Solderless connection method for lithium batteries

Abstract

The present application relates to the technical field of battery, in particular to a lithium battery welding-free connecting method. The lithium battery welding-free connecting method comprises the following steps: (a) processing a plurality of tabs in a pole group to make the tabs inclined; (b) spraying a suspension of adhesive onto a current collecting disc, pressing the pole group above the current collecting disc to the current collecting disc, and simultaneously vibrating and / or rotating the pole group until a contact pressure is generated between any tab on the pole group and the current collecting disc to form an acute angle region, and the adhesive is accumulated in each acute angle region; (c) heating the current collecting disc to melt the adhesive to form a molten body, and then cooling to complete the bonding of the tabs and the current collecting disc. The method can reduce the risk of self-discharge of the battery cell, reduce equipment investment, improve the connection yield, reduce production cost, and improve the energy of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a solderless connection method for lithium batteries. Background Technology

[0002] Laser penetration welding is a crucial step in the manufacturing process of large cylindrical batteries. Its principle is to use high-density laser energy to irradiate the current collector, forming a keyhole that penetrates the current collector and melts the tabs below the current collector. However, because the tabs are not neatly overlapped and are very loose, with a large number of lateral air gaps, when the keyhole reaches the stacked tabs, the metal vapor formed by the tab vaporization can easily escape from the lateral air gaps, which seriously reduces the welding quality. Furthermore, when the metal vapor re-solidifies into solid metal, it is highly likely to enter the electrode assembly, becoming a hidden danger of internal short circuit.

[0003] As the requirements for welding yield and efficiency become increasingly stringent, welding technology is constantly being innovated. For example, new welding technologies use green lasers with high copper and aluminum absorption rates, claiming to be completely free of metal spatter, but ultimately can only use heat conduction to weld the tabs. Due to the presence of a dense oxide layer on the current collector, traditional laser welding cannot guarantee effective welding of the tabs before the current collector plate melts and collapses; at the same time, the high cost of new green lasers will seriously offset the cost advantage of large cylinders.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One objective of this invention is to provide a solderless connection method for lithium batteries to solve many problems and defects caused by laser penetration welding in the prior art.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] A solderless connection method for lithium batteries includes the following steps:

[0008] (a) Several tabs in the electrode group are processed to tilt the tabs; the electrode group includes a wound electrode group or a stacked electrode group; in the wound electrode group, the tabs are tilted in the direction of increasing radius of the circumferential end face where they are located; in the stacked electrode group, the tabs are tilted in one direction.

[0009] (b) The adhesive suspension is evenly sprayed onto the collector plate, the electrode assembly located above the collector plate is pressed against the collector plate, and the electrode assembly is vibrated and / or rotated until contact pressure is generated between any electrode tab on the electrode assembly and the collector plate, forming an acute angle region, and the adhesive is accumulated in each of the acute angle regions.

[0010] (c) The collector plate is heated to melt the adhesive and form a melt, which is then cooled to complete the bonding of the tab and the collector plate.

[0011] In one embodiment, the angle of the acute angle region is 30° to 45°.

[0012] In one embodiment, in step (b), the amount of adhesive added within a single acute angle region is 50% to 70%; the amount of adhesive added is defined as the percentage of the total volume of the adhesive to the volume of the acute angle region to which it belongs.

[0013] In one embodiment, the heating temperature is 120–150°C.

[0014] In one embodiment, the heating time is 5 to 10 seconds.

[0015] In one embodiment, the contact angle between the melt and the manifold is 60° to 150°.

[0016] In one embodiment, the adhesive comprises PE microspheres.

[0017] In one embodiment, step (a) further includes: flattening the electrode group after the electrode tabs are tilted.

[0018] In one embodiment, the tab cutting is performed using a laser and / or a rotating cutter.

[0019] In one embodiment, the flatness of the electrode tab after cutting is 0.09 to 0.1 mm.

[0020] In one embodiment, the manifold is pretreated; the pretreatment includes pickling, washing with water, and drying.

[0021] In one embodiment, the pull-out force after the collector plate is bonded to the electrode tab is 50-80N.

