Flattening Method of Core, Core and All-Pole-Ear Cylindrical Battery

Abstract

The present invention belongs to the technical field of battery processing, and discloses a method for flattening a wound core, a wound core, and a full-tab cylindrical battery. The method for flattening the wound core includes: S10: Pre-pressing, folding inwards the multiple layers of positive electrode sheets and multiple layers of negative electrode sheets at both ends of the wound core; S20: Dynamic flattening, a dynamic flattening mechanism compresses the wound core from both ends of the wound core towards the middle of the wound core at a preset flattening speed, and stops when the wound core reaches a predetermined expansion amount; S30: Static flattening, a static flattening mechanism squeezes both ends of the wound core with a fixed pressure and maintains for a preset time; The wound core is made by the above method for flattening the wound core. The full-tab cylindrical battery includes the above wound core. For this method for flattening the wound core, the wound core, and the full-tab cylindrical battery, the welding between the wound core and the current collector is stable, the internal situation of false soldering is reduced, the internal impedance of the battery is decreased, 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 method for flattening a wound core, a wound core, and a full-tab cylindrical battery. Background Art

[0002] In order to significantly improve the overcurrent capacity of a battery, reduce the heat generation of the battery, and break through the bottleneck of cylindrical batteries, the full-tab process is mostly adopted for lithium batteries. In the full-tab process of lithium batteries, the full tab needs to be flattened first, and after it has a certain strength, subsequent current collector welding can be carried out. The flattening process of the full-tab wound core mostly adopts mechanical kneading and simple pressing methods. When mechanically kneading the tab, it is easily damaged and metal debris is generated. When using the pressing method, in the subsequent welding process of the finished wound core, it is difficult to weld with the current collector, and it is easy to cause false soldering. This results in a small overcurrent area inside the battery, a large impedance, affecting the performance of the battery, and reducing the quality of the finished battery.

[0003] Therefore, there is an urgent need to design a method for flattening a wound core, a wound core, and a full-tab 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 wound core. After being flattened by using this method, the wound core is easy to weld with the current collector, and the welding quality is good, ensuring excellent battery performance.

[0005] Another object of the present invention is to provide a wound core that can be stably welded with the current collector, reduce the phenomenon of false soldering, and improve the performance of the battery.

[0006] Still another object of the present invention is to provide a full-tab cylindrical battery in which the wound core and the current collector are stably welded, the internal false soldering situation is reduced, the internal impedance of the battery is reduced, and the performance is improved.

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

[0008] A method for flattening a wound core, the wound core is wound by 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 wound 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 wound core. The blank foils of the positive electrode sheet and the negative electrode sheet face in opposite directions; either one or both of the blank foils of the positive electrode sheet and the blank foils of the negative electrode sheet have a flat surface formed by bending and overlapping towards the central axis of the wound core, and a groove is formed on the flat surface;

[0009] The method for flattening the wound core includes:

[0010] S10: Pre-pressing. The blank foils of multiple layers of the above-mentioned positive electrode sheets and / or the blank foils of multiple layers of the above-mentioned negative electrode sheets at the end of the above-mentioned core are folded inward by a pre-pressing device to form the above-mentioned groove.

[0011] S20: Dynamic flattening. The dynamic flattening mechanism compresses the above-mentioned core from both ends of the above-mentioned core to the middle of the above-mentioned core at a preset flattening speed, and stops when the above-mentioned core reaches a predetermined expansion amount.

[0012] S30: Static flattening. The static flattening mechanism squeezes both ends of the above-mentioned core with a fixed pressure and maintains it for a preset time.

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

[0014] As an optional solution, the above-mentioned fixed pressure and the above-mentioned preset time are in a negative correlation relationship.

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

[0016] As an optional solution, S10 includes:

[0017] S11: Fix the above-mentioned core on a fixing device located at the pre-pressing position. Pre-pressing components are respectively arranged at both ends of the above-mentioned core. The pre-pressing components fold the blank foils of multiple layers of the above-mentioned positive electrode sheets and / or the blank foils of multiple layers of the above-mentioned negative electrode sheets at the end of the above-mentioned core inward to form the above-mentioned groove.

[0018] S12: The transport mechanism transfers the fixing device to the dynamic flattening position.

[0019] Between the above-mentioned S20 and the above-mentioned S30, there is also S21: The transport mechanism transfers the above-mentioned fixing device from the above-mentioned dynamic flattening position to the static flattening position, and the above-mentioned static flattening mechanism performs static flattening on the above-mentioned core at the static flattening position.

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

[0021] The overall flatness of the above-mentioned negative electrode flat surface is less than or equal to 0.22mm. The above-mentioned negative electrode flat surface is divided into several independent fan-shaped second welding areas by the above-mentioned groove, and the flatness of each above-mentioned second welding area is less than or equal to 0.2mm.

