Abstract :
[en] Rechargeable batteries occupy a predominant position in energy storage systems, thanks to their versatility and performance. Indeed, they can be used in a wide range of applications such as portable devices, electric vehicles or grid storage. The development of high-performance energy storage systems has to meet actual energy and technology needs and requirements but also fulfill environmental considerations. In this context, this thesis included two research axes: the development of green and flexible Li4Ti5O12 electrodes for Li-ion batteries, based on aqueous formulation, and the study and optimisation of Na2Ti3O7 anode material for Na-ion batteries.
Therefore, the first part of this thesis concerned the development of new aqueous suspensions for the preparation of free-standing and flexible electrodes. Li4Ti5O12, which is a promising anode material for Li-ion batteries, was synthesized via a spray-drying route in aqueous media. Crack-free and free-standing electrodes were obtained with the use of polyvinyl alcohol and polyethylene glycol as the binder and plasticizer, respectively. Good electrochemical performance was obtained in half-cell configuration and also in full-cell configuration with LiFePO4 flexible cathode.
The second part of this thesis concerns the development of Na2Ti3O7 (NTO) as anode material for Na-ion batteries. In-situ high-temperature XRD was coupled with ex-situ XRD, TGA/DSC, SEM and TEM to investigate the formation of NTO. Na2Ti6O13 and Na4Ti5O12 were identified as intermediate phases and the chemical equations for a three-step formation mechanism were established. The observed influence of the heat-treatment duration on the electrochemical performance of NTO material was elucidated by in-situ XRD technique. Indeed, for the first time different mechanisms for Na+ ions insertion/extraction in the structure were identified and studied, regarding the calcination time. Rietveld refinement showed that the increase of the calcination duration leads to a more ordered structure, which explained the higher performance and stability of the material heat-treated 48 h compared to 8 h. In addition to this study, the formation of in-situ carbon was considered in order to decrease the irreversibility at the first cycle and limiting the surface degradation of Na2Ti3O7 during cycling.
Finally, the electrochemical performance in Na-ion full-cell configuration was investigated using Na3V2(PO4)2F3 (NVPF) as cathode material. The system NTO/NVPF has been reported for the first time in this study. A high excess of NVPF was required to compensate the sodium consumption due to SEI formation and side reactions at NTO anode. Moreover, the presodiation of the NTO anode allowed to improve the stability
and enhance the performance of the NVPF/NTO batteries of more than 300 % during the rate capability test, compared to the batterie assembled with non-presodiated NTO.
