Negative electrode sheet, secondary battery, electric device, and hard carbon material

Abstract

The invention provides a negative pole piece, a secondary battery, an electric device and a hard carbon material.The negative pole piece comprises a negative current collector and a negative film layer located on at least one surface of the negative current collector, the negative film layer comprises the hard carbon material, and the hard carbon material comprises a graphene sheet layer; the space volume H1 between the graphene sheet layers with the interlayer spacing larger than 0.4 nm and the total space volume Htotal between the layers in the graphene sheet layers meet the condition that H1 / Htotal is larger than or equal to 40% and smaller than or equal to 60%. As a result, the dynamic performance and the first coulombic efficiency of the secondary battery can be achieved at the same time.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a negative electrode sheet, a secondary battery, an electrical device, and a hard carbon material. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, and aerospace. With the application and promotion of rechargeable batteries, the performance requirements are becoming increasingly stringent. As a crucial component of rechargeable batteries, the negative electrode active material plays a vital role in their performance. Currently, hard carbon is commonly used as the negative electrode active material for rechargeable batteries. However, when used as a negative electrode active material, hard carbon cannot simultaneously achieve optimal kinetic performance and initial coulombic efficiency. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode, a secondary battery, an electrical device, and a hard carbon material, through which the secondary battery can have both excellent kinetic performance and first coulombic efficiency.

[0004] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer comprises a hard carbon material, the hard carbon material comprising graphene sheets, wherein the space volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total space volume H between the individual layers of the graphene sheets are... 总 Satisfy: 40% ≤ H1 / H 总 ≤60%.

[0005] In this application, by ensuring that the proportion of the space volume between graphene sheets with an interlayer spacing greater than 0.4 nm in the hard carbon material is within the aforementioned specific range, the secondary battery can possess both excellent kinetic performance and first-time coulombic efficiency.

[0006] In some implementations, 40% ≤ H1 / H 总 ≤55%.

[0007] By adjusting the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the aforementioned range, it is even more conducive to achieving both excellent dynamic performance and first-round coulomb efficiency.

[0008] In some embodiments, the space volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is related to the total space volume H between the individual layers of the graphene sheet. 总Satisfying: 22% ≤ H2 / H 总 ≤60%.

[0009] In this application, the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is compared with the total spatial volume H between each layer in the graphene sheet. 总 Within the aforementioned range, it is possible to improve the capacity of the secondary battery while simultaneously enhancing its kinetics.

[0010] In some embodiments, the space volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm is related to the total space volume H between the individual layers in the graphene sheet. 总 Satisfy: H3 / H 总 ≤18%.

[0011] By adjusting the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the above range, the risk of sodium deposition can be reduced, the cathode capacity can be improved, and the energy density of the secondary battery can be increased.

[0012] In some embodiments, the hard carbon material further includes micropores with a pore size of 2 nm or less and mesopores with a pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5 ≤ V 1 / V2≤9.7.

[0013] By setting the pore volume V1 of micropores and the pore volume V2 of mesopores to satisfy the above relationship, it is beneficial to enable secondary batteries to have both excellent capacity and kinetic performance.

[0014] In some embodiments, the hard carbon material, as determined by nitrogen adsorption, contains pores with a diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)). The hard carbon material provided in this application has an optimized pore structure. Specifically, the characteristic dV / d(logD) of the hard carbon material with pore sizes of 1.0nm-1.5nm corresponds to the pore volume contributed per unit pore size, with a maximum value of 0.001cm. 3 / (g·log(nm))-0.009cm 3 Within the range of / (g·log(nm)), it is beneficial to reduce gas generation and bubbling during the pulping process.

[0015] In some embodiments, the hard carbon material has a pore size of 1.0 nm to 1.5 nm, and the maximum value of dV / d(logD) is 0.001 cm⁻¹. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0016] In some embodiments, the pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm-2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b At 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g. The pore volume of hard carbon materials with pore size below 2nm is within the above range, which is more conducive to reducing gas generation and bubbling during the pulping process while maintaining the specific capacity.

[0017] In some embodiments, the V of the hard carbon material a +V b At 0.0020cm 3 / g to 0.0030cm 3 Within the range of / g.

[0018] In some embodiments, the pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%. When the proportion of micropore volume in the total pore volume is within the above range, it is beneficial to improve the capacity of the secondary battery.

[0019] In some embodiments, the pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 2.5% ≤ V² / V 总 ≤10%. A mesopore volume within the above range is beneficial for improving the kinetic performance of secondary batteries.

[0020] In some implementations, 0.0003cm 3 / g≤V2≤0.0012cm 3 / g. A mesoporous pore volume within the above range is beneficial for improving the kinetic performance of the secondary battery.

[0021] In some embodiments, the hard carbon material includes heteroatoms, which account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material. In some embodiments, the heteroatoms include at least one of O, N, S, P, B, and F. The presence of heteroatoms can increase the interlayer spacing of the graphene sheets in the hard carbon material, making the spacing between the graphene sheets greater than 0.4 nm, which is beneficial to the kinetics of the secondary battery. In addition, the mass percentage of heteroatoms in the hard carbon material within the above-mentioned range ensures that the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the total graphene sheets is within the above-mentioned range, which is beneficial to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0022] In some embodiments, the hard carbon material I D / I G It is 1.1-1.35; where, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location. By making the I of the hard carbon material... D / I G Within the aforementioned range, the high degree of carbon order and fewer surface defects on the surface of hard carbon materials are beneficial for improving the initial coulombic efficiency of the battery and also for increasing the compaction density.

[0023] In some embodiments, the surface oxygen content of the hard carbon material is 5% to 15%.

[0024] When the surface oxygen content of the hard carbon material is within the above-mentioned range, the viscosity of the slurry containing the hard carbon material is within a suitable range, which is beneficial to improving the processing performance of secondary batteries.

[0025] In some embodiments, the powder compaction density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial to increase the cold-pressed density of the negative electrode sheet, which in turn is beneficial to increase the volumetric energy density of the secondary battery.

[0026] In some embodiments, the hard carbon material satisfies at least one of the following:

[0027] (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; The specific surface area of ​​hard carbon materials is within the above range, which is beneficial to improving the first coulombic efficiency of secondary batteries.

[0028] (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 When the tap density of hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film and improve the energy density of the secondary battery.

[0029] (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 When the true density of hard carbon materials is within the above range, it is beneficial to improve the capacity of secondary batteries.

[0030] (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm;

[0031] (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm;

[0032] (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

[0033] When the particle size distribution of hard carbon materials falls within the aforementioned range (Dv10, Dv50, Dv90), it is beneficial to reduce the specific surface area of ​​the hard carbon materials, thereby reducing the occurrence of side reactions and improving the initial coulombic efficiency of the secondary battery. Simultaneously, it can also shorten the bulk transport path of active ions, further enhancing the kinetic performance of the secondary battery.

[0034] A second aspect of this application provides a secondary battery, including the negative electrode sheet described in the first aspect of this application.

[0035] The secondary battery in this application possesses both excellent kinetic performance and initial coulombic efficiency.

[0036] A third aspect of this application provides an electrical device, including the secondary battery of the second aspect of this application.

[0037] The electrical device of this application includes the secondary battery of this application, and therefore has at least the same advantages as the secondary battery.

[0038] A fourth aspect of this application provides a hard carbon material comprising graphene sheets, wherein the space volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total space volume H between the individual layers of the graphene sheets are also provided. 总 Satisfy: 40% ≤ H1 / H 总 ≤60%.

[0039] In this application, by ensuring that the proportion of the space volume between graphene sheets with an interlayer spacing greater than 0.4 nm in the hard carbon material is within the aforementioned specific range, the secondary battery can possess both excellent kinetic performance and first-time coulombic efficiency.

[0040] In some implementations, 40% ≤ H1 / H 总 ≤55%.

[0041] By adjusting the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the aforementioned range, it is even more conducive to achieving both excellent dynamic performance and first-round coulomb efficiency.

[0042] In some embodiments, the space volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is related to the total space volume H between the individual layers of the graphene sheet. 总 Satisfying: 22% ≤ H2 / H 总 ≤60%.

[0043] In this application, the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is compared with the total spatial volume H between each layer in the graphene sheet. 总 Within the aforementioned range, it is possible to improve the capacity of the secondary battery while simultaneously enhancing its kinetics.

[0044] In some embodiments, the space volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm is related to the total space volume H between the individual layers in the graphene sheet. 总 Satisfy: H3 / H 总 ≤18%.

[0045] By adjusting the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the above range, the risk of sodium deposition can be reduced, the cathode capacity can be improved, and the energy density of the secondary battery can be increased.

[0046] In some embodiments, the hard carbon material further includes micropores with a pore size of 2 nm or less and mesopores with a pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5 ≤ V 1 / V2≤9.7.

[0047] By setting the pore volume V1 of micropores and the pore volume V2 of mesopores to satisfy the above relationship, it is beneficial to enable secondary batteries to have both excellent capacity and kinetic performance.

[0048] In some embodiments, the hard carbon material, as determined by nitrogen adsorption, contains pores with a diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))0.009cm 3 / (g·log(nm)). The hard carbon material provided in this application has an optimized pore structure. Specifically, the characteristic dV / d(logD) of the hard carbon material with pore sizes of 1.0nm-1.5nm corresponds to the pore volume contributed per unit pore size, with a maximum value of 0.001cm. 3 / (g·log(nm))-0.009cm 3 Within the range of / (g·log(nm)), it is beneficial to reduce gas generation and bubbling during the pulping process.

[0049] In some embodiments, the hard carbon material has a pore size of 1.0 nm to 1.5 nm, and the maximum value of dV / d(logD) is 0.001 cm⁻¹. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0050] In some embodiments, the pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b At 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g. The pore volume of hard carbon materials with pore size below 2nm is within the above range, which is more conducive to reducing gas generation and bubbling during the pulping process while maintaining the specific capacity.

