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

Abstract

The present disclosure provides a negative electrode sheet, a secondary battery, an electric device, a hard carbon material, and a preparation method therefor. The negative electrode sheet 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 a hard carbon material; the hard carbon material comprises a core and an organic coating layer wrapping the core; and the core comprises porous carbon. The total pore volume A of the porous carbon satisfies: 0.2cm3 / g≤A≤0.6cm3 / g; and the methylene blue adsorption value Z of the hard carbon material is less than or equal to 8 mg / g.

Description

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

[0001] Cross-reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202410544841.2, filed on April 30, 2024, entitled “Negative electrode sheet, secondary battery, electric device, hard carbon material and preparation method thereof”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a negative electrode sheet, a secondary battery, an electric device, a hard carbon material and a preparation method thereof. BACKGROUND

[0004] In recent years, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. With the application and promotion of secondary batteries, people have higher and higher requirements for the energy density, cycle performance and large-rate charging performance of secondary batteries, and the performance of the negative active material, as an important component of the secondary battery, to some extent, affects the performance of the secondary battery. Currently, hard carbon is usually used as the negative active material of the secondary battery, but the charge gram capacity and the initial coulombic efficiency of the hard carbon as the negative active material are low.

[0005] SUMMARY

[0006] The present disclosure is made in view of the above-mentioned problems, and aims to provide a negative electrode sheet, a secondary battery, an electric device, a hard carbon material and a preparation method thereof, wherein the negative electrode sheet is used as a secondary battery with improved charge gram capacity and initial coulombic efficiency.

[0007] To achieve the above-mentioned purpose, the first aspect of the present disclosure provides a negative electrode sheet, comprising a negative current collector and a negative film layer located on at least one surface of the negative current collector, the negative film layer comprising a hard carbon material, the hard carbon material comprising a core and an organic coating layer coating the core, the core comprising porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3 / g; the methylene blue adsorption value Z of the hard carbon material is ≤8 mg / g.

[0008] In the present disclosure, by setting the total pore volume of the porous carbon in the hard carbon material within the above range, the carbon skeleton of the hard carbon material can have appropriate strength and stability, and the hard carbon material can have improved charge gram capacity and initial coulombic efficiency of the secondary battery without collapse during the insertion and extraction of active ions. In addition, by providing the organic coating layer on the outer surface of the porous carbon core, the electrolyte molecules can be blocked from entering the pore structure of the porous carbon, which is conducive to improving the charge gram capacity and initial coulombic efficiency of the secondary battery. Further, the methylene blue adsorption value of the hard carbon material is within the above range, so that the organic coating layer has high compactness, can effectively isolate the electrolyte, inhibit the electrolyte molecules from entering the inside of the porous carbon, and further improve the charge gram capacity and initial coulombic efficiency of the secondary battery.

[0009] In some embodiments, the methylene blue adsorption value of the hard carbon material is Z≤4 mg / g. The smaller the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charge gram capacity and initial coulombic efficiency of the secondary battery.

[0010] In some embodiments, the porous carbon includes micropores with a pore size of 0.4 nm-2.5 nm and mesopores with a pore size of 2.5 nm-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. In this way, the storage space inside the hard carbon material can be maximized, and the active ions can be reversibly inserted and extracted, which is conducive to the charge gram capacity and initial coulombic efficiency of the secondary battery.

[0011] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy: 85%≤X / A≤97%. In this way, more storage space for active ions can be provided, which is conducive to improving the discharge gram capacity of the hard carbon material.

[0012] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy: 3%≤Y / A≤15%. In this way, a proper amount of transmission channels for active ions can be provided, which improves the utilization rate of the micropores and is conducive to improving the charge gram capacity and initial coulombic efficiency of the secondary battery.

[0013] In some embodiments, the thickness of the organic coating layer is 1 nm-90 nm. In this way, the kinetic performance of the secondary battery and the charge gram capacity and initial coulombic efficiency of the secondary battery can be considered.

[0014] In some embodiments, in the hard carbon material, the mass of the organic coating layer is 0.5 wt%-10 wt% of the porous carbon. In this way, the kinetic performance of the secondary battery and the charge gram capacity and initial coulombic efficiency of the secondary battery can be considered.

[0015] In some embodiments, the hard carbon material satisfies at least one of the following:

[0016] (1) The compaction density of 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.

[0017] (2) The tap density of 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.

[0018] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0μm-7.9μm;

[0019] (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm. When the volume distribution particle size 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.

[0020] (5) The specific surface area (BET) of 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.

[0021] A second aspect of this disclosure provides a secondary battery, including the negative electrode sheet of the first aspect of this disclosure.

[0022] In some embodiments, the secondary battery further includes a positive electrode. The positive electrode includes at least one selected from transition metal oxides, polyanionic compounds, and Prussian blue compounds as the positive electrode active material.

[0023] The secondary battery of this disclosure has improved charge capacity and initial coulombic efficiency.

[0024] A third aspect of this disclosure provides an electrical device including a secondary battery as described in the second aspect of this disclosure.

[0025] The power consuming device of the present disclosure comprises the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery.

[0026] The fourth aspect of the present disclosure provides a hard carbon material comprising a core and an organic material coating layer coating the core, wherein the core comprises porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3 / g; and the methylene blue adsorption value Z of the hard carbon material is ≤8 mg / g.

[0027] In the present disclosure, by setting the total pore volume of the porous carbon in the hard carbon material within the above range, the carbon skeleton of the hard carbon material has appropriate strength and stability, and will not collapse during the insertion and extraction of active ions, thereby improving the charge gram capacity and the initial coulombic efficiency of the secondary battery. In addition, by setting the organic material coating layer on the outer surface of the porous carbon core, the electrolyte molecules can be blocked from entering the pore structure of the porous carbon, which is conducive to improving the charge gram capacity and the initial coulombic efficiency of the secondary battery. Further, the methylene blue adsorption value of the hard carbon material is within the above range, so that the compactness of the organic material coating layer is high, which can effectively isolate the electrolyte and inhibit the electrolyte molecules from entering the interior of the porous carbon, thereby further improving the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0028] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g. The smaller the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0029] 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. In this way, the storage space inside the hard carbon material can be maximized, and the active ions can be reversibly inserted and extracted, which is conducive to the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0030] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy: 85%≤X / A≤97%. In this way, more storage space for active ions can be provided, which is conducive to improving the discharge gram capacity of the hard carbon material.

[0031] In some embodiments, the total pore volume Y of the mesopores satisfies 3%≤Y / A≤15% with respect to the total pore volume A of the porous carbon. In this way, a proper amount of transport channels for active ions can be provided, thereby improving the utilization of micropores and facilitating the improvement of the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0032] In some embodiments, the thickness of the organic coating layer is 1 nm-90 nm. In this way, the kinetic performance of the secondary battery and the charge gram capacity and the initial coulombic efficiency of the secondary battery can be balanced.

[0033] In some embodiments, the mass of the organic coating layer in the hard carbon material is 0.5wt%-10wt% of the porous carbon. In this way, the kinetic performance of the secondary battery and the charge gram capacity and the initial coulombic efficiency of the secondary battery can be balanced.

[0034] In some embodiments, the hard carbon material satisfies at least one of the following:

[0035] (1) The compaction density of the hard carbon material at 5t is 0.55g / cm 3 -1.0g / cm 3 ; when the powder compaction density of the hard carbon material is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the transport performance of active ions and electrons, and further improve the kinetic performance of the secondary battery.

[0036] (2) The tap density of the hard carbon material is 0.34g / cm 3 -0.8g / cm 3 ; when the tap density of the hard carbon material is within the above range, it is beneficial to improve the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0037] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0μm-7.9μm;

[0038] (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 and reduce the occurrence of side reactions, thereby improving the initial coulombic efficiency of the secondary battery. At the same time, the bulk transport path of active ions can be shortened, thereby improving the kinetic performance of the secondary battery.

[0039] (5) The specific surface area BET of the hard carbon material is 0.1m 2 / g-0.8m 2 / g. When the specific surface area of the hard carbon material is within the above range, the consumption of active ions during the first charging can be reduced, which is beneficial to improve the initial coulombic efficiency of the secondary battery.

