CN106654212A - Preparation method and application of tricobalt tetroxide/graphene composite material (Co3O4/N‑RGO) - Google Patents

Abstract

The invention relates to a preparation method of a cobaltosic oxide/graphene composite material (Co<3>O<4>/N-RGO), and an application of the composite material in a nickel-metal hydride battery and a lithium ion battery. The composite material is prepared by the steps as follows: a, preparing graphite oxide according to an improved Hummers method; b, performing hydrolysis and oxidization of cobalt acetate under the regulation effect of ammonium hydroxide, and carrying out in-situ growth of extra-small Co<3>O<4> nanoparticles on the surface of the graphite oxide; and c, performing further crystallization of the Co<3>O<4> nanoparticles and reduction of the graphite oxide. When the Co<3>O<4>/N-RGO composite material is used as an electrode material, due to the unique structural characteristic and the synergistic effect between the Co<3>O<4> and the N-RGO, the high-rate discharging performance of the nickel-metal hydride battery and the lithium ion battery is obviously improved; for the nickel-metal hydride battery, at discharge current density of 3A/g, the discharge capacity can be as high as 223.1mAh/g which is 3.2 times (68.7mAh/g) of that of a commercial hydrogen storage alloy; and for the lithium ion battery, at discharge current density of 10A/g, relatively high discharge capacity which is 423.6mAh/g is still maintained. A new thought is provided for research and development of a high-power type battery.

Description

The preparation method of tricobalt tetroxide/graphene composite material (Co3O4/N-RGO) and application

Technical field:

The invention relates to the preparation of tricobalt tetroxide/graphene composite material (Co ₃ O ₄ /N-RGO) and its application as negative electrode material of nickel hydrogen battery and lithium ion battery.

Background technique:

There is an increasing demand for high-power batteries in new energy vehicles, electric tools and military equipment. Therefore, considerable research efforts have focused on developing electrode materials with excellent rate performance. Transition metal oxides are considered as one of the ideal materials for batteries and capacitors. Among them, _Co3O4 has _attracted extensive attention due to its high capacity, low cost, and high catalytic activity. However, their electrochemical performance is usually limited by low conductance and slow ion diffusion rate. Researchers have proposed several effective methods to alleviate these problems: preparing nanomaterials to shorten the ion diffusion distance and increase the specific surface area; compounding with carbon materials to improve the conductivity of electrodes, etc. Here, based on the synergistic effect, we prepared a composite of Co3O4 _nanocubes and nitrogen _- doped graphene, and applied it as an electrode material in NiMH and Li-ion batteries. In this composite material, nitrogen-doped graphene as a conductive substrate can uniformly load Co ₃ O ₄ nanocubes to improve the conductivity of Co ₃ O ₄ ; at the same time, Co ₃ O ₄ nanocubes can provide high discharge capacity and electrical conductivity. catalytic activity. In addition, Co ₃ O ₄ nanocubes are pinned on nitrogen-doped graphene, and nitrogen-doped graphene supports Co ₃ O ₄ , which together form a three-dimensional conductive network structure, which is conducive to shortening the ion diffusion distance and improving ion and ion density. electron diffusion rate.

Invention content:

The object of the present invention is to relate to the preparation method of tricobalt tetroxide/graphene composite material (Co ₃ O ₄ /RGO) and its application as negative electrode material of nickel hydrogen battery and lithium ion battery. Through the synergistic effect of Co ₃ O ₄ nanocubes and N-RGO, the Co ₃ O ₄ /N-RGO composite material has a small electrode internal resistance, fast electron and ion diffusion rate, and is excellent as a battery electrode material. rate discharge performance.

Above-mentioned purpose of the present invention is achieved through the following technical solutions:

A preparation method of tricobalt tetroxide/graphene composite material (Co ₃ O ₄ /RGO), comprising the following steps:

a, synthesize graphite oxide according to the improved Hummers method;

b. Add 1-2ml of 0.2M cobalt acetate and 1-2ml of 4.5mg/ml graphite oxide into 34-36ml of absolute ethanol at 22-25°C, ultrasonically disperse for 20-30min, and then dissolve at 75-85 Heating at ℃ for 9-10 hours to hydrolyze and oxidize cobalt acetate and grow ultra-small Co ₃ O ₄ nanoparticles in situ on the surface of graphite oxide;

c. Heating at 145-155°C for 2.5-3.5 hours by hydrothermal method to further crystallize Co ₃ O ₄ nanoparticles and reduce graphite oxide. Thoroughly wash with water 4 to 6 times, and dry in a vacuum oven at 22 to 25°C for 10 to 12 hours.

