Thermal Stability Study of Commercial Lithium-Ion Batteries As a Function of Cathode Chemistry and State-of-Charge

The safety of lithium-ion batteries is mainly quantified by thermal runaway characteristics such as onset temperature, peak heating rate (HR), and maximum pressure release. This talk evaluates the materials aspects of thermal runaway of commercial lithium-ion batteries by correlating the contributions from individual cell components to thermal runaway trends. An accelerating rate calorimeter was used to define the thermal runaway behavior of three commercial 18650 lithium-ion batteries (LiCoO 2 , LiFePO 4 , and LiNi x Co y Al 1-x-y­ O 2 ) at various states of charge (SOC). Cells were also disassembled and the thermal properties of their component materials was evaluated by thermogravimetric analysis, differential scanning calorimetry, and temperature-resolved X-ray diffraction. Broadly, lithium-ion battery thermal runaway process begins with solid-electrolyte interface and negative active material decomposition followed by the positive active material breakdown. The experimental results show that the onset temperature is generally independent of SOC and peak HR increases with SOC as a result of cathode destabilization. Overall, LiNi x Co y Al 1-x-y O 2 decomposes readily, and charged LiCoO 2 is also metastable, although it decomposes more gradually than LiNi x Co y Al 1-x-y . Contrary to the layered transition metal oxides, LiFePO 4 is stable to > 500 o C, even when charged. The results are aimed at informing future engineering and fire protection of commercial lithium-ion batteries. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2018-3360 A