A modified current collector base film, its preparation method, composite copper current collector and application

Abstract

The present invention provides a modified current collector base film, a preparation method thereof, a composite copper current collector, and applications. The modified current collector base film includes a polymer material and modified silica aerogel, and the modified silica aerogel has a porous structure, and short fibers with nano-copper seeds attached to the surface are filled in the pores. In the present invention, silica aerogel is introduced into the polymer material, and at the same time, short fibers with nano-copper seeds attached to the surface are filled in its pores for modification. The short fiber material can form interpenetrating crosslinks in the pores to increase the interfacial friction force. At the same time, the nano-copper seeds can serve as active sites to provide nucleation sites for the subsequent preparation of the copper layer, thereby refining the copper grains and enabling the copper grains to grow directionally, so that the modified current collector base film has a significant improvement in electrical conductivity, interfacial adhesion, and mechanical properties. It solves the problems existing in the composite copper current collector, such as reduced interfacial adhesion, low electrical conductivity, low mechanical properties, and low heat resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a modified current collector base film, a preparation method thereof, a composite copper current collector and an application. Background Art

[0002] With the rapid development of the new energy vehicle and energy storage fields, the demand for lithium-ion power batteries has increased rapidly, and thus higher requirements are put forward for the performance of current collectors. Therefore, current collectors are developing in the direction of being thinner, lighter and safer. As a new current collector material with the most potential for substitution, the composite current collector subverts the traditional current collector with its "metal-polymer material-metal" sandwich structure, enabling it to improve safety performance while increasing energy density and reducing raw material costs. At present, the processes for preparing composite current collectors by mainstream manufacturers are divided into two-step and three-step routes, both mainly based on magnetron sputtering and electroplating with water. The specific process is as follows: First, a conductive metal is sputtered on the surface of a polymer substrate with good tensile strength (usually polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), etc.) to metallize it, and then through the electroplating process with water, copper ions in the electrolytic cell are reduced and deposited on the surface of the magnetron film to thicken the copper layer, obtaining a product that meets the process standards.

[0003] Currently, the development of composite copper current collectors based on polymer membranes is one of the most popular sub-research fields in the power battery industry. However, the composite copper current collectors based on polymer substrates produced currently face disadvantages such as general tensile strength, poor adhesion and low heat resistance, and are prone to fracture in a physical vapor deposition environment (such as winding tension, metal ion bombardment, vacuum pumping, and high temperature generated during sputtering), which limits their further application.

[0004] Therefore, it is necessary to develop a new current collector base film to solve the problems of reduced interfacial adhesion, lower conductivity and mechanical properties, and low heat resistance existing in composite copper current collectors. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a modified current collector base film, a preparation method thereof, a composite copper current collector and an application. The present invention introduces silica aerogel with physical and chemical properties such as low density, low thermal conductivity, high porosity and large specific surface area into the polymer material, and at the same time fills short-cut fibers with nano copper crystal seeds attached to the surface in its pores for modification. The short-cut fiber material can form interpenetrating crosslinks in the pores, resulting in a mechanical interlocking effect between materials, thereby increasing interfacial friction and hindering the movement of the interface. At the same time, the nano copper crystal seeds can serve as active sites to provide nucleation sites for the subsequent preparation of the copper layer and refine the copper grains, enabling the copper layer to grow in the (111) direction, so that the modified current collector base film is greatly improved in terms of conductivity, interfacial adhesion, and mechanical properties.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a modified current collector base film, which includes a polymer material and modified silica aerogel. The modified silica aerogel has a porous structure, and short fibers with nano-copper seeds attached to their surfaces are filled in the pores.

[0008] The present invention introduces silica aerogel with physical and chemical properties such as low density, low thermal conductivity, high porosity, and large specific surface area into the polymer material. At the same time, short fibers with nano-copper seeds attached to their surfaces are filled in its pores for modification. The short fiber material can form interpenetrating cross-links in the pores, resulting in a mechanical interlocking effect between the materials, thereby increasing the interfacial friction and hindering the movement of the interface. At the same time, the nano-copper seeds can serve as active sites to provide nucleation sites for the subsequent preparation of the copper layer and refine the copper grains, enabling the copper layer to grow in the (111) direction, so that the modified current collector base film has a significant improvement in electrical conductivity, interfacial adhesion, and mechanical properties.

