Separation, preparation method therefor, and battery

Abstract

A separator, a preparation method therefor, and a battery. The separator comprises a porous polymer matrix and solid electrolyte particles; and the solid electrolyte particles are dispersed in the porous polymer matrix with a dispersion range of 1–6 μm and a particle coverage rate of 5-20%.

Description

A diaphragm and its preparation method, and battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on November 30, 2023, with application number 202311636881.1 and titled “A diaphragm and its preparation method, battery, and electrical equipment,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present application belongs to the technical field of battery materials, and specifically relates to a diaphragm and a preparation method thereof, and a battery. Background Art

[0004] Polymer separators prepared by stretching have been widely used in the production of lithium-ion battery separator materials. Traditional polymer separators mainly provide channels for ions to shuttle between the positive and negative electrodes. However, traditional polymer separators have performance deficiencies, such as poor heat resistance and poor electrolyte wettability, which cannot help improve the electrochemical performance of the battery. Some studies have improved separator performance by extruding inorganic particles and polymer blends, but in fact, the addition of inorganic particles has limited improvement in the heat resistance of polymer separators and will cause the tensile strength of polymer separators to decrease. On the other hand, the addition of inorganic particles will reduce the lithium ion conductivity of the separator and affect the wettability of the electrolyte to the separator, thereby affecting the ionic conductivity of the separator, increasing the internal resistance of the battery, and leading to uneven lithium ion deposition and black spots, which are not conducive to the battery's capacity at low temperatures.

[0005] Summary of the Invention

[0006] In response to the problems of decreased tensile strength and decreased ion conductivity in existing polymer membranes with added inorganic particles, the present application provides a membrane, a preparation method thereof, and a battery.

[0007] The technical solutions adopted by this application to solve the above technical problems are as follows:

[0008] In one aspect, the present application provides a membrane comprising:

[0009] a porous polymer matrix; and,

[0010] Solid electrolyte particles are dispersed in the porous polymer matrix, and the dispersion range of the solid electrolyte particles in the porous polymer matrix is ​​1 μm to 6 μm, and the particle coverage is 5% to 20%.

[0011] In some embodiments, the dispersion range of the solid electrolyte particles in the porous polymer matrix is ​​1 μm to 4.5 μm, and the particle coverage is 12% to 19%.

[0012] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​50% to 90%, and the mass content of the solid electrolyte particles is 10% to 50%.

[0013] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​50% to 80%, and the mass content of the solid electrolyte particles is 20% to 50%.

[0014] In some embodiments, the melting point of the porous polymer matrix is ​​80°C to 180°C.

[0015] In some embodiments, the material of the porous polymer matrix includes one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide and polyvinylidene fluoride. In the present disclosure, low-density polyethylene may include but is not limited to linear low-density polyethylene.

[0016] In some embodiments, the solid electrolyte particles include Li 1.3 Al 0.3 Ti 1.7 (PO4)3、Li7La3Zr2O 12 、Li 0.34 La 0.56 TiO3 and Li 1.5 Al 0.5 Ge 1.5 One or more of (PO4)3.

[0017] In some embodiments, the particle size D50 of the solid electrolyte particles is 0.5 μm to 5 μm.

[0018] In some embodiments, the diaphragm satisfies at least one of the following conditions:

[0019] The tensile strength of the diaphragm is 150MPa to 300MPa;

[0020] The pore size of the diaphragm is 20nm to 70nm;

[0021] The porosity of the diaphragm is 20% to 70%;

[0022] The air permeability of the diaphragm is 50s / 100cc to 500s / 100cc;

[0023] The electrolyte diffusion radius of the diaphragm is 0.2 cm to 3 cm.

[0024] In some embodiments, the thickness of the separator is 2 μm to 20 μm.

[0025] On the other hand, the present application provides a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0026] Pre-dispersing the solid electrolyte particles in paraffin oil to form a suspension;

[0027] mixing the suspension with a polymer material to prepare a membrane precursor;

[0028] The paraffin oil in the membrane precursor is removed to obtain the membrane.

