Separator, and electrochemical device and electronic device comprising same

Abstract

The present application discloses a separator, and an electrochemical device and electronic device comprising same. The separator comprises a porous base material and a porous coating located on at least one side of the porous base material; the porous coating comprises filler particles and a binder; the separator has a maximum pore size recorded as Dmax, a minimum pore size recorded as Dmin, and an average pore size recorded as Davg, all with the unit of nm, wherein Dmax is 35 nm to 75 nm, Dmin is 10 nm to 20 nm, Davg is 25 nm to 45 nm, and Dmax / Davg is 1.20 to 2.99. According to the present application, the electrochemical device has both good low temperature cycle performance and good high temperature stability.

Description

Separator, and electrochemical device and electronic device containing the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 15, 2024, with application number 202410056354.1 and invention name “Diaphragm, and electrochemical device and electronic device containing the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of electrochemical technology, and specifically relates to a diaphragm, and an electrochemical device and an electronic device containing the same. Background Art

[0003] With the demand for high energy density and long cycle life in lithium-ion batteries, stricter requirements are being placed on the performance of separators. Existing separators typically pursue uniform pore sizes. However, during the actual charge and discharge process of lithium-ion batteries, due to the significant difference in the migration rate of lithium ions between the positive and negative electrodes, the use of separators with uniform pore sizes results in lithium ions escaping from the positive electrode not having enough time to embed at the negative electrode, resulting in purple spots and lithium deposition at the negative electrode, which affects the battery's cycle performance. Summary of the Invention

[0004] The present application provides a diaphragm, and an electrochemical device and an electronic device comprising the same, which can enable the electrochemical device to have both good low-temperature cycle performance and high-temperature stability.

[0005] In a first aspect, the present application provides a membrane comprising a porous substrate and a porous coating located on at least one side of the porous substrate, wherein the porous coating comprises filler particles and a binder; the maximum pore size of the membrane is denoted as D max , the minimum aperture is recorded as D min The average pore size is recorded as D avg , the unit is nm, D max 35nm to 75nm, D min 10nm to 20nm, D avg 25nm to 45nm, D max / D avg It ranges from 1.20 to 2.99.

[0006] By adjusting the range of the maximum pore size, minimum pore size, and average pore size of the diaphragm, the pore size of the diaphragm can be made to present a non-homogeneous characteristic, so that the diaphragm provided in the embodiment of the present application can balance the mobility of lithium ions on the positive electrode side of the diaphragm and the mobility of lithium ions on the negative electrode side of the diaphragm, thereby facilitating the smooth embedding of lithium ions into the negative electrode and effectively reducing the problem of purple lithium precipitation at the negative electrode, thereby facilitating the improvement of the low-temperature cycle performance of the electrochemical device. At the same time, the diaphragm provided in the embodiment of the present application includes a porous coating, which can also have good thermal stability and a low degree of thermal shrinkage, thereby also facilitating the electrochemical device to have good high-temperature stability. Therefore, the diaphragm provided in the embodiment of the present application can enable the electrochemical device to have both good low-temperature cycle performance and high-temperature stability.

[0007] In some embodiments, D max / D avg 1.20 to 2.62, and / or, D min / D avg It is 0.35 to 0.59.

[0008] Optionally, D max / D avg 1.60 to 2.23, and / or, D min / D avg It is 0.43 to 0.57.

[0009] By further adjusting the relationship between the maximum pore size, minimum pore size and average pore size of the diaphragm max / D avg and / or D min / D avg Within the above range, the pore size of the diaphragm can better present non-uniform characteristics, which can better balance the low-temperature cycling performance and high-temperature stability of the electrochemical device.

[0010] In some embodiments, D max / D min 3.39 to 6.05.

[0011] Optionally, D max / D min 3.67 to 4.54.

[0012] By further adjusting the relationship between the maximum pore size and the minimum pore size of the diaphragm max / D min Within the above range, the low-temperature cycle performance and high-temperature stability of the electrochemical device can be better balanced.

[0013] In some embodiments, the total pore area of ​​pores with a pore diameter of 30 nm to 45 nm in the membrane accounts for 10% to 35%, and optionally 14% to 27% of the total pore area of ​​the membrane.

[0014] By further adjusting the total pore area ratio of pores with a pore size of 30 nm to 45 nm within the above range, the ion transport properties of the diaphragm can be improved, and the circulation of the electrolyte can be facilitated, thereby better improving the low-temperature cycle performance of the electrochemical device.

[0015] In some embodiments, the porous substrate has a porosity of 20% to 50%.

[0016] In some embodiments, the porous substrate has an average pore size of 30 nm to 60 nm.

[0017] In some embodiments, the porous substrate has a thickness of 4 μm to 15 μm.

[0018] In some embodiments, the porosity of the separator after heating at 130° C. for 1 hour is 30% to 60%.

[0019] In some embodiments, the membrane has an area density of 1 g / m 2 Up to 5g / m 2 .

[0020] In some embodiments, the total thickness of the separator is 10 μm to 17 μm.

[0021] In some embodiments, the porous coating has a thickness of 2 μm to 10 μm.

[0022] In some embodiments, the filler particles include at least one of organic particles and inorganic particles.

[0023] In some embodiments, the organic particles include vinylidene fluoride-based resin particles, and the volume distribution particle size Dv50 of the organic particles is 0.8 μm to 2 μm, Dv90 is 1.5 μm to 4 μm, and Dv10 is 0.1 μm to 1.8 μm.

[0024] By adjusting the volume distribution particle size of the organic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to the circulation of the electrolyte, and is also beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm, thereby better balancing the low-temperature cycle performance and high-temperature stability of the electrochemical device.

[0025] In some embodiments, the aspect ratio of the organic particles is (1-1.5):1.

[0026] By adjusting the aspect ratio of the organic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm. It can also bring into play the adhesion of the organic particles, improve the bonding strength between the filler particles in the porous coating and the bonding strength between the porous coating and the porous substrate, thereby reducing the impedance of the diaphragm and improving the low-temperature cycling performance of the electrochemical device.

[0027] In some embodiments, the inorganic particles include ceramic particles, and the volume distribution particle size Dv50 of the inorganic particles is 1 μm to 4 μm, Dv90 is 2 μm to 6 μm, and Dv10 is 0.6 μm to 1.2 μm.

[0028] By adjusting the volume distribution particle size of the inorganic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to the circulation of the electrolyte, and is also beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm, thereby better balancing the low-temperature cycle performance and high-temperature stability of the electrochemical device.

[0029] In some embodiments, the aspect ratio of the inorganic particles is (2-5):1.

[0030] By adjusting the aspect ratio of the inorganic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to improving the thermal stability of the diaphragm, reducing the degree of thermal shrinkage of the diaphragm, and thereby improving the low-temperature cycle performance of the electrochemical device.

[0031] In some embodiments, the binder includes a copolymer containing at least two structural units, wherein the at least two structural units are derived from monomers containing unsaturated double bonds, at least one of the monomers containing unsaturated double bonds contains an ester group and at least one does not contain an ester group, and the weight average molecular weight of the binder is 800,000 to 1.8 million.

[0032] By making the comonomer of the binder include both monomers containing ester groups and monomers not containing ester groups, the diaphragm can have good lyophilicity and good heat resistance, thereby further improving the low-temperature cycle performance and high-temperature stability of the electrochemical device.

[0033] In some embodiments, the ester-containing monomer includes at least one of methyl methacrylate, ethyl methacrylate, isooctyl acrylate, n-propyl acrylate, butyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. By adjusting the ester-containing monomer within the above range, the lyophilicity of the separator can be further improved.

[0034] In some embodiments, the monomer not containing an ester group includes at least one of styrene, butadiene, methacrylamide, acrylamide, and acrylonitrile. By adjusting the monomer not containing an ester group within the above range, the heat resistance of the separator can be further improved.

[0035] In some embodiments, the binder comprises a copolymer of the following three monomers: styrene, methyl methacrylate, and isooctyl acrylate. Based on 100 parts by weight of the three monomers, the weight of styrene is 75 to 90 parts, the weight of methyl methacrylate is 2 to 5 parts, and the balance is isooctyl acrylate. This helps improve the low-temperature cycling performance and high-temperature stability of the electrochemical device.

[0036] In some embodiments, the binder comprises a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is (1-5): 1. This is beneficial for improving the low-temperature cycling performance and high-temperature stability of the electrochemical device.

[0037] In a second aspect, the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a diaphragm, wherein the diaphragm comprises the diaphragm of the first aspect of the present application.

