Self-supporting high-energy-density electrode material and preparation method and application thereof

Abstract

The invention belongs to the field of electrode materials, and discloses a self-supporting high-energy-density electrode material and a preparation method and application thereof. The electrode material is flaky and is prepared by laminating a graphene compound, and the graphene compound comprises lamellar graphene and a metal oxide dispersed in the graphene lamellar layer; when the total weight of the electrode material is 100 wt%, the content of the graphene is 15-40 wt%, and the content of the metal oxide is 60-85 wt%; the total content of carboxylic acid groups and phenolic hydroxyl groups in the graphene compound is not less than 0.01 mol / g. The electrode material provided by the invention avoids the use of a binder, a conductive agent and a current collector, has relatively high mass density and energy density, and also has relatively high rate capability and cycle performance of the battery. After the electrode plate obtained by the method is further crushed, the self-supporting plate can be obtained again after the electrode plate is extruded again, namely, the electrode material also has processability and reusability.

Description

Technical Field

[0001] The present invention belongs to the field of electrode materials, and relates to a self-supporting high-energy density electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] The non-renewability of fossil energy and serious air pollution have led to an urgent need for clean energy as an alternative energy solution. As one of the optimal commercialized energy storage solutions today, the improvement of the mass and volume energy density of the positive and negative electrode materials of lithium-ion batteries is the main focus of lithium-ion battery research. In addition, the development of lithium-ion batteries towards miniaturization, flexibility, and curvature to meet the growing demands of wearable devices and curved 3C (computer, communication & consumer electronics) electronic devices has gradually become a research hotspot among vast scientific researchers.

[0003] For traditional commercial lithium-ion battery systems, the battery manufacturing method involves stirring active materials with binders and conductive agents such as carbon black and carbon nanotubes, and then coating them on current collectors such as aluminum foil (positive electrode) and copper foil (negative electrode). The addition amount of the conductive agent is generally less than 10% because it does not contribute to the capacity. Excessive addition of the conductive agent will only lead to a decrease in the mass energy density of the electrode. The use of non-conductive binders will exacerbate the polarization phenomenon of the active materials. At the same time, due to the potential possibility of side reactions caused by their presence, the binders have an adverse impact on the electrochemical performance of lithium-ion batteries. In addition, since binders are generally polymer materials, their operating temperature is also limited. Current collectors are the skeletons that support the electrode structure. Copper foil and aluminum foil have good electrical conductivity and are good solutions for current collectors. However, the use of current collectors will increase the electrode mass (10-15%), thereby reducing the mass energy density of the electrode. In recent years, studies have shown that self-supporting flexible electrodes can replace the traditional coating method to improve battery performance. The skeleton of flexible electrodes generally adopts a three-dimensional conductive network, which can directly support active electrode materials. During the preparation of flexible electrodes, the use of binders, conductive agents, and current collectors can be avoided, greatly reducing the proportion of inactive materials and avoiding the negative impacts of the addition of the above materials on the mass energy density and the electrochemical performance of the battery, and the electrochemical performance can be further improved. Patent document CN112151766A uses a vacuum filtration method to prepare a multi-layer flexible electrode using carbon nanotubes and electrode materials. The electrode has extremely strong flexibility, can be bent arbitrarily, and can integrate multiple layers of electrodes at the same time, doubling the areal capacity of the electrode. However, a binder needs to be added between the multi-layer electrode sheets and the electrode thickness is large, weakening the cycling performance of the battery. Patent document CN114242951A uses a magnetically assisted supersonic flame spraying technique to spray an iron oxide-graphene composite powder onto the surface of a copper substrate to obtain an iron oxide-graphene composite coating electrode sheet. The electrode obtained by this method is not easily pulverized and exhibits good electrochemical performance. However, this flexible electrode still uses a copper current collector, reducing the total mass of the battery, bringing negative impacts and involving relatively expensive instrument equipment, resulting in high production costs.

[0004] A method that truly avoids the use of binders, conductive agents, and current collectors and can prepare flexible electrodes with large area and low cost is still rarely reported. At present, a method that can rapidly fabricate flexible electrodes with large area and low cost remains a great challenge. Summary of the Invention

[0005] In view of the limitations of existing preparation methods, the present invention aims to obtain a high-capacity electrode material with a self-supporting structure by means of a new, rapid and convenient preparation method. The electrode material of the present invention avoids the use of binders, conductive agents and current collectors, and can improve the specific capacity per unit electrode mass. At the same time, the extrusion preparation method can combine cutting and punching to customize self-supporting flexible electrode sheets according to different sizes. The electrode material with a self-supporting structure of the present invention has a relatively high mass density and energy density, and also has relatively high battery rate performance and cycling performance. After the electrode sheets obtained by this method are further crushed and then extruded again, self-supporting sheets can be obtained again, that is, this electrode material also has processability and reusability.

[0006] The first aspect of the present invention is to provide an electrode material. The electrode material is in sheet form and is prepared by pressing a graphene composite. The graphene composite includes sheet-like graphene and metal oxides dispersed in the graphene sheets; based on the total weight of the electrode material being 100 wt%, the content of graphene is 15-40 wt%, and the content of metal oxides is 60-85 wt%; the total content of carboxyl groups and phenolic hydroxyl groups in the graphene composite is not less than 0.01 mol / g.

