Tailoring solvation chemistry in carbonate electrolytes for all-climate, high-voltage lithium-rich batteries

Abstract

High-voltage Li-rich layered oxide materials (LLOs) are considered as the promising next-generation cathode materials because of their high energy density and low cost. However, their electrochemical performance continues to deteriorate under high voltages when using traditional lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes, mostly due to the detrimental reactions with free anions, unstable electrode interface and limited Li+ kinetic process. Here, we demonstrate a highly oxidation-resistant carbonate electrolyte by incorporating multifunctional lithium difluoro(oxalato)borate (LiDFOB) and Tris(trimethylsilyl) Phosphite (TMSPi) additives. It is discovered that the introduction of LiDFOB and TMSPi can manipulate the electrolyte solvation structure by reducing the number of coordinated solvent molecules and free PF6−anions at the electrolyte-electrode interface, thus promoting the desolvation process of Li+, suppressing the generation of harmful HF species and conducive to forming a thin and robust cathode electrolyte interphase (CEI) layer. As a result, the Li||LLO cells with dual additives show excellent cycle stability and improved rate capability in a wide temperature ranged from -20 °C to 55 °C, and the retention rate of LLO||graphite pouch cell (2.5 Ah) using EEDB-TMSPi electrolyte is up to 91.1% after 200 cycles. It is anticipated that the work provides a promising strategy for realizing long-cycle stability of layered cathode materials under high-voltage and wide-temperature conditions.