Large cylindrical lithium battery negative collector plate and ultrasonic point bottom welding method

Abstract

The invention discloses a large cylindrical lithium battery negative collector plate and an ultrasonic point bottom welding method. The large cylindrical lithium battery negative collector plate comprises an ultrasonic welding needle, an ultrasonic welding needle protruding welding head, a roll core, a steel shell, an ultrasonic welding bottom film, a collector plate and a laser welding groove. The steel shell is made of SPCC, the collector plate is round or strip-shaped, the collector plate is made of pure copper T2, the hardness of the collector plate is M-state HV48-59, the collector plate is plated with nickel on a single side, and the collector plate is used for preventing laser high reflection, an ultrasonic spot bottom welding surface is not plated with nickel, and self-discharge abnormity caused by nickel powder generated by ultrasonic spot bottom welding high-frequency vibration is prevented. And nickel plating affects the hardness of the collector plate and prevents the hardness from affecting the ultrasonic point bottom welding strength. According to the invention, the resistance and the point bottom pseudo soldering rate are reduced, the point bottom welding strength and the welding area are increased, so that the internal resistance of the battery is reduced to achieve the purpose of low charge-discharge temperature rise, the safety performance is improved, and high-rate charge-discharge can be realized; and the problem of rusting at a laser penetration welding shell bottom weld bead is solved.

Description

Technical Field

[0001] The invention relates to the technical field of negative current collecting plates of lithium batteries, and in particular to a negative current collecting plate of a large cylindrical lithium battery and an ultrasonic point bottom welding method. Background Art

[0002] The existing large cylindrical steel shell lithium battery has a full-ear structure, and the mainstream manufacturing process for the negative electrode collector and the shell bottom is resistance point bottom welding or laser penetration welding. The disadvantages of resistance point bottom welding are that the negative electrode collector and the shell bottom are fixed by only one welding point, the welding area is small, the current capacity is low, and it is easy to have cold welding, which leads to increased internal resistance and excessive temperature rise, affecting the safety performance of the battery. Although laser penetration welding can solve the shortcomings of small welding area and low strength, it also has another disadvantage. The laser penetration welding will damage the nickel layer at the bottom of the steel shell, causing the shell bottom to rust, reducing the service life of the battery, and the investment cost of laser penetration welding equipment is high. Summary of the invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a new type of welding method for the negative collector of a large cylindrical battery and the bottom of the shell through ultrasonic spot bottom welding. The negative collector is designed as a single-sided copper-nickel-plated structure, in which the side in contact with the ultrasonic welding needle is not nickel-plated, and the non-nickel-plated surface retains the soft state characteristics of copper itself and is easy to weld; the other laser welding surface is nickel-plated to prevent the problem of high-reflection of laser welding. The welding head of the ultrasonic welding needle is designed as a plurality of convex point structures. Under the action of high-frequency vibration and pressure, the negative collector and the surface of the shell bottom are rubbed against each other to form a fusion between the molecular layers to form a plurality of small molten cores. This welding has high strength and large welding area, improves the abnormality of the bottom of the resistance point and the small area causing the internal resistance to rise in charge and discharge temperature, and improves the problem of rust on the bottom of the shell due to laser penetration welding; compared with resistance welding and laser penetration welding, ultrasonic welding is a green, environmentally friendly and energy-saving welding method.

