Full-tab cylindrical battery and roll core leveling method

Abstract

The invention belongs to the technical field of battery processing, and discloses a full-tab cylindrical battery and a roll core leveling method. The full-tab cylindrical battery comprises a roll core and two current collecting pieces, flat surfaces are formed at the two ends of the roll core, the flat surfaces are divided into a positive pole flat surface and a negative pole flat surface which are located at the two ends of the roll core, the overall flatness of the positive pole flat surface is smaller than or equal to 0.25 mm, and the positive pole flat surface is divided into a plurality of independent fan-shaped first welding areas by grooves; the flatness of each first welding area is smaller than or equal to 0.2 mm; the overall flatness of the negative electrode flat surface is smaller than or equal to 0.22 mm, the negative electrode flat surface is divided into a plurality of independent fan-shaped second welding areas by the grooves, and the flatness of each second welding area is smaller than or equal to 0.2 mm; and the first welding area and / or the second welding area are / is spirally welded with the corresponding current collecting pieces through linear welding lines. According to the full-tab cylindrical battery and the leveling method of the roll core, the stability of connection between the flat surface and the current collector is improved, and the anti-collision performance of the battery is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery processing, and in particular to a full-ear cylindrical battery and a winding core flattening method. Background Art

[0002] In order to significantly improve the battery's overcurrent capability, reduce battery heat generation, and break through the bottleneck of cylindrical batteries, lithium batteries mostly use a full-ear process. In the full-ear process of lithium batteries, the full-ear (that is, the two ends of the core) needs to be flattened first, and the flat surface has a certain strength before the subsequent current collector welding can be carried out. In the subsequent current collector welding process, technicians found that the welding between the flat surface of the core and the current collector was not stable enough. When the battery is impacted, the core is easy to separate from the current collector, causing battery failure.

[0003] Therefore, it is urgent to design a full-ear cylindrical battery and a flattening method for the winding core to solve the above problems. Summary of the invention

[0004] One object of the present invention is to provide a full-ear cylindrical battery, in which the welding of the winding core and the current collector is more stable, thereby improving the impact resistance of the battery.

[0005] Another object of the present invention is to provide a method for flattening a winding core, wherein the welding between the winding core and the current collecting sheet after flattening by the method is more stable, and the impact resistance of the battery is improved.

[0006] A full-ear cylindrical battery, comprising a winding core and a current collecting sheet, wherein the winding core is formed by winding a positive electrode sheet, a separator, a negative electrode sheet and a separator stacked in sequence, the positive electrode foil of the positive electrode sheet has a positive electrode active material layer and a blank foil located at the axial end of the winding core, the negative electrode foil of the negative electrode sheet has a negative electrode active material layer and a blank foil located at the axial end of the winding core, and the blank foils of the positive electrode sheet and the negative electrode sheet face opposite directions; either or both of the blank foil of the positive electrode sheet and the blank foil of the negative electrode sheet have a flat surface formed by bending toward the central axis of the winding core and overlapping, and a groove is formed on the flat surface;

[0007] The flat surface is divided into a positive electrode flat surface and a negative electrode flat surface located at both ends of the winding core, the overall flatness of the positive electrode flat surface is less than or equal to 0.25 mm, and the positive electrode flat surface is divided into a plurality of independent and fan-shaped first welding areas by the groove, and the flatness of each of the first welding areas is less than or equal to 0.2 mm; and / or

[0008] The overall flatness of the negative electrode flat surface is less than or equal to 0.22 mm, and the negative electrode flat surface is divided into a plurality of independent fan-shaped second welding areas by the grooves, and the flatness of each second welding area is less than or equal to 0.2 mm;

[0009] At least one of the first welding area and / or at least one of the second welding area is welded to the corresponding current collecting piece through a linear welding wire, and the welding wire is arranged along the outer circumference of the winding core toward the central axis of the winding core.

[0010] As an optional scheme, several of the above-mentioned first welding areas form an annular surface and / or several of the above-mentioned second welding areas form an annular surface and are arranged concentrically with the above-mentioned winding core, and the above-mentioned welding line is located inside the first welding area or the second welding area; the distance between the outer side of the above-mentioned first welding area and / or the second welding area and the outer wall of the winding core is c1, c1=n*Gap, 4≤n≤8, Gap=T1+T2+2*T3, the thickness of the above-mentioned positive electrode sheet is T1, the thickness of the above-mentioned negative electrode sheet is T2, and the thickness of the above-mentioned diaphragm is T3; the distance between the inner side of the above-mentioned first welding area and / or the second welding area and the inner wall of the winding core is c2, 0.3mm≤c2≤1.0mm, the width of the above-mentioned first welding area and / or the second welding area is C, and the thickness of the winding core is X, C=X-c1-c2.

[0011] As an optional solution, the welding wire includes an effective welding wire, the length of the effective welding wire is A, and 65%≤A / C≤86%.

[0012] The above welding wire is a spiral welding wire.

[0013] As an optional solution, the spiral diameter of the welding wire is D, 0.2mm≤D≤1mm, the pitch of the welding wire is Y, 0.2mm≤Y≤0.7mm, and D>Y.

[0014] As an optional solution, the grooves on the positive electrode flat surface are provided with eight, the first welding areas are provided with eight, the eight first welding areas are evenly spaced in a fan shape along the center of the positive electrode flat surface, each of the first welding areas is formed with a corresponding welding line, and the welding line is formed at the center of the first welding area; and / or

[0015] There are eight grooves on the flat surface of the negative electrode, and eight second welding areas are arranged. The eight second welding areas are evenly distributed in a fan shape along the center of the flat surface of the negative electrode. A corresponding welding wire is formed in each of the second welding areas, and the welding wire is formed at the center of the second welding area.

[0016] As an optional solution, it also includes a positive electrode current collector and a negative electrode current collector. The positive electrode flat surface is welded to the positive electrode current collector with a welding yield of more than 99%, and the negative electrode flat surface is welded to the negative electrode current collector with a welding yield of more than 99%.

[0017] The core flattening method is used to flatten the end surface of the core, and the core flattening method comprises:

[0018] S10: pre-pressing, the blank foils of the multi-layer positive electrode sheet and / or the blank foils of the multi-layer negative electrode sheet at the end of the winding core are gathered inward by a pre-pressing device to form the above-mentioned groove;

[0019] S20: Dynamic flattening: the dynamic flattening mechanism compresses the winding core from both ends of the winding core toward the middle of the winding core at a preset flattening speed, and stops when the winding core reaches a predetermined expansion and contraction amount;

[0020] S30: static flattening, the static flattening mechanism presses the two ends of the winding core with a fixed pressure and maintains it for a preset time.

[0021] As an optional scheme, in the above S30, the total feed amount of the above-mentioned static flattening mechanism is greater than that of the two-step flattening, and is configured so that the final core height after three-step flattening is the same as the core height after two-step flattening, and the ratio of the core height before flattening to the core height after flattening is 1.09.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a full-ear cylindrical battery, which greatly improves the bonding strength between the current collector and the flat surface by reducing the flatness of the flat surface, the first welding area and the second welding area, and adopts a linear welding wire, thereby improving the impact resistance of the battery. Even under external force, the flat surface and the current collector are still in a stable joint state and are not easy to separate.

