Solid Solutions of () Obtained via a Combustion Synthesis Route and Their Electrochemical Characteristics

Pure, single-phase and layered materials with good cation ordering are not easy to synthesize. In this work, solid solutions of (x = 0, 0.1, …, 0.9) are synthesized using a self-propagating combustion route and characterized. All the materials are observed to be phase pure giving materials of hexagonal crystal system with R-3m space group. The RIR and R factor values of stoichiometries of (x = 0.1, 0.2, 0.3, 0.4, and 0.5) show good cation ordering. Their electrochemical properties are investigated by a series of charge-discharge cycling in the voltage range of 3.0 to 4.3？V. It is found that some of the stoichiometries exhibit specific capacities comparable or better than those of LiCoO2, but the voltage plateau is slightly more slopping than that for the LiCoO2 reference material. 1. Introduction Layered oxides are more advantageous over those of the spinels due to their higher theoretical specific capacities which are about double those of the spinels. The present commercial cathode material, LiCoO2, suffers from three major restrictions which are toxicity, cost, and scarcity. Therefore, it is logical to produce materials with less Co content [1] for commercial applications. LiNiO2 has the advantage of being cheaper, but it is more difficult to synthesize and does not cycle well [1, 2]. It is thermodynamically as well as electrochemically unstable [3]. Thus, it is unsuitable for use in commercial Li-ion batteries. Cobalt substitution in LiNiO2 is, however, more stable than its pure form [1]. can be a potential commercial cathode if a relatively simple synthesis method yielding pure single-phase compounds is found. Many groups of researchers [4–8] have attempted to synthesize some stoichiometries of , but their XRD results show the presence of impurities. Others such as Xie et al. [9] and Lu and Wang [10] have produced hexagonal structure but with poor cation ordering with high (104) peaks relative to the (003) peak. We present here a simple self-propagating combustion synthesis which produces pure, single-phase, and layered hexagonal-structured materials for the whole range of solid solutions of ( ) with relatively good cation ordering especially for materials with stoichiometries. Electrochemical behaviour of the materials was investigated, and it was found that some stoichiometries show comparable performance to LiCoO2 reference material. 2. Experimental ( ) materials were synthesized using a self propagating combustion method [11]. For the synthesis, lithium nitrate (LiNO3, Fluka), cobalt (II) nitrate hexahydrate (Co (NO3)3·6H2O, Aldrich), and