Composite hard carbon material and preparation method thereof, negative electrode slurry and pole piece, secondary battery and device

Abstract

The invention provides a composite hard carbon material and a preparation method thereof, negative electrode slurry, a negative electrode plate, a secondary battery and an electric device. The composite hard carbon material comprises a hard carbon material and a hydrophobic compound filled in pores of the hard carbon material, wherein the hydrophobic compound is a compound represented by the following formula (I). The composite hard carbon material provided by the invention can reduce foaming of the negative electrode slurry, so that the cycle performance of the secondary battery is improved. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the technical field of alkali metal ion batteries, and in particular to a composite hard carbon material and its preparation method, a negative electrode paste and electrode sheet, a secondary battery and a device. Background Art

[0002] In recent years, with the increasingly wide application range of alkali metal ion batteries, alkali metal ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of alkali metal ion batteries, higher requirements have also been put forward for their energy density, cycle performance, and safety performance.

[0003] Currently, in order to improve the energy density, cycle performance, and safety performance of alkali metal ion batteries, it is necessary to improve the stability of the negative electrode sheet of alkali metal ion batteries. In other words, it is necessary to improve the stability of the negative electrode paste that forms the negative electrode sheet. Therefore, how to improve the stability of the negative electrode paste and thus improve the performance of alkali metal ion batteries has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a composite hard carbon material and its preparation method to reduce the foaming of the negative electrode paste and thus improve the cycle performance of the secondary battery. In addition, the purpose of the present application is also to provide a negative electrode paste and electrode sheet, a secondary battery and a device including the composite hard carbon material.

[0005] To achieve the above purpose, the present application provides a composite hard carbon material and its preparation method, a negative electrode paste and electrode sheet, a secondary battery and a device.

[0006] The first aspect of the present application provides a composite hard carbon material, which includes: a hard carbon material and a hydrophobic compound filled in the pores of the hard carbon material, and the hydrophobic compound is a compound represented by the following formula (I):

[0007]

[0008] In the formula (I), X is O, S, C═O, CR 11 R 12 , NR 21 , PR 31 , P(═O)R 32 or P(═S)R 33 ;

[0009] wherein, R 11 , R 12 , R 21 , R 31, R 32 , R 33 Each independently selected from H, SH, OH, NH 2 , halogen, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted 5- to 10-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 8-membered cycloalkyl or heterocycloalkyl, amido or thiocarboxamide group; when the C1-C10 alkyl, 5- to 10-membered heteroaryl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include OH, NH 2 , halogen, at least one of C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl;

[0010] R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 Each independently selected from any one of R, OR, C(=O)R, COOR, 6- to 10-membered aryl and halogen, wherein R is each independently selected from any one of H and C1-C10 alkyl.

[0011] Thus, the composite hard carbon material provided by the present application includes a hard carbon material and a hydrophobic compound filled in the pores of the hard carbon material, that is, the hydrophobic compound occupies the pores of the hard carbon material; during the subsequent process of forming a negative electrode paste using the above composite hard carbon material, solvents in the negative electrode paste, such as water molecules, cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode paste and further improving the stability of the negative electrode paste.

[0012] In some embodiments, in the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH 2 , halogen, unsubstituted or substituted C1-C4 alkyl, unsubstituted or substituted 5- to 6-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 6-membered cycloalkyl or heterocycloalkyl, amido or thiocarboxamide group; when the C1-C4 alkyl, 5- to 6-membered heteroaryl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include OH, NH 2, at least one of a halogen, a C1-C4 alkyl group, a 6- to 10-membered aryl group, a 3- to 6-membered cycloalkyl group, or a heterocycloalkyl group;

[0013] R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 each independently selected from any one of R, OR, C(=O)R, COOR, phenyl, and a halogen, wherein each R is independently selected from any one of H and a C1-C4 alkyl group.

[0014] In any embodiment, in the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 each independently selected from H, SH, OH, NH 2 , phenyl, 4-hydroxyphenyl, furyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, piperidinyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxiranyl, thioxiranyl, cyclohexyl, benzyl, thiocarboxamide, 1-pyrrolidin-2-yl-methyl, and any one of C1-C4 alkyl groups.

[0015] In some embodiments, the hydrophobic compound is selected from at least one of the following compounds:

[0016]

[0017] In some embodiments, in the composite hard carbon material, the weight ratio of the hydrophobic compound to the hard carbon material is 0.1-5:100.

[0018] By defining the mixing weight ratio range between the hydrophobic compound and the hard carbon material, the hydrophobic compound can enter the pores of the hard carbon material and occupy the pores of the hard carbon material to form a composite hard carbon material; subsequently, solvents such as water molecules in the negative electrode slurry cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode slurry.

[0019] In some embodiments, the hydrophobic compound is fixed in the pores of the hard carbon material through π-π conjugate interaction and / or van der Waals force interaction.

[0020] Hydrophobic compounds can be fixed in the pores of the hard carbon material through π-π conjugate interaction and / or van der Waals force interaction to form a composite hard carbon material; even when using this composite hard carbon material to form a negative electrode slurry, the hydrophobic compounds have occupied the pores of the hard carbon material, thereby reducing the probability of solvents such as water molecules in the negative electrode slurry entering the pores of the composite hard carbon material, and further reducing the foaming of the negative electrode slurry.

[0021] The second aspect of the present application provides a method for preparing a composite hard carbon material, the method comprising:

[0022] Mix the hard carbon material and the hydrophobic compound evenly and then put them into a reaction kettle;

[0023] Fill the reaction kettle with a supercritical fluid so that the hard carbon material and the hydrophobic compound react in the supercritical fluid to obtain a composite hard carbon material;

[0024] Wherein, the hydrophobic compound is a compound represented by the following formula (I):

[0025]

[0026] In the formula (I), X is O, S, C=O, CR 11 R 12 、NR 21 、PR 31 、P(=O)R 32 Or P(=S)R 33 ;

[0027] Wherein, R 11 、R 12 、R 21 、R 31 、R 32 、R 33 Each independently selected from H, SH, OH, NH 2 、halogen, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted 5- to 10-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 8-membered cycloalkyl or heterocycloalkyl, amide group or thiocarboxamide group; when the C1-C10 alkyl, 5- to 10-membered heteroaryl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include OH, NH 2 、halogen, C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl of at least one;

[0028] R 1 、R 2 、R 3 、R 4 、R 5 、R6 , R 7 , R 8 , R 9 , R 10 Each independently selected from any one of R, OR, C(=O)R, COOR, 6- to 10-membered aryl, and halogen, wherein each R is independently selected from any one of H and C1-C10 alkyl.

