Modified diaphragm, preparation method and application thereof and lithium ion battery

Abstract

The invention relates to the technical field of battery materials, in particular to a modified diaphragm, a preparation method and application thereof and a lithium ion battery. The modified diaphragm comprises a base membrane and a modified layer compounded on at least one surface of the base membrane, and the modified layer comprises a binder and polymer microspheres; the mass ratio of the binder to the polymer in the polymer microspheres is (0.05-0.2): 1; wherein the average particle size of the polymer microspheres is 1-10 [mu] m. The modified diaphragm is prepared by adopting an electrostatic spraying technology, the modified diaphragm has excellent thermal dimensional stability and ionic conductivity, the cycle performance and electrochemical performance of the lithium ion battery are improved, and large-scale application is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a modified diaphragm, a preparation method and application thereof, and a lithium ion battery. Background Art

[0002] As one of the core components of lithium-ion batteries, the diaphragm is known as the "third pole". The diaphragm is essentially a plastic film with a porous structure, located between the positive electrode and the negative electrode. Its main function is to separate the positive and negative active materials to prevent the two electrodes from contacting and causing a short circuit. At the same time, during the electrochemical reaction, it forms an ion movement channel to allow ions to pass freely. The diaphragm itself does not participate in the chemical reaction, but its material type and structure greatly affect the internal resistance and interface properties of the battery, and ultimately affect the actual working parameters of the battery, such as capacity and cycle life. Therefore, it is particularly important to develop a battery diaphragm with excellent performance and stability.

[0003] Polyolefin materials have become one of the commercial diaphragm materials due to their excellent mechanical, chemical and electrochemical stability and low price. However, the performance of polyolefin diaphragms needs to be further improved. The polyolefin materials in polyolefin diaphragms have a low melting point, poor thermal stability at high temperatures, obvious dimensional shrinkage and deformation, and serious safety hazards. In addition, due to the hydrophobicity of polyolefin materials, they have poor affinity with highly polar electrolytes, making the assembled battery have a high interfacial resistance, which ultimately affects the battery's cycle and rate performance.

[0004] At present, the modification of polyolefin diaphragms is mainly carried out by surface coating, and inorganic ceramics or high-temperature resistant polymers are usually used to coat polyolefin diaphragms. This modification method will inevitably bring about a certain pore blocking effect, reducing the ionic conductivity of the diaphragm. In addition, the density of inorganic ceramics is relatively large, and the surface density of the polyolefin diaphragm coated on the surface increases, which will reduce the energy density of lithium-ion batteries. Moreover, when the temperature is higher than the melting point of polyolefins, the base film melts and shrinks, which will cause the inorganic coating layer to fall off and break, causing a short circuit in the battery; the polymer coating is limited to its own structure. Once the polyolefin diaphragm melts and shrinks, the coating itself does not have good mechanical properties and it is difficult to meet the needs of lithium-ion batteries with increasing energy density.

[0005] Therefore, the development of new coating materials and technologies has become a research hotspot in recent years. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem of poor heat shrinkage resistance of polyolefin diaphragms in the prior art, and to provide a modified diaphragm and its preparation method and application as well as a lithium-ion battery. Electrostatic spraying technology is used to form a polymer microsphere coating on the surface of the base film. The obtained modified diaphragm has excellent thermal dimensional stability and improves the cycle performance and electrochemical performance of the lithium-ion battery.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a modified diaphragm, wherein the diaphragm comprises a base film, and a modified layer composited on at least one surface of the base film, wherein the modified layer comprises a binder and polymer microspheres; the mass ratio of the binder to the polymer in the polymer microspheres is 0.05-0.2:1;

[0008] Wherein, the average particle size of the polymer microspheres is 1-10 μm.

[0009] The second aspect of the present invention provides a method for preparing the modified diaphragm according to the first aspect, wherein the method comprises the following steps:

[0010] (1) dispersing a polymer and a binder in a dispersion medium and mixing them to obtain an electrostatic spray precursor solution;

[0011] (2) Electrostatically spraying the electrostatic spray precursor liquid on at least one surface of the base film to form polymer microspheres on the surface of the base film, and then drying to obtain the modified diaphragm.

