Diaphragm and lithium ion battery

Abstract

In order to solve the problem of insufficient electrolyte infiltration in the middle position of a pole piece of a winding type long and narrow battery in the prior art, the utility model provides a diaphragm and a lithium ion battery, the diaphragm comprises a base membrane layer and a PVDF (Polyvinylidene Fluoride) coating layer, the PVDF coating layer is arranged on the surface of the base membrane layer and comprises a first area and two second areas, and the first area and the second area are arranged on the surface of the base membrane layer. The first area is arranged in the middle of the diaphragm, the two second areas extend from the edge of the first area to the end part of the diaphragm in the length direction, and the porosity of the first area is greater than that of the second areas. According to the diaphragm provided by the utility model, the second region with small porosity is relatively high in overall density, so that the rigidity and the tensile resistance of the diaphragm are improved, that is, through the combination of the first region and the second region, the overall wettability of the diaphragm can be improved, and the mechanical strength of the diaphragm can be ensured; the electrochemical performance and the service life of the lithium ion battery are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of lithium ion battery manufacturing, in particular to a diaphragm and a lithium ion battery. Background Art

[0002] With the widespread application of lithium-ion battery products, and in order to enhance product differentiation and competitiveness, lithium-ion battery sizes have become diversified. For example, under the same pack size, long and narrow batteries can be designed with higher capacity and higher discharge power. However, due to the characteristics of small width and large length of wound long and narrow batteries, after injection, the electrolyte flows from the edge positions (head and bottom) along the length of the battery to infiltrate the pole piece, and gradually diffuses to the middle of the pole piece. However, due to the longer battery length, under the same infiltration process conditions, the self-driving force for the electrolyte to infiltrate from the edge of the pole piece to the middle of the pole piece is insufficient, and the difficulty of electrolyte infiltration into the middle of the pole piece is greatly increased. Abnormal infiltration in the middle of the pole piece can easily cause black spots and lithium precipitation in the middle of the pole piece after cycling, affecting battery performance and service life. How to improve the infiltration degree of the middle position of the pole piece of long and narrow batteries becomes the key. Utility Model Content

[0003] The technical problem to be solved by the utility model is to provide a diaphragm and a lithium ion battery in view of the problem of insufficient electrolyte infiltration in the middle of the pole piece of a wound long narrow battery in the prior art.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0005] On the one hand, the utility model provides a diaphragm, including a base membrane layer and a PVDF coating layer, the PVDF coating layer is arranged on the surface of the base membrane layer, the PVDF coating layer includes a first region and two second regions, the first region is arranged in the middle position of the diaphragm, and the two second regions extend from the edge of the first region to the end of the length direction of the diaphragm, and the porosity of the first region is greater than the porosity of the second region.

[0006] Optionally, the porosity of the first region is 30% to 45%, and is greater than the porosity of the second region.

[0007] Optionally, the porosity of the second region is 20% to 35%, and is smaller than the porosity of the first region.

[0008] Optionally, the coverage of the first region on the surface of the base film layer is 10% to 30%.

[0009] Optionally, the coverage of the second region on the surface of the base film layer is 70% to 90%.

[0010] Optionally, the average coating thickness of the second region is 2.5 μm to 4.0 μm, and the average coating thickness of the first region is 1.5 μm to 3.0 μm.

[0011] Optionally, the diaphragm further includes a ceramic layer, the ceramic layer is disposed between the base membrane layer and the PVDF coating layer, the ceramic layer includes ceramic particles, and the average thickness of the ceramic layer is 0.5 μm to 2.0 μm;

[0012] The ceramic particles are boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide or silicon dioxide.

[0013] Optionally, the first region is a spray coating, and the second region is a roller coating.

[0014] Optionally, the base film layer is a polyethylene film layer, a polypropylene film layer, a non-woven fabric film layer or a polyimide film layer.

[0015] On the other hand, the present invention provides a lithium-ion battery, comprising a pole piece, a pole tab and the diaphragm, wherein the pole tab is led out from the pole piece, and the pole piece and the diaphragm are wound to form a battery core.

