The three SEB cells show very close rates of capacity fade within 1000 cycles (Fig. 4A). Beyond 1000 cycles, SEB-3 shows a much lower rate of capacity fade than the other two SEB cells, as expected from its lowest reactivity. In comparison with the baseline cell, the stability and long cycle life of SEB cells are clearly evident, the reasons of which can be delineated from the differences in the capacity retention trend at various stages of aging. For the baseline cell, we see a sharp decrease in C/3 capacity retention during the initial stage and a slow decrease in the secondary stage. This is primarily attributed to the loss of lithium inventory during the quick and slow growth of the SEI layer. For the SEB cells, the capacity fade is linear with cycle number, indicating that there is no quick growth in the initial stage of aging as SEI layer growth is suppressed by in situ formation of the flame-retardant protective layer. Moreover, a sharp, nonlinear capacity loss due to lithium plating can usually be observed in the baseline cell at room temperature and at low temperatures in final stages of cell aging (11). In all SEB cells operated at 60°C, this lithium plating-induced capacity loss is, however, absent, indicative of no lithium plating in SEB cells. The SEB cell free of Li plating offers a significant improvement in safety over conventional LIB cells.