Battery diaphragm, secondary battery and electric device

Abstract

The invention provides a battery diaphragm, a secondary battery and an electric device, and belongs to the technical field of batteries. The battery diaphragm comprises a porous base membrane, and the porous base membrane comprises polyether sulfone, a low-melting-point polymer, a reaction type compatilizer and nano ceramic particles; the melting point of the low-melting-point polymer is 100-160 DEG C, and the reactive compatilizer enables the polyether sulfone and the low-melting-point polymer to form an interpenetrating network structure; through interaction of the components, the battery diaphragm not only has relatively good electrolyte wettability, but also can realize in-advance hole closing at low temperature and complete structure at high temperature, and avoids contact short circuit of positive and negative electrodes, so that the safety of a secondary battery is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery separator, a secondary battery and a power utilization device. BACKGROUND

[0002] Traditional polyolefin separators have poor thermal stability and poor wetting effect, which to some extent affects the safety and cycle performance of secondary batteries. Polyarylether sulfone (PSF) is a thermoplastic polymer material with high glass transition temperature (190-225℃), high decomposition temperature (>400℃) and excellent thermal stability, and also has good mechanical properties and processing properties. Polyarylether sulfone has good film-forming performance and chemical stability. Due to the presence of polar groups such as sulfone groups (-SO2-) in the molecule, it has good wetting properties for polar electrolyte; the benzene ring and sulfone group ensure the rigidity of the molecular chain, and endow polyarylether sulfone with good mechanical properties and heat resistance; the ether bond in the main chain provides good flexibility for the polymer molecular chain. Polyarylether sulfone has excellent chemical stability and can exist stably in common organic solvents, so it can be used as a new type of high-temperature-resistant lithium ion battery separator to ensure that the battery separator will not break and cause the positive and negative electrodes to come into contact. However, the complete pore structure of the polyarylether sulfone separator at high temperature will also cause the continuous passage of Li ions, causing the positive and negative electrodes to continue to react, and the temperature to continue to rise, and various side reactions to continue to occur, leading to thermal runaway. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provides a battery separator, a secondary battery and a power utilization device.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: in the first aspect, a battery separator is provided, which comprises a porous base film, the porous base film comprises polyarylether sulfone, a low-melting-point polymer, a reactive compatibilizer and nano ceramic particles; the melting point of the low-melting-point polymer is 100-160℃, and the reactive compatibilizer forms a network structure penetrating each other between the polyarylether sulfone and the low-melting-point polymer.

[0005] In some embodiments, the mass ratio of the polyarylether sulfone to the low-melting-point polymer is (50-70):(24-38).

[0006] In some embodiments, the mass ratio of the polyarylether sulfone to the reactive compatibilizer is (50-70):(4-7).

[0007] In some embodiments, the mass ratio of the polyarylether sulfone to the nano ceramic particles is (50-70):(2-5).

[0008] In some embodiments, the low-melting-point polymer comprises at least one of polyethylene, thermoplastic polyurethane, polylactic acid, polybutylene succinate, polybutylene adipate / terephthalate, copolymer nylon.

[0009] In some embodiments, the reactive compatibilizer comprises a polymer comprising at least one functional group of maleic anhydride group, epoxy group, oxazoline group, isocyanate group.

[0010] In some embodiments, the nano-ceramic particle comprises at least one of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, zinc oxide, barium oxide, magnesium oxide, beryllium oxide, calcium oxide, thorium oxide, aluminum nitride, titanium nitride, brucite, apatite, aluminum hydroxide, magnesium hydroxide, barium sulfate, boron nitride, silicon carbide, silicon nitride, cubic boron nitride, hexagonal boron nitride, graphite, graphene.

[0011] In some embodiments, the nano-ceramic particle has an elastic modulus ≥ 300 GPa.

[0012] In some embodiments, the nano-ceramic particle has an average particle size ≤ 100 nm.

[0013] In some embodiments, the porous base film has a closed pore temperature of 100-160 °C, and a film breaking temperature of 180-350 °C.

[0014] In some embodiments, the porous base film has a thickness of 5-30 μm.

[0015] In some embodiments, the porous base film has a porosity of 30-60 %.

[0016] In some embodiments, the porous base film has a longitudinal shrinkage of ≤ 5 % and a transverse shrinkage of ≤ 5 % at 180 °C for 1 h.

[0017] In some embodiments, the porous base film has a transverse tensile strength ≥ 200 MPa and a longitudinal tensile strength ≥ 250 MPa.

[0018] In some embodiments, the porous base film has a puncture strength > 400 gf.

[0019] In some embodiments, the battery separator further comprises an organic coating layer covering at least one side surface of the porous base film.

[0020] In some embodiments, the organic coating layer comprises a first polymer; the first polymer comprises a homopolymer or copolymer of at least one monomer of ethylene, propylene, vinylidene fluoride, hexafluoropropylene, acrylic acid, acrylic ester, vinyl acetate, styrene, acrylonitrile, maleic anhydride, vinyl chloride, chloropropylene.

[0021] In a second aspect, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and the battery separator, which is located between the positive electrode sheet and the negative electrode sheet.

[0022] In a third aspect, a power device is provided, comprising the secondary battery.

[0023] Compared with the prior art, the battery separator has the following beneficial effects: the battery separator can balance the pores by adding a low-melting polymer to the polyarylether sulfone to form pores together, and can timely close the pore structure to prevent the positive and negative electrode reactions when the secondary battery is in thermal runaway by using the low melting point of the low-melting polymer. The thermodynamic difference between the polyarylether sulfone and the low-melting polymer leads to a weak interface bonding strength between the two, and the reactive compatibilizer can form a "bridging" effect by being respectively affined to the polyarylether sulfone and the low-melting polymer through molecular segments, thereby reducing the interface separation between the polyarylether sulfone and the low-melting polymer. The nano ceramic particles can prevent the stress generated when the low-melting polymer melts and prevent the structure of the polyarylether sulfone from collapsing. Moreover, the nano ceramic particles are filled at the interface between the polyarylether sulfone and the low-melting polymer, thereby buffering the stress concentration when the pores are closed and preventing brittle fracture of the battery separator. The battery separator not only has good electrolyte wettability, but also can realize early closing of the pores at low temperature, complete structure at high temperature, and avoidance of short circuit of the positive and negative electrodes, thereby effectively improving the safety of the secondary battery. DETAILED DESCRIPTION

[0024] For the purpose of promoting an understanding of the application, the application will be described in greater detail below. However, the application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the application.

[0025] As used herein the terms "a", "an" and "the" mean "one or more".

