WO2025054877A1 - Separator, electrochemical apparatus and electronic device - Google Patents

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, electrochemical device and electronic device Technical Field

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

As the application scope of lithium-ion batteries becomes wider and wider, higher requirements are put forward for their safety performance, especially their thermal safety performance. Battery separators with excellent thermal safety performance should have a lower risk of thermal runaway, so as to avoid thermal runaway of the battery cell when the battery short-circuits or other abnormalities occur. Thermal runaway will eventually lead to large-scale short circuits in the battery, causing fire or explosion.

At present, the closed-cell design of the isolation membrane mainly focuses on the closed-cell base membrane. The effect of the closed-cell base membrane on reducing the risk of thermal runaway has been widely used and verified, but the performance of the base 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 base membrane cannot be reduced indefinitely. Therefore, it is urgent to provide an isolation membrane that can improve the closed-cell performance of the base membrane, so as to improve the pass rate of the hot box test of lithium-ion batteries.

Summary of the invention

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.

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 disposed on the base membrane, wherein the functional coating includes a first coating, wherein the first coating is disposed on at least one surface of the base membrane, and wherein 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 and the anode, and the reducing substances in the functional particles can also reduce the electromotive force of the electrochemical device in a high temperature environment, and the reducing substances cooperate with the first material in the functional particles to improve thermal runaway of the battery.

In some embodiments, the functional particle has a core-shell structure, wherein the core-shell structure comprises a core and an outer shell. The inner core contains the reducing substance and a first material, wherein the first material is a low melting point component and has a high melting index and a large heat absorption power. The outer shell contains a second material, and the glass transition temperature of the second material is significantly higher than the glass transition temperature of the first material to prevent the functional particles from melting and blocking the base membrane pores during the formation stage.

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.

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. The oxidation potential of the reducing substance is within the above range, which 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.

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.

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

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 block 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, its heat absorption power range is suitable and its melting index range is suitable, which is more conducive to improving its fluidity after melting, thereby achieving rapid melting and pore 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 polyethylene wax, small fraction At least one of polyvinyl chloride, polymethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, terpolymer polyacrylonitrile, polystyrene or polyester resin.

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), does not affect the normal charging and discharging of the battery cell, and melts and breaks at high temperatures (100°C to 130°C). The low melting point component of the core (i.e., the first material) quickly melts and flows to open the plug hole, thereby preventing the short circuit of the cathode and cathode, the interaction of materials between the cathode 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 exemplary 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 its melting point in a suitable range. The specific means of regulation can refer to the conventional means of the prior art, which will not be repeated. In some embodiments, the reducing substance is selected from at least one of the compounds of formula I, formula II, formula III, or compounds containing Fe ³⁺ /Fe ²⁺ electrode pairs;

Wherein, _R1 to _R7 are each independently selected from any one of hydrogen and _C1 to _C6 alkyl.

In some embodiments, R ₁ and R ₂ are each independently any one of C ₃ to C ₄ alkyl groups, and R ₃ to R ₇ are each independently selected from any one of C ₁ to C ₂ alkyl groups.

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. In the coating synthesis, the reducing substance is added to the core, and at high temperature, as the shell melts and breaks, the reducing substance flows out and is oxidized by the strong oxidizing cathode, reducing the cathode potential, and part of the oxidation product diffuses to the anode, which can be reduced by the anode, increasing the anode potential, thereby reducing the overall cell potential and improving the hot box pass rate.

In some embodiments, based on the mass of the first coating, the mass percentage of the core is 50wt% to 80wt%, based on the mass of the 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%. Preferably, based on the mass of the first coating, the mass percentage of the core is 60wt% to 70wt%, based on the mass of the core, the mass percentage of the reducing substance is 20wt% to 30wt%, based on the mass of the functional particles, the mass percentage of the second material is 30wt% to 40wt%.

In some embodiments, the film breaking temperature of the base film is 150° C. to 180° C., and the closed-cell temperature of the base film is 134° C. to 140° C. It can be seen that the closed-cell temperature of the actual commercial base film usually does not reach 130° C. Therefore, the present application further provides the first coating on the basis of the commercial base film, so that the base film can achieve closed-cell operation in an environment below 130° C. At the same time, the closed-cell operation of the coating can further enhance the short-circuit current between the anode and cathode, and improve thermal runaway.

