Technology Overview

How the Vanadium Battery Works

An ionic membrane divides each cell. The electrolytes are acid vanadium sulphate.
The oxidation states of the vanadium are V²⁺ to V³⁺ on the negative side, and V⁵⁺ to V⁴⁺ on the positive side.
The open circuit potential across each cell is 1.35V in the 50% charged state.
The power (kW) depends on the membrane area. The capacity (Ah) depends on the volume of electrolyte.

Electrical shunt currents in the channels feeding the electrolytes to the cells bypass the intended electrical path through the cells
These shunt currents cause corrosion, loss of energy efficiency, and non-uniform distribution of the current to the cells
To ensure uniform electrolyte distribution to the cells and prevent blockages, flow rates are higher than needed for the electrochemical reactions

In the charging mode shown the reactions are V³⁺ + e^{- =}V²⁺ on the negative side of the membrane and V⁴⁺ = V⁵⁺ + ^e- on the positive side. These reactions are reversed when the battery delivers electrical power.
The open circuit potential across each cell varies from 1.1 volts in the uncharged state to 1.6 volts in the fully charged state.

The cells are horizontal in a vertical pile with electrolytes fed upwards through the cells in series
This almost eliminates bypass currents
It is safe because a blockage would be detected at once and the electrolysis of water can be quickly prevented
It is also efficient because electrolyte flow rates (and pumping power) needed are lower than with parallel feed

They are expected to last at least 20 years
They are not affected by rapid charging and discharging variations
They operate normally at 80 degrees C
The life-cycle costs of conventional vanadium batteries have been estimated at 60% of lead-acid systems. The new systems will make life-cycle costs even less

Commercially available V2O5 is only slightly soluble in sulfuric acid
Existing chemical methods of electrolyte preparation are costly
This new method reduces the vanadium at the negative electrodes, but oxidation at the positive electrode is prevented by the small area
Measured amounts of V2O5 powder and H2SO4 are added in a continuous process

Left: An "auto-transformer" for stepping up the voltage of a continuous direct current.
Right: The principle of the inductionless inverter for delivering alternating current from the battery.

Electrical taps connected to the electrodes control the voltage of the input and output currents with the help of electronic power switching circuits
The alternating current drawn directly from the battery is practically harmonic-free

The cells are divided into elements, each having a separate membrane
The separators between cells are electrical insulators impervious to the electrolytes
Switches enable the number of operating electrodes and membranes to be varied
The use of monopolar electrodes enables one to control the voltage as the current load varies by varying the membrane area
Individual cells in a stack may have different numbers of built-in elements; this is important when a sinusoidal output is created using the switching method
There is no hydraulic pressure stress across the electrodes
Different materials can be used for the positive and negative electrodes