Reevaluating the Stability of the PEO-Based Solid-State Electrolytes for High Voltage Solid-State Batteries

Whitacre, Jay

Poly(ethylene oxide) (PEO) is a very popular polymer-based solid electrolyte material with relatively high ionic conductivity and dielectric constant¹. However, many previous works mentioned that it could not be used in high voltage cells for its low oxidation potential (~3.9V vs. Li/Li+)². However, only a handful of prior investigations evaluated the stability of the PEO-based solid-state electrolyte considering the contribution of the cathode surface chemistry to electrolyte oxidation and decomposition. Since most of the previous research exploring high voltage cathodes with PEO used LiCoO₂, it could be possible the other cathode compositions will erode the PEO-based solid electrolyte in different and less extreme ways.

Our work revisits the high voltage electrochemical stability of PEO-based solid state-electrolyte materials. Potentiodynamic and galvanostatic tests were performed in test cells using PEO electrolyte layers with either LiNi_xMn_yCo_zO₂ or LiCoO₂ cathode materials. We found that the high voltage instability of PEO-based solid-state cells is profoundly affected by the instability of the cathode material used. Specifically, the LiCoO₂ electrodes were observed to undergo an irreversible oxidation process where they shattered into small pieces, which then led 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 cathodes stably at a voltage up to 4.5V vs. Li/Li+ over many cycles with minimal capacity deterioration.

K. Chrissopoulou, K. S. Andrikopoulos, S. Fotiadou, S. Bollas, C. Karageorgaki, D. Christofilos, G. A. Voyiatzis, and S. H. Anastasiadis, 44, 9710–9722 (2011).
J. Qiu, X. Liu, R. Chen, Q. Li, Y. Wang, P. Chen, L. Gan, S.-J. Lee, D. Nordlund, Y. Liu, X. Yu, X. Bai, H. Li, and L. Chen, Adv. Funct. Mater., 30, 1909392 (2020).