[0029] In some embodiments, the mass ratio of the polymer material to the paraffin oil is (25-35): (65-75).

[0030] In some embodiments, the paraffin oil removal method is organic extraction.

[0031] On the other hand, the present application provides a battery comprising a positive electrode, a negative electrode, and the separator as described above, wherein the separator is located between the positive electrode and the negative electrode.

[0032] According to the diaphragm provided by the present application, solid electrolyte particles are used as fillers in the porous polymer matrix. Compared with conventional inorganic particles, solid electrolyte particles can not only improve the high temperature resistance of the diaphragm, but also the lattice defects and voids inside them can realize the transmission of lithium ions, which can effectively improve the ion transmission capacity of the diaphragm. At the same time, the inventors have found that the extremely poor dispersion of solid electrolyte particles in the porous polymer matrix and the particle coverage rate affect the tensile strength of the diaphragm and the wetting performance of the electrolyte. When the extremely poor dispersion of solid electrolyte particles in the porous polymer matrix is ​​between 1μm and 6μm, and the particle coverage rate is 5% to 20%, the tensile strength of the diaphragm itself can be effectively guaranteed. At the same time, the wetting ability of the electrolyte for the diaphragm is improved, avoiding the problem of negative electrode black spots caused by poor diffusion of the electrolyte, and effectively avoiding the problem of lithium dendrites caused by uneven deposition of lithium ions, thereby improving the ion conductivity of the diaphragm and improving the electrochemical performance of the battery at low temperatures. DETAILED DESCRIPTION

[0033] In the embodiments of this application, the term "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0034] In order to make the technical problems, technical solutions and beneficial effects solved by this application more clearly understood, this application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0035] The present application provides a diaphragm, comprising:

[0036] a porous polymer matrix; and,

[0037] The solid electrolyte particles are dispersed in the porous polymer matrix, and the dispersion range of the solid electrolyte particles in the porous polymer matrix is ​​1 μm to 6 μm, and the particle coverage is 5% to 20%.

[0038] The diaphragm uses solid electrolyte particles as fillers in a porous polymer matrix. Compared to conventional inorganic particles, solid electrolyte particles can not only improve the high temperature resistance of the diaphragm, but also the lattice defects and voids inside them can realize the transmission of lithium ions, which can effectively improve the ion transmission capacity of the diaphragm. At the same time, the inventors found that the extremely poor dispersion of solid electrolyte particles in the porous polymer matrix and the particle coverage rate affect the tensile strength of the diaphragm and the wettability of the electrolyte. When the extremely poor dispersion of solid electrolyte particles in the porous polymer matrix is ​​between 1μm and 6μm, and the particle coverage rate is 5% to 20%, the tensile strength of the diaphragm itself can be effectively guaranteed. At the same time, the wettability of the electrolyte to the diaphragm is improved, avoiding the problem of negative electrode black spots caused by poor diffusion of the electrolyte. It can also effectively avoid the problem of lithium dendrites caused by uneven deposition of lithium ions, improve the ionic conductivity of the diaphragm, and thus improve the electrochemical performance of the battery at low temperatures.

[0039] In the description of this application, the term "extremely poor dispersion" reflects the dispersion state of the solid electrolyte particles in the polymer matrix. The extremely poor dispersion can be measured by the following methods:

[0040] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance L (μm) between adjacent solid electrolyte particles in the area was measured. The maximum value L1 (μm) and the minimum value L2 (μm) of the distance between the solid electrolyte particles were subtracted from each other, and the difference (L1-L2) obtained was the extremely poor dispersion of the solid electrolyte particles in the porous polymer matrix.

[0041] In the description of this application, the term "particle coverage" reflects the coverage state of solid electrolyte particles in the polymer matrix. Particle coverage can be measured by the following methods:

[0042] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, which was the particle coverage.

