Olive-like heterogeneous symbiotic oxide / graphene composite material as well as preparation method and application thereof

Abstract

The invention relates to an electrode material, and discloses an olive-shaped heterogeneous symbiotic oxide / graphene composite electrode material and a preparation method and application thereof. The oxide / graphene composite electrode material comprises graphene and two kinds of metal oxide particles dispersed in the graphene, the two kinds of metal oxide particles are respectively one-dimensional nano-particles. The oxide / graphene composite material disclosed by the invention has relatively high cycle efficiency and specific capacity, the rate capability is greatly improved, and the oxide / graphene composite material has relatively high charge-discharge stability; the preparation method disclosed by the invention is simple and quick, and has great application value.

Description

Technical Field

[0001] The present invention relates to an electrode material, and particularly to an olive-shaped heterogeneous symbiotic oxide / graphene composite electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] As a key component of a lithium battery, the anode material directly affects the first cycle efficiency, cycle life, rate performance, and safety performance of the battery. Currently, the commercially available anode materials on a large scale are still mainly graphite-based carbon materials. Their main advantage lies in the stable structure during lithium ion insertion and extraction, high cycle life, and relatively low material cost. After the large screen and diversified functions of digital terminal products of lithium ion batteries, new requirements for battery endurance have been put forward. The theoretical capacity of the anode materials in the existing system is relatively low, and their battery performance is difficult to meet the requirements in fields such as electric vehicles. The research and industrialization of new battery technologies are imminent.

[0003] Transition metal oxide materials represented by iron-based and manganese-based materials are regarded as potential anode materials because they are inexpensive, environmentally friendly, and can be matched with high-voltage (4V or 5V) cathode materials. However, metal oxides also have disadvantages that limit their further practical applications. First, transition metal oxides often have poor electronic conductivity. As a result, a large amount of Joule heat is generated during the continuous insertion and extraction of lithium ions, posing a safety hazard. Second, the ion transport rate of transition metal oxides is poor, and the rate performance test is not good. Third, during the lithiation and delithiation processes of transition metal oxides, there is an obvious phenomenon of volume expansion and contraction, resulting in pulverization of the electrode material. General solutions can be roughly divided into two categories. First, composite metal oxides with other materials (such as carbon materials, etc.) to give play to the advantages of both and improve the lithium storage performance. Second, nanometerize the materials to prepare metal oxide nanoparticles with special morphologies, such as nanowires, nanorods, hollow structures, etc. For example, CN112151804A uses a carbon-coated transition metal oxide based on a Prussian blue analogue and applies it to the preparation of lithium batteries. The unique nanostructure can effectively shorten the transport distance of electrons and ions and improve the transport rate; at the same time, the nanoscale cubic particles of the carbon coating layer can effectively alleviate the volume expansion problem during charge and discharge. However, the dispersion of its nanoparticles is poor, and the aggregation effect is enhanced during long cycling. For example, CN114759164A invented a core-shell structured magnetic nanotemplate with polyaniline as the shell and Fe3O4 as the core, which is mixed evenly with the anode material, binder, conductive agent, and solvent water, and then a magnetic field is applied to direct the assembly of magnetic nanoscale Fe3O4 on the surface of the current collector to obtain the anode electrode sheet. Its three-dimensional network channels of conductivity can effectively improve the conductivity of the electrode, shorten the ion and electron migration paths, enhance the wettability of the electrolyte, and promote the high-speed conduction of lithium ions. However, the preparation process is relatively cumbersome and needs to be further optimized. At present, a simple and fast method for preparing nanocomposite anode materials is still extremely challenging. Summary of the Invention

[0004] Aiming at the limitations of the existing preparation methods, the present invention aims to obtain an olive-shaped heterogeneous symbiotic oxide / graphene composite material and its application by a simple and fast new preparation method. It is planned to use the hydrothermal method to composite graphene with two metal oxides to prepare a high-energy-density anode material for lithium-ion batteries. In the growth system of two oxides, namely heterogeneous oxides, each oxide acts as a dispersant for each other, which not only limits the further growth of the oxides but also alleviates the aggregation effect caused by them during charge and discharge to a certain extent. By optimizing the particle size, the transport paths of electrons and ions can be greatly reduced, thereby increasing the transport rate and the contact area between the electrode and the electrolyte, and rapid charge and discharge can be achieved. In addition, the good synergistic effect between the heterogeneous oxides and graphene can disperse the oxides, thus avoiding aggregation and enhancing the energy storage performance.

