Positive pole piece, roll core and single battery

Abstract

The utility model provides a positive pole piece, a roll core and a single battery, and relates to the technical field of batteries, the positive pole piece comprises a positive pole current collector and active material layers coated on two surfaces of the positive pole current collector, the active material layer at the winding inner side of the positive pole piece is provided with a stress buffer structure in a plurality of bending areas at the winding starting end, the stress buffer structure comprises at least one groove, and the groove is formed by locally thinning the active material layer. In the winding and circulating process, the positive pole piece bears the dual effects of stretching and extruding at the corner, and the stress at the corner is dispersed or weakened due to the design of the groove, so that the fracture of the positive pole piece caused by overlarge stress is avoided. Through the design, the problem that the positive pole piece is easy to break in the prior art is fundamentally solved, the reliability of the battery is remarkably improved, and the service life of the battery is remarkably prolonged.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a positive electrode sheet, a winding core, and a single battery cell. Background Technology

[0002] With the widespread application of rechargeable batteries in electric vehicles, energy storage systems, and other fields, the market demands increasingly higher battery performance, especially in terms of high energy density and fast charging capabilities. To meet these requirements, the design of battery positive electrode sheets tends to employ higher active material areal density and thicker film layers to improve battery energy density. However, this design also brings a series of technical challenges during battery manufacturing and use.

[0003] During the cell manufacturing process, when using a winding technique, the positive electrode sheet has a small radius of curvature at the initial folds, making it prone to cracking during winding or hot pressing. Furthermore, during battery charging and discharging, the negative electrode material expands in volume at full charge, causing a rebound in negative electrode thickness and further increasing stress concentration at the corners. These factors can lead to positive electrode sheet breakage, resulting not only in battery capacity loss but also potential safety hazards.

[0004] Currently, some companies are attempting to address the breakage problem of high areal density positive electrode sheets by attaching adhesive tape to both sides of the electrode corners, utilizing the tape's toughness to maintain the electrode's integrity. However, this method has significant limitations: in the early stages of battery life, the tape can obscure some active material, preventing full capacity utilization and potentially causing edge lithium plating; and after long-term cycling, the adhesive force of the tape gradually decreases, while the expansion force of the negative electrode continues to increase, making breakage of the positive electrode sheet still possible, thus failing to fundamentally solve the problem.

[0005] Other companies are attempting to address the tensile deformation of the electrode at corners by using aluminum foil with higher elongation as the current collector. However, the elongation of existing aluminum foil is already close to the material's limit, and further increasing the elongation requires complex modification methods. This not only significantly increases processing costs but may also lead to a decrease in the tensile strength of the electrode due to excessive elongation. Furthermore, in the cold pressing process, excessively high elongation can cause uneven stretching of the electrode film surface, resulting in fluctuations in areal density and breakage of the conductive network, thereby affecting the overall performance of the battery. Utility Model Content

[0006] In view of this, this utility model proposes a positive electrode sheet, a winding core, and a single battery cell to solve the problem of electrode sheet extrusion and breakage caused by stress concentration at the corner of the positive electrode sheet.

[0007] The technical solution of this utility model is implemented as follows:

[0008] In a first aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and an active material layer coated on both sides of the positive current collector. The active material layer on the inner side of the positive electrode sheet is provided with a stress buffer structure in several bending areas at the starting end of the winding. The stress buffer structure includes at least one groove, which is formed by local thinning of the active material layer.

[0009] Based on the above technical solution, preferably, the stress buffer structure is disposed in at least one bending area of ​​the first to tenth folds in the wound core.

[0010] Based on the above technical solution, preferably, the stress buffer structure includes a plurality of parallel grooves, which extend perpendicular to the winding direction.

[0011] Based on the above technical solution, preferably, the spacing between adjacent grooves is consistent, and the width of all grooves is consistent.

[0012] Based on the above technical solution, preferably, the depth of the plurality of grooves increases in a gradient from the outside to the inside.

[0013] Based on the above technical solution, preferably, the sum of the widths of all grooves ΣW and the radius of curvature r of the corresponding bending region of the positive electrode sheet satisfy: 6.7%πr < ΣW < 2πr.

