A diaphragm and electrochemical device

Abstract

This invention discloses a diaphragm and an electrochemical device. The resistivity R of the diaphragm of this invention is 0.8-50.0 Ωcm. 2 And it satisfies the following condition: within a pressure range of 0-100 MPa, γ is 0-0.08 Ωcm. 2 / MPa; where γ is the rate of change of resistivity, Ωcm 2 / MPa; ΔR is the resistivity change, Ωcm 2 △P represents the pressure change value in MPa. The diaphragm of this invention has good pressure resistance, and the resistivity of the diaphragm changes little with increasing pressure, exhibiting good pressure resistance and effectively avoiding lithium plating and improving the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to a diaphragm and an electrochemical device. Background Technology

[0002] The separator, or diaphragm, is the membrane separating the positive and negative electrodes in a lithium-ion battery. It's a thin film that allows ion conduction while providing electronic insulation. Therefore, the performance of the separator significantly impacts the performance of the lithium-ion battery. Separators generally require good ionic conductivity, mechanical properties (elastic modulus and strength), and wettability. A separator with excellent overall performance can improve the battery's long-cycle stability and safety.

[0003] Conventional base films (such as PP and PE) have simple structures and compositions, limiting their overall performance and making it difficult to meet the practical needs of batteries. Currently, coating the base film with a coating is considered an effective way to improve performance. The composition and structure of the coating can be designed according to actual needs, thereby improving the overall performance of the separator. Although the overall performance of the separator is improved, the continuous volume expansion during long-term battery cycling still reduces the stability of the separator. The volume changes of the positive / negative electrodes inside the cell during charging and discharging lead to increased stress at the positive / separator and negative / separator interfaces, increasing the pressure on the separator and causing a rapid increase in separator resistivity, which easily induces lithium plating. On the one hand, the electrodes in the battery continuously expand in volume during long-term cycling, leading to increased internal stress in the cell and a gradual increase in pressure on the separator. Although the separator can cope with the expansion and contraction of the electrodes, it will still undergo performance changes (such as resistivity and tortuosity) after being subjected to pressure. The increase in resistivity directly hinders the insertion / extraction of lithium ions on the electrode surface, easily inducing lithium plating, and long-term vicious cycling causes battery failure. On the other hand, there are currently no other patent reports on the changes in parameters such as resistivity and resistivity growth rate caused by pressure on the diaphragm, so it is necessary to conduct a systematic study on it.

[0004] Therefore, the resistivity change caused by pressure on the diaphragm needs to be investigated in order to guide diaphragm development and cell design. Summary of the Invention

[0005] To overcome the problems in existing technologies where the performance of the separator changes under pressure (such as resistivity and tortuosity), further hindering the insertion / extraction of lithium ions on the electrode surface, easily inducing lithium plating, and causing battery failure due to long-term vicious cycling, this invention provides a separator and an electrochemical device. The separator of this invention has good pressure resistance, and its resistivity changes little with increasing pressure, exhibiting good pressure resistance and effectively avoiding lithium plating and improving battery cycle performance.

[0006] In a first aspect, the present invention provides a diaphragm having a resistivity of 0.8-50.0 Ωcm. 2 ;

[0007] Furthermore, the diaphragm satisfies the following condition: γ is 0-0.08 Ωcm within a pressure range of 0-100 MPa. 2 / MPa; where

[0008]

[0009] Where γ is the rate of change of resistivity, in Ωcm 2 / MPa; ΔR is the resistivity change, Ωcm 2 ; △P is the pressure change value, MPa.

[0010] In a second aspect, the present invention provides an electrochemical device comprising the diaphragm as described above.

[0011] The positive and progressive effects of this invention are as follows:

[0012] The separator of this invention has good pressure resistance and its resistivity changes little with increasing pressure, which can effectively avoid lithium plating and improve the cycle performance of the battery. Furthermore, this invention explores the parameter changes of the separator under different pressures and clarifies the range of resistivity change with pressure, which can guide the development and design of separators and the performance design of battery cells. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a device for testing the electrochemical resistivity of a membrane.

[0014] Figure 2 The resistivity of the diaphragms prepared in Examples 1-3 changes with pressure. Detailed Implementation

[0015] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0016] The key terms and technical abbreviations in this invention are explained as follows:

[0017] Diaphragm impedance: The resistance of the diaphragm, that is, its opposition to the current in the circuit.

