Preparation Of In-situ Nitrogen-doping Carbon Aerogel And Study On The Electrochemical Performance Of Lithium-sulfur Batteries

Lithium-sulfur battery(LSB)has been attracting worldwide attention and in-depth research due to excellent characteristics including high specific energy density,high theoretical specific capacity,environment-friendly and non-toxic,and abundant sulfur storage in the earth.The popular strategies focus on combining sulfur with highly conductive materials to improve the electrochemical performance of LSB.Carbon aerogel(CA)has become a key supporting material for sulfur electrode owing to its large specific surface area and high electrical conductivity.In our work,in-situ N-doping carbon aerogel with specific structure has been prepared by the facile method,and the composite electrode with sulfur is formed,effectively inhibiting the "shuttle effect" and significantly enhancing the electrochemical performance of LSB.Carbon aerogel with high content N-doping(NCA)is successfully prepared via m-phenylenediamine and formaldehyde reaction through the facile sol-gel method and subsequent high-temperature carbonization process.The prepared NCA nanospheres have the specific cross-linked framework structure and present the characteristics of large specific surface area and high loading sulfur.NCA cathode materials with N possess active sites and realize the adsorption of lithium polysulfide(Li PSs),presenting excellent electrochemical performance.The NCA/S composite electrode exhibits the first discharge capacity of 1247 m Ah/g at 0.2 C.NCA/S cathode still displays a capacity of 797 m Ah/g and low capacity attenuation rate of 0.083% after300 cycles at 0.5 C,presenting excellent cycle stability.The remarkable properties are mainly attributed to strong adsorption of evenly-distributed nitrogen in the material,effectively preventing the escape of PSs,restraining shuttle effect and increasing utilization of active sulfur.On the basis of the above work,Cu-N co-doped carbon aerogel(Cu-NCA)is prepared via using m-phenylenediamine,formaldehyde and copper nitrate.Cu-NCA material not only inherits evenly distributed nitrogen,but also successfully realizes the uniform distribution of copper element.Cu-N co-doped spherical carbon aerogel as a supporting material for sulfur has abundant active sites,which can effectively immobilize PSs,retard their migration and diffusion and inhibit the shuttle effect,exhibiting excellent electrochemical performance.Particularly,the 2-Cu-NCA/S composite cathode presents a high discharge capacity of 1305 m Ah/g at 0.2 C.LSB with 2-Cu-NCA/S electrode still demonstrates a capacity of over 890 m Ah/g and the capacity decay rate per cycle of only 0.075% after 300 cycles at 0.5 C during charge and discharge cycle.The structure of three-dimensional network of the carbon sulfur electrode is conducive to enhancing the electron conductivity and increasing the specific discharge capacity of the positive electrode.At the same time,the synergistic effect of Cu and N in the composite cathode can anchor Li PSs,enhance the utilization of sulfur and improve the electrochemical performance of the battery.