Reasons why redox flow battery becomes energy storage products

1. Redox flow battery is a safer energy storage option
2. Advantages and disadvantages of redox flow battery
3. Redox flow battery is back to the market
4. Expand the flow battery energy storage industry system
5. Summary

In the past, lithium batteries were the absolute focus of the market, and they were widely used in mobile phones, home appliances, new energy vehicles and the recently rapidly emerging energy storage industry. But now lithium batteries have ushered in a new opponent – redox flow battery.

Statistic pointed out that ternary lithium batteries should not be used in medium and large electrochemical energy storage power stations, and it is not appropriate to use cascade utilization power batteries, mainly from lithium batteries. However, there are still some famous ternary battery manufacturers in China which focus on making ternary battery. In this way,  we can read the top 10 ternary power battery manufacturers in China. 

In this case, redox flow battery began to become the focus of development. But in fact, flow battery as an electrochemical energy storage technology is not a new thing. All-vanadium, iron-chromium, zinc-iron and other flow battery technologies have experienced nearly half a century of development.

Redox flow battery were born during the energy crisis and have been developing slowly since then. Until recent years, the energy storage market has regained attention with the development of new energy. This technology has begun to receive attention in China, and may affect the new energy storage pattern dominated by lithium batteries in the future.

1. Redox flow battery is a safer energy storage option

Redox flow battery (RFB) is one of the technical routes in electrochemical energy storage. It is a technology that utilizes the energy difference generated in the process of metal redox (Redox) to realize the conversion of chemical energy and electrical energy. Unlike lithium batteries, which store the electrolyte inside the battery, the electrolyte of the flow battery is stored in the outer container of the battery stack.

During charging and discharging, the positive and negative electrolytes will be pumped into the battery stack respectively for oxidation reaction. After the reaction is completed, the electrolyte will be It is re-pumped back to the outer container to restore its original state, and the cycle repeats.

In the past few years, few people have paid attention to redox flow battery, and more attention has been paid to electrochemical energy storage technologies such as lithium batteries and lead-acid batteries. Lithium-ion batteries have become the focus of the energy storage market due to their mature technology and degree of commercialization.

According to statistics, in 2021, lithium batteries will account for more than 90% of the installed electrochemical energy storage capacity in China, followed by lead batteries, accounting for 5.5%, redox flow battery and other electrochemical energy storage technologies, accounting for 2.9% and 0.6% respectively. 

Lithium ranks in the front row of the periodic table, so lithium ions are extremely active. Due to its advantages of light weight, large capacity and high energy density, it is widely used in all walks of life. But on the other hand, lithium batteries also have their shortcomings. Excessive charging and discharging of lithium batteries, short circuits, and battery overheating and runaway caused by extrusion are the main reasons for the instability of lithium batteries.

Lead-acid battery technology is the most mature, with stable performance and extremely short service life, which directly affects the application scope of lead-acid technology. Within 300~350℃. So the advantages of redox flow battery began to emerge.

2. Advantages and disadvantages of redox flow battery

Since the redox flow battery stores energy in an aqueous electrolyte, and the energy conversion does not depend on solid electrodes, there is almost no risk of combustion and explosion, which meets the safety requirements of energy storage. On the other hand, this technical path can flexibly adjust the battery capacity, and easily expand the capacity by adding electrolyte, without going through complicated disassembly procedures.

More importantly, the raw materials for redox flow battery are abundant in China and cheap in price. They do not depend on imports and are extremely cost-effective. Therefore, some experts said that in the case of large-scale long-term energy storage, redox flow battery have significant economic advantages and have broad application prospects in the field of power system energy storage.

At present, the concept stocks of all-vanadium redox redox flow battery are collectively rising. There are mainly four types of redox flow battery on the market: all-vanadium, iron-chromium, zinc-iron, and iron-bromine. The difference is mainly in the use of metal compounds in the electrolyte.

Vanadium, iron, chromium, bromine, zinc and other metals used by flow battery technology are all located in the fourth cycle of the periodic table of chemical elements, and are chemically more stable than lithium, which ranks first in the second cycle. This is also the reason why the flow battery is more stable.

Redox flow battery also have obvious advantages in terms of charge and discharge times. The number of charge and discharge times of redox flow battery is generally more than 15,000 times, which is more than 3 times that of lithium batteries. Experts say that the all-vanadium redox flow battery has more than 20,000 charge-discharge cycles and a lifespan of more than 20 years.

Weview Energy Storage, which focuses on zinc-iron redox flow battery, also revealed that its technical team has achieved more than 1 million charge and discharge experiments in the laboratory environment. In the energy storage scenario, the service life of the flow battery is far more than 20 years.

