Skip to main content

All Organic Redox Flow Batteries

Periodic Reporting for period 1 - GLOBE (All Organic Redox Flow Batteries)

Reporting period: 2015-09-01 to 2017-08-31

Transition to renewable energy sources depends on proper electrical energy storage (EES) technology for renewable energy management in order to handle the varying solar and wind generated electricity. The project’s main objective was to provide a low-cost solution for EES, based on organic redox active species for both redox flow and solid-state batteries. This could facilitate the EU’s transition to renewable energy sources. Several important breakthroughs were achieved during this project. A great number of redox active species was screened, where a great number of them is electrochemically stable and reversible, some are very soluble in water, however there are chemical stability issues with some organic redox species. A number of redox active species for the positive side were developed, which have great solubility in water and are electrochemically reversible however not sufficiently chemically stable. A method has been developed to improve the cell potential of organic redox flow batteries with pH dependent redox potential. New type of nickel hydroxide-oligomer battery was developed. A semi organic redox flow battery was developed and directly fully charged directly using the solar energy and the home-made semiconductor. Overall, a sound knowledge has been gathered on organic redox active species and their application in redox flow, solid-state and directly solar charged redox flow batteries.
Within the first year of the project GLOBE we have successfully adapted electrochemical techniques and performed a large screening of a commercially available organic redox species to learn about their redox potential, water solubility and chemical stability. This allowed our group to establish its own library of species and decide on the subsequent directions in the project. Several important conclusions were drawn from the initial screening:
• Many of the organic species were found not to have sufficient chemical stability in water, and this concerns both the negative and the positive side, however it is much more severe for the positive side of the redox flow battery. There seem to be viable strategies to overcome this problem.
• Cell voltage of all organic redox flow battery is limited to 1 V, which is significantly smaller than that of commercial vanadium redox flow battery. However, many of the species have pH dependent redox potential and this property was exploited to increase the cell potential.
• Many of the species were insoluble in water, however redox active. This property was exploited for their use in solid state batteries.
• Organic redox species have a tunable redox potential, i.e. addition of certain functional groups changes the redox potential of quinone based species. This property was exploited in direct solar charging of redox flow batteries where redox potential was tuned so that it fits the energy level of a semiconductor.
Progress beyond state of the art
• Project GLOBE has identified a number of organic redox active species, addressed their chemical stability and measured their solubility in water.
• We have increased the potential of anthraquinone disulfonic acid/bromine battery from 0.86 V to 1.3 V (40%) and managed to operate the battery at differential pH, at mild pH conditions, improved conditions compared to harsh acidic conditions of the original battery.
• We have developed new very water soluble organic redox active species for the positive side, however there are chemical stability issues. One type includes azo disulfonate species, another includes derivatives of hydroquinone. We have now started with new research into water soluble and chemically stable species for the positive side.
• We have applied anthraquinone oligomers/polymers in nickel solid state battery, instead of metal hydride and cadmium. This resulted in a new battery that is able to deliver around 1000 cycles, however the battery losses around 70% of its capacity.
• We have directly fully solar charged a semi-organic redox flow battery.

The GLOBE’s outcomes will have both social and economic impact, by sharing the new insights publicly, and by using our current knowledge to establish foundations for a new type of semi organic redox flow battery, that could be commercialized within the next 6 years (in ORBAT project funded currently by Innovation Fond Denmark). GLOBE’s results are expected to promote innovation in the field of organic redox flow and solid-state batteries, given the developed new types of species, however there are also future plans on developing new types of organic solid-state batteries. Our results will strengthen the global competitiveness of the European electrical energy storage industry.
Differential pH concept