CN215266583U

CN215266583U - Pole piece, electric core subassembly and battery

Info

Publication number: CN215266583U
Application number: CN202120989654.7U
Authority: CN
Inventors: 李晓杰; 郭敏
Original assignee: Xiamen Haichen New Energy Technology Co Ltd
Current assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2021-05-10
Filing date: 2021-05-10
Publication date: 2021-12-21
Anticipated expiration: 2031-05-10

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 pole ear of the pole piece has a welding area, the welding area comprises a plurality of welding imprints, cracks are arranged between at least two adjacent welding imprints, and the number of the cracks with the width not less than 20 mu m is 1-10. The welding effect of the tab with the welding mark and the crack structure is good, and the probability of occurrence of over-welding and insufficient welding is reduced. The sheet resistance of the structure is small, so that the battery cell has high battery cell capacity and long cycle life.

Description

Pole piece, electric core subassembly and battery

Technical Field

The application relates to the technical field of lithium batteries, in particular to a pole piece, an electric core assembly and a battery.

Background

With the development of science and technology, lithium ion batteries are applied more and more in the fields of electric vehicles and the like, and the quality and performance of the lithium ion batteries are concerned more and more. In a lithium battery, a tab and an adapter plate are often connected by welding. Generally, ultrasonic welding or laser welding is adopted. In the welding process, the problem of insufficient soldering or over soldering is easily caused, the connection between the pole lug and the adapter sheet is influenced, and the electrical properties of the pole piece and the battery cell are influenced.

SUMMERY OF THE UTILITY MODEL

The utility model provides a pole piece, electric core subassembly and battery to reduce the probability of rosin joint or the overweld that utmost point ear welding appears.

In a first aspect, the present application provides a pole piece, a tab of the pole piece has a welding area, the welding area includes a plurality of welding imprints, at least two adjacent welding imprints have cracks therebetween, and the number of cracks having a width of not less than 20 μm is 1-10.

The application provides a utmost point ear of pole piece has on the utmost point ear and welds seal and crackle for the utmost point ear after the switching welds. The cracks have a direct effect on the resistance of the tab. The inventor of the application finds that the influence of the cracks with the width smaller than 20 mu m on the structure of the tab is small, and further the influence on the resistance of the tab is small. However, the crack with the width indicates that the welding strength is low, so that the problem of insufficient welding is likely to occur, and the use performance of the tab is affected. When the width of the crack between two adjacent welding marks is not less than 20 mu m, the welding process can realize the connection of the pole lug and the adapter plate and ensure the connection stability. And the number of the cracks is 1-10, which shows that the welding process has moderate effect on the pole lug and is not easy to generate the over-welding condition. The pole piece with the pole lug of the structure has small resistance, is beneficial to improving the electric capacity and the multiplying power of the battery core and the battery, and prolongs the cycle life of the battery.

In one possible implementation, the width of the crack is 20 μm to 300 μm.

The inventors of the present application have found that if the width of the crack is larger than 300 μm, the welding process is not suitable, and the crack is wider while causing other problems such as over-welding. The width of the crack is within the above range. The pole piece has good electrical property.

In one possible implementation, the length of the crack is 60% -99% of the shortest distance between two adjacent solder marks.

Cracks within this length range can indicate that the tab is subjected to a more suitable welding action. If the length of the crack on the tab is short, the influence on the structure of the tab is not great, possibly due to the small welding effect. If the welding action is small, insufficient welding may occur. If the length of the crack is too long, the influence of the crack on the tab is large, which also indicates that the welding action is too large, and the over-welding condition may occur, which may cause the welding mark to have the crack and influence the welding effect.

In one possible implementation manner, the direction in which the root of the tab extends from the pole piece defines the length direction of the tab, and the extension direction of the plurality of cracks of the tab is parallel to the length direction of the tab.

The current has the transmission direction in the transmission process, namely the current passes to the adaptor plate from the pole piece body through the pole ear. Cracks in the transmission direction have a large influence on the electrical properties of the tab. If the extending direction of the crack is vertical to the length direction of the tab, the crack is easy to block the transmission of current on the tab. The extending direction of the cracks is parallel to the length direction of the tab, so that the influence of the cracks on current transmission can be reduced, and the resistance of the tab is reduced.

In one possible implementation, the number of cracks having a width of not less than 20 μm between each two adjacent solder marks is the same.

