A square lithium-ion battery with wound electrode assembly

Abstract

This invention discloses a square lithium-ion battery with wound electrode assemblies, comprising a hollow cell casing; two wound electrode assemblies are disposed within the cell casing; the two wound electrode assemblies are horizontally aligned and vertically arranged; a cell cover plate is disposed on the top of the cell casing; positive electrode posts and negative electrode posts are respectively disposed at the left and right ends of the cell cover plate; the positive electrode tabs of the two wound electrode assemblies are electrically connected to the lower ends of the positive electrode posts; the negative electrode tabs of the two wound electrode assemblies are electrically connected to the lower ends of the negative electrode posts; wherein, each wound electrode assembly includes a central planar portion and two corner portions; the two corner portions are located at the left and right ends of the central planar portion; an elastic insulating pad is disposed on the outer side of the cell casing. This invention, by providing an elastic insulating pad on the outer surface of the cell casing of the square lithium-ion battery, helps to reduce the external forces generated between adjacent cells and improves the cycle life of the cells.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a square lithium-ion battery with a wound electrode assembly. Background Technology

[0002] Currently, lithium-ion batteries are rapidly being adopted and promoted in the field of electric vehicles due to their advantages such as high energy density and long cycle life. With the increasing demand for longer driving range, the cycle life of lithium-ion batteries in the vehicle battery system must be fully utilized to ensure the lifespan of electric vehicles.

[0003] Electric vehicles are generally high-voltage power systems composed of hundreds of battery cells. Their structure can be divided into three types from bottom to top: the first type is cell-module-pack (C to M to P), the second type is cell-pack (C to P), and the third type is cell-chassis (C to C).

[0004] In battery systems of various structures, cells are integrated and arranged together in series and parallel, with the ends of parallel cell stacks rigidly fixed. Furthermore, based on the design principle of maximizing volumetric energy density, the space reserved for the cells is very limited. During charging and discharging, the cells undergo lateral expansion, generating external forces between them.

[0005] As the number of battery cell cycles increases, the electrode thickness expands, leading to a continuous increase in cell thickness. Consequently, the external forces generated between adjacent cells also increase. Since the electrodes and separators used in the cell are porous structures, these external forces affect the ionic pore resistance. Furthermore, the structural differences in wound electrode assemblies result in varying degrees of stress.

[0006] Therefore, there is an urgent need to develop a technology that can reduce the external forces generated between adjacent cells and improve the cycle life of the cells, taking into account the structural differences in the electrode groups. Summary of the Invention

[0007] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a square lithium-ion battery with a wound electrode assembly.

[0008] Therefore, the present invention provides a square lithium-ion battery with a wound electrode assembly, characterized in that it includes a hollow cell casing;

[0009] Inside the cell casing, two wound electrode groups are installed;

[0010] The two wound pole groups are horizontally aligned and vertically arranged.

[0011] A cell cover plate is provided on the top of the cell casing;

[0012] Positive and negative terminals are respectively provided at the left and right ends of the battery cell cover.

[0013] The positive tabs of the two wound-type electrode groups are electrically connected to the lower end of the positive electrode post;

[0014] The negative tabs of the two wound-type electrode groups are electrically connected to the lower end of the negative electrode post;

[0015] Each wound pole group includes a central planar portion and two corner portions;

[0016] The two corner sections are located at the left and right ends of the middle plane section;

[0017] At least one elastic insulating pad is provided on the front and rear outer surfaces of the battery cell housing. The elastic insulating pad is provided on the wound electrode assembly in any of the following structural forms:

[0018] The first structural form: When the elastic insulating pad is a hollow U-shaped structure, an elastic insulating pad is provided on the front and rear sides of the cell housing respectively. The inner side of the four sides of each elastic insulating pad is aligned with the left and right sides and the top and bottom sides of the wound electrode assembly, and the outer side of the four sides of the elastic insulating pad is aligned with the four sides of the cell housing.

[0019] The second structural form: When the elastic insulating pad is a solid rectangular pad, a vertically distributed rectangular elastic insulating pad is provided on the front and rear sides of the cell housing respectively. The two elastic insulating pads are respectively provided on the front and rear sides of the middle plane part of the wound electrode assembly. The vertical height of each elastic insulating pad is the same as the vertical height of the cell housing.