[0007] The inventors of the present invention have found through research that: common composites of graphene and metal oxides that can be used as electrode materials cannot obtain electrode sheets by direct pressing. Because whether a self-supporting electrode sheet can be obtained is mainly related to the reduction degree of graphene oxide and the mass ratio of graphene and metal oxides in the composite material. At the same time, these are also closely related to the energy density of the electrode sheet, the battery rate performance and the cycling performance. When the content of graphene and metal oxides in the electrode material is within this range and the total content of carboxyl groups and phenolic hydroxyl groups is within the above range, the present invention can obtain an electrode material with a self-supporting structure, and has a relatively high mass density and energy density, and also has relatively high battery rate performance and cycling performance.

[0008] According to some preferred embodiments of the present invention, the total content of carboxyl groups and phenolic hydroxyl groups in the graphene composite is 0.01-0.05 mol / g, preferably 0.02-0.04 mol / g, such as 0.02, 0.025, 0.03, 0.035, 0.04 mol / g, and any two values or any interval of any two values. In this preferred embodiment, the mass density and energy density of the electrode material are further improved, and the battery rate performance and cycling performance are also greatly improved.

[0009] According to some preferred embodiments of the present invention, the graphene in the graphene composite is nitrogen-doped graphene.

[0010] According to some preferred embodiments of the present invention, before pressing, the graphene composite has a porous structure. Preferably, the pore size is 3 - 10 μm, and / or, before pressing, the graphene composite has a foamy shape.

[0011] According to some preferred embodiments of the present invention, based on the total weight of the electrode material being 100 wt%, the content of graphene is 25 - 40 wt%, such as 25, 30, 35, 40 wt%, as well as any two values or any interval of any two values, and the content of the metal oxide is 60 - 75 wt%, such as 60, 65, 70, 75 wt%, as well as any two values or any interval of any two values. In this preferred embodiment, the mass density and energy density of the electrode material are further improved, and the battery rate performance and cycling performance are also greatly enhanced.

[0012] According to some preferred embodiments of the present invention, the thickness of the electrode material is 0.1 - 0.8 mm, preferably 0.3 - 0.5 mm.

[0013] According to some preferred embodiments of the present invention, the graphene composite self - bonds under external pressure to obtain the electrode material; preferably, the electrode material is a self - supporting flexible electrode sheet; more preferably, the electrode material does not contain a binder, a conductive agent, and a current collector.

[0014] According to the present invention, the metal element of the metal oxide can be selected within a relatively wide range. In a preferred embodiment of the present invention, the metal element of the metal oxide is a transition metal element; preferably, the transition metal element is selected from active metal elements for batteries, and more preferably, the transition metal element includes at least one of iron, cobalt, and manganese.

[0015] According to some preferred embodiments of the present invention, the preparation method of the electrode material includes: subjecting a mixed solution containing graphene oxide and a metal element source to a hydrothermal reaction in the presence of a nitrogen - containing precipitant, freeze - drying the obtained product, and sintering it under a protective atmosphere to obtain a graphene composite; pressing the graphene composite into a sheet to obtain the electrode material.

[0016] The second aspect of the present invention is to provide a preparation method of an electrode material, preferably for the preparation method of the electrode material described in the first aspect, including: subjecting a mixed solution containing graphene oxide and a metal element source to a hydrothermal reaction in the presence of a nitrogen - containing precipitant, freeze - drying the obtained product, and sintering it under a protective atmosphere to obtain a graphene composite; pressing the graphene composite into a sheet to obtain the electrode material.

[0017] The present invention effectively composites graphene with the active material of a lithium-ion battery in a self-supporting manner. After hydrothermal synthesis, freeze-drying treatment, and sintering, the foam electrode is pressed into tablets by "one-step extrusion". Graphene oxide is reduced during hydrothermal synthesis and sintering. The interaction between the small amount of residual derivative carboxylic acid groups and phenolic hydroxyl groups on the reduced graphene oxide (foam electrode material) and the intermolecular π-π force are like glue. With the help of a strong external force (extrusion force), the foam electrode material can be connected to obtain a paper-like self-supporting electrode sheet. This process avoids the use of binders, conductive agents, and current collectors, and can significantly improve the specific capacity per unit electrode mass.

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

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

[0020] Step 2: Perform a hydrothermal reaction on mixed solution A. For example, react in a polymerization reaction kettle, and then wash the reaction mixture with water, for example, wash 3-4 times, and retain the precipitate, which is denoted as product B;

[0021] Step 3: Lyophilize product B, and then sinter it under a protective atmosphere to obtain a foam-like solid C; the foam-like solid C is a graphene composite;

[0022] Step 4: Press the foam-like solid C into a sheet.

[0023] According to some more preferred embodiments of the present invention, in step 1: relative to 1 g of graphene oxide, the dosage of the metal element source is 8-50 mmol, preferably 10-40 mmol, such as 10, 15, 20, 25, 30, 35, 40 mmol, and any two values or any interval of any two values. The dosage of the metal element source is calculated based on the content of the metal element.