[0012] The third aspect of the present invention provides a use of the modified diaphragm described in the first aspect or the modified diaphragm prepared by the method described in the second aspect in a lithium ion battery.

[0013] A fourth aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the separator is the modified separator described in the first aspect or the modified separator obtained by the method described in the second aspect.

[0014] Through the above technical solution, the present invention can achieve the following technical effects:

[0015] (1) The modified diaphragm provided by the present invention uses electrostatic spraying technology to form a modified layer containing polymer microspheres on the surface of the base film. The particle size of the polymer microspheres is controllable and has good temperature resistance. The polymer microspheres are distributed on the surface of the base film to improve the thermal dimensional stability of the modified diaphragm, thereby improving the high-temperature use safety of the lithium-ion battery diaphragm;

[0016] (2) The modified diaphragm provided by the present invention, the gaps between the polymer microspheres provide a rapid migration channel for lithium ions, giving the modified diaphragm a higher ion mobility. Compared with the traditional polymer and ceramic coated modified diaphragms, the modified diaphragm has a higher mass energy density and cycle life, and has better electrochemical performance;

[0017] (3) The modified membrane provided by the present invention has excellent wettability of the polymer microspheres, so that the modified membrane has higher electrolyte wettability and improves the ionic conductivity of the modified membrane; and the process flow is simple, the production efficiency is high, the application range is wide, and it is conducive to large-scale application. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] The first aspect of the present invention provides a modified diaphragm, wherein the diaphragm comprises a base film and a modified layer composited on at least one surface of the base film, wherein the modified layer comprises a binder and polymer microspheres; the mass ratio of the binder to the polymer in the polymer microspheres is 0.05-0.2:1;

[0020] Wherein, the average particle size of the polymer microspheres is 1-10 μm.

[0021] The inventors of the present invention have discovered that the surface of the base film is modified by electrostatic spraying technology, and the surface of the modified diaphragm contains polymer microspheres and a binder, which greatly improves the thermal dimensional stability and electrolyte wettability of the modified diaphragm. The gaps between the polymer microspheres provide a rapid migration channel for lithium ions, giving the modified diaphragm a higher ion mobility, so that the modified diaphragm has a higher mass energy density and cycle life, and has better electrochemical properties.

[0022] In some embodiments of the present invention, preferably, the mass ratio of the binder to the polymer in the polymer microspheres is 0.1-0.15:1.

[0023] In the present invention, the mass ratio of the binder to the polymer obtained in the polymer microspheres is controlled within the above range, which is beneficial to making the average particle size of the obtained polymer microspheres 1-10 μm, so that the modified diaphragm has better comprehensive performance; the mass ratio of the binder to the polymer obtained in the polymer microspheres is less than 0.05:1, the binder content is relatively low, and the modified diaphragm has the risk of powdering during long-term use; the mass ratio of the binder to the polymer obtained in the polymer microspheres is greater than 0.2:1, the binder content is relatively high, the viscosity of the obtained electrostatic spray precursor solution is relatively high, it is difficult to form polymer microspheres, and the particle size of the formed polymer microspheres is relatively large, which does not meet the use range.

[0024] In some embodiments of the present invention, preferably, the average particle size of the polymer microspheres is 1.2-9.7 μm, preferably 4.5-7.5 μm. As a non-limiting example, the average particle size of the polymer microspheres can be 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm and 7.5 μm and any value in the range formed by any two of these point values. Meeting this range is more conducive to making the modified diaphragm have better thermal dimensional stability and electrolyte wettability, and has higher mass energy density and cycle life.

[0025] In the present invention, the average particle size of the polymer microspheres is less than 1 μm, which is relatively small and will produce a pore blocking effect to a certain extent, affecting the ionic conductivity of the modified diaphragm and reducing the electrochemical performance; the average particle size of the polymer microspheres is greater than 10 μm, which is relatively large, resulting in a weak interaction between the modified layer containing the polymer microspheres and the base membrane, and there is a risk of falling off during long-term use.

[0026] In the present invention, the average particle size of the polymer microspheres is preferably in the range of 1.2-9.7 μm and further preferably in the range of 4.5-7.5 μm, which is more conducive to making the modified diaphragm have excellent comprehensive properties.

