Xavier Arnauld De Sartre

Justin Missaghieh-Poncet

Deep

Deep geothermal energy policies within the context

come

 Main unfavourable remarks :

• The technical capabilities of the industry and the maturity of the technology;

• The financial soundness of the company and insurance;

• The issue of risks: protection of the aquifer, induced seismicity, corrosion of the pipes, and swelling of the soil.

10 • The swiss case-study remains interesting…

Generate a debate on subsurface issues for energy transition?



  Context: Depoliticization of subsurface in France  Case study of geothermy France -Strasbourg  Insights of the seismicity in Strasbourg  Conclusions  Public debate • 3 favourable remarks, 3 favourable remarks with reservations, 885 unfavourable remarks

••

  Case study -Seismicity in Strasbourg: context Even like that, the projects went on  12 november 2019 : series of earthquakes  Hydrogeological tests to remove uncertainty  October 2020 : series of earthquakes (1.1, 2.7) → local media coverage  December 2020: new serie of earthquake, national media coverage  Prefecture will then suspend current geothermal project 11 Case study -Seismicity in Strasbourg: earthquakes The end of the project is due to earthquakes management Prefecture administrative investigation : lack of control and leadership: Not possible to reach a consensual expertise on the origins of seismicity • Drilled deeper than planned (5,000m of 4,200m) • Discrepancy in the sampling pressure (150 bars instead of 100 bars) Huge gap between intentions and achievements, that is quite common in France 13

Context -

Depoliticisation of sub-surface in France

 Politicization: the fact that a topic becomes a matter of concern for political actors 24/03/2022

 In France, a slow disapperence of subsurface from political debates:


Brunelle Marche
email: brunelle.marche@univ-lorraine.fr

Vincent Boly
email: vincent.boly@univ-lorraine.fr

Frédérique Mayer
email: frederique.mayer@univ-lorraine.fr

J Roland Ortt
email: j.r.ortt@tudelft.nl

A collaborative tool to design the product/supply chain couple in a high-tech environment: application to an electromagnetic sensor

Keywords: Supply chain, Innovation, Collaborative tools, Case Study

The emergence of innovative products involves several stakeholders and impacts the supply chain. Innovation is often a collective and open process. As the product is interlinked with its supply chain, companies involved in the innovation process have a strong interest in focusing on the product/supply chain pair rather than on the product alone. However, there are many collaborative tools dedicated to product design but they are not necessarily adapted to the design of the product/supply chain couple. Therefore, we suggest in this article that an instantiated supply chain model can help companies collaborate to design their product/supply chain couple. A case study illustrates our proposal and highlights the importance of digital tools in the innovation process.

I. INTRODUCTION

New products become more and more complex, involving an increased number of stakeholders. Consequently, innovation cannot always be driven by the company alone [START_REF] Boly | Ingénierie de l'innovation, 3è édition[END_REF], it is often a collective and open process. Indeed, the new product often requires new resources, a new mode of delivery, and a distribution of tasks of realization between several companies. Therefore, innovation occurs within wide collaborative systems between customers and suppliers [START_REF] Maniak | Shifting from co-development to coinnovation[END_REF] or between final customers and manufacturers [START_REF] Garel | La fabrique de l'innovation[END_REF]. Thus, it is important to have a vision of the sequence of stakeholders involved in the launching of an innovation [START_REF] Boly | Ingénierie de l'innovation, 3è édition[END_REF], i.e. a vision of the supply chain of the product.

The supply chain has to meet the specification of the new product and vice-versa. Indeed, the design of a supply chain depends on product characteristics [START_REF] Fisher | What Is the Right Supply Chain for Your Product?[END_REF]- [START_REF] Vonderembse | Designing supply chains: Towards theory development[END_REF], because the structure of the supply chain is influenced by the technical choices made to manufacture the product [START_REF] Blackhurst | PCDM: a decision support modeling methodology for supply chain, product and process design decisions[END_REF], [START_REF] Childerhouse | Analysis and design of focused demand chains[END_REF]. The product is both the cause and the effect of the supply chain. So, the product and the supply chain are interrelated. Hence in a context of innovation, collaboration between companies could facilitate the achievement of an "optimal" product/supply chain couple. This collaboration may help to consider the complexity inherent in the product/supply chain relationship (regulatory constraints, specific skills, available technology among others).

However, at present, many collaborative tools facilitate product design such as computer-aided design software or augmented reality [START_REF] Shen | Augmented reality for collaborative product design and development[END_REF], [START_REF] Morosi | Analysis of Co-Design Scenarios and Activities for the Development of A Spatial-Augmented Reality Design Platform[END_REF] or project management tools without being adapted to supply chain design. Thus, this article raises the following question: How to extend collaborative tools to the product/supply chain couple? This research shows how the instantiated supply chain model [START_REF] Marche | Innovative product's supply chain: How to model it[END_REF] can support collaboration between companies designing the product/supply chain couple. This article is structured as follows. Initially, existing theories related to our research work will be proposed. Then, the methodology is presented and the results are detailed. The model is described in detail. Finally, the analysis and conclusion of this research are presented.

II. RELATION TO EXISTING THEORIES AND WORK

A. Characterization of the studied system: the product and Supply Chain couple

This study integrates two closely related and interacting subjects: the product and the supply chain. The product is the result of a sequence of processes that also characterizes the supply chain. So, the product and the supply chain are linked by activities and tasks [START_REF] Meinadier | Le métier d'intégration de systèmes[END_REF] within processes involving specific skills, equipment, decisions and know-how Whatever the innovation is (product, service, processes, organization, way to sell…), the supply chain is impacted following the changes within the innovation. An innovation can lead to consequential changes requiring a partial or complete reconfiguration of the supply chain [START_REF] Marche | Overview of phenomena occurring in supply chains during the emergence of innovation[END_REF].

The choice of a supply chain is directly linked to the expected results in terms of value creation. However, each supply chain evolves in an environment with external factors (political, economic, socio-cultural, technological, ecological and legal) to be considered because they can change and have an impact on operations in the supply chain [START_REF] Marche | Overview of phenomena occurring in supply chains during the emergence of innovation[END_REF]. Furthermore, each supply chain is characterized by the exchange between its stakeholders, by the mastering of processes (supplying, manufacturing, distribution) and by the individual and Pre-print version, please cite as: collective decisions [START_REF] Fixson | Product architecture assessment: a tool to link product, process and supply chain design decisions[END_REF]. Thus, the functioning of the supply chain depends on the balance between all these components. So, there is a mutual dynamic influence between the product and the supply chain: the product and the supply chain form a couple and evolve in a complex environment.

The product/supply chain couple is a part of a larger Technology Innovation System, containing both social and technical elements , all of which need to be aligned: product price and performance, production, complementary product/service, stakeholders (subcontracting, supply, manufacture, distribution, sales…), customers, institutions, knowledge technology and application, financial, human and natural resources, economic, strategic or socio-cultural context, unexpected events among others [START_REF] Marche | From product design to supply chain design : Which methodologies for the upstream stages of innovation?[END_REF].

Thus, when designing the product/supply chain couple as part of the innovation process can help to consider the complex interactions with the environment [START_REF] Marche | From product design to supply chain design : Which methodologies for the upstream stages of innovation?[END_REF]. Indeed, the link between the product and the supply chain is possible through the processes that make it possible to produce the product and define the supply chain. This vision is complementary to a "Concurrent Engineering" (CE) approach of the 90s that is intended for "designing concurrently a product and its processes, such as: manufacturing, assembly, test, support and recycling" [START_REF] Winner | The Role of Concurrent Engineering in Weapons System Acquisition[END_REF]- [START_REF] Fine | Modeling tradeoffs in threedimensional concurrent engineering: a goal programming approach[END_REF]. Consequently, as multiple stakeholders are involved in the co-design of a product/supply chain tools are developed to collaboratively design and implement the product/supply chain.

B. Importance of the collaboration for the ajustment between Product and Supply Chain

Companies rely on R&D collaborations to access external sources of knowledge which can represent a substantial part of the complementary inputs necessary for the development of successful innovations [START_REF] Chesbrough | New Frontiers in Open Innovation[END_REF], [START_REF] Fey | External Sources of Knowledge, Governance Mode, and R&D Performance[END_REF]. R&D collaboration for innovation offers a number of substantive benefits, such as the possibility for mutual knowledge sharing, combining complementary skills with partners, scale economies in research, as well as the sharing of costs and risks [START_REF] Ahuja | The duality of collaboration: inducements and opportunities in the formation of interfirm linkages[END_REF], [START_REF] Belderbos | The antecedents of new R&D collaborations with different partner types: On the dynamics of past R&D collaboration and innovative performance[END_REF]. A large body of literature has shown that R&D collaboration can contribute to different outcomes such as innovation [START_REF] Rothaermel | Exploration and exploitation alliances in biotechnology: a system of new product development[END_REF]- [START_REF] Belderbos | Intertemporal patterns of R&D collaboration and innovative performance[END_REF], patenting [START_REF] Gittelman | Does Good Science Lead to Valuable Knowledge? Biotechnology Firms and the Evolutionary Logic of Citation Patterns[END_REF], organization growth [START_REF] Mitsuhashi | A matching theory of alliance formation and organizational success: Complementarity and compatibility[END_REF] and manufacturing procurement efficiency [START_REF] Gulati | Dependence Asymmetry and Joint Dependence in Interorganizational Relationships: Effects of Embeddedness on a Manufacturer's Performance in Procurement Relationships[END_REF]. There are differences between institutional (universities and research institutes), vertical (buyers and suppliers) and horizontal (competitors) R&D collaborations [START_REF] Belderbos | The antecedents of new R&D collaborations with different partner types: On the dynamics of past R&D collaboration and innovative performance[END_REF].

