Progress of MOFs as templates for preparation of lithium-ion batteries anode materials

Abstract

Lithium-ion batteries (LIBs) with high energy density have been widely used in portable electronics and electric vehicles. Unfortunately, commercialized graphite encounters with limited theoretical capacity due to the generation of the intercalation compound LiC6. Simultaneously, metal oxides suffer from serious capacity loss due to the slow diffusion of lithium ions and high polarization during the lithium storage process. Consequently, numerous efforts have been focused on developing alternative anode materials with higher capacities and rate capabilities to meet the ever-growing demands of energy storages. Interestingly, metal-organic frameworks (MOFs), as a very promising kind of multifunctional materials, have been widely fabricated for environmental and energy-related applications due to their simply preparation, high porosity, large specific surface area, adjustable pore size, abundant diversity in structure and composition. Recent reports highlight that MOFs materials are prospective self-sacrificing templates for the fabrication of multifunctional materials. This paper summarizes the advances in the application of MOFs and MOFs-derived porous materials in LIBs. Firstly, a brief summary of pristine MOFs for particular application in LIBs is provided. In this regard, the lithium storage mechanism is mainly divided into two aspects: insertion/desertion mechanism and conversion mechanism. In order to improve the electrochemical performance, it is particularly important to select appropriate organic ligands with relatively low molecular weight and reactive functional groups (amino, carboxyl, benzene rings, etc.), as well as variable valence metal centers to construct rigid and porous MOFs and provide more lithium storage active site. Afterward, a comprehensive overview of the synthetic methods of MOF-derived materials (porous carbon, transition metal oxides, metal oxides/carbon composites, metal/metal oxides) and their applications in the anode of LIBs are described in details, including the important issues and research challenges. MOFs can be easily converted into traditional inorganic functional materials (metal compounds or carbon) through high temperature calcination or controlled chemical reaction. Especially, many advantages such as adjustable structure, chemical composition, and secondary building units, can further enhance the electrochemical performance and solve the key scientific issues in the field of electrochemical energy. There are several effective methods to improve the capacities and cycling stability: (1) fabrication of multicomponent active electrode material with unique structure (such as mixed metal oxides, metal/metal oxide and C/N doping), which can effectively reduce the activation energy of electron transfer and provide richer redox chemical kinetics; (2) introduction of conductive materials (such as graphene, carbon fibers, carbon nanotubes, copper foam and nickel foam), which can enhance electrical conductivity for fast charge transfer; (3) creation of hollow nanostructure with high specific surface area porosity, which can increase the contact area between the electrolyte and the material, effectively buffer the volume expansion, ensuring the integrity and stability of the structure. Lastly, topics of the development directions and prospect applications of these MOF-derived materials for electrochemical energy storage and conversion are outlined, providing meaningful experimental basis and theoretical value for the directional synthesis of these materials in electrochemistry.