[0029] Thus, in this application, by treating the hard carbon material, the hard carbon material and the hydrophobic compound are reacted in a supercritical fluid to obtain a composite hard carbon material, and the pores of the composite hard carbon material are filled with the hydrophobic compound. Subsequently, during the process of using the above composite hard carbon material to form the negative electrode paste, solvents such as water molecules in the negative electrode paste cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode paste and further improving the stability of the negative electrode paste.

[0030] In some embodiments, in the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH 2 , halogen, unsubstituted or substituted C1-C4 alkyl, unsubstituted or substituted 5- to 6-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 6-membered cycloalkyl or heterocycloalkyl, amide group or thiocarboxamide group; when C1-C4 alkyl, 5- to 6-membered heteroaryl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl are substituted, their substituents each independently include OH, NH 2 , halogen, C1-C4 alkyl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl;

[0031] R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 Each independently selected from any one of R, OR, C(=O)R, COOR, phenyl, and halogen, wherein each R is independently selected from any one of H and C1-C4 alkyl.

[0032] In some embodiments, in the formula (I), R 11 , R 12 , R 21, R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH 2 , phenyl, 4-hydroxyphenyl, furyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, piperidyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxiranyl, thiooxiranyl, cyclohexyl, benzyl, thiocarboxamide, 1-pyrrolidin-2-yl-methyl, any one of C1-C4 alkyl groups.

[0033] In some embodiments, the hydrophobic compound is selected from at least one of the following compounds:

[0034]

[0035]

[0036] In some embodiments, the hydrophobic compound and the hard carbon material are mixed evenly at a weight ratio of 0.1-5:100.

[0037] By defining the mixing weight ratio range between the hydrophobic compound and the hard carbon material, the hydrophobic compound can enter the pores of the hard carbon material and occupy the pores of the hard carbon material to form a composite hard carbon material; solvents in the negative electrode slurry, such as water molecules, cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode slurry.

[0038] In some embodiments, the supercritical fluid is selected from supercritical carbon dioxide, supercritical nitric oxide, supercritical acetylene, supercritical trifluoromethane, supercritical trichloromethane, supercritical methane, supercritical ethane, supercritical propane, supercritical ethylene, supercritical propylene, supercritical methanol, supercritical ethanol, supercritical acetone, supercritical chlorofluorocarbon or supercritical xenon.

[0039] In some embodiments, the reaction duration of the hard carbon material and the hydrophobic compound in the supercritical fluid is 2h to 10h.

[0040] By defining the reaction duration of the hard carbon material and the hydrophobic compound in the supercritical fluid, it is beneficial for the hard carbon material and the hydrophobic compound to react fully, so that the hydrophobic compound enters the pores of the hard carbon material to form a composite hard carbon material.

[0041] The third aspect of the present application provides a negative electrode slurry, which includes the composite hard carbon material of the first aspect of the present application and a solvent, as well as at least one of a conductive agent, a dispersant and a binder.

[0042] Accordingly, the negative electrode slurry provided by the present application includes the composite hard carbon material in the above technical solution. The pores of the composite hard carbon material include a hydrophobic compound, so that solvents such as water molecules in the negative electrode slurry cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode slurry and further improving the stability of the negative electrode slurry. Even if it is left for several days, the negative electrode slurry will not foam, and the viscosity remains stable.

[0043] In some embodiments, based on the solid content in the negative electrode slurry, the content of the composite hard carbon material is 85 wt% to 97 wt%; the content of the conductive agent is 0 to 5 wt%; the content of the dispersant is 0.5 wt% to 5 wt%; the content of the binder is 0.5 wt% to 5 wt%.

[0044] In some embodiments, the solvent is water.

[0045] In some embodiments, based on the total weight of the negative electrode slurry, the total solid content of the negative electrode slurry is 40 wt% to 65 wt%.

[0046] In some embodiments, the conductive agent is selected from at least one of carbon black, carbon nanotubes, and graphene;

[0047] and / or, the dispersant is selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose;

[0048] and / or, the binder is selected from at least one of styrene-butadiene rubber, styrene-acrylic emulsion, and modified polyacrylic acids.

[0049] The fourth aspect of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes the composite hard carbon material of the first aspect of the present application.

[0050] Accordingly, the negative electrode film layer provided by the present application includes the composite hard carbon material in the above technical solution. The stability of the negative electrode slurry is high and it will not foam even if left for several days; subsequently, using the above negative electrode plate to form a secondary battery can effectively improve the cycling performance of the secondary battery.

[0051] The fifth aspect of the present application provides a secondary battery, which includes the negative electrode plate of the fourth aspect of the present application.

[0052] Accordingly, the secondary battery provided by the present application includes the negative electrode plate in the above technical solution, which can effectively improve the cycling performance of the secondary battery.

[0053] The sixth aspect of the present application provides an electrical device, which includes the secondary battery of the fifth aspect of the present application.

[0054] The present application provides a composite hard carbon material, a preparation method thereof, a negative electrode slurry, a pole piece, a secondary battery and a device. The composite hard carbon material includes a hard carbon material and a hydrophobic compound filled in the pores of the hard carbon material. Subsequently, using the above composite hard carbon material to form a negative electrode slurry can effectively reduce the foaming of the negative electrode slurry, thereby improving the stability of the negative electrode slurry. Description of the Drawings

[0055] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0056] Figure 2 is Figure 1 An exploded view of the battery cell shown in an embodiment of the present application.

[0057] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0058] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0059] Figure 5 is Figure 4 An exploded view of the battery pack shown in an embodiment of the present application.

[0060] Figure 6 It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0061] Figure 7 It is a photo of a negative electrode slurry containing the composite hard carbon material of Example 1. Among them, (a) is a photo of the negative electrode slurry after stirring; (b) is a photo of the negative electrode slurry after being placed for 7 days.

[0062] Figure 8 It is a photo of a negative electrode slurry containing the hard carbon material of Comparative Example 1. Among them, (a) is a photo of the negative electrode slurry after stirring; (b) is a photo of the negative electrode slurry after being placed for 12 hours.