[0014] Based on the above technical solution, preferably, the cross-section of the groove is U-shaped or V-shaped.

[0015] Secondly, this utility model provides a winding core, including a negative electrode sheet, a diaphragm, and the positive electrode sheet described in the first aspect, wherein the diaphragm is disposed between the negative electrode sheet and the positive electrode sheet.

[0016] Thirdly, this utility model provides a single battery cell, including a casing and the winding core described in the second aspect, wherein the winding core is housed in the casing.

[0017] The present invention has the following advantages over the prior art:

[0018] (1) By incorporating stress buffer structures in several bending areas at the starting point of the winding of the active material layer on the inner side of the positive electrode sheet, and by forming grooves through local thinning of the active material layer as stress buffer structures, the stress concentration problem during winding is effectively alleviated. Especially in the bending areas of the first few folds, the presence of grooves thins the active material layer, reduces the rigidity of the area, and makes the bending of this part more flexible, thereby effectively reducing stress concentration. Since the positive electrode sheet is subjected to both tension and compression at the corners during winding and cycling, the groove design allows the stress at these points to be dispersed or weakened, avoiding the breakage of the positive electrode sheet due to excessive stress. This design fundamentally solves the problem of easy breakage of the positive electrode sheet in the prior art, significantly improving the reliability and service life of the battery.

[0019] (2) The reasonable design of the total width of the groove can ensure that the stress buffer structure can bend smoothly during the winding process, effectively disperse the stress, avoid stress concentration, and maintain the consistent thickness of the active material layer, thereby ensuring that the battery capacity is not affected. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a planar sectional view of the positive electrode sheet disclosed in this utility model;

[0022] Figure 2 This is a top view of the positive electrode sheet disclosed in this utility model;

[0023] Figure label:

[0024] 1. Positive current collector; 2. Active material layer; 3. Stress buffer structure; 31. Groove. Detailed Implementation

[0025] The technical solutions of this utility model will be clearly and completely described below with reference to the embodiments of this utility model. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0026] like Figure 1 As shown, combined with Figure 2This utility model discloses a positive electrode sheet, including a positive current collector 1 and an active material layer 2.

[0027] Among them, the positive current collector 1 is a metal foil, preferably an aluminum foil, which serves to carry the active material and provide a current conduction path.

[0028] The active material layer 2, coated on both sides of the positive electrode current collector 1, is the main material of the battery's positive electrode. Its function is to store and release electrical energy, and it is a key component determining battery performance (such as capacity and energy density). The active material layer 2 can be one or a mixture of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium cobalt oxide, and sodium ion positive electrode materials (layered oxides, polyanionic compounds, and Prussian blue compounds).

[0029] During battery manufacturing, in the winding process, the positive electrode sheet is wound into a tight core, especially at the inner corner at the beginning of the winding. Due to material deformation, the corner area usually experiences significant stress concentration. As the negative electrode material expands and contracts during charging and discharging, these stresses are further aggravated, easily leading to breakage of the positive electrode sheet.

[0030] To solve the above problems, the solution adopted in this embodiment is as follows: the active material layer 2 on the inner side of the positive electrode sheet is provided with a stress buffer structure 3 in several bending areas at the starting end of the winding. The stress buffer structure 3 includes at least one groove 31, which is formed by local thinning of the active material layer 2.

[0031] In this embodiment, the first few folds of the wound core have the smallest radius of curvature and the highest stress concentration. The groove 31, designed to alleviate stress, reduces the rigidity of this area by thinning the active material layer 2, making the bending more flexible and effectively reducing stress concentration during winding. Because the positive electrode sheet is subjected to both stretching and compression during winding and cycling, the groove 31 design disperses or weakens the stress at the corners, thus reducing stress concentration. This design effectively prevents cracks in the positive electrode sheet caused by excessive stress during winding, fundamentally solving the problem of positive electrode sheet breakage in the prior art.

[0032] In this embodiment, the cross-section of the groove 31 is U-shaped or V-shaped, and the groove 31 can be made by laser etching, argon ion etching, or mechanical engraving.

