Electrochimica Acta 55 (2010) 4441–4450 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Synthesis of compounds, Li(MMn 11/6 )O 4 (M = Mn 1/6 , Co 1/6 , (Co 1/12 Cr 1/12 ), (Co 1/12 Al 1/12 ), (Cr 1/12 Al 1/12 )) by polymer precursor method and its electrochemical performance for lithium-ion batteries A. Sakunthala a,b , M.V. Reddy a , S. Selvasekarapandian b,c,∗ , B.V.R. Chowdari a,∗∗ , P. Christopher Selvin d a Department of Physics, National University of Singapore, Singapore 117542, Singapore b DRDO-BU, Centre for Life Sciences, Bharathiar University, Coimbatore 641046, India c Kalasalingam University, Krishnankoil, Virudhunagar 626190, Tamil Nadu, India d NGM College, Pollachi, Tamil Nadu, India article info Article history: Received 4 January 2010 Received in revised form 15 February 2010 Accepted 22 February 2010 Available online 1 March 2010 Keywords: Doped LiMn2O4 Cycling stability Cathodes X-ray absorption fine structure Electrochemical properties Lithium batteries abstract The compounds, Li(MMn 11/6 )O 4 (M = Mn 1/6 , Co 1/6 , (Co 1/12 Cr 1/12 ), (Co 1/12 Al 1/12 ), (Cr 1/12 Al 1/12 )) are synthe- sised by the polymer precursor method. The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, respectively. Density and the Brunauer, Emmet and Teller surface area (BET) of the compounds are also studied. The cobalt doped compound, Li(Co 1/6 Mn 11/6 )O 4 is found to be nanosized particles in the range of 60–100 nm, when compared to the other compounds in our present study. The oxidation state and the local structure of the compounds are analysed by the X-ray absorption spectroscopy (XAS) technique. Cyclic voltammetry (CV) and the galvanostatic charge–discharge cycling (30 mA g -1 ) studies are made in the voltage range of 3.5–4.3 V at room temperature for all the compounds under study. The bare and (Co 1/6 ), and (Co 1/12 Cr 1/12 ) substituted spinels are cycled at high current rates of 1, 2 and 5C (assuming 1C∼120 mA g -1 ). Cycling results of Co-substituted spinels show better and long-term capacity retention at all the current rates. At the end of the second cycle, Li(Co 1/6 Mn 11/6 )O 4 compound delivers a discharge capacity value of 100 (±3) and 87 (±3) mAh g -1 for the current rate of 2 and 5C, respectively. An excellent capacity retention value of 94% is observed at the end of the 1000 cycles for both 2 and 5C rates. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction The high cost, toxicity, safety concerns and the chemical insta- bility of the currently used layered lithium cobalt oxide, LiCoO 2 (4 V) cathode material invoke the serious research on alterna- tive materials for lithium-ion batteries. Lithium manganese oxide, LiMn 2 O 4 (4 V vs. Li), is considered as an alternative cathode material for its better advantages like easy preparation, cheaper, environ- mentally friendly, excellent voltage profile characteristics, safety, Mn 3+/4+ redox couple and excellent rate capability [1–5]. But it pos- sesses 10% less energy density when compared to LiCoO 2 and also found to suffer from poor cycling stability. The main reasons con- sidered for the capacity fading are, Jahn–Teller distortion occurring because of t 2g 3 –e g 1 electronic configuration of Mn 3+ ion, forma- ∗ Corresponding author at: DRDO-BU, Centre for Life Sciences, Bharathiar Univer- sity, Coimbatore 641046, India. ∗∗ Corresponding authors at: Department of Physics, National University of Singa- pore, Singapore 117542, Singapore Tel.: +65 65162605; fax: +65 67776126. E-mail addresses: phymvvr@nus.edu.sg (M.V. Reddy), sekarapandian@yahoo.com (S. Selvasekarapandian), phychowd@nus.edu.sg (B.V.R. Chowdari). tion of two cubic phases with different lattice parameters during charge/discharge cycle, active material dissolution, loss of crys- tallinity during cycling and the higher irreversible capacity loss (ICL) [2,6–8]. Varying the morphology of the particles by adopt- ing different synthesis methods, doping with different metal ions and surface coating are considered to improve the electrochemi- cal properties of LiMn 2 O 4 [9–13]. The electrochemical performance was found to strongly depend on its synthesis conditions and varies with the phase purity, particle morphology, specific surface area, crystallinity, cation distributions and composition of the materials [3,14,15]. Though LiMn 2 O 4 prepared by conventional solid state reaction method has the advantage of mass production, the prod- uct usually contains some impure phases and oxygen deficiency which is detrimental to its electrochemical performance and also it involves higher preparation temperature with long heating time followed by several grinding and annealing process [3,15,16]. Hence, so far LiMn 2 O 4 and the substituted compounds have been studied by preparation through many different chemical methods like sol–gel [17,18], ultrasonic spray pyrolysis [3,19], sucrose aided combustion [20], spray-drying [21], flame spray pyrolysis [22], rheological phase assisted microwave synthesis [23], hydrothermal method [24], colloidal templating process 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.02.080