Role of Cu in Mo₆S₈ and Cu Mixture Cathodes for Magnesium Ion Batteries

Abstract

The reversible capacity of Chevrel Mo6S8 cathode can be increased by the simple addition of the Cu metal to Mo6S8 electrodes. However, the exact reaction mechanism of the additional reversible capacity for the Mo6S8 and Cu mixture cathode has not been clearly understood yet. To clarify this unusual behavior, we synthesize a novel Cu nanoparticle/graphene composite for the preparation of the mixture electrode. We thoroughly investigate the electrochemical behaviors of the Mo6S8 and Cu mixture cathode with the relevant structural verifications during Mg(2+) insertion and extraction. The in situ formation of Cu(x)Mo6S8 is observed, indicating the spontaneous electrochemical insertion of Cu to the Mo6S8 host from the Cu nanoparticle/graphene composite. The reversible electrochemical replacement reaction of Cu in the Mo6S8 structure is clarified with the direct evidence for the solid state Cu deposition/dissolution at the surface of Mo6S8 particles. Moreover, the Mo6S8 and Cu mixture cathode improves the rate capability compared to the pristine. We believe that our finding will contribute to understanding the origin of the additional capacity of the Mo6S8 cathode arising from Cu addition and improve the electrochemical performance of the Mo6S8 cathode for rechargeable Mg batteries.

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

“…Optimized Mg-Cu repulsion effects were cited as the reason for the high performance of Cu 1.3 Mo 6 S 8 , whereas higher copper concentrations block diffusion. The same group recently contributed to understanding the mechanism of Cu insertion and extraction [155]. They used a Cu nanoparticle/graphene composite as an additive to study the formation of Cu x CP and its interaction with Mg…”

A High-Performance Rechargeable Mg2+/Li+ Hybrid Battery Using One-Dimensional Mesoporous TiO2(B) Nanoflakes as the Cathode

“…The intrinsic strong coulombic interactions between bivalent Mg 2+ ions and the host materials, however, causes sluggish Mg 2+ diffusion and large polarization, and consequently, low Mg 2+ intercalation levels and/or rapid capacity decay. 3,4 To circumvent the issues associated with the intercalation but still take advantage of the high capacity and high safety associated with Mg deposition and dissolution, Mg 2+ /Li + hybrid batteries have recently been constructed combining an Mg anode, an Li + -intercalation electrode, and an electrolyte containing both Mg 2+ and Li + . [5][6][7][8][9][10] These batteries have been reported to outperform all the previously reported magnesium batteries in terms of specific capacity, cycling stability, and rate capability.…”

Self‐Established Rapid Magnesiation/De‐Magnesiation Pathways in Binary Selenium–Copper Mixtures with Significantly Enhanced Mg‐Ion Storage Reversibility

“…This result resembles the in situ chemical intercalation of Cu into Mo 6 S 8 cathode when the Cu powder and Mo 6 S 8 powder are mixed together for several hours. [18] …”