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.