Hard carbon secondary particle and preparation method thereof, negative electrode plate and sodium battery

Abstract

The invention provides hard carbon secondary particles and a preparation method thereof, a negative electrode plate and a sodium battery. The hard carbon secondary particle is formed by aggregating a plurality of hard carbon primary particles, and the median particle diameter D50 of the hard carbon primary particles is larger than or equal to 200 nm and smaller than or equal to 500 nm.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a hard carbon secondary particle and its preparation method, a negative electrode sheet, and a sodium battery. Background Technology

[0002] Sodium-ion batteries, with their advantages of abundant and widely distributed sodium resources and low cost, are considered a highly promising large-scale energy storage solution and have received widespread attention in recent years. Hard carbon is considered one of the most likely anode materials for commercial application in sodium-ion batteries. However, hard carbon has a small interlayer spacing and a large sodium ion radius, resulting in poor rate performance and slow charge / discharge speeds. Summary of the Invention

[0003] This application provides a hard carbon secondary particle with high rate performance.

[0004] In a first aspect, embodiments of this application provide a hard carbon secondary particle, which is formed by the aggregation of multiple hard carbon primary particles, wherein the median particle size D50 of the hard carbon primary particles is in the range of 200nm≤D50≤500nm.

[0005] Optionally, the hard carbon primary particles are spherical or near-spherical, and the average value F of the shape factor of the hard carbon primary particles is in the range of 0.9 ≤ F ≤ 1.0.

[0006] Optionally, the hard carbon secondary particles include multiple pores, and the pore volume of the hard carbon secondary particles ranges from 0.02 cm³. 3 / g to 0.04cm 3 / g.

[0007] Optionally, the median particle size D50' of the hard carbon secondary particles ranges from 2.5 μm ≤ D50' ≤ 6 μm.

[0008] Optionally, the specific surface area of ​​the hard carbon secondary particles ranges from 2m². 2 / g to 8m 2 / g.

[0009] Optionally, the hard carbon secondary particles include an active core and a carbon coating layer. The active core is formed by the aggregation of the plurality of hard carbon primary particles, and the carbon coating layer is wrapped around the surface of the active core. The thickness of the carbon coating layer ranges from 10 nm to 200 nm.

[0010] Secondly, embodiments of this application also provide a method for preparing hard carbon secondary particles, the preparation method comprising:

[0011] A primary particle precursor is provided, wherein the average particle size of the primary particle precursor ranges from 200 nm to 500 nm;

[0012] The primary particle precursor is pre-carbonized at a first temperature to obtain pre-carbonized secondary particles; and

[0013] The pre-carbonized secondary particles are carbonized at a second temperature to obtain hard carbon secondary particles, wherein the first temperature is lower than the second temperature; the hard carbon secondary particles are formed by the aggregation of multiple hard carbon primary particles, and the median particle size D50 of the hard carbon primary particles is in the range of 200nm≤D50≤500nm.

[0014] Optionally, the provision of the primary particulate precursor includes:

[0015] Provide a reactive monomer, a catalyst, and a surfactant, wherein the residual carbon content of the surfactant is less than or equal to 1%;

[0016] The reactants, catalyst, and surfactant are mixed and stirred at a first stirring rate at a temperature of 80°C to 90°C; and

[0017] The temperature is raised to 100°C to 130°C, and the mixture is stirred at a second stirring rate for 8 to 12 hours to obtain a primary particle precursor; wherein the first stirring rate is greater than the second stirring rate.

[0018] Optionally, the first stirring rate ranges from 200 rpm to 500 rpm; the second stirring rate ranges from 50 rpm to 300 rpm.

[0019] Optionally, the step of pre-carbonizing the primary particle precursor at a first temperature to obtain pre-carbonized secondary particles includes:

[0020] The primary particle precursor is pre-carbonized at a first temperature of 500°C to 600°C to obtain first intermediate particles; and

[0021] The first intermediate particles are subjected to air jet milling to obtain pre-carbonized secondary particles, wherein the particle size of the pre-carbonized secondary particles is 2μm to 5μm.

[0022] Optionally, the step of carbonizing the pre-carbonized secondary particles at a second temperature includes: carbonizing the pre-carbonized secondary particles at a second temperature ranging from 1200°C to 1500°C.

[0023] Before placing the pre-carbonized secondary particles at a second temperature for carbonization, the preparation method further includes:

[0024] The pre-carbonized secondary particles are mixed with a carbon source to obtain second intermediate particles;

[0025] The step of carbonizing the pre-carbonized secondary particles at a second temperature includes: carbonizing the second intermediate particles at a second temperature to form an active core in the pre-carbonized secondary particles, and forming a carbon coating layer in the carbon source; wherein the hard carbon secondary particles include an active core and a carbon coating layer, the active core is formed by the aggregation of the plurality of hard carbon primary particles, the carbon coating layer is wrapped around the surface of the active core, and the thickness of the carbon coating layer ranges from 10 nm to 200 nm.

[0026] Thirdly, embodiments of this application also provide a negative electrode sheet, which includes:

[0027] Negative current collector; and

[0028] A negative electrode active layer is disposed on the surface of the negative electrode current collector, and the negative electrode active layer includes the hard carbon secondary particles described in the embodiments of this application.

[0029] Fourthly, embodiments of this application also provide a sodium battery, the sodium battery comprising: an electrolyte, a positive electrode, a separator, and the negative electrode described in embodiments of this application.

[0030] The hard carbon secondary particles in this application are formed by the aggregation of multiple hard carbon primary particles, wherein the median particle size D50 of the hard carbon primary particles ranges from 200 nm to 500 nm. The sodium storage mechanism of the hard carbon secondary particles includes a sodium storage model of "adsorption-intercalation-pore filling". The ion diffusion rate in the intercalation stage is lower than that in the adsorption and pore filling stages. Therefore, improving the ion diffusion rate in the intercalation stage can more effectively improve the rate performance of hard carbon. Sodium ions must diffuse into the pore-filling sodium storage stage before entering, so reducing the interlayer diffusion distance is the key to improving rate performance. This application, through the design of the median particle size of the hard carbon primary particles, can shorten the diffusion path and transport distance of sodium ions, improve the kinetic performance of the hard carbon secondary particles, thereby improving the rate performance of the sodium battery and the charge / discharge rate of the sodium battery. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of hard carbon secondary particles according to an embodiment of this application.

[0033] Figure 2 This is a scanning electron microscope image of hard carbon secondary particles according to an embodiment of this application.

[0034] Figure 3 This is a schematic diagram of the structure of hard carbon secondary particles according to another embodiment of this application.

[0035] Figure 4 This is a schematic flowchart of a method for preparing hard carbon secondary particles according to an embodiment of this application.

[0036] Figure 5 This is a schematic flowchart of a method for preparing a primary particulate precursor according to an embodiment of this application.

[0037] Figure 6 This is a schematic diagram of the pre-carbonization process in the preparation method of hard carbon secondary particles according to an embodiment of this application.

[0038] Figure 7 This is a schematic flowchart of a method for preparing hard carbon secondary particles according to another embodiment of this application.

[0039] Figure 8 This is a cross-sectional view of the negative electrode sheet according to an embodiment of this application.

[0040] Figure 9 This is a schematic diagram of the structure of a sodium battery according to an embodiment of this application.

[0041] Figure 10 This application describes a sodium battery according to an embodiment of the present application. Figure 9 A schematic diagram of the cross-sectional structure along the AA direction.

[0042] Figure 11 This is a cross-sectional view of the positive electrode sheet according to an embodiment of this application.

[0043] Figure 12 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0044] Figure 13 This is a structural block diagram of an energy storage system according to an embodiment of this application.

[0045] Figure 14 This is an application scenario diagram of an energy storage system according to an embodiment of this application.