[0063] Description of the Reference Numerals:

[0064] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Embodiments

[0065] Hereinafter, embodiments of the composite hard carbon material, its manufacturing method, negative electrode slurry and electrode sheet, secondary battery and device of the present application will be specifically described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent 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 for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0066] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 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 application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0068] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0069] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0070] Hard carbon refers to a carbon material that will not be converted into graphite even at temperatures above 3000 °C. Hard carbon materials have the advantages of low energy storage voltage, high capacity, and good cycle stability, and also have advantages such as rich sources and simple preparation processes. They are one of the most promising anode materials at present and have a large application market in alkali metal ion batteries. The synthesis of hard carbon is mainly obtained by heating or chemical processes based on organic compounds or biomass-derived precursors. For example, natural or synthetic macromolecular polymer structures will decompose when the pyrolysis temperature rises, and a series of small molecules will be released during the carbonization process of the precursor, such as H 2 O, CO 2 and N 2 etc. This process of releasing gas usually leads to an increase in the porosity of the hard carbon material. For hard carbon materials with particularly developed pores, during the process of standing after the negative electrode slurry stirring is completed, solvents in the negative electrode slurry, such as water molecules, are likely to enter the pores and expel the gas in the pores, resulting in foaming of the negative electrode slurry. Thus, when the negative electrode film layer prepared using the foamed negative electrode slurry is applied to a secondary battery, it will cause serious deterioration of the cycle performance of the secondary battery.

[0071] Based on this, this application proposes a composite hard carbon material and its preparation method, negative electrode slurry and electrode sheet, secondary battery and device.

[0072] In the first aspect of this application, a composite hard carbon material is provided. The composite hard carbon material includes: a hard carbon material and a hydrophobic compound filled in the pores of the hard carbon material. The hydrophobic compound is a compound represented by the following formula (I):

[0073]

[0074] In the formula (I), X is O, S, C═O, CR 11 R 12 , NR 21 , PR 31 , P(═O)R 32 or P(═S)R 33 ;

[0075] Among them, R 11 , R 12 , R 21 , R 31 , R 32 , R 33 are each independently selected from H, SH, OH, NH 2 , halogen, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted 5- to 10-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 8-membered cycloalkyl or heterocycloalkyl, amido or thiocarboxamide group; when the C1-C10 alkyl, 5- to 10-membered heteroaryl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include OH, NH 2 , halogen, C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl at least one of;

[0076] R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 are each independently selected from any one of R, OR, C(=O)R, COOR, 6- to 10-membered aryl and halogen, wherein, R is each independently selected from any one of H and C1-C10 alkyl.

[0077] The term "halogen" in this application includes fluorine, chlorine, bromine or iodine, optionally fluorine or chlorine.

[0078] The term "C1-C10 alkyl" in this application includes straight-chain alkyl or branched-chain alkyl having 1 to 10 carbon atoms. Optionally, C1-C10 alkyl includes straight-chain or branched-chain C1-C8 alkyl having 1 to 8 carbon atoms. Optionally, C1-C10 alkyl includes straight-chain or branched-chain C1-C6 alkyl having 1 to 6 carbon atoms. Optionally, C1-C10 alkyl includes straight-chain or branched-chain C1-C4 alkyl having 1 to 4 carbon atoms. Optionally, C1-C10 alkyl includes C1-C2 alkyl having 1 to 2 carbon atoms. Examples of C1-C10 alkyl include but are not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl.

[0079] The term "heteroaryl" in this application refers to an aryl group having 1 to 3 heteroatoms selected from O, N, and S in the ring structure. Examples of heteroaryl include, but are not limited to, pyrrolyl, furyl, thienyl, thiazolyl, isothiazolyl, imidazolyl, triazolyl, tetrazolyl, pyrazolyl, oxazolyl, isoxazolyl, pyridyl, pyrazinyl, pyridazinyl, pyrimidinyl, etc.

[0080] The term "aryl" in this application refers to a 6- to 14-membered fully carbon monocyclic or fused polycyclic group having a conjugated π-electron system, preferably 6- to 10-membered. Examples of aryl include, but are not limited to, phenyl, naphthyl, etc.

[0081] The term "cycloalkyl" in this application refers to a saturated or unsaturated non-aromatic hydrocarbon monocyclic or polycyclic (e.g., fused ring, bridged ring, or spiro ring) system having 3 to 30 carbon atoms (e.g., C 3 ~C 12 、C 3 ~C 10 or C 3 ~C 8 ). Examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, 1,2,3,4-tetrahydronaphthyl, adamantyl.

[0082] The term "heterocycloalkyl" in this application refers to a saturated or unsaturated non-aromatic 3- to 8-membered monocyclic, 7- to 12-membered bicyclic (fused ring, bridged ring, or spiro ring), or 11- to 14-membered tricyclic system (fused ring, bridged ring, or spiro ring) containing 1 to 3 heteroatoms selected from O, N, or S, unless otherwise specified. Examples of heterocycloalkyl include, but are not limited to, piperidinyl, piperazinyl, pyrrolidinyl, dioxolanyl, tetrahydrofuryl, isoindolinyl, indolinyl, imidazolidinyl, pyrazolidinyl, oxazolidinyl, isoxazolidinyl, triazolidinyl, oxiranyl, thioranyl, azetidinyl, oxetanyl, thietanyl, 1,2,3,6-tetrahydropyridyl, tetrahydropyranyl, dihydropyranyl, pyranyl, morpholinyl, tetrahydrothianyl.

[0083] The terms "alkyl", "cycloalkyl", "heterocycloalkyl", "aryl", and "heteroaryl" in this application may be substituted or unsubstituted. When the above groups are substituted, their substituents each independently include at least one of OH, NH 2 , halogen, C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl.

[0084] The term "thiocarboxamido" in this application refers to C(=S)NH 2 .

[0085] The term "amido" in this application refers to C(=O)NH 2 .

[0086] The "pores of the hard carbon material" mentioned herein refer to the pores inherent in the hard carbon material itself, rather than the gaps between the particles of the hard carbon material.

