Positive plate and battery cell

Abstract

The positive plate comprises a current collector and a coating, the surface of the current collector is coated with the coating, the coating comprises a first area and a second area which are sequentially and alternately distributed in the length direction of the current collector, and the first area and the second area are arranged on the surface of the current collector. The percentage content of the active substance in the second area is lower than that of the active substance in the first area; wherein the positive plate is configured as follows: when the positive plate is wound to form a battery cell, the battery cell is provided with a straight part and arc parts connected to two opposite sides of the straight part, and the second area at least forms the arc parts. According to the positive plate, by reducing the percentage content of the active material in the second region, the number of lithium ions in the arc part formed in the second region is reduced, so that the probability of lithium precipitation is reduced, and the use safety and the structural stability are improved. The utility model is applied to the field of secondary batteries.

Description

Technical Field

[0001] The utility model relates to the field of secondary batteries, in particular to a positive electrode sheet and a battery core. Background Art

[0002] In the related art, when the cell of a square battery is made by winding, the cell has a straight portion and an arc portion. During the winding process, the stress on the arc portion is greater than that on the straight portion. During the charging process of the battery in a cyclic use, the negative electrode sheet has a large volume effect, which further increases the stress on the arc portion, thereby causing lithium deposition on the surface of the electrode sheet in the arc portion, affecting the safety of use and the stability of the structure. The reason why the negative electrode sheet has a large volume effect during charging is that during the charging process, the lithium ions in the positive electrode sheet are embedded in the negative electrode sheet. Utility Model Content

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a positive electrode sheet that can reduce the probability of lithium deposition and improve the safety of use and structural stability.

[0004] The positive electrode sheet according to the first embodiment of the utility model comprises:

[0005] current collector;

[0006] A coating layer, applied to the surface of the current collector, the coating layer comprising a first region and a second region alternately distributed in sequence along the length direction of the current collector, wherein the percentage of active material in the second region is lower than the percentage of active material in the first region;

[0007] Wherein, the positive electrode sheet is configured such that when the battery cell is wound to form a battery cell, the battery cell has a straight portion and arc portions connected to two opposite sides of the straight portion, and the second area at least forms the arc portion.

[0008] The positive electrode sheet according to the embodiment of the first aspect of the utility model has at least the following beneficial effects: during the charging process, because the percentage of active material in the positive electrode sheet in the area where the arc portion is located is reduced, the number of ions that can be deintercalated by the positive electrode sheet in the area where the arc portion is located is reduced, thereby reducing the volume effect of the negative electrode sheet in the arc portion, reducing the stress on the arc portion, reducing the probability of lithium deposition, and improving the safety of use and structural stability.

[0009] According to some embodiments of the present invention, the percentage of active material in the first zone is W1, the percentage of active material in the second zone is W2, and the positive electrode sheet satisfies: 95%≤W1≤97%, 60%≤W2≤70%.

[0010] According to some embodiments of the present invention, the coating has a first layer and a second layer along a direction away from the current collector.

[0011] According to some embodiments of the utility model, a surface of the first layer away from the current collector is provided with a plurality of first interlocking portions, a surface of the second layer opposite to the first layer is provided with a plurality of second interlocking portions, the first interlocking portions correspond one-to-one to the second interlocking portions, and the first interlocking portions are interlocked in the corresponding second interlocking portions.

[0012] According to some embodiments of the present invention, the positive electrode sheet is configured such that, when forming a battery cell, the first region forms the straight portion, and the second region forms the arc portion.

[0013] According to some embodiments of the present invention, the distance of the first region along the length direction of the current collector is L2, and the positive electrode sheet satisfies: L2 = L k ;

[0014] L k : When forming a battery cell, the width of the straight portion between the two arc portions.

[0015] According to some embodiments of the present invention, the coating is provided with n second groups sequentially distributed along the length direction of the current collector, the second group includes two second regions of equal length along the length direction of the current collector, along the length direction of the current collector, the length of the second regions in the n second groups along the length direction of the current collector increases gradually, and the distance of the second regions in the second group along the length direction of the current collector is L n , the positive electrode sheet satisfies: L n =πR n ;

[0016] R n : The radius of the arc portion of the battery cell during the nth winding.

[0017] According to some embodiments of the present invention, the coating includes 2n+1 second regions, 2n second regions form n second groups, n second groups and 2n+1 second regions are sequentially distributed along the length direction of the current collector, and the distance between the 2n+1 second regions along the length direction of the current collector is L. n+1 , the positive electrode sheet satisfies: L n+1 =πR n+1 .

