Ki Won Kim

Electrochemical properties and interfacial stability of (PEO)10LiCF3SO3–TinO2n−1 composite polymer electrolytes for lithium/sulfur battery

Abstract Electrochemical properties and interfacial stability of (PEO)10LiCF3SO3 composite polymer electrolytes (CPEs) with titanium oxide (TinO2n−1, n=1, 2) prepared by ball milling as ceramic filler are presented. The amount of titanium oxide powders introduced was between 5 and 15 wt.% into the (PEO)10LiCF3SO3 polymer electrolyte. The addition of titanium oxide which consisted of plate-like spherical shape ranging from sub-micron to several microns increases the ionic conductivity by an order of magnitude compared with (PEO)10LiCF3SO3 polymer electrolyte without titanium oxide, and also have the higher ionic conductivity at low temperature. Li/CPEs/50% S cells have a initial discharge capacity of between 1400 and 1600 mA h g−1-sulfur with current rate of 100 mA g−1-sulfur at 90xa0°C and show the higher initial charge/discharge performance than without titanium oxide. The interfacial stability was remarkably improved by the addition of titanium oxide into the (PEO)10LiCF3SO3 polymer electrolyte.

Preparation and characterization of plasticized polymer electrolytes based on the PVdF-HFP copolymer for lithium/sulfur battery

PVdF-TG-LiX polymer electrolytes comprised of polyvinylidene fluoride (PVdF)-hexafluoropropylene (HFP) copolymer, tetra(ethylene glycol) dimethyl ether as plasticizer, LiCF3SO3, LiBF4 and LiPF6 as lithium salt and acetone as solvent have been prepared by solvent casting of slurry that mixed PVdF-HFP copolymer with acetone and salt using a ball-milling technique, which was performed for 2 and 12 h with a ball-to-material ratio of 400:1, and their electrochemical and thermal properties were studied. The ball-milled PVdF-TG-LiX polymer electrolytes have higher ionic conductivity as well as lower glass transition temperature and melting points than the magnetically stirred one. The PVdF-TG-LiPF6 polymer electrolytes prepared by ball-milling, for, 12 h, in particular, resulted in a maximum value in the ionic conductivity, which was 4.99×10−4 S cm−1 at room temperature. The ball-milled PVdF-TG-LiX polymer electrolytes were introduced into Li/S cells with sulfur as cathode and lithium as the anode. The first specific discharge capacities with discharge rate of 0.14 mA cm−2 at room temperature were about 575 and 765 mA h g–cathode−1 for magnetic stirring and 12 h ball milling.

Effect of ball milling on structural and electrochemical properties of (PEO)nLiX (lix = LiCF3SO3 and LiBF4) polymer electrolytes

Polymer electrolytes consisting of poly(ethylene oxide) (PEO) and lithium salts, such as LiCF3SO3 and LiBF4 are prepared by the ballmilling method. This is performed at various times (2, 4, 8, 12 h) with ball:sample ratio of 400:1. The electrochemical and thermal characteristics of the electrolytes are evaluated. The structure and morphology of PEO–LiX polymer electrolyte is changed to amorphous and smaller spherulite texture by ball milling. The ionic conductivity of the PEO–LiX polymer electrolytes increases by about one order of magnitude than that of electrolytes prepared without ball milling. Also, the ball milled electrolytes have remarkably higher ionic conductivity at low temperature. Maximum ionic conductivity is found for the PEO–LiX prepared by ball milling for 12 h, viz. 2:52 � 10 � 4 Sc m � 1 for LiCF3SO3 and 4:99 � 10 � 4 Sc m � 1 for LiBF4 at 90 8C. The first discharge capacity of Li/S cells increases with increasing ball milling time. (PEO)10LiCF3SO3 polymer electrolyte prepared by ball milling show the typical two plateau discharge curves in a Li/S battery. The upper voltage plateau for the polymer electrolyte containing LiBF4 differs markedly from the typical shape.# 2002 Elsevier Science B.V. All rights reserved.

Growth behavior of β-Ga2O3 nanomaterials synthesized by catalyst-free thermal evaporation

Various kinds of β-Ga2O3 nanomaterials such as nanowires, nanorods, nanobelts, nanosheets and nanocolumns have been successfully synthesized by simple evaporation of gallium powder with no assisted catalyst in a flow of argon gas. The as-synthesized materials were pure, structurally uniform, single crystalline with monoclinic β-Ga2O3 structure (space group: C2 m−1) and free from defects. The synthesized nanomaterials were deposited with a growth order of nanocolumn/nanorod, nanowire/nanobelt and nanosheet with synthesis time. The nucleation site was looked over in detail. We present evidence that the surface, edge and tip of previously grown β-Ga2O3 nanomaterials again provide a nucleation site of new β-Ga2O3 nanomaterials. Because no metal catalysts were introduced into our growth, a vapor–liquid–solid (VLS) growth is not the likely process in this work, indicating that the observed nanomaterials were grown via a vapor–solid (VS) mechanism.