[0087] The applicant has found that during the process of forming the negative electrode paste using the hard carbon material, solvent molecules such as water molecules in the negative electrode paste are likely to enter the pores of the hard carbon material during placement and expel the gas in the pores, resulting in foaming of the negative electrode paste. Therefore, the applicant treats the hard carbon material with a hydrophobic compound so that the hydrophobic compound enters the pores of the hard carbon material, that is, the hydrophobic compound occupies the pores of the hard carbon material to form a composite hard carbon material; during the subsequent process of forming the negative electrode paste using the above composite hard carbon material, solvent molecules such as water molecules in the negative electrode paste cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode paste and further improving the stability of the negative electrode paste.

[0088] In some embodiments of this application, in the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 are each independently selected from H, SH, OH, NH 2 , halogen, unsubstituted or substituted C1-C4 alkyl, unsubstituted or substituted 5- to 6-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 6-membered cycloalkyl or heterocycloalkyl, amido or thioformamido; when the C1-C4 alkyl, 5- to 6-membered heteroaryl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include at least one of OH, NH 2 , halogen, C1-C4 alkyl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl;

[0089] R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 are each independently selected from any one of R, OR, C(=O)R, COOR, phenyl and halogen, where R is each independently selected from any one of H and C1-C4 alkyl.

[0090] The term "C1-C4 alkyl" in this application includes straight-chain alkyl or branched-chain alkyl having 1 to 4 carbon atoms. Optionally, C1-C4 alkyl includes C1-C2 alkyl having 1 to 2 carbon atoms. Examples of C1-C4 alkyl include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl.

[0091] In some embodiments of this application, in the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 are each independently selected from H, SH, OH, NH 2 , phenyl, 4-hydroxyphenyl, furyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, piperidyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxiranyl, thietanyl, cyclohexyl, benzyl, thiocarboxamide, 1-pyrrolidin-2-yl-methyl, and any one of C1-C4 alkyl.

[0092] Exemplarily, the hydrophobic compound in this application can be the following:

[0093]

[0094]

[0095] In some embodiments of this application, in the composite hard carbon material, the weight ratio of the hydrophobic compound to the hard carbon material is 0.1-5:100.

[0096] Optionally, in the composite hard carbon material, the weight ratio of the hydrophobic compound to the hard carbon material is 1.0-4.0:100. Exemplarily, the weight ratio of the hydrophobic compound to the hard carbon material is 1.5:100, 2.0:100, 2.5:100, 3.0:100, or 3.5:100.

[0097] By defining the weight ratio range between the hydrophobic compound and the hard carbon material, the hydrophobic compound can enter the pores of the hard carbon material and occupy the pores of the hard carbon material to form a composite hard carbon material; subsequently, solvents such as water molecules in the negative electrode slurry cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode slurry.

[0098] In some embodiments of this application, the hydrophobic compound is fixed in the pores of the hard carbon material through π-π conjugate interaction and / or van der Waals force interaction.

[0099] Hydrophobic compounds can be fixed in the pores of the hard carbon material through π-π conjugate interaction and / or van der Waals force interaction to form a composite hard carbon material. Even when using the composite hard carbon material to form a negative electrode paste, the hydrophobic compounds have occupied the pores of the hard carbon material, thereby reducing the probability of solvents such as water molecules in the negative electrode paste entering the pores of the composite hard carbon material, and further reducing the foaming of the negative electrode paste.

[0100] The second aspect of the present application provides a method for preparing a composite hard carbon material, the method comprising:

[0101] After uniformly mixing the hard carbon material and the hydrophobic compound, put them into a reaction kettle;

[0102] Charge a supercritical fluid into the reaction kettle, so that the hard carbon material and the hydrophobic compound react in the supercritical fluid to obtain a composite hard carbon material; wherein, the hydrophobic compound has the same definition as the compound represented by the foregoing formula (I).

[0103] The term "supercritical fluid" in the present application refers to a state where the temperature and pressure of a substance are both above the critical temperature and critical pressure. In this state, the properties of gases and liquids gradually tend to be similar, and finally a homogeneous fluid is formed. Supercritical fluids have characteristics different from those of gases and liquids, including but not limited to: (1) The density of supercritical fluids is not much different from that of liquids, but the density of supercritical fluids is much greater than that of gases, which helps supercritical fluids dissolve the dispersion medium; (2) The viscosity of supercritical fluids is closer to that of gases and has good fluidity; (3) The diffusion coefficient of supercritical fluids is between the diffusion coefficients of gases and liquids; (4) Supercritical fluids have low viscosity, high density, and low surface tension, and have good mass transfer performance.

[0104] When it is mentioned herein that "the hard carbon material and the hydrophobic compound react in the supercritical fluid", it means that the reaction temperature and reaction pressure in the reaction kettle and other conditions are within the temperature range and pressure range that satisfy the formation of the supercritical fluid, whereby the hard carbon material and the hydrophobic compound react in the supercritical fluid.

[0105] In this application, by treating the hard carbon material, the hard carbon material and the hydrophobic compound react in a supercritical fluid to form a composite hard carbon material. The pores of the composite hard carbon material are filled with the hydrophobic compound. Subsequently, during the process of forming the negative electrode paste using the above composite hard carbon material, solvents in the negative electrode paste, such as water molecules, cannot enter the pores of the composite hard carbon material, thus effectively reducing the foaming of the negative electrode paste and further improving the stability of the negative electrode paste. Here, by utilizing the characteristics of supercritical carbon dioxide fluid, the hydrophobic compound is introduced into the pores of the hard carbon material. Due to π-π conjugate interaction and / or van der Waals force interaction, the hydrophobic compound is fixed in the pores of the hard carbon material. During the process of preparing the aqueous paste, under the combined action of the hydrophobic compound and steric hindrance, water molecules cannot enter the pores of the hard carbon material, and there is no situation of air expulsion.

[0106] In addition, by using supercritical fluid to introduce the hydrophobic compound into the pores of the hard carbon material, the use of traditional solvents is reduced, and pollution is lowered.

[0107] In some embodiments, the hydrophobic compound and the hard carbon material are mixed evenly at a weight ratio of 0.1 - 5:100. Exemplarily, the weight ratio of the hydrophobic compound to the hard carbon material is 1.0:100, 1.5:100, 2.0:100, 2.5:100, 3.0:100, 3.5:100, or 4.0:100.

[0108] By defining the range of the mixing weight ratio between the hydrophobic compound and the hard carbon material, the hydrophobic compound can enter the pores of the hard carbon material, occupy the pores of the hard carbon material, and form a composite hard carbon material; solvents in the negative electrode paste, such as water molecules, cannot enter the pores of the composite hard carbon material, thus effectively reducing the foaming of the negative electrode paste.

