Effect of the Crystalline Structure of Cu_xMo₆S₈ on the Capacity of Mg-Based Secondary Batteries

Abstract

Mo 6 S 8 Chevrel-phase (CP) cathode materials, for Mg secondary batteries, have been reported to be better suited and superior to other cathode materials. We synthesized Cu x Mo 6 S 8 (Cu-CP) by varying the temperature and time and found different crystalline structures of Cu-CP, depending on the time and temperature of the growth process. Using these structures as precursors for preparing cathodes was shown to influence the performance of the electrochemical cell. After etching Cu from Cu-CP, the structure was stabilized as the rhombohedral phase of Mo 6 S 8 (CP). The morphologies of Cu-CP and CP were examined by scanning electron microscopy, and the structures were confirmed using X-ray diffraction. The coin-cell structure was fabricated, and the electrochemical properties of CP were evaluated and compared for different crystalline structures of Cu-CP. The discharge capacities were improved from 84.2 to 122.9 mAh•g −1 as the structure of Cu-CP changed from rhombohedral to triclinic.

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage

“…The maximum volume expansion of Mo 6 S 8 is only 5.23% (156 mAh g −1 at 500 mA g −1 ), smaller than that of Mo 6 S 8 in other multivalent ion systems (Zn 2+ : 5.3% (134 mAh g −1 at 6.4 mA g −1 ), Mg 2+ : 7.9% (123.3 mAh g −1 at 5 mA g −1 )). 37,38 In addition, the evolution of the lattice parameters and volume changes is smooth, and no sharp fluctuation is observed, demonstrating that Mo 6 S 8 maintains a high structural adaptability and stability during the cycling process (Figure S18). Based on the above electrochemical and o-SXRD analysis, it can be deduced that Mo 6 S 8 undergoes a reversible multiple phase transition during the (de)copperization process.…”

“…Benefiting from the Cu 2+ (de)­intercalation electronic structure evolution, Mo 6 S 8 demonstrates the best discharge specific capacity and is superior to other Mo 6 S 8 cathode-based secondary ion batteries in the literature, such as aluminum ion batteries (AIBs), magnesium ion batteries (MIBs), zinc ion batteries (ZIBs), sodium ion batteries (SIBs), and lithium-ion battery (LIB) systems (Figures f and S23–S25). ,,− …”