Negative pole piece, secondary battery, electric device, hard carbon material and preparation method of hard carbon material

Abstract

The invention provides a negative electrode piece, a secondary battery, an electric device, a hard carbon material and a preparation method thereof, the negative electrode piece comprises 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 comprises the hard carbon material, the hard carbon material comprises an inner core and an organic matter coating layer coating the inner core, and the organic matter coating layer is located between the inner core and the negative electrode film layer. The inner core comprises porous carbon; the total pore volume A of the porous carbon is more than or equal to 0.2 cm < 3 > / g and less than or equal to 0.6 cm < 3 > / g; the methylene blue adsorption value Z of the hard carbon material is less than or equal to 8mg / g. The negative pole piece disclosed by the invention is used as a secondary battery, and has improved charging gram volume and improved first coulombic efficiency.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, an electrical device, a hard carbon material, and a method for preparing the same. 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 power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, the requirements for their energy density, cycle performance, and high-rate charging performance are becoming increasingly stringent. As a crucial component of rechargeable batteries, the performance of the negative electrode active material significantly impacts the overall battery performance. Currently, hard carbon is commonly used as the negative electrode active material in rechargeable batteries; however, hard carbon exhibits low specific capacity and initial coulombic efficiency when used as the negative electrode active material. 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 sheet, a secondary battery, an electrical device, a hard carbon material and a method for preparing the same, wherein the negative electrode sheet used as a secondary battery has improved charging specific capacity and initial 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 a core and an organic coating layer covering the core, the core comprising porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material Z≤8mg / g.

[0005] In this application, by ensuring the total pore volume of the porous carbon in the hard carbon material is within the aforementioned range, the specific capacity of the hard carbon material can be increased while simultaneously ensuring that the carbon skeleton possesses suitable strength and stability, preventing collapse during the insertion and extraction of active ions, thereby improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Furthermore, by providing an organic coating layer on the outer surface of the porous carbon core, electrolyte molecules can be prevented from entering the pore structure of the porous carbon, which is beneficial for improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Moreover, the methylene blue adsorption value of this hard carbon material is within the aforementioned range, resulting in a high density of the organic coating layer, which can effectively isolate the electrolyte and inhibit electrolyte molecules from entering the porous carbon interior, further contributing to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0006] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g. The lower the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0007] In some embodiments, the porous carbon comprises micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A. In some embodiments, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7 ≤ X / Y ≤ 16. Therefore, the internal storage space of the hard carbon material can be maximized, and the reversible insertion and extraction of active ions can be enabled, which is beneficial to the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0008] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the condition: 85% ≤ X / A ≤ 97%. This provides more storage space for active ions, which is beneficial for improving the discharge specific capacity of hard carbon materials.

[0009] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the condition: 3% ≤ Y / A ≤ 15%. This provides a suitable number of transport channels for active ions, thereby improving the utilization rate of the micropores and contributing to increased specific capacity and initial coulombic efficiency of the secondary battery.

[0010] In some embodiments, the thickness of the organic coating layer is 1 nm to 90 nm. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0011] In some embodiments, the organic coating layer in the hard carbon material comprises 0.5 wt% to 10 wt% of the porous carbon. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0012] In some embodiments, the hard carbon material satisfies at least one of the following:

[0013] (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial for the formation of a reasonable pore structure between the particles of the negative electrode film, which improves the active ion and electron transport performance, thereby improving the kinetic performance of the secondary battery.

[0014] (2) The tap density of the hard carbon material is 0.34 g / cm³.3 -0.8g / 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.

[0015] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm;

[0016] (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above range, it is beneficial to reduce the specific surface area of ​​the hard carbon material, reduce the occurrence of side reactions, and thus improve the initial coulombic efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of active ions, thereby improving the kinetic performance of the secondary battery.

[0017] (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g. The specific surface area of ​​hard carbon materials is within the above range, which can reduce the consumption of active ions during the first charge and help improve the first coulombic efficiency of the secondary battery.

[0018] A second aspect of this application provides a secondary battery, including the negative electrode sheet described in the first aspect of this application.

[0019] In some embodiments, the secondary battery further includes a positive electrode. The positive electrode comprises at least one selected from transition metal oxides, polyanionic compounds, and Prussian blue compounds as the positive electrode active material.

[0020] The secondary battery in this application has improved charge capacity and initial coulombic efficiency.

[0021] A third aspect of this application provides an electrical device, including the secondary battery of the second aspect of this application.

[0022] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0023] A fourth aspect of this application provides a hard carbon material, comprising a core and an organic coating layer covering the core, wherein the core comprises porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material Z≤8mg / g.

[0024] In this application, by ensuring the total pore volume of the porous carbon in the hard carbon material is within the aforementioned range, the specific capacity of the hard carbon material can be increased while simultaneously ensuring that the carbon skeleton possesses suitable strength and stability, preventing collapse during the insertion and extraction of active ions, thereby improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Furthermore, by providing an organic coating layer on the outer surface of the porous carbon core, electrolyte molecules can be prevented from entering the pore structure of the porous carbon, which is beneficial for improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Moreover, the methylene blue adsorption value of this hard carbon material is within the aforementioned range, resulting in a high density of the organic coating layer, which can effectively isolate the electrolyte and inhibit electrolyte molecules from entering the porous carbon interior, further contributing to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0025] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g. The lower the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0026] In some embodiments, the porous carbon comprises micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A. In some embodiments, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7 ≤ X / Y ≤ 16. Therefore, the internal storage space of the hard carbon material can be maximized, and the reversible insertion and extraction of active ions can be enabled, which is beneficial to the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0027] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the condition: 85% ≤ X / A ≤ 97%. This provides more storage space for active ions, which is beneficial for improving the discharge specific capacity of hard carbon materials.

[0028] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the condition: 3% ≤ Y / A ≤ 15%. This provides a suitable number of transport channels for active ions, thereby improving the utilization rate of the micropores and contributing to increased specific capacity and initial coulombic efficiency of the secondary battery.

[0029] In some embodiments, the thickness of the organic coating layer is 1 nm to 90 nm. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0030] In some embodiments, the organic coating layer in the hard carbon material comprises 0.5 wt% to 10 wt% of the porous carbon. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0031] In some embodiments, the hard carbon material satisfies at least one of the following:

[0032] (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial for the formation of a reasonable pore structure between the particles of the negative electrode film, which improves the active ion and electron transport performance, thereby improving the kinetic performance of the secondary battery.

[0033] (2) The tap density of the hard carbon material is 0.34 g / cm³. 3 -0.8g / 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.

[0034] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm;

[0035] (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above range, it is beneficial to reduce the specific surface area of ​​the hard carbon material, reduce the occurrence of side reactions, and thus improve the initial coulombic efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of active ions, thereby improving the kinetic performance of the secondary battery.

[0036] (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g. The specific surface area of ​​hard carbon materials is within the above range, which can reduce the consumption of active ions during the first charge and help improve the first coulombic efficiency of the secondary battery.

