Evaluation method and control method of winding tension

Abstract

The invention provides a winding tension evaluation method and a winding tension control method, and relates to the technical field of batteries. According to the method for evaluating the winding tension, provided by the invention, the evaluation of the layer gap is simplified and converted into the evaluation of the tab dislocation quantity, the difference between the layer gap and the tightness of the battery cell can be evaluated through the tab dislocation quantity, and the relationship between the tab dislocation quantity and the winding tension is further obtained according to the relationship between the layer gap and the winding tension; and the winding tension can be evaluated through the tab dislocation quantity. According to the control method of the winding tension provided by the invention, the winding tension is adjusted in real time to enable the layer gap to be the target layer gap by detecting the tab dislocation amount in the preparation process of the winding battery cell according to the relationship between the tab dislocation amount and the winding tension obtained by the evaluation method, so that the consistency of the layer gap of the battery cell is realized, and the improvement of the performance of the battery cell is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a winding tension evaluation method and a control method. Background Art

[0002] The wound battery cell is composed of a positive electrode sheet, a negative electrode sheet and a separator. During the winding process, the positive and negative electrode sheets and separators maintain the stability of the tape under a certain tension and control the tightness of the battery cell. If the tension is too large, the electrode sheet is easy to break during the winding process, and the electrode sheet is easy to be pulled to death, affecting the correction effect. At the same time, it will cause the battery cell to be too tight, the infiltration effect to deteriorate, the internal stress of the battery cell is too large, and the battery cell is deformed, thereby inducing performance deterioration; if the tension is too small, the battery cell is loose, it is easy to have poor core pulling, the gap between the battery cell layers is too large, the internal impedance increases, and the battery performance deteriorates. However, there is currently no effective evaluation and control method for winding tension.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The first object of the present invention is to provide a method for evaluating winding tension to solve the above technical problems.

[0005] The second object of the present invention is to provide a method for controlling winding tension to solve the above-mentioned technical problem.

[0006] In order to achieve the above objectives, the following technical solutions are adopted:

[0007] In a first aspect, the present invention provides a method for evaluating winding tension, comprising the following steps:

[0008] a. Confirm the target layer gap of the wound battery cell;

[0009] b. Conduct a single factor experiment on winding tension during the preparation of wound cells to obtain the relationship between winding tension and layer gap;

[0010] c. The relationship between the tab misalignment and the interlayer gap is: S1 = (n-1)*a1+(n-1)*(n-2)*π*(δ1-δ);

[0011] Among them, S1 is the misalignment of the tab between the nth and first turns of the wound cell; n is the number of turns of the wound cell; a1 is the misalignment of the tab between the second and first turns of the wound cell; π is the circumference of pi; δ1 is the layer gap when the tab misalignment is S1; δ is the target layer gap;

[0012] d. According to steps b and c, the relationship between the tab misalignment and the winding tension is obtained, and the winding tension is evaluated by detecting the tab misalignment during the preparation of the wound battery cell.

[0013] As a further technical solution, the winding tension includes the negative electrode sheet winding tension, the positive electrode sheet winding tension and the separator winding tension;

[0014] The winding tension of the negative electrode sheet, the winding tension of the positive electrode sheet and the winding tension of the separator are each independently 80-2000 gf.

[0015] As a further technical solution, the interlayer gap includes the negative electrode tension contribution layer gap, the positive electrode tension contribution layer gap and the separator tension contribution layer gap;

[0016] Interlayer gap = δa + δc + δs;

[0017] Among them, δa is the gap of the negative electrode tension contribution layer; δc is the gap of the positive electrode tension contribution layer; δs is the gap of the separator tension contribution layer.

[0018] As a further technical solution, the relationship between the winding tension and the layer gap is:

[0019] δa=λaln(Fa)+μa;

[0020] δc=λcln(Fc)+μc;

[0021] δs=λsln(Fs)+μs;

[0022] Among them, λa, λc, λs, μa, μc and μs are all constants; Fa is the winding tension of the negative electrode sheet; Fc is the winding tension of the positive electrode sheet; Fs is the winding tension of the separator;

[0023] According to the single-factor experimental results in step b, determine the values ​​of λa, λc, λs, μa, μc and μs.

[0024] As a further technical solution, in the process of preparing the wound battery cell in step b and step d, other preparation parameters except the winding tension are the same.

[0025] As a further technical solution, the other preparation parameters include the circumference of the winding needle, the thickness of the positive and negative electrode sheets, the thickness of the separator and the P roller pressure.

[0026] In a second aspect, the present invention provides a method for controlling winding tension. The relationship between the tab misalignment and the winding tension is obtained through the above-mentioned evaluation method. By detecting the tab misalignment during the preparation of the wound battery cell, the winding tension is adjusted in real time so that the layer gap is the target layer gap.

