Conductive connection structure, preparation method thereof and battery cell

Abstract

The invention provides a conductive connection structure, a preparation method thereof and a battery cell, and relates to the technical field of batteries. The conductive connection structure is characterized by comprising a current collector, a conductive adhesive, gradient foam metal, a conductive adhesive and a tab which are sequentially abutted against one another, the gradient foam metal is provided with two or three metal layers with different porosity, and the porosity of the metal layers ranges from 30% to 99%. The gradient foam metal layer or the conductive connection structure adopted in the battery cell can absorb vibration energy, and the elastic modulus of the gradient foam metal layer or the conductive connection structure can provide a buffer effect, so that the connection reliability and shock resistance are greatly improved; furthermore, the foam metal in the connecting structure combining the gradient foam metal layer and the conductive adhesive can provide more low-resistance paths, and the conductive adhesive can further reduce the interface resistance, so that the conductivity is optimized, the internal resistance of the battery cell is reduced, and the performance of the battery cell is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a conductive connection structure, its preparation method, and a battery cell. Background Technology

[0002] In the electrical connection between battery cells and external tabs / posts, various welding methods are commonly used, including resistance welding, ultrasonic welding, and laser welding. Resistance welding utilizes the resistance heat generated by current passing through the workpiece to locally melt the contact surface, forming a weld point or weld seam under pressure. It is simple to operate and low in cost, but it has safety hazards, low weld strength, and high equipment and maintenance costs. Ultrasonic welding uses the high-frequency vibration energy of ultrasound to cause metal surfaces to rub against each other to form a weld. It is fast, energy-saving, and environmentally friendly, but it produces metal dust and is prone to poor welds and cracking of weld joints. Laser welding uses a high-energy-density laser beam to irradiate the material, causing it to melt and solidify rapidly to form a weld seam. Laser welding has high precision and speed, but it has low energy conversion efficiency, high cost, and risks of slag spatter and burn-through.

[0003] Besides the connection methods mentioned above, there are also non-welding methods, such as conductive adhesive bonding. Conductive adhesive bonding has advantages such as simple operation, no special equipment required, and low cost. In addition, conductive adhesive bonding can provide good conductivity and mechanical strength. However, ordinary epoxy resin conductive adhesive / conductive blocks have poor conductivity, and the resistance at the connection is higher than that of welding. It is suitable for battery cells with low conductivity requirements. Moreover, conductive adhesive is expensive. If improperly handled, conductive adhesive may fall into the battery cell and become free conductive particles after electrolyte injection. These particles can easily react and deposit on the surface of the separator, leading to excessive self-discharge of the battery cell or causing a short circuit risk.

[0004] In existing connection methods, welding can cause high temperatures that damage the battery cell material and is prone to producing incomplete welds. Welding is also prone to producing slag. In addition, ordinary conductive adhesive connection methods have poor conductivity and the adhesive block can easily cause safety hazards such as self-discharge or short circuit of the battery cell. Summary of the Invention

[0005] In the electrical connection technology between battery cells and external tabs / posts, in order to reduce thermal damage and ensure process safety, a non-welding method is adopted to improve connection reliability and shock resistance, optimize conductivity and reduce internal resistance, reduce costs and simplify process complexity. This patent provides a conductive connection structure, its preparation method and battery cell.

[0006] Firstly, this application provides a conductive connection structure:

[0007] A conductive connection structure includes a current collector, a conductive adhesive, a gradient foam metal, a conductive adhesive, and a tab that are sequentially connected; the gradient foam metal has two or three metal layers with different porosities, the porosity of the metal layers ranging from 30% to 99%.

[0008] Furthermore, the gradient foam metal includes shapes such as cuboids, cubes, and rings.

[0009] Furthermore, the gradient foam metal is a gradient foam metal with a surface porosity of 30-40%, a middle layer porosity of 40-60%, and a bottom layer porosity of 80-99%.

[0010] Furthermore, the gradient foam metal is an aluminum-based gradient foam metal ring with a surface porosity of 40% and a bottom porosity of 85%.

