CN113097656B - Pole pieces, cell assemblies and batteries - Google Patents

Abstract

The application provides a pole piece, an electric core component and a battery, and relates to the technical field of lithium batteries. A pole piece, the tab of the pole piece is provided with a welding area, the welding area comprises a plurality of welding positions, and the thickness ratio of the thickness of the tab of the welding positions to the thickness of the non-welded part of the tab is (2-12): (3-30). The welding effect of this utmost point ear is better, avoids appearing the condition of overselding and rosin joint, and the resistance of utmost point ear is less, and the electric core has higher electric core capacity and longer cycle life.

Description

Electrode, cell assembly and battery

Technical Field

The present application relates to the technical field of lithium batteries, and more specifically, to pole pieces, battery cell assemblies and batteries.

Background Art

With the development of science and technology, lithium-ion batteries are increasingly used in electric vehicles and other fields, and the quality and performance of lithium-ion batteries are also receiving more and more attention. In lithium batteries, the pole tabs and connecting pieces are mostly connected by welding. Generally, ultrasonic welding or laser welding is used. During the welding process, it is easy to produce problems such as cold welding or over-welding, which affects the connection between the pole tabs and the connecting pieces, and affects the electrical performance of the pole pieces and the battery cells.

Summary of the invention

The purpose of the present application is to provide a pole piece, a battery cell assembly and a battery to reduce the probability of cold welding or over welding in the welding of the pole tab.

In a first aspect, an embodiment of the present application provides a pole piece, wherein a pole ear of the pole piece has a welding area, the welding area includes a plurality of welding positions, and the thickness of the pole ear at the welding position to the thickness of the unwelded portion of the pole ear has a ratio of (2-12):(3-30).

The pole piece of the pole piece provided in the present application is a pole piece after welding, and the thickness of the pole piece is reduced compared with the pole piece that has not been welded. The change in the thickness of the pole piece has an impact on the electrical properties of the pole piece, such as the resistance. If the thickness of the pole piece changes greatly, the welding pressure may be large, and the power is too large, which will lead to an increase in cracks in the conductive layer, and then the pole piece resistance increases, the battery cell IMP (AC resistance) increases, and the capacity of the battery cell decreases, the multiple is reduced, and the cycle life is reduced. If the thickness of the pole piece changes less, the welding effect may be too low, the welding is poor, and then the situation of cold welding occurs. It will also cause the pole piece resistance to increase, the battery cell IMP (AC resistance) increases, and the capacity of the battery cell decreases, the multiple is reduced, and the cycle life is reduced. The inventor of the present application has found through research that when the thickness ratio of the pole piece before and after welding is in the range of (2-12): (3-30), the welding effect of the pole piece is better, avoiding the situation of over-welding and cold welding, the resistance of the pole piece is small, and the battery cell has a higher battery cell capacity and cycle life.

In a possible implementation, there is an extrusion zone around the welding position, and the thickness of the pole ear in the extrusion zone, the thickness of the pole ear at the welding position and the thickness of the unwelded portion of the pole ear are in the ratio of (4-32):(2-12):(3-30).

During the welding process, the thickness of the tab at the welding position decreases, and the extruded material will bulge around the welding position to form an extrusion area. Since the extrusion area is thicker, it will affect the resistance of the tab. If the thickness change of the extrusion area after welding is within the above range, the welding effect of the tab is better and the resistance is smaller.

In a possible implementation, the tab includes a base film and a conductive layer disposed on both sides of the base film, and the thickness ratio of the base film of the tab at the welding position to the thickness ratio of the base film of the tab not welded is 4:(5-7).

During the welding process, the thickness of the base film and the thickness of the conductive layer will change. The thickness of the base film can reflect the degree of welding effect on the tab. When the base film is within this thickness variation range, the welding effect of the tab is better and the resistance is smaller.

In a possible implementation, the ratio of the thickness of the conductive layer on one side of the electrode tab at the welding position to the thickness of the conductive layer on one side of the electrode tab that has not been welded is (7-9):10.

