Method for preparing electrode sheet for wound battery cell and wound battery cell

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses a method for preparing an electrode sheet for a wound cell and a wound cell. The method comprises: S1, preparing positive and negative electrode slurries respectively; S2, coating the positive and negative electrode slurries on both sides of the positive and negative electrode current collectors respectively; S3, calculating the N / P value of the flat area of the wound cell under uniform coating; S4, calculating the N / P value of the corner area of the wound cell under uniform coating; calculating the difference between the N / P value of the corner area of the wound cell and the N / P value of the flat area of the wound cell to determine a compensation value; and using a laser cleaning process to remove the active material in the corresponding corner area according to the compensation value. Through the technical solution of the present invention, the N / P value of the corner area is made more reasonable, the lithium deposition phenomenon in the corner is improved, and a coating process is omitted, thereby improving production efficiency. The invention can be applied to wound cells of the same design and different widths, and has greater versatility and flexibility.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for preparing a pole piece for a wound-type battery cell and the wound-type battery cell. Background Art

[0002] Due to the rise of emerging electronic products such as tablets and laptops, lithium batteries such as 3C batteries have gradually developed towards large capacity, high rate, and flexible batteries, and the performance requirements for 3C lithium batteries such as safety, reliability, and service life are becoming increasingly higher.

[0003] The coating thickness of all areas on the pole piece in the wound lithium-ion battery is consistent, resulting in the N / P value of the corner arc area being smaller than that of the flat area. Moreover, the corner arc area is subjected to poor stress during the formation stage, and the contact between the pole pieces is poor. During the cycle, the corners are prone to high ion transfer resistance due to insufficient lithium insertion space and poor contact between the pole pieces. In the later stage of the cycle, this area is very prone to lithium deposition. As lithium deposition intensifies the side reactions, the battery cell cycle fails. In the related art, the N / P ratio of the outer ring of the negative electrode is usually increased by designing a "yin-yang surface" to improve corner lithium deposition and thus improve the cycle, or, as in the patent document CN115084428A, the corner compensation area of the pole piece is first coated by extrusion coating, and then a second layer of continuous coating is performed. The two layers of coating slurry are required to be consistent and there is no gap between the coated pole pieces. The following technical defects exist:

[0004] (1) The design of the “yin and yang sides” comes at the expense of the energy density of the battery cell. The weight of the negative electrode coating on one side increases, and the overall thickness of the battery cell increases.

[0005] (2) The extrusion coating method is used to first coat the corner compensation area of the electrode, and then the second layer of continuous coating is performed. Each model needs to be coated twice, which has low production efficiency and serious waste of slurry. Summary of the Invention

[0006] In view of this, it is necessary to provide a method for preparing electrode sheets for wound battery cells, positive and negative electrode sheets for wound battery cells, and wound battery cells. The N / P value of the flat area is used as a reference to calculate the N / P compensation value of the corner area, and the active material layer in the corresponding corner area of the positive electrode sheet or the negative electrode sheet is compensated through a laser cleaning process, so that the N / P value of the corner area is more reasonable, the lithium plating phenomenon at the corner is improved, and one coating process is omitted, thereby improving production efficiency. It can be applied to wound battery cells of the same design and different widths, and has greater versatility and flexibility.

[0007] To achieve the above object, the present invention adopts the following technical solution: a method for preparing an electrode sheet for a wound battery cell, comprising the following steps:

[0008] S1, prepare positive electrode slurry and negative electrode slurry respectively, wherein the weight percentage of active material in the positive electrode slurry is W c , the gram capacity of the active material in the positive electrode slurry is C c The weight percentage of active material in the negative electrode slurry is W a , the gram capacity of the active material in the negative electrode slurry is C a ;

[0009] S2, the positive electrode slurry and the negative electrode slurry are coated on both sides of the positive electrode collector and the negative electrode collector respectively, wherein the density of the positive electrode collector coating surface is ρ c , the density of the negative electrode current collector coating surface is ρ a ;

[0010] S3, calculate the N / P value of the flat area of the wound cell under uniform coating, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c );

[0011] S4, calculate the N / P value of the corner area of the wound cell under uniform coating, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i It is represented by the arc radius of the positive electrode sheet of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n;

[0012] S5, calculating the difference between the N / P value of the corner area of the wound battery cell and the N / P value of the flat area of the wound battery cell to determine a compensation value;

[0013] S6, removing the active material in the corresponding corner area using a laser cleaning process according to the compensation value.

[0014] Preferably, according to the compensation value, a laser cleaning process is used to remove the active material in the corresponding corner area, including the following steps: if the positive electrode sheet in the corner area covers the negative electrode sheet, a laser cleaning process is used to physically remove the active material in the corner area corresponding to the positive electrode sheet according to the compensation value.

