Composite current collector and preparation method thereof

Abstract

The invention provides a composite current collector. The composite current collector comprises an adhesive polymer base film and electroplated metal b films compounded on the two sides of the adhesive polymer base film. According to the composite current collector provided by the invention, on one hand, various problems caused by a vacuum coating process are avoided, and on the other hand, materials such as an adhesive do not need to be used for strengthening the adhesive force of an electroplated metal film and a polymer base film; 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 electroplated 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 present invention belongs to the technical field of electrochemical devices, and in particular relates to a composite current collector and a preparation method thereof. Background Art

[0002] The current collector is one of the indispensable components of an electrochemical device. It not only carries active substances, but also collects and outputs the current generated by the electrode active substances, which helps to reduce the internal resistance of the electrochemical device and improve the coulombic efficiency, cycle stability and rate performance of the electrochemical device.

[0003] Modifying traditional single metal foil current collectors into composite current collectors comprising a thin film support layer and a metal conductive layer can enhance the current collector's toughness and improve its mechanical properties. The current process for composite current collectors involves first applying a conductive pre-coated copper layer to a thin film substrate using vacuum coating methods such as magnetron sputtering and / or evaporation to metallize the polymer film. The copper layer is then thickened to 1μm using conventional wet electroplating to ensure the composite copper foil's conductivity meets application requirements. However, this method results in a weak bond between the film substrate and the metal conductive layer. Furthermore, during vacuum coating, the film substrate is susceptible to burns or wrinkling due to the high-temperature copper vapor, which can reach temperatures exceeding 1000°C. Mechanical impact from metal particles on the film substrate also leads to varying degrees of attenuation of the film substrate's tensile strength and elongation at break. Furthermore, vacuum coating production is inefficient and the process cost is high. These shortcomings significantly impact the application of composite current collectors in electrochemical devices, hindering their widespread replacement and mass production for pure metal foil current collectors in electrochemical devices.

[0004] In addition, existing composite current collector preparation technologies also employ multi-layer structures, in which a binder material is added between the film substrate and the metal conductive layer to enhance adhesion between the two. However, the addition of a binder layer inevitably increases the thickness of the composite current collector and complicates the preparation process, thereby increasing its cost and reducing its performance.

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

[0006] In view of this, the technical problem to be solved by the present invention is to provide a composite current collector and a preparation method thereof, which 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 adhesives and other materials to strengthen the adhesion between the electroplated metal film and the polymer base film, and can obtain a low-cost composite current collector with ultra-thin, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion to the electroplated metal film, simple production process, high efficiency and high yield, so that the composite current collector can achieve large-scale replacement and mass production of pure metal foil current collectors in electrochemical devices.

[0007] The invention provides a composite current collector, comprising a bondable polymer base film and an electroplated metal B film composited on both sides of the bondable polymer base film.

[0008] Preferably, the adhesive polymer base film is selected from adhesive polyimide or its composite film, preferably soluble adhesive polyimide or its composite film; the thickness of the adhesive polymer base film is 1 to 6 μm, preferably 2 to 3 μm.

[0009] Preferably, the metal b of the electroplated 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 electroplated metal b film is 0.5 to 5 μm, preferably 0.5 to 1.5 μm.

[0010] Preferably, the peel strength of the electroplated metal b film and the adhesive polymer base film in the composite current collector is not less than 6N / 25mm; the difference in thermal expansion coefficient between the electroplated metal b film and the adhesive polymer base film is not greater than 50ppm / ℃, preferably not greater than 30ppm / ℃.

[0011] The present invention provides a roll-to-roll method for preparing a composite current collector, comprising the following steps:

[0012] A) electroplating metal b on the surface of metal foil a to obtain semi-finished product 1;

[0013] B) coating a bondable polymer film on the surface of the metal b of the semi-finished product 1 to obtain a semi-finished product 2;

[0014] C) superimposing the two adhesive polymer films of the semi-finished product 2 and laminating them at high temperature to obtain a semi-finished product 3;

[0015] D) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0016] The present invention also provides a roll-to-roll method for preparing a composite current collector, comprising the following steps:

[0017] a) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1;

[0018] b) coating a bondable polymer film on the metal surface b of the semi-finished product 1 to obtain a semi-finished product 2;

[0019] c) superimposing the metal b of the semi-finished product 1 and the adhesive polymer film of the semi-finished product 2 and pressing them at high temperature to obtain a semi-finished product 3;

[0020] d) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0021] Another roll-to-roll method for preparing a composite current collector provided by the present invention comprises the following steps:

[0022] 1) Electroplating metal b on the surface of metal foil a to obtain semi-finished product 1;

[0023] 2) coating a bondable polymer on the surface of the porous membrane to obtain a bondable polymer composite film;

[0024] 3) superimposing the metal b of the semi-finished product 1, the bondable polymer composite film, and the metal b of the semi-finished product 1 and performing high-temperature pressing to obtain a semi-finished product 3;

[0025] 4) Peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0026] Preferably, the metal foil a is at least one of titanium foil, stainless steel foil, copper foil and alloys thereof.

