An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode sheet, a negative electrode sheet and a porous separator layer between the positive electrode sheet and the negative electrode sheet; by using infrared spectrum testing, the porous separator layer has a first absorption peak in the range of 835 cm ‑1 to 845 cm ‑1 , a second absorption peak in the range of 760 cm ‑1 to 770 cm ‑1 , and the peak height I1 of the first absorption peak and the peak height I2 of the second absorption peak satisfy I1>I2. The electrochemical device has low self-discharge and high safety.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrochemical device and an electronic device. Background Technology

[0002] Lithium-ion batteries possess numerous advantages, including high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, making them widely used in consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, the requirements for the energy density, safety, cycle performance, and other related properties of lithium-ion batteries are becoming increasingly stringent. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide an electrochemical device and an electronic device for reducing the self-discharge of the electrochemical device and improving its safety.

[0004] The first aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, and a porous insulating layer located between the positive and negative electrode; using infrared spectroscopy, the porous insulating layer is detected at a wavenumber of 835 cm⁻¹. -1 Up to 845cm -1 It has a first absorption peak in the range of , at a wavenumber of 760 cm⁻¹ -1 Up to 770cm -1 The second absorption peak is present within the range of [value missing], and the peak heights I1 and I2 of the first and second absorption peaks satisfy the condition: I1 > I2. The wavenumber is [value missing] at 835 cm⁻¹. -1 Up to 845cm -1 The first absorption peak within the range is the absorption peak of the β-crystalline phase in fluoropolymers, with a wavenumber of 760 cm⁻¹. -1 Up to 770cm -1 The second absorption peak within the range is the absorption peak of the α-crystalline phase in the fluoropolymer. The inventors of this application have discovered that fluoropolymers have low CF bond polarization, dense molecular structure, good hydrophobicity, heat resistance, and excellent chemical stability. Furthermore, the β-crystalline phase of the fluoropolymer exhibits better compressive strength and thermal stability compared to the α-crystalline phase. By controlling the peak heights I1 of the first absorption peak and I2 of the second absorption peak in the porous insulating layer to satisfy I1 > I2, the compressive strength and thermal stability of the fibers in the porous insulating layer can be improved. This reduces the self-discharge of the electrochemical device and enhances its safety.

[0005] In some implementations, 1.5 ≤ I1 / I2 ≤ 4.5. Controlling the value of I1 / I2 within this range helps to further reduce the self-discharge of the electrochemical device and improve its safety. Further, 2 ≤ I1 / I2 ≤ 4.

[0006] In some embodiments, the half-peak width W1 of the first absorption peak and the half-peak width W2 of the second absorption peak satisfy: 0.5≤W1 / W2≤1. In this way, the self-discharge of the electrochemical device is reduced, and the safety of the electrochemical device is improved. Further, 0.85≤W1 / W2≤1.

[0007] In some embodiments, the porous separator layer includes a polymer material, the polymer material includes a fluoropolymer, the fluoropolymer includes an alpha crystal phase and a beta crystal phase, which is conducive to reducing the self-discharge of the electrochemical device and improving the safety of the electrochemical device.

[0008] In some embodiments, the fluoropolymer includes a vinylidene fluoride polymer segment.

[0009] In some embodiments, the fluoropolymer includes at least one of polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer. The porous separator layer prepared by using the above-mentioned material has good compression resistance and thermal stability, which is conducive to reducing the self-discharge of the electrochemical device and improving the safety of the electrochemical device.

[0010] In some embodiments, the alpha crystal phase accounts for 35% to 80% of the fluoropolymer based on the total of the alpha crystal phase and the beta crystal phase in the fluoropolymer, and the beta crystal phase accounts for 20% to 65% of the fluoropolymer. By controlling the proportions of the alpha crystal phase and the beta crystal phase in the fluoropolymer within the above-mentioned ranges, the porous separator layer has good compression resistance, thermal stability and manufacturability, which is conducive to reducing the self-discharge of the electrochemical device and improving the safety of the electrochemical device.

[0011] In some embodiments, the porous separator layer further includes an inorganic material. The further addition of the inorganic material in the porous separator layer can improve the mechanical strength of the porous separator layer, thereby being conducive to improving the compression resistance and thermal stability of the porous separator layer, reducing the self-discharge of the electrochemical device, and improving the safety of the electrochemical device.

[0012] In some embodiments, the inorganic material includes at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate.

[0013] In some embodiments, the mass percentage content of the inorganic material in the porous separator layer is 5% to 60%.

[0014] In some embodiments, the polymer material further includes at least one of polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, polyacrylate or polyethylene terephthalate.

[0015] In some embodiments, the polymer material comprises 40% to 100% by mass in the porous isolation layer.

