Porous graphene / transition metal oxide composite microrod, preparation method thereof and application of porous graphene / transition metal oxide composite microrod in negative electrode of lithium ion battery

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a porous graphene / transition metal oxide composite microrod, a preparation method thereof and application of the porous graphene / transition metal oxide composite microrod in a negative electrode of a lithium ion battery. The preparation method comprises the following steps: injecting a mixed slurry composed of graphene oxide and an organic small molecule ligand into a rotating turntable containing a transition metal salt solution coagulating bath through a needle tube to obtain a composite gel microrod suspension; carrying out hydrothermal reaction on the suspension, cooling, filtering, washing, drying and grinding; and carrying out high-temperature calcination treatment on the graphene / MOF composite microrod powder and a strong alkali mixture in a protective atmosphere, and synchronously realizing activation etching and high-temperature carbonization of the microrod. The prepared composite microrod effectively relieves the volume effect of the transition metal oxide in the charging and discharging process, obviously reduces the interface resistance and accelerates lithium ion transmission and electrolyte permeation, so that the cycling stability and the rate capability of an electrode are greatly improved, the structural stability of the electrode is obviously improved, and the cycle life of the electrode is obviously prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and particularly to a porous graphene / transition metal oxide composite micro-rod, a preparation method thereof, and an application thereof in an anode of a lithium-ion battery. Background Art

[0002] Graphene has become a research focus in the field of materials science due to its excellent electrical, mechanical, and thermal properties. However, graphene often faces the problems of agglomeration and sheet stacking in practical applications, significantly limiting the full play of its performance. Transition metal oxides, such as zinc oxide (ZnO), have become one of the hotspots in the research of anode materials for lithium-ion batteries due to their high theoretical specific capacity of 978 mAh / g, rich resource reserves, and good chemical stability. Compared with traditional graphite anode materials, transition metal oxides have higher energy storage potential and can meet the requirements of next-generation high-energy-density energy storage devices. However, transition metal oxides face two key challenges in practical applications: firstly, during charge and discharge processes, transition metal oxides will experience severe volume expansion and contraction (>200%), resulting in the destruction of the electrode structure, the shedding of active materials, and the rapid decay of cycle performance; secondly, transition metal oxides have poor conductivity, for example, the conductivity of ZnO is <10 -6 S / cm, which limits their electrochemical performance under high-rate conditions. In addition, transition metal oxide particles are prone to agglomeration in electrode materials, further reducing their active area and electrochemical stability. Therefore, how to overcome the problems of volume effect, insufficient conductivity, and particle agglomeration has become the core problem in the practical application of transition metal oxides. Summary of the Invention

[0003] The purpose of the present invention is to propose a porous graphene / transition metal oxide composite micro-rod, a preparation method thereof, and an application thereof in an anode of a lithium-ion battery, aiming at the above deficiencies of the prior art. The volume effect of transition metal oxides during charge and discharge processes is effectively alleviated, the interfacial resistance is significantly reduced, the lithium-ion transmission and electrolyte penetration are accelerated, thereby greatly improving the cycle stability and rate performance of the electrode, and significantly enhancing the structural stability and cycle life of the electrode.

[0004] The first object of the present invention is to provide a preparation method of a porous graphene / transition metal oxide composite micro-rod, comprising the following steps:

[0005] Step S1: Inject a mixed slurry composed of graphene oxide and an organic small molecule ligand into a rotating turntable containing a coagulation bath of a transition metal salt solution through a syringe to obtain a composite gel micro-rod suspension;

[0006] Step S2: Perform a hydrothermal reaction on the composite gel micro-rod suspension, and then naturally cool it to room temperature;

[0007] Step S3: Filter the micron rod slurry cooled in Step S2, wash it with a volatile organic solvent to obtain a graphene / MOF composite micron rod mixed slurry, and then dry and grind it to obtain graphene / MOF composite micron rods;

[0008] Step S4: Calcinate the graphene / MOF composite micron rod powder at high temperature under a protective atmosphere with a strong base mixture to simultaneously activate and etch the micron rods and perform high-temperature carbonization.

