阅读说明：本技术 涂层隔膜及其制备方法和电化学装置 (Coated separator, method for preparing same, and electrochemical device ) 是由 吴斌 刘子英 周旭苗 徐建伟 王莉 王小记 李华锋 柳青 于 2020-11-02 设计创作，主要内容包括：本发明公开了一种涂层隔膜及其制备方法和电化学装置,该涂层隔膜材料包括微孔基膜以及陶瓷涂层,所述陶瓷涂层设在所述微孔基膜的至少一部分上,微孔基膜的透气度为10～100s/100cc,陶瓷涂层的透气度为180～250s/100cc。由此,该涂层隔膜一致性好,将其应用于锂离子电池可以保证电流的均匀性,从而解决现有锂离子电池内部电流分布不均匀导致的电池循环容量低以及电池内部短路的问题,并且该涂层隔膜具有良好的离子电导率和热稳定性。(The invention discloses a coating diaphragm and a preparation method and an electrochemical device thereof, wherein the coating diaphragm material comprises a microporous base film and a ceramic coating, the ceramic coating is arranged on at least one part of the microporous base film, the air permeability of the microporous base film is 10-100 s/100cc, and the air permeability of the ceramic coating is 180-250 s/100 cc. Therefore, the coating diaphragm has good consistency, can ensure the uniformity of current when applied to the lithium ion battery, solves the problems of low battery cycle capacity and short circuit in the battery caused by uneven distribution of the internal current of the existing lithium ion battery, and has good ionic conductivity and thermal stability.)

1. A coated separator, comprising:

a microporous base film;

a ceramic coating disposed on at least a portion of the microporous base film,

wherein the air permeability of the microporous base film is 10-100 s/100cc, and the air permeability of the ceramic coating is 180-250 s/100 cc.

2. The coated membrane of claim 1, wherein the microporous base membrane is selected from at least one of a polyolefin microporous base membrane, a polyethylene terephthalate microporous base membrane, a polyamide microporous base membrane, a polyimide microporous base membrane, a polyetheretherketone microporous base membrane, a polyethersulfone microporous base membrane, a polyvinylidene fluoride microporous base membrane, and a polytetrafluoroethylene microporous base membrane;

optionally, the microporous base membrane is prepared by a dry or wet stretching process.

3. The coated separator according to claim 1, wherein the thickness of the microporous base film is 5 to 12 μm.

4. The coated separator of claim 1, wherein the ceramic coating is provided on the upper surface and/or the lower surface of the microporous base membrane.

5. The coated separator according to claim 1, wherein the ratio of the thickness of the ceramic coating layer to the thickness of the microporous base film is (1-2): (1-5).

6. The coated separator of claim 1, wherein the inorganic ceramic particles in the ceramic coating are at least one of aluminum oxide, silicon dioxide, zirconium dioxide, titanium dioxide, barium sulfate, magnesium oxide, magnesium hydroxide, boehmite, and silicon nitride.

7. A method of making the coated separator of any one of claims 1-6, comprising:

(1) mixing inorganic ceramic particles, a wetting agent, a dispersant, a thickener, a binder and water to obtain a coating slurry;

(2) the coating slurry is applied on a part of the surface of the microporous base film and then dried, so that a coated separator is obtained.

8. The method according to claim 7, wherein in step (1), the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickener, the binder, and water are mixed in a mass ratio of 1: (0.0030-0.009): (0.0039-0.0160): (0.0030-0.03): (0.03-0.09): (1.2-5.6) mixing;

optionally, the wetting agent comprises at least one of polyols, polyoxyethylene ethers, and organosiloxanes;

optionally, the dispersant comprises at least one of ammonium polyacrylate salt, trimethylammonium hydrochloride salt;

optionally, the thickener comprises at least one of sodium carboxymethyl cellulose, sodium carboxymethyl acrylate;

optionally, the binder comprises at least one of an acrylic aqueous binder, a polyacrylate emulsion based binder, and polyvinyl alcohol;

optionally, in the step (2), the applying manner includes at least one of gravure roll coating, anilox roll coating, sleeve coating, and screen printing.

