Electrochimica Acta 123 (2014) 378–386 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom ep age: www.elsevier.com/locate/elec tacta Improved electrochemical activity of nanostructured Li 2 FeSiO 4 /MWCNTs composite cathode Shivani Singh, Sagar Mitra ∗ 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 11 November 2013 Received in revised form 21 December 2013 Accepted 6 January 2014 Available online 22 January 2014 Keywords: Cathode material Electrical conductivity Lithium-ion batteries Li2FeSiO4 Multi-walled carbon nanotubes a b s t r a c t Electrochemical activity of nano Li 2 FeSiO 4 material with the Pmn2 1 symmetry is reported against lithium. Small amount of carboxylic group impurity distributed heterogeneously over the Li 2 FeSiO 4 surface is concluded with Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The electrode material with Pmn2 1 symmetry is prepared by simple sol-gel technique and further modified with multi-walled carbon nanotubes (MWCNTs) to achieve better electron passage to the particle-particle boundaries. Our strategy helps to improve the electrochemical performance and storage capacity to a level compared to bare material. The Li 2 FeSiO 4 /MWCNT composite electrode deliv- ered first discharge capacity of 240 mAh g -1 at 16.5 mA g -1 , when it is cycled between 1.5 V- 4.8 V at 20 ◦ C. This indicates more than one lithium is extracted. The voltage plateau of second charge is different and lower than that of first charge plateau whereas first and second discharge plateaus are almost similar, structural rearrangement involving the lithium and iron exchange between their sites and pre-activation during first oxidation step are the possible reasons for this phenomenon. Since silicates are inexpensive compared to other electrode materials, we have undertaken this work to improve the electrochemical activity and power performance by nanosizing of particle and adding MWCNTs as conductive additives. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Energy security is probably one of the most important pillars for successful modern economies. Finiteness of fossil fuels is an impending threat that looms over today’s world, making it really important to search for other energy alternatives. Electrochemical energy storage technologies such as Li-ion battery and electro- chemical capacitors are among those promising alternatives. Li-ion batteries have been in use for quite some time in portable electronic devices. However, it’s high time that they should move up in the hierarchy and present themselves as an attractive alternative for high scale energy applications such as electric vehicles. To make Li-ion battery greener and sustainable source of energy, research is directed to increase the energy density, lower its cost and improve safety, which are few fundamental challenges. Cathode of a Li-ion battery plays a pivotal role in increasing energy density and life cycle. As reported by Tarascon et.al. that in order to improve energy density of battery by 57%, cathode capacity needs to be doubled whereas an anode needs to have an enhanced capacity by 10 times to increase energy density by 47% [1,2]. Hence, it is quite obvious that the key to achieve high energy density bat- tery lies in the choice of a promising cathode material. Lithium ∗ Corresponding author. Tel.: +91 222576 7849; fax: +91 22 2576 4890. E-mail address: sagar.mitra@iitb.ac.in (S. Mitra). based orthosilicates (Li 2 MSiO 4 ; where M = Fe, Ni, Mn) as cathode materials is definitely one class of such materials. Silicate materi- als can deliver a theoretical capacity up to 333 mAh g -1 when two Li ions are extracted from the host matrix [3]. Moreover, iron and silicon are among the most abundant, non-toxic and economical elements which lead to lower cost and safe cathode material for high energy applications. Li-Fe-Si-O system has same lattice stabi- lization as in the case of LiFePO 4 because of strong Si-O bond leading to thermal stability [4]. Furthermore, silicates also show polymor- phism, three commonly reported polymorphs of silicate (Li 2 MSiO 4 ) are Pmn2 1 , Pmnb (orthorhombic) and P2 1 /n (monoclinic). The cation within the tetrahedral sites can order themselves in different ways leading to polymorphism [5–8]. Apart from various advantages, it suffers from low electrical conductivity [9], which leads to poor rate performance. It is well reported in literature that poor elec- trical conductivity can be overcome by nanostructuring and using carbon additives [10–12]. Since, electrical conductivity is an intrin- sic property of a material therefore it is difficult to change such property. However, claims have been made in the literature and that the enhanced electrochemical activity can be achieved by few factors like 1) providing proper channels for electron and ions to react inside the material (by nanostructuring process) and 2) con- ductive carbon coating on electrode material, which would benefit the electron transfer to the adjacent particles, thereby making elec- tronic bridge between them and hence reducing grain boundary impedance for mass and electron transfer [13,14]. 0013-4686/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2014.01.045