Building on earlier work, researchers in China have fabricated a hierarchical metal-organic nanocomposite for use as a cathode in sodium-ion batteries (SIBs). Their electrode—metal-organic cuprous tetracyanoquino-dimethane (CuTCNQ) in a three-dimensional (3D) conductive carbon nanofibers (CNFs) network (CuTCNQ)—exhibits a capacity of 252 mAh g-1 at 0.1 C and highly reversible stability for 1200 cycles within the voltage range of 2.5 - 4.1 V (vs. Na+/Na). They obtained a high specific energy of 762 Wh kg-1 with high average potential of 3.2 V (vs. Na+/Na).
In a paper published in the journal ChemSusChem, the team from Yunnan University, Huazhong University of Science and Technology, and Tongji University suggest that such in-situ formed electroactive metal-organic composites with tailored nanoarchitecture are a promising alternative choice for high-performance cathode materials in high-energy sodium-ion batteries.
Recently, room temperature sodium-ion batteries (SIBs) have received tremendous attention for electrochemical energy storage applications owing to their low cost and the abundant resource of sodium compared with lithium. For SIBs, great progress has been achieved on anode materials, but cathode materials face a big challenge due to limited capacity and some other unsatisfactory performances. … Recently, metal-organic compounds, which are composed of metal ions coordinated to organic ligands, are emerging as state-of-the-art electrode materials and have drawn more and more interests.
… The metal-organic compounds can be designed to consist of electroactive metal ions and organic ligands ions, so that multiple-electron transfer redox reactions can be achieved to enhance the Na-storage capacity. Moreover, the transition metal ions participate in the electrochemical reaction at high potentials that is helpful to raise the battery voltage.—Huang et al.
The research team had already shown that CuTCNQ functions as a high-energy SIB cathode; they found that the cationic Cu+ and anionic TCNQ- could simultaneously participate in the redox reaction with a three-electron transfer process. The theoretical specific energy density is more than 900 Wh kg-1; however, since CuTCNQ is an organic-based compound, one concern is its structural stability and electronic conductivity.
In this latest work, they address that issue by devising a simple in-situ synthetic method that combines electrospinning and solution reaction to anchor CuTCNQ nanorods on carbon fibers.
We believe that this work not only proves that the metal-organic compounds can serve as stable high-energy electrodes for SIBs, but also provides a facile method to fabricate the advanced composite of electroactive metal-organic compounds and conductive carbon network with superior electrochemical performance.—Huang et al.
Huang, Y., Fang, C., Zeng, R., Liu, Y., Zhang, W., Wang, Y., Liu, Q. and Huang, Y. (2017) “In-Situ Formed Hierarchical Metal-Organic Flexible Cathode for High-Energy Sodium-Ion Batteries” ChemSusChemdoi: 10.1002/cssc.201701484