[0038] In some embodiments, the electrolyte contains 1,3-propane sultone and vinyl sulfate, the mass fraction of the 1,3-propane sultone in the total mass of the electrolyte is A, the mass fraction of the vinyl sulfate in the total mass of the electrolyte is B, and 2.0≤A / B≤8.0. When the ratio between 1,3-propane sultone and vinyl sulfate is adjusted to meet the scope of this application, a synergistic effect will occur between the two additives, so that a structurally stable and uniform solid electrolyte interface film with a thickness of tens of nanometers can be formed on the surface of the positive electrode active material during the cycle of the electrochemical device. The formation of this film can reduce the oxidative decomposition of the electrolyte, and by capturing gas molecules on the interface, the temperature rise of the electrochemical device under the fast charge test is reduced, thereby improving the fast charge performance and high temperature cycle stability of the electrochemical device.

[0039] Optionally, 3.5≤A / B≤7.25. This can more effectively reduce the temperature rise of the electrochemical device during a fast charge test, thereby improving the fast charge performance and high-temperature cycle stability of the electrochemical device.

[0040] Optionally, 4.0≤A / B≤6.5. This can better reduce the temperature rise of the electrochemical device during a fast charge test, thereby improving the fast charge performance and high-temperature cycle stability of the electrochemical device.

[0041] In some embodiments, the positive electrode plate includes a positive electrode active material having a powder volume resistivity of 100 kΩ·cm to 450 kΩ·cm at 15 MPa. When the positive electrode active material has a powder volume resistivity within this range, lithium ion migration between the positive and negative electrodes can be maintained at a suitable rate, thereby effectively improving the low-temperature cycling performance of the electrochemical device.

[0042] In a third aspect, the present application provides an electronic device comprising the electrochemical device according to the second aspect of the present application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. Based on the technical solutions and embodiments provided in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0044] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0045] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0046] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of each parameter mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0047] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0048] The term "plurality" means more than two.

[0049] The charging process of a lithium-ion battery refers to the process in which lithium ions are released from the positive electrode under the drive of an electric field, pass through the electrolyte and separator, and are embedded in the negative electrode. However, when abnormal situations occur, such as when lithium ions are successfully released from the positive electrode but cannot be embedded in the negative electrode in equal quantities, the lithium ions that cannot be embedded in the negative electrode can only obtain electrons on the negative electrode surface, thereby forming silvery-white metallic lithium on the negative electrode surface, which is the problem of lithium plating.

[0050] Existing separators typically pursue a uniform pore size. However, during the actual charge and discharge process of lithium-ion batteries, due to differences in the rate at which lithium ions escape from the positive electrode, the rate at which they embed into the negative electrode, and the rate at which lithium ions migrate between the positive and negative electrodes, a separator with a uniform pore size results in lithium ions escaping from the positive electrode being unable to embed equally into the negative electrode. This results in purple lithium deposition at the negative electrode, impacting the battery's cycling performance. Particularly at low temperatures, the electrolyte's ionic conductivity further decreases. This increases the resistance to lithium ion escape from the positive electrode and the resistance to lithium ion embedding into the negative electrode. Simultaneously, the migration resistance of solvated lithium ions in the electrolyte increases significantly, while their migration rate decreases significantly, further exacerbating the purple lithium deposition problem at the negative electrode.

[0051] Based on this, this application first takes the perspective of the diaphragm and adjusts the pore size of the diaphragm to enable the electrochemical device to have both good low-temperature cycling performance and high-temperature stability. Furthermore, this application also selects a more suitable electrolyte from the perspective of the compatibility between the electrolyte and the diaphragm, thereby further improving the high-temperature stability and fast-charging performance of the electrochemical device.

[0052] In a first aspect, an embodiment of the present application provides a diaphragm.

[0053] The membrane includes a porous substrate and a porous coating located on at least one side of the porous substrate. The porous coating includes filler particles and a binder. The maximum pore size of the membrane is denoted as D max , the minimum aperture is recorded as D min The average pore size is recorded as Davg , the unit is nm, D max 35nm to 75nm, D min 10nm to 20nm, D avg 25nm to 45nm, D max / D avg It ranges from 1.20 to 2.99.

[0054] The diaphragm provided in the embodiment of the present application meets the requirements of D max 35nm to 75nm, D min 10nm to 20nm, D avg 25nm to 45nm, D max / D avg is 1.20 to 2.99. By adjusting the range of the maximum pore size, minimum pore size and average pore size of the diaphragm, the pore size of the diaphragm can be made to present a non-uniform characteristic. Compared with the diaphragm with uniform pore size pursued by the prior art, the diaphragm provided in the embodiment of the present application can balance the mobility of lithium ions on the positive electrode side of the diaphragm and the mobility of lithium ions on the negative electrode side of the diaphragm, thereby facilitating the smooth embedding of lithium ions into the negative electrode, and effectively reducing the problem of purple lithium precipitation at the negative electrode, thereby facilitating the improvement of the low-temperature cycle performance of the electrochemical device. At the same time, the diaphragm provided in the embodiment of the present application includes a porous coating, thereby also having good thermal stability and a low degree of thermal shrinkage, which is also beneficial for the electrochemical device to have good high-temperature stability.

[0055] Therefore, the diaphragm provided in the embodiments of the present application can enable the electrochemical device to have both good low-temperature cycle performance and high-temperature stability.

[0056] In some embodiments, D max / D avg The molecular weight of the present invention is 1.20 to 2.80, for example, 1.20, 1.28, 1.34, 1.37, 1.40, 1.43, 1.48, 1.52, 1.60, 1.70, 1.80, 1.90, 2.01, 2.09, 2.17, 2.20, 2.23, 2.35, 2.48, 2.62, 2.80, or a range consisting of any of the above values.

[0057] In some embodiments, D min / D avg The range is 0.35 to 0.67, for example, 0.35, 0.37, 0.40, 0.43, 0.45, 0.47, 0.49, 0.52, 0.55, 0.57, 0.59, 0.61, 0.63, 0.65, 0.67, or any range thereof.

[0058] In some embodiments, D max / D avg1.20 to 2.62, and / or, D min / D avg It is 0.35 to 0.59.

[0059] By further adjusting the relationship between the maximum pore size, minimum pore size and average pore size of the diaphragm max / D avg and / or D min / D avg Within the above range, the pore size of the diaphragm can better present non-uniform characteristics, which can better balance the low-temperature cycling performance and high-temperature stability of the electrochemical device.

[0060] D max / D avg Smaller and / or D min / D avg When the pore size is larger, the pore size of the separator tends to be uniform, which is not conducive to balancing the mobility of lithium ions on the positive electrode side of the separator and the mobility of lithium ions on the negative electrode side of the separator, thereby affecting the low-temperature cycle performance of the electrochemical device.

[0061] D max / D avg Larger and / or D min / D avg When the D is small, the maximum pore size of the diaphragm is large and the minimum pore size is small, which is not conducive to balancing the mobility of lithium ions on the positive electrode side of the diaphragm and the mobility of lithium ions on the negative electrode side of the diaphragm, thereby affecting the low-temperature cycle performance of the electrochemical device; at the same time, D max / D avg When the value is larger, the thermal stability of the entire diaphragm will deteriorate, the degree of thermal shrinkage will be higher, and the high-temperature stability of the electrochemical device will be affected.

[0062] Optionally, D max / D avg 1.60 to 2.23, and / or, D min / D avg The low-temperature cycle performance and high-temperature stability of the electrochemical device can be further balanced.

[0063] In some embodiments, D max / D min5.40, 5.50, 5.60, 5.70, 5.80, 5.90, 6.05, 6.20, 6.35, 6.50, or a range consisting of any of the above values.

[0064] By further adjusting the relationship between the maximum pore size and the minimum pore size of the diaphragm max / D min Within the above range, the low-temperature cycle performance and high-temperature stability of the electrochemical device can be better balanced.

[0065] D max / D min When the pore size is smaller, the pore size of the separator tends to be uniform, which is not conducive to balancing the mobility of lithium ions on the positive electrode side of the separator and the mobility of lithium ions on the negative electrode side of the separator, thereby affecting the low-temperature cycle performance of the electrochemical device.

[0066] D max / D min When it is larger, the maximum pore size of the diaphragm is larger and the minimum pore size is smaller, which is not conducive to balancing the mobility of lithium ions on the positive electrode side of the diaphragm and the mobility of lithium ions on the negative electrode side of the diaphragm, thereby affecting the low-temperature cycle performance of the electrochemical device; at the same time, the overall thermal stability of the diaphragm will deteriorate, and the degree of thermal shrinkage will be higher, which will also affect the high-temperature stability of the electrochemical device.

[0067] Optionally, D max / D min is 3.39 to 6.05. More preferably, D max / D min The low-temperature cycle performance and high-temperature stability of the electrochemical device can be further balanced.

