Solar panels and wind turbines can generate low-carbon electricity, but their output does not always coincide with the hours when homes and businesses need power. The challenge is not simply producing renewable energy; it is storing enough of it and releasing that energy reliably when generation falls.
A new study in Nature Sustainability reports a promising development in the chemistry of batteries designed for stationary storage. Researchers made a recyclable, water-based flow-battery material that retained 98.1% of its capacity after 2,200 laboratory charge-discharge cycles under specific test conditions.
The team also demonstrated a 63 watt-hour (Wh) experimental battery stack and a process for recovering its active material. Their results bring together three aims that are difficult to achieve in the same storage chemistry: accessible capacity, repeated operation and a route to material reuse.
Published on 23 October 2026, the work is a materials and engineering demonstration, not evidence of a commercially deployed grid battery. Its significance is that a sulfur-based molecule could be used for electrical storage while also offering a recycling pathway.
Why electricity grids need different kinds of batteries
Electricity grids must balance supply and demand continuously. Solar generation rises in daylight and declines after sunset, while wind output changes with weather. Storage is one way to shift electricity from periods of production to periods when it is more valuable.
The ideal battery depends on the job. Electric vehicles need compact packs capable of delivering substantial power without excessive weight. Large stationary storage systems can sometimes accommodate external tanks and supporting equipment if doing so improves economics or durability.
This is where redox flow batteries become interesting. They hold their energy-bearing liquids in reservoirs and pump those liquids through an electrochemical cell. Charging changes the chemical states of active species; discharging reverses the reaction and releases electrical energy.
Increasing the volume of active fluid can provide more storage capacity, while changing the size or number of cells can affect power output. In practice, the relationship is not perfectly independent, but the design offers flexibility for stationary installations.
Vanadium-based flow batteries are among the existing technologies. Researchers continue exploring alternatives because material costs, supply chains, performance and end-of-life recovery can all affect whether a storage system makes economic sense.
A recyclable sulfur-based energy-storage liquid
Qiliang Chen, Hongjuan Ou and colleagues at Zhengzhou University developed an anolyte, the active liquid associated with the negative side of a redox flow battery.
The central material was an oligo(disulfide): relatively short molecular chains containing sulfur–sulfur bonds that can participate in reversible oxidation and reduction reactions. Through those chemical changes, the liquid can store and release electrical energy.
The scientists prepared the material by ring-opening polymerization of a potassium form of thioctic acid, also called alpha-lipoic acid. This process provided a concentrated source of electrochemically active sulfur bonds.
Although thioctic acid occurs in biological chemistry, that does not establish that industrial production would be cheap or environmentally harmless. Raw materials, processing, solvents, energy use and waste would still need to be assessed at scale.
The researchers paired the sulfur-based anolyte with a sulfonated cobalt phthalocyanine catalyst. A catalyst speeds reactions that might otherwise proceed too slowly for useful battery operation. Here the cobalt-containing molecular catalyst helped the reversible sulfur chemistry work within the cell.
The experiment therefore tested an integrated electrochemical design, not just a promising liquid in isolation. That distinction is important when assessing whether the result could eventually be reproduced in a larger battery.
The battery’s capacity: what 128 Ah/L means
In one laboratory test, the new liquid achieved a capacity density of 128 ampere-hours per litre (Ah/L) at a current density of 50 milliamperes per square centimetre (mA/cm²).
The researchers reported 95.5% material utilization under that test condition. In this context, utilization describes how much of the active material’s theoretically available charge was accessed during the experiment.
Neither figure should be mistaken for electricity-to-electricity efficiency. Ampere-hours per litre measure charge relative to volume, while energy density also depends on voltage. Material utilization describes access to chemical capacity, not what proportion of input electricity is recovered.
The result suggests that the sulfur-based solution can store a substantial amount of accessible charge at the tested concentration. Whether that translates into economical system-level energy storage requires additional evidence about voltage, pumps, membranes, processing and operating costs.
Why 2,200 charge-discharge cycles matter
For the longer durability experiment, the team used a more specific arrangement with a carbon-coated sulfonated poly(ether ether ketone) membrane and a sulfur–sulfur bond concentration of 0.25 molar.