[0043] In different embodiments, the dispersion range of the solid electrolyte particles in the porous polymer matrix can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 5 μm, 4.8 μm, 5.0 μm, 5.4 μm, 5.8 μm or 6.0 μm. The particle coverage of the solid electrolyte particles in the porous polymer matrix can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0044] In some embodiments, the dispersion of the solid electrolyte particles in the porous polymer matrix ranges from 1 μm to 4.5 μm, and the particle coverage is 12% to 19%.

[0045] When the dispersion of the solid electrolyte particles in the porous polymer matrix is ​​extremely poor and the particle coverage is within the above range, it is beneficial to further improve the tensile strength, ionic conductivity and the wettability of the electrolyte to the diaphragm.

[0046] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​50% to 90%, and the mass content of the solid electrolyte particles is 10% to 50%.

[0047] The porous polymer matrix is ​​the main matrix for maintaining the shape and toughness of the diaphragm, and is also the main matrix for forming the porous structure. Among them, the porous structure has the permeability of the electrolyte, and the polymer material itself has affinity and wettability for the electrolyte, ensuring the ion exchange of the electrolyte on both sides of the diaphragm; and the solid electrolyte particles are used to improve the ionic conductivity and high temperature resistance of the diaphragm. When the mass content of the porous polymer matrix and the solid electrolyte particles is within the above range, it can be ensured that the diaphragm has both high tensile strength, good high temperature resistance and ion conduction.

[0048] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​50% to 80%, and the mass content of the solid electrolyte particles is 20% to 50%.

[0049] In some embodiments, the porous polymer matrix has a melting point of 80°C to 180°C.

[0050] When the melting point of the porous polymer matrix is ​​within the above range, the porous polymer matrix has good heat resistance and flexibility.

[0051] In some embodiments, the material of the porous polymer matrix includes one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide and polyvinylidene fluoride. In the present disclosure, low-density polyethylene may include but is not limited to linear low-density polyethylene. Among them, high-density polyethylene refers to a density of 0.94 to 0.95 g / m 3 Ultra-high density polyethylene refers to a density greater than 0.96g / m 3 ; Low-density polyethylene refers to a density of 0.91g / m 3 The density of high-density polypropylene is about 0.89~0.91g / m 3 ;Ultra-high-density polypropylene has a density greater than 0.91g / m 3 .

[0052] In some embodiments, the solid electrolyte particles include LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3)、LLZO(Li7La3Zr2O 12 )、LLTO(Li 0.34 La 0.56 TiO3) and LAGP(Li 1.5 Al 0.5 Ge 1.5 (PO4)3) or more.

[0053] By selecting LATP(Li 1.3 Al 0.3 Ti 1.7 (PO4)3), LLZO(Li7La3Zr2O 12 )、LLTO(Li 0.34 La 0.56 TiO3) and LAGP(Li 1.5 Al 0.5 Ge 1.5 One or more (PO4)3) solid electrolyte particles offer the advantages of high lithium ion conductivity and thermal stability, helping to reduce battery internal resistance and improve battery safety. These solid electrolyte particles can be undoped or modified by doping, and their surfaces may or may not have a conductive coating. The material and thickness of the conductive coating can be selected as needed and are not further detailed in this disclosure.

[0054] In some embodiments, the particle size (D50) of the solid electrolyte particles is 0.5 μm to 5 μm.

[0055] In different embodiments, the particle size (D50) of the solid electrolyte particles may be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm or 5 μm.

[0056] The particle size (D50) of the solid electrolyte particles is related to the degree of dispersion thereof in the porous polymer matrix. When the particle size (D50) of the solid electrolyte particles is within the above range, compared with conventional inorganic fillers, the particle size (D50) is larger, which can effectively avoid the agglomeration problem caused by the van der Waals force or electrostatic force between the particles, improve the dispersion uniformity of the solid electrolyte particles in the porous polymer matrix, and improve the consistency of the performance of each region of the diaphragm. The particle size D50 of the solid electrolyte particles refers to the median particle size of the solid electrolyte particles, also known as the volume average particle size, which indicates the particle size corresponding to the cumulative volume distribution percentage of the solid electrolyte particles reaching 50%. The D50 of the solid electrolyte particles can be obtained by testing with a laser particle size tester.

