Preparation method of electrode assembly and battery

Abstract

The invention provides an electrode assembly, a preparation method thereof and a battery. The preparation method comprises the following steps: overlapping a positive plate, a diaphragm and a negative plate, and winding to form a winding core; wherein the initial winding tension of the positive plate is Z0, the first-section decline coefficient is Z1, the second-section decline coefficient is Z2, the third-section decline coefficient is Z3, and Z1, Z2 and Z3 meet the condition that Z3 > Z2 > Z1; the initial winding tension of the negative plate is F0, the first-section decline coefficient is F1, the second-section decline coefficient is F2, the third-section decline coefficient is F3, and F1, F2 and F3 meet the condition that F3 > F2 > F1; the initial winding tension of the diaphragm is G0, and the decreasing coefficient of the diaphragm is G1; z0 > = Z0 > = 3G0, Z1 > = F1, Z2 > = F2, Z3 > = F3, 3G1 > = Z1 > = F1 > = 2G1; and baking and hot-pressing the roll core to form the electrode assembly. By setting the winding tension, the winding tension of the winding core is rapidly and progressively decreased, and the performance of the battery core is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery preparation technology, and in particular to an electrode assembly, a preparation method thereof, and a battery. Background Art

[0002] Batteries have a wide range of applications in modern society, including electric vehicles, mobile power supplies, and portable electronic devices. Battery performance and production efficiency are crucial to many industries. A battery typically consists of a casing and an electrode assembly located within the casing. The electrode assembly typically includes a positive electrode, a negative electrode, and a separator. Electrode assemblies are primarily categorized as wound or laminated. Wound electrode assemblies utilize a winding needle to stack the negative electrode, separator, and positive electrode, then wind them together. During the winding process, the positive, negative, and separator are compressed to ensure a stable winding shape and enhance battery performance.

[0003] However, the winding tension control and hot pressing conditions during the winding process have a significant impact on the quality and production efficiency of the final product. Winding tension control involves applying appropriate winding tension to components such as the positive electrode, negative electrode, and separator during the winding process, with the aim of ensuring stable contact between components and a uniform winding shape. In particular, for prismatic batteries, due to the presence of the R corner (i.e., the corner area) of the electrode assembly after winding, improper winding tension control may lead to poor contact, deformation, scratches, and other problems between components, affecting the performance, safety, and production efficiency of the electrode assembly.

[0004] Hot pressing is the process of heating and applying pressure to the large surfaces of a wound electrode assembly to enhance its mechanical stability and sealing performance. During hot pressing, the electrode assembly is typically heated to a specific temperature and pressure is applied to ensure close contact between internal components and form a stable structure. Improper hot pressing conditions can lead to deterioration in electrode assembly performance, safety issues, and reduced production efficiency.

[0005] In the traditional electrode assembly manufacturing process, during the winding process, the winding tension control of components such as the positive electrode, negative electrode and separator is usually based on experience or manual adjustment, which is difficult to achieve precise control. The large surface of the electrode assembly is subjected to uneven stress, resulting in wrinkles on the electrode sheets. The wrinkles have a serious impact on subsequent battery cycles and other electrical properties, reducing battery quality.

[0006] Therefore, improving the preparation method of electrode assemblies and reducing the wrinkles of pole pieces are crucial to improving battery performance and production efficiency. Summary of the Invention

[0007] The main purpose of the present invention is to provide an electrode assembly, a preparation method thereof and a battery, so as to solve the problem in the prior art that wound battery pole sheets are prone to wrinkles.

[0008] In order to achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing an electrode assembly is provided, the method comprising: stacking a positive electrode sheet, a separator and a negative electrode sheet and winding them to form a winding core; wherein the starting winding tension of the positive electrode sheet is Z0, the first section decreasing coefficient is Z1, the second section decreasing coefficient is Z2, the third section decreasing coefficient is Z3, and Z1, Z2 and Z3 satisfy Z3>Z2>Z1; the starting winding tension of the negative electrode sheet is F0, the first section decreasing coefficient is F1, the second section decreasing coefficient is F2, the third section decreasing coefficient is F3, and F1, F2 and F3 satisfy F3>F2>F1; the starting winding tension of the separator is is G0, and the diaphragm decrease coefficient is G1; F0≥Z0>3G0, Z1≥F1, Z2≥F2, Z3≥F3, 3G1≥Z1≥F1≥2G1; the total number of turns of the core is X turns, the number of turns corresponding to the first section of the decrease coefficient is the 1st turn to the Q1th turn, the number of turns corresponding to the second section of the decrease coefficient is the (Q1+1)th turn to the Q2th turn, and the number of turns corresponding to the third section of the decrease coefficient is the (Q2+1)th turn to the Xth turn, wherein Q1 is an integer in the range of X / 6-2 to X / 6+2, and Q2 is an integer in the range of 2X / 3-2 to 2X / 3+2; the core is baked and hot-pressed to form an electrode assembly.

[0009] Furthermore, the winding tension during winding satisfies: 6gf≥Z1≥F1≥3gf;

[0010] and / or, 12gf≥Z2≥F2≥9gf;

[0011] and / or, 18gf≥Z3≥F3≥15gf.

