Mn2+-Doped MoS2/MXene Heterostructure Composites as Cathodes for Aqueous Zinc-Ion Batteries

Typical layered transition-metal chalcogenide materials, especially MoS2, are gradually attracting widespread attention as aqueous Zn-ion battery (AZIB) cathode materials by virtue of their two-dimensional structure, tunable band gap, and abundant edges. The metastable phase 1T-MoS2 exhibits better electrical conductivity, electrochemical activity, and zinc storage capacity compared to the thermodynamically stable 2H-MoS2. However, 1T-MoS2 is still limited by the phase stability and layered structure destruction for AZIB application. Thus, a three-dimensional interconnected network heterostructure (Mn-MoS2/MXene) consisting of Mn2+-doped MoS2 and MXene with a high percentage of 1T phase (82.9%) was synthesized by hydrothermal methods and investigated as the cathode for AZIBs. It was found that S-Mn-S covalent bonds between MoS2 interlayers and Ti-O-Mo bonds at heterogeneous interfaces can act as "electron bridges" to facilitate electron and charge transfer. And the doping of Mn2+ and the combination of MXene not only expanded the interlayer spacing of MoS2 but also maintained the metastable structure of 1T-MoS2 nanosheets, acting to reduce the activation energy for Zn2+ intercalation and enhance specific capacity. The obtained Mn-MoS2/MXene contains more 1T-MoS2 and provides an improved specific capacity of 191.7 mAh g-1 at 0.1 A g-1. Compared with Mn-MoS2 and pure MoS2, it also exhibits enhanced cycling stability with a capacity retention of 80.3% after 500 cycles at 1 A g-1. Besides, the conductivity of Mn-MoS2/MXene is significantly improved, which induces a lower activation energy of the zinc ions during intercalation/deintercalation.