[0009] In summary, the modified current collector base film solves the problems existing in the composite copper current collector, such as reduced interfacial adhesion, low electrical conductivity, low mechanical properties, and low temperature resistance. Based on this, the energy density of the prepared battery is significantly improved.

[0010] It should be noted that the present invention does not limit the specific type of the polymer material. Exemplarily, for example, it can be any one or at least two combinations of materials such as polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

[0011] Preferably, the short fibers include any one or at least two combinations of short carbon fibers, short glass fibers, or chemical staple fibers.

[0012] It should be noted that short carbon fibers are cut from carbon fiber filaments by a fiber cutting machine, and their basic properties mainly depend on the properties of their raw material - carbon fiber filaments. Short glass fibers, also known as chopped glass fiber rovings, are raw filaments drawn from quartz sand through high-temperature melting using a special wetting agent (softener), and are cut into short lengths online by wet method or by cutting the product glass fiber. Chemical staple fibers, commonly known as "staple fibers" or "filaments", are products obtained by cutting chemical fibers into a certain length after forming.

[0013] Preferably, the length of the chopped fibers is 100 - 1000 nm, for example, it can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 1000 nm, etc.

[0014] Preferably, the diameter of the chopped fibers is 10 - 100 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc.

[0015] Preferably, the diameter of the nano - copper seeds ≤ 100 nm, for example, it can be 50 nm, 70 nm or 100 nm, etc.

[0016] In the present invention, nano - copper seeds with appropriate particle size are beneficial to serve as active sites for subsequent copper plating, providing nucleation points to refine copper grains, thereby improving mechanical properties and electrical conductivity.

[0017] Preferably, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the modified silica aerogel is 0 - 20%, and 0 is not included, for example, it can be 2%, 5%, 8%, 11%, 15% or 18%, etc., preferably 5 - 15%.

[0018] In the present invention, if the mass content of the modified silica aerogel is too large, it will cause a sharp drop in the tensile strength of the composite material, because the mechanical strength of the modified silica aerogel is lower than that of the polymer material.

[0019] Preferably, the porosity of the modified silica aerogel is 80 - 99.8%, for example, it can be 80%, 85% or 90%, etc.

[0020] Preferably, the average pore diameter of the modified silica aerogel is 50 - 100 nm, for example, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc.

[0021] The modified silica aerogel provided by the present invention has characteristics such as low density (for example, 0.03 g / cm 3 )、low thermal conductivity, high porosity and high specific surface area, etc., making the made current collector have a lighter density and can further improve the battery energy density.

[0022] In the second aspect, the present invention provides a preparation method of a modified current collector - based film as described in the first aspect, and the preparation method includes the following steps:

[0023] (1) Mix the polymer material and silica aerogel, and then successively carry out melt extrusion, plasticizing molding and stretching treatment to obtain a semi-treated film;

[0024] (2) Coat the two side surfaces of the semi-treated film with a solution of short-cut fibers with nano copper seeds attached to the surface, and after drying, wind it up to obtain the modified current collector base film.

[0025] Preferably, during the melt extrusion in step (1), the heating and melting temperature is higher than the melting point of the polymer material. Exemplarily, if the polymer material is polypropylene PP, the heating and melting temperature can be 200 °C.

[0026] Preferably, the difference between the heating and melting temperature and the melting point temperature of the polymer material is 15 - 30 °C, for example, it can be 15 °C, 20 °C, 25 °C or 30 °C, etc.

[0027] Preferably, during the plasticizing molding in step (1), the molding temperature < 45 °C, for example, it can be 40 °C, 35 °C, 30 °C or 25 °C, etc.

[0028] Preferably, the stretching treatment in step (1) includes longitudinal stretching and transverse stretching.