But redox flow battery also have drawbacks. At present, the energy density of lithium batteries is close to 500Wh/L, and the application scenarios are rich. In addition to energy storage, it can also be applied to electric vehicles and large digital products. However, the flow battery is limited by the low energy density (15~85Wh/L) and is only suitable for the energy storage scenario.

3. Redox flow battery is back to the market

According to statistics, among China’s power storage projects, pumped water storage accounts for 86.3%, new energy storage accounts for 12.5%, and molten salt heat storage accounts for 1.2%. Among them, redox flow battery account for only 0.9% of the emerging energy storage market. Due to geographical constraints, many pumped hydro storage resources are actually far away from the electricity side, and are not suitable for areas with flat terrain or lack of water resources.

The market demand for energy storage is huge and urgent, which also lays the foundation for the development prospects of new energy storage. More than a decade ago, Chinese flow battery entrepreneurs have begun to enter the market. In 2007, VRB was established. In the second year, Dalian Hengrong and Dalian Institute of Chemical Physics jointly established Dalian Rongke. In 2009, Shanghai Electric Energy Storage was established, focusing on the development and manufacture of all-vanadium redox flow battery for a long time.

At that time, China’s energy storage had not developed rapidly. Although redox flow battery have been used in some energy storage projects in the United States, Japan and other places, in China, they are still in the laboratory stage. The first to enter the market is the all-vanadium flow battery, which is also the flow battery technology path with the most mature technology and the highest degree of commercialization in China.

In 2009, VRB acquired VRB POWER, a Canadian all-vanadium flow battery company. Up to now, VRB has put into operation more than 70 all-vanadium flow battery projects in 12 countries around the world. Dalian Rongke is the largest all-vanadium flow battery in China. A service provider for the whole industry chain of redox flow battery, with the technology development and production capacity of the whole industry chain of all-vanadium redox flow battery.

In February this year, the world’s largest flow battery energy storage power station – Dalian 100MW/400MWh flow battery energy storage has entered the single commissioning stage. Another technical route, iron-chromium redox flow battery, is currently in commercial mass production. The research and development of zinc-iron redox flow battery in China started late.

At that time, the technical path of lithium battery was very mature, and it was a fully competitive market. In contrast, redox flow battery are more suitable for the needs of new energy storage scenarios, and after decades of development, redox flow battery has formed a relatively complete technical system. Research shows that the supply of zinc and iron raw materials is large, the price is low, and it is more competitive.

Last year, China’s energy storage industry ushered in a clear policy inflection point, and put forward quantitative requirements for new energy storage construction, opening up more development space for new energy storage technologies such as redox flow battery, gravity energy storage, and thermal energy storage.

4. Expand the flow battery energy storage industry system

The 200kW/600kWh Smart Energy Demonstration Project in Yugan County, Jiangxi Province, a cooperation between Weview and Power China, was successfully connected to the grid. This year, the secondary market has also shown its intention to develop redox flow battery. Since the market’s attention to vanadium batteries goes far beyond the main concept of redox flow battery, a series of vanadium raw material suppliers have emerged, such as Pangang Group, CNNC and so on.

Redox flow battery still has a long way to go. The initial installation cost is one of the problems that restrict the landing of redox flow battery. At the beginning of 2022, the cost of lithium battery energy storage is about 1.8RMB/Wh. At present, the industry average price for initial installation of redox flow battery is around 3RMB/Wh. Experts pointed out that the vanadium industry has just emerged, and although the industrial chain is basically perfect, it has not yet reached the stage where the scale effect appears.

In terms of technology, redox flow battery and lithium batteries also face the problem of relying on imports of ion exchange membranes. redox flow battery of various technical paths are also facing difficulties to be broken through. Although the all-vanadium flow battery is the most mature technology for commercialization, its operating temperature is limited to 5~40°C, and its application range is limited. The working temperature of the battery is 20~50℃, which is also very restrictive.

In contrast, the working temperature of iron-chromium and zinc-iron redox flow battery is more universal. The working temperature of the former is -40~70℃, and the latter is -10~45℃. However, the energy density of iron-chromium redox flow battery can only reach a maximum of 20Wh/L, which is the bottom of almost all redox flow battery, while zinc-iron redox flow battery are faced with the hidden danger of the electrolyte forming zinc dendrites penetrating the separator and causing the battery to short-circuit.

5. Summary

Overall, the flow battery market is small in scale, low in market awareness, and insufficient in production capacity. According to forecasts, redox flow battery are expected to enter a stage of rapid growth in the next 10 years. As a market where demand is ahead of supply, the biggest problem of energy storage at present is to provide a more reliable, more diversified and more flexible solution to achieve the “dual carbon” goal, and redox flow battery is one of the options.

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