[0057] The tensile strength of the diaphragm is affected by the porous polymer matrix and is also affected by the extreme dispersion of the added solid electrolyte particles and the particle coverage. When the extreme dispersion of the solid electrolyte particles is controlled to be between 1 μm and 6 μm and the particle coverage is between 5% and 20%, it is beneficial to ensure that the tensile strength of the diaphragm is at a higher level.

[0058] In some embodiments, the membrane satisfies at least one of the following conditions:

[0059] The tensile strength of the diaphragm is 150MPa to 300MPa;

[0060] The pore size of the diaphragm is 20nm to 70nm;

[0061] The porosity of the diaphragm is 20% to 70%;

[0062] The air permeability of the diaphragm is 50s / 100cc to 500s / 100cc;

[0063] The electrolyte diffusion radius of the diaphragm is 0.2 cm to 3 cm.

[0064] In some embodiments, the tensile strength of the separator is 150 MPa to 300 MPa.

[0065] In some embodiments, the pore size of the membrane is 20 nm to 70 nm, and the porosity of the membrane is 20% to 70%.

[0066] The pore size and porosity of the separator affect both its electrolyte permeability and its barrier effect on the positive and negative electrodes. When the pore size and porosity of the separator are within the above ranges, it prevents short circuits between the positive and negative electrodes, reducing self-discharge rates while also providing good electrolyte permeability and enhancing ionic conductivity.

[0067] In some embodiments, the membrane has an air permeability of 50s / 100cc to 500s / 100cc.

[0068] The air permeability of the separator is affected to a certain extent by the porosity of the separator. When the air permeability of the separator is within the above range, it is beneficial to improve the permeation efficiency of lithium ions.

[0069] In some embodiments, the electrolyte diffusion radius of the separator is 0.2 cm to 3 cm.

[0070] The electrolyte diffusion radius of the diaphragm is used to characterize the penetration and wetting effect of the electrolyte on the diaphragm.

[0071] In the description of this application, the "electrolyte diffusion radius of the diaphragm" can be obtained by testing using the following method:

[0072] Place the diaphragm in a circular hollow fixture with a radius of 3 cm, so that the diaphragm is suspended in the air. Use a pipette to take 30 μL of electrolyte and drop it into the middle of the diaphragm. After 30 seconds, measure the radius of the electrolyte diffusion.

[0073] In some embodiments, the thickness of the separator is 2 μm to 20 μm.

[0074] When the thickness of the separator is within the above range, it can effectively block the positive electrode and the negative electrode while taking into account the ion permeability and at the same time has a certain mechanical strength to prevent puncture.

[0075] Another embodiment of the present application provides a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0076] dispersing the solid electrolyte particles in paraffin oil to form a suspension;

[0077] mixing the suspension with a polymer material to prepare a membrane precursor; and,

[0078] The paraffin oil of the membrane precursor is removed to obtain the membrane.

[0079] Compared to the existing diaphragm preparation method, the present application changes the material processing sequence before extrusion. Specifically, unlike the existing blending method of inorganic fillers, in this preparation method, the solid electrolyte particles are first dispersed in paraffin oil to form a suspension, and then the suspension is mixed with the polymer material to obtain a diaphragm precursor. Among them, paraffin oil has a pore-forming effect. During the blending process, the paraffin oil and the polymer material are fully mixed. After the subsequent removal of the paraffin oil operation, the paraffin oil is removed to form holes in the polymer material to obtain a porous polymer matrix. Pre-mixing the solid electrolyte particles with paraffin oil to form a suspension is also an important operation to reduce the extremely poor dispersion of the solid electrolyte particles in the porous polymer matrix and improve the particle coverage. Through the dispersion of paraffin oil, the agglomeration phenomenon of the solid electrolyte particles can be reduced, thereby improving the dispersibility of the solid electrolyte particles in the porous polymer matrix, making the solid electrolyte particles in the prepared diaphragm more uniform, which is beneficial to improving the tensile strength and ion conductivity of the diaphragm. More importantly, since the solid electrolyte particles are dispersed in paraffin oil, the surface of the solid electrolyte particles can be fully exposed on the inner wall of the pores during the process of removing the paraffin oil to form pores, thereby avoiding the coating of the solid electrolyte particles by the polymer material, which is conducive to fully leveraging the advantages of the high ionic conductivity of the solid electrolyte particles and improving the particle coverage of the diaphragm without increasing the amount of solid electrolyte particles added.

