Reduction of Tortuosity in Porous Electrodes through Macropore Patterning

In porous electrodes, limitations exist on how quickly ionic current can be transferred through electrolyte, partly determined by the "tortuosity," a factor describing the effective length an ion must travel through the microstructure's pores. To facilitate ionic conduction and adsorption into electric double-layers, we show that macroscopic pores can be added to reduce the effective tortuosity by providing more direct paths to capacitive interfaces. We show experimental and simulated results in fabricating and testing electrodes that are machined to create these macro-pores aligned normal to current collectors. Through the reduction of tortuosity, these "bi-tortuous" electrodes surpass unpatterned electrodes in effective conductivity, rate capability, and capacitance. The degree of improvement is dependent on the electrodes' thickness and the time scale of the charging.