Preparation Of Iodine Containing Composites And Electrochemical Performance Studies Of Rechargeable Magnesium-Iodine Batteries

The ever-increasing development of science and technology has put forward new requirements on the performance of the storage batteries,looking for a new kind of clean,safe and efficient battery system is imperative.Recently,rechargeable lithium-iodine batteries have received extensive attentions of researchers due to high energy density and rate performance,but exist serious security problems when used as anode of batteries on account of the growing of lithium dendrites.Magnesium is an ideal anode material,it has negative electrode potential(-2.36 V vs.NHE)and high volume energy density(3833 mAh cm-3),magnesium-iodine batteries take magnesium as anode,iodine as cathode has well application prospect.In this paper,we study the electrochemical properties of magnesium-iodine batteries by using beta-cyclodextrin and activated carbon fiber to immobilize iodine,and further studies were made by using LiTFSI as electrolyte additives.First,we use beta-cyclodextrin to immobilize iodine,the content of iodine in beta-cyclodextrin/iodine complex is 17% by the UV spectrum tests.The XPS tests demonnstrate that the interactron between iodine and beta-cyclodextrin were mostly physical,thermogravimetric analysis shows the thermal stability of iodine increased significantly through the adsorption in beta-cyclodextrin.Taking beta-cyclodextrin/iodine composite as cathode,magnesium as anode,0.75 mol L-1 Mg(ClO4)2 in DMSO as electrolyte to assemble batteries.The beta-cyclodextrin/iodine composite cathode delivers an initial discharge capacity of 138 mAh g-1 at rate of 0.1 C for discharging and 0.2 C for charging,after 20 cycles,discharge capacity is 50 mAh g-1.The charge and discharge coulombic efficiency is about 70%.By using beta-cyclodextrin/iodine composite as anode of magnesium-iodine batteries has merit of inexpensive price and simplely preparation,beta-cyclodextrin with the property of adsorption and disadsorption of iodine molecular has certain significance for further study the mechanism of magnesium-iodine batteries.Secondly,we use activated carbon fiber to immobilize iodine,activated carbon fiber has strong adsorption ability of iodine.Taking activated carbon fiber/iodine composite as cathode,magnesium as anode,0.3 mol L-1 [Mg(THF)6][AlCl4]2/PYR14TFSI:THF(V:V=1:1)as electrolyte to assemble batteries.For CV test of magnesium-iodine batteries,there are two pairs of electrochemical redox peaks corresponding to I2/I3-and I3-/I-redox pairs.The initial discharge capacity is 142 mAh g-1 at rate of 0.1 C for discharging and 0.2 C for charging,but the capacity decay quickly,the discharge capacity is 58 mAh g-1 only after 5 cycles.The as-prepared activated carbon fiber/iodine composite cathode leaves out the use of conductive additives,binder and current collector,which simplify the manufacture process and reduce the cost of batteries,but the cycle performance of the batteries need to further improve.At last,in order to improve the electrochemical performance of the batteries,we add high concentration of Li TFSI into the electrolyte as additives to study the electrochemical performance of activated carbon fiber/iodine composite cathode.The charge and discharge results show that the cycle performance is significantly better than the system without lithium salt,the initial discharge capacity is 231 mAh g-1 and also keep around 60 mAh g-1 after 50 cycles.Activated carbon fiber is an ideal material to immobilize iodine,which has the merit of low price,good conductivity,strong adsorption ability of iodine,magnesium-iodine batteries with activated carbon fiber/iodine composite cathode have well application prospect.