Composite current collector and electrochemical device

Abstract

The utility model provides a composite current collector. The composite current collector comprises an adhesive polymer base film and metal b films compounded on the two sides of the adhesive polymer base film. According to the composite current collector provided by the utility model, on one hand, various problems caused by a vacuum coating process can be avoided, and on the other hand, the adhesive force between the metal film and the polymer base film does not need to be strengthened by using materials such as an adhesive; the composite current collector which is ultrathin, high in tensile strength, large in elongation at break, good in thermal stability, good in electrochemical stability, good in metal film adhesive force, simple in production process, high in efficiency, high in yield and low in cost can be obtained, and large-scale replacement and batch production of pure metal foil current collectors in an electrochemical device can be achieved through the composite current collector.

Description

Technical Field

[0001] The utility model belongs to the technical field of electrochemical devices, and particularly relates to a composite current collector and an electrochemical device. Background Art

[0002] The current collector is one of the indispensable components in the electrochemical device. It can not only carry the active material, but also collect and output the current generated by the electrode active material, which is beneficial to reducing the internal resistance of the electrochemical device and improving the Coulomb efficiency, cycle stability and rate performance of the electrochemical device.

[0003] Modifying the traditional single-metal foil current collector into a composite current collector including a thin film support layer and a metal conductive layer can enhance the toughness of the current collector, making the current collector have higher mechanical properties. At present, the process route of the composite current collector is to first process a conductive pre-coated copper layer on the thin film substrate by vacuum coating methods such as magnetron sputtering and / or evaporation plating to metallize the polymer film, and then use traditional wet electroplating to thicken the copper layer to 1 μm to ensure that the conductivity of the composite copper foil meets the application requirements. However, this method has a weak bonding force between the thin film substrate and the metal conductive layer; moreover, the thin film substrate is extremely prone to burning or wrinkling of the thin film substrate due to the high-temperature vapor of metallic copper reaching above 1000 °C during the vacuum coating process, and the mechanical impact of metal particles on the thin film substrate causes different degrees of attenuation of the tensile strength and elongation at break of the thin film substrate; in addition, the vacuum coating production efficiency is low and the process cost is high; all these disadvantages will seriously affect the application of the composite current collector in the electrochemical device, resulting in the fact that the composite current collector still cannot achieve large-scale substitution and mass production of the pure metal foil current collector in the electrochemical device so far.

[0004] In addition, in the existing technologies for preparing composite current collectors, there are also technical solutions using multi-layer structures, that is, adding an adhesive material between the thin film substrate and the metal conductive layer to enhance the adhesion between the thin film substrate and the metal conductive layer. However, the addition of the adhesive layer will inevitably increase the thickness of the composite current collector, and will also inevitably complicate the preparation process of the composite current collector, thereby increasing the cost of the composite current collector and reducing its performance.

[0005] Therefore, in order to avoid various problems caused by the vacuum coating process on the one hand, and on the other hand, there is no need to use materials such as adhesives to strengthen the adhesion between the metal film and the polymer-based film, developing a low-cost composite current collector with ultra-thin, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion of the metal film, simple production process, high efficiency and high yield has become an urgent problem to be solved. Summary of the Utility Model

[0006] In view of this, the technical problem to be solved by the present utility model is to provide a composite current collector and an electrochemical device. On the one hand, various problems caused by the vacuum coating process can be avoided. On the other hand, materials such as adhesives do not need to be used to strengthen the adhesion between the metal film and the polymer-based film. A low-cost composite current collector with ultra-thin thickness, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion of the metal film, simple production process, high efficiency and high yield can be obtained, enabling the composite current collector to achieve large-scale replacement and mass production of pure metal foil current collectors in electrochemical devices.

[0007] The present utility model provides a composite current collector, comprising a bondable polymer-based film and metal b films laminated on both sides of the bondable polymer-based film.

[0008] Preferably, the bondable polymer-based film is selected from bondable polyimide or its composite film.

[0009] Preferably, the bondable polymer-based film is selected from soluble bondable polyimide or its composite film.

[0010] Preferably, the thickness of the bondable polymer-based film is 1 - 6 μm, preferably 2 - 3 μm.

[0011] Preferably, the metal b of the metal b film is at least one of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, iridium, indium and their alloys.

[0012] Preferably, the metal b of the metal b film is at least one of copper, aluminum and their alloys.

[0013] Preferably, the thickness of the metal b film is 0.5 - 5 μm, preferably 0.5 - 1.5 μm.

[0014] Preferably, the metal b film is an aluminum conductive layer, the aluminum conductive layer is a single-layer structure, and the surface on the side in contact with the polymer film is a rough surface.

[0015] Preferably, the surface on the side of the aluminum conductive layer in contact with the polymer film has a number of concave structures, the depth of the concave structures is 0.1 - 1 μm, the width of the concave structures is 10 - 100 nm, and the thickness of the aluminum conductive layer with concave structures is 0.5 - 6 μm.

[0016] The present utility model also provides an electrochemical device, comprising the above composite current collector.

[0017] Compared with the prior art, the present utility model provides a composite current collector, which includes an adhesive polymer-based film and metal B films laminated on both sides of the adhesive polymer-based film. The composite current collector provided by the present utility model can, on the one hand, avoid various problems caused by the vacuum coating process, and on the other hand, does not require the use of materials such as adhesives to enhance the adhesion between the metal film and the polymer-based film. A low-cost composite current collector with ultra-thin thickness, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion of the metal film, simple production process, high efficiency and high yield can be obtained, enabling the composite current collector to achieve large-scale substitution and mass production of pure metal foil current collectors in electrochemical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of the composite current collector provided by the present utility model;

[0019] Figure 2 is a schematic structural diagram of the composite current collector provided by the present utility model;

[0020] Figure 3 is a schematic process flow diagram of the preparation of the composite current collector provided by the present utility model;

[0021] Figure 4 is a schematic process flow diagram of the preparation of the composite current collector provided by the present utility model;

[0022] Figure 5 is a schematic process flow diagram of the preparation of the composite current collector provided by the present utility model;

[0023] Figure 6 is a schematic structural diagram of the aluminum composite current collector provided by the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The present utility model provides a composite current collector, which includes an adhesive polymer-based film and metal B films laminated on both sides of the adhesive polymer-based film.

[0025] The metal B of the metal B film is at least one of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, iridium, indium and their alloys.

[0026] In some specific embodiments of the present utility model, when the metal B of the metal B film is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and their alloys, refer to Figure 1 , Figure 1 which is a schematic structural diagram of the composite current collector provided by the present utility model, Figure 1 where 1 and 3 are metal B films, and 2 is an adhesive polymer-based film.

