Polymer Electrolyte–Cathode Surface Bonding Suppresses Oxygen Evolution and Cation Mixing in Ni‐Rich Layered Oxides for Lithium Batteries

Although lithium nickel manganese cobalt oxides (NMC‐811) exhibit high practical capacity and voltage, they face severe structural degradation at high states of delithiation, including oxygen evolution, Li/Ni mixing, transition‐metal (TM) dissolution, etc. These phenomena are dependent on the interactions with the electrolyte. Here, we systematically studied interfacial O–TM bonding between three distinct solid polymer electrolytes and the NMC‐811 surface using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The polymers considered include poly(ethylene oxide) (PEO), poly‐ε‐caprolactone (PCL), and poly(trimethylene carbonate) (PTMC). The DFT results indicate that PTMC exhibits the strongest Ni–O polymer bonding strength due to the highly negative charge of its carbonyl oxygen. This strong PTMC–NMC bond further enhances the Ni–O NMC bonding strength, and both the Ni–O polymer and Ni–O NMC bonds are strengthened after delithiation. Consequently, PTMC can stabilize undercoordinated surface Ni ions. The AIMD simulations support this observation, showing the fewest oxygen‐evolution and Li/Ni‐mixing events in the PTMC‐based system. We propose that strong hybridization between the donor oxygen and surface Ni facilitates Ni 2+ oxidation and reduces the redox activity of lattice oxygen. Thereby, this study highlights that the structural stability of NMC can be tuned by selecting polymer functional groups.