[0024] The present invention has no special requirements for the dosage of water in 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%.

[0025] In the present invention, the role of the nitrogen-containing precipitant is: 1) regulate the solution pH to form a precipitate with the soluble metal salt; 2) react with graphene oxide to form nitrogen-doped graphene oxide. Therefore, there are various choices for the nitrogen-containing precipitant according to the above roles. 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.

[0026] According to some more preferred embodiments of the present invention, the addition amount of the nitrogen-containing precipitant is such that the pH of the mixed solution A is controlled between 9 and 11. Further more preferably, the concentration of the nitrogen-containing precipitant in the mixed solution A is 0.1-3 wt%, preferably 0.5-1 wt%, and / or, further more preferably, the nitrogen-containing precipitant is added in the form of a solution. Preferably, when the nitrogen-containing precipitant is ammonia water, the dropping rate of the ammonia water is 0.01-2 ml / min, preferably 0.5-1 ml / min.

[0027] 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. The hydrothermal reaction of the present invention is carried out in a closed environment (such as a polymerization reaction kettle).

[0028] According to some preferred embodiments of the present invention, in step 3: the sintering temperature is 400-800 °C, preferably 500-600 °C; and / or, the sintering time is 2-8 h, preferably 3-5 h.

[0029] According to some preferred embodiments of the present invention, in step 4, a roll press is used for pressing. Preferably, the gap of the roll press is 0.1-0.8 mm, preferably 0.3-0.5 mm. A paper-like electrode is obtained by one-step extrusion. A self-supporting high-capacity electrode sheet can be obtained by cutting.

[0030] The weight of the electrode sheet can be freely controlled according to the thickness of the roll press, and it is applicable to various positive and negative electrode materials of lithium batteries, that is, this preparation method has processability and reusability.

[0031] According to the present invention, by way of example, step 1 can be carried out by the following method: dissolving a metal element source in a mixed solution containing graphene oxide, for example, ultrasonic mixing can be carried out, and then a nitrogen-containing precipitant is added. After mixing, for example, ultrasonic treatment can be carried out, which is denoted as mixed solution A.

[0032] In the present invention, the conditions for freeze-drying in step 3 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 h.

[0033] The protective atmosphere in step 3 includes but is not limited to nitrogen and / or inert gas (such as argon).

[0034] According to the present invention, the graphene oxide is produced from graphite raw material (no special requirements) using the Hummers method, which is a prior art method. This method includes, but is not limited to, the following: weighing an appropriate amount of graphite and concentrated sulfuric acid into a beaker, stirring for 24 hours, adding an appropriate amount of NaNO3, and then slowly adding KMnO4 at a temperature close to 0°C. The mixture is then briefly placed in a 35°C water bath, followed by the addition of water and then H2O2 to the beaker (the solution is now bright yellow), and allowed to settle naturally for at least 2 hours. The mixture is then washed once with dilute hydrochloric acid and once with water, and centrifuged multiple times to obtain the graphene oxide.

[0035] According to some preferred embodiments of the present invention, the metal element source is selected from a soluble salt of the corresponding metal element, preferably at least one of a hydrochloride, a sulfate, and a nitrate. For 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; and the manganese source includes but is not limited to at least one of manganese chloride, manganese sulfate, and manganese nitrate.

[0036] The present invention uses a one-step extrusion method to prepare electrode sheets. The principle of the present invention is that through the ratio and method of the present invention, hydrothermal reaction and post-sintering thermal reduction are adopted to greatly reduce the functional groups on graphene oxide (foam-like composite material), and the interaction between the small amount of residual derivative carboxylic acid groups and phenolic hydroxyl groups and the intermolecular π-π force is like glue. With the help of strong external force, the freeze-dried foam-like composite material is connected to obtain paper-like electrode sheets. This simple production method overcomes the cumbersome preparation steps of traditional electrode production methods, avoids the use of binders and conductive carbon black, thereby reducing the weight of the electrode and increasing the energy density. The present invention not only prepares electrode sheets (i.e., self-supporting electrode materials) by a one-step extrusion method, but also the self-supporting electrode material obtained by the present invention has a higher energy density. In particular, under the preferred hydrothermal reaction and sintering conditions of the present invention, the self-supporting electrode material obtained has a better energy density, higher cycle efficiency and specific capacity.

[0037] The one-step extrusion method is the first of its kind in this invention. Other patents use traditional coating methods, which are cumbersome, result in heavy electrode sheets, and low energy density. For example, the electrode sheet described in CN101982408A is manufactured using this traditional method. Furthermore, CN101982408A uses hydrazine hydrate for reduction, which is highly toxic and unsuitable for large-scale production, industrial use, or use in biomedicine. The self-supporting electrode material and preparation method of this invention achieve unexpected technical results and possess extremely high application value.

[0038] The third aspect of the present invention is to provide an application of the electrode material described in the first aspect or the electrode material obtained by the preparation method described in the second aspect in a battery;

[0039] According to some preferred embodiments of the present invention, it is preferably used as an electrode sheet in a battery.

