A method and apparatus for coating an electrode

Abstract

The application provides a cell coating method and a coating device, and particularly relates to the technical field of battery manufacturing. MD The elastic modulus E TD of the insulation film along the width direction is 105 MPa-125 MPa; the unwinding section of the insulation film is positioned under tension, and the cutting section is pulled; at least part of the insulation film is pressed and attached to the outer surface of the shell at a first position between the unwinding section and the cutting section and corresponding to the outer surface of the shell, and the at least part of the insulation film corresponding to the first position is defined as a starting part of the attachment; the tension between the starting part of the attachment and the unwinding section is continuously controlled, the cell is moved, and the insulation film is continuously pressed and attached to the outer surface of the shell under the tension, wherein the continuously controlled tension is 30 N-50 N. The application can improve the residual stress in the coating process to cause bubbles, wrinkles and other defects.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a method and equipment for coating a battery cell. Background Technology

[0002] With the rapid development of the new energy vehicle and energy storage industries, the safety performance and lifespan of power batteries have received widespread attention. As the core power source of new energy equipment, the safety performance of battery modules directly determines the reliability of equipment operation. Battery modules are typically assembled from several individual battery cells connected in series and parallel. Among them, the insulation protection of the cell casing is a crucial aspect of ensuring the safety of battery modules and preventing safety accidents such as short circuits.

[0003] Currently, the mainstream insulating coating for battery cell casings uses a blue PET (polyethylene terephthalate) based adhesive film (referred to as "blue film"), which is applied to the outer surface of the cell casing to achieve insulation isolation between the casing and the module structural components and to manage localized heat. However, during the coating process, the blue film undergoes tensile deformation, resulting in tensile strain and potential localized stress concentration in the blue film. These factors lead to defects such as bubbles and wrinkles after blue film coating, which not only affect the appearance quality and insulation performance of the battery cell but may also pose safety hazards and increase production costs. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a coating method for a battery cell and a battery cell to improve the technical problem of defects such as bubbles and wrinkles caused by residual stress during the coating process.

[0005] To achieve the above and other related objectives, the present invention provides a coating method for a battery cell, comprising the following steps: A battery cell is provided, the battery cell including a housing; An insulating film is provided, wherein the elastic modulus E along the unwinding length direction is... MD The elastic modulus E along the width direction is 90MPa~105MPa. TD The pressure is 105MPa~125MPa; the unwinding section of the insulating film is tensioned and positioned, and the cut section of the insulating film is pulled. At a first position between the unwinding section and the cutting section, and corresponding to the outer surface of the housing, at least a portion of the insulating film is pressed and adhered to the outer surface of the housing, and the at least portion of the insulating film corresponding to the first position on the outer surface of the housing is defined as the adhesive starting portion of the insulating film; The tension between the initial bonding portion of the insulating film and the unwinding section is continuously controlled. The battery cell is moved and the insulating film is continuously pressed and bonded to the outer surface of the housing under the tension. The tension is continuously controlled to be 30N~50N.

[0006] In an embodiment of the present invention, the specified non-proportional extension strength R of the insulating film p0.2 is 10 MPa to 16 MPa, and said R p0.2 represents the critical tensile stress at which the insulating film undergoes 0.2% non-proportional plastic elongation.

[0007] In an embodiment of the present invention, the elastic modulus E of the insulating film in the unwinding length direction MD and the elastic modulus E in the width direction TD satisfy: |E MD –E TD | / max(E MD ,E TD )≤5%.

[0008] In an embodiment of the present invention, when the electric core is moved, the pressing operation is continuously performed on the insulating film, and the pressing operation continuously moves from a first position on the outer surface of the casing to a second position on the outer surface of the casing, so that at least part of the pressed insulating film is attached to the outer surface of the casing, wherein the casing comprises a plurality of side walls arranged at an angle and connected end to end along the film wrapping direction; the insulating film is wrapped on the side walls along the film wrapping direction, the side walls have a film wrapping width W along the film wrapping direction, and the film wrapping width W is ≤ 120 mm; or the film wrapping width W is ≤ 92 mm.

[0009] In an embodiment of the present invention, the side walls include a first side wall and a second side wall, the first side wall and the second side wall are integrally connected at an angle, the film wrapping width of the first side wall is smaller than the film wrapping width of the second side wall, the film wrapping width of the first side wall is ≥ 21 mm, or the film wrapping width of the first side wall is ≥ 26 mm.

[0010] In an embodiment of the present invention, the insulating film satisfies the following relational expression: F= , where E is the elastic modulus of the insulating film in MPa, and the value of E is the smaller one of said elastic modulus E MD and said elastic modulus E TD ; t is the thickness of the insulating film in mm; w represents the film wrapping width in mm; F is the wrapping adaptation coefficient of the insulating film, and F ∈ [6.3×10 -5 , 1.25×10 -4 .

[0011] In an embodiment of the present invention, the film wrapping speed v of the electric core and the stress relaxation time τ of the insulating film satisfy the relational expression: v·τ < L / 3, where L represents the total length of the pressing operation acting on the outer surface of the casing along the film wrapping direction, and L ≥ b, where b is the width of the insulating film.

[0012] The present invention also provides a coating apparatus for the above-described coating method, the coating apparatus comprising: a feeding unit, a cell conveying unit, a tension control unit, and a pressing and applying unit, wherein the feeding unit is used to output the insulating film, the cell conveying unit is configured to convey the cell, the tension control unit is configured to apply tension force to the tension section of the insulating film, and the pressing and applying unit is used to press and apply the insulating film to the outer surface of the housing.

[0013] In one embodiment of the present invention, the tension control unit includes a tension roller, which tensions the tensioning section of the insulating film and adjusts the tension force by adjusting its torque. The torque of the tension roller is controlled within the range of 10 N / m to 14 N / m.

[0014] In one embodiment of the present invention, the tension control unit controls the tension of the insulating film through any of the following torque control modes: The first mode: The tension control unit detects the change in the roll diameter of the insulating film after unwinding in real time, so as to dynamically adjust the torque of the tension roller to keep the torque of the tension roller in the range of 10 N / m to 14 N / m, and at the same time keep the tension force constant and maintain the first tension force. The second mode: The tension control unit fixes the torque of the tension roller to a constant value within the range of 10 N / m to 14 N / m; The third mode: The tension control unit detects the change in the roll diameter of the insulating film after unwinding in real time, so as to dynamically adjust the torque of the tension roller to keep the torque of the tension roller in the range of 10 N / m to 14 N / m, and at the same time keep the tension force constant and maintain the first tension force; the housing includes a planar first sidewall, a planar second sidewall, and a rounded transition section integrally connected between the first sidewall and the second sidewall. When the pressed position of the insulating film corresponds to the rounded transition section, the tension roller automatically adjusts the torque to keep the tension force constant and maintain the second tension force, which is less than the first tension force.