Universities and research institutes are important centres for the creation and dissemination of scientific knowledge [START_REF] Hemmert | The influence of institutional factors on the technology acquisition performance of high-tech firms: survey results from Germany and Japan[END_REF]. Suppliers have greater expertise and more comprehensive knowledge regarding the parts and components which may be critical to a company's new product development [START_REF] Tsai | Collaborative networks and product innovation performance: Toward a contingency perspective[END_REF].

Customers can help to identify market opportunities for technology development but also reduce the likelihood of poor design in the early stages of development [START_REF] Tsai | Collaborative networks and product innovation performance: Toward a contingency perspective[END_REF]. Furthermore, involving customers can help to gain new ideas about solutions [START_REF] Von | Creating breakthroughs at 3M[END_REF] and to identify market trends, thereby increasing the chances of new product development and success [START_REF] Tsai | Collaborative networks and product innovation performance: Toward a contingency perspective[END_REF]. Finally, competitors can share technological knowledge and skills in order to produce a synergistic effect on solving common problems outside the competitor's area of influence [START_REF] Tether | Who co-operates for innovation, and why: An empirical analysis[END_REF].

In a co-design approach for the product/supply chain couple, vertical collaborations are particularly interesting because the stakeholders are likely to participate in the industrialisation of the product. As a result, vertical collaborations can be at the origin of the future supply chain of the innovative product.

Many tools have been developed to facilitate collaboration between several stakeholders, among others: (i) Digital tools to facilitate the exchange of information such as computer-aided design software or augmented reality [START_REF] Shen | Augmented reality for collaborative product design and development[END_REF], [START_REF] Morosi | Analysis of Co-Design Scenarios and Activities for the Development of A Spatial-Augmented Reality Design Platform[END_REF]; (ii) Organizational tools or methodologies to facilitate project management [START_REF] Brocke | Managing collaborative research projects: A synthesis of project management literature and directives for future research[END_REF], [START_REF] Kerzner | Project Management 2.0: Leveraging Tools, Distributed Collaboration, and Metrics for Project Success[END_REF] such as Enterprise Resource Planning tools [START_REF] Aloini | Benefits and barriers of social/collaborative ERP systems: a state of the art and research agenda[END_REF], collaborative platforms or scrum methods [START_REF] Mollahoseini Ardakani | Adapting the scrum methodology for establishing the dynamic interorganizational collaboration[END_REF].

However, there is a lack of strategic approaches characterizing collaboration and addressing important questions such as Why collaborate? How to collaborate? Under what conditions? How long?

So, characterizing collaboration prior to launch and defining its role in the future supply chain (i.e. anticipating its evolution) can be useful to increase the chances of success of the product on the market.

C. An instantiated supply chain model as a collaborative tool

Product design is a complex phenomenon that depends on the interaction between many stakeholders. Design research aims to understand what drives the improvement of the practice of product design in order to increase the chances of producing a successful product [START_REF] Blessing | A design research methodology[END_REF], [START_REF] Chakrabarti | A Review of Theories and Models of Design[END_REF]. Therefore, human interactions are an important part of the design process that contain main uncertainties [START_REF] Swann | Action Research and the Practice of Design[END_REF], [START_REF] Muratovski | Research for Designers: A Guide to Methods and Practice[END_REF].

Collaboration results from these human interactions. Common models can help describe and implement collaboration by providing a common vision of the object to be created. However, in our case, the object to create is the product/supply chain couple. This couple is characterized by common descriptive elements such as processes, skills and activities. Thus, a collaboration set up before the launch of the new product contributes to the simultaneous design of the product and the supply chain.

However, although there are international standards and reference models for collaboration such as SCOR for supply chain management or ISO 10303-21 STEP for product information exchange, there is no collaboration model in the literature leading to the design of the product/supply chain couple. Based on a literature review and an observation campaign, Marche et al [START_REF] Marche | Innovative product's supply chain: How to model it[END_REF] created an instantiated supply chain model to detail the supply chain architecture of a product taking into account stakeholders, flows between stakeholders, processes and value at each step of the supply chain, one step being represented by a process. This model is based on system engineering to represent the product/supply chain couple and its complexity and the relationships between the different constitutive elements [START_REF] Bonjour | Pilotage des activités de conception par l'Ingénierie Système (IS)[END_REF] necessary for a coherent description of the studied couple. In the context of product and supply chain development, this approach breaks down the complex system into different layers, identifies and organizes activities and controls the information needed to develop the product and supply chain [START_REF] Bonjour | Pilotage des activités de conception par l'Ingénierie Système (IS)[END_REF]. To transmit the information, the use of modeling language, standardized formalism, is required. UML are discursive languages where information is communicated as text [START_REF] Durand | La systémique, 10e édition mise à jour[END_REF]. The UML language is a standardized visual specification language for modeling objects that includes a graphical notation used to create an abstract model of a system. It is based on a decomposition of the model into "views", represented in diagrams. Each view is dedicated to the representation of a particular aspect of the system: requirements, structures, behaviors [START_REF] Rochet | Formalization of System Engineering Processes : Proposal of a method to adapt generic processes to different application contexts[END_REF]. In addition, MEGA International Software is a software solution for system modeling. It facilitates process definition, control of operations. To represent a model, the system engineering approach uses entities linked by relationships. Cardinalities and constraints give information to get as close as possible to reality.

Pre-print version

Within the model, each stakeholder has a role: producer, influence, resources or specialist. The producer stakeholders are involved in a process using skills, resources and decisions to realize a product or a part of the product contributing to the flows within the supply chain. Each stakeholder is connected to the other ones through flows: financial flow, material flow or information flow. A process can be decomposed into at least one activity generating value [START_REF] Marche | Innovative product's supply chain: How to model it[END_REF].

Therefore, the supply chain is described as many times as there are processes. III. RESEARCH APPROACH The empirical approach considers that knowledge is constructed from the observation of phenomena, it is a discovery of the world through experience [START_REF] Bulinge | Maîtriser l'information stratégique : Méthodes et techniques d'analyse[END_REF]. It contributes to the constructivist paradigm which considers that reality is constructed and that it is self-organized around a finality [START_REF] Bulinge | Maîtriser l'information stratégique : Méthodes et techniques d'analyse[END_REF]. In a constructivist approach, observation is a phase in the progressive construction of a research project, and the definition of new representations [START_REF] Boly | Processus d'innovation: contribution à la modélisation et approches méthodologiques[END_REF], [START_REF] Le Moigne | La théorie du système général : Théorie de la modélisation[END_REF]. To collect and exploit data about the innovative product/supply chain couple, a case study approach was used.

A. Aim of the study

In this empirical study, we seek to validate the use of the instantiated supply chain model as a tool to describe and implement a collaboration. We mainly focus on the vertical collaboration between two companies involved in the development and the launch of an electromagnetic sensor. This case study is chosen for the following reasons: (i) the product is obtained as the result of an inter-company collaboration; (ii) the collaboration evolves throughout the innovation process and product life cycle; (iii) the product and the supply chain are codesigned.

From the early stages of the project, collaboration was important: the preferred concept for the new product required concurrent engineering from the beginning of the collaboration and contributed to its sustainability. Moreover, in this case, it can be said that collaboration is not limited to the development of a new product: the two main stakeholders are also willing to rely on each other to create new markets in the medium and long term. Indeed, based on their expertise and knowledge of new markets, these two companies are seeking to enrich their technological systems and business models. The use of the instantiated supply chain model seems consistent with a constructivist approach because: (i) it facilitates decision-making; (ii) it is reproducible, adapts to different situations and makes it possible to characterize situations.

B. Methodology 1) Data collection

The research includes a collection of data compiled throughout the innovation process through interviews and work sessions. The data highlight how product design impacts the relationships and collaboration between companies in the supply chain. The instantiated supply chain model was used to collect data from the two companies studied. Indeed, the model enables to translate product design data into supply chain design data. At each stage of the supply chain, the model must be completed to accurately describe how the supply chain works and to consider the form of possible collaboration during the product launch.

2) Data processing

During data processing, several dimensions are considered such as skills, processes, stakeholders, added value and equipment. This step aims to identify the processes and/or activities that could enrich collaboration.

In order to describe scenarios of a supply chain for the product, a detailed description of each process involved in the production of the future product was proposed thanks to the instantiated supply chain model. In this article, the process highlighting the outcome of the collaboration will be detailed. This supply chain study has several advantages: (i) it describes in detail on which elements (processes, equipment, skills) possible collaborations are based; (ii) it considers possible collaborations based on the value (financial, strategic for example) generated within the supply chain. The model is completed as follows: (i) the product has been decomposed into modules and components; (ii) each module or component has been decomposed into processes; (iii) activities have been assigned to each process; (iv) skills, resources and decisions were assigned to each activity; (v) actors have been defined according to the skills and resources used to carry out the activities (related activities assigned to actors are seen as tasks); (vi) the generated value of the assembly operation has been determined.

Using the instantiated supply chain model, the functioning of the supply chain is analysed to visualize when collaboration can emerge. It can be based on a specific combination of skills from both companies, on the sharing of equipment or specific knowhow or on high value-added activities for both partners.

3) Result from data processing

Following the data processing, the partners can decide on the type, intensity and timing of collaboration strategies.

IV. FINDINGS Firstly, following a presentation of the case study, the instantiated supply chain model will be used to illustrate its interest in setting up a collaboration between two companies. Secondly, we will look at the collaborative strategy favoured by the two companies within the framework of this project.

A. Factual description of the innovative project development 1) Brief description of the product

The innovative product is an electromagnetic sensor integrated into ABS technology. The Automatic Break System (ABS) is used in the automotive industry. It consists of a magnet and a sensor, sensitive to the external magnetic field to vary the electrical resistance of the assembly. The product is a so-called active technology, consisting of various separate components: a ball bearing, an encoded seal, a magnetic sensor and a sensor body. The innovation is at the level of magnetic sensor, based on a magneto-resistive element and an integrated electronic part.