[0018] Resistivity: The resistance of a diaphragm per unit area; surface resistance = impedance * area, unit is Ωcm 2 The diaphragm area is 2 cm². 2 .

[0019] Resistivity change rate: The percentage increase in resistivity caused by pressure on the diaphragm.

[0020] The particle size distribution dispersion is calculated using the following formula: Dispersion = (D90 - D10) / D50.

[0021] Air permeability: the ease with which gas passes through the diaphragm. In this invention, it refers to the time required for a certain volume of gas to pass through a diaphragm of a certain area under a certain pressure.

[0022] Porosity: The percentage of pore volume to total volume in a membrane.

[0023] Electrolyte conductivity: The ease with which ions can flow in an electrolyte.

[0024] In the diaphragm of the first aspect of the present invention:

[0025] This invention addresses the parameter changes of diaphragms under different pressures, clarifies the range of resistivity variation with pressure, and guides diaphragm development and design as well as cell performance design.

[0026] In this invention, R and γ are measured by stacking three layers of the diaphragm.

[0027] In this invention, within a pressure range of 0-100 MPa, when the resistivity is 0.8-3.0 Ωcm 2 When the resistivity is between 3-50 Ωcm, no lithium plating occurs during use; 2 While lithium plating does occur between these thresholds, it is weak and has little impact on the battery's electrochemical performance; however, above 50 Ωcm... 2 At this time, severe lithium plating occurs, which seriously affects electrochemical performance. In this invention, the resistivity is preferably 0.8-3.0 Ωcm within the pressure range of 0-100 MPa. 2 .

[0028] In this invention, within a pressure range of 0-100 MPa, the resistivity change rate γ is preferably 0-0.05 Ωcm. 2 / MPa, more preferably 0-0.04Ωcm 2 / MPa. The resistivity change rate γ is in the range of 0-0.04Ωcm. 2 Within the range of / Ma, this indicates good pressure resistance of the diaphragm; if the resistivity change rate γ is greater than 0.08Ωcm 2 / MPa indicates that the resistivity of the separator increases significantly due to pressure, which seriously affects the dynamic performance of the battery and will cause lithium plating.

[0029] In this invention, within a pressure range of 0-100 MPa, when ΔP is 25-80 MPa, ΔR is preferably 0-10 Ωcm. 2 .

[0030] In this invention, the diaphragm satisfies the following condition: within a pressure range of 100 MPa to 300 MPa, the resistivity change rate γ is 0.05-0.14 Ωcm. 2 / MPa; preferably 0.05-0.13Ωcm 2 / MPa, more preferably 0.05-0.1cm 2 / MPa.

[0031] In this invention, the diaphragm includes a substrate and a coating applied to at least one side of the substrate surface.

[0032] The substrate is a polyolefin porous substrate.

[0033] Preferably, the substrate is selected from polyethylene film (PE), polypropylene film (PP), or polypropylene-polyethylene composite film (PP / PE / PP), for example, polyethylene film.

[0034] Preferably, the thickness of the substrate is 6-12 μm, more preferably 9-12 μm.

[0035] Preferably, the air permeability of the substrate is 60s / 100mL-300s / 100mL, and more preferably 150s / 100mL-300s / 100mL.

[0036] Preferably, the porosity of the substrate is 30-50%, more preferably 35-50%, for example 38%.

[0037] Preferably, the pore diameter of the substrate is 0.02-0.08 μm, and more preferably 0.04-0.08 μm.

[0038] The coating comprises inorganic particles and a binder.

[0039] Preferably, the particle size distribution dispersion of the inorganic particles is 0.5-2; more preferably, the particle size distribution dispersion of the inorganic particles is 0.5-1, for example, 0.9.

[0040] Preferably, the particle size of the inorganic particles satisfies D10 > 0.4 μm, 0.6 μm < D50 < 0.8 μm, and D90 < 2.0 μm.

[0041] In one specific embodiment of the present invention, the particle size of the inorganic particles satisfies D10 of 0.5 μm, D50 of 0.7 μm, and D90 of 1.85 μm.

[0042] In one specific embodiment of the present invention, the particle size of the inorganic particles satisfies D10 of 0.5 μm, D50 of 0.7 μm, and D90 of 0.85 μm.

[0043] In one specific embodiment of the present invention, the particle size of the inorganic particles satisfies D10 of 0.6 μm, D50 of 0.7 μm, and D90 of 1.2 μm.

[0044] In one specific embodiment of the present invention, the particle size of the inorganic particles satisfies D10 of 0.5 μm, D50 of 0.7 μm, and D90 of 1.23 μm.

