A composite current collector, its preparation method, electrode and battery

Abstract

This invention discloses a composite current collector, its preparation method, an electrode, and a battery. The current collector includes an insulating interlayer, a first polymer film and a second polymer film adhered to opposite sides of the insulating interlayer, a first metal layer deposited on the surface of the first polymer film, and a second metal layer deposited on the surface of the second polymer film. Both the first and second polymer films are conductive. At least one arched cavity is provided between the first and / or second polymer films and the insulating interlayer, and the polymer film at the location of the arched cavity is cut into thin strips. This structural design can improve the loading and adhesion of the active material.

Description

Technical Field

[0001] This invention belongs to the field of current collector technology, specifically relating to a composite current collector, its preparation method, electrode sheet, and battery. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries are widely used in various electronic fields and the electric vehicle industry due to their excellent characteristics such as environmental friendliness, high energy density, and long cycle life.

[0004] Current collectors are a crucial component in lithium-ion batteries, collecting the current generated by the active materials to produce a larger output current. The preparation of the positive and negative electrodes involves mixing active materials, binders, and conductive agents to form a slurry. This slurry is then coated onto the current collector to create a dried electrode granule coating, followed by compaction, densification, and cutting or slitting. Lithium-ion battery current collectors are typically made of copper / aluminum foil. The smooth surface of copper / aluminum foil makes it easy for the coated active material to detach, and the electrodes are prone to breakage during rolling. To increase foil flexibility, current commercially available current collectors use PP or PE as a base and employ evaporation coating. While this increases flexibility, the adhesion between the active material slurry and the current collector remains relatively low. To further improve the adhesion of active materials to the surface of the current collector and reduce the shedding of active materials, some technologies have been developed to make the surface of the current collector uneven to increase the surface roughness. However, this method has limited effect on improving the adhesion of active materials to the surface of the current collector, and by only increasing the surface roughness, the increase in the loading of active materials is limited. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite current collector, its preparation method, electrode, and battery.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a composite current collector, comprising an insulating interlayer, a first polymer film and a second polymer film adhered to opposite sides of the insulating interlayer, a first metal layer deposited on the surface of the first polymer film, and a second metal layer deposited on the surface of the second polymer film; both the first polymer film and the second polymer film are conductive.

[0008] At least one arched cavity is left between the first polymer film and / or the second polymer film and the insulating intermediate layer, and the polymer film at the location of the arched cavity is cut into a thin strip structure.

[0009] At least one arched cavity is left between the first and / or second polymer films and the insulating interlayer. The polymer films at the arched cavity locations are cut into thin strips. During the coating process of the active material slurry, the thin strips of polymer films are compressed and deformed, allowing some of the active material slurry to enter the arched cavity, while the remaining active material slurry is coated on the outer surface of the polymer films. This structural design can improve the loading capacity and adhesion of the active material in the following ways:

[0010] The arched cavity has a relatively large capacity, which can effectively increase the loading of active material. After the active material is coated, the thin strip-shaped polymer film is reset. The gaps between the thin strip structures are small. At this time, the arched cavity forms a receiving cavity, which can play a good role in supporting the active material and can effectively prevent the active material from falling off.

[0011] When the active material slurry is coated, the slurry inside the arched cavity and the slurry outside the arched cavity are continuous. After the active material slurry dries, the dried active material layers inside and outside the arched cavity are continuous. That is, the active material inside the arched cavity can exert a certain pulling force on the active material outside, which further improves the adhesion of the active material on the surface of the polymer film.

[0012] The presence of the fine strip structure also increases the surface roughness of the polymer film, which in turn helps to improve the adhesion of the polymer surface to the active substance.

[0013] The substrate of the current collector is made of polymer film, which can effectively improve the flexibility of the current collector and thus effectively prevent the current collector from being crushed during the rolling process.

[0014] In some embodiments, the height of the arched cavity is 0.1-3 mm.

