Determination of degradation modes of lithium-ion batteries considering aging-induced changes in the half-cell open-circuit potential curve of silicon–graphite

The shape of the open-circuit potential (OCP) curve of silicon–graphite blend electrodes changes during cycle aging due to the faster degradation of the silicon in comparison to the graphite. In this study, the impact of these changes on the open-circuit voltage (OCV) curve of full-cells is investigated. Reconstructing the OCV curve of aged cells by shifting and linearly scaling pristine half-cell OCP curves is an established diagnostic method of determining the degradation modes occurring in lithium-ion cells. We reconstruct the full-cell OCV curves of cycle-aged commercial cells with silicon–graphite anodes using both pristine and aged silicon–graphite OCP curves. Lower estimates are obtained for the loss of anode active material and higher estimates for the loss of both cathode active material and lithium inventory, when aging-induced changes in the shape of the silicon–graphite OCP are considered. Aging-induced changes in the shape of silicon–graphite OCP curves are integrated in the diagnostic method by using a blend electrode OCP model. This not only improves the validity of the determined degradation modes, but also enables the non-destructive estimation of the anode capacity fraction provided by silicon, based on full-cell OCV measurements.