The thickness of the conductive layer has a great influence on the thickness of the pole ear and pole piece. If the conductive layer changes greatly, over-welding may occur. If the conductive layer changes slightly, cold soldering may occur. Within the above thickness variation range, the resistance of the conductive layer is small.

In a possible implementation, the ratio of the resistance of the welded tab to the resistance of the unwelded tab is (5-6): 10. Through a suitable welding process, the resistance of the conductive layer after welding is small.

In a second aspect, a battery cell assembly is provided, including a connecting sheet and a battery cell, wherein the battery cell includes the above-mentioned pole piece, and the connecting sheet is welded to the pole ear of the pole piece to form a plurality of welding positions.

The battery cell assembly adopts the above-mentioned pole piece, the resistance of the battery cell assembly is small, and the resistance of the battery cell is small.

In one possible implementation, the tab includes a base film and a conductive layer arranged on both sides of the base film, the conductive layer on one side of the base film and a connecting piece welded to the conductive layer form a transfer layer, and the ratio of the sum of the thickness of the conductive layer and the connecting piece of the tab that has not been welded to the thickness of the transfer layer is (7-8):6.

After the welding process, the conductive layer and the connecting piece are welded together, and the thickness of the formed transfer layer can reflect the degree of welding. Within the above-mentioned thickness variation range, the welding effect of the tab is better and the resistance is smaller.

In a possible implementation, connecting sheets are provided on both sides of the tab, and the tab is welded to the connecting sheets on both sides to form a tab assembly, and the ratio of the thickness of the welded tab assembly to the thickness of the unwelded tab assembly is 2:(3-5). In a possible implementation, there are extrusion areas on both sides of the welding position, and the ratio of the thickness of the tab area corresponding to the extrusion area, the thickness of the welded tab assembly to the thickness of the unwelded tab assembly is 6:2:(3-5).

The lug assembly within this thickness ratio range undergoes an appropriate welding process, and the welding effect will not be too low or too high, thereby avoiding poor welding of the lug assembly or excessive welding power, and avoiding increased resistance of the lug assembly after welding, reduced cycle life, and increased cell resistance.

In a second aspect, a battery is provided, comprising a shell, an insulating member, a top cover assembly and the above-mentioned battery cell assembly, wherein the battery cell assembly is accommodated inside the shell, the insulating member is arranged between the battery cell and the shell, and the top cover assembly is covered on the shell and connected to the battery cell through a pole ear.

The battery adopts the above-mentioned battery cell assembly and has good electric capacity and cycle life.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the structure of a tab assembly provided in an embodiment of the present application;

FIG. 2 is a schematic diagram of a detection resistor according to an embodiment of the present application.

Icon: 10-ear assembly; 100-ear; 101-welding position; 103-extrusion area; 110-base film; 120-conductive layer; 200-connecting piece.

DETAILED DESCRIPTION

To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians of the art without making creative work are within the scope of protection of the present application.

In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application 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 a limitation on the present application.

Some implementation methods of the present application are described in detail below in conjunction with the accompanying drawings.

Please refer to FIG. 1, which is a schematic diagram of the structure of the battery cell assembly provided in this embodiment. This embodiment provides a battery cell assembly, including a connecting sheet 200 and a battery cell, wherein the battery cell includes a first polarity pole piece, a second polarity pole piece, and a diaphragm disposed between the first polarity pole piece and the second polarity pole piece. Each pole piece (including the first polarity pole piece and the second polarity pole piece) has a pole ear 100, and the current is drawn out by connecting the pole ear 100 with the connecting sheet 200.

