Lithium batteries essentially rule our world now. Our phones, cordless tools, and cars, to name a few, all rely on the technology, and it, in turn, relies on our ability to mine and process lithium. And while deposits such as the 2.3 million metric tons of lithium in the Appalachian Mountains suggest that we'll have a steady supply of the metal for many years to come, it doesn't change the fact that lithium is relatively expensive, trading at about $26,000 per tonne as of mid-May 2026. That's not necessarily exorbitant, admittedly, but there are plenty of cheaper metals out there: Iron ore, for example, trades at just over $110 per tonne. It may have a bright future as a material in more affordable batteries, too: In April 2026, scientists from the Chinese Academy of Sciences' Institute of Metal Research (IMR) announced that they had developed an "all-iron" flow battery that, according to a research paper published in Advanced Energy Materials, will last 6,000 charge cycles — or about 16 years of daily use — without losing any capacity. For context, the lithium-ion battery in your smartphone will last fewer than 1,000 cycles, while larger batteries may endure up to 5,000 cycles.
Flow batteries differ from conventional lithium-ion batteries in that they submerge the battery elements in an electrolyte fluid. This particular battery uses a new electrolyte that "effectively prevents hydroxide ions from attacking the iron center," per an IMR press release. This protection for the iron core results in a longer-lasting battery that overcomes the longevity and durability issues associated with previous designs, which tend to degrade very quickly. The concept of flow batteries is not new; they have been studied for decades as a potential solution for stationary energy storage because of their scalability and decoupled energy and power ratings. Traditional flow batteries often use vanadium, but vanadium is also expensive and toxic. Iron, being abundant and inexpensive, has long been a dream material for flow batteries, but earlier versions suffered from hydrogen evolution and side reactions that limited cycle life.
A Leap in Coulombic Efficiency
Saying that a battery will last for 16 years without losing capacity is all well and good, but can we quantify this durability? Actually, yes. In the same IMR press release, the researchers claim that their iron battery achieved an average coulombic efficiency — the number of electrons transferred between battery electrodes during charging — of 99.4% over more than 6,000 cycles at a current of 80 mA/cm², with no reduction in capacity. It performed impressively at higher currents, too, with 78.5% efficiency at 150 mA/cm². High coulombic efficiency is associated with longer battery life, so this tech looks to have quite a lot of potential indeed. For comparison, typical lithium-ion batteries have coulombic efficiencies around 99.9% or higher, but they degrade in capacity over time due to side reactions and structural changes. The all-iron battery's ability to maintain capacity over thousands of cycles is remarkable, especially at such a low materials cost.
The key innovation lies in the electrolyte formulation. The IMR team developed a complexing agent that forms a protective barrier around the iron ions, preventing hydroxide ions from reacting with iron in a way that would cause precipitation or passivation. This allows the iron to cycle between Fe²⁺ and Fe³⁺ states without losing active material. Similar strategies have been attempted before, but the Chinese team's specific combination of ligands and pH control appears to be the breakthrough. They also optimized the carbon felt electrodes to improve reaction kinetics and reduce overpotentials.
From Lab to Grid: Applications and Challenges
While this development is certainly promising, we're unlikely to see all-iron flow batteries in consumer electronics any time soon, if ever. Instead, this tech is intended for long-term grid-scale energy storage, most likely in battery facilities such as California's massive Darden Clean Energy Project, and will play a big part in the worldwide push toward renewable energy. The primary advantage of flow batteries for grid storage is that they can be scaled up simply by increasing the size of the electrolyte tanks, making them ideal for multi-hour to multi-day storage durations. Lithium-ion batteries, while excellent for short-duration storage, become prohibitively expensive for long-duration applications due to the cost of the cells and the need for thermal management.
