Hard carbon negative electrode slurry, preparation method thereof, hard carbon negative electrode plate and sodium ion battery

Abstract

The invention relates to a hard carbon negative electrode slurry, a preparation method thereof, a hard carbon negative electrode plate and a sodium ion battery, the formula of the hard carbon negative electrode slurry is improved, a stable conductive network skeleton is constructed through a non-polar solvent, and agglomeration of a conductive agent is avoided; meanwhile, gradient coating is realized by utilizing a polar solvent. Through the optimized formula, the stability and dispersion uniformity of the hard carbon negative electrode slurry are improved, and the viscosity in the preparation process is maintained at 3000 mPa.s to 5000 mPa.s. The hard carbon negative electrode plate prepared from the hard carbon negative electrode slurry has uniform membrane density, can reduce stress concentration in a sodion deintercalation process, and inhibits volume expansion, so that the cycle performance is improved. Besides, the hard carbon negative plate forms a compact and stable solid electrolyte interface (SEI) film in the first charging and discharging process, and the irreversible capacity loss is effectively reduced, so that the first coulombic efficiency of the sodium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a negative electrode slurry, in particular to a hard carbon negative electrode slurry, a preparation method thereof, a hard carbon negative electrode sheet and a sodium ion battery. Background Art

[0002] Graphite is currently widely used as the negative electrode material in lithium-ion batteries. However, the small interlayer spacing of graphite hinders the embedding of sodium ions. Furthermore, graphite compounds with high sodium content are thermodynamically unstable, making graphite unusable in sodium batteries. Hard carbon materials offer advantages such as structural diversity, low cost, good conductivity, high sodium storage capacity, and low redox potential. However, as a carbon material that is difficult to graphitize, hard carbon has a complex morphology, with disordered internal carbon layers and numerous pores. This results in poor dispersion in aqueous slurries, making screening difficult and prone to clogging.

[0003] CN118281222A discloses a sodium ion battery negative electrode slurry, a preparation method and application thereof. The negative electrode slurry is prepared by gradually mixing and stirring a hard carbon active material, a conductive agent, a suspension stabilizer A, a suspension stabilizer B, a binder and a solvent in a certain ratio. The preparation method is to first mix the suspension stabilizer A and the suspension stabilizer B in a solvent, then sequentially add the conductive agent powder and the hard carbon active material, and finally add the binder and stir evenly under vacuum conditions.

[0004] However, hard carbon materials suffer from numerous surface defects, low initial coulombic efficiency, and poor interfacial compatibility with binders, leading to slurry sedimentation and uneven coating. The significant volume expansion of sodium ions during intercalation and deintercalation makes traditional hard carbon anode slurry formulations unstable, and existing dispersion processes struggle to achieve a uniform dispersion of the conductive agent and hard carbon.

[0005] Therefore, it is necessary to provide a hard carbon negative electrode slurry and a preparation method thereof that can achieve uniform dispersion of a conductive agent and hard carbon. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a hard carbon negative electrode slurry, a preparation method thereof, a hard carbon negative electrode sheet and a sodium ion battery. By improving the formula of the hard carbon negative electrode slurry and the preparation method thereof, the hard carbon negative electrode sheet prepared from the hard carbon negative electrode slurry has a uniform film density and a higher compaction density, thereby improving the electrochemical performance of the sodium ion battery.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a hard carbon negative electrode slurry, wherein the raw materials of the hard carbon negative electrode slurry include hard carbon, a conductive agent, a composite binder, a silane coupling agent, a thixotropic agent, a non-polar solvent and a polar solvent;

[0009] The mass ratio of the hard carbon, the conductive agent, the composite binder, the silane coupling agent and the thixotropic agent is (92-95):(2-3):(2-3):(0.1-0.3):0.2.

