Lithium-ion batteries now represent the most common type of rechargeable battery. They are used in a wide range of applications from consumer electronics (e.g., batteries for smartphones and laptop computers) to electric vehicles to utility-scale energy storage systems. However, many alternative battery technologies have emerged in the recent years and are poised to compete head-to-head against lithium-ion batteries. The development of the next-generation energy storage solutions, in particular, has been focusing on better safety performance. The new kinds of batteries seek to address the most dangerous attribute of the traditional battery technologies, namely the high degree of flammability and combustibility. Recently, researchers at the Korea Institute of Science and Technology (KIST) in South Korea have devised zinc-ion batteries that not only eliminate the risk of fires and explosions but are also more environment-friendly than conventional lithium-ion batteries.
Zinc has long been used in single-use batteries. As for rechargeable zinc-ion batteries, the major challenges in their development include the corrosiveness of the electrolyte and the formation of dendrite on the anode. The latter issue also afflicts lithium-ion batteries. As a rechargeable battery goes through numerous charging and discharging cycles, clumps of metal ions start to deposit on the surface of the anode. They then grow into dendrites or crystalline branches that will eventually damage the separator of the battery, thereby affecting the performance and the operational lifespan of the whole device. Researchers at KIST target the formation of dendrite because resolving this issue will lead to a competitive type of zinc-ion battery that uses no toxic materials, costs not much to manufacture, and is safe for users.
The KIST team has stated that its zinc-ion batteries contain a water-based electrolyte. Unlike the flammable electrolyte that is in conventional lithium-ion batteries, it does not catch fire or explode. As for the problem of dendrites, the team has come up with a “periodic anodizing method” that alternatingly blocks and permits the flow of current on the surface of the anode. This technique, which modifies the surface coating morphology and the pattern of the zinc oxide film, prevents the formation of crystalline branches.
To put this method into practice, the team alters the surface of the anode so that hexagonal pyramids or needle-like structures protrude from it. The design stifles the formation of dendrites during the electrochemical reaction. The zinc oxide covering the top part of the pyramid is thick, whereas the film covering the sides of the pyramid is thin. This unevenness induces zinc ions to accumulate on the sides rather than piling up vertically and turning into branches. The same zinc oxide film that expands horizontally actually serves as an effective buffer between the anode and the corrosive electrolyte, thereby inhibiting side reactions at the same time.
The study on the zinc-ion batteries developed by the KIST team shows that the device kept almost 100% of its capacity after 1,000 cycles under extreme conditions (i.e., 9,000mA/g fully charged and discharged for two minutes respectively). The device has demonstrated remarkable electrochemical and structural stability. These attributes have also allowed the team to create zinc-batteries that are bendable and can be incorporated into the materials of clothes and bags.
Dr. Joong-kee Lee, senior researcher at KIST and leader of this research project, has said that zinc-ion batteries have a much lower risk of a fire hazard compared with lithium-ion batteries. Moreover, zinc-ion batteries are safer for human body and offer a performance on par with the existing energy storage devices. The KIST team hopes that its study will attract more attention to this next-generation energy storage technology. Further improvements in electrochemical stability and performance have to be made in order for rechargeable zinc-ion batteries to enter real-life applications. Additionally, the manufacturing process has to become more streamlined and less costly.
(The photo at the top of the article is a representation image of batteries in general. Photo credit: Shutterstock.)