[0027] In the present invention, the average particle size of the polymer microspheres is measured using a static laser particle size analyzer.

[0028] In some embodiments of the present invention, preferably, the thickness of the modified layer is 2-20 μm, preferably 3-10 μm. The modified layer provided by the present invention contains polymer microspheres and a binder, and the polymer microspheres have a certain number of polar groups and have affinity for the electrolyte. Controlling the thickness of the modified layer within the above range is conducive to improving the electrolyte wettability of the modified diaphragm.

[0029] In the present invention, as the modified layer becomes thicker, the ionic conductivity of the separator decreases, resulting in a decrease in the energy density of the battery; when the thickness of the modified layer is less than 2 μm, the thermal dimensional stability, liquid retention rate and capacity retention rate of the modified separator decrease. The thickness of the modified layer is tested using an ellipsometer.

[0030] In some embodiments of the present invention, preferably, the base membrane is a polymer membrane, preferably a polyolefin membrane, more preferably any one selected from a polypropylene membrane, a polyethylene membrane and a polypropylene / polyethylene composite membrane.

[0031] In the present invention, the modified membrane comprises a polymer base membrane and a modified layer composited on at least one surface of the polymer base membrane. The effect is better when the polymer base membrane is a polyolefin membrane, and the obtained modified membrane has more excellent comprehensive performance.

[0032] In some embodiments of the present invention, preferably, the base film has a thickness of 5-15 μm, preferably 6-12 μm; an average pore size of 600-1200 nm, preferably 800-1000 nm; and a porosity of 30-60%, preferably 35-50%.

[0033] In the present invention, controlling the thickness, average pore size and porosity of the base film within the above ranges is conducive to making the obtained modified diaphragm have excellent thermal dimensional stability and ionic conductivity, and excellent electrochemical properties; controlling the thickness, average pore size and porosity of the base film within the above preferred ranges is more conducive to making the modified diaphragm have excellent electrochemical properties. The base film is commercially available.

[0034] In some embodiments of the present invention, preferably, the binder is selected from at least one of polyvinylidene fluoride, polyacrylonitrile, polyurethane and polyimide.

[0035] In some embodiments of the present invention, preferably, the polymer in the polymer microspheres is selected from at least one of poly(arylethersulfoneketone), polyethylene terephthalate, polyetheretherketone, polyetherketone, polyphenylene phthalamide and cellulose acetate.

[0036] In some embodiments of the present invention, preferably, the polymer microspheres are obtained by subjecting a polymer to electrostatic spraying.

[0037] The second aspect of the present invention provides a method for preparing the modified diaphragm according to the first aspect, wherein the method comprises the following steps:

[0038] (1) dispersing a polymer and a binder in a dispersion medium and mixing them to obtain an electrostatic spray precursor solution;

[0039] (2) Electrostatically spraying the electrostatic spray precursor liquid on at least one surface of the base film to form polymer microspheres on the surface of the base film, and then drying to obtain the modified diaphragm.

[0040] In some embodiments of the present invention, preferably, in step (1), based on the total amount of the electrostatic spray precursor solution, the mass fraction of the polymer is 0.5-5wt%, preferably 0.8-3wt%.

[0041] In the present invention, controlling the mass fraction of the polymer within the above range is conducive to forming polymer microspheres with an average particle size of 1-10 μm.

[0042] In some embodiments of the present invention, preferably, the mass ratio of the binder to the polymer is 0.05-0.2:1, preferably 0.1-0.15:1.

[0043] In the present invention, controlling the mass ratio of the binder to the polymer within the above-mentioned range is beneficial to making the average particle size of the obtained polymer microspheres 1-10 μm, improving the thermal dimensional stability and electrolyte wettability of the modified diaphragm, having a higher mass energy density and cycle life, and having excellent electrochemical properties; controlling the mass ratio of the binder to the polymer within the above-mentioned preferred range is more beneficial to improving the comprehensive performance of the modified diaphragm.