[0009] Further, the specific operation of Step S4 is: ultrasonically disperse the graphene / MOF composite micron rod powder in ethanol to form a suspension, then dropwise add an aqueous strong base solution to the suspension, stir and react, and then dry;

[0010] Carbonize the dried product at high temperature, cool it, wash and dry it to obtain porous graphene / transition metal oxide composite micron rods.

[0011] Further, in Step S1, the mixed slurry is obtained by liquid-liquid mixing of a graphene oxide solution and an organic small molecule ligand dispersion solution, and ultrasonically oscillating and dispersing; wherein the solvent in the graphene oxide solution is one of water, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, and the concentration is 5-45 mg / ml; the molar ratio of graphene oxide to the organic small molecule ligand is 1:3-12.

[0012] Further, the organic ligand in the organic small molecule ligand dispersion solution is one of 2-methylimidazole, 2,6-naphthalenedicarboxylic acid, terephthalic acid, and 2,5-dihydroxyterephthalic acid, and the solvent is one of water, ethanol, methanol, and N,N-dimethylformamide, and the concentration is 0.01-45 mol / L.

[0013] Further, in Step S1, the transition metal salt in the coagulation bath of the transition metal salt solution is Zn 2+ 、Co 2+ 、Ni 2+ 、Fe 3+ 、Cu 2+ 、Zr 4+ One of them, and the corresponding solvent is one of water, ethanol, methanol, and N,N-dimethylformamide or a mixed solution of two.

[0014] Further, in Step S1, the syringe is a screw-threaded syringe with a volume of 5-100 ml, the matching needle is a 100-200 mm long needle, the inner diameter of the needle is between 50-550 μm, and the injection speed is controlled between 0.1-3.0 ml / min.

[0015] Further, in Step S2, perform a hydrothermal reaction at 60-150 °C for 3-24 hours, and then naturally cool to room temperature;

[0016] In step S3, the volatile organic solvent is acetone, and it is filtered and washed with a 200-1000 mesh filter screen, and the filtration and washing are repeated 2-4 times;

[0017] In step S3, drying is to transfer it to a polytetrafluoroethylene container and dry it in an oven at 60-120 °C; grinding is to quickly grind it with a micro grinder for 5-120 seconds to obtain the corresponding graphene / MOF composite micro-rods;

[0018] In step S3, the graphene / MOF composite micro-rod mixed slurry is a suspension obtained after acetone filtration and washing and adding 10-150 ml of acetone.

[0019] Furthermore, in step S4, the mass-to-volume ratio of the graphene / MOF composite micro-rod powder to ethanol is 0.5-5 g: 5-50 ml; the concentration of the strong alkali aqueous solution is 0.5-15 M; stirring reaction is carried out for 1-10 h; drying is carried out in an oven at 60-120 °C.

[0020] Furthermore, in step S5, transfer it to a tube furnace and calcine it at 600-1000 °C for 1-10 h; wrap the powder material naturally cooled to room temperature with a 200-1000 mesh sieve, fully immerse and wash it in deionized water until the pH is neutral, and then redisperse it in an acetone solution and dry it in an oven at 60-120 °C to obtain the corresponding porous graphene / transition metal oxide composite micro-rods.

[0021] The second object of the present invention is to provide a porous graphene / transition metal oxide composite micro-rod prepared by the preparation method as described above.

[0022] The third object of the present invention is to provide an application of the porous graphene / transition metal oxide composite micro-rod as described above in the negative electrode of a lithium-ion battery.

