Due to global warming, the world is transitioning towards a low-carbon model. Energy storage, as an indispensable part of this process, has seen rapid development in the past two years. Currently, the main energy storage battery is the lithium-ion battery, but due to the increasingly exorbitant prices of lithium battery raw materials, capital is turning its attention to the high-performance flow battery.
Development history of vanadium batteries
Flow batteries have a very rich history of development. Research on them began in 1973 by NASA in the United States, with the initial research system mainly consisting of the Fe(3+)/Cr(2+) redox couple.
In 1976, researchers discovered that vanadium could be used as an active material in flow batteries; in 1958, scholars theoretically proved the feasibility of vanadium batteries, and the following year, the all-vanadium ion redox flow battery was officially launched and patented.
As researchers continue their in-depth studies, numerous articles have emerged concerning vanadium battery electrodes, electrolytes, and separators. The advantages and disadvantages of vanadium batteries are gradually becoming known.
Vanadium batteries have the following advantages compared to other energy storage batteries. First, their capacity and output power are relatively independent; the capacity depends only on the electrolyte concentration and quantity, while the output power depends on the size of the battery stack. Second, charging and discharging vanadium batteries only involve changes in the valence state of vanadium ions, enabling deep discharge. Furthermore, only one type of ion reacts, without other interference, resulting in a theoretically unlimited lifespan. When the vanadium battery system is shut down, there is no self-discharge; the response speed is fast, allowing for instantaneous charging without any safety hazards. Finally, battery recycling and disposal are simpler and more convenient than other batteries, and they pose no harm to the environment.
The disadvantages are also obvious. Vanadium batteries currently have low energy density, reaching only 40Wh/kg, which is more than ten times lower than that of first-tier lithium-ion batteries. Vanadium batteries are also much more expensive than other flow batteries such as iron-zinc batteries, and they occupy a large area and have a narrow operating temperature range, which limits the application areas of vanadium batteries.
Vanadium battery principle and materials
Vanadium batteries mainly consist of electrolyte, electrodes, selective proton exchange membranes, bipolar plates, and current collectors.
Among these costs, the electrolyte accounts for the highest proportion, reaching 50%. The main components of the positive and negative electrode electrolytes are sulfuric acid solutions of vanadium ions in different valence states. In the industrial field, the most critical raw material for electrolytes is vanadium pentoxide, and the mainstream source of vanadium pentoxide in China is currently the extraction of vanadium pentoxide from vanadium slag produced during the steelmaking process of vanadium-titanium magnetite.
Currently, there are three main methods for preparing vanadium electrolyte: physical dissolution, chemical reduction, and electrolysis.
The physical dissolution method involves directly dissolving high-concentration vanadium oxysulfate solid with sulfuric acid.
The chemical reduction method uses reducing agents such as elemental sulfur and sulfurous acid under certain conditions to reduce pentavalent vanadium to tetravalent or trivalent vanadium;
Electrolysis is currently the mainstream preparation method, which uses vanadium pentoxide as raw material and is prepared in sulfuric acid. The operating temperature is generally between -5°C and 50°C.
In addition, adding certain additives to the electrolyte can also affect its performance. For example, adding additives such as methanesulfonic acid, glycerol, and n-propanol can improve the electrolyte's energy efficiency or energy density.
In the field of electrodes, vanadium battery electrodes mainly include carbon-based electrodes, metal electrodes, and composite electrodes. Among them, carbon electrodes have the characteristics of high stability, corrosion resistance, good conductivity, and low cost, but their electrochemical activity is poor and needs further improvement.
Metal electrodes have advantages such as good conductivity, high mechanical properties, and high electrochemical activity, but they are prone to forming a passivation film during discharge, which seriously affects the reaction.
Composite electrodes are generally made by mixing and molding high molecular polymers and carbon materials, and have advantages such as low internal resistance, good electrochemical stability and high conductivity.
In terms of separators, the most widely used cation exchange membrane is the Nafion membrane, which has a voltage efficiency of over 90%, good conductivity, and can effectively improve battery efficiency by increasing the membrane thickness, but the cost will increase.
In vanadium batteries, anion exchange membranes facilitate carrier transport by exchanging anions such as sulfate ions from electrolysis within the membrane with anions from electrolysis.
In addition, zwitterionic exchange membranes are currently a research hotspot, as they possess the characteristics of both cation and anion exchange membranes.