[0015] Preferably, the laser cleaning process for physically removing the active material in the corresponding corner area of the positive electrode sheet comprises the following steps:

[0016] determining a target area density of the first active material in a corresponding corner area of the positive electrode sheet according to the compensation value;

[0017] Determine the first positive electrode sheet laser cleaning process parameters according to the target surface density of the first active material, and perform a first laser cleaning to remove the active material in the corresponding corner area of the positive electrode sheet according to the first positive electrode sheet laser cleaning process parameters. The first positive electrode sheet laser cleaning process parameters include: power 4kW to 5kW, speed 11000mm / s to 15000mm / s, frequency 100kHz to 200kHz, unwinding tension 30N to 90N, rewinding tension 60N to 120N, and tape speed 400mm / s to 900mm / s.

[0018] The positive electrode sheet after the first laser cleaning is weighed and visually observed. Based on the results of the first laser cleaning, the second positive electrode sheet laser cleaning process parameters are determined. According to the second positive electrode sheet laser cleaning process parameters, the active material in the corresponding corner area of the positive electrode sheet is laser cleaned and removed for a second time. The second positive electrode sheet laser cleaning process parameters include: power of 4kW~5kW, speed of 14000mm / s~18000mm / s, frequency of 400kHz~600Khz, unwinding tension of 30N~90N, winding tension of 60N~120N, and tape speed of 400mm / s~900mm / s.

[0019] Preferably, a laser cleaning process is used to remove the active material in the corresponding corner area, and the following steps are also included: if the negative electrode sheet in the corner area covers the positive electrode sheet, a laser cleaning process is used to physically remove the active material in the corner area corresponding to the negative electrode sheet according to the compensation value.

[0020] Preferably, the laser cleaning process for physically removing the active material in the corner area of the negative electrode sheet includes the following steps:

[0021] determining a target area density of the second active material in a corresponding corner area of the negative electrode sheet according to the compensation value;

[0022] Determine the laser cleaning process parameters for the first negative electrode sheet according to the target surface density of the second active material, and perform a first laser cleaning to remove the active material in the corresponding corner area of the negative electrode sheet according to the first negative electrode sheet laser cleaning process parameters. The first negative electrode sheet laser cleaning process parameters include: power 7.2kW to 8kW, speed 11000mm / s to 15000mm / s, frequency 100kHz to 200kHz, unwinding tension 30N to 90N, rewinding tension 60N to 120N, and tape speed 400mm / s to 900mm / s.

[0023] The negative electrode sheet after the first laser cleaning is weighed and visually observed. Based on the results of the first laser cleaning, the second negative electrode sheet laser cleaning parameters are determined. According to the second negative electrode sheet laser cleaning process parameters, the active material in the corresponding corner area of the negative electrode sheet is laser cleaned and removed for the second time. The second negative electrode sheet laser cleaning process parameters include: power 1.6kW~2.4kW, speed 11000mm / s~15000mm / s, frequency 400kHz~600kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s.

[0024] Preferably, the active material in the positive electrode slurry is any one of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese oxide, or a combination of at least two thereof.

[0025] Preferably, the active material in the negative electrode slurry is any one of silicon material, mesocarbon microbeads, hard carbon, soft carbon and lithium metal, or a combination of at least two thereof.

[0026] A positive electrode sheet for a wound battery cell is prepared using the method for preparing an electrode sheet for a wound battery cell in the above-mentioned technical solution, comprising a positive electrode current collector, a first active material layer and a second active material layer respectively coated on both sides of the positive electrode current collector, wherein the first active material layer is distributed in high and low intervals, corresponding to the flat area and corner area of the wound battery cell, respectively.

[0027] A negative electrode sheet for a wound battery cell is prepared using the electrode sheet preparation method for a wound battery cell in the above-mentioned technical solution, comprising a negative electrode current collector, a third active material layer and a fourth active material layer respectively coated on both sides of the negative electrode current collector, wherein the fourth active material layer is distributed in high and low intervals, corresponding to the flat area and corner area of the wound battery cell, respectively.

[0028] A wound battery cell is formed by winding the positive electrode sheet for a wound battery cell and the negative electrode sheet for a wound battery cell in the above technical solution.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention calculates the N / P compensation value of the corner area based on the N / P value of the flat area, and compensates the active material layer in the corner area of the positive electrode sheet or the negative electrode sheet through a laser cleaning process, thereby making the N / P value of the corner area more reasonable, which can not only improve the lithium deposition phenomenon in the corner, but also save coating slurry.

[0031] (2) The coating process of the present invention is simpler, and compared with the prior art, one coating process is reduced, thereby greatly improving production efficiency.

[0032] (3) The present invention can adjust parameters according to the actual coating thickness and surface density, so as to make the N / P value of the corner area more reasonable and improve the performance of the wound battery cell.

