Winding method of winding core and application thereof

Abstract

The invention provides a winding method of a winding core and application of the winding core, and relates to the technical field of batteries. The expansion amount of the pole pieces with different turns is calculated according to the thickness change of the pole pieces with different turns after charging and discharging circulation, so that the tension of the positive pole pieces with different turns, the negative pole pieces with different turns and the diaphragm is adjusted to control the layer gap during winding, the problem that the stress borne by the pole pieces with different turns is not uniform is solved, and the cycle life of the battery cell is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a winding method of a winding core and application thereof. Background Art

[0002] For cylindrical lithium-ion batteries, the management and release of internal stress is one of the key factors affecting its cycle performance and overall life. During the charge and discharge cycle of the battery, the thickness of the positive and negative electrodes continues to expand and shrink due to the embedding and de-embedding of lithium ions. At the same time, due to the constraints of the cylindrical shell and the winding structure, the stress generated inside the core cannot be released. As the cycle progresses, the thickness of the electrode continues to increase, causing the internal stress of the core to continue to increase, which will cause the electrode to break and affect the cycle performance. At the same time, during the cycle, the outer ring electrode of the core is only subject to the binding force of the shell, resulting in less internal stress, while the inner and middle electrodes are not only subject to the stress generated by their own expansion, but also the pressure generated by the expansion of the outer ring electrode, resulting in greater internal stress; therefore, the expansion of electrodes with different numbers of turns is inconsistent, resulting in differences in electrode performance. As the cycle progresses, the electrode with a specific number of turns will deteriorate first, resulting in a rapid decline in the overall battery performance.

[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 winding method for a winding core to solve the above-mentioned technical problem.

[0005] The second object of the present invention is to provide application of the above winding method in preparing cylindrical batteries.

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

[0007] In a first aspect, the present invention provides a winding method of a winding core, wherein the winding core is mainly obtained by winding a positive electrode sheet, a separator, a negative electrode sheet and a separator; one winding is regarded as a basic unit, and is sequentially recorded as the first to the nth turns from the inside to the outside;

[0008] a. Obtaining a core of 100% SOC at which the diameter no longer increases after charge and discharge cycles, and measuring the expansion of each basic unit, wherein the core is wound using a constant winding tension;

[0009] b. Obtain the relationship between the core winding tension and the layer gap:

[0010] Fc=γc*ln(δ)+λc;

[0011] Fa=γa*ln(δ)+λa;

[0012] Fs=γs*ln(δ)+λs;

[0013] Among them, Fc is the tension of the positive electrode sheet; Fa is the tension of the negative electrode sheet; Fs is the tension of the separator; δ is the interlayer gap of the basic unit; γc, γa, γs, λc, λa and λs are constants, λc is 1700~2000gf, λa is 1900~2200gf, and λs is 700~900gf;

[0014] c. Winding the core according to the following winding tension:

[0015] Fcn = γc*ln(K-ΔHn)+λc;

[0016] Fan=γa*ln(K-ΔHn)+λa;

[0017] Fsn=γs*ln(K-ΔHn)+λs;

[0018] Among them, Fcn is the tension of the positive electrode sheet of the nth circle; Fan is the tension of the negative electrode sheet of the nth circle; Fsn is the tension of the diaphragm of the nth circle; K is the correction value of the electrode expansion, which is 15~25μm; ΔHn is the expansion of the basic unit of the nth circle.

[0019] As a further technical solution, step a also includes the step of measuring the full-charge expansion rate of each circle of positive electrode sheet and the full-charge expansion rate of the negative electrode sheet, then ΔHn is:

[0020] ΔHn=ηcn*Hc+ηan*Ha;

[0021] Among them, Hc is the thickness of the positive electrode sheet during winding; Ha is the thickness of the negative electrode sheet during winding; ηcn is the full-charge expansion rate of the n-th circle positive electrode sheet; ηan is the full-charge expansion rate of the n-th circle negative electrode sheet.

[0022] As a further technical solution, the Hc may be, for example, but not limited to, 50 μm, 100 μm or 220 μm;

[0023] The Ha may be, for example, but not limited to, 40 μm, 100 μm or 200 μm;

[0024] The thickness of the separator may be, for example, but not limited to, 7 μm, 15 μm or 30 μm.