[0045] In one specific embodiment of the present invention, the particle size of the inorganic particles satisfies D10 of 0.5 μm, D50 of 0.7 μm, and D90 of 1.13 μm.

[0046] Preferably, the inorganic particles are selected from at least one of silicon oxide, aluminum oxide, boehmite, zirconium oxide, titanium dioxide, silicon nitride, aluminum nitride, zirconium nitride, titanium nitride, orthosilicic acid, aluminum hydroxide, zirconium hydroxide, and titanium hydroxide, for example, aluminum oxide or titanium oxide.

[0047] Preferably, the adhesive is selected from one or more of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, pure acrylic emulsion and styrene-butadiene rubber, for example, polyvinylidene fluoride.

[0048] Preferably, the mass ratio of the inorganic particles to the adhesive is (1-999):1, more preferably (200-999):1.

[0049] In this invention, the thickness of the coating can be 2-6 μm, for example 3 μm.

[0050] In this invention, the thickness ratio of the substrate to the coating can be (1-5):1, for example, 3:1.

[0051] In a preferred embodiment of the present invention, the resistivity of the diaphragm is 0.8-3.0 Ωcm. 2 ;

[0052] Within a pressure range of 0-100 MPa, the resistivity change rate γ is 0-0.04 Ωcm. 2 / MPa; within a pressure range of 100MPa-300MPa, the resistivity change rate γ is 0.05-0.1Ωcm. 2 / MPa;

[0053] The diaphragm includes a substrate and a coating applied to at least one surface of the substrate; the coating includes inorganic particles and an adhesive.

[0054] The particle size distribution dispersion of the inorganic particles is 0.5-1; the particle size of the inorganic particles satisfies D10 > 0.4 μm, 0.6 μm < D50 < 0.8 μm, and D90 < 2.0 μm; the inorganic particles are alumina and / or titanium oxide.

[0055] The substrate is a polyethylene film; the thickness of the substrate is 9-12 μm; the air permeability of the substrate is 150s / 100mL-300s / 100mL; the porosity of the substrate is 35-50%; the pore diameter of the substrate is 0.04-0.08 μm; the thickness of the coating can be 2-6 μm; the thickness ratio of the substrate to the coating is (1-5):1.

[0056] In this invention, the diaphragm can be prepared using conventional methods in the art. Preferably, the preparation method of the diaphragm includes the following steps: preparing a substrate using a wet biaxial stretching process, and then coating at least one side of the substrate surface with a microgravure roller.

[0057] In the electrochemical device of the second aspect of the present invention:

[0058] In this invention, the electrochemical device can generally be a conventional device in the art containing a membrane as described above, such as a battery or capacitor. Preferably, the battery includes a primary battery or a secondary battery, such as a lithium-ion battery or a sodium-ion battery.

[0059] In some preferred embodiments, the electrochemical device is a lithium-ion battery. The lithium-ion battery typically includes a negative electrode, a positive electrode, an electrolyte, and a separator as described above.

[0060] Preferably, the positive electrode typically includes a positive electrode active material, a binder, and a conductive agent.

[0061] The weight ratio of the positive electrode active material, the binder, and the conductive agent can be 98:1:1.

[0062] The positive electrode active material can be a conventional positive electrode active material used in the field for lithium-ion battery positive electrodes, such as lithium iron phosphate (LFP).

[0063] The binder may be a conventional binder used in the field for lithium-ion battery cathodes, such as polyvinylidene fluoride (PVDF).

[0064] The conductive agent can be a conductive agent commonly used in the field for the positive electrode of lithium-ion batteries, such as conductive carbon black (Super P).

[0065] Preferably, the negative electrode typically includes a negative electrode active material, a thickener, a binder, and a conductive agent.

[0066] The weight ratio of the negative electrode active material, the thickener, the binder, and the conductive agent can be 96:1:1:2.

[0067] The negative electrode active material can be a negative electrode active material conventionally used in the field for lithium-ion battery negative electrodes, such as artificial graphite.

[0068] The binder may be a conventional binder used in the field for lithium-ion battery anodes, such as styrene-butadiene rubber (SBR).

[0069] The conductive agent can be a conductive agent conventionally used in the field for the negative electrode of lithium-ion batteries, such as conductive carbon black (Super P).

[0070] The thickener may be a thickener conventionally used in the field for lithium-ion battery anodes, such as sodium carboxymethyl cellulose (CMC-Na).