[0068] In some embodiments, the total pore area of ​​pores with a pore size of 30 nm to 45 nm in the membrane accounts for 10% to 35% of the total pore area of ​​the membrane, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, or a range consisting of any of the above values.

[0069] By further adjusting the total pore area ratio of pores with a pore size of 30 nm to 45 nm within the above range, the ion transport properties of the diaphragm can be improved, and the circulation of the electrolyte can be facilitated, thereby better improving the low-temperature cycle performance of the electrochemical device.

[0070] Optionally, the total pore area of ​​pores with a pore diameter of 30 nm to 45 nm in the separator accounts for 14% to 27% of the total pore area of ​​the separator, thereby further improving the low-temperature cycle performance of the electrochemical device.

[0071] The pore size and pore size distribution of the diaphragm can be adjusted by adjusting the parameters of the porous substrate, such as pore size, pore size distribution, porosity, and the parameters of the porous coating, such as the weight content of filler particles, the weight content of binder, the morphology of filler particles and the particle size.

[0072] In some embodiments, the porous substrate may have a porosity of 20% to 50%, for example, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any range thereof. A porosity within this range may be more conducive to improving the low-temperature cycling performance of the electrochemical device.

[0073] In some embodiments, the average pore size of the porous substrate may be 30 nm to 60 nm, for example, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm, or any range thereof. A porous substrate having such an average pore size may be more conducive to improving the low-temperature cycling performance of an electrochemical device.

[0074] In some embodiments, the porous substrate may have a thickness of 4 μm to 15 μm, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any range thereof. When the thickness of the porous substrate falls within this range, it may be more conducive to improving the low-temperature cycling performance of the electrochemical device.

[0075] The present application has no particular restrictions on the material of the porous substrate, as long as the purpose of the present application can be achieved. For example, the porous substrate can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the porous substrate can include at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate, polyimide, polyamide, spandex and aramid. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0076] In some embodiments, the preparation method of the porous substrate may include the following steps: mixing a first pore-forming agent and a first polymer particle in a predetermined ratio to obtain a mixture 1; mixing a second pore-forming agent and a second polymer particle in a predetermined ratio to obtain a mixture 2, wherein the weight average molecular weight of the first polymer particle is greater than the weight average molecular weight of the second polymer particle; adding the above-mentioned mixture 1 and mixture 2 to the two grinding heads of a double-head extruder respectively, extruding through a two-layer die, cooling the mixture 1 and the mixture 2 on a casting roller and finally mixing to form a membrane; stretching the obtained membrane, and then extracting the pore-forming agent with a solvent, and obtaining a porous substrate intermediate with pores after drying; and subjecting the obtained porous substrate intermediate to a secondary stretching treatment, and then heat setting treatment to obtain a porous substrate.

[0077] Optionally, the first pore-forming agent and the second pore-forming agent may independently include one or more of paraffin oil and white oil.

[0078] Optionally, the molecular weights of the first pore-forming agent and the second pore-forming agent may be independently 200 to 1500. Pore-forming agents within this molecular weight range can better achieve the pore-forming effect required by the present application, thereby helping to improve the cycle performance of the electrochemical device.

[0079] Optionally, the weight average molecular weight of the first polymer particles may be 700,000 to 1.4 million, and optionally 1.2 million to 1.4 million.

[0080] Optionally, the weight average molecular weight of the second polymer particles may be 200,000 to 600,000, or optionally 300,000 to 500,000.

[0081] The weight average molecular weight of the first polymer particles and the weight average molecular weight of the second polymer particles can be measured by gel permeation chromatography (GPC).

[0082] Alternatively, the weight ratio of the first pore-forming agent to the first polymer particles may be 65:35 to 80:20. As the weight ratio of the first pore-forming agent to the first polymer particles increases, the pore size of the porous substrate increases under the same preparation process conditions; and as the weight ratio of the first pore-forming agent to the first polymer particles decreases, the pore size of the porous substrate decreases under the same preparation process conditions.

[0083] Alternatively, the weight ratio of the second pore-forming agent to the second polymer particles may be 65:35 to 80:20. As the weight ratio of the second pore-forming agent to the second polymer particles increases, the pore size of the porous substrate increases under the same preparation process conditions; and as the weight ratio of the second pore-forming agent to the second polymer particles decreases, the pore size of the porous substrate decreases under the same preparation process conditions.

[0084] Alternatively, the weight ratio of the first polymer particles to the second polymer particles may be 45:55 to 25:75.

[0085] The screw temperature of the twin-head extruder can be between 180°C and 220°C.

[0086] The cooling temperature of the casting roll of the twin-head extruder can be 60°C to 90°C.

[0087] Optionally, the step of stretching the obtained film includes transverse stretching and longitudinal stretching, for example, the film may be stretched transversely and longitudinally simultaneously, stretched transversely first and then longitudinally, or stretched longitudinally first and then transversely.

[0088] Optionally, the transverse stretching ratio may be 5 to 8 times, more preferably 6 to 7 times.

[0089] Optionally, the longitudinal stretching ratio may be 5 to 8 times, more preferably 6 to 7 times.

[0090] As the stretching ratio increases, the pore size of the porous substrate becomes larger under the same preparation process conditions; as the stretching ratio decreases, the pore size of the porous substrate becomes smaller under the same preparation process conditions.

[0091] The temperature for stretching the obtained film may be 105° C. to 115° C. The transverse stretching temperature and the longitudinal stretching temperature may be the same or different.

[0092] Alternatively, the solvent for extracting the pore former may include dichloromethane.

[0093] Optionally, the step of subjecting the obtained porous substrate intermediate to secondary stretching treatment includes transverse stretching and longitudinal stretching, for example, stretching in both the transverse and longitudinal directions simultaneously, stretching in the transverse direction first and then in the longitudinal direction, or stretching in the longitudinal direction first and then in the transverse direction.

[0094] Optionally, the transverse stretching ratio may be 1 to 2 times.

[0095] Optionally, the longitudinal stretching ratio may be 1 to 2 times.

[0096] As the secondary stretching multiple increases, the pore size of the porous substrate becomes larger under the same preparation process conditions; as the secondary stretching multiple decreases, the pore size of the porous substrate becomes smaller under the same preparation process conditions.

[0097] The temperature for performing the secondary stretching treatment on the obtained porous substrate intermediate may be 105°C to 115°C.

[0098] Alternatively, the heat setting temperature may be 108°C to 115°C.

[0099] As the heat setting temperature increases, the pore size of the porous substrate becomes smaller under the same preparation process conditions; as the heat setting temperature decreases, the pore size of the porous substrate becomes larger under the same preparation process conditions.

[0100] Optionally, the heat setting time may be 20 seconds to 40 seconds.

[0101] As the heat setting time increases, the pore size of the porous substrate decreases under the same preparation process conditions; as the heat setting time decreases, the pore size of the porous substrate increases under the same preparation process conditions.

[0102] In some embodiments, the porous coating layer may have a thickness of 2 μm to 10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any range thereof. The thickness of the porous coating layer refers to the thickness of the porous coating layer on a single side of the porous substrate.

[0103] The porous coating includes filler particles and a binder. By adjusting the thickness of the porous coating within the above range, it is beneficial to improve the thermal stability of the diaphragm, reduce the thermal shrinkage of the diaphragm, and also help to improve the energy density of the electrochemical device.

[0104] In some embodiments, the weight content of the filler particles in the porous coating can be 85 wt % to 98 wt %, for example, 85 wt %, 86 wt %, 87 wt %, 88 wt %, 89 wt %, 90 wt %, 91 wt %, 92 wt %, 93 wt %, 94 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, or a range consisting of any of the above values.

[0105] In some embodiments, the weight content of the binder in the porous coating can be 2 wt % to 15 wt %, for example, it can be 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt %, 15 wt %, or a range consisting of any of the above values.

[0106] By adjusting the weight content of filler particles and binder in the porous coating within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, improve the thermal stability of the diaphragm, reduce the thermal shrinkage of the diaphragm, and improve the bonding strength between the filler particles in the porous coating and the bonding strength between the porous coating and the porous substrate.

[0107] Under the same preparation process conditions, as the binder content increases, the minimum pore size of the diaphragm becomes larger; under the same preparation process conditions, as the binder content decreases, the minimum pore size of the diaphragm becomes smaller.

[0108] In some embodiments, the filler particles may include at least one of organic particles and inorganic particles.

[0109] In some embodiments, the organic particles may include vinylidene fluoride-based resin particles, for example, polyvinylidene fluoride (PVDF).

[0110] In some embodiments, the organic particles may have an aspect ratio of (1-1.5):1.

