New Insights in the Electrochemical Stability of Various Solid Polymer Electrolytes/Layered Positive Metal‐Oxide Electrode Interfaces in Solid‐State Lithium‐Ion Battery

All‐solid‐state battery is a promising solution to make lithium batteries safer while boosting their energy density. Solid polymer electrolytes offer a cheaper alternative to inorganic solid electrolyte. Solid polymer electrolytes even outperform inorganic solid electrolytes in some domains; for example, they are less prone to mechanical failure or to contact loss with electrodes upon cycles. However, there are still a couple of challenges to address, including the solid electrolyte/positive electrode interface degradation. The interface between solid polymer electrolyte and the positive electrode is largely overlooked in favor of that of the negative electrode. Ab initio molecular dynamics was combined with relative bond length change analysis and X‐ray photoelectron spectroscopy to study the compatibility of a broad selection of functional groups with two grades of Ni‐rich NMC cathode (NMC622, NMC811). The results emphasize the relative reactivity of NMC811 compared to NMC622. It was observed that Li is mostly responsible for triggering chemical degradation by interacting with negatively charged atoms from functional groups. Results revealed that hydroxyl or amine deprotonation is a major mechanism of interface degradation that leads to capacity fading. The role of the electric field during cycling was also investigated, showing how it affects functional group orientation and interactions with the NMC electrode.