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

Abstract

Disclosed in the present disclosure are a negative electrode sheet, a secondary battery, an electric device, and 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, wherein the negative electrode film layer comprises a hard carbon material, and the hard carbon material comprises a core and a carbon coating layer that coats the core; the core comprises porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm3 / g≤A≤0.6 cm3 / g; and the methylene blue adsorption capacity Z of the hard carbon material is less than or equal to 10 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. 202410544868.1, 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 hydropower, thermal power, wind power 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 coulomb 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 and has improved charge gram capacity and initial coulomb 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 a carbon coating layer coating the core; the core comprises porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3mg / g. 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, and collapse does not occur during the insertion and extraction of active ions, which is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery. In addition, by providing a carbon 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 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 carbon coating layer has high compactness, can effectively isolate the electrolyte, and inhibit the electrolyte molecules from entering the interior of the porous carbon, which is further conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0008] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤5 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.

[0009] In some embodiments, the porous carbon includes micropores with a pore size of 0.4-2.5 nm and mesopores with a pore size of 2.5-10 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: 8≤X / Y≤13. 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 the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0010] 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.

[0011] 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 the first coulombic efficiency of the secondary battery.

[0012] In some embodiments, the I D / I G is 0.83-1.26; wherein, I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 , and I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1G peak intensity. The I D / I G Within the above range, it is reflected that the surface coating layer has a suitable degree of order and a suitable reactivity, so as to enable the active ions to be transported.

[0013] In some embodiments, the hard carbon material satisfies at least one of the following:

[0014] (1) The hard carbon material has a tap density of 0.6 g / cm 3 -1.05 g / cm 3 When the powder 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 thus to improve the kinetic performance of the secondary battery.

[0015] (2) The hard carbon material has a tap density of 0.4 g / cm 3 -0.85 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.

[0016] (3) The hard carbon material has a volume distribution particle size Dv50 of 3.0 μm-7.9 μm;

[0017] (4) The hard carbon material has a volume distribution particle size Dv90 of 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 and to 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 the active ions can be shortened, and thus the kinetic performance of the secondary battery is improved.

[0018] (5) The hard carbon material has a specific surface area BET of 0.1 m 2 / g-10 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 can be reduced, and it is beneficial to improve the initial coulombic efficiency of the secondary battery.

[0019] A second aspect of the present disclosure provides a secondary battery comprising the negative electrode sheet of the first aspect of the present disclosure.

[0020] In some embodiments, the secondary battery further comprises a positive electrode sheet. The positive electrode sheet comprises at least one selected from transition metal oxides, polyanion compounds, and Prussian blue compounds as a positive electrode active material.

[0021] The secondary battery in the present disclosure has improved charge specific capacity and initial coulombic efficiency.

[0022] The third aspect of the present disclosure provides a power consuming device comprising the secondary battery of the second aspect of the present disclosure.

[0023] 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.

[0024] The fourth aspect of the present disclosure provides a hard carbon material comprising a core and a carbon coating layer coating the core; 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 ≤10 mg / g. 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, which is conducive to improving the charge gram capacity and the initial coulombic efficiency of the secondary battery. In addition, by setting the carbon 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 carbon coating layer has high compactness, can effectively isolate the electrolyte, and inhibit the electrolyte molecules from entering the interior of the porous carbon, which is further conducive to improving the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0025] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤5 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.

[0026] In some embodiments, the porous carbon comprises micropores with a pore size of 0.4 nm to 2.5 nm and mesopores with a pore size of 2.5 nm to 10 nm; the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 5.6%≤X / Y≤33%, and X+Y=A. In some embodiments, the total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 8≤X / Y≤13. 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.

[0027] 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.

[0028] 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 transmission channels for active ions can be provided, thereby improving the utilization of micropores and facilitating the improvement of the charge capacity and the initial coulombic efficiency of the secondary battery.

[0029] In some embodiments, the I D / I G of the hard carbon material is 0.83-1.26; wherein, I D represents the D-peak intensity of the Raman spectrum at 1350±50 cm -1 -1; I G represents the G-peak intensity of the Raman spectrum at 1580±50 cm -1 -1. The I D / I G of the hard carbon material is within the above range, which reflects that the surface coating layer has a proper degree of order and a proper reactivity, and can enable the transmission of active ions.

[0030] In some embodiments, the hard carbon material satisfies at least one of the following:

[0031] (1) The hard carbon material has a tap density of 0.6 g / cm 3 -1.05 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 transmission performance of active ions and electrons, and to further improve the kinetic performance of the secondary battery.

[0032] (2) The hard carbon material has a tap density of 0.4 g / cm 3 -0.85 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.

[0033] (3) The hard carbon material has a volume distribution particle size Dv50 of 3.0 μm-7.9 μm;

[0034] (4) The hard carbon material has a volume distribution particle size Dv90 of 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 and to reduce the occurrence of side reactions, thereby improving the initial coulombic efficiency of the secondary battery. At the same time, the bulk transmission path of active ions can be shortened, thereby improving the kinetic performance of the secondary battery.

[0035] (5) The hard carbon material has a specific surface area BET of 0.1 m 2 / g-10 m 2g. The specific surface area of the hard carbon material in the above range can reduce the consumption of active ions in the first charging, and is beneficial to improve the first coulombic efficiency of the secondary battery.

[0036] The fifth aspect of the present disclosure also provides a method for preparing a hard carbon material, the method comprising:

[0037] performing a pre-carbonization treatment on the hard carbon precursor to obtain a pre-carbonized body;

[0038] performing an activation treatment on the pre-carbonized body to obtain a porous carbon precursor;

[0039] performing a coating treatment on the porous carbon precursor to form a hard carbon precursor; wherein the coating treatment comprises a kneading treatment of kneading a kneaded mixture formed by the porous carbon precursor and an aqueous solution of a coating raw material, and a solidification treatment of solidifying the product of the kneading treatment; the solid content of the kneaded mixture is 55wt%-75wt%;

[0040] performing a carbonization treatment on the hard carbon precursor to obtain a hard carbon material.