[0051] In some embodiments, the V of the hard carbon material a +V b At 0.0020cm 3 / g to 0.0030cm 3 Within the range of / g.

[0052] In some embodiments, the pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%. When the proportion of micropore volume in the total pore volume is within the above range, it is beneficial to improve the capacity of the secondary battery.

[0053] In some embodiments, the pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material are... 总Satisfies: 2.5% ≤ V² / V 总 ≤10%. A mesopore volume within the above range is beneficial for improving the kinetic performance of secondary batteries.

[0054] In some implementations, 0.0003cm 3 / g≤V2≤0.0012cm 3 / g. A mesoporous pore volume within the above range is beneficial for improving the kinetic performance of the secondary battery.

[0055] In some embodiments, the hard carbon material includes heteroatoms, which account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material. In some embodiments, the heteroatoms include at least one of O, N, S, P, B, and F. The presence of heteroatoms can increase the interlayer spacing of the graphene sheets in the hard carbon material, making the spacing between the graphene sheets greater than 0.4 nm, which is beneficial to the kinetics of the secondary battery. In addition, the mass percentage of heteroatoms in the hard carbon material within the above-mentioned range ensures that the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the total graphene sheets is within the above-mentioned range, which is beneficial to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0056] In some embodiments, the hard carbon material I D / I G It is 1.1-1.35; where, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location. By making the I of the hard carbon material... D / I G Within the aforementioned range, the high degree of carbon order and fewer surface defects on the surface of hard carbon materials are beneficial for improving the initial coulombic efficiency of the battery and also for increasing the compaction density.

[0057] In some embodiments, the surface oxygen content of the hard carbon material is 5% to 15%.

[0058] When the surface oxygen content of the hard carbon material is within the above-mentioned range, the viscosity of the slurry containing the hard carbon material is within a suitable range, which is beneficial to improving the processing performance of secondary batteries.

[0059] In some embodiments, the powder compaction density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3When the compaction density of hard carbon material powder is within the above range, it is beneficial to increase the cold-pressed density of the negative electrode sheet, which in turn is beneficial to increase the volumetric energy density of the secondary battery.

[0060] In some embodiments, the hard carbon material satisfies at least one of the following:

[0061] (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; The specific surface area of ​​hard carbon materials is within the above range, which is beneficial to improving the first coulombic efficiency of secondary batteries.

[0062] (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 When the tap density of hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film and improve the energy density of the secondary battery.

[0063] (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 When the true density of hard carbon materials is within the above range, it is beneficial to improve the capacity of secondary batteries.

[0064] (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm;

[0065] (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm;

[0066] (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

[0067] When the particle size distribution of hard carbon materials falls within the aforementioned range (Dv10, Dv50, Dv90), it is beneficial to reduce the specific surface area of ​​the hard carbon materials, thereby reducing the occurrence of side reactions and improving the initial coulombic efficiency of the secondary battery. Simultaneously, it can also shorten the bulk transport path of active ions, further enhancing the kinetic performance of the secondary battery. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0069] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0070] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0071] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0072] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0073] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0074] Figure 7 The X-ray diffraction pattern of the hard carbon material in Example 1 of this application is shown.

[0075] Figure 8 The lithium intercalation capacity diagrams are for the hard carbon materials of Example 1 and Comparative Example 1 of this application when used as negative electrode active materials in secondary batteries.

[0076] Figure 9 for Figure 8 A magnified view of a portion of the image;

[0077] Figure 10 The pore size distribution of the hard carbon material prepared in Example 11 of this application is measured by nitrogen adsorption method.

[0078] Figure 11 The pore size distribution of the hard carbon material prepared in Example 12 of this application is measured by nitrogen adsorption method.

[0079] Explanation of reference numerals in the attached figures:

[0080] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0081] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, secondary battery, power supply device, and hard carbon material of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0082] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0084] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0085] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0086] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0087] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0088] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to sodium ions.

[0089] In this application, the term "spatial volume" refers to the size of the space formed between adjacent graphene sheets.

[0090] Currently, due to sodium's advantages in resources and cost, sodium-ion batteries have become an important development direction for energy storage batteries. Hard carbon materials have a large interlayer spacing, abundant pore structure, and good electronic conductivity. Sodium ions are relatively stable during their insertion and extraction processes, making them the most promising anode material for sodium storage. However, currently, hard carbon as an anode active material cannot simultaneously achieve good kinetic performance and first-coulombic efficiency.

[0091] In view of this, this application provides a negative electrode sheet, a secondary battery, an electrical device, and a hard carbon material, wherein the hard carbon material, when used as the negative electrode active material of the secondary battery, can simultaneously achieve both kinetic performance and initial coulombic efficiency.

[0092] Negative electrode sheet

[0093] A first aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer comprises a hard carbon material, the hard carbon material comprising graphene sheets with different interlayer spacings, wherein the space volume H1 between graphene sheets with interlayer spacing greater than 0.4 nm and the total space volume H between all layers in the graphene sheets are... 总 Satisfy: 40% ≤ H1 / H 总 ≤60%.

[0094] When hard carbon materials are used as negative electrode active materials in secondary batteries, their capacity includes both ramp capacity and plateau capacity. The ramp capacity has a voltage >0.1V, while the plateau capacity has a voltage between 0V and 0.1V. Studies have found that during fast charging, if the plateau capacity ratio is large, the longer the time spent at low voltage during sodium storage, the more likely sodium deposition will occur. Therefore, increasing the proportion of ramp capacity can reduce the risk of sodium deposition and improve the kinetic performance of hard carbon materials. However, an excessively high ramp capacity can affect the initial coulombic efficiency. This is because active ions are adsorbed on the surface of large-interlayer-spacing microcrystals or amorphous carbon in the ramp section for energy storage. However, large-interlayer-spacing microcrystals also contain numerous defects and dangling bonds, which can easily form stable chemical bonds with active ions, making it impossible for the active ions to reversibly escape, thus affecting the initial coulombic efficiency. Therefore, the proportion of ramp capacity in the material should be within an appropriate range to balance the kinetic performance and initial coulombic efficiency of the secondary battery.

[0095] Hard carbon materials contain stacked graphene sheets with varying interlayer spacing. The size of the space between adjacent graphene sheets affects the insertion and extraction of sodium ions. For ease of description, we define H1 as the space between graphene sheets with an interlayer spacing greater than 0.4 nm, H2 as the space between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm, and H3 as the space between graphene sheets with an interlayer spacing less than 0.36 nm. 总 H refers to the total spatial volume between the graphene sheets in hard carbon materials, specifically the sum of the spatial volumes between graphene sheets with different interlayer spacings. 总 =H1+H2+H3.

[0096] The inventors discovered that graphene sheets with an interlayer spacing greater than 0.4 nm, due to the large space volume between the sheets, allow for easier embedding of active ions, enabling sodium storage through an "adsorption" mechanism, thus achieving a high ramp capacity above 0.1 V. Therefore, in hard carbon materials, the H1 / H... 总 This reflects the proportion of capacity in the slope section of the material to a certain extent. However, the excessively large volume ratio between graphene sheets with an interlayer spacing greater than 0.4 nm leads to an excessively high capacity in the slope section, thus affecting the initial coulombic efficiency of the secondary battery.

[0097] Therefore, in this application, by making H1 / H 总 The ratio is within the specific range mentioned above, so that the ratio of the slope section capacity is within an appropriate range. On the one hand, this allows active ions to be adsorbed on the graphene sheet surface for energy storage, and on the other hand, it can control the number of defects, thus taking into account both the kinetic performance and the initial coulombic efficiency of the secondary battery.

[0098] In some implementations, 40% ≤ H1 / H 总 ≤55%.

[0099] The spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between all layers in the graphene sheet. 总 Within the aforementioned range, the proportion of the portion with an interlayer spacing greater than 0.4 nm in the hard carbon material is placed within a more suitable range, thus ensuring that the proportion of the ramp section capacity is within a more suitable range, which is more conducive to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0100] In some embodiments, the space volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is related to the total space volume H between the individual layers of the graphene sheet. 总 Satisfying: 22% ≤ H2 / H 总 ≤60%.

[0101] Graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm mainly store sodium through interlayer intercalation, thus exhibiting high capacity at a low voltage plateau (i.e., obtaining plateau capacity). However, if the proportion of interlayer spacing of 0.36 nm to 0.4 nm is too large, it is easy to cause sodium deposition, which affects the reversible capacity of the secondary battery and further affects the first coulombic efficiency of the secondary battery.

[0102] In this application, the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm and the total spatial volume H between each layer in the graphene sheet are set. 总 Within the aforementioned range, ensuring that the proportion of graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm in the hard carbon material is within a suitable range can improve the kinetic performance of the secondary battery while increasing its capacity.

[0103] In some embodiments, the space volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm is related to the total space volume H between the individual layers in the graphene sheet. 总 Satisfy: H3 / H 总 ≤18%.

[0104] Graphene sheets with interlayer spacing less than 0.36 nm are difficult to store sodium due to their small space. However, these graphene sheets can provide slip, which is beneficial for improving the compaction density of the negative electrode. In this application, the space volume H3 between graphene sheets with interlayer spacing less than 0.36 nm and the total space volume H between all layers in the graphene sheet are set... 总 Within the aforementioned range, ensuring that the proportion of graphene sheets with an interlayer spacing of less than 0.36 nm in hard carbon materials is within a suitable range can reduce the risk of sodium deposition, improve the cathode capacity utilization, and benefit the energy density of secondary batteries.