[0026] "Made from" is synonymous with "comprising". The terms "comprising", "including", "having" and "containing" and any variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0027] The conjunctive word "comprising" excludes any element, step, or ingredient not specified. If used in a claim, the phrase "comprising" will be construed to implicate a closed-ended limitation that does not invoke 35 U.S.C. § 112(f) unless otherwise specifically recited. The transitional phrase "consisting of" excludes any element, step, or ingredient not specified. If used in a claim, the phrase "consisting of" will be construed to implicate a closed-ended limitation that does not invoke 35 U.S.C. § 112(f) unless otherwise specifically recited. The transitional phrase "consisting essentially of" excludes any element, step, or ingredient not specified, but does not exclude materials or steps that affect the basic and novel characteristics of the claimed application. If used in a claim, the phrase "consisting essentially of" will be construed to implicate a closed-ended limitation that does not invoke 35 U.S.C. § 112(f) unless otherwise specifically recited.

[0028] When expressing a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values for an equivalent, concentration, or other value or parameter, it is to be understood that all ranges formed by any pair of an upper or preferred value and a lower or preferred value of that range, whether or not the range is expressly disclosed, are specifically disclosed. For example, where a range "1-5" is disclosed, the described range is to be interpreted to include the ranges "1-4," "1-3," "1-2," "1-2 and 4-5," "1-3 and 5," etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within that range.

[0029] In these embodiments, unless otherwise indicated, the parts and percentages are by mass.

[0030] "Mass parts" refers to a basic unit of measurement that represents the mass ratio relationship of multiple components, 1 part can represent any unit mass, such as 1 g, 2.689 g, etc. If we say that the mass parts of component A is a parts, and the mass parts of component B is b parts, it means that the mass ratio of component A and component B is a:b. It should not be misunderstood that, unlike the mass percentage, the sum of the mass parts of all components is not limited to 100 parts.

[0031] "and / or" is used to indicate one or both of the stated circumstances can occur, for example, A and / or B includes (A and B) and (A or B).

[0032] In a first aspect of the present application, a battery separator is provided, comprising a porous base film, the porous base film comprising a polyarylether sulfone, a low-melting polymer, a reactive compatibilizer, and nano-ceramic particles; the low-melting polymer has a melting point of 100-160°C, and the reactive compatibilizer forms a network structure with the polyarylether sulfone and the low-melting polymer.

[0033] The battery separator of the present application, by adding a low-melting-point polymer into the polyarylether sulfone to co-pore, balances the porosity, and at the same time, utilizes the low melting temperature of the low-melting-point polymer to timely close the pore structure to prevent the positive and negative electrode reactions when the secondary battery is in thermal runaway; the thermodynamic difference between the polyarylether sulfone and the low-melting-point polymer leads to weak interface bonding strength between the two, the reactive compatibilizer can form a "bridging" effect by respectively affining with the polyarylether sulfone and the low-melting-point polymer through molecular chain segments, and reduces the interface separation between the polyarylether sulfone and the low-melting-point polymer; the nano ceramic particles can prevent the stress generated when the low-melting-point polymer melts and prevent the structure of the polyarylether sulfone from collapsing; and the nano ceramic particles are filled at the interface between the polyarylether sulfone and the low-melting-point polymer to buffer the stress concentration when the pores are closed and prevent brittle fracture of the battery separator. The battery separator of the present application not only has good electrolyte wettability, but also can realize early closing of the pores at low temperature, complete structure at high temperature, and avoidance of positive and negative electrode contact short circuit, thereby effectively improving the safety of the secondary battery.

[0034] Specifically, the melting point of the low-melting-point polymer can be one or a range value between any two of 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃.

[0035] Specifically, in the battery separator of the present application, the melting point of the low-melting-point polymer can be obtained by a differential scanning calorimeter. As an example, specifically, a differential scanning calorimeter is used, nitrogen is used as the test atmosphere; the heating rate is 10℃ / min, the heat flow change of the unit mass sample is recorded during the heating process, and the peak temperature of the curve is the melting point of the polymer or refers to GB / T19466.1-2004 Differential Scanning Calorimetry (DSC) for Plastics Part 1: General Principles; GB / T 19466.3-2004 / ISO 11357-3:1999 Differential Scanning Calorimetry (DSC) for Plastics Part 3: Determination of the Melting and Crystallization Temperatures and Heat of Fusion.

[0036] In some embodiments, the mass ratio of the polyarylether sulfone and the low-melting-point polymer is (50-70):(24-38).

[0037] In some embodiments, the mass ratio of the polyarylether sulfone and the reactive compatibilizer is (50-70):(4-7).

[0038] In some embodiments, the mass ratio of the polyarylether sulfone and the nano ceramic particles is (50-70):(2-5).

[0039] In some embodiments, the mass ratio of the polyarylether sulfone, the low-melting polymer, the reactive compatibilizer, and the nano-ceramic particles is (50-70):(24-38):(4-7):(2-5); for example, it can be one of 50:38:7:5, 55:35:6:4, 60:32:5:3, 65:28:4:3, 70:24:4:2 or a range value between any two of them.

[0040] Specifically, the mass ratio of the polyarylether sulfone, the low-melting polymer, the reactive compatibilizer, and the nano-ceramic particles is within the above range, and the overall performance of the battery separator is better.

[0041] In some embodiments, the low-melting polymer includes at least one of polyethylene, thermoplastic polyurethane, polylactic acid, polybutylene succinate, polybutylene adipate / terephthalate, and copolymer nylon.

[0042] Using the above-mentioned kind of polymer as a low-melting polymer, when the temperature is raised to the melting point of the low-melting polymer, it can better melt and plug the holes, further inhibit the reaction between the positive and negative electrodes, prevent the occurrence of thermal runaway, and improve the stability of the secondary battery.

[0043] In some embodiments, the reactive compatibilizer includes a polymer containing at least one functional group of maleic anhydride group, epoxy group, oxazoline group, and isocyanate group. As a specific example of a polymer containing a maleic anhydride group, maleic anhydride grafted polyethylene can be listed; as a specific example of a polymer containing an epoxy group, an epoxy functionalized acrylate copolymer can be listed; as a specific example of a polymer containing an oxazoline group, a polystyrene-oxazoline copolymer can be listed; as a specific example of a polymer containing an isocyanate group, a hexamethylene diisocyanate-based prepolymer can be listed.

[0044] Using the above-mentioned kind of substance as a reactive compatibilizer, the interfacial bonding strength between the low-melting polymer and the polyarylether sulfone can be further improved, thereby improving the mechanical strength of the battery separator.

