Importance of uniformly redistributing external pressure on cycling of pouch-type Li-metal batteries

Abstract

Li-metal anode (LMA) is considered promising for overcoming the energy density limit of current Li-ion batteries. However, LMAs in large-scale cells are limited by uneven and excessive anode swelling, owing to the notorious buildup of a highly porous passivation ("dead" Li) layer. To demonstrate the impact of the pressure environment on the LMA swelling behavior and cycling stability, the distribution of the actual stack pressure was visualized in pouch cell platforms using pressure-sensitive films. If the stack pressure is not uniform, pouch cell failure occurs regardless of how high the applied pressure is. Conformal stack pressure assisted by the modified pressure setup with force redistributing pads enabled stable cycling even at a lower external pressure. By correlating with the thickness distribution of the "dead" Li layer over the LMA surfaces after cycling, it is suggested that a uniform stack pressure is crucial for mitigating anode swelling and the stable cycling of Li metal pouch cells.