This Water Battery Beats Lithium-Ion for Home Solar Storage?
Australian engineers have achieved a breakthrough in water-based flow battery technology, potentially revolutionising home energy storage. A next-generation design overcomes the limitations of earlier flow batteries, offering a safer, cheaper, and more efficient alternative to lithium-ion systems for storing rooftop solar energy.
What is a Water Battery?
A water battery (scientifically known as an aqueous battery) is an energy storage system that uses water-based solutions as its electrolyte instead of the flammable organic solvents found in conventional lithium-ion batteries.
Broadly, water battery technology falls into two categories:
- Aqueous Redox Flow Batteries: Systems where liquid electrolytes are pumped through an electrochemical cell to store and release energy.
- Aqueous Metal-Ion Batteries: Solid-state batteries that use water-based electrolytes instead of organic polymer gels, often employing abundant metals like zinc, magnesium, or sodium.
Because the core medium is water, these batteries are inherently non-flammable, non-toxic, and highly recyclable, positioning them as the ultimate safety-first alternative for residential and grid-scale energy storage.
Flow Batteries: A Key Technology for Energy Storage
Flow batteries have been around for decades, traditionally utilised for large-scale energy storage due to their size and slow charging speeds. Unlike lithium-ion batteries that store energy in solid materials, flow batteries store energy in liquid electrolytes. This offers several advantages:
- Safety: Water-based flow batteries are non-flammable and non-toxic, making them safer than lithium-ion batteries, which pose a fire risk.
- Cost-Effectiveness: Flow batteries can be manufactured using abundant and inexpensive materials, potentially leading to lower costs than lithium-ion systems.
- Scalability: The energy storage capacity of a flow battery is determined by the size of its electrolyte tanks, allowing for easy customisation and scaling.
- Long Lifespan: Redox flow batteries can withstand numerous charge and discharge cycles without significant degradation, making them ideal for renewable energy storage.
However, previous flow battery designs have been too bulky and slow for residential use. The new water-based battery developed by researchers at Monash University overcomes these limitations, making it a promising candidate for home energy storage.
Monash University's Membrane Breakthrough
The key to Monash University's breakthrough lies in a newly engineered membrane that allows for faster charging speeds. This innovation addresses a major drawback of earlier flow battery designs, making them suitable for capturing rooftop solar energy in real-time.
The Ultra-Ion-Selective SPEEK-SX Membrane
The study highlights an ultra-ion-selective SPEEK-SX membrane, enabling 600 cycles at 160 mA cm-2 with only 0.00935% per cycle capacity decay. This outperforms the industry-standard Nafion-212 membrane and offers a fluorine-free alternative.
Outperforming the Industry Standard
According to Wanqiao Liang, a PhD candidate at the Department of Materials Science and Engineering at Monash University and the study's lead author, the new membrane design is at the heart of the team's breakthrough.
“The key was improving ion selectivity; letting the good ions through quickly while keeping unwanted ones out,” says Liang. “Our new membrane achieves this balance, allowing fast, stable operation even at high current densities.”
In testing, the technology outperformed the industry-standard membrane in both speed and stability, running 600 high-current cycles with virtually no capacity loss.
Aims for Rooftop Solar and Home Use
The engineers state that their next-generation flow battery is expected to be much cheaper than current £8,000 (US$10,000) lithium-ion systems and enables compact, high-performance battery systems for homes.
“This is the kind of battery you'd want in your garage,” Liang said. “It's non-toxic, non-flammable, and made from abundant materials, all while keeping up with solar power on a sunny day.”
Publishing the Results
The team's findings have been published in Angewandte Chemie International Edition (2025) in a paper titled “Flow Battery with Remarkably Stable Performance at High Current Density: Development of A Nonfluorinated Separator with Concurrent Rejection and Conductivity”.
How Does It Work?
The Monash team's flow battery design incorporates a non-fluorinated separator with concurrent rejection and conductivity. Unlike lithium-ion batteries, which rely on solid materials, flow batteries store energy in liquid form, offering safer and more sustainable operation.
Redox Flow Batteries Explained
Redox flow batteries store energy in liquid solutions called electrolytes, which contain chemical compounds that can change from an oxidised to a reduced state and vice versa. During operation, two types of electrolytes are pumped from separate tanks through a central electrochemical cell. In this cell, the electrolytes interact through an ion-exchange membrane, generating electricity that can be used or stored.
The Membrane's Role
The membrane plays a crucial role in the battery's performance by selectively allowing ions to pass through while blocking unwanted substances. This improves the battery's efficiency, stability, and lifespan. The new membrane developed by the Monash team achieves this balance, allowing for fast and stable operation even at high current densities.
Overcoming the Voltage Limits of Water
One of the fundamental challenges of any water battery is the narrow electrochemical stability window of water. Thermodynamically, water splits into hydrogen and oxygen gas at a relatively low voltage:
2H2O→O2+4H++4e−(E0=−1.23 V)When a water battery exceeds this voltage threshold, electrolysis occurs, consuming the water electrolyte and creating gas buildup. The Monash SPEEK-SX membrane and advanced electrolyte formulations overcome this chemical limit by suppressing water-splitting side reactions, allowing the battery to operate at higher voltages and currents without degrading.
