Square battery cell assembly, preparation method thereof and square battery

Abstract

The invention provides a square battery cell assembly and a preparation method thereof and a square battery, the preparation method comprises the following steps: (1) providing a positive plate, a negative plate, a diaphragm and a rectangular gasket, and respectively carrying out laser die cutting on blank areas of the positive plate and the negative plate to obtain tab parts; (2) respectively carrying out slit cleaning on the active material areas of the positive plate and the negative plate to form a plurality of groups of paired gap parts; (3) winding the positive plate, the diaphragm and the negative plate along the periphery of the rectangular gasket, so that the paired gap parts are respectively positioned at the corners of the positive plate and the negative plate to obtain a roll core main body with a square structure, and collecting the positive tab cluster and the negative tab cluster at the two sides of the roll core main body respectively; and (IV) respectively welding the positive tab cluster and the negative tab cluster to form a positive tab and a negative tab. The winding battery cell with the cuboid structure is adopted, so that the space utilization rate of the battery reaches the maximum value, and the cycle performance of the battery is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of new energy lithium batteries and relates to a square battery core assembly and a preparation method thereof and a square battery. Background Art

[0002] The basic structure of square power and energy storage batteries is generally composed of a roll core or stacked core (collectively referred to as a battery cell), a transfer plate, a top cover and a shell. The roll core or stacked core is mainly composed of positive and negative electrodes and tabs. The positive and negative electrodes are the core components that directly undergo electrochemical reactions and determine the capacity and performance of the battery, while the tabs act as current collectors that guide current from the inside to the outside.

[0003] Existing wound cells have the advantages of relatively simple production control and high production efficiency, but their disadvantages are also quite obvious. For example, the cell structure has arc-shaped corners in the width direction, which makes the reaction in the dead corners incomplete, the space utilization rate is low, and the energy density is low. In addition, under long-term circulation and storage, the pole pieces expand, the cells are prone to deformation and arching, and the dead corners are prone to powder loss under cyclic stress, which poses certain safety risks. In addition, wound cells also generally have the problems of high internal resistance and low discharge rate (current), which affects battery performance.

[0004] For laminated cells, the advantages are high space utilization, high energy density, about 5% capacity increase, high discharge rate, excellent cycle performance, and the cell resistance is 10% lower than that of wound cells of the same size. However, the production efficiency of laminated cells is very low, only 20% to 25% of that of wound cells, and the investment in production equipment is large, which limits the promotion of laminated cells, and the production process is relatively complicated, adding cutting and lamination processes. Among them, the cutting process includes cutting of four edges, which greatly increases the probability and risk of burrs, powder removal and other defects; the lamination process adopts the form of single-piece back-and-forth stacking, which requires the alignment and alignment of the four edges, and requires high production control accuracy, which limits the application of laminated batteries in power or energy storage batteries. Furthermore, the space on the side of the laminated battery structure has not been utilized. Although the energy density has been improved relative to the wound cell, there is still a problem of low space utilization, which needs to be improved.

[0005] In addition, for cells with a thickness exceeding a certain value, the traditional winding process and lamination process must be divided into two cells for assembly, which not only reduces the space utilization rate, but also increases the difficulty and precision of production control. Therefore, how to achieve the maximum energy density of the cell in a fixed size space without changing the electrochemical system, so that the space utilization rate can be greatly improved, is one of the main research directions. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a square battery cell assembly and a preparation method thereof and a square battery, which improves the stability of the battery structure, is not easy to deform, and has a high volume energy density, thereby greatly improving the battery cycle performance.

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

[0008] In a first aspect, the present invention provides a method for preparing a square battery cell assembly, the method comprising:

[0009] (I) providing a positive electrode sheet, a negative electrode sheet, a separator and a rectangular gasket, wherein the positive electrode sheet and the negative electrode sheet independently include a blank area and an active material area, laser die-cutting the blank area of ​​the positive electrode sheet to obtain a plurality of first electrode lugs arranged at intervals, and laser die-cutting the blank area of ​​the negative electrode sheet to obtain a plurality of second electrode lugs arranged at intervals;

[0010] (II) performing slit cleaning on the active material area of ​​the positive electrode sheet to remove the positive electrode active material to form a plurality of pairs of first interstices, and performing slit cleaning on the active material area of ​​the negative electrode sheet to remove the negative electrode active material to form a plurality of pairs of second interstices;

[0011] (III) Winding the positive electrode sheet, the separator and the negative electrode sheet along the outer periphery of the rectangular gasket so that the paired first gap portions and the paired second gap portions are respectively located at the corners of the positive electrode sheet and the negative electrode sheet to obtain a winding core body with a square structure, and performing hot pressing shaping, and a plurality of first pole ear portions are concentrated on one side of the rectangular gasket to form a positive electrode pole ear cluster, and a plurality of second pole ear portions are concentrated on the other side of the rectangular gasket to form a negative electrode pole ear cluster;

[0012] (IV) The positive electrode tab cluster and the negative electrode tab cluster are welded to form a positive electrode tab and a negative electrode tab, respectively, to obtain a square battery cell assembly.

[0013] The present invention utilizes a rectangular gasket as a support during the winding process to stabilize the winding core body having a rectangular structure, thereby avoiding deformation or wrinkling of the battery core. At the same time, the voids from which the active material is removed correspond to the four corners of the rectangular parallelepiped to release the stress of the pole piece expansion, thereby greatly improving the battery energy density.

[0014] It should be noted that the active material area in the present invention refers to the area on the pole piece coated with active material; the blank area refers to the area located at the edge of the pole piece and not coated with active material.

