A comparative study on the substitution of divalent, trivalent and tetravalent metal ions in LiNi 1− xM xO 2 (M = Cu 2+, Al 3+ and Ti 4+)

Abstract

Stabilized lithium nickelate is receiving increased attention as a low-cost alternative to the LiCoO 2 cathode now used in lithium batteries. Layered LiNi 1− x M x O 2 samples (M= Cu 2+, Al 3+ and Ti 4+, where 0.025≤ x≤0.2) were prepared by solid state reaction at 750 °C under an oxygen stream and subjected to powder X-ray diffraction analysis and coin-cell tests. The Cu 2+-substituted samples showed poor structural stability and electrochemical performance, while the Al 3+- and Ti 4+-substituted samples formed highly ordered and phase-pure layered compounds. Of the three compounds tested, the LiNi 1− x Ti x O 2 electrodes exhibited the highest capacity and best electrochemical reversibility. Indeed, the LiNi 0.975Ti 0.025O 2 electrode achieved the highest reversible capacity and energy density (900 Wh/kg) of all known layered LiNiO 2 or LiCoO 2 electrodes. Indications are that the structural integrity of the LiNi 1− x Ti x O 2 materials was preserved because the Ti 4+ ions prevented impurity Ni 2+ migration into the lithium sites. The substitution of tetravalent titanium into lithium nickelate has proved to yield promising cathode materials and further studies are needed to optimize electrode composition and processing conditions.