[0037] A fifth aspect of this application also provides a method for preparing a hard carbon material, the method comprising:

[0038] The hard carbon precursor is pre-carbonized to obtain a pre-carbonized body; the pre-carbonized body is activated to obtain a porous carbon precursor; the porous carbon precursor is carbonized to obtain porous carbon; the porous carbon is coated, wherein the coating treatment includes kneading a kneading mixture formed by the porous carbon and an aqueous solution of the coating material, wherein the solid content of the kneading mixture is 55wt%-75wt%, and the pH value of the aqueous solution of the coating material is ≤3.

[0039] This application obtains a porous carbon precursor by pre-carbonizing and activating a hard carbon precursor to create pores. The porous carbon precursor is then carbonized to obtain porous carbon. Finally, the porous carbon and an aqueous solution of a coating material are kneaded to form a hard carbon material with a coating layer. Kneading the porous carbon and coating material under the aforementioned solid content and pH conditions of the aqueous solution of the coating material allows for more thorough mixing and shearing, resulting in a coating layer with good density. Therefore, it can prevent electrolyte molecules from entering the interior of the porous carbon, which is beneficial for improving the specific capacity and initial coulombic efficiency of the secondary battery.

[0040] In some embodiments, the solid content of the kneaded mixture is 63wt%-67wt%, and the pH value of the aqueous solution of the coating material is 1.2-1.8. This facilitates the formation of a coating layer with suitable density, enabling the secondary battery to improve its specific charging capacity and initial coulombic efficiency without affecting its kinetic performance.

[0041] In some embodiments, the coating material includes at least one of polyacrylic acid, polyacrylate, and copolymers of polyacrylic acid. The carboxyl groups on the polyacrylic acid molecular chain can react with the oxygen-containing functional groups on the porous carbon surface to form carbon-oxygen covalent bonds. These covalent bonds tightly connect the organic coating layer and the porous carbon, forming a stable and highly dense organic coating layer. This organic coating layer can inhibit the intrusion of electrolyte into the porous carbon, which is beneficial for improving the specific capacity and initial coulombic efficiency of the secondary battery.

[0042] In some embodiments, the mass of the coating material is 0.5%-10% of the mass of the porous carbon, and the kneading treatment is performed for at least 0.5 hours. This allows for the formation of a coating layer with suitable density, which can improve the specific capacity and initial coulombic efficiency of the secondary battery without affecting its kinetic performance or increasing its impedance.

[0043] In some embodiments, the kneading process is carried out in a twin-screw kneader at a rotation speed of 10 rpm to 50 rpm. Kneading under these conditions can yield a uniformly coated organic layer.

[0044] In some embodiments, the activation treatment includes treating the pre-carbonized body at 700°C-950°C under a preset mixed gas, wherein the preset mixed gas includes carbon dioxide gas, water vapor, and an inert gas, and the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is ≥2. Activation treatment performed at the above temperature can form an appropriate amount of mesopores and micropores, which is beneficial for improving the discharge specific capacity of the secondary battery.

[0045] In some embodiments, the volume percentage of carbon dioxide gas in the preset mixed gas is 5%-20%, and the volume percentage of water vapor in the mixed gas is 1%-5%. A volume percentage of carbon dioxide gas within the above range allows for the formation of an appropriate amount of micropores, which is beneficial for improving the discharge specific capacity of the secondary battery. A volume percentage of water vapor within the above range allows for the formation of an appropriate amount of mesopores, which is beneficial for improving the charge specific capacity and initial coulombic efficiency of the secondary battery.

[0046] In some embodiments, the activation treatment includes immersing the pre-carbonized body in a pore-forming solution for at least 2 hours; the pore-forming solution includes a phosphorus-containing pore-forming solution or a zinc-containing pore-forming solution, wherein the phosphorus content in the phosphorus-containing pore-forming solution is 9.5%-32.4% of the mass of the porous carbon, and the zinc content in the zinc-containing pore-forming solution is 14%-50% of the mass of the porous carbon. This allows for the formation of appropriate amounts of micropores and mesopores, which is beneficial for improving the discharge specific capacity, charge specific capacity, and initial coulombic efficiency of the secondary battery.

[0047] In some embodiments, the solid content of the impregnation mixture formed by the pre-carbonized body and the pore-forming liquid is 50 wt% to 70 wt%.

[0048] In some embodiments, the activation treatment further includes holding the impregnation mixture formed by the impregnated precarbide and the pore-forming solution at 400°C-750°C for 1-12 hours. This allows the phosphorus-containing pore-forming solution and the precarbide to chemically react, enabling etching through chemical activation and introducing numerous pore structures into the precarbide framework.

[0049] In some embodiments, the pre-carbonization treatment involves heating to 400°C-600°C at a rate of 1°C / min-20°C / min and holding for 1-12 hours. Pre-carbonization under these conditions facilitates the formation of a basic carbon framework structure, which is beneficial for subsequent pore formation.

[0050] In some embodiments, the carbonization process involves heating to 1000℃-1800℃ at a rate of 2℃ / min-20℃ / min and holding for 1h-12h. During carbonization, the precursor loses heteroatoms such as H and O to form a stable hard carbon framework.

[0051] In some embodiments, the hard carbon precursor includes at least one of a biomass precursor and a synthetic polymer precursor; the synthetic polymer precursor includes a compound composed of C, H, and O elements. Hard carbon materials prepared using the above precursors exhibit relatively ordered carbon formation after activation, and are capable of forming appropriate amounts of micropores and mesopores. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0053] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0054] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0055] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0056] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0057] 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.

[0058] Explanation of reference numerals in the attached figures:

[0059] 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

[0060] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet, secondary battery, electrical device, hard carbon material, and preparation method thereof. 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.

[0061] 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.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0063] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0064] 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.

[0065] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0066] 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.

[0067] 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 lithium ions.

[0068] Currently, hard carbon is commonly used as the negative electrode active material for secondary batteries. However, when hard carbon is used as the negative electrode active material, both the charge capacity and the initial coulombic efficiency are relatively low.

[0069] In view of this, the present application provides a new hard carbon material, which, as a negative electrode material for secondary batteries, has improved charge capacity and initial coulombic efficiency.

[0070] Negative electrode sheet

[0071] A first aspect of this application provides an 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 a core and an organic coating layer covering the core, the core comprising porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material Z≤8mg / g.

[0072] When hard carbon materials are used as negative electrode active materials in secondary batteries, active ions are first transported to defect sites in the hard carbon material for adsorption, and then transported to fill the pores of the hard carbon material. The active ions exist in the form of clusters in the pores, providing specific capacity. In related technologies, the specific capacity of hard carbon materials is improved by forming more and larger pore structures. However, a large number of pore structures leads to a decrease in the strength and stability of the carbon skeleton of hard carbon materials. During charge-discharge cycles, the insertion and extraction of active ions can easily cause the carbon skeleton of hard carbon materials to collapse, affecting the charging specific capacity and the first coulombic efficiency. In addition, the large pore structure makes it easier for electrolyte molecules to enter. Electrolyte molecules entering the pore structure not only occupy the storage sites of active ions, but also consume more active ions to form a solid electrolyte interface (SEI film), further reducing the charging specific capacity and the first coulombic efficiency.

