阅读说明：本技术 一种金属-陶瓷微球、含有该金属-陶瓷微球的隔膜及含有该隔膜的锂离子电池 (Metal-ceramic microsphere, diaphragm containing metal-ceramic microsphere and lithium ion battery containing diaphragm ) 是由 张祖来 李素丽 唐伟超 李俊义 徐延铭 于 2019-09-18 设计创作，主要内容包括：本发明提供了一种金属-陶瓷微球、含有该金属-陶瓷微球的隔膜及含有该隔膜的锂离子电池。所述微球具有核壳结构,即包括壳层和核芯,形成所述壳层的材料包括热敏聚合物和金属粉,形成所述核芯的材料包括陶瓷材料。本发明区别于传统的锂离子电池隔膜,采用聚合物定向设计包覆的方法,筛选热敏聚合物和金属粉包覆陶瓷材料,在不影响锂离子电池性能的前提下,在隔膜表面涂覆含有热敏聚合物和金属粉包覆陶瓷材料的微球,能有效改善锂离子电池的高温安全性能。(The invention provides a metal-ceramic microsphere, a diaphragm containing the metal-ceramic microsphere and a lithium ion battery containing the diaphragm. The microsphere has a core-shell structure, namely comprises a shell layer and a core, wherein the shell layer is made of a thermosensitive polymer and metal powder, and the core is made of a ceramic material. The invention is different from the traditional lithium ion battery diaphragm, adopts the polymer orientation design coating method to screen the thermosensitive polymer and metal powder coated ceramic material, and coats the microsphere containing the thermosensitive polymer and metal powder coated ceramic material on the surface of the diaphragm on the premise of not influencing the performance of the lithium ion battery, thereby effectively improving the high-temperature safety performance of the lithium ion battery.)

1. The metal-ceramic microsphere has a core-shell structure, namely comprises a shell layer and a core, wherein the shell layer is formed by a material comprising a thermosensitive polymer and metal powder, and the core is formed by a material comprising a ceramic material.

2. The metal-ceramic microsphere according to claim 1, wherein, in the microsphere, the mass ratio of the shell layer to the core layer is (15-1200): 100-500);

and/or in the shell layer, the mass ratio of the thermosensitive polymer to the metal powder is (1-50) to 1;

and/or in the microsphere, the thickness of a shell layer is 1nm-1000 nm;

and/or, in the microsphere, the average particle size of the microsphere is 0.01-10 μm.

3. The metal-ceramic microspheres of claim 1 or 2, wherein said metal powder is selected from at least one of copper, iron, zinc, nickel and aluminum;

preferably, the metal powder has a particle size of 1nm to 200 nm.

4. A method of preparing metal-ceramic microspheres as claimed in any one of the claims 1-3, said method comprising the steps of:

coating a shell forming material comprising a thermosensitive polymer and metal powder on the surface of a core forming material comprising a ceramic material by adopting a liquid phase coating method or a solid phase coating method to prepare the microsphere; the microsphere has a core-shell structure, namely comprises a shell layer and a core, wherein the shell layer is made of a material comprising a thermosensitive polymer and metal powder, and the core is made of a material comprising a ceramic material.

5. The production method according to claim 4, wherein, in the case of using a liquid phase coating method, the liquid phase coating method comprises the steps of:

dissolving the material for forming the shell layer in a solvent in a stirring manner to form a solution containing the material for forming the shell layer; adding a material for forming a core into the solution, and stirring and mixing uniformly; removing a solvent in a mixed system through vacuum heating drying or spray drying and the like to obtain the microsphere, wherein the microsphere has a core-shell structure, namely comprises a shell layer and a core, the shell layer is formed by a material comprising a thermosensitive polymer and metal powder, and the core is formed by a material comprising a ceramic material;

alternatively, in the case of a solid phase coating method, the solid phase coating method includes the steps of:

and (3) performing solid phase coating on the material for forming the shell layer and the material for forming the core in a stirring, ball milling and mechanical fusion mode, and then heating to the temperature of the thermosensitive interval of the thermosensitive polymer to form a coating layer on the surface of the material for forming the core by the material for forming the shell layer.