[0020] The third structural form: When the elastic insulating pad is a solid rectangular pad, two elastic insulating pads are respectively provided on the front and rear sides of the cell housing, and a vertically distributed rectangular elastic insulating pad is respectively provided on the front and rear sides of the two corner parts at the left and right ends of the wound electrode group. The vertical height of each elastic insulating pad is the same as the vertical height of the cell housing.

[0021] The fourth structural form: When the elastic insulating pad is a hollow U-shaped structure, an elastic insulating pad is provided on the front and rear sides of the battery cell housing, and a vertically distributed U-shaped elastic insulating pad is provided on the front and rear sides of the middle plane part of the wound electrode assembly. The vertical height of each elastic insulating pad is the same as the vertical height of the battery cell housing, and the center of each elastic insulating pad has a rectangular cavity.

[0022] Preferably, the middle plane portion of the wound electrode assembly is the portion of the wound electrode assembly that is linearly distributed.

[0023] The two corner sections at the left and right ends of the wound pole assembly are the parts of the wound pole assembly other than the middle planar section.

[0024] Preferably, the elastic insulating pads are applied to different positions of the wound electrode assembly and are connected to the outer surface of the battery cell housing by thermally conductive structural adhesive or double-sided adhesive.

[0025] Preferably, the wound electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, negative electrode sheet, and separator in the wound electrode assembly each include a central planar portion and a corner portion; the separator is located between the positive electrode sheet and the negative electrode sheet.

[0026] Preferably, the elastic insulating gasket is made of polypropylene microporous foam material (MPP).

[0027] Preferably, the thickness of the elastic insulating gasket is 0.50 mm.

[0028] Preferably, for the first structural form, the overall lateral width of the inner frame of each elastic insulating pad is equal to the overall lateral length of the wound electrode assembly.

[0029] Preferably, for the second structural form, the lateral width of each elastic insulating pad is less than or equal to the lateral width of the intermediate plane portion, and the two elastic insulating pads cover the front and rear sides of the intermediate plane portion of the wound electrode assembly.

[0030] Preferably, for the third structural form, the lateral length of the elastic insulating pad is greater than or equal to the radius of the arc of the semi-circular corner portion of the wound electrode assembly.

[0031] Preferably, for the fourth structural form, the overall outer frame lateral width of each elastic insulating pad is less than or equal to the lateral width of the middle plane portion.

[0032] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides a square lithium-ion battery with a wound electrode assembly. Its structure is scientifically designed. By setting an elastic insulating pad on the outer surface of the cell shell of the square lithium-ion battery, it is beneficial to reduce the external forces generated between adjacent cells (i.e., two adjacent wound electrode assemblies) and improve the cycle life of the cell, which has great practical significance. Attached Figure Description

[0033] Figure 1a A schematic diagram of the structure of a square lithium-ion battery with a wound electrode assembly provided by the present invention (in this case, an elastic insulating pad of the second structural form is used);

[0034] Figure 1b for Figure 1a The diagram shown is a simplified structural representation of a square lithium-ion battery with a wound electrode assembly provided by the present invention, without showing the elastic insulating pad.

[0035] Figure 1c for Figure 1a The diagram shown is a simplified structural diagram of a square lithium-ion battery with a wound electrode assembly provided by the present invention, with an elastic insulating pad provided.

[0036] Figure 1d for Figure 1a The diagram shown is a simplified structural diagram of a square lithium-ion battery with wound electrode groups provided by the present invention, wherein the battery cell housing contains two wound electrode groups.

[0037] Figure 1e A schematic diagram (cross-sectional view) of the structure of two wound electrode groups located inside the cell casing of a square lithium-ion battery with wound electrode groups provided by the present invention;

[0038] Figure 1f This invention provides a schematic diagram of the structure of one embodiment of a wound electrode assembly in a square lithium-ion battery with a wound electrode assembly (in this case, no elastic insulating pad is provided);

[0039] Figure 2a A schematic diagram of a square lithium-ion battery structure without the addition of elastic insulating pads for a conventional wound electrode assembly.

[0040] Figure 2b This invention provides a square lithium-ion battery with a wound electrode assembly, and a schematic diagram of the structure of the wound electrode assembly when an elastic insulating pad of the first structural form is provided.

[0041] Figure 2cThis invention provides a schematic diagram of a square lithium-ion battery with a wound electrode assembly, wherein the wound electrode assembly is provided with an elastic insulating pad of a second structural form.