[0027] Preferably, when the metal foil a is titanium foil or stainless steel foil and its alloy, the grain size of the metal foil a is not less than level 7; or, when the metal foil a is copper foil and its alloy, a thin membrane layer is also included between the metal foil a and the electroplated metal b, and the isolation layer is prepared by coating an organic compound and / or electroplating a metal or its alloy.

[0028] Preferably, the electroplating method is to connect the metal foil a to the cathode of the power supply, and the metal b plate to the anode of the power supply, and place them together in an electroplating solution containing metal b cations, and apply an external electric field to electroplate a dense and uniform metal b film on the surface of the metal foil a;

[0029] Preferably, in step C) or step c), the temperature of the high-temperature pressing is 120 to 350° C., and the pressure is 20 to 200 kgf;

[0030] Preferably, in step 2) or step 3), the drying temperature is 80-230°C.

[0031] The present invention also provides an electrochemical device comprising the composite current collector.

[0032] Compared to the prior art, the present invention provides a composite current collector comprising an adhesive polymer base film and an electroplated metal film b composited to both sides of the adhesive polymer base film. The composite current collector provided by the present invention 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 base film. A low-cost composite current collector can be obtained that is ultra-thin, has high tensile strength, high elongation at break, good thermal stability, good electrochemical stability, good adhesion to the electroplated metal film, simple production process, high efficiency, and high yield. This allows the composite current collector to achieve large-scale replacement and mass production of pure metal foil current collectors in electrochemical devices.

[0033] The present invention provides a method for preparing a composite current collector, comprising the following steps: A) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1; B) coating a bondable polymer film on the surface of metal b of the semi-finished product 1 to obtain a semi-finished product 2; C) superimposing the bondable polymer films of two semi-finished products 2 and performing high-temperature pressing to obtain a semi-finished product 3; and D) peeling off the upper and lower layers of metal foil a of the semi-finished product 3 to obtain a composite current collector.

[0034] The present invention also provides a method for preparing a composite current collector, comprising the following steps: a) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1; b) coating a bondable polymer film on the surface of the metal b of the semi-finished product 1 to obtain a semi-finished product 2; c) superimposing the metal b of the semi-finished product 1 and the bondable polymer film of the semi-finished product 2, and then performing high-temperature pressing to obtain a semi-finished product 3; d) peeling off the upper and lower layers of metal foil a of the semi-finished product 3 to obtain a composite current collector. The present invention provides another method for preparing a composite current collector, comprising the following steps: 1) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1; 2) coating a bondable polymer on the surface of a porous membrane to obtain a bondable polymer composite film; 3) superimposing the metal b of the semi-finished product 1, the bondable polymer composite film, and the metal b of the semi-finished product 1, and then performing high-temperature pressing to obtain a semi-finished product 3; 4) peeling off the upper and lower layers of metal foil a of the semi-finished product 3 to obtain a composite current collector.

[0035] The composite current collector and preparation method provided by the present invention can, on the one hand, avoid various problems caused by the vacuum coating process, and on the other hand, do not need to use materials such as adhesives to strengthen the adhesion between the electroplated metal film and the polymer base film. A low-cost composite current collector with ultra-thinness, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion to the electroplated metal film, simple production process, high efficiency and high yield can be obtained, so that the composite current collector can achieve large-scale replacement and mass production of pure metal foil current collectors in electrochemical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the preparation process of the composite current collector provided by the present invention;

[0037] Figure 2 A schematic diagram of the preparation process of the composite current collector provided by the present invention;

[0038] Figure 3 This is a schematic diagram of the preparation process of the composite current collector provided by the present invention. DETAILED DESCRIPTION

[0039] The invention provides a composite current collector, comprising a bondable polymer base film and an electroplated metal B film composited on both sides of the bondable polymer base film.

[0040] The adhesive polymer base film is selected from adhesive polyimide or its composite film, preferably soluble adhesive polyimide or its composite film.

[0041] In the present invention, when the adhesive polymer base film is selected from a soluble adhesive polyimide film, the soluble adhesive polyimide film is a single-layer structure prepared from a soluble adhesive polyimide. The soluble adhesive polyimide can be dissolved in a solvent and directly coated on a substrate (semi-finished product 1 or adhesive composite film) without the need for a secondary imidization reaction. This greatly simplifies the production process of the composite current collector by avoiding the vacuum coating process. It is also unnecessary to use a binder or other material to strengthen the adhesion between the electroplated metal film and the polymer base film. This greatly reduces the thickness of the composite current collector by avoiding the use of a binder. The solvent is selected from one or more solvents selected from N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone, and cyclopentanone. The solid content of the resulting soluble adhesive polyimide slurry is 5% to 12%, preferably 5% to 8%.

