A method for solving the wrinkles of negative electrode sheets

Abstract

The present invention relates to the field of battery manufacturing technology, and specifically to a method for solving the wrinkles of negative electrode sheets, comprising the following steps: shortening a variable length support plate to a suitable length inside a winding core by low temperature treatment; placing the shortened variable length support plate inside the winding core as a winding core liner during winding; after winding, restoring the variable length support plate to room temperature, and restoring its length to its initial length. The present invention introduces a variable length support plate inside the winding core to ensure that the internal winding core is uniformly stressed and to avoid the generation of wrinkles. The length of the variable length support plate changes significantly at low temperatures, and the length changes are negligible at room temperature and high temperatures. Place the support plate inside the winding core at low temperatures, and wait for the support plate to return to room temperature before its length becomes longer, thereby providing support force to the internal electrode sheet.

Description

Technical Field

[0001] The invention relates to the technical field of battery manufacturing, and in particular to a method for solving the wrinkling of negative electrode sheets. Background Art

[0002] The proportion of wind and solar power generation is increasing year by year. This type of intermittent energy will aggravate the instability of the power grid, so it is necessary to match energy storage power stations to alleviate its damage to the power grid. Square aluminum shell lithium-ion batteries are widely used in the field of energy storage due to their high energy density, high space utilization, and low cost. However, due to the stress problem of the outer ring of the square aluminum shell battery roll core, the inner ring negative electrode sheet will have wrinkles after being assembled into a battery cell. These wrinkles will cause the interface between the positive and negative electrodes to deteriorate, resulting in problems such as inability to exert capacity and dendrites, which will seriously affect the battery cycle and safety issues.

[0003] In the existing field, the method to solve the problem of wrinkles on the negative electrode sheet inside the winding core is:

[0004] (1) Variable tension winding, with a larger tension on the inside and a smaller tension on the outside. This method can alleviate the wrinkle problem to a certain extent through process improvements, but it cannot fundamentally solve the problem.

[0005] (2) Use PVDF coated separator to bond the positive and negative electrodes and limit the wrinkling of the negative electrode. The double-layer PVDF coated separator can firmly fix the positive and negative electrodes and prevent the wrinkling of the negative electrode, but the cost of the double-layer coated separator increases significantly and is not suitable for large-scale mass production.

[0006] (3) Use thicker copper foil to improve the anti-wrinkle performance of the negative electrode. Thicker copper foil can improve the anti-bending performance of the current collector, but the cost of copper foil in the battery cell will increase significantly. At the same time, thicker thickness will reduce the proportion of active materials in the battery cell and reduce the energy density of the battery. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide a method for solving the wrinkles of negative electrode sheets.

[0008] The technical solution to achieve the purpose of the present invention is: a method for solving the wrinkles of negative electrode sheets, comprising the following steps:

[0009] S1, shortening the variable length support plate to a length suitable for the inside of the winding core through low temperature treatment;

[0010] S2, during winding, the shortened variable length support plate is placed inside the winding core as a winding core lining;

[0011] S3, after winding, the variable length support plate is restored to room temperature and its length is restored to the initial length.

[0012] The material of the variable-length support plate described in the above technical solution is a thermally expandable and thermally contractible material.

[0013] The material of the variable-length support plate described in the above technical solution is a composite of one or more of high molecular polymer, resin and rubber.

[0014] The high molecular polymer described in the above technical solution is one or more of polystyrene, polypropylene, polyethylene, polytetrafluoroethylene, and polymethyl methacrylate.

[0015] The volume shrinkage rate of the variable-length support plate described in the above technical solution at low temperatures is greater than the volume expansion rate at room temperature or high temperatures.

[0016] The length change rate of the variable-length support plate described in the above technical solution is 0-10% at 0-25°C, and is 0-1% at a temperature greater than 25°C.

[0017] The variable-length support plate described in the above technical solution is a porous structure.

[0018] The porosity of the variable-length support plate described in the above technical solution is 10% to 50%.

[0019] The variable-length support plate described in the above technical solution has the characteristics of oxidation resistance and electrolyte resistance.

[0020] The variable-length support plate described in the above technical solution is compressible and can be compressed to a force of 0.01 MPa to 1 MPa.

[0021] After adopting the above technical solution, the present invention has the following positive effects:

[0022] (1) The present invention introduces a variable-length support plate inside the winding core to ensure uniform force on the internal winding core and avoid wrinkles. The length of the variable-length support plate changes significantly at low temperatures, and the length changes are negligible at room temperature and high temperatures. The support plate is placed inside the winding core at low temperatures, and the length of the support plate becomes longer after it returns to room temperature, thereby providing support force to the internal pole piece.

