阅读说明：本技术 一种安全隔膜及其制备方法、锂离子电池 (Safety diaphragm, preparation method thereof and lithium ion battery ) 是由 邓豪 马斌 陈杰 于 2021-08-03 设计创作，主要内容包括：本发明属于锂离子电池技术领域,尤其涉及一种安全隔膜及其制备方法、锂离子电池,包括基膜以及设置于所述基膜至少一侧面的安全涂层,所述安全涂层包括热熔添加剂,所述热熔添加剂用于吸收热量后融化堵塞基膜的膜孔。本发明的一种安全隔膜,具有安全涂层能够在高温环境下吸收热量,降低基膜温度,提升基膜耐热性,同时能够融化堵塞基膜的膜孔,从而避免电芯短路起火。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a safety diaphragm and a preparation method thereof, and a lithium ion battery. The safety diaphragm provided by the invention has the advantages that the safety coating can absorb heat in a high-temperature environment, the temperature of the base film is reduced, the heat resistance of the base film is improved, and meanwhile, the film holes blocking the base film can be melted, so that the short circuit and the fire of a battery core are avoided.)

1. A rupture disc, comprising:

a base film having a film hole;

the safety coating is arranged on at least one side face of the base film and comprises a hot melt additive, and the hot melt additive is used for melting and blocking the film holes after absorbing heat.

2. The rupture disk of claim 1, wherein the hot melt additive has a particle size of 0.2 to 5 um.

3. The safety diaphragm of claim 1 wherein the safety coating has a thickness of 1-5 um.

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

step (A): adding a polymer and a hot-melt additive into an organic solvent, stirring and mixing to form a mixed glue solution;

step (B): and coating the mixed glue solution on at least one side surface of the base film, washing with water, and drying to form a safety coating, thereby preparing the safety diaphragm.

5. The method for preparing a security diaphragm according to claim 4, further comprising an inorganic filler, wherein the inorganic filler is added into the mixed glue solution and stirred and mixed to form a coating slurry, the coating slurry is coated on at least one side surface of the base film, and the base film is washed and dried to form a security coating, so that the security diaphragm is prepared.

6. The method for producing a safety diaphragm according to claim 5, wherein the weight ratio of the polymer to the hot-melt additive to the inorganic filler is 60 to 70:5 to 50:30 to 80.

7. The method for producing a safety separator according to claim 5, wherein the inorganic filler is at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silica, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

8. The method for producing a safety diaphragm according to claim 4, wherein the polymer is at least one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene oxide, epoxy resin, and epoxy resin derivative.

9. The method of manufacturing a safety separator according to claim 4, wherein the hot-melt additive is at least one of polyethylene, polyethylene wax, polyethylene oxide wax, and polypropylene wax.

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 lithium ion batteries, and particularly relates to a safety diaphragm, a preparation method of the safety diaphragm, and a lithium ion battery.

Background

The lithium ion battery has the characteristics of high energy density, good rate capability, environmental protection and the like, and is widely applied to the fields of 3C digital products and electric automobiles; the lithium ion battery mainly comprises an anode, a cathode, a diaphragm, electrolyte, an aluminum plastic film and the like, wherein the diaphragm plays an important role in conducting ions, isolating the anode and the cathode and preventing short circuit in the lithium ion battery; most of commercially used lithium ion battery separators are made of polyolefin materials, and serious shrinkage occurs at a temperature higher than 130 ℃, so that the contact between the positive electrode and the negative electrode of the battery causes the risk of short circuit and fire, and therefore, a technical method for solving the problems is needed.

Disclosure of Invention

One of the objects of the present invention is: to prior art not enough, and provide a rupture disk, have safety coating and can absorb the heat under high temperature environment, reduce the base film temperature, promote the base film heat resistance, can melt the diaphragm orifice that blocks up the base film simultaneously to avoid electric core short circuit to catch fire.

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

a safety diaphragm comprises a base film and a safety coating arranged on at least one side surface of the base film, wherein the safety coating comprises a hot melt additive which is used for melting and blocking film holes of the base film after absorbing heat.

As an improvement of the preparation method of the safety diaphragm, the particle size of the hot-melt additive is 0.2-5 um.

As an improvement of the preparation method of the safety diaphragm, the thickness of the safety coating is 1-5 um.

The second purpose of the invention is: aiming at the defects of the prior art, the preparation method of the safety diaphragm is simple, good in controllability 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): adding a polymer and a hot-melt additive into an organic solvent, stirring and mixing to form a mixed glue solution; step (B): and coating the mixed glue solution on at least one side surface of the base film, washing with water, and drying to form a safety coating, thereby preparing the safety diaphragm.

