| The electrochemical performance of current lithium secondary batteries is too low to meet the rapid developed energy-intensive technologies such as the electrical vehicles. Therefore, it is highly desirable to develop novel electrode materials with much higher energy density. The construction of high-energy lithium secondary battery strongly depends on the regulation of the composition, structure and functional characteristics of electrochemically active materials to improve the structure thermodynamic stability and reaction kinetics. In this study, we focus on the design and synthesis of carbon-based nanohybrids as high performance electrode materials for lithium secondary batteries by improving or optimizing their surface characteristics, morphology, and porous structure to achieving high capacity and superior lifespan. The detailed study includes:Polycyanamide coupled graphene hybrids have been developed by in-situ polymerization of the cyanamide on graphene nanosheets, which greatly inherits the conductivity and stability of graphene nanosheets. The presence of polycyanamide layer with extremely high nitrogen content modifies the interfacial properties and facilitates the strong coupling of ultrafine Fe3O4 nanoparticles on the surface, which leads to the formation of nitrogen-rich carbon coupled Fe3O4/graphene nanohybrids. The nanostructure decreases the transport path of Li+ and electrons and enhances the integral structure and interfacial stability. As a result, the nanohybrids exhibit excellent durability for long-term cycling and superior rate response, as characterized by high capacity retention of over 80% for as long as 1000 cycles at high current densities of 2-5 A g"1. Remarkably, comparable capacities of 443 mA h g-1 can still remain at a high current density of 10 A g-1.High reactive hydrothermal carbon coupled graphene nanosheets have been constructed by in-situ polymerization of glucose on graphene nanosheets. With the help of the adsorption and nanosized confinement effect of hydrothermal carbon on graphene surface, two-dimensional nanohybrids made of microporous carbon coated graphene with Fe3O4 quantum dots (QDs) embedded is successfully constructed. Benefiting from the ultrashort ion transport path and high reactivity of FesCU QDs, as well as the protection effect of the microporous carbon, the as-synthesized Fe3O4-QDs/CNs exhibit excellent lithium storage performance with a high capacity of 420 mA h g-1 retained after 1000 cycles at an ultrahigh current density of 10 A g-1, which is superior to Fe3O4/Nx/rGO hybrids in the above chapter.A flexible TiO2(B)-based battery electrode with superior power rate and ultralong cycle life have been developed by anchoring TiO2(B) nanosheets on non-woven activated carbon fabric (ACF) via in-situ hydrothermal deposition. The integral electrode is directly employed as the anode of lithium-ion battery, which avoids the use of auxiliary binders, conductive additives, and high weight metal collector. As a result, the nanoarchitectured TiO2(B)/ACF electrode exhibits exceptional lithium storage performance with a high capacity of 130 mA h g-1 after 2000 cycles capacities at an ultrahigh current density of 20 C (6.7 A g-1). In addition, the TiO2(B)/ACF electrode can still exhibit excellent performance even after being folded many times.With polystyrene spheres as templates, free-standing and hierarchically porous carbon nanotube (FHP-CNT) film made of macro and mesopores is successfully fabricated by the self-assembly of carbon nanotubes. Benefiting from the optimized porous structure, the FHP-CNT electrode exhibits a specific capacity 4683 mA h g-1 at the current density of 50 mA g-1 with high gravimetric energies of 1870-2570 W h kg-1 based on the overall mass of CNT and discharged products (Li2O2), which is much better than that of commercial LiCoO2 cathode for lithium-ion batteries. |
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