Synthesis And Electrochemical Performance Of SiO₂@rGO Anode Materials For Lithium-ion Batteries

With the pursuit of the“dual carbon”goal,energy has become the cornerstone of the scientific and technological development of modern society,presenting a new set of challenges.As a critical component in the field of energy storage batteries,lithium-ion battery（LIBs）are extensively employed in various electronic intelligent devices due to their environmental friendliness,high specific capacity,high working voltage（3.7-3.8 V）,and excellent cycle performance.The anode material plays a significant role in determining the cycle life and energy density of LIBs,making it a vital components of these batteries.Silica（SiO₂）,an abundant materials on the earth,exhibits high electrochemical activity for Li⁺.SiO₂ holds promise as an anode material due to its higher energy density(theoretical specific capacity 1965 mAh g^-1)and lower discharge voltage platform.However,SiO₂ as an anode material also has certain drawbacks.Firstly,during the charge-discharge cycle,SiO₂undergoes volume expansion caused by alloying and dealloying,leading to the pulverization of the electrode material and the fragmentation and regeneration of the solid electrolyte interface.This results in irreversible capacity loss and capacity attenuation.Secondly,the high bond energy of Si-O in SiO₂hampers its electrical conductivity,thereby affecting its rate performance and long cycle performance.To address these issues,the preparation of nano-sized SiO₂ materials or their composites with high conductive materials proves effective.Based on this,nano-SiO₂carbon composites anode materials with yolk shell and tubular structures were synthesized using sol-gel method,hydrothermal method,and high temperature calcination methods,focusing on their structural modifications.The main contents are as follows:（1）The yolk-shell SiO₂@rGO composite was prepared by incorporating carbon-coated SiO₂ into a reduced graphene oxide（rGO）conductive network.The unique yolk shell structure allowed the SiO₂to undergo volume changes without destroying the carbon layer.the combination of rGO and carbon layer formed an efficient pathway for electron transfer.By selectively etching a portion of SiO₂with sodium hydroxide,a gap was created between the SiO₂core and carbon layer,which effectively limited the volume expansion of SiO₂ and improve its electrical conductivity.Electrochemical performance tests demonstrated that the carbon-coated SiO₂ with this special structure maintained a capacity of 616 mAh g^-1 even after 358 cycles at a current density of 0.1A g^-1.Furthermore,the material exhibited good stability throughout the charge-discharge cycling process.The rational design of yolk-shell SiO₂ composite rGO with provided a promising approach for developing anode materials and energy storage systems.（2）On the basis of the successful synthesis of yolk-shell SiO₂@rGO,the next step involved N atom doping of rGO through a hydrothermal method using urea as nitrogen dopant,resulting in the formation of yolk-shell SiO₂@N-rGO.The introduction of nitrogen atoms served to adjust the electron distribution and create abundant defect sites,thereby enhancing the electron transfer rate and improving the electrical conductivity.Electrochemical impedance spectroscopy and charge-discharge test were conducted,revealing that the cyclic specific capacity of yolk-shell SiO₂@N-rGO was 45%higher compared to the unmodified materials at the current density of 0.1 A g^-1.Remarkably,the yolk-shell SiO₂@N-rGO exhibited a capacity of 352 mAh g^-1 after undergoing 534cycles at 0.2 A g^-1.After the charge-discharge cycle,the yolk-shell SiO₂@N-rGO was analyzed,demonstrating that the material remained relatively intact,and excellent stability.（3）SiO₂ nanotubes@nitrogen-doped carbon（SNT@N-C）compositewere synthesized through a sol-gel method and high temperature sintering process,utilizing ammonium tartrate as a template and chitosan as a nitrogen-carbon precursor.The resulting SNT@N-C composite exhibited a unique tubular structure,offering a large specific surface area(20.830 m²g^-1)and nitrogen-containing carbon materials,which provided ample space for volume expansion,Li⁺active sites,and facilitated high electron transfer rate for SiO₂ anode materials.Following a series of electrochemical tests,the SNT@N-C composite demonstrated remarkable performance.Under the test conditions of 0.1 A g^-1,it maintained a specific capacity of 577.6 mAh g^-1 after 200cycles.After the charge-discharge cycle,the SNT@N-C was analyzed,demonstrating that the material remained relatively intact,and excellent stability.（4）Carbon-coated SiO₂ nanotubes（SNT@C）,prepared using ammonium tartrate as a template,were incorporated onto rGO to create a high-performance anode composite,SNT@C@rGO.This composite exhibited stable cycling performance and excellent electrochemical performance.As the negative electrode in lithium-ion battery,SNT provided an abundant of active sites for Li⁺due to its tubular structure,while the carbon layer served as a pathway for efficient electron transport.Additionally,the three-dimensional transport structure formed by the combination of SNT@C and rGO enhanced the mobility of Li⁺and electrons within the composite.After 148 cycles at a current density of 0.1 A g^-1,the SNT@C@rGO composite retained a significant capacity of 580 mAh g^-1.