2) Origin of the project

Company A is at the origin of this project, it is a company specializing in ball bearings for the automotive industry. It designs and develops different ranges of bearings, encoders and seals for vehicles. These products need to be combined with sensors to provide data to drivers. A market study highlighted that the demand for magnetic field sensors, reading heads and so-called "active" applications are growing rapidly. Indeed, it is used in many fields of applications such as automotive, household appliances or micro computing. More than 100 million sensors are used in ABS systems in vehicles (25 million vehicles being equipped on each wheel). Based on its current production and by considering that it is outcompeting alternative systems and the company is not challenged by another company, this enables company A to make fairly accurate production forecasts: a daily mass production is envisaged. The research and development focus on a Tunnel Magneto Resistance sensor and involve two stakeholders in addition to company A, selected according to their expertise: (i) Jean Lamour Institute (University of Lorraine) is an academic research laboratory specialized in material sciences. It is in charge of the scientific supervision; (ii) one company, called Company X, focuses on the specifications of the sensitive elements and provides qualified personnel and infrastructure. They have been selected in particular for their design and manufacturing capacities. The company X will be involved in the industrialization of the future sensor.

3) Description of the collaboration during the innovation process

This project is the result of the desire of company A and the Jean Lamour Institute to industrially develop the magnetoresistance with a tunnel effect (TMR), controlled in the laboratory. The industrial stakeholder, i.e. company A, has developed a network of R&D partners to develop the new product. Company A being in charge of the manufacture of ball bearings, Company X has joined this network in order to develop the product/process specifications. The choice of Company X was based on several criteria: (i) existing facilities and skilled staff; (ii) experience in thin magnetic layers deposition and process; (iii) industrialization solution for the future sensor; (iv) partner already present and recognized in the sensor market. The product design was based on a strong collaboration between these three stakeholders reinforced by the use of a common platform to share all data. Both the Jean Lamour Institute and Company X give their expertise to the project. Note that unlike Company A, Company X was not involved in an automotive supply chain prior to this project. There was even a technological academic/industry transfer between the Jean Lamour Institute and Company X.

A supply chain analysis was requested from the ERPI Laboratory (secondary stakeholder not involved in product development) by the Jean Lamour Institute for three reasons: (i) study and model the future supply chain of ABS technology; (ii) study the role and future relationships between the stakeholders involved in the development project; (iii) reflect on the collaborative strategy to be put in place to facilitate the industrialization of the product. The functioning between the main stakeholders of the project are described in figure 1

B. Factual description of the supply chain design decisions

The organisation of the supply chain is the result of decisions taken before the innovation process.

Company A manages the manufacture of the ball bearing integrating magnetic encoders. From the outset of the project, company A excluded in-house production of the sensor in order to avoid investments in facilities, machines and skills that were too high. As a result, it preferred to subcontract this part of the technology by collaborating with company X with the capacity to implement a manufacturing process linked to the structure of the read-head layers. Thus, the preferred manufacturing process influenced the choice of the subcontractor, i.e. company X. The co-design of the sensor leads to the filing of a patent and common management of associated licenses which link Company A and Company X for at least five years. The figure 2 represents the material results of the collaboration between companies A and X.

To better understand the role of the instantiated supply chain model, we focused on the "thermocompression assembly" process because the ABS technology is the result of the assembly of TMR Read Head and a Flex circuit by thermocompression. The thermocompression assembly process is a necessary step to obtain the active sensor. The active sensor is composed of several components who are need to be manufactured prior to assembly. To achieve this, three stakeholders have to work in a coordinated manner: company A, the read-head manufacturer (company X) and the electronic components supplier, the latter not being an essential stakeholder in the development of the innovative product given the availability of electronic components on the market. Company A implements this process by means of the following activities: (i) reception of the necessary components (TMR Read-Head, Flex circuit equipped with differential amplifiers, electronic components and copper threads); (ii) positioning the read-head on the flex circuit; (iii) assembly of the read-head and flex circuit by thermocompression on copper threads; (iv) check component operations.

Thus, the implementation of this process relies on the company's skills in inventory and production management, assembly, thermocompression equipment mastery, equipment calibration or metrology. The production of the active sensor follows a production order for a certain product volume. Figure 3 shows the application of the model to the example "thermocompression assembly process".

In a context of innovation and when stakeholders desire to create sustainable collaborations, the instantiated supply chain model can be considered as the functional specifications of collaboration, highlighting the foundations on which it is based, clarifying the role and technical contributions of each stakeholder. It is used as a collaborative design tool.

C. Study of the evolution of the collaboration

In an innovation context, collaboration between different stakeholders may evolve, as may the supply chain [START_REF] Vonderembse | Designing supply chains: Towards theory development[END_REF]. The intensity of industrial collaboration may vary depending on the context. In our case, we note that R&D collaboration has led to a privileged relationship between stakeholders when the product is introduced to the market and evolves according to the product life cycle: the collaboration is gradually established and stems from the strategy. At the beginning of the project, Company X worked jointly with the Jean Lamour Institute to develop technical innovation. The collaboration between Company A and X was minimal. As technical decisions were made within the project where industrialization became possible, collaboration increased. When the product was launched on the market, Company A and X jointly filed a patent on the innovative product obtained, the result of their collaboration.

The industrialisation of the product (market launch, prediffusion phase and mass production) has led to several business guidelines: (i) companies A and X can sell the TMR sensor and/or use existing or new patented solutions for any customer in their own field or in "other fields"; (ii) company A can purchase the TMR sensing elements exclusively from Company X. These business guidelines are valid for 5 years. Beyond these 5 years, business guidelines evolve: (i) companies A and X can sell TMR sensor sensors and/or use existing or new patented solutions for any customer in their own field or in "other fields"; (ii) company A can purchase TMR sensing elements from any other manufacturer. Company X will allow Company A to use secondary sources for production with cost compensation for the transfer of processes and know-how; (iii) if third parties apply for a manufacturing licence, Companies A and X must agree on such a licence. Licensing costs are shared between companies A and X according to the number of patents each party contributes.

These business guidelines mark an evolution in collaboration around the industrialized product.

Based on our study [START_REF] Marche | Innovative product's supply chain: How to model it[END_REF], [START_REF] Marche | From product design to supply chain design : Which methodologies for the upstream stages of innovation?[END_REF], the evolution could be represented as follows in figure 4 . At the moment, the product is still in a growth phase. Two solutions are possible for the future:

1. Company A chooses new subcontractors and gradually orchestrates the end of the collaboration with company X;

2. Company A chooses to keep Company X as a subcontractor.

Other scenarios are possible, including a compromise that would consist in keeping Company X as a subcontractor while using other companies in parallel. Describing the supply chain and therefore the collaboration requires a large amount of information to be considered in order to make the most appropriate decisions for the context and strategy of companies. The instantiated supply chain model can be used throughout the product life cycle to describe the relationships between companies. Then, modelling provides a framework for future collaboration: it highlights the contributions of each stakeholder in terms of skills, resources, it stipulates the tasks performed by each stakeholder, the value generated and thus facilitates contractualization between the stakeholders. Its use is useful when making critical decisions such as launching the project, launching the product on the market or ending the collaboration because it reflects the impact of these decisions on the supply chain. For example, the disappearance of a major stakeholder implies changes that need to be compensated to ensure that the production of the product will always be effective. The instantiated model therefore provides information on the characteristics of the stakeholders to be integrated.

Like the model, collaboration is built phase by phase. Thus, the instantiated model describing the supply chain at time t reveals the technical and organizational evolutions of the planned collaborations. The business guidelines appear in the "decisions" box of the model. Thus, by superimposing each model of the same process at a given time in the supply chain, it is possible to study the evolution of collaboration. Collaboration and its evolution over time are the result of the strategy of the companies involved: it goes beyond the boundaries of the individual company. Thus, strategic decisions impact the supply chain of the product and the functioning of stakeholders. There are therefore organizational, operational and temporal repercussions.

V. CONCLUSION

The results presented here highlight the importance of a good knowledge of what characterizes collaboration between two or more companies: Which actors? Which processes? What decisions? What types of flows? What added value? However, this process is time-consuming and requires a significant amount of information that is not always easy to collect and capitalize. Indeed, the use of this model requires to describe the collaboration at each moment. Collaboration can be considered as the beginning of the supply chain of a new innovative product. In the literature, collaboration is addressed in several ways: (i) a legal contractual aspect based on trust and the contractualization of relationships. Many technologies such as blockchain support this aspect by guaranteeing the transparency of exchanges; (ii) a flow aspect of the supply chain based on logistics and the exchange of products and information between the various partners. This aspect is considered in supply chain management; (iii) an organizational aspect emphasizing the importance of network configuration to create strong and sustainable relationships. However, the literature reveals a lack of information regarding the implementation of these collaborations. Consequently, this article proposes an engineering approach as a functional approach to support companies in the implementation of collaborative relationships in a context of innovation. The use of the instantiated supply chain model has highlighted the logical link between collaboration and supply chain, as collaboration can lead to the initiation of a supply chain. In order to encourage and support companies to collaborate with each other, it seems particularly appropriate to describe collaboration from a functional point of view and to facilitate decision-making and to anticipate the usage scenarios in order to reduce the gap between "perceived needs and real needs". Two perspectives are then possible. First, the development of a database seems judicious in order to collect the processes, skills, technologies mobilized in the supply chain supporting the collaboration. The instantiated supply chain model presented in this document can serve as a specification in the design of this database, i.e. at the conceptual level, for several reasons: (i) It gathers all types of data to be integrated into the database (processes, activities, type of stakeholders, skills, equipment, decisions and so on). This information will be used to determine the tables and fields present in the database; (ii) it offers a visual representation of our database. Each box in the diagram represents a table in the database; (iii) It highlights the relationships between the tables. Cardinality plays an important role. For example, a process requires several activities.