[0109] In some embodiments, the supercritical fluid is selected from supercritical carbon dioxide, supercritical nitric oxide, supercritical acetylene, supercritical trifluoromethane, supercritical trichloromethane, supercritical methane, supercritical ethane, supercritical propane, supercritical ethylene, supercritical propylene, supercritical methanol, supercritical ethanol, supercritical acetone, supercritical chlorofluorocarbon, or supercritical xenon. Optionally, the supercritical fluid is supercritical carbon dioxide.

[0110] For example, the supercritical fluid can be supercritical carbon dioxide. The supercritical state of carbon dioxide is relatively easy to achieve, with a critical temperature of 304.2 K (i.e., 31.05 °C), a critical pressure of 7.38 MPa, and supercritical carbon dioxide has the advantages of stable chemical properties, non-toxic and harmless, and low cost. During the process of treating hard carbon materials and hydrophobic compounds with supercritical carbon dioxide, the reaction temperature range is from 35 °C to 100 °C, and the reaction pressure range is from 8 MPa to 15 MPa. Optionally, the reaction temperature range is from 38 °C to 90 °C. Optionally, the reaction temperature range can be from 40 °C to 80 °C. Optionally, the reaction pressure range is from 9 MPa to 14 MPa. Optionally, the reaction pressure range can be from 9 MPa to 13 MPa.

[0111] It should be noted that the hard carbon material and the hydrophobic compound react in the supercritical fluid to obtain a composite hard carbon material. The temperature conditions and pressure conditions for different types of supercritical fluids to achieve the supercritical state are different. According to the type of supercritical fluid selected, appropriate temperature conditions and pressure conditions can be selected as the reaction temperature and reaction pressure for preparing the composite hard carbon material.

[0112] In some embodiments, the reaction duration of the hard carbon material and the hydrophobic compound in the supercritical fluid is from 2 h to 10 h. Optionally, the reaction duration is from 3 h to 9 h. Optionally, the reaction duration can be from 4 h to 8 h. For example, the reaction duration can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or 9 h.

[0113] By limiting the reaction duration of the hard carbon material and the hydrophobic compound in the supercritical fluid, it is beneficial for the hard carbon material and the hydrophobic compound to react fully, so that the hydrophobic compound enters the pores of the hard carbon material to form a composite hard carbon material.

[0114] The third aspect of the present application provides a negative electrode slurry, which includes the composite hard carbon material of the first aspect of the present application and a solvent, as well as at least one of a conductive agent, a dispersant, and a binder.

[0115] Therefore, the negative electrode slurry provided by the present application includes the composite hard carbon material in the above technical solution. The pores of the composite hard carbon material include hydrophobic compounds, so that solvents such as water molecules in the negative electrode slurry cannot enter the pores of the composite hard carbon material, thereby effectively reducing the foaming of the negative electrode slurry and further improving the stability of the negative electrode slurry. Even if it is placed for several days, the negative electrode slurry will not foam, and the viscosity remains stable.

[0116] In some embodiments, based on the solid content in the negative electrode paste, the content of the composite hard carbon material is 85 wt% to 97 wt%; the content of the conductive agent is 0 to 5 wt%; the content of the dispersant is 0.5 wt% to 5 wt%; and the content of the binder is 0.5 wt% to 5 wt%.

[0117] Optionally, the content of the composite hard carbon material is 90% to 96%. Optionally, the content of the composite hard carbon material can be 90% to 93%.

[0118] Optionally, the content of the conductive agent is 0.5% to 4%. Optionally, the content of the conductive agent can be 1% to 2%.

[0119] Optionally, the content of the dispersant is 0.8% to 3%. Optionally, the content of the dispersant can be 1.5% to 2%.

[0120] Optionally, the content of the binder is 1.0 to 4%. Optionally, the content of the binder can be 2.4% to 3%.

[0121] In some embodiments, the solvent is water.

[0122] In some embodiments, based on the total weight of the negative electrode paste, the total solid content of the negative electrode paste is 40 wt% to 65 wt%.

[0123] Optionally, the total solid content of the negative electrode paste can be 45% to 62%. Optionally, the total solid content of the negative electrode paste can be 50% to 60%.

[0124] In some embodiments, the conductive agent is selected from at least one of carbon black, carbon nanotubes, and graphene;

[0125] and / or, the dispersant is selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose;

[0126] and / or, the binder is selected from at least one of styrene-butadiene rubber, styrene-acrylic emulsion, and modified polyacrylic acids.

[0127] The fourth aspect of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes the composite hard carbon material of the first aspect of the present application.

[0128] Negative electrode plate

[0129] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes the composite hard carbon material of the first aspect of the present application.

[0130] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0131] 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 substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0132] In some embodiments, the negative electrode sheet can be prepared by the following method: dispersing the above components for preparing the negative electrode sheet, such as the composite hard carbon material, the conductive agent, the binder, the dispersant, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0133] In addition, the secondary battery and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0134] The fifth aspect of the present application provides a secondary battery, and the secondary battery includes the negative electrode sheet of the fourth aspect of the present application.

[0135] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. The following will be described separately.

[0136] Generally, a secondary battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth 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 disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0137] Positive electrode sheet

[0138] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0139] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0140] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0141] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM811 )), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 )) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), the composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), the composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of the composite material of lithium manganese iron phosphate and carbon.

[0142] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material can adopt the positive electrode active material for sodium-ion batteries well-known in the art. As an example, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds (phosphates, fluorophosphates, pyrophosphates, sulfates), Prussian blue compounds, etc. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery can also be used.

[0143] As an optional technical solution of the present application, 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 MO 2 , where M is one or several of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. For example, sodium iron composite oxide (NaFeO 2 ), sodium cobalt composite oxide (NaCoO 2 ), sodium chromium composite oxide (NaCrO 2 ), sodium manganese composite oxide (NaMnO 2 ), sodium nickel composite oxide (NaNiO 2 ), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O 2 ), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O 2 ), sodium iron manganese composite oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O 2 ), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ).

[0144] As an alternative technical solution of the present application, the polyanionic compound may be a type of compound having sodium ions, transition metal ions, and tetrahedral (YO 4 ) n- anion units. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si; n represents the valence state of (YO 4 ) n- .