[0041] In some embodiments, the mass ratio of the coating raw material to the porous carbon precursor is 0.5:10-2:10, and the kneading treatment is performed for at least 0.5h. The mass of the coating raw material in the above range can form a coating layer with suitable density, and can improve the charge capacity and the first coulombic efficiency of the secondary battery without affecting the kinetic performance of the secondary battery and increasing the impedance of the secondary battery.

[0042] In some embodiments, the solidification treatment is performed at 120°C-250°C for at least 1h. The solidification under the above conditions can improve the crosslinking degree of the carbon coating raw material, thereby improving the thermal stability of the carbon coating layer and reducing the volume shrinkage of the carbon coating layer in the subsequent carbonization process, so that the carbon coating layer will not be broken in the subsequent carbonization process, thereby improving the density of the coating layer.

[0043] In some embodiments, the coating raw material comprises a prepolymer of a thermosetting resin.

[0044] In some embodiments, the thermosetting resin comprises at least one of a phenolic resin, an epoxy resin, an unsaturated polyester resin, and a furan resin. Using the above thermosetting resin as the coating raw material of the carbon coating layer has the advantages of high uniformity, high density, and high coating integrity.

[0045] 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.

[0046] In some embodiments, the activation treatment comprises subjecting the pre-carbonized body to a preset mixed gas at 700-950°C, 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 at the above temperature can form appropriate amounts of mesopores and micropores, which is conducive to improving the discharge gram capacity of the secondary battery.

[0047] 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 in the above 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 in the above 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.

[0048] In some embodiments, the activation treatment comprises subjecting the pre-carbonized body to a P-containing pore-forming liquid or a Zn-containing pore-forming liquid for at least 2h; the added amount of P element in the P-containing pore-forming liquid is 9.5-32.4% of the mass of the pre-carbonized body, and the added amount of Zn element in the Zn-containing pore-forming liquid is 14-50% of the mass of the pre-carbonized body. The added amount of P element or Zn element in the pore-forming liquid in the above range can form appropriate amounts of micropores and mesopores, which is conducive to improving the discharge gram capacity, the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0049] In some embodiments, the solid content of the pre-carbonized body in the impregnation mixture formed by the pre-carbonized body and the pore-forming liquid is 50-70wt%. By setting the solid content of the impregnation mixture in the above range, 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 activation treatment further comprises subjecting the impregnation mixture formed by the impregnated pre-carbonized body and the pore-forming liquid to heat preservation at 400-750°C for 1-12h. In this way, the P-containing or Zn-containing pore-forming liquid and the pre-carbonized body can be chemically reacted, etching is carried out by chemical activation, and a large number of pore structures are introduced into the pre-carbonized body skeleton structure.

[0051] In some embodiments, the pre-carbonization treatment is carried out at a temperature increasing rate of 1-20°C / min to 400-600°C and maintained for 1-12h. The pre-carbonization treatment under the above conditions is conducive to forming a carbon basic skeleton structure, which is convenient for subsequent pore-forming.

[0052] In some embodiments, the carbonization treatment is performed at a temperature increasing rate of 2-20 ℃ / min to 1000-1800 ℃ and maintained for 1-12 h. During the carbonization process, the precursor releases H, O and other heteroatoms to form a stable hard carbon skeleton, and the coating layer is more compact, which is beneficial to the charge capacity and the initial coulombic efficiency of the secondary battery.

[0053] 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 prepared by using the above-mentioned precursor has ordered carbon formed after activation, and can form appropriate micropores and mesopores. BRIEF DESCRIPTION OF DRAWINGS

[0054] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0055] FIG. 2 is an exploded view of the battery cell according to an embodiment of the present disclosure shown in FIG. 1.

[0056] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0057] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0058] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present disclosure shown in FIG. 4.

[0059] FIG. 6 is a schematic view of a power-using device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0060] REFERENCE NUMERALS:

[0061] 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 power-using device, the hard carbon material and the method for manufacturing the same according to the present disclosure will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description 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 sodium ions.

[0070] Currently, hard carbon is generally 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 a carbon 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 ≤10 mg / g.

[0074] When the hard carbon material is used as the negative active material of a secondary battery, active ions are first transmitted to defect sites in the hard carbon material for adsorption, and then transmitted to the pores of the hard carbon material for filling. The active ions exist in the form of clusters in the pores to provide gram capacity. In the related art, the gram capacity of the hard carbon material is improved by forming a large number of pores with large sizes. 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 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, large-size pore structures easily allow electrolyte molecules to enter. The entry of electrolyte molecules into the pore structures not only occupies the storage sites of 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 in 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 hard carbon material will not collapse during the insertion and extraction of active ions, which is beneficial to improve the charging gram capacity and the first coulomb efficiency of the secondary battery. In addition, by providing a carbon 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 in the above range, so that the carbon coating layer has high density, can effectively isolate the electrolyte, inhibit the electrolyte molecules from entering the inside of the porous carbon, and further improve the charging gram capacity and the first coulomb efficiency of the secondary battery.

[0076] In addition, the presence of the carbon coating layer improves the stability of the SEI film in the secondary battery, thereby achieving high charging gram capacity and first coulomb efficiency.

[0077] It should be noted that since the molecular diameter of methylene blue is close to the size of the commonly used ester solvent of electrolyte (about 1 nm), the methylene blue adsorption value can accurately characterize the area that the electrolyte can enter, that is, the density of the carbon 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 Z of the hard carbon material is ≤5 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, 0.38 cm 3 / g, 0.4 cm 3 / g, 0.41 cm 3 / g, 0.42 cm 3 / g, 0.43 cm 3 / g, 0.44 cm 3 / g, 0.45 cm 3 / g, 0.46 cm 3 / g, 0.47 cm 3 / g, 0.48 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, 1.5 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, 6.0 mg / g, 7.0 mg / g, 8.0 mg / g, 9.0 mg / g, 10 mg / g, or any value within a range defined by any two of the values.

[0081] In some embodiments, the material of the carbon coating layer is a prepolymer of a thermosetting resin. For example, the thermosetting resin can be at least one of a phenolic resin, an epoxy resin, an unsaturated polyester resin, and a furan resin. Using the prepolymer of the thermosetting resin as the carbon coating layer has the advantages of high uniformity, high density, and high completeness of coating.

