A negative electrode composite material, a preparation method thereof, a battery, and an electronic device

Abstract

The present application relates to a kind of negative composite material and its preparation method, battery and electronic device, the preparation method includes: biomass material is carried out pre-oxidation treatment, and obtain pre-oxidized biomass material;The first calcination is carried out to the obtained pre-oxidized biomass material in mixed gas atmosphere, pickling, second calcination is carried out in inert gas atmosphere, and obtain porous hard carbon material;In inert gas atmosphere, nitrogen-containing polymer and the obtained porous hard carbon material are placed in the same equipment in different carrier simultaneously third calcination is carried out, cooling, the negative composite material is obtained.The sodium ion battery equipped with the negative composite material has excellent initial efficiency and cycle performance.The preparation method is simple and controllable, and can be applied to mass production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a negative electrode composite material, a preparation method thereof, a battery and an electronic device. BACKGROUND

[0002] In the face of increasingly severe environmental challenges and energy crises, people urgently need to develop renewable and sustainable energy, such as wind and solar energy. However, the effective conversion and utilization of these intermittent energy sources cannot be achieved without the strong support of large-scale energy storage systems. In this context, sodium ion batteries are considered as the most potential lithium ion battery substitutes for large-scale energy storage due to their low cost, abundant sodium resources and similar "rocking chair" working mechanism as lithium ion batteries.

[0003] In the past decade, significant progress has been made in the research and application of sodium ion battery cathode materials, including polyanion compounds, layered oxides and prussian analogues. In terms of negative electrode materials, carbonaceous materials, alloy metals, metal chalcogen compounds and other materials have been widely explored. However, due to their complex preparation process and inherent electrochemical defects, most of the candidate materials show serious shortcomings in large-scale application.

[0004] Carbonaceous materials are considered as the most promising negative electrode material due to their low cost, simple preparation and good repeatability. Unlike the successful application of graphite in traditional lithium ion batteries, the narrow interlayer spacing (0.335 nm) and thermodynamic instability of graphite intercalation compounds hinder the intercalation of sodium ions, so it is generally recognized that graphite cannot be directly used as the negative electrode material of sodium ion batteries. In contrast, hard carbon is composed of interlaced graphite crystalline layers, abundant micropores and defects, which has a relatively large interlayer spacing and can store a large amount of sodium ions, thus having a large reversible capacity.

[0005] Therefore, in order to meet the requirements of full batteries in practical applications, it is urgent to develop a hard carbon sodium ion negative electrode material with high reversible capacity and appropriate low potential platform capacity. SUMMARY

[0006] Therefore, the present application provides a negative electrode composite material, a preparation method thereof, a battery and an electronic device to solve at least one problem in the background art.

[0007] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:

[0008] The first aspect of the present application provides a preparation method of a negative electrode composite material, comprising the following steps:

[0009] S1: pre-oxidizing a biomass material to obtain a pre-oxidized biomass material;

[0010] S2: performing first calcination on the pre-oxidized biomass material obtained in step S1 under a mixed gas atmosphere, acid washing, and performing second calcination under an inert gas atmosphere to obtain a porous hard carbon material;

[0011] S3: simultaneously performing third calcination and cooling of the nitrogen-containing polymer and the porous hard carbon material obtained in step S2 in different carriers in the same device under an inert gas atmosphere to obtain the negative electrode composite material.

[0012] Preferably, in step S1, the biomass material is selected from one or more of cellulose, bamboo fiber, flax fiber, lignin, bagasse, and straw.

[0013] Preferably, in step S1, the pre-oxidation treatment is performed at a temperature of 200-350°C, a temperature rising rate of 1-10°C / min, and a holding time of 2-15 hours under an air atmosphere.

[0014] Preferably, in step S2, the mixed gas is a mixture of hydrogen and an inert gas, and the volume ratio of the hydrogen to the inert gas is 1:(14-24), and the inert gas is selected from at least one of argon, helium, and nitrogen.

[0015] Preferably, in step S2, the mixed gas is introduced at a flow rate of 50-100 ml / min, the first calcination is performed at a temperature of 600-800°C, a temperature rising rate of 1-10°C / min, and a holding time of 1-5 hours.

[0016] Preferably, in step S2, the acid washing is stirring acid washing in a hydrochloric acid solution, the concentration of the hydrochloric acid solution is 0.5-1.5 mol / L, the stirring time is 8-16 hours, and the ratio of the mass (g) of the pre-oxidized biomass material to the volume (ml) of the hydrochloric acid solution is 1:(50-100).

[0017] Preferably, in step S2, after the acid washing, the method further comprises the steps of washing to neutral with deionized water and drying.

[0018] Preferably, in step S2, the inert gas is selected from at least one of argon, helium, and nitrogen.

[0019] Preferably, the second calcination is performed at a temperature of 1000-1600°C, a temperature rising rate of 1-5°C / min, and a holding time of 2-8 hours.

[0020] Preferably, in step S3, the distance between the carrier where the nitrogen-containing polymer is placed and the inlet of the inert gas of the device is less than the distance between the carrier where the porous hard carbon material is placed and the inlet of the inert gas of the device.

