Method for calculating square lithium battery winding tab center distance and winding tab length

Abstract

The application discloses a calculation method of square lithium battery winding tab center distance and winding tab length, which determines the single cell core thickness F and the adjacent folding arc length thickness increment delta, respectively calculates the tab winding layer number, the tab folding number, the diaphragm layer number and the cell thickness in sequence, and further calculates the tab folding arc length and the tab full length, and the adjacent tab center distance. The method can quickly confirm the distance between the tabs and the total length of the winding tabs, ensure that the tab alignment and the tab margin meet the process requirements, and does not need to be rewound for many times, so that the problems of low efficiency, material waste and large workload caused by the method are solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery processing technology, and particularly relates to a method for calculating the center distance of the wound tabs and the length of the wound electrode sheets of a square lithium battery. Background Technology

[0002] Currently, there are two cell structures in the design of polymer lithium-ion battery multi-tab cells: stacked structure and wound structure. In the stacked structure, each electrode is punched out using a corresponding positive electrode die or negative electrode die; each electrode has tabs punched on it.

[0003] The challenges of stacking cells are: 1. High precision is required for the stacking equipment; misalignment must be avoided during the stacking of positive and negative electrode films; 2. If misalignment occurs, meaning the negative electrode film area fails to completely cover the positive electrode film area, it is difficult to detect and alarm using ordinary X-ray inspection technology, making effective risk management impossible. In a wound structure, each of the positive and negative electrode films of the battery has only one electrode sheet. During winding, the positive and negative electrodes are separated by a separator and rotated layer by layer around the core; the tabs of each layer are punched out from the blank current collector reserved in the coating width direction during coating.

[0004] Features of the winding structure: 1. The winding equipment is simple and the technology is mature, making it difficult for the negative electrode film area to fail to cover the positive electrode film area due to misalignment; 2. If film area misalignment occurs, it is easy to pre-detect and alarm using ordinary X-ray detection technology, thus controlling the risk. Challenges of the multi-tab winding structure: In the winding body, the inner layer segment is narrower, while the outer layer segment is relatively wider. The distance between the upper tabs of the inner and outer layers continuously increases, not remaining constant. To ensure that each layer of positive or negative electrode tabs in the winding body overlaps, the precise cutting position of the upper tabs in each layer segment from the inside to the outside of the core must be carefully considered. The current practice involves engineers determining the punching position of each layer of tabs based on their work experience and continuous manual adjustments during the sample preparation process. However, this method is problematic because: 1. It relies too heavily on the engineer's experience and understanding of the equipment's capabilities; 2. Precisely determining the position of multiple tabs requires constant trial and error, resulting in a long cycle, reduced production efficiency, and extended product development time, failing to achieve the intended design goals; 3. It cannot handle the design of multiple-tab cells with various models, leading to a larger workload and longer processing time; 4. It cannot guarantee accuracy. In multi-tab winding structures, precise tab positioning is crucial. If precise positioning is not achieved, misalignment will occur between tabs on adjacent layers during winding. This misalignment worsens with the number of winding layers, affecting not only the center distance between tabs but also potentially causing tab "fence" phenomena, ultimately rendering the entire winding unusable.

[0005] The prior art discloses a method for accurately locating the tabs of a multi-tab wound lithium-ion battery, as disclosed in Chinese patent application number CN201710574761.1. The method comprises the following steps: Step 1: Establishing an ideal physical model for tab positioning; Step 2: Deriving a unified mathematical expression for each tab layer based on the ideal physical model; Step 3: Introducing a correction factor into the unified mathematical expression to numerically correct the final mathematical expression; Step 4: Using the tab position number as the independent variable, substituting the design parameters under actual working conditions (including tab center distance, winding needle width, correction factor, thickness of positive and negative electrodes, and thickness of the separator) into the final mathematical expression to calculate the precise position of each tab.