[0027] As a further technical solution, the deviation of the current layer gap from the target layer gap is evaluated according to the amount of tab misalignment;

[0028] If the interlayer gap is too large, increase the winding tension; if the interlayer gap is too small, reduce the winding tension.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The method for evaluating winding tension provided by the present invention simplifies the evaluation of layer gap and converts it into the evaluation of tab misalignment. The difference in layer gap and tightness of the battery cell can be evaluated through the tab misalignment. The relationship between the tab misalignment and the winding tension is further obtained based on the relationship between the layer gap and the winding tension. The winding tension can be evaluated through the tab misalignment.

[0031] The method for controlling winding tension provided by the present invention, based on the relationship between the tab misalignment and the winding tension obtained by the above-mentioned evaluation method, detects the tab misalignment in the process of preparing the wound battery cell, and adjusts the winding tension in real time so that the layer gap is the target layer gap, thereby achieving consistency in the battery cell layer gap, which is beneficial to improving the battery cell performance. DETAILED DESCRIPTION

[0032] The embodiments of the present invention will be described in detail below in conjunction with the embodiments and examples, but it will be appreciated by those skilled in the art that the following embodiments and examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified, proceed according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0033] In a first aspect, the present invention provides a method for evaluating winding tension, comprising the following steps:

[0034] a. Confirm the target layer gap of the wound battery cell;

[0035] b. Conduct a single factor experiment on winding tension during the preparation of wound cells to obtain the relationship between winding tension and layer gap;

[0036] c. From the second tab span (the distance from the previous tab to the next tab) to the second-to-last tab span, the tab span satisfies the trend of arithmetic progression, then:

[0037] When the tab misalignment is 0, the incremental value of the tab span is:

[0038] D = 2*π*(da+dc+2*ds+δ);

[0039] When the tab misalignment is S1, the incremental value of the tab span is:

[0040] D1=2*π*(da+dc+2*ds+δ1);

[0041] According to the first n-1 terms and formula of the arithmetic progression: S1 = (n-1)*a1 + (n-1)*(n-2) / 2*d, where d = D1-D;

[0042] Then, the relationship between the tab misalignment and the interlayer gap is:

[0043] S1=(n-1)*a1+(n-1)*(n-2)*π*(δ1-δ);

[0044] Among them, da is the thickness of the negative electrode sheet; dc is the thickness of the positive electrode sheet; ds is the thickness of the separator; S1 is the misalignment of the tab between the nth and first turns of the wound cell; n is the number of turns of the wound cell; a1 is the misalignment of the tab between the second and first turns of the wound cell; π is the circumference of pi; δ1 is the interlayer gap when the tab misalignment is S1; δ is the target interlayer gap;

[0045] d. According to steps b and c, the relationship between the tab misalignment and the winding tension is obtained, and the winding tension is evaluated by detecting the tab misalignment during the preparation of the wound battery cell.

[0046] The method for evaluating winding tension provided by the present invention simplifies the evaluation of layer gap and converts it into the evaluation of tab misalignment. The difference in layer gap and tightness of the battery cell can be evaluated through the tab misalignment. The relationship between the tab misalignment and the winding tension is further obtained based on the relationship between the layer gap and the winding tension. The winding tension can be evaluated through the tab misalignment.

[0047] In some optional embodiments, the winding tension includes a negative electrode sheet winding tension, a positive electrode sheet winding tension and a separator winding tension;

[0048] The winding tension of the negative electrode sheet, the winding tension of the positive electrode sheet and the winding tension of the separator are each independently 80-2000 gf. The winding tension is related to the control capability of the winding machine. Usually, the tension control range of the winding machine is 80-2000 gf.

[0049] In some optional embodiments, the interlayer gap includes a negative electrode tension contribution layer gap, a positive electrode tension contribution layer gap, and a separator tension contribution layer gap;

[0050] Interlayer gap = δa + δc + δs;

[0051] Among them, δa is the gap of the negative electrode tension contribution layer; δc is the gap of the positive electrode tension contribution layer; δs is the gap of the separator tension contribution layer.

[0052] In some optional embodiments, the relationship between the winding tension and the layer gap is:

[0053] δa=λaln(Fa)+μa;

[0054] δc=λcln(Fc)+μc;

[0055] δs=λsln(Fs)+μs;

[0056] Among them, λa, λc, λs, μa, μc and μs are all constants; Fa is the winding tension of the negative electrode sheet; Fc is the winding tension of the positive electrode sheet; Fs is the winding tension of the separator;

[0057] According to the single-factor experimental results in step b, determine the values ​​of λa, λc, λs, μa, μc and μs.

