Study On Construction Of Tungsten Disulfide-Based Composite Structures And Their Electrochemical Potassium Storage Mechanism

Tungsten disulfide（WS₂）is a metal sulfide of layered structure.Its layers are combined by weak van der Waals force.And its interlayer spacing is relatively large,d（002）=6.18 ?.The large interlayer spacing and weak interlayer bonding are favorable for the intercalation and deintercalation of potassium ions,which make WS₂ have great potential in the field of potassium storage anode materials.However,when WS₂ is used as an anode material for potassium-ion batteries,there are still two problems.Firstly,the poor conductivity of tungsten disulfide material leads to slow charge transport kinetics.Secondly,the conversion reaction of tungsten disulfide material during the electrochemical reaction will produce large volume changes,which will affect and destroy its structural stability.At present,the method of compounding with carbon is mostly used to modify it.However,the capacity of the obtained tungsten disulfide/carbon composite material is low and the charging and discharging mechanism is not clear enough.So further research on the design of the composite structure and the mechanism of potassium storage is needed.Therefore,in this paper,different WS₂-based composite structures were constructed to improve their potassium storage performance.Besides,the potassium storage mechanism of each structure was analyzed,and the reasons for the performance improvement of each structure were explored.The details are as follows:（1）Through the combination of liquid-phase synthesis and high-temperature heat treatment,a hollow C/WS₂ composite structure was synthesized in multiple steps as an anode material for potassium storage.The composite electrode still has a capacity of 273.8 mAh·g^-1 after 100 cycles at a current density of 0.2 A·g^-1,and a capacity of 133.5 mAh·g^-1 at a high current density of 5 A·g^-1.The hollow C/WS₂ composite structure can effectively alleviate the large volume change of the material during the conversion reaction,thereby improving its structural stability.The introduction of carbon materials with good conductivity improves the conductivity of the overall composite electrode.And the synergistic effect of them makes the composite electrode exhibit fast electron transport and ion diffusion kinetics,thereby achieving rapid potassium storage.（2）Using tungsten hexachloride as the tungsten source,cuprous oxide as the copper source,and dopamine hydrochloride as the carbon source,a carbon-coated WS₂/Cu₉S₅ mixed metal sulfide structure（WS₂/Cu₉S₅@C）was synthesized in multiple steps as a high-capacity potassium storage anode material.The electrode has a capacity of 401.8 mAh·g^-1 after 180 cycles at a low current density of 0.2 A·g^-1,showing good cycle stability and high potassium storage capacity.At 10 A·g^-1 high current density,there is still a specific capacity of 109.7 mAh·g^-1.The synergy between the components of the composite structure enables high capacity,high stability,and high pseudocapacitive potassium storage.（3）Using the copper-containing hollow carbon shell as the matrix,a hollow C/WS₂/Cu₉S₅ composite structure was synthesized in multiple steps through a combination of solvothermal reaction and high-temperature heat treatment.Applying it to the anode material of potassium ion battery,it can still maintain a high capacity of 406.2 mAh·g^-1 after 150 cycles at a current density of 0.2 A·g^-1.And at high current densities of 10 A·g^-1 and 20 A·g^-1,it can exhibit high capacities of 285.4 mAh·g^-1 and 251.6 mAh·g^-1,respectively.The introduction of carbon materials and Cu₉S₅ materials with good conductivity improves the conductivity of the overall composite electrode.The confinement effect of the carbon matrix is conducive to improving the cycle stability of the composite electrode.The hollow composite structure shortens the diffusion path of ions and accelerates the transport of electrons.And the synergistic effect of them makes the composite electrode exhibit high capacity and excellent potassium storage kinetics.