[0145] The polyanionic compound may also be a type of compound having sodium ions, transition metal ions, tetrahedral (YO 4 ) n- anion units, and halogen anions. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be at least one of P, S, and Si, n represents the valence state of (YO 4 ) n- ; the halogen may be at least one of F, Cl, and Br.

[0146] The polyanionic compound may also be a type of compound having sodium ions, tetrahedral (YO 4 ) n- anion units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y may be at least one of P, S, and Si, n represents the valence state of (YO 4 ) n- ; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents the valence state of (ZO y ) m+ ; the halogen may be at least one of F, Cl, and Br.

[0147] Examples of the polyanionic compound are NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaM’PO 4 F (M’ is one or more of V, Fe, Mn, and Ni) and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ≤ y ≤ 1), etc.

[0148] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me’ c (CN) 6 , where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0149] 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.

[0150] 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.

[0151] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the 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.

[0152] Electrolyte

[0153] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel or all-solid state.

[0154] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0155] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate and lithium tetrafluorooxalate phosphate.

[0156] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl 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.

[0157] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0158] Separator

[0159] In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0160] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0161] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator may be made into an electrode assembly by a winding process or a stacking process.

[0162] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0163] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0164] The present application does not particularly limit the shape of the battery cell, and it may be cylindrical, square or any other shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0165] In some embodiments, refer to Figure 2, the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0166] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0167] Figure 3 is a battery module 4 as an example. Refer to Figure 3 , in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0168] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0169] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0170] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , the battery pack 1 may 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. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0171] In addition, the present application also provides an electrical device, which includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0172] As the electrical device, the battery cell, battery module or battery pack can be selected according to its usage requirements.

[0173] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0174] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery cell can be adopted as the power source.

[0175] Embodiment

[0176] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0177] Preparation of hard carbon material

[0178] Put the coconut shell / starch / lignin at 200°C to 300°C for pre-carbonization treatment of the coconut shell / starch / lignin; use a roller press to crush the pre-carbonized coconut shell into particles with a diameter of about 2 mm, and remove impurities by screening; heat-treat the particles at 400°C to 800°C, and optionally introduce halogen or hydrogen halide gas to remove ash, to obtain particles that are easy to be ball-milled; perform ball milling on the particles; place the ball-milled particles in an inert atmosphere and keep the temperature at 1150°C to carbonize the ball-milled particles. Optionally, acetylene gas can be introduced to perform vapor deposition carbon coating on the ball-milled particles, thereby preparing hard carbon particles with irregular shapes.

[0179] Preparation of composite hard carbon material

[0180] Embodiment 1

[0181] After uniformly mixing the hard carbon material and the hydrophobic compound 1, put them into a reaction kettle; among them, the weight ratio between the hydrophobic compound 1 and the hard carbon material is 2:100; charge supercritical carbon dioxide into the reaction kettle so that the hard carbon material and the hydrophobic compound 1 react in supercritical carbon dioxide to obtain a composite hard carbon material; among them, the reaction temperature is 50 °C, the reaction pressure is 8 MPa, and the reaction duration is 8 h. The chemical formula of the hydrophobic compound 1 is as follows:

[0182]

[0183] Examples 2 to 24

[0184] Under the same conditions as in Example 1, the difference is that the hydrophobic compound 1 is successively replaced by the hydrophobic compounds 2 to 24. The chemical formulas of the hydrophobic compounds 2 to 24 are as follows:

[0185]

[0186]

[0187] Examples 25 to 26

[0188] Under the same conditions as in Example 1, the difference is that the weight ratios between the hydrophobic compound 1 and the hard carbon material are 0.1:100 and 5:100, respectively.

[0189] Comparative Example 1

[0190] The hard carbon material of Comparative Example 1 is the hard carbon material prepared by the above-mentioned preparation method of the hard carbon material without any treatment. That is, the pores of the hard carbon material are not filled with a hydrophobic compound.

[0191] As shown in Table 1, in Examples 1 to 24, the composite hard carbon materials were prepared using the hydrophobic compounds 1 to 24, respectively. The X group and the substituents R on the benzene ring in each hydrophobic compound 1 to R 10 can be referred to as shown in Table 1.

[0192] Table 1

[0193]

[0194]

[0195] Preparation of the negative electrode slurry

[0196] Disperse and stir the composite hard carbon material, conductive agent carbon black, dispersant carboxymethyl cellulose sodium, and binder styrene-acrylic emulsion in Example 1 in water according to a weight ratio of 95:1:1.2:2.8 to obtain a negative electrode slurry with a solid content of 55%.

[0197] Similarly, the composite hard carbon materials in Examples 2 to 26 and the hard carbon material in Comparative Example 1 were used to replace the composite hard carbon material in Example 1, respectively, to prepare the corresponding negative electrode slurries.

[0198] Testing of the negative electrode slurry

[0199] (1) Testing of the foaming situation of the negative electrode slurry

[0200] It was visually observed whether the negative electrode slurry foamed after standing still after sufficient stirring. For example, it was observed whether the volume of the slurry changed and whether it showed a sponge-like state, and a photo was taken for record.

[0201] (2) Testing of the viscosity stability of the negative electrode slurry

[0202] The viscosity of the negative electrode slurry was measured at room temperature (20 - 35 °C) by a viscometer (model DVESLVTJ0, a viscometer purchased from Brookfield). After the negative electrode slurry was sufficiently stirred and then allowed to stand for 5 min, the viscosity of the negative electrode slurry was measured. The viscosity was measured every 2 h for a total of 24 h, and the viscosity change was observed. If the viscosity change rate within 24 h ≤ 2000 mPa·s, it was considered that the viscosity was stable.

[0203] Preparation of the secondary battery

[0204] (1) Preparation of the positive electrode sheet

[0205] The positive electrode active material sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O 2 )), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were sufficiently stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) according to a weight ratio of 92:5:3 to form a uniform positive electrode slurry; the positive electrode slurry was coated on a positive electrode current collector aluminum foil with a thickness of 13 μm, and after drying at 100 °C, it was pressed to obtain a positive electrode sheet.

[0206] (2) Preparation of the negative electrode sheet

[0207] After the above-mentioned negative electrode slurry was sufficiently stirred and then allowed to stand for 24 h, it was coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8 μm, and after drying at 100 °C, it was pressed to obtain a negative electrode sheet.