[0080] In some embodiments, the polymeric material includes one or more of high density polyethylene, ultra high density polyethylene, low density polyethylene, high density polypropylene, ultra high density polypropylene, polyimide, and polyvinylidene fluoride.

[0081] In some embodiments, the mass ratio of the polymer material to the paraffin oil is (25-35):(65-75).

[0082] By controlling the mass ratio of the polymer material to the paraffin oil within the above range, it is beneficial to regulate the pore size and porosity of the diaphragm, thereby ensuring the ion conductivity of the diaphragm.

[0083] In some embodiments, the solid electrolyte particles are dispersed in the paraffin oil by one or more of stirring, ultrasonic treatment, and mechanical grinding.

[0084] In some embodiments, the membrane precursor is prepared by extrusion.

[0085] In some embodiments, the paraffin oil removal method is organic extraction.

[0086] Specifically, the membrane precursor is placed in an organic solvent, the paraffin oil in the membrane precursor is dissolved and removed by the organic solvent, and then the membrane precursor from which the paraffin oil has been removed is dried to obtain the membrane.

[0087] In some embodiments, the membrane precursor is stretched after the extrusion operation to obtain a membrane precursor with a desired thickness.

[0088] Another embodiment of the present application provides a battery, comprising a positive electrode, a negative electrode, and the separator as described above, wherein the separator is located between the positive electrode and the negative electrode.

[0089] The use of the diaphragm as described above can significantly improve the battery's resistance to lithium dendrite growth due to the diaphragm's high tensile strength and ionic conductivity, thereby preventing the diaphragm from being pierced by lithium dendrites and causing a short circuit. At the same time, it reduces the battery impedance and improves the battery's low-temperature performance.

[0090] The present application is further described below through examples.

[0091] Example 1

[0092] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0093] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 59% by mass;

[0094] The solid electrolyte particles are LLZO (Li7La3Zr2O) with a particle size (D50) of 1.5 μm. 12 ), quality accounts for 41%;

[0095] The solid electrolyte particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. The suspension is then mixed with the polymer material and extruded and stretched by co-extrusion to prepare a diaphragm precursor. The paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0096] Dispersion extreme test: Take an SEM photograph of the membrane surface at a magnification of 5000 times, select an area with a length and width of 0.5cm*0.5cm in the SEM photograph, and measure the distance between adjacent solid electrolyte particles in the area. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion extreme of the solid electrolyte particles in the porous polymer matrix, which is 1.5μm.

[0097] Particle coverage test: An SEM photograph of the diaphragm surface was taken at a magnification of 5000 times. An area with a length and width of 0.5 cm * 0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the diaphragm area was calculated, and the particle coverage was obtained to be 18.5%.

[0098] Air permeability test: Take a diaphragm with a TD (transverse) length greater than 10 cm and use an air permeability tester (brand: SYSTESTER, model: GTR) to perform an air permeability test.

[0099] Porosity test: Take a 10*10cm square diaphragm, measure the average thickness d of the diaphragm, weigh the mass m of the sample, and calculate the porosity of the diaphragm according to the formula: P = (1-m / (L×b×d×p0))×100%. Among them, P is the porosity of the diaphragm, %; m is the mass of the diaphragm, in grams (g); L is the length of the diaphragm, in centimeters (cm); b is the width of the diaphragm, in centimeters (cm); d is the thickness of the diaphragm, in micrometers (μm); p0 is the density of the diaphragm, in g / cm 3 ). Wherein, L and b are both 10 cm.