[0042] Figure 2d This invention provides a schematic diagram of a square lithium-ion battery with a wound electrode assembly, wherein the wound electrode assembly is provided with an elastic insulating pad of a third structural form.

[0043] Figure 2e This invention provides a schematic diagram of a square lithium-ion battery with a wound electrode assembly, wherein the wound electrode assembly is provided with an elastic insulating pad of a fourth structural form.

[0044] Figure 3a A three-dimensional structural diagram of two clamping plates used in a prismatic lithium-ion battery with a wound electrode assembly provided by the present invention during cycle testing.

[0045] Figure 3b A schematic diagram of the front structure of the clamping plate used in the cycle test of a square lithium-ion battery with a wound electrode assembly provided by the present invention.

[0046] Figure 3c A schematic diagram of the engagement state of a square lithium-ion battery with a wound electrode assembly provided by the present invention with a clamping plate during a cycle test.

[0047] Figure 4 This diagram illustrates the capacity retention rate of a conventional wound electrode assembly without added elastic insulating pads and a square lithium-ion battery with four structural forms provided by this invention after cycle testing. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0049] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0050] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] See Figures 1a to 1f , Figures 2b to 2e , Figures 3a to 3c , Figure 4 The present invention provides a square lithium-ion battery with a wound electrode assembly, including a hollow cell housing 1 (specifically a cuboid shape);

[0053] Inside the cell housing 1, there are two wound electrode groups 2 (i.e., cells);

[0054] The two wound pole groups are horizontally aligned and vertically arranged.

[0055] A cell cover plate is provided on the top of the cell housing 1;

[0056] Positive terminal 3 and negative terminal 4 are respectively provided at the left and right ends of the battery cell cover.

[0057] The positive tabs of the two wound-type electrode groups are electrically connected to the lower end of the positive electrode post 3;

[0058] The negative electrode tabs of the two wound electrode groups are electrically connected to the lower end of the negative electrode post 4;

[0059] Each wound pole group 2 includes a central planar portion 201 and two corner portions 202.

[0060] The two corner sections 202 are located at the left and right ends of the middle plane section 201;

[0061] The middle plane portion 201 of the wound pole group 2 is the portion of the wound pole group 2 that is linearly distributed.

[0062] The two corner portions 202 at the left and right ends of the wound pole group 2 are the remaining portions of the wound pole group 2, excluding the middle planar portion.

[0063] At least one elastic insulating pad 5 is provided on the outer surfaces of the front and rear sides of the battery cell housing 1. The elastic insulating pad 5 is provided on the wound electrode assembly 2 in any of the following structural forms:

[0064] The first structural form: When the elastic insulating pad 5 is a hollow U-shaped structure, an elastic insulating pad 5 is provided on the front and rear sides of the battery cell housing 1 respectively. The inner side of the four sides of each elastic insulating pad 5 is aligned with the left and right sides and the top and bottom sides of the wound electrode group 2, and the outer side of the four sides of the elastic insulating pad 5 is aligned with the four sides of the battery cell housing 1.

[0065] The second structural form: When the elastic insulating pad 5 is a solid rectangular pad, a vertically distributed rectangular elastic insulating pad 5 is provided on the front and rear sides of the battery cell housing 1 respectively. The two elastic insulating pads 5 are respectively provided on the front and rear sides of the middle plane part 201 of the wound electrode group 2. The vertical height of each elastic insulating pad 5 is the same as the vertical height of the battery cell housing 1.

[0066] The third structural form: When the elastic insulating pad 5 is a solid rectangular pad, two elastic insulating pads 5 are respectively provided on the front and rear sides of the battery cell housing 1, and a vertically distributed rectangular elastic insulating pad 5 is respectively provided on the front and rear sides of the two corner parts 202 at the left and right ends of the wound electrode group 2. The vertical height of each elastic insulating pad 5 is the same as the vertical height of the battery cell housing 1.

[0067] The fourth structural form: When the elastic insulating pad 5 is a hollow U-shaped structure, an elastic insulating pad 5 is provided on the front and rear sides of the battery cell housing 1, and a vertically distributed U-shaped elastic insulating pad 5 is provided on the front and rear sides of the middle plane portion 201 of the wound electrode group 2. The vertical height of each elastic insulating pad 5 is the same as the vertical height of the battery cell housing 1, and the center of each elastic insulating pad 5 has a rectangular cavity.