[0046] Explanation of reference numerals in the attached figures:

[0047] 100-Hard carbon secondary particles, 10-Hard carbon primary particles, 20-Porosity, 10a-Active core, 30-Carbon coating layer, 400-Negative electrode sheet, 410-Negative electrode current collector, 420-Negative electrode active layer, 500-Sodium battery, 510-Positive electrode sheet, 511-Positive electrode current collector, 512-Positive electrode active layer, 520-Separator, 540-Shell, 550-End cap assembly, 600-Energy storage device, 610-Box, 700-Energy storage system, 710-Electric power conversion device. Detailed Implementation

[0048] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0050] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0051] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0052] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0053] Batteries are the smallest energy storage unit in energy storage devices and systems, and their performance directly affects the performance and application of these devices and systems. Batteries include lithium batteries and sodium batteries.

[0054] Sodium-ion batteries, with their advantages of abundant and widely distributed sodium resources and low cost, are considered a highly promising large-scale energy storage solution and have received widespread attention in recent years. Hard carbon is considered one of the most likely anode materials for commercial application in sodium-ion batteries. However, hard carbon has a small interlayer spacing and a large sodium ion radius, resulting in poor rate performance and slow charge / discharge speeds.

[0055] See Figure 1 This application provides a hard carbon secondary particle 100, which is formed by the aggregation of multiple hard carbon primary particles 10. The median particle size D50 of the hard carbon primary particles 10 is in the range of 200nm≤D50≤500nm.

[0056] The hard carbon secondary particles 100 of this application embodiment can be applied to sodium batteries (such as sodium-ion batteries) as negative electrode active materials of the negative electrode active layer of the positive electrode sheet of sodium batteries.

[0057] Understandably, the hard carbon secondary particles 100 comprise a plurality of hard carbon primary particles 10. The plurality of hard carbon primary particles 10 are closely arranged and stacked to form a hard carbon secondary particle 100 resembling a "grape bunch structure." A scanning electron microscope (SEM) image of the hard carbon secondary particles 100 according to an embodiment of this application is shown below. Figure 2 As shown, Figure 2 As shown, multiple primary hard carbon particles 10 are tightly packed together to form secondary hard carbon particles 100 that resemble a "grape bunch deconstruction".

[0058] Understandably, the hard carbon primary particles 10 of this application are submicron in size.

[0059] Optionally, the sodium battery can be, but is not limited to, a sodium-ion battery, a lithium-sodium hybrid battery, or a sodium metal battery.

[0060] The term "secondary particle" refers to a larger composite particle structure formed by the aggregation of multiple primary particles through physical or chemical processes.

[0061] "Median particle size D50" refers to the particle size corresponding to a cumulative volumetric particle size distribution percentage of 50%.

[0062] Specifically, the median particle size D50 of the hard carbon primary particles 10 can be, but is not limited to, 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, etc. If the median particle size D50 of the hard carbon primary particles 10 is too small, the specific surface area of ​​the hard carbon secondary particles 100 will be too large, increasing the side reactions between the hard carbon secondary particles 100 and the electrolyte, and reducing the initial efficiency and cycle capacity retention of the sodium battery. If the median particle size D50 of the hard carbon primary particles 10 is too large, the transport distance of sodium ions will be increased, resulting in a deterioration in the rate performance and kinetic performance of the sodium battery. When the median particle size D50 of the hard carbon primary particles 10 is in the range of 200 nm to 500 nm, the diffusion path and transport distance of sodium ions can be shortened better, the kinetic performance of the hard carbon secondary particles 100 can be improved, thereby improving the rate performance of the sodium battery and the charge and discharge rate of the sodium battery.

[0063] The hard carbon secondary particles 100 of this application embodiment are formed by the aggregation of multiple hard carbon primary particles 10, wherein the median particle size D50 of the hard carbon primary particles 10 ranges from 200nm to 500nm. The sodium storage mechanism of the hard carbon secondary particles 100 includes a sodium storage model of "adsorption-intercalation-pore filling". The ion diffusion rate in the intercalation stage is lower than that in the adsorption and pore filling stages. Therefore, improving the ion diffusion rate in the intercalation stage can more effectively improve the rate performance of hard carbon. Sodium ions must diffuse into the pore-filling sodium storage stage before entering, so reducing the interlayer diffusion distance is the key to improving rate performance. This application, through the design of the median particle size of the hard carbon primary particles 10, can shorten the diffusion path and transport distance of sodium ions, improve the kinetic performance of the hard carbon secondary particles 100, thereby improving the rate performance of the sodium battery and the charge / discharge rate of the sodium battery.

[0064] Optionally, the interlayer orientation within the hard carbon primary particles 10 is isotropic (i.e., the interlayer orientation is random). This is beneficial for improving the kinetic performance of the hard carbon secondary particles 100 and increasing the rate performance of the battery.

[0065] In some embodiments, the hard carbon primary particles 10 are spherical or near-spherical, and the average value F of the shape factor of the hard carbon primary particles 10 is in the range of 0.9 ≤ F ≤ 1.0.

[0066] In the embodiments of this application, when the numerical range a to b is involved, unless otherwise specified, the numerical value can be any value between a and b, including the endpoint value a and the endpoint value b.

[0067] It should be noted that the shape factor F of the primary hard carbon particles 10 can be expressed by the formula F = 4πA / P. 2 The calculation is performed, where P is the maximum perimeter of the hard carbon primary particle 10, and A is the cross-sectional area corresponding to the maximum perimeter of the hard carbon primary particle 10. When the hard carbon primary particle 10 is spherical, F = 1. Therefore, the closer F is to 1, the better the sphericity of the hard carbon primary particle 10.

[0068] Specifically, the average value of the shape factor of the hard carbon primary particles 10 can be, but is not limited to, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, etc.

[0069] In this embodiment, the average shape factor of the hard carbon primary particles 10 is too small, which reduces the compaction density of the hard carbon secondary particles 100 and reduces the energy density of the sodium battery.

[0070] Please see again Figure 1 In some embodiments, the hard carbon secondary particles 100 include a plurality of pores 20, the pore volume of the hard carbon secondary particles 100 ranging from 0.02 cm³. 3 / g to 0.04cm 3 / g.

[0071] It should be noted that the pores 20 of the hard carbon secondary particles 100 described in this application are gaps or holes left by the accumulation of multiple hard carbon primary particles 10.

[0072] "Pore volume" refers to the total volume of all pores 20 in a unit mass of hard carbon secondary particles 100. In this application, the pore volume refers to the BJH pore volume, i.e., the pore volume measured using the Barrett-Joyner-Halenda (BJH) method. In other words, pore volume is the total volume of mesopores in a unit mass of hard carbon secondary particles 100.

[0073] Specifically, the pore volume of the hard carbon secondary particles 100 can be, but is not limited to, 0.02 cm. 3 / g, 0.022cm 3 / g, 0.024cm 3 / g, 0.026cm 3 / g, 0.028cm 3 / g, 0.03cm 3 / g, 0.032cm 3 / g, 0.034cm 3 / g, 0.036cm 3 / g, 0.038cm 3 / g, 0.04cm 3 / g etc.

[0074] In this embodiment, if the pore volume of the hard carbon secondary particles 100 is too small, the amount of sodium ions that the hard carbon secondary particles 100 can adsorb is reduced, thus reducing the kinetic performance of the hard carbon secondary particles 100; if the pore volume of the hard carbon secondary particles 100 is too large, the specific surface area of ​​the hard carbon secondary particles 100 is increased, the side reactions between the hard carbon secondary particles 100 and the electrolyte are increased, thus reducing the initial efficiency and cycle capacity retention of the sodium battery.

[0075] In some embodiments, the median particle size D50' of the hard carbon secondary particles 100 ranges from 2.5 μm ≤ D50' ≤ 6 μm.

[0076] Specifically, the median particle size D50' of the hard carbon secondary particles 100 can be, but is not limited to, 2.5μm, 2.8μm, 3.0μm, 3.3μm, 3.5μm, 3.8μm, 4.0μm, 4.3μm, 4.5μm, 4.8μm, 5.0μm, 5.3μm, 5.5μm, 5.8μm, 6μm, etc.

[0077] "Median particle size D50" refers to the particle size corresponding to the cumulative volumetric particle size distribution percentage of the hard carbon secondary particles 100 reaching 50%.

