Schmitt Julien

Paradis Anne-Lise

Boucher Mathieu

Andrieu Laurent

Barnéoud Pascal

Rondi-Reig Laure
email: laure.rondi-reig@upmc.fr

Affiliations

Validation of memory assessment in the Starmaze task: Data from 14 month-old APPPS1 mice and controls. Authors

Keywords: Spatio-temporal memory, sequence memory, Aging, Navigation behavior, APPPS1, transgenic mouse model, Alzheimer's Disease (AD), robustness assessment

This article describes navigation data of 14 month-old APPPS1 and C57Bl6 in the Starmaze task. These data were acquired as positive controls of memory deficit in a model of the familial form of Alzheimers's disease (see Schmitt et al., Flexibility as a marker of early cognitive decline in humanized Apolipoprotein E ε4 (ApoE4) mice, Neurobiol Aging, 2021). They were acquired in a reduced version of the Starmaze environment and accompanied by a number of acquisitions in different control groups at 6 and 14 months to assess the robustness of the procedure and its associated memory scores. These data illustrate the extraction of a variety of navigation scores (including search strategy, spatial learning and memory) and provide a reference of navigation data in the Starmaze task for healthy 6-month-old controls, normal aging and a model of pathological memory deficit.

Value of the Data

• These data highlight robust navigation scores that evaluate spatial and sequence aspects of episodic-like memory and validate the ability of the Starmaze task to detect a deficit of this memory in APPPS1 mice, a model of the familial form of Alzheimer's disease.

• These data can be useful to labs or companies needing a behavioral paradigm to assess spatial and sequence memory in transgenic mice models and/or mice treated with pharmacological agents targeting memory.

• These data may be used as reference when assessing spatial and sequence memory in mice during normal or pathological aging.

Data Description

To first ensure the robustness of the scores used to evaluate memory from the Starmaze task, we tested if their values were stable (i.e., did not significantly differ) across different batches of control mice at 6 or 14 months (see data files 'Robustness_6months.xslx' and 'Robustness_14months.xlsx' respectively, in Navigation and Memory Scores). We thus compared a C57BL/6 (N=15, 'manip 8') and two ApoE3 batches (N=14, 'manip 9' and N=15, 'manip 7') at 6 months, as well as two batches of C57/BL6 (N=15, 'manip 8' and N=12, 'manip 4') at 14 months. The data for each score are reported on separate sheets named according to the score (Travelled distance, Localization Score, repeated sequence score, Recall sequence score and Number of dead ends revisits). Each sheet consists of 10 columns detailing the identification code of the mice, their group and their individual scores at each experimental session (8 in total). Note that the repeated sequence score is only available from session 4, and that the recall sequence score is computed between consecutive sessions (Sn/Sn+1).

Additional raw scores ('Time', 'Number of visited alleys', 'Direct Path Score', '% correct 1st turn' and '% of direct path') are provided for the sake of completeness but were not further analyzed in the following because they were considered less informative and globally redundant with the other ones. In particular, the time and number of visited alleys relate to distance, and the orientation choice at the first intersection, which determines the percentage of correct first turns by session, also contributes to the localization score, just as the direct path score and the associated percentage of direct path can be considered special cases of the localization score as well.

We also eliminated the recall sequence score from further analysis because of a significant difference between the two C57BL/6 groups at 14 months (Genotype effect: F(1, 53.9) = 5.04, p = 0.0289, two-way ANOVA-type). The four other analyzed parameters were considered as robust (Table 1).

These four scores were then compared between 14-month-old APPPS1 mice (N=10) and 14-month-old C57BL/6 control mice (N=12) to evaluate the ability of a reduced configuration of the Starmaze to detect memory deficits (see data file 'Starmaze_APPPPS1_14months.xlsx', in Navigation and Memory Scores). Data for each score are reported in separate sheets organized in columns. The first two columns provide the identification code and group of the mice. The 40 following columns report their individual score at each experimental trial (5 trials per session multiplied by 8 days). We observed consistent impairments of the APPPS1 on the 4 parameters (Fig. 1). For each parameter (travelled distance -TD-, localization score -LS-, repeated sequence score -RSS-and dead end revisit number -DERN-), there was a genotype effect (TD: F(1, 20) = 20.05, p = 0.0002; LS: F(1, 33) = 14.03, p = 0.0013; RSS: F(1, 25) = 14.71, p = 0.008; DERN: F(1, 31.3) = 12.40, p = 0.0013). All parameters but the repeated sequence score also showed a session effect (TD: F(7, 140) = 22.76, p < 0.0001, two-way ANOVA; LS: F(5.14, 154) = 19.61, p < 0.0001; DERN: F(4.82, 148) = 18.70, p < 0.001 but RSS: F(3.22, 97.7) = 0.85, p = 0.4745) and an interaction effect was found for the localization score (F(5.14, 154) = 2.16, p = 0.0537). Post-hoc tests for each session showed that APPPS1 were impaired in particular in session S2 and in sessions S4 to S7 for the travelled distance, in sessions S4 to S8 for the localization score, in sessions S4, S5 and S7 for the repeated sequence score, and in sessions S4, S5, S7 and S8 for the dead end revisit number (Table 2).

We further analyzed the trajectories of the APPPS1 mice and their controls (see associated raw trajectories) to determine which search strategies they used when learning the task (see Fig. 1 F). These trajectories are recorded as separate text files for the X and Y coordinates. There is one file per trial and per mouse, named JxEy-IC.txt, where x is the day of recording, y the trial number and IC the identification code of the mouse. The files are arranged in directories by day of recording (from day 1 to day 8). We thus observed that APPPS1 mice performed more trials without strategy, confirming the learning impairment of APPPS1 mice (see Table 2, second part for statistics) (Fig. 1 F).

To ensure that the deficits of the APPPS1 in the Starmaze were not explained by a visuomotor impairment, we verified that their performances were not significantly different from those of C57BL/6 mice in the cued version of the Morris water maze (see Table 2 and data file 'Cued_Watermaze_Distance_APPPS1_14months.xslx', in Navigation and Memory Scores). The data file reports for each mouse the distance travelled between the start point and the visible goal platform at each trial (8 trials in total). Comparisons across control groups were performed separately at 6 months (3 batches: 2 ApoE3, n = 14 and n = 15, and 1 C57BL/6, n = 15) and 14 months (2 batches of C57BL/6, n = 15 and n = 12) using a two-way ANOVA with factors Group and Session. The grey background highlights a score that significantly varies across the 14-month-old batches for the Group factor, and is therefore considered as a non-robust parameter. *Bold: p-value<0.05.

Fig. 1. The Starmaze reveals memory deficits in

Experimental Design, Materials and Methods

Mice. C10 homozygous Thy1.APPmutxPS1M146L (hereafter called APPPS1) [START_REF] Blanchard | Time sequence of maturation of dystrophic neurites associated with Aβ deposits in APP/PS1 transgenic mice[END_REF] were used as positive controls for spatio-temporal memory deficit at middle-aging stage. Mice were obtained from Charles River France (Saint Germain Nuelles, France). C57BL/6JRj male mice aged 14 months (n=12) were obtained from Charles River France (Saint Germain Nuelles, France) to be used as controls for the APPPS1 mice. Additional C57BL/6JRj male mice aged 6 months (n=15) and 14 months (n=15) were obtained from Janvier Labs (Saint Berthevin, France). The ApoE3 mice were obtained from Taconic Biosciences (Germantown, USA). All 6 month-old mice were used as controls in Schmitt et al, 2021 [START_REF] Schmitt | Flexibility as a marker of early cognitive decline in humanized Apolipoprotein E ε4 (ApoE4) mice[END_REF].

The list of the mice used in this dataset is provided in the data file 'List_of _mice_and_genotypes.xlsx' with their identification code and genotype.

Animals were housed in a 12 hours dark/light cycle in a temperature-controlled room (20 +/-1 °C) with food and water ad libitum. They were housed by groups of 3 or 4 mice per cage until one week before the start of the experiment, at which point mice were isolated in individual cages until the end of the first experiment, which lasted approximately 1 month.

Mice performed the tests in the following order: Shirpa protocol [START_REF] Rogers | Behavioral and functional analysis of mouse phenotype: SHIRPA, a proposed protocol for comprehensive phenotype assessment[END_REF], Starmaze [START_REF] Rondi-Reig | The starmaze: a new paradigm to characterize multiple spatial navigation strategies[END_REF] and cued Morris water maze [START_REF] Morris | Place navigation impaired in rats with hippocampal lesions[END_REF].

Starmaze paradigm.

The Starmaze is a star-shaped water maze consisting of 5 central alleys forming a pentagon and 5 peripheral alleys starting from each vertex of the pentagon. In order to reduce the acquisition period, we here used a reduced Starmaze: some alleys were made inaccessible by blocking them with walls (see Fig. 1E). The alleys are 42 (central) or 47 (peripheral) cm long, 25 cm wide and 30 cm high [START_REF] Rogers | Behavioral and functional analysis of mouse phenotype: SHIRPA, a proposed protocol for comprehensive phenotype assessment[END_REF]. The Starmaze is filled with water made opaque with a non-toxic dye (Accuscan OP 301) up to about 5 cm from the top of the walls. A platform is immersed 1 cm below the water surface. The Starmaze is surrounded by black curtains arranged in square on which 2D and 3D visual cues are attached. The cues are grouped into groups of 2 or 3. All cues are present in two copies but each configuration of 2 or 3 cues is unique. The brightness of the room was between 90 and 100 lux. A white noise of 50 decibels was broadcast via 4 loudspeakers during all trials. A trial begins with the mouse released by the experimenter always at the same departure point. The mouse is then left to swim until it finds the platform or 90 seconds maximum. If the mouse finds the platform, it is left 20 seconds on the platform before being picked up by the experimenter. If the mouse does not find the platform before the end of the 90 seconds, it is placed on the platform for 20 seconds. At the end of each trial, the mouse is placed in a cage containing a towel for drying before being returned to its home cage while waiting for the next trial, during 30 to 60 minutes. The acquisition phase consisted of 5 trials per day for 8 days (also named sessions in the data files).

