Who will dominate the future of flow batteries

1. The principle of flow battery technology is the same
2. Flow batteries have their own strengths
3. Completion of the flow battery industry chain
4. Summary

Recently, the Dalian 200MW/800MWh flow battery energy storage peak-shaving power station with the largest power and the largest capacity in the world has been connected to the grid to generate electricity.

CNNC Huineng won the bid for the 1GWh flow battery project of energy storage system centralized procurement of new energy projects in 2022-2023. At the same time, a number of large-scale production and manufacturing plants related to flow batteries have been signed for construction.

Whether from the market side or the industrial chain level, it has become an indisputable fact that flow batteries are striding towards industrialization. Flow batteries have many advantages, such as high safety, long cycle life, recyclable electrolyte, cost-effective life cycle, and environmental friendliness.

They are considered to be one of the preferred technologies for large-scale energy storage technology and have broad application prospects.

According to the different active substances in the electrolyte, flow batteries can be divided into many types. The more typical ones are iron-chromium flow batteries, all-vanadium flow batteries, and zinc-bromine flow batteries. These three technologies have their own advantages and disadvantages. Thus, who will dominate the future?

The principle of flow battery technology is the same

Vanadium batteries, iron-chromium batteries and zinc-bromine batteries are all redox flow battery, so their technical principles are the same.

The all-vanadium redox flow battery mainly realizes electric energy storage and release through the change of the valence state of vanadium ions. The electrolytic hydraulic pressure is injected into the battery stack through an external pump.

The electrolyte solution flows through the electrode surface in parallel and electrochemical reaction occurs, and the current is collected and conducted through the double electrode plate, so that the chemical energy stored in the solution is converted into electrical energy. This reversible reaction process enables the vanadium battery to smoothly charge, discharge and recharge.

The iron-chromium flow battery uses the difference in the valence of iron and chromium ions dissolved in hydrochloric acid solution to charge and discharge. The positive and negative electrolyte solutions are stored in the storage tank outside the battery, and are transported to the inside of the battery through pumps and pipelines.

The positive and negative electrolytes of the zinc-bromine flow battery are both ZnBr2 aqueous solutions, and the electrolytes circulate through the surfaces of the positive and negative electrodes through a pump.

Zinc is deposited on the negative electrode during charging, and the bromine generated in the positive electrode will be immediately complexed into an oily substance by the bromine complexing agent in the electrolyte, so that the bromine content in the aqueous phase is greatly reduced, and the density of the substance is greater than that of the electrolyte.

It will gradually deposit on the bottom of the storage tank during the liquid circulation process, which greatly reduces the volatility of bromine in the electrolyte and improves the safety of the system.

During discharge, the zinc on the surface of the negative electrode dissolves, and the complexed bromine is re-pumped into the circulation loop and dispersed, converted into bromide ions, and the electrolyte returns to the state of zinc bromide, and the reaction is completely reversible.

Flow batteries have their own strengths

The most obvious advantage of the flow battery in the long-term energy storage track is that the power unit and the capacity unit of the battery are independent “decoupling design”.

The number of stacks determines the output power of the entire system, and the amount of its electrolyte determines the capacity of the entire flow battery system. For example, for a 1 MW project, the capacity of the flow battery can be 0.5 MWh, 1 MWh, 2 MWh, and of course it can be configured to 10 MWh, which is more flexible. Especially suitable for large-scale long-term energy storage.

However, among the three main bodies of flow batteries, vanadium batteries, iron-chromium flow batteries and zinc-bromine flow batteries also have their own advantages and disadvantages.

The most prominent advantages of vanadium batteries are long cycle life and high conversion efficiency. The service life of vanadium battery is often more than 10 years, it can be charged and discharged more than 15,000 times, and the conversion efficiency can reach 80%. In contrast, zinc-bromine flow batteries have the shortest cycle life, less than one-third that of vanadium batteries, and the lowest energy conversion efficiency.

However, the initial installation cost of vanadium battery is relatively high, and its installation cost is about 3-3.2RMB/Wh. The high installation cost means that the initial investment of the all-vanadium redox flow battery is relatively large, which limits the development of industrialization to a certain extent.

In addition, the working temperature range of vanadium batteries is narrow, and the ideal working environment is 4-45 °C. Once higher than this temperature, the precipitate in the cathode solution will block the flow channel and make it scrapped. Below this temperature, the electrolyte solidifies and the battery cannot operate.

The electrolyte solution of Fe-Cr flow battery is rich in iron and chromium resources, and its cost is lower than that of all-vanadium redox flow battery (under the condition that other hardware devices remain unchanged, the proportion of electrolyte cost is reduced from 50% of all-vanadium to Fe-Cr 9%), there will be no short-term resource constraints on development, and it has stronger sustainable development.

However, there are some major problems in the zinc-bromine flow battery itself. First, the bromine in the zinc-bromine liquid flow is a volatile solution, which is difficult to solve.

Second, bromine is corrosive and penetrating, and its corrosiveness is not Caused by its acidity and alkalinity, it is the corrosion caused by the penetration of bromine. In addition, during the reaction, the electrode where the zinc is located is prone to produce some zinc dendrites, which can pierce the separator and reduce the performance of the entire battery.

Completion of the flow battery industry chain

In the field of flow batteries, vanadium flow batteries are currently leading in terms of the integrity of the industrial chain and the process of industrialization. At present, the vanadium battery industry chain mainly forms three major links: upstream vanadium pentoxide raw material production, midstream components matching and downstream assembly production.

The vanadium battery industry chain is relatively complete, so its industrialization is also accelerating, and the development of GW-level energy storage power station projects has been realized. Here is a list of top 10 vanadium battery factories in China for your reference. However, issues such as cost and technology are still problems that need to be broken through in the commercialization of vanadium batteries.

The iron-chromium flow battery is still in its infancy, and the related projects are all small-scale demonstrations. Large-scale commercial projects have not yet started, and the number of mature enterprises is still small.

In terms of upstream raw materials, the overall market of the chromium salt industry is characterized by small scale, high concentration, and regional exclusive dominance. Zhenhua was established in 2003. It is an early chromium salt enterprise in the industry to deploy iron-chromium flow batteries, and it is also the world’s leading chromium salt company.

At present, in terms of technology research and development and industrialization development, zinc-bromine flow batteries are very different from vanadium batteries, but individual companies such as Jiangsu Hengan are still actively exploring in this field.

Through independent innovation, Jiangsu Hengan Energy Storage Technology has successfully developed my country’s first set of zinc-bromine flow batteries and key materials such as battery separators, plates and electrolytes, filling the technical gap in this technical field in China.

Summary

On the whole, vanadium batteries have obvious advantages, the industrial chain is relatively complete, and the industrialization process is accelerating. The long-term cost advantage of iron-chromium flow batteries is also very obvious.

Experts predict that vanadium batteries and iron-chromium flow batteries will show increased competition in the long-term energy storage market in the future, while the future of zinc-bromine flow batteries does not look so optimistic.

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