Secondly, block chains could prove to be an interesting solution for processing this information on a large scale. It is a technology for storing and transmitting information by being transparent, secure and without a control organ [START_REF] Badinet | La blockchain décryptée[END_REF]. In concrete terms, a block chain is a forgery-proof digital database on which all exchanges between its users since its creation are recorded. Unlike a traditional database, a block chain is a distributed database [START_REF] Badinet | La blockchain décryptée[END_REF]. It can be used as an information collection network shared between nodes that are all known and individually identified [START_REF] Hug | Un nouvel outil numérique pour la fiabilisation des supply chains: la blockchain[END_REF], i.e. stakeholders involved in the collaboration (suppliers, manufacturing companies, distributors and even institutional among others). This technology is interesting because it considers the legal, flow and organizational aspects while supporting the functional aspect of collaboration, as the instantiated supply chain model can serve as the specifications for the architecture of the future blockchain by: (i) guaranteeing the transparency of relations; (ii) storing a lot of relevant information for the companies involved (product data, source of raw materials, skills used, added value, etc.); (iii) highlighting the relationships between different companies; (iv) tracking the processes used to design products. Thus, the collaboration is simplified by improving information transfer between the stakeholders and by fostering collective intelligence through a better distribution of resources and by distributing more fairly and transparently the value generated by the collaboration.

  , please cite as: Marche, B., Boly, V., Mayer, F., & Ortt, J. R. (2019). A collaborative tool to design the product/supply chain couple in a high-tech environment: Application to an electromagnetic sensor. In 2019 IEEE International Conference on Engineering, Technology and Innovation (ICE/ITMC) (pp. 1-9). IEEE. 10.1109/ICE.2019.8792625

  Pre-print version, please cite as: Marche, B., Boly, V., Mayer, F., & Ortt, J. R. (2019). A collaborative tool to design the product/supply chain couple in a high-tech environment: Application to an electromagnetic sensor. In 2019 IEEE International Conference on Engineering, Technology and Innovation (ICE/ITMC) (pp. 1-9). IEEE. 10.1109/ICE.2019.8792625

  . Pre-print version, please cite as: Marche, B., Boly, V., Mayer, F., & Ortt, J. R. (2019). A collaborative tool to design the product/supply chain couple in a high-tech environment: Application to an electromagnetic sensor. In 2019 IEEE International Conference on Engineering, Technology and Innovation (ICE/ITMC) (pp. 1-9). IEEE. 10.1109/ICE.2019.8792625

Fig 1 .

 1 Fig 1. Overview of the functioning between the main stakeholders during the development of the project

Fig 2 .

 2 Fig 2. Material results of the collaboration between companies A and X

Fig 3 .

 3 Fig 3.

  version, please cite as: Marche, B., Boly, V., Mayer, F., & Ortt, J. R. (2019). A collaborative tool to design the product/supply chain couple in a high-tech environment: Application to an electromagnetic sensor. In 2019 IEEE International Conference on Engineering, Technology and Innovation (ICE/ITMC) (pp. 1-9). IEEE. 10.1109/ICE.2019.8792625

Fig 4 .

 4 Fig 4. Evolution of the collaboration following the product evolution (our research)


Anna Windmüller
email: a.windmueller@fz-juelich.de

Tatiana Renzi

Hans Kungl

Svitlana Taranenko

Emmanuelle Suard

François Fauth

Mathieu Duttine

Chih-Long Tsai

Yasin Ruoheng Sun

Emre Durmus

Yasin Emre Durmus

Hermann Tempel

Peter Jakes

Christian Masquelier

Rüdiger-A Eichel

Laurence Croguennec

Helmut Ehrenberg

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Current approaches to enhance the volumetric and gravimetric energy density of positive electrodes for Li-ion batteries (LIB) follow two lines of development. One is to enhance the specific capacities of the used electrode materials and the other is to increase their working voltages. [1][2][3][4][5] In the materials class of Li-Mn spinels, higher voltages are achieved by substituting Mn with transition metals like Ni, Fe or Co. The redox potentials associated to these cations in spinels are around 5 V vs. Li/Li + . 3,6,7 Research has been mostly focused on LiNi 0.5 Mn 1.5 O 4 , where a two-electron process involving the Ni 4+/2+ redox couple provides a cell voltage of 4.7 V vs. Li/Li + , making available a specific capacity of 148 mAh/g at high voltage. 2 Attractive alternatives to LiNi 0.5 Mn 1.5 O 4 are LiFe x Mn 2-x O 4 spinels, as Fe is non-toxic and more sustainable and low-cost than Ni. Furthermore, substituting Mn by Fe results in even higher voltages (~5.1 V vs. Li/Li + ). 5,[8][9][10] However, a high degree of substitution of Fe for Mn (ideally beyond x = 0.5) has to be achieved to profit from the high voltage as the electrochemically active redox couple Fe 4+/3+ provides a one-electron process only. 8,9 LiFe x Mn 2-x O 4 crystallizes in the Fd-3m space group, with Li occupying the tetrahedral site (8a Wyckoff position) and the transition metals (TM) occupying the octahedral site (16d Wyckoff position). 10,11 This so-called normal spinel is the preferred structure for most of the known high voltage spinels. 2 However, the ligand field of the high spin Fe 3+ ion gives no energetic preference for octahedral or tetrahedral oxygen coordination [START_REF] Burns | Mineralogical Applications of Crystal Field Theory[END_REF] , thus Fe can partially occupy the tetrahedral 8a (Li) site, while Li partially occupies the octahedral 16d (TM) site, especially for compositions with x > 0.5 in LiFe x Mn 2-x O 4 . [START_REF] Gracia | [END_REF][14][15] Exclusive occupancy of the tetrahedral site by Fe would yield the so-called inverse spinel. The onset of spinel inversion was identified at x = 0.57 and a gradual increase of Fe localization in the tetrahedral 8a site was reported with increasing of x in LiFe x Mn 2-x O 4 . [START_REF] Gracia | [END_REF]16 In the LiFe x Mn 2-x O 4 p w x ≤ 0.5 olution between LiMn 3+ Mn 4+ O 4 (x = 0) and LiFe 0.5 3+ Mn 0.5 3+ Mn 4+ O 4 (x = 0.5) is established, with Mn being substituted by Fe on the octahedral 16d site. [START_REF] Gracia | [END_REF]16,17 With increasing Fe substitution for Mn, the lattice parameter is reported to increase linearly. [START_REF] Gracia | [END_REF]14,[16][17][18][19][START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF][21][22] However, the increase in lattice parameter cannot be explained by the isovalent substitution of high spin Mn 3+ by high spin Fe 3+ , as they exhibit the same ionic radius for the octahedral coordination (0.645 Å). 23 Therefore, different hypothesis to explain the increase in lattice parameter are postulated: Talik et al. suggest Fe 3+ substitution for Mn 4+ or Mn 3+ in the low spin state, as they exhibit smaller ionic radii. [START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF] Whereas, Tsuji et al. and Gracia et al. found a hint to the existence of a small fraction of Fe 4+ via Mössbauer spectroscopy. [START_REF] Gracia | [END_REF]17 The existence of Fe 4+ would explain the increase of lattice parameters due to the substitution of Fe 4+ for Mn 4+ . [START_REF] Gracia | [END_REF]17 However, this Mössbauer signal has been center of debates in literature and was also assigned to Fe 3+ in a tetrahedral environment 16,19,22 or Fe 3+ in an oxygen deficient octahedral environment. 21 Up to now, the reason for the increasing lattice parameters in LiFe x Mn 2-x O 4 high voltage spinels remains as an open question.

First reports on the high voltage performance of LiFe x Mn 2-x O 4 spinel date back to 1998 by Kawai et al. 9 They reported a total specific capacity of 125 mAh/g encompassing a high voltage capacity (> 4.5 V vs. Li/Li + ) of more than 40 mAh/g after charging the battery to 5.3 V vs. Li/Li + . After 37 cycles, the total discharge capacity was reduced to less than 90 mAh/g. Several follow up studies focused on improving the specific capacity and cycling stability by optimizing the synthesis and processing conditions for LiFe 0.5 Mn 1.5 O 4 , 8,16,[24][25][26][27][28][29][30] as well as for the series of LiFe x Mn 2-x O 4 spinels. 7, 10, 14, 16-21, 27, 31-33 Despite the broad variety of different synthesis and processing conditions, such as precursors, synthesis temperatures and atmospheres, number of synthesis steps and electrode fabrication, three reasons can be identified for the specific capacity fading and low cycling stabilities: i) powder morphology and surface area 8,29,[START_REF] Kuppan | Physical chemistry chemical physics[END_REF] , ii) amount of Fe in LiFe x Mn 2-x O 4 17, 21 , and iii) upper charging cut-off voltage 25,29 . All three parameters determine the exposure of the LiFe x Mn 2-x O 4 electrode material at the interface with the organic electrolyte at high voltage. It is generally agreed that the operation of high voltage positive electrode materials -well beyond the electrochemical stability window of the commonly used liquid electrolytes 8,35,36 -causes fast capacity fading due to electrolyte oxidation. 3,37 Recently, the tremendous effort in research and development for high voltage stable electrolytes 38,39 might bring forward compatible electrode-electrolyte combinations for realizing high voltage LIB in the near future.

In the present work, a series of LiFe x Mn 2-x O 4 spinels with x = 0.2 to 0.9 is analyzed aiming for the maximal utilization of the Fe 4+/3+ redox couple for LIB. As previous studies relied on laboratory diffractometers with Cu sources, especially for the compositions beyond x = 0.5 [START_REF] Gracia | [END_REF]14,16,24 , we hope to improve the understanding of the phase stabilities, spinel inversion characteristics and Fe solubility limitations by high resolution synchrotron radiation powder diffraction (SRPD) in combination with neutron diffraction (NPD). The crystal chemistry of the thereby identified spinel samples with successful Fe incorporation, but low levels of spinel inversion (i.e. x < 0.6 with < 5 % Fe occupancy on the tetrahedral site), is analyzed further by Mössbauer spectroscopy for the electronic configuration and local environment of Fe, while cyclic voltammetry (CV) is used to identify the redox active species.

