Jin Gu Kang

Long-term, high-rate lithium storage capabilities of TiO2 nanostructured electrodes using 3D self-supported indium tin oxide conducting nanowire arrays

Core/shell, indium tin oxide (ITO)/TiO2 hybrid nanostructured electrodes for high-power lithium ion rechargeable batteries have been synthesized via a thermal evaporation method followed by pulsed laser deposition (PLD). Lithium-active TiO2 nanoparticles were uniformly assembled onto high-conductivity ITO nanowire arrays that were directly grown on metallic current collectors. This configuration resulted in superior rate capabilities and long-term cycle life. Such high electrochemical performances result from the unique 3 dimensional (3D) geometrical features of nanoarchitectured electrodes, which enable efficient electronic pathways upon prolonged cycling.

Sn-induced low-temperature growth of Ge nanowire electrodes with a large lithium storage capacity

We herein present the synthesis of germanium (Ge) nanowires on Au-catalyzed low-temperature substrates using a simple thermal Ge/Sn co-evaporation method. Incorporation of a low-melting point metal (Sn) enables the efficient delivery of Ge vapor to the substrate, even at a source temperature below 600 °C. The as-synthesized nanowires were found to be a core/shell heterostructure, exhibiting a uniform single crystalline Ge sheathed within a thin amorphous germanium suboxide (GeO(x)) layer. Furthermore, these high-density Ge nanowires grown directly on metal current collectors can offer good electrical connection and easy strain relaxation due to huge volume expansion during Li ion insertion/extraction. Therefore, the self-supported Ge nanowire electrodes provided excellent large capacity with little fading upon cycling (a capacity of ∼900 mA h g(-1) at 1C rate).

Origin of Capacity Fading in Nano-Sized Co3O4Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co3O4, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co3O4with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co3O4anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.

Three-dimensional hierarchical self-supported multi-walled carbon nanotubes/tin(iv) disulfide nanosheets heterostructure electrodes for high power Li ion batteries

It is of great significance to improve the power density of Li ion batteries (LIBs) in pursuit of high-end products and technologies. Herein, we investigated the three-dimensional (3D) hierarchical self-supported multi-walled carbon nanotubes (MWCNTs)/tin(IV) disulfide nanosheets (SnS2 NS) heterostructured electrodes, demonstrating superior rate capabilities of 480 and 420 mAh g−1 even at the very high c-rates of 5C and 10C (charging in 6 min), respectively. The origins of the enhancement of the rate capabilities were discussed in detail by focusing on the roles of MWCNTs, which were directly grown on the metallic current collector. Furthermore, we have delicately dealt with the in-plane and plane-normal growth mechanisms of hexagonal SnS2 NS from the crystallographic point of view.

The effect of the concentration and oxidation state of Sn on the structural and electrical properties of indium tin oxide nanowires.

High quality single-crystalline indium tin oxide (ITO) nanowires with controlled Sn contents of up to 32.5 at.% were successfully synthesized via a thermal metal co-evaporation method, based on a vapor-liquid-solid growth mode, at a substrate temperature of as low as 540 °C. The high solubility of Sn in the nanowires was explained with the existence of Sn(2+) ions along with Sn(4+) ions: the coexistence of Sn(2+) and Sn(4+) ions facilitated their high substitutional incorporation into the In(2)O(3) lattice by relaxing structural and electrical disturbances due to the differences in ionic radii and electrical charges between Sn and In(3+) ions. It was revealed that, while the lattice parameter of the ITO nanowires had a minimum value at a Sn content of 6.3 at.%, the electrical resistivity had a minimum value of about 10(-3) Ω cm at a Sn content of 14 at.%. These structural and electrical behaviors were explained by variation in the relative and total amounts of the two species, Sn(2+) and Sn(4+).

Germanium microflower-on-nanostem as a high-performance lithium ion battery electrode

We demonstrate a new design of Ge-based electrodes comprising three-dimensional (3-D) spherical microflowers containing crystalline nanorod networks on sturdy 1-D nanostems directly grown on a metallic current collector by facile thermal evaporation. The Ge nanorod networks were observed to self-replicate their tetrahedron structures and form a diamond cubic lattice-like inner network. After etching and subsequent carbon coating, the treated Ge nanostructures provide good electrical conductivity and are resistant to gradual deterioration, resulting in superior electrochemical performance as anode materials for LIBs, with a charge capacity retention of 96% after 100 cycles and a high specific capacity of 1360 mA h g−1 at 1 C and a high-rate capability with reversible capacities of 1080 and 850 mA h g−1 at the rates of 5 and 10 C, respectively. The improved electrochemical performance can be attributed to the fast electron transport and good strain accommodation of the carbon-filled Ge microflower-on-nanostem hybrid electrode.