[0071] Preferably, the electrolyte can be a conventional electrolyte used in lithium-ion batteries, generally including a non-aqueous solvent, lithium salt, and additives.

[0072] The non-aqueous solvent can be a conventional non-aqueous solvent in the art, preferably an ester solvent, and more preferably a carbonate solvent. The carbonate solvent is preferably one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).

[0073] The lithium salt can be a conventional lithium salt in the art, preferably LiPF6, LiBF4, LiN(SO2F)2 (LiFSI), LiClO4, LiAsF6, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiDFOB), or LiN(SO2R) F 2. LiN(SO2F)(SO2R) F At least one of the following: . The lithium salt content in the electrolyte is preferably 5%-20%, where the percentage is the percentage of the lithium salt by mass of the electrolyte.

[0074] The additive is preferably one or more selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), vinylene sulfate, 1,3-propane sulfonyl lactone (PS), propylene sulfonate lactone, and 1,4-butane sulfonate lactone. The amount of the additive used is conventional in the art, preferably 1%-4%, for example, 2%, where the percentage is the percentage of the additive to the total mass of the electrolyte.

[0075] The conductivity of the electrolyte is preferably 9-12 mS / cm, for example, 10.79 mS / cm.

[0076] In this invention, the positive electrode can be prepared using conventional methods in the art. Preferably, the preparation method of the positive electrode includes the following steps: mixing the positive electrode active material, the binder and the conductive agent, adding N-methylpyrrolidone (NMP), and stirring under a vacuum mixer until the system is uniform and transparent to obtain a positive electrode slurry; uniformly coating the positive electrode slurry onto an aluminum foil; drying the aluminum foil at room temperature and then transferring it to an oven for drying, followed by cold pressing and slitting to obtain the positive electrode.

[0077] In this invention, the negative electrode can be prepared using conventional methods in the art. Preferably, the preparation method of the negative electrode includes the following steps: mixing the negative electrode active material, the thickener, the binder and the conductive agent, adding deionized water, and stirring evenly under a vacuum mixer to obtain a negative electrode slurry; uniformly coating the negative electrode slurry onto a negative electrode current collector copper foil; drying the copper foil at room temperature and then transferring it to an oven for drying, followed by cold pressing and slitting to obtain the negative electrode.

[0078] In this invention, the electrolyte can be prepared using conventional methods in the art, preferably including the following steps: in an argon atmosphere glove box with a water content of <10ppm, a fully dried lithium salt is dissolved in a solvent, and the electrolyte is obtained after being mixed evenly.

[0079] In this invention, the lithium-ion battery can be prepared using conventional methods in the art, preferably including the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, with the separator positioned between the positive electrode and the negative electrode to act as an separator, then wrapping with an aluminum-plastic film, transferring to a vacuum oven to dry at 120°C, injecting the electrolyte as described above, sealing, and performing electrolyte liquefaction to finally obtain the lithium-ion battery.

[0080] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0081] Example 1

[0082] Preparation of the diaphragm: The PE film was prepared into a PE substrate using a wet biaxial stretching process. The thickness of the substrate was 12 μm, the air permeability was 150 s / 100 mL, the porosity was 38%, and the pore size of the substrate was about 0.04 μm.

[0083] Examples 2-13 and Comparative Example 1

[0084] PE film was prepared into PE substrate using a wet biaxial stretching process. Then, a coating was applied to one side of the substrate using a microgravure roller. The coating consisted of inorganic particles and polyvinylidene fluoride (PVDF) adhesive. The thickness, air permeability, porosity, pore size, alumina particle size, and particle size distribution dispersion of the substrate are shown in Table 1.

[0085] Table 1. Parameters of coatings and substrates for the diaphragms of Examples 1-13 and Comparative Example 1

[0086]

[0087]

[0088] Effect Example

[0089] Preparation of EIS fixture for diaphragm pressure testing

[0090] ① Assembly of diaphragm pressure-bearing tooling mold

[0091] A schematic diagram of the EIS fixture for measuring the electrochemical resistivity of a diaphragm under pressure is shown below. Figure 1 As shown. The upper and lower clamps are made of stainless steel, and the middle cylindrical sealing sleeve is made of polytetrafluoroethylene. It is sealed with an acid- and alkali-resistant, high- and low-temperature resistant sealing ring.

