Method for improving binding power of positive pole piece of lithium battery

Abstract

The invention discloses a method for improving the binding power of a positive pole piece of a lithium battery. The method comprises the following steps: S1, arranging a heating device on a cold press; and S2, in the transmission process of the positive pole piece, heating the positive pole piece by a heating device. According to the method for improving the binding power of the positive pole piece of the lithium battery, the positive pole piece is heated, and the binding agent in the positive pole piece is softened, so that a binding network of the binding agent and the active substance is increased, the binding power between the active substance and the foil is improved, and the active substance is prevented from falling off in the electrolyte soaking and battery using process; and meanwhile, the flexibility of the positive pole piece is improved, so that the cycle service life of the battery is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery manufacturing, and in particular, relates to a method for improving the bonding force of a lithium battery positive electrode sheet. Background Art

[0002] With the rapid development of new energy vehicles, the demand for lithium-ion batteries with high cycle stability and high safety is more urgent.

[0003] In the current lithium-ion battery manufacturing process, cold pressing technology is used to roll the battery pole piece. During the cold pressing process, if the ambient humidity is not controlled, the active material in the pole piece will absorb moisture in the air, which will not only affect the alkalinity of the active material surface, but also affect the thickness rebound; if the ambient humidity is controlled, the ambient temperature will be low, and the material deformation resistance will increase with the decrease in temperature, and the plastic deformation will also decrease. Most importantly, there will be insufficient adhesion between the active material and the current collector, causing the active material to separate and fall off during the battery charging and discharging process, thereby affecting the battery cycle life.

[0004] It is hoped to provide a method for improving the bonding strength of the positive electrode sheet of a lithium battery, especially how to improve the bonding strength between the active material and the current collector, reduce the shedding of the active material during immersion in the electrolyte and use of the battery, thereby extending the cycle life of the battery. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for improving the bonding strength of a lithium battery positive electrode sheet, the purpose of which is to improve the bonding strength between the active material and the current collector during the rolling process of the battery electrode sheet using the cold pressing technology, and reduce the shedding of the active material during the electrolyte immersion and battery use process.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for improving the bonding strength of a positive electrode sheet of a lithium battery, comprising the steps of:

[0007] S1. A heating device is provided on the cold press;

[0008] S2. During the transmission of the positive electrode plate, the heating device heats the positive electrode plate.

[0009] The heating device is arranged at the unwinding driving roller position of the cold press.

[0010] The heating method of the heating device is infrared heating.

[0011] The heating method of the heating device is electromagnetic heating.

[0012] In the step S2, the heating device heats the positive electrode plate to 80-200°C.

[0013] In the step S2, the heating device heats the positive electrode plate to 100-180°C.

[0014] In the step S2, the heating device heats the positive electrode plate for 0.3 to 3 seconds.

[0015] In the step S2, the heating device heats the positive electrode plate for 0.5 to 2 seconds.

[0016] The method for improving the bonding strength of the positive electrode sheet of a lithium battery of the present invention heats the positive electrode sheet to soften the bonding agent in the positive electrode sheet, thereby increasing the bonding network between the bonding agent and the active material, improving the bonding strength between the active material and the foil, reducing the shedding of the active material during electrolyte immersion and battery use, and improving the flexibility of the positive electrode sheet, thereby extending the cycle service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] This specification includes the following drawings, which show the following contents:

[0018] Figure 1 It is a flow chart of the method for improving the bonding force of the positive electrode sheet of a lithium battery according to the present invention;

[0019] Figure 2 is a graph of the electrode peeling strength and its growth rate at different hot pressing temperatures in Example 1;

[0020] Figure 3 This is a graph of peel strength and growth rate of different PVDF contents under hot pressing at 150°C in Example 2. DETAILED DESCRIPTION

[0021] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the present invention and facilitating its implementation.

[0022] like Figure 1 As shown, the present invention provides a method for improving the bonding strength of a positive electrode sheet of a lithium battery, comprising the following steps:

[0023] S1. A heating device is provided on the cold press;

[0024] S2. During the transmission of the positive electrode plate, the heating device heats the positive electrode plate.

[0025] Specifically, in the above step S1, the heating device is arranged at the unwinding drive roller position of the cold press, and the heating method of the heating device is infrared heating or electromagnetic heating.

[0026] In the above step S2, when the heating is started, the heating device heats the positive electrode plate to 100-180°C. Exemplarily, the heating device heats the positive electrode plate to 110°C, 120°C, 130°C, 140°C, 150°C or 160°C. In the above step S2, the heating device heats the positive electrode plate for 0.5 to 2S. Exemplarily, the heating time can be 0.8S, 1.0S, 1.2S, 1.5S or 1.8S. Generally, the actual operating speed of the equipment is 30-50m / min, and the retention time of the electrode in the equipment is about 0.5 to 2S. The heating time can be affected by adjusting the operating speed of the equipment. In addition, the equipment runs very fast, and the time gradient of a few tenths of a second does not significantly affect the electrode, so there is no need to verify the time gradient.