[0044] In some embodiments of the present invention, preferably, in step (1), the mixing temperature is 60-120°C, the time is 6-12h, and the speed is 500-800r / min;

[0045] In the present invention, in step (1), the temperature-resistant polymer and the binder are dispersed in a dispersion medium, stirred at a temperature of 70-90° C. for 8-10 hours, and after being uniformly mixed, an electrostatic spray precursor solution is obtained for standby use.

[0046] In some embodiments of the present invention, preferably, the dispersion medium is an organic solvent, preferably at least one selected from tetrahydrofuran, acetone, ethanol, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, ethyl acetate, dimethyl sulfoxide, ethyl methyl carbonate and cyclohexane.

[0047] In the present invention, the dispersion medium ensures that the polymer and the binder are fully dissolved, thereby obtaining a uniformly dispersed electrostatic spray precursor solution.

[0048] In some embodiments of the present invention, preferably, based on the total amount of the electrostatic spray precursor solution, the mass fraction of the dispersion medium is 94-99.5wt%, preferably 97-99.2wt%.

[0049] In the present invention, the amount of the dispersion medium is controlled within the above range so that the viscosity of the obtained electrostatic spray precursor liquid meets the requirements of the electrostatic spray technology, which is conducive to the formation of polymer microspheres with an average particle size that meets the requirements, thereby making the obtained modified diaphragm have better electrical properties.

[0050] In the present invention, in step (2), a polymer base film is used as a receiving material, and electrostatic spraying technology is adopted to adjust the spinning process parameters. The electrostatic spray precursor liquid obtained in step (1) forms polymer microspheres on the surface of the base film under the action of the electric field force, and the polymer microspheres not adhering to the surface of the base film are removed by washing, and the modified diaphragm is obtained after drying.

[0051] In the present invention, the electrostatic spraying technology is a method well known to those skilled in the art and will not be described in detail here.

[0052] In some embodiments of the present invention, preferably, in step (2), the process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2-3mm, preferably 0.5-2.5mm; the spinning voltage is 5-30kV, preferably 10-25kV; the receiving distance is 10-20cm, preferably 12-18cm; the electrostatic spraying precursor injection speed is 0.5-3mL / h, preferably 1.0-2mL / h; the ambient temperature is 10-35°C; and the relative humidity is 15-40%.

[0053] In the present invention, the electrostatic spraying is carried out in an electrospinning machine, and the process conditions of the electrostatic spraying are controlled within the above-mentioned range, which is conducive to forming a modified layer containing polymer microspheres with an average particle size of 1-10 μm on the surface of the base film, thereby improving the thermal dimensional stability and electrolyte wettability of the modified diaphragm, having a higher mass energy density and cycle life, and making the modified diaphragm have excellent electrochemical properties.

[0054] In some embodiments of the present invention, preferably, the drying temperature is 60-90° C. and the drying time is 8-24 h.

[0055] In the present invention, the drying equipment is not particularly limited, and it is preferably carried out in a vacuum drying oven.

[0056] In the present invention, the ionic conductivity of the modified diaphragm is 0.77-0.92 mS / cm, and the thermal shrinkage rate after being kept at 105° C. for 1 hour is 0.5-1.8%.

[0057] In the present invention, the ionic conductivity (σ) of the modified membrane is calculated according to the following formula:

[0058] σ=L / (R b A)

[0059] Where, L is the thickness of the diaphragm (cm); A is the measurement area of ​​the diaphragm (cm 2 );R b is the bulk resistance of the battery (Ω), which was tested using an electrochemical workstation.

[0060] In the present invention, the test method of the thermal shrinkage rate of the modified diaphragm includes: cutting the modified diaphragm into a 5cm×5cm size diaphragm and placing it in an oven, keeping it at 105°C for 1 hour, and the test method of the thermal shrinkage rate refers to the standard of GB / T3519. The thermal shrinkage rate of the modified diaphragm is measured in the longitudinal and transverse directions respectively, and then the higher value of the thermal shrinkage rate in the longitudinal and transverse directions is defined as the thermal shrinkage rate of the modified diaphragm.

[0061] The third aspect of the present invention provides a use of the modified diaphragm described in the first aspect or the modified diaphragm prepared by the method described in the second aspect in a lithium ion battery.

[0062] A fourth aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the separator is the modified separator described in the first aspect or the modified separator obtained by the method described in the second aspect.

