In-Depth Understanding of Cycling Degradation Mechanisms in Lithium Metal Batteries

Lithium metal batteries (LMBs) are widely recognized for their substantial advantages in energy density, but their cycle life and safety still face the challenges of lithium dendrites and the generation of dead lithium, which limit their practical applications. LMBs experience dramatic volume changes during charge and discharge cycles, thereby requiring external pressure to ensure normal operation. Additionally, the charge and discharge conditions equally influence their self-generated pressure. To better understand the degradation mechanisms of LMBs, we analyzed the intricate correlation between external pressure, charge–discharge rates, and cycle life of LMBs based on recent literature. Using a 420 Wh/kg (9.8 Ah) LMB pouch cell, we conducted long-term cycling tests under various charge–discharge rates. After 710 cycles at 0.2C-3C rates, the capacity retention remained as high as 91%. Furthermore, through in situ high-resolution pressure sensing, we measured the expansion force of the lithium metal pouch cell under slow charge/fast discharge and fast charge/slow discharge conditions. Applying appropriate external pressure in combination with slow charge/fast discharge can effectively mitigate battery volume changes and enhance cycle life.