Preparation And Electrochemical Performance Of Biomass Porous Silicon Lithium-ion Battery Anode Materials Derived From Xiequia

Silicon has attracted more interest because of its ultra-high theoretical capacity(4200 mAh/g),abundant sources and suitable working voltage(<0.5V vs.Li⁺/Li).However,there are many problems in Si anode materials,which hinder its commercial application.On the one hand,Si anode materials suffer from the volume expansion(>300%)during the process of lithiation/delithiation,which can cause pulverization of Si electrode,resulting in irreversible attenuation of its electrochemical performance.On the other hand,the existing methods to prepare Si-based materials are complex and costly.To overcome these obstacles mentioned above,in this paper,low-cost Equisetum Fluviatile as raw materials are employed to construct the porous Si-based anode materials with excellent electrochemical performance for lithium-ion battery.The research contents of this paper are as follows:(1)Firstly,porous 3D-bio-SiO₂ was synthesized from Equisetum Fluviatile.It reveals that this porous 3D-bio-SiO₂ is composed of primary particles of about 9-15nm in diameter.The clustering of these primary particles leads to a porous structure with a surface area of 227 m²/g and a pore volume of 0.43cm³/g.Subsequently,the3D-bio-SiO₂ was reduced to 3D-bio-Si which consists of 30 nm primary particles by deep reduction-mild oxidation route.Finally,the 3D-bio-Si/C anode with a surface area of 232 m²/g was prepared through the carbon coating of the 3D-bio-Si.As an anode material for lithium-ion battery,the 3D-bio-Si/C can deliver a reversible specific capacity of 933.4 mAh/g at a current density of 1 A/g even after 400 cycles with the capacity retention rate of 89%.(2)Porous SiO₂/C composites were synthesized by HCl-leaching and then carbonization of low-cost Equisetum Fluviatile which served as both carbon and silicon sources.The prepared porous SiO₂/C composites with high specific surface area(181.139 m²/g)and pore volume(0.223 cm³/g)have a three-dimensional network structure composed of primary particles of SiO₂/C about 14.6 nm.The SiO₂/C composites show ultra-high electrochemical performance,and retain the specific capacity of 526.9 mAh/g after 95 cycles at the current density of 0.5 A/g.(3)The porous Si/C composites were successfully prepared by in-situ low-temperature magnesiothermic reduction process under the molten salts of Al Cl₃ at250?,which avoids the formation of high stability Si C.The XRD results show that the maximum reduction of SiO₂/C composites to Si/C composites can be achieved when the reaction time is 48h under the in-situ low-temperature magnesiothermic reduction process.The Si/C composites are composed of a special structure in which silicon nanocrystals with a diameter of about 13.66 nm are uniformly dispersed in the carbon matrix.In the first cycle,the Si/C composite can deliver a high specific capacity of 4010.3(Discharge)and 2100.3 mAh/g(Charge).After 95 cycles,the capacity of the Si/C composites can still remain at 990.7 mAh/g at a current density of 0.5 A/g.Benefiting from the three-dimensional network structure,in which the primary silicon particles uniformly dispersed in the amorphous carbon matrix,the Si/C composite shows excellent electrochemical performance.This three-dimensional network structure not only greatly buffers the volume expansion of silicon because of the abundant mespores therein,but also greatly improves the electronic conductivity of the anode because of the insitu formed carbon matrix,ensuring the rapid transportation of Li⁺during cycling.This work provides a simple,green,low-cost,and scalable approach for the preparation of silicon-based anode materials for lithium-ion battery.