High-Voltage Electrolyte and Interface Design for Mid-Nickel High-Energy Li-Ion Batteries

Elevating the charge cutoff voltage of mid-nickel (mid-Ni) LiNixCoyMnzO2 (NCM; x = 0.5–0.6) Li-ion batteries (LIBs) beyond the traditional 4.2 V generates capacities comparable to those of high-Ni NCMs along with more stable performance and improved safety. Considering the critical issues associated with residual lithium on high-Ni NCMs regarding greatly increased cost, deteriorated cycle life, and safety hazards, mid-Ni is recognized as a more reliable cathode to meet the urgent needs for cost reduction and safety enhancement pursued by LIB and electric vehicle manufacturers. To enable high-voltage mid-Ni LIBs, high anodic stability of electrolyte and cathode–electrolyte interface (CEI) are essential. Utilization of additives is a cost-effective strategy, and recent trends include the exploration of high-voltage solvents for better working electrolytes. This Perspective aims to highlight and discuss the key compounds that are usable as additives and/or solvents in high-voltage electrolytes at standard salt concentrations, specifically for mid-Ni LIBs, which are less flammable and form an inorganics-enriched robust CEI, and to provide insights into their function and applicability to improve the energy density, overall performance, and safety for next-phase LIBs.