[0029] Preferably, the stretching ratio of the longitudinal stretching in step (1) is (3.2 - 6.1):1, for example, it can be 3.2:1, 4:1, 5:1 or 6:1, etc., the stretching temperature of the longitudinal stretching is 50 - 180 °C, for example, it can be 50 °C, 80 °C, 100 °C, 150 °C or 180 °C, etc., the stretching ratio of the transverse stretching is (3.4 - 5.5):1, for example, it can be 3.5:1, 4:1, 4.5:1 or 5:1, etc., and the stretching temperature of the transverse stretching is 50 - 180 °C, for example, it can be 50 °C, 80 °C, 100 °C, 150 °C or 180 °C, etc.

[0030] Preferably, the coating method in step (2) includes the spraying method, preferably the ultrasonic spraying method.

[0031] Preferably, the concentration of the solution of short-cut fibers with nano copper seeds attached to the surface in step (2) is 0 - 0.15 g / L, and does not include 0, for example, it can be 0.02 g / L, 0.05 g / L, 0.08 g / L, 0.1 g / L, 0.12 g / L or 0.15 g / L, etc., preferably 0.05 - 0.1 g / L. It should be noted that the concentration refers to the ratio of the mass of short-cut fibers with nano copper seeds attached to the surface to the total volume of the solution.

[0032] In the present invention, if the concentration of the short fiber solution with nano copper seeds attached to its surface is too high, it will lead to uneven distribution, and it is difficult to form crosslinks due to pore blockage, resulting in an insignificant improvement in mechanical properties.

[0033] Preferably, the preparation steps of the short fiber solution with nano copper seeds attached to its surface in step (2) include:

[0034] Mix a copper source, short fibers, a complexing buffer, a dispersant, a reducing agent, and a non-organic solvent to obtain the short fiber solution with nano copper seeds attached to its surface.

[0035] It should be noted that the copper source provides copper atoms for the generation of copper seeds, the complexing buffer has a dual effect of complexing and buffering, the dispersant is used to prevent the aggregation of copper ions, and the reducing agent is used to convert copper ions into copper atoms.

[0036] Preferably, the copper source includes a solution of tetrachlorocupric acid. Exemplarily, for example, 1 g of tetrachlorocupric acid is dissolved in 50 mL of water to obtain a 0.02 g / mL solution of tetrachlorocupric acid.

[0037] Preferably, the complexing buffer includes a sodium citrate solution. Exemplarily, the concentration of the sodium citrate solution can be, for example, 0.04 mol / L.

[0038] Preferably, the dispersant includes a polyvinylpyrrolidone solution. Exemplarily, the concentration of the polyvinylpyrrolidone solution can be, for example, 5 mol / L.

[0039] Preferably, the reducing agent includes a sodium borohydride solution. Exemplarily, the concentration of the sodium borohydride solution can be, for example, 0.1 mol / L.

[0040] Preferably, the ratio of the copper source, short fibers, complexing buffer, dispersant, and reducing agent is (0.5 - 1) mL: 1 g: (0.8 - 1.2) mL: (3 - 5) mL: (0.9 - 1.1) mL. Among them, the selection range of the copper source "(0.5 - 1) mL" can be, for example, 0.5 mL, 0.6 mL, 0.7 mL, 0.8 mL, 0.9 mL, or 1 mL, etc.; the selection range of the complexing buffer "(0.8 - 1.2) mL" can be, for example, 0.8 mL, 0.9 mL, 1 mL, 1.1 mL, or 1.2 mL, etc.; the selection range of the dispersant "(3 - 5) mL" can be, for example, 3 mL, 3.5 mL, 4 mL, 4.5 mL, or 5 mL, etc.; the selection range of the reducing agent "(0.9 - 1.1) mL" can be, for example, 0.9 mL, 1 mL, or 1.1 mL, etc. Preferably, it is 0.7 mL: 1 g: 1 mL: 4 mL: 1 mL.

[0041] Preferably, the non-organic solvent includes water.