6. A separator comprising a separator base layer and a coating layer on at least one side surface of the separator base layer, the coating layer being coated on at least one side surface of the separator base layer from a hybrid system comprising the metal-ceramic microspheres according to any one of claims 1 to 3.

7. A diaphragm according to claim 6, wherein the mixed system further comprises at least one of a polymeric binder and an auxiliary agent;

preferably, the mass parts of the components in the mixed system are as follows:

50-90 parts by mass of the metal-ceramic microspheres, 0-50 parts by mass of a polymer binder and 0-10 parts by mass of an auxiliary agent;

also preferably, the mass parts of the components in the mixed system are as follows:

50-90 parts by mass of the metal-ceramic microspheres, 1-50 parts by mass of a polymer binder and 1-10 parts by mass of an auxiliary agent.

8. The method for preparing the separator according to claim 6 or 7, wherein the method comprises the steps of:

(a) adding the metal-ceramic microspheres, optional polymer binder and optional auxiliary agent into a solvent, and mixing to obtain mixed slurry;

(b) and (b) coating the mixed slurry obtained in the step (a) on the surface of a diaphragm base layer, and drying to obtain the diaphragm.

9. The method for preparing a separator according to claim 8, wherein, in the step (b), the porosity of the separator base layer is 20 to 80%, the thickness is 5 to 50 μm, and the pore size is D <80 nm;

preferably, the material system of the diaphragm base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polynaphthalene, polyimide, polyamide, aramid, and poly (p-phenylene benzobisoxazole).

10. A lithium ion battery comprising the separator of claim 6 or 7.

Technical Field

The invention belongs to the technical field of microspheres and lithium ion batteries, and particularly relates to a metal-ceramic microsphere, a diaphragm containing the metal-ceramic microsphere and a lithium ion battery containing the diaphragm, wherein the diaphragm has high safety performance.

Background

With the popularization of 3C products and the rise of the electric automobile market, the demand for lithium ion secondary batteries is increasing. The diaphragm is used as a key component of the lithium ion battery, the performance of the diaphragm determines the interface structure, internal resistance and the like of the battery, the characteristics of the battery such as capacity, cycle and safety performance are directly influenced, and the diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery. Therefore, the development of high-performance separators has become an important direction for improving the performance of lithium batteries, and particularly, the safety of separators has become a focus of our attention. The safety of lithium ion batteries is a major concern in the industry, and the safety of separators is an important factor. This requires separators with excellent mechanical properties, lower closed cell temperatures and the ability to retain shape at higher temperatures. At present, polyolefin materials such as polypropylene and polyethylene are mainly adopted for large-scale commercialized lithium battery diaphragms, and with the fact that the performance requirements of lithium batteries are higher and higher, the thermal safety and the electrolyte maintaining capacity of diaphragms made of the two materials are difficult to meet the requirements, and the research and preparation of high-performance composite diaphragms made of other materials and polyolefin become the most important direction for diaphragm modification at present.

The traditional method for improving the heat resistance of the diaphragm mainly comprises the step of coating one or more heat-resistant coatings on the surface of a polyolefin substrate. If the literature mentions that the heat resistance of the diaphragm is improved by coating a layer of inorganic ceramic particles on the surface of the polyolefin substrate diaphragm, the safety performance of the battery cannot be fundamentally solved; the literature also mentions that the surface of the polyolefin substrate diaphragm is coated with a layer of modified inorganic ceramic particles, so that the heat resistance of the diaphragm is improved, and the safety performance of the battery cannot be fundamentally solved; in addition, the literature mentions that a layer of heat-sensitive coating is coated on the surface of the polyolefin substrate diaphragm to improve the overcharge resistance of the battery, and because a large amount of polymer thermal expansion microspheres are added into the coating, the cycle and rate performance of the battery are reduced.

Disclosure of Invention

The traditional method for solving the heat resistance of the diaphragm is to coat one or more layers of heat-resistant coatings on the surface of the polyolefin substrate diaphragm so as to improve the heat resistance of the diaphragm, but the method only improves the safety performance of the battery and cannot fundamentally solve the safety problem of the battery.