[0078] In this embodiment, if the median particle size D50' of the hard carbon secondary particles 100 is too small, the specific surface area of ​​the hard carbon secondary particles 100 will be too large, which will increase the side reactions between the hard carbon secondary particles 100 and the electrolyte and reduce the initial efficiency and cycle capacity retention of the sodium battery; if the median particle size D50' of the hard carbon secondary particles 100 is too large, the transport path of sodium ions will be increased and the kinetic performance of the hard carbon secondary particles 100 will be reduced.

[0079] In some embodiments, the specific surface area of ​​the hard carbon secondary particles 100 ranges from 2m². 2 / g to 8m 2 / g.

[0080] Specifically, the specific surface area of ​​the hard carbon secondary particles 100 can be, but is not limited to, 2 m². 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g etc.

[0081] In this embodiment, the specific surface area of ​​the hard carbon secondary particles 100 is too small, which reduces the contact area between the hard carbon secondary particles 100 and the electrolyte, making it difficult for the electrolyte to wet the hard carbon secondary particles 100. This reduces the area on which sodium ions can be intercalated on the hard carbon secondary particles 100, thereby reducing the kinetic performance of the hard carbon secondary particles 100. On the other hand, if the specific surface area of ​​the hard carbon secondary particles 100 is too large, it increases the side reactions between the hard carbon secondary particles 100 and the electrolyte, reducing the initial efficiency and cycle capacity retention of the sodium battery.

[0082] See Figure 3 In some embodiments, the hard carbon secondary particles 100 include an active core 10a and a carbon coating layer 30. The active core 10a is formed by the aggregation of the plurality of hard carbon primary particles 10, and the carbon coating layer 30 is wrapped around the surface of the active core 10a. The thickness of the carbon coating layer 30 ranges from 10 nm to 200 nm.

[0083] Optionally, the carbon coating layer 30 can be soft carbon.

[0084] Specifically, the thickness of the carbon coating layer 30 can be, but is not limited to, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, etc.

[0085] When the hard carbon secondary particles 100 do not have a carbon coating layer 30 (i.e., only an active core 10a of multiple hard carbon primary particles 10 stacked together), when the hard carbon secondary particles 100 are used to prepare the negative electrode slurry, the hard carbon secondary particles 100 are easily destroyed, forming multiple hard carbon primary particles 10. The particle size of the hard carbon primary particles 10 is in the nanometer range, and their specific surface area is too large, which will lead to the viscosity of the slurry being too high, affecting the coating of the negative electrode slurry. In this embodiment, a carbon coating layer 30 is formed on the surface of the active core 10a, which improves the stability of the hard carbon secondary particles 100 during the formation of the negative electrode slurry from the pulp. Furthermore, the carbon coating layer 30 reduces the specific surface area of ​​the hard carbon secondary particles 100, reduces side reactions between the hard carbon secondary particles 100 and the electrolyte, and improves the initial efficiency and cycle capacity retention of the sodium battery. Moreover, the carbon coating layer 30 is made of soft carbon, which has higher conductivity than the active core 10a, thereby better improving the electronic conductivity of the hard carbon secondary particles 100 and enhancing their kinetic performance. If the carbon coating layer 30 is too thin, it is detrimental to improving the stability of the hard carbon secondary particles 100, reducing side reactions between the hard carbon secondary particles 100 and the electrolyte, improving the initial efficiency and cycle capacity retention of the sodium battery, and also detrimental to improving the conductivity and kinetic performance of the hard carbon secondary particles 100. If the carbon coating layer 30 is too thick, it will reduce the specific capacity of the hard carbon secondary particles 100 and reduce the energy density of the sodium battery.

[0086] The hard carbon secondary particles 100 of this application embodiment can be prepared by the methods described in the following embodiments of this application. In addition, they can also be prepared by other methods. The preparation methods of this application embodiment are merely one or more preparation methods of the hard carbon secondary particles 100 of this application and should not be construed as limiting the hard carbon secondary particles 100 provided in the embodiments of this application.

[0087] See Figure 4 This application provides a method for preparing hard carbon secondary particles 100, the preparation method comprising:

[0088] S201, providing a primary particle precursor, the primary particle precursor having an average particle size ranging from 200 nm to 500 nm;

[0089] Specifically, the average particle size of the primary particle precursor can be, but is not limited to, 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, and 500nm. If the average particle size of the primary particle precursor is too small, the median particle size D50 of the hard carbon primary particles 10 will be too small, and the specific surface area of ​​the hard carbon secondary particles 100 will be too large, increasing the side reactions between the hard carbon secondary particles 100 and the electrolyte, and reducing the initial efficiency and cycle capacity retention of the sodium battery. If the average particle size of the primary particle precursor is too large, the median particle size D50 of the hard carbon primary particles 10 will be too large, and the transport distance of sodium ions will be too long, resulting in poor rate performance and poor kinetic performance of the sodium battery.

[0090] S202, the primary particle precursor is pre-carbonized at a first temperature to obtain pre-carbonized secondary particles; and

[0091] S203, the pre-carbonized secondary particles are carbonized at a second temperature to obtain hard carbon secondary particles 100, wherein the first temperature is lower than the second temperature; the hard carbon secondary particles 100 are formed by the aggregation of multiple hard carbon primary particles 10, and the median particle size D50 of the hard carbon primary particles 10 is in the range of 200nm≤D50≤500nm.

[0092] For further detailed descriptions of other aspects of the hard carbon secondary particles 100 and hard carbon primary particles 10, please refer to the descriptions of the corresponding sections of the above embodiments, which will not be repeated here.

[0093] The hard carbon secondary particles 100 of this application embodiment are formed by the aggregation of multiple hard carbon primary particles 10, wherein the median particle size D50 of the hard carbon primary particles 10 ranges from 200nm to 500nm. The sodium storage mechanism of the hard carbon secondary particles 100 includes a sodium storage model of "adsorption-intercalation-pore filling". The ion diffusion rate in the intercalation stage is lower than that in the adsorption and pore filling stages. Therefore, improving the ion diffusion rate in the intercalation stage can more effectively improve the rate performance of hard carbon. Sodium ions must diffuse into the pore-filling sodium storage stage before entering, so reducing the interlayer diffusion distance is the key to improving rate performance. This application, through the design of the median particle size of the hard carbon primary particles 10, can shorten the diffusion path and transport distance of sodium ions, improve the kinetic performance of the hard carbon secondary particles 100, thereby improving the rate performance of the sodium battery and the charge / discharge rate of the sodium battery.

[0094] See Figure 5 In some embodiments, in S201, providing the primary particulate precursor includes:

[0095] S2011, providing a reactive monomer, a catalyst and a surfactant, wherein the residual carbon content of the surfactant is less than or equal to 1%;

[0096] The term "residual carbon content" refers to the percentage of solid carbon material remaining after the surfactant has been completely pyrolyzed in an inert atmosphere (such as nitrogen or argon) during high-temperature pyrolysis or carbonization, relative to the total initial mass.

[0097] Specifically, the residual carbon content of the surfactant can be, but is not limited to, less than or equal to 1%, less than or equal to 0.9%, less than or equal to 0.8%, less than or equal to 0.7%, less than or equal to 0.6%, less than or equal to 0.5%, less than or equal to 0.4%, less than or equal to 0.3%, less than or equal to 0.2%, less than or equal to 0.1%, or 0%. If the residual carbon content of the surfactant is too high, the specific capacity of the obtained hard carbon secondary particles 100 is reduced, thus lowering the energy density of the battery.

[0098] Optionally, the primary particulate precursor may be, but is not limited to, at least one of polymers such as phenolic resin, furfural resin, and epoxy resin. In the following description and embodiments of this application, phenolic resin is used as an example of the primary particulate precursor, and this should not be construed as limiting the primary particulate precursor used in the embodiments of this application.

[0099] In a specific example, if the primary particle precursor is phenolic resin, then the reactant monomers include phenol and formaldehyde, the catalyst can be ammonia water with a mass concentration of 25%, and the surfactant can be, but is not limited to, polyethylene glycol (PEG).