[0010] The present invention improves the hard carbon negative electrode slurry formulation, utilizing a non-polar solvent to form a conductive network skeleton to prevent conductive agent agglomeration; and utilizes a polar solvent to achieve gradient coating. This optimized formulation improves the stability and dispersion uniformity of the hard carbon negative electrode slurry, maintaining a viscosity of 3000-5000 mPa·s during the preparation process. The hard carbon negative electrode sheet prepared from the hard carbon negative electrode slurry of the present invention has a uniform film density, which can reduce stress concentration during sodium ion intercalation and deintercalation, inhibit volume expansion, and thus improve cycle performance. Furthermore, the hard carbon negative electrode sheet forms a dense and stable solid electrolyte interface (SEI) film during the initial charge and discharge process, effectively reducing irreversible capacity loss and thereby improving the initial coulombic efficiency of the sodium ion battery.

[0011] The mass ratio of hard carbon to thixotropic agent is 92:0.2-95:0.2, for example, 92:0.2, 93:0.2, 94:0.2 or 95:0.2, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0012] The mass ratio of the conductive agent to the thixotropic agent is 2:0.2-3:0.2, for example, 2:0.2, 2.2:0.2, 2.5:0.2, 2.7:0.2, 2.8:0.2 or 3:0.2, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0013] The mass ratio of the composite adhesive to the thixotropic agent is 2:0.2-3:0.2, for example, it can be 2:0.2, 2.2:0.2, 2.5:0.2, 2.7:0.2, 2.8:0.2 or 3:0.2, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0014] The mass ratio of the silane coupling agent to the thixotropic agent is 0.1:0.2-0.3:0.2, for example, 0.1:0.2, 0.2:0.2 or 0.3:0.2, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, the solid content of the hard carbon negative electrode slurry is 40wt%-50wt%, for example, it can be 40wt%, 42wt%, 45wt%, 48wt% or 50wt%, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0016] The non-polar solvent in the present invention is used to form a conductive network skeleton.

[0017] Preferably, the non-polar solvent comprises any one or a combination of at least two of toluene, benzene or carbon tetrachloride, and a typical but non-limiting skeleton comprises a combination of toluene and benzene, a combination of toluene and carbon tetrachloride, a combination of benzene and carbon tetrachloride, or a combination of toluene, benzene and carbon tetrachloride.

[0018] In the present invention, the polar solvent is used to dissolve the composite binder and improve the uniformity of the hard carbon negative electrode slurry.

[0019] Preferably, the polar solvent comprises any one or a combination of at least two of N-methylpyrrolidone (NMP), water, glycerol or dimethyl sulfoxide (DMSO). Typical but non-limiting combinations include a combination of NMP and water, a combination of NMP and glycerol, a combination of NMP and DMSO, a combination of NMP, glycerol and DMSO, or a combination of NMP, water, glycerol and DMSO.

[0020] The present invention improves the stability of the hard carbon negative electrode slurry by synergistically combining a non-polar solvent and a polar solvent, so that the hard carbon and the conductive agent therein can be evenly dispersed.

[0021] Preferably, the volume ratio of the non-polar solvent to the polar solvent is 1:2-1:3, for example, it can be 1:2, 1:2.2, 1:2.4, 1:2.5, 1:2.7, 1:2.8 or 1:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the conductive agent includes carbon nanotubes and / or conductive carbon.

[0023] Optionally, the carbon nanotubes include any one of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) or double-walled carbon nanotubes (DWCNTs) or a combination of at least two of them. Typical but non-limiting combinations include a combination of SWCNTs and MWCNTs, a combination of SWCNTs and DWCNTs, a combination of MWCNTs and DWCNTs, or a combination of SWCNTs, MWCNTs and DWCNTs.

[0024] Optionally, the conductive carbon includes any one or a combination of at least two of conductive carbon black, graphite or activated carbon. Typical but non-limiting combinations include a combination of conductive carbon black and graphite, a combination of graphite and activated carbon, a combination of conductive carbon black and activated carbon, or a combination of conductive carbon black, graphite and activated carbon.

[0025] Carbon nanotubes, with their superior one-dimensional nanostructure and extremely high carrier mobility, can form efficient electron transport channels. Conductive carbon, with its large specific surface area and rich porous structure, can increase the contact area with hard carbon and improve electron transport efficiency. Therefore, the synergistic effect of carbon nanotubes and conductive carbon in an appropriate mass ratio helps improve the coating performance of the slurry, helping to maintain the integrity of the electrode structure during the cycling of sodium-ion batteries, thereby extending the cycle life.