[0016] In some implementations, the thickness of the porous isolation layer is between 4 μm and 20 μm. Controlling the thickness of the porous isolation layer within this range is beneficial for the electrochemical device to achieve high energy density while maintaining low self-discharge and high safety.

[0017] In some implementations, the porosity of the porous isolation layer is between 30% and 75%. By controlling the porosity of the porous isolation layer within this range, the liquid retention capacity of the porous isolation layer is stronger, which is beneficial to improving the cycle performance of the electrochemical device.

[0018] In some implementations, the average pore size of the porous isolation layer is between 90 nm and 200 nm. Controlling the average pore size of the porous isolation layer within this range is beneficial for the electrochemical device to have lower self-discharge, higher safety, and better cycle performance.

[0019] A second aspect of this application provides an electronic device comprising the electrochemical device described in any of the foregoing embodiments. Therefore, the electronic device exhibits good performance in use. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0021] Figure 1 This is a schematic diagram of the planar structure of polyvinylidene fluoride in the α-crystal phase in some embodiments of this application;

[0022] Figure 2 This is a schematic diagram of the planar structure of polyvinylidene fluoride in the β-crystal phase in some embodiments of this application;

[0023] Figure 3 This is a schematic diagram of the structure of an electrode sheet with a porous isolation layer disposed on one side in some embodiments of this application;

[0024] Figure 4 This is a schematic diagram of a structure in which a porous insulating layer is disposed on a double-coated positive electrode sheet in some embodiments of this application;

[0025] Figure 5 This is a schematic diagram of a structure in which a porous insulating layer is disposed on a double-coated negative electrode sheet in some embodiments of this application;

[0026] Figure 6Infrared spectra of the porous isolation layers in Examples 1-6 of this application;

[0027] Figure 7 This is a fiber morphology diagram of the porous isolation layer in Embodiment 1-1 of this application after being compressed;

[0028] Figure 8 This is a fiber morphology diagram of the porous isolation layer of Comparative Example 1 of this application after being subjected to pressure. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0030] The first aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, and a porous insulating layer located between the positive and negative electrodes; the porous insulating layer is located between the positive and negative electrodes to conduct ions and isolate electrons. Infrared spectroscopy was used to measure the porous insulating layer at a wavenumber of 835 cm⁻¹. -1 Up to 845cm -1 It has a first absorption peak in the range of , at a wavenumber of 760 cm⁻¹ -1 Up to 770cm -1 The porous isolation layer exhibits a second absorption peak within a certain range, and the peak heights I1 of the first absorption peak and I2 of the second absorption peak satisfy the condition: I1 > I2. -1 Up to 845cm -1 The presence of a first absorption peak within the range indicates that the porous isolation layer contains a β-phase fluoropolymer; the porous isolation layer exhibits an absorption peak at a wavenumber of 760 cm⁻¹. -1 Up to 770cm -1 The presence of a second absorption peak within the specified range indicates that the porous insulating layer contains an α-crystalline phase fluoropolymer. Extensive research by the inventors revealed that fluoropolymers exhibit low CF bond polarization, a dense molecular structure, good hydrophobicity, heat resistance, and excellent chemical stability. Furthermore, β-crystalline phase fluoropolymers demonstrate better compressive strength and thermal stability compared to α-crystalline phase fluoropolymers. By adjusting the peak heights I1 and I2 of the first and second absorption peaks in the porous insulating layer to satisfy I1 > I2, the compressive strength and thermal stability of the fibers in the porous insulating layer can be improved. Therefore, applying this porous insulating layer to electrochemical devices can reduce self-discharge and improve device safety. The peak heights I1 and I2 of the first and second absorption peaks are defined as the distance from the lowest point of the absorption peak in the infrared spectrum to the baseline.

[0031] In some embodiments, 1.5 ≤ I1 / I2 ≤ 4.5. For example, the value of I1 / I2 can be 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or a range consisting of any two of the above values. Adjusting the value of I1 / I2 within the above range indicates a higher content of the β-phase fluoropolymer in the porous insulating layer, which is beneficial for improving the compressive strength and thermal stability of the fibers in the porous insulating layer, thereby reducing the self-discharge of the electrochemical device and improving its safety. Further, in some embodiments, 2 ≤ I1 / I2 ≤ 4.

[0032] In some embodiments, the full width at half maximum (FWHM) W1 of the first absorption peak and the full width at half maximum (FWHM) W2 of the second absorption peak satisfy the condition: 0.5 ≤ W1 / W2 ≤ 1. For example, the value of W1 / W2 is 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 1, or any two of the above values. Adjusting the value of W1 / W2 within the above range is beneficial for improving the compressive strength and thermal stability of the fibers in the porous insulating layer, thereby reducing the self-discharge of the electrochemical device and improving its safety. Further, in some embodiments, 0.85 ≤ W1 / W2 ≤ 1.

