Preparation method and application of pole piece of composite current collector

Abstract

The invention discloses a preparation method and application of a pole piece of a composite current collector. The pole piece comprises a composite polymer film with an adhesive layer on the surface of a polymer layer; holes penetrate through the composite polymer film at equal intervals; performing composite molding on two surfaces of the composite polymer film and aluminum foil, and performing high-temperature curing; etching the aluminum foils on the two sides to a target thickness; after drying, slitting along the edge of the hole to obtain a composite current collector with a welding area on one side edge; one end of the tab is arranged in the groove of the welding area, and the tab-aluminum foil-aluminum foil welding is realized by adopting ultrasonic welding. According to the invention, a polymer layer is canceled at a local fixed point of the composite current collector to obtain a pure metal tab welding site, the pure metal tab can be directly welded with the tab through the pure metal site, and an external aluminum foil switching process is removed; the process of composite current collector transfer welding is reduced, the overall yield of battery cell manufacturing is improved by more than 5%, and the preparation time of the battery cell is shortened to 8 h; moreover, transfer welding positions are reduced, the head space of the battery cell is narrowed, and the energy density is improved by more than 2%.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium batteries, and specifically relates to a method for preparing a composite current collector electrode and its application. Background Art

[0002] With the continuous updating and development of lithium-ion battery technology, the application field of lithium-ion batteries is also expanding. The resulting battery safety issues are receiving more and more public attention. Lithium-ion battery safety accidents characterized by thermal failure after mechanical damage to the battery cell occur frequently, which brings certain resistance to the development of lithium-ion batteries. How to solve the battery safety problem is a difficult problem that the current lithium battery industry has to face. Often, the performance improvement of the four major materials will lead to the loss of the electrical performance and mechanical energy density of the battery cell, and the conventional battery cell safety protection method can only delay thermal failure, but cannot completely solve the safety problems caused by mechanical damage to the battery cell, and there are great limitations in application. The composite current collector (Metal polymer film, MPF) adopts a metal-polymer-metal three-layer sandwich structure, which can greatly reduce the thickness of the metal layer, bring a certain weight reduction, and improve the weight energy density of the battery cell; at the same time, due to the thinning of the metal layer, the metal burrs generated when the battery cell is mechanically damaged by the outside world become less, thereby reducing the risk of short circuit failure between the aluminum metal and the anode inside the battery cell; the main mechanical support layer of the composite current collector is polymer, because the deformation and ductility of polymer are better than metal, it has a wider operating window in processing, so the composite current collector takes into account the multiple advantages of weight reduction, increased energy density, battery cell mechanical safety and processing;

[0003] At present, the processing bottleneck of composite current collectors used in battery cells lies in the electrode ear connection welding process. Due to the presence of the polymer layer in the middle of the composite current collector, the electrode ear and the current collector cannot be effectively eutectic welded. The commonly used welding method is to achieve the connection between the composite current collector and the electrode ear through the transfer metal foil. This solution will increase the battery cell production process and increase the battery cell manufacturing cost. In addition, the transfer metal foil will leave welding marks, which cannot be squeezed and bent during the battery cell processing process, resulting in the loss of part of the battery cell shell space, that is, the internal space of the battery cell is lost and the battery cell energy density is reduced. Summary of the invention

[0004] In view of the above problems, the present application provides a method for preparing a pole piece of a composite current collector and its application, which can reduce the composite current collector transfer welding process, improve the overall quality and efficiency of battery cell manufacturing, reduce the transfer welding position, narrow the battery cell head space, and improve the energy density.

[0005] In a first aspect, the present application provides a method for preparing a composite current collector electrode, comprising the following steps:

[0006] ① Obtaining a composite polymer film with an adhesive layer on the surface of the polymer layer;

[0007] ② Through laser cutting or die cutting, holes of specific sizes are set in the composite polymer film at equal distances along the length direction;

[0008] ③ Directly heat-composite the two surfaces of the composite polymer film with the aluminum foil, and the aluminum foil on both sides is concave inward to form a welding area, and then cured at high temperature;

[0009] ④ Use strong alkaline solution to etch the aluminum foil on both sides to the target thickness, then wash away the residual alkaline solution on the surface with acid and water, and dry for later use;

[0010] ⑤ After drying, cut along the edge of the hole to obtain a composite current collector with one side including the welding area;

[0011] ⑥ Place one end of the pole ear in the groove of the welding area, and use ultrasonic welding to achieve welding between the pole ear-aluminum foil-aluminum foil.

