Separator, electrochemical apparatus, and electronic device

Abstract

A separator (101), an electrochemical apparatus, and an electronic device. The separator (101) comprises a base film (11) and a functional coating (12) disposed on the base film (11), wherein the functional coating (12) comprises a first coating (121), the first coating (121) is arranged on one side surface of the base film (11), the first coating (121) contains functional particles (13), and the functional particles (13) are used for melting during a thermal safety test, so as to block pores of the base film. The separator (101) is configured in an electrochemical apparatus, so as to improve the thermal safety performance of the electrochemical apparatus. In a formation stage, the separator (101) does not melt to block pores, and in a high-temperature stage, the separator (101) can quickly melt to block the pores of a base film, so as to hinder a short-circuit current between a cathode and an anode; and the separator (101) is configured in an electrochemical apparatus, such that the thermal safety performance of the electrochemical apparatus can be improved.

Description

Separator membranes, electrochemical devices, and electronic devices

[0001] This application claims priority to Chinese patent application No. 2023111837038, filed on September 14, 2023, with invention name “Isolation membrane, electrochemical device and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] 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

[0003] 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.

[0004] 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 further improve the closed-cell performance of the basement membrane, so as to improve the pass rate of the hot box test and the needle penetration test of lithium-ion batteries.

[0005] Summary of the Invention

[0006] In view of this, the present application provides an isolation membrane, an electrochemical device and an electronic device, wherein the isolation membrane does not melt and block the pores in the high-temperature formation stage (80°C to 90°C) of the lithium-ion battery, but can quickly melt and block the base membrane pores in the high-temperature section (110°C to 130°C) of its thermal safety test to hinder the short-circuit current between the anode and cathode. The isolation membrane is arranged in the electrochemical device to improve the thermal safety performance of the electrochemical device.

[0007] In the first aspect, the present application provides an isolation membrane, which includes a base membrane and a functional coating arranged on the base membrane, wherein the functional coating includes a first coating, which is arranged on one side surface of the base membrane, and the first coating contains functional particles, which are used to melt and block the pores of the base membrane in a temperature range of 110°C to 130°C. The isolation membrane is configured in an electrochemical device to improve the thermal safety performance of the electrochemical device.

[0008] The functional particles were immersed in a specific solution at a temperature of 98°C to 102°C for 1 hour, and the mass increase was 20% to 30%. The specific solution included a solvent and LiPF6. The solvent included ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate. The mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate was (0.8-1.2):(0.8-1.2):(0.8-1.2). The mass proportion of LiPF6 in the specific solution was 12wt% to 13wt%. At this time, the functional particles had better pore plugging performance at high temperature, which was more conducive to their melting and plugging the base film pores in the high temperature section of the hot box test.

[0009] In some embodiments, the base film is a low-cell-closure-temperature base film, preferably having a closed-cell temperature of 134°C to 140°C. The closed-cell temperature of commercial base films generally does not reach 130°C. Therefore, the present application further provides a functional coating on one surface of the low-cell-closure-temperature base film to enable the low-cell-closure-temperature base film to achieve closed-cell operation in an environment below 130°C, thereby improving battery thermal runaway.

[0010] In some embodiments, the functional particles have a core-shell structure, which includes a core and an outer shell, the core containing a first component, the glass transition temperature / melting point of the first component is 30°C to 110°C, and the endothermic power of the first component is 1mW / mg to 12mW / mg, and the outer shell contains a second component, the glass transition temperature / melting point of the second component is 110°C to 130°C.

[0011] On the one hand, the functional particles described in this application can remain stable in the high-temperature formation stage (80°C to 90°C) and do not affect the normal charging and discharging of the battery cell. In the high-temperature section of the thermal safety test (110°C to 130°C), the shell melts and breaks, and the low-melting-point component (first component) in the core can quickly melt and flow to block the base membrane pores, and some of the melted material will also adhere to the cathode surface, hindering the electrolyte and the cathode from continuing to react with each other, thereby improving thermal safety. On the other hand, the isolation membrane described in this application has significant improvements in the needle puncture test. In the needle puncture test, the burrs of the copper and aluminum foil generated by the puncture of the steel needle will cause a short circuit. Among them, the short-circuit mode with the largest heat generation and the most dangerous is the contact between the aluminum foil and the anode active material. The aluminum burr short-circuit will melt the closed-pore coating (first coating) of the diaphragm when heated. After the functional particles melt, they can isolate the short-circuit point, thereby improving the needle puncture test.