[0012] Furthermore, the initial winding tension Z0 of the positive electrode sheet is 500 gf to 600 gf;

[0013] and / or, the initial winding tension F0 of the negative electrode sheet is 500 gf to 600 gf;

[0014] and / or, the initial winding tension G0 of the separator is 100 gf to 200 gf;

[0015] And / or, the decreasing coefficient G1 of the separator is 1 gf to 3 gf.

[0016] Furthermore, the baking temperature is 80° C.-90° C. and the baking time is 1 h-2 h.

[0017] Furthermore, the hot pressing temperature is 80° C.-110° C., the hot pressing time is 40s-80s, and the hot pressing pressure is 5000Kgf-10000Kgf.

[0018] To achieve the above object, according to one aspect of the present invention, a battery is provided, comprising a battery cell group, the battery cell group comprising at least one electrode assembly, wherein the electrode assembly is prepared by any of the above methods for preparing an electrode assembly.

[0019] Furthermore, the surface of the battery cell group is provided with restraining glue and bundling glue; the restraining glue is located on the bottom surface and two opposite large surfaces of the battery cell group, and the bundling glue is wrapped around the battery cell group along the winding direction of the electrode on the surface of the battery cell group.

[0020] Furthermore, the width of the binding glue is Ts mm, and the width of the electrode assembly is T J mm, 9mm≥(T J -Ts) / 2≥6mm; the R corner radius of the electrode assembly is R0 mm, the distance from the edge of the binding glue to the R corner edge is L mm, and L satisfies: (T J -Ts) / 2-R0+3≥L≥(T J -Ts) / 2-R0-3;

[0021] Preferably, the upper edge of the diaphragm exceeds the upper edge of the binding glue by 5-15 mm.

[0022] Furthermore, the upper edge of the diaphragm extends beyond the upper edge of the binding adhesive by 3-6 mm;

[0023] Preferably, the width of the binding glue is 15-25 mm.

[0024] Furthermore, the thickness of the binding glue is 20-150 μm;

[0025] The thickness of the binding glue is 20-100μm;

[0026] Preferably, the materials of the binding adhesive and the restraining adhesive are independently selected from any one or more of polyimide, polyester and polytetrafluoroethylene.

[0027] By applying the technical solution of the present invention, by setting the winding tension of the positive electrode sheet, the negative electrode sheet and the diaphragm, the winding tension of the core decreases rapidly, and the relatively outer electrode sheet of the core exerts less pressure on the relatively inner electrode sheet; and in order to further improve the through-type electrode sheet wrinkles, different sections require different decreasing coefficients, and the winding tension of the core starts to decrease from the beginning of winding, which can reduce the self-binding force between the inner circle electrode sheets corresponding to the first section of decreasing turns; and as the number of winding turns increases, the R angle gradually increases, and the excessive self-binding between adjacent electrode sheets evolves into the second electrode sheet layer formed by all electrode sheets corresponding to the second section of decreasing turns and the first section of decreasing turns. The self-binding between the first electrode layer formed by all the electrodes corresponding to the number of reduced turns is too large; and maintaining the same fixed decreasing coefficient cannot distinguish the number of electrode layers that need to be rapidly decreased. The winding tension between the electrodes decreases regularly, and the binding force between the electrode layers still exists. Therefore, the core is divided into three sections, and the decreasing coefficient of each section becomes larger and larger, so as to timely reduce the binding force between the electrode layers (that is, reduce the self-binding force between the second electrode layer and the first electrode layer, and reduce the self-binding force between the third electrode layer and the second electrode layer formed by all the electrodes corresponding to the third section with the number of reduced turns). After the wound core is baked, the stress of the electrode is released and it is immediately hot-pressed into shape. The stress between the internal parts of the core is greatly reduced compared with the conventional process battery cell, which greatly improves the electrode wrinkles and enhances the battery cell performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 A schematic structural diagram of a battery cell according to an embodiment of the present invention is shown;

[0030] Figure 2 shows a schematic cross-sectional structure diagram of a battery cell according to an embodiment of the present invention;

[0031] Figure 3 It shows an interface diagram of a disassembled negative electrode sheet of a battery after capacity division according to Example 1 of the present invention;

[0032] Figure 4 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Example 2 of the present invention;

[0033] Figure 5 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Example 3 of the present invention;

[0034] Figure 6 It shows an interface diagram of a disassembled negative electrode sheet of a battery after capacity division according to Example 4 of the present invention;

[0035] Figure 7 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Example 5 of the present invention;

[0036] Figure 8 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Comparative Example 1 of the present invention;

[0037] Figure 9 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Comparative Example 2 of the present invention;

[0038] Figure 10 It shows an interface diagram of the negative electrode sheet after disassembly of a battery after capacity division according to Comparative Example 3 of the present invention;

[0039] Figure 11 The figure shows the interface of the negative electrode sheet after disassembly of the battery after capacity division according to comparative example 4 of the present invention.