[0100] Optionally, the molar ratio of phenol to formaldehyde is from 1:1 to 1:1.5. Specifically, the molar ratio of phenol to formaldehyde can be, but is not limited to, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc. During the preparation of the primary particulate precursor, formaldehyde is in excess compared to phenol, which better ensures more complete hydroxymethylation.

[0101] Optionally, the amount of 25% ammonia added is 5% to 10% of the mass of phenol. Specifically, the amount of 25% ammonia added can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10% of the mass of phenol.

[0102] Optionally, the amount of surfactant added is 1% to 5% of the mass of the reactant monomers (such as the total mass of phenol and formaldehyde). Specifically, the amount of surfactant added can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, etc., of the mass of the reactant monomers. Adding surfactant during the synthesis of the primary particle precursor can prevent the primary particle precursor from agglomerating and ensure the presence of primary particles. If the amount of surfactant added is too small, the primary particle precursor is prone to agglomeration and it is difficult to ensure sphericity, which reduces the compaction density of the obtained hard carbon secondary particles 100; if the amount of surfactant added is too large, it reduces the molecular weight of the primary particle precursor and reduces the specific mass of the obtained hard carbon secondary particles 100.

[0103] In a specific example, the number average molecular weight of polyethylene glycol (PEG) is between 500 and 1200. Specifically, the number average molecular weight of PEG can be, but is not limited to, 500, 600, 700, 800, 900, 1000, 1100, 1200, etc. If the number average molecular weight of PEG is too high, PEG will be insoluble in water, reducing its solubility in water. This makes the primary particle precursor prone to aggregation, which is not conducive to the formation of single spherical particles from the primary particle precursor.

[0104] S2012, the reactants, catalyst, and surfactant are mixed and stirred at a first stirring rate at a temperature of 80°C to 90°C; and

[0105] In one specific example, phenol, formaldehyde, ammonia (25% by mass), and polyethylene glycol are dissolved in water and mixed. The mixture is then placed at a temperature of 80°C to 90°C and stirred at a first stirring rate to ensure that the components are fully mixed and the reaction is more complete, thus obtaining a reaction slurry.

[0106] Specifically, the mixing temperature of each reactant (reactant monomer, catalyst, and surfactant, etc.) can be, but is not limited to, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, etc. If the mixing temperature of each reactant is too low, it is not conducive to the uniform mixing of the reactants; if the mixing temperature of each reactant is too high, part of the polymer reaction will take place before the reactants are uniformly mixed, which will reduce the gram capacity of the obtained hard carbon secondary particles 100.

[0107] In some embodiments, the first stirring rate ranges from 200 rpm to 500 rpm. Specifically, the first stirring rate can be, but is not limited to, 200 rpm, 230 rpm, 250 rpm, 280 rpm, 300 rpm, 330 rpm, 350 rpm, 380 rpm, 400 rpm, 430 rpm, 450 rpm, 480 rpm, 500 rpm, etc. If the first stirring rate is too low, the solvent in the system will be unevenly dispersed; if the first stirring rate is too high, ineffective energy consumption will be wasted, increasing the production cost of hard carbon secondary particles.

[0108] In some embodiments, the stirring and mixing time ranges from 2 hours to 6 hours. Specifically, the stirring and mixing time can be, but is not limited to, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc. If the stirring and mixing time is too short, the solvent in the system will not be dispersed evenly; if the stirring and mixing time is too long, it will waste ineffective energy consumption and increase the production cost of hard carbon secondary particles.

[0109] S2013, the temperature is raised to 100℃ to 130℃, stirred at the second stirring rate, and the polymerization reaction is carried out for 8h to 12h to obtain a primary particle precursor; wherein, the first stirring rate is greater than the second stirring rate.

[0110] When the temperature is raised to 100℃ to 130℃, the monomers undergo polymerization under the action of a catalyst. After the reaction is completed, centrifugation is performed to obtain a primary particle precursor with an average particle size of 200nm to 500nm. Compared with the method of obtaining the primary particle precursor by spray drying, this embodiment uses centrifugation to obtain the precursor, which can avoid the granulation that occurs with spray drying and can better reduce the difficulty of air jet milling after pre-carbonization (i.e., spray drying increases the difficulty of air jet milling after pre-carbonization); in addition, it can also reduce energy consumption.

[0111] Specifically, the polymerization temperature can be, but is not limited to, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃, 124℃, 126℃, 128℃, 130℃, etc. If the polymerization temperature is too low, the reactants will not undergo cross-linking or polymerization, and thermosetting resin cannot be formed, thus failing to obtain the primary particle precursor. If the polymerization temperature is too high, the formed primary particle precursor is prone to agglomeration and cannot form spherical shapes. In addition, it will also result in an excessively large particle size of the obtained primary particle precursor, increasing the particle size of the hard carbon primary particles 10 in the obtained hard carbon secondary particles 100, increasing the sodium ion transport distance, and thus deteriorating the rate performance and kinetic performance of the sodium battery.

[0112] Specifically, the polymerization reaction time can be, but is not limited to, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, etc. If the polymerization reaction time is too short, the particle size of the primary particle precursor obtained will be too small, resulting in excessively small particle size of the primary hard carbon particles 10 in the resulting hard carbon secondary particles 100. This leads to an excessively large specific surface area of ​​the hard carbon secondary particles 100, increasing side reactions between the hard carbon secondary particles 100 and the electrolyte, and reducing the initial efficiency and cycle capacity retention of the sodium battery. If the polymerization reaction time is too long, the particle size of the primary particle precursor obtained will be too large, resulting in excessively large particle size of the primary hard carbon particles 10 in the resulting hard carbon secondary particles 100. This increases the transport distance of sodium ions, leading to poor rate performance and kinetic performance of the sodium battery. Furthermore, it makes the primary particle precursor prone to agglomeration, making it difficult to obtain spherical primary particle precursors and reducing the compaction density of the hard carbon secondary particles 100.

[0113] In some implementations, the second stirring rate ranges from 50 rpm to 300 rpm. Specifically, the second stirring rate can be, but is not limited to, 50 rpm, 80 rpm, 100 rpm, 130 rpm, 150 rpm, 180 rpm, 200 rpm, 230 rpm, 250 rpm, 280 rpm, 300 rpm, etc. If the second stirring rate is too low, the primary particle precursor is difficult to form into spherical shapes, reducing the compaction density of the hard carbon secondary particles 100. In addition, it makes the primary particle precursor too large, resulting in an excessively large particle size of the hard carbon primary particles 10 in the hard carbon secondary particles 100, increasing the sodium ion transport distance, and thus deteriorating the rate performance and kinetic performance of the battery. If the second stirring rate is too high, the particle size of the primary particle precursor is too small, increasing the specific surface area of ​​the hard carbon secondary particles 100, increasing the side reactions between the hard carbon secondary particles 100 and the electrolyte, and reducing the initial efficiency and cycle capacity retention of the sodium battery.

[0114] In one specific example, a reaction slurry containing phenol, formaldehyde, 25% ammonia (by mass), and polyethylene glycol is heated to 100°C to 130°C, stirred at a second stirring rate ranging from 50 rpm to 300 rpm, and kept at this temperature for 8 to 12 hours. The mixture is then centrifuged to obtain a primary phenolic resin particle precursor. Understandably, in this embodiment, the primary phenolic resin particle precursor is synthesized using a liquid-phase method.

[0115] See Figure 6 In some embodiments, in S202, the step of pre-carbonizing the primary particle precursor at a first temperature to obtain pre-carbonized secondary particles includes:

[0116] S2021, the primary particle precursor is pre-carbonized at a first temperature of 500°C to 600°C to obtain first intermediate particles; and

[0117] Specifically, the first temperature (i.e., the pre-carbonization temperature) can be, but is not limited to, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, etc. In this embodiment, if the first temperature is too low, there will be too much residual volatile matter in the first intermediate particles, which is not conducive to the bonding and agglomeration of the pre-carbonized primary particles and not conducive to the formation of pre-carbonized secondary particles of the preset size; if the first temperature is too high, the hardness of the first intermediate particles will be too high, which is not conducive to airflow pulverization, increases energy consumption, and increases the preparation cost of hard carbon secondary particles 100.