[0018] According to the battery cell of the embodiment of the second aspect of the utility model, a winding body is formed by winding a stack, and the winding body includes a straight portion and an arc portion connected to two opposite sides of the straight portion. The stack includes the positive electrode sheet described in the embodiment of the first aspect of the utility model, and the second area of ​​the positive electrode sheet at least forms the arc portion.

[0019] The battery cell according to the embodiment of the second aspect of the utility model has at least the following beneficial effects: using the positive electrode sheet of the embodiment of the first aspect of the utility model can reduce the probability of lithium deposition in the arc portion, thereby improving the safety of use and structural stability.

[0020] According to some embodiments of the utility model, the stack includes a first diaphragm, a first pole piece, a second diaphragm and a second pole piece stacked in sequence, the polarity of the first pole piece is opposite to that of the second pole piece, and the first pole piece or the second pole piece is the positive pole piece.

[0021] According to some embodiments of the present invention, the second electrode is the positive electrode, and the positive electrode satisfies: R n =(h1+h3+h4)*n+h2*(n-1);

[0022] n: the number of windings of the second pole piece;

[0023] R n : The radius of the arc portion of the battery cell during the nth winding;

[0024] h1: the total thickness of the double-sided coating and the current collector of the first pole piece in the double-sided coating area;

[0025] h2: the total thickness of the double-sided coating and the current collector of the second pole piece in the double-sided coating area;

[0026] h3: thickness of the first diaphragm;

[0027] h4: thickness of the second diaphragm.

[0028] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is further described below with reference to the accompanying drawings and embodiments, wherein:

[0030] Figure 1 This is a schematic structural diagram of a positive electrode sheet according to an embodiment of the utility model;

[0031] Figure 2 This is an exploded schematic diagram of a positive electrode sheet according to an embodiment of the utility model;

[0032] Figure 3 The figure is a schematic diagram of the structure of a battery cell according to an embodiment of the utility model.

[0033] Figure Number:

[0034] Current collector 100;

[0035] Coating 200; first zone 210; second zone 220; first layer 230; first interlocking portion 231; second layer 240; second interlocking portion 241;

[0036] Straight portion 300;

[0037] Arc portion 400. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0039] In the description of the present invention, it should be understood that the descriptions involving orientation, such as the orientation or positional relationship indicated as up, down, etc., are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0040] In the description of the present utility model, "several" refers to one or more, and "multiple" refers to two or more. If there is a description of "first" or "second", it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0041] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0042] In the related art, a square battery includes a shell and a battery cell. The shell is generally in the shape of a rectangle, so it is called a square battery cell. The shell also has a rectangular chamber. The battery cell is arranged in the chamber and is electrically connected to the shell. After the battery cell is wound, in order to be placed in the rectangular chamber, a rectangular clamp is generally used as a winding axis. The wound battery cell will have a straight portion 300 and two arc portions 400. The two arc portions 400 are respectively located on two opposite sides of the straight portion 300. The straight portion 300 is in the shape of a rectangle to fully fill the space in the chamber. Among them, during the winding process of the battery cell, there will be winding tension so that the winding body can be shaped after winding, and the arc portion 400 is the concentrated area of ​​the winding tension, so it is subjected to greater stress. The negative electrode sheet located at the arc portion 400 is affected by the stress, resulting in a decrease in the pores of the negative electrode sheet. Some pores will not be able to allow lithium ions to enter, causing the lithium ions to concentrate on the surface of the negative electrode sheet, causing lithium precipitation. During the charging process of the negative electrode sheet, the increase in the volume of the negative electrode sheet causes an increase in pressure, which will further aggravate the precipitation of lithium ions.

[0043] Reference Figures 1 to 3 As shown, the first embodiment of the utility model proposes a positive electrode sheet, including: a current collector 100 and a coating 200, the coating 200 is coated on the surface of the current collector 100, the coating 200 includes a first area 210 and a second area 220 alternately distributed in sequence along the length direction of the current collector 100, the percentage of active material in the second area 220 is lower than the percentage of active material in the first area 210; wherein, the positive electrode sheet is configured as follows: when winding to form a battery cell, the battery cell has a straight portion 300 and an arc portion 400 connected to two opposite sides of the straight portion 300, and the second area 220 at least forms the arc portion 400. The positive electrode sheet in this embodiment reduces the percentage of active material in the second area 220 to reduce the number of lithium ions in the arc portion 400 formed by the second area 220, thereby reducing the probability of lithium precipitation and improving the safety of use and structural stability.

