Redox flow batteries

Redox flow batteries use a liquid solution to store energy, rather than storing it in a solid material like lithium-ion batteries. Flow batteries consist of two electrolytes contained in tanks separated by an ion-selective membrane that allows only certain ions to pass through during the charging or discharging process. Negative and positive electrolytes contain dissolved atoms or molecules that can react electrochemically to release or store electrons. During discharge, an electron is released from the anode (negative electrolyte) via an oxidation reaction, travels through an external circuit and is accepted at the cathode (positive electrolyte) via a reduction reaction. During charging, the opposite flows and reactions take place as the battery stores energy. The separation of the energy (the electrolyte tanks) and power (the membrane) components allows a tailored design: larger storage tanks increase energy storage capacity. Flow batteries are less sensitive to deep discharge, have a long life cycle and unlimited energy capacity. However, they also have a lower volumetric energy density. Several chemistries can be used, but the most mature is the vanadium redox battery (VRB), which uses vanadium ions as the charge carrier. However, the supply of vanadium is limited and cheaper alternatives are being investigated.