阅读说明：本技术 一种安全隔膜以及制备方法、锂离子电池 (Safety diaphragm, preparation method and lithium ion battery ) 是由 符宽 赖旭伦 孙先维 陈杰 杨山 于 2021-08-03 设计创作，主要内容包括：本发明属于电池技术领域,尤其涉及一种安全隔膜以及制备方法、锂离子电池,包括基膜,所述基膜具有膜孔；安全涂层,所述安全涂层设置于所述基膜至少一侧面,所述安全涂层具有热熔材料,所述热熔材料的熔点低于所述基膜的熔点,所述热熔材料融化后用于填补所述膜孔。本发明的一种安全隔膜,能够在较低温度下实现闭孔,将基膜的膜孔堵住,避免破孔而导致短路,从而避免热失控,提高安全性。(The invention belongs to the technical field of batteries, and particularly relates to a safety diaphragm, a preparation method of the safety diaphragm and a lithium ion battery, wherein the safety diaphragm comprises a base film, and the base film is provided with a film hole; the safety coating is arranged on at least one side face of the base film and is provided with a hot-melt material, the melting point of the hot-melt material is lower than that of the base film, and the hot-melt material is used for filling the film holes after being melted. According to the safety diaphragm, the closed hole can be realized at a lower temperature, the diaphragm hole of the base diaphragm is blocked, and short circuit caused by broken hole is avoided, so that thermal runaway is avoided, and the safety is improved.)

1. A rupture disc, comprising:

a base film having a pore;

the safety coating is arranged on at least one side face of the base film and is provided with a hot-melt material, the melting point of the hot-melt material is lower than that of the base film, and the hot-melt material is used for filling the film holes after being melted.

2. The rupture disc of claim 1, wherein said hot melt material has a melting point of 90 ℃ to 130 ℃.

3. The rupture disc according to claim 1, wherein the thickness of the safety coating layer is 1 to 5 μm.

4. A method for preparing a safety diaphragm, comprising the following steps:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on at least one side surface of the base film, and drying to form the safety coating to obtain the safety diaphragm.

5. The method for preparing a safety diaphragm according to claim 4, wherein the weight ratio of the ceramic powder, the hot-melt material, the thickening agent, the wetting agent and the binder is 60-75: 15-25: 0.5-1.5: 0.1-1: 5-10.

6. The method for producing a safety separator according to claim 4, wherein the hot-melt material is a polyethylene micro-wax emulsion.

7. The method for preparing a safety diaphragm according to claim 4, wherein the solid content of the hot-melt material is 30% to 50%.

8. The method for producing a safety diaphragm according to claim 4, wherein the ceramic powder comprises one or a mixture of two or more of alumina, boehmite, and aluminum hydroxide.

9. The method of manufacturing a safety diaphragm according to claim 4, wherein the binder has a solid content of 15% to 25%.

10. A lithium ion battery comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a case, wherein the separator is used for separating the positive electrode and the negative electrode, and the separator is the safety separator according to any one of claims 1 to 3.

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a safety diaphragm, a preparation method of the safety diaphragm and a lithium ion battery.

Background

At present, in order to reduce the thickness of a battery core, most of digital 3c consumer batteries use a PE diaphragm, and the PE diaphragm has a thinner thickness than other polyolefin diaphragms. And the PE diaphragm has a hole closing effect at about 130 ℃, so that the further reaction of the anode and the cathode is blocked, and the thermal runaway is prevented. However, the temperature of 130 ℃ is still high, and the membrane is at risk of breaking pores when reaching this temperature, so that the membrane needs to be closed before 130 ℃ to prevent thermal runaway. In addition, in order to increase the adhesion between the pole piece and the diaphragm, the current water-based diaphragm coating needs to coat a PMMA or PVDF layer on the surface of the diaphragm, and the structure process is complicated.

Disclosure of Invention

One of the objects of the present invention is: the safety diaphragm can realize closed pore at lower temperature and below the melting point of the base film, block the pore of the base film, and avoid short circuit caused by hole breaking, thereby avoiding thermal runaway and improving safety.

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

a safety diaphragm comprising:

a base film having a pore;

the safety coating is arranged on at least one side face of the base film and is provided with a hot-melt material, the melting point of the hot-melt material is lower than that of the base film, and the hot-melt material is used for filling the film holes after being melted.