[0118] S2022, the first intermediate particles are subjected to airflow pulverization to obtain pre-carbonized secondary particles, wherein the particle size of the pre-carbonized secondary particles is 2μm to 5μm.

[0119] Specifically, the first intermediate particles can be pulverized by an airflow with a pressure of 0.4 MPa to 1 MPa (e.g., but not limited to 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, etc.) to obtain pre-carbonized secondary particles with a particle size of 3 μm to 5 μm.

[0120] Specifically, the particle size of the pre-carbonized secondary particles can be, but is not limited to, 2.0 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.3 μm, 4.5 μm, 4.8 μm, and 5.0 μm. If the particle size of the pre-carbonized secondary particles is too small, the median particle size D50' of the resulting hard carbon secondary particles 100 will be too small, resulting in an excessively large specific surface area of ​​the hard carbon secondary particles 100. This increases the side reactions between the hard carbon secondary particles 100 and the electrolyte, reducing the initial efficiency and cycle capacity retention of the sodium battery. If the particle size of the pre-carbonized secondary particles is too large, the median particle size D50' of the hard carbon secondary particles 100 will be too large, increasing the sodium ion transport path and reducing the kinetic performance of the hard carbon secondary particles 100.

[0121] In some embodiments, in S203, placing the pre-carbonized secondary particles at a second temperature for carbonization includes: placing the pre-carbonized secondary particles at a second temperature ranging from 1200°C to 1500°C for carbonization.

[0122] Specifically, the second temperature (i.e., the carbonization temperature) can be, but is not limited to, 1200℃, 1230℃, 1250℃, 1280℃, 1300℃, 1330℃, 1350℃, 1380℃, 1400℃, 1430℃, 1450℃, 1480℃, 1500℃, etc. If the carbonization temperature is too low, the degree of carbonization of the hard carbon secondary particles 100 is reduced, the reversible specific capacity of the hard carbon secondary particles 100 is reduced, and thus the energy density of the battery is reduced; if the carbonization temperature is too high, the interlayer spacing of the hard carbon primary particles 10 in the hard carbon secondary particles 100 will be too small, which is not conducive to the intercalation of sodium ions and reduces the kinetic performance of the hard carbon secondary particles 100.

[0123] See Figure 7 This application provides a method for preparing hard carbon secondary particles 100, the preparation method comprising:

[0124] S301, providing a primary particle precursor, the primary particle precursor having an average particle size ranging from 200 nm to 500 nm;

[0125] S302, the primary particle precursor is pre-carbonized at a first temperature of 500°C to 600°C to obtain the first intermediate particles.

[0126] S303, the first intermediate particles are subjected to airflow pulverization to obtain pre-carbonized secondary particles, wherein the particle size of the pre-carbonized secondary particles is 2μm to 5μm;

[0127] For a detailed description of S301 to S303, please refer to the description of the corresponding parts of the above embodiments, which will not be repeated here.

[0128] S304, the pre-carbonized secondary particles are mixed with a carbon source to obtain second intermediate particles; and

[0129] Optionally, the particle size of the second intermediate particle is 3 μm to 7 μm. Specifically, the particle size of the second intermediate particle can be, but is not limited to, 3.0 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.3 μm, 4.5 μm, 4.8 μm, 5.0 μm, 5.3 μm, 5.5 μm, 5.8 μm, 6 μm, 6.3 μm, 6.5 μm, 6.8 μm, 7.0 μm, etc. If the particle size of the second intermediate particle is too small, the median particle size of the hard carbon secondary particle 100 will be too small, and the specific surface area of ​​the hard carbon secondary particle 100 will be too large, increasing the side reactions between the hard carbon secondary particle 100 and the electrolyte, and reducing the initial efficiency and cycle capacity retention of the sodium battery. If the particle size of the second intermediate particle is too large, the median particle size of the hard carbon secondary particle 100 will be too large, which will increase the transport path of sodium ions and reduce the kinetic performance of the hard carbon secondary particle 100.

[0130] Optionally, the carbon source can be, but is not limited to, at least one of asphalt, petroleum coke, etc. In this embodiment, asphalt is used as an example; this should not be construed as limiting the carbon source and the hard carbon secondary particles 100 in this embodiment.

[0131] S305, the second intermediate particles are carbonized at a second temperature of 1200°C to 1500°C to form an active core 10a from the pre-carbonized secondary particles, and the carbon source forms a carbon coating layer 30; hard carbon secondary particles 100 are obtained; wherein, the hard carbon secondary particles 100 include an active core 10a and a carbon coating layer 30, the active core 10a is formed by the aggregation of the plurality of hard carbon primary particles 10, the carbon coating layer 30 is wrapped around the surface of the active core 10a, and the thickness of the carbon coating layer 30 is in the range of 10 nm to 200 nm.

[0132] For detailed descriptions of other aspects such as pre-carbonized secondary particles, second temperature, active core 10a, carbon coating layer 30, hard carbon secondary particles 100, and hard carbon primary particles 10, please refer to the descriptions in the corresponding sections of the above embodiments, which will not be repeated here.

[0133] In this embodiment, the pre-carbonized secondary particles are coated with a carbon source before carbonization, thereby forming a carbon coating layer 30 on the surface of the active core 10a. This makes the hard carbon secondary particles 100 less prone to damage during the preparation of the negative electrode slurry, resulting in multiple hard carbon primary particles 10, which is beneficial for the coating of the negative electrode slurry. Furthermore, forming a carbon coating layer 30 on the surface of the active core 10a can reduce the specific surface area of ​​the hard carbon secondary particles 100, reduce side reactions between the hard carbon secondary particles 100 and the electrolyte, and improve the initial efficiency and cycle capacity retention of the sodium battery. Moreover, the carbon coating layer 30 is made of soft carbon, which has higher conductivity than the active core 10a, thereby better improving the electronic conductivity of the hard carbon secondary particles 100 and enhancing their kinetic performance.

[0134] See Figure 8 This application embodiment also provides a negative electrode sheet 400, which includes a negative electrode current collector 410 and a negative electrode active layer 420. The negative electrode active layer 420 is disposed on the surface of the negative electrode current collector 410, and the negative electrode active layer 420 includes the hard carbon secondary particles 100 described in this application embodiment.

[0135] For a detailed description of other aspects of the hard carbon secondary particles 100, please refer to the description of the corresponding section of the above embodiments, which will not be repeated here.

[0136] Understandably, hard carbon secondary particles 100 serve as the negative electrode active material of the negative electrode active layer 420.

[0137] It should be noted that the negative electrode active layer 420 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the negative electrode current collector 410. In the schematic diagram of the accompanying drawings of this application, the negative electrode active layer 420 is disposed on two opposite surfaces of the negative electrode current collector 410 as an example, which should not be construed as a limitation on the negative electrode active layer 420 and the negative electrode sheet 400 of the embodiments of this application.

[0138] Optionally, the negative electrode current collector 410 can be, but is not limited to, a copper sheet, copper foil, etc.

[0139] Optionally, the negative electrode active layer 420 may further include at least one of a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener.

[0140] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0141] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0142] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethyl methacrylate (PMA).

[0143] See Figure 9 and Figure 10 This application also provides a sodium battery 500, which includes an electrolyte, a positive electrode 510, a separator 520, and a negative electrode 400 as described in this application embodiment.

[0144] For a detailed description of other aspects of the negative electrode 400, please refer to the description of the corresponding part of the above embodiment, which will not be repeated here.

[0145] It should be noted that the sodium battery 500 in this application embodiment can be, but is not limited to, at least one of sodium-ion batteries, sodium metal batteries, lithium-sodium hybrid batteries, etc.

