Preparation And Properties Of High-performance Anode Materials With Microwave-modified Spent Graphite From Lithium Ion Battery

Lithium-ion battery has become an indispensable part of life and social development,whose output and consumption are rising year by year.Recycling and reusing graphite from waste batteries will not only reduces the pollution caused by waste landfill and incineration,but also brings economic benefits and social benefits of sustainable development.In this paper,the recycled spent graphite was modified via microwave-irradiation as the anode material,and the lithium-storage capacity was studied.And the composites material of nano-SnO₂/rGO/recycled graphite is synthesized using as-prepared graphite as the carbon matrix to overcome the volume expansion of SnO₂,and to improve cycling stability and electric conductivity.This work innovatively optimized the value-added of waste resources via microwave modification and developed a new design of SnO₂/C-based materials which composited with recycling graphite.The comprehensive performances for lithium-ion battery anode were evaluated systematically.The main contents are as follows:（1）Microwave modification of recycling graphite and lithium-storage properties.The recycled graphite powder was purified,and then it was modified by microwave taking advantage of the properties and high-absorption of cycled graphite for microwave.A certain amount of defects and pores were formed on the surface and layer spacing was expanded,which became additional active sites for Li⁺storage and diffusion.In this case,the specific capacity and the diffusion of Li⁺is improved.When microwave time is 15 s,the resultant sample shows the outstanding Li-storage performance with initial coulombic efficiency of 86.4%.It exhibits an excellent reversible capacity of 428.2 mAh g^-1 at a current density of 0.1 A g^-1 after initial cycling and maintains a stable capacity of 412.6 mAh g^-1 after 50 cycles,which is significantly higher than that of spent graphite without microwave treatment and commercial carbon MCMB(～300 mAh g^-1).And the rate performance is significantly improved.This work provides a method for the regeneration and modification of recycled graphite.（2）Preparation of“SnO₂/rGO/recycled graphite”anode material and its energy storage performance based on microwave-modified recycled graphite.SnO₂/rGO/recycled graphite（SnO₂@rGO/SG）ternary composite was prepared under normal pressure by microwave-assisted and mechanical method to reduce the capacity fading of SnO₂@rGO,using modified recycled graphite,Sn Cl₂ and GO as raw materials.Also the effect of graphite content on Li-storage performance was studied.The prepared SnO₂ nanoparticles with a size of～4 nm were uniformly anchored on rGO nanosheets,which can shorten Li⁺transmission distance.Graphite particles can further stabilize the electrode structure,buffer expansion and contribute capacity.And the ions and charges transmission is improved.Remarkably,when the graphite content is 15 wt.%,resultant sample exhibits an excellent initial capacity of 1567.5 mAh g^-1 at a current density of 0.2 A g^-1 and maintains at a stable capacity of 1025.0 mAh g^-1 after100 cycles.At high current density of 1 A g^-1,SnO₂@rGO/SG also shows an excellent specific capacity of 704.7 mAh g^-1 after 100 cycles.This work provides an efficient and a low-cost approach to achieve high performance SnO₂/C-based composite.（3）Effect of preparation technology on energy-storage properties of SnO₂@rGO/SG composites.Under the optimal content of graphite（15 wt.%）,the effects of microwave time on the structure,composition and Li-storage properties of SnO₂@rGO/SG composite was studied to determine the relatively optimal synthesis process parameters.This work found that the sample had the highest crystallinity and content of SnO₂ when microwave for 7 min.In this case,more active sites for Li⁺storage are existed.The cyclic stability,rate performance and ions diffusion are obviously better than those of other samples.It exhibits an excellent initial capacity of904.5 mAh g^-1 at a current density of 0.2 A g^-1 after 300 cycles.At 1 A g^-1,the capacity retention rate is 81.6%after 100 cycles.It can be concluded that the optimum condition for the preparation of SnO₂@rGO/SG ternary composite by microwave-assisted hydrothermal is the microwave irradiation at 500 W for 7 min.