Are Lithium Ion Cells Intrinsically Safe?

National Institute for Occupational Safety and Health researchers are studying the potential for Li-ion-battery thermal runaway from an internal short circuit in equipment approved as permissible for use in underground coal mines. Researchers used a plastic wedge to induce internal short circuits for thermal runaway susceptibility evaluation purposes, which proved to be a more severe test than the flat plate method for selected Li-ion cells. Researchers conducted cell crush tests within a 20-L chamber filled with 6.5% CH₄-air to simulate the mining hazard. Results indicate that LG Chem ICR18650S2 LiCoO₂ cells pose a CH₄ explosion hazard from a cell internal short circuit. Under specified test conditions, A123 Systems 26650 LiFePO₄ cells were safer than the LG Chem ICR18650S2 LiCoO₂ cells at a conservative statistical significance level.