A Molybdenum Polysulfide In-Situ Generated from Ammonium Tetrathiomolybdate for High-Capacity and High-Power Rechargeable Magnesium Cathodes

Rechargeable magnesium batteries (RMBs) are a promising large-scale energy-storage technology with low cost and high reliability. However, developing high-performance cathode materials remains the most prominent obstacle because of the insufficient magnesium-storage active sites and unfavor-able magnesium cation transport paths, as well as the strong interaction between the cathode material and the bivalent magnesium cation. Herein, ammonium tetrathiomolybdate is demonstrated to be a high-performance RMB cathode material. Ammonium tetrathiomolybdate exhibits a high capacity of 333 mAh g-1 at 50 mA g-1 and a good rate performance of 129 mAh g-1 at 5.0 A g-1 (similar to 15 C). An amorphous structure with plenty of efficient magnesium-storage active sites and open magnesium transport paths is in situ formed during the first cycle via ammonium extraction. The covalent-like bond between the molybdenum and sulfur delocalizes the negative charge, weakening the interaction with the bivalent magnesium cation and accelerating the kinetics. The covalent-like molybdenum-sulfur bond also promotes the simultaneous redox of molybdenum and sulfur, leading to a high specific capacity. The present work introduces a high-capacity and high-power RMB cathode material, elucidates the origin of the high performance, and provides insights for the design and optimization of RMB cathode materials.

Automated summary

Rechargeable magnesium batteries (RMBs) are a promising energy-storage technology, but the development of high-performance cathode materials is a major challenge. This study demonstrates the high performance of ammonium tetrathiomolybdate as an RMB cathode material, which forms an amorphous structure with efficient magnesium-storage active sites and open transport pathways through ammonium extraction. The covalent-like molybdenum-sulfur bond weakens the interaction with magnesium ions and promotes simultaneous redox of molybdenum and sulfur, leading to high capacity.