Starmaze scores. Mice trajectories were tracked and the distances travelled during a trial were measured using SMART 2.5 (Bioseb) software. X and Y trajectory coordinates were recorded every 0.04 seconds during the navigation task, and processed with our own developed software, NAT (Navigation Analysis Tool) [START_REF] Jarlier | A Navigation Analysis Tool (NAT) to assess spatial behavior in open-field and structured mazes[END_REF], to extract the following behavioral parameters: -the localization score, calculated by allocating a mark at each choice point (100 if the mouse moves toward the platform, 0 otherwise) and averaging the marks allocated at all the intersections encountered during a trial [START_REF] Fouquet | A new approach for modeling episodic memory from rodents to humans: The temporal order memory[END_REF]; -the repeated sequence score, attributing a maximal mark if the moves made at each choice point of trial Ti+1 reproduce the choices made at trial Ti, in a same learning session [START_REF] Bellassen | Temporal Order Memory Assessed during Spatiotemporal Navigation As a Behavioral Cognitive Marker for Differential Alzheimer's Disease Diagnosis[END_REF]; --the recall sequence score, calculated like the repeated sequence score, to compare the sequence performed in the first trial on day X+1 with the most repeated sequence performed on day X; -the number of dead ends (peripheral arms not containing the platform) revisits; -the time to reach the platform, capped at 90 seconds per trial; -the percentage of correct first turns, which indicates the proportion of trials per session where the mouse makes a correct decision at the first intersection; -the number of visited alleys averaged across trials. All these scores are reported at the session level in the data files 'Robustness_6months.xslx' and 'Robustness_14months.xlsx' for the 6 and 14-month-old control mice.

Search strategies. The visualization of the trajectories (see raw trajectories) allowed to identify two types of trajectories that reveal an efficient strategy to reach the goal during the acquisition of the task: -the direct trajectory, which corresponds to the most efficient sequence of turns to the goal with no visit of dead ends; -the serial strategy, which includes a systematic visit of the dead end between the start and the platform. The other types of trajectories corresponded to mice travelling more alleys to reach the platform, and were labelled as 'no strategy'.

Morris water maze in cued version.

The 14-month-old APPPS1 mice (N=10) and their C57BL/6 controls (N=12) were subjected to a navigation task in the Morris water maze with a visible platform to ensure that possible deficits observed during the Starmaze task are not due to vision or swimming deficits. The pool is a circular tank of 150 cm in diameter. It is filled with water at 20 +/-1°C made opaque with a non-toxic dye (Accuscan OP 301). An opaque black curtain is placed around the pool so that the mouse cannot use distal landmarks and a flag is placed on the platform (12 cm in diameter) to make it visible. The protocol is carried out in 2 days with 4 trials per day separated by 45 to 60 minutes each. The platform location is changed at each trial; the starting point is always opposite to the platform and the head of the mouse is directed towards the center of the water maze at the beginning of each trial. A trial lasts a maximum of 90 seconds. If the mouse does not find the platform during those 90 seconds, it is guided to the platform. The success at this task is monitored using the distance travelled by the mouse from the starting point to the visible platform. Distances were recorded by the tracking software (SMART 2.5, Bioseb). They are reported for each mouse and each trial (8 in total) in the data file 'Cued_Watermaze_Distance_APPPS1_14months.xslx'.

Table 1 . Robustness assessment for the different Starmaze Scores.

 1

	Starmaze Parameters	Cognitive function	Age (months)	Statistical model	Group factor F value	Group effect P value
	Travelled distance	Learning of the	6	Two-way	F(2, 41) = 0.77	0.4718
	(cm)	task	14	ANOVA	F(1, 25) = 0.33	0.5724
	Repeated	Sequence memory	6		F(2, 52.3) = 0.49	0.6178
	sequence score	inside sessions	14		F(1, 32.9) = 0.00	0.9938
	Recall sequence	Sequence memory	6		F(2, 80.8) = 0.57	0.5678
	score	between sessions	14	Two-way ANOVA-TYPE	F(1, 53.9) = 5.04	0.0289 *
	Number of revisits in dead ends	Working memory	6 14		F(2, 88.3) = 0.82 F(1, 49.7) = 2.22	0.4440 0.1425
			6		F(2, 52.4) = 0.47	0.6245
	Localization score	Spatial memory
			14		F(1,49.2) = 0.29	0.5934

14 months APPPS1 mice.

  Comparison of APPPS1 (N=10) and C57Bl6 (N=12) behavior at 14 months in the Starmaze. A: Travelled distance. Data are represented as mean +/sem. B: Localization score. Data are represented as median +/mad (median absolute deviation). C: Repeated sequence score. Data are represented as median +/mad. D: Dead end revisit number. Data are represented as median +/mad. E: Examples of trials illustrating search strategies. Failed: the mouse does not reach the platform in the allotted time. Direct: efficient sequence of turns to the goal with no dead-end visit. Serial strategy: visit of the dead-end between the start and the goal. No strategy: all other situations. Dark red lines show the blocking walls added to reduce the Starmaze. F: Distribution of trial types by session and genotype. *: Genotype effect p < 0.05, Post hoc analysis with Student's t-test performed after a two-way ANOVA for distance or with Fisher's test performed after two-way ANOVA-type for other parameters in a specific session (Table2).

	Statistical model	Parameters	Factor	F value	p-value
			Genotype	F(1, 20) = 20.05	0.0002
	Two-way ANOVA	Travelled distance	Session	F(7, 140) = 22.76	<0.0001
			Genotype*Session	F(7, 140) = 1.73	0.1067
			Genotype	F(1, 33) = 14.03	0.0013
		Localization score	Session	F(5.14, 154) = 19.61	<0.0001
			Genotype*Session	F(5.14, 154) = 2.16	0.0537
			Genotype	F(1, 25) = 14.71	0.0008
	Two-way ANOVA-type	Repeated sequence score	Session	F(3.22, 97.7) = 0.85	0.4745
			Genotype*Session F(3.22, 97.7) = 0.76	0.5255
			Genotype	F(1, 31.3) = 12.40	0.0013
		Dead end revisit number	Session	F(4.82, 148) = 18.70	<0.0001
			Genotype*Session	F(4.82, 148) = 1.75	0.122
			Genotype	F(1, 20) = 0.87	0.3524
		Direct strategy	Session	F(7, 140) = 7.82	<0.0001
			Genotype*Session	F(7, 140) = 1.12	0.3552
	Two-way		Genotype	F(1, 20) = 2.62	0.1076
	binomial	Serial strategy	Session	F(7, 140) = 6.3	<0.0001
	GLMM		Genotype*Session	F(7, 20) = 1.28	0.2633
			Genotype	F(1, 140) = 14.51	0.0002
		No Strategy	Session	F(7, 140) = 3.32	0.0026
			Genotype*Session	F(7, 140) = 4.01	0.0005
	Two-way ANOVA	Distance to cued platform in Morris water maze	Genotype Session Genotype*Session	F(1, 20) = 0.155 F(7, 140) = 2.033 F(7, 140) = 0.292	0.6978 0.055 0.9563

Acknowledgments

We thank Jean Vincent for help with behavioral experiments. We thank the IBPS animal facility for helping in taking care of mice.

Declaration of Competing Interest

JS, PB and LA were full-time employees of Sanofi when this study was performed. The CNRS, LRR and her lab have financial interest in the sale of the Starmaze task. This work was supported by Sanofi (PB, JS, LA), the CNRS and Sorbonne University through UMR 8246 (LRR). The group of LRR is a member of the Labex BioPsy and ENP Foundation. This work also received support under the program Investissements d'Avenir launched by the French Government and implemented by the ANR, with the references ANR-10-LABX-BioPsy (LRR). Labex are supported by French State funds managed by the ANR within the Investissements d'Avenir programme under reference ANR-11-IDEX-0004-02.

Specifications Table

Subject

Neuroscience: Behavioral

Specific subject area

Behavioral assessment of memory using a navigation task as a behavioral assessment of memory Top: Effects of factors Genotype, Session (repeated) and their interaction on each parameter of the Starmaze, and on the distance travelled in the cued version of the Morris water maze. Bottom: Post-hoc analyses comparing 14-month-old APPPS1 and C57BL/6 mice at each session in all above parameters. The repeated sequence score was computed only from session S4. A two-way ANOVA analysis was followed by Student's T-tests and a two-way ANOVA-type analysis was followed by Fisher's tests. Failed, Direct and Serial refer to the search strategies used by the mice to reach the platform. The results of the cued morris water maze are provided to ensure that the learning deficits of the APPPS1 in the Starmaze are not due to visuo-motor deficits compared to C57bl6. Bold: p-value<0.05 for main effects, p<0.1 for interaction.

Type of data

Statistical analysis. The distance travelled in the Starmaze was analyzed using a two-way analysis of variance (ANOVA) with factors Genotype, Session and their interaction, performed on raw data for the robustness assessment (Table 1) and the comparison of APPPS1 vs. C57Bl6 at 14 months (Table 2). Repeated measures on the factor session were taken into account in each model and AR(1) variance-covariance structure was used. The Localization score was analyzed using a two-way ANOVA-type with factors Group, Session and their interaction on ranked data for the robustness assessment (Table 1) and the comparison of APPPS1 with C57Bl6 at 14 months (Table 2).

For the other three Starmaze parameters, i.e. repeated sequence score, recall sequence score and Dead end revisit number, a two way ANOVA-type was performed on ranked data for the score robustness assessment (Table 1), the comparison of APPPS1 vs C57Bl6 at 14 months (Table 2). The analysis was followed by comparisons of groups with post hoc tests at each session.

To compare the use of search strategies between groups, a two-way GLMM with binomial distribution was performed on raw data for the number of Direct, Serial and No strategy trials (Table 2) followed by Bonferroni-Holm adjustment if necessary.

A two-way analysis of variance (ANOVA) on factors Genotype and Session (repeated) was also performed on the travelled distance in the indexed version of the Morris water maze, when significant deficits were found in the Starmaze task (Table 2).

Ethics Statement

All experiments were approved by Sorbonne University Ethical Committee and conducted in full compliance with standards for the care and use of laboratory animals, according to French and European Community (Directive 2010/63/EU) legislation.

CRediT author statement


For aqueous technologies, the energy performances are limited. The energy of the pack allows only less than one hour drive in normal use. But the batteries technologies are adapted only for slow discharge, for example, a three hours discharge specification. On vehicle, energy delivery is lower than specified, for example half of the specification. Aqueous technologies are not adapted for electric vehicles. For lithium batteries, there's only the additional weight of the mechanic of the pack.

