Recently, CGN New Energy Gong'an County 50MW/100MWh iron-based flow battery energy storage power station demonstration project officially launched EPC bidding. The project is located in Yangjiachang Town, Gong'an County, Jingzhou City, Hubei Province. It is invested and developed by CGN New Energy Gong'an County Co., Ltd. The planned construction capacity is 200MW/800MWh, of which the current construction capacity is 50MW/100MWh. The project is scheduled to start on May 10, 2025, and is expected to complete full-capacity grid-connected power generation before June 30, 2025.
What is iron flow battery
Iron-based flow batteries (IBFB) are a type of electrochemical energy storage technology that uses iron salt solution as electrolyte and realizes energy storage and release through the redox reaction of iron ions.
How does iron flow battery work
Its core principle is to use iron ions dissolved in the electrolyte as active substances, and complete the charging and discharging process through the circulation of positive and negative electrolytes. Compared with other flow batteries (such as all-vanadium flow batteries), the advantages of iron-based flow batteries are low raw material costs, abundant resources, and high safety.
For example, iron resources are abundant, with a content of about 5% in the earth's crust, and the electrolyte cost is low, with the price of FeCl₂ being about 1 yuan/kg. In addition, aqueous electrolytes have no combustion risk and are suitable for large-scale energy storage scenarios. The theoretical number of cycles exceeds 10,000 times, and in actual applications it can reach more than 5,000 times. There is no heavy metal pollution, and the electrolyte can also be recycled.
Indicators Iron-based flow battery All-vanadium flow battery Lithium-ion battery
Cost (yuan/kWh) 150-300 3500-4500 500-800
Cycle life (times) >5000 >15000 3000-5000
Energy density (Wh/L) 10-15 20-25 300-600
Safety High (no risk of explosion) High Medium (risk of thermal runaway)
Applicable scenarios Grid-level long-term energy storage Large energy storage power station Mobile devices, short-term energy storage
Iron-based flow batteries are developing rapidly
At present, there are three main technical routes for iron-based flow batteries: all-iron flow batteries, which use iron-based active materials for both positive and negative electrodes to avoid cross-contamination; iron-chromium flow batteries, with positive electrodes Fe³⁺/Fe²⁺ and negative electrodes Cr³⁺/Cr²⁺, but limited by the side reaction of hydrogen evolution from Cr²⁺; and zinc-iron flow batteries, with positive electrodes Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ and negative electrodes Zn²⁺/Zn, which need to solve the problem of zinc dendrites.
For example, State Power Investment Corporation has built the world's first 250kW/1.5MWh iron-chromium flow battery demonstration project (Ronghe No. 1) in Zhangjiakou, Hebei, and promoted a 1MW/6MWh project in Huolin River, Inner Mongolia, verifying the feasibility of this technology in power grid peak regulation. Iron-chromium flow batteries use hydrochloric acid electrolytes, with a cycle life of more than 20,000 times and an energy density of about 25-35Wh/L, which is suitable for long-term energy storage.
However, the initial manufacturing cost of iron-chromium flow batteries is currently high, key materials such as proton exchange membranes rely on imports, and the energy density is lower than that of lithium batteries. However, through large-scale production and localization of materials, costs are expected to drop significantly.
In the all-iron flow battery, the Institute of Metal Research of the Chinese Academy of Sciences has improved the reversibility of the iron negative electrode through electrode interface defect design and polar solvent regulation, and achieved stable operation for 100 hours at a low temperature of -20°C. This technology reduces the freezing point of the electrolyte to below -20°C, and by optimizing the uniformity of iron deposition, the cycle stability is increased by 10 times, and the power density reaches 80mW/cm².
In the field of zinc-iron flow batteries, Weijing Energy Storage has built a 3GW zinc-iron flow battery intelligent manufacturing base in Baotou, Inner Mongolia, which is expected to be put into production in 2025. Zinc-iron flow batteries use zinc as the negative electrode and iron as the positive electrode. They are lower in cost and safer, and are suitable for large-scale long-term energy storage.
