Amorphous MoS₃ Derived from (NH₄)₂MoS₄: Structural Insights and Applications in All-Solid-State Batteries

Amorphous molybdenum polysulfides (a-MoS_x) have attracted considerable attention because of their unique physical and chemical properties, which enable their use in a wide range of applications including energy-storage materials. Among various synthesis methods, thermal decomposition provides an effective route for synthesizing a-MoS_x. In particular, amorphous molybdenum trisulfide (a-MoS₃) prepared via thermal decomposition has emerged as a promising active material for energy-storage applications owing to its unique structural and electrochemical characteristics. However, owing to its amorphous nature, the detailed structure of a-MoS₃ remains unclear. In this study, a-MoS₃ was synthesized via thermal decomposition of (NH₄)₂MoS₄, and its structure and electrochemical properties were investigated. It was revealed that a-MoS₃ exhibited an amorphous nature with a MoS₂-like structure but without disulfide bonds. Moreover, in the a-MoS₃ structure, Mo was coordinated with more than six sulfur atoms and at least two sulfur species with different electronic states were identified. The presence of sulfur with high binding energy would likely contribute significantly to the high electrochemical capacity as an active material in batteries. All-solid-state lithium cells using a-MoS₃ exhibited high reversible capacities of approximately 313 mAh g^-1 and excellent cycling stability over 3000 cycles, demonstrating that a-MoS₃ is a promising high-performance active material.