The Beneficial Effect of Pressure for Lithium Ion Battery Cells through Gas Dissipation

Pressure is often applied to improve the performance of lithium ion batteries (LIBs) during cyclic aging. However, the reasons for the performance impact of compression is still unclear. For this, LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) based LIB pouch cells with graphite based and SiO x based negative electrodes were used. Further, the electrolyte composition was varied between vinylene carbonate (VC) -containing and VC-free electrolytes. The cells were cyclic aged at 20 or 60 °C under three different conditions: without compression, compression (∼1.9 bar) only during formation and compression during formation and cyclic aging. Compression during formation increased obtainable capacity and decreased capacity loss, if gassing was present. However, no additional long-term effect of cells where pressure was applied during formation was observed during cyclic aging without compression at 20 and 60 °C. Compression during cyclic aging increased the obtainable capacity, when the cells were gassing during cycling as at 60 °C. Otherwise, if the cells were not gassing, as at 20 °C, no further effect of compression was observed during cycling. The results highlight that pressure only had a beneficial effect if cells were gassing.