In order to overcome the defects of the prior art, the invention aims to provide a diaphragm containing a coating layer and a lithium ion battery containing the diaphragm, wherein the coating layer is coated by a mixed system containing microspheres with a core-shell structure, the microspheres have the core-shell structure and comprise a shell layer and a core, the shell layer is formed by a material comprising a thermosensitive polymer and metal powder, and the core is formed by a material comprising a ceramic material. The diaphragm containing the coating layer can not change in the conventional use process, but when the lithium ion battery is heated to reach a thermosensitive temperature range, the thermosensitive polymer can be melted to release metal powder, meanwhile, the thermosensitive polymer can be melted to form a multilayer protective layer to prevent lithium ions from passing through, the metal powder can form a plurality of electronic channels, a plurality of micro short circuits are formed inside the battery, the energy of the battery is reduced, the phenomenon that the thermal runaway is caused by a large amount of heat released by the further reaction of the positive electrode and the negative electrode of the battery is avoided, and the safety performance of the battery is fundamentally solved.

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

the metal-ceramic microsphere has a core-shell structure, namely comprises a shell layer and a core, wherein the shell layer is formed by a material comprising a thermosensitive polymer and metal powder, and the core is formed by a material comprising a ceramic material.

According to the invention, the metal-ceramic microspheres can be used in the field of lithium ion batteries, and also can be used in the field of semiconductors, coatings and primary batteries or secondary batteries of other ionic systems.

According to the invention, in the microsphere, the mass ratio of the shell layer to the core is (15-1200): 100-500).

According to the invention, in the shell layer, the mass ratio of the thermosensitive polymer to the metal powder is (1-50): 1.

According to the present invention, the metal powder is at least one selected from the group consisting of copper, iron, zinc, nickel, and aluminum.

According to the invention, the particle size of the metal powder is 1nm to 200nm, preferably 10 to 100 nm.

According to the invention, in the microsphere, the shell layer has a thickness of 1nm-1000nm, preferably 50nm-100 nm. For example 1nm, 10nm, 50nm, 100nm, 200nm, 500nm or 1000 nm.

According to the invention, the microspheres have an average particle size of 0.01 μm to 10 μm. For example, 0.01. mu.m, 0.05. mu.m, 0.1. mu.m, 0.5. mu.m, 1. mu.m, 4. mu.m, 5. mu.m, 8. mu.m or 10 μm.

According to the invention, the heat-sensitive polymer is chosen from thermoplastic polymers which can form a relatively stable system with the electrolyte and which have phase-changing properties. The thermosensitive temperature range of the thermosensitive polymer is, for example, 100 ℃ to 140 ℃. Illustratively, the thermosensitive polymer is selected from at least one of polystyrene, polyethylene, polymethyl methacrylate, polyacrylic acid-butadiene-styrene, polylactic acid, polyvinyl chloride, polyvinyl butyral, and the like, or a monomer-modified copolymerized polymer thereof.

According to the invention, the particle size of the ceramic material is between 0.01 and 20 μm. For example, 0.01. mu.m, 0.05. mu.m, 0.1. mu.m, 0.5. mu.m, 1. mu.m, 4. mu.m, 5. mu.m, 8. mu.m, 10. mu.m, 12. mu.m, 15. mu.m, 18. mu.m or 20. mu.m.

According to the present invention, the ceramic material is at least one selected from the group consisting of silica, alumina, zirconia, magnesium hydroxide, boehmite, barium sulfate, fluorophlogopite, fluoroapatite, mullite, cordierite, aluminum titanate, titania, copper oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, attapulgite and the like.

According to the invention, when the temperature of the microsphere reaches a thermosensitive interval, the thermosensitive polymer is melted to release metal powder, the thermosensitive polymer is melted to form a multi-layer protective layer to prevent lithium ions from passing through, the metal powder can form a plurality of electronic channels, a plurality of micro short circuits are formed in the battery, the energy of the battery is reduced, the thermal runaway caused by a large amount of heat released by the further reaction of the anode and the cathode of the battery is avoided, and the safety performance of the battery is fundamentally solved.