[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 8≤X / Y≤13. For example, X / Y can be 5.7, 7.6, 8.0, 6.0, 10.4, 11.0, 12.1, 13, 15, 20, 25, 30, 33, or any value within a range defined by any two of the values.

[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 transport channels for active ions, enabling the active ions to be effectively transported into the micropores, thereby improving the utilization rate of the micropores and the discharge gram capacity and the initial coulombic efficiency of the secondary battery.

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

[0085] In some embodiments, the total pore volume of the micropores X satisfies 85%≤X / A≤97% with respect to the total pore volume A of the porous carbon. Alternatively, the total pore volume of the micropores X satisfies 90≤X / A≤93 with respect to the total pore volume A of the porous carbon. Exemplarily, X / A can be any value within a range consisting of 85%, 86%, 87%, 90%, 91%, 93%, 95%, 97%, or any two of them. The total pore volume of the micropores X 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 pore volume of the mesopores Y satisfies 3%≤Y / A≤15% with respect to the total pore volume A of the porous carbon. Alternatively, the total pore volume of the mesopores Y satisfies 7≤Y / A≤10 with respect to the total pore volume A of the porous carbon. Exemplarily, Y / A can be any value within a range consisting of 3%, 5%, 7%, 8%, 10%, 12%, 15%, or any two of them. The total pore volume of the mesopores Y 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 micropores and being beneficial to improve the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0087] In some embodiments, the I D / I G of the hard carbon material is 0.83-1.26; wherein, I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 -1.26; wherein, I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1 -1.26; wherein, I D / I G of the hard carbon material is 0.83, 0.9, 1.0, 1.1, 1.2, 1.26, or any value within a range consisting of any two of them. The I D / I G Within the above range, it reflects that the surface coating layer has a proper order degree and a proper reactivity, which can enable the transport of active ions.

[0088] In some embodiments, the hard carbon material satisfies at least one of the following:

[0089] (1) The compact density of the hard carbon material at 5t is 0.6 g / cm 3 -1.05 g / cm 3 . When the powder compact 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 transport performance of active ions and electrons, and to further improve the kinetic performance of the secondary battery.

[0090] (2) The tap density of the hard carbon material is 0.4 g / cm 3 -0.85 g / 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.

[0091] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm.

[0092] (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 and reduce the occurrence of side reactions, thereby improving 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.

[0093] (5) The specific surface area BET of the hard carbon material is 0.1 m 2 / g-10 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 charge, which is beneficial to improve the initial coulombic efficiency of the secondary battery.

[0094] 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.

[0095] 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 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 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.

[0096] In the present disclosure, before testing the pore volume of the porous carbon, the hard carbon material is pretreated to break the carbon coating layer so that the gas of nitrogen adsorption / desorption test can enter the porous carbon. An exemplary treatment procedure includes adding 2 g of hard carbon powder into a 250 ml beaker, adding 1 g of NaNO3, slowly adding 46 ml of concentrated sulfuric acid and stirring uniformly. The beaker is placed in an ice water bath, 6 g of KMnO4 is slowly added under stirring, and the temperature is kept below 20°C during the process. After 5 minutes, the ice water bath is removed, and the temperature is raised to 35°C for 30 min. Then 92 ml of deionized water is added, stirred for 15 minutes, and finally 80 ml of 3% H2O2 solution at 60°C is added to reduce the excess KMnO4 until no obvious bubbles are generated. Finally, filtration is performed, the filter cake is washed repeatedly with deionized water and anhydrous ethanol until the pH of the filtrate is > 6. The washed filter cake is dried in a vacuum oven at 80°C for 24 hours.

[0097] In the present disclosure, the I D / I G value of the hard carbon material can be tested using 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: excitation wavelength of 532 nm, grating of 600 lines, objective lens of 50 times, integration time of 10 s, cumulative number of 3 times, surface scanning, 100 points of D peak and G peak intensity are obtained, 100 points of I D / I G are calculated, 30 I D / I G with the largest and the smallest are removed, and the average value of the remaining 40 points is the I D / I G of the material. The test instrument can use a Horiba LabRAM HR800 Raman spectrometer.

[0098] In the present disclosure, the compaction density of the hard carbon material is the meaning known in the art, and can be determined by instruments and methods known in the art. For example, GB / T 24533-2009 can be referred to, and the compaction density of the material at 5 t pressure can be determined by an electronic pressure testing machine (for example, a UTM7305 type electronic pressure testing machine). An exemplary test method is as follows: 1 g of sample powder is weighed and added into a mold with a bottom area of 1.327 cm 2 , and is pressed to 5 t, kept for 30 s, then released, kept for 10 s, and then recorded and calculated to obtain the powder compaction density of the material at 5 t pressure.

[0099] In the present disclosure, the tap density of the hard carbon material is in the meaning known in the art and can be measured by using the instruments and methods known in the art. For example, it can be measured by referring to GB / T 5162-2006 using a powder tap density tester. The testing instrument can be Dandong Bitai 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 cylinder volume 25 mL.

[0100] In the present disclosure, the volume distribution particle size Dv50 and Dv90 of the hard carbon material are in the meaning known in the art, which respectively represent the particle size corresponding to the cumulative volume distribution percentage of 50% and 90% of the material, and can be measured by using the instruments and methods known in the art. For example, it can be measured 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.

[0101] 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 measured by using the instruments and methods known in the art. For example, it can be measured 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.

[0102] In the present disclosure, the microstructure of the hard carbon material can be observed by a scanning electron microscope or a transmission electron microscope.

[0103] 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.

[0104] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper 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 (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.).

[0105] In some embodiments, the negative active material comprises the hard carbon material provided in the above embodiments or prepared according to the preparation method in the above embodiments.

[0106] In some embodiments, the negative film layer further optionally comprises 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).

[0107] In some embodiments, the negative film layer further optionally comprises a conductive agent. The conductive agent can be selected from at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the negative film layer further optionally comprises other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0109] 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 a negative current collector, and after drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0110] Secondary battery

[0111] 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.

[0112] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack. The following are described respectively.

[0113] Generally, a secondary battery cell comprises a positive electrode sheet, a negative electrode sheet in the above embodiments, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0114] [Positive electrode sheet]

[0115] The positive electrode sheet comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector, and the positive film layer comprises the positive active material of the first aspect of the present disclosure.

