Winding battery cell and battery

Abstract

The utility model provides a winding battery cell and a battery, the winding battery cell comprises a positive plate, a negative plate and a diaphragm, the positive plate comprises a current collector, and a protective coating and an active material layer which are sequentially coated on at least one surface of the current collector, the positive plate is provided with a plurality of grooves, the grooves correspond to the areas, with paste, of the negative plate, and the active material layer is arranged in the grooves. The grooves are recessed from one surface of the positive plate along the thickness direction of the positive plate and protrude from the other surface of the positive plate, and the periphery of the projection of each groove in the direction perpendicular to the thickness direction of the positive plate forms a smooth transition and end-to-end connection shape. According to the winding battery cell provided by the invention, when the battery is extruded by external force or impacted by a heavy object, the positive plate is more easily broken from the groove, and the fracture is more tidy, so that the probability of short circuit caused by metal burrs and negative active material scraps at the fracture of the positive plate can be effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of battery devices, and in particular to a wound battery cell and a battery. Background Art

[0002] The factors that affect the safety performance of secondary batteries are mainly thermal abuse and mechanical abuse. Among them, mechanical abuse (such as needle puncture, extrusion, and heavy object impact) will cause battery short circuit at the moment the secondary battery is damaged. The most dangerous short circuit is the short circuit between the positive electrode collector and the negative electrode active material layer. This short circuit method will instantly gather a large amount of heat and cause fire or explosion. In the field of lithium batteries, the positive electrode base coating is usually designed to improve the short circuit between the positive electrode collector and the negative electrode active material layer. However, this method has a more obvious effect on improving needle puncture safety, but it does not significantly improve the safety of extrusion and heavy object impact. Therefore, the safety performance of lithium batteries in terms of extrusion and heavy object impact needs to be improved urgently. Utility Model Content

[0003] The present application provides a wound battery cell, which is provided with a certain groove structure. When the wound battery cell is squeezed or impacted by a heavy object, the positive electrode sheet is easier to break from the groove and the fracture is more neat, which can effectively reduce the short circuit probability between the positive electrode collector and the negative electrode active material layer.

[0004] The present application also provides a battery. Since the battery includes the above-mentioned wound battery core, the battery still has good safety performance when it is squeezed and impacted by heavy objects.

[0005] On the one hand, the present application provides a wound battery cell, including a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet including a current collector and a protective coating and an active material layer sequentially coated on at least one surface of the current collector, the positive electrode sheet is provided with a plurality of grooves, the grooves corresponding to the areas where the negative electrode is coated with paste, the grooves are recessed from one surface of the positive electrode sheet along the thickness direction of the positive electrode sheet and protrude from the other surface, and each of the grooves forms a shape with a smooth transition and a connected end at the projected periphery perpendicular to the thickness direction of the positive electrode sheet.

[0006] In an optional implementation, the groove satisfies the following formula 1 and / or formula 2:

[0007] 0.05≤a / b≤0.99 Formula 1,

[0008] 0.05≤c / d≤1 Formula 2,

[0009] Among them, a is the width of the area where the groove is located, b is the width of the positive electrode sheet, c is the length of the area where the groove is located, and d is the length of the positive electrode sheet.

[0010] In an optional embodiment, 0.1≤a / b≤0.6,

[0011] and / or, 0.5 ≤ c / d ≤ 0.9.

[0012] In an alternative embodiment, the groove satisfies the following formula 3 and / or formula 4:

[0013] 0.7 ≤ e / f ≤ 1 Formula 3,

[0014] j ≥ 1 mm Formula 4;

[0015] Wherein, e is the thickness of the positive electrode sheet in the area where the groove is located, f is the thickness of the positive electrode sheet in the area where there is no groove, and j is the distance between the end of the groove closest to the edge of the positive electrode sheet and the edge of the positive electrode sheet.

[0016] In an alternative embodiment, the groove satisfies the following formula 5 and / or formula 6:

[0017] 1 ≤ g / k ≤ 20 Formula 5,

[0018] 0.1 ≤ m / f < 1 Formula 6,

[0019] Wherein, g is the distance between two adjacent grooves, k is the size of the projection of the groove in the thickness direction perpendicular to the positive electrode sheet, m is the distance from the bottom of the groove to the end face, and f is the thickness of the positive electrode sheet in the area where there is no groove.