[0024] The present invention also provides a method for flattening a winding core, in which the flat surface of the winding core is flattened by a three-step method, the overall flatness of the positive electrode flat surface and the negative electrode flat surface is less than or equal to 0.25 mm, the flatness of the first welding area and the second welding area is less than or equal to 0.2 mm, and the heights of the outer circle and the inner circle of the flat surface of the winding core tend to be consistent, so that a larger area of ​​the flat surface can be used for welding with the current collector, and the yield of welding the current collector is improved, the internal resistance of the battery is reduced, and the battery performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is an exploded view of welding the winding core and two current collecting sheets provided by an embodiment of the present invention;

[0026] Figure 2 is a cross-sectional view of a winding core before pre-pressing provided by an embodiment of the present invention;

[0027] Figure 3 is a cross-sectional view of a rolled core after pressing provided by an embodiment of the present invention;

[0028] Figure 4 is a layered diagram of the interior of a winding core provided by an embodiment of the present invention;

[0029] Figure 51 is a schematic diagram of the partitioning of the flat surface of the winding core and a schematic diagram of the spiral welding line provided by an embodiment of the present invention;

[0030] Figure 6 It is a schematic diagram of the partitions of the flat surface of the winding core provided by an embodiment of the present invention, and each distance is marked;

[0031] Figure 7 Schematic diagram of height change of a two-step flattening core in the prior art provided by an embodiment of the present invention;

[0032] Figure 8 is a schematic diagram of height change of a three-step flattening core provided by an embodiment of the present invention;

[0033] Fig. 9 This is a CT image of the welding between the positive electrode flat surface of the winding core and the positive electrode current collector after two-step flattening in the prior art;

[0034] Fig.10 This is a CT image of the welding between the negative electrode flat surface of the winding core and the negative electrode current collector after two-step flattening in the prior art;

[0035] Fig.11 This is a CT image of the welding between the positive electrode flat surface of the winding core and the positive electrode current collector after three-step flattening provided by an embodiment of the present invention;

[0036] Fig.12 This is a CT image of the welding between the negative electrode flat surface of the winding core and the negative electrode current collector after three-step flattening provided by an embodiment of the present invention;

[0037] Fig.13 This is a style diagram of the negative terminal surface after pre-compression provided by an embodiment of the present invention;

[0038] Fig.14 This is a pattern diagram of the negative terminal surface after dynamic flattening provided by an embodiment of the present invention;

[0039] Fig.15 This is a style diagram of the negative terminal surface after static flattening provided by an embodiment of the present invention;

[0040] Fig.16 This is a style diagram of the positive terminal surface after pre-compression provided by an embodiment of the present invention;

[0041] Fig.17 This is a pattern diagram of the positive terminal surface after dynamic flattening provided by an embodiment of the present invention;

[0042] Fig.18 This is a style diagram of the positive terminal surface after static flattening provided by an embodiment of the present invention.

[0043] In the figure:

[0044] 10. Roll core;

[0045] 11. flat surface; 111. first welding area; 1111. welding line; 112. groove;

[0046] 13. positive electrode sheet; 131. first empty foil area; 132. positive electrode active material layer; 14. negative electrode sheet; 15. separator;

[0047] 16. Flat surface of positive electrode; 17. Flat surface of negative electrode;

[0048] 20. Current collector; 30. Positive electrode current collector; 40. Negative electrode current collector. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0050] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0052] In the description of this embodiment, the terms "upper", "lower", "left", "right" and other directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0053] like Figure 1The structure of a full-ear cylindrical battery according to an embodiment of the present invention (only the winding core 10 and two current collectors 20 are shown), and see Figure 2 The winding core 10 is formed by winding the positive electrode sheet 13, the separator 15, the negative electrode sheet 14 and the separator 15 stacked in sequence, and the whole is cylindrical. Figure 2 As shown, in an optional embodiment, the positive electrode active material layer 132 covers most of the positive electrode foil, and the negative electrode active material layer covers most of the negative electrode foil. When unfolded, both ends of the positive electrode sheet 13 and the negative electrode sheet 14 in the width direction (i.e., the positions where the active material is not coated) form the aforementioned blank foil. Figure 2 As shown, taking the positive electrode sheet 13 as an example, the position on the positive electrode foil where the positive electrode active material layer 132 is not coated forms a first empty foil area 131. Of course, see Figure 4 The portion of the negative electrode foil not coated with the negative electrode active material forms a second blank foil (not marked, Figure 4 The center is located at the end of the winding core 10 away from the first empty foil area 131). Figure 2 As shown, when the winding core 10 is wound, in the axial direction, the positive electrode active material layer 132 and the negative electrode active material layer (not shown in the figure) are staggered so that the blank foils of the positive electrode sheet 13 and the negative electrode sheet 14 face oppositely to form the winding core 10, and the upper and lower end surfaces (the lower end surface is not shown) are pressed into a flat surface 11 by a flattening device, and a groove 112 is formed on the flat surface 11 (see Figure 6 ), wherein the arrangement of the groove 112 can absorb the wrinkles formed by the inward bending of the blank foil of the multi-layer positive electrode sheet 13 and the blank foil of the negative electrode sheet 14, thereby reducing the wrinkling of the flat surface 11 and improving the flatness of the flat surface 11.

[0054] like Figure 2 and Figure 4 As shown, the winding core 10 is contained in the battery case in a state of being impregnated with electrolyte. The positive electrode foil may be a metal foil made of aluminum or aluminum alloy, and the negative electrode foil may be a metal foil made of copper or copper alloy.

[0055] like Figure 2 As shown, in an optional embodiment, there is a through hole 18 in the central axis of the winding core 10, and the through hole 18 is used to insert a positioning pin (not shown in the figure), and the positioning pin is used for welding the current collector 20 and the bottom of the battery housing. Figure 3 and Figure 4 As shown, the blank foils of the positive electrode sheet 13 and the blank foils of the negative electrode sheet 14 are bent into the flat surface 11 , and the bending direction is from the outer periphery of the winding core 10 toward the through hole 18 . The adjacent blank foils of the positive electrode sheet 13 or the negative electrode sheet 14 are bent so as to overlap each other.

[0056] like Figure 1 and Figure 3As shown, in an optional embodiment, the current collector 20 is divided into a positive current collector 30 and a negative current collector 40. The positive current collector 30 is welded to the flat surface 11 formed by the first empty foil area 131. The positive current collector 30 can be a metal plate or metal sheet made of a monomer or composite material of aluminum or aluminum alloy. The negative current collector 40 is welded to the flat surface 11 formed by the negative blank foil. The negative current collector 40 can be a metal plate or metal sheet made of a monomer or composite material of nickel, nickel alloy, copper, copper alloy. A hole is opened near the center of the positive current collector 30, and the position of the hole is the position corresponding to the through hole 18. The negative current collector 40 can be a whole circular current collector, or a circular current collector with a circular protrusion in the center. The center position of the current collector 20 at one end of the negative electrode is further welded to the bottom of the battery housing through an external positioning pin.

[0057] It is understandable that the present invention Figures 1 to 7 They are only schematic diagrams. For example, the actual number of layers of the core 10 is subject to the embodiment. In an optional embodiment, the positive electrode active material layer 132 includes any one or more of the positive electrode materials that can embed and deintercalate lithium. The positive electrode active material layer 132 may also further include any one or more of other materials such as a positive electrode binder and a positive electrode conductor. The positive electrode material can be lithium iron phosphate or nickel-cobalt-manganese system, nickel-cobalt-aluminum system ternary materials and other lithium-ion battery positive electrode materials already available in the prior art.

[0058] In an optional embodiment, the negative electrode material can be a carbon material, such as artificial graphite and natural graphite, or a graphite composite negative electrode material doped with a certain amount of silicon oxygen or silicon carbon, as well as other lithium-ion battery negative electrode materials available in the prior art.

[0059] In an optional embodiment, the diaphragm 15 can be a single-layer PP, single-layer PE, PP+ceramic coating, PE+ceramic coating, double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP, as well as other lithium-ion battery diaphragm materials available in the prior art.

[0060] In an optional embodiment, the electrolyte includes a solvent and an electrolyte salt. In addition, the electrolyte may further include any one or more of other materials such as additives.

[0061] In an optional embodiment, the solvent includes any one or more of non-aqueous solvents such as organic solvents. The electrolyte of the non-aqueous solvent is a so-called non-aqueous electrolyte, and the non-aqueous solvent can be, for example, cyclic carbonate, chain carbonate, lactone, chain carboxylic acid ester, nitrile (mononitrile), etc.

[0062] In an optional embodiment, the electrolyte salt may include any one or more of lithium salts, etc. In addition, the electrolyte salt may also include salts other than lithium salts, etc. The salts other than lithium salts may be light metal salts other than lithium, etc.

[0063] In one embodiment, the battery shell is a metal shell, which may be a steel shell or an aluminum shell, and is more preferably a steel shell.