Control the hydrolysis and oxidation rate of cobalt acetate by regulating the amount of ethanol and the reaction temperature in the step b.

In step c, the crystal morphology of Co ₃ O ₄ is controlled by adjusting the temperature of the hydrothermal heat.

In step c, 0.5-1 g of hydrogen-storage alloy powder is added before the hydrothermal reaction at 145-155° C. to prepare the composite material Co ₃ O ₄ /RGO/HSAs of tricobalt tetroxide/graphene and hydrogen-storage alloy.

In step b, add 0.5-0.8ml of ammonia water to hydrolyze and oxidize cobalt acetate under the regulation of ammonia water to prepare cobalt tetroxide/nitrogen-doped graphene composite material Co ₃ O ₄ /N-RGO.

In step b, add 0.5-0.8ml of ammonia water to hydrolyze and oxidize cobalt acetate under the regulation of ammonia water. In step c, add 0.5-1g of hydrogen storage alloy powder before the hydrothermal reaction at 145-155°C to prepare cobalt tetroxide/nitrogen doped Composites of graphene and hydrogen storage alloys Co ₃ O ₄ /N-RGO/HSAs.

The composite material Co ₃ O ₄ /RGO/HSAs obtained according to the above preparation method and the composite material Co ₃ O ₄ /N-RGO/ HSAs, the two are used as electrode materials for nickel-metal hydride batteries for electrochemical performance testing, including the following steps:

a. Mix 0.25-0.255g active material with 1.0-1.02g carbonyl nickel powder evenly, and press it into an electrode sheet with a diameter of 10-15mm by a tablet press under a pressure of 8-20MPa;

B, the electrode sheet prepared in step a is used as working electrode, the Ni(OH) ₂ /NiOOH sheet of sintering is used as counter electrode, the mercuric oxide electrode is used as reference electrode, and the KOH solution of 25～35wt% is electrolyte, forms the standard Three-electrode system for electrochemical testing;

c. When carrying out the capacity test, the charge and discharge current density is 0.06A/g (0.2C), and the number of activation circles is 4; when carrying out the high-rate discharge performance test, the charge current density is 0.3A/g (1C), and the discharge current The densities are 0.3, 0.6, 0.9, 1.2, 1.5, 2.4 and 3A/g (10C);

d. The electrochemical performance test is carried out on the IVIUM electrochemical workstation. The AC impedance test is performed when the amplitude relative to the open circuit potential (OCP) is 5mV, and the frequency range of the test is from 100kHz to 5mHz; under the condition of 50% depth of discharge , when the potential scanning range relative to OCP is -5 to 5mV, a linear polarization curve test with a scanning rate of 0.05mV/s is performed; under the condition of 50% depth of discharge, the potential scanning range relative to OCP is 0 to At 1.5V, conduct an anodic polarization curve test with a scan rate of 5mV/s; in a 100% charged state, perform a 4000s current-time curve test at a potential step of +500mV relative to Hg/HgO.

Cobalt tetroxide/graphene composite material (Co ₃ O ₄ /RGO) and tricobalt tetroxide/nitrogen-doped graphene composite material (Co ₃ O ₄ /N-RGO) obtained according to the above-mentioned preparation method are used as electrodes for lithium-ion batteries The electrochemical performance test of the material includes the following steps:

a. The active material is used as the working electrode, the lithium sheet is used as the counter electrode/reference electrode, the diaphragm is a Celgard 2500 membrane, and the electrolyte is 1M LiPF ₆ dissolved in ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1:1 CR2016 button cells were assembled in an argon-filled glove box ([O ₂ ]<1ppm, [H ₂ O]<1ppm) in a mixture of ester and ethyl methyl carbonate;

b. The preparation method of the working electrode is to uniformly mix 80% active material, 10% super P and 10% binder polyvinylidene fluoride PVDF, and dissolve them in N-methyl-2- In pyrrolidone NMP, the mixture was ground with an agate mortar for 30 minutes, and then the slurry was evenly coated on copper foil, and the weight of each copper foil was 0.5-0.6 mg, and dried at 100°C for 10 hours;

c. The charge and discharge test is carried out on the LAND CT2001A battery test system, and its potential range is relative to Li ⁺ /Li0.01-3.0V; the cyclic voltammetry curve is carried out on the IVIUM electrochemical workstation, and its potential range is Relative to Li ⁺ /Li0.01-3.0V, the sweep speed is 0.2mV/s; the AC impedance test is performed when the amplitude is 10mV, and the frequency range of the test is from 100kHz to 10mHz.