The preparation method of the safety diaphragm further comprises the steps of adding the inorganic filler into the mixed glue solution, stirring and mixing to form coating slurry, coating the coating slurry on at least one side surface of the base film, washing, drying to form the safety coating, and thus the safety diaphragm is prepared.

As an improvement of the preparation method of the safety diaphragm, the weight part ratio of the polymer, the hot-melt additive and the inorganic filler is 60-70: 5-50: 30-80.

As an improvement of the method for manufacturing a safety diaphragm of the present invention, the inorganic filler is at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silica, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, and boehmite.

As an improvement of a method for manufacturing a safety diaphragm of the present invention, the polymer is at least one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene oxide, epoxy resin, and epoxy resin derivative.

As an improvement of the preparation method of the safety diaphragm, the hot melt additive is at least one of polyethylene, polyethylene wax, polyethylene oxide wax and polypropylene wax.

The third purpose of the invention is that: aiming at the defects of the prior art, the lithium ion battery is good in safety and long in 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 has the beneficial effects that: the utility model provides a safety diaphragm, has safety coating and can absorb the heat under high temperature environment, reduces the base film temperature, promotes the base film heat resistance, can melt the diaphragm orifice that blocks up the base film simultaneously to avoid electric core short circuit to catch fire.

Drawings

Fig. 1 is an enlarged view of the safety diaphragm of the present invention.

Figure 2 is a graph comparing the closed cell temperature curves of the separators of example 1, example 2, and comparative 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.

1. A safety diaphragm comprises a base film and a safety coating arranged on at least one side surface of the base film, wherein the safety coating comprises a hot melt additive which is used for melting and blocking film holes of the base film after absorbing heat. As shown in fig. 1, the safety diaphragm of the present invention has uniform distribution of micropores, can absorb a portion of heat during the abnormal heating process of the diaphragm, and forms closed pores when the temperature rises to the melting point of the hot melt additive, thereby melting and blocking the base membrane, and further effectively preventing the short circuit and the fire of the battery core.

Preferably, the particle size of the hot-melt additive is 0.2-5 um. When the electric core is out of control due to heat, the hot melt additive blocks the diaphragm micropores through phase state change, so that the generation of short-circuit current is inhibited, and the hot box test passing rate of the electric core is improved. The particle size of the hot-melt additive is too small, so that the material cannot completely block micropores after the phase state of the material is changed, and the hot box test performance is poor; the particle size of the hot-melt additive is too large, the physical volume of the material before deformation is larger than the pore size of the diaphragm micropores of the organic solvent system, and the diaphragm micropores are blocked when thermal runaway does not occur, so that the lithium ion transmission channels are reduced under the normal working state of the diaphragm, and the performance of a lithium ion battery cell is influenced. Preferably, the particle size of the hot-melt additive is 1-4 um. Preferably, the particle size of the hot melt additive is 1um, 2um, 3um, 4um, 5 um.

Preferably, the thickness of the base film is 3-200 um, the porosity is 20-80%, and the air permeability is 50-200 s/100 cc. Too small porosity of the base film easily affects the ion moving rate, and too large porosity easily causes particles in the safety coating to block the pores of the base film under normal work, thereby affecting the ion moving speed and the conductivity. Preferably, the thickness of the base film is 10-100 um, the porosity is 40-70%, and the air permeability is 100-150 s/100 cc. The base film is any one of polyethylene microporous diaphragm, polypropylene/polyethylene/polypropylene three-layer composite microporous diaphragm, polyvinylidene fluoride-hexafluoropropylene microporous diaphragm, polyimide microporous diaphragm, polyethylene non-woven fabric, polypropylene non-woven fabric, polyester non-woven fabric, polyimide non-woven fabric, aramid non-woven fabric and spandex non-woven fabric.

Preferably, the thickness of the security coating is 1-5 um. Preferably, the thickness of the security coating is 1um, 2um, 3um, 4um, 5 um. The thickness of the safety coating is too thick, so that the thickness of the whole diaphragm is too thick, the electrical property is influenced, the safety coating is too thin, the heat resistance of the base film cannot be improved, and the safety coating is easy to damage.

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

step (A): adding a polymer and a hot-melt additive into an organic solvent, stirring and mixing to form a mixed glue solution;

step (B): and coating the mixed glue solution on at least one side surface of the base film, washing with water, and drying to form a safety coating, thereby preparing the safety diaphragm.

The hot melt additive is a substance which is melted at a high temperature of 90-130 ℃, so that the hot melt additive can be melted at the high temperature to absorb partial heat, and micropores of a base film are blocked after the heat is melted, so that the transmission of ions is reduced, the heat can not be gathered and increased in a certain area, and the thermal runaway is effectively controlled.