All-iron flow batteries could also be manufactured with locally sourced materials, reducing supply chain risks. Iron is mined in many countries, including the United States, Australia, and Brazil, and does not rely on politically sensitive regions like the Democratic Republic of Congo for cobalt or China for processed lithium. However, there are still challenges to commercialization. The energy density of flow batteries is much lower than that of lithium-ion, meaning they take up more physical space. For grid applications, this is often acceptable, but for residential or commercial buildings, space constraints could limit deployment. Additionally, the all-iron system must prove its long-term stability beyond the lab. The 6,000 cycles tested correspond to about 16 years, but real-world operation includes varying temperatures, impurities, and occasional deep discharges. The IMR team will need to conduct field trials to validate the longevity.
The Global Context: Flow Battery Renaissance
Flow batteries, regardless of the tech, look to be the hot new thing in energy storage. Japan and China brought massive flow battery facilities online in April and July 2022, respectively, while U.S.-based startup Ess Tech Inc teamed up with Arizona's Salt River Project in 2025 to supply flow batteries for Project New Horizon, a 5-megawatt, 50-MWh battery system capable of powering more than 1,000 homes for 10 hours. Time will tell whether the Chinese Academy of Sciences' battery tech will be deployed on similarly large scales. Other iron-based flow battery companies, such as ESS Inc. (which is different from Ess Tech Inc.) and Energy Storage Systems Pty Ltd, have also made progress with iron-chromium and all-iron chemistries, but the IMR battery's performance metrics appear to be the best reported so far.
The push for renewable energy integration has accelerated the need for long-duration storage. Solar and wind power are intermittent, and grid operators need reliable backup for periods when the sun doesn't shine or the wind doesn't blow. Lithium-ion batteries can cover a few hours, but for longer periods, alternatives like pumped hydro, compressed air, or flow batteries are required. Flow batteries offer the advantage of independent scaling of power and energy: adding more electrolyte increases energy capacity without changing the power rating. This makes them exceptionally flexible for utilities planning storage systems that need to discharge for 10 to 20 hours.
Iron-based flow batteries also have an environmental edge. Lithium-ion batteries require significant water for mining and processing, and their disposal poses pollution risks. Iron is non-toxic and abundant. The electrolyte in an all-iron flow battery is typically water-based and can be recycled or disposed of safely. The carbon felt electrodes can be reused or repurposed. This aligns with the circular economy principles that many governments are promoting.
One of the hurdles for all-iron flow batteries is improving the power density, which affects the cost of the power conversion system and the stack itself. The IMR team reported a peak power density of about 0.2 W/cm², which is competitive with vanadium redox flow batteries but lower than some emerging non-flow chemistries. However, the low cost of materials compensates, making the levelized cost of storage very attractive. A recent study by the National Renewable Energy Laboratory estimated that iron flow batteries could achieve a cost of $50 per kWh for long-duration storage, compared to $150-$200 per kWh for lithium-ion. The Chinese development could bring that cost down further.
What does this mean for consumers? In the short term, little change. But over the next decade, if all-iron flow batteries prove reliable, homeowners with solar panels might be able to install a flow battery in the garage that stores a full day's energy without the fire risk associated with lithium-ion. Utilities could build storage facilities that support entire neighborhoods during peak demand, reducing the need for fossil fuel peaker plants. The technology could be particularly transformative in developing countries where grid infrastructure is weak and energy access is limited. Iron-based batteries could be produced locally with less imported material, enabling energy independence.
The IMR is now working with commercial partners to scale up production. A pilot plant is expected within the next two years, and if successful, full-scale manufacturing could begin by 2030. The researchers are also exploring hybrid systems that combine iron flow batteries with supercapacitors for applications requiring both high power and high energy. Meanwhile, competitors are not standing still. Redflow Limited in Australia continues to deploy zinc-bromine flow batteries, and Primus Power in the U.S. developed zinc-iron flow batteries for military applications. But the all-iron chemistry's simplicity and cost advantage make it a strong candidate for the future of energy storage.
Source: SlashGear News