[0011] Furthermore, the surface layer is 0.2-0.5mm thick. A thinner layer can reduce material usage and lower costs while ensuring good conductivity and adhesion. The middle layer is 0.5-1.0mm thick. An appropriate thickness can provide good mechanical properties and energy absorption capacity while also ensuring a certain level of conductivity. The bottom layer is 1.0-1.5mm thick. The bottom layer mainly provides support and has high porosity. A thicker bottom layer can increase the stability of the structure and energy absorption capacity, while high porosity helps with air permeability and weight reduction.

[0012] Secondly, this application provides a method for preparing a conductive connection structure:

[0013] A method for preparing a conductive connection structure, wherein the method for preparing the gradient foam metal includes the following preparation steps:

[0014] S1 metal powder particle size selection: surface powder particle size 10-50μm, middle powder particle size 50-100μm, bottom powder particle size 100-300μm;

[0015] S2 Gradient Structure Formation: After mixing metal powder of different layers with foaming agent, copper powder is filled in sections and pressed, and then kept at 950-1400℃ in an inert gas atmosphere for 0.5-2 hours to form a gradient foam metal preform with a surface porosity of 30-40%, a middle layer porosity of 40-60%, and a bottom layer porosity of 80-99%.

[0016] S3 post-treatment: Impregnation with silicone oil to improve elasticity or annealing to reduce internal stress, resulting in gradient foam metal.

[0017] Furthermore, the metal powder includes aluminum, nickel, and copper, and the foaming agent includes ammonium chloride and carbonates.

[0018] Furthermore, the impregnation time with silicone oil is 10-30 minutes; the annealing temperature is 500-600℃ and the time is 20-30 minutes.

[0019] The specific steps for gradient foam metal molding are as follows:

[0020] S1 selects metal material powder as raw material, requiring the powder to have a certain purity, and the powder particle size (10-300μm) is segmented to meet the needs of different levels.

[0021] S2 performs gradient pressing, setting the corresponding porosity (30-99%) and pressing pressure according to different layers to form a gradient structure.

[0022] After adding a foaming agent, S3 is sintered under specific atmosphere and temperature conditions to form a connected pore structure.

[0023] S4 then undergoes post-processing, including impregnation with silicone oil to improve elasticity and annealing to reduce internal stress, thereby improving product performance.

[0024] As a preferred technical solution of the present invention, the metal material powder may be, but is not limited to, aluminum, nickel and copper, wherein the particle size of the powder used in the surface layer is controlled between 10-50 μm, the particle size of the powder in the middle layer is 50-100 μm, and the particle size of the powder in the bottom layer is 100-300 μm.

[0025] As a preferred embodiment of the present invention, in the S2 gradient pressing, the surface porosity is 30-40% and the pressing pressure is 300-500MPa; the intermediate layer porosity is 40-60% and the pressing pressure is 200-300MPa; and the bottom layer porosity is 80-99% and the pressing pressure is 150MPa.

[0026] As a preferred technical solution of the present invention, the foaming agent mentioned in S3 is generally ammonium chloride (NH4Cl), carbonates (such as calcium carbonate, magnesium carbonate, sodium bicarbonate) and polyurethane foam skeleton.

[0027] As a preferred embodiment of the present invention, the time for impregnating silicone oil in S4 is 10-30 minutes, the annealing temperature is set to 500-600°C, and the time at the set temperature is maintained for 20-30 minutes.

[0028] The specific steps for applying and curing conductive adhesive are as follows:

[0029] S1 uses screen printing, dispensing, or spraying of conductive adhesive onto foam metal or current collectors, with the adhesive layer thickness controlled between 0.1-5μm.

[0030] S2 is then cured under specific temperature and pressure conditions.

