Cylindrical winding core, cylindrical battery and cylindrical winding core preparation method

Abstract

The application relates to the technical field of battery production and discloses a cylindrical winding core, a cylindrical battery and a cylindrical winding core preparation method. The cylindrical winding core prepared by the method comprises a winding head and a winding tail which are connected with each other along the length direction of the pole piece; the tab comprises a first tab and a second tab, the first tab is located at the winding head, and the second tab is located at the winding tail; the height of the first tab is set to be not greater than the rolling height, and the height of the second tab is set to be greater than the rolling height. Through the design of the tabs with different heights, after the winding of the pole piece to form the cylindrical winding core and the rolling of the tabs, at least part of the outer ring tabs is covered on the inner ring tabs, the support effect of the inner ring tabs on the outer ring tabs is realized, the distance of the outer ring tabs to the center hole of the cylindrical winding core is close to 0, the distance of the tabs to the center hole after the rolling of the cylindrical winding core can be reduced, and the short circuit caused by the tab insertion can be effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery production, and in particular relates to a cylindrical winding core, a cylindrical battery and a method for preparing the cylindrical winding core. Background Art

[0002] Current energy crises and environmental pollution have drawn widespread attention. Consequently, in our rapidly developing modern society, people are increasingly demanding sustainable energy. Among various energy conversion and storage systems, batteries, with their high specific energy density, long cycle life, and lack of memory effects, are an ideal choice as a power source for clean energy devices.

[0003] There are three common packaging forms of batteries, which are divided into soft-pack batteries, square batteries and cylindrical batteries according to their appearance. Among them, large cylindrical batteries have the advantages of good consistency, good heat dissipation, and small expansion effect. At the same time, the energy density is improved, fast charging safety is achieved, and both battery life and economy are taken into account.

[0004] In existing technologies, increasing the diameter of cylindrical batteries can lead to problems with effective thermal management due to a decrease in the battery's surface area to volume ratio. To address these issues, a "full-tab" structure has been proposed. This structure uses the current collector foil itself to collect current, resulting in a more uniform current distribution within the battery.

[0005] However, after the full-tab structure completes the flattening process, the tabs of the cylindrical core are easily inserted into the center hole due to force, causing the tabs to contact the pole pieces, thereby causing a short circuit and resulting in low production yield.

[0006] Therefore, there is an urgent need to improve its production process in order to increase the production yield of cylindrical batteries. Summary of the Invention

[0007] In order to address the deficiencies of the prior art, the present invention provides a pole piece, a cylindrical winding core and a cylindrical battery. The pole piece is designed with pole ears of different heights, and the height of the first pole ear located at the winding head is set to be no greater than the flattened height, and the height of the second pole ear located at the winding tail is set to be greater than the flattened height. Therefore, after the pole piece is wound to form a cylindrical winding core and the pole ear is flattened, the distance that the pole ear is inserted into the center hole after being flattened can be reduced, thereby effectively reducing the inverted insertion of the pole ear and improving the production yield.

[0008] The technical effects to be achieved by the present invention are achieved through the following aspects:

[0009] In a first aspect, the present invention provides a pole piece, the pole piece extending in a length direction, the pole piece including a current collector and a pole tab connected to each other in a height direction, the current collector being coated with an active material, and the pole piece including a winding head and a winding tail connected to each other in the length direction;

[0010] The tabs include a first tab and a second tab, wherein the first tab is located at the winding head and the second tab is located at the winding tail;

[0011] The height of the first tab is set to a first preset height, and the height of the second tab is set to a second preset height;

[0012] In which, the first preset height is not greater than the flattened height, and the second preset height is greater than the flattened height. The electrode can be wound to form a cylindrical core, a center hole is formed inside the cylindrical core, the winding head forms an inner ring electrode, the first electrode tab forms an inner ring electrode tab, the winding tail forms an outer ring electrode tab, and the second electrode tab forms an outer ring electrode tab. After the electrode tabs of the cylindrical core are flattened to the flattened height, at least part of the outer ring electrode tabs covers the inner ring electrode tabs, and the distance of the electrode tabs of the cylindrical core inserted inverted to the center hole is close to 0.

[0013] In some implementations, the first preset height is equal to the flattened height.

[0014] In the second aspect, the present invention provides a cylindrical winding core, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the cylindrical winding core is formed by winding the positive electrode sheet, the negative electrode sheet and the separator, and a center hole is formed inside the cylindrical winding core; the positive electrode sheet and the negative electrode sheet adopt the above-mentioned electrode sheet, and the tabs of the cylindrical winding core are flattened to the flattened height, at least part of the outer ring tabs covers the inner ring tabs, and the distance of the tabs of the cylindrical winding core from being inverted to the center hole is close to 0.

[0015] In some implementations, the outermost tab in the outer ring of tabs covers the innermost tabs sequentially from the outside to the inside until the innermost tab in the outer ring of tabs covers the inner ring of tabs.