[0020] In an alternative embodiment, 1 ≤ g / k ≤ 10,

[0021] and / or, 0.2 ≤ m / f ≤ 0.8.

[0022] In an alternative embodiment, the width of the area where there is no groove ≥ the depth of the tab welding.

[0023] In an alternative embodiment, the convex surface of the groove faces the outside of the wound battery cell.

[0024] On the other hand, the present application provides a battery, including a housing and the above-mentioned wound battery cell, and a ceramic insulating coating is provided on one side of the end of the positive electrode sheet facing the housing.

[0025] In an alternative embodiment, the ceramic insulating coating surrounds the entire circumference of the wound battery cell.

[0026] By introducing special grooves on the surface of the positive electrode sheet in the present application, when the battery is squeezed or impacted by a heavy object, the positive electrode sheet is more likely to break and the fracture surface is more neat, thereby reducing the number of metal burrs at the fracture surface and reducing the probability of short circuit of the battery cell due to the contact between the metal burrs and the debris of the negative active material. Description of the Drawings

[0027] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0028] Figure 1 It is a partial schematic view of the positive electrode sheet of a specific embodiment of the present application;

[0029] In the figure, 001: positive electrode sheet, 002: groove, 003: area where the groove is located, 004: active material layer, 007: tab, a: width of the area where the groove is located, b: width of the positive electrode sheet, c: length of the area where the groove is located, d: length of the positive electrode sheet;

[0030] Figure 2 It is a partial longitudinal sectional view of the positive electrode sheet of a specific embodiment of the present application;

[0031] In the figure, 002: groove, 003: area where the groove is located, 004: active material layer, 005: protective coating, 006: current collector, g: distance between two adjacent grooves, k: size of the projection of the groove in the direction perpendicular to the thickness of the positive electrode sheet;

[0032] Figure 3 It is a partial schematic view of the positive electrode sheet of another specific embodiment of the present application;

[0033] In the figure, 001: positive electrode sheet, 002: groove, 003: area where the groove is located, 004: active material layer, 007 tab, j: distance between the end of the groove closest to the edge of the positive electrode sheet and the edge of the positive electrode sheet;

[0034] Figure 4 It is a partial schematic view of the laminated positive electrode sheet of a specific embodiment of the present application;

[0035] In the figure, 001: positive electrode sheet, 002: groove, 003: area where the groove is located, 004: active material layer, 007 tab;

[0036] Figure 5 It is a partial longitudinal sectional view of the positive electrode sheet of a specific embodiment of the present application, where 001: positive electrode sheet, 002: groove, m: distance from the bottom of the groove to the end face, f: thickness of the positive electrode sheet in the area where there is no groove, e: thickness of the positive electrode sheet in the area where the groove is located;

[0037] Figure 6 It is a CT test picture of the fracture of the battery cell corresponding to the positive electrode sheet of Example 1;

[0038] Figure 7 It is a CT test picture of the fracture of the battery cell corresponding to the positive electrode sheet of Comparative Example 1.

[0039] Through the above-mentioned drawings, specific embodiments of the present application have been shown, and more detailed descriptions will be provided hereinafter. These drawings and written descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. Detailed Description of the Embodiments

[0040] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the protection scope of the present application.

[0041] In the drawings of the embodiments of the present application, the same or similar reference numerals correspond to the same or similar components; in the description of the present application, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation of the present application. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0042] On the one hand, the present application provides a wound battery cell, including a positive electrode sheet, a negative electrode sheet and a separator. As shown in combination with Figure 2 the positive electrode sheet includes a current collector 006 and a protective coating 005 and an active material layer 004 sequentially coated on at least one surface of the current collector; the positive electrode sheet is provided with a plurality of grooves 002, the grooves correspond to the areas where the negative electrode is pasted, the grooves are recessed from one surface of the positive electrode sheet along the thickness direction of the positive electrode sheet and protrude from the other surface, and the projection periphery of each groove in the direction perpendicular to the thickness direction of the positive electrode sheet forms a smooth transition and is connected end to end.