The invention also provides a preparation method of the metal-ceramic microsphere, which comprises the following steps:

coating a shell forming material comprising a thermosensitive polymer and metal powder on the surface of a core forming material comprising a ceramic material by adopting a liquid phase coating method or a solid phase coating method to prepare the microsphere; the microsphere has a core-shell structure, namely comprises a shell layer and a core, wherein the shell layer is made of a material comprising a thermosensitive polymer and metal powder, and the core is made of a material comprising a ceramic material.

Illustratively, in the case of the liquid phase coating method, the liquid phase coating method includes the steps of:

dissolving the material for forming the shell layer in a solvent in a stirring manner to form a solution containing the material for forming the shell layer; adding a material for forming a core into the solution, and stirring and mixing uniformly; and removing the solvent in the mixed system through vacuum heating drying or spray drying and the like to obtain the microsphere, wherein the microsphere has a core-shell structure, namely comprises a shell layer and a core, the shell layer is formed by a material comprising a thermosensitive polymer and metal powder, and the core is formed by a material comprising a ceramic material.

Wherein the solvent is at least one selected from cresol, benzene, acetone, N-methyl-2-pyrrolidone, N-dimethylacetamide, N-dimethylformamide and tetrahydrofuran.

Illustratively, in the case of the solid phase coating method, the solid phase coating method includes the steps of:

and (3) performing solid phase coating on the material for forming the shell layer and the material for forming the core in a stirring, ball milling and mechanical fusion mode, and then heating to the temperature of the thermosensitive interval of the thermosensitive polymer to form a coating layer on the surface of the material for forming the core by the material for forming the shell layer.

The invention also provides a diaphragm which comprises a diaphragm base layer and a coating layer positioned on at least one side surface of the diaphragm base layer, wherein the coating layer is obtained by coating at least one side surface of the diaphragm base layer by using the mixed system comprising the metal-ceramic microspheres.

According to the invention, the thickness of the coating layer is 1-10 μm, for example 2-5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, and the coating layer may be applied once or several times.

According to the present invention, if the separator includes a separator base layer and coating layers on both side surfaces of the separator base layer, the thicknesses of the coating layers on both side surfaces may be the same or different.

According to the invention, the mixed system also comprises at least one of a polymer binder and an auxiliary agent. For example, the mixed system also comprises a polymer binder and an auxiliary agent.

According to the invention, the mixed system comprises the following components in parts by weight:

50-90 parts by mass of the metal-ceramic microspheres, 0-50 parts by mass of a polymer binder and 0-10 parts by mass of an auxiliary agent.

For example, the mass parts of the components in the mixed system are as follows:

50-90 parts by mass of the metal-ceramic microspheres, 1-50 parts by mass of a polymer binder and 1-10 parts by mass of an auxiliary agent.

For example, the metal-ceramic microspheres are 50, 55, 60, 65, 70, 75, 80, 85, or 90 parts by mass.

For example, the above-mentioned polymer binder is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45 or 50 parts by mass.

For example, the mass part of the above-mentioned auxiliary is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mass parts.

According to the present invention, the mixed system further comprises 100-5000 parts by mass of a solvent.

According to the invention, the polymer binder is selected from polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, poly (methyl) acrylate, aramid resin, poly (meth) acrylic acid, Styrene Butadiene Rubber (SBR), polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, aqueous polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, polystyrene lithium sulfonate, aqueous silicone resin, butyronitrile-polyvinyl chloride blend, styrene-acrylic latex, pure benzene latex and the like, and one or more combinations of blends and copolymers derived from the modification of the aforementioned polymers.

According to the present invention, the auxiliary agent is selected from at least one of polybranched alcohol, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, stearic acid, sodium dodecylbenzenesulfonate, sodium hexadecylsulfonate, fatty acid glyceride, sorbitan fatty acid ester and polysorbate.

According to the present invention, the solvent is at least one selected from the group consisting of water, methanol, ethanol, acetone, N-methyl-2-pyrrolidone (NMP), chloroform, xylene, tetrahydrofuran, o-chlorobenzaldehyde, hexafluoroisopropanol, N-dimethylformamide, methyl ethyl ketone and acetonitrile.

