Enhanced Aluminium Passivation properties of lithium nonafluoro-tert-butoxide: Designing Electrolyte Additives for High-Voltage 4.8 V LiNi0.5Mn1.5O4-graphite batteries

LiNi0.5Mn1.5O4 (LNMO) cathodes offer high energy density in Li-ion batteries due to their higher operational potential than conventional cathode materials. However, their practical application in Li-ion batteries is limited by the active metal (e.g., Mn) dissolution, which irreversibly compromises the graphite anode of a Li-ion battery. In this work, lithium nonafluoro-tert-butoxyborate (LiONFtb) has been tested as an additive in LNMO-graphite system. The electrochemical stability analysis of the LiONFtb salt on the aluminium current collector revealed a new passivation mechanism, without the formation of cracks and pits, which are otherwise commonly observed in the case of LiPF6-containing electrolytes. Adding 1 wt% LiONFtb to the commercial LiPF6-based electrolyte is demonstrated to improve the high voltage stability of the electrolyte in LNMO-Li half-cell. The LiONFtb additive was also found to promote better Li+ de-/intercalation behaviour in graphite-Li half-cell. The long-term cycling of the LNMO-graphite full cell with the 1% LiONFtb additive electrolyte demonstrated higher initial discharge capacity (121 mAh/g) and higher capacity retention (62%) than the LiPF6 containing electrolyte (105 mAh/g and 9.2%, respectively) after 100 cycles. The post-cycling analysis reveals that the LiONFtb additive helps to retain the morphology of the LNMO particles and reduces the Mn dissolution during cycling. The positive influence of the LiONFtb additive on reducing the cathode particle cracking and active metal dissolution makes it a viable electrolyte additive candidate for next-generation high-voltage Li-ion batteries.