[0040] According to some preferred embodiments of the present invention, preferably, the battery is a lithium-ion battery.

[0041] The beneficial effects of the present invention are as follows:

[0042] (1) The self-supporting electrode sheet of the present invention has a relatively high mass density and energy density, and the battery rate performance and cycle performance are also relatively high. The self-supporting electrode sheet prepared by the present invention has a significantly reduced weight, which can effectively increase the energy density by 20 - 30%. At a current density of 1000 mA g -1 , the capacity can still remain above 1000 mA h g after 500 cycles, having relatively high charge-discharge cycle stability. -1

[0043] (2) The preparation method is simple and fast, overcoming the cumbersome preparation steps of the traditional electrode manufacturing method, and avoiding the use of binders, conductive carbon black, and current collectors. Only through simple extrusion by a roller press, a self-supporting paper-like electrode sheet (electrode material) can be obtained.

[0044] (3) After the electrode sheet prepared by the extrusion method is crushed, it can be extruded again to re-prepare a complete electrode sheet, that is, this method has the property of being processable and recyclable. The scraps cut from the original electrode material can also be processed by this preparation method for secondary roller pressing into sheets, avoiding the waste of composite materials.

[0045] (4) The weight of the electrode sheet can be freely controlled according to the thickness of the roller press, and it is applicable to various anode and cathode materials of lithium batteries, that is, this preparation method has the property of being processable and recyclable. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1a , Figure 1b , Figure 1c are electron micrographs of the graphene / iron oxide composite in Example 1;

[0047] Figure 2 is a schematic diagram of the electrode preparation process by the extrusion method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] 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 used for further illustration of the present invention and should not 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.

[0049] In the following examples, graphene oxide was synthesized by the Hummers method using purchased graphite raw materials (without special requirements): An appropriate amount of graphite and concentrated sulfuric acid were weighed and added to a beaker and stirred for 24 h. Then, an appropriate amount of NaNO3 was added, and KMnO4 was slowly added under conditions close to 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.

[0050] In the following examples, the Boehm titration method was used to detect the contents of carboxylic groups and phenolic hydroxyl groups: Sodium bicarbonate (NaHCO3) only undergoes a neutralization reaction with the carboxyl groups on the surface of the graphene powder material, sodium carbonate (Na2CO3) can undergo a neutralization reaction with the carboxyl groups and lactone groups on the surface, and sodium hydroxide (NaOH) can undergo a neutralization reaction with the carboxyl groups, lactone groups and phenolic hydroxyl groups on the surface.

[0051] The detection methods for the content of graphene and the content of metal oxides in the graphene / iron oxide composite are as follows:

[0052] Thermogravimetric analysis was performed. 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, it was heated from room temperature, the heating rate was 10 °C / min, it was 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.

[0053] In the following examples and comparative examples, the reactions in the polymerization reactor in step 2 were all carried out under closed conditions.

[0054] Example 1

[0055] Step 1: 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O were dissolved in 30 ml of water. Then, 0.2 ml of concentrated ammonia water was added using a peristaltic pump at a speed of 0.5 ml / min, and it was sonicated appropriately for 1 h, denoted as mixture A (pH 9 - 11).

[0056] Step 2: Mixture A was transferred to a 50 ml polymerization reactor and reacted at 180 °C for 12 h. After taking it out, it was washed 3 - 4 times with deionized water, denoted as product B.

[0057] Step 3: Product B was placed in a -4 °C refrigerator and frozen overnight, then transferred to a freeze dryer and dried by suction for 48 h, and then transferred to a tube furnace and sintered at 500 °C in a nitrogen atmosphere for 3 h to obtain a foamy solid C (i.e., the graphene / iron oxide composite).

[0058] The morphology was observed by electron microscopy as Figure 1aAs shown, macropores with a size of about 5 μm are evenly distributed in three-dimensional graphene. Compared with traditional two-dimensional graphene, it not only retains the abundant nanopores in graphene but also increases the lithium-ion transport channels at the macroscopic level, thereby greatly increasing the lithium storage sites and improving the energy storage capacity. Through further electron microscopy analysis ( Figure 1b and 1c ), metal oxide particles are evenly dispersed in the graphite layer.

[0059] Taking the total weight of the foamy solid C as 100 wt%, the content of the graphene is 33 wt%, and the content of the metal oxide is 67 wt%.

[0060] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.03 mol / g.

[0061] Step 4: Take 50 mg of the foam electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode (i.e., the electrode material) can be obtained by one-step extrusion. After cutting into a disc with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0062] As Figure 2 shown, through mechanical extrusion by the roll press, the paper-like electrode sheet can be obtained in one step. This simple manufacturing method overcomes the cumbersome preparation steps of the traditional electrode manufacturing method and avoids the use of binders and conductive carbon black, thereby reducing the electrode weight and increasing the energy density.