The invention also provides a preparation method of the diaphragm, wherein the method comprises the following steps:

(a) adding the metal-ceramic microspheres, optional polymer binder and optional auxiliary agent into a solvent, and mixing to obtain mixed slurry;

(b) and (b) coating the mixed slurry obtained in the step (a) on the surface of a diaphragm base layer, and drying to obtain the diaphragm.

According to the invention, in the step (a), the mass parts of the metal-ceramic microspheres, the optional polymer binder, the optional auxiliary agent and the solvent in the mixed slurry are as follows: 50-90 parts by mass of the metal-ceramic microspheres, 0-50 parts by mass of a polymer binder (for example, 1-50 parts by mass), 0-10 parts by mass of an auxiliary agent (for example, 1-10 parts by mass), and 100 parts by mass of a solvent (5000 parts by mass).

According to the present invention, in the step (b), the coating is performed by, for example, spray coating, dip coating, gravure printing, extrusion coating, transfer coating, or the like.

According to the invention, in step (b), the porosity of the membrane substrate is 20-80%, the thickness is 5-50 μm, and the pore size is D <80 nm; the material system of the diaphragm base layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polynaphthalene, polyimide, polyamide, aramid fiber, poly (p-phenylene benzobisoxazole) and the like.

The invention also provides a lithium ion battery which comprises the diaphragm.

According to the invention, when the lithium ion battery is at thermal runaway or heat-sensitive temperature, a micro short circuit is formed inside the lithium ion battery, and the safety of the lithium ion battery is higher than that of the conventional lithium ion battery.

The invention has the beneficial effects that:

the invention provides a metal-ceramic microsphere, a diaphragm containing the metal-ceramic microsphere and a lithium ion battery containing the diaphragm. The invention is different from the traditional lithium ion battery diaphragm, adopts the polymer orientation design coating method to screen the thermosensitive polymer and metal powder coated ceramic material, and coats the microsphere containing the thermosensitive polymer and metal powder coated ceramic material on the surface of the diaphragm on the premise of not influencing the performance of the lithium ion battery, thereby effectively improving the high-temperature safety performance of the lithium ion battery.

The invention screens the heat-sensitive polymer and the metal powder which are stable in the electrolyte as shell materials of the microspheres, the heat-sensitive polymer and the metal powder do not dissolve, swell and the like in the electrolyte, the heat-sensitive polymer and the metal powder are taken as coating layers, the microspheres of the ceramic material uniformly coated by the heat-sensitive polymer and the metal powder are prepared by adopting a solid phase coating method or a liquid phase coating method, the microspheres are directly sprayed, dip-coated, gravure-printed, extrusion-coated, transfer-coated and other technologies on the surface of a diaphragm substrate after being uniformly mixed with an optional polymer binder, an optional auxiliary agent, a solvent and the like, so as to obtain a diaphragm with heat-sensitive barrier property, and the diaphragm, a positive electrode, a negative electrode, the electrolyte and other assembled lithium ion batteries have good safety.

Compared with the conventional safety lithium ion battery with high-temperature defects, the lithium ion battery has the following advantages:

1. the microsphere is relatively stable with most of solvents and electrolytes, can not be dissolved or swelled, effectively coats a ceramic material and has a heat-sensitive effect. The lithium ion battery is formed at a temperature of 60-90 ℃ in the production process, and the lithium ion battery is easy to generate heat and lose control in an environment of more than 160 ℃ so as to effectively improve the safety of the lithium ion battery, so that a thermosensitive polymer with a thermosensitive interval temperature of 100-140 ℃ is selected as one of coating materials of the microspheres;

2. the microsphere has good compatibility with the existing lithium ion battery manufacturing system, can be directly introduced into a production system, and reduces the processing cost;

3. the microsphere does not need to be additionally provided with an additional coating layer, can effectively reduce the influence on the performance of the lithium ion battery, and has good safety performance;

4. when the microspheres are heated to reach a thermosensitive interval, the coating layer containing the thermosensitive polymer and the metal powder begins to melt, and the thermosensitive polymer forms one or more isolating layers on the surface and inside the diaphragm substrate, so that lithium ions in the lithium ion battery can be effectively prevented from freely shuttling; the metal powder is released to form a plurality of electronic channels, a plurality of micro short circuits are formed in the battery, and the energy of the battery is reduced, so that the thermal runaway degree of the lithium ion battery is reduced or the thermal runaway is avoided.