[0111] By adjusting the aspect ratio of the organic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm. It can also bring into play the adhesion of the organic particles, improve the bonding strength between the filler particles in the porous coating and the bonding strength between the porous coating and the porous substrate, thereby reducing the impedance of the diaphragm and improving the low-temperature cycling performance of the electrochemical device.

[0112] In some embodiments, the volume distribution particle size Dv50 of the organic particles may be 0.8 μm to 2 μm, Dv90 may be 1.5 μm to 4 μm, and Dv10 may be 0.1 μm to 1.8 μm.

[0113] By adjusting the volume distribution particle size of the organic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to the circulation of the electrolyte, and is also beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm, thereby better balancing the low-temperature cycle performance and high-temperature stability of the electrochemical device.

[0114] In some embodiments, the inorganic particles may have an aspect ratio of (2-5):1.

[0115] By adjusting the aspect ratio of the inorganic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to improving the thermal stability of the diaphragm, reducing the degree of thermal shrinkage of the diaphragm, and thereby improving the low-temperature cycle performance of the electrochemical device.

[0116] In some embodiments, the inorganic particles may include ceramic particles, and the volume distribution particle size Dv50 of the inorganic particles may be 1 μm to 4 μm, Dv90 may be 2 μm to 6 μm, and Dv10 may be 0.6 μm to 1.2 μm.

[0117] By adjusting the volume distribution particle size of the inorganic particles within the above range, it is beneficial to adjust the pore size and pore size distribution of the diaphragm, which is beneficial to the circulation of the electrolyte, and is also beneficial to improving the thermal stability of the diaphragm and reducing the degree of thermal shrinkage of the diaphragm, thereby better balancing the low-temperature cycle performance and high-temperature stability of the electrochemical device.

[0118] Dv10 indicates the particle size at which 10% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv50 indicates the particle size at which 50% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv90 indicates the particle size at which 90% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0119] In some embodiments, the ceramic may include, but is not limited to, at least one of alumina, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium hydroxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, and aluminum nitride.

[0120] In some embodiments, the binder in the porous coating layer may be in the form of particles or films.

[0121] Optionally, the aspect ratio of the granular binder may be (1-1.5):1.

[0122] Alternatively, the volume distribution particle size Dv50 of the particulate binder may be 0.8 μm to 2 μm.

[0123] In some embodiments, the binder may include a copolymer containing at least two structural units, both of which are derived from monomers containing unsaturated double bonds, at least one of which contains an ester group and at least one does not contain an ester group.

[0124] Monomers containing ester groups can improve the lyophilicity of the separator, thereby improving the low-temperature cycling performance of the electrochemical device, but they will reduce the heat resistance of the separator.

[0125] By making the comonomers of the binder include both monomers containing ester groups and monomers without ester groups, the separator can be made to have good lyophilicity and good heat resistance, thereby further improving the low-temperature cycling performance and high-temperature stability of the electrochemical device. The monomer containing an ester group can include at least one of methyl methacrylate, ethyl methacrylate, isooctyl acrylate, n-propyl acrylate, butyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. By adjusting the monomer containing an ester group within the above range, the lyophilicity of the separator can be further improved.

[0126] The monomer not containing an ester group may include at least one of styrene, butadiene, methacrylamide, acrylamide, and acrylonitrile, and may optionally include styrene.

[0127] By adjusting the content of the monomer not containing an ester group within the above range, the heat resistance of the separator can be further improved.

[0128] In some embodiments, the binder may include a copolymer formed by the following three monomers: styrene, methyl methacrylate, and isooctyl acrylate, and based on the total mass of the three monomers as 100 parts, the mass of styrene is 75 to 90 parts, the mass of methyl methacrylate is 2 to 5 parts, and the balance is isooctyl acrylate.

[0129] This is beneficial to improving the low-temperature cycle performance and high-temperature stability of electrochemical devices.

[0130] In some embodiments, the binder may include a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers may be (1-5):1, optionally (2-4):1.

[0131] This is beneficial to improving the low-temperature cycle performance and high-temperature stability of electrochemical devices.

[0132] In some embodiments, the weight average molecular weight of the binder may be 800,000 to 1.8 million.

[0133] The weight average molecular weight of the binder can be measured by gel permeation chromatography (GPC).

[0134] In some embodiments, the porous coating may further include a dispersant.

[0135] In some embodiments, the dispersant may include at least one of polyethylene glycol, polyvinyl alcohol compounds, and sodium dodecylbenzene sulfonate.

[0136] In some embodiments, the weight content of the dispersant in the porous coating layer may be less than or equal to 2 wt %.

[0137] By making the porous coating include a small amount of dispersant, it is beneficial to improve the thickness consistency of the porous coating, reduce the problem of purple spot lithium precipitation in the negative electrode, and thus improve the low-temperature cycle performance of the electrochemical device.

[0138] The method for preparing the porous coating layer may include the following steps: coating a porous coating layer slurry on at least one side of a porous substrate and drying the porous coating layer to form the porous coating layer. The porous coating layer slurry includes filler particles, a binder, and a solvent.

[0139] In some embodiments, the solvent in the porous coating slurry may include water.

[0140] In some embodiments, the porous coating slurry may have a solid content of 30% to 50%.

[0141] As the solid content of the porous coating slurry increases, the pore size of the diaphragm becomes smaller under the same preparation process conditions; as the solid content of the porous coating slurry decreases, the pore size of the diaphragm becomes larger under the same preparation process conditions.

[0142] In some embodiments, the viscosity of the porous coating slurry may be 25 mPa·s to 35 mPa·s.

[0143] As the viscosity of the porous coating slurry increases, the pore size of the diaphragm becomes smaller under the same preparation process conditions; as the viscosity of the porous coating slurry decreases, the pore size of the diaphragm becomes larger under the same preparation process conditions.

[0144] In some embodiments, the drying process of the porous coating slurry may be vacuum drying.

[0145] In some embodiments, the drying temperature of the porous coating slurry may be 30°C to 80°C.

[0146] In some embodiments, the porosity of the separator after heating at 130° C. for 1 hour may be 30% to 60%.

[0147] In some embodiments, the transverse direction (TD) thermal shrinkage of the separator after heating at 130° C. for 1 hour may be less than or equal to 4%, and optionally less than or equal to 3%.

[0148] In some embodiments, the separator may have a machine direction (MD) thermal shrinkage of less than or equal to 4%, and optionally less than or equal to 3%, after being heated at 130° C. for 1 hour.

[0149] In some embodiments, the membrane may have an areal density of 1 g / m 2 Up to 5g / m 2 .

[0150] In some embodiments, the total thickness of the separator may be 10 μm to 17 μm.

[0151] By adjusting the total thickness of the diaphragm within the above range, it is beneficial to improve the puncture resistance of the diaphragm and to improve the energy density of the electrochemical device.

[0152] The method for preparing the separator may include the following steps: coating the porous coating slurry on at least one side of the porous substrate, and drying to obtain the separator.

[0153] electrochemical devices

[0154] In a second aspect, embodiments of the present application provide an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, and specific examples thereof include all types of lithium primary batteries or lithium secondary batteries. In particular, lithium secondary batteries include lithium-ion secondary batteries.

[0155] During the use of electrochemical devices, oxidation and reduction reactions occur in the electrode active materials during charge and discharge. The negative electrode is the electrode where lithium ions are absorbed or lithiated during charge and lithium is released or delithiated during discharge. The positive electrode is the electrode where lithium ions are released or delithiated during charge and lithium is absorbed or lithiated during discharge.

[0156] In some embodiments, the electrochemical device may include a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator used in the electrochemical device is the separator of the first aspect of the embodiment of the present application. Therefore, the electrochemical device provided by the embodiment of the present application can have both good low-temperature cycling performance and high-temperature stability.

[0157] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0158] The electrochemical device also includes an outer packaging for encapsulating the electrode assembly and electrolyte. In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell, or a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of aluminum-plastic film, polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0159] The electrolyte solution may include an electrolyte salt and a solvent, wherein the electrolyte salt contains lithium ions. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to needs.

[0160] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium bis(oxalatoborate) (LiBOB). The above electrolyte salts may be used alone or in combination of two or more.

[0161] In some embodiments, the solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, and a sulfone compound. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MPC), propionic acid At least one of ethyl acetate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), methyl sulfolane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, and N,N-dimethylformamide. The above solvents may be used alone or in combination of two or more.