[0042] In some preferred embodiments of the present invention, the adhesive polymer base film is a composite film prepared by coating a soluble adhesive polyimide on an ultra-high molecular weight polyolefin porous membrane, that is, the middle layer is an ultra-high molecular weight polyolefin porous membrane, the two sides are soluble adhesive polyimide films, and the pores are filled with soluble adhesive polyimide to form a composite film.

[0043] The thickness of the adhesive polymer base film is 1 to 6 μm, preferably 2 to 3 μm.

[0044] The metal b of the electroplated metal b film is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and alloys thereof, preferably copper and alloys thereof. The thickness of the electroplated metal b film is 0.5 to 5 μm, preferably 0.5 to 1.5 μm.

[0045] In the present invention, the composite current collector is ultrathin, has high tensile strength, high elongation at break, good thermal and electrochemical stability, and excellent adhesion of the electroplated metal film. The peel strength between the electroplated metal film (b) and the adhesive polymer base film in the composite current collector is no less than 6 N / 25 mm, preferably 6.6 to 8.0 N / 25 mm. The difference in thermal expansion coefficient between the electroplated metal film (b) and the adhesive polymer base film is no greater than 50 ppm / °C, preferably no greater than 30 ppm / °C.

[0046] The present invention provides a roll-to-roll method for preparing a composite current collector, comprising the following steps:

[0047] A) electroplating copper metal b on the surface of metal foil a to obtain a semi-finished product 1;

[0048] B) coating a bondable polymer film on the surface of the metal b of the semi-finished product 1 to obtain a semi-finished product 2;

[0049] C) superimposing the two adhesive polymer films of the semi-finished product 2 and laminating them at high temperature to obtain a semi-finished product 3;

[0050] D) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0051] See also Figure 1 , Figure 1 This is a schematic diagram of the preparation process of the composite current collector provided by the present invention.

[0052] Wherein, the metal foil a is at least one of titanium foil, stainless steel foil, copper foil and alloys thereof.

[0053] When the metal foil a is titanium foil or stainless steel foil and its alloy, the grain size of the metal foil a of the present invention is not less than level 7; or, when the metal foil a is copper foil and its alloy, a thin membrane layer is also included between the metal foil a and the electroplated metal b, and the isolation layer is prepared by coating an organic compound and / or electroplating a metal or its alloy.

[0054] When the thin separator layer is formed by coating an organic compound, the organic compound is selected from 5-carboxybenzotriazole and 4-carboxybenzotriazole in a mass ratio of 3.5 to 30:1. The 5-carboxybenzotriazole is denoted as 5CBTA, and the 4-carboxybenzotriazole is denoted as 4CBTA. A specific method involves contacting a CBTA solution containing 5CBTA and, if necessary, 4CBTA with at least one surface of a carrier foil to fix the CBTA component to the surface of the carrier foil. The CBTA solution preferably contains 50 to 6000 ppm of 5CBTA, 0 to 3000 ppm of 4CBTA, and a 5CBTA / 4CBTA concentration ratio of 2 or greater. More preferably, it contains 300 to 800 ppm of 5CBTA, 0 to 150 ppm of 4CBTA, and a 5CBTA / 4CBTA concentration ratio of 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 seconds, more preferably 30 to 60 seconds. The carrier foil can be brought into contact with the CBTA solution by immersion in the CBTA solution, spraying the CBTA solution, or by dripping or pouring the CBTA solution. CBTA can also be fixed to the carrier foil surface by adsorption or drying of the CBTA solution, or by electrodeposition of the CBTA component from the CBTA solution. For example, when using copper foil as the carrier foil, the formation of the separator layer is preferably achieved by simultaneously adsorbing the CBTA component during pickling of 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. This allows the surface of the carrier foil to be pickled and dissolved while the eluted metal ions form metal complexes with the CBTA component, precipitating and adsorbing them onto the carrier foil. As a result, the adsorption structure of the CBTA component by precipitation adsorption becomes finer, and the CBTA component can be adsorbed more uniformly compared to the case of precipitation adsorption by contact with an aqueous solution in which only the CBTA component is dispersed.

[0055] When the barrier layer is prepared by electroplating a metal or its alloy, at least one side of the carrier copper foil is smoothed by chemical grinding, electrochemical dissolution, electroplating, or a combination of these methods, or in combination with mechanical grinding, to an average surface roughness Rz of 0.01 to 2.0 μm. The barrier layer is then laminated onto the surface of the smoothed carrier copper foil. The barrier layer can be a layer of chromium, nickel, cobalt, iron, molybdenum, titanium, tungsten, phosphorus, or / and their alloys or hydrated oxides. The metals and hydrated oxides forming the barrier layer can be formed by electroplating.