[0043] In the prior art, coating a safety protection coating on the surface of the current collector can improve the safety of the battery under nail penetration, but it has no obvious improvement on extrusion and heavy object impact. Therefore, in this application, a number of grooves are provided on the surface of the positive electrode sheet. The projection periphery (outer edge of the projection) of the groove in the direction perpendicular to the thickness of the positive electrode sheet is a smooth curve. When the battery is subjected to extrusion or heavy object impact, the positive electrode sheet is more likely to break along the area where it is located, and the fracture surface is neater, reducing the metal burrs generated during the irregular fracture of the positive electrode sheet, thereby reducing the probability of short circuit between the metal burrs and the debris of the negative active material and improving the safety performance of the battery when it is subjected to extrusion or heavy object impact. However, if the projection periphery of the groove along the thickness direction of the positive electrode sheet contains non-smooth curve parts, for example, its projection periphery contains sharp corners, this will cause sharp cracks to be easily generated during the process of pressing the groove on the positive electrode sheet, making the positive electrode sheet more likely to generate debris during the heavy object impact process, triggering potential safety hazards of the lithium-ion battery and resulting in the failure of the battery cell.

[0044] Furthermore, since the most dangerous short-circuit mode in the battery is the short circuit between the positive current collector and the debris of the negative active material, and the grooves in this application correspond to the areas where the negative electrode has a coating paste, this can further reduce the probability of this short-circuit mode occurring and thus improve the safety of the battery cell.

[0045] In addition, compared with punching holes in the positive electrode sheet, the grooves on the positive electrode sheet in this application are integrated with the positive electrode sheet. While improving the safety performance of the lithium-ion battery, the content of the active material remains unchanged and the capacity of the lithium-ion battery will not be reduced.

[0046] This application does not specifically limit the material of the above-mentioned current collector. For example, it can be selected from any one or several of copper foil, titanium foil, tin foil, chromium foil, aluminum foil and composite foil materials of the above metals.

[0047] This application does not specifically limit the composition of the protective coating 005. Those skilled in the art can select a conventional protective coating according to needs. Exemplarily, the protective coating is composed of a main material, an insulating filler and an adhesive. Further, the above main material is conductive titanium dioxide particles containing elements such as tin and antimony doped or coated with oxides of tin and antimony (in the coating layer, the doping amounts of tin and antimony are in the range of 0.5 wt% - 30 wt%); the above insulating filler is at least one of inorganic oxides such as silicon dioxide, aluminum oxide, and titanium dioxide; the above adhesive includes at least one of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, carboxylic acid-modified PVDF, polymethyl methacrylate (PMMA), polyimide (PI), polyacrylic acid, and polyacrylic acid copolymers.

[0048] Similarly, the present application does not specifically limit the composition of the active material layer 004. Those skilled in the art can select a conventional active material layer according to needs. Exemplarily, the active material of the above-mentioned active material layer includes one or more of lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium manganese oxide, and lithium-rich manganese-based lithium, etc.

[0049] In a specific embodiment, the projection shape of the groove in the direction perpendicular to the thickness of the positive electrode sheet is circular, elliptical, or a shape surrounded by other arc curves.

[0050] As for the cross-sectional shape of the groove along the thickness direction of the positive electrode sheet, the present application does not make a special limitation. Those skilled in the art can adjust it according to actual needs. In a specific embodiment, the cross-sectional shape of the groove along the thickness direction of the positive electrode sheet is one or several of a semicircle, an ellipse, a semi-ellipse, and a cylinder.

[0051] In a specific embodiment, the size of the projection of the groove in the direction perpendicular to the thickness of the positive electrode sheet is in the micron level, millimeter level, or centimeter level; wherein, the above size can be understood as the maximum size of the projection plane of the groove in the direction perpendicular to the thickness of the positive electrode sheet. For example, it is the major axis or diagonal of the projection plane. In addition, in order to better reduce the impact of heavy object impact on battery short circuit, the size is preferably in the millimeter level.

[0052] Exemplarily, the size is one or several of 100 - 500μm, 200 - 400μm, 300 - 800μm, 450 - 750μm, 550 - 650μm, 1mm - 9mm, 1.5mm - 8.5mm, 2mm - 7mm, 3mm - 6mm, 3.5mm - 5.5mm, 4mm - 5mm, 1cm - 3cm, 2cm - 4cm, 1.5 - 2.5cm, etc. Further, the size is one or several of 1mm, 1.3mm, 1.5mm, 2mm, 2.2mm, 2.5mm, 2.7mm, 3mm, 3.1mm, 3.2mm, 3.5mm, 3.4mm, 4mm, 4.2mm, 4.5mm, 4.7mm, etc.

