CN112952297B - Ceramic diaphragm, preparation method thereof and lithium battery - Google Patents
Ceramic diaphragm, preparation method thereof and lithium battery Download PDFInfo
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- CN112952297B CN112952297B CN202110454425.XA CN202110454425A CN112952297B CN 112952297 B CN112952297 B CN 112952297B CN 202110454425 A CN202110454425 A CN 202110454425A CN 112952297 B CN112952297 B CN 112952297B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a ceramic diaphragm, a preparation method thereof and a lithium battery, wherein the ceramic diaphragm comprises the following components: the ceramic coating is formed by coating ceramic slurry on at least one side surface of the base film and curing, and comprises ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion type copolymer binder and a surfactant. Therefore, the ceramic diaphragm has good high-temperature resistance, gives consideration to low-temperature performance, is applied to the lithium battery, and is beneficial to reducing the risk of thermal runaway of the lithium battery and the risk of shedding of the ceramic coating from the base film in winter application, thereby meeting the high safety requirement of the existing lithium battery.
Description
Technical Field
The invention belongs to the field of batteries, and particularly relates to a ceramic diaphragm, a preparation method thereof and a lithium battery.
Background
The lithium ion battery mainly comprises a positive/negative electrode material, electrolyte, a diaphragm and a battery packaging material. The diaphragm is used for isolating the positive electrode and the negative electrode, so that short circuit inside the lithium ion battery is prevented, and lithium ions can freely pass through the diaphragm to complete the electrochemical charging and discharging process. The performance of the separator determines the interface performance, internal resistance and the like of the battery, and directly influences the safety performance (high temperature resistance), electrical performance, cycle performance and other characteristics of the battery.
In recent years, the rapidly-developed new energy automobile industry puts higher demands on the safety, energy density, electrical performance and cycle life of lithium ion batteries. The traditional polyolefin diaphragm can not meet the high safety requirement of the existing users on the lithium ion battery, and the polyolefin ceramic coating diaphragm has great improvement on oxidation resistance, high temperature resistance and safety, and becomes the mainstream of the lithium ion battery technology at present. However, the size stability of the current commercial ceramic-coated polyolefin separator is still poor at high temperature (30-80% of 1h heat shrinkage at 150 ℃).
Patent CN201610191479.0 effectively improves thermal stability of the separator and reduces water content of the inorganic coating by introducing a water emulsion type polymer binder with surface tension of 40-50 dyne/cm and a water soluble polymer binder with glass transition temperature of 100-150 ℃, thereby improving safety performance and long-term cycling stability of the battery. However, the surface tension of the polyolefin base film in the invention is between 30 and 35 dyne/cm, and under the condition of not introducing a surfactant or a wetting agent, the ceramic slurry does not have the condition of spreading and wetting on the base film; the water-soluble polymer adhesive introduced in the invention is polyacrylic acid or polyacrylate, the structural unit is a single monomer, the polyacrylic acid or polyacrylate of the single monomer has too strong water absorption, the water content and the heat resistance of the ceramic coating are influenced, and the affinity with the base film is relatively poor.
Patent CN201810685986.9 can effectively reduce the thickness of the inorganic functional layer and ensure the uniformity of the thickness by introducing the plate-shaped boehmite particles, and simultaneously reduces the abrasion of the coating material to the machine due to the characteristic of low hardness of the plate-shaped boehmite particles, but boehmite easily loses physical adsorption water at high temperature, which is fatal to the lithium ion battery, and the invention does not improve the low-temperature performance of the ceramic-coated separator.
Thus, the existing ceramic separator is yet to be improved.
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 ceramic separator, a preparation method thereof, and a lithium battery, wherein the ceramic separator has good high temperature resistance and low temperature performance, and can meet the high safety requirement of the existing lithium battery when applied to the lithium battery.
In one aspect of the invention, a ceramic diaphragm is provided. According to an embodiment of the present invention, the ceramic diaphragm includes:
a base film;
the ceramic coating is formed by coating ceramic slurry on at least one side surface of the base film and curing, and comprises ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion copolymer binder and a surfactant.
The ceramic diaphragm comprises a base film and a ceramic coating, wherein the ceramic coating is formed by coating ceramic slurry on at least one side surface of the base film and curing, and the ceramic coating comprises ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion type copolymer binder and a surfactant. Wherein, the ceramic particles can greatly improve the oxidation resistance, high temperature resistance and safety of the ceramic coating; the water-soluble lithium polyacrylate copolymer adhesive can improve the high-temperature resistance of the ceramic coating and can also improve the film forming property of the ceramic coating; the emulsion copolymer binder can prevent ceramic particles from falling off from the base film in the use of the power battery in winter, and improves the safety of the power battery in the use in winter; meanwhile, the surfactant is beneficial to spreading and wetting the ceramic slurry on the base film. The invention adopts two adhesives, namely water-soluble lithium acrylate copolymer adhesive and emulsion copolymer adhesive, and the first function is to adhere ceramic particles and a base film as well as ceramic particles and ceramic particles together; secondly, the difference between the glass transition temperatures of the two adhesives is large, and the two adhesives complement each other, so that the application temperature range of the ceramic diaphragm is expanded; furthermore, the emulsion copolymer adhesive has high affinity with the base film, and the problem of low peeling strength of the water-soluble lithium acrylate copolymer adhesive and the base film which are singly used can be obviously improved. The surfactant can significantly reduce the surface tension of the entire ceramic slurry system and also facilitate a more intimate adhesion of the two binders and ceramic particles to the surface of the base film. Therefore, the ceramic diaphragm has good high-temperature resistance and low-temperature performance, and can meet the high safety requirement of the existing lithium battery when being applied to the lithium battery.
