Stabilizing High‐Nickel Cathodes with High‐Voltage Electrolytes

Electrolytes connect the two electrodes in a lithium battery by providing Li+ transport channels between them. Advanced electrolytes are being explored with high‐nickel cathodes and the lithium‐metal anode to meet the high energy density and cycle life goals, but the origin of the performance differences with different electrolytes is not fully understood. Here, the mechanisms involved in protecting the high‐capacity, cobalt‐free cathode LiNiO2 with a model high‐voltage electrolyte (HVE) are delineated. The kinetic barrier posed by a thick surface degradation layer with poor Li+‐ion transport is found to be the major contributor to the fast capacity fade of LiNiO2 with the conventional carbonate electrolyte. In contrast, HVE reduces the side reactions between the electrolyte and the electrodes, leading to a thinner nano‐interphase layer comprised of more beneficial species. Crucially, the HVE leads to a different surface reorganization pathway involving the formation of a thinner nanoscale LiNi2O4 spinel phase on the LiNiO2 surface. With a high 3D Li+‐ion and electronic conductivity, the spinel LiNi2O4 reorganization nanolayer preserves fast Li+ transport across the cathode–electrolyte interface, reduces reaction heterogeneity in the electrode and alleviates intergranular cracking within secondary particles, resulting in superior long‐term cycle life. Advanced characterizations delineate the mechanisms behind significantly improved cycling stability of high‐nickel cathodes with high‐voltage electrolytes (HVE). By forming a thin interphase layer with beneficial species and altering surface reconstruction pathways, the HVE preserves fast lithium‐ion transport across the interface, reduces reaction heterogeneity in the electrode and alleviates intergranular cracking, resulting in superior long‐term cycling life.