The first polarity pole piece in the embodiment of the present application is a pole piece containing a composite current collector, the composite current collector includes a base film 110 and a conductive layer 120 disposed on both sides of the base film 110, and active materials are coated on both sides of the composite current collector. The pole tab 100 of the first polarity pole piece includes a base film 110 and a conductive layer 120 disposed on both sides of the base film 110. In the present embodiment, two connecting sheets 200 are respectively provided on both sides of each pole tab 100, and the two connecting sheets 200 are welded with the pole tab 100 to form a pole tab assembly 10. The connecting sheet 200 in the embodiment of the present application is a metal sheet.

The material of the base film 110 in the present application can be o-phenylphenol (OPP), polyethylene terephthalate (PET), polyimide (PI), polyphenylene sulfide (PPS), cast polypropylene (CPP), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), preferably, the material of the base film 110 is PET, PPS or PEN. The base film 110 can be made of any material, or a composite film can be obtained by using two or more materials. The material of the conductive layer 120 can be selected from at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn and their combinations (alloys). The materials of the conductive layers 120 on both sides of the base film 110 can be the same or different. The conductive layer 120 can be formed by sputtering, vacuum deposition, ion plating, laser pulse deposition and the like.

The inventor of the present application has found through experimental research that the microstructure of the tab 100 and the connecting piece 200 obtained by welding the tab 100 and the connecting piece 200 through a certain welding process is closely related to the resistance characteristics, capacity, rate and cycle life of the tab 100 after welding. The microstructure of the tab 100 and the connecting piece 200 is described below.

After the connecting piece 200 and the pole tab 100 are welded, a welding area is formed on the pole tab 100. The embodiment of the present application adopts ultrasonic welding or laser welding process for welding, and multiple welding positions 101 will be formed in the welding area of the pole tab 100, and the pole tab 100 and the connecting piece 200 are tightly connected at the welding position 101. In this embodiment, multiple welding positions 101 are arranged in a matrix, so there is a certain distance between two or more welding positions 101, and there is an unwelded position. The connecting piece 200 and the pole tab 100 are welded or have a certain gap. The specific structure is determined according to the welding degree of the welding position 101. Before welding, the connecting piece 200 and the pole tab 100 are fitted and contacted, which can be understood as the gap between the connecting piece 200 and the pole tab 100 is small. After welding, there will be a gap between the pole tab 100 and the connecting piece 200 that have not been welded near the welding position 101.

When the thickness of the tab 100 and the connecting piece 200 at the welding position 101 decreases a lot, it means that the welding pressure is relatively large; the greater the welding pressure, the larger the gap between the tab 100 and the connecting piece 200 that have not been welded near the welding position 101, making the flatness of the tab assembly 10 worse. At the same time, the greater the welding pressure, the more likely it is that over-welding will occur. When the thickness of the tab 100 and the connecting piece 200 at the welding position 101 decreases a little, it means that the welding pressure is relatively small, then the gap between the tab 100 and the connecting piece 200 that have not been welded near the welding position 101 is relatively small, and the flatness change is relatively small. However, a relatively small welding pressure may result in a cold weld, that is, a poor welding effect and poor welding.

In some embodiments of the present application, the thickness ratio of the pole tab assembly 10 after welding to the thickness ratio of the pole tab assembly 10 not after welding is 2:(3-5). Furthermore, during the welding process, the thickness of the pole tab 100 and the connecting piece 200 at the welding position 101 decreases, and correspondingly, the thickness of the pole tab 100 and the connecting piece 200 near the welding position 101 increases. During the welding process, the thickness of the pole tab assembly 10 at the welding position 101 decreases, and the extruded material bulges around the welding position 101 to form an extrusion area 103. Since the extrusion area 103 is relatively thick, it will affect the resistance of the pole tab assembly 10. In some embodiments of the present application, the thickness ratio of the pole tab assembly 10 corresponding to the extrusion area 103, the thickness of the pole tab assembly 10 after welding, and the thickness of the pole tab assembly 10 not after welding is 6:2:(3-5).

