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

Abstract

Potassium-Oxygen (KÀ O 2 ) batteries have a high theoretical energy density of 935 Wh kg À 1 due to a single-electron redox process in the reversible formation of potassium superoxide. Despite this advantage, standard KÀ O 2 batteries have limited cycle-life (5-10) due to molecular oxygen crossover from cathode to anode, resulting in side reactions forming undesired superoxide on the anode. In this article, a KÀ O 2 battery fabricated with a functionally-graded cathode (FGC) architecture is presented to address oxygen crossover at the cathode. This KÀ O 2 battery lasts > 125 cycles with minimal loss in coulombic efficiency when charged/discharged to 300 μAh (238 μAh cm À 2 ). The FGC is comprised of a carbon fiber layer, microporous carbon and polypyrrole doped with hexafluorophosphate. It provides a scalable architecture for regulating K + ion and oxygen transport at the cathode trilayer (liquid-solidair) interface. The PPy(PF 6 ) formed on the cathode is observed to have an ORR rate two orders greater than that of carbonbased electrodes, as it promotes the reversible formation of potassium superoxide at the cathode, minimizes the transport of molecular oxygen into the electrolyte, and subsequently improves anode stability and cycle-life of the KÀ O 2 battery. These improvements in performance with FGC come at a marginal increase in KÀ O 2 battery material cost, which is estimated to be $44 kWh À 1 . The combination of performance and cost kWh À 1 makes this architecture the most cost-effective electrochemical energy storage device for stationary applications.

Carbon‐based cathode materials for rechargeable zinc‐air batteries: From current collectors to bifunctional integrated air electrodes

“…Carbon-based materials offer a new avenue to the integrated GDEs in practical rechargeable ZABs, which can also be expanded to other metal-air battery chemistries. 109,110 Some development directions for follow-up are listed below:…”

“…Based on these principles, proper selection and fabrication of carbon‐based materials would be very promising to design a unique interphase between air, cathode, and electrolyte in the rechargeable ZABs. Carbon‐based materials offer a new avenue to the integrated GDEs in practical rechargeable ZABs, which can also be expanded to other metal‐air battery chemistries 109,110 . Some development directions for follow‐up are listed below: Devices with stretchability and flexibility have shown great prospects in various technologies, 111 triggering the hot research topic of flexible ZAB 112 .…”

Prospects of Electrode Materials and Electrolytes for Practical Potassium‐Based Batteries

“…The conversion materials, such as, chalcogen elements (O 2 , [36,38,[127][128][129][130][131] S, [41,42,[132][133][134][135][136][137] Se, [138][139][140][141][142][143] Te [144,145] ), CO 2 , [39,40] and I 2 , [146,147] usually possess a high theoretical capacity and operating voltage when used as a cathode for PIBs, leading to a high theoretical energy density. Also, the low-cost and potential economic advantages of conversion materials make them more attractive in large-scale EESs.…”

Critical advances in re-engineering the cathode-electrolyte interface in alkali metal-oxygen batteries

“…Researchers have improved the cathode-electrolyte interface by redesigning the cathode [39,49,53,57] . These modification methods generally include structural redesign and chemical composition improvements.…”

“…Ge et al [57] proposed a 3D honeycomb graphene composite loaded with a Mo/Mo 2 C heterojunction and used it directly as a LOB cathode. The layered porous structure facilitated the penetration of liquid electrolyte, thereby enlarging the cathode-electrolyte interface and providing the necessary conditions for the rapid movement of electrons and the diffusion of Li + and oxygen.…”