[0105] In this application, the above H1 / H 总 H2 / H 总 H3 / H 总 It can be obtained by peak fitting of the XRD pattern of hard carbon materials.

[0106] Specifically, the XRD diffraction pattern of the hard carbon material was first tested using the following method: The XRD diffraction pattern of the hard carbon material can be tested using an X-ray diffractometer according to JIS K 0131-1996. The test conditions were as follows: the hard carbon material and silicon powder were uniformly mixed at a mass ratio of 5:1, and the sample was prepared using the plate sample preparation method. CuKα rays were used as the radiation source, and a copper target was used as the anode target. The wavelength λ of the copper target was... The scanning 2θ angle range is 10°–40°, and the scanning rate is 1° / min. A Bruker D8 Discover X-ray diffractometer can be used as the testing instrument.

[0107] Next, the XRD diffraction pattern of the hard carbon material was fitted using XPS peak software. The XRD pattern of the hard carbon material was fitted into three small peaks, namely the first fitted peak A, the second fitted peak B, and the third fitted peak C. The fitting criteria were: the 2θ angle of the first fitted peak A was less than 22.2°, the 2θ angle of the second fitted peak B was 22.2° to 24.7°, and the 2θ angle of the third fitted peak C was greater than 24.7°.

[0108] The interlayer spacing and the 2θ angle satisfy Bragg's law: 2dsinθ=kλ, where d is the interlayer spacing of the hard carbon (002) crystal plane, θ is the diffraction angle, k is the reflection order, and λ is the wavelength of the copper target. In this application, k is 1, and λ is... According to Bragg's formula, the 2θ angle corresponding to graphene sheets with an interlayer spacing greater than 0.4 nm is less than 22.2°, the 2θ angle corresponding to graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is 22.2° to 24.7°, and the 2θ angle corresponding to graphene sheets with an interlayer spacing of < 0.36 nm is greater than 24.7°.

[0109] Finally, the ratio of the area of ​​the first fitted peak to the total area of ​​the three fitted peaks is equal to the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between the layers in the graphene sheet. 总 The ratio (H1 / H) 总 The ratio of the area of ​​the second fitting peak to the total area of ​​the three fitting peaks is equal to the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm and the total spatial volume H between the layers in the graphene sheet. 总 The ratio (H2 / H) 总 The ratio of the area of ​​the third fitting peak to the total area of ​​the three fitting peaks is equal to the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between the layers in the graphene sheet. 总 The ratio (H3 / H) 总 ).

[0110] For example, H1 / H 总 H2 / H 总 and H3 / H 总 The area of ​​the graphene sheet can be calculated as follows: 15.24 mm². 2 In the case of H1 / H 总 =15.24mm 2 *Sum of interlayer spacings greater than 0.4 nm in hard carbon materials / 15.24 mm 2*The total interlayer spacing in hard carbon materials = 15.24 mm 2 *Area of ​​the first fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the first fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the first fitted peak / Total area of ​​the three fitted peaks. H2 / H 总 =15.24mm 2 *The sum of interlayer spacings from 0.36 nm to 0.4 nm in hard carbon materials / 15.24 mm 2 * The total interlayer spacing in hard carbon materials is 15.24 mm. 2 *Area of ​​the second fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the second fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the second fitted peak / Total area of ​​the three fitted peaks. H3 / H 总 =15.24mm 2 *Sum of interlayer spacings smaller than 0.36 nm in hard carbon materials / 15.24 mm 2 * The total interlayer spacing in hard carbon materials is 15.24 mm. 2 *Area of ​​the third fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the third fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the third fitted peak / Total area of ​​the three fitted peaks.

[0111] In some embodiments, the hard carbon material further includes micropores of 2 nm or less and mesopores of pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5 ≤ V 1 / V2≤9.7.

[0112] Micropores with a pore size of 2 nm or less in hard carbon materials can store sodium, but due to their small pore size, sodium ions are not easily released. In contrast, mesopores with a pore size greater than 2 nm and less than 10 nm in hard carbon materials allow for easier adsorption and release of active ions, which is beneficial to the kinetics of the secondary battery. In this application, the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy the above relationship, which is beneficial for balancing the capacity and kinetic performance of the secondary battery.

[0113] In some embodiments, the micropores, as determined by nitrogen adsorption, comprise pores with diameters in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)).

[0114] This application proposes that pores with a diameter of 1.0 nm to 1.5 nm have a significant impact on continuous gas production and bubbling. By controlling the pore size within this specific range, the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), can be achieved within 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 The value of / (g·log(nm)) can significantly reduce continuous bubbling. Studies have found that larger pore sizes (pores larger than 1.5 nm) have less impact on processability, presumably because the bubbling duration caused by these pores is shorter. Smaller pore sizes (pores smaller than 1.0 nm) may have limited impact on processability due to their smaller gas storage capacity. However, by limiting the maximum value of the volume contribution change rate (dV / d(logD)) of pores with diameters between 1.0 nm and 1.5 nm to within the aforementioned range, gas generation and bubbling during pulping can be effectively reduced, while also considering the sodium storage effect of this type of pore size.

[0115] For example, the maximum dV / d(logD) value for a pore with a diameter of 1.0 nm to 1.5 nm is 0.001 cm. 3 / (g·log(nm)), 0.002cm 3 / (g·log(nm)), 0.003cm 3 / (g·log(nm)), 0.004cm 3 / (g·log(nm)), 0.005cm 3 / (g·log(nm)), 0.006cm 3 / (g·log(nm)), 0.007cm 3 / (g·log(nm)), 0.008cm 3 / (g·log(nm)), 0.009cm 3 / (g·log(nm)) can be any value between any two of these values.

[0116] The dV / d(logD) mentioned in this application reflects the pore volume contributed per unit pore size. This value can be obtained by measuring hard carbon materials using conventional methods in the field. For example, it can be determined using a surface area analyzer-static volumetric method. Specifically, according to embodiments of this application, a flow-type gas adsorption surface area measuring device (device model Micromeritics ASAP-2460) can be used to measure the adsorption and desorption isotherms of nitrogen adsorption, and a DFT model can be used to fit the distribution curve of dV / d(logD) relative to the pore size D, with the maximum value read in the pore size range of 1.0-1.5 nm. The hard carbon material can be a hard carbon material used as a raw material, or it can be hard carbon material obtained from the disassembly and separation of secondary batteries.

[0117] In some embodiments, the hard carbon material has a pore size of 1.0 nm to 1.5 nm, and the maximum value of dV / d(logD) is 0.001 cm⁻¹. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0118] In some embodiments, the hard carbon material has pores with a diameter of 1.0 nm to 1.5 nm and a pore volume of 0.0003 cm³. 3 / g-0.0017cm 3 / g. This is more conducive to reducing gas generation during pulping while also considering specific volume. For example, the pore volume of pores with a pore size of 1.0nm-1.5nm is 0.0003cm³. 3 / g, 0.0005cm 3 / g, 0.0007cm 3 / g, 0.0009cm 3 / g, 0.0011cm 3 / g, 0.0013cm 3 / g, 0.0015cm 3 / g, 0.0017cm 3 / g or a value within a range of any two of these values. Optionally, the total pore volume of pores with a diameter of 1.0 nm to 1.5 nm is 0.0009 cm³. 3 / g-0.0014cm 3 / g.

[0119] The pore volume of the aforementioned 1.0 nm-1.5 nm pores was also obtained by measuring hard carbon materials using conventional methods in the field, such as the N2 adsorption-desorption pore volume and pore size test method. For example, referring to GB / T 19587-2017, the N2 adsorption method can be used to test adsorption and desorption isotherms, and a DFT model can be used to fit the distribution curve of cumulative pore volume relative to pore size, thus obtaining the pore volume of pores in the specific pore size range of 1.0 nm-1.5 nm.

[0120] In some embodiments, the pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b (i.e., V1) at 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g.

[0121] Further research revealed that during the preparation of the negative electrode slurry, pores with a diameter of less than 2 nm all caused a certain degree of gas generation and bubbling. While pores with a diameter less than 1 nm did not cause a large amount of bubbling, the excessive pore volume resulted in a longer duration of bubbling. Pores with a diameter of 1.5-2 nm also caused some bubbling, but the bubbling duration was shorter. Pores with a diameter of less than 2 nm in the material could contribute to the specific capacity. Further limiting V... a +V b Within the aforementioned range, further reduction of continuous bubbling is achieved while balancing specific capacity and processability. For example, the pore volume of pores with a diameter of less than 2 nm is 0.0006 cm³. 3 / g, 0.0010cm 3 / g, 0.0013cm 3 / g, 0.0015cm 3 / g, 0.0018cm 3 / g, 0.0020cm 3 / g, 0.0023cm 3 / g, 0.0025cm 3 / g, 0.0028cm 3 / g, 0.0030cm 3 / g, 0.0033cm 3 / g, 0.0035cm 3 / g can be a value between any two of these values. Alternatively, V a +V b At 0.0020cm3 / g to 0.0030cm 3 Within the range of / g.

[0122] For the hard carbon material with pore sizes less than 1 nm, the pore volume V a The pore volume can be determined using conventional methods in the art. For example, the CO2 adsorption-desorption pore volume and pore size measurement method. This method typically measures the pore volume of pores with a diameter less than 1 nm, particularly those greater than 0.4 nm but less than 1 nm. For instance, referring to GB / T 34709-2017, adsorption and desorption isotherms can be measured using the CO2 adsorption method. A DFT model can be used to fit the cumulative pore volume distribution curve relative to the pore size, and the total pore volume V of pores within a specific diameter range less than 1 nm can be obtained. a .

[0123] The pore volume V of the hard carbon material with a pore size of 1nm-2nm b The distribution curve of cumulative pore volume relative to pore size can be determined using a method similar to that described above, and V can be obtained by integrating over a specific pore size range of 1 nm to 2 nm. b .