According to the invention, the organic solvent is used for mixing the polymer and the hot-melt additive to form an organic solvent system, the prepared diaphragm has good bonding force, the electrolyte has good wettability, the air permeability increment is small, and the uniformly distributed microporous structure can be seen on the surface of the diaphragm obtained by the organic solvent system through SEM observation. The preparation method is simple, the production process is mature, the material cost is lower, the stable mass production capacity is realized, the prepared diaphragm and the prepared pole piece have good adhesion, the adhesion is more than or equal to 5N/m, and the hardness and the consistency of the obtained battery cell are good.

Preferably, the preparation method of the safety diaphragm further comprises the steps of adding the inorganic filler into the mixed glue solution, stirring and mixing to form coating slurry, coating the coating slurry on at least one side surface of the base film, washing with water, and drying to form the safety coating, so as to obtain the safety diaphragm.

Preferably, the weight part ratio of the polymer to the hot-melt additive to the inorganic filler is 60-70: 5-50: 30-80.

Preferably, the inorganic filler is at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silica, titania, zirconia, magnesium hydroxide, aluminum hydroxide, boehmite. The inorganic filler provided by the invention has good heat resistance, and mainly plays a role in improving the heat resistance of the diaphragm in the coating, so that the short circuit of the positive electrode and the negative electrode caused by the contraction of the diaphragm under a high-temperature condition is avoided, the fire probability is reduced, and the safety is improved.

Preferably, the polymer is at least one of polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyurethane, polyphenylene oxide, epoxy resin, and epoxy resin derivative. The polymer of the invention is used as a main body for obtaining a coating diaphragm, plays a role of a framework and obtains a lithium ion transmission channel through pore forming.

Preferably, the hot melt additive is polyethylene, polyethyleneWax, polyethylene oxide wax, polypropylene wax. The hot-melt additive can improve the performance of the diaphragm hot box of an organic solvent system, when the battery core is out of control due to heat, the material absorbs heat and changes phases, and blocks the micropores of the diaphragm after melting, so that the generation of short-circuit current is inhibited, and the test passing rate of the battery core under the high-temperature condition is improved. The melting point of the hot-melt additive is between 90 and 130 ℃, the particle size is between 0.2 and 5 mu m, and the particle size is too small, so that the material cannot completely block micropores after the phase state changes, and the hot box test performance is poor; the aperture is too large, the physical volume of the material before deformation is larger than the aperture of the diaphragm micropores of the organic solvent system, and the diaphragm micropores are already blocked when thermal runaway does not occur, so that the lithium ion transmission channels are reduced under the normal working state of the diaphragm, and the performance of the lithium ion battery cell is influenced. The proportion of the hot melt additive is 5-50%, preferably 10-30%. Preferably the hot melt additive is present in a proportion of 10%, 15%, 20%, 25%, 30%. Preferably, the polyethylene is low-density polyethylene with the density of 0.91-0.93 g/cm³Preferably linear low density polyethylene, and also low molecular weight polyethylene, the molecular weight of polyethylene is 500-2000.

2. 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. The lithium ion battery of the invention uses the safety diaphragm of the invention, and has good safety and long service life.

Example 1

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

step (A): adding a polymer and a hot-melt additive into an organic solvent, stirring and mixing to form a mixed glue solution;

step (B): adding an inorganic filler into the mixed glue solution, stirring and mixing to form coating slurry;

step (C): and coating the coating slurry on two side surfaces of the base film, washing with water, and drying to form a safety coating, thereby preparing the safety diaphragm.

Wherein the weight part ratio of the polymer to the hot melt additive to the inorganic filler is 70:25: 55.

Wherein the inorganic filler is alumina.

Wherein the polymer is polytetrafluoroethylene.

Wherein the hot melt additive is low molecular weight polyethylene.

Wherein the base film is a polypropylene base film.

Wherein the organic solvent is ethanol.

A safety diaphragm comprises a base film and safety coatings arranged on two side faces of the base film, wherein the safety coatings comprise hot melt additives which are used for melting and blocking film holes of the base film after absorbing heat. Wherein the thickness of the base film is 120um, the porosity is 60 percent, and the air permeability is 160s/100 cc.

Example 2

The difference from example 1 is that:

the weight part ratio of the polymer to the hot melt additive to the inorganic filler is 65:5: 30.

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

Example 3

The difference from example 1 is that:

the weight part ratio of the polymer to the hot melt additive to the inorganic filler is 60:20: 45.

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

Example 4

The difference from example 1 is that:

the weight portion ratio of the polymer to the hot melt additive to the inorganic filler is 60:45: 55.

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

Example 5

The difference from the embodiment example 1 is that:

the weight part ratio of the polymer to the hot melt additive to the inorganic filler is 60:15: 35.