[0015] Preferably, the arched cavity accounts for 10-80% of the total area of ​​the polymer film.

[0016] More preferably, the arched cavity accounts for 30-60% of the total area of ​​the polymer film.

[0017] In some embodiments, the width of the strip structure is 1-4 mm.

[0018] Preferably, the spacing between two adjacent thin strip structures is 0.1-3 mm.

[0019] More preferably, the spacing between two adjacent thin strip structures is 0.5-2 mm.

[0020] Preferably, the thin strip structure is arranged along the axial direction of the arched cavity.

[0021] In some embodiments, the thin strip structures on the first polymer film and the second polymer film are symmetrically arranged.

[0022] In some embodiments, the material of the insulating interlayer is selected from at least one of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyphenylene ether (PPO), polypropylene carbonate (PPC), polyethylene oxide (PEO), and their derivatives.

[0023] In some embodiments, the conductive polymers in the first and second polymer films are selected from at least one of polyethylene glycol, polycarbonate, cyclic polyolefins, polyphenylene sulfide, polyvinyl acetate, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), vinylon, polyether nitrile, polyphenylene ether, polyester, polysulfone, and their derivatives.

[0024] Preferably, the non-conductive polymers in the first and second polymer films are selected from polyethylene terephthalate, polypropylene, polyethylene, polyvinyl chloride, or polyimide.

[0025] Preferably, the thickness of the first polymer film and the second polymer film is 1-10 μm.

[0026] Preferably, the thickness of the insulating intermediate layer is 1-3 μm.

[0027] In some embodiments, the first metal layer and the second metal layer are made of at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn or alloys thereof.

[0028] Preferably, the thickness of the first metal layer and the second metal layer is 0.5-1.5 μm.

[0029] Secondly, the present invention provides a method for preparing a composite current collector, comprising the following steps: laying a first polymer film and a second polymer film on both sides of an insulating intermediate layer; before hot pressing, fixing the edges of the polymer film; blowing an inert gas between the polymer film and the insulating intermediate layer to make the first polymer film and the second polymer film bulge outward relative to the insulating intermediate layer; and then performing strip hot pressing composite to form an arched cavity between the polymer film and the insulating intermediate layer.

[0030] A first metal layer and a second metal layer are respectively deposited on the surfaces of the first polymer film and the second polymer film;

[0031] The polymer film at the arched cavity is cut to form a thin strip structure. Inert gas (such as nitrogen or argon) is blown between the polymer film and the insulating intermediate layer to ensure the safety of the hot-pressing composite process.

[0032] In some embodiments, the cutting method is a laser cutting method or a wave cutting method.

[0033] In some embodiments, the first metal layer and the second metal layer are prepared by sputtering, vacuum deposition, ion plating or laser pulse deposition.

[0034] In some embodiments, the first polymer film and / or the second polymer film are prepared by co-spinning of conductive polymers and non-conductive polymers using electrospinning technology.

[0035] Preferably, in the first polymer film and / or the second polymer film, the mass ratio of conductive polymer to non-conductive polymer is 1:1.5-3, and more preferably 1:2.

[0036] Thirdly, the present invention provides an electrode sheet comprising a current collector and an active material layer loaded on the surface of the current collector, wherein the current collector is the composite current collector.

[0037] In some embodiments, when the electrode is a positive electrode, the active material is lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0038] Alternatively, when the electrode is a negative electrode, the active material is graphite, silicon carbide, or lithium titanate.

[0039] Fourthly, the present invention provides a battery in which the positive electrode and / or negative electrode are prepared from the current collector.

[0040] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0041] The composite current collector and electrode sheet provided in this invention include a polymer substrate layer and a metal conductive layer disposed on the polymer substrate layer. At least one arched cavity is left between the first and / or second polymer films of the composite current collector and the insulating intermediate layer. The polymer films at the arched cavity locations are cut into thin strip structures. This composite current collector has suitable flexibility, ensuring high mechanical properties and preventing deformation during the production and processing of lithium-ion batteries, thus avoiding breakage. Simultaneously, the adhesion of the active material to the composite current collector is enhanced, reducing the loss of active material and ensuring good conductivity and current collection performance.