[0064] In an optional embodiment, the lithium salt is, for example, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrachloroaluminate (LiAlCl4), lithium hexafluorosilicate (Li2SF6), lithium chloride (LiCl) and lithium bromide (LiBr). Among them, the lithium salt can be any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate and lithium hexafluoroarsenate; the lithium salt more preferably includes lithium hexafluorophosphate. The content of the electrolyte salt is not particularly limited, and preferably 0.3 mol / kg to 3 mol / kg relative to the solvent.

[0065] In the subsequent current collector welding process, technicians found that the welding between the flat surface 11 of the winding core 10 and the current collector 20 was not stable enough. When the battery was impacted, the winding core 10 was easy to separate from the current collector 20, causing battery failure.

[0066] In order to solve the above problems, this embodiment provides a full-ear cylindrical battery, such as Figure 1 , Figure 2 and Figure 5 As shown, the flat surface 11 is divided into a positive flat surface 16 and a negative flat surface 17 located at both ends of the winding core 10. The overall flatness of the positive flat surface 16 is less than or equal to 0.25 mm. The positive flat surface 16 is divided into a plurality of independent and fan-shaped first welding areas 111 by the groove 112. The flatness of each first welding area 111 is less than or equal to 0.2 mm; the overall flatness of the negative flat surface 17 is less than or equal to 0.22 mm. The negative flat surface 17 is divided into a plurality of independent and fan-shaped second welding areas by the groove 112. The flatness of each second welding area is less than or equal to 0.2 mm; at least one first welding area 111 and at least one second welding area are respectively welded with a current collector 20 through a linear welding line 1111, and the welding line 1111 is arranged along the outer periphery of the winding core 10 toward the central axis of the winding core 10.

[0067] In an optional embodiment, if Figure 5As shown, for the number M of the grooves 112, generally a symmetrical number or a number that can equally divide the circumference can be selected. Generally speaking, the number M should be greater than or equal to 4. M can be selected as 4, 5, 6, 8, 9, 10, 12, etc. All point values ​​or ranges greater than or equal to 4 and less than or equal to 12 are within the protection scope of this optional embodiment. Among them, based on the size of the commonly used model of the winding core 10, the number M of this optional embodiment can be selected as 8.

[0068] In an optional embodiment, if Figure 5 As shown, the grooves 112 on the flat surface 11 can be evenly arranged in the entire circumferential area, and the angles of the grooves 112 are the same, so as to ensure the uniformity of the overall strength and hardness of the flat surface 11 and the overall flatness, and ensure the stable welding effect between the flat surface 11 and the current collecting sheet 20. Of course, in other optional embodiments, it is not ruled out that some areas may not be arranged with grooves 112, or the grooves 112 may also be arranged in the form of unequal spacing, and the arrangement of different grooves 112 is within the protection scope of the present application.

[0069] In an optional embodiment, if Figure 5 As shown, the arrangement of the grooves 112 should extend from the inner periphery to the outer periphery of the winding core 10 and run through the entire winding core 10. This design divides the flat surface 11 into several independent fan-shaped areas, which are used to weld with the current collector 20. Taking the positive flat surface 16 as an example, these fan-shaped areas are the above-mentioned first welding areas 111, and for the negative flat surface 17, these fan-shaped areas are the second welding areas. The following is an example of the positive flat surface 16, and the same is true for the negative flat surface 17, which will not be emphasized later. Multiple first welding areas 111 can be the same fan-shaped areas, which are the same, independent and not connected to each other. For example, in this embodiment, the preferred scheme is to be divided into eight fan-shaped first welding areas 111 with equal areas by eight grooves 112 spaced at the same angle of 45°.

[0070] Combination Figure 5 The flatness of the flat surface 11 is obtained as follows: Figure 6 As shown, in the experiment, a 3D profilometer is used to test the flatness of the flat surface 11 of the core 10. The plane to be measured is selected, and the machine identifies the highest point and the lowest point of the selected area, and automatically calculates the difference between the high and low points, that is, the flatness.

[0071] The calculation formula for flatness is as follows:

[0072] F = H1-H2;

[0073] Among them, F is the flatness of the test area of ​​the flat surface 11 of the core 10, H1 is the height of the highest point of the test area of ​​the flat surface 11 of the core 10, and H2 is the height of the lowest point of the test area of ​​the flat surface 11 of the core 10. Figure 5 The shaded area is the eight overall plane areas to be measured. In a specific embodiment, the flatness measured by the present invention is the flatness of the entire end surface of the winding core 10 (including the eight first welding areas 111).

[0074] Taking the positive electrode flat surface 16 as an example, the negative electrode flat surface 17 will not be described in detail. Figure 5 The shaded area in the middle is the eight first welding areas 111 measured. Each first welding area 111 is used for welding with the positive electrode current collector 30. Those skilled in the art can measure the flatness of the entire flat surface 11 as needed, or measure the flatness of each first welding area 111 separately.

[0075] That is to say, the scheme of this embodiment controls the overall flatness of the positive electrode flat surface 16 to be less than or equal to 0.25 mm, and controls the flatness in each first welding area 111 to be within 0.2 mm. When welding with the positive electrode collector 30, the first welding area 111 has a better fit with the positive electrode collector 30. The gap within 0.2 mm allows the positive electrode flat surface 16 and the positive electrode collector 30 to be completely melted under the high temperature of the welding gun during welding, thereby reducing the occurrence of cold welding, thereby ensuring that after the core 10 is assembled, the internal resistance of the battery is reduced, thereby ensuring the excellent performance of the battery.

[0076] Similarly, the overall flatness of the negative electrode flat surface 17 is controlled to be less than or equal to 0.22 mm, and the flatness in each second welding area is controlled within 0.2 mm. When welded with the negative electrode collector 40, the second welding area has a better fit with the negative electrode collector 40. The gap within 0.2 mm allows the negative electrode flat surface 17 and the negative electrode collector 40 to be completely melted under the high temperature of the welding gun during welding, thereby reducing the occurrence of cold welding. That is, the flatness of the two end faces of the winding core 10 is reduced compared with the prior art, so the welding is more complete, cold welding is avoided, and the overall performance of the battery is improved.

[0077] Optionally, the welding wire 1111 is a spiral welding wire.

[0078] It can be understood that by changing the existing direct welding form to spiral welding, the laser trajectory is no longer set in a straight line or spot welding. Laser swing welding can disperse the heat accumulation of the laser, significantly widen the molten width of the weld line 1111, reduce the molten depth of the weld line 1111, and effectively improve the collapse problem; there is a huge difference in the energy distribution between laser swing and conventional laser welding, and the heat transfer behavior of the molten pool and the morphology of the weld line 1111 change. The core of spiral welding is mainly to affect the energy distribution of the laser at the welding position and the dynamic behavior of the molten pool keyhole (speed and frequency stirring the molten pool). As the laser beam moves along the spiral path, the upper surface of the molten pool is approximately circular and the boundary is smooth. As the welding process proceeds, the molten pool moves forward as a whole. Due to the long spiral trajectory of the laser motion trajectory, the line energy is low, the average laser scanning speed is increased, the energy concentration is reduced, the energy distribution on the molten pool surface is more uniform, the molten pool shape fluctuates very little, and the heat action area and the molten pool are expanded, the temperature gradient is reduced, and the molten liquid metal has enough time to fill the weld line 1111, thereby improving the stability of the weld line 1111 and reducing welding defects. That is to say, in this embodiment, the flatness of the flat surface 11, the first welding area 111 and the second welding area is reduced, and spiral welding is used to greatly improve the bonding strength between the current collecting sheet 20 and the flat surface 11, thereby improving the impact resistance of the battery. Even under external force, the flat surface 11 and the current collecting sheet 20 are still in a stably engaged state and are not prone to detachment.