[0012] In some embodiments, the composite polymer film is formed by simultaneously stretching a polymer layer and a thermosetting adhesive solution into a film.

[0013] In some embodiments, a hole is provided at least at 1\3, 1\2 or 2\3 in the width direction of the composite polymer film.

[0014] In some embodiments, the thermal composite forming adopts a heating roller composite tape, the pressure on the composite layer is 5 to 10 KN, the temperature of the heating roller is 80 to 85°C, the tape speed is 30 to 50 m / min, and then it is cooled and rolled up by cold air; it is placed in a heating room for glue aging, the aging temperature is 85 to 100°C, and the aging time is greater than or equal to 72 hours to obtain a composite aluminum foil.

[0015] In some embodiments, the aged composite aluminum foil is passed through a strong alkaline solution with a concentration of 5±1 mol / L by belt conveyor at a speed of 8±1 m / min, and the thickness of the single-sided aluminum foil is controlled at 0.5 um to 5 um. After drying, the composite aluminum foil is rolled up for use.

[0016] In some embodiments, the thickness of the polymer layer is 1.5 to 10 um; the thickness of the adhesive layer is 0.1 to 2 um.

[0017] In some embodiments, the polymer layer is a PET layer or a PP layer.

[0018] In some embodiments, the size of the hole is 18-28 mm in length and 8-16 mm in width.

[0019] In a second aspect, the present application provides an application of a pole piece in a negative electrode, wherein the pole piece is the pole piece of the composite current collector in the above-mentioned embodiment.

[0020] In a third aspect, the present application provides a battery comprising the negative electrode sheet in the above embodiment.

[0021] Beneficial effects of the present invention: The present invention optimizes the structure of the composite current collector and its preparation method, obtains a composite polymer film with a glue layer on the surface by synchronously stretching the polymer layer and the thermosetting glue liquid, obtains holes of specific size in the specified area of ​​the composite polymer film by laser cutting and other methods, and then directly heat-compounds the composite polymer film with the holes etched by laser with aluminum foil, and then matures at high temperature, and then etches the aluminum foil to the target thickness by corrosion with sodium hydroxide solution, and then washes the residual alkali liquid on the surface with acid and water, and cuts it after drying to obtain the composite current collector, and finally connects the welding area of ​​the hole with the pole ear by ultrasonic welding. The invention cancels the polymer layer at the local fixed point of the composite current collector to obtain a pure metal pole ear welding site, and can be directly welded with the pole ear through the pure metal site, eliminating the external aluminum foil transfer process; and reduces the composite current collector transfer welding process, the overall quality rate of battery cell manufacturing is increased by more than 5% and the battery cell preparation time is shortened by 8h; and the transfer welding position is reduced, the battery cell head space is narrowed, and the energy density is increased by more than 2%.

[0022] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0024] Figure 1 A preparation flow chart of a method for preparing a composite current collector electrode according to some embodiments of the present application;

[0025] Figure 2 A schematic diagram of the structure of a composite current collector electrode obtained by a method for preparing a composite current collector electrode in some embodiments of the present application;

[0026] Figure 3 A cross-sectional view of a composite current collector electrode piece obtained by a method for preparing a composite current collector electrode piece according to some embodiments of the present application.

