Evidence for Al doping in lithium sublattice of LiFePO4

In this work, we applied various measurement techniques in order to evaluate the possibility of the introduction of Al and its actual level at Li site in LiFePO4 positive electrode material for Li-ion batteries. Rietveld refinement of neutron diffraction data indicated that Al is incorporated into Li site, however, in lower amount than expected, and that lithium content is substantially depressed. The observed trends were qualitatively supported by results of ICP OES analysis. In addition, the oxygen content in Li1-3xAlxFePO4 was found to decrease with Al doping. The introduction of relatively small amount of dopant could be an effective route to produce single-phase, highly lithium-deficient lithium iron phosphate. Spectroscopic methods (EXAFS and XANES) do not allow to unambiguously confirm the substitution; nevertheless, all the obtained results are compatible with the substitution taking place. Interestingly, electrochemical studies indicated improvement of the performance of a LiFePO4 cathode material upon partial substitution of lithium by aluminum, possibly as the effect of increase of concentration of lithium vacancies. (C) 2014 Elsevier By. All rights reserved.