Lead Acid

NiCd

NimH ZEBRA LiFePO4

  Aqueous technologies : Lead acid, NiCd, NimH, Electrolyte made of water and sulfurous acid or KOH A lot of parasitic reactions: water electrolyze,… Disadvantages : -Self discharge -Water loses -Waste of energy, lower efficiency, especially if overcharge -End of charge cooling for large batteries -Difficulty of the end of charge detection For NimH, negative dV/dt and temperature rise is adapted for fast charge at ambient temperature -Difficulty to have a precise gauge Advantages : -Intrinsic clamping -End of charge balancing only done by overcharge -No electronic for each stage of accumulators in series reaction can be simulated by a zener diode, in parallel with each cell. Battery cell | 9 RESULTS ON ELECTRIC VEHICLES IN THE 1990'S 2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux

-

  Only one electrochemical reaction -Process with deposition of layers on metallic sheets -Low or very low internal resistance => adapted for fast charge and discharge for months or years -End of charge detection is very easy -Faradic efficiency near 100% (discharge capacitance / charge ) -Gauge with voltage measurement or coulombmetry (charge counting) Disadvantages: -Overvoltage and undervoltage detection is necessary for each stages of accumulators in series -Electronic for balancing for each stages Other specificities: -Process is done in dry room (expensive) -Electrolyte filling is done under inert gas -Balancing is necessary but not at each cycle -The choice of Lithium ion chemistry is a compromise between energy, life time, number of cycle, power, security, cost -Low internal resistance -Charge in some minutes are possible -High level of short circuit current -Efficiency as high as 95% are possible | 12 LITHIUM-ION ELECTROCHEMICAL ACCUMULATORS 2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux Other specificities : -Graphite electrode is limiting because of instability in the electrolyte, but protected by the SEI (like aluminum) -Lithium metal deposition potential is near graphite one. => risk at low temperature below 0°C => no fast charge => life time impact -Titanate hasn't these limits => adapted for fast charge => adapted for low temperature => high number of cycles But lower energy (one volt less) -Discharge at low temperature => loss of energy. Heating or keep in temperature. -Only two standard formats: 18650 (Laptop and electric tools) 26650 (power tools) Bluecar of Bolloré is a Lithium metal electrochemistry and not a Lithium-ion one. To avoid dendrite problem a full solid polymer electrolyte is used. For polymer electrolyte conduction, battery is keep hot (60°C). time and high number of cycles -Cobalt cost Nickel Manganese Cobalt (NMC) -Reactivity, cost, life time and number of cycle depending of the percentages of Nickel and Cobalt (from 1/3, 1/3, 1/3 up to 5% 90% 5%) Manganese oxide -Lowest cost material -Low reactivity -Low life time at high temperature -Low number of cycles | 15 THE DIFFERENT LITHIUM-ION CHEMISTRIES 2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux Iron phosphate -Safest chemistry -Good life time -High number of cycle -Low cost raw material -Nano-structuration and doping of phosphate is necessary -3,3V plateau from 10% to 90% of state of charge -Lower energy -Can be used to 3,3V +/-10% (3V -3,3V -3,6V) -Overvoltage tolerance => 4,5V -Matrix of accumulators with fuses or electronics for defect tolerance developed in CEA for five years The safety of the chemistry allows: -High capacity accumulators mainly in China (hundreds of Ah) with moderate energy density (safety) -Used by Valence for ten years to provide modules to replace lead acid batteries by matrix of 18650 with BMS in an adapted package. Replacement or used is made by the customer/integrator.

  Electrochemistry of the accumulator is only one link in the security chain Security is a system approach with a lot of aspects: -Lithium ion chemistry -Electrolyte solvent (combustible now), gel electrolyte, polymer -Separator (fusing to stop ion diffusion at high temperature, ceramic…) -Internal fuses (CTP or pressure switches) -Mechanical conception of the cell -Overpressure protection -Module conception, cells distance to avoid defect propagation, thermal barrier -Module electric architecture -Electric protections of the pack (vacuum or gas relays, high power fuses…) -Mechanical protection of the packs, fire protection, auto extinguishing polymers... -Electronic (for laptop MOSFET are used to open the circuit in case of overdischarge, overcharge or internal defect)

and risks

		Lead	NiCd	NimH	ZEBRA	LiFePO4	Li ion (1) Li Polymer
		acid				Iron
						phosphate
						Li-ion
	Gravimetric	30-50	45-80	60-110	120	120-140	150-190	150-190
	energy
	Hydrogen (Wh/kg) Energy Gasoline Diesel density (Wh/l) (W/kg) density (2) Power	75-120 0 up to 70	33 000 80-150 13 000 12 400	2.75 (gas -1bar) 220-330 180 2100 (liquid) 9 800 10 500 up to 900 200	50 % (fuel cell) 190-220 220-330 Explosion 220-330 15 to 40 % (combustion engine efficiency Fast combustion, risks with (3) 1500 some explosion up to 800 up to up to 250
	Number of	400-600	2000	1500	800	curves) >2000	gasoline 500-1000 200-300
	Wood cycles Electrochemical (1) 1200(2) Accumulators Self 5% discharge pe r month voltage Nominal 2V	4 000 40 to 200 20% 1,2V	1600-2000 70 to 300 30% (4) 12 % per day (5) 1,2V 2,6 V	15 to 40 % 80 to 95% 5% (6) 3,2V	Slow combustion 10% Fast combustion, low 10% explosion risk, electric risk 3,6V 3,7V

| 5 2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux

THE DIFFERENT LITHIUM-ION CHEMISTRIES

	Material		Charge (mAh/g)	Nominal (V vs. Li) voltage	Energy (Wh/kg) density	Advantages	Drawbacks
	LiCoO 2	LCO	150	3.9	585	High energy	Cost -unstable
	LiNiMnCoO 2	NMC	160-180	3.85	615-695	High energy -stable	Cost
	LiNiCoAlO 2	NCA	190-200	3.75	710-750	The highest energy	unstable
	LiFePO 4	LFP	150-160	3.45	515-550	Low cost-safe	Lowest energy
							Low energy -
	LiMn 2 O 4	LMO	105-120	4.1	430-490	Very low cost-safe	low calendar life at high te
							mperature
	Graphite	G	330-360	0.15	NA	Low cost high energy	Charge at low temperature
						High power,
	Li 4 Ti 5 O 12	LTO	150-165	1.55	NA	calendar life,	Low energy
						safe
							Very low
	Silicium	Si/C -Si 500-2000	0.4	NA	Energy density	number of
							cycles
	Hard carbon	HC	200-300	0.4	NA	High power	Low energy
				2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux

| 17 SECURITY OF LITHIUM-ION BATTERY PACKS 2/11/2016 -4/11/2016 | ESARS ITEC 2016 | Daniel Chatroux

Lithium ion accumulator is a big progress for:

• long term storage,

• energy density,

• fast charge and discharge (some minutes, or tenth of minutes)

Lithium seems to be complicated, but end of detection and gauge are easier. •NiCd / NimH => Lithium

•Lithium pack is a multi tool product (work in autonomy in building site)

•Due to the huge market of laptop computer market, the constant progress of performance and decrease of cost allow commutation of all a application domain to Lithium ion.

For electric or plug-in hybrid vehicles, we are in a transition phase.

Two solution are used :

•Associate thousand of low cost high quality and performance of small standard accumulators with a lot of know-how in the association to provide thermal management, safety and security

•Associate only hundred accumulators in series. The performances, thermal exchange, security and cost are directed linked to the accumulator. Now a specific product, in low quantity production. Possibility of higher performances and lower cost when the electric and plug-in hybrid market will start.

| 26


Fuel cell provides around 50% of conversion efficiency. Efficiency has a low dependence of level of power. The efficiency is dependent of auxiliaries 'management, especially for low power requirements. Gasoline provides high gravimetric and volumetric energy density with an easy management because it is a liquid chemical storage. Conversion efficiency may be higher than 30-35 % at high power, but is lower at low charge. Risks are related with ignition temperature point. So, risks are more important with gasoline than for diesel. Chemical risks are linked to energy level but are very dependent of kinetic. Wood provides a high level of energy (4 kWh/kg) with low risk because his combustion with air is slow. Electrochemical storage with accumulators provides a very good storage efficiency, near 100% for Lithium ones, but with poor gravimetric and volumetric density. Hybrid vehicles may combine gasoline engine in high charge (high torque) at lower speed rotation mode (or stop mode) to provide higher efficiency and a battery to provides an additional power if an acceleration is required [START_REF] Chatroux | Toyota PRIUS: battery in microcycle mode: the cost of use is divided by five[END_REF].

Electrochemical accumulators 2.1. Accumulators supplier specifications for different technologies

The document [START_REF] Schwarz | Le stockage électrochimique[END_REF] indicates the level of performance specified by the suppliers for different technologies of electro-chemical accumulators. This synthesis is a good overview with a lot of information.

The table can be completed with new results or some precisions:

(1) Li ion has several main families with different behaviors; this will be presented in this document [START_REF] Schwarz | Le stockage électrochimique[END_REF] For all accumulators, there are energy versions optimized for energy with less power, and power versions with less energy density, [START_REF] Béranger | Sébastien Fiette CEA-LITEN Experience feedback on electric vehicles of the French car fleet -battery impact PCIM[END_REF] The A123Systems company designed LiFePO4 cells for electric tools at 2 600 W/kg (for 10 s discharge) and Saft VL10VFe cell have 5 kW/kg continuous dis-charge, [START_REF]Chatroux Comparison batteries technologies for electric vehicles application PCIM[END_REF] For high quality NimH, the initial self-discharge is high (30% for example) but decrease a lot in a second phase. We measure that a NimH battery of a Vectrix scooter from GP is only half discharged after more than one year of storage (5) ZEBRA is a high temperature accumulator with high temperature conditioning. Resistors are used to maintain the temperature in storage. Per year, the electricity needed to warm the accumulators in storage increases significantly the electricity bill (6) For example, a 26650 A123Systems cell have low discharge after more than three years of storage. (7)

As for LiFePO4, most of Lithium ion technologies are adapted for discharge at negative temperatures, but for charge the minimum temperature is around 0°C. The charge below 0°C is critical. The recommendations of the supplier have to be followed. In real use, it is possible to charge at negative temperatures but with lower current. The low temperature charge has a great impact on the number of cycles. Specific tests on this point may be necessary according the applications requirements. (8)

Lanthanum, a rare earth, is used in non-plugin Hydrid cars (9)

Since 2005, the battery costs have decreased. Cost is very dependent of market. In 2015, an example of good quality LiFePO4 Lithium ion module is 1000€/kWh. Accumulators (cells) for computers cost is around 200-300€/kWh.

Aqueous batteries

The three main aqueous technologies (lead acid, NiCd and NimH) have a lot of parasitic electrochemical reactions in parallel with the main one. These parasitic reactions have different electrochemical potentials, and so have different chemical kinetics depending of the accumulator voltage.