[0063] Example 2

[0064] Step 1: Dissolve 0.03 g of graphene oxide and 0.16 g of Co(NO3)2·6H2O in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water at a speed of 0.5 ml / min using a peristaltic pump, and ultrasonicate appropriately for 1 h, denoted as mixture A (pH is 9 - 11).

[0065] Step 2: Transfer mixture A to a 50 ml polymerization reaction kettle and react at 180 °C for 12 h. After taking it out, wash it 3 - 4 times with deionized water, denoted as product B.

[0066] Step 3: Place product B in a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tubular furnace and sinter it at 500 °C for 3 h in a nitrogen atmosphere to obtain a foamy solid C (i.e., graphene / cobalt oxide composite).

[0067] Step 4: Take 50 mg of the foam electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained by one-step extrusion. After cutting into a disc with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0068] Example 3

[0069] Step 1: Take 0.03 g of graphene oxide and 0.16 g of Mn(NO3)2·6H2O and dissolve them in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water to it with a peristaltic pump at a speed of 0.5 ml / min, and then ultrasonicate it appropriately for 1 h, which is recorded as mixture A.

[0070] Step 2: Transfer mixture A to a 50-ml polymerization reactor and react it at 180 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, which is recorded as product B.

[0071] Step 3: Put product B into a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tubular furnace and sinter it at 500 °C for 3 h in a nitrogen atmosphere to obtain a foamy solid C (i.e., graphene / manganese oxide composite).

[0072] Step 4: Take 50 mg of the foamy electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained by one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0073] Example 4

[0074] Step 1: Take 0.03 g of graphene oxide and 0.3 g of Fe(NO3)3·6H2O and dissolve them in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water to it with a peristaltic pump at a speed of 0.5 ml / min, and then ultrasonicate it appropriately for 1 h, which is recorded as mixture A (pH is 9 - 11).

[0075] Step 2: Transfer mixture A to a 50-ml polymerization reactor and react it at 180 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, which is recorded as product B.

[0076] Step 3: Put product B into a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tubular furnace and sinter it at 500 °C for 3 h in a nitrogen atmosphere to obtain a foamy solid C.

[0077] Taking the total weight of the foamy solid C as 100 wt%, the content of the graphene is 25 wt%, and the content of the metal oxide is 75 wt%.

[0078] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.025 mol / g.

[0079] Step 4: Take 50 mg of the foamy electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained by one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0080] Example 5

[0081] Step 1: Take 0.03 g of graphene oxide and 0.3 g of Co(NO3)2·6H2O 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, and then ultrasonicate appropriately for 1 h, which is recorded as mixture A (pH is 9 - 11).

[0082] Step 2: Transfer mixture A to a 50 ml polymerization reactor and react at 180 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, which is recorded as product B.

[0083] Step 3: Put product B into a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0084] Step 4: Take 50 mg of the foam electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained by one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0085] Example 6

[0086] Step 1: Take 0.03 g of graphene oxide and 0.3 g of Mn(NO3)2·6H2O 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, and then ultrasonicate appropriately for 1 h, which is recorded as mixture A (pH is 9 - 11).

[0087] Step 2: Transfer mixture A to a 50 ml polymerization reactor and react at 180 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, which is recorded as product B.

[0088] Step 3: Put product B into a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0089] Step 4: Take 50 mg of the foam electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained by one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0090] Example 7

[0091] Step 1: Take 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O 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, and then ultrasonicate appropriately for 1 h, which is recorded as mixture A (pH is 9 - 11).

[0092] Step 2: Transfer the mixture A to a 50 ml polymerization reactor and react at 120 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, and denote it as product B.

[0093] Step 3: Put product B into a refrigerator at -4 °C and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 500 °C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0094] Based on the total weight of the foamy solid C being 100 wt%, the content of graphene is 31 wt%, and the content of metal oxide is 69 wt%.

[0095] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.05 mol / g.

[0096] Step 4: Take 50 mg of the foamy electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and obtain a paper-like electrode by one-step extrusion. After cutting to obtain a disc with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0097] Example 8

[0098] Step 1: Take 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O 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, and ultrasonicate appropriately for 1 h, and denote it as mixture A (pH is 9 - 11).

[0099] Step 2: Transfer the mixture A to a 50 ml polymerization reactor and react at 180 °C for 12 h. After taking it out, wash it with deionized water 3 - 4 times, and denote it as product B.

[0100] Step 3: Put product B into a refrigerator at -4 °C and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 200 °C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0101] Based on the total weight of the foamy solid C being 100 wt%, the content of graphene is 32 wt%, and the content of metal oxide is 68 wt%.

[0102] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.05 mol / g.

[0103] Step 4: Take 50 mg of the foamy electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and obtain a paper-like electrode by one-step extrusion. After cutting to obtain a disc with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0104] Example 9

[0105] Step 1: Dissolve 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O 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, and ultrasonicate appropriately for 1 h. Denote it as mixture A (pH = 9 - 11).

[0106] Step 2: Transfer mixture A to a 50-ml polymerization reactor and react at 150 °C for 15 h. After taking it out, wash it 3 - 4 times with deionized water, and denote it as product B.