[0015] As a preferred technical solution of the present invention, in step (I), during the laser die-cutting process, the first first pole ear portion is cut from the middle portion in the length direction of the positive electrode sheet, and the distance between two adjacent first pole ear portions in the remaining first pole ear portions increases successively along the length direction of the positive electrode sheet.

[0016] At the same time, the first second pole ear portion is cut from the middle portion in the length direction of the negative electrode sheet, and the distance between two adjacent second pole ear portions in the remaining second pole ear portions increases successively along the length direction of the negative electrode sheet.

[0017] The present invention forms the first pole ear portion by cutting the blank area at least half of the length of the positive electrode sheet and the negative electrode sheet, so that the plurality of pole ear portions after winding are just folded on the side of the winding core body in the length direction of its end face. In addition, the cutting positions of the first pole ear portions of the positive electrode sheet and the negative electrode sheet in the present invention are not the same, and the spacing between the two adjacent first pole ear portions and the spacing between the two adjacent second pole ear portions need to be adjusted respectively, so that the first pole ear portion and the second pole ear portion are folded on the opposite sides of the rectangular gasket.

[0018] As a preferred technical solution of the present invention, in step (II), the spacing between two adjacent groups of paired first gaps increases gradually along the length direction of the positive electrode sheet, and the spacing between two adjacent groups of paired second gaps increases gradually along the length direction of the negative electrode sheet.

[0019] During the winding process, the present invention ensures that the paired first gap portions or the paired second gap portions correspond to the two right-angled corners of the rectangular gasket in the width direction of its end face, and for each winding, a group of paired first gap portions and a group of paired second gap portions correspond to the four right-angled corners of the rectangular gasket, so as to provide a release and buffer area for the stress caused by the expansion of the electrode during the charging and discharging process.

[0020] Preferably, the width of the first gap is greater than the width of the second gap, so that the active material area of ​​the negative electrode sheet after winding covers the active material area of ​​the positive electrode sheet.

[0021] Preferably, the width of the first gap portion is 2 to 3 mm, for example, it can be 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm or 3 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the width of the second gap is ≥5 mm.

[0023] Preferably, the strip crack cleaning comprises: firstly laser cleaning the active material in the active material area, and then performing a gap forming process to form a first gap portion or a second gap portion.

[0024] The present invention firstly cleans the active material area by laser to remove the active material in the corresponding area, and then performs gap forming processing to ensure that the shape of the material-free gap is flat and smooth.

[0025] As a preferred technical solution of the present invention, in step (III), the negative electrode sheet, the separator, the positive electrode sheet and the separator are wound in sequence so that the negative electrode sheet is close to the rectangular gasket.

[0026] Preferably, the hot pressing shaping includes: using a hot pressing flat clamp to apply pressure and clamp the two sides of the winding core body.

[0027] Preferably, the pressure of the hot pressing shaping is 1T to 15T, for example, it can be 1T, 2T, 3T, 4T, 5T, 6T, 7T, 8T, 9T, 10T, 11T, 12T, 13T, 14T or 15T, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the temperature of the hot pressing shaping is 70°C to 100°C, for example, it can be 70°C, 75°C, 78°C, 80°C, 85°C, 90°C, 93°C, 95°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the hot pressing shaping time is 40s to 60s, for example, it can be 40s, 42s, 45s, 48s, 50s, 52s, 55s, 56s, 58s or 60s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the diaphragm is a double-sided glue-coated diaphragm.

[0031] The present invention uses a double-sided glue-coated diaphragm so that the diaphragm is completely attached to the positive electrode sheet and the negative electrode sheet on both sides thereof to avoid a gap.

[0032] As a preferred technical solution of the present invention, in step (IV), the welding process includes: performing a primary pre-welding, a secondary pre-welding and a shaping process on the positive electrode tab cluster and the negative electrode tab cluster, respectively, to obtain the positive electrode tab and the negative electrode tab.

[0033] Preferably, the one-time pre-welding comprises: selecting a first welding point for ultrasonic welding to gather the positive electrode tab cluster or the negative electrode tab cluster.

[0034] Preferably, the welding amplitude of the pre-welding is 30-40 μm, for example, it can be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm or 40 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the welding pressure of the primary pre-welding is 0.2-0.4 MPa, for example, it can be 0.2 MPa, 0.23 MPa, 0.25 MPa, 0.28 MPa, 0.3 MPa, 0.32 MPa, 0.35 MPa, 0.36 MPa or 0.4 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the welding energy of the primary pre-welding is 100-600 J, for example, 100 J, 200 J, 300 J, 400 J, 500 J or 600 J, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the delay time of the primary pre-welding is 400-1000 ms, for example, 400 ms, 500 ms, 600 ms, 700 ms, 800 ms, 900 ms or 1000 ms, and other unlisted values ​​within this numerical range are also applicable.

[0038] Preferably, the secondary pre-welding includes: selecting a second welding point for ultrasonic welding so that the gathered positive electrode tab cluster or negative electrode tab cluster is fused and flattened, and the first welding point and the second welding point are arranged along the extension direction of the positive electrode tab cluster or the negative electrode tab cluster.

[0039] Preferably, the welding amplitude of the secondary pre-welding is 20 to 30 μm, for example, it can be 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the welding pressure of the secondary pre-welding is 0.1-0.2 MPa, for example, it can be 0.1 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.18 MPa or 0.2 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the welding energy of the secondary pre-welding is 100-400 J, for example, 100 J, 200 J, 300 J or 400 J, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the delay time of the secondary pre-welding is 500-1000 ms, for example, 500 ms, 600 ms, 700 ms, 800 ms, 900 ms or 1000 ms, and other unlisted values ​​within this numerical range are also applicable.