The inventors of the present application have found that the electrode tab assembly 10 within the thickness ratio range is subjected to a suitable welding process, and the welding effect is neither too low nor too high, so as to avoid the electrode tab assembly 10 from having poor welding or excessive welding power, and to avoid the electrode tab assembly 10 after welding from having increased resistance, reduced cycle life, and increased cell resistance. Optionally, the thickness of the electrode tab assembly 10 corresponding to the extrusion zone 103, the thickness of the welded electrode tab assembly 10, and the thickness of the unwelded electrode tab assembly 10 are 6:2:3 or 3:1:2 or 6:2:5.

In some embodiments of the present application, since the conductive layer 120 of the tab 100 and the connecting piece 200 welded to the conductive layer 120 are both made of metal, after welding, the conductive layer 120 is tightly connected to the connecting piece 200. In this embodiment, the conductive layer 120 and the connecting piece 200 welded to the conductive layer 120 form a transition layer. The ratio of the thickness of the welded transition layer to the thickness of the unwelded transition layer is 6:(7-8).

The welding effect of the conductive layer 120 and the connecting layer within the thickness ratio range is better. If the thickness ratio is lower than the ratio range, the welding pressure may be large and the power may be too large, which will cause the conductive layer 120 to have more cracks, and then the pole sheet resistance will increase, the battery cell IMP (AC resistance) will increase, and the capacity of the battery cell will decrease, the rate will decrease, and the cycle life will decrease. If the thickness ratio is higher than the ratio range, the welding effect may be too low, the welding is poor, and then the situation of cold welding will occur. It will also cause the pole sheet resistance to increase, the battery cell IMP (AC resistance) to increase, and the capacity of the battery cell will decrease, the rate will decrease, and the cycle life will decrease.

In some embodiments of the present application, the thickness of the tab 100 at the welding position 101 is in a ratio of (2-12):(3-30). The thickness of the tab 100 at the welding position 101 is less than the thickness of the tab 100 that has not been welded. The welding position 101 has an extrusion area 103 on both sides, and the thickness of the tab 100 in the extrusion area 103, the thickness of the tab 100 at the welding position 101, and the thickness of the tab 100 that has not been welded are in a ratio of (4-32):(2-12):(3-30). Furthermore, the thickness of the base film 110 of the tab 100 at the welding position 101 is in a ratio of (2-6):(3-9). The ratio of the thickness of the conductive layer 120 on one side of the electrode tab 100 at the welding position 101 to the thickness of the conductive layer 120 on one side of the electrode tab 100 that has not been welded is (7-9):10.

After welding, the tab 100 and the conductive layer 120 within the thickness ratio range have a smaller resistance, and the IMP of the battery cell is smaller, which avoids the negative impact on the pole piece and the battery cell due to improper welding and reduces the electrical performance. Optionally, the thickness ratio of the base film 110 of the tab 100 at the welding position 101 to the thickness ratio of the base film 110 of the tab 100 that has not been welded is 2:3, 2:5, 2:6, 2:9, 3:5, 4:7, 4:9, 5:6, 5:8, 3:8 or 6:9. The thickness ratio of the tab 100 in the extrusion area 103, the thickness of the tab 100 at the welding position 101 to the thickness ratio of the tab 100 that has not been welded is 4:2:3 or 5:3:4 or 15:10:13. The thickness ratio of the conductive layer 120 on one side of the electrode tab 100 at the welding position 101 to the thickness ratio of the conductive layer 120 on one side of the electrode tab 100 that has not been welded is 9:10, 8:10 or 7:10.

It should be noted that the thickness in the present application refers to the thickness of the tab 100 and the connecting sheet 200 at 50% of the welding position 101 , and FIG. 1 is a cross-sectional view of the tab assembly 10 at 50% of the welding position 101 .

The present application also provides a battery (not shown), comprising a housing, an insulating member, a top cover assembly and the above-mentioned battery cell assembly, wherein the battery cell assembly is accommodated inside the housing, the insulating member is arranged between the battery cell and the housing, and the top cover assembly is arranged on the housing and connected to the battery cell through a tab 100. The battery adopts the above-mentioned battery cell assembly and has good electric capacity and cycle life.