[0022] In one embodiment, the internal resistance of the lithium battery is less than or equal to 1.103 mΩ.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The technical problems to be solved by the solderless connection process for electrode tabs are as follows:

[0025] The weldless connection technology of this invention can solve the problem of metal foreign objects caused by laser penetration welding and reduce the risk of cell self-discharge; at the same time, it can reduce equipment investment, improve connection yield, and reduce production costs; it can also improve the utilization rate of the internal space of the cell and increase the energy of the cell. Overall, the cost of the cell will be significantly reduced. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the pole group pressing against the collector disk in Example 2;

[0028] Figure 2 This is a schematic diagram showing the electrode tip tilted outwards;

[0029] Figure 3 A schematic diagram showing the accumulation of PE microspheres in the acute-angle region formed by the tab and the collector plate;

[0030] Figure 4 A schematic diagram showing the connection between the electrode tab and the manifold via molten PE.

[0031] Figure 5 The images show the molten morphology of PE microspheres at different temperature ranges in Example 1. Detailed Implementation

[0032] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0033] A solderless connection method for lithium batteries includes the following steps:

[0034] (a) Several tabs in the electrode group are processed to tilt the tabs; the electrode group includes a wound electrode group or a stacked electrode group; in the wound electrode group, the tabs are tilted in the direction of increasing radius of the circumferential end face where they are located; in the stacked electrode group, the tabs are tilted in one direction.

[0035] (b) The adhesive suspension is evenly sprayed onto the collector plate, the electrode assembly located above the collector plate is pressed against the collector plate, and the electrode assembly is vibrated and / or rotated until contact pressure is generated between any electrode tab on the electrode assembly and the collector plate, forming an acute angle region, and the adhesive is accumulated in each of the acute angle regions.

[0036] (c) The collector plate is heated to melt the adhesive and form a melt, which is then cooled to complete the bonding of the tab and the collector plate.

[0037] This invention improves the process technology for connecting the tabs and current collectors, reducing reliance on laser penetration welding; it eliminates the risk of introducing foreign metal objects during laser penetration welding, reducing battery self-discharge; it addresses the issue of low welding yield in laser penetration welding, improving production efficiency and reducing production costs; it also addresses the high cost of laser welding equipment, reducing cell costs; and by using physical bonding, it reduces the tab width, effectively increasing the electrode width and cell capacity. Overall, the weldless tab connection process solves the self-discharge problem and cost pressure associated with laser penetration welding.

[0038] It should be noted that the acute angle of the acute angle region in this invention is obtained by calculating the ratio of the distance d between the current collector and the electrode assembly to the length L of the electrode tab, i.e. Different tab lengths L correspond to different spacings d, therefore, it is only necessary to control the angle x of the acute angle region. In one embodiment, the tab length L is a fixed value, and by adjusting the spacing d between the collector plate and the electrode group, the tabs on the electrode group and the collector plate form acute angle regions of different angles, thus forming different acute angle regions in each embodiment.

[0039] In one embodiment, the binder comprises PE microspheres.

[0040] To ensure elastic contact between the tabs and the current collector, during or after winding or stacking, a specially designed arc-shaped tooling should be used to tilt the tabs layer by layer towards the outer radius (cylinder) or one side (stacked) at a certain angle. Furthermore, to avoid interference between adjacent tabs, the blank tabs need to be cut before winding / stacking, i.e., die-cutting the tabs. Traditional die-cut tabs are 6–8 mm wide. Using a solderless connection process, the tab width can be reduced to 3–5 mm, and the corresponding coating width can be increased by about 3 mm, significantly improving the battery's energy density.

[0041] In one embodiment, step (a) further includes: flattening the electrode assembly after the tabs are tilted, specifically including: vertically clamping the electrode assembly, using a laser or a high-speed rotating cutter to flatten the uneven lower end of the tabs along the winding direction, which is expected to achieve a flatness of 0.1 mm (refer to semiconductor silicon wafers), and the splashed metal residue will fall downwards, and then the metal debris flying upwards into the electrode assembly will be cleaned up by appropriate vibration or light blowing (without causing plastic deformation of the tabs).

[0042] In one embodiment, the manifold undergoes pretreatment, which includes pickling, washing, and drying to remove the oxide layer from the manifold. It is then transported in a vacuum / protective atmosphere sealed package. During use, to avoid the formation of a new oxide layer, the opening and usage time need to be controlled.

