Carbon-coated aluminum foil for lithium battery cell and method for manufacturing the same

Abstract

The application discloses a carbon-coated aluminum foil for lithium cells and a preparation method thereof, and the preparation method comprises the following steps: (1) performing corona treatment on the surface of a BOPP base film; (2) performing cleaning and electrostatic removal treatment on the BOPP base film subjected to the corona treatment, and performing surface drying and the like treatment; (3) mixing graphene, polyurethane conductive adhesive and sodium bicarbonate, and adding deionized water to form a porous carbon-coated layer slurry; (4) uniformly coating the porous carbon-coated layer slurry on the surface of the treated BOPP base film, drying, volatilizing the sodium bicarbonate, and forming a first porous carbon-coated layer; (5) spraying an aluminum foil layer on the surface of the porous carbon-coated layer in a magnetron sputtering mode; (6) uniformly coating the porous carbon-coated layer slurry on the surface of the treated BOPP base film to form a second porous carbon-coated layer, and drying to obtain the carbon-coated aluminum foil. Compared with the prior art, the carbon-coated aluminum foil prepared by the application has the advantages of good adhesion, difficulty in interlayer separation, and high heat dissipation.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and particularly relates to a carbon-coated aluminum foil for lithium battery and a preparation method thereof. BACKGROUND

[0002] The performance of a lithium ion battery is greatly related to the properties of each component, and the positive current collector is one of the most critical components in the lithium ion battery. The aluminum foil or carbon-coated aluminum foil is commonly used as the positive current collector in the lithium ion battery, but it is gradually eliminated due to the problems of poor adhesion and high contact resistance between the aluminum foil and the positive electrode material. The carbon-coated aluminum foil is coated with a layer of current collector on the aluminum foil substrate. The current collector serves to connect the aluminum foil and the positive electrode material, solving the problems of poor adhesion and high contact resistance.

[0003] CN105018799A discloses an aluminum foil for lithium battery, which belongs to the technical field of aluminum alloy materials. The composition and mass percentage of the aluminum foil for lithium battery are as follows: Fe: 0.38-0.45%; Si: 0.1-0.15%; Cu: 0.03-0.06%; Ti: 0.015-0.02%; Mn: ≤0.03%; Mg: ≤0.03%; Zn: ≤0.03%; and the balance is Al and unavoidable impurities. The aluminum foil for lithium battery can be prepared by the following steps: smelting, and casting and rolling process: heating and smelting the aluminum foil raw material for lithium battery into an aluminum alloy melt; sequentially performing refining and slag removal, grain refinement, degassing and deslagging, and filtration treatment; continuously casting and rolling the filtered aluminum alloy melt into a blank; cold rolling process: cold rolling the blank, and then performing first annealing treatment, rough rolling, and second annealing treatment; foil pressing treatment: finishing rolling the aluminum foil after annealing treatment, and finally cutting to obtain the finished product of the aluminum foil for lithium battery. By adjusting the composition of the aluminum alloy, adding Cu element, and changing the synergistic effect between the elements, the performance of the aluminum foil is improved to meet the requirements for preparing the aluminum foil for lithium battery.

[0004] CN111864210A discloses a carbon-coated aluminum foil for lithium ion battery and a preparation method thereof. The carbon-coated aluminum foil is composed of a conductive carbon layer and an aluminum foil, and the preparation method comprises the following steps: 1) aluminum foil surface treatment; 2) conductive slurry preparation and carbon coating treatment; and 3) heat treatment of the aluminum foil coated with the conductive slurry. The aluminum foil is treated by plasma, effectively cleaning the surface of the aluminum foil and removing the oxide layer without damaging the aluminum foil. After high-temperature heat treatment of the aluminum foil coated with the conductive slurry, the polyacrylonitrile is cyclized on the surface of the graphene, and part of it is carbonized to form a three-dimensional conductive network with the graphene, while the polyacrylonitrile that is not carbonized firmly fixes the graphene on the aluminum foil, effectively improving the adhesion between the carbon coating and the aluminum foil. The prepared carbon-coated aluminum foil has significantly improved conductive performance, and can effectively improve the conductivity of the carbon coating layer and the adhesion between the carbon coating layer and the aluminum foil, thereby improving the high-rate charge and discharge and cycle performance of the lithium ion battery.