[0124] In some embodiments, the pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%. When the proportion of micropore volume in the total pore volume is within the above range, it is beneficial to improve the capacity of the secondary battery.

[0125] In some embodiments, the pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 2.5% ≤ V² / V 总 ≤10%. A mesopore volume within the above range is beneficial for improving the kinetic performance of secondary batteries.

[0126] In some implementations, 0.0003cm 3 / g≤V2≤0.0012cm 3 / g. A mesoporous pore volume within the above range is beneficial for improving the kinetic performance of the secondary battery.

[0127] In some embodiments, the hard carbon material includes heteroatoms.

[0128] The presence of heteroatoms can increase the interlayer spacing of graphene sheets in hard carbon materials, making the spacing between graphene sheets greater than 0.4 nm. This allows active ions to enter more easily and perform adsorption-based sodium storage, which is beneficial to the kinetics of secondary batteries.

[0129] In some embodiments, the heteroatom may include at least one atom selected from O, N, S, P, B, and F. Exemplarily, hard carbon materials may include O and N, or O and S, or O and P, or O and B, or O and F, or O, N, and S, or O, N, and P, or O, N, and B, or O, N, and F, or O, N, S, and P, or O, N, S, and B, or O, N, S, and F, or O, N, S, P, and B, or O, N, S, P, and F, or O, N, S, P, B, and F, or N and S, Or, N and P, or, N and B, or, N and F, or, N, S and P, or, N, S and B, or, N, S and B, or, N, S, P and B, or, N, S, P and F, or, N, S, P, B and F, or, S and P, or, S and B, or, S and F, or, S, P and B, or, S, P and F, or, S, P, B and F, or, P and B, or, P and F, or, P, B and F, or, B and F.

[0130] In some embodiments, heteroatoms account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material. For example, heteroatoms may account for 0.4 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt% of the total mass of the hard carbon material, or any value within the range of any two of these values. Having a heteroatomium percentage within this range ensures that the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the total graphene sheets is within this range, which is beneficial for balancing kinetic performance and first-pass coulombic efficiency.

[0131] In some embodiments, the hard carbon material I D / I G It is 1.1-1.35; where, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location. For example, the I peak intensity of the hard carbon material. D / I G It can be 1.1, 1.2, 1.3, 1.35, or any value within the range of any two values. I of hard carbon materials D / I G Within the aforementioned range, the high degree of carbon order and fewer surface defects on the surface of hard carbon materials are beneficial for improving the initial coulombic efficiency of the battery and also for increasing the compaction density.

[0132] In some embodiments, the surface oxygen content of the hard carbon material is 5% to 15%. Exemplarily, the surface oxygen content of the hard carbon material is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range of any two values. Having the surface oxygen content of the hard carbon material within the above range allows the viscosity of the slurry containing the hard carbon material to be within a suitable range, which is beneficial for improving the processing performance of the secondary battery.

[0133] In some embodiments, the powder compaction density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial to increase the cold-pressed density of the negative electrode sheet, which in turn is beneficial to increase the volumetric energy density of the secondary battery.

[0134] In some embodiments, the hard carbon material satisfies at least one of the following:

[0135] (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; The specific surface area of ​​hard carbon materials is within the above range, which is beneficial to improving the first coulombic efficiency of secondary batteries.

[0136] (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 When the tap density of hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film and improve the energy density of the secondary battery.

[0137] (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 When the true density of hard carbon materials is within the above range, it is beneficial to improve the capacity of secondary batteries.

[0138] It should be noted that true density refers to the mass of a material in an absolutely dense state, per unit actual volume (excluding internal voids, i.e., excluding open and closed pores and interparticle voids).

[0139] (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm;

[0140] (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm;

[0141] (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

[0142] When the particle size distribution of hard carbon materials falls within the aforementioned range (Dv10, Dv50, Dv90), it is beneficial to reduce the specific surface area of ​​the hard carbon materials, thereby reducing the occurrence of side reactions and improving the initial coulombic efficiency of the secondary battery. Simultaneously, it can also shorten the bulk transport path of active ions, further enhancing the kinetic performance of the secondary battery.

[0143] In this application, the pore volumes V1, V2 and V of the micropores and mesopores of the hard carbon material are specified. 总 The determination can be performed with reference to GB / T 19587-2017.

[0144] In this application, the I of hard carbon material D / I G The value can be measured using a Raman spectrometer. D This indicates that the Raman spectrum of the material is at 1350±50 cm⁻¹. -1 The intensity of peak D at I G This indicates that the Raman spectrum of the material is at 1580±50 cm⁻¹. -1 The intensity of the G peak at the location was measured. The test conditions were: excitation wavelength 532 nm, power 0.5%, grating 600 lines, objective lens 50x, integration time 10 s, cumulative scan 3 times, area scan, obtaining the D and G peak intensities at 100 points, and calculating the I values ​​at 100 points. D / I G Remove the largest and smallest 30 I's. D / I G The average of the remaining 40 points is the material's I. D / I G The testing instrument can be a Horiba LabRAMHR800 Raman spectrometer.

[0145] In this application, the surface oxygen content of the hard carbon material can be obtained through semi-quantitative analysis of the surface functional groups of the hard carbon material. Specifically, X-ray photoelectron spectroscopy (XPS) is performed on the hard carbon material, and the signal intensity measured by XPS is converted into elemental content, and the peak area is converted into the corresponding elemental content. The equipment used is an Axis Supra / Supra+, a 450W Al Kα / Ag Lα monochromatic X-ray source with an energy resolution ≤0.45 eV. Specifically, the XPS spectrum of the hard carbon material is fitted using the XPS peak41 software. A suitable baseline is set, fitted peaks are added, and then Gaussian fitting is performed until the residual is less than 10.

[0146] In this application, the compaction density of hard carbon materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine) in accordance with GB / T 24533-2009. An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 2t, held for 30s, then the pressure is released and held for 10s. The compaction density of the powder under 2t pressure is then recorded and calculated.

[0147] In this application, the specific surface area (BET) of hard carbon materials has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0148] In this application, the tap density of hard carbon materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a 25mL graduated cylinder.

[0149] In this application, the true density of hard carbon has a meaning known in the art and can be tested using methods known in the art. As an example, a mass M of hard carbon is weighed and placed in a true density analyzer (AccuPyc II 1340 analyzer) at room temperature (15℃-25℃). The test system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, and then calculating the gas volume in the sample chamber and the expansion chamber respectively according to the ideal gas law, the difference between the two is used to obtain the volume of gas displaced by the hard carbon under certain temperature and pressure conditions, which is the true volume V of the hard carbon. The true density of hard carbon is calculated as the hard carbon mass M / the hard carbon true volume V, and the unit of true density is g / cm³. 3 .

[0150] In this application, the volumetric particle sizes Dv10, Dv50, and Dv90 of hard carbon materials have meanings known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0151] In this application, the content of heteroatoms S, B, P, and F in the hard carbon material can be determined using instruments and methods known in the art. For example, the elements and their contents in the hard carbon material can be measured with reference to EPA 6010D-2014 inductively coupled plasma atomic emission spectrometry.

[0152] In this application, the content of heteroatoms O and N in the hard carbon material can be determined using instruments and methods known in the art. For example, it can be tested using a nitrogen, hydrogen, and oxygen analyzer.

[0153] In this application, the microstructure of hard carbon materials can be observed using a scanning electron microscope or a transmission electron microscope.

[0154] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0155] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0156] In some embodiments, the negative electrode active material includes the hard carbon material provided in the above embodiments or the hard carbon material prepared according to the preparation method of the above embodiments.

[0157] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0158] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0159] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0160] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0161] Secondary batteries

[0162] The second aspect of this application provides a secondary battery, which will be described below with appropriate reference to the accompanying drawings.

[0163] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0164] Typically, a single secondary battery cell includes a positive electrode, a negative electrode as described in the first aspect, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0165] [Positive electrode plate]

[0166] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0167] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0168] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, the battery cell is a sodium-ion battery, and the positive electrode active material can be any positive electrode active material known in the art for use in sodium-ion batteries. As examples, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, etc., but this application is not limited to these materials; other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used. For example, as an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, Pb, and Ce. The sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0170] As an optional technical approach in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0171] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y )m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- Valence state: Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2(PO4)3. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0172] As an optional technical approach in this application, the polyanionic compound can be Na... x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0173] As an optional technical approach in this application, the polyanionic compound can be Na... x R y (PO4)2P2O7, where x = 3.5-4.5, y = 2.75-3.25, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0174] As an optional technical approach in this application, the polyanionic compound can be Na... 4+x R 3-y P 4-m O15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0175] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, Prussian blue compounds are Na a Me b Me’ c (CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0176] In other embodiments, the battery cell can also be a lithium-ion battery, and the positive electrode active material can be the positive electrode active material known in the art for lithium-ion batteries.

[0177] In the enumeration of the positive electrode active material in this application, the molar content of oxygen is only the theoretical value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0178] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0179] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0180] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0181] [Electrolyte]

[0182] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0183] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0184] In some embodiments, when the battery cell is a sodium-ion battery, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium difluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorophosphate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0185] In some embodiments, when the battery cell is a lithium-ion battery, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0186] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0187] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0188] [Isolation membrane]

[0189] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0190] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0191] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0192] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0193] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0194] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0195] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0196] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0197] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0198] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0199] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0200] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0201] In some embodiments, in the first discharge curve of the coin cell prepared using the negative electrode sheet of this application, the discharge capacity corresponding to a voltage greater than 0.1V accounts for 28% to 55% of the total discharge capacity.