[0033] This application does not impose any particular restrictions on the method of controlling the parameters related to the first and second absorption peaks (such as I1 / I2, W1 / W2, etc.), as long as the purpose of this application can be achieved. For example, it can be achieved by controlling the magnitude of the electrospinning voltage during the preparation of the porous isolation layer, or by controlling the type of fluoropolymer and / or the weight-average molecular weight (Mw).

[0034] In some embodiments, the porous insulating layer comprises a polymer material, which includes a fluoropolymer, comprising an α-phase and a β-phase. The α-phase fluoropolymer, such as polyvinylidene fluoride (PVDF), has helical molecular chains (e.g., α-phase). Figure 1 As shown in the diagram, hydrogen and fluorine atoms are alternately distributed on both sides of the molecular chain in a disordered "top-bottom" arrangement, resulting in poor compressibility and a crystal density of 1.92 g / cm³. 3 ; β-phase fluoropolymers, such as β-phase PVDF, have planar serrated molecular chains (e.g. Figure 2 As shown in the figure, the molecular chains are regularly arranged, exhibiting high spontaneous polarization. After orientation, the dielectric constant is significantly increased, resulting in excellent piezoelectricity. The crystal density is 1.97 g / cm³. 3 It possesses excellent compressive strength and mechanical properties. During the preparation of the porous isolation layer, a high-voltage electric field can be applied to increase the crystallinity of PVDF, causing the α-phase to transform into the β-phase, thereby improving the compressive strength and thermal stability of the porous isolation layer.

[0035] In some embodiments, the fluoropolymer includes vinylidene fluoride polymer segments.

[0036] In some embodiments, the fluorine-containing polymer comprises at least one of polyvinylidene fluoride (PVDF) or vinylidene fluoride-hexafluoropropylene copolymer. The porous isolation layer prepared by using the above-mentioned material has good compression resistance and thermal stability, which is conducive to reducing the self-discharge of the electrochemical device and improving the safety of the electrochemical device.

[0037] In some embodiments, the proportion of the a crystal phase in the fluorine-containing polymer is W α 35% to 80%, and the proportion of the b crystal phase in the fluorine-containing polymer is W β 20% to 65%. For example, the proportion of the a crystal phase in the fluorine-containing polymer is 35%, 40%, 50%, 60%, 70%, 80%, or a range formed by any two of the above values. The proportion of the b crystal phase in the fluorine-containing polymer is 20%, 30%, 40%, 50%, 60%, 65%, or a range formed by any two of the above values. By adjusting the proportions of the a crystal phase and the b crystal phase in the fluorine-containing polymer within the above ranges, the porous isolation layer has good compression resistance, thermal stability, and manufacturability, which is conducive to reducing the self-discharge of the electrochemical device and improving the safety of the electrochemical device.

[0038] The application does not have a particular limitation on the adjustment method of the crystal form and the relative content of different crystal forms of the fluorine-containing polymer in the porous isolation layer, as long as the purpose of the application can be achieved. For example, it can be achieved by selecting raw materials with different weight average molecular weights and contents. For example, PVDF-1 and PVDF-2 are mixed in a weight ratio m1 / m2 that satisfies 0.5≤m1 / m2≤2, so that the a crystal phase and the b crystal phase of PVDF in the porous isolation layer satisfy the purpose of the application, wherein the weight average molecular weight of PVDF-1 is 300 000 to 330 000, and the weight average molecular weight of PVDF-2 is 380 000 to 700 000.

[0039] In some embodiments, the polymer material can further comprise at least one of polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenyl ether, polypropylene carbonate, polyacrylate, or polyethylene terephthalate.

[0040] The application does not have a particular limitation on the mass percentage content of the polymer material in the porous isolation layer, as long as the purpose of the application can be achieved. For example, the mass percentage content of the polymer material in the porous isolation layer is 40% to 100%. For example, the mass percentage content of the polymer material in the porous isolation layer is 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range formed by any two of the above values. Further, the mass percentage content of the polymer material in the porous isolation layer is 50% to 90%.

[0041] In some embodiments, the porous isolation layer further includes inorganic materials. The addition of inorganic materials to the porous isolation layer can improve its mechanical strength, thereby enhancing its compressive strength and thermal stability, reducing self-discharge of the electrochemical device, and improving its safety.

[0042] In some embodiments, the inorganic material includes at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.

