Preparation Of Two-Dimensional Silicon-Carbon Composites And Lithium Storage Properties

As a green energy storage device with a broad application prospect,lithium-ion battery not only profoundly affects the development of portable electronics,but also will strongly support the large-scale application of new energy vehicles.As an important component for storing electric energy in lithium-ion batteries,cathode material has become a key factor to enhance the performance of lithium-ion batteries.The low specific capacity and slow diffusion kinetics of graphite make it difficult to meet the demand for high-performance energy storage devices.Silicon-based materials are candidates for next-generation anode materials due to their high specific capacity and low cost,but the huge volume change and inherent low electron/ion conductivity hinder their further development.To overcome these bottlenecks,this thesis utilizes the ice template method to prepare high performance porous carbon nanosheets from water-soluble carbon precursors（sulfonated naphthalene and gelatin）by directional assembly with high temperature carbonization,and utilizes the excellent electrical conductivity and high mechanical strength of carbon nanosheets to construct two-dimensional silicon-carbon composites through the organic combination of both,which effectively improves the structural stability and electrochemical properties of silicon anode.The porous carbon nanosheets（SN-CNS）were prepared by the ice template method using sulfonated naphthalene（SN）as the carbon source.SN-CNS has a high specific surface area(374 m² g^-1)and high pore volume(0.621 cm³ g^-1),as well as a hierarchical pore structure dominated by mesopores and macropores and rich in S and O functional groups.The SN-CNS exhibited an initial specific capacity of 856m Ah/g at a initial Coulomb efficiency of 50.2%at a current density of 0.1 A/g,and maintained a reversible specific capacity of 366 m Ah/g at 56.3%capacity retention when the current density was increased to 2 A/g.After 600 cycles at a current density of 1 A/g,the specific capacity gradually increased to 602 m Ah/g,demonstrating excellent reversible capacity,rate performance and cycling stability as an anode material for Li-ion batteries.The Si@SCNS composites were prepared by homogeneously mixing Si NPs（silicon nanoparticles）with SN through ice templates using SN as the carbon source,and the effect of the mass ratio of SN to Si NPs on the structure and properties of the composites was investigated.When the mass ratio of Si NPs to SN was 1:2,the two-dimensional Si-C composites were successfully prepared.When the composites were used as anode materials for Li-ion batteries,Si@SCNS-1 had high reversible specific capacity（2094 m Ah/g）and first Coulomb efficiency（84.4%）,while Si@SCNS-3 maintained a high reversible specific capacity of 378 m Ah/g at 5 A/g.After 300 cycles at a current density of 200 m Ah/g,Si@SCNS-3 has a high reversible specific capacity of 820 m Ah/g and a capacity retention rate of 95.3%.The two-dimensional Si-C composites prepared by the ice template method have outstanding performance in terms of rate performance and cycling performance.Green,renewable gelatin was used as the carbon precursor to take advantage of the hydrophilic nature and the richness of heteroatoms such as N/O.The nitrogen-doped carbon nanosheets were prepared by the directed assembly of gelatin macro peptide chains through ice templates and the effects of different carbonization temperatures on their microstructure and electrochemical properties were investigated.The gelatin-derived carbon nanosheets（GCNS-800）with high specific surface area（389.3 m²/g）and pore volume（0.512 cm³/g）,as well as the hierarchical pore structure composed of microporous mesopores and the cooperation of N/O functional groups,enabled GCNS-800 to exhibit the optimal cycling and multiplicative properties.A reversible specific capacity of up to 842 m Ah/g is obtained at a initial coulomb efficiency of 53.4%at 0.1 A/g.When at a high current density of 5 A/g,a high specific capacity of 320 m Ah/g is still maintained.After 300cycles at 1 A/g,the reversible specific capacity gradually increases to 612 m Ah/g,demonstrating high rate performance and excellent long cycle stability.The N-doped two-dimensional Si@GCNS composites were prepared by the ice template method with high temperature carbonization using gelatin as the carbon source.Si@GCNS composites were characterized by gelatin-derived carbon nanosheets that uniformly encapsulated silicon spheres in carbon sheets,and the high mechanical strength and electrical conductivity of carbon nanosheets made the composites have excellent structural stability.The anode material for Li-ion batteries exhibits excellent electrochemical performance,with a reversible capacity of 3035m Ah/g and 85.9%initial coulomb efficiency at 0.2 A/g,and a high specific capacity of 1502 m Ah/g when at a current density of 5 A/g.After 300 cycles at a current density of 1 A/g,the reversible capacity is maintained at 1853 m Ah/g.The reversible capacity,rate performance and cycling stability at high currents are demonstrated.