[0023] By combining graphene with transition metal oxides, the present invention constructs a unique micro-rod framework structure of highly conductive graphene. On the basis of effectively encapsulating transition metal oxide nanoparticles, a unique "scallion roll" axial orientation charge transport network is formed, which greatly reduces the interface resistance and charge transfer impedance of the composite material, thereby significantly improving the rate performance of the electrode. Secondly, the high specific surface area of graphene (theoretical specific surface area 2630 m 2 / g) provides a carrier for the uniform dispersion of transition metal oxide particles, avoiding the agglomeration of transition metal oxide particles. Meanwhile, it increases the contact area between the electrode and the electrolyte, accelerating the diffusion kinetics of lithium ions. In addition, the mechanical flexibility of graphene effectively buffers the volume expansion of transition metal oxides during charge and discharge, significantly improving the structural stability and cycle life of the electrode. Further, by chemically etching to create in-plane pores in graphene, the lithium ion transport and electrolyte penetration can be accelerated, further reducing the interfacial impedance and enhancing the rate performance and cycle stability. Therefore, the preparation of porous graphene / transition metal oxide composite micro-rods is not only innovative in structural design but also provides new ideas for solving the key problems in the application of transition metal oxides as anode materials for lithium ion batteries.

[0024] In the preparation process of the porous graphene / transition metal oxide composite micro-rods of the present invention, first, RGO / MOF composite micro-rods are prepared by in-situ growth. Then, using the RGO / MOF composite micro-rods as raw materials, through strong base high-temperature activation etching and high-temperature carbonization, the uniform loading of transition metal oxide nanoparticles in the three-dimensional space of the graphene-based micro-rods and the effective etching of graphene are realized. This structure significantly alleviates the volume effect of transition metal oxides in the anode materials of lithium ion batteries, improves the conductivity, and avoids the problem of particle agglomeration, thus enhancing the cycle stability and rate performance of the electrode.

[0025] In the present invention, by adjusting the mass ratio between the RGO / MOF composite micro-rod powder and the strong base, the type of strong base, as well as the calcination temperature and time, the pore distribution and pore size of the porous graphene / transition metal oxide composite micro-rods can be adjusted.

[0026] In the present invention, by selecting RGO / MOF composite micro-rods with different MOF contents, the precise regulation of the transition metal oxide loading in the composite material can be achieved, and porous graphene / transition metal oxide composite micro-rods with different transition metal oxide contents can be obtained to meet the design requirements of different anode materials for lithium ion batteries. Description of the Drawings

[0027] Figure 1 is the scanning electron microscope photograph of the RGO / ZIF-8 composite micro-rods;

[0028] Figure 2 is the X-ray diffraction pattern of the RGO / ZIF-8 composite micro-rods;

[0029] Figure 3 is the N2 adsorption-desorption isotherm and pore size distribution curve graph of pure RGO micro-rods, pure ZIF-8 particles, and RGO / ZIF-8 composite micro-rods;

[0030] Figure 4Scanning electron microscope images of RGO / ZnO composite microrods without activation treatment (a) and porous RGO / ZnO composite microrods activated with KOH;

[0031] Figure 5 N2 adsorption-desorption isotherms of RGO / ZnO composite microrods without activation treatment (a) and porous RGO / ZnO composite microrods activated with KOH;

[0032] Figure 6 X-ray diffraction patterns of pure RGO and porous RGO / ZnO composite microrods;

[0033] Figure 7 This is a comparison chart of the rate performance of CZIF-8, unactivated RGO / ZnO and KOH activated porous RGO / ZnO microrod composite electrodes;

[0034] Figure 8 This is a scanning electron microscope photo of RGO / ZIF-67 composite microrods;

[0035] Figure 9 This is the X-ray diffraction pattern of RGO / ZIF-67 composite microrods;

[0036] Figure 10 This is a scanning electron microscope photo of RGO / NiFe MOFs composite microrods;

[0037] Figure 11 This is the X-ray diffraction pattern of RGO / NiFe MOFs composite microrods. DETAILED DESCRIPTION

[0038] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0039] Example 1

[0040] The preparation process of porous graphene / ZnO composite microrods is as follows:

[0041] First, prepare the graphene oxide / 2-methylimidazole composite slurry, weigh 11.9g of 2-methylimidazole with an electronic balance, add it to a test tube containing 10ml of deionized water, and ultrasonically vibrate until it is completely dissolved. Subsequently, slowly pour the solution into 100ml of graphene oxide solution with a concentration of 11.9mg / ml, and ultrasonically vibrate again to ensure uniform mixing to prepare a composite slurry for use. At the same time, weigh 5.39g of Zn(NO3)2.6H2O, dissolve it in a mixed solution consisting of 200ml of deionized water and 300ml of ethanol to prepare a coagulation bath solution.

