Flow battery is an electrochemical energy storage technology proposed by American scientist Thaller L.H. (NASA Lewis Research Center) in 1974. It is a secondary battery technology in which active substances exist in a liquid electrolyte. The electrolyte is placed outside the stack and flows through the stack driven by the circulation pump, where it undergoes an electrochemical reaction to convert chemical energy into electrical energy, thereby realizing the storage and release of electrical energy. When charging, an oxidation reaction occurs at the positive electrode and the valence state of the active material increases; a reduction reaction occurs at the negative electrode and the valence state of the active material decreases. During discharge, the opposite is true. A reduction reaction occurs at the positive electrode, and the valence state of the active material decreases; an oxidation reaction occurs at the negative electrode, and the valence state of the active material increases.

　　Unlike traditional secondary batteries that directly use active materials as electrodes, the electrodes of flow energy storage batteries are inert electrodes that only provide reaction sites for electrode reactions. Active materials are usually stored in the electrolyte in an ionic state. The positive and negative electrolytes are installed in two storage tanks respectively, and the electrolyte is circulated in the pipeline system through a liquid delivery pump. During operation, the redox reaction of all-liquid flow batteries is manifested as changes in the valence state of ions, while the deposition-type flow batteries are manifested as the deposition and dissolution of metals.

　　According to different active materials, flow batteries can be divided into various technical routes such as all-vanadium, zinc/bromine, sodium polysulfide/bromine, iron/chromium, etc. At present, the all-vanadium flow battery is the most popular one. The energy storage capacity of the flow battery is easy to adjust the scale. The energy storage capacity depends on the electrolyte capacity and concentration. Therefore, the scale design of the flow battery is very flexible. The flow battery has a large degree of freedom in site selection, and the system can be fully automatically closed and operates without pollution. , simple maintenance, low operating cost; the most important thing is that the flow battery has high safety, its electrolyte solution is an aqueous solution, the battery system has no potential explosion or fire hazard, and has high safety.

　　The scientific research community is widely concerned. How is the research progress?

　　We all know that the most popular flow battery is the all-vanadium flow battery. Because it is all vanadium, there is no pollution problem. It has high safety and long life.

　　MIT

　　MIT recently developed a flow battery that can "breathe air" and store energy for a long time. When the air flow battery is discharging, it will inhale air from the outside world; when charging, it can discharge the air: during the inhalation process, the battery will produce negatively charged hydroxide ions in the catholyte. ; When oxygen is exhaled, positively charged hydrogen ions will appear in the anolyte. Researchers say the principle is similar to how humans breathe, balancing charges by getting oxygen in the system.

　　At the same energy density, the cost of this flow battery is only 1/5 of that of lithium-ion batteries. If the upgraded version of this battery is put into commercial use, the energy storage cost is expected to be controlled between US$20 and US$30 per kilowatt hour. The current prototype of this battery is only the size of a coffee cup. In the next step, they plan to use this design in larger-scale systems and further improve the efficiency, cost performance, and working life of the battery (currently only 1,500 hours).

　　Sumitomo Japan

　　Japan's Sumitomo Electric began research and development of all-vanadium flow battery technology as early as the 1990s, and has leading system integration and engineering application technology. In May 2016, the company's subsidiaries signed a demonstration implementation agreement with San Diego Gas & Electric, a large U.S. power company, on a power storage system using an all-vanadium redox flow battery. In the third quarter of 2016, the project began practical operation on the distribution network.

　　AVL

　　AVL has been focusing on the research and development of all-vanadium redox flow batteries. AVL is collaborating with the University of Western Australia and developed the first all-vanadium flow battery in December 2016. However, since local manufacturers do not have the ability to produce vanadium electrolyte with energy storage function, AVL imported vanadium electrolyte from Austrian Gildermeister Company.

　　UniEnergyTechnologies USA

　　UniEnergy Technologies has the world's leading hybrid acid all-vanadium redox flow battery technology and is responsible for the construction of the first megawatt-hour all-vanadium redox flow battery energy storage power station in the United States. Currently, the U.S. Department of Energy is supporting the U.S. company UniEnergy Technologies to implement a new flow battery energy storage project. The goal is to be able to integrate flow batteries and lithium-ion batteries based on Tesla batteries when the project reaches large-scale and grid integration. Compare and contrast.

　　Dalian Rongke

　　At present, Dalian Rongke has achieved a cumulative installed capacity of all-vanadium redox flow batteries of more than 12MW, accounting for 40% of the world's total installed capacity. In 2013, the world's largest 5MW/10MWh all-vanadium redox flow battery energy storage system jointly developed by Dalian Raycom and Dalian Institute of Chemical Physics successfully passed the owner's acceptance. This is the first 5MW large-scale system in the world that is actually connected to the grid. All indicators of industrial energy storage devices are at the leading international level.

　　In 2014, Dalian Raycom cooperated with Bosch Group to build a 250KW/1MWh all-vanadium redox flow battery energy storage system in a wind farm in northern Germany. It also cooperated with the American company UniEnergy Technologies to build the first megawatt-level all-vanadium redox flow energy storage battery power station in the United States.

　　Dali Electrician

　　Dali Electric has focused on the research and development of all-vanadium redox flow battery energy storage systems for many years. Up to now, the company has applied for 24 patents in the field of vanadium batteries, authorized 17 invention patents, and established 7 company standards. It has successively launched projects in India, Singapore and China. 12 vanadium battery energy storage system demonstration projects have been carried out in other places, and the products are exported to South Korea, the United States and other places.

　　The modular vanadium battery energy storage system independently developed by the company in February 2017 recently received its first order from South Korea in 2017. The company has been supplying to multiple projects in South Korea for two consecutive years, and the first batch of products has been prepared, tested and shipped.

　　Conclusion: The commercialization of flow batteries may be expected

　　The advancement of energy storage technology has driven the development of the energy storage industry, and various energy storage technologies have their suitable application fields. In the field of large-scale energy storage applications, all-vanadium redox flow batteries are slightly better than lithium-ion batteries with relatively low lifespan. However, due to limitations such as low energy density and high cost, they are still being tested in large-scale energy storage fields such as wind power. stage. On October 11, five ministries and commissions jointly announced the "Guiding Opinions on Promoting the Development of Energy Storage Technology and Industry". The "Opinions" pointed out that a number of energy storage technologies and products with independent intellectual property rights should be applied and promoted, including the 100MW class. All-vanadium redox flow battery energy storage power station. It can be seen that the application value of all-vanadium redox flow batteries has received increasing attention from the country. In recent years, various battery technologies have emerged one after another, and the industry has shown a situation of "letting a hundred flowers blossom and a hundred schools of thought contend". Let us wait and see whether all-vanadium redox flow batteries can be commercialized in the future.

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