• Bulletin of the Korean Chemical Society
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• 제22권5호
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• pp.481-487
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• 2001

Surface films formed prior to bulk reduction of lithium have been studied at gold, platinum, and copper electrodes in rigorously dried propylene carbonate solutions using electrochemical quartz crystal microbalance (EQCM) and secondary ion mass spectrometry experiments. The results indicate that the passive film formation takes place at a potential as positive as about 2.0 V vs. Li/Li+ , and the passive film thus formed in this potential region is thicker than a monolayer. Quantitative analysis of the EQCM results indicates that electrogenerated lithium reacts with solvent molecules to produce a passive film consisting of lithium carbonate and other compounds of larger molecular weights. The presence of lithium carbonate is verified by SIMS, whereas the lithium compounds of low molecular weights, including lithium hydroxide and oxide, are not detected. Further lithium reduction takes place underneath the passive film at potentials lower than 1.2 V with a voltammetric current peak at about 0.6 V.

• 한국분말재료학회지
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• 제31권2호
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• pp.163-168
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• 2024

As the demand for lithium-ion batteries for electric vehicles is increasing, it is important to recover valuable metals from waste lithium-ion batteries. In this study, the effects of gas flow rate and hydrogen partial pressure on hydrogen reduction of NCM-based lithium-ion battery cathode materials were investigated. As the gas flow rate and hydrogen partial pressure increased, the weight loss rate increased significantly from the beginning of the reaction due to the reduction of NiO and CoO by hydrogen. At 700 ℃ and hydrogen partial pressure above 0.5 atm, Ni and Li₂O were produced by hydrogen reduction. From the reduction product and Li recovery rate, the hydrogen reduction of NCM-based cathode materials was significantly affected by hydrogen partial pressure. The Li compounds recovered from the solution after water leaching of the reduction products were LiOH, LiOH·H₂O, and Li₂CO₃, with about 0.02 wt% Al as an impurity.

• 자원리싸이클링
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• 제33권1호
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• pp.15-21
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• 2024

전기차용 리튬이온배터리의 수요가 증가함에 따라 향후 발생할 폐리튬이온배터리 중의 유가금속 회수가 필요하다. 본 연구에서는 리튬이온배터리의 NCM계 양극재를 수소환원과 수침출에 의해 리튬을 수산화리튬으로 회수할 때의 회수율에 미치는 반응온도의 영향을 조사하였다. 반응온도가 상승함에 따라 수소에 의한 NiO, CoO의 환원에 의해 무게 감소율이 반응초기부터 급격하게 증가하였으며 동시에 H₂O 발생량도 증가하였다. 602 ℃ 이상에서는 양극재 중의 Ni, Co가 전부 환원되어 금속상으로 존재하였다. 그리고 수소환원 온도의 상승과 함께 Li 회수률도 증가하였으나 704 ℃ 이상에서는 약 92 % 이상의 유사한 수준을 나타내었다. 따라서 폐Li이온 배터리의 전처리로 수소환원하는 것에 의해 리튬만 사전에 회수하고 잔사를 재처리하면 효율적으로 유가금속을 분리하여 회수할 수 있을 것으로 기대된다.

• Bulletin of the Korean Chemical Society
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• 제4권1호
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• pp.14-17
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• 1983

The effects of trialkylborane on the stereochemistry of ketone reduction with lithium borohydride were studied for the four representative ketones, namely 4-t-butylcyclohexanone, 2-methylcyclohexanone, norcamphor, and camphor. The presence of trialkylborane increased the yields of the less stable alcohols. For example, in the presence of tri-s-butylborane, 42 % yield of cis-4-t-butylcyclohexanol was observed whereas only 8 % yield with lithium borohydride alone in the reduction of 4-t-butylcyclohexanone. The in situ formation of lithium trialkylborohydride, by the hydride transfer from lithium trialkoxyborohydride to trialkylborane, was demonstrated as a possible mechanism for the catalytic effect of trialkylborane.