[0043] Preferably, the shaping process includes: bending the positive electrode ear or the negative electrode ear in a first direction to extend out of the winding core body, and then folding it in a second direction to form a "V" shape, wherein the first direction is opposite to the second direction.

[0044] Preferably, the first direction is the length direction of the winding core body.

[0045] The present invention realizes the convergence of the positive electrode ear cluster and the negative electrode ear cluster by one pre-welding, and then realizes the fusion of the ear parts by secondary pre-welding, thereby ensuring the flatness of the surface and facilitating the subsequent final welding process; through the shaping process, the height space is reduced, which is conducive to further improving the battery energy density.

[0046] It should be noted that the length direction of the core body refers to the length direction of the end surface of the core body.

[0047] In the second aspect, the present invention provides a square battery cell assembly, which is prepared by the preparation method described in the first aspect, and the square battery cell assembly includes a core body, which is formed by stacking a positive electrode sheet, a separator and a negative electrode sheet and then winding them, and a rectangular gasket is arranged at the center of the core body, and the core body is wound in a square shape with the rectangular gasket as the winding center; a positive electrode ear and a negative electrode ear are arranged on the core body, and the positive electrode ear and the negative electrode ear are located on the same side of the core body, and are respectively arranged at both ends of the rectangular gasket along the length direction of the core body.

[0048] A rectangular gasket is left in the core body of the present invention, which has a stable structure and is not easy to deform. The core as a whole is a rectangular structure, which greatly improves the volume energy density of the battery. The positive and negative ears are located on the sides of the core body, which not only reduces the risk of internal short circuit caused by the ears hitting the wall, but also can further improve the energy density.

[0049] It should be noted that the length direction of the core body refers to the length direction of the end surface of the core body.

[0050] As a preferred technical solution of the present invention, the positive electrode sheet is provided with a first right-angle portion around the corner of the rectangular gasket; the negative electrode sheet is provided with a second right-angle portion around the corner of the rectangular gasket; the first right-angle portion covers the second right-angle portion, so that the active material area of ​​the negative electrode sheet covers the active material area of ​​the positive electrode sheet.

[0051] In the present invention, both the first right-angle portion and the second right-angle portion are gaps without active materials, which can buffer or release the stress caused by the expansion of the pole piece during the charging and discharging process of the battery cell, so that the cycle performance of the battery cell is greatly improved.

[0052] As a preferred technical solution of the present invention, the thickness of the rectangular gasket is 2 to 3 mm, for example, it can be 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm or 3 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] As a preferred technical solution of the present invention, the positive electrode ear and the negative electrode ear independently present a "V"-shaped structure.

[0054] In a third aspect, the present invention provides a square battery, comprising a shell, a cover plate and a cell assembly, wherein the cell assembly is the square cell assembly described in the second aspect, the core body is located in the shell, the cover plate is buckled on the shell, and the positive pole ear and the negative pole ear of the core body are electrically connected to the cover plate respectively.

[0055] The square battery of the present invention has high space utilization, high energy density, excellent cycle performance, and is not easy to deform or bulge, thereby ensuring the stability and safety of the battery.

[0056] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The present invention provides a square cell assembly, a preparation method thereof and a square battery, which manufacture standard rectangular cells by laser die-cutting the tabs, stabilizing the core structure with rectangular gaskets, hot pressing and tab welding, thereby maximizing the volume energy density of the battery, achieving excellent cycle performance, reducing safety risks such as internal short circuits, and having high stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in Example 1 of the present invention.

[0060] Figure 2 A schematic diagram of laser die-cutting the blank area provided in Example 1 of the present invention.

[0061] Figure 3A schematic diagram of cleaning the seams of the active material area of ​​the positive electrode sheet provided in Example 1 of the present invention.

[0062] Figure 4 A schematic diagram of cleaning the seams of the active material area of ​​the negative electrode sheet provided in Example 1 of the present invention.

[0063] Figure 5 This is a front view of the winding core body provided in Example 1 of the present invention.

[0064] Figure 6 This is a top view of the winding core body provided in Example 1 of the present invention.

[0065] Figure 7 A schematic diagram of welding the positive electrode tab and the negative electrode tab provided in Example 1 of the present invention.

[0066] Figure 8 Schematic diagram of welding the positive electrode ear and the cover plate provided in Example 1 of the present invention.

[0067] Fig. 9 Schematic diagram of welding the negative electrode ear and the cover plate provided in Example 1 of the present invention.

[0068] Fig.10 This is a top view of the battery cell provided in Comparative Example 1 of the present invention.

[0069] Fig.11 A schematic diagram of laser die-cutting the blank area provided for comparative example 1 of the present invention.

[0070] Fig.12 This is a schematic diagram of the preparation process of the battery provided in Comparative Example 1 of the present invention.

[0071] Among them, 100-shell; 200-cover plate; 300-core body; 400-positive electrode ear; 500-negative electrode ear; 600-rectangular gasket; 1-active material area; 2-blank area; 3-ear part; 10-positive electrode ear cluster; 20-negative electrode ear cluster; a-first welding point; b-second welding point. DETAILED DESCRIPTION

[0072] It should be understood that, in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, 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 therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0073] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0074] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0075] In a specific embodiment, the present invention provides a method for preparing a square battery cell assembly, the preparation method comprising:

[0076] Step (1) provides a positive electrode sheet, a negative electrode sheet, a diaphragm and a rectangular gasket, wherein the positive electrode sheet and the negative electrode sheet independently include a blank area and an active material area, the blank area of ​​the positive electrode sheet is laser die-cut to obtain a plurality of first electrode ear portions spaced apart, and the blank area of ​​the negative electrode sheet is laser die-cut to obtain a plurality of second electrode ear portions spaced apart.

