Winding cell and battery

Abstract

The application relates to a winding battery cell and a battery, the winding battery cell comprising a positive electrode sheet, a negative electrode sheet and a diaphragm which are stacked, the negative electrode sheet comprising a first layer section and a second layer section connected with each other and a first bending part formed by backfolding, the positive electrode sheet comprising a third layer section and a fourth layer section connected with each other and a second bending part formed by backfolding, the positive electrode sheet being a double-sided coating electrode sheet, a negative electrode protection layer being arranged on the inner side of the second bending part, one end of the first layer section away from the first bending part being arranged opposite to the negative electrode protection layer, and the starting end of the first layer section in the negative electrode protection layer being a double-sided coating electrode sheet. By arranging the winding starting end of the negative electrode sheet as a double-sided coating electrode sheet, the first layer section of the negative electrode sheet and the third layer section of the positive electrode sheet are alternately and mutually stacked to form the winding battery cell, the second bending part of the positive electrode sheet is provided with the negative electrode protection layer to protect the starting end of the negative electrode sheet opposite to the second bending part, the lithium precipitation can be avoided, the thickness of the battery cell is not additionally increased, and the energy density of the battery cell is effectively increased.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, and particularly relates to a wound battery cell and battery. Background Technology

[0002] The charging and discharging of a rechargeable battery occurs through the migration of lithium ions between the positive and negative electrodes. When the battery is charged, lithium ions are generated at the positive electrode. These lithium ions travel through the electrolyte to the negative electrode and embed themselves in the negative electrode plate. The more lithium ions embedded, the higher the charging capacity. Similarly, when the battery is discharged (i.e., when we use the battery), the lithium ions embedded in the negative electrode are released and move back to the positive electrode. The more lithium ions return to the positive electrode, the higher the discharge capacity. In wound batteries, the cell is formed by winding positive and negative electrode plates. The innermost ring of a wound lithium battery cell typically has a single-sided negative electrode area. Due to the uneven stress on both sides of the copper foil, this area is prone to curling, increasing manufacturing difficulties. The curled area also increases the lithium ion transport distance, leading to lithium plating. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a wound cell and battery. By changing the single-sided negative electrode area of ​​the innermost ring of the wound cell to a double-sided coated negative electrode, and forming a tight integral design with the positive electrode, the problem of easy curling of the single-sided negative electrode area of ​​the inner ring can be solved, and the waste of copper foil and separator can be reduced. This can improve the volumetric energy density of the cell to a certain extent, while reducing material costs.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A wound battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator stacked together. The separator is disposed between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet includes a first layer segment and a second layer segment. The first layer segment is located at the winding start end of the negative electrode sheet. The second layer segment is connected to the first layer segment and folded back relative to the first layer segment. The folded-back point is a first bend.

[0006] The positive electrode sheet includes a third layer and a fourth layer. The third layer is located at the starting end of the winding of the positive electrode sheet. The fourth layer is connected to the third layer and folded back relative to the third layer. This fold-back point is the second bend. The positive electrode sheet is a double-coated electrode sheet, and a negative electrode protective layer is provided on the inner side of the second bend.

[0007] The first layer is disposed between the third layer and the fourth layer. The end of the first layer away from the first bend is disposed opposite to the negative electrode protection layer. The starting end of the first layer in the negative electrode protection layer is a double-sided coated electrode sheet. The third layer is disposed between the first layer and the second layer.

[0008] Preferably, the negative electrode protective layer is any one of single-sided protective adhesive, double-sided protective adhesive, or ceramic insulating layer.

[0009] Preferably, the second bent portion has a recessed area on the inward side, and the negative electrode protective layer is disposed in the recessed area.

[0010] Preferably, the recessed area is the active coating thinning area on the surface of the positive electrode sheet, and the thinning thickness T1 of the thinning area and the active coating thickness T satisfy the following relationship: 0 < T1 < T.

[0011] Preferably, the recessed area is the active coating thinning area on the surface of the positive electrode sheet, and the thinning thickness T1 of the thinning area and the active coating thickness T satisfy the following relationship: 60%T < T1 < 80%T.

[0012] Preferably, the recessed area is an empty foil area on the surface of the positive electrode sheet, and the empty foil area has the same size as the negative electrode protective layer.

[0013] Preferably, the negative electrode sheet is a double-coated electrode sheet, and a separator is provided on both sides of the negative electrode sheet in the thickness direction. A positive electrode protective layer is provided on the inner side of the first bending portion, and the positive electrode protective layer is disposed between the negative electrode sheet and the separator. The positive electrode protective layer is any one of single-sided protective adhesive, double-sided protective adhesive or ceramic insulating layer.