[0033] (4) The same process parameters in the present invention can be applied to wound cells with the same surface density design and different widths, which is more versatile and flexible.

[0034] (5) The present invention can adjust parameters such as laser cleaning according to the actual coating thickness and surface density, thereby optimizing the N / P value, improving the performance of the wound battery cell, and further increasing the cycle life of the lithium battery. By adjusting the laser cleaning parameters for physical removal, the surface density of the positive and negative active materials can be changed, thereby achieving a more reasonable N / P value. The target surface density of the active material is further determined based on the calculated compensation value, which facilitates the adjustment of the laser cleaning parameters. The cleaning results are then confirmed by visual inspection, weighing, etc., and the laser cleaning process parameters are further adjusted to achieve the target cleaning effect and the effect of optimizing the N / P value.

[0035] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0037] Figure 1 A schematic flow chart of a method for preparing a wound-type battery cell electrode sheet according to an embodiment of the present invention is shown;

[0038] Figure 2 A schematic structural diagram of a positive electrode sheet for a wound battery cell according to an embodiment of the present invention is shown;

[0039] Figure 3 A schematic structural diagram of a negative electrode sheet for a wound battery cell according to an embodiment of the present invention is shown;

[0040] Figure 4A schematic structural diagram of a wound battery cell according to an embodiment of the present invention is shown;

[0041] Figure 5 A comparison chart of the cycle life of the wound battery cells obtained according to Example 3 of the present invention and Comparative Example 1 is shown;

[0042] Figure 6 The figure shows the cycle life comparison of the wound battery cells obtained according to Example 6 of the invention and Comparative Example 2.

[0043] in, Figures 2 to 4 The corresponding relationship between the reference numerals and components is as follows:

[0044] 202 positive electrode current collector, 204 first active material layer, 206 second active material layer, 302 negative electrode current collector, 304 third active material layer, 306 fourth active material layer, 402 flat area, 406 corner area. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further clearly and completely described below in conjunction with the embodiments of the present invention. It should be noted that the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] like Figure 1 As shown, the method for preparing a wound-type battery cell electrode sheet according to an embodiment of the present invention includes the following steps:

[0047] S102, prepare positive electrode slurry and negative electrode slurry respectively, wherein the weight percentage of active material in the positive electrode slurry is W c , the gram capacity of the active material in the positive electrode slurry is C c The weight percentage of active material in the negative electrode slurry is W a , the gram capacity of the active material in the negative electrode slurry is C a ; The positive electrode slurry and the negative electrode slurry can be prepared by dry or wet method,

[0048] S104, coating the positive electrode slurry and the negative electrode slurry on both sides of the positive electrode collector and the negative electrode collector respectively, wherein the density of the positive electrode collector coating surface is ρ c , the density of the negative electrode current collector coating surface is ρ a ; It can be coated by extrusion or transfer coating,

[0049] S106, calculating the N / P value of the flat area of the wound battery cell under uniform coating, recorded as (N / P)0, where (N / P)0=(ρ a *W a *C a ) / (ρ c *W c *C c );

[0050] S108, calculating the N / P value of the corner area of the wound battery cell under uniform coating, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i It is represented by the arc radius of the positive electrode sheet of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n;

[0051] S110, calculating the difference between the N / P value of the corner area of the wound battery cell and the N / P value of the flat area of the wound battery cell to determine a compensation value;

[0052] S112 , removing the active material in the corresponding corner area using a laser cleaning process according to the compensation value.

[0053] By calculating the N / P compensation value of the corner area based on the N / P value of the flat area, the active material layer in the corresponding corner area of the positive or negative electrode sheet is compensated through a laser cleaning process, thereby making the N / P value in the corner area more reasonable. This not only improves the lithium deposition phenomenon in the corner, but also saves coating slurry. The coating process is simpler and one coating process is eliminated compared to existing technologies, greatly improving production efficiency.

[0054] It's important to note that in a wound cell, the positive and negative electrodes have two contact surfaces between the layers. In the first contact surface, the positive electrode is outside the negative electrode, effectively enveloping the negative electrode. In the second contact surface, the negative electrode is outside the positive electrode, effectively enveloping the positive electrode. The N / P ratio is the ratio of the negative electrode's reversible capacity to the positive electrode's reversible capacity when viewed face-to-face.

[0055] For the outer ring of the negative electrode, the positive electrode covers the negative electrode. Due to the curvature relationship, the length of the positive electrode is longer than that of the negative electrode in the area where the positive and negative electrodes are facing each other. According to the normally designed N / P ratio, the actual N / P ratio is smaller than the designed value, and there is a risk of lithium plating. The present invention physically removes the active material layer in the corner area corresponding to the positive electrode here.

