Vanadium redox battery

The vanadium redox battery (VRB), also known as the vanadium flow battery (VFB) or vanadium redox flow battery (VRFB), is a type of rechargeable flow battery. It employs vanadium ions as charge carriers. The battery uses vanadium's ability to exist in a solution in four different oxidation states to make a battery with a single electroactive element instead of two. For several reasons, including their relative bulkiness, vanadium batteries are typically used for grid energy storage, i.e., attached to power plants/electrical grids.

Pissoort explored the possibility of VRFB's in the 1930s.P. A. Pissoort, in FR Patent 754065 (1933) NASA researchers and Pellegri and Spaziante followed suit in the 1970s,A. Pelligri and P. M. Spaziante, in GB Patent 2030349 (1978), to Oronzio de Nori Impianti Elettrochimici S.p.A. but neither was successful. Maria Skyllas-Kazacos presented the first successful demonstration of dissolved vanadium in a solution of sulfuric acid in the 1980s.M. Rychcik and M. Skyllas-Kazacos, J. Power Sources, 22 (1988) 59–67 Her design used sulfuric acid electrolytes, and was patented by the University of New South Wales in Australia in 1986.

Numerous companies and organizations are involved in funding and developing vanadium redox batteries.

Advantages and disadvantages

Advantages

VRFB's main advantages over other types of battery:

* no limit on energy capacity
* can remain discharged indefinitely without damage
* mixing electrolytes causes no permanent damage
* single charge state across the electrolytes avoids capacity degradation
* safe, non-flammable aqueous electrolyte;UniEnergy Technologies Products
Accessed 21 Jan 2016.
* wide operating temperature range including passive coolingMiller, Kelsey

, Clean Tech Alliance, 7 July 2014. Accessed 21 Jan 2016.
* long charge/discharge cycle lives: 15,000-20,000 cycles.
* low levelized cost: (a few tens of cents), approaching the 2016 $0.05 target stated by the US Department of Energy and the European Commission Strategic Energy Technology Plan €0.05 target.

Disadvantages

VRFB's main disadvantages compared to other types of battery:

* relatively poor energy-to-volume ratio compared to standard storage batteries
* relatively poor round trip efficiency
* high weight of aqueous electrolyte
* relatively high toxicity of oxides of vanadium

Materials

A vanadium redox battery consists of an assembly of power cells in which two electrolytes are separated by a proton exchange membrane. The electrodes in a VRB cell are carbon based. The most common types are carbon felt, carbon paper, carbon cloth, and graphite felt. Recently, carbon nanotube-based electrodes have attracted interest from the scientific community.

Both electrolytes are vanadium-based. The electrolyte in the positive half-cells contains VO₂⁺ and VO²⁺ ions, while the electrolyte in the negative half-cells consists of V³⁺ and V²⁺ ions. The electrolytes can be prepared by several processes, including electrolytically dissolving vanadium pentoxide (V₂O₅) in sulfuric acid (H₂SO₄). The solution remains strongly acidic in use.

The membrane is another critical component. The most common membrane material is perfluorinated sulfonic acid (PFSA) (Nafion). However, vanadium ions tend to penetrate the membrane and destabilize the cell. A 2021 Chinese study found that this penetration is reduced with hybrid sheets made by growing tungsten trioxide nanoparticles on the surface of single-layered graphene oxide sheets. These hybrid sheets are then embedded into a sandwich structured PFSA membrane reinforced with polytetrafluoroethylene (Teflon). The tungsten trioxide nanoparticles also promote proton transport, offering high Coulombic efficiency and energy efficiency of more than 98.1 percent and 88.9 percent, respectively.