The welding of the pole lug and the adapter plate is local welding, so that the joint of a welding area and a non-welding area and the pole lug of the welding area are possibly subjected to different welding actions, and further, cracks with different distributions are generated in the welding area. Various conditions may occur, such as different crack widths, different crack lengths, and different crack propagation directions, which may adversely affect the electrical performance of the tab. The structure enables the distribution condition of cracks to have small influence on the resistance of the pole lug, and simultaneously shows that the pole lug is subjected to uniform welding action, thereby being beneficial to reducing the condition of over-welding or insufficient welding at the local part of a welding area.

In one possible implementation, the size of the solder marks is (1-2) mm x (1-2) mm, and the shortest distance between two adjacent solder marks is 2mm-4 mm.

The size of the weld mark and the spacing helps to reduce the formation of cracks. If the pitch is small, a large number of cracks are easily formed, and if the pitch is large, the welding effect may be reduced.

In one possible implementation mode, a plurality of welding imprints are arranged in a matrix mode, and the arrangement direction of any one row of welding imprints is parallel to or perpendicular to the length direction of the tab.

In one possible implementation, the pole piece is a pole piece containing a composite current collector.

In a second aspect, an electric core assembly is provided, which comprises an adapter sheet and the above-mentioned pole piece, wherein the adapter sheet and the pole lug of the pole piece are welded to form a welding mark. The battery core has better electric capacity.

The third aspect provides a battery, including casing, top cap subassembly and above-mentioned electric core subassembly, the electric core subassembly is acceptd in the inside of casing, and the casing is located to top cap subassembly lid, and is connected with the electric core subassembly through utmost point ear. The battery adopts the above-mentioned electric core assembly, has better electric capacity and cycle life.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.

Fig. 1 is a structural schematic diagram of cracks of a tab after welding according to an embodiment of the present application;

fig. 2 is a structural schematic diagram of cracks of another post-welded tab provided in the embodiment of the present application;

fig. 3 is a schematic diagram of tab resistance detection according to the test example of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Some embodiments of the present application will be described in detail below with reference to the accompanying drawings.

The embodiment provides a pole piece, and the pole piece is welded with a patch to realize the leading-out of current. In some embodiments of the present application, the pole piece and the interposer are welded by ultrasonic welding and/or laser welding, and in the welding process, improper welding process may cause damage to the tab, such as cracks in the tab, increase the resistance of the tab, and affect the electrical properties of the pole piece and the electrical core. The inventor of the application finds that the current welding process is easy to generate cracks on the tab and affect the electrical property of the tab, but not all cracks have obvious influence on the electrical property of the tab.

The present embodiment provides a pole piece, which is electrically connected to positive and negative poles of a battery cell through an adapter sheet. The electrode plate adopted in the embodiment of the application is an electrode plate containing a composite current collector, and the material of the base film in the composite current collector may be at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, polyethylene glycol, polyamide imide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, polyvinylidene fluoride-hexafluoropropylene, poly (vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene oxide, polyester, polysulfone, and derivatives thereof. The conductive layers on both sides of the base film may be made of 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 combinations (alloys) thereof.

The pole piece is welded and then provided with a welding area, and the welding area comprises a plurality of welding imprints. At least two adjacent solder marks have cracks between them. Wherein the number of cracks having a width of not less than 20 μm is 1 to 10. The cracks with small width can be generated in the welding process, and the research of the inventor of the application finds that the cracks with the width less than 20 mu m have small influence on the structure of the tab, and further have small influence on the resistance of the tab. However, the crack with the width indicates that the welding strength is low, so that the problem of insufficient welding is likely to occur, and the use performance of the tab is affected. The width of the crack is more than or equal to 20 mu m, which shows that the welding process can realize the connection of the pole lug and the adapter plate and ensure the connection stability. Further, the width of the crack is 20 μm to 300 μm. If the width of the crack is greater than 300 μm, the welding process is not suitable, and the crack may be wider while causing other problems, such as over-welding. Therefore, the inventor obtains the welded pole piece with better electrical property through the relation between the cracks on the pole lug and the welding process, and the current on the pole lug is better transmitted.

The inventors of the present application have also found that in addition to its width having an effect on electrical performance, the length of the cracks on the tab also has an effect. The length of the crack is 60% -99% of the shortest distance between two adjacent welding marks. Cracks within this length range can indicate that the tab is subjected to a more suitable welding action. If the length of the crack on the tab is short, the influence on the structure of the tab is not great, possibly due to the small welding effect. If the welding action is small, insufficient welding may occur. If the length of the crack is too long, the influence of the crack on the tab is large, which also indicates that the welding action is too large, the over-welding condition may occur, and the welding effect may be influenced by the crack of the welding mark. Optionally, the length of the crack is 65%, 75%, 80%, 85%, 90%, 95%, or 99% of the shortest distance between two adjacent solder marks.

