CN112436234A

CN112436234A - Ceramic micro-composite diaphragm and preparation method thereof

Info

Publication number: CN112436234A
Application number: CN201910735430.0A
Authority: CN
Inventors: 周素霞; 王晓明; 杨浩田; 黄云; 王婷
Original assignee: Ningde Zhuogao New Material Technology Co Ltd
Current assignee: Ningde Zhuogao New Material Technology Co Ltd
Priority date: 2019-08-09
Filing date: 2019-08-09
Publication date: 2021-03-02

Abstract

The invention relates to a ceramic micro-composite diaphragm and a preparation method thereof, wherein the ceramic micro-composite diaphragm comprises: a base film; a ceramic layer disposed on at least one surface of the base film; and a modified barium sulfate micro-layer arranged on the outer surface of the ceramic layer, wherein the modified barium sulfate is barium sulfate modified by a coupling agent. The ceramic micro-composite diaphragm provided by the invention has improved diaphragm heat shrinkage performance and electrolyte retention performance.

Description

Ceramic micro-composite diaphragm and preparation method thereof

Technical Field

The invention belongs to the technical field of diaphragms, and relates to a ceramic micro-composite diaphragm and a preparation method thereof.

Background

The lithium ion battery is used as a novel high-energy chemical power supply, and under the conditions of high temperature or high-efficiency charge and discharge and the like, the heat effect of a battery system can cause heat accumulation inside the battery, so that the lithium ion battery is extremely easy to combust and explode. Therefore, the safety of lithium batteries is a primary consideration. Meanwhile, in the field of new energy automobiles, the demand of lithium ion batteries is increasing year by year, the demand of high-capacity and high-power batteries is imminent, and the development of lithium ion batteries with high safety and good cycle performance/conductivity is very urgent.

CN201310518815.4 discloses a barium sulfate diaphragm for a lithium ion battery and a preparation method thereof, wherein nano-scale barium sulfate particles, a binder, a solvent and a dressing are mixed together and stirred, then slurry is coated on the front and back surfaces of the lithium ion battery diaphragm to form a coating, and the coating is dried to prepare the barium sulfate diaphragm, so that the puncture resistance and the heat shrinkage resistance of the film are improved, meanwhile, the wettability, the void ratio and the chemical stability are improved, and the energy density of the lithium ion battery is improved. However, the pore diameter of the polyolefin diaphragm of the conventional lithium battery is less than 1 μm, wherein the pore diameter of the polyolefin wet diaphragm is 0.01-0.1 μm, and the pore diameter of the dry diaphragm is 0.1-0.3 μm. The inventor finds that in CN201310518815.4, barium sulfate coats the diaphragm, the particle size of barium sulfate in the embodiment is 0.1-0.25 μm, and barium sulfate is mixed with glue solution or additives and coated on the surface of the diaphragm to form a compact coating, so that the air permeability of the diaphragm is rapidly reduced, and lithium precipitation or lithium dendrite formation is caused in the battery circulation process.

Therefore, there is a need to further develop a novel high temperature resistant high performance separator.

Disclosure of Invention

The present inventors have made various attempts to solve the above problems, and have unexpectedly found that when a ceramic layer is coated on the surface of a base film and then a nano barium sulfate layer modified with a coupling agent is coated, the resulting separator has improved heat shrinkage properties and electrolyte retention properties, thereby completing the present invention.

In one aspect, the present invention provides a ceramic micro-composite separator, including: a base film; a ceramic layer disposed on at least one surface of the base film; and a modified barium sulfate micro-layer arranged on the outer surface of the ceramic layer, wherein the modified barium sulfate is barium sulfate modified by a coupling agent.

Fig. 1 shows a ceramic micro-composite separator according to one embodiment of the present invention, including a base film, a ceramic layer disposed on one surface of the base film, and a modified barium sulfate micro-layer disposed on the ceramic layer. In addition, in an embodiment, the ceramic micro-composite separator according to the present invention may also include a base film, first and second ceramic layers disposed on both surfaces of the base film, respectively, and a modified barium sulfate micro-layer disposed on at least one of the first and second ceramic layers. In addition, the ceramic micro-composite diaphragm according to the invention can be provided with a graphite layer, an electrostatic spinning layer, a thermal closing layer, a nano flame-retardant layer and the like according to requirements.

The base film may be any base film known in the art to be suitable for a lithium battery, and for example, it may be a microporous film, a porous film, or a nonwoven fabric film. The microporous and porous films may be polyolefin films, for example, polyethylene or polypropylene films. In embodiments, the polyolefin-based film may be a single layer Polyethylene (PE) or polypropylene (PP) separator film, or a polyethylene and polypropylene multi-layer composite film (e.g., a polypropylene/polyethylene two-layer film, a polypropylene/polypropylene two-layer film, a polypropylene/polyethylene/polypropylene three-layer composite film, etc.). The polyolefin base film can be prepared by adopting a wet method or a dry method for unidirectional or bidirectional stretching, or adopting a thermally induced phase separation method. The material and the production method of the nonwoven fabric film are not particularly limited, and for example, one or more selected from polypropylene, polyethylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyether ether ketone, polyphenylene sulfide, polyacrylate, polyphenylene amide, polyarylethersulfone ketone, aramid, and polysulfonamide may be used as the material, and one or more selected from melt blowing, spun bonding, wet papermaking, spunlacing, needle punching, and hot rolling may be used for the production.