[0027] The reference numerals in the specific implementation manner are as follows:

[0028] Polymer layer 1; adhesive layer 2; hole 3; aluminum foil 4; welding area 41; pole ear 5. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0031] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0034] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0035] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0037] Reference Figure 1-3 A method for preparing a composite current collector electrode comprises the following steps:

[0038] ① Obtaining a composite polymer film having a polymer layer 1 and an adhesive layer 2 on its surface;

[0039] ② Through laser cutting or die cutting, holes of specific size are set equidistantly in the length direction of the composite polymer film 3;

[0040] ③ The two surfaces of the composite polymer film are directly thermally composited with the aluminum foil 4, and the aluminum foil 4 on both sides is recessed inward to form a welding area 41, and then cured at high temperature;

[0041] ④ Etch the aluminum foils 4 on both sides to the target thickness by using a sodium hydroxide solution, then wash away the residual alkali solution on the surface with an acid solution and clean water, and dry for later use;

[0042] ⑤ After drying, cutting along the edge of the hole 3 to obtain a composite current collector having a welding area 41 on one side;

[0043] ⑥ Place one end of the pole tab 5 in the groove of the welding area 41, and use ultrasonic welding to achieve welding between the pole tab 5-aluminum foil 4-aluminum foil 4.

[0044] The aluminum foil 4 needs to be surface cleaned before lamination, and the cleaning liquid uses a corrosive salt solution or a solution with both acidity and alkalinity.

[0045] The composite rollers for hot composite molding are polymer rubber rollers and rubber rollers.

[0046] The composite current collector is part of the electrode sheet. The composite current collector is coated with slurry to obtain a negative or positive electrode sheet. The composite current collector is not fully coated with slurry. A welding ear 5 area is reserved in the welding area 41 and is not coated with slurry.

[0047] Copper and aluminum are conventional metal conductive materials. The aluminum foil 4 can be replaced with copper foil according to application requirements.

[0048] According to some embodiments of the present application, the composite polymer film is formed by synchronously stretching the polymer layer 1 and the thermosetting adhesive solution into a film.

[0049] According to some embodiments of the present application, a hole 3 is provided at least at 1\3, 1\2 or 2\3 in the width direction of the composite polymer film.

[0050] The single layer of aluminum foil 4 of the composite current collector is only 0.5um to 5um thick, and the double layer is 1 to 8um, which is about 10um compared to conventional metal foil. The ability to transmit electrons will be weakened. By increasing the number of welding areas 41, that is, the number of tabs 5, the charge and discharge rate of the battery cell can be increased, which is suitable for fast charge and discharge needs.

[0051] According to some embodiments of the present application, the thermal composite forming adopts a heating roller composite tape and a pressure of 5 to 10 kN on the composite layer, so that the composite layer is closely fitted and the aluminum foil is prevented from breaking; the temperature of the heating roller is 80 to 85°C. If the temperature is too high, the fluidity of the glue increases, which is not conducive to fitting; the tape speed is 30 to 50 m / min, and the glue is softened at high temperature and then matured. If the speed is too slow, the fluidity of the glue will deteriorate, which is not conducive to the combination of the polymer and the aluminum foil; if the speed is too fast, the glue is not able to fully fill the gap between the polymer and the aluminum foil, and bubbles are easily formed between the layers; then the glue is cooled and rolled up with cold air; the glue is placed in a heating room for curing, the curing temperature is 85 to 100°C, and the curing time is ≥72h. If the time is short, the curing effect is poor, that is, the glue cross-linking effect is poor, and the polymer and the aluminum foil are easily separated; if the time is too long, the production efficiency will be reduced; high temperature accelerates the curing to avoid high temperature damage to the polymer; and a composite aluminum foil 4 is obtained.

[0052] According to some embodiments of the present application, the aged composite aluminum foil 4 is conveyed through a sodium hydroxide solution with a concentration of 5±1 mol / L at a conveyor speed of 8±1 m / min to ensure the depth of corrosion of the aluminum foil. The concentration of the alkali solution and the conveyor speed must be maintained within a certain range, otherwise the thickness of the aluminum layer will be too thick or too thin. The thickness of the single-sided aluminum foil 4 is controlled at 0.5um to 5um, and is rolled up for use after drying.

[0053] The thickness of the aluminum foil 4 is to ensure the electrical performance and safety performance of the battery cell. If it is too thick, the electrical performance is excellent, but the safety performance drops sharply.

[0054] According to some embodiments of the present application, the thickness of the polymer layer 1 is 1.5-10 um; the thickness of the adhesive layer 2 is 0.1-2 um.

