Correlating volume expansion and cycle life in anode-free lithium-metal pouch cells

Persistent swelling and rapid capacity decay remain coupled challenges in anode-free lithium-metal batteries (AF-LMBs). Here, we use operando swelling monitoring to examine the relation between mechanical swelling and Li reversibility in AF-LMB pouch cells. The maximum swelling at 100% state of charge (S max ) is decomposed into irreversible (S ir ) and reversible (S re ) components, thereby linking the evolution of swelling to Li-inventory loss. On this basis, a reversible-swelling ratio (Re-ratio, S re /S max ) is introduced as an operando descriptor of Li reversibility. By comparing different mechanical constraints and cycling protocols, we show that the approximately constant-thickness mode with intermediate initial pressure (0.3 MPa) and a slow-charge/fast-discharge protocol suppresses swelling accumulation, maintains a higher Re-ratio, promotes denser Li deposition, and improves cycling stability. Guided by this analysis, 100 mAh-level pouch cells achieve 88% capacity retention after 150 cycles at 450 Wh/kg and last for 190 cycles at 420 Wh/kg. These results indicate that operando swelling analysis can serve as a useful tool for diagnosing degradation and guiding the optimization of pouch-type AF-LMBs.