Separator, electrochemical device, and electronic apparatus

Abstract

The invention relates to the technical field of electrochemical energy storage, and discloses a diaphragm, an electrochemical device and electronic equipment, the diaphragm comprises a base film, a first protective layer and a second protective layer, the base film is provided with an anode side surface and a cathode side surface opposite to each other at an interval along the thickness direction; the first protective layer is connected to the positive side surface; the second protective layer is connected to the side surface of the negative electrode and is of a flexible porous structure; wherein the hardness of the first protective layer is greater than that of the second protective layer, so that the safety performance of the electrochemical device can be improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a diaphragm, an electrochemical device, and an electronic device. Background Technology

[0002] The separator is one of the core structures of a lithium-ion battery. Its core function is to separate the positive and negative electrodes, prevent direct contact between the positive and negative electrodes and short circuits, and at the same time provide a stable channel for the migration of lithium ions.

[0003] Currently, the separator can be punctured by burrs, particles, etc., affecting the safety performance of the battery. Summary of the Invention

[0004] This invention aims to address at least one of the technical problems existing in the prior art. To this end, this invention proposes a diaphragm that can improve the safety performance of electrochemical devices.

[0005] The present invention also proposes an electrochemical device having the above-mentioned diaphragm, and an electronic device having the electrochemical device.

[0006] According to a first aspect of the present invention, the separator includes a base film, a first protective layer, and a second protective layer. The base film has a positive electrode side surface and a negative electrode side surface spaced apart and opposite to each other along the thickness direction. The first protective layer is connected to the positive electrode side surface. The second protective layer is connected to the negative electrode side surface and has a flexible porous structure. The hardness of the first protective layer is greater than that of the second protective layer.

[0007] The separator according to embodiments of the present invention has at least the following beneficial effects: the base membrane has a positive electrode side surface and a negative electrode side surface spaced apart along the thickness direction; a first protective layer is connected to the positive electrode side surface; and a second protective layer is connected to the negative electrode side surface, thereby improving the structural strength of the separator and reducing the possibility of the separator being punctured. The hardness of the first protective layer is greater than that of the second protective layer, thereby increasing the hardness of the first protective layer. On the one hand, the high hardness of the first protective layer can suppress the thermal shrinkage of the separator under high temperature conditions, helping to avoid short circuits between the positive and negative electrode plates due to thermal shrinkage of the separator. On the other hand, the positive electrode particles of the positive electrode plate are relatively hard, and the high hardness of the first protective layer can reduce the possibility of the positive electrode particles of the positive electrode plate puncturing the first protective layer. The second protective layer is a flexible porous structure. On the one hand, the porous structure of the second protective layer can provide a smoother channel for lithium-ion transport and reduce the transport impedance. On the other hand, during the cycling process of the electrochemical device, the expansion and contraction of the negative electrode is relatively violent. The flexible second protective layer can provide a buffer for the expansion of the negative electrode, reducing stress concentration. Moreover, the flexible second protective layer can better restore its original shape after being squeezed by the negative electrode, which helps to reduce the deformation and blockage of the pores in the second protective layer.

[0008] According to some embodiments of the present invention, a plurality of first protrusions are provided on the surface of the first protective layer facing away from the positive electrode side and / or the surface of the second protective layer facing away from the negative electrode side.

[0009] According to some embodiments of the present invention, the first protrusions are spaced apart, and the distance between any two adjacent first protrusions is ≥10 micrometers and ≤50 micrometers; and / or, the protrusion height of the first protrusion is ≥3 micrometers and ≤5 micrometers.

[0010] According to some embodiments of the present invention, the first protective layer is a ceramic layer.

[0011] According to some embodiments of the present invention, the porosity of the second protective layer is ≥40% and ≤50%; and / or, the thickness of the first protective layer along the thickness direction is ≥2 micrometers and ≤10 micrometers; and / or, the thickness of the second protective layer along the thickness direction is ≥4.5 micrometers and ≤7.5 micrometers.

[0012] An electrochemical device according to a second aspect of the present invention includes an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator as described in any of the above embodiments, the separator being disposed between the positive electrode and the negative electrode, the positive electrode, the separator, and the negative electrode being sequentially stacked and wound into a core structure; wherein the positive electrode is in contact with a first protective layer, and the negative electrode is in contact with a second protective layer.