One first impact of these parasitic reactions is self-discharge phenomenon. At nominal voltage, these parasitic reactions are still active. It is a consumption of energy with a discharge rate of some weeks or months. This is a disadvantage of aqueous electrochemical accumulators.

The second impact is intrinsic voltage clamping at the end of the charge.

For example, at the end of the charge for a lead acid battery, the main electrochemical reaction is finished, so the voltage drops up to the water dissociation voltage. If the charge goes on, the current generates heat and gas from the water dissociation but the voltage stay the same: it is the voltage clamping behavior of the accumulator cell which can be simulated by a "zener diode", as in the figure 1. This parasitic reaction is an advantage when charging multiple cells connected in series (a battery of electrochemical accumulators). As all cells are not identical, or not in the same state of charge, a cell will end its charge first. As other cells are not fully charged, the current is maintained to charge these cells. The first cell stays fully charged and produce heat and water dissociation: it's a natural balancing that allows the end of charge for other cells. Thanks to the parasitic reaction, there is an intrinsic voltage clamping with the possibility to balance the different accumulators in series only by the prolongation of the charging phase without any additional electronic circuit. However, balancing phase duration has to be minimized because of its great impact on battery life time and charge efficiency.

2.3.

Lithium ions batteries

The composition of Lithium ion accumulator is for standard design: a copper foil with graphite layers (the two faces) for the negative electrode, a separator with electrolyte impregnation, a positive electrode with aluminum foil and layers of a positive active material. The electrochemical reaction is based on Lithium ion insertion (intercalation) in graphite or in positive active material for charge and discharge. The reaction mechanism of lithium-ion batteries is presented in the Figure 2. The positive and negative materials usually have a layered structure to facilitate lithium ions insertion. The main effect of the charge and discharge reaction is the back and forth movement of lithium ions between the electrodes, matched by a corresponding flow of electrons in the external circuit. This electrochemical process is sometimes called a "rocking-chair" mechanism. The Lithium ion electrochemistry is a dry one.

Because water is a pollutant in this chemistry, the accumulators are built in dry room. The need of dry room has an important impact on accumulator process cost. Except long term ageing, there is no parasitic reaction, so:

• No discharge current
o Good quality Lithium ion accumulator stores energy for years. It's a great advantage in the application to get the battery charged. For example, a portative electric tool may operate after some months of storage.

• No intrinsic voltage clamping reaction

o There is no natural balancing, minimum and maximum voltage detections are required to cut the charge or discharge current and an external electronic balancing circuit is necessary when accumulators are connected in series

Lithium ion battery management specificity

For safety reason and to provide a high lifetime, the voltage of each accumulator is monitored. Charge has to be stopped when one accumulator reach the maximum voltage specified. Discharge has to be stopped when the first accumulator reach the minimum specified voltage. For balancing, good quality Lithium ion accumulators are nearly perfect. Leakage currents are very low, so unbalancing is a very slow mechanism. It's not necessary to balance after each charge. For example, after a fast charge the unbalancing may be 0.4%. It's only 400m for a 100 km range. But it's a cumulative phenomenon so a balancing circuit is necessary. A standard dissipative circuit is adapted low cost solution. At the end of the charge, the accumulators with higher voltages are discharges at the same level as lower ones, before a cycle of charge. After some cycles balance of all the accumulators is provided.

Specific circuits are designed for balancing. Other designs used linked microcontrollers for each level of accumulators in series.

Balancing circuit is necessary because of very small differences of leakage currents or faradic efficiencies between accumulators in series. The goal of balancing circuit is not to manage the dispersion of accumulators in series. The capacity of a series of accumulator is the capacity of the lower. So an additional circuit to manage the dispersion of accumulators in series seems to be interesting. For this function power electronic is necessary. Because of low voltage, high efficiency is difficult. And at the end, the cost of the function is too high, and production improvements allow to limits the dispersion when high volume occurs.

In our realization, balancing current is 250 mA with a 1W resistor. In automotive batteries, the balancing current may be as low as 10 mA for cost reason. A single PCB manages around hundred stages of accumulators in series. With 10 mA an external MOSFET is not necessary. The power may be dissipated on a single cart.

Because of low power, it is not possible to balance the battery after production, if the accumulators are not at the same state of charge. With 10 mA circuit, an unbalance of 1Ah needs 100 hours to be corrected! Accumulators with the same state of charge may be assembled. It's not a problem, because when accumulators are processed, it's necessary to form the accumulators with some charge and discharge cycles. So capacity is measured and the last charge may be finished exactly at the same state of charge; without over costs.

Another important specificity of Lithium ion batteries is short circuit current level.

Because of low internal resistance, Lithium ion batteries are adapted for fast charge and discharge but the disadvantage is the level of short circuit current for example three or five times more important than other technologies. A small LiFePO4 cell for electric tool with a capacitance of 2.5 Ah has a short circuit current of 350A! With these cells a 40Ah pack has a 5.6 kA short circuit current. Short circuit current levels are higher with Lithium ion batteries. This parameter is important for fuse choice.

Differences between aqueous and lithium ion technologies

The faradic efficiency is the ratio between the charge extracted from the battery in discharge compared and the charge injected. For aqueous battery, the faradic efficiency is about 90% because of the loss of electrons in parasitic reaction and in the overcharge during the balancing phase.

For Lithium accumulator, the Faradic efficiency is near 100%.

The energy efficiency takes into account the faradic efficiency and the energy losses in the serial resistance: it's the reason why the energy efficiency is directly linked with the levels of charge and discharge currents.

For lithium accumulator, energy efficiency is higher than 90-95%, typically 10 to 20% higher than aqueous ones.

End of charge detection is very interesting for the applications, especially for electric vehicle one.

NiCd and NimH end of charge detections are well known for room temperature and around one hour charge. At the end of the charge, the voltage rise first and decrease, and the temperature rises. Chargers used a combination of negative dV/dt and temperature rise detections. At higher temperature, after a ride when the battery is hot, this mechanism disappeared. Voltage charging curve is nearly flat, and it's difficult to discriminate the end of charge with the only temperature evolution. An existing solution is cooling the battery in a first phase, before starting the charge but it may a loss of time. Another solution is charge counter to inject an amount of charge correlated to the discharge. This solution is not perfect because faradic efficiency is not 100% and the battery managing systems has to estimate the charge losses.

Security

The security of a battery pack is a system problem with a lot of parameters: -Chemistry (thermal stability of positive material and negative material) -Solvent (combustible in most cases) -Separator (separator fusion can stop ion diffusion in case of over-temperature (if the voltage applied is not too high) -Internal fuse or CTP (Polyswitch®) or pressure mechanical switch in the cell can open the circuit (if the voltage applied is not too high). -Cells (accumulator) design -Module design for example distance between the cells to avoid thermal runaway propagation -Pack design (fire resistant enclosure, impact absorption, cooling to avoid thermal runaway propagation, fire resistant polymer, exhaust pipe for gases) -Electronic of battery management system to keep the cells in the voltage and temperature limitations, MOSFET to open the circuit for low voltage packs -Electromechanical architecture (vacuum or gas contactor to open the circuit, DC current breaker, fuses able to cut the very high level or short circuit current The security of a battery pack is a combination of all these aspects, with a lot of different solutions and choices.

In laboratory, the standard solution to extinguish a battery fire is neutral gas injection to inert the volume. For car fires, the firefighters uses water pulverization and inert the battery pack with water. The water is very efficient for cooling and stopping the thermal runaway.

3.

Application and associated costs in the different markets

Main applications for lead-acid, NiCd, NimH

A first market for lead-acid battery is the thermal engine start, with the evolution to stop and start applications. In this application, the thermal range of lead acid battery is an advantage. Another market is energy storage for UPS (uninterruptible power supply) or telecom centrals.

NiCd batteries are used in aircraft to start the engines and for safety power supply. The other important market is railway application. Now there are batteries in the locomotives and nearly each cars. NiCd has a large temperature range and a good lifetime in these applications, but with maintenance needs (water adding).

Nimh batteries are generally used in non-plug-in hybrid cars, and it is a small size designed for high power (1.2 kWh, 20 kW, for Toyota Prius). In this application, the battery is used mainly in micro-cycle mode (5%) in a small allowed window of charge (20%) [START_REF] Chatroux | Toyota PRIUS: battery in microcycle mode: the cost of use is divided by five[END_REF]. Millions of batteries were manufactured.

Batteries technologies for electric or plug-in hybrid vehicles

Electric vehicles of the 90's-00's were designed with the batteries technologies of that time.

With aqueous solutions (lead acid, NiCd, NimH) the energy storage provide less than one hour of continuous driving, and these technologies are not adapted for these rates of discharge, for a discharge in one hour or less. The impacts measured one vehicle are: -a smaller energy storage than expected, -a decreasing of lifetime, -a kilometric cost tree times more important than gasoline engine ones [START_REF] Béranger | Sébastien Fiette CEA-LITEN Experience feedback on electric vehicles of the French car fleet -battery impact PCIM[END_REF] The gravimetric energy measured on vehicles is typically half than expected [START_REF]Chatroux Comparison batteries technologies for electric vehicles application PCIM[END_REF]: Aqueous electrochemical technologies (lead acid, NiCd, NimH) are not adapted for electric or plug-in hybrid vehicles.

NimH is used on millions of hybrid vehicle (non-plug-in ones), because for this application battery is only used for micro-cycles [START_REF] Chatroux | Toyota PRIUS: battery in microcycle mode: the cost of use is divided by five[END_REF] Lithium batteries are adapted for electric vehicles or plug-in hybrid ones: -With the same weight, twice or three times more energy is provided -Charge and discharge may be less than an hour without important loss of energy -

The battery has a good efficiency between 95 and 90%, depending of discharge rate -End of charge detection is very easy and reliable

Lithium ion big markets

The first market for Lithium-ion accumulators is laptop. The standard accumulator size is 18650: a cylinder of 18mm of diameter and 65 mm long. The main parameter for this market is laptop autonomy so Cobalt oxide has been used first and now the chemistry are the most energetic ones (NCA, NMC). To provide security, the quality level of accumulator must be high. There may be internal protection in the accumulator (CTP, mechanical switch). A polymer closed enclosure protects the accumulators and local electronic. This electronic manage the battery and is able to open the circuit in case of short circuit at the output of the battery, or in case of risk of overcharge. In this application the charge is for example one hour and the discharge is a three hours.