In addition, the ceramic diaphragm 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 ceramic slurry includes 40 to 50 parts by weight of the ceramic particles, 0.5 to 3 parts by weight of the water-soluble lithium acrylate copolymer binder, 0.4 to 2 parts by weight of the emulsion type copolymer binder, 0.01 to 0.1 part by weight of the surfactant, and 50 to 80 parts by weight of the water. Therefore, the optimal air permeability and peel strength of the ceramic coating can be ensured, and the coating is facilitated, so that the high-temperature resistance and low-temperature resistance of the ceramic diaphragm are improved, and the energy density and safety performance of the lithium battery are improved.
In some embodiments of the invention, the ceramic particles have an average particle size of 200 to 1500nm, preferably 300 to 800nm. Thus, the consistency, appearance of the ceramic coating and energy density of the lithium battery can be improved.
In some embodiments of the present invention, the ceramic particles comprise at least one of aluminum oxide, barium sulfate, magnesium oxide, and magnesium hydroxide. Thus, the consistency, appearance of the ceramic coating and energy density of the lithium battery can be improved.
In some embodiments of the invention, the water-soluble lithium acrylate copolymer binder has a glass transition temperature of not less than 80 ℃. Thereby, the high temperature structural stability of the ceramic coating is facilitated.
In some embodiments of the invention, the water-soluble lithium acrylate copolymer binder comprises at least two water-soluble monomers and at least one water-insoluble monomer. Therefore, the thermal stability, water solubility and flexibility of the polymer are improved, and the safety of the lithium battery is improved.
In some embodiments of the invention, the water-soluble monomer comprises lithium acrylate and at least one selected from acrylamide, methacrylic acid and an unsaturated fatty acid salt, and the water-insoluble monomer comprises at least one of a fluorine-containing acrylate, methyl methacrylate, styrene, epoxy acrylate and a phenol aldehyde. Therefore, the problem of low peeling strength of the water-soluble lithium acrylate copolymer adhesive and the base film when the water-soluble lithium acrylate copolymer adhesive is used alone can be remarkably improved.
In some embodiments of the invention, the glass transition temperature of the emulsion copolymer binder is not greater than-10 deg.C, preferably not greater than-30 deg.C. Therefore, the adhesive effect of the ceramic coating and the base film at low temperature is facilitated.
In some embodiments of the present invention, the emulsion copolymer binder comprises at least one of a polyacrylate copolymer emulsion, a polyvinylidene fluoride-hexafluoropropylene copolymer emulsion, and a fluorine-containing polyacrylate emulsion. Thus, the low temperature performance of the ceramic diaphragm is improved.
In some embodiments of the invention, the surfactant comprises at least one of polyethylene glycol, docusate sodium, polyether modified organosiloxane, and fluorocarbon type surfactant. Thereby, the surface tension of the whole ceramic slurry system is significantly reduced, and it is also advantageous to adhere the two binders and the ceramic particles more closely to the surface of the base film.
In some embodiments of the invention, the ceramic coating further comprises at least one of a thickener and a dispersant. Thus, the viscosity and uniformity of the ceramic slurry can be improved by adding the thickener to the ceramic coating, and the uniformity of the ceramic slurry can be improved by adding the dispersant to the ceramic coating, thereby preventing the sedimentation and aggregation of particles.
In some embodiments of the present invention, the thickener is added in an amount of 0.05 to 1 part by weight. This can further improve the viscosity and uniformity of the ceramic slurry.
In some embodiments of the present invention, the dispersant is added in an amount of 0.05 to 0.5 parts by weight. This can further improve the uniformity of the ceramic slurry and prevent the particles from settling and agglomerating.
In some embodiments of the invention, the thickener comprises at least one of lithium carboxymethyl cellulose, ammonium carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium polyacrylate. Thus, the viscosity and uniformity of the ceramic slurry can be further improved, and the agglomeration of ceramic particles can be prevented.
In some embodiments of the invention, the dispersant comprises at least one of ammonium polyacrylate, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, and polyvinyl pyrrolidone. Thus, the uniformity of the ceramic slurry can be further improved, and the agglomeration of particles can be prevented.