[0016] In a third aspect, the present invention provides a method for preparing the cylindrical core, comprising the following steps:

[0017] S1. Determine the diameter range ΔD of the inner pole piece of the cylindrical winding core;

[0018] S2. Determine the length d of the inner electrode sheet of the cylindrical core according to the diameter range ΔD of the inner electrode sheet of the cylindrical core, and further determine the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet;

[0019] S3. Prepare a positive electrode sheet, a negative electrode sheet, and a separator, set the height of the first electrode tab at the winding head of the positive electrode sheet to the first preset height, set the height of the second electrode tab at the winding tail of the positive electrode sheet to the second preset height, set the height of the first electrode tab at the winding head of the negative electrode sheet to the first preset height, and set the height of the second electrode tab at the winding tail of the negative electrode sheet to the second preset height;

[0020] S4, winding the positive electrode sheet, the negative electrode sheet, and the separator to form the cylindrical winding core, wherein a central hole is formed inside the cylindrical winding core;

[0021] S5. Flatten the tabs of the cylindrical core to a flattened height so that at least a portion of the outer ring tabs covers the inner ring tabs, and the distance between the tabs of the cylindrical core and the center hole is close to 0.

[0022] In some implementations, in step S1, determining the diameter range ΔD of the inner pole piece of the cylindrical winding core includes the following steps:

[0023] S11. Prepare a test positive electrode sheet, a test negative electrode sheet, and a test separator, wherein the test positive electrode sheet differs from the positive electrode sheet only in that the height of the tabs of the test positive electrode sheet is set to the second preset height, the test negative electrode sheet differs from the negative electrode sheet only in that the height of the tabs of the test negative electrode sheet is set to the second preset height, and the test separator is the same as the separator;

[0024] S12, winding the test positive electrode sheet, the test negative electrode sheet, and the test separator into a test cylindrical core using the same winding method as step S4, with a central hole formed inside the test cylindrical core;

[0025] S13, flattening the tabs of the test cylindrical core to the flattened height using the same flattening method as in step S5;

[0026] S14. Measure and calculate the reduction value ΔL of the diameter of the central hole of the test cylindrical core, assuming that the diameter range ΔD of the inner ring pole piece of the cylindrical core is equal to the reduction value ΔL of the diameter of the central hole of the test cylindrical core.

[0027] In some implementations, in step S14, measuring and calculating the reduction value ΔL of the diameter of the central hole of the test cylindrical winding core includes the following steps:

[0028] S141. Before flattening the tabs of the test cylindrical core, measure the diameter L1 of the center hole thereof;

[0029] S142, after the tabs of the test cylindrical core are flattened, measuring the diameter L2 of the center hole thereof;

[0030] S143. Calculate the reduction value of the diameter of the central hole of the test cylindrical core, ΔL = L1 - L2.

[0031] In some implementations, in step S2, determining the length d of the inner electrode sheet of the cylindrical core according to the diameter range ΔD of the inner electrode sheet of the cylindrical core, and further determining the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet includes the following steps:

[0032] S21. Assume that the inner diameter D2 of the inner ring electrode of the cylindrical winding core is equal to the diameter L1 of the center hole of the test cylindrical winding core before the tab is flattened.

[0033] S22, calculating the outer diameter D1 of the inner ring pole piece of the cylindrical winding core = D2 + ΔD;

[0034] S23, using the Archimedean spiral formula to calculate the length d of the inner pole piece of the cylindrical winding core;

[0035] S24. The length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet are both equal to the length d of the inner ring electrode sheet of the cylindrical winding core.

[0036] In some implementations, in step S23, the Archimedean spiral formula is ;

[0037] Wherein, π is the ratio of circumference to circumference, T is the thickness of the basic unit of the cylindrical core, and the thickness of the basic unit of the cylindrical core is the sum of the thickness of the positive electrode sheet, the thickness of the negative electrode sheet, and twice the thickness of the separator.

[0038] In a fourth aspect, the present invention provides a cylindrical battery comprising the above-mentioned cylindrical winding core.

[0039] In summary, the present invention has at least the following benefits:

[0040] 1. The electrode sheet, cylindrical core, and cylindrical battery provided by the present invention utilize tabs of varying heights. The height of the first tab at the beginning of the winding is set to be no greater than the flattened height, while the height of the second tab at the end of the winding is set to be greater than the flattened height. The first tab forms the inner tab, and the second tab forms the outer tab. Therefore, after the electrode sheet is wound to form the cylindrical core and the tabs are flattened, at least a portion of the outer tab overlaps the inner tab, providing support for the inner tab. The distance the outer tab is inverted into the center hole of the cylindrical core approaches zero. Furthermore, the inner tab is not subjected to force or pressure from the outer tab during the flattening process, allowing it to be inverted into the center hole. This means that the distance the inner tab is inverted into the center hole of the cylindrical core also approaches zero. This reduces the distance the tab is inverted into the center hole of the cylindrical core after flattening, effectively reducing short circuits caused by inverted tab insertion and improving production yield.

[0041] 2. The cylindrical winding core preparation method provided by the present invention first determines the diameter range △D of the inner ring electrode of the cylindrical winding core; secondly, according to the diameter range △D of the inner ring electrode of the cylindrical winding core, determines the length d of the inner ring electrode of the cylindrical winding core; then sets the height of the first electrode tab and the second electrode tab; finally, winds the positive electrode tab, the negative electrode tab and the separator to form a cylindrical winding core, and flattens the electrode tab to the flattened height. By adopting this method, the inner ring electrode tab, because its height is not greater than the flattened height, will not be forced to be inserted into the center hole due to the flattening process. The outer ring electrode tab, because its height is greater than the flattened height, at least part of the outer ring electrode tab is flattened and covers the inner ring electrode tab, and the distance of the outer ring electrode tab inserted into the center hole approaches 0, which can effectively reduce the short circuit caused by the inverted insertion of the electrode tab and improve the production yield. The method is simple and convenient to operate and is suitable for mass production operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a structural diagram of the electrode in Example 1.