Benefits of the New Water Flow Battery
While sharing the baseline safety, longevity, and scalability advantages of standard aqueous flow batteries, the Monash University design introduces several unique performance benefits:
- High-Rate Charging: The novel SPEEK-SX membrane enables much faster charging and discharging speeds, making it practical for capturing highly variable rooftop solar energy in real-time.
- Fluorine-Free Construction: By utilising a fluorine-free alternative to industry-standard membranes, the battery reduces manufacturing complexity, environmental impact, and production costs.
- Stable High-Current Operation: The system can withstand hundreds of high-current cycles with negligible capacity decay, ensuring long-term operational reliability.
How Water Batteries Compare to Lithium-Ion
To understand why this water battery technology is highly anticipated, it is helpful to compare it directly to traditional lithium-ion systems and other emerging aqueous designs.
| Feature | Lithium-Ion Battery | Aqueous Flow Battery (Monash) | Aqueous Metal-Ion Battery (RMIT) |
|---|---|---|---|
| Electrolyte Type | Flammable organic solvents | Water-based liquid | Water-based liquid or gel |
| Fire Risk | High (thermal runaway risk) | Absolute zero (non-flammable) | Absolute zero (non-flammable) |
| Typical Lifespan | 5,000 to 10,000 cycles | 10,000 to 20,000+ cycles | Up to 10,000 cycles |
| Energy Density | High (150 to 250 Wh/kg) | Low to Medium (15 to 40 Wh/kg) | Medium (50 to 100 Wh/kg) |
| Primary Use Case | EVs, compact electronic devices | Long-duration home & grid storage | Residential storage, lead-acid swap |
| Recyclability | Complex, costly, toxic chemicals | High (mostly water & stable salts) | Extremely high (biodegradable metals) |
Real-World Testing and Future Prospects
The Monash University engineering team is currently 3D printing prototype systems and testing them under real-world conditions. If the prototypes continue to perform as expected, the battery could be commercially available in a few years.
Monash's Microgrid
Monash University has already demonstrated its commitment to renewable energy with the installation of a 1 MWh redT energy (now known as Invinity Energy Systems) storage system in 2018. This system is a core part of the microgrid at its Clayton, Victoria campus and plays a central role in the university's goal to become 100% energy self-sufficient and achieve Net Zero emissions.
The Competition
While Monash University's design stands out for its combination of safety, low cost, and high-speed performance, other organisations and companies are also developing water battery systems for residential and commercial use.
AQUABATTERY
AQUABATTERY, developed in the Netherlands, is another novel flow battery that uses an acid-base reaction based on reversible water dissociation. It stores electricity in the form of chemical energy in acid, base, and saltwater solutions. Pumps circulate these fluids through a power stack with electrodes separated by membranes. The membranes allow ion exchange between electrolytes to generate electricity. This design is also customisable and suitable for long-duration applications and utility-scale deployment.
RMIT University's Aqueous Metal-Ion "Water Battery"
In another major Australian breakthrough, researchers at RMIT University in Melbourne developed an alternative type of water battery: a solid-state aqueous metal-ion design.
Rather than using flowing liquid tanks, RMIT’s system uses simple metals like magnesium or zinc to replace toxic materials like lead and cadmium. By using water as the electrolyte, the RMIT team successfully prevented the growth of dendritic structures—sharp, needle-like metallic formations that cause short circuits in traditional lithium-ion batteries. This makes the RMIT water battery highly durable, safe, and a direct physical alternative to domestic lead-acid or lithium batteries.
Potential Applications
The new water flow battery has the potential to revolutionise home energy storage and accelerate the transition to a cleaner energy future. It could also be used in other applications, such as:
- Grid-scale energy storage: Flow batteries can be used to store large amounts of energy from renewable sources, such as solar and wind power, helping to stabilise the grid.
- Microgrids: Flow batteries can be used to create self-sufficient microgrids that provide reliable power to communities and businesses.
- Electric vehicle charging stations: Flow batteries can be used to store energy for electric vehicle charging stations, reducing the strain on the grid.
Challenges and Opportunities
While the new water flow battery technology is promising, there are also challenges to overcome before it can be widely adopted. These challenges include:
- Energy Density: Flow batteries typically have lower energy density than lithium-ion batteries, meaning they require larger tanks to store the same amount of energy.
- Cost Reduction: While flow batteries have the potential to be cheaper than lithium-ion batteries, further cost reductions are needed to make them competitive in the market.
- Commercialisation: More companies need to invest in the development and commercialisation of flow battery technology to accelerate its adoption.
Despite these challenges, the opportunities for flow batteries are vast. As the world transitions to a cleaner energy future, energy storage will become increasingly important. Flow batteries offer a safe, cost-effective, and scalable solution for storing renewable energy, making them a key technology for the future.
