Enhanced Cycle Stability of LiNiO₂ in a Highly Concentrated Ionic Liquid Electrolyte

LiNiO₂ (LNO) is a promising positive material for next-generation vehicle batteries because of its high theoretical capacity and lower cost compared to the Co analogues. However, its unstable performance such as Ni dissolution results in capacity fade and poor cycle life, impeding its practical application. Since hydrogen fluoride (HF), the hydrolysis product of LiPF₆, is highly reactive with LNO positive electrodes, exploring LiPF₆-free electrolytes is attractive to improve cycle stability and eliminate parasitic reactions. Herein, a series of ionic liquids (ILs) with Li[FSA] ([FSA]^- = bis(fluorosulfonyl)amide) salts are investigated as electrolytes compatible with the LNO positive electrode. The use of IL electrolytes enhances cycle performance, achieving a high capacity retention of 73.1% in Li/LNO cells after 500 cycles with a high Li salt concentration. Further characterizations confirm that the cathode electrolyte interphase formed on the LNO positive electrode in the highly Li-salt concentrated ILs suppresses Ni dissolution, structural degradation, and side reactions. Meanwhile, the above electrolyte is capable of effectively alleviating Al corrosion at high potentials. This work highlights the role of electrolytes and contributes to addressing the stability concerns of positive electrode components at high voltages.