[0043] This application does not impose any particular limitation on the volume average particle size Dv50 of inorganic materials, as long as it achieves the purpose of this application. For example, the volume average particle size Dv50 of inorganic materials is 50 nm to 500 nm, and further, the volume average particle size Dv50 of inorganic materials is 50 nm to 200 nm. In this application, the volume average particle size Dv50 refers to the particle size that, in the particle size distribution based on volume, accumulates to 50% of the total volume from the smallest particle size side.

[0044] This application does not impose any particular limitation on the mass percentage of inorganic materials in the porous isolation layer, as long as the purpose of this application is achieved. For example, the mass percentage of inorganic materials in the porous isolation layer may be between 5% and 60%. For example, the mass percentage of inorganic materials in the porous isolation layer may be 5%, 10%, 20%, 30%, 40%, 50%, 60%, or any combination of two of the above values. Further, the mass percentage of inorganic materials in the porous isolation layer may be between 10% and 40%.

[0045] In some embodiments, the thickness of the porous isolation layer is from 4 μm to 20 μm. For example, the thickness of the porous isolation layer is 4 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 20 μm, or any combination of two of the above values. By controlling the thickness of the porous isolation layer within the above range, the porous isolation layer exhibits good compressive strength and thermal stability, which is beneficial for electrochemical devices to achieve high energy density while maintaining low self-discharge and high safety.

[0046] In some embodiments, the porosity of the porous isolation layer is 30% to 75%. For example, the porosity of the porous isolation layer is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a range between any two of the aforementioned values. By adjusting the porosity of the porous isolation layer within the aforementioned range, the liquid retention capacity of the porous isolation layer is improved, which is conducive to improving the cycle performance of the electrochemical device. The method for adjusting the porosity of the porous isolation layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the density of the fibers deposited on the surface of the electrode sheet can be adjusted.

[0047] In some embodiments, the average pore size of the porous isolation layer is 90 nm to 200 nm. For example, the average pore size of the porous isolation layer is 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 170 nm, 200 nm, or a range between any two of the aforementioned values. By adjusting the average pore size of the porous isolation layer within the aforementioned range, the electrochemical device has lower self-discharge, higher safety, and higher cycle performance. The method for adjusting the average pore size of the porous isolation layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the density of the fibers deposited on the surface of the electrode sheet can be adjusted.

[0048] The method for preparing the porous isolation layer is not particularly limited in the present application, and any method known to those skilled in the art can be used, as long as the purpose of the present application can be achieved.

[0049] In some embodiments of the present application, the porous isolation layer comprises a polymer material, and the preparation steps of the porous isolation layer can include but are not limited to the following steps: (1) dispersing polymer materials with different weight average molecular weights (such as PVDF-1 and PVDF-2 in a weight ratio of m1:m2=1:2 to 2:1) in a solvent and stirring uniformly until the slurry viscosity is stable, to obtain a spinning solution; (2) preparing the porous isolation layer on a predetermined surface by electrospinning the spinning solution.

[0050] In some embodiments of the present application, the porous isolation layer comprises a polymer material and an inorganic material, and the preparation steps of the porous isolation layer can include but are not limited to the following steps: (1) dispersing polymer materials with different weight average molecular weights (such as PVDF-1 and PVDF-2 in a weight ratio of m1:m2=1:2 to 2:1) in a solvent and stirring uniformly until the slurry viscosity is stable, to obtain a spinning solution; (2) dispersing an inorganic material in a solvent and stirring uniformly until the slurry viscosity is stable, to obtain a suspension; (3) arranging the fibers on a predetermined surface under a high-voltage electrostatic field by electrospinning the spinning solution; and arranging the suspension on the predetermined surface by electro-spraying at the same time, to prepare the porous isolation layer.

[0051] In some embodiments of the present application, the porous separator layer comprises a polymer material and an inorganic material, and the preparation steps of the porous separator layer can include, but are not limited to, the following steps: (1) dispersing polymer materials of different weight average molecular weights (such as PVDF-1 and PVDF-2 in a weight ratio of m1:m2=1:2 to 2:1) in a solvent and stirring uniformly until the slurry viscosity is stable to obtain a spinning solution; (2) dispersing the inorganic material in the solvent and stirring uniformly until the slurry viscosity is stable to obtain a suspension; (3) uniformly mixing the spinning solution and the suspension to obtain a mixed slurry, and arranging the mixed slurry on a pre-set surface by electrospinning to prepare the porous separator layer.

[0052] The kind of the above-mentioned solvent is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the solvent includes at least one of acetone, N,N-dimethylformamide (DMF) or dimethyl ether (DME).

[0053] The electrospinning voltage in the electrospinning process is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, it can be 1.2 MV / cm (megavolt / cm) to 1.5 MV / cm.

