How it works
The VisBlue battery is based on an all-vanadium redox flow battery (VRFB), which is the most mature Redox Flow Batteries technology.
The basic chemical principles are schematically shown in the Figure below. Electricity is stored electrochemically by changing the oxidation states of vanadium redox species that are dissolved in sulphuric acid and stored in two separate tanks. While charging or discharging, the two solutions are circulated through a flow cell, where the electrochemical energy is converted into electricity or vice versa.
The basic chemical principles used in redox flow batteries are similar to that of Li-ion batteries or lead-acid batteries, where electricity is stored in solid redox electrolytes. In Redox Flow Batteries, liquid redox species are used. Moreover, redox Flow batteries can be described as reversible fuel cells with fuels/electrolytes other than O2 and H2. Redox flow batteries have high (70-90 %) cyclic charge/discharge energy efficiencies, depending on the charge/discharge current. One of the attractive features of redox flow batteries is scalability between storage capacity and power because the storage tank and power generation are two separate units.
Compared to redox flow batteries, based on redox species other than vanadium, the vanadium redox flow batteries have the advantage that cross contamination of ions inside the flow cell is less detrimental than in mixed species battery and will only result in slow self-discharge. This means, VRFBs, in principle, has an infinite lifetime. However, mechanical deterioration of the flow cell gives finite lifetime. Depending on the quality of the flow cell, the lifetime is expected to be at least 10-15 years (>3500-5500 cycles). At the same time, the vanadium species that constitutes about 30-50 % of the battery cost has significant scrap value and can be reused in a new installation. Such lifetimes are significantly higher than that of a standard Li-ion and lead-acid batteries (< 3000 cycles and <1000 cycles respectively), which together with the low cost of the vanadium redox species is the main reason for the lower cost of storage in vanadium redox flow batteries.