Preparation And Properties Of Silicon And Lithium Metal Anode Materials With High Specific Capacity For Lithium Ion Batteries

With the increasing requirement of the market for higher energy density lithium ion battery(LIB),it is difficult for commercial graphite anode to meet the demand.Therefore,it is very urgent to develop anode materials with high specific capacity.Silicon and lithium metal anode has attracted extensive attention due to its extremely high theoretical specific capacity,which are expected to be used in high-capacity power lithium ion batteries in the future.However,their volume variation is large during cycling,making the SEI film unstable.In addition,the lithium metal anode has the problem of dendrite growth.In this paper,carbon materials were used to modify them,and materials with different nanostructures were designed,so that the electrochemical properties were effectively improved.The main research content are introduced as following:1.We designed Si/graphite/graphene composite with low Si content(5 wt%)through a simple self-assembly method.Firstly,silicon nanoparticles were ball-milled with commercial graphite to obtain the Si/G composite.Then,the Si/G composite were homogeneously dispersed in graphene solution.After the addition of reducing agent,the graphene sheets self-assembled into a three-dimensional frame structure with tight encapsulation of Si/G composite in it.Due to the low Si content,the effectively maintaining the stability of the electrode by 3D graphene and graphite,and the enhanced conductivity,high specifc capacity and long cycle life were simultaneously achieved in the Si/G/GF-5 electrode(Si:5 wt%)when compared to graphite and Si/G composite.It shows a reversible capacity of 548 mA h/g at 372 mA/g,high capacity retention of 90%over 100 cycles as well as a superior rate performance of 310 mA h/g even at 2232 mA/g.2.The metal-organic frameworks(MOF)modified three dimensional carbon cloth(HZS@CC)composite was prepared through a template method.First,a polystyrene template is deposited on the carbon cloth.Then a layer of ZIF-8 material is grown on the surface.After the removing of template,the ZIF-8 hollow spheres modified carbon cloth was obtained.ZIF-8 can induce the deposition of lithium metal and reduce the nucleation overpotential.At the same time,carbon cloth can act as the host material,alleviate the volume change of the electrode to maintain the stability of the SEI film on the surface.Due to the synergistic effect of them,the composite shows longer cycling time when compared with carbon cloth and Cu foil.The symmetrical cell has a stable cycle of 700 hours at the condition of 1 mA h/cm2,1 mA/cm2,and the cyclic electrode surface is smooth without any lithium dendrite formation.What’s more,the coulombic efficiency is still 99%after 200 cycles at 6 mA h/cm2,2 mA/cm2.