The laptop battery of Figure 3 store 60 Wh for 388 g. The energy densities are 154 Wh/kg and 310 Wh/l. The final price for battery replacement is 30€. So, the level of price for the customer is 500€/kWh

Application of Lithium ion for electric cars market

The last and new market is car and other vehicles applications. It is an emerging market with first interesting vehicles and different approaches. There is not any accumulator dedicated for electric car manufactured by quantity. There is not standard dimension for accumulators for this market.

Tesla approach is to design a high acceleration and speed car with a large range with thousands of laptop standard accumulators. Because of high volume production, the cost is low, for example 200€/kWh, the energy density and the level of quality are high. The energy in each accumulator is limited by the small volume, so it is possible to limit thermal runaway propagation in the pack by specific designs: air space between accumulators or water cooling pipe between the accumulators. Battery pack is very thin and is a part of the vehicle mechanical structure [5]. As said before, the 500 km range is possible but with limited speed around 90 km/h.

Conclusion

Lead acid and NiCd technologies are well adapted for engine starting or energy storage for applications where uninterruptible power supply is necessary. Laptop, cellular phones and tablet use Lithium ion battery to provide the autonomy. The mutation of electric tools has just been done from NiCd and NimH to Lithium ion. The improvement is very interesting with no self-discharge and autonomy improvement with an affordable cost. Lead acid, NiCd, and NimH have too poor real performances on electric vehicle to be a viable solution. The mutation to Lithium allows good vehicle performances, a sufficient level of range, the possibility of promising improvement and good cost perspectives. We are in this mutation phase.

A large accumulator should be less expensive than twenty small ones, but because of the mass production of small accumulators, the level of cost is lower. The association of thousands of them is used by some manufacturers, for module production or car production.

It should be only a transition phase of starting of the electric and hybrid vehicle market. Range is presented as the main problem for electric vehicle. In 2009, we gave a presentation to indicate that the main brake to electric and plug-in hybrid vehicles was the cost of battery storage used. In fact, the battery cost was three times too expensive. Five years later, the level of cost seems to be competitive and an important progress margin is in front of us..

5.

Figure 1 :

 1 Figure 1: parasitic reactions simulation in aqueous batteries technologies

Figure 2 :

 2 Figure 2: Lithium ion technologies

Figure 3 Figure 4 :

 34 Figure 3: laptop battery

Figure 5 :

 5 Figure 5: standard format for electric tools

Figure 6 :

 6 Figure 6: TESLA model S battery concept Figure 7: BMW i3 battery Figure 8: accumulator and module Renault Zoé, BMW i3 are designed with specific design of accumulators with a specific size of accumulator. These cars provide a good level of customer services. The ranges are now

Figure 9 :

 9 Figure 9: Electric or plug-in vehicles: Audi, BMW, Bolloré , Chevrolet, Citroën, Courb, Fisker, Ford, Mercedes, Mitsubishi ,Nissan, Opel, Peugeot, Porsche, Renault ,Smart ,Tazzari, Tesla, Toyota , Volkswagen, Volvo

Compared to the aqueous technologies, lithium ion end of charge may be perfectly detected

  (Nickel Manganese Cobalt oxide) performances depend on the percentage of Co and Ni. Energy is high. Safety behavior and cost depend of Cobalt percentage. Now most accumulators for laptops, electric tools and vehicles are NMC ones.

	Positive and negative material performances are:
	Material		Charge (mAh/g)	Nominal voltage Li) (V vs.	Energy (Wh/kg) density	Advantages Drawbacks
	by the voltage of the accumulators. The advantages and disadvantages of accumulator technologies are the following: LiCoO 2 LCO 150 3.9 High Cost -585 energy unstable
	Parameter LiNiMnCoO 2 NMC Balancing End of charge detection Self-discharge LiNiCoAlO 2 NCA	160-180 190-200	Aqueous technologies ☺ 3.85 615-695 3.75 710-750 The highest High energy -stable energy	Lithium ion Cost ☺ ☺☺ unstable
	Energy Safety LiFePO 4	LFP	150-160	3.45	☺	515-550	Low cost-safe	☺☺ or Lowest energy
	Hydrogen risk Temperature range Cost 2.6. Different Lithium ion technologies ☺ Constant LiMn 2 O 4 LMO 105-120 4.1 430-490	Very low cost-safe	☺ Low energy Decrease -low calendar life at high
								temperature
	Graphite	G	330-360	0.15		NA	Low cost -high energy	Charge at low temperature
							High
	Li 4 Ti 5 O 12	LTO	150-165	1.55		NA	power, calendar	Low energy
							life, safe
	Silicium	Si/C -Si	500-2000	0.4		NA	Energy density	Very low number of cycle
	Hard carbon HC	200-300	0.4		NA	High power Low energy
	Iron Phosphate is the safest material, because dissociation is not possible. The energy is
	lower because voltage and capacity are lower. The voltage curve is near flat at 3.3V. The
	end of charge is 3.6V. The end of discharge is 2V, but there is a very low energy between 2V
	and 3V. So this accumulator technology can provide a stable voltage with only +/-10%
	variation. It's an advantage for power electronic dimensioning. Iron phosphate has good
	calendar life and provides a high number of cycles. Iron phosphate high volume
	accumulators are designed in China for automotive or buses applications.

There are different Lithium-ion technologies with different energy and safety performances. The main differences are due to positive material: Cobalt oxide is the oldest material. It's a very reactive one. In case of failure or abusive conditions, dissociation occurs at a low level of temperature and oxygen reacts with combustible materials of the accumulator. Cobalt has a high cost.

NCA (Nickel Cobalt Aluminum oxide) is reactive. It provides a level of energy as high as 200 Wh/kg. Calendar aging is good. TESLA used PANASONIC accumulators of this technology.

Manganese oxide is a low cost material but a poor calendar aging. Energy is high. Number of charge discharge cycles is low. NMC


Dr Ismail Hamdi
email: ismail.hamdi@u-paris.fr

Amit Guy Buntinx
email: guy.buntinx@univ-lille.fr

Kumar Tiwari

Dr Stéphanie Delbaere
email: stephanie.delbaere@univ-lille.fr

Dr Michinori Takeshita

Dr Stéphane Aloïse
email: stephane.aloise@univ-lille.fr

Dr Amit Kumar Tiwari
email: amit.tiwari.chem@gmail.com

Cyclization Dynamics and Competitive Processes of Photochromic Perfluorocyclopentene Dithienylethylene in Solution

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

Designing of the photochromic materials which convert reversibly its color upon light stimulation [START_REF] Crano | Organic Photochromic and Thermochromic Compounds[END_REF][START_REF] Feringa | Molecular Switches[END_REF][START_REF] Bouas-Laurent | Organic Photochromism[END_REF][START_REF] Tian | Photochromic Materials: Preparation, Properties and Applications[END_REF] have gained the attraction of material scientist due to its various applications in holography, [START_REF] Pu | Photochromic Diarylethene for Polarization Holographic Optical Recording[END_REF] information storage/processing, [START_REF] Andréasson | Storage and Processing of Information Using Molecules: The All-Photonic Approach with Simple and Multi-Photochromic Switches[END_REF] biosensors, [START_REF] Avella-Oliver | Towards Photochromic and Thermochromic Biosensing[END_REF][START_REF] Cheng | Recent Advances in the Use of Photochromic Dyes for Photocontrol in Biomedicine[END_REF] fluorescent probe, [START_REF] Metivier | Novel Fluorophores: Efficient Synthesis and Photophysical Properties[END_REF][START_REF] Metivier | A Highly Sensitive and Selective Fluorescent Molecular Sensor for Pb(II) Based on a Calix 4 Arene Bearing Four Dansyl Groups[END_REF] smart materials [START_REF] Goulet-Hanssens | Enlightening Materials with Photoswitches[END_REF][START_REF] Russew | Photoswitches: From Molecules to Materials[END_REF] etc. Among the different molecular switches necessary to elaborate such applications, [START_REF] Crano | Organic Photochromic and Thermochromic Compounds[END_REF][START_REF] Feringa | Molecular Switches[END_REF][START_REF] Bouas-Laurent | Organic Photochromism[END_REF][START_REF] Tian | Photochromic Materials: Preparation, Properties and Applications[END_REF] diarylethenes (DAEs) and more specifically dithienylethenes (DTEs) [START_REF] Irie | Diarylethenes for Memories and Switches[END_REF][START_REF] Irie | Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators[END_REF] are often used due to their good photochromic properties especially in terms of fatigue resistance. [START_REF] Herder | Improving the Fatigue Resistance of Diarylethene Switches[END_REF] DTEs in solution are having property to undergo efficient photocyclization (ϕcycl~0.2-0.5) between uncolored open form (OF) and colored closed form (CF) in presence of UV light, whereas photoreversion reactions are known to be less efficient ( ~0.01) when expose towards the visible light. [START_REF] Irie | Diarylethenes for Memories and Switches[END_REF][START_REF] Irie | Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators[END_REF] During the last decades, the quantum yield of carbon-carbon photoelectrocyclization limited to 0.5 was a subject of interest explained in term of coexistence of two OF isomers having parallel (P) and anti-parallel (AP) conformations in equal proportions but only the latter being photoactive. [START_REF] Uchida | Substitution Effect on the Coloration Quantum Yield of a Photochromic Bisbenzothienylethene[END_REF][START_REF] Morimitsu | Large Geometrical Structure Changes of Photochromic Diarylethenes upon Photoirradiation[END_REF] To overpass such limitation some researchers focused their efforts on exploring purposed-designed synthetic approach [START_REF] Takeshita | A Photochromic Thiophenophan-1-Ene[END_REF][START_REF] Takeshita | Syntheses and Photochromic Properties of Metacyclothiophenophan-1-Enes[END_REF][START_REF] Takeshita | Enantioselective Photochromic Reaction of a 2.2 Metacyclophan-1-Ene[END_REF][START_REF] Fukumoto | Intramolecular Hydrogen Bonding in a Triangular Dithiazolyl-Azaindole for Efficient Photoreactivity in Polar and Nonpolar Solvents[END_REF] or specific excited-state reactivity. [START_REF] Ishibashi | Multiphoton-Gated Cycloreversion Reactions of Photochromic Diarylethene Derivatives with Low Reaction Yields upon One-Photon Visible Excitation[END_REF][START_REF] Ishibashi | One-and Multi-Photon Cycloreversion Reaction Dynamics of Diarylethene Derivative with Asymmetrical Structure, as Revealed by Ultrafast Laser Spectroscopy[END_REF] Indeed, the rationalization of complex excited state mechanisms are highly desired to still improve photochromic performances and so considerable investigations have been devoted worldwide to explore the excited state topologies of DTEs (or DAEs) via advanced optical spectroscopies [START_REF] Kumpulainen | Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution[END_REF][START_REF] Sotome | Cyclization Reaction Dynamics of an Inverse Type Diarylethene Derivative as Revealed by Time-Resolved Absorption and Fluorescence Spectroscopies[END_REF][START_REF] Jarota | A Deeper Look into the Photocycloreversion of a Yellow Diarylethene Photoswitch: Why Is It so Fast?[END_REF][START_REF] Seo | Ring Closure Reaction Pathway of a Diarylethene in Solution Using Femtosecond Time-Resolved Fluorescence Spectra[END_REF] and/or computational chemistry. [START_REF] Nakamura | Theoretical Investigation on Photochromic Diarylethene: A Short Review[END_REF][START_REF] Perrier | Inverse versus Normal Dithienylethenes: Computational Investigation of the Photocyclization Reaction[END_REF][START_REF] Boggio-Pasqua | Can Diarylethene Photochromism Be Explained by a Reaction Path Alone? A CASSCF Study with Model MMVB Dynamics[END_REF] In this perspective, our group has actively investigated the spectrokinetic features on the series of bridged DAEs, [START_REF] Aloise | Bridged Photochromic Diarylethenes Investigated by Ultrafast Absorption Spectroscopy: Evidence for Two Distinct Photocyclization Pathways[END_REF] bridged DTEs [START_REF] Perrier | Inverse versus Normal Dithienylethenes: Computational Investigation of the Photocyclization Reaction[END_REF][START_REF] Hamdi | New Insights into the Photoswitching Mechanisms of Normal Dithienylethenes[END_REF][START_REF] Hamdi | Unraveling Ultrafast Dynamics of the Photoswitchable Bridged Dithienylethenes under Structural Constraints[END_REF] or DTEs dedicated to supramolecular chemistry [START_REF] Hamdi | Excited-State Dynamics of Dithienylethenes Functionalized for Self-Supramolecular Assembly[END_REF] DTE, hereafter) has become a photoswitch of reference, [START_REF] Jarota | A Deeper Look into the Photocycloreversion of a Yellow Diarylethene Photoswitch: Why Is It so Fast?[END_REF][START_REF] Irie | Photochromic Diarylethenes for Photonic Devices[END_REF][START_REF] Kobatake | Excited State Energy Migration and Photochromic Reaction in 1,2-Bis(2,4-Dimethyl-3-Thienyl)Perfluorocyclopentene Single Crystal[END_REF][START_REF] Irie | Photochromism of Dithienylethenes with Electron-Donating Substituents[END_REF][START_REF] Irie | Photochromism of Diarylethenes Having Thiophene Oligomers as the Aryl Groups[END_REF] reason why we reinvestigated its photochemistry together with a series of polyether bridged analogs. The main outcomes [START_REF] Hamdi | New Insights into the Photoswitching Mechanisms of Normal Dithienylethenes[END_REF] unidentified species (denoted as "X" hereafter) have been reported with variable statistical weight (0-50%) along with the two triplet states within µs regime.

