阅读说明：本技术 一种陶瓷隔膜及其制备方法和应用 (Ceramic diaphragm and preparation method and application thereof ) 是由 鲁丹 赵文文 于 2020-06-11 设计创作，主要内容包括：本发明涉及一种陶瓷隔膜及其制备方法和电池。该陶瓷隔膜包括多孔基体和覆盖在所述多孔基体上的陶瓷涂层,陶瓷涂层包括陶瓷颗粒和粘结剂,陶瓷颗粒包括大粒径陶瓷颗粒和小粒径陶瓷颗粒；粘结剂为聚合单元聚合得到的聚合物,聚合单元包括乙烯基吡啶及其衍生物、丙烯腈及其衍生物、丙烯酸酯及其衍生物和离子型烯烃单体。本发明通过在陶瓷涂层中引入两种粒径大小不同的陶瓷颗粒,以及粘结剂可得到热稳定性能优异的陶瓷涂层,该陶瓷涂层用于制备陶瓷隔膜时,在较小的厚度下也具有较好的热稳定性。同时该陶瓷隔膜还能进一步吸收氟化氢,改善电解液的稳定性。(The invention relates to a ceramic diaphragm, a preparation method thereof and a battery. The ceramic diaphragm comprises a porous substrate and a ceramic coating covering the porous substrate, wherein the ceramic coating comprises ceramic particles and a binder, and the ceramic particles comprise large-particle-size ceramic particles and small-particle-size ceramic particles; the adhesive is a polymer obtained by polymerizing polymerization units, wherein the polymerization units comprise vinyl pyridine and derivatives thereof, acrylonitrile and derivatives thereof, acrylic ester and derivatives thereof and ionic olefin monomers. According to the invention, two ceramic particles with different particle sizes and a binder are introduced into the ceramic coating to obtain the ceramic coating with excellent thermal stability, and the ceramic coating has better thermal stability under a smaller thickness when being used for preparing the ceramic diaphragm. Meanwhile, the ceramic diaphragm can further absorb hydrogen fluoride, and the stability of the electrolyte is improved.)

1. A ceramic separator comprising a porous substrate and a ceramic coating overlying the porous substrate, wherein the ceramic coating comprises ceramic particles and a binder;

the ceramic particles comprise large-particle-size ceramic particles and small-particle-size ceramic particles, the average particle size ratio of the small-particle-size ceramic particles to the large-particle-size ceramic particles is 1/8-3/5, and the mass percentage of the large-particle-size ceramic particles in the ceramic particles is 60-95%;

the adhesive is a polymer obtained by polymerizing a polymerization monomer, and the polymerization monomer comprises the following components in percentage by mass:

30 to 65 percent of vinylpyridine and derivatives thereof,

15 to 40 percent of acrylonitrile and derivatives thereof,

15 to 55 percent of acrylic ester and derivatives thereof,

the content of the ionic olefin monomer is 0.5-2% of the total amount of the binder.

2. The ceramic separator according to claim 1, wherein the small-particle-size ceramic particles are small-particle-size ceramic particles subjected to surface treatment with a coupling agent.

3. The ceramic separator according to claim 1, wherein the mass ratio of the binder to the ceramic particles is 3 to 10%.

4. The ceramic separator according to claim 1, wherein the branched chain of the acrylate or the derivative thereof has 1 to 14 carbon atoms.

5. The ceramic separator according to claim 1, wherein the vinylpyridine derivative is selected from one or more of 4-vinylpyridine, 2-methyl-5-vinylpyridine, 2-vinylpyridine, and 2 fluoro-4-vinylpyridine.

6. The ceramic separator of claim 1, wherein the acrylonitrile derivative is methacrylonitrile; the acrylate and the derivatives thereof are selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, isooctyl acrylate, lauryl acrylate, methacrylate, ethyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate and lauryl methacrylate; the ionic olefin monomer is one or more selected from acrylic acid, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, sodium styrene sulfonate and lithium styrene sulfonate.