The pore size and porosity of the base film are not particularly limited as long as it is suitable for use as a separator for a lithium battery. Generally, the pore diameter is required to be in the range of 0.01 to 0.1. mu.m, for example, 0.02. mu.m, 0.03. mu.m, 0.04. mu.m, 0.05. mu.m, 0.06. mu.m, 0.07. mu.m, 0.08. mu.m, 0.09. mu.m. When the pore diameter is less than 0.01 μm, the lithium ion penetrating ability is too small; the aperture is larger than 0.1 μm, and the battery is easy to be short-circuited when dendrites are generated in the battery. The porosity is generally between 20% and 80%, in particular between 30% and 50%, for example 35%, 40%, 45%, 55%, 60%, 65%, 70%, etc.

The thickness of the base film is not particularly limited as long as it is suitable for use as a separator for a lithium battery. The thickness is generally 30 μm or less, and may be, for example, 3 to 20 μm, 5 to 20 μm or 3 to 16 μm, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

The ceramic layer may be formed using a method of forming a ceramic layer known in the art. Without being limited to any theory, the thermal stability and the mechanical property of the diaphragm can be improved by adding the ceramic layer on the base film, and the wettability of the diaphragm on an electrolyte is improved, so that the rate capability and the cycle performance are improved.

In one embodiment, the ceramic layer may include, preferably consists essentially of, ceramic particulates, a binder, a thickener, and a dispersant. Wherein, the ceramic layer comprises the following components in parts by weight: 70 to 95 parts, preferably 75 to 90 parts, of ceramic fine particles, for example 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 parts, etc.; 2-20 parts of binder, preferably 5-15 parts, such as 6, 7, 8, 9, 10, 11, 12, 13, 14 parts and the like; 1-15 parts of thickening agent, preferably 1-10 parts, such as 1.5, 2, 3, 4, 5, 6, 7, 8, 9 parts and the like; 0.1 to 3 parts of a dispersant, preferably 0.3 to 2 parts, for example, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, etc.

In one embodiment, the thickness of the ceramic layer may be 0.5 to 10 μm, preferably 1 to 5 μm, for example, the thickness of the ceramic layer may be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. In the case where the thickness is less than 0.5 μm, it may result in less change in shrinkage than the base film, and less remarkable improvement in shrinkage; and in the case that the thickness is more than 10 μm, the ceramic layer is likely to fall off and the gas permeation of the separator is greatly increased.

In the ceramic layer, the ceramic fine particles are those having a particle diameter of 0.1 to 5 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm.

The ceramic particles may be one or more selected from alumina, titania, magnesia, magnesium hydroxide, boehmite, etc.

In the ceramic layer, the dispersant is used to promote dispersion of the ceramic particles in the aqueous slurry, and may be, for example, one or more selected from polyacrylate, polyglycol ether, and phosphate compounds. The polyacrylate salt is, for example, sodium polyacrylate.

In addition to using modified barium sulfate, the modified barium sulfate micro-layer may be formed using a method of forming a barium sulfate layer known in the art. Without being limited to any theory, the thermal shrinkage performance of the diaphragm and the electrolyte retention performance can be further improved by adding the modified barium sulfate micro-layer on the ceramic layer. In addition, the barium sulfate is modified by the coupling agent, so that the surface of the barium sulfate can be coated with a multifunctional coupling agent which can be crosslinked with a binder, and discontinuous barium sulfate particles form a continuous network micro-layer, so that the coating thickness cannot be greatly increased, and the barium sulfate particles with small particle size can be randomly distributed in fluctuation gaps or on the surface of ceramic particles, and the ventilation loss cannot be caused. In addition, under the condition that the surface of the diaphragm is coated with the barium sulfate micro-layer, the barium sulfate is used as a developer, has a self-identification function during X-ray detection, can be used as a basis for judging that the battery diaphragm exceeds the negative pole piece, ensures the separation of the positive pole piece and the negative pole piece, and avoids potential safety hazards of the battery caused by the dislocation of the battery diaphragm.

In one embodiment, the modified barium sulfate microlayer may include, preferably consists essentially of, a coupling agent modified barium sulfate, a binder, a thickener, and a wetting agent. Wherein, the proportion of each component in the modified barium sulfate micro-layer in parts by weight of solid can be as follows: 75-95 parts, preferably 80-90 parts, of coupling agent modified barium sulfate, such as 81, 82, 83, 84, 85, 86, 87, 88, 89 parts and the like; 2-20 parts of binder, preferably 5-15 parts, such as 6, 7, 8, 9, 10, 11, 12, 13, 14 parts and the like; 1-15 parts of thickening agent, preferably 1-10 parts, such as 1.5, 2, 3, 4, 5, 6, 7, 8, 9 parts and the like; the wetting agent is 0.1 to 3 parts, preferably 0.2 to 2 parts, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, etc., but is not limited thereto.

