Electrochimica Acta 108 (2013) 135–144 Contents lists available at ScienceDirect Electrochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/electacta Li 2 MnO 3 rich-LiMn 0.33 Co 0.33 Ni 0.33 O 2 integrated nano-composites as high energy density lithium-ion battery cathode materials Senthilkumar Rajarathinam, Sagar Mitra ∗ , Ramesh Kumar Petla Electrochemical Energy Laboratory, Department of Energy Science and Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India a r t i c l e i n f o Article history: Received 5 April 2013 Received in revised form 12 June 2013 Accepted 17 June 2013 Available online 2 July 2013 Keywords: High energy density integrated positive electrode Lithium manganese oxide rich layered–layered composite Lithium-ion battery Solid-state method Self combustion synthesis a b s t r a c t Alternative to LiCoO 2 cathode without sacrificing its structure and capacity, layered–layered compos- ites with Li 2 MnO 3 –LiMO 2 formula have been pursued in this article. In this study, we have optimized the Li 2 MnO 3 content in the composite based on its electrochemical performances (in terms of specific capacity, mAh g -1 ). All the samples are synthesized either by self-combustion reaction (SCR) or solid- state method. Phase composition, morphology, particle size and distribution are characterized by using X-ray diffraction (XRD), field emission gun scanning electron microscope (FEG-SEM) and high resolution transmission electron microscope (HR-TEM), respectively. The X-ray diffraction study confirms that the material has layered LiNi 0.3 Co 0.3 Mn 0.3 O 2 structure with a space group of R ¯ 3m along with the formation of Li 2 MnO 3 phase with super lattice ordering (C2/m). Charge/discharge capacity of the composite cathode materials increases with cycle number due to more and more activation of the Li 2 MnO 3 and get stabilized after 20th cycle with good coulombic efficiency. A composite of 0.7Li 2 MnO 3 –0.3LiMn 0.33 Co 0.33 Ni 0.33 O 2 composition delivered a maximum stable specific discharge capacity of ∼190 mAh g -1 over 50 cycles at C/10 rate at 20 ◦ C once it reaches the activation stage. A detail electrochemical study has been performed to understand the complicated electrochemistry during charge–discharge reaction at 20 ◦ C. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Lithium-ion batteries (LIBs) are the state of the art power sources of modern consumer’s electronics. It has highest energy density and operating potential among all the rechargeable battery technologies [1–9]. Its overall electrochemical performance truly depends on the cathode materials since it exhibits lower capacity compared to the anode materials. Though, layered LiCoO 2 -based cathode is commercialized in today’s LIBs however it suffers by limited e - (0.5 Li + -ion) transfer, operating cost, structural insta- bility during cycling and also contained hazardous cobalt in the structure lead to development of other alternative cathodes. In recent past, LiMn 0.33 Co 0.33 Ni 0.33 O 2 -based cathode materials have been introduced as promising positive electrode materials for LIBs in which Co ions are doubly substituted by Mn and Ni while preventing the LiCoO 2 structure [10]. Surprisingly, transition metal cations found in such positive materials are Mn 4+ , Co 3+ and Ni 2+ but in most of the cases Ni 2+/4+ and Co 2+/3+ redox couples are electro- chemically active during lithium-ion interaction–deintercalation reaction. Double substitution of Ni and Mn to Co site may reduce the cost of the electrode material; however it was observed that rate ∗ Corresponding author. Tel.: +91 2225767849; fax: +91 2225764890. E-mail address: sagar.mitra@iitb.ac.in (S. Mitra). performance tends to degrade with decreasing Co content in the structure [11]. Few reports also present the lower apparent lithium- ion diffusion coefficient while Co content is low in the matrix [12]. It is now well accepted that the reason behind the low power rate performance is mainly due to the structural instability in the matrix in other term cation disordering. Due to similar ionic radii of Li (0.74 ˚ A) and Ni 2+ (0.69 ˚ A), Ni 2+ can easily occupy the Li position in LiMn 0.33 Co 0.33 Ni 0.33 O 2 material. To overcome the problem associated with LiMn 0.33 Co 0.33 Ni 0.33 O 2 cathode and achieve higher voltage cathode mate- rials, Thackeray et al. [13–15] have proposed an alternative high potential (>3 V) integrated layered–layered composite like xLi 2 MnO 3 –(1 - x)LiMn 0.33 Co 0.33 Ni 0.33 O 2 (where M = Co, Mn, Ni) [16–19] as cathode materials which outcast the existing cathodes with superior performance and structural stability. Among all these, lithium rich layered–layered structure opted to be the most promising candidate as it exhibited high energy density (>230 mAh g -1 ) [20–22] and are limited as an active cathode mate- rials due to large polarization, continuous structural transitions and poor coulombic efficiency in the beginning (Li 2 MnO 3 needs electrochemical stabilization). Hence, to foresee these composites as a practical positive electrode in LIBs applications, the following problems to be addressed first [14,23]: (1) highly stable potential plateau; (2) structural stability (due to O 2 evolution during charg- ing); (3) better rate performance by thorough investigation of its 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.06.102