7. The ceramic separator according to any one of claims 1 to 6, wherein the ceramic coating has a thickness of 1.5 to 3 μm on one surface.

8. The ceramic separator according to claim 1, wherein the large-particle-diameter ceramic particles have an average particle diameter in the range of 300 to 1100 nm; the average particle size range of the small-particle-size ceramic particles is 50-600 nm.

9. The method for preparing a ceramic separator according to any one of claims 1 to 8, comprising the steps of: and mixing the ceramic particles with the binder, stirring and dispersing, coating on a porous matrix, and drying to obtain the ceramic diaphragm.

10. A battery comprising a positive electrode, a negative electrode and the ceramic separator according to any one of claims 1 to 8.

Technical Field

The invention belongs to the field of lithium ion battery diaphragms, and particularly relates to a ceramic diaphragm and a preparation method and application thereof.

Background

The lithium ion battery has the advantages of high voltage, large specific energy, large specific power, wide working temperature range, no memory effect, long storage time and the like, and is widely applied to the fields of mobile phones, notebook computers, power tools, automobiles and the like. Meanwhile, with the continuous increase of energy density, thermal runaway is more and more easy to occur, and the safety risk is also larger and larger. The diaphragm is one of four main materials of the battery cell, plays roles in isolating the positive electrode and the negative electrode and conducting lithium ions, and plays an important role in the safety and the output characteristics of the battery cell.

Because the melting points of the traditional polyethylene diaphragm and the polypropylene diaphragm are only 135 ℃ and 165 ℃ respectively, the thermal stability of the common diaphragm is poor, and the common diaphragm is difficult to bear instant high temperature to melt when safety matters occur to the battery cell, so that the anode and the cathode are in short circuit, the thermal runaway of the battery cell is further aggravated, and finally safety accidents are caused. In order to make up for the defects of polyethylene and polypropylene and improve the heat resistance of the diaphragm, ceramic diaphragms are invented, and ceramic coatings are coated on two sides of the polyethylene or polypropylene diaphragm to further improve the heat resistance of the diaphragm. Both LG chemistry and Celgard report ceramic coated separators that significantly improve the thermal stability of the separator. Then, as the requirement on the energy density of the cell is higher, higher requirements on the thickness of the diaphragm are also provided. That is, the thickness of the substrate and coating layer will be reduced to accommodate the use of separator membranes in high energy density battery systems. However, as the thickness of the coating layer is reduced, the thermal stability of the coating layer is gradually reduced, so that how to improve the thermal stability of the ceramic separator at a low coating thickness is a problem which needs to be solved urgently in the field of the current separator. Meanwhile, the improvement effect of the separator on the battery cell is further improved by functionalizing the ceramic separator through the introduction of functional groups.

Disclosure of Invention

The invention aims to overcome the defect or deficiency of poor thermal stability after the coating thickness of the diaphragm is reduced in the prior art, and provides a ceramic diaphragm, which obviously improves the thermal stability of the ceramic diaphragm by optimizing the collocation among ceramic particles, the composition of a binder and the collocation among the ceramic particles and the binder. The vinylpyridine group is introduced into the ceramic coating in the ceramic diaphragm, so that hydrogen fluoride can be further absorbed in the battery cell, the stability of the electrolyte is improved, and the electrolyte is endowed with functionalization.

The invention also aims to provide a preparation method of the ceramic diaphragm.

