The future of the energy transition depends on how effectively we can store renewable energy. Until now, lithium-ion batteries have dominated both electric vehicles and household storage systems, but more advanced alternatives are already emerging. A research group at Monash University in Australia has proposed one such option: a redox flow battery — or, in simpler terms, a water-based liquid battery that is affordable, safe, and capable of replacing lithium systems, which can cost up to ten thousand euros when installed at home. But what makes this new generation of liquid batteries so promising?

The team’s proposal is based on a seemingly simple idea: a battery that uses water-based materials to deliver greater thermal stability, a longer lifespan, and lower costs.

How does that translate into practice? The breakthrough lies in the membrane that separates the electrolytes. The researchers have developed a non-fluorinated membrane that improves ion selectivity — in essence, it lets the “good” ions pass more easily while blocking the “bad” ones. This allows the battery to operate at high current density without losing stability.

In laboratory tests, the device has achieved around 600 high-current cycles with no significant capacity loss — a notable improvement over many existing flow batteries. The Monash team is already producing prototypes using 3D printing as a step towards future commercialisation.

Unlike conventional batteries, where the electrodes and electrolyte are housed within a solid structure, liquid or “flow” batteries store energy in liquids that circulate between separate tanks.

These liquids contain chemical compounds capable of releasing or absorbing electrons through redox (reduction–oxidation) reactions. When the battery is charged, the electrolytes store energy; when discharged, they release it. The two tanks are separated by a membrane that allows ions to move between them while keeping the liquids from mixing, thereby maintaining electrical balance.

The main advantage of this design lies in its flexibility: storage capacity depends on the volume of liquid, while power output is determined by the size of the electrochemical cell. In other words, the amount of energy stored and the charging speed can be adjusted independently — a major advantage for scalable systems.

If the technology sounds so promising, why has it not yet been widely adopted? The main limitation is energy density — the amount of energy that can be stored per unit of volume or weight — which remains lower than that of lithium-ion batteries. This makes flow batteries unsuitable for compact applications such as mobile devices or electric vehicles, where space and weight are critical. Nobody wants to carry a rucksack-sized phone battery.

Another significant hurdle is cost. Although the active materials themselves are relatively inexpensive, the required infrastructure — tanks, pumps, valves, and membranes — drives up the overall price, particularly for small-scale systems. Finally, the membranes that separate the liquids remain a weak point: they must selectively allow ions to pass while keeping the electrolytes from mixing, which demands advanced materials and precision engineering. The Monash researchers’ recent membrane innovation directly tackles this challenge.

Although the progress made by Monash University is encouraging, the gap between academic success and large-scale commercial deployment remains wide. The technology will need to be tested under real-world conditions, undergo safety certification, standardise its production processes and, crucially, prove that its total long-term cost can compete with lithium.

As the demand for distributed energy storage grows alongside the expansion of renewables, liquid batteries could emerge as a key intermediary solution — bridging the gap between household systems and large-scale grid storage.

Source:

• TechXplore