[0023] (2) The variable length support plate ensures both the feasibility of assembly and the support force for the internal pole piece.

[0024] (3) The variable length support plate has a certain compressibility, which can effectively alleviate the expansion of the winding core during the cycle while ensuring good interface contact of the electrode.

[0025] (4) The variable-length support plate has a porous structure and a certain liquid retention capacity. It can slowly release the electrolyte in the later stage of the cycle, thus improving the cycle performance to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1It is a schematic diagram of the structure of a variable length support plate of the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of placing the variable length support plate into the winding core of the present invention.

[0028] In the figure: a variable length support plate 1, a variable length support plate aperture 1-1, and a winding core 2. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] See Figure 1 and Figure 2 The present invention provides a method for solving the wrinkles of negative electrode sheets, comprising the following steps:

[0032] S1, shortening the variable length support plate 1 to a length suitable for the interior of the winding core 2 by low temperature treatment;

[0033] S2, when winding, the shortened variable-length support plate 1 is placed inside the core 2 as the inner lining of the core 2; by introducing the variable-length support plate into the core 2, it is ensured that the force on the inside and outside of the core 2 is uniform, thus avoiding the generation of wrinkles.

[0034] S3, after winding, the variable length support plate 1 is restored to room temperature and its length is restored to the initial length.

[0035] The variable length support plate 1 is made of a thermal expansion and contraction material, which is a composite of one or more polymers, resins, and rubbers. The polymer is one or more of polystyrene, polypropylene, polyethylene, polytetrafluoroethylene, and polymethyl methacrylate. The variable length support plate 1 has the characteristics of oxidation resistance and electrolyte resistance.

[0036] The volume shrinkage rate of the variable length support plate 1 at low temperature is greater than the volume expansion rate at room temperature or high temperature. The length change of the variable length support plate 1 at low temperature is obvious, and the length change at room temperature and high temperature is negligible, so as to avoid the core 2 being broken due to the increase of the battery cell temperature during the cycle.

[0037] Specifically, the length change rate of the variable-length support plate 1 is 0-10% at 0-25°C, and is 0-1% at a temperature greater than 25°C.

[0038] The variable length support plate 1 is a porous structure, and the variable length support plate 1 is provided with a variable length support plate pore 1-1. The porosity of the variable length support plate 1 is 10% to 50%. The variable length support plate pore 1-1 of the variable length support plate 1 can absorb excess electrolyte and slowly release electrolyte in the later stage of the cycle, thereby improving the cycle performance to a certain extent.

[0039] The variable length support plate 1 is compressible, and the compressible force is 0.01MPa-1Mpa. The variable length support plate 1 has a certain compressibility, which can effectively alleviate the expansion of the winding core 2 during the cycle, while ensuring good contact between the electrode interface.

[0040] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for solving the wrinkles of negative electrode sheets, characterized in that: The following steps are involved: S1, shortening the variable length support plate to a length suitable for the inside of the winding core through low temperature treatment; S2, during winding, the shortened variable length support plate is placed inside the winding core as a winding core lining; S3, after winding, the variable length support plate is restored to room temperature and its length is restored to the initial length; The volume shrinkage rate of the variable-length support plate at low temperature is greater than the volume expansion rate at room temperature or high temperature; The length change rate of the variable-length support plate is 0-10% at 0-25°C, and is 0-1% at a temperature greater than 25°C.

2. A method for solving wrinkles on negative electrode sheets according to claim 1, characterized in that: The variable-length support plate is made of a thermally expandable and thermally contractible material.

3. A method for solving wrinkles of negative electrode sheets according to claim 2, characterized in that: The variable-length support plate is made of a material selected from the group consisting of high molecular polymer, resin, and rubber.

4. The method for solving the wrinkles of the negative electrode sheet according to claim 3, characterized in that: The high molecular polymer is one or more of polystyrene, polypropylene, polyethylene, polytetrafluoroethylene, and polymethyl methacrylate.

5. The method for solving the wrinkles of negative electrode sheets according to claim 1, characterized in that: The variable-length support plate is a porous structure.

6. A method for solving wrinkles on negative electrode sheets according to claim 5, characterized in that: The porosity of the variable-length support plate is 10% to 50%.

7. The method for solving the wrinkles of negative electrode sheets according to claim 1, characterized in that: The variable-length support plate has the characteristics of oxidation resistance and electrolyte resistance.

8. The method for solving the wrinkles of negative electrode sheets according to claim 1, characterized in that: The variable-length support plate is compressible, and the compressible force is 0.01 MPa to 1 MPa.

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