[0013] According to some embodiments of the present invention, the electrochemical device further includes a housing, a negative electrode tab, and a temperature-sensitive element. The negative electrode tab is connected to the negative electrode plate and is at least partially disposed outside the electrode assembly. The temperature-sensitive element is at least partially connected to the negative electrode tab and configured to change color when the temperature reaches a threshold temperature. The electrode assembly and the temperature-sensitive element are both disposed within the housing, and the negative electrode tab is at least partially disposed within the housing. The housing includes a light-transmitting portion, and the light-transmitting portion and the temperature-sensitive element are disposed opposite to each other.

[0014] According to some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is connected to the surface of the negative electrode current collector and has a first groove to expose a portion of the negative electrode current collector. The first groove penetrates the edge of the negative electrode active material layer along one side of the axial direction of the electrode assembly. The negative electrode tab includes a connecting portion and an extension portion connected to each other. The connecting portion is disposed in the first groove and connected to the negative electrode current collector, and the extension portion is located outside the electrode assembly. The temperature-sensitive element is at least partially connected to the extension portion.

[0015] According to some embodiments of the present invention, the electrochemical device further includes a conductive adhesive layer disposed in the first groove and bonded between the negative electrode current collector and the connecting portion; the temperature-sensitive element includes a first temperature-sensitive portion and a second temperature-sensitive portion connected to each other, the first temperature-sensitive portion being disposed between the conductive adhesive layer and the connecting portion; the second temperature-sensitive portion being connected to the epitaxial portion, and the light-transmitting portion and the second temperature-sensitive portion being opposite to each other.

[0016] An electronic device according to a third aspect of the present invention is characterized in that it includes the electrochemical device in any of the above embodiments.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 A schematic diagram of the structure of the electrochemical device provided in an embodiment of the present invention is shown; Figure 2 This diagram illustrates the structure of the electrode assembly, positive electrode tab, and negative electrode tab provided in an embodiment of the present invention. Figure 3 This diagram shows a cross-sectional view of the negative electrode sheet, negative electrode tab, temperature-sensitive element, and conductive adhesive layer provided in an embodiment of the present invention. Figure 4 A partial cross-sectional structural diagram of the housing provided in an embodiment of the present invention is shown; Figure 5 A cross-sectional structural diagram of the diaphragm provided in an embodiment of the present invention is shown; Figure 6 A partial cross-sectional structural diagram of the electrode assembly provided in an embodiment of the present invention is shown.

[0019] Figure label: Electrochemical device 100; electrode assembly 110; positive electrode 111; negative electrode 113; negative electrode current collector 1131; negative electrode active material layer 1133; first groove 1135; separator 115; base film 1151; first protective layer 1153; first protrusion 1157; second protective layer 1155; negative electrode tab 130; connecting part 131; extension part 133; positive electrode tab 150; shell 170; light-transmitting part 171; scratch-resistant layer 1711; glass layer 1713; light-concentrating layer 1715; light-filtering layer 1717; shell body 173; accommodating cavity 1731; window 175; Temperature-sensitive element 190; first temperature-sensitive part 191; second temperature-sensitive part 193; conductive adhesive layer 210. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. 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.

[0021] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0023] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0024] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0025] Please see Figure 1 This application provides an electronic device, which includes an electrochemical device 100. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art.

[0026] The electronic devices described in this application are not particularly limited in their application and can be used with any electronic device known in the prior art. These electronic devices include, but are not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, and android robots.

[0027] In some embodiments, the electrochemical device 100 includes any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, and specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device 100 is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0028] Please see Figures 1 to 2 In some embodiments, the electrochemical device 100 includes an electrode assembly 110, which includes a positive electrode 111, a negative electrode 113, and a separator 115 disposed between the positive electrode 111 and the negative electrode 113. The positive electrode 111, the separator 115, and the negative electrode 113 are stacked and wound into a core structure. The specific structure of the core structure can refer to the prior art and will not be described in detail here.

[0029] In some embodiments, the electrochemical device 100 further includes a positive electrode tab 150, which can be connected to the positive electrode plate 111 and is at least partially located outside the electrode assembly 110 for connecting to an external circuit.

[0030] In some embodiments, the electrochemical device 100 further includes a negative electrode tab 130, which can be connected to the negative electrode plate 113 and is at least partially disposed outside the electrode assembly 110 for connecting to an external circuit.

[0031] In some embodiments, the electrochemical device 100 further includes a housing 170, within which the electrode assembly 110 may be disposed. The housing 170 may be a steel shell or a flexible encapsulation shell. The negative electrode tab 130 and the positive electrode tab 150 are at least partially located within the housing 170.

