Graphite-based current collector and tab welding method

Abstract

The invention discloses a graphite-based current collector and tab welding method, and belongs to the technical field of current collectors, the graphite-based current collector comprises a conductive supporting layer, the supporting layer is made of a graphite-based thin film material, and the conductive supporting layer is provided with two surfaces in the thickness direction of the conductive supporting layer; a plurality of first holes are formed in a tab welding area of the conductive supporting layer at least corresponding to a welding surface, the first holes do not penetrate through the conductive supporting layer, at least one second hole communicated with the first holes is formed in the conductive supporting layer in the thickness direction, and the outer diameter of the first holes is larger than that of the second holes; the bonding filling layer is filled into the first hole and the second hole and forms a bonding effect with the tab, and the tab and the conductive supporting layer form an excellent thermal and electric conduction interface in the welding area. According to the invention, based on a graphite-based matrix material, an anchoring structure is formed in the tab welding area and the adapter body, so that the connection firmness of the current collector welding area and the adapter body is improved.

Description

Technical Field

[0001] The invention relates to the technical field of current collectors, and in particular to a graphite-based current collector and a pole tab welding method. Background Art

[0002] In secondary batteries, a current collector is needed as the part for current convergence, and its material is generally aluminum foil or copper foil. In the prior art, for safety reasons, a graphite-based current collector is proposed, which includes a polymer support layer and a metal layer arranged on both sides of the support layer.

[0003] For traditional metal foil as current collector, due to the thicker metal layer, it has relatively good welding performance in the tab welding area and the welding difficulty is relatively low; for graphite-based current collector, since the formed metal conductive layer is thinner and the mechanical strength and weldability of the middle polymer layer are quite different from those of the metal, the current common practice is to use ultrasonic transfer welding to weld the transfer body (usually foil) to the metal layer of the current collector, and then weld the transfer body to make the upper and lower metal layers conductive.

[0004] In the lug area, the current density is relatively large, and the thermal effect at the conductive layer causes the local temperature to rise, which can easily cause desoldering or melting of the supporting layer, resulting in battery failure or short circuit. High temperature can also easily cause safety problems. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least some extent. To this end, one object of the present invention is to provide a graphite-based current collector, based on a graphite-based matrix material, to form an anchoring structure between the electrode tab welding area and the transition body, thereby improving the connection reliability between the current collector welding area and the transition body.

[0006] The technical solution of the present invention is as follows:

[0007] A graphite-based current collector, comprising:

[0008] A conductive support layer, wherein the support layer is configured as a graphite-based film material, and the conductive support layer has two surfaces in a thickness direction thereof;

[0009] A plurality of first holes are provided in the tab welding area of ​​the conductive support layer at least corresponding to the welding surface, the first holes do not penetrate the conductive support layer, and at least one second hole connected to the first hole is provided in the conductive support layer along the thickness direction, and the outer diameter of the first hole is larger than that of the second hole;

[0010] It also includes a bonding filling layer, which is filled into the first hole and the second hole and forms a bonding effect with the pole ear. The pole ear forms an excellent thermal and electrical conduction interface with the conductive support layer in the welding area.

[0011] Based on the above technical solution, the bonding surface can be increased while the anchoring effect of the first filling layer and the second filling layer with the corresponding hole wall surface can ensure that the tab and the conductive support layer are in contact with each other.

[0012] Furthermore, two or more second holes may be provided corresponding to the first holes.

[0013] Based on the above technical solution, the anchor points can be further increased and the bonding surface can be increased.

[0014] Furthermore, a thin layer of a partially bonded filling layer is dispersed on the outer edge of the first hole and / or the second hole to form a third filling layer and a fourth filling layer laid on the outer extension of the corresponding hole.

[0015] Based on the above technical solution, the adhesive filling layer is further spread out on the outer edge of the hole to form a filling layer, which can be further anchored on the surface of the conductive support layer.

[0016] The above-mentioned current collector welding method is as follows: a first hole and a second hole connected to the first hole are formed in the welding area of ​​the conductive support layer; an adhesive filling layer is filled in the gap between the transition body and the conductive support layer under hot pressing to form an anchoring filling structure.

[0017] Based on the above technical solution, the tabs can be welded conveniently.

[0018] Furthermore, the welding method satisfies any of the following hot pressing methods:

[0019] The bonding filling layer is arranged on the welding surface, and is hot pressed with the tab once, and then welded after cooling under pressure;

[0020] The bonding filling layer is arranged on the welding surface, and after the first heat pressing, the connecting body is applied to the welding surface for the second heat pressing, and after the pressure is maintained and cooled, it is welded to the connecting body.

