What is a flow battery?

A flow battery is a type of rechargeable battery that stores and releases energy through the flow of electroactive materials dissolved in liquid electrolytes. Unlike traditional batteries where the energy storage occurs within the battery cells, flow batteries separate the energy storage from the power generation components.

In a flow battery, two electrolyte solutions, typically stored in separate tanks, flow through a cell stack consisting of two compartments separated by an ion-exchange membrane. Each compartment contains an electroactive species dissolved in the electrolyte solution. When the battery is charging or discharging, the electrolyte flows through the cell stack, while the electroactive species react at the electrodes and ions are exchanged through the membrane.

The capacity of a flow battery is determined by the size of the electrolyte storage tanks, which can be scaled independently of the power rating. This design allows for flexible and scalable energy storage solutions. By simply increasing the size of the tanks, the energy storage capacity can be increased without affecting the power output.

Flow batteries have several advantages, including a long cycle life, high energy efficiency, and the ability to decouple power and energy. They are particularly suitable for large-scale energy storage applications, such as grid-level energy storage, renewable energy integration, and load balancing. Flow batteries are also known for their relatively fast response times and the ability to store energy for extended durations.

Different types of flow batteries exist, such as the vanadium redox flow battery (VRFB), zinc-bromine flow battery, and iron-chromium flow battery, among others. Each type uses different electroactive materials and electrolyte solutions, but they all operate on the basic principle of flowing electrolytes to store and release electrical energy.