Electrochemical, Postmortem, and Safety Evaluation of Practical High-Voltage (NMC-811) Li Metal Batteries with Hybrid Ceramic Polymer Electrolyte

In this work, cycling and safety performance of high-voltage lithium polymer batteries, in multilayer pouch cell configuration, are studied. The batteries encompass a hybrid ceramic polymer electrolyte, high loading cathode based on LiNi0.8Mn0.1Co0.1O2 (NMC-811), and 40 µm-thick self-standing Li metal anodes. Solid state NMC-811-based cathodes for the multilayer pouch cells were produced with practical areal capacities of 2.7 mAh∙cm−2. Pouch cells with nominal capacity of 1 Ah reached specific energy of 358 Wh∙kg−1. Cells cycled at 60 °C and C/10 showed 85% capacity retention at the 90th cycle, followed by rapid failure before the 100th cycle. Postmortem analysis indicated that rapid failure is caused by lithium anode exhaustion, exacerbated by the large areal capacity, in accordance with observations in Li||Li symmetric cells. Finally, overtemperature tests in closed calorimeter were performed on 1 Ah and 3 Ah pouch Li/NMC811 cells. The cells showed similar safety behavior to commercial lithium-ion batteries. The released energy was higher, which is attributed to the contribution of the lithium metal as the anode. This study demonstrates the possibilities and challenges of high-voltage lithium metal batteries with polyether-based electrolytes, in terms of performance and safety, in a realistic cell configuration.