[0056] For the inner circle of the negative electrode, the negative electrode wraps the positive electrode. Due to the curvature relationship, the length of the negative electrode is longer than the positive electrode in the area where the positive and negative electrodes are facing each other. According to the normally designed N / P ratio, the actual N / P ratio is larger than the designed value, resulting in a waste of slurry materials, which is not conducive to improving the energy density. The present invention physically removes the active material layer in the corner area corresponding to the negative electrode here.

[0057] Example 1

[0058] Taking the specific model 506582 as an example, this model has 11 turns, the thickness of the isolation film is 9um, the thickness of the positive electrode sheet is 74um, the thickness of the negative electrode sheet is 91um, and the wound battery cell has a left-right symmetrical structure. Each turn has two corners, and the corner compensation value of the same turn is the same.

[0059] For the outer ring of the negative electrode, the positive electrode covers the negative electrode, and the active material in the corner area corresponding to the positive electrode is physically removed, including the following steps:

[0060] Calculate the N / P value of the flat area of the wound cell under uniform coating conditions, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c ), where ρ a Characterized by the density of the negative electrode current collector coating surface, W a Characterized by the weight percentage of active material in the negative electrode slurry, C a Characterized by the gram capacity of the active material in the negative electrode slurry, ρ c Characterized by the density of the positive electrode current collector coating surface, W c Characterized by the weight percentage of active material in the positive electrode slurry, C c It is characterized by the gram capacity of the active material in the positive electrode slurry, and the calculation results are shown in Table 1 below; it should be noted that the active material in the positive electrode slurry is any one or a combination of at least two of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese, and the active material in the negative electrode slurry is any one or a combination of at least two of silicon material, mesophase carbon microbeads, hard carbon, soft carbon and lithium metal.

[0061] Calculate the N / P value of the corner area of the wound cell under uniform coating conditions, recorded as (N / P) i , where (N / P)i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i Characterized by the arc radius of the positive electrode sheet in the i-th circle of the wound battery cell, (N / P) i It is characterized by the N / P value of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n, and the calculation results are shown in Table 1 below;

[0062] The difference between the N / P value of the corner area of the wound cell and the N / P value of the flat area of the wound cell was calculated to determine the compensation value. The calculation results are shown in Table 1 below.

[0063] According to the compensation value, a laser cleaning process is used to physically remove the active material in the corresponding corner area of the positive electrode sheet. The laser cleaning process parameters are determined according to the target surface density of the active material determined by the compensation value. According to a correspondence table between the compensation value and the target surface density of the active material established in advance through a large number of experimental studies, the target surface density of the active material is determined by the compensation value. According to the target surface density of the active material, the laser cleaning process parameters of the first positive electrode sheet are determined, including: power 4kW~5kW, speed 11000mm / s~15000mm / s, frequency 100kHz~200kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning is performed according to the laser cleaning process parameters of the first positive electrode sheet. The positive electrode sheet after the first laser cleaning is weighed and visually observed. According to the results of the first laser cleaning, the laser cleaning process parameters of the second positive electrode sheet are determined. The laser cleaning process parameters of the second positive electrode sheet include: power of 4kW to 5kW, speed of 14000mm / s to 18000mm / s, frequency of 400kHz to 600Khz, unwinding tension of 30N to 90N, winding tension of 60N to 120N, and tape speed of 400mm / s to 900mm / s. Laser cleaning and removal are continued according to the laser cleaning process parameters of the second positive electrode sheet, thereby obtaining the target positive electrode sheet. The structure of the positive electrode sheet is as follows Figure 2 As shown, it includes a positive electrode current collector 202, a first active material layer 204 and a second active material layer 206 coated on both sides of the positive electrode current collector 202, and the first active material layer 204 is distributed in high and low intervals, corresponding to the flat area 402 and the corner area 404 of the wound battery cell respectively.

[0064] Table 1 Compensation value calculation results of different turns of positive electrode

[0065] Number of laps N / P ratio Compensation value flat area 1.065 0.000 Lap 1 1.161 0.096 Lap 2 1.099 0.034 Lap 3 1.086 0.021 Lap 4 1.080 0.015 Lap 5 1.077 0.012 Lap 6 1.074 0.009 Lap 7 1.073 0.008 Lap 8 1.072 0.007 Lap 9 1.071 0.006 Lap 10 1.070 0.005 Lap 11 1.070 0.005

[0066] Example 2

[0067] Taking the specific model 506582 as an example, this model has 11 turns, the thickness of the isolation film is 9um, the thickness of the positive electrode sheet is 74um, the thickness of the negative electrode sheet is 91um, and the wound battery cell has a left-right symmetrical structure. Each turn has two corners, and the corner compensation value of the same turn is the same.