[0005] However, the current carbon-coated aluminum foil still has the following problems: 1) the adhesion between the primer slurry and the foil and the positive electrode material is still poor, and interlayer separation easily occurs, resulting in low yield; 2) the carbon-coated layer has poor heat conduction and heat dissipation performance, and heat is difficult to transfer and release to the outside, which accelerates the decomposition of various active substances in the battery, reduces the service life of the battery, and also brings safety hazards caused by overheating in the battery. 3) The content of aluminum foil in the carbon-coated aluminum foil is high, resulting in high cost of the foil. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of a carbon-coated aluminum foil for lithium battery, which overcomes the problems of high cost, poor adhesion, easy interlayer separation and poor heat dissipation of the existing carbon-coated aluminum foil. The method is to perform corona treatment on the BOPP base film, and add polyurethane conductive adhesive and carbon nanotubes to the porous carbon coating layer, so that the carbonyl or hydroxyl group generated by the corona treatment of the BOPP base film and the active group isocyanate (-NCO) in the polyurethane conductive adhesive form a firm chemical bond, and the carbon nanotubes have high thermal conductivity, thereby effectively preventing the separation of the composite layer and effectively improving the heat dissipation of the carbon-coated aluminum foil.

[0007] In order to achieve the above purpose, the present application provides the following technical scheme:

[0008] The present application provides a preparation method of a carbon-coated aluminum foil for lithium battery, comprising the following steps:

[0009] (1) Corona treatment of BOPP base film;

[0010] (2) washing and destaticizing the BOPP base film treated by corona, and drying the surface to obtain the surface-treated BOPP base film;

[0011] (3) mixing conductive carbon black, carbon nanotubes, polyurethane conductive adhesive and sodium bicarbonate according to the weight ratio of (58-64):(28-32):(3-5):(3-5), and adding deionized water to form a porous carbon coating layer slurry;

[0012] (4) uniformly coating the porous carbon coating layer slurry on the surface of the treated BOPP base film, drying, and volatilizing sodium bicarbonate to form a first porous carbon coating layer;

[0013] (5) spraying an aluminum foil layer of the same thickness on the surface of the first porous carbon coating layer by magnetic control sputtering;

[0014] (6) uniformly coating the porous carbon coating layer slurry on the surface of the aluminum foil layer, drying to form a second porous carbon coating layer, i.e. the carbon-coated aluminum foil.

[0015] Preferably, in step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s.

[0016] Preferably, in step (1), the surface treatment of the BOPP base film satisfies the relationship A = 20Ra + 15μs + c, wherein 30 ≤ c ≤ 35, between the surface wetting tension A (dyn), the surface roughness Ra (μm), and the friction coefficient μs.

[0017] Preferably, the thickness ratio of the BOPP base film, the porous carbon coating layer, and the aluminum foil layer is (2-12):1:(2-10).

[0018] Preferably, the thickness of the BOPP base film is 3-6 μm, the thickness of the porous carbon coating layer is 0.5-1.5 μm, and the thickness of the aluminum foil layer is 3-5 μm.

[0019] Preferably, in step (3), the drying temperature is 80-120 °C.

[0020] Preferably, in step (1), after the corona treatment, the surface of the BOPP base film presents a concave-convex undulating shape, and the pit depth is 50-70 nm.

[0021] Preferably, in step (6), before the porous carbon coating layer slurry is uniformly coated on the surface of the aluminum foil layer, the aluminum foil layer is subjected to a corona treatment, and the surface of the aluminum foil layer subjected to the corona treatment is subjected to a cleaning and destaticizing treatment, and after drying, the porous carbon coating layer slurry is uniformly coated on the surface of the aluminum foil layer.

[0022] Preferably, in step 3), 5% of solid-solid phase change material by total mass of the slurry is added to the porous carbon coating layer slurry, and the phase change temperature of the solid-solid phase change material is 37-41 °C. Preferably, the solid-solid phase change material uses polyethylene glycol with an average relative molecular mass of 950-1050.

[0023] Preferably, in step 6), 5% of crown ether-lithium complex by total mass of the slurry is added to the porous carbon coating layer slurry. The crown ether is an oxygen-containing heterocyclic compound, and the oxygen atoms in the crown ether can stably coordinate lithium ions. The crown ether-lithium complex can provide a stable and controllable lithium source, can effectively supplement the lithium ions consumed in the first cycle process, and can improve the first efficiency and cycle performance of the battery.