[0208] (3) Preparation of the electrolyte

[0209] Ethylene carbonate (EC) and propylene carbonate (PC) in equal volumes were mixed evenly to obtain an organic solvent, and then NaPF 6 was uniformly dissolved in the above-mentioned organic solvent to obtain an electrolyte, where NaPF6 The concentration is 1 mol / L.

[0210] (4) Preparation of secondary battery

[0211] Using a polyethylene film (PE) as the separator. Stack the prepared positive electrode sheet, separator, negative electrode sheet prepared using the composite hard carbon materials in Examples 1 to 26, or the negative electrode sheet prepared using the hard carbon material in Comparative Example 1 in sequence, with the separator in the middle of the positive and negative electrode sheets to play a separating role, wind to obtain a bare battery core, weld the electrode tabs, place the bare battery core in the outer package, inject the above electrolytes into the dried battery core respectively, and perform encapsulation, standing, formation, shaping, capacity testing, etc. to prepare a secondary battery.

[0212] Porosity test of hard carbon materials and composite hard carbon materials

[0213] The porosity of the hard carbon material was measured using a specific surface area and porosity analyzer, and the equipment was TriStar II 3020. The porosity of the hard carbon material in Comparative Example 1 was obtained, and the porosity of the composite hard carbon materials in Examples 1 to 26 was also tested.

[0214] Testing of secondary batteries

[0215] Testing of cycle performance

[0216] At 25 °C, the secondary battery was charged at a constant current of 1 / 3C to 4.0V, then charged at a constant voltage of 4.2V until the current was 0.05C, left standing for 5 min, and then discharged at 1 / 3C to 2.8V. The obtained capacity was recorded as the initial capacity C0. Repeat the above steps for the same battery, and at the same time record the discharge capacity Cn of the battery after the nth cycle. Then the battery capacity retention rate Pn = Cn / C0 * 100%. The minimum n value corresponding to Pn ≤ 80% was used as the cycle life of the secondary battery.

[0217] Table 2

[0218]

[0219]

[0220] As shown in Table 2, in Examples 1 to 26, hydrophobic compounds 1 to 26 were respectively used to treat the hard carbon materials, and composite hard carbon materials with hydrophobic compounds filled in the pores were obtained. In Comparative Example 1, the hard carbon materials were not treated with hydrophobic compounds, and no hydrophobic compounds were filled in the pores of the hard carbon materials. Compared with the porosity of the hard carbon materials in Comparative Example 1, in Examples 1 to 24, different hydrophobic compounds were respectively filled in the pores of the hard carbon materials, and the weight ratio between the hydrophobic compounds and the hard carbon materials was the same, both being 2:100. It can be seen from the data in Table 1 that after filling the hydrophobic compounds, the porosity of the composite hard carbon materials all became smaller. Compared with the porosity of the hard carbon materials in Comparative Example 1, in Examples 1, 25, and 26, after filling hydrophobic compound 1 in the pores of the hard carbon materials, the weight ratio between the hydrophobic compounds and the hard carbon materials was different, being 2:100, 0.1:100, and 5:100 in sequence. It can be seen from the data in Table 1 that after filling the hydrophobic compounds, the porosity of the composite hard carbon materials all became smaller.

[0221] Table 3

[0222]

[0223]

[0224] Table 3 also shows the foaming conditions of the negative electrode slurries prepared using the composite hard carbon materials in Examples 1 to 26 and the negative electrode slurry prepared using the hard carbon materials in Comparative Example 1. The negative electrode slurries prepared using the composite hard carbon materials in Examples 1 to 26 can all be placed for 6 days or 7 days without foaming. However, the negative electrode slurry prepared using the hard carbon materials in Comparative Example 1 foams after being placed for only 12 hours.

[0225] Figure 7 shows the state of the negative electrode slurry prepared from the composite hard carbon material in Example 1 after sufficient stirring. As Figure 7 shown in Figure (a) therein, when the negative electrode slurry is prepared using the composite hard carbon material in Example 1, after stirring, the negative electrode slurry is a uniform slurry system; as Figure 7 shown in Figure (b) therein, after the negative electrode slurry is left standing for 7 days, the negative electrode slurry still remains a uniform slurry system.

[0226] As Figure 8 shown in Figure (a) therein, when the negative electrode slurry is prepared using the hard carbon material in Comparative Example 1, after stirring, the negative electrode slurry is a uniform slurry system; as Figure 8 shown in Figure (b) therein, after the negative electrode slurry is left standing for only 12 h, the negative electrode slurry foams and becomes a non-uniform slurry system.

[0227] As still shown in Table 3, the negative electrode slurries corresponding to the composite hard carbon materials provided in Examples 1 to 26 remained as uniform slurry systems after being placed for 24 h. Therefore, the viscosity fluctuation within 24 h was ≤2000 mPa·s; for the negative electrode slurry corresponding to the hard carbon material provided in Comparative Example 1, the negative electrode slurry had foamed and become a non-uniform slurry system after being placed for 12 h. Therefore, the viscosity fluctuation within 24 h was >10,000 mPa·s.

[0228] As still shown in Table 3, the cycling performance of the secondary batteries corresponding to the composite hard carbon materials provided in Examples 1 to 26 was significantly better than that of the secondary batteries corresponding to the hard carbon material provided in Comparative Example 1. This was because the negative electrode slurry corresponding to the composite hard carbon material foamed and became a non-uniform slurry system, resulting in poor uniformity and a large weight loss rate of the negative electrode sheet formed by coating and cold pressing, and ultimately leading to the deterioration of the cycling performance of the secondary battery.

[0229] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same function and effect as the technical idea within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other modes constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A composite hard carbon material, characterized in that: The composite hard carbon material comprises: a hard carbon material and a hydrophobic compound filled in the pores of the hard carbon material, wherein the hydrophobic compound is a compound represented by the following formula (I): In the formula (I), X is O, S, C=O, CR 11 R 12 NR 21 , PR 31 、P(=O)R 32 or P(=S)R 33 ; Among them, R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH2, halogen, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted 5- to 10-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 8-membered cycloalkyl or heterocycloalkyl, amide or thiocarboxamido; when the C1-C10 alkyl, 5- to 10-membered heteroaryl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include at least one of OH, NH2, halogen, C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl; R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from any one of R, OR, C(=O)R, COOR, 6-membered to 10-membered aryl and halogen, wherein each R is independently selected from any one of H and C1-C10 alkyl.