Technical effect of the present invention is:

The Co ₃ O ₄ /N-RGO composite material prepared by the invention has a large specific surface area, excellent electrical conductivity and a fast electrochemical reaction rate, and exhibits excellent rate discharge performance as a battery electrode material.

Description of drawings:

Figure 1. Rate performance curves of HS3, HS4 and commercial hydrogen storage alloys at different discharge current densities.

Figure 2. Schematic diagram of the preparation of HS1.

Figure 3. Raman spectra of HS1 and HS2.

Figure 4. Raman spectra of HS3 and HS4.

Figure 5. XRD patterns of HS1 and HS2.

Figure 6. XRD patterns of HS3 and HS4.

Figure 7. TGA curves of HS1 and HS2.

Figure 8. XPS full spectrum of HS1.

Fig. 9. High-resolution Co 2p spectrum of HS1.

Figure 10. High-resolution N 1s spectrum of HS1.

Fig. 11, SEM photo of HS1.

Fig. 12, SEM photo of HS2.

Fig. 13, SEM photo of HS3.

Fig. 14, SEM photo of HS4.

Figure 15. SEM photographs of commercial hydrogen storage alloys.

Fig. 16, TEM photo of HS1.

Figure 17. TEM photograph of HS2.

Figure 18. HRTEM photograph of HS1.

Figure 19. HRTEM photograph of HS2.

Figure 20. Discharge capacity curves of HS3, HS4 and commercial hydrogen storage alloys.

Figure 21. Linear polarization curves of HS3, HS4 and commercial hydrogen storage alloys.

Figure 22. Electrochemical impedance spectra of HS3, HS4 and commercial hydrogen storage alloys.

Figure 23. Anodic polarization curves of HS3, HS4 and commercial hydrogen storage alloys.

Figure 24. Discharge current-time curves of HS3, HS4 and commercial hydrogen storage alloys at 100% charge state.

Figure 25. Cyclic voltammetry curves of HS1 and HS2.

Figure 26. Constant current charge and discharge curves of HS1 and HS2.

Figure 27. Cycle performance curves of HS1 and HS2 at a current density of 0.1A/g.

Figure 28. Rate performance curves of HS1 and HS2 at different discharge current densities.

Figure 29. AC impedance spectra of HS1 and HS2.

Figure 30. Cycle performance curves of HS1 and HS2 at a current density of 5A/g.

detailed description:

The specific content and specific implementation of the present invention will be further described below in conjunction with the examples. However, the example is only an example of implementing the present invention and cannot constitute a limitation to the technical solution of the present invention.

Example

The preparation process and steps in this embodiment are as follows:

(1) Graphite oxide was synthesized according to the improved Hummers method; 1.77ml of cobalt acetate with a concentration of 0.2M, 0.74ml of ammonia water and 1.77ml of graphite oxide were added to 35.4ml of absolute ethanol, ultrasonically dispersed for 30min, and then heated at 80°C for 10h. Cobalt acetate was hydrolyzed and oxidized, and ultra-small Co ₃ O ₄ nanoparticles were grown in situ on the surface of graphite oxide; then, the reaction product was transferred to a 40ml reactor, and heated at 150°C for 3 hours by hydrothermal method to make Co ₃ O ₄ Nanoparticles are further crystallized and graphite oxide reduced to prepare Co ₃ O ₄ /N-RGO composite material. The as-prepared composite was then filtered through an inorganic membrane with a pore size of 0.2-μm and thoroughly washed with ethanol and water, respectively. Finally, the product was dried in a vacuum oven at 25° C. for 12 h. Co ₃ O ₄ /RGO composites were prepared without adding ammonia water during the reaction at 80°C; Co ₃ O ₄ /N-RGO was prepared by adding 0.8g hydrogen storage alloy powder (MmNi _3.55 Co _0.75 Mn _0.4 Al _0.3 ) before the hydrothermal reaction /HSAs composite material; no ammonia water was added during the reaction at 80°C, and 0.8g hydrogen storage alloy powder was added before the hydrothermal reaction to prepare Co ₃ O ₄ /RGO/HSAs composite material. Here, the MmNi _3.55 Co _0.75 Mn _0.4 Al _0.3 hydrogen storage alloy is prepared by radio frequency induction melting, and the average diameter of alloy particles is 50±10 μm. We denote the above Co ₃ O ₄ /N-RGO, Co ₃ O ₄ /RGO, Co ₃ O ₄ /N-RGO/HSAs and Co ₃ O ₄ /RGO/HSAs by HS1, HS2, HS3 and HS4 respectively. Four composite materials. The preparation flow chart of HS1 is shown in Figure 2.

