| Developing rechargeable lithium-ion batteries(Li Bs) with high energy density, superb rate capability and satisfactory cycle life is of great importance to meet the ever-increasing power demands in consumer electronics, low-emission electrical vehicles and grid-scale energy storage systems. Increasing the specific capacity of anode materials is considered as one of the most effective and significant routes to build advanced battery system. However, the widespread application of these high-capacity anode materials into LIBs has remained as several common and significant challenges including severe volume change associated with lithiation/delithiation processes, particle aggregation and excessive growth of solid electrolyte interphase(SEI). In this thesis, we focused on improving the electrochemical performance of Co3O4 and Si anodes by synthesizing special graphene-based nanocomposites. Porous graphene sheets with large amounts of well-dispersed in-plane vacancies and 3-dimensional sealed graphene hollow spheres were fabricated and used for Co3O4 and Si anodes, respectively. With the help of these special-structured graphene, the electrochemical performance of Co3O4 and Si anodes has been significantly improved.Considering the severe volume effect and particle aggregation issue of Co3O4, we designed a new strategy to in-situ grow ultra-high loading(93 wt.%) Co3O4 NPs with particle size around 10 nm onto the acid-sonication pretreated graphene oxide through a lowtemperature hydrothermal reaction. Nitric acid-sonication treatment can create large amounts of uniform in-plane vacancies(approximate 5-10 nm in diameter) with carboxylate groups decorating the defect edge sites. In the subsequent hydrothermal process, such inplane vacancies can act as active sites for the formation of Co3O4 NPs since Co2+ ions have a strong bonding effect with these carboxylates, in which nucleation, growth and crystallization of Co3O4 NPs are well separated and confined in a several nanometer region. In particular, the strong binding effect between the Co3O4 NPs and the in-plane vacancies can prevent the particle aggregation and keep the integrity of the composite during the long-term cycles. Therefore the composite exhibits high reversible capacity, high Coulombic efficiency, superb rate capability and much prolonged cycle life.Considering the severe volume effect and SEI excessive growth issue of Si anode, we first proposed a bottom-up route to controllably synthesize a polycrystalline graphene hollow sphere isolated Si NP nanocomposite(Si@void@graphene) through an in-situ pyrolysis and metal-catalyzed graphitization reaction. To create desired void space between the graphene shell and Si core, a silver(Ag) sacrificial layer with calculated thickness was conformally coated on Si NPs surface through a well-known silver mirror reaction and removed after the growth of graphene hollow spheres. Considering the high degree of crystallinity, excellent electronic conductivity and superb mechanical strength of the graphene, the obtained polycrystalline graphene hollow spheres can not only maintain a stable structural and electrical environment for the inner Si NPs even the created voids don’t match the volume expansion, but also effectively prevent the electrolyte from reaching the Si NPs inside the shell and inhibit the excessive growth of the SEI layer on Si surface under repeated volume change. As a result, even the insufficient void space was designed assuming that Si has only 250% volume change in this work, the Si@void@graphene electrode exhibits high reversible capacity, superior rate capability, high Coulombic efficiency and much prolonged cycle life as compared to that of the Si@void@amorphous carbon electrode.
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