All Organic Quinone Solid State Batteries for Environmentally Friendly and Chemical Robust Alternatives Beyond Lithium-Ion Batteries

Introduction: Organic solid-state quinone batteries have unparalleled properties that can meet the most urgent challenges the industry faces. It can create an energy system that is environmentally friendly and electrochemically robust, while being cost efficient enough for industry to adopt and invest in. The inspiration for fully organic solid-state batteries came from extended studies on our all-organic aqueous redox flow batteries, where much of the science of organic redox coupling molecules were understood. Like redox flow batteries, organic solid state quinone batteries utilizes the breaking and reforming of bonds to generate electrical energy. However, it doesn’t require the constant flow of charge carrier solution like the flow batteries. Consequently, this avoids the cost of an extra pumping system and significantly reduce the size of the batteries compared to flow battery systems. Furthermore, the downsized battery system allows for the cell to be implemented into applications such as EV and portable devices. The redox species are directly deposited onto the electrodes. This deposition of active material on carbon paper enables higher surface area for charge transfer, which increases the capacity for fast charge and discharge compared to flow batteries. Additionally, the active materials are of organic quinone nature providing great robustness that other battery systems like lithium-ion batteries don’t allow. The redox chemistry of these quinones still happens in aqueous system, which allows us to use very small amount of aqueous electrolyte instead of the combustible organic solvent used in lithium batteries. Results and discussion: The appropriate quinone species for this solid-state battery must be electrochemically stable and dissolution free in the aqueous system. Various quinones with different substituents were tested. One of the promising redox couples discovered is 2-methylanthraquinone (MAQ) and duroquinone (DQ). The couple displayed a cell voltage of 400 mV (0.4 V) as shown in Figure 1. This value was found to correspond to the redox potential difference between DQ and MAQ. New methods of deposition of active materials onto the electrodes were developed. High conductivity was achieved by introducing CNT with appropriate binder, which resulted in improvements to the cell’s charge and discharge performance (Figure 2). Figure 1 . Cyclic voltammetry study of 10 mM 2-Methylanthraquinone (MAQ) and 10 mM Duroquinone (DQ) in 1 M sulfuric acid with 20% ethanol, MSE reference electrode, glassy carbon, 50 mV/s. (Refer to image file) Figure 2 : Charge and discharge of solid-state batteries of 2-Methylanthraquinone (MAQ) and Duroquinone (DQ) at 10 mA. (Refer to image file) For the positive side, 0.164 g of duroquinone was deposited on 25 cm 2 carbon paper with 0.05 g of CNT. Correspondingly, 0.222 g of 2-Methylantroquinone was deposited for the negative side. The cell was assembled with Nafion 117 as separator and small amount of 1 M sulfuric acid as the supporting electrolyte. The initial charge and discharge curve of this cell showed 97% columbic efficiency. Long-term cycling to test the stability was performed and other redox couples also showed higher cell voltage with high efficiency. The next step for this study is to explore different redox couples that might have better compatibility and higher cell voltage compared to the current redox couple. This will be done through studying the large library of organic compounds including quinones and other redox active organic compounds. Figure 1