Battery assembly and secondary battery

Abstract

The utility model relates to a battery assembly and a secondary battery, belongs to the technical field of secondary batteries, and is used for solving at least one of the problems of lithium / sodium precipitation at the corner of the existing secondary battery, poor cycle performance of the battery and the like. The thickness of the diaphragm thinning area in the battery assembly is different from the thicknesses of the diaphragm straight area and the diaphragm bending area, the expansion rate of the first area and the expansion rate of the second area on the negative plate are different, and the expansion rate of the first area is larger than that of the second area. The diaphragm thinning area can release expansive force, the pole piece fitting property at the corner is better, the problem of lithium / sodium precipitation at the battery corner is reduced, the safety performance of the battery is improved, and the circulation of the battery is improved.

Description

Technical Field

[0001] This utility model relates to the field of secondary battery technology, and in particular to a battery assembly and a secondary battery. Background Technology

[0002] With the growing global demand for clean energy and sustainable transportation solutions, secondary batteries, as a key energy storage medium, are increasingly being used in new energy vehicles (NEVs) and energy storage systems (ESS). The development of secondary battery technology has not only driven improvements in the driving range and performance of electric vehicles but also provided strong support for smart grids and the stable supply of renewable energy. However, with the expansion of application areas, the safety requirements for secondary batteries are becoming increasingly stringent.

[0003] Square batteries are increasingly used in new energy vehicles and energy storage systems, but lithium / sodium plating at their corners poses a significant threat to battery safety and lifespan. Lithium / sodium plating is typically caused by uneven lithium / sodium ion insertion during charging, and is more likely to occur under high energy density and fast charging conditions. This leads to lithium / sodium metal deposition, increased risk of internal short circuits, and may cause battery overheating, thermal runaway, or even combustion and explosion. Furthermore, lithium / sodium plating also causes battery capacity decay and performance degradation.

[0004] Therefore, there is a need to propose a square battery that can solve the problem of lithium / sodium plating at the corners of the square battery, and has high safety and good cycle life. Utility Model Content

[0005] Based on the above analysis, the present invention aims to provide a battery assembly and a secondary battery to solve at least one of the following problems in existing secondary batteries: lithium / sodium plating at corners and poor battery cycle performance.

[0006] In a first aspect, the present invention provides a battery assembly, including a positive electrode sheet, a negative electrode sheet and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form an integral unit;

[0007] The diaphragm includes a straight diaphragm region and a bent diaphragm region; a diaphragm thinning region is provided at the connection between the straight diaphragm region and the bent diaphragm region; the thickness of the diaphragm thinning region is h, and the thickness of the straight diaphragm region is H, where 0.6≤h / H≤0.8;

[0008] The negative electrode sheet includes a first region and a second region, with the first region corresponding to the thinned region of the separator; the area on the negative electrode sheet other than the first region is the second region; the expansion rate of the first region is greater than the expansion rate of the second region.

[0009] In this invention, the thickness of the thinned separator region in the battery assembly differs from the thickness of the straight and bent separator regions. Furthermore, the expansion rates of the first and second regions on the negative electrode are different, with the first region having a higher expansion rate than the second region. This design allows the thinned separator region to release expansion force when the battery assembly expands during cycling, resulting in better electrode adhesion at corners. This reduces lithium / sodium plating issues at battery corners, improves battery safety, and enhances battery cycle life.

[0010] Furthermore, the negative electrode sheet includes a current collector and a negative electrode slurry coating layer, wherein the expansion rate of the coating layer in the first region is 30-60%, and the expansion rate of the coating layer in the second region is 10-20%.

[0011] It should be noted that the expansion rate mentioned in this invention refers to the electrode thickness in a fully charged state / initial electrode thickness × 100%. The different expansion rates of the first and second regions on the negative electrode are determined by the different materials of the negative electrode slurry coating layer. The materials of the coating layer mentioned in this invention are all commercially available raw materials. The current collector in the negative electrode is located in the middle, and the negative electrode slurry is coated on both sides to form the negative electrode.

[0012] The expansion rates of the coating in the first region and the coating in the second region are within the above range, which allows the positive and negative electrodes to fit tightly together without lifting the separator and affecting charge transfer.

[0013] Specifically, the current collector of the negative electrode is aluminum foil.

