High zinc-ion intercalation reaction activity of MoS2 cathode based on regulation of thermodynamic metastability and interlayer water

Divalent zinc-ion with sluggish reaction kinetics limits the choice of cathode materials for aqueous zinc-ion batteries. Metastable 1T-MoS2 shows higher electrochemical activity of ion intercalation reaction in comparison with the thermodynamically stable 2H-MoS2. Herein, the monolayer water inserted 1T-MoS2 nanosheets have been prepared by solvothermal method, investigated as the cathode in zinc-ion batteries. The monolayer water between interlayers can not only expand interlayer spacing but also maintain the metastable structure of 1T-MoS2 nanosheets, conducing to reduce activation energy for Zn2+ intercalation and enhance specific capacity. The obtained 1T-MoS2 cathode with changed 4d orbitals of Mo4+ delivers specific capacity of 164.1 mAh g-1 at 100 mA g-1 and 120.1 mAh g- 1 at 2000 mA g-1, which is 6-8 times that of 2H-MoS2 cathode. The open circuit voltage of the 1T-MoS2 cathode increased to 0.96 V compared with 0.64 V of 2H-MoS2. The DFT calculations are executed to explore the influence of interlayer water on interlayer spacing and the energy storage behavior of Zn2+. Combined with the experimental results and DFT calculations, the roles of the crystalline phase and interlayer water in electronic configuration varies of Mo 4d orbitals are discussed and the Zn2+ intercalation process and storage mechanism are revealed.