[0079] Optionally, a welding line 1111 is formed in each first welding area 111, and the welding line 1111 extends radially along the positive flat surface 16, and the positive current collector 30 and the positive flat surface 16 of the winding core 10 are fully welded at each welding line 1111. It can be understood that during welding, the welding gun welds along the welding line 1111, rather than welding all of the first welding areas 111, to avoid large-area welding causing extended processing time, and the full welding technique ensures the continuity and firmness of the welding. Among them, the full welding connection means that after the welding line 1111 is welded, after testing, the welding line 1111 and the positive current collector 30 are all welded, and there is no false welding position in the welding line 1111.

[0080] Optionally, each second welding area forms a welding line 1111, and the welding line 1111 extends along the radial direction of the negative electrode flat surface 17, and the negative electrode current collector 40 and the negative electrode flat surface 17 of the winding core 10 are fully welded at each welding line 1111. During welding, the welding gun welds along the welding line 1111 instead of welding all the second welding areas, so as to avoid the extension of processing time caused by large-area welding, and the full welding technique ensures the continuity and firmness of the welding.

[0081] Alternatively, if Figure 5As shown, eight first welding areas 111 are provided, and the eight first welding areas 111 are evenly spaced in a fan shape along the center of the positive flat surface 16, and two adjacent first welding areas 111 are separated by the above-mentioned groove 112; eight second welding areas are provided, and the eight second welding areas are evenly spaced in a fan shape along the center of the negative flat surface 17, and two adjacent second welding areas are separated by the above-mentioned groove 112. The groove 112 is generated when the pre-pressing device pushes the positive electrode sheet 13 or the negative electrode sheet 14 inward during the pre-pressing process, and the formation of the groove 112 can also press the residual material of the outer ring into the groove 112.

[0082] Optionally, the tension F1 between the positive current collector sheet 30 and the positive flat surface 16 of the winding core 10 is ≥5N; the tension F2 between the negative current collector sheet 40 and the negative flat surface 17 of the winding core 10 is ≥15N. In the prior art, the tension between the positive flat surface 16 and the positive current collector sheet 30 and the tension between the negative flat surface 17 and the negative current collector sheet 40 are approximately between 2N and 8N, the connection force is small and the fluctuation is large. When the welding tension meets the above conditions, the connection between the winding core 10 and the positive current collector sheet 30 or the negative current collector sheet 40 is also more secure. When the battery is subjected to external impact, the winding core 10 and the positive current collector sheet 30 and the negative current collector sheet 40 are not easily separated, and the strength of the battery, that is, the anti-collision performance, is also improved.

[0083] Furthermore, the positive electrode flat surface 16 is welded to the positive electrode current collector 30 with a welding yield of more than 99%, and the negative electrode flat surface 17 is welded to the negative electrode current collector 40 with a welding yield of more than 99%. In other words, the improvement of the flatness improves the welding stability of the positive electrode flat surface 16 and the positive electrode current collector 30, and improves the welding stability of the negative electrode flat surface 17 and the negative electrode current collector 40.

[0084] Alternatively, if Figure 4 As shown, the positive electrode sheet 13 includes from top to bottom a first empty foil area 131 (also referred to as a positive electrode current collector) and a positive electrode active material layer 132 (the positive electrode active material layer 132 is coated on the positive electrode current collector, and the area of ​​the positive electrode current collector not coated with the positive electrode active material is the first empty foil area 131), the upper portion of the multi-layer first empty foil area 131 is bent inward (that is, the bending portion L in the figure) to form the positive electrode flat surface 16 of the winding core 10, the lower portion of the first empty foil area 131 forms a vertical area, and the top of the negative electrode sheet 14 is located in the vertical area.

[0085] The blank foil of the positive electrode sheet 13 (that is, the first empty foil area 131) and the blank foil of the negative electrode sheet 14 are discussed separately for positive and negative electrodes due to the different flattening structures. The blank foil of the positive electrode sheet 13 can be divided into the form of L+W, where L is the vertical area and W is the bending area. Due to the design of the electrode structure, the negative electrode sheet 14 will be larger than the positive electrode sheet 13 in the width direction, and the entire negative electrode sheet 14 will cover the positive electrode sheet 13. Therefore, in the width direction of the electrode sheet (that is, the length direction of the winding core 10), the vertical area can be further divided into an outer vertical area L1 and an inner vertical area L2, L=L1+L2, and the blank foil of the entire positive electrode sheet 13 is L+W. Generally speaking, since the physical rigidity requirements of L1 and L2 are much greater than those of the W part, in the actual coil design, L2 will be coated with ceramic slurry or insulating glue and other materials to increase the rigidity of L2 to resist bending. At the same time, its insulating coating can effectively alleviate the internal short of the positive electrode sheet 13 and the negative electrode sheet 14. For the L1 part, as needed, we will also apply ceramic slurry or insulating glue and other materials on most or all of L1 to increase the rigidity of L1 to resist bending. The coating on L1 and the coating on L2 are continuous coatings, and the materials of the two can be the same and applied at the same time. It can be understood that the vertical area has stronger physical rigidity than the bending area, ensuring that the vertical area maintains a generally vertical direction during the flattening process to prevent excessive interference with the negative electrode sheet 14.

[0086] At the same time, if Figure 4 As shown, the outer vertical area L2 is arranged in this way to ensure that the projection of the positive electrode active material layer 132 completely falls into the negative electrode active material layer, thereby preventing the edge of the negative electrode sheet 14 from piercing the separator 15 and contacting the positive electrode active material layer 132 to cause a short circuit.

[0087] Through long-term practical exploration by technicians, when L1 / L2<0.2 is too small, it cannot effectively protect the negative electrode sheet 14, and at the same time affects the alignment accuracy of the winding (this part mostly considers the use of glue coating). When L1 / L2>2 is too large, the battery energy density will be affected, and the battery capacity will be reduced by about 2.5%-5%. In an optional embodiment, 0.2≤L1 / L2≤2 is adopted. Through this setting method, it can simultaneously protect the negative electrode sheet 14, ensure the alignment accuracy of the winding, and the energy density of the battery will not be affected.

[0088] For the negative electrode, its structure is basically the same as that of the positive electrode. The main difference is that: on the positive electrode side, there is a situation where the negative electrode sheet 14 is larger than the positive electrode sheet 13 in the width direction. On the negative electrode side, the above structure does not exist, and the entire negative electrode protrudes from the positive electrode sheet 13. Of course, we can also divide the blank foil on the negative electrode side into the form of L+W (not shown in the figure), but L does not need to be further divided into L1 and L2. For the L part of the negative electrode side, we can also choose to apply ceramic slurry or insulating glue and other materials to increase the rigidity of L, but considering the flattening process, if the L part of the negative electrode itself can meet the rigidity requirement of flattening, it is also possible not to apply ceramic slurry or insulating glue and other materials. The core reason is that the negative electrode side does not need to consider the problem of internal short caused by the negative electrode sheet 14 and the positive electrode touching each other, so the ceramic slurry or insulating glue coating on the negative electrode side is an option, which can be selected according to actual needs.

[0089] It should be noted that in actual products, the vertical area and the bending area can be directly connected or smoothly transitioned through a transition structure. In the present invention, a direct connection method is adopted.

[0090] Alternatively, if Figure 5 As shown, the weldable length of the flat surface 11 is more than 1 / 2 of the diameter of the winding core 10. By extending the weldable length of the flat surface 11 to more than 1 / 2 of the diameter of the winding core 10, it can be used for welding with the corresponding collector plate 20, thereby increasing the welding area between the flat surface 11 and the collector plate 20, thereby increasing the stability of the connection between the flat surface 11 and the collector plate 20, and thereby improving the anti-collision performance of the battery.

[0091] Among them, taking the positive electrode flat surface 16 as an example, the weldable area refers to the multiple layers of first empty foil areas 131 that are bent inward and stacked layer by layer to form the positive electrode flat surface 16. The number of stacked layers of the first empty foil areas 131 in the positive electrode flat surface 16 is greater than or equal to five layers. In this area, the number of stacked layers of the blank foil of the positive electrode sheet 13 (that is, the first empty foil area 131 in the figure) is sufficient to withstand the high temperature of welding, thereby ensuring that the internal performance of the core 10 is not affected by welding.