[0056] Using only a thin separator layer of the release metal facilitates peeling of the carrier and copper foil at high temperatures. However, the presence of hydrated oxides on the metal surface further enhances peelability. Controlling grain size and / or using a thin separator layer can help reduce the peeling force during the subsequent steps of peeling metal (B) from foil (A), allowing for complete separation of metal (B) from foil (A).

[0057] Then, metal b is electroplated on the surface of metal foil a to obtain a semi-finished product 1.

[0058] Among them, the method of electroplating metal b is: connecting metal foil a to the cathode of the power supply, connecting the metal b plate to the anode of the power supply, placing them together in an electroplating solution containing metal b cations, applying an external electric field, and electroplating a dense and uniform metal b film on the surface of metal foil a.

[0059] The metal b is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and alloys thereof.

[0060] The thickness of the electroplated metal b film is 0.5 to 5 μm, preferably 0.5 to 1.5 μm.

[0061] The present invention has no special restrictions on the composition of the electroplating solution used for electroplating the metal b, and any electroplating solution used for electroplating the metal b known to those skilled in the art can be used.

[0062] After obtaining semi-finished product 1, the metal b surface of the semi-finished product 1 is coated with a bondable polymer film to obtain semi-finished product 2. Wherein, the bondable polymer film is selected from bondable polyimide or its composite film, preferably soluble bondable polyimide or its composite film, more preferably soluble bondable polyimide is coated on the composite film prepared from ultra-high molecular weight polyolefin porous film. The soluble bondable polyimide can be dissolved in a solvent and directly coated on substrate (semi-finished product 1), and it is not necessary to carry out imidization again, because it circumvents vacuum coating process and greatly simplifies the production process of composite current collector; it is also not necessary to use materials such as adhesives to strengthen the adhesion of electroplated metal film and polymer base film, because it circumvents the use of adhesive and greatly reduces the thickness of composite current collector.

[0063] The present invention has no particular limitation on the coating method, and any coating method known to those skilled in the art may be used.

[0064] In the present invention, the method for coating the soluble and adhesive polyimide is preferably as follows: the semi-finished product 1 enters a floating roller tension system, adjusts its tension, and then enters a coating head, and the diluted soluble and adhesive polyimide slurry is coated according to a program set by the coating system. The wet semi-finished product after coating enters an oven and is dried by hot air to obtain a semi-finished product 2;

[0065] The thickness of the adhesive polymer film is 1 to 6 μm, preferably 2 to 3 μm.

[0066] Next, two semi-finished products 2 are prepared, and the adhesive polymer films of the two semi-finished products 2 are superimposed on each other and then pressed at high temperature to obtain a semi-finished product 3;

[0067] The temperature of the high-temperature pressing is 120-350°C, preferably 120, 150, 200, 250, 300, 350, or any value between 120 and 350°C, and the pressure is 20-200Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 and 200Kgf.

[0068] After high-temperature lamination, the two adhesive polymer films of the semi-finished product 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.

[0069] The present invention also provides a method for preparing a composite current collector, comprising the following steps:

[0070] a) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1;

[0071] b) coating a bondable polymer film on the metal surface b of the semi-finished product 1 to obtain a semi-finished product 2;

[0072] c) superimposing the metal b of the semi-finished product 1 and the adhesive polymer film of the semi-finished product 2 and pressing them at high temperature to obtain a semi-finished product 3;

[0073] d) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0074] See also Figure 2 , Figure 2 This is a schematic diagram of the preparation process of the composite current collector provided by the present invention.

[0075] The preparation methods of step a) and step b) are the same as those of step A) and step B) above, and are not described in detail here. The metal foil a may also be surface treated before being electroplated with the metal b, using the same treatment method as described above.

[0076] Then, the metal b of the semi-finished product 1 and the adhesive polymer film of the semi-finished product 2 are superimposed on each other and pressed at high temperature to obtain the semi-finished product 3;

[0077] The temperature of the high-temperature pressing is 120-350°C, preferably 120, 150, 200, 250, 300, 350, or any value between 120 and 350°C, and the pressure is 20-200Kgf, preferably 20, 40, 50, 100, 150, 200, or any value between 20 and 200Kgf.

[0078] Finally, the upper and lower metal foils a of the semi-finished product 3 are peeled off to obtain a composite current collector.

[0079] The present invention also provides a method for preparing a composite current collector, comprising the following steps:

[0080] 1) Electroplating metal b on the surface of metal foil a to obtain semi-finished product 1;

[0081] 2) coating a bondable polymer on the surface of the porous membrane to obtain a bondable polymer composite film;

[0082] 3) superimposing the metal b of the semi-finished product 1, the bondable polymer composite film, and the metal b of the semi-finished product 1 and performing high-temperature pressing to obtain a semi-finished product 3;

[0083] 4) Peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

[0084] See also Figure 3 , Figure 3 This is a schematic diagram of the preparation process of the composite current collector provided by the present invention.

