Winding structure for reducing internal resistance of lithium ion battery, battery and preparation method

Abstract

The invention provides a winding structure for reducing the internal resistance of a lithium ion battery, the battery and a preparation method, the winding structure comprises an inner-layer diaphragm, a positive plate, a middle-layer diaphragm and a negative plate which are sequentially laminated and wound to form a pole group, and a current collector of the negative plate forms the outermost layer of the pole group so as to be in contact with the inner wall of a battery shell and form electric connection with the inner wall of the battery shell. According to the preparation method of the battery with the winding structure, after the battery cell is formed, at least partial area of the negative electrode current collector can be directly and fully contacted with the metal shell of the battery, so that a parallel conductive path except a tab welding point is formed. The method has the beneficial effects that the alternating-current internal resistance and the direct-current internal resistance of the battery can be greatly reduced and the performance of the battery is improved on the premise that the number of the tabs and the process complexity are not increased.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, and in particular relates to a winding structure, battery and preparation method for reducing the internal resistance of lithium-ion batteries. Background Technology

[0002] In existing technologies, the outermost layer of the electrode assembly in cylindrical lithium-ion batteries is typically an insulating separator. Current relies entirely on tabs welded to the positive and negative current collectors for collection and extraction. This presents several challenges: Due to cell size limitations, only one tab is typically welded to each of the positive and negative electrodes (single-tab structure). This forces current to travel a long distance along the current collector to the tab weld, resulting in high current collector resistance and overall high internal resistance, thus limiting high-rate discharge performance. If a double-tab structure is used to reduce internal resistance, such as welding one tab to each end of the negative electrode and then bending and overlapping the two tabs before welding them to the cell casing, it not only increases the use of tabs and insulating protective film but also reduces the space for active material filling, lowering the cell's volumetric energy density. Furthermore, the tab bending and overlapping welding process is complex, reducing the overall battery production yield. Additionally, the reliability of the double-tab overlapping welding is difficult to guarantee, posing a risk of poor soldering. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a winding structure, a battery, and a preparation method for reducing the internal resistance of lithium-ion batteries, which is particularly suitable for reducing the internal resistance of lithium-ion batteries without increasing the complexity of the manufacturing process.

[0004] The technical solution adopted in this invention is: a winding structure for reducing the internal resistance of a lithium-ion battery, comprising an inner separator, a positive electrode, a middle separator, and a negative electrode formed by sequentially stacking and winding them into an electrode assembly. The current collector of the negative electrode forms the outermost layer of the electrode assembly to contact the inner wall of the battery casing and form an electrical connection.

[0005] Furthermore, the negative electrode sheet is provided with a negative electrode tab, and the negative electrode tab is located in the winding start area of ​​the negative electrode sheet.

[0006] Furthermore, the negative electrode tab is configured to be connected to the battery casing by welding.

[0007] Furthermore, a positive electrode tab is provided on the positive electrode sheet, and the positive electrode tab is located in the winding start area of ​​the positive electrode sheet.

[0008] Furthermore, the positive electrode tab is configured to be connected to the battery cap by welding.

[0009] On the other hand, the present invention also provides a lithium-ion battery, including a housing, a cap connected to the housing, and an electrode assembly placed inside the housing, wherein the electrode assembly is the aforementioned wound structure for reducing the internal resistance of the lithium-ion battery.

[0010] On the other hand, the present invention also provides a method for preparing a lithium-ion battery, comprising the following steps:

[0011] The starting areas of the inner and middle diaphragms are fixed using a winding device;

[0012] The drive winding equipment winds the negative electrode sheet to the outside of the middle layer separator and winds it in, and then guides the positive electrode sheet to the space between the inner layer separator and the middle layer separator and winds it in.

[0013] After winding, fix the end of the negative electrode sheet.

[0014] Furthermore, after the step of fixing the tail end of the negative electrode after winding, a welding step is also included: connecting the negative electrode tab connected to the negative electrode to the shell by resistance welding; and connecting the positive electrode tab connected to the positive electrode to the cap by laser welding.

[0015] Furthermore, the welding step is followed by an assembly step: the electrode assembly is placed into the housing, and after baking, liquid injection, and sealing, it undergoes a formation process. During the formation process, the electrode expands, and the outermost negative current collector contacts the inner wall of the housing and forms an electrical connection.

