Separator, preparation method therefor, and battery

Abstract

A separator and a preparation method therefor, and a battery. The separator comprises the following components: a porous polymer matrix and lithium-rich material particles; the lithium-rich material particles are dispersed in the porous polymer matrix, the dispersion degree range of the lithium-rich material particles in the porous polymer matrix is 4-10 μm, and the particle coverage rate is 5-12%.

Description

A diaphragm and its preparation method, and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 30, 2023, with application number 202311637518.1 and application name “A diaphragm and its preparation method, battery, and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of battery materials, and more specifically, to a diaphragm and a preparation method thereof, and a battery. Background Art

[0003] Polymer membranes prepared by the stretching method have been widely used in the production of lithium-ion battery membranes. Traditional polymer membranes mainly serve as ion transport channels, but traditional polymer membranes have insufficient performance, such as poor heat resistance and poor electrolyte wettability, which cannot help improve the electrochemical performance of the battery. Some studies have improved the performance of membranes by extruding inorganic particles and polymers, but in fact, the addition of inorganic particles has limited improvement in the heat resistance of polymer membranes; at the same time, it will cause the tensile strength of the polymer membrane to decrease. On the other hand, the addition of inorganic particles will affect the wettability of the electrolyte to the membrane, thereby affecting the ionic conductivity of the membrane, increasing the internal resistance of the battery, and leading to uneven deposition of lithium ions and black spots. During the initial formation of the battery, some lithium salts will be consumed to form the SEI film, which reduces the concentration of lithium salts in the electrolyte, resulting in irreversible capacity loss and low initial efficiency of the battery.

[0004] Summary of the Invention

[0005] In view of the problems of low initial efficiency, easy occurrence of black spots and insufficient tensile strength of the diaphragm in existing batteries, the purpose of this application is to provide a diaphragm and its preparation method, and a battery.

[0006] The technical solutions adopted by this application to solve the above technical problems are as follows:

[0007] In a first aspect, the present application discloses a separator comprising the following components:

[0008] a porous polymer matrix; and,

[0009] Lithium-rich material particles are dispersed in the porous polymer matrix, and the dispersion range of the lithium-rich material particles in the porous polymer matrix is ​​4 μm to 10 μm, and the particle coverage is 5% to 12%.

[0010] In another aspect, the present application discloses a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0011] dispersing the lithium-rich material particles in paraffin oil to form a suspension;

[0012] mixing the suspension with a polymer material to prepare a membrane precursor;

[0013] The paraffin oil in the membrane precursor is removed to obtain the membrane.

[0014] In another aspect, the present application discloses 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.

[0015] In combination with the above technical solutions, the diaphragm disclosed in this application uses lithium-rich material particles as fillers in a porous polymer matrix. Compared with conventional inorganic particles, lithium-rich material particles can not only improve the high temperature resistance of the diaphragm, but also can decompose and release lithium ions under high voltage conditions, thereby replenishing lithium for the battery during the formation stage and improving the battery's initial efficiency. At the same time, the applicant's research found that the extremely poor dispersion of lithium-rich material 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 lithium-rich material particles in the porous polymer matrix is ​​between 4μm and 10μm, and the particle coverage rate is 5% to 12%, the tensile strength of the diaphragm itself can be effectively guaranteed. At the same time, the wetting ability of the electrolyte on the diaphragm is improved, avoiding the problem of negative electrode black spots caused by poor diffusion of the electrolyte, and can also effectively avoid the problem of lithium dendrites caused by uneven deposition of lithium ions. DETAILED DESCRIPTION

[0016] 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.

[0017] 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.

[0018] The present invention provides a membrane comprising the following components:

[0019] Porous polymer matrix and lithium-rich material particles;

[0020] The lithium-rich material particles are dispersed in the porous polymer matrix, and the dispersion degree of the lithium-rich material particles in the porous polymer matrix is ​​4 to 10, and the particle coverage is 5% to 12%.

