CN107256951B - A kind of CoO/reduced graphene oxide composite negative electrode material and preparation method thereof - Google Patents

Abstract

The invention relates to a CoO/reduced graphene oxide composite negative electrode material and a preparation method thereof. First, oleylamine and oleic acid are added to an isopropanol solution to obtain A; a cobalt source and a precipitating agent are added to A, and stirred Obtain B evenly; add graphene oxide into B, stir evenly to obtain C; ultrasonically treat C, and then conduct an oil bath reaction to form a precipitate; separate the precipitate and wash and dry it, and then in an atmosphere of 300-500°C Keeping the temperature in the furnace for 0.5-2 hours, cooling to room temperature, and obtaining the CoO/reduced graphene oxide composite negative electrode material. The particle size of CoO in the compound prepared by the present invention is small, which is conducive to the intercalation and extraction of lithium ions in the process of charging and discharging, and improves the specific capacity of the electrode. Help to slow down the volume expansion effect of materials, coupled with the auxiliary effect of carbon materials to improve electrical conductivity, improve the electrochemical performance of materials.

Description

A kind of CoO/reduced graphene oxide composite negative electrode material and preparation method thereof

technical field

The invention belongs to the field of ion battery negative electrode materials, and in particular relates to a CoO/reduced graphene oxide composite negative electrode material and a preparation method thereof.

Background technique

With the rapid development of lithium/sodium-ion batteries, commercially used carbon-based anode materials have been difficult to meet the market demand due to their low theoretical dosage and poor charge-discharge resistance. People urgently need to develop new anode materials to replace carbon anodes. Material. Among them, transition metal oxides (such as CoO, Co ₃ O ₄ , Mn ₃ O ₄ , Fe ₂ O ₃ , etc.) have higher theoretical specific capacity (600-1000mAh/g, about 2-3 times that of carbon materials), In recent years, it has become a hot spot of research and attention. The charging and discharging mechanism of transition metal oxides is different from the lithium intercalation/extraction mechanism of traditional materials. They can undergo a reversible redox reaction with Li to achieve the function of lithium storage, which makes the charging and discharging process faster. CoO in transition metal oxides is a material with a wide range of raw materials, easy preparation, and stable physical and chemical properties. The theoretical capacity is 719mAh/g, which is about twice the theoretical capacity of graphite. However, the mechanical stress generated by the volume expansion and contraction of CoO caused by the lithium-deintercalation reaction can easily lead to the crushing and peeling of the electrode material during the charging and discharging process, affecting its cycle performance. Therefore, it is possible to design nanomaterials and compound them with other substances Effective way to improve performance.

Shasha Chu et al[Shasha Chu, Chao Yang, Xin Xia, Jide Wang, Yanglong Hou and Xintai Su.Controlled synthesis of CoO/C and Co/C nanocomposites via a molten salt method and their lithium-storage properties[J].New J.Chem .,2016,40:2722-2729.] Using sodium oleate and cobalt nitrate as raw materials to obtain CoO/C composites, CoO is dispersed on carbon nanosheets decomposed by oleic acid, and the particle size of CoO is about 3~5nm, the distribution is relatively uniform, but the cycle stability is not very good, and the capacity is also low. The reversible capacity of 50 cycles at a current density of 70mA/g is ~640mAh/g. Jincheng Liu et al[JinchengLiu, Yuejiao Xu, Xiaojian Ma, Jinkui Feng, Yitai Qiana, ShenglinXiong.Multifunctional CoO@C metasequoia arrays for enhanced lithium storage[J].Nano Energy,2014,7:52-62.] Metasequoia-like Co ₃ O ₄ was prepared on the surface, and then it was put into a tube furnace with acetylene gas and argon gas, and the metasequoia-like Co ₃ O ₄ grown on nickel foam was reduced to CoO by CVD method, and A carbon layer decomposed from acetylene is wrapped on the surface of CoO, and the capacity can reach 1200mAh/g at a current density of 500mA/g, but the capacity retention rate is not very good and the decay is fast. Weiwei Yuan et al [Weiwei Yuan, Jun Zhanga, Dong Xie, Zimin Dong, Qingmei Su, Gaohui Du. Porous CoO/C polyhedra asanode material for Li-ion batteries [J]. Electrochimica Acta, 2013, 108:506-511.] The prepared Co ₃ O ₄ was used as a precursor, and sucrose was used as a carbon source to obtain a porous CoO/C octahedral complex. The size of CoO particles is about 50-80nm, but due to the large size and compact structure of CoO/C octahedron, the electrochemical performance is not very ideal, and the capacity is only ~600mAh/g at a current density of 50mA/g. Ming Zhang et al [Ming Zhang, Evan Uchaker, Shan Hu, Qifeng Zhang, Taihong Wang, Guozhong Cao and Jiangyu Li. CoO–carbon nanofiber networks prepared by electrospinning as binder-free anodematerials for lithium-ion batteries with enhanced properties[J].Nanoscale ,2013,5:12342-12349.] CoO/carbon fiber composites were prepared by electrospinning. CoO particles with a size of about 10nm were uniformly distributed in the carbon fibers, and the capacity after 52 cycles at a current density of 100mA/g It is 633mAh/g. The structural design of the composite of CoO and carbon materials is a key part. Although carbon materials will provide high conductivity and stability, CoO itself should also have a smaller particle size, a stable structure, and a larger ratio. Surface area, in order to improve its own electrochemical performance, there is no relevant technical report.

