ATO with a specific surface area

We have established a straightforward synthesis protocol for highly conductive nanocrystalline ATO with a cassiterite crystal structure and an Sb doping level of 5 mol%. The employed hydrothermal synthesis uses low-cost chloride-free precursors and yields nanocrystalline ATO with a specific surface area of 190 m2/g and a mean primary particle size of 4.5 nm. Subsequent calcination at 600°C in the air increases the conductivity by four orders of magnitude to 2 S/cm, which is sufficient for an application as cathode material for Li-O2 batteries. Additional low-energy wet ball milling is suitable to break up agglomerates of several hundred micrometers formed during calcination, thus limiting the maximum agglomerate size to 15 μm. This allows us to produce smooth ATO electrode coatings with low PTFE binder content. In aprotic Li-O2 battery cells, a different discharge product distribution is obtained with ATO cathodes than with carbon cathodes. We propose that a Li2O boundary layer is formed on the ATO surface in analogy to the Li2CO3 layer formed on carbon, with Li2O2 deposited on top in one continuous discharge process. Li2O2 and Li2O are decomposed in two consecutive charge processes at ∼3.3 V and ∼5.2 V. Although the Li2O charging potential is too high for any currently available electrolyte to withstand, future combination with catalysts that lower the Li2O charging potential without lowering the electrolyte oxidation potential may lead to a practically rechargeable cell with a potentially higher energy density than a cell producing only Li2O2.

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