[0015] The beneficial effects of this invention are as follows: The present invention proposes a coating method and coating equipment for battery cells. By controlling the tension of the insulating film during the coating process and selecting an insulating film with an appropriate elastic modulus, the material mechanical properties and process parameters are effectively matched. The insulating film has good bidirectional mechanical property synergy. When stretched under tension, it has both flexibility and supporting rigidity, which can smoothly cover the outer surface of the battery cell and avoid stress concentration in local positions caused by high modulus, thereby reducing the problems of bubbles and cracks. At the same time, the sufficient supporting rigidity makes it less likely to have lateral wrinkles and dimensional deviations during the rolling process. It fundamentally improves the defects of bubbles and wrinkles caused by stretching deformation and stress concentration in the annular coating process, and effectively improves the flatness of the insulating film and the coating yield. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] In the attached diagram: Figure 1 This is a flowchart of a cell coating method provided in one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a battery cell provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of the cell coating process provided in one embodiment of the present invention.

[0018] The attached figures are labeled as follows: 100. Square-shell battery cell; 110. Bottom wall; 120. Side wall; 121. First side wall; 122. Second side wall; 123. Rounded corner transition section; 130. End cap; 131. Terminal post; 200. Wrapping equipment; 210. Insulating film roll; 211. Insulating film; 220. Reseller paper take-up roller; 230. Edge correction device; 240. Passing roller; 250. Tension roller; 260. Ionizing air device; 270. Film pulling rod; 280. Pressing and laminating unit; 281. First laminating roller; 282. Second laminating roller; 283. First transition roller; 284. Second transition roller; 285. First finishing roller; 286. Second finishing roller; 290. Battery cell conveying unit. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0020] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0021] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0023] The terms or phrases used in this article have the following meanings: In this article, the terms "multiple," "various," and "multiple times" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0024] In this document, terms such as “preferred,” “ideal,” “further,” “even more,” and “particularly” are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0025] Elastic modulus: This is a key characteristic parameter of insulating film, characterizing its rigidity, support, and resistance to elastic deformation. It is an important indicator that determines whether the insulating film is prone to stretching, wrinkling, or other defects during the coating process.

[0026] The specified non-proportional elongation strength R p0.2The critical stress corresponding to 0.2% non-proportional plastic elongation of the sample is the critical stress that characterizes the insulating film to begin irreversible plastic deformation. It directly determines whether the insulating film will undergo irreversible permanent deformation during the stretching and coating process, affecting the dimensional stability and appearance yield of the coating.

[0027] To achieve insulation and surface protection for battery cells, the industry commonly uses PET-based pressure-sensitive adhesive insulating films, which are then wrapped in a ring shape using automated wrapping equipment. In existing processes, the battery cell moves along a specific direction. Simultaneously, the wrapping equipment applies the insulating film to specific positions on the cell and continuously unwinds it under a set tension. During unwinding, a pressing device presses the insulating film, sequentially pressing and bonding it to the outer surface of the battery cell, ultimately forming an insulating protective layer on at least part of the outer surface of the casing. However, defects such as bubbles and wrinkles are prone to occur on the surface of the wrapped battery cell. In the wrapping process, the pressing device can be a film-applying roller with an arc-shaped pressing surface.

[0028] When using the aforementioned automated coating method to coat the battery cells, the insulating film simultaneously bears the tension force provided by the tension control unit, the friction force provided by the guide roller, and the roller pressure provided by the coating roller during the coating process. Especially when the coated battery cell is a prismatic cell, due to the geometric discontinuity of the outer surface of the prismatic cell and the rounded transition sections (R-corners) between the planar parts of the outer surface, the insulating film is prone to complex bending-tensile coupling stress during coating. If the elastic modulus of the insulating film is too high, or the film material is too rigid, the insulating film needs to overcome a great bending resistance when wrapping the R-corners with a small radius of curvature, which easily leads to the insulating film not adhering tightly at the R-corners, difficulty in wrapping the corners, and stress concentration that easily causes cracking. Conversely, if the elastic modulus is too low and the film material is too soft, the insulating film is prone to stretching, wrinkling, and dimensional instability under the action of tension force, and may even produce irreversible plastic tensile deformation, causing the insulating film to become thinner and narrower, and wrinkles or curling at the end due to the slow release of internal stress after coating. In addition, tension control during the wrapping process is also crucial: if the tension is too high, the deformation of the insulating film will increase, and the stress will be even higher after it is applied to the battery cell housing. During the static period after wrapping, wrinkles are likely to occur at the end due to the gradual release of stress, and the plastic deformation of the insulating film will also be aggravated. If the tension is too low, the insulating film will not only be prone to forming air bubbles due to poor adhesion, but the flatness of the insulating film before application cannot be guaranteed.

[0029] Based on this, the present invention provides a coating method and coating equipment for battery cells. The coating method achieves effective matching of material mechanical properties and process parameters by adjusting the coating tension during the coating process and selecting an insulating film with an appropriate elastic modulus. This improves defects such as bubbles, wrinkles, and warping caused by tensile deformation and stress concentration in the annular coating process, effectively improves the flatness of the insulating film, and thus improves the coating yield of the battery cells.

[0030] Please see Figures 1 to 3 The present invention provides a coating method for a battery cell, the coating method comprising the following steps: S1. Provide a battery cell, which includes a housing; S2. Provide an insulating film 211, the elastic modulus E of the insulating film 211 along the unwinding length direction. MD The elastic modulus E along the width direction is 90MPa~105MPa. TD The pressure is 105MPa~125MPa; and the unwinding section of the insulating film 211 is tensioned and positioned, while the cutting section is pulled. S3. At a first position between the unwinding section and the cutting section, and corresponding to the outer surface of the housing, at least a portion of the insulating film 211 is pressed and adhered to the outer surface of the housing, and the at least portion of the insulating film corresponding to the first position on the outer surface of the housing is defined as the adhesive starting portion of the insulating film. S4. Continuously control the tension between the initial bonding portion and the unwinding portion of the insulating film 211, move the battery cell and continuously press and adhere the insulating film 211 to the outer surface of the housing under the tension, wherein the continuously controlled tension is 30N~50N.