In a second aspect of the invention, a method of making a ceramic diaphragm is provided. According to an embodiment of the invention, the method comprises:
(1) Mixing the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion-type copolymer binder, the surfactant, and water to obtain a ceramic slurry;
(2) The ceramic slurry is applied on at least one side surface of a base film and cured, so that a ceramic separator is obtained.
According to the method of manufacturing a separator of an embodiment of the present invention, a ceramic slurry may be obtained by mixing ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion type copolymer binder, a surfactant, and water, and then the obtained ceramic slurry may be applied on at least one side surface of a base film and cured, so that a ceramic separator may be obtained. Wherein, the oxidation resistance, high temperature resistance and safety of the ceramic diaphragm can be greatly improved by introducing ceramic particles into the ceramic coating; the high-temperature resistance of the ceramic coating can be improved and the film forming property of the ceramic coating can be improved by introducing the water-soluble lithium polyacrylate copolymer adhesive into the ceramic coating; secondly, by introducing the emulsion copolymer binder into the ceramic coating, ceramic particles are prevented from falling off from the base film in the use of the power battery in winter, and the safety of the power battery in the use in winter is improved; the invention adopts two adhesives, namely water-soluble lithium acrylate copolymer adhesive and emulsion copolymer adhesive, and the first function is to adhere ceramic particles and the base film together, and the ceramic particles together; secondly, the difference between the glass transition temperatures of the two adhesives is large, and the two adhesives complement each other, so that the application temperature range of the ceramic diaphragm is expanded; furthermore, the emulsion copolymer adhesive has high affinity with the base film, and the problem of low peeling strength of the water-soluble lithium acrylate copolymer adhesive and the base film which are singly used can be obviously improved. The surfactant can significantly reduce the surface tension of the entire ceramic slurry system and also facilitate a more intimate adhesion of the two binders and ceramic particles to the surface of the base film. Therefore, the ceramic diaphragm obtained by the method has good high-temperature resistance and low-temperature performance, and can meet the high safety requirement of the existing lithium battery when being applied to the lithium battery.
In addition, the method of manufacturing the ceramic separator according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the present invention, in step (1), at least one of a thickener and a dispersant is mixed with the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion-type copolymer binder, the surfactant, and the water.
In a third aspect of the present invention, the present invention provides a lithium battery, and according to an embodiment of the present invention, the electrochemical device has the ceramic separator or the ceramic separator obtained by the method. Therefore, the ceramic diaphragm which has both low-temperature performance and high-temperature resistance is loaded, the risk of thermal runaway of the lithium ion battery and the risk of shedding of the ceramic coating from the base film in winter application are reduced, and the cycle performance and the safety performance of the lithium ion battery 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 ceramic diaphragm according to one embodiment of the present invention;
FIG. 2 is a schematic structural view of a ceramic diaphragm according to yet another embodiment of the present invention;
fig. 3 is a schematic flow diagram of a method of manufacturing a ceramic diaphragm according to one embodiment of the present 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 elements or elements having the same or similar function 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 ceramic diaphragm is provided. Referring to fig. 1-2, the ceramic separator includes a base film 100 and a ceramic coating layer 200 according to an embodiment of the present invention.
According to the embodiment of the present invention, a person skilled in the art may select a specific type of the base film 100 according to actual needs, for example, the base film 100 may be a polyethylene separator (PE), a polypropylene separator (PP), or a polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer co-extruded separator.
According to an embodiment of the present invention, the ceramic coating 200 is formed by coating a ceramic slurry on at least one side surface of the base film 100 and curing, for example, the ceramic coating 200 is formed on a single side surface of the base film 100 or the ceramic coating 200 is formed on both side surfaces of the base film 100 (refer to fig. 2), and the ceramic coating 200 includes ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion-type copolymer binder, and a surfactant. The inventor finds that the ceramic particles can greatly improve the oxidation resistance, high temperature resistance and safety of the ceramic coating; the water-soluble lithium polyacrylate copolymer adhesive can improve the high-temperature resistance of the ceramic coating and can also improve the film forming property of the ceramic coating; the emulsion copolymer binder can prevent ceramic particles from falling off from the base film in the use of the power battery in winter, and improves the safety of the power battery in the use in winter; meanwhile, the surfactant is beneficial to spreading and wetting the ceramic slurry on the base film. The invention adopts two adhesives, namely a water-soluble lithium acrylate copolymer adhesive and an emulsion type copolymer adhesive, and the first function is to adhere ceramic particles and a base film as well as the ceramic particles and the ceramic particles together; secondly, the difference between the glass transition temperatures of the two adhesives is large, and the two adhesives complement each other, so that the application temperature range of the ceramic diaphragm is expanded; furthermore, the emulsion copolymer adhesive has high affinity with the base film, and the problem of low peeling strength of the water-soluble lithium acrylate copolymer adhesive and the base film which are singly used can be obviously improved. The surfactant can significantly reduce the surface tension of the entire ceramic slurry system and also facilitate a more intimate adhesion of the two binders and ceramic particles to the surface of the base film. Therefore, the ceramic diaphragm has good high-temperature resistance and low-temperature performance, and can meet the high safety requirement of the existing lithium battery when being applied to the lithium battery.
