Degradation Diagnostics on Si/C-Graphite Composite Anode with Different Conductive Agent

A degradation diagnostic method was applied on Si/C-graphite composite anode basing on discharge curves and corresponding dV/dQ curves of full cell. The impact of conductive additives, specifically vapor-grown carbon fibers (VGCF) and single-walled carbon nanotubes (SWCNT), on capacity fade is examined. When VGCF is replaced by SWCNT, capacity retention of half cell is obviously promoted from 91.5% to 103.7%. Meanwhile, the degradation of a full cell slows down in the early cycles but accelerates in the late cycles, which leads to similar capacity retention of 76.3% and 76.0% for cell with VGCF and that with SWCNT, respectively. The analysis on the charge curves and corresponding dV/dQ curves in half cells indicate that the capacity fading in half cell is mainly caused by the electric inactivation of Si. Quantitative analysis of full-cell discharge curves and dV/dQ profiles reveals distinct capacity loss contributions. In VGCF-containing cells, 12.6% capacity loss is attributed to reversible lithium inventory loss, and 11.1% to Si electrical inactivation. Conversely, in SWCNT cells, the total capacity loss (25.1%, closely matching the experimental 24.0%) is solely due to reversible lithium inventory loss, demonstrating complete suppression of Si inactivation.