[0025] As a further technical solution, it also includes fitting ηcn and n to obtain a fitting curve of ηcn and n.

[0026] As a further technical solution, y=ax 2 +bx+c equation is used to fit ηan and n;

[0027] Among them, a, b and c are constants.

[0028] As a further technical solution, the value of a is (2-4)*10 -6 , b is (-2~-3)*10 -4 , c ranges from -0.02 to -0.04.

[0029] As a further technical solution, it also includes fitting ηan and n to obtain a fitting curve of ηan and n.

[0030] As a further technical solution, adopt y=dx 2 +ex+f equation is used to fit ηan and n;

[0031] Among them, d, e and f are constants.

[0032] As a further technical solution, d is taken as (3-5)*10 -5 , the value of e is (-2~-4)*10 -3 , f ranges from 0.09 to 0.13.

[0033] In a second aspect, the present invention provides application of the above-mentioned winding method in preparing cylindrical batteries.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention calculates the expansion of pole pieces with different numbers of turns by adjusting the tension of positive pole pieces, negative pole pieces and diaphragms with different numbers of turns after charge and discharge cycles to control the interlayer gap during winding, thereby solving the problem of uneven stress on pole pieces with different numbers of turns and improving the cycle life of the battery cell. DETAILED DESCRIPTION

[0036] 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.

[0037] In some optional embodiments

[0038] In a first aspect, the present invention provides a winding method of a winding core, wherein the winding core is mainly obtained by winding a positive electrode sheet, a separator, a negative electrode sheet and a separator; one winding is regarded as a basic unit, and is sequentially recorded as the first to the nth turns from the inside to the outside;

[0039] a. Obtaining a core of 100% SOC at which the diameter no longer increases after charge and discharge cycles, and measuring the expansion of each basic unit, wherein the core is wound using a constant winding tension;

[0040] b. Obtain the relationship between the core winding tension and the layer gap:

[0041] Fc=γc*ln(δ)+λc;

[0042] Fa=γa*ln(δ)+λa;

[0043] Fs=γs*ln(δ)+λs;

[0044] Among them, Fc is the tension of the positive electrode sheet; Fa is the tension of the negative electrode sheet; Fs is the tension of the separator; δ is the interlayer gap of the basic unit; γc, γa, γs, λc, λa and λs are constants, λc is 1700~2000gf, λa is 1900~2200gf, and λs is 700~900gf;

[0045] c. Winding the core according to the following winding tension:

[0046] Fcn = γc*ln(K-ΔHn)+λc;

[0047] Fan=γa*ln(K-ΔHn)+λa;

[0048] Fsn=γs*ln(K-ΔHn)+λs;

[0049] Among them, Fcn is the tension of the positive electrode sheet of the nth circle; Fan is the tension of the negative electrode sheet of the nth circle; Fsn is the tension of the diaphragm of the nth circle; K is the correction value of the electrode expansion, which is 15~25μm; ΔHn is the expansion of the basic unit of the nth circle.

[0050] The present invention calculates the expansion of pole pieces with different numbers of turns by adjusting the tension of positive pole pieces, negative pole pieces and diaphragms with different numbers of turns after charge and discharge cycles to control the interlayer gap during winding, thereby solving the problem of uneven stress on pole pieces with different numbers of turns and improving the cycle life of the battery cell.

[0051] In some optional embodiments, step a further includes measuring the full charge expansion rate of the positive electrode sheet and the full charge expansion rate of the negative electrode sheet in each cycle, and the thickness of the positive and negative electrode sheets at 100% SOC after the cycle satisfies the following relationship:

[0052] Hcn=Hc*(1+ηcn);

[0053] Among them, Hcn is the thickness of the positive electrode sheet at the nth cycle at 100% SOC state after cycling; ηcn is the full charge expansion rate of the positive electrode sheet at the nth cycle; Hc is the thickness of the positive electrode sheet during winding;

[0054] Han = Ha*(1+ηan);

[0055] Among them, Han is the thickness of the negative electrode sheet at the nth cycle at 100% SOC state after cycling, ηan is the full charge expansion rate of the negative electrode sheet at the nth cycle; Ha is the thickness of the negative electrode during winding;

