Negative electrode material and preparation method thereof, sodium ion battery, battery pack and electric equipment

Abstract

The invention discloses a negative electrode material and a preparation method thereof, a sodium-ion battery, a battery pack and electric equipment, relates to the technical field of sodium-ion batteries, and aims to solve the problem that the specific capacity of the sodium-ion battery is relatively low due to the fact that reaction sites, capable of being embedded and removed by sodium ions, of a negative electrode material are few. The negative electrode material comprises first amorphous carbon and second amorphous carbon attached to the surface of the first amorphous carbon. The average particle size of the first amorphous carbon is larger than the average particle size of the second amorphous carbon.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a negative electrode material and a preparation method thereof, a sodium ion battery, a battery pack, and electrical equipment. Background Art

[0002] Sodium-ion batteries have great application potential in the field of large-scale energy storage due to the abundant reserves and low cost of sodium raw materials. Sodium-ion batteries have good thermal stability in high-temperature environments and can still maintain high capacity and good cycle performance in low-temperature environments (such as minus 20 degrees Celsius). They are widely used in power grid energy storage, electric vehicles (such as electric bicycles, electric motorcycles and electric vehicles), distributed energy storage (such as home energy storage and community energy storage), smart homes, wearable devices, communication base stations and other fields.

[0003] However, the negative electrode material has fewer reaction sites for sodium ions to embed and release, so that during the charging and discharging process, the amount of charge that the sodium ion battery can store and release will be correspondingly reduced, resulting in a relatively low specific capacity of the sodium ion battery. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material and a preparation method thereof, a sodium ion battery, a battery pack, and an electrical device, aiming to solve the problem of how to increase the reaction sites of the negative electrode material for sodium ion embedding and extraction, thereby increasing the specific capacity of sodium ions.

[0005] In a first aspect, a negative electrode material is provided. The negative electrode material comprises: a first amorphous carbon and a second amorphous carbon attached to a surface of the first amorphous carbon. The average particle size of the first amorphous carbon is larger than the average particle size of the second amorphous carbon.

[0006] In the negative electrode material of the present application, first, the first amorphous carbon and the second amorphous carbon both contain graphite crystallites with large interlayer spacing and nanoscale micropores formed by random arrangement of carbon layers, so that the amorphous carbon has a variety of active sites for sodium ion embedding, which is conducive to the embedding and extraction of sodium ions, and the volume of the first amorphous carbon and the second amorphous carbon is reduced after embedding sodium, and the cycle performance is good, thereby improving the specific capacity of the negative electrode material. Secondly, the second amorphous carbon with a smaller average particle size is attached to the surface of the first amorphous carbon with a larger average particle size. On the one hand, the first amorphous carbon can provide a more stable structural support and provide good mechanical support during the charge and discharge process, which helps to reduce the structural damage caused by the expansion and contraction of the negative electrode material; on the other hand, the first amorphous carbon and the second amorphous carbon can construct a rich heterogeneous contact interface, enhance the contact between the first amorphous carbon and the second amorphous carbon, realize the composite of the first amorphous carbon and the second amorphous carbon, and provide sufficient reaction sites for the embedding and extraction of sodium ions, so that more sodium ions can reach the active sites of the negative electrode material, further improving the specific capacity of the negative electrode material.

[0007] Optionally, the average particle size of the second amorphous carbon is in the range of 0.1 μm to 1 μm.

[0008] Optionally, the average particle size of the first amorphous carbon is in the range of 2 μm to 10 μm.

[0009] Optionally, the material of the first amorphous carbon includes: hard carbon.

[0010] Optionally, the material of the second amorphous carbon includes at least one of soft carbon and hard carbon.

[0011] Optionally, the surface area of ​​the negative electrode material ranges from 3m 2 / g~10m 2 / g.

[0012] Optionally, the true density of the negative electrode material is in the range of 1.9 g / cm 3 ~2.1g / cm 3 .

[0013] In a second aspect, a method for preparing a negative electrode material is also provided. The method for preparing the negative electrode material comprises:

[0014] The second amorphous carbon precursor is dispersed in a solvent to obtain a second amorphous carbon precursor solution.

[0015] The second amorphous carbon precursor solution is atomized and brought into contact with the first amorphous carbon dispersed under the action of the first protective gas, and dried at the same time to obtain an initial negative electrode material.

[0016] The initial negative electrode material is calcined under a second protective gas to obtain a negative electrode material. The negative electrode material includes: a first amorphous carbon and a second amorphous carbon attached to a surface of the first amorphous carbon; the average particle size of the first amorphous carbon is larger than the average particle size of the second amorphous carbon.

[0017] It can be understood that the present application provides a method for preparing a negative electrode material. The beneficial effects that can be achieved can refer to the beneficial effects of the negative electrode material above, and will not be repeated here.

[0018] Optionally, during the calcination of the initial negative electrode material, the calcination temperature rise rate ranges from 1° C. / min to 20° C. / min.

[0019] Optionally, the initial negative electrode material is calcined at a temperature ranging from 700°C to 1500°C.

[0020] Optionally, the material of the first amorphous carbon includes: hard carbon.

[0021] Optionally, the second amorphous carbon precursor includes at least one of asphalt, phenolic resin, epoxy resin, polyfurfuryl alcohol resin, polyvinyl pyrrolidone, polyvinyl alcohol, chitosan and sucrose.

[0022] Optionally, the solvent includes at least one of N-methylpyrrolidone, acetone, and xylene.

