Understanding the Thermal Safety of Solid-State Lithium Battery: An in-Situ Thermal Study

Abstract

The state-of-the-art solid-state lithium batteries (SLBs) using solid electrolytes attracted wide attention due to their high energy density and superior thermal safety. Previously, the thermal safety of SLBs were investigated by thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), or flammability testing. However, these methods can only study the thermal safety of independent electrolyte, not the entire battery simultaneously. A method to quantitatively evaluate the thermal safety of entire SLBs is lacking. Herein, we developed a novel in-situ method to study the thermal safety of an entire coin cell employing multiple module calorimeter (MMC) and battery tester. The MMC can detect the heat flow of a coin cell in the temperature range of 20 to 300 °C with different heating rates, while the coupled battery tester records its open-circuit voltage (OCV). In this work, poly(vinylidene fluoride) (PVDF)-based composite solid-state electrolyte was employed as the model solid electrolyte due to the outstanding compatibility with both cathode and lithium anode, good film forming features, and excellent thermal stability. The all-solid-state LiNi1/3Co1/3Mn1/3O2/Li coin cell was assembled simply by using LiNi1/3Co1/3Mn1/3O2 cathode, PVDF-based solid electrolyte, and Li metal anode without the addition of any liquid electrolyte. For demonstration purpose, the thermal safety of entire solid cell was in-situ investigated and compared with the analogous cell using traditional liquid electrolyte. It is worth noting that the solid-state cell exhibited a thermal stable window up to 177 °C and a small heat release of 189 J g-1 during the thermal runaway of the entire cell. In contrast, the cell using liquid electrolyte delivered a reduced thermal stable window (157 °C) and release a significant amount of heat (812 J g-1). The superior thermal safety of SLBs can be ascribed to the solid-state property and outstanding thermal stability of the PVDF-based solid electrolyte. To the best of our knowledge, this is the first in-situ quantitative study on the thermal safety of the entire solid-state lithium battery. This work highlights a reference for the in-situ quantitative study on the thermal safety of entire SLBs.