A method for winding a lithium-ion battery cell with variable diameter

Abstract

The present invention relates to the field of battery cell winding, and in particular to a variable diameter winding method for lithium ion battery cells. The present invention performs a winding-derived deformation test on each layer of a to-be-wound object to obtain the derived deformation characteristics of the to-be-wound object in a targeted manner, determines the specific contour segment of the winding needle to obtain the number and protrusion characteristics of the specific contour segment for the winding needle, determines the subsequent winding process according to the deformation tendency characterization value, and obtains the discrete difference value of the force on each winding wheel when each winding object covers the specific contour segment of the winding needle during the winding process to determine whether it is in line with the adjustment of the winding speed, determines the force condition of each winding object during the winding process based on the discrete difference value of the force on each winding wheel, continuously monitors the winding process, determines the influence of the different expansion and contraction rates of each winding object on the winding during the battery cell winding process through the relative displacement, adjusts the winding parameters in a targeted manner, and effectively improves the winding efficiency of the battery cell.

Description

Technical Field

[0001] The invention relates to the field of battery core winding, and in particular to a lithium ion battery core variable diameter winding method. Background Art

[0002] As a kind of clean energy, lithium-ion batteries have been widely used in various electronic products, such as smart phones, laptops, digital cameras and portable small appliances, due to their many advantages such as high voltage, long cycle charge and discharge life, low environmental pollution and low self-discharge rate. The main structure of a lithium-ion battery includes a shell and a lithium-ion battery cell arranged in the shell. Usually, a lithium-ion battery cell is formed by winding a battery cell material, such as a positive electrode sheet, an upper diaphragm, a negative electrode sheet and a lower diaphragm, into a battery cell using a winding device.

[0003] Chinese Patent Publication No.: CN104934644A, discloses a battery cell winding mechanism and a battery cell winding method, the battery cell winding mechanism, including a first winding needle shaft, a second winding needle shaft, a transmission shaft, a first connecting plate, a second connecting plate and a first driving mechanism. The first winding needle shaft is connected to one end of the first connecting plate, the second winding needle shaft is connected to one end of the second connecting plate, the first winding needle shaft and the second winding needle shaft are coaxial and arranged oppositely, the first winding needle shaft and the second winding needle shaft can rotate synchronously, and can move closer to or away from each other. The transmission shaft is connected between the other end of the first connecting plate and the other end of the second connecting plate, the first driving mechanism is connected to the first connecting plate or the second connecting plate and can drive the first winding needle shaft, the second winding needle shaft, the first connecting plate and the second connecting plate to swing together around the axis direction of the transmission shaft.

[0004] However, the prior art still has the following problems:

[0005] 1. In the prior art, the influence of different expansion and contraction rates of each winding material on the winding process of the battery cell is not considered, and the winding speed cannot be adjusted accordingly;

[0006] 2. In the prior art, the different shapes of the winding needles are not taken into account. During the winding process, the sharp corners of the winding needles cause the winding material to be subjected to different tensions at different winding points, and the deformation of the winding material cannot be determined;

[0007] 3. In the prior art, the winding process is not monitored and the winding parameters cannot be adjusted in a targeted manner, which affects the winding efficiency of the battery cell. Summary of the invention

[0008] To this end, the present invention provides a lithium-ion battery cell variable diameter winding method to overcome the problem in the prior art that the winding process is not monitored and the winding parameters cannot be adjusted specifically, which affects the winding efficiency of the cell winding.