[0021] The diaphragm uses lithium-rich material particles as fillers in a porous polymer matrix. Compared with conventional inorganic particles, lithium-rich material particles can not only improve the high temperature resistance of the diaphragm, but also can decompose and release lithium ions under high voltage conditions, thereby replenishing lithium to the battery during the formation stage and improving the battery's initial efficiency. At the same time, the applicant's research found that the extremely poor dispersion of lithium-rich material particles in the porous polymer matrix and the particle coverage affect the tensile strength of the diaphragm and the wetting performance of the electrolyte. When the extremely poor dispersion of lithium-rich material particles in the porous polymer matrix is ​​between 4μm and 10μm, and the particle coverage is between 5% and 12%, the tensile strength of the diaphragm itself can be effectively guaranteed. At the same time, the wetting ability of the electrolyte on the diaphragm is improved, avoiding the problem of negative electrode black spots caused by poor diffusion of the electrolyte, and can also effectively avoid the problem of lithium dendrites caused by uneven deposition of lithium ions.

[0022] In the description of this application, the term "extremely poor dispersion" reflects the dispersion state of the lithium-rich material particles in the polymer matrix. The extremely poor dispersion can be measured by the following methods:

[0023] An SEM photograph of the diaphragm 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 lithium-rich material particles in the area was measured. The difference (L1-L2) obtained from the maximum value L1 (μm) and the minimum value L2 (μm) of the distance between adjacent lithium-rich material particles obtained by measurement is the extremely poor dispersion degree of the lithium-rich material particles in the porous polymer matrix.

[0024] In the description of this application, the term "particle coverage" reflects the coverage of lithium-rich material particles in the polymer matrix. Particle coverage can be measured by the following methods:

[0025] An SEM photograph of the diaphragm 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 lithium-rich material particles therein were stained using software. The ratio of the stained area to the non-stained area of ​​the diaphragm area was calculated, which is the particle coverage.

[0026] In various embodiments, the dispersion range of the lithium-rich material particles in the porous polymer matrix may be 5 μm, 4.8 μm, 5.0 μm, 5.4 μm, 5.8 μm, 6.0 μm, 6.9 μm, 7.2 μm, 8.0 μm, 8.5 μm, 9.3 μm, 9.6 μm, or 10 μm. The particle coverage of the lithium-rich material particles in the porous polymer matrix may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%.

[0027] In some embodiments, the dispersion range of lithium-rich material particles in the porous polymer matrix is ​​5 μm to 8.5 μm, and the particle coverage is 6% to 9%.

[0028] When the dispersion degree of lithium-rich material 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 electrolyte wetting performance of the diaphragm.

[0029] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​90% to 99%, and the mass content of the lithium-rich material particles is 1% to 10%.

[0030] In some embodiments, based on 100% of the total weight of the separator, the mass content of the porous polymer matrix is ​​93% to 99.5%, and the mass content of the lithium-rich material particles is 0.5% to 7%.

[0031] The porous polymer matrix is ​​the main matrix structure for maintaining the shape and toughness of the diaphragm, and is also the main structure for forming the porous structure, wherein the porous structure has the permeability of the electrolyte, and the polymer material itself has affinity and wettability for the electrolyte, that is, it ensures the ion exchange of the electrolyte on both sides of the diaphragm. The lithium-rich material particles are used to improve the high temperature resistance of the diaphragm and replenish the lithium ions consumed in the formation stage; when the mass content of the porous polymer matrix and the lithium-rich material particles is within the above range, it can ensure that the diaphragm has high tensile strength, good high temperature resistance and high battery first efficiency.

[0032] In some embodiments, the porous polymer matrix has a melting point of 80°C to 180°C.

[0033] When the melting point of the porous polymer matrix is ​​within the above range, the porous polymer matrix has good heat resistance and flexibility.

[0034] In some embodiments, the porous polymer matrix has a melting point of 100°C to 170°C.

[0035] 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. 3 ~0.95g / 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 3About; the density of high-density polypropylene is 0.89g / m 3 ~0.91g / m 3 ;Ultra-high-density polypropylene has a density greater than 0.91g / m 3 The low-density polyethylene as described above may be a linear low-density polyethylene.