[0092] ② Preparation of electrolyte

[0093] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0094] ③ Preparation of the diaphragm

[0095] The diaphragms obtained in Examples 1-3 were cut into circles with a diameter of 1.6 cm for later use. Diaphragm area: approximately 2 cm². 2 .

[0096] (1) Test of diaphragm pressure resistance

[0097] The pressure sensor is placed under the diaphragm testing fixture, and pressure is applied using hydraulic equipment. The pressure applied to the diaphragm is precisely controlled by the reading of the pressure sensor.

[0098] (2) Test of the resistivity of the diaphragm as a function of pressure

[0099] Transfer the components of the tooling battery mold into the glove box, place three separators into the lower housing, and add 40 μL of electrolyte. After allowing it to settle, place the tooling battery into a high and low temperature test chamber, set the chamber temperature to 25°C, and connect the electrochemical workstation test leads (e.g., ...). Figure 1 (As shown), allow the battery to stand for 3 hours to allow the temperature of the tooling battery to match the temperature of the test chamber; after 3 hours of standing, perform the test using an electrochemical workstation, selecting the "Impedance" AC impedance method, voltage perturbation, and a frequency range of 10. -1 -10 6 The frequency was Hz, the amplitude was 5mV, and the results are shown in Table 2. Based on the experimental data, the resistivity of the diaphragm in Examples 1-3 as a function of pressure was plotted, as shown in Table 2. Figure 2 As shown.

[0100] Table 2. Resistivity values ​​of the diaphragms prepared in Examples 1-13 and Comparative Example 1

[0101]

[0102]

[0103] Referring to Table 2, the resistivity of the membranes prepared in Examples 1 and 2 changes less with pressure and has good pressure resistance. Comparing Examples 1 and 2 reveals that reducing the substrate thickness from 12 μm to 9 μm reduces ion transport resistivity. Example 2 constructed an alumina coating, but the particle size distribution dispersion of the alumina was 1.86, resulting in a larger change in membrane resistivity with pressure compared to Example 1, and a lower pressure resistance. This led to a significant increase in resistivity of the membrane in Example 2 under high pressure conditions. When the pressure exceeded 100 MPa, the resistivity change rate of the membrane prepared in Example 2 ranged from 0.0493 to 0.1233 Ωcm. 2 The resistivity values ​​are between 4 Ω / MPa and those of Example 1. Furthermore, the resistivity values ​​of both Example 1 and Example 2 are on the baseline of the fitted line, and the rate of change of resistivity is greater than 4 Ω / cm. 2 At pressures of 100 MPa, the resistivity increases significantly, and pressures exceeding 100 MPa severely affect the battery's kinetic processes. Based on experimental data, a plot was created... Figure 2 ,Depend on Figure 2 It can be seen that as the pressure increases, the resistivity of both Example 1 and Example 2 increases exponentially, and the growth exponent of Example 2 is greater than that of Example 1, indicating that under high pressure conditions, the resistivity of Example 2 increases faster than that of Example 1.

[0104] Comparing Examples 1 and 3 reveals that the alumina particle size distribution dispersion of Example 3 is 0.5, resulting in a membrane resistivity that changes less with pressure and a significantly increased pressure resistance. When the pressure reaches 100 MPa, the resistivity of the membrane prepared in Example 3 is 4.59 Ωcm. 2 The resistivity change rate is 0.0367 Ωcm 2 The resistivity of Example 3 was also found to be lower than that of Example 1 when the pressure increased to 200 MPa. Furthermore, when the pressure increased to 200 MPa, the resistivity of Example 3 also appeared on the baseline of the fitted line, and the rate of change of resistivity was greater than 4 Ωcm. 2 At / MPa, the resistivity increases significantly; further increases in pressure will also affect the battery's kinetic processes. Figure 2 It can be seen that as the pressure increases, the resistivity of Example 3 also increases exponentially, but the growth exponent of Example 3 is less than that of Example 1, indicating that under high pressure conditions, the resistivity of Example 3 increases more slowly than that of Example 1.

