Quantifying the Thermochemistry of Solid-State Lithium Metal Battery Reactions Using Differential Scanning Calorimetry

Abstract

It is commonly assumed that the introduction of solid-state electrolytes implies the improved safety of high-energy batteries due to the removal of the combustible organic solvents in present Li-ion cells. However, safety is a multifaceted issue that involves thermal runaway onset temperature, self-heating rates, total generated energy, maximum temperature, gas or other material releases from a cell, thermal runaway prevention mechanisms, etc.1 In addition, the use of lithium metal anodes (which melt at 180°C) for high energy density cells may introduce previously unconsidered safety issues not faced by Li-ion cells, in which no molten and reactive lithium metal is present during a thermal runaway. Quantitative heat flow data on reaction thermochemistry among solid-state battery cell components can be gathered using differential scanning calorimetry on milligram-scale samples that include the key components of a full cell stack. While a principal exothermic reaction observed in previous DSC work2 is the formation of Li2O from molten Li and O2 released upon metal oxide cathode decomposition, this work did not include current collectors or carbon and binder, which add further competing reactions such as the oxidation of binder, and lithium/current collector alloying. In addition, the measured heat flows in a DSC test that includes several cell components are critically dependent on the mass ratio of materials present in the cell, for example the electrode capacity ratio. In this talk we present our own DSC measurements on the onset temperatures, total heat release, and rate of heat release for numerous combinations of cell components (e.g., Li metal, solid electrolyte separators, cathode active materials, cathode inactive components) for prospective solid-state batteries.