Kwang Man Kim

Imprintable, Bendable, and Shape‐Conformable Polymer Electrolytes for Versatile‐Shaped Lithium‐Ion Batteries

A class of imprintable, bendable, and shape-conformable polymer electrolyte with excellent electrochemical performance in a lithium battery system is reported. The material consists of a UV-cured polymer matrix, high-boiling point liquid electrolyte, and Al2 O3 nanoparticles, formulated for use in lithium-ion batteries with 3D-structured electrodes or flexible characteristics. The unique structural design and well-tuned rheological characteristics of the UV-curable electrolyte mixture, in combination with direct UV-assisted nanoimprint lithography, allow the successful fabrication of polymer electrolytes in geometries not accessible with conventional materials.

Electrochemical and physical characterization of lithium ionic salt doped polyaniline as a polymer electrode of lithium secondary battery

Abstract Polyaniline films doped with lithium ionic salts such as LiPF 6 and LiBF 4 were prepared by using the electrolyte solution mixture of ethylene carbonate and dimethyl carbonate. The doping level of the polyaniline films was confirmed by X-ray photoelectron spectroscopy and dc conductivity experiments. A doping mechanism of lithium ion through the interaction with a nitrogen at imine site is proposed. Electrochemical cells of Lipolyaniline-LiPF 6 or Lipolyaniline-LiBF 4 were assembled to investigate electrical capacity and its trends over the repeated charge/discharge cycles. The capacity of Lipolyaniline cell was increased and then saturated over 15 cycles. However, it did not reach the half of theoretical capacity of polyaniline material. The mechanism of electrochemical reaction during charge/discharge process of Lipolyaniline cell is presented.

Dye-Sensitized TiO2 Solar Cells Using Polymer Gel Electrolytes Based on PVdF-HFP

The open-circuit voltage increases substantially and stability of dye-sensitized TiO 2 solar cells is improved when polymer gel containing poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) in N-methyl-2-pyrrolidone replaces commonly used solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). The energy conversion efficiency of the cell with 6 wt % PVdF-HFP is comparable to that obtainable in ACN and in MPN. The promising effect of PVdF-HFP as a gelator is attributed to its interaction with Li + ions.

Characterization of poly(vinylidenefluoride-co-hexafluoropropylene)-based polymer electrolyte filled with rutile TiO2 nanoparticles

Various amounts of nanoscale rutile TiO2 particle are used as fillers in the preparation of poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)-based porous polymer electrolytes. Physical, electrochemical and transport properties of the electrolyte films are investigated in terms of surface morphology, thermal and crystalline properties, swelling behavior after absorbing electrolyte solution, chemical and electrochemical stabilities, ionic conductivity, and compatibility with lithium electrode. Contrary to reported inorganic fillers showing the maximum content lower than 50 wt.%, the self-supporting polymer electrolyte films can be obtained even when using higher content of 70 wt.% rutile TiO2 nanoparticles. The physical and electrochemical properties of polymer membrane are highly improved by the addition of TiO2 nanoparticles as good dispersion of fillers, low liquid uptake but adequate ionic conductivity, excellent electrochemical stability, and stabilized interfacial resistance with lithium electrode. An emphasis should be put on the fact that the sufficient ionic conductivity obtained is led by the liquid medium within nano-pores as well as effective ion transport supported by rutile TiO2. As a result, the sample with 30–40 wt.% rutile TiO2 is confirmed as the best polymer electrolyte for rechargeable lithium batteries.

Redox supercapacitor using polyaniline doped with Li salt as electrode

Abstract We prepared polyaniline powder doped with LiPF 6 and utilized it as an electrode material in a polymer redox supercapacitor. The electrode sheet was fabricated by coating the slurry directly on a charge collector. We also compared the performance of porous polyolefin separator as supplied and the polymer electrolyte as prepared. The redox supercapacitor using the polyolefin separator exhibits ∼100 F/g specific capacitance at the initial discharge and retains ∼70 F/g after 5000 cycles, while the initial specific capacitance using the polymer electrolyte is ∼80 F/g and retains ∼60 F/g after 5000 cycles.

