| Lithium ion batteries?LIBs?have attracted more and more attention due to their excellent performance,and finding negative electrode materials with good cycle and rate performance has become a breakthrough in improving the performance of LIBs.Molybdenum-based composite materials possess excellent electrochemical properties owing to their unique morphology,high theoretical capacity and good conductivity,they are considered to be a promising class of anode materials for LIBs.Based on this,a variety of molybdenum-based composites have been successfully prepared with molybdenum-based compounds as the core of construction,and they have been used as anode materials in lithium-ion batteries.While developing the preparation method of molybdenum-based composite materials,its lithium storage performance was also studied.This study established a method of synthesizing a molybdenum-based polyacid-based organometallic framework?POMOF?,and showed that the molybdenum-based composite material has the advantages of high specific capacity and good cycle stability in LIBs.The related works are shown as follows:?1?MIL-88A@PMo12 microrod composites were synthesized by one-step hydrothermal method.Firstly,Fe Cl3 was dissolved in water,and fumaric acid was dissolved in ethanol.After the two solutions were mixed and stirred,phosphomolybdic acid was added to the above mixed solution and kept stirred at room temperature,Afterwards,mixed solution was transferred to a Teflon-lined autoclave and reacted at 65°C for 72 h.Finally,MIL-88A@PMo12microrods were obtained after natural cooling.MIL-88A@PMo12 microrods exhibited excellent electrochemical performance when used as the negative electrode of lithium ion batteries,and showed a high specific capacity of1062.1 m Ah g-1 after 100 cycles at 0.2 A g-1.300 cycles at 1 A g-1 current density can still provide a specific capacity of 490.8 m Ah g-1.The specific capacity of pure MIL-88A under equivalent conditions is only 553 m Ah g-1 and 358 m Ah g-1.Compared to pure MIL-88A microrods,MIL-88A@PMo12 microrods are superior in both large and small current cycling and rate performance.The reason is that the excellent electrochemical performance of phosphomolybdate(PMo12)combined with the unique framework structure of MIL-88A has given full play to their advantages,which make the material has a faster kinetic rate in the electrode reaction.Because the addition of alcohol reduces the reactivity of fumaric acid anions,PMo12 has successfully compounded with MIL-88A,so this work also proposes a construction idea about a polyacid-based organometallic framework?POMOF?.?2?C@Mo O2@C hollow nanosphere composite material was synthesized by layered coating method.First,hollow carbon spheres?HCS?were prepared by using phenolic resin coated Si O2 spheres treated with hydrofluoric acid pickling and annealing in two steps.Subsequently,the hollow carbon spheres were layer-by-layer coated with Mo O2 and C,and finally the C@Mo O2@C hollow nanosphere composite material was obtained and used as the anode of a lithium-ion battery to study its lithium battery performance.For comparison,C@Mo O2 has also conducted equivalent electrochemical tests.After circulating 250 cycles at a current density of 0.2 A g-1,C@Mo O2@C and C@Mo O2 have specific capacities of750 m A h g-1 and 319 m A h g-1,respectively.It is proved that the molybdenum dioxide composite material has good performance in LIBs.After the additional carbon layer is coated,the performance has been significantly improved,which is attributed to the high stability of the three-layer structure and the high electrical conductivity after carbon composite.?3?MIL-88B@PMo12 nano-octahedral composite material was synthesized by one-step hydrothermal method.MOFs with carboxylic acid as the ligand are also used as the basis,which is MIL-88B.By introducing alcohol into the reaction system to promote the compounding of PMo12 and MIL-88B,the effect of different reactant concentrations on the product morphology was also explored.Excellent rate performance and outstanding cycle stability at low current density are demonstrated,when MIL-88B@PMo12nano-octahedral composite material is used as the anode of LIBs.The initial discharge capacity was 1952 m Ah g-1,and after a current density of 0.2 A g-1 for 130 cycles,it showed a specific capacity of 549.8 m Ah g-1.The successful synthesis of this new POMOF provides a template for further research,and provides verification for the construction of the POMOF mentioned above. |
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