The invention also aims to provide application of the ceramic diaphragm in preparation of a lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

a ceramic separator includes a porous substrate and a ceramic coating layer covering the porous substrate, the ceramic coating layer including ceramic particles and a binder; the ceramic particles comprise large-particle size ceramic particles and small-particle size ceramic particles; the average particle size ratio of the small-particle-size ceramic particles to the large-particle-size ceramic particles is 1/8-3/5, and the mass fraction of the large-particle-size ceramic particles in the ceramic particles is 60-95%;

the adhesive is a polymer obtained by polymerizing polymerization units, wherein the polymerization units comprise the following components in percentage by mass:

30 to 65 percent of vinylpyridine and derivatives thereof,

15 to 40 percent of acrylonitrile and derivatives thereof,

15-55% of acrylate and derivatives thereof;

the content of the ionic olefin monomer is 0.5-2% of the total amount of the binder.

According to the technical scheme, two kinds of ceramic particles with different particle sizes are introduced into the ceramic coating and are matched with the binder to obtain the ceramic coating with excellent thermal stability, and when the ceramic coating is used for preparing the ceramic diaphragm, the ceramic coating also has better thermal stability under a smaller thickness.

Specifically, the inventors of the present invention found through studies that the average particle size range, the average particle size ratio, and the specific gravities of the large-particle size ceramic particles and the small-particle size ceramic particles affect the performance of the ceramic coating.

If the average particle size of the large-particle-size ceramic particles is too large, the thickness of the coating layer is difficult to be made thin; when the average particle size of the large-particle-size ceramic particles is too small, the entire ceramic particles are too small and difficult to disperse. If the average particle size of the small-particle size ceramic particles is too large, the coating thickness is difficult to be thin, and if the average particle size of the small-particle size ceramic particles is too small, dispersion is difficult. When the average particle size range of the large-particle-size ceramic particles is controlled to be 300-1100 nm and the average particle size range of the small-particle-size ceramic particles is controlled to be 50-600 nm, the coating thickness can be thinner, and the dispersibility is better. Preferably, the average particle size of the large-particle-size ceramic particles is in the range of 400-1000 nm; the average particle size of the small-particle-size ceramic particles is 100 to 500 nm.

If the ratio of the average particle size of the small-particle-size ceramic particles to the average particle size of the large-particle-size ceramic particles is too large or too small, the ceramic particles are difficult to be effectively matched, and the high-thermal-stability ceramic coating and the ceramic diaphragm are difficult to be prepared. When the ratio of the average particle size of the ceramic coating to the average particle size of the ceramic diaphragm is controlled to be 1/8-3/5, the thermal stability of the ceramic coating and the ceramic diaphragm can be remarkably improved, and preferably, the ratio of the average particle size of the small-particle-size ceramic particles to the average particle size of the large-particle-size ceramic particles is 1/7-2/3.

For example, the ceramic coating layer having a high bulk density is difficult to be obtained because the specific gravity of the ceramic particles having a large particle size is too large and the specific gravity of the ceramic particles having a small particle size is insufficient, and thus the thermal stability of the obtained ceramic coating layer and the ceramic separator is insufficient. Similarly, when the specific gravity of the small-particle-size ceramic particles is too high, it is difficult to produce a ceramic coating having a high bulk density, and the thermal stability of the obtained ceramic coating and ceramic separator is insufficient. When the average particle size ratio of the ceramic coating to the ceramic diaphragm is controlled to be 1/8-3/5, the thermal stability of the ceramic coating and the ceramic diaphragm can be obviously improved.

The mass fraction of the ceramic particles with large particle size in the ceramic particles is 60-95%, and preferably, the mass fraction of the ceramic particles with large particle size in the ceramic particles is 65-90%. The mass fraction of the large-particle-size particles is too low, so that the stacking density is difficult to effectively improve, and the thermal stability of the obtained ceramic diaphragm is insufficient. The mass fraction of the large-particle-size particles is too high, so that the packing density is difficult to effectively improve, and the thermal stability of the obtained ceramic diaphragm is insufficient.

The adhesive is a polymer obtained by polymerizing polymerization monomers, wherein the polymerization monomers comprise vinyl pyridine and derivatives thereof, acrylonitrile and derivatives thereof, acrylic ester and derivatives thereof and ionic olefin monomers.