[0073] Based on this, by ensuring the total pore volume of the porous carbon in the hard carbon material is within the aforementioned range, this application can improve the specific capacity of the hard carbon material while simultaneously ensuring the carbon framework possesses suitable strength and stability, preventing collapse during active ion insertion and extraction, thereby improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Furthermore, by providing an organic coating layer on the outer surface of the porous carbon core, electrolyte molecules can be prevented from entering the porous structure of the carbon, which is beneficial for improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Further, the methylene blue adsorption value of this hard carbon material is within the aforementioned range, resulting in a high density of the organic coating layer, which can effectively isolate the electrolyte and inhibit electrolyte molecules from entering the porous carbon interior, further contributing to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0074] In addition, the presence of the organic coating layer is equivalent to constructing an artificial organic SEI layer on the porous carbon surface, which improves the stability of the SEI film in the secondary battery and reduces the amount of active ions required for subsequent SEI film formation, thereby achieving high charging specific capacity and first coulombic efficiency.

[0075] It should be noted that since the molecular diameter of methylene blue is close to the size of commonly used ester solvents in electrolytes (about 1 nm), the methylene blue adsorption value can accurately characterize the area that the electrolyte can enter, that is, characterize the density of the organic coating layer.

[0076] The lower the methylene blue adsorption value, the better the coating effect. In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g.

[0077] For example, the total pore volume A of the porous carbon is 0.2 cm³. 3 / g, 0.25cm 3 / g, 0.3cm 3 / g, 0.32cm 3 / g, 0.35cm 3 / g, 0.37cm 3 / g, 0.38cm 3 / g, 0.39cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g, 0.6cm 3 / g or any value within the range of any two numerical values.

[0078] For example, the methylene blue adsorption value Z of the hard carbon material can be any value within the range of 1.0 mg / g, 1.2 mg / g, 1.3 mg / g, 1.4 mg / g, 1.5 mg / g, 1.6 mg / g, 1.7 mg / g, 1.8 mg / g, 1.9 mg / g, 2.0 mg / g, 2.5 mg / g, 3.0 mg / g, 3.5 mg / g, 4.0 mg / g, 4.5 mg / g, 5.0 mg / g, 5.2 mg / g, 5.5 mg / g, 5.8 mg / g, 6.0 mg / g, 6.5 mg / g, 7.0 mg / g, 7.5 mg / g, 8.0 mg / g, or any two of these values.

[0079] In some embodiments, the organic coating material includes at least one of polyacrylic acid, polyacrylic acid copolymers, and polyacrylates. Exemplary examples include polyacrylic acid, polyacrylic acid copolymers (e.g., copolymers of polyacrylic acid and carboxymethyl cellulose fragments, copolymers of polyacrylic acid and polyethylene oxide fragments), sodium polyacrylate (PAANa), polyrotaxane (PR) and polyacrylic acid (PAA) complexes, etc., but are not limited thereto. Using such organic materials as coating layers offers advantages such as resistance to electrolyte swelling and strong adhesion, enabling the formation of an SEI-like coating layer on the surface of porous carbon particles. This inhibits the entry of electrolyte into the internal pore structure of the porous carbon particles and reduces the active ions consumed in the subsequent formation of the SEI film.

[0080] In some embodiments, the porous carbon comprises micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A. Optionally, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7 ≤ X / Y ≤ 16. Exemplarily, X / Y can be 5.6, 6.5, 7.0, 7.5, 8.0, 8.5, 10, 11.0, 12, 13, 13.5, 14, 14.5, 15, 20, 25, 30, or 33.

[0081] Research has shown that the micropores with a pore size of 0.4 nm to 2.5 nm in the hard carbon material of this application enable reversible insertion and extraction of active ions. In other words, increasing the number of micropores with a pore size of 0.4 nm to 2.5 nm in the hard carbon material can improve the discharge specific capacity. The mesopores with a pore size of 2.5 nm to 10 nm in the hard carbon material can serve as transport channels for active ions, allowing them to be transported into the micropores, improving the utilization rate of the micropores, and thus increasing the discharge specific capacity and initial coulombic efficiency of the secondary battery.

[0082] In the hard carbon material of this application, the ratio of the total pore volume X of the micropores to the total pore volume Y of the mesopores in the porous carbon core is within the above-mentioned range, which can maximize the utilization of the internal storage space of the hard carbon material and enable the reversible insertion and extraction of active ions, which is beneficial to the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0083] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the following condition: 85% ≤ X / A ≤ 97%. Optionally, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the following condition: 88 ≤ X / A ≤ 94. Exemplarily, X / A can be 85%, 86%, 87%, 88%, 90%, 93%, 94%, or 97%. The fact that the total pore volume X of the micropores and the total pore volume A of the porous carbon in the hard carbon material satisfy the above relationship provides more storage space for active ions, which is beneficial for improving the discharge specific capacity of the hard carbon material.

[0084] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the following condition: 3% ≤ Y / A ≤ 15%. Optionally, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the following condition: 6 ≤ Y / A ≤ 12. Exemplarily, Y / A can be 3%, 5%, 6%, 8%, 10%, 12%, 13%, or 15%. The fact that the total pore volume Y of the mesopores and the total pore volume A of the porous carbon in the hard carbon material satisfy the above relationship provides a suitable number of transport channels for active ions, thereby improving the utilization rate of micropores and contributing to increasing the specific capacity and initial coulombic efficiency of the secondary battery.

[0085] In some embodiments, the thickness of the organic coating layer is 1 nm to 90 nm. Optionally, the thickness of the organic coating layer is 30 nm to 50 nm. Exemplary examples include thicknesses of 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, and 90 nm. By setting the thickness of the organic coating layer within the above ranges, both the kinetic performance of the secondary battery and its charge capacity and initial coulombic efficiency can be considered.

[0086] In some embodiments, the organic coating layer in the hard carbon material has a mass of 0.5 wt% to 10 wt% of the porous carbon. For example, the mass of the organic coating layer is 0.5%, 3%, 5%, 8%, or 10% of the porous carbon. By setting the mass of the organic coating layer in the hard carbon material within the above range, it is possible to balance the kinetic performance of the secondary battery with its specific charging capacity and initial coulombic efficiency.

[0087] In some embodiments, the hard carbon material satisfies at least one of the following:

[0088] (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial for the formation of a reasonable pore structure between particles in the negative electrode film, which improves the active ion and electron transport performance, thereby enhancing the kinetic performance of the secondary battery.

[0089] (2) The tap density of the hard carbon material is 0.34 g / cm³. 3 -0.8g / cm 3 When the tap density of hard carbon materials is within the above-mentioned range, it is beneficial to increase the tap density of the negative electrode film and thus improve the energy density of the secondary battery.

[0090] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0μm-7.9μm.

[0091] (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material are within the above range, it is beneficial to reduce the specific surface area of ​​the hard carbon material, reduce the occurrence of side reactions, and thus improve the initial coulombic efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of active ions, thereby improving the kinetic performance of the secondary battery.

[0092] (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g. The specific surface area of ​​hard carbon materials is within the above range, which can reduce the consumption of active ions during the first charge and help improve the first coulombic efficiency of the secondary battery.

[0093] In this application, the methylene blue adsorption value of the hard carbon material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested according to GB / T 12496.10-1999.