[0005] To achieve the object of the invention, the first aspect of the present invention is to provide an oxide / graphene composite material, comprising graphene and two metal oxide particles dispersed in the graphene; the two metal oxide particles are each one-dimensional nanoparticles.

[0006] According to some preferred embodiments of the present invention, based on the total weight of the oxide / graphene composite material being 100 wt%, the content of graphene is 10-45 wt%, preferably 20-40 wt%, and the total content of the two metal oxides is 55-90 wt%, preferably 60-80 wt%.

[0007] According to some preferred embodiments of the present invention, the molar ratio of the two metal oxides is 0.5-2, preferably 0.9-1.4, based on the molar amount of the metal elements.

[0008] According to some preferred embodiments of the present invention, the metal elements in the metal oxides are selected from two transition metal elements, preferably two of cobalt, manganese, iron, copper, and zinc.

[0009] According to some preferred embodiments of the present invention, the two metal oxide particles are heterogeneously symbiotic.

[0010] According to some preferred embodiments of the present invention, the two metal oxide particles are each olive-shaped one-dimensional nanoparticles. More preferably, the particle size of the two metal oxide particles is each 20-50 nm, and the length is 50-150 nm.

[0011] According to some preferred embodiments of the present invention, the oxide / graphene composite material has a porous foam structure. Preferably, the size of the pores is 2-10 μm.

[0012] According to some preferred embodiments of the present invention, the graphene in the oxide / graphene composite material is nitrogen-doped graphene.

[0013] According to some more preferred embodiments of the present invention, the two metal oxide particles grow in-situ between the layers of the graphene and are heterogeneously symbiotic as olive-shaped one-dimensional nanoparticles.

[0014] According to some more preferred embodiments of the present invention, the oxide / graphene composite material is prepared by a hydrothermal reaction of a mixed solution containing graphene oxide and two gold element sources in a nitrogen-containing precipitating agent, and the obtained product is freeze-dried and sintered under a protective atmosphere.

[0015] According to the present invention, heterogeneous symbiosis refers to the symbiosis of two different oxides. Since each oxide is a phase and each phase is uniform; the two oxides are different phases, that is, non-uniform phases. According to the present invention, by using the symbiosis of two different oxides, when a single oxide A grows, the growth of another oxide B beside it will hinder the further growth of A, and vice versa, when B grows, A will also hinder B; due to this mutual hindrance effect, the oxide particle size becomes smaller, achieving the purpose of optimizing the particle size.

[0016] The second aspect of the present invention is to provide a method for preparing an oxide / graphene composite material, preferably for the method for preparing the oxide / graphene composite material described in the first aspect, including:

[0017] A hydrothermal reaction is carried out on a solution containing graphene oxide and a metal element source in a nitrogen-containing precipitant, and the obtained product is freeze-dried and sintered under a protective atmosphere to obtain the oxide / graphene composite material.

[0018] According to some preferred embodiments of the present invention, the preparation method includes:

[0019] Step 1: Dissolve two metal element sources in a mixed solution containing graphene oxide, add a nitrogen-containing precipitant, and after mixing, it is denoted as solution A;

[0020] Step 2: Carry out a hydrothermal reaction on solution A, then wash the reaction mixture with water, retain the solid, and then freeze-dry to obtain a precursor;

[0021] Step 3: Sinter the obtained precursor under a protective atmosphere to obtain the oxide / graphene composite material.

[0022] According to some preferred embodiments of the present invention, relative to 1 g of graphene oxide, the total amount of the two metal element sources is 15 - 70 mmol, preferably 25 - 50 mmol, such as 25, 30, 35, 40, 45, 50 mmol, and any two values or any interval of any two values. The amounts of the two metal element sources are calculated based on the content of their respective metal elements.

[0023] According to the present invention, the metal elements in the two metal element sources are selected from two transition metal elements, preferably two of cobalt, manganese, iron, copper, and zinc.

[0024] According to some preferred embodiments of the present invention, the molar ratio of the two metal element sources is 0.5 - 2, preferably 0.9 - 1.4, calculated based on the molar amount of the metal elements.