[0085] The preparation method of step 1) is the same as that of step A) or step a) above, and will not be described in detail here. The metal foil a may also be surface treated before being electroplated with the metal b, and the treatment method is as described above.

[0086] After obtaining the semi-finished product 1, a bondable polymer is coated on the surface of the porous membrane to obtain a bondable polymer composite film. Wherein, 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 bondable polymer composite film obtained in step 2) and step 3) has a thickness of 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;

[0087] Wherein, the drying temperature in step 2) and step 3) is 80-230°C.

[0088] Finally, the upper and lower metal foils a of the semi-finished product 3 are peeled off to obtain a composite current collector.

[0089] The present invention also provides an electrochemical device comprising the composite current collector. In the present invention, the electrochemical device is selected from a battery or a capacitor.

[0090] The composite current collector and preparation method provided by the present invention can, on the one hand, avoid various problems caused by the vacuum coating process, and on the other hand, do not need to use materials such as adhesives to strengthen the adhesion between the electroplated metal film and the polymer base film. A low-cost composite current collector with ultra-thinness, high tensile strength, large elongation at break, good thermal stability, good electrochemical stability, good adhesion to the electroplated metal film, simple production process, high efficiency and high yield can be obtained, so that the composite current collector can achieve large-scale replacement and mass production of pure metal foil current collectors.

[0091] In order to further understand the present invention, the composite current collector and the preparation method thereof provided by the present invention are described below with reference to the following examples. The protection scope of the present invention is not limited by the following examples.

[0092] The commercial titanium alloy mentioned in the embodiments of the present invention is obtained from Shanghai Boyangte Metal Materials Co., Ltd.

[0093] The commercial copper foil mentioned in the embodiments of the present invention is obtained from Jiangxi Copper Yezi Copper Foil Co., Ltd.

[0094] The adhesive polyimide mentioned in the embodiment of the present invention is a soluble adhesive polyimide, specifically a heat-resistant polyimide varnish with the model number Q-VR-1714.

[0095] In the following examples, the soluble and adhesive polyimide used for coating was prepared from N-methyl-2-pyrrolidone solvent and had a solid content of 6%.

[0096] In Comparative Example 3, the non-adhesive polyimide film was purchased from Wuxi Shunjinrui New Materials Co., Ltd.

[0097] The copper plating solution used in the following examples was prepared by uniformly mixing copper sulfate at a concentration of 200 g / L, sulfuric acid at a concentration of 50 g / L, and chloride ion solution at a concentration of 8 mg / L.

[0098] Example 1

[0099] A method for preparing a composite current collector comprises the following steps:

[0100] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7 was selected;

[0101] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0102] (3) Electroplating copper film: Place the sample in step (2) in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0103] (4) Polymer coating: coating the copper film surface of the sample obtained in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 2 μm;

[0104] (5) Laminating the two adhesive polyimide film layers of the samples obtained in step (4) together, and fusing the two adhesive polyimide films together by thermal lamination at 320° C. and 100 kgf;

[0105] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0106] Example 2

[0107] A method for preparing a composite current collector comprises the following steps:

[0108] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7 was selected;

[0109] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0110] (3) Electroplating copper film: Place the sample surface in step (2) in the electroplating solution for electroplating at a current density of 4A / dm 2 , the electroplating time is 40min;

[0111] (4) Polymer coating: coating the copper film surface of the sample obtained in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 2 μm;

[0112] (5) Laminating the two adhesive polyimide film layers of the samples obtained in step (4) together, and fusing the two adhesive polyimide films together by thermal lamination at 320° C. and 100 kgf;

[0113] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0114] Example 3

[0115] A method for preparing a composite current collector comprises the following steps:

[0116] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7 was selected;

[0117] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0118] (3) Electroplating of copper film: Place the surface of the sample in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0119] (4) Polymer coating: coating the surface of the copper film in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 4 μm;

[0120] (5) laminating the copper film of step (3) and the adhesive polyimide film of step (4) together, and bonding them by thermal lamination at 320° C. and 100 kgf;

[0121] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0122] Example 4

[0123] A method for preparing a composite current collector comprises the following steps:

[0124] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7 was selected;

[0125] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0126] (3) Electroplating of copper film: Place the surface of the sample in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 40min;

[0127] (4) Polymer coating: coating the copper film surface of the sample obtained in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 3 μm;

[0128] (5) laminating the copper film of step (3) and the adhesive polyimide film of step (4) together, and bonding them by thermal lamination at 320° C. and 150 kgf;

[0129] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0130] Example 5

[0131] A method for preparing a composite current collector comprises the following steps:

[0132] (1) Carrier layer: Commercial copper foil with a thickness of 18 μm and a surface roughness Rz of less than 6 μm on at least one side;

[0133] (2) Smoothing of carrier foil: The copper foil described in step (1) was used as an anode and the current density was set to 25 A / dm in an electrolyte with a sulfuric acid concentration of 50 g / L. 2 A current of 1000 Nm was passed through the foil for 20 seconds to dissolve the surface and smooth it, resulting in a smooth surface with an Rz of 0.65 μm. The electrolytic copper foil with this smoothed surface was used as the carrier copper foil.

