Separator, electrochemical apparatus and electronic device

Abstract

A separator, an electrochemical apparatus and an electronic device. The separator comprises a base membrane and a functional coating, wherein the functional coating comprises a first coating, the first coating being at least arranged on one side surface of the base membrane and containing functional particles. The functional particles are used for melting in a temperature interval of 110 to 130ºC in a thermal safety test to block pores of the base membrane and further comprise a reducing substance, and the reducing substance is used for reducing the electromotive force of an electrochemical device in a temperature interval of 110 to 130ºC in a thermal safety test and ameliorating thermal runaway. The separator can be quickly melted at a high-temperature section of a hot box test to block pores of the base membrane, so as to block a short-circuit current between a cathode and an anode; and the separator can further reduce the cathode potential, which is beneficial to improving the thermal performance of a battery.

Description

Separator membranes, electrochemical devices, and electronic devices Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an isolation membrane, an electrochemical device, and an electronic device. Background Art

[0002] As lithium-ion batteries become increasingly widely used, higher requirements are placed on their safety performance, especially their thermal safety. Battery separators with excellent thermal safety performance should have a low risk of thermal runaway, thereby preventing thermal runaway in the battery cells when a short circuit or other abnormality occurs. Thermal runaway can ultimately lead to a large-scale short circuit in the battery, causing fire or explosion.

[0003] At present, the closed-cell design of the separator mainly focuses on the closed-cell basement membrane. The effect of the closed-cell basement membrane on reducing the risk of thermal runaway has been widely used and verified. However, the performance of the basement membrane needs to take into account the reduction of the closed-cell temperature, the tensile strength of the separator, the heat shrinkage resistance and the processability. Therefore, the closed-cell performance of the basement membrane cannot be reduced indefinitely. Therefore, there is an urgent need to provide a separator that can improve the closed-cell performance of the basement membrane to improve the pass rate of the hot box test of lithium-ion batteries.

[0004] Summary of the Invention

[0005] In view of this, the present application provides an isolation membrane, an electrochemical device and an electronic device, wherein the first coating in the isolation membrane can quickly melt and block the base membrane pores in the high temperature section (110°C to 130°C) of the hot box test to hinder the short-circuit current between the cathode / anode, and the isolation membrane can also reduce the cathode potential of the electrochemical device, which is beneficial to improving the pass rate of the battery hot box test and improving thermal runaway.

[0006] In the first aspect, the present application provides an isolation membrane for use in an electrochemical device, wherein the isolation membrane includes a base membrane and a functional coating provided on the base membrane, wherein the functional coating includes a first coating, wherein the first coating is provided on at least one side surface of the base membrane, and the first coating contains functional particles, wherein the functional particles include reducing substances. The isolation membrane is configured in the electrochemical device so that in a high temperature environment of 110°C to 130°C, the functional particles can melt and block the pores of the base membrane to block the short-circuit current between the cathode / anode, and the reducing substance in the functional particles can also reduce the electromotive force of the electrochemical device in a high temperature environment. The reducing substance cooperates with the first material in the functional particles to improve battery thermal runaway.

[0007] In some embodiments, the functional particles have a core-shell structure, which includes a core and an outer shell. The core contains the reducing substance and a first material, the first material is a low melting point component and has a high melt index and a large heat absorption power, and the outer shell contains a second material. The glass transition temperature of the second material is significantly higher than the glass transition temperature of the first material to avoid the functional particles from melting and blocking the base membrane pores during the formation stage.

[0008] The functional particles described in the present application can remain stable during the formation stage of the lithium-ion battery (80°C to 90°C) without affecting the normal charging and discharging of the battery cell. In the high-temperature section (110 to 130°C) of the hot box test, the outer shell melts and breaks, and the low-melting-point component (first material) in the inner core can quickly melt and flow to block the base membrane pores. At the same time, the reducing substance in the functional particles flows out with the first material and adheres to the cathode surface, is oxidized by the cathode, and thus reduces the cathode potential. Before the first material blocks the pores (i.e., the base membrane pores, the same below), part of the generated oxidation products will diffuse to the anode and be reduced by the anode, thereby increasing the anode potential, thereby reducing the overall electromotive force of the battery cell, thereby improving the pass rate of the hot box test, and the battery cell performance is normal at room temperature.

[0009] In some embodiments, the oxidation potential of the reducing substance is 3.3 V to 4.2 V. Preferably, the oxidation potential of the reducing substance is 3.3 V to 4.05 V. When the oxidation potential of the reducing substance is within the above range, it can significantly reduce the cathode potential of the electrochemical device, thereby reducing the electromotive force of the electrochemical device, which is conducive to improving thermal runaway.

[0010] In some embodiments, the first coating is disposed on the cathode-facing side of the base film, which helps the reducing substances flow to the cathode surface to reduce the overall electromotive force and improve the thermal safety performance of the electrochemical device.

[0011] In some embodiments, the concentration S of the reducing substance dissolved in the electrolyte is 0.5 mol / L to 1.5 mol / L. When the concentration of the reducing substance dissolved in the electrolyte is within the above range, the reducing substance dissolves in the electrolyte after the core-shell structure breaks, which helps to disperse more evenly and react with the cathode surface, and is more effective in preventing overcharge. The fluidity helps the reducing substance to directly shuttle between the positive and negative electrodes, enhancing the overcharge prevention effect. Preferably, the concentration S of the reducing substance dissolved in the electrolyte is 0.8 mol / L to 1.0 mol / L.