[0012] In some embodiments, the first component 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; and the second component is selected from at least one of high molecular weight polyvinyl chloride, polyethylene, polyethylene naphthalate, or a mixture of polyethylene and polypropylene. The above are merely illustrative examples, and this application does not limit the selection of other substances, as long as their glass transition temperature or melting point is within the above range. In particular, the melting point / glass transition temperature of the polymer can be adjusted by regulating its molecular weight to achieve a melting point / glass transition temperature within a suitable range. Specific control methods can be found in conventional methods of the prior art and will not be elaborated upon.

[0013] In some embodiments, the functional coating further comprises a second coating, which is a solid filler coating. In this case, the porosity of the base film is 20% to 55%, and the porosity of the separator is 25% to 60%. After the cell containing the separator with the first coating and the second coating is subjected to high-temperature formation, the separator is disassembled and its porosity is 25% to 50%. It can be seen that the first coating has little effect on the porosity of the separator after high-temperature formation. However, after the separator is baked at 115°C to 125°C for 1h to 2h, its porosity is only 5% to 30%. It can be seen that after high-temperature baking, the melting and closed pores of the first coating have a great influence on the porosity. Preferably, the porosity of the base film is 30% to 55%, the porosity of the separator is 35% to 55%, and the porosity of the separator after baking at 115°C to 125°C for 1h to 2h is 5% to 22%. More preferably, the porosity of the base film is 30% to 40%, and the porosity of the isolation film after being baked at 115° C. to 125° C. for 1 hour to 2 hours is 5 to 10%.

[0014] In some embodiments, using a Gurley air permeability meter, the air permeability of a fresh separator increases (relative to a separator without a first coating and containing only a solid filler coating) by 20s / 100cc to 120s / 100cc. The air permeability of a separator removed from a fresh battery cell increases to (80-300)s / 100cc. After baking at 115°C to 125°C for 20-30 minutes, the air permeability of the separator increases to (800-10000)s / 100cc. It can be seen that the separator described in the present application does not increase much in air permeability at room temperature, and does not increase much in air permeability when the separator is removed from a fresh battery cell. However, after high-temperature baking, the air permeability of the separator increases significantly. In the present application, the fresh separator refers to a separator that has been coated on both sides, and the fresh battery cell refers to a battery cell that has been encapsulated by winding the positive electrode sheet, the negative electrode sheet, and the separator in order, placing them in an outer packaging foil, leaving an injection port, and pouring electrolyte from the injection port.

[0015] In some embodiments, the functional particles have a melting range of 5°C to 25°C, and a D50 value of 0.4 μm to 2 μm. The D50 value of the functional particles is denoted as D1, and the D50 value of the core is denoted as D2, satisfying the following relationship: 0.5 ≤ D2 / D1 ≤ 1. Preferably, the following relationship: 0.5 ≤ D2 / D1 ≤ 0.7 is satisfied. Preferably, the functional particles have a melting range of 10°C to 15°C.

[0016] In some embodiments, the isolation membrane is configured in an electrochemical device. 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 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 150J / g to 200J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 150J / g to 200J / g.

[0017] In a second aspect, the present application provides an electrochemical device comprising an isolating membrane and an electrolyte, wherein the isolating membrane is the isolating membrane described above, and the electrolyte comprises an organic solvent and an additive, wherein the organic solvent comprises a linear carbonate and a cyclic carbonate, and the additive comprises a nitrile compound, wherein the nitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile, or acrylonitrile. By adapting the above-mentioned isolating membrane to a suitable electrolyte, the present application can better enhance the closed-cell performance of the isolating membrane and further improve thermal safety. The full charge voltage of the electrochemical device is 4.45V to 4.5V.

[0018] In some embodiments, the mass ratio of the organic solvent to the additive is (3-5):(0.1-0.2).

[0019] In some embodiments, based on the mass of the organic solvent, the mass percentage of the linear carbonate is 15wt% to 40wt%, and the mass percentage of the cyclic carbonate is 60wt% to 85wt%. The proportion of linear carbonate should not be less than 15%. If it is too low, it will lead to high viscosity of the solvent system and low overall conductivity, affecting electrical performance. The upper limit should not exceed 40%. If the linear carbonate is too high, it is easy to boil and prone to flash explosion during safety testing. When the mass percentages of the linear carbonate and the cyclic carbonate are both within the above range, it is conducive to coordinated adaptation with the isolation membrane and can better coordinate the molten material to block the base membrane pores.

[0020] In some embodiments, the nitrile compound has a weight percentage of 0.15 wt % to 0.5 wt % based on the weight of the additive. A suitable amount of the nitrile compound facilitates film formation at the cathode, enhances cathode stability at high temperatures, avoids heat generation from side reactions between the cathode and the electrolyte, and further improves thermal safety.