[0077] Different from the die-cutting process of traditional power / energy storage cells, in the laser die-cutting process of the present invention, the first first pole ear portion is cut from the middle portion in the length direction of the positive electrode sheet, and the distance between two adjacent first pole ear portions among the remaining first pole ear portions increases successively along the length direction of the positive electrode sheet; at the same time, the first second pole ear portion is cut from the middle portion in the length direction of the negative electrode sheet, and the distance between two adjacent second pole ear portions among the remaining second pole ear portions increases successively along the length direction of the negative electrode sheet.

[0078] The middle part of the pole piece (the pole piece refers to the positive pole piece and the negative pole piece) in the length direction includes the center position of the pole piece length and the position behind the center. Before laser die-cutting, the width of each pole ear portion (the pole ear portion refers to the first pole ear portion and the second pole ear portion) and the spacing between adjacent pole ear portions can be calculated in advance, so that the several pole ear portions after winding are just collected on the side of the winding core body in its length direction. In addition, the cutting position of the first first pole ear portion in the present invention is not the same as the cutting position of the first second pole ear portion, and the spacing between the two adjacent first pole ear portions and the spacing between the two adjacent second pole ear portions need to be calculated separately, so that the first pole ear portion and the second pole ear portion are respectively collected on the opposite sides of the rectangular gasket.

[0079] The positive and negative electrode sheets in the present invention are prepared by conventional processes such as batching, active material coating, rolling and slitting known to those skilled in the art to obtain active material areas, and uncoated areas are left along the edges of the length direction of the electrode sheets to form blank areas.

[0080] Step (2) performs slit cleaning on the active material area of ​​the positive electrode sheet to remove the positive electrode active material to form a plurality of pairs of first gaps, and performs slit cleaning on the active material area of ​​the negative electrode sheet to remove the negative electrode active material to form a plurality of pairs of second gaps.

[0081] Since the right-angled corners of a cuboid cannot expand and contract in all directions like arc corners, the present invention utilizes the material-free gaps after the active material is removed to provide a release and buffer area for the stress caused by the expansion of the pole pieces during the charge and discharge process of the cuboid winding core body.

[0082] Among them, the spacing between two adjacent groups of paired first gaps increases successively along the length direction of the positive electrode sheet, that is, the distances between different groups of paired first gaps are different. The spacing between two adjacent groups of paired second gaps increases successively along the length direction of the negative electrode sheet, that is, the distances between different groups of paired second gaps are different. Before the material seam is cleaned, the width of the first gap and the second gap, as well as the spacing between adjacent pairs of first gaps and the spacing between two adjacent pairs of second gaps need to be calculated respectively to ensure that the paired first gaps or the paired second gaps correspond to the two right-angled corners of the rectangular gasket in the width direction of its end face, and for each winding, a group of paired first gaps and a group of paired second gaps correspond to the four right-angled corners of the rectangular gasket.

[0083] Specifically, the width of the first gap is greater than the width of the second gap, so that the active material area of ​​the negative electrode sheet after winding covers the active material area of ​​the positive electrode sheet. Preferably, the width of the first gap is 2-3 mm, and the width of the second gap is ≥5 mm.

[0084] In some embodiments, the strip crack cleaning includes: first laser cleaning the active material in the active material area, and then performing a gap forming process to form a first gap portion or a second gap portion.

[0085] The present invention does not specifically limit the method of gap forming processing, and can adopt any one or a combination of at least two of the commonly used vacuum suction forming, air knife blowing forming, infiltration forming using a cleaning agent or corrosive liquid, and scraping forming by a scraper.

[0086] Step (3) winds the positive electrode sheet, the separator and the negative electrode sheet along the outer circumference of the rectangular gasket so that the paired first gap portions and the paired second gap portions are respectively located at the corners of the positive electrode sheet and the negative electrode sheet to obtain a winding core body with a square structure, and performs hot pressing shaping, and a plurality of first pole ear portions are concentrated on one side of the rectangular gasket to form a positive pole ear cluster, and a plurality of second pole ear portions are concentrated on the other side of the rectangular gasket to form a negative pole ear cluster.

[0087] Since the core body is easily deformed and wrinkled during the subsequent hot pressing shaping process and the battery cell charge and discharge expansion process, which in turn affects the performance of the battery, the present invention adds a rectangular spacer with a cuboid structure that can be completely assembled with the inner circle of the core body during winding to support and stabilize the core body. Moreover, after winding is completed, the rectangular spacer remains inside the core body to ensure stability during electrical charge and discharge expansion.

[0088] The material of the rectangular gasket includes but is not limited to stainless steel, ceramic, titanium alloy and the like.

[0089] Specifically, the negative electrode sheet, the separator, the positive electrode sheet and the separator are wound in sequence, so that the negative electrode sheet is close to the rectangular gasket.

[0090] Preferably, the diaphragm is a double-sided glue-coated diaphragm.

[0091] In some embodiments, the hot pressing shaping includes: using a hot pressing flat clamp to press and clamp the two sides of the winding core body. That is, the present invention adopts a double-sided hot pressing method to make the gap between the positive electrode sheet, the negative electrode sheet and the rectangular gasket completely fit, and shape it into a standard rectangular battery cell.

[0092] Specifically, the pressure of the hot pressing shaping is 1T to 15T, the temperature is 70° C. to 100° C., and the time is 40s to 60s.