[0012] In some embodiments, the glass transition temperature or melting point of the first material is 40°C to 110°C. In this way, it is conducive to rapid flow in the high temperature section of the hot box test to achieve blocking of the base film pores. The first material will melt rapidly in the high temperature section (110°C to 130°C), and the melting range is narrow, and it can be completely melted in a very narrow temperature range. At the same time, the range of its heat absorption power is appropriate and the range of its melt index is appropriate, which is more conducive to improving its fluidity after melting, thereby achieving rapid melting and closure in the temperature range of 110°C to 130°C, thereby improving the pass rate of the battery hot box test. The first material is selected from at least one of polyethylene wax, low molecular weight polyvinyl chloride, polymethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, ternary copolymer polyacrylonitrile, polystyrene or polyester resin.

[0013] In some embodiments, the glass transition temperature or melting point of the second material is 115°C to 135°C. The second material with the above-mentioned glass transition temperature is conducive to ensuring that the first coating is stable at low temperatures (≤90°C) and does not affect the normal charging and discharging of the battery cell. In the high temperature section (100°C to 130°C), the outer shell melts and breaks, and the low-melting-point component of the inner core (i.e., the first material) quickly melts and flows to open and block the holes, thereby preventing the anode and cathode short circuit and the interaction of materials between the anode and cathode, reducing the heat generation of the battery cell, and thus improving the hot box pass rate of the battery cell. The second material is selected from at least one of high molecular weight polyvinyl chloride, polyethylene, polyethylene naphthalate, or a mixture of polyethylene and polypropylene. It should be noted that the present application does not limit the selection of specific substances in the first material and / or the second material. The above is only an illustrative example. The present application does not limit the selection of other substances, as long as at least one of its glass transition temperature or melting point is within the above range. In particular, for the melting point of the polymer, its molecular weight can be adjusted to achieve a melting point within a suitable range. The specific control methods can refer to the conventional methods of the prior art and will not be described in detail. In some embodiments, the reducing substance is selected from the compound of formula I, the compound of formula II, the compound of formula III or a compound containing Fe 3+ / Fe 2+ At least one of the charge pairs;

[0014] Wherein, R1 to R7 are each independently selected from any one of hydrogen and C1 to C6 alkyl.

[0015] In some embodiments, R1 and R2 are each independently any one of C3 to C4 alkyl groups, and R3 to R7 are each independently selected from any one of C1 to C2 alkyl groups.

[0016] In some embodiments, the reducing substance is selected from at least one of 3,5-di-tert-butyl-1,2-dimethoxybenzene, ferrocene, 10-methylphenothiazine, tetramethylpiperidinyl oxide (TEMPO), 1,2,3,4-tetrahydro-6,7-dimethylnaphthalene, dimethoxybenzene compounds, or 2,2,6,6-tetramethylpiperidinyl oxide. During the coating synthesis, a reducing substance is added to the core. At high temperatures, as the shell melts and ruptures, the reducing substance flows out and is oxidized by the strong oxidizing cathode, reducing the cathode potential. Part of the oxidation product diffuses to the anode and can be reduced by the anode, increasing the anode potential, thereby reducing the overall cell potential and improving the hot box pass rate.

[0017] In some embodiments, the core comprises 50 wt % to 80 wt % based on the mass of the first coating layer, the reducing substance comprises 10 wt % to 35 wt % based on the mass of the core, and the second material comprises 20 wt % to 50 wt % based on the mass of the functional particles. Preferably, the core comprises 60 wt % to 70 wt % based on the mass of the first coating layer, the reducing substance comprises 20 wt % to 30 wt % based on the mass of the core, and the second material comprises 30 wt % to 40 wt % based on the mass of the functional particles.

[0018] In some embodiments, the base film has a rupture temperature of 150°C to 180°C, and a closed-pore temperature of 134°C to 140°C. It can be seen that the closed-pore temperature of actual commercial base films generally does not reach 130°C. Therefore, based on the commercial base film, the present application further provides the first coating so that the base film can achieve closed-pore operation in an environment below 130°C. At the same time, the closed-pore coating can further enhance the ability to prevent short-circuit current between the anode and cathode, thereby improving thermal runaway.

[0019] At high temperatures, the heat generated by the side reactions of the cathode / anode with the electrolyte will cause heat accumulation in the battery cell, which can easily cause the separator to melt and shrink during the hot box test, resulting in a short circuit between the cathode and anode, which in turn causes thermal runaway and ultimately a fire in the battery cell. Therefore, in some embodiments, the functional coating further includes a second coating, which is disposed on the other side of the base film facing away from the first coating. The first coating and the second coating can be disposed relative to each other, and the second coating contains ceramic particles. Based on the mass of the second coating, the mass percentage of the ceramic particles is 70wt% to 95wt%. In this way, the second coating can provide better mechanical support for the base film and the first coating to prevent the separator from melting and shrinking during the hot box test.

[0020] In some embodiments, the D50 value of the functional particles is 0.5 μm to 1.8 μm to maintain fluidity. Preferably, the D50 value of the functional particles is 0.6 μm to 1.0 μm.