In one embodiment, the modified barium sulfate micro-layer may have a thickness of 0.03 to 1 μm, preferably 0.05 to 0.5 μm, for example, the modified barium sulfate micro-layer may have a thickness of 0.06 μm, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 μm, 0.45 μm, or the like. Under the condition that the thickness is less than 0.03 mu m, incomplete coverage of the modified barium sulfate micro-layer can be caused, and the heat shrinkage performance of the diaphragm and the liquid retention performance of the electrolyte are not obviously improved; and in the case of a thickness greater than 1 μm, it may result in the formation of a dense coating by stacking, resulting in a sharp decrease in the gas permeability of the separator, thereby causing the formation of lithium precipitates or lithium dendrites during battery cycling.

In the ceramic layer and the modified barium sulfate micro-layer, the binder (also referred to as binder, adhesive) may be any aqueous binder known in the art for binding ceramic or barium sulfate, for binding ceramic or barium sulfate particles into an integral layer. For example, it may be one or more aqueous binders selected from poly (meth) acrylic acid, poly (meth) acrylates (e.g., acrylic emulsion, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, etc.), butadiene-styrene copolymers (e.g., styrene-butadiene emulsion, etc.), styrene-acrylate copolymers (e.g., styrene-acrylic emulsion, etc.), polyvinylidene fluoride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyacrylonitrile, polyurethane, (meth) acrylic acid- (meth) acrylate copolymers, etc., but is not limited thereto.

In the ceramic layer and the modified barium sulfate micro-layer, the thickener is used for adjusting the viscosity of the aqueous slurry and improving the coatability of the slurry, and may be, for example, one or more selected from carboxymethyl cellulose (CMC), carboxyethyl cellulose, polyvinyl alcohol, sodium alginate, polyethylene oxide, polyurethane, polyacrylamide, guar gum, and the like, but is not limited thereto. In preparing the ceramic layer, the thickener is generally prepared in the form of a premixed aqueous solution having a solid content of 0.1 to 5 wt% before use, but is not limited thereto.

In the modified barium sulfate micro-layer, the wetting agent is used to reduce the surface tension of the aqueous slurry and improve the wettability of the slurry on the surface of the base film, and for example, it may be one or more selected from polyoxyethylene alkylamine, fluoroalkyl methoxy alcohol ether, alkyl naphthalene sodium sulfonate (e.g., butyl naphthalene sodium sulfonate, isopropyl naphthalene sodium sulfonate), aryl naphthalene sodium sulfonate, alkyl benzene sodium sulfonate (e.g., dodecyl benzene sodium sulfonate) or alkyl sodium sulfate, fatty alcohol polyoxyethylene ether, and the like, but is not limited thereto.

The coupling agent modified barium sulfate refers to a product obtained by modifying the surface of nano barium sulfate particles by using a coupling agent. Through modification, the surface of the nano barium sulfate can be coated with a layer of multifunctional coupling agent which can be crosslinked with a binder, so that the discontinuous barium sulfate particles form a continuous micro-layer after coating. There is no particular requirement for the coupling agent, so long as it is a coupling agent that can be used in the art for surface modification of inorganic fillers and is capable of performing the above-described functions. In particular, titanate coupling agents (e.g., isopropoxytriisooctanoyltitanate, isopropoxytriisostearoyltitanate, dioleoyltitanate, isopropyl trioleate, tetrabutyltitanate, etc.), aluminate coupling agents (e.g., aluminate coupling agents F-1, F-2, F-3, F-4, Dl-471, DL-472, DL-492, HY-1108, HY-988, AL-822, L-1A, etc.), or combinations thereof may be used.

The particle size of the coupling agent-modified barium sulfate is not particularly limited as long as it is suitable for a lithium battery and can exert an improving effect, and may be, for example, 500nm or less, 400nm or less, 300nm or less, 200nm or less, or 100nm or less. The lower limit of the particle size of the barium sulfate fine particles is not particularly limited, but may be 2nm or more, for example, 5nm or more for the sake of convenience. In one example, the coupling agent modified barium sulfate has a particle size of 5 to 100nm, such as 10 to 80 nm.

The particle size of the barium sulfate fine particles used for preparing the coupling agent-modified barium sulfate is not particularly limited as long as it is suitable for a lithium battery and can exert an improving effect, and may be, for example, 500nm or less, 400nm or less, 300nm or less, 200nm or less, or 100nm or less. The lower limit of the particle size of the barium sulfate fine particles is not particularly limited, but may be 2nm or more, for example, 5nm or more for the sake of convenience. In one example, the barium sulfate may have a particle size of 5 to 100nm, for example, 10 to 50 nm.

In the coupling agent-modified barium sulfate of the present invention, the coupling agent may be 0.1% to 2.0%, preferably 0.2% to 1.5%, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, or 1.4% by mass of barium sulfate. In the case where the amount of the coupling agent is less than 0.1% by mass of the barium sulfate, the amount of the coupling agent coated on the surface of the nano barium sulfate may be insufficient, so that the crosslinking with the binder is limited, thereby failing to form a continuous microlayer of the discontinuous barium sulfate particles after coating. And under the condition that the using amount of the coupling agent is more than 2.0 percent of the mass of the barium sulfate, the coupling agent coated on the surface of the nano barium sulfate is excessive, so that excessive crosslinking is generated between the coupling agent and the binder, and the non-continuous barium sulfate particles form a compact coating after coating, so that the air permeability of the diaphragm is rapidly reduced, and lithium precipitation or lithium dendrite formation is caused in the battery circulation process.

