Mechanism investigation on microstructure degradation and thermal runaway propagation of batteries undergoing high-rate cycling process

With the increasing application of lithium-ion batteries under high-rate operation, safety concerns such as thermal runaway (TR) and thermal runaway propagation (TRP) have become critical. In this study, the TRP action of batteries undergoing high-rate cycling is systematically investigated. Microanalysis results reveal that the crystallinity and I(003)/I(104) of the cathode are decreased by 32.95% and 13.01% after 4 C cycling, while the layered structure of the anode is seriously damaged. As revealed, the TR interval time (Δt) of batteries cycled at 4 C is decreased by 83.23% compared with that for batteries cycled at 1 C. Meanwhile, the maximum mass loss (ML) rate of Battery 2# is increased by 32.35%. We have further investigated the influence of battery spacing on TRP action. The maximum TR temperature of Battery 2# at 1.5 cm spacing is reduced by 26.21% compared with the value at 0 cm spacing. When increasing the spacing from 0 to 1.5 cm, the ML of batteries is reduced by 20.73%. ML increases and decreases with the elevation of the charging rate and battery spacing, respectively. Compared with a battery cycled at 1 C, a battery cycled at 4 C shows reduced heat required to trigger TR. The corresponding decreases can reach 68.28%, 70.10%, 76.88%, and 26.15% when setting the spacing at 0, 0.6, 1.5, and 2.1 cm, respectively. This indicates that Battery 2# can enter TR with much lower heat after high-rate cycling. Overall, high-rate cycling and low spacing accelerate the TRP of the battery and aggravate the TR severity of the battery. This work can provide insights for the practical safety design of energy storage systems.