(2) When testing the electrochemical performance of nickel-metal hydride batteries, mix 0.25g HS3 or HS4 and 1.0g carbonyl nickel powder evenly, and press it into an electrode sheet with a diameter of 15mm under a pressure of 8MPa, and use this electrode sheet as a working electrode. Ni The (OH) ₂ /NiOOH sheet is used as the counter electrode, the mercury oxide electrode is used as the reference electrode, and the 30wt% KOH solution is used as the electrolyte to form a standard three-electrode system for electrochemical testing; when performing capacity testing, the charge and discharge current densities are both 0.06 A/g (0.2C), the number of activation circles is 4; when performing high-rate discharge performance tests, the charge current density is 0.3A/g (1C), and the discharge current density is 0.3, 0.6, 0.9, 1.2, 1.5, 2.4 And 3A/g (10C); The electrochemical performance test was carried out on the IVIUM electrochemical workstation. The AC impedance test is carried out when the amplitude relative to OCP is 5mV, and the frequency range of the test is from 100kHz to 5mHz; under the condition of 50% depth of discharge, when the potential scanning range relative to OCP is -5 to 5mV, the scanning speed is: 0.05mV/s linear polarization curve test; under the condition of 50% depth of discharge, when the potential scanning range relative to OCP is 0 to 1.5V, conduct an anodic polarization curve test with a sweep rate of 5mV/s; at 100 Under the state of charge, under the potential step of +500mV relative to Hg/HgO, the test of the current-time curve was carried out for 4000s.

(3) In order to test the electrochemical performance of lithium-ion batteries, CR2016 button cells were first assembled in an argon-filled glove box ([O ₂ ]<1ppm, [H ₂ O]<1ppm). Here, the lithium sheet is used as the counter electrode/reference electrode, the diaphragm is Celgard2500 membrane, and the electrolyte is 1M LiPF ₆ dissolved in a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate with a volume ratio of 1:1:1 in the liquid. The preparation method of the working electrode is to uniformly mix HS1 or HS2 with a mass fraction of 80%, 10% conductive medium super P and 10% binder polyvinylidene fluoride PVDF, and dissolve them in N-methyl-2 -Pyrrolidone NMP. Grind the above mixture with an agate mortar for 30 minutes, and then evenly coat the slurry on copper foil with a weight of 0.5-0.6 mg per copper foil, and dry it at 100°C for 10 hours; the charge and discharge test is carried out at LAND CT2001A Conducted on the battery test system, the potential range is 0.01-3.0V relative to Li ⁺ /Li; the cyclic voltammetry curve is carried out on the IVIUM electrochemical workstation, and the potential range is 0.01-3.0V relative to Li ⁺ /Li , the sweep speed is 0.2mV/s; the AC impedance test is performed when the amplitude is 10mV, and the frequency range of the test is from 100kHz to 10mHz.