[0043] Figure 2 This is another structural diagram of the electrode in Example 1.

[0044] Figure 3 This is a schematic structural diagram of the cylindrical winding core in Example 2.

[0045] Figure 4 Schematic diagram of the process flow of the method for preparing the cylindrical core in Example 3.

[0046] Figure 5 Schematic diagram of the process of determining the diameter range ΔD of the inner pole piece in Example 3.

[0047] Figure 6A Schematic diagram of the tab height status of the test cylindrical winding core before the flattening process of Example 3.

[0048] Figure 6B Schematic diagram of the tab height status of the test cylindrical winding core after the flattening process of Example 3.

[0049] Figure 7 Schematic diagram of the process of measuring and calculating the reduction value ΔL of the diameter of the central hole of the test cylindrical winding core in Example 3.

[0050] Figure 8A Schematic diagram of the diameter of the center hole of the experimental cylindrical core before the flattening process in Example 3.

[0051] Figure 8B Schematic diagram of the diameter of the center hole of the experimental cylindrical core after the flattening process in Example 3.

[0052] Figure 9 Schematic diagram of the process of determining the length d of the inner pole piece of the cylindrical winding core in Example 3.

[0053] Figure 10 This is a structural diagram of the diameter range of the inner ring pole piece of the cylindrical winding core in Example 3.

[0054] Markings in the figure:

[0055] 1. Pole piece, 11. Current collector, 111. Winding head, 112. Winding tail, 12. Pole tab, 12A. First pole tab, 12B. Second pole tab; 1A. Positive pole piece, 1B. Negative pole piece, 2. Diaphragm; 3. Center hole; H1. Height of the first pole tab, H2. Height of the second pole tab; H3. Flattening height, H4. Second preset height; △D. Diameter range of the inner ring pole piece, D1. Outer diameter of the inner ring pole piece, D2. Inner diameter of the inner ring pole piece; L1. Diameter of the center hole before the pole tab is flattened, L2. Diameter of the center hole after the pole tab is flattened, △L. Reduction value of the diameter of the center hole. DETAILED DESCRIPTION

[0056] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0057] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0058] In order to facilitate the explanation of the structure of the pole piece of the present invention, the direction of the pole piece can be defined first, and an orthogonal rectangular coordinate axis can be established. The X-axis direction in the coordinate axis is parallel to the length direction of the pole piece, and the Y-axis direction is parallel to the height direction of the pole piece, so as to more clearly describe the specific implementation of the present invention.

[0059] Example 1:

[0060] Please see the attached Figure 1 -Attached Figure 3 This embodiment provides a pole piece 1, which extends along the length direction. The pole piece 1 includes a current collector 11 and a pole tab 12 connected to each other along the height direction. The current collector 11 is coated with an active material. The pole piece 1 includes a winding head 111 and a winding tail 112 connected to each other along the length direction. The pole tab 12 includes a first pole tab 12A and a second pole tab 12B. The first pole tab 12A is located at the winding head 111, and the second pole tab 12B is located at the winding tail 112. The height of the first pole tab 12A is set to a first preset height, and the height of the second pole tab 12B is set to a second preset height. It should be noted that the first preset height can be no greater than the flattened height, and the second preset height can be greater than the flattened height. Among them, the pole piece 1 can be wound to form a cylindrical core, a center hole 3 is formed inside the cylindrical core, the winding head 111 forms an inner ring pole piece, the first pole ear 12A forms an inner ring pole ear, the winding tail 112 forms an outer ring pole piece, and the second pole ear 12B forms an outer ring pole ear. After the pole ears of the cylindrical core are flattened to the flattening height, at least part of the outer ring pole ears cover the inner ring pole ears, and the distance of the pole ears of the cylindrical core from the center hole 3 to the inverted insertion is close to 0.

[0061] The electrode piece of this embodiment is provided with first and second electrode tabs of different heights. When the electrode tab flattening process is performed, the outer ring electrode tab shrinks inwardly toward the center hole 3. Since the height of the inner ring electrode tab is not greater than the flattening height, the inner ring electrode tab is not affected by the flattening effect, that is, the distance of the inner ring electrode tab being inverted into the center hole of the cylindrical core approaches 0. Moreover, since the height of the outer ring electrode tab is greater than the flattening height, at least a portion of the outer ring electrode tab just covers the inner ring electrode tab, which not only realizes the supporting effect of the inner ring electrode tab on the outer ring electrode tab, but also the distance of the outer ring electrode tab being inverted into the center hole approaches 0, making the distance of the electrode tab of the cylindrical core being inverted into the center hole approach 0, which can reduce the distance of the electrode tab of the cylindrical core being inverted into the center hole 3 after being flattened, effectively reducing the short circuit caused by the inverted insertion of the electrode tab, thereby improving the production yield.

[0062] In addition, after the flattening process, the tabs need to be welded with connecting pieces to connect to the poles. Since the outer ring tabs cover the inner ring tabs, the phenomenon of cold welding and hot spots when the connecting pieces are directly welded to the inner ring tabs that have not been flattened can be reduced, effectively ensuring production quality.

