Preparation And Lithium Storage Properties Of Silicon Anode Materials Based On Slicing Waste From Photovoltaic Industry

Silicon-based materials are indispensable core materials for the development of new energy sources,electronic information,energy saving,environmental protection and other national strategic emerging industries.In recent years,with the rapid development of the photovoltaic industry,and more than 50,000 tons of silicon waste has been produced every year.Based on abundant silicon resources in Xinjiang,the development of the photovoltaic industry is particularly dominant.How to recycle the slicing waste from photovoltaic industry which is related to the future development of silicon industry chain in Xinjiang.Therefore,if the silicon waste is successfully applied to lithium-ion batteries（LIBs）,it will bring a great economic and social value.As anodes for LIBs,silicon is one of the most promising materials for commercial applications due to its many advantages of high theoretical mass specific capacity(～4200 m Ah g^-1),low operating voltage platform and environmental friendliness,etc.However,silicon-based materials also have serious defects of huge volume expansion in the electrochemical reaction,which greatly limits their further development and application.At present,nanometerization,porous structure and composite are common and effective methods to improve the electrochemical performance of silicon.Based on the above considerations,the polycrystalline silicon slicing waste from Xinjiang Xinte Energy Co.,Ltd.is acted as the object of research.It is modified physically and chemically using simple and efficient methods.Its application in the anode materials for LIBs is discussed in detail.The contents of the research are as follows:1.Preparation and lithium storage properties of polycrystalline silicon powder materials:Slicing waste silicon usually has an irregular and large structure,which can be nanometerized by a solid-phase ball milling method.The effects of different milling times on particle size and electrochemical properties of silicon waste are systematically explored by the ball milling method.It is found that waste silicon blocks changed to smaller particles obviously with about 140 nm-240 nm after the ball milling for 15h.The capacity of the sample Si-15h maintained at 397.1 m Ah g^-1 after 100 cycles at 200 m A g^-1,which was much better than that of the pristine silicon.It is because the rupture possibility of SEI film gradually decreases as the decreasing size of silicon particles.Meanwhile,nano-sized silicon particles can shorten the diffusion path of Li⁺,leading to the improved electrochemical performance.2.Preparation and lithium storage properties of porous silicon materials:Although the cycling performance of nano-silicon particles after ball milling is improved,there is still a serious of problems leading to the capacity attenuation.Based on the above research,the ball-milled polycrystalline silicon powder was modified by the acid and alkali etching.Then,the porous silicon materials were obtained.The effects of pore structure and composition on the lithium storage performance of the product were discussed.It was found that the waste silicon after the acid and alkali etching took on a thin sheet morphology and rich pore structure.At a current density of 200 m A g^-1 after100 cycles,the capacity of H8-6 after HF etching maintained at 1055.1 m Ah g^-1 and N1.0-60 after Na OH etching maintained at 711.7 m Ah g^-1,which were higher than the discharge capacity of Si-15h at the same condition.In addition,the porous silicon after Na OH etching has good cycling stability,which is attributed to porous structure and the Si O_xlayer that can effectively buffer the volume change of silicon during the charging/discharging process,and also facilitates the rapid transport of lithium ions to improve its electrochemical performance significantly.3.Preparation and lithium storage properties of boron doped Si/C composites:Although porous silicon has better electrochemical properties,its conductivity is still low.To solve the problem,boron doped porous silicon（B-Si）and boron doped silicon/carbon composites（B-Si/C）were prepared by boron doping and carbon coating.The effects of boron doping and carbon coating on the structure and electrochemical properties of waste silicon are discussed.In addition,B-Si owns the porous structure and B-Si/C presents the porous hollow structure.At a current density of 420 m A g^-1,the capacity of B-Si maintained at 932 m Ah g^-1 and B-Si/C maintained at 1240.1 m Ah g^-1 after 100 cycles,demonstrating excellent cycling performances than porous silicon.The porous silicon material after boron-doped produces local lattice expansion,which provides a hierarchical ion transport path.It not only shortens the ion transport distance,but also enhances the inherent conductivity of ions in the solid phase,improving cycling performance greatly.Moreover,the coating carbon layer further improves the conductivity of the material and effectively inhibits the volume expansion resulting from the alloy of Si and Li,which provides an effective guarantee for the optimization of the electrochemical properties of waste silicon.