Optimization of fluorinated orthoformate based electrolytes for practical high-voltage lithium metal batteries

Abstract

• TFEO is a good diluent due to formation of large amount of aggregates in LHCEs. • Optimized LHCE compositions are sensitive to the electrolyte amount used in the LMBs. • Optimized TFEO-based LHCE enables long cycling of LMBs under practical conditions. Lithium (Li) metal batteries (LMBs) have been revitalized in recent years in response to the increasing demand for high energy density batteries. However, the instability of Li metal anode (LMA) is still a critical barrier that limits large scale applications of these batteries. This work optimizes tris(2,2,2-trifluoroethyl) orthoformate (TFEO) based electrolytes and reveals the fundamental mechanisms behind their stability towards both LMA and cathodes. It is also found that the optimized composition of the electrolytes is sensitive to the electrolyte amount used in the batteries due to the consumption of the salt during the cycling process. The optimized TFEO based electrolytes create highly effective solid electrolyte interphase and cathode electrolyte interphase, which prevent continuous electrode/electrolyte side reactions and significantly prolong the cycle life of LMBs with a NMC811 cathode under very challenging conditions (4.2 mAh cm −2 cathode loading, 50 µm Li and lean electrolyte of 3 g (Ah) −1 ). The design principles discovered in this work provide guidance for further development of electrolytes for the stable operation of high energy density LMBs.