Operation

The reaction uses the half-reactions:
: ()
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Other useful properties of vanadium flow batteries are their very fast response to changing loads and their extremely large overload capacities. Studies by the University of New South Wales have shown that they can achieve a response time of under half a millisecond for a 100% load change, and allowed overloads of as much as 400% for 10 seconds. The response time is mostly limited by the electrical equipment. Unless specifically designed for colder or warmer climates, most sulfuric acid-based vanadium batteries work only between about 10 and 40 °C. Below that temperature range, the ion-infused sulfuric acid crystallizes. Round trip efficiency in practical applications is around 65–75 %.VRB Power Systems FAQ

Proposed improvements

Second generation vanadium redox batteries ( vanadium/bromine) may approximately double the energy density and increase the temperature range in which the battery can operate. The vanadium/bromine and other vanadium based systems also reduce the cost of vanadium redox batteries by replacing the vanadium at the positive or negative electrolyte by cheaper alternatives such as cerium.

Typically, perfluorinated sulfonic acid (PFSA) is used as the separator membrane. However, vanadium ions can cross the membrane and destabilize the battery. Researchers grew tungsten trioxide nanoparticles on the surface of graphene oxide sheets and embedded them in a polytetrafluoroethylene-reinforced, sandwich-structured PFSA system. This reduced penetration and promoted proton transport, yielding Coulumbic efficiency and energy efficiency of greater than 98.1% and 88.9%, respectively.

Specific energy and energy density

Current production vanadium redox batteries achieve a specific energy of about 20 Wh/kg (72 kJ/kg) of electrolyte.
More recent research at UNSW indicates that the use of precipitation inhibitors can increase the density to about 35 Wh/kg (126 kJ/kg), with even higher densities made possible by controlling the electrolyte temperature. The current specific energy is quite low compared to other rechargeable battery types (e.g., lead–acid, 30–40 Wh/kg (108–144 kJ/kg); and lithium ion, 80–200 Wh/kg (288–720 kJ/kg)). However, using precipitation inhibitors would place vanadium redox batteries on par with lead-acid batteries.

Applications

VRFB's large potential capacity may be best-suited to buffer the irregular output of utility-scale wind and solar systems.

Their reduced self-discharge makes them potentially appropriate in applications that require long-term battery storage with little maintenance as in military equipment, such as the sensor components of the GATOR mine system.Allbright, Greg, et al
A Comparison of Lead Acid to Lithium-ion in Stationary Storage Applications
All Cell, March 2012

They feature rapid response times well suited to uninterruptible power supply (UPS) applications, where they can replace lead–acid batteries or diesel generators. Fast response time is also appropriate for frequency regulation. These capabilities make VRBF's an effective "all-in-one" solution for microgrids, frequency regulation and load shifting.

Largest vanadium grid batteries

A 200 MW, 800 MWh (4 hours) vanadium redox battery is under construction in China; it was expected to be completed by 2018 and its 250 kW/ 1 MWh first stage was in operation in late 2018

Companies funding or developing vanadium redox batteries

Companies include CellCube (Enerox), UniEnergy Technologies, StorEn Technologies, Largo Energy and Ashlawn Energy in the United States; H2 in South Korea; Renewable Energy Dynamics Technology, Invinity Energy and VoltStorage in Europe; Prudent Energy in China; Australian Vanadium in Australia; EverFlow Energy JV SABIC SCHMID Group in Saudi Arabia and Bushveld Minerals in South Africa.

See also

* List of battery types
* Polysulfide bromide battery
* Electric battery
* Fuel cell
* Energy storage

References

Additional references

Presentation paper from the IEEE summer 2001 conference

UNSW Site on Vanadium batteries

Report by World Energy

World Map Of Global Vanadium Deposits
Vanadium geology is fairly unusual compared to a base metals ore body.
*

External links

The U.S. made a breakthrough battery discovery — then gave the technology to China
''The U.S. made a breakthrough battery discovery — then gave the technology to China''

VRFB developments at UNSW

VRB at everything2

The Need for Vanadium Redox Energy Storage in Wind Turbine Generators
''Net electricity generation from all forms of renewable energies in America increased by over 15% between 2005 and 2009.''

redT and Avalon have merged as Invinity Energy Systems, a global leader in Vanadium Flow Batteries

{{Galvanic cells

Flow batteries
Vanadium
Grid energy storage