[0058] In some optional embodiments, during the preparation of the wound battery cell in step b and step d, other preparation parameters except the winding tension are the same.

[0059] Avoid differences in other preparation parameters that may affect the accuracy of the evaluation results.

[0060] In some optional embodiments, the other preparation parameters include the circumference of the winding needle, the thickness of the positive and negative electrode sheets, the thickness of the separator and the P roller pressure (there is a mechanism on the winding machine to emboss the surface of the positive electrode sheet, and the P roller pressure is the pressure for embossing the positive electrode surface).

[0061] In a second aspect, the present invention provides a method for controlling winding tension. The relationship between the tab misalignment and the winding tension is obtained through the above-mentioned evaluation method. By detecting the tab misalignment during the preparation of the wound battery cell, the winding tension is adjusted in real time so that the layer gap is the target layer gap.

[0062] The method for controlling winding tension provided by the present invention, based on the relationship between the tab misalignment and the winding tension obtained by the above-mentioned evaluation method, detects the tab misalignment in the process of preparing the wound battery cell, and adjusts the winding tension in real time so that the layer gap is the target layer gap, thereby achieving consistency in the battery cell layer gap, which is beneficial to improving the battery cell performance.

[0063] In some optional embodiments, the deviation of the current layer gap from the target layer gap is evaluated based on the amount of tab misalignment;

[0064] If the interlayer gap is too large, increase the winding tension; if the interlayer gap is too small, reduce the winding tension.

[0065] The present invention is further described below by means of specific examples. However, it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0066] Example 1

[0067] A method for evaluating winding tension comprises the following steps:

[0068] a. Confirm the target layer gap of the wound battery cell;

[0069] b. Conduct a single factor experiment on winding tension during the preparation of wound cells to obtain the relationship between winding tension and layer gap;

[0070] The winding tension includes the negative electrode sheet winding tension, the positive electrode sheet winding tension and the separator winding tension;

[0071] The interlayer gap includes the positive electrode tension contribution layer gap, the negative electrode tension contribution layer gap and the separator tension contribution layer gap;

[0072] Interlayer gap = δa + δc + δs;

[0073] Among them, δa is the gap between the negative electrode tension contribution layer; δc is the gap between the positive electrode tension contribution layer; δs is the gap between the separator tension contribution layer;

[0074] The relationship between the winding tension and the layer gap is:

[0075] δa=λaln(Fa)+μa;

[0076] δc=λcln(Fc)+μc;

[0077] δs=λsln(Fs)+μs;

[0078] Among them, λa, λc, λs, μa, μc and μs are all constants; Fa is the winding tension of the negative electrode sheet; Fc is the winding tension of the positive electrode sheet; Fs is the winding tension of the separator;

[0079] According to the obtained single factor experimental results, the values ​​of λa, λc, λs, μa, μc and μs are determined;

[0080] c. The relationship between the tab misalignment and the layer gap is:

[0081] S1=(n-1)*a1+(n-1)*(n-2)*π*(δ1-δ);

[0082] Among them, da is the thickness of the negative electrode sheet; dc is the thickness of the positive electrode sheet; ds is the thickness of the separator; S1 is the misalignment of the tab between the n-1th and 1st turns of the wound cell; n is the number of turns of the wound cell; a1 is the misalignment of the tab between the 2nd and 1st turns of the wound cell; π is the circumference of pi; δ1 is the interlayer gap when the tab misalignment is S1; δ is the target interlayer gap;

[0083] d. According to steps b and c, the relationship between the tab misalignment and the winding tension is obtained, and the winding tension is evaluated by detecting the tab misalignment during the preparation of the wound battery cell.

[0084] Test Example 1

[0085] The battery is designed to:

[0086] The positive electrode sheet is: 31 tabs, with a thickness of 150μm; the current collector of each positive electrode sheet is aluminum foil, and the current collector is coated with a slurry layer, which is composed of a positive electrode active material (lithium iron phosphate), a conductive agent (conductive carbon black) and a binder (PVDF), with a mass ratio of 94.9%:2.9%:2.2%;

[0087] The negative electrode sheet is: 32 tabs, with a thickness of 120μm; the current collector of each negative electrode sheet is copper foil, and the current collector is coated with a slurry layer, which is composed of a negative electrode active material (graphite), a conductive agent (conductive carbon black), and a binder (CMC and SBR, with a mass ratio of 1:1), with a mass ratio of 93.2%: 2.98%: 3.82%;

[0088] The diaphragm is a PP diaphragm with a thickness of 12 μm.