The method for modifying barium sulfate by using the coupling agent in the present invention is not particularly limited as long as the coupling agent can react with barium sulfate to prepare coupling agent modified barium sulfate which can perform corresponding functions.

In one embodiment, the modified barium sulfate is prepared as follows:

(1) mixing 30-80 parts of barium sulfate, 4-8 parts of sodium chloride, 30-100 parts of DI water and 20-80 parts of ethanol to prepare barium sulfate suspension;

(2) and adding 0.2-4 parts of coupling agent into the barium sulfate suspension for reaction, and filtering, washing and drying to obtain the modified nano barium sulfate.

The step (1) can be carried out by mixing and stirring at 60-75 ℃ and 1000-1500 rpm for 0.5-2 h, and the final solid content can be 20-60 wt%.

The reaction of the step (2) can be carried out by using a high-speed shearing emulsifying machine. The rotating speed of the emulsifying machine can be 8000-15000 rpm/min, the temperature can be 60-80 ℃, and the shearing and emulsifying time can be 20-30 min. Under the condition, the full modification of the coupling agent to the barium sulfate is favorably realized.

Another aspect of the present invention relates to a method of preparing a separator according to the present invention, comprising the steps of:

1) ceramic particles, a binder, a thickening agent, a dispersing agent and deionized water (DI water) are uniformly mixed to obtain ceramic slurry,

2) uniformly mixing coupling agent modified barium sulfate, a binder, a thickening agent, a wetting agent and deionized water to obtain barium sulfate slurry,

3) coating the ceramic slurry on at least one surface of a base film to form a ceramic layer, and drying;

4) the barium sulfate slurry was coated on the outer surface of the ceramic layer and dried, thereby obtaining a separator.

The above steps (1) and (2) are only used for distinguishing the two operations, and do not represent the order of the operations. The two can be performed simultaneously or sequentially.

In the step 1), there is no particular limitation on the method of uniformly mixing the ceramic fine particles, the binder, the thickener, the dispersant, and the deionized water as long as they are uniformly mixed, and for example, a planetary mixer, a homogenizer, or the like may be used. In one embodiment, the binder and DI water may be mixed, and stirred at 20-40 ℃ and 300-500 rpm/min for 10-30 min; adding ceramic particles and a thickening agent, stirring at the temperature of 20-40 ℃ and the rpm of 1500-2500 for 1-2.5 h; and finally, adding a dispersing agent, and stirring at 20-40 ℃ and 100-500 rpm/min for 10-20 min to obtain the ceramic slurry. In this way, it is helpful to reduce particle agglomeration and promote uniform mixing. The solid content of the ceramic slurry is not particularly limited as long as it does not adversely affect the coating, and may be appropriately selected depending on the coating method employed. Generally, the solid content may be 20 to 50 wt%.

In the step 2), there is no particular limitation on the method for uniformly mixing the coupling agent modified barium sulfate, the binder, the thickener, the wetting agent, and the deionized water as long as they are uniformly mixed, and for example, a planetary mixer, a homogenizer, or the like may be used. In one embodiment, the binder, the thickener and the DI water may be mixed, and stirred at a temperature of 20 to 40 ℃ and a speed of 300 to 500rpm/min for 10 to 30 min; adding coupling agent modified barium sulfate, and stirring for 1-2 h at 800-1500 rpm/min; and finally, adding a wetting agent, and stirring at 100-300 rpm/min for 20-40 min to obtain the barium sulfate slurry. In this way, it is helpful to reduce particle agglomeration and promote uniform mixing. The solid content of the barium sulfate slurry is not particularly limited as long as it does not adversely affect the coating, and may be appropriately selected depending on the coating method employed. Generally, the solid content may be 10 to 20 wt%.

In the step 3), the ceramic slurry in the step 1) may be coated on both sides of the base film by a micro-gravure coating method, and dried to obtain the ceramic layer.

In the step 4), the barium sulfate slurry in the step 2) may be coated on the outer surface of the ceramic layer and dried to obtain a barium sulfate layer.

There is no limitation on the drying method of the ceramic layer and the barium sulfate layer as long as it is suitable for preparing the separator. For example, drying may be employed. For example, drying the mixture by using an oven at 30-65 ℃.

The method for preparing the separator according to the present invention may further include operations of preparing a graphite layer, an electrostatic spinning layer, a thermal closure layer, a nano flame retardant layer, etc., as necessary. The above-described operations for preparing the graphite layer, the electrospinning layer, the thermal sealing layer, the nano flame-retardant layer, etc. may be performed by using conventional operations in the art for preparing these layers.

In the method of manufacturing a separator of the present invention, descriptions about the thickness of the layer, the composition of the layer, material selection, and the like are the same as those described above and will not be repeated here.

Yet another aspect of the present invention relates to a lithium battery including the separator described above.

In addition to the above-described separator, the lithium battery may have a structure and components conventional in the art for lithium batteries, for example, a negative electrode, a positive electrode, an electrolyte, an aluminum plastic film, and the like. There is no particular limitation on the negative electrode, the positive electrode, the electrolyte, and the aluminum plastic film, and any negative electrode, positive electrode, electrolyte, and aluminum plastic film known in the art that can be used for a lithium battery can be used. For example, the negative electrode may include a negative electrode sheet and a negative electrode active material layer coated on the negative electrode sheet; the positive electrode may include a positive electrode sheet and a positive electrode active material layer coated on the positive electrode sheet; the electrolyte can be one or more of carbonate, carbonate alkene and carboxylate electrolytes. In addition, there is no particular limitation in the structure and assembly method of the lithium battery, and any structure and assembly method known in the art that can be used for a lithium battery may be employed.

