(Digital Presentation) Protective Effects of Lithium Plating on High Temperature Degradation of Lithium-Ion Cells

Abstract

Lithium plating and solid electrolyte interphase (SEI) growth are two main degradation mechanisms of lithium-ion cells. While lithium plating can occur during low temperature charging and/or fast charging, SEI growth is accelerated during high temperature operation. Here we report an interesting observation that lithium plating shows protective effects on high temperature degradation of lithium-ion cells. As shown in Figure 1, two baseline commercially available lithium-ion cells were cycled only at 60 °C. They rapidly degraded which can be attributed to SEI growth. In comparison, the other two cells were pre-cycled at 5 °C and experienced rapid degradation due to lithium plating. But when these two cells with lithium plating were further cycled at 60 °C, they showed slower degradation than the baseline cells. Similar results were also observed for cells cycled at 45 °C as shown in Figure 2. These preliminary results suggest that lithium plating has protective effects for high temperature cycling of lithium-ion cells. Such effects were further observed in lab-made lithium-ion cells with low negative/positive (N/P) ratio. As shown in Figure 3, baseline cells (N/P ratio=1.25) degraded quickly during 60 °C cycling (21 mA constant current charging to 4.2 V and 21 mA constant current discharging to 2.8 V). In comparison, low N/P ratio cells (N/P ratio=0.8) that had lithium plating induced during formation showed very stable discharge capacity for more than 600 cycles before abrupt degradation. Further analysis of these results will be reported. Figure 1