In Situ Monitoring of Fast Li-Ion Conductor Li7P3S11 Crystallization Inside a Hot-Press Setup

Rechargeable solid-state lithium ion batteries (SSLB) require fast ion conducting solid electrolytes (SEs) to enable high charge and discharge rates. Li7P3S11 is a particularly promising lithium solid electrolyte, exhibiting very high room temperature conductivities of up to 17 mS·cm–1 and high ductility, allowing fast ion transport through the bulk and intimate contact to high surface electrodes. Here we present a novel hot-press setup that facilitates the synthesis of solid electrolytes by combining in situ electrochemical impedance spectroscopy (EIS) with simultaneous temperature- and pressure-monitoring. While a high room temperature conductivity in the order of 10 mS·cm–1 is readily achieved for phase pure Li7P3S11 with this design, it further enables monitoring of the different steps of crystallization from an amorphous Li2S–P2S5 glass to triclinic Li7P3S11. Nucleation, crystallization andat temperatures exceeding 280 °Cdecomposition of the material are analyzed in real time, enabling process optimization. The results are supported ex situ by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and Raman spectroscopy. Proof-of-principle experiments show the promising cycling- and rate capability of Li0.3In0.7/Li7P3S11/S-composite all-solid-state batteries. It is furthermore presented that discharging below a limit of 1.2 V results in decomposition of the SE/cathode interface.