In one embodiment, the lithium battery includes: a positive electrode sheet provided with a positive electrode active material layer, the separator, a negative electrode sheet provided with a negative electrode active material layer, and an electrolyte solution.

In one embodiment, the positive electrode sheet is an aluminum foil, and has a thickness of 8 to 15 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or the like; the negative electrode sheet is a copper foil, and has a thickness of 5-20 μm, such as 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, and the like.

The present invention has been described in detail hereinabove, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. Furthermore, there is no intention to be bound by any theory presented in the preceding prior art or the summary or the following examples.

Unless expressly stated otherwise, a numerical range throughout this specification includes any sub-range therein and any numerical value incremented by the smallest sub-unit within a given value. Unless expressly stated otherwise, numerical values throughout this specification represent approximate measures or limitations to the extent that such deviations from the given values, as well as embodiments having approximately the stated values and having the exact values stated, are included. Other than in the operating examples provided at the end of the detailed description, all numbers expressing quantities or conditions of parameters (e.g., quantities or conditions) used in the specification (including the appended claims) are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the number. "about" means that the numerical value so stated is allowed to be somewhat imprecise (with some approach to exactness in that value; about or reasonably close to that value; approximately). As used herein, "about" refers to at least variations that can be produced by ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" can include less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5% variation, and in some aspects, less than or equal to 0.1% variation.

Unless otherwise expressly stated, the terms "comprising," "including," "having," "containing," or any other similar term in this specification are intended to be open-ended terms that indicate that a composition or article may include other elements not expressly listed or inherent to such composition or article. Furthermore, in this document, the terms "comprising," including, "" having, "" containing, "and" containing "are to be construed as specifically disclosed and to cover both closed and semi-closed conjunctions, such as" consisting of … "and" consisting essentially of …. By "consisting essentially of …," it is meant that the elements listed herein constitute greater than 95%, greater than 97%, or in some aspects, greater than 99% of the composition or article.

Advantageous effects

The ceramic micro-composite diaphragm and the preparation method thereof have the following advantages:

(1) the material cost is low, the process is simple, and no environmental pollution is caused;

(2) the surface of the polyolefin diaphragm is coated with a ceramic layer of 1-5 mu m, so that the heat shrinkage performance and the liquid storage performance of the diaphragm are improved.

(3) The surface of the modified nano barium sulfate is coated with a layer of multifunctional coupling agent and crosslinked with a binder, so that the discontinuous barium sulfate particles form a continuous micro-coating, and the barium sulfate particles with smaller particle size can be randomly distributed in the fluctuation gaps or on the surface of the ceramic particles, so that the coating is not increased, and the barium sulfate is distributed in the gaps or on the surface of the ceramic particles in a staggered manner, so that the ventilation loss is not caused;

(4) barium sulfate is used as a developer, has a self-recognition function during X-ray detection, is used as a basis for judging that the battery diaphragm exceeds the negative pole piece, ensures the separation of the positive pole piece and the negative pole piece, and avoids the potential safety hazard of the battery caused by the dislocation of the battery diaphragm.

Drawings

FIG. 1 is a schematic view of a septum according to one embodiment of the invention.

Detailed Description

The technical solution of the present invention is further illustrated by the following examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Reagent and apparatus

Unless otherwise indicated, all materials and reagents used are commercially available products which are conventionally used in the manufacture of lithium battery-related materials.

The stirring is carried out by adopting a DJ200 planetary stirrer manufactured by Shenzhen Xinjia Tuo automation technology Limited.

Preparation example: preparation of modified nano barium sulfate

(1) 50 parts of 20nm barium sulfate, 6 parts of sodium chloride, 80 parts of DI water and 50 parts of ethanol, and mixing and stirring the components at 60 ℃ and 1000rpm for 0.5h to prepare a nano barium sulfate suspension with the solid content of 30 wt%;

(2) adding 0.5 part of titanate coupling agent into a reaction kettle, carrying out shearing emulsification at 8000rpm/min for 20min by adopting a high-speed shearing emulsifying machine to modify the nano barium sulfate, and filtering, washing, drying and carrying out jet milling to obtain modified barium sulfate powder.

The detection shows that the average particle size of the obtained modified barium sulfate powder is 25nm

Example 1

(1) Ceramic slurry preparation

15 parts of butylbenzene emulsion with the solid content of 50 wt% and 37 parts of DI water are mixed and stirred for 20min at 25 ℃ at 500 rpm/min; adding 80 parts of alumina and 100 parts of thickener (5 wt% CMC premixed water solution), and stirring at 1500rpm for 1.5h at 25 ℃; finally, 0.5 part of sodium polyacrylate is added, and the mixture is stirred for 10min at the temperature of 25 ℃ at the rpm/min, so that ceramic slurry with the solid content of 40 wt% is obtained;

(2) preparation of modified barium sulfate slurry

Mixing 20 parts of polymethacrylic acid with the solid content of 20 wt%, 60 parts of thickening agent (5 wt% CMC premixed aqueous solution) and 369 parts of water, and stirring at 30 ℃ at 500rpm/min for 10 min; adding 70 parts of modified barium sulfate powder prepared in the preparation example, and stirring at 1000rpm/min for 1 h; and finally, adding 1 part of sodium polyacrylate, and stirring at 300rpm/min for 20min to obtain modified barium sulfate slurry with the solid content of 15 wt%.