[0094] In this application, the pore volume of porous carbon has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested according to Part 3 of GB / T 21650.3. Porous carbon powder is placed in a sample tube and degassed under vacuum at 200°C for 12 hours. The adsorption capacity of the hard carbon material for nitrogen under different pressures is tested using an ASAP2460 physical adsorption analyzer, and adsorption and desorption isotherms are plotted. The pore shape is determined based on the shape of the hysteresis loop, and the pore size distribution curve of the micropores is fitted using a DFT model. The pore volume X of the micropores, the pore volume Y of the mesopores, and the total pore volume A in the hard carbon material are calculated.

[0095] In this application, before testing the pore volume of porous carbon, the hard carbon material is pretreated to break down the organic coating layer, allowing the nitrogen adsorption-desorption test gas to enter the porous carbon. An exemplary treatment step includes adding 2g of hard carbon powder to a 250ml beaker, adding 1g of NaOH, and stirring until homogeneous. The beaker is placed in a water bath and heated to 80°C for 30 minutes with stirring. Then, the mixture is filtered, and the filter cake is repeatedly washed with deionized water until the filtrate is neutral. The washed filter cake is then dried in an 80°C vacuum oven for 24 hours.

[0096] In this application, the thickness of the organic coating layer in the hard carbon material can be determined by measuring the cross-sectional morphology (CP) of the negative electrode using an ion polishing instrument. Specifically, the hard carbon material can be cut into a sample of a certain size (e.g., 2cm × 2cm) and fixed on a sample stage. The sample stage is then installed and locked in place on a sample holder. The power of the argon ion cross-sectional polishing instrument (e.g., the IB-09010CP argon ion cross-sectional polishing instrument from JEOL Corporation, Japan) is turned on and a vacuum is applied (e.g., 10⁻⁷ Pa). The argon flow rate (e.g., 0.12 MPa) and polishing time (e.g., 90 min) are set, and the sample stage is adjusted to rocking mode to begin polishing. After polishing, energy dispersive spectroscopy (EDS) is performed on the cross-section. The difference in oxygen content can distinguish between the organic coating layer and porous carbon, thus determining the thickness of the organic coating layer.

[0097] In this application, the mass of the organic coating layer in the hard carbon material can be determined using thermogravimetric (TG) testing. By measuring the weight loss of the hard carbon material under a nitrogen atmosphere at temperatures ranging from 150°C to 500°C, the content of the organic coating layer can be calculated.

[0098] 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, 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 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 GThe testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0099] 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 5t, held for 30s, then released and held for 10s. The compaction density of the powder under 5t pressure is then recorded and calculated.

[0100] 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.

[0101] In this application, the volumetric particle sizes 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 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 / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0102] 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.

[0103] In this application, the microstructure of hard carbon materials can be observed using a scanning electron microscope or a transmission electron microscope.

[0104] 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.

[0105] 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.).

[0106] 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.

[0107] 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).

[0108] 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.

[0109] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0110] 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.

[0111] Secondary batteries

[0112] A second aspect of the embodiments of this application provides a secondary battery, which will be described below with appropriate reference to the accompanying drawings.

[0113] 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.

[0114] Typically, a single secondary battery cell includes a positive electrode, a negative electrode as described in the above embodiment, an electrolyte, and a separator. During battery 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.

[0115] [Positive electrode plate]

[0116] 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.

[0117] 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.

[0118] 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.).

[0119] 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 of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, 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。

[0120] 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.

[0121] 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).

[0122] As an optional implementation of this application, the general chemical formula of the polyanionic compound may be Na. x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d, wherein the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, and the Q element 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, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0123] As an optional embodiment of the present application, the general chemical formula of 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.

[0124] As an optional embodiment of the present application, the general chemical formula of the polyanionic compound can be Na 4+x R 3-y P 4- m O 15 / 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.

[0125] 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. Prussian blue compounds are, for example, 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, 0 < c < 1.

[0126] In other embodiments, the battery cell can also be a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries.

[0127] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0128] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0131] [Electrolytes]

[0132] 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.

[0133] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] [Isolation membrane]

[0139] 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.

[0140] 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.

[0141] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In some implementations, refer to Figure 2The 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.

[0146] 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.

[0147] 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.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0149] 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.

[0150] 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.

[0151] Electrical appliances

[0152] 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.

[0153] 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.

[0154] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0155] 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.

[0156] 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.

[0157] Hard carbon materials

[0158] 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 includes a core and an organic coating layer covering the core, wherein the core comprises porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material Z≤8mg / g.

[0159] In this application, by ensuring the total pore volume of the porous carbon in the hard carbon material is within the aforementioned range, the specific capacity of the hard carbon material can be increased while simultaneously ensuring that the carbon skeleton possesses suitable strength and stability, preventing collapse during the insertion and extraction of active ions, thereby improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Furthermore, by providing an organic coating layer on the outer surface of the porous carbon core, electrolyte molecules can be prevented from entering the pore structure of the porous carbon, which is beneficial for improving the charging specific capacity and initial coulombic efficiency of the secondary battery. Moreover, the methylene blue adsorption value of this hard carbon material is within the aforementioned range, resulting in a high density of the organic coating layer, which can effectively isolate the electrolyte and inhibit electrolyte molecules from entering the porous carbon interior, further contributing to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0160] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g. The lower the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0161] In some embodiments, the porous carbon comprises micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A. In some embodiments, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7 ≤ X / Y ≤ 16. Therefore, the internal storage space of the hard carbon material can be maximized, and the reversible insertion and extraction of active ions can be enabled, which is beneficial to the charging specific capacity and initial coulombic efficiency of the secondary battery.

[0162] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the condition: 85% ≤ X / A ≤ 97%. This provides more storage space for active ions, which is beneficial for improving the discharge specific capacity of hard carbon materials.

[0163] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the condition: 3% ≤ Y / A ≤ 15%. This provides a suitable number of transport channels for active ions, thereby improving the utilization rate of the micropores and contributing to increased specific capacity and initial coulombic efficiency of the secondary battery.

[0164] In some embodiments, the thickness of the organic coating layer is 1 nm to 90 nm. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0165] In some embodiments, the organic coating layer in the hard carbon material comprises 0.5 wt% to 10 wt% of the porous carbon. This allows for a balance between the kinetic performance of the secondary battery and its specific charging capacity and initial coulombic efficiency.

[0166] In some embodiments, the hard carbon material satisfies at least one of the following:

[0167] (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 When the compaction density of hard carbon material powder is within the above range, it is beneficial for the formation of a reasonable pore structure between the particles of the negative electrode film, which improves the active ion and electron transport performance, thereby improving the kinetic performance of the secondary battery.

[0168] (2) The tap density of the hard carbon material is 0.34 g / cm³.3 -0.8g / 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.

[0169] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm;

[0170] (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above range, it is beneficial to reduce the specific surface area of ​​the hard carbon material, reduce the occurrence of side reactions, and thus improve the initial coulombic efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of active ions, thereby improving the kinetic performance of the secondary battery.

[0171] (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g. The specific surface area of ​​hard carbon materials is within the above range, which can reduce the consumption of active ions during the first charge and help improve the first coulombic efficiency of the secondary battery.