[0032] As an example, when the housing 170 is a flexible encapsulation housing, the positive tab 150 and the negative tab 130 may be partially located inside the housing 170 and partially extend outside the housing 170 for connection to external circuitry.

[0033] As another example, when the housing 170 is a steel housing, the housing 170 may include a positive conductive part and a negative conductive part, both the positive electrode tab 150 and the negative electrode tab 130 are disposed inside the housing 170, and the positive electrode tab 150 can be electrically connected to the positive conductive part, and the negative electrode tab 130 can be connected to the negative conductive part.

[0034] In some embodiments, the electrochemical device 100 may further include an electrolyte that fills the housing 170 to wet the electrode assembly 110.

[0035] Please see Figures 1 to 3In some embodiments, the electrochemical device 100 further includes a temperature-sensitive element 190, which is at least partially connected to the negative electrode tab 130 and configured to change color when the temperature reaches a threshold temperature. Thus, the temperature-sensitive element 190 can generate a color-changing reaction according to the temperature of the negative electrode tab 130, which helps to provide early warning of thermal runaway of the electrochemical device 100, reduce the risk of thermal runaway, and improve the safety performance of the electrochemical device 100.

[0036] Furthermore, the negative electrode surface is the main area for lithium-ion deposition. The growth and deposition of lithium dendrites generate a strong exothermic reaction. Placing the temperature sensor 190 on the negative electrode tab 130 can more accurately detect the temperature of the highest temperature area of ​​the electrode assembly 110, which helps to make the detection results more accurate. In addition, during the cycle of the electrochemical device 100, the negative electrode is in a low voltage region, and the reduction reaction of the electrolyte is milder. Placing the temperature sensor 190 on the negative electrode tab 130 can also improve the corrosion of the temperature sensor 190 by acidic substances generated in the electrolyte, thus extending the service life of the temperature sensor 190.

[0037] As an example, the temperature-sensitive element 190 can be bonded to the surface of the negative electrode tab 130.

[0038] The temperature-sensitive element 190 can be disposed inside the housing 170. The housing 170 includes a light-transmitting part 171, which is disposed opposite to the temperature-sensitive element 190. The temperature-sensitive element 190 can be observed through the light-transmitting part 171 to conveniently observe the color change of the temperature-sensitive element 190.

[0039] It should be noted that the temperature-sensitive component 190 can be observed with the naked eye or by scanning and identifying it through equipment to improve the identification accuracy.

[0040] As an example, taking device scanning and recognition as an example, scanning and recognition are performed using a mobile APP and CIE Lab color space analysis. Specifically, the mobile phone camera captures an image of the temperature-sensitive component 190 through the light-transmitting part 171. The APP converts the image from RGB to Lab color space, extracts the b-channel data, and compares the b-value with a preset threshold (the preset threshold corresponds to a threshold temperature) to determine whether a thermal runaway warning has been triggered. If the b-value is greater than or equal to the preset threshold, it indicates that the temperature-sensitive component 190 has shown a color change reaction, and the mobile APP outputs thermal runaway warning information. This method has higher detection accuracy and helps avoid situations where the color change of the temperature-sensitive component 190 is weak and difficult to detect with the naked eye.

[0041] The threshold temperature can be flexibly controlled according to the material ratio of the temperature-sensitive element 190. The threshold temperature can be lower than the critical temperature for thermal runaway of the electrochemical device 100, thus enabling the temperature-sensitive element 190 to provide early warning of thermal runaway. For example, the threshold temperature can be 60 degrees Celsius, or other temperatures.

[0042] In some embodiments, the temperature-sensitive element 190 may be a spiropyran-graphene temperature-sensitive element, a polyacetylene nanorod temperature-sensitive element, a thermotropic liquid crystal microcapsule temperature-sensitive element, or other temperature-sensitive materials.

[0043] In some embodiments, the negative electrode 113 may include a negative electrode current collector 1131 and a negative electrode active material layer 1133.

[0044] The negative electrode active material layer 1133 is connected to the surface of the negative electrode current collector 1131. Specifically, when the negative electrode sheet 113 is unfolded and laid flat, the negative electrode active material can be connected to at least one side of the surface of the negative electrode current collector 1131 along the thickness direction.