The present application provides a welding process for a tab and a connecting piece having the above-mentioned welding structure, which is welded by ultrasonic welding, and includes:

A 40KHz ultrasonic horn is used, and the diameter of the ultrasonic horn is about 100mm. The pole ear and the connecting piece are welded under the conditions of a welding pressure (cylinder pressure) of 0.2-0.5MPa, a linear speed of the ultrasonic horn of 30m/min-50m/min, and an ultrasonic amplitude of 10μm-16μm. Optionally, the welding pressure is 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa. The linear speed of the ultrasonic horn is 30m/min, 35m/min, 40m/min, 45m/min or 50m/min. The ultrasonic amplitude is 10μm, 12μm, 13μm, 15μm or 16μm.

Under the same other conditions, adjusting different ultrasonic welding pressures will produce different welding effects: if the ultrasonic welding pressure is too high, the welding head will exert too much pressure on the pole ear part of the welding part. Since the thickness of the pole ear material is only 50μm, it is easy to deform, wrinkle and break. The greater the welding pressure, the greater the deformation. When the deformation is large enough, it will cause the crack combing of the conductive layer on the current collector to gradually increase, and even directly transform from cracks to fractures, resulting in interruption of the conductive network; when the welding pressure is too small, due to insufficient physical bonding, the welding head cannot effectively fit the welding pole ear, resulting in the inability to transmit the ultrasonic energy in time, resulting in a false weld. The smaller the pressure, the smaller the tensile test value after welding, and the conductive network cannot be effectively formed.

Different line speeds will determine the cracks caused by the longitudinal pulling force on the surface of the pole piece after welding. When the speed ratio between the winding and unwinding line speed of the pole piece and the rotation speed of the welding head is large (such as greater than 1.3), it will cause excessive longitudinal pulling force on the surface, so that the conductive layer on the surface of the pole piece is stretched in the winding and unwinding direction, resulting in more cracks. When the ratio is larger, it will cause the conductive layer to break and the conductive network to break.

The influence of amplitude on welding effect mainly lies in the effect of ultrasonic energy. If the amplitude is too large, the energy penetration is strong and it is easy to weld through; if the amplitude is too small, the energy penetration is insufficient and cold welding is easy to occur.

The thickness of the composite current collector may be 5 μm-15 μm, preferably 8 μm-12 μm; the thickness of the copper foil of the connecting sheet may be 4 μm-12 μm, preferably 6 μm-10 μm. It should be noted that the thickness of the connecting sheet is the thickness of the connecting sheet on one side of the composite current collector.

The resistance value of the pole ear (composite current collector) of the single-layer pole piece obtained by the above welding process is 20Ω-65Ω, and the pulling force is 5-80N. The IMP (AC resistance) of the 280 battery cell is 0.15mΩ-0.2mΩ. The resistance of the pole ear of the single-layer pole piece before welding is 33Ω-130Ω. The ratio of the resistance of the conductive layer at the welding position after welding to the resistance of the conductive layer without welding is (5-6):10. It shows that the pole ear and battery cell have better electrical properties after welding.

The features and performance of the present application are further described in detail below in conjunction with the embodiments.

Example 1

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 13 μm, of which the polymer layer (base film) is 12 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 13 μm, and the thickness of the tab assembly is 40 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, welding cylinder pressure is 0.3 MPa, ultrasonic amplitude is 16 μm, and welding head linear speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 20 μm, the thickness of the tab assembly corresponding to the extrusion area is 60 μm, and the thickness of the unwelded tab assembly is 40 μm.

The thickness of the transfer layer corresponding to the welding position is 12 μm, and the thickness of the transfer layer corresponding to the extrusion area is 15 μm.

The thickness of the tab at the welding position is 21.6 μm, and the thickness of the tab at the extrusion area is 24.6 μm.

