The deposition of Li2O2 and Li2O will advance simultaneously if Li2O formation is favored over Li2O2 formation on the ATO surface, but Li2O2 buildup on top of Li2O is kinetically favored over further Li2O deposition on ATO. As both products are electrically insulating, the Li2O/Li2O2 ratio and the discharge capacity are determined by the total thickness of the Li2O/Li2O2 layer that provides enough electrical resistance to prevent any further deposition of Li2O2 on top. This is an analog to the widely accepted capacity limitation by Li2O2 resistivity observed for carbon cathodes. The approximate layer thicknesses on discharged electrodes in ML shown are calculated from the 1st discharge capacities of ∼792 μC/cm2BET for ATO (from this work) and ∼474 μC/cm2BET for Vulcan carbon. With ATO, 44 and 42% of the 1st discharge capacity are stored in Li2O2 and Li2O, respectively. With Vulcan Carbon, 92% and 8% are stored in Li2O2 and Li2CO3, respectively. We assume that 260, 300, and 150 μC/cm2BET are required to form one Li2O2, Li2O, and Li2CO3 monolayer, respectively. These numbers are derived from the calculated number of unit cells per cm2 of electrode surface according to the lattice parameters of each salt, as described in our previous work and the SI of this work. The same surface-normalized discharge rate was applied in Ref. and this work to ensure comparability. Though the depicted layer thicknesses should only be regarded as rough estimations, it is most likely that the Li2O surface film on ATO is much more continuous than the partial Li2CO3 boundary layer on Vulcan carbon.
In contrast, the average thickness of the Li2O2 layer seems to be comparable on both cathode materials. As expected at low discharge rates in glyme electrolytes under water-free conditions, no toroidal or disc-shaped deposits of discharge products can be observed by SEM on the surface of carbon or ATO cathodes (not shown). If you are looking for high quality, high purity, and cost-effective ATO, or if you require the latest price of ATO, please feel free to email contact mis-asia.
