A carbon-coated foil material and a low-expansion silicon-based negative electrode sheet and a battery using the same

Abstract

The application relates to the technical field of battery materials, and particularly discloses a carbon-coated foil and a low-expansion silicon-based negative electrode sheet and a battery using the same. The carbon-coated foil comprises a foil and a carbon-coated layer arranged on at least one surface of the foil, and the carbon-coated layer comprises polyimide and carbon nanotubes. The application has the advantages that the expansion rate of the silicon-based negative electrode is effectively inhibited, the pulverization and crushing of particles and the damage of SEI film are prevented, and the rate of the battery and the cycle life are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a carbon-coated foil and a low-expansion silicon-based negative electrode sheet and battery using the same. BACKGROUND

[0002] With the wide application of lithium ion batteries in electric vehicles, renewable energy storage systems and other fields, users have increasingly significant demands for long endurance and fast charging of lithium ion batteries. However, the commonly used graphite negative electrode material has reached the theoretical limit of 372 mAh / g and cannot meet the demand for high-performance lithium ion battery negative electrode materials.

[0003] Among the currently known negative electrode materials, silicon-based negative electrode materials have the highest theoretical capacity, more than 10 times that of graphite negative electrode materials. At the same time, the lithium intercalation potential of silicon-based negative electrode materials is slightly higher than that of graphite, which can effectively prevent the occurrence of lithium precipitation reaction and form a relatively wide potential window with the positive electrode material, showing good safety and high energy density, and is expected to replace graphite as the first choice for the next generation of negative electrode materials.

[0004] However, the huge lithium intercalation capacity and Li x The complex phase transition of Si alloy and the phase transition enthalpy loss during the process of changing from crystalline state to amorphous state after the first lithium intercalation cause serious volume expansion (nearly 300%) and structural changes in the lithium intercalation process of silicon-based negative electrode materials, which further causes the surface particles of silicon-based negative electrode materials to pulverize, fall off, deactivate and damage the SEI film, which is manifested as a decrease in the rate of lithium ion batteries and a deterioration in the cycle performance. SUMMARY

[0005] In order to effectively suppress the expansion rate of silicon-based negative electrodes, prevent the pulverization and fragmentation of particles and the damage of SEI film, and further improve the rate and cycle life of the battery, the present application provides a carbon-coated foil and a low-expansion silicon-based negative electrode sheet and battery using the same.

[0006] In a first aspect, the present application provides a carbon-coated foil, which adopts the following technical solution:

[0007] A carbon-coated foil, the carbon-coated foil comprising a foil and a carbon-coated layer provided on at least one surface of the foil, the carbon-coated layer comprising polyimide and carbon nanotubes.

[0008] Optionally, the carbon nanotubes are single-walled carbon nanotubes.

[0009] By adopting the above technical scheme, since the carbon-coated foil is prepared by using the composite conductive slurry containing polyimide and single-walled carbon nanotubes, on the one hand, the polyimide can promote the single-walled carbon nanotubes to form a "closed" conductive path in the composite conductive slurry, thereby improving the conductive performance of the carbon-coated foil; and the polyimide can improve the flexibility of the carbon-coated layer, thereby reducing the expansion rate of the silicon-based negative electrode during the use of the battery, and thereby significantly improving the rate and cycle life of the battery; on the other hand, the polyimide and the single-walled carbon nanotubes jointly act to enable the carbon-coated layer to have good average dispersibility, reduce the agglomeration of the single-walled carbon nanotubes, and enable the carbon-coated layer to be evenly distributed on the surface of the foil, thereby reducing the probability that different electrochemical reactions occur due to different conductivities at different places during the charging and discharging of the electrode and that a complex SEI film is generated at the negative electrode, and reducing the occurrence of local overcharging, thereby reducing the safety hazard.

[0010] Optionally, the coating thickness of the carbon-coated layer on at least one surface of the foil is 1.2-1.8 μm.

[0011] Optionally, the coating thickness of the carbon-coated layer on at least one surface of the foil is 1.2-1.8 μm.