[0093] Step (4) respectively performs a primary pre-welding, a secondary pre-welding and a shaping process on the positive electrode tab cluster and the negative electrode tab cluster to form a positive electrode tab and a negative electrode tab, thereby obtaining a square battery cell assembly.

[0094] The primary pre-welding includes: selecting a first welding point for ultrasonic welding to gather the positive electrode tab cluster or the negative electrode tab cluster. Specifically, the primary pre-welding has a welding amplitude of 30-40 μm, a welding pressure of 0.2-0.4 MPa, a welding energy of 100-600 J, and a delay time of 400-1000 ms.

[0095] For example, the one-time pre-welding in the present invention can be performed by a cantilever ultrasonic welding device or a direct pressure ultrasonic welding device known to those skilled in the art. When a cantilever ultrasonic welding device is used, a diamond welding head can be used for welding; when a direct pressure ultrasonic welding device is used, a micro-grid or non-grid welding head can be used for welding. Those skilled in the art can use other types of ultrasonic welding devices according to actual conditions, and the present invention does not specifically limit this.

[0096] The secondary pre-welding includes: selecting a second welding point for ultrasonic welding, so that the gathered positive electrode tab cluster or negative electrode tab cluster is fused and flat, and the first welding point and the second welding point are arranged along the extension direction of the positive electrode tab cluster or the negative electrode tab cluster. Specifically, the welding amplitude of the secondary pre-welding is 20-30 μm, the welding pressure is 0.1-0.2 Mpa, the welding energy is 100-400 J, and the delay time is 500-1000 ms.

[0097] Exemplarily, the secondary pre-welding in the present invention adopts a direct pressure ultrasonic welding device and uses a micro-textured or non-textured welding head for welding.

[0098] The shaping process includes: bending the positive electrode ear or the negative electrode ear in a first direction to extend out of the winding core body, and then folding it in a second direction to form a "V" shape, wherein the first direction is opposite to the second direction. Specifically, the first direction is the length direction of the end surface of the winding core body.

[0099] Since the tab cluster has a large span in the thickness direction of conventional battery cells, there is little space for bending the tabs, and welding the folded tabs can easily cause the risk of the tabs hitting the wall. However, there is plenty of space in the width direction of the battery cell, and the tab cluster has a small span and is easy to bend. The present invention uses a double V-shaped tab welding process to greatly reduce the risk of the tabs hitting the wall and avoid internal short circuit problems. In addition, the present invention can weld the tabs directly to the poles of the battery cover by means of side tabs, without the need for connecting plate welding, saving at least 3 to 5 mm of space in height, further improving the energy density.

[0100] In order to help those skilled in the art better understand the overall technical solution and working process of the present invention, the present invention exemplarily provides the following final welding processing method for square battery cell components and battery cover plates, which specifically includes the following steps:

[0101] S1: bending the positive electrode ear or the negative electrode ear in a first direction and extending it out of the winding core body, and laser welding it to the positive electrode column on the cover plate;

[0102] S2: Flip the cover plate to the top of the winding core body, and press the cover plate downward along the height direction of the shell until the cover plate and the shell form an angle of 30° to 70°, so that the positive electrode ear or the negative electrode ear is folded in a second direction to form a "V" shape;

[0103] S3: Then, the negative electrode ear or the positive electrode ear is bent along the first direction, and then folded in the second direction to form a "V" shape, and laser welded to the negative electrode column of the cover plate.

[0104] The positions of the second welding points of the secondary pre-welding of the positive and negative tabs are respectively subjected to final welding with the positive and negative poles of the cover plate, and the weld size of the final welding is smaller than the weld size of the secondary pre-welding. It should be noted that the weld size in the present invention refers to the outer contour size of the weld, and according to the different structures of the weld, the weld size can be the width and length of the weld, or the outer diameter of the weld.

[0105] In the present invention, the folding angles of the positive electrode ear and the negative electrode ear may be the same or different. Those skilled in the art may adjust the folding angles according to the final welding processing sequence of the positive electrode ear and the negative electrode ear.

[0106] Specifically, when the final welding of the positive ear is performed first and then the final welding of the negative ear is performed, the folding angle of the negative ear is greater than that of the positive ear, that is, the negative ear is a large-angle V-shape and the positive ear is a small-angle V-shape. Since the folding angle of the negative ear is large, there is a certain gap distance so that the laser welding machine welding head can be inserted, the pressing block and the laser are kept perpendicular to the positive pole column, and laser welding is performed.

[0107] On the contrary, when the final welding of the negative ear is performed first and then the final welding of the positive ear, the folding angle of the positive ear is greater than that of the negative ear, that is, the positive ear is a large-angle V-shape and the negative ear is a small-angle V-shape. Due to the large folding angle of the positive ear, there is a certain gap distance to allow the laser welding machine welding head to be inserted, keep the pressing block and the laser perpendicular to the negative pole, and perform laser welding.

[0108] In another specific embodiment, the present invention provides a square battery cell assembly, which is prepared by the preparation method described in a specific embodiment, and the square battery cell assembly includes a core body, which is formed by stacking and winding a positive electrode sheet, a separator and a negative electrode sheet, and a rectangular gasket is arranged at the center of the core body, and the core body is wound in a square shape with the rectangular gasket as the winding center; a positive electrode ear and a negative electrode ear are arranged on the core body, and the positive electrode ear and the negative electrode ear are located on the same side of the core body, and are respectively arranged at both ends of the rectangular gasket along the length direction of the end face of the core body.

