Preparation And Electrochemical Properties Of Silicon-Based Anode Materials For Lithium Ion Batteries Prepared By Silicon-Calcium Alloy

With the large-scale development of electric vehicles,the demand for lithium-ion batteries with high power density and high energy density has increased.Graphite,the most widely used anode,cannot meet market demand due to its low specific capacity.Compared with other anodes,silicon-based anode materials have become one of the most promising electrode materials to replace graphite in lithium-ion batteries(LIB)due to their high specific capacity.Although silicon-based anodes have an energy capacity that is up to 11 times greater than their graphite-based equivalents,the fast capacity decay caused by huge volume expansion and low electronic conductivity also limits the electrochemical performances.The expensive production method to maintain modified structure limits its commercial application.Therefore,seeking a low-cost synthesis method for high-performance silicon-based anode materials is the focus of current research on the synthesis of silicon-based anode materials.Silicon-calcium alloy is a common deoxidizer in the iron and steel industry.Because of its layered structure and low price,it can be used as a raw material for the synthesis of multilayer silicon.Herein,layer by layer B-doped Si is designed and constructed by a facile molten-salt chemical exfoliation from CaSi2,CaCO3 and B2O3.The effects of the ratio of B2O3 to CaCO3 and the pressing method on the morphology,structure and electrochemical properties of the Si/B/C composites were studied.The products were characterized by XRD and SEM.The research results show that:(1)Silicon-based materials can be prepared by molten salts method,and the silicon-based materials mainly exist in the form of multi-layer silicon flakes.(2)With the decreasing of boron-to-carbon ratio,layered structure of the prepared Si/B/C composite materials become more obvious and composites exhibit better electrochemical performance.The compression method affects the carbon content in the composite material.(3)The Si/B/C composite,obtained with a boron-to-carbon ratio of 2:3,CaSi2 pressed with CaCO3 has excellent electrochemical performance,it can deliver a specific capacity of 764.3 mAh·g-1 at a current density of 2000 mA·g-1 after 200 cycles.(4)The Si/B composites,B atoms in Si contribute to the increase of the conductivity and the expansion of lattices.Layer-by layer structure shorten the lithium ion diffusion pathway,promote electron diffusion and enlarge the electrode-electrolyte interface.(5)The electrochemical performance of B-doped Si flakes is better than that of B-doped Si particles and nano silicon.B-doped Si flakes electrodes maintain 85%specific capacity after 200 cycles at a current density of 2 A·g-1.