[0021] In some embodiments, the functional particles are immersed in the electrolyte at 75°C to 85°C for 1 hour, and their mass increases by 5% to 15%. After the low-melting-point material in the core flows out, its swelling increases with increasing temperature in the electrolyte environment. This property helps the low-melting-point material further swell and plug the pores.

[0022] In some embodiments, the ohmic internal resistance of the electrochemical device is denoted as R. The voltage range of the electrochemical device in the discharge state is 3.0V to 3.5V, and the ohmic internal resistance after baking at 115°C to 125°C for 20min to 30min is (1.2 to 5.0)R. This characteristic is used to indicate the increase in the impedance of the isolation membrane after the functional particles block the pores.

[0023] In a third aspect, the present application provides an electronic device comprising the above-mentioned electrochemical device.

[0024] The present application provides an isolation membrane, an electrochemical device, and an electronic device, wherein the isolation membrane includes functional particles, the functional particles having a core-shell structure, the glass transition temperature / melting point of the shell material being significantly higher than the glass transition temperature / melting point of the core material, the functional particles can remain stable during the formation stage of the battery, and will not affect 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 base membrane pores to hinder the short-circuit current between the cathode and the cathode, and the partially melted material will also adhere to the cathode surface, hindering the electrolyte and the cathode from continuing to react with each other, thereby improving thermal safety. Moreover, the isolation membrane described in the present application has a significant improvement in the needle puncture test. In the needle puncture test, the burrs of the copper and aluminum foil generated by the puncture of the steel needle will cause a short circuit. Among them, the short-circuit mode with the largest heat generation and the most dangerous is the contact between the aluminum foil and the anode active material. The aluminum burr short-circuit will melt the diaphragm closed-pore coating (first coating) when heated. After the functional particles are melted, they can isolate the short-circuit point, thereby improving the needle puncture test. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] FIG1 is a schematic structural diagram of the isolation membrane described in this application;

[0027] FIG2 is a DSC test spectrum of the isolation film described in Example 1-1 of the present application;

[0028] FIG3 shows the coating morphology of the isolation film described in Example 1-1 of the present application after coating;

[0029] FIG4 is a coating morphology of the isolation film after high-temperature formation described in Example 1-1 of the present application;

[0030] FIG5 is a coating morphology of the isolation film after thermal safety testing according to Example 1-1 of the present application;

[0031] FIG6 shows the coating morphology of the isolation membrane described in Examples 1-9 of the present application after melting and plugging at high temperature;

[0032] FIG7 is a diagram showing the puncture effect of the separator described in Examples 1-9 of the present application passing through a battery cell in a puncture test;

[0033] FIG8 is a diagram showing the puncture effect of the isolation membrane described in Comparative Example 1-1 of the present application passing through a battery cell in a puncture test. DETAILED DESCRIPTION

[0034] 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.

[0035] The improvement of thermal safety brought by the closed-pore design of the diaphragm is obvious. Under the condition that the low closed-pore temperature of the base membrane is limited, this application proposes to design a coating with closed-pore function in the coating to further improve the overall closed-pore performance of the separator. The closed-pore design can close the channel of the separator, prevent ion conduction between the positive and negative electrodes, and prevent material exchange between the positive electrodes. The reducing substances on the negative electrode side will not reach the positive electrode, and the oxidizing substances on the positive electrode side will not reach the negative electrode, thereby reducing the side reaction heat inside the battery. At the same time, the coating also helps to improve the pass rate of the needle puncture test of the battery cell.

[0036] Currently, the use of closed-cell coatings has the following problems: first, closed-cell coatings may melt and plug the pores after hot pressing, resulting in high impedance; second, the closed-cell response speed is slow at high temperatures (no time for rapid pore closure), leading to rapid thermal runaway of the battery cell. Common methods to solve these common problems include: increasing the Tg (melting point) of the material to prevent the material from melting during processing (especially high-temperature forming at 80°C to 90°C). This can improve the melting and plugging of pores after forming to a certain extent. However, as the melting point temperature increases, it is difficult to achieve rapid pore closure in the high temperature range (110°C to 130°C) where rapid pore closure is required, resulting in poor improvement in thermal safety.

[0037] In order to solve the above technical problems, the present application provides an isolation membrane, which does not melt and block the pores in the high-temperature formation stage (80℃~90℃), but can quickly melt and block the pores of the base membrane in the high-temperature section (110℃~130℃) to hinder the short-circuit current between the anode and cathode. The isolation membrane is arranged in an electrochemical device to improve the thermal safety performance of the electrochemical device.