The solder prints in the embodiments of the present application are generally arranged in a matrix. Furthermore, the direction of the lug extending from the pole piece from the root of the lug is defined as the length direction of the lug, a plurality of welding prints are arranged in a matrix, and the arrangement direction of any one row of welding prints is parallel or vertical to the length direction of the lug. The weld marks structure enables the extension direction of cracks between the weld marks to be parallel or perpendicular to the length direction of the tab. The current has the transmission direction in the transmission process, namely the current passes to the adaptor plate from the pole piece body through the pole ear. Cracks in the transmission direction have a large influence on the electrical properties of the tab.

The number of the cracks in the embodiment of the application is 1-10, and the number range enables the influence of the cracks vertical to the length direction of the tab on the electrical property of the tab to be low, so that the transmission of current blocked by the cracks is avoided. Optionally, the number of cracks is 2, 3, 4, 5, 7 or 8. The cracks in the embodiment of the application can be detected by a microscopic scanning detection instrument, the specific detection method is a conventional technology in the technical field, and the application does not limit the detection method. In addition, other conventional detection instruments can be used for detection.

In the present application, the extending direction of the crack between two adjacent welds is the same, that is, the crack receives the same action, and no crossing crack is generated.

The welding of the pole lug and the adapter plate is local welding, so that the joint of a welding area and a non-welding area and the pole lug of the welding area are possibly subjected to different welding actions, and further, cracks with different distributions are generated in the welding area. Various conditions may occur, such as different crack widths, different crack lengths, and different crack propagation directions, which may adversely affect the electrical performance of the tab. Through the research of the inventor of the application, the inventor finds that the influence on the resistance of the tab is small when the number of cracks with the width not less than 20 mu m between every two adjacent welding marks is the same, and also shows that the tab is subjected to uniform welding action, so that the condition of over-welding or insufficient welding is avoided locally on the welding area.

In the research process, the inventor of the application finds that the distance between the welding marks can also influence the welding effect. In some embodiments of the present application, the size of the solder marks is (1-2) mm x (1-2) mm, and the shortest distance between two adjacent solder marks is 2mm-4 mm. The size of the weld mark and the spacing helps to reduce the formation of cracks. If the pitch is small, a large number of cracks are easily formed, and if the pitch is large, the welding effect may be reduced. Optionally, each solder mark has the same size, and the distance between two adjacent solder marks is the same.

The application also provides an electric core component, including adaptor piece and above-mentioned pole piece, the soldering of utmost point ear welding formation of adaptor piece and pole piece welds the seal. The battery core has better electric capacity.

The application also provides a battery, including casing, top cap subassembly and above-mentioned electric core subassembly, the electric core subassembly is acceptd in the inside of casing, and the casing is located to top cap subassembly lid, and is connected with the electric core subassembly through utmost point ear. The battery adopts the above-mentioned electric core assembly, has better electric capacity and cycle life.

The embodiment of the application mainly adopts an ultrasonic welding process to weld, and comprises the following steps:

a40 KHz ultrasonic horn is used, the diameter of which is about 100 mm. The pole ear and the adapter plate are welded under the conditions that the welding pressure (cylinder pressure) is 0.2-0.5MPa, the linear speed of the ultrasonic welding head is 30-50 m/min, and the amplitude of ultrasonic waves is 10-16 mu m. Optionally, the welding pressure is 0.2MPa, 0.3MPa, 0.4MPa, or 0.5 MPa. The linear speed of the ultrasonic welding head is 30m/min, 35m/min, 40m/min, 45m/min or 50 m/min. The amplitude of the ultrasonic wave is 10 μm, 12 μm, 13 μm, 15 μm or 16 μm.

Under the same other conditions, different ultrasonic welding pressures are adjusted to form different welding effects: the ultrasonic welding pressure is too high, and the welding head generates too high pressure on the lug part of the welding part. Since the thickness of the material of the tab part is only 50 μm, deformation, wrinkling and fracture are easily generated, and the deformation is larger as the welding pressure is larger. When the deformation is large enough, the crack carding of the conductive layer on the current collector is gradually increased, and even the crack is directly converted into fracture, so that the conductive network is interrupted; when the welding pressure is too small, the welding head cannot be effectively attached to weld the lug due to insufficient physical attachment, so that the energy of ultrasonic waves cannot be transmitted in time, a cold joint is generated, the pressure is smaller, the welded tensile force test value is smaller, and a conductive network cannot be effectively formed.