Contents of the invention

The purpose of the present invention is to overcome the problems existing in the prior art, to provide a CoO/reduced graphene oxide composite negative electrode material and its preparation method, by preparing CoO particles with a size of about 5-10nm and thus assembling them into a three-dimensional layer The fluffy structure with a shape size of 1-2 μm realizes the joint improvement of capacity, stability and rate performance.

In order to achieve the above object, the present invention adopts following technical scheme:

Include the following steps:

1) According to the volume ratio (0.5~2):(0.5~2):80, add oleylamine and oleic acid into the isopropanol solution to obtain solution A;

2) Add the cobalt source and the precipitating agent into solution A, and stir evenly to obtain solution B; wherein, the ratio of the cobalt source to the isopropanol solution in step 1) is (1-5) mmol: 80 mL;

3) adding graphene oxide into solution B, stirring evenly to obtain suspension C; wherein, the ratio of graphene oxide and isopropanol solution in step 1) is (0.08～0.24) g: 80 mL;

4) Ultrasonic treatment of the suspension C, followed by an oil bath reaction to generate a precipitate;

5) separating the precipitate and washing and drying to obtain a precursor;

6) Keeping the precursor in an atmosphere furnace at 300-500° C. for 0.5-2 hours, and then cooling to room temperature to obtain a CoO/reduced graphene oxide composite negative electrode material.

Further, in step 1), every 80 mL of isopropanol solution contains 70-78 mL of isopropanol; the volume ratio of oleylamine to oleic acid is 1:1.

Further, stirring in step 1) for 5-10 min to obtain solution A; stirring in step 2) for 10-30 min to obtain solution B.

Further, in step 2), the cobalt source is CoCl ₂ ·6H ₂ O, and the precipitating agent is urea.

Further, the molar ratio of cobalt source and precipitant in step 2) is 1:10.

Further, in step 3), magnetic stirring was performed for 30-60 min to obtain suspension C.

Further, in step 4), the suspension C is ultrasonically treated for 8-15 hours; the temperature in the oil bath reaction is 90-120° C., and the time is 6-10 hours.

Further, in step 5), the precipitate is separated by centrifugation, washed with absolute ethanol and hexane for 3-6 times, and then put into a vacuum drying oven at 70-90° C. for 6-10 hours.

Further, in step 6), the precursor is placed in an atmosphere tube furnace with an atmosphere of argon, the temperature rise rate is 3-10°C·min ^-1 , and the flow rate of argon gas is 0.1-0.5 sccm·min ^-1 .

A CoO/reduced graphene oxide composite negative electrode material prepared by the above-mentioned preparation method, the size of CoO in the material is 5-10nm; the average specific capacity of the material is 1001-1041mAh/g.