[0043] This invention involves applying a layer of adhesive to the surface of a collector plate after removing the oxide layer. The electrode assembly is then pressed onto the collector plate from top to bottom by vibration or rotation along the winding direction. This forces the adhesive to be pushed aside without affecting the contact between the electrode tabs and the collector plate. Appropriate pressure is applied to cause the electrode tabs to tilt and bend elastically, ensuring sufficient contact pressure with the collector plate. The tilt angle of the electrode tabs is a critical control factor. If the tilt angle is too large, the adhesive cannot form an effective contact surface when melting, failing to effectively connect and secure the electrode tabs and the collector. If the tilt angle is too small, the adhesive also cannot effectively accumulate in the acute angle area, which is also detrimental to the connection after melting. In one embodiment, the angle of the acute angle area is 30° to 45°, for example, 30°, 35°, 40°, 45°, etc.

[0044] In one embodiment, the present invention prepares the binder into a suspension, which is then uniformly sprayed onto the manifold using a particle sprayer. By controlling the concentration and spraying amount of the binder suspension, precise control of the binder is achieved, while simultaneously ensuring uniform distribution of the binder on the manifold. Further, through rotational vibration and extrusion, effective contact is formed with the tabs in the acute-angle area. Then, by uniform heating, the solvent of the suspension is evaporated and the binder is melted, achieving adhesion between the tabs and the manifold.

[0045] In one embodiment, the wound electrode core is rotated along the axis (cylinder) or tilted in the direction of the electrode tab bending (stacked), so that the adhesive is deposited at the acute angle of the electrode tab bend by centrifugal force or gravity, avoiding the obtuse angle position where the electrode tab contacts the current collector. The amount of adhesive added is a key control factor. When the amount added is too much, it is not conducive to melting the adhesive and will increase the contact resistance between the electrode tab and the current collector. When the amount added is too little, the adhesive cannot form an effective melting area and cannot effectively connect the electrode tab and the current collector. In one embodiment, the amount of adhesive added in a single acute angle region is 50% to 70%, for example, 52%, 55%, 58%, 60%, 65%, or 70%, etc. The amount of adhesive added is defined as: the percentage of the total volume of adhesive V1 to the volume V2 of its corresponding acute angle region, i.e.

[0046] In one embodiment, the collector plate is uniformly and rapidly heated using a laser or other method, melting the adhesive on the collector plate to form a molten zone, thus bonding the tab to the collector plate. Heating temperature is a critical control factor; too low a temperature will prevent the formation of a good molten zone, while too high a temperature will cause the molten adhesive to expand to the contact area between the tab and the collector plate, affecting normal electrical connection and increasing contact resistance. In one embodiment, the heating temperature is 120–150°C, for example, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, or 150°C. In one embodiment, the heating time is 5–10 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, or 10 seconds. After bonding, forced rapid cooling using air cooling prevents high temperatures from damaging the diaphragm of the electrode assembly. Simultaneously, the adhesive solidifies and shrinks, further tightening the electrical contact between the tab and the collector plate, truly achieving a "full connection" between the tab and the collector plate.

[0047] The above operations should be performed in a non-oxygen-protective atmosphere as much as possible to avoid oxidation at the contact point between the electrode tab and the collector plate, which would reduce the conductivity.

[0048] In one embodiment, the contact angle with the collector plate is 60° to 150°, such as 70°, 80°, 90°, 100°, 120°, 130° or 150°.

[0049] In one embodiment, the pull-out force after the collector plate is bonded to the electrode tab is 50-80N.

[0050] In one embodiment, the internal resistance of the lithium battery is less than or equal to 1.103 mΩ.

[0051] The method of this invention is applicable to specific cylindrical or square models, and is not limited to the connection between the tab and the current collector; it is also applicable to the connection between the tab and the housing. This method can be used in power-type 18650, 21700, and 46 series large cylindrical cells, and can also be applied to the direct connection between the tab and the top / side current collector in square laminated cells, thereby improving the utilization rate of the internal space of the cell.

[0052] The following explanation, in conjunction with specific embodiments, further clarifies the situation.