[0031] As a preferred embodiment of the present invention, the adhesive matrix in S1 is an epoxy resin adhesive with a viscosity of 6000-20000 mPa·s, which can cure quickly and has good flexibility, adhesion, electrolyte resistance, and resistance to high and low temperature aging. The conductive powder is preferably carbon nanotubes or copper powder (with a resistivity of 10 Ω·cm). -3 -10 -6 Ω·cm).

[0032] As a preferred embodiment of the present invention, the pressure for adhesive coating and curing in step S2 is 3-9 kg / cm². 2 Curing temperature: 80-150℃; Curing time: 2-5 minutes.

[0033] To address thermal damage and ensure process safety, improve connection reliability and shock resistance, optimize conductivity and reduce internal resistance, lower costs and simplify process complexity, this application proposes a novel connection method combining gradient foam metal with conductive adhesive for application in various battery cell products. It offers the following advantages:

[0034] Better thermal stability: Traditional welding can easily damage heat-sensitive materials inside the battery cell, such as the separator and electrolyte, due to high temperatures (>500℃), leading to performance degradation or safety hazards. This new solution uses low-temperature curing (≤120℃), which can effectively protect heat-sensitive materials such as PE separator and silicon anode, preventing them from being damaged by high temperatures, thereby ensuring the performance and safety of the battery cell.

[0035] Better conductivity: Pure conductive adhesive has high resistivity and exhibits significant temperature rise under high current. The new design features a high-density foam metal surface layer that provides a low-resistance pathway, while the conductive adhesive fills the pores, further reducing interfacial resistance. This optimizes conductivity, lowers the cell's internal resistance, and improves cell performance.

[0036] Enhanced seismic resistance: Traditional welded rigid connections have poor seismic resistance and are prone to breakage due to vibration. Pure conductive adhesives, due to their high rigidity, are prone to cracking and fail after long-term cycling. The new solution's gradient foam metal bottom layer's low-density area can absorb vibration energy, and its elastic modulus provides a buffering effect. At the same time, the conductive adhesive with an elongation at break ≥150% enhances the resistance to deformation, greatly improving the reliability and seismic resistance of the connection.

[0037] Lower costs: Traditional welding equipment is expensive and has high maintenance costs. The new solution reduces material costs by using copper powder instead of silver powder, simplifies equipment by eliminating the need for laser welding machines, and is compatible with winding / stacking production lines, reducing equipment investment and maintenance costs, simplifying production process complexity, and improving production efficiency.

[0038] Thirdly, this application provides a battery cell:

[0039] A battery cell employing the conductive connection structure described in this application.

[0040] Furthermore, the gradient foam metal is a gradient foam metal ring.

[0041] Furthermore, the aluminum-based gradient foam metal ring in the positive electrode adhesive metal layer of the cylindrical cell includes a bottom layer, a middle layer, and a surface layer; the diameter of the bottom layer is larger than the diameter of the hollow core inside the cylindrical cell.

[0042] In the cylindrical battery cell, the area of ​​the adhesive metal layer on the negative electrode is larger than that of the negative electrode current collector, and the outer region of the adhesive metal layer on the negative electrode is in contact with the negative electrode's busbar.

[0043] Beneficial effects: 1. The gradient foam metal layer or conductive connection structure used in this invention can absorb vibration energy, and its elastic modulus can provide a buffering effect, greatly improving the reliability and shock resistance of the connection; furthermore, in the connection structure of the gradient foam metal layer combined with conductive adhesive used in this invention, the foam metal can provide more low-resistance paths, and the conductive adhesive (conductivity not less than 1.8 × 10⁻⁶) -2 (Ω·cm) can further reduce interface resistance, thereby optimizing conductivity, reducing cell internal resistance, and improving cell performance.

[0044] 2. The conductive connection structure used in this invention can reduce production costs and simplify process equipment; the preparation of the conductive connection structure does not require welding, which can solve the heat damage caused by welding and ensure production safety.

