Assessing the Thermal Safety of a Li Metal Solid-State Battery Material Set Using Differential Scanning Calorimetry.

At the earliest stage of battery development, differential scanning calorimetry (DSC) of a sample with all battery cell stack materials can provide quantitative data on the reaction thermochemistry. The resulting quantitative thermochemical map of expected reactions upon heating can then guide chemistry and component development toward improved cell safety. In this work, we construct Li0.43CoO2 + C + PVDF|Li6.4La3Zr1.4Ta0.6O12|Li microcell DSC samples with capacity-matched electrodes and test to 500 °C. Notable observations are: (1) ∼74% of the O2 released from the Li0.43CoO2 cathode reacts with C to form CO2 rather than with molten Li to produce Li2O, (2) PVDF pyrolysis (>400 °C) releases HF gas that exothermically reacts with Li to form LiF, and (3) reactions involving oxygen (e.g., CO2 and Li2O formation) account for ∼60% of the total heat released, and reactions involving HF (e.g., LiF formation) account for ∼36% of the total heat released.