Current zinc-based batteries often have relatively short lifespans because their materials gradually degrade with repeated charge-discharge cycles.
By changing the chemistry of the battery’s cathode, Chinese researchers have developed a new liquid zinc-ion battery that retains almost 90 percent of its capacity even after more than 10,000 charge-discharge cycles.
According to the team, this equates to more than 3,500 hours of continuous operation.
The researchers said their strategy could help pave the way for the development of longer-lasting aqueous energy storage systems.
Changing chemistry improves service life
Existing aqueous zinc-ion batteries (ZIBs) are typically based on iodine-based cathodes because they offer long cycle stability, rapid charge-discharge capability, and the potential to store large amounts of energy.
However, iodine-based cathodes also have several limitations. They conduct electricity poorly, change structurally when the battery is charged and discharged, and allow iodine ions to migrate through the battery. This so-called shuttle effect reduces efficiency, accelerates material degradation and shortens battery life.
To overcome these challenges, researchers from Jilin University and Changchun Institute of Applied Chemistry modified the chemistry of the cathode’s functional groups to develop self-supporting carbon nanotube cathodes (SSCC).
In their experiments, they compared the iodine adsorption ability of modified carbon nanotubes with that of unmodified ones. The team examined nanotubes functionalized with hydroxyl (‒OH), carboxyl (‒COOH), and amine (‒NH₂) groups to find out which surface chemistry worked best.
Using spectroscopy and microscopy techniques, the researchers confirmed the successful introduction of the functional groups and the uniform iodine loading throughout the cathode material.
They found that the hydroxyl-modified nanotubes acted like tiny anchors, trapping iodine ions where they belong rather than allowing them to travel through the battery. This reduced energy loss while improving both efficiency and long-term stability.
Laboratory tests showed that the new cathode stored a high amount of electrical charge and delivered an initial reversible capacity of 175.5 mAh/g (milliamperes per gram) at a current density of 1 A/g (amps per gram), while maintaining excellent durability.
Even after more than 10,000 charge-discharge cycles, the battery still retained 89.34 percent of its original capacity.
At a higher current density of 10 A/g, the battery delivered a capacity of 120 mAh/g while achieving an exceptionally long cycle life of 93,400 charge-discharge cycles.
Shuttle effect lost
Advanced characterization techniques, including in situ Raman spectroscopy during battery operation and ex situ X-ray photoelectron spectroscopy after charging, confirmed that the iodine species were repeatedly and reversibly converted during charging and discharging.
The researchers also found that the modified cathode effectively eliminated the unwanted iodine shuttle effect, preventing iodine ions from remaining in the electrolyte, reducing energy loss and improving battery stability.
To demonstrate its practical potential, the team built a larger pouch cell prototype containing 150 mg of iodine. The battery operated at 1.1 volts, delivered an actual capacity of 23.8 mAh and retained 91.7 percent of its original capacity after 350 charge-discharge cycles, showing promising performance under more realistic operating conditions.
The researchers concluded that modifying the cathode functional group chemistry represents a simple and effective way to improve iodine conversion kinetics while stabilizing aqueous zinc-iodine batteries. They added that the approach could guide future design of long-lasting aqueous energy storage systems based on naturally occurring zinc metal.
The results were published in Science China Chemistry.