[0038] electrochemical devices

[0039] 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.

[0040] Isolation film

[0041] The isolation membrane 101 includes a base membrane 11 and a functional coating 12 arranged on the base membrane 11. The functional coating 12 includes a first coating 121. The first coating 121 is arranged on one side surface of the base membrane 11. The first coating 121 contains functional particles 13. The functional particles 13 are used to melt and block the base membrane pores during the thermal safety test. The isolation membrane 101 is configured in an electrochemical device to improve the thermal safety performance of the electrochemical device.

[0042] In some embodiments, the functional particle 13 has a core-shell structure, comprising a core 131 and an outer shell 132. The core 131 contains a first component having a glass transition temperature / melting point of 30° C. to 110° C. and an endothermic power of 1 mW / mg to 12 mW / mg. The outer shell 132 contains a second component having a glass transition temperature / melting point of 110° C. to 130° C. Preferably, the endothermic power of the first component is 8 mW / mg to 12 mW / mg.

[0043] Illustratively, the glass transition temperature / melting point of the first component is 30°C, 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.

[0044] Illustratively, the endothermic power of the first component is 1 mW / mg, 3 mW / mg, 5 mW / mg, 6 mW / mg, 8 mW / mg, 10 mW / mg, 12 mW / mg, or a range consisting of any two of the above values.

[0045] Illustratively, the glass transition temperature / melting point of the second component is 110° C., 115° C., 120° C., 125° C., 130° C., or a range consisting of any two of the above values.

[0046] In some embodiments, the functional coating 12 further includes a second coating 122, which is a solid filler coating. The porosity of the base film 11 is 20% to 55%, the porosity of the isolation film 101 is 25% to 60%, and the porosity of the isolation film 101 after baking at 115°C to 125°C for 1 hour to 2 hours is 5% to 30%. Preferably, the porosity of the base film is 30% to 55%, the porosity of the isolation film is 35% to 55%, and the porosity of the isolation film after baking at 115°C to 125°C for 1 hour to 2 hours is 5% to 22%.

[0047] Exemplarily, the porosity of the base film 11 is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or a range consisting of any two of the above values.

[0048] Illustratively, the porosity of the isolation film 101 is 25%, 35%, 45%, 50%, 55%, 60%, or a range consisting of any two of the above values.

[0049] Exemplarily, the porosity of the isolation film 101 after baking at 115°C to 125°C for 1h to 2h is 5%, 8%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30% or a range consisting of any two of the above values.

[0050] In some embodiments, the melting range of the functional particles is 5° C. to 25° C., and the D50 value of the functional particles is 0.4 μm to 2 μm.

[0051] Illustratively, the melting range of the functional particles is 5°C, 8°C, 10°C, 13°C, 15°C, 18°C, 20°C, 23°C, 25°C, or a range consisting of any two of the above values.

[0052] Illustratively, the D50 value of the functional particles is 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or a range consisting of any two of the above values.

[0053] In some embodiments, the D50 value of the functional particles is recorded as D1, and the D50 value of the core is recorded as D2, satisfying: 0.5≤D2 / D1≤1.

[0054] Illustratively, the D2 / D1 value is 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of the above values.

[0055] In some embodiments, the isolation membrane is configured in an electrochemical device. 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 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 150J / g to 200J / g, and the peak area of ​​the main melting peak of the characteristic peak B1 is 150J / g to 200J / g.

[0056] Illustratively, the peak area of ​​the main melting peak of the characteristic peak A1 is 150 J / g, 160 J / g, 170 J / g, 180 J / g, 190 J / g, 200 J / g or a range consisting of any two of the above values.

[0057] Illustratively, the peak area of ​​the main melting peak of the characteristic peak B1 is 150 J / g, 160 J / g, 170 J / g, 180 J / g, 190 J / g, 200 J / g or a range consisting of any two of the above values.

[0058] Exemplary preparation method of the isolation film:

[0059] (1) Preparation of functional particles;

[0060] 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°C to 65°C, rotate at 550r / min to 650r / min, stir for 10min to 20min, add an emulsifier and then pass hydrogen to raise the pressure gauge to 1Mpa to 1.5Mpa, adjust the speed to 750r / min to 850r / min and react for 3h to 4h. After the reaction is completed, release the pressure and keep warm for 1h to 2h, then add the shell monomer and an appropriate amount of cross-linking agent, stir, keep warm for 2h to 3h, cool to room temperature, and freeze to break the emulsion to obtain the product.