[0040] Among them, the above drawings include the following figure marks: 10, winding core; 11, tab; 20, binding glue; 30, bundling glue. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] As analyzed in the background of this application, the prior art presents the problem of wrinkles in wound battery pole pieces. Specifically, a winding core, which sequentially winds the negative electrode, separator, and positive electrode together using a winding needle, can easily become tight if the winding tension is unreasonable. This can lead to excessive pressure from the outer pole piece on the inner pole piece, resulting in severe through-wrinkles in the inner pole piece after formation and full charge. To address this issue, this application provides an electrode assembly, a method for preparing the same, and a battery.

[0043] According to a typical embodiment of the present application, a method for preparing an electrode assembly is provided, the method comprising: stacking a positive electrode sheet, a separator, and a negative electrode sheet and then winding them to form a winding core 10; wherein the starting winding tension of the positive electrode sheet is Z0, the first section decreasing coefficient is Z1, the second section decreasing coefficient is Z2, the third section decreasing coefficient is Z3, and Z1, Z2, and Z3 satisfy Z3>Z2>Z1; the starting winding tension of the negative electrode sheet is F0, the first section decreasing coefficient is F1, the second section decreasing coefficient is F2, the third section decreasing coefficient is F3, and F1, F2, and F3 satisfy F3>F2>F1; the starting winding tension of the separator is G0, and the separator is G1. The membrane decrease coefficient is G1; F0≥Z0>3G0, Z1≥F1, Z2≥F2, Z3≥F3, 3G1≥Z1≥F1≥2G1; the total number of turns of the core 10 is X turns, the number of turns corresponding to the first section of the decrease coefficient is the 1st turn to the Q1th turn, the number of turns corresponding to the second section of the decrease coefficient is the (Q1+1)th turn to the Q2th turn, and the number of turns corresponding to the third section of the decrease coefficient is the (Q2+1)th turn to the Xth turn, wherein Q1 is an integer in the range of X / 6-2 to X / 6+2, and Q2 is an integer in the range of 2X / 3-2 to 2X / 3+2; the core 10 is baked and hot-pressed to form the electrode assembly.

[0044] The present application sets the winding tension of the positive electrode sheet, the negative electrode sheet and the diaphragm, and the winding tension of the core 10 decreases rapidly, and the electrode sheet on the relatively outer side of the core 10 exerts less pressure on the electrode sheet on the relatively inner side; and in order to further improve the through-type electrode wrinkles, different sections require different decreasing coefficients, and the winding tension of the core 10 starts to decrease from the beginning of winding, which can reduce the self-binding force between the inner circle electrode sheets corresponding to the first section of decreasing turns; and as the number of winding turns increases, the R angle gradually increases, and the excessive self-binding between adjacent electrode sheets evolves into a second electrode sheet layer formed by all electrode sheets corresponding to the second section of decreasing turns and a decrease in the self-binding force between the first section of decreasing turns. The self-binding between the first electrode layer formed by all the electrode sheets corresponding to the number of turns is too large; and maintaining the same fixed decreasing coefficient cannot distinguish the number of electrode layers that need to be rapidly decreased. The winding tension between the electrode sheets decreases regularly, and the binding force between the electrode layers still exists; therefore, the core 10 is divided into three sections, and the decreasing coefficient of each section becomes larger and larger, so as to timely reduce the binding force between the electrode layers (that is, reduce the self-binding force between the second electrode layer and the first electrode layer, and reduce the self-binding force between the third electrode layer and the second electrode layer formed by all the electrode sheets corresponding to the third section with decreasing turns). After the wound core 10 is baked, the stress of the electrode is released and it is immediately hot-pressed into shape. The stress inside the core 10 is greatly reduced compared with the conventional process battery cell, which greatly improves the electrode wrinkles and enhances the battery cell performance.

[0045] It is understood that the decreasing coefficient in this application represents the value of the reduction in tension of the electrode or diaphragm from the nth turn to the n+1th turn during the winding process. For example, the first-stage decreasing coefficient Z1 of the positive electrode is the value of the reduction in the tension of the positive electrode for each additional turn of the electrode from the inside to the outside within the first stage of decreasing turns. Similarly, the second-stage decreasing coefficient Z2 of the positive electrode is the value of the reduction in the tension of the positive electrode for each additional turn of the electrode from the inside to the outside within the second stage of decreasing turns. The third-stage decreasing coefficient Z3 of the positive electrode is the value of the reduction in the tension of the positive electrode for each additional turn of the electrode from the inside to the outside within the third stage of decreasing turns. Correspondingly, the decreasing coefficients F1, F2, and F3 of the negative electrode are the reductions in the winding tension of the negative electrode within the corresponding decreasing turns, and G1 is the reduction in the tension of the diaphragm from the nth turn to the n+1th turn during the winding process.

