Study On Modification Of Cathode Materials For Li-Se Batteries By Carbon Framework

The secondary batteries play a great role in improving pollution caused by fossil energy,but the energy density of lithium-ion batteries is increasingly difficult to meet the actual industrial needs.Due to the ultra-high volume capacity density and long-term cycle stability of lithium-sulfur batteries,it has become the most potential development direction for next-generation energy storage equipment.However,poor conductivity,the volume changes during charging and discharging,and the famous"shuttle effect"dramatically increase the difficulty of research and practical application for sulfur electrodes.Selenium is the same main group element as sulfur.When it is used as an electrode material,it also has a considerable volumetric capacity density,and its conductivity has been qualitatively improved compared to sulfur.These all indicate the superior performance of lithium selenium batteries.However,the selenium electrode material also has defects such as irreversible dissolution of intermediate products,volume changes and electrode powdering during cycling.Therefore,this article constructs and improves the selenium loaded on the porous carbon support frame as a cathode material by sacrificing the precursor method,the pitting method and the doping of nitrogen and sulfur elements on carbon support,thereby improving the cycle stability and rate capability of the lithium selenium batteries.The main works of this paper are as follow:MnO₂,as a kind of metal oxide with a simple preparation method,has a very stable micro-morphology and maintains a good structure at high temperatures.However,it is easy to dissolve in hydrochloric acid solution,so it is very suitable as a precursor material for pore formation.In this experiment,porous carbon supporting materials were constructed using polyvinylpyrrolidone as the carbon source,mixed with rod-shaped Mn O₂ synthesized by hydrothermal method as the precursor,a porous carbon supporting material was constructed through high-temperature sintering and acid washing.By adjusting the mass ratio of Mn O₂ pore-forming material to the carbon source to control the pore distribution of the porous carbon material,the carbon support material with the most reasonable pore distribution and the most stable structure is finally selected to load selenium,and then subjected to the characterization and electrochemical testing of the electrode material.It shows that the rich pore structure can effectively load selenium into the inside of the support material,and can further improve the conductivity of the electrode material,thereby improving the energy storage capacity of the batteries.Inspired by the precursor sacrificing method,we designed another porous etching method to prepare porous carbon.After carbonizing the metal chelate manganese tartrate synthesized by hydrothermal method,the acid etching method was used to remove Mn O₂ in the carbon material.A porous carbon support material with a rich pore structure was synthesized,and then we carried out controllable single and double atom doping on the porous carbon surface through hydrothermal and heat treatment to enhance the immobilization of selenium cathode materials and their charge/discharge intermediates.The results show that the discharge specific capacity of the composite electrode is much higher than that of the pure selenium cathode under the synergistic effect of physical limitation of porous carbon on selenium and chemical adsorption of doped atoms.In addition,we also found that compared with the single doping of nitrogen atom,the conductivity and energy storage capacity of the double-doped composite electrode decreased because the sulfur atom occupied the position of nitrogen atom,which indicated that the chemical force between the selenium electrode material and nitrogen atom was stronger than sulfur atom.In summary,this article provides a method for modifying the cathode material of lithium selenium batteries by sacrificing precursor method、etching hole method and doping of carbon materials with nitrogen and sulfur atoms to construct and modify the support material of the cathode materials for lithium selenium batteries.