[0146] Optionally, the sodium battery 500 may be, but is not limited to, at least one of cylindrical sodium batteries, prismatic sodium batteries, and blade sodium batteries. The accompanying drawings of this application merely illustrate one or more possible forms of the sodium battery 500 and should not be construed as limiting the sodium battery 500 of the embodiments of this application, nor should they be construed as limiting the hard carbon secondary particles 100 of the embodiments of this application.

[0147] Understandably, the positive electrode 510 and the negative electrode 400 are located on opposite sides of the separator 520, that is, the separator 520 is located between the positive electrode 510 and the negative electrode 400, separating the positive electrode 510 and the negative electrode 400.

[0148] It should be noted that the positive electrode 510, the separator 520, and the negative electrode 400 are all at least partially immersed in the electrolyte.

[0149] See Figure 11Optionally, the positive electrode 510 further includes a positive current collector 511 and a positive active layer 512, wherein the positive active layer 512 is disposed on the surface of the positive current collector 511.

[0150] It should be noted that the positive electrode active layer 512 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the positive electrode current collector 511. In the schematic diagram of the accompanying drawings of this application, the positive electrode active layer 512 is disposed on two opposite surfaces of the positive electrode current collector 511 as an example, which should not be construed as a limitation on the positive electrode active layer 512 and the positive electrode sheet 510 of the embodiments of this application.

[0151] Optionally, the positive current collector 511 can be, but is not limited to, an aluminum sheet, aluminum foil, etc.

[0152] Optionally, the positive electrode active layer 512 may also include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0153] Optionally, the positive electrode active material may be, but is not limited to, sodium iron pyrophosphate.

[0154] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0155] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0156] Optionally, the electrolyte includes an electrolyte salt, an organic solvent, and a film-forming additive.

[0157] Optionally, the electrolyte salt may include, but is not limited to, sodium salts. Optionally, the sodium salt may be, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalatoborate), sodium difluorodioxalatophosphate, sodium difluorooxalatoborate, sodium difluorophosphate (NaPO2F2), sodium trifluoromethanesulfonate (CF3SO3Na), etc.

[0158] Optionally, the organic solvent may include at least one of cyclic carbonates and chain carbonates. Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and can better promote the formation of a solid electrolyte interface membrane (SEI). Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Optionally, the organic solvent may also include at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0159] Optionally, the film-forming additive may include, but is not limited to, at least one of the following: propargylbenzenesulfonic acid, vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methanedisulfonate (MMDS), butyl sulfonate lactone (BS), and 1,3-propenyl sulfonate lactone (PST).

[0160] Optionally, the diaphragm 520 can be, but is not limited to, at least one of a polypropylene membrane (PP membrane), a polyethylene membrane (PE membrane), and a ceramic diaphragm 520. Optionally, the thickness of the diaphragm 520 is from 10 μm to 18 μm, specifically, the thickness of the diaphragm 520 can be, but is not limited to, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, and 18 μm.

[0161] Please see again Figure 9 and Figure 10 Optionally, the sodium battery 500 further includes a housing 540 and an end cap assembly 550, the housing 540 and the end cap assembly 550 forming a closed receiving cavity (not shown) for housing the electrolyte, the positive electrode 510, the separator 520, and the negative electrode 400. Understandably, the end cap assembly 550 electrically connects the positive electrode 510 and the negative electrode 400, respectively, leading out the positive electrode 510 and the negative electrode 400 for electrical connection to external devices or other sodium batteries 500.

[0162] The following specific embodiments further describe the hard carbon secondary particles 100 and the sodium battery 500 of this application.

[0163] Examples 1 to 9, Comparative Examples 1 to 6

[0164] The hard carbon secondary particles 100 of each embodiment and comparative example were prepared by the following steps:

[0165] (1) Phenol, formaldehyde, ammonia water with a mass concentration of 25% and polyethylene glycol are placed in a reaction vessel, wherein the molar ratio of phenol to formaldehyde is 1:1.3, the amount of ammonia water added is 8% of the mass of phenol, and the amount of polyethylene glycol added is 3% of the mass of phenol and formaldehyde.

[0166] (2) Place it at 85°C and stir at a first stirring rate of 350 rpm;

[0167] (3) A polymerization reaction is carried out. During the reaction, the mixture is stirred at the second stirring rate. After centrifugation, a phenolic resin primary particle precursor is obtained. The polymerization temperature, the second stirring rate, the polymerization time, and the particle size of the primary particle precursor are shown in Table 1 below.

[0168] (4) The primary particle precursor is pre-carbonized at 550°C and then subjected to air jet milling to obtain pre-carbonized secondary particles.

[0169] (5) The pre-carbonized secondary particles are mixed with asphalt and granulated to obtain second intermediate particles; and

[0170] (6) The second intermediate particles are carbonized at a temperature of 1300°C to obtain hard carbon secondary particles 100. The particle size of the hard carbon secondary particles 100 in each embodiment is shown in Table 1 below.

[0171] Comparative Example 7

[0172] The difference between this comparative example and Example 3 is that this comparative example does not perform step (2) of Example 3.

[0173] Sodium battery 500 assembly:

[0174] (1) Preparation of positive electrode 510: Sodium iron pyrophosphate, conductive carbon black SP (positive electrode conductive agent), and binder PVDF (positive electrode binder) are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:0.7:2.3 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is coated on positive electrode current collector 511 aluminum foil, and after drying, cold pressing, slitting and cutting, positive electrode 510 is obtained;

[0175] (2) The hard carbon secondary particles 100 (negative electrode active material), conductive carbon black SP (negative electrode conductive agent), thickener CMC (negative electrode thickener) and negative electrode binder SBR of each embodiment and comparative example are dispersed in deionized water at a mass ratio of 96.5:0.5:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector 410 copper foil. After drying, cold pressing, slitting and cutting, a negative electrode sheet 400 is obtained.

[0176] (3) Electrolyte preparation: In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 2:1:2 to obtain a mixed solvent. Then, the dried electrolyte salt, sodium hexafluorophosphate, is dissolved in the mixed solvent and stirred until completely dissolved and homogeneous. Finally, fluoroethylene carbonate (FEC) and ethylene sulfate (PST) are added and mixed thoroughly to obtain the electrolyte. The molar concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L.

[0177] (4) Diaphragm 520: A 16μm polyethylene film is used as diaphragm 520.

[0178] (5) Assembly of sodium battery 500: The positive electrode 510, separator 520 and negative electrode 400 are stacked in sequence to form an electrode assembly. After the electrode assembly is wound, a bare cell is obtained. After welding the tabs, the cell is assembled into the outer packaging. After injecting the prepared electrolyte, the cell is packaged, left to stand, formed, shaped and capacity tested, etc., and finally sodium battery 500 is prepared.

[0179] Performance tests were conducted on the hard carbon secondary particles 100 and the sodium battery 500 of each embodiment:

[0180] (1) Average particle size (D50) of primary hard carbon particles 10 and average particle size (D50') of secondary hard carbon particles 100: measured using a laser particle size analyzer.

[0181] (2) Test of the average shape factor F of the hard carbon primary particles 10: First, scanning electron microscope images (i.e., SEM images) of the hard carbon secondary particles 100 were taken. Then, the perimeter and area of ​​the 10 hard carbon primary particles 10 were counted using the image processing software Image Pro. Finally, the formula F = 4πA / P was used. 2 Calculate the shape factor of each hard carbon primary particle 10, and finally obtain the average value F of the shape factor of the hard carbon primary particle 10.

[0182] (3) Pore volume of hard carbon secondary particles 100: The pore volume of hard carbon secondary particles 100 was measured using the nitrogen adsorption-desorption method. The pore volume is the sum of the BJH pore volume and the HK pore volume. First, the hard carbon secondary particles 100 were heated and degassed, and then transferred to a low-temperature environment for nitrogen adsorption and desorption. Complete adsorption-desorption curves were obtained based on measurements under different relative pressures. Then, the pore volume was calculated according to the BJH and HK models, and the specific surface area was calculated using the BET model multi-point BET method. In other words, points were taken on the adsorption-desorption curves, and then software was used to fit and calculate according to the BET model.