[0006] However, in order to ensure that the negative electrode completely covers the positive electrode, the negative electrode is pre-wound 1 turn or 1.5 turns earlier than the positive electrode in the current square wound lithium battery. The tail of the negative electrode is usually at the arc, and the length of the negative electrode at the tail is longer than that of the positive electrode. Therefore, when calculating the center distance of the tabs, the distance between the first and last tabs also needs to be calculated. The patent does not mention how to calculate the distance between the first and last tabs, or the calculation method for the total length of the 1ea electrode sheet. Summary of the Invention

[0007] To address the problems of existing technical requirements, this invention proposes the following technical solution:

[0008] A method for calculating the center distance of the wound tabs and the length of the wound electrode sheet in a square lithium battery, wherein the method is as follows:

[0009] Determine the thickness F of the single core and the arc length thickness increment δ at adjacent folds, where the thickness of the positive electrode sheet after roll forming and rebound is G, the thickness of the negative electrode sheet is H, and the thickness of the separator is I.

[0010] Calculate the number of positive electrode winding layers J = F / (G+H+2I), the number of negative electrode winding layers K = J+2, the number of positive electrode folds L = J-1, the number of negative electrode folds M = K-1, the number of separator layers N = J+6, and the cell thickness O = J*G+K*H+N*I;

[0011] The arc length S of the arc-shaped region at the Lth bend of the positive electrode is calculated as follows:

[0012] S 1、2 = Π*(4I+H), L = 1 or 2;

[0013] S 偶 = Π*(4I+H)+Π*(2I+G+H)*(L-2) / 2, where L is an even number greater than 2;

[0014] S 奇 = Π*(4I+H)+Π*(2I+G+H)*(L-1) / 2, where L is an odd number greater than 2;

[0015] Calculate the arc length of all the folded arc regions of the positive electrode:

[0016] Calculate the total length of the positive electrode: Y = J*Ro / 2 + H;

[0017] Calculate the distance in front of the first electrode ear of the positive electrode (the head of the lower 1EA electrode):

[0018] U=Ro / 2-e+Π*(4I+H)+a / 2+cO / 2;

[0019] Calculate the distance between the first electrode ear and the tail of the positive electrode (the tail of the upper 1EA electrode plate):

[0020] X = Ro / 2 - ea / 2 - (cO / 2);

[0021] In the above formula, the width of the positive electrode tab of the winding core is a, the width of the negative electrode tab is b, the edge distance of the winding core is c, the circumference of the circular winding needle is Ro, and O is the thickness of the battery cell; if the head and tail of the negative electrode are in contact with the ear of the arc area, the head and tail of the positive electrode are shorter than the negative electrode by e due to the negative-to-positive factor.

[0022] Calculate the center distance Z between the Lth electrode and the (L-1)th electrode:

[0023] Z1=Ro+Π*(4I+H)+Π*(2I+G+H), L=2;

[0024] Z=Ro+Π*(4I+H)*(2L-4) / 2+Π*(4I+H)*(2L-2) / 2;

[0025] In the above technical solution, the calculation method for the thickness F of a single core is as follows:

[0026] F = (A - 2B - 2C) * D / E, where A is the thickness of the aluminum shell, B is the thickness of the mylar film, C is the thickness of the tape, D is the assembly ratio, and E is the number of battery cells.

[0027] In the above technical solution, E is 5-10 mm.

[0028] The beneficial effects of this invention are as follows:

[0029] The method of this application can quickly confirm the distance between the tabs and the total length of the wound electrode sheet, ensuring that the tab alignment and tab edge distance meet the process requirements. It eliminates the need for multiple rewindings, thus solving problems such as low efficiency, material waste, and large workload that may result. Attached Figure Description

[0030] Figure 1 The image shown is a front view of a lithium battery core.

[0031] Figure 2 The diagram shown is a schematic of the winding structure of the core.

[0032] Figure 3 The diagram shows the unfolded state of the core. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0034] Figure 1 This is a front view of a lithium battery core. Figure 2 The diagram shown is a schematic of the winding structure of the core. Figure 3 The diagram shows the unfolded state of the core.

[0035] like Figure 2 As shown, when the core is wound, the diaphragm is pre-wound 0.7 turns ahead of the negative electrode, the negative electrode begins to be pre-wound, and after the negative electrode is pre-wound 1 turn, the positive electrode is then wound in. At the end, the negative electrode extends 10mm beyond the positive electrode, and the diaphragm is wound 2.5 turns at the end. The winding needle used is a round winding needle.