Different linear velocities can decide the crackle that the vertical power of pulling in utmost point ear surface after the welding produced, when the speed ratio proportion of the rotation rate of the receipts of pole piece and unreeling linear velocity and bonding tool is great (if be greater than 1.3), can lead to the vertical power of pulling in surface too big to make utmost point ear surface conducting layer receive the drawing of receiving and unreeling the direction, produce more crackles, when the proportion is bigger, can lead to the conducting layer fracture, electrically conductive network fracture.

The influence of the amplitude on the welding effect mainly lies in the effect of ultrasonic energy action, the amplitude is overlarge, the energy penetrability is strong, and the welding penetration is easy; too small amplitude, insufficient energy penetration, and easy cold joint.

The thickness of the tab (composite current collector) is 5-15 μm, after welding, the size of a welding mark formed on the tab is (1-2) mmx (1-2) mm, the shortest distance between two adjacent welding marks is 2-4 mm, and a crack is formed between the two adjacent welding marks. Referring to fig. 1 and 2, fig. 1 and 2 are schematic structural diagrams of cracks of a tab after welding in two welding processes, respectively. The cracks between the welding imprints of the electrode lug in the figure 1 are mainly distributed in the transverse direction, the number of the cracks (the width is more than 20 mu m) between two adjacent welding imprints is 1-2, and the length of the cracks is 80% -90% of the distance between two adjacent welding imprints. The cracks between the welding imprints of the tab in fig. 2 are distributed in the transverse direction and the longitudinal direction, the number of the cracks (the width is more than 20 μm) between two adjacent welding imprints is 1, and the length of the cracks is 80-90% of the distance between two adjacent welding imprints. If the resistance of the tab of the single pole piece before welding is 90 omega, the resistance of the tab of the single pole piece after welding is 45 omega. The welded tab has better electrical property.

The features and properties of the present application are described in further detail below with reference to examples.

Example 1

The embodiment provides an electric core assembly, mainly welds utmost point ear and adaptor piece through following welding process:

an ultrasonic welding device is adopted, the diameter of a welding head is 100mm, the diameter of a welding tooth is 1-2mm, and the power of a welding machine is 40 KHz. The pole pieces are subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 100 mu m, the linear speed of a welding head is 80m/min, and the tape speed is 50 m/min. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 20 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 1mm, the number of cracks is 4-6, the length of each crack is 0.8mm-0.9mm, and the width of each crack is 200 mu m.

Example 2

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 100 mu m, the linear speed of the welding head is 100m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head diameter of 100mm, a welding tooth diameter of 1-2mm and welding machine power of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 24 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 1mm, the number of cracks is 4-6, the length of each crack is 0.9mm-0.95mm, and the width of each crack is 300 mu m.

Example 3

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 100 mu m, the linear speed of the welding head is 70m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head diameter of 100mm, a welding tooth diameter of 1-2mm and welding machine power of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 20 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 1.5mm, the number of cracks is 1, the length of each crack is 0.7mm-0.75mm, and the width of each crack is 60 micrometers.

Example 4

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 150 mu m, the linear speed of the welding head is 70m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head diameter of 100mm, a welding tooth diameter of 1-2mm and welding machine power of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 24 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 1.5mm, the number of cracks is 1, the length of each crack is 0.85mm-0.9mm, and the width of each crack is 100 micrometers.

Example 5

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 100 mu m, the linear speed of the welding head is 100m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head diameter of 100mm, a welding tooth diameter of 1-2mm and welding machine power of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 20 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 2mm, the number of cracks is 3-4, the length of each crack is 1.3mm-1.4mm, and the width of each crack is 20 micrometers.

Example 6

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 2mm, the number of cracks is 3-4, the length of each crack is 1.3mm-1.4mm, and the width of each crack is 40 micrometers.

Example 7

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 150 mu m, the linear speed of the welding head is 140m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head with the diameter of 100mm, the diameter of welding teeth of 1-2mm and the power of a welding machine of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 30 omega.

After welding, the sizes of the welding marks on the electrode lugs are 1mm multiplied by 1mm, the distance between every two adjacent welding marks is 5mm, the number of cracks is 3-4, the length of each crack is 4mm-4.2mm, and the width of each crack is 340 micrometers.

Example 8

the electrode plate is subjected to transfer welding under the process conditions that the pressure of a welding cylinder is 0.3MPa, the amplitude of ultrasonic waves is 100 mu m, the linear speed of the welding head is 80m/min and the tape speed is 50m/min by adopting ultrasonic welding equipment with a welding head diameter of 100mm, a welding tooth diameter of 1-2mm and welding machine power of 40 KHz. The pole piece of the battery cell is a pole piece containing a composite current collector, and the resistance of the pole lug of the single-layer pole piece is 30 omega.

