Selective Charging Behavior in an Ionic Mixture Electrolyte-Supercapacitor System for Higher Energy and Power

Abstract

Ion-ion interactions in supercapacitor (SC) electrolytes are considered to have significant influence over the charging process and therefore the overall performance of the SC system. Current strategies used to weaken ionic interactions can enhance the power of SCs, but consequently, the energy density will decrease due to the increased distance between adjacent electrolyte ions at the electrode surface. Herein, we report on the simultaneous enhancement of the power and energy densities of a SC using an ionic mixture electrolyte with different types of ionic interactions. Two types of cations with stronger ionic interactions can be packed in a denser arrangement in mesopores to increase the capacitance, whereas only cations with weaker ionic interactions are allowed to enter micropores without sacrificing the power density. This unique selective charging behavior in different confined porous structure was investigated by solid-state nuclear magnetic resonance experiments and further confirmed theoretically by both density functional theory and molecular dynamics simulations. Our results offer a distinct insight into pairing ionic mixture electrolytes with materials with confined porous characteristics and further propose that it is possible to control the charging process resulting in comprehensive enhancements in SC performance.

Perspective on High‐Energy Carbon‐Based Supercapacitors

“…88%, 1000 cycles @ 1 A g −1 BDA/rGO 266 m 2 g −1 [81] TEA-BF 4 /ACN 2.7 V 34 Wh kg −1 @ 425 W kg −1 >90%, 10 000 cycles @ 5 A g −1 Tris/rGO 327 m 2 g −1 [81] BMIM-BF 4 3. 82.4%, 10 000 cycles @ 5 A g −1 Meso-2.0 nm 3140 m 2 g −1 [175] TMA-BF 4 /EMIM-BF 4 3.5 V 113 Wh kg −1 @ 500 W kg −1 71 Wh kg −1 @ 7.5 kW kg −1 84%, 5000 cycles @ 1 A g −1 GNW//NGNW [136] TEA-BF 4 /PC…”

Enhanced Rate Capability of Ion‐Accessible Ti3C2Tx‐NbN Hybrid Electrodes

“…[ 1–6 ] Because of high power density, long cycle life, and superior rate capability, supercapacitors (SCs) have attracted increased attention. [ 7–12 ] SCs can provide power density in excess of 10 kW kg −1 since charges are stored through highly reversible ion adsorption or fast redox reactions (in the case of pseudocapacitors), which is at least ten times higher than commercially available lithium‐ion batteries. [ 13–16 ] This meets the requirements of the applications where high‐rate charge/discharge is demanded, which include but are not limited to energy harvesting/recapturing and delivery in electric vehicles, elevators, trains, smart grids, and backup power for electronics, electric utilities, and factories.…”

Recent advances in carbon-based supercapacitors

“…Gogotsi's group demonstrated the in-cell charging selectivity in the TMABF 4 /EMIMBF 4 ionic mixture electrolyte for simultaneously improved power/ energy densities. 203 Two cations (TMA + /EMIM + ) with strong cationic interactions could be arranged in denser distribution at the electrode/electrolyte interface to increase the capacitance, while the selective sieving effect of TMA + with weaker interactions allowed fast ion dynamics in micropores without reducing the power output (Fig. 13).…”