Preparation And Electrochemical Properties Of Silicon-Based Anode Materials For Lithium Ion Batteries

The development of lithium ion batteries with higher energy density has become the main direction of the development of power batteries.The research of high capacity anode and cathode materials with excellent performance is needed.In terms of anode materials,the theoretical capacity of the most widely used graphite anode material is 372 mAh g-1,and the practical capacity of commercial graphite materials reaches 365 mAh g-1,which is close to the capacity limit.Therefore,the development of high capacity anode materials for next-generation lithium-ion batteries is imminent.Silicon-based materials are considered to be the most promising next-generation high capacity lithium ion battery anode materials because of high theoretical capacity,suitable lithium insertion potential,abundant resources,and environmental friendliness.However,the commercialization of Si anode still faces great obstacle.A key factor is that Si anode suffers huge volume change(?300%)during cycles,leading to serious pulverization,rapid electrode deterioration,and capacity loss.Therefore,holding structural integrity with Si electrode against unavoidable volume change is an enormous challenge.Therefore,to solve the main problems of silicon anodes,material structure design and binder are designed to improve the electrochemical performance,which is mainly included the following aspects:(1)First,we synthesized a novel structural microspheres consisting of cross-linked CNT,porous Si/SiOx nanoparticles,CNT,and carbon coating(CNT/SFDP-Si/SiOx@C microspheres)by combining an inverse water-in-oil microemulsion approach with magnesiothermic reduction,in which silica fume,an inexpensive industrial by-product,is used as the porous Si precursor.The size of the microsphere is 1-10 ?m,which can effectively increase the tap density.The reversible capacity of the prepared microspheres is still 675.8 mAh g-1 after 1000 long cycles at 2 C with 81.2%retention and a negligible capacity decay rate of 0.018%.Matching with LiFePO4 cathode material,the initial coulombic efficiency of the full cell is 91.2%at 0.2 C.After 40 cycles,the capacity retention rate is 93.2%,demonstrating the possibility of application.(2)Using tetraethyl orthosilicate as silicon source and CTAB as surfactant,carbon-coated mesoporous hollow silicon oxide were prepared by modified stober method and carbothermal reduction.The ratio of alcohol to water has an important influence on the size,morphology and properties.The silicon oxide nanospheres coated carbon are about 300 nm when the ratio of alcohol to water is 0.45,and the electrochemical performance is the best.The reversible capacity of 813 mAh g-1 can be achieved after 200 cycles at a current density of 100 mA g-1.After 1200 cycles at the current density of 500 mA g-1,the capacity maintain to be 704 mAh g-1 with the retention rate of 82%and the capacity decay rate of 0.015%.(3)Using carbon dioxide as a template and bitumen as carbon source,the carbon-coated hollow silicon oxide anode material was prepared,meanwhile,a cross-linked three-dimensional binder was synthesized in situ on the current collector.The mechanical properties of the electrode are excellent.In the half-cell,the as-prepared collaborative electrode presents a reversible capacity of 696 mAh g-1 without obvious capacity decay after 500 cycles at 0.5 A g-1.The full cell fabricated with prelithiated NCM 523?Void@SiOx@C delivers a reversible capacity of 157 mAh g-1 at 0.5 C and an excellent capacity retention of 94%after 160 cycles,showing a great commercial prospect.