Electrochimica Acta 108 (2013) 32–38 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom ep age: www.elsevier.com/locate/elec tacta Characterization of Li-rich xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co 1-y-z ]O 2 as cathode active materials for Li-ion batteries Yong Nam Jo a , K. Prasanna a , Suk Joon Park b , Chang Woo Lee a,∗ a Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Gihung, Yongin, Gyeonggi 446-701, South Korea b Ecopro, 316-3 Songdae, Ochang, Cheongwon 363-883, South Korea a r t i c l e i n f o Article history: Received 1 March 2013 Received in revised form 18 June 2013 Accepted 22 June 2013 Available online 27 June 2013 Keywords: Li-ion battery Cathode active materials Li-rich Overlithiated oxide Cycling properties Rate capability a b s t r a c t We have investigated the crystallographical, morphological, and electrochemical behaviors of synthe- sized four different compositions of xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co 1-y-z ]O 2 cathode active materials using X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), and galvanostatic cycler. The four different compositions of cathode active materials demonstratea commonly angular shape of primary particles, but agglomerated spherical shape in appearance. All the attempted compo- sitions of xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co 1-y-z ]O 2 cathodes deliver a specific discharge capacity of between 220 and 242 mAh/g at room temperature when cycled between 2.5 and 4.6 V versus Li/Li + at C/10 rate. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction The Li-ion batteries have become an indispensable part of our lives from potable application such as mobile, digital camera and power tool to the large application, for example hybrid electric vehicle (HEV), electric vehicle (EV), energy storage system (ESS) and so on. During the last decades, plenty of materials have been synthesized and estimated as cathode active materials for Li-ion rechargeable batteries [1–4]. To increase the energy density of Li-ion batteries, it is necessary to enlarge the capacity of the cathode because the usable capacity of graphite as an anode, about 350mAh/g, is much larger than that of LiCoO 2 as a cathode which has 150 mAh/g of practical specific discharge capacity, the LiCoO 2 material that is widely used as the cathode in Li-ion rechargeable batteries [5–9]. In order to increase the energy density of cathode materials, recent researches have focused on the Li-rich NCM compounds that have high specific dis- charge capacity. Electrodes based on Li-rich NCM compositions can provide at high anodic potentials of 4.6 V vs. Li/Li + and offer high capacities(>200 mAh/g) [10,11]. In order to develop alternatives of LiCoO 2 and/or conven- tional cathode materials, we investigated the different composition ∗ Corresponding author. Tel.: +82 31 201 3825; fax: +82 31 204 8114. E-mail address: cwlee@khu.ac.kr (C.W. Lee). of xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co 1-y-z ]O 2 cathode active materials. Many researchers already studied that type of Li-rich cathode active materials. In this research we tried to find out the optimum compo- sition of xLi 2 MnO 3 ·(1-x)Li[Mn y Ni z Co 1-y-z ]O 2 for electric vehicles and/or energy storage systems at room and elevated temperature. So as to study the electrochemical behavior, 2032-type coin cells are assembled using four different compositions of cathode active materials and carried out the intensive studies on potential pro- file, cycle life, and so on. Furthermore, crystallographies of the attempted cathode active materials were investigated. 2. Experimental All the cathode active materials were synthesized by Ecopro using the co-precipitation method. In order to fabricate the cathode electrode, each 90 wt% of Li-rich powder was mixed with 5 wt% of conductive carbon agent, 5 wt% of polyvinylidene fluoride (PVDF) which acts as a binder and N-methyl-2-pyrrolidone (NMP). The mixed slurry was laminated on Al foil. The electrochemical prop- erties of Li-rich materials were evaluated using 2032-type coin cells assembled in an argon filled glove box. The 2032-type coin cell consisted of fabricated Li-rich cathode electrode, pure lithium metal as the counter electrode, microporous membrane as the separator and 1 M LiPF 6 in ethylene carbonate (EC): diethylene car- bonate (DEC) (1:1 vol%) as the electrolyte. The morphology analysis of the each cathode active materials was observed using a field 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.06.062