Compared with the prior art, the present invention has the following beneficial technical effects:

In the present invention, the Venus flytrap-like CoO/graphene composite is synthesized by adding the cobalt source and the precipitating agent into the water-alcohol solution system, adding graphene oxide and ultrasonically dispersing for a period of time, and using the oil bath method combined with heat treatment, and the preparation process is simple Mild, short preparation cycle, improve the electrochemical performance of CoO negative electrode more efficiently; CoO particles in the prepared composite are small in size, which is helpful for the intercalation and extraction of lithium ions in the process of charging and discharging, and improves the specific capacity of the electrode. The reasonable structure design on the surface generates a Venus flytrap-like compound, which is of great help to maintain the stability of the material and slow down the volume expansion effect of the material. In addition, the auxiliary effect of the carbon material to improve the electrical conductivity has a great impact on the electrochemical performance of the material. The performance has been greatly improved; in the present invention, the combination of nano-particles and reasonable structural design plays a synergistic effect, and at the same time, the high conductivity provided by carbon materials is added to finally achieve the common improvement of capacity, stability and rate performance.

The present invention obtains flytrap-like CoO/graphene composites through oil bath method and heat treatment. The flytrap-like CoO is snapped together by two CoO sheets with jagged edges, leaving gaps and holes in the middle. The size is about 300nm and it consists of CoO with a size of 5-10nm. Small CoO particles shorten the distance of electron and ion transmission, increase the specific surface area in contact with the electrolyte, and increase the active sites of the reaction. The fluffy structure with voids and holes also makes the contact between the material and the electrolyte more sufficient. At the same time, it can also alleviate the volume expansion problem caused by the de-lithiation/intercalation process. The reduced graphene oxide matrix supports such a structure, which not only improves the conductivity but also stabilizes the structure of CoO. These structural features improve the electrochemical performance of the material. The average specific capacity of the composite is 1001-1041mAh/g . The special morphology of CoO also has certain reference value for the research of other transition metal oxides.

Description of drawings

FIG. 1 is an X-ray diffraction (XRD) spectrum of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention.

Fig. 2 is the scanning electron microscope (SEM) photo of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention at a magnification of 20.0K

Fig. 3 is a scanning electron microscope (SEM) photo at a magnification of 100.0K of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention.

The transmission electron microscope (TEM) photograph of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention at a magnification of 200nm

Fig. 5 is a transmission electron microscope (TEM) photo at a magnification of 500 nm of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention.

Fig. 6 is an HRTEM image at a magnification of 5 nm of the Venus flytrap-like CoO/reduced graphene oxide composite negative electrode material prepared in Example 1 of the present invention.

Fig. 7 is a graph of the cycle performance of the Venus flytrap-like CoO/reduced graphene oxide composite anode material prepared in Example 1 of the present invention at a current density of 500mA/g for 50 cycles.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

The present invention comprises the steps:

1) Add 2~10mL deionized water into 78~70mL isopropanol to make 80mL mixed solvent A;

2) Add 0.5-2mL oleylamine and 0.5-2mL oleic acid to the mixed solvent A according to the volume ratio of 1:1, and stir for 5-10min to obtain solution B;

3) Take 1-5 mmol of CoCl ₂ ·6H ₂ O and 10-50 mmol of CO(NH ₂ ) ₂ , add them to solution B in sequence according to the molar ratio of 1:10, and stir for 10-30 minutes to obtain solution C;

4) Add 0.08-0.24 g of graphene oxide into solution C, and magnetically stir for 30-60 minutes to obtain suspension D;

5) ultrasonically treat the suspension D for 8-15 hours;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature at 90-120°C, and the holding time at 6-10 hours, then naturally cool to room temperature to obtain the precipitate E;

7) Centrifuge the precipitate and wash it with absolute ethanol and hexane for 3 to 6 times respectively, then put it into a vacuum drying oven for 6 to 10 hours at 70 to 90° C. to dry to obtain the precursor F;

8) Put the precursor F in an atmosphere tube furnace, set the heating rate at 3-10°C·min ^-1 , the flow rate of argon flow at 0.1-0.5 sccm·min ^-1 , the reaction temperature at 300-500°C, and the holding time for After 0.5-2 hours, after the reaction is completed, it is naturally cooled to room temperature, and the Venus flytrap-like CoO/reduced graphene oxide composite can be obtained.

The present invention prepares CoO particles with a size of about 5nm and assembles them into a three-dimensional fluffy flytrap-like structure, which not only shortens the distance of electron and ion transmission, but also makes the contact between the material and the electrolyte more sufficient and increases the reaction rate. The active sites promote the electrochemical reaction. The graphene matrix connects CoO to each other, improving the conductivity and stabilizing the structure.