[0116] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0117] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum 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 (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.).

[0118] In some embodiments, the battery cell is a sodium ion battery, and the positive electrode active material can employ 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.

[0119] As an alternative technical solution of the present disclosure, the polyanion compound can be a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4) n- anion unit. 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 the valence of (YO4) n- . The polyanion compound can also be a compound having a sodium ion, a tetrahedral (YO4) n- anion unit, and a halogen anion. 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 the valence of (YO4) n- ; and the halogen can be at least one of F, Cl, and Br.

[0120] The polyanion compound can also be a compound having a sodium ion, a tetrahedral (YO4)n- anionic units, polyhedral units (ZO y ) m+ and optional halide anions. Y can be at least one of P, S, and Si, and n represents the valence state of (YO4) n- Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence state of (ZO y ) m+ Halide can be at least one of F, Cl, and Br. Polyanionic compounds are, for example, NaFePO4, Na3V2(PO4)3, NaM’PO4F (M’ is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y at least one of (0≤y≤1).

[0121] As an optional embodiment of the present disclosure, the chemical formula of the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d wherein the A element represents an alkali metal element that dopes and substitutes the Na element, the M element represents a metal element that substitutes the V element, the D element represents a doping element that substitutes the P element, the Q element represents a doping element that substitutes the F element, the D element includes at least one of Si and S, and the Q element includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, 0≤d≤0.2z. Optionally, the A element includes at least one of K and Li; and the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0122] 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.

[0123] As an optional embodiment of the present disclosure, the chemical formula of the polyanionic compound can be Na4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0124] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na a Me b Me’ c (CN)6, wherein Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0125] In other embodiments, the battery cell can also be a lithium-ion battery, and the positive electrode active material can be the positive electrode active material known in the art for lithium-ion batteries.

[0126] In the listing of the positive electrode active material in the present disclosure, the molar content of oxygen is only the theoretical value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0127] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0128] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0130] [Electrolyte]

[0131] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The kind of electrolyte is not particularly limited in the present disclosure, and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0132] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0133] 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-trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorobisoxalate borate, sodium bisoxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorodioxalate phosphate.

[0134] 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-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0135] 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0136] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also 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.

[0137] [Separator]

[0138] In some embodiments, the battery cell further includes a separator. The kind of separator is not particularly limited in the present disclosure, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0139] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0140] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly through a winding process or a stacking process.

[0141] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0142] 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, or the like. 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 plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0143] The present disclosure does not particularly limit the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG. 1 is a battery cell 5 of a square structure as an example.

[0144] In some embodiments, referring to FIG. 2, the outer package can include a shell 51 and a top cover assembly 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated 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 a person skilled in the art according to specific actual needs.

[0145] 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 a person skilled in the art according to the application and capacity of the battery module.

[0146] 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 arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0147] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0148] In some embodiments, the above 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, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0149] 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 an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0150] Electric device

[0151] 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.

[0152] The electric 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 supply of the electric device or as an energy storage unit of the electric device. The electric 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.

[0153] As the electric device, the battery monomer, the battery module or the battery pack can be selected according to the use requirement thereof.

[0154] FIG. 6 is an electric device as an example. The electric 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 electric device, the battery pack or the battery module can be used.

[0155] 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 supply.

[0156] Hard carbon material

[0157] A 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 a carbon coating layer coating the core; the core includes porous carbon; the total pore volume A of the porous carbon satisfies: 0.2 cm 3 / g≤A≤0.6 cm 3mg / g. 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, and collapse does not occur during the insertion and extraction of active ions, which is conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery. In addition, by providing a carbon 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 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 carbon coating layer has high compactness, which can effectively isolate the electrolyte and inhibit the electrolyte molecules from entering the interior of the porous carbon, further conducive to improving the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0158] In some embodiments, the methylene blue adsorption value Z of the hard carbon material is ≤5 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.

[0159] In some embodiments, the porous carbon includes micropores with a pore size of 0.4-2.5 nm and mesopores with a pore size of 2.5-10 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: 8≤X / Y≤13. 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 the charge gram capacity and the first coulombic efficiency of the secondary battery.

[0160] 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.

[0161] 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, an appropriate 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.

[0162] In some embodiments, the I D / I G is 0.83-1.26; wherein, I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 , and I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1G peak intensity. The I D / I G Within the above range, it is reflected that the surface coating layer has a suitable degree of order and a suitable reactivity, so as to enable the active ions to be transported.

[0163] In some embodiments, the hard carbon material satisfies at least one of the following:

[0164] (1) The hard carbon material has a tap density of 0.6 g / cm 3 -1.05 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 transport performance of the active ions and electrons, and thus to improve the kinetic performance of the secondary battery.

[0165] (2) The hard carbon material has a tap density of 0.4 g / cm 3 -0.85 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.

[0166] (3) The hard carbon material has a volume distribution particle size Dv50 of 3.0 μm-7.9 μm;

[0167] (4) The hard carbon material has a volume distribution particle size Dv90 of 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 and to reduce the occurrence of side reactions, so as to improve the initial coulombic efficiency of the secondary battery. At the same time, it can also shorten the bulk transport path of the active ions, and thus improve the kinetic performance of the secondary battery.

[0168] (5) The hard carbon material has a specific surface area BET of 0.1 m 2 / g-10 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 initial coulombic efficiency of the secondary battery.

[0169] Method for preparing hard carbon material

[0170] In a fifth aspect, the present disclosure provides a method for preparing the 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 coating treatment on the porous carbon precursor to form a hard carbon precursor; wherein the coating treatment comprises a kneading treatment of kneading a kneading mixture formed by the porous carbon precursor and an aqueous solution of a coating raw material, and a solidification treatment of solidifying a product of the kneading treatment; a solid content of the kneading mixture is 55wt%-75wt%; and performing a carbonization treatment on the hard carbon precursor to obtain the hard carbon material. The total pore volume A of the formed porous carbon satisfies: 0.2cm 3 / g≤A≤0.6cm 3 / g; and a methylene blue adsorption value Z of the formed hard carbon material is ≤10mg / g.