[0061] (2) Preparation of the first coating;

[0062] 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.

[0063] (3) Preparation of the second coating;

[0064] Exemplarily: Step c. Mix 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 disperse them in a blender to obtain a slurry B to be coated; Step d. Evenly apply the slurry B to be coated in step c on the other side surface of the base film, and complete the preparation of the second coating after drying to obtain an isolation film.

[0065] electrolyte

[0066] The electrolyte includes an organic solvent and an additive. The organic solvent includes a linear carbonate and a cyclic carbonate. The additive includes a nitrile compound. The nitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile or acrylonitrile.

[0067] In some embodiments, the mass ratio of the organic solvent to the additive is (3-5):(0.1-0.2).

[0068] In some embodiments, based on the mass of the organic solvent, the mass percentage of the linear carbonate is 15 wt % to 40 wt %, and the mass percentage of the cyclic carbonate is 60 wt % to 85 wt %.

[0069] Illustratively, the mass percentage of the linear carbonate is 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or a range consisting of any two of the above values.

[0070] Illustratively, the mass percentage of the cyclic carbonate is 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt% or a range consisting of any two of the above values.

[0071] In some embodiments, based on the mass of the additive, the mass percentage of the nitrile compound is 0.15 wt % to 0.5 wt %.

[0072] Illustratively, based on the mass of the additive, the mass percentage of the nitrile compound is 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt% or a range consisting of any two of the above values.

[0073] In some embodiments, the functional particles are immersed in the electrolyte at 75° C. to 85° C. for 1 hour, and the mass increase thereof is 5% to 15%.

[0074] Illustratively, the mass increase of the functional particles after being immersed in the electrolyte at 75° C. to 85° C. for 1 hour is 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of the above values.

[0075] The electrolyte can be prepared according to conventional methods in the art.

[0076] other

[0077] The cathode electrode sheet includes a cathode current collector and a cathode active material layer provided on at least one surface of the cathode current collector. The present application does not particularly limit the thickness of the cathode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the cathode active material layer is 30 μm to 120 μm. The cathode active material in the cathode 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. The cathode 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 cathode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the cathode current collector is 5 μm to 12 μm.

[0078] In some embodiments, the gram capacity of the cathode active material is 175 mAh / g to 185 mAh / g, and the gram capacity of the cathode active material after baking at 115° C. to 125° C. for 1 h to 2 h is 40 mAh / g to 120 mAh / g.

[0079] Illustratively, the gram capacity of the cathode active material is 175 mAh / g, 178 mAh / g, 180 mAh / g, 183 mAh / g, 185 mAh / g, or a range consisting of any two of the above values.

[0080] Illustratively, the gram capacity of the cathode active material after baking at 115° C. to 125° C. for 1 h to 2 h is 40 mAh / g, 60 mAh / g, 80 mAh / g, 100 mAh / g, 120 mAh / g, or a range consisting of any two of the above values.

[0081] The cathode plate can be prepared according to conventional methods in the art.

[0082] The anode electrode sheet includes an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector. The present application does not particularly limit the thickness of the anode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the anode active material layer is 30μm to 120μm. The anode active material layer contains an anode active material. In some embodiments, the anode 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 material, or a silicon-carbon composite material. The present application does not particularly limit the thickness of the anode 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, nickel foam, copper foam, or a composite current collector (for example, a composite current collector with a metal layer disposed on the surface of a polymer layer). The present application does not particularly limit the thickness of the anode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the anode current collector is 5μm to 12μm. The anode active layer may also include a binder and a thickener. This application does not specifically limit the types of binders and thickeners, 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 anode active layer may also include a conductive agent. This application does not specifically limit the types of conductive agents, as long as they 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 ratios of the negative electrode active material, conductive agent, binder, and thickener in the anode active layer. Those skilled in the art may select these ratios based on actual needs, as long as they can achieve the objectives of this application. Optionally, the anode plate may also include a conductive layer positioned between the anode current collector and the anode 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.

[0083] The anode plate can be prepared according to conventional methods in the art.

[0084] 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.

[0085] electronic devices

[0086] 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.

[0087] Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples.

[0088] Example 1-1

[0089] (1) Preparation of lithium-ion batteries

[0090] (1) Preparation of lithium-ion battery separators

[0091] A base film with a closed-cell temperature of 135°C was selected. Coating slurry A was applied to one side of the base film and dried to form a first coating layer. Coating slurry B was applied to the other side of the base film and dried to form a second coating layer. This resulted in a separator membrane. A schematic structural diagram of the separator membrane is shown in Figure 1, and a DSC spectrum of the separator membrane is shown in Figure 2. Figure 2 shows that the main melting peak of the core component is at 114°C, while the main melting peak of the shell component is at 127°C.