Example 1:

1) Add 10mL deionized water into 70mL isopropanol to make 80mL mixed solvent A;

2) Add 0.5mL oleylamine and 0.5mL oleic acid into the mixed solvent A according to the volume ratio of 1:1, and stir for 5min to obtain solution B;

3) Take 1mmol of CoCl ₂ ·6H ₂ O and 10mmol of CO(NH ₂ ) ₂ , add them to solution B sequentially according to the molar ratio of 1:10, and stir for 10min to obtain solution C;

4) 0.08g of graphene oxide was added to solution C, and magnetically stirred for 30min to obtain suspension D;

5) ultrasonically treat the suspension D for 8 hours;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature to 90°C, and set the holding time to 10h, then naturally cool to room temperature to obtain the precipitate E;

7) Centrifuge the precipitate and wash it with absolute ethanol and hexane for 3 times respectively, then put it into a vacuum drying oven for 10 hours at 70°C to obtain the precursor F;

8) Place the precursor F in an atmosphere tube furnace, set the heating rate to 3°C·min ^-1 , the flow rate of argon flow to 0.1sccm·min ^-1 , the reaction temperature to 300°C, and the holding time to 0.5h. After the reaction is completed After natural cooling to room temperature, the Flytrap-like CoO/reduced graphene oxide composite can be obtained.

As shown in Figure 1, it is the XRD spectrum of the obtained CoO/reduced graphene oxide product. The characteristic diffraction peaks in the figure are consistent with the standard card of CoO (JCPDS No.: 43-1004), and the diffraction angle is between 20 and 30 degrees. The less obvious diffraction peaks appearing between them are the characteristic peaks of graphene. Figure 2 and Figure 3 are the SEM images of the product at 20K and 100K magnifications. It can be clearly seen from the figures that the Venus flytrap-like CoO structure grows on graphene, with a size of 1-2 μm. Figure 4 and Figure 5 are the TEM images of Venus flytrap-like CoO/reduced graphene oxide taken from different angles of view. The angle of view seen in Figure 4 is the same as that seen in the SEM image. The internal structure of the Venus flytrap-like CoO can be seen from the side, which is composed of two relatively symmetrical multi-sheet assemblies, and there are gaps between the sheets, and there are also gaps between the two symmetrical structures. Figure 6 is HRTEM. It can be seen from the figure that the size of CoO particles is 5-10nm. The interplanar spacing obtained from the lattice fringes is consistent with the XRD results, indicating that the flytrap-like structure is indeed CoO.

Comparative example 1: If the volume ratio of oleic acid and oleylamine is changed, the electrochemical performance of the resulting product will be attenuated. As shown in Figure 7, when the volume ratio of oleic acid and oleylamine becomes 2:1, and the oil When the volume ratio of acid and oleylamine becomes 1:2, the cycle performance of the product will decrease. The original average specific capacity of 1041mAh/g decayed to 646mAh/g and 376mAh/g respectively.

Example 2:

1) Add 5mL deionized water into 75mL isopropanol to make 80mL mixed solvent A;

2) Add 1mL oleylamine and 1mL oleic acid into the mixed solvent A according to the volume ratio of 1:1, and stir for 5min to obtain solution B;

3) Take 2mmol of CoCl ₂ ·6H ₂ O and 20mmol of CO(NH ₂ ) ₂ , add them to solution B sequentially according to the molar ratio of 1:10, and stir for 10 minutes to obtain solution C;

4) 0.12g of graphene oxide was added to solution C, and magnetically stirred for 40min to obtain suspension D;

5) ultrasonically treat the suspension D for 10 h;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature to 100°C, and set the holding time to 8h, then naturally cool to room temperature to obtain the precipitate E;

7) Centrifuge the precipitate and wash it with absolute ethanol and hexane for 4 times, then put it into a vacuum drying oven at 80°C for 8 hours to obtain the precursor F;

8) Place the precursor F in an atmosphere tube furnace, set the heating rate at 5°C·min ^-1 , the flow rate of argon flow at 0.2 sccm·min ^-1 , the reaction temperature at 400°C, and the holding time for 1 h. After the reaction is completed, After natural cooling to room temperature, the flytrap-like CoO/reduced graphene oxide composite can be obtained, and the average specific capacity of the composite is 1039mAh/g.