[0202] Electrical appliances

[0203] A third aspect of the embodiments of this application also provides an electrical device, and the secondary battery of this application will be described below with appropriate reference to the accompanying drawings.

[0204] The electrical device mentioned in the embodiments of this application includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0205] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0206] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0207] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0208] The fourth aspect of this application provides a hard carbon material included in the negative electrode sheet of the first aspect of this application. The hard carbon material comprises graphene sheets, wherein the space volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total space volume H between all layers in the graphene sheets are... 总 Satisfy: 40% ≤ H1 / H 总 ≤60%.

[0209] In this application, by ensuring that the proportion of the space volume between graphene sheets with an interlayer spacing greater than 0.4 nm in the hard carbon material is within the aforementioned specific range, the secondary battery can possess both excellent kinetic performance and first-time coulombic efficiency.

[0210] In some implementations, 40% ≤ H1 / H 总 ≤55%.

[0211] By adjusting the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the aforementioned range, it is even more conducive to achieving both excellent dynamic performance and first-round coulomb efficiency.

[0212] In some embodiments, the space volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is related to the total space volume H between the individual layers of the graphene sheet. 总 Satisfying: 22% ≤ H2 / H 总 ≤60%.

[0213] In this application, the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm is compared with the total spatial volume H between each layer in the graphene sheet. 总 Within the aforementioned range, it is possible to improve the capacity of the secondary battery while simultaneously enhancing its kinetics.

[0214] In some embodiments, the space volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm is related to the total space volume H between the individual layers in the graphene sheet. 总 Satisfy: H3 / H 总 ≤18%.

[0215] By adjusting the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between all layers in the graphene sheet... 总 Within the above range, the risk of sodium deposition can be reduced, the cathode capacity can be improved, and the energy density of the secondary battery can be increased.

[0216] In some embodiments, the hard carbon material further includes micropores with a pore size of 2 nm or less and mesopores with a pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5 ≤ V 1 / V2≤9.7.

[0217] By setting the pore volume V1 of micropores and the pore volume V2 of mesopores to satisfy the above relationship, it is beneficial to enable secondary batteries to have both excellent capacity and kinetic performance.

[0218] In some embodiments, the hard carbon material, as determined by nitrogen adsorption, contains pores with a diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)). The hard carbon material provided in this application has an optimized pore structure. Specifically, the characteristic dV / d(logD) of the hard carbon material with pore sizes of 1.0nm-1.5nm corresponds to the pore volume contributed per unit pore size, with a maximum value of 0.001cm. 3 / (g·log(nm))-0.009cm 3 Within the range of / (g·log(nm)), it is beneficial to reduce gas generation and bubbling during the pulping process.

[0219] In some embodiments, the hard carbon material has a pore size of 1.0 nm to 1.5 nm, and the maximum value of dV / d(logD) is 0.001 cm⁻¹. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0220] In some embodiments, the pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b At 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g. The pore volume of hard carbon materials with pore size below 2nm is within the above range, which is more conducive to reducing gas generation and bubbling during the pulping process while maintaining the specific capacity.

[0221] In some embodiments, the V of the hard carbon material a +Vb At 0.0020cm 3 / g to 0.0030cm 3 Within the range of / g.

[0222] In some embodiments, the pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%. When the proportion of micropore volume in the total pore volume is within the above range, it is beneficial to improve the capacity of the secondary battery.

[0223] In some embodiments, the pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material are... 总 Satisfies: 2.5% ≤ V² / V 总 ≤10%. A mesopore volume within the above range is beneficial for improving the kinetic performance of secondary batteries.

[0224] In some implementations, 0.0003cm 3 / g≤V2≤0.0012cm 3 / g. A mesoporous pore volume within the above range is beneficial for improving the kinetic performance of the secondary battery.

[0225] In some embodiments, the hard carbon material includes heteroatoms, which account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material. In some embodiments, the heteroatoms include at least one of O, N, S, P, B, and F. The presence of heteroatoms can increase the interlayer spacing of the graphene sheets in the hard carbon material, making the spacing between the graphene sheets greater than 0.4 nm, which is beneficial to the kinetics of the secondary battery. In addition, the mass percentage of heteroatoms in the hard carbon material within the above-mentioned range ensures that the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the total graphene sheets is within the above-mentioned range, which is beneficial to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0226] In some embodiments, the hard carbon material I D / I G It is 1.1-1.35; where, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location. By making the I of the hard carbon material... D / I GWithin the aforementioned range, the high degree of carbon order and fewer surface defects on the surface of hard carbon materials are beneficial for improving the initial coulombic efficiency of the battery and also for increasing the compaction density.

[0227] In some embodiments, the surface oxygen content of the hard carbon material is 5% to 15%.

[0228] When the surface oxygen content of the hard carbon material is within the above-mentioned range, the viscosity of the slurry containing the hard carbon material is within a suitable range, which is beneficial to improving the processing performance of secondary batteries.

[0229] In some embodiments, the powder compaction density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial to increase the cold-pressed density of the negative electrode sheet, which in turn is beneficial to increase the volumetric energy density of the secondary battery.

[0230] In some embodiments, the hard carbon material satisfies at least one of the following:

[0231] (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; The specific surface area of ​​hard carbon materials is within the above range, which is beneficial to improving the first coulombic efficiency of secondary batteries.

[0232] (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 When the tap density of hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film and improve the energy density of the secondary battery.

[0233] (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 When the true density of hard carbon materials is within the above range, it is beneficial to improve the capacity of secondary batteries.

[0234] (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm;

[0235] (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm;

[0236] (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

[0237] When the particle size distribution of hard carbon materials falls within the aforementioned range (Dv10, Dv50, Dv90), it is beneficial to reduce the specific surface area of ​​the hard carbon materials, thereby reducing the occurrence of side reactions and improving the initial coulombic efficiency of the secondary battery. Simultaneously, it can also shorten the bulk transport path of active ions, further enhancing the kinetic performance of the secondary battery.

[0238] Preparation method of hard carbon materials

[0239] In the preparation of the hard carbon material described in this application, the carbon sources that can be used include biomass materials and synthetic polymer materials. In some embodiments, different carbon sources can also be combined with each other; for example, synthetic polymer materials can be combined with other carbon sources to obtain hard carbon materials with more favorable internal / external structures. The hard carbon material described above can be prepared by adjusting the process conditions.

[0240] Biomass materials are widely available, such as coconut shells, rice husks, bamboo, wheat husks, straw, lignin, and so on. Using biomass materials as a carbon source has both economic and environmental benefits.

[0241] In some embodiments, the above-mentioned hard carbon material can be prepared by the following preparation method, specifically including: a pre-carbonization step, a doping step, and a carbonization step; the pre-carbonization step includes pre-carbonizing the biomass precursor at 300℃-500℃; the carbonization step includes carbonizing at 1000℃-1200℃.

[0242] In this application, the pre-carbonization step, doping step, and carbonization step are performed under the above conditions during the preparation of hard carbon materials, so that the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the prepared hard carbon materials is within the above range, which is beneficial to balance the kinetic performance and first coulombic efficiency of the secondary battery.

[0243] Furthermore, a carbonization temperature within the aforementioned range can also ensure that the amount of active sites (i.e. defects) in the hard carbon material is within a suitable range, which is beneficial for balancing the initial coulombic efficiency and reversible capacity of the hard carbon material as a negative electrode active material for secondary batteries.

[0244] In some embodiments, the biomass precursor includes cellulose, hemicellulose, and lignin, wherein the mass percentage of cellulose in the biomass precursor is 40% to 60%, the mass percentage of hemicellulose in the biomass precursor is <40%, and the mass percentage of lignin in the biomass precursor is 20% to 40%.

[0245] Because hemicellulose in biomass precursors has high crystallinity, it easily stacks to form long-range ordered carbon layers during high-temperature pyrolysis. In contrast, lignin and cellulose are mostly amorphous components, which can prevent the graphitization of carbon layers and increase the interlayer spacing during high-temperature pyrolysis. Therefore, by setting the proportions of cellulose, lignin, and hemicellulose in the biomass carbon precursors within the above-mentioned range, the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the formed hard carbon material is within the above-mentioned range, which is beneficial to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0246] In some embodiments, the biomass precursor is formed through the following steps: dissolving a carbon source in a solvent and stirring to form a homogeneous solution; transferring the mixed solution to a reaction vessel for thermal reaction, followed by cooling and filtration to obtain the carbon precursor. The carbon source includes one or more of lignin, cellulose, and sugars; the solvent is one or more of water, methanol, ethanol, and acetone. The above thermal reaction can, for example, be carried out in an oven at 180°C–250°C for 4–12 hours.

[0247] In this application, the thermal reaction in the preparation process of the biomass precursor is carried out at the above-mentioned temperature, which allows the carbon source reaction to be more complete and prevents the prepared carbon precursor from fusion.

[0248] In some embodiments, after preparing the biomass precursor, the sample is further purified by acid washing and water washing to remove or reduce the ash content in the biomass precursor.

[0249] In some embodiments, heteroatom doping is performed during the doping step, such that the hard carbon material comprises 0.4 wt% to 5 wt% heteroatoms. In some embodiments, the heteroatoms include at least one of O, N, S, P, B, and F.

[0250] In this application, the total mass percentage of heteroatoms in the hard carbon material is within the above-mentioned range, which enables the proportion of graphene sheets with an interlayer spacing greater than 0.4 nm in the total graphene sheets to be within a suitable range, which is beneficial to balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0251] In some embodiments, during the pre-carbonization step, a carrier gas is introduced, and the temperature is increased to 200℃-500℃ at a heating rate of 1℃ / min-10℃ / min, and maintained for 0.5h-3h; the flow rate of the carrier gas is 10mL / min-30mL / min. Pre-carbonization, performed in the above steps, can form a carbon framework with suitable spacing, which is beneficial for the subsequent formation of graphene sheets with suitable interlayer spacing.