[0107] Step 3: Place product B in a -4 °C refrigerator and freeze it overnight. Then, transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 400 °C for 8 h under a nitrogen atmosphere to obtain a foamy solid C.

[0108] Based on the total weight of the foamy solid C being 100 wt%, the content of graphene is 29 wt%, and the content of metal oxide is 71 wt%.

[0109] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.035 mol / g.

[0110] Step 4: Take 50 mg of the foamy electrode and directly put it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and obtain a paper-like electrode by one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0111] Example 10

[0112] Step 1: Dissolve 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O 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, and ultrasonicate appropriately for 1 h. Denote it as mixture A (pH = 9 - 11).

[0113] Step 2: Transfer mixture A to a 50-ml polymerization reactor and react at 200 °C for 10 h. After taking it out, wash it 3 - 4 times with deionized water, and denote it as product B.

[0114] Step 3: Place product B in a -4 °C refrigerator and freeze it overnight. Then, transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 800 °C for 2 h under a nitrogen atmosphere to obtain a foamy solid C.

[0115] Based on the total weight of the foamy solid C being 100 wt%, the content of graphene is 27 wt%, and the content of metal oxide is 73 wt%.

[0116] The total content of carboxyl groups and phenolic hydroxyl groups in the foamed solid C is 0.02 mol / g.

[0117] Step 4: Take 50 mg of the foamed electrode and directly place it into an experimental roll press. Adjust the gap of the roll press to 0.3 mm, and a paper-like electrode can be obtained through one-step extrusion. After cutting to obtain a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0118] It has been verified that the electrode sheets prepared by the extrusion method in the above Examples 1-10 can be re-extruded to prepare complete electrode sheets again after being crushed, that is, this method has processability and reusability. The scraps cut from the original electrode materials can also be processed by this preparation method for secondary roll pressing and sheet making, avoiding the waste of composite materials.

[0119] Comparative Example 1

[0120] Step 1: Dissolve 0.03 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water to it with a peristaltic pump at a speed of 0.5 ml / min, and ultrasonicate appropriately for 1 h. Record it as the mixed solution A (pH is 9-11).

[0121] Step 2: Transfer the mixed solution A to a 50 ml polymerization reactor and react at 180 °C for 12 h. After taking it out, wash it with deionized water 3-4 times, and record it as the product B.

[0122] Step 3: Place the product B in a -4 °C refrigerator and freeze it overnight, then transfer it to a freeze dryer and dry it for 48 h. Transfer it to a tube furnace and sinter it at 500 °C in a nitrogen atmosphere for 3 h to obtain the foamed solid C.

[0123] Step 4: Take 100 mg of C, place the sample, acetylene black, and PVDF in a weighing bottle according to the ratio of 8:1:1, add 100 mg of N-methylpyrrolidone and stir for more than 6 h. 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 load, and perform double-roll to prepare an electrode sheet cut into a diameter of 1 cm.

[0124] Comparative Example 2

[0125] Step 1: Dissolve 1 g of graphene oxide and 0.16 g of Fe(NO3)3·9H2O in 30 ml of water. Then, add 0.2 ml of concentrated ammonia water to it with a peristaltic pump at a speed of 0.5 ml / min, and ultrasonicate appropriately for 1 h. Record it as the mixed solution A.

[0126] Step 2: Transfer the mixed solution A to a 50 ml polymerization reactor and react at 180 °C for 12 h. After taking it out, wash it with deionized water 3-4 times, and record it as the product B.

[0127] In Step 3, the product B was placed in a refrigerator at -4°C and frozen overnight, then transferred to a freeze dryer and dried for 48 h, and then transferred to a tube furnace and sintered at 500°C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0128] Based on the total weight of the foamy solid C being 100 wt%, the content of the graphene is 91 wt%, and the content of the metal oxide is 9 wt%.

[0129] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.1 mol / g.

[0130] In Step 4, 50 mg of the foamy electrode was directly placed into a laboratory roll press, the gap of the roll press was adjusted to 0.3 mm, and a paper-like electrode was obtained by one-step extrusion. After cutting into a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0131] Comparative Example 3

[0132] In Step 1, 0.03 g of graphene oxide and 1 g of Fe(NO3)3·6H2O were dissolved in 30 ml of water, then 0.2 ml of concentrated ammonia water was added at a speed of 0.5 ml / min using a peristaltic pump, and then appropriately ultrasonicated for 1 h, denoted as mixture A.

[0133] In Step 2, the mixture A was transferred to a 50 ml polymerization reactor and reacted at 180°C for 12 h. After taking it out, it was washed 3 - 4 times with deionized water, denoted as product B.

[0134] In Step 3, the product B was placed in a refrigerator at -4°C and frozen overnight, then transferred to a freeze dryer and dried for 48 h, and then transferred to a tube furnace and sintered at 500°C for 3 h under a nitrogen atmosphere to obtain a foamy solid C.

[0135] Based on the total weight of the foamy solid C being 100 wt%, the content of the graphene is 10 wt%, and the content of the metal oxide is 90 wt%.

[0136] The total content of carboxyl groups and phenolic hydroxyl groups in the foamy solid C is 0.012 mol / g.

