Realizing poly(ethylene oxide) as a polymer for solid electrolytes in high voltage lithium batteries via simple modification of the cell setup

Pure, i.e., linear poly(ethylene oxide)-based solid polymer electrolyte (PEO-based SPE) as a common benchmark system for Li metal batteries (LMBs) is frequently assumed to be unsuitable for high voltage applications e.g., with LiNi0.6Mn0.2Co0.2O2 (NMC622)-based cathodes. In fact, a destructive failure appears immediately after cell operation, seen by a random-like voltage noise during charge, rendering continuous charge/discharge cycling in e.g., NMC622||Li cells not possible. Counterintuitively, this failure is a result of short-circuits in the course of e.g., Li dendrite penetration. It is shown that the distance between the electrodes plays a crucial role. This failure is more likely with a lower distance, particularly when the SPE is mechanically prone to shrinkage, for example at higher temperatures as systematically revealed by mechanical compression tests. Additionally, the active mass loading has a crucial impact on short circuits, and thus the voltage noise failure, as well. An effective and practically simple solution to realize cell operation with a PEO-based SPE is the incorporation of a spacer between the electrodes. This modification prevents the detrimental shrinkage and enables charge/discharge cycling performance in NMC622||Li cells with a defined and constant electrode distance, thus without voltage noise, and finally fulfills a reasonable benchmark for systematic R&D with specific capacities above 150 mA h g(-1) even at 40 degrees C.

Automated summary

Pure PEO-based solid polymer electrolyte is often considered unsuitable for high voltage applications in Li metal batteries due to destructive failure caused by short circuits during dendrite penetration. This failure can be prevented by increasing electrode distance or incorporating a spacer to enable stable operation and fulfill benchmark standards in systematic R&D.