Nanoparticle–Nanorod Core–Shell LiNi0.5Mn1.5O4 Spinel Cathodes with High Energy Density for Li-Ion Batteries

with distilled water and was vacuum-dried at 120°C. An as-prepared MnO2 template was used to prepare LiNi0.5Mn1.5O4, and appropriate amounts of LiC2H3O2·H2O and NiNO32·6H2O were completely dissolved in distilled water and mixed with MnO2 in a molar ratio of 1:0.5:1.5 LiC2H3O2·H2O:NiNO32·6H2O:MnO2. After drying it in an oven, the product was ground using mortar and pestle, fol- lowed by firing at 400 and 700°C for 2 and 8 h, respectively. For comparison, the cathode powder was obtained using the sol-gel pro- cess, LiC2H3O2·H2O was first dissolved in distilled water, and then MnC2H3O2·4H2O and NiNO32·6H2O were continuously dissolved into it with a molar ratio of 1:1.5:0.5 Li:Mn:Ni. Finally, poly vinylpyrrolidene as a chelating agent was mixed together, and NH4OH was added to adjust pH 8.5 to 9.0. The solution was dried at

The effect of silica addition on the properties of poly((vinylidene fluoride)-co-hexafluoropropylene)-based polymer electrolytes

The effect of fumed silica(SiO 2 ) addition on the physical and electrochemical properties of poly((vinylidene fluoride)-co-hexafluoropropylene) based polymer electrolyte was investigated by various methods including morphology observation, thermal and crystallinity evaluations, impregnation test using an electrolyte solution, electrochemical stability analysis and impedance measurement. About 38 wt.-% of silica content proved to be the upper limit at which the silica could be no longer added to obtain a self-sustained polymer electrolyte film. As the silica content increased, a finer pore structure developed, a greater amount of electrolyte solution was absorbed, and thus higher ionic conductivity was shown. The electrochemical stability was preserved up to about 4.5 V for all the polymer electrolytes prepared. The interfacial resistance between the polymer electrolyte and the lithium electrode was reduced with the silica content and also showed a diminishing growth rate with time.

Synergistic multi-doping effects on the Li7La3Zr2O12 solid electrolyte for fast lithium ion conduction.

Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li7La3Zr2O12 (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al3+ plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10−4 S cm−1 than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition.

Graphite/Silicon Hybrid Electrodes using a 3D Current Collector for Flexible Batteries

A flexible hybrid anode from graphite and thin film silicon is realized by the concept of a 3D sandwich current collector by the combination of micro-contact printing and RF magnetron sputtering. Flexible lithium-ion batteries with a new hybrid anode demonstrate not only enhanced specific capacity but also improved rate capability compared to that of a conventional graphite anode under bending deformation.

Electrochemical properties of vanadium oxide thin film deposited by R.F. sputtering

Vanadium oxide (V2O5) thin films with various thicknesses have been prepared by using the radio frequency (R.F.) sputtering method from V2O5 (ceramic) or V (metal) target. The electrochemical properties of the films were characterized as a function of the thickness. The films with thickness of 500 nm fabricated from V2O5 ceramic target showed proper discharge capacity and cycle performance. However, the electrochemical property for the film with thickness of over 500 nm could not be observed due to the low deposition rate from V2O5 ceramic target and instability of interface between the surface and the film. The discharge capacity and cyclic performance of vanadium oxide films deposited from V metal target degraded with increasing thickness of the films. Considering the electrochemical properties of the films and the requirement of current density for the application field of thin film battery, appropriate thickness of vanadium oxide film for thin film battery was less than 1000 nm in our work. D 2002 Elsevier Science B.V. All rights reserved.