[0024] The application also provides a carbon-coated aluminum foil for a lithium cell, which is prepared by the above-mentioned method for preparing a carbon-coated aluminum foil for a lithium cell.

[0025] The application also provides a positive electrode sheet, which comprises the carbon-coated aluminum foil prepared above and a positive electrode active material layer coated on the carbon-coated aluminum foil.

[0026] The application also provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator spaced between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet as described above.

[0027] Compared with the prior art, the application has at least the following beneficial effects:

[0028] 1) The application can make the surface of the BOPP base film rough by strong impact of the electron flow on the BOPP base film under the action of the corona current, and the surface tension of the BOPP base film is increased, which is helpful to the adhesion and bonding of the conductive adhesive. When the conductive adhesive contacts the surface, good wetting can be generated, and the base film is firmly bonded. If observed under a high-power magnifying glass, the surface of the treated base film is obviously uneven and rough compared with the untreated base film. In addition, under the action of the high-voltage electric field, a large amount of ozone is generated, and ozone is a strong oxidant that can oxidize polypropylene molecules to generate carbonyl and peroxide groups with strong polarity. After such a structure, the polarity of the base film molecules is increased, the surface tension is increased, the affinity to the conductive adhesive is increased, and the bonding strength between the composite films is increased. In addition, the generation of carbonyl groups will also generate new alpha-carbon atoms in the molecular chain, and active hydrogen will appear. The active hydrogen can chemically react with the active group isocyanate (-NCO) in the polyurethane conductive adhesive, so that a firm chemical bond is generated between the adherend and the conductive adhesive, and the bonding strength is further increased, thereby effectively avoiding the separation phenomenon between the layers.

[0029] 2) The application can effectively transfer heat by setting the porous carbon coating layer and carbon nanotubes with high thermal conductivity, can quickly conduct and release the heat of the substrate to the external environment, and effectively improve the heat dissipation performance of the carbon-coated aluminum foil. In addition, the sodium bicarbonate added in the porous carbon coating layer can be decomposed to leave voids in the subsequent drying process, increase the pore structure of the point heat dissipation layer, and further improve the heat dissipation effect of the carbon-coated aluminum foil, and the surface pores can also increase the adhesion with the aluminum foil layer or the positive active material layer. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the carbon-coated aluminum foil in an embodiment of the application.

[0031] Among them, 1-BOPP base film, 2-first porous carbon coating layer, 3-aluminum foil layer, 4-second porous carbon coating layer. DETAILED DESCRIPTION

[0032] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in combination with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0033] According to a first aspect of the present application, the present application provides a preparation method of a carbon-coated aluminum foil for a lithium cell, comprising the following steps:

[0034] (1) performing corona treatment on a BOPP base film;

[0035] (2) performing cleaning and electrostatic removal treatment on the BOPP base film subjected to the corona treatment, and obtaining a surface-treated BOPP base film after drying the surface;

[0036] (3) mixing conductive carbon black, carbon nanotubes, polyurethane conductive adhesive and sodium bicarbonate according to a weight ratio of (58-64):(28-32):(3-5):(3-5), and adding deionized water to form a porous carbon coating layer slurry;

[0037] (4) uniformly coating the porous carbon coating layer slurry on the surface of the treated BOPP base film, drying, and volatilizing sodium bicarbonate to form a first porous carbon coating layer;

[0038] (5) spraying an aluminum foil layer of the same thickness on the surface of the first porous carbon coating layer by means of magnetron sputtering;

[0039] (6) uniformly coating the porous carbon coating layer slurry on the surface of the aluminum foil layer, drying to form a second porous carbon coating layer, thereby obtaining the carbon-coated aluminum foil.

[0040] In an embodiment according to the present application, in step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s. Through the test of the adhesion and firmness of the first porous carbon coating layer, the inventors found that the adhesion and firmness of the first porous carbon coating layer on the BOPP base film subjected to the corona treatment were significantly improved, and when the corona current reached 8 A, the firmness of the first porous carbon coating layer on the surface of the BOPP base film was the highest, and when the corona current was greater than 8 A, the adhesion of the first porous carbon coating layer showed a sharp downward trend. Therefore, the size of the corona current has a decisive effect on the adhesion of the BOPP base film.