[0089] The above materials were used to prepare wound cells. During the preparation process, the winding tension was evaluated using the evaluation method of Example 1:

[0090] 1. Confirm that the target layer gap of the wound cell is 15μm;

[0091] 2. During the preparation of the wound battery cell, a single factor experiment was conducted on the winding tension, and the calculated values ​​were -5.944 for λa, -5.319 for λc, -2.466 for λs, 53.940 for μa, 53.056 for μc, and 33.067 for μs;

[0092] Then, the relationship between winding tension and layer gap is:

[0093] δa=-5.944ln(Fa)+53.940;

[0094] δc=-5.319ln(Fc)+53.056;

[0095] δs=-2.466ln(Fs)+33.067;

[0096] 3. Prepare the roll core.

[0097] If the target gap is 15mm and the actual tab misalignment is 10mm, then according to the formula:

[0098] S1=(n-1)*a1+(n-1)*(n-2)*π*(δ1-δ);

[0099] It can be calculated that the actual layer gap δ1 = 18.659 μm, and the actual layer gap correction amount is -3.659 μm.

[0100] △δ=△δa+△δc+△δs, where △δ=-3.659μm.

[0101] The initial winding tension is 500gf for the positive electrode, 500gf for the negative electrode, and 200gf for the separator. Then:

[0102] △δa=-5.944ln(Fa)+5.944ln(500);

[0103] △δc=-5.319ln(Fc)+5.319ln(500);

[0104] Δδs=-2.466ln(Fs)+2.466ln(500).

[0105] According to the gap contribution ratio, the positive electrode / negative electrode each contributes 40%, and the diaphragm adjustment contributes 20%, then:

[0106] △δa=△δc=0.4*△δ=-1.463μm;

[0107] △δs=0.2*△δ=-0.732μm;

[0108] Then, the adjusted tension is Fa=639gf, Fc=658gf, Fs=269gf.

[0109] The tabs of the battery finally prepared are aligned and meet the interlayer gap requirements.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating winding tension, characterized in that: The following steps are involved: a. Confirm the target layer gap of the wound battery cell; b. Conduct a single factor experiment on winding tension during the preparation of wound cells to obtain the relationship between winding tension and layer gap; c. The relationship between the tab misalignment and the interlayer gap is: S1 = (n-1)*a1+(n-1)*(n-2)*π*(δ1-δ); Among them, S1 is the misalignment of the tab between the nth and first turns of the wound cell; n is the number of turns of the wound cell; a1 is the misalignment of the tab between the second and first turns of the wound cell; π is the circumference of pi; δ1 is the layer gap when the tab misalignment is S1; δ is the target layer gap; d. According to steps b and c, the relationship between the tab misalignment and the winding tension is obtained, and the winding tension is evaluated by detecting the tab misalignment during the preparation of the wound battery cell.

2. The evaluation method according to claim 1, characterized in that: The winding tension includes the negative electrode sheet winding tension, the positive electrode sheet winding tension and the separator winding tension; The winding tension of the negative electrode sheet, the winding tension of the positive electrode sheet and the winding tension of the separator are each independently 80-2000 gf.

3. The evaluation method according to claim 1, characterized in that: The interlayer gap includes the negative electrode tension contribution layer gap, the positive electrode tension contribution layer gap and the separator tension contribution layer gap; Interlayer gap = δa + δc + δs; Among them, δa is the gap of the negative electrode tension contribution layer; δc is the gap of the positive electrode tension contribution layer; δs is the gap of the separator tension contribution layer.

4. The evaluation method according to claim 3, characterized in that: The relationship between the winding tension and the layer gap is: δa=-λaln(Fa)+μa; δc=-λcln(Fc)+μc; δs=-λsln(Fs)+μs; Among them, λa, λc, λs, μa, μc and μs are all constants; Fa is the winding tension of the negative electrode sheet; Fc is the winding tension of the positive electrode sheet; Fs is the winding tension of the separator; According to the single-factor experimental results in step b, determine the values ​​of λa, λc, λs, μa, μc and μs.

5. The evaluation method according to claim 1, characterized in that: During the preparation process of the wound battery cell in step b and step d, other preparation parameters except the winding tension are the same.

6. The evaluation method according to claim 5, characterized in that: The other preparation parameters include the winding needle circumference, the thickness of the positive and negative electrode sheets, the thickness of the separator and the P roller pressure.

7. A method for controlling winding tension, characterized in that: The relationship between the tab misalignment and the winding tension is obtained by the evaluation method described in any one of claims 1 to 6. By detecting the tab misalignment during the preparation of the wound battery cell, the winding tension is adjusted in real time so that the layer gap is the target layer gap.

8. The control method according to claim 7, characterized in that: The deviation of the current layer gap from the target layer gap is evaluated based on the amount of tab misalignment; If the interlayer gap is too large, increase the winding tension; if the interlayer gap is too small, reduce the winding tension.