Current zinc-based batteries often have relatively short lifespans because their materials gradually degrade during 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 nearly 90 percent of its capacity even after more than 10,000 charge-discharge cycles.According to the team, this corresponds to more than 3,500 hours of continuous operation.The researchers said their strategy could help pave the way for designing longer-lasting aqueous energy storage systems.Altered chemistry improves lifespanExisting aqueous zinc-ion batteries (ZIBs) typically rely on iodine-based cathodes because they offer long cycling stability, fast charge-discharge capability, and the potential to store large amounts of energy.However, iodine-based cathodes also suffer from several limitations. They conduct electricity poorly, undergo structural changes as the battery charges and discharges, 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 the Changchun Institute of Applied Chemistry modified the functional group chemistry of the cathode to develop self-supporting carbon nanotube cathodes (SSCC).In their experiments, they compared the iodine adsorption capability of modified carbon nanotubes with that of unmodified ones. The team investigated nanotubes functionalized with hydroxyl (‒OH), carboxyl (‒COOH), and amine (‒NH₂) groups to determine which surface chemistry performed best.Using spectroscopy and microscopy techniques, the researchers confirmed the successful introduction of the functional groups and the uniform loading of iodine throughout the cathode material.They found that the hydroxyl-modified nanotubes acted like tiny anchors, trapping iodine ions where they belonged rather than letting them migrate 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, delivering an initial reversible capacity of 175.5 mAh/g (milliampere-hours per gram) at a current density of 1 A/g (ampere per gram) while maintaining excellent durability.Even after more than 10,000 charge-discharge cycles, the battery 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 cycling life of 93,400 charge-discharge cycles.Shuttle effect lostAdvanced characterization techniques, including in situ Raman spectroscopy performed during battery operation and ex situ X-ray photoelectron spectroscopy conducted after cycling, 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 lingering in the electrolyte, reducing energy loss, and improving battery stability.To demonstrate 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, demonstrating promising performance under more realistic operating conditions.The researchers concluded that modifying the cathode’s functional group chemistry provides a simple and effective way to improve iodine conversion kinetics while stabilizing aqueous zinc-iodine batteries. They added that the approach could guide the future design of long-life aqueous energy storage systems based on naturally abundant zinc metal.The findings were published in Science China Chemistry.