Further, the ceramic slurry includes 40 to 50 parts by weight of ceramic particles, 0.5 to 3 parts by weight of a water-soluble lithium acrylate copolymer binder, 0.4 to 2 parts by weight of an emulsion type copolymer binder, 0.01 to 0.1 part by weight of a surfactant, and 50 to 80 parts by weight of water. The inventors have found that when the proportion of the ceramic particles is too high, the ceramic particles are not firmly adhered to the base film because the amount of the binder and other materials is reduced, the peel strength of the ceramic coating is reduced, and the ceramic particles are reduced; on the other hand, if the proportion of the ceramic particles is too low, it means that the proportion of the material such as the binder is too high, and the air permeability of the ceramic coating layer increases, resulting in deterioration of the air permeability and increase in the lithium ion transport resistance. If the proportion of the water-soluble lithium acrylate copolymer binder is too high, the water content of the ceramic separator may be increased in addition to the above negative effects; if the proportion of the water-soluble lithium acrylate copolymer binder is too low, the film forming property of the ceramic coating is poor, and the high temperature resistance of the ceramic diaphragm cannot be effectively improved. If the proportion of the emulsion copolymer adhesive is too high, the air permeability value of the ceramic coating is increased, and the air permeability is deteriorated; if the proportion of the emulsion copolymer binder is too low, the peel strength of the ceramic coating is reduced. If the proportion of the surfactant is too high, the air permeability value of the ceramic coating is increased, and the air permeability is poor; if the proportion of the surfactant is too low, the ceramic slurry cannot be spread rapidly on the base film during coating, thereby reducing the production efficiency. If the proportion of the water is too high, the cost of coating and drying the ceramic slurry is increased, and the time is prolonged; on the other hand, if the water content is too low, the viscosity of the ceramic slurry increases, which is not favorable for coating. Therefore, the ceramic slurry adopts the mixing proportion, can ensure the optimal air permeability and peel strength of the ceramic coating, and is beneficial to coating, thereby improving the high-temperature resistance and low-temperature resistance of the ceramic diaphragm and improving the energy density and safety performance of the lithium battery.
Further, the average particle diameter of the ceramic particles is 200 to 1500nm, preferably 300 to 800nm. The inventors found that if the particle size of the ceramic particles is too large, the uniformity and appearance of the ceramic coating are deteriorated; on the other hand, if the particle size of the ceramic particles is too small, the bulk density of the ceramic coating layer becomes large, which is not advantageous for increasing the energy density of the lithium battery. It should be noted that the specific type of the ceramic particles can be selected by those skilled in the art according to actual needs, and for example, the ceramic particles include at least one of aluminum oxide, barium sulfate, magnesium oxide and magnesium hydroxide.
Further, the glass transition temperature of the above water-soluble lithium acrylate copolymer binder is not lower than 80 ℃. The inventors have found that if the glass transition temperature of the water-soluble lithium acrylate copolymer binder is too low, the high temperature structural stability of the ceramic coating is reduced. In addition, the water-soluble lithium acrylate copolymer binder comprises at least two water-soluble monomers and at least one water-insoluble monomer, the water-insoluble monomer is added to improve the affinity and the thermal stability of the water-soluble adhesive and a substrate, the heat stability and the water solubility of the polymer can be improved by introducing the water-soluble monomer, such as acrylamide, the flexibility of the polymer can be improved, and the separation of a membrane bending coating caused by a ceramic membrane in a battery lamination process can be avoided. Preferably, the molar ratio of the water-soluble monomer to the water-insoluble monomer is (3 to 6): 1. the inventors have found that if the proportion of the water-soluble monomer is too high, the water content of the ceramic coating increases, whereas if the proportion of the water-soluble monomer is too low, the water solubility of the polymer decreases, and the copolymer binder polymer segment is insoluble in water, thereby being disadvantageous in the film-forming property of the ceramic coating. It should be noted that the specific types of the water-soluble monomer and the water-insoluble monomer can be selected by those skilled in the art according to actual needs, for example, the water-soluble monomer includes lithium acrylate and at least one selected from acrylamide, methacrylic acid and unsaturated fatty acid salt; the water-insoluble monomer includes at least one of fluorine-containing acrylate, methyl methacrylate, styrene, epoxy acrylate, and phenol aldehyde.
Further, the glass transition temperature of the above emulsion type copolymer binder is not higher than-10 ℃ and preferably not higher than-30 ℃. The inventors have found that if the glass transition temperature of the emulsion copolymer binder is too high, the adhesion of the ceramic coating to the base film at low temperatures is affected. It should be noted that the specific type of the emulsion copolymer binder can be selected by those skilled in the art according to actual needs, and for example, the emulsion copolymer binder includes at least one of polyacrylate copolymer emulsion, polyvinylidene fluoride-hexafluoropropylene copolymer emulsion, and fluorine-containing polyacrylate emulsion.