[0044] In this embodiment, the current collector 100 is an aluminum foil, which is generally in the shape of a long strip. The coating 200 is a positive electrode coating. The positive electrode coating includes active substances and other substances. The other substances generally include conductive agents and adhesives. The active substances contain conductive ions, such as lithium ions, sodium ions, etc. Taking the active substances containing lithium ions as an example, the active substances can generally be lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese oxide or lithium iron phosphate, etc.

[0045] The percentage of active material refers to the content of active material in the entire positive electrode coating. When the percentage of active material decreases, the lithium ion content contained in the positive electrode coating also decreases accordingly. When the percentage of active material in the second area 220 of the positive electrode sheet decreases, the lithium ion content of the arc portion 400 formed by the second area 220 decreases, thereby reducing the probability of lithium precipitation.

[0046] In addition, when the percentage of active material in the second area 220 decreases, it will be reduced to the overall capacity of the battery. In order to avoid the reduction of the overall capacity of the battery, the active material reduced in the second area 220 can be added to the first area 210, so that the total percentage of active material in the positive electrode sheet remains unchanged, so as to maintain the overall capacity of the battery unchanged.

[0047] It is worth understanding that during the charging process, because the percentage of active material in the positive electrode sheet in the area where the arc portion 400 is located is reduced, the number of ions that can be deintercalated by the positive electrode sheet in the area where the arc portion 400 is located is reduced, thereby reducing the volume effect of the negative electrode sheet in the arc portion 400, reducing the stress on the arc portion 400, reducing the probability of lithium deposition, and improving safety of use and structural stability.

[0048] Reference Figure 1 As shown, in some specific embodiments of the present invention, the percentage content of active material in the first area 210 is W1, the percentage content of active material in the second area 220 is W2, and the positive electrode sheet satisfies: 95%≤W1≤97%, 60%≤W2≤70%.

[0049] It should be noted that the mass of active material in the first zone 210 and the second zone 220 is not necessarily the same, which is specifically related to the length of all straight portions 300 and the length of all arc portions 400. When the length of all straight portions 300 is much greater than the length of all arc portions 400, the mass of active material in the first zone 210 is much greater than the mass of active material in the second zone 220. Even if the active material reduced in the second zone 220 is added to the first zone 210, the increase in the percentage of active material in the first zone 210 is still limited, and the impact on the first zone 210 is also limited. The straight portion 300 corresponding to the first zone 210 will not have the risk of lithium plating during charging due to the increase in active material.

[0050] Specifically, the percentage of active material in the positive electrode sheet is generally above 90%. In this embodiment, when the positive electrode sheet is uniformly coated, the percentage of active material in the positive electrode sheet is 95%, and when the percentage of active material in the second zone 220 is reduced to 60%, the percentage of active material in the first zone 210 is 97%.

[0051] Reference Figure 2 As shown, in some specific embodiments of the present invention, the coating 200 has a first layer 230 and a second layer 240 along a direction away from the current collector 100 .

[0052] It is worth understanding that the coating 200 has a first layer 230 and a second layer 240, and the content of other substances in the first layer 230 may be different from the content of other substances in the second layer 240. Specifically, the content of the conductive agent in the first layer 230 is greater than the content of the conductive agent in the second layer 240, so that the lithium ions in the coating 200 attached to the surface of the current collector 100 can have more conductive channels to move to the surface of the coating 200 and enter the negative electrode sheet, thereby reducing the internal resistance of the battery and improving the performance of the battery.

[0053] Reference Figure 2 As shown, in some specific embodiments of the present invention, a first layer 230 is provided with a plurality of first interlocking portions 231 on a side away from the current collector 100, and a second layer 240 is provided with a plurality of second interlocking portions 241 on a side relative to the first layer 230, and the first interlocking portions 231 correspond to the second interlocking portions 241 one by one, and the first interlocking portions 231 are interlocked in the corresponding second interlocking portions 241.

[0054] It is worth understanding that the first layer 230 and the second layer 240 are embedded as a whole through the first embedding portion 231 and the second embedding portion 241, so that the connection between the first layer 230 and the second layer 240 is more reliable, and when the first layer 230 and the second layer 240 are wound, part of the stress will be converted into the embedding force of the first embedding portion 231 and the second embedding portion 241 to reduce the stress and strengthen the connection tightness between the first layer 230 and the second layer 240.

[0055] In this embodiment, the first fitting part 231 includes a first convex part and a first recessed part, the second fitting part 241 includes a second convex part and a second recessed part, the second convex part corresponds to the first recessed part, so as to fit into the first recessed part, and the second recessed part corresponds to the first convex part, so as to fit into the first convex part, to realize the fitting of the first fitting part 231 and the second fitting part 241.