[0036] After the roll-pressing rebound, the thickness of the positive electrode sheet is set to G, the thickness of the negative electrode sheet to H, and the thickness of the separator to I. Since the thickness increment between adjacent arc lengths of odd-numbered and even-numbered folds in the winding structure is 2 layers of separator, 1 layer of positive electrode, and 1 layer of negative electrode, the arc length increment between adjacent odd-numbered and even-numbered folds is Π*(2I+G+H).

[0037] Based on the aluminum shell thickness A, the mylar film thickness B, the tape thickness C, the assembly ratio D, and the number of battery cells E, calculate the thickness F of a single core: F = (A - 2B - 2C) * D / E.

[0038] Calculate the number of positive electrode winding layers J: J = F / (G + H + 2I);

[0039] The number of negative electrode winding layers K = the number of positive electrode winding layers J + 2 layers;

[0040] Positive electrode fold number L = positive electrode winding layer number J-1;

[0041] The number of folds in the negative electrode M = the number of layers of the negative electrode winding K-1;

[0042] Number of membrane layers N = J + 6;

[0043] Cell thickness O = J*G + K*H + N*I.

[0044] The total length of the positive electrode sheet = the number of positive electrode sheet layers * the circumference of the winding needle / 2 + the length of the odd-numbered folded arc region of the positive electrode + the length of the even-numbered folded arc region of the positive electrode;

[0045] The first and second fold arc regions of the positive electrode have 4 layers of separator and 1 layer of negative electrode thickness. Therefore, the arc length of the first and second fold arc regions of the positive electrode is: Π*(4I+H).

[0046] Therefore, the arc lengths of the third and fourth arc regions of the positive electrode are: Π*(4I+H)+Π*(2I+G+H)...and so on;

[0047] Assuming the number of folds L on the positive electrode is odd, the arc lengths of the arc regions of the (L-1)th and (L-2)th folds on the positive electrode are Π*(4I+H)+Π*(2I+G+H)*(L-3) / 2; the arc length of the arc region of the Lth fold on the positive electrode is Π*(4I+H)+Π*(2I+G+H)*(L-1) / 2.

[0048] Assuming the positive electrode fold number L is even, the arc length of the arc region of the L-1th fold and the Lth fold of the positive electrode is Π*(4I+H)+Π*(2I+G+H)*L / 2;

[0049] The arc length S of the arc-shaped region at the Lth bend of the positive electrode is uniformly defined as:

[0050] S = Π*(4I+H), L = 1 or 2;

[0051] S = Π*(4I+H)+Π*(2I+G+H)*(L-2) / 2, where L is an even number greater than 2;

[0052] S = Π*(4I+H)+Π*(2I+G+H)*(L-1) / 2, where L is an odd number greater than 2;

[0053] Assuming the positive electrode fold number L is odd, the length P of the odd-numbered fold arc region of the positive electrode = the length of the first fold arc + the length of the third fold arc + ... the length of the Lth fold arc, and the length Q of the even-numbered fold arc region of the positive electrode = the length of the second fold arc + the length of the fourth fold arc + ... the length of the L-1th fold arc;

[0054] Assuming the positive electrode fold number L is even, the length R of the positive electrode odd-numbered fold arc region is equal to the length of the first fold arc + the length of the third fold arc + ... the length of the (L-1)th fold arc, and the length S of the positive electrode even-numbered fold arc region is equal to the length of the second fold arc + the length of the fourth fold arc + ... the length of the Lth fold arc;

[0055] Assuming the number of folds L on the positive electrode is odd, the total length of the positive electrode sheet = number of positive electrode sheet layers * circumference of the winding needle / 2 + length of the arc-shaped region with odd folds on the positive electrode + length of the arc-shaped region with even folds on the positive electrode = J * Ro / 2 + P + Q;

[0056] Assuming the positive electrode fold number L is even, the total length of the positive electrode plate = J*Ro / 2 + R + S;

[0057] Calculate the arc length of all the folded arc regions of the positive electrode:

[0058] Calculate the total length of the positive electrode: Y = J * G + H; the calculation method for the negative electrode is the same.