[0068] For the inner circle of the negative electrode, where the negative electrode covers the positive electrode, the active material in the corner area corresponding to the negative electrode is physically removed, including the following steps:

[0069] Calculate the N / P value of the flat area of the wound cell under uniform coating conditions, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c ), where ρ a Characterized by the density of the negative electrode current collector coating surface, W a Characterized by the weight percentage of active material in the negative electrode slurry, C a Characterized by the gram capacity of the active material in the negative electrode slurry, ρ c Characterized by the density of the positive electrode current collector coating surface, W c Characterized by the weight percentage of active material in the positive electrode slurry, C c Characterized by the gram capacity of the active material in the positive electrode slurry, the calculation results are shown in Table 2 below; it should be noted that the active material in the positive electrode slurry is any one or a combination of at least two of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese, and the active material in the negative electrode slurry is any one or a combination of at least two of silicon material, mesophase carbon microbeads, hard carbon, soft carbon and lithium metal.

[0070] Calculate the N / P value of the corner area of the wound cell under uniform coating conditions, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 iCharacterized by the arc radius of the positive electrode sheet in the i-th circle of the wound battery cell, (N / P) i It is characterized by the N / P value of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n, and the calculation results are shown in Table 2 below;

[0071] The difference between the N / P value of the corner area of the wound cell and the N / P value of the flat area of the wound cell was calculated to determine the compensation value. The calculation results are shown in Table 2 below.

[0072] According to the compensation value, a laser cleaning process is used to physically remove the active material in the corresponding corner area of the negative electrode sheet. The laser cleaning process parameters are determined according to the target surface density of the active material determined by the compensation value. According to a correspondence table between the compensation value and the target surface density of the active material established in advance through a large number of experimental studies, the target surface density of the active material is determined by the compensation value. According to the target surface density of the active material, the laser cleaning process parameters of the first negative electrode sheet are determined, including: power 7.2kW~8kW, speed 11000mm / s~15000mm / s, frequency 100kHz~200kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning is performed according to the laser cleaning process parameters of the first negative electrode sheet. The negative electrode sheet after the first laser cleaning is weighed and visually observed. According to the results of the first laser cleaning, the laser cleaning process parameters of the second negative electrode sheet are determined, including: power 1.6kW~2.4kW, speed 11000mm / s~15000mm / s, frequency 400kHz~600kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning and removal are continued according to the laser cleaning process parameters of the second negative electrode sheet, thereby obtaining the target negative electrode sheet. The structure of the negative electrode sheet is as follows Figure 3 As shown, it includes a negative electrode current collector 302, a third active material layer 304 and a fourth active material layer 306 coated on both sides of the negative electrode current collector 302, and the fourth active material layer 306 is distributed in high and low intervals, corresponding to the flat area 402 and the corner area 404 of the wound battery cell, respectively.

[0073] Table 2 Compensation value calculation results of different turns of negative electrode

[0074]

[0075]

[0076] Example 3

[0077] The target positive electrode sheet prepared in Example 1 and the target negative electrode sheet prepared in Example 2 are assembled to form a wound battery cell, such as Figure 4As shown, there is a flat area 402 in the middle and symmetrical corner areas 404 on both sides.

[0078] Example 4

[0079] Taking the specific model 496488 as an example, this model has 9 turns, the isolation film thickness is 8um, the positive electrode sheet thickness is 91um, the negative electrode sheet thickness is 110um, and the wound battery cell has a left-right symmetrical structure. Each turn has two corners, and the corner compensation value of the same turn is the same.

[0080] For the outer ring of the negative electrode, the positive electrode covers the negative electrode, and the active material in the corner area corresponding to the positive electrode is physically removed, including the following steps:

[0081] Calculate the N / P value of the flat area of the wound cell under uniform coating conditions, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c ), where ρ a Characterized by the density of the negative electrode current collector coating surface, W a Characterized by the weight percentage of active material in the negative electrode slurry, C a Characterized by the gram capacity of the active material in the negative electrode slurry, ρ c Characterized by the density of the positive electrode current collector coating surface, W c Characterized by the weight percentage of active material in the positive electrode slurry, C c It is characterized by the gram capacity of the active material in the positive electrode slurry, and the calculation results are shown in Table 1 below; it should be noted that the active material in the positive electrode slurry is any one or a combination of at least two of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese, and the active material in the negative electrode slurry is any one or a combination of at least two of silicon material, mesophase carbon microbeads, hard carbon, soft carbon and lithium metal.

[0082] Calculate the N / P value of the corner area of the wound cell under uniform coating conditions, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i Characterized by the arc radius of the positive electrode sheet in the i-th circle of the wound battery cell, (N / P)i It is characterized by the N / P value of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n, and the calculation results are shown in Table 1 below;

[0083] The difference between the N / P value of the corner area of the wound cell and the N / P value of the flat area of the wound cell was calculated to determine the compensation value. The calculation results are shown in Table 3 below.