[0031] Specifically, the battery cell in step S1 includes a housing and an end cap 130. The housing includes multiple sidewalls arranged at an angle and connected end-to-end along the coating direction, wherein the coating direction is defined as the direction in which the insulating film 211 sequentially wraps around each sidewall. The multiple sidewalls together form a receiving cavity, which is used to accommodate internal components of the battery cell such as electrode assemblies and electrolyte. The end cap 130 is used to seal the receiving cavity, and an electrode post 131 for conducting the internal current of the battery cell is mounted on the end cap 130. The housings of prismatic and cylindrical battery cells are usually formed by stamping or deep drawing processes from metal materials such as aluminum alloy and stainless steel, and the shape of the housing can be flexibly adapted and adjusted according to the type of battery cell. The housing of soft-pack battery cells is different from that of rigid metal housings and usually uses aluminum-plastic composite film (hereinafter referred to as aluminum-plastic film). The coating method provided by this invention is applicable to coating the housings of various types of battery cells.

[0032] To facilitate understanding of the coating method of the present invention, the following description will first take the structure of the square-shell battery cell 100 as an example to illustrate the relevant shell structure features.

[0033] Please see Figure 2In one embodiment, the casing of the square-shell battery cell 100 is an approximately rectangular cylindrical structure with one end open and the other end closed. The casing includes a bottom wall 110 and multiple side walls 120 arranged at an angle around the bottom wall 110 and connected end-to-end along the coating direction. Each side wall 120 includes two opposing first side walls 121 and two opposing second side walls 122, with the area of ​​the second side walls 122 being larger than the area of ​​the first side walls 121. Specifically, the two first side walls 121 (smaller side walls) are arranged opposite each other along the width direction of the bottom wall 110, and the two second side walls 122 (larger side walls) are arranged opposite each other along the length direction of the bottom wall 110. One end of each side wall 120 facing away from the bottom wall 110 forms an opening for inserting internal components of the battery cell, such as electrode assemblies and electrolyte. The internal components of the battery cell are not described in detail here, but can be selected and configured according to conventional techniques in the art. The end cap 130 is sealed to the opening. The end cap 130 can be installed in various ways, such as by laser welding, adhesive bonding, or mechanical connection, to form a sealed connection between the end cap 130 and the opening of the housing. In this embodiment, both the positive and negative terminals of the square-shell cell 100 are connected to the end cap 130.

[0034] In other embodiments, the housing may also be an approximately rectangular cylindrical structure with openings at both ends. In this case, the housing only includes the aforementioned plurality of sidewalls 120, and the openings at both ends of the housing are sealed by end caps 130. In some embodiments, the positive and negative terminals of the prismatic cell 100 are respectively connected to the end caps 130 at both ends. The coating method of this application is applicable to both of the above-described prismatic cell 100 structures.

[0035] In some embodiments, adjacent first sidewalls 121 and second sidewalls 122 are connected by a rounded transition section 123, that is, on any cross section parallel to the end cap 130, the first sidewalls 121 and second sidewalls 122 are connected by rounded corners.

[0036] In step S2, the provided insulating film 211 uses polyethylene terephthalate (PET) film as a substrate, and an adhesive layer is coated on the side facing the battery cell. The elastic modulus E of the insulating film 211 along its unwinding length direction (machine direction, abbreviated as MD) is... MD For example, E is 90MPa~105MPa. MD The pressure can be 90MPa, 95MPa, 100MPa, or 105MPa, preferably 105MPa; the elastic modulus E of the insulating film 211 along its own width direction (transverse direction, abbreviated as TD) is... TD For example, E is 105MPa~125MPa. TDThe pressure can be 105MPa, 110MPa, 115MPa, 120MPa or 105MPa, preferably 105MPa. The insulating film 211 with an elastic modulus in the above range has both moderate longitudinal flexibility when stretched by unwinding tension, which can smoothly wrap the rounded transition section 123 of the battery cell and reduce bubbles or cracks caused by stress concentration at the corners due to excessively high modulus; and sufficient supporting rigidity, which is not easy to cause lateral wrinkles and dimensional deformation when pressed by the film-applying roller.

[0037] The above-mentioned test of the elastic modulus of the insulating film is based on GB / T 1040.3-2018. The test conditions are: sample width 25 mm, test spacing 100 mm, tensile speed 50 mm / min, and calculated thickness 110 μm. The test equipment is a universal testing machine with an indication accuracy of ±0.5% FS, equipped with a pneumatic flat-mouth clamp that is anti-slip and anti-pinch.

[0038] The insulating film 211 includes an unwinding section and a cutting section. Before the wrapping operation, the unwinding section of the insulating film 211 is pre-tensioned and positioned, and the cutting section of the insulating film 211 can be pulled and moved under the action of external force.

[0039] Before covering the battery cell casing, a film-applying positioning step, namely step S3, is performed in advance. The specific operation is as follows: Select the film-applying area between the unwinding section and the cutting section of the insulating film 211, align the insulating film 211 with the first position on the outer surface of the battery cell casing, and press the insulating film 211 so that the insulating film 211 is at least partially attached to the outer surface of the casing; wherein, the section of insulating film 211 that is attached to the first position on the outer surface of the casing is defined as the starting part of the adhesive application of the insulating film 211.

[0040] In one embodiment, any one of the two first sidewalls 121 of the square-shell cell 100 is selected as the first position of the outer surface of the shell, and the area of ​​the insulating film 211 pressed against the surface of the first sidewall 121 in step S3 is the starting part of the bonding of the insulating film 211.

[0041] After completing the pre-positioning film application operation in step S3, proceed to the overmolding step S4; the specific process of step S4 is as follows: The tension of the insulating film 211 is adjusted so that the film segment between the initial bonding part of the insulating film 211 and the unwinding section of the insulating film has tension, and the tension value is controlled to be 30N to 50N; then the battery cell is moved along the preset direction, and under the continuous action of the above tension, the insulating film 211 is continuously pressed and adhered to the outer surface of the shell, and finally the complete covering of each side wall of the shell is completed, effectively avoiding defects such as loosening, wrinkling, and displacement of the insulating film during the covering process.

[0042] In some embodiments, the elastic modulus E of the insulating film 211 described above is... MDand elastic modulus E TD The tension force can be set to any value within the above range (i.e., constant tension force), such as 30N, 40N, or 50N. In other embodiments, the tension force can also be controlled to vary within the above range (i.e., variable tension force). For example, by setting the tension roller of the tension control unit of the wrapping equipment to have a constant torque, the tension force will decrease as the insulating film roll is unwound. However, it needs to be controlled to maintain a tension force value of 30N to 50N during the wrapping process, regardless of how the tension force changes due to the unwinding action. The tension force during wrapping determines the flatness of the insulating film 211 surface before application and the initial contact pressure between the adhesive layer and the surface of the battery cell during application. If the tension is too low (less than 30N), the insulating film 211 will lack sufficient tension, making it prone to shaking and loosening during unwinding and conveying. This results in tiny wavy lines on the surface before lamination. After being pressed by the laminating roller, these wavy lines will be directly compacted and locked onto the surface of the battery cell, forming wrinkles and bubbles that cannot be eliminated. If the tension is too high (greater than 50N), although the flatness of the film material can be ensured, the tensile stress inside the insulating film 211 will increase sharply, easily exceeding its elastic limit and causing irreversible plastic tensile deformation. This will not only cause the insulating film 211 to become thinner and narrower, but will also cause wrinkles at the end during the lamination process or during the resting period after lamination, as stress is released. Therefore, the tension should be controlled at 30N. Within the range of 50 N, and in conjunction with the specific range of the bidirectional elastic modulus mentioned above, the tensile stress generated by the insulating film 211 throughout the entire coating process is always within an appropriate range, without irreversible plastic deformation. This fundamentally improves the defects of bubbles and wrinkles caused by tensile deformation and stress concentration during the annular coating process of the battery cell, significantly improves the flatness of the coating adhesion, and increases the coating yield.