[0063] Preferably, the first preset height can be equal to the flattened height, that is, the height of the first tab 12A is set to be equal to the flattened height. This setting can ensure that the inner and outer tabs are in close contact after the tabs are flattened, further reducing the phenomenon of cold welding and hot spots when the tabs are welded to the connecting tabs, while avoiding an increase in internal resistance, and effectively ensuring production quality.

[0064] Example 2:

[0065] This embodiment provides a cylindrical winding core based on the above embodiment 1. Figure 3 , including a positive electrode sheet 1A, a negative electrode sheet 1B and a separator 2, the separator 2 is arranged between the positive electrode sheet 1A and the negative electrode sheet 1B, the cylindrical core is formed by winding the positive electrode sheet 1A, the negative electrode sheet 1B and the separator 2, and a central hole 3 is formed inside the cylindrical core; the positive electrode sheet 1A and the negative electrode sheet 1B adopt the above-mentioned electrode sheet 1, the tabs of the cylindrical core are flattened to the flattened height, at least part of the outer ring tabs cover the inner ring tabs, and the distance of the tabs of the cylindrical core from the center hole 3 to the inverted insertion is close to 0.

[0066] By adopting the above-mentioned electrode piece 1 to prepare a cylindrical winding core, when the electrode ear is flattened, the outer ring electrode ear shrinks inward toward the center hole 3. Since the height of the inner ring electrode ear is not greater than the flattened height, and the height of the outer ring electrode ear is greater than the flattened height, at least part of the outer ring electrode ear covers the inner ring electrode ear, thereby realizing the supporting effect of the inner ring electrode ear on the outer ring electrode ear, effectively reducing the distance of the electrode ear of the cylindrical winding core being inserted into the center hole 3, and realizing the distance of the electrode ear of the cylindrical winding core being inserted into the center hole 3 being close to 0, which can reduce the occurrence of inverted insertion of the electrode ear, and further effectively avoid contact between the electrode ear and the electrode piece, thereby avoiding short circuit of the cylindrical winding core and improving the production yield of the cylindrical winding core.

[0067] In some embodiments, the outermost tab of the outer ring of tabs sequentially covers the innermost tab from the outside to the inside, until the innermost tab of the outer ring of tabs covers the inner ring of tabs. The outermost tab of the outer ring of tabs sequentially covers the innermost tab from the outside to the inside, that is, the outer tabs are in close contact with the inner tabs in sequence, which can further reduce the phenomenon of cold welding and hot spots when welding the tabs to the connecting pieces.

[0068] Example 3:

[0069] This embodiment provides a method for preparing a cylindrical core based on embodiment 2. Figure 4 , including the following steps:

[0070] S1. Determine the diameter range △D of the inner ring pole piece of the cylindrical winding core;

[0071] S2. Determine the length d of the inner electrode sheet of the cylindrical core based on the diameter range ΔD of the inner electrode sheet of the cylindrical core, and further determine the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet;

[0072] S3. Prepare a positive electrode sheet, a negative electrode sheet, and a separator, set the height H1 of the first electrode tab at the winding head of the positive electrode sheet to a first preset height, set the height H2 of the second electrode tab at the winding tail of the positive electrode sheet to a second preset height, set the height H1 of the first electrode tab at the winding head of the negative electrode sheet to the first preset height, and set the height H2 of the second electrode tab at the winding tail of the negative electrode sheet to the second preset height;

[0073] S4, winding the positive electrode sheet, the negative electrode sheet and the separator into a cylindrical core, and forming a central hole inside the cylindrical core;

[0074] S5. Flatten the tabs of the cylindrical core to a flattening height so that at least a portion of the outer ring tabs covers the inner ring tabs, and the distance between the tabs of the cylindrical core and the center hole is close to 0.

[0075] In some embodiments, see Figure 5 In step S1, determining the diameter range ΔD of the inner pole piece of the cylindrical winding core includes the following steps:

[0076] S11. Prepare a test positive electrode sheet, a test negative electrode sheet, and a test separator. The test positive electrode sheet differs from the positive electrode sheet only in that the height of the tabs of the test positive electrode sheet is set to the second preset height. The test negative electrode sheet differs from the negative electrode sheet only in that the height of the tabs of the test negative electrode sheet is set to the second preset height. The test separator is identical to the separator.

[0077] S12, winding the test positive electrode sheet, the test negative electrode sheet, and the test separator into a test cylindrical core using the same winding method as step S4, and forming a central hole inside the test cylindrical core;

[0078] S13, flattening the tabs of the test cylindrical core to a flattened height using the same flattening method as in step S5;

[0079] S14. Measure and calculate the reduction value △L of the diameter of the center hole of the test cylindrical core, assuming that the diameter range △D of the inner ring pole piece of the cylindrical core is equal to the reduction value △L of the diameter of the center hole of the test cylindrical core.

[0080] It should be noted that in order to reduce the short circuit caused by the inverted insertion of the tabs of the cylindrical core, it is necessary to set the height of the inner ring tabs of the cylindrical core to a first preset height, and set the height of the outer ring tabs of the cylindrical core to a second preset height, so that after the tabs of the cylindrical core are flattened from the preset tab height to the flattened height, the outer ring tabs of the cylindrical core are retracted from the outside to the inside and at least part of the outer ring tabs covers the inner ring tabs, and the distance of the tabs of the cylindrical core that are inverted to the center hole of the cylindrical core approaches 0.