[0009] To achieve the above object, the present invention provides a lithium ion battery cell variable diameter winding method, comprising:

[0010] Step S1, after a plurality of objects to be wound overlap, a plurality of marking points arranged at equal intervals are set along the winding direction to perform a winding-derived deformation test, including winding the objects to be wound, obtaining a scanning image of the winding section where the marking points are located, so as to determine the relative displacement of a single marking point on the surface of different objects to be wound, and determining a derived deformation characteristic value according to the relative displacement of each marking point;

[0011] Step S2, obtaining a cross-sectional image of the winding needle, identifying a specific contour segment according to the curvature of different contour segments of the cross-sectional contour, determining the protrusion features of the specific contour segment, and calculating a deformation tendency characterization value based on the number of specific contour segments, the protrusion features and the derived deformation characteristic value;

[0012] Step S3, determining the deformation tendency according to the deformation tendency characterization value, and controlling the process parameters in the winding process based on the determination result, including:

[0013] Obtain discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process, determine whether it meets the stress diffusion standard, and adjust the winding speed;

[0014] Or, maintain the current winding speed.

[0015] Furthermore, in the step S1, the relative displacement of a single marking point on the surface of different objects to be wound is determined, and the process of determining the derived deformation characteristic value according to the relative displacement of each marking point includes:

[0016] Determine the coordinates of a single marking point on the surface of different objects to be wound based on the scanned image to solve the average distance between the coordinates, and determine the average distance as the relative displacement of the marking point;

[0017] The mean of the relative displacement of each marking point is calculated to obtain the derived deformation eigenvalue.

[0018] Furthermore, in step S2, the process of identifying the specific contour segment according to the curvature of different contour segments of the cross-sectional contour includes:

[0019] Divide the cross-sectional profile into several profile segments and calculate the curvature of each profile segment;

[0020] For the curvature of a single contour segment, the average difference ratio between the curvature of the single contour segment and the curvature of the adjacent contour segments is calculated respectively;

[0021] If the average difference ratio is less than or equal to a predetermined difference ratio threshold, the contour segment is determined to be a non-specific contour segment;

[0022] If the average difference ratio is greater than a predetermined difference ratio threshold, the contour segment is determined to be a specific contour segment.

[0023] Furthermore, in step S2, the process of determining the protrusion feature of the specific contour segment includes:

[0024] For a single unique contour segment, a connecting line is drawn between its two end points to obtain a standard segment for the single unique contour segment;

[0025] The distance between the unique contour segment and the standard segment is obtained, and the maximum value among the distances is determined as the protrusion feature for the single unique contour segment.

[0026] Furthermore, in step S2, the deformation tendency characterization value is calculated according to formula (1):

[0027]

[0028] Wherein, B is the deformation tendency characterization value, n represents the number of specific contour segments, i=1,2,3...,n, Li is the protrusion feature of the i-th specific contour segment, C is the derived deformation feature value, n0 is the mean value of the number of specific contour segments corresponding to each winding needle in history, L0 is the mean value of the protrusion features of each winding needle in history, C0 is the mean value of the derived deformation feature values ​​corresponding to the historical objects to be wound, α is the specific number weight coefficient, β is the protrusion number weight coefficient, and γ is the derived deformation weight coefficient.

[0029] Furthermore, in the step S3, the process of determining the deformation tendency according to the deformation tendency characterization value includes:

[0030] If the deformation tendency representation value is less than or equal to the preset deformation tendency representation value, it is classified as a weak deformation tendency category;

[0031] If the deformation tendency characterization value is greater than the preset deformation tendency characterization value, it is classified into a strong deformation tendency category.

[0032] Furthermore, in step S3, the process of controlling the process parameters in the winding process based on the determination result of the deformation tendency includes:

[0033] If the object to be wound is of the type with weak deformation tendency, the winding is completed by maintaining the current winding speed;

[0034] If the object to be wound is of the strong deformation tendency category, the discrete difference values ​​of the forces on different winding wheels when the object to be wound covers the specific contour segment during the winding process are obtained to determine whether it meets the stress diffusion standard so as to adjust the winding speed.

[0035] Furthermore, in the step S3, the process of obtaining the discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process is as follows:

[0036] The variance of the force values ​​of each winding wheel is calculated and the variance is determined as a discrete difference value.

[0037] Furthermore, in step S3, the process of determining whether the stress diffusion standard is met includes:

[0038] If the discrete difference value is less than or equal to the preset discrete difference value, it is determined that the stress diffusion standard is met;

[0039] If the discrete difference value is greater than the preset discrete difference value, it is determined that the stress diffusion standard is not met.