[0056] In some specific embodiments of the present invention, the positive electrode sheet is configured as follows: when forming a battery cell, the first area 210 forms a straight portion 300, and the second area 220 forms an arc portion 400. The winding body formed by winding the positive electrode sheet one circle includes two arc portions 400 and two layers of upper and lower straight portions, and the two layers of straight portions are stacked to form a straight portion 300. One first area 210 corresponds to one straight portion, and one second area 220 corresponds to one arc portion. Therefore, each circle of the positive electrode sheet includes two first areas 210 and two second areas 220, wherein the two first areas 210 included in one circle of the positive electrode sheet form a first group, and the two second areas 220 included in one circle of the positive electrode sheet form a second group.

[0057] It is worth understanding that the first area 210 forms the straight portion 300, and the second area 220 forms the arc portion 400, so that the active material in the first area 210 can be fully utilized, and the active material in the second area 220 can also reduce the risk. However, in actual use, due to the influence of errors, it is impossible to ensure that the second area 220 just completely forms the arc portion 400. Generally, it is necessary to increase the length of the second area 220 along the length direction so that the second area 220 forms the arc portion 400 and forms part of the straight portion 300 to ensure that the second area 220 can completely form the arc portion 400.

[0058] When the straight portion 300 is formed in the first region 210, the distance of the first region 210 along the length direction of the current collector 100 is L2, and the positive electrode sheet satisfies: L2 = L k ; L k : The width of the straight portion 300 between the two arc portions 400 when forming a battery cell.

[0059] When the arc portion 400 is formed in the second region 220, the length of the second region 220 increases with the number of windings, and when winding one circle, two second regions 220 form two arc portions 400, and the lengths of the two second regions 220 along the length direction of the current collector 100 are equal, so the specific situation includes the following:

[0060] 1. When the number of the second regions 220 is an even number and the number is 2n, the coating 200 is provided with n second groups distributed in sequence along the length direction of the current collector 100, and the second group includes two second regions 220 of equal length along the length direction of the current collector 100. Along the length direction of the current collector 100, the lengths of the second regions 220 in the n second groups along the length direction of the current collector 100 increase gradually, and the distance between the second regions 220 in the second group along the length direction of the current collector 100 is L n , the positive electrode satisfies: L n =πR n ;

[0061] R n : The radius of the arc portion 400 of the battery cell during the n-th winding.

[0062] 2. When the number of the second regions 220 is odd, the coating 200 includes 2n+1 second regions 220, the 2n second regions 220 form n second groups, the n second groups and the 2n+1 second regions 220 are sequentially distributed along the length direction of the current collector 100, and the distance between the 2n+1 second regions 220 along the length direction of the current collector 100 is L n+1 , the positive electrode satisfies: L n+1 =πR n+1 .

[0063] Reference Figure 1 and Figure 3 As shown, the second embodiment of the present invention proposes a battery cell, which is formed by winding a stacked body, the wound body includes a straight portion 300 and an arc portion 400 connected to two opposite sides of the straight portion 300, the stacked body includes the positive electrode sheet of the first embodiment of the present invention, and the second area 220 of the positive electrode sheet at least forms the arc portion 400.

[0064] In this embodiment, the stack includes a first diaphragm, a first electrode sheet, a second diaphragm and a second electrode sheet stacked in sequence, the polarity of the first electrode sheet is opposite to that of the second electrode sheet, and when the stack is wound along one end of its length direction to form a wound body, the wound body has a straight portion 300 and an arc portion 400 connected to two opposite sides of the straight portion 300, the first electrode sheet, the second electrode sheet, the first diaphragm and the second diaphragm together form the arc portion 400, wherein the first pole sheet or the second pole sheet is a positive electrode sheet, the second area 220 of the positive electrode sheet forms the arc portion 400, and the first area 210 of the positive electrode sheet forms the straight portion 300, so as to reduce the probability of lithium deposition in the arc portion 400, thereby improving the safety of use and the structural stability.

[0065] In some specific embodiments of the present invention, the second electrode is a positive electrode, and the positive electrode satisfies: R n =(h1+h3+h4)*n+h2*(n-1);

[0066] n: the number of windings of the second pole piece;

[0067] R n : The radius of the arc portion 400 of the battery cell during the nth winding;

[0068] h1: the total thickness of the double-sided coating and the current collector of the first pole piece in the double-sided coating area;

[0069] h2: the total thickness of the double-sided coating and the current collector of the second pole piece in the double-sided coating area;

[0070] h3: thickness of the first diaphragm;

[0071] h4: thickness of the second diaphragm.