[0040] The fifth aspect of the present disclosure also provides a method for preparing a hard carbon material, the method comprising:

[0041] The hard carbon precursor is subjected to a pre-carbonization treatment to obtain a pre-carbonized body, the pre-carbonized body is subjected to an activation treatment to obtain a porous carbon precursor, the porous carbon precursor is subjected to a carbonization treatment to obtain a porous carbon, and the porous carbon is subjected to a coating treatment, wherein the coating treatment comprises a kneading treatment of a kneading mixture formed by the porous carbon and an aqueous solution of a coating raw material, wherein the solid content of the kneading mixture is 55wt%-75wt%, and the pH value of the aqueous solution of the coating raw material is ≤3.

[0042] The present disclosure obtains a porous carbon precursor by pre-carbonization and activation pore-forming treatment of a hard carbon precursor, obtains a porous carbon by carbonization treatment of the porous carbon precursor, and forms a hard carbon material with a coating layer by kneading treatment of the porous carbon and an aqueous solution of a coating raw material. Under the above-mentioned solid content and pH conditions of the aqueous solution of the coating raw material, the porous carbon and the coating raw material are kneaded to make them more fully mixed and sheared, so that the coating layer formed has good compactness, thus being able to block electrolyte molecules from entering the interior of the porous carbon and being conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0043] In some embodiments, the solid content of the kneading mixture is 63wt%-67wt%, and the pH value of the aqueous solution of the coating raw material is 1.2-1.8. In this way, it is conducive to forming a coating layer with suitable compactness, and the charge gram capacity and the first coulombic efficiency of the secondary battery can be improved without affecting the kinetic performance of the secondary battery.

[0044] In some embodiments, the coating raw material comprises at least one of polyacrylic acid, a polyacrylic acid salt, and a copolymer of polyacrylic acid. The carboxyl groups on the molecular chain of the polyacrylic acid can react with the oxygen-containing functional groups on the surface of the porous carbon to form carbon-oxygen covalent bonds, which make the organic coating layer and the porous carbon tightly connected, forming a stable and highly compact organic coating layer. The organic coating layer can inhibit the electrolyte from entering the interior of the porous carbon, and is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0045] In some embodiments, the mass of the coating raw material is 0.5%-10% of the mass of the porous carbon, and the kneading treatment is performed for at least 0.5h. In this way, a coating layer with suitable compactness can be formed, and the charge gram capacity and the first coulombic efficiency of the secondary battery can be improved without affecting the kinetic performance of the secondary battery and without increasing the impedance of the secondary battery.

[0046] In some embodiments, the kneading treatment is performed in a double-screw kneader, and the rotation speed of the double-screw kneader is 10rpm-50rpm. Under the above-mentioned conditions, a uniformly coated organic coating layer can be obtained.

[0047] In some embodiments, the activation treatment comprises treating the pre-carbonized body at 700-950°C under a preset mixed gas, the preset mixed gas comprising carbon dioxide gas, water vapor and inert gas, and the volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas is ≥2. The activation treatment is performed at the above-mentioned temperature, which can form appropriate amounts of mesopores and micropores, and is conducive to improving the discharge gram capacity of the secondary battery.

[0048] In some embodiments, the volume ratio of the carbon dioxide gas in the preset mixed gas is 5%-20%, and the volume ratio of the water vapor in the mixed gas is 1%-5%. The volume ratio of the carbon dioxide gas in the preset mixed gas within the above-mentioned range can form appropriate amounts of micropores, which is conducive to improving the discharge gram capacity of the secondary battery. The volume ratio of the water vapor in the preset mixed gas within the above-mentioned range can form appropriate amounts of mesopores, which is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0049] In some embodiments, the activation treatment comprises at least immersing the pre-carbonized body in a pore-forming liquid for 2h; the pore-forming liquid comprises a P-containing pore-forming liquid or a Zn-containing pore-forming liquid, wherein the added amount of P element in the P-containing pore-forming liquid is 9.5%-32.4% of the mass of the porous carbon, and the added amount of Zn element in the Zn-containing pore-forming liquid is 14%-50% of the mass of the porous carbon. In this way, appropriate amounts of micropores and mesopores can be formed, which is conducive to improving the discharge gram capacity, the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0050] In some embodiments, the solid content of the immersion mixture formed by the pre-carbonized body and the pore-forming liquid is 50wt%-70wt%.

[0051] In some embodiments, the activation treatment further comprises heat treating the immersion mixture formed by the immersed pre-carbonized body and the pore-forming liquid at 400-750°C for 1h-12h. In this way, the P-containing pore-forming liquid and the pre-carbonized body can be chemically reacted, etching is performed by chemical activation, and a large number of pore structures are introduced into the pre-carbonized body skeleton structure.

[0052] In some embodiments, the pre-carbonization treatment is heated to 400-600°C at a heating rate of 1°C / min-20°C / min and maintained for 1h-12h. The pre-carbonization treatment is performed under the above-mentioned conditions, which is conducive to forming a basic carbon skeleton structure and facilitating subsequent pore formation.

[0053] In some embodiments, the carbonization treatment is heated to 1000-1800°C at a heating rate of 2°C / min-20°C / min and maintained for 1h-12h. During the carbonization process, the precursor loses H, O and other heteroatoms to form a stable hard carbon skeleton.

[0054] 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. The hard carbon material is prepared using the above-mentioned precursor, and the carbon formed after activation is relatively ordered and can form an appropriate amount of micropores and mesopores. BRIEF DESCRIPTION OF DRAWINGS

[0055] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0056] FIG. 2 is an exploded view of the battery cell shown in FIG. 1 according to an embodiment of the present disclosure.

[0057] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0058] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0059] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0060] FIG. 6 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0061] REFERENCE NUMERALS: 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: top cap assembly. DETAILED DESCRIPTION

[0062] Hereinafter, specific embodiments of the negative electrode sheet, the secondary battery, the electric device, the hard carbon material, and the method of manufacturing the same according to the present disclosure are explained in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed explanations are omitted. For example, there can be cases where detailed explanations of matters well known in the art, repeated explanations of actually identical structures are omitted. This is to avoid the following explanation from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following explanation are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0063] The ranges disclosed herein are defined by their lower and upper endpoints, and given that a range is defined by selecting a lower endpoint and an upper endpoint, the selected lower and upper endpoints define the boundaries of the particular range. Ranges defined by endpoints can be inclusive or exclusive of the endpoints, and can be arbitrarily combined, i.e., any lower endpoint can be combined with any upper endpoint to form a range. For example, if ranges of 60-120 and 80-110 are listed, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, 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 contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all of the individual real combinations of values that are within the range of a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all of the real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0066] Unless otherwise specified, all steps of the present disclosure can be performed in sequence or randomly, and are preferably performed in sequence. For example, a method comprising steps (a) and (b) indicates that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further comprise step (c), which indicates that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0067] Unless otherwise specified, the terms used in the present disclosure have the commonly understood meanings understood by those skilled in the art.

[0068] Unless otherwise specified, the values of the parameters mentioned in the present disclosure can be measured by various test methods commonly used in the art, for example, can be measured according to the test methods given in the present disclosure.

[0069] Unless otherwise specified, in the present disclosure, the term "active ion" refers to an ion capable of being reversibly intercalated and deintercalated between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0070] Currently, hard carbon is commonly used as the negative active material of a secondary battery, but the charge gram capacity and the initial coulombic efficiency are both low when hard carbon is used as the negative active material.

[0071] Therefore, the embodiments of the present disclosure provide a new hard carbon material, which has improved charge gram capacity and initial coulombic efficiency as a negative material of a secondary battery.

[0072] Negative electrode sheet

[0073] A first aspect of the embodiments of the present disclosure provides a negative electrode sheet, comprising a negative current collector and a negative film layer on at least one surface of the negative current collector, the negative film layer comprising a hard carbon material, the hard carbon material comprising a core and an organic coating layer coating the core, the core comprising porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3 / g; and the methylene blue adsorption value Z of the hard carbon material is ≤8 mg / g.

