Zn-Br flow battery is a type of battery for power energy storage system with high performance, low cost and large capacity. The solution of zinc bromide is stored in two tanks as dielectric. One tank is used to store the electrolyte for the positive electrode reactions and the other for the negative, and respectively connect with positive electrode and negative electrode on the battery stack, and battery are discharged or charged due to oxidation and reduction reactions simultaneously.

Composition of Zinc-Bromine flow battery

The Zinc-Bromine redox flow battery is mainly composed of three parts： electrolyte, battery stack, fluid circulation and auxiliary system.

1) Electrolyte

The electrolyte is stored in the external storage tank, and pumped through each cell in parallel via the boosting system, Electrochemical reactions take place where the electro-active chemicals flow through the reactor. While improving the power density of the battery, the parallel structure of electrolyte path ensure the consistency between the cell chips. The capacity of the battery depends on the volume of the electrolyte storage tank and the amount of electrolyte solution.

2) Battery stack

The battery stack is composed of multiple double electrode units. Each cell forms a series system on the circuit through bipolar plates. The battery power is determined by the specification of the battery stack.

3) Fluid circulation and auxiliary system

Mainly consists of storage tank, pipe pump, two-phase valve and various sensors. While circulating the electrolyte, it provides instant feedback for various information of the battery such as liquid level, temperature, etc.

Features of Zn-Br redox flow battery

1) Low-cost energy storage solution

The electrolyte of zinc bromine flow battery is zinc bromide solution, which has an inherent advantage in cost. According to general cost of energy storage battery, the cost of electrolyte accounts for 30% of the total cost of flow battery, so the price of electrolyte components greatly determines the overall cost of storage energy battery. Zinc and bromine are the main components of electrolyte for zinc bromine redox battery, and zinc is a very common metal, which is easy to obtain in large quantities and has lower price, the other component, bromine is more common and can even be extracted from sewage. This innate characteristic determines the advantages of zinc bromide battery in cost.

2) Long service life flow battery

Both the positive and negative electrolyte are zinc bromide solution, so there will be no cross contamination of electrolyte. The discharge capacity of battery is affacted by the zinc load on the electrode surface. The electrode doesn’t participate in the charge and discharge reaction, The metal zinc deposited on the surface during discharge can be completely dissolved into the electrolyte. Therefore, the Zn-Br flow battery can frequently perform 100% deep discharge without affecting the performance and service life of flow batteries. Generally, the cycle life of battery stack is more than 3000 times in the depth charging and discharging working status, and can prolong the service life by replacing the stack.

3) Modularization of energy storage system

The energy storage battery system is based on modular design, which has independent power and capacity and flexible configuration. As a component unit, the module can be rapidly expanded to MW level energy storage system. In addition, in large-scale energy storage system, when a single module fails, it can be taken out and replaced immediately to realize maintenance without shutdown, greatly improve system reliability.

4) Environmentally friendly and safety

The flow of electrolyte in the flow battery is beneficial to thermal management of the energy storage system, and can effectively avoid overheating problems and risk of fire and explosion. The main components of the electrode and membrane materials are based on plastic, free of heavy metals and low price, it’s recyclable and environmentally friendly.

Development of zinc bromine flow batteries

Since the 1970s, zinc bromine flow battery technology has developed rapidly in the United States, Japan, Australia and other countries, and has developed many listed companies and technology enterprises. Since the 1990s, the research on non-circulating zinc bromine batteries in China has been carriedout, scientific research institutes and some enterprises, are committed to the development of non-circulating Zn-Br power batteries which are applied to large electric buses. The industrialization research and development of zinc bromine flow battery started relatively late in China. At present, only a few domestic enterprises including XNHY are engaged in zinc bromine flow battery technology.

With the gradual depletion of fossil energy and the continuous progress of new energy technologies, new energy power generation technologies such as wind energy and solar energy will achieve large-scale development in the direction of both grid-connected mode and island mode, and eventually occupy an increasing proportion in the overall power generation. However, due to its inherent instability and discontinuity, it will have an impact on the power grid in practical applications, and will also have an adverse impact on the power consumption of off-grid users. The introduction of energy storage system will provide important technical support for renewable energy access. At the same time, it can realize various functions such as frequency regulation, voltage regulation, delay capacity expansion, emergency standby power supply, etc, increasingly become an important part of smart grid construction.

There are many types of energy storage technologies. As one of them, the flow battery technology is valued in the field of large-scale energy storage technology due to its great flexibility and scalability in system design. On the other hand, zinc system rechargeable battery has been considered to be highly competitive in the application of large-scale energy storage system due to its high energy density and low cost. As a combination of these two technologies, zinc bromine flow battery has received more and more attention in recent years. In the field of energy storage, Zinc bromine flow battery have great potential and can simultaneously solve the reliability and economic problems for large-scale energy storage.