[0042] Preferably, the preparation method includes the following steps:

[0043] (1) Mix the polymer material and silica aerogel, then add them to a twin-screw extruder for heat melting treatment. Then, under the push of pressure, the obtained melt is extruded through a die. Subsequently, the extruded stream is cast onto a casting roll and formed by cooling with the casting roll and cooling water. The cooling temperature is < 45°C to obtain a formed casting sheet. Then, the formed casting sheet is stretched step by step longitudinally and transversely. The longitudinal stretching parameters include: the stretching ratio is (3.2 - 6.1):1, and the stretching temperature is 50 - 180°C; the transverse stretching parameters include: the stretching ratio is (3.4 - 5.5):1, and the stretching temperature is 50 - 180°C. After stretching, a semi-treated film is obtained.

[0044] Among them, the heat melting temperature is higher than the melting point of the polymer material, and the difference is 15 - 30°C.

[0045] (2) Ultrasonically spray the solution of short-cut fibers with nano-copper seeds attached to the two side surfaces of the semi-treated film, and then dry it with a main roll at a surface temperature of 30 - 50°C and wind it up to obtain the modified current collector base film.

[0046] Among them, the concentration of the solution of short-cut fibers with nano-copper seeds attached is 0 - 0.15 g / L and not 0. The preparation steps include: adding a copper source to water, then adding a complexing buffer and a dispersant, and then adding short-cut fibers and stirring for 1 h, and then adding a reducing agent to obtain the solution of short-cut fibers with nano-copper seeds attached; the ratio of the copper source, short-cut fibers, complexing buffer, dispersant, and reducing agent is (0.5 - 1) mL:1 g:(0.8 - 1.2) mL:(3 - 5) mL:(0.9 - 1.1) mL.

[0047] In the third aspect, the present invention provides a composite copper current collector, which includes a back conductive copper layer, a modified current collector base film as described in the first aspect, and a front conductive copper layer stacked.

[0048] In the present invention, the back conductive copper layer and the front conductive copper layer are respectively located on both sides of the modified current collector base film and serve as current-carrying layers in subsequent battery production, with the negative electrode material carried on the surface.

[0049] It should be noted that the present invention does not limit the preparation method of the copper layer. Exemplarily, for example, it can be an electron beam evaporation coating process or a magnetron sputtering plus electroplating coating process, etc.

[0050] Preferably, the materials of the back conductive copper layer and the front conductive copper layer independently include copper metal or copper alloy.

[0051] Preferably, the thicknesses of the back conductive copper layer and the front conductive copper layer are independently 500 - 2500 nm. For example, they can be 100 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, etc., and are preferably 900 - 1200 nm.

[0052] In the present invention, in order to balance the conductivity of the current collector and the improvement of the battery energy density, the thickness is preferably between 900 nm and 1200 nm.

[0053] In a fourth aspect, the present invention provides a lithium-ion battery, and the negative electrode sheet of the lithium-ion battery includes the composite copper current collector as described in the third aspect, or includes a composite copper current collector made based on the modified current collector base film described in the first aspect.

[0054] The numerical ranges described in the present invention not only include the exemplified point values above, but also include any point values between the above numerical ranges not exemplified. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The present invention introduces silica aerogel with physical and chemical properties such as low density, low thermal conductivity, high porosity, and large specific surface area into the polymer material. At the same time, short fibers with nano copper seeds attached to their surfaces are filled in its pores for modification. The short fiber material can form an interpenetrating crosslinking in the pores, resulting in a mechanical interlocking effect between materials, thereby increasing the interfacial friction force and hindering the movement of the interface. At the same time, the nano copper seeds can serve as active sites to provide nucleation sites for the subsequent preparation of the copper layer and refine the copper grains, enabling the copper layer to grow in the (111) direction, so that the modified current collector base film is greatly improved in terms of conductivity, interfacial adhesion, and mechanical properties. In summary, the modified current collector base film solves the problems existing in the composite copper current collector, such as reduced interfacial adhesion, low conductivity, low mechanical properties, and low temperature resistance. Based on this, the energy density of the prepared battery is significantly improved. Specific Embodiments

