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 Li 0.43 CoO 2 + C + PVDF|Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 |Li microcell DSC samples with capacity-matched electrodes and test to 500 °C. Notable observations are: (1) ∼74% of the O 2 released from the Li 0.43 CoO 2 cathode reacts with C to form CO 2 rather than with molten Li to produce Li 2 O, (2) PVDF pyrolysis (>400 °C) releases HF gas that exothermically reacts with Li to form LiF, and (3) reactions involving oxygen (e.g., CO 2 and Li 2 O 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.