[0074] When the hard carbon material is used as the negative active material of a secondary battery, the active ions are first transmitted to the defect sites in the hard carbon material for adsorption, and then transmitted to the pores in the hard carbon material for filling. The active ions exist in the form of clusters in the pores to provide the gram capacity. In the related art, the gram capacity of the hard carbon material is improved by forming more and larger pore structures. However, a large number of pore structures lead to a decrease in the strength of the carbon skeleton of the hard carbon material and poor stability. In the charge and discharge cycle, the intercalation and deintercalation of the active ions easily lead to the collapse of the carbon skeleton of the hard carbon material, affecting the charge gram capacity and the initial coulombic efficiency. In addition, the large pore structures easily allow electrolyte molecules to enter. The entry of the electrolyte molecules into the pore structures not only occupies the storage sites of the active ions, but also consumes more active ions to form a solid electrolyte interface (SEI) film, further reducing the charge gram capacity and the initial coulombic efficiency.

[0075] Based on this, in the present disclosure, by making the total pore volume of the porous carbon in the hard carbon material within the above range, the carbon skeleton of the hard carbon material can have appropriate strength and stability while improving the gram capacity of the hard carbon material, and the collapse during the active ion insertion and extraction process will not occur, thereby improving the charging gram capacity and the first coulombic efficiency of the secondary battery. In addition, by providing the organic coating layer on the outer surface of the porous carbon core, the electrolyte molecules can be blocked from entering the pore structure of the porous carbon, which is conducive to improving the charging gram capacity and the first coulombic efficiency of the secondary battery. Further, the methylene blue adsorption value of the hard carbon material is within the above range, so that the compactness of the organic coating layer is higher, which can effectively isolate the electrolyte and inhibit the electrolyte molecules from entering the inside of the porous carbon, thereby further improving the charging gram capacity and the first coulombic efficiency of the secondary battery.

[0076] In addition, the presence of the organic coating layer is equivalent to constructing an artificial organic SEI layer on the surface of the porous carbon, which improves the stability of the SEI film in the secondary battery, and reduces the amount of active ions consumed for subsequent SEI film generation, thereby achieving high charging gram capacity and first coulombic efficiency.

[0077] It should be noted that since the molecular diameter of methylene blue and the size of the commonly used ester solvent of electrolyte are close (about 1 nm), the methylene blue adsorption value can accurately characterize the area that the electrolyte can enter, i.e., the compactness of the organic coating layer.

[0078] The smaller the methylene blue adsorption value is, the better the coating effect is. In some embodiments, the methylene blue adsorption value of the hard carbon material is Z≤4 mg / g.

[0079] For example, the total pore volume A of the porous carbon is 0.2 cm 3 / g, 0.25 cm 3 / g, 0.3 cm 3 / g, 0.32 cm 3 / g, 0.35 cm 3 / g, 0.37 cm 3 / g, 0.38 cm 3 / g, 0.39 cm 3 / g, 0.4 cm 3 / g, 0.45 cm 3 / g, 0.5 cm 3 / g, 0.55 cm 3 / g, 0.6 cm 3 / g or any value within the range consisting of any two numerical values.

[0080] For example, the methylene blue adsorption value Z of the hard carbon material can be 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 value within a range defined by any two of the values.

[0081] In some embodiments, the material of the organic coating layer includes at least one of polyacrylic acid, a polyacrylic acid copolymer, and a polyacrylic acid salt. For example, the material of the organic coating layer can be polyacrylic acid, a polyacrylic acid copolymer (such as a copolymer of polyacrylic acid and a carboxymethyl cellulose segment, a copolymer of polyacrylic acid and a polyethylene oxide segment), polyacrylic acid sodium (PAANa), a polyrotaxane (PR) and polyacrylic acid (PAA) composite, or the like, but is not limited thereto. Using such an organic material as the coating layer has the advantages of resistance to electrolyte swelling and strong adhesion, and can form a coating layer similar to an SEI film on the surface of the porous carbon particles, thereby inhibiting the entry of the electrolyte into the internal pore structure of the porous carbon particles and reducing the consumption of active ions in the subsequent formation of the SEI film.

[0082] In some embodiments, 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. Alternatively, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy 7≤X / Y≤16. For example, 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, 33.

[0083] It has been found through research that the micropores with a pore size of 0.4 nm to 2.5 nm in the hard carbon material of the present disclosure can enable reversible insertion and extraction of active ions, i.e., an increase in 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 gram capacity of the hard carbon material. The mesopores with a pore size of 2.5 nm to 10 nm in the hard carbon material can serve as a transport channel for active ions, enabling the active ions to be transported into the micropores, thereby improving the utilization rate of the micropores and improving the discharge gram capacity and the initial coulombic efficiency of the secondary battery.

[0084] The ratio of the total micropore volume X of the micropores of the porous carbon inner core to the total mesopore volume Y of the mesopores of the hard carbon material in the present disclosure is within the above range, the storage space inside the hard carbon material can be maximally utilized, and the reversible insertion and extraction of active ions can be achieved, which is beneficial to the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0085] In some embodiments, the total micropore volume X of the micropores satisfies 85%≤X / A≤97% with respect to the total pore volume A of the porous carbon. Alternatively, the total micropore volume X of the micropores satisfies 88≤X / A≤94 with respect to the total pore volume A of the porous carbon. Exemplarily, X / A can be 85%, 86%, 87%, 88%, 90%, 93%, 94%, 97%. The total micropore volume X of the micropores of the hard carbon material satisfies the above relationship with respect to the total pore volume A of the porous carbon, which can provide more storage space for active ions, and is beneficial to improve the discharge gram capacity of the hard carbon material.

[0086] In some embodiments, the total mesopore volume Y of the mesopores satisfies 3%≤Y / A≤15% with respect to the total pore volume A of the porous carbon. Alternatively, the total mesopore volume Y of the mesopores satisfies 6≤Y / A≤12 with respect to the total pore volume A of the porous carbon. Exemplarily, Y / A can be 3%, 5%, 6%, 8%, 10%, 12%, 13%, 15%. The total mesopore volume Y of the mesopores of the hard carbon material satisfies the above relationship with respect to the total pore volume A of the porous carbon, which can provide a proper amount of transport channels for active ions, thereby improving the utilization rate of the micropores and being beneficial to improve the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0087] In some embodiments, the thickness of the organic coating layer is 1 nm-90 nm. Alternatively, the thickness of the organic coating layer is 30 nm-50 nm. Exemplarily, the thickness of the organic coating layer is 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm. By setting the thickness of the organic coating layer within the above range, the kinetic performance of the secondary battery and the charge gram capacity and the initial coulombic efficiency of the secondary battery can be considered.

[0088] In some embodiments, the mass of the organic coating layer in the hard carbon material is 0.5wt%-10wt% of the porous carbon. Exemplarily, the mass of the organic coating layer is 0.5%, 3%, 5%, 8%, 10% of the porous carbon. By setting the mass of the organic coating layer in the hard carbon material within the above range, the kinetic performance of the secondary battery and the charge gram capacity and the initial coulombic efficiency of the secondary battery can be considered.

[0089] In some embodiments, the hard carbon material satisfies at least one of the following:

[0090] (1) The compaction density of the hard carbon material at 5 t is 0.55 g / cm3 -1.0 g / cm 3 When the tap density of the hard carbon material is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, to improve the active ion and electron transport performance, and further to improve the kinetic performance of the secondary battery.

[0091] (2) The tap density of the hard carbon material is 0.34 g / cm 3 -0.8 g / cm 3 When the tap density of the hard carbon material is within the above range, it is beneficial to improve the tap density of the negative electrode film layer, and to improve the energy density of the secondary battery.

[0092] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm.

[0093] (4) The volume distribution particle size Dv90 of the hard carbon material is 8 μm-15 μm. 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, to reduce the occurrence of side reactions, and to improve the first coulomb efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of the active ion, and further improve the kinetic performance of the secondary battery.

[0094] (5) The specific surface area BET of the hard carbon material is 0.1 m 2 / g-0.8 m 2 / g. When the specific surface area of the hard carbon material is within the above range, it can reduce the consumption of active ions during the first charging, and is beneficial to improve the first coulomb efficiency of the secondary battery.

[0095] In the present disclosure, the methylene blue adsorption value of the hard carbon material is the meaning known in the art, which can be determined by instruments and methods known in the art. For example, GB / T 12496.10-1999 can be referred to for testing.