Drawings

Fig. 1 is a schematic view showing a structure of a separator in a normal state according to a preferred embodiment of the present invention.

Fig. 2 is a schematic structural view of a separator in a high temperature state according to a preferred embodiment of the present invention.

FIG. 3 is a schematic structural diagram of the microsphere according to a preferred embodiment of the present invention; wherein, the 'organic layer' refers to a shell layer of the microsphere, and materials for forming the shell layer comprise thermosensitive polymers and metal powder; "inorganic layer" refers to the core of the microspheres of the invention, the material forming the core comprising a ceramic material.

Figure 4 is a plot of cell ARC test "temperature-voltage-time" for example 1 and comparative example 1 separators.

Fig. 5 is a graph showing the results of rate tests of batteries assembled by the separators of example 1 and comparative example 1.

Fig. 6 is a graph showing the results of cycle tests of batteries assembled by the separators of example 1 and comparative example 1.

Detailed Description

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1

20g of polymethyl methacrylate and 1 part of copper powder with the particle size of 30nm are dissolved in N, N-dimethylacetamide by a stirring mode to form a mixed solution, 200g of aluminum oxide is added, after uniform stirring and mixing, the solvent in the mixture is removed by a spray drying technology, and the microspheres of the thermosensitive polymer coated ceramic material are obtained.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate and copper powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 21:200, the thickness of the shell layer is 50nm, and the average grain diameter of the microsphere is about 1.0 μm.

And adding 90g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene and 1g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The membrane has a thickness ofA 12 mu m wet-process substrate diaphragm, one side of which is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 2

Dissolving 1000g of polymethyl methacrylate and 100g of aluminum powder with the particle size of 60nm in N, N-dimethylacetamide by a stirring mode to form a mixed solution, adding 400g of aluminum oxide, stirring and mixing uniformly, and removing the solvent in the mixture by a spray drying technology to obtain the microsphere of the thermosensitive polymer coated ceramic material.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate and aluminum powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 1100:400, the thickness of the shell layer is 500nm, and the average grain diameter of the microsphere is about 1.5 mu m.

And adding 90g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene and 1g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 3

Dissolving 20g of polyethylene and 1g of copper powder with the particle size of 30nm in N, N-dimethylacetamide by a stirring mode to form a mixed solution, adding 200g of boehmite, uniformly stirring and mixing, and removing the solvent in the mixture by a spray drying technology to obtain the microsphere of the thermosensitive polymer coated ceramic material.

In the prepared microsphere, the shell layer is a mixed coating of polyethylene and copper powder, and the core is boehmite; the mass ratio of the shell layer to the core is 21:200, the thickness of the shell layer is 50nm, and the average grain diameter of the microsphere is about 1.0 μm.

And adding 90g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene and 1g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 4

Dissolving 250g of polymethyl methacrylate, 250g of polyvinyl butyral and 20g of copper powder with the particle size of 30nm in N, N-dimethylacetamide in a stirring manner to form a mixed solution, adding 200g of aluminum oxide, stirring and mixing uniformly, and removing the solvent in the mixture by a spray drying technology to obtain the microsphere of the thermosensitive polymer coated ceramic material.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate, polyvinyl butyral and copper powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 520:200, the thickness of the shell layer is 300nm, and the average grain diameter of the microsphere is about 1.2 mu m.

And adding 90g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene and 1g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 5

20g of polymethyl methacrylate and 1g of copper powder with the particle size of 30nm are dissolved in N, N-dimethylacetamide by a stirring mode to form a mixed solution, 200g of aluminum oxide is added, after uniform stirring and mixing, the solvent in the mixture is removed by a spray drying technology, and the microspheres of the thermosensitive polymer coated ceramic material are obtained.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate and copper powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 21:200, the thickness of the shell layer is 50nm, and the average grain diameter of the microsphere is about 1.0 μm.