Example 3:

1) Add 8mL deionized water to 72mL isopropanol to make 80mL mixed solvent A;

2) Add 1.5mL oleylamine and 1.5mL oleic acid into the mixed solvent A according to the volume ratio of 1:1, and stir for 8min to obtain solution B;

3) Take 3mmol of CoCl ₂ ·6H ₂ O and 30mmol of CO(NH ₂ ) ₂ , add them to solution B sequentially according to the molar ratio of 1:10, and stir for 20min to obtain solution C;

4) 0.16g of graphene oxide was added to solution C, and magnetically stirred for 50min to obtain suspension D;

5) ultrasonically treat the suspension D for 12 hours;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature to 110°C, and set the holding time to 7h, then naturally cool to room temperature to obtain the precipitate E;

7) Centrifuge the precipitate and wash it with absolute ethanol and hexane for 5 times respectively, then put it into a vacuum drying oven at 90°C for 6 hours to obtain the precursor F;

8) Put the precursor F in an atmosphere tube furnace, set the heating rate to 10°C·min ^-1 , the flow rate of argon flow to 0.5 sccm·min ^-1 , the reaction temperature to 500°C, and the holding time to 2h. After the reaction is completed, After natural cooling to room temperature, the flytrap-like CoO/reduced graphene oxide composite can be obtained, and the average specific capacity of the composite is 1022mAh/g.

Example 4:

1) Add 10mL deionized water into 70mL isopropanol to make 80mL mixed solvent A;

2) Add 2 mL of oleylamine and 2 mL of oleic acid into the mixed solvent A according to the volume ratio of 1:1, and stir for 10 min to obtain solution B;

3) Take 4mmol of CoCl ₂ ·6H ₂ O and 40mmol of CO(NH ₂ ) ₂ , add them to solution B sequentially according to the molar ratio of 1:10, and stir for 30min to obtain solution C;

4) 0.2g of graphene oxide was added to solution C, and magnetically stirred for 60min to obtain suspension D;

5) ultrasonically treat the suspension D for 12 hours;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature to 120°C, and set the holding time to 6h, then naturally cool to room temperature to obtain the precipitate E;

7) Centrifuge the precipitate and wash it with absolute ethanol and hexane for 6 times respectively, then put it into a vacuum drying oven for 8 hours at 70°C to obtain the precursor F;

8) Put the precursor F in the atmosphere tube furnace, set the heating rate at 3°C·min ^-1 , the flow rate of argon flow at 0.5 sccm·min ^-1 , the reaction temperature at 300°C, and the holding time at 2h. After the reaction is completed, After natural cooling to room temperature, the flytrap-like CoO/reduced graphene oxide composite can be obtained, and the average specific capacity of the composite is 1007mAh/g.

Example 5:

1) Add 2mL deionized water into 70mL isopropanol to make 80mL mixed solvent A;

2) Add 0.5mL oleylamine and 0.5mL oleic acid into the mixed solvent A according to the volume ratio of 1:1, and stir for 5min to obtain solution B;

3) Take 5mmol of CoCl ₂ ·6H ₂ O and 50mmol of CO(NH ₂ ) ₂ , add them to solution B sequentially according to the molar ratio of 1:10, and stir for 30min to obtain solution C;

4) 0.24g of graphene oxide was added to solution C, and magnetically stirred for 60min to obtain suspension D;

5) ultrasonically treat the suspension D for 15 hours;

6) Put the ultrasonic suspension D in an oil bath, set the holding temperature to 90°C, and set the holding time to 6h, then naturally cool to room temperature to obtain the precipitate E;

7) The precipitate was centrifuged and washed 6 times with absolute ethanol and hexane respectively, and then dried in a vacuum oven at 90°C for 6 hours to obtain the precursor F;

8) Put the precursor F in the atmosphere tube furnace, set the heating rate to 10°C·min ^-1 , the flow rate of argon flow to 0.1sccm·min ^-1 , the reaction temperature to 400°C, and the holding time to 1.5h. After the reaction is completed After natural cooling to room temperature, the flytrap-like CoO/reduced graphene oxide composite can be obtained, and the average specific capacity of the composite is 1001mAh/g.