[0054] Those skilled in the art should understand that the above-mentioned "pre-set surface" can refer to the surface of the positive electrode sheet and / or the negative electrode sheet, and the porous separator layer can be prepared on the surface of the positive electrode sheet, or on the surface of the negative electrode sheet, or on the surfaces of the positive electrode sheet and the negative electrode sheet at the same time, as long as the positive electrode sheet and the negative electrode sheet are separated by the porous separator layer. These should all belong to the protection scope of the present application.

[0055] In some embodiments of the present application, the porous separator layer of the present application can be arranged on at least one surface of the electrode sheet, wherein the electrode sheet comprises a positive electrode sheet and / or a negative electrode sheet, as shown in Figures 3 to 5 The positive electrode sheet comprises a positive electrode current collector 10 and a positive electrode active material layer 20, and the negative electrode sheet comprises a negative electrode current collector 50 and a negative electrode active material layer 40. For example, it can be a structure in which the porous separator layer 30 is arranged on one side of the positive electrode sheet or the negative electrode sheet as shown in Figure 3 It can also be a structure in which the porous separator layer 30 is arranged on both sides of the positive electrode sheet as shown in Figure 4 It can also be a structure in which the porous separator layer 30 is arranged on both sides of the positive electrode sheet as shown in Figure 5 It can also be a structure in which the porous separator layer 30 is arranged on both sides of the positive electrode sheet as shown in

[0056] The positive electrode tab in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the positive electrode tab generally comprises a positive current collector and a positive active material layer. Among them, the positive current collector is not particularly limited and can be any positive current collector known in the art, such as an aluminum foil or an aluminum alloy foil, etc. The positive active material layer comprises a positive active material, which is not particularly limited and can use any positive active material known in the art, for example, can comprise at least one of nickel cobalt manganese lithium (NCM811, NCM622, NCM523, NCM111), nickel cobalt aluminum lithium, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate or lithium manganese iron phosphate. In the present application, the thickness of the positive current collector and the positive active material layer is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5 μm to 20 μm. The thickness of the single-sided positive active material layer is 30 μm to 120 μm. In the present application, the positive active material layer can be disposed on one surface in the thickness direction of the positive current collector, or can be disposed on both surfaces in the thickness direction of the positive current collector.

[0057] The negative electrode tab in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the negative electrode tab generally comprises a negative current collector and a negative active material layer. Among them, the negative current collector is not particularly limited and can use any negative current collector known in the art, such as a copper foil, an aluminum foil or an aluminum alloy foil, etc. The negative active material layer comprises a negative active material, which is not particularly limited and can use any negative active material known in the art. For example, can comprise at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, silicon-carbon composite material or silicon-oxygen composite material. In the present application, the thickness of the negative current collector and the negative active material layer is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the negative current collector is 6 μm to 10 μm, and the thickness of the negative active material layer is 30 μm to 130 μm. In the present application, the negative active material layer can be disposed on one surface in the thickness direction of the negative current collector, or can be disposed on both surfaces in the thickness direction of the negative current collector.

[0058] The electrochemical device of the present application can further comprise a shell and an electrolyte, and the shell and the electrolyte in the present application are not particularly limited and can be any shell and electrolyte known in the art as long as the purpose of the present application can be achieved.

[0059] The preparation method of the electrochemical device is not particularly limited in the present application, and any method known to those skilled in the art can be used as long as the purpose of the present application can be achieved. For example, the electrochemical device can be manufactured by the following process: separating the positive electrode sheet and the negative electrode sheet via a porous separator layer, and winding, folding, etc. as needed, and then placing it in a case, injecting an electrolyte into the case and sealing, wherein the porous separator layer used is the above-mentioned porous separator layer provided by the present application.

[0060] The type of electrochemical device is not particularly limited in the present application, and it can include any device that undergoes an electrochemical reaction. For example, the electrochemical device can include, but is not limited to, a lithium ion battery, a sodium ion battery.

[0061] The second aspect of the present application provides an electronic device comprising the electrochemical device according to any one of the preceding embodiments. Therefore, the electronic device has good use performance.

[0062] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device can include, but is not limited to, a mobile phone, a notebook computer, a tablet computer, a drone, an electric vehicle, an electric bicycle, an electric motorcycle, an electric tool, a game console and a Bluetooth headset.

[0063] Embodiments

[0064] Hereinafter, embodiments and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations were carried out according to the following methods.

[0065] Test methods and apparatus:

[0066] Infrared test method:

[0067] The sample was dissolved in dimethyl ether (DME), coated on KBr, pressed into a tablet, and then measured by an infrared spectrometer after the solvent was volatilized into a film.

[0068] Sample requirements: The porous separator layer removed from the lithium ion battery was soaked in dimethyl carbonate (DMC) for more than half an hour, washed with alcohol and then dried or oven dried for standby use.

