This Small Business Innovation Research (SBIR) Phase II project will develop a novel ion gate membrane with controlled pore size for redox flow battery. Redox flow battery is one of the most promising electric energy storage (EES) technologies. However, the cost of the state-of-the-art (SOA) membrane used in such battery has to come down dramatically in order to reach the overall system cost target for EES applications. Moreover, the ion selectivity of the SOA membrane is also very poor, leading to ion cross-over and lower energy efficiency for the battery. In the proposed approach, an ultra thin composite membrane will be developed to address the issues. Due to its thin thickness, tight pore size control and material selection, the membrane is expected to have excellent ion selectivity, proton conductivity and chemical stability. Once fully developed, it will be able to meet the stringent requirements of large scale redox flow batteries for EES applications.<br/><br/>The broader impact/commercial potential of this project includes promoting the widespread adoption of redox flow battery as the low cost EES systems and facilitating the rapid deployment of smart grids. In order to satisfy the surging energy demand and mitigate the environment impact of fossil fuel usage, renewable energy sources are becoming more and more important in the power generation. However, renewable energy sources, such as wind power, suffer the drawback of fluctuation. To mitigate the problem, smart grids are now being proposed and developed. The EES system is considered as the key components of the smart grids. The market for such batteries is expected to grow rapidly. According to a study, the EES market could reach $52 billion if 10% of wind plants adopt EES. This work if successful will lead to a breakthrough product: a low cost, high performance ion gate membrane as a key component for the redox flow battery. Such a breakthrough product could accelerate the penetration of redox flow battery in this market. In addition, development of this innovative membrane will help maintain our nations leading position in this important field, creating new business opportunities and high tech jobs.