[0027] In some specific embodiments of the present utility model, the bondable polymer-based film is selected from bondable polyimide or its composite film, preferably soluble bondable polyimide or its composite film.

[0028] In the present utility model, when the bondable polymer-based film is selected from soluble bondable polyimide films, the soluble bondable polyimide film is a single-layer structure prepared from soluble bondable polyimide.

[0029] In some preferred embodiments of the present utility model, the bondable polymer-based film is a composite film prepared by coating soluble bondable polyimide on a ultra-high molecular weight polyolefin porous film, that is, the middle layer is a ultra-high molecular weight polyolefin porous film, and the two sides are soluble bondable polyimide films, and the pores are filled with soluble bondable polyimide to form a composite film.

[0030] See Figure 2 , Figure 2 which is a schematic structural diagram of the composite current collector provided by the present utility model. Figure 2 In it, 4 and 8 are metal b films, 5, 6, and 7 together form a composite film, 5 and 7 are bondable polymer films, and 6 is a ultra-high molecular weight polyolefin porous film.

[0031] Among them, the soluble bondable polyimide can be dissolved in a solvent and directly coated on a substrate (semi-finished product 1 or bondable composite film), and no further imidization reaction is required. Because the vacuum coating process is avoided, the production process of the composite current collector is greatly simplified; nor is it necessary to use materials such as adhesives to strengthen the adhesion between the metal film and the polymer-based film. Because the use of adhesives is avoided, the thickness of the composite current collector is greatly reduced. Among them, the solvent is selected from one or more of N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone, and cyclopentanone. The solid content of the formed soluble bondable polyimide slurry is 5% to 12%, preferably 5% to 8%.

[0032] The thickness of the bondable polymer-based film is 1 to 6 μm, preferably 2 to 3 μm.

[0033] The metal b of the metal b film is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and their alloys, preferably copper and its alloys. The thickness of the metal b film is 0.5 to 5 μm, preferably 0.5 to 1.5 μm.

[0034] In the present utility model, the composite current collector is ultra-thin, has high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, and good adhesion of the metal film. The peel strength between the metal b film and the bondable polymer base film in the composite current collector is not less than 6 N / 25 mm; the difference in the coefficient of thermal expansion between the metal b film and the bondable polymer base film is not more than 50 ppm / °C, preferably not more than 30 ppm / °C.

[0035] The present utility model provides a roll-to-roll method for preparing the above-mentioned composite current collector, which includes the following steps:

[0036] A) Coating metal b on the surface of metal foil a to obtain semi-finished product 1;

[0037] B) Coating a bondable polymer film on the surface of the metal b of the semi-finished product 1 to obtain semi-finished product 2;

[0038] C) Stacking the bondable polymer films of two semi-finished products 2 on top of each other and then performing high-temperature pressing to obtain semi-finished product 3;

[0039] D) Peeling off the upper and lower layers of metal foil a of the semi-finished product 3 to obtain the composite current collector.

[0040] See Figure 3 , Figure 3 which is a schematic process flow diagram of the preparation of the composite current collector provided by the present utility model.

[0041] Among them, the metal foil a is at least one of titanium foil, stainless steel foil, copper foil and their alloys.

[0042] When the metal foil a is titanium foil or stainless steel foil and their alloys, the grain size of the metal foil a of the present utility model is not less than grade 7; or, when the metal foil a is copper foil and its alloys, a diaphragm thin layer is further included between the metal foil a and the metal b, and the isolation thin layer is prepared by coating an organic compound and / or a metal or its alloy.

[0043] When the diaphragm thin layer is obtained by coating an organic compound, the organic compound is selected from 5-carboxybenzotriazole and 4-carboxybenzotriazole with a mass ratio of 3.5 to 30:1. The 5-carboxybenzotriazole is denoted as 5CBTA, and the 4-carboxybenzotriazole is denoted as 4CBTA. The specific method is as follows: A CBTA solution containing 5CBTA and optionally 4CBTA is brought into contact with at least one surface of the carrier foil, and the CBTA component is fixed on the surface of the carrier foil. The CBTA solution preferably contains 50 to 6000 ppm of 5CBTA, 0 to 3000 ppm of 4CBTA, and the concentration ratio of 5CBTA / 4CBTA is 2 or more. More preferably, it contains 300 to 800 ppm of 5CBTA, 0 to 150 ppm of 4CBTA, and the concentration ratio of 5CBTA / 4CBTA is 2 to 8. The liquid temperature of the CBTA solution is preferably in the range of 20 to 60 °C, more preferably 30 to 40 °C. The treatment time with the CBTA solution is preferably in the range of 5 to 120 s, more preferably 30 to 60 s. The contact between the carrier foil and the CBTA solution can be carried out by dipping in the CBTA solution, spraying the CBTA solution, flowing down or dropping the CBTA solution. In addition, the fixation of CBTA on the surface of the carrier foil can be carried out by adsorption or drying of the CBTA solution, electrodeposition of the CBTA component in the CBTA solution, etc. For example, when using a copper foil as the carrier foil, the formation of the diaphragm thin layer preferably adsorbs the CBTA component while performing pickling treatment on the carrier foil. In this case, the CBTA solution preferably has a sulfuric acid concentration of 50 to 250 g / L and a copper concentration of 2 to 20 g / L, more preferably a sulfuric acid concentration of 100 to 200 g / L and a copper concentration of 5 to 15 g / L. Thus, while the surface of the carrier foil is pickled and dissolved, the eluted metal ions form metal complexes with the CBTA component and are precipitated and adsorbed on the carrier foil. As a result, the adsorption structure of the precipitated and adsorbed CBTA component becomes fine, and compared with the case of precipitating and adsorbing by contacting only an aqueous solution in which the CBTA component is dispersed, the CBTA component can be adsorbed uniformly.

[0044] When the isolation thin layer is prepared by electroplating a metal or its alloy, at least one surface of the carrier copper foil is smoothed by chemical polishing, electrochemical dissolution, electroplating, or a combination of these methods, or by further combining mechanical polishing, so that the average surface roughness Rz reaches 0.01 to 2.0 μm, and then an isolation thin layer is laminated on the surface of the smoothed carrier copper foil. The isolation thin layer is a layer of chromium, nickel, cobalt, iron, molybdenum, titanium, tungsten, phosphorus, or / and their alloys, or their hydrated oxide layers. The metals and their hydrated oxides for forming these isolation thin layers can be electroplated to form the isolation thin layer.

[0045] Forming a diaphragm thin layer only with the stripping material metal can make the stripping of the carrier and the copper foil at high temperature easier. However, if there is still hydrated oxide on its metal surface layer, the peelability will be further improved. Controlling the grain size and / or using an isolation thin layer is beneficial to reducing the stripping force when metal b is stripped from metal foil a in subsequent steps, so that metal b can be completely stripped from metal foil a.