[0069] Test method of self-discharge rate:

[0070] (1) The lithium ion battery was discharged at a constant current of 0.5C to a cut-off voltage of 3.0V at room temperature 25℃, and then charged at a constant current of 0.7C to 50% SOC (state of charge), and then left to stand at room temperature 25℃ for 24 hours, and the voltage of the lithium ion battery was tested as OCV1;

[0071] (2) Then left to stand at room temperature 25℃ for another 48 hours, and the voltage of the lithium ion battery was tested as OCVB;

[0072] (3) The self-discharge rate calculation method of lithium ion battery is: self-discharge rate (mV / hr) = (OCV1-OCVB) x 1000 / 48.

[0073] Forced internal short circuit test method:

[0074] (1) At room temperature 25℃, during the preparation of lithium ion battery, a nickel sheet is placed in the winding core (between the negative electrode sheet and the porous separator), and after the preparation of lithium ion battery is completed, it is placed at 60℃ for 45±15min;

[0075] (2) Take out the lithium ion battery after standing, and press the above battery at a pressing speed of 0.1mm / s, and monitor the voltage of lithium ion battery.

[0076] If it is observed that the voltage reduction of lithium ion battery is caused by internal short circuit, stop pressing immediately, and fix the pressing clamp for 30s, and then release the pressure. The voltage monitoring sampling time is 10ms. If the voltage is reduced by more than 50mV compared with the initial voltage, it can be indicated that internal short circuit occurs. If the maximum pressure reaches 400N, stop the pressing device immediately, and the test is ended.

[0077] Test method of thermal abuse safety temperature:

[0078] Charge the lithium ion battery at 0.5C constant current to 4.25V at room temperature 25℃, and then charge at 4.25V constant voltage until the current is 0.05C, so that the lithium ion battery reaches full charge state. Then place the lithium ion battery in full charge state in a high temperature oven, and heat for 1 hour. The upper limit temperature at which the battery does not catch fire and explode is the thermal abuse safety temperature of the battery.

[0079] Observation method of fiber morphology in porous separator:

[0080] The morphology of fibers in the porous separator is observed by scanning electron microscope, and a photo is taken.

[0081] Test method of average pore size and porosity of porous separator:

[0082] The average pore size and porosity of the porous separator are determined by nitrogen low temperature adsorption method. The porous separator sample is degassed by heating and vacuumizing to remove the impurity gas adsorbed on the surface. Weigh, and then place in liquid nitrogen. At different pressure points, the nitrogen adsorption amount of the sample is determined at liquid nitrogen temperature to obtain the adsorption isotherm. Through computer processing data, the pore volume V 孔 , average pore size are calculated from the adsorption isotherm; according to the thickness T and area S of the porous separator sample, the apparent volume V 表观 = T x S is calculated, and the porosity ε = V 孔 / V 表观 .

[0083] Methods for testing the proportion of α- and β-phase in fluoropolymers:

[0084] The relative contents of α-phase and β-phase in fluoropolymer samples were determined by infrared spectroscopy. The content of β-phase in the sample could be determined according to the method proposed in the literature (Salimi A, Yousefi A. Analysis method: FTIR studies of β-phase crystal formation instretched PVDF films[J]. Polymer Testing,2003,22(6):699-704.).

[0085] relative content of β phase

[0086] In the formula: A α and A β These are the intensities of the second absorption peak and the first absorption peak, respectively.

[0087] The relative content of the α phase is F(α) = 1 - F(β).

[0088] Example 1-1

[0089] <Preparation of the positive electrode>

[0090] Lithium cobalt oxide (CCO), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The positive electrode slurry was uniformly coated on one surface of a 10 μm thick aluminum foil for positive electrode current collectors and dried at 90 °C to obtain a positive electrode sheet with a single-sided coating of positive active material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material. After cold pressing, cutting, and welding of tabs, the positive electrode sheet was ready for use.

[0091] <Preparation of a Porous Electrode with a Double-Sided Integrated Porous Insulation Layer>

[0092] Preparation of spinning solution: PVDF-1 (weight average molecular weight Mw1 = 310000) and PVDF-2 (weight average molecular weight Mw2 = 640000) were dispersed in a mixed solvent at a mass ratio of m1:m2 = 2:1 and stirred until the slurry viscosity stabilized to obtain a spinning solution with a solid content of 20 wt%; wherein, the mixed solvent was composed of DMF and acetone mixed at a mass ratio of 7:3.