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

Example 6

The difference from the embodiment example 1 is that:

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

step (A): adding a polymer and a hot-melt additive into an organic solvent, stirring and mixing to form a mixed glue solution;

step (B): and coating the mixed glue solution on two side surfaces of the base film, washing with water, and drying to form a safety coating, thereby preparing the safety diaphragm.

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

Comparative example 1 is a polypropylene separator.

Comparative example 2 is an aqueous solvent coated separator.

Performance testing

1. Closed cell temperature test: preparing a stainless steel clamp with a cavity inside, isolating the left part and the right part of the stainless steel clamp by using resin sealing gaskets, placing a diaphragm in the clamp, filling the cavity with electrolyte, and then respectively connecting the left part and the right part of the clamp with a temperature detector and a resistance detector. The clamp is placed in the oven with the heating function, the oven is heated, the temperature and the resistance value are recorded, the micropores of the diaphragm are smooth at the beginning, the left part and the right part of the clamp are conducted through electrolyte, the resistance value is small, when the clamp is heated to a certain temperature, the diaphragm forms a closed hole, the micropore channel is blocked, and the resistance value of the clamp is sharply increased. The closed cell temperature of the separator was obtained by recording and the test structure is reported in table 1. Figure 2 records the closed cell temperature curves for the membranes of example 1, example 2 and comparative example 1.

2. Testing the hardness of the battery core: the three-point bending method is characterized in that two ends of a battery cell are horizontally arranged on two sides of a fixed position, no shielding object is arranged below a battery cell main body, a circular rod provided with a force detector is aligned to the center of the battery cell, then the circular rod is moved downwards, the magnitude of force is recorded, the peak force is the magnitude of battery cell hardness, and a test result is recorded in a table 2.

3. Charging the lithium ion battery to 4.3V at a constant current of 1C at 25 ℃, then charging to a current of less than 0.05C at a constant voltage of 4.3V, and stopping charging; the lithium ion battery is placed in a hot box, the temperature is increased from 25 ℃ to 150 ℃ at the temperature increase rate of 5 ℃/min, the temperature is kept unchanged after the temperature reaches 150 ℃, then timing is started until the surface of the lithium ion battery starts to smoke, each test is carried out for 5 times, the passing times are recorded, and the test result is recorded in a table 3.

TABLE 1

Item	Example 1	Example 2	Example 3	Example 4
					Closed cell temperature (. degree. C.)	139	142	138	136
Item	Example 5	Example 6	Comparative example 1	Comparative example 2
					Closed cell temperature (. degree. C.)	135	136	145	144

TABLE 2

Item	Example 1	Example 2	Example 3	Example 4
					Cell hardness/N	215	215	216	214
Item	Example 5	Example 6	Comparative example 1	Comparative example 2
					Cell hardness/N	219	216	202	210

TABLE 3

Item	132℃/30mins	135℃/30mins	Item	132℃/30mins	135℃/30mins
						Example 1	5/5	5/5	Example 2	5/5	5/5
Example 3	5/5	5/5	Example 4	5/5	5/5
						Example 5	5/5	5/5	Example 6	5/5	5/5
Comparative example 1	1/5	0/5	Comparative example 2	1/5	0/5

As a result of comparing examples 1 to 6 and comparative examples 1 and 2 described above, the safety separator according to the present invention has a lower closing temperature, a higher cell hardness, and a higher heat resistance than the separators of the prior art. Specifically, as can be seen from table 1, the closed-cell temperature of the present invention is lower, and can reach 135 ℃, which indicates that the separator of the present invention has a more sensitive temperature response compared to the conventional PP separator, and can realize closed-cell at a lower temperature, thereby isolating the contact between the positive electrode and the negative electrode and further avoiding thermal runaway. More specifically, as can be seen from a comparison of FIG. 2, examples 1 and 2 prepared according to the present invention have lower closed cell temperatures, with example 1 having a closed cell temperature of 139℃ and example 2 having a closed cell temperature of 142℃. As can be seen from table 2, the cell hardness of the present invention is higher, up to 218N, has stronger mechanical strength, and is stronger and safer than those of comparative example 1 and comparative example 2. As can be seen from Table 3, the prepared cell of the invention has better heat resistance, and passes through the 132 ℃/30mins and 135 ℃/30mins hot box tests respectively, and has good heat resistance, while the polypropylene diaphragm of the comparative example 1 and the water-based solvent coating diaphragm of the comparative example 2 only pass through the 132 ℃/30mins test for 1 time, but do not pass through the 135 ℃/30mins hot box test. Also from the comparison of examples 1-6, when the weight part ratio of the polymer, the hot melt additive and the inorganic filler is set to 60:15:35, the prepared separator cell has lower closed cell temperature, higher heat resistance and stronger mechanical strength.

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.