[0084] According to the compensation value, the laser cleaning process parameters are determined according to the target surface density of the active material determined by the compensation value. According to a correspondence table between the compensation value and the target surface density of the active material established in advance through a large number of experimental studies, the target surface density of the active material is determined by the compensation value. According to the target surface density of the active material, the laser cleaning process parameters of the first positive electrode sheet are determined, including: power 4kW~5kW, speed 11000mm / s~15000mm / s, frequency 100kHz~200kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning is performed according to the laser cleaning process parameters of the first positive electrode sheet. The positive electrode sheet after the first laser cleaning is weighed and visually observed. Based on the results of the first laser cleaning, the laser cleaning process parameters of the second positive electrode sheet are determined, including: power of 4kW to 5kW, speed of 14000mm / s to 18000mm / s, frequency of 400kHz to 600Khz, unwinding tension of 30N to 90N, winding tension of 60N to 120N, and tape speed of 400mm / s to 900mm / s. Laser cleaning and removal are continued according to the laser cleaning process parameters of the second positive electrode sheet to obtain the target positive electrode sheet. The structure of the positive electrode sheet is as follows: Figure 2 As shown, it includes a positive electrode current collector 202, a first active material layer 204 and a second active material layer 206 coated on both sides of the positive electrode current collector 202, and the first active material layer 204 is distributed in high and low intervals, corresponding to the flat area 402 and the corner area 404 of the wound battery cell respectively.

[0085] Table 3 Compensation value calculation results of different number of positive electrode turns

[0086]

[0087] Example 5

[0088] Taking the specific model 496488 as an example, this model has 9 turns, the isolation film thickness is 8um, the positive electrode sheet thickness is 91um, the negative electrode sheet thickness is 110um, and the wound battery cell has a left-right symmetrical structure. Each turn has two corners, and the corner compensation value of the same turn is the same.

[0089] For the inner circle of the negative electrode, where the negative electrode covers the positive electrode, the active material in the corner area corresponding to the negative electrode is physically removed, including the following steps:

[0090] Calculate the N / P value of the flat area of the wound cell under uniform coating conditions, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c ), where ρ a Characterized by the density of the negative electrode current collector coating surface, W a Characterized by the weight percentage of active material in the negative electrode slurry, C a Characterized by the gram capacity of the active material in the negative electrode slurry, ρ c Characterized by the density of the positive electrode current collector coating surface, W c Characterized by the weight percentage of active material in the positive electrode slurry, C c Characterized by the gram capacity of the active material in the positive electrode slurry, the calculation results are shown in Table 2 below; it should be noted that the active material in the positive electrode slurry is any one or a combination of at least two of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese, and the active material in the negative electrode slurry is any one or a combination of at least two of silicon material, mesophase carbon microbeads, hard carbon, soft carbon and lithium metal.

[0091] Calculate the N / P value of the corner area of the wound cell under uniform coating conditions, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i Characterized by the arc radius of the positive electrode sheet in the i-th circle of the wound battery cell, (N / P) i It is characterized by the N / P value of the i-th circle of the wound battery cell, i = 1, 2, 3, .... n, and the calculation results are shown in Table 2 below;

[0092] The difference between the N / P value of the corner area of the wound cell and the N / P value of the flat area of the wound cell was calculated to determine the compensation value. The calculation results are shown in Table 4 below.

[0093] According to the compensation value, a laser cleaning process is used to physically remove the active material in the corresponding corner area of the negative electrode sheet. The laser cleaning process parameters are determined according to the target surface density of the active material determined by the compensation value. According to a correspondence table between the compensation value and the target surface density of the active material established in advance through a large number of experimental studies, the target surface density of the active material is determined by the compensation value. According to the target surface density of the active material, the laser cleaning process parameters of the first negative electrode sheet are determined, including: power 7.2kW~8kW, speed 11000mm / s~15000mm / s, frequency 100kHz~200kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning is performed according to the first negative electrode sheet laser cleaning process parameters. The negative electrode sheet after the first laser cleaning is weighed and visually observed. Based on the first laser cleaning results, the second negative electrode sheet laser cleaning process parameters are determined: power 1.6kW~2.4kW, speed 11000mm / s~15000mm / s, frequency 400kHz~600kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s. Laser cleaning and removal are continued according to the second negative electrode sheet laser cleaning process parameters, thereby obtaining the target negative electrode sheet. The structure of the negative electrode sheet is as follows: Figure 3 As shown, it includes a negative electrode current collector 302, a third active material layer 304 and a fourth active material layer 306 coated on both sides of the negative electrode current collector 302, and the fourth active material layer 306 is distributed in high and low intervals, corresponding to the flat area 402 and the corner area 404 of the wound battery cell, respectively.

[0094] Table 4 Compensation value calculation results of different turns of negative electrode

[0095]

[0096]

[0097] Example 6

[0098] The target positive electrode sheet prepared in Example 4 and the target negative electrode sheet prepared in Example 5 are assembled to form a wound battery cell, such as Figure 4 As shown, there is a flat area 402 in the middle and symmetrical corner areas 404 on both sides.