[0042] Place a crystallization dish with a diameter of 180 mm on an automatic horizontal turntable, add about 100 ml of coagulation bath solution, and adjust the rotation speed to 110 - 160 rpm. Use a plastic syringe to draw about 15 ml of the pre-mixed and evenly dispersed graphene oxide / 2-methylimidazole composite slurry. After switching to a long injection needle with a length of 120 - 180 mm, adjust the needle direction to be tangent to the rotation direction of the turntable. The inner diameter of the needle is between 50 - 350 μm, and control the injection speed at 0.5 - 2 ml / min. Under the combined action of shear force, ionic cross-linking, and coordination, graphene oxide and 2-methylimidazole small molecule ligands cross-link and coordinate with zinc ions in the coagulation bath in the solution to self-assemble into composite gel micro-rods. Transfer the obtained mixture of gel micro-rods to a 500 ml autoclave and carry out a hydrothermal reaction at 85 - 150 °C for 12 hours. After the reaction is completed, cool it naturally to room temperature. Filter the cooled micro-rods with gauze and rinse them repeatedly with acetone. Then redisperse them in a small amount of acetone and dry them in an oven at 80 - 120 °C. After drying, use a micro grinder to grind them quickly for 10 - 60 seconds to obtain the RGO / ZIF-8 composite micro-rod powder.

[0043] Disperse 2 g of the obtained RGO / ZIF-8 composite micro-rod powder in 10 ml of ethanol under ultrasonic oscillation conditions to prepare suspension A; subsequently, weigh 2.4 g of KOH and dissolve it in 5 ml of deionized water under ultrasonic oscillation conditions to obtain solution B; then, under magnetic stirring conditions, drop solution B into suspension A and continuously stir and react for 2 - 3 hours. Then dry it in an oven at 90 °C to obtain mixture C; next, transfer mixture C to a tubular furnace and calcine it at 800 °C for 3 h under a protective atmosphere, and cool it naturally to room temperature; finally, wrap the powder material cooled to room temperature with a 300-mesh filter screen, fully immerse and wash it with deionized water until the pH is neutral, and then redisperse it in 10 ml of acetone solution and dry it in an oven at 80 °C to obtain the corresponding porous graphene / ZnO composite micro-rods.

[0044] Comparative Example 1

[0045] Directly transfer 2 g of the obtained RGO / ZIF-8 composite micro-rod powder to a tubular furnace and calcine it at 800 °C for 3 h under a protective atmosphere. The other steps are the same as those in Example 1 to prepare RGO / ZnO composite micro-rods without activation treatment.

[0046] As Figure 1As shown, the scanning electron microscope (SEM) results indicate that the as-prepared RGO / ZIF-8 composite material is overall in the shape of micron-sized rods, with a diameter ranging from 30 to 100 μm, and has a typical flaky wrinkled structure of graphene (RGO) on the surface. ZIF-8 particles are evenly distributed on the RGO micron-rod framework, with a uniform particle size (about 50 - 300 nm) and no obvious agglomeration. This indicates that the tight composite of RGO and ZIF-8 has been successfully achieved by the in-situ growth method.

[0047] The corresponding X-ray powder diffraction (XRD) pattern ( Figure 2 ) shows that the diffraction peaks of the RGO / ZIF-8 composite material are highly consistent with the simulated standard diffraction peaks of ZIF-8, further confirming that the MOF particles in the composite material are ZIF-8 particles with high crystallinity.