[0023] Optionally, dispersing the second amorphous carbon precursor in a solvent comprises:

[0024] The second amorphous carbon precursor and the solvent are mixed, the concentration of the second amorphous carbon precursor is in the range of 18 wt% to 22 wt%, and the mixture is ball-milled.

[0025] Optionally, the first amorphous carbon dispersed under the action of the first protective gas includes:

[0026] A first protective gas with a temperature range of 120° C. to 180° C. is blown into the bottom of the atomizing drying device to disperse the first amorphous carbon in the atomizing drying device.

[0027] Optionally, the second amorphous carbon precursor solution is atomized, and the atomization treatment time range is controlled within 15 minutes to 120 minutes.

[0028] Optionally, the second amorphous carbon precursor solution is atomized and brought into contact with the first amorphous carbon dispersed under the action of the first protective gas, and the mass loading of the second amorphous carbon precursor on the surface of the first amorphous carbon is in the range of 1% to 10%.

[0029] In a third aspect, a sodium ion battery is provided. The sodium ion battery includes a positive electrode and a negative electrode disposed opposite the positive electrode. The negative electrode material includes a negative electrode material.

[0030] It can be understood that the present application provides a sodium ion battery, and the beneficial effects that can be achieved can refer to the beneficial effects of the negative electrode material mentioned above, which will not be repeated here.

[0031] In a fourth aspect, a battery pack is provided, comprising at least two sodium-ion batteries.

[0032] It can be understood that the present application provides a battery pack, and the beneficial effects that can be achieved can refer to the beneficial effects of the negative electrode material mentioned above, which will not be repeated here.

[0033] In a fifth aspect, an electric device is provided, which includes a battery pack.

[0034] It can be understood that the present application provides an electrical device, and the beneficial effects that can be achieved can refer to the beneficial effects of the negative electrode material mentioned above, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 A flow chart of a method for preparing a negative electrode material provided in an embodiment of the present application;

[0037] Figure 2 is a SEM image of the negative electrode material of Example 1;

[0038] Figure 3 TEM image of the negative electrode material of Example 1;

[0039] Figure 4 This is a Raman spectrum of the negative electrode material of Example 1;

[0040] Figure 5 is the XRD pattern of the negative electrode material of Example 1;

[0041] Figure 6 Electrochemical charge-discharge curves of sodium ion batteries made with the negative electrode materials of Example 1 and Comparative Example 1;

[0042] Figure 7 The figure shows the rate-capacity retention curve of the sodium ion battery made from the negative electrode materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0043] In the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0044] In the embodiments of the present application, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0045] In the description of the embodiments of the present application, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0046] As "carbon peak and carbon neutrality" become a global consensus, the proportion of new clean energy in the overall energy system will rapidly increase. However, due to the intermittent and unstable characteristics of clean energy such as solar and wind power, it is difficult to meet the needs of large-scale centralized use. Developing economical, environmentally friendly, and efficient large-scale energy storage systems is the most effective strategy to address these issues and integrate electricity generated by renewable energy into large-scale battery systems. Energy storage is experiencing explosive growth.

[0047] With the rapid development of lithium-ion batteries, existing lithium resources may not be able to meet future human needs. Sodium-ion batteries, which have similar electrochemical properties to lithium-ion batteries and more abundant raw material reserves, are gradually showing broad commercial prospects, especially in the field of large-scale energy storage. They have huge application potential and are considered to be an ideal alternative to lithium-ion batteries.

[0048] Sodium-ion batteries (SIBs) have enormous potential for large-scale energy storage due to the abundance and low cost of sodium raw materials. Furthermore, SIBs exhibit excellent thermal stability at high temperatures, and maintain high capacity and cycle performance at low temperatures (e.g., -20°C). These batteries are widely used in various fields, including grid energy storage, electric vehicles, distributed energy storage, smart homes, wearable devices, and communication base stations. These fields encompass a wide range of electrical devices.

[0049] Electrical equipment refers to various equipment, devices or systems that use electrical energy to work, including various electrical mechanical equipment, electronic equipment, etc.

[0050] Exemplarily, the electrical equipment may be grid energy storage equipment (such as battery energy storage systems), electric vehicles (such as electric bicycles, electric motorcycles, and electric vehicles), distributed energy storage equipment (such as household energy storage equipment, community energy storage equipment), smart home equipment (such as smart lighting, security systems, and automatic control equipment), wearable devices (such as smart bracelets and smart watches), and communication base station equipment (such as base station power supplies and communication terminal equipment), etc.

[0051] An embodiment of the present application provides an electric device, which includes a battery pack.

[0052] As can be understood, a battery pack can be used as a device to store electrical energy and provide power to electrical devices. For example, it can provide portable, continuous power support when no external power source is available, or provide emergency power during a power outage or failure.

[0053] An embodiment of the present application provides a battery pack comprising at least two sodium-ion batteries.

[0054] It is understood that the battery pack contains two sodium ion batteries, which can be connected in series, parallel or other ways to meet the capacity or voltage requirements.

[0055] An embodiment of the present application provides a sodium ion battery. The sodium ion battery includes: a positive electrode and a negative electrode disposed opposite the positive electrode. The material of the negative electrode includes: a negative electrode material.

[0056] Sodium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of sodium ions between the positive and negative electrodes to work, which is similar to the working principle of lithium-ion battery.