[0025] The present invention has no special requirements for the amount of water in the mixed solution A, and those skilled in the art can flexibly adjust it, including but not limited to: before adding the nitrogen-containing precipitant, the content of graphene oxide in the mixed solution is 0.01-1 wt%, preferably 0.05-0.1 wt%, based on the total amount of water being 100 wt%.

[0026] In the present invention, the function of the nitrogen-containing precipitant is as follows: 1) regulating the solution pH to form a precipitate with the soluble metal salt so as to better form metal oxides later; 2) reacting with graphene oxide to form nitrogen-doped graphene oxide. Therefore, the nitrogen-containing precipitant can have various selections according to the above functions. According to some more preferred embodiments of the present invention, the nitrogen-containing precipitant is selected from at least one of ammonia water, ammonium bicarbonate, and ammonium carbonate.

[0027] According to some preferred embodiments of the present invention, the addition amount of the nitrogen-containing precipitant controls the pH of the mixed solution A between 9 and 12. Preferably, the concentration of the nitrogen-containing precipitant in the mixed solution A is 0.2-4 wt%, preferably 1-2 wt%; and / or, preferably, the nitrogen-containing precipitant is added in the form of a solution. More preferably, when the nitrogen-containing precipitant is ammonia water, the dropping rate of ammonia water is 0.01-2 ml / min, preferably 0.5-1 ml / min.

[0028] The purpose of hydrothermal treatment and sintering in the present invention is to form two in-situ generated metal oxides and simultaneously reduce graphene oxide.

[0029] The hydrothermal reaction of the present invention is carried out in a closed environment (such as a polymerization reaction kettle).

[0030] According to some preferred embodiments of the present invention, in step 2: the reaction temperature is 150-200 °C, and / or the reaction time is 10-15 h.

[0031] According to some preferred embodiments of the present invention, in step 3: the furnace sintering temperature is 400-800 °C, preferably 500-600 °C; and / or the sintering time is 2-8 h, preferably 3-5 h.

[0032] According to some preferred embodiments of the present invention, the metal element source is selected from soluble salts corresponding to the metal elements, preferably at least one of hydrochlorides, sulfates, and nitrates. By way of example, the iron source includes but is not limited to at least one of ferric chloride, ferric sulfate, and ferric nitrate; the cobalt source includes but is not limited to at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate; the manganese source includes but is not limited to at least one of manganese chloride, manganese sulfate, and manganese nitrate.

[0033] According to the present invention, for example, Step 1 can be carried out by the following method: Dissolve two metal element sources in a mixed solution containing graphene oxide. For example, ultrasonic mixing can be carried out, and then a nitrogen-containing precipitating agent is added. After mixing, ultrasonic treatment can be carried out, for example, and it is denoted as mixed solution A.

[0034] In the present invention, the conditions for freeze-drying in Step 2 are conventional operating conditions. For example, it can be placed in a -4°C refrigerator and frozen overnight, and then transferred to a freeze-dryer to be dried for 48 hours.

[0035] In the present invention, the protective atmosphere in Step 3 includes but is not limited to nitrogen and / or inert gas (such as argon).

[0036] According to the present invention, the graphene oxide is prepared by the Hummers method using graphite raw materials (without special requirements), which is the prior art. It includes but is not limited to the following methods: Weigh an appropriate amount of graphite and concentrated sulfuric acid and add them to a beaker and stir for 24 hours. Then add an appropriate amount of NaNO3 and slowly add KMnO4 under the condition close to 0°C. After that, keep it in a water bath at 35°C for a while. Add water and then add H2O2 to the beaker again (at this time, the solution is bright yellow), and let it naturally settle for more than 2 hours. Wash it once with dilute hydrochloric acid and water respectively, and obtain graphene oxide after centrifuging multiple times.

[0037] The third aspect of the present invention is to provide an application of the oxide / graphene composite material described in the first aspect or the oxide / graphene composite material prepared by the preparation method described in the second aspect as an electrode material, preferably as an anode material.

[0038] According to a preferred embodiment of the present invention, the application includes mixing the oxide / graphene composite material with a conductive agent to obtain a slurry, and coating the slurry on a current collector to obtain an electrode sheet. Specifically, the method for preparing the electrode sheet is a conventional means in the prior art, including but not limited to the method described in the embodiments of the present invention: Take out the electrode material and place the sample, acetylene black, and PVDF in a weighing bottle in a ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone and stir for more than 6 hours. Coat the obtained slurry evenly on the copper foil with a coater and place it in an oven at 90°C to dry. Punch holes in the obtained copper foil with a load, and roll it to prepare an electrode sheet cut into a diameter of 1 cm.