[0045] In some embodiments, the nano-ceramic particles include at least one of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, zinc oxide, barium oxide, magnesium oxide, beryllium oxide, calcium oxide, thorium oxide, aluminum nitride, titanium nitride, bormite, apatite, aluminum hydroxide, magnesium hydroxide, barium sulfate, boron nitride, silicon carbide, silicon nitride, cubic boron nitride, hexagonal boron nitride, graphite, and graphene.

[0046] In this application, when the nano-ceramic particles are of the above-mentioned kind, the strength of the battery separator at high temperature can be further enhanced, and the thermal shrinkage of the battery separator at high temperature can be further reduced.

[0047] In some embodiments, the nano-ceramic particles have an elastic modulus ≥ 300 GPa, such as 300-500 GPa, such as one or a range between any two of 300 GPa, 320 GPa, 350 GPa, 370 GPa, 400 GPa, 450 GPa, 500 GPa.

[0048] The elastic modulus of the nano-ceramic particles in the above range can further resist the stress generated when the low-melting-point polymer melts and shrinks, further preventing the collapse of the polyarylethersulfone skeleton, thereby improving the structural stability of the battery separator.

[0049] In the present application, the elastic modulus of the nano-ceramic particles is tested by the following method, specifically: using a three-point bending test, which is divided into the following steps: 1. Sample preparation: cut the nano-ceramic into a cuboid with length x width x thickness = 30 x 4 x 3 mm; 2. Span setting: adjust the distance L between the lower support rollers; 3. Loading test: place the sample on the lower support roller, making sure it is centered; slowly load at a displacement rate of 0.5 mm / min; record the load-displacement curve (stop before the sample breaks to avoid damaging the indenter); 4. Modulus calculation: E = L 3 / (4bh 3 )*ΔF / Δd L: span b: sample width h: sample thickness ΔF / Δd: load-displacement curve.

[0050] In some embodiments, the nano-ceramic particles have a melting point ≥ 300 °C, such as 300-3000 °C, such as one or a range between any two of 300 °C, 320 °C, 350 °C, 400 °C, 500 °C, 600 °C, 900 °C, 1200 °C, 1500 °C, 1800 °C, 2100 °C, 2400 °C, 2700 °C, 3000 °C. When the melting point of the nano-ceramic particles is in the above range, the nano-ceramic particles will not melt during the thermal runaway of the battery, improving the structural stability of the battery separator.

[0051] In some embodiments, the nano-ceramic particles have an average particle size ≤ 100 nm, such as one or a range between any two of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm.

[0052] The average particle size of the nano-ceramic particles in the above range can further limit the molecular chain movement of the polyarylethersulfone and the low-melting-point polymer, thereby improving the film breaking temperature of the battery separator.

[0053] In the present application, the average particle size of the nano ceramic particles is tested by the following method, specifically by using the DLS test method, which can be divided into the following four steps: 1. Ultrasonic dispersion: uniformly disperse the nanoparticles in the solvent; 2. Laser irradiation: irradiate the solution with laser, and detect the fluctuation of scattered light intensity; 3. Correlation analysis: calculate the diffusion coefficient by autocorrelation function; 4. Particle size output.

[0054] In some embodiments, the closed pore temperature of the porous base film is 100-160℃, for example, it can be one of 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, or a range value between any two of them; the film breaking temperature of the porous base film is 200-350℃, for example, it can be one of 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 330℃, 350℃, or a range value between any two of them.

[0055] In the present application, the closed pore temperature and the film breaking temperature of the porous base film are tested by the following method, specifically by TMA method, i.e. thermal mechanical method, according to GB / T 36800.1-2018 Plastics - Thermomechanical analysis (TMA) - Part 1: General principles, the first peak inflection point of the first derivative is the closed pore temperature, and the membrane breaking temperature is the film breaking temperature.

[0056] In some embodiments, the thickness of the porous base film is 5-30μm, for example, it can be one of 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 19μm, 22μm, 24μm, 26μm, 28μm, 30μm, or a range value between any two of them.

[0057] In the present application, the thickness of the porous base film is within the above range, which is beneficial to obtain appropriate secondary battery internal resistance and reduce the safety risk of the secondary battery.

[0058] In the present application, the measurement method of the thickness of the porous base film includes the following steps: referring to GB-T 6672-2001 Mechanical measurement method for determining the thickness of plastic film and sheet.

[0059] In some embodiments, the porosity of the porous base film is 30-60%, for example, it can be one of 30%, 32%, 35%, 37%, 40%, 45%, 50%, 53%, 55%, 58%, 60%, or a range value between any two of them.

[0060] In the present application, the porosity of the porous base film is within the above range, which can effectively ensure the ionic conductivity of the lithium ion battery separator. In the present application, the measurement method of the porosity of the porous base film includes: cutting a porous base film of a specific size (for example, 6 cm x 6 cm), weighing, then immersing the porous base film sample in isobutyl alcohol, and measuring the sample weight after adsorption equilibrium, the porosity = 1- (mass after adsorption-mass before adsorption) / mass before adsorption x 100%.

[0061] In some embodiments, the porous base film has a longitudinal shrinkage (MD) of ≤5% at 180°C for 1h, for example, it can be one or a range value between any two of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%; a transverse shrinkage (TD) of ≤5%, for example, it can be one or a range value between any two of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0062] In the present application, the longitudinal shrinkage of the porous base film at 180°C for 1h is ≤5%, which can promote the shrinkage of the pore size of the porous base film at high temperature, prevent the occurrence of thermal runaway, and better prevent the longitudinal shrinkage of the separator at the pore closing temperature, causing local membrane rupture and reducing the timeliness of closing; the transverse shrinkage of the porous base film at 180°C for 1h is ≤5%, which can prevent the transverse shrinkage of the separator at the pore closing temperature, causing short circuit between the positive and negative electrodes.

[0063] In the present application, the measurement method of the shrinkage of the porous base film includes: stacking the porous base film into 3 stacks, stacking flat, and then cutting the sample with a size of 140*70mm to obtain the sample to be measured, and measuring the length A1 and the width B1 of the sample to be measured respectively, placing the sample to be measured in an oven, and keeping it at 180°C for 1h, after the heat preservation is completed, taking out the sample to be measured, and after cooling for 10min, measuring the length A2 and the width B2 of the sample to be measured after heat preservation respectively; the longitudinal shrinkage and the transverse shrinkage of the porous base film are calculated according to the following formula; longitudinal shrinkage = (A1-A2) / A1*100%, transverse shrinkage = (B1-B2) / B1*100%.