[0016] The advantages and positive effects of this invention are as follows: By adopting the above technical solution, a large-area negative electrode current collector contacts the metal battery casing and forms a low-resistance current path in parallel with the negative electrode tab. Without increasing the number of tabs or the complexity of the process, the AC internal resistance and DC internal resistance of the battery are significantly reduced, thereby improving the battery performance. It also has the advantages of simple manufacturing process, which helps to reduce the internal resistance of the battery, improve the volumetric energy density of the cell, and increase the overall yield and reliability of battery production. Attached Figure Description

[0017] Figure 1 This is a cross-sectional schematic diagram of an embodiment of the winding structure of the present invention during the winding process;

[0018] Figure 2 This is a schematic diagram of the structure of one embodiment of the battery of the present invention.

[0019] In the picture:

[0020] 1. Inner diaphragm; 2. Positive electrode plate; 3. Middle diaphragm; 4. Negative electrode plate; 5. Positive electrode tab; 6. Negative electrode tab; 7. Shell; 8. Cap. Detailed Implementation

[0021] The embodiments of the present invention will now be described with reference to the accompanying drawings. The described embodiments are only some embodiments of the invention, and not all embodiments.

[0022] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar units or units having the same or similar functions throughout.

[0023] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that terms such as "installation," "connection," and "fixing" should be interpreted broadly, and can refer to direct connection, installation, or fixing, or indirect connection, installation, or fixing. The present invention does not impose any limitations in this regard.

[0024] like Figure 1 The diagram illustrates an embodiment of a winding structure for reducing the internal resistance of a lithium-ion battery according to the present invention. It includes an inner separator 1, a positive electrode 2, a middle separator 3, and a negative electrode 4, which are sequentially stacked and wound to form an electrode assembly. The current collector of the negative electrode 4 forms the outermost layer of the electrode assembly, contacting and electrically connecting with the inner wall of the battery casing 7, thereby forming a conductive path in parallel with the negative electrode tab 6. In this embodiment, the electrode assembly is a cylindrical battery electrode assembly. By setting the negative electrode 4 as the outermost layer of the electrode assembly and contacting the negative electrode current collector with the battery casing 7, the present invention forms an additional conductive path in parallel with the conventional electrode tab welding point, effectively reducing the battery's internal resistance and improving current transmission efficiency.

[0025] The negative electrode sheet 4 is provided with a negative electrode tab 6, which is located in the winding start area of ​​the negative electrode sheet 4. The winding start area is the area that is first wound during the winding process, close to the winding needle side of the winding equipment. The single negative electrode tab 6 design simplifies the structure, reduces the tab material and welding steps, lowers production costs and process complexity, and thus improves the battery production yield. The negative electrode tab 6 being located in the start area optimizes the current path, which helps to improve the battery charging and discharging efficiency.

[0026] The negative electrode tab 6 is configured to be connected to the battery casing 7 by resistance welding. Connecting the negative electrode tab 6 to the casing 7 by resistance welding improves connection reliability and stability, and reduces the risk of poor soldering.

[0027] The positive electrode 2 is provided with a positive electrode tab 5, and the positive electrode tab 5 is located in the winding start area of ​​the positive electrode 2. The positive electrode 2 is provided with a single positive electrode tab 5, which maintains the symmetry and balance of the structure and avoids the process complexity caused by too many tabs.

[0028] The positive electrode tab 5 is configured to be connected to the battery cap 8 via laser welding. Connecting the positive electrode tab 5 and the cap 8 via laser welding improves welding precision and strength, ensuring a higher battery production yield.

[0029] like Figure 2As shown, the present invention also provides a lithium-ion battery, including a housing 7, a cap 8 connected to the battery housing 7, and an electrode assembly placed inside the housing 7. The electrode assembly is the aforementioned wound structure for reducing the internal resistance of the lithium-ion battery. Preferably, the lithium-ion battery is cylindrical, with a battery diameter D1, the value of D1 being 12mm≤D1≤30mm; and a battery height H1, the value of H1 being 30mm≤H1≤98mm.