[0068] In this invention, it should be noted that the wound electrode assembly 2 includes a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, negative electrode sheet, and separator in the wound electrode assembly 2 each include a central planar portion and a corner portion; the separator is located between the positive electrode sheet and the negative electrode sheet.

[0069] In this invention, specifically, the elastic insulating pad 5 is applied to different positions of the wound electrode assembly 2 and is connected to the outer surface of the battery cell housing 1 by thermally conductive structural adhesive or double-sided adhesive.

[0070] It should be noted that, in this invention, the cell casing 1 is made of aluminum (3003 series H14, hardness 42, yield strength 125), with a thickness of 0.6-0.5 mm. Under stress, the casing can deform by 130%. During battery cycling, the force of the electrode expansion acts on the cell casing, causing deformation, which is then transmitted to the outside and interacts with the external gasket (i.e., the elastic insulating gasket). However, due to the structural differences of the electrode assembly, different structural parts generate different forces, thus requiring optimization of the gasket's function to mitigate these force differences.

[0071] To better understand the technical solution of the present invention, the following specific embodiments will be used to illustrate the technical solution of the present invention.

[0072] The embodiments described in the specific implementation details are only some, not all, of the embodiments of this invention. For example, the parameters involved, such as gasket size, cell type, gasket specifications and materials, and cycle regime, are not limited to these. Based on the technologies and specific embodiments involved in this invention, other examples obtained in the art without substantial technical improvements are all within the scope of protection of this invention.

[0073] In this invention, by scientifically designing the shape and structure of the elastic insulating pad 5 and its matching installation position on the wound electrode assembly 2, the cycle performance of the lithium-ion battery cell can be effectively improved.

[0074] In this invention, see Figures 2a to 2e In this square lithium-ion battery, the positive electrode post 3 and the negative electrode post 4 are placed vertically upwards. This direction is defined as the Z-axis direction of the cell casing 1. The direction parallel to the positive electrode post 3 and the negative electrode post 4 is the X-axis direction, and the direction perpendicular to the XZ plane is the y-axis direction. For this invention, the elastic insulating pad 5 mainly functions on the two XZ planes of the wound electrode assembly 2. The electrode assembly plane corresponding to this plane includes the large surface of the electrode assembly and the two left and right corners. Furthermore, the XZ planes are the two largest surfaces (i.e., the front and rear sides) on the outer surface of the square lithium-ion battery. Figure 2a The coordinate axis indicators in the text;

[0075] See Figures 2a to 2e The following section presents five scenarios for cell cycle testing: four different structural forms including no gasket, elastic insulating gasket 5 on the outside of the cell housing 1, and cycle testing under rigid clamping. By comparing the cycle performance, the effect of the elastic insulating gasket 5 on the cell cycle performance is explained, and the optimal usage of the elastic insulating gasket 5 under the condition of optimal cycle life is determined.

[0076] See Figure 2a As shown, the lithium-ion power cell (wound electrode group 2) implemented in the following embodiments of the present invention has dimensions of 26.5mm (y-axis direction) * 148mm (x-axis direction) * 103mm (z-axis direction) (excluding electrode height, electrode height 2.5mm), nominal cell capacity of 58Ah, and voltage window of 2.8-4.35V. The battery cell housing 1 contains two pole groups (i.e., wound pole groups 2). The pole groups are wound (see Figure 3). The dimensions of the pole groups are 11.3mm (y-axis direction) * 144mm (x-axis direction) * 95mm (z-axis direction). The radius of the two left and right corners is 5.65mm. The elastic insulating pad 5 applies to the plane of the battery cell housing 1 with dimensions of 148mm * 103mm (XZ). The two pole group planes (i.e., the middle plane part 201) corresponding to the XZ plane of the battery cell housing have dimensions of 144.0mm * 95mm (XZ).

[0077] Referring to Figure 1, the design of the elastic insulating pad 5 addresses the structural differences between the left and right corner portions 202 and the middle planar portion 201 of the wound electrode assembly 2. The specific design is as follows:

[0078] Example 1.

