Preparation And Potassium Storage Performance Research Of Two-dimensional MoS₂ Based Electrode Materials

Two-dimensional（2D）electrodes used in potassium ion batteries（PIBs）have high energy density and large capacity.However,the serious volume changes due to the large size of K⁺and the slow diffusion kinetics at the electrode interface during charge and discharge limit the improvement of the electrochemical performance.Based on this,this paper takes the two-dimensional layered transition metal sulfide MoS₂ electrode as the research object,and realizes the interface ion defect regulation of the two-dimensional composite electrode by introducing the conductive matrix MXene and defect engineering modification strategy,so as to further adjust the potassium storage performance of two-dimensional MoS₂-based electrode.In this paper,not only the potassium storage characteristics,diffusion behavior and structural changes before and after cycles of the fabricated electrode materials are studied in detail,but also the energy storage mechanisms of the composite electrodes are explored and elucidated by dynamic in-situ spectroscopy and first-principles calculations.The implementation and results of this project will provide important fundamental research data for the study of the relationship between structural modification of 2D electrodes and electrochemical energy storage,and open up new ideas for the preparation and application of electrode materials for high-capacity potassium ion batteries.（1）The two-dimensional layered MoS₂ material has a polycrystalline structure,and different crystalline forms have different atomic arrangements,thus exhibiting different physical and chemical properties.Therefore,in this paper,MoS₂ and 1T-MoS₂ materials with different crystalline forms are firstly prepared by hydrothermal and magneto-hydrothermal methods,respectively,and used as the anodes for potassium-ion batteries,so as to compare and study the effects of different crystalline forms on the electrode structure and electrochemical performance.The results show that the 1T-MoS₂ anode exhibits better potassium storage performance at the same current density:the reversible capacity is 628 m A h g^-1 at 0.1 A g^-1;the capacity is 494m A h g-1 at 2.0 A g^-1;and at 0.1 A g^-1,the reversible capacity remains 412 m A h g^-1 after 500cycles,which is mainly attributed to the higher conductivity and larger interlayer spacing of1T-MoS₂ material compared to MoS₂,thus giving it better energy storage characteristics.（2）In view of the disadvantages of MoS₂-based electrode materials such as low intrinsic conductivity,obvious volume change and easy aggregation,MoS₂@V₂CT_x and1T-MoS₂@V₂CT_x composites have been constructed as anodes for potassium ion batteries by introducing conductive matrix V₂CT_xMXene through hydrothermal method,magneto-hydrothermal method and in-situ growth strategy.The results show that the1T-MoS₂@V₂CT_x anode has superior potassium storage performance compared to the MoS₂@V₂CT_x anode:the capacity reaches 887.3 m A h g^-1 at 0.1 A g^-1 and 563.6 m A h g^-1 at 2.0A g^-1,indicating good rate performance.On the other hand,at 1.0 and 2.0 A g^-1,the capacities of the 1T-MoS₂@V₂CT_x anode remain 601.2 and 374.7 m A h g^-1 after 2000 cycles,and the corresponding capacity retentions are 69.4%and 56.5%,respectively,which confirms its good cycle performance.The better potassium storage characteristics of 1T-MoS₂@V₂CT_x anode are a result of the combination of the higher capacity of 1T-MoS₂ and the larger specific surface area of 1T-MoS₂@V₂CT_x.In addition,the reversible energy storage mechanism,stable structure and enhanced ion diffusion kinetic behavior of the 1T-MoS₂@V₂CT_x anode have been confirmed by in-situ tests and DFT calculations,which are also the source of its good electrochemical performance.（3）Mo vacancy defects have been introduced into the 1T-MoS₂@V₂CT_x electrode by a simple organic solvent dragging method to realize the interface ion defect regulation of the two-dimensional composite electrode,so as to further adjust the ion diffusion and potassium storage characteristics of the composite electrode.The results show that the D-1T-MoS₂@V₂CT_x electrode after introducing defects has enhanced potassium storage performance compared to the 1T-MoS₂@V₂CT_x electrode:the capacity reaches 959.9 m A h g^-1at 0.1 A g^-1 and 632.1 m A h g^-1 at 2.0 A g^-1,indicating good rate performance.On the other hand,at 0.1 A g^-1,the capacity of D-1T-MoS₂@V₂CT_x anode remains 820.7 m A h g^-1 after 500 cycles,and the corresponding capacity retention is 90.6%,confirming its good cycle performance.The better potassium storage performance of D-1T-MoS₂@V₂CT_x electrode indicates that the vacancies in it not only provide more abundant adsorption/storage/active sites for K⁺,but also facilitate K⁺diffusion across the vacancies to promote K⁺migration/transport and interface charge transfer.