Multielectron Conversion: Peculiar Transition Metal Sulfides with Mixed Vulcanized States toward High‐Capacity Metal‐Ion Storage

Abstract Transition metal sulfides with mixed vulcanized states (TMS‐mVs) possess tremendous potential to realize highcapacity, superior redox reactions, and structural reversibility for metal‐ion (Mⁿ⁺) storage owing to their multielectron reactions caused by the simultaneous participation of transition metal (TM) cations and S₂²⁻ anions as well as multifarious TM or S valence states. Here, recent advances are systematically introduced regarding the mainstream TMS‐mVs that can be applied to Mⁿ⁺ storage. These TMS‐mVs can be divided into two categories of TMS, those with mixed sulfur‐valence states (TMS‐mSs) and those with mixed metal‐valence states (TMS‐mMs). It is found that TMS‐mV anodes mainly experience three reaction mechanisms, inculding insertion‐accompanied conversion, insertion, and conversion reactions. During the reversible charge process, Li₂S is possibly oxidized into polysulfides or even S. TMS‐mVs have the ability to transfer more electrons than other homogeneous TMSs. TMS‐mS anodes usually present higher theoretical specific capacities than TMS‐mM anodes. In these TMS‐mV anodes, Mo‐based, V‐based, and Co‐based TMS‐mM anodes exhibit good electrochemical reversibility, Ni‐based TMS‐mM anodes exhibit moderate electrochemical reversibility, and Fe‐based TMS‐mM and TMS‐mS anodes exhibit poor electrochemical reversibility. The strategies for enhancement of their electrochemical performance are classified into composite, coating, nanostructure, heterointerface, and lattice engineering.