Flow Battery Definition, Comparison and Problems Explained

Flow battery is a rechargeable energy storage system which operates using electrolytes that are in a state of continuous flow across membranes or tanks in the battery. This article discusses flow battery definition, comparison and problems, as follows;


-Flow Battery Definition: 4 Ways to Define Flow Batteries

-Flow Battery Vs Lithium-ion Battery

-Problems of Flow Batteries





Flow Battery Definition: 4 Ways to Define Flow Batteries

A flow battery is an electrochemical device whose internal structure comprises of tanks through which two isolated electrolytes flow and exchange ions, in reactions that lead to the continuous storage and discharge of energy [1].

Flow Battery Definition: Some Components of a Flow Battery (Credit: Earth-Rare 2014 .CC BY-SA 3.0.)
Flow Battery Definition: Some Components of a Flow Battery (Credit: Earth-Rare 2014 .CC BY-SA 3.0.)


The design and operation of flow batteries are based on electrochemical processes, which are also the basis of one of the types of energy storage (i.e. electrochemical storage). Below is an alternative flow battery definition that highlights the basic conversion process that occurs in this device;

A flow battery is a rechargeable energy storage system that converts electricity or kineto-mechanical energy to chemical energy in order to store it in an electrolyte, from which it may be released or discharged through electrochemical reactions.

As implied above, energy storage in a flow battery is achieved through electrochemical energy conversion and electricity generation. The reactions involved are further highlighted in the flow battery definition below;

A flow battery is an energy storage device in which reduction and oxidation reactions occur, leading to the exchange of ions between internal electrolytes and external energy sources, in order for energy to be stored and discharged repeatedly.

Based on the factors mentioned above, a flow battery may also be referred to as a redox flow battery.

Lastly, some types of flow batteries are listed in the flow battery definition below;

A flow battery is an electrochemical energy storage device which could be any of redox, full-flow, semi-flow, membrane-less, hybrid, and flexible types, that uses electrolytes to store and release energy in a rechargeable manner [2].


Flow Battery Vs Lithium-ion Battery

The differences between flow battery and lithium-ion battery include exterior and interior design, mode of operation, capacity, versatility, adoption, and energy efficiency. Flow batteries are generally of lower energy density, performance, depth of discharge, adoption; and larger size and complexity, than lithium-ion batteries.

In terms of structural configuration, the flow battery is more complex than lithium-ion battery. Its components include liquid electrolytes, membranes, tanks and pumps for fluid circulation.

On the contrary, lithium-ion battery is relatively simple, with no mechanical or mobile components and a more compact structure.

As a result of its configurational complexity, flow battery tends to be larger than lithium-ion. Its size is directly proportional to its storage capacity, which is generally lower than that of lithium-ion battery.

The risk of fire hazard is lower for flow batteries than lithium ion batteries. Also, flow batteries are less reactive to the influences of the external environment, than lithium-ion batteries.

Flow batteries are more containerized than lithium-ion batteries; and have low relative depth of discharge and energy density.

Lastly, the scale and rate adoption of flow batteries are both lower than for lithium-ion batteries. This can be attributed to the fact that lithium-ion batteries are more versatile and easy to operate/maintain than flow batteries.

As a result, lithium-ion batteries are more likely to be used for energy storage with electric cars, solar panels and wind turbines.

Comparison Criteria Flow Battery Lithium-Ion Battery
Structural Complexity High Low
Relative Flammability/Hazard Risk Low High
Versatility Low High
Relative Adoption Low High
Maintenance High Low
Relative Size Large Small
Relative Energy Density Low High
Relative Performance Low High


Problems of Flow Batteries

The main problem with flow batteries is low storage capacity per unit weight. Because their energy storage capacity depends directly on electrolyte volume, flow batteries tend to be very heavy, often reaching several thousand kilograms.

Other problems of flow batteries include;

1. Structural complexity

2. Lack of flexibility in usage and innovation

3. High cost of components like Vanadium

4. Corrosivity of electrolytes

5. Relative low performance



Flow battery is an energy storage system which uses electrochemical conversion through redox reactions in electrolytes, to store energy in a rechargeable manner.

Compared to lithium-ion batteries, flow batteries have larger size and higher complexity, with lower energy density, efficiency, versatility and adoption.



1). Puleston, T.; Clemente, A.; Costa-Castelló, R.; Serra, M. (2022). “Modelling and Estimation of Vanadium Redox Flow Batteries: A Review.” Batteries 8(9):121. Available at: https://doi.org/10.3390/batteries8090121. (Accessed 31 October 2022).

2). Sanchez-Diez, E.; Ventosa, E.; Guanieri, M.; Trovò, A.; Flox, C.; Marcilla, R.; Soavi, F.; Mazúr, P.; Aranzabe, E.; Ferret, R. (2021). “Redox flow batteries: Status and perspective towards sustainable stationary energy storage.” Journal of Power Sources 481:228804. Available at: https://doi.org/10.1016/j.jpowsour.2020.228804. (Accessed 31 October 2022).

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