CN106601967A - Composite ceramic diaphragm and application thereof - Google Patents

Abstract

The invention discloses a composite ceramic diaphragm and a battery containing the diaphragm. The composite ceramic diaphragm includes a polymer diaphragm base material and a ceramic layer. The composite ceramic diaphragm is made into a slurry made of anionic surfactant, sepiolite powder and dispersant, and is coated on one side and both sides of the polymer diaphragm base material. Covering or dipping to make a ceramic layer, and further drying. Sepiolite ceramic powder has the properties of large specific surface, strong adsorption, light weight, heat insulation, insulation, corrosion resistance and thermal stability. In addition, the anionic surfactant has a debundling effect on the sepiolite, transforming the fibrous sepiolite into a uniformly dispersed fiber, increasing the stress of the diaphragm, and the formed ceramic layer improves the infiltration of the polymer diaphragm substrate. It can be used as a high-safety separator for lithium-ion secondary batteries due to its high temperature and thermal stability.

Description

A kind of composite ceramic diaphragm and its application

technical field

The invention belongs to the field of electrochemistry, and in particular relates to a sepiolite composite ceramic diaphragm, and also relates to the application of the composite ceramic diaphragm in chemical power systems such as lithium ion batteries.

Background technique

As a chemical power system with high energy density, high output voltage, no memory effect, excellent cycle performance, and environmental friendliness, lithium-ion battery has good economic benefits, social benefits and strategic significance, and has been widely used in mobile communications, Digital products and other fields, and it is very likely to become the most important power supply system in the field of energy storage and electric vehicles.

In lithium-ion batteries, the separator mainly plays the role of preventing positive and negative electrodes from contacting and allowing ion conduction, and is an important part of the battery. At present, commercial lithium-ion batteries mainly use polyolefin diaphragm materials with microporous structures, such as single-layer or multi-layer films of polyethylene (Polyethylene, PE) and polypropylene (Polypropylene, PP). Due to the characteristics of the polymer itself, although the polyolefin separator can provide sufficient mechanical strength and chemical stability at room temperature, it exhibits large thermal shrinkage at high temperatures, which causes the positive and negative electrodes to contact and quickly accumulate a large amount of heat. , although the PP/PE composite separator can firstly melt the micropores in the polymer to block the ion conduction at a lower temperature (120°C), and PP still plays a supporting role to prevent further electrode reactions, but due to The melting temperature of PP is only 150°C. When the temperature rises rapidly and exceeds the melting temperature of PP, the melting of the separator will cause a large area of short circuit and cause thermal runaway, which will aggravate the accumulation of heat, generate high pressure inside the battery, and cause the battery to burn or explode. The internal short circuit of the battery is the biggest hidden danger to the safety of lithium-ion batteries. In order to meet the needs of the development of large-capacity lithium-ion batteries, the development of high-safety separators has become an urgent task for the industry. Among them, the excellent temperature resistance and high safety of ceramic diaphragms make them one of the main choices to replace traditional polyolefin diaphragms.

Ceramic-coated Separators are coated on one or both sides of the surface of the existing polyolefin microporous membrane substrate with a uniform protective layer composed of ceramic particles to form a porous membrane. Safety function diaphragm. On the basis of ensuring the original basic characteristics of the polyolefin microporous separator, the separator is endowed with a high heat resistance function, which reduces the thermal shrinkage of the separator, thereby more effectively reducing the internal short circuit of the lithium-ion battery and preventing the battery from heat caused by the internal short circuit of the battery. out of control.

Since the polyolefin membrane is a hydrophobic material and has poor affinity with the highly polar electrolyte, the polyolefin membrane cannot quickly absorb the electrolyte and effectively retain the electrolyte, which will greatly affect the performance of the polyolefin membrane in lithium-ion batteries And there is a risk of leakage. At present, the preparation method of ceramic diaphragm is mainly to disperse ceramic powder (mainly nanometer or submicron oxide powder, such as Al ₂ O ₃ , SiO ₂ , TiO ₂ , etc.), binder, etc. in a solvent to form a slurry. , and then form a ceramic coating on the surface of the polyolefin separator substrate by casting or dipping (see Journal of Power Sources 195 (2010) 6192-6196, CN200580036709.6CN200780035135.X, etc.). The ceramic coating will improve the affinity between the ceramic powder and the diaphragm substrate, and improve the performance of the polyolefin film in lithium-ion batteries. However, the existing ceramic coating requires the action of a binder because the ceramic powder exists in granular form, and is easy to fall off. Its thermal stability is not good, and there is still a certain risk of liquid leakage.