The thickness of the conductive layer at the welding position is 0.8 μm, and the thickness of the polymer layer at the welding position is 8 μm.

The resistance of the tab before welding is 130mΩ, and the resistance of the tab after welding is about 65mΩ. The tensile force is about 25N, the IMP of the battery cell is 0.18Ω, and the DCR of the battery cell is 0.252Ω.

Example 2

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 13 μm, of which the polymer layer (base film) is 12 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 13 μm, and the thickness of the tab assembly is 40 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.4 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 15 μm, the thickness of the tab assembly corresponding to the extrusion area is 65 μm, and the thickness of the unwelded tab assembly is 40 μm.

The thickness of the transfer layer corresponding to the welding position is 9 μm, and the thickness of the transfer layer corresponding to the extrusion area is 14 μm.

The thickness of the tab at the welding position is 16.4 μm, and the thickness of the tab at the extrusion area is 21.4 μm.

The thickness of the conductive layer at the welding position is 0.7 μm, and the thickness of the polymer layer at the welding position is 6 μm.

The resistance of the tab before welding is 130mΩ. After welding, the resistance of the tab is about 80mΩ, the tensile force is about 19N, the IMP of the battery cell is 0.19Ω, and the DCR of the battery cell is 0.266Ω.

Example 3

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 13 μm, of which the polymer layer (base film) is 12 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 13 μm, and the thickness of the tab assembly is 40 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.2 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 35 μm, the thickness of the tab assembly corresponding to the extrusion area is 45 μm, and the thickness of the unwelded tab assembly is 40 μm.

The thickness of the transfer layer corresponding to the welding position is 14 μm, and the thickness of the transfer layer corresponding to the extrusion area is 16 μm.

The thickness of the tab at the welding position is 27.8 μm, and the thickness of the tab at the extrusion area is 29.8 μm.

The thickness of the conductive layer at the welding position is 0.9 μm, and the thickness of the polymer layer at the welding position is 12 μm.

The resistance of the tab before welding is 130mΩ. After welding, the resistance of the tab is about 90mΩ, the tensile force is about 15N, the IMP of the battery cell is 0.195Ω, and the DCR of the battery cell is 0.273Ω.

Example 4

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 5.5 μm, of which the polymer layer (base film) is 4.5 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 8 μm, and the thickness of the tab assembly is 22.5 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.3 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 14 μm, the thickness of the tab assembly corresponding to the extrusion area is 28 μm, and the thickness of the unwelded tab assembly is 22.5 μm.

The thickness of the transfer layer corresponding to the welding position is 10 μm, and the thickness of the transfer layer corresponding to the extrusion area is 11 μm.

The thickness of the tab at the welding position is 15.6 μm, and the thickness of the tab at the extrusion area is 16.6 μm.

The thickness of the conductive layer at the welding position is 0.8 μm, and the thickness of the polymer layer at the welding position is 4 μm.

The resistance of the tab before welding is 40mΩ. After welding, the resistance of the tab is about 20mΩ. The tensile force is about 19N. The IMP of the battery cell is 0.16Ω, and the DCR of the battery cell is 0.224Ω.

Example 5

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 5.5 μm, of which the polymer layer (base film) is 4.5 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 8 μm, and the thickness of the tab assembly is 22.5 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.4 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 8 μm, the thickness of the tab assembly corresponding to the extrusion area is 32 μm, and the thickness of the unwelded tab assembly is 22.5 μm.

The thickness of the transfer layer corresponding to the welding position is 5 μm, and the thickness of the transfer layer corresponding to the extrusion area is 9 μm.

The thickness of the tab at the welding position is 9.4 μm, and the thickness of the tab at the extrusion area is 13.4 μm.

The thickness of the conductive layer at the welding position is 0.7 μm, and the thickness of the polymer layer at the welding position is 3 μm.

The resistance of the tab before welding is 40mΩ. After welding, the resistance of the tab is about 25mΩ. The pulling force is about 18N. The IMP of the battery cell is 0.165Ω, and the DCR of the battery cell is 0.231Ω.

