Are lithium ion cells Intrinsically Safe?

Abstract

National Institute for Occupational Safety and Health (NIOSH) researchers are studying the potential for Liion 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% CH 4 -air to simulate the mining hazard. Results indicate that LG Chem ICR18650S2 LiCoO 2 cells pose a CH 4 explosion hazard from a cell internal short circuit. Under specified test conditions, A123 Systems 26650 LiFePO 4 cells were safer than the LG Chem ICR18650S2 LiCoO 2 cells at a conservative statistical significance level.

Further study of the intrinsic safety of internally shorted lithium and lithium-ion cells within methane-air

“…This new provision suggests that a cell may deform by 10% at forces significantly less than the 13 kN maximum force, at which point the force is released. Previous research (Dubaniewicz and DuCarme, 2013) found that a sample of cylindrical Li-ion cells crushed by flat plates deformed by approximately 18% without any adverse outcomes; similar cells readily ignited when crushed by a plastic wedge. IEC 62133 edition 2 has also eliminated a narrow side crush test of prismatic cells.…”

“…The relative safety of LiFePO 4 is generally attributed to limited O 2 release upon high temperature decomposition. Previous research (Dubaniewicz and DuCarme, 2013) found that selected LiFePO 4 cells did not cause ignition when crushed within CH 4 -air mixtures under specified test conditions. In the current study, additional tests were conducted to crush selected LiFePO 4 cells while charging within normal charging conditions.…”

“…Neither ACRI2001 nor ANSI/ISA 60079-11 requirements for distance through solid insulation are currently applied to internal Li-ion cell constructions. These standards rely on other cell level standards to help ensure intrinsic safety in potentially explosive environments (Dubaniewicz and DuCarme, 2013). …”

“…Portable electronics often use Li-ion batteries with lithium cobalt oxide (LiCoO 2 ) cathodes, which offer high energy density, but have well-known thermal runaway safety concerns. Safety concerns specific to underground coal mine fire and explosion hazards from LiCoO 2 cells were described previously (Dubaniewicz and DuCarme, 2013). A Li-ion powered Mine Safety and Health Administration (MSHA) permissible device was involved in a thermal event in an underground coal mine.…”

“…The study focused on internal short circuits induced by external mechanical damage, with this failure mechanism known to produce thermal runaway in Li-ion cells. NIOSH researchers previously reported on a new method of inducing internal short circuit for thermal runaway susceptibility evaluation purposes that overcomes some limitations of the flat plate and nail penetration methods (Dubaniewicz and DuCarme, 2013). The present work extends earlier findings to include a study of:

LiFePO 4 cells crushed while under charge.

prismatic form factor LiCoO 2 cells.

crush speed influence on thermal runaway susceptibility.

primary, spiral-wound constructed LiMnO 2 cells.

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