[0041] With the increase of the corona current, the kinetic energy of the particles generated during the corona discharge increases, which is conducive to breaking the chemical bonds of the long molecular chains on the surface of the plastic, and the surface activity gradually increases, and the surface tension also increases accordingly. Therefore, the surface tension of the BOPP base film increases with the increase of the corona current, which is helpful for the adhesion and bonding of the conductive adhesive. Further research shows that the peak value of the surface tension of the BOPP base film appears when the corona current is about 8A, and when the current increases, the surface tension of the BOPP base film decreases. This is because the amount of air between the electrode and the corona roller has reached a relatively stable state, and the content of oxygen molecules in the air is constant. Even if the voltage and current of the electrode are increased, more oxygen molecules cannot be activated, and more oxygen-containing functional groups remain on the surface of the BOPP base film. In addition, due to excessive corona, the surface structure of the base film is severely damaged, so when the corona current increases, the surface tension of the BOPP base film decreases rapidly. Compared with the BOPP base film without corona treatment, the firmness of the porous carbon coating layer on the surface of the BOPP base film after corona treatment is significantly improved. With the increase of the corona current, the firmness of the ink film on the surface of the BOPP base film is greatly improved, and the surface tension of the BOPP base film after 8A current corona treatment reaches the maximum.

[0042] In addition, when the corona speed is too fast or the corona treatment time is too short, the corona treatment will be insufficient, which will lead to a decrease in the adhesion of the base film. When the corona speed is too slow or the corona treatment time is too long, the base film is prone to corona breakdown, which will lead to the reverse adhesion of the conductive adhesive. Therefore, the corona speed and the corona time also need to be controlled within a suitable range.

[0043] In an embodiment according to the present application, in step (1), the surface wetting tension A (dyn), the surface roughness Ra (μm) and the friction coefficient μs of the BOPP base film after surface treatment satisfy the relationship: A = 20Ra + 15μs + c, wherein 30 ≤ c ≤ 35. This relationship shows that there is a specific linear relationship between the surface wetting tension A of the BOPP base film and the surface roughness Ra and the friction coefficient μs. When the friction coefficient μs or the surface roughness Ra increases, the surface wetting tension A also increases accordingly, indicating that the greater the friction between the object and the slurry, the better the surface wetting effect. Through this relationship, the required surface wetting tension can be determined according to the control of the surface roughness and the friction coefficient in the actual preparation process, so as to better coat the porous carbon coating slurry, thereby improving the adhesion and performance stability of the high-temperature-resistant green adhesive.

[0044] In an embodiment according to the present application, A is in the range of 38-42 dyn, Ra is in the range of 0.08-0.16 pm, and us is in the range of 0.4-0.7. As the surface roughness increases, the surface contact area increases, and the tension of the slurry also increases. However, when the surface is too rough, the slurry is not evenly distributed, resulting in a smaller contact angle and a decrease in the surface wetting tension. Therefore, the above parameters need to be controlled within a suitable range. Therefore, the above relationship and parameter range can be used to control the properties of the BOPP base film surface during actual preparation. By controlling the relationship between the surface wetting tension, surface roughness and friction coefficient of the BOPP base film after surface treatment, the surface of the base film can have good wettability and roughness, which is beneficial to the coating and adhesion of the first porous carbon coating layer to the base film.

[0045] In an embodiment according to the present application, in step (6), before uniformly coating the porous carbon coating layer slurry on the surface of the aluminum foil layer, the aluminum foil layer is subjected to corona treatment. The surface of the aluminum foil layer subjected to corona treatment is cleaned, destaticized and dried, and then the porous carbon coating layer slurry is uniformly coated on the surface of the aluminum foil layer.

[0046] In an embodiment according to the present application, in step (4), the thickness ratio of the BOPP base film, the first porous carbon coating layer, the second porous carbon coating layer and the aluminum foil layer is (2-12): 1: 1: 1: (2-10). By controlling the thickness ratio of the BOPP base film and the porous carbon coating layer, the conductive performance and heat dissipation performance of the carbon-coated aluminum foil can be further optimized. This design makes the thickness of the BOPP base film and the porous carbon coating layer match better, avoiding unstable performance caused by uneven thickness; and a proper thickness ratio helps to optimize the heat conduction path and improve the heat dissipation effect.

