Churl Kyoung Lee

Reductive leaching of cathodic active materials from lithium ion battery wastes

Abstract Reductive leaching of LiCoO2 from spent lithium ion battery was investigated in terms of reaction variables. The leaching efficiency of LiCoO2 increased with increasing temperature, and concentration of HNO3, but with decreasing solid/liquid (S/L) ratio. Li and Co from LiCoO2 were leached over 95% with the addition of 1.7 vol.% H2O2 as a reducing agent. This is due to the reduction of Co3+ to Co2+ which can be readily dissolved. The dissolution rates of Co and Li were inversely proportional to their respective concentrations in the solution. Apparent activation energies of 12.5 and 11.4 kcal/mol were obtained for Co and Li, respectively. This indicates that the dissolution of LiCoO2 is controlled by surface chemical reaction.

Surface modification of precipitated calcium carbonate using aqueous fluosilicic acid

Abstract Surface modification of calcium carbonate using aqueous fluosilicic acid (H2SiF6) was carried out in terms of the mole ratio of fluosilicic acid to calcium carbonate as well contact time. The resulting surface compounds of amorphous silica and calcium fluoride after surface modification were visualized on the surface of calcium carbonate. Amorphous silica was generated by the hydrolysis of silicon hexafluoride (SiF62−) dissociated from fluosilicic acid. Calcium fluoride was generated by the reaction of dissociated fluoride ion and calcium ion. The compounds were widely distributed throughout the surface of calcium carbonate like thin coating layer. An effect of fluosilicic acid concentration on the formation of surface compounds was more significant than contact time. The surface compounds contributed to enhance an acid resistance of calcium carbonate compared to unmodified calcium carbonate.

Silicon Diphosphide: A Si-Based Three-Dimensional Crystalline Framework as a High-Performance Li-Ion Battery Anode

The development of an electrode material for rechargeable Li-ion batteries (LIBs) and the understanding of its reaction mechanism play key roles in enhancing the electrochemical characteristics of LIBs for use in various portable electronics and electric vehicles. Here, we report a three-dimensional (3D) crystalline-framework-structured silicon diphosphide (SiP2) and its interesting electrochemical behaviors for superior LIBs. During Li insertion in the SiP2, a three-step electrochemical reaction mechanism, sequentially comprised of a topotactic transition (0.55-2 V), an amorphization (0.25-2 V), and a conversion (0-2 V), was thoroughly analyzed. On the basis of the three-step electrochemical reaction mechanism, excellent electrochemical properties, such as high initial capacities, high initial Coulombic efficiencies, stable cycle behaviors, and fast-rate capabilities, were attained from the preparation of a nanostructured SiP2/C composite. This 3D crystalline-framework-structured SiP2 compound will be a promising alternative anode material in the realization and mass production of excellent, rechargeable LIBs.

Application of Ionic Liquids in Hydrometallurgy

Ionic liquids, low temperature molten salts, have various advantages manifesting themselves as durable and environmentally friendly solvents. Their application is expanding into various fields including hydrometallurgy due to their unique properties such as non-volatility, inflammability, low toxicity, good ionic conductivity, and wide electrochemical potential window. This paper reviews previous literatures and our recent results adopting ionic liquids in extraction, synthesis and processing of metals with an emphasis on the electrolysis of active/light, rare earth, and platinum group metals. Because the research and development of ionic liquids in this area are still emerging, various, more fundamental approaches are expected to popularize ionic liquids in the metal manufacturing industry.

Nanostructured cobalt oxide-based composites for rechargeable Li-ion batteries

Cobalt oxide-based nanocomposites are prepared using Co3O4, various metals (Al, Mg), carbon powders, and a simple high-energy mechanical milling technique. X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy show that the cobalt oxide-based composites are mainly composed of nanostructured CoO/Al2O3, CoO/MgO, and Co3O4/C composites, respectively. Based on concepts related to the enhanced electrical conductivity of the Co3O4/C nanocomposite using conducting carbon matrix and to the resistance of inactive ceramic matrices (Al2O3, MgO) against active CoO particle growth during cycling, various nanostructured cobalt oxide-based composites are tested for use as anode materials. Among the composites, the Co3O4/C nanocomposite anode exhibits good electrochemical characteristics, such as high-capacity, good initial Coulombic efficiency, and long cycle behavior for Li-ion batteries.

