Battery safety: abuse and thermal runaway

Lithium-ion safety on one page: nail penetration, overcharge and oven abuse tests, the thermal-runaway temperature ladder from SEI decomposition to oxygen release, a shutdown separator, and runaway spreading through a module. Every caption and temperature is quoted from the cited papers.

1. Nail penetration: Mechanical, electrical and thermal abuse initiate internal short circuits and heat accumulation that show as smoke, fire or explosion. Penetration can instantly breach the separator, connecting anode and cathode: the localized short triggers rapid local Joule heating, then electrolyte decomposition, gas release and potentially runaway; penetration, compression and crushing are the most frequent and hazardous mechanical abuses (Yang 2026). 2. Overcharge: Overcharge forces lithium insertion beyond the anode capacity, causing lithium plating, SEI decomposition and gas evolution; overdischarge can dissolve copper from the current collector and form dendrites; an external short at a high state of charge reaches several hundred amperes within milliseconds (Yang 2026). 3. Oven test: Abuse can be mechanical (deformation), electrical (overcharge) or thermal (heating above the permitted temperature); exothermic reactions then start a feedback loop of self-heating that leads to thermal runaway. From about 70 °C LiPF₆ decomposes to POF₃ and HF, and the first gases appeared near 70–80 °C; at 130 °C gas evolution may raise the pressure fast enough to vent the cell (Schmidt 2025). 4. The temperature ladder: Heat accumulation starts with SEI decomposition and anode–electrolyte reactions at 80–110 °C; intense thermal runaway follows at 130–300 °C. Polyolefin separators melt at ≈ 130 °C, causing internal short circuits; above 200 °C cathode materials such as Li-rich layered oxides decompose and release oxygen, which reacts with the carbonate solvents (> 2000 J g⁻¹) and drives the cell over 800 °C within seconds (Nan 2026). The cell vents its contents violently at the peak, and the runaway stops only once the reactants are exhausted (Zhou 2025). 5. Shutdown separator: In a commercial PP/PE/PP separator (Celgard 2325) the PE layer can close its pores above 115 °C, impeding ion transport and inhibiting the spread of thermal runaway, though that temperature is still high enough to add risk (Zhou 2025). Inorganic coatings, or high-melting films with low shrinkage such as polyimide, cellulose and polyesters, improve thermal stability (Nan 2026). Moss-like deposits and dendrites can pierce the separator and short the cell (Agubra 2013). 6. Propagation in a module: Once one cell runs away its heat, gases and flames can cascade through a module: by conduction through casings and tabs, convection by vented gases and radiation from flames or hot surfaces. Smaller gaps between cells shorten propagation times, while larger spacing or thermal barriers, which block conduction, buffer heat and shield flames and vent-gas jets, delay and suppress it (Su 2026).

Yang et al., “A Review of Failure Modes and Safety Strategies of Lithium-Ion Batteries from Materials to Systems”, Adv. Sci. 2026 (doi:10.1002/advs.76228); Schmidt et al., “High temperature in situ gas analysis for identifying degradation mechanisms of lithium-ion batteries”, Chem. Sci. 2025 (doi:10.1039/d4sc08105f); Nan et al., “Materials design for thermally improved safety in lithium-ion batteries”, Chem. Sci. 2026 (doi:10.1039/d5sc08060f); Zhou et al., “Critical Perspectives on the Design of Polymeric Materials for Mitigating Thermal Runaway in Lithium-Ion Batteries”, Polymers 2025 (doi:10.3390/polym17091227); Su et al., “Engineering Strategies to Suppress Thermal Runaway Propagation in Lithium-Ion Battery: Mechanisms, Metrics, Materials, and Evaluation Methods”, Adv. Sci. 2026 (doi:10.1002/advs.76502); Agubra & Fergus, “Lithium Ion Battery Anode Aging Mechanisms”, Materials 2013 (doi:10.3390/ma6041310).

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