[0172] Preparation method of hard carbon materials

[0173] A fifth aspect of this application provides a method for preparing the above-mentioned hard carbon material, the method comprising: pre-carbonizing a hard carbon precursor to obtain a pre-carbonized body; activating the pre-carbonized body to obtain a porous carbon precursor; carbonizing the porous carbon precursor to obtain porous carbon; and coating the porous carbon, wherein the coating treatment includes kneading a kneading mixture formed by the porous carbon and an aqueous solution of a coating material, wherein the solid content of the kneading mixture is 55wt%-75wt%, and the pH value of the aqueous solution of the coating material is ≤3. The total pore volume A of the formed porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the formed hard carbon material Z≤8mg / g.

[0174] This application obtains a porous carbon precursor by pre-carbonizing and activating a hard carbon precursor to create pores. The porous carbon precursor is then carbonized to obtain porous carbon. Finally, the porous carbon and an aqueous solution of a coating material are kneaded to form a hard carbon material with a coating layer. Kneading the porous carbon and coating material under the aforementioned solid content and pH conditions of the aqueous solution of the coating material allows for more thorough mixing and shearing, resulting in a coating layer with good density. Therefore, it can prevent electrolyte molecules from entering the interior of the porous carbon, which is beneficial for improving the specific capacity and initial coulombic efficiency of the secondary battery.

[0175] For example, the solid content of the kneaded mixture is 55 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 71 wt%, and 75 wt%.

[0176] In some embodiments, the solid content of the kneaded mixture is 63wt%-67wt%, and the pH value of the aqueous solution of the coating material is 1.2-1.8. A solid content within this range facilitates the formation of a coating layer with suitable density, thereby improving the specific charge capacity and initial coulombic efficiency of the secondary battery without affecting its kinetic performance. A pH value within the above range during the kneading process allows for the rapid formation of a coating layer with suitable density, further enhancing the specific charge capacity and initial coulombic efficiency of the secondary battery.

[0177] In some embodiments, the coating material includes at least polyacrylic acid. Exemplarily, the coating material includes at least one of: polyacrylic acid, polyacrylic acid copolymer, sodium polyacrylate, and a polyrotaxane-polyacrylic acid composite. During the kneading process, the carboxyl groups on the polyacrylic acid molecular chains react with the oxygen-containing functional groups on the porous carbon surface to form carbon-oxygen covalent bonds. These covalent bonds tightly connect the organic coating layer and the porous carbon, forming a stable and highly dense organic coating layer. The organic coating layer can inhibit the entry of electrolyte into the porous carbon, which is beneficial for improving the charging capacity and initial coulombic efficiency of the secondary battery. Furthermore, since polyacrylic acid does not swell in the electrolyte, it can effectively isolate the electrolyte.

[0178] In some embodiments, the mass of the coating material is 0.5%-10% of the mass of the porous carbon, and the kneading treatment is performed for at least 0.5 hours, optionally for 9-12 hours. For example, the mass of the coating material is 5% of the mass of the porous carbon, and the kneading time is 12 hours. When the mass of the coating material is within the above range, a coating layer with suitable density can be formed, which can improve the specific charge capacity and initial coulombic efficiency of the secondary battery without affecting its kinetic performance or increasing its impedance.

[0179] In some embodiments, the kneading process is carried out in a twin-screw kneader at a rotation speed of 10-50 rpm. Kneading under these conditions can yield a uniformly coated organic layer.

[0180] In some embodiments, the aqueous solution may be an aqueous solution, an ethanol solution, or an isopropanol solution, or a mixture of at least two of the aqueous solution, ethanol solution, and isopropanol solution.

[0181] In some implementations, the kneading process described above is carried out at room temperature.

[0182] In some embodiments, the activation treatment includes treating the pre-carbonized body at 700°C-950°C under a preset mixed gas. Optionally, the pre-carbonized body is treated at 830°C-870°C. Exemplarily, the activation treatment temperature can be 700°C, 850°C, or 900°C. Activation treatment performed at these temperatures can form an appropriate amount of mesopores and micropores, which is beneficial for improving the discharge capacity of the secondary battery.

[0183] In some embodiments, the preset mixed gas includes carbon dioxide gas, water vapor, and an inert gas, wherein the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is ≥2. Optionally, the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is 4-6. Exemplarily, the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas can be 2, 3, 4, 5, 6, 8, or 10. When the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is within the above range, it can form an appropriate amount of mesopores and micropores, which is beneficial for improving the discharge capacity of the secondary battery.

[0184] In some embodiments, the inert gas in the above-mentioned mixed gas includes helium, neon, argon, etc.

[0185] In some embodiments, the volume percentage of carbon dioxide gas in the preset mixed gas is 5%-20%; optionally, the volume percentage of carbon dioxide gas in the preset mixed gas is 8%-12%. For example, the volume percentage of carbon dioxide gas in the preset mixed gas can be 4%, 5%, 6%, 10%, 15%, or 20%. A volume percentage of carbon dioxide gas in the preset mixed gas within the above range can form an appropriate amount of micropores, which is beneficial for improving the discharge capacity of the secondary battery.

[0186] In some embodiments, the water vapor accounts for 1%-5% of the volume of the mixed gas; optionally, the water vapor accounts for 1.5%-2.5% of the volume of the mixed gas. For example, the volume percentage of water vapor in the mixed gas can be 1%, 1.5%, 2%, 2.5%, 3%, 4%, or 5%. A water vapor volume percentage within the above range in the preset mixed gas can form an appropriate amount of mesopores, which is beneficial for improving the specific charging capacity and initial coulombic efficiency of the secondary battery.

[0187] In some embodiments, the activation treatment includes immersing the pre-carbonized body in a pore-forming solution for at least 2 hours; the pore-forming solution includes a phosphorus-containing pore-forming solution or a zinc-containing pore-forming solution, wherein the amount of phosphorus added in the phosphorus-containing pore-forming solution is 9.5%-32.4% of the mass of the porous carbon, optionally, the amount of phosphorus added in the phosphorus-containing pore-forming solution is 18%-24% of the mass of the porous carbon; the amount of zinc added in the zinc-containing pore-forming solution is 14%-50% of the mass of the porous carbon, optionally, the amount of zinc added in the zinc-containing pore-forming solution is 25%-35% of the mass of the porous carbon. For example, the amount of phosphorus (P) added to the pore-forming solution can be 9.5%, 12%, 15%, 18%, 20%, 24%, 27%, 30%, or 32% of the mass of the porous carbon; and the amount of zinc (Zn) added to the pore-forming solution can be 14%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% of the mass of the porous carbon. When the amount of P or Zn added to the pore-forming solution is within the above ranges, an appropriate amount of micropores and mesopores can be formed, which is beneficial to improving the discharge capacity, charge capacity, and initial coulombic efficiency of the secondary battery. Furthermore, by setting the immersion time of the pre-carbonized body in the pore-forming solution as described above, an appropriate amount of micropores and mesopores can be formed, which is beneficial to improving the discharge capacity, charge capacity, and initial coulombic efficiency of the secondary battery.

[0188] For example, a phosphoric acid-containing pore-forming solution may include at least one of a phosphoric acid solution, a polyphosphoric acid solution, or a phosphate ester solution.

[0189] For example, a Zn-containing pore-forming solution can be an aqueous solution of zinc chloride.

