Efficient Charge Storage In Zinc-Iodine Batteries Based On Pre-Embedded Iodine-Ions

Rechargeable aqueous metal batteries have the advantages of high Coulomb efficiency,long cycle life,pollution-free operation and low maintenance cost,Thus,rechargeable metal ion batteries are prospective for large-scale grid energy storage.Among aqueous metal batteries,Zn-I₂cells have received extensive research attention because of their abundant reserves（75 ppm of zinc in the earth’s crust and 55μg of iodine in seawater）,cost effectiveness,safe operating environment,high capacity,excellent energy density and 1.29 V output voltage.In cyclic voltammetry,the zinc metal anode undergoes a plating/stripping process with a theoretical capacity of up to820 m Ah g^-1and an electrochemical redox potential as low as-0.76 V（vs.standard hydrogen electrode,SHE）.However,the slow kinetics of I^-/I₃^-redox reaction limit the successful realization of Zn-I₂batteries.In addition,the irreversible shuttle and loss/escape of polyiodide during this reaction leads to unstable operation and poor cyclability,greatly limiting the further development of large-scale grid storage.Therefore,this paper is dedicated to solving the problems and challenges of low Coulomb efficiency,poor cycling stability,and poor multiplicity performance in Zn-I₂batteries due to the self-shuttle effect of I₃^-,slow kinetics of I^-/I₃^-redox reactions,etc.We selected a suitable iodine ion reaction host-Prussian blue material（PB）,and then we pre-embedded iodine ions in the Prussian blue material（PBI）,so that the PBI electrode utilizes electrode-electrolyte coupling to achieve high Coulomb efficiency,long cycle stability,and excellent multiplicity performance of the zinc-iodine cell.This thesis contains the following two main areas of work:（1）Design and performance comparison of PB and PBI electrode materialsPrussian blue materials（PB）are used as hosts for iodide ions because they possess versatility due to their high porosity,open metal species and controlled chemical composition.The intrinsically porous structure of PBAs enables a facile guests’ions（such as I^-）infiltration and ion transportation.However,the PB material acts as an iodine ion host and its active site is not effectively utilized,and iodine ion transport to the PB material for oxidation reactions requires overcoming potential barriers.Meanwhile,PB electrodes are subject to physical adsorption only,and the self-shuttle effect of polyiodide I₃^-is not significantly inhibited,resulting in low coulomb efficiency and poor cycling stability of the electrode.Prussian blue is plasma etched under hydrogen atmosphere and then heat treated in a high concentration iodine ion solution to obtain pre-embedded iodine ion Prussian blue material（PBI）.By this pre-bridging effect,the utilization of iodine ions in the redox electrolyte by the electrode material can be improved.The PBI electrode has a high capacity of 110m Ah g^-1at a current density of 1 A g^-1.Meanwhile,the self-shuttle effect of I₃^-is effectively suppressed by the formation of Fe-I bonds,and the PBI electrode can maintain a capacity retention of 84.7%after 3500 cycles,while the Coulomb efficiency is close to 100%.Finally,asymmetric capacitors（PPINF and PPNF devices）were assembled using Fe₂O₃as the negative electrode,and the PPINF（PBI electrode）still has good performance.This simple and effective strategy can provide a new strategy for the efficient utilization of electrolytes for redox reactions.（2）Construction of a novel aqueous zinc iodine batteryIn this work,we constructed an aqueous Zn-iodine cell using PBI and PB materials as the positive electrode,1 M Zn SO₄+50×10^-4M KI（ZSPI）and 1 M Zn SO4+25×10^-4M KI（ZSPSI）solution as the electrolyte,and zinc flakes as the negative electrode,respectively.As a result,the Zinc-iodine double-ion battery in the high concentration of iodine ion ZSPI electrolyte delivers a high specific capacity of242 m Ah g^-1at the current density of 0.2 A g^-1with an excellent CE of≈100%,demonstrating excellent battery reversibility and shuttling suppression.The battery exhibits a high multiplicity performance of 82%in the current density range of 0.2 to10 A g^-1.Furthermore,the battery exhibits a retention rate of 94%after 1500charge/discharge cycles at a current density of 4 A g^-1and delivers a high energy density of 142 W h kg^-1at a power density of 5538 W kg^-1.Similarly,PBI//Zn zinc iodine cells still outperform PB//Zn cells in ZSPSI electrolyte with low iodine ion concentration.Thes excellent performances show a good application prospect for PBI//Zn Zn-iodine batteries and provide a solution for further commercialization of Zn-iodine batteries.