Mass Balancing of Hybrid Ion Capacitor Electrodes: A Simple and Generalized Semiempirical Approach

Hybrid
ion capacitors (HICs) are emerging as promising energy-storage
devices exhibiting the advantages of both batteries and supercapacitors.
However, the difference in the electrodes’ specific capacities
and rate capabilities makes it extremely challenging to achieve optimum
mass balancing for a full-cell HIC device. Here, we demonstrate a
method to predict well-performing mass ratios of electrodes for a
Na-HIC by analyzing the capacities of anodes and cathodes as a function
of the actual current densities experienced by the individual electrodes.
We employ a simple design tool, a “Ragone Plot Simulator”,
to predict specific energy and specific power on Ragone plots and
study the performance trend of devices with varying electrode mass
ratios. The validation of the proposed method is done based on the
experimental data obtained from several hybrid ion capacitor devices
reported in the literature, which closely matches with the simulated
Ragone plots. Further, we exemplify the validity of our calculations
by comparing the simulated Ragone plot with that of a Na-HIC fabricated
using in-house-made carbon. This unique approach presents a simple,
generalized, yet never reported, method, which could be employed as
a design tool to guide the selection of optimized HIC devices for
the intended applications.