Preparation And Property Of T-Nb₂O₅ Negative Electrodes For Lithium-ion Batteries

As the development of portable electronics and electric vehicles, future mobile power is required to be more safe, fast charging（within seconds） as well as long-term cycling. Exploring anode materials that possessing outstanding cycling stability and fascinating rate performance is one of the most decisive factors in oeder to achieve the aim. Recently, T-Nb₂O₅, as one of classic materials behaving excellent stability, has received much attention. However, its low conductivity leads to a large charge transfer resistance as using it in Li ion battery anodes, which can decrease the batteries energy density. To settle this issue, it is essential to improve the conductivity of Nb₂O₅ without harming its high rate capability. Thus, Nb₂O₅-based materials were chosen as our research subjects to enhance its conductivity, energy density and rate capability. Our work mainly includes as follows:（1） We present a composite of T-Nb₂O₅ with N-GO by hydrothermal meathod. It is clearly seen that Nb₂O₅ homogeneously decorated onto the N-doped graphene nanosheets efficiently increase the conductivity of the electrode, prevent the restacking of nanoparticles.Compared with pure T-Nb₂O₅ or T-Nb₂O₅/GO, the composite material exhibited higher specific capacity as well as perfect cycling stability. After 500 cycles at the current density of 3 A g-1, the capacity retention rate of T-Nb₂O₅/N-GO was 94 %, performing excellent cycling stability. Then, in order to obtain the best electrochemical performance, we systematically investigated the electrochemical performance of samples with different mass proportion（MN-GO:MNb₂O₅=1:1,1:2,2:1）.The results showed that the best ratio is 2:1,which exhibits a larger capacity（175 mAh g-1） and good stability after 500 cycles at the current density of 3 A g-1.（2） In order to futher enhance the energy density of T-Nb₂O₅-based material, we demonstrate a novel T-Nb₂O₅/ mesocarbon microbead（MCMB） composite with unique three-dimensional nanoporous networks fabricated by hot water bath method and sintered process. The three-dimensional nanoporous networks were generated by the homogeneous intercalation of T-Nb₂O₅ nanoparticles into the gap between graphene layers of MCMB, which provided electrically conducting channels to promote electrolyte penetration and endowed the composite both high capacity and rate capability. The specific capacity was 100 mAh g-1 after 500 cycles at a current density of 90 A g–1. On the other hand the deposited Nb₂O₅ covered the functional groups and the sintering process led the enlarged MCMB recrystallizing, which all helped the as-prepared materials more rechargeable. The fist irreversible capacity of the composite is only 8.7 %. Furthermore, the biger tap density of the composite compared with expanded MCMB let it has more larger capacity energy（200 Ah L-1）, at the current density of 3 A g-1.（3） In order to explore a facile and accessible method to improve electronic conductivity of T-Nb₂O₅, we report a Ti@T-Nb₂O₅ core-shell nanowire array prepared by electrodepositing Nb₂O₅ nanoparticles on Ti nanowire arrays which can directly used as a free-standing electrode, without adding other conducting additive, or polymer binders. Specially, T-Nb₂O₅ with size of several nanometers（quantum dots） anchoring on the Ti nanowire arrays, which show excellent rate performances, releasing more than 260 mAh g-1 at a rate current density of 6 A g-1, more larger than T-Nb₂O₅/N-GO and T-Nb₂O₅/GO. Such excellent durability at high rate cycling all owing to their unique structure, comprising stable components and abundant inner space, especially their superior conductivity.