[0030] The battery adopts the above-mentioned winding structure, which reduces the overall internal resistance. The outermost layer of the electrode group is in direct contact with the shell 7 to form a parallel path, which significantly increases the current conduction area and reduces heat generation and energy loss.

[0031] On the other hand, the present invention also provides a method for preparing a lithium-ion battery, comprising the following winding step:

[0032] The starting areas of the inner diaphragm 1 and the middle diaphragm 3 are clamped using a winding device.

[0033] The driving winding equipment performs winding, guiding the negative electrode sheet 4 to the outside of the middle layer diaphragm 3 and winding it in, and then guiding the positive electrode sheet 2 between the inner layer diaphragm 1 and the middle layer diaphragm 3 and winding it in. During the winding process, the negative electrode tab 6 and the positive electrode tab 5 are controlled to be exposed.

[0034] After winding, the negative electrode sheet 4 of the electrode assembly is fixed with terminating tape, and the adhesion area of ​​the terminating tape is controlled so that at least part of the surface of the outermost negative electrode current collector of the electrode assembly remains exposed.

[0035] After the step of fixing the tail end of the negative electrode 4 after winding is completed, the following welding steps are also included: connecting the negative electrode tab 6 connected to the negative electrode 4 to the housing 7 by resistance welding; and / or connecting the positive electrode tab 5 connected to the positive electrode 2 to the cap 8 by laser welding.

[0036] Following the welding step is the assembly step: the wound electrode assembly is placed into the battery casing 7, and after baking, electrolyte injection, and sealing, it undergoes a formation process. During the formation process, the electrode sheets expand, causing the outermost negative electrode current collector to contact the inner wall of the casing 7 and form an electrical connection, creating an additional current path in parallel with the welding point of the conventional negative electrode tab 6. This parallel path effectively reduces the total resistance of the current transmission path.

[0037] The present invention has the following significant advantages:

[0038] Significantly reduced internal resistance: The outermost layer of the electrode assembly is a large-area negative electrode current collector. After cell formation, the expansion of the electrode sheets ensures that the negative electrode current collector and the metal casing 7 are in full and tight contact. This contact surface forms a low-resistance current path in parallel with the negative electrode tab 6, significantly reducing current transmission losses in the current collector, thereby significantly reducing the battery's AC internal resistance (ACIR) and DC internal resistance (DCIR). Experiments show that the internal resistance can be reduced by more than 25%.

[0039] Simplified process and improved reliability: The use of a single tab design avoids the complex bending, overlapping, and welding processes of bipolar structures, improving production yield and efficiency. Furthermore, with only one welding point between the positive or negative tab and the housing 7, welding quality is easier to control, resulting in higher connection reliability.

[0040] Maintaining high energy density: Compared to the monopole structure, no additional tabs, adhesive tape, or other non-active materials are used, thus maximizing the space inside the cell for filling active materials and ensuring the cell's high volumetric energy density.

[0041] Improved electrical performance: The reduction in internal resistance directly results in a higher discharge voltage platform and better high-rate discharge performance, while reducing heat generation during charging and discharging, thus improving battery safety and cycle life.

[0042] Example 1:

[0043] A 2.5Ah capacity 18650 lithium-ion battery. The specifications of the electrodes, separator, and tab design are as follows:

[0044] Positive electrode 2: Length 630mm, width 57mm, thickness 130μm (of which the positive current collector is a 12μm thick aluminum foil).

[0045] Negative electrode 4: Length 690mm, width 59mm, thickness 150μm (of which the negative electrode current collector is an 8μm thick copper foil).

[0046] Diaphragm (inner and middle layers): 730 mm in length, 61 mm in width, and 16 μm in thickness.

[0047] Positive electrode tab 5: 51mm in length, 4mm in width, and 0.1mm in thickness. Its welding position is located 100mm from the starting end of the positive electrode plate 2 (near the coiling needle side). The exposed part of the positive electrode tab 5 is connected to the positive electrode cap 8 of the battery cell by laser welding.

[0048] Negative electrode tab 6: 36mm in length, 4mm in width, and 0.1mm in thickness. Its welding position is adjusted to 5mm from the starting end of the negative electrode plate 4 (near the coiling needle side). The exposed part of the negative electrode tab 6 is connected to the negative electrode shell 7 of the battery cell by resistance welding.