[0252] In some embodiments, the carrier gas is an inert gas, such as nitrogen or inert gases such as helium, neon, argon, krypton, or xenon.

[0253] In some embodiments, the pre-carbonization step is performed simultaneously with the doping step; in the doping step, doping is performed using a doping gas or a dopant.

[0254] It should be noted that since the pre-carbonization process is the process of forming a carbon skeleton, heteroatoms are mixed in during this process. Since the radius of heteroatoms is larger than that of carbon atoms, this can increase the interlayer spacing of the carbon layers, making it easier for active ions to enter and perform adsorption-type sodium storage, which is beneficial to the kinetics of the secondary battery.

[0255] In some embodiments, the dopant gas includes at least one of an oxygen-containing gas, a nitrogen-containing gas, or a fluorine-containing gas; the volume ratio of the dopant gas to the carrier gas is 0.02:1 to 0.11:1. Maintaining the dopant gas volume ratio within this range ensures that the amount of heteroatoms in the hard carbon material is within a suitable range, which is beneficial for balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0256] In some embodiments, the oxygen-containing gas may be, for example, oxygen or ozone; the nitrogen-containing gas may be, for example, ammonia or nitric oxide; and the fluorine-containing gas may be, for example, fluorine or hydrogen fluoride.

[0257] In some embodiments, examples of dopants include polypyrrole, polyaniline, triphenylphosphine, sulfur, cyanuric acid, dicyandiamide, boric acid, melamine, thiourea, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Preferably, the dopant includes at least one of boric acid, melamine, thiourea, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the mass ratio of the dopant to the carbon precursor is 0.05:1 to 2:1. A mass ratio of dopant to carbon precursor within the above range ensures that the amount of heteroatoms in the hard carbon material is within a suitable range, which is beneficial for balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0258] In some embodiments, after the pre-carbonization step, the pre-carbonized product is pulverized to break the biomass precursor to the target particle size. This benefits the subsequent pulping process and improves the electrochemical performance of hard carbon materials as a negative electrode active material in secondary batteries.

[0259] In some embodiments, the pulverization process is carried out by an air jet mill or a mechanical mill.

[0260] In some embodiments, the carbonization treatment is carried out under an inert atmosphere for 1-6 hours. The carbonization treatment can remove moisture, volatiles, and surface groups from the pre-carbonized product, and can also adjust the structure of the hard carbon, which is beneficial to the electrochemical performance of the secondary battery.

[0261] In some embodiments, the doping step is performed after the carbonization step; in the doping step, at least one doping solution selected from nitric acid solution, sulfuric acid solution, potassium permanganate solution, and hydrogen peroxide is used for doping for 0.5 h to 5 h; the mass ratio of the solute in the doping solution to the hard carbon material obtained in the carbonization step is (3 to 40): 1.

[0262] Because nitric acid solution, sulfuric acid solution, potassium permanganate solution, hydrogen peroxide, and other solutions have strong oxidizing properties, they can be used to dope the hard carbon material obtained in the carbonization step with oxygen atoms, thereby expanding the interlayer spacing of the hard carbon material. Furthermore, by using doping solutions with appropriate treatment time and maintaining the mass ratio of solute in the doping solution to the hard carbon material obtained in the carbonization step within the aforementioned ranges, the amount of heteroatoms doped in the hard carbon material can be kept within a suitable range, which is beneficial for balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0263] In some embodiments, the doping solution may be a nitric acid solution with a mass concentration of 10% to 40%, a sulfuric acid solution with a mass concentration of 10% to 60%, a potassium permanganate solution with a mass concentration of 0.5% to 10%, or hydrogen peroxide with a mass concentration of 1% to 10%.

[0264] In some embodiments, after the carbonization step or the doping step, a grading and demagnetization process is further included.

[0265] In some embodiments, the above-mentioned hard carbon material can also be prepared by the following preparation method, specifically including: a pre-carbonization step, in which the biomass material is heated at 300-500℃, optionally 400-500℃, for 2-6 hours. The pre-carbonization step can remove volatiles from the biomass; a crushing step, in which the pre-carbonized product is crushed to a particle size of Dv10≤3μm, Dv50≤8μm, and Dv90≤30μm. The crushing step enables the final hard carbon material to have a suitable particle size distribution; a deashing step, in which the product is soaked in an acid washing kettle with 1-5M acid to remove metal impurities. Biomass contains a lot of metal impurities, and the deashing step can reduce the content of metal impurities; a pre-compression step, in which the deashed product is compressed into a cake shape with tightly packed particles to reduce the exposed area, prevent the oxidation and destruction of carbon by sintering volatiles, and control the porosity; and a carbonization step, in which the material is heated at 1300-1600℃ for 2-6 hours to remove the remaining volatiles.

[0266] Exemplarily, the crushing can be performed by an air jet mill or a mechanical mill, and this disclosure does not impose any particular limitation on this method. In some embodiments, the crushing results in a particle Dv50 of 4μm-8μm, which is more conducive to adjusting the pore structure of the pre-carbonized product to obtain a suitable pore structure during subsequent high-temperature carbonization, and also facilitates the full dissolution of impurities and results in a suitable particle size distribution of the final hard carbon.

[0267] For example, the acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, etc. The deashing process reduces the ash content, which consists of various metals and their oxides.

[0268] In some implementations, the amount of metal ions volatilized from the interior remaining on the surface can be adjusted by further washing after carbonization. For example, using coconut shell as a carbon source, the ion content can be further reduced by washing 3-4 times after carbonization. By combining this with the preceding deashing step, the cation content in the final hard carbon material can be adjusted, which is beneficial to the electrode preparation process.

[0269] In the above method, porosity and pore structure are adjusted by steps such as crushing and pre-oxidizing the pre-carbonized products, sintering temperature and time, so as to obtain hard carbon materials with reduced or eliminated bubbling in the pulping process.

[0270] Example

[0271] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0272] Example 1

[0273] Preparation of hard carbon materials:

[0274] (1) Pre-carbonization step and doping step: Under the condition of introducing carrier gas nitrogen and doping gas oxygen, the biomass carbon precursor coconut shell is placed in a box furnace and heated to 300°C at a heating rate of 5°C / min and held for 3h for pre-carbonization treatment. The volume ratio of oxygen to nitrogen is 0.05:1; the flow rate of the mixed gas of nitrogen and oxygen is 10mL / min.

[0275] (2) Carbonization step: Under the condition of nitrogen gas, heat to 1100℃ and hold for 2 hours, then cool to room temperature;

[0276] (3) The sample obtained by the above carbonization step is crushed, graded, sieved, demagnetized and other processes are carried out to finally obtain hard carbon anode material.

[0277] Tests related to hard carbon materials:

[0278] 1) XRD testing

[0279] The hard carbon material prepared in Example 1 was uniformly mixed with silicon powder at a mass ratio of 5:1, and a sample was prepared using the plate preparation method. A Bruker D8 Discover X-ray diffractometer was used for testing. CuKα rays were used as the radiation source, and a copper target was used as the anode target. The scanning angle range was 10°–40°, and the scanning rate was 1° / min. The XRD diffraction pattern of the hard carbon material was obtained, as shown below. Figure 7 As shown, the blue data with noise represents the original data, and the red data represents the fitted data.

[0280] The XRD spectrum of the hard carbon material, after fitting, includes three fitting peaks. The strongest peak of the first fitting peak (orange) corresponds to an angle of 2θ = 21.16°. The area of ​​the first fitting peak represents the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm in the hard carbon material. The ratio of the area of ​​the first fitting peak to the total area of ​​the three fitting peaks is equal to the spatial volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm in the hard carbon material, which is the total spatial volume H between the graphene sheets. 总 The proportion of H1 / H 总 The percentage is 52.41%. The strongest peak of the second fitting peak (blue) corresponds to an angle of 2θ = 23.53°. The area of ​​the second fitting peak represents the spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm in the hard carbon material. The ratio of the area of ​​the second fitting peak to the total area of ​​the three fitting peaks is equal to the total spatial volume H2 between the graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm in the hard carbon material. 总 The proportion of H2 / H 总 The percentage is 33.77%. The strongest peak of the third fitting peak (green) corresponds to an angle of 2θ = 25.46°. The area of ​​the third fitting peak represents the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm in the hard carbon material. The ratio of the area of ​​the third fitting peak to the total area of ​​the three fitting peaks is equal to the spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm in the hard carbon material and the total spatial volume H between the layers in the graphene sheet. 总 The proportion of H3 / H 总 It is 13.82%.

[0281] 2) Aperture and pore volume testing

[0282] For hard carbon materials, adsorption and desorption isotherms were tested using nitrogen and carbon dioxide adsorption methods, respectively, in accordance with GB / T 19587-2017. The nitrogen adsorption method employed a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA), and the carbon dioxide adsorption method also employed a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA). For the adsorption and desorption isotherms obtained by the nitrogen adsorption method, a DFT model was used to fit the pore size distribution curves, yielding the pore volume and total specific surface area for specific pore size ranges (1.0 nm-1.5 nm, 1 nm-2 nm, and above 2 nm). For the adsorption and desorption isotherms obtained by the carbon dioxide adsorption method, a DFT model was used to fit the pore size distribution curves, and the pore volume for pores with diameters smaller than 1 nm was calculated using mathematical methods. These methods yielded the pore size and pore volume parameters V1, V2, and Vtotal.

[0283] Battery manufacturing:

[0284] The hard carbon material prepared in Example 1 was mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CCMC-Na) as a thickener, and Superp as a conductive agent in a mass ratio of 96:2.5:0.8:0.7 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil of the negative electrode current collector, dried in a vacuum oven at 80°C for 12 hours, and then sliced ​​to form a negative electrode sheet.

