| Rechargeable batteries are becoming one of the most favorable options for energy storage systems (EESs) which could reduce our dependence on fossil fuels. Lithium ion batteries (LIBs) have been successfully commercialized in the past decades and extensively integrated into portable electronics, automobiles and hybrid electric vehicles. However, the unevenly distributed of lithium resources and low abundance of Li element in Earth’s crust could not satisfy the growing global Li consumption. Recently, sodium ion batteries (NIBs) have gained significant attention as an ideal alternative to LIBs due to the eco-friendliness, low cost and natural abundance of sodium element.To develop high energy/power density, long cycle life of electrodes still has many tough challenges especially for negative electrodes. Unfortunately, some commercialized and common anodes for LIBs are not appropriate for NIBs. For example, the graphite presents small capacity in NIBs which may be ascribed to the insufficient interlayer distance to meet larger Na cation radii (1.02 A). In LIBs, many attempts have been adopted to seek the substitute for the commercial carbonaceous anode materials which is limited to the low theoretical capacity (372 mAh g-1) and inherent safety risks. Among the investigated system, alloying-type and conversion-type materials have been extensively studied due to the large specific capacity higher than graphite. Additionally, large volume change during repeated lithiation/delithiation and sodiation/desodiation leads to unstable solid electrolyte interphase (SEI) film which is an important factor to achieve long cycling stability. Limited several approaches have been adopted to overcome the above mentioned drawbacks, including control on the component, structure, and surface of electrodes.(1) Hydrogenated TiO2 branches coated Mn3O4 nanorods as an advanced anode material for lithium ion batteries.Designing hierarchical nanostructures used as anodes involving high capacity and long cycling ability to meet the demand of better lithium ion batteries has received wide attention. TiO2 with oxygen vacancies showing advantages of small volume change (～ 4%), high theoretical capacity (～1340 mAh cm-3), improved electronic conductivity, excellent cycling stability as well as good thermal stability, has been firstly used as interface materials for hybrid structure to achieve a good capacity retention and a high specific capacity. In this structure, Mn3O4@H-TiO2 with Mn2O4 nanorod as a core and hydrogenated TiO2 branches as a shell, has been successfully synthesized via a stepwise process. As a result, such a hierarchical structure Mn3O4@H-TiO2 exhibit improved cycling stability (560 mAh g-1 even after 1500 cycles at the current density of 1 A g-1) as well as the outstanding rate capacity comparing to Mn3O4@TiO2, Mn3O4, and TiO2, suggesting that TiO2 with oxygen vacancies used as a conductive scaffold pave a new way to construct better anode materials.(2) Sb@TiO2-x nanotubes as a superior high-rate and ultralong lifespan anode material for Na-ion and Li-ion batteries.Sb@H-TiO2 nanotubes are synthesized by the calcination of Sb2S3@TiO2 nanorods in Ar/H2, obtained by the hydrolysis of tetrabutyl titanate on Sb2S3 nanorods. The reducing atmosphere promotes the decomposition of Sb2S3 into metallic Sb. The good binding affinity of Sb to TiO2 makes it attached to the inner surface of the TiO2-x shell and inhibits the growth of the as-obtained Sb nanoparticles, generating unique double-walled structures that also benefit the structure stability upon cycling. Another effect of the reducing atmosphere is to induce oxygen vacancies and Ti3+ species in the TiO2-x shell. The double-walled nanotubes well combine the high capacity of Sb and the good stability of TiO2-x together, realizing excellent performances both in LIBs and in NIBs. They could deliver a capacity of 424 mAh g-1 after 1000 cycles at 6.6 A g-1 in a half cell of lithium ion batteries or～300 mAh g-1 after 1000 cycles at 2.64 A g-1 in a half cell of sodium ion batteries. In the full cell, the energy density of lithium ion batteries approaches～360 Wh kg-1 at 77 W kg-1. Even at 3.77 kW kg-1, it is still about 262 Wh kg-1. As to the full cell of sodium ion batteries, the energy density comes to 151 Wh kg-1 at 21 W kg-1, or 61 Wh kg-1 at 1.83 kW kg-1.(3) Sb-P-TiO2-x yolk-shell structure used in sodium ion batteries.Sodium ion batteries, have attracted growing attention due to the abundance and non- toxicity of sodium resources. Phosphorus possesses highest known theoretical capacity (～2600 mAh g-1) but limited to insulation and huge volume change (～292%). Here we introduce an in situ oxidation-reduction reaction to synthesize york-shell nanorods of Sb-P-TiO2-x composite, instead of traditional ball-milling and vaporization-condensation method. In this composite, P is very uniformly distributed in TiO2-x shells invigated by mapping and line scanning via a redox reaction. The high capacity of phosphorus, high conductivity of metallic Sb, the stable framework TiO2-x and the void space exists in york-shell nanostructure ensure the improved capacity and stable cycling of Sb-P-TiO2-x composite. In addition, the full battery Sb-P-TiO2-x/NasV2(PO4)-C presents the high output voltage (2.72 V) and stable cycling performance (392 mAh g-1anode after 150 cycles at 1 A g-1anode).(4) Porous micro/nano structured binary metallic oxides and their application in Li-ion batteriesPorous electrode materials with both long cycle lives and high specific capabilities are significant to satisfy the increasing demand of energy storage. Here, hierarchically porous ZnMn2O4 microspheres composed of interconnected nanosized building blocks have been prepared via a thermal treatment of metal carbonates obtained by a solvothermal reaction. ZnMn2O4 microspheres not only deliver a high reversible capacity of 800 mAh g-1 at a current of 500 mA g-1 and with 99.2% capacity retention over 300 cycles, but they also display excellent rate capability. Meanwhile, porous MnFe2O4 microrods have been successfully prepared by a room temperature reaction and then moderate thermal calcination of metal oxalates in Ar atmosphere. The porous MnFe2O4 electrodes exhibit high reversible capacity and outstanding cycling stability (after 1000 cycles still keep about 630 mAh g-1 at the current density of 1A g-1), as well as a high coulombic efficiency (> 98%). And MFe2O4 (M=Zn, Co, Ni) nanorods are synthesized by a template-engaged reaction, with (3-FeOOH nanorods as precursors which are prepared by a hydrothermal method. The reversible capacity of 800,625 and 520 mAh g-1 are obtained for CoFe2O4, ZnFe2O4 and NiFe2O4, respectively, at the high current density of 1000 mA g"1 even after 300 cycles. The outstanding electrochemical performance could be ascribed to the porous miacro/nano structure of the ZnMn2O4 microspheres and MnFe2O4 microrods. The porous miacro/nano structure could provide a large number of active sites for charge-transfer reactions, facilitate the molecular diffusion kinetics and accommodate volume change during the electrochemical reaction. These results suggest that ZnMn2O4 microspheres, MnFe2O4 microrods and MFe2O4 (M=Zn, Co, Ni) nanorods are promising anode materials in advanced Li-ion batteries, owing to their facile preparation as well as their good lithium storage properties. |
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