[0021] Preferably, in step S3, the mass ratio of the nitrogen-containing polymer and the porous hard carbon material is (3-5):1, and the nitrogen-containing polymer is selected from one or more of melamine resin, polyurethane resin, urea-formaldehyde resin, polysilazane resin, polyamide resin and ABS resin.

[0022] Preferably, in step S3, the inert gas is at least one selected from argon, helium and nitrogen, the flow rate of the inert gas is 50-100 ml / min, the temperature of the third calcination is 400-800℃, the heating rate of the third calcination is 1-5℃ / min, and the holding time of the third calcination is 1-5 hours.

[0023] Preferably, in step S3, the cooling is first cooled to a first temperature at a first cooling rate, and then naturally cooled to room temperature, the first cooling rate is 1-10℃ / min, and the first temperature is 400-600℃.

[0024] The second aspect of the present application provides a negative electrode composite material, which is prepared according to the preparation method of the negative electrode composite material provided in the first aspect of the present application.

[0025] Preferably, the negative electrode composite material comprises the porous hard carbon material and a coating layer coated on the surface of the porous hard carbon material, the porous hard carbon material has a closed pore structure, the coating layer is a nitrogen-doped hard carbon coating layer, the thickness of the coating layer is 3-10 nm, the closed pore size of the negative electrode composite material is 0.8-2.0 nm, and the interlayer spacing of the negative electrode composite material is 0.37-0.385 nm.

[0026] Preferably, the atomic percentage of nitrogen atoms in the coating layer is 2at%-5at%, and the C:O atomic ratio of the negative electrode composite material is (100-200):1.

[0027] Preferably, the true density of the negative electrode composite material is 1.3-1.6 g / cm 3 , the median particle size Dv50 of the negative electrode composite material is 2-10 μm, and the specific surface area of the negative electrode composite material is 2-10 m 2 / g.

[0028] The third aspect of the present application provides a battery, which comprises a negative electrode sheet, and the negative electrode sheet comprises the negative electrode composite material provided in the second aspect of the present application.

[0029] The fourth aspect of the present application provides an electronic device comprising the battery of the third aspect of the present application.

[0030] Compared with the prior art, the present application has the beneficial effects that:

[0031] The preparation method of the negative electrode composite provided by the present application first improves the proportion of oxygen elements in the biomass material by pre-oxidizing the biomass material with a long molecular chain structure, which is beneficial to making the hard carbon structure more disordered; then the oxygen elements in the surface and bulk phase of the pre-oxidized biomass material are reduced by hydrogen, which enriches the defect sites in the material, and the water molecules produced by the reduction of hydrogen can effectively pore the material; and through high-temperature calcination, a porous hard carbon material rich in closed pores is generated, which is beneficial to the effective filling of sodium ions; finally, the surface of the porous hard carbon material is doped and coated with N elements by skillfully utilizing the emission of nitrogen-containing small molecule gases during the decomposition of the nitrogen-containing polymer, which effectively reduces the specific surface area of the material and improves the interface stability, thereby forming a negative electrode composite with the internal porous hard carbon material rich in closed pores and the external nitrogen-doped hard carbon coating layer, which can effectively improve the initial efficiency and cycle performance of the sodium ion battery equipped with the negative electrode composite, and make it have more excellent electrochemical performance. In addition, the preparation method of the negative electrode composite is simple and controllable, and can be suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which are included to provide a further understanding of the present application, form a part of the present application and illustrate the illustrative embodiments of the present application and together with the description serve to explain the present application. In the drawings:

[0033] Figure 1 SEM image of the nitrogen-doped hard carbon sodium ion battery negative electrode composite obtained in Example 1.

[0034] Figure 2 HRTEM image of the nitrogen-doped hard carbon sodium ion battery negative electrode composite obtained in Example 1.

[0035] Figure 3 XRD pattern of the nitrogen-doped hard carbon sodium ion battery negative electrode composite obtained in Example 1.

[0036] Figure 4 SAXS graph of the nitrogen-doped hard carbon sodium ion battery negative electrode composite obtained in Example 1, wherein the red line is the fitting line, and the flat part in the curve represents that the material has a closed pore structure; the lower left corner in the graph is the closed pore size. DETAILED DESCRIPTION

[0037] In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by listing specific examples. The drawings are not necessarily drawn to scale, and local features can be enlarged or reduced to more clearly show the details of the local features. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods in the following examples, if not specified, are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available, unless otherwise specified.

[0038] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the application. One skilled in the relevant art will recognize, however, that the application can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures have not been described in detail in order to avoid obscuring the application. According to the knowledge of those skilled in the art, the technical features in the present application can be implemented in various ways. In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by listing specific examples. The drawings are not necessarily drawn to scale, and local features can be enlarged or reduced to more clearly show the details of the local features. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods in the following examples, if not specified, are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available, unless otherwise specified.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0040] For a thorough understanding of the present application, detailed steps and detailed structures will be presented in the following description, in order to explain the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows, however, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0042] Unless otherwise specified, the experimental methods in the following examples are generally carried out according to the conventional techniques or conditions described in the literature, or according to the product instructions and manufacturer's recommendations. The numerical ranges in the following examples include the end point values.

