Progress has been made in the research of membrane materials for alkaline‑system flow batteries.

Recently, the research team led by Researcher Xianfeng Li at the Energy Storage Technology Research Department of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made significant progress in the large-scale preparation and application of membrane materials for high-performance, low-cost alkaline redox flow batteries. By employing a continuous roll-to-roll membrane‑forming process, they have achieved the large-area fabrication of non-fluorinated cation-exchange membranes and demonstrated their integration into alkaline redox flow battery energy storage systems.

Energy storage is a key enabling technology for building a new type of power system dominated by renewable energy. Redox flow battery technology, with its advantages of safety, reliability, long lifespan, and high efficiency, is the preferred choice for large-scale energy storage. Consequently, reducing costs—particularly the cost of the critical material in redox flow batteries, ion-conducting membranes—is of paramount importance for accelerating the practical deployment of this technology.

At present, research on ion-conducting membranes for alkaline‑system redox flow batteries remains quite limited. Perfluorosulfonic acid ion‑exchange membranes (Nafion), owing to their excellent stability, have become the material of choice for both conventional redox flow batteries and those operating in alkaline media. However, Nafion membranes suffer from several drawbacks: a complex manufacturing process, significant environmental and health risks posed by by‑products generated during production, high cost, and low ionic conductivity under alkaline conditions, which in turn leads to reduced battery efficiency. Developing low‑cost, structurally tunable, and easily fabricated non‑fluorinated anion‑exchange membranes holds promise for addressing these issues. Nevertheless, in alkaline environments, the quaternary ammonium groups on traditional non‑fluorinated anion‑exchange membranes—specifically, quaternary ammonium‑type ion‑conducting membranes—undergo Hofmann elimination and nucleophilic substitution reactions, resulting in poor membrane stability.

In this work, the research team, building on their prior design of ion-conducting membranes for alkaline systems (Nat. Commun., 2018; Angew. Chem. Int. Ed., 2020; J. Am. Chem. Soc., 2021; Adv. Funct. Mater., 2021) and a deep understanding of ion transport mechanisms (Nat. Commun., 2021), synthesized kilogram-scale sulfonated polyetheretherketone polymer resin via electrophilic substitution. Subsequently, employing a continuous roll-to-roll membrane‑fabrication process, they prepared large‑area, high‑throughput non‑fluorinated cation‑exchange membrane materials and demonstrated their application in alkaline‑system flow batteries. The study revealed that the membrane’s rigid backbone structure and its charge characteristics confer excellent alkali resistance; moreover, the discrete –SO3H groups along the polymer chain form a continuous hydrogen‑bonding network within the membrane, enabling rapid OH− transport via the Grotthuss mechanism and thereby enhancing the membrane’s electrical conductivity. In addition, using this newly developed membrane, the team assembled a 4 kW‑class alkaline zinc–iron flow battery stack, which achieved an energy efficiency exceeding 85% at a current density of 80 mA cm⁻². This research holds promise for improving the performance of next‑generation flow batteries, accelerating their transition from laboratory prototypes to large‑scale applications, and contributing to cost reduction and the practical deployment of flow‑battery energy‑storage technologies.

The relevant research findings, titled “Low-cost Hydrocarbon Membrane Enables Commercial-scale Flow Batteries for Long-duration Energy Storage,” were recently published in Joule. This work was supported by projects funded by the National Natural Science Foundation of China, the CAS Engineering Laboratory for Electrochemical Energy Storage Technology, and the Chinese Academy of Sciences Youth Innovation Promotion Association, among others.

The Dalian Institute of Chemical Physics has developed a high-performance, low-cost membrane material for alkaline‑system flow batteries.

Source: Dalian Institute of Chemical Physics, Chinese Academy of Sciences