[0171] The present disclosure obtains a porous carbon precursor by performing a pre-carbonization and an activation pore-forming treatment on a hard carbon precursor, and forms a hard carbon precursor with a coating layer by performing a kneading treatment of the porous carbon precursor and an aqueous solution of a coating raw material, and a solidification treatment of a product of the kneading treatment, and then obtains a hard carbon material with a coating layer by performing a carbonization treatment on the hard carbon precursor with a coating layer. Under the above solid content condition, the porous carbon precursor and the coating raw material are kneaded to make them more fully mixed and sheared, so that the formed coating layer has good compactness, and on this basis, the thermal stability of the coating layer is further improved by the solidification treatment, so that the carbon coating layer will not be broken in the subsequent carbonization process. Therefore, the coating layer in the present disclosure can block electrolyte molecules from entering the inside of the porous carbon, which is conducive to improving the charge gram capacity and the initial coulombic efficiency of the secondary battery.

[0172] For example, the solid content of the kneading mixture is 55wt%, 60wt%, 62wt%, 65wt%, 68wt%, 71wt%, or 75wt%.

[0173] In some embodiments, the solid content of the kneading mixture is 62wt%-68wt%. The solid content of the kneading mixture in the above range is conducive to forming a coating layer with suitable compactness, which can improve the charge gram capacity and the initial coulombic efficiency of the secondary battery without affecting the kinetic performance of the secondary battery.

[0174] In some embodiments, the mass ratio of the coating raw material to the porous carbon precursor is 0.5:10-2:10, and the kneading process is performed for at least 0.5 h. Alternatively, the mass ratio of the coating raw material to the porous carbon precursor is 1.0:10-1.5:10, and the kneading process is performed for at least 5 h-7 h. The mass of the coating raw material in the above range can form a coating layer with a suitable density, which can improve the charge gram capacity and the first coulomb efficiency of the secondary battery without affecting the kinetic performance of the secondary battery and increasing the impedance of the secondary battery. In addition, the kneading time in the above range enables the coating raw material to be uniformly distributed on the surface of the porous carbon, thereby facilitating the formation of a carbon coating layer with a higher density, and further facilitating the improvement of the charge gram capacity and the first coulomb efficiency of the secondary battery.

[0175] In some embodiments, the aqueous solution can be an aqueous solution, an ethanol solution, or a mixed solution of an aqueous solution and an ethanol solution.

[0176] In some embodiments, the above kneading process is performed at room temperature.

[0177] In some embodiments, the solidification process is performed at 120°C-250°C for at least 1 h. Alternatively, the temperature increasing rate in the solidification process can be 5°C / min-15°C / min, the temperature in the solidification process can be 160°C-200°C, and the time in the solidification process can be 5 h-7 h. Exemplarily, the temperature in the solidification process is 180°C, and the time in the solidification process is 6 h. The solidification under the above conditions can improve the cross-linking degree of the carbon coating raw material, thereby improving the thermal stability of the carbon coating layer and reducing the volume shrinkage of the carbon coating layer in the subsequent carbonization process, so that the carbon coating layer will not be broken in the subsequent carbonization process, thereby improving the density of the coating layer. The high density of the carbon coating layer is beneficial to improve the charge gram capacity and the first coulomb efficiency of the secondary battery.

[0178] In some embodiments, the coating raw material includes a prepolymer of a thermosetting resin. Exemplarily, the thermosetting resin includes at least one of a phenolic resin, an epoxy resin, an unsaturated polyester resin, and a furan resin. Using the above thermosetting resin prepolymer as the coating raw material of the carbon coating layer has the advantages of high uniformity, high density, and high coating integrity.

[0179] In some embodiments, the coating raw material can further include a compound containing C, H, and O elements such as a sugar.

[0180] In some embodiments, the kneading process is performed in a double-screw kneader with a rotation speed of 10 rpm-50 rpm. Under the above conditions, the carbon coating layer can be uniformly coated.

[0181] In some embodiments, the activation treatment includes treating the pre-carbonized body at 700-950°C under a preset mixed gas. Optionally, the pre-carbonized body is treated at 820-880°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.

[0182] In some embodiments, the preset mixed gas includes 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 2.25-7.5. Exemplarily, the volume ratio of the carbon dioxide gas to the water vapor in the preset mixed gas can be 2, 4, 6, 8, 10, 12. 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.

[0183] In some embodiments, the inert gas in the above mixed gas includes helium, neon, argon and the like.

[0184] 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 9%-15%. Exemplarily, the volume percentage of the carbon dioxide gas in the preset mixed gas can be 6%, 9%, 10%, 12%, 15%, 18%, 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.

[0185] 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 2%-4%. Exemplarily, the volume percentage of the water vapor in the mixed gas can be 1%, 2%, 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.

[0186] 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, and the Zn-containing pore-forming liquid has a Zn element addition amount of 14% to 50% of the mass of the porous carbon. For example, the P-containing pore-forming liquid has a P element addition amount of 9.5%, 10%, 15%, 19%, 25%, 30%, or 32.4% of the mass of the porous carbon. For example, the Zn-containing pore-forming liquid has a Zn element addition amount of 14%, 20%, 25%, 30%, 35%, 40%, 45%, or 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.

[0187] For example, the P-containing pore-forming liquid can comprise at least one of phosphoric acid, polyphosphoric acid, and phosphoric acid ester.

[0188] For example, the Zn-containing pore-forming liquid can be zinc chloride.

[0189] 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%, or 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.

[0190] 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 temperature is raised to 600°C at a rate of 5°C / min under the flow of nitrogen 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 or Zn-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.

[0191] In some embodiments, the pre-carbonization treatment is performed at a temperature increasing rate of 1-20℃ / min to 400-600℃ and maintained for 1-12h. For example, the pre-carbonization temperature can be 500℃ and the pre-carbonization treatment time can be 2h. The pre-carbonization treatment under the above conditions is conducive to the formation of a carbon basic skeleton structure, which facilitates the subsequent pore formation.

[0192] In some embodiments, the carbonization treatment is performed at a temperature increasing rate of 2-20℃ / min to 1000-1800℃ and maintained for 1-12h. For example, the carbonization temperature can be 1200℃ and the carbonization treatment time can be 12h. During the carbonization process, the precursor is removed of H, O and other heteroatoms to form a stable hard carbon skeleton, and the carbonization process makes the coating layer more dense, which is conducive to the charge capacity and the first coulombic efficiency of the secondary battery.