[0022] There are eight of the above-mentioned grooves on the above-mentioned flat surface of the positive electrode, and there are eight of the above-mentioned first welding areas. The eight above-mentioned first welding areas are evenly distributed at intervals in a fan shape along the center of the above-mentioned flat surface of the positive electrode; and / or

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

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

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

[0026] As an optional solution, the tensile force F1 between the above-mentioned positive current collector and the above-mentioned flat surface of the positive electrode is ≥5N; and / or

[0027] The tensile force F2 between the above-mentioned negative current collector and the above-mentioned flat surface of the negative electrode is ≥15N.

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

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

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

[0031] The present invention provides a method for flattening a core. The flat surface of the core 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 flat surface of the core tend to be the same. When the current collector is placed on the flat surface of the core for welding, the spacing between the current collector and the corresponding flat surface of the core at each position is reduced. After the same welding, the current collector and the flat surface of the core at the positions passed by the welding torch are both melted in place, the current collector is welded firmly, the phenomenon of false welding is reduced, and the performance of the battery is improved.

[0032] The present invention further provides a core, which is made by the above-mentioned method for flattening a core, and can be welded firmly with the current collector, reduce the phenomenon of false welding, and improve the performance of the battery.

[0033] The present invention also provides a full-tab cylindrical battery, which includes the above-mentioned wound core, a positive current collector, and a 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 wound core and the current collector is firm, the internal soldering voids are reduced, the internal impedance of the battery is decreased, and the performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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

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

[0041] Figure 8 is a schematic diagram of the height change of the prior art two-step flattened wound core provided by an embodiment of the present invention;

[0042] Figure 9 is a schematic diagram of the height change of the three-step flattened wound core provided by an embodiment of the present invention;

[0043] Figure 10 is a CT diagram of the welding of the positive flat surface of the wound core and the positive current collector after two-step flattening in the prior art;

[0044] Figure 11 is a CT diagram of the welding of the negative flat surface of the wound core and the negative current collector after two-step flattening in the prior art;

[0045] Figure 12 is a CT diagram of the welding of the positive flat surface of the wound core and the positive current collector after three-step flattening provided by an embodiment of the present invention;

[0046] Figure 13 is a CT diagram of the welding of the negative flat surface of the wound core and the negative current collector after three-step flattening provided by an embodiment of the present invention;

[0047] Figure 14 It is the style diagram after pre - pressing the negative extreme surface provided by the embodiment of the present invention;

[0048] Figure 15 It is the style diagram after dynamically flattening the negative extreme surface provided by the embodiment of the present invention;

[0049] Figure 16 It is the style diagram after statically flattening the negative extreme surface provided by the embodiment of the present invention;

[0050] Figure 17 It is the style diagram after pre - pressing the positive extreme surface provided by the embodiment of the present invention;

[0051] Figure 18 It is the style diagram after dynamically flattening the positive extreme surface provided by the embodiment of the present invention;

[0052] Figure 19 It is the style diagram after statically flattening the positive extreme surface provided by the embodiment of the present invention.

[0053] In the figure:

[0054] 10. Core; 11. Flat surface; 111. First welding area; 1111. First wire bonding 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 implementation manners

[0056] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the present invention are shown in the drawings, rather than all the structures.

[0057] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected to", and "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0058] In the present invention, unless otherwise clearly specified or limited, the first feature being "on" or "under" the second feature may include direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is less than that of the second feature.

[0059] In the description of this embodiment, the orientation or positional relationships such as "up", "down", "left", "right" are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0060] Such as Figure 1 is the structure of a full-tab cylindrical battery according to an embodiment of the present invention (only the wound core 10 and two current collectors 20 are shown). At the same time, referring to Figure 2 , the wound core 10 is wound by stacking a positive electrode sheet 13, a separator 15, a negative electrode sheet 14 and a separator 15 in sequence, and is in a cylindrical shape as a whole. Such as Figure 2 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 in the unfolded state, at both ends of the positive electrode sheet 13 and the negative electrode sheet 14 in the width direction (that is, the positions where the active material is not coated), the aforementioned blank foils are formed. Such as Figure 2 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, referring to Figure 4 , the part of the negative electrode foil where the negative electrode active material is not coated forms a second blank foil (not marked, Figure 4 at one end of the wound core 10 away from the first blank foil 131 in Figure 2 shown, when the wound 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 staggeredly arranged, so that the blank foils of the positive electrode sheet 13 and the negative electrode sheet 14 face in opposite directions and are wound into the wound core 10, and the upper and lower two end faces (the lower end face is not shown) are pressed into a flat surface 11 by a pressing device, and a groove 112 is formed on the flat surface 11 (refer to Figure 6), wherein the arrangement of the groove 112 can absorb the wrinkles formed by the inward bending of the blank foils of the multi-layer positive electrode sheet 13 and the blank foil of the negative electrode sheet 14, reduce the wrinkling of the flat surface 11, and improve the flatness of the flat surface 11.

[0061] As Figure 2 and Figure 4 shown, the core 10 is accommodated in the battery case in a state where the electrolyte is infiltrated. The positive electrode foil can be a metal foil made of aluminum or an aluminum alloy, and the material of the negative electrode foil can be a metal foil made of copper or a copper alloy.