[0053] Example 1

[0054] The first step is to determine the optimal heating temperature for the PE microspheres. The test method involves using a graduated measuring tool to place an equal amount of PE microspheres onto the manifold. After removing the measuring tool, the manifold is heated. Once the temperature probe reaches the preset temperature, heating continues for 5 seconds. The PE microspheres melt and adhere to the manifold after being heated. The melting effect is confirmed by measuring their microstructure. The determination is based on the angle between the melt and the manifold, thus selecting the optimal melting temperature range.

[0055] In this embodiment, we set five temperature ranges: T1 (100≤T1<110℃), T2 (110≤T2<120℃), T3 (120≤T3<130℃), T4 (130≤T4<140℃), and T5 (140≤T5≤150℃). The morphology of the melt is related to the amount of PE microspheres added; the higher the amount added, the higher the required heating temperature. See Appendix. Figure 5 ,in, Figure 5 Figure (A) corresponds to the melt morphology in the T1 temperature range, Figure (B) corresponds to the melt morphology in the T2 range, Figure (C) corresponds to the melt morphology in the T3 range, and Figure (D) corresponds to the melt morphology in the T4 and T5 ranges. It can be seen that the optimal heating temperature range is 120–150℃, and the optimal angle between the PE melt and the manifold is 60°–150°.

[0056] Example 2

[0057] For solderless connection methods for lithium batteries, please refer to [link / reference]. Figure 1 , Figure 2 , Figure 3 , Figure 4 This includes the following steps:

[0058] (a) Several tabs in the pole group are processed to tilt the tabs; the pole group is a wound pole group; in the wound pole group, the tabs are tilted in the direction of increasing radius of the end face of the circumference on which they are located.

[0059] (b) The suspension of PE microspheres is evenly sprayed onto the collector plate through a particle sprayer, and the electrode assembly located above the collector plate is pressed against the collector plate. At the same time, the electrode assembly is vibrated and / or rotated until contact pressure is generated between any electrode on the electrode assembly and the collector plate, forming several acute angle regions. Each of the acute angle regions is filled with PE microspheres.

[0060] (c) The current collector is heated to 130°C to melt the PE microspheres and form a melt. Then it is cooled and the PE microspheres solidify and shrink, which further tightens the electrical contact surface between the tab and the current collector (to realize the electrical connection between the current collector and the tab), thus completing the bonding between the tab and the current collector.

[0061] The acute angle formed between any of the electrodes and the current collector is 30°;

[0062] The amount of PE microspheres added can be controlled by adjusting the concentration of the PE microsphere suspension and the spraying amount; within a single acute-angled region, the amount of PE microspheres added is 50%.

[0063] Example 3

[0064] The lithium battery solderless connection method differs from Example 2 in that the amount of PE microspheres added in a single acute-angle region is 70%.

[0065] Example 4

[0066] The lithium battery solderless connection method differs from that in Example 2 in that: within a single acute angle region, the acute angle formed between any of the electrode sheets and the current collector is 45°.

[0067] Example 5

[0068] The difference between the solderless connection method for lithium batteries and Example 4 is that the amount of PE microspheres added is 70%.

[0069] Comparative Example 1

[0070] The lithium battery solderless connection method differs from Example 2 in that the amount of PE microspheres added in a single acute-angle region is 30%.

[0071] Comparative Example 2

[0072] The lithium battery solderless connection method differs from Example 4 in that the amount of PE microspheres added in a single acute-angle region is 30%.

[0073] Comparative Example 3

[0074] The lithium battery solderless connection method differs from Example 2 in that: the acute angle formed between any of the electrodes and the current collector is 60°; and the amount of PE microspheres added within a single acute angle region is 30%.

[0075] Comparative Example 4

[0076] The lithium battery solderless connection method differs from that in Example 2 in that the acute angle formed between any of the electrode sheets and the current collector is 60°.

[0077] Comparative Example 5

[0078] The lithium battery solderless connection method differs from Example 2 in that: the acute angle formed between any of the electrodes and the current collector is 60°; and the amount of PE microspheres added within a single acute angle region is 70%.

[0079] Experimental Example

[0080] I. Pull-out force and internal resistance tests were performed on the lithium batteries obtained after connecting Examples 2-5 and Comparative Examples 1-5. The results are shown in Table 1.