[0046] Then, metal b is electroplated on the surface of metal foil a to obtain semi-finished product 1.

[0047] Among them, the method of electroplating metal b is: connecting metal foil a to the cathode of the power supply and metal b plate to the anode of the power supply, and placing them together in an electroplating solution containing metal b cations. Applying an external electric field to electroplate a dense and uniform metal b film on the surface of metal foil a.

[0048] The metal b is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and their alloys.

[0049] The thickness of the electroplated metal b film is 0.5 - 5 μm, preferably 0.5 - 1.5 μm.

[0050] The present utility model has no special restrictions on the composition of the electroplating solution used for electroplating metal b, and the electroplating solution for electroplating metal b well-known to those skilled in the art can be used.

[0051] After obtaining semi-finished product 1, a bondable polymer film is coated on the metal b surface of the semi-finished product 1 to obtain semi-finished product 2. Among them, the bondable polymer film is selected from bondable polyimide or its composite film, preferably soluble bondable polyimide or its composite film, and more preferably a composite film prepared by coating soluble bondable polyimide on a porous ultra-high molecular weight polyolefin film. The soluble bondable polyimide can be dissolved in a solvent and directly coated on the substrate (semi-finished product 1), without the need for an imidization reaction again, because the vacuum coating process is avoided and the production process of the composite current collector is greatly simplified; nor is it necessary to use materials such as adhesives to strengthen the adhesion between the electroplated metal film and the polymer base film, because the use of adhesives is avoided and the thickness of the composite current collector is greatly reduced.

[0052] The present utility model has no special restrictions on the coating method, and the coating methods well-known to those skilled in the art can be used.

[0053] In the present utility model, the method of coating soluble bondable polyimide is preferably to put semi-finished product 1 into a floating roller tension system, adjust its tension and then enter the coating head, and coat the diluted soluble bondable polyimide slurry according to the program set by the coating system. The wet semi-finished product after coating enters the oven and is dried by hot air to obtain semi-finished product 2;

[0054] Among them, the thickness of the bondable polymer film is 1 to 6 μm, preferably 2 to 3 μm.

[0055] Next, two semi-finished products 2 are prepared. After the bondable polymer films of the two semi-finished products 2 are superposed on each other, they are hot-pressed at a high temperature to obtain a semi-finished product 3;

[0056] Among them, the temperature of the high-temperature hot pressing is 120 to 350 °C, preferably 120, 150, 200, 250, 300, 350, or any value between 120 and 350 °C, and the pressure is 20 to 200 Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 and 200 Kgf.

[0057] After high-temperature hot pressing, the bondable polymer films of the two semi-finished products 2 are fused together. Finally, the upper and lower metal foils a of the semi-finished product 3 are peeled off to obtain a composite current collector.

[0058] The present invention also provides a method for preparing a composite current collector, including the following steps:

[0059] a) Electroplate metal b on the surface of metal foil a to obtain a semi-finished product 1;

[0060] b) Coat a bondable polymer film on the surface of metal b of the semi-finished product 1 to obtain a semi-finished product 2;

[0061] c) Superpose the metal b of the semi-finished product 1 and the bondable polymer film of the semi-finished product 2, and then perform high-temperature hot pressing to obtain a semi-finished product 3;

[0062] d) Peel off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0063] See Figure 4 , Figure 4 which is a schematic process flow diagram of the composite current collector provided by the present invention.

[0064] Among them, the preparation methods of steps a) and b) are the same as those of steps A) and B) in the above text, and will not be elaborated here. Before electroplating metal b on metal foil a, surface treatment can also be performed, and the treatment method is as described above.

[0065] Then, the metal b of the semi-finished product 1 and the bondable polymer film of the semi-finished product 2 are superposed on each other and then hot-pressed at a high temperature to obtain a semi-finished product 3;

[0066] Among them, the temperature of the high-temperature pressing is 120 to 350 °C, preferably 120, 150, 200, 250, 300, 350, or any value between 120 and 350 °C, and the pressure is 20 to 200 Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 and 200 Kgf.

[0067] Finally, strip the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0068] The present utility model also provides a method for preparing a composite current collector, including the following steps:

[0069] 1) Electroplate metal b on the surface of metal foil a to obtain semi-finished product 1;

[0070] 2) Coating a bondable polymer on the surface of the porous membrane to obtain a bondable polymer composite film;

[0071] 3) Stack the metal b of the semi-finished product 1, the bondable polymer composite film, and the metal b of the semi-finished product 1 on top of each other and then perform high-temperature pressing to obtain semi-finished product 3;

[0072] 4) Strip the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0073] See Figure 5 , Figure 5 which is a schematic process flow diagram of the composite current collector provided by the present utility model.

[0074] Among them, the preparation method in step 1) is the same as that in step A) or step a) in the above text, and will not be elaborated here. Before electroplating metal b on metal foil a, surface treatment can also be performed, and the treatment method is as described above.

[0075] After obtaining the semi-finished product 1, coat a bondable polymer on the surface of the porous membrane to obtain a bondable polymer composite film. Among them, the bondable polymer is selected from bondable polyimide, preferably soluble bondable polyimide. The method for coating the bondable polymer composite film is as described above. The difference is that the thickness of the bondable polymer composite film prepared in steps 2) and 3) is 1 to 6 μm, preferably 2 to 3 μm; the porous membrane in step 2) has a thickness of 0.5 to 4 μm, preferably 1 to 2 μm;

[0076] Among them, the drying temperature in steps 2) and 3) is 80 to 230 °C.

[0077] Finally, strip the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0078] In some specific embodiments of the present utility model, when the metal b film is an aluminum conductive layer, the current collector provided by the present utility model is an aluminum composite current collector.

[0079] See Figure 6 , Figure 6 is a schematic structural diagram of the aluminum composite current collector provided by the present utility model. Figure 6 In it, 9 and 11 are aluminum conductive layers, 10 is a bondable polymer base film, and 12 is a concave structure formed on the surface of the aluminum conductive layer after treatment.

[0080] Among them, the aluminum composite current collector includes a bondable polymer base film. The thickness of the bondable polymer base film is 1 - 6 μm, preferably 1, 2, 3, 4, 5, 6, or any value between 1 - 6 μm. The bondable polymer base film is a soluble thermoplastic polyimide. When a soluble thermoplastic polyimide is selected, on the one hand, the soluble thermoplastic polyimide can be dissolved in a solvent, and its fluidity can be used to directly coat the rough surface of the aluminum foil, improving the contact surface between the polyimide and the rough surface of the aluminum foil; on the other hand, the soluble thermoplastic polyimide has excellent mechanical strength and bonding properties, and can be used to prepare an ultra-thin and high-tensile-strength aluminum composite current collector.