[0042] The present invention has an arched cavity between the polymer film and the insulating intermediate layer. The arched cavity can accommodate more active material, and the bonding strength between the active material in the arched cavity and the active material on the surface of the composite current collector is increased, which can prevent the active material from falling off and thus avoid the loss of active material.

[0043] In this invention, the presence of the arched cavity with its fine strip structure increases the roughness of the composite current collector, thereby increasing the adhesion of the active material to the composite current collector and slowing down the shedding of the active material. The fine strip structure has good flexibility and can provide good elastic support during rolling, thus acting as a buffer and reducing electrode breakage.

[0044] The thin film substrate of the composite current collector in this invention adopts a typical insulating ion conductor intermediate layer, which is beneficial to the rapid transport of ions. Attached Figure Description

[0045] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0046] Figure 1 This is a top view of a composite current collector according to an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram of the cross-sectional structure of a composite current collector according to an embodiment of the present invention.

[0048] Figure 3 This is a schematic cross-sectional view of a composite current collector coated with an active material according to an embodiment of the present invention.

[0049] In the figure, 1-insulating intermediate layer; 11-first polymer film; 12-second polymer film; 111-first metal layer; 121-second metal layer; 211-first active material layer; 212-second active material layer. Detailed Implementation

[0050] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0051] The technical solution of the present invention will be further described below through specific embodiments.

[0052] Example 1

[0053] like Figure 1 and Figure 2A composite current collector includes an insulating interlayer, a first polymer film and a second polymer film adhered to opposite sides of the insulating interlayer, a first metal layer deposited on the surface of the first polymer film, and a second metal layer deposited on the surface of the second polymer film; both the first polymer film and the second polymer film are conductive.

[0054] An arched cavity is left between the first and second polymer films and the insulating intermediate layer. The polymer film at the location of the arched cavity is cut into a thin strip structure.

[0055] The height of the arched cavity is 1 mm.

[0056] The area of ​​the arched cavity polymer film accounts for 50% of the total area of ​​the polymer film.

[0057] The width of the thin strip structure is 2mm.

[0058] The spacing between two adjacent thin strip structures is 0.5 mm. The thin strip structures are arranged along the axial direction of the arched cavity.

[0059] The first and second metal layers are made of copper and have a thickness of 1 μm.

[0060] The preparation method of this composite current collector includes the following steps:

[0061] 1) A polymer film with a thickness of 4 μm was obtained by existing electrospinning technology. In the polymer film, the conductive polymer is polyphenylene sulfide and the non-conductive polymer is polypropylene. The mass percentage of the conductive polymer is 33 wt%.

[0062] 2) The polymer film is hot-pressed onto the insulating interlayer, which is made of polyvinylidene fluoride and has a thickness of 2μm.

[0063] A first and second polymer film were laid on both sides of an insulating interlayer. Before hot pressing, the edges of the polymer films were fixed, and nitrogen gas was blown between the first and second polymer films and the insulating interlayer, causing both polymer films to bulge outward relative to the insulating interlayer. Then, strip-shaped hot pressing was performed to form an arched shape (the distance from the arched film to the insulating interlayer was 1 mm, and the area ratio was 50%). The polymer film on the other side of the insulating interlayer was then subjected to the same equidistant extrusion to form an arched shape. Finally, it was placed in an oven and baked at 80℃ for 12 hours to obtain the composite film.

[0064] 4) A metal layer is deposited on the above composite film by means of evaporation metal deposition technology, and finally a current collector is formed (this metal layer is copper metal with a thickness of 1μm).

