Preparation Of Silicon - Carbon Composite Nanomaterials And Silica Nanomaterials And Their Lithium Storage Properties

As anode materials for lithium-ion batteries (LIBs), silicon-based materials possess higher specific capacities and improved safety, and thus have been considered to be ideal anodic candidates to replace commercial carbon materials. Among them, silicon-based nanomaterials especially silicon-carbon hybrid nanomaterials and SiO2 nanomaterials possess the superiorities of nanomaterials and conducting/buffering effects from carbon or Li2O matrix, and are able to exhibit higher structural stability and charge-transport capability in comparison with pure silicon materials and bulk silicon-based materials. Therefore, silicon-carbon hybrid nanomaterials and SiO2 nanomaterials are anticipated to manifest higher specific capacity, good cycling stability, and high rate capability, and meet the performance requirements of advanced LIBs.Herein, we rationally design and synthesize a series of silicon-carbon hybrid nanomaterials and SiO2 nanomaterials through the hydrolysis-condensation processes of TEOS combined with template-directed approach, PVDF pyrolysis method, layer-by-layer assembly and magnesiothermic-reduction processes. Owing to their unique compositional and structural features, the as-prepared silicon-carbon hybrid nanomaterials and SiO2 nanomaterials all demonstrate enhanced lithium-storage performance in terms of specific capacity, cycling stability, and rate capability. The main innovative results are displayed as follows: (1) By using SiO2 spheres as precursors, porous Si spheres encapsulated in carbon shells (porous Si@C spheres) has been constructed through the pyrolysis of PVDF and subsequent magnesiothermic reduction methodology. The as-synthesized porous Si@C spheres have been applied as anode materials for LIBs, and exhibit enhanced anodic performance in term of cycling stability compared with bare Si spheres. For example, the porous Si@C spheres are able to exhibit a high reversible capacity of 900.0 mA h g-1 after 20 cycles at a current density of 0.05 C (1 C= 4200 mA g-1), which is much higher than that of bare Si spheres (430.7 mAh g-1). (2) By using SiO2 spheres as precursors, three-dimensional (3D) interconnected network of graphene-wrapped porous silicon spheres (3D porous Si@G network) was constructed through layer-by-layer assembly and subsequent in situ magnesiothermic-reduction methodology. Compared with bare Si spheres, the as-synthesized Si@G network exhibits markedly enhanced anodic performance in terms of specific capacity, cycling stability, and rate capability. For example, the 3D porous Si@G network able to deliver a high reversible capacity of 1299.6 mA h g-1 after 25 cycles at a current density of 0.05 C, which is much higher than that of bare Si spheres (431.5 mA h g-1).(3) By using CuO nanobelts as templates, hollow porous SiO2 nanobelts was obtained through the hydrolysis-condensation of TEOS and subsequent template-removal processes. When applied as an anode material for LIBs, the hollow porous SiO2 nanobelts demonstrates high reversible capacities, excellent capacity retention, and high rate capability. For example, the capacity fading is only 0.07% per cycle from 2 to 100 cycles, and a high discharge capacity of 1012.5 mA h g-1 can be retained after 100 cycles at a current density of 100 mA g-1.(4) By using ZnO nanorods as templates, graphene-wrapped SiO2 nanotube network (SiO2-NT@G network) was prepared through the hydrolysis-condensation of TEOS, layer-by-layer assembly, and subsequent template-removal processes. When utilized as an anode material for LIBs, the as-synthesized SiO2-NT@G network manifests good lithium-storage performance in terms of specific capacities, cycle life, and rate capability. For example, an ultrahigh discharge capacity of 1145.3 mA h g’1 is retained after 100 cycles (100 mA g-1), and high reversible capacities of 811.1 and 628.6 mAh g-1 can still be delivered even under current densities as high as 500 and 1000 mA g-1, respectively.