Finally, galvanostatic cycling at different C-rates allows for the understanding of the electrochemical performances and cycling stabilities. The results provide a baseline for further improvements of LiFe x Mn 2-x O 4 spinels.

Experimental

LiFe x Mn 2-x O 4 , with x ranging from 0.2 to 0.9, were prepared by a solid state reaction process. 40 Stoichiometric amounts of Li The particle size and the morphology of the calcined powders were investigated with a scanning electron microscope (SEM) (Quanta FEG 650 FEI, USA). The images were recorded operating the SEM at an accelerating voltage of 20.0 kV at magnifications of 10000

x with a secondary electron detector (ETD).

SRPD data were collected from fine-grained samples sealed in 0.7 mm diameter glass capillaries using the MSPD diffractometer at ALBA Synchrotron (Barcelona, Spain) 41 , in Debye-g y 0.82411 Å 2θ g g f 0.5° -72° with 0.006° 2θ-steps and an accumulation time of 5 minutes per pattern for the samples x = 0.2, 0.3, 0.5.

For the samples with x = 0.4 and x = 0.6 to 0.9, the SRPD data were collected at 0.9532 Å in 2θ g g f 3.5° -62° applying the same step size and accumulation time.

Complementary, NPD measurements were performed on the high-resolution powder diffractometer D2B at the Institut Laue Langevin (ILL, Grenoble, France). 42 The powders were placed in 8 mm diameter vanadium sample holders each. The diffraction patterns were p w w g f 1.5947(1) Å 2θ g g f 0° -150° w 0.05° 2θ-steps during a total accumulation time of 6h per pattern. For cross comparison, the results obtained from NPD and SRPD at different wavelengths will be

expressed independe f w g (λ) Q-space as Q = 4•π• (θ)/λ.
analysis 43 of NPD and SRPD data was carried out using the GSAS II software package. 44 57 Fe Mössbauer spectroscopy measurements were performed for x = 0.2 to 0.5 at room temperature using a constant acceleration Halder-type spectrometer operating in transmission geometry with a room temperature 57 Co source (embedded in a Rh matrix). The velocity scale w g p α-Fe 0 foil as reference material. The polycrystalline absorbers were prepared in order to contain less than 5 mg/cm 2 of Fe and thus, avoid saturation effects.

Results and Discussion

After calcination at 800°C, LiFe x Mn 2-x O 4 powders consist of primary particles being 0.5 -2 µm in size. Partially, these particles aggregate or form up to 10 µm sized sintered agglomerates. The SEM images of LiFe x Mn 2-x O 4 with x = 0.2, 0.4 and 0.7 are shown in Figure 1. No substantial differences in particle size or morphology could be seen for the materials as a function of the Fe content.

Figure 2 displays the SRPD patterns of the LiFe x Mn 2-x O 4 samples for x = 0.2 to x = 0.9.

Materials with spinel as single phase are obtained with a low Fe content (x < 0.4). For x = 0.4, 0.5 and 0.6 secondary phase reflections rise from the background with small intensities (closer inspection is offered in figure S1). They can be indexed to a Li 2 MnO 3 layered oxide that crystallizes in the monoclinic C2/m space group with the cell parameters a = 4.9292(2) Å, b = 8.5315(2) Å, c = 5.0251(1) Å β = 109.337(2)° . 45,46 Li 2 MnO 3 is a well-known secondary phase in the Li-Mn-O system. 47 Since it is structurally related to spinel, many of its main reflections are superimposed by the reflections of the main spinel phase. The intensity of Li 2 MnO 3 f g f y f x ≥ 0.7. F p easily identified in Figure 2 from its typical 020, 110 and 11-1 reflections (marked by * in the Q range from 1.5 to 2 Å -1 ) with their well-known heterogeneous peak profile broadening due to stacking faults. 48 Additionally, shoulders emerge at the high angle sides of the spinel reflections that also can be attributed to Li 2 MnO 3 .

Besides the obvious presence of Li 2 MnO 3 , shoulders at the low angle side of some spinel reflections, especially at the 220, 311, 400 and 511 reflections are visible for x ≥ 0.5.

Additionally, freestanding reflections at Q = 3.75 Å -1 and Q = 4.4 Å -1 emerge for these compositions. The positions of these shoulders and freestanding reflections can be attributed to a LiFe 5 O 8 spinel with a = 8.33 Å. 49 The intensities of the additional reflections increase with the Fe content in the samples. This phase has not been identified in the LiFe x Mn 2-x O 4 system before. In previous studies, however, powder diffraction was exclusively carried out on laboratory diffractometers with Cu sources. [START_REF] Gracia | [END_REF]14,16,24 The lower signal to noise ratio and the lower instrumental resolution might have hidden any LiFe 5 O 8 contribution or at least make its identification rather difficult. 16 The appearance of LiFe 5 O 8 in the current study and its increase beyond x > 0.4 suggests that the solubility limit of Fe in LiFe x Mn 2-x O 4 under the given synthesis conditions is reached in between x = 0.4 to 0.5.

The structural parameters of the main spinel phase in the samples were further investigated by Rietveld analysis based on the synchrotron und neutron diffraction data. The SRPD data are collected with high resolution, and thus give high accuracy for the cell parameters and atomic positions, whereas the NPD data allow the localization of the light element Li and the discrimination between the Mn and Fe due to the different sign of their coherent scattering lengths (-3.73 pm for Mn and 9.45 pm for Fe). Thus, structural parameters, such as lattice parameters and atomic positions, which allow for the determination of average bond distances, as well as cation occupancies and cation mixing on tetrahedral and octahedral sites, can be evaluated.

The refinement of the structural parameters starts from a Fd-3m model structure as were freed to converge. The refined structural parameters from SRPD were used as starting values for the combined fit of the SRPD and NPD data. Site occupancies of Fe and Mn on the octahedral site, as well as Fe or Mn and Li on the tetrahedral site were constrained to 100% at each site and refined against the SRPD and NPD data in the combined approach. Additionally, the phases LiFe 5 O 8 and Li 2 MnO 3 were considered. This applied three phase model leads to a reasonable difference minimization of observed and calculated data for the samples x ≤ 0.5

[Li , TM] 8a [Fe , Mn] 16d 2 O 32e 4 ,
(Table 1, Table S1).

For x = 0.6, the data could no more be reasonably described by the aforementioned three phase model. The calculated pattern leaves unfitted intensity residuals due to asymmetric peak shapes for the measured data that could not be calculated by the applied model. Figures S2 andS3 allow closer inspections of measured and calculated data and their difference plot for the x = 0.6 sample. The most reasonable explanation for the misfit is a large inhomogeneity of the main spinel phase, that might arise from accelerated Li 2 MnO 3 and LiFe 5 O 8 segregation, which points out the really low thermodynamic stability of the spinel, for the given synthesis temperature and atmosphere.

Table 1 gives a summary of the refined parameters for the LiFe x Mn 2-x O 4 samples with x = 0.2 to x = 0.5 and Figure 3a and 3b display the measured and calculated data of SRPD and NDP and their difference plot exemplarily for x = 0.3. The refined lattice parameters a increase slightly from a = 8.2476 Å ± 0.00003 Å for x = 0.2 to a = 8.2582 Å ± 0.00003 Å for x = 0.5, which is an increase of 0.13 %, in good agreement with the observed increase in lattice parameters for LiFe x Mn 2-x O 4 with x ≤ 0.5 in literature. 16,[18][19][START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF][21] Equally to the debate in literature, we have no direct explanation for the observation of increasing lattice parameters, as for the isovalent substitution of high spin Fe 3+ (0.645 Å) for high spin Mn 3+ (0.645 Å) in

LiFe 3+

x Mn 3+ 1-x Mn 4+ O 4 an increase in lattice parameter is not expected. We will discuss the problem again later after the evaluation of more obtained results.

The refinement of TM occupancies on the octahedral 16d site agrees to the expected cation mixing of Fe and Mn (Table 1 While the increase of Fe occupation on the octahedral site is expected, the steady increase of Fe occupation on the tetrahedral 8a site for x < 0.5 with increasing x is surprising.

It suggests that spinel inversion starts much earlier than reported by Ohzuku et al. who defined the onset of spinel inversion sharply at x = 0.57 from the evaluation of the intensity ratios of the 220 and 400 spinel reflections. 16 It is in line with the SRPD and NPD studies of Shigemura et al. who found ~ 3 % of Fe occupying the 8a site for x = 0.5. 19 These results point out the difficulties in targeting normal spinel type LiFe x Mn 2-x O 4 materials, given the nature of the ligand field of the Fe 3+ ion, with equal stabilization energies for the tetrahedral and the octahedral coordination. [START_REF] Burns | Mineralogical Applications of Crystal Field Theory[END_REF] Aliovalent substitution of Li + by Fe 3+ on tetrahedral sites should affect the distance in between the cationic 8a and anionic 32e atomic site positions. Inspections of the bond lengths determined from the Rietveld refinement (Table 1) show that the 8a-32e atomic distance decreases slightly from 1.967 ± 0.0005 Å for x = 0.2 to 1.965 ± 0.0005 Å for x = 0.5, in correlation to the rising Fe occupancy on the 8a site. Surprisingly, not only the 8a-32e atomic distance shows changes with x, but also the 16d-32e atomic distance. Cationic sites (8a at 1/8, 1/8, 1/8 and 16d at 1/2, 1/2, 1/2) are special positions with no free variables. Thus, the atomic distances of cations and anions in spinels are determined by the unit cell dimensions and the fractional coordinates of the oxygen position (32e at x, x, x), only. The changes in the oxygen position will determine the relative sizes of the octahedra and the tetrahedra in the unit cell.