Further, the specific type of surfactant can be selected by those skilled in the art according to actual needs, for example, the surfactant includes at least one of polyethylene glycol, docusate sodium, polyether modified organosiloxane, and fluorocarbon type surfactant.
Further, the ceramic coating layer further includes at least one of a thickener and a dispersant. The inventors have found that by adding a thickener to the ceramic coating, the viscosity and uniformity of the ceramic slurry can be improved; by adding the dispersant to the ceramic coating, the uniformity of the ceramic slurry can be improved, and the particles are prevented from settling and agglomerating.
Further, the thickener is added in an amount of 0.05 to 1 part by weight. The inventor finds that if the addition amount of the thickening agent is too high, the viscosity of the ceramic slurry is too high, the ceramic slurry is not beneficial to coating, and the water content of the ceramic coating is increased; on the other hand, if the amount of the thickener added is too low, the storage stability of the ceramic slurry is deteriorated. It should be noted that the specific type of the thickener can be selected by those skilled in the art according to actual needs, and for example, the thickener includes at least one of lithium carboxymethyl cellulose, ammonium carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium polyacrylate.
Further, the amount of the dispersant is 0.05 to 0.5 part by weight. The inventors found that if the amount of the dispersant added is too high, the cost rises; on the other hand, if the amount of the dispersant is too small, the dispersion of the ceramic particles in water is not favorable. It should be noted that the specific type of the dispersing agent can be selected by those skilled in the art according to actual needs, and for example, the dispersing agent includes at least one of ammonium polyacrylate, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, and polyvinyl pyrrolidone.
In a second aspect of the present invention, the present invention provides a method for preparing the above ceramic separator. According to an embodiment of the invention, referring to fig. 3, the method comprises:
s100: mixing ceramic particles, water-soluble lithium acrylate copolymer binder, emulsion type copolymer binder, surfactant and water
In the step, ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion type copolymer binder, a surfactant and water are mixed and uniformly mixed to obtain ceramic slurry. Wherein the glass transition temperature of the water-soluble lithium acrylate copolymer binder is not lower than 80 ℃; the glass transition temperature of the emulsion copolymer binder is not higher than-10 deg.C, preferably not higher than-30 deg.C. The inventor finds that the oxidation resistance, high temperature resistance and safety of the ceramic diaphragm can be greatly improved by introducing ceramic particles into the ceramic coating; the water-soluble lithium polyacrylate copolymer adhesive with higher glass transition temperature is introduced into the ceramic coating, so that the high-temperature resistance of the ceramic coating can be improved, and the film forming property of the ceramic coating can be improved; secondly, by introducing the emulsion type copolymer adhesive with the glass transition temperature lower than minus 10 ℃ into the ceramic coating, ceramic particles are prevented from falling off from the base film in the use of the power battery in winter, and the safety of the power battery in the use in winter is improved; meanwhile, the surface active agent is introduced into the ceramic coating, so that the ceramic slurry is favorably spread and wetted on the base film. Therefore, the ceramic diaphragm has good high-temperature resistance and low-temperature performance. The invention adopts two adhesives, namely a water-soluble lithium acrylate copolymer adhesive and an emulsion type copolymer adhesive, and the first function is to adhere ceramic particles and a base film as well as the ceramic particles and the ceramic particles together; secondly, the difference between the glass transition temperatures of the two adhesives is large, and the two adhesives complement each other, so that the application temperature range of the ceramic diaphragm is expanded; furthermore, the emulsion copolymer adhesive has high affinity with the base film, and the problem of low peeling strength of the water-soluble lithium acrylate copolymer adhesive and the base film which are singly used can be obviously improved. The surfactant can significantly reduce the surface tension of the entire ceramic slurry system and also facilitate a more intimate adhesion of the two binders and ceramic particles to the surface of the base film. It should be noted that the specific types and mixing ratios of the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion type copolymer binder and the surfactant are the same as those described above, and are not described herein again.
Further, the above step further comprises mixing at least one of a thickener and a dispersant with the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion-type copolymer binder, the surfactant, and water. The inventors have found that by adding a thickener to the ceramic coating, the viscosity and uniformity of the ceramic slurry can be improved; by adding the dispersant to the ceramic coating, the uniformity of the ceramic slurry can be improved, and the particles are prevented from settling and agglomerating. It should be noted that the addition amounts and specific types of the above thickeners and dispersants are the same as those described above, and are not described herein again.
S200: applying a ceramic slurry on at least one side surface of a base film and curing
In this step, a ceramic separator may be obtained by applying and curing a ceramic slurry on at least one side surface of a base film. Specifically, the ceramic 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 is performed on the base film. It should be noted that, a person skilled in the art may select the type of the base film, the application manner and the curing manner of the ceramic slurry according to actual needs, for example, the base film may be a polyethylene separator (PE), a polypropylene separator (PP), or a polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer co-extrusion separator; the application mode of the coating slurry can be at least one of gravure roll coating, anilox roll coating, sleeve coating and screen printing; the curing means may be drying or the like.