[0092] In an alternative embodiment, see Figure 4 and Figure 6The first welding area 111 and / or the second welding area is annular and concentrically arranged with the winding core 10; the distance between the outer side of the first welding area 111 and / or the second welding area and the outer wall of the winding core 10 is c1, c1=n*Gap, Gap=T1+T2+2*T3, the thickness of the positive electrode sheet 13 is T1, the thickness of the negative electrode sheet 14 is T2, and the thickness of the separator 15 is T3, 4≤n≤8, preferably 4≤n≤6; the distance between the inner side of the first welding area 111 and / or the second welding area and the inner wall of the winding core 10 is c2, which is 0.3-1.0 mm; the width C of the first welding area 111 or the second welding area, the thickness of the winding core 10 is X, C=X-c1-c2.

[0093] Among them, the edges of the first welding area 111 and / or the second welding area adjacent to the groove 112 also have a small distance. This distance is caused by the inevitable transition zone adjacent to the groove 112 in the preparation process. It will not be elaborated here. It can be considered that the edges of the first welding area 111 and / or the second welding area adjacent to the groove 112 are basically parallel and the distance between them is very small.

[0094] It can be understood that the setting of the first welding area 111 and the second welding area is for us to further understand the mechanism of welding and the problems faced, and is a targeted innovation made in the present invention when facing specific technical problems. This innovation ensures the operability, success rate and stability of welding the flat surface 11 and the collector 20.

[0095] Specifically, for the outer side of the first welding zone 111 and / or the second welding zone and the outer wall of the winding core 10, the spacing is c1, c1=n*Gap, Gap=T1+T2+2*T3, the thickness of the positive electrode sheet 13 is T1, the thickness of the negative electrode sheet 14 is T2, and the thickness of the separator 15 is T3. In actual preparation, all our welding points need to ensure that the number of stacked layers is at least maintained at more than 4 layers, that is, we need to ensure that the entire welding line 1111 must be welded from the inside to the outside. More than 4 layers must be welded. If the minimum stacking is less than 4 layers, accidents such as melt-through and internal short circuit will occur. Therefore, we choose c1, c1=n*Gap, 4≤n≤8, preferably, 4≤n≤6. When n=4, the minimum stacking number of the tabs at the starting position of the outermost welding zone is exactly 4 layers, which is the minimum number of layers that can be welded. Similarly, we need to note that in order to achieve a minimum stacking number of 4 tabs, the prerequisite must be W≥m*Gap (see Figure 4 and Figure 6 ), 4≤m≤16, m is preferably 7≤m≤13.

[0096] Combination Figure 3 and Figure 4Taking the outermost positive electrode sheet 13 as an example, the outermost positive electrode sheet 13 is overlapped on the fifth layer of the positive electrode sheet 13 after being flanged. From the fifth layer inward, a visible multi-layer flanged positive electrode sheet 13 is formed, and at this position, the area plane is formed after the pressing is completed due to the setting of the groove 112, which is conducive to subsequent welding.

[0097] At the same time, with the center hole as the boundary, the spacing between the inner side of the first welding zone 111 and / or the second welding zone and the inner wall of the core 10 is c2 0.3-1.0 mm, preferably c2 0.5 mm; it is understandable why the internal reserved spacing needs to be set. The first reason is that the internal multi-layer tabs are seriously piled up here. The deeper into the center of the core 10, the more serious the accumulation and the more complicated the internal situation are. Therefore, the area closer to the center (close to the inner wall of the inner core 10) is no longer the best welding area. Another reason is that due to the problem of fixing the laser welding instrument, during welding, the laser welding instrument needs to clamp the two ends of the core 10, and the part of the core 10 close to the inner periphery is used for the laser welding instrument to clamp the force. Therefore, based on the above two reasons, we need to set the spacing between the inner side of the first welding zone 111 and the second welding zone on the core 10 and the inner wall of the core 10 to be c2 0.3-1.0 mm.

[0098] Optionally, the welding wire 1111 includes an effective welding wire, and the length of the effective welding wire is A, wherein the effective welding wire refers to the actual welded part of the welding wire 1111, and the unwelded part is the virtual welding area, 65%≤A / C≤86%. Exemplarily, the width of the weldable area (that is, the first welding area 111 or the second welding area) is 7mm, and the length of the welding wire 1111 is about 5mm to 6mm. It is difficult to achieve more than 6mm. On the basis of being achievable, the longer the length of the welding wire 1111, the better. It is understandable that the improvement of flatness will significantly increase the length of the welding wire 1111. Therefore, on the basis of achieving a significant improvement in the flatness of the positive electrode flat surface 16 and the negative electrode flat surface 17, the effectiveness of the welding wire 1111 is also greatly improved (that is, the effective welding wire). For example, in the prior art, since the flatness of the positive electrode flat surface 16 or the negative electrode flat surface 17 is not high, it can be observed that although the welding wire 1111 is also 6mm during the preparation process, its actual effective welding wire is only 3mm, and the remaining 3mm belongs to the virtual welding area, and only 3mm can play a real electrical connection. However, in the present invention, after the flatness of the positive electrode flat surface 16 is increased to 0.25mm, and the flatness of the negative electrode flat surface 17 is increased to 0.20mm, although the welding wire 1111 is also only 6mm during the preparation process, due to the improvement of flatness, its effective welding wire reaches 5mm (measured by CT image), which is a huge improvement. It can be said that in the technical field of flattening battery cells, how to improve the flatness of the flat surface 11 becomes a huge technical difficulty, and the present invention solves this technical problem very cleverly.

[0099] As an embodiment, the effective welding line is measured by using a CT image of the battery core after welding.

[0100] For a specific embodiment, detailed specific parameters are given:

[0101] The size of the winding core 10 is, in the present invention, taking the 21700 type battery cell as an example (the present invention is not limited to the battery cell model, and other models can also achieve the technical effect of the present invention), the inner diameter is 1.5 mm and the outer diameter is 10.2 mm. Therefore, the thickness X of the winding core 10 is 8.7 mm;

[0102] c1=n*Gap, Gap=T1+T2+2*T3, T1=85μm, T2=80μm and T3=12μm respectively, 1Gap=189μm, n=11, and the value of c1=1.89mm is obtained.

[0103] The width of the first welding area 111 and / or the second welding area is C, C=X-c1-c2, X=8.7mm, c1=n*Gap, n is 4, then c1=0.756mm, c2 is 0.5mm, then C=7.444mm.

[0104] In the present invention, the effective welding length / welding area, ie, A / C, is 65%≤A / C≤86%.

[0105] As another embodiment, the length of the welding line 1111 is measured to be 6 mm, and the effective welding length is measured by CT image to be 5.8 mm, and the effective welding rate is 96.7%. Then, the effective welding length / welding area, A / C=82.8%, is within the range of 65%≤A / C≤86%.

[0106] As another embodiment, as the size of the roll varies, such as 18 series or 21 series and other larger series, the length of the welding wire 1111 and the weldable area are always maintained in a reasonably same ratio. For example, in this embodiment, A / C is above 70%, more preferably above 75%, and can reach up to 85%.

[0107] Alternatively, if Figure 5As shown, the thickness of the core 10 is X, a through hole 18 is formed in the center of the core 10, the outer radius of the core 10 is R1, the radius of the through hole 18 is R2, X=R4-R2, the length of the welding line 1111 is set to B, 25%≤B / X≤80%, and the preferred range is 45-70%. For example, the core 10 of series 21 is selected. In a specific embodiment, the diameter of the core 10 is 20.45 mm, the diameter of the through hole 18 on the inner circumference is 3.5 mm, and the thickness X (inner and outer diameters) of the core 10 are The diameter) is 8.475mm, then the range of the welding wire 1111 is 2.1mm≤B≤6.78mm, and the preferred length of the welding wire 1111 is 3.8mm≤B≤6mm. Optionally, the length B of the welding wire 1111 can be 2mm, 2.5mm, 2.8mm, 3mm, 3.3mm, 3.5mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm, 5.5; 5.7; 5.9; 6, 6.4; 6.7, etc., which is not limited here.