(3) Preparation of coating film

Coating the ceramic slurry on one side of a 7-micron polyethylene diaphragm at a coating speed of 30m/min, and drying the ceramic diaphragm in ovens at 30, 45 and 30 ℃ in sequence to obtain a ceramic diaphragm with a coating of 3 microns; and then coating the modified barium sulfate slurry on the surface of the ceramic layer at a coating speed of 20m/min, and drying the ceramic layer by drying ovens at 40, 55 and 50 ℃ in sequence to obtain the ceramic micro-composite diaphragm.

Example 2

(1) Ceramic slurry preparation

15 parts of styrene-acrylic emulsion with the solid content of 50 wt% and 37 parts of DI water are mixed and stirred for 20min at the temperature of 25 ℃ and the rpm/min of 500; 80 parts of boehmite, 100 parts of thickener (5 wt% aqueous CMC premix) were added and stirred at 1500rpm for 1.5h at 25 ℃; finally, 0.5 part of sodium polyacrylate is added, and the mixture is stirred for 10min at the temperature of 25 ℃ and at the rpm/min of 300, so that ceramic slurry with the solid content of 40 wt% is obtained;

(2) preparation of modified barium sulfate slurry

Mixing 20 parts of polymethacrylate with the solid content of 20 wt%, 60 parts of thickening agent (5 wt% CMC premixed aqueous solution) and 369 parts of water, and stirring at 30 ℃ at 500rpm/min for 10 min; adding 70 parts of modified barium sulfate powder prepared in the preparation example, and stirring at 1000rpm/min for 1 h; and finally, adding 1 part of sodium polyacrylate, and stirring at 300rpm/min for 20min to obtain modified barium sulfate slurry with the solid content of 15 wt%.

(3) Preparation of coating film

Example 3

(1) Ceramic slurry preparation

20 parts of polymethacrylic acid with a solid content of 50 wt% and 74 parts of DI water, and stirring at 30 ℃ and 500rpm/min for 30 min; adding 85 parts of alumina and 100 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution), and stirring at 1500rpm for 2h at 30 ℃; finally, 1 part of polyethylene glycol ether is added, and the mixture is stirred for 20min at the temperature of 30 ℃ and at the rpm/min of 300, so that ceramic slurry with the solid content of 35 wt% is obtained;

(2) preparation of modified barium sulfate slurry

Mixing 20 parts of polymethacrylic acid with the solid content of 50 wt%, 200 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution) and 219 parts of water, and stirring at the temperature of 30 ℃ at 500rpm/min for 10 min; adding 60 parts of modified barium sulfate powder prepared in the preparation example, and stirring at 1500rpm/min for 1 h; and finally, adding 1 part of polyethylene glycol ether, and stirring at 300rpm/min for 20min to obtain the modified barium sulfate slurry with the solid content of 15 wt%.

(3) Preparation of coating film

Coating the ceramic slurry on one side of a 7-micron polyethylene diaphragm at a coating speed of 30m/min, and drying the ceramic diaphragm in ovens at 30, 45 and 30 ℃ in sequence to obtain a ceramic diaphragm with a coating layer of 4 microns; and then coating the modified barium sulfate slurry on the surface of the ceramic layer at a coating speed of 20m/min, and drying the ceramic layer by drying ovens at 40, 55 and 50 ℃ in sequence to obtain the ceramic micro-composite diaphragm.

Example 4

(1) Ceramic slurry preparation

20 parts of butylbenzene emulsion with the solid content of 50 wt% and 74 parts of DI water are mixed and stirred for 30min at the temperature of 30 ℃ at 500 rpm/min; adding 85 parts of silicon oxide and 100 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution), and stirring at 1500rpm for 2h at 30 ℃; finally, 1 part of polyethylene glycol ether is added, and the mixture is stirred for 20min at the temperature of 30 ℃ and at the rpm/min of 300, so that ceramic slurry with the solid content of 35 wt% is obtained;

(2) preparation of modified barium sulfate slurry

Mixing 20 parts of styrene-acrylic emulsion with the solid content of 50 wt%, 200 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution) and 219 parts of water, and stirring at the temperature of 30 ℃ at 500rpm/min for 10 min; adding 60 parts of modified barium sulfate powder prepared in the preparation example, and stirring at 1500rpm/min for 1 h; and finally, adding 1 part of polyethylene glycol ether, and stirring at 300rpm/min for 20min to obtain the modified barium sulfate slurry with the solid content of 15 wt%.

(3) Preparation of coating film

Comparative example 1

(1) Ceramic slurry preparation

(2) preparation of coating film

Coating the ceramic slurry on one side of a 7-micron polyethylene diaphragm at a coating speed of 30m/min, and drying in ovens at 30, 45 and 30 ℃ in sequence to obtain the ceramic diaphragm with a coating of 3 microns.

