Influence of pressure peaks occurring during battery module production on performance

This study investigates the impact of short-term pressure peaks occurring during battery module production on lithium-ion cell performance. A specialized test bench and procedure were developed to simulate the pressures experienced by cells during module production and to operate the cells in a rigidly constrained setup. Cell stacks are compressed and constrained to a specific dimension in the production process to fit in the designated installation space. Due to the partly viscous compression behavior of the cell components, a short-term pressure peak occurs. The magnitude of this peak depends on the strain rate. After reaching the desired dimension, the pressure decreases while the compressive strain remains constant. In this study, different peak pressures from 0.2 MPa to 2.5 MPa were applied to the cells before operation. After the pressure peak, the cells were constrained at a fixed displacement with an identical initial preload pressure of 0.2 MPa. The results demonstrate that higher pressure peaks during compression lead to greater irreversible compression, which indicates a reduction in the porosity of the cell components. This reduction in porosity initially deteriorates the rate capability at C-rates above 1 C, while the discharge capacity at lower C-rates remains unaffected. During operation, the rate capability at high C-rates (>1 C) declines further, whereas the capacity at lower C-rates showed no significant variation across the cases. This decrease in rate capability at higher C-rates is attributed to a reduced concentration of conducting salt, which causes earlier depletion of lithium ions. This effect becomes more pronounced with lower porosity as the diffusion paths increase. Consequently, cells subjected to higher pressure peaks are more affected. The findings indicate that short-term pressure peaks during battery module production can reduce rate capability and amplify the effects of aging mechanisms, such as conducting salt depletion, further impacting rate performance.