Indirect regulation of solvation structure in all-fluorinated electrolyte by introducing carboxylate for stable 5 V battery

Abstract

All-fluorinated electrolytes are crucial for achieving long-term application of 5 V-class batteries. As an alternative to carbonates, carboxylates have low viscosities and freezing points but are still confined to chemistry batteries with cutoff voltage < 4.3 V. Therefore, it is urgent to expand the electrochemical window of carboxylate-based electrolytes to over 5 V to inhibit their oxidative decomposition when paired with high-voltage cathodes. Herein, surrounding ethyl trifluoroacetate (TFEA), we designed 1.2 m LiPF6 in fluoroethylene carbonate (FEC)/TFEA/1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) electrolyte to simultaneously accomplish the reversibility of aggressive high voltage cathode and Li metal/graphite anodes. This performance is attributed to the solvent-anion hybrid chemistry at the electrode-electroyte interface. By theoretical calculations, we inspired a universal approach that the TFEA with weak solvation ability indirectly induces Li+ to form FEC- and anion-rich solvation environment. Based on the above features, the FEC/TFEA/TTE electrolyte provides 300 and 500 stable cycles for LNMO-Li cells and LNMO-graphite cells. This work demonstrates the feasibility of carboxylate application in high voltage electrolytes for 5 V-class batteries and opens up the possibility for the futural development of ultra-low temperature ultra-high voltage batteries.