[0079] See Figure 2b In the first structural form shown, the elastic insulating pad 5 located outside the wound electrode assembly is a hollow U-shaped structure with an overall rectangular shape. The hollow U-shaped area is rectangular and avoids the entire wound electrode assembly 2. The solid frame of the elastic insulating pad 5 is fixed to the four sides of the cell housing 1. Specifically, the inner side of the four sides of each elastic insulating pad 5 is aligned with the left and right sides and the top and bottom sides of the wound electrode assembly 2, and the outer side of the four sides of the elastic insulating pad 5 is aligned with the four sides of the cell housing 1.

[0080] See Figure 2b The elastic insulating pad 5 is a hollow U-shaped structure. The size of the hollow area avoids the entire pole group. The outer frame size of the elastic insulating pad 5 is a1*B1=148mm*103mm (X*Z direction), the width of the solid frame in the X direction is a1=2mm, the width of the solid frame in the height (Z) direction is b1=4mm, and the hollow area is 144mm*95mm.

[0081] In specific implementation, for the first structural form, the preferred configuration is that the overall lateral width of the inner frame of each elastic insulating pad 5 is equal to the overall lateral length L1 of the wound electrode assembly 2 (L1 is equal to the sum of the radius R1 of the two corner portions and the lateral length L2 of the middle planar portion 201), see [reference]. Figure 2b As shown in Figure 1.

[0082] Example 2.

[0083] See Figure 2c The second structural form shown is a solid rectangular pad for the elastic insulating pad 5 located outside the wound pole group. It acts on the middle plane portion 201 of the wound pole group 2, avoiding the corner portions 202 at the left and right ends of the wound pole group 2.

[0084] In specific implementation, for the second structural form, it is preferred that the lateral width of each elastic insulating pad 5 is less than or equal to the lateral width of the middle plane portion 201 (i.e., L2 shown in Figure 1), and the two elastic insulating pads 5 cover the front and rear sides of the middle plane portion 201 of the wound electrode assembly 2.

[0085] See Figure 2c The elastic insulating pad 5 is a solid rectangular pad that avoids the left and right corners of the wound pole assembly and acts on the middle plane of the pole assembly. The size of the pad is A2*B2=108mm*103mm (X*Z direction). The reserved width of the left and right corners of the wound pole assembly 2 without the pad is 20mm (reserved width a2=20mm), which is larger than the radius of the left and right corners of the pole assembly, which is 5.65mm.

[0086] Example 3.

[0087] See Figure 2d The third structural form shown is that the elastic insulating pad 5 located outside the cell housing 1 is four solid rectangular pads, which act on the left and right corners 202 of the electrode group respectively.

[0088] In specific implementation, for the third structural form, the lateral length of the elastic insulating pad 5 is greater than or equal to the radius R1 of the semi-circular corner portion 202 of the wound pole group 2.

[0089] See Figure 2d The elastic insulating pad 5 consists of four rectangular solid sheets, which are respectively applied to the front and rear sides of the left and right corners of the wound pole group 2. The size of the pad is a3*B3=20mm*103mm (X*Z direction). The X-direction size of the pad is 20mm, which is greater than the radius R15.65mm of the corner of the pole group.

[0090] Example 4.

[0091] See Figure 2e The fourth structural form shown is that the elastic insulating pad 5 located outside the wound electrode group is a hollow square structure with a rectangular shape. The solid frame of the elastic insulating pad 5 acts on the cell plane, and the width of the elastic insulating pad 5 avoids the two corners 202 at the left and right ends of the wound electrode group 2.

[0092] In specific implementation, for the fourth structural form, it is preferable that the overall outer frame lateral width of each elastic insulating pad 5 is less than or equal to the lateral width of the middle plane portion 201 (i.e., L2 as shown in Figure 1).

[0093] See Figure 2e The elastic insulating pad 5 is a hollow U-shaped structure with a rectangular shape. The solid frame serves as the middle plane of the wound pole group 2 of the battery cell, avoiding the two corners of the pole group. The outer frame is A4*B4=108mm*103mm (X*Z direction). The width of the solid frame in the X direction is a4=10mm, and the width of the solid frame in the Z direction is b4=10mm. The left and right corners of the wound pole group 2 do not have the function of pads. A width of c4=20mm is reserved for each corner, which is larger than the radius of the arc R1 (5.65mm) of the left and right corners of the pole group.

[0094] The technical performance and effects of the present invention will be illustrated through the following experiments.

[0095] See Figures 2b to 2e The above four types of elastic insulating pads 5 are fixed to the two XZ surfaces (corresponding to the pole group surfaces: including the middle flat part 201 and the two corner parts 202 at the left and right ends) on the outside of the four identical battery cell housings 1 with double-sided adhesive.