[0190] In some embodiments, the solid content of the impregnation mixture formed by the pre-carbonized body and the pore-forming liquid is 50 wt% to 70 wt%. For example, the solid content of the impregnation mixture formed by the pre-carbonized body and the pore-forming liquid can be 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%. By setting the solid content of the impregnation mixture within the above range, an appropriate amount of micropores and mesopores can be formed, which is beneficial for improving the discharge specific capacity, charge specific capacity, and initial coulombic efficiency of the secondary battery.

[0191] In some embodiments, the activation treatment further includes holding the impregnation mixture formed by the impregnated precarbide and the pore-forming liquid at 400°C-750°C for 1-12 hours. Optionally, the temperature is increased at a rate of 1°C / min-20°C / min under nitrogen or inert gas. For example, the heat treatment process involves increasing the temperature to 600°C at a rate of 5°C / min and holding it for 2 hours while purging nitrogen. Holding at 400°C-750°C for 1-12 hours allows the phosphorus-containing pore-forming liquid and the precarbide to chemically react, resulting in etching through chemical activation and introducing a large number of pore structures into the precarbide framework.

[0192] In some embodiments, the pre-carbonization treatment involves heating to 400°C-600°C at a rate of 1°C / min-20°C / min and holding for 1-12 hours. For example, the pre-carbonization temperature can be 550°C, and the pre-carbonization treatment time can be 6 hours. Pre-carbonization under these conditions facilitates the formation of a basic carbon framework structure, which is beneficial for subsequent pore formation.

[0193] In some embodiments, the carbonization process involves heating to 1000℃-1800℃ at a rate of 2℃ / min-20℃ / min and holding for 1h-12h. For example, the carbonization temperature can be 1250℃, and the carbonization time can be 10h. During carbonization, the precursor loses heteroatoms such as H and O to form a stable hard carbon framework.

[0194] In some embodiments, the pre-carbonization and carbonization processes described above are carried out under nitrogen or an inert atmosphere. Optionally, the inert atmosphere is argon.

[0195] In some embodiments, the pre-carbonization treatment is further followed by a pulverization process. The pulverization process is performed using ball milling. This pulverization process can reduce the pre-carbonized material to a suitable particle size, facilitating subsequent activation treatment.

[0196] In some embodiments, the hard carbon precursor includes at least one of a biomass precursor and a synthetic polymer precursor; the synthetic polymer precursor includes a compound composed of C, H, and O elements. Exemplarily, the biomass precursor can be coconut shell, pine powder, walnut shell, reed, straw, etc.; the synthetic polymer precursor can be phenolic resin, epoxy resin, or unsaturated polyester resin. Hard carbon materials prepared using the above precursors exhibit relatively ordered carbon formation after activation and are capable of forming appropriate amounts of micropores and mesopores.

[0197] In some embodiments, when a biomass precursor is used as the hard carbon precursor, a deashing process is further included after the pulverization treatment. The deashing process involves soaking the pre-carbonized material in an acidic aqueous solution at room temperature to 95°C for 1-12 hours, repeated 1-5 times. The deashing process removes ash such as minerals and metal oxides from the pre-carbonized material, improving its purity.

[0198] In some embodiments, a deashing process is included after the activation step. The deashing process involves immersing the sample in an acidic aqueous solution at room temperature to 95°C for 1-12 hours, repeated 1-5 times. The deashing process is used to remove residual P or Zn elements from the porous carbon precursor.

[0199] Example

[0200] 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.

[0201] Example 1

[0202] Preparation of hard carbon materials:

[0203] 1) Pre-carbonization treatment: When nitrogen is introduced, the hard carbon precursor pine powder is placed in a tube furnace and heated to 550℃ at a heating rate of 10℃ / min and held for 6h to obtain a pre-carbonized body. The nitrogen flow rate is 500mL / min.

[0204] 2) Crushing treatment; The precarbide obtained above was crushed by ball milling using zirconia grinding balls and a zirconia grinding jar. The mass ratio of precarbide to grinding balls was 1:3. The speed of the ball mill was 800 rpm and the milling time was 8 hours. After removing the grinding balls, a precarbide with a volumetric particle size distribution Dv50 of 5.4 μm and a volumetric particle size distribution Dv90 of 11.3 μm was obtained.

[0205] 3) Deashing treatment; The pre-carbonized body after crushing treatment in step 2) above is washed with hydrochloric acid aqueous solution. The acid washing temperature range is 60℃, the acid washing time is 3h, and the washing process is repeated 4 times. Then, it is filtered, and the filter cake is taken and washed repeatedly with deionized water and anhydrous ethanol until the pH of the filtrate is >6. The washed filter cake is dried in a vacuum oven at 80℃ for 24 hours.

[0206] 4) Activation treatment; The pre-carbonized body after the deashing treatment in step 3) above is activated at 700°C under a preset mixed gas to obtain a porous carbon precursor; wherein, the preset mixed gas includes carbon dioxide gas, water vapor and inert gas, the proportion of carbon dioxide gas in the preset mixed gas is 12% and the proportion of water vapor in the preset mixed gas is 3%.

[0207] 5) Carbonization treatment; while introducing nitrogen, the porous carbon precursor prepared in step 4) above is placed in a tube furnace and heated to 1250°C at a heating rate of 10°C / min and held for 10h to obtain porous carbon.

[0208] 6) Coating treatment; Prepare a polyacrylic acid aqueous solution with a pH of 1.5, mix the porous carbon prepared in step 5) with the prepared acrylic acid aqueous solution to form a kneading mixture, place the kneading mixture in a twin-screw kneader and knead for 6 hours to obtain hard carbon material; the rotation speed of the twin-screw kneader is 40 rpm, the solid content of the kneading mixture is 65 wt%, and the mass of polyacrylic acid in the kneading mixture is 5% of the mass of the porous carbon.

[0209] Tests related to hard carbon materials:

[0210] 1) Pore volume test

[0211] First, the hard carbon material is pretreated to obtain porous carbon material. Specifically, 2g of hard carbon powder is added to a 250ml beaker, along with 1g of NaOH, and stirred until homogeneous. The beaker is placed in a water bath and heated to 80℃ for 30 minutes with stirring. Then, the mixture is filtered, and the filter cake is repeatedly washed with deionized water until the filtrate is neutral. The washed filter cake is then dried in a vacuum oven at 80℃ for 24 hours.

[0212] Next, porous carbon material powder was placed in a sample tube and degassed under vacuum at 200℃ for 12 hours. The adsorption capacity of the hard carbon material for nitrogen under different pressures was measured using an ASAP2460 physical adsorption analyzer, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the shape of the hysteresis loop, and the pore size distribution curve of the micropores was fitted using a DFT model. The pore volume X of the micropores, the pore volume Y of the mesopores, and the total pore volume A in the hard carbon material were calculated.