[0096] In the present disclosure, the pore volume of the porous carbon is the meaning known in the art, which can be determined by instruments and methods known in the art. For example, GB / T 21650.3 Part 3 can be referred to for testing. The porous carbon powder is placed in a sample tube and vacuum degassed at 200°C for 12h. The adsorption amount of nitrogen by the hard carbon material under different pressures is tested by an ASAP2460-physical adsorption analyzer, and the adsorption and desorption isotherms are drawn. The shape of the pores is determined according to the shape of the hysteresis loop, the pore size distribution curve of the micropores is fitted using the DFT model, and the pore volume X of the micropores, the pore volume Y of the mesopores, and the total pore volume A of the hard carbon material are calculated.

[0097] In the present disclosure, before testing the pore volume of the porous carbon, the hard carbon material is pretreated to break the organic coating layer so that the gas of nitrogen adsorption / desorption test can enter the porous carbon. An exemplary treatment step includes adding 2 g of hard carbon powder into a 250 ml beaker, adding 1 g of NaOH, and stirring until uniform. The beaker is placed in a water bath and heated to 80°C for 30 min with stirring. Then, the filter cake is filtered, washed repeatedly with deionized water until the filtrate is neutral. The washed filter cake is dried in a vacuum oven at 80°C for 24 h.

[0098] In the present disclosure, the thickness of the organic coating layer in the hard carbon material can be tested by ion polishing cross-section morphology (CP) test of the negative electrode sheet using a cross-section polisher. Specifically, the hard carbon material can be cut into a sample to be tested (for example, 2 cm x 2 cm), and the hard carbon material is fixed on a sample stage; the sample stage is locked and fixed on a sample holder, the power of the argon ion cross-section polisher (for example, the IB-09010CP argon ion cross-section polisher of Japan JEOL Co.) is turned on and vacuumed (for example, 10-7Pa), the argon flow (for example, 0.12 MPa) and the polishing time (for example, 90 min) are set, and the sample stage is adjusted to the swing mode to start polishing. After polishing is completed, the cross-section is analyzed by energy spectrum element analysis, and the difference in O element can be used to distinguish the organic coating layer and the porous carbon, so that the thickness of the organic coating layer can be obtained.

[0099] In the present disclosure, the mass of the organic coating layer in the hard carbon material can be tested by thermogravimetric (TG) test. The weight loss of the hard carbon material at 150°C-500°C under nitrogen atmosphere can be measured, and the content of the organic coating layer can be calculated.

[0100] In the present disclosure, the I D / I G value of the hard carbon material can be tested by a Raman spectrometer, I D represents the D peak intensity of the Raman spectrum of the material at 1350±50 cm -1 , I G represents the G peak intensity of the Raman spectrum of the material at 1580±50 cm -1 . The test conditions are as follows: the excitation wavelength is 532 nm, the grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the cumulative number is 3 times, the surface scanning is performed, the D peak and G peak intensities of 100 points are obtained, and the average value of the remaining 40 points is the I D / I G of the material after removing the maximum and minimum I D / I G of 30. D / I GThe testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0101] In the present disclosure, the tap density of the hard carbon material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by referring to GB / T 5162-2006 using a powder tap density tester. The testing instrument can be a Dandong Baita BT-301, and the testing parameters are as follows: vibration frequency 250 ± 15 times / min, vibration amplitude 3 ± 0.2 mm, vibration times 5000 times, and graduated cylinder 25 mL. 2

[0102] In the present disclosure, the tap density of the hard carbon material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by referring to GB / T 5162-2006 using a powder tap density tester. The testing instrument can be a Dandong Baita BT-301, and the testing parameters are as follows: vibration frequency 250 ± 15 times / min, vibration amplitude 3 ± 0.2 mm, vibration times 5000 times, and graduated cylinder 25 mL.

[0103] In the present disclosure, the volume distribution particle size Dv50, Dv90 of the hard carbon material is in the meaning known in the art, which respectively represents the particle size corresponding to the cumulative volume distribution percentage of 50% and 90% of the material, and can be determined by using instruments and methods known in the art. For example, it can be determined by referring to GB / T 19077-2016 using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0104] In the present disclosure, the specific surface area BET of the hard carbon material is in the meaning known in the art and can be determined by using instruments and methods known in the art. For example, it can be determined by referring to GB / T 19587-2017 using a nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area and pore size analysis tester of Micromeritics, USA.

[0105] In the present disclosure, the microstructure of the hard carbon material can be observed by a scanning electron microscope or a transmission electron microscope.

[0106] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two opposite surfaces of the negative electrode current collector. ​

[0107] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0108] In some embodiments, the negative active material includes the hard carbon material provided in the above embodiments or prepared according to the preparation method of the above embodiments.

[0109] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0110] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0112] In some embodiments, the negative electrode sheet can be prepared by dispersing the above components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0113] Secondary battery

[0114] In a second aspect of the embodiments of the present disclosure, a secondary battery is provided, and the secondary battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0115] The term "secondary battery" referred to herein means a battery cell, a battery module, or a battery pack. Each is described below.

[0116] Generally, the secondary battery cell includes a positive electrode sheet, the negative electrode sheet in the above embodiments, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent short circuiting between the positive electrode and the negative electrode, while allowing ions to pass through.

[0117] [Positive electrode sheet]

[0118] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present disclosure.

[0119] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0120] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In some embodiments, the battery cell is a sodium ion battery, and the positive electrode active material can be a positive electrode active material known in the art for use in sodium ion batteries. As an example, the positive electrode active material can include a sodium transition metal oxide, a polyanion compound, a Prussian blue compound, etc., but the present disclosure is not limited to these materials, and 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 alternative technical solution of the present disclosure, in the sodium transition metal oxide, the transition metal 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, and 0 < x ≤ 1.

[0122] As an alternative technical solution of the present disclosure, the polyanion compound can be a compound having sodium ions, transition metal ions, and a tetrahedral (YO4) 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.

[0123] 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).

[0124] As an optional embodiment of this disclosure, 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 dwherein A represents an alkali metal element doped to substitute Na, M represents a metal element to substitute V, D represents a doping element to substitute P, Q represents a doping element to substitute F, D includes at least one of Si and S, and Q includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, and 0≤d≤0.2z. Optionally, A includes at least one of K and Li; and M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0125] As an optional embodiment of the present disclosure, the chemical formula of the polyanionic compound can be Na x R y (PO4)2P2O7, wherein 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.

[0126] As an optional embodiment of the present disclosure, the chemical formula of the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein 0

[0127] The Prussian blue compound can be a compound 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. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, wherein Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0

[0128] In other embodiments, the battery cell can also be a lithium ion battery, and the positive active material can be a positive active material known in the art for use in lithium ion batteries.

[0129] In the enumeration of the positive electrode active material in the present disclosure, the molar content of oxygen is only the theoretical state value, and the lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of oxygen will appear to be floating.

[0130] In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0131] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0132] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (for example, N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, and the like, the positive electrode tab can be obtained.

[0133] [Electrolyte]

[0134] The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The present disclosure does not have a specific limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0135] In some embodiments, the electrolyte adopts an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0136] In some embodiments, when the battery cell is a sodium ion battery, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethylsulfonylimide, sodium triflate, sodium difluorophosphate, sodium difluoro-bis-oxalate-phosphate, sodium bis-oxalate-borate, and sodium difluoro-tetrafluoro-oxalate-phosphate.

[0137] In some embodiments, when the battery cell is a lithium ion battery, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium triflate, lithium difluorophosphate, lithium difluoro-bis-oxalate-borate, lithium bis-oxalate-borate, and lithium difluoro-tetrafluoro-oxalate-phosphate.

[0138] In some embodiments, the solvent can 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, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanediol sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0139] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0140] [Separator]

[0141] In some embodiments, a separator can be further included in the battery cell. The type of the separator is not particularly limited in the present disclosure, and any publicly known porous structure separator having good chemical stability and mechanical stability can be used.

[0142] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0143] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0144] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte solution.

[0145] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0146] The shape of the battery cell is not particularly limited in the present disclosure, and can be a cylindrical shape, a square shape, or any other shape. For example, FIG. 1 is a battery cell 5 of a square structure as one example.