[0045] In some embodiments, the negative electrode tab 130 can be integrally formed with the negative electrode current collector 1131, or the negative electrode tab 130 and the negative electrode current collector 1131 can be two separate structural components.

[0046] In some embodiments, the negative electrode active material layer 1133 is provided with a first groove 1135 to expose a portion of the negative electrode current collector 1131. The first groove 1135 extends through the edge of the negative electrode active material layer 1133 along one side of the electrode assembly 110 axial direction.

[0047] The negative electrode tab 130 includes a connecting portion 131 and an extension portion 133 connected to each other. The connecting portion 131 can be disposed in the first groove 1135 and connected to the negative electrode current collector 1131. The extension portion 133 can be located outside the electrode assembly 110. The temperature-sensitive element 190 is at least partially connected to the extension portion 133, so that the temperature-sensitive element 190 can be at least partially exposed outside the electrode assembly 110 to avoid being blocked by the electrode assembly 110 and to facilitate observation of the temperature-sensitive element 190 through the light-transmitting portion 171.

[0048] In some embodiments, the electrochemical device 100 may also include a conductive adhesive layer 210.

[0049] The conductive adhesive layer 210 can be disposed in the first groove 1135 and bonded between the negative current collector 1131 and the connecting part 131, thereby avoiding the solder marks caused by welding of the negative current collector 1131 and the connecting part 131, and helping to avoid the situation where the burrs at the solder mark position puncture the diaphragm 115.

[0050] In some embodiments, the temperature-sensitive element 190 includes a first temperature-sensitive part 191 and a second temperature-sensitive part 193 connected together.

[0051] The first temperature-sensitive part 191 is disposed between the conductive adhesive layer 210 and the connecting part 131, and the second temperature-sensitive part 193 is connected to the extension part 133. The conductive adhesive layer 210 can bond and fix the first temperature-sensitive part 191, which helps to reduce the possibility of the temperature-sensitive part 190 falling off. In addition, the first temperature-sensitive part 191 can more directly reflect the temperature of the negative electrode tab 130 through the color change reaction.

[0052] The light-transmitting part 171 and the second temperature-sensitive part 193 are opposite each other so that the second temperature-sensitive part 193 can be observed through the light-transmitting part 171.

[0053] In some embodiments, the temperature-sensitive element 190 is a conductive temperature-sensitive element, which helps to prevent the temperature-sensitive element 190 from blocking the current transmission path, allowing the current to flow more smoothly. For example, the temperature-sensitive element 190 may include a thermochromic material and a conductive material.

[0054] In some embodiments, the volume resistivity of the conductive adhesive layer 210 is ≤10. -3 Ω·cm.

[0055] In some embodiments, the conductive adhesive layer 210 is an elastic conductive adhesive layer, which helps to provide buffer space for the expansion of the negative electrode 113 and reduces stress concentration.

[0056] In some embodiments, the elastic modulus of the conductive adhesive layer 210 is ≥0.5GPa and ≤1.2GPa.

[0057] Please see Figure 1 , Figure 3 and Figure 4 In some embodiments, the housing 170 may include a housing body 173. The housing body 173 has a receiving cavity 1731, and the housing wall may have a window 175 communicating with the receiving cavity 1731. The electrode assembly 110 and the temperature-sensitive element 190 may both be disposed within the receiving cavity 1731, and the positive electrode tab 150 and the negative electrode tab 130 are both at least partially disposed within the receiving cavity 1731.

[0058] The light-transmitting part 171 can be provided in the window 175 and the window 175 can be closed.

[0059] The light-transmitting portion 171 may include a scratch-resistant layer 1711, a glass layer 1713, a light-concentrating layer 1715, and a light-filtering layer 1717 connected in sequence. All three layers are light-transmitting materials. The scratch-resistant layer 1711 may be located on the surface of the light-transmitting portion 171 facing away from the receiving cavity 1731, helping to reduce the likelihood of the light-transmitting portion 171 being scratched by external structures. The glass layer 1713 can support the scratch-resistant layer 1711, the light-concentrating layer 1715, and the light-filtering layer 1717. The light-concentrating layer 1715 can focus the light, allowing for clearer observation of the temperature-sensitive element 190 through the light-transmitting portion 171. The light-filtering layer 1717 can filter out stray light unrelated to the color of the temperature-sensitive element 190, thereby enhancing the color light reflected by the temperature-sensitive element 190 and further improving recognition accuracy.

