Lattice volume change during charge/discharge reaction and cycle performance of Li[NixCoyMnz]O2

The structural change of Li[NixCoyMnz]O2 cathode materials (x + y + z = 1) during the electrochemical delithiation/lithiation was studied with the in-situ X-ray diffraction. It was found that the cathode having the larger Ni fraction of Ni gave the larger unit cell volume change (ΔV) during the reaction. While the initial capacity increased with an increase in the Ni fraction, the capacity fading became much significant for the cathode with high Ni fraction. It was shown that the impedance originating from the cathode grew after the cycling and its degree increased with the Ni fraction. Additionally, micro-cracks were frequently observed for the cathode particles after the cycling evaluation, and the development feature of the micro-cracks was affected by the chemical composition of the cathode compounds. The capacity fading was discussed from the view-points of the lattice volume change, the impedance growth and the microstructure variation.