[0108] Optionally, for another parameter of the welding wire 1111, the spiral diameter D of the welding wire 1111 and the pitch Y of the welding wire 1111, as the size of the winding core 10 changes, the diameter D of the welding wire 1111 can be adjusted accordingly according to the product requirements, and its range is 0.2mm≤D≤1mm, and its pitch can be selected as 0.2mm≤Y≤0.7mm, but in order to make the spiral welding cross each other, it needs to be set to D>Y. The above parameter settings make the laser running trajectory overlap between the previous spiral and the next spiral, ensuring the adequacy of the spiral welding.

[0109] Optionally, the width of the welding wire 1111 is W1, 0.5 mm≤W1≤0.7 mm. Exemplarily, W1 can be 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, etc., which is not limited here.

[0110] Alternatively, if Figure 3 As shown, a welding line 1111 is formed in each first welding area 111, and the welding line 1111 is formed at the center of the first welding area 111, and a welding line 1111 is formed in each second welding area, and the welding line 1111 is formed at the center of the second welding area. The uniform distribution of welding positions is further improved, thereby improving the uniform distribution of welding connection force when the current collector 20 is welded to the flat surface 11.

[0111] This embodiment provides a core flattening method for flattening the end face of the core 10. Each end face of the core 10 is pressed three times, and the flatness of the flat surface 11 formed is smaller. It can be understood that the flattening method of the prior art generally undergoes two flattenings. After the core 10 is flattened, the flatness is ≥0.8mm. At this time, the welding yield of the collector 20 welded to the end face of the core 10 is low, and there are many cases of false welding. After the core 10 is pressed three times provided by this embodiment, the overall flatness of the positive flat surface 16 and the negative flat surface 17 is less than or equal to 0.25mm, the flatness of the first welding area 111 and the second welding area is less than or equal to 0.2mm, the height of the outer circle and the inner circle of the end face of the core 10 tends to be consistent, the yield of the welding collector 20 is improved, the internal resistance of the battery is reduced, and the battery performance is improved.

[0112] Specifically, the core flattening methods include:

[0113] S10: Pre-pressing, the blank foils of the multi-layer positive electrode sheet 13 and / or the blank foils of the multi-layer negative electrode sheet 14 at the end of the winding core 10 are gathered inward by the pre-pressing device to form a groove 112; wherein, Figure 2 The state before pre-pressing, the first empty foil area 131 is in a fully stretched state, the core 10 is placed horizontally, and both ends of the core 10 are provided with pre-pressing devices. After the pre-pressing is completed, since the pressure head of the pre-pressing device is provided with a convex pressure rib, each end surface of the core 10 is provided with eight pressure heads. After the pre-pressing, eight pre-pressing grooves 112 are formed, and at the same time, the multi-layer positive electrode sheet 13 and the multi-layer negative electrode sheet 14 are all retracted inward at a certain angle (see Figure 1 ). Each pressing head of the pre-pressing device rotates to pre-press the multi-layer positive electrode sheet 13 or the negative electrode sheet 14 at a certain angle. For the pre-pressing technology and device equipment, reference can be made to the technical Chinese patent application No. 2024115037125 A battery cell tab pre-pressing device and pre-pressing equipment, and Chinese patent application No. 202411503713X A battery cell tab pre-pressing device and pre-pressing equipment.

[0114] S20: Dynamic flattening: The dynamic flattening mechanism compresses the core 10 from both ends of the core 10 to the middle of the core 10 at a preset flattening speed, and stops when the core 10 reaches a preset expansion and contraction amount; after dynamic flattening, Figure 1 Taking the positive electrode flat surface 16 in the winding core 10 as an example, the plurality of positive electrode sheets 13 continue to be flattened by force. At this time, the flatness of the positive electrode flat surface 16 is approximately between 0.75 mm and 0.8 mm, and the feed amount accounts for approximately 7.4% of the original height of the winding core 10.

[0115] S30: static flattening, the static flattening mechanism presses the two ends of the core 10 with a fixed pressure and maintains it for a preset time. The static flattening mechanism is different from the dynamic flattening mechanism. The static flattening mechanism uses a fixed pressure to flatten and press the two ends of the core 10 after dynamic flattening. Under the condition of fixed pressure, the height of the core 10 is still reduced.

[0116] After many tests, it was found that it is difficult to weld the core 10 and the current collecting sheet 20. The main reason is that after the flattening method of the prior art is completed, the heights of the outer electrode sheet (referring to the positive electrode sheet 13 or the negative electrode sheet 14, which will not be repeated when the electrode sheet is mentioned below) and the inner electrode sheet are different. The outer layer is often higher and the inner layer is lower. The current collecting sheet 20 is a flat piece. When the current collecting sheet 20 is placed on the end face of the core 10, the gap with the end face of the core 10 is different, which makes it difficult to weld the core 10 and the current collecting sheet 20. Cold solder joints are very likely to occur at positions with larger spacing.

[0117] The core 10 made by the above-mentioned core flattening method is flattened through three steps of pre-pressing-dynamic flattening-static flattening. After static flattening, the heights of the outer layer and the inner layer of the end face of the core 10 tend to be consistent. When the current collecting sheet 20 is placed on the end face of the core 10 for welding, the spacing difference between the current collecting sheet 20 and the corresponding end face of the core 10 at each position is reduced. After the same welding, the current collecting sheet 20 and the end face of the core 10 at the position where the welding gun passes are melted in place, the current collecting sheet 20 is firmly welded, the cold welding phenomenon is reduced, and the performance of the battery is improved.

[0118] It can be seen that in the dynamic flattening step, this process cannot control the pressure, and only uses a single preset expansion amount as a single parameter. Regardless of the flattening pressure, it is based on the final flattening position. Static flattening uses a preset pressure for static regulation and maintains a certain static flattening time. The expansion amount of the battery cell will be further reduced by a small amount to achieve the length of the entire winding core 10 required by the cylindrical battery.

[0119] Optionally, S10 includes:

[0120] S11: Fix the winding core 10 on a fixing device at a pre-pressing position, and set pre-pressing components at both ends of the winding core 10. The pre-pressing components gather the blank foils of the multi-layer positive electrode sheet 13 (i.e., the first blank foil 131 in the figure) and / or the blank foils 14 of the multi-layer negative electrode sheet 14 at the end of the winding core 10 inward to form a groove 112;

[0121] S12: The transport mechanism transfers the fixture to the dynamic flattening position;

[0122] The process between S20 and S30 also includes S21: the transport mechanism transfers the fixing device from the dynamic flattening position to the static flattening position, and the static flattening mechanism statically flattens the winding core 10 at the static flattening position.

[0123] It can be understood that the winding core 10 is fixed by a fixing device, and then the fixing device is transported to each workstation by a transportation mechanism, thereby realizing a continuous three-step flattening operation.

[0124] Optionally, the static flattening pressure is controlled within the range of 5N-15N, and the flattening time lasts for 2s-10s. The greater the pressure, the shorter the flattening time, and the fixed pressure is negatively correlated with the preset time. This can ensure that the flatness of the end surface of the core 10 is improved without damaging the core 10.

[0125] Optionally, in S30, the total feed amount of the static flattening mechanism is 0.5 mm more than the two-step flattening of the prior art. The total feed amount of the static flattening mechanism at both ends of the winding core 10 is 0.5 mm. It can be considered that the feed amount on the positive side is 0.25 mm more, and the feed amount on the negative side is also 0.25 mm more, and the feed amount on both sides is 0.5 mm more. In order to ensure the final height of the winding core 10, during the early design of the product, the blank foil height of the positive electrode sheet 13 is increased by 0.25 mm, and the blank foil height of the negative electrode sheet 14 is increased by 0.25 mm. Of course, in some embodiments, due to the difference between the positive and negative electrodes being aluminum foil and copper foil, and the difference in material and hardness, the feed amount of the two will be slightly different. For example, the feed amount of the negative electrode may be slightly higher than that of the positive electrode.

