Electrochemical Performance Of Carbon Based Composite Cathode Materials In Zinc-iodine Batteries

With high electrochemical reversibility and low cost,metal-iodine batteries（MIBs）have broad application prospects in the new generation of electrochemical energy storage systems.Although the technology of rechargeable MIBs has made great progress,there are still problems such as low energy density and poor cycling stability,which hinder their wide application.Zinc is abundant in resources and has the advantages of high energy density and low cost.Compared with other MIBs,zinc-iodine（Zn-I₂）batteries are simpler and more convenient to assemble.However,the selection of a suitable cathode substrate material to control the reaction process,suppress the by-product generation,and avoid the corrosion of the zinc anode are key factors.The pore structure of porous carbon materials can limit the diffusion of iodine,while the heterogeneous doping can improve the utilization of iodine and provide more active sites for the reaction,which can further enhance the electrochemical performance.In this thesis,porous carbon/iodine composites were prepared using three carbon materials as the cathode matrix,and their electrochemical properties were tested and investigated.The following aspects of research are mainly carried out.（1）ZIF-8 derived porous carbon（ZPC）is used as a matrix for iodine in Zn-I₂batteries.The porous structure gives it a large specific surface area,which can effectively adsorb iodine by physical adsorption while promoting ion diffusion and electrolyte infiltration.ZPC also contains a large amount of N,Zn,and Zn O heterogeneity,which can provide a large number of active sites to form a chemical connection with iodine and effectively inhibit the shuttle effect of iodine,several advantages above make ZPC an excellent cathode matrix for Zn-I₂ batteries.The ZPC/I₂ composite electrode exhibits a high specific capacity(156 m Ah g^-1 at a current density of 100 m A g^-1),good rate performance and excellent cycling stability.The high coulomb efficiency and excellent self-discharge test results also show that the"shuttle effect"is effectively suppressed,and the kinetic study shows that the battery is diffusion-controlled and has fast reaction kinetics.（2）Considering that Zn-I₂ batteries are inherently cheap and environmentally friendly,it is ideal to use cheap and easily available biomass-derived porous carbon as the cathode substrate from this point of view.Using ginkgo as the carbon source and potassium hydroxide as the activator,hierarchical biomass-derived porous carbon(BC_HP)is produced by a two-step carbonization method,there are smaller pores within pores,and BC_HP has a high specific surface area(1176 m² g^-1).The special hierarchical structure not only provides a large number of channels for rapid electrolyte infiltration,but also provides abundant active sites to physically adsorb iodine,and these effects improve iodine utilization and accelerate the reaction kinetics,allowing the battery to achieve excellent cycling stability and high Coulomb efficiency.It provides a new idea for the development of cheap,safe and environmentally friendly Zn-I₂ batteries.（3）Based on the second work,the biomass-derived porous carbon was further modified by high-temperature carbonization with litchi shell as the carbon source,potassium hydroxide as the activator,and urea as the nitrogen source to generate nitrogen-doped litchi shell-derived porous carbon（N-LPC）materials.The nitrogen doping provides more active sites for the reaction of iodine and increases the adsorption effect on iodine,while the rich pore structure and high specific surface area facilitate the performance.When assembled into batteries for testing,the specific capacity was 126m Ah g^-1 at a current density of 100 m A g^-1,while the rate performance and cycling stability were also superior.This method provides an idea to further enhance the performance of carbon materials as a matrix for iodine.