After welding, the size of the welding marks on the tab is 1mm multiplied by 1mm, the distance between two adjacent welding marks is 0.5mm, the number of cracks is 10-13, the length of the crack is 0.4-0.5mm, and the width of the crack is 10-30 μm.

Test examples

Parameters of the welding process of examples 1 to 6 are shown in table 1, and the tab obtained in examples 1 to 6 was subjected to electrical property detection, the detection method including:

the cell prepared from the pole pieces provided in examples 1 to 6 was selected, and the number of layers was 280, and the positive electrode 105 and the negative electrode 105 or 106 in a single cell. And respectively carrying out resistance detection on the corresponding battery cores.

Selecting six welded single-layer pole pieces provided in examples 1-6, selecting a tab with the size of 120 x 90, referring to fig. 3, selecting two test points a and B at two ends of the tab surface, and placing a resistance test probe at point A, B for detection.

Detecting the cell resistance: IMP (alternating current resistance) is detected under the condition that the alternating current is 1KHZ/m omega, and the standard is 0.10m omega-0.20 m omega. DCR (direct current resistance) is detected under the conditions of 500A DC/37A CC, 30S, 50% SOC, 25 ℃ and BOL, and the standard is that DC is less than or equal to 0.5m omega, and CC is less than or equal to 0.5m omega. The detection results are shown in table 1:

because the welding imprints on the lugs of the welded single-layer pole pieces provided by the embodiments 1-6 are of a square structure, the resistance test is carried out on the welding imprints by adopting a four-probe method, and the test method comprises the following steps: the four probes for double electricity measurement are arranged in a straight line at equal intervals and are arranged at equal intervals. The tips of the probes are pressed on the surfaces of the tabs, the outer two probes are electrified by current I, and the inner two probes are used for measuring voltage V, and generally by using a potentiometer. The calculation formula of the resistance is:

where c is a correction coefficient, and c is 4.53.

The results are shown in Table 1:

TABLE 1 welding Process parameters and test results

As can be seen from the test results, in example 1-2, the distribution of cracks on the welded tab of example 1 was relatively uniform, and the width and length of the cracks were relatively small, indicating that the surface damage of the tab of example 1 was relatively small, the sheet resistance of the tab before and after welding was substantially unchanged, and the resistance of the tab after welding was substantially equal to one-half of the resistance of the tab without welding. The surface of the tab of example 2 was damaged more, the sheet resistance of the tab after welding was increased more, and the resistance of the tab after welding was greater than one-half of the resistance of the tab without welding. The resistance of the cell provided in example 1 is less than the resistance of the cell of example 2.

The resistance of the welding mark can be used for judging the extending direction of the crack, and the resistance with problems can be found out by detecting the resistance of each welding mark so as to adjust the welding process and eliminate the abnormity.

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

Claims

1. A pole piece, characterized in that a tab of the pole piece has a weld zone comprising a plurality of weld imprints with cracks between at least two adjacent weld imprints, wherein the number of cracks having a width not less than 20 μm is 1-10.

2. The pole piece of claim 1 wherein the cracks are 20 μ ι η to 300 μ ι η in width.

3. The pole piece of claim 2 wherein the length of the crack is 60% to 99% of the shortest distance between two adjacent welds.

4. The pole piece of claim 2, wherein the direction in which the tab extends from the pole piece from the root of the tab is defined as a longitudinal direction of the tab, and the direction in which the crack extends is parallel to the longitudinal direction of the tab.

5. The pole piece of claim 2 wherein there are the same number of cracks between each two adjacent welds of width no less than 20 μm.

6. The pole piece of claim 2, wherein the solder marks have a size of (1-2) mm x (1-2) mm, and a shortest distance between two adjacent solder marks is 2mm-4 mm.

7. The pole piece of claim 4, wherein a plurality of said solder prints are arranged in a matrix, and the direction of arrangement of any one row of said solder prints is parallel or perpendicular to the length direction of said tab.

8. The pole piece of claim 1, wherein the pole piece is a pole piece containing a composite current collector.

9. An electric core assembly comprising an adaptor sheet and a pole piece as claimed in any one of claims 1 to 8, said adaptor sheet being welded to a tab of said pole piece.

10. A battery comprising a housing, a cap assembly and the electric core assembly of claim 9, wherein the electric core assembly is contained in the housing, and the cap assembly covers the housing and is connected to the electric core assembly via tabs.