[0026] Preferably, the conductive agent comprises carbon nanotubes and conductive carbon in a mass ratio of (1-2):(1-2), for example, 1:1, 1:2 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the composite binder comprises sodium carboxymethylcellulose (CMC) and / or polyacrylic acid (PAA).

[0028] The molecular chain of CMC contains a large number of polar groups such as hydroxyl and carboxyl groups, which can form hydrogen bonds with the hydroxyl groups on the surface of hard carbon; PAA contains a large number of carboxyl groups, which can form physical adsorption and chemical bonding with hard carbon, thereby improving the strong bonding force; the synergistic cooperation of CMC and PAA in a suitable mass ratio is beneficial to the stability of the hard carbon negative electrode slurry, and is also beneficial to ensuring the coating uniformity of the hard carbon negative electrode slurry, and is also beneficial to the structural stability of the hard carbon negative electrode sheet, so that the sodium ion battery has good cycle stability.

[0029] Preferably, the composite binder comprises sodium carboxymethyl cellulose and polyacrylic acid in a mass ratio of (1-3):(1-3), for example, it can be 1:1, 1:2, 1:3, 3:2 or 3:1, but is not limited to the listed values, and the remaining values ​​within the numerical range not listed are also applicable.

[0030] Preferably, the silane coupling agent includes any one or a combination of at least two of 3-aminopropyltriethoxysilane (APTES), methyltrimethoxysilane (MTMS), vinyltriethoxysilane (VTES) or mercaptopropyltrimethoxysilane (MPTMS). Typical but non-limiting combinations include a combination of APTES and MTMS, a combination of MTMS and VTES, a combination of VTES and MPTMS, a combination of MTMS, VTES and MPTMS, or a combination of APTES, MTMS, VTES and MPTMS, preferably 3-aminopropyltriethoxysilane.

[0031] Preferably, the raw materials of the hard carbon negative electrode slurry further include a pH regulator.

[0032] The present invention can suppress the residual alkali on the surface of hard carbon by using a pH regulator.

[0033] Optionally, the pH adjuster includes citric acid.

[0034] Preferably, the pH value of the hard carbon negative electrode slurry is 4-5, for example, 4, 4.5 or 5, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] The present invention improves the static stability of the hard carbon negative electrode slurry by using a thixotropic agent.

[0036] Preferably, the thixotropic agent comprises nano-silica aerogel.

[0037] The present invention uses nano-silica aerogel, can utilize the physical adsorption effect of the nano-silica aerogel to increase thixotropy and inhibit the sedimentation of hard carbon particles.

[0038] Optionally, the specific surface area of ​​the nano-silica aerogel is 600m 2 / g~1000m 2 / g, for example, it can be 600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g or 1000m 2 / g, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In a second aspect, the present invention provides a method for preparing a hard carbon negative electrode slurry, the preparation method comprising the following steps:

[0040] (1) mixing hard carbon, a conductive agent, and a non-polar solvent to obtain a first mixed solution;

[0041] (2) mixing a polar solvent, a composite binder, a silane coupling agent and the first mixed solution obtained in step (1) to obtain a second mixed solution;

[0042] (3) Mixing a thixotropic agent with the second mixed solution of step (2) to obtain the hard carbon negative electrode slurry described in the first aspect.

[0043] The preparation method provided by the present invention first mixes hard carbon, a conductive agent, and a non-polar solvent, using the non-polar solvent to form a conductive network skeleton. A polar solvent, a composite binder, and a silane coupling agent are then added to the first mixed solution and mixed, achieving gradient coating by utilizing the polarity difference between the polar and non-polar solvents. A thixotropic agent is then added to achieve stable dispersion of the slurry. The preparation method provided by the present invention can maintain the slurry viscosity between 3000mPa·s and 5000mPa·s throughout the preparation process, facilitating processing and production.

[0044] Preferably, the mixing method in step (1) includes first planetary stirring mixing.

