Mechanical abuse simulation and thermal runaway risks of large-format Li-ion batteries

Abstract

Internal short circuit of large-format Li-ion pouch cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ~40% maximum compressive loading force during the pinch test. The cell was twisted about 5 degrees to the side by horizontally pulling a wire attached to the anode tab. The combined torsioncompression force created small failure at the separator yet allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4-6 cells at each state-of-charge (SOC). Commercially available 18 Ahr LiFePO 4 (LFP) and 25 Ahr Li(NiMnCo) 1/3 O 2 (NMC) cells were tested, and a thermal runaway risk (TRR) score system was used to evaluate the safety of the cells under the same testing conditions. The aim was to provide the cell manufacturers and end users with a tool to compare different designs and safety features.

Thermal runaway detection of cylindrical 18650 lithium-ion battery under quasi-static loading conditions

“…Eqs. (9) and (10), shows linear fit for three point bending "ε " represents failure strain and σ ft represents failure stress for three point bending test.…”

“…Assumptions based on past research were that the cell voltage could be used to identify the initiation of mechanical failure [8] [9]. Tension (stress: strain ratio) causes an initiation of cutoff [4] [10].…”

“…Temperature variations are not considered in battery abuse failure, and is useful to predict battery degradation and short circuit; however sudden force and voltage drop are used as a failure of battery and initiation of the short circuit [9]. Short circuit leading to thermal runaway is not found in detail but extreme abuse conditions according to battery testing standards SAE, J2464 [15] is found in literature where nail penetration, oven test, crush test internal and external short circuits are used to evaluate thermal runaway and spreading of thermal runaway into adjacent cells [17] [18].…”

Direct Assessment of Separator Strain in Li-Ion Batteries at the Onset of Mechanically Induced Short Circuit

“…In the literature, studies related to the internal short circuit of lithium-ion batteries have been reported experimentally using nail penetration, indentation and pinch tests [2][3][4][5][6][7][8]. These types of abuse tests are fairly common to ensure the robustness of the battery systems.…”

“…Thermal and electrochemical failure modes in LIB has also been reported in the literature. Progressive damage in pouch cells also have been conducted and damage evolution have been mapped including presence of slant fracture modes in the battery cross-section and application of Mohr-Coulomb type failure models [1,[3][4][5]. It is Careful sectioning through the deformed region is also needed to image the deformed stage of the internal layers.…”