[0193] 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.

[0194] In some embodiments, after the pre-carbonization treatment, a further crushing treatment is performed. The crushing treatment is performed by ball milling. The crushing treatment can crush the pre-carbonized body to a suitable particle size, which facilitates the subsequent activation treatment.

[0195] In some embodiments, 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. For example, the biomass precursor can be coconut shell, walnut shell, bamboo cane, straw, etc.; the synthetic polymer precursor can be phenolic resin, epoxy resin, unsaturated polyester resin, etc. The use of the above-mentioned precursors to prepare hard carbon materials can form ordered carbon after activation, and can form an appropriate amount of micropores and mesopores.

[0196] In some embodiments, when the hard carbon precursor is a biomass precursor, after the crushing treatment, a further deashing treatment is performed. The deashing treatment is performed by immersing the acid aqueous solution at room temperature-95℃ for 1-12h, and repeating 1-5 times. The deashing treatment can remove the ash such as minerals and metal oxides in the pre-carbonized body, and improve the purity of the pre-carbonized body.

[0197] Examples

[0198] Hereinafter, examples of the present disclosure are described. The examples described below are exemplary and are only used to explain the present disclosure, and cannot be understood as a limitation of the present disclosure. If a specific technology or condition is not specified in the examples, it is performed according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0199] Example 1

[0200] Preparation of hard carbon material:

[0201] 1) Pre-carbonization treatment; the hard carbon precursor coconut shell was placed in a tube furnace while nitrogen was flowing, and the temperature was raised to 500°C at a rate of 5°C / min and maintained for 2h, to obtain a pre-carbonized body, the flow rate of nitrogen was 500mL / min;

[0202] 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 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 4.9um and a volume particle size distribution Dv90 of 10.3um was obtained;

[0203] 3) Deashing treatment; the pre-carbonized body after breaking treatment in step 2) above was washed in hydrochloric acid aqueous solution, the acid washing temperature range was 50°C, the acid washing time was 4h, the washing process was repeated for 3 times, then filtered, the filter cake was washed repeatedly 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 24;

[0204] 4) Activation treatment; the pre-carbonized body after 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 includes 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%;

[0205] 5) Coating treatment; the porous carbon prepared in step 4) above and a water solution of coating raw material phenolic resin were mixed uniformly to form a kneading mixture, the kneading mixture was placed in a double screw kneader for kneading for 6h, the speed of the double screw kneader was 30rpm, the solid content of the kneading mixture was 65wt%, in the kneading mixture, the mass ratio of coating raw material phenolic resin to porous carbon precursor was 1.2:10; the above kneaded product was placed in a tube furnace while nitrogen was flowing, and the temperature was raised to 180°C at a rate of 5°C / min and maintained for 6h for solidification treatment, to obtain a hard carbon precursor, the flow rate of nitrogen was 500mL / min;

[0206] 6) Carbonization treatment; the hard carbon precursor prepared in step 5) above was placed in a tube furnace while nitrogen was flowing, and the temperature was raised to 1200°C at a rate of 5°C / min and maintained for 12h, to obtain a hard carbon material.

[0207] Hard carbon material related tests:

[0208] 1) Pore volume test

[0209] 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 NaNO3 is added, 46 ml of concentrated sulfuric acid is slowly added and stirred evenly. The beaker is placed in an ice water bath, 6 g of KMnO4 is slowly added under stirring, and the temperature is kept below 20°C during the process. After 5 minutes, remove the ice water bath and warm up to 35°C for 30 min. Then add 92 ml of deionized water, stir for 15 minutes, and finally add 80 ml of 3% H2O2 solution at 60°C to reduce the excess KMnO4 until no obvious bubbles are generated. Finally, filter and wash the filter cake with deionized water and anhydrous ethanol repeatedly until the filtrate pH > 6. The washed filter cake is dried in a vacuum oven at 80°C for 24 h to obtain a porous carbon material.

[0210] Second, the porous carbon material powder is placed in a sample tube and vacuum degassed at 200°C for 12 h. The nitrogen adsorption amount of 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.

[0211] 2) Methylene blue adsorption value test

[0212] The methylene blue adsorption value test is carried out according to the following steps:

[0213] 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.

[0214] Preparation of button cell:

[0215] 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.

[0216] Performance test of button cell

[0217] 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.

[0218] First coulombic efficiency (%) = first circle charge capacity / first circle discharge gram capacity × 100%.

[0219] Example 2-11

[0220] The hard carbon material was prepared according to the similar method of Example 1 and assembled into a button-type half cell, with the only difference being that when preparing the hard carbon material, the process conditions of the activation treatment and the coating treatment were adjusted according to Table 1 below to obtain a hard carbon material with a total pore volume A of 0.437 cm

[0221] Comparative Example 1

[0222] The hard carbon material was prepared according to the similar method of Example 1 and assembled into a button-type half cell, with the only difference being that when preparing the hard carbon material, the process conditions of the activation treatment and the coating treatment were adjusted according to Table 1 below to obtain a hard carbon material with a total pore volume A of 0.437 cm 3 / g and a methylene blue adsorption value greater than 10 mg / g.

[0223] Comparative Example 2

[0224] The hard carbon material was prepared according to the similar method of Example 1 and assembled into a button-type half cell, with the only difference being that when preparing the hard carbon material, the process conditions of the activation treatment and the coating treatment were adjusted according to Table 1 below to obtain a hard carbon material with a total pore volume A of 0.437 cm 3 / g and a methylene blue adsorption value less than 10 mg / g.

[0225] Comparative Example 3

[0226] The hard carbon material was prepared according to the similar method of Example 1 and assembled into a button-type half cell, with the only difference being that when preparing the hard carbon material, the process conditions of the activation treatment and the coating treatment were adjusted according to Table 1 below to obtain a hard carbon material with a total pore volume A of 0.437 cm 3 / g and a methylene blue adsorption value greater than 10 mg / g.

[0227] The process parameters for preparing the hard carbon material in Examples 1-11 and Comparative Examples 1-3 are shown in Table 1 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 2 below.

