High capacity surface route discharge at the potassium-O2 electrode

Abstract

Discharge by a surface route at the cathode of an aprotic metal-O2 battery typically results in surface passivation by the non-conducting oxide product. This leads to low capacity and early cell death. Here we investigate the cathode discharge reaction in the potassium-O2 battery and demonstrate that discharge by a surface route is not limited to growth of thin (<10 nm) metal oxide layers. Electrochemical analysis and in situ Raman confirmed that the product of the cathode reaction is a combination of KO2 and K2O2, depending on the applied potential. Use of the low donor number solvent, acetonitrile, allows us to directly probe the surface route. Rotating ring-disk electrode, electrochemical quartz crystal microbalance and scanning electron microscope characterisations clearly demonstrate the formation of a thick > 1 µm product layer, far in excess of that possible in the related lithium-O2 battery. These results demonstrate a high-capacity surface route in a metal-O2 battery for the first time and the insights revealed here have significant implications for the design of the K-O2 battery.

A Functionally Graded Cathode Architecture for Extending the Cycle‐Life of Potassium‐Oxygen Batteries

“…At the end of cycling the membrane in battery charging/discharging tests, the cathodes are rinsed in DME, and a post-mortem SEM and EDX of the PPy side is performed. [27] In the characterization studies reported in this paper, the discharge potentials largely remain outside of this window (in charge/discharge data in Figure 4) and therefore KO 2 is the expected discharge product. This indicates that KO 2 is formed at the cathode/ separator interface and not just at the air-facing side of the cathode.…”

“…It should also be noted that recent reports indicate the formation of K 2 O 2 at low potentials (~2.25 V vs K/ K + ) on gold electrodes in acetonitrile. [27] In the characterization studies reported in this paper, the discharge potentials largely remain outside of this window (in charge/discharge data in Figure 4) and therefore KO 2 is the expected discharge product. Previous studies have shown that the average crystal size of KO 2 decreases with increasing discharge rate.…”

Strategies Toward Stable Nonaqueous Alkali Metal–O2 Batteries

“…Nonetheless, the reaction pathways can also be tuned similarly. For example, Bruce's group found that the surface route can achieve high discharge capacity in K–O 2 battery, which was entirely different from that in Li–O 2 and Na–O 2 systems . Although the mechanism remains obscure, it may provide some helpful information in developing high‐performance K–O 2 battery.…”

Alkali‐Oxygen Batteries Based on Reversible Superoxide Chemistry

“…Due to the kinetic preference for superoxide and enhanced stability of KO 2 with respect to its peroxide, the potassium‐oxygen battery has demonstrated selectivity for KO 2 formation. Only in the case of a gold electrode has potassium peroxide been reported, indicating that pursuing electrodes with higher catalytic activity may result in the formation of undesired potassium peroxide …”

“…Only in the case of ag olde lectrode has potassium peroxide been reported, indicating that pursuing electrodes with higher catalytic activity may result in the formation of undesiredp otassium peroxide. [40] The formation and morphology of KO 2 has been investigated as af unctiono fa ppliedc urrent and solvent. The discharge current or growth rate of KO 2 can affect the crystallite size distribution ( Figure 8).…”