[0014] Preferably, the end of the third layer segment away from the second bend is disposed opposite to the positive electrode protective layer inside the first bend.

[0015] Preferably, the first layer and the third layer are bonded together to form the innermost ring of the wound cell.

[0016] Preferably, the axial distance between the foremost end of the first layer segment furthest from the first bend and the negative electrode protective layer is A, and the value of A is 0 < A ≤ 50 mm.

[0017] Preferably, the foremost end of the first layer segment away from the first bend is a double-sided empty foil area with an empty length of B, where the value of B is 0 < B ≤ 10 mm.

[0018] Preferably, the protective length of the negative electrode protective layer after being symmetrically bent and wrapped at the second bending part is C, which satisfies the following relationship: C≥A+B.

[0019] A battery comprising the wound cell described in any of the above claims.

[0020] Compared to existing technologies, the advantages of this invention are as follows: the starting end of the negative electrode is a double-coated electrode, which only needs to be bent once to form the first and second layers to cover the starting end of the positive electrode. The wound cell is arranged in alternating layers, and the second bending part of the positive electrode has a negative electrode protective layer to protect the starting end of the negative electrode. This avoids lithium plating without increasing the cell thickness, effectively increasing the cell's energy density. Moreover, it avoids the problem of curling easily occurring on one side of the negative electrode in existing designs, while reducing the use of copper foil and separator, thus reducing production costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the wound battery cell of the present invention.

[0022] Figure 2 This is a partial structural diagram of the wound battery cell according to Embodiments 1 and 2 of the present invention.

[0023] Figure 3 This is a partial structural diagram of the wound battery cell according to Embodiment 3 of the present invention.

[0024] Figure 4 This is a schematic diagram of the overall structure of the wound battery cell according to Embodiment 4 of the present invention.

[0025] Figure 5 yes Figure 4 A magnified view of part A.

[0026] Figure 6 This is a schematic diagram of the overall structure of the wound battery cell according to Embodiment 5 of the present invention.

[0027] Figure label:

[0028] 1. Positive electrode plate; 11. Third layer; 12. Fourth layer; 13. Second bend; 14. Negative electrode protective layer; 15. Recessed area.

[0029] 2. Negative electrode sheet; 21. First layer; 22. Second layer; 23. First bend; 24. Positive electrode protective layer;

[0030] 3. Diaphragm. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] See Figure 1-2 The present invention provides a wound battery cell comprising a positive electrode 1, a negative electrode 2 and a separator 3 stacked together. The separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The negative electrode 2 includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the winding start end of the negative electrode 2. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21. The folded-back part is a first bend 23.

[0034] The positive electrode 1 includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the starting end of the winding of the positive electrode 1. The fourth layer segment 12 is connected to the third layer segment 11 and folds back relative to the third layer segment 11. The folding point is the second bending part 13. The positive electrode 1 is a double-coated electrode. A negative electrode protective layer 14 is provided on the inner side of the second bending part 13.

[0035] The first layer 21 is located between the third layer 11 and the fourth layer 12. The end of the first layer 21 away from the first bend 23 is opposite to the negative electrode protection layer 14. The starting end of the first layer 21 in the negative electrode protection layer 14 is a double-sided coated electrode sheet. The third layer 11 is located between the first layer 21 and the second layer 22.

[0036] The negative electrode protective layer 14 can be any one of a single-sided protective adhesive, a double-sided protective adhesive, or a ceramic insulating layer. When the negative electrode protective layer 14 is a single-sided or double-sided protective adhesive, its protective adhesive substrate is any one of BOPP, PET, or PI. If it is a single-sided protective adhesive, its adhesive layer is bonded to the positive electrode active material layer, and the other non-adhesive side faces the first layer segment 21 and covers and protects it. If it is a double-sided protective adhesive, in addition to being bonded to the positive electrode active material layer, it can also be used to bond and position the second layer segment 22. The above selections can be appropriately replaced according to actual production. Preferably, in this embodiment, the negative electrode protective layer 14 is a single-sided protective adhesive, and the substrate of this single-sided protective adhesive is PET.

[0037] As described above, by changing the starting end of the negative electrode 2, which is coated with active material on one side in the original design, to be coated on both sides, and by stacking the positive electrode 1 and the negative electrode 2 in a U-shape, the single-sided negative electrode area of ​​the innermost ring of the cell is eliminated. This directly avoids the problem of curling of the single-sided negative electrode area. In the existing design, the starting end of the negative current collector is only coated with negative active material on one side. The coated side has a cohesive force on the current collector, while the uncoated side has no effect on it. Therefore, the starting end of the negative electrode 2 is prone to curling towards the side coated with negative active material, which causes deformation of the innermost ring of the cell and may even lead to lithium plating. At the same time, it avoids the useless negative electrode in the innermost ring occupying the cell volume and effectively increases the energy density of the cell. By setting a negative electrode protective layer 14 at the corresponding position of the positive electrode 1, the first layer segment 21 of the negative electrode 2 is prevented from directly contacting the second bending portion 13 of the positive electrode 1, thus avoiding adverse conditions such as short circuit or puncture of the positive electrode 1.