[0057] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0058] Example 1

[0059] This example provides a modified current collector base film, which includes a polymer material and modified silica aerogel. The modified silica aerogel has a porous structure, and short fibers with nano copper seeds attached to their surfaces are filled in the pores;

[0060] The polymer material is polyethylene terephthalate, the length of the chopped fibers is 500 nm, the diameter is 40 nm, the chopped fibers are chopped carbon fibers, and the diameter of the nano copper seeds is 50 nm;

[0061] Based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 85%, and the mass content of the modified silica aerogel is 15%;

[0062] The porosity of the modified silica aerogel is 85%, and the average pore diameter of the modified silica aerogel is 100 nm.

[0063] This embodiment also provides a method for preparing the above-mentioned modified current collector base film, which includes the following steps:

[0064] (1) Mix polyethylene terephthalate and silica aerogel, then add them to a twin-screw extruder, melt and process them at 280 °C, and then under the push of pressure, extrude the obtained melt through a die, and then cast the extruded material onto a casting roll, and cool and shape it through the casting roll and cooling water. The cooling temperature is 25 °C to obtain a shaped casting, and then stretch the shaped casting step by step longitudinally and transversely. The stretching parameters in the longitudinal direction include: the stretching ratio is 4.4:1, and the stretching temperature is 175 °C; the stretching parameters in the transverse direction include: the stretching ratio is 4:1, and the stretching temperature is 165 °C; after stretching, a semi-processed film is obtained;

[0065] (2) Heat-treat the semi-processed film at 160 °C and then send it to a cooling system to cool it to room temperature of 25 °C. Then, spray the cooled semi-processed film through an ultrasonic spraying system. Select a chopped carbon fiber solution with nano copper seeds attached to the surface with a concentration of 0.05 g / L as the spraying liquid, the spraying amount is 0.01 mL / min, the tape running speed is 4 m / min. After spraying, dry it through a main roller with a surface temperature of 40 °C, and then enter the winding system through a traction system for winding to obtain the modified current collector base film;

[0066] Among them, the preparation steps of the short-cut fiber solution with nano copper seeds attached to the surface include: adding a copper tetrachloride acid solution with a concentration of 0.02 g / mL into water and stirring, then adding a trisodium citrate solution with a concentration of 0.04 mol / L and a polyvinylpyrrolidone solution with a concentration of 5 mol / L, subsequently adding 1 g of short-cut carbon fiber and stirring for 1 h, then adding a sodium borohydride solution with a concentration of 0.1 mol / L, observing the precipitation of copper seeds and their attachment to the surface of the short-cut carbon fiber, and after continuous stirring for 1 h, obtaining a short-cut carbon fiber solution with nano copper seeds attached to the surface; among them, the ratio of the copper tetrachloride acid solution, short-cut carbon fiber, trisodium citrate solution, polyvinylpyrrolidone solution, and sodium borohydride solution is 0.7 mL:1 g:1 mL:4 mL:1 mL.

[0067] This embodiment also provides a composite copper current collector, which includes a back conductive copper layer, the modified current collector base film as above, and a front conductive copper layer that are stacked;

[0068] The materials of the back conductive copper layer and the front conductive copper layer are both copper metal, and their thicknesses are both 1000 nm.

[0069] This embodiment also provides a preparation method of the above composite copper current collector, and the specific steps include:

[0070] In a magnetron sputtering system, conductive copper layers with a thickness of 1000 nm are respectively sputtered on both surfaces of the modified current collector base film, the background vacuum is 3×10 -3 Pa, the sputtering gas flow is 100 sccm, the sputtering gas pressure is 2×10 -1 Pa, the sputtering power is 15 kW, and the main roller cooling temperature is -15 °C; subsequently, the obtained semi-finished product is placed in a chemical copper plating solution with a pH of 12 and electroplated at 30 °C, and the tape running speed is 3 m / min to obtain a composite copper current collector.

