| Lithium-ion batteries（LIBs）as efficient power sources have been predominantly applied in consumer electronics,electric vehicles and so on,thanks to the merits of high energy density and excellent cycling stability.LIBs with longer cycle life and enhanced endurance are still demanded,the properties of which mainly depend on the key components of LIBs.The negative electrode,one of the most critical parts,largely determines the performance of LIBs.In this thesis,tin-based materials are systematically investigated,owing to the merits of high theoretical capacity,low cost and natural abundance.However,tin-based materials still suffer from severe capacity degradation,stemming from the poor conductivity and huge volume expansion.To alleviate these critical obstacles as electrodes for LIBs,hollow structures and heterostructures have been designed.The design of nanomaterials with special structures and the combination of conductive carbon can effectively improve the conductivity and alleviate the volume expansion,thereby improving the cycle stability.In chapter 3,we successfully demonstrate a facile self-templating method for the preparation of carbon-encapsulated Sn O2 hollow spheres（Sn O2@C-6H）.Briefly,carbon-coated Sn/Sn O2 hybrid hollow spheres were fabricated by employing Sn spheres as a self-template and glucose as a carbon source,followed by hydrothermal oxidization of the Sn spheres and high-temperature calcination.High-temperature annealing（e.g.,700?°C）inevitably led to the formation of Sn on the exterior surface,which was disadvantageous for long-term cycling.In contrast,the preparation at an optimal annealing temperature of 600?°C coupled with subsequent acid etching completely encapsulated the Sn O2 within a carbon shell while maintaining a stable hollow structure.The as-prepared Sn O2@C-6H after acid etching exhibited enhanced electrochemical performance for LIBs characterized by high cycling stability and rate capacity.Specifically,Sn O2@C-6H displayed a reversible capacity of 897.9?m Ah g-1 at 200?m A?g-1 after 120 cycles and a promising rate capacity of 549.8?m Ah g-1 at a high current density of up to 2000?m A?g-1.The obtained high-performance could be attributed to the formation of a unique hollow structure with an enlarged specific surface area of 215.18?m2?g-1 and a relatively high degree of graphitization（i.e.,ID/IG?=?0.84）of the carbon shell.A plausible cause for this performance was that the acquired hollow spheres not only provide a barrier effect for volume expansion and the aggregation of Sn O2,but also promote lithium storage.Flexible electrodes are indispensable for flexible LIBs and thus the emerging flexible/bendable electronic devices.In comparison to a series of flexible substrates,carbon cloth（CC）generally exhibits outstanding electrical conductivity,excellent flexibility and mechanical strength.In chapter 4,we present flexible carbon cloth supported Sn O2/Sn Sx heterostructured arrays coated with carbon（Sn O2/Sn Sx@C）as a robust anode for LIBs.Sn O2/Sn Sx@C was prepared by facile hydrothermal method and carbonization.The resulting Sn O2/Sn Sx@C exhibited high specific capacity,superior long-term stability and the excellent rate performance.Specifically,Sn O2/Sn Sx@C showed an initial discharge specific capacity of 1898.7 m Ah g-1 with its initial coulombic efficiency of 77.5%,and retained the specific capacity of 1047.5 m Ah g-1after 100 cycles at 0.2 A g-1.The excellent electrochemical performance of Sn O2/Sn Sx@C is attributed to the well-established unique structure:（1）the carbon cloth offers a flexible framework which can enhance the integrity of nanostructures and facilitate the charge transfer;（2）Sn O2/Sn Sx heterostructures act as a buffer framework to mitigate the volume expansion,and accelerate the charge transfer by constructing an electric field;and（3）carbon arrays are favor to prevent the Sn O2/Sn Sx electrode from pulverization and enhance the charge transfer by promoting the graphitization degree. |