[0053] In a specific embodiment, in the width direction of the positive electrode sheet, the above-mentioned groove always extends from the center of the positive electrode sheet to both side edges. As for the arrangement of the grooves, the present application does not make a specific limitation. For example, several grooves can be arranged in parallel or non-parallel, can be in one row or multiple rows, can be continuously arranged or intermittently distributed along the width direction of the positive electrode sheet, or can be continuously or intermittently distributed along the length direction of the positive electrode sheet. However, in order to further reduce the burrs generated during the irregular rupture of the positive electrode sheet, preferably, the grooves are arranged in an array.

[0054] In a specific embodiment, the groove satisfies the following formula 1 and / or formula 2:

[0055] 0.05 ≤ a / b ≤ 0.99, Equation 1

[0056] 0.05 ≤ c / d ≤ 1, Equation 2

[0057] wherein, in combination with Figure 1 , a is the width of the groove area 003, b is the width of the positive electrode plate, c is the length of the groove area 003, and d is the length of the positive electrode plate.

[0058] For the impact of heavy objects, when the width of the groove satisfies Equation 1 and / or Equation 2, it can further ensure that the positive electrode plate is easily broken along the groove and ensure that the fracture surface is neater, thereby reducing the short-circuit probability between the metal burrs and the debris of the negative active material.

[0059] In a specific embodiment, to further ensure that the positive and negative electrode plates are broken along the groove and ensure that the fracture surface is neater, 0.1 ≤ a / b ≤ 0.6, and / or, 0.5 ≤ c / d ≤ 0.9.

[0060] Exemplarily, a / b is 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, etc., and c / d is 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0061] In a specific embodiment, the groove satisfies the following Equation 3 and / or Equation 4:

[0062] 0.7 ≤ e / f ≤ 1, Equation 3

[0063] j ≥ 1 mm, Equation 4

[0064] wherein, in combination with Figure 5 , e is the thickness of the positive electrode plate in the groove area, f is the thickness of the positive electrode plate in the non-groove area, and in combination with Figure 3 , j is the distance between the end of the groove closest to the edge of the positive electrode plate and the edge of the positive electrode plate.

[0065] If the groove satisfies Equation 3, the occurrence of cracks at the edge of the groove can be reduced, thus avoiding affecting the normal use of the battery. If e / f is less than 0.7, the groove is under excessive pressure, cracks appear at the edge of the groove, and more debris appears at the fracture surface after the battery is impacted or squeezed by a heavy object, increasing the short-circuit probability of the battery. Exemplarily, e / f is 0.75, 0.77, 0.8, 0.85, 0.87, 0.9, 0.92, 0.95, 0.97, etc.

[0066] If the groove satisfies Equation 4, cracking of the positive electrode plate along the edge can be avoided during the formation of the groove. Exemplarily, j is 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, etc.

[0067] In a specific embodiment, the groove satisfies the following formula 5 and / or formula 6:

[0068] 1 ≤ g / k ≤ 20, formula 5,

[0069] 0.1 ≤ m / f < 1, formula 6,

[0070] wherein, in combination Figure 2 , g is the distance between two adjacent grooves, k is the size of the projection of the groove in the thickness direction perpendicular to the positive electrode sheet, and in combination Figure 5 , m is the distance from the bottom of the groove to the end face, and f is the thickness of the positive electrode sheet in the area where there is no groove.

[0071] The groove satisfying formula 5 and / or formula 6 can further make the fracture surface of the battery neater after being squeezed. Moreover, the groove satisfying formula 6 is beneficial to the storage of free electrolyte, and can further ensure that the battery does not deteriorate its cycle performance on the premise of having good safety performance; if m / f is less than 0.1, the distance from the bottom of the groove to the end face is short, that is, the groove depth is too shallow, and the degree of compression of the electrode sheet is insufficient, which is not conducive to the appearance of a neat fracture surface of the battery after being impacted or squeezed by a heavy object. If m / f is greater than 1, the groove depth is too deep, and the positive electrode sheet is severely over-pressed, resulting in cracks in the positive electrode sheet. The existence of cracks will block the transmission of electrons, thereby deteriorating the cycle performance, and it is easy to cause more debris at the fracture surface and increase the probability of battery short circuit.