[0147] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be wound or stacked to form an electrode assembly 52. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0148] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0149] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0150] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0151] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0152] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0153] Electric device

[0154] A third aspect of the embodiments of the present disclosure also provides an electric device, and the secondary battery of the present disclosure is described below with reference to the accompanying drawings as appropriate.

[0155] The power consuming device mentioned in the embodiments of the present disclosure includes the secondary battery provided by the present disclosure. The secondary battery can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0156] As the power consuming device, the battery monomer, the battery module or the battery pack can be selected according to the use requirement thereof.

[0157] FIG. 6 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consuming device, the battery pack or the battery module can be used.

[0158] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery monomer can be used as a power source.

[0159] Hard carbon material

[0160] The fourth aspect of the present disclosure provides the hard carbon material included in the negative electrode tab of the first aspect of the present disclosure. The hard carbon material includes a core and an organic material coating layer coating the core, the core including porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3 / g; and the methylene blue adsorption value Z of the hard carbon material is ≤8 mg / g.

[0161] In the present disclosure, by making the total pore volume of the porous carbon in the hard carbon material within the above range, the carbon skeleton of the hard carbon material has appropriate strength and stability, and will not collapse during the process of active ion insertion and extraction, thereby improving the charging gram capacity and the first coulomb efficiency of the secondary battery. In addition, by providing the organic material coating layer on the outer surface of the porous carbon core, the electrolyte molecules can be blocked from entering the pore structure of the porous carbon, which is beneficial to improve the charging gram capacity and the first coulomb efficiency of the secondary battery. Further, the methylene blue adsorption value of the hard carbon material is within the above range, so that the compactness of the organic material coating layer is higher, which can effectively isolate the electrolyte and inhibit the electrolyte molecules from entering the inside of the porous carbon, thereby further improving the charging gram capacity and the first coulomb efficiency of the secondary battery.

[0162] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤4 mg / g. The smaller the methylene blue adsorption value, the better the coating effect, which is more conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0163] In some embodiments, the porous carbon includes micropores with a pore size of 0.4 nm-2.5 nm and mesopores with a pore size of 2.5 nm-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. In this way, the storage space inside the hard carbon material can be maximally utilized, and the active ions can be reversibly inserted and extracted, which is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0164] In some embodiments, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy: 85%≤X / A≤97%. In this way, more storage space for active ions can be provided, which is conducive to improving the discharge gram capacity of the hard carbon material.

[0165] In some embodiments, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy: 3%≤Y / A≤15%. In this way, a proper amount of transport channels for active ions can be provided, which improves the utilization rate of the micropores and is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0166] In some embodiments, the thickness of the organic coating layer is 1 nm-90 nm. In this way, the kinetic performance of the secondary battery and the charge gram capacity and the first coulombic efficiency of the secondary battery can be taken into account.

[0167] In some embodiments, the mass of the organic coating layer in the hard carbon material is 0.5wt%-10wt% of the porous carbon. In this way, the kinetic performance of the secondary battery and the charge gram capacity and the first coulombic efficiency of the secondary battery can be taken into account.

[0168] In some embodiments, the hard carbon material satisfies at least one of the following:

[0169] (1) The compaction density of the hard carbon material at 5t is 0.55 g / cm 3 -1.0 g / cm 3 When the powder compaction density of the hard carbon material is within the above range, a reasonable pore structure can be formed between the particles of the negative electrode film layer, the active ion and electron transport performance is improved, and thus the kinetic performance of the secondary battery is improved.

[0170] (2) The tap density of the hard carbon material is 0.34 g / cm 3 -0.8 g / cm 3; when the tap density of the hard carbon material is within the above range, the compaction density of the negative electrode film layer is improved, and the energy density of the secondary battery is improved.

[0171] (3) the volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm;

[0172] (4) the volume distribution particle size Dv90 of the hard carbon material is 8 μm-15 μm; when the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above range, the specific surface area of the hard carbon material is reduced, the occurrence of side reactions is reduced, and thus the first coulombic efficiency of the secondary battery is improved. At the same time, the bulk transport path of active ions is shortened, and thus the kinetic performance of the secondary battery is improved.

[0173] (5) the specific surface area BET of the hard carbon material is 0.1 m 2 / g-0.8 m 2 / g. When the specific surface area of the hard carbon material is within the above range, the consumption of active ions during the first charging is reduced, and the first coulombic efficiency of the secondary battery is improved.

[0174] Preparation method of hard carbon material

[0175] A fifth aspect of the embodiments of the present disclosure provides a preparation method of the above hard carbon material, the method comprising: performing pre-carbonization treatment on a hard carbon precursor to obtain a pre-carbonized body; performing activation treatment on the pre-carbonized body to obtain a porous carbon precursor; performing carbonization treatment on the porous carbon precursor to obtain a porous carbon; and performing coating treatment on the porous carbon, wherein the coating treatment comprises performing kneading treatment on a kneading mixture formed by the porous carbon and an aqueous solution of a coating raw material, the solid content of the kneading mixture being 55 wt%-75 wt%, and the pH value of the aqueous solution of the coating raw material being ≤3. The total pore volume A of the formed porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3 / g; and the methylene blue adsorption value Z of the formed hard carbon material is ≤8 mg / g.

[0176] The present disclosure obtains a porous carbon precursor by performing pre-carbonization and activation pore-forming treatment on a hard carbon precursor, and obtains a porous carbon by performing carbonization treatment on the porous carbon precursor. Then, the porous carbon and an aqueous solution of a coating raw material are subjected to kneading treatment to form a hard carbon material with a coating layer. Under the above solid content and pH conditions of the aqueous solution of the coating raw material, the porous carbon and the coating raw material are more fully mixed and sheared, so that the formed coating layer has good compactness, and thus the electrolyte molecules can be blocked from entering the interior of the porous carbon, which is beneficial to improving the charge capacity and the first coulombic efficiency of the secondary battery.

[0177] Exemplarily, the solid content of the kneaded mixture is 55 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 71 wt%, 75 wt%.

[0178] In some embodiments, the solid content of the kneaded mixture is 63 wt%-67 wt%, and the pH value of the aqueous solution of the coating raw material is 1.2-1.8. The solid content of the kneaded mixture within the above range is conducive to forming a coating layer with a suitable density, and can improve the charge gram capacity and the first coulombic efficiency of the secondary battery without affecting the kinetics of the secondary battery. The pH value of the aqueous solution of the coating raw material within the above range during the kneading process can quickly form a coating layer with a suitable density, and is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0179] In some embodiments, the coating raw material at least includes polyacrylic acid. Exemplarily, the coating raw material includes at least one of polyacrylic acid, polyacrylic acid copolymer, sodium polyacrylate, polyrotaxane and polyacrylic acid composite. During the kneading process, the carboxyl on the polyacrylic acid molecular chain can react with the oxygen-containing functional groups on the surface of the porous carbon to form carbon-oxygen covalent bonds, which tightly connect the organic coating layer and the porous carbon, forming a stable and high-density organic coating layer. The organic coating layer can inhibit the electrolyte from entering the interior of the porous carbon, and is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery. In addition, since the polyacrylic acid does not swell in the electrolyte, it can achieve the effect of isolating the electrolyte.

[0180] In some embodiments, the mass of the coating raw material is 0.5%-10% of the mass of the porous carbon, and the kneading process is performed for at least 0.5 h, and optionally, the kneading process is performed for 9 h-12 h. Exemplarily, the mass of the coating raw material is 5% of the mass of the porous carbon, and the time of the kneading process is 12 h. The mass of the coating raw material within the above range can form a coating layer with a suitable density, and can improve the charge gram capacity and the first coulombic efficiency of the secondary battery without affecting the kinetics of the secondary battery and without increasing the impedance of the secondary battery.

[0181] In some embodiments, the kneading process is performed in a double-screw kneader, and the rotation speed of the double-screw kneader is 10-50 rpm. Under the above conditions, the organic coating layer can be uniformly coated.

[0182] In some embodiments, the aqueous solution can be an aqueous solution, an ethanol solution or an isopropanol solution, or a mixed solution of at least two of the aqueous solution, the ethanol solution and the isopropanol solution.

[0183] In some embodiments, the above kneading process is performed at room temperature.