[0063] In the present invention, the positive electrode is made of a positive electrode material, a conductive agent and a binder for lithium-ion batteries, and the positive electrode material can be any existing one, for example, at least one of lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA). The negative electrode can be made of any negative electrode material, a conductive agent and a binder, and the negative electrode material can be any negative electrode material, for example, at least one of graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen carbon and metallic lithium.

[0064] In the present invention, the lithium-ion battery has all the characteristics and advantages of the modified diaphragm described above, which will not be described in detail here.

[0065] The present invention will be described in detail below through examples.

[0066] The testing methods for the average particle size of polymer microspheres, thickness of the modified layer, ionic conductivity and shrinkage of the modified diaphragm in the following examples and comparative examples are the same as those in the specific embodiments, and will not be repeated here.

[0067] Battery capacity retention rate and coulombic efficiency: LiCoO2 material was used as the positive electrode, lithium sheet was used as the negative electrode, polypropylene membrane Celgard 2325 was used as the original membrane, and the electrolyte was a mixed solution of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (wt / wt / wt=1:1:1) containing 1 mol / L lithium hexafluorophosphate (LiPF6) to make a lithium ion battery;

[0068] The lithium-ion battery was cycled at 0.5C, and the ratio of the discharge capacity at 100 cycles to the discharge capacity at the first cycle was used as the capacity retention rate; and the ratio of the discharge capacity at 100 cycles to the charge capacity at 100 cycles was used as the coulomb efficiency.

[0069] The raw materials used in the following examples and comparative examples are respectively:

[0070] Polyphenylene phthalamide was purchased from Taihe New Materials, with a number average molecular weight of 100,000 g / mol;

[0071] Polyvinylidene fluoride was purchased from Arkema, France;

[0072] N'N-dimethylacetamide was purchased from Sinopharm;

[0073] Polyimide was purchased from Saudi Arabia Basic Materials Co., Ltd. with the brand name Ultem1000.

[0074] Example 1

[0075] (1) dissolving 1 g of poly(phenylene phthalamide) and 0.15 g of poly(vinylidene fluoride) in 50 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 r / min for 12 h to obtain an electrostatic spray precursor solution;

[0076] (2) depositing the electrostatic spray precursor solution on one side of the base film by electrostatic spraying, and forming a modified layer containing polymer microspheres on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 10 μm, an average pore size of 800 nm, a porosity of 44%, a modified layer thickness of 8 μm, and a polymer microsphere diameter of 5.5 μm;

[0077] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 15 kV, the receiving distance is 15 cm, the electrostatic spraying precursor liquid injection speed is 1.5 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0078] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0079] Example 2

[0080] (1) dissolving 1 g of soluble polyimide and 0.1 g of polyvinylidene fluoride in 50 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 r / min for 10 h to obtain an electrostatic spray precursor solution;

[0081] (2) depositing the electrostatic spray precursor liquid on one side surface of the base film by electrostatic spraying, and forming a modified layer containing polymer microspheres on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 10 μm, an average pore size of 800 nm, a porosity of 44%, a modified layer thickness of 7 μm, and a polymer microsphere diameter of 4.5 μm;

[0082] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 15 kV, the receiving distance is 15 cm, the electrostatic spraying precursor liquid injection speed is 1.5 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0083] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0084] Example 3

[0085] (1) dissolving 1 g of soluble polyimide and 0.15 g of polyvinylidene fluoride in 50 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 r / min for 10 h to obtain an electrostatic spray precursor solution;

[0086] (2) depositing the electrostatic spray precursor liquid on one side surface of the base film by electrostatic spraying, and forming a modified layer containing a polymer microsphere layer on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 12 μm, an average pore diameter of 750 nm, a porosity of 35%, a modified layer thickness of 10 μm, and a polymer microsphere diameter of 6.1 μm;

[0087] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 15 kV, the receiving distance is 15 cm, the electrostatic spraying precursor liquid injection speed is 3 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0088] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0089] Example 4

[0090] (1) dissolving 1 g of poly(phenylene phthalamide) and 0.15 g of poly(vinylidene fluoride) in 50 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 / min for 12 h to obtain an electrostatic spray precursor solution;