[0099] Comparative Example 1

[0100] The same positive electrode slurry as that in Example 1 was applied to both sides of the positive electrode current collector according to the set value, without any compensation treatment on the corner area of the positive electrode sheet, to obtain the target positive electrode sheet;

[0101] The same negative electrode slurry as in Example 2 was applied to both sides of the negative electrode current collector according to the set value, without any compensation treatment on the corner area of the negative electrode sheet, to obtain the target negative electrode sheet;

[0102] Assemble the above target positive electrode sheet and target negative electrode sheet into a wound battery cell.

[0103] Comparative Example 2

[0104] The same positive electrode slurry as that in Example 4 was applied to both sides of the positive electrode current collector according to the set value, without any compensation treatment on the corner area of the positive electrode sheet, to obtain the target positive electrode sheet;

[0105] The same negative electrode slurry as that in Example 5 was applied to both sides of the negative electrode current collector according to the set value, without any compensation treatment on the corner area of the negative electrode sheet, to obtain the target negative electrode sheet;

[0106] Assemble the above target positive electrode sheet and target negative electrode sheet into a wound battery cell.

[0107] The wound cells obtained in Example 3 and Comparative Example 1 were subjected to cycle performance tests, and the test results are shown in FIG. Figure 5 As shown by Figure 5 It can be seen that the wound battery cell prepared in Example 3 of the present invention has a longer cycle life. Although the difference is not obvious in the early stage of the cycle, in the later stage of the cycle, the cycle performance of Example 3 of the present invention is significantly better than that of Comparative Example 1. It can be seen that in Comparative Example 1, in the later stage of the cycle, lithium plating at the corners becomes more and more serious, and the contact effect between the pole pieces becomes worse and worse, which easily causes the battery cell cycle failure. However, Example 3 of the present invention significantly improves the problem of lithium plating at the corners, and the contact effect between the pole pieces is better, the cycle period is longer, and the capacity retention rate can still reach about 95% after 500 cycles.

[0108] The wound cells obtained in Example 6 and Comparative Example 2 were subjected to cycle performance tests. The test results are shown in FIG. Figure 6 As shown by Figure 6 It can be seen that the wound battery cell prepared in Example 6 of the present invention has a longer cycle life. Although the difference is not obvious in the early stage of the cycle, in the later stage of the cycle, the cycle performance of Example 6 of the present invention is significantly better than that of Comparative Example 2. It can be seen that in Comparative Example 2, in the later stage of the cycle, lithium plating at the corners becomes more and more serious, and the contact effect between the pole pieces becomes worse and worse, which easily causes the battery cell cycle failure. However, Example 6 of the present invention significantly improves the problem of lithium plating at the corners, and the contact effect between the pole pieces is better, the cycle period is longer, and the capacity retention rate can still reach about 85% after 500 cycles.

[0109] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a pole piece for a wound battery cell, characterized in that: The following steps are involved: S1, prepare positive electrode slurry and negative electrode slurry respectively, wherein the weight percentage of active material in the positive electrode slurry is W c , the gram capacity of the active material in the positive electrode slurry is C c The weight percentage of active material in the negative electrode slurry is W a , the gram capacity of the active material in the negative electrode slurry is C a ; S2, the positive electrode slurry and the negative electrode slurry are coated on both sides of the positive electrode collector and the negative electrode collector respectively, wherein the density of the positive electrode collector coating surface is ρ c , the density of the negative electrode current collector coating surface is ρ a ; S3, calculate the N / P value of the flat area of the wound cell under uniform coating, recorded as (N / P)0, where (N / P)0 = (ρ a *W a *C a ) / (ρ c *W c *C c ); S4, calculate the N / P value of the corner area of the wound cell under uniform coating, recorded as (N / P) i , where (N / P) i =(ρ a *W a *C a *π*R1 i ) / (ρ c *W c *C c *π*R2 i ), R1 i Characterized by the arc radius of the negative electrode sheet of the i-th circle of the wound battery cell, R2 i Characterized by the arc radius of the positive electrode sheet in the i-th circle of the wound battery cell, (N / P) i Characterized by the N / P value of the i-th turn of the wound cell, i = 1, 2, 3, .... n; S5, calculating the difference between the N / P value of the corner area of the wound battery cell and the N / P value of the flat area of the wound battery cell to determine a compensation value; S6, removing the active material in the corresponding corner area using a laser cleaning process according to the compensation value.

2. The method for preparing a pole piece for a wound battery cell according to claim 1, wherein: According to the compensation value, a laser cleaning process is used to remove the active material in the corresponding corner area, including the following steps: If the positive electrode sheet in the corner area covers the negative electrode sheet, a laser cleaning process is used to physically remove the active material in the corresponding corner area of the positive electrode sheet according to the compensation value.

