Leveling method of roll core, roll core and full-tab cylindrical battery

Abstract

The invention belongs to the technical field of battery processing, and discloses a roll core leveling method, a roll core and a full-tab cylindrical battery, and the roll core leveling method comprises the following steps: S10: pre-pressing: folding multiple layers of positive plates and multiple layers of negative plates at two ends of the roll core inwards; s20, dynamic flattening is conducted, specifically, a dynamic flattening mechanism compresses the roll core from the two ends of the roll core to the middle of the roll core at the preset flattening speed and stops when the roll core reaches the preset stretching amount; s30, static flattening is conducted, specifically, a static flattening mechanism extrudes the two ends of the roll core with fixed pressure and keeps for preset time; the roll core is manufactured by the roll core leveling method, the full-tab cylindrical battery comprises the roll core, the roll core leveling method, the roll core and the full-tab cylindrical battery, the roll core and the current collector are stably welded, the internal pseudo soldering condition is reduced, the internal impedance of the battery is reduced, and the performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery processing, and in particular to a winding core flattening method, a winding core and a full-ear cylindrical battery. 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 needs to be flattened first, and only after it has a certain strength can the subsequent current collector welding be carried out. The flattening process of the full-ear winding core mostly uses mechanical flattening and simple flattening methods. Mechanical flattening of the ears is easy to damage and produce metal debris. Using the flattening method, the finished winding core is difficult to weld with the current collector during the subsequent welding process, which is easy to cause cold welding. This results in a small internal overcurrent area and large impedance in the battery, which affects the performance of the battery and reduces the quality of the finished battery.

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

[0004] One object of the present invention is to provide a method for flattening a winding core, by which the winding core and the current collecting sheet can be easily welded after being flattened, the welding quality is good, and the excellent performance of the battery is ensured.

[0005] Another object of the present invention is to provide a winding core that can be firmly welded to a current collector, thereby reducing the phenomenon of cold welding and improving the performance of the battery.

[0006] Another object of the present invention is to provide a full-ear cylindrical battery, in which the welding between the winding core and the current collector is stable, the internal cold welding is reduced, the internal impedance of the battery is reduced, and the performance is improved.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] A method for flattening a winding core, 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 foil of the positive electrode sheet and the blank foil of 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;

[0009] The flattening method of the core includes:

[0010] S10: pre-pressing, using a pre-pressing device to gather the blank foils of the multiple layers of the positive electrode sheet and / or the multiple layers of the blank foils of the negative electrode sheet at the end of the winding core inward to form the groove;

[0011] 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;

[0012] 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.

[0013] As an optional solution, the fixed pressure is F, 5N≤F≤15N, and the preset time is T, 2s≤T≤10s.

[0014] As an optional solution, the above-mentioned fixed pressure is negatively correlated with the above-mentioned preset time.

[0015] As an optional solution, in the above S30, the total feed amount of the above static flattening mechanism at both ends of the above winding core is 0.2-0.7 mm.

[0016] As an optional solution, S10 includes:

[0017] S11: fixing the winding core on a fixing device located at a pre-pressing position, and providing pre-pressing components at both ends of the winding core respectively, and the pre-pressing components gather the blank foils of the multiple layers of the positive electrode sheet and / or the blank foils of the multiple layers of the negative electrode sheet at the ends of the winding core inward to form the grooves;

[0018] S12: The transport mechanism transfers the fixture to the dynamic flattening position;

[0019] The above-mentioned step S21 is also included between S20 and S30: the above-mentioned fixing device is transferred from the above-mentioned dynamic flattening position to the static flattening position by the transportation mechanism, and the above-mentioned static flattening mechanism statically flattens the above-mentioned winding core at the above-mentioned static flattening position.

[0020] A winding core manufactured by the above-mentioned winding core flattening method, wherein the above-mentioned flat surface is divided into a positive electrode flat surface and a negative electrode flat surface located at both ends of the above-mentioned winding core, the overall flatness of the above-mentioned positive electrode flat surface is less than or equal to 0.25 mm, and the above-mentioned positive electrode flat surface is divided into a plurality of independent and fan-shaped first welding areas by the above-mentioned grooves, and the flatness of each of the above-mentioned first welding areas is less than or equal to 0.2 mm; and / or

[0021] The overall flatness of the negative electrode flat surface is less 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. The flatness of each second welding area is less than or equal to 0.2 mm.