[0057] During the charge and discharge process, sodium ions are intercalated and released back and forth between the two electrodes: During the charge process, sodium ions are released from the positive electrode material, migrate through the electrolyte to the negative electrode material, and are embedded in the negative electrode's crystal lattice. At this point, the negative electrode material is loaded with sodium ions, which is equivalent to storing electrical energy. During the discharge process, sodium ions are released from the negative electrode material, migrate back to the positive electrode material through the electrolyte, and are embedded in the positive electrode's crystal lattice, releasing the stored electrical energy. The negative electrode material plays the role of loading and releasing sodium ions and serves as a storage medium for sodium ions.

[0058] However, the negative electrode material has fewer reaction sites for sodium ions to embed and release, so that during the charging and discharging process, the amount of charge that the sodium ion battery can store and release will be correspondingly reduced, resulting in a relatively low specific capacity of the sodium ion battery.

[0059] In some examples, the specific capacity of the negative electrode material is controlled by regulating the composition of the electrolyte. This method lacks the control over the structure and composition of the negative electrode material itself, which limits the use conditions of the negative electrode.

[0060] Based on this, an embodiment of the present application provides a negative electrode material. The negative electrode material includes: a first amorphous carbon and a second amorphous carbon attached to a surface of the first amorphous carbon. The average particle size of the first amorphous carbon is larger than the average particle size of the second amorphous carbon.

[0061] It can be understood that, first of all, the first amorphous carbon and the second amorphous carbon both contain graphite crystallites with a large interlayer spacing and nanoscale micropores formed by the disordered arrangement of carbon layers, so that the amorphous carbon has a variety of active sites for sodium ions to be embedded, which is beneficial to the embedding and extraction of sodium ions. In addition, the volume deformation of the first amorphous carbon and the second amorphous carbon after sodium embedding is reduced, which improves the kinetic performance of the negative electrode material during the charge and discharge process and improves the specific capacity of the sodium ion battery.

[0062] Secondly, the second amorphous carbon with a smaller average particle size is attached to the surface of the first amorphous carbon with a larger average particle size. On the one hand, the first amorphous carbon can provide a more stable structural support and provide good mechanical support during the charge and discharge process, which helps to reduce the structural damage caused by the expansion and contraction of the negative electrode material; on the other hand, the first amorphous carbon and the second amorphous carbon can construct a rich heterogeneous contact interface, enhance the contact between the first amorphous carbon and the second amorphous carbon, and realize the composite of the first amorphous carbon and the second amorphous carbon, which can provide sufficient reaction sites for the embedding and extraction of sodium ions, so that more sodium ions can reach the active sites of the negative electrode material, improve the kinetic performance of the negative electrode material during the charge and discharge process, and further improve the specific capacity of the sodium ion battery.

[0063] Moreover, the second amorphous carbon is attached to the surface of the first amorphous carbon, which is not only beneficial to the performance of the first amorphous carbon and the second amorphous carbon, but also beneficial to the efficient utilization of the second amorphous carbon. At the same time, it can improve the conductivity of the negative electrode material and enhance the overall activity of the negative electrode material.

[0064] Here, the first amorphous carbon may be distributed in a dotted manner on the surface of the second amorphous carbon, or the first amorphous carbon may be coated on the surface of the second amorphous carbon in a layered manner.

[0065] In some embodiments, the second amorphous carbon has an average particle size ranging from 0.1 μm to 1 μm.

[0066] For example, the average particle size of the second amorphous carbon may be 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm or 1 μm, etc., which is not limited here.

[0067] It can be understood that the particle size of the second amorphous carbon is maintained in the range of 0.1μm to 1μm, indicating that the particle size of the second amorphous carbon is small, which can ensure that the second amorphous carbon has a larger specific surface area, which helps to increase the contact area between the second amorphous carbon and sodium ions, provide more reaction sites, thereby promoting the occurrence of electrochemical reactions, and responding to the insertion and deintercalation of sodium ions more quickly, thereby improving the kinetic performance of the negative electrode material during the charge and discharge process, and further improving the specific capacity of the sodium ion battery; and the particle size of the second amorphous carbon is small, which shortens the diffusion path of sodium ions and can quickly provide current, thereby improving the rate performance of the battery, enabling the sodium ion battery to release energy at a higher power in a short time.

[0068] In some embodiments, the average particle size of the first amorphous carbon is in a range of 2 μm to 10 μm.

[0069] For example, the average particle size of the first amorphous carbon may be 2 μm, 4 μm, 6 μm, 8 μm, or 10 μm, etc., which is not limited here.

[0070] For example, the median particle size of the first amorphous carbon is in the range of 4 μm to 8 μm. For example, the median particle size of the first amorphous carbon can be 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm, etc., which is not limited here.

[0071] It can be understood that the average particle size of the first amorphous carbon is maintained in the range of 2μm to 10μm, which can provide a more solid structural support, can maintain its shape under high mechanical stress, and is not easy to break or pulverize, thereby enhancing the cycle life and reliability of the sodium ion battery. At the same time, the first amorphous carbon with an average particle size range of 2μm to 10μm is combined with the second amorphous carbon with a smaller particle size to form an effective composite structure, which helps to form a good electronic conductive network. The larger first amorphous carbon can promote sufficient electron flow, enhance the overall electronic conductivity of the negative electrode material, and effectively improve the performance of the sodium ion battery.

[0072] In some embodiments, the first amorphous carbon material includes hard carbon.