[0038] Specifically, the second bend 13 has a recessed area 15 on one side, and the negative electrode protective layer 14 is disposed in the recessed area 15. The thickness of the negative electrode protective layer 14 is the same as the depth of the recessed area 15. After the negative electrode protective layer 14 is embedded in the recessed area 15, the surface of the second bend 13 remains a flat surface after unfolding.

[0039] Specifically, the recessed region 15 is a thinned area of ​​the active coating on the surface of the positive electrode 1, and the thinning thickness T1 of the thinned area is 50%-90% of the active coating thickness T. Preferably, the thinning thickness T1 is 50%, 60%, 70%, 80%, or 90%, etc. In this embodiment, the thinning thickness T1 is 50%.

[0040] Specifically, the negative electrode 2 is a double-coated electrode, and a separator 3 is provided on both sides of the negative electrode 2 in the thickness direction. The separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent the starting end of the third layer segment 11 of the positive electrode 1 from directly contacting the first bend 23 of the negative electrode 2, thus avoiding short circuits or punctures to the negative electrode 2. More specifically, a positive electrode protective layer 24 is provided inside the first bend 23, and the positive electrode protective layer 24 is disposed between the negative electrode 2 and the separator 3; the positive electrode protective layer 24 can be any one of single-sided protective adhesive, double-sided protective adhesive, or ceramic insulating layer. In this embodiment, the positive electrode protective layer 24 is a double-sided protective adhesive. The negative electrode 2 also has an active coating thinning area to accommodate the positive electrode protective layer 24.

[0041] Specifically, the end of the third layer 11 away from the second bend 13 is positioned opposite to the positive electrode protection layer 24 inside the first bend 23. This allows the first layer 21 and the third layer 11 to be stacked at the innermost layer of the cell, serving as the starting point for winding the entire cell, and enabling the subsequent second layer 22 and fourth layer 12 to be wound in this manner.

[0042] Specifically, the axial distance between the foremost end of the first layer segment 21 away from the first bend 23 and the negative electrode protective layer 14 is A, and the value of A is 0 < A ≤ 50 mm. More specifically, A can be 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 25 mm, 40 mm, and 50 mm, etc. In this embodiment, A is 10 mm.

[0043] Specifically, the protective length of the negative electrode protective layer after symmetrical bending and covering at the second bending section is C, satisfying the following relationship: C≥A. More specifically, C can be 1mm, 5mm, 8mm, 10mm, 20mm, 25mm, 40mm, and 50mm, etc. In this embodiment, C is 15mm.

[0044] Example 2:

[0045] See Figure 1-2 The present invention provides a wound battery cell comprising a positive electrode 1, a negative electrode 2 and a separator 3 stacked together. The separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The negative electrode 2 includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the winding start end of the negative electrode 2. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21. The folded-back part is a first bend 23.

[0046] The positive electrode 1 includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the starting end of the winding of the positive electrode 1. The fourth layer segment 12 is connected to the third layer segment 11 and folds back relative to the third layer segment 11. The folding point is the second bending part 13. The positive electrode 1 is a double-coated electrode. A negative electrode protective layer 14 is provided on the inner side of the second bending part 13.

[0047] The first layer 21 is located between the third layer 11 and the fourth layer 12. The end of the first layer 21 away from the first bend 23 is opposite to the negative electrode protection layer 14. The starting end of the first layer 21 in the negative electrode protection layer 14 is a double-sided coated electrode sheet. The third layer 11 is located between the first layer 21 and the second layer 22.

[0048] The negative electrode protective layer 14 can be any one of a single-sided protective adhesive, a double-sided protective adhesive, or a ceramic insulating layer. When the negative electrode protective layer 14 is a single-sided or double-sided protective adhesive, its protective adhesive substrate is any one of BOPP, PET, or PI. If it is a single-sided protective adhesive, its adhesive layer is bonded to the positive electrode active material layer, and the other non-adhesive side faces the first layer segment 21 and covers and protects it. If it is a double-sided protective adhesive, in addition to being bonded to the positive electrode active material layer, it can also be used to bond and position the second layer segment 22. The above selections can be appropriately replaced according to actual production. Preferably, in this embodiment, the negative electrode protective layer 14 is a double-sided protective adhesive, and the substrate of this double-sided protective adhesive is PET.