[0043] In order to achieve the above-mentioned object of the present application, the present application provides the following technical solutions:

[0044] [Preparation of negative electrode composite material]

[0045] The first aspect of the present application provides a preparation method of a negative electrode composite material, comprising the following steps:

[0046] S1: performing pre-oxidation treatment on a biomass material to obtain a pre-oxidized biomass material;

[0047] S2: performing first calcination on the pre-oxidized biomass material obtained in step S1 under a mixed gas atmosphere, acid pickling, and performing second calcination under an inert gas atmosphere to obtain a porous hard carbon material;

[0048] S3: placing a nitrogen-containing polymer and the porous hard carbon material obtained in step S2 in different carriers of the same device under an inert gas atmosphere to simultaneously perform third calcination and cooling, thereby obtaining the negative electrode composite material.

[0049] The preparation method provided in the present application first increases the proportion of oxygen elements in the biomass material by performing pre-oxidation treatment on the biomass material with a long molecular chain structure, which is conducive to making the hard carbon structure more disordered; then reduces the oxygen elements on the surface and in the bulk phase of the pre-oxidized biomass material by hydrogen, enriches the defect sites in the material, and the water molecules produced by hydrogen reduction can effectively pore the material; and generates a porous hard carbon material rich in closed pores through high-temperature calcination, which is conducive to the effective filling of sodium ions; finally, the nitrogen-containing small molecule gas emitted during the decomposition of the nitrogen-containing polymer is used to dopedly coat the surface of the porous hard carbon material, effectively reducing the specific surface area of the material and improving the interface stability, thereby forming a negative electrode composite material with a porous hard carbon material rich in closed pores inside and a nitrogen-doped hard carbon coating layer outside, so that the sodium ion battery equipped with the negative electrode composite material has more excellent electrochemical performance.

[0050] In some embodiments, in step S1, the biomass material is selected from one or more of cellulose, bamboo fiber, flax fiber, lignin, bagasse and straw.

[0051] In some embodiments, the biomass material is cellulose, bamboo fiber, flax fiber, or bagasse.

[0052] The above biomass material has a long molecular chain structure, so a rich network structure can be formed during crosslinking reaction, and a more abundant closed pore structure can be formed after carbonization, which is conducive to the effective filling of sodium ions, thereby significantly increasing the platform capacity, and thus the sodium ion battery equipped with the negative electrode composite material has more excellent electrochemical performance.

[0053] In some embodiments, in step S1, the temperature of the pre-oxidation treatment is 200-350°C, for example 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C, but is not limited to the listed values, and other values not listed in the value range are also applicable; the temperature rising rate of the pre-oxidation treatment is 1-10°C / min, for example 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values not listed in the value range are also applicable; the holding time of the pre-oxidation treatment is 2-15 hours, for example 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, but is not limited to the listed values, and other values not listed in the value range are also applicable; the pre-oxidation treatment is carried out in an air atmosphere.

[0054] In the present application, by pre-oxidation treatment of the biomass material, the introduction of oxygen-containing functional groups by oxidative crosslinking, and the increase of the proportion of oxygen elements in the biomass material, the hard carbon structure can be effectively optimized to become more disordered; the platform capacity of the material can be effectively improved, and thus the sodium ion battery equipped with the negative electrode composite material has more excellent electrochemical performance.

[0055] In some embodiments, in step S2, the mixed gas is a mixture of hydrogen and inert gas, the volume ratio of the hydrogen and inert gas is 1:(14-24), for example 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23 or 1:24, but is not limited to the listed values, and other values not listed in the value range are also applicable, and the inert gas is selected from at least one of argon, helium and nitrogen;

[0056] In some embodiments, in step S2, the mixed gas is a mixture of hydrogen and argon, the volume ratio of the hydrogen and argon is 1:(14-24), for example 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23 or 1:24, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0057] In step S2 of the present application, the oxygen elements in the surface and bulk phase of the pre-oxidized biomass material are reduced by hydrogen, enriching the defect sites of the material, and the water molecules produced by the hydrogen reduction can effectively pore the material, thereby effectively improving the electrochemical performance of the sodium ion battery equipped with the negative electrode composite material.

[0058] In step S2 of the present application, the reaction mechanism for pore-forming the material with water molecules is as follows:

[0059] H2O+C x →H2+CO+C x-1

[0060] 2H2O+C→2H2+CO2

[0061] In some embodiments, in step S2, the flow rate of the mixed gas is 50-100 ml / min, for example 50 ml / min, 60 ml / min, 70 ml / min, 80 ml / min, 90 ml / min or 100 ml / min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0062] In some embodiments, in step S2, the temperature of the first calcination is 600-800℃, for example 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃ or 800℃, but is not limited to the listed values, and other values not listed in the value range are also applicable; the heating rate of the first calcination is 1-10℃ / min, for example 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values, and other values not listed in the value range are also applicable; the holding time of the first calcination is 1-5 hours, for example 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0063] In some embodiments, in step S2, the acid washing is stirring acid washing in a hydrochloric acid solution, the concentration of the hydrochloric acid solution is 0.5-1.5 mol / L, for example 0.5 mol / L, 1 mol / L or 1.5 mol / L, but not limited to the listed values, other values not listed in the value range are also applicable; the stirring time is 8-16 hours, for example 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or 16 hours, but not limited to the listed values, other values not listed in the value range are also applicable; the ratio of the mass (g) of the pre-oxidized biomass material to the volume (ml) of the hydrochloric acid solution is 1:(50-100), for example 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95 or 1:100, but not limited to the listed values, other values not listed in the value range are also applicable.