[0040] Further, in step S3, the winding speed is determined based on the discrete difference value, wherein:

[0041] The determined winding speed is negatively correlated with the discrete difference value.

[0042] Compared with the prior art, the present invention conducts a winding-derived deformation test on each layer of the object to be wound to obtain the derived deformation characteristics of the object to be wound in a targeted manner, determines the specific contour segment of the winding needle to obtain the number and protrusion characteristics of the specific contour segment for the winding needle, determines the subsequent winding process according to the deformation tendency characterization value, and obtains the discrete difference value of the force on each winding wheel when each object to be wound covers the specific contour segment of the winding needle during the winding process to determine whether it is in compliance with the adjustment of the winding speed, determines the force condition of each object to be wound during the winding process based on the discrete difference value of the force on each winding wheel, and continuously monitors the winding process, determines the influence of the different expansion and contraction rates of each object to be wound on the winding during the winding process of the battery cell through the relative displacement, and adjusts the winding parameters in a targeted manner, thereby effectively improving the winding efficiency of the battery cell.

[0043] Furthermore, the deformation tendency characterization value is calculated and determined by the relative displacement of the object to be wound on the surface of different objects to be wound, the number of specific contour segments of the cross-sectional contour of the winding needle and the protrusion characteristics. Different objects to be wound have different expansion and contraction rates, and winding needles of different shapes apply different tensions to the objects to be wound during the winding process. A lower winding speed is required during the winding process to reduce the uneven internal stress caused by the inconsistent expansion and contraction of the objects to be wound during the charging and discharging process of the battery, so as to improve the battery performance. The larger the derived deformation characteristic value, the greater the difference in expansion and contraction of the objects to be wound when subjected to the same force, and the more likely it is that wrinkles and other problems will occur during the winding process, affecting the quality of the battery. The winding speed needs to be reduced to keep the battery interface flat and the current evenly distributed to avoid wavy deformation caused by inconsistent internal stress. In order to improve the safety and cycle life of the battery, the more specific contour segments of the winding needle, the more unstable the winding process of each object to be wound, the larger the protrusion feature, the sharper the sharp corners of the cross section of the winding needle, the greater the tension to be exerted on the object to be wound, and the winding speed is reduced to reduce defects such as bending, wrinkling and even breakage that may occur in the winding process. Therefore, the present invention provides data support by calculating the deformation tendency characterization value to divide the deformation tendency, and then, it is convenient to determine the specific parameters of the subsequent winding process, and then, the properties of the object to be wound mapped during the winding process of each object to be wound on the winding needle are digitized, and when the deformation tendency is a strong deformation tendency, the winding speed is adjusted according to the discrete difference values ​​of the forces on different winding wheels when the object to be wound covers the specific contour segment. While improving the quality of the wound battery cell, the production efficiency of the wound battery cell is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of the steps of the variable diameter winding method of a lithium-ion battery cell according to an embodiment of the invention;

[0045] Figure 2 A logical decision diagram for identifying unique contour segments for an embodiment of the invention;

[0046] Figure 3 A logical decision diagram for determining deformation tendency for an embodiment of the invention;

[0047] Figure 4 This is a logic decision diagram for controlling process parameters in a winding process based on a decision result of deformation tendency according to an embodiment of the invention. DETAILED DESCRIPTION

[0048] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0049] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0050] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0051] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "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 components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] See also Figure 1 , Figure 2 , Figure 3 as well as Figure 4 As shown, they are respectively a flow chart of the steps of the variable diameter winding method of the lithium ion battery cell according to the embodiment of the present invention, a logic determination diagram for identifying a specific contour segment, a logic determination diagram for determining a deformation tendency, and a logic determination diagram for controlling a process parameter in the winding process based on a determination result of the deformation tendency; the variable diameter winding method of the lithium ion battery cell according to the embodiment of the present invention comprises:

