Variations in Open Circuit Voltage of Cycle-Aged Lithium-Ion Batteries due to Silicon-Enhanced Anodes

We present the outcomes of cycle aging tests performed on 16 lithium-ion battery cells of different types, both commercially available: INR21700M50LT produced by LG Energy Solution and INR18650M35A produced by Molicel. These cells exhibit differences in silicon content within the anode, coupled with the utilization of two different cathode materials. Throughout the testing process, the cells underwent cycling with different state of charge (SOC) windows: 0-90%, 0-30%, 30-60% and 60-90% as well as routine checkup phases, which include a measurement of the residual capacity and of the quasi-open circuit voltage (qOCV) curve. After 260 equivalent full cycles, we found substantial differences in the aging of the two cell types, evident in both their state of health and in the variations of the qOCV curve. The LG M50LT displayed a notably slower capacity fade up to 3x less with respect to the Molicel M35A under identical testing conditions. We also found out that cycling in the SOC window 0-90% produced the least pronounced variations in the qOCV curve of the LG M50LT, while the opposite is true for the Molicel M35A. This discrepancy cannot be explained only in terms of a different silicon content, therefore the reasons have to be searched in the complex interactions between the two anode materials, as well as in cathode material degradation.