The Interplay between Stack Pressure, Mechanical Expansion and Degradation Pathways in Lithium-ion Batteries

While electrochemical degradation mechanisms in lithium-ion batteries are well-studied, the influence of mechanical factors remains poorly understood. Here, we introduce a high-precision stack-pressure control and dilatometry tool to apply a uniform and constant stack pressure on electrodes independent of electrode swelling. By increasing stack-pressure four-fold over typical initial values, we double the lifetime of graphite ‖ NMC811 cells, an industrially relevant battery chemistry, without altering active materials or electrolytes. This suggests that many lithium-ion batteries operate under sub-optimal stack-pressure conditions, leading to curtailed lifetimes. We demonstrate that different degradation mechanisms emerge outside the optimal pressure window: low stack pressure accelerates cathode cracking, whereas high pressure promotes lithium plating. Our findings highlight coupled mechanical-electrochemical degradation mechanisms and identify stack pressure optimisation as a practical solution for increasing cycling stability.