[0072] It is worth understanding that when the second electrode is the positive electrode, the first electrode is located at the center of the winding. When the first winding is performed, the first electrode is located on the side of the second electrode facing the winding center. Therefore, the radius of the arc portion 400 of the positive electrode needs to be added with the thickness of the first electrode, and the thickness of the first diaphragm and the second diaphragm. Then, the radius of the positive electrode when the first winding is performed is calculated, and the above formula is obtained by analogy, R nThe radius of the positive electrode sheet corresponding to the nth winding is designed based on the distance of the second area 220 of the positive electrode sheet along the length direction of the positive electrode sheet. In addition, when the first substrate is the positive electrode sheet, the first substrate is located at the center of the winding. When the first winding is completed, the radius of the arc portion 400 of the positive electrode sheet only needs to be added with the thickness of the first diaphragm to calculate the radius of the positive electrode sheet when the first winding is completed. By analogy, the calculation formula is R n =h1*n+(h2+h3+h4)*(n-1), R n Corresponding to the nth winding, the radius of the positive electrode sheet is designed based on the distance of the second area 220 of the positive electrode sheet along the length direction of the positive electrode sheet.

[0073] In addition, the length of the straight portion 300 is determined by the size of the battery cell. Battery cells of different sizes have straight portions 300 of different sizes, and can be designed according to actual needs. Moreover, the length of the first area 210 of the positive electrode sheet corresponding to the straight portion 300 along the length direction of the positive electrode sheet is equal. Therefore, after the size of the battery cell is determined, the length of the straight portion 300 of the battery cell is determined, and the length of the first area 210 of the positive electrode sheet can also be directly calculated. When the length of the first area 210 and the length of the second area 220 are determined, the overall size of the positive electrode sheet is determined.

[0074] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: current collector; A coating layer, applied to the surface of the current collector, the coating layer comprising a first region and a second region alternately distributed in sequence along the length direction of the current collector, wherein the percentage of active material in the second region is lower than the percentage of active material in the first region; Wherein, the positive electrode sheet is configured such that when the battery cell is wound to form a battery cell, the battery cell has a straight portion and arc portions connected to two opposite sides of the straight portion, and the second area at least forms the arc portion.

2. The positive electrode sheet according to claim 1, characterized in that: The coating layer has a first layer and a second layer along a direction away from the current collector.

3. The positive electrode sheet according to claim 2, characterized in that: A surface of the first layer away from the current collector is provided with a plurality of first embedding parts, a surface of the second layer opposite to the first layer is provided with a plurality of second embedding parts, the first embedding parts correspond to the second embedding parts one by one, and the first embedding parts are embedded in the corresponding second embedding parts.

4. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet is configured such that, when forming a battery cell, the first region forms the straight portion, and the second region forms the arc portion.

5. The positive electrode sheet according to claim 4, characterized in that: The coating is provided with n second groups sequentially distributed along the length direction of the current collector, the second group includes two second regions with equal lengths along the length direction of the current collector, along the length direction of the current collector, the lengths of the second regions in the n second groups along the length direction of the current collector increase gradually, and the distance of the second regions in the second group along the length direction of the current collector is L n , the positive electrode sheet satisfies: L n =πR n ; R n : The radius of the arc portion of the battery cell during the nth winding.

6. The positive electrode sheet according to claim 5, characterized in that: The coating includes 2n+1 second regions, 2n second regions form n second groups, n second groups and the 2n+1 second region are sequentially distributed along the length direction of the current collector, and the distance between the 2n+1 second region and the 2n+1 second region along the length direction of the current collector is L. n+1 , the positive electrode sheet satisfies: L n+1 =πR n+1 .

7. A battery cell, characterized in that: A wound body is formed by winding a stack, the wound body comprising a straight portion and arc portions connected to two opposite sides of the straight portion, the stack comprising the positive electrode sheet according to any one of claims 1 to 6, and the second area of ​​the positive electrode sheet at least forms the arc portion.

8. The battery cell according to claim 7, characterized in that: The stacked body includes a first diaphragm, a first pole piece, a second diaphragm, and a second pole piece stacked in sequence, the first pole piece and the second pole piece have opposite polarities, and the first pole piece or the second pole piece is the positive pole piece.

9. The battery cell according to claim 8, characterized in that: The second electrode is the positive electrode, and the positive electrode satisfies: R n =(h1+h3+h4)*n+h2*(n-1); n: the number of windings of the second pole piece; R n : The radius of the arc portion of the battery cell during the nth winding; h1: the total thickness of the double-sided coating and the current collector of the first pole piece in the double-sided coating area; h2: the total thickness of the double-sided coating and the current collector of the second pole piece in the double-sided coating area; h3: thickness of the first diaphragm; h4: thickness of the second diaphragm.

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