[0045] 3. This invention simplifies equipment and is compatible with winding / stacking production lines, reducing equipment investment and maintenance costs, simplifying production process complexity, and improving production efficiency. This invention has universal applicability to cell layers, suitable not only for cylindrical cells but also for different types of pouch cells. This invention optimizes the cell structure, maintaining the flowability of the hollow core to provide high porosity and good air permeability, while also possessing good mechanical properties and conductivity. Attached Figure Description

[0046] Figure 1 This is a top view schematic diagram of the conductive connection structure 4 in the soft-pack battery cell of Example 1;

[0047] Figure 2 This is a front view schematic diagram of the conductive connection structure 4 in the soft-pack battery cell of Example 1;

[0048] Figure 3 This is a schematic diagram of the cylindrical battery cell in Example 2;

[0049] Figure 4 This is a schematic diagram of the structure of the positive electrode adhesive metal layer 7 and the positive electrode current collector 6 on the positive electrode side of the battery cell in Example 2;

[0050] Figure 5 This is a schematic diagram of the structure of the positive electrode adhesive metal layer 7, the positive electrode current collector 6, and the hollow core 13 on the positive electrode side of the battery cell in Example 2;

[0051] Figure 6 This is a schematic diagram of the structure at the bottom of the negative electrode of the battery cell in Example 2.

[0052] Figure label:

[0053] 1. Soft-pack battery cell current collector; 2. Adhesive-coated foam metal; 3. Tab; 4. Conductive connection structure; 5. Core; 6. Positive current collector; 7. Positive electrode adhesive-coated metal layer; 8. Busbar; 9. Top cover; 10. Shell bottom; 11. Negative electrode adhesive-coated metal layer; 12. Negative current collector; 13. Hollow core; 14. Shell. Detailed Implementation

[0054] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Example 1: A soft-pack battery cell using gradient foam metal combined with conductive adhesive:

[0056] Preparation of gradient foam metal: Copper powder was used as the matrix material. The surface layer used copper powder with a particle size of 40 μm, the middle layer used copper powder with a particle size of 80 μm, and the bottom layer used copper powder with a particle size of 250 μm. This mixture was combined with the foaming agent NH4Cl, and then filled and pressed in sections to form a three-layer gradient. Argon gas was then introduced into a tube furnace, and the furnace was held at 950℃ for 1.5 hours, causing the NH4Cl foaming agent to decompose and form gradient pores. The product was then placed in silicone oil for 20 minutes to improve elasticity, followed by annealing in a furnace at 600℃ for 30 minutes to increase internal stress, resulting in a gradient foam metal with a surface layer of 40% porosity, a middle layer of 60% porosity, and a bottom layer of 98% porosity.

[0057] Corresponding to the conductive connection structure in the pouch cell: a gradient foam metal (1*3.5cm) is placed on a conductive adhesive containing copper powder (resistivity 2.4×10⁻⁶). -2 A conductive adhesive containing a carbon tube (resistivity 2.4 × 10⁻⁶ Ω·cm) is applied to a current collector (4*5cm) with a current collector of the same size (1*3.5cm). -2 (Ω·cm), then place the electrode on top, and heat cure under pressure at 80℃ and 0.5Mpa for 5min to obtain the corresponding conductive connection structure.

[0058] Soft-pack battery cells: structure as follows Figure 1 and Figure 2 The main body of the soft-pack battery cell includes a conductive connection structure 4, which includes a soft-pack battery cell current collector 1, a metal foam with adhesive backing 2, and a tab 3.

[0059] The surface layer is 0.2 mm thick, the middle layer is 0.3 mm thick, and the bottom layer is 1.0 mm thick.

[0060] Example 2: Cylindrical battery cell using aluminum-based gradient foam metal rings:

[0061] The aluminum-based gradient foam metal ring consists of a surface layer with 40% porosity, a middle layer with 40% porosity, and a bottom layer with 85% porosity. The thickness of the surface and middle layers is 0.3 mm, and the diameter of the bottom layer is 1.0 mm.

