I-Corps: Electron-Donating Phenothiazines for Non-Aqueous Redox Flow Batteries

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The broader impact/commercial potential of this I-Corps project involves enabling increased utilization of renewable energy power sources such as solar and wind. Due to the intermittency of these power sources, energy storage systems must be connected to our electrical grid in increased amounts to help stabilize the grid through storage of energy during peak production times and release of energy during peak consumption. The technology developed consists of stable carbon-based materials that can store charge for extended periods of time. These materials may allow for the production of batteries with organic electrolytes, specifically called redox flow batteries, which can be charged at higher power densities and have higher energy capacities than current aqueous-based counterparts. In addition to stationary energy storage, these materials could serve as additives in lithium-ion batteries that can extend lifetimes and prevent catastrophic failure through protection during abusive conditions that result from charging batteries to too-high potentials. Yet another possibility is to use these materials to initiate chemical reactions that allow for lower-cost preparation of polymer coatings through the elimination of metal complexes.This I-Corps project involves the exploration of potential markets for stable, electron-donating phenothiazine derivatives as potential materials for energy-storage applications and polymerization initiators. These materials were developed as a result of studying a variety of fused-ring heterocyclic organic compounds with varying substituent identity and position, which led to identification of characteristics that led to greater stability in multiple states of oxidation (neutral, radical cation, and dication). The most stable derivatives were tested as redox shuttle additives that limit voltage in overcharging lithium-ion batteries and were found to have extensive performance in batteries containing commercially utilized electrode materials due to their high stability. High solubility led to their incorporation into battery electrolytes at high concentrations, which allowed for high-rate overcharge protection. More recently, the study of these materials as catholytes for non-aqueous redox flow batteries showed extensive lifetimes in symmetric cells at high concentrations and with high charging currents. In fact, in many cases, high stability has allowed for their isolation as crystalline radical-cation salts. Furthermore, these materials have been shown to initiate cationic polymerizations using visible light, which may lead to their use as photo-redox catalysts.