[0048] In addition, the N adsorption - desorption isotherm and pore size distribution curve ( Figure 3 ) show that the specific surface area of the RGO / ZIF-8 composite micron-rods is significantly higher than that of the pure RGO micron-rods, and slightly lower than that of the pure ZIF-8. This indicates that the in-situ introduction of ZIF-8 effectively inhibits the agglomeration and stacking of graphene, and at the same time realizes the precise regulation of pore size.

[0049] Figure 4 Scanning electron microscope photos of the RGO / ZnO composite micron-rods without activation treatment (a) and the porous RGO / ZnO composite micron-rods treated with KOH activation; as Figure 4 shown, both the RGO / ZnO without high-temperature KOH activation treatment and the porous RGO / ZnO composite material treated with KOH activation are overall in the shape of micron-sized rods, with a diameter ranging from 30 to 200 μm, and have a typical flaky wrinkled structure of graphene (RGO) on the surface. ZnO particles are evenly distributed on the RGO micron-rod framework, with a uniform particle size (about 50 - 300 nm), and are overall in the shape of a collapsed rhombic dodecahedron, without obvious agglomeration. Compared with the RGO / ZnO micron-rods without activation treatment, the porous RGO / ZnO micron-rod material is overall more porous, with obvious pore structures on the surface. This indicates that after the high-temperature KOH activation treatment, the ZIF-8 nanoparticle structure has undergone high-temperature carbonization transformation in-situ within the three-dimensional space of the graphene-based micron-rods, and at the same time, graphene has been effectively etched.

[0050] Figure 5 N2 adsorption - desorption isotherms of the RGO / ZnO composite micron-rods without activation treatment (a) and the porous RGO / ZnO composite micron-rods treated with KOH activation, Figure 5 show that the specific surface area of the porous graphene / ZnO micron-rods obtained by KOH activation treatment is much larger than that of the graphene / ZnO micron-rods without activation treatment, further confirming the activation and etching effect of KOH.

[0051] Figure 6 X-ray diffraction patterns of pure RGO and porous RGO / ZnO composite microrods are shown in Figure 6 As shown, the diffraction peaks of the porous graphene / ZnO composite material are highly consistent with the diffraction peaks of standard zincite ZnO, indicating that the collapsed rhombic dodecahedral nanoparticles in the composite material are ZnO nanoparticles with high crystallinity.

[0052] Figure 7 The figure is a comparison of the rate performance of CZIF-8, unactivated RGO / ZnO and KOH activated porous RGO / ZnO microrod composite electrodes. The specific capacity, rate performance and cycle stability of the porous RGO / ZnO microrod-based composite electrode are significantly higher than those of pure carbonized ZIF-8 (CZIF-8) and unactivated RGO / ZnO-based composite electrodes. This shows that the prepared composite material can achieve uniform dispersion of ZnO particles in the porous graphene micro-frame and form a "scallion roll" coating structure, which effectively alleviates the volume effect of ZnO during the charge and discharge process, significantly reduces the interface resistance, accelerates lithium ion transmission and electrolyte penetration, thereby greatly improving the cycle stability and rate performance of the electrode, further revealing the significant structural advantages and electrochemical performance advantages of porous RGO / ZnO composite microrods in the design of negative electrode materials for lithium-ion batteries.

[0053] Example 2

[0054] This embodiment is different from Example 1 in that the corresponding KOH is replaced with NaOH of the same mass, and the calcination time is changed to 5 hours. The rest is the same as Example 1.

[0055] Example 3

[0056] This embodiment differs from the specific embodiment 1 in that the calcination is performed at 600° C. for 3 h under a protective atmosphere, and the rest is the same as the specific embodiment 1.

[0057] Example 4

[0058] Here is the preparation of porous graphene / CoO composite microrods. The specific process is as follows:

[0059] First, prepare the graphene oxide / 2-methylimidazole composite slurry, weigh 0.66g of 2-methylimidazole with an electronic balance, add it to a test tube containing 3ml of deionized water, and ultrasonically vibrate until it is completely dissolved. Subsequently, slowly pour the solution into 20ml of 6.2mg / ml graphene oxide solution, and ultrasonically vibrate again to ensure uniform mixing to prepare a composite slurry for use. At the same time, weigh 0.55g of Co(NO3)2.6H2O, dissolve it in a mixture of 200ml of deionized water and 300ml of ethanol to prepare a coagulation bath solution.

