Redox-Active Macrocycles for Organic Rechargeable Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Organic Chemistry

Background:

• Organic rechargeable batteries offer advantages like cost-effectiveness and high capacity over lithium-ion batteries.
• A major challenge is controlling the redox potential of organic molecules for a stable battery voltage.
• Current organic materials often exhibit multiple voltage plateaus, limiting their performance.

Purpose of the Study:

• To identify a molecular structure that enables a single, well-defined voltage output in organic rechargeable batteries.
• To investigate the relationship between molecular structure, electron delocalization, and voltage profiles.
• To advance the design of high-performance organic electrode materials.

Main Methods:

• Density Functional Theory (DFT) calculations to model electron delocalization.
• Synthesis and electrochemical characterization of triangular macrocyclic molecules, a dimer, and an acyclic derivative.
• Techniques including differential pulse voltammetry, spectroelectrochemistry, and galvanostatic measurements.

Main Results:

• A triangular macrocycle with three pyromellitic diimide (PMDI) units exhibited a single output voltage at 2.33 V.
• Acyclic and dimeric PMDI derivatives showed multiple voltage plateaus during reduction and oxidation.
• Through-space electron delocalization in the triangular structure was identified as key to the single voltage profile.

Conclusions:

• Controlling the conformational arrangement of redox-active units in macrocycles is crucial for stable battery voltage.
• Triangular macrocyclic structures promote electron delocalization, leading to desirable single voltage plateaus.
• This research provides a pathway for designing high energy density and long cycle-life organic electrodes.