[0081] To set the height of the inner tab of the cylindrical core to a first predetermined height and the height of the outer tab of the cylindrical core to a second predetermined height, it is necessary to first determine the diameter range of the inner tab of the cylindrical core, that is, the diameter range ΔD of the inner pole piece of the cylindrical core. Because the outer tab of the cylindrical core converges from the outside to the inside and at least partially covers the inner tab, the inward contraction distance of the outer tab of the cylindrical core should be similar to the diameter range of the inner tab of the cylindrical core. Therefore, it can be assumed that the diameter range ΔD of the inner pole piece of the cylindrical core is equal to the inward contraction distance of the outer tab of the cylindrical core.

[0082] At this point, it is necessary to first determine the retraction distance of the outer tabs of the cylindrical core. However, due to factors such as the preset tab height, flattening height, tab thickness, and flattening method, after the outer tabs of the cylindrical core are flattened from the second preset height to the flattened height, the retraction distance of the outer tabs of the cylindrical core will be less than the difference between the second preset height and the flattening height. Therefore, the retraction distance of the outer tabs of the cylindrical core can be evaluated by preparing a test cylindrical core.

[0083] When preparing the test positive electrode sheet, the height of the tabs of the test positive electrode sheet is set to the second preset height; when preparing the test negative electrode sheet, the height of the tabs of the test negative electrode sheet is set to the second preset height; after the test positive electrode sheet, the test negative electrode sheet and the test separator are wound to form a test cylindrical core, the height of the tabs of the test cylindrical core is all the second preset height. Figure 6A and Figure 6B As shown, Figure 6A Schematic diagram of the test cylindrical core structure before flattening. At this time, the tab height in the test cylindrical core is the second preset height H4.

[0084] Please continue to see Figure 6B , Figure 6B This is a schematic diagram of the structure of the test cylindrical core after flattening. Figure 6A The second preset height H4 is flattened to Figure 6B When the tabs of the test cylindrical core are flattened from the second preset height to the flattened height, the inner tabs of the test cylindrical core are subjected to force or squeezed by the outer tabs during the flattening process and shrink from the outside to the inside and are inserted upside down into the center hole of the test cylindrical core, so that the diameter of the center hole of the test cylindrical core is reduced.

[0085] It can be understood that the retracted distance of the inner tab of the test cylindrical core is equal to the reduction value ΔL of the diameter of the center hole of the test cylindrical core. By actually measuring and calculating the reduction value ΔL of the diameter of the center hole of the test cylindrical core, the retracted distance of the inner tab of the test cylindrical core can be obtained.

[0086] Since the test positive electrode sheet and the test negative electrode sheet are identical except for the tab height, and the test negative electrode sheet and the test cylindrical core tabs are identical except for the tab height, and the tabs of the test cylindrical core and the outer tabs of the cylindrical core are flattened from the second preset height to the flattened height using the same flattening method, the inward contraction distance of the inner tabs of the test cylindrical core should be similar to the inward contraction distance of the outer tabs of the cylindrical core. Therefore, it can be assumed that the diameter range ΔD of the inner tabs of the cylindrical core is equal to the reduction value ΔL of the diameter of the center hole of the test cylindrical core.

[0087] It can be understood that the above operation can obtain a more accurate diameter range △D of the inner ring pole piece of the cylindrical core, and then after the pole ear of the cylindrical core is flattened from the preset height of the pole ear to the flattened height, it is ensured that the inward shrinkage distance of the outer ring pole ear of the cylindrical core is close to the diameter range △D of the inner ring pole piece, thereby better ensuring that the distance of the outer ring pole ear of the cylindrical core inserted into the center hole is close to 0; it can also ensure that the outer ring pole ear of the cylindrical core is almost completely covered on the inner ring pole ear, thereby effectively preventing cold welding and explosion points when welding the connecting piece.

[0088] In some embodiments, in step S11, the tabs of the test positive electrode sheet are all set to the same height, and the tabs of the test negative electrode sheet are all set to the same height. Through this arrangement, the tabs of the test positive electrode sheet and the test negative electrode sheet are both formed into a full tab structure, which facilitates the tab formation of the test positive electrode sheet and the test negative electrode sheet.

[0089] In some embodiments, see Figure 7 、 Figure 8A and Figure 8B ,in, Figure 7 Flow chart of the steps for measuring and calculating the reduction value ΔL of the diameter of the central hole of the test cylindrical winding core. Figure 8A The diameter of the center hole of the test cylindrical core before the flattening process is shown. Figure 8B The diagram shows the diameter of the center hole of the test cylindrical core after the flattening process and the reduction value ΔL of the diameter of the center hole. In step S14, measuring and calculating the reduction value ΔL of the diameter of the center hole 3 of the test cylindrical core includes the following steps:

[0090] S141. Before flattening the tabs on the test cylindrical core, measure the diameter L1 of the center hole;

[0091] S142. After the tabs of the test cylindrical core are flattened, the diameter L2 of the center hole is measured;

[0092] S143. Calculate the reduction in diameter of the center hole of the test cylindrical core by △L = L1 - L2.

[0093] The above method can more accurately obtain the reduction value △L of the diameter of the center hole of the test cylindrical core based on the flattening process, providing a basis for the subsequent determination of the diameter range △D of the inner ring pole piece of the cylindrical core. The method is simple, easy to operate, highly accurate, and conducive to wide use.