[0043] To verify the rationality and optimization effect of the tension control range during the coating process of this application, the applicant set up multiple sets of control tests. The tests were conducted under the same conditions: using the same batch and specification of PET insulating film (110μm thickness), on the same coating equipment, and using a constant tension scheme, the 100 square-shell battery cells with identical dimensional parameters were coated. The sample size for each test was 2000 pieces, and the core evaluation indicators were coating bubbles, static wrinkles, and total defect rate. The test results are shown in Table 1.

[0044] Table 1: Comparison of cell coating effects under different coating tensions

[0045] The experimental data shows that when the tension of the insulating film 211 is controlled within the range of 30-50N during the coating process, the coating effect of the battery cell is better, and the total defect rate is controlled within 2%. When the tension exceeds 50N, the insulating film 211 is overstretched, resulting in large residual stress inside after being applied to the battery cell casing. During the resting process, wrinkles are easily generated at the end due to stress release. When the tension is below 30N, the tension of the insulating film 211 is insufficient, resulting in poor adhesion to the battery cell surface and easy formation of coating bubbles, which also leads to an increase in the defect rate. The above results indicate that the tension control range proposed in this application can effectively balance the tensile deformation of the insulating film and the adhesion tightness, significantly reduce bubble and wrinkle defects, and improve the coating yield.

[0046] In some embodiments, the specified non-proportional elongation strength R of the insulating film 211 is further controlled. p0.2 The pressure ranges from 10 MPa to 16 MPa, where R p0.2 This represents the critical tensile stress at which the insulating film undergoes 0.2% non-proportional plastic elongation. For example, R... p0.2 Specifically, it can be 10MPa, 12MPa, 14MPa, or 16MPa, etc. The R of the insulating film 211... p0.2 By controlling the tension within the range of 10MPa to 16MPa, the selection of the appropriate tension force is better adapted. This ensures that within this controlled tension range, the insulating film 211 remains in a safe elastic deformation stage during the encapsulation, hot pressing, and expansion processes, without undergoing plastic deformation. Because no plastic deformation occurs, the material possesses elastic recovery capability after the external force is removed, preventing the generation of continuously released residual stress on the cell surface. This avoids springback, warping, and delamination problems caused by plastic deformation, ensuring the insulation stability of the cell during long-term use.

[0047] In some embodiments, the elastic modulus E of the insulating film 211 along the unwinding length direction is further controlled. MD With the elastic modulus E along the width direction TD The relative deviation is ≤5%, i.e., E MD With E TD Satisfy: |E MD –E TD | / max(E MD E TDThe difference in elastic modulus is ≤5%, thus achieving a high degree of balance in the bidirectional mechanical properties of the insulating film 211. During high-speed unwinding and wrapping, the insulating film 211 exhibits good synchronization in both directions of stretching and retraction, making it less prone to unilateral stress concentration and avoiding film deviation and wrinkling caused by uneven force on both sides during high-speed unwinding. Specifically, when the film is subjected to longitudinal tension, according to the Poisson effect, it will generate lateral shrinkage strain. If the bidirectional elastic modulus is extremely uneven, longitudinal stretching will induce severe and uneven lateral shrinkage, causing asymmetrical lateral oscillation during the film-laying process of the insulating film 211, i.e., deviation. This not only leads to deviation in the film application position but also easily causes oblique stretching wrinkles during application due to uneven lateral force, severely reducing the wrapping yield. This embodiment achieves a high degree of isotropy in the bidirectional mechanical properties of the insulating film 211 by controlling the difference in bidirectional elastic modulus to ≤5%. During high-speed unwinding and wrapping, the insulating film 211 can evenly distribute the tension force, and its lateral shrinkage and longitudinal stretching have a highly linear and symmetrical relationship. This effectively suppresses asymmetric shear instability during high-speed unwinding, maintains the straightness of the film trajectory, and thus enables extremely precise alignment during bonding, completely eliminating oblique wrinkles.

[0048] In one embodiment, during step S4, a pressing action is performed on the insulating film 211, more specifically, a rolling and smoothing action is performed on the insulating film 211 by a film-applying roller, and the battery cell is moved. Figure 3 The arrows in the diagram indicate the direction of cell movement, causing the position of the insulating film 211 to move from a first position on the outer surface of the housing to a second position on the outer surface of the housing. At least a portion of the insulating film 211, which has been rolled and smoothed, is adhered to the outer surface of the housing. As the cell continues to feed, the contact position between the film-applying roller and the insulating film 211, as well as the cell housing, is simultaneously displaced, and the contact point gradually moves from the first position on the outer surface of the housing to the second position on the outer surface of the housing. Under the continuous rolling and smoothing action, at least a section of the insulating film 211 is tightly adhered to the outer surface of the cell housing. The air between the insulating film 211 and the housing is expelled by the rolling pressure, avoiding appearance defects such as bubbles, wrinkles, and curling edges after coating, and ensuring that the insulating film 211 is firmly adhered to the side wall of the housing.

[0049] The sidewall 120 of the casing has a wrapping width along the wrapping direction. The wrapping width is defined as the width of the insulating film 211 attached to the sidewall 120, that is, the width of the area of ​​the sidewall 120 that needs to be covered with the insulating film 211. Currently, the market demand for high-capacity power batteries continues to increase, the overall size of the cells is constantly increasing, and the size of the casing sidewall is increasing accordingly, resulting in a corresponding increase in the wrapping width. The larger the wrapping width, the more stress accumulates inside the insulating film 211 during the wrapping process, and the stress accumulated in the early stage is difficult to be completely released in the subsequent wrapping finishing process, which can easily cause the insulating film 211 to lift at the finishing position, reducing the wrapping yield.

[0050] In order to improve the above-mentioned defects and increase the yield of coated products, the coating method of this application limits the coating width W: the coating width W≤120mm, and further, the coating width W≤92mm.

