Structural, electrical and electrochemical behaviours of LiNi0·4 M 0·1Mn1·5O4 (M = Al, Bi) as cathode material for Li-ion batteries

In order to improve the cycling performance of LiMn2O4 based cathode materials, we have synthesized a new composition, LiNi0·4 M 0·1Mn1·5O4 (M = Al, Bi), by the sol–gel method. The formation of solid solutions is confirmed by structural characterization using TG/DTA, XRD, FT–IR, EPR, SEM and EPR. A.c.-impedance (Nyquist plot) showed a high frequency semicircle and a sloping line in the low-frequency region. The semicircle is ascribed to the Li-ion migration through the interface from the surface layer of the particles to the electrolyte. Cyclic voltammogram (between 3·5 and 4·9 V) for these materials using CR2032 coin-type cell shows two pairs of redox peaks corresponding to two-step reversible intercalation process, wherein Li-ions occupy two different tetragonal 8a sites in spinel Li x Mn2O4 (x < 1) lattice. The galvanostatic charge/discharge curves for M = Al (77 mAh g–1) showed reasonably good capacity retention than that of M = Bi (11 mAh g–1) at the end of 17th cycle.