[0021] Based on the above technical solution, the bonding filling layer suitable for different materials is filled and thinned, and hot-pressed and welded with the tab; the secondary hot-pressing process can further thin the anchoring layer between the interfaces.

[0022] Furthermore, the thickness of the conductive support layer is 6-50 μm.

[0023] Based on the above technical solution, the conductive support layer is controlled within a suitable range, which can avoid the overall thickness of the film while ensuring the strength.

[0024] Furthermore, the maximum width of the first hole is 5-15 mm, and the depth does not exceed 1 / 2 of the thickness of the conductive support layer.

[0025] Furthermore, the maximum width of the second hole is 0.5-3 mm.

[0026] Based on the above technical solution, the size of the hole is controlled to control the film strength in the electrode tab welding area, which also facilitates subsequent processing.

[0027] Furthermore, the pressure of the hot pressing is controlled within the range of 50-5000N, the action time is controlled within the range of 0.5-5s, and the temperature is controlled above the softening temperature of the bonding filling layer.

[0028] Based on the above technical solution, the material of the bonding filling layer can be fully filled into the gaps at the holes and interfaces, and cooled and crystallized to form a connection and anchoring of the tabs.

[0029] Furthermore, during the hot pressing process, the temperature of the non-welding surface of the conductive support layer is within the temperature range of crystallization of the adhesive filling layer.

[0030] Based on the above technical solution, the material of the adhesive filling layer filled into the second hole can be preferably solidified, so as to seal the filling material and reduce overflow.

[0031] Furthermore, the bonding filling layer material is selected from high molecular polymers and / or metals with a lower melting point than the conductive support layer.

[0032] Based on the above technical solution, a good connection anchoring strength can be formed; at the same time, the selection of metal bonding materials can further improve the electrical conductivity and thermal conductivity at the interface.

[0033] Furthermore, a conductive layer is formed on the surface of the conductive support layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 It is a schematic diagram of the structure of the tab welding area after welding when only the graphite film is used as the current collector;

[0036] Figure 2 for Figure 1 A schematic diagram of a welding method for a central current collector;

[0037] Figure 3 for Figure 1 Schematic diagram of another welding method for the middle current collector;

[0038] Figure 4 It is a schematic diagram of the structure of the pressure roller.

[0039] In the figure:

[0040] 0-welding area;

[0041] 1-conductive support layer; 10-first surface; 20-second surface;

[0042] 2-First hole;

[0043] 3- Second hole;

[0044] 4-bonding filling layer; 41-first filling layer; 42-second filling layer; 43-third filling layer; 44-fourth filling layer;

[0045] 5-Pole ear;

[0046] 6-pressing roller; 61-punch; 62-piercing die; 621-first hole die; 622-second hole die. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0048] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0049] In the prior art, conventional metal foils or composite current collectors have relatively poor thermal conductivity, and the current density at the tabs is relatively large, resulting in high heat generation and relatively poor thermal conductivity, which affects the overall safety of the secondary battery.

[0050] In view of the above problems, in some embodiments of the present application, reference is made to Figure 1 , a graphite-based current collector is proposed, comprising:

[0051] The conductive support layer 1 is configured as a graphite-based (graphite film) material, so it has good thermal and electrical conductivity; the conductive support layer 1 has two surfaces in its thickness direction, namely, corresponding Figure 1 In the first surface 10 and the second surface 20, in some embodiments of the present application, welding is performed on the first surface 10;

[0052] A plurality of first holes 2 are provided in the tab welding area 0 of the conductive support layer 1 at least corresponding to the welding surface, the first holes 2 do not penetrate the conductive support layer (i.e., are blind holes), and at least one second hole 3 connected to the first hole 2 is provided on the conductive support layer 1 along the thickness direction, and the outer diameter of the first hole 2 is larger than the second hole 3; in some embodiments of the present application, the first holes 2 are distributed in the welding area 0 in an array, or they can be distributed in the welding area according to a certain arrangement rule or based on the tolerance value of the setting position; the number of the second holes 3 can also be set to two or more corresponding to the first hole 2, that is, one first hole 2 corresponds to multiple second holes 3;

[0053] It also includes a bonding filling layer 4, which is filled into the first hole 2 and the second hole 3 and forms a bonding effect with the pole tab 5. The pole tab 5 forms an excellent thermal and electrical conduction interface with the conductive support layer 1 in the welding area 0.