[0045] Preferably, the revolution speed of the first planetary stirring and mixing is 10 rpm-20 rpm, the rotation speed is 80 rpm-120 rpm, and the time is 8 min-12 min.

[0046] The revolution speed of the first planetary stirring and mixing is 10 rpm-20 rpm, for example, it can be 10 rpm, 12 rpm, 15 rpm, 16 rpm, 18 rpm or 20 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] The rotation speed of the first planetary stirring and mixing is 80 rpm-120 rpm, for example, it can be 80 rpm, 90 rpm, 100 rpm, 110 rpm or 120 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] The time for the first planetary stirring and mixing is 8 min-12 min, for example, 8 min, 9 min, 10 min, 11 min or 12 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the mixing method in step (2) includes second planetary stirring mixing.

[0050] Preferably, the second planetary stirring and mixing device has an orbital speed of 25 rpm-35 rpm, a rotational speed of 1800 rpm-2200 rpm, and a stirring time of 25 min-35 min.

[0051] The revolution speed of the second planetary stirring mixer is 25 rpm-35 rpm, for example, it can be 25 rpm, 28 rpm, 30 rpm, 32 rpm or 35 rpm, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0052] The rotation speed of the second planetary stirring mixer is 1800 rpm-2200 rpm, for example, it can be 1800 rpm, 1900 rpm, 2000 rpm, 2100 rpm or 2200 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0053] The second planetary stirring and mixing time is 25 min-35 min, for example, it can be 25 min, 28 min, 30 min, 32 min or 35 min, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0054] Preferably, the mixing in step (3) includes a third planetary stirring and a fourth planetary stirring carried out sequentially under vacuum conditions.

[0055] Preferably, the revolution speed of the third planetary agitator is 10 rpm-20 rpm, the rotation speed is 180 rpm-220 rpm, and the time is 8 min-12 min.

[0056] The revolution speed of the third planetary agitator is 10 rpm-20 rpm, for example, it can be 10 rpm, 12 rpm, 15 rpm, 16 rpm, 18 rpm or 20 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] The rotation speed of the third planetary agitator is 180 rpm-220 rpm, for example, it can be 180 rpm, 190 rpm, 200 rpm, 210 rpm or 220 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] The time of the third planetary stirring is 8 minutes to 12 minutes, for example, it can be 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] Preferably, the fourth planetary stirring device has an orbital speed of 20 rpm-30 rpm, a rotational speed of 2200 rpm-2600 rpm, and a stirring time of 80 min-100 min.

[0060] The revolution speed of the fourth planetary agitator is 20 rpm-30 rpm, for example, it can be 20 rpm, 22 rpm, 24 rpm, 25 rpm, 27 rpm, 28 rpm or 30 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] The rotation speed of the fourth planetary agitator is 2200rpm-2600rpm, for example, it can be 2200rpm, 2250rpm, 2300rpm, 2400rpm, 2500rpm or 2600rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0062] The fourth planetary stirring time is 80 min-100 min, for example, 80 min, 85 min, 90 min, 95 min or 100 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0063] Preferably, a pH regulator is also added during the mixing in step (3).

[0064] In a third aspect, the present invention provides a hard carbon negative electrode sheet, which is prepared from the hard carbon negative electrode slurry described in the first aspect.

[0065] Illustratively, the hard carbon negative electrode slurry of the first aspect is coated on the surface of a current collector and dried to obtain the hard carbon negative electrode sheet.

[0066] Preferably, the coating density of the hard carbon negative electrode sheet is 8 mg / cm 2 -10mg / cm 2 , for example, it can be 8 mg / cm 2 、8.5mg / cm 2 , 9mg / cm 2 , 9.5mg / cm 2 or 10 mg / cm 2 , but not limited to the listed values, the remaining values ​​not listed in the numerical range are also applicable.

[0067] Preferably, the moisture content of the hard carbon negative electrode sheet is ≤200 ppm.

[0068] Preferably, the compaction density of the hard carbon negative electrode sheet is 1g / cm 3 -1.05g / cm 3 , for example, it can be 1g / cm 3 , 1.01g / cm 3 , 1.02g / cm 3 , 1.03g / cm 3 , 1.04g / cm 3 or 1.05g / cm 3 , but not limited to the listed values, the remaining values ​​not listed in the numerical range are also applicable.