[0092] The coating slurry A and the coating slurry B were prepared according to the following method:

[0093] Preparation of functional particles:

[0094] The raw material linear liquid polyethylene wax (melting point 105°C) was prepared into a 10% solution and added to 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 three times to expel the air in the reactor. Triisobutylaluminum and nickel cyclohexaneate were prepared as a catalyst in a molar ratio of 6:1. The prepared catalyst was placed in a constant temperature water bath and kept constant for 30 minutes. It was then slowly pumped into the reactor and stirred at 60°C and 600r / min for 15 minutes. Then, 200g of sodium carboxymethyl cellulose emulsifier was added. Then, hydrogen was introduced to raise the pressure gauge to 1MPa and the speed was 800r / min for 3 hours. After the reaction was completed, the pressure was released and the reaction was kept warm for 1 hour. The shell monomer vinyl chloride was added in an amount of 11% of the core mass. At the same time, an appropriate amount of crosslinking agent acrylic acid ester was added in an amount of 0.5% of the core mass. The mixture was slowly stirred at 300r / min and kept warm for 2 hours. Finally, it was cooled to room temperature and frozen to break the emulsion to obtain functional particles with a core-shell structure. The prepared functional particles have a mass increase of 23% when immersed in a specific solution at 100°C for 1 hour. The specific solution includes a solvent and LiPF6. The solvent includes ethylene carbonate, ethyl methyl carbonate and diethyl carbonate. The mass ratio of the ethylene carbonate, the ethyl methyl carbonate and the diethyl carbonate is 1:1:1. The mass proportion of LiPF6 in the specific solution is 12.5wt%.

[0095] Preparation of coating slurry A:

[0096] Deionized water, the functional particles, PVDF 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.

[0097] Preparation of coating slurry B:

[0098] 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.

[0099] 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 coating slurry A in Comparative Example 1-1, the functional particles are replaced with boehmite, and the rest are the same as Example 1-1.

[0100] The difference between Comparative Examples 1-2 and 1-3 and Example 1 is that the parameters of the first component of the core and the second component of the shell in the functional particles are adjusted in Comparative Examples 1-2 and 1-3, respectively. See Table 2 for details.

[0101] The difference between Examples 1-2 to 1-15 and Example 1-1 is that Examples 1-2 to 1-15 respectively adjust the parameters of the first component of the core and the second component of the shell in the functional particles. In particular, for polymers with similar melting points, for example, the second component in Example 1-9 has a melting point of 110°C polyethylene and the second component in Example 1-10 has a melting point of 115°C polyethylene. Although their molecular weight ranges are the same, the difference in melting point can be achieved by fine-tuning the proportion of macromolecules. Specific parameters are shown in Table 2.

[0102] Examples 2-1 to 2-14 further adjusted the D50 value of the functional particles, the melting range of the functional particles, and the porosity of the base film, as shown in Table 3.

[0103] (2) Preparation of cathode electrode

[0104] The cathode active material - lithium cobalt oxide 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 cathode slurry; the cathode 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.

[0105] (3) Preparation of anode electrode

[0106] The anode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium methyl cellulose (CMC) were mixed uniformly 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 an anode electrode sheet coated with an anode active layer on both sides. After cold pressing and cutting, the negative electrode sheet was obtained.

[0107] (4) Preparation of electrolyte

[0108] 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 (additive) 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.

[0109] Examples 3-1 to 3-8 further adjusted the components of the organic solvent in the electrolyte and the content of each component, as shown in Table 4.

[0110] (5) Preparation of lithium-ion batteries

[0111] The cathode electrode, isolation membrane and anode electrode are stacked in sequence, and the isolation membrane separates the cathode electrode and the anode electrode. 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.

[0112] Examples 4-1 to 4-5 further adjusted the empty voltage (the voltage of the lithium-ion battery in the empty state) and the gram capacity of the cathode active material of the prepared lithium-ion battery, as shown in Table 5 for details.

[0113] Figure 3 shows the coating morphology of the isolation membrane described in Example 1-1 of the present application after coating, Figure 4 shows the coating morphology of the isolation membrane described in Example 1-1 of the present application after high-temperature formation, and Figure 5 shows the coating morphology of the isolation membrane described in Example 1-1 of the present application after thermal safety testing. It can be seen from Figures 3 to 5 that the isolation membrane described in the present application can quickly melt and block the pores of the base membrane in the high-temperature section.