[0100] Diaphragm pore diameter test: Place the diaphragm under a microscope and observe it, and calculate the average value of 100 pore diameters. If the pores are irregular in shape, the longest pore diameter is selected as the diaphragm diameter.

[0101] The above-mentioned separator has a porosity of 51%, a pore diameter of 54 nm, an air permeability of 75 s / 100 cc, and a thickness of 7 μm.

[0102] Example 2

[0103] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0104] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 62% by mass;

[0105] The solid electrolyte particles are LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3), accounting for 38% by mass;

[0106] The solid electrolyte particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. The suspension is then mixed with the polymer material and extruded and stretched by co-extrusion to prepare a diaphragm precursor. The paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0107] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion range of the solid electrolyte particles in the porous polymer matrix, which is 1.63 μm.

[0108] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 15.0%.

[0109] The porosity of the above-mentioned diaphragm is 43%, the pore diameter is 50 nm, the air permeability is 110 s / 100 cc, and the thickness is 9 μm; the testing method is the same as that of Example 1.

[0110] Example 3

[0111] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0112] The polymer material is high-density polypropylene with a melting point of 165°C, accounting for 80% by mass;

[0113] The solid electrolyte particles are LLZO (Li7La3Zr2O) with a particle size (D50) of 0.6 μm. 12 ), quality accounts for 20%;

[0114] The solid electrolyte particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. The suspension is then mixed with the polymer material and extruded and stretched by co-extrusion to prepare a diaphragm precursor. The paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0115] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the solid electrolyte particles in the porous polymer matrix, which is an extreme difference of 4.2 μm.

[0116] An SEM photograph of the membrane surface at a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 12.5%.

[0117] The porosity of the above-mentioned diaphragm is 38%, the pore diameter is 42 nm, the air permeability is 120 s / 100 cc, and the thickness is 10 μm; the testing method is the same as that of Example 1.

[0118] Example 4

[0119] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0120] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 52% by mass;

[0121] The solid electrolyte particles are LLZO (Li7La3Zr2O) with a particle size (D50) of 1.5 μm. 12 ), quality accounts for 48%;

[0122] The solid electrolyte particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. The suspension is then mixed with the polymer material and extruded and stretched by co-extrusion to prepare a diaphragm precursor. The paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0123] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the solid electrolyte particles in the porous polymer matrix, and the extreme difference is 1.0 μm.

[0124] An SEM photograph of the membrane surface at a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 19.5%.

[0125] The porosity of the above-mentioned diaphragm is 52%, the pore diameter is 54 nm, the air permeability is 70 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0126] Example 5

[0127] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0128] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 88% by mass;

[0129] The solid electrolyte particles are LLZO (Li7La3Zr2O) with a particle size (D50) of 1.5 μm. 12 ), quality accounts for 12%;

[0130] The solid electrolyte particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. The suspension is then mixed with the polymer material and extruded and stretched by co-extrusion to prepare a diaphragm precursor. The paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0131] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion range of the solid electrolyte particles in the porous polymer matrix, which is 5.5 μm.

[0132] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 9%.

[0133] The porosity of the above-mentioned diaphragm is 38%, the pore diameter is 45 nm, the air permeability is 130 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0134] Comparative Example 1

[0135] This comparative example is used to compare and illustrate the separator, battery, and preparation method thereof disclosed in this application, and includes the following steps:

[0136] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 45% by mass;

[0137] The solid electrolyte particles are LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3), accounting for 55% by mass;

[0138] The solid electrolyte particles, paraffin oil and polymer material are directly blended and then co-extruded and stretched to prepare a membrane precursor, where the mass ratio of paraffin oil to polymer material is 70:30; the paraffin oil in the membrane precursor is removed by organic extraction to obtain a membrane.

[0139] An SEM photograph of the membrane surface at a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion range of the solid electrolyte particles in the porous polymer matrix, which is 0.6 μm.