[0069] In a fourth aspect, the present invention provides a sodium ion battery, comprising the hard carbon negative electrode sheet described in the third aspect.

[0070] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] The present invention improves the hard carbon negative electrode slurry formulation, utilizing a non-polar solvent to form a conductive network skeleton to prevent conductive agent agglomeration; and utilizes a polar solvent to achieve gradient coating. This optimized formulation improves the stability and dispersion uniformity of the hard carbon negative electrode slurry, maintaining a viscosity of 3000-5000 mPa·s during the preparation process. The hard carbon negative electrode sheet prepared from the hard carbon negative electrode slurry of the present invention has a uniform film density, which can reduce stress concentration during sodium ion intercalation and deintercalation, inhibit volume expansion, and thus improve cycle performance. Furthermore, the hard carbon negative electrode sheet forms a dense and stable solid electrolyte interface (SEI) film during the initial charge and discharge process, effectively reducing irreversible capacity loss and thereby improving the initial coulombic efficiency of the sodium ion battery. DETAILED DESCRIPTION

[0073] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0074] Example 1

[0075] The present embodiment provides a hard carbon negative electrode slurry, wherein the solid content of the hard carbon negative electrode slurry is 45 wt%, and the raw materials include hard carbon (KURANODE Type 2-5 μm), a conductive agent (carbon nanotubes (single-walled carbon nanotubes) and conductive carbon (conductive carbon black) in a mass ratio of 1:2), a composite binder (CMC (Hua Teng MAC 500LC) and PAA (Indile LA136D) in a mass ratio of 3:1), a silane coupling agent (3-aminopropyltriethoxysilane), a thixotropic agent (nanosilica aerogel), a non-polar solvent (toluene) and a polar solvent (water).

[0076] The mass ratio of hard carbon, conductive agent, composite binder, silane coupling agent and thixotropic agent is 94:2:2:0.2:0.2; the volume ratio of non-polar solvent to polar solvent is 1:2.5;

[0077] The raw materials for preparing the hard carbon negative electrode slurry also include a pH regulator, citric acid, and the amount of citric acid used is such that the pH value of the hard carbon negative electrode slurry is 4.

[0078] The preparation method of the hard carbon negative electrode slurry provided in this embodiment includes the following steps:

[0079] (1) a first planetary stirring device mixes hard carbon, a conductive agent, and a non-polar solvent to obtain a first mixed solution;

[0080] The first planetary stirring and mixing has an orbital speed of 15 rpm and an autorotation speed of 100 rpm for 10 minutes;

[0081] (2) mixing the polar solvent, the composite binder, the silane coupling agent and the first mixed solution obtained in step (1) by a second planetary stirring device to obtain a second mixed solution;

[0082] The second planetary stirring and mixing has an orbital speed of 30 rpm and a rotation speed of 2000 rpm for 30 minutes;

[0083] (3) performing a third planetary stirring and a fourth planetary stirring in sequence under vacuum conditions to mix the thixotropic agent, the pH adjuster and the second mixed solution of step (2) to obtain the hard carbon negative electrode slurry;

[0084] The revolution speed of the third planetary stirring is 15 rpm, the rotation speed is 200 rpm, and the time is 10 minutes;

[0085] The fourth planetary stirring device has an orbital speed of 25 rpm, a rotational speed of 2400 rpm, and a stirring time of 90 min.

[0086] Example 2

[0087] The present embodiment provides a hard carbon negative electrode slurry, wherein the solid content of the hard carbon negative electrode slurry is 40 wt%, and the raw materials include hard carbon (KURANODE Type 2-5 μm), a conductive agent (carbon nanotubes (single-walled carbon nanotubes) and conductive carbon (conductive carbon black) in a mass ratio of 2:1), a composite binder (CMC (Hua Teng MAC 500LC) and PAA (Indile LA136D) in a mass ratio of 1:3), a silane coupling agent (3-aminopropyltriethoxysilane), a thixotropic agent (nanosilica aerogel), a non-polar solvent (toluene) and a polar solvent (water).

