Toward Deciphering the Internal Menace of Battery Safety: Soft Short Circuit Versus Hard Short Circuit?

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Abstract
Internal short circuits (ISC) from Li dendrites pose crucial challenges to the safety and reliability of electric vehicle power batteries. However, fundamental knowledge of how local/microscopic Li‐dendrites initiate ISC and early identification remains unclear. Particularly for soft ISC, presents the transient shorting and un‐shorting that occurs on the microsecond‐to‐seconds timescale. Herein, a general phase‐field‐based multiscale ISC model is developed to monitor the “real‐time” life cycle of Li dendrite‐induced ISC from a physics‐based perspective across micro‐to‐cell level. Validated by ISC experiments, the results show: 1) hard short‐circuits exhibit < 1 Ω contact resistance, while soft short‐circuits range from 10 2 –10 3 Ω, 2) soft short‐circuits involve dozens/hundreds of competitive Li‐deposition‐dissolving cycles. For each cycle, Li dissolving persists for ≈70% cycle time where Li local self‐discharge and dissolution counteract Li growth, consistent with experimentally observed “stagnant” dendrite growth, 3) “Fake stable” voltage behavior is observed during soft ISC, where voltage increases despite Li filaments connecting the cathode, 4) when capacity loss rate >0.005mAh s −1 , soft ISC permanently transition to hard ISC. These results demonstrate the dominant mechanism of the Li‐dendrite re‐dissolving (i.e., voltage recovery, resulting in un‐shorting) is local self‐discharge current density, which defeat critical current density of Li‐deposition at the dendrite tip region.

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