[0012] By adopting the above technical scheme, when the thickness of the carbon-coated layer on the foil is within a certain range, the polarization of the negative electrode sheet can be maximally alleviated, and the internal resistance of the battery can be reduced, thereby reducing the probability of heating of the battery during use, effectively improving the use performance of the battery and prolonging the cycle life of the battery.

[0013] Optionally, the weight ratio of polyimide to carbon nanotubes in the carbon-coated layer is 1:3-5.

[0014] Optionally, the weight ratio of polyimide to carbon nanotubes in the composite conductive slurry is 1:4.

[0015] Optionally, the diameter of the carbon nanotubes is 1-2 nm, the length is 10-30 μm, and the purity is greater than 97%.

[0016] By adopting the above technical scheme, the carbon nanotubes with a length-diameter ratio within a certain range are more likely to form a "closed" conductive path in the composite conductive slurry, and are uniformly dispersed in the polyimide-single-walled carbon nanotube system, thereby improving the adhesion of the composite conductive slurry to the surface material of the negative electrode, reducing the expansion rate of the silicon-based negative electrode, and improving the conductive performance and high-temperature resistance of the silicon-based negative electrode.

[0017] Optionally, the foil is selected from any one of a copper foil or an aluminum foil.

[0018] Optionally, the thickness of the copper foil is 6-10 μm, and the thickness of the aluminum foil is 10-16 μm.

[0019] Optionally, the thickness of the copper foil is 6 μm, and the thickness of the aluminum foil is 12 μm.

[0020] Optionally, the method for preparing the carbon-coated foil comprises the following steps: coating a composite conductive paste on at least one surface of the foil, and forming the carbon coating layer on the surface of the foil by using the composite conductive paste; wherein the composite conductive paste comprises the polyimide and the carbon nanotube.

[0021] Optionally, during the preparation of the composite conductive paste, the stirring speed is 300-800 rpm, the stirring time is 5-10 h, the heating temperature is 40-150 ℃, the heating time is 0.1-2 h, the ultrasonic time is 0.1-5 h, the continuous stirring speed is 300-600 rpm, and the continuous stirring time is 5-10 h.

[0022] Optionally, the viscosity of the composite conductive paste is 50-400 cp, and the particle size is 0.1-2 nm.

[0023] By using the above technical solution, the composite conductive paste has excellent sedimentation stability and rheological properties, which can meet the requirements of the coating process of the electrode plate, and at the same time, the thickness of the composite conductive paste at the center and the edge of the foil is as uniform as possible, so that a carbon coating layer with uniform thickness is obtained.

[0024] Optionally, during the preparation of the carbon-coated foil, an electrostatic spinning spraying process is used to coat the composite conductive paste on the surface of the foil.

[0025] Optionally, in the electrostatic spinning spraying process, the flow rate of the electrostatic spinning liquid is 0.6-1 mL / h, the spinning temperature is 25-35 ℃, and the spinning humidity is 32-37%.

[0026] By using the above technical solution, the composite conductive paste can be uniformly and continuously distributed on the surface of the foil, and the thickness consistency of the carbon coating layer on the surface of the foil is further improved.

[0027] In a second aspect, the present application provides a silicon-based negative electrode plate with low expansion rate, comprising a current collector and a negative active coating layer arranged on at least one surface of the current collector, wherein the current collector is the carbon-coated foil according to any one of claims 1-9, the negative active coating layer comprises a negative active material, and the negative active material comprises a silicon-based material.

[0028] By using the above technical solution, the silicon-based negative electrode plate prepared by the present application can effectively reduce the expansion rate of the silicon-based negative electrode during the lithium intercalation process, so that the expansion rate of the silicon-based negative electrode is as low as 12-20%, and the conductivity of the silicon-based negative electrode is further improved.

[0029] In a third aspect, the application provides a battery comprising a positive electrode sheet and the silicon-based negative electrode sheet according to claim 10.

[0030] By adopting the technical scheme, the battery prepared by the application has high rate and high cycle performance. DETAILED DESCRIPTION

[0031] In order to enable persons skilled in the art to better understand the technical solutions in the application, the technical solutions in the application will be clearly and completely described below in combination with the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by persons skilled in the art without creative effort should fall within the protection scope of the application.