[0073] Understandably, hard carbon is considered to be the most promising negative electrode material for sodium ion batteries due to its wide availability, low cost, environmental friendliness, good conductivity and low redox potential (0.1V~1V). In addition, hard carbon has the following advantages: (1) Hard carbon has a high theoretical specific capacity and can effectively intercalate and deintercalate sodium ions, especially exhibiting good cycle stability at low operating voltages. (2) The structure of hard carbon is relatively strong and can maintain good shape and integrity during multiple charge and discharge processes, resisting the mechanical stress caused by volume changes. (3) Hard carbon can provide a sufficient electronic conductive network, so that sodium ion batteries exhibit good conductivity during discharge. (4) The amorphous structure of hard carbon facilitates the movement of electrons and sodium ions, providing a smoother current path for sodium ion batteries. (5) Hard carbon materials exhibit low capacity decay during multiple charge and discharge cycles, can maintain good sodium ion battery performance, and make sodium ion batteries more durable for a long time when used in electric vehicles and renewable energy storage systems, etc., so that hard carbon, as the first amorphous carbon material, can significantly improve the performance of sodium ion batteries.

[0074] In addition, as an amorphous carbon material, hard carbon has a microstructure with disordered graphite-like layers, abundant edge and surface defects, and a unique nanopore structure. When used as a negative electrode material for sodium-ion batteries, hard carbon exhibits dual voltage region characteristics during the charge and discharge process, with the slope region being an important region. The charge and discharge curve of hard carbon can generally be divided into two parts: the slope region under high voltage (>0.1V) and the platform region under low voltage (<0.1V). The slope region exhibits faster kinetics and better rate capability. The higher average potential helps to inhibit the electroplating of sodium ions during the cycle, thereby improving the cycle stability of sodium-ion batteries.

[0075] In some embodiments, the material of the second amorphous carbon includes at least one of soft carbon and hard carbon.

[0076] Understandably, soft carbon has a higher specific surface area, which helps to increase the insertion and extraction reaction rate of sodium ions, thereby improving the charge and discharge performance. The flexibility and moderate volume change of soft carbon enable it to better adapt to stress during the charge and discharge process; soft carbon has amorphous or partially amorphous characteristics, which results in more defects and voids in the soft carbon, which can serve as channels for sodium ions, reducing the barriers to the migration of sodium ions within the material and allowing sodium ions to diffuse rapidly within it; soft carbon usually has good conductivity, which can improve the conductivity of the overall electrode and help achieve higher power density.

[0077] Moreover, the soft carbon has a higher capacity percentage in the slope region (>0.1V) and better kinetic performance. Therefore, loading the soft carbon, which is the second amorphous carbon material, on the surface of the hard carbon, which is the first amorphous carbon material, can increase the capacity and proportion of the hard carbon in the slope region, effectively improving its kinetic performance and avoiding the problem of sodium precipitation at the negative electrode.

[0078] For example, loading hard carbon on the surface of hard carbon after activation and pore formation can effectively reduce the specific surface area of ​​hard carbon, reduce the contact between hard carbon and electrolyte, and reduce the total surface area of ​​direct contact between negative electrode material and electrolyte, thereby reducing the intensity of side reactions (such as the formation of solid electrolyte interface film), helping to reduce the capacity loss of the battery during the first charge and discharge process, thereby improving the first charge and discharge efficiency.

[0079] In some embodiments, the specific surface area of ​​the negative electrode material is in the range of 3 m 2 / g~10m 2 / g.

[0080] For example, the specific surface area of ​​the negative electrode material can be 3m 2 / g, 5m 2 / g、7m 2 / g、9m 2 / g or 10m 2 / g, etc., are not limited here.

[0081] It is understandable that the specific surface area of ​​hard carbon is generally around 50 m 2 / g~300m 2 / g, the specific surface area of ​​soft carbon is generally between 10m 2 / g~100m 2 / g, indicating that the specific surface area of ​​the negative electrode material of the present application is small, which can reduce the total surface area of ​​direct contact between the negative electrode material and the electrolyte, thereby reducing the intensity of side reactions (such as the formation of solid electrolyte interface film), thereby improving the overall efficiency and initial cycle efficiency of the battery.

[0082] In some embodiments, the true density of the negative electrode material is in the range of 1.9 g / cm 3 ~2.1g / cm 3 .

[0083] For example, the true density of the negative electrode material can be 1.9 m 2 / g, 1.95m 2 / g, 2m 2 / g, 2.05m 2 / g or 2.1m 2 / g, etc., are not limited here.

[0084] It can be understood that the above configuration can enable the negative electrode material to maintain good electrical conductivity and ion conductivity, and a higher true density (>2.1 g / cm 3 ) or lower true density (<1.9g / cm 3 ) may lead to an unsatisfactory pore structure of the material, thereby affecting the charge and discharge efficiency and rate performance of the battery.

[0085] The above is a description of the negative electrode material. The following describes a method for preparing the negative electrode material.

[0086] In some examples, a composite material is obtained by physically mixing a first amorphous carbon and a second amorphous carbon, followed by a high-temperature carbonization process. However, this simple solid-phase mixing process results in poor contact between the first and second amorphous carbons in the final product, making it impossible to achieve uniform bonding between the first and second amorphous carbons, thus affecting the performance of the final product.

[0087] In other examples, a liquid-phase mixing process, where a first amorphous carbon is dispersed in a liquid precursor of a second amorphous carbon, can achieve uniform composite formation of the first and second amorphous carbons. However, this process is complex, and the ratio of the first to second amorphous carbons in the composite material is difficult to control. Chemical vapor deposition, while a method that can address these issues, is costly and places significant pressure on mass production.

[0088] The embodiment of the present application provides a method for preparing a negative electrode material. Figure 1 As shown, the preparation method of the negative electrode material includes: S1 to S3.

[0089] S1: dispersing a second amorphous carbon precursor in a solvent to obtain a second amorphous carbon precursor solution.