As an improvement of the safety diaphragm, the melting point of the hot-melt material is 90-130 ℃. Preferably, the melting point of the hot melt material is from 100 ℃ to 125 ℃.

As an improvement of the safety diaphragm, the thickness of the safety coating is 1-5 mu m.

The second purpose of the invention is: aiming at the defects of the prior art, the preparation method of the safety diaphragm is simple in preparation, easy to control and capable of being produced in large batch.

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

a method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on at least one side surface of the base film, and drying to form the safety coating to obtain the safety diaphragm.

As an improvement of the preparation method of the safety diaphragm, the weight part ratio of the ceramic powder, the hot melting material, the thickening agent, the wetting agent and the binder is 60-75: 15-25: 0.5-1.5: 0.1-1: 5-10. The increase in the content of the hot-melt material can improve the closed cell capacity of the separator, but too high a content of the hot-melt material leads to a decrease in the thermal shrinkage of the separator. The solid content of the prepared low-temperature pore-closing slurry is set to be 20-40%, the solid content is too low, the viscosity is low, the slurry stability is poor, the coating thickness cannot meet the requirement, the solid content is too high, the viscosity is high, the leveling property of the coating slurry is poor, and the film surface is uneven. The solid content of the binder is 10-20%, and preferably, the solid content of the binder is 20%.

As an improvement of the preparation method of the safety diaphragm, the hot-melt material is polyethylene micro-wax emulsion. The high-density polyethylene has good heat resistance and cold resistance, good chemical stability, higher rigidity and toughness and good mechanical strength. The dielectric property and the environmental stress cracking resistance are also better. The hardness, tensile strength and creep property are better than those of low-density polyethylene; the wear resistance, the electrical insulation, the toughness and the cold resistance are good, the chemical stability is good, and the paint is insoluble in any organic solvent and resistant to corrosion of acid, alkali and various salts at room temperature; and has a melting point lower than that of the PE film used in the cell. Compared with the wax powder, the polyethylene wax emulsion has smaller particle size, does not need subsequent ball milling treatment, and can be well and uniformly dispersed in an aqueous solution.

As an improvement of the preparation method of the safety diaphragm, the solid content of the hot-melt material is 30-50%.

As an improvement of the preparation method of the safety diaphragm, the ceramic powder comprises one or a mixture of more than two of aluminum oxide, boehmite and aluminum hydroxide.

As an improvement of the preparation method of the safety diaphragm, the solid content of the binder is 15-25%.

The third purpose of the invention is that: aiming at the defects of the prior art, the lithium ion battery has the characteristics of low-temperature closed pores, good safety and long service life.

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

a lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Compared with the prior art, the invention is characterized in that:

1. according to the safety diaphragm, the closed hole can be realized at a lower temperature which is lower than the melting point of the base film, the film hole of the base film is blocked, and short circuit caused by hole breakage is avoided, so that thermal runaway is avoided, and the safety is improved.

2. The safety coating has the effect of closing the diaphragm in advance to form open circuit, so that the reaction of the anode and the cathode is blocked, and the effect of preventing the thermal runaway of the battery cell is achieved.

3. The blended safety coating has the property of bonding to pole pieces, the bonding force of the blended safety coating meets the use requirement of a battery core, as shown in fig. 4, a data graph of the bonding force of the safety coating to the pole pieces and fig. 5 of a picture of a torn diaphragm of the safety coating bonded pole piece of the invention are shown, and the safety coating is still bonded on the pole pieces after the safety coating is torn from fig. 5, which shows that the safety coating has good bonding property with the pole pieces.

4. In the preparation process, the electrode plate is bonded after the blending coating is coated, so that the coating of a PMMA/PVDF coating is omitted, the process flow is reduced, and the time cost is saved.

Drawings

Fig. 1 is a DSC diagram of a security coating of the present invention.

FIG. 2 is a line graph showing the shrinkage of the separator prepared by adding different amounts of the hot-melt material according to the present invention.

FIG. 3 is a bar graph of air permeability at different temperatures for membranes made with different levels of hot melt material added in accordance with the present invention.

FIG. 4 is a graph comparing the wet-press bond strength of the separator of example 1 of the present invention and a PMMA coated separator to the cathode.

Fig. 5 is a schematic view of the interface between the separator and the pole piece after tearing open according to example 1 of the present invention.

FIG. 6 is a schematic diagram of the interface between the PMMA coated membrane and the pole piece after being torn.

