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Nam K.-M.,Chungnam National University | Kim H.-J.,Chungnam National University | Kang D.-H.,EMT Co. | Kim Y.-S.,EMT Co. | Song S.-W.,Chungnam National University
Green Chemistry | Year: 2015

The ammonia-free green coprecipitation process has successfully produced a micro-sized spherical Ni0.5Co0.2Mn0.3(OH)2 precursor with a homogeneous elemental distribution. The replacement of ammonia with citric acid as a chelating agent was the key for this eco-friendly and cost-effective process. The pH of coprecipitation was determined from solubility and complex formation diagrams calculated using solubility products and formation constants. By varying the relative ratio of citric acid to metals, the optimized particle morphology, size and robustness of the precursor were obtained. The cathode material LiNi0.5Co0.2Mn0.3O2, prepared using the hydroxide coprecipitate precursor, showed a good charge-discharge cycling performance in lithium cells, delivering high capacity and cycling stability (≥94% retention) at 3.0-4.3 V as well as upon high-voltage operation at 4.6 V. © 2015 The Royal Society of Chemistry.

Kang J.,Chungnam National University | Pham H.Q.,Chungnam National University | Kang D.-H.,EMT Co. | Park H.-Y.,IPI Technology Inc. | Song S.-W.,Chungnam National University
Journal of Alloys and Compounds | Year: 2016

High loading level of micron cathode active material is essential for high energy density Li-ion batteries. High loading level and thick cathode however limit not only rate capability but also cycle life, which is mainly caused by inhomogeneous current distribution from bottom (current collector side) to the top (interface side to electrolyte) of the cathode. Here we report a significant improvement of rate performance of micron LiNi0.6Co0.2Mn0.2O2 cathode material with high loading level of more than 10 mgcm-2, through simple and homogeneous dispersion and interweaving of bulk carbon fibers (CF) to active material. This microstructure permits the building-up of 3D electrical conduction network over the thick cathode. While the interwoven carbon fiber network guarantees fast electron transfer, porous characteristic of a thick cathode leads to a rapid access of Li+-ion through a good electrolyte wetting, and favorable rate capability and cycling stability. The resulting highly loaded CF-interwoven cathode achieves rate capability upto 5 C, high capacity of 163 mAhg-1 at 1 C and stable 1 C cycling performance even under an aggressive test condition between 3.0 and 4.6 V utilizing high-voltage electrolyte additive. © 2015 Elsevier B.V.

Lee Y.-M.,Chungnam National University | Nam K.-M.,Chungnam National University | Hwang E.-H.,Leechem Co. | Kwon Y.-G.,Leechem Co. | And 3 more authors.
Journal of Physical Chemistry C | Year: 2014

The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi0.5Co0.2Mn0.3O2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0-4.6 V versus Li/Li+ results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205-182 mAhg-1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and -CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi0.5Co0.2Mn0.3O2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes. © 2014 American Chemical Society.

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