Structural and Morphological Characterization of Composite Materials:

Figure 3 shows the Raman spectra of HS1 and HS2, in which 194, 482, 524, 619 and 691cm ^-1 correspond to the F _2g , E _g , F _2g , F _2g and A _1g vibration modes of Co ₃ O ₄ with spinel structure. The characteristic peaks of HS2 are similar to those of HS1, but its A _1g peak is shifted to 709cm ^-1 and narrowed, indicating that the size of Co ₃ O ₄ in HS2 is larger than that in HS1. Graphene in Fig. 3 shows typical D band (1353cm ^-1 ) and G band (1604cm ^-1 ). The I _D / _IG values of HS1 and HS2 are 1.49 and 1.25, respectively, indicating that the topological defects in HS1 are increased due to N doping. Figure 4 is a comparison of Raman spectra of HS3 and HS4. It can be seen that the Raman characteristic peaks of HS3 and HS4 are similar to those of HS1 and HS2. Fig. 5 is the X-ray diffraction (XRD) pattern of HS1 and HS2, it can be seen that there are characteristic peaks of graphene and Co ₃ O ₄ of spinel structure in the composite material. The XRD patterns of HS3, HS4 and commercial hydrogen storage alloys are shown in Figure 6. It can be seen that both HS3 and HS4 maintain the CaCu ₅ type hexagonal structure, because the contents of Co ₃ O ₄ and RGO in the composite materials are very low , by ICP test, the mass fractions of Co ₃ O ₄ and RGO in HS3 (or HS4) are 0.9wt% and 1.8wt%, respectively. According to thermogravimetric analysis (TGA), it is known that the content of RGO in HS1 and HS2 is about 26wt% (see Figure 7), and the thermogravimetric curve of HS1 has three obvious weight losses at 248, 300 and 473 °C, and the weight loss at 248 and 300 °C The loss may be attributed to the oxidation of disordered carbon caused by N doping, and the weight loss at 473 °C may be attributed to the oxidation of carbon in the graphene framework. Figure 8 is the XPS full spectrum of HS1, from which it is known that the composite material contains elements C, N, O and Co, and the content of N atoms is 3.31 at%. Figure 9 is the high-resolution 2p XPS spectrum of Co, which shows that Co element exists in the form of oxide in the composite material. The high-resolution 1s XPS spectrum of N is shown in Fig. 10, indicating that N is composed of pyridine nitrogen and pyrrole nitrogen. The surface morphology of HS1 and HS2 was observed by scanning electron microscope (SEM), see Figs. 11 and 12 . It can be seen from the figure that the Co ₃ O ₄ nanocubes are pinned on the graphene sheets, and the graphene sheets are covered with Co ₃ O ₄ . The Co ₃ O ₄ nanocubes in HS1 have side lengths of 50–80 nm, while the Co ₃ O ₄ nanocubes in HS2 have side lengths of 150–200 nm. The SEM morphologies of HS3 and HS4 are shown in Figures 13 and 14. It can be seen that Co ₃ O ₄ is pinned on graphene nanosheets, which is different from the smooth surface of commercial hydrogen storage alloys (see Figure 15). It can be clearly seen that the distribution of Co ₃ O ₄ nanocubes in HS3 is more uniform than that in HS4, and there is no obvious segregation. This may be due to the introduction of more nucleation sites by the N functional group in HS3. 16 and 17 are transmission electron microscope (TEM) photographs of HS1 and HS2. It can also be seen that graphene nanosheets wrap Co ₃ O ₄ nanocubes, and HS1 has a smaller size of Co ₃ O ₄ . This is attributed to more nucleation sites in HS1 ([Co(NH ₃ ) ₆ ] ²⁺ formed by Co ²⁺ and NH ₃ can serve as a kind of crystal nucleus of Co ₃ O ₄ ). See Figures 18 and 19 for high resolution transmission electron microscope (HRTEM) photos of HS1 and HS2. Interplanar distances of 0.286, 0.244 and 0.202nm correspond to (220), (311) and (400) crystal planes of Co ₃ O ₄ , respectively. The inset of Figure ₁₈ demonstrates the good contact between Co3O4 and N _- RGO.

Electrochemical performance characterization of HS3 and HS4 Ni-MH batteries:

Figure 20 shows the discharge curves of HS3, HS4 and commercial hydrogen storage alloy electrodes. It can be seen from the figure that the three have similar discharge capacities. The rate performance of the three electrodes can be seen in Figure 1. It can be seen from this figure that the high rate discharge performance of the HS3 electrode is better than that of the other two electrodes at all discharge current densities I _d , and it is more obvious when the I _d is larger . At a discharge current density of 3 A/g, the capacity of HS3 is as high as 223.1 mAh/g, which is 3.2 times that of commercial hydrogen storage alloys (68.7 mAh/g). The high-rate discharge performance of metal hydride electrodes is determined by the electrochemical reaction speed on the electrode surface and the hydrogen atom diffusion speed inside the alloy. The former can be characterized by the exchange current density I ₀ , the contact resistance R _c and the charge transfer resistance R _ct of the electrode, The latter can be evaluated from the limiting current density _IL and the _hydrogen atom diffusion coefficient DH. Figure 21 shows the linear polarization curves of HS3, HS4 and commercial hydrogen storage alloys at 50% depth of discharge. The I ₀ value can be calculated from the slope of the straight line in the figure. Figure 22 shows the test results of electrochemical impedance spectroscopy, and R _c and R _ct can be obtained by fitting according to the equivalent circuit diagram in the figure. _IL (see Figure 23) and _DH (see Figure 24) can be used to characterize the rate of hydrogen diffusion from the interior of the alloy to the surface. It is known from the calculation that the HS3 electrode has the largest I ₀ , _IL and D _H , and has the smallest R _c and R _ct , indicating its best high-rate discharge performance. The advantages of the HS3 electrode are: (1) heteroatom defects, high electrical conductivity and excellent electrode/electrolyte wettability of N-RGO are beneficial to the adsorption of H and the transport of electrons and ions; (2) the small size of Co ₃ The uniform distribution of O ₄ nanocubes on the surface of N-RGO improves the catalytic activity of Co ₃ O ₄ to the Volmer reaction: H ₂ O+e ^- →H+OH ^- and improves the discharge capacity; (3) hydrogen storage alloys with Co The seamless integration of ₃ O ₄ /N-RGO reduces the internal resistance of the electrode.

Electrochemical performance characterization of lithium-ion batteries of HS1 and HS2:

Figure 25 shows the cyclic voltammetry (CV) curves of HS1 and HS2. For the HS1 electrode, the first cathode scan has a strong peak (0.68V) and a weak shoulder (1.31V), corresponding to amorphous Li ₂ O formation and multistep transformation from Co ₃ O ₄ to Co. In addition, this strong peak also corresponds to the formation of an irreversible solid electrolyte interfacial film (SEI film). From the second lap, the position of the weak shoulder remains basically unchanged, however, the strong peak shifts to 0.89 V, accompanied by a significant drop in current density. The third circle of the CV curve of the HS1 electrode basically coincides with the second circle, indicating its good cycle stability. Furthermore, the anodic part in the CV curve of the HS1 electrode does not change much during cycling, and the two anodic peaks at 1.37 V and _2.12 V correspond to the transformation _of Co to CoO and Co3O4, respectively. The CV curve of HS2 is similar to that of HS1, except that the two cathodic peaks are shifted to 0.66V and 1.21V, and the two anodic peaks are shifted to 1.46V and 2.16V, respectively, reflecting that the HS2 electrode has a larger electrochemical electrode. change. The constant current charge and discharge curve also verifies this point (see Figure 26). It is known from this figure that the HS1 electrode has a higher discharge platform than the HS2 electrode, indicating that HS1 has a smaller electrochemical polarization in the electrochemical reaction. It can also be seen from the figure that both electrodes have high initial discharge capacity (1493.5mAh/g for HS1 and 1492.7mAh/g for HS2). However, the second cycle discharge capacity of the HS2 electrode dropped significantly to 806.2mAh/g, a loss of 46%. On the contrary, the discharge capacity of HS1 remained basically unchanged in the second, third and even fiftieth laps, which were 1305.0, 1297.5 and 1251.2mAh/g respectively. In addition, the first cycle Coulombic efficiency (87.8%) of HS1 electrode is significantly higher than that of HS2 (51.2%). This indicates that N doping can inhibit the decomposition of the electrolyte to a certain extent and improve the reversibility of lithium storage. Figure 27 shows the cycle performance curves of HS1 and HS2 at a current density of 0.1A/g. The Coulombic efficiencies of the two electrodes are maintained at close to 100%, indicating good reversible lithium storage characteristics. HS1 had a capacity of 1251.2mAh/g after 50 cycles, a loss of 4.1% (compared to the second-cycle discharge capacity), while HS2 had a capacity of only 753.9mAh/g after 50 cycles. HS1 has excellent rate discharge performance, see Figure 28. The average discharge capacity of the HS1 electrode at different current densities from 0.2 to 10A/g is 1174.5, 1058.4, 934.6, 800.3, 658.4, 538.1 and 423.6mAh/g, and when the current returns to 0.2A/g, its discharge capacity rapidly It recovered to 1088.2mAh/g, and remained basically stable in subsequent charge-discharge cycles. The HS1 electrode exhibits excellent rate discharge performance, which is mainly attributed to the synergistic effect between Co ₃ O ₄ and N-RGO: (1) The smaller size of Co ₃ O ₄ in HS1 can provide greater electrochemical activity area, shortening the ion diffusion distance; (2) N-RGO has better electrode/electrolyte wettability, which can promote good contact between electrolyte and electrode active material, and enhance the transport kinetics of Li ⁺ ; (3) N-RGO With more topological defects, it can provide more active sites, which is beneficial to the adsorption and diffusion of Li ⁺ ; (4) Co ₃ O ₄ has stronger interaction and better electrical contact with N-RGO , improving the electrode conductivity. This is consistent with the test results of AC impedance (see Figure 29), where the semicircle corresponds to the charge transfer resistance, and the straight line corresponds to the Warburg impedance that characterizes the diffusion performance. The smaller the diameter of the semicircle, the smaller the charge transfer resistance, and the better the electrochemical reaction kinetics of the electrode. Compared with HS2, the HS1 electrode has smaller charge transfer resistance (91.2vs.122.8Ω) and smaller electrochemical polarization. Figure 30 is the cycle characteristic curves of HS1 and HS2 electrodes at a current density of 5A/g. The HS1 electrode has higher discharge capacity and better cycle stability. This is also attributed to the synergistic effect between _Co3O4 and N _- RGO. _On the one hand, Co ₃ O ₄ is pinned on the graphene sheet, or graphene supports ^and covers Co ₃ O _{4 .} The volume change produced in the process can also inhibit the agglomeration of Co ₃ O ₄ nanocubes during the cycle and prevent the pulverization of electrode materials; on the other hand, Co ₃ O ₄ nanocubes are pinned between the graphene sheets , can inhibit the stacking of graphene sheets in the cycle process like nano gaskets, avoid the graphitization of graphene, keep it high specific surface area, loose three-dimensional conductive network structure and maintain fast electron and ion transport. The good rate performance and cycle stability of HS1 indicate that our prepared composite has certain potential in the practical application of high-power batteries.

