Study On The Preparation Of Nano-silicon Materials For Lithium Ion Batteries Based On Rapid Solidification

Lithium-ion batteries have been widely used in modern life,but its power and energy density still can not meet the requirements of the rapid development of electric vehicles and portable electronic devices.At present,the anode material of commercial lithium batteries is mainly graphite,but its theoretical specific capacity is low(372 m Ah/g).At present,graphite is mainly used as anode material for commercial lithium batteries.Silicon is one of the most promising anode candidates for the next-generation Li-ion batteries due to its high specific capacity(with the highest theoretical capacity reported at 4200 m Ah/g(Li₂₂Si₅)),low charge/discharge platform(<0.5 V vs.Li/Li⁺),and abundant crustal reserves.However,practical application of silicon anodes is currently hindered by multiple challenges including the enormous volume change(>300%)during lithiation/delithiation processes,low intrinsic electrical conductivity,and instability of the solid electrolyte interface(SEI).Meanwhile,most of the preparation methods for the modification of silicon anodes are complicated,and the cost is high,which makes it difficult to achieve industrialization of silicon-based composite material systems.How to solve the above problems and find a method with large-scale industrial production is the focus of this chapter.In view of the above problems,this article first combined the rapid solidification and de-alloying method to prepare nano-silicon anode materials which of diameter is below100 nm.By controlling the alloy composition ratio,preparation conditions,etc.to control the size of the silicon particles,the obtained nano-silicon anode shows excellent electrochemical performance.In this paper,nano-silicon particles(c-Si and r-Si)are prepared by suction casting and melt spinning respectively.After simple coating,systematic characterization and analysis are performed.The main research contents include:1.Nano silicon particles(c-Si)with uniform rod shape can be obtained by suction casting method with Al-Si alloy as precursor and de-alloying method with average size is72 to 162 nm.The effects of alloy composition and diameter of suction-mold copper mold on the size of c-Si particles were investigated,and it was found that when the alloy composition was 14.0 wt.%Si,nano-sized silicon powder with uniform size and no coarse particles could be obtained to the greatest extent.The particle size of c-Si decreases as the size of the suction-cast copper mold gradually decreases.Electrochemical performance tests also show that c-Si has a higher initial Coulomb efficiency(83.7%),and has a higher specific capacity and more stable cycle performance than m-Si.2.A more uniform ellipsoidal nano-silicon particle(r-Si)with an average size of 40nm was prepared by the spinning method and de-alloying.We also combined graphene oxide reduction coating graphene layer(r-Si/GO)and simple amorphous carbon coating(r-Si/C)to improve the cycling performance of the electrode.In a half-cell assembled with r-Si/C and metallic lithium,there is a reversible capacity of 758.4 m Ah/g at a current density of 200 m A/g and a superior capacity retention of 69.2%after 200 cycles.In summary,our research methods are more simple,low-cost and easy to realize industrial batch production compared with other methods for preparing silicon anode materials.It provides a new idea for large-scale production of high-performance nano-silicon particles in lithium ion batteries.