Fig. 7 is an enlarged view of the safety coating of example 1 of the present invention.

FIG. 8 is an enlarged view of the baking time at 90 deg.C/0.5 h of example 1 of the present invention.

FIG. 9 is an enlarged view of the baking time at 120 deg.C/0.5 h for example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.

Example 1

A method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on two side surfaces of the base film, and drying to form a safety coating to obtain the safety diaphragm.

Wherein the weight part ratio of the ceramic powder to the hot-melt material to the thickening agent to the wetting agent to the binder is 71:20:0.8:0.2: 8.

Wherein the ceramic powder is aluminum oxide.

Wherein the solid content of the hot-melt material is 40%, the hot-melt material is polyethylene micro-wax emulsion, and the melting point is 121.14 ℃.

Wherein the binder has a solids content of 20%.

Wherein the wetting agent is alkyl sulfate.

Wherein the thickening agent is carboxymethyl cellulose.

Wherein the binder is polyacrylic binder.

DSC analysis is carried out on the prepared low-temperature closed-pore slurry, and as shown in figure 1, when the temperature reaches 121.14 ℃, a curve shows that the curve is obviously raised upwards, which indicates that the low-temperature closed-pore slurry is melted, so that the membrane pores of the base membrane are blocked, and the short circuit between the anode and the cathode is avoided. Meanwhile, the manufactured rupture disk was observed at room temperature (A), after baking at 90 ℃/0.5h (B) and after baking at 120 ℃/0.5h (C) under magnification, and the results are shown in FIGS. 7 to 9, respectively.

A safety diaphragm comprising:

a base film having a pore;

the safety coating is arranged on at least one side face of the base film and is provided with a hot-melt material, the melting point of the hot-melt material is lower than that of the base film, and the hot-melt material is used for filling the film holes after being melted.

Wherein the thickness of the base film is 0.1 mm.

Wherein the thickness of the security coating is 4 μm.

A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Example 2

A method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on two side surfaces of the base film to form a safety coating to obtain the safety diaphragm.

Wherein the weight part ratio of the ceramic powder to the hot-melt material to the thickening agent to the wetting agent to the binder is 75:25:1:1: 8.

Wherein the ceramic powder is boehmite.

Wherein the solid content of the hot-melt material is 45%, and the hot-melt material is polyethylene micro-wax emulsion.

Wherein the binder has a solids content of 23%.

Wherein the wetting agent is alkyl sulfate.

Wherein the thickening agent is carboxymethyl cellulose.

Wherein the binder is polyacrylic binder.

A safety diaphragm comprises a base film and safety coatings arranged on two side faces of the base film, wherein hot-melt materials are used for filling film holes after being melted.

Wherein the thickness of the base film is 0.2 mm.

Wherein the thickness of the security coating is 5 μm.

A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Example 3

A method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on two side surfaces of the base film to form a safety coating to obtain the safety diaphragm.

The ceramic powder, the hot-melt material, the thickening agent, the wetting agent and the binder are mixed according to the weight ratio of 60:15:0.5:1: 5.

Wherein the ceramic powder is aluminum hydroxide.

Wherein the solid content of the hot-melt material is 30%, and the hot-melt material is polyethylene micro-wax emulsion.

Wherein the binder has a solids content of 15%.

A safety diaphragm comprises a base film and safety coatings arranged on two side faces of the base film, wherein hot-melt materials are used for filling film holes after being melted.

Wherein the thickness of the base film is 0.3 mm.

Wherein the thickness of the security coating is 3 μm.

A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Example 4

A method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on two side surfaces of the base film to form a safety coating to obtain the safety diaphragm.

Wherein the weight part ratio of the ceramic powder to the hot-melt material to the thickening agent to the wetting agent to the binder is 65:18:1.2:0.1: 6.

Wherein the ceramic powder is aluminum hydroxide.

Wherein the solid content of the hot-melt material is 35%, and the hot-melt material is polyethylene micro-wax emulsion.

Wherein the binder has a solids content of 20%.

A safety diaphragm comprises a base film and safety coatings arranged on two side faces of the base film, wherein hot-melt materials are used for filling film holes after being melted.

Wherein the thickness of the base film is 0.5 mm.

Wherein the thickness of the security coating is 5 μm.

