Mitigating interfacial instability of high-voltage sodium layered oxide cathodes with coordinative polymeric structure

Abstract

High operating voltage ensures high sodium utilization and high specific capacity of sodium-based layered oxides for sodium-ion batteries (SIBs), but charging to high voltage (>4.2 V vs. Na+/Na) may facilitate the irreversible phase transformation and undesirable interfacial reactions with electrolyte, resulting in severe capacity fading. Herein, we demonstrate an organic surface modification strategy to remarkably enhance the interfacial stability and electrochemical performance of high-voltage sodium-based layered oxides through a copolymer nanolayer of methacrylic acid and acrylonitrile (PMAA-AN). The copolymer nanolayer with strong electron-donating groups could anchor transition metal ions by coordinative interaction and prevent cathode materials from being corroded by electrolyte, thus slowing down interfacial structural degradation during cycling. The Na0.67Li0.16Ni0.33Mn0.67O2+δ (NLNM) coated with moderate PMAA-AN (0.5 wt%) exhibits remarkable improvement and excellent electrochemical performance with an initial capacity of 173.4 mAh g−1 and 86.0% capacity retention after 100 cycles, a superior rate capability of 100.1 mAh g−1 at 5 C within the wide voltage range of 1.5–4.5 V. This work provides new insights on the protective mechanism of polymeric coatings with coordinative structure and pave a way to advance high‐voltage layered oxides for high‐energy‐density SIBs.