Nonflammable single-solvent electrolyte towards highly stable Li-rich Mn-based cathode materials

Abstract

Li-rich Mn-based cathode materials (LRMs) with high specific capacity are considered as one of the most promising cathodes in the next-generation lithium-ion batteries. However, the mismatch between high-voltage LRM cathodes and conventional carbonate electrolytes causes a series of problems such as cathode structure degradation, transition metal dissolution, and continuous electrolyte decomposition. Herein, we demonstrate a nonflammable and highly oxidation-resistant electrolyte by introducing methyl (2,2,2-trifluoroethyl) carbonate (FEMC) as the single solvent. Theoretical calculations show that the low binding energy between FEMC and Li⁺ promotes the desolvation process of Li⁺ while reducing the competition with anions, which is beneficial for more anions to enter the first solvation shell structure of Li⁺. This regulation in solvation structure optimizes the cathode–electrolyte interphase (CEI) components and forms a durable and inorganic-rich CEI layer on the cathode interface. Meanwhile, the low viscosity and flame-retardant properties of the FEMC molecule also improve the wettability and safety of the electrolyte. Therefore, the assembled Li‖LRM batteries with the single-solvent electrolyte exhibit a high capacity retention of 83.9% after 400 cycles in the voltage range of 2–4.8 V at 1C. Even at the high cut-off voltage of 5 V, a high capacity retention of 91.9% is achieved after 150 cycles. This work provides new insights into the development of high-safety and high-voltage electrolytes for high-energy-density lithium-ion batteries.