[0096] Then, see Figures 2b to 2e The four battery cell housings 1, each with a different structure of elastic insulating pad 5, are fixed using two clamping plates 6 with positioning posts. Figure 2a The cell housing 1 shown, which has no spacer, is directly fixed by a clamp 6 with positioning posts. Therefore, the clamp 6 with positioning posts simulates the rigid fixing of a square lithium-ion battery in an electric vehicle.

[0097] Then, square lithium-ion batteries with elastic insulating pads 5 having the above four structural forms and square lithium-ion batteries without pads were placed in a constant temperature chamber with the temperature set at 25℃±2℃. Cyclic tests were conducted at 25℃ using an existing battery testing system. By comparing the capacity retention rate of the cycle performance, the influence of elastic insulating pads 5 on the cycle performance of the battery (i.e., square lithium-ion battery) and the optimal pad structure were evaluated.

[0098] In practice, the constant temperature chamber is a high and low temperature test chamber manufactured by High Frequency Jufu Instruments (Suzhou) Co., Ltd., with an adjustable temperature range of -40℃ to 150℃. The cyclic test temperature is set at 25℃±2℃. The battery testing equipment is an Arbin battery testing system, which performs cyclic tests on the battery at 25℃±2℃. The upper limit voltage of the testing equipment is 100A, and the upper limit voltage is 5V. The cyclic test procedure is as follows: 1C (58A) constant current charging to 4.3V, 0.33C (19.33A) constant current charging to the upper limit cutoff voltage of 4.35V, then switching to constant voltage charging mode until the current drops to 0.05C (2.9A), resting for 30 minutes, 1C discharging to the lower limit cutoff voltage (2.8V), and resting for 30 minutes, which constitutes one cycle. By comparing the battery's cycle capacity retention rate, the role of the gasket is evaluated, and the structural form of the gasket under the optimal cycle conditions is determined.

[0099] The effect of the elastic insulating pad 5 on the battery cycle performance was evaluated by comparing cycle data, and the optimal usage of the elastic insulating pad 5 under the condition of optimal cycle life was determined. The specific operation method for comparing cycle data is as follows:

[0100] See Figure 4 By processing the battery's cycle data, after 1125 cycles without the pad, the remaining capacity is 80.0% (without the pad: 1125 cycles @ 80.0%).

[0101] Under the action of external gasket 1 (i.e., elastic insulating gasket 5 of the first structural form), after 1780 cycles, the remaining capacity is 80% (external gasket 1: 1780 cycles @ 80.0%).

[0102] Under the action of external gasket 2 (i.e., elastic insulating gasket 5 of the second structural form), after 1911 cycles, the remaining capacity is 81.8% (external gasket 2: 1911 cycles @ 81.8%).

[0103] Under the action of external gasket 3 (i.e., elastic insulating gasket 5 of the third structural form), after 1660 cycles, the remaining capacity is 80.0% (external gasket 3: 1660 cycles @ 80.0%).

[0104] Under the action of external gasket 4 (i.e., elastic insulating gasket 5 of the fourth structural form), after 1200 cycles, the remaining capacity is 80.0% (external gasket 4: 1200 cycles @ 80.0%).

[0105] The order of cycle life based on the mode of action is as follows: External gasket 2 (1911 cycles @ 81.8%) > External gasket 1 (1780 cycles @ 80.0%) > External gasket 3 (1660 cycles @ 80.0%) > External gasket 4 (1200 cycles @ 80.0%) > No gasket: 1125 cycles @ 80.0%.

[0106] By comparing the cycle life, it was found that the cycle life with external gaskets was better than that without external gaskets. Under different gasket types, external gasket type 2 (i.e., the second type of elastic insulating gasket 5) is a solid rectangular gasket and has the best cycle performance.

[0107] For the present invention, see Figure 4 As shown, through comparison of cycle data, it is concluded that the cycle performance of batteries using elastic insulating pads 5 is better than that of batteries without pads, that is, elastic insulating pads 5 can improve the cycle life of the battery cell; the structural form with the longest cycle life is the second structural form, that is, a solid rectangular pad, which acts on the middle plane part of the wound electrode group 2 (i.e., battery cell) in the battery cell housing 1, avoiding the left and right corner parts of the wound electrode group 2.