At 100 mA/cm², the battery retained 98.1% of its capacity after 2,200 charge-discharge cycles. Under the reported conditions, measured capacity fell by only 1.9% over the cycling sequence.
That is encouraging because battery materials can degrade repeatedly through unwanted side reactions, chemical breakdown, active species crossing the membrane or becoming unavailable for further reactions.
But 2,200 laboratory cycles cannot be translated directly into a guaranteed number of years of commercial life. Operational installations experience changing temperatures, periods of rest, irregular charging, pump wear and fluid-management demands that controlled tests do not fully reproduce.
There is another essential distinction: capacity retention is not energy efficiency. High retention means the system preserved much of its storage capacity across cycles. It does not reveal how much electricity is lost on each cycle.
That second measure was approximately 70% energy efficiency at the reported current density of 100 mA/cm². Some of the electrical energy supplied during charging was therefore not recovered as output under those conditions.
A battery can maintain stable capacity while still facing efficiency trade-offs. Both figures must be considered when comparing technologies for an actual electricity project.
The membrane is part of the result
A flow battery’s membrane must permit appropriate ions to move between the cell’s two sides while limiting the migration of active substances that should remain separated. Excessive crossover can erode useful capacity; too much resistance can lower energy efficiency.
The carbon-coated membrane was part of the test configuration that achieved strong capacity retention. This means the long-cycling result reflects the combination of the active liquid, catalyst, membrane and operating conditions.
It would be misleading to credit every benefit solely to a single molecule or to assume that changing one component would preserve the same result. Membrane manufacturing, durability, maintenance and cost are also important engineering considerations.
A 63 Wh stack moves beyond a single cell
The researchers built a 63 Wh stack, combining cells into a larger experimental assembly. This allowed the team to investigate practical aspects of their chemistry beyond one small laboratory cell.
The scale matters: 63 Wh is 0.063 kilowatt-hours, tiny compared with storage installations intended to support an electricity grid. The demonstration is a step toward scale-up, not proof of commercial-scale operation.
Larger systems would require greater volumes of electrolyte as well as pumps, controllers, membranes, reservoirs and connections between multiple cells. Increasing size can reveal problems involving leaks, uneven flow, chemical degradation and electrical differences across the stack.
The stack was also used to validate the researchers’ approach to closed-loop recycling of the active sulfur-based material. That second function makes it more interesting than a demonstration focused only on initial battery performance.
What the recycling claim does—and does not—establish
Battery sustainability requires attention to how materials are obtained, manufactured, used and recovered at the end of service life. Materials that are difficult to recycle may create new environmental challenges even when they support low-carbon electricity generation.
The study demonstrated a route to recover and reuse its oligo(disulfide) active chemistry, including validation in the experimental stack. The result suggests that the energy-bearing material could potentially be cycled through more than one material-use life.
But this is not proof that every part of a commercial flow-battery installation is recyclable. Tanks, membranes, catalysts, pumps and electronic components have their own manufacturing and end-of-life requirements.
Nor does recyclability alone establish a lower environmental impact. Industrial recovery consumes materials and energy, and an independent lifecycle assessment would be needed to compare the entire system with alternatives.
The significance of the reported recycling experiment is that the researchers went beyond describing a theoretical possibility. They tested a recovery pathway for the specific active material they developed.
Why efficiency and cost could limit adoption
The approximate 70% energy efficiency reported for the long-term cycling arrangement deserves attention alongside the excellent capacity retention. A system that loses more energy during storage must justify those losses through other benefits, such as lower cost, safety, durability or longer storage duration.
Different applications face different trade-offs. Storage used for occasional backup may be evaluated differently from a unit that charges and discharges every day in a competitive electricity market.
The paper does not establish a commercial cost per kilowatt-hour or prove that this chemistry is cheaper than lithium-ion or vanadium-based flow batteries. Manufacturing, catalyst and membrane expenses, efficiency, maintenance and replacement intervals all matter.
Additional research would need to assess cost, process energy and performance under actual operating schedules before comparing economic competitiveness with established technologies.