[0060] As an example, the scratch-resistant layer 1711 can be made of diamond-like carbon or other scratch-resistant materials. The glass layer 1713 can be made of sapphire glass, tempered glass-polyurethane composite matrix, or other glass. The light-concentrating layer 1715 can be made of a microprism array layer or other light-concentrating structure layer. The filter layer 1717 can select a suitable filter film according to the color change of the temperature-sensitive element 190 to enhance light of the same color as the temperature-sensitive element 190 and weaken light of different colors from the temperature-sensitive element 190.

[0061] The edges of the light-transmitting part 171 and the window 175 can be glued, welded or connected in other ways. This application embodiment does not limit this, as long as the light-transmitting part 171 can seal the window 175.

[0062] Please see Figure 2 , Figure 5 and Figure 6 In some embodiments, the diaphragm 115 includes a base membrane 1151, a first protective layer 1153, and a second protective layer 1155.

[0063] The base membrane 1151 has a positive electrode side surface and a negative electrode side surface spaced apart along its thickness direction. A first protective layer 1153 is connected to the positive electrode side surface, and a second protective layer 1155 is connected to the negative electrode side surface, thereby improving the structural strength of the separator 115 and reducing the possibility of the separator 115 being punctured. Understandably, when the negative electrode sheet 113 and the separator 115 are stacked and laid flat, the thickness direction of the base membrane 1151 is the same as the thickness direction of the negative electrode current collector 1131.

[0064] When the separator 115 is applied to the electrode assembly 110, the positive electrode 111 and the negative electrode 113 are respectively disposed on opposite sides of the separator 115 along the thickness direction. The positive electrode side surface is the surface of the base film 1151 facing the positive electrode 111, and the negative electrode side surface is the surface of the base film 1151 facing the negative electrode 113. Specifically, the positive electrode 111 is in contact with the first protective layer 1153, and the negative electrode 113 is in contact with the second protective layer 1155.

[0065] The hardness of the first protective layer 1153 is greater than that of the second protective layer 1155, thereby increasing the hardness of the first protective layer 1153. On the one hand, the high hardness of the first protective layer 1153 can suppress the thermal shrinkage of the separator 115 under high temperature environment, which helps to avoid the short circuit caused by the thermal shrinkage of the separator 115. On the other hand, the positive electrode particles of the positive electrode 111 are relatively hard, and the high hardness of the first protective layer 1153 can reduce the possibility of the positive electrode particles of the positive electrode 111 puncturing the first protective layer 1153.

[0066] The second protective layer 1155 has a flexible porous structure. On the one hand, the porous structure of the second protective layer 1155 provides a smoother channel for lithium-ion transport and reduces the transport impedance. On the other hand, during the cycling process of the electrochemical device 100, the expansion and contraction of the negative electrode 113 are relatively intense. The flexible second protective layer 1155 can provide a buffer for the expansion of the negative electrode 113, reducing stress concentration. Moreover, the flexible second protective layer 1155 can better recover its original shape after being squeezed by the negative electrode 113, which helps to reduce the deformation and blockage of the pores in the second protective layer 1155.

[0067] In some embodiments, the negative electrode active material layer 1133 may be a silicon-doped active material layer. Silicon has a large specific capacity, which helps to improve the energy density of the electrochemical device 100.

[0068] The volume expansion of the silicon-doped active material layer is more dramatic, and the second protective layer 1155 can better buffer the silicon-doped active material layer, thereby increasing the energy density of the electrochemical device 100 while reducing the risk of the diaphragm 115 being punctured.

[0069] In some embodiments, the base film 1151 may be a polyethylene (PE) film or other materials.

[0070] In some embodiments, the first protective layer 1153 may be a ceramic layer. The ceramic layer has high hardness, which helps to suppress the thermal shrinkage of the separator 115 under high temperature environment, reduces the possibility of the positive electrode particles of the positive electrode sheet 111 puncturing the first protective layer 1153, and the ceramic layer is an alkaline material, which can neutralize the acidic substances generated by the decomposition of the electrolyte, and reduces the possibility of acidic substances eroding the solid electrolyte interphase (SEI) membrane.

[0071] In some embodiments, the ceramic layer is an alumina layer, a silicon dioxide layer (SiO2 layer), a boron nitride layer (BN layer), or a hybrid material layer of polyvinylidene fluoride-hexafluoropropylene copolymer / alumina (PVDF-HFP / Al2O3 hybrid material layer). The ceramic layer may also be made of other ceramic materials besides those mentioned above.

