Behavior of Solid Electrolyte in Li-Polymer Battery with NMC Cathode via in-Situ Scanning Electron Microscopy

We present the first results of in situ scanning electron microscopy (SEM) of an all-solid Li battery with a nickel-manganese-cobalt-oxide (NMC-622) cathode at 50 °C and an operating voltage of 2.7-4.3 V. Experiments were conducted under a constant current at several C rates (nC rate: cycling in 1/n h): C/12, C/6, and C/3. The microstructure evolution during cycling was monitored by continuous secondary electron imaging. We found that the chemical degradation of the solid polymer electrolyte (SPE) was the main mechanism for battery failure. This degradation was observed in the form of a gradual thinning of the SPE as a function of cycling time, resulting in gas generation from the cell. We also present various dynamic electrochemical and mechanical phenomena, as observed by SEM images, and compare the performance of this battery with that of an all-solid Li battery with a LiFePO₄ cathode.