[0072] In order to further ensure that the fracture surface of the battery is neater after being impacted or squeezed by a heavy object, in a specific embodiment, 1 ≤ g / k ≤ 10, and / or, 0.2 ≤ m / f ≤ 0.8.

[0073] Exemplarily, g / k is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, etc., and m / f is 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, etc.

[0074] Figure 5 It is a schematic cross-sectional view of the positive electrode sheet of a specific embodiment of the present application. Among them, 002 is the groove, 001 is the positive electrode sheet, m is the distance from the bottom of the groove to the end face, and f is the thickness of the positive electrode sheet in the area where there is no groove.

[0075] Furthermore, when the convex surface of the groove faces the outside of the core, when the battery core is impacted, the electrode sheet of the convex surface of the impact groove is more likely to break, thereby reducing the exposure of empty metal debris at the fracture surface. Therefore, in a specific embodiment, the convex surface of the groove faces the outside of the wound battery core.

[0076] To avoid the fracture of the foil or poor welding during the welding of the tab, the width direction of the tab welding depth area is a non-groove area. Figure 1 FIG. Figure 1 is a partial schematic view of the positive electrode sheet of a specific embodiment of the present application, and the tab of this embodiment is at the tail of the positive current collector. Figure 3 FIG. Figure 3 is a partial schematic view of the positive electrode sheet of another specific embodiment of the present application, and the tab of this embodiment is in the middle of the positive current collector. Figure 4 FIG. Figure 4 is a partial schematic view of the laminated positive electrode sheet of another specific embodiment of the present application; in the figure, 001 is the positive electrode sheet, 002 is the groove, 003 is the area where the groove is located, 004 is the active material layer, and 007 is the tab; in order to avoid the fracture of the foil or poor welding during the welding of the tab, preferably, any of the above positive electrode sheets satisfies that the width of the non-groove area ≥ the tab welding depth.

[0077] On the other hand, the present application provides a battery, including a housing and the above-mentioned wound battery cell, and a ceramic insulating coating is provided on one side of the end of the positive electrode sheet facing the housing.

[0078] In a specific embodiment, the ceramic insulating coating surrounds the entire circumference of the wound battery cell.

[0079] The following further elaborates on the present invention in conjunction with specific embodiments:

[0080] Embodiment 1

[0081] Combined with Figure 1 and Figure 2 , this example provides a wound battery cell, including a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a current collector 006 and a protective coating 005 and an active material layer 004 sequentially coated on two surfaces of the current collector; the positive electrode sheet is also provided with a plurality of grooves 002, and the grooves correspond to the areas with pasted paste on the negative electrode. The grooves are recessed from one surface of the positive electrode sheet along the thickness direction of the positive electrode sheet and protrude from the other surface. The protruding surface of the groove faces the outside of the winding core, and the projection of each groove in the direction perpendicular to the thickness direction of the positive electrode sheet is circular.

[0082] Among them, the thickness of the current collector 006 is 8 μm, and the material is aluminum foil;

[0083] The thickness of the protective coating 005 is 2 μm, and it is composed of 85 parts by mass of conductive titanium dioxide particles (doped with tin and antimony elements on the surface, particle size Dv50 < 0.5 μm), 10 parts by mass of nano-silica (particle size < 50 nm) and 5 parts by mass of polyvinylidene fluoride (PVDF).

[0084] The thickness of the single-sided active material layer 004 is 36 μm. The active material layer is composed of 97.6 parts by mass of lithium cobaltate, 1.05 parts by mass of PVDF, and 1.35 parts by mass of conductive agent. Among them, the conductive agent is composed of conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes with a mass ratio of 30:13:2.

[0085] There are 5 rows of parallel circular grooves in the longitudinal direction of the positive electrode plate. The diameter of the circular grooves is 2 mm. The gap between the grooves is equal to the diameter of the grooves. The distance from the bottom of the grooves to the end face is equal to 45% of the thickness of the positive electrode plate. The width of the grooves is 18 mm (the width of the positive electrode plate is 86.5 mm).