[0285] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1 to obtain an organic solvent. NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.4 mol / L.

[0286] Then, using a sodium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, a CR2430 coin cell was assembled in a glove box.

[0287] Battery performance test

[0288] First Coulomb efficiency and dynamic performance

[0289] At 25°C, the prepared coin cell was first discharged at a constant current density of 0.1C to 0.1V, and the capacity above 0.1V of the coin cell was recorded. Then, it was discharged at a constant current density of 0.1C to 0V, and the first discharge capacity (i.e., the first sodium insertion capacity) of the coin cell was recorded. After that, it was charged at a constant current density of 0.1C to 2.0V, and the first charge capacity (i.e., the first sodium removal capacity) of the coin cell was recorded.

[0290] The initial coulombic efficiency (%) of a secondary battery = initial sodium removal capacity / initial sodium insertion capacity × 100%;

[0291] Percentage of capacity above 0.1V (%) = Capacity above 0.1V / Initial sodium intercalation capacity × 100%;

[0292] The 0.1V capacity ratio can reflect the dynamic performance of a secondary battery. The higher the 0.1V capacity ratio, the better the dynamic performance of the secondary battery.

[0293] Based on the original capacity-voltage data of the first discharge capacity, a lithium intercalation capacity diagram is plotted, as follows: Figure 8 and Figure 9 As shown by the solid line in the image, Figure 9 for Figure 8 A magnified view of a portion of the secondary battery. In Example 1, the proportion of the ramp segment above 0.1V is as high as 39.6%, and the capacity above 0.1V is 129.6mAh / g.

[0294] Examples 2-4

[0295] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into secondary batteries. The only difference was that the pre-carbonization temperature and the amount of heteroatom doping were adjusted during the preparation of the hard carbon materials to obtain different H1 / H ratios. 总 For details on the hard carbon materials, please refer to Tables 1 and 2.

[0296] Example 5

[0297] Preparation of hard carbon materials:

[0298] (1) Pre-carbonization step: Under the condition of introducing carrier gas nitrogen, the biomass carbon precursor coconut shell is placed in a box furnace and heated to 400℃ at a heating rate of 5℃ / min and kept for 3h for pre-carbonization treatment. The nitrogen flow rate is 10mL / min.

[0299] (2) Carbonization step: Under the condition of nitrogen gas, heat to 1200℃ and hold for 2 hours, then cool to room temperature;

[0300] (3) Doping step: Mix the above carbonized hard carbon material with a nitric acid solution with a mass concentration of 15% and keep it for 1.5h to obtain the doped hard carbon material.

[0301] (4) The above-mentioned doped hard carbon material samples are subjected to crushing, grading, sieving, and demagnetizing processes to finally obtain H1 / H 总 It is a hard carbon anode material with 60% hard carbon content.

[0302] Next, the battery is assembled into a secondary battery using a method similar to that in Example 1.

[0303] Examples 6, 8, and 10

[0304] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into secondary batteries. The only difference was that the pre-carbonization temperature and the amount of heteroatom doping were adjusted during the preparation of the hard carbon materials to obtain hard carbon materials with different V1 / V2 ratios, as detailed in Tables 1 and 2.

[0305] Examples 7 and 9

[0306] Hard carbon materials were prepared using a method similar to that in Example 5 and assembled into a secondary battery. The only difference was that the pre-carbonization temperature and the amount of heteroatom doping were adjusted during the preparation of the hard carbon materials to obtain hard carbon materials with different V1 / V2 ratios, as detailed in Tables 1 and 2.

[0307] Comparative Example 1

[0308] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into a secondary battery. The only difference was that the pre-carbonization temperature and the amount of heteroatom doping were adjusted during the preparation of the hard carbon materials to obtain H1 / H. 总 Hard carbon materials with less than 40% content are detailed in Tables 1 and 2.

[0309] The secondary battery in Comparative Example 1 was subjected to charge-discharge tests in the same manner as in Example 1. A lithium intercalation capacity diagram was plotted based on the original capacity-voltage data of the first discharge charge capacity of the secondary battery in Comparative Example 1. Figure 8 and Figure 9 As shown by the dashed line in the figure. In Comparative Example 1, the proportion of the ramp segment above 0.1V in the secondary battery is 24.4%, and the capacity above 0.1V is 89.4mAh / g.

[0310] Comparative Example 2

[0311] Hard carbon materials were prepared using a method similar to that in Example 5 and assembled into a secondary battery. The only difference was that the pre-carbonization temperature and the amount of heteroatom doping were adjusted during the preparation of the hard carbon materials to obtain H1 / H. 总 Hard carbon materials with a content greater than 60% are detailed in Tables 1 and 2.

[0312] The parameters of the hard carbon materials prepared in Examples 1-10 and Comparative Examples 1 and 2, as well as the performance test results of the secondary batteries, are shown in Tables 1-3 below.

[0313] Table 1:

[0314]

[0315] In Table 1, " / " indicates that the item does not exist.

[0316] Table 2:

[0317]

[0318]

[0319] Table 3:

[0320]

[0321] As can be seen from Tables 2 and 3 above, compared to Comparative Example 1 (H1 / H of hard carbon materials) 总 <40%) and Comparative Example 2 (H1 / H 总 >60%), in Examples 1-10, by making the H1 / H of the hard carbon material 总 A value between 40% and 60% ensures that the capacity of the secondary battery above 0.1V accounts for more than 28.5%, and that the initial coulombic efficiency of the secondary battery is greater than 87%, thus balancing the kinetic performance and initial coulombic efficiency of the secondary battery.

[0322] Furthermore, compared to Example 9 (V1 / V2 of hard carbon material < 0.5) and Example 10 (V1 / V2 of hard carbon material > 9.7), in Examples 1-8, by keeping the V1 / V2 of the hard carbon material between 0.5 and 9.7, the proportion of secondary battery capacity above 0.1V was further increased, resulting in better performance.

[0323] Example 11

[0324] Preparation of hard carbon materials using biomass as the carbon source:

[0325] 1) Pre-carbonization: Using lignin as raw material, it is treated at 400℃ for 2 hours under normal pressure and N2 atmosphere in a hot press furnace (Dingli Technology, VHP-777) to obtain pre-carbonized product.

[0326] 2) Crushing; The pre-carbonized product obtained in step 1) above is subjected to air jet mill (Shengxing Environmental Protection: SX1210) to obtain products with Dv10 of 2μm, Dv50 of 5μm and Dv90 of 12μm.

[0327] 3) Deashing: The product crushed in step 2) above is soaked in a pickling kettle with 2M hydrochloric acid aqueous solution for 10 hours at room temperature, filtered, washed with water 3 times, and then dried in a continuous kiln at 100°C.

[0328] 4) Pre-compression: The product obtained in step 3) above is pressurized in a hot press (manufacturer: Dingli Technology, model: VHP-777) at 50T pressure for 1 hour.

[0329] 5) Carbonization: The product obtained in step 4) above is sintered for 2 hours at 1400℃ for a normal pressure N2 atmosphere at a heating rate of 2℃ / min, washed with water 3 times, and then dried at 100℃ in a continuous kiln to obtain hard carbon material.

[0330] Preparation of negative electrode slurry:

[0331] The hard carbon material, conductive agent, and dispersant prepared above were dispersed in deionized water in a ratio of 8:1:1 to form a uniform negative electrode slurry, wherein the dispersant was sodium carboxymethyl cellulose and the conductive agent was conductive carbon black.

[0332] Preparation of negative electrode sheet:

[0333] The uniformly stirred negative electrode slurry is coated onto both sides of the Al foil using a double-sided coating machine. After double-sided coating is completed, the negative electrode sheet is prepared by vacuum drying at 80°C, cold pressing, slitting, and sheet forming.

[0334] Preparation of secondary batteries:

[0335] The prepared negative electrode sheet was used for battery assembly in a glove box. The sodium metal sheet was used as the counter electrode. The electrolyte was a solvent in which NaPF6 was dissolved in EC:DMC (volume ratio) = 1:1, and 10 v / v% FEC was added.

[0336] The positive electrode, separator, and negative electrode are stacked in sequence, and the electrolyte is added. After processes such as encapsulation, standing, formation, and aging, a button cell is made.

[0337] Example 12

[0338] Hard carbon materials were prepared using a method similar to that in Example 11, except that the high-temperature carbonization temperature was 1000°C.

[0339] Gas adsorption test

[0340] The time it took for the hard carbon materials prepared in the above embodiments to stop bubbling was observed during the preparation of the negative electrode slurry. Records were made of samples that continued to bubble 2 hours after mixing the components of the negative electrode slurry.

[0341] For the hard carbon materials of Examples 11 and 12 above, adsorption and desorption isotherms were tested using nitrogen and carbon dioxide adsorption methods, respectively, in accordance with GB / T 19587-2017. Both nitrogen and carbon dioxide adsorption methods were analyzed using a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA). The specific surface area of ​​the hard carbon material was calculated using the BET (Brunauer Emmett Teller) method based on the adsorption and desorption isotherms measured by the nitrogen adsorption method. A DFT model was used to fit the distribution curve of dV / d(logD) relative to the pore size D, and the maximum value was read within the pore size range of 1.0 nm to 1.5 nm. Simultaneously, the distribution curve of the cumulative pore volume relative to the pore size was fitted to obtain the pore volume for specific pore size ranges (1.0 nm-1.5 nm and 1 nm-2 nm). The adsorption and desorption isotherms measured by the carbon dioxide adsorption method were used to fit the cumulative pore volume distribution curve relative to the pore size using a DFT model, and the pore volume of pores with a pore size range of less than 1 nm was obtained. The test results of the hard carbon materials prepared in Examples 11 and 12 are shown in Table 4 below. Figure 10 and Figure 11 The graphs show the dV / d(logD) versus pore size range for the hard carbon materials prepared in Examples 11 and 12, respectively, based on nitrogen adsorption. See also... Figure 10 The hard carbon material prepared in Example 11 of this application has a maximum dV / d(logD) value of 0.006 cm in the pore size range of 1.0 nm to 1.5 nm. 3 / (g·log(nm)). See also Figure 11 The hard carbon material prepared in Example 12 of this application has a maximum dV / d(logD) value of 0.013 cm in the pore size range of 1.0 nm to 1.5 nm. 3 / (g·log(nm)). It can be seen that the dV / d(logD) of the hard carbon in Examples 11 and 12 with pore sizes of 1.0nm-1.5nm are significantly different.

