Strategies for replacing LiPF6 salt by LiFSI for various cathodes chemistries, LiFePO4, LiNixMnyCozO2 and LiNi0.5Mn1.5O4
Ann Mari Svensson
NTNU
The dominating salt for conventional Li-ion batteries is LiPF6. One major disadvantage of LiPF6 is the fact that HF is inevitably formed in the presence of trace amounts of H2O, causing challenges with respect to etching of active materials (in particular cathodes and silicon anodes), recycling process, and in the case of hazardous events. An alternative salt, not susceptible to hydrolysis, is LiFSI, which has many advantages, like improved thermal stability, higher Li+ transport number and good SEI forming properties. However, due to the absence of HF, LiFSI-based electrolytes fail to form passivation layers on the aluminium current collector. The corrosion of the current collector is thus a major challenge that needs to be overcome, in particular for high voltage cathodes. In the presentation, strategies for enabling the use of electrolytes based primarily on LiFSI are presented, going from low-voltage cathodes like LiFePO4 (LFP), to medium voltage cathodes like LiNi0.6Mn0.6Co0.2O2 (NMC622) and high voltage cathodes, like LiNi0.5Mn1.5O4 (LNMO). These strategies include studies of salt additives (LiDFOB and LiBF4), ex-situ treatments of the current collector, highly concentrated electrolytes, as well as replacing the carbonate solvent with ionic liquids.