Vanadium Redox Flow Batteries - How they work

Vanadium has a unique characteristic of having four different stages of oxidation. In each of the four stages, Vanadium contains a different electrical charge and is therefore used as a catalyst to store energy. In order to convert this electrical energy into a chemical compound, it requires two electrodes, called a “stack”.

This stack consists of many cells; each one contains two half-cells that are separated by a membrane. In the half-cells the electrochemical reactions take place as soon as electrolytes flow past the membranes. Hence, the reduction or oxidation leads to the charging or discharging of the battery.

The stack is connected to two different tanks and one electrolyte tank contains the positive V4+ and V5+ redox couples, the other the negative V2+ and V3+ redox couples. These energy-carrying liquids circulate through the stack by pumps.

Vanadium electrolyte in its four stages of oxidisation

Diagram showing how a VRFB works

In VRFB’s batteries, these materials are liquid and have different electric charges. Both liquids (V2+/V3+ and VO2+/VO2+) are pumped into a tank and a thin membrane separates the two liquids, however the liquids are able to react and an electric current is generated.

Vanadium is used because it can convert back and forth from its various different states which carry different positive charges. The risk of cross contamination is eliminated as only one material is used, which makes VRFB’s safer, as the two liquids don’t mix causing a sudden release of energy.

Advantages Over Other Storage Solutions

VRFBs have emerged as a promising solution for grid services due to their long lifecycle potential and high energy capacity, which can provide extended discharge times. Given the ability to scale power and energy of a system independently, VRFB technology offers a long-term solution for off-grid power systems and micro-grids. These systems can be used to support residential, community, military, and commercial end-users, and to fulfill remote-energy-access needs of remote rural areas in countries like Australia.

VRFB’s are the most efficient battery technology suitable for utility scale renewable energy storage for both wind and solar.

“We see $548 billion being invested in battery capacity by 2050, two thirds of that at the grid level and one third installed behind-the-meter by households and businesses”- BLOOMBERG NEF

The VRFB, given its unlimited storage capacity, long battery life, low maintenance requirements, adaptability and almost non-existent environmental footprint, is today’s answer to efficiently storing and accessing energy. The stored electricity will reduce Australia’s reliance on fossil fuels into the future, cutting pollution and CO2 emissions.

Benefits of VRFB vs lithium-ion battery