[0047] In an embodiment according to the present application, in step (4), the thickness of the BOPP base film is 3-6 pm; for example, it can be 3 pm, 3.1 pm, 3.2 pm, 3.3 pm, 3.4 pm, 3.5 pm, 3.6 pm, 3.7 pm, 3.8 pm, 3.9 pm, 4.1 pm, 4.2 pm, 4.3 pm, 4.4 pm, 4.5 pm, 4.6 pm, 4.7 pm, 4.8 pm, 4.9 pm, 5 pm, 5.1 pm, 5.2 pm, 5.3 pm, 5.4 pm, 5.5 pm, 5.6 pm, 5.7 pm, 5.8 pm, 5.9 pm, 6 pm.

[0048] The thickness of the porous carbon coating layer is 0.5-1.5 pm; for example, it can be 0.5 pm, 0.6 pm, 0.7 pm, 0.8 pm, 0.9 pm, 1 pm, 1.1 pm, 1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm.

[0049] The thickness of the aluminum foil layer is 3-5 μm. For example, it can be 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, or 5 μm.

[0050] In an embodiment according to the present application, in step (3), the drying temperature is 80-120 ℃. Drying allows the porous carbon coating layer to be cured and sodium carbonate and sodium bicarbonate to be volatilized to form a pore structure.

[0051] In an embodiment according to the present application, after the corona treatment in step (1), the surface of the BOPP base film presents a concave-convex undulating shape with a pit depth of 50-70 nm. The inventors found through comparison of the BOPP base film before and after the corona treatment that the maximum depth of the surface of the BOPP film without the corona treatment is not more than 28 nm, and the maximum depth after the corona treatment can reach 70 nm, and the surface presents a clear concave-convex undulating shape, the convex part is brighter in color, and analysis shows that these brighter parts are granular substances, mainly composed of low-molecular-weight oxides. The change in surface micro-roughness and the increase in micro-real area truly reflect the influence of the corona treatment on the structure and composition of the BOPP film.

[0052] In an embodiment according to the present application, in step (3), 5% of the total mass of the porous carbon coating layer slurry is added with a solid-solid phase change material, and the phase change temperature of the solid-solid phase change material is 37-41 ℃. Preferably, the solid-solid phase change material uses polyethylene glycol with an average relative molecular mass of 950-1050. The polyethylene glycol is an organic solid-solid phase change material (solid-state ordered molecular connection structure changes into solid-state disordered molecular connection structure), and its phase change temperature increases with the increase of the polymerization degree, so its average relative molecular mass cannot be too high or too low. When it reaches its phase change temperature (37-41 ℃), solid-solid phase change occurs, heat is absorbed, and the heat dissipation effect of the porous carbon coating layer is further improved.

[0053] In an embodiment according to the present application, in step (3), 5% of the total mass of the porous carbon coating layer slurry is added with a crown ether-lithium complex. The crown ether is an oxygen-containing heterocyclic compound, and the oxygen atoms in it can stably coordinate with lithium ions. The crown ether-lithium complex can provide stable and controllable lithium sources, effectively supplement the lithium ions consumed in the first cycle process, and improve the first efficiency and cycle performance of the battery.

[0054] According to the second aspect of the present application, the present application also provides a carbon-coated aluminum foil for a lithium cell, which is prepared by the above-mentioned method for preparing a carbon-coated aluminum foil for a lithium cell.

[0055] According to a third aspect of this application, this application also provides a positive electrode sheet, which includes the carbon-coated aluminum foil prepared above and a positive electrode active material layer coated on the carbon-coated aluminum foil.

[0056] According to a fourth aspect of this application, this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0057] The present application will be further described below with reference to specific embodiments.

[0058] Example 1

[0059] like Figure 1 As shown, the carbon-coated aluminum foil for lithium battery cells provided in this embodiment includes a BOPP base film 1, a first porous carbon coating layer 2 disposed on both sides of the BOPP base film, an aluminum foil layer 3 disposed on the surface of the first porous carbon coating layer 2, and a second porous carbon coating layer 4 disposed on the surface of the aluminum foil layer.