[0183] (4) Rate performance test: After the assembled sodium battery 500 is divided into different capacities, a 25°C room temperature rate charging test is conducted, with the 4C charging capacity / 0.5C charging capacity as the rate performance index.

[0184] (5) Cycle Capacity Retention Test: The sodium battery 500 was subjected to charge-discharge cycle test on a charge-discharge apparatus at a test temperature of 25℃. The cycle rate was 1C (i.e., both the charge and discharge rates were 1C), and the charge-discharge voltage range was 1.5V to 3.5V. The capacity retention rate after the cycle was calculated. The formula for calculating the capacity retention rate is: Capacity retention rate after the nth cycle = (Charging capacity after the nth cycle / Maximum value of the cycle charging capacity) × 100%.

[0185] It is understood that the term "cycle" in this application refers to the number of times the sodium battery 500 is charged and discharged at a preset rate. One complete charge-discharge cycle of the sodium battery 500 is called one cycle. 1C / 1C 500-cycle capacity retention rate: refers to the capacity retention rate of the sodium battery 500 after 500 charge-discharge cycles at a test temperature of 25°C with a 1C charging rate and a 1C discharging rate.

[0186] (6) Specific capacity and initial coulombic efficiency (hereinafter referred to as initial efficiency or first effect): Hard carbon secondary particles 100 (negative electrode active material), conductive carbon black SP (negative electrode conductive agent), thickener CMC (negative electrode thickener) and negative electrode binder SBR were dispersed in deionized water at a mass ratio of 96:1:1.5:1.5 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, and after drying, cold pressing and cutting, a negative electrode sheet was obtained. A coin cell was assembled with a pure sodium sheet as the counter electrode. In the Blue Electric test cabinet, it was discharged to 5mV in a step-discharge manner of 0.1C-0.05C, and then charged to 2V at 0.1C to obtain the reversible specific capacity.

[0187] (7) Initial Coulombic Efficiency Calculation: The assembled 500 coin cell sodium batteries were charged and discharged using a CT2001A Blue Battery Test System. The batteries were discharged to 5mV at 0.1C and 0.05C rates, respectively; this was the discharge phase. They were then charged to 2.0V at 0.1C rate; this was the charging phase. The discharge specific capacity and charge specific capacity were recorded at these times. Initial Coulombic Efficiency = Charge Specific Capacity / Discharge Specific Capacity × 100%.

[0188] (8) Powder compaction density: The LD43.305 powder compaction density meter was used to test the powder compaction density of hard carbon secondary particles 100. The data after 5 tons of pressure relief was taken as the powder compaction density of hard carbon secondary particles 100.

[0189] The performance parameters of the hard carbon secondary particles 100 and the sodium battery 500 in each embodiment are shown in Tables 1 and 2 below.

[0190] Table 1 Performance parameters of hard carbon secondary particles 100 in each embodiment and comparative example

[0191]

[0192]

[0193] Table 2 Performance parameters of hard carbon secondary particles 100 in each embodiment and comparative example

[0194]

[0195] As shown in Tables 1 and 2, the test results of Examples 1 to 4, Comparative Examples 1 and 2 reveal that, with increasing polymerization temperature during the preparation of the primary particle precursor, the particle size of the hard carbon secondary particles 100 gradually increases, as does the particle size of the hard carbon primary particles 10; however, the shape factor F of the hard carbon primary particles 10 gradually decreases, meaning the sphericity of the hard carbon primary particles 10 gradually decreases; the pore volume of the hard carbon secondary particles 100 also gradually decreases; and the specific surface area of ​​the hard carbon secondary particles 100 also gradually decreases. Furthermore, with increasing polymerization temperature during the preparation of the primary particle precursor, the powder compaction density of the hard carbon secondary particles 100 first gradually increases and then gradually decreases; the specific capacity of the hard carbon secondary particles 100 gradually increases. Moreover, with increasing polymerization temperature during the preparation of the primary particle precursor, the initial coulombic efficiency of the sodium battery 500 gradually increases; the rate performance of the sodium battery 500 gradually decreases; and the capacity retention after 500 cycles of the sodium battery 500 first gradually increases and then gradually decreases.

[0196] As shown in Tables 1 and 2, the test results of Examples 3, 5, 6, Comparative Examples 3 and 4 indicate that as the polymerization reaction time during the preparation of the primary particle precursor increases, the particle size of the obtained hard carbon secondary particles 100 gradually increases, and the particle size of the hard carbon primary particles 10 also gradually increases. However, the shape factor F of the hard carbon primary particles 10 gradually decreases, meaning the sphericity of the hard carbon primary particles 10 gradually decreases; the pore volume of the obtained hard carbon secondary particles 100 also gradually decreases; and the specific surface area of ​​the hard carbon secondary particles 100 also gradually decreases. Furthermore, as the polymerization reaction time during the preparation of the primary particle precursor increases, the powder compaction density of the hard carbon secondary particles 100 first gradually increases and then gradually decreases; and the specific capacity of the hard carbon secondary particles 100 gradually increases. Furthermore, as the polymerization reaction time during the preparation of the primary particulate precursor increases, the initial coulombic efficiency of the sodium battery 500 gradually increases; the rate performance of the sodium battery 500 gradually decreases; and the capacity of the sodium battery 500 after 500 cycles initially increases gradually, and then gradually decreases.

[0197] As shown in Tables 1 and 2, the test results of Examples 3, 7 to 9, Comparative Examples 5 and 6 indicate that, with the increase of the second stirring rate during the preparation of the primary particle precursor, the particle size of the hard carbon secondary particles 100 gradually decreases, and the particle size of the hard carbon primary particles 10 also gradually decreases. However, the shape factor F of the hard carbon primary particles 10 gradually increases, meaning the sphericity of the hard carbon primary particles 10 gradually increases; the pore volume of the hard carbon secondary particles 100 also gradually increases; and the specific surface area of ​​the hard carbon secondary particles 100 also gradually increases. Furthermore, with the increase of the second stirring rate during the preparation of the primary particle precursor, the powder compaction density of the hard carbon secondary particles 100 first gradually increases and then gradually decreases; and the specific capacity of the hard carbon secondary particles 100 gradually decreases. Furthermore, as the second stirring rate increases during the preparation of the primary particle precursor, the initial coulombic efficiency of the sodium battery 500 gradually decreases; the rate performance of the sodium battery 500 gradually increases; and the capacity of the sodium battery 500 after 500 cycles initially increases gradually and then gradually decreases.

[0198] In summary, when the median particle size D50 of the hard carbon primary particles 10 is in the range of 200nm≤D50≤500nm, the hard carbon secondary particles 100 can have a higher specific capacity, and the sodium battery 500 can have a higher initial coulombic efficiency, a higher rate performance, and a higher cycle capacity retention rate.

[0199] The test results of Example 3 and Comparative Example 7 show that when the reaction system is not stirred before the polymerization reaction to prepare the primary particle precursor (as in Comparative Example 7), the resulting hard carbon secondary particles 100 and hard carbon primary particles 10 will have excessively large particle sizes, a reduced shape factor F of the hard carbon primary particles 10, excessively small pore volume of the hard carbon secondary particles 100, a small specific surface area of ​​the hard carbon secondary particles 100, and low powder compaction density, resulting in reduced specific capacity. Furthermore, the initial coulombic efficiency, rate performance, and cycle capacity retention of the sodium battery 500 will all decrease. This indicates that stirring can reduce the particle size of the hard carbon secondary particles 100 and hard carbon primary particles 10, increase the sphericity of the hard carbon primary particles 10, increase the pore volume and specific surface area of ​​the hard carbon secondary particles 100, increase the powder compaction density and specific capacity of the secondary hard carbon particles, and improve the initial coulombic efficiency, rate performance, and cycle capacity retention of the sodium battery 500.

[0200] See Figure 12 This application also provides an energy storage device 600, which includes a housing 610 and a sodium battery 500 as described in this application embodiment, wherein the sodium battery 500 is housed within the housing 610.