Comparative example 2

(1) Ceramic slurry preparation

20 parts of polymethacrylic acid with a solid content of 50 wt% and 74 parts of DI water, and stirring at 30 ℃ and 500rpm/min for 30 min; adding 85 parts of alumina and 100 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution), and stirring at 1500rpm for 2h at 30 ℃; finally, 1 part of polyethylene glycol ether is added, and the mixture is stirred for 20min at the temperature of 30 ℃ at the rpm/min, so that ceramic slurry with the solid content of 35 wt% is obtained;

(2) preparation of coating film

Coating the ceramic slurry on one side of a 7-micron polyethylene diaphragm at a coating speed of 30m/min, and drying in ovens at 30, 45 and 30 ℃ in sequence to obtain the ceramic diaphragm with a coating layer of 4 microns.

Comparative example 3

(1) Ceramic slurry preparation

(2) preparation of barium sulfate slurry

Mixing 20 parts of styrene-acrylic emulsion with the solid content of 50 wt%, 200 parts of thickening agent (2 wt% sodium alginate premixed aqueous solution) and 219 parts of water, and stirring at the temperature of 30 ℃ at 500rpm/min for 10 min; adding 60 parts of unmodified barium sulfate powder, and stirring at 1500rpm/min for 1 h; and finally, adding 1 part of polyethylene glycol ether, and stirring at 300rpm/min for 20min to obtain the barium sulfate slurry with the solid content of 15 wt%.

(3) Preparation of coating film

Coating the ceramic slurry on one side of a 7-micron polyethylene diaphragm at a coating speed of 30m/min, and drying the ceramic diaphragm in ovens at 30, 45 and 30 ℃ in sequence to obtain a ceramic diaphragm with a coating of 3 microns; and then coating the barium sulfate slurry on the surface of the ceramic layer at the coating speed of 20m/min, and drying the barium sulfate slurry in 40, 55 and 50 ℃ drying ovens in sequence to obtain the unmodified ceramic micro-composite diaphragm.

Experimental example 1 thickness measurement

The measuring method comprises the following steps: the thicknesses of the polyethylene-based films, the separators after the ceramic layer was coated, and the separators after the barium sulfate layer was coated according to examples 1 to 4 and comparative examples 1 to 3 were measured using a ten-thousandth micrometer, respectively, and the results are shown in table 1 below.

TABLE 1

Item	Example 1	Example 2	Example 3	Example 4	Comparative example 1	Comparative example 2	Comparative example 3
								Polyethylene-based film	6.8	7.0	7.2	6.9	7.0	7.1	7.0
Ceramic diaphragm	9.8	10.1	11.1	11.0	10.0	10.2	10.3
								Micro-composite diaphragm	9.9	10.2	11.3	11.2	/	/	10.5

The results in table 1 show that the modified or unmodified barium sulfate microlayers did not result in a significant increase in coating thickness.

Experimental example 2 air permeability measurement

The measuring method comprises the following steps: the base films, ceramic separators and micro composite separators of examples 1 to 4 and comparative examples 1 to 3 were used to test air permeability values using an asahi jowar air permeability tester. The results are shown in Table 2.

The air permeability value, which reflects the permeability of the membrane, is the time (seconds) it takes 100ml of air to penetrate a certain area of the membrane under a certain pressure in an air permeameter.

TABLE 2 ceramic coating Permeability growth value (sec/100cc)

As can be seen from the results in Table 2, the gas permeability of the ceramic coatings of examples 1-4 is increased by 15 or more and increased by 30 or less, and the gas permeability of the barium sulfate micro-layer is not increased obviously, wherein the negative value is that the gas permeability of the ceramic coating at different positions fluctuates up and down, and the fluctuation tolerance of the same roll of the diaphragm is +/-10, so that the modified or unmodified barium sulfate micro-layer basically does not cause gas permeability loss.

Experimental example 3 shrinkage test

The measuring method comprises the following steps: the base films, ceramic separators and micro-composite separators of experimental examples 1 to 4 and comparative examples 1 to 3 were subjected to a heat shrinkage test, with a sample size of 200mm × 100mm (MD × TD), MD being the separator longitudinal direction, and TD being the separator transverse direction. Thermal shrinkage test temperature: the substrate film is 120 ℃/1h, and the ceramic diaphragm and the micro-composite diaphragm are 130 ℃/1 h. The results of the heat shrinkage test in the MD and TD directions are shown in table 3.

TABLE 3

As can be seen from table 3, the heat shrinkage performance of the micro composite separators using the modified barium sulfate micro layers according to examples 1 to 4 of the present invention was significantly improved relative to the ceramic separator, while the heat shrinkage performance of the micro composite separator using the unmodified barium sulfate micro layers of comparative example 3 was not substantially improved relative to the ceramic separator.

Experimental example 4 electrolyte retention amount

Samples of the micro-composite separators of examples 1 to 4 and comparative example 3 and the ceramic separators of comparative examples 1 and 2 were taken for standby and had a size of 100cm². Firstly, respectively measuring the weight of a diaphragm sample by using a precision density balance, soaking the diaphragm sample in electrolyte (the electrolyte composition EC: EMC: DEC: PC: 3:2:1) at 85 ℃ for 24h, taking out the sample, wiping off residual electrolyte on the surface by using dust-free paper, weighing, and calculating the liquid absorption rate as an index of the liquid retention capacity of the diaphragm electrolyte. The results are shown in Table 4.

