The rival of energy storage 26650 battery, all-vanadium flow battery

Lithium-ion battery has been the hot commodity in the energy storage industry in recent years. According to statistics, lithium-ion battery accounted for the largest proportion of 74% of the newly installed energy storage technology in 2014. Tesla's super battery factory chose lithium-ion battery technology for research and development and production. They also launched Powerwall for the small energy storage market, which is widely welcomed by the market. But in fact, according to the different requirements of energy storage technology in the application field, various energy storage technologies have their suitable application fields. When dealing with large-scale energy storage applications, lithium-ion batteries have encountered opponents. According to foreign media reports, the US Department of Energy is supporting the US UniEnergyTechnologies to implement a new type of liquid flow battery energy storage project. The goal is to compare and contrast liquid flow batteries and lithium-ion batteries mainly based on Tesla batteries when the project reaches large-scale and grid integration.

Generally speaking of energy storage technology, everyone thinks that Japan and the United States are the best, but in the field of liquid flow batteries, China can be said to be the world's No. 1. At present, the world's largest all-vanadium liquid flow battery energy storage system is developed by Chinese companies, and the international liquid flow battery standard system is also organized and developed by Chinese scientists. Nengdoujun visited Professor Zhang Huamin, who is responsible for the formulation of the standard system and is also the chief engineer of the world's largest all-vanadium liquid flow battery system project.

Professor Zhang is currently the chief researcher of the Dalian Institute of Chemical Physics, director of the National Energy Liquid Flow Battery Energy Storage Technology Key Laboratory, and deputy general manager and chief engineer of Dalian Rongke Energy Storage Technology Development Co., Ltd. Professor Zhang Huamin returned to China in 2000 as a talent of the Chinese Academy of Sciences to work at the Dalian Institute of Chemical Physics. Before that, he studied in Japan and engaged in fuel cell research. After returning to China, Professor Zhang Huamin successively served as the director of the Fuel Cell Research Center, assistant director, and director of the Energy Storage Technology Department.

Why did Professor Zhang Huamin switch from fuel cells to liquid flow batteries? What has happened to China's energy storage in the past 15 years since 2000? What is the future development prospect of energy storage technology? Please pay attention to EnergyTalk, the 2015 Annual Summit of All Powers. Professor Zhang Huamin will share his wonderful experience and his judgment on the future blue ocean of energy storage technology with Energy Bean fans as a special guest.

Today, Energy Bean will first take you to popularize what flow batteries are in advance and see why the future of large-scale energy storage is here.

ABC of flow batteries

1. What is a flow battery?

Flow battery is a secondary battery technology in which active substances exist in liquid electrolytes. The electrolyte is placed outside the battery stack and flows through the battery stack under the impetus of a circulating pump, and an electrochemical reaction occurs to achieve the conversion of chemical energy and electrical energy, thereby achieving the storage and release of electrical energy.

2. What are the characteristics of flow batteries?

① The energy storage capacity is easy to adjust the scale. The output power of the battery depends on the size and number of the battery stack, and the energy storage capacity depends on the capacity and concentration of the electrolyte. Therefore, the scale design of the flow battery is very flexible: as long as the area of the battery stack and the number of battery stacks are increased, the output power can be increased; as long as the volume of the electrolyte is increased, the energy storage capacity can be increased.

② Flow batteries have a large degree of freedom in site selection. The system can be fully automatically closed and operated, pollution-free, simple to maintain, and low in operating costs.

③ High safety. The electrolyte solution is an aqueous solution, and the battery system has no potential explosion or fire hazard, and is highly safe.

3. Types of flow batteries

Depending on the active material, flow batteries can be divided into a variety of technical routes such as all-vanadium, zinc/bromine, sodium polysulfide/bromine, and iron/chromium. To date, the total installed capacity of flow batteries worldwide is about 68MW, of which all-vanadium flow batteries account for 40%. Judging from the current technical maturity and engineering application effects, all-vanadium flow battery technology has entered the stage of engineering application and market development, and has begun to achieve commercialization; zinc-bromine flow battery technology has entered the stage of application demonstration and market development; other flow batteries are still in the research stage.

