An overview of iron-chromium flow battery technology, advantages, disadvantages and economics

The rapid development of energy storage has inevitably produced some problems.

For example, with the large-scale integration of renewable energy sources such as wind farms, photovoltaic power stations, and hydropower into the grid, my country's power grid acceptance capacity has begun to appear inadequate. In response to this problem, the market has put forward major Scale energy storage is a solution.

Among the many large-scale energy storage technologies, iron-chromium flow batteries are one of the strong competitors in the future large-scale storage market.

　Four Kings of Flow Batteries

　　Flow batteries consist of positive and negative electrolyte storage tanks, positive and negative electrodes It is composed of electrolyte, stack system and managementcontrol system.

Currently, the popular flow batteries on the market are mainly divided into four categories: iron-chromium flow batteries, all-vanadium flow batteries, lead-acid flow batteries and lithium Ion flow batteries.

First, Iron-chromium flow battery has long life, low cost, mature technology, abundant raw materials, and wide operating temperature range. There is huge potential in areas such as large-scale long-duration energy storage.

Second, All-vanadium redox flow battery has the most mature technology and the most sufficient marketization. The disadvantage is that the cost of electrolyte is high.

On the 30th of last month, the Dalian flow battery energy storage power station, which ranks first in capacity and power in the world, was successfully connected to the grid to generate electricity.

Third, Lead-acid flow battery has low initial design cost, but its shortcomings are short life and high later maintenance costs, so it has not been widely used.

Fourth, lithium-ion flow battery has no obvious market advantages. In terms of large and medium-sized energy storage, it is not as good as iron-chromium flow battery and all-vanadium flow battery. Batteries may have applications in small-scale energy storage and short-term energy storage in the future.

　Iron-chromium flow battery VS all-vanadium flow battery

The mainstream commercial flow batteries are iron-chromium flow batteries and all-vanadium flow batteries.

Comparing the two, Iron-chromium flow battery has obvious advantages in terms of operating temperature and raw material cost.

First, in terms of operating temperature, the operating temperature of iron-chromium flow battery is -20~70℃ , the operating temperature of all-vanadium flow batteries is 5~50°C, and the operating temperature range of iron-chromium is significantly larger.

Second, In terms of raw material costs, the key raw materials for iron-chromium flow batteries and all-vanadium flow batteries are chromite and vanadium respectively.

According to the price trend in Shanghai on November 10, 2022, the price of 50-base ferrovanadium is 15.6 times that of 50-base ferrochromium. The key raw materials of ferrochrome flow batteries are cheaper.

In addition, the crustal content of chromium is 0.01%, ranking 17th. Globally, chromite resources are abundant. In 2020, global chromium ore resources were approximately 9 billion tons, and global chromium ore production was 34.8 million tons in 2021. In China, the chromium industry chain is complete and relevant technology reserves are comprehensive.

　However, in terms of technological maturity and self-sufficiency of raw materials, all-vanadium redox flow batteries are superior.

First, in terms of technological maturity, all-vanadium flow batteries are more mature than iron-chromium flow batteries.

At present, in all-vanadium redox flow battery projects, the power of a single stack can reach 400V, while in iron-chromium flow battery projects, the power of a single stack is only 30-40V. The gap is obvious. .

Industry insiders predict that with the development of related technologies, the power of a single stack of iron-chromium flow batteries can reach 400V by the end of 2025.

Second, In terms of self-sufficiency in raw materials, my country has the largest vanadium ore reserves in the world, but it relies heavily on imported chromium ore.

China’s chromium ore reserves are only 4.07 million tons, accounting for less than 1% of the world. However, the demand is huge, self-sufficiency accounts for less than 10%, and it relies heavily on foreign imports.
 

In comparison, according to relevant USUG data, my country's vanadium ore reserves will be 9.5 million tons in 2021, accounting for 40% of global reserves. It is the country with the largest vanadium ore reserves in the world.

　Large-scale long-term energy storage adapter

　Iron-chromium flow battery has long life, Low cost, high safety, high performance, large capacity, weak toxicity, weak corrosiveness and other advantages.

In terms of low cost, the cost of electricity per kilowatt hour is only 0.4 yuan/kWh, which is lower than The price of all-vanadium redox flow battery is 0.8~1.3 yuan/degree.

　In terms of high safety, the positive and negative electrolytes of the iron-chromium flow battery are both aqueous solutions and are packed in two independent liquid storage tanks. , the electric stack is separated from the liquid storage tank, and there is no risk of explosion.

　In terms of high performance, the energy density of iron-chromium flow batteries is 10~20Wh/liter.

At present, the iron-chromium flow battery energy storage projects that have been put into operation in our country include the Zhanshigou Photovoltaic Power Station 250kW/1.5MWh Iron-Chromium of Zhangjiakou Branch of Hebei Electric Power Co., Ltd. of State Power Investment Group Flow battery energy storage demonstration project, and 1MW/4MWh iron-chromium flow battery long-term energy storage project in the Science and Technology City New District of Mianyang City, Sichuan.

In terms of shortcomings, the current commercialization limitation of iron-chromium flow batteries is mainly that the power of the single stack is still low, only 30~40V.

Based on the advantages and disadvantages of iron-chromium flow batteries, iron-chromium flow batteries will be the king of adaptation in large-scale long-term energy storage fields such as wind and solar distribution and storage.

　Bright prospects

In recent years, the industry has worked hard to tackle key problems and solved theproblems that have always plagued iron-chromium flow batteries. Three problems: electrolyte mixing problem, cathode hydrogen evolution problem and electrolyte attenuation problem.

Among them, the problem of electrolyte mixing was solved by using a mixed solution of iron ions and chromium ions; the problem of hydrogen evolution at the cathode was solved by using a catalyst; and the problem of hydrogen evolution at the cathode was solved by designing and installing a rebalancing system. Electrolyte attenuation problem.

With the further improvement of iron-chromium flow battery technology, the current shortcomings of low power of single cell stacks, once solved, iron-chromium flow batteries will usher in a bright future.