In this paper, we decided to reinvestigate a smaller structural analogue of DTE without the two terminal phenyl groups, the 1,2bis(2,5-dimethyl-3-thienyl)-perfluorocyclopentene noticed in the following DMTPF. Such molecule has been studied in the past in crystalline phase [START_REF] Irie | Photochromic Diarylethenes for Photonic Devices[END_REF][START_REF] Kobatake | Excited State Energy Migration and Photochromic Reaction in 1,2-Bis(2,4-Dimethyl-3-Thienyl)Perfluorocyclopentene Single Crystal[END_REF] and in solution [START_REF] Irie | Photochromism of Dithienylethenes with Electron-Donating Substituents[END_REF][START_REF] Irie | Photochromism of Diarylethenes Having Thiophene Oligomers as the Aryl Groups[END_REF] with the main features to present a photocyclization more efficient in crystalline phase (φcycl=0.5) as compared to hexane solution (φcycl=0.21) while photoreversion yields are almost identical (φcycl=0.12) in both phases. Knowing that AP population was restricted to 17% in the solid state (compared to almost 50% in solution), the authors concluded for an excited state energy migration during photoconversion, the P conformer acting as a sensitizer.

So, focalizing our attention on photocyclization process, we have applied transient absorption spectroscopy on the microfemtosecond timescale in order to elucidate the excited states dynamics of DMTPF in solution with a systematic comparison with the previous study dealing with DTE molecule. We will pay attention on the possible existence of triplet or X species and discuss the previous results found in the literature under the light on our new results.

Results and Discussion

General photochemical features in solution.

The photochromism of DMTPF in chloroform is illustrated in Figure 1a through absorption spectra under continuous UV irradiation for less than 10 min. For uncoloured solution, OF has a peak at ∼ 235 nm. Upon UV irradiation with dramatically changes and has a peak at 351 nm and broad absorption band at 535 nm corresponding to the absorption of CF.

After 350 s irradiation time with continuous UV, the absorbance of CF does not increase further and a plateau is reached (see Figure 1b) which indicates the photo-stationary state (PSS).

However, with further UV irradiation, the solution turns to pale yellow and as seen in Figure 1c, a new band appears at ∼300 nm with a concomitant decrease of the band at 532 nm responsible for the decrease of the curve in Figure 1b mainly produced through 1 P species upon rapid interconversion.

Computational estimation of the potential barrier between 1 AP and 1 P will be published elsewhere. By the way, we will discuss this point below with the aid of transient spectroscopy. Indeed, in the following we will describe the ultrafast dynamics of this molecule knowing that the photocyclization mechanism and the competitive process (P photophysics) are very similar to DTE molecule. For that reason, we will keep the same notations compare to our first article (we also present the results in a short manner) but we will present the transient species following the natural deexcitation timescale, femtosecond/picosecond regime and then nanosecond regime for which the two molecules display some different features.

Excited States dynamics in the pico-femtosecond regime.

The early photophysics just after laser excitation is now investigated. the ESA peaking at 450 nm decreases with a characteristic time of 300 fs. This evolution is attributed to the relaxation of the FC region for P conformer ( S P → S ! P . Note that this spectral evolution was more difficult to detect for DTE, and can be related to the higher percent of P conformer population for DMTPF than for DTE (80% vs 52%). Finally, for pump-probe delay times higher , and P conformer S ! P → P " . Interestingly, the effect of introducing phenyl groups into the photochromic core does not affect the ISC of the AP species (1.2 ps vs 1.0 ps) contrary to the P species. This effect of structure can be nicely rationalized in terms of unpaired electrons well localized on the reactive carbons suggesting also a possible steric effect for the parallel species. Indeed, the faster ISC for DTE P conformer (55 ps instead of 80 ps) has to be related with torsional effect induced by the phenyl groups.

In summary, the ultrafast photocyclization from the FC region gives birth to the CF is in competition with the ISC of both AP and P conformers. The deactivation pathways of both triplet states are now under examination. Quenching rate constants (10 8 M -1 s -1 ) of AP, P and CF species are also indicated (see text). direct precursors of the by-product in scheme 4 and scheme 5 in ref [START_REF] Higashiguchi | Fatigue Mechanism of Photochromic 1,2-Bis(2,5-Dimethyl-3-Thienyl)Perfluorocyclopentene[END_REF] Such signal is insensitive to oxygen addition bringing evidence for a pure photocyclization route in the singlet manifold.

Excited state dynamics in the nano

Conclusion

In

Experimental Section

DMTPF was synthesized following already published protocol. [START_REF] Irie | Photochromism of Dithienylethenes with Electron-Donating Substituents[END_REF] Chloroform solvents (spectroscopic grade, Sigma-Aldrich) were used as received. The stationary absorption spectra

were measured with CARY 100bio absorption spectrometer. Rest in peace Olivier.

Keywords: Photochromism, Photophysics, Photochemistry, Transient Absorption, Ultrafast dynamics.

  Scheme 1. UV/Vis Photochromic reactions of DMTPF (R= H) and DTE (R=C6H5) between the OF and CF. Thermal Interconversion between AP and P conformers is indicated.

  were pointed as follow: (i) for the P* conformer, an Intersystem crossing (ISC) occurred (40-150 ps) to produce a first triplet state ( 3 P) after ultrafast relaxation toward S1 relaxed state. Later on the 3 P state relaxed within few tens of µs to the ground state; (ii) for the AP* conformer, the photocyclization reaction occur immediately after light absorption (100-200 fs) starting from the Franck-Condon (FC) region while the relaxed singlet state is populated in parallel way and evolves through an ISC reaction (1-40 ps) and generate a second triplet state, 3 AP with a lifetime depending on the structural constraints; (iii) interconversion between the two triplet states has been experimentally identified, e.g. 3 AP↔ 3 P only for some polyether bridged DTE (DTE-O6 in ref 33 ); (iv) an

Figure 1 .

 1 Figure 1. (a) Absorption spectral change of DMTPF in chloroform (50 µM) upon UV irradiation (302 nm) up to 10 minutes and (b) up to 1 hour (c) Absorbance evolution @ 532 nm with time for an UV irradiation starting at 60s after the beginning of the recording.

Table 2 .

 2 photodegradation. In the case of DMTPF, by analogy with previous work dealing on neighbouring molecules,[START_REF] Higashiguchi | Fatigue Mechanism of Photochromic 1,2-Bis(3-Thienyl)Perfluorocyclopentene[END_REF][START_REF] Higashiguchi | Fatigue Mechanism of Photochromic 1,2-Bis(2,5-Dimethyl-3-Thienyl)Perfluorocyclopentene[END_REF] such drastic spectral modifications are probably due to the well-known condensed rings by-product formation resulting from UV excitation of the CF (see inset of Figure1c). Such by-product species is well characterized by the band around 300 nm and the vanishing contribution in the visible region. This result indicates that the presence of the phenyl groups drastically increases the stability of the CF of DTE compared to DMTPF. Note that for the time-resolved studies here below, we have chosen experimental conditions in order to neglect as much as possible the by-product contamination. Some important photochemical parameters were measured in chloroform and gathered in Table1. The P:AP ratio for DMTPF has been determined based on 1 H-NMR measurements to be 80:20 at ambient temperature in d-chloroform (Figure S.2). For DTE, we have recover the same 52:48 ratio that was previously reported by Irie and co-workers.[START_REF] Irie | Photochromism of Dithienylethenes with Electron-Donating Substituents[END_REF] The main indicative results concern the proportion of P conformers from 52% for DTE to 80% for DMTPF. It immediately rationalizes the quantum yields of the cyclization for DMTPF (0.22) being more than 2 times lower compared to DTE (0.46) paralleling the decrease of AP population from 48 to 20%. Another important findings concerns the triplet quantum yields measured by the method of energy transfer with beta-carotene we already applied to DTE 32 indicated in the table 1. For DMTPF this value is as high as 0.75 while for DTE, it decreases down to 0.4. Actually, it is tempting to correlate the high triplet formation efficiency with the high proportion of parallel conformer. Indeed, a quantitative estimation for the intrinsic cyclization yield gives almost an unit value (≈0.22/0.2) indicating that almost all photoexcited AP is converted to CF with no population accumulated in the triplet state 3 AP. First, such efficient mechanism is consistent with a ring closing process from the Franck-Condon region in proximity with conical intersection for which competitive routes are not taken. Then, the apparent discrepancy between the high intrinsic cyclization yield and high triplet formation yield can be explained in term of 1 AP species

Figure 2 .

