Study On Metal Organic Frameworks And Derivatives As Anode Materials For Lithium Ion Batteries

As a new generation of green power source,lithium ion battery has been widely used in the fields of portable electronic products and electric vehicles because of its advantages of high energy,high working voltage and long cycle life.Metal organic frameworks?MOFs?as a new kind of electrode material for lithium ion batteries has attracted great attention due to these advantages of high porosity,large specific surface area and adjustable aperture.In this paper,a series of M₂?NDC?₂DMF₂(M=Co²⁺,Mn²⁺,Cd²⁺)with the same topology,one bimetallic organic framework CoMn-NDC and their dierivatives were synthesized by using1,4-naphthalenedicarboxylic acid as the organic ligand.,The electrochemical properties of these materials as anodes for lithium ion batterywere studied systematically.1.Three organic frameworks,namely,Co₂?NDC?₂DMF₂,Mn₂?NDC?₂DMF₂ and Cd₂?NDC?₂DMF₂ were prepared by solvothermal method.Their structures were characterized by XRD and FTIR.The results showed that these three structureshad the same topology.They were used for the first time as electrode materials to explore their applications in the field of lithium ion storage.The electrochemical experimental results indicated that the three materials had potential application as anode materials for lithium ion batteries since all of them showed certain electrochemical properties.However,the electrochemical performances of these three materials with the same topology are not the same which may attribute to the different central metal ions,in which Mn₂?NDC?₂DMF₂ had the highest discharge capacity with a discharge specific capacity of 731.4 mAh/g at the current density of 200 mA/g,Co₂?NDC?₂DMF₂ and Cd₂?NDC?₂DMF₂ had a discharge specific capacity of is 627.1 and401.8 mAh/g,respectively.2.Co₂?NDC?₂DMF₂ and Mn₂?NDC?₂DMF₂ were used as precursors to synthesize their derivatives Co₃O₄ and Mn₂O₃ by calcinating at different temperatures?350?,500?,700??in airThe results showed that the grain size of the metal oxides increases obviously with the raise of calcination temperature.the larger grain size is not good for the ion migration and electrolyte diffusion,resulting in the decrease of reversible capacity.Co₃O₄ and Mn₂O₃calcined at a low temperature of 350?had higher specific discharge capacity of 1058.9 and1218.4 mAh/g under 200 mA/g current density,respectively.3.Co₃O₄/C and Mn₂O₃/C composites were obtained by calcinating Co₂?NDC?₂DMF₂ and Mn₂?NDC?₂DMF₂precursors.Compared with the pure Co₃O₄,the presence of carbon in Co₃O₄/C obviously improved the electrochemical performance.Under the current density of200 mA/g,the discharge specific capacity maintained at about 1000 mAh/g from second to200th cycles.However,the electrochemical performance of Mn₂O₃/C composites did not improved significantly when compared with pure Mn₂O₃.It is necessary to carry out further optimal experiments to find out the reason behind..4.The bimetallic organic framework CoMn-NDC was prepared by a solvothermal method,and the derivative?Co,Mn??Co,Mn?₂O₄ was obtained through a heating treatment.The results showed that CoMn-NDC had good cyclic stability.Under the current density of200 mA/g,the specific capacity after 350 cycles maintained at about 600 mAh/g.The derivative?Co,Mn??Co,Mn?₂O₄-350 obtained by calcinating at 350?in air had a higher discharge specific capacity of 1278.8 mAh/g after 200 cycles at a current density of 200 mA/g than its precusor CoMn-NDC.