[0032] Preparation example of the composite conductive paste

[0033] Preparation example 1

[0034] A composite conductive paste, wherein the weight ratio of the polyimide to the single-walled carbon nanotube is 1:3.

[0035] A composite conductive paste is prepared by the following steps:

[0036] The polyimide and the single-walled carbon nanotube are mixed, the obtained mixture is stirred at a speed of 300 rpm for 10 h, heated at 40℃ for 2 h, then ultrasonically treated for 0.1 h, and continuously stirred at a speed of 300 rpm for 10 h to obtain the composite conductive paste.

[0037] Preparation example 2

[0038] A composite conductive paste, wherein the weight ratio of the polyimide to the single-walled carbon nanotube is 1:5.

[0039] A composite conductive paste is prepared by the following steps:

[0040] The polyimide and the single-walled carbon nanotube are mixed, the obtained mixture is stirred at a speed of 800 rpm for 5 h, heated at 150℃ for 0.1 h, then ultrasonically treated for 5 h, and continuously stirred at a speed of 600 rpm for 5 h to obtain the composite conductive paste.

[0041] Preparation example 3

[0042] A composite conductive paste, wherein the weight ratio of the polyimide to the single-walled carbon nanotube is 1:4.

[0043] A composite conductive paste is prepared by the following steps:

[0044] The polyimide and single-walled carbon nanotubes are mixed, the mixture is stirred at a speed of 550 rpm for 7.5 h, heated at 95°C for 1 h, then ultrasonically treated for 2.5 h, and continuously stirred at a speed of 450 rpm for 7.5 h to obtain a composite conductive slurry.

[0045] Preparation Example 4

[0046] A composite conductive slurry, wherein the weight ratio of the polyimide to the single-walled carbon nanotubes is 1:4.5.

[0047] A composite conductive slurry is prepared by the following steps:

[0048] The polyimide and single-walled carbon nanotubes are mixed, the mixture is stirred at a speed of 600 rpm for 7 h, heated at 80°C for 1.5 h, then ultrasonically treated for 2.5 h, and continuously stirred at a speed of 400 rpm for 8 h to obtain a composite conductive slurry.

[0049] Preparation Example 5

[0050] A composite conductive slurry, which is different from that of Preparation Example 3 in that the weight ratio of the polyimide to the single-walled carbon nanotubes in the preparation process is 1:2.5.

[0051] Preparation Example 6

[0052] A composite conductive slurry, which is different from that of Preparation Example 3 in that the weight ratio of the polyimide to the single-walled carbon nanotubes in the preparation process is 1:5.5.

[0053] Preparation Example 7

[0054] A composite conductive slurry, which is different from that of Preparation Example 3 in that the diameter of the single-walled carbon nanotubes used in the preparation process is 0.75-0.9 nm.

[0055] Preparation Example 8

[0056] A composite conductive slurry, which is different from that of Preparation Example 3 in that the diameter of the single-walled carbon nanotubes used in the preparation process is 2.5-3 nm.

[0057] Preparation Example 9

[0058] A composite conductive slurry, which is different from that of Preparation Example 3 in that the length of the single-walled carbon nanotubes used in the preparation process is 1-5 μm.

[0059] Preparation Example 10

[0060] A composite conductive slurry, which is different from that of Preparation Example 3 in that the length of the single-walled carbon nanotubes used in the preparation process is 35-45 μm.

[0061] Preparation Example 11

[0062] A composite conductive paste, which is different from Preparation Example 3 in that equal weight of polyimide is used instead of single-walled carbon nanotubes in the preparation process.

[0063] Preparation Example 12

[0064] A composite conductive paste, which is different from Preparation Example 3 in that equal weight of single-walled carbon nanotubes is used instead of polyimide in the preparation process.