[0071] Example 2

[0072] The difference between this embodiment and Example 1 is that based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 98%, and the mass content of the modified silica aerogel is 2%.

[0073] The remaining preparation methods and parameters are the same as those in Example 1.

[0074] Example 3

[0075] The difference between this embodiment and Example 1 is that based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 95%, and the mass content of the modified silica aerogel is 5%.

[0076] The remaining preparation methods and parameters are the same as those in Example 1.

[0077] Example 4

[0078] The difference between this example and Example 1 is that, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 92%, and the mass content of the modified silica aerogel is 8%.

[0079] The remaining preparation methods and parameters are the same as those in Example 1.

[0080] Example 5

[0081] The difference between this example and Example 1 is that, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 89%, and the mass content of the modified silica aerogel is 11%.

[0082] The remaining preparation methods and parameters are the same as those in Example 1.

[0083] Example 6

[0084] The difference between this example and Example 1 is that, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 82%, and the mass content of the modified silica aerogel is 18%.

[0085] The remaining preparation methods and parameters are the same as those in Example 1.

[0086] Example 7

[0087] The difference between this example and Example 1 is that, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 80%, and the mass content of the modified silica aerogel is 20%.

[0088] The remaining preparation methods and parameters are the same as those in Example 1.

[0089] Example 8

[0090] The difference between this example and Example 1 is that the concentration of the short carbon fiber solution with nano copper seeds attached to the surface is 0.1 g / L.

[0091] The remaining preparation methods and parameters are the same as those in Example 1.

[0092] Example 9

[0093] The difference between this example and Example 1 is that the concentration of the short carbon fiber solution with nano copper seeds attached to the surface is 0.15 g / L.

[0094] The remaining preparation methods and parameters are the same as those in Example 1.

[0095] Example 10

[0096] The difference between this example and Example 1 is that, based on the total mass of the polymer material and the modified silica aerogel, the mass content of the polymer material is 70%, and the mass content of the modified silica aerogel is 30%.

[0097] The remaining preparation methods and parameters are the same as those in Example 1.

[0098] Example 11

[0099] The difference between this example and Example 1 is that the concentration of the chopped carbon fiber solution with nano copper seeds attached to the surface is 0.2 g / L.

[0100] The remaining preparation methods and parameters are the same as those in Example 1.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that the spraying treatment of the chopped carbon fiber solution with nano copper seeds attached to the surface in step (2) is not carried out, that is, the pores of the silica aerogel are not filled with chopped fibers with nano copper seeds attached to the surface.

[0103] The remaining preparation methods and parameters are the same as those in Example 1.

[0104] Comparative Example 2

[0105] The difference between this comparative example and Example 1 is that in the preparation method of the chopped carbon fiber solution with nano copper seeds attached to the surface in step (2), copper tetrachloride acid is not added, that is, nano copper seeds are not attached to the surface of the chopped fibers.

[0106] The remaining preparation methods and parameters are the same as those in Example 1.

[0107] Performance Test

[0108] The tensile strength of the modified current collector base film and the composite copper current collector provided in the above examples and comparative examples was tested respectively. The test standard refers to the national standard GB / T 1040.3 - 2006; the sheet resistance of the composite copper current collector was measured using a four-probe tester, and pay attention to flattening the current collector during the test; refer to the "Test Method for the Bonding Strength of Composite Current Collectors" of the China Automobile Association to test the bonding strength of the composite copper current collector; the flame retardancy of the composite copper current collector was inspected according to the UL94 standard.

[0109] The above test results are shown in Table 1.

[0110] Table 1

[0111]

[0112] Analysis:

[0113] As can be seen from the above results, in the present invention, by introducing silica aerogel into the polymer material and simultaneously filling the pores of the silica aerogel with short fibers having nano copper seeds attached to their surfaces for modification, a modified current collector base film with better mechanical properties is prepared. Moreover, due to the introduction of the short fibers with copper seeds, nucleation sites are provided for the growth of copper grains, the copper grains are refined, and it is beneficial for the copper grains to grow along specific crystal directions. This not only improves the bonding effect between the conductive copper layer and the modified current collector base film, but also greatly improves the conductivity and tensile strength of the current collector. In addition, due to the good thermal conductivity of the modified silica aerogel, the subsequently prepared current collector has better heat resistance, thus providing a direction for the subsequent process optimization and change, and accelerating the effective application of the composite copper current collector.

