Here,
as with previous work, atomic layer deposition (ALD) has been used
to deposit Al2O3 on positive electrode active
materials, LiCoO2, to create a protective barrier layer,
suppress the high potential phase transition, and thus reduce the
subsequent Co dissolution. However, in this study it was found that
it also resulted in the reduction of the charge transfer resistance
at the positive electrode–electrolyte interface, thus enhancing
the performance of the battery. Energy-dispersive X-ray spectroscopy,
in conjunction with transmission electron microscopy, shows that a
discrete Al2O3 shell was not formed under the
selected growth conditions and that the Al diffused into the bulk
LiCoO2. The resulting active oxide material, which was
significantly thicker than the nominally ALD growth rate would predict,
is proposed to be of the form LiCoO2:Al with amorphous
and crystalline regions depending on the Al content. The cells consisting
of the modified electrodes were found to have good cycling stability
and discharge capacities of ∼110 mA h g–1 (0.12 mA h cm–2) and ∼35 mA h g–1 (0.04 mA h cm–2) at 50 and 100 C, respectively.
The Aurivillius layer-structures, described by the general formula Bi2O2(Am-1BmO3m+1), are naturally 2-dimensionally nanostructured. They are very flexible frameworks for a wide variety of applications, given that different types of cations can beaccommodated both at the A- and B-sites. In this review article, we describe how the Aurivillius phases are a particularly attractive class of oxides for the design of prospective single phase multiferroic systems for multi-state data storage applications, as they offer the potential to include substantial amounts of magnetic cations within a strongly ferroelectric system. The ability to vary m yields differing numbers of symmetrically distinct B-site locations over which the magnetic cations can be distributed and generates driving forces for cation partitioning and magnetic ordering. We discuss how out-of-phase boundary and stacking fault defects can further influence local stoichiometry and the extent of cation partitioning in these intriguing material systems.
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