[0064] In some embodiments, the porous base film has a longitudinal tensile strength ≥ 200 MPa, for example, can be 200-400 MPa, for example, can be one or a range value between any two of 200 MPa, 210 MPa, 220 MPa, 230 MPa, 250 MPa, 270 MPa, 300 MPa, 350 MPa, 400 MPa; a transverse tensile strength ≥ 250 MPa; for example, can be 250-400 MPa, for example, can be one or a range value between any two of 250 MPa, 270 MPa, 290 MPa, 310 MPa, 330 MPa, 350 MPa, 360 MPa, 370 MPa, 380 MPa, 400 MPa.

[0065] In this application, the measurement method of the tensile strength of the porous base film refers to GB / T 1040.1-2018 Determination of tensile properties of plastics Part 1: General principles; GB / T 1040.3-2006 Determination of tensile properties of plastics Part 3: Test conditions for films and sheets; GB / T 36363-2018 Polyolefin separators for lithium ion batteries.

[0066] In some embodiments, the puncture strength of the porous base film is > 400 gf, for example, can be one or a range value between any two of 405 gf, 450 gf, 500 gf, 550 gf, 600 gf, 650 gf, 700 gf, 750 gf.

[0067] In this application, the measurement method of the puncture strength of the porous base film includes: placing the porous base film in the puncture clamp of the universal testing machine, clamping to ensure that the porous base film is smooth and wrinkle-free, then starting the measurement, the 5 mm diameter needle of the puncture clamp is lowered at a speed of 5 mm / min, and the corresponding load stress value at a displacement of 2 mm is recorded. The value is the puncture strength.

[0068] In some embodiments, the battery separator further comprises an organic coating layer covering at least one side surface of the porous base film.

[0069] Forming an organic coating layer on the surface of the porous base film can improve the adhesion between the battery separator and the positive and negative electrodes, increase the stability of the battery separator, and improve the safety performance of the secondary battery.

[0070] In some embodiments, the organic coating layer comprises a first adhesive; the first adhesive comprises a homopolymer or copolymer of at least one monomer of ethylene, propylene, vinylidene fluoride, hexafluoropropylene, acrylic acid, acrylic ester, vinyl acetate, styrene, acrylonitrile, maleic anhydride, vinyl chloride, chloropropylene.

[0071] When the organic coating layer comprises the first binder, the battery separator has not only good high-temperature heat shrinkage resistance, but also higher bonding strength and ionic conductivity.

[0072] In some embodiments, the organic coating layer further comprises a second binder; the second binder comprises at least one of polyacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylic acid copolymer and silica sol.

[0073] When the organic coating layer comprises the first binder and the second binder, the first binder and the second binder jointly facilitate the battery separator coating layer to have no powder falling and good bonding effect with the positive and negative electrode sheets.

[0074] The thickness of the organic coating layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the organic coating layer can be 0.5-3 μm. In the present application, the thickness of the organic coating layer can be obtained by SEM scanning electron microscope test.

[0075] In another aspect, the present application also provides a preparation method of the porous base film, comprising the following steps:

[0076] S1: uniformly mixing polyarylether sulfone, low-melting-point polymer, reactive compatibilizer and nano ceramic particles to obtain a premix; adding a solvent to the premix and uniformly stirring to obtain a slurry;

[0077] S2: coating the slurry on a release film, volatilizing the solvent in the slurry to form a first substrate having a first pore size and a second pore size; the first pore size is 0.3-1 μm, and the second pore size is 0.1-0.3 μm;

[0078] S3: heat treating the first substrate to form a porous base film having a heat-responsive switch structure.

[0079] In step S1, in order to improve the uniformity of mixing polyarylether sulfone and low-melting-point polymer, the polyarylether sulfone and the low-melting-point polymer are respectively subjected to crushing treatment before mixing.

[0080] Specifically, the crushing treatment of the polyarylether sulfone comprises grinding the polyarylether sulfone to obtain polyarylether sulfone with an average particle size <50 μm.

[0081] Specifically, the crushing treatment of the low-melting-point polymer comprises freezing the low-melting-point polymer in liquid nitrogen for at least 10 min, and then grinding to obtain low-melting-point polymer with an average particle size <30 μm.

[0082] In step S1, the solvent can be any of various existing inert liquid substances capable of dissolving the polyarylether sulfone and low-melting polymer and dispersing the nanoceramic material, specific examples of which include, but are not limited to, at least one of N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), toluene, acetone, tetrahydrofuran, etc. Preferably, N,N-dimethylacetamide (DMAC) and acetone.

[0083] In step S2, the slurry is coated on a release film, and the solvent in the slurry is volatilized to form a first substrate having a first pore size and a second pore size. The specific steps are as follows:

[0084] S21: The slurry is coated on a release film to obtain a first wet film;

[0085] S22: The first wet film is soaked in an ethanol / water solution at a temperature of 30-50°C for 10-20s to obtain a second wet film;

[0086] S23: The second wet film is soaked in ice water at a temperature of 0-7°C for 3-7s to obtain a first substrate.

[0087] Soaking the first wet film in the ethanol / water solution induces the polyarylether sulfone in the first wet film to form a main skeleton macropore (0.3-1 μm); soaking the second wet film in ice water at a temperature of 0-7°C induces the low-melting polymer to form a dendritic micropore 0.1-0.3 μm, so that the first substrate forms a double network structure with two different pore sizes.

[0088] In step S3, the first substrate is heat treated to form a porous base film having a heat-responsive switch structure. The specific steps are as follows:

[0089] S31: The first substrate is heat treated at a temperature of 100-115°C for 3-7min to obtain a second substrate;

[0090] S32: The second substrate is heat treated at a temperature of 130-140°C for 2-4min to obtain a third substrate;

[0091] S33: The third substrate is placed in liquid nitrogen and frozen for 3-7min to obtain a porous base film having a heat-responsive switch structure.

[0092] Specifically, in step S31, the reactive compatibilizer forms a chemical bond with the polyarylether sulfone and the low-melting polymer, respectively; in step S32, the low-melting polymer partially melts and wraps the polyarylether sulfone skeleton; in step S33, the fluidity of the low-melting polymer in a molten state is locked to form a heat-responsive switch structure.

[0093] In a second aspect, a secondary battery is provided, comprising a positive electrode, a negative electrode, an electrolyte, and a battery separator, wherein the battery separator is located between the positive electrode and the negative electrode.

[0094] In one embodiment of this application, the negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector, and the positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector.

[0095] The lithium-ion battery in this application embodiment can adopt a stacked or wound design inside the battery. It is understood that, due to the stacked or wound design inside the battery, the current collectors (including positive electrode current collectors and negative electrode current collectors) can be coated on one side or on both sides. That is, active material layers are formed on both sides of the current collector, or an active material layer is formed on one side.