[0049] As described above, by changing the starting end of the negative electrode 2, which is coated with active material on one side in the original design, to be coated on both sides, and by stacking the positive electrode 1 and the negative electrode 2 in a U-shape, the single-sided negative electrode area of ​​the innermost ring of the cell is eliminated. This directly avoids the problem of curling of the single-sided negative electrode area. In the existing design, the starting end of the negative current collector is only coated with negative active material on one side. The coated side has a cohesive force on the current collector, while the uncoated side has no effect on it. Therefore, the starting end of the negative electrode 2 is prone to curling towards the side coated with negative active material, which causes deformation of the innermost ring of the cell and may even lead to lithium plating. At the same time, it avoids the useless negative electrode in the innermost ring occupying the cell volume and effectively increases the energy density of the cell. By setting a negative electrode protective layer 14 at the corresponding position of the positive electrode 1, the first layer segment 21 of the negative electrode 2 is prevented from directly contacting the second bending portion 13 of the positive electrode 1, thus avoiding adverse conditions such as short circuit or puncture of the positive electrode 1.

[0050] Specifically, the second bend 13 has a recessed area 15 on one side, and the negative electrode protective layer 14 is disposed in the recessed area 15. The thickness of the negative electrode protective layer 14 is the same as the depth of the recessed area 15. After the negative electrode protective layer 14 is embedded in the recessed area 15, the surface of the second bend 13 remains a flat surface after unfolding.

[0051] Specifically, the recessed region 15 is a thinned area of ​​the active coating on the surface of the positive electrode 1, and the thinning thickness T1 of the thinned area is 60%-80% of the active coating thickness T. Preferably, the thinning thickness T1 is 60%, 65%, 70%, 75%, or 80%, etc. In this embodiment, the thinning thickness T1 is 70%.

[0052] Specifically, the negative electrode 2 is a double-coated electrode, and a separator 3 is provided on both sides of the negative electrode 2 in the thickness direction. The separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent the starting end of the third layer segment 11 of the positive electrode 1 from directly contacting the first bend 23 of the negative electrode 2, thus avoiding short circuits or punctures to the negative electrode 2. More specifically, a positive electrode protective layer 24 is provided inside the first bend 23, and the positive electrode protective layer 24 is disposed between the negative electrode 2 and the separator 3; the positive electrode protective layer 24 can be any one of single-sided protective adhesive, double-sided protective adhesive, or ceramic insulating layer. In this embodiment, the positive electrode protective layer 24 is a double-sided protective adhesive. The negative electrode 2 also has an active coating thinning area to accommodate the positive electrode protective layer 24.

[0053] Specifically, the end of the third layer 11 away from the second bend 13 is positioned opposite to the positive electrode protection layer 24 inside the first bend 23. This allows the first layer 21 and the third layer 11 to be stacked at the innermost layer of the cell, serving as the starting point for winding the entire cell, and enabling the subsequent second layer 22 and fourth layer 12 to be wound in this manner.

[0054] Specifically, the axial distance between the foremost end of the first layer segment 21 away from the first bend 23 and the negative electrode protective layer 14 is A, and the value of A is 0 < A ≤ 50 mm. More specifically, A can be 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 25 mm, 40 mm, and 50 mm, etc. In this embodiment, A is 8 mm.

[0055] Specifically, the protective length of the negative electrode protective layer after symmetrical bending and covering at the second bending section is C, satisfying the following relationship: C≥A. More specifically, C can be 1mm, 5mm, 8mm, 10mm, 20mm, 25mm, 40mm, and 50mm, etc. In this embodiment, C is 10mm.

[0056] Example 3:

[0057] See Figure 1 and Figure 3 The present invention provides a wound battery cell comprising a positive electrode 1, a negative electrode 2 and a separator 3 stacked together. The separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The negative electrode 2 includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the winding start end of the negative electrode 2. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21. The folded-back part is a first bend 23.

[0058] The positive electrode 1 includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the starting end of the winding of the positive electrode 1. The fourth layer segment 12 is connected to the third layer segment 11 and folds back relative to the third layer segment 11. The folding point is the second bending part 13. The positive electrode 1 is a double-coated electrode. A negative electrode protective layer 14 is provided on the inner side of the second bending part 13.

[0059] The first layer 21 is located between the third layer 11 and the fourth layer 12. The end of the first layer 21 away from the first bend 23 is opposite to the negative electrode protection layer 14. The starting end of the first layer 21 in the negative electrode protection layer 14 is a double-sided coated electrode sheet. The third layer 11 is located between the first layer 21 and the second layer 22.