[0114] Figure 6 shows the coating morphology of the isolation membrane described in Examples 1-9 of the present application after melting and plugging at high temperature. It can be seen from Figure 6 that the melted low-melting-point material flows and adheres to the burrs to isolate the short-circuit points, which can reduce the short-circuit area and improve the pass rate of the puncture test.

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

[0116] (1) Thermal safety test

[0117] (a) Hot box test

[0118] 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;

[0119] 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;

[0120] Step 3: Heat the box to 130°C at a rate of 5°C and maintain for 60 minutes.

[0121] Judging criteria: The battery passes if it does not catch fire or explode.

[0122] (b) Needle prick test

[0123] The lithium-ion batteries prepared in Comparative Example 1-1 and Example 1-9 were subjected to needle puncture tests according to the conditions in Table 1, using a 4 mm steel needle at a puncture speed of 30 mm / s.

[0124] Table 1

[0125] Figure 7 is a diagram showing the puncture effect of the isolation membrane described in Examples 1-9 of the present application passing through the battery cell in the puncture test, and Figure 8 is a diagram showing the puncture effect of the isolation membrane described in Comparative Example 1-1 of the present application passing through the battery cell in the puncture test. Comparing Figure 7 and Figure 8, it can be seen that the burning area and burning degree of the short-circuit area of ​​the electrode using the closed-pore coating in Examples 1-9 are both milder than those in the control group.

[0126] (2) Cathode heat generation test

[0127] Fully charge the battery cell (0.2C charge to 4.5V, then 4.5V constant voltage charge to 0.05C), then disassemble the battery cell, take out the cathode electrode, and place it in an adiabatic calorimeter for testing.

[0128] (3) Battery cell internal resistance test

[0129] After formation, the cell voltage is within the range of 3.8V to 4.2V. Place the cell at a high temperature of 45℃±5℃ for 24h±3h, then place it at room temperature of 25℃ for 24h±3h. Use an internal resistance meter to connect the positive and negative tabs of the cell to test the internal resistance of the cell.

[0130] (4) Swelling test

[0131] The functional particles were immersed in a specific solution at 100°C for 1 hour, and their mass increase was calculated. The specific solution included a solvent and LiPF6, wherein the solvent included ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate was 1:1:1. The mass proportion of LiPF6 in the specific solution was 12.5 wt%.

[0132] Table 2

[0133] Comparing Comparative Example 1-1 with Example 1-1, it can be seen that the isolation membrane containing the functional particles can significantly improve the hot box test pass rate and the needle penetration test pass rate of the lithium-ion battery, and the internal resistance of the battery cell after formation is appropriate, while the internal resistance of the battery cell of Comparative Example 1-1 after formation is too high, which is not conducive to the normal use of the battery cell.

[0134] Comparing Comparative Examples 1-2 and 1-3 with Example 1-1, it can be seen that the swelling of the functional particles needs to be within an appropriate range. When within the appropriate range, the greater the swelling, the more obvious the effect of improving the thermal safety performance. However, if the swelling is too large, for example, the mass increase exceeds 30%, it will seriously block the pores, resulting in excessive internal resistance of the battery cell, affecting the electrical performance of the battery cell. The swelling of the functional particles cannot be too small, for example, the mass increase is less than 20%. At this time, the thermal safety performance of the battery cell cannot be improved.

[0135] Comparing Comparative Examples 1-2 to 1-3 and Examples 1-1 to 1-4, it can be seen that the Tg / melting point of the first component in the core is appropriate, which is more conducive to improving the pass rate of the thermal safety test of the lithium-ion battery, and the internal resistance of the battery cell after formation increases more significantly within a suitable range, thereby improving the thermal safety performance.

[0136] Comparing Examples 1-5 to 1-9 and 1-14 with 1-15, it can be seen that the Tg / melting point of the second component in the shell is within a suitable range, which is more conducive to improving the pass rate of the thermal safety test of the lithium-ion battery.

[0137] Comparing Examples 1-10 to 1-13, it can be seen that the heat absorption power of the first component in the core is appropriate, which is also beneficial to improving the pass rate of the thermal safety test of the lithium-ion battery and increasing the internal resistance of the battery cell after formation within an appropriate range.

[0138] Table 3

[0139] It can be seen from Table 3 that further adjusting the D50 value of the functional particles, the melting range thereof, the porosity of the base film and other parameters are all within an appropriate range, which is more conducive to improving the pass rate of the thermal safety test of lithium-ion batteries.