• Bulletin of the Korean Chemical Society
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• 제7권1호
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• pp.66-69
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• 1986

The reaction of potassium trialkoxyborohydrides of varying steric requirements with lithium chloride in tetrahydrofuran(THF) was examined in detail to establish the generality of this synthesis of the corresponding lithium trialkoxyborohydrides. The metal ion exchange reaction between potassium triisopropoxyborohydride and lithium chloride in THF proceeded instantly at room temperature and the corresponding lithium salt was very stable toward disproportionation. However, for R = s-Bu, t-Bu and 2-methylcyclohexyl, with increasing steric requirement, the lithium derivatives were unstable and thus dissociated into $(RO)BH_3^-\;and\; (RO)_4B^-$. The stereoselectivity of lithium triisopropoxyborohydride(LIPBH) in the reduction of representative cyclic ketones was examined and compared with that of the potassium derivative.

• 한국재료학회지
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• 제24권5호
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• pp.243-248
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• 2014

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

• Bulletin of the Korean Chemical Society
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• 제23권12호
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• pp.1695-1696
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• 2002

• Bulletin of the Korean Chemical Society
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• 제22권7호
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• pp.661-662
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• 2001

• Bulletin of the Korean Chemical Society
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• 제16권5호
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• pp.416-421
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• 1995

The approximate rates and stoichiometry of the reaction of excess lithium gallium hydride with selected organic compounds containing representative functional groups were examined under the standard conditions (diethyl ether, 0 $^{\circ}C)$ in order to compare its reducing characteristics with lithium aluminum hydride and lithium borohydride previously reported, and enlarge the scope of its applicability as a reducing agent. Alcohols, phenol, and amines evolve hydrogen rapidly and quantitatively. However lithium gallium hydride reacts with only one active hydrogen of primary amine. Aldehydes and ketones of diverse structure are rapidly reduced to the corresponding alcohols. Conjugated aldehyde and ketone such as cinnamaldehyde and methyl vinyl ketone are rapidly reduced to the corresponding saturated alcohols. p-Benzoquinone is mainly reduces to hydroquinone. Caproic acid and benzoic acid liberate hydrogen rapidly and quantitatively, but reduction proceeds slowly. The acid chlorides and esters tested are all rapidly reduced to the corresponding alcohols. Alkyl halides and epoxides are reduced rapidly with an uptake of 1 equiv of hydride. Styrene oxide is reduced to give 1-phenylethanol quantitatively. Primary amides are reduced slowly. Benzonitrile consumes 2.0 equiv of hydride rapidly, whereas capronitrile is reduced slowly. Nitro compounds consumed 2.9 equiv of hydride, of which 1.9 equiv is for reduction, whereas azobenzene, and azoxybenzene are inert toward this reagent. Cyclohexanone oxime is reduced consuming 2.0 equiv of hydride for reduction at a moderate rate. Pyridine is inert toward this reagent. Disulfides and sulfoxides are reduced slowly, whereas sulfide, sulfone, and sulfonate are inert under these reaction conditions. Sulfonic acid evolves 1 equiv of hydrogen instantly, but reduction is not proceeded.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.670-676
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• 1992

A systematic study of the partial reduction of carboxylic acids and their derivatives to the corresponding aldehydes with lithium tris(dialkylamino)aluminum hydrides under practical conditions has been carried out. The diethylaminosubstituted derivative of lithium aluminum hydride, lithium tris(diethylamino)aluminum hydride (LTDEA), shows quite general applicability in the conversion of carboxylic acids, carboxylic esters, and primary carboxamides to the corresponding aldehydes. Lithium tripiperidinoaluminum hydride (LTPDA) also appears to be a reagent of choice for such partial transformation of primary carboxamides. In additioin, both LTDEA and LTPDA reduce tertiary carboxyamides to aldehydes in high yields. Finally, lithium tris(dihexylamino)aluminum hydride (LTDHA) is capable of achieving the chemoselective reduction of aromatic nitriles to aldehydes in the presence of aliphatic nitriles under practical conditions.