[0093] Preparation of the porous separator layer: using the above prepared spinning solution as raw material, spinning is carried out on one side surface of the positive electrode sheet by electrospinning, wherein the electrospinning voltage is 1.25 MV / cm, and a porous separator layer with a thickness of 8 μm is prepared. After the above steps are completed, the preparation of the single-sided porous separator layer is completed. The porosity of the porous separator layer is 50%, and the average pore size of the porous separator layer is 150 nm. The above steps are repeated on the other side surface of the positive electrode sheet, and vacuum drying is carried out at 40°C, thereby obtaining a positive electrode sheet integrated with a double-sided porous separator layer.

[0094] <Preparation of the negative electrode sheet>

[0095] The negative electrode active material graphite, the conductive agent conductive carbon black (Super P), and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96:1.5:2.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 70 wt%, and the mixture is stirred uniformly. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. Then, the above steps are repeated on the other surface of the copper foil, thereby obtaining a negative electrode sheet coated with a negative electrode active material layer on both sides. After cold pressing, cutting, and welding of the tabs, the negative electrode sheet is obtained for use.

[0096] <Preparation of the electrolyte>

[0097] In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC: EMC: DEC = 30:50:20 to obtain an organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix uniformly, thereby obtaining an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0098] <Preparation of the lithium ion battery>

[0099] The above prepared double-sided integrated porous separator layer positive electrode sheet and the negative electrode sheet are stacked and wound opposite to each other, thereby obtaining an electrode assembly with a wound structure. The electrode assembly is placed in an aluminum plastic film packaging bag, dried, and then injected with electrolyte, and then subjected to vacuum packaging, standing, formation, degassing, edge cutting, and other processes to obtain a lithium ion battery.

[0100] Examples 1-2 to 1-8

[0101] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0102] Example 2-1

[0103] <Preparation of the double-sided integrated porous separator layer positive electrode sheet>

[0104] Preparation of the spinning solution: PVDF-1 (weight average molecular weight Mw1 = 310000) and PVDF-2 (weight average molecular weight Mw2 = 640000) were dispersed in the mixed solvent according to the mass ratio m1:m2 = 1:1, and stirred uniformly until the slurry viscosity was stable, to obtain a spinning solution with a solid content of 20wt%; wherein the mixed solvent was obtained by mixing DMF and acetone according to the mass ratio 7:3.

[0105] Preparation of the suspension: inorganic material boehmite, acrylonitrile and boron trifluoride were dispersed in the mixed solvent according to the mass ratio 95:4.5:0.5, and stirred uniformly until the slurry viscosity was stable, to obtain a suspension with a solid content of 40wt%; wherein the mixed solvent was obtained by mixing DMF and acetone according to the mass ratio 7:3; the average volume particle size of boehmite was 800nm.

[0106] Preparation of the porous isolation layer: the spinning solution prepared above was used as raw material, and electrospinning was performed on one side surface of the positive electrode sheet, wherein the electrospinning voltage was 1.25MV / cm; at the same time, the suspension prepared above was used as raw material, and electro-spraying was performed on the surface of the positive electrode sheet, to deposit the inorganic material into the porous isolation layer, to obtain a porous isolation layer with a thickness of 8μm. After the above steps were completed, the preparation of the single-sided porous isolation layer was completed. The average pore size of the porous isolation layer was 150nm. The above steps were repeated on the other side surface of the positive electrode sheet, and vacuum drying was performed at 40℃, to obtain a positive electrode sheet with a double-sided integrated porous isolation layer.

[0107] The rest was the same as in Examples 1-5.

[0108] Example 2-2

[0109] Except for adjusting the relevant preparation parameters according to Table 2, the rest was the same as in Example 2-1.

[0110] Comparative Example 1

[0111] <Preparation of a positive electrode sheet with a double-sided integrated porous isolation layer>

[0112] Preparation of the spinning solution: PVDF-1 (weight average molecular weight Mw1 = 170000) was dispersed in the mixed solvent, and stirred uniformly until the slurry viscosity was stable, to obtain a spinning solution with a solid content of 20wt%; wherein the mixed solvent was obtained by mixing DMF and acetone according to the mass ratio 7:3.

[0113] Preparation of the porous separator layer: using the prepared spinning solution as raw material, spinning was performed on one side surface of the positive electrode sheet by electrospinning, wherein the electrospinning voltage was 1.25 MV / cm, and a porous separator layer with a thickness of 8 μm was prepared. After the above steps were completed, the preparation of the single-sided porous separator layer was completed. The porosity of the porous separator layer was 50%, and the average pore size of the porous separator layer was 150 nm. The above steps were repeated on the other side surface of the positive electrode sheet, and vacuum drying was performed at 40°C, thereby obtaining a positive electrode sheet with a double-sided integrated porous separator layer.

[0114] The rest was the same as in Example 1-1.

[0115] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 and Table 2.

[0116] Table 1

[0117]

[0118] Note: “\” in Table 1 indicates no corresponding parameter.

