Coating Modification Of Separators And Their Electrochemical Performance Of Zinc-Iodine Batteries

With the increasing requirements for energy storage devices in our lives,it is urgent to explore the new battery systems with higher energy density and lower cost than the current lithium-ion batteries.Among few options,the metal-iodine battery is a promising alternative to the embedded cathode due to its low cost,abundant iodine supply and the two-electron redox reaction.In particular,zinc-iodine battery has attracted wide attention owing to its advantages such as the simple assembly and the high relative specific capacity of iodine and zinc(211 m Ah·g^-1).However,the poor thermal stability and electrical conductivity of iodine,as well as the serious shuttle effect have inhibited the further development of Zn-iodine battery.It was found that porous carbon-based materials can suppress the diffusion of active iodine to the anode effectively,thus improved the capacity retention of Zn-iodine battery.However,the porous carbon shows weak physical adsorption of active iodine,thus establishing stronger interactions between iodine and the material is an effective and feasible strategy.In this thesis,three carbon-based materials were used as coating materials for modified separators,through a combination of chemical and physical interactions to limit the shuttle effect of active iodine effectively.The main work carried as follows:（1）The B₂O₃/PC composite（BPC）was used as a coating material for modified separator and applied to zinc-iodine battery.The porous structure can increase the utilization of active substances by the physical adsorption of iodine.In addition,the B₂O₃particles loaded on the carbon skeleton,which have the chemical bonding effect on iodine species can inhibit the shuttle effect effectively.The battery with BPC modified separator exhibits excellent electrochemical performance.The initial discharge capacity of battery was 228 m Ah g^-1 at 100 m A g^-1,and the capacity retention was around 91.2%after 175cycles.This study provides a novel idea for the development and design of the high-performance zinc-iodine battery.（2）Herein,a nitrogen and sulfur co-doped porous carbon material（NSPC）was successfully prepared by carbonization and hydrothermal method,and the adsorption tests showed that the adsorption capacity of NSPC material for polyiodide and iodine was higher than that of the compared sample,which was attributable to the physical adsorption of iodine by the porous structure,while the doping of N and S provided abundant chemical anchor sites for active iodine.Therefore,the battery with the NSPC modified separator exhibited excellent electrochemical performance:the specific capacity of the battery could still be maintained around 248 m Ah g^-1 after 115 cycles at 100 m A g^-1;it showed the excellent rate performance and self-discharge was well suppressed.This work provides a novel idea to prepare the porous carbon materials based on heteroatom doping for the application of high-performance zinc-iodine battery.（3）Based on the second work,we continued to explore economical and heteroatom-rich carbon-based materials.Here,a biomass-derived porous carbon（GBC）was prepared by high-temperature carbonization.The porous structure and heteroatom doping can provide abundant and robust active sites,which improve the utilization of active iodine and accelerate the reaction kinetics.Therefore,the battery with BPC modified separator exhibited excellent cycling stability and rate performance.The initial discharge capacity of the battery with the modified separator was 140.8 m Ah g^-1 at 100 m A g^-1,and the capacity retention rate was 76.9%after 200 cycles.This work provides an economical and environmental-friendly strategy for preparing high-performance zinc-iodine battery.