[0046] It should be pointed out that the range of the number of winding turns corresponding to the first-stage decreasing coefficient of the positive and negative electrodes is the same, both of which are 1 to Q1 (i.e., integers in the range of X / 6-2 to X / 6+2). Specifically, Q1 can be X / 6-2 or an integer adjacent to it in the range of X / 6-2 to X / 6+2, X / 6-1, X / 6, X / 6+1 or X / 6+2. If the value of X / 6 is not an integer, the above values are all integers adjacent to it in the above range. Accordingly, the number of winding turns in the first stage can be 1 to (X / 6-2) turns, 1 to (X / 6-1) turns, 1 to X / 6 turns, 1 to (X / 6+1) turns or 1 to (X / 6+2) turns.

[0047] The range of the number of winding turns corresponding to the second-stage decreasing coefficient of the positive and negative electrodes is also the same, which is (Q1+1) turns to Q2 turns. Specifically, Q2 can be 2X / 3-2, 2X / 3-1, 2X / 3, 2X / 3+1 or 2X / 3+2. If the value of 2X / 3 is not an integer, the above values are all integers corresponding to the adjacent ones within the above range. Those skilled in the art can determine the range of the number of turns of the first stage, the second stage and the third stage according to the values of Q1 and Q2.

[0048] Those skilled in the art will appreciate that the number of turns of the core 10 can be determined by counting the tabs 11. For example, for a half-tab core 10, starting from the innermost tab 11, the Nth tab 11 corresponds to the N-1th turn of the core 10. For a full-tab core 10, starting from the innermost tab 11, with the center of the core 10 as the dividing line, count half of the tabs 11 on one side of the core 10, and the Nth tab 11 corresponds to the N-1th turn of the core 10.

[0049] In some preferred embodiments of the present application, in order to further reduce the wrinkling of the electrode sheets in the inner layer of the winding core 10 during the winding process, the decreasing coefficients of the positive and negative electrode sheets in the first section during winding satisfy the following requirements: 6gf ≥ Z1 ≥ F1 ≥ 3gf. If Z1 is less than F1, the tension of the number of turns corresponding to the positive electrode sheet is greater than that of the negative electrode sheet, causing the outer positive electrode sheet to bind the inner negative electrode sheet. The binding force parallel to the transverse direction of the winding core 10 can easily cause wrinkles in the negative electrode sheet. For example, the decreasing coefficient Z1 of the positive electrode sheet in the first section is 5gf, and the decreasing coefficient F1 of the negative electrode sheet in the first section is 5gf, 4gf, or 3gf; for another example, the decreasing coefficient Z1 of the positive electrode sheet in the first section is 4gf, and the decreasing coefficient F1 of the negative electrode sheet in the first section is 4gf, 3.5gf, or 3gf, etc. Preferably, the difference between the decreasing coefficients Z1 and F1 of the positive and negative electrode sheets in the first section during winding is 0gf to 3gf, specifically 0gf, 0.5gf, 1gf, 1.5gf, 2gf, 2.5gf, 3gf, etc., or other values within the above range, which is particularly effective in reducing electrode wrinkles near the inner layer.

[0050] In some preferred embodiments of the present application, to further reduce electrode wrinkles in the middle layer of the winding core 10 during winding, the decreasing coefficients of the positive and negative electrode sheets in the second section during winding satisfy the following requirements: 12gf ≥ Z2 ≥ F2 ≥ 9gf. For example, the decreasing coefficient Z2 of the positive electrode sheet in the second section is 12gf, and the decreasing coefficient F2 of the negative electrode sheet in the second section is 12gf, 11gf, 10gf, or 9gf; for another example, the decreasing coefficient Z2 of the positive electrode sheet in the second section is 11gf, and the decreasing coefficient F2 of the negative electrode sheet in the second section is 11gf, 10gf, or 9gf, etc. Preferably, the difference between the decreasing coefficients Z2 and F2 of the positive and negative electrode sheets in the second section during winding is 0gf to 3gf, specifically 0gf, 0.5gf, 1gf, 1.5gf, 2gf, 2.5gf, 3gf, etc., or other values within the above range, which is particularly effective in reducing the wrinkles of the electrode sheets in the middle layer.

[0051] In some preferred embodiments of the present application, to further reduce electrode wrinkles on the outer layer of the winding core 10 during winding, the decreasing coefficients of the positive and negative electrode sheets in the third section during winding satisfy the following requirements: 18gf ≥ Z3 ≥ F3 ≥ 15gf. For example, the decreasing coefficient Z3 of the positive electrode sheet in the third section is 18gf, and the decreasing coefficient F3 of the negative electrode sheet in the third section is 18gf, 17gf, 16gf, or 15gf; for another example, the decreasing coefficient Z3 of the positive electrode sheet in the third section is 17gf, and the decreasing coefficient F3 of the negative electrode sheet in the third section is 17gf, 16gf, or 15gf, etc. Preferably, the difference between the decreasing coefficients Z1 and F1 of the positive and negative electrode sheets in the third section during winding is 0gf to 3gf, specifically 0gf, 0.5gf, 1gf, 1.5gf, 2gf, 2.5gf, 3gf, etc., or other values within the above range, which is particularly effective in reducing wrinkles on the outer electrode sheet.