[0036] In some embodiments, the above-mentioned includes one or more of Li5FeO4, Li2Ni5O4, Li2MnO3, LiCoO4, Li6MnO4 and LiReO6.

[0037] By selecting one or more of Li5FeO4, Li2Ni5O4, Li2MnO3, LiCoO4, Li6MnO4, and LiReO6 as lithium-rich material particles, they have the advantages of high lithium content and decomposition and release of lithium ions at high voltages (decomposition at 3.5V to 4.1V), which is conducive to improving the initial efficiency of battery formation. The above lithium-rich material particles can be undoped or doped, and their surfaces can have a conductive coating or not.

[0038] In some embodiments, the particle size (D50) of the lithium-rich material particles is 0.5 μm to 5 μm.

[0039] In different embodiments, the particle size (D50) of the lithium-rich material 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.

[0040] In some embodiments, the particle size (D50) of the lithium-rich material particles is 0.5 μm to 2 μm.

[0041] The particle size (D50) of the lithium-rich material particles is related to their degree of dispersion in the porous polymer matrix. When the particle size (D50) of the lithium-rich material particles is within the above range, compared with conventional inorganic fillers, it has a larger particle size (D50), which can effectively avoid the agglomeration problem caused by van der Waals forces or electrostatic forces between particles, improve the dispersion uniformity of lithium-rich material particles in the porous polymer matrix, and improve the consistency of performance of various regions of the diaphragm. The particle size D50 refers to the median particle size of the lithium-rich material particles, also known as the volume average particle size, which indicates the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. The particle size D50 of the lithium-rich material particles can be obtained by testing with a laser force tester.

[0042] The tensile strength of the diaphragm is affected by the porous polymer matrix, and is also affected by the extreme dispersion degree and particle coverage of the added lithium-rich material particles. When the extreme dispersion degree of the lithium-rich material particles is controlled to be between 4μm and 10μm and the particle coverage is between 5% and 12%, it is beneficial to ensure that the tensile strength of the diaphragm is at a higher level.

[0043] In some embodiments, the diaphragm satisfies at least one of the following conditions:

[0044] The tensile strength of the diaphragm is 150MPa to 300MPa;

[0045] The pore size of the diaphragm is 20nm to 70nm;

[0046] The porosity of the diaphragm is 20% to 70%;

[0047] The air permeability of the diaphragm is 50s to 500s / 100cc;

[0048] The electrolyte diffusion radius of the diaphragm is 0.2 cm to 3 cm.

[0049] In some embodiments, the tensile strength of the separator is 150 MPa to 300 MPa.

[0050] 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%.

[0051] The pore size and porosity of the diaphragm affect the electrolyte permeability of the diaphragm on the one hand, and on the other hand, they also affect the barrier effect of the diaphragm for the positive and negative electrodes; when the pore size and porosity of the diaphragm are within the above range, short circuits between the positive and negative electrodes are prevented, and the self-discharge rate is reduced; at the same time, it also has good electrolyte permeability and improves ion conductivity.

[0052] In some embodiments, the porosity of the separator is 40% to 60%.

[0053] In some embodiments, the membrane has an air permeability of 50s to 500s / 100cc.

[0054] In some embodiments, the membrane has an air permeability of 50s to 200s / 100cc.

[0055] The air permeability of the diaphragm is affected to a certain extent by the porosity of the diaphragm. When the air permeability of the diaphragm is within the above range, it is beneficial to improve the permeation efficiency of lithium ions and increase the rate performance of the battery.

[0056] In some embodiments, the thickness of the separator is 1 μm to 50 μm.

[0057] In some embodiments, the electrolyte diffusion radius of the separator is 0.2 cm to 3 cm.

[0058] The electrolyte diffusion radius of the diaphragm is used to characterize the penetration and wetting effect of the electrolyte on the diaphragm.