[0088] The mass ratio of hard carbon, conductive agent, composite binder, silane coupling agent and thixotropic agent is 92:2:2:0.1:0.2; the volume ratio of non-polar solvent to polar solvent is 1:2;

[0089] The raw materials for preparing the hard carbon negative electrode slurry also include a pH regulator, citric acid, and the amount of citric acid used is such that the pH value of the hard carbon negative electrode slurry is 4.

[0090] The preparation method of the hard carbon negative electrode slurry provided in this embodiment includes the following steps:

[0091] (1) a first planetary stirring device mixes hard carbon, a conductive agent, and a non-polar solvent to obtain a first mixed solution;

[0092] The first planetary stirring and mixing has an orbital speed of 10 rpm and an autorotation speed of 80 rpm for 12 minutes;

[0093] (2) mixing the polar solvent, the composite binder, the silane coupling agent and the first mixed solution obtained in step (1) by a second planetary stirring device to obtain a second mixed solution;

[0094] The second planetary stirring and mixing has an orbital speed of 25 rpm and an autorotational speed of 1800 rpm for 35 min.

[0095] (3) performing a third planetary stirring and a fourth planetary stirring in sequence under vacuum conditions to mix the thixotropic agent, the pH adjuster and the second mixed solution of step (2) to obtain the hard carbon negative electrode slurry;

[0096] The revolution speed of the third planetary stirring is 10 rpm, the rotation speed is 180 rpm, and the stirring time is 12 minutes;

[0097] The fourth planetary stirring device has an orbital speed of 20 rpm, a rotational speed of 2200 rpm, and a stirring time of 100 min.

[0098] Example 3

[0099] The present embodiment provides a hard carbon negative electrode slurry, wherein the solid content of the hard carbon negative electrode slurry is 50 wt%, and the raw materials include hard carbon (KURANODE Type 2-5 μm), a conductive agent (carbon nanotubes (single-walled carbon nanotubes) and conductive carbon (conductive carbon black) in a mass ratio of 1:2), a composite binder (CMC (Hua Teng MAC 500LC) and PAA (Indile LA136D) in a mass ratio of 3:1), a silane coupling agent (3-aminopropyltriethoxysilane), a thixotropic agent (nanosilica aerogel), a non-polar solvent (toluene) and a polar solvent (water).

[0100] The mass ratio of hard carbon, conductive agent, composite binder, silane coupling agent and thixotropic agent is 95:3:3:0.3:0.2; the volume ratio of non-polar solvent to polar solvent is 1:3;

[0101] The raw materials for preparing the hard carbon negative electrode slurry also include a pH regulator, citric acid, and the amount of citric acid used is such that the pH value of the hard carbon negative electrode slurry is 5.

[0102] The preparation method of the hard carbon negative electrode slurry provided in this embodiment includes the following steps:

[0103] (1) a first planetary stirring device mixes hard carbon, a conductive agent, and a non-polar solvent to obtain a first mixed solution;

[0104] The first planetary stirring and mixing has an orbital speed of 20 rpm and an autorotational speed of 120 rpm for 8 minutes;

[0105] (2) mixing the polar solvent, the composite binder, the silane coupling agent and the first mixed solution obtained in step (1) by a second planetary stirring device to obtain a second mixed solution;

[0106] The second planetary stirring and mixing has an orbital speed of 35 rpm and a rotation speed of 2200 rpm for 25 minutes;

[0107] (3) performing a third planetary stirring and a fourth planetary stirring in sequence under vacuum conditions to mix the thixotropic agent, the pH adjuster and the second mixed solution of step (2) to obtain the hard carbon negative electrode slurry;

[0108] The revolution speed of the third planetary stirring is 20 rpm, the rotation speed is 220 rpm, and the stirring time is 8 minutes;

[0109] The fourth planetary stirring device has an orbital speed of 30 rpm, a rotational speed of 2600 rpm, and a stirring time of 80 min.

[0110] Example 4

[0111] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of embodiment 1 except that the conductive agent is only carbon nanotubes.