[0004] The present invention proposes a method for ultrasonic spot welding of a negative current collector of a large cylindrical lithium battery, including an ultrasonic welding needle, an ultrasonic welding needle protruding welding head, a winding core, a steel shell, an ultrasonic welding bottom film, a current collector and a laser welding groove; The material of the steel shell is SPCC; The collector plate is one of a circular shape and a strip shape; The material of the collector plate is pure copper T2, with a hardness of M state HV48-59, and single-sided nickel plating for preventing laser high reflection. The ultrasonic spot bottom welding surface is not nickel-plated to prevent the high-frequency vibration of the ultrasonic spot bottom welding from generating nickel powder and causing abnormal self-discharge. The nickel plating affects the hardness of the collector plate to prevent the hardness from affecting the ultrasonic spot bottom welding strength. The welding place between the collecting plate and the winding core is provided with two grooves, which fits the winding core more closely without gaps, thus preventing abnormal explosion during welding; The current collecting plate is provided with two elliptical notches and two circular notches, which are convenient for electrolyte infiltration during injection and achieve the effect of weight reduction; The collector plate is provided with two reinforcing ribs, which effectively increase the overall rigidity of the collector plate and prevent the collector plate from deforming; The collector plate is provided with a foolproof notch to prevent assembly errors when the collector plate is welded to the negative end of the winding core; The ultrasonic welding needle and the ultrasonic welding base film are both made of tool steel; The ultrasonic welding needle raised welding head is provided with a plurality of convex point structures, the number of which can be adjusted according to the welding effect. During the welding process, under the action of high-frequency vibration and pressure, a plurality of convex point designs at the ultrasonic welding head form a plurality of small molten nuggets to achieve the welding purpose. The welding area is large and the welding strength is high. The edges of the ultrasonic welding needle raised welding head are provided with rounded corners to prevent the sharp edge of the welding needle head from breaking the collecting plate after welding. A cavity is provided at the center of the ultrasonic welding bottom film to prevent the shell bottom from being rubbed out and nickel from falling off during high-frequency vibration of ultrasonic point bottom welding.

[0005] A method for ultrasonic spot bottom welding of a negative current collector of a large cylindrical lithium battery comprises the following steps: S1: The negative terminal of the winding core is assembled and welded with the negative current collector. The raised side of the laser welding groove of the negative current collector is not nickel-plated and contacts the negative terminal surface. The other side of the negative current collector that is laser welded is nickel-plated. The positive terminal of the winding core is welded with the positive current collector. The positive terminal of the winding core is covered with an insulating sheet and high-temperature tape and then placed in a steel shell. S2: After entering the steel shell, the negative electrode current collector is tightly fitted to the bottom of the steel shell; S3: After entering the steel shell, the coil core is inserted into the ultrasonic welding needle. The negative electrode current collector and the bottom of the steel shell are melted together under the action of the pressure, pre-pressing time, welding time, welding frequency and holding time of the ultrasonic welding machine. Multiple small welding nuggets are formed at the multiple convex points designed at the raised welding head of the ultrasonic welding needle to achieve the purpose of welding. S4: Carry out the subsequent production process of the battery.

[0006] The beneficial effects of the present invention are: reducing the resistance and the spot bottom false welding rate, increasing the spot bottom welding strength and welding area, thereby reducing the internal resistance of the battery to achieve the purpose of low charging and discharging temperature rise, improving safety performance, and enabling high-rate charging and discharging; improving the rust problem at the shell bottom weld of laser penetration welding; A negative electrode current collector is not nickel-plated on the ultrasonic spot bottom welding surface, but is nickel-plated on the laser welding surface; an ultrasonic spot bottom welding process is used to replace traditional resistance spot bottom welding and laser penetration welding processes; the ultrasonic spot bottom welding needle head is designed with a structure of multiple convex points, which makes it easier to weld the negative current collector to the shell under pressure and high-frequency vibration, thereby increasing the welding area and welding strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 A is a schematic diagram of the structure of the present invention; Figure 3 It is a schematic diagram of the structure of the ultrasonic welding needle raised welding head in the present invention; Figure 4 A is a schematic diagram of the A-section structure of the current collecting plate in the present invention; Figure 5 It is a schematic diagram of the B-section structure of the current collecting plate in the present invention; Figure 6 It is a schematic diagram of the C-section structure of the current collecting plate in the present invention; Figure 7 It is the ultrasonic point bottom welding form of the present invention; Figure 8 It is a structural schematic diagram of the nickel-plated welding surface in the present invention; Fig. 9 It is a schematic diagram of the side structure of the B section of the current collecting plate in the present invention.