[0039] On the basis of the above technical solutions, preferably, the dosage of the electrode material is 100 - 500 mg, preferably 200 - 300 mg; and / or, the dosage of the N-methylpyrrolidone material is 100 - 500 mg, preferably 200 - 300 mg.

[0040] The beneficial effects of the present invention are:

[0041] The oxide / graphene composite material of the present invention has high cycle efficiency and specific capacity, and its rate performance is greatly improved, with high charge-discharge stability; the preparation method of the present invention is simple and fast. More specifically:

[0042] (1) By utilizing the confinement effect between the growth of different metal oxides, on the one hand, the particle size of metal oxides can be optimized, and on the other hand, it can act as a dispersant for each other, reducing particle agglomeration. The particle size distribution of the nanoparticles is uniform and the dispersibility is good, which can better exert the nano characteristics, reduce the transmission distance of lithium ions and electrons, and increase the rate performance.

[0043] (2) Using cheap, easily available, safe and harmless raw materials, the synthesis method is simple and feasible and has universality, and there is no specific limitation on the selection of metal oxide types, so it can be extended to a variety of oxides, which helps to achieve large-scale production.

[0044] (3) The synergistic effect between graphene and metal oxides can, on the one hand, enhance the overall conductivity of the material, and on the other hand, effectively separate the metal oxide particles by means of the space confinement effect of the graphene layer, limit the transmission distance to a single particle, and greatly reduce the transmission path.

[0045] (4) The rate performance of the composite material prepared by the present invention is greatly improved. Even when tested at a current density as high as 10000 mA g -1 -1, after 100 cycles, the reversible capacity can still remain above 94% of the initial capacity. Description of the Drawings

[0046] Figure 1 Electron microscope image of the oxide / graphene composite material in Example 1;

[0047] Figure 2 Electron microscope image of the olive-shaped heterogeneous symbiotic oxide / graphite negative electrode material in Example 1;

[0048] Figure 3 Rate performance test curve of the electrode material in Example 1;

[0049] Figure 4 Electron microscope image of the single oxide / graphene composite electrode material in Comparative Example 1. Detailed Embodiments

[0050] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0051] In the following examples, graphene oxide was synthesized by the Hummers method using purchased graphite raw materials (no special requirements): An appropriate amount of graphite and concentrated sulfuric acid were weighed and added to a beaker, stirred for 24 h, then an appropriate amount of NaNO3 was added, and KMnO4 was slowly added under the condition of approaching 0 °C. After that, it was kept in a water bath at 35 °C for a moment, water was added, and then H2O2 was added to the beaker again (at this time, the solution was bright yellow), and it was allowed to settle naturally for more than 2 h. It was washed once with dilute hydrochloric acid and once with water, and graphene oxide was obtained after centrifugation multiple times.

[0052] The detection method for the content of graphene and metal oxide in the graphene / iron oxide composite is as follows:

[0053] Thermogravimetric method was used for testing. That is, the sample was placed in the sample chamber of a thermogravimetric analyzer, the gas was nitrogen, the gas flow rate was 150 ml / min, heated from room temperature at a heating rate of 10 °C / min, heated to 120 °C, held for 5 minutes, and then heated again at a rate of 10 °C / min to 800 °C and reacted for 5 hours until the reaction ended.

[0054] In the following examples and comparative examples, the pH of the mixed solution obtained in step 1 was between 9 and 12; the reactions in the polymerization reactor in step 2 were all carried out under closed conditions;

[0055] Example 1

[0056] Step 1: 0.16 g of Fe(NO3)3·9H2O, 0.12 g of Co(NO3)2·6H2O, and 0.03 g of graphene oxide were dissolved in 30 ml of water, and then 0.2 ml of concentrated ammonia water was added with a peristaltic pump at a speed of 0.5 ml / min. To ensure the uniformity of this solution, it was appropriately sonicated for 1 h.