[0090] Exemplarily, the second amorphous carbon precursor includes at least one of asphalt, phenolic resin, epoxy resin, polyfurfuryl alcohol resin, polyvinyl pyrrolidone, polyvinyl alcohol, chitosan, and sucrose.

[0091] S2: Atomizing the second amorphous carbon precursor solution, contacting the solution with the first amorphous carbon dispersed under the first protective gas, and drying the solution to obtain an initial negative electrode material. The negative electrode material includes the first amorphous carbon and the second amorphous carbon attached to the surface of the first amorphous carbon; the average particle size of the first amorphous carbon is larger than the average particle size of the second amorphous carbon.

[0092] Exemplarily, the material of the first amorphous carbon includes: hard carbon.

[0093] Exemplarily, the drying time of the atomization treatment is controlled to be 15 minutes to 120 minutes.

[0094] In this step, the second amorphous carbon precursor is loaded on the surface of the first amorphous carbon. Exemplarily, the mass loading amount of the second amorphous carbon precursor on the surface of the first amorphous carbon is in the range of 1% to 10%.

[0095] For example, the mass loading amount of the second amorphous carbon precursor on the surface of the first amorphous carbon may be 1%, 3%, 5%, 7%, 9% or 10%, etc., which is not limited here.

[0096] Exemplarily, the first shielding gas includes argon.

[0097] S3: calcining the initial negative electrode material under the second protective gas to obtain a negative electrode material.

[0098] In this step, the calcined second amorphous carbon precursor forms second amorphous carbon and is loaded on the surface of the first amorphous carbon, thereby obtaining the negative electrode material as described in any of the above embodiments.

[0099] Exemplarily, the second shielding gas includes argon.

[0100] Exemplarily, the heating rate of calcination is in the range of 1°C / min to 20°C / min.

[0101] For example, the heating rate of calcination can be 1° C. / min, 5° C. / min, 10° C. / min, 15° C. / min, or 20° C. / min, etc., which is not limited here.

[0102] Exemplarily, the calcination temperature ranges from 700°C to 1500°C.

[0103] For example, the calcination temperature may be 700° C., 900° C., 1000° C., 1100° C., 1300° C., or 1500° C., etc., which is not limited here.

[0104] It can be understood that the present application adopts a liquid phase atomization coating process, that is, the second amorphous carbon precursor is prepared into a solution, and then atomized to make it evenly adhere to the surface of the hard carbon particles and dry quickly, and finally through high-temperature carbonization treatment, a uniformly composited negative electrode material can be obtained, cleverly achieving the uniform composite of the first amorphous carbon and the second amorphous carbon, and the process is relatively simple, and the ratio of the first amorphous carbon and the second amorphous carbon can be controlled, the cost is low, and the pressure of mass production is small.

[0105] Moreover, by introducing the atomization drying process into the process of compounding the first amorphous carbon and the second amorphous carbon precursor, the second amorphous carbon can be evenly distributed on the surface of the first amorphous carbon. Thanks to the special process of atomization drying, after high-temperature calcination, the second amorphous carbon is evenly distributed in the form of particles and dots on the surface of the first amorphous carbon particles, forming a heterojunction. Compared with ordinary coating, it has a larger specific surface area, which can enhance the contact between the negative electrode material and the electrolyte, so that the prepared soft carbon negative electrode material exhibits higher specific capacity and kinetic performance. Moreover, the preparation method of the negative electrode material is also applicable to the compounding or coating process of the first amorphous carbon and the second amorphous carbon, which can achieve uniform compounding of the first amorphous carbon and the second amorphous carbon.

[0106] In addition, the micro defects of the negative electrode material can be controlled by setting the calcination heating rate. By increasing the micro defects of the negative electrode material, it is beneficial to the deintercalation of sodium ions, thereby improving the performance of sodium ion batteries.

[0107] In some embodiments, in S1, dispersing the second amorphous carbon precursor in a solvent comprises:

[0108] The second amorphous carbon precursor and the solvent are mixed, the concentration of the second amorphous carbon precursor is in the range of 18 wt% to 22 wt%, and the mixture is ball-milled.

[0109] For example, the concentration of the second amorphous carbon precursor may be 18 wt %, 19 wt %, 20 wt %, 21 wt % or 22 wt %, etc., which is not limited here.

[0110] In some embodiments, in S2, the first amorphous carbon is dispersed under the action of the first protective gas, including:

[0111] A first protective gas with a temperature range of 120° C. to 180° C. is blown into the bottom of the atomizing drying device to disperse the first amorphous carbon in the atomizing drying device.

[0112] For example, the temperature of the first protective gas may be 120° C., 140° C., 160° C., 170° C., or 180° C., etc., which is not limited here.

[0113] The present application is further described in detail below by taking specific experiments as examples and in conjunction with the accompanying drawings. These implementation cases are only for illustrating the technical solution of the present application and cannot be regarded as limiting the content of the present application. In the examples, the raw materials used are all commonly used chemical materials in the laboratory, the hard carbon is homemade in the laboratory, N-methylpyrrolidone is purchased from Shanghai Aladdin Reagent Co., Ltd., asphalt is purchased from Sinopharm Chemical Reagent Co., Ltd., and deionized water is homemade in the laboratory (17.25MΩ·cm).