[0062] As Figure 2 shown, in an optional embodiment, there is a through hole 18 on the central axis of the core 10, and a positioning pin (not shown in the figure) is used to be inserted into the through hole 18 for welding the current collector 20 and the bottom of the battery case. As Figure 3 and Figure 4 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 circumference of the core 10 towards the through hole 18, and the adjacent blank foils of the positive electrode sheet 13 or the negative electrode sheet 14 are bent overlapping each other.

[0063] As Figure 1 and Figure 3 shown, in an optional embodiment, the current collector 20 is divided into a positive electrode current collector 30 and a negative electrode current collector 40. The positive electrode current collector 30 is welded to the flat surface 11 formed by the positive electrode blank foil. The positive electrode current collector 30 can be a metal plate or a metal sheet made of a single body or a composite material of aluminum or an aluminum alloy. The negative electrode current collector 40 is welded to the flat surface 11 formed by the negative electrode blank foil. The negative electrode current collector 40 can be a metal plate or a metal sheet made of a single body or a composite material of nickel, a nickel alloy, copper, or a copper alloy. A hole is provided near the center of the positive electrode current collector 30, and the position of the hole is a position corresponding to the through hole 18. The negative electrode current collector 40 can be an entire circular current collector or a circular current collector with a circular convex portion at the center. The center position of the current collector 20 at the negative electrode end is further welded to the bottom of the battery case through an externally inserted positioning pin.

[0064] It can be understood that the Figures 1 to 7 in the present invention are all 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 two or more of the positive electrode materials capable of intercalating and deintercalating lithium. The positive electrode active material layer 132 can further include any one or two or more of other materials such as a positive electrode binder and a positive electrode conductive agent. The positive electrode material can be lithium iron phosphate or a ternary material of nickel cobalt manganese system or nickel cobalt aluminum system, and other positive electrode materials of lithium ion batteries existing in the prior art.

[0065] In an alternative embodiment, the negative electrode material may be a carbon material, such as artificial graphite and natural graphite, or a graphite-based composite negative electrode material doped with a certain amount of silicon oxide or silicon carbide, as well as other negative electrode materials for lithium-ion batteries existing in the prior art.

[0066] In an alternative embodiment, the separator 15 may be a single-layer PP, single-layer PE, PP + ceramic coating, PE + ceramic coating, double-layer PP / PE, double-layer PP / PP, or triple-layer PP / PE / PP separator, as well as other separator materials for lithium-ion batteries existing in the prior art.

[0067] In an alternative 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 alternative embodiment, the aforementioned solvent includes any one or more of non-aqueous solvents such as organic solvents. Among them, the electrolyte with a non-aqueous solvent is a so-called non-aqueous electrolyte, and the non-aqueous solvent may be, for example, a cyclic carbonate, a chain carbonate, a lactone, a chain carboxylate, a nitrile (mononitrile), etc.

[0069] In an alternative embodiment, the aforementioned electrolyte salt may include any one or more of salts such as lithium salts. In addition, the electrolyte salt may also include salts other than lithium salts. The salts other than lithium salts may be, for example, light metal salts other than lithium.

[0070] In one embodiment, the battery casing is a metal casing, and the metal casing may be a steel casing or an aluminum casing, and is further preferably a steel casing.

[0071] In an alternative embodiment, the aforementioned lithium salt is, for example, lithium hexafluorophosphate (LiPF 6 )、lithium tetrafluoroborate (LiBF 4 )、lithium perchlorate (LiClO 4 )、lithium hexafluoroarsenate (LiAsF 6 )、lithium tetraphenylborate (LiB(C 6 H 5 ) 4 )、lithium methanesulfonate (LiCH 3 SO 3 )、lithium trifluoromethanesulfonate (LiCF 3 SO 3 )、lithium tetrachloroaluminate (LiAlCl 4 )、lithium bis(hexafluorosilicate) (Li 2 SF 6), lithium chloride (LiCl), lithium bromide (LiBr), etc. Among them, the aforementioned lithium salts can be any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate; the aforementioned lithium salts are more preferably lithium hexafluorophosphate. The content of the electrolyte salt is not particularly limited, and preferably, it is 0.3 mol / kg to 3 mol / kg relative to the solvent.

[0072] In the prior art, in a full-tab cylindrical battery, the flattening process of the wound core 10 mostly adopts mechanical kneading and simple flattening methods. At the end of the spiral wound core 10 where the positive current collector coated with the active material and the negative current collector are wound with the separator 15 in between, there is a current collector exposed part without the active material coated. When mechanically kneading the current collector, the tab is easily damaged and metal debris is generated. In the simple flattening method, several grooves 112 are pre-pressed in the tab area first to form an inwardly inclined tab, and then flattened to avoid damage to the tab and generation of metal debris. However, the inwardly stacked tabs are likely to cause the entire flattening end face to sink inward, and the height of the outer ring gradually decreases towards the inner ring.

