Amorphous bimetallic polysulfide for all-solid-state batteries with superior capacity and low-temperature tolerance

Abstract

Transition-metal sulfides with high capacity and low cost have been widely acknowledged as promising cathode candidate for all-solid-state batteries (ASSBs). However, the solid-solid conversion reaction mechanism based on ordered crystal structures and the high concentration of metal element result in sluggish reaction kinetics and sacrificed specific capacity. Herein, an amorphous bimetallic polysulfide (Mo0.5Ti0.5S4) is designed to create abundant reaction sites, improve diffusion kinetics and attain sulfur-equivalent capacity. As a result of the decreased elastic modulus through the introduction of Ti, the amorphization of crystalline MoS2 is accelerated during ball milling. Compared with its counterpart (MoS4, 757 mAh g−1), Mo0.5Ti0.5S4 ASSB delivers a much higher reversible capacity (914 mAh g−1), thanks to the abundant reaction sites and suppressed S/Li2S separation from amorphous Mo-Sx matrix. Moreover, due to the improved diffusion kinetics and pseudocapacitive contribution, the capacity retention of Mo0.5Ti0.5S4 at 4 C current rate increases from 47.2 % to 65.8 %. In addition, Mo0.5Ti0.5S4 shows excellent low-temperature performances, including good long-term cycle stability and rate capability (with a capacity retention of 50.5 % at 0.5 C) at −20 ℃, and increased capacity retention (from 35.1 % to 50.7 %) at −40 ℃. Therefore, Mo0.5Ti0.5S4 with bimetallic amorphous structure and enriched sulfur anions has enormous potential on high-rate and low-temperature ASSB applications.