[0119] From the comparison of Example 1-1 to Example 1-8 and Comparative Example 1, it can be seen that the peak height I1 of the first absorption peak and the peak height I2 of the second absorption peak of the porous separator layer of the examples satisfy I1>I2, and further, 1.5≤I1 / I2≤4.5. When the porous separator layer satisfying the above condition is applied to a lithium ion battery, the forced internal short circuit voltage drop and the self-discharge rate of the lithium ion battery are reduced, and the thermal abuse safety temperature is increased, indicating that the self-discharge of the lithium ion battery is reduced and the safety is improved.

[0120] wherein, Figure 6 is the infrared spectrum of the porous separator layer of Example 1-6. From Figure 6 It can be seen that the peak height I1 of the first absorption peak is greater than the peak height I2 of the second absorption peak. Figure 7 shows the fiber morphology of the porous separator layer of Example 1-1 after being pressed, Figure 8 shows the fiber morphology of the porous separator layer of Comparative Example 1 after being pressed, from Figure 7 and Figure 8 It can be seen that the porous separator layer of the examples contains PVDF with β crystal phase, and satisfies I1>I2, and after being pressed, no obvious deformation occurs. The porous separator layer of Comparative Example 1 does not satisfy I1>I2, and after being pressed, the fibers are severely deformed, indicating that the porous separator layer of the examples has better compression resistance than the comparative example.

[0121] The proportion of the alpha crystal phase and the beta crystal phase in the fluorine-containing polymer also generally affects the self-discharge and thermal stability of the lithium ion battery. As can be seen from Examples 1-1 to 1-8, the lithium ion battery selected with the proportion of the alpha crystal phase and the beta crystal phase within the range of the present application has a lower forced internal short circuit voltage drop and self-discharge rate, and has a higher thermal abuse safety temperature, indicating that the lithium ion battery has a lower self-discharge and good safety.

[0122] Table 2

[0123]

[0124] Note: “\” in Table 2 represents no corresponding parameter.

[0125] As can be seen from Examples 1-5, 2-1 and 2-2, when the inorganic material is further added to the porous isolation layer, the lithium ion battery has a lower forced internal short circuit voltage drop and self-discharge rate, and has a higher thermal abuse safety temperature, indicating that the lithium ion battery has a lower self-discharge and good safety.

[0126] It should be noted that in this document, the terms “comprising”, “containing” or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article or apparatus that includes a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, article or apparatus.

[0127] The above description is merely preferred embodiments of the present application, but not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrochemical device, comprising a positive electrode, a negative electrode, and a porous insulating layer located between the positive electrode and the negative electrode; the porous insulating layer comprises a polymer material, the polymer material comprising a fluoropolymer, the fluoropolymer comprising an α-phase and a β-phase; Infrared spectroscopy was used to test the porous insulating layer at a wavenumber of 835 cm⁻¹. -1 Up to 845cm -1 It has a first absorption peak in the range of , at a wavenumber of 760 cm⁻¹ -1 Up to 770cm -1 The first absorption peak has a second absorption peak within the range of , and the peak height I1 of the first absorption peak and the peak height I2 of the second absorption peak satisfy: I1>I2, 1.5≤I1 / I2≤4.5; The electrochemical device satisfies at least one of the following conditions: (1) The fluoropolymer includes vinylidene fluoride polymer segments; (2) The fluoropolymer includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; (3) Based on the sum of the α-phase and β-phase in the fluoropolymer, the α-phase accounts for 35% to 80% of the fluoropolymer, and the β-phase accounts for 20% to 65% of the fluoropolymer.

2. The electrochemical device according to claim 1, wherein, 2≤I1 / I2≤4.

3. The electrochemical device according to claim 1, wherein, The full width at half maximum (FWHM) W1 of the first absorption peak and the full width at half maximum (FWHM) W2 of the second absorption peak satisfy the condition: 0.5 ≤ W1 / W2 ≤ 1.

4. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following conditions: (1) The porous isolation layer further includes inorganic materials; (2) The polymer material further includes at least one of polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, polyacrylate or polyethylene terephthalate; (3) The polymer material in the porous isolation layer has a mass percentage content of 40% to 100%.

5. The electrochemical device according to claim 4, wherein, The electrochemical device satisfies at least one of the following conditions: (1) The inorganic material includes at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate; (2) The inorganic material in the porous isolation layer has a mass percentage content of 5% to 60%.

6. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following conditions: (1) The thickness of the porous isolation layer is 4 μm to 20 μm; (2) The porosity of the porous isolation layer is 30% to 75%; (3) The average pore size of the porous isolation layer is 90 nm to 200 nm.

7. An electronic device comprising the electrochemical device according to any one of claims 1 to 6.

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