[0055] If the thickness of the bonding layer is too small, poor bonding will occur; if it is too large, the overall current collector will become thicker, affecting the overall energy density of the battery cell; the polymer layer 1 provides mechanical support; if it is too large, the overall current collector will become thicker, affecting the overall energy density of the battery cell; if it is too small, it will lack mechanical properties, resulting in the current collector being unable to be processed into the battery cell.

[0056] According to some embodiments of the present application, the polymer layer 1 is a PET layer or a PP layer.

[0057] According to some embodiments of the present application, the size of the hole 3 is 18-28 mm in length and 8-16 mm in width.

[0058] An application of a pole piece in a negative electrode, the pole piece is the pole piece of the composite current collector in the above embodiment.

[0059] A battery comprises the negative electrode plate in the above embodiment.

[0060] Example

[0061] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0062] A method for preparing a composite current collector electrode comprises the following steps:

[0063] S100: Provide polymer film and punching equipment

[0064] Select PET or PP as the polymer film material, and laser cutting or chip punching as the punching device, depending on the actual situation;

[0065] Among them, the raw material of the polymer film is PET, and the surface is subjected to a synchronous stretching process to increase the adhesive layer. The thickness of the PET layer is 3.4um and the thickness of the adhesive layer is 0.7um. The stretching ratio is increased from 200um to 4.1um, which is nearly 50 times.

[0066] Use laser cutting equipment to make holes of specified size 16*16mm on the polymer film, with a length interval of 1m and a width interval of 80mm. The laser power is 500W and the speed is 3m / min.

[0067] S200: providing aluminum foil, cleaning the surface of aluminum foil, and the porous polymer film prepared in S100

[0068] The thickness of the selected aluminum foil is 5um, and the cleaning agent is a corrosive solution with acidic, alkaline, oxidizing and other properties. The oxidizing corrosive solution (1M / L chromate solution) is coated on the surface of the aluminum foil using a gravure machine, and then dried to corrode the surface of the aluminum foil to achieve the purpose of surface cleaning; then the washed aluminum foil-perforated PET film-washed aluminum foil laminate is composited and passed through a heating roller at a temperature of 85°C and a speed of 30m / min; then it is cooled and rolled up with cold air, placed in a heating room for glue aging at a aging temperature of 85°C and an aging time of 72h, and then taken out for use;

[0069] S300: Provides sodium hydroxide solution and composite aluminum foil after S200 aging

[0070] The concentration of sodium hydroxide solution is 5 mol / L. The S200 aged thickness composite aluminum foil is passed through the sodium hydroxide solution at a speed of 8 m / min. The thickness of one side of the aluminum foil is etched to 1 um. After drying, it is rolled up for use.

[0071] A battery, the assembly mainly includes the following steps:

[0072] S10: Provide some composite current collectors and lithium cobaltate slurry

[0073] The composite current collector is prepared according to the above embodiment;

[0074] Use the battery core electrode coating mechanism to coat the lithium cobaltate slurry on the surface of the composite current collector, where the holes in the polymer layer of the composite current collector are not coated, and the coating weight is 160g / m 2 , drying temperature 120℃, speed 20m / min, after winding, pass through the pressing roller to obtain the cathode electrode sheet of specified thickness for use;

[0075] S20: Provide S10 composite current collector pole piece, battery cell pole ear, ultrasonic welding machine

[0076] The uncoated area of ​​the composite current collector electrode sheet prepared in step S10 is overlapped with the electrode ear, and an ultrasonic welding machine is used for welding, with a welding time of 0.02s, a welding power of 20KW, and a welding area between 4mm×4mm-10mm×10mm, which can be 4mm×4mm, 5mm×8mm, 10mm×10mm, etc.; after welding, a composite current collector cathode electrode sheet with an electrode ear is obtained;

[0077] S30: Provide S20 composite current collector electrode, diaphragm, anode electrode, battery cell packaging bag, electrolyte

[0078] Among them: the thickness of the diaphragm is 7-10um, the main material of the anode is pure graphite, pure silicon, or graphite mixed with silicon, the thickness is 70-110um, the thickness of the battery pack is 70-130um, and the electrolyte concentration is 1-3mol / L lithium hexafluorophosphate organic solvent;