[0060] Preparation of carbon-coated aluminum foil:

[0061] This embodiment provides a method for preparing carbon-coated aluminum foil for lithium battery cells, including the following steps:

[0062] (1) A BOPP base film 1 with a thickness of 6 μm was subjected to corona treatment, wherein the corona treatment voltage was 2.0 kV, the current was 8 A, the corona velocity was 40 m / min, and the treatment time was 8 s;

[0063] (2) The BOPP base film 1 after corona treatment is cleaned, destaticated, and dried to obtain the surface-treated BOPP base film 1.

[0064] (3) The conductive carbon black, carbon nanotubes, polyurethane conductive adhesive and sodium bicarbonate are mixed in a weight ratio of 60:30:5:5 and deionized water is added to form a porous carbon coating slurry.

[0065] (4) The porous carbon coating slurry is uniformly coated on the surface of the treated BOPP base film 1 and dried at 80°C. Sodium bicarbonate evaporates to form a first porous carbon coating layer 2 with a thickness of 1μm.

[0066] (5) A layer of aluminum foil 3 of the same thickness is sprayed onto the surface of the first porous carbon coating layer by magnetron sputtering;

[0067] (6) The porous carbon coating slurry is uniformly coated on the surface of the aluminum foil layer and dried at 80°C to form a second porous carbon coating layer 4 with a thickness of 1μm, thus obtaining the carbon-coated aluminum foil.

[0068] Preparation of positive electrode:

[0069] The carbon-coated aluminum foil is coated with a positive active material layer to form a positive electrode sheet; wherein the positive active material layer uses a positive active material of lithium cobaltate.

[0070] Preparation of the lithium battery:

[0071] The negative electrode sheet, the positive electrode sheet, the separator and the electrolyte are made into a lithium ion battery according to a conventional process; wherein the lithium salt of the electrolyte used is 1M LiPF6, the solvent is EC:DEC:DMC 3:4:3; and the separator is a BOPP film.

[0072] Example 2

[0073] Different from Example 1, the thickness of the base film 1 in this embodiment is 4μm, the thickness of the first porous carbon-coated layer 2 and the second porous carbon-coated layer 4 is 0.5μm, and the thickness of the aluminum foil layer 3 is 6μm.

[0074] The rest is the same as Example 1, which will not be repeated here.

[0075] Example 3

[0076] Different from Example 1, in the preparation step (3) of the carbon-coated aluminum foil, the conductive carbon black, the carbon nanotube, the polyurethane conductive adhesive and the sodium bicarbonate are mixed in a weight ratio of 64:30:3:3.

[0077] The rest is the same as Example 1, which will not be repeated here.

[0078] Example 4

[0079] Different from Example 1, in the preparation step (1) of the carbon-coated aluminum foil, the surface wetting tension A of the BOPP base film 1 after surface treatment is 40dyn, the surface roughness Ra is 0.1μm and the friction coefficient is 0.4μs, wherein the three satisfy the relationship: A=20Ra+15μs+c, and 30≤c≤35.

[0080] The rest is the same as Example 1, which will not be repeated here.

[0081] Example 5

[0082] Different from Example 1, in the preparation step (1) of the carbon-coated aluminum foil, after the corona treatment, the surface of the BOPP base film presents a concave-convex undulating shape, and the pit depth is 60-70nm.

[0083] The rest is the same as Example 1, which will not be repeated here.

[0084] Example 6

[0085] Different from Example 1, in the preparation step (3) of the carbon-coated aluminum foil, 5% of solid-solid phase change material in total mass of the slurry is added into the porous carbon-coated layer slurry, and the solid-solid phase change material is polyethylene glycol with average relative molecular mass of 950-1050.

[0086] Other than Example 1, which will not be repeated here.

[0087] Example 7

[0088] Different from Example 1, in the preparation step (6) of the carbon-coated aluminum foil, 5% of crown ether-lithium complex in total mass of the slurry is added into the porous carbon-coated layer slurry.

[0089] Other than Example 1, which will not be repeated here.

[0090] Comparative Example 1

[0091] Different from Example 1, the preparation method of the carbon-coated aluminum foil in the comparative example is that the same thickness of conductive carbon black coating is directly sprayed on the aluminum foil.

[0092] Other than Example 1, which will not be repeated here.