[0081] The aluminum composite current collector provided by the present utility model further includes aluminum conductive layers compounded on both sides of the polymer film. The aluminum conductive layer is a single-layer structure, and the surface on the side that fits with the bondable polymer base film is a rough surface. Preferably, the surface on the side of the aluminum conductive layer that fits with the bondable polymer base film has a number of concave structures. The depth of the concave structure is 0.1 - 1 μm, preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any value between 0.1 - 1.0 μm, and the width of the concave structure is 10 - 100 nm, preferably 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or any value between 10 - 100 nm.

[0082] In the present utility model, the thickness of the aluminum conductive layer with a concave structure is 0.5 - 6 μm, preferably 1.0, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5, 6, or any value between 0.5 - 6 μm.

[0083] In the present utility model, the concave structure on the surface of the aluminum conductive layer can improve the bonding force with the bondable polymer-based film. Since the bondable polymer has fluidity and can penetrate into the concave structure on the surface of the aluminum conductive layer to produce an anchoring effect, and the concave structure on the surface of the aluminum conductive layer is mainly composed of an alumina film, and the outermost surface of the alumina film is AlOOH, and the -OH group in AlOOH is prone to form hydrogen bonds with the -C=O and -N= groups in the polymer, bonding the polymer and the aluminum conductive layer together.

[0084] The present utility model provides a method for preparing the above-mentioned aluminum composite current collector, comprising the following steps:

[0085] A) Surface-treat the aluminum foil to obtain an aluminum foil with a rough surface;

[0086] B) Coat a bondable polymer film on the rough surface of the aluminum foil to obtain a semi-finished product;

[0087] C) Overlap the bondable polymer films of two semi-finished products and press them at a high temperature to obtain the aluminum composite current collector.

[0088] First, provide the aluminum foil. The present utility model has no special restrictions on the specific source of the aluminum foil, which can be commercially available or prepared by itself. Among them, the aluminum foil can be prepared by rolling or vacuum coating. In the present utility model, the thickness of the aluminum foil without surface treatment is 1 - 7 μm, preferably 1, 2, 3, 4, 5, 6, 7, or any value between 1 - 7 μm.

[0089] Next, surface-treat the aluminum foil. The surface treatment methods include at least one of electrolytic oxidation method, chemical oxidation method, and surface etching method.

[0090] Specifically, the electrolytic oxidation method is: Place the surface of the aluminum foil in a NaOH solution and connect it to the anode, select a stainless steel disc as the cathode, and provide alternating current for electrolysis at room temperature to form an alumina film on the surface of the aluminum foil.

[0091] Among them, the concentration of the NaOH solution is 0.5 - 4 mol / L, preferably 1, 2, 3, 4 mol / L, or any value between 0.5 - 4 mol / L. The electrolysis conditions are at room temperature, the electrode spacing is 10 mm, and the voltage range is 8 - 28 V, preferably 12, 16, 20, 28 V, or any value between 8 - 28 V. The surface of the alumina film has a longitudinally staggered porous concave structure.

[0092] The surface of the electrolytically oxidized aluminum foil is evenly distributed with recessed structures having a depth of 0.1 to 0.5 μm and a width of 10 to 40 nm. Among them, the depth of the recessed structure is preferably 0.1, 0.2, 0.3, 0.4, 0.5, or any value between 0.1 and 0.5 μm, and the width is preferably 10, 20, 30, 40, or any value between 10 and 40 nm.

[0093] The chemical oxidation method is as follows: at a certain temperature, the aluminum foil is used as the anode and placed in an electrolyte solution, and an aluminum oxide film is formed on its surface by electrolysis.

[0094] Among them, the reaction temperature is 15 to 25 °C, the current density is 0.3 to 1 A / dm 2 , the oxidation time is 5 to 20 min, and the cathode material is a lead plate. The electrolyte solution includes at least one of sulfuric acid, chromic acid, phosphoric acid, and oxalic acid, and preferably a chromic acid electrolyte solution with a concentration of 50 to 100 g / L.

[0095] The surface of the chemically oxidized aluminum foil is evenly distributed with recessed structures having a depth of 0.1 to 0.7 μm and a width of 30 to 70 nm; among them, the depth of the recessed structure is preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or any value between 0.1 and 0.7 μm, and the width is preferably 30, 40, 50, 60, 70, or any value between 30 and 70 nm.

[0096] The surface etching method is as follows: the aluminum foil is placed in an alkaline solution for reaction.

[0097] Among them, the alkaline solution is at least one of NaOH and Na2CO3, preferably a NaOH solution, the concentration of the NaOH solution is 0.5 to 2 mol / L, and the etching time is 3 to 10 min.

[0098] The surface of the surface-etched aluminum foil is evenly distributed with recessed structures having a depth of 0.1 to 1 μm and a width of 50 to 100 nm. Among them, the depth of the recessed structure is preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any value between 0.1 and 1.0 μm, and the width is preferably 50, 60, 70, 80, 90, 100, or any value between 50 and 100 nm.

[0099] The above surface treatment method of the aluminum foil can reduce the thickness of the aluminum foil, and the thickness of the thinned aluminum foil is 0.5 to 6 μm, preferably 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4, 4.5, 5, 5.5, 6, or any value between 0.5 and 6 μm.

[0100] Then, a bondable polymer film is coated on the surface of the surface-treated aluminum foil to obtain a semi-finished product. The present utility model does not impose any special restrictions on the coating method, and any method known to those skilled in the art can be used. Preferably, the bondable polymer is dissolved in a solvent to obtain a bondable polymer solution, and then the bondable polymer solution is coated on the surface of the surface-treated aluminum foil, and the solvent is removed by drying to obtain an aluminum foil semi-finished product coated with a bondable polymer film.

[0101] The bondable polymer film is at least one of polyimide, polyolefin film, or a composite material of the two, and is preferably a soluble bondable thermoplastic polyimide.

[0102] The polymer films of the two semi-finished products are overlapped and hot-pressed at a high temperature to obtain an aluminum composite current collector.

[0103] The temperature of the hot pressing is 150 - 350 °C, preferably 150, 200, 250, 300, 350, or any value between 150 - 350 °C, and the pressure is 20 - 200 Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 - 200 Kgf.

[0104] The present utility model also provides a method for preparing a composite current collector, comprising the following steps:

[0105] a) Surface-treat the aluminum foil to obtain an aluminum foil with a rough surface;

[0106] b) Coat a bondable polymer film on the rough surface of the aluminum foil to obtain a semi-finished product;

[0107] c) Overlap the rough surface of the aluminum foil in a) with the bondable polymer film of the semi-finished product and hot-press at a high temperature to obtain an aluminum composite current collector.

[0108] Among them, the preparation methods of steps a) and b) are the same as those of steps A) and B) in the above text, and will not be elaborated here.