[0057] Step 2: The sonicated solution was introduced into a 50 ml polymerization reactor and reacted at 180 °C for 12 h. After the hydrothermal kettle was naturally cooled, it was washed four times with deionized water. The obtained solid was then transferred to a freeze dryer and freeze-dried for 48 h to be fully dried.

[0058] Step 3: The obtained freeze-dried sample was transferred to a tube furnace and sintered at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, the electrode material (i.e., the oxide / graphene composite material) was taken out.

[0059] After testing by electron microscopy as Figure 1As shown, the electrode material has a foamy porous structure; from a spatial perspective, due to the uniform coating of metal oxides by graphene, the structure of the nanoparticles is fully protected. Conversely, because the oxides are embedded in the graphene nanolayers, it is better to exfoliate graphene. That is, in step 2 of the preparation process, metal oxides grow on graphene, so it is equivalent to separating graphene layers one by one. Exfoliating graphene, single-layer graphene or graphene with fewer layers has better electrical conductivity and mechanical properties. It not only maintains the abundant nanopores in graphene but also increases the lithium-ion transport channels at the macroscopic level, thus greatly increasing the lithium storage sites and improving the energy storage capacity.

[0060] Through further electron microscopy analysis such as Figure 2 , olive-shaped metal oxide particles are uniformly dispersed in the graphite layer. The nanoparticle sizes are relatively uniform, with a particle size of about 30 nm and a length in the range of 80 - 120 nm. This unique morphology mainly comes from the synergistic effect between graphene and nanoparticles and between different types of oxides. The two oxides act as each other's dispersants and restrictors, which can reduce the agglomeration between particles and further reduce the nanoparticle size. In addition, since the metal oxides grow in-situ within the graphene interlayers, their growth space is restricted within the graphene protective layer, which will cause two or more particles to fuse, thus becoming a long and narrow nanostructure.

[0061] Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 21 wt%, and the total content of the two metal oxides is 79 wt%.

[0062] Place 100 mg of the electrode material, the sample, acetylene black, and PVDF in a weighing bottle according to a ratio of 8:1:1, add 100 mg of an appropriate amount of N-methylpyrrolidone, and stir for more than 6 h. Then, uniformly coat the obtained slurry on the copper foil with a coater and place it in an oven at 90 °C to dry. Punch holes in the obtained copper foil-coated sheet and roll it to prepare an electrode sheet cut into a diameter of 1 cm.

[0063] Example 2

[0064] Step 1: Take 0.16 g of Fe(NO3)3·9H2O, 0.11 g of Mn(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, use a peristaltic pump to add 0.2 ml of concentrated ammonia water at a speed of 0.5 ml / min. To ensure the uniformity of this solution, ultrasonicate it appropriately for 1 h.

[0065] Step 2: Transfer the ultrasonically treated solution into a 50 ml polymerization reactor and react at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, and then transfer it to a freeze dryer to freeze-dry for 48 h to ensure complete drying.

[0066] Step 3 Transfer the obtained freeze-dried sample to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, take out the electrode material.

[0067] Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 20 wt%, and the total content of the two metal oxides is 80 wt%.

[0068] Example 3

[0069] Step 1 Take 0.12 g of Co(NO3)3·6H2O, 0.11 g of Mn(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, use a peristaltic pump to add 0.2 ml of concentrated ammonia water at a speed of 0.5 ml / min. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0070] Step 2 Transfer the sonicated solution into a 50 ml polymerization reactor and react it at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, and then transfer it to a freeze-dryer and freeze-dry it for 48 h to dry it thoroughly.

[0071] Step 3 Transfer the obtained freeze-dried sample to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, take out the electrode material. Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 21 wt%, and the total content of the two metal oxides is 79 wt%.

[0072] Example 4

[0073] Step 1 Take 0.3 g of Fe(NO3)3·9H2O, 0.22 g of Co(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, use a peristaltic pump to add 0.5 ml of concentrated ammonia water at a speed of 0.5 ml / min. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0074] Step 2 Transfer the sonicated solution into a 50 ml polymerization reactor and react it at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, and then transfer it to a freeze-dryer and freeze-dry it for 48 h to dry it thoroughly.

[0075] Step 3 Transfer the obtained freeze-dried sample to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, take out the electrode material. Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 11 wt%, and the total content of the two metal oxides is 89 wt%.

