ORIGINAL PAPER Influence of sol–gel derived lithium cobalt phosphate in alkaline rechargeable battery Manickam Minakshi • Sathiyaraj Kandhasamy Received: 27 December 2011 / Accepted: 22 June 2012 / Published online: 3 July 2012 Ó Springer Science+Business Media, LLC 2012 Abstract A lithium cobalt phosphate (LiCoPO 4 ) cathode was synthesised by citric acid assisted sol–gel method and its electrochemical behaviour in alkaline secondary battery (using novel lithium hydroxide as the electrolyte) is reported. The sol–gel method using metal acetate precur- sors with citric acid as a chelating agent influenced the particle size and the homogeneity while yielding a single phase LiCoPO 4 at a considerably lower temperature and shortened heating time, compared to that of the conven- tional solid state reaction. The cyclic voltammogram of LiCoPO 4 showed a reversible redox process implying that de-intercalation and intercalation of lithium can occur in aqueous electrolyte. This was supported by X-ray diffrac- tion (XRD) and Infra-red (IR) studies. The charge–dis- charge performance of the Zn/LiCoPO 4 battery showed good capacity retention (after 25 cycles it delivered 90 % of its initial capacity). This enhanced capacity retention was attributed to the synergistic effect of particle homo- geneity, reduced Li ? diffusion path and stability of the non-reactive aqueous electrolyte between the electrode and the electrolyte interface. Keywords LiCoPO 4 Á Sol–gel synthesis Á Aqueous electrolyte Á Battery 1 Introduction In today’s world, technological developments have increased the demand for batteries in high power applications. To meet this requirement, olivine-phase lithium transition metal phosphates, LiMPO 4 (M = Fe, Mn, Co and Ni), showed potential as cathode materials for rechargeable batteries [1]. High discharge rate, excellent capacity retention, high energy density and structural stability favours olivine-phosphates as next generation cathodes for high energy batteries [2]. Among the available olivine phosphates, lithium nickel phosphate (LiNiPO 4 ) is not attractive due to its high redox potential (*5 V vs. Li ? /Li). The currently available non- aqueous electrolytes are not stable beyond 4.5 V, hence, LiNiPO 4 was not proven to be suitable cathode for a bat- tery system. In the case of manganese and iron substitu- tions in the olivine phosphate, during oxidation the phase transition occurs in LiFePO 4 /FePO 4 and LiMnPO 4 /MnPO 4 which are isostructural with the same space group (Pnma) but the difference in cell parameters has been shown to be quite large i.e. 7 and 9 %, respectively [3, 4]. In the case of cobalt substitution, the phase transition occurs in LiCoPO 4 / CoPO 4 with the evolution of new secondary phase (Li 0.7 CoPO 4 ), nevertheless the difference in cell parameter is shown to be only 2 %. This smaller difference leads to lower energy loss in Li ? hopping [5, 6] and makes the LiCoPO 4 material versatile for battery applications. LiCoPO 4 cathode has excellent redox behaviour but its electronic conductivity need to be improved to achieve a full efficiency of this material. This limitation had been overcome through various processes including suitable doping [7], conductive carbon coatings [8], and carbon composites [9, 10]. In this context, sol–gel synthesis has unique advantages in fulfilling this limitation to achieve better electronic conductivity and controlled particle size with homogeneity [11]. The formation of a percolate net- work with carbon as the conducting agent gives high electronic conductivity [10, 11]. Here, we show that, by adding citric acid as a chelating agent and metal acetates as M. Minakshi (&) Á S. Kandhasamy School of Chemical and Mathematical Sciences, Murdoch University, Murdoch, WA 6150, Australia e-mail: minakshi@murdoch.edu.au; lithiumbattery@hotmail.com 123 J Sol-Gel Sci Technol (2012) 64:47–53 DOI 10.1007/s10971-012-2826-3