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

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.