How it fits into the wider battery landscape
Not every battery breakthrough addresses the same problem. Some scientists work on electrode structure, others on chemistry, separators, controls or making recycling easier.
A previous Research Today article on a sodium-ion cathode examined a material retaining 82% capacity after 1,000 cycles. Those numbers cannot be ranked directly against the current result because the chemistry and test arrangements differ.
Other studies have focused on controlling battery charging to reduce simulated peak electricity demand. That concerns when energy is used, rather than the composition of the storage medium.
And battery research directed at electric vehicles often prioritizes compactness, weight and the safety of densely packed cells. Stationary flow batteries face another set of engineering constraints and may ultimately serve different purposes.
For that reason, this sulfur-based flow-battery work should be viewed as one development among several possible future energy-storage options, rather than a replacement for every rechargeable battery.
What it could mean for South Africa
South Africa and other countries expanding solar and wind generation may benefit from a broader range of dependable electricity-storage technologies. Storage can help align fluctuating renewable output with evening demand and other periods when generation is limited.
However, the researchers did not test the chemistry on South Africa’s grid, model local electricity tariffs or demonstrate operation in a commercial power plant. It would therefore be premature to claim the technology will reduce local electricity prices or solve power interruptions.
Its regional relevance is potential: if future development makes recyclable flow batteries competitive and reliable, they could become another option for stationary applications. That possibility must still be evaluated through engineering, economic and environmental studies.
Important limitations of the research
The paper combines molecular design, electrochemical tests, durability measurements and a larger experimental stack, which makes it stronger than an investigation reporting only a single laboratory performance figure.
Nevertheless, the battery has not been demonstrated at grid scale. The 63 Wh stack is a proof of concept, and 2,200 controlled charge-discharge cycles do not establish years of field operation.
The headline measurements also come from distinct experimental conditions. The 128 Ah/L capacity density and the 98.1% retention with approximately 70% energy efficiency should not be combined into an imaginary specification for one commercial product.
Other unresolved questions include the costs of producing and recycling the sulfur material, manufacturing and replacing membranes, catalyst requirements, operational safety, and performance when temperatures and workloads vary.
Future research could examine much larger stacks, multiple recovery cycles, independent comparisons against existing technologies and a full lifecycle environmental assessment.
A meaningful step, not a finished grid battery
The central advance is the combination of stable cycling and demonstrated active-material recovery. The oligo(disulfide) anolyte supplied useful charge capacity, retained almost all its measured capacity through extensive laboratory cycling and supported a small recycling demonstrator.
That is encouraging for scientists exploring water-based, more circular storage systems. It also illustrates why new battery claims need careful interpretation: capacity, retention, electrical efficiency, system scale and recyclability answer different questions.
The next test is whether the chemistry can retain those useful properties when deployed at much larger scale, operated under real conditions and manufactured at a competitive cost. Until then, it represents a promising research platform rather than a commercially proven solution.
Looking for studies on this topic? Use the Research Today Research Paper Finder to search scholarly research by topic, question, author or keyword.
Source Information
Study title: A circular oligo(disulfide) anolyte enables practical aqueous redox flow batteries
Authors: Qiliang Chen, Hongjuan Ou, Xiaoting Zhao, Yajie Jin, Wei Guo and Yongzhu Fu
Journal: Nature Sustainability
Publication date: 23 October 2026
Study design: Experimental materials-development study involving molecular synthesis, catalyst-assisted aqueous redox flow-cell tests, long-term charge-discharge cycling, membrane testing and a 63 Wh stack demonstration of active-material recycling
Sample or scope: Oligo(disulfide) anolyte tested in laboratory aqueous redox flow cells, including capacity testing at 50 mA/cm² and cycling at 100 mA/cm² with 0.25 M sulfur–sulfur bonds; a 63 Wh experimental stack
Key finding: The anolyte reached 128 Ah/L capacity density with 95.5% material utilization; a separate cycling configuration retained 98.1% capacity after 2,200 cycles at approximately 70% energy efficiency, while a 63 Wh stack supported recycling tests