[0008] In the figure: 1. Ultrasonic welding needle; 2. Raised welding head of ultrasonic welding needle; 3. Winding core; 4. Negative electrode current collector; 5. Steel shell; 6. Ultrasonic welding base film; 8. Elliptical notch; 9. Reinforcement rib; 10. Laser welding groove; 11. Anti-fool notch; 12. Circular notch. DETAILED DESCRIPTION

[0009] The present invention will be further explained below in conjunction with specific embodiments. Example

[0010] refer to Figure 1-9 In this embodiment, a method for ultrasonic spot welding of a negative current collector of a large cylindrical lithium battery is proposed, including an ultrasonic welding needle 1, an ultrasonic welding needle raised welding head 2, a winding core 3, a steel shell 5, an ultrasonic welding bottom film 6, a current collector, and a laser welding groove 10; The material of the steel shell 5 is SPCC; The collector plate is one of a circular shape and a strip shape; The material of the collector plate is pure copper T2, with a hardness of M state HV48-59, and single-sided nickel plating for preventing laser high reflection. The ultrasonic spot bottom welding surface is not nickel-plated to prevent the high-frequency vibration of the ultrasonic spot bottom welding from generating nickel powder and causing abnormal self-discharge. The nickel plating affects the hardness of the collector plate to prevent the hardness from affecting the ultrasonic spot bottom welding strength. The welding place between the collecting plate and the winding core 3 is provided with two grooves, which fits the winding core 3 more closely without gaps, thus preventing abnormal explosion during welding; The collector plate is provided with two elliptical notches 8 and two circular notches 12, which facilitate the infiltration of electrolyte during injection and achieve the effect of weight reduction; The collector plate is provided with two reinforcing ribs 9, which effectively increase the overall rigidity of the collector plate and prevent the collector plate from deforming; The collector plate is provided with a foolproof notch 11 to prevent assembly errors when the collector plate is welded to the negative end of the winding core 3; The ultrasonic welding needle 1 and the ultrasonic welding base film 6 are both made of tool steel; The ultrasonic welding needle raised welding head 2 is provided with a plurality of convex point structures, the number of which can be adjusted according to the welding effect. During the welding process, under the action of high-frequency vibration and pressure, a plurality of convex point designs at the ultrasonic welding head form a plurality of small molten nuggets to achieve the welding purpose. The welding area is large and the welding strength is high. The edges of the ultrasonic welding needle raised welding head 2 are provided with rounded corners to prevent the sharp edge of the welding needle head from breaking the collecting plate after welding. A cavity is provided at the center of the ultrasonic welding bottom film 6 to prevent the shell bottom from being rubbed out and nickel from falling off during high-frequency vibration of ultrasonic point bottom welding.

[0011] A method for ultrasonic spot bottom welding of a negative current collector of a large cylindrical lithium battery comprises the following steps: S1: The negative terminal of the winding core 3 is assembled and welded with the negative electrode current collecting plate 4. The raised side of the laser welding groove of the negative electrode current collecting plate 4 is not nickel-plated and contacts the negative terminal surface. The other side of the laser welding surface of the negative electrode current collecting plate 4 is nickel-plated. The positive terminal of the winding core 3 is welded with the positive electrode current collecting plate. The positive terminal of the winding core 3 is covered with an insulating sheet and a high-temperature tape and then placed in the steel shell 5. S2: After entering the steel shell 5, the negative electrode current collecting plate 4 is tightly fitted to the bottom of the steel shell 5; S3: After entering the steel shell 5, the winding core 3 is inserted into the ultrasonic welding needle 1, and the negative electrode current collector 4 and the shell bottom of the steel shell 5 are melted together under the action of the pressure, pre-pressing time, welding time, welding frequency and holding time of the ultrasonic welding machine, and multiple small welding nuggets are formed at the multiple convex points of the convex welding head 2 of the ultrasonic welding needle to achieve the purpose of welding; S4: Carry out the subsequent production process of the battery.

[0012] In this embodiment, the steel shell 5 is made of SPCC nickel-plated, the shell bottom thickness is 0.7mm, the negative electrode current collector 4 is made of pure copper T2, the surface laser-welded with the negative end surface of the winding core 3 is nickel-plated, and the other surface in contact with the ultrasonic welding needle 1 is not nickel-plated. The copper state is M state, the hardness is HV48-59, the outer diameter is φ38.5mm, and the raw material thickness is 0.3mm. After the winding core 3 is welded with the positive and negative electrode current collectors 4, an insulating sheet is wrapped with high-temperature tape and put into the shell; Insert ultrasonic welding needle 1, such as Figure 6 and Figure 7As shown, ultrasonic point bottom welding is used to weld the negative electrode current collector 4 to the shell bottom. The ultrasonic welding head is designed with 19 convex points that transmit high-frequency vibration waves to the negative electrode current collector 4 and the shell bottom. Under pressure, the negative electrode current collector 4 and the shell bottom surface rub against each other to form fusion between molecular layers, forming multiple small molten cores, thereby improving the welding strength and welding area.