[0065] Embodiment

[0066] In this embodiment, when the foil used in the process of preparing the carbon-coated foil is copper foil, all the examples of preparing the carbon-coated copper foil are recorded as Group A, and when the foil used in the process of preparing the carbon-coated foil is aluminum foil, the examples of preparing the carbon-coated aluminum foil are recorded as Group B, the difference between Group B and Group A is that the copper foil is replaced by the aluminum foil, and correspondingly, the thickness of the aluminum foil is selected within the range of the thickness of the aluminum foil recorded in the specification of the present application; that is, in Group A, the thickness of the copper foil in Examples 1-4 is selected to be 8 μm, 10 μm, 6 μm, and 10 μm, respectively, and in Group B, the thickness of the aluminum foil in Examples 1-4 is selected to be 14 μm, 16 μm, 12 μm, and 10 μm, respectively.

[0067] In this embodiment, when the composite conductive paste is sprayed onto the foil using the electrostatic spraying process, the voltage is 15 kV, and the rotating speed of the metal drum is 700 rpm; the process parameters for the spraying part are designed as follows: the coating temperature is 40-113°C, and the preferable value is 50-55°C; the coating stretch difference is 0.01-22%, and the preferable value is 0.2%-2%; after spraying, rewinding is performed, and the rewinding temperature is 50-113°C, and the preferable value is 55-70°C; the take-up and let-off tension is 0.01-76 N, and the preferable value is 0.01-1 N; after rewinding, slitting is performed, and the take-up and let-off tension for slitting is 0.01-24 N, and the preferable value is 0.1-5 N; the contact pressure is 0.01-20 N, and the preferable value is 0.2-5 N.

[0068] Example 1

[0069] A carbon-coated foil is prepared by the following steps:

[0070] The composite conductive paste prepared in Preparation Example 1 is sprayed on the surface of a copper foil with a thickness of 8 μm by the electrostatic spraying process, and the thickness of the composite conductive paste on the surface of the copper foil is 1.2 μm.

[0071] In the electrostatic spraying process, the flow rate of the electrospinning solution is 0.6 mL / h, the spinning temperature is 25°C, and the spinning humidity is 32%.

[0072] Example 2

[0073] A carbon-coated foil is prepared by the following steps:

[0074] The composite conductive paste prepared in Preparation Example 2 was sprayed on the surface of a copper foil having a thickness of 10 μm by an electrospinning spraying process, and the thickness of the composite conductive paste on the surface of the copper foil was 1.8 μm.

[0075] In the electrospinning process, the flow rate of the electrospinning solution was 1 mL / h, the spinning temperature was 35°C, and the spinning humidity was 37%.

[0076] Example 3

[0077] A carbon-coated foil was prepared by the following steps:

[0078] The composite conductive paste prepared in Preparation Example 3 was sprayed on the surface of a copper foil having a thickness of 6 μm by an electrospinning spraying process, and the thickness of the composite conductive paste on the surface of the copper foil was 1.5 μm.

[0079] In the electrospinning process, the flow rate of the electrospinning solution was 0.8 mL / h, the spinning temperature was 30°C, and the spinning humidity was 35%.

[0080] Example 4

[0081] A carbon-coated foil was prepared by the following steps:

[0082] The composite conductive paste prepared in Preparation Example 4 was sprayed on the surface of a copper foil having a thickness of 10 μm by an electrospinning spraying process, and the thickness of the composite conductive paste on the surface of the copper foil was 1.6 μm.

[0083] In the electrospinning process, the flow rate of the electrospinning solution was 0.9 mL / h, the spinning temperature was 27°C, and the spinning humidity was 33%.

[0084] Example 5

[0085] A carbon-coated foil was prepared by the following steps, except that the composite conductive paste used in the process of preparing the carbon-coated foil was prepared in Preparation Example 5.

[0086] Example 6

[0087] A carbon-coated foil was prepared by the following steps, except that the composite conductive paste used in the process of preparing the carbon-coated foil was prepared in Preparation Example 6.

[0088] Example 7

[0089] A carbon-coated foil was prepared by the following steps, except that the composite conductive paste used in the process of preparing the carbon-coated foil was prepared in Preparation Example 7.

[0090] Example 8

[0091] A carbon-coated foil, which differs from Example 3 in that the composite conductive paste used in the process of preparing the carbon-coated foil is prepared from Preparation Example 8.