[0109] In step c), the rough surface of the aluminum foil in a) is overlapped with the polymer film of the semi-finished product and hot-pressed at a high temperature to obtain an aluminum composite current collector;

[0110] Among them, the temperature of the hot pressing is 150 - 350 °C, preferably 150, 200, 250, 300, 350, or any value between 150 - 350 °C, and the pressure is 20 - 200 Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 - 200 Kgf.

[0111] The present utility model also provides an electrochemical device, which includes the above-mentioned composite current collector. In the present utility model, the electrochemical device is selected from a battery or a capacitor.

[0112] The composite current collector provided by the present utility model can, on the one hand, avoid various problems caused by the vacuum coating process, and on the other hand, does not require the use of materials such as adhesives to strengthen the adhesion of the electroplated metal film to the polymer-based film. A low-cost composite current collector with ultra-thin thickness, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion of the electroplated metal film, simple production process, high efficiency and high yield can be obtained, enabling the composite current collector to achieve large-scale replacement and mass production of pure metal foil current collectors.

[0113] To further understand the present utility model, the following describes the composite current collector and an electrochemical device provided by the present utility model in conjunction with embodiments. The protection scope of the present utility model is not limited by the following embodiments.

[0114] The commercial titanium alloy mentioned in the embodiments of the present utility model was obtained from Shanghai Boyangte Metal Materials Co., Ltd.

[0115] The commercial copper foil mentioned in the embodiments of the present utility model was obtained from Jiangxi Copper Yez Copper Foil Co., Ltd.

[0116] The bondable polyimide mentioned in the embodiments of the present utility model is a soluble bondable polyimide, specifically a heat-resistant polyimide varnish with the model Q-VR-1714.

[0117] In the following embodiments, the soluble bondable polyimide used for coating was prepared with N-methyl-2-pyrrolidone solvent, and the solid content was 6%.

[0118] In Comparative Example 3, the non-bondable polyimide film was purchased from Wuxi Shunjinrui New Materials Co., Ltd.

[0119] The copper plating electroplating solution used in the following embodiments was prepared by uniformly mixing in the ratio of copper sulfate concentration 200 g / L, sulfuric acid concentration 50 g / L, and chloride ion solution concentration 8 mg / L.

[0120] Example 1

[0121] A preparation method of a composite current collector includes the following steps:

[0122] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of 7 grades;

[0123] (2) Surface cleaning: Scrub the surface oil stain of the above titanium alloy with anhydrous ethanol and rinse it clean with pure water;

[0124] (3) Electroplating a copper film: Place the specimen from step (2) in an electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0125] (4) Polymer coating: Coat a soluble and bondable polyimide film with a film thickness of 2 μm on the surface of the copper film of the sample obtained in step (3);

[0126] (5) Bond the bondable polyimide film layers of the two samples obtained in step (4) together, and fuse the two bondable polyimide films together by thermal lamination at 320 °C and 100 Kgf;

[0127] (6) Peel off the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0128] Example 2

[0129] A method for preparing a composite current collector, comprising the following steps:

[0130] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7;

[0131] (2) Surface cleaning: Scrub the oil stain on the surface of the above titanium alloy with anhydrous ethanol and rinse it clean with pure water;

[0132] (3) Electroplating a copper film: Place the surface of the specimen in step (2) in an electroplating solution for electroplating, with a current density of 4 A / dm 2 , and the electroplating time is 40 min;

[0133] (4) Polymer coating: Coat a soluble and bondable polyimide film with a film thickness of 2 μm on the surface of the copper film of the sample obtained in step (3);

[0134] (5) Bond the bondable polyimide film layers of the two samples obtained in step (4) together, and fuse the two bondable polyimide films together by thermal lamination at 320 °C and 100 Kgf;

[0135] (6) Peel off the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0136] Example 3

[0137] A method for preparing a composite current collector, comprising the following steps:

[0138] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7;

[0139] (2) Surface cleaning: Scrub the oil stains on the surface of the above titanium alloy with anhydrous ethanol and rinse it clean with pure water;

[0140] (3) Electroplating a copper film: Place the surface of the above specimen in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0141] (4) Polymer coating: Coat a soluble and bondable polyimide film with a film thickness of 4 μm on the surface of the copper film in step (3);

[0142] (5) Bond the copper film in step (3) and the bondable polyimide film in step (4) together and bond them by thermal lamination at 320 °C and 100 Kgf;

[0143] (6) Peel the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0144] Example 4

[0145] A method for preparing a composite current collector, comprising the following steps:

[0146] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7;

[0147] (2) Surface cleaning: Scrub the oil stains on the surface of the above titanium alloy with anhydrous ethanol and rinse it clean with pure water;

[0148] (3) Electroplating a copper film: Place the surface of the above specimen in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 40 min;

[0149] (4) Polymer coating: Coat a soluble and bondable polyimide film with a film thickness of 3 μm on the copper film surface of the sample obtained in step (3);

[0150] (5) Bond the copper film in step (3) and the bondable polyimide film in step (4) together and bond them by thermal lamination at 320 °C and 150 Kgf;

[0151] (6) Peel the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0152] Example 5

[0153] A method for preparing a composite current collector, comprising the following steps:

[0154] (1) Carrier layer: Select a commercial copper foil with a thickness of 18 μm and a surface roughness Rz of less than 6 μm on at least one side;

[0155] (2) Smoothing of the carrier foil: Using the copper foil described in step (1) as the anode, in an electrolytic solution with a sulfuric acid concentration of 50 g / L, allow a current density of 25 A / dm 2 of current to flow for 20 seconds to dissolve the surface and achieve smoothing, obtaining a smooth surface with an Rz of 0.65 μm. Use the electrolytic copper foil with this smoothed surface as the carrier copper foil;

[0156] (3) Formation of the diaphragm thin layer: Continuously electroplate chromium on the smoothed surface of the carrier copper foil smoothed in step (2) to form a chromium-plated diaphragm thin layer with an adhesion amount of 0.50 mg / dm 2 ;

[0157] (4) Electroplating a copper film: Place the surface of the sample in step (3) in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0158] (5) Polymer coating: Coat a 2-μm-thick soluble and bondable polyimide film on the copper film surface of the sample obtained in step (4);

[0159] (6) Bond the bondable polyimide film layers in the two samples obtained in step (5) together, and fuse the two bondable polyimide films together by thermal lamination at 320 °C and 100 Kgf;

[0160] (7) Peel off the upper and lower layers of commercial copper foil of the sample obtained in step (6) to obtain the finished composite current collector.