9. The method of claim 7, wherein step (1) is performed as a series of steps:

(1-1) mixing and dispersing the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickener and water with stirring to obtain a pre-dispersed ceramic slurry;

(1-2) dispersing the pre-dispersed ceramic slurry in a sand mill or a high shear dispersing device to obtain a ceramic slurry;

(1-3) mixing the ceramic slurry and the binder with stirring to obtain the coating slurry.

10. An electrochemical device comprising the coated separator of any one of claims 1 to 6 or a coated separator obtained by the method of any one of claims 7 to 9.

Technical Field

The invention belongs to the field of materials, and particularly relates to a coating diaphragm, a preparation method thereof and an electrochemical device.

Background

The lithium ion battery is composed of anode, cathode, electrolyte, diaphragm and other materials. The diaphragm is an important component and plays a role in separating the positive electrode from the negative electrode, preventing the positive electrode from being directly contacted with the negative electrode and avoiding internal short circuit. The separator allows only electrolyte ions to pass freely, and its properties determine the interface structure and internal resistance of the battery, etc.

The uniformity of the current inside the lithium ion battery affects the cycle performance and safety performance. The non-uniform current distribution can cause lithium precipitation at the negative electrode of the battery. The occurrence of the lithium separation phenomenon can cause negative effects on the battery in two aspects. On one hand, active lithium precipitated from the negative electrode continuously reacts with an electrolyte to generate a solid electrolyte interphase (SEI film), which causes the reduction of the cycle capacity of the battery and the increase of the internal resistance of the battery; on the other hand, lithium dendrites formed during the cycle pierce the separator, causing an internal short circuit of the battery, and increasing the safety risk of the battery.

The uniformity of the separator, including porosity, pore size distribution, and film resistance, can affect cell performance. The production and manufacture process of microporous polyolefin diaphragm relates to drawing process, and the ion transmission channel in the diaphragm is oriented along the drawing direction, and has different drawing multiplying power and different orientation degree. The porous membrane diaphragm prepared by the existing stretching method can not ensure the complete consistency of the diaphragm structure no matter in a dry process or a wet process, and the problem of poor uniformity of the transmission of lithium ions in the polyolefin diaphragm exists. When the diaphragm is applied to a battery, particularly in the process of large-current charging and discharging, the current at the interface of the diaphragm and an electrode is not uniform, and the phenomenon of lithium precipitation is easily generated, so that the capacity of the battery is attenuated.

To address the issue of coating membrane uniformity, solutions for organic-inorganic composite membranes have emerged. CN 111446402 a reports the preparation process of a separator. Firstly, uniformly mixing a diaphragm substrate, superfine ceramic powder and one of PVDF and PMMA in a mixer according to a proportion, and grinding to obtain a mixed material with a required granularity; secondly, transferring the obtained mixed material to a heater with stirring to melt the material, and then adding an organic solvent to adjust the viscosity of the material; and finally, transferring the melted material into a material injector of the 3D printer, and pushing a piston of the injector to enable the material to be sprayed on the substrate through a 3D printer nozzle to form the composite diaphragm. The composite diaphragm has uniform aperture structure, less local defects and good diaphragm consistency. However, the diaphragm related to the patent has complex preparation process and low production efficiency.

CN 110265608A discloses a preparation method of a nanometer diaphragm, which relates to a grafted nanometer inorganic oxide layer on the surface of a base film layer. Firstly, carrying out irradiation treatment on the surface of a polyolefin diaphragm; then, coating the water-based slurry of the nano inorganic oxide on the surface of the polyolefin diaphragm by adopting a micro gravure roller coating mode; and finally, drying the water at 40-60 ℃ to obtain the composite film of the polyolefin surface grafted with the nano inorganic particles. The composite diaphragm has good thermal stability and excellent battery cycle performance. However, this preparation method takes a long time, and the coating slurry preparation process uses an organic solvent, which is harmful to the environment.