The vinylpyridine and the derivative component thereof are beneficial to improving the bonding strength and the bulk density among ceramic particles. The content of the vinylpyridine and the derivatives thereof accounts for 30-65% of the total amount of the binder, and less than 30% of the total amount of the binder is not beneficial to improving the bonding strength and the stacking density among ceramic particles, thereby influencing the bonding strength of a coating and the thermal stability of a ceramic diaphragm, and more than 65% of the total amount of the binder is not beneficial to the air permeability of the ceramic coating.

Specifically, the vinylpyridine derivative is selected from one or more of 4-vinylpyridine, 2-methyl-5-vinylpyridine, 2-vinylpyridine and 2 fluoro-4-vinylpyridine.

The acrylonitrile and the derivatives thereof account for 15-40% of the total amount of the binder, and the acrylonitrile and the derivatives thereof are beneficial to improving the cohesive energy of the binder and increasing the adhesive force among ceramic particles and between the ceramic particles and a matrix. The content of acrylonitrile and derivatives thereof is lower than 15%, the cohesive energy of the binder is insufficient, the adhesive strength of the coating is poor, and the content of polyacrylonitrile and derivatives thereof exceeds 40%, so that the flexibility of the polymer is insufficient, and the improvement of the adhesive strength of the coating is not facilitated.

Specifically, the acrylonitrile derivative is methacrylonitrile.

The acrylate and its derivatives are useful for improving the bond strength between the ceramic coating and the substrate. The acrylic ester and the derivatives thereof account for 15-55% of the total amount of the binder. The specific gravity is too low, the bonding strength of the ceramic coating and the porous matrix is weak, and the bonding strength of the coating is influenced. The specific gravity of the ceramic particles influences the packing density of the ceramic particles, and therefore influences the thermal shrinkage of the ceramic diaphragm.

Specifically, the acrylate and the derivative thereof are selected from one or more of acrylate and the derivative thereof selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, isooctyl acrylate, lauryl acrylate, methacrylate, ethyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate and lauryl methacrylate.

The ionic olefin monomer can improve the dispersibility of the polymer in water, thereby further improving the bond strength. The content of the binder is 0.5-2% of the total amount of the binder. When the content of the ionic olefin monomer is within the range, the dispersibility of the protective adhesive in water can be better dispersed, so that the adhesive strength of the coating is better improved.

Preferably, the ionic olefin monomer is one or more of acrylic acid, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, sodium styrene sulfonate and lithium styrene sulfonate.

In addition to improving thermal stability, vinylpyridine and its derivatives can absorb hydrofluoric acid (HF) in the electrolyte, improve the stability of the electrolyte, improve the electrochemical performance of the battery, and impart functionality thereto. The electrolyte stabilization mechanism is as follows:

hydrogen fluoride is absorbed through acid-base neutralization reaction, and the stability of the electrolyte is improved.

Preferably, the small-particle-size ceramic particles are small-particle-size ceramic particles subjected to surface treatment by using a coupling agent, and the small-particle-size ceramic particles subjected to surface treatment by using the coupling agent have better compatibility with a binder, so that the bonding strength of a ceramic coating and a ceramic diaphragm can be further improved; the coupling agent can be selected from coupling agents commonly used in the art, and more preferably, the coupling agent is selected from one or more of KH560, KH570 or KH 550.

Preferably, the mass ratio of the binder to the ceramic particles is 3-10%. If the specific gravity of the binder to the ceramic particles is too low, the peel strength is insufficient. If the specific gravity of the binder to the ceramic particles is too high, the air permeability is affected.

Preferably, the ceramic coating also contains a rheological additive, which is conventional in the art and can be used in the invention, and the rheological additive is one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxymethyl cellulose, or polyacrylate.

Other functional additives may also be added to the ceramic coating to further enhance its performance.

Preferably, the ceramic coating also comprises one or more of surfactants such as sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, cetyl trimethyl ammonium bromide, octyl phenol polyoxyethylene or polyethylene glycol.