[0162] In some embodiments, the electrolyte may further contain additives. Optionally, the electrolyte contains 1,3-propane sultone and vinyl sulfate, where the mass fraction of 1,3-propane sultone in the total mass of the electrolyte is A, the mass fraction of vinyl sulfate in the total mass of the electrolyte is B, and 2.0≤A / B≤8.0. For example, A / B can be 2.0, 2.5, 3.0, 3.5, 3.75, 4.0, 4.25, 4.5, 4.75, 5.0, 5.5, 5.75, 6.0, 6.25, 6.5, 6.75, 7.0, 7.25, 7.5, 8.0, or a range consisting of any of the above values. When the ratio between 1,3-propane sultone and vinyl sulfate is adjusted to meet the scope of this application, a synergistic effect will occur between the two additives, so that during the cycle of the electrochemical device, a structurally stable, uniform solid electrolyte interface film with a thickness of tens of nanometers can be formed on the surface of the positive electrode active material. The formation of this film can reduce the oxidative decomposition of the electrolyte, and by capturing gas molecules on the interface, reduce the temperature rise of the electrochemical device under fast charging test, thereby improving the fast charging performance and high-temperature cycle stability of the electrochemical device.

[0163] Optionally, 3.5≤A / B≤7.25. By further adjusting the ratio between 1,3-propane sultone and vinyl sulfate, the temperature rise of the electrochemical device during a fast charge test can be more effectively reduced, thereby improving the fast charge performance and high-temperature cycle stability of the electrochemical device.

[0164] More preferably, 4.0≤A / B≤6.5. By further adjusting the ratio between 1,3-propane sultone and vinyl sulfate, the temperature rise of the electrochemical device during fast charge testing can be further reduced, thereby improving the fast charge performance and high-temperature cycle stability of the electrochemical device.

[0165] Optionally, the mass fraction of 1,3-propane sultone in the total mass of the electrolyte is 1.6% to 6.4%, optionally 2.8% to 5.8%, or 3.2% to 5.2%.

[0166] The electrolyte solution can be prepared according to conventional methods in the art. For example, the solvent, electrolyte salt, and optional additives can be mixed uniformly to obtain the electrolyte solution. The order of adding the materials is not particularly limited. For example, the electrolyte salt and optional additives can be added to the solvent and mixed uniformly to obtain the electrolyte solution.

[0167] The components and their contents in the electrolyte can be determined by conventional methods in the art, for example, by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0168] [Positive electrode]

[0169] The material, composition and manufacturing method of the positive electrode sheet may include any technology known in the prior art.

[0170] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0171] In some embodiments, the shape of the positive electrode current collector may be plate-shaped or foil-shaped, which is not limited in the embodiments of the present application.

[0172] In some embodiments, the thickness of the positive electrode current collector may be 6 μm to 25 μm.

[0173] In some embodiments, the material of the positive electrode current collector is not particularly limited, and a material having electronic conductivity can be selected. For example, a single element or an alloy (e.g., stainless steel) containing at least one of C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al can be used.

[0174] From the viewpoint of high conductivity, high stability in the electrolyte and good oxidation resistance, C layer, Al foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production cost, Al foil is optional. Those skilled in the art can adjust according to actual conditions.

[0175] The positive electrode active material layer includes a positive electrode active material, which may be selected from materials capable of absorbing and releasing lithium.

[0176] The specific type of the positive electrode active material is not specifically limited and can be selected according to requirements. As an example, the positive electrode active material may include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide, layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium-rich materials (such as lithium-rich nickel cobalt manganese oxide), manganese dioxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and at least one of their respective modified compounds. These materials can be used alone or in combination of two or more.

[0177] Optionally, the positive electrode active material may include at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, spinel-type lithium nickel manganese oxide, and their respective modified compounds.

[0178] As an example, the molecular formula of lithium nickel cobalt aluminum oxide may be LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, and for example, it may include, but is not limited to, LiNi 0.8 Co 0.15 Al 0.05 O2.

[0179] As an example, the molecular formula of lithium nickel cobalt manganese oxide may be LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, and for example, it may include, but is not limited to, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn0.1 At least one of O2.

[0180] As an example, spinel-type lithium nickel manganese oxide may include but is not limited to LiNi 0.5 Mn 1.5 O4.

[0181] The modified compounds of the above-mentioned positive electrode active materials can be used to modify the positive electrode active materials by doping, surface coating, or both doping and coating.

[0182] In some embodiments, the powder volume resistivity of the positive electrode active material at 15 MPa can be 100 kΩ·cm to 450 kΩ·cm, for example, 100 kΩ·cm, 150 kΩ·cm, 200 kΩ·cm, 250 kΩ·cm, 300 kΩ·cm, 350 kΩ·cm, 400 kΩ·cm, 450 kΩ·cm, or a range consisting of any of the foregoing values. When the positive electrode active material has a powder volume resistivity within this range, the lithium ion migration between the positive and negative electrodes can be maintained at a suitable rate, thereby effectively improving the low-temperature cycling performance of the electrochemical device.

[0183] The volume resistivity of the positive electrode active material powder at 15 MPa can be measured using a four-probe method. For example, the test method may include the following steps: placing a 2g sample on a sample table, applying a pressure of 15 MPa to the powder using a press, and then reading the test result using a powder resistivity tester after the powder stabilizes.

[0184] The positive electrode active material sample can be obtained as follows: fully discharge the electrochemical device, disassemble and remove the positive electrode sheet, dry the positive electrode sheet, use a scraper to scrape an appropriate amount of powder from the positive electrode current collector, dry the scraped powder, and take an appropriate amount to test the powder volume resistivity.

[0185] In some embodiments, the porosity of the positive active material layer may be 20% to 35%.

[0186] In some embodiments, the thickness of the positive electrode active material layer may be 15 μm to 150 μm, which is not limited in the present embodiment. The thickness of the positive electrode active material layer refers to the thickness of the positive electrode active material layer located on a single side of the positive electrode current collector.

[0187] In some embodiments, the positive electrode active material layer may include a positive electrode conductive agent. The positive electrode conductive agent may include conductive carbon powder. As an example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube (CNT). These materials may be used alone or in combination of two or more.

[0188] In some embodiments, the positive electrode active material layer may include a positive electrode binder. The positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinyl alcohol (PVA).

[0189] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode active material and optional positive electrode conductive agent, positive electrode binder, etc. are dispersed in a solvent to form a positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. The positive electrode sheet is obtained through processes such as drying and compaction. The solvent can be N-methylpyrrolidone (NMP), but the present application is not limited thereto.

[0190] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0191] [Negative electrode]

[0192] The material, composition and manufacturing method of the negative electrode sheet may include any technology known in the prior art.

[0193] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0194] In some embodiments, the negative electrode current collector may be in the shape of a plate or foil, which is not limited in the embodiments of the present application.

[0195] In some embodiments, the thickness of the negative electrode current collector may be 4 μm to 25 μm.

[0196] In some embodiments, the negative electrode current collector material is not particularly limited, and materials with good electronic conductivity can be selected. For example, a single element or alloy (such as stainless steel) containing at least one of C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Ag can be used. Alternatively, a composite material can be formed by plating a conductive material with a different conductive material, such as Fe plated with Cu.

[0197] From the viewpoint of high conductivity, high stability in electrolyte and good oxidation resistance, Cu foil, Ni foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production cost, Cu foil and Ni foil are optional. Those skilled in the art can adjust according to actual conditions.

[0198] The negative electrode active material layer includes a negative electrode active material, which may include at least one of a carbon material and a silicon-based material.

[0199] The weight content of the silicon-based material in the negative electrode active material may be 0% to 25%. A weight content of the silicon-based material of 0% indicates that the negative electrode active material does not contain the silicon-based material.

[0200] As an example, the carbon material may include natural graphite, artificial graphite, or a mixture thereof.

[0201] As an example, the silicon-based material may include at least one of elemental silicon, silicon oxide, a silicon-carbon composite material, and a silicon alloy.

[0202] In some embodiments, the porosity of the negative active material layer may be 25% to 45%.

[0203] In some embodiments, the thickness of the negative electrode active material layer may be 30 μm to 150 μm, which is not limited in the present embodiment. The thickness of the negative electrode active material layer refers to the thickness of the negative electrode active material layer located on one side of the negative electrode current collector.

[0204] In some embodiments, the negative electrode active material layer may include a negative electrode conductive agent. The negative electrode conductive agent may include conductive carbon powder. As an example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube (CNT). These materials may be used alone or in combination of two or more.

[0205] In some embodiments, the negative electrode active material layer may include a negative electrode binder. The negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), acrylonitrile copolymers (e.g., LA-type water-based binders, optionally LA132 or LA133), polyacrylic acid (PAA) and its salts, styrene-acrylic resin, polyvinyl alcohol (PVA), and their respective derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0206] In some embodiments, the negative electrode active material layer may further include a negative electrode dispersant, thereby improving the film-forming quality of the negative electrode active material layer. As an example, the negative electrode dispersant may include, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC) and its derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups (e.g., amino groups).

