Graphene-based Nanocomposites For Rechargeable Lithium Batteries

The rapid development of portable electronic devices, electric vehicles, smart power grids, and aerospace fields has boosted the demands for sustainable and cost-effective rechargeable lithium batteries with high energy and power densities. State-of-the-art lithium-ion batteries(LIBs) are confronting their development bottleneck in performance owing to the low theoretical capacity of present electrode materials. Extensive efforts have been devoted to the exploration of novel electrode materials for rechargeable lithium batteries, including LIBs, lithium-organic batteries, and lithium-sulfur batteries, which has promoted the sustainable development of energy storage systems. Aiming at solving the bottleneck problems in electrode materials such as huge volume change of tin oxide anodes, high solubility of organics in electrolytes, and the “shuttle effect” of polysulfides, graphene-based two-dimensional(2D) nanomaterials with morphological anisotropy and excellent electrical conductivity demonstrate great potential for applications as electrode materials in rechargeable lithium batteries. The following is the main contents and results:1. Boron(B)-doped carbon coated tin oxide/graphene hybrids were fabricated by the hydrothermal carbonization of sucrose in the presence of tin oxide/graphene nanosheets and boric acid/phenylboronic acid as dopants, and following thermal treatment. The hybrids attain high synergy effect of unique 2D core-shell architecture and B-doped carbon shells, which enhance the conductivity of the sandwich-liked nanosheets and provide extra active sites for lithium storage, as well as accommodate the volume variation of tin oxides. With phenylboronic acid as B source, the resulting hybrid exhibits superior electrochemical performance as a LIB anode.2. Compact 2D coupled graphene and porous polyaryltriazine-derived frameworks with tailormade pore structures are fabricated by employing the polyacrylonitrile-functionalized graphene nanosheets as templates and using various molecular building blocks under ionothermal conditions. The porous nanosheets display nanoscale thickness, high specific surface areas, and strong coupling of electroactive polyaryltriazine-derived frameworks with graphene through covalent bonding. All these features make it possible to efficiently depress the dissolution of redox moieties in electrolytes and to boost the electrical conductivity of whole electrode. When employed as a cathode in rechargeable lithium batteries, the porous nanosheets exhibit ultralong cycle life and ultrahigh charge-discharge rates, which surpass the previously reported non-inorganic cathode materials.3. Given the benefits of the aforementioned porous nanohybrids with nanoscale thickness, high specific surface areas, tailormade pore structures, nitrogen-doping, and excellent electrical conductivity, graphene-based porous carbon/sulfur composites were synthesized by melt diffusion of sulfur into the pores of carbon matrix. The “shuttle effect” of polysulfides can be effectively restrained and the electrical conductivity of electrode materials can be greatly enhanced. Serving as a cathode in lithium-sulfur batteries, the composite with optimal pore structure exhibits outstanding cycle stability and excellent rate capability.