[0072] In some embodiments, the thickness of the first protective layer 1153 along the thickness direction is ≥2 micrometers and ≤10 micrometers, thereby controlling the thickness of the first protective layer 1153 within a suitable range, improving the structural strength of the first protective layer 1153, helping to avoid the situation where the thickness of the first protective layer 1153 is too thin, which would increase the risk of the first protective layer 1153 being punctured, and also helping to avoid the situation where the thickness of the first protective layer 1153 is too thick, which would affect the flexibility of the diaphragm 115.

[0073] The thickness of the first protective layer 1153 along the thickness direction can be 2 micrometers, 5 micrometers, 6.5 micrometers, 8 micrometers, 10 micrometers, or any other value between any two of the above values.

[0074] In some embodiments, the second protective layer 1155 may be a porous polymer layer, which helps the second protective layer 1155 to have better flexibility and higher porosity.

[0075] In some embodiments, the second protective layer 1155 is a composite layer of polyethylene and polyvinylidene fluoride, a polyimide layer (PI layer), an aromatic polyamide fiber layer, or a three-layer composite layer of polypropylene / polyethylene / polypropylene (PP / PE / PP). The second protective layer 1155 may also be made of other materials besides those mentioned above.

[0076] In some embodiments, the thickness of the second protective layer 1155 along the thickness direction is ≥4.5 micrometers and ≤7.5 micrometers, thereby controlling the thickness of the second protective layer 1155 within a suitable range. This helps to avoid the situation where the thickness of the second protective layer 1155 is too thin and prone to collapse, and also helps to avoid the situation where the thickness of the second protective layer 1155 is too thick and affects the size of the electrode assembly 110.

[0077] The thickness of the second protective layer 1155 along the thickness direction can be 4.5 micrometers, 5 micrometers, 5.8 micrometers, 6.2 micrometers, 7.5 micrometers, or any other value between any two of the above values.

[0078] In some embodiments, the porosity of the second protective layer 1155 is ≥40% and ≤50%, thereby controlling the porosity of the second protective layer 1155 within a suitable range. The second protective layer 1155 can have enough pores for lithium ions to pass through, which helps to avoid the impact of lithium ion transport efficiency due to excessively small porosity, and also helps to avoid the impact of structural strength of the second protective layer 1155 due to excessively large porosity.

[0079] The porosity of the second protective layer 1155 can be 40%, 42%, 45%, 48.5%, 50%, or any other value between any two of the above percentage values.

[0080] In some embodiments, the surface of the first protective layer 1153 facing away from the positive electrode side is provided with a plurality of first protrusions 1157, thereby forming a gap at the interface between the first protective layer 1153 and the positive electrode 111. The electrolyte can enter the gap to quickly wet the positive electrode 111 and the separator 115, thereby improving the wetting speed of the electrolyte, helping lithium ions to migrate more smoothly, and reducing the transmission impedance.

[0081] The first protrusion 1157 can be a cylindrical protrusion, a semi-cylindrical protrusion, an elliptical protrusion, a polygonal protrusion, or a protrusion of other shapes. This application embodiment does not limit the type of protrusion.

[0082] Each of the first protrusions 1157 can be arranged in an array, a non-array, a local distribution, a periodic distribution, or other arrangements. This application does not limit the arrangement.

[0083] In some embodiments, the first protrusion 1157 on the first protective layer 1153 may contact the surface of the positive electrode 111. The surface of the positive electrode 111 facing the first protective layer 1153 may be a plane, or the surface of the positive electrode 111 facing the first protective layer 1153 may be provided with a plurality of first recesses, and each first protrusion 1157 on the first protective layer 1153 may partially protrude into the first recess.

[0084] When the first protrusion 1157 on the first protective layer 1153 protrudes into the first recess, it helps to reduce the relative slippage between the positive electrode 111 and the separator 115, and can reduce the size of the electrode assembly 110, thereby increasing the energy density of the electrochemical device 100.

[0085] In some embodiments, the surface of the second protective layer 1155 facing away from the positive electrode may also be provided with a plurality of first protrusions 1157, thereby forming a gap at the interface between the second protective layer 1155 and the negative electrode 113. The electrolyte can enter the gap to quickly wet the negative electrode 113 and the separator 115, thereby improving the wetting speed of the electrolyte, helping lithium ions to migrate more smoothly, and reducing the transmission impedance.

