Reversible Multielectron Transfer Chemistry of I-Activated Voltage-Enhanced Ferrocene-Based Organic Cathodes

Organic molecule engineering has the potential to design materials with multiple electroactive centers, affording high energy storage capabilities and low-cost chemistry. The discovery of ferrocenes contributes significantly to the broad applications of organometallic compounds. Even though their reversible redox reactions can be used in batteries, their low potential and limited electron density per unit mass pose some challenges. Here, we report an I-activated voltage-enhanced ferrocene-based molecule, (ferrocenylmethyl) trimethylammonium iodide (FcNI), featuring a dual redox center by decorating the ferrocene backbone with designed functional groups to regulate the electron energy of Fe^3+/2+ redox couples. It enables multielectron transfer of I^0/- and Fe^3+/2+, a sharply increased potential of Fe^3+/2+ redox couples, and high-power energy storage with cycling stability. An organic cathode based on FcNI molecules displays a discharge capacity of over 400 mAh g^-1 at 2 A g^-1 with high-voltage plateaus up to 1.7 and 3.5 V when coupled with a zinc or lithium anode, respectively, and an excellent rate capability. Our results show that organic molecules can be programmed with multiple redox sites to develop high-voltage, fast-charging, and high-capacity organic rechargeable batteries.