Liquid-phase synthesis of a Li3PS4 solid electrolyte using N-methylformamide for all-solid-state lithium batteries

Abstract

A Li 3 PS 4 solid electrolyte was directly synthesized from Li 2 S and P 2 S 5 by a liquid-phase reaction using N-methylformamide (NMF) and n-hexane as reaction media. After the reaction of Li 2 S and P 2 S 5 , a yellow NMF solution was obtained. The NMF solution was dried at 180 C for 3 hours under vacuum to remove NMF and to obtain a powder. A crystalline phase of the obtained powder from the NMF solution was attributed to Li 3 PS 4 crystals, and the ionic conductivity of the obtained powder was 2.3 Â 10 À6 S cm À1 at 25 C. Electrode-electrolyte composite materials for all-solid-state lithium batteries were prepared by coating the Li 3 PS 4 solid electrolyte onto LiCoO 2 particles using the NMF solution. SEM and EDX analysis showed that LiCoO 2 particles were uniformly coated with the Li 3 PS 4 solid electrolyte. An all-solid-state cell using the LiCoO 2 particles coated with the Li 3 PS 4 solid electrolyte as a positive electrode operated as a secondary battery.

Preparation of Li₃PS₄ Solid Electrolyte by Liquid-Phase Shaking Using Organic Solvents with Carbonyl Group as Complex Forming Medium

“…Thus, the electron density of oxygen atom will take the important role in the synthetic process and the reactivity of the solvents is expected to be in this order DMC > EA > MPK. In the liquid-phase synthesis process, the products directly precipitated from the solvents were reported to be the co-crystalline of solid electrolytes and solvents [9][10][11][12] . It is also reported that the bonds between solid electrolytes and solvents originated from Li ion of the electrolytes and C=O group in solvents.…”

“…Atsunori MATSUDA, Hiroyuki MUTO and Nguyen H.H. PHUC N-methylformamide (NMF), in which the reaction between NMF and P 2 S 5 was proved to be the initial step [9][10][11][12]15) . Thus, the electron density of oxygen atom will take the important role in the synthetic process and the reactivity of the solvents is expected to be in this order DMC > EA > MPK.…”

“…However, nearly all the reports focus on the preparation of Li 3 PS 4 (LPS), which can be considered as the simplest member of the sulfide electrolytes [8][9][10][11] .…”

“…Recently we have also successfully prepared LPS by liquid-phase shaking using ester (dimethyl carbonate and ethyl acetate) as a complex forming medium [8][9][10][11][12][13][14][15][16] . Solvent containing ketone group is still omitted from the usage of preparation of sulfide solid electrolyte till now.…”

“…They are ether (tetrahydrofuran, dimethoxy ethane), amide (formamide), alcohol (ethanol), nitrile (acetonitrile), amine (hydrazine) [8][9][10][11][12][13][14][15][16] .…”