Vanadium Redox Battery - Energy Density

Energy Density

Current production vanadium redox batteries achieve an energy density of about 25 Wh/kg of electrolyte. More recent research at UNSW indicates that the use of precipitation inhibitors can increase the density to about 35 Wh/kg, with even higher densities made possible by controlling the electrolyte temperature. This energy density is quite low as compared to other rechargeable battery types (e.g., lead–acid, 30–40 Wh/kg; and lithium ion, 80–200 Wh/kg).

Researchers at the Fraunhofer Institute for Chemical Technology claim to have built a prototype for an improved cell stating “We can now increase the mileage four or fivefold, to approximately that of lithium-ion batteries,”. This same article makes a very optimistic claim that vanadium flow batteries can be recharged at a gas station by simply filling the vehicle tanks with fresh electrolytes.

There are at least two problems with this claim. First, the electrolytes used in flow batteries are dangerously acidic. Pouring acids is a very different exercise from pouring gasoline and is much more dangerous. Face shields and other protective gear is necessary for handling strongly acidic solutions. Second, any electrolyte still in the vehicle will need to be drained into a recycling system. This means that self-service will not be a possibility unless and until the fluid transfer processes can be fully automated. Until the processes are fully automated, it will be necessary for carefully trained attendants to do this job for the station's customers. This is something that is unlikely to be done by existing fueling facilities with the level of training given to existing fuel station personnel. There are at least as many liability issues with this plan as there would be with a gaseous fuel such as hydrogen or methane, but this technology does hold out the promise that the necessity for burning any kind of fuel in an automobile might be eliminated in the foreseeable future.