[0092] Example 9

[0093] A carbon-coated foil, which differs from Example 3 in that the composite conductive paste used in the process of preparing the carbon-coated foil is prepared from Preparation Example 9.

[0094] Example 10

[0095] A carbon-coated foil, which differs from Example 3 in that the composite conductive paste used in the process of preparing the carbon-coated foil is prepared from Preparation Example 10.

[0096] Example 11

[0097] A carbon-coated foil, which differs from Example 3 in that the thickness of the composite conductive paste on the surface of the copper foil is 1 μm, respectively, in the process of preparing.

[0098] Example 12

[0099] A carbon-coated foil, which differs from Example 3 in that the thickness of the composite conductive paste on the surface of the copper foil is 2 μm, respectively, in the process of preparing.

[0100] Example 13

[0101] A carbon-coated foil, which differs from Example 3 in that the flow rate of the electrospinning solution is 0.5 mL / h, the spinning temperature is 20°C, and the spinning humidity is 40% in the process of preparing.

[0102] Example 14

[0103] A carbon-coated foil, which differs from Example 3 in that the flow rate of the electrospinning solution is 1.1 mL / h, the spinning temperature is 38°C, and the spinning humidity is 30% in the process of preparing.

[0104] Comparative Example

[0105] Comparative Example 1

[0106] A carbon-coated foil, which differs from Example 3 in that the composite conductive paste used in the process of preparing the carbon-coated foil is prepared from Preparation Example 11.

[0107] Comparative Example 2

[0108] A carbon-coated foil, which differs from Example 3 in that the composite conductive paste used in the process of preparing the carbon-coated foil is prepared from Preparation Example 12.

[0109] Comparative Example 3

[0110] A carbon-coated foil, different from Example 3 in that an equal weight of polytetrafluoroethylene is used instead of polyimide in the process of preparing the carbon-coated foil.

[0111] Comparative Example 4

[0112] A carbon-coated foil, different from Example 3 in that an equal weight of polytetrafluoroethylene is used instead of polyimide in the process of preparing the carbon-coated foil.

[0113] Application Examples

[0114] In the present application examples, when the carbon-coated foil used in the process of preparing the silicon-based negative electrode sheet is a carbon-coated copper foil, all the application examples are recorded as Group C; when the carbon-coated foil used in the process of preparing the silicon-based negative electrode sheet is a carbon-coated aluminum foil, all the application examples are recorded as Group D.

[0115] Application Example 1

[0116] A silicon-based negative electrode sheet, the copolymer-coated silicon-carbon negative electrode composite material, graphite, conductive agent SP and binder PAA are dissolved in a solvent in a mass percentage of 10:84:3:3, mixed and coated on the carbon-coated copper foil prepared from Example 1, and a silicon-based negative electrode sheet is prepared after vacuum drying.

[0117] Application Example 2

[0118] A silicon-based negative electrode sheet, different from Application Example 1 in that the carbon-coated foil used in the preparation process is prepared from Example 2.

[0119] Application Example 3

[0120] A silicon-based negative electrode sheet, different from Application Example 1 in that the carbon-coated foil used in the preparation process is prepared from Example 3.

[0121] Application Example 4

[0122] A silicon-based negative electrode sheet, different from Application Example 1 in that the carbon-coated foil used in the preparation process is prepared from Example 4.

[0123] Application Example 5

[0124] A silicon-based negative electrode sheet, different from Application Example 1 in that the carbon-coated foil used in the preparation process is prepared from Example 5.

[0125] Application Example 6

[0126] A silicon-based negative electrode sheet, different from Application Example 1 in that the carbon-coated foil used in the preparation process is prepared from Example 6.

[0127] Application Example 7

[0128] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 7.

[0129] Application Example 8

[0130] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 8.

[0131] Application Example 9

[0132] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 9.

[0133] Application Example 10

[0134] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 10.

[0135] Application Example 11

[0136] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 11.

[0137] Application Example 12

[0138] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 12.

[0139] Application Example 13

[0140] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 13.