[0207] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode active material and optional negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are dispersed in a solvent to form a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector and subjected to drying, compaction, and other processes to produce the negative electrode sheet. The solvent may include, but is not limited to, at least one of water, ethanol, acetone, butanone, dimethylformamide, N-methylpyrrolidone, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran.

[0208] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0209] The negative electrode sheets provided in the embodiments of the present application do not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode active material layer; in some embodiments, the negative electrode sheet may further include a protective layer covering the surface of the negative electrode active material layer.

[0210] electronic devices

[0211] In a third aspect, an embodiment of the present application further provides an electronic device, which includes the electrochemical device of the second aspect of the embodiment of the present application.

[0212] The electronic devices provided in the embodiments of the present application are not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic devices can include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0213] Example

[0214] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0215] Test section

[0216] (1) Volume distribution particle size test of filler particles

[0217] The volume distribution particle size of the filler particles is tested with reference to GB / T 19077-2016. The testing equipment may be a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0218] Dv10 indicates the particle size at which 10% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv50 indicates the particle size at which 50% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv90 indicates the particle size at which 90% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0219] (2) Diaphragm pore size test

[0220] The pore size distribution curve of the diaphragm can be obtained by the pore size tester to obtain the maximum pore size D of the diaphragm. max , minimum aperture D min , average pore diameter D avg The ratio of the total pore area of ​​pores with a pore size of 30 nm to 45 nm to the total pore area of ​​the separator was measured. The instrument model was a CFP-1500AE lithium membrane through-hole tester. The infiltration fluid was GalWick. The separator sample was a 24 mm diameter disc.

[0221] (3) Thermal shrinkage test of diaphragm

[0222] Cut the diaphragm into samples with a length of 70 mm in the MD direction and 50 mm in the TD direction, fix the four corners of the sample on a piece of paper with tape, and then bake the above sample in a 130°C oven for 1 hour. After the baking, take out the sample and measure the length L1 of the diaphragm in the MD direction and the length L2 in the TD direction.

[0223] The thermal shrinkage rate of the separator in the MD direction = (70-L1) / 70×100%.

[0224] The thermal shrinkage rate of the separator in the TD direction = (50-L2) / 50×100%.

[0225] To ensure the accuracy of the above test results, 5 samples were taken for testing in each embodiment and comparative example, and the average value was taken as the test result.

[0226] (4) Porosity test of the diaphragm after heating at 130℃ / 1h

[0227] The diaphragm was cut into samples with a length of 70 mm in the MD direction and 50 mm in the TD direction. The four corners of the sample were fixed on a piece of paper with tape. Then the sample was placed in an oven at 130°C and baked for 1 hour. After that, the diaphragm was taken out and the porosity was tested.

[0228] The porosity of the diaphragm is tested using a true density meter. The heated diaphragm is punched into a regular sample and placed on the true density meter to determine the true volume of the diaphragm. The length, width, and height of the sample are measured with a ruler to calculate the apparent volume of the diaphragm. Diaphragm porosity (%) = (apparent volume of diaphragm - true volume of diaphragm) / apparent volume of diaphragm × 100%. The test instrument is an AccuPyc II 1340 true density meter.

[0229] (5) Low temperature cycle performance test of lithium-ion batteries

[0230] The lithium-ion battery was placed at -10°C for 60 minutes, then charged at a constant current rate of 2C to a full charge voltage of 4.25V. The battery was then charged at a constant voltage of 4.25V to a cutoff current of 0.02C. After 5 minutes of rest, the battery was discharged at a constant current rate of 0.5C to 3.0V. This constituted one charge-discharge cycle, and the discharge capacity at the first cycle was recorded. The lithium-ion battery was cycled 500 times using the above steps, and the discharge capacity after 500 cycles was recorded.

[0231] The cycle capacity retention rate of the lithium-ion battery after 500 cycles at -10°C = (discharge capacity after 500 cycles / discharge capacity at the first cycle) × 100%.

[0232] (6) High temperature cycle performance test of lithium-ion batteries

[0233] The lithium-ion battery was left at rest for 60 minutes at 45°C, then charged at a constant current rate of 2C to a full charge voltage of 4.25V. The battery was then charged at a constant voltage of 4.25V to a cutoff current of 0.02C. After resting for 5 minutes, the battery was discharged at a constant current rate of 0.5C to 3.0V. This constituted one charge-discharge cycle, and the discharge capacity at the first cycle was recorded. The lithium-ion battery was cycled 450 times using the above steps, and the discharge capacity after 450 cycles was recorded.

[0234] The cycle capacity retention rate of the lithium-ion battery after 450 cycles at 45° C. = (discharge capacity after 450 cycles / discharge capacity at the first cycle)×100%.

[0235] (7) Hot box performance test of lithium-ion batteries

[0236] At 25°C, charge the lithium-ion battery at a constant current rate of 0.5C to a full charge voltage of 4.25V. Continue charging at a constant voltage of 4.25V to a cutoff current of 0.02C, bringing it to a fully charged state. Inspect the appearance to ensure that the lithium-ion battery is in normal use. Place the fully charged battery in an oven and increase the temperature at a rate of 5°C / min until it reaches the specified hot box test temperature of 130°C. Maintain the temperature for one hour, observing the condition of the lithium-ion battery during this process.

[0237] The criteria for lithium-ion batteries to pass the hot box test are: the lithium-ion batteries do not catch fire or explode.

[0238] Hot box test pass rate = number of lithium-ion batteries that passed the hot box test / total number of lithium-ion batteries.

[0239] (8) Fast charging temperature rise test of lithium-ion batteries

[0240] At 25°C, the lithium-ion battery was fast charged, first at a constant current of 8C to a full charge voltage of 4.25V, and then continued to charge at a constant voltage of 4.25V to a cutoff current of 0.02C. The surface temperature rise of the lithium-ion battery during fast charging was monitored and the maximum temperature rise value was recorded.

[0241] Example 1-1

[0242] (1) Preparation of diaphragm

[0243] Preparation of porous substrates

[0244] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-material weight ratio of 65:35 to obtain a mixture 1.

[0245] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 65:35 to obtain a mixture 2.

[0246] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0247] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0248] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 115° C. to obtain a porous substrate.

[0249] Preparation of porous coating slurry

[0250] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0251] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0252] (2) Preparation of negative electrode sheet

[0253] Artificial graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5. Deionized water was then added as a solvent to create a slurry with a solids content of 70%, which was then stirred thoroughly. The slurry was evenly coated on one surface of an 8μm-thick copper foil. After drying at 110°C and cold pressing, a single-sided negative electrode sheet with a 150μm-thick negative electrode active material layer was obtained. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet. The negative electrode sheet was cut into 80mm x 880mm dimensions and the tabs were welded before use.

[0254] (3) Preparation of positive electrode sheet

[0255] LiCoO2, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) was then added as a solvent to form a slurry with a solid content of 75%, which was then stirred evenly. The slurry was evenly coated on one surface of a 12μm thick aluminum foil. After drying at 90°C and cold pressing, a single-sided positive electrode sheet with a positive electrode active material layer thickness of 100μm was obtained. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet. The positive electrode sheet was cut into a size of 74mm×867mm and the tabs were welded before use.

[0256] (4) Preparation of electrolyte

[0257] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2, and then LiPF6 was added and mixed uniformly to obtain an electrolyte. The mass fraction of LiPF6 in the electrolyte was 8%.

[0258] (5) Preparation of lithium-ion batteries

[0259] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, the porous coating of the separator is brought into contact with the positive electrode sheet, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and the prepared electrolyte is injected. After vacuum packaging, static standing, hot pressing, and shaping, a soft-pack lithium-ion battery is obtained.

[0260] Example 1-2

[0261] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0262] (1) Preparation of diaphragm

[0263] Preparation of porous substrates

[0264] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 68:32 to obtain a mixture 1.

[0265] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-material weight ratio of 68:32 to obtain a mixture 2.

[0266] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0267] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0268] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 115° C. to obtain a porous substrate.

[0269] Preparation of porous coating slurry

[0270] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0271] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0272] Examples 1-3

[0273] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0274] (1) Preparation of diaphragm

[0275] Preparation of porous substrates

[0276] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 75:25 to obtain a mixture 1.

[0277] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 75:25 to obtain a mixture 2.

[0278] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0279] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0280] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0281] Preparation of porous coating slurry

[0282] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.5μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0283] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0284] Examples 1-4

[0285] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0286] (1) Preparation of diaphragm

[0287] Preparation of porous substrates

[0288] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 1.