Electrochemical properties of Fe2O3 thin film fabricated by electrostatic spray deposition for lithium-ion batteries

Fe2O3 thin films are important for the fabrication of rechargeable lithium microbatteries. Thin films of Fe2O3 were prepared by the electrostatic spray deposition (ESD) technique by using iron chloride as the precursor. The thin film electrodes, without inert additives such as polymer binder and conducting material, can deliver a first discharge capacity of 912?mA?h?g?1 and retain a discharge capacity of 537?mA?h?g?1 at a current density of 200?mA?g?1 to the 100th cycle. The coulombic efficiency of the Fe2O3 thin-film electrode was over 96% after several cycles.

Consideration of Fe Nanoparticles and Nanowires Synthesized by Chemical Vapor Condensation Process

Various physical, chemical and mechanical methods, such as inert gas condensation, chemical vapor condensation, sol-gel, pulsed wire evaporation, evaporation technique, and mechanical alloying have been used to synthesize nanoparticles. Among them, chemical vapor condensation(CVC) represents the benefit for its applicability to almost materials because a wide range of precursors are available for large-scale production with a non-agglomerated state. In this work, iron nanoparticles and nanowires have synthesized by chemical vapor condensation(CVC) process, using iron pentacarbonyl(Fe(CO)5) as precursor. The effects of processing parameters on the morphology, microstructure and size of iron nanoparticles and nanowires were studied. Iron nanoparticles and nanowires having various diameters were obtained by controlling the inflow of metallic organic precursor. Both nanoparticles and nanowires were crystallized. Characterization of obtained nanoparticles and nanowires were investigated by using a field emission scanning electron microscopy, transmission microscopy and X-ray diffraction.

Effects of MWNT and GNF on the Performance of Sulfur Electrode for Li/S Battery

We investigated the effects of multi-walled carbon nanotubes (MWNT) and graphitic nanofibers (GNF) on the performance of sulfur electrode for the lithium/sulfur battery. MWNT and GNF were manufactured by a thermal chemical vapor deposition (CVD) method, and then they were added as an additive in the sulfur electrode. The added sulfur electrodes were composed of 60wt% elemental sulfur (Aldrich), 20wt% acetylene black, 5wt% MWNT or GNF, and 15wt% poly ethylene oxide (PEO) dissolved in acetonitrile. No-added sulfur electrodes were prepared by mixing 60wt% elemental sulfur, 25wt% acetylene black, and 15wt% PEO. The addition of MWNT and GNF was found to give good electrochemical effects in sulfur electrode.

Electrochemical and interfacial properties of (PEO)10LiCF3SO3−Al2O3 nanocomposite polymer electrolytes using ball milling

Electrochemical and interfacial properties of (PEO)10LiCF3SO3−Al2O3 composite polymer electrolytes (CPEs) prepared by either ball milling or stirring are reported. Ball milling was introduced into a slurry preparative technique utilizing PEO, lithium salt and Al2O3 powder ranging from 5 to 15 wt.%. The ionic conductivity was increased by ball milling over a range of temperatures. In particular, a significant increase at low temperature below the melting point of crystalline PEO was observed. Interfacial stability between lithium electrode and CPE was significantly improved by the addition of alumina as well as by ball milling. The electrochemical stability window produced by (PEO)10LiCF3SO3−Al2O3 ball milling was higher than that of stirring, which was about 4.4 V. Charge/discharge performance of Li/CPE/S cells with (PEO)10LiCF3SO3−Al2O3-12 hr ball milling was superior to that of a pristine polymer electrolyte due to the low interface resistance and high ionic conductivity.

Effect of Various Lithium Salts in TEGDME Based Electrolyte for Li/Pyrite Battery

The effect of lithium salts such as LiPF6, LiBF4, LiCF3SO3 and LiN(CF3SO2)2 (LiTFSI) in tetra(ethylene glycol) dimethyl ether (TEGDME) electrolyte on the ionic conductivity, interfacial resistance and discharge properties of Li/pyrite cell at room temperature was studied. The electrolytes had good ionic conductivity at room temperature in the range 0.61 to 1.86 × 10-3 S/. The discharge capacities of Li/pyrite cells with 1M LiPF6 and LiBF4 in TEGDME were lower compared to those of the other two non-HF containing salts. The best cycle performance was exhibited by LiTFSI in TEGDME electrolyte, with a discharge capacity of 438 mAhg-1 after 20 cycles, which is ~49% of FeS2 theoretical capacity (894 mAhg-1). The good performance of LiTFSI-TEGDME electrolyte resulted mainly from its low interfacial resistance in Li/FeS2 cells, which showed a decreasing trend with cycling.

Effects of Multiwalled Carbon Nanotubes on the Cycle Performance of Sulfur Electrode for Li/S Secondary Battery

Lithium sulfur cells were prepared by composing with sulfur cathode, 0.5M LiCF3SO3 in tetra ethylene glycol dimethyl ether (TEGDME) solution and lithium anode. Multiwalled carbon nanotubes (MWNTs) were used to form the high electric network and prevent the dissolution of lithium polysulfides in sulfur cathode. The effects of additive contents were investigated by discharge test. The morphology of cathode with MWNTs (20wt.%) has rough and submicro porous. The initial discharge capacity of lithium sulfur cell using multiwalled carbon nanotubes (MWNTs) was 1,200mAh/g-sulfur, which was better than those of acetylene black (AB). The cycle performance of lithium sulfur cell was remarkably improved by the the addition of MWNTs.