Policies and upstream and downstream activities
In recent years, my country has introduced a number of policies and standards related to vanadium batteries. In 2018, the National Energy Administration released the "Maintenance Requirements for Vanadium Redox Flow Batteries" and the "Technical Specifications for Installation of Vanadium Redox Flow Batteries."
In 2019, the National Energy Administration released the "Technical Rules for Safety Guardians of Vanadium Redox Flow Battery Energy Storage Power Stations (Draft for Comments)";
In 2021, the National Energy Administration and the National Development and Reform Commission issued the "Guiding Opinions on Accelerating the Development of New Energy Storage". The Opinions pointed out that we should adhere to the diversification of energy storage technologies and realize the early stage of commercial development of long-term energy storage technologies such as flow batteries; by 2025, we should shift from the early stage of commercialization to large-scale development.
One policy that has attracted the most attention from investors is the "Twenty-Five Key Requirements for Preventing Power Production Accidents (Draft for Comments)" released in June this year, which stipulates that ternary lithium batteries and sodium-sulfur batteries cannot be used in large-scale energy storage power stations. This policy immediately triggered a strong market reaction, with vanadium battery-related stocks surging collectively in July.
The vanadium battery industry chain currently consists of three main segments: upstream vanadium pentoxide raw material production, midstream component supply, and downstream assembly production.
Upstream raw material suppliers include Vanadium Titanium Industry, Hebei Iron & Steel, Sichuan Weiyuan Group, Longbai Group, and CNNC Titanium Dioxide.
Midstream electrolyte production companies include Dalian Rongke, Hunan Yinfeng, and Hebei Iron & Steel; battery stacks are currently supplied internally by vanadium battery manufacturers; separator companies include Chemours, Dongyue Group, and Suzhou Kerun; electrode companies include Liaoning Jingu, Nas New Materials, and Gansu Fulai.
Downstream assembly and manufacturing companies include Dalian Rongke, Beijing Puneng, Weilide, and State Grid Yingda. Currently, upstream and downstream companies have largely completed their partnerships. Vanadium Titanium Industry has partnered with Dalian Rongke, Hebei Iron & Steel Group has partnered with Beijing Puneng, and CNNC Titanium Dioxide has partnered with Weilide.
The projects that have been completed and put into operation include: the 5MW/10MWh all-vanadium redox flow battery energy storage demonstration power station at Woniushi Wind Farm, which was built in 2012 by Rongke Energy Storage in cooperation with Guodian Longyuan, and has been in operation for 10 years.
In March 2021, Beijing Puneng signed an agreement with the Hubei High-tech Zone Management Committee for a "50 MW annual production capacity vanadium battery energy storage system".
In June 2021, Ningxia Weilide's GW-level all-vanadium redox flow battery was officially put into operation;
In September of this year, Yongtai Energy and Haide Group jointly established Detai Energy Storage Company. Currently, the company has also launched a 30MWh all-vanadium redox flow battery energy storage auxiliary frequency regulation project in cooperation with Yongtai Energy's thermal power plants.
In mid-October this year, the Dalian Flow Battery Energy Storage Peak Shaving Power Station, the world's largest and most powerful flow battery energy storage peak shaving power station, was put into operation. One of the shareholders of the power station is Dalian Rongke.
Future Outlook
National policies are promoting the development of the new energy industry and encouraging the development of vanadium redox flow batteries. At the same time, my country has very rich vanadium resources, with reserves ranking first in the world. Vanadium batteries, due to their unique advantages, can be widely used in many fields such as wind power and photovoltaics, grid peak shaving, emergency power supply, and military energy storage, and have broad development prospects.
However, the vanadium battery industry is still in its infancy. Although it has a complete industrial chain, there are still many problems to be solved, such as small market size, low awareness, and insufficient production capacity.
Current research directions mainly include: developing highly stable, high-concentration electrolytes; developing highly ion-selective, low-cost membranes; developing highly conductive, highly electrochemically active electrode materials; further optimizing stack design to improve energy efficiency; and further developing low-cost, highly stable integrated and intelligent control technologies.
According to EVTank data, my country's newly installed vanadium battery capacity was 0.13GW in 2021, and is expected to reach 0.6GW in 2022. By 2025, the newly installed vanadium battery capacity is expected to reach more than 2.3GW.