[0054] In some embodiments of the present application, the bonding filling layer 4 includes a first filling layer 41 filled in the first hole 2 and a second filling layer 42 filled in the second hole 3. Since the size of the first filling layer 41 is larger than the second filling layer 42, and the first filling layer 41 is directly in contact with the pole ear 5, it has a larger bonding surface. Through the anchoring effect of the first filling layer and the second filling layer and the corresponding hole wall, it can ensure that the pole ear 5 and the conductive support layer 1 are in contact and not prone to delamination. The conductive support layer 1 has good thermal conductivity and can quickly export the heat of the welding area 0.

[0055] Furthermore, in some embodiments of the present application, a thin layer of partially bonded filling layer 4 is dispersed on the outer edge of the first hole 2 and / or the second hole 3 to form a third filling layer 43 and a fourth filling layer 44 laid on the extension of the corresponding holes, thereby further forming an anchoring self-locking effect.

[0056] When welding the above current collector, refer to Figure 2 , the method is as follows:

[0057] S1 forming a first hole 2 and a second hole 3 connected to the first hole 2 in a welding area 0 of a conductive support layer 1;

[0058] S2: placing the bonding filling layer 4 on the welding surface, and forming a bonding filling structure after the first hot pressing;

[0059] S3: Apply the connector 5 to the welding surface for a second hot pressing, and weld the connector 5 after cooling under pressure.

[0060] in,

[0061] The conductive support layer 1 is a graphite film (graphite paper) with a thickness of 6-50 μm.

[0062] In step S1, the first hole 2 and the second hole 3 can be formed by Figure 4The pressing roller 6 is formed in one step, and a plurality of convex molds 61 are arranged in the circumferential direction of the pressing roller 6, and a puncture die head 62 is fixed on the convex mold 61. Specifically, the puncture die head 62 includes a first hole mold 621 for forming the first hole 2 and a second hole mold 622 for forming the second hole 3. At this time, a support structure, such as a support roller, is arranged on the second surface side of the conductive support layer, and a support film (plastic film) of a certain thickness is arranged on the surface of the roller body, so that after the hole mold completely penetrates the conductive support layer, it avoids direct rigid contact with the support structure; of course, it can also be based on laser opening, by controlling the laser power, scanning range or spot size, to cut and form the above-mentioned anchoring hole structure. The maximum width of the first hole 2 is preferably 5-15mm, and the depth does not exceed 1 / 2 of the thickness of the conductive support layer; the maximum width (diameter) of the second hole 3 is 0.5-3mm, and the first hole 2 can be evenly covered in the welding area.

[0063] In step S2, the pressure F1 of the first hot pressing is selected in combination with the material adaptability of the bonding filling layer, such as 50-500N, and the holding pressure / heat holding time is 0.5-5s; at the same time, the first surface 10 has a first processing temperature T1, and the first temperature T1 satisfies that under the applied pressure F1, the bonding filling layer 4 is transferred and filled into the first hole and the second hole, and a small amount remains on the surface layer (pores) of the first surface 10, and when the bonding filling layer 4 material is sufficient, it fills the second hole 3 and is transferred to the second surface 20 to form a corresponding filling layer 41-44; the first temperature T1 can be set at the softening temperature of the bonding filling layer 4 (higher than the glass transition temperature Tg), preferably near the melting temperature (Tm); under the action of pressure and heat, due to the large size of the first hole and when the second hole 3 is a through hole, the bonding filling layer material is easier to enter the hole, and an appropriate excess of the bonding filling layer material can be released on the second surface 20, which has little effect on the thermal and electrical conduction of the welding surface;

[0064] Furthermore, the second surface 20 has a second temperature T2, which is lower than the softening temperature (Tg) of the bonding filling layer 4, which is conducive to cooling and solidifying in the end of the second hole 3 close to the second surface 20 to form a seal, thereby avoiding leakage caused by material melting during processing and resulting in insufficient filling.

[0065] In step S3, the connector 5 is hot-pressed and composited under pressure F2, with only the first surface 10 heated. At this time, a relatively larger welding pressure is applied, such as 100-5000N, and the pressure / heat preservation is 0.5-2s. At this time, the third temperature T3 also satisfies the softening and penetration of the second filling layer 42 and the fourth filling layer 44 generated into the pores on the surface of the tab 5, and an anchoring effect is formed after recrystallization. At this time, no additional temperature (normal temperature) is applied to the second surface 20, or the temperature is controlled to keep the filling layer on the other side in a crystalline state.