Key technology breakthroughs and development trends
The current iron-based flow batteries still have some technical bottlenecks, such as dendrite growth. However, the Chinese Academy of Sciences team constructed a defect structure on the surface of the carbon electrode through metal etching to promote uniform iron deposition, successfully inhibited dendrite growth, and increased the current efficiency to 99%, and the cycle stability by 10 times.
In terms of electrolyte, the Chinese Academy of Sciences team introduced polar solvents (such as ethylene glycol) to reduce the freezing point to -20°C, achieving low-temperature stable operation, and increased the FeCl₃ concentration to 3M, with an energy density of 15Wh/L, while the traditional all-vanadium flow battery is about 25Wh/L.
Of course, there are still some challenges to be addressed. For example, the current localization rate of key materials such as proton exchange membranes and bipolar plates is insufficient. Among them, perfluorosulfonic acid membranes (such as Nafion) account for 15%-20% of the cost, the localization rate is less than 30%, and the performance (such as proton conductivity) is inferior to overseas products. It is necessary to accelerate the development of high-performance alternative materials, and graphene composite membranes can be used as substitutes. In addition, the links such as electrolyte recovery and system integration are not yet mature, and a complete industrial chain from raw materials to operation and maintenance needs to be established.
Fortunately, some domestic companies have begun to promote domestic substitution. For example, the ion exchange membrane of Kerun New Materials and the bipolar plate of Dongyue Group have begun to be mass-produced locally, reducing supply chain risks.
At the same time, Shanghai Electric, Dalian Rongke, etc. are planning gigawatt-level battery manufacturing bases, aiming to reduce costs to less than 1,500 yuan/kWh in 2027.
In terms of cost, taking the 4-hour energy storage solution as an example, the initial cost of the all-iron liquid flow battery is about 2,500-3,000 yuan/kWh, of which electrodes and ion exchange membranes account for more than 40%. In 2024, the global iron-based flow battery production capacity is less than 1 GW, and it is difficult to dilute the cost through large-scale production.
Highly active carbon-based composite materials, such as defective carbon felt, can be developed to improve reaction kinetics and reduce hydrogen evolution side reactions. At the same time, wide temperature range solvents (such as ionic liquids) or new iron salts (such as FeCl₃-ethylene glycol complexes) can be introduced to balance low-temperature performance and cost.
In addition, iron-based electrolytes need to be replaced regularly, resulting in increased long-term operation and maintenance costs. For example, the annual loss rate of the iron-chromium system is about 2%. In addition, low-concentration FeCl₂ electrolytes are prone to hydrogen evolution, and some inhibitors such as lead salts need to be added, which will also push up costs.
In terms of market size, the market size of iron-based flow batteries in 2025 will be about 12 billion yuan, and it is expected to exceed 50 billion yuan in 2030, with an annual compound growth rate of more than 30%. In the Chinese market, with the promotion of policies, the installed capacity target in 2025 will reach 10GW, focusing on the storage of northwest wind and solar bases.
From the overall market perspective, the short-term energy storage market is dominated by lithium batteries, which will still account for more than 90% of the global market in 2024. Iron-based flow batteries need to establish differentiated advantages in the field of long-term energy storage. On the other hand, the cost of sodium-ion batteries is falling rapidly, and it is expected to reach 0.3 yuan/Wh by 2027, which may squeeze the space for iron-based flow batteries in the mid- and low-end markets.
Summary
The commercialization challenge of iron-based flow batteries is essentially a comprehensive game of technology maturity, cost control and market ecology. In the short term, it is necessary to break through core technologies such as electrolyte stability and material corrosion resistance to reduce system costs; in the medium and long term, it is necessary to rely on policy support, accumulate data through large-scale demonstration projects, and establish industrial chain synergy. If it can highlight the cost advantage in long-term energy storage (especially in scenarios of more than 10 hours), combined with the global accessibility of iron resources, it is expected to become an important supplementary technology for distributed energy storage and grid peak regulation in the future.
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