[0114] As can be seen from Example 1 and Examples 2 - 7, the introduction of the modified silica aerogel enhances the tensile strength of the base film. This is due to the different interfaces of different materials, resulting in an increase in friction during stretching. However, with a large amount of the modified silica aerogel added, the tensile strength of the current collector decreases rapidly, but the heat resistance changes rapidly.

[0115] As can be seen from Example 1 and Example 10, when the addition amount of the modified silica aerogel is too large, the tensile strength of the base film decreases rapidly. This is because the mechanical properties of the modified silica aerogel are low, and when the content is too high, agglomeration occurs, leading to defects, thus resulting in the above results.

[0116] As can be seen from Example 1, Examples 8 - 9, and Example 11, an appropriate concentration of the short carbon fiber solution with nano copper seeds attached to its surface can effectively increase the interfacial friction, improve the tensile strength of the base film, and improve its bonding force with the conductive copper layer. However, if the concentration of the short carbon fiber solution with nano copper seeds attached to its surface is too high, it will lead to uneven distribution, and it is difficult to form crosslinks due to pore blockage, resulting in no obvious improvement in mechanical properties.

[0117] As can be seen from Example 1 and Comparative Example 1, if the pores of the silica aerogel are not filled with short fibers having nano copper seeds attached to their surfaces, the improvement in the tensile strength of the modified base film is not obvious, and the mechanical properties, bonding force, and conductivity of the prepared current collector change insignificantly.

[0118] As can be seen from Example 1 and Comparative Example 2, if the surface of the short fibers is not attached with nano copper seeds, the bonding force and conductivity between the conductive copper layer and the base film in the prepared current collector cannot be improved.

[0119] The applicant declares that the technical solution of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the present invention product, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a modified current collector-based film, characterized in that, The preparation method includes the following steps: (1) Mix the polymer material and silica aerogel, and then successively perform melt extrusion, plasticizing molding, and stretching treatment to obtain a semi-treated film; (2) Coat the two side surfaces of the semi-treated film with a solution of short-cut fibers with nano copper seeds attached to the surface, and after drying, wind it up to obtain the modified current collector base film; The modified current collector base film includes a polymer material and modified silica aerogel. The modified silica aerogel is a porous structure, and the pores are filled with short-cut fibers with nano copper seeds attached to the surface.

2. The preparation method according to claim 1, characterized in that, The short-cut fibers include any one or at least two combinations of short-cut carbon fibers, short-cut glass fibers, or chemical short fibers.

3. The preparation method according to claim 1, characterized in that, The length of the short-cut fibers is 100-1000 nm.

4. The preparation method according to claim 1, characterized in that, The diameter of the short-cut fibers is 10-100 nm.

5. The preparation method according to claim 1, characterized in that, The diameter of the nano copper seeds ≤ 100 nm.

6. The preparation method according to claim 1, wherein Based on the total mass of the polymer material and modified silica aerogel, the mass content of the modified silica aerogel is 0-20%, and 0 is not included.

7. The preparation method according to claim 6, characterized in that Based on the total mass of the polymer material and modified silica aerogel, the mass content of the modified silica aerogel is 5-15%.

8. The preparation method according to claim 1, characterized in that, The porosity of the modified silica aerogel is 80-99.8%.

9. The preparation method according to claim 1, wherein The average pore diameter of the modified silica aerogel is 50-100 nm.

10. The preparation method according to claim 1, characterized in that, During the melt extrusion in step (1), the heating and melting temperature is higher than the melting point of the polymer material.

11. The preparation method according to claim 10, characterized in that, The difference between the heating and melting temperature and the melting point temperature of the polymer material is 15-30 °C.