[0016] The beneficial effects of the present invention are:

[0017] The diaphragm provided by the present invention includes a base film layer and a PVDF coating layer, the PVDF coating layer includes a first region and two second regions, the porosity of the first region is greater than the porosity of the second region, and under the condition that the porosity of the first region is greater than the porosity of the second region, by arranging the first region in the middle of the base film layer, the injected electrolyte penetrates through the porosity of the first region and quickly diffuses in the first region, which is beneficial to improving the infiltration of the diaphragm corresponding to the first region; the second region with small porosity has a higher overall density, which is beneficial to improving the rigidity and tensile resistance of the diaphragm, that is, the combination of the first region and the second region can not only improve the overall infiltration of the diaphragm but also ensure the mechanical strength of the diaphragm itself; and further, in the subsequent assembly of lithium-ion batteries, the use of the diaphragm provided by the present application can effectively solve the problem of insufficient electrolyte infiltration in the middle of long and narrow batteries, avoid the generation of black spots and lithium precipitation in lithium-ion batteries, and at the same time be beneficial to improving the electrochemical performance and service life of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 This is a schematic diagram of the diaphragm structure provided by the utility model;

[0020] Figure 2 This is a schematic cross-sectional view of the diaphragm corresponding to the first region provided by the present invention;

[0021] Figure 3 is a schematic cross-sectional view of the diaphragm corresponding to the second region provided by the present invention;

[0022] Figure 4 This is a schematic diagram of the lithium-ion battery structure provided by the utility model.

[0023] The reference numerals in the drawings of the specification are as follows:

[0024] 1. Base film layer; 2. PVDF coating layer; 21. First region; 22. Second region; 3. Ceramic layer; 4. Tab; 5. Battery cell. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] In the description of the present invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0027] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0028] An embodiment of the present invention provides a diaphragm, including a base membrane layer 1 and a PVDF coating layer 2, wherein the PVDF coating layer 2 is arranged on the surface of the base membrane layer 1, and the PVDF coating layer 2 includes a first region 21 and two second regions 22, wherein the first region 21 is arranged in the middle position of the diaphragm, and the two second regions 22 extend from the edge of the first region 21 to the end of the length direction of the diaphragm, and the porosity of the first region 21 is greater than the porosity of the second region 22.

[0029] Specifically, the diaphragm provided by the present invention includes a base film layer 1 and a PVDF coating layer 2, the PVDF coating layer 2 includes a first region 21 and two second regions 22, the porosity of the first region 21 is greater than the porosity of the second region 22, and under the condition that the porosity of the first region 21 is greater than the porosity of the second region 22, by arranging the first region 21 in the middle of the base film layer 1, the injected electrolyte penetrates through the porosity of the first region 21 and diffuses rapidly in the first region 21, which is beneficial to improving the infiltration of the diaphragm corresponding to the first region 21; the second region 22 with small porosity has a higher overall density, which is beneficial to improving the rigidity and tensile resistance of the diaphragm, that is, the combination of the first region 21 and the second region 22 can not only improve the overall infiltration of the diaphragm but also ensure the mechanical strength of the diaphragm itself; and further, in the subsequent lithium-ion battery assembly, the use of the diaphragm provided by the present application can effectively solve the problem of insufficient electrolyte infiltration in the middle of the long and narrow battery, avoid the generation of black spots and lithium precipitation in the lithium-ion battery, and at the same time be beneficial to improving the electrochemical performance and service life of the lithium-ion battery.

[0030] In one embodiment, the porosity of the first region 21 is 30%-45% and is higher than the porosity of the second region 22 .

[0031] Specifically, the porosity of the first region 21 can be 35%, 40% or 45%. The porosity within the above range is conducive to ensuring that the first region 21 has good wetting conditions when infiltrating the electrolyte, thereby improving the wettability of the diaphragm, making it easier for the electrolyte to penetrate the diaphragm, and thus improving the overall electrochemical performance of the lithium-ion battery.

