Differential voltage analyses of high-power, lithium-ion cells: 1. Technique and application

The C/25 discharge data from 18650-size cells containing LiNi0.8Co0.1Al0.1O2 cathode and graphite anode laminates were analyzed through the use of the differential voltage, dV/dQ, curves. Using half-cell data, the peaks in the dV/dQ curve of the full cell data were assigned. Analysis of the relative peak shifts allowed for the determination of the source of capacity fade. For cells formed and aged at 45 °C for 40 weeks (capacity fade = 7.5%), the analysis indicated negligible loss of accessible material at the anode and at the cathode. Capacity loss of the cell could be accounted for, largely, by side reactions at the anode. This type of analysis can be used when the introduction of a reference electrode is difficult or impractical.