Preferably, the branched chain of the acrylate and the derivative thereof has 1 to 14 carbon atoms.

The number of carbon atoms of the branches of the acrylate and its derivatives has a different effect on the bonding strength of the ceramic coating for different porous substrates. When the number of carbon of a branched chain of a porous matrix such as polyethylene terephthalate (PET), polyimide and the like is 1-4, the coating has excellent bonding strength. When the number of carbon of branched chains of the porous matrix such as polyolefin is 4-14, the coating has excellent bonding strength

Inorganic oxides or inorganic salts with high thermal stability, which are conventional in the art, may be used as the ceramic particulate material in the present invention, and the ceramic particulate material is one or more selected from alumina, magnesia, boehmite, titania or barium sulfate.

A ceramic separator includes a porous substrate and a ceramic coating layer coated on the porous substrate; the ceramic coating can be coated on one side or two sides and can be selected according to actual use requirements.

A porous substrate conventional in the art may be used in the present invention, and the porous substrate is selected from one or more of a polyolefin-based porous substrate, a polyethylene terephthalate (PET) -based porous substrate, or a polyimide-based porous substrate;

preferably, the polyolefin-based porous matrix is a Polyethylene (PE) porous matrix or a polypropylene (PP) porous matrix.

Most preferably, when the porous matrix is a polyolefin porous matrix, the carbon number of the alkyl carbon chain of the acrylate and the derivatives thereof is 4-14; when the porous matrix is a polyethylene terephthalate (PET) porous matrix or a polyimide porous matrix, the number of carbon atoms of alkyl carbon chains of the acrylate and the derivative thereof is 1-4.

The ceramic coating can meet the thickness requirement of the diaphragm, and the thickness of the ceramic coating is 1.5-3 mu m. If the thickness of the ceramic coating is less than 1.5um, the thermal shrinkage of the separator is affected. If the thickness of the coating is too great, the energy density of the cell is affected.

The invention also claims a preparation method of the ceramic diaphragm, which comprises the following steps: and mixing the ceramic particles with the binder, stirring and dispersing, coating on a porous matrix, and drying to obtain the ceramic diaphragm.

The application of the ceramic diaphragm in the preparation of the lithium ion battery is also within the protection scope of the invention.

The invention obviously improves the thermal stability of the ceramic coating by optimizing the collocation among the ceramic particles, the composition of the binder and the collocation among the ceramic particles and the binder; the ceramic diaphragm obtained by coating the ceramic coating on the porous matrix has better thermal stability; meanwhile, the ceramic diaphragm can further absorb hydrogen fluoride, and the stability of the electrolyte is improved.

Drawings

Fig. 1 is a diagram showing a mechanism of electrolyte stabilization.

Detailed Description

The invention is further illustrated by the following examples. These examples are intended to illustrate the invention and are not intended to limit the scope of the invention. Experimental procedures without specific conditions noted in the examples below, generally according to conditions conventional in the art or as suggested by the manufacturer; the raw materials, reagents and the like used are, unless otherwise specified, those commercially available from the conventional markets and the like. Any insubstantial changes and substitutions made by those skilled in the art based on the present invention are intended to be covered by the claims.

The small-particle-size ceramic particles selected in the embodiments and the comparative examples of the present invention are surface-treated with a coupling agent, taking KH570 as an example, the specific process is as follows: and (2) putting the ceramic particles into methyl ethyl ketone for ball milling and dispersion, then adding 3% KH570, performing reflux reaction, then cooling, filtering and washing to obtain the small-particle-size ceramic particles with the epoxy surfaces.

The average particle size range of the small-particle-size ceramic particles can be 50-600 nm (for example, 70nm, 100nm, 200nm, 300nm, 400nm, 500nm and the like), and the small-particle-size ceramic particles are selected from one or more of aluminum oxide, magnesium oxide, boehmite, titanium oxide and barium sulfate and the like, and can be selected according to actual needs.