[0073] To solve the above problems, this embodiment provides a method for flattening a wound core, which is used to flatten the end face of the above-mentioned wound core 10. Each end face of the wound core 10 is pressed three times, and the flatness of the formed flat surface 11 is smaller. It can be understood that the prior art flattening method generally undergoes two flattenings. After the wound core 10 is flattened, the flatness ≥ 0.8 mm. At this time, the welding yield of the current collector plate 20 welded to the end face of the wound core 10 is relatively low, and there are many cases of virtual welding. After the wound core 10 is pressed three times provided by this embodiment, among them, the flat surfaces 11 at both ends of the wound core 10 are the positive flat surface 16 and the negative flat surface 17 respectively. The positive flat surface 16 is divided into several first welding areas 111 by several grooves 112, and the negative flat surface 17 is divided into several second welding areas by several grooves 112. The overall flatness of the positive flat surface 16 and the negative flat surface 17 is less than or equal to 0.25 mm, and the flatness of the first welding area 111 and the second welding area is less than or equal to 0.2 mm. The height of the outer ring and the inner ring of the end face of the wound core 10 tends to be consistent, the welding yield of the welded current collector plate 20 is improved, the internal resistance of the battery is reduced, and the battery performance is improved.

[0074] Specifically, the method for flattening the wound core includes:

[0075] S10: Pre-pressing, see Figures 6 - 7 , through the pre-pressing device, the blank foils of the multi-layer positive electrode sheets 13 and / or the blank foils of the multi-layer negative electrode sheets 14 at the end of the wound core 10 are folded inward to form grooves 112; among them, Figure 6Before preloading, the first blank foil 131 is in a fully straight state. The core 10 is placed horizontally, and preloading devices are provided at both ends of the core 10. After preloading, due to the ribs protruding from the pressing heads of the preloading devices, eight pressing heads are arranged on each end face of the core 10. After preloading, eight grooves 112 are formed, and at the same time, the multi-layer positive electrode sheets 13 and multi-layer negative electrode sheets 14 are both folded inward by a certain angle ( Figure 7 The inclination state is not shown in). Each pressing head of the preloading device rotates to preload the multi-layer positive electrode sheets 13 or negative electrode sheets 14 by a certain angle. For the preloading technology and device equipment, reference can be made to the Chinese patent application No. 2024115037125, a core tab preloading device and preloading equipment, and Chinese patent application No. 202411503713X, a core tab preloading device and preloading equipment.

[0076] S20: Dynamic flattening. The dynamic flattening mechanism compresses the core 10 from both ends of the core 10 to the middle at a preset flattening speed and stops when the core 10 reaches a predetermined expansion amount; after dynamic flattening, taking Figure 1 the positive flat surface 16 in as an example, multiple positive electrode sheets 13 continue to be stressed and flattened. At this time, the flatness of the positive flat surface 16 is approximately between 0.75 mm and 0.8 mm, and the feed amount accounts for about 7.4% of the original height of the core 10.

[0077] S30: Static flattening. The static flattening mechanism squeezes both ends of the core 10 with a fixed pressure and maintains it for a preset time. The pressing mechanisms of static flattening and dynamic flattening are different. The two ends of the core 10 after dynamic flattening are leveled and pressed with a fixed pressure. In the case of a fixed pressure, the height of the core 10 still decreases.

[0078] After many tests, it is found that it is difficult to weld the core 10 and the current collector 20. The main reason is that after the flattening method of the existing technology is completed, the heights of the outer electrode sheets (referring to the positive electrode sheets 13 or negative electrode sheets 14, and the electrode sheets will not be repeated when mentioned below) and the inner electrode sheets are different. Usually, the outer layer is higher and the inner layer is lower. The current collector 20 is a flat part. When the current collector 20 is placed on the end face of the core 10, the gaps with the end face of the core 10 are different, resulting in difficulty in welding the core 10 and the current collector 20, and virtual welding is likely to occur at the positions with larger gaps.

[0079] The core 10 manufactured by the above-mentioned core flattening method flattens the end face of the core 10 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 the same. When the current collector 20 is placed on the end face of the core 10 for welding, the distance between the current collector 20 and the corresponding end face of the core 10 at each position decreases, and after the same welding, at the positions where the welding torch passes, both the current collector 20 and the end face of the core 10 are melted in place, the current collector 20 is welded firmly, the phenomenon of false soldering 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. It only uses a single preset expansion amount as a single parameter. Regardless of the flattening pressure, it reaches the final flattening position. While static flattening uses a preset pressure for static regulation and maintains a certain static flattening time, and the expansion amount of the battery core will be further reduced by a small part to reach the length of the entire core 10 required for the cylindrical battery.