[0161] Example 6

[0162] A method for preparing a composite current collector, comprising the following steps:

[0163] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7;

[0164] (2) Surface cleaning: Scrub the oil stain on the surface of the above titanium alloy with anhydrous ethanol and rinse it clean with pure water;

[0165] (3) Electroplating a copper film: Place the sample in step (2) in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0166] (4) Porous membrane polymer coating: Coat 0.5 μm of soluble and bondable polyimide on both surfaces of a 2-μm-thick ultra-high molecular weight polyethylene porous membrane to obtain an ultra-high molecular weight polyethylene-polyimide composite film;

[0167] (5) After overlapping the surface of the copper film in step (3), the film surface of the sample obtained in step (4), and the surface of the copper film in step (3), bond them by thermal lamination at 320 °C and 100 Kgf;

[0168] (6) Peel the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0169] Example 7

[0170] A method for preparing a composite current collector, comprising the following steps:

[0171] (1) Carrier layer: Select a commercial copper foil with a thickness of 18 μm;

[0172] (2) In a CBTA aqueous solution containing 300 ppm of 5CBTA, 150 ppm of 4CBTA, a sulfuric acid concentration of 150 g / L, and a copper concentration of 10 g / L, immerse the electrode surface side of the pickled carrier copper foil at a liquid temperature of 30 °C for 30 seconds to adsorb the CBTA component on the electrode surface of the carrier foil; Immerse the carrier foil with the formed organic release layer in a solution made of nickel sulfate with a nickel concentration of 20 g / L, and under the conditions of a liquid temperature of 45 °C, pH = 3, and a current density of 5 A / dm 2 , make nickel adhere to the organic release layer, thereby forming a nickel layer as an auxiliary metal layer on the organic release layer;

[0173] (3) Electroplate a copper film: Place the surface of the sample in step (2) in an electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0174] (4) Polymer coating: Coat a 2-μm-thick soluble and bondable polyimide film on the copper film surface of the sample obtained in step (3);

[0175] (5) Bond the bondable polyimide film layers of the two samples obtained in step (4) together, and fuse the two bondable polyimide films by thermal lamination at 320 °C and 100 Kgf;

[0176] (6) Peel the upper and lower layers of commercial copper foil of the sample obtained in step (5) to obtain the finished composite current collector.

[0177] Comparative Example 1

[0178] A method for preparing a composite current collector, comprising the following steps:

[0179] Select a polypropylene film with a thickness of 4.5 μm as the carrier layer, place it in the vacuum chamber of a vacuum coating equipment, and set the vacuum environment to 3.0×10 -3Pa. Evaporate 99.9% of the copper in the evaporation boat at 1600 °C, maintain the concentration of copper vapor at 120 mol / L, sputter a layer of metallic copper film with a thickness of 40 nm on both sides of the polypropylene film, and then use the electroplating process with water to thicken the copper layers on both sides to 1 μm respectively in a 0.5 mol / L copper sulfate solution, and then a copper composite current collector can be obtained.

[0180] Comparative Example 2

[0181] A preparation method of a composite current collector, comprising the following steps:

[0182] Electroplate a copper film on the surface of a 5-μm commercial titanium alloy according to the steps in Example 2, with the thickness of the copper film being 2 μm. Subsequently, after peeling off the titanium alloy layer on the surface of the copper film, a copper film can be obtained. Then, according to the copper-soluble and bondable polyimide-copper sandwich structure, press and bond the two copper films and a 3-μm thick soluble and bondable polyimide film at 320 °C and 100 Kgf conditions to obtain a composite current collector.

[0183] Comparative Example 3

[0184] A preparation method of a composite current collector, comprising the following steps:

[0185] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7.

[0186] (2) Surface cleaning: Scrub the oil stain on the surface of the above titanium alloy with anhydrous ethanol, rinse it clean with pure water, and after drying, deposit a 20-nm thin layer of nickel-copper alloy on the surface by vacuum plating.

[0187] (3) Electroplate a copper film: Place the surface of the above sample in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min.

[0188] (4) Coating a 1.5-μm thick polyvinylidene fluoride as a binder on both the upper and lower surfaces of a 4-μm thick insoluble thermoplastic polyimide film, and then press and bond the copper film in step (3) with the binders on the upper and lower layers at a temperature of 120 °C.

[0189] (5) Peel off the upper and lower layers of titanium alloy of the sample obtained in step (4), and then a finished composite current collector can be obtained.

[0190] Comparative Example 4

[0191] A preparation method of a composite current collector, comprising the following steps:

[0192] (1) Carrier layer: Select a commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 6.

[0193] (2) Surface cleaning: Scrub the oil stains on the surface of the above titanium alloy with anhydrous ethanol and rinse it thoroughly with pure water;

[0194] (3) Electroplating copper film: Place the specimen in step (2) in the electroplating solution for electroplating, with a current density of 2 A / dm 2 , and the electroplating time is 20 min;

[0195] (4) Polymer coating: Coat a soluble and bondable polyimide film with a film thickness of 2 μm on the copper film surface of the sample obtained in step (3);

[0196] (5) Bond the soluble and bondable polyimide film layers in the two samples obtained in step (4) together, and fuse the two soluble and bondable polyimide films together by thermal lamination at 320 °C and 100 Kgf;

[0197] (6) Peel off the upper and lower layers of titanium alloy of the sample obtained in step (5) to obtain the finished composite current collector.

[0198] Comparative Example 5

[0199] A preparation method of a composite current collector, comprising the following steps:

[0200] This comparative example is compared with Example 5 without the steps of smoothing the carrier copper foil and forming the diaphragm thin layer, and the rest is the same as Example 5.

[0201] The performance detection of this application is carried out in the following manner:

[0202] (1) Thickness test

[0203] Use a precision micrometer or a vertical optical comparator to measure the thickness of a single composite current collector, and the detailed steps are carried out in accordance with GB13542.2-2009.

[0204] (2) Tensile strength and elongation at break test

[0205] The tensile test and elongation at break are carried out on a dynamic mechanical analyzer (TA Instruments, USA, model: DMA Q800 / TA). The composite current collector needs to be cut into a rectangular piece of 3×15 mm 2 for tensile test, and the tensile speed is 0.01-0.05% / min.

[0206] (3) Thermal stability test

[0207] Prepare at least 3 specimens, install the specimens on a thermomechanical analyzer, heat the specimens at a uniform rate within a predetermined temperature range, and record the height change of the specimens moving at the same time. Calculate the coefficient of thermal expansion of the specimens through the following formula:

[0208] α = (ΔH / ΔT) / H

[0209] Wherein, ΔH is the change in the height of the specimen within the temperature interval; ΔT is the temperature interval; H is the height of the specimen. For the detailed steps, reference can be made to IPC-TM-650-2.4.41.3.

