Abstract
Redox-enhanced electrochemical capacitors (redox ECs) are promising energy-storage devices with the potential to deliver both high power and energy performances, although overcoming the severe self-discharge remains a great challenge due to the shuttle effect of redox species such as I−/I3− ions introduced in the electrolytes for gaining additional capacities. Herein, we propose a cation-initiated self-assembly process of Ti3C2Tx MXene nanosheets onto glass fiber membranes to form Janus separators that can mitigate the shuttling of I−/I3− ions in iodine-based redox ECs. The interlayer spacing of the MXene films can be controlled by selecting different cations such as imidazolium (C4mim+), Mg2+, and Al3+, therefore the resulting Janus separators exhibit tailored nanochannels for ion sieving. Both molecular dynamic (MD) simulations and electrochemical tests indicate that C4mim+-intercalated MXene Janus separators (C4mim+-MXene) can block the diffusion of I3− ions while allowing the pass of other electrolyte ions. As a result, self-discharge caused by the shuttle effect can be much reduced in C4mim+-MXene-based redox ECs, which deliver voltage and energy retentions substantially higher than that of the cells using glass fiber membrane separators (voltage retention: 70% vs. 10%, energy retention: 51% vs. 6.5%) after 24-h open-circuit test.
Published Version
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