[0184] In some embodiments, the activation treatment comprises treating the pre-carbonized body at 700-950°C under a preset mixed gas. Optionally, the pre-carbonized body is treated at 830-870°C. Exemplarily, the activation treatment temperature can be 700°C, 850°C, 900°C. The activation treatment at the above temperature can form appropriate amount of mesopores and micropores, which is beneficial to improve the discharge gram capacity of the secondary battery.

[0185] In some embodiments, the preset mixed gas comprises carbon dioxide gas, water vapor and inert gas, and the volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas is ≥2. Optionally, the volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas is 4-6. Exemplarily, the volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas can be 2, 3, 4, 5, 6, 8, 10. The volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas within the above range can form appropriate amount of mesopores and micropores, which is beneficial to improve the discharge gram capacity of the secondary battery.

[0186] In some embodiments, the inert gas in the above mixed gas comprises helium, neon, argon, etc.

[0187] In some embodiments, the volume percentage of the carbon dioxide gas in the preset mixed gas is 5%-20%; optionally, the volume percentage of the carbon dioxide gas in the preset mixed gas is 8%-12%. Exemplarily, the volume percentage of the carbon dioxide gas in the preset mixed gas can be 4%, 5%, 6%, 10%, 15%, 20%. The volume percentage of the carbon dioxide gas in the preset mixed gas within the above range can form appropriate amount of micropores, which is beneficial to improve the discharge gram capacity of the secondary battery.

[0188] In some embodiments, the volume percentage of the water vapor in the mixed gas is 1%-5%; optionally, the volume percentage of the water vapor in the mixed gas is 1.5%-2.5%. Exemplarily, the volume percentage of the water vapor in the mixed gas can be 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%. The volume percentage of the water vapor in the preset mixed gas within the above range can form appropriate amount of mesopores, which is beneficial to improve the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0189] In some embodiments, the activation treatment comprises at least 2 hours of immersion of the pre-carbonized body in a pore-forming liquid; the pore-forming liquid comprises a P-containing pore-forming liquid or a Zn-containing pore-forming liquid, wherein the P-containing pore-forming liquid has a P element addition amount of 9.5% to 32.4% of the mass of the porous carbon, or optionally, the P element addition amount of the P-containing pore-forming liquid is 18% to 24% of the mass of the porous carbon; the Zn-containing pore-forming liquid has a Zn element addition amount of 14% to 50% of the mass of the porous carbon, or optionally, the Zn element addition amount of the Zn-containing pore-forming liquid is 25% to 35% of the mass of the porous carbon. For example, the P element addition amount of the pore-forming liquid can be 9.5%, 12%, 15%, 18%, 20%, 24%, 27%, 30%, 32% of the mass of the porous carbon; for example, the Zn element addition amount of the pore-forming liquid can be 14%, 20%, 25%, 30%, 35%, 40%, 45%, 50% of the mass of the porous carbon. The P element or Zn element addition amount in the pore-forming liquid within the above range can form an appropriate amount of micropores and mesopores, which is conducive to improving the discharge gram capacity, charge gram capacity and first coulombic efficiency of the secondary battery. In addition, by setting the pre-carbonized body to be immersed in the pore-forming liquid for the above time, an appropriate amount of micropores and mesopores can be formed, which is conducive to improving the discharge gram capacity, charge gram capacity and first coulombic efficiency of the secondary battery.

[0190] For example, the P-containing pore-forming liquid can comprise at least one of a phosphoric acid solution, a polyphosphoric acid solution, and a phosphoric ester solution.

[0191] For example, the Zn-containing pore-forming liquid can be an aqueous zinc chloride solution.

[0192] In some embodiments, the solid content of the immersion mixture formed by the pre-carbonized body and the pore-forming liquid is 50wt% to 70wt%. For example, the solid content of the immersion mixture formed by the pre-carbonized body and the pore-forming liquid can be 50wt%, 55wt%, 60wt%, 65wt%, 70wt%. By setting the solid content of the immersion mixture within the above range, an appropriate amount of micropores and mesopores can be formed, which is conducive to improving the discharge gram capacity, charge gram capacity and first coulombic efficiency of the secondary battery.

[0193] In some embodiments, the activation treatment further comprises heat treatment of the immersion mixture formed by the pre-carbonized body and the pore-forming liquid at 400°C to 750°C for 1 hour to 12 hours. Optionally, the temperature is raised at a rate of 1°C / min to 20°C / min under the flow of nitrogen or inert gas. For example, the heat treatment process is carried out under the flow of nitrogen, and the temperature is raised to 600°C at a rate of 5°C / min and maintained for 2 hours. The heat treatment at 400°C to 750°C for 1 hour to 12 hours can cause the P-containing pore-forming liquid and the pre-carbonized body to chemically react, etch by chemical activation, and introduce a large number of pore structures into the skeleton structure of the pre-carbonized body.

[0194] In some embodiments, the pre-carbonization process is performed at a temperature of 400-600°C at a temperature increasing rate of 1-20°C / min and for a time period of 1-12h. For example, the pre-carbonization temperature can be 550°C and the pre-carbonization time period can be 6h. The pre-carbonization process is performed under the above conditions to facilitate the formation of a basic carbon skeleton structure, which is beneficial for subsequent pore formation.

[0195] In some embodiments, the carbonization process is performed at a temperature of 1000-1800°C at a temperature increasing rate of 2-20°C / min and for a time period of 1-12h. For example, the carbonization temperature can be 1250°C and the carbonization time period can be 10h. During the carbonization process, the precursor is dehydrated to form a stable hard carbon skeleton.

[0196] In some embodiments, the pre-carbonization process and the carbonization process are performed under a nitrogen or inert atmosphere. Optionally, the inert atmosphere is argon.

[0197] In some embodiments, after the pre-carbonization process, a crushing process is further included. The crushing process is performed by ball milling. The crushing process can crush the pre-carbonized body to a suitable particle size, which is beneficial for subsequent activation.

[0198] 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. For example, the biomass precursor can be coconut shell, pine wood powder, walnut shell, bamboo cane, straw, etc.; the synthetic polymer precursor can be phenolic resin, epoxy resin, unsaturated polyester resin. The use of the above-mentioned precursors to prepare hard carbon materials can form ordered carbon after activation, and can form appropriate micropores and mesopores.

[0199] In some embodiments, when the hard carbon precursor is a biomass precursor, after the crushing process, a deashing process is further included. The deashing process is performed by immersing the pre-carbonized body in an acidic aqueous solution at room temperature-95°C for 1-12h, and repeating 1-5 times. The deashing process can remove ash such as minerals and metal oxides in the pre-carbonized body, thereby improving the purity of the pre-carbonized body.

[0200] In some embodiments, after the activation process, a deashing process is further included. The deashing process is performed by immersing the pre-carbonized body in an acidic aqueous solution at room temperature-95°C for 1-12h, and repeating 1-5 times. The deashing process is used to remove residual P elements or Zn elements in the porous carbon precursor.

[0201] Examples

[0202] Hereinafter, an embodiment of the present disclosure will be described. The embodiment described below is exemplary and is for the purpose of explanation of the present disclosure and should not be understood as a limitation of the present disclosure. In the embodiment, unless a specific technique or condition is specified, the technique or condition described in the literature in the field or according to the product manual is used. The reagent or instrument used, unless the manufacturer is specified, is a conventional product that can be obtained on the market.

