High-throughput methods to design deformable recrystallized boracite solid electrolytes: challenges and solutions

Abstract

Solid electrolytes for Li batteries continue to be extremely challenging to design as they have such broad material requirements. No single material matches all required properties. Boracites have recently been studied as being potentially ideal in terms of being deformable in a glassy state so that they can be well prepared in a composite with the cathodes, but then be crystallized into an ionic conductor at temperatures that do not damage the cathodes. However, these materials remain poorly explored, primarily due to the time/effort needed to perform the complex synthesis. Herein, we develop a combinatorial workflow that allows reproduction of materials made previously only in bulk quantities. In so doing, we overcome the extreme Cl loss that leaves no Cl in our small samples when we attempt to utilize the same synthesis conditions published previously for larger samples. The Cl loss is mitigated through saturation of the atmosphere such that equilibrium is established to maintain sufficient Cl content. This establishes atmosphere saturation as a method for mitigating extreme elemental loss in combinatorial samples. We further demonstrate that our materials show comparable ionic conductivity to those published previously. We also determine the limits to the stability window for the first time and also identify air stability as a serious problem for these materials as it converts them into proton conductors. Finally, we demonstrate the viability of thorough dopant screening by testing the deformability of a batch of samples made with 62 different dopants and find the property to be highly tunable with composition. This shows that combinatorial methods will be viable and highly efficient in developing these promising materials.