Example 6

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 5.5 μm, of which the polymer layer (base film) is 4.5 μm, the conductive layer is 1 μm, the thickness of the connecting sheet aluminum foil is 8 μm, and the thickness of the tab assembly is 22.5 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.2 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 20 μm, the thickness of the tab assembly corresponding to the extrusion area is 24 μm, and the thickness of the unwelded tab assembly is 22.5 μm.

The thickness of the transfer layer corresponding to the welding position is 8 μm, and the thickness of the transfer layer corresponding to the extrusion area is 13 μm.

The thickness of the tab at the welding position is 14.3 μm, and the thickness of the tab at the extrusion area is 19.3 μm.

The thickness of the conductive layer at the welding position is 0.9 μm, and the thickness of the polymer layer at the welding position is 4.5 μm.

The resistance of the tab before welding is 40mΩ. After welding, the resistance of the tab is about 30mΩ. The pulling force is about 10N. The IMP of the battery cell is 0.17Ω, and the DCR of the battery cell is 0.238Ω.

Example 7

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 5.5 μm, of which the polymer layer (base film) is 4.5 μm, the conductive layer is 1 μm, and the thickness of the connecting piece aluminum foil is 8 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 40 KHz, pressure is 0.5 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 10 μm, the thickness of the tab assembly corresponding to the extrusion area is 26 μm, and the thickness of the unwelded tab assembly is 22.5 μm.

The thickness of the transfer layer corresponding to the welding position is 8 μm, and the thickness of the transfer layer corresponding to the extrusion area is 11 μm.

The thickness of the tab at the welding position is 13.6 μm, and the thickness of the tab at the extrusion area is 16.6 μm.

The thickness of the conductive layer at the welding position is 0.8 μm, and the thickness of the polymer layer at the welding position is 4 μm.

The resistance of the tab before welding is 40mΩ. After welding, the resistance of the tab is about 24mΩ. The pulling force is about 15N. The IMP of the battery cell is 0.163Ω, and the DCR of the battery cell is 0.2282Ω.

Example 8

This embodiment provides a battery cell assembly, and the following process is used to transfer weld the tab:

The thickness of the composite current collector is 5.5 μm, of which the polymer layer (base film) is 4.5 μm, the conductive layer is 1 μm, and the thickness of the connecting piece aluminum foil is 8 μm.

The preset parameters of ultrasonic welding are: welding head diameter is 100 mm, welding machine power is 60 KHz, pressure is 0.3 MPa, amplitude is 16 μm, and speed is 50 m/min.

The thickness of the tab assembly corresponding to the welding position is 9 μm, the thickness of the tab assembly corresponding to the extrusion area is 25 μm, and the thickness of the unwelded tab assembly is 22.5 μm.

The thickness of the transfer layer corresponding to the welding position is 8 μm, and the thickness of the transfer layer corresponding to the extrusion area is 11 μm.

The thickness of the tab at the welding position is 13.6 μm, and the thickness of the tab at the extrusion area is 16.6 μm.

The thickness of the conductive layer at the welding position is 0.8 μm, and the thickness of the polymer layer at the welding position is 4 μm.

The resistance of the tab before welding is 40mΩ. After welding, the resistance of the tab is about 23mΩ. The pulling force is about 16N. The IMP of the battery cell is 0.165Ω, and the DCR of the battery cell is 0.231Ω.

Test example

The parameters of the various thicknesses of the battery cell components of Examples 1-6 and the parameters of the welding process are shown in the following table. The electrical performance of the tabs obtained in Examples 1-6 is tested, and the testing method includes:

A battery cell made of the electrode sheets provided in Examples 1-6 was selected, with 280 layers, 105 positive electrode layers, and 105 or 106 negative electrode layers in a single battery cell. The corresponding battery cells were tested for resistance.