[0064] In step S2 of the present application, the acid washing is beneficial to remove the ash in the material, and further beneficial to generate more pores, beneficial to the effective filling of sodium ions, and further make the sodium ion battery equipped with the negative electrode composite material have more excellent electrochemical performance.

[0065] In some embodiments, in step S2, after the acid washing is completed, the step of washing to neutral with deionized water and drying is further included.

[0066] In some embodiments, in step S2, the inert gas is selected from at least one of argon, helium, nitrogen.

[0067] In some embodiments, in step S2, the inert gas is selected from argon.

[0068] In some embodiments, the temperature of the second calcination is 1000-1600℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃ or 1600℃, but not limited to the listed values, other values not listed in the value range are also applicable; the heating rate of the second calcination is 1-5℃ / min, for example 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but not limited to the listed values, other values not listed in the value range are also applicable; the holding time of the second calcination is 2-8 hours, for example 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but not limited to the listed values, other values not listed in the value range are also applicable. In this way, the carbon atoms in the material can be rearranged at high temperature to graphitize, the carbon layer is bent, and further form nanometer holes, which is beneficial to the effective filling of sodium ions, and further make the sodium ion battery equipped with the negative electrode composite material have more excellent electrochemical performance.

[0069] In some embodiments, the distance between the carrier in which the nitrogen-containing polymer is placed and the inlet of the inert gas of the device is less than the distance between the carrier in which the porous hard carbon material is placed and the inlet of the inert gas of the device. Thus, the nitrogen-containing small molecule gas emitted during the decomposition of the nitrogen-containing polymer can be deposited on the surface of the porous hard carbon material, serving as N element doping coating, which can effectively reduce the specific surface area of the material and improve the interface stability, thereby making the sodium ion battery equipped with the negative electrode composite material have more excellent electrochemical performance.

[0070] In some embodiments, the device is a tube furnace.

[0071] In some embodiments, the carrier is a crucible.

[0072] In some embodiments, in step S3, the mass ratio of the nitrogen-containing polymer to the porous hard carbon material is (3-5): 1, for example, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values, and other values not listed in the value range are also applicable; the nitrogen-containing polymer is selected from one or more of melamine resin, polyurethane resin, urea-formaldehyde resin, polysilazane resin, polyamide resin and ABS resin.

[0073] In some embodiments, the nitrogen-containing polymer is melamine resin.

[0074] Since part of the micropores still exist in the form of open pores during the carbonization process, in order to avoid excessive specific surface area of the material to cause excessive side reactions in the first circle, the nitrogen-containing substance and short-chain molecule gas generated during the pyrolysis of the nitrogen-containing polymer are used to dope and coat the material with N element, which can effectively reduce the specific surface area of the material and improve the interface stability, thereby making the sodium ion battery equipped with the negative electrode composite material have more excellent electrochemical performance.

[0075] In some embodiments, in step S3, the inert gas is selected from at least one of argon, helium, and nitrogen; the flow rate of the inert gas is 50-100 ml / min, for example, 50 ml / min, 60 ml / min, 70 ml / min, 80 ml / min, 90 ml / min, or 100 ml / min, but is not limited to the listed values, and other values not listed in the range are also applicable; the temperature of the third calcination is 400-800℃, for example, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or 800℃, but is not limited to the listed values, and other values not listed in the range are also applicable; the temperature rising rate of the third calcination is 1-5℃ / min, for example, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, but is not limited to the listed values, and other values not listed in the range are also applicable; the holding time of the third calcination is 1-5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0076] In some embodiments, in step S3, the inert gas is nitrogen.

[0077] In some embodiments, in step S3, the cooling is first cooled to a first temperature at a first cooling rate, and then naturally cooled to room temperature; the first cooling rate is 1-10℃ / min, for example, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, but is not limited to the listed values, and other values not listed in the range are also applicable; the first temperature is 400-600℃, for example, 400℃, 450℃, 500℃, 550℃, or 600℃, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0078] [Anode composite material]

[0079] The second aspect of the present application provides an anode composite material, which is prepared according to the preparation method of the anode composite material provided in the first aspect of the present application, wherein the anode composite material comprises the porous hard carbon material and a coating layer coated on the surface of the porous hard carbon material, the porous hard carbon material has a closed pore structure, and the coating layer is a nitrogen-doped hard carbon coating layer.