[0021] In some embodiments, the first coating layer has a thickness of 0.5 μm to 3 μm. A coating thickness less than 0.5 μm may not achieve full coverage and weaken the closed-cell effect. A coating thickness greater than 3 μm may result in accumulation of the closed-cell coating, affecting normal electrical performance and increasing impedance. Preferably, the first coating layer has a thickness of 1.5 μm to 2.5 μm.

[0022] In a second aspect, the present application provides an electrochemical device, which includes the above-mentioned isolation membrane.

[0023] In some embodiments, when the electrochemical device is fully charged (full charge potential is 4.53V), the DSC spectrum of the separator shows a characteristic peak A1 of the core in the range of 80°C to 110°C, a characteristic peak B1 of the shell in the range of 115°C to 135°C, the peak area of ​​the main melting peak of the characteristic peak A1 is 100 J / g to 250 J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 80 J / g to 200 J / g. Preferably, the characteristic peak A1 of the core is present in the range of 95°C to 110°C, the characteristic peak B1 of the shell is present in the range of 115°C to 125°C, the peak area of ​​the main melting peak of the characteristic peak A1 is 150 J / g to 200 J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 150 J / g to 200 J / g. It can be seen that after testing at a high temperature of 110℃ to 130℃ for 15 to 20 minutes, the peak is sharp and presents a "tall and narrow" shape. The reason is that the core-shell structure melts and breaks under high temperature, and the reducing substances are released.

[0024] During the formation stage of the battery cell manufacturing process, if the core material's glass transition temperature is too low, it will melt and deform, lacking mechanical support for the outer shell, which can easily cause the shell to rupture and release the core material. However, if the core material's glass transition temperature is too high, its melting rate will be too slow, its thermal response will be slow, and its melting range will become wider, affecting its high-temperature thermal closed-cell performance. Therefore, the glass transition temperature of the first material must be regulated within an appropriate range to facilitate the presence of a characteristic peak A1 with a peak area of ​​100 J / g to 250 J / g in the range of 95°C to 110°C. Because the outer shell needs to provide mechanical support, encapsulate the core, and prevent pore blocking during the formation stage, it should not melt prematurely. Since the national standard for hot-box testing is 130°C, the outer shell must melt and rupture before the hot-box test temperature, releasing the core material. Therefore, the glass transition temperature of the second material must be regulated within an appropriate range.

[0025] In some embodiments, the initial electromotive force of the electrochemical device is 4.53 V, and after a hot box test at 110° C. to 130° C. for 15 to 20 minutes, the electromotive force of the electrochemical device is 4.0 V to 4.30 V.

[0026] In some embodiments, the initial electrochemical device electromotive force is 4.53 V. After the electrochemical device is subjected to a hot box test at 110° C. to 130° C. for 15 to 20 minutes, the electrochemical device electromotive force is 4.0 V to 4.21 V. The lower electromotive force after the hot box test is more conducive to passing the thermal safety test and improving the stability of the electrochemical device.

[0027] In a third aspect, the present application provides an electronic device comprising the above-mentioned electrochemical device.

[0028] The present application provides an isolation membrane, an electrochemical device, and an electronic device, wherein the isolation membrane includes functional particles having a core-shell structure, wherein the glass transition temperature / melting point of the shell material is significantly higher than the glass transition temperature / melting point of the core material, and wherein the core of the functional particles further contains a reducing substance. The functional particles can remain stable during the formation stage of the battery without affecting the normal charging and discharging of the battery cell, while in the high-temperature test section, the shell material can quickly melt and rupture, and the first material in the core can quickly melt and flow to block the basement membrane pores to hinder the short-circuit current between the cathode and the anode. At the same time, the reducing substance in the core flows out with the first material and adheres to the cathode surface, reducing the cathode potential, thereby reducing the overall electromotive force of the battery cell. The reducing substance and the first material cooperate with each other to improve the thermal runaway of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0030] FIG1 is a schematic structural diagram of the isolation membrane described in this application;

[0031] FIG2 is a DSC test spectrum of the isolation membrane described in Example 1-1 of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] The prior art usually adopts the method of increasing the glass transition temperature of the coating material in the battery separator to avoid the coating material from melting during the processing (especially 80-90°C in the formation stage). This can improve the melting and plugging of the pores after formation to a certain extent. However, as the glass transition temperature of the material increases, the pore closing response speed is slow in the high temperature section of the test (110-130°C), and it is difficult to quickly close the base membrane pores, which is not conducive to blocking the short-circuit current between the anode and cathode, resulting in a low pass rate of the battery's hot box test, which is not conducive to improving the battery's thermal runaway. In order to solve the above technical problems, the present application provides a separator, which can be quickly melted in the high temperature section (110-130°C) of the hot box test, with a narrow melting range, a high melting index, and a large melting enthalpy, thereby achieving rapid melting and spreading to block the base membrane pores, hindering the transmission of lithium ions between the anode and cathode, hindering the interaction of substances between the anode and cathode, and reducing side reactions. The reducing substance in the separator can also reduce the electromotive force of the electrochemical device, which is more conducive to improving the battery's thermal runaway.