[0013] In this embodiment, it can be seen from the above-mentioned large cylindrical current collector and ultrasonic spot bottom welding method that the negative electrode current collector 4 is designed with a notch to facilitate liquid injection and achieve the effect of weight reduction; the reinforcing ribs 9 are designed to increase the rigidity of the current collector to prevent deformation; the anti-mistake notch 11 is designed to distinguish the front and back sides to prevent assembly errors; two laser welding grooves are designed to fit more closely with the winding core 3 without gaps to prevent abnormal explosion during welding; single-sided nickel plating, and the laser welding surface is nickel-plated to prevent laser high reflection; like Figure 8 As shown, the ultrasonic spot bottom welding surface is not nickel-plated to prevent the high-frequency vibration of the ultrasonic spot bottom welding from generating nickel powder and causing abnormal self-discharge, and the nickel plating affects the hardness of the collector plate to prevent the hardness from affecting the ultrasonic spot bottom welding strength.

[0014] The head of the ultrasonic welding needle 1 is designed with a convex structure, and the number of convex points can be adjusted according to the welding effect. During the welding process, under the action of high-frequency vibration and pressure, multiple convex points at the ultrasonic welding head are designed to form multiple small molten cores to achieve the welding purpose. The welding area is large, the welding strength is high, and the production efficiency is high. It improves the problem of point-bottom cold welding and small area causing large internal resistance and high charging and discharging temperature, and improves the problem of rust at the bottom of the laser penetrating welding shell.

[0015] 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 negative current collector for a large cylindrical lithium battery, characterized in that: It comprises an ultrasonic welding needle (1), an ultrasonic welding needle raised welding head (2), a winding core (3), a negative electrode current collecting plate (4), a steel shell (5), an ultrasonic welding base film (6) and a laser welding groove (10); The material of the steel shell (5) is SPCC; The negative electrode current collecting plate (4) is in a circular or strip shape; The negative electrode current collecting plate (4) is made of pure copper T2, with a hardness of M state HV48-59, and is nickel plated on one side to prevent high laser reflection; Two grooves are provided at the welding point between the negative electrode current collecting disc (4) and the winding core (3); The negative electrode current collecting plate (4) is provided with two elliptical notches (8) and two circular notches (12); The negative electrode current collector (4) is provided with two reinforcing ribs (9) for preventing the negative electrode current collector (4) from deforming; The negative electrode current collecting plate (4) is provided with an anti-mistake notch (11); The ultrasonic welding needle (1) and the ultrasonic welding base film (6) are both made of tool steel; The ultrasonic welding needle raised welding head (2) is provided with a plurality of raised point structures, and the edges of the ultrasonic welding needle raised welding head (2) are provided with rounded corners; A cavity is provided at the center of the ultrasonic welding base film (6).

2. The ultrasonic spot bottom welding method for the negative current collector of a large cylindrical lithium battery according to claim 1, characterized in that: The following steps are involved: S1: The negative terminal of the winding core (3) is assembled and welded to the negative electrode current collecting plate (4), the raised side of the laser welding groove of the negative electrode current collecting plate (4) is not nickel-plated and contacts the negative terminal surface, the other side of the laser welding surface of the negative electrode current collecting plate (4) is nickel-plated, the positive terminal of the winding core (3) is welded to the positive electrode current collecting plate, and the positive terminal of the winding core (3) is covered with an insulating sheet and high-temperature tape and then placed in the steel shell (5); S2: After entering the steel shell (5), the negative electrode current collecting plate (4) is tightly fitted to the bottom of the steel shell (5); S3: After entering the steel shell (5), the winding core (3) is inserted into the ultrasonic welding needle (1), and the negative electrode current collector (4) and the bottom of the steel shell (5) are melted together under the action of the pressure, pre-pressing time, welding time, welding frequency and pressure holding time of the ultrasonic welding machine, and multiple small welding nuggets are formed at multiple convex points designed at the convex welding head (2) of the ultrasonic welding needle, thereby achieving the purpose of welding; S4: Carry out the subsequent production process of the battery.

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