Structural and electrochemical characterization of lithium excess and Al-doped nickel oxides synthesized by the sol-gel method

The effects of excess lithium and aluminum doping in nickel oxide were investigated in an attempt to improve electrochemical properties of the layered LiNiO₂. Li_1+xNiO₂ (x = 0-0.02) and LiAl_yNi_1-yO₂ (y = 0-0.3) powders were synthesized by a sol-gel method using adipic acid as a chelating agent. The electrochemical properties of the synthesized materials were explored at room and high temperatures. Gas analysis during decomposition of gel precursors revealed that oxygen might play an important role in the synthesis of highly crystallized LiNiO₂. Although the electrochemical test of the Al-doped samples showed a low initial discharge capacity of about 140 mAh g^-1, the capacity loss with repeated cycling was very small at room temperature. Furthermore the fade in capacity of this cell at high temperature (50 °C) was almost negligible. The Al-doping of the LiNiO₂ cathode material was very effective in improving cycle performance at high temperature due to the enhanced stability of LiNiO₂ structure.