[0203] Example 1

[0204] Preparation of hard carbon material:

[0205] 1) Pre-carbonization treatment; the hard carbon precursor pine wood powder was placed in a tube furnace while nitrogen was introduced, and was heated to 550°C at a heating rate of 10°C / min and maintained for 6h to obtain a pre-carbonized body, and the flow rate of nitrogen was 500mL / min;

[0206] 2) Breaking treatment; the pre-carbonized body obtained above was subjected to ball milling breaking treatment using zirconia material milling beads and zirconia material milling tank, the mass ratio of pre-carbonized body to milling beads was 1:3, the rotation speed of the ball mill was 800rpm, the ball milling time was 8h, the milling beads were removed, and a pre-carbonized body with a volume particle size distribution Dv50 of 5.4um and a volume particle size distribution Dv90 of 11.3um was obtained;

[0207] 3) Deashing treatment; the pre-carbonized body subjected to breaking treatment in step 2) above was washed in hydrochloric acid aqueous solution, the acid washing temperature was in the range of 60°C, the acid washing time was 3h, the washing process was repeated for 4 times, then filtered, and the filter cake was repeatedly washed with deionized water and anhydrous ethanol until the filtrate pH>6; the washed filter cake was dried in a vacuum oven at 80°C for 24h;

[0208] 4) Activation treatment; the pre-carbonized body subjected to deashing treatment in step 3) above was subjected to activation treatment at 700°C under a preset mixed gas to obtain a porous carbon precursor; wherein the preset mixed gas comprises carbon dioxide gas, water vapor and inert gas, the proportion of carbon dioxide gas in the preset mixed gas is 12%, the proportion of water vapor in the preset mixed gas is 3%;

[0209] 5) Carbonization treatment; the porous carbon precursor prepared in step 4) above was placed in a tube furnace while nitrogen was introduced, and was heated to 1250°C at a heating rate of 10°C / min and maintained for 10h to obtain a porous carbon;

[0210] 6) coating treatment; mixing the porous carbon prepared in step 5) above with an aqueous polyacrylic acid solution with pH value of 1.5 to form a kneaded mixture, and placing the kneaded mixture in a double screw kneader for kneading for 6 h to obtain a hard carbon material; the rotation speed of the double screw kneader is 40 rpm, and the solid content of the kneaded mixture is 65 wt%, and in the kneaded mixture, the mass of the polyacrylic acid is 5% of the mass of the porous carbon.

[0211] Hard carbon material related tests:

[0212] 1) Pore volume test

[0213] First, the hard carbon material is pretreated to obtain a porous carbon material. Specifically, 2 g of hard carbon powder is added to a 250 ml beaker, 1 g of NaOH is added, and stirred uniformly. The beaker is placed in a water bath and heated to 80°C for 30 min under stirring. Then filter, wash the filter cake repeatedly with deionized water until the filtrate is neutral. The washed filter cake is dried in a vacuum oven at 80°C for 24.

[0214] Second, the porous carbon material powder is placed in a sample tube and vacuum degassed at 200°C for 12 h. The adsorption amount of nitrogen by the hard carbon material under different pressures is tested by an ASAP2460-physical adsorption analyzer, and the adsorption and desorption isotherms are drawn. The shape of the pores is determined according to the shape of the hysteresis loop, the micropore size distribution curve is fitted using the DFT model, and the micropore volume X, mesopore volume Y and total pore volume A of the hard carbon material are calculated.

[0215] 2) Methylene blue adsorption value test

[0216] The methylene blue adsorption value test is carried out according to the following steps:

[0217] ① Preparation of buffer solution: weigh 3.6 g of potassium dihydrogen phosphate and 14.3 g of sodium hydrogen phosphate, and dissolve in 1000 mL of water. ② Preparation of methylene blue solution: weigh 1.0 g of dry methylene blue, and dissolve in the buffer solution with a temperature of 60±1℃. After complete dissolution, cool to room temperature and filter into a 1000 mL volumetric flask. Wash the filter residue with buffer solution in several portions, and finally dilute to the mark with buffer solution to prepare a methylene blue solution with a concentration of 1000 mg / L. ③ Sample treatment: weigh a certain amount of ground and dried hard carbon material, and mix with the prepared methylene blue solution with a known concentration to absorb. Shake at room temperature for a certain time to allow the hard carbon material to fully adsorb the methylene blue. ④ Filtration: use a medium-speed qualitative filter paper with a diameter of 12.5 cm for filtration to separate the unadsorbed methylene blue solution. ⑤ Determination of absorbance: take the filtrate and determine the absorbance at the maximum absorption wavelength (665 nm) using a UV spectrophotometer. ⑥ Comparison and calculation: compare with the absorbance of copper sulfate standard color solution (0.4% mass fraction aqueous solution), adjust the amount of methylene blue solution added until the absorbance readings of the sample filtrate and copper sulfate standard color solution differ by no more than ±0.02. ⑦ Obtain the methylene blue concentration 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.

[0218] Preparation of button cell:

[0219] The hard carbon material prepared in Example 1 was mixed with the binder styrene-butadiene rubber (SBR), the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of solvent deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on the surface of the negative electrode current collector copper foil, dried in an oven, and then sliced for use. Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then NaPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Then, a metal sodium sheet was used as the counter electrode, and a glass fiber membrane was used as the separator membrane to assemble a CR2430 type button cell in an argon gas protected glove box.

[0220] Performance test of button cell

[0221] At 25℃, the button cell prepared above was first discharged at a current density of 10 mA / g to 0V, and the first circle discharge gram capacity (i.e. discharge gram capacity) of the button cell was recorded. Then, the button cell was charged at a current density of 10 mA / g to 2.0V, and the first circle charge gram capacity (i.e. charge gram capacity) of the button cell was recorded.

[0222] First coulombic efficiency (%) = first circle charge capacity / first circle discharge gram capacity × 100%.

[0223] Example 2-13

[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 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.

[0225] Comparative Example 1

[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 a total pore volume A of less than 0.2 cm³. 3 / g of hard carbon material.

[0227] Comparative Example 2

[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 hard carbon materials with a methylene blue adsorption value greater than 8 mg / g.

[0229] Comparative Example 3

[0230] 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.

[0231] 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.

[0232] Table 1:

[0233] Table 2:

[0234] 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-0.6cm 3 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, and the methylene blue adsorption value of the hard carbon material is greater than 8 mg / g, the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. In Comparative Example 3, because the total pore volume of the porous carbon is less than 0.2 cm3 / g, and the methylene blue adsorption value of the hard carbon material is greater than 8 mg / g, the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. Within the range of the suitable total pore volume and the methylene blue adsorption value, the pore volume ratio X / Y of micropores to mesopores is within the suitable range, for example, 5.6-33, and particularly, 7-16, which can further balance the discharge gram capacity, the charge gram capacity and the first coulombic efficiency. 3 / g, and the methylene blue adsorption value of the hard carbon material is greater than 8 mg / g, the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. In Comparative Example 3, because the total pore volume of the porous carbon is less than 0.2 cm3 / g, and the methylene blue adsorption value of the hard carbon material is greater than 8 mg / g, the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. Within the range of the suitable total pore volume and the methylene blue adsorption value, the pore volume ratio X / Y of micropores to mesopores is within the suitable range, for example, 5.6-33, and particularly, 7-16, which can further balance the discharge gram capacity, the charge gram capacity and the first coulombic efficiency.

[0235] Example 14

[0236] Preparation of the hard carbon material:

[0237] 1) pre-carbonization treatment; the hard carbon precursor epoxy resin was placed in a tube furnace, and heated to 550℃ at a heating rate of 10℃ / min and kept for 6h while nitrogen was introduced, to obtain a pre-carbonized body, and the flow rate of nitrogen was 500 mL / min;

[0238] 2) breaking treatment; the pre-carbonized body obtained above was subjected to ball milling breaking treatment with zirconia material milling beads and zirconia material milling tank, the mass ratio of the pre-carbonized body to the milling beads was 1:3, the rotating speed of the ball mill was 800 rpm, the ball milling time was 8h, the milling beads were removed, and a pre-carbonized body with a volume particle size distribution Dv50 of 5.1 μm and a volume particle size distribution Dv90 of 11 μm was obtained;

[0239] 3) activation treatment; the pre-carbonized body subjected to the breaking treatment in step 2) above was immersed in a pore-forming liquid phosphoric acid aqueous solution for 6h, and then placed in a tube furnace, and heated to 600℃ at a heating rate of 5℃ / min and kept for 2h while nitrogen was introduced, to obtain a porous carbon precursor; wherein, the added amount of P element was 12.2% of the mass of the porous carbon; and the solid content of the impregnated mixture formed by the pre-carbonized body and the pore-forming liquid was 65%;

[0240] 4) deashing treatment; the porous carbon precursor in step 4) above was washed in a hydrochloric acid aqueous solution, the temperature range of acid washing was 60℃, the acid washing time was 3h, the washing process was repeated for 4 times, and then filtered, the filter cake was washed repeatedly with deionized water and anhydrous ethanol until the pH of the filtrate was >6; the washed filter cake was dried in a vacuum oven at 80℃ for 24h;

[0241] 5) carbonization treatment; the porous carbon precursor subjected to the deashing treatment in step 4) above was placed in a tube furnace, and heated to 1250℃ at a heating rate of 10℃ / min and kept for 10h while nitrogen was introduced, to obtain a porous carbon;

[0242] 6) coating treatment; mixing the porous carbon prepared in step 5) above with an aqueous polyacrylic acid solution with pH value of 1.5 to form a kneaded mixture, and placing the kneaded mixture in a twin-screw kneader for kneading for 6 h to obtain a hard carbon material; the rotation speed of the twin-screw kneader is 40 rpm, and the solid content of the kneaded mixture is 65 wt%, and in the kneaded mixture, the mass of the polyacrylic acid is 5% of the mass of the porous carbon.