[0053] Step S1, after a plurality of objects to be wound overlap, a plurality of marking points arranged at equal intervals are set along the winding direction to perform a winding-derived deformation test, including winding the objects to be wound, obtaining a scanning image of the winding section where the marking points are located, so as to determine the relative displacement of a single marking point on the surface of different objects to be wound, and determining a derived deformation characteristic value according to the relative displacement of each marking point;

[0054] Step S2, obtaining a cross-sectional image of the winding needle, identifying a specific contour segment according to the curvature of different contour segments of the cross-sectional contour, determining the protrusion features of the specific contour segment, and calculating a deformation tendency characterization value based on the number of specific contour segments, the protrusion features and the derived deformation characteristic value;

[0055] Step S3, determining the deformation tendency according to the deformation tendency characterization value, and controlling the process parameters in the winding process based on the determination result, including:

[0056] Obtain discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process, determine whether it meets the stress diffusion standard, and adjust the winding speed;

[0057] Or, maintain the current winding speed.

[0058] Specifically, it can be understood that when the battery cell is wound, the material to be wound is usually four layers, including a positive electrode winding, a negative electrode winding, a positive electrode separator and a negative electrode separator, and the material to be wound needs to be wound into the battery cell.

[0059] Specifically, there is no limitation on the marking method of the marking points, and fluorescent marking can be performed by means of fluorescent dyes. It can be understood that in order to obtain the relative displacement of the marking points on each object to be wound on the winding surface, when marking is performed, the objects to be wound are in an overlapping state, and each marking point corresponds to an overlapping state, which will not be elaborated.

[0060] Specifically, there is no limitation on the specific method of obtaining the scanning image of the marking point, and it can be obtained through scanning technology. For example, a high-resolution X-ray fluoroscopic imaging detection device can be used to obtain the scanning image and determine the marking point. Of course, other methods can also be used. It is understandable that the setting method of the marking point must also be able to match the detection equipment so that the detection equipment can obtain the marking point. This will not be repeated.

[0061] Specifically, the specific equipment for winding the battery cells is not limited. It can be understood that the winding is usually required to include a number of winding wheels for respectively supplying each object to be wound, a variable diameter winding needle mechanism for fixing the winding needle and controlling the rotation of the winding needle, a finishing gluing mechanism for gluing and fixing the winding core after the winding is completed, and a unloading and conveying mechanism for automatically removing the winding core from the winding needle. This is the existing technology and will not be repeated here.

[0062] Specifically, the specific method for obtaining the force value of each winding wheel is not limited, and it can be obtained through a pressure sensor set in each wheel. This is a prior art and will not be described in detail.

[0063] Specifically, it can be understood that when adjusting the winding speed, the rotation speed of each winding wheel and winding needle is adjusted synchronously to reduce the tension fluctuation of the pole piece and the diaphragm during the winding process, avoid stretching of the diaphragm due to excessive tension or shrinkage of the diaphragm after winding is completed, thereby reducing deformation and damage to the internal structure of the battery, which will not be elaborated.

[0064] Specifically, the specific method for obtaining the cross-sectional profile is not limited, and the contour features of the winding needle in the cross-sectional image can be obtained by image processing. This is a prior art and will not be described in detail.

[0065] Specifically, a winding-derived deformation test is performed on each layer of the object to be wound to obtain the derived deformation characteristics of the object to be wound in a targeted manner, and the specific contour segment of the winding needle is determined to obtain the number and protrusion characteristics of the specific contour segments for the winding needle, and the subsequent winding process is determined according to the deformation tendency characterization value, and the discrete difference value of the force on each winding wheel when each object to be wound covers the specific contour segment of the winding needle during the winding process is obtained to determine whether it is in compliance with the adjustment of the winding speed, and the force condition of each object to be wound during the winding process is determined based on the discrete difference value of the force on each winding wheel, and the winding process is continuously monitored, and the influence of the different expansion and contraction rates of each object to be wound on the winding process of the battery cell is determined through the relative displacement, and the winding parameters are adjusted in a targeted manner, which effectively improves the winding efficiency of the battery cell.

