CeOx/C nanocomposite derived from a metal-organic framework as high-performance anodes for sodium-ion batteries, developed by researchers at Chung Yuan Christian University (CYCU) and National Cheng Kung University (NCKU) in Taiwan.Sodium offers a potentially cheap and more abundant alternative to commonly used lithium-ion batteries. Now researchers in Taiwan have created high-performance anodes for sodium-ion batteries using a cerium oxide/carbon nanocomposite derived from a metal-organic framework Muruganantham et al., Applied Materials Today 22 (2021) 100935, https://doi.org/10.1016/j.apmt.2021.100935].
“We converted a highly porous metal-organic framework (MOF) into a porous cerium oxide-carbon (CeOx/C) nanocomposite,” explain Chung-Wei Kung of National Cheng Kung University and Wei-Ren Liu of Chung Yuan Christian University, who led the work. “The CeOx/C material shows promising performance as an anode material for sodium-ion batteries.”
MOFs are made up of inorganic metal-based nodes held together by organic linkers. The researchers transformed a cerium-based MOF (Ce-MOF-808) using a one-step process known as calcination into a nanocomposite of CeOx particles (30-100 nm in diameter), made up of agglomerations of tiny nanometer-sized grains, wrapped in conductive layers of carbon. During the process, the hexa-cerium clusters that make up Ce-MOF-808 are converted into crystalline ceria, while the organic linkers are carbonized into a porous carbon coating. The resulting composite is highly porous and much more conductive than Ce-MOF-808, thanks to the presence of carbon.
The CeOx/C nanocomposite shows remarkable electrochemical activity and stable sodium-ion storage performance, according to the researchers. As well as improving conductivity, the researchers believe that the carbon coating also inhibits volume changes during sodium ion absorption and desorption during charging/discharging cycles.
“The porous structure acts as an additional sodium-ion migration pathway during reversible charging and discharging cycles,” explain Kung and Liu. “The redox activity of ceria itself also offers higher reversible capacity for sodium-ion storage,” they add.
The researchers believe that the work is the first demonstration of the possibilities of ceria as an anode material for sodium-ion batteries. The nanocomposite material boasts a higher capacity than other metal oxide-based anodes reported to date.
Although cerium is a relatively Earth-abundant material, MOF production costs still remain high, and the mass production of Ce-MOF is not well developed. To exploit the capabilities of CeOx/C nanocomposites for sodium-ion batteries, large-scale mass production methods need to be developed. Nevertheless, Liu is confident that the significant improvement in conductivity offered by MOF-derived CeOx/C makes the material a viable and practical option for sodium- and other metal ion-based storage applications.
“We are focusing on the production of materials in larger quantities through simple low-cost techniques,” Kung and Liu say. “Such MOF-derived CeOx/C nanomaterials will be utilized as active materials in other types of metal-ion batteries as well.”