[0289] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 2.

[0290] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0291] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0292] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0293] Preparation of porous coating slurry

[0294] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 92:8. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0295] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0296] Examples 1-5

[0297] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0298] (1) Preparation of diaphragm

[0299] Preparation of porous substrates

[0300] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 1.

[0301] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 2.

[0302] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0303] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0304] The porous substrate intermediate was stretched twice in the transverse direction by 1.5 times at 110° C., and then heat-set and rolled at 108° C. to obtain a porous substrate.

[0305] Preparation of porous coating slurry

[0306] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 93:7. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 1.5μm, Dv10 of 0.5μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1,000,000, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0307] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0308] Examples 1-6

[0309] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0310] (1) Preparation of diaphragm

[0311] Preparation of porous substrates

[0312] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0313] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0314] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0315] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0316] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0317] Preparation of porous coating slurry

[0318] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 85:15. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 4μm, Dv90 of 6μm, Dv10 of 1.2μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0319] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0320] Examples 1-7

[0321] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0322] (1) Preparation of diaphragm

[0323] Preparation of porous substrates

[0324] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 75:25 to obtain a mixture 1.

[0325] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 75:25 to obtain a mixture 2.

[0326] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0327] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0328] The porous substrate intermediate was stretched twice in the transverse direction by 1.5 times at 110° C., and then heat-set and rolled at 112° C. to obtain a porous substrate.

[0329] Preparation of porous coating slurry

[0330] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 2. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0331] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0332] Examples 1-8

[0333] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0334] (1) Preparation of diaphragm

[0335] Preparation of porous substrates

[0336] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-material weight ratio of 65:35 to obtain a mixture 1.

[0337] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 65:35 to obtain a mixture 2.

[0338] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0339] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0340] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 115° C. to obtain a porous substrate.

[0341] Preparation of porous coating slurry

[0342] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 90:10. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 5. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0343] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0344] Examples 1-9

[0345] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0346] (1) Preparation of diaphragm

[0347] Preparation of porous substrates

[0348] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 1.

[0349] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 77:23 to obtain a mixture 2.

[0350] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0351] The membrane was stretched to 7 times in the longitudinal direction and 7 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0352] The porous substrate intermediate was stretched twice in the transverse direction by 1.5 times at 110° C., and then heat-set and rolled at 113° C. to obtain a porous substrate.

[0353] Preparation of porous coating slurry

[0354] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0355] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0356] Examples 1-10

[0357] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0358] (1) Preparation of diaphragm

[0359] Preparation of porous substrates

[0360] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 78:22 to obtain a mixture 1.

[0361] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 78:22 to obtain a mixture 2.

[0362] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0363] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0364] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0365] Preparation of porous coating slurry

[0366] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 90:10. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0367] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0368] Examples 1-11

[0369] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0370] (1) Preparation of diaphragm

[0371] Preparation of porous substrates

[0372] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0373] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0374] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0375] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0376] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0377] Preparation of porous coating slurry

[0378] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 3.5μm, Dv90 of 5.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1.5, and the Dv50 is 1.3μm.

[0379] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0380] Examples 1-12

[0381] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0382] (1) Preparation of diaphragm

[0383] Preparation of porous substrates

[0384] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0385] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0386] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0387] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0388] The porous substrate intermediate was stretched twice in the transverse direction by 1.5 times at 110° C., and then heat-set and rolled at 108° C. to obtain a porous substrate.

[0389] Preparation of porous coating slurry

[0390] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 4μm, Dv90 of 6μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0391] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0392] Comparative Example 1-1

[0393] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0394] (1) Preparation of diaphragm

[0395] Preparation of porous substrates

[0396] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 55:45 to obtain a mixture 1.

[0397] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 55:45 to obtain a mixture 2.

[0398] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0399] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0400] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 115° C. to obtain a porous substrate.

[0401] Preparation of porous coating slurry

[0402] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1:0.7, and the Dv50 is 1μm.

[0403] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0404] Comparative Example 1-2

[0405] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0406] (1) Preparation of diaphragm

[0407] Preparation of porous substrates

[0408] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-material weight ratio of 85:15 to obtain a mixture 1.

[0409] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 85:15 to obtain a mixture 2.

[0410] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0411] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0412] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 115° C. to obtain a porous substrate.

[0413] Preparation of porous coating slurry

[0414] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 5μm, Dv90 of 7μm, Dv10 of 2μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1,000,000, the aspect ratio is 1.7, and the Dv50 is 2.5μm.

[0415] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0416] Comparative Examples 1-3

[0417] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0418] (1) Preparation of diaphragm

[0419] Preparation of porous substrates

[0420] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0421] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0422] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0423] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0424] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 130° C. to obtain a porous substrate.

[0425] Preparation of porous coating slurry

[0426] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 99:1. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 4.5μm, Dv90 of 6.5μm, Dv10 of 1.4μm, and an aspect ratio of 6. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0427] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0428] Comparative Examples 1-4

[0429] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0430] (1) Preparation of diaphragm

[0431] Preparation of porous substrates

[0432] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0433] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0434] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0435] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0436] The porous substrate intermediate was stretched transversely for a second time by 1.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0437] Preparation of porous coating slurry

[0438] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 78:22. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0439] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0440] Comparative Examples 1-5

[0441] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0442] (1) Preparation of diaphragm

[0443] Preparation of porous substrates

[0444] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0445] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0446] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0447] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0448] The porous substrate intermediate was stretched twice in the transverse direction by 0.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0449] Preparation of porous coating slurry

[0450] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0451] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0452] Comparative Examples 1-6

[0453] Except for the different preparation parameters of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0454] (1) Preparation of diaphragm

[0455] Preparation of porous substrates

[0456] Paraffin oil and PE particles with a weight average molecular weight of 1.2 million to 1.4 million were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 1.

[0457] Paraffin oil and PE particles with a weight average molecular weight of 300,000 to 500,000 were mixed at an oil-to-fuel weight ratio of 80:20 to obtain a mixture 2.

[0458] Mixture 1 and mixture 2 were added to the two grinding heads of a twin-grinding extruder, extruded through a two-layer die, cooled on a casting roll, and finally mixed to form a film. The mass ratio of mixture 1 to mixture 2 was 45:55.

[0459] The membrane was stretched to 6 times in the longitudinal direction and 6 times in the transverse direction at 105° C., and then extracted with dichloromethane at 25° C. for 0.6 h. After drying, a porous substrate intermediate was obtained.

[0460] The porous substrate intermediate was stretched twice in the transverse direction by 2.5 times at 110° C., and then heat-set and rolled at 110° C. to obtain a porous substrate.

[0461] Preparation of porous coating slurry

[0462] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1.2μm, Dv90 of 3.5μm, Dv10 of 1μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0463] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0464] Table 1

[0465] From the test results in Table 1, it can be seen that by making the diaphragm meet D max 35nm to 75nm, D min 10nm to 20nm, D avg 25nm to 45nm, D max / D avg The diaphragm has a pore size of 1.20 to 2.99, which can make the pore size of the diaphragm present a non-uniform characteristic, thereby balancing the mobility of lithium ions on the positive electrode side of the diaphragm and the mobility of lithium ions on the negative electrode side of the diaphragm, thereby facilitating the smooth embedding of lithium ions into the negative electrode and effectively reducing the problem of purple lithium precipitation at the negative electrode. Therefore, the diaphragm provided in the embodiment of the present application can enable the lithium-ion battery to have good low-temperature cycle performance. The diaphragm provided in the embodiment of the present application also has a low thermal shrinkage rate, thereby also enabling the lithium-ion battery to have good high-temperature stability and reliability.

[0466] It can also be seen from the test results of Examples 1-1 to 1-12 that by further adjusting D max / D avg 、D min / D avg , and / or D max / D min range, which can better balance the low-temperature cycle performance and high-temperature stability of lithium-ion batteries.

[0467] Example 2-1

[0468] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0469] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 80:3:17. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0470] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0471] Example 2-2

[0472] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0473] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 86:4:10. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0474] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0475] Example 2-3

[0476] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0477] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 90:2:8. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0478] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0479] Examples 2-4

[0480] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0481] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 75:5:20. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0482] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0483] Examples 2-5

[0484] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0485] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 95:1:4. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0486] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0487] Examples 2-6

[0488] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0489] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 68:7:25. The weight average molecular weight of the binder is 900,000-1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0490] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0491] Table 2

[0492] From the test results in Table 2, it can be seen that by further adjusting the types and mass ratios of monomers without ester groups and monomers containing ester groups in the binder, the lithium-ion battery can have better high-temperature cycle performance and hot box performance.