[0034] electrochemical devices

[0035] The present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0036] Isolation film

[0037] In some embodiments, as shown in Figure 1, the isolation membrane 101 includes a base membrane 11 and a functional coating 12 disposed on the base membrane 11, the functional coating 12 including a first coating 121 and a second coating 122, the first coating 121 is disposed on one side surface of the base membrane 11, the first coating 121 contains functional particles 13, the functional particles 13 include reducing substances, the second coating 122 is disposed on the side surface of the base membrane facing away from the first coating 121, the first coating 121 and the second coating 122 are disposed opposite to each other, the second coating 122 contains ceramic particles, the isolation membrane 101 is configured in an electrochemical device to block the short-circuit current between the cathode / anode during thermal safety testing, and can reduce the electromotive force of the electrochemical device and improve battery thermal runaway.

[0038] In some embodiments, the functional particles 13 have a core-shell structure, comprising a core 131 and an outer shell 132. The core 131 contains the reducing substance and a first material, wherein the first material is a low-melting-point component having a high melt index and a large heat absorption power. The outer shell 132 contains a second material having a glass transition temperature significantly higher than that of the first material to prevent the functional particles from melting and blocking the pores of the base membrane during the formation stage. When the electrochemical device is fully charged, the DSC spectrum of the separator, as shown in FIG2 , shows a characteristic peak A1 of the core in the range of 80°C to 110°C, and a characteristic peak B1 of the outer shell in the range of 115°C to 135°C. The peak area of ​​the main melting peak of characteristic peak A1 is 100-250 J / g, and the peak area of ​​the main melting peak of characteristic peak B1 is 80-200 J / g.

[0039] In some embodiments, when the electrochemical device is in a fully charged state, in the DSC spectrum of the isolation membrane, there is a characteristic peak A1 of the inner core in the range of 95°C to 110°C, and there is a characteristic peak B1 of the outer shell in the range of 115°C to 125°C. The peak area of ​​the main melting peak of the characteristic peak A1 is 150 to 200 J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 150 to 200 J / g.

[0040] In some embodiments, the oxidation potential of the reducing substance is 3.3V to 4.2V. Preferably, the oxidation potential of the reducing substance is 3.3V to 4.05V.

[0041] Illustratively, the oxidation potential of the reducing substance is 3.3 V, 3.4 V, 3.5 V, 3.6 V, 3.8 V, 4.0 V, 4.2 V, or a range consisting of any two of the above values.

[0042] In some embodiments, the dissolution concentration S of the reducing substance in the electrolyte is 0.5 to 1.5 mol / L.

[0043] Illustratively, the solubility concentration S of the reducing substance in the electrolyte is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.5 mol / L or a range consisting of any two of the above values.

[0044] In some embodiments, the glass transition temperature / melting point of the first material is 40° C. to 110° C. Exemplarily, the glass transition temperature / melting point of the first material is 40° C., 50° C., 60° C., 70° C., 80° C., 90° C., 100° C., 110° C., or a range consisting of any two of the foregoing values.

[0045] In some embodiments, the heat absorption power of the first material is 1.5 to 10 mW / mg, and the melt index of the first material is 2.5 to 30 g / min.

[0046] Illustratively, the heat absorption power of the first material is 1.5 mW / mg, 2 mW / mg, 3 mW / mg, 5 mW / mg, 8 mW / mg, 10 mW / mg, or a range consisting of any two of the above values.

[0047] Illustratively, the melt index of the first material is 2.5 g / min, 3 g / min, 5 g / min, 10 g / min, 15 g / min, 20 g / min, 25 g / min, 30 g / min, or a range consisting of any two of the above values.

[0048] In some embodiments, the first material is selected from at least one of polyethylene wax, low molecular weight polyvinyl chloride, polymethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, terpolymer polyacrylonitrile, polystyrene, or polyester resin.

[0049] In some embodiments, the second material has a glass transition temperature / melting point of 115°C to 135°C.

[0050] Illustratively, the glass transition temperature / melting point of the second material is 115°C, 118°C, 120°C, 122°C, 124°C, 125°C, 128°C, 130°C, 133°C, 135°C, or a range consisting of any two of the above values.

[0051] In some embodiments, the second material is selected from at least one of high molecular weight polyvinyl chloride, polyethylene, polyethylene naphthalate, or a mixture of polyethylene and polypropylene.

[0052] In some embodiments, the reducing substance is selected from at least one of 3,5-di-tert-butyl-1,2-dimethoxybenzene, ferrocene, 10-methylphenothiazine, tetramethylpiperidinium oxide (TEMPO), 1,2,3,4-tetrahydro-6,7-dimethylnaphthalene, dimethoxybenzene compounds or 2,2,6,6-tetramethylpiperidinium oxide.

[0053] In some embodiments, based on the mass of the first coating layer, the mass percentage of the core is 50 wt % to 80 wt %.

[0054] Illustratively, the mass percentage of the inner core is 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt% or a range consisting of any two of the above values.

[0055] In some embodiments, based on the mass of the core, the mass percentage of the reducing substance is 10 wt % to 35 wt %.

[0056] Illustratively, the mass percentage of the reducing substance is 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt% or a range consisting of any two of the above values.

[0057] In some embodiments, based on the mass of the functional particles, the mass percentage of the second material is 20 wt % to 50 wt %.

[0058] Exemplarily, the mass percentage of the second material is 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt% or a range consisting of any two of the above values.

[0059] In some embodiments, the base film has a rupture temperature of 150°C to 180°C, and a closed-cell temperature of 134°C to 148°C.

[0060] Exemplarily, the film breaking temperature of the base film is 150° C., 155° C., 160° C., 170° C., 180° C., or a range consisting of any two of the above values.