[0096] This application does not have any special requirements on the composition or structure of the positive electrode and the negative electrode. Without departing from the inventive concept of this application, any known positive electrode active material, negative electrode active material, current collector, and corresponding auxiliary structure and composition can be used in this application.

[0097] The following is a brief explanation of the positive and negative electrode materials and structures, provided merely as an illustrative example and not to limit the scope of protection.

[0098] The negative electrode is formed from a lithium-based material that can be used as the negative electrode in a lithium-ion battery. For example, the negative electrode may contain a negative electrode active material that can be used as the negative electrode in a battery. The negative electrode active material layer may be composed of multiple negative electrode active materials.

[0099] This application does not specifically limit the type of negative electrode active material. Any known negative electrode active material can be used in this application without departing from the inventive concept.

[0100] In one embodiment, the negative electrode active material comprises lithium metal and / or lithium alloy. In other embodiments, the negative electrode is a silicon-based negative electrode active material comprising silicon, such as silicon alloys, silicon oxide, or combinations thereof, and in some cases may also be mixed with graphite. In other embodiments, the negative electrode may comprise a carbon-based negative electrode active material comprising one or more of graphite, graphene, carbon nanotubes (CNTs), and combinations thereof. In yet another embodiment, the negative electrode comprises one or more lithium-accepting negative electrode active materials, such as lithium titanium oxide (Li4Ti5O4). 12 One or more transition metals (e.g., tin (Sn)), one or more metal oxides (e.g., vanadium oxide (V₂O₅), tin oxide (SnO), titanium dioxide (TiO₂)), titanium niobium oxide (Ti) x Nby O z where 0≤x≤2, 0≤y≤24, and 0≤z≤64), metal alloys (such as copper tin alloy (Cu6Sn5)), and one or more metal sulfides (such as iron sulfide (FeS)).

[0101] In an embodiment, the negative active material in the negative electrode tab can be doped with one or more conductive agents that provide an electronic conduction path and / or at least one polymeric binder material that improves the structural integrity of the negative electrode. For example, the binder can be, optionally, poly(tetrafluoroethylene) (PTFE), sodium carboxymethylcellulose (CMC), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene butadiene styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof. The conductive agent can include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials can include, for example, particles of carbon black, graphite, superP, acetylene black (such as KETCHEN™ black or DENKA™ black), carbon fibers and nanotubes, graphene, and the like. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and the like.

[0102] In an embodiment, the negative electrode tab includes the following mass percentage of components: 90wt%-97wt% of negative active material, 0.2wt%-4wt% of conductive material, 1wt%-4wt% of binder, 1wt%-3wt% of dispersant.

[0103] In an embodiment, the dispersant includes, but is not limited to, sodium carboxymethylcellulose (CMC).

[0104] The positive electrode tab is formed of a plurality of positive active particles including one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. In some embodiments, the positive active material layer further includes an electrolyte, such as a plurality of electrolyte particles. The positive active material layer has a thickness greater than or equal to about 1 pm to less than or equal to about 1000 pm.

[0105] In an embodiment, the positive active material layer is one of a layered oxide cathode, a spinel cathode, and a polyanion cathode. For example, the layered oxide cathode (e.g., a rock-salt layered oxide) includes one or more lithium-based positive active materials selected from the group consisting of LiCoO2(LCO), LiNi x Mn y Co 1-x-yO2(wherein 0≤x≤1 and 0≤y≤1), LiNi 1-x- y Co x Al y O2(wherein 0≤x≤1 and 0≤y≤1), LiNi x Mn 1-x O2(wherein 0≤x≤1), and Li 1+x MO2(wherein M is one of Mn, Ni, Co, and Al and 0≤x≤1). The spinel cathode includes one or more lithium-based positive active materials selected from the group consisting of LiMn2O4(LMO) and LiNi x Mn 1.5 O4. The olivine-type cathode includes one or more lithium-based positive electroactive materials LiMPO4(wherein M is at least one of Fe, Ni, Co, and Mn). The polyanionic cation includes, for example, phosphates such as LiV2(PO4)3 and / or silicates such as LiFeSiO4.

[0106] In one embodiment, the one or more lithium-based positive active materials can be optionally coated (e.g., by LiNbO3 and / or Al2O3) and / or can be doped (e.g., by magnesium (Mg)). Further, in certain embodiments, the one or more lithium-based positive active materials can be optionally mixed with one or more conductive materials that provide an electronic conduction path and / or at least one polymeric binder material that improves the structural integrity of the positive electrode.

[0107] In one embodiment, the positive active material layer includes the following mass percentages of components: 90wt%-98wt% of the one or more lithium-based positive active materials, 0.5wt%-5wt% of the conductive agent, 0.5wt%-5wt% of the binder.

[0108] In one embodiment, the positive active material layer can be optionally mixed with a binder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), nitrile butadiene rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof. The conductive agent can include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials can include, for example, particles of carbon black, graphite, acetylene black (e.g., KETCHEN™ black or DENKA™ black), carbon fibers and nanotubes, graphene, and the like. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like.

[0109] The positive current collector can facilitate the flow of electrons between the positive electrode and an external circuit. The positive current collector can include a metal, such as a metal foil, a metal grid or mesh, or a metal net. For example, the positive current collector can be formed of aluminum, stainless steel, and / or nickel, or any other suitable electrically conductive agent known to one skilled in the art.

[0110] In some embodiments, the secondary battery can include an outer package that can be used to encapsulate the above-described electrode assembly and electrolyte.

[0111] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. As the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, or the like, can be listed.

[0112] The shape of the secondary battery according to the present application is not particularly limited, and can be cylindrical, square, or any other arbitrary shape.

[0113] In one embodiment, in the secondary battery according to the present application, the charging cutoff voltage of the battery can be not less than 4.2 V, i.e., the battery can be used in a high voltage state of not less than 4.2 V. For example, the battery can operate in the range of 4.2 V to 4.9 V, or the battery can operate in the range of 4.3 V to 4.8 V.

[0114] In one embodiment, in the secondary battery according to the present application, the operating temperature of the battery can be greater than 45℃, i.e., the battery can be used in a high temperature state of not less than 45℃. For example, the battery can operate in the range of 45 to 70℃.

[0115] In a fifth aspect of the present application, a power consuming device is provided, which includes the above-described secondary battery.

[0116] For example, the above-described power consuming device can include a mobile device (e.g., a cell phone, a notebook computer, or the like), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, or the like), an electric train, a ship and a satellite, an energy storage system, or the like, but is not limited thereto.