Claims (8)

1. a kind of cobalt oxide/graphene composite (Co₃O₄/ RGO) preparation method, comprise the following steps：

A, according to improved Hummers methods synthesize graphite oxide；

B, at 22～25 DEG C, by the cobalt acetate of 1～2ml 0.2M, the graphite oxide of 1～2ml 4.5mg/ml is added to 34～ In the absolute ethyl alcohol of 36ml, 20～30min of ultrasonic disperse, then 9～10h is heated at 75～85 DEG C makes cobalt acetate hydrolysis, oxidation And grow extra small Co in graphite oxide surface in situ₃O₄Nano-particle；

C, heat 2.5～3.5h at 145～155 DEG C with the method for hydro-thermal and make Co₃O₄The further crystallization of nano-particle, graphite oxide Reduction, afterwards by the inorganic membrane filtration that product aperture is 0.1～0.2 μm, respectively with second alcohol and water thoroughly cleaning 4～6 times, 22～25 DEG C of 10～12h of drying in vacuum drying chamber.

2. cobalt oxide/graphene composite (Co according to claim 1₃O₄/ RGO) preparation method, its feature It is：By adjusting the amount of ethanol and hydrolysis and the oxidation rate of controlling reaction temperature cobalt acetate in step b.

3. cobalt oxide/graphene composite (Co according to claim 1₃O₄/ RGO) preparation method, its feature It is：Co is controlled in step c by adjusting the temperature of hydro-thermal₃O₄Crystallization shape.