[0061] Illustratively, the closed-cell temperature of the base film is 134° C., 135° C., 138° C., 140° C., 148° C., or a range consisting of any two of the above values.

[0062] In some embodiments, based on the mass of the second coating layer, the mass percentage of the ceramic particles is 70 wt % to 95 wt %.

[0063] Illustratively, the mass percentage of the ceramic particles is 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt% or a range consisting of any two of the above values.

[0064] In some embodiments, the functional particles have a D50 value of 0.5 μm to 1.8 μm, a D10 value greater than 0.1 μm, and a molecular weight of 1,500 to 20,000.

[0065] Illustratively, the D50 value of the functional particles is 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.5 μm, 1.6 μm, 1.8 μm, or a range consisting of any two of the above values.

[0066] In some embodiments, the coating weight of the first coating is 1.5 mg / 5000 mm 2 ~3.0mg / 5000mm 2, the coating thickness is 0.5μm~3μm.

[0067] For example, the coating weight of the first coating is 1.5 mg / 5000 mm 2 、1.8mg / 5000mm 2 , 2.0mg / 5000mm 2 , 2.3mg / 5000mm 2 , 2.5mg / 5000mm 2 , 2.8mg / 5000mm 2 、3.0mg / 5000mm 2 Or a range consisting of any two of the above values.

[0068] Illustratively, the coating thickness of the first coating layer is 0.5 μm, 0.8 μm, 1.0 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, or a range consisting of any two of the above values.

[0069] Exemplary preparation method of the isolation film:

[0070] (1) Preparation of functional particles;

[0071] Exemplarily: obtain a reaction solution containing a raw material linear liquid, put the reaction solution and the catalyst into a hydrogenation reactor, stir at 55-65°C and 550-650 r / min, stir for 10-20 min, add a solution containing a reducing substance and an emulsifier, and then pass hydrogen to raise the pressure gauge to 1-1.5 MPa, adjust the speed to 750-850 r / min and react for 3-4 hours. After the reaction is completed, release the pressure and keep warm for 1-2 hours, then add the shell monomer and an appropriate amount of cross-linking agent, stir, keep warm for 2-3 hours, cool to room temperature, and freeze to break the emulsion.

[0072] (2) Preparation of the first coating;

[0073] Exemplarily: step a. mixing deionized water, functional particles, a binder and a wetting agent, wherein the functional particles, the binder and the wetting agent are mixed in a mass ratio of 96.5-99.3%: 0.5-3%: 0.2-0.5% (excluding the dispersion medium deionized water), and fully dispersed in a stirrer to obtain a slurry A to be coated; step b. uniformly coating the slurry A to be coated in step a on one side surface of the base film, and completing the preparation of the first coating after drying.

[0074] (3) Preparation of the second coating;

[0075] Exemplarily: step c. mixing deionized water, solid filler, adhesive and wetting agent, wherein the solid filler, adhesive and wetting agent are mixed in a mass ratio of 94.5-99.3%: 0.5-5%: 0.2-0.5%, and fully dispersed in a blender to obtain a slurry B to be coated; step d. evenly coating the slurry B to be coated in step c on the other side surface of the base film, and completing the preparation of the second coating after drying to obtain an isolation film.

[0076] other

[0077] Positive electrode

[0078] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The present application does not particularly limit the thickness of the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30μm to 120μm. The positive electrode active material in the positive electrode active material layer can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and compounds obtained by adding other transition metals or non-transition metals to the above compounds, and the present application does not particularly limit it. The positive electrode current collector can be made of materials such as metal foil or porous metal plate, for example, foil or porous plate of metals such as aluminum, copper, nickel, titanium or iron or their alloys, such as Al (aluminum) foil. The present application does not particularly limit the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 12μm.

[0079] The positive electrode sheet can be prepared according to conventional methods in the art.

[0080] Negative electrode

[0081] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The present application does not specifically limit the thickness of the negative electrode active material layer, as long as it can achieve the objectives of the present application. For example, the thickness of the negative electrode active material layer is 30 μm to 120 μm. The negative electrode active material layer contains a negative electrode active material. In some embodiments, the negative electrode active material may include at least one of a carbon material or a silicon-based material. In some embodiments, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon. In some embodiments, the silicon-based material includes, but is not limited to, at least one of silicon, a silicon-oxygen composite, or a silicon-carbon composite. The present application does not specifically limit the thickness of the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer). The present application does not specifically limit the thickness of the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The negative electrode active layer may also include a binder and a thickener. This application does not specifically limit the types of binder and thickener, as long as they can achieve the objectives of this application. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The negative electrode active layer may also include a conductive agent. This application does not specifically limit the type of conductive agent, as long as it can achieve the objectives of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, a metallic material, or a conductive polymer. This application does not specifically limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode active layer. Those skilled in the art may select the ratio based on actual needs, as long as it can achieve the objectives of this application. Optionally, the negative electrode plate may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the conductive agent and binder used in the negative electrode active layer described above.

[0082] The negative electrode sheet can be prepared according to conventional methods in the art.

[0083] electrolyte

[0084] The electrolyte includes an organic solvent and a lithium salt, wherein the organic solvent includes a carbonate solvent, a carboxylate solvent, or a combination thereof; wherein the carbonate solvent includes at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC); and the carboxylate solvent includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate. The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiB(C2O4)2, LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0085] The electrolyte may further include an electrolyte additive, which may include but is not limited to at least one of fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VC) or 1,3-propane sultone (PS).