[0051] In one embodiment, the first sidewall 121 and the second sidewall 122 of the prismatic battery cell 100 are integrally formed and connected at a 90° angle, and the coating width of the first sidewall 121 is smaller than the coating width of the second sidewall 122. Here, the coating widths correspond to the width W1 of the first sidewall 121 and the width W2 of the second sidewall 122, respectively.

[0052] Specifically, the larger the width W2 of the second sidewall 122 (large sidewall) of the prismatic cell 100, the longer the extension stroke of the insulating film 211 during the coating process, and the greater the accumulated residual stress inside the insulating film 211. This residual stress cannot be completely released in the conventional coating finishing process, ultimately causing poor lifting at the finishing position of the insulating film 211. In one embodiment, the width W2 of the second sidewall 122 is ≤120mm. Further, the width W2 of the second sidewall 122 is 92mm~120mm. For example, W2 can be 92mm, 95mm, 100mm, 110mm, or 120mm, etc. Even further, the width W2 of the second sidewall 122 is ≤92mm.

[0053] Correspondingly, the first sidewall 121 (small side) of the square-shell battery cell 100 is the final cutting position of the insulating film 211 cutter, and also the finishing roller assembly (see...). Figure 3 The main pressing contact areas are 285 and 286 in the above-mentioned finishing roller group. The aforementioned finishing roller group refers to the roller combination at the end of the coating equipment, which is used to roll-press, flatten, shape, maintain tension, and stabilize the finishing section of the insulating film 211 after the main body of the battery cell shell is completed, ensuring that the finishing section of the insulating film 211 is tightly bonded to the coated surface of the battery cell shell without wrinkles, bubbles, or curling edges. When the width W1 of the first sidewall 121 is larger, that is, the thickness of the square battery cell 100 is larger, the effective contact area between the insulating film 211 and the finishing roller group and the sidewall of the battery cell is larger, which can fully and evenly release the residual stress accumulated in the early stage of coating, and significantly improve the curling defect of the insulating film at the end. In one embodiment, the width W1 of the first sidewall 121 is ≥21mm, and further, W1 can be 21mm~26mm. For example, W1 can be 21mm, 23mm, 25mm or 26mm, etc.; and even further, W1 ≥26mm.

[0054] This application, by coordinating and limiting the width dimensions of the large and small sides of the cell casing, matches the stress accumulation during the coating process with the stress release capability at the final stage, thereby reducing the defect rate of blistering, wrinkling, and lifting at the end of the insulation film 211 from the source and significantly improving the coating yield.

[0055] To verify the rationality of the above-mentioned cell size parameters and the corresponding optimization technology effects, this application sets up a control experiment, and standardizes the test conditions to eliminate interference: the experiment uses PET insulating film of the same specification (2 layers of PET material + 2 layers of adhesive), the overall thickness of the insulating film 211 is 110μm, and the same coating equipment and uniform mass production-level coating process are used throughout the process. During the coating process, the tension of the insulating film 211 is controlled at a constant value within the range of 30N~50N, specifically controlled at 40N; the material properties of the insulating film 211 used in each group of tests, the elastic modulus (E) TD E MD Both are 105 MPa), and the specified non-proportional elongation strength R is specified. P0.2 (16MPa) remained consistent. Multiple groups of square-shell cells with different sidewall dimensions were selected for comparative testing. The sample size for each group was 1000 pieces. The wrinkles after the cells were coated and left to stand were used as the core evaluation index. The specific test results are shown in Table 2 below.

[0056] Table 2: Test results of coating effect for different cell sizes

[0057] The above test data shows that when the width of the second sidewall 122 of the battery cell is limited to ≤120mm and the width of the first sidewall 121 is limited to ≥21mm, the highest rate of warping defects after coating is 6%, which meets the basic quality requirements for mass production of battery cells. Specifically, when the width of the second sidewall 122 is 92mm and the width of the first sidewall 121 is 21mm, the warping defect rate after coating is as low as 1.20%, achieving the best results. This dimensional ratio, while ensuring the internal space of the battery cell and meeting the capacity design requirements, effectively shortens the coating extension stroke of the large sidewall film, reduces residual stress accumulation, and fully releases residual stress by relying on the small sidewall finishing structure with a large contact area. This fundamentally improves defects such as warping and wrinkling of the insulating film finishing, significantly enhancing the forming quality and mass production stability of the annular coating of prismatic battery cells. If the width W2 of the second sidewall 122 exceeds 120 mm and the width W2 of the first sidewall 121 is less than 21 mm (corresponding to comparative test 6), the residual stress accumulated during the coating process of the insulating film 211 cannot be fully released in the finishing process, and the coating warping defect rate increases significantly. Even if the width of the first sidewall 121 is adjusted to more than 21 mm (corresponding to comparative test 5), the coating defect rate decreases slightly, but there is still a significant difference compared with the working conditions within the size limit range of this application.

[0058] The relationship between the casing wrapping speed of the cell and the stress relaxation time of the insulating film 211 also affects the wrapping effect. In some embodiments, the casing wrapping speed v of the prismatic cell 100, the stress relaxation time τ of the insulating film 211, and the cumulative length L of the pressing action acting on the outer surface of the casing along the wrapping direction satisfy the relational expression v τ<L / 3. This relational expression ensures that the action time of the rolling pressing action on the insulating film 211 is significantly longer than its stress relaxation time, so that the tensile residual stress inside the insulating film 211 is fully relaxed and released under the continuous pressing action, fundamentally reducing the later warping and bubble defects caused by residual stress release. At the same time, the design requires L≥b (b is the width of the insulating film), which ensures that the pressing action can completely cover the insulating film in the axial direction, avoiding indentation or uneven local relaxation at the edge of the insulating film due to stress concentration at the pressing edge.

[0059] To adapt to the development trend of large-size cells in the industry, the present application expands the above-mentioned tension force matching rule of the insulating film during casing wrapping to the wrapping working condition of large-size cells, and realizes the parameter matching design for cells of different specifications and different insulating films by establishing a mechanical matching criterion.

[0060] The present application constructs a mechanical matching relational expression: F= ; the definitions of each parameter in the formula are as follows: E is the elastic modulus of the insulating film, taking the elastic modulus E MD and the elastic modulus E TD the smaller value, unit MPa; W is the wrapping width, unit mm; t is the thickness of the insulating film, unit mm; F is the wrapping adaptation coefficient of the insulating film. Fitted through multiple sets of casing wrapping process test data, the value range of the wrapping adaptation coefficient corresponding to the qualified yield of cell casing wrapping is: F∈[6.3×10 -5 , 1.25×10 -4 .

