Materials Science and Engineering B 176 (2011) 1257–1263 Contents lists available at ScienceDirect Materials Science and Engineering B jou rnal h om epage: www.elsevier.com/locate/mseb Crystal habits of LiMn 2 O 4 and their influence on the electrochemical performance K. Ragavendran a,b , H.L. Chou b , L. Lu a,∗ , Man On Lai a , B.J. Hwang b , R. Ravi Kumar c , S. Gopukumar c , Bosco Emmanuel c , D. Vasudevan c , D. Sherwood c a Materials Laboratory, Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore b Nano Electrochemistry Laboratory, National Taiwan University of Science and Technology, Taipei, Taiwan c Central Electrochemical Research Institute, Karaikudi 630 006, Tamilnadu, India a r t i c l e i n f o Article history: Received 8 December 2010 Received in revised form 26 May 2011 Accepted 11 July 2011 Available online 27 July 2011 Keywords: Lithium manganate Crystal habits Crystal shape algorithm Density functional theory Lithium batteries a b s t r a c t Crystal habits of LiMn 2 O 4 prepared through a sol–gel method using different starting materials (metal acetates and metal nitrates) are studied using a crystal shape algorithm. Density functional theory (DFT) as implemented in VASP is employed to study the thermodynamic stabilities and the electronic structure of the different hkl planes of LiMn 2 O 4 , as identified by the crystal shape algorithm. The crystal habit of lithium manganate prepared through the metal acetate route, LiMn 2 O 4 (A), seems to possess a higher thermodynamic stability compared to the metal nitrate route viz. LiMn 2 O 4 (N). Electrochemical cycling measurements show that the capacity retention in LiMn 2 O 4 (A) is better than LiMn 2 O 4 (N) at low (C/10) as well as at higher (5C) rates. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The electrochemical performance of a cathode material in a Li-battery depends upon several factors among which (a) crystal- lographic structure, (b) electronic structure, (c) structure of the solid–electrolyte interface and (d) morphology are the most impor- tant. Size and shape are the two essential attributes that determine the morphology and hence the morphology dependent function- ality of polycrystalline materials. Size as measured from the full width at half maximum (FWHM) of an XRD peak (i.e., hkl) gives the thickness of the crystallite in one particular direction; however only the shape of a material can provide complete 3-D information on its physico-chemical properties. Studies on material’s shapes have recently attracted a lot of interest among the scientists since the report by Ertl, recognized with the award of 2007 Nobel Prize in Chemistry, that the catalytic activity of different planes of Fe differs by several orders of magnitude [1]. In the context of cathode mate- rials for lithium battery applications, crystal habit (shape) which manifests as the morphology of the material is one of the important factors that determine the electrochemical performance. A change in the morphology and hence the electrochemical per- formance of the cathode material can be achieved by changing the ∗ Corresponding author. Tel.: +65 65162236; fax: +65 6779 1459. E-mail address: luli@nus.edu.sg (L. Lu). method of preparation. The influence of morphology of electro- active materials as determined by SEM/TEM on the electrochemical performance is available in the literature [2–4]. However, quan- titative information correlating the crystal shape of the cathode material to its electrochemical performance is not available as yet. This manuscript is our preliminary effort to quantitatively relate the electrochemical performance of a cathode material, such as LiMn 2 O 4 , with a spinel type structure and an Fd3m space group [5], prepared using different starting materials, to their crystal habits. Since LiMn 2 O 4 (A) and LiMn 2 O 4 (N) differ only in the nature of the starting materials used, it is reasonable to believe that a difference in the electrochemical behavior between these cathodes could arise mostly due to the differences in their morphology. We use the crystal shape algorithm [6] which simulates the crystal habit of LiMn 2 O 4 from the 2 and the full width at half maximum (FWHM) values for the X-ray reflections arising from the corresponding Miller indices of the material. DFT computations were carried out to compute the thermodynamic stabilities of the predominant hkl planes as identified by the crystal shape algorithm. It is well known in electrochemistry that many physical and electrochemical properties such as electronic work functions, cat- alytic rates of reactions and adsorption kinetics depend on the surface chemistry/physics. The same holds good with the elec- trochemistry of lithium batteries which needs the so-called 8a sites accessible to the Li ion coming from the electrolyte. Thus the Li intercalation depends not only on the surface density of 8a sites exposed on a given plane but also on the hindrance offered by the surrounding ions on the plane. Both the density and the 0921-5107/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2011.07.005