[0059] The width of the positive electrode lug is A, the width of the negative electrode lug is B, the edge distance of the winding core is C, and the circumference of the circular winding needle is D. If the head and tail of the negative electrode are in contact with the lug of the arc area, the head and tail of the positive electrode are E: 5-10mm shorter than the negative electrode due to the negative-to-positive factor. Figure 2 Structure: The distance in front of the positive electrode head, Dhead = D / 2 - E + length of the positive electrode head fold + A / 2 + CO / 2; Dtail = D / 2 - EA / 2 - (CO / 2); The calculation method for the negative electrode is the same;

[0060] according to Figure 2 The structure is as follows: the center distance between the first and second electrodes is D1 = D + the arc length of the second fold of the positive electrode (even-numbered first fold) + the arc length of the third fold of the positive electrode (odd-numbered second fold); the center distance between the second and third electrodes is D1 = D + the arc length of the fourth fold of the positive electrode (even-numbered second fold) + the arc length of the fifth fold of the positive electrode (odd-numbered third fold)... and so on; D(L-1) / 2 = D + the arc length of the (L-1)th fold of the positive electrode (even-numbered (L-1) / 2nd fold) + the arc length of the Lth fold of the positive electrode (odd-numbered (L+1) / 2nd fold).

[0061] The center distance between the Lth electrode and the (L-1)th electrode is uniformly calculated as follows: Z = Ro + Π*(4I+H)*(2L-4) / 2 + Π*(4I+H)*(2L-2) / 2; the calculation method for the negative electrode is the same.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A method for calculating the center distance of the wound tabs and the length of the wound electrode sheet in a square lithium battery, characterized in that, The method is as follows: Determine the thickness F of the single core and the thickness increment δ of the arc length at adjacent folds, where the thickness of the positive electrode sheet after roll pressing and rebound is G, the thickness of the negative electrode sheet is H, and the thickness of the separator is I. Calculate the number of positive electrode winding layers J=F / (G+H+2I), the number of negative electrode winding layers K=J+2, the number of positive electrode folds L=J-1, the number of negative electrode folds M=K-1, the number of separator layers N=J+6, and the cell thickness O=J*G+K*H+N*I; The arc length S of the arc-shaped region at the Lth bend of the positive electrode is calculated as follows: S 1、2 =Π*(4I+H), L=1 or 2; S 偶 =Π*(4I+H)+Π*(2I+G+H)*(L-2) / 2, where L is an even number greater than 2; S 奇 =Π*(4I+H)+Π*(2I+G+H)*(L-1) / 2, where L is an odd number greater than 2; Calculate the arc length of all the folded arc regions of the positive electrode: ; Calculate the total length of the positive electrode: Y = J*Ro / 2 + H; Calculate the distance in front of the first electrode ear of the positive electrode, i.e., the head of the next 1EA electrode: U=Ro / 2-e+Π*(4I+H)+a / 2+cO / 2; Calculate the distance from the tail of the first electrode ear of the positive electrode, i.e., the tail of the upper 1EA electrode plate: X = Ro / 2 - ea / 2 - (cO / 2); In the above formula, the width of the positive electrode tab of the winding core is a, the width of the negative electrode tab is b, the edge distance of the winding core is c, the circumference of the circular winding needle is Ro, and O is the thickness of the battery cell; if the head and tail of the negative electrode are in contact with the ear of the arc area, the head and tail of the positive electrode are shorter than the negative electrode due to the negative-to-positive factor.

2. The method for calculating the center distance of the wound tabs and the length of the wound electrode sheet of a square lithium battery according to claim 1, characterized in that, The method for calculating the thickness F of a single core is as follows: F = (A - 2B - 2C) * D / E, where A is the thickness of the aluminum shell, B is the thickness of the mylar film, C is the thickness of the tape, D is the assembly ratio, and E is the number of battery cells.

3. The method for calculating the center distance of the wound tabs and the length of the wound electrode sheet of a square lithium battery according to claim 1, characterized in that, E is 5~10mm.

4. The method for calculating the center distance of the wound tabs and the length of the wound electrode sheet of a square lithium battery according to claim 1, characterized in that, Calculate the center distance between the Lth electrode and the (L-1)th electrode: Z1=Ro+Π*(4I+H)+Π*(2I+G+H), L=2; Z=Ro+Π*(4I+H)*(2L-4) / 2+Π*(4I+H)*(2L-2) / 2.

Images