[0114] It should be noted that the scanning electron microscopy (SEM) images used in this application were obtained using a Zeiss Supra-55 field emission scanning electron microscope at an accelerating voltage of 3 kV; the transmission electron microscopy images were obtained using a JEOL JEM-2100F field emission transmission electron microscope at an accelerating voltage of 200 kV; and powder X-ray diffraction (XRD) was performed using a Panalytical X'Pert PRO MPD diffractometer under the test conditions of 40 kV and 40 mA.

[0115] Example 1

[0116] Example 1 provides a negative electrode material, and the preparation method of the negative electrode material includes:

[0117] Step (1): weigh industrial asphalt, place it in N-methylpyrrolidone (NMP), and ball-mill for 40 minutes to obtain an asphalt solution with a mass fraction of 20 wt%.

[0118] Step (2): placing the hard carbon in a sealed container of an atomizing drying device, blowing argon gas at a temperature of 150°C from the bottom of the atomizing drying device to fully disperse the hard carbon particles in the sealed container, and atomizing the asphalt solution obtained in step (1) through a nozzle above the atomizing drying device, and spraying it into the sealed container, so that the asphalt solution obtained in step (1) is fully in contact with the hard carbon particles and adheres to the surface of the hard carbon particles, and then drying is achieved to obtain a solid powder; wherein, the atomizing drying time is controlled to be 60 minutes, so that the asphalt loading amount on the hard carbon surface is about 3%.

[0119] Step (3): The solid powder obtained in step (2) is placed in a tubular furnace, argon is introduced as a protective atmosphere, and then the temperature is increased to 900°C at a heating rate of 10°C / min, and the temperature is kept at 900°C for 2 hours. After the tubular furnace program is completed and the temperature is cooled to room temperature, the black powder obtained is collected as the negative electrode material.

[0120] like Figure 2 is a SEM image of the negative electrode material of Example 1, wherein: Figure 2 a in Figure 2 Figure b is an SEM image of pure hard carbon. It can be seen that the average particle size of pure hard carbon is distributed in the range of 2μm to 10μm. Combined with the particle size test results, the D50 of the particles is about 5μm. Figure 2 c in Figure 2 The d in the figure is the SEM image of the negative electrode material. It can be seen that the particle size distribution and D50 of the hard carbon do not change after loading the soft carbon. The average particle size distribution is 2μm to 10μm. In the local enlarged image ( Figure 2 As can be seen from d), many soft carbon particles with an average diameter of 0.1 μm to 1 μm are evenly distributed on the surface of the hard carbon particles.

[0121] like Figure 3 This is the TEM image of the negative electrode material of Example 1. The measured interlayer spacing of the hard carbon is about 0.372nm, and the interlayer spacing of the soft carbon is about 0.374nm. It can be seen from the TEM image that the soft carbon and the hard carbon are in close contact in the selected area, forming a rich heterogeneous interface.

[0122] like Figure 4 The Raman spectrum of the negative electrode material of Example 1 is shown in FIG. Figure 4 Two characteristic peaks can be seen at about 1580 cm -1 The characteristic peak is the G peak, which corresponds to the ordered carbon in graphite; located at about 1350cm -1 The characteristic peak, D peak, corresponds to disordered carbon. Both G and D peaks are observed in each test result, indicating the presence of both soft and hard carbon in the negative electrode material of Example 1. Furthermore, the area of ​​the G peak is close to that of the D peak, indicating a high content of disordered carbon in the negative electrode material of Example 1. The ratio of the G to D peak areas ranges from 1.21 to 1.72.

[0123] like Figure 5 2 is the XRD pattern of the negative electrode material of Example 1. It can be seen that the soft carbon and hard carbon composite materials formed after treatment exhibit poor crystallinity, which indicates that the composite structure contains rich disordered structures.

[0124] Example 2

[0125] Example 2 provides a negative electrode material. The preparation method of the negative electrode material is the same as that of Example 1, except that the atomization drying time in step (2) is controlled to 30 minutes, so that the asphalt loading on the hard carbon surface is about 1%.

[0126] The particle size distribution test results of the negative electrode material of Example 2 show that the median particle size D50 of the hard carbon particles is 6 μm, D90 is about 12 μm, and the specific surface area is 5.61 m 2 / g; the microcrystalline interlayer spacing of the soft carbon is about 0.376nm; the Raman spectrum results show that the area ratio of the D peak and the G peak is in the range of 1.42 to 1.94, indicating that both soft carbon and hard carbon exist in the negative electrode material of Example 2.

[0127] Example 3

[0128] Example 3 provides a negative electrode material. The preparation method of the negative electrode material is the same as that of Example 1, except that the atomization drying time in step (2) is controlled to 100 minutes, so that the asphalt loading on the hard carbon surface is about 10%.

[0129] The particle size distribution test results of the negative electrode material of Example 3 show that the median particle size D50 of the hard carbon particles is 5.98 μm, D90 is about 20 μm, and the specific surface area is 2.73 m 2 / g, the larger D90 may be due to the excessive use of asphalt, which causes small hard carbon particles to agglomerate into large particles, and the smaller specific surface area (2.73m 2 / g) can also confirm the above inference; the microcrystalline interlayer spacing of soft carbon is about 0.374nm; the Raman spectrum results show that the area ratio of the D peak and the G peak is in the range of 1.02 to 1.53, indicating that both soft carbon and hard carbon exist in the negative electrode material of Example 3. Raman detection shows that the defect content of the negative electrode material of Example 3 is less than that of Example 1, which is mainly because the soft carbon coating amount on the hard carbon surface is large, covering the defects on the hard carbon surface.

[0130] Example 4

[0131] Example 4 provides a negative electrode material. The preparation method of the negative electrode material is the same as that of Example 1, except that the calcination temperature in step (3) is 700°C.

