Suberonitrile (SUN)/PF₆^–-Derived Electrode/Electrolyte Interfacial Chemistry in LiNi_0.5Mn_1.5O₄/Graphite High-Voltage Lithium-Ion Cells Using SUN as an Electrolyte Additive

Enhancing the operating voltage (>4.3 V vs Li/Li+) of cathodes is a critical strategy for increasing the energy density of lithium-ion batteries (LIBs). However, in high-voltage LIBs employing conventional carbonate-based electrolytes, solvent-dominated electrode–electrolyte interfacial reactions hinder the formation of a stable cathode–electrolyte interface, resulting in rapid capacity degradation. In this work, suberonitrile (SUN) is used as an additive to regulate the structure of a commercial carbonate electrolyte (1 M LiPF6+ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3/7, v/v)), and the electrolyte containing SUN has a localized high-concentration electrolyte-like structure. Because the attraction of Li+-SUN is weaker than that of Li+-EC and Li+-EMC, while the attraction of PF6–-SUN is stronger than that of PF6–-EC and PF6–-EMC, SUN closely contacts PF6– by squeezing out the solvent molecules near PF6–, which pulls the PF6– into the Li+ solvation sheath. This unique electrolyte configuration shifts the interfacial chemistry from solvent-derived to SUN/anion-dominated, enhancing the stability of the electrode/electrolyte interface in high-voltage LiNi0.5Mn1.5O4/graphite cells. Consequently, the cell employing the 1.0 wt % SUN-containing electrolyte demonstrates a 14.3% improvement in capacity retention after 200 cycles at a 0.3C rate compared to that with the baseline electrolyte.