[0141] Application Example 14

[0142] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Example 14.

[0143] Application Comparative Example

[0144] Application Comparative Example 1

[0145] A silicon-based negative electrode sheet, which differs from that of Application Example 1 in that the carbon-coated foil material used in the production process is prepared by Comparative Example 1.

[0146] Application Comparative Example 2

[0147] A silicon-based negative electrode sheet, which differs from the application example 1 in that the carbon-coated foil material used in the preparation process is prepared from the comparative example 2.

[0148] Comparative example 3

[0149] A silicon-based negative electrode sheet, which differs from the application example 1 in that the carbon-coated foil material used in the preparation process is prepared from the comparative example 3.

[0150] Comparative example 4

[0151] A silicon-based negative electrode sheet, which differs from the application example 1 in that the carbon-coated foil material used in the preparation process is prepared from the comparative example 4.

[0152] Application example 15

[0153] The silicon-based negative electrode sheets prepared from the application examples 1-14 and the comparative examples 1-4 are used to prepare batteries according to the following scheme.

[0154] The above-mentioned silicon-based negative electrode sheet, a ternary positive electrode sheet (positive electrode active material is NCM811) prepared by a conventional mature process, 1 mol / L LiPF6 / EC+DMC+EMC (v / v=1:1:1) electrolyte, 9+3 boehmite coating film (Zhongcai Lithium Film), and a shell are assembled into a 18650 cylindrical single battery by a conventional production process.

[0155] Detection method

[0156] I. Performance test of carbon-coated copper foil and carbon-coated aluminum foil

[0157] The carbon-coated copper foil and carbon-coated aluminum foil prepared from the application examples 1-14 and the comparative examples 1-4 are tested for tensile strength, elongation, resistance, and tightness with the silicon-based negative electrode. The sheet resistance similarity rate of the carbon-coated copper foil and carbon-coated aluminum foil prepared from the application examples 1-14 and the comparative examples 1-4 relative to the relatively pure carbon nanotube foil, and the tightness enhancement multiple of the carbon-coated copper foil and carbon-coated aluminum foil prepared from the application examples 1-14 and the comparative examples 1-4 relative to the relatively pure carbon nanotube foil on the silicon-based negative electrode are calculated. The test results are shown in Table 1.

[0158] Table 1

[0159]

[0160]

[0161] II. Test of the battery product prepared in the application example 15

[0162] The rate performance of the battery was tested under cylindrical battery test conditions, using a LAND Tianchi test system from Wuhan Jinuo Electronics Co., Ltd. at 25°C, with the charge and discharge voltage limited to 2.5-4.2V. The expansion rate of the full-electricity silicon-based negative electrode, the cycle performance of the battery, and the rate performance were measured, and the relevant parameters are recorded in Table 2.

[0163] Table 2

[0164]

[0165]

[0166] In combination with application examples 1-4, application comparative examples 1-2, Table 1, and Table 2, it can be seen that, whether copper foil or aluminum foil is used to prepare the carbon-coated foil material, the compounding of polyimide and single-walled carbon nanotubes can significantly improve the tensile strength of the carbon-coated foil material and its tightness to the silicon-based negative electrode, thereby significantly reducing the expansion rate of the silicon-based negative electrode material during battery use, and improving the electrical conductivity, the rate, and the cycle life of the battery.

[0167] In combination with application examples 3, 5-6, Table 1, and Table 2, it can be seen that, when the amount ratio of polyimide and single-walled carbon nanotubes is too high or too low, the expansion rate of the silicon-based negative electrode material is increased to some extent, and the electrical conductivity is reduced, which reduces the cycle performance of the battery. This may be due to the fact that when the amount ratio of polyimide and single-walled carbon nanotubes is too high or too low, the viscosity and particle size of the conductive paste change, which is not conducive to the formation of a uniform and stable conductive layer on the surface of the foil material.

[0168] In combination with application examples 3, 7-10, Table 1, and Table 2, it can be seen that, when the diameter or length of the single-walled carbon nanotubes is too large or too small, the electrical conductivity is reduced to some extent. This may be due to the fact that when the diameter or length is too large or too small, the single-walled carbon nanotubes in the composite conductive paste system cannot effectively form a “closed” conductive path.