At high temperatures, the heat generated by the side reactions of the cathode/anode and the electrolyte will cause the battery core to accumulate heat, which is easy to cause the battery core to accumulate heat during the hot box test. The isolation film melts and shrinks, resulting in a short circuit between the cathode and cathode, which in turn causes thermal runaway and eventually 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, and the first coating and the second coating can be disposed relatively to each other, and the second coating contains ceramic particles, and the mass percentage of the ceramic particles is 70wt% to 95wt% based on the mass of the second coating. In this way, the second coating can provide better mechanical support for the base film and the first coating to prevent the isolation film from melting and shrinking during the hot box test.

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.

In some embodiments, the coating thickness of the first coating is 0.5 μm to 3 μm. If the coating thickness is less than 0.5 μm, full coverage of the coating cannot be achieved, and the closed-cell effect will be weakened. If the coating thickness is greater than 3 μm, closed-cell coating will accumulate, which will affect normal electrical properties and increase impedance. Preferably, the coating thickness of the first coating is 1.5 μm to 2.5 μm.

In a second aspect, the present application provides an electrochemical device, wherein the electrochemical device comprises the above-mentioned isolation membrane.

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

During the formation stage of the battery cell preparation process, if the glass transition temperature of the core material is too low, it will melt and deform, lacking mechanical support for the shell, which can easily cause the shell to rupture and the core material to flow out. If the glass transition temperature of the core material is too high, it will cause its melting rate to be too slow, the thermal response speed to be low, and the melting range to become wider, affecting the high-temperature thermal closed-cell performance. Therefore, the glass transition temperature of the first material needs to be regulated within a suitable range to facilitate the realization of a characteristic peak A1 with a peak area of 100J/g to 250J/g in the range of 95°C to 110°C. Since the shell needs to provide mechanical support, cover the core, and avoid plugging holes during the formation stage, Therefore, it should not be melted too early. Since the national standard for hot box test is 130°C, the outer shell needs to melt and break before the hot box test temperature to release the inner core material, so the glass transition temperature of the second material is regulated within an appropriate range.

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.

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

In a third aspect, the present application provides an electronic device, which includes the above-mentioned electrochemical device.

The present application provides a separator, an electrochemical device and an electronic device, wherein the separator includes functional particles, the functional particles have a core-shell structure, 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 the core of the functional particles also contains reducing substances. 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 the shell material can quickly melt and rupture in the high-temperature test section, and the first material in the core can quickly melt and flow to block the base film holes to hinder the short-circuit current between the cathode and the anode, and 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, and 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

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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.

FIG1 is a schematic diagram of the structure of the isolation membrane described in the present application;

FIG. 2 is a DSC test spectrum of the isolation membrane described in Example 1-1 of the present application.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is described below in conjunction with the accompanying drawings and embodiments. Please provide further detailed description. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

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 holes after the formation to a certain extent. However, as the glass transition temperature of the material increases, the closure response speed is slow in the high temperature section of the test (110-130°C), and it is difficult to quickly close the base film pores, which is not conducive to blocking the short-circuit current between the anode and cathode, resulting in a low pass rate of the hot box test of the battery, which is not conducive to improving the thermal runaway of the battery. 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 film pores, hinder the transmission of lithium ions between the anode and cathode, hinder the interaction of substances between the anode and cathode, and reduce 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 thermal runaway of the battery.

Electrochemical Devices

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.

Isolation film

In some embodiments, as shown in FIG1 , the isolation membrane 101 includes a base membrane 11 and a functional coating 12 disposed on the base membrane 11, the functional coating 12 includes 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 one 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 in a thermal safety test, and can reduce the electromotive force of the electrochemical device and improve battery thermal runaway.

In some embodiments, the functional particle 13 has a core-shell structure, the core-shell structure includes a core 131 and an outer shell 132, the core 131 contains the reducing substance and a first material, the first material is a low melting point component and has a high melting index and a large heat absorption power, the outer shell 132 contains a second material, the glass transition temperature of the second material is 0. The transition temperature is significantly higher than the glass transition temperature of the first material to prevent the functional particles from melting and blocking the base film pores during the formation stage. When the electrochemical device is fully charged, the DSC spectrum of the isolation membrane, as shown in FIG2, has a characteristic peak A1 of the inner 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 the characteristic peak A1 is 100 to 250 J/g, and the peak area of the main melting peak of the characteristic peak B1 is 80 to 200 J/g.