[0094] In some embodiments, see Figure 9-10 In step S2, the length d of the inner electrode sheet of the cylindrical core is determined based on the diameter range ΔD of the inner electrode sheet of the cylindrical core, and the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet are further determined. The method includes the following steps:

[0095] S21. Assume that the inner diameter D2 of the inner ring pole piece of the cylindrical core is equal to the diameter L1 of the center hole of the test cylindrical core before the pole tab is flattened.

[0096] It should be noted that when winding the cylindrical core and the test cylindrical core, it is necessary to select a winding needle of appropriate diameter for winding. After the winding is completed, the diameter of the center hole of the cylindrical core before the tab is flattened is close to the diameter of the selected winding needle, and the diameter L1 of the center hole of the test cylindrical core before the tab is flattened is close to the diameter of the selected winding needle. Since the cylindrical core and the test cylindrical core are formed by the same winding method, that is, the diameters of the winding needles selected for the two are equal, it can be assumed that the diameter of the center hole of the cylindrical core before the tab is flattened is equal to the diameter L1 of the center hole of the test cylindrical core before the tab is flattened. It can be understood that the inner diameter D2 of the inner ring pole piece of the cylindrical core is equal to the diameter of the center hole of the cylindrical core before the tab is flattened. Therefore, it can be assumed that the inner diameter D2 of the inner ring pole piece of the cylindrical core is equal to the diameter L1 of the center hole of the test cylindrical core before the tab is flattened, so that the length d of the inner ring pole piece of the cylindrical core can be calculated more accurately.

[0097] S22. Calculate the outer diameter of the inner pole piece of the cylindrical winding core: D1 = D2 + △D.

[0098] S23. Use the Archimedean spiral formula to calculate the length d of the inner pole piece of the cylindrical core.

[0099] S24. The length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet are both equal to the length d of the inner ring electrode sheet of the cylindrical winding core.

[0100] The above method can be used to obtain the length d of the inner ring electrode of the cylindrical core, so that the inner ring electrode of the cylindrical core will not be inserted into the center hole due to the force during the flattening process, and the distance of the outer ring electrode of the cylindrical core inserted into the center hole is close to 0, which can effectively reduce the short circuit caused by the inverted insertion of the electrode and improve the production yield.

[0101] In some embodiments, in step S23, the Archimedean spiral formula is ;

[0102] wherein, π is a constant, T is the thickness of the basic unit of the cylindrical core, and the thickness of the basic unit of the cylindrical core is the sum of the thickness of the positive electrode sheet 1A, the thickness of the negative electrode sheet 1B and 2 times the thickness of the separator 2.

[0103] The length d of the inner ring electrode sheet of the cylindrical core is calculated in this way, which is simple and fast.

[0104] Example 4:

[0105] In this example, the diameters of the center holes of the test cylindrical cores and the cylindrical cores of Example 2 before and after flattening are measured, and short circuit tests are performed.

[0106] (1) Test cylindrical core: 10 test cylindrical cores were prepared using the preparation method of the test cylindrical core in steps S11-S13 of Example 3, and the core numbers were 1-10. The specific preparation process is as follows:

[0107] The test positive electrode sheet, the test negative electrode sheet and the test separator were prepared, wherein the height of the tab of the test positive electrode sheet was set to h1=6mm, and the thickness of the test positive electrode sheet was t1=0.170mm; the height of the tab of the test negative electrode sheet was set to h2=6mm, and the thickness of the test negative electrode sheet was t2=0.132mm; the thickness of the test separator was t3=0.018mm.

[0108] The test positive electrode sheet, the test negative electrode sheet and the test separator were wound to form a test cylindrical core using a winding needle with a diameter of 8mm, and a center hole was formed in the inside of the test cylindrical core. The diameter of the center hole of the test cylindrical core was measured to obtain the diameter L1 of the center hole before the tab was flattened.

[0109] The tab of the test cylindrical core was flattened to a flattening height. The flattening height was 2mm. The diameter of the center hole of the test cylindrical core was measured again to obtain the diameter L2 of the center hole after the tab was flattened.

[0110] The difference between the diameter L1 of the center hole before the tab was flattened and the diameter L2 of the center hole after the tab was flattened was calculated to obtain the reduction AL of the diameter of the center hole of the test cylindrical core.

[0111] The test cylindrical core after flattening was subjected to a Hi-pot short circuit test. The test results are shown in Table 1.

[0112] Table 1 Measurement results of AL of test cylindrical core and short circuit test results

[0113]

[0114] During the preparation of the test cylindrical cores, the height h1 of the test positive electrode tabs was identical to the height h2 of the test negative electrode tabs, and both were greater than the flattened height. Table 1 shows that after the tabs of the test cylindrical cores were flattened to the flattened height, the average reduction in the diameter of the central hole of the test cylindrical cores, ΔL, was 3.93 mm. This indicates that the inner tabs of the test cylindrical cores were subjected to force during the flattening process or were squeezed by the outer tabs, forcing them into the central hole a considerable distance, resulting in a serious case of inverted tab insertion.

[0115] In the short-circuit test, only three test cylindrical cores passed the test, with a production yield of 30%.