[0091] (2) depositing the electrostatic spray precursor liquid on one side surface of the base film by electrostatic spraying, and forming a modified layer containing a polymer microsphere layer on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 12 μm, an average pore diameter of 750 nm, a porosity of 35%, a modified layer thickness of 15 μm, and a polymer microsphere diameter of 7.3 μm;

[0092] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 10 kV, the receiving distance is 15 m, the electrostatic spraying precursor liquid injection speed is 3 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0093] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0094] Example 5

[0095] (1) dissolving 1 g of poly(phenylene phthalamide) and 0.15 g of poly(vinylidene fluoride) in 20 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 r / min for 12 h to obtain an electrostatic spray precursor solution;

[0096] (2) depositing the electrostatic spray precursor liquid on one side surface of the base film by electrostatic spraying, and forming a modified layer containing a polymer microsphere layer on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 12 μm, an average pore diameter of 750 nm, a porosity of 35%, a modified layer thickness of 20 μm, and a polymer microsphere diameter of 9.7 μm;

[0097] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 10 kV, the receiving distance is 10 cm, the electrostatic spraying precursor liquid injection speed is 1.5 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0098] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0099] Example 6

[0100] (1) dissolving 1 g of poly(phenylene phthalamide) and 0.15 g of poly(vinylidene fluoride) in 200 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 rad / min for 12 h to obtain an electrostatic spray precursor solution;

[0101] (2) depositing the electrostatic spray precursor liquid on one side surface of the base film by electrostatic spraying, and forming a modified layer containing a polymer microsphere layer on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 12 μm, an average pore size of 750 nm, a porosity of 35%, a modified layer thickness of 6 μm, and a polymer microsphere diameter of 1.2 μm;

[0102] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 30 kV, the receiving distance is 10 cm, the electrostatic spraying precursor liquid injection speed is 1.5 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0103] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0104] Comparative Example 1

[0105] Different from Example 1, the base film is directly subjected to a cycle performance test. The test results are shown in Table 1.

[0106] Comparative Example 2

[0107] (1) dissolving 1 g of poly(phenylene phthalamide) and 0.02 g of poly(vinylidene fluoride) in 50 mL of N,N-dimethylacetamide, stirring at 90° C. and 500 r / min for 12 h to obtain an electrostatic spray precursor solution;

[0108] (2) depositing the electrostatic spray precursor liquid on one side of the base film by electrostatic spraying, and forming a modified layer containing polymer microspheres on the surface of the base film after drying at 60° C. to obtain the modified diaphragm, wherein the base film has a thickness of 10 μm, an average pore size of 800 nm, a porosity of 44%, a modified layer thickness of 7 μm, and a polymer microsphere diameter of 5.3 μm, but is easy to fall off;

[0109] The specific process conditions of the electrostatic spraying include: the needle nozzle aperture is 0.2 mm, the spinning voltage is 15 kV, the receiving distance is 15 cm, the electrostatic spraying precursor liquid injection speed is 1.5 mL / h, the ambient temperature is 30° C., and the relative humidity is 30%.

[0110] The above modified membrane was subjected to a cycle performance test, and the results are shown in Table 1.

[0111] Table 1

[0112]

[0113] It can be seen from the results in Table 1 that the modified diaphragm prepared by the method of the present invention has excellent thermal dimensional stability and ionic conductivity, and improves the coulombic efficiency and cycle life of the lithium ion battery. It can be seen from Examples 1-4 in Table 1 that the particle size of the polymer microspheres is within the preferred range, the thermal dimensional stability and ionic conductivity of the modified diaphragm are higher, and it has more excellent electrochemical performance; it can be seen from Examples 5 and 6 in Table 1 that the particle size of the polymer microspheres is not within the preferred range, so the thermal dimensional stability and ionic conductivity of the modified diaphragm are slightly reduced, and the electrochemical performance is slightly reduced, indicating that the size of the polymer microspheres has an effect on the performance of the modified diaphragm; Comparative Example 1 in Table 1 does not perform surface modification on the base film, and the ionic conductivity of the obtained modified diaphragm is good, but the thermal dimensional stability is greatly reduced, and the electrochemical performance is poor; the mass ratio of the binder to the polymer in the polymer microspheres in Comparative Example 2 in Table 1 is not within the range specified by the present invention, and the polymer microspheres in the obtained modified diaphragm are very easy to fall off, and performance testing cannot be performed.

