Technological advances in renewable energy allows our society to transition from fossil fuels to sustainable sources. However, the development of efficient batteries remains a major challenge. High-performance Li-ion batteries have proven to be an appropriate but temporary solution, as their availability is rapidly being overtaken by civil needs. In recent years, redox flow batteries (RFB) have gained considerable attention to solve the issues faced with storage of transient energy. In RFBs, energy is stored in solutions which flow through an electrochemical cell and redox term refers to the reduction and oxidation reactions involved in the catholyte and anolyte that are converted to electrical power. Vanadium RFBs possess high durability with significant cyclability, however, the use of metal is associated with high cost and toxicity. Redox-active organic materials with large potential windows and their applications in full organic RFBs, have thus emerged as an alternative for low-cost and large-scale batteries due to their sustainable, synthetically tunable, and inexpensive raw materials. However, cross-contamination problems encountered by the use of distinct redox species still limits the development of reliable organic RFBs. Herein, we report a class of helical carbeniums, with several stable oxidation states, as electrolytes for the development of symmetric cells. Cyclic voltammetry and solubility measurements were assessed to identify critical properties for RFB applications. The stability of different [4]helicenium ions were then evaluated by static GCPL cycling. These lead to 3 all-organic non-aqueous symmetric RFBs models with OCVs of 2.1-3 V, capacity retentions above 550 cycles, and energy density above 12 Wh/L.

Toward full-organic symmetric redox flow battery: From helical redox-active bipolar carbenium ions to applicable RFB models

ACS Spring 2022

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