Preparation And Properties Investigation Of Molybdenum-based Cathode Material For Aqueous Zinc Ion Battery

The transition metal dichalcogenide Mo S₂ is widely used in electrochemical energy storage due to its unique graphene-like layered structure,but its research as a cathode material for aqueous zinc-ion batteries（ZIBs）is still in infancy.The main reasons limit the further development of Mo S₂ cathodes come from the strong electrostatic interaction between the divalent Zn²⁺and the main framework,resulting in high energy barriers for Zn²⁺intercalation as well as insufficient spacing of the pristine Mo S₂ lamellar structure to accommodate the repeated insertion/extraction of large size hydrated Zn²⁺.These couple with the fact that steady-state Mo S₂ generally belongs to the semiconductor 2H phase and often suffers from inherent low ionic/electronic conductivity,making Zn//Mo S₂ batteries exhibit low discharge specific capacity,poor cycling stability and slow electrochemical kinetics,which make it difficult to meet the growing demand for chemical energy storage devices.In this paper,we prepared three modified Mo S₂ electrodes,evaluated their electrochemical properties and investigated the reasons for their enhanced zinc storage,with the following main findings:（1）Preparation and properties investigation of interlayer-expanded Mo S₂ by NH₄⁺intercalationBy using a simple hydrothermal method to inserted NH₄⁺into the interlayer of Mo S₂（the interlayer spacing of Mo S₂ was extended from 0.62nm to 0.92 nm）,which cause lattice distortion and promote the transition from 2H phase to 1T phase.The Mo S₂-5 prepared by using thioacetamide（TAA）as the S source,with controlled Mo/S ratio of 1:2,ammonia addition of 5 ml and hydrothermal temperature of 200°C shows a discharge specific capacity of about 120 m Ah g^-1 at 0.1 A g^-1 and a stable discharge capacity of 90 m Ah g^-1 at 1.0 A g^-1 after 200 cycles.In contrast,the discharge capacity of A-Mo S₂-5 with NH₄⁺removed by annealing shows a significant degradation,indicating that the effect of NH₄⁺layer expansion is critical to the enhancement of the electrochemical performance of Mo S₂.（2）Preparation and properties investigation of oxygen-rich Mo S₂prepared by template-assisted hydrothermalA simple template-assisted hydrothermal method was used to prepare oxygen-rich Mo S₂.Hexadecyl trimethyl ammonium bromide（CTAB）as the templating agent to promoted the heterogeneous nucleation of Mo S₂ to form spherical nanoflake structures.The O element provided by the oil-phase solvent ethylene glycol partially replaced the S element on the framework（the content of O element was 7.87%）and the interlayer spacing of Mo S₂ was expanded from 0.62 nm to 1.01 nm while the changed electronic structure increases the content of 1T phase to 73%.The discharge specific capacity of Mo S₂-C-0.015 prepared by using a CTAB concentration of 0.015 mol L^-1 and a hydrothermal temperature of 180°C was about 197.9 m Ah g^-1 at 0.1 A g^-1 and the capacity retention rate was94%after 500 cycles at 1.0 A g^-1.（3）Preparation and properties investigation of Mo S₂@carbon cloth flexible self-supporting material by seed-assisted hydrothermalMo S₂@carbon composite material（SA-Mo S₂@CC）was prepared by seed-assisted hydrothermal.Mo S₂ nanosheets were in situ grown on carbon cloth fibers with three-dimensional nanoarray structure,which provided large specific surface area to facilitate the permeability between electrolyte and electrode,shortening the Zn²⁺diffusion pathway.The water molecules intercalated in the Mo S₂ lattice enlarged the Mo S₂ layer spacing to 1.0 nm and caused lattice distortion,resulting in the formation of high content 1T phase（76%）.The discharge specific capacity of the prepared SA-Mo S₂@CC electrode is about 259.6 m Ah g^-1 at 0.1 A g^-1 and 122.6 m Ah g^-1 at 2.0 A g^-1 after 1000 cycles.