[0059] In the description of this application, the "electrolyte diffusion radius of the diaphragm" can be obtained by testing using the following method:

[0060] 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 30ul of electrolyte and drop it into the center of the diaphragm. After 30s, measure the radius of the electrolyte diffusion.

[0061] In some embodiments, the thickness of the separator is 2 μm to 20 μm.

[0062] 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.

[0063] Another embodiment of the present application provides a method for preparing the above-mentioned diaphragm, comprising the following steps:

[0064] dispersing the lithium-rich material particles in paraffin oil to form a suspension;

[0065] mixing the suspension with a polymer material to prepare a membrane precursor; and,

[0066] The paraffin oil in the membrane precursor is removed to obtain the membrane; the membrane comprises a porous polymer matrix and lithium-rich material particles dispersed in the porous polymer matrix.

[0067] The polymer 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.

[0068] Compared with the existing diaphragm preparation method, the present application changes the order of material processing before extrusion. Specifically, different from the existing blending method of inorganic fillers, in this preparation method, the lithium-rich material particles are first dispersed in paraffin oil to form a suspension, and then the suspension is mixed with the polymer material for extrusion to obtain a diaphragm precursor, wherein the 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, the paraffin oil is removed to form pores in the polymer material, thereby obtaining a porous polymer matrix. Pre-mixing the lithium-rich material particles with the paraffin oil to form a suspension is also an important operation to reduce the extremely poor dispersion of the lithium-rich material particles in the porous polymer matrix and improve the particle coverage. Through the dispersion of paraffin oil, the agglomeration of the lithium-rich material particles can be reduced, thereby improving the dispersibility of the lithium-rich material particles in the porous polymer matrix, making the lithium-rich material 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 lithium-rich material particles are dispersed in the paraffin oil, the surface of the lithium-rich material particles can be fully exposed on the inner wall of the hole during the process of removing the paraffin oil to form holes, thereby avoiding the coating of the lithium-rich material particles by the polymer material, which is conducive to fully exerting the role of the lithium-rich material particles in decomposing and replenishing lithium, and improving the particle coverage rate of the diaphragm without increasing the amount of lithium-rich material particles added.

[0069] In some embodiments, the mass ratio of the polymer material to the paraffin oil is (25-35):(65-75).

[0070] 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.

[0071] In some embodiments, the lithium-rich material particles are dispersed in the paraffin oil by one or more of stirring, ultrasonic treatment, and mechanical grinding.

[0072] In some embodiments, the membrane precursor is prepared by extrusion.

[0073] In some embodiments, the paraffin oil removal method is organic extraction.

[0074] 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.

[0075] In some embodiments, the membrane precursor is stretched after the extrusion operation to obtain a membrane precursor with a desired thickness.

[0076] 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.

[0077] The use of the diaphragm as described above can significantly improve the battery's resistance to lithium dendrite growth due to its high tensile strength, preventing the diaphragm from being pierced by lithium dendrites and causing a short circuit. At the same time, it can reduce the loss of irreversible capacity in the battery formation stage and improve the battery's initial efficiency.

[0078] The present application is further described below through examples.

[0079] Example 1

[0080] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0081] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 98% by mass;

[0082] The lithium-rich material particles are Li5FeO4 with a particle size (D50) of 1.5 μm, accounting for 2% by mass;

[0083] The lithium-rich material 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.

[0084] Dispersion extreme test: Take an SEM photograph of the diaphragm surface with 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 lithium-rich material particles in the area. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion extreme of the lithium-rich material particles in the porous polymer matrix, which is 6.5μm.

[0085] 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 lithium-rich material 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 8.8%.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The above-mentioned separator has a porosity of 45%, a pore diameter of 50 nm, an air permeability of 95 s / 100 cc, and a thickness of 7 μm.

[0090] Example 2

[0091] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0092] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 99% by mass;

[0093] The lithium-rich material particles are LiCoO4 with a particle size (D50) of 1.2 μm, accounting for 1% by mass;

[0094] The lithium-rich material 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.

[0095] An SEM photograph of the diaphragm 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is extremely poor at 7.2 μm.