[0062] Preparation of conductive structure: Aluminum powder is used as the matrix material. The top and middle layers are made of 40μm aluminum powder, and the bottom layer is made of 250μm copper powder. After being mixed with foaming agent NH4Cl, aluminum powder is filled in sections and pressed to form two gradient layers. Then, argon gas is introduced into a tube furnace and held at 950℃ for 1.5 hours. The foaming agent NH4Cl decomposes to form gradient pores, thus obtaining aluminum-based gradient foam metal rings.

[0063] Assembly of the conductive connection structure: An aluminum-based gradient foam metal ring (40% porosity on the surface and 85% on the bottom layer) is pre-pressed into the groove on the end face of the shell; the electrode tab is coated with copper-containing conductive adhesive, inserted into the foam metal layer, and then heat-cured at 100°C and 0.3 MPa for 4 minutes to obtain the corresponding conductive connection structure, as shown in the figure. Figure 3 .

[0064] Figure 3 This is a schematic diagram of a cylindrical battery cell, which includes an upper cover 9, a core 5, a positive current collector 6, a positive electrode adhesive metal layer 7, a busbar 8, a bottom shell 10, a negative electrode adhesive metal layer 11, a negative electrode current collector 12, and a casing 14.

[0065] Conductive adhesive is applied to the cylindrical positive current collector 6 and covered with an aluminum-based gradient foam metal ring of the same area to form a positive electrode adhesive metal layer 7; the busbar 8 is placed on the positive electrode adhesive metal layer 7 and connected to the top cover 9; for better effect, the current collector 12 on the negative electrode side of the shell bottom is in contact with the negative electrode adhesive metal layer 11, the busbar 8 is in contact with the negative electrode adhesive metal layer 11, and the shell bottom 10 is located outside the shell bottom busbar 8.

[0066] Figure 4 The structure of the positive electrode adhesive metal layer 7 and the positive electrode current collector 6 on the top of the shell is shown. The area of ​​the positive electrode current collector 6 is larger than the area of ​​the adhesive foam metal layer 7.

[0067] Figure 5 For a detailed schematic diagram, the aluminum-based gradient foam metal ring in the positive electrode adhesive metal layer 7 includes a bottom layer 14, a middle layer 15, and a surface layer 16. The bottom layer 14 is slightly larger than the hollow core 13 inside the core 5, maintaining the flowability of the hollow core 13 to provide high porosity and good air permeability. The middle layer 15 is also located in the middle layer of the cylinder and plays a buffering role. The surface layer 16 provides good mechanical properties and conductivity.

[0068] Figure 6 The diagram shows the structure of the negative electrode of the battery cell. The area of ​​the adhesive metal layer 11 of the negative electrode is larger than that of the negative electrode current collector 12. The outer layer (the outer area of ​​the adhesive metal layer of the negative electrode) wraps the entire cylindrical battery cell and is directly the same size as the busbar, providing good conductivity.

[0069] Comparative Example 1: A pouch cell, differing from Example 1 in that it uses uniform foamed metal copper with a porosity of 75% in volume (same shape) instead of gradient foamed metal.

[0070] Comparative Example 2: A soft-pack battery cell, differing from Example 1 in that it does not use the adhesive-coated metal layer 7, but instead uses a conductive adhesive containing copper powder / epoxy resin (resistivity 2.4 × 10⁻⁶). -2 The electrode (Ω·cm) is applied to the current collector, and then the tab is placed on top. The electrode is then heat-cured at 80°C and 0.5 MPa for 3 minutes to obtain the corresponding conductive connection structure.

[0071] Performance testing:

[0072] The performance tests of the embodiments and comparative examples are shown in Table 1.

