Storing renewable energy even when there is no sun or wind

A team from the US Department of Energy’s Berkeley Lab, along with international collaborators, have developed a new type of versatile and affordable grid battery membrane for flow batteries that can store renewable energy. Flow batteries store electricity in tanks of liquid electrolyte, and could help enhance how an electrical grid can be powered by renewable energy. The innovative concept for cheaper and sustainable flow batteries was reported in the journal Joule [Baran et al. Joule (2019) DOI: 10.1016/j.joule.2019.08.025]. It is based on a new class of polymers called AquaPIM, short for aqueous-compatible polymers of intrinsic microporosity, which allow for long-lasting and relatively cheap grid batteries as they are based on easily available materials, including iron, zinc and water. A simple empirical model that compared battery performance to that of various membranes and the effect that a range of battery membranes can have on the lifetime of a flow battery was also developed. It helps show the need for a membrane for different battery chemistries, with the technology and model for the battery’s performance and lifetime improving the assessment of each battery component. The membrane screen significantly reduces the time taken to identify how long a battery will last once the entire cell has been assembled. In addition, the AquaPIM technology does not use fluorinated polymer membranes, an expensive part of the battery, making them more affordable. As study leader Brett Helms points out, “Our AquaPIM membrane technology is well-positioned to accelerate the path to market for flow batteries that use scalable, low-cost, water-based chemistries”. Although the majority of grid battery chemistries comprising highly alkaline electrodes, with a positively charged cathode and a negatively charged anode, current membranes are developed for acidic chemistries, such as the fluorinated membranes used in fuel cells and not for alkaline flow batteries. The team found that the grid battery membranes modified with an “amidoxime” permitted ions to quickly travel between the anode and cathode. AquaPIM membranes lead to stable alkaline cells, with prototypes retaining the integrity of the charge-storing materials in the cathode as well as the anode. When the membranes were characterized, it was found that such characteristics were universal across AquaPIM variants, and that the structure of the polymers in the membrane were very resistant to pore collapse under highly basic conditions in alkaline electrolytes. The researchers now hope to apply AquaPIM membranes across a wider range of aqueous flow battery chemistries, such as metals and inorganics and organics and polymers, and to assess if the membranes are compatible with other aqueous alkaline zinc batteries. Storing renewable energy even when there is no sun or wind