[0033] Battery cores are typically formed by tightly winding the positive electrode, negative electrode, and separator into a cylindrical or other shape. During the winding process, the electrodes undergo multiple bends, each of which generates stress, especially in the initial few folds on the inner side of the core. These areas are where stress is most concentrated, making them prone to cracking or breakage.

[0034] Folds 1 through 10 constitute the initial portion of the winding process, where the bending stress is relatively high. Without optimized design, the electrode is prone to cracking or breakage at these locations.

[0035] Therefore, in this embodiment, the stress buffer structure 3 is disposed in at least one bending area of ​​the 1st to 10th folds in the winding core. This allows for optimized design at the locations most prone to cracking and breakage during battery winding. This design effectively alleviates stress in the most critical parts, preventing unnecessary breakage and ensuring battery stability and performance.

[0036] As a preferred option, stress buffer structures are provided in all bending areas from 1 to 5 folds, which can greatly reduce the risk of positive electrode sheet breakage.

[0037] Optimizing these critical bending points in the winding process not only improves the performance of the positive electrode but also enhances the stability of the battery manufacturing process. Manufacturers can more precisely locate and control these bending areas during production, reducing variations and increasing production controllability. This design also reduces battery losses caused by stress concentration during long charge-discharge cycles, ensuring the battery maintains good performance and safety even after multiple charge-discharge cycles.

[0038] As one implementation, the stress buffer structure 3 includes multiple parallel grooves 31. The design of multiple parallel grooves 31 can more evenly distribute the effect of external force in the bending area. Especially in the initial stage of the winding process, multiple parallel grooves 31 can effectively reduce the stress concentration of the positive electrode sheet during the winding process, so that the stress borne by each groove 31 area is more uniform, avoiding the problem of excessive stress in a single position, thereby effectively preventing the electrode sheet from cracking or breaking.

[0039] During the winding process, the electrode sheet is mainly subjected to tensile and compressive forces along the winding direction. By extending the groove 31 perpendicular to the winding direction, the stress from the winding direction can be effectively dispersed and weakened, reducing stress concentration at the bending point and helping to improve the bending and tensile properties of the electrode sheet.

[0040] To improve the uniformity and consistency of the stress buffer structure 3, this embodiment sets the spacing between adjacent grooves 31 to be consistent, and the width of all grooves 31 to be consistent. This setting ensures that the effective range of each groove 31 is equal, thereby distributing stress more evenly and avoiding the problem of excessive local stress caused by uneven spacing and width.

[0041] In some implementations, the depth of the multiple grooves 31 increases gradually from both sides of the stress buffer structure 3 towards the center. This gradient depth design allows the grooves 31 to be distributed according to the stress requirements at different locations. During the winding process, the center of the bending area experiences greater stress, while the sides of the bending area experience less stress. By setting the grooves 31 with gradually increasing depth, the stress relief effect in different areas can be more balanced.

[0042] Initial contact stage: When the electrode begins to bend, the sidewall of groove 31, due to its gradient depth design (shallow on both sides and deep in the middle), first makes contact at the point of maximum curvature. This gradual contact mode can avoid stress abrupt changes and allow bending energy to be absorbed gradually.

[0043] As the degree of bending increases, the multiple grooves 31 in the stress buffer structure 3 come together at the bend, eliminating any gaps that might have existed. When the winding reaches the designed curvature, all the grooves 31 fit together perfectly to form a dense structure, the cavity of the grooves 31 disappears, and the active material layer 2 recovers its full thickness, ensuring that the battery capacity is not lost in any way.

[0044] To avoid stress concentration leading to breakage of the positive electrode and to prevent battery capacity degradation, this embodiment further sets some limiting conditions. Specifically, the total width ΣW of the groove 31 and the radius of curvature r of the corresponding bending area of ​​the positive electrode satisfy: 6.7%πr < ΣW < 2πr.

[0045] The sum of the widths of grooves 31, ΣW, refers to the sum of the widths of all grooves 31. The width of each groove 31 may be different, but their sum must satisfy the mathematical inequality requirements mentioned above.

[0046] The radius of curvature *r* refers to the radius of curvature of the curved region where the electrode is located during the battery winding process. The radius of curvature is inversely proportional to the degree of curvature; that is, the smaller the radius of curvature, the greater the degree of curvature.

