Enhancing the Li+ storage capability of transition metal sulfides by in situ regulation of the phase conversion in operating batteries

Abstract

Transition metal sulfides (TMSs), with the advantages of high Li⁺-storage capacity and low cost, are attractive conversion-type anode materials for all-solid-state lithium or lithium-ion batteries (ASSLBs and LIBs). However, the intrinsic phase conversion property also conveys structural destruction and a short lifespan in repeated lithiation–delithiation reactions. Herein, size-controlled and phase-controlled failure mechanisms of various TMS species were confirmed in LIB models, which were generated from the binding energy differences of TMS interlayers. In ZnS, MoS₂ and WS₂ groups, a large particle size of more than 10 nm of the secondary phase-converted products Zn/ZnS′, Mo/MoS′₂ and W/WS′₂ led to charge-discharge capacity decay due to the reduced Li⁺/e⁻ transfer efficiency. In the FeS group, although the particle structure was retained without any obvious destruction, phase conversion from pristine hexagonal FeS to low-active tetragonal FeS led to charge-discharge capacity decay owing to the increased Li⁺ transfer energy barrier. In comparison, enhanced Li⁺ storage capability was easily achieved by introducing a metastable amorphous Al₂O₃ nanocoating on the surface of TMS particles. It was found that the modulation characteristic of Al₂O₃ originated from Al₂O₃–TM bonding during long-term cycling processes; thus the size-controlled and phase-controlled failure mechanisms were restrained in situ by the strong interface interaction. This work is expected to provide guidelines for the design and optimization of TMS anodes.