Therefore, the ceramic diaphragm obtained by the method has good high-temperature resistance and low-temperature performance, and can meet the high safety requirement of the existing lithium battery when being applied to the lithium battery. It should be noted that the features and advantages described above for the ceramic membrane are also applicable to the method for preparing the ceramic membrane, and are not described herein again.
In a third aspect of the present invention, the present invention provides a lithium battery, and according to an embodiment of the present invention, the electrochemical device has the ceramic separator or the ceramic separator obtained by the method. Therefore, the high-temperature-resistant ceramic diaphragm with low temperature performance is loaded, the risk of thermal runaway of the lithium ion battery and the risk of shedding of the ceramic coating from the base film in winter application are reduced, and the cycle performance and the safety performance of the lithium ion battery can be improved. It should be noted that the features and advantages described above for the ceramic separator and the preparation method thereof are also applicable to the lithium battery, and are not described herein again.
The following embodiments of the present invention are described in detail, and it should be noted that the following embodiments are exemplary only, and are not to be construed as limiting the present invention. In addition, all reagents used in the following examples are commercially available or can be synthesized according to methods herein or known, and are readily available to one skilled in the art for reaction conditions not listed, if not explicitly stated.
Example 1
Weighing 55 parts by weight of deionized water, adding 0.08 part by weight of ammonium polyacrylate dispersant while stirring, adding 0.4 part by weight of thickening agent CMC1140, and then adding D 50 40 parts by weight of 400nm aluminum oxide; after high-speed stirring for a period of time, sanding once, and adding 1.2 parts by weight of water-soluble lithium acrylate copolymer binder, 0.8 part by weight of polyacrylate copolymer emulsion and 0.08 part by weight of docusate sodium, wherein the water-soluble lithium acrylate copolymer binder is prepared by copolymerizing four monomers, namely lithium acrylate, acrylamide, unsaturated fatty acid lithium and styrene, the molar ratio of water-soluble monomers to water-insoluble monomers is 4; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 12 mu m, and drying to form a ceramic coating with the thickness of 2 mu m to obtain the ceramic coating diaphragm.
Example 2
The ceramic slurry prepared in example 1 was coated on a polyethylene microporous membrane having a thickness of 9 μm, and the thickness of the ceramic coating was 3 μm.
Example 3
Weighing 60 parts by weight of deionized water, adding 0.15 part by weight of sodium polyacrylate dispersant while stirring, adding 0.4 part by weight of thickening agent CMC1220, and then adding D 50 50 parts by weight of 500nm alumina; after stirring for a period of time at a high speed, sanding once, and adding 1.75 parts by weight of water-soluble lithium acrylate copolymer adhesive, 0.75 part by weight of polyacrylate copolymer emulsion and 0.05 part by weight of surfactant polyether modified organosiloxane, wherein the water-soluble lithium acrylate copolymer adhesive is prepared by copolymerizing four monomers, namely lithium acrylate, acrylamide, unsaturated fatty acid lithium and methyl methacrylate, the molar ratio of the water-soluble monomer to the water-insoluble monomer is 4; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 12 mu m, and drying to form a ceramic coating with the thickness of 2 mu m to obtain the ceramic coating diaphragm.
Example 4
Weighing 120 parts by weight of deionized water, adding 0.3 part by weight of ammonium polyacrylate dispersant while stirring, adding 1.0 part by weight of thickening agent CMC1140, and then adding D 50 100 parts by weight of 350nm aluminum oxide; after stirring for a period of time at a high speed, sanding once, and adding 2.5 parts by weight of water-soluble lithium acrylate copolymer binder, 2.5 parts by weight of fluorine-containing polyacrylate emulsion and 0.15 part by weight of surfactant polyethylene glycol, wherein the water-soluble lithium acrylate copolymer binder is prepared by copolymerizing three monomers, namely lithium acrylate, unsaturated fatty acid sodium and methyl methacrylate, the molar ratio of water-soluble monomer to non-water-soluble monomer is 4; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 9 mu m, and drying to form a ceramic coating with the thickness of 3 mu m to obtain the ceramic coating diaphragm.
Example 5
Weighing 115 parts by weight of deionized water, adding 0.2 part by weight of ammonium polyacrylate dispersant, adding 0.6 part by weight of thickening agent CMC1220 while stirring, and then adding D 50 100 parts by weight of 800nm aluminum oxide; after high-speed stirring for a period of time, sanding once, and adding 4.0 parts by weight of water-soluble lithium acrylate copolymer binder, 2.0 parts by weight of fluorine-containing polyacrylate emulsion and 0.05 parts by weight of fluorocarbon surfactant, wherein the water-soluble lithium acrylate copolymer binder is prepared by copolymerizing three monomers, namely lithium acrylate, acrylamide and styrene, the molar ratio of water-soluble monomer to non-water-soluble monomer is 7; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 9 mu m, and drying to form a ceramic coating with the thickness of 3 mu m to obtain the ceramic coating diaphragm.