[0093] Comparative Example 2

[0094] Different from Example 1, the preparation method of the carbon-coated aluminum foil in the comparative example is that the same thickness of aluminum foil layer is directly sprayed on the BOPP base film, and then the same thickness of conductive carbon black coating is directly sprayed on the aluminum foil.

[0095] Other than Example 1, which will not be repeated here.

[0096] Comparative Example 3

[0097] Different from Example 1, the preparation method of the carbon-coated aluminum foil in the comparative example is that in the step (1), the BOPP base film 1 is subjected to corona treatment, wherein the corona treatment voltage is 2.0 kV, the current is 10 A, the corona speed is 40 m / min, and the treatment time is 8 s.

[0098] Other than Example 1, which will not be repeated here.

[0099] Comparative Example 4

[0100] Different from Example 1, the preparation method of the carbon-coated aluminum foil in the comparative example is that in the step (1), the BOPP base film 1 is subjected to corona treatment, wherein the corona treatment voltage is 2.0 kV, the current is 6 A, the corona speed is 40 m / min, and the treatment time is 8 s.

[0101] Other than Example 1, which will not be repeated here.

[0102] Comparative Example 5

[0103] The preparation method of the carbon-coated aluminum foil of the present comparative example is different from that of example 1. In step (2), the conductive carbon black, carbon nanotubes, phenolic resin conductive adhesive and sodium bicarbonate are mixed in a weight ratio of 60:30:5:5.

[0104] Other than example 1, which will not be repeated here.

[0105] Comparative example 6

[0106] The preparation method of the carbon-coated aluminum foil of the present comparative example is different from that of example 1. In step (2), the conductive carbon black, carbon nanotubes and polyurethane conductive adhesive are mixed in a weight ratio of 60:30:10.

[0107] Other than example 1, which will not be repeated here.

[0108] The carbon-coated aluminum foil, positive electrode sheet and lithium ion battery prepared in examples 1-7 and comparative examples 1-6 are respectively tested for performance, and the test results are shown in Table 1:

[0109] Table 1

[0110]

[0111] From the test results of example 1 and comparative examples 1-2, it can be seen that the adhesion of the carbon-coated aluminum foil of example 1 is significantly improved, the positive electrode sheet is effectively cooled, and the high-temperature cycle performance of the lithium ion battery is further improved.

[0112] From the test results of example 1 and comparative example 3, it can be seen that the adhesion of the carbon-coated aluminum foil of example 1 is significantly better than that of comparative example 3, further indicating that the optimal current for corona treatment in step (1) is 8A. When the corona current is greater than 8A, the surface tension of the BOPP base film shows a downward trend, resulting in a sharp decrease in the adhesion of the porous carbon-coated layer. Therefore, the size of the corona current has a decisive effect on the adhesion of the BOPP base film.

[0113] From the test results of example 1 and comparative example 4, it can be seen that the adhesion of the carbon-coated aluminum foil of example 1 is significantly better than that of comparative example 4, further indicating that the optimal current for corona treatment in step (1) is 8A. As the corona current increases, the kinetic energy of the particles generated during corona discharge increases, which is beneficial to opening the chemical bonds of the long molecular chains on the surface of the plastic, gradually increasing the surface activity and the surface tension.

[0114] From the test results of Example 1 and Comparative Example 5, it can be seen that the adhesion of the carbon-coated aluminum foil of Example 1 is significantly better than that of Comparative Example 5, further proving that the adhesion of Example 1 is due to the chemical reaction between the active isocyanate group (-NCO) in the polyurethane conductive adhesive and the active hydrogen generated during the corona treatment of the BOPP base film, generating a strong chemical bond, increasing the adhesion of the BOPP base film and the porous carbon coating layer, thereby effectively avoiding the phenomenon of interlayer separation. The strong polarity groups such as carbonyl groups generated by the BOPP base film under the action of high voltage electric field make new α-carbon atoms appear in the molecular chain, and active hydrogen appears.

[0115] From the test results of Example 1 and Comparative Example 6, it can be seen that the adhesion and heat dissipation performance of the carbon-coated aluminum foil of Example 1 are significantly better than those of Comparative Example 6, and the positive plate has been effectively cooled and effectively avoided the phenomenon of interlayer separation, further illustrating that the addition of sodium bicarbonate in the porous carbon coating layer can form a pore structure in the subsequent drying process, which helps to further improve the heat dissipation effect of the carbon-coated aluminum foil, and the pores on the surface can also increase the adhesion with the aluminum foil layer.

