A comparative study on the substitution of divalent, trivalent and tetravalent metal ions in LiNi1−xMxO2 (M = Cu2+, Al3+ and Ti4+)

Stabilized lithium nickelate is receiving increased attention as a low-cost alternative to the LiCoO2 cathode now used in lithium batteries. Layered LiNi1−xMxO2 samples (M= Cu2+, Al3+ and Ti4+, 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 Cu2+-substituted samples showed poor structural stability and electrochemical performance, while the Al3+- and Ti4+-substituted samples formed highly ordered and phase-pure layered compounds. Of the three compounds tested, the LiNi1−xTixO2 electrodes exhibited the highest capacity and best electrochemical reversibility. Indeed, the LiNi0.975Ti0.025O2 electrode achieved the highest reversible capacity and energy density (900 Wh/kg) of all known layered LiNiO2 or LiCoO2 electrodes. Indications are that the structural integrity of the LiNi1−xTixO2 materials was preserved because the Ti4+ ions prevented impurity Ni2+ 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.