[0022] The above-mentioned grooves of the above-mentioned positive electrode flat surface are provided with eight, the above-mentioned first welding areas are provided with eight, and the eight above-mentioned first welding areas are evenly spaced in a fan shape along the center of the above-mentioned positive electrode flat surface; and / or

[0023] The above-mentioned grooves are arranged on the above-mentioned negative electrode flat surface in eight numbers, and the above-mentioned second welding areas are arranged in eight numbers. The eight above-mentioned second welding areas are evenly distributed in a fan shape along the center of the above-mentioned negative electrode flat surface.

[0024] A full-ear lug cylindrical battery, comprising the above-mentioned winding core, the above-mentioned full-ear lug cylindrical battery also includes a positive electrode current collector, a first welding line area is formed in each of the above-mentioned first welding areas, the above-mentioned first welding line area extends radially along the above-mentioned positive electrode flat surface, and the above-mentioned first welding area is fully welded to the above-mentioned positive electrode current collector at the position of the first welding line area; and / or

[0025] The winding core also includes a negative electrode current collector. A second welding line area is formed in each of the second welding areas. The second welding line area extends radially along the negative electrode flat surface. The second welding area is fully welded to the negative electrode current collector at the position of the second welding line area.

[0026] As an optional solution, the tension F1 between the positive electrode current collector and the positive electrode flat surface is ≥5N; and / or

[0027] The tension F2 between the negative electrode current collector and the negative electrode flat surface is ≥15N.

[0028] As an optional solution, the impedance of the positive electrode flat surface after welding with the positive electrode current collector is less than or equal to 2.5 mΩ; and / or

[0029] The impedance of the negative electrode flat surface after welding with the negative electrode current collector is less than or equal to 2.5 mΩ.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a core flattening method, which flattens the flat surface of the core 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 flat surface of the core tend to be consistent. When the current collecting sheet is placed on the flat surface of the core for welding, the spacing difference between the current collecting sheet and the corresponding flat surface of the core at each position is reduced. After the same welding, the current collecting sheet and the flat surface of the core at the position where the welding gun passes are melted in place, the current collecting sheet is welded firmly, the cold welding phenomenon is reduced, and the performance of the battery is improved.

[0032] The present invention also provides a winding core, which is made by the above-mentioned winding core flattening method, and can be firmly welded with the current collecting sheet, thereby reducing the phenomenon of cold welding and improving the performance of the battery.

[0033] The present invention also provides a full-ear cylindrical battery, which includes the above-mentioned winding core, positive current collector and negative current collector, the positive current collector is welded to the positive flat surface, and the negative current collector is welded to the negative flat surface. The welding between the winding core and the current collector is stable, the internal cold welding is reduced, the internal impedance of the battery is reduced, and the performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is an exploded view of welding the winding core and two current collecting sheets provided by an embodiment of the present invention;

[0035] Figure 2 is a cross-sectional view of a winding core before pre-pressing provided by an embodiment of the present invention;

[0036] Figure 3 is a cross-sectional view of a rolled core after pressing provided by an embodiment of the present invention;

[0037] Figure 4 is a layered diagram of the interior of a winding core provided by an embodiment of the present invention;

[0038] Figure 5 is a schematic diagram of partitioning of a flat surface of a winding core provided by an embodiment of the present invention;

[0039] Figure 6 is a schematic structural diagram of a winding core before pre-pressing provided by an embodiment of the present invention;

[0040] Figure 7 is a schematic structural diagram of a winding core after pre-pressing provided by an embodiment of the present invention;

[0041] Figure 8 Schematic diagram of height change of a two-step flattening core in the prior art provided by an embodiment of the present invention;

[0042] Fig. 9 Schematic diagram of height change of a three-step flattening core provided by an embodiment of the present invention;

[0043] Fig.10 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;

[0044] Fig.11 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;

[0045] Fig.12 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;

[0046] Fig.13 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;

[0047] Fig.14 This is a style diagram of the negative terminal surface after pre-compression provided by an embodiment of the present invention;

[0048] Fig.15 This is a pattern diagram of the negative terminal surface after dynamic flattening provided by an embodiment of the present invention;

[0049] Fig.16 This is a style diagram of the negative terminal surface after static flattening provided by an embodiment of the present invention;

[0050] Fig.17 This is a style diagram of the positive terminal surface after pre-compression provided by an embodiment of the present invention;

[0051] Fig.18 This is a pattern diagram of the positive terminal surface after dynamic flattening provided by an embodiment of the present invention;

[0052] Fig.19 This is a style diagram of the positive terminal surface after static flattening provided by an embodiment of the present invention.