[0086] In some embodiments, the first protrusion 1157 on the second protective layer 1155 may contact the surface of the negative electrode 113. The surface of the negative electrode 113 facing the second protective layer 1155 may be a plane, or the surface of the negative electrode 113 facing the second protective layer 1155 may be provided with a plurality of second recesses, and each first protrusion 1157 on the second protective layer 1155 may partially protrude into the second recess.

[0087] With the first protrusion 1157 on the second protective layer 1155 protruding into the second recess, it helps to reduce the relative slippage between the negative electrode 113 and the separator 115, and can reduce the size of the electrode assembly 110, thereby increasing the energy density of the electrochemical device 100.

[0088] The first protrusion 1157 of the first protective layer 1153 and the first protrusion 1157 of the second protective layer 1155 may have the same shape, number, or distribution pattern, and this application embodiment does not limit them.

[0089] In some embodiments, the first protrusions 1157 may be spaced apart, which helps to increase the gap between the first protrusions 1157 and further improve the wetting speed of the electrolyte.

[0090] In some embodiments, the distance between any two adjacent first protrusions 1157 is ≥10 micrometers and ≤50 micrometers, thereby controlling the distance between adjacent first protrusions 1157 within a suitable range, which can improve the wetting speed of the electrolyte, help avoid the distance between adjacent first protrusions 1157 being too small and affecting the wetting speed of the electrolyte, and also help avoid the situation where the distance between adjacent first protrusions 1157 is too large and causes the electrode assembly 110 to collapse in the gap between adjacent first protrusions 1157.

[0091] The spacing between any two adjacent first protrusions 1157 can be 10 micrometers, 18 micrometers, 25 micrometers, 30.5 micrometers, 50 micrometers, or any other value between any two of the above values.

[0092] In some embodiments, the protrusion height of the first protrusion 1157 is ≥3 micrometers and ≤5 micrometers, thereby controlling the height of the first protrusion 1157 within a suitable range, which can improve the wetting speed of the electrolyte. This helps to avoid the situation where the protrusion height of the first protrusion 1157 is too low and affects the wetting speed of the electrolyte, and also helps to avoid the situation where the protrusion height of the first protrusion 1157 is too high and affects the size of the electrode assembly 110, thereby affecting the energy density of the electrochemical device 100.

[0093] The height of the first protrusion 1157 can be 3 micrometers, 3.2 micrometers, 4 micrometers, 4.8 micrometers, 5 micrometers, or any other value between any two of the above.

[0094] As shown in Table 1, the peak puncture force and thermal shrinkage rate of the three diaphragm structures were tested. The diaphragm 115 in this embodiment uses an alumina ceramic layer (i.e., the first protective layer 1153) + a base membrane 1151 + a composite layer of polyethylene and polyvinylidene fluoride (i.e., the second protective layer 1155). The alumina ceramic layer is 3 micrometers thick, and the composite layer of polyethylene and polyvinylidene fluoride has a porosity of 45%.

[0095] The diaphragm 115 of Comparative Example 1 uses an alumina ceramic layer (i.e., the first protective layer 1153) + a base film 1151, with the alumina ceramic layer having a thickness of 5 micrometers.

[0096] The diaphragm 115 of Comparative Example 2 uses a conventional single-layer PE membrane.

[0097] As can be clearly seen from Table 1, the peak puncture force of the diaphragm 115 in this embodiment is significantly higher than that of the diaphragm 115 in Comparative Example 1 and Comparative Example 2, and the thermal shrinkage rate of the diaphragm 115 is significantly lower than that of the diaphragm 115 in Comparative Example 1 and Comparative Example 2. Therefore, the diaphragm 115 provided in this embodiment has better puncture resistance and thermal shrinkage resistance.