[0096] 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 lithium-rich material 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 7.1%.

[0097] The porosity of the above-mentioned diaphragm is 50%, the pore diameter is 54 nm, the air permeability is 100 s / 100 cc, and the thickness is 9 μm; the testing method is the same as that of Example 1.

[0098] Example 3

[0099] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0100] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 99.3% by mass;

[0101] The lithium-rich material particles are LiCoO4 with a particle size (D50) of 1.8 μm, accounting for 0.7% by mass;

[0102] The lithium-rich material 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.

[0103] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is extremely poor at 8.1 μm.

[0104] 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 lithium-rich material 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 6.5%.

[0105] The porosity of the above-mentioned diaphragm is 50%, the pore diameter is 53 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.

[0106] Example 4

[0107] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0108] The polymer material is high-density polypropylene with a melting point of 165°C, accounting for 99.5% by mass;

[0109] The lithium-rich material particles are Li5FeO4 with a particle size (D50) of 1.5 μm, accounting for 0.5% by mass;

[0110] The lithium-rich material 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.

[0111] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is 9.8 μm.

[0112] 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 lithium-rich material 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 5.2%.

[0113] The porosity of the above-mentioned diaphragm is 40%, the pore diameter is 50 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.

[0114] Example 5

[0115] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0116] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 96.5% by mass;

[0117] The lithium-rich material particles are Li5FeO4 with a particle size (D50) of 1.2 μm, accounting for 3.5% by mass;

[0118] The lithium-rich material 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.

[0119] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is 5.2 μm.

[0120] 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 lithium-rich material 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 11.8%.

[0121] The porosity of the above-mentioned diaphragm is 48%, the pore diameter is 50 nm, the air permeability is 88 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0122] Example 6

[0123] This example is used to illustrate the separator, battery and preparation method disclosed in this application, and includes the following steps:

[0124] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 95.5% by mass;

[0125] The lithium-rich material particles are Li5FeO4 with a particle size (D50) of 1.2 μm, accounting for 4.5% by mass;

[0126] The lithium-rich material 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.

[0127] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is an extreme difference of 4 μm.

[0128] 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 lithium-rich material 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 12.0%.

[0129] The porosity of the above-mentioned diaphragm is 49%, the pore diameter is 49 nm, the air permeability is 89 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0130] Comparative Example 1

[0131] 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:

[0132] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 99.8% by mass;

[0133] The lithium-rich material particles are LiCoO4 with a particle size (D50) of 1.2 μm, accounting for 0.2% by mass;

[0134] The lithium-rich material 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.

[0135] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is an extreme difference of 11.2 μm.

[0136] 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 lithium-rich material 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 4.8%.

[0137] 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.

[0138] Comparative Example 2

[0139] 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:

[0140] The polymer material is ultra-high density polyethylene with a melting point of 135°C, accounting for 92% by mass;

[0141] The lithium-rich material particles are LiCoO4 with a particle size (D50) of 1.2 μm, accounting for 8% by mass;

[0142] The lithium-rich material 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.

[0143] 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 lithium-rich material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the dispersion degree of the lithium-rich material particles in the porous polymer matrix, which is 3.2 μm.

[0144] 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 lithium-rich material 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 12.5%.

[0145] The porosity of the above-mentioned diaphragm is 55%, the pore diameter is 50 nm, the air permeability is 65 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0146] Comparative Example 3

[0147] The difference from Example 1 is that this example is used to illustrate the separator, battery and preparation method thereof disclosed in this application, and includes the following steps:

[0148] The polymer material is polyvinylidene fluoride with a melting point of 155°C, accounting for 98% by mass;

[0149] The particle size (D50) of conventional alumina is selected to be 1.5 μm, accounting for 2% by mass;

[0150] 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.

[0151] An SEM photograph of the diaphragm 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 alumina material particles in the area was measured. The difference between the maximum and minimum values ​​obtained from the measurement is the maximum dispersion degree of the alumina particles in the porous polymer matrix, which is 6.5 μm.