Thus, existing diaphragms are in need of improvement.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide a coating separator, a method for preparing the same, and an electrochemical device, wherein the coating separator has good consistency, and when the coating separator is applied to a lithium ion battery, the uniformity of current can be ensured, so that the problem of serious battery capacity attenuation caused by uneven distribution of internal current in the existing lithium ion battery can be solved, the generation of lithium dendrite can be inhibited, and the coating separator has good ionic conductivity and thermal stability.

In one aspect of the invention, a coated separator is provided. According to an embodiment of the invention, the coated membrane comprises:

a microporous base film;

a ceramic coating disposed on at least a portion of the microporous base film,

wherein the air permeability of the microporous base film is 10-100 s/100cc, and the air permeability of the ceramic coating is 180-250 s/100 cc.

According to the coating diaphragm of the embodiment of the invention, the ceramic coating with uniform internal structure and components is formed on the microporous base film, so that the thermal stability of the coating diaphragm can be improved, the air permeability of the microporous base film is limited to 10-100 s/100cc, and the air permeability of the ceramic coating is 180-250 s/100cc, namely the ceramic coating with the air permeability is arranged on the microporous base film with low air permeability to improve the uniformity of the coating diaphragm, the problem of uneven current density distribution caused by poor base film uniformity is reduced by utilizing the uniform transmission of lithium ions in the ceramic coating, namely the coating diaphragm has good uniformity, the coating diaphragm can be applied to a lithium ion battery to ensure the uniformity of current, so that the problems of low battery circulation capacity and lithium dendrite generation inhibition caused by uneven current distribution in the conventional lithium ion battery are solved, and the ceramic coating has good lyophilic property, thereby improving the ion conductivity of the coated membrane.

In addition, the coated membrane according to the above embodiment of the present invention may further have the following additional technical features:

in some embodiments of the present invention, the microporous base film is prepared using a dry or wet stretching process.

In some embodiments of the present invention, the microporous base membrane is selected from at least one of a polyolefin microporous base membrane, a polyethylene terephthalate microporous base membrane, a polyamide microporous base membrane, a polyimide microporous base membrane, a polyetheretherketone microporous base membrane, a polyethersulfone microporous base membrane, a polyvinylidene fluoride microporous base membrane, and a polytetrafluoroethylene microporous base membrane.

In some embodiments of the present invention, the microporous base film has a thickness of 5 to 12 μm. Therefore, the mechanical property of the coating diaphragm can be improved, and the energy density of the manufactured battery is high.

In some embodiments of the present invention, the ceramic coating is disposed on the upper surface and/or the lower surface of the microporous base film.

In some embodiments of the present invention, the ratio of the thickness of the ceramic coating layer to the thickness of the microporous base film is (1-2): 1-5. Thereby, it is possible to suppress the generation of lithium dendrites and to enhance the thermal stability of the coated separator and the cycle performance of the battery.

In some embodiments of the present invention, the inorganic ceramic particles in the ceramic coating are at least one of aluminum oxide, silicon dioxide, zirconium dioxide, titanium dioxide, barium sulfate, magnesium oxide, magnesium hydroxide, boehmite, and silicon nitride. Thereby, the conductivity can be improved.

In a second aspect of the invention, a method of making a coated separator is provided. According to an embodiment of the invention, the method comprises:

(1) mixing inorganic ceramic particles, a wetting agent, a dispersant, a thickener, a binder and water to obtain a coating slurry;

(2) the coating slurry is applied on a part of the surface of the microporous base film and then dried, so that a coated separator is obtained.

According to the method for preparing the coating diaphragm, the coating slurry obtained by mixing the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickening agent and the binder is applied to the surface of the microporous base film, so that the coating diaphragm with good consistency and thermal stability can be prepared, the uniformity of current can be ensured when the coating diaphragm is applied to a lithium ion battery, the problem of low battery circulation capacity caused by uneven distribution of the current in the conventional lithium ion battery is solved, lithium dendrite can be inhibited from being generated, and the ionic conductivity of the coating diaphragm is improved due to good lyophilic property of the ceramic coating. In addition, the production process is simple, and the slurry system is a water-based system and has little pollution to the environment.