[0080] In certain embodiments, the thickness of the coating layer is 3-10 nm, for example 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0081] In certain embodiments, the closed pore size of the anode composite is 0.8-2.0 nm, for example 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, or 2.0 nm, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0082] In certain embodiments, the interlayer distance of the anode composite is 0.37-0.385 nm, for example 0.37 nm, 0.375 nm, 0.38 nm, or 0.385 nm, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0083] In certain embodiments, the atomic percentage of nitrogen atoms in the coating layer is 2 at% - 5 at%, for example 2 at%, 2.5 at%, 3 at%, 3.5 at%, 4 at%, 4.5 at%, or 5 at%, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0084] In certain embodiments, the C:O atomic ratio of the anode composite is (100-200): 1, for example 100: 1, 110: 1, 120: 1, 130: 1, 140: 1, 150: 1, 160: 1, 170: 1, 180: 1, 190: 1, or 200: 1, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0085] In certain embodiments, the true density of the anode composite is 1.3-1.6 g / cm 3 , for example 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , or 1.6 g / cm 3 , but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0086] In certain embodiments, the median particle size Dv50 of the anode composite is 2-10 μm, for example 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.

[0087] In some embodiments, the specific surface area of the negative electrode composite is 2-10 m 2 / g. For example, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, or 10 m 2 / g, but not limited to the listed values, and other values not listed in the range are also applicable.

[0088] It should be understood that, since the negative electrode composite provided by the present application is prepared according to the preparation method of the negative electrode composite provided by the first aspect of the present application, the beneficial effects of the preparation method of the negative electrode composite in any of the above embodiments are applicable to the negative electrode composite.

[0089] [Battery]

[0090] The third aspect of the present application provides a battery, which comprises a negative electrode sheet, and the negative electrode sheet comprises the negative electrode composite provided by the second aspect of the present application.

[0091] In some embodiments, the battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the above-mentioned battery can be a sodium ion battery, but is not limited thereto. The battery structure of the present application includes but is not limited to a soft package type sodium ion battery, a square hard shell battery, or a cylindrical hard shell battery, etc.

[0092] The battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator film, and the separator film is arranged between the positive electrode sheet and the negative electrode sheet. During the charging and discharging process of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator film is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing the short circuit of the positive / negative electrode, while allowing ions to pass through.

[0093] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector. The negative electrode current collector can be an aluminum foil, a copper foil, a titanium foil, a nickel foil, an iron foil, a zinc foil, etc. The negative electrode active material layer comprises a negative electrode active material. In the present application, the negative electrode active material is the negative electrode composite provided by the second aspect of the present application.

[0094] The negative active material layer can further include one or both of a conductive agent and a binder. The conductive agent serves to improve the conductivity of the electrode. Examples of the negative conductive agent include conductive carbon black, conductive graphite, vapor-grown carbon fiber (VGCF), carbon nanotube, graphene, etc. The binder of the negative electrode improves the adhesion between the negative active material particles and between the negative active material particles and the current collector. Examples of the negative binder include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), cyclodextrin, gelatin, polyvinyl alcohol, polyacrylate, acrylonitrile multi-copolymer, etc. The mass ratio of the components in the negative active material layer can be conventional.

[0095] The preparation method of the negative electrode sheet is not particularly limited in the present application, and a preparation method known in the art can be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the negative electrode sheet includes but is not limited to the following steps: dispersing and mixing the negative active material, the conductive agent and the binder in a solvent to form a uniform negative electrode slurry, coating the negative electrode slurry on the negative electrode current collector, and then drying, cold pressing, cutting, slitting and drying again to obtain the negative electrode sheet. The solvent of the negative electrode slurry can be a conventional solvent in the art, for example, deionized water.

[0096] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector can be an aluminum foil, a copper foil, a titanium foil, a nickel foil, an iron foil, a zinc foil, etc. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material suitable for the present application can be various known positive electrode active materials that can be used in sodium ion batteries and can reversibly intercalate and deintercalate sodium ions. The positive electrode active material can be a sodium ion positive electrode active material commonly used in the art, and is preferably selected from one or more of sodium iron composite oxides (such as NaFeO2), sodium cobalt composite oxides (such as NaCoO2), sodium chromium composite oxides (such as NaCrO2), sodium manganese composite oxides (such as NaMnO2), sodium nickel composite oxides (such as NaNiO2), sodium nickel titanium composite oxides (such as NaNi0 .5 Ti 0.5 O2), sodium nickel manganese composite oxides (such as NaNi 0.5 Mn 0.5 O2), sodium iron manganese composite oxides (such as Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxides (such as NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate compounds (such as NaFePO4), sodium manganese phosphate compounds (such as NaMnPO4), and sodium cobalt phosphate compounds (such as NaCoPO4).

[0097] The positive electrode active material layer can further include one or both of a conductive agent and a binder. The conductive agent serves to improve the conductivity of the electrode. Examples of the conductive agent of the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, ketjen black, graphene, carbon nanotube, and carbon microsphere. The binder of the positive electrode improves the adhesion between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder of the positive electrode include at least one of fluorine-containing resin, polypropylene resin, fiber-type binder, rubber-type binder, and polyimide-type binder. The mass ratio of the components in the positive electrode active material layer can be conventional.

[0098] The application does not have a particular limitation on the preparation method of the positive electrode tab, and a preparation method known in the art can be selected as long as the purpose of the application can be achieved. For example, the preparation method of the positive electrode tab includes but is not limited to the following steps: dispersing and mixing the positive electrode active material, the conductive agent, and the binder in a solvent to form a uniform positive electrode slurry, coating the positive electrode slurry on the positive electrode current collector, and then drying, cold pressing, cutting, slitting, and drying again to obtain the positive electrode tab. The solvent of the positive electrode slurry can be a conventional solvent in the art, such as N-methyl pyrrolidone (NMP).