[0169] In combination with application examples 3, 11-12, Table 1, and Table 2, it can be seen that, when the thickness of the composite conductive paste on the surface of the foil material is too high or too low, it may increase the risk of cracking of the composite conductive coating or be not conducive to the uniform dispersion of the composite conductive paste system on the surface of the foil material, thereby having a certain negative impact on the expansion rate of the silicon-based negative electrode, the electrical conductivity, and the rate and cycle performance of the battery.

[0170] In combination with application example 3, 13-14, table 1 and table 2, it can be seen that when the flow rate of the spinning solution, the spinning temperature and the spinning humidity in the electrospinning process are too high or too low, it is not conducive to the composite conductive slurry to form a carbon coating layer with stable thickness and uniform composition on the surface of the foil, and further negatively affects the various performances of the carbon-coated foil finally prepared, and when it is applied in the battery, it negatively affects the expansion rate of the silicon-based negative electrode, the rate of the battery and the cycle life.

[0171] In combination with application example 3, application comparative examples 3-4, table 1 and table 2, it can be seen that when the polyimide is replaced by the commonly used binder in the art, the expansion rate of the silicon-based negative electrode increases, and when the selection of the polyimide is changed, the expansion rate of the silicon-based negative electrode decreases slightly compared to application comparative examples 3-4, but compared to application example 3, the silicon-based expansion rate of application comparative examples 3-4 increases to a certain extent, and the conductive performance, the rate of the battery and the cycle performance decrease, indicating that the polyimide in the composite conductive slurry system cannot be replaced at will.

[0172] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A carbon-coated foil material, characterized in that: The carbon-coated foil includes a foil and a carbon coating layer disposed on at least one surface of the foil, wherein the carbon coating layer includes polyimide and carbon nanotubes; The weight ratio of polyimide to carbon nanotubes in the carbon coating layer is 1:(3-5); the diameter of the carbon nanotubes is 1-2 nm and the length is 10-30 μm.

2. The carbon-coated foil material according to claim 1, characterized in that: The carbon coating layer has a coating thickness of 1.2-1.8 μm on at least one surface of the foil.

3. The carbon-coated foil material according to claim 1, characterized in that: The purity of the carbon nanotubes is greater than 97%.

4. The carbon-coated foil material according to claim 1, characterized in that: The foil material is selected from either copper foil or aluminum foil.

5. A carbon-coated foil according to any one of claims 1-4, characterized in that, The method for preparing the carbon-coated foil includes the following steps: coating a composite conductive paste onto at least one surface of the foil, and forming the carbon coating layer on the surface of the foil using the composite conductive paste; wherein the composite conductive paste includes the polyimide and the carbon nanotubes.

6. A carbon-coated foil material according to claim 5, characterized in that: During the preparation of the composite conductive paste, the stirring speed is 300-800 rpm, the stirring time is 5-10 h, the heating temperature is 40-150℃, the heating time is 0.1-2 h, the ultrasonic time is 0.1-5 h, the stirring speed is 300-600 rpm, and the stirring time is 5-10 h.

7. A carbon-coated foil material according to claim 5, characterized in that: In preparing the carbon-coated foil, the composite conductive paste is coated onto the surface of the foil using an electrostatic spinning spraying process.

8. A carbon-coated foil according to claim 7, characterized in that: In the electrospinning spraying process, the flow rate of the electrospinning solution is 0.6-1 mL / h, the spinning temperature is 25-35℃, and the spinning humidity is 32-37%.

9. A silicon-based negative electrode with low expansion coefficient, characterized in that: The present invention includes a current collector and a negative electrode active coating disposed on at least one surface of the current collector, wherein the current collector is a carbon-coated foil as described in any one of claims 1-8, and the negative electrode active coating includes a negative electrode active material, wherein the negative electrode active material includes a silicon-based material.

10. A battery, characterized in that: It includes a positive electrode and a silicon-based negative electrode as described in claim 9.

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