[0052] It should be noted that the decreasing coefficients Z1 and F1 of the positive or negative electrode sheets in the first section of decreasing turns may be fixed values or variable values. Preferably, within the same section of decreasing turns, the decreasing coefficient of the winding tension of the positive or negative electrode sheet relative to the outer layer is not less than the decreasing coefficient relative to the inner layer. Similarly, the decreasing coefficient of the positive or negative electrode sheet in the second or third section of decreasing turns may also be fixed. Preferably, within the same section of decreasing turns, the decreasing coefficient of the winding tension of the positive or negative electrode sheet relative to the outer layer is not less than the decreasing coefficient relative to the inner layer.

[0053] In some embodiments of the present application, the starting winding tension Z0 of the positive electrode sheet is 500gf to 600gf (for example, 500gf, 510gf, 520gf, 530gf, 540gf, 550gf, 560gf, 570gf, 580gf, 590gf or 600gf, etc.); the starting winding tension F0 of the negative electrode sheet is 500gf to 600gf (for example, 500gf, 510gf, 520gf, 530gf, 540gf, 550gf, 560gf, 570gf, 580gf, 590gf or 600gf, etc.). The initial winding tension G0 of the separator is 100gf to 200gf (for example, 100gf, 110gf, 120gf, 130gf, 140gf, 150gf, 160gf, 170gf, 180gf, 190gf, or 200gf). By optimizing the initial winding tension of the positive and negative electrode sheets and separators, the manufacturing precision and internal structural stability of the battery can be further improved, deformation and damage during the manufacturing process can be reduced, and the overall performance of the battery can be improved. This optimized battery can better meet the needs of high-power, high-energy-density applications such as electric vehicles and energy storage systems.

[0054] The specific process of baking or hot pressing the wound core 10 can refer to the prior art, and this application has no special limitation on this. In some embodiments of the present application, the baking temperature is 80℃-90℃, specifically 80℃, 82℃, 84℃, 85℃, 87℃, 89℃, etc., or other values within the above range; the baking time is 1h-2h, specifically 1h, 1.3h, 1.5h, 1.8h, 2h, etc., or other values within the above range. Baking within this temperature and time range can effectively remove moisture and gas inside the battery, improve the stability of the internal structure of the battery, reduce the internal pressure of the battery during the charge and discharge process, thereby improving the safety and cycle performance of the battery. It is suitable for various types of lithium-ion batteries, especially high energy density batteries used in electric vehicles and energy storage systems.

[0055] In some embodiments of the present application, the temperature of hot pressing is 80°C-110°C (such as 80°C, 90°C, 100°C, 110°C, etc.), the time of hot pressing is 40s-80s (such as 40s, 50s, 60s, 70s, 80s, etc.), and the pressure of hot pressing is 5000Kgf-10000Kgf (such as 5000Kgf, 6000Kgf, 7000Kgf, 8000Kgf, 9000Kgf, 10000Kgf, etc.), which is conducive to further improving the effect of hot pressing and improving the comprehensive performance of the battery. The optimization of the hot pressing step further ensures the close contact of the internal materials of the battery, reduces the internal voids, and improves the energy density and cycle performance of the battery. Hot pressing treatment within this temperature, time and pressure range can ensure the close contact of the internal materials of the battery, reduce the internal voids, improve the energy density and cycle performance of the battery, and enhance the mechanical strength and thermal stability of the battery, providing a guarantee for the long-term stable operation of the battery. This optimized hot pressing process is particularly suitable for manufacturing batteries with high energy density and high power output, such as electric vehicle power batteries, drone batteries, etc.

[0056] According to another typical embodiment of the present application, a battery is provided, including a battery cell group, the battery cell group including at least one electrode assembly, wherein the electrode assembly is prepared by any of the above-mentioned methods for preparing an electrode assembly.

[0057] The stress inside the winding core 10 of the electrode assembly prepared by the above method is greatly reduced compared with the conventional process battery cell, which greatly improves the wrinkles of the electrode sheet. It not only has high energy density and high cycle performance, but also has good mechanical strength and thermal stability, so that the battery containing it can meet the needs of high-demand application fields such as electric vehicles and energy storage systems, providing more efficient and safer energy solutions for these fields.

[0058] In some typical embodiments of this application, the battery cell pack is provided with restraining tape and bundling tape on its surface. The restraining tape is located on the bottom surface and two opposing large surfaces of the battery cell pack, while the bundling tape wraps around the battery cell pack once along the direction of pole piece winding. The combination of the restraining tape and bundling tape creates a closed-loop restraining force on the large surface of the winding core 10, ensuring a relatively uniform restraining force on both sides of the winding core 10. This prevents stress release in the pole pieces from unevenly applied areas and further reduces pole piece wrinkling.

[0059] In some embodiments of the present application, Figure 1 As shown, the electrode assembly contains two winding cores 10, both welded with tabs 11. One side of the binding adhesive 20 is affixed to the large surface of core A, and then to the large surface of core B via the bottom surface. The binding adhesive 30 is parallel to the separator on the winding core 10 and covers the binding adhesive 20, passing through the rounded corners on both sides, wrapping around the winding core 10 once. The combination of the binding adhesive 20 and the binding adhesive 30 closes the binding force loop over the large surface of the winding core 10, ensuring uniform binding force on both sides of the winding core 10, thus preventing stress release in the electrode sheets due to uneven force.