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.

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.

Exemplarily, 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.

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

Exemplarily, the dissolved 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.

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 above values.

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

Exemplarily, 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.

Exemplarily, 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.

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. A sort of.

In some embodiments, the glass transition temperature/melting point of the second material is 115°C to 135°C.

Exemplarily, 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.

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.

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.

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

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

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

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

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

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.

In some embodiments, the film breaking temperature of the base film is 150°C to 180°C, and the closed-cell temperature of the base film is 134°C to 148°C.

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.

Exemplarily, 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.

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 %.

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

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 1500 to 20000.

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.

In some embodiments, the coating weight of the first coating layer is 1.5 mg/5000 mm ² to 3.0 mg/5000 mm ² , and the coating thickness is 0.5 μm to 3 μm.

Illustratively, the coating weight of the first coating layer is 1.5 mg/5000 mm ² , 1.8 mg/5000 mm ² , 2.0 mg/5000 mm ² , 2.3 mg/5000 mm ² , 2.5 mg/5000 mm ² , 2.8 mg/5000 mm ² , 3.0 mg/5000 mm ² or a range consisting of any two of the above values.

Exemplarily, 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.

Exemplary preparation method of isolation film:

(1) Preparation of functional particles;

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

(2) Preparation of the first coating;

Exemplarily: step a. mix 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. evenly apply the slurry A to be coated in step a on one side of the base film, and complete the preparation of the first coating after drying.

(3) Preparation of the second coating;

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 stirrer to obtain slurry B to be coated; step d. uniformly 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.

other

Positive electrode

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The present application has no particular restrictions on 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 30 μm to 120 μm. 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 has no particular restrictions. The positive electrode current collector can use materials such as metal foil or porous metal plate, such as 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 has no particular restrictions on 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 5 μm to 12 μm.

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

Negative electrode

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 has no particular limitation on the thickness of the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode active material layer is 30 μm to 120 μm. The negative electrode active material layer contains negative electrode active materials. In some embodiments, In the example, 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, silicon-oxygen composite materials or silicon-carbon composite materials. The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or a composite current collector (for example, a composite current collector having a metal layer disposed on the surface of the polymer layer). The present application has no particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 5μm to 12μm. The negative electrode active layer may also include a binder and a thickener. The present application has no particular restrictions on the types of binders and thickeners, as long as the purpose of the present application can be achieved. 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 acrylic (ester) 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, and the present application has no particular restrictions on the type of the conductive agent, as long as the purpose of the present application can be achieved. 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, metal materials or conductive polymers. The present application has no particular restrictions on the mass ratio of the negative electrode active material, conductive agent, binder and thickener in the negative electrode active layer, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. Optionally, the negative electrode sheet may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application has no particular restrictions on the composition of the conductive layer, which may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The present application has no particular limitation on the conductive agent and the binder in the conductive layer. For example, the conductive agent and the binder may be at least one of the conductive agent and the binder in the above-mentioned negative electrode active layer.

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

Electrolyte

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), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) or butylene carbonate (BC). The carboxylate solvent The lithium salt 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 (LiPF ₆ ), lithium bis(oxalatoborate) (LiB(C ₂ O ₄ ) ₂ , LiBOB), lithium difluorooxalatoborate (LiBF ₂ (C ₂ O ₄ ), LiDFOB), lithium tetrafluoroborate (LiBF ₄ ), lithium bis(fluorosulfonyl imide) salt (LiFSI) or lithium bis(trifluoromethanesulfonyl imide) (LiTFSI).

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).

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

The electrochemical device of the present application may include any device that generates an electrochemical reaction, and its specific embodiments include all kinds 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.

Electronic devices

The electronic device described in the present application includes any of the above-mentioned electrochemical devices. The electronic device described in the present application includes, but is not limited to, mobile phones, laptops, tablet computers, game consoles, drones, electric cars, electric bicycles, electric tools, and Bluetooth headsets.

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

Example 1-1

(I) Preparation of lithium-ion batteries

(1) Preparation of lithium-ion battery separator

A base film with a film breaking temperature of 165°C and a closed cell temperature of 135°C was selected, and coating slurry A was coated on the cathode side of the base film, and the first coating was prepared after drying. Coating slurry B was coated on the other side of the base film facing the anode, and the second coating was prepared after drying to obtain an isolating film. The DSC spectrum of the isolating film is shown in Figure 2. It can be seen from Figure 2 that 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.