[0098] Table 1

[0099] In the diaphragm 115, electrochemical device 100, and electronic device provided in this application embodiment, the base film 1151 has a positive electrode side surface and a negative electrode side surface spaced apart along the thickness direction. A first protective layer 1153 is connected to the positive electrode side surface, and a second protective layer 1155 is connected to the negative electrode side surface, thereby improving the structural strength of the diaphragm 115 and reducing the possibility of the diaphragm 115 being punctured. The hardness of the first protective layer 1153 is greater than that of the second protective layer 1155, thereby improving the hardness of the first protective layer 1153. On the one hand, the high hardness of the first protective layer 1153 can suppress the thermal shrinkage of the diaphragm 115 under high temperature conditions, which helps to avoid the short circuit caused by the thermal shrinkage of the diaphragm 115, which could lead to contact between the positive electrode 111 and the negative electrode 113. On the other hand, the positive electrode particles of the positive electrode 111 are relatively hard, and the high hardness of the first protective layer 1153 can reduce the possibility of the positive electrode particles of the positive electrode 111 puncturing the first protective layer 1153. The second protective layer 1155 has a flexible porous structure. On the one hand, the porous structure of the second protective layer 1155 provides a smoother channel for lithium-ion transport and reduces the transport impedance. On the other hand, during the cycling process of the electrochemical device 100, the expansion and contraction of the negative electrode 113 are relatively intense. The flexible second protective layer 1155 can provide a buffer for the expansion of the negative electrode 113, reducing stress concentration. Moreover, the flexible second protective layer 1155 can better recover its original shape after being squeezed by the negative electrode 113, which helps to reduce the deformation and blockage of the pores in the second protective layer 1155.

[0100] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A diaphragm, characterized by The application relates to a separator for an electrochemical device. The separator comprises: a base film having a positive electrode side surface and a negative electrode side surface opposite to each other in a thickness direction; a first protective layer connected to the positive electrode side surface; a second protective layer connected to the negative electrode side surface and having a flexible porous structure; 2. The separator according to claim 1, characterized in that wherein the first protective layer has a higher hardness than the second protective layer.

3. The diaphragm of claim 2, wherein, A surface of the first protective layer opposite to the positive electrode side surface and / or a surface of the second protective layer opposite to the negative electrode side surface is provided with a plurality of first protrusions. The first protrusions are arranged at intervals, and the interval between any two adjacent first protrusions is greater than or equal to 10 microns and less than or equal to 50 microns.

4. The separator of claim 1, wherein The first protrusions have a protrusion height greater than or equal to 3 microns and less than or equal to 5 microns.

5. The separator of claim 1, wherein The first protective layer is a ceramic layer. The second protective layer has a porosity greater than or equal to 40% and less than or equal to 50%. The first protective layer has a thickness greater than or equal to 2 microns and less than or equal to 10 microns in the thickness direction.

6. An electrochemical device, characterized by, The second protective layer has a thickness greater than or equal to 4.5 microns and less than or equal to 7.5 microns in the thickness direction. The application also relates to an electrode assembly comprising a positive electrode sheet, a negative electrode sheet and the separator according to any one of claims 1 to 5, the separator being arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the separator and the negative electrode sheet being sequentially stacked and wound into a jelly-roll structure.

7. The electrochemical device of claim 6, wherein The positive electrode sheet is in contact with the first protective layer, and the negative electrode sheet is in contact with the second protective layer. The electrochemical device further comprises a shell, a negative electrode tab and a temperature-sensitive element, the negative electrode tab being connected to the negative electrode sheet and at least partially arranged outside the electrode assembly, and the temperature-sensitive element being at least partially connected to the negative electrode tab and configured to change color when the temperature reaches a threshold temperature.

8. The electrochemical device of claim 7, wherein, The electrode assembly and the temperature-sensitive element are arranged in the shell, and the negative electrode tab is at least partially arranged in the shell; the shell comprises a light-transmitting portion, and the light-transmitting portion and the temperature-sensitive element are arranged opposite to each other. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being connected to a surface of the negative electrode current collector and provided with a first groove to expose part of the negative electrode current collector, and the first groove extends through the negative electrode active material layer and reaches an edge on one side of the electrode assembly in an axial direction.

9. The electrochemical device of claim 8, wherein, The negative electrode tab comprises a connecting portion and an extension portion connected to each other, the connecting portion is arranged in the first groove and connected to the negative electrode current collector, and the extension portion is located outside the electrode assembly; and the temperature-sensitive element is at least partially connected to the extension portion. The electrochemical device further comprises a conductive adhesive layer arranged in the first groove and bonded between the negative electrode current collector and the connecting portion.

10. An electronic device, comprising: The temperature-sensitive element comprises a first temperature-sensitive portion and a second temperature-sensitive portion connected to each other, the first temperature-sensitive portion is arranged between the conductive adhesive layer and the connecting portion, and the second temperature-sensitive portion is connected to the extension portion, and the light-transmitting portion and the second temperature-sensitive portion are arranged opposite to each other. The application further relates to an electrochemical device comprising the electrochemical device according to any one of claims 6 to 9.

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