In addition, the method of manufacturing the coated separator according to the above embodiment of the present invention may further have the following additional technical features:

in some embodiments of the invention, step (1) above is performed as a series of steps: (1-1) mixing and dispersing the inorganic ceramic particles, the wetting agent, the thickener, the dispersant and water with stirring to obtain a pre-dispersed ceramic slurry; (1-2) dispersing the pre-dispersed ceramic slurry in a sand mill or a high shear dispersing device to obtain a ceramic slurry; (1-3) mixing the ceramic slurry and the binder with stirring to obtain the coating slurry.

In some embodiments of the present invention, in the step (1), the inorganic ceramic particles, the wetting agent, the dispersant, the thickener, the binder and water are mixed in a mass ratio of 1 (0.0030 to 0.009): 0.0039 to 0.0160): 0.0030 to 0.03): 0.03 to 0.09): 1.2 to 5.6.

In some embodiments of the present invention, the wetting agent includes at least one of a polyol polyoxyethylene ether and a silicone ether, thereby improving wetting of the ceramic particles in the pre-dispersed ceramic slurry with water.

In some embodiments of the present invention, the dispersant includes at least one of ammonium polyacrylate salt and trimethylammonium hydrochloride salt, thereby improving the stability of the ceramic particles in the pre-dispersed ceramic slurry in water.

In some embodiments of the present invention, the thickener comprises at least one of sodium carboxymethyl cellulose and sodium carboxymethyl acrylate, thereby increasing the viscosity of the coating paste and enhancing the stability of the paste system.

In some embodiments of the present invention, the binder includes at least one of an acrylic aqueous binder, a polyacrylate emulsion-based binder, and polyvinyl alcohol, and thus, the adhesion of the ceramic particles to the base film may be enhanced.

In some embodiments of the invention, the rotational speed of the sand mill or the high shear dispersing apparatus is 1000 to 3000 rpm. This can improve the dispersibility of the ceramic slurry.

In some embodiments of the invention, the application means comprises at least one of gravure roll coating, anilox roll coating, sleeve coating and screen printing.

In a third aspect of the present invention, the present invention provides an electrochemical device having the above-described coated separator or the coated separator obtained by the above-described method according to an embodiment of the present invention. Thus, by loading the coated separator having the above excellent uniformity, thermal stability and high ionic conductivity, the capacity, cycle performance and safety performance of the electrochemical device can be improved.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic structural view of a coated membrane according to one embodiment of the invention;

FIG. 2 is a schematic structural view of a coated membrane according to yet another embodiment of the invention;

FIG. 3 is a schematic flow diagram of a method of making a coated separator according to one embodiment of the invention;

fig. 4 is a schematic flow diagram of a method of making a coated separator according to yet another embodiment of the invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar components or components having the same or similar functions throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