[0086] The preparation of the above positive electrode plate and battery is as follows:

[0087] First step: Prepare the protective coating. After mixing 85 parts by mass of conductive titanium dioxide particles and 10 parts by mass of nano-silica evenly, add them to the dispersed PVDF adhesive solution. After mixing the slurry evenly, coat it on the aluminum foil by the gravure coating method. After baking and drying, the current collector with the protective coating 002 is obtained. The thickness of this protective coating is 2 μm. After the protective coating is coated, use the skip coating method to coat a ceramic insulating coating with a thickness of 10 μm on the single-sided empty foil area at the tail of the positive electrode.

[0088] Second step: Prepare the active material layer. After mixing the conductive agent and the PVDF adhesive solution evenly, add lithium cobaltate and stir evenly to obtain the active material layer slurry. Coat the slurry on the surface of the safety protection layer by the extrusion coating method. After baking, rolling, and slitting, small strip-shaped positive electrode plates are obtained.

[0089] Third step: Prepare the negative electrode plate. After mixing 97 parts by mass of graphite and 0.5 parts by mass of conductive carbon black evenly, add 1.3 parts by mass of dispersant carboxymethyl cellulose and deionized water in batches. Finally, add 1.2 parts by mass of binder styrene-butadiene rubber and stir evenly to obtain the negative electrode active material layer slurry. Coat the negative electrode slurry on a 10-μm carbon-coated copper foil by the extrusion coating method. After baking, rolling, and slitting, small strip-shaped negative electrode plates are obtained (the thickness of the single-sided negative electrode active material coating after rolling is 47 μm).

[0090] Fourth step: Use an embossing roller with raised patterns to roll the positive electrode plate that has been slit into small strips to obtain the above positive electrode plate.

[0091] Fifth step: Make positive and negative electrode plates. Weld the tabs of the positive and negative electrode plates respectively, and paste tab glue, protective glue, and termination glue.

[0092] Step 6: After processes such as winding the positive electrode sheet, separator, and negative electrode sheet (wherein, the groove corresponds to the area with paste on the negative electrode, and the convex surface of the groove faces the outside of the winding core), encapsulation, baking, liquid injection, formation, secondary sealing, sorting, and OCV, a lithium-ion battery is obtained.

[0093] Example 2

[0094] In this example, the groove introduced on the positive electrode sheet is oval, the major axis of the groove is 2 mm, and the spacing of the grooves is the major axis of the groove. Other conditions are the same as in Example 1.

[0095] Example 3

[0096] In this example, three rows of parallel circular grooves are introduced, the width of the grooves is 10 mm, and other conditions are the same as in Example 1.

[0097] Example 4

[0098] In this example, eight rows of parallel circular grooves are introduced, the width of the grooves is 30 mm, and other conditions are the same as in Example 1.

[0099] Example 5

[0100] In this example, the diameter of the introduced groove is 500 μm, and other conditions are the same as in Example 1.

[0101] Example 6

[0102] In this example, the distance from the bottom of the introduced groove to the end face is 10% of the thickness of the positive electrode sheet, and other conditions are the same as in Example 1.

[0103] Example 7

[0104] In this example, the distance from the bottom of the introduced groove to the end face is 80% of the thickness of the positive electrode sheet, and other conditions are the same as in Example 1.

[0105] Comparative Example 1

[0106] In this example, there is no groove on the positive electrode sheet, that is, the surface of the cut small strip is not pressed to form a groove. Other conditions are the same as in Example 1.

[0107] Comparative Example 2

[0108] In this example, five rows of parallel diamond-shaped grooves are introduced, and other conditions are the same as in Example 1.

[0109] Comparative Example 3

[0110] In this embodiment, after pressing grooves on the positive current collector first and then performing subsequent processes such as coating, rolling, and slitting, the distance from the bottommost part of the groove to the end face is 45% of the thickness of the current collector. Other preparation processes are the same as those in Embodiment 1. Result: After rolling, no obvious grooves that are recessed from one surface of the positive electrode plate along the thickness direction of the positive electrode plate and protrude from the other surface of the positive electrode plate are formed on the surface of the positive electrode plate.