[0066] Specifically, in step S1, the relative displacement of a single marking point on the surface of different objects to be wound is determined, and the process of determining the derived deformation characteristic value according to the relative displacement of each marking point includes:

[0067] Determine the coordinates of a single marking point on the surface of different objects to be wound based on the scanned image to solve the average distance between the coordinates, and determine the average distance as the relative displacement of the marking point;

[0068] The mean of the relative displacement of each marking point is calculated to obtain the derived deformation eigenvalue.

[0069] Specifically, in step S2, the process of identifying the specific contour segment according to the curvature of different contour segments of the cross-sectional contour includes:

[0070] Divide the cross-sectional profile into several profile segments and calculate the curvature of each profile segment;

[0071] For the curvature of a single contour segment, the average difference ratio between the curvature of the single contour segment and the curvature of the adjacent contour segments is calculated respectively;

[0072] If the average difference ratio is less than or equal to a predetermined difference ratio threshold, the contour segment is determined to be a non-specific contour segment;

[0073] If the average difference ratio is greater than a predetermined difference ratio threshold, the contour segment is determined to be a specific contour segment.

[0074] Specifically, the predetermined difference ratio threshold is selected within the interval [0.25, 0.5].

[0075] It can be understood that the difference ratio is the ratio of the difference between the curvature of a contour segment and the curvature of an adjacent contour segment to the curvature of the contour segment.

[0076] Specifically, there is no limitation on the division method of the contour segments, and the contour segments can be divided evenly and equidistantly. It can be understood that the specific contour segments can be captured and obtained, and no further details will be given.

[0077] Specifically, in step S2, the process of determining the protrusion features of the specific contour segment includes:

[0078] For a single unique contour segment, a connecting line is drawn between its two end points to obtain a standard segment for the single unique contour segment;

[0079] The distance between the unique contour segment and the standard segment is obtained, and the maximum value among the distances is determined as the protrusion feature for the single unique contour segment.

[0080] Specifically, in step S2, the deformation tendency characterization value is calculated according to formula (1):

[0081]

[0082] Wherein, B is the deformation tendency characterization value, n represents the number of specific contour segments, i=1,2,3...,n, Li is the protrusion feature of the i-th specific contour segment, C is the derived deformation feature value, n0 is the mean value of the number of specific contour segments corresponding to each winding needle in history, L0 is the mean value of the protrusion features of each winding needle in history, C0 is the mean value of the derived deformation feature values ​​corresponding to the historical objects to be wound, α is the specific number weight coefficient, β is the protrusion number weight coefficient, and γ is the derived deformation weight coefficient.

[0083] It can be understood that the historical information is a number of data collected during the historical winding process of a number of battery cells, which will not be described in detail here.

[0084] Specifically, α is 0.47, β is 0.23, and γ is 0.3.

[0085] Specifically, the deformation tendency characterization value is calculated and determined by the relative displacement of the object to be wound on the surface of different objects to be wound, the number of specific contour segments of the cross-sectional contour of the winding needle and the protrusion characteristics. Different objects to be wound have different expansion and contraction rates, and winding needles of different shapes apply different tensions to the objects to be wound during the winding process. A lower winding speed is required during the winding process to reduce the uneven internal stress caused by the inconsistent expansion and contraction of the objects to be wound during the charging and discharging process of the battery, so as to improve the battery performance. The larger the derived deformation characteristic value, the greater the difference in expansion and contraction of the objects to be wound when subjected to the same force, and the more likely it is that wrinkles and other problems will occur during the winding process, affecting the quality of the battery. The winding speed needs to be reduced to keep the battery interface flat and the current evenly distributed to avoid wavy deformation caused by inconsistent internal stress. In order to improve the safety and cycle life of the battery, the more specific contour segments of the winding needle, the more unstable the winding process of each object to be wound, the larger the protrusion feature, the sharper the sharp corners of the cross section of the winding needle, the greater the tension to be exerted on the object to be wound, and the winding speed is reduced to reduce defects such as bending, wrinkling and even breakage that may occur in the winding process. Therefore, the present invention provides data support by calculating the deformation tendency characterization value to divide the deformation tendency, and then, it is convenient to determine the specific parameters of the subsequent winding process, and then, the properties of the object to be wound mapped during the winding process of each object to be wound on the winding needle are digitized, and when the deformation tendency is a strong deformation tendency, the winding speed is adjusted according to the discrete difference values ​​of the forces on different winding wheels when the object to be wound covers the specific contour segment. While improving the quality of the wound battery cell, the production efficiency of the wound battery cell is further improved.