[0056] The expansion of the 100% SOC cell in the nth cycle after cycling satisfies the following relationship:

[0057] δn=Hn-H;

[0058] Hn=Hcn+Han+2Hs;

[0059] H=Hc+Ha+2Hs;

[0060] Where: Hs is the thickness of the diaphragm; Hn is the thickness of the basic unit of the nth turn of the winding core at 100% SOC; H is the thickness of the basic unit of the winding core during winding;

[0061] Therefore, the expansion of the nth circle can be simplified as:

[0062] ΔHn=ηcn*Hc+ηan*Ha.

[0063] In some optional embodiments, the Hc value is 50 to 220 μm;

[0064] The Ha value is 40 to 200 μm;

[0065] The thickness of the diaphragm is 7 to 30 μm.

[0066] In some optional implementations, the method further includes fitting ηcn and n to obtain a fitting curve of ηcn and n.

[0067] The relationship curve between ηcn and n is obtained by fitting.

[0068] The present invention does not impose any specific restrictions on the fitting equation. In some optional implementations, y=ax 2 +bx+c equation is used to fit ηan and n;

[0069] Among them, a, b and c are constants.

[0070] In some optional implementations, a is (2-4)*10 -6 , b is (-2~-3)*10 -4 , c ranges from -0.02 to -0.04.

[0071] In some optional implementations, the method further includes fitting ηan and n to obtain a fitting curve of ηan and n.

[0072] The relationship curve between ηan and n is obtained by fitting.

[0073] The present invention does not impose any specific restrictions on the fitting equation. In some optional implementations, y=dx 2 +ex+f equation is used to fit ηan and n;

[0074] Among them, d, e and f are constants.

[0075] In some optional implementations, d is (3-5)*10 -5 , the value of e is (-2~-4)*10 -3 , f ranges from 0.09 to 0.13.

[0076] In a second aspect, the present invention provides application of the above-mentioned winding method in preparing cylindrical batteries.

[0077] The winding method provided by the present invention solves the problem of uneven stress on pole pieces with different numbers of turns, and the winding cores prepared by the method have a higher cycle life.

[0078] 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.

[0079] Comparative Example 1

[0080] A winding core is wound with a constant winding tension, the number of winding turns is 70, and the thickness of the positive electrode sheet, the thickness of the negative electrode sheet and the winding tension are shown in Table 1.

[0081] Example 1

[0082] 1. The core of comparative example 1 was charged and discharged for 300 cycles. At this time, the diameter of the core no longer increased. The battery was then disassembled to obtain the thickness and expansion rate of the positive electrode sheet and the thickness and expansion rate of the negative electrode sheet in each cycle under the 100% SOC state, and the charge and discharge cycle performance (25°C 1C / 1C cycle) of the same model battery was measured, as shown in Table 1.

[0083] Table 1

[0084]

[0085] 2. Using the same raw materials as the comparative core, test the data of different winding tensions and layer gaps, and the relationship between winding tension and layer gap is obtained after fitting:

[0086] Fc=γc*ln(δ)+λc;

[0087] Fa=γa*ln(δ)+λa;

[0088] Fs=γs*ln(δ)+λs;

[0089] Among them, Fc is the tension of the positive electrode; Fa is the tension of the negative electrode; Fs is the tension of the separator; δ is the interlayer gap of the basic unit; γc is -526, γa is -572, γs is -205; λc is 1827gf, λa is 2040gf, λs is 852gf;

[0090] 3. Using the same raw materials as in Comparative Example 1, winding is performed at the following winding tension to obtain a winding core, and the winding tension is shown in Table 2.

[0091] Fcn = γc*ln(K-ΔHn)+λc;

[0092] Fan=γa*ln(K-ΔHn)+λa;

[0093] Fsn=γs*ln(K-ΔHn)+λs;

[0094] Among them, Fcn is the tension of the positive electrode sheet of the nth circle; Fan is the tension of the negative electrode sheet of the nth circle; Fsn is the tension of the diaphragm of the nth circle; K is 20μm; ΔHn is the expansion of the basic unit of the nth circle.