[0140] Table 4

[0141] As can be seen from Table 4, pairing the functional coating with a suitable electrolyte not only enhances the functional coating's melt-blocking effect, but also allows the molten, flowing coating to cover the surface of the cathode active material. Furthermore, the nitrile additive in the electrolyte forms a film at the cathode, enhancing cathode stability at high temperatures, hindering side reactions between the cathode and the electrolyte, and reducing heat generation. In Example 3-3, the excessively high proportion of cyclic carbonate results in a high electrolyte viscosity, which is detrimental to lithium ion transport and leads to a high internal resistance in the battery cell.

[0142] Table 5

[0143] As can be seen from Table 5, the functional coating melts and plugs the pores, covering the surface of the cathode active material. As a result, after baking at 115°C to 125°C for 1h to 2h, the cathode electrode piece disassembled and used to assemble into button batteries has low capacity.

[0144] 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 separation film, characterized in that: The isolation film includes a base film and a functional coating disposed on the base film; The functional coating comprises a first coating, the first coating is disposed on one side of the base film, the first coating contains functional particles, and the functional particles are used to melt and block the base film pores in a temperature range of 110° C. to 130° C.; The mass increase of the functional particles when immersed in a specific solution at a temperature of 98°C to 102°C for 1 hour is 20% to 30%; The specific solution includes a solvent and LiPF6, the solvent includes ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, the mass ratio of the ethylene carbonate, the ethyl methyl carbonate and the diethyl carbonate is (0.8-1.2):(0.8-1.2):(0.8-1.2), wherein the mass proportion of LiPF6 in the specific solution is 12wt%-13wt%.

2. The isolation film according to claim 1, characterized in that: The functional particles have a core-shell structure, which includes a core and an outer shell, and meet at least one of the following conditions: (1) The inner core contains a first component, and the glass transition temperature / melting point of the first component is 30° C. to 110° C.; (2) The heat absorption power of the first component is 1 mW / mg to 12 mW / mg; (3) The shell contains a second component, and the glass transition temperature / melting point of the second component is 110°C to 130°C.

3. The isolation film according to claim 1, characterized in that: The functional coating further includes a second coating, which is a solid filler coating, and the isolation film satisfies at least one of the following conditions: (1) The porosity of the base film is 20% to 55%; (2) The porosity of the isolation film after being baked at 115° C. to 125° C. for 1 h to 2 h is 5% to 30%.

4. The isolation membrane according to claim 3, characterized in that: The isolation film satisfies at least one of the following conditions: (1) The porosity of the base film is 30% to 55%; (2) The porosity of the isolation film after being baked at 115° C. to 125° C. for 1 h to 2 h is 5% to 22%.

5. The isolation film according to claim 2, characterized in that: The isolation film satisfies at least one of the following conditions: (1) The melting range of the functional particles is 5°C to 25°C; (2) The D50 value of the functional particles is 0.4 μm to 2 μm; (3) The D50 value of the functional particles is recorded as D1, and the D50 value of the core is recorded as D2, satisfying: 0.5≤D2 / D1≤1.

6. The isolation film according to claim 1, characterized in that: The isolation membrane is arranged in an electrochemical device. In a fully charged state, in a 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 135°C.

7. The isolation film according to claim 6, characterized in that: 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.

8. An electrochemical device, characterized in that: The electrochemical device includes a separator and an electrolyte; The isolation film is the isolation film according to any one of claims 1 to 7; The electrolyte includes an organic solvent and an additive, the organic solvent includes a linear carbonate and a cyclic carbonate, and the additive includes a nitrile compound; The nitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile or acrylonitrile.

9. The electrochemical device according to claim 8, characterized in that At least one of the following conditions is met: (1) The mass ratio of the organic solvent to the additive is (3-5):(0.1-0.2); (2) Based on the mass of the organic solvent, the mass percentage of the linear carbonate is 15wt% to 40wt%, and the mass percentage of the cyclic carbonate is 60wt% to 85wt%; (3) Based on the mass of the additive, the mass percentage of the nitrile compound is 0.15wt% to 0.5wt%.

10. The electrochemical device according to claim 8, characterized in that The functional particles are immersed in the electrolyte at 75° C. to 85° C. for 1 hour, and the mass increment is 5% to 15%.

11. The electrochemical device according to claim 8, characterized in that The voltage range of the electrochemical device in the empty state is 3.0V to 3.5V; The ohmic internal resistance of the electrochemical device is recorded as R, and the ohmic internal resistance after baking at 115° C. to 125° C. for 20 min to 30 min is (1.2 to 5.0)R.

12. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to any one of claims 8 to 11.

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