[0076] Example 5

[0077] Step 1: Take 0.3 g of Fe(NO3)3·9H2O, 0.2 g of Mn(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, add 0.5 ml of concentrated ammonia water at a rate of 0.5 ml / min using a peristaltic pump. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0078] Step 2: Transfer the sonicated solution into a 50-ml polymerization reactor and react it at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, and then transfer it to a freeze dryer and freeze-dry it for 48 h to ensure thorough drying.

[0079] Step 3: Transfer the obtained freeze-dried sample into a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, take out the electrode material. Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 10 wt%, and the total content of the two metal oxides is 90 wt%.

[0080] Example 6

[0081] Step 1: Take 0.22 g of Co(NO3)2·6H2O, 0.2 g of Mn(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, add 0.5 ml of concentrated ammonia water at a rate of 0.5 ml / min using a peristaltic pump. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0082] Step 2: Transfer the sonicated solution into a 50-ml polymerization reactor and react it at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, and then transfer it to a freeze dryer and freeze-dry it for 48 h to ensure thorough drying.

[0083] Step 3: Transfer the obtained freeze-dried sample into a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere. After cooling to room temperature, take out the electrode material. Based on the total weight of the oxide / graphene composite being 100 wt%, the content of graphene is 10 wt%, and the total content of the two metal oxides is 90 wt%.

[0084] It has been verified that by using the hydrothermal reaction conditions and sintering conditions described in the present invention, electrode materials with performance similar to those of the examples can be obtained.

[0085] Comparative Example 1

[0086] Step 1: Take 0.16 g of Fe(NO3)3·9H2O and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water at a rate of 0.5 ml / min using a peristaltic pump. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0087] Step 2: Introduce the solution after ultrasonic treatment into a 50 ml polymerization reactor, react at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, then transfer it to a freeze dryer and freeze-dry for 48 h to ensure complete drying.

[0088] Step 3: Transfer the obtained freeze-dried sample to a tube furnace, sinter it at 500 °C for 3 h under a nitrogen atmosphere, and take out the electrode material after cooling to room temperature.

[0089] Comparative Example 2

[0090] Step 1: Take 0.16 g of Co(NO3)3·6H2O and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, use a peristaltic pump to add 0.2 ml of concentrated ammonia water at a rate of 0.5 ml / min. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0091] Step 2: Introduce the solution after ultrasonic treatment into a 50 ml polymerization reactor, react at 180 °C for 12 h. After the hydrothermal reactor cools naturally, wash it four times with deionized water, then transfer it to a freeze dryer and freeze-dry for 48 h to ensure complete drying.

[0092] Step 3: Transfer the obtained freeze-dried sample to a tube furnace, sinter it at 500 °C for 3 h under a nitrogen atmosphere, and take out the electrode material after cooling to room temperature.

[0093] Comparative Example 3

[0094] Step 1: Take 0.16 g of Fe(NO3)3·9H2O, 0.12 g of Co(NO3)2·6H2O, and 0.03 g of graphene oxide and dissolve them in 30 ml of water. Then, use a peristaltic pump to add 0.2 ml of concentrated ammonia water at a rate of 0.5 ml / min. To ensure the uniformity of this solution, sonicate it appropriately for 1 h.

[0095] Step 2: Mechanically stir the solution after ultrasonic treatment for 4 hours, then place it in the refrigerator and freeze overnight. Then, transfer it to a freeze dryer and freeze-dry for 48 h to ensure complete drying.

[0096] Step 3: Transfer the obtained freeze-dried sample to a tube furnace, sinter it at 500 °C for 3 h under a nitrogen atmosphere, and take out the electrode material after cooling to room temperature.

[0097] After testing, the obtained electrode material is different from the electrode material in the example. In the electrode material of Comparative Example 3, the metal oxide does not grow in-situ on the graphene, but shows a large-area agglomerated state and is dispersed on the surface of the graphene. Moreover, the metal oxide particles are zero-dimensional spherical, with a particle size between 300 - 400 nm.

[0098] It has been verified that the morphologies of the electrode materials in Examples 2-6 of the present invention are similar to that in Example 1. The bimetallic oxide particles are one-dimensional olive-shaped nanoparticles, with particle sizes all within 20-50 nm and the lengths of the one-dimensional nanoparticles all within 50-150 nm.