 2 Figure 2. Femto-picosecond time-resolved absorption spectra of DMTPF in chloroform (2-10 -4 M) using 320 nm excitation wavelength. Transient data are separated into 4 different temporal windows for improved clarity. All spectra are corrected from the GVD. The assignments of the different bands are indicated (see text).

  Figure 2 shows time-resolved transient absorption spectra obtained after the excitation of the DMTPF OF (for DTE, see Figure 6 of ref 32 ) in chloroform solution with a femtosecond 320 laser pulse, recorded in the 380-700 nm spectral range within four temporal windows (-1-0.25, 0.28-0.5, 0.52-1 and 2-500 ps). Global fitting of transient signal with four-exponential functions, convoluted with a Gaussian profile simulating the pump-probe correlation function are shown in supporting information (see Figure S.3). The characteristic times for DMTPF compared to DTE are represented in Table 3. As already said, because of similar results, the interpretations made for DMTPF data of will stick those made for DTE molecule in our previous work. The transient data results are summarized on Figure 4. For short delay times (-1-0.25 ps), just after laser excitation, the spectra present essentially two intense bands peaking at 385 nm and 450 nm, respectively. By analogy with our previous work, these bands are attributed to the excited state absorption (ESA) of S1 states on the Franck-Condon region (FC)for both AP and P conformers, i.e. S AP and S P . For the delay times between 0.28-0.5 ps on the second panel, we observed a decrease of the band peaking at 385 nm while, in the same time, the 550-750 nm edge is maintained constant. Indeed, in this spectral range, the vanishing signal is compensated in the same extent by a rising component which matches perfectly the CF visible band. The related characteristic time can thus be ascribed to the photocyclization of DMTPF (OF→CF) which takes place with a time constant of 90 fs. For the third panel (0.52-1 ps),

than 2

 2 ps, we observed a decrease of both transient signals with two different characteristic times 1.2 ps and 80 ps respectively attributed to the intersystem-crossing (ISC) of the AP conformer S ! AP → AP "

Figure 3 .

 3 Figure 3. (a) Transient absorption spectra of DMTPF in chloroform (5 10 -4 M) for different time delays after nanosecond laser excitation at 290 nm and (b) Kinetic traces measured at 440 nm for solutions initially saturated with N2 gas (blue line) or O2 gas (red line). (c) Stern-Volmer plots concerning experimental decays # $% of two triplet states and X species obtained from kinetics at 440 nm vs diene quencher concentration [Q].

  photodegradation during transient experiment as proved by the presence of the by-product absorption band after the nanosecond measurements as shown in Figure S.4 and Figure S.5. Therefore,it seems reasonable to correlate the X species with a by-product precursor being in the singlet state with probable biradical structure. Following the admitted mechanism would be that the X species is due to the re-excitation of the CF and the X species would be a biradical species either in singlet or triplet states. By the way, among the two propositions emitted byIrie et al., (the

Table 3 .

 3 Lifetimes (in µs) deduced from multi-exponential fitting of transient kinetics obtained from the laser-flash photolysis experiment (the relative contributions are given into parenthesis) for DMTPF and DTE (ref[START_REF] Hamdi | New Insights into the Photoswitching Mechanisms of Normal Dithienylethenes[END_REF] ).

Figure 4 .

 4 Figure 4. Photochemical processes (illustrations) including characteristic times derived according transient spectroscopy.

  Figure S.7.). All the transient spectra presented in this paper are GVD corrected according to the typical extrapolation method[START_REF] Nakayama | Construction of a Subpicosecond Double-Beam Laser[END_REF]45 (the temporal chirp over the white-light 350-800 nm range was about 400 fs). The characteristic times deduced from kinetics are obtained by fitting the data with the of a multi-exponential function convolved with a Gaussian pulse mimicking the pumpprobe cross-correlation function (FWHM at 180 fs).

Table 1 .

 1 Experimental photochromic parameters of DMTPF and DTE (ref[START_REF] Hamdi | New Insights into the Photoswitching Mechanisms of Normal Dithienylethenes[END_REF] ) in chloroform.

  ),

							height of this plateau being proportional to the photo induced CF.
		F	F			F	F
	F			F	F		F
	F			F	F		F
	Me	Me		Me	Me	Me	Me
	S	Me	S	S	Me	S
	Scheme 2. Structure with two unpaired electrons.
	we validate the structure with the two unpaired electrons far away
	compatible with a singlet nature. Such species would have a
	13 µs lifetime.
	At present time, this transient species responsible for
	the photodegradation is thought to originate from the CF excited
	state after UV irradiation. A second hypothesis is valuable as well
	involving the P conformer. Indeed, if we consider the relative
	contribution of triplet states species in the table 4, the results are
	instructive as well keeping in mind that the following discussion is
	3 AP is not delocalized along lateral phenyls implying probable
	similar optical properties for DMTPF; see Figure S.24 of ref 32 ) So,
	upon inspection of table 3, the quite similar relative amplitudes for
	the decays (at around 15-20%) suggest a similar 3 AP triplet
	population. In contrast, among the remaining 3 P population (75-
	80%), one can notice that 50% of the P conformers are turned
	into X species. Based on those results, we can emit a new
	hypothesis concerning the nature of the X species: rather than
	originating from CF reexcitation, the by-product reported for
	diarylethene could come from the triplet of the P conformer of the
	OF. As an evidence, advanced CASSCF/CASPT2 calculations
	already performed for model DTEs 29 are now desired to explore
	the pathways starting from either CF* or from P* species evolving
	trough the X singlet biradical structure to finally giving birth to the
	by-product molecule. Just as challenging, the interconversion
	between AP and P at both singlet and triplet manifold have to be
	included.
	Concerning the exact role of the triplet species in solid state
	DMTPF photochromism, although it exists constraints due to
	crystal lattice, we do not expect any photochromism from the
	triplet route ( 3 AP→CF) because such a route is not observed in
	solution unlike the polyether bridged DTEs analogs. Indeed, the
	nanosecond transient signal acquired @ 550 nm CF maximum
	absorption (see Figure S.6) is a plateau for the long time, the

qualitative. From NMR experiment, we know that the proportion of P conformer (see table

1

) is much higher for DMTPF compared to DTE. Furthermore, it is worth to precise that molar extinction coefficient for the triplet states are expected to be in the same order of magnitude for both molecules (for DTE, spin density of

Acknowledgements

Chevreul Institute (FR 2638), Ministère de l'Enseignement Supérieur et de la Recherche, Région Nord-

Photolysis System Utilizing a Femtosecond Ti:Sapphire Amplifiers (a Regenerative Amplifier and Two Double Passed Linear Amplifiers), and Measurements of the Transient Absorption Spectra by a Pump-Probe Method.

Rev Sci Instrum 1997, 68 (12), 4364-4371.


Daniel Chatroux
email: daniel.chatroux@cea.fr

Julien Chauvin

0 kA switch with MOSFET in avalanche for Lithium-ion battery short-circuit tests

CEA is a technological research center dedicated to nuclear and renewable energies. One department is dedicated to Lithium-ion batteries and fuel cells systems for transportation. Safety is one of the major issue for Lithium-ion batteries and this activity uses abuse test platform for research actions. This presentation focusses on the development of a specific high current switch to short-circuit lithium-ion accumulators or modules and to open the circuit after a 0.2 to 1s duration. The ON resistance is submilliohm, the energy to dissipate at turn-off is some tens of Joule because of the stray inductance and the high level of current. This realization use hundred MOSFETs in parallel in avalanche mode to dissipate the stray inductance energy. A second part of the paper presents an avalanche test schematic, a low cost handmade high voltage probe and some first results for avalanche safety area for different technologies of MOSFET.

1 Realization of a 10 kA 60 V switch for Lithium-ion battery short circuit tests

In CEA, in the abuse tests platforms, short-circuit of accumulator, modules or Lithium-ion battery pack is one of the standard abusive tests. With electromechanical parts a low resistance shortcircuit switch is possible to switch ON the short circuit but it can be open only after full discharge of the tested device. For specific characterization and research tests, it is necessary to switch ON the short circuit and to open the circuit after a specified duration between 0.2 and 1 s. Depending of the parasitic resistance of the Lithium-ion accumulator or module, the level of current is some kilo Amps. Specifications of the equipment are:  60 V maximum voltage for the tested component (accumulator or module),  3 kA nominal current, 10 kA maximum current,  < 1 milliohm ON resistance  0.2 to 1 s duration,  1.5 m cable length between tested devices and the switch.

The two main difficulties of the application are:

 The very low ON resistance to be negligible compared to the accumulator internal resistance,  The high level of energy stored in the cables to dissipate at switch off.

The technological choices of the development of our realization are:

 association of small MOSFET in TO220 package in parallel,  a design adapted to balance the current between the MOSFETs,  the dissipation of all the parasitic energy of the cables in the MOSFETs in parallel in avalanche mode, without active clamping or external clamping,  a fuse is in series with each MOSFET to open the circuit in case of the MOSFET failure.

Avalanche mode is the clamping of the voltage by the component due to the maximum electric field limit in the semiconductor. The component clamps the voltage, and the external circuit limits the current. This phenomena is used in "Zener" diode when the voltage is upper than 6V. A "Zener" diode with a specified voltage higher than 6V works in avalanche mode.