[0014] Furthermore, the diaphragm thinning area includes a first surface, a second surface, and a third surface; the first surface and the third surface have equal areas, are connected to the edge of the second surface and are positioned opposite each other; the first surface and the second surface form an angle greater than 90°; the third surface and the second surface form an angle greater than 90°.

[0015] Furthermore, the diaphragm includes a first diaphragm surface and a second diaphragm surface; the first diaphragm surface is connected to the first diaphragm thinning region surface and the third diaphragm thinning region surface, forming an included angle α.

[0016] It should be noted that the shape of the thinned area of ​​the separator in this utility model is an inverted trapezoidal structure. The thickness of the thinned area is h, and the thickness of the straight area is H. 0.6≤h / H≤0.8. Within the above range, when the battery assembly is compressed, the adhesive material dispersed to both sides of the negative electrode gathers in the thinned area and enters the inverted trapezoidal structure, thereby reducing the thickness of the battery assembly at the corner. The thickness of the thinned area adapts to the expansion of the negative electrode sheet, and also leaves room for the accumulation of adhesive on the separator.

[0017] Furthermore, the included angle α is 150–160°.

[0018] It should be noted that a small angle is not conducive to the transfer of adhesive liquid after being squeezed on the diaphragm, while a large angle is not conducive to bonding in the middle.

[0019] This invention achieves a higher expansion rate in the first region by coating the negative electrode slurry with the aforementioned expansion rate at different positions on the negative electrode sheet. At the same time, the amount of slurry coated in the thinned separator area is reduced. The specific coating method for the thinned area can reduce the thickness change of the slurry that disperses to both sides of the negative electrode after being compressed in the first region, resulting in a tighter fit between the positive and negative electrodes. This solves the problem of lithium / sodium deposition at the battery corners, improves the battery's safety performance, and enhances the battery's cycle life.

[0020] As one feasible approach, the lengths of the separator bending area, separator thinning area, and the first area on the negative electrode sheet at different locations are adopted as follows: specifically, the length of the innermost separator bending area of ​​the battery assembly is a1, and the length of the outermost separator bending area is a n ; satisfy, a n =a n-1 +2c; where c is the total thickness of the positive electrode, negative electrode, and two separator layers; n is an integer greater than 1.

[0021] Furthermore, when the length of the diaphragm bending region is a1, the length of the diaphragm thinning region is b1;

[0022] When the length of the diaphragm bending area is a n At that time, the length of the diaphragm thinning region is b. n ;

[0023] b1 = (0.05 ~ 0.1)a1, b n =b n-1 +(0.05~0.1)c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode and two separator layers.

[0024] Furthermore, when the length of the diaphragm bending region is a1, the length of the first region on the negative electrode sheet is d1;

[0025] When the length of the diaphragm bending area is a n At that time, the length of the first region on the negative electrode is d. n ;

[0026] d1 = (0.05 ~ 0.1)a1, d n =d n-1 +(0.05~0.1)c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode and two separator layers.

[0027] Furthermore, the first and second surfaces of the diaphragm are made of PVDF.

[0028] In this invention, the thickness of the positive electrode, negative electrode, and separator all refer to the total thickness after the surface is coated with the slurry, such as... Figure 2 As shown, the thickness h of the diaphragm thinning area is the vertical distance between the second surface of the diaphragm thinning area and the second surface of the diaphragm, and the thickness H of the diaphragm straight area is the vertical distance between the first surface of the diaphragm and the second surface of the diaphragm.

[0029] Secondly, this utility model provides a secondary battery, including the aforementioned battery assembly.

[0030] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or be learned by practicing this invention. The objectives and other advantages of this invention can be realized and obtained from the details specifically pointed out in the text and accompanying drawings. Attached Figure Description

[0031] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0032] Figure 1 This is a partial cross-sectional structural diagram of a battery assembly according to the present invention;

[0033] Figure 2 This is a schematic diagram of a partial structure of a diaphragm according to the present invention.

[0034] Figure label:

[0035] 11-First zone, 12-Second zone, 21-Straight diaphragm zone, 22-Bent diaphragm zone, 23-Thinned diaphragm zone, 231-First side of thinned diaphragm zone, 232-Second side of thinned diaphragm zone, 233-Third side of thinned diaphragm zone, 24-First side of diaphragm, 25-Second side of diaphragm, 3-Positive electrode plate. Detailed Implementation

[0036] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] Example 1

[0038] One battery assembly in this embodiment, such as Figure 1-2As shown, it includes a positive electrode 3, a negative electrode, and a separator disposed between the positive electrode 3 and the negative electrode. The positive electrode 3, the separator, and the negative electrode are stacked and wound together to form a whole.