[0086] Specifically, in step S3, the process of determining the deformation tendency according to the deformation tendency characterization value includes:

[0087] If the deformation tendency representation value is less than or equal to the preset deformation tendency representation value, it is classified as a weak deformation tendency category;

[0088] If the deformation tendency characterization value is greater than the preset deformation tendency characterization value, it is classified into a strong deformation tendency category.

[0089] Specifically, the preset deformation tendency characterization value B0 is selected within the interval [1.2, 1.35].

[0090] Specifically, in step S3, the process of controlling the process parameters in the winding process based on the determination result of the deformation tendency includes:

[0091] If the object to be wound is of the type with weak deformation tendency, the winding is completed by maintaining the current winding speed;

[0092] If the object to be wound is of the strong deformation tendency category, the discrete difference values ​​of the forces on different winding wheels when the object to be wound covers the specific contour segment during the winding process are obtained to determine whether it meets the stress diffusion standard so as to adjust the winding speed.

[0093] Specifically, in step S3, the process of obtaining the discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process is as follows:

[0094] The variance of the force values ​​of each winding wheel is calculated and the variance is determined as a discrete difference value.

[0095] Specifically, in step S3, the process of determining whether the stress diffusion standard is met includes:

[0096] If the discrete difference value is less than or equal to the preset discrete difference value, it is determined that the stress diffusion standard is met;

[0097] If the discrete difference value is greater than the preset discrete difference value, it is determined that the stress diffusion standard is not met.

[0098] Specifically, the preset discrete difference value Y0 is selected within the interval [1.17S0, 1.4S0], the discrete difference standard value S0 is pre-recorded, the discrete difference values ​​corresponding to each winding wheel in the historical winding process are obtained, and the mean of the discrete difference values ​​is used to determine the discrete difference standard value S0.

[0099] Specifically, in step S3, the winding speed is determined based on the discrete difference value, wherein:

[0100] The determined winding speed is negatively correlated with the discrete difference value.

[0101] In this embodiment, optionally,

[0102] The discrete difference value Y is compared with the preset first preset difference comparison threshold value Y1 and the second preset difference comparison threshold value Y2,

[0103] If Y≤Y1, the winding speed is determined as the first winding speed V1, and V1=0.9V0;

[0104] If Y1<Y≤Y2, the winding speed is determined as the second winding speed V2, and V2=0.8V0 is set;

[0105] If Y>Y2, the winding speed is determined as the third winding speed V3, and V3=0.7V0 is set;

[0106] Among them, V0 is the initial winding speed, Y1=1.2Y0, Y2=1.5Y0.