[0065] 5) The composite current collector formed in step 4) is cut into thin strips of equal spacing in an arch shape using laser cutting technology, targeting the arched position;

[0066] 6) An active material slurry is coated onto the above-mentioned composite current collector to form an electrode sheet. The active material slurry is composed of graphite (96%), conductive carbon black (0.5%), SBR (1.5%), polyacrylic acid PAA (1.3%), and carboxymethyl cellulose CMC (0.7%), where % is by mass percentage; the coating density of the active material slurry on the surface of the current collector is 90 g / m². 2 .

[0067] Example 2

[0068] It is basically the same as Example 1, except that the spacing between the thin strips is 0.1 mm.

[0069] Example 3

[0070] It is basically the same as Example 1, except that the spacing between the thin strips is 3mm.

[0071] Example 4

[0072] It is basically the same as Example 1, except that the distance from the polymer film in the arched cavity to the insulating intermediate layer is 0.1 mm.

[0073] Example 5

[0074] It is basically the same as Example 1, except that the distance from the polymer film in the arched cavity to the insulating intermediate layer is 3 mm.

[0075] Example 6

[0076] It is basically the same as Example 1, except that the area of ​​the polymer film in the arched cavity accounts for 10% of the total area of ​​the current collector.

[0077] Example 7

[0078] It is basically the same as Example 1, except that the area of ​​the polymer film in the arched cavity accounts for 80% of the total area of ​​the current collector.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that nitrogen is not used, i.e. there is no arched cavity; otherwise, they are the same as Example 1.

[0081] Comparative Example 2

[0082] The composite current collector is made of ordinary copper foil with a thickness of 6 μm. The composition and coating amount of the active material slurry are the same as in Example 1.

[0083] The electrode sheets prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to corresponding performance tests, and the test data are shown in Table 1.

[0084] Electrode tensile strength: The current collectors prepared in Examples 1-7 and Comparative Examples 1-2 were made into composite current collectors of 150×20mm; then the narrower ends were placed at both ends of a tensile testing machine and fixed; the tensile testing machine was started to stretch the composite current collector. The data recorded when it broke was the tensile strength.

[0085] Electrode adhesion test:

[0086] 1. Cut the current collector into strips measuring 2cm × 10cm;

[0087] 2. Apply double-sided tape to a steel plate with a length of 125±1mm, a width of 50±1mm, and a thickness of 1.5-2mm. Attach the current collector from the composite sample prepared in step 1 onto the double-sided tape. Use a utility knife and ruler to cut the test sample into pieces 80mm long and 15mm wide.

[0088] 3. Turn on the INSTRON 3365 electronic universal testing machine and select the 180° peel test item to prepare for the test: Fold the free end of the sample 180° and peel off the adhesive surface from the test plate by about 25mm. Clamp the free end of the sample and the test plate on the upper and lower clamps respectively, and make sure that the sensor is not under any force. When clamping, the peel surface should be aligned with the force line of the tensile testing machine.

[0089] 4. Press the test button on the control panel to start the test. After the test stroke is completed, the upper clamp of the tensile testing machine will return to its original position. When the upper clamp has returned to its original position, remove the test plate from the lower clamp. Take at least three data points for each test, and use the average value to represent the adhesion force of the sample.

[0090] Table 1

[0091]