[0060] Place a crystallization dish with a diameter of 150 mm on an automatic horizontal turntable, add about 50 ml of coagulation bath solution, and adjust the rotation speed to 130 - 150 rpm. Use a plastic syringe to draw about 10 ml of pre - mixed and homogeneous graphene oxide / 2 - methylimidazole composite slurry. After switching to a long injection needle with a length of 120 - 180 mm, adjust the needle direction to be tangent to the rotation direction of the turntable. The inner diameter of the needle is between 100 - 250 μm, and control the injection speed at 0.5 - 1.5 ml / min. Under the combined action of shear force, ionic cross - linking and coordination, graphene oxide and 2 - methylimidazole small - molecule ligands cross - link and coordinate with cobalt ions in the coagulation bath in the solution to form composite gel micro - rods by self - assembly. Transfer the obtained mixture of gel micro - rods to a 200 - ml autoclave and carry out a hydrothermal reaction at 90 °C for 12 hours. After the reaction is completed, cool it to room temperature naturally. Filter the cooled micro - rods with gauze and rinse them repeatedly with acetone, then redisperse them in a small amount of acetone and dry them in an oven at 80 - 120 °C. After drying, use a micro - grinder to grind quickly for 10 - 60 seconds to obtain RGO / ZIF - 67 composite micro - rod powder.

[0061] Disperse 2 g of the obtained RGO / ZIF - 67 composite micro - rod powder in 10 ml of ethanol under ultrasonic oscillation conditions to prepare suspension A; subsequently, weigh 2.4 g of KOH and dissolve it in 5 ml of deionized water under ultrasonic oscillation conditions to obtain solution B; then, under magnetic stirring conditions, add solution B dropwise to suspension A and continuously stir and react for 2 - 3 hours, and then dry it in an oven at 90 °C to obtain mixture C; then, transfer mixture C to a tubular furnace and calcine it at 800 °C for 3 h under a protective atmosphere and cool it to room temperature naturally; finally, wrap the powder material cooled to room temperature with a 300 - mesh filter screen, impregnate and wash it thoroughly with deionized water until the pH is neutral, and then redisperse it in 10 ml of acetone solution and dry it in an oven at 80 °C to obtain the corresponding porous graphene / CoO composite micro - rods.

[0062] Figure 8 is the scanning electron microscope photograph of RGO / ZIF - 67 composite micro - rods. From Figure 7 It can be seen that the results of scanning electron microscope (SEM) show that the prepared RGO / MOF composite material as a whole presents a micro - rod - like morphology, with a diameter range between 5 - 15 μm, and has a typical flaky wrinkled structure of graphene (RGO) on the surface. MOF particles are evenly distributed on the RGO micro - rod framework, with uniform particle size (about 50 - 350 nm) and no obvious agglomeration phenomenon. This indicates that the tight composite of RGO and MOF has been successfully achieved by the in - situ growth method.

[0063] Figure 9is the X-ray diffraction pattern of RGO / ZIF-67 composite microrods. Figure 8 It can be seen that the diffraction peaks of the RGO / MOF composite material are highly consistent with the simulated standard diffraction peaks of ZIF-67, further confirming that the MOF particles in the composite material are highly crystalline ZIF-67 nanoparticles.

