Preparation, Characterization And Property Of Copper Phosphide Nano/Micro Material、 Copper Phosphide/Graphene Nanocomposites

Recently, extensive efforts have been carried out to explore transition metal phosphides(M-P, where M= Fe, Co, Ni, Cu, etc.) owing to their high gravimetric and volumetric capacity associated with the low polarization and good cycling stability. Among transition metal phosphides, copper phosphide have drawn great attention because of their promising utilizations as anodes for lithium ion batteries. Although its gravimetric capacity is close to that of graphite, its volumetric capacity is almost three times higher than that of graphite. Similar to transition metal oxides, the large volume expansion that occurs during the lithium insertion/exaction processes destabilizes the structure of the electrode, resulting in a significant capacity fade during cycling. A variety of appealing strategies have been utilized to alleviate these intractable problems. Size miniaturization and control of morphology were shown to effectively enhance the electrochemical performance. Additionally, combining highly conductive carbon materials also helps in enhancing average electronic conductivity of active material, providing conductive electronic wiring between active particles and the current collector.Graphene is the most popular and intriguing two-dimensional carbon material due to its superior electrical conductivity, large surface area, chemical stability, and structural flexibility. It has been demonstrated that graphene-based anode materials have large initial discharge capacity and reversible capacity, although they suffer from large irreversible capacity, low initial Coulombic efficiency, and fast capacity fading. More importantly, graphene can also be used in composites with transition metal phosphides NPs to improve the electrochemical performance of these particles. The addressing of graphene could not only provide a support for anchoring well-dispersed NPs, increase conductivity and surface area of the electrodes but also can effectively prevent the volume expansion/contraction and aggregation of NPs during Li charge/discharge process. Meanwhile, the anchoring of NPs on graphene can effectively reduce the degree of restacking of graphene sheets and consequently keep their high active surface area and, to some extent, increase the lithium storage capacity and cyclic performance of graphene-based material. Therefore, it is believed that the composite of flexible and electrically conductive graphene anchored with nanostructured Cu3 P particles can efficiently utilize the combinative merits of nanosized Cu3 P and graphene and obtain LIBs with superior performance.In this paper, the copper phosphide nano/micro materials with special morphology and Cu3P/graphene hybrids were designed and prepared, the growth mechanism and electrochemical performances were also discussed. The main contents are summarized as follows:(1) In this paper, well-defined copper phosphide(Cu3P) hollow sphere was successfully synthesized by hydrothermal method, using copper sulfate pentahydrate and white phosphorus as starting material, ethylenediaminetetraacetic acid disodiumsalt and polyethylene glycol 10000 were used as the mixed shape-controlling agents. X-ray powder diffraction(XRD) and field emission scanning electron microscopy(FE-SEM) indicated that the as-obtained Cu3 P nanocrystal had a well-crystallized hexagonal phase. As anode materials for lithium ion batteries, the electrochemical property of the Cu3 P hollow sphere was examined. The results revealed that the initial discharge capacity of Cu3 P reached 947.4 m A·h/g and relatively constanted at 224 m A h/g after 10 cycles. This phenomenon might be related to the size of Cu3 P particles and their hollow structures.(2) Copper phosphide(Cu3P) nanotube was successfully synthesized via a solvothermal method, using N, N-dimethylformamide(DMF) as solvent with the help of hexadecyl trimethyl ammonium bromide(CTAB). The phase and morphology of the products were characterized by means of XRD, EDS, FE-SEM and TEM. The as-obtained Cu3 P nanotube had a well-crystallized hexagonal phase. It was found that the CTAB played a crucial role in the formation of Cu3 P. Furthermore, the effects of the experimental parameters(such as the reaction time, reaction temperature) on the products were also investigated. It was found that the optimum preparation conditions were that the reaction temperature was 180 ℃ and the reaction time was 16 h. The possible growth mechanisms was also discussed in detail. The electrochemical test results of the nanotubes showed that the initial discharge capacity exceeded 1078 m A·h/g and retained at least 600 m A h/g after 20 cycles.(3) We reported a facile strategy to synthesize such composite of Cu3 P NPs anchored on conducting graphene as an advanced anode material for high performance LIBs. The Cu3P/graphene hybrids were synthesized through a facile solvothermal methods with the presence of CTAB. The products were characterized by XRD, EDS, FE-SEM and TEM. The results showed that the as-prepared Cu3 P was pure hexagonal phase and Cu3 P NPs with the diameter of 80~120 nm were homogeneously anchored on the thin graphene layers. The Cu3 P nanoparticles were hexagonal plate-like. The role of CTAB and the possible growth mechanisms was also briefly discussed. The electrochemical test results of the hybrids showed that the initial discharge capacity of Cu3 P exceeded 1244.69 m A·h/g and retained at least 600 m A h/g after 100 cycles. The results demonstrated that the graphene layer contributed to the improvement of cyclability anodes.