[0060] The negative electrode protective layer 14 can be any one of a single-sided protective adhesive, a double-sided protective adhesive, or a ceramic insulating layer. When the negative electrode protective layer 14 is a single-sided or double-sided protective adhesive, its protective adhesive substrate is any one of BOPP, PET, or PI. If it is a single-sided protective adhesive, its adhesive layer is bonded to the positive electrode active material layer, and the other non-adhesive side faces the first layer segment 21 and covers and protects it. If it is a double-sided protective adhesive, in addition to being bonded to the positive electrode active material layer, it can also be used to bond and position the second layer segment 22. The above selections can be appropriately replaced according to actual production. Preferably, in this embodiment, the negative electrode protective layer 14 is a single-sided protective adhesive, and the substrate of this single-sided protective adhesive is PET.

[0061] As described above, by changing the single-sided coating of the negative electrode 2 to double-sided coating in the original design, and by stacking the positive electrode 1 and negative electrode 2 in a U-shape, the single-sided negative electrode area of ​​the innermost ring of the cell is eliminated, directly avoiding the problems that easily occur in the single-sided negative electrode area. That is, in the existing design, the negative electrode current collector is only coated with negative electrode active material on one side. The coated side has a cohesive force on the current collector, while the uncoated side has no effect on it. Therefore, the starting end of the negative electrode 2 is prone to curling towards the side coated with negative electrode active material, which causes deformation of the innermost ring of the cell and may even lead to lithium plating. At the same time, it avoids the useless negative electrode in the innermost ring occupying the cell volume, effectively increasing the cell energy density. By setting a negative electrode protective layer 14 at the corresponding position of the positive electrode 1, the first layer 21 of the negative electrode 2 is prevented from directly contacting the second bent part 13 of the positive electrode 1, avoiding adverse conditions such as short circuits or punctures to the positive electrode 1.

[0062] Specifically, the second bend 13 has a recessed area 15 on one side, and the negative electrode protective layer 14 is disposed in the recessed area 15. The thickness of the negative electrode protective layer 14 is the same as the depth of the recessed area 15. After the negative electrode protective layer 14 is embedded in the recessed area 15, the surface of the second bend 13 remains a flat surface after unfolding.

[0063] Specifically, the recessed area 15 is an empty foil area on the surface of the positive electrode sheet 1, and the empty foil area has the same size as the negative electrode protective layer 14. This empty foil area is the region on the current collector of the positive electrode sheet 1 that is not coated with positive electrode active material. The thickness of the negative electrode protective layer 14 is the same as the thickness of the positive electrode active material layer to form a flat surface. In this embodiment, the empty foil area is located on the side of the second bend 13 facing the winding start end of the negative electrode sheet 2.

[0064] Specifically, the negative electrode 2 is a double-coated electrode, and a separator 3 is provided on both sides of the negative electrode 2 in the thickness direction. The separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent the starting end of the third layer segment 11 of the positive electrode 1 from directly contacting the first bend portion 23 of the negative electrode 2, thus avoiding adverse conditions such as short circuits or punctures to the negative electrode 2. More specifically, a positive electrode protective layer 24 is provided inside the first bend portion 23, and the positive electrode protective layer 24 is disposed between the negative electrode 2 and the separator 3; the positive electrode protective layer 24 can be any one of single-sided protective adhesive, double-sided protective adhesive, or ceramic insulating layer. In this embodiment, a hollow foil area is also provided on the surface of the negative electrode 2 corresponding to the first bend portion 23 to accommodate the positive electrode protective layer 24.

[0065] Specifically, the end of the third layer segment 11 away from the second bend 13 is positioned opposite to the diaphragm 3 inside the first bend 23. This allows the first layer segment 21 and the third layer segment 11 to be stacked at the innermost layer of the battery cell, serving as the starting point for winding the entire battery cell, and allowing the subsequent second layer segment 22 and fourth layer segment 12 to be wound in this manner.

[0066] Specifically, the axial distance between the foremost end of the first layer segment 21 away from the first bend 23 and the negative electrode protective layer 14 is A, and the value of A is 0 < A ≤ 50 mm. More specifically, A can be 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 25 mm, 40 mm, and 50 mm, etc. In this embodiment, A is 8 mm.

[0067] Specifically, the protective length of the negative electrode protective layer after symmetrical bending and covering at the second bending section is C, satisfying the following relationship: C≥A. More specifically, C can be 1mm, 5mm, 8mm, 10mm, 20mm, 25mm, 40mm, and 50mm, etc. In this embodiment, C is 10mm.

