Effect of Mg doping and MgO-surface modification on the cycling stability of LiCoO2 electrodes

Two synthetic routes including Mg doping and MgO-surface modification were applied to the preparation of LiCoO2 showing enhanced reversible cycling behaviour as cathode material in lithium ion batteries. Mg-doped LiCoO2 was obtained by the citrate precursor method in the temperature range 750¯900°C. The surface of LiCoO2 was modified by coating with Mg (CH3COO)2 and subsequent heating at 600°C. XRD, chemical oxidative analysis and electron paramagnetic resonance (EPR) of Ni3+ spin probes were used to characterize the Mg distribution in LiCoO2. Substitution of Co by Mg in the CoO2-layers was found to have a positive effect on the cycling stability, while Mg dopants in LiO2-layers did not influence the capacity fade. The accumulation of MgO on the surface of LiCoO2 improves the cycling stability without loss of initial capacity.