In one aspect of the invention, a coated separator is provided. According to an embodiment of the present invention, referring to fig. 1, the coated membrane includes: a microporous base film 100 and a ceramic coating layer 200, wherein the ceramic coating layer 200 is provided on at least a portion of the microporous base film 100, wherein the microporous base film 100 has a permeability of 10 to 100s/100cc, and the ceramic coating layer 200 has a permeability of 180 to 250s/100 cc. The inventors found that the thermal stability of the coated separator can be improved by forming the ceramic coating 200 having a uniform internal structure and composition on the microporous base film 100, and surprisingly found that, if the porosity of the microporous base film 100 is less than 10s/100cc, the porosity of the base film is high, so that lithium ions are not uniformly transferred in the coated separator, lithium dendrites are easily generated, which may pierce the coated separator to cause internal short circuit of the battery, the safety risk of the battery increases, and the self-discharge of the battery is large; and if the air permeability value of the microporous base film 100 is higher than 100s/100cc, the air permeability of the obtained coated membrane is high, the ionic resistance is high, and the conductivity of the obtained coated membrane is low. Meanwhile, if the air permeability of the ceramic coating 200 is lower than 180s/100cc, the thermal shrinkage rate of the coating diaphragm is large, even if the thermal stability of the coating diaphragm is poor; and if the ceramic coating 200 has a permeability of more than 250s/100cc, the ion conductivity of the coated separator is low, thereby reducing the cycle performance of the battery. And the air permeability of the microporous base film 100 is limited to 10-100 s/100cc, and the air permeability of the ceramic coating 200 is limited to 180-250 s/100cc, so that under the condition, good ion conduction and low thermal shrinkage rate of the coating diaphragm can be ensured, and the internal current of the battery is uniform. This application sets up the ceramic coating 200 of above-mentioned air permeability on the micropore base film 100 of above-mentioned air permeability and improves the uniformity of coating diaphragm from this, utilize lithium ion even transmission to reduce the poor inhomogeneous problem of current density distribution that causes of base film uniformity in ceramic coating 200, this application coating diaphragm uniformity is good that to say, thereby it can guarantee the homogeneity of electric current to be applied to lithium ion battery with it, and then solve the problem of the inside short circuit of battery that the inside electric current distribution of current in current lithium ion battery is inhomogeneous to lead to that battery cycle capacity is low and the battery, and because ceramic coating 200 lyophilic is good, thereby improve the ionic conductivity of coating diaphragm.

Further, the microporous base film 100 is prepared by a dry or wet stretching process. Specifically, the microporous base film 100 obtained by the stretching process has local defects inside, which results in poor consistency, so that the ceramic coating 200 with uniform internal structure and components is formed on the surface of the microporous base film, and the consistency and stability of the microporous base film can be improved. Preferably, the microporous base film 100 may be a polyolefin base film or other base film, for example, at least one of a polyethylene terephthalate microporous base film, a polyamide microporous base film, a polyimide microporous base film, a polyetheretherketone microporous base film, a polyethersulfone microporous base film, a polyvinylidene fluoride microporous base film, a polytetrafluoroethylene microporous base film.

Further, the thickness of the microporous base film 100 is 5 to 12 μm. The inventors found that if the microporous base film 100 is less than 5 μm thick, the mechanical properties of the coated separator are poor; if the thickness of the microporous base film 100 is larger than 12 μm, the ionic resistance of the coating diaphragm is higher, and the energy density of the manufactured battery is low. Therefore, the microporous base film 100 with the thickness of 5-12 mu m can improve the mechanical strength of the coating diaphragm and simultaneously avoid the problem of higher ionic resistance of the coating diaphragm. The inventors have also found that if the ratio of the thickness of the ceramic coating 200 to the microporous base film 100 is less than 1: 5, the ceramic coating has a thickness of 200. thin, which causes uneven lithium ion transmission in the coating diaphragm, and the battery is easy to generate lithium dendrite, and the high thermal yield of the coating diaphragm causes poor thermal stability of the coating diaphragm; and if the thickness ratio of the ceramic coating layer 200 to the microporous base film 100 is more than 2: 1, the coated separator 200 has low conductivity and poor battery cycle performance. Therefore, the thickness ratio of the ceramic coating 200 to the microporous base film 100 in the coating diaphragm adopted by the application is (1-2) to (1-5), so that the current distribution on the coating diaphragm can be ensured to be uniform, and the battery cycle performance can be improved. It is emphasized that the "ceramic coating thickness" in the ratio of the ceramic coating to the microporous base film thickness herein refers to the single-sided ceramic coating thickness, unless otherwise specified.

