Interfacial degradation of PEO-based polymer electrolytes on the NMC cathode and CEI components prediction

All-solid-state Li-metal batteries using solid polymer electrolytes (SPEs) in combination with high-voltage cathodes such as lithium nickel manganese cobalt oxide (NMC) promise enhanced battery safety, energy density, and flexibility. However, understanding the oxidative decomposition of SPEs on the cathode surfaces and characterizing the resulting cathode-electrolyte interphase (CEI) remain challenging both experimentally and computationally. This study introduces a new computational protocol based on ab initio molecular dynamics for simulating the decomposition of PEO:LiTFSI SPE on the NMC-811 cathode surface using a combined electron- and Li+-removal simulation approach. This method incorporates the effects of the applied electric potential and Li+ migration on electrolyte oxidation during battery charging. The calculations indicate that electrons are withdrawn from both the C-C bonds of PEO and the Ni-O bonds of NMC-811, resulting in C-C bond cleavage and the formation of decomposition fragments. The created Li vacancies in the NMC facilitate coupling between decomposed PEO and exposed surface oxygen. The ROCH2O-M species, identified as the major degradation product on the NMC-811 cathode surface, is in agreement with the experimental XPS spectra. This approach provides detailed insights into the oxidative decomposition of PEO-based SPEs and demonstrates its effectiveness in exploring CEI component formation.