[0132] The particle size distribution test results of the negative electrode material of Example 4 show that the median particle size D50 of the hard carbon particles is 6.23 μm, D90 is about 11.2 μm, and the specific surface area is 6.25 m 2 / g; the soft carbon crystallite spacing was approximately 0.398 nm; and Raman spectroscopy results showed that the area ratio of the D peak to the G peak ranged from 1.48 to 1.76, indicating the presence of both soft and hard carbon in the negative electrode material of Example 4. Raman spectroscopy revealed that the negative electrode material of Example 4 contained relatively high levels of defects and a larger crystallite spacing of the soft carbon, primarily due to the lower calcination temperature.

[0133] Example 5

[0134] Example 5 provides a negative electrode material. The preparation method of the negative electrode material is the same as that of Example 1, except that the calcination temperature in step (3) is 1100°C.

[0135] The particle size distribution test results of the negative electrode material of Example 5 show that the median particle size D50 of the hard carbon particles is 5.92 μm, D90 is about 12.1 μm, and the specific surface area is 5.02 m 2 / g; the soft carbon crystallite spacing was approximately 0.382nm; and Raman spectroscopy results showed that the area ratio of the D peak to the G peak ranged from 0.92 to 1.56, indicating the presence of both soft and hard carbon in the negative electrode material of Example 5. Raman spectroscopy revealed that the negative electrode material of Example 5 contained relatively few defects and had a smaller crystallite spacing of the soft carbon, primarily due to the higher calcination temperature.

[0136] Example 6

[0137] Example 6 provides a negative electrode material. The preparation method of the negative electrode material is the same as that of Example 1, except that the industrial asphalt in step (1) is replaced by phenolic resin.

[0138] Comparative Example 1

[0139] Comparative Example 1 provides a negative electrode material, which is a commercially available hard carbon product.

[0140] Comparative Example 2

[0141] Comparative Example 2 provides a negative electrode material, and the preparation method of the negative electrode material includes:

[0142] Step (1): weigh industrial asphalt, place it in N-methylpyrrolidone (NMP), and ball-mill for 40 minutes to obtain an asphalt solution with a mass fraction of 20 wt%.

[0143] Step (2): Mixing the hard carbon with the asphalt solution obtained in step (1) to obtain a mixed solution.

[0144] Step (3): The mixed solution obtained in step (2) was placed in a tubular furnace, argon was introduced as a protective atmosphere, and then the temperature was increased to 900°C at a heating rate of 10°C / min, and the mixture was kept at 900°C for 2h to obtain a negative electrode material.

[0145] Comparative Example 3

[0146] Comparative Example 3 provides a negative electrode material, and the preparation method of the negative electrode material includes:

[0147] Step (1): weigh industrial asphalt and place it in N-methylpyrrolidone (NMP) to obtain an asphalt solution with a mass fraction of 20 wt%.

[0148] Step (2): mixing the hard carbon with the asphalt solution obtained in step (1), and then performing solid-liquid separation and drying to obtain solid powder.

[0149] Step (3): The solid powder obtained in step (2) was placed in a tube furnace, argon was introduced as a protective atmosphere, and then the temperature was increased to 900°C at a heating rate of 10°C / min, and the temperature was kept at 900°C for 2h to obtain the negative electrode material.

[0150] Performance Testing

[0151] The negative electrode materials of the embodiment and the comparative example were made into CR2032 button-type sodium ion batteries for evaluation.

[0152] Specifically, the negative electrode material of the embodiment and comparative example: conductive agent: carboxymethyl cellulose: maleic acid rubber in a ratio of 92:2:2:4 were uniformly mixed in deionized water to form a slurry. An appropriate amount of N-methylpyrrolidone was then added and mixed until uniform. The mixed slurry was then evenly coated on a carbon-coated aluminum foil current collector and transferred to an 80°C oven to dry for 1 hour. Finally, the dried electrode sheets were rolled on a roller press and cut into electrode discs with a diameter of 14 mm. Prior to assembly of button-type sodium-ion batteries, the electrode discs were dried in a 110°C oven for 3 hours. The dried electrode discs were transferred to a glove box (with H₂O and O₂ concentrations not exceeding 0.1 ppm) and assembled into CR2032 button-type batteries using a sodium sheet as the counter electrode, glass fiber as the separator, and NaPF₂ / (EC+DMC) as the electrolyte.

[0153] Test 1: (1) A constant current charge and discharge test was performed on a CR2032 button cell made of the negative electrode materials of Example 1 and Comparative Example 1. The constant current charge and discharge test was performed on a BlueDian multi-channel battery test system. The test voltage range was 0.005 to 2.0 V, and the test temperature was 25°C.

[0154] like Figure 6 The electrochemical charge-discharge curves of the sodium ion batteries made of the negative electrode materials of Example 1 and Comparative Example 1 are shown. At a current density of 0.1C, the first-cycle discharge capacity of the CR2032 button battery made of the negative electrode material of Example 1 is 307.82 mAh g -1 , the charge capacity is 269.55mAhg -1 The first cycle coulombic efficiency is 87.57%. In the discharge capacity, the slope area (>0.1V) capacity is as high as 133.03mAhg -1 The slope area capacity accounts for as high as 43.32%, which is significantly higher than the data of the CR2032 button battery made of the negative electrode materials of Comparative Example 1 and Japan Kuraray Type-2. The CR2032 button battery made of the negative electrode material of Example 1 has a higher charge and discharge voltage platform and slope area capacity.

