Doping of Self-Standing CNT Fibers: Promising Flexible Air-Cathodes for High-Energy-Density Structural Zn–Air Batteries

Finding proper electrocatalysts capable of efficiently catalyzing both ORR and OER is of great importance for metal–air batteries. With increasing attention focused on structural and flexible battery systems, one is encouraged to develop a high-performance self-standing air-cathode. This is challenging, as most of the oxygen catalysts are in a powder format and need to be further processed. Here, we construct a highly bifunctional air catalyst from macroscopic CNT fibers (CNTfs) through direct CVD spinning followed by a hydrothermal method. The electrocatalytic properties of the samples were tuned by altering nitrogen doping and defect densities which can be readily adjusted by using different hydrothermal reaction temperatures. The treated CNTfs showed excellent bifunctional activity (ΔE = E j=10 – E 1/2 = 0.81 V) and demonstrated exceptional performance as carbon-based self-standing air-cathodes in both liquid- and solid-state rechargeable Zn–air batteries, with a high capacity of 698 mAh g–1 and an ultrahigh energy density of 838 Wh kg–1 (liquid-state). The rechargeable Zn–air batteries exhibit a low discharge–charge overpotential and excellent stability. This work represents a novel and easily achievable method of preparing self-standing air electrodes with exceptional performance for structural Zn–air batteries.