Design of Thick Electrodes with Vertical Channels for Aqueous Batteries: Experimental and Numerical Analysis

Developing thick electrodes with high-area loadings is a direct method for boosting the energy density. However, this approach also leads to a proportional increase in the resistance to charge transport. Optimizing the microstructure of the electrode can effectively enhance the charge transport kinetics in thick electrodes. Herein, a low-tortuosity nickel electrode with vertical channels (VC-Ni) is fabricated using a phase inversion method. A high-loading VC-Ni electrode (26.7 mg cm^-2) delivers a superior specific capacity of 134.0 mAh g^-1 at a 5 C rate, significantly outperforming the conventional nickel electrode (Con-Ni). Numerical simulations reveal the fast transport kinetics within the vertical channel electrodes. For the thick electrode, the VC-Ni electrode shows a substantially lower concentration gradient of OH^- and H⁺ compared to the Con-Ni electrode. Notably, beyond a critical loading of 26.5 mg cm^-2, the specific capacity initially increases with volume fraction, peaking at 50%, and then diminishes. The specific capacity increases as the channel size decreases, but the tendency to increase gradually decreases. The highest specific capacity is achieved with an inverted trapezoidal channel shape, characterized by larger pores near the separator and smaller pores near the current collector. This work is of guidance for the design of thick electrodes for high-performance aqueous batteries.