[0064] Example 5

[0065] Here is the preparation of porous graphene / NiFe oxide composite microrods. The specific process is as follows:

[0066] First, prepare the graphene oxide / 1,4-naphthalene dicarboxylic acid composite slurry, weigh 0.5g of 1,4-naphthalene dicarboxylic acid with an electronic balance, add it to a test tube containing 4ml of N, N-dimethylformamide (DMF), and ultrasonically vibrate until it is completely dissolved. Subsequently, slowly pour the solution into 15ml of 7.1mg / ml graphene oxide solution, and ultrasonically vibrate again to ensure uniform mixing to prepare a composite slurry for use. At the same time, weigh 0.1g of Fe(NO3)3.9H2O and 0.4g of Ni(Ac)2, dissolve them in a mixture of 37.5ml of deionized water and 37.5ml of ethanol to prepare a coagulation bath solution.

[0067] Place a 180mm diameter crystallization dish on an automatic horizontal turntable, add about 50ml of coagulation bath solution, and adjust the speed to 100-120rpm. Use a plastic syringe to extract about 10ml of pre-mixed graphene oxide / 2-methylimidazole composite slurry, switch to a 120-180mm long injection needle, adjust the needle direction to be tangent to the direction of rotation of the turntable, the inner diameter of the needle is between 150-200μm, and the injection speed is controlled at 1.0-1.5ml / min. Under the combined action of shear force, ionic crosslinking and coordination, graphene oxide and 1,4-naphthalene dicarboxylic acid small molecule ligands crosslink and coordinate self-assemble with metal ions in the coagulation bath in the solution to form composite gel microrods. The resulting gel microrod mixture was transferred to a 200ml reactor and subjected to hydrothermal reaction at 80℃ for 12 hours. After the reaction was completed, it was naturally cooled to room temperature. The cooled microrods were filtered with gauze, rinsed repeatedly with acetone, and then redispersed in a small amount of acetone and dried in an oven at 80-120° C. After drying, the RGO / NiFe MOFs composite microrod powder was obtained by rapid grinding with a micro grinder for 10-60 seconds.

[0068] The obtained 2 g of RGO / NiFe MOFs composite micro-rod powder was dispersed in 10 ml of ethanol under ultrasonic oscillation conditions to prepare suspension A. Subsequently, 2.4 g of KOH was weighed and dissolved in 5 ml of deionized water under ultrasonic oscillation conditions to obtain solution B. Then, under magnetic stirring conditions, solution B was dropped into suspension A and continuously stirred for 2 - 3 hours. Subsequently, it was dried in an oven at 90 °C to obtain mixture C. Then, mixture C was transferred to a tube furnace and calcined at 800 °C for 3 h under a protective atmosphere and naturally cooled to room temperature. Finally, the powder material cooled to room temperature naturally was wrapped with a 300-mesh filter screen and fully immersed and washed with deionized water until the pH was neutral. Subsequently, it was redispersed in 10 ml of acetone solution and dried in an oven at 80 °C to obtain the corresponding porous graphene / NiFe oxide composite micro-rods.

[0069] Figure 10 is the scanning electron microscope photograph of the RGO / NiFe MOFs composite micro-rods. From Figure 9 it can be seen that the MOF particles in the prepared RGO / MOF composite micro-rod material present a uniform nano-sphere morphology, and there is no obvious agglomeration phenomenon. The diameter range is between 400 - 500 nm. The flaky and wrinkled graphene (RGO) uniformly wraps the MOF nano-particles. This indicates that the tight composite of RGO and MOF has been successfully achieved by the in-situ growth method.

[0070] Figure 11 is the X-ray diffraction pattern of the RGO / NiFe MOFs composite micro-rods. From Figure 10 it can be seen that the diffraction peaks of the RGO / MOF composite material coincide with the diffraction peaks of the standard NiFe MOFs, further confirming that the MOF spherical nano-particles in the composite material are NiFe MOFs nano-particles.

[0071] Where not otherwise involved, the prior art shall apply.