[0099] The separator film can be a polymer porous separator film, an inorganic porous separator film, or a polymer-inorganic composite porous separator film. The polymer porous separator film includes a single-layer polymer porous separator film and a multi-layer polymer porous separator film.

[0100] The electrolyte generally contains a solvent and a sodium salt. The electrolyte suitable for the application can be conventional, for example, the solvent can be one or more selected from dimethyl carbonate (DMC), propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), or 1,4-butyne carbonate, more preferably one or more of PC, EC, and EMC. The sodium salt can be selected from one or more of sodium tetrafluoroborate, sodium hexafluorophosphate, sodium triflate, or sodium perchlorate.

[0101] The battery of the application further includes a packaging shell for containing the positive electrode tab, the separator film, the negative electrode tab, and the electrolyte, as well as other components known in the art in a sodium ion battery, and the application does not limit the above-mentioned other components. The application does not have a particular limitation on the packaging shell, which can be a packaging shell known in the art as long as the purpose of the application can be achieved.

[0102] [Electronic device]

[0103] The fourth aspect of the application provides an electronic device, which includes the battery provided by the third aspect of the application

[0104] The use of the battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the battery of the present application can be used in, but not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, unmanned aerial vehicles, and sodium-ion capacitors, etc.

[0105] It should be understood that, since the electronic device provided by the present application comprises the battery described in the third aspect of the present application, the beneficial effects of the preparation method of the negative electrode material described in any of the above embodiments are applicable to the electronic device.

[0106] The method of the present application is described below through specific examples, and it should be understood that these examples are used to illustrate the basic principles, main features and advantages of the present application, and the present application is not limited in scope by the following examples; the implementation conditions used in the examples can be further adjusted according to specific requirements, and the implementation conditions not noted are usually the conditions in conventional experiments.

[0107] Example 1

[0108] S101: 50g of cellulose (i.e. biomass material) was loaded into a crucible and placed in a tube furnace, and pre-oxidation was carried out by increasing the temperature from 25 degrees Celsius to 260 degrees Celsius at a rate of 2 degrees per minute under an air atmosphere, and the pre-oxidation process was carried out for 10 hours, to obtain a pre-oxidized biomass material;

[0109] S102: 30g of the pre-oxidized biomass material was placed in a tube furnace, and calcination was carried out by increasing the temperature from 25 degrees Celsius to 700 degrees Celsius at a rate of 2 degrees per minute under an H2 / Ar mixed gas atmosphere (wherein H2 accounts for 5% of the mixed gas), and the calcination was carried out for 2 hours, and after the calcination was completed, the material was placed in 2.4L of 1mol / L hydrochloric acid solution and stirred for 12 hours, and after the acid washing was completed, the material was washed to neutral with deionized water and dried, and then the acid-washed material was placed in a crucible, and calcination was carried out by increasing the temperature to 1300 degrees Celsius at a rate of 2 degrees per minute under an argon atmosphere, and the calcination was carried out for 5 hours, to obtain a porous hard carbon material;

[0110] S103: Put 20 g of nitrogen-containing polymer (melamine resin) and 5 g of porous hard carbon material into two side-by-side crucibles, respectively, in a tube furnace, and place the crucible containing the nitrogen-containing polymer near the gas inlet of the tube furnace. Under a nitrogen atmosphere, heat from 25 degrees Celsius to 600 degrees Celsius at a rate of 2 degrees Celsius per minute, and maintain the temperature for 2 hours. Then, cool down to 500 degrees Celsius at a rate of 5 degrees Celsius per minute, and then cool down to room temperature naturally. A high-performance nitrogen-doped hard carbon sodium-ion battery anode material is obtained.

[0111] Example 2

[0112] The difference between Example 2 and Example 1 is only that the cellulose in step S101 of Example 1 is replaced by bamboo fiber.

[0113] Example 3

[0114] The difference between Example 3 and Example 1 is only that the cellulose in step S101 of Example 1 is replaced by flax fiber.

[0115] Example 4

[0116] The difference between Example 4 and Example 1 is only that the cellulose in step S101 of Example 1 is replaced by bagasse.

[0117] Comparative Example 1

[0118] Put 50 g of cellulose into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat from 25 degrees Celsius to 1300 degrees Celsius at a rate of 2 degrees Celsius per minute, and maintain the temperature for 10 hours. A sodium-ion battery anode material is obtained.

[0119] Comparative Example 2

[0120] The difference between Comparative Example 2 and Example 1 is only that Comparative Example 2 does not include step S103 in Example 1, and only porous hard carbon material is prepared by steps S101 and S102 in Example 1.