[0116] From the test results of Example 1 and Example 6, it can be seen that the heat dissipation performance of the carbon-coated aluminum foil of Example 6 is further improved, indicating that the addition of 5% polyethylene glycol in the porous carbon coating layer can effectively cool the positive plate and improve the high-temperature cycle performance of the lithium ion battery.

[0117] From the test results of Example 1 and Example 7, it can be seen that the cycle performance of the lithium ion battery of the carbon-coated aluminum foil of Example 7 is better, indicating that the addition of 5% crown ether-lithium complex in the porous carbon coating layer can provide stable and controllable lithium source, which can effectively supplement the lithium ions consumed during the first cycle, improve the initial efficiency and cycle performance of the battery.

[0118] Based on the disclosure and teachings of the above specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. A method for producing a carbon-coated aluminum foil for a lithium cell, characterized by, The method comprises the following steps: (1) performing corona treatment on the surface of a BOPP base film; the surface wetting tension A, surface roughness Ra and friction coefficient μs of the BOPP base film after surface treatment satisfy the relationship: A = 20Ra + 15μs + c, wherein 30 ≤ c ≤ 35, the unit of the surface wetting tension A is dyn, and the unit of the surface roughness Ra is μm; (2) performing cleaning and electrostatic removal treatment on the BOPP base film after corona treatment, and obtaining the BOPP base film after surface treatment after drying; (3) mixing conductive carbon black, carbon nanotubes, polyurethane conductive adhesive and sodium bicarbonate according to a weight ratio of (58-64):(28-32):(3-5):(3-5), and adding deionized water to form a porous carbon coating layer slurry; (4) uniformly coating the porous carbon coating layer slurry on the surface of the treated BOPP base film, drying, volatilizing sodium bicarbonate, and forming a first porous carbon coating layer; (5) spraying an aluminum foil layer of the same thickness on the surface of the first porous carbon coating layer by using a magnetron sputtering method; (6) uniformly coating the porous carbon coating layer slurry on the surface of the aluminum foil layer, drying, volatilizing sodium bicarbonate, and forming a second porous carbon coating layer, thereby obtaining the carbon-coated aluminum foil.

2. The method for preparing carbon-coated aluminum foil for lithium battery cells according to claim 1, characterized in that, In step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s.

3. The method for preparing carbon-coated aluminum foil for lithium battery cells according to claim 1, characterized in that, The thickness ratio of the BOPP base film, the first porous carbon coating layer, the second porous carbon coating layer and the aluminum foil layer is (2-12):1:1:(2-10).

4. The method for preparing carbon-coated aluminum foil for lithium battery cells according to claim 3, characterized in that, The thickness of the BOPP base film is 3-6 μm, the thickness of the first and second porous carbon coating layers is 0.5-1.5 μm, and the thickness of the aluminum foil layer is 3-5 μm.

5. The method for preparing carbon-coated aluminum foil for lithium battery cells according to claim 1, characterized in that, In step (1), after the corona treatment, the surface of the BOPP base film presents a concave-convex undulating shape, and the pit depth is 50-70 nm.

6. The method of claim 1, wherein the carbon-coated aluminum foil for a lithium cell is prepared by the steps of: In step (6), before uniformly coating the porous carbon coating layer slurry on the surface of the aluminum foil layer, the aluminum foil layer is subjected to corona treatment, the surface of the aluminum foil layer after the corona treatment is subjected to cleaning and electrostatic removal treatment, and then the porous carbon coating layer slurry is uniformly coated on the surface of the aluminum foil layer after drying.

7. The method for preparing carbon-coated aluminum foil for lithium-ion battery cells according to claim 1, characterized in that, In step (3), 5% of solid-solid phase change materials based on the total mass of the slurry are added to the porous carbon coating layer slurry, and the phase change temperature of the solid-solid phase change materials is 37-41 ℃.

8. The method of claim 1 to 7, wherein the method is characterized by, In step (6), 5% of crown ether-lithium complex based on the total mass of the slurry is added to the porous carbon coating layer slurry.

9. A carbon-coated aluminum foil for a lithium cell, characterized by: The carbon-coated aluminum foil for a lithium cell is prepared by the method according to any one of claims 1-8.

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