The liquid absorption rate calculation method comprises the following steps: the liquid absorption rate (%) - (M-M0)/M0%

Wherein, M0: diaphragm sample initial weight; m: weight of membrane sample after soaking.

TABLE 4

Item	Example 1	Example 2	Example 3	Example 4	Comparative example 1	Comparative example 2	Comparative example 3
								M0g/m²	9.5	9.3	11.0	11.2	9.5	11.3	9.4
Mg/m²	15.2	14.8	15	15.3	14	16.8	13.9
								The liquid absorption rate%	60	59	70	69	47	49	48

As can be seen from the results in table 4, the liquid retention amounts of the micro composite separators according to examples 1 to 4 of the present invention were significantly increased, which was advantageous for lithium ion cycle in lithium batteries, and increased the battery rate. The liquid retention of the micro-composite diaphragm adopting the unmodified barium sulfate micro-layer in the comparative example 3 is basically the same as that of the ceramic diaphragms in the comparative examples 1 and 2, namely, the unmodified barium sulfate micro-layer does not substantially contribute to the liquid retention of the diaphragm.

Claims

1. A ceramic micro-composite separator, comprising: a base film; a ceramic layer disposed on at least one surface of the base film; and a modified barium sulfate micro-layer arranged on the outer surface of the ceramic layer, wherein the modified barium sulfate is barium sulfate modified by a coupling agent.

2. The ceramic microcomposite separator of claim 1, wherein the base film is a polyolefin film, e.g., a polyethylene or polypropylene film, and/or the base film has a pore size in the range of 0.01 to 0.1 μ ι η, and/or a porosity of between 20% and 80%, in particular between 30% and 50%, and/or a thickness of 30 μ ι η or less, e.g., 3 to 20 μ ι η.

3. The ceramic micro-composite separator according to claim 1, wherein the thickness of the ceramic layer is 0.5-10 μm, preferably 1-5 μm, and/or the ceramic layer comprises ceramic particles, a binder, a thickener and a dispersant, wherein the ceramic layer comprises the following components in parts by weight of solid: 70-95 parts of ceramic particles, preferably 75-90 parts; 2-20 parts of binder, preferably 5-15 parts; 1-15 parts of thickening agent, preferably 1-10 parts; 0.1-3 parts of dispersing agent, preferably 0.3-2 parts, and/or the ceramic particles are one or more selected from alumina, titanium oxide, magnesium hydroxide and boehmite, and/or the particle size is 0.1-5 mu m.

4. The ceramic micro-composite membrane according to claim 1, wherein the modified barium sulfate micro-layer comprises a coupling agent modified barium sulfate, a binder, a thickener and a wetting agent, wherein the modified barium sulfate micro-layer comprises the following components in parts by weight: 75-95 parts of coupling agent modified barium sulfate, preferably 80-90 parts; 2-20 parts of binder, preferably 5-15 parts; 1-15 parts of thickening agent, preferably 1-10 parts; 0.1-3 parts of wetting agent, preferably 0.2-2 parts, and/or the thickness of the modified barium sulfate micro-layer is 0.03-1 μm, preferably 0.05-0.5 μm.

5. The ceramic micro-composite membrane according to claim 1, wherein the coupling agent is a titanate coupling agent, an aluminate coupling agent, or a combination thereof, and/or the coupling agent is 0.1% to 2.0%, preferably 0.2% to 1.5% by mass of barium sulfate, and/or the coupling agent modified barium sulfate has a particle size of 5 to 100nm, for example 10 to 80 nm.

6. The ceramic micro-composite separator according to claim 1, wherein the coupling agent modified barium sulfate is prepared by:

7. A method of making the ceramic microcomposite separator of any one of claims 1-6 comprising the steps of:

1) ceramic particles, a binder, a thickening agent, a dispersing agent and deionized water are uniformly mixed to obtain ceramic slurry,

8. The method of claim 7, wherein,

step 1) is carried out as follows: mixing the binder and deionized water, and stirring at 20-40 ℃ and 300-500 rpm/min for 10-30 min; adding ceramic particles and a thickening agent, stirring at the temperature of 20-40 ℃ and the rpm of 1500-2500 for 1-2.5 h; finally, adding a dispersing agent, and stirring at 20-40 ℃ and 100-500 rpm/min for 10-20 min to obtain ceramic slurry; and/or

Step 2), mixing the binder, the thickening agent and deionized water, and stirring at the temperature of 20-40 ℃ and at the speed of 300-500 rpm/min for 10-30 min; adding coupling agent modified barium sulfate, and stirring for 1-2 h at 800-1500 rpm/min; and finally, adding a wetting agent, and stirring at 100-300 rpm/min for 20-40 min to obtain the barium sulfate slurry.

9. A lithium battery comprising the ceramic microcomposite separator of any one of claims 1-6.

10. The lithium battery of claim 9, wherein the lithium battery comprises: a positive electrode sheet provided with a positive electrode active material layer, the separator according to any one of claims 1 to 6, a negative electrode sheet provided with a negative electrode active material layer, and an electrolyte, and/or the positive electrode sheet is an aluminum foil and has a thickness of 8 to 15 μm; the negative plate is a copper foil, and the thickness of the negative plate is 5-20 mu m.