MOF-derived Metal Oxide/Graphene Composites Used In Lithium Ion Batteries

Lithium-ion batteries are expected to be the main solution for electric vehicles and fixed energy storage systems.As the most critical component of lithium-ion batteries,the performance of cathode materials plays a decisive role.At present,the traditional graphite anode is difficult to meet the requirements,so the research and development focus of lithium-ion batteries with high energy density lies in the design and preparation of anode materials.Metal oxides derived from MOF have been widely used as cathode materials for lithium-ion batteries due to their super high theoretical capacity and various properties.As a new two-dimensional material,graphene has been widely used in the field of electrochemical energy storage and conversion due to its controllable synthesis method,excellent conductivity,adjustable functional surface functional groups and other characteristics.Due to the inevitable lamination caused by the interaction between Van Der Waals forces and-in two-dimensional materials,their mass-energy density is low and their performance is limited.In view of this,in this paper,two kinds of graphene-based three-dimensional porous materials were constructed by means of three-dimensional self-assembly,electrostatic adsorption,in-situ growth,heteroatom doping and MOF derivation,etc.,and their electrochemical properties as anode materials for lithium ion batteries were studied.The detailed research contents,results and discussion are summarized as the following aspects:(1)We designed assembly of porous Fe₂O₃ nano framework into three-dimensional P-doped graphene framework composites(PGF@p Fe₂O₃NF)via using Metal-organic frameworks as the precursor of porous Fe₂O₃ and thermal treatment to obtain P doped graphene.The hierarchical structure with flexible macroporous P-doped graphene network and Fe₂O₃ nanoporous framework can effectively promote the lithium diffusion and charge transport during the lithiation/delithiation processes.The flexible PGF@p Fe₂O₃NF is directly compressed with binder-free anodes for LIBs.It showed excellent capacity(1106 m Ah g^-1 at100 m A g^-1),rate performance(410 m Ah g^-1 at 4000 m A g^-1),and super long cycling performance(452 m Ah g^-1 at 3000 m A g^-1 after 6000 cycles).Moreover,the PGF@p Fe₂O₃NF-based LIB full cell also delivers high energy of 350.8 Wh kg^-1.This work offersd a strategy to develop advanced porous Fe₂O₃-based anode for high-performance LIBs.(2)The ZIF-67/graphene composites were obtained by the solvent thermal reaction,and then three-dimensional graphene-coated porous cobalt oxide composites were prepared by calcination.The accumulation and volume change of the ZIF-67 derived porous cobalt oxide particles during the electrochemical process which can be effectively inhibited by coating them in a 3D graphene framework.Co₃O₄ particles/3D graphene composites were obtained from the in-situ metal-organic skeleton grown on 3D graphene sheets through thermal decomposition.Under the 100 m A g^-1,the reversible capacity was 1516 m Ah g^-1 after 180cycles.Under the ultra-high current density of 4000 m A g^-1,the reversible capacity could still reach 926 m Ah g^-1.This excellent performance is due to the clear hollow structure of the porous particles derived from ZIF-67.In addition to high performance,the porous crosslinking structure of 3D graphene also ensures the stability of the whole composite.To summery,this paper has made a series of achievements in the use of porous metal oxides derived from the controllable 3D graphene framework and MOF as well as heteroatomic doping for lithium anode materials.The results are helpful to understand the influence mechanism of graphene's chemical composition,structure and thermal stability on its electrochemical performance,accelerate the practical process of graphene and its composite materials,and promote the development of new energy technologies...