Crystal structures and electrochemical properties of LiAlyNi1−yO2 solid solution

We describe the synthesis, structure and electrochemical properties of LiAlyNi1−yO2 solid solutions. LiNiO2 charged to 4.1 V versus lithium metal can de-intercalate lithium to x=0.7 in Li1−xNiO2. Additional lithium can be removed above 4.1 V, but this degrades cell performance because the cathode structure is destabilized beyond x=0.7. In an overcharged Li1−xNiO2 cathode most of the nickel atoms are in the unstable Ni4+ state. Since LiAlO2 is isostructural with LiNiO2, we reasoned that substituting trivalent aluminium for nickel may limit the amount of lithium which can be withdrawn from the cathode. Single-phase LiAlyNi1−yO2 solid solutions were synthesized for y≤0.3. They were structurally characterized by X-ray diffraction and evaluated as the cathode in LiAlyNi1−yO2/Li coin cells. Although the substitution of aluminium for nickel had the desired effect of reducing the amount of lithium that can be removed on overcharge, it also reduced the reversible capacity of the cathode.