[0342] Testing of bubbling during the preparation of negative electrode slurry

[0343] 50g of the hard carbon materials prepared in Examples 11 and 12 were added to sealed reaction vessels equipped with temperature and pressure sensors, respectively. After adding 200ml of water, the reaction vessels were quickly closed, and stirring was started until the temperature and pressure remained constant. The volume of gas emitted per unit mass of hard carbon was calculated based on the pressure change and the ideal gas equation, and this volume was used as a measure of the bubbling amount. The test results of the hard carbon materials prepared in Examples 11 and 12 are shown in Table 5 below.

[0344] Specific capacity testing of hard carbon materials

[0345] For the coin cells prepared in Examples 11 and 12, the capacity obtained by inserting sodium at a rate of 0.05C to 0V is the initial charge capacity; the capacity obtained by desodiuming at a rate of 0.1C to 2.5V is the initial discharge capacity. The mass of the hard carbon material in the negative electrode was calculated based on the coating weight and area of ​​the slurry during the electrode preparation process. Total sodium storage capacity Q = initial charge capacity / mass of hard carbon material. The test results of the hard carbon materials prepared in Examples 11 and 12 are shown in Table 5 below.

[0346] Table 4 shows the pore characteristics and interlayer spacing characteristics of the hard carbon materials prepared in Examples 11 and 12, and Table 5 shows the bubbling amount and specific capacity test results of the hard carbon materials prepared in Examples 11 and 12.

[0347] Table 4:

[0348]

[0349]

[0350] Table 5:

[0351] Serial Number Bubbling volume (mL / g) Stir directly and observe whether bubbles appear. Observe for 2 hours to see if bubbles appear. Capacity (mAh / g) Example 11 1.08 no no 310 Example 12 1.34 yes yes 350

[0352] As can be seen from Tables 4 and 5, the maximum value of dV / d(logD) is 0.006cm. 3 When the value is / (g·log(nm)), continuous bubbling can be effectively reduced.

[0353] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a hard carbon material, characterized in that, The hard carbon material comprises graphene sheets, wherein the space volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm is equal to the total space volume H between all layers in the graphene sheet. 总 satisfy: 40%≤H1 / H 总 ≤60%。 2. The negative electrode sheet according to claim 1, characterized in that, 40%≤H1 / H 总 ≤55%。 3. The negative electrode sheet according to claim 1 or 2, characterized in that, The spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm and the total spatial volume H between all layers in the graphene sheet. 总 satisfy: 22%≤H2 / H 总 ≤60%。 4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between all layers in the graphene sheet. 总 satisfy: H3 / H 总 ≤18%。 5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The hard carbon material also includes micropores with a pore size of less than or equal to 2 nm and mesopores with a pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5≤V1 / V2≤9.

7.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, Determined by nitrogen adsorption, the hard carbon material contains pores with a diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)).

7. The negative electrode sheet according to claim 6, wherein the hard carbon material has a pore size of 1.0 nm-1.5 nm and a maximum dV / d(logD) value of 0.001 cm⁻¹. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)).

8. The negative electrode sheet according to any one of claims 1-7, characterized in that, The pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm-2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b At 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g.

9. The negative electrode sheet according to claim 8, wherein the hard carbon material has a V... a +V b At 0.0020cm 3 / g to 0.0030cm 3 Within the range of / g.

10. The negative electrode sheet according to claim 5, characterized in that, The pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%.

11. The negative electrode sheet according to claim 5 or 10, characterized in that, The pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material 总 Satisfies: 2.5% ≤ V² / V 总 ≤10%.

12. The negative electrode sheet according to claim 10 or 11, characterized in that, The pore volume V2 of the mesopore satisfies: 0.0003 cm 3 / g≤V2≤0.0012cm 3 / g.

13. The negative electrode sheet according to any one of claims 1-12, characterized in that, The hard carbon material includes heteroatoms, which account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material.

14. The negative electrode sheet according to claim 13, characterized in that, The heteroatom includes at least one of O, N, S, P, B, and F.

15. The negative electrode sheet according to any one of claims 1-14, characterized in that, The hard carbon material I D / I G It ranges from 1.1 to 1.35; Among them, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

16. The negative electrode sheet according to any one of claims 1-15, characterized in that, The surface oxygen content of the hard carbon material is 5% to 15%.

17. The negative electrode sheet according to any one of claims 1-16, characterized in that, The compacted density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3 .

18. The negative electrode sheet according to any one of claims 1-17, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 ; (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 ; (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm; (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm; (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

19. A secondary battery, the secondary battery comprising the negative electrode sheet according to any one of claims 1 to 18.

20. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 19.

21. A hard carbon material, characterized in that, The hard carbon material comprises graphene sheets, wherein the space volume H1 between graphene sheets with an interlayer spacing greater than 0.4 nm is equal to the total space volume H between all layers in the graphene sheet. 总 satisfy: 40%≤H1 / H 总 ≤60%。 22. The hard carbon material according to claim 21, characterized in that, 40%≤H1 / H 总 ≤55%。 23. The hard carbon material according to claim 21 or 22, characterized in that, The spatial volume H2 between graphene sheets with an interlayer spacing of 0.36 nm to 0.4 nm and the total spatial volume H between all layers in the graphene sheet. 总 satisfy: 22%≤H2 / H 总 ≤60%。 24. The hard carbon material according to any one of claims 21-23, characterized in that, The spatial volume H3 between graphene sheets with an interlayer spacing of less than 0.36 nm and the total spatial volume H between all layers in the graphene sheet. 总 satisfy: H3 / H 总 ≤18%。 25. The hard carbon material according to any one of claims 21-24, characterized in that, The hard carbon material also includes micropores with a pore size of less than or equal to 2 nm and mesopores with a pore size greater than 2 nm and less than 10 nm; the pore volume V1 of the micropores and the pore volume V2 of the mesopores satisfy: 0.5≤V1 / V2≤9.

7.

26. The hard carbon material according to any one of claims 21-25, characterized in that, Determined by nitrogen adsorption, the hard carbon material contains pores with a diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore diameter D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)).

27. The hard carbon material according to claim 26, wherein the maximum value of dV / d(logD) for pores with a diameter of 1.0 nm to 1.5 nm is 0.001 cm. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)).

28. The hard carbon material according to any one of claims 21-27, characterized in that, The pore volume of the hard carbon material with a pore size of less than 1 nm, determined by carbon dioxide adsorption, is expressed as V. a The pore volume of the hard carbon material with a pore size of 1 nm-2 nm, determined by nitrogen adsorption, is expressed as V. b Then V a +V b At 0.0006cm 3 / g to 0.0035cm 3 Within the range of / g.

29. The hard carbon material according to claim 28, wherein the V of the hard carbon material a +V b At 0.0020cm 3 / g to 0.0030cm 3 Within the range of / g.

30. The hard carbon material according to claim 25, characterized in that, The pore volume V1 of the micropores with a pore size of less than or equal to 2 nm and the total pore volume V of the hard carbon material 总 Satisfies: 4.5% ≤ V1 / V 总 ≤30%.

31. The hard carbon material according to claim 25 or 30, characterized in that, The pore volume V2 of the mesopores with a pore size greater than 2 nm and less than 10 nm and the total pore volume V of the hard carbon material 总 Satisfies: 2.5% ≤ V² / V 总 ≤10%.

32. The hard carbon material according to claim 30 or 31, characterized in that, The pore volume V2 of the mesopore satisfies: 0.0003 cm 3 / g≤V2≤0.0012cm 3 / g.

33. The hard carbon material according to any one of claims 21-32, characterized in that, The hard carbon material includes heteroatoms, which account for 0.4 wt% to 5 wt% of the total mass of the hard carbon material.

34. The hard carbon material according to claim 33, characterized in that, The heteroatom includes at least one of O, N, S, P, B, and F.

35. The hard carbon material according to any one of claims 21-34, characterized in that, The hard carbon material I D / I G It ranges from 1.1 to 1.35; Among them, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

36. The hard carbon material according to any one of claims 21-35, characterized in that, The surface oxygen content of the hard carbon material is 5% to 15%.

37. The hard carbon material according to any one of claims 21-36, characterized in that, The compacted density of the hard carbon material at 2t is 0.9 g / cm³. 3 -1.2g / cm 3 .

38. The hard carbon material according to any one of claims 21-37, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) The specific surface area of ​​the hard carbon material is 2m². 2 / g-8m 2 / g; (2) The tap density of the hard carbon material is 0.78 g / cm³. 3 -0.9g / cm 3 ; (3) The true density of the hard carbon material is 2.0 g / cm³. 3 -2.3g / cm 3 ; (4) The volume distribution particle size Dv10 of the hard carbon material is 1.8μm-3μm; (5) The volume distribution particle size Dv50 of the hard carbon material is 4μm-7μm; (6) The volume distribution particle size Dv90 of the hard carbon material is 9μm-15μm.

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