[0210] (4) Test for the adhesion (peel strength) of the electroplated metal film

[0211] Fix the specimen on the base of the testing machine with the metal foil facing upwards, make the peeling angle reach 90°, use a vertical pulling force, perform at a speed of 5 cm per minute, and test the minimum pulling force according to the recorder. Repeat the specimen 5 times. For the detailed steps, reference can be made to IPC-TM-650-2.4.8.1.

[0212] (5) Electrochemical stability

[0213] The battery test system is the Wuhan Blue Electric multi-channel battery test system. Perform constant current charge and discharge cycle performance tests on the lithium-ion battery system, and perform cyclic voltammetry tests (test conditions: scanning speed is 0.1 mV / s) on the electrochemical workstation (VMP-3). It is required that the number of cycles measured for the battery > 400 times.

[0214] (6) Energy density test

[0215] Test object: It is a lithium-ion battery and is consistent with the test object of GB 38031-2020. Among them, the positive electrode is lithium iron phosphate, the negative electrode is the composite current collector prepared in the embodiment and the graphite layer on the surface of the current collector, the separator is a polyolefin microporous separator, and the electrolyte is a liquid electrolyte with lithium hexafluorophosphate as the solute.

[0216] Test steps: Use a battery charge and discharge tester to charge the assembled lithium-ion battery at a constant current of 0.33C to 4.25V at 25°C ± 2°C, then charge at a constant voltage until the current drops to 0.02C, let it stand for 5 minutes, and then discharge the battery at a constant current of 0.33C to 2.5V, record the first discharge capacity Q discharge and the first discharge energy E 放 , repeat the above experimental steps, take the average value of the 3 discharge energies E 放 , weigh the battery weight and record it as W, and calculate the energy density ED = E 放 / W.

[0217] Table 1

[0218]

[0219] In Table 1, the difference in the coefficient of thermal expansion is the difference in the coefficient of thermal expansion between the electroplated metal b film and the bondable polymer-based film.

[0220] As can be seen from Table 1, compared with Comparative Example 1, magnetron sputtering is carried out under high-temperature conditions, which will damage the mechanical properties of the film, resulting in a decrease in tensile strength and puncture strength. Moreover, the bonding force between the film substrate and the copper layer in the copper composite current collector prepared by this method is poor, greatly shortening the service life of the battery; compared with Comparative Example 2, when preparing the ultra-thin composite current collector, due to the low thickness of the copper film, fractures and wrinkles are likely to occur during the lamination process, resulting in a very low product yield. Therefore, no relevant data tests were carried out on Comparative Example 2; compared with Comparative Example 3, the selected polyimide film must use a binder to ensure the adhesion between the copper foil and the polyimide film, but the thickness of the composite current collector increases significantly, the battery energy density decreases, and the adhesion of the product is difficult to maintain for a long time; if no binder is used, since the polyimide film used in Comparative Example 3 is a thermosetting film and has no adhesiveness, a composite current collector cannot be prepared; compared with Comparative Example 4, the difference from Example 1 is the grain size on the surface of the commercial titanium alloy. When the grain size on the surface of the titanium alloy is lower than the limit of Grade 7, the surface grains become larger, resulting in an uneven surface, increasing the surface roughness, improving the bonding force between the electroplated metallic copper and it, and causing electroplated metallic copper film to remain on the surface of the titanium alloy during peeling; compared with Comparative Example 5, the difference from Example 5 is that the surface of the carrier copper foil is not smoothed and there is no diaphragm thin layer on the surface, so that the electroplated metallic copper and the carrier copper foil cannot be peeled off after electroplating

[0221] From the difference in the coefficient of thermal expansion in Table 1, it can be seen that the difference in the coefficient of thermal expansion between the electroplated metallic b film and the bondable polymer-based film is not greater than 30 ppm / °C. Therefore, after the polymer film and the electroplated copper film are compounded with each other, during the repeated process of thermal expansion and contraction during multiple charge and discharge operations of the battery, excellent peel force stability and durability can be maintained between the two

[0222] Example 8

[0223] A method for preparing an aluminum composite current collector, comprising the following steps:

[0224] (1) Prepare an aluminum foil with a thickness of 4 μm by the rolling method, place it in a 2 mol / L NaOH solution and connect it to the anode, select a stainless steel disc as the cathode, at room temperature, the electrode spacing is 10 mm, and electrolyze under 20 V alternating current. After electrolysis, the surface of the aluminum foil is distributed with concave structures with an average depth of 0.2 μm and an average width of 10 nm, and its thickness is 3.8 μm;

[0225] (2) Coat a polyimide film with a film thickness of 2 μm on the surface of the aluminum foil treated in step (1);

[0226] (3) Bond the polymer layers in the two samples obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain an aluminum composite current collector

[0227] Example 9

[0228] A method for preparing an aluminum composite current collector, comprising the following steps:

[0229] (1) Prepare an aluminum foil with a thickness of 4 μm by rolling. At 25 °C, place the aluminum foil as the anode in an H2CrO4 electrolyte with a concentration of 80 g / L. The cathode material is a lead plate, and the current density is 0.5 A / dm 2 , and the oxidation time is 5 min. The obtained aluminum foil has a concave structure with an average depth of 0.3 μm and an average width of 60 nm on its surface, and its thickness is 3.7 μm;

[0230] (2) Coat a polyimide film with a thickness of 2 μm on the surface of the aluminum foil treated in step (1);

[0231] (3) Bond the polymer layers of the two samples obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain an aluminum composite current collector.

[0232] Example 10

[0233] A method for preparing an aluminum composite current collector, comprising the following steps:

[0234] (1) Prepare an aluminum foil with a thickness of 4 μm by rolling. Place it in a 0.5 mol / L NaOH solution, and the etching time is 3 min. After taking it out, rinse it with pure water until clean. The obtained aluminum foil has a concave structure with an average depth of 0.6 μm and an average width of 100 nm on its surface, and its thickness is 3.5 μm;

[0235] (2) Coat a polyimide film with a thickness of 2 μm on the surface of the aluminum foil treated in step (1);

[0236] (3) Bond the polymer layers of the two samples obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain an aluminum composite current collector.

[0237] Example 11

[0238] A method for preparing an aluminum composite current collector, comprising the following steps:

[0239] (1) Prepare an aluminum foil with a thickness of 4 μm by the calendering method, place it in a 2 mol / L NaOH solution and connect it to the anode. Select a stainless steel disc as the cathode. Under room temperature conditions, with an electrode spacing of 10 mm, electrolyze under 20 V alternating current. After electrolysis, the surface of the aluminum foil is distributed with concave structures with an average depth of 0.2 μm and an average width of 10 nm, and its thickness is 3.8 μm;

[0240] (2) Coat a polyimide film with a film thickness of 2 μm on the surface of the aluminum foil treated in step (1);

[0241] (3) Bond the surface of the aluminum foil treated in step (1) and the polymer layer in the sample obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain an aluminum composite current collector.