Example 6
Weighing 240 parts by weight of deionized water, adding 0.2 part by weight of ammonium polyacrylate dispersant while stirring, adding 1.6 parts by weight of thickening agent CMC1220, and then adding D 50 200 parts by weight of 600nm aluminum oxide; after stirring for a period of time at a high speed, sanding once, and adding 7 parts by weight of water-soluble lithium acrylate copolymer binder, 4 parts by weight of fluorine-containing polyacrylate emulsion and 0.2 part by weight of surfactant polyethylene glycol, wherein the water-soluble lithium acrylate copolymer binder is prepared by copolymerizing three monomers, namely lithium acrylate, unsaturated fatty acid sodium and methyl methacrylate, the molar ratio of water-soluble monomers to water-insoluble monomers is 4; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 9 mu m, and drying to form a ceramic coating with the thickness of 3 mu m to obtain the ceramic coating diaphragm.
Example 7
Weighing 130 parts by weight of deionized water, adding 0.3 part by weight of ammonium polyacrylate dispersant and 0.2 part by weight of thickening agent polyvinyl alcohol while stirring, and then adding D 50 100 parts by weight of 500nm alumina; after stirring for a period of time at a high speed, sanding once, and adding 5 parts by weight of water-soluble lithium acrylate copolymer binder, 2 parts by weight of fluorine-containing polyacrylate copolymer emulsion and 0.15 part by weight of surfactant polyether modified organosiloxane, wherein the water-soluble lithium acrylate copolymer binder is prepared by copolymerizing four monomers, namely lithium acrylate, acrylamide, unsaturated fatty acid lithium and methyl methacrylate, the molar ratio of water-soluble monomers to water-insoluble monomers is 4; fully stirring and filtering to obtain the water-based ceramic slurry.
And coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 9 mu m, and drying to form a ceramic coating with the thickness of 3 mu m to obtain the ceramic coating diaphragm.
Comparative example 1
Weighing130 parts by weight of deionized water, 0.35 part by weight of dispersant sodium polyacrylate while stirring, 1220 2 parts by weight of thickener CMC, and D 50 100 parts by weight of 700nm aluminum oxide; after stirring at a high speed for a period of time, sanding once, and adding 6 parts by weight of adhesive and 0.2 part by weight of surfactant, wherein the adhesive is polyacrylate copolymer emulsion and the surfactant is polyethylene glycol; fully stirring and filtering to obtain the water-based ceramic slurry.
And respectively coating the ceramic slurry on a polyethylene microporous membrane with the thickness of 12 mu m through a wire rod, and drying to form a ceramic coating with the thickness of 2 mu m to obtain the ceramic coating diaphragm.
Comparative example 2
The ceramic slurry prepared in comparative example 1 was coated on a polyethylene microporous membrane having a thickness of 9 μm, and dried to form a ceramic coating layer having a thickness of 3 μm, to obtain a ceramic-coated separator.
The results of measuring the thickness, peel strength, heat shrinkage, air permeability and water content of the ceramic separators of examples 1 to 7 and comparative examples 1 to 2 are shown in table 1.
TABLE 1 ceramic separator Properties of examples 1-7 and comparative examples 1-2
The above test of the ceramic separator in table 1 uses the following method:
1. and (3) thickness testing: and directly carrying out thickness test on multiple points of the ceramic diaphragm product by adopting a Mark thickness gauge, and taking an average value.
2. And (3) testing the peel strength: the test was carried out according to method 3 of GB/T2792-2014 test methods for peel Strength of adhesive tapes.
3. Testing the thermal shrinkage rate: the ceramic diaphragm was cut into 12cm × 12cm pieces.
Drawing two lines perpendicular to each other and having a length of about 10cm in the middle of the sample, marking the longitudinal direction and the transverse direction, and measuring the length L of the two lines by using an Abbe's comparator 0 And recorded, the swatches were placed on the weighing paper. Placed in (150 ℃. + -. 1 ℃)Oven drying for 1h, taking out the sample wafer, standing for 30min to cool the sample wafer to room temperature, and measuring the length L of two lines 1 And recorded, and the heat shrinkage ratio (% = (L) was calculated from the change in length of the two lines before and after baking 0 -L 1 )/L 0 ) And taking an average value in three parallel determinations as an experimental result of the direction, wherein two decimal places are reserved in the experimental result.
4. And (3) testing air permeability: the test was carried out according to the Gerlay method of GB/T458-2008 "determination of air Permeability of paper and cardboard", and the time required for 100mL of air to pass was recorded.
5. Testing the water content: taking a sample with a diaphragm of about 0.1g, and accurately weighing the sample by mass m 0 (g) The sample was placed in a dry and clean jar, and sealed with a sealer.
The Karl Fei autumn moisture meter is set at 150 ℃ and 4 r/s in rotation speed, and the absolute water content mu of the empty bottle is respectively tested Air conditioner And absolute water content mu of sample bottle Absolute The formula for calculating the water content X of the sample is shown in formula (1).
