Application of metal-organic frameworks as cathode materials for lithium-ion batteries

With the popularity of rechargeable devices, lithium-ion batteries are being widely used in mobile electronic devices and transportation owing to their high specific capacity and high energy density. However, phenomena of dissolution and side reactions leading to an increase in interface resistance still exist in traditional cathode materials, which drastically reduce their specific capacity and cycling performance. Due to these obvious defects, microstructure control of cathode materials has a decisive effect on their performance. Interestingly, metal-organic frameworks (MOFs), as a class of porous materials formed by self-assembly of organic ligands and metal ions or metal clusters, have been widely concerned in the field of energy storage for their advantages such as easy preparation, high porosity, large capacity and diversity. Recent research highlights that MOFs are excellent templates for building electrode materials. This paper reviews the application of MOFs and MOF-derived derivatives in lithium-ion batteries cathode materials. Herein, a summary of direct application of MOFs in cathode materials is provided. When MOFs are working as cathodes, the redox reaction of metal ions or organic active groups realizes the intercalation/deintercalation of lithium-ions. To improve the electrochemical performance of MOFs cathodes, it is important to choose organic ligands with high conductivity, high stability, porous structure and redox active sites at high density. Afterwards, the preparation methods of MOF-derived composite (MOFs as precursors or modifiers) and their application in cathodes of lithium-ion batteries are described in detail. Metal compounds or porous carbon with specific structures can be easily obtained by calcining MOFs at different temperatures under various gas atmospheres and other simple chemical reactions. Since MOF-derived derivatives retain the original morphology of MOFs, MOFs can be regarded as accurate templates for the synthesis of electrode materials. Compared with pristine MOFs, MOF-derived derivatives involve a more extensive level and have better research prospects in the storage and conversion of electrochemical energy sources due to their adjustable structure and composition, which combine the advantages of multiple materials. The following issues should be considered when developing MOF-derived materials as positive electrodes: (1) Introducing conductive materials such as porous carbon to improve the conductivity; (2) providing protective layers for the active material and reduce its dissolution to improve the cycling stability; (3) improving the specific surface area of the composite to increase the contact area between the active substance and the electrolyte for higher reactivity; (4) retaining the inherent porous structure of MOFs so as to provide channels for the transmission of lithium-ions and electrons. Finally, topic of application directions of MOFs and their derivatives in cathode materials for lithium-ion batteries is outlined, providing future prospects for the development of new electrode materials.