[0108] Based on the above description, it can be seen that the wound electrode assembly, under four different structural gasket methods and without gaskets, underwent cyclic testing fixed by rigid clamps. The comparison of cyclic performance shows that the elastic insulating gasket 5 used in this invention can improve the cyclic performance of the battery cell. The technical features of this patent are simple operation, strong applicability, and significant improvement in cyclic performance.

[0109] In practice, the two clamping plates 6 that fix the battery cell housing 1 are two aluminum alloy plates with a rectangular shape.

[0110] The lateral length of the clamping plate 6 is greater than the lateral length of the cell casing 1;

[0111] The battery cell housing 1 is placed in the longitudinal gap between two vertically arranged and laterally distributed clamping plates 6;

[0112] Each clamping plate 6 has a round hole 61 on the upper and lower sides of both ends;

[0113] The four round holes on the two clamping plates 6 are arranged symmetrically front and back;

[0114] The left and right ends of the two clamping plates 6 are respectively fixedly connected by four positioning pins;

[0115] Each positioning post has a screw hole at both its front and rear ends;

[0116] Each positioning post has its front and rear ends passing through the round holes on the two clamping plates 6, and then being threadedly connected to a screw, that is, the screw is connected to the screw hole on the positioning post.

[0117] It should be noted that the diameter of the screw nut is larger than the diameter of the round hole 61.

[0118] It should be noted that each clamping plate 6 has four round holes at its four corners, and a positioning post is located between two clamping plates 6. The positioning post is cylindrical, with screw holes at both ends. The diameter of the positioning post is smaller than the diameter of the round holes at the four corners of the clamping plate. The front and rear ends of the positioning post pass through the round holes of the two clamping plates respectively. Each positioning post is connected and fixed to the two clamping plates with two screws. See [reference needed]. Figure 3a , Figure 3b As shown, the clamps simulate the rigid fixation of a square lithium-ion battery within an electric vehicle.

[0119] It should be noted that the two clamping plates fixing the battery cell housing 1 are two rectangular aluminum alloy plates, with a length * width of 188mm * 103mm. Each aluminum alloy plate is 10mm thick, and each clamping plate has round holes at its four corners. There are four cylindrical positioning posts between the two plates. The positioning posts are 14mm in diameter and have screw holes at both ends. The positioning post is 27mm long, and both ends of the positioning post pass through the round holes in the clamping plate. The positioning post and the clamping plate are connected by... For screw connection and fixation, see [link / reference] Figure 2b As shown.

[0120] In this invention, specifically, the elastic insulating gasket 5 is made of MPP (microporous polypropylene foam). MPP can be a porous polypropylene (PP) foam material with a pore size of less than 100μm, possessing a certain degree of compressive elasticity and allowing for cutting. The elastic insulating gasket 5 has a specific thickness of 0.50mm, and its shape can be achieved by cutting with scissors.

[0121] It should be noted that, through practical testing, by applying this invention and using an external spacer between two adjacent square lithium-ion cells, the external forces between the cells can be reduced, thereby improving the cycle life of the cells.

[0122] Furthermore, due to the structural differences in the large surface and the two corners of the wound electrode assembly of the square power cell, different ways of using external pads will cause different stress distributions in the electrode assembly, thus affecting the cycle performance of the cell. In order to further improve the cycle performance of lithium-ion batteries, this invention provides the optimal way to use external pads for lithium-ion cells by studying the relationship between the different ways of using external pads and the cycle performance of lithium-ion batteries.

[0123] In summary, compared with the prior art, the square lithium-ion battery with wound electrode assembly provided by the present invention has a scientific structural design. By setting an elastic insulating pad on the outer surface of the cell shell of the square lithium-ion battery, it is beneficial to reduce the external forces generated between adjacent cells (i.e., two adjacent wound electrode assemblies) and improve the cycle life of the cells, which has significant practical significance.