[0053] In the figure:

[0054] 10. winding core; 11. flat surface; 111. first welding area; 1111. first welding line area; 112. groove; 13. positive electrode sheet; 131. first blank foil; 132. positive electrode active material layer; 14. negative electrode sheet; 15. separator; 16. positive electrode flat surface; 17. negative electrode flat surface; 18. through hole; 20. current collector;

[0055] 30. Positive electrode current collector; 40. Negative electrode current collector. DETAILED DESCRIPTION

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] like Figure 1 The 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. In the unfolded state, 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 blank foil 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 blank foil 131). Figure 2 As shown, when the winding core 10 is wound, the positive electrode active material layer 132 and the negative electrode active material layer (not shown in the figure) are staggered in the axial direction, 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.

[0061] 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.

[0062] 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 positive electrode blank foil and the negative electrode blank foil are bent into a flat surface 11 , and the bending direction is from the outer periphery of the winding core 10 toward the through hole 18 , and the blank foils of the adjacent positive electrode sheets 13 or negative electrode sheets 14 are bent so as to overlap each other.

[0063] like Figure 1 and Figure 3 As 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 positive blank foil. The positive current collector 30 can be a metal plate or metal sheet made of a single body 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 single body 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] In an optional embodiment, the solvent includes any one or more 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In the prior art, in full-ear cylindrical batteries, the flattening process of the winding core 10 is mostly carried out by mechanical flattening and simple flattening. The end of the spiral winding core 10, in which the positive electrode current collector coated with active material and the negative electrode current collector are wound through the diaphragm 15, has an exposed portion of the current collector that is not coated with active material. Mechanical flattening of the current collector can easily damage the ear and generate metal debris. The simple flattening method first pre-presses a plurality of grooves 112 in the ear area to form an inwardly inclined ear, and then flattens it to avoid damage to the ear and the generation of metal debris. However, the inwardly stacked ears can easily cause the flattened end surface to be concave as a whole, and the height of the outer circle gradually decreases from the inner circle.

[0073] In order to solve the above problems, the present embodiment provides a core flattening method for flattening the end surface of the core 10. Each end surface of the core 10 is pressed three times, and the flat surface 11 formed has a smaller flatness. 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 current collector 20 welded to the end face of the core 10 is low, and there are many cases of cold welding. After the three pressings provided by the core 10 in this embodiment, the flat surfaces 11 located at both ends of the core 10 are respectively the positive flat surface 16 and the negative flat surface 17. The positive flat surface 16 is divided into a plurality of first welding areas 111 by a plurality of grooves 112, and the negative flat surface 17 is divided into a plurality of second welding areas by a plurality of grooves 112. The overall flatness of the positive flat surface 16 and the negative flat surface 17 is less than or equal to 0.25mm, and the flatness of the first welding area 111 and the second welding area is less than or equal to 0.2mm. The heights of the outer circle and the inner circle of the end face of the core 10 tend to be consistent, the yield of the welding current collector 20 is improved, the internal resistance of the battery is reduced, and the battery performance is improved.

[0074] Specifically, the core flattening methods include:

[0075] S10: Preload, see Figure 6-Figure 7 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 6 The state before pre-pressing, the first blank foil 131 is in a completely straight 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 there are convex ribs on the pressure head of the pre-pressing device, each end face of the core 10 is provided with eight pressure heads. After the pre-pressing, eight 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 ( Figure 7There is no tilt state in the figure). 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.

[0076] 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.

[0077] 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.

[0078] 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, and 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.

[0079] 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.

[0080] 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.

[0081] Optionally, S10 includes:

[0082] S11: Fix the winding core 10 on a fixing device located at a pre-pressing position, and set pre-pressing components at both ends of the winding core 10, respectively, and the pre-pressing components gather the multiple layers of positive electrode blank foil and / or multiple layers of negative electrode blank foil at the ends of the winding core 10 inward to form a groove 112;

[0083] S12: The transport mechanism transfers the fixture to the dynamic flattening position;

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Optionally, in S30, the total feed amount of the static flattening mechanism ranges from 0.2 mm to 0.7 mm.