[0047] By constraining the relationship between the total width of the grooves 31 and the radius of curvature of the core, the aim is to ensure that the width of the grooves 31 is moderate so as to effectively relieve stress during the winding process, while ensuring that the electrode can bend smoothly without structural problems.

[0048] The minimum value of 6.7%πr was determined based on experiments and mechanical analysis to avoid excessive stress concentration caused by an excessively small total groove width. The maximum value of 2πr was theoretically set by taking into account the physical limitations of the radius of curvature and stress distribution to ensure that the battery can maintain a stable structure during winding and that the battery capacity and performance will not be affected by an excessively large total groove width.

[0049] Specifically, firstly, the total width of the grooves 31 cannot be too small. If the total width of the grooves 31 is too small, the stress may not be effectively dispersed during the winding process, causing local stress concentration and thus affecting the battery performance. Secondly, the total width of the grooves 31 cannot be too large. If the total width of the grooves 31 is too large, one or more grooves 31 in the stress buffer structure 3 corresponding to the bend cannot be tightly closed, resulting in gaps in the grooves 31. This reduces the thickness of the active material layer 2 to some extent, thus leading to a decrease in battery capacity.

[0050] Therefore, the reasonable design of the total width of the grooves 31 can ensure that the stress buffer structure 3 can bend smoothly during the winding process, effectively disperse stress, avoid stress concentration, and maintain the consistent thickness of the active material layer 2, thereby ensuring that the battery capacity is not affected.

[0051] This utility model also discloses a winding core, including a negative electrode sheet, a separator, and the positive electrode sheet disclosed in the foregoing embodiments, wherein the separator is disposed between the negative electrode sheet and the positive electrode sheet.

[0052] Because the active material layer 2 on the inner side of the positive electrode sheet is provided with stress buffer structure 3 in several bending areas at the beginning of the winding, the stress buffer structure 3 includes at least one groove 31. The design of the groove 31 can disperse or weaken the stress of the positive electrode sheet at the corner, thereby reducing the stress concentration phenomenon and effectively avoiding the formation of positive electrode sheet cracks due to excessive stress during the winding process, thus improving the structural stability and reliability of the core.

[0053] This invention also provides a single-cell battery, including a casing and the winding core described in the second aspect, wherein the winding core is housed within the casing. Because the winding core uses a positive electrode sheet, which possesses superior stability and reliability, the single-cell battery also exhibits high stability and reliability.

[0054] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A positive electrode sheet comprising a positive electrode current collector (1) and an active material layer (2) coated on both sides of the positive electrode current collector (1), characterized by: The active material layer (2) on the inner side of the positive electrode tab winding is provided with a stress buffer structure (3) in the bending area at the winding start end, the stress buffer structure (3) comprising at least one groove (31) formed by local thinning of the active material layer (2).

2. The cathode electrode of claim 1, wherein: The stress buffer structure (3) is arranged in at least one bending area of the first to tenth folds of the winding core.

3. The cathode sheet of claim 1, wherein: The stress buffer structure (3) comprises a plurality of parallel grooves (31) extending perpendicular to the winding direction.

4. The cathode electrode of claim 3, wherein: The spacing between adjacent grooves (31) is uniform, and the width of all grooves (31) is uniform.

5. The cathode sheet of claim 3, wherein: The depths of the plurality of grooves (31) are distributed in a gradient increasing from both sides to the middle of the stress buffer structure (3).

6. The cathode sheet of claim 3, wherein: The sum of the widths of all grooves (31) ΣW and the radius of curvature r of the corresponding bending area of the positive electrode tab satisfy: 6.7%πr<ΣW<2πr.

7. The cathode sheet of claim 1, wherein: The cross section of the groove (31) is U-shaped or V-shaped.

8. A core, characterized in that Comprising: a negative electrode tab, a separator, and the positive electrode tab as claimed in any one of claims 1 to 7, the separator being arranged between the negative electrode tab and the positive electrode tab.

9. A single cell characterized by, Comprising: a housing and the winding core as claimed in claim 8, the winding core being accommodated in the housing.

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