[0242] Example 12

[0243] A method for preparing an aluminum composite current collector, comprising the following steps:

[0244] (1) Prepare an aluminum foil with a thickness of 4 μm by the calendering method, place it in a 4 mol / L NaOH solution and connect it to the anode. Select a stainless steel disc as the cathode. Under room temperature conditions, with an electrode spacing of 10 mm, electrolyze under 28 V alternating current. After electrolysis, the surface of the aluminum foil is distributed with concave structures with an average depth of 0.5 μm and an average width of 40 nm, and its thickness is 3.5 μm;

[0245] (2) Coat a polyimide film with a film thickness of 1 μm on the surface of the aluminum foil treated in step (1);

[0246] (3) Bond the polymer layers in two samples obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain an aluminum composite current collector.

[0247] Example 13

[0248] A method for preparing an aluminum composite current collector, comprising the following steps:

[0249] (1) Prepare an aluminum foil with a thickness of 4 μm by the calendering method, place it in a 2 mol / L NaOH solution and connect it to the anode. Select a stainless steel disc as the cathode. Under room temperature conditions, with an electrode spacing of 10 mm, electrolyze under 20 V alternating current. After electrolysis, the surface of the aluminum foil is distributed with concave structures with an average depth of 0.2 μm and an average width of 10 nm, and its thickness is 3.8 μm;

[0250] (2) Coat a 0.6-μm-thick soluble and bondable polyimide layer on both the surface of the aluminum foil processed in step (1) and the surface of the ultra-high density polyethylene film with a film thickness of 2 μm. Press them together, remove the extruded excess glue, and keep them in an oven at 80 °C for 3 h, then cool to room temperature;

[0251] (3) Coat a 0.6-μm-thick soluble and bondable polyimide layer on the other surface of the ultra-high density polyethylene film in step (2) and the surface of the aluminum foil processed in step (1). Press them together, remove the extruded excess glue, and keep them in an oven at 80 °C for 3 h. Then place them in an oven at 210 °C for drying and curing, and cool to room temperature to obtain the aluminum composite current collector.

[0252] Comparative Example 6

[0253] A method for preparing an aluminum composite current collector, comprising the following steps:

[0254] Select a PET base film with a thickness of 6 μm as the carrier layer, and place it on a vacuum evaporation device together with a high-purity aluminum ingot with a purity of 99.9%. Set the vacuum environment to 5.0×10 -2 Pa, the evaporation rate is 50 m / min, and the evaporation temperature is 700 °C. Deposit aluminum on both the upper and lower surfaces of the PET base film through the vacuum evaporation device to obtain an aluminum coating layer. The single-sided aluminum coating layer needs to be evaporated dozens of times, and the thickness of the single-sided aluminum coating layer is 1 μm. After evaporation, wind it up to obtain the aluminum composite current collector.

[0255] Comparative Example 7

[0256] A method for preparing an aluminum composite current collector, comprising the following steps:

[0257] (1) Prepare an aluminum foil with a thickness of 4 μm by the rolling method, remove the surface oil stain with ethanol, and rinse it clean with pure water;

[0258] (2) Coat a polyimide film with a film thickness of 2 μm on the surface of the aluminum foil processed in step (1);

[0259] (3) Bond the polymer layers of the two samples obtained in step (2) together, and fuse the two polymer films together by hot pressing at 300 °C and 100 Kgf to obtain the aluminum composite current collector.

[0260] Comparative Example 8

[0261] A method for preparing an aluminum composite current collector, comprising the following steps:

[0262] (1) Prepare an aluminum foil with a thickness of 4 μm by the calendering method, place it in a 2 mol / L NaOH solution and connect it to the anode. Select a stainless steel disc as the cathode. At room temperature, with an electrode spacing of 10 mm, electrolyze under 20 V alternating current. After electrolysis, the surface of the aluminum foil is distributed with concave structures with an average depth of 0.2 μm and an average width of 10 nm, and its thickness is 3.8 μm;

[0263] (2) Stack the aluminum foils treated in step (1) on both sides of a polyamic acid film with a thickness of 4 μm to form a laminated material, and then dry it at 120 °C and 100 Kgf;

[0264] (3) Place the dried sample under the condition of 300 °C for imidization treatment, and the aluminum composite current collector is obtained after cooling.

[0265] The performance detection of this application is shown in the following table:

[0266] Table 2

[0267]

[0268] As can be seen from Table 2, for the aluminum composite current collectors prepared by the electrolytic oxidation method, such as Example 8 and Example 11, they have the highest peel strength. The main reason is that after the aluminum foil is treated by the electrolytic oxidation method, a porous concave structure with longitudinal intersections is formed on its surface. Coupled with the fact that the polyimide film used is a soluble polyimide and has excellent adhesiveness, its fluidity can penetrate into the concave structure on the surface of the aluminum foil to produce an anchoring effect, thus significantly improving the bonding strength between the aluminum foil and the polyimide film.

[0269] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that: The structure comprises a bondable polymer base film and a single-layer metal b film compounded on both sides of the bondable polymer base film, wherein the metal b of the single-layer metal b film is one of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, iridium, indium and alloys thereof; the bondable polymer base film is selected from bondable polyimide or its composite film.

2. The composite current collector according to claim 1, characterized in that: The bondable polymer base film is selected from soluble bondable polyimide or a composite film thereof.

3. The composite current collector according to claim 1, characterized in that: The thickness of the adhesive polymer base film is 1 to 6 μm.

4. The composite current collector according to claim 1, characterized in that: The thickness of the adhesive polymer base film is 2-3 μm.

5. The composite current collector according to claim 1, characterized in that: The metal b of the single-layer metal b film is one of copper, aluminum and their alloys.

6. The composite current collector according to claim 1, characterized in that: The thickness of the single-layer metal b film is 0.5-5 μm.

7. The composite current collector according to claim 1, characterized in that: The thickness of the single-layer metal b film is 0.5-1.5 μm.

8. The composite current collector according to claim 1, characterized in that: The single-layer metal b film is an aluminum conductive layer, the aluminum conductive layer is a single-layer structure, and the surface of the aluminum conductive layer on the side that is bonded to the polymer base film is a rough surface.

9. The composite current collector according to claim 8, characterized in that: The surface of the aluminum conductive layer on the side where it is bonded to the polymer base film has a plurality of concave structures, the depth of the concave structures is 0.1-1 μm, the width of the concave structures is 10-100 nm, and the thickness of the aluminum conductive layer with the concave structures is 0.5-6 μm.

10. An electrochemical device, characterized in that: A composite current collector comprising any one of claims 1 to 9.

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