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Overview: Comparison of Types and Performance of Liquid Flow Batteries
2023/3/18
Liquid flow batteries have the characteristics of high capacity, wide range of applications (environment), and long cycle life, making them a new energy product. The significant feature of liquid flow batteries is large-scale energy storage. With the increasing demand for the widespread use of renewable energy, it can be foreseen that liquid flow batteries will usher in a period of rapid development. Liquid flow battery. Different types of liquid flow batteries have different chemical compositions, including commonly used vanadium, as well as less commonly used zinc bromine, polysulfide bromine, iron chromium, and iron iron.
1. Iron chromium flow battery:
Iron chromium flow battery is an early proposed flow battery technology. At present, there are still some technical issues with ferrochrome flow batteries, such as:
-The negative hydrogen evolution problem reduces the energy efficiency of the battery;
-Cross contamination of positive and negative ions can reduce battery capacity and efficiency, leading to the need for high selectivity in the ion conduction membrane used. Currently, the cost of imported perfluorinated sulfonic acid membranes is relatively high;
-The redox performance of chromium is poor, and the optimal operating temperature of the battery is higher.
2. All vanadium flow battery:
All vanadium flow battery is currently a highly commercialized and technologically mature flow battery technology. Featuring high energy efficiency, long cycle life, and high power density, it is suitable for large and medium-sized energy storage scenarios. But for all vanadium flow batteries, the cost of vanadium electrolyte accounts for about 60% of the battery cost, greatly increasing the initial investment threshold.
3. Zinc Bromine Flow Battery
The zinc bromide flow battery uses Br -/Br2 pairs for positive * and Zn2+/Zn pairs for negative *. When the cathode is charged, Br - is oxidized into Br2 elemental substance, which combines with relevant substances in the solution and settles at the bottom of the electrolyte. Therefore, zinc bromide flow batteries are single deposition flow batteries. Zinc bromide flow battery is a more successful commercial flow battery technology besides all vanadium flow battery.
In terms of application, due to its excellent modular design, low cost, and high safety, early zinc bromide flow batteries were more used for user side arbitrage and improving power supply stability, with a smaller scale of use. In recent years, the rapid development of renewable energy has driven the large-scale application of zinc bromide flow batteries on the power generation and grid sides.
4. Zinc iron flow battery
In 1981, alkaline zinc iron flow batteries were proposed, followed by neutral and acidic zinc iron flow batteries, but neither of them reached the level of engineering application. Alkaline zinc iron flow battery has a high open circuit voltage, and can cycle for a long time under high current density when combined with porous film and porous battery. The acidic zinc iron flow battery fully utilizes the advantages of high solubility of iron ions in acidic media and stable electrochemical performance, but the positive side is greatly affected by pH value.
Neutral zinc iron flow batteries are gradually receiving attention due to their non-toxic, harmless, and environmentally friendly characteristics. Combining with porous membranes can effectively reduce battery costs. Regardless of the type of zinc iron flow battery, there are zinc dendrites on the positive side and the surface capacity is limited, which has become a problem that must be considered in the industrialization of zinc iron flow batteries.
Technically, zinc iron flow batteries, like other deposition batteries and zinc batteries, face issues such as incomplete decoupling of zinc dendrites from power and capacity, and low negative surface capacity. At the same time, as a relatively new type of liquid flow battery, the industrial chain of its ion conductive film and related components is not yet mature, which greatly restricts its commercial promotion and application.
5. Zinc nickel single flow battery
Zinc nickel monomer flow battery combines the advantages of zinc nickel secondary battery and flow battery. Similar to the structure of zinc bromine single flow batteries, zinc nickel single flow batteries use the same electrolyte for positive and negative ions, without the need for ion exchange membranes, and have a simple structure.
In terms of application, zinc nickel flow batteries are still in the commercial demonstration stage. The comprehensive performance of the zinc nickel flow battery in the laboratory stage is good, and preliminary application demonstrations have also been conducted. However, due to the rapid increase in nickel prices, the price competitiveness of zinc nickel single flow batteries has rapidly weakened, and technology development and deployment are in a relatively stagnant stage.
At the technical level, further research is needed on the reduction of battery life caused by short circuits and zinc dendrites and accumulation. The positive and negative area capacity of zinc nickel single flow batteries is low, and the power and capacity cannot be completely decoupled. The problem of high cost sintered nickel for battery positive and negative battery life needs to be solved.
6. All iron flow battery
Compared to vanadium, iron has higher utility and lower cost. All iron flow batteries are divided into acidic and alkaline systems, and the commercial development of acidic all iron flow batteries is relatively mature.
The technical issues of all iron flow batteries mainly lie in the negative hydrogen evolution reaction similar to iron chromium flow batteries and the need to suppress the formation of iron hydroxide precipitates.
These issues will greatly reduce the operational efficiency of the battery, reduce battery capacity, and pose a risk of blocking the ion conductive film. There are few reports on the research and commercial development of this flow battery system in China.
7. High performance zinc based flow battery
In addition, in 2022, based on a deep understanding of the redox reaction mechanism of iodine, researchers proposed an iodine positive solution based on polyiodide complexes. Effectively releasing the capacity of iodine positive *, achieving high-energy and long cycle operation of zinc iodine flow batteries.
The improved zinc iodine flow battery significantly increases its discharge capacity by 58% and can stably cycle 600 times at 70% energy efficiency, providing a new approach for the development of high-performance zinc iodine flow batteries
8. Zinc air flow battery
During the charging process of a zinc air flow battery, the anion undergoes an oxygen evolution reaction, and zinc ions are deposited on the metal cation in the form of metallic zinc. During the discharge process, the anion undergoes an oxygen reduction reaction, and the zinc on the cation dissolves and is stored in the electrolyte as zinc ions.
Technically speaking, zinc air flow batteries, like most other zinc flow batteries, also face the problem of zinc dendrites. At the same time, it also faces problems such as low current density and incomplete development of dual effect catalysts for oxygen evolution and reduction.
conclusion
In the long run, all vanadium flow batteries will replace lithium batteries in the energy storage direction. All vanadium flow battery is a widely used flow battery technology, which has advantages such as suitability for large-scale energy storage, high energy conversion efficiency, long cycle life, and convenient charging. Moreover, the power and capacity of the battery system are independent of each other, making it suitable for large-scale energy storage scenarios. Meanwhile, all vanadium flow batteries have good charging and discharging performance and high energy conversion efficiency. From the perspective of downstream application scenarios, the value of liquid flow batteries is mainly applied in fields such as power grid peak shaving, emergency power generation devices, and electric vehicle power supplies.
At the policy level, with the establishment of China's dual carbon goals, the adjustment of energy structure is constantly accelerating, the installed capacity of new energy generation is constantly increasing, and the demand for energy storage is also rapidly increasing. The country has successively introduced a series of policies to encourage the development of new energy storage technologies, which will greatly promote the rapid development of all vanadium flow batteries in the energy storage field.
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