Preparation Of Transition Metal Sulfide/Carbon Hollow Sphere Composites In Lithium-Sulfur Batteries

The limitation of fossil energy and the importance of energy conservation and carbon reduction has promoted the vigorous development of the new energy industry.Lithium-sulfur batteries have high performance,low cost and environmental protection,which are very suitable for current energy market applications.However,there are still drawbacks such as volume expansion,shuttle effect and poor conductivity in the positive sulfur electrode of Lithium-sulfur batteries,which seriously hinder the pace of Lithium-sulfur batteries entering the energy market.The electrochemical reaction of lithium-sulfur battery in the charge and discharge process mainly occurs in the positive electrode of sulfur,so it is necessary to further optimize and prepare new positive electrode host materials.In this paper,a transition metal sulfide/carbon hollow sphere composite material was designed as a host material for lithium-sulfur batteries in response to the problems existing in sulfur-positive electrodes.Transition metal sulfides have strong interactions with polysulfides.The huge internal cavities of carbon hollow spheres can store sulfur,and carbon materials have excellent electrical conductivity.Therefore,when transition metal sulfide/carbon hollow spheres are for lithium-sulfur batteries,they can effectively improve the conductivity of the sulfur cathode and inhibit the shuttle effect of polysulfides during charging and discharging,thereby improving the battery capacity and cycle performance of lithium-sulfur batteries.The main research contents and conclusions of this article are as follows:（1）Using Si O2 spheres as the template,phenolic resin as a carbon source,and sublimated sulfur as a sulfur source,carbon hollow sphere host materials C-HS with different carbon wall thicknesses were obtained by high-temperature carbonization and etching with Na₂S aqueous solution.Prepared by low-temperature melting method C-HS@S The electrode material was assembled into a button type half cell for electrochemical performance testing.The test results show that,2-C-HS@S The electrode material has good cycling performance,and the CV test shows that2-C-HS@S The electrode material has good cyclic reversibility,and the AC impedance test results show that it has a small resistance value,so it exhibits good electrochemical performance.（2）When using the above process to prepare carbon hollow spheres,cobalt salts were added to prepare cobalt disulfide/carbon hollow spheres（Co S₂/C-HS）composite materials,which were used as positive electrode carriers for lithium-sulfur batteries.The test results show that Co S₂nanoparticles are embedded on the surface of the carbon layer to form a Co S₂/C-HS composite material.Using the low-temperature melting method,elemental sulfur was loaded into the interior of the Co S₂/C-HS cavity to obtain Co S₂/C-HS@S Electrode material.The electrochemical performance results indicate that Co S₂/C-HS@S The electrode material exhibits a charge discharge specific capacity of 1115.4 m Ah g^-1in the first cycle,and after 500 cycles at a current density of 335 m A g^-1,it still maintains a high discharge specific capacity of 476.1m Ah g^-1.CV curve display Co S₂/C-HS@S The reduction peak potential of the electrode material shows a significant positive shift,indicating that the nanostructured Co S₂has good catalytic performance.EIS testing indicates Co S₂/C-HS@S The electrode material has a smaller electrochemical impedance.The improvement in electrochemical performance can be attributed to the synergistic effect of transition metal sulfide nanoparticles and carbon hollow spheres.（3）On the basis of Chapter 4,a dual transition metal sulfide/carbon hollow sphere（Ni Co₂S₄/C-HS）composite material was prepared and used as a positive electrode carrier material for lithium-sulfur batteries.Compared to single metal sulfides,Ni Co₂S₄/C-HS carrier materials have better conductivity and strong interactions with polysulfides.Therefore,Ni Co₂S₄/C-HS@S The electrode material exhibits excellent electrochemical performance,exhibiting a charge discharge specific capacity of 1341.1 m Ah g^-1in the first cycle and a high discharge capacity of 524.3m Ah g^-1after 500 cycles at a current density of 335 m A g^-1.Through CV testing at different current densities,it was found that Ni Co₂S₄/C-HS@S The electrode material has better Li⁺diffusion performance.