[0140] An SEM photograph of the membrane surface at a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 23%.

[0141] The porosity of the above-mentioned diaphragm is 55%, the pore diameter is 50 nm, the air permeability is 60 s / 100 cc, and the thickness is 9 μm; the testing method is the same as that of Example 1.

[0142] Comparative Example 2

[0143] This comparative example is used to compare and illustrate the separator, battery, and preparation method thereof disclosed in this application, and includes the following steps:

[0144] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 92% by mass;

[0145] The solid electrolyte particles are LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3), accounting for 8% by mass;

[0146] The solid electrolyte particles, paraffin oil and polymer material are directly blended and then co-extruded and stretched to prepare a membrane precursor, where the mass ratio of paraffin oil to polymer material is 70:30; the paraffin oil in the membrane precursor is removed by organic extraction to obtain a membrane.

[0147] An SEM photograph of the membrane surface with a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent solid electrolyte particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the solid electrolyte particles in the porous polymer matrix, which is an extreme difference of 7 μm.

[0148] An SEM photograph of the membrane surface was taken at a magnification of 5000 times. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 4.8%.

[0149] The porosity of the above-mentioned diaphragm is 38%, the pore diameter is 45 nm, the air permeability is 150 s / 100 cc, and the thickness is 9 μm; the testing method is the same as that of Example 1.

[0150] Comparative Example 3

[0151] This comparative example is used to compare and illustrate the separator, battery, and preparation method thereof disclosed in this application, and includes the following steps:

[0152] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 59% by mass;

[0153] The particle size (D50) of conventional alumina particles is 1.5 μm, accounting for 41% by mass;

[0154] The above-mentioned aluminum oxide particles are first dispersed in a paraffin oil system by stirring to form a suspension, with the mass ratio of paraffin oil to polymer material being 70:30. Then, after mixing with the polymer material, the suspension is extruded and stretched by co-extrusion to prepare a diaphragm precursor; the paraffin oil in the diaphragm precursor is removed by organic extraction to obtain a diaphragm.

[0155] An SEM photograph of the diaphragm surface at a magnification of 5000 times was taken. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the distance between adjacent alumina particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the alumina particles in the porous polymer matrix, which is an extreme difference of 1.6 μm.

[0156] An SEM photograph of the membrane surface was taken at a magnification of 5000 times. An area with a length and width of 0.5 cm*0.5 cm was selected in the SEM photograph, and the solid electrolyte particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the membrane area was calculated, and the particle coverage was obtained to be 18.1%.

[0157] The porosity of the above-mentioned diaphragm is 43%, the pore diameter is 50 nm, the air permeability is 110 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0158] Performance Testing

[0159] The following performance tests were performed on the diaphragm prepared above:

[0160] 1. Electrolyte Diffusion Radius Test: Place the separator in a circular hollow fixture with a radius of 3 cm, leaving it suspended above the table. Use a pipette to dispense 30 μL of electrolyte onto the center of the separator. After 30 seconds, measure the electrolyte diffusion radius. The electrolyte composition is: DMC:EMC:DEC:EC = 1:3:1:4, plus 1 mol / L LiPF6.

[0161] 2. Low-temperature ionic conductivity test: Assemble the separator with the positive electrode, negative electrode, and electrolyte to form a battery. Place the prepared battery in a -20°C thermostat for 5 hours, and then perform an ionic conductivity test according to the national standard GB-T36363 for ionic conductivity. For the positive electrode, PVDF is dissolved in a certain amount of NMP, lithium iron phosphate and a conductive agent are added, and then coated on aluminum foil by coating. The mass ratio of lithium iron phosphate, conductive agent (carbon black), and PVDF is 96:2:2. For the negative electrode, SBR, graphite material, and conductive agent are added to water, and then coated on copper foil by coating. The mass ratio of graphite, conductive agent (carbon black), and SBR is 96:2:2.