[0081] Optionally, S10 includes:

[0082] S11: Fix the core 10 on the fixing device located at the pre-pressing position, and pre-pressing components are respectively arranged at both ends of the core 10. The pre-pressing components gather the multi-layered positive blank foils and / or multi-layered negative blank foils at the end of the core 10 inward to form a groove 112;

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

[0084] Between S20 and S30, there is also S21: The transport mechanism transfers the fixing device from the dynamic flattening position to the static flattening position, and the static flattening mechanism performs static flattening on the core 10 at the static flattening position.

[0085] It can be understood that the core 10 is fixed by the fixing device, and then the fixing device is transported at each working station by the transport mechanism, thereby realizing the continuous operation of three-step flattening.

[0086] Optionally, the pressure of static flattening is controlled within the range of 5N - 15N, and the flattening time lasts for 2s - 10s. The greater the pressure applied, the shorter the flattening time lasts. The fixed pressure and the preset time are in a negative correlation relationship. It can ensure the flatness of the end face of the core 10 without damaging the core 10.

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

[0088] It can be understood that in S30, the total feed of the static flattening mechanism is 0.2 mm - 0.7 mm more than that of the two-step flattening in the prior art, preferably 0.5 mm. Exemplarily, the total feed of the static flattening mechanism at both ends of the core 10 is 0.5 mm. It can be considered that the feed on the positive electrode side is 0.25 mm more, and the feed on the negative electrode side is also 0.25 mm more, and the combined feed on both sides is 0.5 mm more. In order to ensure the final height of the core 10, during the preliminary design of the product, the blank foil height of the positive electrode 13 is increased by 0.25 mm, and the blank foil height of the negative electrode 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 their materials and hardness, the feeds of the two may be slightly different. For example, the feed of the negative electrode may be slightly higher than that of the positive electrode.

[0089] Among them, Figure 8 For the prior art, the height change data of the core 10 in two-step flattening are as follows:

[0090] L 0 : The total height of the core before two-step flattening;

[0091] L 1 : The total height of the core after flattening;

[0092] L 2 : The height of the separator;

[0093] L 3 : The height of the positive electrode tab before two-step flattening;

[0094] L 4 : The height of the negative electrode tab before two-step flattening;

[0095] L 5 : The feed of the positive electrode in two-step flattening;

[0096] L 6 : The feed of the negative electrode in two-step flattening;

[0097] L 7 : The height of the positive electrode tab after flattening;

[0098] L 8 : The height of the negative electrode tab after flattening;

[0099] In this embodiment, Figure 9 For the three-step flattening, the height change data of the core 10 are as follows:

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

[0101] L 3-1 : The height of the positive electrode tab before flattening, L 3-1 = L3 +0.25;

[0102] L 4-1 : Height of the negative tab before flattening, L 4-1 = L 4 +0.25;

[0103] L 5-1 : Positive feed rate, L 5-1 = L 5 +0.25;

[0104] L 6-1 : Negative feed rate, L 6-1 = L 6 +0.25;

[0105] After three-step flattening, the thickness of the dense area accounts for 8.25% of the height of the tab area before flattening, that is, the height ratio of the rolled core 10 before and after flattening is increased from 1.08 to 1.09, ensuring that the height of the rolled core 10 remains unchanged after flattening and the normal progress of the assembly process.

[0106] To further illustrate the technical effects of the rolled core leveling method in this embodiment, Table 1 shows the overall flatness data of the negative flat surface 17 of the rolled core 10 with a diameter of 20.45 mm. Table 2 shows the data of the wire bonding length, impedance, and welding tensile force of the negative flat surface 17 of the rolled core 10.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111] As can be seen from Table 1, the maximum flatness of a single piece of the negative flat surface 17 of the rolled core 10 after two-step flattening reaches 0.8 mm, and most are concentrated in the range of 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, reducing the stability of the wire bonding depth and length. After welding the current collector 20 and performing a CT test on the welding penetration depth, there are a large number of virtual welds, and the average value of the effective wire bonding length only reaches half.

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

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

[0114] Table 3

[0115]

[0116] Table 4

[0117]

[0118] As can be seen from Table 3, the maximum flatness of the first welding area 111 of the positive flat surface 16 of the core 10 after two-step flattening reaches 0.78 mm, and most of them are concentrated in the range of 0.5 - 0.6 mm. The foil material is not compacted, and the entire flat foil material is in a warped state. The strength of the foil material is not conducive to the welding of the current collector 20, reducing the stability of the wire bonding depth and length. After welding the current collector 20 and taking a CT test on the welding penetration depth, there are large areas of false soldering, and the average value of the effective wire bonding length only reaches half. After adding the third step of flattening, the flatness of a single block 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 relatively good. The foil materials in the dense area can be closely bonded layer by layer, and there is no gap between the foil materials, avoiding problems such as false soldering, welding through and poor penetration depth consistency. Therefore, the penetration depth stability after welding is better, there is no false soldering and it meets the requirements of welding tensile force, current-carrying area and impedance.

