They published their work on Mar. 15th in Energy Material Advances.
"It is highly necessary to design highly conductive and high-performance materials for application in alkaline ion batteries," said paper author Xijun Xu, associate Professor at the College of Chemical Engineering and Light Industry, Guangdong University of Technology.
"In recent years, with the development of large-scale power systems such as electric vehicles, the demand for secondary batteries has gradually shifted towards high power and low cost. Furthermore, in light of the increasing energy and environmental concerns, the exploration of green and renewable resources has become a research hotspot. Among them, lithium-ion batteries are currently the mainstream energy storage devices. However, due to the uneven distribution and expensive price of lithium resources, the research and development of high-performance and highly safe alkaline ion secondary batteries hold significant practical significance."
Xu said that covalent organic framework (COF) materials exhibit several advantageous characteristics and demonstrate excellent electrochemical performance. Their unique network framework provides good structural stability and outstanding cycling performance, offering broad prospects in electronic devices and energy storage applications.
"The ability of COFs to pre-design oxidation-reduction active sites with precise density and position provides them with the flexibility to alter the energy density of electrode materials. Additionally, the introduction of organic functional groups into COF structures promotes the migration of metal ions, demonstrating the potential to address the issue of slow ion transport in batteries."
"Typically, the introduction of functional groups or heteroatoms with strong electron-withdrawing characteristics is a common method to effectively reduce the bandgap and increase conjugation to enhance the intrinsic conductivity of organic electrode materials. Structural design is necessary to achieve highly stable and high-capacity COF materials. It is worth noting that in alkali metal ion batteries, larger ion sizes imply slower ion transport rates and larger volume changes during reversible cycling. Therefore, the influence of larger ion sizes should be considered in the design process. The design principles of COFs in metal ion battery systems mainly involve the regulation of pore structures, chemical reaction sites, and surface functional groups. Thus, by designing the structure and properties of COFs in a rational manner, high-performance, stable, and sustainable alkaline ion battery systems can be achieved."
"Currently, the development of COF batteries is still in its early stages and faces several challenges. For instance, the synthesis conditions for obtaining most COFs are complex and not amenable to large-scale production. Additionally, polycrystalline COFs suffer from various structural defects," Xu said, "The significant correlation between the adaptable structure of COFs and the electrochemical functionality of batteries is evident. The extensive application of COFs in batteries is still ongoing, and many areas require improvement. Furthermore, a thorough understanding of the electrochemical reaction mechanisms is equally crucial for the design of high-performance materials. In general, further research is needed for the application of COFs in batteries, and in the future, overcoming the aforementioned challenges is necessary to enhance the electrochemical properties of COFs. Simplification of reaction conditions would also be advantageous for practical applications."
Other contributors include Tao Yang, Shaomin Ji and Yanping Huo, College of Chemical Engineering and Light Industry, Guangdong University of Technology; Yan Yang and Jun Liu, School of Materials Science and Engineering, Guangdong Provincial Key Laboratory of Advanced Energy Storage Materials, South China University of Technology; Weizhen Fan and Jingwei Zhao, Research and Development Center, Guangzhou Tinci Materials Technology Co., Ltd.; Yanxue Wu and Yanping Huo, Analytical&Testing Center, Guangdong University of Technology.
The National Key Research and Development Program of China (no. 2022YFB2502000), the National Natural Science Foundation of China (no. U21A2033251771076, 52301266), Guangdong Basic and Applied Basic Research Foundation (nos. 2020B1515120049, 2021A1515010332), and R&D Program in Key Areas of Guangdong Province (no. 2020B0101030005) supported this work.
