Studies on the local structures for the trigonal Ni3+ centers in cathode materials LiAlyCo1-yO2 (y = 0, 0.1, 0.5, and 0.8).

The local angular distortions Δθ are theoretically studied for the various Ni3+ centers in LiAlyCo1-yO2 at different Al concentrations (y = 0, 0.1, 0.5, and 0.8) based on the perturbation calculations of electron paramagnetic resonance g factors for a trigonally distorted octahedral 3d7 cluster with low spin (S = 1/2). Due to the Jahn-Teller effect, the [NiO6]9- clusters are found to experience the local angular distortions (Δθ ≈ 5°-9°) along the C3 axis. The variation trend of Δθ with y is in accordance with that of anisotropy (Δg = g|| - g⊥). As the substitutions can weaken bond strengths between transition metal and oxygen and the structural stability plays an important role in cathode performances, detailed investigations on the structural properties of the cathode materials LiAlyCo1-yO2 can be practically helpful to understand the performances of these materials. The oxy-redox properties of LiAlyCo1-yO2 systems are comprehensible in the framework of Ni3+/Ni4+ couples, and the trigonally compressed octahedral [NiO6]9- clusters are applicable to the clarification of the electrochemical properties of lithium nickel oxide batteries. It appears that LiAl0.8Co0.2O2 with the largest Al concentration may correspond to the smallest distortion among the mixing systems. [ABSTRACT FROM AUTHOR]