Early-Stage Evaluation of Battery Safety Based on Materials, Component, and Microcell Calorimetry Measurements

Abstract

There are numerous “beyond lithium ion” battery chemistries under development at universities, national labs, companies, and other organizations. Early-stage battery chemistry work typically focuses on demonstrating performance at the materials, coin, and pouch cell level, with evaluation and design for safety left for later stages.1 In this talk, we will describe the opportunities for assessing the safety of a battery chemistry at the earliest stages of its development, as soon as the active materials and electrolyte have been identified.2 With carefully designed and quantitative experiments, key information such as the amounts of heat released by the reactions of and among cell components, the temperatures at which that heat is released, the release of toxic or otherwise dangerous gases, the material heat capacities, and other key properties can be measured with differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and other approaches. We have demonstrated the value of this approach for a LixCoO2+C+PVDF cathode sheet /LLZO/Li metal material set, where we identified the previously under-appreciated role of the cathode sheet conductive additive and binder in the reaction pathways upon heating to 500°C in a DSC pan.3 Despite this material set containing no liquid electrolyte, delithiated LixCoO2 releases oxygen upon heating to >~230°C, and that oxygen can react exothermically with the Li metal and conductive carbon. In addition, PVDF binder releases HF gas at >400°C, which can also react exothermically with Li metal.This talk will focus on the methodology required to obtain accurate measurements on milligram-scale samples, with an emphasis on the sample preparation and DSC methods to obtain accurate, repeatable results. Approaches associated with DSC baselining and integration methods will be presented. The talk will also present results from our recent work on material sets that are more commercially relevant for electric vehicle applications than the LixCoO2 cathode sheet/ LLZO / Li material set. In particular, results from material sets such as NMC532 cathode sheet / LLZO / Li, NMC811 cathode sheet / LLZO / Li, and NMC811 cathode sheet / LPSCl / Li metal will be presented. Finally, we will discuss the implications of our early-stage, material-scale work for future large-format cells.1. See Category 3 in the ARPA-E EVS4ALL program, https://arpa-e.energy.gov/technologies/programs/evs4all2. Joule 6, 742–755, April 20, 2022.3. ACS Appl. Mater. Interfaces 2023, 15, 49, 57134–57143