Crystal structures and electrochemical properties of LiAl yNi 1− yO 2 solid solution

Abstract

We describe the synthesis, structure and electrochemical properties of LiAl y Ni 1− y O 2 solid solutions. LiNiO 2 charged to 4.1 V versus lithium metal can de-intercalate lithium to x=0.7 in Li 1− x NiO 2. 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 Li 1− x NiO 2 cathode most of the nickel atoms are in the unstable Ni 4+ state. Since LiAlO 2 is isostructural with LiNiO 2, we reasoned that substituting trivalent aluminium for nickel may limit the amount of lithium which can be withdrawn from the cathode. Single-phase LiAl y Ni 1− y O 2 solid solutions were synthesized for y≤0.3. They were structurally characterized by X-ray diffraction and evaluated as the cathode in LiAl y Ni 1−y O 2 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.