[0117] The polyarylene ether sulfone and the low-melting polymer used in the following examples and comparative examples were subjected to a pulverization treatment,

[0118] The step of the pulverization treatment of the polyarylene ether sulfone was to grind the polyarylene ether sulfone to obtain a polyarylene ether sulfone having an average particle size of < 50 μm.

[0119] The step of the pulverization treatment of the low-melting polymer was to freeze the low-melting polymer in liquid nitrogen for at least 10 min, and then grind it to obtain a low-melting polymer having an average particle size of < 30 μm.

[0120] Example 1

[0121] The embodiment provides a battery separator, and a preparation method thereof comprises the following steps:

[0122] S1: polyarylether sulfone, linear low-density polyethylene with a melting point of 130 DEG C, maleic anhydride grafted polyethylene and aluminum oxide particles with an average particle size of 50 nm are mixed in a mass ratio of 60:30:5:5 at a temperature of 80 DEG C and a rotating speed of 300 r / min for 30 min to obtain a premix; the solvent is evenly divided into 3 parts, and the 3 parts of the solvent are added into the premix at a rotating speed of 500 r / min, and the addition is performed in 3 times with an interval of 10 min to obtain a slurry; wherein the mass ratio of the solvent to the premix is 5:1, the solvent is a DMAC / acetone mixture, and the volume ratio of DMAC to acetone is 7:3;

[0123] S2: the slurry is coated on a polyester release film through a double-screw extruder to obtain a first wet film with a thickness of 250 mu m; the first wet film is soaked in an ethanol / water solution at a temperature of 40 DEG C for 10 s to obtain a second wet film; the second wet film is soaked in ice water at a temperature of 5 DEG C for 120 s to obtain a first base material with a first pore size and a second pore size; the first pore size is 0.3-1 mu m, and the second pore size is 0.1-0.3 mu m;

[0124] S3: the first base material is heat-treated at a temperature of 110 DEG C for 5 min to obtain a second base material; the second base material is heat-treated at a temperature of 135 DEG C for 3 min to obtain a third base material; the third base material is immediately placed in liquid nitrogen and frozen for 5 min to obtain a battery separator with a thickness of 20 mu m.

[0125] Embodiment 2

[0126] The embodiment provides a battery separator, and a preparation method thereof, wherein the difference between the preparation method and the embodiment 1 is that the melting point of the linear low-density polyethylene is 110 DEG C.

[0127] Embodiment 3

[0128] The embodiment provides a battery separator, and a preparation method thereof, wherein the difference between the preparation method and the embodiment 1 is that the melting point of the linear low-density polyethylene is 150 DEG C.

[0129] Embodiment 4

[0130] The embodiment provides a battery separator, and a preparation method thereof, wherein the difference between the preparation method and the embodiment 1 is that the melting point of the linear low-density polyethylene is 100 DEG C.

[0131] Embodiment 5

[0132] The embodiment provides a battery separator, and a preparation method thereof, wherein the difference between the preparation method and the embodiment 1 is that the melting point of the linear low-density polyethylene is 160 DEG C.

[0133] Example 6

[0134] The present example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130℃, maleic anhydride grafted polyethylene, and nano-aluminum oxide particles with an average particle size of 50nm is 55:35:6:4.

[0135] Example 7

[0136] The present example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130℃, maleic anhydride grafted polyethylene, and nano-aluminum oxide particles with an average particle size of 50nm is 65:28:4:3.

[0137] Example 8

[0138] The present example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130℃, maleic anhydride grafted polyethylene, and nano-aluminum oxide particles with an average particle size of 50nm is 50:38:7:5.

[0139] Example 9

[0140] The present example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130℃, maleic anhydride grafted polyethylene, and nano-aluminum oxide particles with an average particle size of 50nm is 70:24:4:2.

[0141] Example 10

[0142] The present example provides a battery separator, the preparation method of which is different from that of Example 1 in that the composition of the premix is different, and the preparation method of the premix of the present example is as follows: polyarylether sulfone, polylactic acid with a melting point of 130℃, epoxy-functionalized acrylate copolymer, and cubic boron nitride particles with an average particle size of 50nm are mixed at a mass ratio of 60:30:5:5 at a temperature of 80℃ and a rotation speed of 300r / min for 30min to obtain the premix.

[0143] Example 11

[0144] The present example provides a battery separator, the preparation method of which comprises the following steps:

[0145] S1: linear low density polyethylene with a melting point of 130℃, maleic anhydride grafted polyethylene and aluminum oxide particles with an average particle size of 50 nm were mixed in a mass ratio of 60:30:5:5 at a temperature of 80℃ and a rotation speed of 300 r / min for 30 min to obtain a premix; the solvent was evenly divided into 3 parts, and added to the premix under the condition of a rotation speed of 500 r / min, 3 times, with an interval of 10 min to obtain a slurry; wherein the mass ratio of solvent to premix is 5:1, the solvent is a DMAC / acetone mixture, and the volume ratio of DMAC to acetone is 7:3;

[0146] S2: the slurry was coated on a polyester release film by a twin-screw extruder to obtain a first wet film with a thickness of 250 μm; the first wet film was soaked in an ethanol / water solution at a temperature of 40℃ for 10 s to obtain a second wet film; the second wet film was soaked in ice water at a temperature of 5℃ for 120 s to obtain a first substrate with a first pore size and a second pore size; the first pore size is 0.3-1 μm, and the second pore size is 0.1-0.3 μm;

[0147] S3: the first substrate was heat treated at a temperature of 110℃ for 5 min to obtain a second substrate; the second substrate was heat treated at a temperature of 135℃ for 3 min to obtain a third substrate; the third substrate was immediately placed in liquid nitrogen and frozen for 5 min to obtain a porous separator with a thickness of 20 μm;

[0148] S4: polyvinylidene fluoride and acrylonitrile were added to water and stirred uniformly to obtain an organic slurry; wherein, based on 100% of the mass of the organic slurry, the mass percentage of polyvinylidene fluoride is 15%, and the mass percentage of acrylonitrile is 3%;

[0149] The organic slurry was sprayed on one side surface of the porous base film obtained in step S3 by rotary spraying to form an organic coating layer with a thickness of 5 μm to obtain a battery separator.

[0150] Example 12

[0151] The battery separator provided in this example has a preparation method different from that of Example 1, which is different in that the organic slurry in step S4 is different, and in this example, based on 100% of the mass of the organic slurry, it contains the following mass percentage of components: polyvinylidene fluoride 15%, acrylonitrile 3%, sodium carboxymethyl cellulose 2%, and the balance is water.