[0032] In one embodiment, the porosity of the second region 22 is 20%-35%, which is lower than the porosity of the first region 21 .

[0033] Specifically, the porosity of the second region 22 can be 20%, 25% or 30%. The porosity within the above range ensures that the second region 22 has good electrolyte infiltration ability while improving the mechanical strength and puncture resistance of the diaphragm; specifically, the second region 22 with a small porosity has a higher overall density, which increases the rigidity and tensile resistance of the diaphragm. Secondly, during the use of lithium-ion batteries, there is a risk of puncturing the diaphragm due to the growth of lithium dendrites or burrs on the edge of the electrode and other sharp objects. In this application, by arranging the second region 22 with a smaller porosity at both ends of the diaphragm, the risk of puncture can be effectively reduced, thereby improving the safety of the battery.

[0034] In one embodiment, the coverage of the first region 21 on the surface of the base film layer 1 is 10% to 30%.

[0035] Specifically, the pore coverage of the first region 21 is controlled within the range of 10% to 30%, which can not only ensure good electrolyte infiltration ability and improve the electrochemical properties of the diaphragm, but also enable the diaphragm to have sufficient mechanical strength and puncture resistance; the coverage of the first region 21 on the surface of the base film layer 1 can be 10%, 20% or 30%.

[0036] In one embodiment, the coverage of the second region 22 on the surface of the base film layer 1 is 70% to 90%.

[0037] Specifically, the coverage rate of the second region 22 on the surface of the base film layer 1 can be 70%, 80% or 90%; specifically, during the hot pressing process of assembling the electrode with the diaphragm, when the coverage rate of the second region 22 on the surface of the base film layer 1 is within the above range, the contact area between the second region 22 and the electrode can be ensured, thereby ensuring the bonding strength between the diaphragm and the electrode.

[0038] In one embodiment, the average coating thickness of the second region 22 is 2.5 μm to 4.0 μm, and the average coating thickness of the first region 21 is 1.5 μm to 3.0 μm.

[0039] Specifically, the average coating thickness of the second region 22 can be 2.5 μm, 3.0 μm or 4.0 μm, and the average coating thickness of the first region 21 can be 1.5 μm, 2 μm or 3.0 μm; specifically, when the thickness of the first region 21 and the thickness of the second region 22 are too thick, the thickness of the diaphragm increases, so that the number of layers that can be wound of the diaphragm is smaller, and accordingly, the capacity of the lithium-ion battery will also decrease. In addition, when the thickness of the first region 21 and the thickness of the second region 22 are too thin, the thickness of the diaphragm is also reduced accordingly, and its puncture resistance performance is also reduced, which is not conducive to improving the safety performance of the lithium-ion battery.

[0040] In one embodiment, the diaphragm further includes a ceramic layer 3, which is disposed between the base membrane layer 1 and the PVDF coating layer 2. The ceramic layer 3 includes ceramic particles, and the average thickness of the ceramic layer is 0.5 μm to 2 μm.

[0041] The ceramic particles are boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide or silicon dioxide.

[0042] Specifically, setting the ceramic layer 3 is beneficial to improving the high temperature resistance and mechanical strength of the diaphragm. In this application, the ceramic layer 3 is set between the base film layer 1 and the PVDF coating layer 2. This multi-layer structure not only optimizes the performance of the diaphragm, but also increases its mechanical strength. The high hardness and good dispersion of the ceramic particles in the ceramic layer 3 effectively prevent puncture due to external physical damage or lithium dendrite growth, thereby reducing the risk of internal short circuit of the battery. In addition, the porous structure of the ceramic layer 3 provides good wettability for the electrolyte and ensures the transmission of lithium ions, which helps the battery to work stably under high load conditions and improves the charge and discharge efficiency of the battery.

[0043] In one embodiment, the first region 21 is a spray coating, and the second region 22 is a roller coating.