X＝(μ Absolute -μ Air conditioner )/m 0 …………………………(1)
In the formula:
x represents the water content of the sample in ppm;
m 0 -mass of the membrane sample in grams (g);
μ air conditioner Absolute water content of the empty bottle in milligrams (. Mu.g);
μ absolute Absolute water content of the sample vial in milligrams (. Mu.g).
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 will be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, 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.
Claims (15)
1. A ceramic diaphragm, comprising:
a base film;
the ceramic coating is formed by coating ceramic slurry on at least one side surface of the base film and curing, and comprises ceramic particles, a water-soluble lithium acrylate copolymer binder, an emulsion type copolymer binder and a surfactant, wherein the water-soluble lithium acrylate copolymer binder is formed by copolymerizing four monomers including lithium acrylate, acrylamide, unsaturated fatty acid lithium and methyl methacrylate, and the ratio of the total molar amount of the lithium acrylate, the acrylamide and the unsaturated fatty acid lithium to the molar amount of the methyl methacrylate is (3-6): 1,
the ceramic slurry includes 40 to 50 parts by weight of the ceramic particles, 0.5 to 3 parts by weight of the water-soluble lithium acrylate copolymer binder, 0.4 to 2 parts by weight of the emulsion type copolymer binder, 0.01 to 0.1 part by weight of the surfactant, and 50 to 80 parts by weight of the water,
the glass transition temperature of the emulsion copolymer binder is-45 ℃ to-38 ℃.
2. The ceramic separator according to claim 1, wherein the water-soluble lithium acrylate copolymer binder has a glass transition temperature of not less than 80 ℃.
3. The ceramic separator of claim 1, wherein the emulsion-type copolymer binder comprises at least one of a polyacrylate copolymer emulsion, a polyvinylidene fluoride-hexafluoropropylene copolymer emulsion, and a fluorine-containing polyacrylate emulsion.
4. The ceramic separator according to claim 1, wherein the ceramic particles have an average particle diameter of 200 to 1500nm.
5. The ceramic separator according to claim 4, wherein the ceramic particles have an average particle diameter of 300 to 800nm.
6. The ceramic separator according to claim 1, wherein the ceramic particles comprise at least one of aluminum oxide, barium sulfate, magnesium oxide, and magnesium hydroxide.
7. The ceramic membrane of claim 1, wherein the surfactant comprises at least one of polyethylene glycol, docusate sodium, polyether modified organosiloxane, and fluorocarbon-based surfactant.
8. The ceramic separator of claim 1, wherein the ceramic coating further comprises at least one of a thickener and a dispersant.
9. The ceramic separator according to claim 8, wherein the thickener is added in an amount of 0.05 to 1 part by weight.
10. The ceramic separator according to claim 8, wherein the dispersant is added in an amount of 0.05 to 0.5 parts by weight.
11. The ceramic separator of claim 8, wherein the thickener comprises at least one of lithium carboxymethyl cellulose, ammonium carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium polyacrylate.
12. The ceramic separator of claim 8, wherein the dispersant comprises at least one of ammonium polyacrylate, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, and polyvinyl pyrrolidone.
13. A method of making the ceramic membrane of any one of claims 1-12, comprising:
(1) Mixing the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion-type copolymer binder, the surfactant, and water to obtain a ceramic slurry;
(2) The ceramic slurry is applied on at least one side surface of a base film and cured, so as to obtain a ceramic separator.
14. The method according to claim 13, wherein in step (1), at least one of a thickener and a dispersant is mixed with the ceramic particles, the water-soluble lithium acrylate copolymer binder, the emulsion-type copolymer binder, the surfactant, and the water.
15. A lithium battery having a ceramic separator as claimed in any one of claims 1 to 12 or obtained by the method as claimed in claim 13 or 14.
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| CN113611984B (en) * | 2021-08-02 | 2022-11-18 | 江苏厚生新能源科技有限公司 | Coating slurry with low moisture, high temperature resistance and high peel strength and application thereof |
| CN114361718A (en) * | 2021-12-14 | 2022-04-15 | 乐凯胶片股份有限公司 | Diaphragm for lithium ion battery and lithium ion battery |
| CN114447523B (en) * | 2021-12-23 | 2024-03-22 | 山东华夏神舟新材料有限公司 | Polyvinylidene fluoride emulsion for lithium ion secondary battery diaphragm and preparation method thereof |
| CN114709563B (en) * | 2022-06-07 | 2022-08-05 | 中材锂膜(宁乡)有限公司 | Battery isolation membrane, preparation method thereof and secondary battery |
| CN116285434A (en) * | 2022-12-22 | 2023-06-23 | 乐凯胶片股份有限公司 | Ceramic slurry, ceramic coating diaphragm and lithium ion battery |
| CN116247374A (en) * | 2023-03-17 | 2023-06-09 | 江苏北星新材料科技有限公司 | High-temperature-resistant ceramic composite lithium battery diaphragm and preparation method thereof |
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