[0134] (3) Formation of the diaphragm thin layer: The smoothed surface of the carrier copper foil smoothed in step (2) is continuously electroplated with chromium to form a deposition amount of 0.50 mg / dm 2 A thin layer of chrome-plated diaphragm;

[0135] (4) Electroplating copper film: Place the sample surface in step (3) in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0136] (5) Polymer coating: coating the copper film surface of the sample obtained in step (4) with a layer of soluble and adhesive polyimide film with a thickness of 2 μm;

[0137] (6) Laminating the two adhesive polyimide film layers of the samples obtained in step (5) together, and fusing the two adhesive polyimide films together by thermal lamination at 320° C. and 100 kgf;

[0138] (7) Peeling off the upper and lower layers of commercial copper foil of the sample obtained in step (6) to obtain a finished composite current collector.

[0139] Example 6

[0140] A method for preparing a composite current collector comprises the following steps:

[0141] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 7 was selected;

[0142] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0143] (3) Electroplating copper film: Place the sample in step (2) in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0144] (4) Porous film polymer coating: 0.5 μm of soluble and adhesive polyimide was coated on both sides of a 2 μm thick ultra-high molecular weight polyethylene porous membrane to obtain an ultra-high molecular weight polyethylene-polyimide composite film;

[0145] (5) superimposing the surface of the copper film obtained in step (3), the surface of the film of the sample obtained in step (4), and the surface of the copper film obtained in step (3), and bonding them by thermal lamination at 320° C. and 100 kgf;

[0146] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0147] Example 7

[0148] A method for preparing a composite current collector comprises the following steps:

[0149] (1) Carrier layer: Commercial copper foil with a thickness of 18 μm is used;

[0150] (2) The electrode side of the pickled copper foil was immersed in a CBTA aqueous solution containing 300 ppm of 5CBTA and 150 ppm of 4CBTA, a sulfuric acid concentration of 150 g / L, and a copper concentration of 10 g / L at a liquid temperature of 30°C for 30 seconds to allow the CBTA component to be adsorbed on the electrode side of the foil. The foil formed with the organic release layer was immersed in a nickel solution of 20 g / L made of nickel sulfate at a liquid temperature of 45°C, a pH of 3, and a current density of 5 A / dm 2 Under the conditions of , nickel is attached to the organic peeling layer, thereby forming a nickel layer as an auxiliary metal layer on the organic peeling layer;

[0151] (3) Electroplating copper film: Place the sample surface in step (2) in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0152] (4) Polymer coating: coating the copper film surface of the sample obtained in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 2 μm;

[0153] (5) Laminating the two adhesive polyimide film layers of the samples obtained in step (4) together, and fusing the two adhesive polyimide films together by thermal lamination at 320° C. and 100 kgf;

[0154] (6) Peeling off the upper and lower layers of commercial copper foil of the sample obtained in step (5) to obtain a finished composite current collector.

[0155] Comparative Example 1

[0156] A method for preparing a composite current collector comprises the following steps:

[0157] A polypropylene film with a thickness of 4.5 μm was selected as the carrier layer and placed in the vacuum chamber of the vacuum coating equipment. The vacuum environment was set to 3.0×10 -3Pa, evaporate 99.9% of the copper in the evaporation boat at 1600℃, maintain the concentration of copper vapor at 120mol / L, and sputter a 40nm thick metal copper film on both sides of the polypropylene film. Then, use a water electroplating process to thicken the copper layers on both sides to 1μm by electroplating in a 0.5mol / L copper sulfate solution to obtain a copper composite current collector.

[0158] Comparative Example 2

[0159] A method for preparing a composite current collector comprises the following steps:

[0160] According to the steps in Example 2, a copper film is electroplated on the surface of a 5μm commercial titanium alloy, and the copper film has a thickness of 2μm. Subsequently, the titanium alloy layer on the surface of the copper film is peeled off to obtain a copper film. Then, according to the sandwich structure of copper-soluble and adhesive polyimide-copper, the two layers of copper film and the 3μm thick soluble and adhesive polyimide film are pressed at 320°C and 100Kgf to obtain a composite current collector.

[0161] Comparative Example 3

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

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

[0164] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, rinse it with pure water, and after drying, deposit a 20 nm nickel-copper alloy thin layer on the surface by vacuum plating;

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

[0166] (4) A 1.5 μm thick layer of polyvinylidene fluoride is coated on both sides of a 4 μm thick non-soluble thermoplastic polyimide film as an adhesive, and then the copper film from step (3) is pressurized and laminated with the upper and lower layers of adhesive at a temperature of 120°C.

