Electrochimica Acta 143 (2014) 152–160 Contents lists available at ScienceDirect Electrochimica Acta j our na l ho me pa g e: www.elsevier.com/locate/electacta Porous lithium rich Li 1.2 Mn 0.54 Ni 0.22 Fe 0.04 O 2 prepared by microemulsion route as a high capacity and high rate capability positive electrode material Tirupathi Rao Penki, D. Shanmughasundaram, N. Munichandraiah ∗ Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore - 560012, India a r t i c l e i n f o Article history: Received 12 June 2014 Accepted 28 July 2014 Available online 13 August 2014 Keywords: Lithium rich manganese oxides Ferrite composites Inverse microemulsion Porous materials High discharge capacity High rate capability. a b s t r a c t A porous layered composite of Li 2 MnO 3 and LiMn 0.35 Ni 0.55 Fe 0.1 O 2 (composition:Li 1.2 Mn 0.54 Ni 0.22 Fe 0.04 O 2 ) is prepared by inverse microemulsion method and studied as a positive electrode material. The pre- cursor is heated at several temperatures between 500 and 900 ◦ C. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies suggested that well crystalline sub- micronsized particles are obtained. The product samples possess mesoporosity with broadly distributed pores around 10∼50 nm diameter. Pore volume and surface area decrease by increasing the tempera- ture of preparation. However, the electrochemical activity of the composite samples increases with an increase in temperature. The discharge capacity values of the samples prepared at 900 ◦ C are about 186 mAh g -1 at a specific current of 25 mA g -1 with an excellent cycling stability. The composite sample also possesses high rate capability. The high rate capability is attributed to the porous nature of the material. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Research activities on lithium-ion batteries have been exten- sive in the recent past because of their attractive energy density [1]. These batteries are used successfully in small sizes at present and they are anticipated to be useful in large sizes for future applications such as electric vehicles. Although the energy density of the present Li-ion batteries is the highest among the exist- ing rechargeable batteries, applications such as electric vehicles require still greater energy density. The commercially available electrode materials in the market such as LiCoO 2 , LiMn 2 O 4 , LiFePO 4 and LiMn 1/3 Co 1/3 Ni 1/3 O 2 deliver discharge capacity of 140, 130,170 and 160 mAh g -1 , respectively, typically at C/10 rate [2]. The lithium rich transition metal oxide, namely, Li 2 MnO 3 is a potentially important cathode material for the next generation lithium-ion battery [3]. In addition to its very high theoretical capacity (460 mAh g -1 ), Li 2 MnO 3 is inexpensive and environmental friendly. Li 2 MnO 3 has layered structure similar to LiCoO 2 , but elec- trochemically inactive. As the oxidation state of Mn in Li 2 MnO 3 is +4 state, it cannot undergo further oxidation to +5 state when Li is extracted from it during charging [4]. To overcome this problem, ∗ Corresponding author. E-mail addresses: muni@ipc.iisc.ernet.in, tiru.penki@gmail.com (N. Munichandraiah). Li 2 MnO 3 is integrated with LiMO 2 (M= Co, Ni, Mn, etc.) and such a composite becomes electrochemically active [5,6]. These compos- ites have been considered as promising positive electrode materials for the next generation lithium ion batteries, because of their high capacity and good cycling stability [7–11]. Novel positive electrode materials based on solid solutions of Li 2 MnO 3 and LiMO 2 delivered discharge capacity values greater than 200 mAh g -1 for M= Co[10,11], Fe[12], Ni[13], Cr[14]. Thack- eray et al., studied a composite of Li 2 MnO 3 and LiMn 0.5 Ni 0.5 O 2 and reported that cations of the transition metal layers were not homogenously distributed in solid solutions, but were distributed in an irregular manner in domains with short range disorder [7]. Amalraj et al., prepared the Li 2 MnO 3 with LiMn 1/3 Ni 1/3 Co 1/3 O 2 by self-combustion reaction route, and obtained a capacity of 250 mAh g -1 [15]. On initial charging, extraction of lithium occurs from LiMO 2 (M= Ni, Mn, Co) component by oxidation of Ni 2+ and Co 3+ ions below 4.5 V. At potentials above 4.5 V, Li 2 O extraction occurs from Li 2 MnO 3 , thus converting the inactive component into an electrochemically active phase during the first charging process [15]. Composites of Li 2 MnO 3 with layered compounds consisting of Fe are attractive because of low cost, environmental compatibil- ity and safety. Moreover, the Fe and Ni cosubstituted L 2 MnO 3 has a high average potential compared to pristine Li 2 MnO 3 . Tabuchi et al., reported (Li 1+x (Fe y Mn 1-y ) 1-x O 2 (0≤x≤1/3, 0.3≤y≤0.7) samples as 4 V cathode materials, which were prepared by http://dx.doi.org/10.1016/j.electacta.2014.07.155 0013-4686/© 2014 Elsevier Ltd. All rights reserved.