Surface ‒OH Termination‐Reduced Ti3C2Tx Pseudo‐capacitors with Reinforced Ionic Liquid Accessibility to Achieve High Energy Density.

Highly conductive Ti3C2Tx pseudo‐capacitors hold promise to expand energy density by utilizing ionic liquid (IL) electrolytes (e.g., 1‐ethyl‐3‐methylimidazolium bis trifluoromethane sulfonyl imide, EMITFSI) that possesses broaden voltage window, resulting in various applications involving hybrid vehicle, rail transportation, and power system. However, abundantly random surface ‒OH terminations cannot maintain an extremely stabilized Ti3C2Tx layer spacing framework for efficient ion arrangements, increase ionic diffusion barriers, and decline in energy density. Herein, intensely chemical covalent bonding interactions of ‒SH, ‒COOH, and ‒NH2 terminated L‐cysteine molecules with ‒OH terminations are proposed to stabilize Ti3C2Tx and expand interlayer structure, allowing sufficient ionic transport and realizing high energy‐density Ti3C2Tx pseudo‐capacitors. It is found that, with cysteine molecules stayed flat to Ti3C2Tx layer, superior hydrophilic surface, and increased interlayer spacing to 1.51 nm, 2.16‐folds higher than Ti3C2Tx electrode, the Ti3C2Tx‒cysteine electrode delivered high capacitance of 279 F g−1 in EMITFSI/acetonitrile electrolyte. Assembled asymmetric Ti3C2Tx‒cysteine//activated carbon flexible device exhibited a high voltage of 2.9 V and a high energy density of 72.1 Wh kg−1 at a power density of 874 W kg−1, which could power various colored smart rollable flexible electronics at bent angle of 90°. Additionally, identical mechanisms are found in Ti3C2Tx‐amino acid systems, wherein amino acid stayed flat between Ti3C2Tx layers with optimized content, interlayer spacing, and capacitance, no matter amino acid in different charged feature and different sidechain lengths (e.g., glutamine, cysteine, and lysine). The present study provides systematically experimental evidence for improving ion accessibility in IL electrolytes based on an organic‐modified Ti3C2Tx electrode structure. [ABSTRACT FROM AUTHOR]