Correlation of electrochemical and mechanical responses: Differential analysis of rechargeable lithium metal cells

Recently, interest in high energy rechargeable lithium metal batteries has increased. Application of pressure has been identified as a distinct means to increase cycle life for these cells, but there is still a disconnect between the evolution of electrochemical and mechanical responses. For this study, lithium/NMC622 pouch cells are cycled under two different pressure conditions and pressure evolution is monitored. Applying pressure with an appropriate experimental setup not only improves performance, but also enables collection of additional information that compliments cell electrochemistry. By jointly comparing differential pressure (dP dV(-1)) and differential capacity (dQ dV(-1)) analysis, the combined electrochemical and mechanical cell responses are analyzed. It is found that while little change in cell capacity and dQ dV(-1) are observed, changes in cell pressure can be used to provide in operando information on the lithium metal electrode for full pouch cells. The changes in pressure suggest it is possible to track the evolution of electrode structure from a flatter electrode early in life to a more porous negative electrode prior to the point where cell capacity begins to dramatically fade.