Preparation And Properties Of Polymer-based Composite Silicon Anodes

Lithium-ion(Li-ion)battery,a kind of green renewable energy,is an inevitable product of the development of new age,under the circumstances that natural gas,oil and other traditional energy materials are drying up.Compared with other secondary batteries,Li-ion battery has greater energy density,higher operating voltages,longer working life,and also be friendly to environment.Much attention has been focused on it for a long time.The anode material is one of most perspective aspects among all the ingredients of Li-ion battery.Along with carbon materials,transition metal oxides and alloy materials in recent years,new findings of anode material with wonderful performance arise one by one,promoting the development of Li-ion battery.Si,a kind of new anode materials that be abundant,safe and friendly to environment,has low discharge potential(<0.2V vs Li/Li~+)and high theoretical capacity up to 4200 mAh/g,more than ten times higher than that of commercialized graphite.However,it suffers from poor cycle stability,resulting from great volumetric expansion up to 300%during lithiation and delithiation.Great internal stress and electrode destroy may arise accordingly.Consequently,the loss of electrical between Si and collector is unavoidable.To make up this weakness has been the target of researchers.In the paper,polymer is a new element added to the Si-based anode material.Liquid rubber with higher elasticity and better adhesion than PVDF acts as structural material in Si-based composite anode.The main aspects are shown as follows.(1)LT(LNBR)acted as matrix material.Si nanoparticles and acetylene black were dispersed in it to form Si/LT(Si/LNBR)composite,which was coated on Cu foil.It was showed that Si/LT got a thin layer of LT,the volumetric expansion of Si might be controlled by which.The first reversible specific capacity was 1500 mAh/g under the current density of 200 mA/g.After 50 cycles 48 percent of it was remained.The average decay rate was 0.7%.Comparatively,Si/LNBR composite gained an integrated dense thick coating layer,paving the way for next research.(2)Si@a-C composite was obtained by carbonization of Si/LNBR.LNBR was transformed into amorphous carbon as a coating layer on Si and also a conductive agent,improving electric conductivity.In addition,the current collector was changed to foam-Ni that provided interpenetrating channel for diffusion of Li-ion.Under the same conditions,the first reversible specific capacity was 2000 mAh/g,and the average decay rate was 0.8%in 50 cycles.(3)Based on Si@a-C composite,FACS was added to improve mechanical strength and porosity,which might contribute to structural stability and diffusion of Li-ion.Comparatively,the first reversible specific capacity was 2500 mAh/g,and 80percent was remained after 50 cycles.The average decay rate was down to 0.4%.Charge/discharge capacity and the cycling stability both were promoted to a great degree obviously.Moreover,the Si@a-C composite modified by FACS still showed nice capacity and cycling stability under higher current density,indicating its practical value.