[0137] In Step 4, 50 mg of the foamy electrode was directly placed into a laboratory roll press, the gap of the roll press was adjusted to 0.3 mm, and a paper-like electrode was obtained by one-step extrusion. After cutting into a circular piece with a diameter of 1 cm for testing, a self-supporting high-capacity electrode sheet can be obtained.

[0138] Test Example

[0139] The battery test process for assembling the electrode sheets of the examples and comparative examples is as follows: The electrode sheets were assembled into 2032-type button batteries and then subjected to electrochemical tests. The electrolyte used in the tests was 1 mol L -1Lithium hexafluorophosphate is dissolved in ethylene carbonate: diethyl carbonate with a mass ratio of 1:1. The test diaphragm is Celgard 2400. In the battery test, the electrode sheet serves as the positive electrode, and a lithium sheet is used as the counter electrode. The test is carried out at room temperature. The assembled button battery is first subjected to charge-discharge tests in a Blue Electric test system. The test method is as follows: the test diaphragm is Celgard 2400, and the test is carried out at room temperature. The assembled button battery is first subjected to charge-discharge tests in a Blue Electric test system (Wuhan Blue Electric Co., Ltd.) to verify its rate performance and long-cycle performance. The test voltage range is 0.01 - 3.00 V, and the current density is 100 - 10000 mA g -1 . The cyclic voltammetry test uses an Autolab PGSTAT302N electrochemical workstation. The cyclic voltammetry test voltage range is 0 - 3 V, and the scanning rate is 0.1 mV s -1 .

[0140] Verify the cycle efficiency and long-cycle performance, and the current density is 100 mA g -1 , and the test results are shown in Table 1.

[0141] Table 1

[0142]

[0143] After detection, the detection results of the self-supporting high-capacity electrode sheets obtained in Example 9 and Example 10 are similar to those in Example 6, both are better than all Comparative Examples 1 - 3, and are better than Example 7 and Example 8.

[0144] Common composites of graphene and metal oxides that can be used as electrode materials cannot be pressed into electrode sheets. This is mainly related to the reduction degree of graphene oxide and the mass ratio of graphene and metal oxides in the composite material. If the reduction degree of graphene is too high, a self-supporting electrode sheet cannot be formed. For example, when the sintering temperature is too high and the sintering time is too long, and the total content of carboxylic acid groups and phenolic hydroxyl groups in the reduced graphene oxide is less than 0.01 mol / g, the material itself is brittle and fragile, and a self-supporting electrode sheet cannot be obtained by pressing; if the reduction degree is too low, the conductivity of the electrode material is poor, and conductive carbon black must be added during the subsequent production of the electrode, increasing the weight of the electrode material and reducing the energy density; if the graphene content in the electrode material is too high (such as in Comparative Example 2), the energy density of the electrode material is too low; if the graphene content is too low (such as in Comparative Example 3), the metal oxides are prone to agglomeration, resulting in poor conductivity of the electrode material and poor battery cycle performance.

[0145] The present invention uses a one-step extrusion method to prepare electrode sheets. The principle of the present invention lies in that through the formulation and method of the present invention, by means of hydrothermal reaction and subsequent sintering and thermal reduction, the functional groups on graphene oxide are greatly reduced. The remaining small amount of derivative carboxylic groups and the interaction between phenolic hydroxyl groups, as well as the intermolecular π-π interaction, are like glue. With the help of strong external force, the freeze-dried foam-like composite materials are connected to obtain paper-like electrode sheets. This simple manufacturing method overcomes the cumbersome preparation steps of traditional electrode manufacturing methods, avoids the use of binders and conductive carbon black, thereby reducing the weight of the electrode and increasing the energy density. The present invention not only prepares electrode sheets (i.e., self-supporting electrode materials) by a one-step extrusion method, but also, the self-supporting electrode materials obtained by the present invention have a relatively high energy density. Especially under the hydrothermal reaction and sintering conditions preferably used in the present invention, the obtained self-supporting electrode materials have a better energy density, higher cycle efficiency and specific capacity.

[0146] The one-step extrusion method is pioneered by the present invention. Other patent documents use the traditional coating method, which has cumbersome steps, a large weight of electrode sheets, and a low energy density. For example, the electrode sheets involved in CN101982408A are made by traditional methods. In addition, hydrazine hydrate reduction is used in CN101982408A. Hydrazine hydrate is highly toxic and is not suitable for use in large-scale production, nor for industrial and biomedical applications. The self-supporting electrode materials and preparation methods of the present invention have achieved unexpected technical effects and have extremely high application value.

[0147] The above-mentioned content is only a preferred embodiment under the concept of the present invention and is not used to limit the present invention. Those skilled in the art can make various modifications within the scope of the appended claims. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

[0148] It should be noted that the above-mentioned 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 restrictive words. Modifications can be made to the present invention within the scope of the claims of the present invention as stipulated, 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.

[0149] 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 those of ordinary skill in the art. In case of conflict, the definitions in this specification shall prevail.

