Synthesis Of Cobalt-Based MOF And Its Derivatives As Advanced Anode Materials For Lithium/Sodium Ion Batteries

The rapid development of portable electronic devices and electric vehicles requires that the rechargeable batteries have high power,high energy density and fast charging capability.Lithium-ion batteries(LIBs)have been considered as one of the major breakthroughs in the field of electrochemical energy storage in recent decades due to their advantages such as low cost,long cycle performance,small size,high energy density,large reversible capacity,and no memory effect.Large-scale applications such as power grid energy storage,however,require cost effectiveness and performance characteristics.The insufficient reserves of lithium resources limit the long-term and large-scale use of LIBs.The electrochemical and kinetic characteristics of sodium ion batteries(SIBs)and LIBs are consistent.The development of highperformance SIBs electrode materials can be based on and utilized by the current achievements of LIBs.Therefore,SIBs is the only viable post-lithium technology with the necessary cost and performance characteristics.In this article,the electrode material with high electrochemical performances were synthesized by morphology and structural design.The main contents are as follows:(1)To obtain MOFs materials with good electrochemical performance in both lithium-ion batteries(LIBs)and sodium-ionbatteries(SIBs),a kind of hollow urchins Co-MOF with doping fluorine(F)was in-situ assembled on reduced graphene oxide(rGO)using a simple solvothermal reaction.The doping of F can not only improve the crystallinity of the material,but also effectively improve the reversibility of lithium insertion/delithiation and the lithium storage performance.According to XRD,XPS and EDS mapping analysis,the molecular structure should be Co2[Fx(OH)1-x]2(C8O4H4)(denoted as F-Co-MOF).When the composite material is used as active material to assemble LIBs,it not only presents the outstanding reversible capacity(1202.0 mA h g-1 at 0.1 A g-1),but also gives the excellent rate performance and cycle performance(771.5 mA h g-1 at 2 A g-1 after 550 repeated cycles).The remarkable lithium storage capacity of F-Co-MOF/rGO is also reflected in the full cell,where it can still maintain a high capacity of 165.2 mA h g-1 after 300 cycles at 0.2 A g-1.(2)A double-layer carbon coated hollow nanocube MnS-CoS2-NC@NC was prepared by a simple one-step calcination process.The double-layer carbon structure can not only significantly increase the overall conductivity of the material to promote electron transport,but also effectively alleviate the volume expansion during charging and discharging.In the half cell,the MnS-CoS2-NC@NC electrode not only provides an ultra-high specific capacity of 608.5 mA h g-1 at 0.2 A g-1 for 100 cycles,but also shows an outstanding rate performance of 560.5 mA h g-1 at 5.0 A g-1 for 1100 cycles.Even in a full cell composed with Na3V2(PO4)3,it can still maintain a capacity of 436.7 mA h g-1 after 900 cycles at 1.0 A g-1.Compared with the MnS-CoS2-NC electrode calcined without PDA coating,the rate performance and cycle stability have been significantly improved.In order to explore its sodium storage mechanism,in-situ and ex-situ XRD tests are carried out to prove the mechanism of its conversion reaction.