Research Of In-Situ Cross-Linked Binder And Protecting Layer In High Capacity Lithium Battery Electrode

The limited energy density of lithium-ion battery now can not meet the need of electric vehicle's development.The theoretical capacity of silicon material is more than ten times that of graphite.Replacing graphite with high capacity silicon/carbon(Si@C)material would obviously increase the energy density of lithium-ion battery.The choice of binder would influence the performance of Si@C composite material seriously,and the traditional binder could no longer meet the need of high capacity Si@C material.So it's quite necessary to develop a novel binder,which is suited to the high specific capacity Si@C material.Because of the limited potential of lithium-ion battery cathode material,it's necessary to develop new energy storage device to get higher energy density.Lithiumsulfur(Li-S)battery has a theoretical energy density of 2500 Wh/Kg,and is regarded as ideal energy storage device for the next generation.The main problems of Li-S battery include the shuttle effect of the polysulfide,the volume expansion of sulfur and so on.The strategies of sulfur/carbon composite material and interlayer could obviously improve the performance of Li-S battery.But the strategies above would introduce a large amount of inactive material and decrease the energy density of Li-S battery.There is a need to develop strategies which introduce no or little inactive material and improve the performance of Li-S battery at the same time.At first,this paper designed and developed a novel binder by compositing prelithified polyacrylic acid(PAA-Li)and guar gum(GG).At the station of 150 ? and vacuum,the hydroxyl groups on the GG molecule would react with the carboxyl groups on the PAA molecule to form eater groups.So a cross-linked structure could be in-situ formed in the Si@C electrode.the novel cross-linked binder could effectively restrain the volume expansion of silicon,and improve the cycle performance and coulombic efficiency.Secondly,this paper designed and prepared a novel Li-S cathode binder,while Polycarbonate diol(PCDL),triethanolamine(TEA)and hexamethylene diisocyanate(HDI)were used as monomers.By taking advantage of the high activity between hydroxyl groups and diisocyanate groups,those monomers above could be in-situ crosslinked in the Li-S cathode electrode.the cross-linked structure of this novel binder could not only restrain the volume expansion of sulfur,but also adsorb the polysulfide chemically and promote the transportation of Li-ion.So this binder could improve the cycle,rate and high mass loading performance of Li-S battery at the same time.Finally,this paper respectively prepared zinc oxide,zinc and stannum protective layer on the Li-S battery cathode through magnetron sputtering.When preparing membrane through magnetron sputtering,the temperature of base material wouldn't increase obviously.So the magnetron sputtering is proper to be applied in the Li-S battery cathode,which is not stable at high temperature.All kinds of protective layer could resist the polysulfide physically.The oxide protective layer could adsorb the polysulfide chemically,so the cycle performance of Li-S battery could be improved.The metal protective layer could promote the transportation of electron,so the rate performance of Li-S battery could be improved.