Effect of Ni and Ti substitutions on Li1.05Mn2O4-δ electrical conductivities at high temperature

Abstract

Abstract Samples of Li 1.05 Mn 2 O 4-δ , Li 1.05 Mn 1.5 Ni 0.5 O 4-δ , and Li 1.05 Mn 1.0 Ni 0.5 Ti 0.5 O 4-δ were prepared by a solid-state reaction technique and ultimately refined to a space group Fd −3 m of spinel structure by the Rietveld method using synchrotron powder X-ray diffraction data. Comparison of lattice constants suggested that Ni-substitution increased the covalency in the bonding of MO 6 (M: metal ion at 16 d site) octahedrals, but Ni/Ti co-substitution decreased the covalency of M–O bonds and introduced structural distortion. Electrical conductivity measurements by a four-probe method resulted in the determination that electrical conduction (within all samples) exhibits a nonadiabatic hopping process at high temperatures. The activation energies of Li 1.05 Mn 2 O 4-δ and Li 1.05 Mn 1.5 Ni 0.5 O 4-δ were found to be of similar values. The Ni/Ti co-substituted sample of Li 1.05 Mn 1.0 Ni 0.5 Ti 0.5 O 4-δ , on the other hand, showed the highest activation energy among all the measured samples. Substitution reduced the electrical conductivity relative to Li 1.05 Mn 2 O 4-δ ; furthermore, both the substituted samples (Li 1.05 Mn 1.5 Ni 0.5 O 4-δ and Li 1.05 Mn 1.0 Ni 0.5 Ti 0.5 O 4-δ ) were found to exhibit functional independence from oxygen partial pressure ( P O2 ).