Study On Optimization And Electrochemical Performance Of Metal-iodine Secondary Battery Electrolyte

Electrochemical energy storage devices play an important role in people’s daily life.It is particularly important to develop electrochemical energy storage devices with high capacity,high stability and low production cost.As a new cathode material,iodine has a high theoretical capacity(211 m Ah·g^-1).Meanwhile,seaweed,kelp and other plants can selectively absorb and enrich the iodine in seawater,so that the battery based on iodine material has received wide attention and been studied.Iodine-based battery mainly use anhydrous organic solvent.However,the organic electrolyte is toxic,flammable,strict requirements for operating environment,and iodine salt has strong oxidation,corrosive and biotoxicity,bringing safety certain and limiting the widespread use in the field of energy storage.Therefore,the development of green electrolyte for iodine-based battery is of great significance.In this thesis,aqueous electrolyte is used to replace the organic electrolyte and paired with metal anodes with a relatively negative potential.By optimizing the type and content of additives in aqueous electrolyte,the electrochemical performance of the battery is improved.The main researches of this thesis are as follows:（1）A certain amount of potassium iodide and polyethylene glycol（PEG400）was added to water as the electrolyte for the dual-ion secondary battery in the zinc-iodine system.The complexation of PEG400 with iodine inhibited the reaction of iodine and iodine ions to generate iodine triions and reduces the solubility of iodine in the electrolyte.Secondly,the addition of potassium iodide to the electrolyte serves not only as a source of iodine active substances,but also as an additive of potassium salt to increase the ionic conductivity of electrolyte.Finally,the electrolyte is assembled with double carbon cloth as cathode current collector,zinc sheet anode and seperator.At 1 m A·cm^-2current density,iodine displays a capacity of 1.62 m Ah·cm^-2.The percentage of iodine involved in the redox reaction accounts for 47.52%of the total iodine mass in the battery electrolyte,with a comlombic efficiency of93%.The comlombic efficiency increases to about 98%at the high current density of 7m A·cm^-2with a capacity retention of 58.33%after 1200 cycles.This stragtegy,simple in operation and low cost,works well,displaying that zinc iodine battery has great potential for further development in energy storage.（2）The aqueous electrolyte of manganese-iodine system is prepared by adding glycine and selenium dioxide additives,potassium iodide and a large amount of sucrose or polyethylene glycol（PEG400）in pure water.Using the complexation of glycine and manganese ion,the deposition of manganese ions at the electrode interface was faciliated.In charge and discharge process,selenium dioxide,in the form of Se O₃^2-in the electrolyte,produces Se on the interface of the manganese metal,inhibiting the evolution of hydrogen.Potassium iodide not only increases the source of iodine,but also improves the ion conductivity of the electrolyte.In addition,by adding large amounts of sucrose and PEG,the electrochemical window of electrolyte was widened,and the evolution of hydrogen and oxygen was largely inhibited.Finally,with tin-plated manganese sheet as anode and iodine cathode materials,the cells displayed a Coulomb efficiency of about 90%at 0.5 C rate and capacity of 190m Ah g^-1.At 1 C rate,the capacity retention rate increases to 93.66%and the coulomb efficiency is about 90%over 100 cycles,displaying good cycle stability.