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Electrochemical cycling of ATO cells

The upper panel shows a representative voltage profile of the first discharge-charge cycle of Li-O2 cells with ATO cathodes, with marked states of charge (SOC) for the subsequent analysis of discharge products #1, #2, and #3. The lower panel depicts the specific discharge capacity as a function of cycle number, with the corresponding voltage profile for the first three cycles shown in the inset. The discharge of Li-O2 cells with ATO cathodes is characterized by a sloping potential rather than a plateau, starting at 2.6 V and declining with increasing steepness until the cutoff of 2.0 V is reached. First discharge capacities typically reach 110 ± 30 mAh/gATO (792 ± 216 μC/cm2BET) (result obtained from 15 cells). Normalized to the cathode's BET surface area, the first discharge capacities obtained with ATO are slightly superior to those with Vulcan carbon cathodes, typically at 183 ± 50 mA/gCarbon (474 ± 130 μC/cm2BET). The charging initiates at a potential plateau of 3.3 V, after which the potential rises to approx. 5 V, at which point 48 ± 6% of the 1st discharge capacity has been recovered (result obtained from 5 cells); subsequently, a charging plateau of around 5.2 V is observed. To avoid overcharging beyond this point, capacity-limited charging is applied instead of a voltage cutoff, which stops the charge once the previous discharge capacity is recharged. Given that only a partial recharge is possible in a potential window up to 4.7 V, the uppermost potential up to which the diglyme electrolyte is expected to be stable, the rapid capacity fading within the first three charge/discharge cycles ending at 5.2 V is not surprising. However, it is noteworthy that unlike cells with carbon cathodes, which exhibit an initial capacity increase over cycles 2–5 due to the formation of electrolyte degradation products that hinder passivation by Li2O2 growth, no such effect is seen with ATO cathodes. This indicates substantial differences in the extent and the electrolyte degradation products on ATO versus carbon surfaces. The striking fact that the 1st discharge capacity is almost completely recovered in cycle two but severely compromised in cycle three corresponds to the voltage rising to > 4.5 V in the 2nd charge. It will be further rationalized in the Section Rechargeability of discharge products. 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.

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