Select the six welded single-layer pole pieces provided in Examples 1-6, select a pole ear with a size of 120*90, refer to FIG. 2 , select two test points A and B at both ends of the pole ear surface, and place the resistance test probes at points A and B for detection.

Cell resistance test: Under the condition of AC 1KHZ/mΩ, test IMP (AC resistance), the standard is 0.10mΩ-0.20mΩ. Under the condition of 500A DC/37A CC, 30S, 50% SOC, 25℃, BOL, test DCR (DC resistance), the standard is DC≤0.5mΩ, CC≤0.5mΩ. The test results are as follows:

Table 1 Thickness parameters, welding process parameters and test results

It can be seen from the test results that compared with Example 2 and Example 3, Example 1 adopts a more suitable welding process. After welding, the thickness of the tabs, connecting sheets, conductive layers, transition layers, and tab assemblies in the welding position, extrusion area, and unwelded area is within the range recorded in this application, and the obtained tab resistance is reduced by half relative to the tab resistance before welding, which is less than the welded tabs provided in Example 2 and Example 3. It shows that the microstructure of the tab assembly provided in Example 1 has better electrical properties. The battery cell obtained by using the pole piece provided in Example 1 has lower resistance, higher capacity and cycle life. Example 4 adopts a more suitable welding process relative to Example 5 and Example 6, and has a better microstructure, so that the resistance of the tab after welding is less than the welded tab provided in Example 5 and Example 6. It can be seen that the battery cell obtained by using the pole piece and welding process provided in Example 4 has lower resistance, higher capacity and cycle life.

The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (9)

1. A pole piece, characterized in that a pole lug of the pole piece is provided with a welding area, a squeezing area and a part which is not welded, the welding area comprises a plurality of welding positions, the periphery of the welding position is provided with the squeezing area, the squeezing area is positioned between the welding position and the part which is not welded, and when in welding, the welding position is squeezed and the squeezing area is formed at the periphery of the welding position;

the thickness ratio of the tab of the extrusion area to the thickness of the tab of the welding position to the thickness of the non-welded part of the tab is (4-32): 2-12): 3-30.

2. The pole piece according to claim 1, wherein the tab comprises a base film and conductive layers arranged on two sides of the base film, and the ratio of the thickness of the base film of the tab at the welding position to the thickness of the base film of the tab which is not welded is 4 (5-7).

3. The pole piece of claim 2, wherein the ratio of the thickness of the conductive layer on one side of the tab of the weld site to the thickness of the conductive layer on one side of the tab that has not been welded is (7-9): 10.

4. A cell assembly comprising a connection tab and a cell, the cell comprising a pole piece according to any one of claims 1 to 3, the connection tab being welded to a tab of the pole piece.

5. The cell assembly of claim 4, wherein the tab comprises a base film and conductive layers disposed on both sides of the base film, the conductive layers on one side of the base film and the connection pads welded to the conductive layers form a transfer layer, and a ratio of a sum of thicknesses of the conductive layers of the tab and the connection pads, which are not welded, to a thickness of the transfer layer is (7-8): 6.

6. The cell assembly according to claim 4, wherein the connecting pieces are respectively arranged on two sides of the tab, the tab and the connecting pieces on two sides are welded to form a tab assembly, and the thickness ratio of the welded tab assembly to the non-welded tab assembly is 2 (3-5).

7. The cell assembly of claim 6, wherein the welding site has a crush zone at a periphery thereof, wherein a thickness of the tab assembly corresponding to the crush zone, a thickness ratio of the welded tab assembly to the non-welded tab assembly is 6:2 (3-5).

8. The cell assembly of claim 4, wherein the ratio of the resistance of the welded tab to the resistance of the non-welded tab is (5-6): 10.

9. a battery, characterized by comprising a shell, an insulating part, a top cover component and the battery cell component as claimed in any one of claims 4 to 8, wherein the battery cell component is contained in the shell, and the top cover component is covered on the shell and is connected with the battery cell component through a tab.

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