External short-circuit damage characterization and rapid hierarchical safety diagnosis of lithium iron phosphate batteries

Current research on external short-circuit mechanisms often decouples thermo-electrochemical failure from resistance variations, lacking comprehensive insights into multi-factor operational scenarios. To bridge this gap, this study systematically evaluates 26700 lithium iron phosphate batteries under nominal external resistance conditions ranging from 10 to 0.01 Ω across diverse operating conditions. By integrating macroscopic electro-thermal evolution, incremental capacity analysis, and post-mortem scanning electron microscopy observations, this study characterizes external-short-circuit-induced degradation from coupled electrical, thermal, and morphological perspectives. Scanning electron microscopy observations suggest severe anode surface deterioration and separator pore densification after low-resistance external short circuits. Under the matched 5 min, 0.01 Ω protocol, the full-SOC group exhibited a mean total absolute ICA peak-height change of 13.21 ± 0.79 Ah/V, 1.62 times that of the charging-state group. In the separate 30 min thermal tests, the maximum measured cell-surface temperature under the 0.01 Ω condition reached 103.2°C at full SOC. Furthermore, parallel topologies are found to mask localized cell-level failure signatures. Based on these observations, a mechanism-informed Multi-Scale Temporal Fusion Hierarchical Detection System is developed by combining electro-thermal model-assisted data augmentation, external-short-circuit-oriented feature extraction, and hierarchical diagnosis. Validation on a held-out real-cell test set separated by battery identity yields an accuracy of 0.981 ± 0.016 (mean ± sample SD, n = 5) and fault-identification times of 0.07–0.96 s under controlled laboratory conditions. These results support rapid battery-safety diagnosis under the tested laboratory conditions.