Electrochemical behaviour of Al-doped Li(Ni<inf>0.5-x</inf>Al<inf>2x</inf>Mn<inf>0.5-x</inf>)O<inf>2</inf> with large Al content by the sol-gel method

Layered Li(Ni _0.5-x Al _2x Mn _0.5-x )O ₂ (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(Ni _0.5 Mn _0.5 )O ₂ , the discharge capacity of Li(Ni _0.4 Al _0.2 Mn _0.4 )O ₂ 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(Ni _0.5-x Al _2x Mn _0.5-x )O ₂ not only replaces Ni ²⁺ as an active materal, but also can substitute Mn ⁴⁺ used for supporting structure. Moreover, the electrochemical impedance spectra of the samples are also discussed.