2. The composite hard carbon material according to claim 1, characterized in that In the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH2, halogen, unsubstituted or substituted C1-C4 alkyl, unsubstituted or substituted 5- to 6-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 6-membered cycloalkyl or heterocycloalkyl, amide or thiocarboxamido; when C1-C4 alkyl, 5- to 6-membered heteroaryl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include at least one of OH, NH2, halogen, C1-C4 alkyl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl; R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from any one of R, OR, C(=O)R, COOR, phenyl and halogen, wherein each R is independently selected from any one of H and C1-C4 alkyl.

3. The composite hard carbon material according to claim 1 or 2, characterized in that: In the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each is independently selected from any one of H, SH, OH, NH2, phenyl, 4-hydroxyphenyl, furanyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, piperidyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxirane, ethylenethiocyanate, cyclohexanyl, benzyl, thiocarboxamido, 1-pyrrolidin-2-yl-methyl, and C1~C4 alkyl.

4. The composite hard carbon material according to any one of claims 1 to 3, characterized in that The hydrophobic compound is selected from at least one of the following compounds:

5. The composite hard carbon material according to any one of claims 1 to 4, characterized in that: In the composite hard carbon material, the weight ratio of the hydrophobic compound to the hard carbon material is 0.1 to 5:

100.

6. The composite hard carbon material according to any one of claims 1 to 5, characterized in that The hydrophobic compound is fixed in the pores of the hard carbon material through π-π conjugated interactions and / or van der Waals interactions.

7. A method for preparing a composite hard carbon material, characterized in that: The method comprises: The hard carbon material and the hydrophobic compound are mixed evenly and then placed in a reaction kettle; Filling the reactor with a supercritical fluid so that the hard carbon material and the hydrophobic compound react in the supercritical fluid to obtain a composite hard carbon material; Wherein, the hydrophobic compound is a compound represented by the following formula (I): In the formula (I), X is O, S, C=O, CR 11 R 12 NR 21 , PR 31 、P(=O)R 32 or P(=S)R 33 ; Among them, R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH2, halogen, unsubstituted or substituted C1-C10 alkyl, unsubstituted or substituted 5- to 10-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 8-membered cycloalkyl or heterocycloalkyl, amide or thiocarboxamido; when the C1-C10 alkyl, 5- to 10-membered heteroaryl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include at least one of OH, NH2, halogen, C1-C10 alkyl, 6- to 10-membered aryl, 3- to 8-membered cycloalkyl or heterocycloalkyl; R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from any one of R, OR, C(=O)R, COOR, 6-membered to 10-membered aryl and halogen, wherein each R is independently selected from any one of H and C1-C10 alkyl.

8. The preparation method according to claim 7, characterized in that: In the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each independently selected from H, SH, OH, NH2, halogen, unsubstituted or substituted C1-C4 alkyl, unsubstituted or substituted 5- to 6-membered heteroaryl or 6- to 10-membered aryl, unsubstituted or substituted 3- to 6-membered cycloalkyl or heterocycloalkyl, amide or thiocarboxamido; when C1-C4 alkyl, 5- to 6-membered heteroaryl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl is substituted, their substituents each independently include at least one of OH, NH2, halogen, C1-C4 alkyl, 6- to 10-membered aryl, 3- to 6-membered cycloalkyl or heterocycloalkyl; R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from any one of R, OR, C(=O)R, COOR, phenyl and halogen, wherein each R is independently selected from any one of H and C1-C4 alkyl.

9. The preparation method according to claim 7 or 8, characterized in that: In the formula (I), R 11 , R 12 , R 21 , R 31 , R 32 , R 33 Each is independently selected from any one of H, SH, OH, NH2, phenyl, 4-hydroxyphenyl, furanyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, piperidyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxirane, ethylenethiocyanate, cyclohexanyl, benzyl, thiocarboxamido, 1-pyrrolidin-2-yl-methyl, and C1~C4 alkyl.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The hydrophobic compound is selected from at least one of the following compounds:

11. The preparation method according to any one of claims 7 to 10, characterized in that: The hydrophobic compound and the hard carbon material are uniformly mixed in a weight ratio of 0.1 to 5:

100.

12. The preparation method according to any one of claims 7 to 11, characterized in that: The supercritical fluid is selected from supercritical carbon dioxide, supercritical nitric oxide, supercritical acetylene, supercritical trifluoromethane, supercritical chloroform, supercritical methane, supercritical ethane, supercritical propane, supercritical ethylene, supercritical propylene, supercritical methanol, supercritical ethanol, supercritical acetone, supercritical chlorofluorocarbon or supercritical xenon.

13. The preparation method according to any one of claims 7 to 12, characterized in that: The reaction time of the hard carbon material and the hydrophobic compound in the supercritical fluid is 2 hours to 10 hours.

14. A negative electrode slurry, characterized in that: The negative electrode slurry includes the composite hard carbon material according to any one of claims 1 to 6 and a solvent, and at least one of a conductive agent, a dispersant, and a binder.

15. The negative electrode slurry according to claim 14, characterized in that: Based on the solid content in the negative electrode slurry, the content of the composite hard carbon material is 85wt% to 97wt%; the content of the conductive agent is 0 to 5wt%; the content of the dispersant is 0.5wt% to 5wt%; and the content of the binder is 0.5wt% to 5wt%.

16. The negative electrode slurry according to claim 14 or 15, characterized in that: The solvent is water.

17. The negative electrode slurry according to any one of claims 14 to 16, characterized in that: The total solid content of the negative electrode slurry is 40 wt % to 65 wt % relative to the total weight of the negative electrode slurry.

18. The negative electrode slurry according to any one of claims 14 to 17, characterized in that: The conductive agent is selected from at least one of carbon black, carbon nanotubes and graphene; And / or, the dispersant is selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; And / or, the binder is selected from at least one of styrene-butadiene rubber, styrene-acrylic emulsion and modified polyacrylic acid.

19. A negative electrode plate, characterized in that: The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the composite hard carbon material according to any one of claims 1 to 6.

20. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet according to claim 19.

21. An electrical device, characterized in that: The electric device comprises the secondary battery according to claim 20.

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