Co-substituted LiLax-yLiyNi1-xO2 cathode materials were synthesized by sol-gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 degrees C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using XRD, SEM, EDAX, TEM, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy. XRD studies revealed a well defined layer structure and a linear variation of lattice parameters with the addition of lanthanum and lithium confirmed phase pure compounds in a rhombohedral structure. TEM and SEM analysis shows that LiLa0.10Li0.10Ni0.80O2 has smaller particle size and regular morphological structure with narrow size distribution than those of LiNiO2. Variations of dual mixing and hexagonal ordering with the substituted elements have enhanced the charge/discharge capacities at both room (25 degrees C) and elevated temperatures (45 degrees C), respectively. LiLa0.10Li0.10Ni0.80O2 had high charge/discharge capacity, low irreversible capacity and better elevated temperature performance. (C) 2013 Elsevier Ltd. All rights reserved.