Nature inspired cathodes using high-density carbon papers with an eddy current effect for high-rate performance lithium-air batteries

Abstract

Phenomena observed in nature can be considered to be the result of optimized outcomes that have been obtained through trial and error for many years. Researchers have thus attempted to apply the lessons provided by nature to real scientific problems. In particular, in nature, the fluidic behavior of eddy currents is frequently observed, such as in a river, whereby the eddy develops into a whirlpool with an increased flow velocity, vorticity, and inner pressure. However, in this study on the design of a cathode for Li-air batteries (LABs), the eddy current of oxygen gas as a fluid can also be found in the gas diffusion layer (GDL) in the cathode fabricated using an imprinting process with micro-scale patterned metal molds. Herein, the cathode with the patterned GDL containing an increased density of carbon paper exhibits increased velocity, vorticity, and inner pressure of O-2 flow due to the increased eddy current effect (the inner structuring). In addition, the patterned cathode increases the catalytic active sites for the oxygen reduction reaction due to the outer structuring effect such as an increased roughness factor. According to the simulated data from COMSOL, an average O-2 gas velocity of the patterned cathode prepared through inner/outer structuring is increased by 45.8%, compared to that of the bare electrode. In the LAB test, the micro-scale patterned cathode shows an increased energy density and decreased IR drop by 79.6% and 23.2%, respectively. Consequently, the inner and outer structured GDL in the cathode for the ORR could be predominantly responsible for the superior LAB performance.