Example 1

The present embodiment provides a ceramic separator. The ceramic diaphragm is prepared by the following steps: 80 parts of alumina with the average particle size of 500nm, 20 parts of alumina with the average particle size of 100nm, 5 parts of adhesive 1 (40 parts of vinylpyridine, 20 parts of acrylonitrile, 40 parts of n-butyl acrylate and 0.5 part of acrylic acid), 1.2 parts of carboxymethyl cellulose and 0.5 part of surfactant (octylphenol polyoxyethylene) are stirred and dispersed, coated on a PE substrate with the diameter of 9 mu m on both sides, dried and coated on the two sides with the diameter of 2 mu m respectively.

Example 2

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected alumina is different, and the details are as follows: 5 parts of alumina particles having an average particle diameter of 100nm and 95 parts of alumina particles having an average particle diameter of 500 nm.

Example 3

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected alumina is different and the coating thickness is controlled differently, and the specific steps are as follows: 40 parts of alumina with the average particle size of 600nm, 60 parts of alumina with the average particle size of 1000nm, and the thickness of the coatings on the two surfaces is 3 mu m.

Example 4

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected alumina is different and the coating thickness is controlled differently, and the specific steps are as follows: 15 parts of alumina with the average particle size of 50nm and 85 parts of alumina with the average particle size of 400nm, and the thickness of the coatings on the two surfaces is 1.5 mu m.

Example 5

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected ceramic particles are different, and the specific steps are as follows: 20 parts of boehmite particles having an average particle size of 200nm and 80 parts of boehmite particles having an average particle size of 600 nm.

Example 6

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected ceramic particles are different, and the specific steps are as follows: 20 parts of boehmite having an average particle size of 100nm and 80 parts of boehmite having an average particle size of 800 nm.

Example 7

Example 7

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the dosage of the selected binder is different, and the specific steps are as follows: the using amount of the binder 1 is 3 parts, and the mass ratio of the binder to the ceramic particles is 3%.

Example 8

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the dosage of the selected binder is different, and the specific steps are as follows: the using amount of the binder 1 is 8 parts, and the mass ratio of the binder to the ceramic particles is 8%.

Example 9

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the selected binder is different, and the specific steps are as follows: the binder 2 comprises 30 parts of vinylpyridine, 40 parts of acrylonitrile, 30 parts of butyl acrylate and 0.5 part of acrylic acid.

Example 10

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the selected binder is different, and the specific steps are as follows: the binder 3 is prepared from 40 parts of vinylpyridine, 15 parts of acrylonitrile, 45 parts of butyl acrylate and 0.5 part of acrylic acid.

Example 11

The present embodiment provides a ceramic separator. The preparation process is the same as that of example 1 except that the selected binder is different and the porous matrix is different, and the specific steps are as follows: the adhesive 4 comprises 40 parts of vinylpyridine, 30 parts of acrylonitrile, 30 parts of methyl acrylate and 0.5 part of acrylic acid, and is coated on a PET porous substrate.

Example 12

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the selected binder is different, and the specific steps are as follows: the adhesive 5 comprises 65 parts of vinyl pyridine, 20 parts of acrylonitrile, 15 parts of butyl acrylate and 0.5 part of acrylic acid.

Example 13

The present embodiment provides a ceramic separator. The preparation process is the same as that of the embodiment 1 except that the selected binder is different, and the specific steps are as follows: the binder 6 comprises 30 parts of vinylpyridine, 15 parts of acrylonitrile, 55 parts of butyl acrylate and 2 parts of acrylic acid.

Comparative example 1

This comparative example provides a ceramic diaphragm, which is the same as example 1 except that the alumina used in the preparation process is different, and specifically includes the following steps: 100 parts of large-particle-size alumina particles having an average particle size of 700nm are selected.