[0121] Comparative Example 3

[0122] Step S101*: Put 50 g of cellulose (i.e. biomass material) into a crucible and place it in a tube furnace. Under a nitrogen atmosphere, heat from 25 degrees Celsius to 1300 degrees Celsius at a rate of 2 degrees Celsius per minute, and maintain the temperature for 10 hours. After the pyrolysis of the biomass material is completed, a pyrolyzed biomass material is obtained;

[0123] Step S102*: Put the nitrogen-containing polymer and the pyrolyzed biomass material into two side-by-side crucibles respectively, place the crucible containing the nitrogen-containing polymer close to the air inlet, and perform calcination under a nitrogen atmosphere at a temperature rising rate of 2 degrees per minute from 25 degrees Celsius to 600 degrees Celsius, and then at a temperature dropping rate of 5 degrees per minute from 600 degrees Celsius to 500 degrees Celsius, and then naturally cool to room temperature, to obtain a sodium-ion battery negative electrode material.

[0124] Electrochemical performance test

[0125] Sodium-ion battery preparation:

[0126] (1) Preparation of negative electrode sheet: the negative electrode material prepared in the above Examples 1-4 and Comparative Examples 1-3 is used as the negative electrode active material, carbon black is used as the conductive agent, and CMC is used as the binder, and the negative electrode active material, the conductive agent, and the binder are mixed in a ratio of 8:1:1, and then uniformly coated on the negative electrode current collector (Cu foil) on a transfer coater, and then roll-pressed and sliced to obtain the negative electrode sheet.

[0127] (2) Preparation of positive electrode sheet: metal sodium sheet is used as the positive electrode sheet.

[0128] (3) Separator: glass fiber separator is used as the separator.

[0129] (4) Electrolyte: the electrolyte is prepared by dissolving 1.0 mol / L NaPF6 in diglyme.

[0130] (5) Assembly of battery: the negative electrode sheet, the separator, and the positive electrode sheet are assembled in sequence, and the electrolyte is used to soak them, and then a CR2032 button cell is assembled in an argon glove box.

[0131] The CR2032 button cells using the negative electrode materials prepared in the above Examples 1-4 and Comparative Examples 1-3 as the negative electrode active material are tested for performance.

[0132] 1. First discharge capacity, first charge capacity, and first coulombic efficiency test: Land battery test system is used to test the discharge and charge at 0.1C / 0.1C rate at 25°C, and the voltage range is 0-2V. Specifically, discharge at 0.1C rate to 0V, and record the discharge capacity at this time as the first discharge capacity; then charge at 0.1C rate to 2V, and record the charge capacity at this time as the first charge capacity; first coulombic efficiency = first charge capacity / first discharge capacity*100%. The test results are shown in Table 1.

[0133] Table 1

[0134] Example Initial discharge capacity mAh / g Initial charge capacity mAh / g Initial coulombic efficiency (%) Example 1 448.3 408.4 91.1 Example 2 449.1 407.8 90.8 Example 3 448.5 407.7 90.9 Example 4 447.6 408.2 91.2 Comparative Example 1 319.3 265.3 83.1 Comparative Example 2 388.4 293.6 75.6 Comparative Example 3 375.4 320.2 85.3

[0135] The button half-batteries with the negative electrode composite materials prepared in Examples 1-4 as the negative electrode active material all have high initial discharge capacity (all more than 400 mAh / g) and the first storage efficiency is more than 90%. Compared with Example 1, Comparative Example 1 does not pre-oxidize the cellulose, but directly pyrolyzes and carbonizes to obtain the negative electrode material; Comparative Example 2 does not include the step of nitrogen coating; Comparative Example 3 directly pyrolyzes the cellulose and then coats with nitrogen, so the first discharge capacity of Comparative Examples 1-3 is only 265.3-320.2 mAh / g, and the first coulombic efficiency is 75.6%-85.3%. This is because after the biomass material is cross-linked by pre-oxidation, more defects can be formed by removal of oxygen atoms, and more closed pores can be generated by rearrangement of carbon atoms at high temperature, and nitrogen doping also provides adsorption capacity, which is beneficial to provide more storage space for sodium ions; in addition, the interface structure of the nitrogen-doped material is beneficial to generate a compact SEI layer, thereby effectively improving the first coulombic efficiency.

[0136] 2. Capacity retention rate test: using a blue battery test system, at 25°C, 1C rate constant current discharge to 0V, then constant current charging to 2V with 1C current, recording the charging capacity at this time as the first cycle charging capacity, which is one cycle; after repeating the process for 500 cycles, record the charging capacity of the 500th cycle, the capacity retention rate = the 500th cycle charging capacity / first cycle charging capacity*100%. The test results are shown in Table 2.

[0137] Table 2

[0138] Example Capacity retention (%) Example 1 92.8 Example 2 93.2 Example 3 93.3 Example 4 93.6 Comparative Example 1 82.8 Comparative Example 2 80.7 Comparative Example 3 87.3

[0139] The button half-batteries with the negative electrode composite materials prepared in Examples 1-4 as the negative electrode active material all have high cycle capacity retention rate of 500 cycles (all more than 92%), and the capacity retention rate of Comparative Examples 1-3 is only 82.8%-87.3% compared with Example 1. This shows that the negative electrode material prepared by the preparation method of the present application has a rich microporous structure which can provide a continuous conductive framework, can shorten the transmission distance in the process of ion and electron transmission, and the good mechanical properties and stable interface help to generate a dense SEI layer, so that the battery has good cycle stability, thereby improving the overall electrochemical performance of the electrode.