[0099] The metal oxide in the electrode material in the embodiments of the present invention is one-dimensional particles (olive-shaped). Compared with zero-dimensional particles (Comparative Example 2 and Comparative Example 3), it has a larger specific surface area, thereby increasing the contact area between the active material and the electrolyte and increasing the lithium storage capacity. This unique morphology mainly results from the interaction between graphene and nanoparticles. Since the metal oxide in the embodiments of the present invention grows in situ within the graphene interlayer, its growth space is restricted within the graphene protective layer, which will cause two or more particles to fuse, thus becoming a long and narrow nanostructure. Such a structure directly proves that the metal oxide particles grow in situ in graphene, different from the composite nanomaterials prepared by the traditional mechanical mixing method (Comparative Example 3).

[0100] Application Example

[0101] The electrode materials in the examples and comparative examples were prepared into electrode sheets according to the following method:

[0102] 100 mg of the electrode material, the sample, acetylene black, and PVDF were placed in a weighing bottle according to a ratio of 8:1:1, and 100 mg of N-methylpyrrolidone was added and stirred for more than 6 h. The obtained slurry was evenly coated on a copper foil with a coater and placed in an oven at 90 °C for drying. The obtained copper foil with the load was punched and roll-pressed to prepare an electrode sheet cut into a diameter of 1 cm.

[0103] The battery test procedures for the examples and Comparative Examples 1-3 were as follows: After assembling the electrode sheets into 2032-type button batteries, electrochemical tests were carried out. The electrolyte used in the tests was 1 mol L -1 Lithium hexafluorophosphate was dissolved in ethylene carbonate:diethyl carbonate with a mass ratio of 1:1. The test separator was Celgard 2400. In the battery test, the electrode sheet was used as the positive electrode, and a lithium sheet was used as the counter electrode. The test was carried out at room temperature. The assembled button battery was first subjected to charge-discharge tests in a BlueTEC test system to verify the rate performance.

[0104] The charge-discharge test method was as follows: The test separator was Celgard 2400, and the test was carried out at room temperature. The assembled button battery was first subjected to charge-discharge tests in a BlueTEC test system (Wuhan BlueTEC Electronic Co., Ltd.) to verify its rate and long-cycle performance. The test voltage range was 0.01-3.00 V, and the current density was 100-5000 mA g -1between. Cyclic voltammetry tests were performed using an Autolab PGSTAT302N electrochemical workstation. The voltage range for cyclic voltammetry tests was 0 - 3V, and the scan rate was 0.1 mV s -1 .

[0105] To verify the cycling efficiency and long - term cycling performance, the current density was 100 mA g -1 The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] The rate performance test of the electrode material in Example 1 is shown in Figure 3 Even when the current density is as high as 5000 mA g -1 and 10000 mA g -1 , the reversible capacity can still be as high as 695 mA h g -1 and 567 mA h g -1 , which is much higher than the theoretical specific capacity of commercial graphite anode materials. Except for the first cycle, the charge - discharge cycling efficiency of the following cycles is close to 100%, indicating good structural stability of this sample.

[0110] It has been verified that the rate performance of the electrode materials prepared in the examples of the present invention has been greatly improved. Even when tested at a current density as high as 10000 mA g -1 , after 100 cycles, the reversible capacity still remains above 94% of the initial capacity.

[0111] In summary, the oxide / graphene composite material of the present invention has high cycling efficiency and specific capacity, and its rate performance has been greatly improved, with high charge - discharge stability; the preparation method of the present invention is simple and fast.

[0112] It should be noted that the above - described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as specified, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

[0113] All publications, patent applications, patents, and other references mentioned in this specification are hereby incorporated by reference in their entirety. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by one of ordinary skill in the art. In case of conflict, the definitions in this specification shall prevail.

[0114] When this specification uses prefixes such as "known to those skilled in the art", "prior art", or similar terms to introduce materials, substances, methods, steps, devices, or components, etc., the objects introduced by such prefixes cover those commonly used in the art at the time when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as suitable for similar purposes.

[0115] In the ranges disclosed in this application document, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following, in principle, various technical solutions can be combined with each other to obtain new technical solutions, and this should also be regarded as specifically disclosed herein.

[0116] In the context of this specification, any matter or thing not mentioned, except as expressly stated, shall directly apply those known in the art without any change.

