Integrating Pseudocapacitive Function into Air-Cathodes with 3D-Wired Nanoscale MnOx: Enabling Pulse-Power for Zn–Air Batteries

Abstract

Metal–air batteries have the highest specific (packaged) energy among common battery chemistries (over 400 Whkg–1 for Zn–air) with the added benefits conferred by aqueous electrolytes of safety and affordability. But air-dependent batteries are power-limited by catalytic and mass-transfer restrictions associated with reduction of molecular oxygen at the air cathode—an electrode that must support multiple tasks: O2 transport, ion transport, electron conduction, and electrocatalytic reactivity. To address this power limitation, we have redesigned the air cathode using an architectural and nanoscopic perspective that marries complementary characteristics of batteries and electrochemical capacitors. We demonstrate that air cathodes comprising fiber paper–supported carbon nanofoams modified with conformal nanoscale coatings of Na+-birnessite-type MnOx (10–20 nm thick) exhibit dual functionality: (i) oxygen reduction to sustain long-term energy delivery and (ii) faradaic pseudocapacitance associated with Mn(III/IV) redox to provide intermittent, farads-worth discharge pulses over 10s of seconds [1,2]. Manganese (III) sites in the post-pulsed oxide spontaneously recharge to Mn(IV) in the presence of oxygen from air, making the oxide ready and available for subsequent pulse-power discharge. [1] Redesigning air cathodes for metal–air batteries using MnOx-functionalized carbon nanofoam architectures. C.N. Chervin, J.W. Long, N.L. Brandell, J.M. Wallace, and D.R. Rolison, J. Power Sources 2012, 207, 191–199. [2] Dual-function air cathode nanoarchitectures for metal–air batteries with air-independent pulse power capability. J.W. Long, C.N. Chervin, N.W. Kucko, E.S. Nelson, and D.R. Rolison, Adv. Energy Mater. 2013, 3, 584–588.