Co–Sb intermetallic compounds and their disproportionated nanocomposites as high-performance anodes for rechargeable Li-ion batteries

Co–Sb intermetallic compounds (CoSb, CoSb2, and CoSb3) were simply synthesized by solid-state synthesis routes and their potential as anode materials for Li-ion batteries was investigated. The CoSb3 electrode showed poor electrochemical behavior, but the CoSb and CoSb2 electrodes showed relatively good electrochemical performance. Additionally, the reaction mechanisms of CoSb, CoSb2, and CoSb3 with Li were identified using ex situ X-ray diffraction. To improve the electrochemical performance of the Co–Sb intermetallic compounds, nanostructured composites of these compounds modified with carbon were prepared using a high-energy mechanical milling technique. Among the fabricated nanocomposites, the CoSb2/C nanocomposite electrode comprising disproportionated nanocrystalline CoSb, amorphous Sb, and an amorphous carbon matrix showed excellent electrochemical properties, such as a high energy density (1st charge: 578 mA h g−1, or ∼2895 mA h cm−3), cycling durability over 100 cycles (above 490 mA h g−1, or ∼2450 mA h cm−3), high initial Coulombic efficiency (∼78.1%), and a fast rate capability (1 C: 472 mA h g−1, 3 C: 415 mA h g−1). These excellent electrochemical properties demonstrated by the CoSb2/C nanocomposite electrode confirm its potential as an alternative anode material for Li-ion batteries.

Tellurium recovery from cemented tellurium with minimum waste disposal

Abstract A waste minimization hydrometallurgical process with near zero-discharge has been developed for the treatment of cemented tellurium from copper refining. Tellurium is recovered by a series of leaching, precipitation and electrowinning steps, and the barren electrolyte is recycled to the leaching step of fresh cemented tellurium feed with a replenished NaOH solution. In the leaching step, more than 95% of tellurium is selectively extracted in the form of TeO32− within 10 min at 80°C and 200 g/l pulp density. The leach residue is leached with H2SO4 solution and can be sent to the existing Cu electrowinning circuit. In the next step, most of the remaining Cu and Pb impurities are precipitated with Na2S. Then, tellurium of 99.9% purity is electrowon from the purified pregnant solution, leaving most of Se and As behind in the solution. Impurity levels of Se and As can be lowered by the addition of hydrazine hydrate at every fifth cycle, and the purified NaOH solution is recirculated to the leaching step.

Amorphized ZnSb-based composite anodes for high-performance Li-ion batteries

We report a simple, rapid, and straightforward hybrid mechanochemical synthesis for intermetallic compound-based nanocomposites, which can be used as anode materials for high-performance Li-ion batteries.

Modeling of solid-state electrotransport for purification of gadolinium

Modeling of solid state electrotransport (SSE) was formulated to understand the transport phenomena of the interstitial impurities in gadolinium, are of the rare earth metals. Through numerical analysis, the optimum conditions for SSE are theoretically predicted. The processing parameters such as pressure, temperature, and reaction time can be determined to attain maximum effectiveness. The concentration profiles of interstitial impurities such as oxygen, nitrogen, and carbon were calculated based on this model. The electromigration of oxygen is faster than nitrogen and carbon because of its greater diffusivity and mobility. When the reaction time was 105 seconds, the oxygen and nitrogen were refined up to 92%–95% at 10−5Pa while carbon was refined to 98% at 10−6Pa. The increase in temperature gives rise to a shorter reaction time, but extremely low pressure is required.

Synthesis of Silicon Thin Film by Electrodeposition from Ionic Liquid

The synthesis of a silicon thin film by room-temperature electrodeposition was investigated in the ionic liquids 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]Tf2N) and 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMPy]Tf2N) with SiCl4. Cyclic voltammetry on a gold working electrode showed the possibility of the electrodeposition of elemental silicon. The reduction current of silicon in [EMIM]Tf2N was higher than in [BMPy]Tf2N. The elemental silicon thin film could be synthesized on the gold electrode under potentiostatic conditions, as confirmed by various analytical techniques including X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy-dispersive spectroscopy. In the [EMIM]Tf2N electrolyte with dissolved SiCl4, the electrodeposited Si surface was more uniform than in [BMPy]Tf2N and no impurity was detected except trace oxygen caused by contamination during handling for analysis