Controlled Large-Area Lithium Deposition to Reduce Swelling of High-Energy Lithium Metal Pouch Cells in Liquid Electrolytes

Lithium (Li) metal battery technology has attracted world-wide attention because of its high energy density, but its practical application is hindered by several challenges, with one significant issue being the large volume change and cell swelling. While external pressure is known to have a profound effect on cell performance, there are currently no reports exploring the relationship between external pressure and the electroplating of Li+ in large-format pouch cells to enhance overall performance. Here we investigate the influence of externally applied pressure on the electroplating and stripping of lithium metal in 350 Wh/kg pouch cells. A hybrid constant gap and constant pressure design is designed to apply a minimal external pressure for practical application. The self-generated pressures are monitored and quantified which are further correlated to the observed charge-discharge processes. A two-stage cycling process is observed. In the first stage, Li+ ions utilized are mainly supplied by the cathode which shuttle between the cathode and anode with minimal Li loss which minimizes cell swelling but only happens when pressure is applied appropriately. In the second stage, Li from the Li foil anode participates in the reaction and the thickness of the anode gradually increases. However, even after extensive cycling, cell swelling remains less than 10%, comparable to that of state-of-the-art Li-ion batteries. In addition, the pressure distribution along the horizontal direction across the surface of Li metal pouch cell reveals a complex behavior of Li+ migration during the electroplating (charge) process. The external pressure encourages a preferred plating process of Li in the central region, necessitating the development of new strategies to address uneven Li plating and utilization to advance Li metal battery technology.