[0152] Comparative Example 1

[0153] The comparative example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130°C, maleic anhydride grafted polyethylene, and aluminum oxide particles with an average particle size of 50 nm is 65:30:5:0, i.e., the comparative example does not contain maleic anhydride grafted polyethylene.

[0154] Comparative Example 2

[0155] The comparative example provides a battery separator, the preparation method of which is different from that of Example 1 in that the mass ratio of polyarylether sulfone, linear low-density polyethylene with a melting point of 130°C, maleic anhydride grafted polyethylene, and aluminum oxide particles with an average particle size of 50 nm is 65:30:0:5, i.e., the comparative example does not contain maleic anhydride grafted polyethylene.

[0156] Comparative Example 3

[0157] The comparative example provides a battery separator, the preparation method of which is different from that of Example 1 in that the composition of the premix is different, and the mass ratio of polyarylether sulfone, polybutylene succinate with a melting point of 130°C, glycidyl methacrylate grafted polyethylene, and aluminum oxide particles with an average particle size of 50 nm is 60:30:5:5.

[0158] Comparative Example 4

[0159] The comparative example provides a battery separator, the preparation method of which is different from that of Example 1 in that the average particle size of the aluminum oxide particles is 0.8 μm.

[0160] Comparative Example 5

[0161] The comparative example provides a battery separator, which is a polyethylene separator purchased from Shenzhen Xingyuan Material Co., Ltd., with a thickness of 25 μm.

[0162] Comparative Example 6

[0163] The comparative example provides a battery separator, which is a polypropylene separator purchased from Shenzhen Xingyuan Material Co., Ltd., with a thickness of 25 μm.

[0164] Performance Test

[0165] The battery separators obtained in the examples and comparative examples were subjected to performance tests, and the test methods were as follows:

[0166] (1) Closed pore temperature and membrane rupture temperature: refer to GB / T 36800.1-2018 Plastics - Thermomechanical analysis (TMA) - Part 1: General principles - First order derivative, the first peak inflection point is the closed pore temperature, and the membrane rupture temperature is the membrane rupture temperature. The specific steps are as follows: cut the membrane along the MD and TD directions into 4mm wide test samples, place the test sample in the length of 8mm scale groove position clamp, lock with screw, and cut off the excess part of the test sample outside the clamp; the test process of the thermal mechanical analyzer is as follows: preheat and set the nitrogen flow rate to 50ml / min→thin film probe correction and zero→sample is placed in the measurement accurate length→close the heating furnace and set the test conditions: preloading force is 0.1N, temperature rising range is 40-200℃, temperature rising rate is 5℃ / min→complete the test and data analysis.

[0167] (2) Heat shrinkage rate: stack the battery separator into 3 stacks, flatten, and then cut with a cutting plate with a size of 140*70mm to obtain 3 test samples. Measure the length A1 and width B1 of the test sample, respectively. Place the test sample in an oven at different temperatures for different times. After the heat preservation is completed, take out the test sample and cool it for 10 minutes. Then measure the length A2 and width B2 of the test sample after heat preservation, respectively. Calculate the longitudinal shrinkage rate and transverse shrinkage rate of the battery separator according to the following formula: longitudinal shrinkage rate=(A1-A2) / A1*100%, transverse shrinkage rate=(B1-B2) / B1*100%.

[0168] (3) Air permeability test: refer to GB-T 36363-2018 Lithium ion battery polyolefin separator; the air permeability increase of the separator after 130℃&1h baking=sample air permeability after 130℃&1h baking-fresh sample air permeability.

[0169] (4) Liquid absorption rate: cut the battery separator into 5cm*5cm samples, weigh W1, then place the sample in the electrolyte, and place it at room temperature for 10 minutes. Take out and dry the surface electrolyte with filter paper. Weigh W2, and the liquid absorption rate=(W2-W1) / W1*100%, repeat 5 times and take the average value; wherein the electrolyte is a solution of LiPF6 with a concentration of 1mol / L, which is composed of dimethyl carbonate DMC, ethylene carbonate EC and methyl ethyl carbonate EMC with a volume ratio of 1:1:1.

[0170] (5) Puncture strength: place the battery separator in the puncture clamp of the universal testing machine, clamp it tightly, and ensure that the battery separator is smooth and wrinkle-free. Then start measuring. The 5mm diameter needle of the puncture clamp moves down at a speed of 5mm / min. Record the load stress value corresponding to the displacement of 2mm. This value is the puncture strength.

[0171] (6) Foreign matter puncture resistance: the negative electrode sheet / battery separator / N particle / positive electrode sheet were stacked in turn, wherein the Ni particle was 40 mesh, and was placed on a hot press under the condition of a temperature of 85°C and a pressure of 2 MPa for 15 s to obtain a product to be tested, then an ohmmeter was used to test whether the internal resistance of the product to be tested changed, the internal resistance did not change all the time, that is, it was passed, the passing rate was recorded, the sample size was 30, and the foreign matter resistance = the number of passing / the sample size * 100%.

[0172] (7) Breakdown voltage: a battery separator with a width less than the distance between the upper and lower electrodes of the voltage resistance tester and greater than the diameter of the electrode was placed between the upper and lower electrodes, the battery separator was ensured to be flat and wrinkle-free, then the voltage was gradually increased until the battery separator was broken down and the instrument emitted a buzzing alarm sound, and the voltage value at this time was recorded as the breakdown voltage.

[0173] (8) Ionic conductivity: a symmetric battery was assembled by sequentially placing stainless steel, a battery separator and stainless steel in a battery shell, the symmetric battery was subjected to electrochemical impedance spectroscopy test by a CHI-604E type electrochemical workstation under the condition of a working range of 0.1 MHz-0.1 Hz and a vibration amplitude of 10 mV, the test curve was fitted by Z-view software to obtain an impedance value R, and the ionic conductivity σ of the solid electrolyte was calculated by the following formula: σ = L / (A*R), the unit was mS / cm; wherein L was the thickness of the battery separator, A was the area of the stainless steel with a diameter of 1 cm 2 ).

[0174] (9) Short circuit performance and cycle performance:

[0175] The battery separator obtained by using each example and the comparative example was used to prepare a lithium ion battery according to the following method.