The coating slurry A and the coating slurry B are prepared according to the following method:

Preparation of functional particles:

The raw material linear liquid polyethylene wax (melting point 105℃) was prepared into a 10% solution and added into a 2L hydrogenation reactor with a rotor. The solution mass was 1200g. The reactor was tightened to prevent air leakage, and then flushed with high-purity nitrogen for 3 times to exhaust the air in the reactor. Triisobutylaluminum and nickel cyclohexaneate were prepared as catalysts in a molar ratio of 6:1. The prepared catalyst was placed in a constant temperature water bath for 30 minutes, then slowly injected into the reactor and stirred at 60℃ and 600r/min for 15 minutes, and then 3,5-di-tert-butyl-1,2- -400g of dimethoxybenzene solution (reducing substances account for 8% by mass), 200g of sodium carboxymethyl cellulose emulsifier was added, and then hydrogen was introduced to raise the pressure gauge to 1Mpa, and the speed was 800r/min for 3h. After the reaction was completed, the pressure was released and the mixture was kept warm for 1h. The shell monomer vinyl chloride was added in an amount of 11% of the mass of the inner core, and an appropriate amount of cross-linking agent acrylic ester was added in an amount of 0.5% of the mass of the core layer. The mixture was slowly stirred at 300r/min and kept warm for 2h. Finally, it was cooled to room temperature and frozen to break the emulsion to obtain a functional core-shell material.

Preparation of coating slurry A:

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 and evenly dispersed in a stirrer to obtain a slurry A to be coated.

Preparation of coating slurry B:

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

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.

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 are adjusted when preparing the functional particles, as shown in Table 1 for details.

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.

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

Examples 3-1 to 3-10 further adjusted the particle size and coating thickness of the functional particles, see Table 3 for details.

(2) Preparation of positive electrode sheet

The positive electrode active material - lithium cobalt oxide active material _LiCoO2 , conductive carbon black Super-P, and binder PVDF are fully stirred in an N-methylpyrrolidone NMP solvent system in a weight ratio of 97.6:1.3:1.1 by a vacuum mixer 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 280mg, 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.

(3) Preparation of negative electrode sheet

The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium methyl cellulose (CMC) are mixed evenly in a deionized water solvent at a mass ratio of 95:2:2:1, coated on one side of a 9μm Cu foil and dried, and the above steps are 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. After cold pressing and cutting, a negative electrode sheet is obtained.

(4) Preparation of electrolyte

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. LiPF ₆ is dissolved in the organic solvent, and vinylene carbonate is added and mixed to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF ₆ is 12.5% and the mass percentage of vinylene carbonate is 3%.

(5) Preparation of lithium-ion batteries

The positive electrode sheet, the isolation membrane and the negative electrode sheet are stacked in sequence, the isolation membrane separates the positive electrode sheet and the negative electrode sheet, and a bare battery cell is formed by winding. The bare battery cell is placed in an aluminum-plastic film shell to be sealed, and a lithium-ion battery is obtained after processes such as high-temperature baking, electrolyte injection, vacuum packaging, standing, formation, shaping and capacity testing.

(II) Testing of lithium-ion batteries

(1) Hot box test

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

Step 2: Attach the temperature-sensing wire to the fully charged battery, attach it between the two poles, connect the two poles to monitor the voltage, and place the battery vertically. Hang directly in the box;

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

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

(2) Heat shrinkage test

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

MD heat shrinkage = (72.5-X1)/72.5*100%;

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

(3) Electromotive force test

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

(4) Normal temperature cycle performance test

At 25°C, charge the lithium-ion battery to 4.5V at a constant current of 0.7C, then charge it at a constant voltage to a current of 0.5C. At this time, the lithium-ion battery is fully charged. Record the charging capacity at this time, which is the first cycle charging capacity. After the lithium-ion battery is left to stand for 5 minutes, discharge it to 3V at a constant current of 0.5C and leave it to stand for 5 minutes. This is a cycle of charging and discharging. Record the discharge capacity at this time, which is the first cycle discharge capacity. Cycle 400 times under this condition and calculate the capacity retention rate of the 400th cycle. Among them, capacity retention rate % = discharge capacity of the current cycle/first cycle discharge capacity.

Table 1

Compared with Example 1-1, it can be seen that coating the coating containing functional particles on the base film 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 coating containing functional particles on the base film is beneficial to improving the thermal safety performance of the lithium-ion battery.