[0117] Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas thus formed shall be regarded as part of the original disclosure or original record of the present invention, and shall not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider such combination to be obviously unreasonable.

Claims

1. An oxide / graphene composite material, comprising graphene and two metal oxide particles dispersed in the graphene; the two metal oxide particles are each one-dimensional nanoparticles.

2. The oxide / graphene composite material according to claim 1, wherein: Based on the total weight of the oxide / graphene composite material being 100 wt%, the content of the graphene is 10 - 45 wt%, preferably 20 - 40 wt%, and the total content of the two metal oxides is 55 - 90 wt%, preferably 60 - 80 wt%.

3. The oxide / graphene composite material according to claim 1, wherein: The molar ratio of the two metal oxides is 0.5 - 2, preferably 0.9 - 1.4, based on the molar amount of the metal element; and / or, The metal element in the metal oxide is selected from two transition metal elements, preferably two of cobalt, manganese, iron, copper, and zinc.

4. The oxide / graphene composite material according to claim 1, wherein: The two metal oxide particles are heterogeneously symbiotic; and / or, The two metal oxide particles are each olive-shaped one-dimensional nanoparticles, preferably, the particle size of the two metal oxide particles is each 20 - 50 nm, and the length is 50 - 150 nm; and / or, The oxide / graphene composite material has a porous foam structure, preferably, the pore size is 2 - 10 μm; and / or, The graphene in the oxide / graphene composite material is nitrogen-doped graphene.

5. The oxide / graphene composite material according to any one of claims 1 - 4, wherein: The two metal oxide particles grow in-situ between the layers of the graphene and are heterogeneously symbiotic as olive-shaped one-dimensional nanoparticles; preferably, The oxide / graphene composite material is prepared by subjecting a mixed solution containing graphene oxide and two metal element sources to a hydrothermal reaction in a nitrogen-containing precipitating agent, and the obtained product is freeze-dried and sintered under a protective atmosphere.

6. A method for preparing an oxide / graphene composite material, preferably a method for preparing the oxide / graphene composite material according to any one of claims 1 - 5, comprising: Subjecting a solution containing graphene oxide and a metal element source to a hydrothermal reaction in a nitrogen-containing precipitating agent, and the obtained product is freeze-dried and sintered under a protective atmosphere to obtain the oxide / graphene composite material.

7. The preparation method according to claim 6, characterized in that The preparation method comprises: Step 1: Dissolve two metal element sources in a mixed solution containing graphene oxide, add a nitrogen-containing precipitating agent, and after mixing, denote it as solution A; Step 2: Subject solution A to a hydrothermal reaction, then wash the reaction mixture with water, retain the solid, and then freeze-dry to obtain a precursor; Step 3: Sinter the obtained precursor under a protective atmosphere to obtain the oxide / graphene composite material.

8. The preparation method according to claim 7, wherein: In step 1: The total amount of the two metal element sources is 15 - 70 mmol, preferably 25 - 50 mmol, based on the content of each metal element, relative to 1 g of graphene oxide; and / or, The molar ratio of the two metal element sources is 0.5 - 2, preferably 0.9 - 1.4, based on the molar amount of the metal elements; and / or, The nitrogen-containing precipitant is selected from at least one of ammonia water, ammonium bicarbonate, and ammonium carbonate; and / or, The addition amount of the nitrogen-containing precipitant is such that the pH of the mixed solution A is controlled between 9 and 12.

9. The preparation method according to claim 7, wherein: In step 2: the reaction temperature is 150 - 200 °C, and / or, the reaction time is 10 - 15 h; and / or, In step 3: the furnace sintering temperature is 400 - 800 °C, preferably 500 - 600 °C; and / or, the sintering time is 2 - 8 h, preferably 3 - 5 h.

10. The preparation method according to claim 7, wherein: The graphene oxide is prepared by the Hummers method; and / or, The two metal element sources are selected from the soluble salts of the two metal elements respectively, preferably at least one of hydrochlorides, sulfates, and nitrates.

11. Application of the oxide / graphene composite material according to any one of claims 1 - 5 or the oxide / graphene composite material prepared by the preparation method according to any one of claims 6 - 10 as an electrode material, preferably as a negative electrode material; preferably, It includes mixing the oxide / graphene composite material with a conductive agent to obtain a slurry, and coating the slurry on a current collector to obtain an electrode sheet.

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