3. The method for preparing a pole piece for a wound battery cell according to claim 2, wherein: The laser cleaning process is used to physically remove the active material in the corresponding corner area of the positive electrode sheet, including the following steps: determining a target area density of the first active material in a corresponding corner area of the positive electrode sheet according to the compensation value; Determine the first positive electrode sheet laser cleaning process parameters according to the target surface density of the first active material, and perform a first laser cleaning to remove the active material in the corresponding corner area of the positive electrode sheet according to the first positive electrode sheet laser cleaning process parameters. The first positive electrode sheet laser cleaning process parameters include: power 4kW to 5kW, speed 11000mm / s to 15000mm / s, frequency 100kHz to 200kHz, unwinding tension 30N to 90N, rewinding tension 60N to 120N, and tape speed 400mm / s to 900mm / s. The positive electrode sheet after the first laser cleaning is weighed and visually observed. Based on the results of the first laser cleaning, the second positive electrode sheet laser cleaning process parameters are determined. According to the second positive electrode sheet laser cleaning process parameters, the active material in the corresponding corner area of the positive electrode sheet is laser cleaned and removed for a second time. The second positive electrode sheet laser cleaning process parameters include: power of 4kW~5kW, speed of 14000mm / s~18000mm / s, frequency of 400kHz~600Khz, unwinding tension of 30N~90N, winding tension of 60N~120N, and tape speed of 400mm / s~900mm / s.

4. The method for preparing a wound-type battery cell electrode sheet according to any one of claims 1 to 3, characterized in that: The laser cleaning process is used to remove the active material in the corresponding corner area, and further includes the following steps: If the negative electrode sheet in the corner area covers the positive electrode sheet, a laser cleaning process is used to physically remove the active material in the corner area corresponding to the negative electrode sheet according to the compensation value.

5. The method for preparing a pole piece for a wound battery cell according to claim 4, wherein: The laser cleaning process for physically removing the active material from the corner area of the negative electrode sheet includes the following steps: determining a target area density of the second active material in a corresponding corner area of the negative electrode sheet according to the compensation value; Determine the laser cleaning process parameters for the first negative electrode sheet according to the target surface density of the second active material, and perform a first laser cleaning to remove the active material in the corresponding corner area of the negative electrode sheet according to the first negative electrode sheet laser cleaning process parameters. The first negative electrode sheet laser cleaning process parameters include: power 7.2kW to 8kW, speed 11000mm / s to 15000mm / s, frequency 100kHz to 200kHz, unwinding tension 30N to 90N, rewinding tension 60N to 120N, and tape speed 400mm / s to 900mm / s. The negative electrode sheet after the first laser cleaning is weighed and visually observed. Based on the results of the first laser cleaning, the second negative electrode sheet laser cleaning parameters are determined. According to the second negative electrode sheet laser cleaning process parameters, the active material in the corresponding corner area of the negative electrode sheet is laser cleaned and removed for the second time. The second negative electrode sheet laser cleaning process parameters include: power 1.6kW~2.4kW, speed 11000mm / s~15000mm / s, frequency 400kHz~600kHz, unwinding tension 30N~90N, winding tension 60N~120N, and tape speed 400mm / s~900mm / s.

6. The method for preparing a pole piece for a wound battery cell according to claim 5, characterized in that: The active material in the positive electrode slurry is any one of lithium cobalt oxide, ternary material, lithium iron phosphate, lithium manganese oxide and lithium-rich manganese oxide, or a combination of at least two thereof.

7. The method for preparing a wound-type battery cell electrode according to claim 6, wherein: The active material in the negative electrode slurry is any one of silicon material, mesophase carbon microbeads, hard carbon, soft carbon and lithium metal, or a combination of at least two of them.

8. A positive electrode sheet for a wound battery cell, characterized in that: The electrode sheet is prepared by the method for preparing a wound battery cell according to any one of claims 1 to 7, and includes a positive electrode current collector, a first active material layer and a second active material layer respectively coated on both sides of the positive electrode current collector, and the first active material layer is distributed in high and low intervals, corresponding to the flat area and corner area of the wound battery cell respectively.

9. A negative electrode sheet for a wound battery cell, characterized in that: The electrode sheet is prepared by the method for preparing a wound battery cell according to any one of claims 1 to 7, and includes a negative electrode current collector, a third active material layer and a fourth active material layer respectively coated on both sides of the negative electrode current collector, and the fourth active material layer is distributed in high and low intervals, corresponding to the flat area and corner area of the wound battery cell respectively.

10. A wound battery cell, characterized in that: The positive electrode sheet for a wound battery cell according to claim 8 and the negative electrode sheet for a wound battery cell according to claim 9 are wound together.

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