INVESTIGATING THE NATURE OF LINE BROADENING IN ELECTROCHEMICALLY DELITHIATED Li-XmMnrXwNirX8CorX-Om

The anomalous line broadening behaviour exhibited by Li1.2Mn0.4Ni0.3Co0.1O2 during charging to high voltage (> 4.4V) has been investigated. Previous hypotheses attributing the phenomena to stacking faults can not explain all of the broadening features, as some of them (e.g. 003) disobey the selection rules expected of stacking faults in a cubic close-packed system (H-K = 3N ± 1). An alternative explanation has been developed, that describes the broadening in terms of an inhomogeneity of the residual lithium within the crystal structure. The hkl dependence of the broadening has been formulated in a reciprocal space relationship dependant on the c reciprocal space vector, L, and the distribution of lithium in the material δ. It was found that the observed asymmetry can be modelled using the same hkl relationship. The hkl-dependant broadening and asymmetry corrections have been added to Topas script files for structural Rietveld refinements in the R-3m space group. The inhomogeneity approach produced profile fits very similar to those obtained using a model-independent spherical harmonics correction for both broadening and asymmetry. This would suggest that lithium inhomogeneity is the dominant cause of broadening in these samples. INTRODUCTION Lithium-ion batteries have largely replaced nickel-cadmium and nickel-metal hydride batteries for consumer electronics applications. Ever increasing energy demands are being made by smaller and smaller devices. The increased energy density of lithium-ion technology has made them a natural successor in this market. Lithium ion batteries rely on the ‘shuttling’ of lithium ions between a positive cathode material and negative anode on charge and discharge. The deintercalation and intercalation processes have to be highly reversible to obtain long service life. One of the more costly components of a lithium-ion battery is the cathode material, usually a lithiated transition metal oxide such as LiCoO2. These materials have a layered structure for 149