Kinzan, South Korea
Kinzan, South Korea

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Pham H.Q.,Chungnam National University | Hwang E.-H.,Leechem Co. | Kwon Y.-G.,Leechem Co. | Song S.-W.,Chungnam National University
Journal of Power Sources | Year: 2016

Research progress of high-energy performance and interfacial phenomena of Li1.13Mn0.463Ni0.203Co0.203O2 cathode and graphite anode in a 55 °C full-cell under an aggressive charge cut-off voltage to 4.7 V (4.75 V vs. Li/Li+) is reported. Although anodic instability of conventional electrolyte is the critical issue on high-voltage and high-temperature cell operation, interfacial phenomena and the solution to performance improvement have not been reported. Surface spectroscopic evidence revealed that structural degradation of both cathode and anode materials, instability of surface film at cathode, and metal-dissolution from cathode and -deposition at anode, and a rise of interfacial resistance with high-voltage cycling in 55 °C conventional electrolyte are resolved by the formation of a stable surface film with organic/inorganic mixtures at cathode and solid electrolyte interphase (SEI) at anode using blended additives of fluorinated linear carbonate and vinylene carbonate. As a result, significantly improved cycling stability of 77% capacity retention delivering 227-174 mAhg-1 after 50 cycles is obtained, corresponding to 819-609 Wh per kg of cathode active material. Interfacial stabilization approach would pave the way of controlling the performance and safety, and widening the practical application of Li-rich layered oxide cathode materials and high-voltage electrolyte materials in various high-energy density Li-ion batteries. © 2016 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.

Pham H.Q.,Chungnam National University | Nam K.-M.,Chungnam National University | Hwang E.-H.,Leechem Co. | Kwon Y.-G.,Leechem Co. | And 2 more authors.
Journal of the Electrochemical Society | Year: 2014

High-capacity Li-rich layered composite oxide, xLi2MnO3 · (1-x)LiMO2 (M = Mn, Ni, Co), is a promising candidate cathode material for high-energy electrochemical energy storage. Enabling the high-performance of high-voltage cathode relies on an electrolyte breakthrough and the solid electrolyte interface (SEI) stabilization. In this study, the 0.6Li2MnO3 · 0.4LiNi0.45Co0.25Mn0.3O2 (Li1.2Mn0.525Ni0.175Co0.1O2, LMNC) cathode is operated at 2.5-4.8 V with 5 wt% fluorinated linear carbonate, di-(2, 2, 2 trifluo-roethyl)carbonate (DFDEC), as a high-voltage electrolyte additive, for the first time and applied to a high-energy lithium-ion battery. The cathode with DFDEC outperforms that in electrolyte only, delivering a high capacity of 250 mAhg-1 with an excellent charge-discharge cycling stability at the rate of 0.2C. Upon the use of DFDEC, the cathode surface is effectively passivated by a stable SEI composed of DFDEC decomposition products, which inhibit a detrimental metal dissolution and structural cathode degradation. A full-cell based on the SEI-stabilized LMNC cathode and graphite anode successfully demonstrates doubled energy density (∼278 Whkg-1) compared to ∼136 Whkg-1 of a commercialized cell of graphite//LiCoO2 and an excellent cycling stability. © 2014 The Electrochemical Society.

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