[0086] The electrolyte can be prepared according to conventional methods in the art.

[0087] The electrochemical device of the present application may include any device that generates an electrochemical reaction, and specific embodiments thereof include all types of primary batteries or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0088] electronic devices

[0089] The electronic devices described in this application include any of the above-mentioned electrochemical devices. The electronic devices described in this application include, but are not limited to, mobile phones, laptops, tablet computers, game consoles, drones, electric cars, electric bicycles, power tools, and Bluetooth headsets.

[0090] Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples.

[0091] Example 1-1

[0092] (1) Preparation of lithium-ion batteries

[0093] (1) Preparation of lithium-ion battery separators

[0094] A base membrane with a rupture temperature of 165°C and a closure temperature of 135°C was selected. Coating slurry A was applied to the cathode-facing side of the base membrane and dried to complete the first coating. Coating slurry B was applied to the anode-facing side of the base membrane and dried to complete the second coating. The separator membrane was obtained. The DSC spectrum of the separator membrane is shown in Figure 2. As can be seen from Figure 2, the main melting peak of the core component is at 110°C, and the main melting peak of the shell component is at 127°C.

[0095] The coating slurry A and the coating slurry B were prepared according to the following method:

[0096] Preparation of functional particles:

[0097] Prepare a 10% solution of linear liquid polyethylene wax (melting point 105°C) as the raw material and add it to a 2L hydrogenation reactor with a rotor. The solution mass is 1200g. Tighten the reactor to prevent air leakage, then flush it with high-purity nitrogen three times to exhaust the air in the reactor. Prepare a catalyst with triisobutylaluminum and nickel cyclohexane at a molar ratio of 6:1. Place the prepared catalyst in a constant temperature water bath for 30 minutes, then slowly inject it into the reactor and stir it at 60°C and 600r / min for 15 minutes. Then add 3,5-di-tert-butyl-1,2-diol. -400 g of dimethoxybenzene solution (reducing substances account for 8% by mass) was added to 200 g of sodium carboxymethyl cellulose emulsifier, and then hydrogen was introduced to raise the pressure gauge to 1 MPa, the speed was 800 r / min, and the reaction was carried out for 3 hours. After the reaction was completed, the pressure was released and the mixture was kept warm for 1 hour. The shell monomer vinyl chloride was added in an amount of 11% of the mass of the core, and an appropriate amount of cross-linking agent acrylic acid ester was added in an amount of 0.5% of the mass of the core layer. The mixture was slowly stirred at 300 r / min and kept warm for 2 hours. Finally, the mixture was cooled to room temperature and frozen to break the emulsion to obtain a functional core-shell material.

[0098] Preparation of coating slurry A:

[0099] Deionized water, functional particles, PMMA and polyoxyethylene alkylphenol ether are mixed in a mass ratio of 98%:2%:0.3% (excluding the dispersion medium deionized water), and are fully dispersed in a stirrer to obtain a slurry A to be coated.

[0100] Preparation of coating slurry B:

[0101] Deionized water, boehmite, PVA and polyoxyethylene alkylphenol ether were mixed in a mass ratio of 99%:0.5%:0.5%, and the mixture was fully and evenly dispersed in a stirrer to obtain a slurry B to be coated.

[0102] The difference between Comparative Example 1-1 and Example 1-1 is that in Comparative Example 1-1, both sides of the base film are coated with ceramic particles, that is, when preparing the coating slurry A in Comparative Example 1-1, the functional particles are replaced with boehmite.

[0103] The difference between Example 1-0, Example 1-2 to Example 1-26 and Example 1-1 is that the parameters of some raw materials were adjusted when preparing the functional particles, as shown in Table 1 for details.

[0104] The difference between Example 1-27 and Example 1-1 is that both sides of the base film are coated with functional coatings, that is, both sides of the base film are coated with coating slurry A. See Table 1 for details.

[0105] Examples 2-1 to 2-11 further adjusted the contents of the core, reducing substance, and second material in the functional particles, as shown in Table 2 for details.

[0106] Examples 3-1 to 3-10 further adjusted the particle size of the functional particles and the coating thickness, as shown in Table 3.

[0107] (2) Preparation of positive electrode sheet

[0108] The positive electrode active material - lithium cobalt oxide active material LiCoO2, conductive carbon black Super-P, and binder PVDF are mixed in an N-methylpyrrolidone NMP solvent system in a weight ratio of 97.6:1.3:1.1 by a vacuum mixer and fully stirred to obtain a positive electrode slurry; the positive electrode slurry is coated on both surfaces of a 9μm Al foil substrate with a coating weight of 280 mg, and then dried, cold pressed, slit, and cut to obtain a positive electrode sheet. The thickness of the positive electrode sheet after cold pressing is 95μm.

[0109] (3) Preparation of negative electrode sheet

[0110] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium methyl cellulose (CMC) were mixed evenly in a deionized water solvent in a mass ratio of 95:2:2:1, coated on one side of a 9 μm Cu foil and dried, and the above steps were repeated on the other side of the Cu foil to obtain a negative electrode sheet coated with a negative electrode active layer on both sides. The negative electrode sheet was obtained by cold pressing and cutting.

