CIC energiGUNE validates 10,000 cycles in a new redox flow battery for long-duration energy storage

The development is part of CIC energiGUNE’s commitment to a new generation of more affordable and durable redox flow batteries with reduced dependence on critical raw materials.

CIC energiGUNE, the Basque research centre specialising in energy storage and conversion, is working on a new generation of redox flow batteries designed to store electricity generated by solar or wind power for several hours when there is surplus production and release it when the grid actually needs it — one of the major challenges facing an increasingly renewable energy system.

Among the centre’s developments is an innovative single-flow iron-lead battery, designed for long-duration stationary energy storage, which has already completed 10,000 validation cycles at temperatures between 25 and 30 °C. The technology uses iron and lead as active materials, avoids the use of critical raw materials and simplifies the conventional architecture of flow batteries by using a single electrolyte circuit.

The goal is to move towards systems capable of storing large amounts of renewable electricity for long periods while providing high safety, long service life and competitive costs over the entire lifetime of the installation.

“When we think about integrating increasing amounts of solar and wind energy, we do not just need to store electricity: we need technologies capable of doing so again and again for many years. That is where flow batteries can offer distinctive value,” explains Raquel Ferret, Business Development Director at CIC energiGUNE.

The development has evolved from initial laboratory cells to larger stacks, and the next step will be to progress towards kW-scale modules, combining simulation, system design and experimental validation.

A battery designed to last

One of the main advantages of redox flow batteries is that they store energy in electrolytes contained in external tanks. This makes it possible to increase the amount of energy stored by increasing the volume of electrolyte without having to increase the system’s power output by the same proportion. 

This characteristic, combined with their high level of safety and ability to withstand a large number of cycles, makes them particularly attractive for applications such as the integration of solar and wind farms, grid-scale energy storage, microgrids and energy management for large industrial consumers.

However, the most established commercial technology currently uses vanadium, whose cost and concentrated supply chain represent two of the main obstacles to wider deployment.

For this reason, one of the major challenges facing the sector is to find alternatives that retain the advantages of flow batteries while reducing both costs and dependence on critical raw materials.

The iron-lead solution developed by CIC energiGUNE is a step in this direction. Its single-flow configuration simplifies the system and reduces the number of components associated with conventional dual-circuit designs, while the active materials used benefit from well-established industrial and recycling supply chains.

The architecture also incorporates a fluorine-free membrane developed to reduce internal resistance and limit the unwanted crossover of species between the two sides of the battery. This solution helps simplify the system and strengthens the technology’s potential to compete in stationary energy storage applications, particularly where the aim is to reduce dependence on critical materials while maintaining competitive costs throughout the installation’s service life.

“A low-cost battery is of little use if it quickly loses performance, while a highly durable battery will struggle to reach the market if its materials or components are too expensive. Our work is precisely about finding that balance between cost, stability, efficiency and manufacturability,” says Ferret.

The iron-lead battery is one of the developments that exemplifies CIC energiGUNE’s strategy in this field, but the centre’s activity in redox flow batteries encompasses a range of different chemistries and components.

The research teams are working on new electrolytes and organic molecules, membranes adapted to different chemistries, electrodes, bipolar plates and stack components, as well as strategies aimed at reducing the cost and consumption of vanadium in current systems.

What distinguishes this approach is that development does not stop at the material level. CIC energiGUNE has the capabilities to study material behaviour from the molecular scale through to its integration into cells and stacks, subsequently incorporating modelling, system design, prototyping, and cost and sustainability analysis. 

“Many technologies deliver very promising results when tested in a small cell. The real challenge begins when that performance has to be maintained over thousands of cycles and then transferred to higher-power stacks and modules,” explains the researcher.

The growing share of renewable energy sources is making this challenge increasingly relevant. Redox flow batteries are not intended to replace every energy storage technology, but they can play a particularly important role in applications where energy needs to be stored for many hours, cycled intensively and kept in operation for long periods with limited degradation.