The positive electrode pair of the all-vanadium liquid flow energy storage battery is VO2+/VO2+, and the negative electrode pair is V2+/V3+. The electrodes undergo the following electrochemical reactions:

4. Technical features of all-vanadium liquid flow batteries

① Long cycle life: The charge and discharge cycle life of the all-vanadium liquid flow energy storage battery can reach more than 13,000 times, and the calendar life exceeds 15 years.

② Good charge and discharge characteristics: The all-vanadium liquid flow battery energy storage system has the characteristics of fast and deep charge and discharge without affecting the service life of the battery, and the uniformity of each single battery is good. In addition, the electrochemical reversibility of vanadium ions is high and the electrochemical polarization is also small, so it is very suitable for large current rapid charge and discharge.

③ Independent design of power and capacity: The power of the all-vanadium liquid flow battery is determined by the specifications and number of the battery stack, and the capacity is determined by the concentration and volume of the electrolyte. Therefore, the power expansion can be achieved by increasing the battery stack power and increasing the number of battery stacks, and the capacity increase can be achieved by increasing the volume of the electrolyte.

④Safety and environmental protection: The all-vanadium liquid flow battery energy storage system works under normal temperature and pressure conditions, which not only prolongs the service life of the battery components, but also shows very good safety performance. In addition, the electrolyte solution can be recycled and reused, which is environmentally friendly and saves resources. Most battery components are cheap carbon materials and engineering plastics, with long service life, rich material sources, mature processing technology, and easy recycling.

Overall, the all-vanadium liquid flow battery has obvious advantages in large-scale fixed energy storage occasions with output power of hundreds of kilowatts to hundreds of megawatts and energy storage capacity of hundreds of kilowatt-hours to hundreds of megawatt-hours. It is one of the preferred technologies for large-scale and efficient energy storage technology.

5. What are the challenges facing all-vanadium liquid flow batteries?

① Ion exchange membrane technology. Ion exchange membranes can affect the mutual permeability of ions between the positive and negative electrolytes, thereby affecting the energy efficiency and life of the liquid flow battery. It is necessary to study and develop highly selective and highly conductive ion exchange membranes for liquid flow batteries.

② High-concentration and high-stability electrolyte preparation technology. Previously, the electrolyte cost accounted for nearly 50% of the total cost. Currently, due to the decline in battery costs, the electrolyte cost accounts for a larger proportion.

③ Low energy density and large volume. The battery system needs to be equipped with a large number of auxiliary components such as pipelines, valves, electrolyte circulation pumps, heat exchangers, etc., which makes the flow battery more complex and puts higher requirements on the reliability of the battery system.

6. What is the current status and prospects of the development of flow batteries?

All-vanadium flow batteries are suitable for peak-shaving power systems, large-scale photovoltaic power systems, wind power generation systems, energy storage, and uninterruptible power supplies or emergency power supply systems.

Global all-vanadium flow battery manufacturers mainly include: Japan's Sumitomo Electric Industries, Dalian Rongke Energy Storage Technology Development Co., Ltd. (hereinafter referred to as: Rongke Energy Storage Company), the United States UniEnergy Technologies and Austria's Gildemeister.

Japan's Sumitomo Electric Industries began to develop all-vanadium flow battery technology as early as the 1990s, and has leading system integration and engineering application technologies, but its key functional materials and components rely on outsourcing, and the cost is relatively high. UniEnergy Technologies of the United States has the world's leading mixed acid all-vanadium liquid flow battery technology and is responsible for building the first megawatt-hour all-vanadium liquid flow battery energy storage power station in the United States. Gildemeister has been developing all-vanadium liquid flow energy storage batteries since 2002. Its products are mainly matched with solar photovoltaic cells and are used in power supply in remote areas, electric vehicle charging stations and other fields.

my country's all-vanadium liquid flow energy storage technology and industrial development are at the world's leading level. At present, Rongke Energy Storage Company has achieved a total installed capacity of more than 12MW of all-vanadium liquid flow batteries, accounting for 40% of the world's total installed capacity. In 2013, the world's largest 5MW/10MWh all-vanadium liquid flow battery energy storage system jointly developed by Rongke Energy Storage Company and Dalian Institute of Chemical Physics successfully passed the owner's acceptance. This is currently the world's first 5MW-class large-scale industrial energy storage device that is actually connected to the grid and operates, and all indicators are at the international leading level.

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