[0228] Table 1:

[0229] Table 2:

[0230] As can be seen from Table 1 and Table 2 above, in Examples 1-11, by making the total pore volume of the porous carbon be 0.2 cm 3 / g-0.6 cm 3between 0.2 cm3 / g and 0.4 cm3 / g, and the methylene blue adsorption value of the hard carbon material is less than 10 mg / g, the first coulombic efficiency and the charge gram capacity are obviously improved, and the high discharge gram capacity is also considered. In Comparative Example 1, the methylene blue adsorption value of the hard carbon material is greater than 10 mg / g, although the discharge gram capacity is high, the first coulombic efficiency and the charge gram capacity are low. In Comparative Example 2, the total pore volume of the porous carbon is less than 0.2 cm3 / g, and the discharge gram capacity is low. In Comparative Example 3, 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 10 mg / g, so the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. 3 / g, and the methylene blue adsorption value of the hard carbon material is less than 10 mg / g, the first coulombic efficiency and the charge gram capacity are obviously improved, and the high discharge gram capacity is also considered. In Comparative Example 1, the methylene blue adsorption value of the hard carbon material is greater than 10 mg / g, although the discharge gram capacity is high, the first coulombic efficiency and the charge gram capacity are low. In Comparative Example 2, the total pore volume of the porous carbon is less than 0.2 cm3 / g, and the discharge gram capacity is low. In Comparative Example 3, 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 10 mg / g, so the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low. 3 / g, and the methylene blue adsorption value of the hard carbon material is less than 10 mg / g, the first coulombic efficiency and the charge gram capacity are obviously improved, and the high discharge gram capacity is also considered. In Comparative Example 1, the methylene blue adsorption value of the hard carbon material is greater than 10 mg / g, although the discharge gram capacity is high, the first coulombic efficiency and the charge gram capacity are low. In Comparative Example 2, the total pore volume of the porous carbon is less than 0.2 cm3 / g, and the discharge gram capacity is low. In Comparative Example 3, 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 10 mg / g, so the discharge gram capacity, the charge gram capacity and the first coulombic efficiency are all low.

[0231] Example 12

[0232] Preparation of the hard carbon material:

[0233] 1) Pre-carbonization treatment: the hard carbon precursor coconut shell was placed in a tube furnace while nitrogen was flowing, and the temperature was raised to 500℃ at a rate of 5℃ / min and maintained for 2h, to obtain a pre-carbonized body, and the flow rate of nitrogen was 500 mL / min;

[0234] 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 pre-carbonized body to milling beads was 1:3, the rotating speed of the ball mill was 800 rpm, the ball milling time was 8h, and the milling beads were removed, to obtain a pre-carbonized body with a volume particle size distribution Dv50 of 4.9um and a volume particle size distribution Dv90 of 10.3um;

[0235] 3) Activation treatment: the pre-carbonized body subjected to 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 while nitrogen was flowing, and the temperature was raised to 600℃ at a rate of 5℃ / min and maintained for 2h, and the flow rate of nitrogen was 500 mL / min, to obtain a porous carbon precursor; wherein the added amount of P element in the pore-forming liquid phosphoric acid aqueous solution was 10.8% of the mass of the pre-carbonized body; and the solid content of the impregnated mixture formed by the pre-carbonized body and the pore-forming liquid was 65%;

[0236] 4) Deashing treatment: the porous carbon precursor in step 3) above was washed in a hydrochloric acid aqueous solution, the acid washing temperature was 50℃, the acid washing time was 4h, the washing process was repeated for 3 times, and then filtered, and the filter cake was washed repeatedly with deionized water and anhydrous ethanol until the filtrate pH>6; the washed filter cake was dried in a vacuum oven at 80℃ for 24h;

[0237] 5) coating treatment; the water solution of coating raw material phenol formaldehyde resin and the porous carbon precursor after the descaling treatment in step 4) above are mixed uniformly to form a kneaded mixture, the kneaded mixture is placed in a double screw kneader for kneading for 6h, the rotating speed of the double screw kneader is 30rpm, the solid content of the kneaded mixture is 65wt%, the mass ratio of the coating raw material phenol formaldehyde resin and the porous carbon precursor in the kneaded mixture is 1.2:10; the product after the kneading above is placed in a tube furnace for curing treatment at a temperature raising rate of 5℃ / min to 180℃ and keeping for 6h, the nitrogen gas is introduced, the flow rate of the nitrogen gas is 500mL / min, to obtain a hard carbon precursor;

[0238] 6) carbonization treatment; the hard carbon precursor prepared in step 5) above is placed in a tube furnace for carbonization treatment at a temperature raising rate of 5℃ / min to 1200℃ and keeping for 12h, the nitrogen gas is introduced, to obtain a hard carbon material.

[0239] The button-type half cell is assembled in a similar way as in Example 1.

[0240] Examples 13-16

[0241] The hard carbon material is prepared in a similar way as in Example 12, and is assembled into a button-type half cell, the only difference is that the process conditions of the activation treatment are adjusted according to Table 3 below when the hard carbon material is prepared, to obtain the hard carbon material with different total pore volume A of the porous carbon, see Table 3 below.

[0242] The process parameters for preparing the hard carbon material in Examples 12-16 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.

[0243] Table 3:

[0244] Table 4:

[0245] From the above Table 3 and Table 4, it can be seen that in Examples 12-16, by making the total pore volume of the porous carbon between 0.2cm 3 / g-0.6cm 3 / g, and making the methylene blue adsorption value of the hard carbon material less than 10mg / g, the first coulombic efficiency and the charge gram capacity are obviously improved, while the high discharge gram capacity is also taken into account.

[0246] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present disclosure are included in the technical scope of the present disclosure. Furthermore, various modifications that can be thought of by those skilled in the art, and other modes of embodiment constructed by combining part of the configurations of the embodiments, are also included in the scope of the present disclosure without departing from the spirit of the present disclosure.

Claims

1. A negative electrode sheet, comprising a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer comprising a hard carbon material, the hard carbon material comprising a core and a carbon coating layer covering the core; the core comprising porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value Z of the hard carbon material is ≤10 mg / g.

2. The negative electrode sheet according to claim 1, wherein, The methylene blue adsorption value of the hard carbon material is Z≤5mg / g.

