Sol-gel synthesis of LiCoO₂ and LiCo₀.₄Ni₀.₆O₂, their electrochemical performances and applications in Li-Ion batteries as cathode material

Abstract

Lithium cobalt oxide (LiCoO₂) is extensively used as a cathode material in commercially available Li-ion batteries due its high energy density and good cycle-life performances. However, the high cost of this material and toxicity of cobalt are some drawbacks. Recently, the cathodes of the type LiMₓNiᵧ0₂ where M is one of the transition or alkaline earth metals are being extensively used as less-costly cathodic material in Li-ion batteries. The aims of the present work are to study the structural and electrochemical properties of LiCoO₂ and lithiated nickel cobalt oxide, LiCo₀.₄Ni₀.₆O₂, and to assess their applications in Li-ion batteries. LiCoO₂ and LiCo₀.₄Ni₀.₆O₂ were synthesized by using the sol-gel technique. The properties of the compounds were studied using XRD, ITIR and DSC. The oxides LiCoO₂ and LiCo₀.₄Ni₀.₆O₂ were used as cathode materials for rechargeable lithium-batteries and their electrochemical performances were studied. The potentiostat and galvanostat techniques were used to determine the electrochemical characteristics. The discharge capacities of the LiCoO₂ were 155 and 145 mA h g⁻¹ of the LiCo₀.₄Ni₀.₆O₂ were 19 and 15 mA h g⁻¹ for the 1st and 15th cycles, respectively. The overall electrochemical capacity of LiCo₀.₄Ni₀.₆O₂ oxide has been drastically reduced due to the s-block or p-block metal substitution and impurity remained during the synthesis and showed very poor cycleability. However, more stable charge-discharge cycling performances have been observed for LiCoO₂ oxide at different current rates. Differences and similarities between these two cathode materials are also discussed. Using the synthesized LiCoO₂ as the cathode and natural untreated vein graphite of Sri Lanka as anode with 1 M LiPF₆ in EC/DMC as liquid electrolyte Li-ion batteries were assembled and tested.