[0111] Summarize the partial structural parameters of the above positive electrode plates in the above embodiments and comparative examples in Table 1. Among them, the width of the area where the groove is located is denoted as a, the width of the positive electrode plate is denoted as b, the length of the area where the groove is located is denoted as c, and the length of the positive electrode plate is denoted as d; the thickness of the positive electrode plate in the non-groove area is denoted as f, and the distance from the bottommost part of the groove to the end face is denoted as m.

[0112] Table 1:

[0113] Item a / b c / d m / f Example 1 0.2 0.98 0.45 Example 2 0.2 0.98 0.45 Example 3 0.11 0.98 0.45 Example 4 0.34 0.98 0.45 Example 5 0.2 0.98 0.45 Example 6 0.2 0.98 0.1 Example 7 0.2 0.98 0.8

[0114] Conduct the following safety tests on the batteries in the above embodiments and comparative examples (the results are recorded in Table 2):

[0115] 1. Heavy object impact test: At room temperature, after discharging the battery at 0.5C to 3.0V, then charging it at 0.2C to 4.5V, with the constant voltage charging cut-off current being 0.02C, discharging it at 0.5C to 3.0V, cycling 5 times in sequence, then charging the battery cell at a constant current of 0.7C charging rate to 4.5V, with the constant voltage cut-off current being 0.02C. Finally, place the fully charged battery cell on a flat surface, place a steel column with a diameter of 15.8 ± 0.2 mm at the center of the battery cell, with the longitudinal axis of the steel column parallel to the plane, and let a heavy object with a mass of 9.1 ± 0.1 Kg freely fall from a height of 610 ± 25 mm onto the steel column above the center of the battery cell. Pass if the battery cell does not catch fire or explode. The heavy object impact test needs to be completed within 48 hours after the battery is fully charged. Among them, the fracture CT test pictures of the battery cell corresponding to the positive electrode plate of Embodiment 1 are shown in Figure 6 , and the fracture CT test pictures of the battery cell corresponding to the positive electrode plate of Comparative Example 1 are shown in Figure 7 , and it can be seen by comparison that there are fewer scraps and the fracture is neater at the fracture of the battery cell corresponding to the positive electrode plate after pressing grooves in Embodiment 1.

[0116] 2. Unilateral extrusion test: At room temperature, charge and discharge the battery cell in a cycle of 0.7C / 1C (cut-off current is 0.02C) for 5 times, then place the battery cell on an 8-mm-thick platform for extrusion test. The pressing block descends at a speed of 150 mm / s, the total stroke height between the pressing block and the bottom of the platform is 300 mm, the descending stroke is 294 mm, the distance between the pressing block and the fixed platform is 0.3 ± 0.1 mm, the distance between the pressing block and the bottom of the platform is <0.1 mm, and the extrusion time is 1 s. Test the left and right sides of the battery cell respectively. The test needs to be completed within 48 hours after the battery cell is fully charged.

[0117] 3. Needle puncture test: At room temperature, discharge the battery cell to 3.0V at 1C, then charge it to 4.5V at 0.7C constant current with a cut-off current of 0.02C, discharge it to 3.0V at 1C for 5 cycles, then charge it to 4.5V at 0.7C constant current with a cut-off current of 0.02C. Within 48 hours after the test is completed, use a 2.5mm diameter steel needle to vertically penetrate the left, middle and right positions of the lithium-ion battery at a speed of 30mm / s. If there is no fire or explosion within 5 minutes, it passes the test.

[0118] The following cycle performance tests were performed on the batteries of the above embodiments and comparative examples:

[0119] 25℃ cycle system: (1) stand at 25℃±2℃ for 4 hours;

[0120] (2) 0.2C discharge to the lower limit voltage, and let stand for 10 minutes;

[0121] (3) Charge at 0.2C to the upper voltage limit, cut off at 0.05C, and let stand for 10 minutes;

[0122] (4) 0.2C discharge to the lower limit voltage (for initial capacity test);

[0123] (5) Let stand for 10 minutes;

[0124] (6) Charge at 1.5C to 4.25V, then charge at 1.2C to 4.5V, then charge at 0.8C to 4.55V (cut-off at 0.19C), let stand for 5 min, then switch to 4.5V constant voltage, cut-off current at 0.05C, let stand for 10 min;

[0125] (7) 1.0C discharge to the lower limit voltage of 3.0V, and let it stand for 10 minutes;

[0126] Steps (6) to (7) were cycled 1200 times, and the 25°C cycle capacity retention rate of each battery was recorded in Table 1.