[0111] (4) Preparation of electrolyte

[0112] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent. LiPF6 is dissolved in the organic solvent, and vinylene carbonate is added and mixed to obtain an electrolyte. The mass percentage of LiPF6 is 12.5% ​​and the mass percentage of vinylene carbonate is 3% based on the total mass of the electrolyte.

[0113] (5) Preparation of lithium-ion batteries

[0114] The positive electrode sheet, separator and negative electrode sheet are stacked in sequence, and the separator separates the positive electrode sheet and the negative electrode sheet. The bare battery cell is formed by winding, and the bare battery cell is placed in the aluminum-plastic film shell to be sealed. After high-temperature baking, electrolyte injection, vacuum packaging, standing, formation, shaping and capacity testing, a lithium-ion battery is obtained.

[0115] (2) Testing of lithium-ion batteries

[0116] (1) Hot box test

[0117] Step 1: Charge the prepared battery at a constant current of 0.5C to a cut-off voltage of 4.5V, then charge it at a constant voltage to a cut-off current of 200mA, and then let it stand for 5 minutes;

[0118] Step 2: Attach the temperature-sensing wire to the fully charged battery between the two tabs, connect the two tabs to monitor the voltage, and hang the battery cell vertically in the box;

[0119] Step 3: Heat the box to 130°C at a rate of 5°C and maintain for 60 minutes.

[0120] Judging criteria: The battery passes if it does not catch fire or explode.

[0121] (2) Thermal shrinkage test

[0122] Use a specific mold to punch out the separator to be tested into a length and width of 72.5cm and 54.2cm respectively. Place the punched separator flatly between two A4 papers and bake it in a 130℃ oven for 20 minutes. Take out the baked separator and measure the length and width as X1 and X2 respectively. The heat shrinkage calculation formula is as follows:

[0123] MD thermal shrinkage = (72.5-X1) / 72.5*100%;

[0124] TD thermal shrinkage = (54.2-X2) / 54.2*100%.

[0125] (3) Electromotive force test

[0126] The initial electromotive force of the assembled batteries was 4.53 V, and the battery electromotive force value was detected in real time during the hot box test.

[0127] (4) Normal temperature cycle performance test

[0128] At 25°C, charge the lithium-ion battery at a constant current of 0.7C to 4.5V, then charge it at a constant voltage to a current of 0.5C. At this point, the lithium-ion battery is fully charged. Record the charge capacity at this point, which is the first-cycle charge capacity. After the lithium-ion battery rests for 5 minutes, discharge it at a constant current of 0.5C to 3V and rest for 5 minutes. This is a cycle of charge and discharge. Record the discharge capacity at this point, which is the first-cycle discharge capacity. Cycle 400 times under these conditions and calculate the capacity retention rate at the 400th cycle. Wherein, capacity retention rate (%) = discharge capacity of the current cycle / first-cycle discharge capacity.

[0129] Table 1

[0130] Comparing Comparative Example 1-1 with Example 1-1, it can be seen that coating the base film with a coating containing functional particles can significantly reduce the electromotive force of the lithium-ion battery at high temperature, and the pass rate of the hot box test is significantly improved. It can be seen that coating the base film with a coating containing functional particles is beneficial to improving the thermal safety performance of the lithium-ion battery.

[0131] Comparing Example 1-0 with Example 1-1, it can be seen that the appropriate oxidation potential of the reducing substance in the functional particles is more conducive to reducing the electromotive force of the lithium-ion battery at high temperature, and further improving the hot box test pass rate of the lithium-ion battery.

[0132] Comparing Examples 1-2 and 1-3 with Examples 1-4 and 1-5, it can be seen that the suitable reducing substance is more compatible with the first material having a melting point or glass transition temperature of 40°C to 110°C. The two work together to better balance reducing the electromotive force of the electrochemical device and improving the battery hot box pass rate, thereby improving battery thermal runaway.

[0133] Comparing Example 1-6 with Example 1-1 shows that the solubility of the reducing substance in the electrolyte is appropriate, which is conducive to further improving the battery hot box pass rate. Compared with Example 1-1, Examples 1-7 and 1-8 show that the melting point / glass transition temperature of the second material is too high (above 135°C), which is not conducive to improving battery thermal runaway. At the same time, compared with Example 1-1, the melting point / glass transition temperature of the second material in Example 1-9 is too low (below 115°C), which is also not conducive to improving battery thermal runaway.

[0134] Compared with Example 1-1, it can be seen from Examples 1-13 to 1-16 that the oxidation potential of the reducing substance is too high (higher than 4.2 V) or too low (lower than 3.3 V), which is not conducive to improving the thermal runaway of the battery.

[0135] Compared with Example 1-1, it can be seen from Examples 1-17 to 1-19 that the oxidation potential of the reducing substance and the solubility concentration in the electrolyte are both appropriate, which is more conducive to improving the thermal safety performance of the battery.

[0136] Examples 1-20 to 1-26 are all parallel examples of Example 1-1, and the results obtained are similar.

[0137] Table 2

[0138] As can be seen from Table 2, a moderate proportion of the low-melting-point material (first material) in the core improves the hot box test pass rate, but also reduces the mechanical properties of the coating. High-temperature and high-pressure core formation is prone to collapse, flattening, and blocking pores. Increasing the proportion of the first material increases internal resistance. In Example 2-12, when the proportion of the first material is too low, the high content of the external high-melting-point material also leads to an increase in internal resistance. Among them, Example 2-6 has the best overall effect.