[0176] a. Preparation of the positive electrode sheet: lithium iron phosphate, super P and PVDF were added to an NMP solvent in a mass ratio of 97:1:2, and were fully stirred to form a positive electrode slurry with a solid content of 58% and a viscosity of 4000 mPa·s, then the slurry was coated on an aluminum foil, dried, rolled, and cut for standby;

[0177] b. Preparation of the negative electrode sheet: artificial graphite, super P, CMC and SBR were added to a deionized water solvent in a mass ratio of 96.5:0.5:1.2:1.8, and were fully stirred to form a negative electrode slurry with a solid content of 53% and a viscosity of 3000 mPa·s, then the slurry was coated on a copper foil, dried, rolled, and cut for standby;

[0178] c. Preparation of the electrolyte:

[0179] Lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1:1.5:1 to obtain an electrolyte, wherein the molar concentration of lithium hexafluorophosphate is 1 mol / L.

[0180] d. Preparation of lithium ion battery: the positive electrode sheet, the negative electrode sheet and the separator film of the above examples and comparative examples are respectively wound into a bare battery cell, and then preheated, hot-pressed and paired into a shell (the number of inner cores is 2). Then, the electrolyte is injected into the aluminum shell, and then the processes of standing, formation, secondary liquid supplement, welding, capacity distribution, self-discharge test and the like are carried out, to prepare a lithium ion battery with a capacity of 136 Ah and a cutoff voltage of 2.5 V-3.65 V.

[0181] Short circuit performance: the obtained lithium ion battery is fully charged to 3.65 V and placed in an environment of 20±5℃, and when the surface temperature of the battery reaches 20±5℃, it is placed for 30 min; a wire with an internal resistance of 3 mΩ is used to connect the positive and negative electrodes of the battery for 10 min, and the change of the surface temperature of the lithium ion battery is monitored, and after the test is completed, it is observed for 1 h at ambient temperature to see if explosion or fire occurs; the sample size is 5.

[0182] Cycle performance: at 25℃, the lithium ion battery is placed for 5 minutes, charged to 3.65 V at 1C rate, then charged to a current less than or equal to 0.05C, then placed for 5 minutes, and then discharged to 2.5 V at 1C rate, which is one charge-discharge cycle. The discharge capacity of this cycle is recorded as the discharge capacity of the first cycle of the lithium ion secondary battery. The lithium ion battery is cycled according to the above method for 1500 cycles, and the discharge capacity at 1500 cycles is recorded. The capacity retention rate (%) = the discharge capacity of the 1500th cycle / the discharge capacity of the first cycle x 100%.

[0183] The above test results are shown in Tables 1-2.

[0184] Table 1

[0185]

[0186]

[0187] Note: " / " in Table 1 indicates that the battery separator is broken and cannot be tested.

[0188] Table 2

[0189]

[0190]

[0191] As can be seen from the experimental data in Table 1 and Table 2, the closed pore temperature of the battery separator of the application is 100-160℃, the broken membrane temperature is 180-350℃, the longitudinal shrinkage rate at 180℃ for 1h is ≤5%, the transverse shrinkage rate is ≤5%, the battery separator permeability increases by >5000s / 100cc after baking at 130℃ for 1h, the liquid absorption rate is ≥260%, the puncture strength is >400gf, the foreign matter puncture resistance is ≥93%, the breakdown voltage is ≥4kV, the ion conductivity is ≥2.4mS / cm, the surface temperature of the secondary battery containing the battery separator is ≤140℃, the number of fires is 0, and the capacity retention rate after 1500 cycles is ≥93.4%; it is shown that the battery separator of the application can effectively improve the safety of the secondary battery.

[0192] Finally, it should be noted that the above examples are used to illustrate the technical solutions of the application and not to limit the scope of protection of the application. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the application.

Claims

1. A battery separator, characterized in that, The membrane includes a porous base membrane comprising polyarylene ether sulfone, a low-melting-point polymer, a reactive compatibilizer, and nano-ceramic particles; the low-melting-point polymer has a melting point of 100-160°C, and the reactive compatibilizer enables the polyarylene ether sulfone and the low-melting-point polymer to form an interpenetrating network structure.

2. The battery separator as described in claim 1, characterized in that, The mass ratio of the polyarylether sulfone to the low-melting-point polymer is (50-70):(24-38).

3. The battery separator as described in claim 1, characterized in that, The mass ratio of the polyarylether sulfone to the reactive compatibilizer is (50-70):(4-7).

4. The battery separator as described in claim 1, characterized in that, The mass ratio of the polyarylether sulfone to the nano-ceramic particles is (50-70):(2-5).

5. The battery separator as described in claim 1, characterized in that, The low-melting-point polymer includes at least one of polyethylene, thermoplastic polyurethane, polylactic acid, polybutylene succinate, polybutylene adipate / terephthalate, and copolynylon; And / or, the reactive compatibilizer comprises a polymer containing at least one functional group selected from maleic anhydride, epoxy, oxazoline, and isocyanate groups; And / or, the nanoceramic particles comprise at least one of the following: alumina, silicon oxide, titanium oxide, zirconium oxide, zinc oxide, barium oxide, magnesium oxide, beryllium oxide, calcium oxide, thorium oxide, aluminum nitride, titanium nitride, boehmite, apatite, aluminum hydroxide, magnesium hydroxide, barium sulfate, boron nitride, silicon carbide, silicon nitride, cubic boron nitride, hexagonal boron nitride, graphite, and graphene. And / or, the elastic modulus of the nano-ceramic particles is ≥300 GPa; And / or, the average particle size of the nano-ceramic particles is ≤100nm.

6. The battery separator as described in claim 1, characterized in that, The pore-closing temperature of the porous base membrane is 100-160℃, and the membrane-breaking temperature of the porous base membrane is 180-350℃.

7. The battery separator as described in claim 1, characterized in that, The thickness of the porous base membrane is 5-30 μm; and / or the porosity of the porous base membrane is 30-60%.

8. The battery separator as described in claim 1, characterized in that, The porous base membrane has a longitudinal shrinkage rate of ≤5% and a transverse shrinkage rate of ≤5% at 180℃ for 1 hour. And / or, the porous base membrane has a transverse tensile strength ≥200MPa and a longitudinal tensile strength ≥250MPa; And / or, the puncture strength of the porous base membrane is >400gf.

9. The battery separator as described in claim 1, characterized in that, The battery separator also includes an organic coating covering at least one side surface of the porous base membrane.

10. The battery separator as described in claim 9, characterized in that, The organic coating comprises a first polymer; the first polymer comprises a homopolymer or copolymer of at least one monomer selected from ethylene, propylene, vinylidene fluoride, hexafluoropropylene, acrylic acid, acrylate, vinyl acetate, styrene, acrylonitrile, maleic anhydride, vinyl chloride, and propylene chloride.

11. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a battery separator as described in any one of claims 1-10, wherein the battery separator is located between the positive electrode and the negative electrode.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

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