Further, the ceramic coating 200 formed on the microporous base film 100 is a single-sided ceramic coating (refer to fig. 1) or a double-sided ceramic coating (refer to fig. 2), preferably a double-sided ceramic coating, and more preferably a double-sided ceramic coating having the same thickness. The inventor finds that the double-sided ceramic coating not only can effectively improve the wettability of the coating diaphragm to electrolyte and is beneficial to ion conduction, but also has low thermal shrinkage of the double-sided ceramic coating diaphragm, thereby improving the thermal stability of the coating diaphragm. Further, the inorganic particles in the ceramic coating 200 are one or more of aluminum oxide, silicon dioxide, zirconium dioxide, titanium dioxide, barium sulfate, magnesium oxide, magnesium hydroxide, boehmite, and silicon nitride.

In a second aspect of the present invention, the present invention provides a method for preparing the above-described coated separator. According to an embodiment of the invention, referring to fig. 3, the method comprises:

s100: mixing inorganic ceramic particles, a wetting agent, a dispersing agent, a thickening agent, a binder and water

In this step, inorganic ceramic particles, a wetting agent, a dispersant, a thickener, a binder and water are mixed to obtain a coating slurry. Further, the mixing ratio of the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickening agent, the binder and the water is not particularly limited, and for example, the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickening agent, the binder and the water are in a mass ratio of 1 (0.0030-0.009): (0.0039-0.0160): (0.0030-0.03): (0.03-0.09): (1.2-5.6). The inventor finds that the proportion of ceramic components is low, and the thermal shrinkage rate of the coating diaphragm is low; the ceramic component ratio is high, and the production cost is increased. The proportion of the wetting agent is low, and the ceramic particles have poor wettability to water; the proportion of the wetting agent is high, the phenomenon of pore blocking of a coating diaphragm is serious, and the air permeability value is large. The proportion of the dispersing agent is low, and the dispersing effect of the ceramic particles is poor; the proportion of the dispersant is high, and the cycle performance of the battery is influenced. The proportion of the thickening agent is low, and a slurry system is unstable and easy to layer; the proportion of the thickening agent is high, the viscosity of a slurry system is high, and the dispersion is difficult. The proportion of the binder is low, and finally, ceramic particles are easy to fall off, so that the phenomenon of serious powder falling of a coating diaphragm is caused; the proportion of the binder is high, the phenomenon of pore blocking of the coating diaphragm is serious, and the air permeability value is large. Therefore, the ionic conductivity and the thermal stability of the coating diaphragm can be improved by adopting the mixing proportion.

According to an embodiment of the present invention, referring to fig. 4, mixing the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickening agent, and the binder may be performed using the following steps:

s110: mixing and dispersing inorganic ceramic particles, a wetting agent, a thickening agent, a dispersing agent and water with stirring

In this step, the above inorganic ceramic particles, wetting agent, thickener and dispersant are mixed and dispersed in water with stirring to obtain a pre-dispersed ceramic slurry. Meanwhile, the types of the wetting agent, the dispersing agent and the thickener are not particularly limited, for example, the wetting agent includes at least one of polyhydric alcohol polyoxyethylene ethers, silicone ethers; the dispersant comprises at least one of polyacrylic acid ammonium salt and trimethylammonium hydrochloride; the thickener comprises at least one of sodium carboxymethyl cellulose and sodium carboxymethyl acrylate.

S120: dispersing the pre-dispersed ceramic slurry in a sand mill or high shear dispersing equipment

In the step, the pre-dispersed ceramic slurry obtained in the step is dispersed in a sand mill or high-shear dispersing equipment to obtain ceramic slurry with higher dispersibility. Further, the rotation speed of the sand mill or the high shear dispersion apparatus is 1000-3000 rpm. The inventor finds that if the rotating speed is lower than 1000rpm, the slurry dispersing effect is poor, and the slurry is easy to settle; and if the rotating speed is higher than 3000rpm, the energy consumption of dispersing equipment is high, and the cost is increased. Therefore, by adopting the rotating speed, the energy consumption cost can be reduced while the slurry dispersing effect is improved.

S130: mixing the ceramic slurry and the binder with stirring

In this step, the ceramic slurry and the binder are mixed with stirring to obtain a coating slurry. Meanwhile, the type of the binder is not particularly limited, and for example, the binder includes at least one of an acrylic aqueous binder, a polyacrylate emulsion-based binder, and a polyvinyl alcohol-based binder.