Adding 50g of the prepared microspheres, 50g of polyimide and 5g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 6

20g of polymethyl methacrylate and 1g of iron powder with the particle size of 30nm are dissolved in N-methyl-2-pyrrolidone in a stirring mode to form a mixed solution, 200g of aluminum oxide is added, after uniform stirring and mixing, the solvent in the mixture is removed through a spray drying technology, and the microspheres of the thermosensitive polymer coated ceramic material are obtained.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate and iron powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 21:200, the thickness of the shell layer is 50nm, and the average grain diameter of the microsphere is about 1.0 μm.

And adding 90g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene and 1g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Example 7

20g of polymethyl methacrylate and 1g of copper powder with the particle size of 30nm are dissolved in N, N-dimethylacetamide by stirring to form a mixed solution, 200g of aluminum oxide is added, after uniform stirring and mixing, the solvent in the mixture is removed by a spray drying technology, and the microspheres of the thermosensitive polymer coated ceramic material are obtained.

In the prepared microsphere, the shell layer is a mixed coating of polymethyl methacrylate and copper powder, and the core is aluminum oxide; the mass ratio of the shell layer to the core is 21:200, the thickness of the shell layer is 50nm, and the average grain diameter of the microsphere is about 1.0 μm.

Adding 80g of the prepared microspheres, 10g of polyvinylidene fluoride-hexafluoropropylene, 10g of poly (meth) acrylic acid and 1g of polyethylene glycol into 900g of N-methyl-2-pyrrolidone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.6g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Comparative example 1

Adding 80g of aluminum oxide, 20g of polyvinylidene fluoride-hexafluoropropylene and 2g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.4g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Comparative example 2

Adding 20g of polymethyl methacrylate, 1g of copper powder with the particle size of 30nm, 60g of aluminum oxide, 20g of polyvinylidene fluoride-hexafluoropropylene and 2g of polyethylene glycol into 900g of acetone, uniformly mixing to obtain mixed slurry, coating the mixed slurry on the surface of a diaphragm base layer through a micro-gravure, and drying to obtain the diaphragm.

The diaphragm is a wet-process substrate diaphragm with the thickness of 12 mu m, the single surface of the diaphragm is coated, the coating thickness is 4 mu m, and the total areal density of the diaphragm is 14.4g/m²。

And preparing a lithium ion battery cell by laminating or winding the diaphragm, the anode and the cathode, and the like, and baking, injecting, forming and packaging to obtain the high-safety lithium ion battery.

Test example 1

The lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2 were subjected to a voltage test and an internal resistance test, in which the lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2 were fully charged, then placed in an environment of 25 ℃ and 50% humidity, and the voltage and the internal resistance of the batteries in a full-charge state were measured using a voltage internal resistance meter (Anbo-Applent, model AT526B), and the results are shown in Table 1.

TABLE 1 results of Voltage test and internal resistance test of lithium ion batteries of examples 1 to 7 and comparative examples 1 to 2

Sample numbering	Average voltage of lithium battery	Lithium ion battery internal resistance
			Example 1	4.2011V	11.23mΩ
Example 2	4.2012V	11.33mΩ
			Example 3	4.2011V	11.62mΩ
Example 4	4.2005V	11.45mΩ
			Example 5	4.2004V	11.12mΩ
Example 6	4.2013V	11.87mΩ
			Example 7	4.2009V	11.11mΩ
Comparative example 1	4.2011V	12.02mΩ
			Comparative example 2	1.0265V	0.25mΩ

Examples 1 to 7 use microspheres of a thermosensitive polymer coated ceramic material to be applied in a separator and assembled into a lithium ion battery, and it is known from the data in table 1 that after the lithium ion batteries prepared in examples 1 to 7 and comparative example 1 are sorted, the voltage and internal resistance are normal, but the voltage and internal resistance of comparative example 2 are significantly reduced, because metal powder is directly added into the slurry to cause micro short circuit inside the battery;

the lithium ion batteries prepared in example 1 and comparative example 1 were subjected to charge-discharge cycle and rate performance tests, and the charge-discharge cycle test was carried out by using a 1C charge/1C discharge system; the rate performance test was performed using a 0.2C charge/0.2C, 0.5C, 1C, 3C, 5C discharge regime, and the results are shown in fig. 5 and 6.