Compared with Example 1-1, it can be seen that the oxidation potential of the reducing substance in the functional particles is It is more conducive to reducing the electromotive force of lithium-ion batteries at high temperatures and further improving the pass rate of hot box tests for lithium-ion batteries.

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 a glass transition temperature of 40°C to 110°C, and the synergistic cooperation of the two is more conducive to both reducing the electromotive force of the electrochemical device and improving the battery hot box pass rate, thereby improving battery thermal runaway.

Compared with Example 1-1, Example 1-6 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, Example 1-7 and Example 1-8 show that the melting point/glass transition temperature of the second material is too high (higher than 135°C), which is not conducive to improving the battery thermal runaway. At the same time, compared with Example 1-1, Example 1-9 shows that the melting point/glass transition temperature of the second material is too low (lower than 115°C), which is also not conducive to improving the battery thermal runaway.

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 4.2V) or too low (lower than 3.3V), which is not conducive to improving the thermal runaway of the battery.

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 dissolution concentration in the electrolyte are both appropriate, which is more conducive to improving the thermal safety performance of the battery.

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

Table 2

It can be seen from Table 2 that the appropriate proportion of low melting point material (first material) in the core will increase the pass rate of the hot box test. The mechanical properties of the coating will also be reduced, the core will be easily collapsed and flattened under high temperature and high pressure, the proportion of the first material will increase, and the internal resistance will increase. In Example 2-12, when the proportion of the first material is too small, the internal resistance will also increase due to the high content of the external high melting point substance. Among them, Example 2-6 has the best comprehensive effect.

Table 3

Note: Air permeability increment = (air permeability after baking at 130℃_20min) – (air permeability before baking)

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 closed-cell effect of the coating is better, and the pass rate will be better in the hot box test. As can be seen from Table 3, the D50 value and coating thickness of the functional particles are both in a suitable range, which is conducive to improving the electrochemical properties and closed-cell effect of the coating, thereby improving the pass rate of the hot box test. The best comprehensive performance is preferably obtained from Example 3-2.

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

Claims (15)

A separator used in an electrochemical device, characterized in that the separator comprises 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. The isolation membrane according to claim 1, characterized in that the functional particles have a core-shell structure, the core-shell structure comprises 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. The isolation film according to claim 2, characterized in that at least one of the following conditions is satisfied: (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. The isolation membrane according to claim 1, characterized in that the reducing substance is selected from at least one of the compounds of formula I, formula II, formula III or compounds containing Fe ³⁺ /Fe ²⁺ electrode pairs;

Wherein, _R1 to _R7 are each independently selected from any one of hydrogen and _C1 to _C6 alkyl. The isolation film according to claim 4, characterized in that R ₁ and R ₂ are each independently selected from any one of C ₃ -C ₄ alkyl groups, and R ₃ to R ₇ are each independently selected from any one of C ₁ to C ₂ alkyl groups; The compound containing the Fe ³⁺ /Fe ²⁺ electrode pair includes ferrocene. The isolation film according to claim 2 is characterized in that it satisfies: 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%. The isolation membrane according to claim 1, characterized in that the first coating is provided on a side of the base membrane facing the cathode. The isolation membrane according to claim 1 is characterized in that the reducing substance is dissolved in the electrolyte at a concentration of 0.5 mol/L to 1.5 mol/L. The isolation film according to claim 1, characterized in that at least one of the following conditions is satisfied: (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. An electrochemical device, characterized in that it contains the separator according to any one of claims 1 to 9. The electrochemical device according to claim 10, characterized in that when the electrochemical device is fully charged, 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. The electrochemical device according to claim 11, characterized in that when the electrochemical device is fully charged, 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. The electrochemical device according to claim 10 is characterized in that the initial electromotive force of the electrochemical device is 4.53V, and the electromotive force of the electrochemical device is 4.0V to 4.30V after the hot box test at 110°C to 130°C for 15 to 20 minutes. The electrochemical device according to claim 13 is characterized in that the initial electromotive force of the electrochemical device is 4.53V, and the electromotive force of the electrochemical device is 4.0V to 4.21V after the hot box test of the electrochemical device at 110°C to 130°C for 15 to 20 minutes. An electronic device, characterized in that the electronic device comprises the electrochemical device according to any one of claims 10 to 14.