[0044] Specifically, the first region 21 is a spray coating layer, which uses a spraying technology to spray the corresponding coating onto the surface of the base film layer 1 at the corresponding position, so that irregular pores are formed in the corresponding spray coating area of ​​the diaphragm, which is conducive to the electrolyte to penetrate and diffuse quickly through the pores, thereby improving the infiltration speed and infiltration degree of the electrolyte in the middle area of ​​the electrode in subsequent assembly; the roller coating layer of the second region 22 provides good mechanical strength due to its highly uniform and dense characteristics.

[0045] In one embodiment, the base film layer 1 is a polyethylene film layer, a polypropylene film layer, a non-woven fabric film layer or a polyimide film layer.

[0046] Specifically, the base membrane layer 1 generally adopts a porous structure, which helps to isolate the positive and negative electrodes of the battery while allowing lithium ions to pass freely during charging and discharging. The base membrane layer 1 not only plays a mechanical isolation role, but also can close micropores at high temperatures, limit current to prevent short circuits, and thus improve the safety of the battery.

[0047] Another embodiment of the present invention provides a lithium-ion battery, comprising a pole piece, a pole tab 4 and the above-mentioned separator, wherein the pole tab 4 is led out from the pole piece, and the pole piece and the separator are wound to form a battery cell 5.

[0048] Specifically, the electrode sheets include positive electrode sheets and negative electrode sheets. After the positive electrode sheets, the negative electrode sheets and the diaphragm are placed in sequence, a battery cell 5 is formed through a winding process. The battery cell 5 is placed in a corresponding battery shell and injected with liquid to form a fully assembled lithium-ion battery. The lithium-ion battery includes the diaphragm provided by the present application, which can effectively solve the problem of poor electrolyte infiltration in the middle of a long and narrow battery, avoid the generation of black spots and lithium plating in the lithium-ion battery, and improve the electrochemical performance and service life of the lithium-ion battery.

[0049] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. 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 make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: The invention comprises a base membrane layer (1) and a PVDF coating layer (2), wherein the PVDF coating layer (2) is arranged on the surface of the base membrane layer (1), and the PVDF coating layer (2) comprises a first region (21) and two second regions (22), wherein the first region (21) is arranged in the middle of the diaphragm, and the two second regions (22) extend from the edge of the first region (21) to the end of the length direction of the diaphragm, and the porosity of the first region (21) is greater than the porosity of the second region (22).

2. A diaphragm according to claim 1, characterized in that: The porosity of the first region (21) is 30% to 45%, and is higher than the porosity of the second region (22).

3. A diaphragm according to claim 1, characterized in that: The porosity of the second region (22) is 20% to 35%, and is lower than the porosity of the first region (21).

4. A diaphragm according to claim 1, characterized in that: The coverage of the first region (21) on the surface of the base film layer (1) is 10% to 30%.

5. The diaphragm according to claim 1, characterized in that: The coverage of the second region (22) on the surface of the base film layer (1) is 70% to 90%.

6. The diaphragm according to claim 1, characterized in that: The average coating thickness of the second region (22) is 2.5 μm to 4.0 μm, and the average coating thickness of the first region (21) is 1.5 μm to 3.0 μm.

7. The diaphragm according to claim 1, characterized in that: The diaphragm further comprises a ceramic layer (3), the ceramic layer (3) being arranged between the base membrane layer (1) and the PVDF coating layer (2), the ceramic layer (3) comprising ceramic particles, and the average thickness of the ceramic layer being 0.5 μm to 2.0 μm; The ceramic particles are boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide or silicon dioxide.

8. A diaphragm according to claim 7, characterized in that: The first region (21) is a spray coating, and the second region (22) is a roller coating.

9. The diaphragm according to claim 1, characterized in that: The base film layer (1) is a polyethylene film layer, a polypropylene film layer, a non-woven fabric film layer or a polyimide film layer.

10. A lithium ion battery, characterized in that: It comprises a pole piece, a pole ear (4) and a separator according to any one of claims 1 to 9, wherein the pole ear (4) is led out from the pole piece, and the pole piece and the separator are wound to form a battery core (5).

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