Study On Preparation And Properties Of Organic Materials Coated Silicon Anode Material

With the rapid development of new energy vehicles,the existing graphite negative electrode cannot meet the needs of high energy density batteries.As a new generation of anode material with high specific capacity,silicon is expected to replace graphite and greatly improve the energy density of lithium-ion batteries.However,the huge volume expansion caused by the insertion and removal of lithium ions during charge and discharge will lead to the damage and regeneration of the SEI layer,and even the pulverization of the electrode materials,resulting in a rapid decline in the capacity of the battery.In order to solve the problems of silicon-based anode electrode,a new type of silicon-based composite was prepared by coating organic matter on the surface of silicon material,which effectively improved the electrochemical performance of silicon anode electrode.The main research contents are as follows:（1）Using acid-washed discarded micron Si as silicon source,by a simple one-pot method,coating a layer of covalent organic framework（COF）on micron Si surface through Schiff base condensation reaction,a novel silicon-based composite material Si@COF was prepared.The COF material on silicon surface has the characteristics of porous channel,cavity structure and particle gap,which can not only improve the lithium-ion transport but also restrain the volume expansion of silicon material.As the anode electrode of lithium-ion battery,the prepared composites showed excellent electrochemical performance.Under the current density of 500 m Ah·g^-1,the initial Coulomb efficiency is 77.4%.After 100charge-discharge tests,it has a charge specific capacity of 1800 mAh·g^-1.（2）Using acid-washed discarded micron Si as silicon source,the surface of micron Si was coated with protocatechuic acid（PCA）,and a new type of silicon-based composite Si@PCA was prepared.The PCA coated on the surface of micron Si suppresses the volume expansion of silicon and improves the cycling performance of silicon anode.As the anode electrode of lithium-ion battery,the electrochemical performance of Si@PCA composite is good.Under the current density of 500 m Ah·g^-1,the initial Coulomb efficiency is 73.3%,and the charge specific capacity of 1093 m Ah·g^-1is obtained after 200 charge-discharge tests.（3）From the aspects of surface modification and functionalization,the silicon-based composite Si@GA was prepared by coating a layer of Gallic acid on the nano-Si particles.Gallic acid was coating on the surface of nano-Si reduces the decomposition of electrolyte on the surface of Si and improves the electrochemical performance of silicon-based materials.As the anode electrode of lithium-ion battery,the initial charge-discharge specific capacity of Si@GA composite is 2977 m Ah·g^-1and 3318 m Ah·g^-1,respectively,and the initial Coulomb efficiency is 89.7%.After100 charge-discharge tests,Si@GA composite has the charge specific capacity of2340 m Ah·g^-1.Even at a large current density of 1 A·g^-1,Si@GA composite still shows excellent cycle performance.