[0120] As can be seen from the data in Table 4, the overall flatness of the positive flat surface 16 of the core 10 is reduced from ≤0.85 mm to ≤0.2 mm, the effective welding rate is increased from 60% to 100%, the value of A / C is increased from 4.28% to 71.4%, and there is no false soldering and it meets the requirements that the positive welding tensile force is greater than or equal to 5 N, the current-carrying area and the impedance are less than 2.3 ± 0.2 mΩ. After testing, for the core 10 with a diameter of 20.45 mm, the current-carrying area of the positive flat surface 16 after static flattening is about 20 mm², the current-carrying area is significantly increased, and the impedance is correspondingly reduced.

[0121] As can be seen from the accompanying drawings, compared with the two-step flattening, for the three-step flattening proposed by the present invention, since the third-step static flattening is added and the static flattening will consume a certain amount of feed, therefore, an additional feed allowance L needs to be given in the design of the core 10. 5-1 and L 6-1 , relative to the final feed L in the two-step method 5 and L 6 , L 5-1 >L 5 , L 6-1 >L 6 . At the same time, we can see that whether it is three-step flattening or two-step flattening, the height of the core 10 brought by the two methods is the same, and the total height of the finally obtained core 10 is H = L 2 +L 7 +L 8 . For the three-step flattening proposed by the present invention, the positive electrode side L 5-1 =L 5 +0.25, the negative electrode feed, L 6-1 =L 6 +0.25. It can be understood in this way that the feed given by the third-step static flattening for the positive and negative electrodes is 0.25 mm and 0.25 mm respectively. Table 5 shows the data of the influence of two-step flattening and three-step flattening on the welding yield of the core 10.

[0122] Table 5

[0123]

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

[0125] The above table uses the two-step flattening of the controlled dynamic flattening mechanism to directly adjust the feed to compress L 5-1 and L 6-1 , and directly compress to the positions of L 7 and L 8 . While the three-step flattening method is that the normal dynamic flattening consumes the feed L 5 and L 6 , and then the static flattening consumes the feed of 0.25 mm and 0.25 mm respectively. Considering that the positive electrode side L 5-1 =L 5 +0.25, the negative electrode side, L 6-1 =L 6 +0.25, the final feed consumed by 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 =L 5 +0.25, negative side, L 6-1 =L 6 +0.25 and still using the two-step flattening method, it will cause serious accumulation of the tabs in the bending area during 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] Flattening in two steps for 1000 cores 10. For 500 cores 10, the positive current collector 30 is welded first. For 500 cores 10, the negative current collector 40 is welded first. The defective rate of positive Hi-pot is 11.8%, and the defective rate of negative Hi-pot is 9.8%. The end faces of the cores 10 are uneven. What is in close contact with the current collector 20 is not the entire plane. There are a large number of gaps between the current collector 20 and the concave position of the foil, which is likely to cause defects such as false soldering, black spots or welding through. The main manifestations are insufficient tensile strength, poor appearance detected by the naked eye, and welding hitting the separator 15 resulting in defective Hi-pot; Flattening in three steps for 1000 cores 10. For 500 cores 10, the positive current collector 30 is welded first. For 500 cores 10, the negative current collector 40 is welded first. The defective rate of positive Hi-pot is 0.2%, and the defective rate of negative Hi-pot is 0.4%. That is to say, the method of flattening in three steps in this embodiment greatly improves the welding yield of the cores 10, and further improves the qualification rate of the final finished battery.

[0131] In addition, in the third step of this embodiment, static flattening is adopted, which is also an important means to ensure the battery yield. It is known through experiments that for cores 10 of the same height, flattening them twice or three times with a certain speed in the third flattening cannot reduce the defective rate to the value in Table 5.

[0132] As Figure 10 and Figure 11 shown, after flattening in two steps, the actual welding wires at the positive and negative poles are only about half of the theoretical welding wires. As Figure 12 and Figure 13 shown, after flattening in three steps, the actual welding wire length is the same as the theoretical welding wire length, which is a full-weld situation without false soldering areas ( Figures 10 - 13 The part indicated by the green line is the actual welding wire).

[0133] Figures 14 - 16 They are the states of the end face of the negative pole of the core 10 after pre-pressing, dynamic flattening, and static flattening in sequence. Figures 17 - 19 is the state of the end face of the positive pole of the core 10 after pre-pressing, dynamic flattening, and static flattening in sequence. It can be seen that after flattening in three steps, the flatness of the visually flat surface 11 is better.

[0134] Optionally, as Figure 5 shown, the overall flatness of the positive flat surface 16 is less than or equal to 0.25 mm. A number of first welding areas 111 are independent of each other and each first welding area is fan-shaped. 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. A number of second welding areas are independent of each other and each second welding area is fan-shaped. The flatness of each second welding area is less than or equal to 0.2 mm.

[0135] In an alternative embodiment, as Figure 5 shown, for the number M of the slots 112, generally, a symmetric number or a number that can evenly divide the circumference can be selected. Generally speaking, the number of M should be greater than or equal to 4. M can be selected as different numbers such 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 alternative embodiment. Among them, starting from the size of the commonly used core 10, the number M of this alternative embodiment can be selected as 8.