S200: applying the coating slurry to a portion of the surface of the microporous base film and drying

In this step, the above coating slurry is applied to a portion of the surface of the microporous base film and then dried at 55 to 65 ℃ (preferably 60 ℃) to obtain a coated separator. Specifically, the coating slurry may be applied to the upper surface and/or the lower surface of the microporous base film, i.e., single-sided coating or double-sided coating may be performed on the microporous base film.

The application method of the coating paste is not particularly limited, and for example, at least one of gravure roll coating, anilox roll coating, blanket coating, and screen printing may be used as the application method of the coating paste.

According to the method for preparing the coating diaphragm, the coating slurry obtained by mixing the inorganic ceramic particles, the wetting agent, the dispersing agent, the thickening agent and the binder is applied to the surface of the microporous base film, so that the coating diaphragm with good consistency and thermal stability can be prepared, the uniformity of current can be ensured when the coating diaphragm is applied to a lithium ion battery, the problems of low battery circulation capacity and short circuit inside the battery caused by uneven distribution of the current inside the lithium ion battery are solved, and the ionic conductivity of the coating diaphragm is improved due to good lyophilic property of the ceramic coating. And the production process is simple, and the slurry system is a water-based system and has small pollution to the environment. It should be noted that the features and advantages described above for the coated separator are also applicable to the method for preparing the coated separator, and are not described in detail here.

In a third aspect of the present invention, an electrochemical device is provided. According to an embodiment of the present invention, the electrochemical device includes the above-described coated separator or the coated separator obtained by the above-described method. Thus, by loading the above-described coated separator having excellent uniformity, thermal stability and ionic conductivity, the capacity, cycle performance and safety performance of the electrochemical device can be improved. It should be noted that, the structure of the electrochemical device other than the coated separator may be selected by those skilled in the art according to actual needs, and the features and advantages described above for the coated separator and the preparation method thereof are also applicable to the electrochemical device, and will not be described herein again.

The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.

General procedure

The method of preparing the coated separator includes the steps of:

(1) mixing and dispersing inorganic ceramic particles, a wetting agent, a thickening agent, a dispersing agent and water with stirring to obtain pre-dispersed ceramic slurry;

(2) dispersing the pre-dispersed ceramic slurry in a sand mill or high-shear dispersing equipment to obtain ceramic slurry;

(3) mixing a ceramic slurry and a binder with stirring to obtain the coating slurry;

(4) and (3) applying the coating slurry on a part of the surface of the microporous base film, and drying at 60 ℃ to obtain the coating diaphragm.

The method of preparing the coated separator in examples 1 to 5 and comparative examples 1 to 3 is the same as the above general method, and wherein the microporous base film, the inorganic ceramic particles, the wetting agent, the dispersant, the thickener, the binder, the rotation speed of the sand mill or high-shear dispersion apparatus, and the addition ratio of each component are shown in table 1, and the thickness and air permeability of the microporous base film, the air permeability of the ceramic coating layer, the thickness ratio of the ceramic coating layer to the microporous base film, and the structure of the ceramic coating layer are shown in table 2, for example.

Table 1 example formulations

Table 2 structure of the embodiment

Note: in table 2, "ceramic coating thickness" in the ratio of the ceramic coating to the thickness of the microporous base film means the thickness of the single-sided ceramic coating.

The air permeability test and the coating membrane thickness test in table 2 used the following methods:

and (3) testing air permeability: selecting a base film or a coating diaphragm flat part, cutting each sample to be tested into 3 pieces of samples with the thickness of 100mm multiplied by 100mm, and testing the air permeability value by adopting a Gurley-4100 air permeability instrument. The air permeability of the coated separator or base film was measured by the time T for 100ml of air to pass through an area of the coated separator or base film under a certain pressure at an ambient temperature of 25 ℃. Wherein T is₁Is the permeability value, T, of the coating membrane₀Is the air permeability value of the base film, and is the air permeability value of the ceramic coating, wherein T is T₁-T₀；

Testing the thickness of the coating diaphragm: and selecting a part to be measured of the coating diaphragm, testing the coating diaphragm by using a thickness gauge, reading the measurement results for 5 times, and taking an average value.

