Two Architected Battery Electrodes are Better than One!

Having removed the roadblock to rechargeable aqueous alkaline batteries by architecting the zinc in a sponge form factor, thus thwarting formation of cell-shorting zinc dendrites, our team at the US Naval Research Laboratory has turned to improving the performance of the opposing electrode. To do so, we again bring an architectural perspective to the positive electrode. Keeping the zinc sponge anode as a constant factor, we demonstrate two classes of Zn-based alkaline cells that derive improved discharge areal capacity and capacity retention, namely Ni–Zn and Zn–air, when the respective cathodes adopt either an architected form factor or deploy architected catalysts. We nucleate and grow Al(III)-substituted α-Ni(OH)₂ onto carbon nanofiber paper and achieve 1.5 electrons per Ni rather than the 1 electron per Ni characteristic of Ni cathodes. Using the 3D electron-wired cathode, the cell retains that extra per Ni capacity without fade over 80 cycles. To catalyze oxygen reduction (ORR) and evolution (OER) in the air electrode, we use aerogels as the design architecture. By blending aerogel versions of an excellent ORR catalyst (the 2×2 tunneled polymorph of MnO₂, cryptomelane) with an excellent OER catalyst (nickel ferrite) in a powder-composite electrode structure, we attain high areal capacity (mAh per geometric area) while achieving state-of-the-art low voltage hysteresis (700 mV) and charging voltage <2 V.