4. cobalt oxide/graphene composite (Co according to claim 1₃O₄/ RGO) preparation method, its feature It is：0.5～1g hydrogen storing alloy powders were added before 145～155 DEG C of hydro-thermal reactions in step c, cobaltosic oxide/graphite is prepared The composite Co of alkene and hydrogen bearing alloy₃O₄/RGO/HSAs。

5. cobalt oxide/graphene composite (Co according to claim 1₃O₄/ RGO) preparation method, its feature It is：0.5～0.8ml ammoniacal liquor is added in step b, cobalt acetate hydrolyzed under the adjustment effect of ammoniacal liquor, aoxidized, prepared four and aoxidize Three cobalts/nitrogen-doped graphene composite Co₃O₄/N-RGO。

6. cobalt oxide/graphene composite (Co according to claim 1₃O₄/ RGO) preparation method, its feature It is：In step b add 0.5～0.8ml ammoniacal liquor, cobalt acetate hydrolyzed under the adjustment effect of ammoniacal liquor, aoxidized, in step c 0.5～1g hydrogen storing alloy powders are added before 145～155 DEG C of hydro-thermal reactions, cobaltosic oxide/nitrogen-doped graphene and hydrogen storage is prepared The composite Co of alloy₃O₄/N-RGO/HSAs。

7. the preparation method according to claim 4 or 6 is obtained cobalt oxide/graphene and the composite wood of hydrogen bearing alloy Material Co₃O₄The composite Co of/RGO/HSAs and cobaltosic oxide/nitrogen-doped graphene and hydrogen bearing alloy₃O₄/ N-RGO/HSAs, Electrochemical property test is carried out both as the electrode material of Ni-MH battery, is comprised the following steps：

A, 0.25～0.255g active materials are well mixed with 1.0～1.02g carbonyl nickel powders, by tablet press machine 8～20MPa's The electrode slice of a diameter of 10～15mm is pressed under pressure；

B, using electrode slice prepared in step a as working electrode, the Ni (OH) of sintering₂/ NiOOH pieces are used as to electrode, oxidation Used as reference electrode, the KOH solution of 25～35wt% is electrolyte to mercury electrode, and constituting the three-electrode system of standard carries out electrochemistry Test；

C, when carrying out volume test, charging and discharging currents density is 0.06A/g (0.2C), and the activation number of turns is 4；Carry out high magnification to put During electric performance test, the density of charging current is 0.3A/g (1C), and discharge current density is respectively 0.3,0.6,0.9,1.2,1.5, 2.4 and 3A/g (10C)；

D, electrochemical property test are carried out on IVIUM electrochemical workstations, in the amplitude relative to OCP (OCP) For 5mV when carry out ac impedance measurement, the frequency range of test is by 100kHz to 5mHz；Under the conditions of 50% depth of discharge, When relative to the potential scan scope of OCP being -5 to 5mV, carry out sweeping speed and test for the linear polarisation curves of 0.05mV/s； Under the conditions of 50% depth of discharge, when the potential scan scope relative to OCP is 0 to 1.5V, carry out sweeping anode of the speed for 5mV/s Polarization curve is tested；Under 100% charged state, under the potential step of+500mV relative to Hg/HgO, carry out 4000s's The test of current versus time curve.

8. the cobalt oxide/graphene composite that the preparation method according to any one of claims 1 to 3 or 5 is obtained (Co₃O₄/ RGO) and cobaltosic oxide/nitrogen-doped graphene composite (Co₃O₄/ N-RGO), both as lithium ion battery Electrode material carries out electrochemical property test, comprises the following steps：

A, using active material as working electrode, used as to counter/reference electrode, barrier film is the films of Celgard 2500 to lithium piece, electricity Solution liquid is the LiPF of 1M₆Volume ratio is dissolved in for 1:1:The mixed liquor of 1 ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate In, in the glove box ([O full of argon gas₂]<1ppm,[H₂O]<CR2016 type button cells are assembled in 1ppm)；

B, the preparation method of working electrode be by active material that mass fraction is 80%, 10% super P and 10% it is viscous Knot agent polyvinylidene fluoride PVDF is homogenously mixed together, in being dissolved in METHYLPYRROLIDONE NMP, by mixture agate Nao mortar grinder 30min, are then uniformly coated on slurries on Copper Foil, and the quality of each Copper Foil load is 0.5-0.6mg, 10h is dried under conditions of 100 DEG C；

C, charge-discharge test are carried out on LAND CT2001A battery test systems, and its potential interval is relative to Li⁺/Li 0.01-3.0V；Cyclic voltammetry curve is carried out on IVIUM electrochemical workstations, and its potential interval is relative to Li⁺/Li 0.01-3.0V, sweeps speed for 0.2mV/s；Ac impedance measurement is carried out when amplitude is 10mV, the frequency range of test is by 100kHz To 10mHz.