Superior high-temperature rate performance of LiFePO4 cathode: The stabilizing effect of a multicomponent gel biopolymer binder

A quasi-solid-state polymer gel binder (PGB) has been prepared and investigated for application in high-temperature lithium-ion batteries. The effects of binder on the aging behavior of LiFePO4 (LFP) cathodes were investigated by electrochemical methods and post mortem analysis. Conventional binder polyvinylidene difluoride (PVDF) was used as a benchmark. At 60 degrees C, LFP/PGB half cells delivered a capacity of 98 mAh which corresponds to 92% of the initial value 140 mA g(-1) over 1000 cycles at 10C. These results were far superior to the ones obtained for LFP with PVDF which only exhibited a capacity of 58 mAh g(-1). We showed that a significant degradation of LFP in the LFP/PVDF electrode accompanied by iron dissolution in the electrolyte and deposition on the anodic surface together with a strong swelling of PVDF in the electrolyte as well as some contact loss between the electrode and the current collector represent the main reasons for the capacity fading at 60 degrees C. In contrast, these effects were much less pronounced in the LFP/PGB electrode. Furthermore, thick LFP/ PGB electrodes with 450 mu m thickness, corresponding to a 4.5 mg cm(-2) mass loading, showed a better cycling performance and more favorable electrochemical kinetics than the electrode incorporating PVDF.