Structural Modification Of Molybdenum Disulfide And Its Zinc Storage Properties

As a new type of energy storage device,aqueous zinc ion batteries offer ideal prospects in the field of large-scale energy storage.At present,research on aqueous zinc ion batteries has focused on the exploration of cathode materials.Among the various types of zinc ion intercalation active materials commonly available,molybdenum disulphide（Mo S₂）occupies a place by virtue of its two-dimensional structure,tunable band gap and rich edges.Compared to the thermodynamically stable 2H phase Mo S₂,1Tphase Mo S₂ has superior hydrophilicity,electrical conductivity and better Zn²⁺storage capacity.However,1Tphase Mo S₂ is a metastable phase and is prone to spontaneous conversion to the stable 2H-phase,resulting in poor electronic and ionic conductivity and significant degradation of battery performance.In this paper,the morphology,layer spacing,phase structure and stability of Mo S₂ are regulated by both Mn²⁺doping and compounding with MXene,a highly conductive material,in order to improve its zinc storage performance.1.To address the problems of small Mo S₂ layer spacing and unstable 1T phase structure,we used Mn²⁺doping to modify the Mo S₂ interlayer to improve its structural morphology and electrochemical properties through the"pillar effect"of Mn²⁺.It was found that doping with different amounts of Mn²⁺could effectively adjust the layer spacing of Mo S₂,and the layer spacing could be expanded to 0.9 nm when doping with0.2 mmol of Mn²⁺.Meanwhile,the doping of Mn²⁺could also induce the formation of1T phase Mo S₂,and the best effect was achieved when the doping amount of Mn²⁺was0.2 mmol,which increased the percentage of 1T phase to 78.47%.In the structural analysis,it was found that Mn²⁺can form S-Mn-S covalent bonds between Mo S₂ layers and build"electron bridges"to promote electron transfer,thus enhancing the zinc storage capacity and electrical conductivity of Mo S₂.The initial charge/discharge specific capacity of 0.2Mn-Mo S₂ can be increased from 156.5 m Ah/g of Pure Mo S₂ to192.1 m Ah/g at a current density of 0.1 A/g.Therefore,the appropriate amount of Mn²⁺doping can promote more Zn²⁺embedding/exfoliation,improve the cycle life of Mo S₂and transfer higher specific capacity.2.Based on our work on Mn²⁺-doped molybdenum disulphide,we found that although Mn²⁺can enhance the electrical conductivity of Mo S₂ and promote more Zn²⁺participation in the reaction,0.2Mn-Mo S₂ still undergoes some volume expansion and structural damage when Zn²⁺is embedded and exited,resulting in rapid decay of specific capacity at low currents and poor cycling stability.Therefore,with the help of the high electrical conductivity and good chemical stability of Ti3C2Tx（MXene）material,we synthesized a three-dimensional interconnected network heterostructure of Mn²⁺-doped Mo S₂ and MXene（0.2Mn-Mo S₂/MXene）by hydrothermal method and studied it as an aqueous zinc ion battery cathode.We found that the S-Mn-S covalent bond formed between the Mo S₂ layers and the Ti-O-Mo bond at the heterogeneous interface by Mn²⁺can act as an"electron bridge"to promote electron transfer and induce the formation of 1T-phase Mo S₂.Meanwhile,the doping of Mn²⁺and compounding with MXene not only expand the interlayer spacing of Mo S₂,but also maintain the sub-stable structure of 1T-phase Mo S₂ nanosheets,which reduces the intercalation activation energy of Zn²⁺and increases the specific capacity of the cell.The obtained high-occupancy 1T-phase 0.2Mn-Mo S₂/MXene electrode has a high specific capacity of 191.7 m Ah/g at 0.1 A/g,and the capacity is maintained at 143.9m Ah/g after 90 cycles,with a capacity retention rate of 82.55%.At a current density of1.0 A/g,the specific capacity of 0.2Mn-Mo S₂/MXene can reach 161.5 m Ah/g with a capacity retention rate of 80.37%after 500 cycles,which demonstrates the high specific capacity and more excellent cycling stability of 0.2Mn-Mo S₂/MXene.In addition,the diffusion coefficient of Zn²⁺(D_Zn²⁺)in the 0.2Mn-Mo S₂/MXene electrode was calculated to be greater and the electrical conductivity was significantly improved.