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.

The presence of residual alkaline compounds in the ultrahigh-nickel layered oxide cathodes (LiNi_xCo_yMn_1−x−yO₂, x ≥ 0.9) aggravates structural degradation, increases surface reactivity, and promotes slurry gelation, leading to the capacity decay of batteries with these cathodes and complicating their manufacturing. Traditional approaches for addressing this issue, including direct removal, coverage, and utilization, are complex and require surface regeneration. Herein, we propose neutralizing residual alkaline compounds with 3-thiopheneboronic acid (3-TBA) to improve the performance of LiNi_0.95Co_0.04Mn_0.01O₂ (NCM) cathode material, a facile strategy that does not require any post-treatment. The suggested reaction yields a uniform and thin organic-modified layer on the surface of the NCM cathode, improving its chemical stability toward the electrolyte, as demonstrated by multiple characterization methods. The modified NCM cathode exhibited impressive cyclic and rate performances, achieving a capacity retention of 83.34% after 200 cycles at 1.0 C and a specific capacity of 162.00 mAh·g⁻¹ at 10.0 C. Most importantly, the proposed approach can efficiently suppress unfavorable phase transitions, severe electrolyte degradation, and CO₂ gas evolution, improving the application potential of ultrahigh-nickel layered oxide cathode materials.