[0068] Example 4:

[0069] See Figure 1 , Figure 4 and Figure 5 The present invention provides a wound battery cell comprising a positive electrode 1, a negative electrode 2 and a separator 3 stacked together. The separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The negative electrode 2 includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the winding start end of the negative electrode 2. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21. The folded-back part is a first bend 23.

[0070] The positive electrode 1 includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the starting end of the winding of the positive electrode 1. The fourth layer segment 12 is connected to the third layer segment 11 and folds back relative to the third layer segment 11. The folding point is the second bending part 13. The positive electrode 1 is a double-coated electrode. A negative electrode protective layer 14 is provided on the inner side of the second bending part 13.

[0071] The first layer 21 is located between the third layer 11 and the fourth layer 12. The end of the first layer 21 away from the first bend 23 is opposite to the negative electrode protection layer 14. The starting end of the first layer 21 in the negative electrode protection layer 14 is a double-sided coated electrode sheet. The third layer 11 is located between the first layer 21 and the second layer 22.

[0072] The negative electrode protective layer 14 can be any one of a single-sided protective adhesive, a double-sided protective adhesive, or a ceramic insulating layer. When the negative electrode protective layer 14 is a single-sided or double-sided protective adhesive, its protective adhesive substrate is any one of BOPP, PET, or PI. If it is a single-sided protective adhesive, its adhesive layer is bonded to the positive electrode active material layer, and the other non-adhesive side faces the first layer segment 21 and covers and protects it. If it is a double-sided protective adhesive, in addition to being bonded to the positive electrode active material layer, it can also be used to bond and position the second layer segment 22. The above selections can be appropriately replaced according to actual production. Preferably, in this embodiment, the negative electrode protective layer 14 is a double-sided protective adhesive, and the substrate of this double-sided protective adhesive is PET.

[0073] As described above, by changing the starting end of the negative electrode 2, which is coated with active material on one side in the original design, to be coated on both sides, and by stacking the positive electrode 1 and the negative electrode 2 in a U-shape, the single-sided negative electrode area of ​​the innermost ring of the cell is eliminated. This directly avoids the problem of curling of the single-sided negative electrode area. In the existing design, the starting end of the negative current collector is only coated with negative active material on one side. The coated side has a cohesive force on the current collector, while the uncoated side has no effect on it. Therefore, the starting end of the negative electrode 2 is prone to curling towards the side coated with negative active material, which causes deformation of the innermost ring of the cell and may even lead to lithium plating. At the same time, it avoids the useless negative electrode in the innermost ring occupying the cell volume and effectively increases the energy density of the cell. By setting a negative electrode protective layer 14 at the corresponding position of the positive electrode 1, the first layer segment 21 of the negative electrode 2 is prevented from directly contacting the second bending portion 13 of the positive electrode 1, thus avoiding adverse conditions such as short circuit or puncture of the positive electrode 1.

[0074] Specifically, the second bend 13 has a recessed area 15 on one side, and the negative electrode protective layer 14 is disposed in the recessed area 15. The thickness of the negative electrode protective layer 14 is the same as the depth of the recessed area 15. After the negative electrode protective layer 14 is embedded in the recessed area 15, the surface of the second bend 13 remains a flat surface after unfolding.

[0075] Specifically, the recessed region 15 is a thinned area of ​​the active coating on the surface of the positive electrode 1, and the thinning thickness T1 of the thinned area is 60%-80% of the active coating thickness T. Preferably, the thinning thickness T1 is 60%, 65%, 70%, 75%, or 80%, etc. In this embodiment, the thinning thickness T1 is 70%.

[0076] Specifically, the negative electrode 2 is a double-coated electrode, and a separator 3 is provided on both sides of the negative electrode 2 in the thickness direction. The separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent the starting end of the third layer segment 11 of the positive electrode 1 from directly contacting the first bend 23 of the negative electrode 2, thus avoiding short circuits or punctures to the negative electrode 2. More specifically, a positive electrode protective layer 24 is provided inside the first bend 23, and the positive electrode protective layer 24 is disposed between the negative electrode 2 and the separator 3; the positive electrode protective layer 24 can be any one of single-sided protective adhesive, double-sided protective adhesive, or ceramic insulating layer. In this embodiment, the positive electrode protective layer 24 is a double-sided protective adhesive. The negative electrode 2 also has an active coating thinning area to accommodate the positive electrode protective layer 24.

[0077] Specifically, the end of the third layer 11 away from the second bend 13 is positioned opposite to the positive electrode protection layer 24 inside the first bend 23. This allows the first layer 21 and the third layer 11 to be stacked at the innermost layer of the cell, serving as the starting point for winding the entire cell, and enabling the subsequent second layer 22 and fourth layer 12 to be wound in this manner.

