Reevaluating the stability of the PEO-based solid-state electrolytes for high voltage solid-state batteries

This work shows how PEO-based solid state-electrolyte materials can be more stable than commonly expected when used with some types of high voltage cathode materials. Potentiodynamic and galvanostatic tests were performed in test cells using PEO electrolyte layers with either LiNixMnyCozO2 or LiCoO2 cathode materials. We found that the high voltage instability of PEO-based solid-state cells is profoundly affected by the interfacial instability of the cathode material used Specifically, the in the presence of PEO electrolyte, LiCoO2 electrodes were observed to undergo an irreversible oxidation process where they eventually shattered into small pieces, thus leading to a rapid irreversible loss in capacity. In contrast, we found that the PEO-based solid-state electrolytes could be stably cycled with high-nickel content cathode materials (NCM 811, 532, and 111) stably at a cell potential up to 4.5 V vs. Li/Li+ over many cycles with minimal capacity deterioration; this unexpected degree of stability in light of possible PEO/cathode interfacial stability concepts.