[0107] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A lithium-ion battery cell variable diameter winding method, characterized in that: include: Step S1, after a plurality of objects to be wound overlap, a plurality of marking points arranged at equal intervals are set along the winding direction to perform a winding-derived deformation test, including winding the objects to be wound, obtaining a scanning image of the winding section where the marking points are located, so as to determine the relative displacement of a single marking point on the surface of different objects to be wound, and determining a derived deformation characteristic value according to the relative displacement of each marking point; Step S2, obtaining a cross-sectional image of the winding needle, identifying a specific contour segment according to the curvature of different contour segments of the cross-sectional contour, determining the protrusion features of the specific contour segment, and calculating a deformation tendency characterization value based on the number of specific contour segments, the protrusion features and the derived deformation characteristic value; Step S3, determining the deformation tendency according to the deformation tendency characterization value, and controlling the process parameters in the winding process based on the determination result, including: Obtain discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process, determine whether it meets the stress diffusion standard, and adjust the winding speed; Or, maintain the current winding speed; In step S1, the relative displacement of a single marking point on the surface of different objects to be wound is determined, and the process of determining the derived deformation characteristic value according to the relative displacement of each marking point includes: Determine the coordinates of a single marking point on the surface of different objects to be wound based on the scanned image to solve the average distance between the coordinates, and determine the average distance as the relative displacement of the marking point; Calculate the mean of the relative displacement of each marking point to obtain the derived deformation eigenvalue; In step S2, the process of identifying the specific contour segment according to the curvature of different contour segments of the cross-sectional contour includes: Divide the cross-sectional profile into several profile segments and calculate the curvature of each profile segment; For the curvature of a single contour segment, the average difference ratio between the curvature of the single contour segment and the curvature of the adjacent contour segments is calculated respectively; If the average difference ratio is less than or equal to a predetermined difference ratio threshold, the contour segment is determined to be a non-specific contour segment; If the average difference ratio is greater than a predetermined difference ratio threshold, the contour segment is determined to be a specific contour segment; In step S2, the process of determining the protrusion features of the unique contour segment includes: For a single unique contour segment, a connecting line is drawn between its two end points to obtain a standard segment for the single unique contour segment; Obtaining the distance between the unique contour segment and the standard segment, and determining the maximum value among the distances as the protrusion feature for the single unique contour segment; In step S2, the deformation tendency characterization value is calculated according to formula (1): Wherein, B is the deformation tendency characterization value, n represents the number of specific contour segments, i=1,2,3...,n, Li is the protrusion feature of the i-th specific contour segment, C is the derived deformation feature value, n0 is the mean value of the number of specific contour segments corresponding to each winding needle in history, L0 is the mean value of the protrusion features of each winding needle in history, C0 is the mean value of the derived deformation feature values ​​corresponding to the historical objects to be wound, α is the specific number weight coefficient, β is the protrusion number weight coefficient, γ is the derived deformation weight coefficient, α is 0.47, β is 0.23, γ is 0.3; In step S3, the process of determining the deformation tendency according to the deformation tendency characterization value includes: If the deformation tendency representation value is less than or equal to the preset deformation tendency representation value, it is classified as a weak deformation tendency category; If the deformation tendency representation value is greater than the preset deformation tendency representation value, the strong deformation tendency category is classified; In step S3, the process of controlling the process parameters in the winding process based on the determination result of the deformation tendency includes: If the object to be wound is of the type with weak deformation tendency, the winding is completed by maintaining the current winding speed; If the object to be wound is of the strong deformation tendency category, the discrete difference values ​​of the forces on different winding wheels when the object to be wound covers the specific contour segment during the winding process are obtained to determine whether it meets the stress diffusion standard so as to adjust the winding speed.

2. The lithium-ion battery core variable diameter winding method according to claim 1, characterized in that: In step S3, the process of obtaining the discrete difference values ​​of the forces on different winding wheels when the winding object covers the specific contour segment during the winding process is as follows: The variance of the force values ​​of each winding wheel is calculated and the variance is determined as a discrete difference value.

3. The method for reducing the diameter of a lithium-ion battery cell according to claim 2, characterized in that: In step S3, the process of determining whether the stress diffusion standard is met includes: If the discrete difference value is less than or equal to the preset discrete difference value, it is determined that the stress diffusion standard is met; If the discrete difference value is greater than the preset discrete difference value, it is determined that the stress diffusion standard is not met.

4. The lithium-ion battery cell variable diameter winding method according to claim 1, characterized in that: In step S3, the winding speed is determined based on the discrete difference value, wherein: The determined winding speed is negatively correlated with the discrete difference value.

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