[0136] In an alternative embodiment, as Figure 5 shown, the slots 112 on the flat surface 11 can be evenly arranged in the entire circumferential area, and the angles between them 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 collector 20. Of course, in other alternative embodiments, it is not excluded that some areas may not be provided with the slots 112, or the slots 112 can also be arranged in a non-uniform pitch form. Different arrangement methods of the slots 112 are within the protection scope of this application.

[0137] In an alternative embodiment, as Figure 5 shown, the arrangement of the slots 112 should extend from the inner circumference to the outer circumference of the core 10 and penetrate the entire core 10. This design divides the flat surface 11 into several independent fan-shaped areas, which are used for welding 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. For the negative flat surface 17, these fan-shaped areas are the second welding areas. Hereinafter, the positive flat surface 16 will be used as an example for illustration, and the negative flat surface 17 is the same, and will not be emphasized later. The multiple first welding areas 111 can be the same fan-shaped areas, and these fan-shaped areas are independent of each other and do not connect. For example, in this embodiment, the preferred solution is that the eight slots 112 spaced at the same angle of 45° divide the flat surface 16 into eight first welding areas 111 with equal areas and in a fan shape.

[0138] Combined with Figure 5 the description of obtaining the flatness of the flat surface 11, as Figure 5 shown, in the experiment, a 3D profiler is used to measure 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 in the selected area, and automatically calculates the difference between the high and low points, which is the flatness.

[0139] The calculation formula of the 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 part in Figure 5 is the eight measured overall flat areas. In a specific embodiment, the flatness measured in the present invention is the flatness of the entire end face of the core 10 (including the eight first welding areas 111).

[0142] Taking the positive flat surface 16 as an example, the negative flat surface 17 will not be elaborated. Figure 5 The shaded part in Figure 5 is the eight measured first welding areas 111. Each first welding area 111 is used for welding with the positive 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, in the solution of this embodiment, by controlling the overall flatness of the positive flat surface 16 within the range of less than or equal to 0.25 mm and controlling the flatness within each first welding area 111 within 0.2 mm, when welding with the positive current collector 30, the fit between the first welding area 111 and the positive current collector 30 is better. The gap within 0.2 mm enables the positive flat surface 16 and the positive current collector 30 to be completely melted under the high temperature of the welding torch during welding, reducing the occurrence of false soldering. Furthermore, after the core 10 is assembled, the internal resistance of the battery is reduced, ensuring excellent battery performance.

[0144] Similarly, by controlling the overall flatness of the negative flat surface 17 within the range of less than or equal to 0.22 mm and controlling the flatness within each second welding area within 0.2 mm, when welding with the negative current collector 40, the fit between the second welding area and the negative current collector 40 is better. The gap within 0.2 mm enables the negative flat surface 17 and the negative current collector 40 to be completely melted under the high temperature of the welding torch during welding, reducing the occurrence of false soldering. That is, the flatness of the two end faces of the core 10 is reduced compared with the prior art, the welding is more sufficient, false soldering is avoided, and the overall performance of the battery is improved.

[0145] Optionally, a first bonding wire area 1111 is formed within each first welding area 111. The first bonding wire area 1111 extends along the radial direction of the positive electrode flat surface 16. The positive electrode current collector 30 and the positive electrode flat surface 16 are fully welded at each first bonding wire area 1111. It can be understood that during welding, the welding torch performs welding along the first bonding wire area 1111, rather than welding the entire first welding area 111, so as to avoid the extension of processing time caused by large-area welding. The full-welding method ensures the continuity and firmness of welding. Here, the full-welding connection means that after welding in the first bonding wire area 1111, after inspection, all welds between the first bonding wire area 1111 and the positive electrode current collector 30 are complete, and there is no unfused position within the first bonding wire area 1111.

[0146] Optionally, a second bonding wire area is formed within each second welding area. The second bonding wire area extends along the radial direction of the negative electrode flat surface 17. The negative electrode current collector 40 and the negative electrode flat surface 17 are fully welded at each second bonding wire area. During welding, the welding torch performs welding along the second bonding wire area, rather than welding the entire second welding area, so as to avoid the extension of processing time caused by large-area welding. The full-welding method ensures the continuity and firmness of welding.

[0147] Optionally, as Figure 5 shown, there are eight first welding areas 111. The eight first welding areas 111 are evenly distributed at intervals in a fan shape around the center of the positive electrode flat surface 16. Adjacent two first welding areas 111 are separated by the above-mentioned groove 112; there are eight second welding areas. The eight second welding areas are evenly distributed at intervals in a fan shape around the center of the negative electrode flat surface 17. Adjacent two 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 plate 13 or the negative electrode plate 14 inward during the pre-pressing process. At the same time, the generation of the pre-pressing groove can also press the surplus material on the outer ring into the groove 112.

