| In recent years,as a new high-performance lithium ion battery anode material,transition metal phosphide(TMP)has attracted extensive attention due to its high theoretical capacity and abundant sources.Nevertheless,the poor electrical conductivity and the huge volume changes associated with lithiation-delithiation process,make TMP exhibits poor cycling stability and rate capability,which impose restrictions on their commercial implementation.In order to solve the above problems,the transition metal(iron,cobalt and nickel)phosphide materials with different structures and compositions were designed and prepared.The structures and compositions of the materials and the electrochemical properties when the materials as the anodes for lithium-ion batteries were studied.The main research contents and results are as follows:(1)The Fe,Ni2-xP/P-C nanorods were prepared in one step by using Fe2Ni MIL-88 as the precursor and NaH2PO2 as the precursor.The method can obtain a transition metal phosphide and carbon composite material while simplifying the preparation of the transition metal phosphide process and reducing the oxygen content in the material.As a negative electrode material for lithium ion batteries,it exhibits excellent electrochemical lithium storage capacity,which is mainly attributed to the porosities of Fe,Ni2-xP materials and the rich carbon in the materials.(2)Based on the characteristics of phytic acid pyrolysis to produce P under a reducing atmosphere,the complexes of phytic acid and transition metal ions are used as precursors to synthesize transition metal phosphides.In reducing atmosphere,P produced by in-situ decomposition of phytic acid reacts with metal ions to form transition metal phosphides.This method can make full use of phosphorus source,reduce pollution and reduce the cost of preparing transition metal phosphide.CoP/C nanoboxes were successfully prepared by this method.It shows excellent electrochemical performance when used as lithium-ion battery anode electrode.In addition,the CoP/C nanoboxes can also be used as a high activity and long life HER catalyst.(3)An integrated flexible CoP@CC electrode was prepared using carbon cloth as substrate and phytic acid as phosphorus source.The preparation method is simple and environmentally friendly,and can effectively improve the rate performance of lithium ion batteries while simplifying the process of assembling lithium ion batteries.This method can also be used to prepare other transition metal phosphide integrated electrodes.(4)Since ATMP has the property of pyrolysis under a reducing atmosphere to produce a carbon matrix and P,the step of preparing a transition metal phosphide is further optimized by using ATMP as an in-situ phosphorus source.The precursor of Co-ATMP was synthesized by complexing ATMP with Co2+,and then the precursor was heat treated in reducing atmosphere to obtain CoP.This method can compound transition metal phosphides with nitrogen and phosphorus co-doped carbon substrates to form an effective conductive network at the same time,it can delay the collapse of the structure of the electrode material in the process of deintercalation and improve the electrochemical performance of the material.The prepared CoP/NPC exhibits excellent lithium storage performance when it is used as anode material for lithium-ion batteries.(5)A series of two-dimensional zinc-cobalt oxide porous nanosheets were synthesized by using ZIF-L with different ratios of zinc to cobalt as precursors.Different electrochemical properties were obtained by adjusting the different zinc/cobalt ratios in the materials.The effects of different ratios of zinc and cobalt on the electrochemical properties of the materials and the reaction mechanism of zinc and cobalt in the electrochemical process were discussed.Through analysis and comparison,the zinc/cobalt ratio with the best lithium storage performance is obtained. |
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