[0088] It is understandable that in S30, the total feed amount of the static flattening mechanism is 0.2mm-0.7mm more than the two-step flattening of the prior art, preferably 0.5mm. Exemplarily, the total feed amount of the static flattening mechanism at both ends of the winding core 10 is 0.5mm. It can be considered that the feed amount on the positive side is 0.25mm more, and the feed amount on the negative side is also 0.25mm more, and the feed amount on both sides is 0.5mm more. In order to ensure the final height of the winding core 10, in the early design of the product, the blank foil height of the positive electrode sheet 13 is increased by 0.25mm, and the blank foil height of the negative electrode sheet 14 is increased by 0.25mm. Of course, in some embodiments, due to the difference between the positive and negative electrodes, which are 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.

[0089] in, Figure 8 The height variation data of the winding core 10 flattened in two steps in the prior art are as follows:

[0090] L0: total height of the core before two-step flattening;

[0091] L1: total height of the core after flattening;

[0092] L2: Diaphragm height;

[0093] L3: height of positive ear before two-step flattening;

[0094] L4: Height of negative pole ear before two-step flattening;

[0095] L5: two-step flattening of positive electrode feed;

[0096] L6: two-step flattening of negative electrode feed;

[0097] L7: height of positive ear after flattening;

[0098] L8: height of negative pole ear after flattening;

[0099] In this embodiment, Fig. 9 The height change data of the three-step flattening core 10 is:

[0100] L 0-1 : Total height of the roll core before three-step flattening, L 0-1 =L0+0.5;

[0101] L 3-1 : Height of positive ear before flattening, L 3-1 =L3+0.25;

[0102] L 4-1 : Height of negative pole ear before flattening, L 4-1 =L4+0.25;

[0103] L 5-1 : Positive electrode feed amount, L 5-1 =L5+0.25;

[0104] L 6-1 : Negative electrode feed amount, L 6-1 =L6+0.25;

[0105] 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.

[0106] To further illustrate the technical effect of the core 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 data of the welding wire length, impedance and welding tension of the negative electrode flat surface 17 of the core 10.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111] 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 line are reduced. After welding the current collector 20, a CT test was taken to test the welding penetration depth, and there was a large area of ​​cold welding, and the average effective welding line length was only half.

[0112] After adding the third step of static flattening, it can be seen from Table 2 that the flatness of the second welding area of ​​the negative electrode flat surface 17 of the winding core 10 is reduced from ≤0.96mm to ≤0.22mm, the effective welding rate is increased from 60% to 100%, and the A / C value is increased from 42.8% to 71.4%. There is no false welding and the requirements of welding tension greater than or equal to 15N, flow area and impedance less than 2.5mΩ are met. After testing, for the winding core 10 with a diameter of 20.45mm, the flow area of ​​the negative electrode flat surface 17 after the three pressings is about 20mm², the flow area is also significantly improved, and the impedance is correspondingly reduced.

[0113] Table 3 shows the flatness data of the first welding area 111 of the positive electrode flat surface 16 of the winding core 10 with a diameter of 20.45 mm. Table 4 shows the data of the welding wire length, impedance and welding tension of the positive electrode flat surface 16 of the winding core 10.

[0114] Table 3

[0115]

[0116] Table 4

[0117]

[0118] It can be seen from Table 3 that the flatness of the first welding area 111 of the positive flat surface 16 of the two-step flattened winding 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, which reduces the depth and length stability of the weld line. After welding the current collector 20, a CT test is taken to test the welding penetration depth. There is a large area of ​​cold welding, and the average effective weld line length is only half. After adding the third step of flattening, the single piece flatness of the positive flat surface 16 is optimized to ≤0.25 mm.

[0119] 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.

[0120] 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 ≤0.2mm, the effective welding rate is increased from 60% to 100%, and the A / C value is increased from 4.28% to 71.4%. There is no void welding and the positive electrode welding tensile force is greater than or equal to 5N, 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 16 after static flattening is about 20mm², the flow area is significantly increased, and the impedance is correspondingly reduced.

[0121] 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 coil core 10.

[0122] Table 5

[0123]

[0124] In order to demonstrate the protection of the core 10 by the three-step flattening method and its unexpected technical effect, we use the height of the core 10 in the three-step flattening method, and the feed amount of the positive and negative electrodes is unified as L 5-1 and L 6-1 .

[0125] The above table uses a controlled dynamic flattening mechanism to use two-step flattening to directly adjust the feed amount and compress L 5-1 and L 6-1 , directly compressed to the position 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 the positive side L 5-1 =L5+0.25, negative side, L 6-1 =L6+0.25, the final feed consumption of both is L 5-1 , L 6-1 .

[0126] However, the flatness of the core 10 obtained by the two-step flattening method has increased significantly compared to the previous 0.8mm, to 0.4mm-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 the welding process meets the required welding yield requirements, which are 0.2% for the positive electrode and 0.4% for the negative electrode.

