Cross-talk and internal resistance in high-voltage graphite‖LiNi0.5Mn1.5O4 cells: sulfolane vs. carbonate-based electrolytes

Abstract

High-voltage cathode active materials such as LiNi_0.5Mn_1.5O₄ offer promises of high-energy density lithium-ion batteries (LIBs), but their implementation is hindered by electrolyte instability and cross-talk phenomena that compromise cycling performance. This study presents a comprehensive investigation of interfacial degradation mechanisms in graphite‖LNMO full cells, comparing a conventional carbonate-based electrolyte (1.0 M LiPF₆ in EC/DEC + 1 wt% LiBOB) with a sulfolane (SL)-based alternative (0.7 M LiBOB in SL + 0.2 M LiTFSI). Using the latter electrolyte results in reduced transition metal dissolution, but significant graphite coulombic efficiency degradation persists, as shown by a holistic assessment using graphite-limited cell configurations, post mortem analysis, and intermittent current interruption measurements. The cells with the SL-based electrolyte exhibit lower initial discharge capacities, reduced average coulombic efficiencies, and substantially higher LNMO interfacial resistances. They also produce organic rich interphases and soluble oxidation products affecting the anode performance, which rather than transition metal dissolution alone, constitute the dominant degradation pathway. Overall, the revealed complex interplay between electrolyte formulation, interfacial chemistry, and cross-talk mechanisms offers valuable insights for rational design of a next generation of electrolytes capable of supporting stable high-voltage LIB operation.