[0116] (2) Cylindrical cores: Ten cylindrical cores were prepared using the method for preparing cylindrical cores provided in Example 3. The cores were numbered 11-20. The specific preparation process is as follows:

[0117] The inner diameter D2 of the inner ring pole piece of the cylindrical winding core is set to be equal to the diameter L1 of the center hole of the test cylindrical winding core before the pole tab is flattened. Here, L1 is the average value of 8.05mm, that is, D2=L1=8.05mm.

[0118] The diameter range △D of the inner ring pole piece of the cylindrical core is set to be equal to the reduction value △L of the diameter of the central hole of the test cylindrical core, where △L is an average value of 3.93mm, that is, △D=△L=3.93mm.

[0119] Calculate the outer diameter of the inner pole piece of the cylindrical winding core: D1 = D2 + △D = 8.05 + 3.93 = 11.98 mm.

[0120] Calculate the thickness of the basic unit of the cylindrical core ;

[0121] Using the Archimedean spiral formula, calculate the length d of the inner pole piece of the cylindrical core.

[0122] .

[0123] Where π is the ratio of circumference to circumference. Substituting the above data into the actual calculation, we get d=π*(11.98 2 - 8.05 2 ) / (4*0.338)≈182.91mm.

[0124] Positive electrode sheets, negative electrode sheets, and separators were prepared, wherein the thickness of the positive electrode sheet was set to 0.170 mm, the thickness of the negative electrode sheet was set to 0.132 mm, and the thickness of the separator was set to 0.018 mm. The lengths of the winding heads of the positive electrode sheet and the winding heads of the negative electrode sheet were both equal to the length d of the inner ring electrode sheet of the cylindrical winding core. That is, from the winding head end of the positive electrode sheet to the winding tail end of the positive electrode sheet, the portion of the positive electrode sheet near the winding head end equal to d was the winding head of the positive electrode sheet, and the remaining portion was the winding tail of the positive electrode sheet; from the winding head end of the negative electrode sheet to the winding tail end of the negative electrode sheet, the portion of the negative electrode sheet near the winding head end equal to d was the winding head of the negative electrode sheet, and the remaining portion was the winding tail of the negative electrode sheet.

[0125] The height H1 of the first tab at the beginning of the winding of the positive electrode sheet is set to 2 mm, i.e., H1 = 2 mm. Similarly, the height H1 of the first tab at the beginning of the winding of the negative electrode sheet is also set to 2 mm. This ensures that the height of the inner ring tabs of the inner ring electrode sheets is 2 mm.

[0126] The height H2 of the second tab at the end of the positive electrode sheet is set to 6 mm, i.e., H2 = 6 mm. Similarly, the height H2 of the second tab at the end of the negative electrode sheet is also set to 6 mm. This ensures that the height of the outer tabs on the outer electrode sheets is uniformly 6 mm.

[0127] Using an 8mm diameter winding needle, the positive electrode sheet, negative electrode sheet, and separator are wound into a cylindrical core with a central hole formed inside. The diameter of the central hole of the cylindrical core is measured to obtain the diameter L1 of the central hole before the tab is flattened.

[0128] The tabs of the cylindrical winding core are flattened to a flattened height of 2 mm. At this point, the height H1 of the first tab at the beginning of the winding of the positive and negative electrode sheets is equal to the flattened height, and the height H2 of the second tab at the end of the winding of the positive and negative electrode sheets is greater than the flattened height. This ensures that the height of the inner tabs of the inner ring electrode sheets is equal to the flattened height, and the height of the outer tabs of the outer ring electrode sheets is greater than the flattened height, so that at least part of the outer tabs cover the inner tabs after being flattened. The diameter of the center hole of the cylindrical winding core is measured again to obtain the diameter L2 of the center hole after the tabs are flattened.

[0129] The difference between the diameter L1 of the center hole before the tab is flattened and the diameter L2 of the center hole after the tab is flattened is calculated to obtain the reduction value ΔL of the diameter of the center hole of the cylindrical winding core.

[0130] The flattened cylindrical core was subjected to a Hi-pot short-circuit test. The test results are shown in Table 2.

[0131] Table 2 △L measurement results and short-circuit test results of cylindrical core

[0132]

[0133] In the cylindrical cores with core numbers 11-20 prepared, the tabs of the cylindrical cores are flattened to a flattened height, and at least part of the outer ring tabs covers the inner ring tabs, thereby achieving the supporting effect of the inner ring tabs on the outer ring tabs.

[0134] As shown in Table 2, after the tabs of the cylindrical core are flattened to the flattened height, the average reduction in the diameter of the center hole of the cylindrical core, ΔL, is 0.79 mm. Compared with the experimental cylindrical core, the cylindrical core provided by this embodiment reduces the distance required for the tabs to be inserted into the center hole after being flattened, thereby effectively reducing short circuits caused by inverted tab insertion and improving production yield.

[0135] In the short-circuit test, all 10 cylindrical cores passed the test, with a production yield of 100%.

[0136] Example 5:

[0137] This embodiment provides a cylindrical battery based on Example 2. The cylindrical battery includes the cylindrical core described above. In addition, the cylindrical battery also includes a housing, a cover plate, and other structures. This embodiment does not limit the specific structures and connection methods included therein.

[0138] The use of the above-mentioned cylindrical winding core with high production yield can improve the production quality of cylindrical batteries.