[0148] Optionally, the tensile force F1 between the positive electrode current collector 30 and the positive electrode flat surface 16 is ≥5N; the tensile force F2 between the negative electrode current collector 40 and the negative electrode flat surface 17 is ≥15N. In the prior art, the tensile force between the positive electrode flat surface and the positive electrode current collector and the tensile force between the negative electrode flat surface and the negative electrode current collector are approximately between 2N - 8N, with a small connection force and large fluctuations. In this embodiment, when the welding tensile force 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 firm. When the battery is impacted externally, it is not easy for the winding core 10 and the positive electrode current collector 30 and the negative electrode current collector 40 to separate, and the strength of the battery, that is, the anti-collision performance, is also improved.

[0149] Furthermore, the flat surface 16 of the positive electrode is welded to the positive current collector 30 with a welding yield rate of over 99%, and the welding yield rate of the flat surface 17 of the negative electrode and the negative current collector 40 is over 99%. That is to say, the improvement in flatness enhances the welding stability between the flat surface 16 of the positive electrode and the positive current collector 30, as well as the welding stability between the flat surface 17 of the negative electrode and the negative current collector 40.

[0150] Optionally, as Figure 4 shown, the positive electrode sheet 13 includes a first blank foil 131 (which can also be referred to as the positive current collector) and a positive electrode active material layer 132 from top to bottom (the positive electrode active material layer 132 is coated on the positive current collector, and the area of the positive current collector without the coating of 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 the flat surface 16 of the positive electrode, and the lower part of the first blank foil 131 forms a vertical part. As Figure 4 shown, the height of the vertical part is L, and the top of the negative electrode sheet 14 is located within the vertical part.

[0151] Regarding the blank foils of the positive electrode sheet 13 (i.e., the first blank foil) and the negative electrode sheet 14, due to the different flattening structures, we will discuss them separately for the positive and negative electrodes. 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 sheet structure, the negative electrode sheet 14 will be wider 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 (i.e., the length direction of the 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 entire blank foil of the positive electrode sheet 13 is L + W. Generally speaking, since the physical stiffness requirements of L1 and L2 are much greater than those of the W part, in the actual design of the winding, ceramic slurry or insulating glue and other substances will be coated on L2 to increase the stiffness of L2 to resist bending. At the same time, its insulating coating can effectively alleviate the internal short circuit between the positive electrode sheet 13 and the negative electrode sheet 14. For the L1 part, according to needs, we will also coat most or all of L1 with ceramic slurry or insulating glue and other substances to increase the stiffness of L1 to resist bending. The coatings on L1 and L2 are continuous coatings, and the two materials can be the same and are coated simultaneously. It can be understood that the vertical area L has stronger physical stiffness than the bending area W, ensuring that the vertical area L remains generally vertical during the flattening process and preventing excessive interference with the negative electrode sheet 14.

[0152] At the same time, as Figure 4 shown, the outer vertical area L2 is set in this way to ensure that the projection of the positive electrode active material layer 132 completely falls within the negative electrode active material layer, avoiding the edge of the negative electrode sheet 14 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 is too small, i.e., L1 / L2 < 0.2, it cannot effectively protect the negative electrode sheet 14, and at the same time, it affects the winding alignment accuracy (this part mainly considers the method of applying glue). When L1 / L2 is too large, i.e., L1 / L2 > 2, 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. By this setting method, it can achieve the effect of protecting the negative electrode sheet 14, ensuring the winding alignment accuracy, and not affecting the battery energy density.

[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 may be a situation where the negative electrode sheet 14 is wider than the positive electrode sheet 13 in the width direction. On the negative electrode side, such a structure does not exist, and the entire negative electrode protrudes beyond the positive electrode sheet 13. Of course, the blank foil on the negative electrode side can also be divided 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 on the negative electrode side, we can also choose to coat ceramic slurry or insulating glue and other substances to increase the stiffness of L. However, considering that during the flattening process, if the L part of the negative electrode itself can meet the requirement of being rigid during flattening, then it is also possible not to coat ceramic slurry or insulating glue and other substances. The core reason is that on the negative electrode side, there is no need to consider the problem of internal short circuit caused by the contact between the negative electrode sheet 14 and the positive electrode. Therefore, the ceramic slurry or insulating glue coating on the negative electrode side is an optional item and can be selected according to actual needs.

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

[0156] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, various obvious changes, re-adjustments, and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall 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, the static flattening mechanism presses the two ends of the winding core with a fixed pressure and maintains it for a preset time, the fixed pressure is F, 5N≤F≤15N; In S30, the total feed amount of the static flattening mechanism at both ends of the winding core is 0.2-0.7 mm.

2. The method for flattening a winding core according to claim 1, characterized in that: 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: 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.

5. A winding core, characterized in that: Manufactured by the flattening method of the winding core according to any one of claims 1 to 4, 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.

6. The winding core according to claim 5, 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).

7. Full-ear cylindrical battery, characterized in that: Comprising the winding core as claimed in claim 5 or 6, 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.

8. The full-ear cylindrical battery according to claim 7, 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.

9. The full-ear cylindrical battery according to claim 7, 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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