Dissolution and Recrystallization Behavior of Li3PS4 in Different Organic Solvents

TL;DR

This study investigates the dissolution and recrystallization of beta-Li3PS4 in various solvents, revealing optimal conditions and structural changes that impact ionic conductivity, with implications for battery recycling.

Contribution

It provides a detailed analysis of recrystallization processes of beta-Li3PS4 in polar solvents, including structural characterization of intermediate phases and effects on ionic transport.

Findings

Recrystallization occurs in polar, slightly protic solvents like NMF.

An intermediate phase Li3PS4*2NMF is structurally characterized.

Recrystallization increases amorphous content, reducing activation energy to 0.2 eV.

Abstract

Solid state batteries can be built based on thiophosphate electrolytes such as beta-Li3PS4. For the preparation of these electrolytes, various solvent-based routes have been reported. For recycling of end-of-life solid state batteries based on such thiophosphates, we consider the development of dissolution and recrystallization strategies for the recovery of the model compound beta-Li3PS4. We show that recrystallization can only be performed in polar, slightly protic solvents such as N-methylformamide (NMF). The recrystallization is comprehensively studied, showing that it proceeds via an intermediate phase with composition Li3PS4*2NMF, which is structurally characterized. This phase has a high resistivity for the transport of lithium ions and must be removed in order to obtain a recrystallized product with a conductivity similar to the pristine material. Moreover, the recrystallization from solution results in an increase of the amorphous phase fraction next to crystalline beta-Li3PS4, which results in a decrease of the activation energy to 0.2 eV compared to 0.38 eV for the pristine phase.