[0167] (5) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (4) to obtain a finished composite current collector.

[0168] Comparative Example 4

[0169] A method for preparing a composite current collector comprises the following steps:

[0170] (1) Carrier layer: A commercial titanium alloy with a thickness of 5 μm and a surface grain size of grade 6 was selected;

[0171] (2) Surface cleaning: Use anhydrous ethanol to clean the oil stains on the surface of the titanium alloy, and then rinse with pure water;

[0172] (3) Electroplating copper film: Place the sample in step (2) in the electroplating solution for electroplating at a current density of 2A / dm 2 , the electroplating time is 20min;

[0173] (4) Polymer coating: coating the copper film surface of the sample obtained in step (3) with a layer of soluble and adhesive polyimide film with a thickness of 2 μm;

[0174] (5) Laminating the two soluble adhesive polyimide film layers in the samples obtained in step (4) together, and fusing the two soluble adhesive polyimide films together by thermal lamination at 320° C. and 100 kgf;

[0175] (6) Peeling off the upper and lower titanium alloy layers of the sample obtained in step (5) to obtain a finished composite current collector.

[0176] Comparative Example 5

[0177] A method for preparing a composite current collector comprises the following steps:

[0178] Compared with Example 5, this comparative example does not include the steps of smoothing the carrier copper foil and forming the diaphragm thin layer. The rest is the same as Example 5.

[0179] The performance test of this application is carried out in the following manner:

[0180] (1) Thickness test

[0181] Use a precision micrometer or a vertical optical gauge to measure the thickness of a single composite current collector. The detailed steps are carried out in accordance with GB13542.2-2009.

[0182] (2) Tensile strength and elongation at break test

[0183] The tensile test and elongation at break were performed on a dynamic mechanical analyzer (TA Instruments, USA, model: DMA Q800 / TA). The composite current collector was cut into 3×15 mm 2 The rectangular piece was subjected to tensile test with a tensile speed of 0.01-0.05% / min.

[0184] (3) Thermal stability test

[0185] Prepare at least three samples and place them on a thermomechanical analyzer. Heat the samples at a uniform rate within a predetermined temperature range while recording the height change of the sample. Calculate the thermal expansion coefficient of the sample using the following formula:

[0186] ɑ=(ΔH / ΔT) / H

[0187] Where ΔH is the change in specimen height within the temperature interval; ΔT is the temperature interval; and H is the specimen height. For detailed procedures, refer to IPC-TM-650-2.4.41.3.

[0188] (4) Electroplated metal film adhesion test

[0189] Secure the specimen to the tester base with the foil facing upward, maintaining a 90° peel angle. Apply vertical tension at a rate of 5 cm / min, measuring the minimum tension as recorded by the recorder. Repeat this test five times. For detailed procedures, refer to IPC-TM-650-2.4.8.1.

[0190] (5) Electrochemical stability

[0191] The battery testing system is a Wuhan Landian multi-channel battery testing system. Constant current charge-discharge cycle performance tests are performed on lithium-ion battery systems. Cyclic voltammetry tests (test conditions: scan rate of 0.1mV / s) are performed on an electrochemical workstation (VMP-3). The battery test cycle is required to be >400 times.

[0192] (6) Energy density test

[0193] Test object: A lithium-ion battery, consistent with the test object in GB 38031-2020. The positive electrode is lithium iron phosphate, the negative electrode is the composite current collector prepared in the example and the graphite layer on the current collector surface, the separator is a polyolefin microporous separator, and the electrolyte is a liquid electrolyte with lithium hexafluorophosphate as the solute.

[0194] Test steps: Use a battery charge and discharge tester to charge the assembled lithium-ion battery at 25℃±2℃ at a constant current of 0.33C to 4.25V, then charge at a constant voltage until the current drops to 0.02C. After standing for 5 minutes, discharge the battery at a constant current of 0.33C to 2.5V, and record the battery's first discharge capacity Q and first discharge energy E. 放 Repeat the above experimental steps and take 3 discharge energy E 放 The average value of the battery weight is recorded as W, and the energy density is calculated as ED=E 放 / W.

[0195] Table 1

[0196]

[0197] In Table 1, the difference in thermal expansion coefficient is the difference in thermal expansion coefficient between the electroplated metal b film and the bondable polymer base film.