[0060] In some embodiments of the present application, Figure 2 As shown, the width of the binding glue 20 is Ts mm, and the width of the electrode assembly, that is, the winding core 10 is T J mm, 9mm≥(T J -Ts) / 2≥6mm. For example (T J -Ts) / 2 can be 6, 6.5, 7, 7.5, 8, 8.5, 9, etc., to ensure that the binding glue 20 can cover the entire winding core 10 while leaving enough space to avoid excessive constraint on the material. Figure 2 The radius of the R corner of the core 10) is R0 mm, the distance between the edge of the binding glue 20 and the edge of the R corner is L mm, and L satisfies: (T J -Ts) / 2-R0+3≥L≥(T J In some embodiments, the distance between the upper edge of the diaphragm and the upper edge of the binding glue 20 is 5-15 mm.

[0061] In some embodiments of the present application, the upper edge of the diaphragm exceeds the upper edge of the binding glue 30 by 3-6 mm. In this way, the binding glue can better cooperate with the restraining glue, making the force on the electrode more uniform, thereby reducing the occurrence of electrode wrinkles.

[0062] In some embodiments of the present application, the width of the binding adhesive is 15-25 mm, which provides a more secure adhesion and helps to make the binding force more uniform across the large surface of the roll core. Specifically, the width of the binding adhesive can be 15 mm, 17 mm, 19 mm, 20 mm, 22 mm, 24 mm, etc., or other values within the above range, and is not limited here.

[0063] In some embodiments of the present application, in order to make the above-mentioned binding glue and bundling glue play a better role, the thickness of the binding glue is 20-150μm, such as 30μm, 50μm, 70μm, 90μm, 110μm, 130μm, etc., to ensure that it does not adversely affect the performance of the battery while providing mechanical support. The thickness of the bundling glue is preferably set between 20μm and 100μm, such as 30μm, 40μm, 55μm, 70μm, 85μm, etc., which not only ensures the mechanical strength of the core 10, but also avoids excessive impact on the internal structure of the battery.

[0064] The materials for the binding glue 30 and the binding glue 20 can be selected from the existing technology and are not limited in this application. The materials for the binding glue 20 and the binding glue 30 are preferably selected from materials with high insulation and heat resistance, such as polyimide, polyester, polyethylene terephthalate (PET) or polytetrafluoroethylene (PTFE). These materials not only provide good mechanical properties, but also remain stable in high temperature environments, effectively enhancing the thermal stability of the battery and providing a guarantee for the long-term stable operation of the battery.

[0065] The following examples and comparative examples will further illustrate the beneficial effects that can be achieved by the present application.

[0066] Example 1

[0067] (1) Winding core 10, the specific method is as follows:

[0068] The total number of turns of the winding core 10 is 30, the number of turns in the first section is set to be 1-5 turns, the number of turns in the second section is set to be 6-18 turns, and the number of turns in the third section is set to be 19-30 turns.

[0069] Set the starting winding tension Z0 of the positive electrode sheet to 600gf, the first-stage decreasing coefficient Z1 to 5gf, the second-stage decreasing coefficient Z2 to 8gf, and the third-stage decreasing coefficient Z3 to 12gf;

[0070] Set the starting winding tension F0 of the negative electrode sheet to 600gf, the first-stage decreasing coefficient F1 to 5gf, the second-stage decreasing coefficient F2 to 8gf, and the third-stage decreasing coefficient F3 to 12gf;

[0071] The initial winding tension G0 of the separator is 180 gf, and the separator reduction coefficient G1 is 2 gf.

[0072] (2) The winding core 10 wound with the above-set winding tension is baked at a temperature of 85°C for 1.5 hours. After baking, the winding core 10 is immediately hot-pressed at a temperature of 100°C for 40 seconds and a pressure of 6000 kgf. After hot-pressing, the electrode assembly is transferred to the top cover and the adapter plate for welding according to conventional processes.

[0073] (3) After the two electrode assemblies are combined into a battery cell group, the battery cell group is affixed with binding glue and bundling glue, wherein the binding glue and bundling glue are both made of PET material. The specific method is as follows:

[0074] The large surfaces of the two electrode assemblies are bonded together. For ease of understanding, one electrode assembly is referred to as electrode assembly A and the other is referred to as electrode assembly B. One side of the binding glue 20 is attached to the large surface of electrode assembly A that faces away from electrode assembly B, and then the bottom surface is attached to the large surface of electrode assembly B that faces away from electrode assembly A. The width Ts of the binding glue 20 is 170 mm, the thickness is 80 μm, and the electrode assembly width T J The electrode assembly has an R corner radius R0 of 3 mm, and a distance L between the edge of the binding glue 20 and the R corner edge of 2 mm; the upper edge of the diaphragm extends beyond the upper edge of the binding glue 20 by 10 mm, and the thickness of the binding glue is 80 μm;

[0075] It should be noted that the width Ts of the binding rubber 20 is the width of the binding rubber 20. Figure 1 The dimension in the X direction, the width of the electrode assembly is T J For electrode components Figure 1 The size in the X direction.