In the present invention, cobalt chloride is used as cobalt source, urea is used as precipitant, and the two are added in a certain ratio to the water-alcoholic solution system containing a certain amount of oleylamine and oleic acid, and graphene oxide is added at the same time after ultrasonic dispersion for a period of time , using the oil bath method combined with heat treatment, the Venus flytrap-like CoO/reduced graphene oxide composite assembled from CoO nanoparticles can be obtained. The size of CoO nanoparticles is about 5nm, and the size of the assembled Flytrap-like structure is about 300nm. The three-dimensional Flytrap-like structure can be seen macroscopically by two sheets with jagged ends occluded. Together, there are gaps and holes inside, which is conducive to the immersion of electrolyte and the full occurrence of electrochemical reactions. Such Venus flytrap-like CoO grows on the surface of reduced graphene oxide and binds firmly to it, which is conducive to the rapid transport of electrons during charge and discharge. Nano-scale particle size, three-dimensional CoO structure and strong combination with reduced graphene oxide all play a key role in the improvement of electrochemical performance, and the synthesis method is simple, which is an important reference for the synthesis of other transition metal oxide anode materials value.

Claims (9)

1. a preparation method of CoO/reduced graphene oxide composite negative electrode material, is characterized in that: comprise the following steps: 1) According to the volume ratio (0.5~2):(0.5~2):80, add oleylamine and oleic acid into the isopropanol solution to obtain solution A; 2) Add cobalt source and precipitant to solution A, stir evenly to obtain solution B; wherein, cobalt source is CoCl ₂ 6H ₂ O, precipitant is urea, CoCl ₂ 6H ₂ O and isopropyl The ratio of alcohol solution is (1~5)mmol:80mL; 3) adding graphene oxide into solution B, stirring evenly to obtain suspension C; wherein, the ratio of graphene oxide and isopropanol solution in step 1) is (0.08～0.24) g: 80 mL; 4) Ultrasonic treatment is performed on the suspension C, and then an oil bath reaction is carried out at 90-120° C. for 6-10 hours to form a precipitate; 5) separating the precipitate and washing and drying to obtain a precursor; 6) Keeping the precursor in an atmosphere furnace at 300-500° C. for 0.5-2 hours, and then cooling to room temperature to obtain a CoO/reduced graphene oxide composite negative electrode material. 2. the preparation method of a kind of CoO/reduced graphene oxide composite negative electrode material according to claim 1, is characterized in that: step 1) contains the isopropanol of 70～78mL in the isopropanol solution of every 80mL; The volume ratio of amine and oleic acid is 1:1. 3. A method for preparing a CoO/reduced graphene oxide composite negative electrode material according to claim 1, characterized in that: step 1) stirs for 5-10 minutes to obtain solution A; step 2) stirs for 10-30 minutes , to obtain solution B. 4. The method for preparing a CoO/reduced graphene oxide composite negative electrode material according to claim 1, wherein the molar ratio of the cobalt source and the precipitating agent in step 2) is 1:10. 5 . The method for preparing a CoO/reduced graphene oxide composite negative electrode material according to claim 1 , characterized in that: in step 3), the suspension C is obtained by magnetically stirring for 30-60 minutes. 6. The method for preparing a CoO/reduced graphene oxide composite negative electrode material according to claim 1, characterized in that: in step 4), the suspension C is ultrasonically treated for 8-15 hours. 7. The preparation method of a kind of CoO/reduced graphene oxide composite negative electrode material according to claim 1, it is characterized in that: in step 5), by centrifugal separation, precipitate is washed with dehydrated alcohol and hexane respectively for 3～ After 6 times, put it into a vacuum drying oven for 6-10 hours at 70-90°C. 8. The preparation method of a kind of CoO/reduced graphene oxide composite negative electrode material according to claim 1, it is characterized in that: in step 6), the precursor is placed in the atmosphere tube furnace whose atmosphere is argon, and the heating rate 3-10°C·min ^-1 , and the flow rate of argon gas is 0.1-0.5 sccm·min ^-1 . 9. A CoO/reduced graphene oxide composite negative electrode material prepared by the preparation method according to claim 1, characterized in that: the size of CoO in the material is 5-10 nm; the average specific capacity of the material is 1001-1041mAh /g.