[0109] In some embodiments, the positive electrode sheet is provided with a first right angle portion around the corner of the rectangular gasket, and the negative electrode sheet is provided with a second right angle portion around the corner of the rectangular gasket, and the first right angle portion covers the second right angle portion, so that the active material area of ​​the negative electrode sheet covers the active material area of ​​the positive electrode sheet. That is, during the preparation process, the paired first gap portions without material are bent along the rectangular gasket to form two first right angle portions at two corners, and at the same time, the paired second gap portions without material are bent along the rectangular gasket to form two second right angle portions at two corners.

[0110] Specifically, the thickness of the rectangular gasket is 2 to 3 mm.

[0111] Specifically, the positive electrode ear and the negative electrode ear independently present a "V"-shaped structure.

[0112] In another specific embodiment, the present invention provides a square battery, which includes a shell, a cover plate and a battery cell assembly. The battery cell assembly is a square battery cell assembly described in a specific embodiment, the core body is located in the shell, the cover plate is buckled on the shell, and the positive and negative ears of the core body are electrically connected to the cover plate respectively.

[0113] The square battery of the present invention adopts a square battery cell assembly with a standard rectangular structure, and the square battery cell assembly is assembled into a shell, and the shell filling ratio is close to 100%. The cover plate and the positive electrode ear and the negative electrode ear are finally welded, and then it is made through conventional processes such as baking, liquid injection, and chemical formation that are familiar to those skilled in the art. Compared with the existing stacked core structure or rolled core structure, the maximum energy density can be obtained under the same volume.

[0114] Example 1

[0115] The present embodiment provides a square battery and a method for preparing the same. The square battery includes a shell 100, a cover plate 200 and a square battery cell assembly. The square battery cell assembly includes a core body 300, the core body 300 is located in the shell 100, the cover plate 200 is buckled on the shell 100, and the cover plate 200 is provided with a positive pole and a negative pole. The core body 300 is formed by stacking the positive electrode sheet, the glue-coated diaphragm and the negative electrode sheet in sequence and then winding them. A 2mm thick rectangular gasket made of stainless steel is provided in the center of the core body 300, and the core body 300 is wound in a square shape with the rectangular gasket as the winding center. A positive electrode ear 400 and a negative electrode ear 500 are provided on the core body 300. The positive electrode ear 400 and the negative electrode ear 500 are located on the same side of the core body 300 and are respectively arranged at both ends of the rectangular gasket along the length direction of the end face of the core body 300. The positive electrode ear 400 and the negative electrode ear 500 are respectively electrically connected to the positive electrode column and the negative electrode column on the cover plate 200.

[0116] The preparation method of this embodiment specifically comprises the following steps:

[0117] (1) Provide positive electrode sheet, negative electrode sheet, glue-coated diaphragm and rectangular gasket, such as Figure 1 As shown, the positive electrode sheet and the negative electrode sheet independently include a blank area 2 and an active material area 1;

[0118] (2) Laser die cutting is performed on the blank area 2 of the positive electrode sheet to obtain a plurality of first electrode ears 3 arranged at intervals, such as Figure 2 As shown, the first first pole ear portion 3 is cut from the middle of the positive electrode sheet in the length direction, and the distance between two adjacent first pole ear portions 3 in the remaining first pole ear portions 3 increases in sequence along the length direction of the positive electrode sheet. The distance between each first pole ear portion 3 is calculated in advance to ensure that the first pole ear portion 3 after winding is located on one side of the winding core body 300;

[0119] (3) Laser die-cutting is performed on the blank area 2 of the negative electrode sheet to obtain a plurality of second electrode lugs 3 arranged at intervals. The first second electrode lug 3 is cut from the middle of the length direction of the negative electrode sheet. The intervals between two adjacent second electrode lugs 3 in the remaining second electrode lugs 3 are increased in sequence along the length direction of the negative electrode sheet. The interval between each second electrode lug 3 is calculated in advance to ensure that the first electrode lug 3 after winding is located on the other side of the winding core body 300.

[0120] (4) Figure 3 As shown, the active material area 1 of the positive electrode sheet is laser cleaned to remove the positive electrode active material to form a plurality of pairs of first gaps with a width greater than 5 mm, which are sequentially denoted as J1, J2, ..., J n (where n is an integer greater than 2, J1, J2...J n The number of each is two), and J1, J2, ... J nThe spacing increases in sequence along the length direction of the positive electrode sheet, and then the fallen positive electrode active material powder is cleaned out by using air knife blowing and negative pressure;

[0121] (5) Figure 4 As shown, the active material area 1 of the negative electrode sheet is laser cleaned to remove the negative electrode active material to form a plurality of pairs of second gaps with a width of 2 to 3 mm, which are sequentially denoted as G1, G2, ..., G n (where n is an integer greater than 2, G1, G2...G n The number of each is two), and G1, G2, ... G n The spacing increases in sequence along the length direction of the negative electrode sheet, and then the powder of the negative electrode active material that has fallen off is cleaned out by using air knife blowing and negative pressure;

[0122] (6) Figure 5 and Figure 6 As shown, the positive electrode sheet, the glue-coated separator and the negative electrode sheet are respectively placed on the winding machine, and are wound in sequence along the outer circumference of the rectangular gasket in the order of the negative electrode sheet, the glue-coated separator, the positive electrode sheet and the glue-coated separator, so that after winding, the paired first gap portions and the second gap portions correspond to the four right-angled corners of the rectangular gasket, and the plurality of first pole ear portions 3 are concentrated on the left side of the rectangular gasket to form a positive pole ear cluster 10, and the plurality of second pole ear portions 3 are concentrated on the right side of the rectangular gasket to form a negative pole ear cluster 20, thereby obtaining a winding core body 300 with a square structure;

