Mo₃S₁₃ Cluster-Based Cathodes for Rechargeable Magnesium Batteries: Reversible Magnesium Association/Dissociation at the Bridging Disulfur along with Sulfur–Sulfur Bond Break/Formation

Multivalent cation batteries are attracting increasing attention in energy-storage applications, but reversible storage of highly polarizing multivalent cations is a major difficulty for the electrode materials. In the present study, charge-delocalizing Mo3S13 cluster-based materials (crystalline (NH4)2Mo3S13 and amorphous MoSx) are designed and investigated as cathodes for rechargeable magnesium batteries. Both of the cathodes show high magnesium storage capacities (296 and 302 mAh g–1 at 100 mA g–1) and superior rate performances (76 and 80 mAh g–1 at 15 A g–1). A high area loading of 3.0 mg cm–2 could be achieved. These performances are of the highest level compared with those of reported magnesium storage materials. Further mechanism study and theoretical computation demonstrate the magnesium storage active sites are the bridging disulfur groups of the Mo3S13 cluster. The valence state of bridging disulfur decreases/increases largely during magnesiation/demagnesiation along with breaking/formation of the sulfur–sulfur bond, which makes the Mg-association/dissociation highly reversible. The sulfur–sulfur bond breaking and formation provides high reversible capacities. Prominently, the valence state increase and sulfur–sulfur bond formation of the bridging disulfur during charge weakens the bonding with Mg2+, significantly assisting the magnesium dissociation. The present study not only develops high-performance magnesium storage cathode materials but also demonstrates the importance of constructing favorable magnesium storage active sites in the high-performance cathode materials design. The findings presented herein are of great significance for the development of electrode materials for the storage of multivalent cations.多价阳离子电池在储能领域正受到越来越多的关注，但对于电极材料而言，实现高极化多价阳离子的可逆存储仍是一项重大挑战。本研究设计并研究了基于电荷离域Mo₃S₁₃团簇的材料（结晶态(NH₄)₂Mo₃S₁₃与非晶态MoSₓ），将其用作可充电镁电池的正极材料。两种正极材料均展现出优异的镁存储容量（在100 mA g⁻¹电流密度下分别可达296和302 mAh g⁻¹）及卓越的倍率性能（在15 A g⁻¹下仍能保持76和80 mAh g⁻¹），其面积负载量可达到3.0 mg cm⁻²。该性能在已报道的镁存储材料中处于顶尖水平。进一步的机理研究与理论计算表明，Mo₃S₁₃团簇的桥连二硫基团为镁存储的活性位点。在镁化/脱镁化过程中，桥连二硫基团的价态会发生显著的降低/升高，同时伴随硫-硫键的断裂/生成，这使得Mg²⁺的结合/解离过程具备高度可逆性；硫-硫键的断裂与生成也为高可逆容量提供了支撑。尤为值得注意的是，充电过程中桥连二硫基团的价态升高与硫-硫键生成，会削弱其与Mg²⁺的相互作用，显著助力Mg²⁺的解离过程。本研究不仅开发出高性能的镁存储正极材料，同时证实了在高性能正极材料设计中，构建适配的镁存储活性位点的重要性。本文所报道的研究成果，对于多价阳离子存储用电极材料的开发具有重要意义。