Electrochemical behaviour of Al-doped Li(Ni0.5-xAl2xMn0.5-x)O2 with large Al content by the sol-gel method

Layered Li(Ni0.5-xAl2xMn0.5-x)O2 (x=0 and 0.1) (Mn/Ni = 1) were synthesized by sol-gel method using citric acid as a chelating agent. The Structure, electrochemical properties of prepared cathode materials were measured by means of X-ray diffraction, cyclic voltammetry, galvanostatic charge-discharge test and AC impedance spectra. The measured results indicate that, (1) the Al-doped sample has the better layered-structure; (2) compared to Li(Ni0.5Mn0.5)O2, the discharge capacity of Li(Ni0.4Al0.2Mn0.4)O2 is evidently increased and reaches 160 mAhg⁻¹ between 2.8 and 4.2V at the rate of 20 mAg⁻¹; (3) Al ion in Li(Ni0.5-xAl2xMn0.5-x)O2 not only replaces Ni²⁺ as an active materal, but also can substitute Mn⁴⁺ used for supporting structure. Moreover, the electrochemical impedance spectra of the samples are also discussed.