[0112] Example 5

[0113] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of Example 1 except that the conductive agent is only conductive carbon.

[0114] Example 6

[0115] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of Example 1 except that the composite binder is only sodium carboxymethyl cellulose.

[0116] Example 7

[0117] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of Example 1 except that the composite binder is only polyacrylic acid.

[0118] Example 8

[0119] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of Example 1 except that the volume ratio of the non-polar solvent to the polar solvent is 1:1.

[0120] Example 9

[0121] This embodiment provides a hard carbon negative electrode slurry, which is the same as that of Example 1 except that the volume ratio of the non-polar solvent to the polar solvent is 1:4.

[0122] Comparative Example 1

[0123] This comparative example provides a hard carbon negative electrode slurry, which is the same as Example 1 except that no non-polar solvent is used.

[0124] Preparation of hard carbon negative electrode sheets

[0125] The hard carbon negative electrode slurry provided in Examples 1 to 9 and Comparative Example 1 was coated on the surface of the current collector copper foil and dried to obtain a hard carbon negative electrode sheet with a moisture content of ≤ 200 ppm as the negative electrode sheet. The double-sided film density of the coating was 9 mg / cm 2 , compacted density is 1.05g / cm 3 .

[0126] Sodium-ion battery assembly

[0127] A sodium metal foil was used as the counter electrode, a glass fiber separator (GF / A) as the separator, and the electrolyte was a mixture of 1M sodium hexafluorophosphate (NaPF6) dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio EC:DMC:EMC = 3:5:2). The hard carbon anode sheet, separator, and sodium foil were stacked in order, and after the electrolyte was added dropwise, the cells were packaged into CR2032 button cells in an inert atmosphere glove box (H2O / O2 <0.1ppm).

[0128] Performance Testing

[0129] Cycle capacity retention rate: Under constant temperature of 25±2℃, the assembled CR2032 button sodium ion battery was tested using a blue battery test system (LAND CT3001A) with a constant current density of 300mAg - 1 (based on the mass of hard carbon negative electrode active material), the charge and discharge voltage range is set to 0V (discharge cut-off) to 2.0V (charge cut-off, vs. Na + / Na), and the cycle capacity retention rate was calculated by the formula: cycle capacity retention rate = 500th charge specific capacity / first charge specific capacity × 100%.

[0130] Coulombic efficiency: The constant current charge and discharge test was performed using a LAND battery test system (LAND CT3001A) at a constant temperature of 25±2°C, with a current density of 30mAg - 1. Charge and discharge cut-off conditions: Charge end voltage upper limit 2.0V (vs.Na + / Na), the lower limit of discharge termination voltage is 0.01V (vs.Na + The first coulombic efficiency is calculated by the formula: first coulombic efficiency = first charge specific capacity / first discharge specific capacity × 100%.

[0131] Table 1

[0132] Capacity cycle retention rate First coulombic efficiency Example 1 93％ 90％ Example 2 90％ 91％ Example 3 92％ 90％ Example 4 85％ 90％ Example 5 86％ 87％ Example 6 87％ 88％ Example 7 88％ 86％ Example 8 89％ 88％ Example 9 85％ 84％ Comparative Example 1 83％ 85％

[0133] In summary, the present invention improves the formula of the hard carbon negative electrode slurry, constructs a stable conductive network skeleton through non-polar solvents, avoids the agglomeration of the conductive agent; and at the same time uses polar solvents to achieve gradient coating. The optimized formula improves the stability and dispersion uniformity of the hard carbon negative electrode slurry, and the viscosity during the preparation process is maintained at 3000mPa·s-5000mPa·s. The hard carbon negative electrode sheet prepared by the hard carbon negative electrode slurry of the present invention has a uniform film density, which can reduce stress concentration during the sodium ion intercalation and deintercalation process, inhibit volume expansion, and thus improve the cycle performance. In addition, the hard carbon negative electrode sheet forms a dense and stable solid electrolyte interface (SEI) film during the first charge and discharge process, which effectively reduces the irreversible capacity loss, thereby improving the first coulombic efficiency of the sodium ion battery.