[0039] The diaphragm includes a flat diaphragm region 21 and a bent diaphragm region 22; a thinning diaphragm region 23 is provided at the connection between the flat diaphragm region 21 and the bent diaphragm region 22; the thickness of the thinning diaphragm region 23 is h, the thickness of the flat diaphragm region is H, and h / H = 0.6;

[0040] The negative electrode sheet includes a first region 11 and a second region 12. The first region 11 is correspondingly disposed to the membrane thinning region 23. The area on the negative electrode sheet other than the first region 11 is the second region 12. The expansion rate of the first region 11 is greater than the expansion rate of the second region 12.

[0041] The negative electrode includes a current collector and a negative electrode slurry coating layer coated on the current collector. The expansion rate of the coating layer in the first region 11 is 30%, and the expansion rate of the coating layer in the second region 12 is 10%.

[0042] Specifically, such as Figure 2 As shown, the diaphragm thinning area 23 includes a first surface 231, a second surface 232, and a third surface 233. The first surface 231 and the third surface 233 have equal areas and are connected to the edge of the second surface 232 and are positioned opposite each other. The first surface 231 and the second surface 232 form an angle greater than 90°. The third surface 233 and the second surface 232 also form an angle greater than 90°. The diaphragm includes a first surface 24 and a second surface 25. The first surface 24 is connected to the first surface 231 and the third surface 233, forming an angle α, where α = 160°.

[0043] As one feasible approach, the lengths of the diaphragm bending region 22, the diaphragm thinning region 23, and the first region 11 on the negative electrode sheet at different locations are set in the following manner.

[0044] Specifically, the length of the innermost membrane bending area of ​​the battery assembly is a1, and the length of the outermost membrane bending area is a. n ; satisfy, a n =a n-1 +2c; where c is the total thickness of the positive electrode, negative electrode, and two separator layers; n is an integer greater than 1.

[0045] When the length of the diaphragm bending region is a1, the length of the diaphragm thinning region is b1;

[0046] When the length of the diaphragm bending area is an At that time, the length of the diaphragm thinning region is b. n ;

[0047] b1 = 0.05a1, b n =b n-1 +0.05c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode, and two separator layers.

[0048] In a further embodiment, when the length of the diaphragm bending region is a1, the length of the first region on the negative electrode sheet is d1;

[0049] When the length of the diaphragm bending area is a n At that time, the length of the first region on the negative electrode is d. n ;

[0050] d1 = 0.05a1, d n =d n-1 +0.05c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode, and two separator layers.

[0051] The first and second sides of the separator are made of PVDF, and the current collector of the negative electrode is aluminum foil.

[0052] Example 2

[0053] This embodiment of the battery assembly is the same as that in Embodiment 1, except that the coating expansion rate of the first region 11 is 45%; the coating expansion rate of the second region 12 is 15%, h / H = 0.7, α = 155°, b1 = 0.075a1, b n =b n-1 +0.075c, d1=0.075a1, d n =d n-1 +0.075c.

[0054] Example 3

[0055] This embodiment of the battery assembly is the same as that in Embodiment 1, except that the coating expansion rate of the first region 11 is 60%; the coating expansion rate of the second region 12 is 20%, h / H = 0.8, α = 150°, b1 = 0.1a1, b n =b n-1 +0.1c, d1=0.1a1, d n =d n-1 +0.1c.

[0056] Comparative Example 1

[0057] This comparative example uses a battery assembly that is the same as that in Example 1, except that α is 10°.

[0058] Comparative Example 2

[0059] This comparative example uses a battery assembly that is the same as that in Example 1, except that h = 0.5H.

[0060] Comparative Example 3

[0061] This comparative example of a battery assembly is the same as that in Example 1, except that the coating expansion rate of the first region 11 is 25% and the coating expansion rate of the second region 12 is 8%.

[0062] Application Example 1

[0063] Sodium-ion batteries were assembled using the battery module core alignment, adhesive application, tab welding, casing insertion, and sealing methods of Examples 1-3 and Comparative Examples 1-3, respectively. The positive electrode material was a layered sodium-ion positive electrode material, the negative electrode was hard carbon, and the electrolyte was sodium hexafluorophosphate and the organic solvent methyl ethyl carbonate. The performance of the sodium-ion batteries was tested according to standard T / CIAPS0031—2023, and the results are shown in Table 1.