[0066] After secondary heating and application of pressure, the filling layers in the second filling layer 42 and the fourth filling layer 44 that have been crystallized and solidified melt again because the surface of the pole ear 5 occupies a position and is close to the surface of the conductive support layer 1. The volume of the filling layer increases after melting and further diffuses under the action of pressure. Therefore, the fourth filling layer 44 has a larger effective surface after cooling; and a protrusion or embossing can be further formed on the pressurized effective surface (the protrusion corresponds to the first hole 2 setting), and the deformed pole ear 5 is squeezed into the first hole 2. After cooling under pressure, a matching structure is formed in the first hole 2, and the coverage area of ​​the fourth filling layer 44 can be further increased.

[0067] The bonding filling layer material can be a high molecular polymer or a metal with a lower melting point than the conductive support layer. After softening / melting, it recrystallizes to form a connection with the connector 5. For example, polymer molecules such as PE, PP, PET, etc. can be selected, which have good bonding force with graphite. The metal can be made of tin foil, aluminum foil, copper foil and other materials. When welding pressure is applied, an isolation layer, such as a smooth metal foil, can be applied to the welding head to avoid contaminating the welding head.

[0068] Figure 2 The method shown in the figure is a method of welding and forming after secondary hot pressing. By adopting the secondary pressurization method, the filling rate in the first hole and the second hole can be larger and fuller, and the thickness of the bonding filling layer on the first surface 10 can be improved or thinned. The fourth filling layer formed by overflow can be more evenly distributed in the pores between the layers at the connection interface, and sufficient contact surface is ensured between the connector 5 and the conductive support layer 1.

[0069] Further references Figure 3 The main difference between the welding methods is that the bonding filling layer 4 is arranged on the welding surface, and is hot pressed once with the connecting body, and then welded after cooling under pressure.

[0070] At this time, a pressure F is applied, and a fourth temperature T4 is applied to the first surface 10, and a fifth temperature T5 is applied to the second surface 20. The pressure is preferably 200-5000N, and the temperature / pressure is maintained for 1-5s to promote the penetration and filling of the bonding filling layer 4.

[0071] The fourth temperature T4 is preferably close to the Tm temperature to promote softening and penetration of the material; the fifth temperature T5 is lower than the Tg temperature and ensures that crystallization and solidification can be achieved within the pressure-maintaining cooling time.

[0072] The one-time welding forming method is particularly suitable for selecting a metal bonding filling layer, which can quickly fill the first hole 2 and the second hole 3 of the first surface 10 after melting, and will not affect the electrical or thermal conductivity due to a relatively larger amount retained on the first surface 10.

[0073] And when a material with a conductivity greater than that of the conductive support layer 1, such as a metal material, is selected, the setting of the filling layers 41-44 improves the current flow capacity at the pole ear to a certain extent, and the generated heat can be discharged through the graphite conductive support layer 1 with high thermal conductivity; at the same time, the first hole 2 at the welding interface has a larger cross-sectional area, so the heat generation can be reduced to a certain extent, and the impact on the composite interface can also be reduced, thereby ensuring the anchoring welding effect.

[0074] In some other embodiments of the present application, in order to increase the conductivity of the conductive support layer 1, a conductive layer can be further formed on its surface; the conductive layer can be formed by plating, such as sputtering, evaporation, chemical plating, etc., or it can be formed by directly coating a conductive paste. Based on the formation method of the conductive layer, its material can be selected from metal materials, such as one or a combination of silver, copper, gold, aluminum, tungsten, nickel, chromium, etc. The relevant plating method belongs to the existing conventional technical means and will not be repeated.

[0075] Of course, the first hole 2 communicating with the second hole 3 may be further provided on the second surface 20, that is, the first hole is provided on both surfaces of the conductive support layer 1. In this case, the anchoring ability and the welding performance may be further increased.

[0076] Preparation Example

[0077] Take a 20μm graphite paper film, open a first hole with a diameter of 5mm (blind hole depth is about 6μm) and a second hole with a diameter of 1mm (through hole) in the welding area of ​​the tab area, and the center interval of the holes is 2cm. Cover the 0.1mm aluminum foil tab, set a 0.1mm tin foil between the graphite paper and the tab, and set aluminum foil on the other surface of the graphite paper for isolation. The welding head performs hot pressing welding at 320℃ and a pressure of 100N. The other side of the graphite paper is not heated. After keeping the temperature and pressure for 3s, it is naturally cooled under pressure.

[0078] Comparative Example 1

[0079] Take a 20μm graphite paper film, cover it with a 0.1mm aluminum foil tab, set a 0.1mm tin foil between the graphite paper and the tab, and perform hot pressing welding at 320℃ with a pressure of 100N. After keeping the temperature and pressure for 3s, cool it naturally while keeping the pressure.

[0080] Comparative Example 2

[0081] The difference from the preparation example is that only the first hole is opened.