[0201] The energy storage device 600 of this application can be applied to, but is not limited to, energy storage on the generation side, energy storage on the grid side, and energy storage on the consumption side.

[0202] Optionally, the energy storage device 600 may include, but is not limited to, sodium battery 500 modules, sodium battery 500 packs, sodium battery 500 systems, energy storage boxes, energy storage cabinets, energy storage containers, etc. The actual application form of the energy storage device 600 provided in this application embodiment can be, but is not limited to, the listed products, and can also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 600. The accompanying drawings of this application embodiment are only illustrative of the energy storage device 600 including multiple sodium batteries 500, and should not be construed as limiting the energy storage device 600 of this application embodiment.

[0203] Optionally, the number of sodium batteries 500 can be, but is not limited to, one or more. When there are multiple sodium batteries 500, they are stacked within the housing 610. It is understood that the stacked arrangement of the multiple sodium batteries 500 can be either arranged sequentially abutting each other, or arranged sequentially with intervals between them. Furthermore, the multiple sodium batteries 500 can be stacked laterally (e.g., horizontally) or longitudinally (e.g., along the direction of gravity). The stacking method and direction of the multiple sodium batteries 500 can be designed according to actual conditions, and this application does not impose specific limitations.

[0204] The term "multiple" refers to two or more.

[0205] Understandably, the multiple sodium batteries 500 of the energy storage device 600 can be connected in parallel, or in series, or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple sodium batteries 500 of the same energy storage device 600.

[0206] Understandably, the housing 610 has a receiving cavity in which one or more sodium batteries 500 are received. In some embodiments, each receiving cavity receives one sodium battery 500. In other embodiments, each receiving cavity receives multiple sodium batteries 500.

[0207] See Figure 13 and Figure 14 This application also provides an energy storage system 700, which includes the energy storage device 600 described in this application embodiment; and an energy conversion device 710, wherein the energy conversion device 710 is electrically connected to the energy storage device 600, the energy conversion device 710 is used to convert other forms of energy into electrical energy, and the energy storage device 600 is used to store the electrical energy.

[0208] It should be noted that energy storage (i.e., energy storage) has a wide range of applications, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The energy storage system 700 in this application embodiment is described in detail using generation-side energy storage as an example. This should not be construed as limiting the energy storage system 700, nor should it be construed as limiting the energy storage device 600, sodium battery 500, etc., in this application embodiment.

[0209] During operation, the power conversion device 710 converts other forms of energy into electrical energy and stores it in the energy storage device 600. The electrical energy stored in the energy storage device 600 can be used to supply electrical loads such as streetlights and household appliances during peak electricity prices, or to supply power when the power grid experiences a power outage. The electrical energy generated by the power conversion device 710 can also be supplied to the power grid through high-voltage cables to alleviate the power supply pressure on the power grid during peak periods.

[0210] Optionally, the power conversion device 710 can convert at least one other form of energy, such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy, into electrical energy.

[0211] Optionally, the number of power conversion devices 710 can be one or more. When there are multiple power conversion devices 710, the multiple power conversion devices 710 can be connected in series, in parallel or in a mixed manner. This application does not make specific limitations.

[0212] Optionally, the power conversion device 710 may be, but is not limited to, at least one of photovoltaic panels, wind power generation devices, hydropower generation devices, etc.

[0213] Optionally, the number of energy storage devices 600 can be one or more. When there are multiple energy storage devices 600, the multiple energy storage devices 600 can be connected in series or in parallel. This application does not make specific limitations.

[0214] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0215] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A type of hard carbon secondary granules, characterized in that, The hard carbon secondary particles are formed by the aggregation of multiple hard carbon primary particles, and the median particle size D50 of the hard carbon primary particles ranges from 200nm to 500nm.

2. The hard carbon secondary particles according to claim 1, characterized in that, The hard carbon primary particles are spherical or near-spherical, and the average value F of the shape factor of the hard carbon primary particles is in the range of 0.9 ≤ F ≤ 1.

0.

3. The hard carbon secondary particles according to claim 1, characterized in that, Hard carbon secondary particles satisfy at least one of the following conditions: The hard carbon secondary particles comprise multiple pores, with a pore volume ranging from 0.02 cm³. 3 / g to 0.04cm 3 / g; The median particle size D50' of the hard carbon secondary particles ranges from 2.5 μm to D50' to 6 μm.

4. The hard carbon secondary particles according to claim 1, characterized in that, The specific surface area of ​​the hard carbon secondary particles ranges from 2m². 2 / g to 8m 2 / g.

5. The hard carbon secondary particles according to any one of claims 1-4, characterized in that, The hard carbon secondary particles include an active core and a carbon coating layer. The active core is formed by the aggregation of multiple hard carbon primary particles. The carbon coating layer is wrapped around the surface of the active core, and the thickness of the carbon coating layer ranges from 10 nm to 200 nm.

6. A method for preparing hard carbon secondary particles, characterized in that, The preparation method includes: A primary particle precursor is provided, wherein the average particle size of the primary particle precursor ranges from 200 nm to 500 nm; The primary particle precursor is pre-carbonized at a first temperature to obtain pre-carbonized secondary particles; and The pre-carbonized secondary particles are carbonized at a second temperature to obtain hard carbon secondary particles, wherein the first temperature is lower than the second temperature; the hard carbon secondary particles are formed by the aggregation of multiple hard carbon primary particles, and the median particle size D50 of the hard carbon primary particles is in the range of 200nm≤D50≤500nm.

7. The method for preparing hard carbon secondary particles according to claim 6, characterized in that, The provision of the primary particulate precursor includes: Provide a reactive monomer, a catalyst, and a surfactant, wherein the residual carbon content of the surfactant is less than or equal to 1%; The reactants, catalyst, and surfactant are mixed and stirred at a first stirring rate at a temperature of 80°C to 90°C; and The temperature is raised to 100°C to 130°C, and the mixture is stirred at a second stirring rate for 8 to 12 hours to obtain a primary particle precursor; wherein the first stirring rate is greater than the second stirring rate.

8. The method for preparing hard carbon secondary particles according to claim 7, characterized in that, The first stirring rate ranges from 200 rpm to 500 rpm; the second stirring rate ranges from 50 rpm to 300 rpm.

9. The method for preparing hard carbon secondary particles according to claim 6, characterized in that, The step of pre-carbonizing the primary particle precursor at a first temperature to obtain pre-carbonized secondary particles includes: The primary particle precursor is pre-carbonized at a first temperature of 500°C to 600°C to obtain first intermediate particles; and The first intermediate particles are subjected to air jet milling to obtain pre-carbonized secondary particles, wherein the particle size of the pre-carbonized secondary particles is 2μm to 5μm.

10. The method for preparing hard carbon secondary particles according to any one of claims 6-9, characterized in that, The step of carbonizing the pre-carbonized secondary particles at a second temperature includes: carbonizing the pre-carbonized secondary particles at a second temperature ranging from 1200°C to 1500°C. Before placing the pre-carbonized secondary particles at a second temperature for carbonization, the preparation method further includes: The pre-carbonized secondary particles are mixed with a carbon source to obtain second intermediate particles; The step of carbonizing the pre-carbonized secondary particles at a second temperature includes: carbonizing the second intermediate particles at a second temperature to form an active core in the pre-carbonized secondary particles, and forming a carbon coating layer in the carbon source; wherein the hard carbon secondary particles include an active core and a carbon coating layer, the active core is formed by the aggregation of the plurality of hard carbon primary particles, the carbon coating layer is wrapped around the surface of the active core, and the thickness of the carbon coating layer ranges from 10 nm to 200 nm.

11. A negative electrode sheet, characterized in that, The negative electrode current collector includes: Negative current collector; and A negative electrode active layer is disposed on the surface of the negative electrode current collector, and the negative electrode active layer includes the hard carbon secondary particles as described in any one of claims 1 to 5.

12. A sodium battery, characterized in that, The sodium battery comprises: an electrolyte, a positive electrode, a separator, and the negative electrode as described in claim 11.

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