[0064] Table 1

[0065] Group Sodium deposition during charging Cycle retention rate % / 500 cycles Example 1 Sodium not precipitated 93.7 Example 2 Sodium not precipitated 94.4 Example 3 Sodium not precipitated 93.5 Comparative Example 1 Sodium precipitation at corner 90.1 Comparative Example 2 Sodium precipitation at corner 90.3 Comparative Example 3 Sodium precipitation at corner 89.7

[0066] Table 1 shows that comparing Examples 1-3 with Comparisons 1-3, it can be seen that when the ratio of the thickness h of the separator thinning region to the separator thickness H is limited to 0.6 to 0.8, the angle of the separator thinning region α is set between 150°C and 160°C, and the expansion rate of the slurry coating layer in the first region of the negative electrode is set between 30% and 60%, and the expansion rate of the slurry coating layer in the second region of the negative electrode is set between 10% and 20%, the battery cycle performance can be improved and the problem of sodium deposition at the battery corner can be alleviated.

[0067] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present utility model should be included within the protection scope of the present utility model.

Claims

1. A battery assembly, characterized in that, It includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode, the separator, and the negative electrode are stacked and wound together to form a whole; The diaphragm includes a straight diaphragm region and a bent diaphragm region; a diaphragm thinning region is provided at the connection between the straight diaphragm region and the bent diaphragm region; the thickness of the diaphragm thinning region is h, and the thickness of the straight diaphragm region is H, where 0.6≤h / H≤0.8; The negative electrode sheet includes a first region and a second region, with the first region corresponding to the thinned region of the separator. The area on the negative electrode that is not in the first region is the second region; the expansion rate of the first region is greater than that of the second region.

2. A battery assembly according to claim 1, characterized in that, The negative electrode sheet includes a current collector and a negative electrode slurry coating layer. The expansion rate of the coating layer in the first region is 30-60%, and the expansion rate of the coating layer in the second region is 10-20%.

3. A battery assembly according to claim 1, characterized in that, The diaphragm thinning area includes a first surface of the diaphragm thinning area, a second surface of the diaphragm thinning area, and a third surface of the diaphragm thinning area; The first surface of the diaphragm thinning area and the third surface of the diaphragm thinning area have the same area, and are connected to and opposite to the edge of the second surface of the diaphragm thinning area; The angle between the first surface of the diaphragm thinning zone and the second surface of the diaphragm thinning zone is greater than 90°. The angle between the third surface of the diaphragm thinning zone and the second surface of the diaphragm thinning zone is greater than 90°.

4. A battery assembly according to claim 3, characterized in that, The diaphragm includes a first diaphragm surface and a second diaphragm surface; the first diaphragm surface is connected to the first diaphragm thinning area surface and the third diaphragm thinning area surface, forming an included angle α.

5. A battery assembly according to claim 4, characterized in that, The included angle α is 150° to 160°.

6. A battery assembly according to any one of claims 1-5, characterized in that, The length of the innermost membrane bending zone of the battery assembly is a1, and the length of the outermost membrane bending zone is a. n ; satisfy, a n =a n-1 +2c; where c is the total thickness of the positive electrode, negative electrode and two separators, and n is an integer greater than 1.

7. A battery assembly according to claim 6, characterized in that, When the length of the diaphragm bending region is a1, the length of the diaphragm thinning region is b1; When the length of the diaphragm bending area is a n At that time, the length of the diaphragm thinning region is b. n ; b1 = (0.05 ~ 0.1)a1, b n =b n-1 +(0.05~0.1)c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode and two separator layers.

8. A battery assembly according to claim 6, characterized in that, When the length of the diaphragm bending region is a1, the length of the first region on the negative electrode sheet is d1; When the length of the diaphragm bending area is a n At that time, the length of the first region on the negative electrode is d. n ; d1 = (0.05 ~ 0.1)a1, d n =d n-1 +(0.05~0.1)c; where n is an integer greater than 1, and c is the total thickness of the positive electrode, negative electrode and two separator layers.

9. A battery assembly according to claim 4, characterized in that, The first and second surfaces of the diaphragm are made of PVDF.

10. A secondary battery, characterized in that, Includes the battery assembly as described in any one of claims 1-9.

Images