[0105] As shown in Examples 3-6 and Comparative Example 1, when the particle size distribution dispersion of the inorganic particles is greater than 2, the resistivity of the prepared diaphragm changes significantly with pressure, resulting in poor pressure resistance. For example, in Comparative Example 1, the particle size distribution dispersion of the inorganic particles is 3. When the pressure is 100 MPa, the resistivity change rate of the diaphragm prepared in Comparative Example 1 is as high as 0.0767 Ωcm. 2 At pressures of 300 MPa, the resistivity of the diaphragm increases rapidly with pressure changes, reaching a rate of change as high as 0.1615 Ωcm. 2 / MPa. When the particle size distribution dispersion of the inorganic particles is between 0.5 and 1, the resistivity of the prepared diaphragm changes less with pressure, and the pressure resistance is significantly increased. When the pressure is below 100MPa, the resistivity change rate of the diaphragm prepared in Example 6 is the largest, but it is only 0.0451 Ωcm. 2 / MPa, lower than in Examples 1 and 2; the resistivity of the diaphragm increases slowly with pressure changes, and the resistivity change rate of the diaphragms prepared in Examples 4-6 is 0.0443-0.0834 Ωcm when the pressure is between 100-300 MPa. 2 / MPa, 0.0448-0.0833Ωcm 2 / MPa, 0.0451-0.0832Ωcm 2 / MPa, all less than 0.9Ωcm 2 / MPa. The above results show that when the particle size distribution dispersion of inorganic particles is between 0.5 and 2, the prepared diaphragm has good pressure resistance, while when the particle size distribution dispersion of inorganic particles is between 0.5 and 1, the pressure resistance of the prepared diaphragm will be significantly improved.

[0106] Examples 7 and 8 show that when the mass ratio of inorganic particles to binder is between (1-999):1, the resistivity of the prepared diaphragm changes little with pressure, and it has good pressure resistance.

[0107] As can be seen from Examples 9 and 10, when the thickness of the coating is between 2 and 6, the thickness of the substrate is between 6 and 12, and the thickness ratio of the substrate to the diaphragm is (1-5):1, the resistivity of the diaphragm changes little with pressure and has good pressure resistance.

[0108] As can be seen from Examples 11 and 12, when the air permeability of the substrate is between 60s / 100mL and 300s / 100mL, the porosity is between 30% and 50%, and the pore diameter is between 0.02 and 0.08μm, the resistivity of the prepared diaphragm changes little with pressure and has good pressure resistance.

[0109] Example 13 uses titanium oxide as the coating of inorganic particles. As shown in Table 2, the resistivity of the diaphragm prepared in Example 13 also changes little with pressure and has good pressure resistance.

[0110] In summary, the resistivity of different separators increases linearly with increasing pressure. When the particle size distribution dispersion of the inorganic particles is between 0.5 and 2, this coating can improve the pressure resistance of the separator, reduce the rate of resistivity change, resist the volume expansion caused by long-term cycling of lithium batteries, and improve the cycle stability of the battery. Furthermore, within the experimental range, the preferred relatively stable resistivity range of the separator under pressure is 0.8-50 Ωcm. 2 (Corresponding to a resistivity change rate of 0-0.08Ωcm) 2 ( / MPa). The reference values ​​from the above experiments can guide the development and design of diaphragms and the performance design of battery cells.

[0111] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A diaphragm, characterized by The electrical resistivity R of the separator is 0.8-50.0 Ω cm 2 ; And the diaphragm satisfies: in the range of 0-100 MPa pressure, γ is 0-0.08 Ω cm 2 / MPa; in the range of 100-300 MPa pressure, γ is 0.05-0.1 Ω cm 2 / MPa; wherein, ； wherein γ is the resistivity change rate, Ω cm 2 ΔR is the resistivity change value, Ω cm 2 ΔP is the pressure change value, Mpa; The separator includes a substrate and a coating layer coated on at least one side surface of the substrate, the coating layer including inorganic particles and a binder; the inorganic particles have a particle size distribution dispersion degree of 0.5-1; the inorganic particles have a particle size satisfying D10>0.4 μm, 0.6 μm 2. The septum of claim 1, wherein ΔR is 0-10 Ω cm when ΔP is 25-100 MPa in the range of 0-100 MPa 2 .

3. The septum of claim 1, wherein One or more of the following conditions (a)-(c) are satisfied: (a) the thickness of the coating layer is 2-6 μm; (b) the thickness of the substrate is 6-12 μm; (c) the thickness ratio of the substrate to the coating layer is (1-5):

1.

4. The septum of claim 1 wherein, The substrate is a polyolefin porous substrate; the polyolefin porous substrate satisfies one or more of the following conditions (d)-(f): (d) the air permeability of the substrate is 60 s / 100 mL-300 s / 100 mL; (e) the porosity of the substrate is 30%-50%; (f) the pore diameter of the substrate is 0.02-0.08 μm.

5. An electrochemical device, characterized by, It includes the separator according to any one of claims 1-4.

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