[0072] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways for substitution, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing porous graphene / transition metal oxide composite microrods, characterized in that: The steps include: Step S1: injecting a mixed slurry consisting of graphene oxide and organic small molecule ligands into a rotating turntable containing a transition metal salt solution coagulation bath through a syringe to obtain a composite gel microrod suspension; Step S2: subjecting the composite gel microrod suspension to a hydrothermal reaction, followed by natural cooling to room temperature; Step S3: filtering the cooled microrod slurry obtained in step S2, washing it with a volatile organic solvent to obtain a graphene / MOF composite microrod mixed slurry, and then drying and grinding it to obtain graphene / MOF composite microrods; Step S4: calcining the graphene / MOF composite microrod powder and the strong alkali mixture at high temperature under a protective atmosphere to simultaneously achieve activation etching and high-temperature carbonization of the microrods.

2. The preparation method according to claim 1, characterized in that: The specific operation of step S4 is: ultrasonically dispersing the graphene / MOF composite microrod powder in ethanol to form a suspension, then dropping a strong alkali aqueous solution into the suspension, stirring for reaction, and then drying; The dried product is carbonized at high temperature, cooled, washed and dried to obtain porous graphene / transition metal oxide composite microrods.

3. The preparation method according to claim 1, characterized in that: In step S1, the mixed slurry is obtained by liquid-liquid mixing of a graphene oxide solution and an organic small molecule ligand dispersion, and then dispersing the mixture by ultrasonic vibration; wherein the solvent in the graphene oxide solution is one of water, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, and the concentration is 5-45 mg / ml; and the molar ratio of graphene oxide to organic small molecule ligand is 1:3-12; The organic ligand in the organic small molecule ligand dispersion is one of 2-methylimidazole, 2,6-naphthalene dicarboxylic acid, terephthalic acid, and 2,5-dihydroxyterephthalic acid, and the solvent is one of water, ethanol, methanol, and N,N-dimethylformamide, and the concentration is 0.01-45 mol / L.

4. The preparation method according to claim 1, characterized in that: In step S1, the transition metal salt in the transition metal salt solution coagulation bath is Zn 2+ 、Co 2+ 、Ni 2+ , Fe 3+ , Cu 2+ 、Zr 4+ The corresponding solvent is one of water, ethanol, methanol, N, N-dimethylformamide or a mixture of two of them.

5. The preparation method according to claim 1, characterized in that: In step S1, the needle tube is a screw-mouth needle tube with a volume of 5-100 ml, the matching needle is a 100-200 mm long needle, the inner diameter of the needle is between 50-550 μm, and the injection speed is controlled between 0.1-3.0 ml / min.

6. The preparation method according to claim 1, characterized in that: In step S2, a hydrothermal reaction is carried out at 60-150° C. for 3-24 hours, followed by natural cooling to room temperature; In step S3, the volatile organic solvent is acetone, which is filtered and washed with a 200-1000 mesh filter screen, and the filtering and washing are repeated 2-4 times; In step S3, drying is performed by transferring the obtained graphene to a polytetrafluoroethylene container and drying the obtained graphene in an oven at 60-120° C.; grinding is performed by rapidly grinding the obtained graphene using a micro grinder for 5-120 seconds to obtain the corresponding graphene / MOF composite microrods; In step S3, the graphene / MOF composite microrod mixed slurry is a suspension obtained after filtering and washing with acetone and adding 10-150 ml of acetone.

7. The preparation method according to claim 1, characterized in that: In step S4, the mass volume ratio of graphene / MOF composite microrod powder to ethanol is 0.5-5g:5-50ml; the concentration of the strong alkali aqueous solution is 0.5-15M; the reaction is stirred for 1-10h; and the mixture is dried in an oven at 60-120°C.

8. The preparation method according to claim 1, characterized in that: In step S4, the powder material is transferred to a tubular furnace and calcined at 600-1000°C under a protective atmosphere for 1-10h; the powder material naturally cooled to room temperature is wrapped with a 200-1000 mesh sieve, fully immersed and washed in deionized water until the pH is neutral, and then redispersed in an acetone solution, and dried in an oven at 60-120°C to obtain the corresponding porous graphene / transition metal oxide composite microrods.

9. A porous graphene / transition metal oxide composite microrod prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the porous graphene / transition metal oxide composite microrods as claimed in claim 9 in a negative electrode of a lithium ion battery.

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