[0162] 3. Low-temperature cycling performance test: Assemble the separator with the positive electrode, negative electrode, and electrolyte to form a battery. Place the prepared battery in a -10°C constant temperature chamber for 5 hours. Then, perform 50 charge and discharge cycles at 0.5C / 0.5C. Record the first and last discharge capacities, and calculate the capacity retention rate. After 50 charge and discharge cycles, disassemble the battery, remove the negative electrode, and observe and record the observation results.

[0163] 4. Tensile strength test: The tensile strength test refers to the national standard GB / T36363-2018.

[0164] The test results are entered in Table 1.

[0165] Table 1

[0166] From the test results in Table 1, it can be seen that by controlling the dispersion range of the solid electrolyte particles in the porous polymer matrix to be between 1 μm and 6 μm, and the particle coverage rate to be between 5% and 20%, the tensile strength of the diaphragm can be improved while effectively ensuring the wettability of the electrolyte and the ionic conductivity of the diaphragm. At the same time, the capacity retention rate of the battery during cycling at low temperatures is effectively improved, the formation of lithium dendrites and the occurrence of negative electrode black spots are inhibited, thereby improving the safety performance and low-temperature performance of the battery.

[0167] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A diaphragm, characterized in that: Includes the following components: a porous polymer matrix; and, The solid electrolyte particles are dispersed in the porous polymer matrix, and the dispersion range of the solid electrolyte particles in the porous polymer matrix is ​​1 μm to 6 μm, and the particle coverage is 5% to 20%.

2. The diaphragm according to claim 1, characterized in that The dispersion degree of the solid electrolyte particles in the porous polymer matrix is ​​extremely poor, ranging from 1 μm to 4.5 μm, and the particle coverage is 12% to 19%.

3. The diaphragm according to claim 1 or 2, characterized in that: Based on the total weight of the separator being 100%, the mass content of the porous polymer matrix is ​​50% to 90%, and the mass content of the solid electrolyte particles is 10% to 50%.

4. The diaphragm according to any one of claims 1 to 3, characterized in that: Based on the total weight of the separator being 100%, the mass content of the porous polymer matrix is ​​50% to 80%, and the mass content of the solid electrolyte particles is 20% to 50%.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The melting point of the porous polymer matrix is ​​80°C to 180°C.

6. The diaphragm according to any one of claims 1 to 5, characterized in that: The material of the porous polymer matrix includes one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide and polyvinylidene fluoride.

7. The diaphragm according to any one of claims 1 to 6, characterized in that: The solid electrolyte particles include Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , Li 0.34 La 0.56 TiO3 and Li 1.5 Al 0.5 Ge 1.5 (PO4)3 or more.

8. The diaphragm according to any one of claims 1 to 7, characterized in that: The particle size D50 of the solid electrolyte particles is 0.5 μm to 5 μm.

9. The diaphragm according to any one of claims 1 to 8, characterized in that: The diaphragm satisfies at least one of the following conditions: The tensile strength of the diaphragm is 150MPa to 300MPa; The pore size of the diaphragm is 20nm to 70nm; The porosity of the diaphragm is 20% to 70%; The air permeability of the diaphragm is 50s / 100cc to 500s / 100cc; The electrolyte diffusion radius of the diaphragm is 0.2 cm to 3 cm.

10. The diaphragm according to any one of claims 1 to 9, characterized in that: The thickness of the separator is 2 μm to 20 μm.

11. A method for preparing the diaphragm according to any one of claims 1 to 10, characterized in that: The steps include: dispersing the solid electrolyte particles in paraffin oil to form a suspension; mixing the suspension with a polymer material to prepare a membrane precursor; and, The paraffin oil of the diaphragm precursor is removed to obtain the diaphragm.

12. The method for preparing a diaphragm according to claim 11, characterized in that: The mass ratio of the polymer material to the paraffin oil is (25-35):(65-75).

13. The method for preparing a diaphragm according to claim 11 or 12, characterized in that: The paraffin oil removal method is organic extraction.

14. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a separator according to any one of claims 1 to 10, wherein the separator is located between the positive electrode and the negative electrode.

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