Performance of Lithium-Ion Pouch Cells with Silicon Composite Anodes under External Mechanical Pressure

The external forces have significant effects on the mechanical and electrochemical properties of lithium-ion pouch cells with silicon composite electrodes, but the behaviors under the constant pressure condition have been lacking for a long time. In this study, on the basis of the in situ testing equipment that can provide good precision and good stability under constant pressure conditions, the mechanical and electrochemical performance of silicon-composite-based batteries is studied in detail. First, the optimal constant pressure for the battery is proposed with the value of 0.02 MPa. Then, the cycle life is started on the basis of this pressure, but it is found that the improvement in the capacity retention rate is limited. Through non-destructive computed tomography detection and morphology characterization, the silicon composite electrode under a constant pressure leads to a change in the battery spacing, which, in turn, increases the polarization and results in lithium precipitation on the surface, and lithium precipitation consumes the electrolyte and causes the gas formation and eventually battery failure. Finally, an improved strategy that can effectively prolong the battery cycle period is proposed. In the experiment, it is observed that, when the battery operates under a constant pressure, its capacity undergoes a slow decline followed by a rapid drop at a specific capacity point known as the "inflection point". When the inflection point occurs, increasing the external pressure applied to the battery can delay the aging behavior of the battery. This work has certain guidance for improving the cycle life of silicon-based lithium-ion batteries and pushes their engineering applications in battery pack systems.