[0152] 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 alumina particles were stained using software. The ratio of the stained area to the non-stained area was calculated, and the particle coverage was obtained to be 8.0%.

[0153] The porosity of the above-mentioned diaphragm is 45%, the pore diameter is 50 nm, the air permeability is 95 s / 100 cc, and the thickness is 7 μm; the testing method is the same as that of Example 1.

[0154] Performance Testing

[0155] The following performance tests were performed on the diaphragm prepared above:

[0156] 1. Electrolyte Diffusion Radius Test: Place the diaphragm in a circular hollow fixture with a radius of 3 cm, leaving it suspended above the table. Use a pipette to drop 30 μL of electrolyte onto the center of the diaphragm. 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.

[0157] 2. Battery Initial Performance Test: Assemble the separator with the positive electrode, negative electrode, and electrolyte to form a battery. Charge the battery at 0.2C constant current and constant voltage to 3.75V, with a cutoff current of 0.05C and a rest period of 5 minutes. Record the charge capacity (C1). Discharge the battery at 0.5C constant current to 2V and a rest period of 5 minutes. Record the discharge capacity (C2). Initial performance = C2 / C1 * 100%. For the positive electrode, dissolve PVDF in a certain amount of NMP, then add lithium iron phosphate and a conductive agent, then apply the coating to the electrode. For the negative electrode, dissolve SBR, graphite material, and a conductive agent in water, then apply the coating to the electrode.

[0158] 3. Battery Capacity Retention Test: Assemble the separator with the positive electrode, negative electrode, and electrolyte to form a battery. After formation, subject the battery to 500 cycles of 1C / 1C charge and discharge. The 500-cycle capacity retention rate = 500-cycle capacity / first-cycle capacity * 100%. After 500 cycles, disassemble the battery, remove the negative electrode, and observe and record the results.

[0159] 4. Tensile strength test: The tensile strength test refers to the national standard GB / T36363-2018.

[0160] The test results are entered in Table 1.

[0161] Table 1

[0162] From the test results in Table 1, it can be seen that by controlling the dispersion range of lithium-rich material particles in the porous polymer matrix to 4μm to 10μm and the particle coverage rate to 5% to 12%, the tensile strength of the separator can be effectively improved while ensuring the wettability of the electrolyte and the first effect of the battery. At the same time, the capacity retention rate of the battery in long-term cycles is effectively improved, the formation of lithium dendrites and the occurrence of negative electrode black spots are inhibited, thereby improving the safety performance and cycle life of the battery.

[0163] 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, Lithium-rich material particles; the lithium-rich material particles are dispersed in the porous polymer matrix, and the dispersion range of the lithium-rich material particles in the porous polymer matrix is ​​4μm to 10μm, and the particle coverage is 5% to 12%.

2. The diaphragm according to claim 1, characterized in that The dispersion degree of the lithium-rich material particles in the porous polymer matrix is ​​5 μm to 8.5 μm, and the particle coverage is 6% to 9%.

3. The diaphragm according to claim 1 or 2, characterized in that: Based on the total weight of the diaphragm being 100%, the mass content of the porous polymer matrix is ​​93% to 99.5%, and the mass content of the lithium-rich material particles is 0.5% to 7%.

4. The diaphragm according to any one of claims 1 to 3, characterized in that: Based on the total weight of the diaphragm being 100%, the mass content of the porous polymer matrix is ​​90% to 99%, and the mass content of the lithium-rich material particles is 1% to 10%.

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 lithium-rich material particles include one or more of Li5FeO4, Li2Ni5O4, Li2MnO3, LiCoO4, Li6MnO4 and LiReO6.

8. The diaphragm according to any one of claims 1 to 7, characterized in that: The particle size D50 of the lithium-rich material 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 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 1 μm to 50 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 lithium-rich material particles in paraffin oil to form a suspension; Mixing the suspension with a polymer material to prepare a membrane precursor; The paraffin oil in the membrane precursor is removed to obtain the membrane.

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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