The Zener effect is a low voltage phenomenon, mainly lower than 6V. This clamping effect acts with a soft transition with leakage current under the clamping voltage. For higher voltage, in a "Zener diode" the clamping is due to avalanche effect with a good transition between none conducting and clamping voltage in avalanche mode, and low leakage current under the clamping voltage For 5 or 6 Volts voltage, both phenomenon coexist in the "Zener" diode. The advantage is a low temperature coefficient due to compensation of the opposite temperature coefficients of the two effects. In the 90's, for a nuclear research application, high voltage switches were designed with MOSFETs and diodes in avalanche mode. These components were not specified to be used in avalanche but some references were tested and proved a good behavior in avalanche mode [START_REF] Chatroux | Power switch: the standard small components strategy[END_REF]. Some realization are still used after twenty years. At PCIM, in 2020, another paper presents this point [START_REF] Chatroux | Small standard components strategy, twenty years later[END_REF]. These research works indicates that the good avalanche behavior is linked with the conception of the components. One supplier's reference is qualified by avalanche test, and individual test of each component is not necessary.

Another key point is that the avalanche limitation is maximum current level. The criteria for safety use is avalanche current and not energy as specified by some suppliers. Energy has only a thermal effect as switching losses, with maximum temperature to limit and cycle thermal fatigue.

Now some MOSFETs have some avalanche specifications. For example, the IPP023N10N5 is a 120A MOSFET with a specification for 100A avalanche current and 979mJ of energy for single pulse for this level of current. Some application notes are focus on avalanche current and not only on energy [START_REF]Power MOSFET Avalanche Design Guidelines[END_REF].

Nevertheless, avalanche is still considered as dangerous for components, and especially for components in parallel because of the risk of unbalancing of avalanche currents between the components.

For the switch realization, the avalanche was studied for three MOSFETs in parallel, to prove the current balancing efficiency between the MOSFET in parallel. The performances of the switch design for Lithium-ion accumulators and modules is conform to specifications. The global resistance of the entire current loop with all the wiring is 600 micro ohm. The energy stored in the cable is dissipated during avalanche mode in the MOSFETs in parallel with a good balancing.

As describe, for laboratory test, an electrochemical capacitor bank is used to provide the 10 kA current. After this laboratory test, the switch was tested in the abuse test platform on a Lithium-ion module. The current level was 6 kA. Because of higher wire length between module and switch for safety reason in case of fire, the level of current must be reduce to limit the stored energy. Through this part, we are going to see how make a silicon MOSFET transistor benchmark with low prototyping means. Most particularly, the realization and the bandwidth qualification of a handmade 5kΩ oscilloscope probe, which allows performing kilovolts measurements and low-rise time, with low cost and good performances compared to classics oscilloscope probes.

In a second part, we will also deal with an analysis of three different technology of power MOSFET during avalanche phase.

For the purposes of our analysis, we need a prototyping platform that allow us to manage the parameters in term of current and dissipated energy during the avalanche phase. In fact, the aim of the test is to reproduce avalanche phenomenon during opening the current on an inductive load. For this, the use of handmade air inductors of different values is used. The schema of the prototyping benchmark is simple and do not requires specific materials. With this test bench, the research work proves than some MOSFET of some suppliers have a good behavior in avalanche mode, and so avalanche mode can be used in a design, for example for high voltage switches [START_REF] Chatroux | Power switch: the standard small components strategy[END_REF].

For avalanche, energy is not the good criterion.

The limiting physic parameter is the avalanche current. Test of components of the same reference have the same level of maximum avalanche current for 200 ns and 2 µs avalanche duration. Energy is ten times higher. It is not the good parameter.

As the good parameter is the avalanche current level and not energy, the shape of the current has no impact, so a very simple test bench as opening the current of an air inductor as Fig. 8 is adapted.

MOSFET suppliers for avalanche MOSFET specification use this diagram. The power supply voltage is 50V for example. This voltage value is interesting because a safe low voltage laboratory power supply can be used. For the human protection, the dangerous zone is limited to the drain of the MOSFET and the connected components. Another advantage of this voltage is the possibility to use a high frequency low impedance probe for voltage measurement. In order to make such probe, it is essential to pay attention to electromagnetic compatibility aspects. Use coaxial cable with a good shielding recovery without useless length; minimize the distance between two resistors while maintaining sufficient insulation distances. Finally, make a precision measurement of your probe including an external 50Ω adapter. To qualify the frequency bandwidth of the probe and to optimize the design, a spectrum analyzer is a good tool. Because of the low impedance and the 50 Ohms output adaptation, the probe can be tested between the internal calibration oscillator and the input of the spectrum analyzer. As we can see on the picture above, the bandwidth of the probe is about 200 MHz. In addition to its great stability, the maximum avalanche current before breakage is higher than the datasheet specification. The device n°1 is capable of conducting during the avalanche phase a current of 630A, more than 1.3 x the maximal specified pulsed current (480A), 5x the nominal current (120A) and 6 x the specified avalanche current (100A).

-In comparison, the device n°2 (vertical engraving type MOSFET -CoolMOS), although avalanche specified, has a much unsafe avalanche behavior. Tests have shown that the device n°2 has instability during the avalanche phase and break easily. The figure 15 shows the maximal current in avalanche mode measured. The maximum avalanche current for this device is 27 A, compared to its 20.7 A nominal current and 20A specified avalanche current.

Regarding the third component, device n°3 (SiC MOSFET), its avalanche behavior is probably the better in terms of stability for a high voltage component. As shown on the figure 16, the avalanche phase represent a cut-off power about 143kW. The maximum avalanche current (97A) is as high as the specified pulse current (90A), 2.7 times the nominal current (36A). This component is avalanche energy specified for a test current of 22A.

Conclusion

This paper describes a specific high current switch with high wiring inductance energy dissipated in the hundred MOSFET in avalanche mode. This proves the good spreading of the avalanche current between the hundred MOSFET in parallel.

Because of the first key parameter for avalanche is the current and not the energy. Very simple test schematic with opening of the current of an inductor is adapted. For voltage measurement, we propose a low cost high frequency high voltage probe as well as the associated characterization test with a standard spectrum analyzer for CEM tests.

With our very easy test bench, some the maximum avalanche current of different MOSFET of different technologies is presented and compared with the safe operating area specification.

The 100 V tested MOSFET and the SiC one proves a very good of avalanche current and behavior in avalanche mode without oscillation risk. The 100 V MOSFET maximum avalanche current is 5 times the nominal current. The SiC one is 2.7 times the nominal current.

The model of the avalanche is a clamping diode in series with a resistance. For the 100 V MOSFET the dependence between the clamping voltage and the resistance with temperature is measured. The avalanche voltage coefficient is positive. The resistance value is nearly constant from 25°C to 150°C. These values are the inputs to model the impact of avalanche voltage dispersion on avalanche currents in the case of MOSFET in parallel.

5 References:

Fig. 1 :Fig. 2 :

 12 Fig. 1: Test of three MOSFETs in parallel

Fig. 3 :

 3 Fig. 3: Power stage and driver for 20 MOSFETs

Fig. 4 :

 4 Fig. 4: Twenty MOSFETs PCB For safety reasons, first tests of the switch uses an electrolytic capacitive bank and not real Lithium-ion accumulators or modules. The global switch is an association of 100 MOSFETs on five PCB in parallel. Copper busbar provides a low resistance and balances the MOSFET currents.

Fig. 5 :Fig. 6 :

 56 Fig. 5: PCB in parallel top view

Fig. 7 :

 7 Fig. 7: Current measurement qualification The final test on the capacitive bank is a maximum current of 10kA delivered by the capacitive bank on the voltage of 55V. The energy dissipated in the hundred MOSFETs in parallel is 48.8J.

Fig. 8 :

 8 Fig. 8: Benchmark schematicIn the 2000', the avalanche characterization[START_REF] Lausenaz | Component evaluation facility for high current (200A), short time (2µs) avalanche testing PCIM[END_REF] in CEA uses specific avalanche test benches based on high voltage power supply, a resistor and a high voltage switch. This test bench provides constant current pulses for a duration from 200 ns to 2 µs.

Fig. 9 :Fig. 10 :

 910 Fig. 9: Benchmark diagram for rectangular avalanche current shape

Fig. 11 :

 11 Fig.11: Benchmark realization On Fig.11, an electrolytic capacitor bank provides the current. Depending of the choose pulse duration, one or more air inductor are used to supply the current to the MOSFET.Regarding measurement tools, typical high frequency oscilloscope probes are adapted for voltages under 500 V. Above 500 V, voltage probe are specific ones and offers lower bandwidth. Low impedance handmade voltage probe are a known solution in pulse power application, mainly for high voltage, or for EMC tests. The impedance of the probe is 5 kohm for example. An additional capacitor can cut the continuous or the low frequency voltage level. The 5 kohm probe is a divider by 100 between a 4950 ohm resistor in series with a adapted 50 ohm cable and a 50 ohm charge on the oscilloscope. Because of the low impedance, and the transmission at the impedance of 50 ohm, a bandwidth of some 100 MHz is possible.

Fig. 12 :

 12 Fig.12: Handmade 5kΩ probe

Fig. 13 :

 13 Fig.13: Bandwidth of the 5kΩ probe With optimization of resistors value, distances between components, and length of the wiring, higher frequency bandwidth are accessible.

3

  Benchmark result: comparison of different MOSFET technologiesThere are various technologies for the internal conception of silicon transistors. Standard etching usually uses planar engraving, while manufacturers are innovating and offering different types of vertical etching. Lately, the reliability of SiC transistors also makes it a fullyfledged player on the market. But what are the performance in avalanche of these three types of component? What is the maximum avalanche current compared to the safe operating area of these three types of component? We have compared three references of different manufacturers: -Device (1) is a low voltage transistor use in the 10kA switch (Vds: 100V, Id: 120A) -Device (2) is a vertical etching transistor (CoolMOS, Vds: 650V, Id: 20.7A) -Device (3) is a silicon carbide transistor (Vds: 900V, Id: 36A) The result of these tests are the following: -As shown on the figure 14, the device N°1 (low voltage MOSFET) has excellent avalanche behavior.

Fig. 14 :

 14 Fig.14: Device n°1 safe operating area during avalanche

Fig. 15 :

 15 Fig.15: Device n°2 safe operating area during avalanche

Fig. 16 :

 16 Fig.16: Device n°3 safe operating area during avalanche The avalanche voltage depends on the current level and on the temperature. The figure 17 is the dependence of the avalanche voltage to the temperature for the 100V MOSFET (device n°1). The MOSFET is positioned on a controlled heating plate for soldering. The avalanche voltage increases from 0.04 V per °C. The equivalent internal resistance of avalanche is near constant from 50 milliohm at 20°C to 60 milliohm at 150°C. This value is 20 times more important as the RdsON of the MOSFET.

  Power avalanche diodes are used for clamping voltage or transient voltage limitation. Different commercial references exists like Transil® for example. The maximum voltage of theses diodes is 200V. Upper voltages exist but with chips in series in the same component.