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

4. The negative electrode sheet according to claim 3, wherein, The total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 8 ≤ X / Y ≤ 13.

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 the following condition: 85% ≤ X / A ≤ 97%.

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

7. The negative electrode sheet according to any one of claims 1-6, wherein, The hard carbon material I D / I G The range is 0.83-1.26; Among them, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹. -1 D peak intensity at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

8. The negative electrode sheet according to any one of claims 1-7, wherein, The hard carbon material satisfies at least one of the following conditions: (1) The compaction density of the hard carbon material at 5t is 0.6 g / cm³. 3 -1.05g / cm 3 ; (2) The tap density of the hard carbon material is 0.4 g / cm³. 3 -0.85g / cm 3 ; (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm; (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm; (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-10m 2 / g.

9. A secondary battery, the secondary battery comprising the negative electrode sheet according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein, The secondary battery also includes a positive electrode sheet, wherein the positive electrode sheet comprises at least one selected from transition metal oxides, polyanionic compounds and Prussian blue compounds as the positive electrode active material.

11. An electrical device comprising the secondary battery as described in claim 9 or 10.

12. A hard carbon material, comprising a core and a carbon coating layer covering the core; the core comprising porous carbon; The total pore volume A of the porous carbon satisfies: 0.2 cm³. 3 / g≤A≤0.6cm 3 / g; The methylene blue adsorption value Z of the hard carbon material is ≤10 mg / g.

13. The hard carbon material according to claim 12, wherein, The methylene blue adsorption value of the hard carbon material is Z≤5mg / g.

14. The hard carbon material according to claim 12 or 13, wherein, 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.

15. The hard carbon material according to claim 14, wherein, The total pore volume X of the micropores and the total pore volume Y of the mesopores satisfy: 8 ≤ X / Y ≤ 13.

16. The hard carbon material according to claim 14 or 15, wherein, The total pore volume X of the micropores and the total pore volume A of the porous carbon satisfy the following condition: 85% ≤ X / A ≤ 97%.

17. The hard carbon material according to any one of claims 14-16, wherein, The total pore volume Y of the mesopores and the total pore volume A of the porous carbon satisfy the following condition: 3% ≤ Y / A ≤ 15%.

18. The hard carbon material according to any one of claims 12-17, wherein, The hard carbon material I D / I G The range is 0.83-1.26; Among them, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹. -1 D peak intensity at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

19. The hard carbon material according to any one of claims 12-18, wherein, The hard carbon material satisfies at least one of the following conditions: (1) The compaction density of the hard carbon material at 5t is 0.6 g / cm³. 3 -1.05g / cm 3 ; (2) The tap density of the hard carbon material is 0.4 g / cm³. 3 -0.85g / cm 3 ; (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm; (4) The volume distribution particle size Dv90 of the hard carbon material is 8μm-15μm; (5) The specific surface area (BET) of the hard carbon material is 0.1 m². 2 / g-10m 2 / g.

20. A method for preparing a hard carbon material, the method comprising: The hard carbon precursor is pre-carbonized to obtain a pre-carbonized body; The pre-carbonized body is activated to obtain a porous carbon precursor; The porous carbon precursor is coated to form a hard carbon precursor; The coating process includes a kneading process of kneading a mixture of the porous carbon precursor and the coating material in an aqueous solution, and a curing process of curing the product of the kneading process; the solid content of the kneading mixture is 55wt%-75wt%. The hard carbon precursor is subjected to carbonization treatment to obtain the hard carbon material.

21. The preparation method according to claim 20, wherein, The mass ratio of the coating material to the porous carbon precursor is 0.5:10-2:10, and the kneading process is carried out for at least 0.5 hours.

22. The preparation method according to claim 20 or 21, wherein, The curing process shall be carried out at 120℃-250℃ for at least 1 hour.

23. The preparation method according to any one of claims 20-22, wherein, The coating material includes a prepolymer of a thermosetting resin.

24. The preparation method according to claim 23, wherein, The thermosetting resin includes at least one of phenolic resin, epoxy resin, unsaturated polyester resin, and furan resin.

25. The preparation method according to any one of claims 20-24, wherein, The kneading process is carried out in a twin-screw kneader, the twin-screw kneader rotating at a speed of 10 rpm to 50 rpm.

26. The preparation method according to any one of claims 20-25, wherein, The activation treatment includes subjecting the pre-carbonized body to a preset mixed gas at 700℃-950℃. The preset mixed gas includes carbon dioxide gas, water vapor, and an inert gas, wherein the volume ratio of carbon dioxide gas to water vapor in the preset mixed gas is ≥2.

27. The preparation method according to claim 26, wherein, The carbon dioxide gas accounts for 5%-20% of the volume of the preset mixed gas, and the water vapor accounts for 1%-5% of the volume of the mixed gas.

28. The preparation method according to any one of claims 20-27, wherein, The activation treatment includes immersing the pre-carbonized body in a P-containing pore-forming solution or a Zn-containing pore-forming solution for at least 2 hours; the amount of P added in the P-containing pore-forming solution is 9.5%-32.4% of the mass of the pre-carbonized body, and the amount of Zn added in the Zn-containing pore-forming solution is 14%-50% of the mass of the pre-carbonized body.

29. The preparation method according to claim 28, wherein, The solid content of the pre-carbonized body in the impregnation mixture formed with the pore-forming liquid is 50 wt% to 70 wt%.

30. The preparation method according to claim 28 or 29, wherein, The activation treatment also includes keeping the impregnated mixture of the pre-carbonized body and the pore-forming liquid at 400℃-750℃ for 1h-12h.

31. The preparation method according to any one of claims 20-30, wherein, The pre-carbonization treatment involves heating to 400℃-600℃ at a rate of 1℃ / min-20℃ / min and holding for 1h-12h.

32. The preparation method according to any one of claims 20-31, wherein, The carbonization process involves heating the temperature to 1000℃-1800℃ at a rate of 2℃ / min-20℃ / min and holding it for 1h-12h.

33. The preparation method according to any one of claims 20-32, wherein, The hard carbon precursor includes at least one of biomass precursor and synthetic polymer precursor; The synthetic polymer precursors include compounds composed of C, H, and O elements.

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