[0092] Table 1 shows that Example 1 exhibits improved electrode tensile strength and electrode adhesion compared to Comparative Examples 1 and 2, indicating that the presence of arched strips enhances the flexibility of the composite current collector and mitigates active material detachment. However, Examples 2 and 3 show lower performance data compared to Example 1. This is because the spacing between the strips is either too dense or too sparse, resulting in ineffective performance. When the spacing is too dense, the slurry cannot easily penetrate the arch, adhering to the surface and causing the active material to detach. When the spacing is too sparse, the slurry is unobstructed inside and outside the arch, similar to coating on a foil, thus also causing active material detachment. Examples 4 and 5 are comparable to Examples 3 and 4, but their performance is slightly lower than Example 1. Compared to Example 1, Examples 6 and 7 show that too few arched strips result in insufficient flexibility and adhesion to the active material in the composite current collector. While too many arched strips increase flexibility, the slurry coating is loose, leading to decreased adhesion.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite current collector, characterized in that: It includes an insulating interlayer, a first polymer film and a second polymer film adhered to opposite sides of the insulating interlayer, a first metal layer deposited on the surface of the first polymer film, and a second metal layer deposited on the surface of the second polymer film; both the first polymer film and the second polymer film are conductive. At least one arched cavity is left between the first polymer film and / or the second polymer film and the insulating intermediate layer. The height of the arched cavity is 0.7-1 mm. The polymer film at the location of the arched cavity is cut into thin strip structures, and the spacing between two adjacent thin strip structures is 0.1-3 mm.

2. The composite current collector according to claim 1, characterized in that: The arched cavity accounts for 10-80% of the total area of ​​the polymer film.

3. The composite current collector according to claim 1, characterized in that: The width of the thin strip structure is 1-4 mm.

4. The composite current collector according to claim 3, characterized in that: The thin strip-shaped structure is arranged along the axial direction of the arched cavity.

5. The composite current collector according to claim 1, characterized in that: The thin strip-like structures on the first and second polymer films are symmetrically arranged.

6. The composite current collector according to claim 1, characterized in that: The material of the insulating intermediate layer is selected from at least one of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyphenylene ether, polypropylene carbonate, polyethylene oxide and its derivatives.

7. The composite current collector according to claim 1, characterized in that: The conductive polymers in the first and second polymer films are selected from at least one of polyethylene glycol, polycarbonate, cyclic polyolefin, polyvinyl acetate, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), vinylon, polyether nitrile, polyphenylene ether, polysulfone and their derivatives.

8. The composite current collector according to claim 7, characterized in that: The non-conductive polymers in the first and second polymer films are selected from polyethylene terephthalate, polypropylene, polyethylene, polyvinyl chloride, or polyimide.

9. The composite current collector according to claim 1, characterized in that: The thicknesses of the first and second polymer films are 1-10 μm.

10. The composite current collector according to claim 1, characterized in that: The thickness of the insulating intermediate layer is 1-3 μm.

11. The method for preparing the composite current collector according to any one of claims 1-10, characterized in that: The process includes the following steps: laying the first polymer film and the second polymer film flat on both sides of the insulating intermediate layer; before hot pressing, fixing the edges of the polymer film; blowing inert gas between the polymer film and the insulating intermediate layer to make the first polymer film and the second polymer film bulge outward relative to the insulating intermediate layer; and then performing strip hot pressing composite to form an arched cavity between the polymer film and the insulating intermediate layer. A first metal layer and a second metal layer are respectively deposited on the surfaces of the first polymer film and the second polymer film; The polymer film at the arched cavity is cut to form a thin strip structure.

12. The method for preparing the composite current collector according to claim 11, characterized in that: The cutting method is either laser cutting or wave cutting. The first polymer film and / or the second polymer film are prepared by electrospinning conductive polymers and non-conductive polymers together.

13. The method for preparing the composite current collector according to claim 12, characterized in that: In the first polymer film and / or the second polymer film, the mass ratio of conductive polymer to non-conductive polymer is 1:1.5-3.

14. The method for preparing the composite current collector according to claim 13, characterized in that: In the first polymer film and / or the second polymer film, the mass ratio of conductive polymer to non-conductive polymer is 1:

2.

15. An electrode sheet, characterized in that: It includes a current collector and an active material layer loaded on the surface of the current collector, wherein the current collector is the composite current collector as described in any one of claims 1-10; When the electrode is a positive electrode, the active material is lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. Alternatively, when the electrode is a negative electrode, the active material is graphite, silicon carbide, or lithium titanate.

16. A battery, characterized in that: Its positive and / or negative electrode sheets are prepared from the current collectors described in any one of claims 1-10.

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