[0126] in, Figure 7 The height variation data of the winding core 10 flattened in two steps in the prior art are as follows:

[0127] L0: total height of the core before two-step flattening;

[0128] L1: total height of the core after flattening;

[0129] L2: Diaphragm height;

[0130] L3: height of positive ear before two-step flattening;

[0131] L4: Height of negative pole ear before two-step flattening;

[0132] L5: two-step flattening of positive electrode feed;

[0133] L6: two-step flattening of negative electrode feed;

[0134] L7: height of positive ear after flattening;

[0135] L8: height of negative pole ear after flattening;

[0136] In this embodiment, Figure 8 The height change data of the three-step flattening core 10 is:

[0137] L 0-1: Total height of the roll core before three-step flattening, L 0-1 =L0+0.5;

[0138] L 3-1 : Height of positive ear before flattening, L 3-1 =L3+0.25;

[0139] L 4-1 : Height of negative pole ear before flattening, L 4-1 =L4+0.25;

[0140] L 5-1 : Positive electrode feed amount, L 5-1 =L5+0.25;

[0141] L 6-1 : Negative electrode feed amount, L 6-1 =L6+0.25;

[0142] The thickness of the dense area after three-step flattening accounts for 8.25% of the height of the tab area before flattening, that is, the height ratio of the core 10 before and after flattening is increased from 1.08 to 1.09, ensuring that the height of the core 10 remains unchanged after flattening and the assembly process proceeds normally.

[0143] To further illustrate the technical effect of the core 10 flattening method in this embodiment, Table 1 shows the overall flatness data of the negative electrode flat surface 17 of the core 10 with a diameter of 20.45 mm. Table 2 shows the length, impedance and welding tension data of the welding wire 1111 of the negative electrode flat surface 17 of the core 10.

[0144] Table 1

[0145]

[0146] Table 2

[0147]

[0148] It can be seen from Table 1 that the single-piece flatness of the negative electrode flat surface 17 of the two-step flattened core 10 reaches a maximum of 0.8 mm, and most of them are concentrated in 0.4-0.5 mm. The foil is not compacted, and the entire flat foil is in a warped state. The strength of the foil is not conducive to the welding of the current collector 20, and the depth and length stability of the welding wire 1111 are reduced. After welding the current collector 20, a CT test is taken to test the welding penetration, and there is a large area of ​​cold welding, and the average effective welding wire length is only half.

[0149] It can be seen from Table 2 that the welding area width C is selected as 7mm.

[0150] After adding the third step of static flattening, the overall flatness of the negative electrode flat surface 17 of the core 10 is reduced from ≤0.96mm to ≤0.22mm, the effective welding rate is increased from 60% to 100%, and the effective welding wire length / weldable length of the negative electrode flat surface 17 of the core 10 is increased from 42.8% to 71.4%, without false welding and meeting the requirements of welding tension greater than or equal to 5N, flow area and impedance less than 2.5mΩ. After testing, for a core 10 with a diameter of 20.45mm, the flow area of ​​the negative electrode flat surface 17 after three pressings is 20mm 2 The flow area is significantly increased and the impedance is reduced accordingly. Table 3 shows the overall flatness data of the positive electrode flat surface 16 of the winding core 10 with a diameter of 20.45 mm. Table 4 shows the length, impedance and welding tension of the welding wire 1111 of the negative electrode flat surface 17 of the winding core 10.

[0151] Table 3

[0152]

[0153] Table 4

[0154]

[0155] It can be seen from Table 3 that the single-piece flatness of the positive electrode flat surface 16 of the two-step flattened core 10 reaches a maximum of 0.78 mm, and most of them are concentrated in 0.5-0.6 mm. The foil is not compacted, and the entire flat foil is in a warped state. The strength of the foil is not conducive to the welding of the current collector 20, and the depth and length stability of the welding line 1111 are reduced. After welding the current collector 20, a CT test is taken to test the welding penetration depth. There is a large area of ​​virtual welding, and the average effective welding line length is only half. After adding the third step of flattening, the single-piece flatness of the positive electrode flat surface 16 is optimized to ≤0.25 mm.

[0156] After the third step of flattening, the thickness consistency of the dense area of ​​the core 10 is better, the dense area foil can achieve close fit between layers, and there is no gap between the foils to avoid problems such as cold welding, welding penetration and poor consistency of penetration depth. Therefore, the penetration depth stability after welding is better, there is no cold welding, and the welding tension, flow area and impedance requirements are met.

[0157] It can be seen from the data in Table 4 that the overall flatness of the positive electrode flat surface 16 of the winding core 10 is reduced from ≤0.85mm to ≤0.25mm, the effective welding rate is increased from 60% to 100%, and the A / C is increased from 42.8% to 71.4%. There is no virtual welding and the negative electrode welding tensile force is greater than or equal to 10N, and the flow area and impedance are less than 2.3±0.2mΩ. After testing, for the winding core 10 with a diameter of 20.45mm, the flow area of ​​the positive electrode flat surface 12 after static flattening is 20mm 2 The flow area is significantly increased and the impedance is reduced accordingly.

[0158] It can be seen from the accompanying drawings that the three-step flattening proposed by the present invention is compared with the two-step flattening. Since the third step of static flattening is added, static flattening will consume a certain amount of feed. Therefore, an additional feed margin L needs to be provided in the design of the winding core 10. 5-1 and L 6-1 , relative to the final feed amounts L5 and L6 in the two-step method, L 5-1 >L5,L 6-1 >L6. At the same time, we can see that the height of the core 10 obtained by the three-step flattening method is the same as that of the two-step flattening method, and the total height of the core 10 obtained by both methods is H=L2+L7+L8. 5-1 =L5+0.25, negative electrode feed amount, L 6-1 =L6+0.25, it can be understood that the positive and negative feed amounts given by the third step static flattening are 0.25mm and 0.25mm respectively. Table 5 shows the data on the influence of two-step flattening and three-step flattening on the welding yield of the core 10.

[0159] Table 5

[0160]

[0161] In order to demonstrate the protection of the core 10 by the three-step flattening method and its unexpected technical effect, we used the height of the core 10 in the three-step flattening method, and the feed amounts of the positive and negative electrodes were unified as L5-1 and L6-1.

[0162] The above table uses a two-step flattening mechanism to directly adjust the feed amount to compress L5-1 and L6-1, directly compressing them to the positions of L7 and L8. The three-step flattening rule is that the normal dynamic flattening consumes the feed amount L5 and L6, and then the static flattening consumes the feed amount of 0.25mm and 0.25mm respectively. Considering that L5-1=L5+0.25 on the positive side and L6-1=L6+0.25 on the negative side, the final feed amount consumed by both is L5-1 and L6-1.

[0163] However, the flatness of the core 10 obtained by the two-step flattening method has increased significantly compared to the previous 0.8mm, to 0.4-0.6mm. The overall flatness of the positive electrode is 0.55m, and the overall flatness of the negative electrode is 0.5mm, which is higher than the flatness of the normal two-step flattening method. The flatness of the positive electrode and the negative electrode is 0.82mm. However, the defective rate of welding has increased significantly to 11.8% and 9.8%, which is unbearable in mass production. Similarly, the flatness of the core 10 obtained by the three-step flattening method is less than 0.25mm and less than 0.22, and at the same time, it has met the welding yield requirements required by the two fields, which are 0.2% for the positive electrode and 0.4% for the negative electrode.

[0164] As a preference, the welding yield of the present invention is above 99%, and preferably the welding yield of the present invention is above 99.5%.

[0165] Therefore, we can see that even if the same feed rate is used to replace the three-step flattening method with the two-step flattening method, the welding yield obtained by the present invention, such as a welding yield of more than 99%, cannot be obtained. The reason is that if the positive side L 5-1 =L5+0.25, negative side, L 6-1 =L6+0.25, but the two-step flattening method is still used, which will cause serious accumulation of the tabs in the bending area in the dynamic flattening step, and the pressure is too large and cannot be released slowly. There may be huge downward pressure in some parts, which cannot be released in time and then transmitted to the material area of ​​the coating of the winding core 10, thereby crushing the positive and negative pole pieces. What is more dangerous is that due to excessive feed volume, the compression in the dynamic flattening step at one time may cause the local blank foil to reverse downward, puncture the diaphragm 15 or approach the pole piece of the opposite polarity to form an internal short, causing a huge safety risk.