Evaluation:

1. evaluating the thermal shrinkage, the conductivity, the cycle capacity retention rate and the short circuit time of the coating diaphragms obtained in the examples 1 to 5 and the comparative examples 1 to 3;

2. the evaluation method comprises the following steps:

testing the thermal shrinkage rate of the coating diaphragm:

the high-temperature resistance of the coating diaphragm sample is characterized by adopting the thermal shrinkage rate, the test method is carried out with reference to GB/T12027-2004, and the specific method is as follows: the actual dimensions (LM) of the samples were measured in the MD and TD directions of the coated separator, respectively, taking 5 pieces each of the samples of 100mm x 100mm or more in the MD and TD directions of the coated separator₀、LT₀) Then, the sample was sandwiched between two sheets of A4 paper, and after the temperature of the oven was stabilized, the sample was put into the oven, heated at 135 ℃ for 1 hour, taken out, and the heated size (LM) was measured₁、LT₁) The heat shrinkage ratios in the MD and TD directions were calculated by the following formulas, respectively. (η M, η T): η i ═ L_i0-L_i1)/L_i0X 100%, where i ═ M, T, test results are given in table 3.

And (3) testing the conductivity of the coating membrane:

and (3) clamping the coating diaphragm by using two stainless steel sheets, and injecting electrolyte to assemble the CR2032 type battery. Testing the resistance of the coating diaphragm through the alternating current impedance of an electrochemical workstation at the room temperature of 25 DEG CUsing the formula: sigma-L/SR_bWherein L is the thickness of the coating diaphragm, S is the area of the stainless steel sheet, and R_bTo measure the resistance of the resulting coated separator, the test results are shown in table 3.

Cycle capacity retention ratio:

the coated diaphragm and the electrode are assembled into a battery for testing, wherein the positive active material NCM523 is used as the positive active material, and the negative active material is graphite. The battery assembly is completed in a glove box (high-purity argon atmosphere), the button battery (CR2032) is obtained, and the assembled button battery is kept still for 24 hours, so that the electrode and the coating diaphragm are fully soaked by the electrolyte. First, the cells were activated by cycling at a constant current of 0.1C rate for 2 weeks. The cycle performance of the battery is in the range of 3.0-4.2V and under the condition of 1C multiplying power, 100-week cycle test is carried out, and the capacity retention rate is calculated. The charging mode is a constant current-constant voltage mode, and the discharging mode is a constant current mode. Capacity retention rate ═ C₁-C₀)/C₀100% of C₁Is 100 cycles capacity, C₀The test results are shown in table 3 for the initial discharge capacity.

Short-circuit time test:

and short circuit time, namely the time of lithium dendrites penetrating through the ceramic coating diaphragm, and the metal lithium and the coating diaphragm are assembled into a metal lithium/coating diaphragm/metal lithium symmetrical battery. At a discharge capacity of 1mAh/cm²The current density is 0.5mA/cm²And (0.5C) carrying out a lithium/lithium symmetric battery polarization test under the test condition, judging the influence of the coating diaphragm on lithium dendrites by utilizing the short-circuit time relation, and evaluating the inhibition capability of the coating diaphragm on the growth of the lithium dendrites, wherein the test result is shown in Table 3.

TABLE 3 Performance results

In conclusion, as can be seen from table 3, compared with comparative examples 1 to 3, the performance of the coated separator of examples 1 to 5 is superior to that of the coated separator obtained in comparative examples 1 to 3, which shows that the method of the present invention not only can significantly improve the conductivity, thermal stability and capacity retention rate of the coated separator, but also can ensure that lithium ions are uniformly transferred in the coated separator, and inhibit the generation of lithium dendrites, thereby satisfying the use requirements of consumers.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.