[0139] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0140] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like indicate positions or locations based on the positions shown in the accompanying drawings, or the positions or locations in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0141] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0142] In the present invention, unless otherwise expressly specified or limited, a first feature being above or below a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being above, above, and above the second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being below, below, and below the second feature includes the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0143] Although the present invention has been described with reference to the above specific embodiments, it will be apparent to those skilled in the art that many substitutions, modifications, and variations can be made based on the above. Therefore, all such substitutions, modifications, and variations are intended to be encompassed within the spirit and scope of the appended claims.

Claims

1. A method for preparing a cylindrical core, characterized in that: The cylindrical winding core includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, and each of the positive electrode sheet and the negative electrode sheet includes a winding head and a winding tail connected to each other along the length direction; the preparation method includes the following steps: S1. Determine the diameter range ΔD of the inner pole piece of the cylindrical winding core; S2. Determine the length d of the inner electrode sheet of the cylindrical core according to the diameter range ΔD of the inner electrode sheet of the cylindrical core, and further determine the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet; S3. Prepare a positive electrode sheet, a negative electrode sheet, and a separator, set the height of the first electrode tab at the winding head of the positive electrode sheet to a first preset height, set the height of the second electrode tab at the winding tail of the positive electrode sheet to a second preset height, set the height of the first electrode tab at the winding head of the negative electrode sheet to the first preset height, and set the height of the second electrode tab at the winding tail of the negative electrode sheet to the second preset height; the first preset height is not greater than the flattened height, and the second preset height is greater than the flattened height; S4. Winding the positive electrode sheet, the negative electrode sheet, and the separator to form the cylindrical core, forming a central hole inside the cylindrical core, the winding head forming the inner ring electrode sheet, the first electrode tab forming the inner ring electrode tab, the winding tail forming the outer ring electrode sheet, and the second electrode tab forming the outer ring electrode tab; S5, flattening the tabs of the cylindrical core to a flattening height, so that at least a portion of the outer ring tabs covers the inner ring tabs, and the distance between the tabs of the cylindrical core and the center hole is close to zero; Wherein, in step S1, determining the diameter range ΔD of the inner ring pole piece of the cylindrical winding core includes the following steps: S11. Prepare a test positive electrode sheet, a test negative electrode sheet, and a test separator, wherein the test positive electrode sheet differs from the positive electrode sheet only in that the height of the tabs of the test positive electrode sheet is set to the second preset height, the test negative electrode sheet differs from the negative electrode sheet only in that the height of the tabs of the test negative electrode sheet is set to the second preset height, and the test separator is the same as the separator; S12, winding the test positive electrode sheet, the test negative electrode sheet, and the test separator into a test cylindrical core using the same winding method as step S4, with a central hole formed inside the test cylindrical core; S13, flattening the tabs of the test cylindrical core to the flattened height using the same flattening method as in step S5; S14. Measure and calculate the reduction value ΔL of the diameter of the central hole of the test cylindrical core, assuming that the diameter range ΔD of the inner ring pole piece of the cylindrical core is equal to the reduction value ΔL of the diameter of the central hole of the test cylindrical core.

2. The method for preparing a cylindrical winding core according to claim 1, characterized in that: In step S14, measuring and calculating the reduction value ΔL of the diameter of the central hole of the test cylindrical winding core includes the following steps: S141. Before flattening the tabs of the test cylindrical core, measure the diameter L1 of the center hole thereof; S142, after the tabs of the test cylindrical core are flattened, measuring the diameter L2 of the center hole thereof; S143. Calculate the reduction value of the diameter of the central hole of the test cylindrical core, ΔL = L1 - L2.

3. The method for preparing a cylindrical winding core according to claim 1, characterized in that: In step S2, determining the length d of the inner electrode sheet of the cylindrical core according to the diameter range ΔD of the inner electrode sheet of the cylindrical core, and further determining the length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet includes the following steps: S21. Assume that the inner diameter D2 of the inner ring electrode of the cylindrical winding core is equal to the diameter L1 of the center hole of the test cylindrical winding core before the tab is flattened. S22, calculating the outer diameter D1 of the inner ring pole piece of the cylindrical winding core = D2 + ΔD; S23, using the Archimedean spiral formula to calculate the length d of the inner pole piece of the cylindrical winding core; S24. The length of the winding head of the positive electrode sheet and the length of the winding head of the negative electrode sheet are both equal to the length d of the inner ring electrode sheet of the cylindrical winding core.

4. The method for preparing a cylindrical winding core according to claim 3, characterized in that: In step S23, the Archimedean spiral formula is ; Wherein, π is the ratio of circumference to circumference, T is the thickness of the basic unit of the cylindrical core, and the thickness of the basic unit of the cylindrical core is the sum of the thickness of the positive electrode sheet, the thickness of the negative electrode sheet, and twice the thickness of the separator.

5. The method for preparing a cylindrical winding core according to claim 1, characterized in that: The first preset height is equal to the flattening height.

6. A cylindrical winding core, characterized in that: The cylindrical winding core is prepared by the method for preparing a cylindrical winding core according to any one of claims 1 to 5.

7. The cylindrical winding core according to claim 6, characterized in that The outermost tab in the outer ring tabs covers the inner tabs in sequence from the outside to the inside, until the innermost tab in the outer ring tabs covers the inner ring tabs.

8. A cylindrical battery, characterized in that: Comprising a cylindrical winding core as claimed in claim 6 or 7.

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