[0166] The three-step flattening method adopts a method of slowly releasing the ear pressure in the bending area, providing more buffer time and buffer space. The pressure is effectively controlled, which effectively improves the yield of the core 10 in the flattening step, greatly reduces the risk of internal shorts, and can also greatly improve the flatness of the flat surface 11.

[0167] 1000 roll cores 10 were flattened in two steps, 500 roll cores 10 were welded with the positive current collector sheet 30 first, and 500 roll cores 10 were welded with the negative current collector sheet 40 first. The positive Hi-pot defective rate was 11.8%, and the negative Hi-pot defective rate was 9.8%. The end surface of the roll core 10 was uneven, and it was not the entire plane that was tightly attached to the current collector sheet 20. There was a large gap between the concave position of the foil and the current collector sheet 20, which could easily cause cold welding, black spots or welding through defects. The main manifestations were insufficient tension, poor appearance detected by naked eye, and welding hitting the diaphragm 15, resulting in Hi-pot defects. 1000 roll cores 10 were flattened in three steps, 500 roll cores 10 were welded with the positive current collector sheet 30 first, and 500 roll cores 10 were welded with the negative current collector sheet 40 first. The positive Hi-pot defective rate was 0.2%, and the negative Hi-pot defective rate was 0.4%. That is, the three-step flattening method in this embodiment greatly improves the welding yield of the core 10, thereby improving the qualification rate of the final finished battery.

[0168] In addition, static flattening is adopted in the third step of this embodiment, which is also an important means to ensure the battery yield. It is found through experiments that flattening the winding core 10 of the same height twice or three times with a certain speed for the third flattening cannot reduce the defective rate to the value in Table 5.

[0169] like Fig. 9 and Fig.10 As shown in FIG. 1 , after two-step flattening, the positive electrode welding line and the negative electrode welding line are only about half of the theoretical welding line 1111. Fig.11 and Fig.12 As shown, after three steps of flattening, the actual length of the welding line 1111 is consistent with the theoretical length of the welding line 1111, which is a full welding situation, and there is no virtual welding area ( Figure 9-12 The green line indicates the actual welding line 1111).

[0170] Figure 13-Figure 15 The states of the negative end pre-pressed, dynamically flattened, and statically flattened rear surfaces of the winding core 10 are shown in sequence. Figure 16-18 The figures show the state of the surface of the winding core 10 after pre-pressing the positive end, after dynamic flattening and after static flattening. It can be seen that after the three-step flattening, the flatness of the flat surface 11 is visually better.

[0171] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A full-ear cylindrical battery, comprising a winding core (10) and a current collector (20), wherein the winding core (10) is formed by winding a positive electrode sheet (13), a separator (15), a negative electrode sheet (14) and a separator (15) stacked in sequence, wherein the positive electrode foil of the positive electrode sheet (13) has a positive electrode active material layer (132) and a blank foil located at the axial end of the winding core (10), and the negative electrode foil of the negative electrode sheet (14) has a negative electrode active material layer and a blank foil located at the axial end of the winding core (10), and the blank foils of the positive electrode sheet (13) and the negative electrode sheet (14) face opposite directions; either or both of the blank foil of the positive electrode sheet (13) and the blank foil of the negative electrode sheet (14) have a flat surface (11) formed by bending toward the central axis of the winding core (10) and overlapping, and a groove (112) is formed on the flat surface (11); It is characterized in that The flat surface (11) is divided into a positive electrode flat surface (16) and a negative electrode flat surface (17) located at both ends of the winding core (10), the overall flatness of the positive electrode flat surface (16) is less than or equal to 0.25 mm, the positive electrode flat surface (16) is divided into a plurality of independent and fan-shaped first welding areas (111) by the groove (112), and the flatness of each first welding area (111) is less than or equal to 0.2 mm; and / or The overall flatness of the negative electrode flat surface (17) is less than or equal to 0.22 mm, and the negative electrode flat surface (17) is divided into a plurality of independent and fan-shaped second welding areas by the groove (112), and the flatness of each second welding area is less than or equal to 0.2 mm; At least one of the first welding areas (111) and / or at least one of the second welding areas is welded to a corresponding current collecting sheet (20) via a straight welding line (1111), and the welding line (1111) is arranged along the outer periphery of the winding core (10) toward the central axis of the winding core (10).

2. The full-ear cylindrical battery according to claim 1, characterized in that: A plurality of the first welding areas (111) form an annular surface and / or a plurality of the second welding areas form an annular surface and are arranged concentrically with the winding core (10); the welding line (1111) is located inside the first welding area (111) or the second welding area; the distance between the outer side of the first welding area (111) and / or the second welding area and the outer wall of the winding core (10) is c1, c1=n*Gap, 4≤n≤8, Gap=T1+T2+2*T 3. The thickness of the positive electrode sheet (13) is T1, the thickness of the negative electrode sheet (14) is T2, and the thickness of the separator (15) is T3; the distance between the inner side of the first welding area (111) and / or the second welding area and the inner wall of the winding core (10) is c2, 0.3 mm ≤ c2 ≤ 1.0 mm, the width of the first welding area (111) and / or the second welding area is C, and the thickness of the winding core (10) is X, C = X-c1-c2.

3. The full-ear cylindrical battery according to claim 2, characterized in that: The welding line (1111) comprises an effective welding line, the length of the effective welding line is A, and 65%≤A / C≤86%.

4. According to the full-tab cylindrical battery according to claim 1, the welding wire (1111) is a spiral welding wire.

5. The full-ear cylindrical battery according to claim 4, characterized in that: The spiral diameter of the welding wire (1111) is D, 0.2mm≤D≤1mm, the pitch of the welding wire (1111) is Y, 0.2mm≤Y≤0.7mm, and D>Y.

6. The full-ear cylindrical battery according to any one of claims 1 to 5, characterized in that: The grooves (112) of the positive electrode flat surface (16) are provided with eight, the first welding areas (111) are provided with eight, the eight first welding areas (111) are evenly spaced in a fan shape along the center of the positive electrode flat surface (16), each of the first welding areas (111) is formed with a corresponding welding line (1111), and the welding line (1111) is formed at the center of the first welding area (111); and / or The negative electrode flat surface (17) is provided with eight grooves (112), and eight second welding areas are provided. The eight second welding areas are evenly spaced in a fan shape along the center of the negative electrode flat surface (17), and a corresponding welding line (1111) is formed in each of the second welding areas. The welding line (1111) is formed at the center of the second welding area.

7. The full-ear cylindrical battery according to any one of claims 1 to 5, characterized in that: It also comprises a positive electrode current collector (30) and a negative electrode current collector (40); the positive electrode flat surface (16) is welded to the positive electrode current collector (30) with a welding yield of more than 99%, and the negative electrode flat surface (17) is welded to the negative electrode current collector (40) with a welding yield of more than 99%.

8. A method for flattening a core, characterized in that: Used to flatten the end surface of the winding core (10) according to any one of claims 1 to 7, the flattening method of the winding core comprising: S10: pre-pressing, using a pre-pressing device to gather the blank foils of the multiple layers of the positive electrode sheet (13) and / or the blank foils of the multiple layers of the negative electrode sheet (14) at the end of the winding core (10) inward to form the groove (112); S20: Dynamic flattening, where a dynamic flattening mechanism compresses the winding core (10) from both ends of the winding core (10) toward the middle of the winding core (10) at a preset flattening speed, and stops when the winding core (10) reaches a predetermined expansion and contraction amount; S30: static flattening, the static flattening mechanism presses the two ends of the winding core (10) with a fixed pressure and maintains it for a preset time.

9. The method for flattening a winding core according to claim 8, characterized in that: In S30, the total feed amount of the static flattening mechanism is greater than that of the two-step flattening, and is configured so that the final height of the core (10) after the three-step flattening is the same as the height of the core (10) after the two-step flattening, and the ratio of the height of the core (10) before flattening to the height of the core (10) after flattening is 1.09.

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