[0082] In order to meet the test conditions, the welding area has a relatively large width, which does not represent the actual welding width of the tab; the actual welding width of the tab is selected according to the current carrying capacity.

[0083] For the peel strength (adhesion) test, a layer of Permacel P-94 double-sided tape is bonded to a 1mm thick aluminum foil, and the graphite paper surface in the electrode tab welding area to be tested is bonded to the double-sided tape. A layer of ethylene acrylic acid copolymer film is covered on the electrode tab (aluminum foil 0.1mm) in the electrode tab welding area, and then hot-pressed at 1.3×105N / m2 and 120℃ for 10s, cooled to room temperature, and cut into 150mm×25mm strips. Finally, the ethylene acrylic acid copolymer film of the sample strip is fixed to the upper fixture of the tensile machine, and the rest is fixed to the lower fixture. After fixing, the two are peeled at an angle of 180° and a speed of 100mm / min, and the maximum value is recorded.

[0084] Preparation example 15.3N / 25mm, comparative example 1 is 9.8N / 25mm, comparative example 2 is 11.4N / 25mm.

[0085] It can be seen that the setting of the relevant holes can increase the connection strength between the pole tab and the current collector after welding. At the same time, further setting a second hole and filling the adhesive layer material to form an anchoring structure can further improve the peeling strength of the pole tab connection.

[0086] In addition, in some embodiments of the present application, an energy storage device based on the above-mentioned graphite-based current collector, such as a secondary battery, is also disclosed.

[0087] In the description of the present invention, it is to be understood that the 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., indicating orientations or positional relationships based on the orientations or positional relationships shown in the drawings or conventionally expressed in the prior art, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0088] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0089] The term "multiple" as used in the present application refers to more than two (including two). Similarly, the term "multiple groups" refers to more than two groups (including two groups), and the term "multiple sheets" refers to more than two sheets (including two sheets).

[0090] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A graphite-based current collector, characterized in that: include: A conductive support layer, wherein the support layer is configured as a graphite-based film material, and the conductive support layer has two surfaces in a thickness direction thereof; A plurality of first holes are provided in the tab welding area of ​​the conductive support layer at least corresponding to the welding surface, the first holes do not penetrate the conductive support layer, and at least one second hole connected to the first hole is provided in the conductive support layer along the thickness direction, and the outer diameter of the first hole is larger than that of the second hole; It also includes a bonding filling layer, which is filled into the first hole and the second hole and forms a bonding effect with the pole ear. The pole ear forms an excellent thermal and electrical conduction interface with the conductive support layer in the welding area.

2. The graphite-based current collector according to claim 1, characterized in that The number of the second holes corresponding to the first holes is two or more.

3. The graphite-based current collector according to claim 1, characterized in that: The thin layer of partially bonded filling layer is dispersed on the outer edge of the first hole and / or the second hole to form a filling layer laid on the outer edge of the corresponding hole.

4. The graphite-based current collector according to any one of claims 1 to 3, characterized in that: The method for welding the tab is as follows: forming a first hole and a second hole connected to the first hole in the welding area of ​​the conductive support layer; filling the bonding filling layer in the gap between the transition body and the conductive support layer under hot pressing to form an anchoring filling structure.

5. The graphite-based current collector according to claim 4, characterized in that Meet any of the following hot pressing methods: The bonding filling layer is arranged on the welding surface, and is hot pressed with the tab once, and then welded after cooling under pressure; The bonding filling layer is arranged on the welding surface, and after the first heat pressing, the connecting body is applied to the welding surface for the second heat pressing, and after the pressure is maintained and cooled, it is welded to the connecting body.

6. The graphite-based current collector according to claim 4 or 5, characterized in that: The thickness of the conductive support layer is 6-50 μm; and / or, the maximum width of the first hole is 5-15 mm, and the depth does not exceed 1 / 2 of the thickness of the conductive support layer; And / or, the maximum width of the second hole is 0.5-3 mm.

7. The graphite-based current collector according to claim 4 or 5, characterized in that: The pressure of hot pressing is controlled at 50-5000N, the action time is controlled at 0.5-5s, and the temperature is controlled above the softening temperature of the bonding filling layer.

8. The graphite-based current collector according to claim 4 or 5, characterized in that: The temperature of the non-welding surface of the conductive support layer during the hot pressing process is within the temperature range of the crystallization of the bonding filler layer.

9. The graphite-based current collector according to claim 4 or 5, characterized in that: The bonding filling layer material is selected from high molecular polymer and / or metal with a lower melting point than the conductive support layer.

10. The graphite-based current collector according to claim 4 or 5, characterized in that: A conductive layer is formed on the surface of the conductive support layer.

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