[0079] The composite current collector electrode prepared by S20 is wound with a 7um diaphragm and an 80um pure graphite anode electrode to obtain a bare battery cell, which is then packaged with a 90um diaphragm for heating and air packaging. The packaging temperature is 135°C, and a liquid injection port is reserved for packaging. The size of the liquid injection port must not be wider than the height of the battery cell; the electrolyte is injected into the battery cell with an injection volume of 4g / piece, and then the liquid injection port is heat-packaged at a packaging temperature of 135°C. After packaging, the battery cell is obtained, and the battery cell is pre-charged and discharged. The charging temperature is 80°C, the charging rate is 1C, the discharging rate is 0.5C, the charging cut-off voltage is 4.5V, and the discharging cut-off voltage is 4.2V; after the charging and discharging are completed, the finished battery cell is obtained.

[0080] Experimental data 1: Composite current collector fabrication and energy density comparison

[0081] Experimental groups Battery cell manufacturing quality rate % Cell energy density Conventional composite current collector 68 620 New composite current collector 73 632

[0082] Experimental data 2: Comparison of welding data of new composite current collectors with different hole sizes

[0083] Experimental groups Glue layer thickness Aluminum foil thickness Punch size Tab welding quality rate 1 1um 0.5um 15mm*25mm 85％ 2 1um 1um 15mm*25mm 88％ 3 1um 1.5um 15mm*25mm 95％ 4 1um 3um 15mm*25mm 96％ 5 1.5um 1.5um 15mm*25mm 95％ 6 0.5um 1.5um 15mm*25mm 95％ 7 1um 1.5um 10mm*15mm 76％ 8 1um 1.5um 18mm*28mm 96％

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for preparing a composite current collector electrode, characterized in that: The following steps are involved: ① Obtaining a composite polymer film with an adhesive layer on the surface of the polymer layer; ② Through laser cutting or die cutting, holes of specific sizes are set in the composite polymer film at equal distances along the length direction; ③ Directly heat-composite the two surfaces of the composite polymer film with the aluminum foil, and the aluminum foil on both sides is concave inward to form a welding area, and then cured at high temperature; ④ Use strong alkaline solution to etch the aluminum foil on both sides to the target thickness, then clean the surface to remove the residual alkali solution, and dry for later use; ⑤ After drying, cut along the edge of the hole to obtain a composite current collector with one side including the welding area; ⑥ Place one end of the pole ear in the groove of the welding area, and use ultrasonic welding to achieve welding between the pole ear-aluminum foil-aluminum foil.

2. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The composite polymer film is formed by synchronously stretching the polymer layer and the thermosetting adhesive solution.

3. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The composite polymer film is provided with holes at at least 1\3, 1\2 or 2\3 locations in the width direction.

4. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The thermal composite forming adopts a heating roller composite belt, the pressure on the composite layer is 5-10KN, the temperature of the heating roller is 80-85°C, the belt speed is 30-50m / min, and then it is cooled and rolled up by cold air; it is placed in a heating room for glue curing, the curing temperature is 85-100°C, and the curing time is ≥72h to obtain a composite aluminum foil.

5. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The cured composite aluminum foil is passed through a strong alkaline solution with a concentration of 5±1 mol / L by belt conveyor at a speed of 8±1 m / min. The thickness of the single-sided aluminum foil is controlled at 0.5 um to 5 um. After drying, it is rolled up for use.

6. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The thickness of the polymer layer is 1.5-10 um; the thickness of the adhesive layer is 0.1-2 um.

7. A method for preparing a composite current collector electrode according to claim 1, 2 or 6, characterized in that: The polymer layer is a PET layer or a PP layer.

8. The method for preparing a composite current collector electrode according to claim 1, characterized in that: The size of the hole is 18-28 mm in length and 8-16 mm in width.

9. Use of an electrode in a negative electrode, the electrode being the electrode of the composite current collector according to any one of claims 1 to 8.

10. A battery comprising the negative electrode sheet according to claim 9.

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