[0127] As a preference, the welding yield rate of the present invention is above 99%, and preferably the welding yield rate of the present invention is above 99.5%.

[0128] 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 coating area 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.

[0129] The three-step flattening method adopts a method of slowly releasing the ear pressure in the bending area, which provides 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.

[0130] 1000 roll cores 10 were flattened in two steps, 500 roll cores 10 were welded with the positive current collector 30 first, and 500 roll cores 10 were welded with the negative current collector 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 20. There was a large gap between the concave position of the foil and the current collector 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 30 first, and 500 roll cores 10 were welded with the negative current collector 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.

[0131] 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.

[0132] like Fig.10 and Fig.11 As shown in Figure 2, the actual positive electrode welding line and the actual negative electrode welding line after two-step flattening are only about half of the theoretical welding line. Fig.12 and Fig.13 As shown in the figure, after three-step flattening, the actual welding wire length is consistent with the theoretical welding wire length, which is a full welding situation with no cold welding area ( Figure 10-13 The green line indicates the actual welding line).

[0133] Figure 14-16 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 17-Figure 19 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.

[0134] Alternatively, if Figure 5 As shown, the overall flatness of the positive electrode flat surface 16 is less than or equal to 0.25 mm, the multiple first welding areas 111 are independent of each other and each of the first welding areas is fan-shaped, and the flatness of each first welding area 111 is less than or equal to 0.2 mm; the overall flatness of the negative electrode flat surface 17 is less than or equal to 0.22 mm, the multiple second welding areas are independent of each other and each of the second welding areas is fan-shaped, and the flatness of each second welding area is less than or equal to 0.2 mm.

[0135] In an optional embodiment, if Figure 5 As 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.

[0136] 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.

[0137] In an optional embodiment, if Figure 5As 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 negative flat surface 17 is the same, and it 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°.

[0138] Combination Figure 5 The flatness of the flat surface 11 is obtained as follows: Figure 5 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.

[0139] The calculation formula for flatness is as follows:

[0140] F = H1-H2;

[0141] 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 in the middle 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).

[0142] 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 to be welded to 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.

[0143] 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.

[0144] 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.

[0145] Optionally, a first welding line area 1111 is formed in each first welding area 111, and the first welding line area 1111 extends radially along the positive electrode flat surface 16. The positive electrode current collector 30 and the positive electrode flat surface 16 are fully welded in each first welding line area 1111. It can be understood that during welding, the welding gun is welded along the first welding line area 1111, rather than welding all the first welding areas 111, so as to avoid large-area welding and prolonging the processing time. The full welding technique ensures the continuity and firmness of the welding. Among them, the full welding connection means that after the first welding line area 1111 is welded, after testing, all the welding of the first welding line area 1111 and the positive electrode current collector 30 is completed, and there is no false welding position in the first welding line area 1111.

[0146] Optionally, each second welding area forms a second welding line area, and the second welding line area extends along the radial direction of the negative electrode flat surface 17. The negative electrode current collector 40 is fully welded to the negative electrode flat surface 17 at each second welding line area. During welding, the welding gun welds along the second welding line area instead of welding all the second welding areas, so as to avoid extended processing time caused by large-area welding. The full welding technique ensures the continuity and firmness of the welding.

[0147] 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. Among them, 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 generation of the pre-pressing groove can also press the residual material of the outer ring into the groove 112.

[0148] Optionally, the tension F1 between the positive electrode current collector 30 and the positive electrode flat surface 16 is ≥5N; the tension F2 between the negative electrode current collector 40 and the negative electrode flat surface 17 is ≥15N. In the prior art, the tension between the positive electrode flat surface and the positive electrode current collector and the tension between the negative electrode flat surface and the negative electrode current collector are approximately between 2N and 8N, and the connection force is small and fluctuates greatly. In this embodiment, when the welding tension meets the above conditions, the connection between the winding core 10 and the positive electrode current collector 30 or the negative electrode current collector 40 is also more secure. When the battery is subjected to external impact, the winding core 10 and the positive electrode current collector 30 and the negative electrode current collector 40 are not easily separated, and the strength of the battery, that is, the anti-collision performance, is also improved.

[0149] 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.