[0078] Specifically, the axial distance between the foremost end of the first layer segment 21 away from the first bend 23 and the negative electrode protective layer 14 is A, and the value of A is 0 < A ≤ 50 mm. More specifically, A can be 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 25 mm, 40 mm, and 50 mm, etc. In this embodiment, A is 10 mm.

[0079] Specifically, a double-sided empty foil area is provided at the starting end of the first layer segment 21 away from the first bend 23, with an empty length of B, where B ranges from 0 to 10 mm. More specifically, C can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm, etc. In this embodiment, A is 5 mm.

[0080] Specifically, the protective length of the negative electrode protective layer after symmetrical bending and covering at the second bending section is C, satisfying the following relationship: C≥A+B. More specifically, C can be 2mm, 5mm, 8mm, 10mm, 20mm, 25mm, 40mm, 50mm, and 60mm, etc. In this embodiment, C is 20mm.

[0081] Example 5:

[0082] See Figure 6 The present invention provides a wound battery cell comprising a positive electrode 1, a negative electrode 2 and a separator 3 stacked together. The separator 3 is disposed between the positive electrode 1 and the negative electrode 2. The negative electrode 2 includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the winding start end of the negative electrode 2. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21. The folded-back part is a first bend 23.

[0083] The positive electrode 1 includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the starting end of the winding of the positive electrode 1. The fourth layer segment 12 is connected to the third layer segment 11 and folds back relative to the third layer segment 11. The folding point is the second bending part 13. The positive electrode 1 is a double-coated electrode. A negative electrode protective layer 14 is provided on the inner side of the second bending part 13.

[0084] The first layer 21 is located between the third layer 11 and the fourth layer 12. The end of the first layer 21 away from the first bend 23 is opposite to the negative electrode protection layer 14. The starting end of the first layer 21 in the negative electrode protection layer 14 is a double-sided coated electrode sheet. The third layer 11 is located between the first layer 21 and the second layer 22.

[0085] The negative electrode protective layer 14 can be any one of a single-sided protective adhesive, a double-sided protective adhesive, or a ceramic insulating layer. When the negative electrode protective layer 14 is a single-sided or double-sided protective adhesive, its protective adhesive substrate is any one of BOPP, PET, or PI. If it is a single-sided protective adhesive, its adhesive layer is bonded to the positive electrode active material layer, and the other non-adhesive side faces the first layer segment 21 and covers and protects it. If it is a double-sided protective adhesive, in addition to being bonded to the positive electrode active material layer, it can also be used to bond and position the second layer segment 22. The above selections can be appropriately replaced according to actual production. Preferably, in this embodiment, the negative electrode protective layer 14 is a single-sided protective adhesive, and the substrate of this single-sided protective adhesive is PET.

[0086] As described above, by changing the starting end of the negative electrode 2, which is coated with active material on one side in the original design, to be coated on both sides, and by stacking the positive electrode 1 and the negative electrode 2 in a U-shape, the single-sided negative electrode area of ​​the innermost ring of the cell is eliminated. This directly avoids the problem of curling of the single-sided negative electrode area. In the existing design, the starting end of the negative current collector is only coated with negative active material on one side. The coated side has a cohesive force on the current collector, while the uncoated side has no effect on it. Therefore, the starting end of the negative electrode 2 is prone to curling towards the side coated with negative active material, which causes deformation of the innermost ring of the cell and may even lead to lithium plating. At the same time, it avoids the useless negative electrode in the innermost ring occupying the cell volume and effectively increases the energy density of the cell. By setting a negative electrode protective layer 14 at the corresponding position of the positive electrode 1, the first layer segment 21 of the negative electrode 2 is prevented from directly contacting the second bending portion 13 of the positive electrode 1, thus avoiding adverse conditions such as short circuit or puncture of the positive electrode 1.

[0087] Specifically, the second bend 13 has a recessed area 15 on one side, and the negative electrode protective layer 14 is disposed in the recessed area 15. The thickness of the negative electrode protective layer 14 is the same as the depth of the recessed area 15. After the negative electrode protective layer 14 is embedded in the recessed area 15, the surface of the second bend 13 remains a flat surface after unfolding.

[0088] Specifically, the recessed region 15 is a thinned area of ​​the active coating on the surface of the positive electrode 1, and the thinning thickness T1 of the thinned area is 50%-90% of the active coating thickness T. Preferably, the thinning thickness T1 is 50%, 60%, 70%, 80%, or 90%, etc. In this embodiment, the thinning thickness T1 is 50%.