Comparative example 2

This comparative example provides a ceramic separator, which is the same as example 1 except that the binder used in the preparation process is different, and specifically includes the following steps: selecting common binder SBR.

Comparative example 3

This comparative example provides a ceramic diaphragm, which is the same as example 1 except that the alumina used in the preparation process is different, and specifically includes the following steps:

100 parts of small-particle-size alumina particles (surface-treated) having an average particle size of 100nm were selected.

Comparative example 4

This comparative example provides a ceramic particle which was prepared in the same manner as in example 1, except that the alumina was used.

55 parts of alumina with the average particle size of 500nm and 45 parts of 100nm alumina are selected

Comparative example 5

This comparative example provides a ceramic particle which was prepared in the same manner as in example 1, except that the alumina was used. In this comparative example, 80 parts of alumina having an average particle diameter of 500nm and 20 parts of alumina having an average particle diameter of 50nm were used.

Comparative example 6

This comparative example provides a ceramic particle which was prepared in the same manner as in example 1, except that the binder was different. Selecting adhesive 6 (vinyl pyridine 70 parts, acrylonitrile 20 parts, n-butyl acrylate 10 parts, acrylic acid 0.5 part)

Performance testing

(1) And (3) testing the air permeability of the diaphragm: test equipment GPI4110, test the time for 100mL of air to pass through the septum.

(2) Testing the peel strength of the diaphragm: cutting the diaphragm into 100 × 15mm samples, adhering the ceramic-coated substrate to two iron plates by using double-sided adhesive tapes, clamping the two iron plates on a stretching clamp, and stretching and stripping.

(3) Testing the stacking density of the diaphragm: the membrane was cut into 5 x 5cm samples, tested for weight m1 and thickness u1, and then the ceramic coating was removed and tested for matrix weight m2 and thickness u 2. The surface density per unit thickness is calculated by the formula: (m1-m2)/[ (u1-u2) × 0.05]

(4) Testing the thermal stability of the diaphragm: the membrane was cut into 10 x 5cm samples, left at 140 ℃ for 1 hour and tested for dimensional change.

(5) And (3) testing the stability of the electrolyte: the separator was placed in a bottle containing an electrolyte (EV/EMC/DEC ═ 1/1/1, 1moL lithium hexafluorophosphate), and left at 45 ℃ for 2 days to test the HF content in the electrolyte.

The test results are shown in Table 1.

Table 1 performance test results of the ceramic separators provided in each of examples and comparative examples

Remarking: (examples 5, 6 use boehmite, since the gram weight of boehmite itself is only 3.1g/cm^3,Much less than the gram weight of alumina 4g/cm³Therefore, the apparent bulk density is low, and the bulk density is more than 2 g/(m) in terms of alumina²·μm))

The ceramic diaphragm provided by each embodiment of the invention has good air permeability, large bonding strength between the ceramic coating and the porous matrix, large stacking density of ceramic particles in the ceramic coating and good thermal stability. In addition, as shown in fig. 1, due to the introduction of the vinylpyridine group, the ceramic coating has the function of absorbing HF, and has more excellent electrolyte stability.

From examples 1 to 13 and comparative example 2, it can be seen that the incorporation of the vinylpyridine component into the binder is significantly reduced in the amount of HF in the electrolyte, as compared with a binder containing no vinylpyridine component, and the stability of the electrolyte can be effectively improved.

From examples 1 to 6 and comparative examples 1, 3, 4 and 5, it can be seen that the bulk density of the ceramic coating and the thermal stability of the separator can be significantly improved by using the ceramic particles of the size, the particle diameter ratio and the weight ratio used in the present invention.

From example 1, example 9-example 13 and comparative examples 2 and 6, we can see that the adhesive using the present invention has better bulk density, peel strength and thermal stability of the separator.

It will be appreciated by those of ordinary skill in the art that the examples provided herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited examples and embodiments. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.