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A square lithium-ion battery having a wound electrode assembly, characterized in that, Includes a hollow cell casing (1); Inside the cell housing (1), two wound electrode groups (2) are provided; The two wound pole groups are horizontally aligned and vertically arranged. A cell cover plate is provided on the top of the cell housing (1); Positive electrode post (3) and negative electrode post (4) are respectively provided at the left and right ends of the battery cell cover plate; The positive tabs of the two wound-type electrode groups are electrically connected to the lower end of the positive electrode post (3); The negative electrode tabs of the two wound electrode groups are electrically connected to the lower end of the negative electrode post (4); Each wound pole group (2) includes a central planar portion (201) and two corner portions (202); The middle plane portion (201) of the wound pole group (2) is the portion of the wound pole group (2) that is in a straight line distribution state; The two corner portions (202) at the left and right ends of the wound pole assembly (2) are the portions of the wound pole assembly (2) excluding the middle planar portion; Two corner sections (202) are located at the left and right ends of the middle plane section (201); At least one elastic insulating pad (5) is provided on the front and rear outer surfaces of the battery cell housing (1). The arrangement of the elastic insulating pad (5) on the wound electrode assembly (2) specifically includes any one of the following structural forms: The first structural form: When the elastic insulating pad (5) is a hollow U-shaped structure, an elastic insulating pad (5) is provided on the front and rear sides of the battery cell housing (1). The inner side of the four sides of each elastic insulating pad (5) is aligned with the left and right sides and the top and bottom sides of the wound electrode assembly (2), and the outer side of the four sides of the elastic insulating pad (5) is aligned with the four sides of the battery cell housing (1). The second structural form: When the elastic insulating pad (5) is a solid rectangular pad, a vertically distributed rectangular elastic insulating pad (5) is provided on the front and rear sides of the battery cell housing (1). The two elastic insulating pads (5) are respectively positioned to correspond to the front and rear sides of the middle plane part (201) of the wound electrode group (2). The vertical height of each elastic insulating pad (5) is the same as the vertical height of the battery cell housing (1). The third structural form: When the elastic insulating pad (5) is a solid rectangular pad, two elastic insulating pads (5) are respectively provided on the front and rear sides of the battery cell housing (1), and a vertically distributed rectangular elastic insulating pad (5) is respectively provided on the front and rear sides of the two corner parts (202) at the left and right ends of the wound electrode group (2). The vertical height of each elastic insulating pad (5) is the same as the vertical height of the battery cell housing (1). The fourth structural form: When the elastic insulating pad (5) is a hollow U-shaped structure, an elastic insulating pad (5) is provided on the front and rear sides of the battery cell housing (1), and a vertically distributed U-shaped elastic insulating pad (5) is provided on the front and rear sides of the middle plane part (201) of the wound electrode group (2). The vertical height of each elastic insulating pad (5) is the same as the vertical height of the battery cell housing (1), and each elastic insulating pad (5) has a rectangular cavity at its center. The elastic insulating pad (5) is applied to different positions of the wound electrode assembly (2) and is connected to the outer surface of the battery cell housing (1) by thermally conductive structural adhesive or double-sided adhesive. The thickness of the elastic insulating pad (5) is 0.50 mm.

2. A square lithium-ion battery with a wound electrode assembly as described in claim 1, characterized in that, The wound electrode assembly (2) includes a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, negative electrode sheet, and separator in the wound electrode assembly (2) each include a central planar portion and a corner portion; the separator is located between the positive electrode sheet and the negative electrode sheet.

3. The square lithium-ion battery with wound electrode assembly as described in claim 1, characterized in that, The elastic insulating pad (5) is made of polypropylene microporous foam material MPP.

4. The square lithium-ion battery with wound electrode assembly as described in any one of claims 1 to 3, characterized in that, For the first structural form, the overall lateral width of the inner frame of each elastic insulating pad (5) is equal to the overall lateral length of the wound pole group (2).

5. The square lithium-ion battery with wound electrode assembly as described in any one of claims 1 to 3, characterized in that, For the second structural form, the lateral width of each elastic insulating pad (5) is less than or equal to the lateral width of the intermediate plane portion (201), and the two elastic insulating pads (5) cover the front and rear sides of the intermediate plane portion (201) of the wound pole assembly (2).

6. The square lithium-ion battery with wound electrode assembly as described in any one of claims 1 to 3, characterized in that, For the third structural form, the lateral length of the elastic insulating pad (5) is greater than or equal to the radius of the semi-circular corner portion (202) of the wound pole assembly (2).

7. The square lithium-ion battery with wound electrode assembly as described in any one of claims 1 to 3, characterized in that, For the fourth structural form, the overall outer frame lateral width of each elastic insulating pad (5) is less than or equal to the lateral width of the middle plane portion (201).

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