[0061] In the present application, the thickness t of the insulating film 211 is limited to 50 μm to 200 μm. In the actual production regulation process for large-size cells, adjustment can be made in the following two ways: first, keep the thickness t of the insulating film 211 unchanged, and adjust the elastic modulus E of the insulating film 211 to make the wrapping adaptation coefficient F fall into the above qualified range; second, keep the elastic modulus E of the insulating film 211 unchanged, and adjust the thickness t of the insulating film 211 to realize the range matching of F. If the wrapping adaptation coefficient F is lower than the lower limit of the range, it means that the overall rigidity of the insulating film is weak, the film body is too soft or the thickness is insufficient, and appearance defects such as film surface bubbling and wrinkles are prone to occur during the wrapping process; if the wrapping adaptation coefficient F is higher than the upper limit of the range, the rigidity of the insulating film is too high, the tensile resistance during wrapping is large, and the attachment stress on the surface of the cell casing is too large, which easily causes defects such as film layer tearing and edge warping. Therefore, F needs to be strictly controlled within the qualified range obtained by fitting during the production process, so as to balance the flatness of large-size cell wrapping and the tensile processing performance of the film material.

[0062] Please see Figure 3 The present invention also provides a coating equipment 200, which is used to automatically coat the insulating film 211 on the outer surface of the sidewall of the square battery cell 100. The equipment includes a feeding unit, a tension control unit, a battery cell conveying unit 290 and a pressing and film-applying unit 280. The units work together to realize the fully automatic coating operation of the insulating film on the sidewall of the square battery cell 100.

[0063] The feeding unit includes an insulating film roll 210, a release paper take-up roller 220, an edge correction device 230, and several guide rollers 240. The insulating film roll 210 continuously releases the insulating film 211 with release paper. The guide rollers 240 are spaced apart along the conveying path of the insulating film 211, guiding and limiting its movement to ensure smooth movement along the preset conveying path. The edge correction device 230 is located downstream of the insulating film conveying path and can detect and correct the conveying offset of the insulating film 211 in real time, effectively preventing film deviation and misalignment, and ensuring the accuracy of the wrapping position. The release paper take-up roller 220 is positioned above the insulating film 211 conveying path. Before the actual wrapping of the battery cell, the release paper is peeled off the insulating film 211. The peeled release paper is guided and conveyed by the corresponding guide roller 240 and finally collected by the release paper take-up roller 220, preventing the release paper from interfering with the wrapping operation.

[0064] The tension control unit includes a tension roller 250, which is used to regulate the tension of the insulating film throughout the conveying process to ensure the quality of film application. The tension roller 250 is mounted on the conveying path of the insulating film 211 and can provide continuous and stable film tension to the insulating film 211 during the conveying process through floating adjustment or active drive control, so as to avoid problems such as loosening, wrinkling or excessive stretching and breakage of the film belt.

[0065] The tension control unit also includes an ionizing air device 260 and a film-pulling rod 270. The ionizing air device 260 is located near the tension roller 250 and can eliminate static electricity on the surface of the insulating film 211, preventing static electricity from attracting dust and impurities, and effectively improving the adhesion and flatness between the insulating film and the battery cell surface. The film-pulling rod 270 is arranged below the wrapping channel and works in conjunction with the tension roller 250 to further fine-tune the local tension and conveying posture of the insulating film to adapt to the tension requirements of the battery cell wrapping.

[0066] The battery cell conveying unit 290 includes a coating channel, a feeding pusher, and a discharging pusher, used to realize automated continuous conveying of battery cells. The battery cells to be coated are pushed by the feeding pusher and move at a constant speed along the coating channel, passing through the film application station, transition station, and finishing station in sequence to complete the entire coating process. After coating, the finished battery cells are smoothly delivered out of the equipment by the discharging pusher to connect with subsequent production processes.

[0067] The pressing and laminating unit 280 is the core execution structure for battery cell lamination, including a laminating roller group, a transition roller group, and a finishing roller group arranged sequentially along the lamination channel. The laminating roller group includes a first laminating roller 281 and a second laminating roller 282 symmetrically arranged on the upper and lower sides of the lamination channel, forming the first pressing station. This station primarily presses and adheres the insulating film 211 to the outer surface of the battery cell sidewall, achieving initial positioning and fixation of the insulating film 211. The transition roller group includes a first transition roller 283 and a second transition roller 284 symmetrically arranged on the upper and lower sides of the lamination channel, forming the second pressing station. This station gradually presses and extends the initially laminated insulating film 211. The finishing roller group includes a first finishing roller 285 and a second finishing roller 286 symmetrically arranged on the upper and lower sides of the lamination channel, forming the third pressing station. This station compacts and seals the ends of the insulating film circumferentially around the battery cell, completing the circumferential full-coverage operation of the battery cell sidewall, ensuring complete and firm insulation film coverage without edge lifting or blistering.

[0068] In one embodiment, the above-mentioned coating equipment 200 is used to perform annular coating on the square-shell cell 100. The specific process is as follows: Step 1: Provide a square-shell battery cell 100 to be coated. The square-shell battery cell 100 includes a housing and an end cap 130. The housing includes a bottom wall 110 and side walls 120 arranged around the bottom wall 110. The side walls 120 include two first side walls 121 and two second side walls 122 arranged opposite to each other. The two first side walls 121 (small side walls) are arranged opposite to each other along the width direction of the bottom wall 110, and the two second side walls 122 (large side walls) are arranged opposite to each other along the length direction of the bottom wall 110.

[0069] Step 2: Provide insulating film 211. The insulating film 211 covering the battery cell is continuously output from the insulating film roll 210 of the coating equipment 200 feeding unit.

[0070] Step 3: Place the square-shell battery cell 100 to be coated into the coating channel, keeping the two second sidewalls 122 horizontal, and ensuring the end cap 130 is parallel to the conveying direction of the battery cell within the coating channel. Press the insulating film 211 against the first sidewall 121 on the front side of the housing along the conveying direction between the unwinding and cutting sections of the insulating film 211, so that the insulating film 211 is at least partially adhered to the housing, completing the initial positioning and fixing of the insulating film 211. The insulating film 211 at the position corresponding to the first sidewall 121 is the initial adhesion part.