Consequently, a changing size of the tetrahedral cation-anion bond length will affect the size of the octahedral cation-anion bond length. 11 However, the observed increase in the 16d-32e atomic distance is far larger than the decrease in the 8a-32e atomic distance. While the 8a-32e atomic distance changes by 0.1% only, the 16d-32e atomic distance changes from 1.9629 ± 0.00004 Å for x = 0.2 to 1.9679 ± 0.00004 Å for x = 0.5, which is a change of 0.25%. Therefore, the changes in the octahedral cation-anion bond length cannot be explained by the counterbalancing effect from the decreased tetrahedral cation-anion bond length alone.

Similar to the unexpected lattice parameter increase, the absolute increase of the 16d-32e atomic distance is unexpected from the cation mixing of Fe 3+ and Mn 3+ on the 16d site because of their identical radius.

One hypothesis to explain the increase in octahedral bond length would be through overstoichiometric fractions of high spin Mn 3+ ions (0.645 Å) at the expense of the smaller Mn 4+ ions (0.53 Å) on the octahedral site. Overstoichiometry in Mn 3+ might result from the reduction of Mn 4+ through oxygen loss during synthesis and formation of an oxygen-deficient spinel, a process that is well known in the Li-Mn-spinel system. 50,51 The presence of oxygen vacancies could no y f f y xyg ' occupancy is highly correlated to the other structural parameters. However, it is worth mentioning that when freed to converge after fixing all refined parameters, the oxygen occupancy converges away from full occupancies to values around 97% to 98%, which might indicate the presence of oxygen defects. Thus, an overstoichiometric fraction of Mn 3+ on the octahedral 16d site could explain an increasing average octahedral bond length with x, if in parallel the oxygen deficiency also increases with x -suggesting a destabilization of the anionic lattice of LiFe x Mn 2-x O 4 spinel because of Fe incorporation. This would agree with the increase of Li 2 MnO 3 fraction with increasing x. Li 2 MnO 3 is known for coexisting with an oxygen deficient spinel, hence its presence indicates oxygen deficiency and lower stability of the spinel. 50 Another hypothesis proposed in literature to explain this unexpected increasing lattice parameter is the presence of the unusual Fe 4+ or mixed Fe 3.5+ valence state. [START_REF] Gracia | [END_REF]17 These different hypotheses will be discussed in the following, especially by considering the Mössbauer spectroscopy results.

The electronic configuration and local environment of Fe in LiFe x Mn 2-x O 4 (0.2 ≤ x ≤ 0.5)

were probed experimentally by 57 Fe Mössbauer spectroscopy in order to get more insight into the Fe oxidation state and coordination. The spectra recorded with a low-velocity scale (-3 ≤ v ≤ +3 mm/s) are presented in Figure 4. The spectra show a characteristic asymmetric doubled that consist of two components: (1) a major quadrupole doublet and (2) a minor quadrupole doublet, in consistence with the Mössbauer data reported in literature for LiFe x Mn 2-x O 4 w x ≤ 0.5. [START_REF] Gracia | [END_REF]16,17,[19][START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF][21][22] Hence, all the spectra were tentatively reconstructed g w p w x f f xp (χ 2 value close to 1). The refined Mössbauer hyperfine parameters of the main signal (1) are given in [START_REF] Gracia | [END_REF]17 The isomer shift associated to the minor component observed in our study (0.2 mm/s) is most close those previously attributed in literature to (ii) Fe 3+ in tetrahedral coordination and (iii) Fe 4+ in octahedral coordination. The presence of Fe in the tetrahedral coordination was proven by Rietveld analysis before, despite in small fractions (less than 4%).

The presence of Fe 4+ cannot be excluded from the Mössbauer data, as its signal would be strongly overlaid by the signal of existing Fe 3+ in tetrahedral coordination.

Additionally, Mössbauer spectra of the LiFe x Mn 2-x O 4 compounds were recorded at room temperature with a high-velocity scale (-12 ≤ v ≤ +12 mm/s) (Figure S4). An additional minor component, characterized by two sextets, was evidenced for the composition x = 0.5.

Considering their hyperfine parameters at room temperature (Table 2), these magnetically-ordered components may be associated with Fe The CVs of LiFe x Mn 2-x O 4 with x = 0.2, 0.3, 0.4 and 0.5 reveal three oxidation and three corresponding reduction reactions (Figure 5). The two peaks in the voltage range between 3.75 to 4.25 V vs. Li/Li + are characteristic for the Mn 4+/3+ redox couple, with an order-disorder phase transition upon removing Li + from the spinel lattice. 52,53 The high voltage peaks between 4.75 and 5.2 V vs. Li/Li + correspond to the Fe 4+/3+ redox couple. 19 With increasing Fe content in LiFe x Mn 2-x O 4 , the integrated normalized current intensities attributed to the Mn 4+/3+ voltage range decrease and those attributed to the Fe 4+/3+ voltage range increase. This confirms the substitution of Fe 3+ for Mn 3+ in LiFe x Mn 2-x O 4 , where 0.2 Mn 3+ is substituted by 0.2 Fe 3+ for x = 0.2, 0.3 Mn 3+ is substituted by 0.3 Fe 3+ for x = 0.3, 0.4

Mn 3+ is substituted by 0.4 Fe 3+ for x = 0.4, and 0.5 Mn 3+ is substituted by 0.5 Fe 3+ for x = 0.5, respectively.

Up to x = 0.4, the normalized current peak intensities of the Mn 4+/3+ redox couple at lower voltages (peak 1, Figure 5) remain almost unchanged, whereas the normalized current peak intensities for the Mn 4+/3+ redox couple at higher voltages (peak 2) are subject to g f . I k w " y" w the two Mn 4+/3+ peaks is reached at electrochemical delithiation states of y = 0.5 in Li 1-y Mn 2 O 4 spinel. At this point, the remaining Li + ions start to order in their own fcc sublattice. 52,53 This very characteristic order-disorder phase transitions in the 4 V region has been observed for Fe substituted LiMn 2 O 4 as well. 18 Consistently, our data show the maintenance of the order-disorder phase transition for Fe substitution levels up to x = 0.4. Peak 1 is unaltered; all samples allow the delithiation up to y = 0.5 at the potential of the first Mn 4+/3+ reaction. The contribution of peak 2 gets lower as the Mn content decreases, and the extraction for y > 0.5 is shifted towards the potential of the Fe 4+/3+ redox couple.

For a stoichiometric LiFe 0.5 Mn 1.5 O 4 (Li + Fe 0.5 3+ Mn 0.5 3+ Mn 4+ O 4 ) with only 0.5 mol Mn 3+ per formula unit, only one Mn 4+/3+ redox peak should be observed, as the first peak of the Mn 4+/3+ reaction is expected for delithiation states y < 0.5 in Li 1-y Fe 0.5 Mn 1.5 O 4 . The second Mn 4+/3+ redox peak (peak 2) should disappear completely. However, a small shoulder is still visible at the high voltage side of the first Mn 4+/3+ redox peak for the LiFe 0.5 Mn 1.5 O 4 sample.

The appearance of this shoulder can have two reasons. The first reason would be an alteration of phase transition characteristics that could be induced by small fractions of Li occupying the 16d site. Indeed, the presence of Li on the 16d site would frustrate the ordering in the fcc sublattice and smears out the sharp double peak characteristics in CV. 52 However, our NPD results falsify this hypothesis since Li was not detected on the 16d site. The other possible reason for the appearance of the shoulder at peak 1 would be a higher fraction of Mn 3+ than expected for the stoichiometric compound LiFe 0.5 Mn 1.5 O 4 . The possibility of Mn 3+ overstoichiometry because of oxygen vacancies (Li + Fe 3+ 0.5 Mn 3+ 0.5+2 Mn 4+ 1-2 O 4- ) was suggested already in the structural section above. The small shoulder at the high voltage side of the first Mn 4+/3+ redox peak for the LiFe 0.5 Mn 1.5 O 4 sample qualitatively matches with the expected level of oxygen defects (<2%) 54,55,56 and the expected induced Mn 3+ overstoichiometry. CV has been proven to be a sensitive method for recognizing the presence of Mn 3+ for different high voltage spinels 56,57,58 and is here again shown to be a helpful tool to gain insight into the crystal chemistry of the studied spinels. Hence, Mn 3+ overstoichiometry and oxygen understoichiometry are strongly suggested by two of our results (CV and Rietveld).

The charge-discharge behavior at a C/20 rate at two different upper cut-off voltages (5.0 and 5.2 V vs. Li/Li + ) w F g 6 6 . T g w "p " 5.0 V vs. Li/Li + and in the range between 4.2 and 4.0 V vs. Li 6a). The discharge curves with a 5.2 V vs. Li/Li + upper charging cut-off voltage deliver higher capacities than the one with a charging cut-off at 5.0 V vs. Li/Li + , (Figure 6b). The samples provide specific capacities of 120-125 mAh/g, which means an increase by ~20% when rising the upper charging cut-off voltage by 0.2 V from 5.0 V to 5.2 V vs. Li/Li + .

Along with the increase of the higher charging cut-off voltage from 5.0 to 5.2 V vs.

Li/Li + , the capacities in the high voltage range (> 4.6 V vs. Li/Li + ) undergo significant changes. In the first cycle for the charging cut-off voltage at 5 V vs. Li/Li + , specific capacities of 11, 15, 18 and 24 mAh/g are obtained for LiFe x Mn 2-x O 4 with x = 0.2, 0.3, 0.4 and 0.5, respectively. Whereas for the charging cut-off voltage at 5.2 V vs. Li/Li + , specific capacities of 24, 30, 35 and 30 mAh/g are obtained for LiFe x Mn 2-x O 4 with x = 0.2, 0.3, 0.4 and 0.5, respectively. This corresponds to 75%, 63%, 57% and 38% of the theoretical capacities associated to the redox couple Fe 4+/3+ for LiFe 0.2 Mn 1.8 O 4 , LiFe 0.3 Mn 1.7 O 4 , LiFe 0.4 Mn 1.6 O 4 and LiFe 0.5 Mn 1.5 O 4 , respectively. The CV results already expressed that cycling to 5 V vs. Li/Li + will not be sufficient to exploit the full Fe 4+/3+ capacity. However, even for the higher charging cut-off voltage at 5.2 vs. Li/Li + , the full Fe 4+/3+ capacity is not yet fully exploit, especially for the samples with higher Fe contents.

