A Universal Highly Concentrated Electrolyte for Improved Cycling Stability in Li(Ni1-x-yMnxCoy)O2-NMC-Based Batteries

While 1 M LiPF6 has been widely adopted as the standard electrolyte in current LIBs, its chemical instability has reduced the battery’s cycling stability by, for instance, accelerating the dissolution of transition metals from electrode materials, particularly in high-voltage cathodes. Lithium bis(fluorosulfonyl)imide (LiFSI) has emerged as a promising alternative salt for next-generation high-voltage energy-dense LIB electrolytes. However, despite extensive research, the optimal concentration and formulation of LiFSI remain unresolved, with variations typically tested across different Li(Ni1-x-yMnxCoy)O2 (NMC) series cathodes. Herein, 6:4.5:8.3 LiFSI/EC/DMC (in molar ratio) is proposed as a universal electrolyte for high-voltage NMC series cathodes. The 6:4.5:8.3 LiFSI/EC/DMC electrolyte decomposes to form a uniform cathode–electrolyte interface with abundant inorganic species, resulting in a lower interface resistance. By adopting the 6:4.5:8.3 LiFSI/EC/DMC electrolyte, NMC series Li-ion half-cells are all able to stably cycle up to 200 cycles at a cut-off voltage of 4.4 V. Especially for high Ni content (NMC 811) cathode, the capacity retention was improved from 43.6% to 87.5% when charged to 4.4 V at 1C rate. This work provides a feasible universal electrolyte formulation for developing next-generation high-voltage LIBs.