[0134] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A hard carbon negative electrode slurry, characterized in that: The raw materials of the hard carbon negative electrode slurry include hard carbon, a conductive agent, a composite binder, a silane coupling agent, a thixotropic agent, a non-polar solvent and a polar solvent; The mass ratio of the hard carbon, the conductive agent, the composite binder, the silane coupling agent and the thixotropic agent is (92-95):(2-3):(2-3):(0.1-0.3):0.

2.

2. The hard carbon negative electrode slurry according to claim 1, characterized in that The solid content of the hard carbon negative electrode slurry is 40wt%-50wt%; Preferably, the non-polar solvent comprises any one of toluene, benzene or carbon tetrachloride or a combination of at least two thereof; Preferably, the polar solvent comprises any one or a combination of at least two of N-methylpyrrolidone, water, glycerol or dimethyl sulfoxide; Preferably, the volume ratio of the non-polar solvent to the polar solvent is 1:2-1:

3.

3. The hard carbon negative electrode slurry according to claim 1 or 2, characterized in that: The conductive agent includes carbon nanotubes and / or conductive carbon; Preferably, the conductive agent comprises carbon nanotubes and conductive carbon in a mass ratio of (1-2):(1-2).

4. The hard carbon negative electrode slurry according to any one of claims 1 to 3, characterized in that: The composite binder includes sodium carboxymethyl cellulose and / or polyacrylic acid; Preferably, the composite binder comprises sodium carboxymethyl cellulose and polyacrylic acid in a mass ratio of (1-3):(1-3).

5. The hard carbon negative electrode slurry according to any one of claims 1 to 4, characterized in that: The silane coupling agent includes any one of 3-aminopropyltriethoxysilane, methyltrimethoxysilane, vinyltriethoxysilane or mercaptopropyltrimethoxysilane, or a combination of at least two thereof, preferably 3-aminopropyltriethoxysilane; Preferably, the raw materials of the hard carbon negative electrode slurry further include a pH regulator; Preferably, the pH value of the hard carbon negative electrode slurry is 4-5; Preferably, the thixotropic agent comprises nano-silica aerogel.

6. A method for preparing a hard carbon negative electrode slurry, characterized in that: The preparation method comprises the following steps: (1) mixing hard carbon, a conductive agent, and a non-polar solvent to obtain a first mixed solution; (2) mixing a polar solvent, a composite binder, a silane coupling agent, and the first mixed solution obtained in step (1) to obtain a second mixed solution; (3) Mixing a thixotropic agent with the second mixed solution of step (2) to obtain the hard carbon negative electrode slurry according to any one of claims 1 to 5.

7. The preparation method according to claim 6, characterized in that The mixing method in step (1) includes first planetary stirring and mixing; Preferably, the revolution speed of the first planetary stirring and mixing is 10 rpm-20 rpm, the rotation speed is 80 rpm-120 rpm, and the time is 8 min-12 min; Preferably, the mixing method in step (2) includes second planetary stirring mixing; Preferably, the second planetary stirring and mixing has an orbital speed of 25 rpm-35 rpm, a rotation speed of 1800 rpm-2200 rpm, and a stirring and mixing time of 25 min-35 min; Preferably, the mixing in step (3) includes a third planetary stirring and a fourth planetary stirring carried out sequentially under vacuum conditions; Preferably, the revolution speed of the third planetary stirring is 10rpm-20rpm, the rotation speed is 180rpm-220rpm, and the time is 8min-12min; Preferably, the fourth planetary stirring device has an orbital speed of 20 rpm-30 rpm, a rotational speed of 2200 rpm-2600 rpm, and a stirring time of 80 min-100 min.

8. The preparation method according to claim 6 or 7, characterized in that A pH regulator is also added during the mixing in step (3).

9. A hard carbon negative electrode sheet, characterized in that: The hard carbon negative electrode sheet is prepared from the hard carbon negative electrode slurry according to any one of claims 1 to 5; The moisture content of the hard carbon negative electrode sheet is ≤200ppm; The compaction density of the hard carbon negative electrode sheet is 1g / cm 3 -1.05g / cm 3 .

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the hard carbon negative electrode sheet according to claim 9.