[0071] Step 4: After pre-positioning, the tension roller 250 of the tension control unit applies tension to the section of insulating film 211 located between the bonding start section and the unwinding section. Simultaneously, the feed pusher of the cell conveying unit 290 pushes the prismatic cell 100 continuously along the coating conveying channel, allowing the cell to pass through each coating station sequentially. During movement, the pressing and bonding unit 280 smoothly extends the insulating film 211 from the first sidewall 121 on the starting side, ensuring the insulating film 211 tightly adheres to the second sidewalls 122 on both the upper and lower sides of the prismatic cell 100, i.e., the large sidewalls of the cell, achieving full coverage of both large sidewalls. After the second sidewalls 122 on both sides of the cell are completely covered, the remaining insulating film 211 continues to extend to the first sidewall 121 on the other side of the prismatic cell 100, i.e., the small end face on the finishing side. At this point, the first finishing roller 285 and the second finishing roller 286 roll and compact the end of the insulating film 211, causing the beginning and end ends of the insulating film 211 to overlap and seal at the small end face of the finishing side. This completes the annular closed-loop wrapping of the square battery cell 100, forming a complete and sealed insulating protective layer around the outer periphery of the square battery cell 100. After the entire annular wrapping process of the battery cell is completed, the finished battery cell with the wrapping formed is sent out of the wrapping equipment 200 by the discharge pusher and transferred to the next production process.

[0072] During the aforementioned wrapping process, the tension T applied to the film segment between the initial bonding portion and the unwinding section of the insulating film 211 is controlled in real-time by the tension control unit of the wrapping equipment 200. Specifically, this includes two adjustment methods adapted to the wrapping conditions: constant tension control and variable tension control. The core calculation logic for the tension of the insulating film 211 follows the formula: Where T is the tension force of the insulating film 211, M is the output torque of the tension roller 250, and D is the real-time roll diameter of the insulating film roll 210 during unwinding.

[0073] In one embodiment, a constant tension control mode is adopted. The tension control unit includes a roll diameter detection sensor, which monitors the real-time roll diameter D of the insulating film roll 210 during the wrapping process. The tension control unit adaptively adjusts the torque M of the tension roller 250 according to the tension calculation formula to compensate for changes in roll diameter during film roll consumption, ensuring that the tension T of the insulating film 211 remains constant throughout the wrapping process. In this application, the tension T set for constant tension control is within the range of 30N to 50N, and any value within this range can be selected for stable operation.

[0074] To ensure that the insulating film undergoes only elastic deformation during the wrapping process, this application selects an insulating film with high yield strength and high elastic modulus, which effectively expands the elastic working range of the insulating film and ensures that the wrapping tension is always within the elastic deformation range of the insulating film throughout the entire process.

[0075] The specified non-proportional elongation strength of an insulating film is defined as R.p0.2 The effective cross-sectional area A of the insulating film 211 is determined by the film width and film thickness, satisfying the calculation formula A=b×h. In some embodiments, the thickness h of the insulating film 211 ranges from 50μm to 200μm, and can be 110μm for example; the width b of the insulating film 211 ranges from 298mm to 302mm, and can be 299.4mm for example.

[0076] To balance the bonding effect of the film and the safety deformation requirements of the insulating film 211, the constant tension setting value of this application satisfies: T 设定 =k×R p0.2 ×A, where k is the tension safety factor, ranging from 0.6 to 0.8. During the conveying process of the insulating film 211, the torque of the tension roller 250 and the tension force of the insulating film 211 follow the formula: Since the tension of the insulating film 211 increases with the torque of the tension roller 250, if the torque is too large, the actual tension will exceed the safety setting value, causing the insulating film 211 to undergo plastic deformation. Therefore, the actual tension corresponding to the torque must be limited to be less than the preset working tension. < k× R p0.2 ×A The torque constraint relationship is obtained by converting and deriving the formula: .

[0077] Based on this torque and the specified non-proportional elongation strength R of the insulating film 211 p0.2 The correlation formula of the insulating film 211 parameters can match the torque parameters of the tension roller 250 according to the performance parameters of insulating films 211 of different specifications, and accurately control the tension of the insulating film 211 during the wrapping process, so as to ensure that the tension of various insulating films 211 is stably within the reasonable range defined in this application, and avoid problems such as stretching deformation of the insulating film 211, film wrinkles, and edge lifting.

[0078] In another embodiment, a variable tension control mode is adopted, that is, the output torque M of the tension roller 250 remains fixed during the operation. As the wrapping operation continues, the roll diameter D of the insulating film roll 210 continuously decreases. According to the tension calculation formula, the tension T of the insulating film will gradually decrease as the insulating film roll 210 is consumed.

[0079] In some optional implementations, the constant torque M ranges from 10 N / m to 14 N / m, with 10 N / m, 12 N / m, and 14 N / m being examples. By setting this torque parameter, the tension T of the insulating film throughout the coating process can be adaptively varied and stably covered within the process requirement range of 30 N to 50 N, adapting to the needs of continuous coating production.

[0080] Furthermore, a rounded transition section 123 exists between the second sidewall 122 and the first sidewall 121 of the square-shell battery cell 100. This rounded transition section 123 experiences a bending and tensile coupling stress effect, which can easily lead to problems such as film blistering, wrinkling, and tensile deformation. To improve this defect, this application uses variable tension adaptive logic to match the battery cell's external structural characteristics: when wrapping the straight section of the large side of the battery cell, a high first tension is maintained to ensure that the insulating film is tightly bonded to the battery cell plane, flat and without looseness; before the insulating film 211 covers the rounded transition section 123, the tension is actively reduced by relying on a constant torque combined with changes in trajectory curvature, lowering the tension from the first tension to the second tension, adaptively offsetting the bending and tensile coupling stress of the rounded transition section 123, and significantly improving the consistency and flatness of the film bonding at the corners and arc positions of the battery cell. In one embodiment, before the insulating film 211 covers the rounded transition section 123, the second tension applied is reduced by 20% to 40% compared to the first tension. For example, it can be 20%, 30%, or 40%, etc.

[0081] Further research by the applicant revealed that the bending stiffness EI of the insulating film 211 is the core physical parameter determining its performance in the cell rounded corner transition section 123. The bending stiffness EI directly determines the bending rebound characteristics during the insulating film coating process: the greater the bending stiffness EI of the insulating film 211, the stronger the film's rigidity and the worse its flexibility. When the insulating film is bonded to the cell rounded corner transition section 123, it generates significant internal bending rebound stress, making it prone to problems such as edge lifting, delamination, and bonding failure after the external force is removed. Conversely, the smaller the bending stiffness EI, the better the film's bending flexibility, the significantly reduced bending rebound stress, and the ability of the film to tightly adhere to the cell's corner structure, resulting in better coating consistency.

[0082] To address the issues of excessive bending stiffness of the insulating film 211 and stress concentration at the rounded corner transition section 123 of the battery cell, which lead to edge curling and poor adhesion, this application proposes an optimized scheme for the coordinated control of the thickness, elastic modulus, and bending stiffness of the insulating film 211. This scheme improves the edge coating effect of the battery cell from the perspectives of material properties and structural parameters.