[0089] Specifically, the negative electrode 2 is a double-coated electrode, and a separator 3 is provided on both sides of the negative electrode 2 in the thickness direction. The separator 3 separates the positive electrode 1 and the negative electrode 2 to prevent the third layer segment 11 of the positive electrode 1 from directly contacting the first bend 23 of the negative electrode 2, thus avoiding adverse conditions such as short circuit or puncture of the negative electrode 2.

[0090] Specifically, the end of the third layer segment 11 away from the second bend 13 is positioned opposite to the diaphragm 3 inside the first bend 23. This allows the first layer segment 21 and the third layer segment 11 to be stacked at the innermost layer of the battery cell, serving as the starting point for winding the entire battery cell, and allowing the subsequent second layer segment 22 and fourth layer segment 12 to be wound in this manner.

[0091] Specifically, the axial distance between the foremost end of the first layer segment 21 away from the first bend 23 and the negative electrode protective layer 14 is A, and the value of A is 0 < A ≤ 50 mm. More specifically, A can be 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 25 mm, 40 mm, and 50 mm, etc. In this embodiment, A is 10 mm.

[0092] Specifically, the protective length of the negative electrode protective layer after symmetrical bending and covering at the second bending section is C, satisfying the following relationship: C≥A. More specifically, C can be 1mm, 5mm, 8mm, 10mm, 20mm, 25mm, 40mm, and 50mm, etc. In this embodiment, C is 15mm.

[0093] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A wound battery cell, comprising a positive electrode (1), a negative electrode (2), and a separator (3) stacked together, wherein the separator (3) is disposed between the positive electrode (1) and the negative electrode (2), characterized in that: The negative electrode (2) includes a first layer segment (21) and a second layer segment (22). The first layer segment (21) is located at the starting end of the winding of the negative electrode (2). The second layer segment (22) is connected to the first layer segment (21) and folded back relative to the first layer segment (21). The folded-back part of the negative electrode (2) is the first bending part (23). The positive electrode (1) includes a third layer (11) and a fourth layer (12). The third layer (11) is located at the starting end of the winding of the positive electrode (1). The fourth layer (12) is connected to the third layer (11) and folds back relative to the third layer (11). The folding point of the positive electrode (1) is the second bending part (13). The positive electrode (1) is a double-coated electrode. A negative electrode protective layer (14) is provided on the inner side of the second bending part (13). The first layer (21) is disposed between the third layer (11) and the fourth layer (12). The end of the first layer (21) away from the first bend (23) is disposed opposite to the negative electrode protection layer (14). The starting end of the first layer (21) in the negative electrode protection layer (14) is a double-sided coated electrode sheet. The third layer (11) is disposed between the first layer (21) and the second layer (22). The negative electrode protective layer (14) is any one of single-sided protective adhesive, double-sided protective adhesive or ceramic insulating layer; The second bend (13) has a recessed area (15) on one side, and the negative electrode protective layer (14) is disposed in the recessed area (15); The negative electrode (2) is a double-coated electrode. The negative electrode (2) has a diaphragm (3) on both sides in the thickness direction. The positive electrode protective layer (24) is provided on the inner side of the first bent part (23). The positive electrode protective layer (24) is located between the negative electrode (2) and the diaphragm (3). The positive electrode protective layer (24) is any one of single-sided protective adhesive, double-sided protective adhesive or ceramic insulating layer. The third layer (11) is disposed opposite to the positive electrode protective layer (24) inside the first bend (23) at one end away from the second bend (13); The first layer (21) and the third layer (11) are bonded together to form the innermost ring of the wound cell; The axial distance between the foremost end of the first layer (21) away from the first bend (23) and the negative electrode protective layer (14) is A, and the value of A is 0 < A ≤ 50 mm. The first layer (21) has a double-sided empty foil area at the starting end away from the first bend (23), and the empty length is B, the value of B is 0 < B ≤ 10 mm. The protective length of the negative electrode protective layer (14) after being symmetrically bent and covered at the second bend (13) is C, which satisfies the following relationship: C≥A+B.

2. The wound battery cell according to claim 1, characterized in that: The recessed area (15) is the active coating thinning area on the surface of the positive electrode (1). The thinning thickness T1 of the thinning area and the active coating thickness T satisfy the following relationship: 0 < T1 < T.

3. The wound battery cell according to claim 2, characterized in that: The recessed area (15) is the active coating thinning area on the surface of the positive electrode (1). The thinning thickness T1 of the thinning area and the active coating thickness T satisfy the following relationship: 60%T < T1 < 80%T.

4. The wound battery cell according to claim 1, characterized in that: The recessed area (15) is the empty foil area on the surface of the positive electrode (1), and the empty foil area has the same size as the negative electrode protective layer (14).

5. A battery, characterized in that, Includes the wound battery cell as described in any one of claims 1-4.

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