[0095] Test Example 1

[0096] The core provided in Example 1 was subjected to 300 charge and discharge cycles, and then the battery was disassembled to measure the thickness and expansion rate of the positive electrode sheet and the thickness and expansion rate of the negative electrode sheet in each cycle at 100% SOC. The charge and discharge cycle performance (25°C 1C / 1C cycle) of the same model battery was measured. The results are shown in Table 2.

[0097] Table 2

[0098]

[0099] Before the tension adjustment, the full-charge expansion rate of the negative electrode sheet changes with the number of turns. The expansion rate of the negative electrode sheet is the lowest between 10 and 40 turns, and the stress of the electrode sheet is relatively large within this range of turns. After the tension adjustment, the expansion rates of the negative electrode sheets with different turns are basically the same, indicating that the changing tension solves the problem of uneven stress on the electrode sheets with different turns. At the same time, the capacity retention rate of the battery cell at 1000cls and 3000cls is improved.

[0100] 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 winding method for a winding core, characterized in that: The winding core is mainly obtained by winding the positive electrode sheet, the separator, the negative electrode sheet and the separator; one winding is regarded as a basic unit, and is recorded as the first to the nth windings from the inside to the outside; a. Obtaining a core of 100% SOC at which the diameter no longer increases after charge and discharge cycles, and measuring the expansion of each basic unit, wherein the core is wound using a constant winding tension; b. Obtain the relationship between the core winding tension and the layer gap: Fc=γc*ln(δ)+λc; Fa=γa*ln(δ)+λa; Fs=γs*ln(δ)+λs; Among them, Fc is the tension of the positive electrode sheet; Fa is the tension of the negative electrode sheet; Fs is the tension of the separator; δ is the interlayer gap of the basic unit; γc, γa, γs, λc, λa and λs are constants, λc is 1700~2000gf, λa is 1900~2200gf, and λs is 700~900gf; c. Winding the core according to the following winding tension: Fcn = γc*ln(K-ΔHn)+λc; Fan=γa*ln(K-ΔHn)+λa; Fsn=γs*ln(K-ΔHn)+λs; Among them, Fcn is the tension of the positive electrode sheet of the nth circle; Fan is the tension of the negative electrode sheet of the nth circle; Fsn is the tension of the diaphragm of the nth circle; K is the correction value of the electrode expansion, which is 15~25μm; ΔHn is the expansion of the basic unit of the nth circle.

2. The winding method according to claim 1, characterized in that: Step a also includes the step of measuring the full-charge expansion rate of each positive electrode sheet and the full-charge expansion rate of each negative electrode sheet, then ΔHn is: ΔHn=ηcn*Hc+ηan*Ha; Among them, Hc is the thickness of the positive electrode sheet during winding; Ha is the thickness of the negative electrode sheet during winding; ηcn is the full-charge expansion rate of the n-th circle positive electrode sheet; ηan is the full-charge expansion rate of the n-th circle negative electrode sheet.

3. The winding method according to claim 2, characterized in that: The Hc value is 50 to 220 μm; The Ha value is 40 to 200 μm; The thickness of the diaphragm is 7 to 30 μm.

4. The winding method according to claim 1, characterized in that: The method also includes fitting ηcn and n to obtain fitting curves of ηcn and n.

5. The winding method according to claim 4, characterized in that: Using y=ax 2 +bx+c equation is used to fit ηan and n; Among them, a, b and c are constants.

6. The winding method according to claim 5, characterized in that: The value of a is (2~4)*10 -6 , b is (-2~-3)*10 -4 , c ranges from -0.02 to -0.

04.

7. The winding method according to claim 1, characterized in that: The method also includes fitting ηan and n to obtain fitting curves of ηan and n.

8. The winding method according to claim 7, characterized in that: Using y=dx 2 +ex+f equation is used to fit ηan and n; Among them, d, e and f are constants.

9. The winding method according to claim 8, characterized in that: The value of d is (3~5)*10 -5 , the value of e is (-2~-4)*10 -3 , f ranges from 0.09 to 0.

13.

10. Use of the winding method according to any one of claims 1 to 9 in preparing cylindrical batteries.

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