From the experimental results of comparative examples 1 to 7 and comparative examples 1 to 2, the following conclusions were drawn:

1. the thermosensitive polymer and the metal powder are directly added into the coating and applied to the lithium ion battery diaphragm, and the metal powder can generate micro short circuit in the battery to cause the internal resistance of the lithium ion battery to be reduced;

2. in the embodiments 1 to 7, the microspheres coated with the ceramic material by the thermosensitive polymer are applied to the lithium ion battery diaphragm, so that the internal resistance, the voltage and the charge-discharge cycle of the lithium ion battery are not influenced, and the application requirements are met.

Test example 2

The lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2 were subjected to internal resistance testing, in which the separators prepared in examples 1 to 7 and comparative examples 1 to 2 were treated at 90 ℃, 100 ℃ and 140 ℃ for 10 minutes, respectively, and then electrolyte was added dropwise to test the internal resistance of the separator, to obtain the results shown in table 2 below.

Table 2 internal resistance test results of lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2

Sample numbering	Treatment at 90 deg.C	Treatment at 100 deg.C	Treatment at 140 deg.C
				Example 1	11.23mΩ	176.22mΩ	0.24mΩ
Example 2	11.35mΩ	182.13mΩ	0.34mΩ
				Example 3	11.42mΩ	179.43mΩ	0.26mΩ
Example 4	11.34mΩ	154.76mΩ	0.33mΩ
				Example 5	11.19mΩ	169.53mΩ	0.13mΩ
Example 6	11.29mΩ	174.87mΩ	0.42mΩ
				Example 7	11.37mΩ	173.98mΩ	0.36mΩ
Comparative example 1	12.26mΩ	12.84mΩ	12.23Ω
				Comparative example 2	0.28mΩ	0.12mΩ	0.04mΩ

From the data in table 2 above, the experimental results of comparative examples 1 to 7, comparative examples 1 to 2, the following conclusions were drawn:

1. the temperature-sensitive interval of the temperature-sensitive polymer is 100-140 ℃;

2. the lithium ion battery using the microspheres containing the thermosensitive polymer coated ceramic material can well control or slow down the occurrence of thermal runaway.

Test example 3

The lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2 were subjected to puncture and extrusion tests, in which a full-charge cell obtained after charging and discharging of the lithium ion battery was treated at 140 ℃ for 10min, then cooled to normal temperature to perform puncture and extrusion experiments, and the battery conditions were observed, with the results shown in table 3.

TABLE 3 puncture and crush test results of lithium ion batteries prepared in examples 1 to 7 and comparative examples 1 to 2

From the data in table 3 above, the following conclusions are drawn: when the microspheres coated with the ceramic material are applied to the diaphragm, the safety of the lithium ion battery can be effectively improved.

Test example 4

The lithium ion batteries prepared in example 1 and comparative example 1 were tested for temperature rise and voltage change due to exothermic reaction inside the cell using an adiabatic accelerated calorimeter test, as shown in fig. 4.

As can be seen from fig. 4, the experimental results comparing example 1 with comparative example 1 show that:

comparative example 1 a full-charge battery, in which the voltage of the battery is reduced as the temperature is increased, comparative example 1 shows thermal runaway of the battery at about 150 ℃, and ignition and explosion occur; example 1 a full-charge battery is characterized in that a thermosensitive polymer coats ceramic material microspheres at a temperature of 100 ℃ and starts to melt, so that the internal blocking of the battery is caused, and the voltage of the battery is reduced; therefore, in the embodiments 1 to 7, when the battery reaches the temperature-sensitive temperature range, the heat-sensitive polymer on the surface of the ceramic material microsphere coated by the heat-sensitive polymer is melted to form an internal micro short circuit, so that the safety performance of the lithium ion battery is effectively improved.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.