[0083] In some alternative embodiments, the simplified formula for the bending stiffness EI of the insulating film 211 is as follows: That is, the bending stiffness EI of the insulating film 211 is positively correlated with the elastic modulus E and proportional to the square of the film thickness t. A small change in film thickness can lead to an exponentially large change in bending stiffness. Based on the above mechanism, the thickness t of the insulating film 211 in this application is 50μm~200μm, and further, it can be 110μm. By reducing the film thickness, the square of the thickness is significantly reduced, thereby achieving a significant reduction in bending stiffness EI. At the same time, the elastic modulus E of the insulating film 211 is limited and controlled to a range of 90MPa~125MPa to avoid the problems of insufficient overall strength, poor tensile properties, and easy breakage caused by simply reducing the film thickness or blindly reducing the modulus.

[0084] This application optimizes the bending stiffness of the insulating film by synergistically matching and controlling the thickness and elastic modulus of the insulating film, significantly reducing the bending rebound stress and corner stress concentration effects. The optimized insulating film exhibits excellent bending flexibility, allowing it to tightly conform to the irregular corner structures of the battery cell. This improves defects such as edge lifting, delamination, and blistering at the corners of the battery cell, effectively enhancing the overall forming quality and coating stability of the annular coating of the battery cell.

[0085] The coating method and equipment for battery cells provided by this invention achieve effective matching of material mechanical properties and process parameters by controlling the tension force during the coating process and selecting an insulating film with an appropriate elastic modulus. The insulating film exhibits excellent synergy in both bidirectional mechanical properties, possessing both flexibility and supporting rigidity when stretched under tension. This allows for smooth coating of the rounded transition sections of the battery cell shell, avoiding stress concentration in localized areas caused by excessively high modulus, thereby reducing problems such as bubbles and cracking. Simultaneously, sufficient supporting rigidity prevents lateral wrinkles and dimensional deviations during the rolling process. This fundamentally improves the bubble and wrinkle defects caused by tensile deformation and stress concentration in the annular coating process, effectively enhancing the flatness of the insulating film adhesion and the appearance quality of the battery cell. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0086] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for coating a battery cell, characterized in that, comprising the following steps: providing a cell, wherein the cell comprises a housing; An insulating film is provided, wherein the elastic modulus E along the unwinding length direction is... MD The elastic modulus E along the width direction is 90MPa~105MPa. TD The pressure is 105MPa~125MPa; the unwinding section of the insulating film is tensioned and positioned, and the cut section of the insulating film is pulled. at a first position between the unwinding section and the cutting section and corresponding to the outer surface of the housing, pressing and attaching at least part of the insulating film to the outer surface of the housing, wherein at least part of the insulating film corresponding to the first position on the outer surface of the housing is defined as the sticking start portion of the insulating film; continuously controlling a tension force to exist between the sticking start portion of the insulating film and the unwinding section, moving the cell and continuously pressing and attaching the insulating film to the outer surface of the housing under the tension force, wherein the tension force is continuously controlled to be 30N to 50N.

2. The coating method according to claim 1, characterized in that, The specified non-proportional elongation strength R of the insulating film p0.2 The value is 10MPa~16MPa, wherein, the R p0.2 This represents the critical tensile stress at which the insulating film undergoes 0.2% non-proportional plastic elongation.

3. The coating method according to claim 1, characterized in that, The elastic modulus E of the insulating film along the unwinding length direction MD With the elastic modulus E along the width direction TD Satisfy: |E MD –E TD | / max(E MD E TD ≤5%.

4. The coating method according to claim 1, characterized in that, When moving the cell, a pressing operation is continuously performed on the insulating film, the pressing operation continuously moves from the first position on the outer surface of the housing to a second position on the outer surface of the housing, so that at least part of the pressed insulating film is attached to the outer surface of the housing; wherein the housing comprises a plurality of side walls arranged at an angle and connected end to end along the film wrapping direction; the insulating film is wrapped around the side walls along the film wrapping direction, the side walls have a film wrapping width W along the film wrapping direction, and the film wrapping width W ≤ 120mm; or, the film wrapping width W ≤ 92mm.

5. The coating method according to claim 4, characterized in that, The side walls include a first side wall and a second side wall, the first side wall and the second side wall are integrally connected at an angle, the film wrapping width of the first side wall is smaller than the film wrapping width of the second side wall, the film wrapping width of the first side wall is ≥ 21mm, or, the film wrapping width of the first side wall is ≥ 26mm.

6. The coating method according to claim 4, characterized in that, The insulating film satisfies the following relationship: F= In the formula, E is the elastic modulus of the insulating film, in MPa, and the value of E is the elastic modulus E. MD and the elastic modulus E TD The smaller of the values; t is the thickness of the insulating film, in mm; W represents the width of the coating, in mm; F ​​is the coating fit coefficient of the insulating film, F∈[6.3×10] -5 1.25×10 -4 ].

7. The coating method according to claim 1, characterized in that, The film wrapping speed v of the cell and the stress relaxation time τ of the insulating film satisfy the relational expression: v·τ < L / 3, where L represents the cumulative length of the pressing operation acting on the outer surface of the housing along the film wrapping direction, and L ≥ b, where b is the width of the insulating film.

8. A coating apparatus for the coating method according to any one of claims 1 to 7, characterized in that, comprising: a feeding unit, configured to output the insulating film; a cell conveying unit, configured to convey the cell; a tension control unit, configured to apply the tension force to the tension section of the insulating film; a pressing and film attaching unit, configured to press and attach the insulating film to the outer surface of the housing.

9. The coating apparatus according to claim 8, characterized in that, The tension control unit comprises a tension roller, the tension roller tensions the tension section of the insulating film, and adjusts the tension force by adjusting its torque, wherein the torque of the tension roller is controlled within the range of 10N / m to 14N / m.

10. The coating apparatus according to claim 9, characterized in that, The tension control unit controls the tension force of the insulating film through any one of the following torque control modes: The first mode: the tension control unit detects the change in the roll diameter of the insulating film roll after the insulating film is unwound in real time, so as to dynamically adjust the torque of the tension roller to keep the torque of the tension roller within the range of 10 N / m to 14 N / m, and at the same time keep the tension force constant at a first tension force; The second mode: the tension control unit fixes the torque of the tension roller to a certain constant value within the range of 10 N / m to 14 N / m; The third mode: The tension control unit detects the change in the roll diameter of the insulating film after unwinding in real time, so as to dynamically adjust the torque of the tension roller to keep the torque of the tension roller in the range of 10 N / m to 14 N / m, and at the same time keep the tension force constant and maintain the first tension force; the housing includes a planar first sidewall, a planar second sidewall, and a rounded transition section integrally connected between the first sidewall and the second sidewall. When the pressed position of the insulating film corresponds to the rounded transition section, the tension roller automatically adjusts the torque to keep the tension force constant and maintain the second tension force, which is less than the first tension force.

Images