Electrochemical behaviour of Al-doped Li(Ni0.5-xAl2xMn0.5-x)O2 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.