[0150] When this specification uses prefixes such as "known to those of ordinary skill in the art", "prior art", or their 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 of filing of this application, but also include those that are not commonly used at present but will become recognized in the art as suitable for similar purposes.

[0151] In the scope disclosed in this application document, the endpoints and any values of the scope are not limited to the exact scope or value. These scopes or values should be understood to include values close to these scopes or values. For numerical ranges, the endpoints of each range, between the endpoints 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 text, 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.

[0152] In the context of this specification, any matters or things not mentioned, except as expressly stated, directly apply those known in the art without any change.

[0153] Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the resulting technical solutions or technical ideas 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 of ordinary skill in the art consider such combination to be obviously unreasonable.

Claims

1. An electrode material, which is in sheet form and is prepared by pressing a graphene composite. The graphene composite includes lamellar graphene and metal oxides dispersed in the graphene lamellae. Based on the total weight of the electrode material being 100 wt%, the content of graphene is 15 - 40 wt%, and the content of the metal oxide is 60 - 85 wt%; the total content of carboxyl groups and phenolic hydroxyl groups in the graphene composite is not less than 0.01 mol / g.

2. The electrode material according to claim 1, wherein: The total content of carboxyl groups and phenolic hydroxyl groups in the graphene composite is 0.01 - 0.05 mol / g, preferably 0.02 - 0.04 mol / g; and / or, The graphene in the graphene composite is nitrogen-doped graphene; and / or, Before pressing, the graphene composite has a porous structure. Preferably, the pore size is 3 - 10 μm, and / or, before pressing, the graphene composite has a foam-like shape.

3. The electrode material according to claim 1, wherein: Based on the total weight of the electrode material being 100 wt%, the content of graphene is 25 - 40 wt%, and the content of the metal oxide is 60 - 75 wt%; and / or, The thickness of the electrode material is 0.1 - 0.8 mm, preferably 0.3 - 0.5 mm; and / or, The graphene composite self-bonds under external pressure to obtain the electrode material; preferably, The electrode material is a self-supporting flexible electrode sheet; more preferably, The electrode material does not contain a binder, a conductive agent, and a current collector.

4. The electrode material according to claim 1, wherein: The metal element of the metal oxide is a transition metal element; preferably, The transition metal element is selected from at least one of iron, cobalt, and manganese.

5. The electrode material according to any one of claims 1 - 4, wherein: The preparation method of the electrode material includes: subjecting a mixed solution containing graphene oxide and a metal element source to a hydrothermal reaction in the presence of a nitrogen-containing precipitant, freeze-drying the obtained product, and sintering it under a protective atmosphere to obtain a graphene composite; pressing the graphene composite into a sheet to obtain the electrode material.

6. A method for preparing an electrode material, preferably for preparing the electrode material according to any one of claims 1-5, comprising: Subjecting a mixed solution containing graphene oxide and a metal element source to a hydrothermal reaction in the presence of a nitrogen-containing precipitant, freeze-drying the obtained product, and sintering it under a protective atmosphere to obtain a graphene composite; pressing the graphene composite into a sheet to obtain the electrode material.

7. The preparation method according to claim 6, wherein It includes the following steps: Step 1 Dissolve the metal element source in the mixed solution containing graphene oxide, add a nitrogen-containing precipitant, and after mixing, denote it as mixed solution A; Step 2 Subject mixed solution A to a hydrothermal reaction, then wash the reaction mixture with water, and retain the precipitate, denoted as product B; Step 3 Freeze-dry product B, and then sinter it under a protective atmosphere to obtain a foam-like solid C; the foam-like solid C is a graphene composite; Step 4 Press the foam-like solid C into a sheet.

8. The preparation method according to claim 7, wherein: In Step 1: relative to 1 g of graphene oxide, the dosage of the metal element source is 8 - 50 mmol, preferably 10 - 40 mmol, and the dosage of the metal element source is based on the content of the metal element; and / or, The nitrogen-containing precipitating agent is selected from at least one of ammonia water, ammonium bicarbonate, and ammonium carbonate; and / or, The addition amount of the nitrogen-containing precipitating agent is such that the pH of the mixed solution A is controlled between 9 and 11. Preferably, the concentration of the nitrogen-containing precipitating agent in the mixed solution A is 0.1 - 3 wt%, preferably 0.5 - 1 wt%.

9. The preparation method according to claim 6, 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 sintering temperature is 400 - 800 °C, preferably 500 - 600 °C; and / or, the sintering time is 2 - 8 h, preferably 3 - 5 h; and / or, In Step 4, rolling press is used for pressing. Preferably, the gap of the rolling press is 0.1 - 0.8 mm, preferably 0.3 - 0.5 mm.

10. The preparation method according to any one of claims 6 - 9, wherein: The graphene oxide is prepared by the Hummers method; and / or, The metal element source is selected from soluble salts corresponding to the metal elements, preferably at least one of hydrochlorides, sulfates, and nitrates.

11. Application of the electrode material according to any one of claims 1 - 5 or the electrode material obtained by the preparation method according to any one of claims 6 - 10 in a battery; Preferably as an electrode sheet in a battery; and / or, Preferably the battery is a lithium-ion battery.

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