[0493] Example 3-1

[0494] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0495] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 1.5 million to 1.6 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0496] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0497] Example 3-2

[0498] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0499] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 500,000 to 600,000, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0500] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0501] Example 3-3

[0502] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0503] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following three monomers: styrene, methyl methacrylate and isooctyl acrylate, and the mass ratio of the three monomers is 76.6:3.8:19.6. The weight average molecular weight of the binder is 1.9 million to 2 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0504] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0505] Table 3

[0506] From the test results in Table 3, it can be seen that by further adjusting the weight-average molecular weight of the binder, the lithium-ion battery can have better high-temperature cycle performance and hot box performance.

[0507] Example 4-1

[0508] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0509] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0510] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0511] Example 4-2

[0512] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0513] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 2:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0514] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0515] Example 4-3

[0516] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0517] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 3:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0518] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0519] Example 4-4

[0520] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0521] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 4:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0522] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0523] Examples 4-5

[0524] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0525] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 5:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0526] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 5 μm.

[0527] Table 4

[0528] From the test results in Table 4, it can be seen that by further adjusting the types and mass ratios of monomers without ester groups and monomers containing ester groups in the binder, the lithium-ion battery can have better high-temperature cycle performance and hot box performance.

[0529] Example 5-1

[0530] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0531] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0532] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating was 3 μm.

[0533] Example 5-2

[0534] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0535] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0536] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating was 8 μm.

[0537] Example 5-3

[0538] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0539] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0540] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating was 10 μm.

[0541] Example 5-4

[0542] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0543] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0544] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating layer was 12 μm.

[0545] Example 5-5

[0546] Except for the different preparation parameters of the porous coating layer of the separator, the rest of the preparation process is the same as that of Example 1-1.

[0547] The filler particles and the binder are first mixed in proportion, and then deionized water is added and stirred evenly to form a porous coating slurry. The solid content of the porous coating slurry is about 40%, and the viscosity is about 30mPa·s. The weight ratio of the filler particles and the binder is 95:5. The filler particles are boehmite particles with a volume distribution particle size Dv50 of 1μm, Dv90 of 2μm, Dv10 of 0.6μm, and an aspect ratio of 3.0. The binder includes a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is 1:1. The weight average molecular weight of the binder is 900,000 to 1 million, the aspect ratio is 1, and the Dv50 is 1.3μm.

[0548] The porous coating slurry was coated on one side of a porous substrate and dried in vacuum at 60° C. to 70° C. to obtain a separator. The thickness of the porous coating was 1.8 μm.

[0549] Table 5

[0550] It can be seen from the test results in Table 5 that by further adjusting the thickness of the porous coating, the lithium-ion battery can have better high-temperature cycle performance and hot box performance.

[0551] Examples 6-1 to 6-17

[0552] Examples 6-1 to 6-17 were prepared based on Example 1-1, except that 1,3-propane sultone and vinyl sulfate, as shown in Table 6, were further added to the electrolyte of Example 1-1. In Table 6, A represents the mass fraction of 1,3-propane sultone in the total mass of the electrolyte, and B represents the mass fraction of vinyl sulfate in the total mass of the electrolyte.

[0553] Table 6

[0554] It can be seen from the test results in Table 6 that by further adjusting the mass ratio of 1,3-propane sultone to vinyl sulfate in the electrolyte, the maximum temperature rise of the lithium-ion battery under the fast charge test can be reduced, thereby improving the fast charge performance and high-temperature cycle stability of the lithium-ion battery.

[0555] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A separator, comprising a porous substrate and a porous coating located on at least one side of the porous substrate, characterized in that, the porous coating comprises filler particles and a binder; The maximum pore diameter of the diaphragm is denoted as D max , the minimum pore diameter is denoted as D min , the average pore diameter is denoted as D avg , and the unit is nm for all. D max is from 35 nm to 75 nm, D min is from 10 nm to 20 nm, D avg is from 25 nm to 45 nm, D max / D avg is from 1.20 to 2.

99.

2. The diaphragm according to claim 1, wherein, D max / D avg is from 1.20 to 2.62, and / or, D min / D avg is from 0.35 to 0.

59.

3. The diaphragm according to claim 2, wherein D max / D avg is from 1.60 to 2.23, and / or, D min / D avg is from 0.43 to 0.

57.

4. The diaphragm according to any one of claims 1 to 3, characterized in that, D max / D min is from 3.39 to 6.

05.

5. The diaphragm according to claim 4, characterized in that, D max / D min is from 3.67 to 4.

54.

6. The diaphragm according to claim 1, wherein the total pore area of the pores with a pore diameter of 30 nm to 45 nm in the separator accounts for 10% to 35% of the total pore area of the separator.

7. The diaphragm according to claim 6, characterized in that, the total pore area of the pores with a pore diameter of 30 nm to 45 nm in the separator accounts for 14% to 27% of the total pore area of the separator.

8. The diaphragm according to claim 1, characterized in that, the porous substrate satisfies at least one of the following conditions (1) to (3): (1) The porosity of the porous substrate is 20% to 50%; (2) The average pore diameter of the porous substrate is 30 nm to 60 nm; (3) The thickness of the porous substrate is 4 μm to 15 μm.

9. The diaphragm according to claim 1, characterized in that, the separator satisfies at least one of the following conditions (1) to (4): (1) The porosity of the separator after being heated at 130 °C for 1 h is 30% to 60%; (2) The areal density of the separator is 1 g / m 2 to 5 g / m 2 ; (3) The total thickness of the separator is 10 μm to 17 μm; (4) The thickness of the porous coating is 2 μm to 10 μm.

10. The diaphragm according to claim 1, wherein the filler particles comprise at least one of organic particles and inorganic particles.

11. The separator according to claim 10, characterized in that, the organic particles comprise vinylidene fluoride resin particles, and the volume distribution particle sizes Dv50 of the organic particles are 0.8 μm to 2 μm, Dv90 are 1.5 μm to 4 μm, and Dv10 are 0.1 μm to 1.8 μm; and / or, the inorganic particles comprise ceramic particles, and the volume distribution particle sizes Dv50 of the inorganic particles are 1 μm to 4 μm, Dv90 are 2 μm to 6 μm, and Dv10 are 0.6 μm to 1.2 μm.

12. The separator according to any one of claims 10 to 11, characterized in that, the aspect ratio of the organic particles is (1 - 1.5):1; and / or, the aspect ratio of the inorganic particles is (2 - 5):

1.

13. The diaphragm according to claim 1, characterized in that, the binder comprises a copolymer containing at least two structural units, and the at least two structural units are both derived from monomers containing unsaturated double bonds. At least one of the monomers containing unsaturated double bonds contains an ester group, and at least one does not contain an ester group. The weight average molecular weight of the binder is 800,000 to 1,800,000; the monomers containing an ester group comprise at least one of methyl methacrylate, ethyl methacrylate, isooctyl acrylate, n-propyl acrylate, butyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate; the monomers not containing an ester group comprise at least one of styrene, butadiene, methacrylamide, acrylamide, and acrylonitrile.

14. The diaphragm according to claim 13, characterized in that, the binder comprises a copolymer formed by the following three monomers: styrene, methyl methacrylate, and isooctyl acrylate. Based on the total mass of the three monomers being 100 parts, the mass of styrene is 75 parts to 90 parts, the mass of methyl methacrylate is 2 parts to 5 parts, and the balance is isooctyl acrylate.

15. The diaphragm according to claim 14, characterized in that, the binder comprises a copolymer formed by the following two monomers: styrene and butyl acrylate, and the mass ratio of the two monomers is (1 - 5):

1.

16. An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, characterized in that, the separator comprises the separator according to any one of claims 1 to 15.

17. The electrochemical device according to claim 16, wherein The electrolyte contains 1,3 - propane sultone and vinylene sulfate. The mass fraction of 1,3 - propane sultone in the total mass of the electrolyte is A, and the mass fraction of vinylene sulfate in the total mass of the electrolyte is B, where 2.0 ≤ A / B ≤ 8.

0.

18. The electrochemical device according to claim 17, wherein, 3.5 ≤ A / B ≤ 7.

25.

19. The electrochemical device according to claim 18, characterized in that, 4.0 ≤ A / B ≤ 6.

5.

20. The electrochemical device according to any one of claims 16 to 19, characterized in that, The positive electrode plate includes a positive electrode active material, and the powder volume resistivity of the positive electrode active material under 15 MPa is from 100 KΩ·cm to 450 KΩ·cm.

21. An electronic device, characterized in that, An electrochemical device according to any one of claims 16 to 20.

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