[0073] Table 1. Performance List of Example 1, Example 2, Comparative Example 1 and Comparative Example 2

[0074] performance Example 1 (Soft Pack) Example 2 (Cylinder) Comparative Example 1 (Soft Packaging) Comparative Example 2 (Soft Packaging) Traditional welding solutions Interface resistance (mΩ) 0.152 0.164 0.177 0.168 0.147 Peel strength (N) 723 698 655 638 700 Electrolyte corrosion resistance (N) 600, not detached 500, not detached 412, partially detached 400, partially detached 612, not detached Risk of heat damage none none none none high Vibration / bending resistance After 200 bends, the resistance changes by +4%. After 24 hours of vibration, the resistance increased by 5%. After 120 bends, the adhesive layer developed cracks, and the resistance increased by 200%. The adhesive layer broke after 70 bends, and the resistance increased by 400%. After 150 bends, the adhesive layer developed cracks, and the resistance increased by 300%.

[0075] Among them, the resistance to electrolyte corrosion was tested by placing the sample in an aluminum-plastic bag, adding electrolyte to two-thirds of the bag's volume, heat-sealing the bag, and then placing it in a 45°C oven. After one month, the sample was removed and subjected to a tensile test again.

[0076] Thermal damage risk refers to the possibility that a sample may be damaged by high temperatures during the production process. Traditional welding generates high temperatures (>500℃) that can easily damage the materials inside the battery cell, such as scalding the diaphragm. In contrast, non-welding methods require lower temperatures and cause less damage to the battery cell.

[0077] Vibration / bending resistance: After repeatedly bending the soft-pack sample, test its resistance on an AC impedance instrument and observe the changes in the state of the sample joints. For cylindrical products, test their resistance and observe their condition after placing them on a vibration table for 24 hours.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A conductive connection structure, characterized in that, It includes a current collector, conductive adhesive, gradient foam metal, conductive adhesive and tabs that are sequentially connected; the gradient foam metal has two or three metal layers with different porosities, the porosity of the metal layers being in the range of 30-99%.

2. The conductive connection structure according to claim 1, characterized in that, The gradient foam metal has shapes including cuboids, cubes, and rings.

3. The conductive connection structure according to claim 1, characterized in that, The gradient foam metal has a surface porosity of 30-40%, a middle layer porosity of 40-60%, and a bottom layer porosity of 80-99%.

4. The conductive connection structure according to claim 1, characterized in that, The gradient foam metal is an aluminum-based gradient foam metal ring with a surface porosity of 40% and a bottom porosity of 85%.

5. The method for preparing a conductive connection structure according to claim 1, characterized in that, The method for preparing the gradient foam metal includes the following preparation steps: S1 metal powder particle size selection: surface powder particle size 10-50μm, middle powder particle size 50-100μm, bottom powder particle size 100-300μm; S2 Gradient Structure Formation: After mixing metal powder of different layers with foaming agent, copper powder is filled in sections and pressed. The mixture is kept at 950-1400℃ in an inert gas atmosphere for 0.5-2 hours to form a gradient foam metal preform with a surface porosity of 30-40%, a middle layer porosity of 40-60%, and a bottom layer porosity of 80-99%. S3 post-treatment: Impregnation with silicone oil to improve elasticity or annealing to reduce internal stress, resulting in gradient foam metal.

6. The method for preparing a conductive connection structure according to claim 5, characterized in that, The metal powder includes aluminum, nickel, and copper, and the foaming agent includes ammonium chloride and carbonates.

7. The method for preparing a conductive connection structure according to claim 5, characterized in that, The impregnation time with silicone oil is 10-30 minutes; the annealing temperature is 500-600℃ and the time is 20-30 minutes.

8. A battery cell, characterized in that, The conductive connection structure described in any one of claims 1-7 is adopted.

9. A battery cell according to claim 8, characterized in that, The gradient foam metal is a gradient foam metal ring.

10. A battery cell according to claim 9, characterized in that, The positive electrode adhesive metal layer of the cylindrical battery cell includes an aluminum-based gradient foam metal ring comprising a bottom layer, a middle layer, and a surface layer; the diameter of the bottom layer is larger than the diameter of the hollow core inside the cylindrical battery cell. In the cylindrical battery cell, the area of ​​the adhesive metal layer on the negative electrode is larger than that of the negative electrode current collector, and the outer region of the adhesive metal layer on the negative electrode is in contact with the current collector of the negative electrode.

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