[0155] (2) The results of testing the first-cycle discharge capacity, first-cycle coulomb efficiency, slope region capacity and slope region capacity ratio of CR2032 button batteries made of the negative electrode materials of the embodiment and the comparative example are shown in Table 1.

[0156] Table 1: First-cycle discharge capacity, first-cycle coulomb efficiency, slope region capacity, and slope region capacity ratio of CR2032 button batteries made of negative electrode materials of the embodiment and comparative example

[0157]

[0158] Test 2: The sodium ion batteries made of the negative electrode materials of Example 1 and Comparative Example 1 were subjected to a rate-capacity retention test.

[0159] like Figure 7 The rate-capacity retention curves of the sodium ion batteries made from the negative electrode materials of Example 1 and Comparative Example 1 show that, compared with Comparative Example 1, the CR2032 button battery made from the negative electrode material of Example 1 exhibits a higher rate-capacity retention, which also indicates that the negative electrode material of Example 1 has higher kinetic performance, which is mainly attributed to the effective composite of soft carbon and hard carbon: (1) The method provided by this patent enables the soft carbon to be evenly distributed on the surface of the hard carbon in the form of dots. Compared with other coating methods, it can not only increase the specific surface area of ​​the composite material and enhance the contact with the electrolyte, but also improve the conductivity of the hard carbon material; (2) A rich heterogeneous interface is formed between the dot-distributed soft carbon and the hard carbon body, which promotes the efficient transfer of substances during the charge and discharge process, which can not only achieve an improvement in the specific capacity of the negative electrode material but also an improvement in the kinetic performance of the negative electrode material.

[0160] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A negative electrode material, characterized in that include: a first amorphous carbon and a second amorphous carbon attached to a surface of the first amorphous carbon; The average particle size of the first amorphous carbon is greater than the average particle size of the second amorphous carbon.

2. The negative electrode material according to claim 1, characterized in that The average particle size of the second amorphous carbon is in the range of 0.1 μm to 1 μm.

3. The negative electrode material according to claim 1, characterized in that The average particle size of the first amorphous carbon is in the range of 2 μm to 10 μm.

4. The negative electrode material according to claim 1, characterized in that The material of the first amorphous carbon includes hard carbon.

5. The negative electrode material according to claim 1, characterized in that The material of the second amorphous carbon includes at least one of soft carbon and hard carbon.

6. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is in the range of 3m 2 / g~10m 2 / g.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that The true density of the negative electrode material is in the range of 1.9 g / cm 3 ~2.1g / cm 3 .

8. A method for preparing a negative electrode material, characterized in that: include: dispersing a second amorphous carbon precursor in a solvent to obtain a second amorphous carbon precursor solution; atomizing the second amorphous carbon precursor solution, contacting the solution with the first amorphous carbon dispersed under the action of the first protective gas, and drying the solution to obtain an initial negative electrode material; The initial negative electrode material is calcined under a second protective gas to obtain the negative electrode material, wherein the negative electrode material includes: a first amorphous carbon and a second amorphous carbon attached to a surface of the first amorphous carbon; the average particle size of the first amorphous carbon is greater than the average particle size of the second amorphous carbon.

9. The method for preparing the negative electrode material according to claim 8, wherein: In the calcining of the initial negative electrode material, the calcination temperature rise rate ranges from 1° C. / min to 20° C. / min.

10. The method for preparing the negative electrode material according to claim 8, wherein: In the calcining of the initial negative electrode material, the calcination temperature ranges from 700°C to 1500°C.

11. The method for preparing the negative electrode material according to claim 8, wherein: The material of the first amorphous carbon includes hard carbon.

12. The method for preparing the negative electrode material according to claim 8, wherein: The second amorphous carbon precursor includes at least one of asphalt, phenolic resin, epoxy resin, polyfurfuryl alcohol resin, polyvinyl pyrrolidone, polyvinyl alcohol, chitosan and sucrose.

13. The method for preparing the negative electrode material according to claim 8, wherein: The solvent includes at least one of N-methylpyrrolidone, acetone, and xylene.

14. The method for preparing the negative electrode material according to claim 8, wherein: The step of dispersing the second amorphous carbon precursor in a solvent comprises: The second amorphous carbon precursor is dispersed in a solvent, wherein the concentration of the second amorphous carbon precursor is in the range of 18 wt % to 22 wt %, and ball milling is performed.

15. The method for preparing the negative electrode material according to claim 8, characterized in that: The first amorphous carbon dispersed under the action of the first protective gas includes: The first protective gas with a temperature range of 120° C. to 180° C. is blown into the bottom of the atomizing drying device to disperse the first amorphous carbon in the atomizing drying device.

16. The method for preparing the negative electrode material according to claim 15, characterized in that: The second amorphous carbon precursor solution is subjected to atomization treatment, and the drying time of the atomization treatment is controlled within a range of 15 minutes to 120 minutes.

17. The method for preparing the negative electrode material according to claim 16, wherein: The second amorphous carbon precursor solution is atomized and brought into contact with the first amorphous carbon dispersed under the action of the first protective gas, and the mass loading of the second amorphous carbon precursor on the surface of the first amorphous carbon is in the range of 1% to 10%.

18. A sodium ion battery, characterized in that: include: a positive electrode and a negative electrode disposed opposite to the positive electrode; The material of the negative electrode includes: the negative electrode material according to any one of claims 1 to 7.

19. A battery pack, characterized in that: include: At least two sodium ion batteries according to claim 18.

20. An electrical device, characterized in that: include: The battery pack as claimed in claim 19.

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