The Need

The growing global demand for electrical energy has increased research efforts towards the integration of renewable energy sources into the electrical grid. Generation of energy from petroleum-based sources dominates the current market, but dependence on renewable energy is expected to grow rapidly. For example, photovoltaic installations have outpaced annual predictions and are approaching terawatt scales at prices <$0.50/W. However, many issues associated with renewable energy impedes their full integration into the electrical grid.

The Technology

We report the development of hybrid RFBs that contain redox-active organic solids (ROSs). Rather than forcing these solids to charge/discharge directly at the electrode, small quantities of solvated redox-active organic molecules (ROMs) will relay electrons between the ROSs and the distal current collectors. The resulting redox relay flow battery (RRFB) will be scalable, have high energy density, and be synthetically modular. The RRFB is a hybrid storage system with a number of key advantages over current RFBs. First, the energy density of the RRFB scales with capacity (mass of ROS added), rather than with solubility. Such systems can function with over 20 mol of actives per kg solvent, which greatly exceeds RFB limits (<1mol/kg solvent). At such energy densities, cost-competitive storage can be achieved at lower cell voltages(~2 V) than current RFB targets. Second, excessively high concentrations of solvated shuttle are not required because energy density is dictated by the loading of the ROS. This lower shuttle concentration reduces solution viscosity, slows bimolecular decomposition pathways of solvated compounds, and eliminates the cost associated with extensive synthetic derivatization to prepare highly soluble ROMs. Finally, the ROSs will be loaded into interchangeable cartridges. This design allows the energy-dense cartridges to be charged at one site and easily transported for discharge to a geographic site where harvesting renewable energy is challenging.

Competitive Advantages

• RRFBs have high energy density and thus are very efficient for their size
• The cartridge-based system allows for easy transportation of energy from one site to another
• Lower concentrations of solvated shuttle are required, significantly reducing the cost per battery

Commercial Applications

• Energy Storage
• Solar Power