[0049] Winding process:

[0050] The inner layer separator 1, the middle layer separator 3, the positive electrode 2, and the negative electrode 4 are provided with the above specifications.

[0051] Use a needle to clamp the starting areas of the inner diaphragm 1 and the middle diaphragm 3.

[0052] Start the winding process. First, place the negative electrode plate 4 (with negative electrode tab 6 at its starting end) outside the middle diaphragm 3 and insert it for winding.

[0053] The positive electrode 2 is then placed between the inner separator 1 and the middle separator 3 and inserted for winding.

[0054] After winding, an electrode assembly structure is formed from the inside out: inner separator 1, positive electrode 2, middle separator 3, and negative electrode 4 (copper foil). The terminating tape only covers a very small area at the end of the electrode to ensure that the vast majority of the negative current collector is exposed.

[0055] Assembly and Effects:

[0056] The wound electrode assembly is then placed into the steel casing 7 and subjected to subsequent processes such as baking, liquid injection, and sealing. During the formation process, the electrode expands, allowing the outermost negative electrode 4 (negative electrode copper foil) to achieve large-area, tight physical contact with the inner wall of the steel casing 7, thereby forming an electrical connection.

[0057] The present invention is not limited to the above embodiments; the winding structure can be applied to cylindrical batteries of different sizes.

[0058] Test results show that, by adopting the winding structure of this invention, the AC internal resistance (ACIR) of the battery is reduced from an average of 35mΩ in the conventional structure to 22mΩ, a reduction of 37.1%. The DC internal resistance (DCIR) at room temperature is also significantly reduced by about 25%. This results in a higher voltage plateau and less heat generation during high-rate discharge, leading to a significant performance improvement.

[0059] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A winding structure for reducing the internal resistance of a lithium-ion battery, characterized in that, The battery assembly includes an inner separator, a positive electrode, a middle separator, and a negative electrode, which are sequentially stacked and wound to form an electrode group. The current collector of the negative electrode forms the outermost layer of the electrode group to contact the inner wall of the battery casing and form an electrical connection.

2. The winding structure for reducing the internal resistance of a lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet is provided with a negative electrode tab, and the negative electrode tab is located in the winding start area of ​​the negative electrode sheet.

3. The winding structure for reducing the internal resistance of a lithium-ion battery according to claim 2, characterized in that, The negative electrode tab is configured to be connected to the battery casing by welding.

4. The winding structure for reducing the internal resistance of a lithium-ion battery according to any one of claims 1-3, characterized in that, The positive electrode sheet is provided with a positive electrode tab, and the positive electrode tab is located in the winding start area of ​​the positive electrode sheet.

5. The winding structure for reducing the internal resistance of a lithium-ion battery according to claim 4, characterized in that, The positive electrode tab is configured to be connected to the battery cap by welding.

6. A lithium-ion battery, comprising a casing, a cap connected to the casing, and an electrode assembly disposed within the casing, characterized in that, The electrode assembly is a wound structure for reducing the internal resistance of a lithium-ion battery as described in any one of claims 1-5.

7. A method for preparing a lithium-ion battery according to claim 6, characterized in that, Includes the following steps: The starting areas of the inner diaphragm and the middle diaphragm are fixed using a winding device; The winding device is driven to wind the negative electrode sheet to the outside of the middle layer membrane and wind it in, and then the positive electrode sheet is guided to the space between the inner layer membrane and the middle layer membrane and wind it in. After winding, fix the tail end of the negative electrode sheet.

8. The method for preparing a lithium-ion battery according to claim 7, characterized in that, After the step of fixing the tail end of the negative electrode sheet after winding is completed, a welding step is also included: The negative electrode tab connected to the negative electrode plate is connected to the housing by resistance welding; The positive electrode tab connected to the positive electrode plate is connected to the cap by laser welding.

9. The method for preparing a lithium-ion battery according to claim 8, characterized in that, The welding step is followed by an assembly step: The electrode assembly is placed inside the housing, and after baking, liquid injection, and sealing, it undergoes a formation process. During the formation process, the electrode expands, and the outermost negative current collector contacts the inner wall of the housing and forms an electrical connection.

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