[0027] When the cold pressing technology is used to roll the positive electrode sheets of the battery, the positive electrode sheets are heated during the transmission process, and the binder in the positive electrode sheets softens, which increases the bonding network between the binder and the active material, improves the bonding force between the active material and the foil, and at the same time improves the flexibility of the positive electrode sheets.

[0028] Compared with the cold-pressed electrode, the bonding strength of the positive electrode obtained by this method is increased by 1-10 times, and the problem of the innermost winding fracture of the electrode is improved.

[0029] In the present invention, the following method can be used to verify the bonding strength of the heated battery electrode sheet, and the verification method includes the following steps:

[0030] Step 1: Take the mass-produced cold-pressed (16.5°C) electrode and test its peel strength A;

[0031] Step 2: Take the mass-produced coated positive electrode sheet, roll it using a cold press with a heating device, the heating temperature is 100-180°C, and test the peel strength B of the electrode sheet;

[0032] Step 3: Take the electrode sheets coated with different PVDF contents (1-2.5%), use a roller press with a heating device to roll them, the heating temperature is 100-180°C, and test the electrode peel strength C;

[0033] Compared with the existing solution using cold pressing technology, the method proposed by the present invention has the following three advantages:

[0034] First, the bonding strength of the positive electrode sheet is significantly improved;

[0035] Second, under the premise that the bonding strength meets the requirements of the battery cell process and electrical performance, the amount of PVDF auxiliary materials used can be reduced by 0.5-1%, thereby improving the energy density of the battery;

[0036] The third is to improve the flexibility of the positive electrode sheet and improve the situation of inner circle winding breakage of the positive electrode sheet during the winding process.

[0037] Example 1

[0038] The method for verifying the bonding strength of the heated battery electrode provided in this embodiment includes the following steps:

[0039] Step 1: Take the mass-produced cold-pressed electrode as the control group and test its peel strength A;

[0040] Step 2: Take the mass-produced coated electrode and roll it using a roller press with a heating device at a heating temperature of 100 to 180°C, and test its peel strength B.

[0041] The verification results are shown in Table 1.

[0042] Table 1 Peel strength and growth rate at different hot pressing temperatures

[0043] Temperature / ℃ Peel strength (N / m) Peel strength growth rate % 16.5 12.5 0.00％ 100 34.7 177.6％ 120 59.4 375.2％ 150 92.6 640.8％ 180 143.5 1048.0％

[0044] Example 2

[0045] The method for verifying the bonding strength of the heated battery electrode provided in this embodiment includes the following steps:

[0046] Step 1: Take the mass-produced cold-pressed rear electrode (PVDF content is 2.0%) A as the control group and test its peel strength;

[0047] Step 2: Take mass-produced pole pieces coated with different PVDF contents (1-2.5%), roll them using a roller press with a heating device at a heating temperature of 150° C., and test their peel strength C.

[0048] The verification results are shown in Table 2.

[0049] Table 2 Peel strength and growth rate of different PVDF contents under hot pressing at 150℃

[0050] PVDF content / % Peel strength N / m 1.0 16.5 1.5 41.7 2.0 92.6

[0051] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above-mentioned concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for improving the bonding strength of a positive electrode sheet of a lithium battery, characterized in that: Includes steps: S1. A heating device is provided on the cold press; S2. During the transmission of the positive electrode plate, the heating device heats the positive electrode plate.

2. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 1, characterized in that: The heating device is arranged at the unwinding driving roller position of the cold press.

3. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 1, characterized in that: The heating method of the heating device is infrared heating.

4. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 1, characterized in that: The heating method of the heating device is electromagnetic heating.

5. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to any one of claims 1 to 4, characterized in that: In the step S2, the heating device heats the positive electrode plate to 80-200°C.

6. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 5, characterized in that: In the step S2, the heating device heats the positive electrode plate to 100-180°C.

7. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to any one of claims 1 to 6, characterized in that: In the step S2, the heating device heats the positive electrode plate for 0.3 to 3 seconds.

8. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 7, characterized in that: In the step S2, the heating device heats the positive electrode plate for 0.5 to 2 seconds.

9. The method for improving the bonding strength of a positive electrode sheet of a lithium battery according to claim 7, characterized in that: In the step S2, the heating device heats the positive electrode plate for 1.5 seconds.

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