[0076] It can be understood that the “distance L between the edge of the binding glue 20 and the edge of the R-angle” is the distance between the edge of the binding glue 20 and the edge of the R-angle in the X direction.

[0077] It is understood that the upper edge of the diaphragm is Figure 1 In the middle Y direction, the side of the diaphragm is close to the tab.

[0078] The upper edge of the diaphragm extends 6mm beyond the upper edge of the bundling glue, has a width of 30mm and a thickness of 60μm. The bundling glue 30 covers the binding glue, passes through the R corners on both sides, and wraps around the battery cell group in one circle; the cooperation of the binding glue 20 and the binding glue 30 makes the binding force of the large surface of the winding core 10 closed-loop, and the large surface of the winding core 10 on both sides is evenly bound, avoiding the stress release of the electrode in the uneven force area and the formation of wrinkles.

[0079] (4) After step (3) is completed, Mylar is wrapped and then helium inspected to prepare a battery. The positive electrode of the battery is composed of lithium iron phosphate (LiFePO4), binder polyvinylidene fluoride (PVDF) and conductive agent carbon black (SP) in a mass ratio of 97.2:2:0.8; the negative electrode is composed of artificial graphite, SBR, CMC, conductive carbon black in a ratio of 96.5:1.5:1.2:0.8; the electrolyte is formed by adding 10wt% lithium hexafluorophosphate (LiPF6), 1wt% vinylene carbonate and 2wt% vinyl sulfate (DTD) to a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 3:5:2 (mass ratio).

[0080] The battery prepared in this embodiment was formed, divided into different capacities and fully charged, and then disassembled. The negative electrode sheet obtained by disassembly is as follows: Figure 3 As shown, it can be seen that there are no wrinkles on the electrode interface.

[0081] The formation steps are shown in Table 1:

[0082] Table 1

[0083] Serial number Steps Current A Time min Cut-off voltage V 1 Charge 0.02C 60 3 2 Let it sit / 1 / 3 Charge 0.05C 60 3.3 4 Let it sit / 1 / 5 discharge 1C 60 2.5 6 Let it sit / 1 / 7 Finish

[0084] The steps of capacity division are shown in Table 2:

[0085] Table 2

[0086] Serial number Working Mode Current A End time min End voltage V 1 Let it sit / 1 / 2 Charge 0.33C 240 / 3 Let it sit / 1 / 4 discharge 1C 90 2.0 5 Let it sit / 1 / 6 Finish

[0087] Example 2

[0088] The difference from Example 1 is that in step (3), no binding glue and bundling glue are applied.

[0089] Example 3

[0090] The difference from Example 1 is that in step (3), the upper edge of the diaphragm exceeds the upper edge of the binding glue by 30 mm.

[0091] Example 4

[0092] The difference from Example 1 is that in step (3), the upper edge of the diaphragm exceeds the upper edge of the binding glue by 10 mm.

[0093] Example 5

[0094] The difference from Example 1 is that Z1 is 8 gf, the second-stage decreasing coefficient Z2 is 11 gf, and the third-stage decreasing coefficient Z3 is 18 gf.

[0095] Comparative Example 1

[0096] (1) The positive electrode sheet, negative electrode sheet, electrolyte composition and battery preparation process of this comparative example are basically the same as those of Example 1, with the only difference being:

[0097] The first-stage decreasing coefficient Z1 of the positive electrode is 0kf.

[0098] The battery prepared in the comparative example was disassembled after full charge and the pole pieces obtained were as follows: Figure 3 As shown, many wrinkles are formed on the electrode interface.

[0099] Comparative Example 2

[0100] The only difference from Example 1 is that in step (1), the winding core 10 is wound according to a fixed decreasing coefficient, specifically as follows:

[0101] The total number of turns of the winding core 10 is 30, and the initial winding tension of the positive electrode sheet is set to 600 gf, with a decreasing coefficient of 10 gf;

[0102] Set the starting winding tension of the negative electrode sheet to 600gf and the decreasing coefficient to 10gf;

[0103] The initial winding tension G0 of the separator is 180 gf, and the separator reduction coefficient G1 is 3 gf.

[0104] Comparative Example 3

[0105] The difference from Example 1 is that the first-stage decreasing coefficient F1 of the negative electrode sheet is 0 kf.

[0106] Comparative Example 4

[0107] The difference from Example 1 is that the number of decreasing turns in the first stage is set to 0-3 turns, the number of decreasing turns in the second stage is set to 4-15 turns, and the number of decreasing turns in the third stage is set to 16-30 turns.

[0108] Depend on Figure 3-7 The following are the interface diagrams of the disassembled negative electrode sheets of Examples 1-5, Figure 8-11 This is an interface diagram of the negative electrode sheet after disassembly of comparative example 1-4; it can be seen that compared with the comparative example, the wrinkles on the negative electrode sheet after disassembly of embodiment 1-5 are significantly reduced.