[0198] 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 needle puncture strength. In addition, the bonding strength between the film substrate and the copper layer in the copper composite current collector prepared by this method is poor, which greatly shortens 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, it is very easy to break and wrinkle during the pressing process, resulting in an extremely low product yield. Therefore, relevant data testing was not performed on Comparative Example 2; compared with Comparative Example 3, the selected polyimide film must use an adhesive to ensure the adhesion between the copper foil and the polyimide film, but the thickness of the composite current collector is significantly increased and the battery energy density is reduced. , and the adhesion of the product is difficult to maintain for a long time; if no adhesive is used, the composite current collector cannot be prepared because the polyimide film used in Comparative Example 3 is a thermosetting film and has no adhesiveness; compared with Comparative Example 4, the difference from Example 1 is that the grain size of the commercial titanium alloy surface is different. When the grain size of the titanium alloy surface is lower than the limit of level 7, the surface grains become larger, resulting in an uneven surface, increasing the surface roughness, and increasing the bonding force of the electroplated metal copper with it, resulting in the electroplated metal copper film remaining on the titanium alloy surface 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 the metal copper and the carrier copper foil cannot be peeled off after electroplating.

[0199] As can be seen from the difference in thermal expansion coefficients in Table 1, the difference in thermal expansion coefficients between the electroplated metal b film and the adhesive polymer base film is no more than 30 ppm / °C. Therefore, after the polymer film and the electroplated copper film are laminated together, the two can maintain excellent peel force stability and durability during repeated thermal expansion and contraction during multiple charge and discharge operations of the battery.

[0200] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A composite current collector, characterized in that: The invention comprises a bondable polymer base film and an electroplated metal b film compounded on both sides of the bondable polymer base film.

2. The composite current collector according to claim 1, characterized in that The adhesive polymer base film is selected from adhesive polyimide or its composite film, preferably soluble adhesive polyimide or its composite film; The thickness of the adhesive polymer base film is 1 to 6 μm, preferably 2 to 3 μm.

3. The composite current collector according to claim 1, wherein: The metal b of the electroplated metal b film is at least one of copper, nickel, chromium, zinc, tin, gold, silver, iridium, indium and alloys thereof, preferably copper and alloys thereof; The thickness of the electroplated metal b film is 0.5 to 5 μm, preferably 0.5 to 1.5 μm.

4. The composite current collector according to claim 1, characterized in that The peel strength between the electroplated metal b film and the adhesive polymer base film in the composite current collector is not less than 6N / 25mm; The difference in thermal expansion coefficient between the electroplated metal b film and the bondable polymer base film is not greater than 50 ppm / °C, preferably not greater than 30 ppm / °C.

5. A roll-to-roll method for preparing a composite current collector, characterized in that: The following steps are involved: A) electroplating metal b on the surface of metal foil a to obtain semi-finished product 1; B) coating a bondable polymer film on the surface of the metal b of the semi-finished product 1 to obtain a semi-finished product 2; C) superimposing the two adhesive polymer films of the semi-finished product 2 and laminating them at high temperature to obtain a semi-finished product 3; D) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

6. A roll-to-roll method for preparing a composite current collector, characterized in that: The following steps are involved: a) electroplating metal b on the surface of metal foil a to obtain a semi-finished product 1; b) coating a bondable polymer film on the metal surface b of the semi-finished product 1 to obtain a semi-finished product 2; c) superimposing the metal b of the semi-finished product 1 and the adhesive polymer film of the semi-finished product 2 and pressing them at high temperature to obtain a semi-finished product 3; d) peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

7. A roll-to-roll method for preparing a composite current collector, characterized in that: The following steps are involved: 1) Electroplating metal b on the surface of metal foil a to obtain semi-finished product 1; 2) coating a bondable polymer on the surface of the porous membrane to obtain a bondable polymer composite film; 3) superimposing the metal b of the semi-finished product 1, the bondable polymer composite film, and the metal b of the semi-finished product 1 and performing high-temperature pressing to obtain a semi-finished product 3; 4) Peeling off the upper and lower metal foils a of the semi-finished product 3 to obtain a composite current collector.

8. The preparation method according to claim 5, 6 or 7, characterized in that: The metal foil a is at least one of titanium foil, stainless steel foil, copper foil and alloys thereof; When the metal foil a is titanium foil or stainless steel foil and its alloy, the grain size of the metal foil a is not less than level 7; or, when the metal foil a is copper foil and its alloy, a thin membrane layer is also included between the metal foil a and the electroplated metal b, and the isolation layer is prepared by coating an organic compound and / or electroplating a metal or its alloy.

9. The preparation method according to claim 5, 6 or 7, characterized in that: The electroplating method comprises connecting a metal foil a to a cathode of a power supply, connecting a metal plate b to an anode of a power supply, placing the metal foil a together in an electroplating solution containing cations of the metal b, applying an external electric field, and electroplating a dense and uniform metal b film on the surface of the metal foil a; In step C) or step c), the high-temperature pressing temperature is 120 to 350° C. and the pressure is 20 to 200 kgf; In step 2) or step 3), the drying temperature is 80-230°C.

10. An electrochemical device, characterized in that The composite current collector comprises the composite current collector according to any one of claims 1 to 4.

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