[0127] Table 2:

[0128]

[0129]

[0130] As can be seen from Table 2, compared with Comparative Example 1, introducing circular or elliptical grooves on the positive electrode sheet of the example has a better improvement effect on heavy object impact and unilateral extrusion, while introducing diamond-shaped grooves on the surface of the positive electrode sheet in Comparative Example 2 will deteriorate the heavy object impact; for heavy object impact, when the width area of the positive electrode groove is greater than 10% of the width area of the positive electrode sheet (Example 1, Example 3, Example 4 vs. Comparative Example 1), the circular groove has a better improvement effect; by comparing the micron-level grooves and millimeter-level grooves, it is found that the millimeter-level grooves have a better improvement effect on heavy object impact (Example 1 vs. Example 5); in addition, introducing appropriate grooves on the surface of the positive electrode sheet is beneficial to the storage of free electrolyte, so it can ensure that the lithium-ion battery does not deteriorate the cycle performance on the premise of having good safety performance. Compared with the grooves on the rolled electrode sheet, the grooves on the current collector have a weaker improvement effect on the safety performance of the battery cell and will deteriorate the cycle stability performance of the battery cell (Example 1 vs. Comparative Example 3). This may be because the unevenness on the current collector causes the uneven distribution of the positive electrode active material, affecting the ratio of the positive and negative electrode active materials and thus deteriorating the cycle performance. At the same time, the grooves on the current collector crack or partially fall off during the subsequent rolling process, resulting in debris easily existing at the fracture, so the improvement effect on the safety performance is limited.

[0131] It should be understood that the present application is not limited to the precise structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A wound battery cell, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet comprises a current collector and a protective coating and an active material layer sequentially coated on at least one surface of the current collector, characterized in that: The positive electrode sheet is provided with a plurality of grooves, which correspond to the areas where the paste is applied to the negative electrode. The grooves are recessed from one surface of the positive electrode sheet along the thickness direction of the positive electrode sheet and protrude from the other surface. Each of the grooves forms a shape with a smooth transition and a connected end at the projected periphery perpendicular to the thickness direction of the positive electrode sheet.

2. The wound battery cell according to claim 1, characterized in that: The groove satisfies the following formula 1 and / or formula 2: 0.05≤a / b≤0.99 Formula 1, 0.05≤c / d≤1 Formula 2, Among them, a is the width of the area where the groove is located, b is the width of the positive electrode sheet, c is the length of the area where the groove is located, and d is the length of the positive electrode sheet.

3. The wound battery cell according to claim 2, characterized in that: 0.1≤a / b≤0.6, And / or, 0.5≤c / d≤0.

9.

4. The wound battery cell according to claim 1, characterized in that: The groove satisfies the following formula 3 and / or formula 4: 0.7≤e / f≤1 Formula 3, j≥1mm Formula 4, Among them, e is the thickness of the positive electrode sheet in the area where the groove is located, f is the thickness of the positive electrode sheet in the area where the groove is not located; j is the distance between the end of the groove closest to the edge of the positive electrode sheet and the edge of the positive electrode sheet.

5. The wound battery cell according to claim 1, characterized in that: The groove satisfies the following formula 5 and / or formula 6: 1≤g / k≤20 Formula 5, 0.1≤m / f<1 Formula 6, Among them, g is the distance between two grooves, k is the size of the projection of the groove in the direction perpendicular to the thickness of the positive electrode sheet, m is the distance from the bottom of the groove to the end face, and f is the thickness of the positive electrode sheet in the area where the groove is not located.

6. The wound battery cell according to claim 5, characterized in that: 1≤g / k≤10, And / or, 0.2≤m / f≤0.

8.

7. The wound battery cell according to claim 1, characterized in that: The width of the non-groove area is ≥ the depth of the lug welding.

8. The wound battery cell according to any one of claims 1 to 7, characterized in that: The protruding surface of the groove faces the outer side of the wound battery core.

9. A battery comprising a housing and a wound battery cell according to any one of claims 1 to 8, characterized in that: A ceramic insulating coating is provided on one side of the positive electrode sheet tail end facing the shell.

10. The battery according to claim 9, characterized in that The ceramic insulating coating surrounds the entire circumference of the wound battery core.

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