Vanadium is an element that can commonly exist in four different oxidation states. That just means that it can exist as an ion with different charges. For example, a vanadium ion that is missing three electrons would have a charge of V3+. If you add an electron to it, it converts to a V2+ ion. This transfer of electrons back and forth is what makes VFBs charge and discharge, as the vanadium ions in the battery swing from V2+ to V5+.
This differs from lithium-ion batteries in that every time lithium charges and discharges it is plating and deplating lithium metal on the cathode. Although this reaction is almost completely reversible, it will lead to degradation after a few thousand cycles and performance will decrease.
A VFB consists of two tanks of electrolyte dissolved in water and separated by a proton exchange membrane. Both electrolytes are vanadium-based. As the batteries are charged and discharged, vanadium ions are simply moved between oxidation states. According to Matt, this can be done tens of thousands of times over a time period measured in decades, with no degradation in the ability of the vanadium solutions to hold charge.
They estimate that every 10-20 years, the membrane that the ionic species crosses over will require a replacement. Again, this is unlike a lithium-ion battery where the entire battery would need to be replaced. They compared this to maintenance on a car. Matt indicated they have products in the field that have done more than 30 years of charging and discharging cycling.
Li-ion batteries do have an advantage in energy density, which is why VFBs are being targeted for stationary applications. However, compared to Li-ion batteries for grid scale storage, there is no fire risk with VFBs. Li-ion batteries need to be spaced farther apart or have sufficient fire suppression. Thus, VFBs can be packed tighter than lithium, so the footprint for grid-scale operation is comparable.
Regarding the cost, Invinity reports that they sell their batteries at a price in the same ballpark as Li-ion per MWh for the industrial market. The benefit of Invinity’s VFB comes in the levelized cost over time because of the decades of service a single device can deliver. VFBs can charge and discharge multiple full cycles daily for 20 years. Even though you may get thousands of cycles with a Li-ion battery, for a utility or commercial storage application where daily cycling is needed that may not be enough to give Li-ion the advantage.
Invinity’s core technology – the “cell stack” at the core of the VFB - is developed and manufactured in Vancouver, Canada.
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I asked about the supply of vanadium. I learned that vanadium is the 13th most abundant metallic element in the earth’s crust. It is more abundant than copper. Further, the supply of vanadium in the battery can be recycled practically endlessly as the vanadium ions are moved between oxidation states, and not destroyed or degraded. In addition to the vanadium electrolyte being infinitely reusable, the balance of Invinity’s VFB is made almost entirely of common materials, like steel and household plastics, that can be easily recycled.
There are large vanadium reserves in the U.S. At present, 90% of the supply goes into steel manufacture. So, steel-producing regions like China are currently the largest producers of vanadium.