The obtained specific discharge capacities agree to the experimental specific discharge capacities reported previously. Indeed, Kawai et al. reported a discharge specific capacity of 125 mAh/g for LiFe 0.5 Mn 1.5 O 4 , with a high voltage capacity (> 4.5 V vs. Li/Li + ) of ~ 40 mAh/g after charging to 5.3 V vs. Li/Li + . 9 For an upper charging cut-off voltage of 5.2 V vs.

Li/Li + , Ohzuku et al. reported a specific discharge capacity of 110 mAh/g during the first cycle. 28 For LiFe x Mn 2-x O 4 with x = 0.1, 0.3 and 0.5, specific discharge capacities of 130, 115 and 120 mAh/g with high voltage capacities (> 4.5 V vs Li/Li + ) of approximately 10, 20 and 40 mAh/g, respectively, were reported when charging the battery to 5.3 V vs. Li/Li + at a C/10 rate. 25 All these studies have in common that the obtained capacities are relatively low compared to the theoretical ones, which is explained by the incomplete Fe 4+/3+ redox reaction despite very high voltage charging cut-off conditions. The chosen cut-off conditions are always compromises between the extra capacity that can be gained and the side reactions coming from liquid electrolyte decomposition at high voltage that should be mitigated, especially upon long term cycling -as it will be discussed later. 600°C and 72% and 59% after 50 and 70 cycles, respectively, for the spinel post-annealed at 1000°C. 25 When cycling the post-annealed LiFe 0.5 Mn 1.5 O 4 for 50 cycles at C/8 to 5.5 V, 68% of the capacity are lost. 33 A similar trend was also observed for LiFe 0.5 Mn 1.5 O 4 prepared by different synthesis routes, e.g., by solvothermal synthesis, impregnation and template methods with subsequent annealing at 700°C. 29 These materials show relatively good stability when cycled to 5.0 V vs. Li/Li + , however, with specific capacities below 70 mAh/g. 29 Increasing the upper charging cut-off voltage for the material prepared from the template method to 5.3 V vs. Li/Li + results in an initial specific capacity of 103 mAh/g, but 27% of the capacity are lost already after 16 cycles 29 . Lower charging cut-off voltages of 5.0 V vs.

Li/Li + result in good cycling stability at moderate capacities, whereas charging to voltages higher than 5.0 V vs. Li/Li + provide enhanced initial specific capacities, but also result in substantial capacity fading.

Capacity fading of electrodes can have several reasons: i) structural changes in the active material; ii) microstructural degradation of the electrode (micro cracks and loss of contacts);

iii) dissolution of soluble elements from the electrode into the electrolyte; 60 vi) surface orientation of crystalline particles, i.e. crystal habitus; 59 and v) cathode-electrolyte interface (CEI) formation. 60 For high voltage electrodes, strong capacity degradation is also generally agreed to be an effect of the instability of the conventional electrolytes, when the operational voltage exceeds the oxidation limitation. 3 It induces electrolyte decomposition and subsequent deposition of resulting organic and inorganic degradation products on the electrode surface, which adds up to the CEI formation 3,36 and can also cause surface structural changes of the electrode structure. 61 All of these effects would primarily come with capacity fade, due to loss of Li-ions or loss of active material and/or the increase in internal cell resistances, i.e. polarization. In fact, we observe strong correlations between cell degradation and cell polarization. The increasing cell polarization hinders the exploitation of the Fe 4+ / 3+ redox capacity (Figures S5 andS6) at thus in itself already causes capacity fading.

From the given data, it is difficult to specifically assign a certain mechanism to the observed degradation of the cells. However, we can deduce correlations between capacity degradation and the upper charging cut-off voltage (5.2 V vs. Li/Li + ) as well as Fe-content. As such, capacity degradation is more severe for higher cut-off voltages and for higher Fe-content.

To investigate further the degradation mechanism observed upon discharge for LiFe 0.5 Mn segregation indicates oxygen deficiencies in the coexisting spinel. Our results suggest that Fe diminishes the stability of the oxygen spinel lattice, leading to oxygen non-stoichiometry and overstoichiometry of Mn 3+ , which explains the increase in lattice parameter with increasing Fe content for x ≤ 0.5. T F 4+/3+ capacity for the studied samples (x = 0.2 to 0.5) is difficult to exploit fully due to the limitations of the electrolyte stability window. Higher cut-off voltages are associated with higher cell-polarization, which causes severe capacity degradation. Part of this capacity is retained when the current density is lowered, as the increased overpotentials cause a steady decrease of the accessible Fe 4+ / 3+ capacity at the given charging cut-off voltage. The fraction of the irreversible capacity fade is still moderate, however, which is a promising starting point for further materials engineering and applicable Fe based high voltage spinels hopefully with compatible electrolytes in the future.

  considering cation mixing of Li and TM on the tetrahedral 8a site and cation mixing of Fe and Mn on the octahedral 16d site. Cation mixing of Li and TMs on the 16d site was not found to improve the fitting quality and was excluded from the model early. The structural parameters, such as lattice parameters, atomic displacement parameters, atomic positions (x=y=z position of oxygen), and site occupancies on tetrahedral and octahedral sites were refined first by SRPD. Cation mixing of Li and TM was allowed on tetrahedral sites and octahedral sites, by constraining the occupancy to 100%. Peak broadening through size and strain effects were treated individually. Finally, all parameters

3 O 4 or

 34 Li x Fe 3-x O 4 spinel, as secondary phase(s), which agrees to the detection of LiFe 5 O 8 spinel by SRPD and NPD and points out the low stability of the LiFe x Mn 2-x O 4 spinel by encountering the Fe solubility limitation in between x = 0.4 to 0.5 already.

  Figure6cand 6d for x = 0.4 and 0.5. Along with the charging cut-off voltage of 5.0 V vs. Li/Li + , both materials show capacity fading of ~ 20 % over 50 cycles. In contrast, when operating the cells with a higher charging cut-off voltage of 5.2 V vs. Li/Li + , pronounced decrease of the capacity is observed, which is 39% and 48% for LiFe 0.4 Mn 1.6 O 4 and LiFe 0.5 Mn 1.5 O 4 respectively. These results appear in good agreement with the reported cycling stabilities for sol-gel derived LiFe 0.5 Mn 1.5 O 4 cycled up to 5.3 V vs. Li/Li + at a cycling rate of C/2 for 70 cycles.25,33 E.g. Bhaskar et. al reported the capacity retention for LiFe 0.5 Mn 1.5 O 4 was 66% after 50 cycles and 58% after 70 cycles for the spinel annealed at

Figure 1 :

 1 Figure 1: SEM of Lithium-Iron-Manganese spinel LiFe x Mn 2-x O 4 , a) x = 0.2, b) x = 0.4 and c) x = 0.7.

Figure 2 :

 2 Figure 2: Synchrotron powder diffraction patterns for LiFe x Mn 2-x O 4 (0.2 ≤ x ≤ 0.9). p f indicated by their hkl Miller indices. Secondary phase reflections are highlighted with the symbol * for Li 2 MnO 3 and arrows pointing to positions of LiFe 5 O 8 reflections. Vertical dashed lines are drawn to guide the eye.

Figure 3 :

 3 Figure 3: Results of Rietveld analysis from SRPD and NPD data: Experimental (I obs ), calculated (I calc ) and difference (I obs -I calc ) for x = 0.3 exemplarily for SRPD in a) and for NPD in b); c) changes of atomic distances in the tetrahedral and octahedral cation coordination polyhedra as a function of x.

Figure 4 :

 4 Figure 4: Room temperature 57 Fe Mössbauer spectra of the series of LiFe x Mn 2-x O 4 p (0.2 ≤ x ≤ 0.5). T f yp f p f ff -spectra (highlighted by the blue lines) are gathered in Table2.

Figure 5 :

 5 Figure 5: CVs for LiFe x Mn 2-x O 4 recorded at a scanning rate of 0.028 mV/s in the range between 3.5 and 5.2 V vs. Li/Li + for LiFe 0.2 Mn 1.8 O 4 , LiFe 0.3 Mn 1.7 O 4 , LiFe 0.4 Mn 1.6 O 4 and LiFe 0.5 Mn 1.5 O 4 . Currents are normalized to the mass of active materials in the positive electrode.

Figure 6 :

 6 Figure 6: Discharge curves for LiFe x Mn 2-x O 4 (x = 0.2 to 0.5) at a C/20 rate with two different charging cut-off voltages: a) 5.0 V and b) 5.2 V vs. Li/Li + . Specific discharge capacities of LiFe x Mn 2-x O 4 for x = 0.4 and x = 0.5 cycled at C/5 rate with two different upper charging cut-off voltages: c) 5.0 V and d) 5.2 V vs. Li/Li + . The lower cut-off discharging voltage is 3.0 V vs. Li/Li + for all the samples.

Figure 7 :

 7 Figure 7: LiFe 0.5 Mn 1.5 O 4 long term cycling performance over ~ 900 hours in between 3.0 V and 5.2 V vs. Li/Li+ at different C-rates: 1C, C/5 and C/10 with intermediate C/20 cycles after 50 cycles each.