12. The preparation method according to claim 1, wherein, The stretching treatment method in step (1) includes longitudinal stretching and transverse stretching.

13. The preparation method according to claim 12, characterized in that, The stretching ratio of the longitudinal stretching is (3.2-6.1):1, the stretching temperature of the longitudinal stretching is 50-180 °C, the stretching ratio of the transverse stretching is (3.4-5.5):1, and the stretching temperature of the transverse stretching is 50-180 °C.

14. The preparation method according to claim 1, characterized in that, The coating method in step (2) includes the spraying method.

15. The preparation method according to claim 1, wherein, The concentration of the solution of short-cut fibers with nano copper seeds attached to the surface in step (2) is 0-0.15 g / L, and it is not 0.

16. The preparation method according to claim 1, characterized in that, The preparation steps of the solution of short-cut fibers with nano copper seeds attached to the surface in step (2) include: Mix a copper source, short-cut fibers, a complexing buffer, a dispersant, a reducing agent, and a non-organic solvent to obtain the solution of short-cut fibers with nano copper seeds attached to the surface.

17. The preparation method according to claim 16, characterized in that, The copper source includes a solution of tetrachlorocupric acid.

18. The preparation method according to claim 16, characterized in that, The complexing buffer includes a solution of trisodium citrate.

19. The preparation method according to claim 16, characterized in that, The dispersant includes a solution of polyvinylpyrrolidone.

20. The preparation method according to claim 16, wherein The reducing agent includes a solution of sodium borohydride.

21. The preparation method according to claim 16, wherein The ratio of the copper source, short-cut fibers, complexing buffer, dispersant, and reducing agent is (0.5-1) mL:1 g:(0.8-1.2) mL:(3-5) mL:(0.9-1.1) mL.

22. The preparation method according to claim 16, characterized in that, The non-organic solvent includes water.

23. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix the polymer material and silica aerogel, then add them to a twin-screw extruder for heat melting treatment. Then, under the push of pressure, the obtained melt is extruded through a die head. Subsequently, the extruded stream is cast onto a casting roll and formed through cooling by the casting roll and cooling water. The cooling temperature is <45°C to obtain a formed cast sheet. Then, the formed cast sheet is stretched step by step longitudinally and transversely. The stretching parameters in the longitudinal direction include: the stretching ratio is (3.2 - 6.1):1, and the stretching temperature is 50 - 180°C; the stretching parameters in the transverse direction include: the stretching ratio is (3.4 - 5.5):1, and the stretching temperature is 50 - 180°C. After stretching, a semi-treated film is obtained. Among them, the temperature of heat melting is higher than the melting point of the polymer material, and the difference is 15 - 30°C. (2) Ultrasonically spray the short-cut fiber solution with nano copper seeds attached to the two side surfaces of the semi-treated film, and then wind it up after drying by a main roll with a surface temperature of 30 - 50°C to obtain the modified current collector base film. Among them, the concentration of the short-cut fiber solution with nano copper seeds attached to the surface is 0 - 0.15 g / L and not 0. The preparation steps include: adding a copper source to water, then adding a complexing buffer and a dispersant, then adding short-cut fibers and stirring for 1 h, and then adding a reducing agent to obtain the short-cut fiber solution with nano copper seeds attached to the surface; the ratio of the copper source, short-cut fibers, complexing buffer, dispersant, and reducing agent is (0.5 - 1) mL:1 g:(0.8 - 1.2) mL:(3 - 5) mL:(0.9 - 1.1) mL.

24. A composite copper current collector, characterized in that, The composite copper current collector includes a back conductive copper layer, a modified current collector base film prepared by the preparation method according to any one of claims 1 - 23, and a front conductive copper layer arranged in a laminated manner.

25. A lithium-ion battery, characterized in that, The negative electrode tab of the lithium-ion battery includes the composite copper current collector according to claim 24, or includes a composite copper current collector made of a modified current collector base film prepared by the preparation method according to any one of claims 1 - 23.

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