[0243] Assembled into a button-type half cell in a similar manner to Example 1.

[0244] Examples 15-18

[0245] The hard carbon material was prepared in a similar manner to Example 14, and was assembled into a button-type half cell, with the only difference being that in the preparation of the hard carbon material, the process conditions of the activation treatment were adjusted according to Table 3 below to obtain hard carbon materials with different total pore volumes A of the porous carbon, as shown in Table 3.

[0246] The process parameters for preparing the hard carbon material in Examples 14-18 are shown in Table 3 below, and the performance parameters of the prepared hard carbon material and the test results of the button-type half cell are shown in Table 4 below.

[0247] Table 3:

[0248] Table 4:

[0249] As can be seen from Table 3 and Table 4 above, in Examples 14-18, by reasonably adjusting the content of phosphoric acid in the pore-forming liquid or the impregnation time, the pore structure of the hard carbon material can be adjusted so that the total pore volume of the porous carbon is between 0.2 cm 3 / g-0.6 cm 3 / g, and the methylene blue adsorption value of the hard carbon material is less than 8 mg / g, which significantly improves the first coulombic efficiency and the charge gram capacity, while taking into account the high discharge gram capacity.

[0250] It should be noted that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect within the scope of the technical solutions of the present disclosure are all included in the technical scope of the present disclosure. In addition, within the scope of the main idea of the present disclosure, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present disclosure.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a hard carbon material, the hard carbon material comprising a core and an organic coating layer coating the core, the core comprising porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g ≤ A ≤ 0.6 cm 3 / g; the hard carbon material has a methylene blue adsorption value Z of 8 mg / g or less.

2. The negative electrode sheet according to claim 1, wherein the hard carbon material has a methylene blue adsorption value Z of 4 mg / g or less.

3. The negative electrode sheet according to claim 1 or 2, wherein 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.

4. The negative electrode sheet according to claim 3, wherein 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, wherein the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy 85%≤X / A≤97%.

6. The negative electrode sheet according to any one of claims 3 to 5, wherein the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy 3%≤Y / A≤15%.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein 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 to 7, wherein in the hard carbon material, the mass of the organic coating layer is 0.5 wt% to 10 wt% of the porous carbon.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein the hard carbon material satisfies at least one of the following: (1) the hard carbon material has a compaction density of 0.55 g / cm3 at 5 t 3 -1.0 g / cm 3 ; (2) the tap density of the hard carbon material is 0.34 g / cm 3 -0.8 g / cm 3 ; (3) the hard carbon material has a volume distribution particle size Dv50 of 3.0 μm to 7.9 μm; (4) the hard carbon material has a volume distribution particle size Dv90 of 8 μm to 15 μm; (5) the specific surface area BET of the hard carbon material is 0.1 m 2 / g - 0.8 m 2 / g. 10.A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 9.

11. The secondary battery according to claim 10, wherein the secondary battery further comprises a positive electrode sheet comprising at least one selected from transition metal oxides, polyanion compounds and Prussian blue compounds as a positive electrode active material. 12.An electric device comprising the secondary battery according to claim 10 or 11. 13.A hard carbon material comprising a core and an organic coating layer coating the core, the core comprising porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g ≤ A ≤ 0.6 cm 3 / g; the hard carbon material has a methylene blue adsorption value Z of 8 mg / g or less.

14. The hard carbon material of claim 13, wherein, the hard carbon material has a methylene blue adsorption value Z of 4 mg / g or less.

15. The hard carbon material of claim 13 or 14, wherein, 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.

16. The hard carbon material of claim 15, wherein, 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 of claim 15 or 16, wherein, the total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy 85%≤X / A≤97%.

18. The hard carbon material of any one of claims 15-17, wherein, the total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy 3%≤Y / A≤15%.

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

20. The hard carbon material of any one of claims 13-19, wherein, in the hard carbon material, the mass of the organic coating layer is 0.5 wt% to 10 wt% of the porous carbon.

21. The hard carbon material of any one of claims 13-20, wherein, the hard carbon material satisfies at least one of the following: (1) the hard carbon material has a compaction density of 0.55 g / cm3 at 5 t 3 -1.0 g / cm 3 ; (2) the tap density of the hard carbon material is 0.34 g / cm 3 -0.8 g / cm 3 ; (3) the hard carbon material has a volume distribution particle size Dv50 of 3.0 μm to 7.9 μm; (4) the hard carbon material has a volume distribution particle size Dv90 of 8 μm to 15 μm; (5) the specific surface area BET of the hard carbon material is 0.1 m 2 / g - 0.8 m 2 / g. 22.A method for preparing a hard carbon material, the method comprising: performing a pre-carbonization treatment on a hard carbon precursor to obtain a pre-carbonized body; performing an activation treatment on the pre-carbonized body to obtain a porous carbon precursor; performing a carbonization treatment on the porous carbon precursor to obtain a porous carbon; performing a coating treatment on the porous carbon, wherein the coating treatment comprises a kneading treatment of a kneading mixture formed by the porous carbon and an aqueous solution of a coating raw material, wherein a solid content of the kneading mixture is 55wt%-75wt%, and a pH value of the aqueous solution of the coating raw material is ≤3.

23. The method of making according to claim 22, wherein, The solid content of the kneading mixture is 63wt%-67wt%, and the pH value of the aqueous solution of the coating raw material is 1.2-1.

8.

24. The method of manufacturing according to claim 22 or 23, wherein, The coating raw material comprises at least one of polyacrylic acid, a polyacrylic acid salt, and a copolymer of polyacrylic acid.

25. The method of making according to any one of claims 22-24, wherein, A mass of the coating raw material is 0.5%-10% of a mass of the porous carbon, and the kneading treatment is performed for at least 0.5h.

26. The method of making according to any one of claims 22-25, wherein, The kneading treatment is performed in a double screw kneader with a rotation speed of 10rpm-50rpm.

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

28. The method of manufacturing according to claim 27, wherein, The volume ratio of the carbon dioxide gas in the preset mixed gas is 5%-20%, and the volume ratio of the water vapor in the mixed gas is 1%-5%.

29. The method of making according to any one of claims 22-28, wherein, The activation treatment comprises immersing the pre-carbonized body in a pore-forming liquid for at least 2h. The pore-forming liquid comprises a P-containing pore-forming liquid or a Zn-containing pore-forming liquid, wherein an added amount of P in the P-containing pore-forming liquid is 9.5%-32.4% of a mass of the porous carbon, and an added amount of Zn in the Zn-containing pore-forming liquid is 14%-50% of the mass of the porous carbon.

30. The method of manufacturing according to claim 29, wherein, A solid content of an immersion mixture formed by the pre-carbonized body and the pore-forming liquid is 50wt%-70wt%.

31. The method of manufacturing according to claim 29 or 30, wherein, The activation treatment further comprises heat-insulating the immersion mixture formed by the pre-carbonized body and the pore-forming liquid after immersion at 400℃-750℃ for 1h-12h.

32. The method of making according to any one of claims 22-31, wherein, The pre-carbonization treatment is performed at a temperature increasing rate of 1℃ / min-20℃ / min to 400℃-600℃ and maintained for 1h-12h.

33. The method of making according to any one of claims 22-32, wherein, The carbonization treatment is performed at a temperature increasing rate of 2℃ / min-20℃ / min to 1000℃-1800℃ and maintained for 1h-12h.

34. The method of making according to any one of claims 22-33, wherein, The hard carbon precursor comprises at least one of a biomass precursor and a synthetic polymer precursor. The synthetic polymer precursor comprises a compound composed of C, H, and O elements.

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