[0123] (7) Using a hot pressing flat fixture to press and clamp the two sides of the winding core body 300 to achieve hot pressing shaping, so that the gaps between the positive electrode sheet, the negative electrode sheet and the rectangular gasket are completely fitted, wherein the hot pressing shaping pressure is 10T, the temperature is 90°C, and the time is 50s;

[0124] (8) Figure 7 As shown, the first welding point a is selected for ultrasonic welding to gather the positive pole ear cluster 10, and then the second welding point b is selected for ultrasonic welding, so that the gathered positive pole ear cluster 10 is flat, and the first welding point a and the second welding point b are arranged along the extension direction of the positive pole ear cluster 10, and the above steps are repeated to achieve the gathering and flattening of the negative pole ear cluster 20, and the positive pole ear 400 and the negative pole ear 500 are obtained, and are loaded into the shell 100, wherein the welding amplitude of the first welding point a during ultrasonic welding is 30μm, the welding pressure is 0.3Mpa, the welding energy is 300J, and the delay time is 600ms, and the welding amplitude of the second welding point b during ultrasonic welding is 20μm, the welding pressure is 0.1Mpa, the welding energy is 300J, and the delay time is 800ms;

[0125] (9) Figure 8As shown, the positive electrode ear 400 is bent in the first direction and extends out of the shell 100, and the second welding point b is laser welded to the positive electrode column on the cover plate 200, and then the cover plate 200 is turned over to the top of the winding core body 300, so that the positive electrode ear 400 is folded in the second direction to form a "V" shape, and the cover plate 200 is pressed downward along the height direction of the shell 100 until the cover plate 200 and the shell 100 are 60°; then, as shown in Fig. 9 As shown, the negative electrode ear 500 is bent along the first direction, and then folded in the second direction to form a "V" shape, and the welding head of the laser welding machine is inserted, and the pressing block and the laser are kept perpendicular to the positive electrode column to laser weld the second welding point b of the negative electrode ear 500 to the negative electrode column of the cover plate 200, and the final welding process is completed to obtain a square battery, wherein the weld mark size of the final welding process is smaller than the weld mark size of the second welding point b.

[0126] Comparative Example 1

[0127] This comparative example provides a spiral wound battery and a preparation method thereof, which is different from Example 1 in that: the battery adopts Fig.10 The 71173207-280Ah battery cell shown has two winding cores, and no rectangular gasket is set in the center of the winding core. The positive and negative ears of the winding core are electrically connected to the cover plate through two connecting pieces respectively.

[0128] The preparation method of this comparative example is as follows Fig.11 and Fig.12 As shown, the difference from Example 1 is that: (1) during the cutting process of the electrode ear, the blank area is laser die-cut by the heads of the positive electrode sheet and the negative electrode sheet; (2) the negative electrode sheet, the diaphragm and the positive electrode sheet stacked in sequence are directly wound without adding a rectangular gasket; (3) during the final welding process, one end of one of the adapter sheets is welded to the positive electrode ear, and the other end is welded to the positive electrode column of the cover plate, and one end of the other adapter sheet is welded to the negative electrode ear, and the other end is welded to the negative electrode column of the cover plate; then the core roll welded with the cover plate is pressed into the shell, and then the cover plate and the shell are buckled and sealed to obtain a core roll battery.

[0129] The present invention calculates the filling volumes of the batteries provided by Example 1 and Comparative Example 1 respectively for comparison.

[0130] The corners of the winding core of Comparative Example 1 are approximately regarded as circles, and the cross-sectional area of ​​the two wound cells is: S 卷 =2×(π×R 2 +w×2R). The cross-sectional area S of the standard rectangular core body of Example 1 is 长 = length × width = (w + 2R) × 4R, h = 4R. Then the difference between the two is S Δ =S 长 -S 卷 =(8-2×π)×R 2The greater the thickness h, the greater the difference between the two. Compared with the 71173207-280Ah battery cell provided in Comparative Example 1, the difference S Δ =(8-2×π)×16×16 / 2 / (π×16×16+170)=24.7%. It can be seen that the volume energy density of the core body of Example 1 is 24.7% higher.

[0131] In addition, compared with Comparative Example 1, the span of the pole ear cluster of the winding core body provided in Example 1 is small, and the positive pole ear and the negative pole ear are in a double V structure, eliminating the risk of the pole ear hitting the wall; at the same time, the positive pole ear and the negative pole ear of Example 1 are directly welded to the pole column of the cover plate, eliminating the welding of the connecting plate, and saving at least 3mm to 5mm of space in height, which greatly improves the battery energy density.

[0132] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a square battery cell assembly, characterized in that: The preparation method comprises: (I) providing a positive electrode sheet, a negative electrode sheet, a separator and a rectangular gasket, wherein the positive electrode sheet and the negative electrode sheet independently include a blank area and an active material area, laser die-cutting the blank area of ​​the positive electrode sheet to obtain a plurality of first electrode lugs arranged at intervals, and laser die-cutting the blank area of ​​the negative electrode sheet to obtain a plurality of second electrode lugs arranged at intervals; (II) performing slit cleaning on the active material area of ​​the positive electrode sheet to remove the positive electrode active material to form a plurality of pairs of first interstices, and performing slit cleaning on the active material area of ​​the negative electrode sheet to remove the negative electrode active material to form a plurality of pairs of second interstices; (III) Winding the positive electrode sheet, the separator and the negative electrode sheet along the outer periphery of the rectangular gasket so that the paired first gap portions and the paired second gap portions are respectively located at the corners of the positive electrode sheet and the negative electrode sheet to obtain a winding core body with a square structure, and performing hot pressing shaping, and a plurality of first pole ear portions are concentrated on one side of the rectangular gasket to form a positive electrode pole ear cluster, and a plurality of second pole ear portions are concentrated on the other side of the rectangular gasket to form a negative electrode pole ear cluster; (IV) The positive electrode tab cluster and the negative electrode tab cluster are welded to form a positive electrode tab and a negative electrode tab, respectively, to obtain a square battery cell assembly.