[0150] Alternatively, if Figure 4 As shown, the positive electrode sheet 13 includes from top to bottom a first blank foil 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 blank foil 131), the upper part of the multi-layer first blank foil 131 is bent inward to form a positive electrode flat surface 16, and the lower part of the first blank foil 131 forms a vertical part, as shown in FIG. Figure 4 As shown, the height of the vertical portion is L, and the top of the negative electrode sheet 14 is located in the vertical portion.

[0151] The blank foil of the positive electrode sheet 13 (also known as the first blank foil) and the blank foil of the negative electrode sheet 14 are discussed separately for positive and negative electrodes due to their 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 L and W is the bending area W. 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 L 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 roll 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 L has stronger physical rigidity than the bending area W, ensuring that the vertical area L maintains a substantially vertical direction during the flattening process to prevent excessive interference with the negative electrode sheet 14.

[0152] 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.

[0153] 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 achieve the effect of protecting the negative electrode sheet 14 at the same time, ensuring the alignment accuracy of the winding, and the energy density of the battery will not be affected.

[0154] 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 requirements 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.

[0155] It should be noted that in actual products, the vertical area L and the bending area W can be directly connected or smoothly transitioned through a transition structure. In the present invention, a direct connection method is adopted.

[0156] 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 method for flattening a core, characterized in that: The winding core is formed by winding a positive electrode sheet (13), a separator (15), a negative electrode sheet (14) and a separator (15) stacked in sequence; 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; 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; the blank foil of the positive electrode sheet (13) and the blank foil of 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 and overlapping, and a groove (112) is formed on the flat surface (11); Characterized in that, the core flattening method comprises: 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 inward to form the groove (112); S20: Dynamic flattening, wherein the dynamic flattening mechanism compresses the core from both ends of the core toward the middle of the core at a preset flattening speed, and stops when the core reaches a predetermined expansion and contraction amount; S30: static flattening, where a static flattening mechanism presses the two ends of the winding core with a fixed pressure and maintains it for a preset time.

2. The method for flattening a winding core according to claim 1, characterized in that: The fixed pressure is F, 5N≤F≤15N, and the preset time is T, 2s≤T≤10s.

3. The method for flattening a winding core according to claim 2, characterized in that: The fixing pressure is negatively correlated with the preset time.

4. The method for flattening a core according to any one of claims 1 to 3, characterized in that: In S30, the total feed amount of the static flattening mechanism at both ends of the winding core is 0.2-0.7 mm.

5. The method for flattening a winding core according to any one of claims 1 to 3, characterized in that: S10 includes: S11: fixing the winding core on a fixing device located at a pre-pressing position, and providing pre-pressing components at both ends of the winding core respectively, and the pre-pressing components 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 ends of the winding core inward to form the groove (112); S12: The transport mechanism transfers the fixture to the dynamic flattening position; The step S21 is also included between S20 and S30: 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 at the static flattening position.

6. A winding core, characterized in that: Manufactured by the flattening method of the winding core according to any one of claims 1 to 5, 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, 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 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.

7. The winding core according to claim 6, wherein the grooves (112) of the positive electrode flat surface (16) are provided with eight, the first welding areas (111) are provided with eight, and the eight first welding areas (111) are evenly spaced in a fan shape along the center of the positive electrode flat surface (16); and / or The negative electrode flat surface (17) is provided with eight grooves (112), and 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 electrode flat surface (17).

8. Full-ear cylindrical battery, characterized in that: Comprising the winding core as claimed in claim 6 or 7, the full-ear cylindrical battery further comprising a positive electrode current collector (30), a first welding line area (1111) is formed in each of the first welding areas (111), the first welding line area (1111) extends along the radial direction of the positive electrode flat surface (16), and the first welding area (111) is fully welded to the positive electrode current collector (30) at the position of the first welding line area (1111); and / or The winding core also includes a negative electrode current collector (40), a second welding line area is formed in each second welding area, the second welding line area extends radially along the negative electrode flat surface (17), and the second welding area is fully welded to the negative electrode current collector (40) at the position of the second welding line area.

9. The full-ear cylindrical battery according to claim 8, characterized in that: The tension F1 between the positive electrode current collector (30) and the positive electrode flat surface (16) is ≥5N; and / or The tension F2 between the negative electrode current collecting sheet (40) and the negative electrode flat surface (17) is ≥15N.

10. The full-ear cylindrical battery according to claim 8, characterized in that: The impedance of the positive electrode flat surface (16) and the positive electrode current collector (30) after welding is less than or equal to 2.5 mΩ; and / or The impedance of the negative electrode flat surface (17) and the negative electrode current collecting sheet (40) after welding is less than or equal to 2.5 mΩ.

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