A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Example 5

A method of making a rupture disc comprising the steps of:

step (A): dissolving a wetting agent and a thickening agent in a solvent, stirring and mixing to obtain a first mixed solution;

step (B): adding the hot-melt material into the first mixed solution, stirring and mixing to obtain a second mixed solution;

step (C): adding ceramic powder and a binder into the second mixed solution, stirring and mixing to obtain low-temperature closed-pore slurry;

step (D): and coating the low-temperature closed-pore slurry on two side surfaces of the base film to form a safety coating to obtain the safety diaphragm.

Wherein the weight part ratio of the ceramic powder to the hot-melt material to the thickening agent to the wetting agent to the binder is 73:18:0.7:0.1: 6.

Wherein, the ceramic powder comprises one or a mixture of more than two of alumina, boehmite and aluminum hydroxide.

Wherein the solid content of the hot-melt material is 38%, and the hot-melt material is polyethylene micro-wax emulsion.

Wherein the binder has a solids content of 18%.

A safety diaphragm comprises a base film and safety coatings arranged on two side faces of the base film, wherein hot-melt materials are used for filling film holes after being melted.

Wherein the thickness of the base film is 0.1 mm.

Wherein the thickness of the security coating is 1 μm.

A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, wherein the diaphragm is used for separating the positive electrode from the negative electrode, and the diaphragm is the safety diaphragm.

Comparative example 1

The difference from example 1 is that:

a diaphragm comprises a base film and PMMA coatings arranged on two side faces of the base film.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 2 used a polypropylene separator.

Performance testing

1. The separators prepared in examples 1 to 6 and comparative example 1 were subjected to tensile strength, puncture strength, heat shrinkage, closing temperature, and rupture temperature tests, and the test results are reported in table 1.

2. The separators prepared in examples 1 to 6 and comparative examples 1 and 2 were bonded to a pole piece and then subjected to adhesion test, and the test results are shown in table 2.

TABLE 1

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative example 1
								Tensile Strength kgf/cm2	3846	3764	3742	3751	3758	3772	3521
Puncture Strength kgf/cm2	312	294	295	296	293	294	267
								Thermal shrinkage rate	4	5.1	5.2	5.2	5.1	5.0	8
Temperature of closed pores (. degree.C.)	116	121	120	119	120	119	/
								Temperature of hole breaking C	146	135	134	136	133	134	130

TABLE 2

	Example 1	Example 2	Example 3	Example 4	Example 5	Comparative example 1	Comparative example 2
								Adhesion (N/m)	23.53	21.67	20.93	22.67	21.33	19.4	22.03

As can be seen from the table 1, the safety diaphragm prepared by the invention has better tensile strength, puncture strength and heat shrinkage rate, lower hole closing temperature and higher hole breaking temperature compared with a PMMA coating diaphragm, and can sensitively react to the temperature, so that thermal runaway is avoided, and the safety diaphragm has good safety. As shown in fig. 2 and 3, when the content of the hot-melt material is set to 10% to 30%, the prepared separator has a low heat shrinkage rate and a large gas permeability value (the gas permeability value is the time required per unit area for gas to permeate therethrough, so that the larger the gas permeability value, the more closed pores are indicated). As can be seen from FIG. 4, the safety diaphragm prepared by the invention has stronger bonding strength to the pole piece compared with the PMMA coating diaphragm, and the safety diaphragm can be well contacted with the pole piece, so that the volume of the monomer is reduced, and the performance is improved. As can be seen from FIG. 5, after the safety diaphragm and the pole piece of the invention are torn, a thin safety diaphragm still remains on the surface of the pole piece, which proves that the safety diaphragm and the pole piece of the invention have good bonding strength, as can be seen from FIG. 6, after the PMMA coating diaphragm and the pole piece of comparative example 1 are torn, the surface of the pole piece is very smooth, which proves that the PMMA coating and the pole piece are not tightly bonded, are easy to fall off, and have poor performance. As can be seen from Table 2, the safety diaphragm prepared by the invention has good adhesive force, coating of PMMA/PVDF coating can be omitted when the battery cell is prepared, the process flow is reduced, and the time cost is saved. Moreover, as shown by comparison of examples 1-6, when the weight ratio of the ceramic powder to the hot-melt material to the thickening agent to the wetting agent to the binder is 71:20:0.8:0.2:8, the solid content of the hot-melt material is 40% and the solid content of the binder is 20%, the prepared safety diaphragm has better performance, has a lower closed pore temperature of 116 ℃, and simultaneously has a higher broken pore degree of 146 ℃, and has good safety performance.

Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.