[0109] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the present application sets the winding tension of the positive electrode sheet, the negative electrode sheet and the diaphragm, and the winding tension of the core 10 decreases rapidly, and the outer electrode sheet exerts less pressure on the inner electrode sheet; and in order to further improve the through-type electrode sheet wrinkles, different sections require different decreasing coefficients. The winding tension of the core 10 starts to decrease from the beginning of winding, which can reduce the self-binding force between the inner circle electrode sheets; and as the number of winding turns increases, the R angle gradually increases, and the excessive self-binding between the electrode sheets evolves into excessive self-binding between layers. A fixed decreasing coefficient cannot distinguish the number of layers that need to be rapidly decreased. The winding tension between the electrode sheets decreases regularly, and the binding force between the layers still exists; therefore, the core 10 is divided into three sections, and the decreasing coefficient of each section becomes larger and larger, so as to timely reduce the binding force between the layers. After the wound core 10 is baked, the stress of the electrode is released and it is immediately hot-pressed into shape. The stress inside the core 10 is greatly reduced compared to the conventional process battery cell, which greatly improves the electrode wrinkles and enhances the battery cell performance.

[0110] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing an electrode assembly, characterized in that: include: The positive electrode sheet, the separator and the negative electrode sheet are stacked and then wound to form a winding core; wherein the starting winding tension of the positive electrode sheet is Z0, the first section decreasing coefficient is Z1, the second section decreasing coefficient is Z2, the third section decreasing coefficient is Z3, and Z1, Z2 and Z3 satisfy Z3>Z2>Z1; the starting winding tension of the negative electrode sheet is F0, the first section decreasing coefficient is F1, the second section decreasing coefficient is F2, the third section decreasing coefficient is F3, and F1, F2 and F3 satisfy F3>F2>F1; the starting winding tension of the separator is G0, and the separator decreasing coefficient is G1 ; F0 ≥ Z0 > 3G0, Z1 ≥ F1, Z2 ≥ F2, Z3 ≥ F3, 3G1 ≥ Z1 ≥ F1 ≥ 2G1; the total number of turns of the winding core is X turns, the number of turns corresponding to the first section of the decreasing coefficient is the 1st turn to the Q1th turn, the number of turns corresponding to the second section of the decreasing coefficient is the (Q1+1)th turn to the Q2th turn, and the number of turns corresponding to the third section of the decreasing coefficient is the (Q2+1)th turn to the Xth turn, wherein Q1 is an integer in the range of X / 6-2 to X / 6+2, and Q2 is an integer in the range of 2X / 3-2 to 2X / 3+2; The winding core is baked and hot-pressed to form the electrode assembly.

2. The method for preparing an electrode assembly according to claim 1, wherein: The winding tension during winding satisfies: 6gf≥Z1≥F1≥3gf; and / or, 12gf≥Z2≥F2≥9gf; and / or, 18gf≥Z3≥F3≥15gf.

3. The method for preparing an electrode assembly according to claim 2, wherein: The initial winding tension Z0 of the positive electrode sheet is 500 gf to 600 gf; and / or, the initial winding tension F0 of the negative electrode sheet is 500 gf to 600 gf; and / or, the initial winding tension G0 of the separator is 100 gf to 200 gf; And / or, the decreasing coefficient G1 of the diaphragm is 1 gf to 3 gf.

4. The method for preparing an electrode assembly according to claim 1, wherein: The baking temperature is 80°C-90°C; The baking time is 1h-2h.

5. The method for preparing an electrode assembly according to claim 1, wherein: The temperature of the hot pressing is 80° C.-110° C., the time of the hot pressing is 40s-80s, and the pressure of the hot pressing is 5000Kgf-10000Kgf.

6. A battery comprising a battery cell group, wherein the battery cell group comprises at least one electrode assembly, and the electrode assembly is prepared by the method for preparing an electrode assembly according to any one of claims 1 to 5.

7. The battery according to claim 6, characterized in that The surface of the battery cell group is provided with restraining glue and bundling glue; the restraining glue is located on the bottom surface and two opposite large surfaces of the battery cell group, and the bundling glue is wrapped around the battery cell group in a circle along the winding direction of the pole piece on the surface of the battery cell group.

8. The battery according to claim 7, characterized in that The width of the binding glue is Ts mm, and the width of the electrode assembly is T J mm, 9mm≥(T J -Ts) / 2≥6mm; the R corner radius of the electrode assembly is R0 mm, the distance between the edge of the binding glue and the edge of the R corner is L mm, and L satisfies: (T J -Ts) / 2-R0+3≥L≥(T J -Ts) / 2-R0-3; Preferably, the upper edge of the diaphragm exceeds the upper edge of the binding glue by 5-15 mm.

9. The battery according to claim 7, characterized in that The upper edge of the diaphragm extends 3-6 mm beyond the upper edge of the binding glue; Preferably, the width of the binding glue is 15-25 mm.

10. The battery according to claim 7, characterized in that The thickness of the binding glue is 20-150 μm; The thickness of the binding glue is 20-100 μm; Preferably, the materials of the bundling adhesive and the restraining adhesive are independently selected from any one or more of polyimide, polyester and polytetrafluoroethylene.

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