How to determine the degradation modes of lithium-ion batteries with silicon–graphite blend electrodes

Silicon–graphite blend anodes, which are used to increase the energy density of lithium-ion batteries, complicate degradation mode analysis because silicon and graphite age independently. Degradation modes are typically inferred by shifting and scaling half-cell open-circuit potentials (OCPs) to align with the full-cell voltage, which requires accurate silicon and graphite OCPs. However, silicon OCPs published in the literature vary widely, which can lead to different estimated degradation modes. In this paper, we present a new method to derive the silicon OCP from the measured blend anode and a graphite half-cell. We analyze the generated and literature silicon OCPs in a degradation mode framework by applying them to commercial cells with silicon–graphite blend anodes. Our results show that the estimated full-cell degradation modes, such as graphite loss, can vary by more than twofold depending on the chosen silicon OCP. By leveraging our generated silicon OCP, we can strongly improve the accuracy of the full-cell voltage reconstruction. Additionally, we demonstrate the enhanced accuracy of the generated silicon OCP in determining degradation modes by comparing the fitted results to measurements from a three-electrode cell setup. The tools are openly available in the GitHub repository https://github.com/tum-ees/DegradationModeAnalysis .