[0140] It should be understood that the above examples are exemplary and are not intended to include all possible embodiments included in the claims. Various modifications and changes can also be made on the basis of the above examples without departing from the scope of the present disclosure. Similarly, any combination of the technical features of the above examples can also be made to form additional embodiments of the present application which have not been explicitly described. Therefore, the above examples only express several embodiments of the present application, and do not limit the protection scope of the present application.

Claims

1. A method for producing a negative electrode composite material, characterized by, The method comprises the following steps: S1: pre-oxidizing a biomass material to obtain a pre-oxidized biomass material; S2: performing first calcination on the pre-oxidized biomass material obtained in step S1 under a mixed gas atmosphere, acid pickling, and performing second calcination under an inert gas and / or nitrogen atmosphere to obtain a porous hard carbon material; S3: placing a nitrogen-containing polymer and the porous hard carbon material obtained in step S2 in different carriers of the same device to simultaneously perform third calcination and cooling under an inert gas and / or nitrogen atmosphere, thereby obtaining the negative electrode composite material; In step S2, the mixed gas is a mixture of hydrogen and inert gas, and the volume ratio of hydrogen to inert gas is 1:(14-24); or the mixed gas is a mixture of hydrogen and nitrogen. The temperature of the first calcination is 600-800 DEG C, and the holding time of the first calcination is 1-5 hours. The temperature of the second calcination is 1000-1600 DEG C, and the holding time of the second calcination is 2-8 hours. In step S3, the distance between the carrier containing the nitrogen-containing polymer and the gas inlet of the inert gas of the device is less than the distance between the carrier containing the porous hard carbon material and the gas inlet of the inert gas of the device. The mass ratio of the nitrogen-containing polymer to the porous hard carbon material is (3-5):1, and the nitrogen-containing polymer is selected from one or more of melamine resin, polyurethane resin, urea-formaldehyde resin, polysilazane resin, polyamide resin, and ABS resin. The temperature of the third calcination is 400-800 DEG C, and the holding time of the third calcination is 1-5 hours.

2. The method of claim 1, wherein the negative electrode composite is prepared by mixing the active material, the binder, and the conductive agent. In step S1, the biomass material is selected from one or more of cellulose, bamboo fiber, flax fiber, lignin, bagasse, and straw. In step S1, the temperature of the pre-oxidation treatment is 200-350 DEG C, the heating rate of the pre-oxidation treatment is 1-10 DEG C / min, the holding time of the pre-oxidation treatment is 2-15 hours, and the pre-oxidation treatment is performed under an air atmosphere.

3. The method of claim 1, wherein the negative electrode composite is prepared by mixing the active material, the binder, and the conductive material. In step S2, the inert gas is selected from argon and / or helium.

4. The method of claim 1, wherein the negative electrode composite is prepared by mixing the active material, the binder, and the conductive material. In step S2, the flow rate of the mixed gas is 50-100 mL / min, and the heating rate of the first calcination is 1-10 DEG C / min.

5. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the electrolyte solution. In step S2, the acid pickling is stirring acid pickling in a hydrochloric acid solution, the concentration of the hydrochloric acid solution is 0.5-1.5 mol / L, the stirring time is 8-16 hours, and the mass ratio of the pre-oxidized biomass material to the volume of the hydrochloric acid solution is 1 g:50-100 mL.

6. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the electrolyte solution. In step S2, after the acid pickling is completed, the method further comprises the steps of washing to neutral with deionized water and drying.

7. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the electrolyte solution. In step S2, the heating rate of the second calcination is 1-5 DEG C / min.

8. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the electrolyte solution. In step S3, the inert gas is selected from argon and / or helium, the flow rate of the inert gas is 50-100 mL / min, and the heating rate of the third calcination is 1-5 DEG C / min.

9. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the electrolyte solution. In step S3, the cooling is first cooling at a first cooling rate to a first temperature, and then natural cooling to room temperature, the first cooling rate is 1-10℃ / min, and the first temperature is 400-600℃.

10. A negative electrode composite material characterized by comprising: The negative electrode composite material is prepared according to the preparation method of the negative electrode composite material in any one of claims 1-9, The negative electrode composite material comprises the porous hard carbon material and a coating layer coated on the surface of the porous hard carbon material, the porous hard carbon material has a closed pore structure, the coating layer is a nitrogen-doped hard carbon coating layer, the thickness of the coating layer is 3-10nm, the closed pore size of the negative electrode composite material is 0.8-2.0nm, and the interlayer spacing of the negative electrode composite material is 0.37-0.385nm.

11. The negative electrode composite of claim 10, wherein The atomic percentage of nitrogen atoms in the coating layer is 2at%-5at%, and the C:O atomic ratio of the negative electrode composite material is (100-200):

1.

12. The negative electrode composite of claim 10, wherein The true density of the negative electrode composite is 1.3-1.6 g / cm 3 , the median particle size Dv50 of the negative electrode composite is 2-10 μm, and the specific surface area of the negative electrode composite is 2-10 m 2 / g.

13. A battery, characterized by The battery comprises a negative electrode sheet, and the negative electrode sheet comprises the negative electrode composite material in any one of claims 10-12.

14. An electronic device, comprising: The electronic device comprises the battery in claim 13.

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