[0213] 2) Methylene blue adsorption value test

[0214] Follow these steps to test the methylene blue adsorption value:

[0215] ① Prepare buffer solution: Weigh 3.6g potassium dihydrogen phosphate and 14.3g disodium hydrogen phosphate, and dissolve in 1000mL water. ② Prepare methylene blue solution: Weigh 1.0g dried methylene blue and dissolve in a buffer solution at 60±1℃. After complete dissolution, cool to room temperature and filter into a 1000mL volumetric flask. Wash the filter residue with buffer solution several times, and finally dilute to the mark with buffer solution to prepare a 1000mg / L methylene blue solution. ③ Sample treatment: Weigh a certain amount of ground and dried hard carbon material and mix it thoroughly with the prepared methylene blue solution of known concentration. Shake at room temperature for a certain period of time to allow the hard carbon material to fully adsorb the methylene blue. ④ Filtration: Filter using 12.5cm diameter medium-speed qualitative filter paper to separate the unadsorbed methylene blue solution. ⑤ Measure absorbance: Take the filtrate and measure the absorbance at the maximum absorption wavelength (665nm) using a UV spectrophotometer. ⑥ Comparison and Calculation: Compare the absorbance of the sample filtrate with that of the copper sulfate standard solution (0.4% aqueous solution by mass), and adjust the amount of methylene blue solution added until the difference in absorbance reading between the sample filtrate and the copper sulfate standard solution does not exceed ±0.02. ⑦ Obtain the concentration of methylene blue in the solution according to the standard curve, and calculate the mass of methylene blue adsorbed per gram of hard carbon material to obtain the Z value.

[0216] Preparation of coin cell half-cells:

[0217] The hard carbon material prepared in Example 1 was mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and carbon black as a conductive agent in a mass ratio of 96.2:1.8:1.2:0.8 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 current collector, dried in an oven, and then sliced ​​for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. A CR2430 coin cell was then assembled in an argon-protected glove box using a sodium metal sheet as the counter electrode and a glass fiber film as the separator.

[0218] Button cell performance test

[0219] At 25°C, the coin cell half-cell prepared above was first discharged to 0V at a constant current density of 10mA / g, and the first discharge capacity (i.e., discharge capacity) of the coin cell half-cell was recorded. Then, it was charged to 2.0V at a constant current density of 10mA / g, and the first charge capacity (i.e., charge capacity) of the coin cell was recorded.

[0220] Initial coulombic efficiency (%) = First charge capacity / First discharge capacity × 100%.

[0221] Example 2-13

[0222] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into coin cells. The only difference was that the activation treatment and kneading treatment conditions were adjusted according to Table 1 below to obtain hard carbon materials with different total pore volumes A and different methylene blue adsorption values ​​Z. See Table 1 for details.

[0223] Comparative Example 1

[0224] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into coin cells. The only difference was that the activation and coating process conditions were adjusted according to Table 1 below during the preparation of the hard carbon materials to obtain a total pore volume A of less than 0.2 cm³. 3 / g of hard carbon material.

[0225] Comparative Example 2

[0226] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into coin cells. The only difference was that the activation and coating process conditions were adjusted according to Table 1 below during the preparation of the hard carbon materials to obtain hard carbon materials with a methylene blue adsorption value greater than 8 mg / g.

[0227] Comparative Example 3

[0228] Hard carbon materials were prepared using a method similar to that in Example 1 and assembled into coin cells. The only difference was that the activation and coating process conditions were adjusted according to Table 1 below during the preparation of the hard carbon materials to obtain a total pore volume A of less than 0.2 cm³. 3 Hard carbon materials with a methylene blue adsorption value greater than 8 mg / g and a methylene blue adsorption value greater than 8 mg / g.

[0229] The process parameters for preparing hard carbon materials in Examples 1-13 and Comparative Examples 1-3 are shown in Table 1 below, and the performance parameters of the prepared hard carbon materials and the test results of coin half-cells are shown in Table 2 below.

[0230] Table 1:

[0231]

[0232] Table 2:

[0233]

[0234]

[0235] As can be seen from Tables 1 and 2 above, in Examples 1-13, the total pore volume of the porous carbon was kept at 0.2 cm³. 3 / g-0.6cm3 The concentration of methylene blue in the hard carbon material was kept between 0.2 mg / g and 1 mg / g, significantly improving the initial coulombic efficiency and charge capacity while maintaining a high discharge capacity. In Comparative Example 1, the total pore volume of the porous carbon was less than 0.2 cm³. 3 / g, with a relatively low discharge specific capacity. In Comparative Example 2, although the discharge specific capacity of the hard carbon material is relatively high due to its methylene blue adsorption value being greater than 8 mg / g, its initial coulombic efficiency and charge specific capacity are relatively low. In Comparative Example 3, the total pore volume of the porous carbon is less than 0.2 cm³. 3 The methylene blue adsorption value of the hard carbon material is greater than 8 mg / g, resulting in low discharge specific capacity, charge specific capacity, and initial coulombic efficiency. Within a suitable range of total pore volume and methylene blue adsorption value, a micropore-to-mesopore pore volume ratio X / Y within a suitable range, such as 5.6-33, and particularly 7-16, can further balance the discharge specific capacity, charge specific capacity, and initial coulombic efficiency.

[0236] Example 14

[0237] Preparation of hard carbon materials:

[0238] 1) Pre-carbonization treatment: When nitrogen is introduced, the hard carbon precursor epoxy resin is placed in a tube furnace and heated to 550℃ at a heating rate of 10℃ / min and held for 6h to obtain a pre-carbonized body. The flow rate of nitrogen is 500mL / min.

[0239] 2) Crushing treatment; The precarbide obtained above was crushed by ball milling using zirconia grinding balls and a zirconia grinding jar. The mass ratio of precarbide to grinding balls was 1:3. The speed of the ball mill was 800 rpm and the milling time was 8 hours. After removing the grinding balls, a precarbide with a volumetric particle size distribution Dv50 of 5.1 μm and a volumetric particle size distribution Dv90 of 11 μm was obtained.

[0240] 3) Activation treatment: The pre-carbonized body after the crushing treatment in step 2) above is immersed in the pore-forming solution of phosphoric acid aqueous solution for 6 hours, and then placed in a tube furnace. While introducing nitrogen gas, the temperature is raised to 600℃ at a heating rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 500mL / min to obtain a porous carbon precursor. The amount of P element added is 12.2% of the mass of porous carbon. The solid content of the impregnation mixture formed by the pre-carbonized body and the pore-forming solution is 65%.

[0241] 4) Deashing treatment; The porous carbon precursor in step 4) above is washed in hydrochloric acid aqueous solution. The acid washing temperature range is 60℃, the acid washing time is 3h, and the washing process is repeated 4 times. Then filter, take the filter cake, and wash it repeatedly with deionized water and anhydrous ethanol until the pH of the filtrate is >6. Dry the washed filter cake in a vacuum oven at 80℃ for 24 hours.

[0242] 5) Carbonization treatment; while introducing nitrogen, the porous carbon precursor after deashing treatment in step 4) above is placed in a tube furnace and heated to 1250°C at a heating rate of 10°C / min and held for 10h to obtain porous carbon.

[0243] 6) Coating treatment; Prepare a polyacrylic acid aqueous solution with a pH of 1.5, mix the porous carbon prepared in step 5) with the prepared acrylic acid aqueous solution to form a kneading mixture, place the kneading mixture in a twin-screw kneader and knead for 6 hours to obtain hard carbon material; the rotation speed of the twin-screw kneader is 40 rpm, the solid content of the kneading mixture is 65 wt%, and the mass of polyacrylic acid in the kneading mixture is 5% of the mass of the porous carbon.

