Synthesis and Characterization of Lithium- Manganese Rich Cathode Materials for Lithium Ion Batteries

Abstract

In this study 0.5LiMn 2 O 3 .0.5LiNi 1/3 Mn 1/3 Co 1/3 O 2 , a layered lithium-manganese rich nickel manganese cobalt (LMR-NMC) oxide, was a carefully selected composition for use as a cathode material in Li ion batteries. The effect of synthesis method and doping on this layered lithium-manganese rich, mixed metal oxides is presented. First part of this study deals with the effect of synthesis route on the electrochemical properties of the 0.5LiMn 2 O 3 .0.5LiNi 1/3 Mn 1/3 Co 1/3 O 2 material. A comparison between Co- precipitation, low temperature (90C) sol-gel synthesised and high temperature (120C) sol- gel synthesised LMR composite materials is presented. The study demonstrated that synthesis procedure and conditions strongly influence the electrochemical properties of the synthesized material. Co-precipitation and sol-gel synthesised LMR composites revealed obvious differences in capacity and cycle life, which give the impression from X-ray photoelectron spectra to be strongly related to the particles‘ surface reactivity. In the second part of study, the LMR-NMC materials were doped with varying amounts of aluminium. Small amounts of Al doping to the sol-gel material were shown to improve the rate capability and cyclability, in addition to decreasing voltage fade. The results were interpreted in terms of charge discharge studies and supported by differential capacity plots, impedance measurements and cyclic voltammetry data. The electrochemistry of an aluminium doped material was revealed to be highly dependent on the degree of aluminium doping – with the behaviour of 1% doped material giving a maximum capacity of 201 mAhg -1 at 150 mAg -1 and a capacity retention of 88% after 200 cycles. An attempt has been made to study the effect of Cr doping as well on the electrochemical properties of the LMR-NMC materials. It results in an increase in the initial charge/discharge capacity of the material while decreasing the capacity retention. However, the Cr as a dopant could not be assigned as an improvement in the LMR mixed metal oxide material. The study established the comparative role of co-precipitation and sol-gel methods on the improvement of electrochemical properties of the LMR-NMC oxides. Additionally, controlled Al doped samples substantially improved the discharge capacity while maintaining capacity retention event at very high C-rate.