NaH₂PO₄as an Electrolyte Additive for Enhanced Thermal Stability of LiNi_0.8Co_0.1Mn_0.1O₂/Graphite Batteries

The wide use of nickel-rich layered cathode materials is plagued by their severe degradation at elevated temperatures. In this study, we introduce monobasic sodium phosphate (NaH2PO4) (P2) as a versatile electrolyte additive that improves the thermal stability of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material. P2 remarkably enhances the cycle and storage performances of NCM811/graphite cells at 60 °C. We elucidate that P2 plays a beneficial role in two ways: (i) it forms a conductive and protective cathode-electrolyte interphase layer that suppresses electrolyte decomposition and NiO-phase formation on the cathode; (ii) it controls the hydrofluoric acid content, and thus decelerates the formation of NiO-phase on the cathode and the degradation of the solid electrolyte interphase layer on the anode. Considering its excellent thermal stability and practical availability, P2 is a promising electrolyte additive for Ni-rich NCM cathodes that suffer from poor thermal stability.