[0114] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A modified diaphragm, characterized in that: The diaphragm comprises a base film and a modified layer compounded on at least one surface of the base film, wherein the modified layer comprises a binder and polymer microspheres; the mass ratio of the binder to the polymer in the polymer microspheres is 0.05-0.2:1; Wherein, the average particle size of the polymer microspheres is 1-10 μm.

2. The diaphragm according to claim 1, wherein The mass ratio of the binder to the polymer in the polymer microspheres is 0.1-0.15:1; Preferably, the average particle size of the polymer microspheres is 1.2-9.7 μm, preferably 4.5-7.5 μm; Preferably, the thickness of the modified layer is 2-20 μm, preferably 3-10 μm.

3. The diaphragm according to claim 1 or 2, wherein: The base membrane is a polymer membrane, preferably a polyolefin membrane, more preferably any one selected from a polypropylene membrane, a polyethylene membrane and a polypropylene / polyethylene composite membrane; Preferably, the base film has a thickness of 5-15 μm, preferably 6-12 μm; an average pore size of 600-1200 nm, preferably 800-1000 nm; and a porosity of 30-60%, preferably 35-50%.

4. The diaphragm according to any one of claims 1 to 3, wherein: The binder is selected from at least one of polyvinylidene fluoride, polyacrylonitrile, polyurethane and polyimide.

5. The diaphragm according to any one of claims 1 to 4, wherein: The polymer in the polymer microspheres is selected from at least one of poly(arylethersulfoneketone), polyethylene terephthalate, polyetheretherketone, polyetherketone, polyphenylene phthalamide and cellulose acetate; Preferably, the polymer microspheres are obtained by subjecting the polymer to electrostatic spraying.

6. A method for preparing the modified diaphragm according to any one of claims 1 to 5, wherein: The method comprises the following steps: (1) dispersing a polymer and a binder in a dispersion medium and mixing them to obtain an electrostatic spray precursor solution; (2) Electrostatically spraying the electrostatic spray precursor liquid on at least one surface of the base film to form polymer microspheres on the surface of the base film, and then drying to obtain the modified diaphragm.

7. The method according to claim 6, wherein: In step (1), based on the total amount of the electrostatic spray precursor solution, the mass fraction of the polymer is 0.5-5wt%, preferably 0.8-3wt%; Preferably, the mass ratio of the binder to the polymer is 0.05-0.2:1, preferably 0.1-0.15:

1.

8. The method according to claim 6 or 7, wherein: In step (1), the mixing temperature is 60-120° C., the mixing time is 6-12 h, and the mixing speed is 500-800 r / min; Preferably, the dispersion medium is an organic solvent, preferably at least one selected from tetrahydrofuran, acetone, ethanol, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, ethyl acetate, dimethyl sulfoxide, ethyl methyl carbonate and cyclohexane; Preferably, based on the total amount of the electrostatic spray precursor solution, the mass fraction of the dispersion medium is 94-99.5wt%, preferably 97-99.2wt%.

9. The method according to any one of claims 6 to 8, wherein: In step (2), the process conditions of the electrostatic spray include: the needle nozzle aperture is 0.2-3mm, preferably 0.5-2.5mm; the spinning voltage is 5-30kV, preferably 10-25kV; the receiving distance is 10-20cm, preferably 12-18cm; the electrostatic spray precursor injection speed is 0.5-3mL / h, preferably 1.0-2mL / h; the ambient temperature is 10-35°C; the relative humidity is 15-40%; Preferably, the drying temperature is 60-90° C. and the drying time is 8-24 h.

10. Use of the modified diaphragm described in any one of claims 1 to 5 or the modified diaphragm prepared by the method described in any one of claims 6 to 9 in lithium ion batteries.

11. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the separator is a modified separator as described in any one of claims 1 to 5 or a modified separator prepared by the method as described in any one of claims 6 to 9.

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