International audienceSafety is one of the most important criteria for electrochemical energy storage devices used in large scale applications such as wind or solar farms. In this context, solid polymer electrolytes based on nanostructured block copolymer electrolytes (BCEs) are promising because their properties can be finely tuned by adjusting simultaneously their block chemistries and polymer architectures. However, there is a need to rationalize the different properties of BCE that are optimal for battery applications. We produced by controlled radical polymerization a large number of BCEs based on either (1) linear poly(ethylene oxide) (PEO) or (2) comb PEO as the ionic conductor block, and polystyrene as the structural block. We varied the molecular weight of the PEO-based block, the composition, and the architecture (diblock vs triblock). We performed a systematic analysis of their thermodynamic, ionic transport, and mechanical properties. To verify the potential of BCEs as electrolytes, we evaluated their electrochemical stabilities. Laboratory scale batteries comprising the best BCEs and LiFePO4 as a positive active material were cycled at different rates and temperatures. This process allows the selection of the best architectures and compositions that had been successfully tested in battery prototypes and cycled for more than 600 cycles at high rates without any dendritic growth

Two Li 1.1 V 3 O 8 samples have been prepared by heating a sol-gel precursor at 350 and 650 uC, i.e. below and above the melting point, respectively. Their electrochemical lithium insertion behavior was investigated after different grinding treatments. Important differences were observed, both in initial capacity and in cyclability. Attempts were made to correlate these differences to the material characteristics (composition, morphology and structure). The importance of grain morphology (size, size distribution and shape) and texture (agglomeration of smaller particles or not) has been evidenced. The size and agglomeration of the grains play a major role on the initial capacity, while their crystal shape (well formed crystals or no crystal shape) seems to be the main factor influencing the cyclability. This latter morphology feature was also shown to affect differently the partial capacity fading occurring on each electrochemical Li insertion process.

Understanding the solid electrolyte interphase (SEI) in lithium batteries is very important to face the major safety issue of lithium dendritic growth during battery charge. The aim of this work is to study the thickness and the chemical nature of the SEI by XPS, as well as their influence on the electrochemical performance of the battery for different liquid organic electrolytes. XPS imaging is also used in this work to get a chemical mapping of the SEI layer components formed on the metallic lithium electrode surface cycled in different conditions. Data processing based on the principal component analysis (PCA) method has been conducted in order to illustrate the SEI layer heterogeneities. The obtained results are compared with energy-dispersive X-ray spectroscopy (EDX) mapping. Thereby, the benefits and the precision of the XPS imaging technique to identify chemical compounds distribution have been highlighted. These different analyses have led to a better knowledge of the redox processes occurring at the top surface of lithium metal electrodes cycled in different liquid electrolytes.

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