  Mn 1.7 O 4 , 3.2% ± 0.2% for LiFe 0.4 Mn 1.6 O 4 , and 4.0% ± 0.2% for LiFe 0.5 Mn 1.5 O 4 . Accordingly, the resulting structural formulas can be written as [Li 0.98 Fe 0.02 ] 8a [Fe 0.2 Mn 1.8 ] 16d O 32e 4 for x = 0.2, [Li 0.98 Fe 0.02 ] 8a [Fe 0.3 Mn 1.7 ] 16d O 32e 4 for x = 0.3, [Li 0.97 Fe 0.03 ] 8a [Fe 0.4 Mn 1.6 ] 16d O 32e 4 for x = 0.4, and [Li 0.96 Fe 0.04 ] 8a [Fe 0.49 Mn 1.51 ] 16d O 32e

	4 for
	x = 0.5, respectively.

). That is, for LiFe 0.2 Mn 1.8 O 4 a Fe fraction of 9.8% ± 0.1% is found on the 16d site (vs. 10% expected). Similarly, 14.9% ± 0.1% (vs. 15% expected), 19.5% ± 0.1% (vs. 20% expected) and 24.2% ± 0.1% (vs. 25% expected) are found for LiFe x Mn 2-x O 4 with x = 0.3, 0.4 and 0.5, respectively. Furthermore, cation mixing of Li and Fe on the tetrahedral 8a sites was found to improve the fit for all compositions. The refined fractions of Fe on the tetrahedral site are 1.5% ± 0.2% for LiFe 0.2 Mn 1.8 O 4 , 1.8% ± 0.2% for LiFe 0.3

Table 2

 2 Shigemura et al. and Li et al. assigned the minor component with an isomer shift ranging between 0.21 mm/s and 0.31 mm/s to Fe 3+ in tetrahedral coordination16,19,22 and further supported their result by NPD19 ; and iii) Tsuji et al. and Gracia et al. assigned an isomer shift smaller than 0.22 mm/s to Fe 4+ or mixed Fe 3.5+ in octahedral coordination.

	( = 0.35 mm/s and  = 0.74 mm/s); they are characteristic of six-fold coordinated
	high-spin Fe 3+ ions (on 16d octahedral site), in perfect agreement to the literature data. 13, 16, 17,
	19-22
	The minor component (2) (relative area: 5%) is characterized by an isomer shift of about
	0.20 mm/s and a smaller quadrupole splitting value (about 0.30 mm/s). The correct
	assignment of this component in the Mössbauer spectra collected for LiFe x Mn 2-x O 4 is center

of debates in literature

[START_REF] Gracia | [END_REF]17,[19][START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF][21][22]

: i) Talik et al. and Shigemura et al. found an isomer shift of the minor component at 0.354 mm/s and 0.23 mm/s respectively, that they both assigned to Fe 3+ in an octahedral site but with different symmetries

[START_REF] E. T K . P Ń K A. G Z K . Z J M. M K M. Z K | Ką z łk -G w ł[END_REF]21

possibly induced by oxygen defects

21

; ii) Later,

  Mn 1.8 O 4 and LiFe 0.3 Mn 1.7 O 4 , whereas in the same potential range a smoother evolution of the voltage is observed for LiFe 0.4 Mn 1.6 O 4 and LiFe 0.5 Mn 1.5 O 4 . When charging to a cut-off voltage of 5.0 V vs. Li/Li + , initial specific capacities of 100-110 mAh/g are obtained (Figure

							/Li + with a broad transition
	g	w . T w	f	"p	"	w	F	. I	g
	range between 4.0 and 4.2 vs. Li/Li + w	"p	"		f f
	LiFe 0.2

  1.5 O 4 for a upper charging cut-off voltage at 5.2 V vs. Li/Li + , we carried out The capacity is mostly restored once the current density is lowered and diffusion limitations due to rising overpotentials are overcome. Accordingly, our data show cell degradation due to two effects: reversible and irreversible degradation. If we consider the capacity fading between the initial cycle at C/20 and the capacity of the intermediate cycle at C/20 after 300h as a measure of the amount of irreversible degradation only, the irreversible and reversible capacities in our experiments can be treated separately. In view of that, we can conclude that the irreversible capacity due to cell degradation is lower than 20% after 150 cycles at 1C. For comparison, the well-known LiNi 0.5 Mn 1.5 O 4 high voltage spinel, operating at 4.7 V vs. Li/Li + , typically shows capacity degradation of ~10% after ~ 150 cycles.62,63 With optimized electrolytes, in the near future, and proper materials engineering, these performances might be realized for LiFe 0.5 Mn 1.5 O 4 , while providing similar theoretical capacities and average potentials (in average 4.6 V vs.Li/Li + and 145 mAh/g) compared to LiNi 0.5 Mn 1.5 O 4 (in average 4.7 V vs. Li/Li + and 145 mAh/g), but utilizing the more environmentally friendly and more abundant Fe-ion. Li 0.97 Fe 0.03 ] 8a [Fe 0.4 Mn 1.6 ] 16d O 32e 4 for x = 0.4, and [Li 0.96 Fe 0.04 ] 8a [Fe 0.49 Mn 1.51 ] 16d O 32e 4 for x = 0.5, respectively. The presence of secondary LiFe 5 O 8 and Li 2 MnO 3 phases as impurities indicate the solubility limit of Fe in between x = 0.4 to 0.5 on the one hand and emphasize the thermodynamic instability -at the given synthesis conditions -on the other hand, as Li 2 MnO 3

	Conclusions
	LiFe x Mn 2-x O 4, w x ≤ 0.5 y	z	Fd-3m spinel structure with partial inversion
	due to Li + and high spin Fe 3+ mixing on the tetrahedral site as
	[Li 0.98 Fe 0.02 ] 8a [Fe 0.2 Mn 1.8 ] 16d O 32e 4 for x = 0.2, [Li 0.98 Fe 0.02 ] 8a [Fe 0.3 Mn 1.7 ] 16d O 32e	4 for x = 0.3,
	[
	experiments with different C-rates (C/10, C/5 and 1C), while allowing intermediate cycles at
	a much lower current density (C/20) (Figure 7). The degradation over the whole experimental
	time increases with the applied C-rate, with 35% degradation for the C/10, 45% for C/5 and
	72% for the 1C cycling. Independent of the C-rate, however, the intermediate cycles at C/20
	display a similar strikingly low capacity fading (~ 30% for all three experiments over ~900 h).

This result emphasizes the effect of increased cell polarization in combination with a charging cut-off voltage at 5.2 V vs. Li/Li + , which is too low to exploit the whole capacity of the Fe 4+/3+ redox. This results in a reversibly retained capacity.

Table 1 :

 1 Refined structural parameters obtained for the LiFe x Mn 2-x O 4 samples with x = 0.2 to 0.5 by Rietveld analysis of SRPD and NPD data. *) wR: Weighted pattern residual

	x in	Lattice	Oxygen	8a Fe	16d Fe	8a-32e	16d-32e	wR*
	LiFe x Mn	parameter	atomic	occupan	occupan	atomic	atomic
	2-x O 4	[Å]	position	cy [%]	cy [%]	distance	distance [Å]
						[Å]
	0.2	8.24764(3)	0.26268(9)	1.5(2)	9.8(1)	1.9667(5)	1.96294(4)	7.5
	0.3	8.24988(3)	0.26258(10)	1.8(2)	14.9(1)	1.9659(5)	1.96420(4)	8.2
	0.4	8.25248(3)	0.26248(10)	3.2(2)	19.5(1)	1.9651(5)	1.96546(4)	8.7
	0.5	8.25816(3)	0.26235(9)	4.0(1)	24.2(1)	1.9646(4)	1.96785(4)	8.1

Table 2 .

 2 57 Fe Mössbauer hyperfine parameters determined from the analysis of room temperature spectra of LiFe x Mn 2-x O 4 p yp w 0.2 ≤ x ≤ 0.5 ( f g 4). [a] δ isomer shift, [b] Δ quadrupole splitting, 2 quadrupole shift [c] B hf hyperfine magnetic field, [d] Γ signal linewidth.

	x in LiFe x Mn 2-x O 4	Component	 [mm.s -1 ] [a]	 or 2 [mm.s -1 ] [b] B hf [T] [c] Γ [mm.s -1 ] [d]	Relative area [%]	Assignment
	0.2	doublet (1)	0.350(1)	0.742(2)	-	0.26(1)	95(2)	Fe 3+ [Oh]
		doublet (2)	0.20(2)	0.27(2)	-	0.27(2)	5(2)	Fe 3+ [Td]
	0.3	doublet (1)	0.350(1)	0.744(2)	-	0.26(1)	95(2)	Fe 3+ [Oh]
		doublet (2)	0.21(2)	0.29(2)	-	0.28(2)	5(2)	Fe 3+ [Td]
	0.4	doublet (1)	0.349(1)	0.739(2)	-	0.28(1)	95(2)	Fe 3+ [Oh]
		doublet (2)	0.22(2)	0.27(2)	-	0.28(2)	5(2)	Fe 3+ [Td]
	0.5	doublet (1)	0.348(1)	0.735(2)	-	0.28(1)	89(2)	Fe 3+ [Oh]
		doublet (2)	0.22(2)	0.29(2)	-	0.27(2)	5(2)	Fe 3+ [Td]
		sextet (1)	0.29(2)	0.01(1)	49(1)	0.45(-)	6(2)	Fe 3 O 4 or
		sextet (2)	0.65(5)	0.02(2)	46(1)	0.45(-)		Li x Fe 3-x O 4

Acknowledgments

The authors would like to thank Alain Wattiaux (ICMCB) for helpful discussion and support. Funding from the German Federal Ministry of Education and Research (BMBF-project DESIREE, grant number 03SF0477A and 03SF0477B), from Region Nouvelle Aquitaine, from the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) and from ILL for the funding of TR PhD thesis, is acknowledged.

Provision of beam time on BL04-MSPD beamline at ALBA was granted through In House proposal 2017042199.