[0244] Assemble a button cell using a method similar to that in Example 1.

[0245] Examples 15-18

[0246] Hard carbon materials were prepared in a manner similar to that in Example 14 and assembled into coin cells. The only difference was that the activation treatment process conditions were adjusted according to Table 3 below to obtain hard carbon materials with different total pore volumes A of porous carbon. See Table 3 for details.

[0247] The process parameters for preparing hard carbon materials in Examples 14-18 are shown in Table 3 below, and the performance parameters of the prepared hard carbon materials and the test results of coin half-cells are shown in Table 4 below.

[0248] Table 3:

[0249]

[0250] Table 4:

[0251]

[0252] As can be seen from Tables 3 and 4 above, in Examples 14-18, the pore structure of the hard carbon material can be adjusted by reasonably regulating the phosphoric acid content or impregnation time in the pore-forming solution, so that the total pore volume of the porous carbon is within 0.2 cm³. 3 / g-0.6cm 3 The methylene blue adsorption value of the hard carbon material is between 8 mg / g and 8 mg / g, which significantly improves the initial coulombic efficiency and charge capacity while also ensuring a high discharge capacity.

[0253] 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 includes a core and an organic coating layer covering the core, wherein the core comprises porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material is Z≤8mg / g.

2. The negative electrode sheet according to claim 1, characterized in that, The methylene blue adsorption value of the hard carbon material is Z≤4mg / g.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The porous carbon includes micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A.

4. The negative electrode sheet according to claim 3, characterized in that, The total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7≤X / Y≤16.

5. The negative electrode sheet according to claim 3 or 4, characterized in that, The total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the following condition: 85% ≤ X / A ≤ 97%.

6. The negative electrode sheet according to any one of claims 3-5, characterized in that, The total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the following condition: 3% ≤ Y / A ≤ 15%.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The thickness of the organic coating layer is 1 nm to 90 nm.

8. The negative electrode sheet according to any one of claims 1-7, characterized in that, In the hard carbon material, the organic coating layer has a mass of 0.5 wt% to 10 wt% of the porous carbon.

9. The negative electrode sheet according to any one of claims 1-8, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 ; (2) The tap density of the hard carbon material is 0.34 g / cm³. 3 -0.8g / cm 3 ; (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm; (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm; (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g.

10. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet as described in any one of claims 1 to 9.

11. The secondary battery according to claim 10, characterized in that, The secondary battery also includes a positive electrode sheet, wherein the positive electrode sheet comprises at least one selected from transition metal oxides, polyanionic compounds and Prussian blue compounds as the positive electrode active material.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 10 or 11.

13. A hard carbon material, characterized in that, It includes a core and an organic coating layer covering the core, the core comprising porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value of the hard carbon material is Z≤8mg / g.

14. The hard carbon material according to claim 13, characterized in that, The methylene blue adsorption value of the hard carbon material is Z≤4mg / g.

15. The hard carbon material according to claim 13 or 14, characterized in that, The porous carbon includes micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6% ≤ X / Y ≤ 33%, and X + Y = A.

16. The hard carbon material according to claim 15, characterized in that, The total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 7≤X / Y≤16.

17. The hard carbon material according to claim 15 or 16, characterized in that, The total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the following condition: 85% ≤ X / A ≤ 97%.

18. The hard carbon material according to any one of claims 15-17, characterized in that, The total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the following condition: 3% ≤ Y / A ≤ 15%.

19. The hard carbon material according to any one of claims 13-18, characterized in that, The thickness of the organic coating layer is 1 nm to 90 nm.

20. The hard carbon material according to any one of claims 13-19, characterized in that, In the hard carbon material, the organic coating layer has a mass of 0.5 wt% to 10 wt% of the porous carbon.

21. The hard carbon material according to any one of claims 13-20, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm³. 3 -1.0g / cm 3 ; (2) The tap density of the hard carbon material is 0.34 g / cm³. 3 -0.8g / cm 3 ; (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm; (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm; (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-0.8m 2 / g.

22. A method for preparing a hard carbon material, characterized in that, The method includes: The hard carbon precursor is pre-carbonized to obtain a pre-carbonized body; The pre-carbonized body is activated to obtain a porous carbon precursor; The porous carbon precursor is subjected to carbonization treatment to obtain porous carbon; The porous carbon is coated, wherein the coating process includes a kneading process of kneading a mixture of the porous carbon and an aqueous solution of the coating material, wherein the solid content of the kneading mixture is 55wt%-75wt%, and the pH value of the aqueous solution of the coating material is ≤3.

23. The preparation method according to claim 22, characterized in that, The solid content of the kneaded mixture is 63wt%-67wt%, and the pH value of the aqueous solution coating the raw material is 1.2-1.

8.

24. The preparation method according to claim 22 or 23, characterized in that, The coating material includes at least one of polyacrylic acid, polyacrylate, and copolymers of polyacrylic acid.

25. The preparation method according to any one of claims 22-24, characterized in that, The mass of the coating material is 0.5%-10% of the mass of the porous carbon, and the kneading process is carried out for at least 0.5 hours.

26. The preparation method according to any one of claims 22-25, characterized in that, The kneading process is carried out in a twin-screw kneader, the twin-screw kneader rotating at a speed of 10 rpm to 50 rpm.

27. The preparation method according to any one of claims 22-26, characterized in that, The activation treatment includes treating the pre-carbonized body at 700℃-950℃ under a preset mixed gas, wherein the preset mixed gas includes carbon dioxide gas, water vapor and inert gas, and the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is ≥2.

28. The preparation method according to claim 27, characterized in that, The carbon dioxide gas accounts for 5%-20% of the volume of the preset mixed gas, and the water vapor accounts for 1%-5% of the volume of the mixed gas.

29. The preparation method according to any one of claims 22-28, characterized in that, The activation treatment includes immersing the pre-carbonized body in the pore-forming solution for at least 2 hours; The pore-forming fluid includes a phosphorus-containing pore-forming fluid or a zinc-containing pore-forming fluid, wherein the amount of phosphorus added in the phosphorus-containing pore-forming fluid is 9.5%-32.4% of the mass of the porous carbon, and the amount of zinc added in the zinc-containing pore-forming fluid is 14%-50% of the mass of the porous carbon.

30. The preparation method according to claim 29, characterized in that, The solid content of the impregnation mixture formed by the pre-carbonized body and the pore-forming liquid is 50 wt% to 70 wt%.

31. The preparation method according to claim 29 or 30, characterized in that, The activation treatment also includes keeping the impregnated mixture of the pre-carbonized body and the pore-forming liquid at 400℃-750℃ for 1h-12h.

32. The preparation method according to any one of claims 22-31, characterized in that, The pre-carbonization treatment involves heating to 400℃-600℃ at a rate of 1℃ / min-20℃ / min and holding for 1h-12h.

33. The preparation method according to any one of claims 22-32, characterized in that, The carbonization process involves heating the temperature to 1000℃-1800℃ at a rate of 2℃ / min-20℃ / min and holding it for 1h-12h.

34. The preparation method according to any one of claims 22-33, characterized in that, The hard carbon precursor includes at least one of biomass precursor and synthetic polymer precursor; The synthetic polymer precursors include compounds composed of C, H, and O elements.

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