[0139] Table 3

[0140] Note: Air permeability increment = (air permeability after baking at 130℃ for 20 minutes) – (air permeability before baking)

[0141] It can be seen that the smaller the particles are, the denser the functional coating is under the same coating quality, and the larger the initial permeability value is, indicating that the initial pore blocking phenomenon is serious and the electrochemical performance will be relatively poor at the beginning. The permeability value increases after baking, and the permeability value increment characterizes the pore blocking of the diaphragm. The larger the increase, the more serious the pore blocking, indicating that the better the closed-cell effect of the coating, and the better the pass rate in the hot box test. As can be seen from Table 3, the D50 value and coating thickness of the functional particles are both within the appropriate range, which is conducive to improving the electrochemical performance and closed-cell effect of the coating, thereby improving the pass rate of the hot box test. Example 3-2 is preferred for the best comprehensive performance.

[0142] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A separator for use in an electrochemical device, characterized in that: The isolation film includes a base film and a functional coating; The functional coating comprises a first coating, the first coating is disposed on at least one side of the base film, the first coating contains functional particles, and the functional particles are used to melt and plug the base film pores in a temperature range of 110° C. to 130° C.; The functional particles further include a reducing substance, and the reducing substance is used to reduce the electromotive force of the electrochemical device in a temperature range of 110° C. to 130° C. to improve thermal runaway.

2. The isolation film according to claim 1, characterized in that: The functional particles have a core-shell structure, the core-shell structure includes a core and an outer shell, and the core contains the reducing substance; The isolation film satisfies at least one of the following conditions: (I) the oxidation potential of the reducing substance is 3.3V to 4.2V; (II) the inner core further comprises a first material, wherein the glass transition temperature / melting point of the first material is 40° C. to 110° C.; (III) The shell contains a second material having a glass transition temperature / melting point of 115°C to 135°C.

3. The isolation film according to claim 2, characterized in that: At least one of the following conditions is met: (i) the oxidation potential of the reducing substance is 3.3V to 4.05V; (ii) the first material is selected from at least one of polyethylene wax, polymethyl methacrylate, polyacrylonitrile, polystyrene or polyethylene terephthalate; (iii) The second material is at least one selected from polyvinyl chloride, polyethylene or a mixture of polyethylene and polypropylene.

4. The isolation film according to claim 1, characterized in that: The reducing substance is selected from the group consisting of a compound of formula I, a compound of formula II, a compound of formula III or a compound containing Fe 3+ / Fe 2+ At least one of the charge pairs; Wherein, R1 to R7 are each independently selected from any one of hydrogen and C1 to C6 alkyl.

5. The isolation film according to claim 4, characterized in that: R1 and R2 are each independently selected from any one of C3-C4 alkyl groups, and R3 to R7 are each independently selected from any one of C1 to C2 alkyl groups; The Fe-containing 3+ / Fe 2+ Electron pairs include ferrocene.

6. The isolation film according to claim 2, characterized in that: The following requirements are met: based on the mass of the first coating, the mass percentage of the inner core is 50wt% to 80wt%; based on the mass of the inner core, the mass percentage of the reducing substance is 10wt% to 35wt%; based on the mass of the functional particles, the mass percentage of the second material is 20wt% to 50wt%.

7. The isolation film according to claim 1, characterized in that: The first coating layer is disposed on a side of the base film facing the cathode.

8. The isolation film according to claim 1, characterized in that: The reducing substance is dissolved in the electrolyte at a concentration of 0.5 mol / L to 1.5 mol / L.

9. The isolation film according to claim 1, characterized in that: At least one of the following conditions is met: (1) The coating thickness of the first coating layer is 0.5 μm to 3 μm; (2) The D50 value of the functional particles is 0.5 μm to 1.8 μm.

10. An electrochemical device, characterized in that: The electrochemical device comprises the separator according to any one of claims 1 to 9.

11. The electrochemical device according to claim 10, characterized in that When the electrochemical device is in a fully charged state, in the DSC spectrum of the isolation membrane, there is a characteristic peak A1 of the inner core in the range of 80°C to 110°C, and there is a characteristic peak B1 of the outer shell in the range of 115°C to 135°C; The peak area of ​​the main melting peak of the characteristic peak A1 is 100 J / g to 250 J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 80 J / g to 200 J / g.

12. The electrochemical device according to claim 11, characterized in that When the electrochemical device is in a fully charged state, in the DSC spectrum of the isolation membrane, there is a characteristic peak A1 of the inner core in the range of 95°C to 110°C, and there is a characteristic peak B1 of the outer shell in the range of 115°C to 125°C; The peak area of ​​the main melting peak of the characteristic peak A1 is 150 J / g to 200 J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 150 J / g to 200 J / g.

13. The electrochemical device according to claim 10, characterized in that The initial electromotive force of the electrochemical device is 4.53 V. After the electrochemical device is subjected to a hot box test at 110° C. to 130° C. for 15 to 20 minutes, the electromotive force thereof is 4.0 V to 4.30 V.

14. The electrochemical device according to claim 13, characterized in that The initial electromotive force of the electrochemical device is 4.53 V. After the electrochemical device is subjected to a hot box test at 110° C. to 130° C. for 15 to 20 minutes, the electromotive force thereof is 4.0 V to 4.21 V.

15. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to any one of claims 10 to 14.

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