2. The preparation method according to claim 1, characterized in that: In step (I), during the laser die-cutting process, the first first pole ear portion is cut from the middle portion of the positive electrode sheet in the length direction, and the distance between two adjacent first pole ear portions of the remaining first pole ear portions increases in sequence along the length direction of the positive electrode sheet; At the same time, the first second pole ear portion is cut from the middle portion in the length direction of the negative electrode sheet, and the distance between two adjacent second pole ear portions in the remaining second pole ear portions increases successively along the length direction of the negative electrode sheet.

3. The preparation method according to claim 1, characterized in that: In step (II), the spacing between two adjacent groups of paired first gaps increases in sequence along the length direction of the positive electrode sheet, and the spacing between two adjacent groups of paired second gaps increases in sequence along the length direction of the negative electrode sheet; Preferably, the width of the first gap is greater than the width of the second gap, so that the active material area of ​​the negative electrode sheet after winding covers the active material area of ​​the positive electrode sheet; Preferably, the width of the first gap is 2 to 3 mm; Preferably, the width of the second gap is ≥5 mm; Preferably, the strip crack cleaning comprises: firstly laser cleaning the active material in the active material area, and then performing a gap forming process to form a first gap portion or a second gap portion.

4. The preparation method according to claim 1, characterized in that: In step (III), the negative electrode sheet, the separator, the positive electrode sheet and the separator are wound in sequence so that the negative electrode sheet is close to the rectangular gasket; Preferably, the hot pressing shaping comprises: using a hot pressing flat clamp to apply pressure and clamp from both sides of the winding core body; Preferably, the pressure of the hot pressing shaping is 1T to 15T; Preferably, the temperature of the hot pressing shaping is 70°C to 100°C; Preferably, the hot pressing shaping time is 40s to 60s; Preferably, the diaphragm is a double-sided glue-coated diaphragm.

5. The preparation method according to claim 1, characterized in that: In step (IV), the welding process includes: performing a primary pre-welding, a secondary pre-welding and a shaping process on the positive electrode tab cluster and the negative electrode tab cluster in sequence to obtain a positive electrode tab and a negative electrode tab; Preferably, the one-time pre-welding comprises: selecting a first welding point for ultrasonic welding to gather the positive electrode tab cluster or the negative electrode tab cluster; Preferably, the welding amplitude of the primary pre-welding is 30-40 μm; Preferably, the welding pressure of the primary pre-welding is 0.2-0.4 MPa; Preferably, the welding energy of the primary pre-welding is 100-600 J; Preferably, the delay time of the pre-welding is 400-1000ms; Preferably, the secondary pre-welding comprises: selecting a second welding point for ultrasonic welding, so that the gathered positive electrode tab cluster or negative electrode tab cluster is fused and flat, and the first welding point and the second welding point are arranged along the extension direction of the positive electrode tab cluster or the negative electrode tab cluster; Preferably, the welding amplitude of the secondary pre-welding is 20-30 μm; Preferably, the welding pressure of the secondary pre-welding is 0.1-0.2 MPa; Preferably, the welding energy of the secondary pre-welding is 100-400 J; Preferably, the delay time of the secondary pre-welding is 500-1000ms; Preferably, the shaping process includes: bending the positive electrode ear or the negative electrode ear in a first direction to extend out of the winding core body, and then folding it in a second direction to form a "V" shape, wherein the first direction is opposite to the second direction; Preferably, the first direction is the length direction of the winding core body.

6. A square battery cell assembly, characterized in that: The square battery cell assembly is prepared by the preparation method according to any one of claims 1 to 5, and the square battery cell assembly comprises a winding core body, which is formed by winding a positive electrode sheet, a separator and a negative electrode sheet after being stacked, and a rectangular gasket is arranged at the center of the winding core body, and the winding core body is wound in a square shape with the rectangular gasket as the winding center; The core body is provided with a positive electrode ear and a negative electrode ear. The positive electrode ear and the negative electrode ear are located on the same side of the core body and are respectively arranged at two ends of the rectangular gasket along the length direction of the core body.

7. The square battery cell assembly according to claim 6, characterized in that: The positive electrode sheet is provided with a first right angle portion around the corner of the rectangular gasket; The negative electrode sheet is provided with a second right-angle portion around the corner of the rectangular gasket; The first right-angle portion covers the second right-angle portion, so that the active material area of ​​the negative electrode sheet covers the active material area of ​​the positive electrode sheet.

8. The square battery cell assembly according to claim 6, characterized in that: The thickness of the rectangular gasket is 2-3 mm.

9. The square battery cell assembly according to claim 6, characterized in that: The positive electrode ear and the negative electrode ear independently present a "V"-shaped structure.

10. A square battery, characterized in that: The square battery includes a shell, a cover plate and a cell assembly. The cell assembly is the square cell assembly according to any one of claims 6 to 9. The core body is located in the shell, the cover plate is buckled on the shell, and the positive and negative ears of the core body are electrically connected to the cover plate respectively.

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