Functionalized carboxylate molecule-enabled quasi-localized high concentration electrolyte for high-stability lithium-ion batteries

Advanced electrolyte engineering is a crucial solution for the development of high-energy lithium-ion batteries (LIBs) coupled with ultrahigh nickel cathode. However, the commercial electrolytes always yield the unstable cathode electrolyte interface (CEI) due to severe electrolyte decomposition and the structure deterioration under high voltage, leading to poor battery lifespan. Herein, this work demonstrates a quasi-localized high concentration electrolyte (Q-LHCE) by replacing cosolvent in conventional carbonate electrolyte with a functional carboxylic ester (methyl difluoro(fluorosulfonyl)acetate, MDFA), which features weak solvation ability, contributes to an favorable CEI layer on cathode for battery performance improvements. Such an interface with multiple inorganic composition benefits from the formation of an anion-rich solvation sheath, enhancing the Li⁺ transport kinetics and concurrently inhibiting the electrolyte decomposition and cathode degradation. Consequently, the LiNi_0.98Co_0.02O₂/Graphite full battery maintains outstanding capacity retentions of 89.13% after 250 cycles at 25 °C and 86.11% after 120 cycles at 45 °C, respectively (vs. 72.18% and 65.70% in the counterpart), accompanying with a higher initial coulombic efficiency (CE). These results provide useful guidance for tailoring the solvation structure and interfacial chemistry to realize the rational electrolyte design for high-performance LIBs.