[0081] Table 1 Test Results

[0082] Group Pull-out force (N) Internal resistance (mΩ) Example 2 70 0.954 Example 3 80 1.103 Example 4 50 1.102 Example 5 70 0.967 Comparative Example 1 40 1.246 Comparative Example 2 30 1.352 Comparative Example 3 20 1.367 Comparative Example 4 50 1.235 Comparative Example 5 60 1.155

[0083] As shown in Table 1, the acute angle region (tilt angle) between the electrode and the current collector of the present invention, combined with the amount of PE microspheres added, makes the connected lithium battery have higher pull-out force and lower internal resistance.

[0084] The acute angle area of ​​the electrode in Comparative Example 1 is small, the amount of PE microspheres added is low, it cannot form an effective melting area, it cannot effectively connect the tab and the current collector, the pull-out force is low, and the internal resistance is high.

[0085] The acute angle region of the electrode in Comparative Example 2 is 45°. Compared with Example 4, the amount of PE microspheres added is lower, which makes it impossible to form an effective melting area, and thus impossible to effectively connect the electrode tab and the current collector. The pull-out force is lower and the internal resistance is higher.

[0086] Comparative Examples 3-5 show that the acute angle of the tab is too high, and the pull-out force increases with the increase of the amount of PE microspheres added. However, the internal resistance of the battery is high and does not meet the usage requirements.

[0087] II. Existing Technology 1: Inward flattening of the tabs + laser welding, with an internal resistance range of 0.90–0.95 mΩ; Existing Technology 2: Vertical tabs + laser welding, with an internal resistance range of 1.1–1.15 mΩ. The battery with the tabs tilted outwards and PE microspheres thermosetting connection in this invention has an internal resistance range of 0.95–1.103 mΩ. This invention meets the internal resistance requirements by controlling the outward tilt angle of the tabs (30–45°), reasonably controlling the amount of PE microspheres added (50%–70%), and reasonably controlling the heating temperature (120–150°C), ensuring that the contact angle between the PE melt and the current collector is within 60°–150°.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for solderless connection of lithium batteries, characterized in that, The method comprises the following steps: (a) processing a plurality of tab ears in a polar group to make the tab ears inclined; the polar group comprises a winding polar group or a laminated polar group; in the winding polar group, the tab ears are inclined towards the direction of increasing radius of the circumferential end face; in the laminated polar group, the tab ears are unidirectionally inclined; (b) uniformly spraying a suspension of a bonding agent onto a current collector plate, pressing the polar group above the current collector plate towards the current collector plate, and simultaneously vibrating and / or rotating the polar group until a contact pressure is generated between any tab ear on the polar group and the current collector plate, and an acute angle region is formed, and the bonding agent is accumulated in each acute angle region; (c) heating the current collector plate to melt the bonding agent to form a molten body, and then cooling to complete the bonding of the tab ears and the current collector plate; The angle of the acute angle region is 30°-45°; In step (b), the addition amount of the bonding agent in a single acute angle region is 50%-70%; The addition amount of the bonding agent is defined as the percentage of the total volume of the bonding agent to the volume of the acute angle region to which the bonding agent belongs; The contact angle between the molten body and the current collector plate is 60°-150°.

2. The lithium battery solderless connection method according to claim 1, characterized in that, The heating temperature is 120-150℃.

3. The lithium battery solderless connection method of claim 1, wherein, The heating time is 5-10s.

4. The lithium battery solderless connection method of claim 1, wherein, The bonding agent comprises PE microspheres.

5. The lithium battery solderless connection method of claim 1, wherein, At least one of the following features (1) to (3) is included: (1) in step (a), further comprising tab ear flattening of the polar group after the tab ears are inclined; (2) the tab ear flattening uses laser and / or a rotating cutter; (3) the flatness after the tab ear flattening is 0.09-0.1mm.

6. The lithium battery solderless connection method of claim 1, wherein, The current collector plate is pretreated; the pretreatment comprises pickling, washing and drying.

7. The lithium battery solderless connection method of claim 1, wherein, At least one of the following features (1) to (2) is included: (1) the pulling force after the bonding of the current collector plate and the tab ears is 50-80N; (2) the internal resistance of the lithium battery is less than or equal to 1.103mΩ.

Images