Contents of the invention

The present invention obtains fibrous sepiolite by dispersing fibrous sepiolite in an anionic surfactant and unbundling, and prepares a composite ceramic diaphragm with fibrous sepiolite as a ceramic matrix, which is used to improve diaphragm stress and thermal stability.

One object of the present invention is to provide a kind of sepiolite fiber that is unbundled with surfactant as the composite ceramic membrane of ceramic element, and described composite ceramic membrane comprises polymer membrane base material and is formed on the surface of described polymer membrane base material The ceramic layer, the thickness of the ceramic layer is 500nm-10μm; the ceramic layer includes sepiolite fiber, the diameter of the sepiolite fiber is 100nm-500nm, and the length is 500nm-5μm; the composite ceramic diaphragm passes Prepared by the following method:

Provide a mass ratio of 1%-30% anionic surfactant, 40-90% dispersant and 5%-30% fibrous sepiolite, adding the anionic surfactant to the dispersant Mix evenly, add the fibrous sepiolite and ultrasonically, continue magnetic stirring for 2 to 5 hours to unbundle the fibrous sepiolite into fibers to obtain a ceramic slurry, which is coated or impregnated on the The ceramic layer is formed on the surface of the polymer diaphragm substrate, and the composite ceramic diaphragm is obtained after drying.

Preferably, the thickness of the ceramic layer is 300nm-30μm.

Preferably, the polymer separator substrate can be a commercially available polyolefin porous polymer film (such as a single-layer or multi-layer composite film of polyethylene or polypropylene), a non-woven fabric, or a Polymer materials for secondary battery polymer electrolytes, such as polyethylene oxide, polyacrylonitrile, polymethylmethacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol, polyimide etc., and include blending and copolymerization systems derived from the above systems, such as acrylonitrile-methyl methacrylate copolymer, etc.

Preferably, the anionic surfactant is at least one of sulfonate, carboxylate, sulfate ester salt, and phosphate ester salt.

Preferably, the anionic surfactant is sodium lignosulfonate.

Preferably, the dispersant is an aqueous solution formed of ethanol and deionized water at a volume ratio of 1:1.

Preferably, the ceramic slurry is coated or impregnated on one or both sides of the polymer membrane substrate.

Sepiolite is a magnesium-rich silicate clay mineral with layered chain structure. Low shrinkage, good plasticity, large specific surface, strong adsorption. Soluble in hydrochloric acid, light in weight. Sepiolite also has the properties of flame retardancy, heat insulation, insulation, corrosion resistance and thermal stability. When sepiolite dissolves in water, it can form a rather viscous solution by itself. Add its powder into the surfactant solution, on the one hand, it can form a ceramic slurry with a certain viscosity without adding a binder; Uniformly dispersed fibrous. The fibrous sepiolite structure has a certain length-to-diameter ratio, which can increase the stress of the separator, thereby improving the thermal stability of the separator. After the process of coating or dipping, the composite ceramic diaphragm can be obtained.

Another object of the present invention is to provide the application of this composite ceramic diaphragm in secondary batteries.

Another object of the present invention is to provide a battery comprising such a composite ceramic separator. The battery provided by the invention includes positive electrode material and negative electrode material, and the composite ceramic diaphragm provided by the invention is arranged between the positive electrode material and the negative electrode material.

Generally, the cathode materials used in lithium ion batteries can be used in the present invention. The positive electrode active material related to the positive electrode can use a compound that can reversibly store-release (intercalate and deintercalate) lithium ions, for example, Li _x MO ₂ or Li _y M ₂ O ₄ (wherein, M is Transition metals, lithium-containing composite oxides represented by 0≤x≤1, 0≤y≤2), spinel-like oxides, layered metal chalcogenides, olivine structures, etc.

Specific examples thereof include lithium cobalt oxides such as LiCoO ₂ , lithium manganese oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium titanium oxides such as Li _4/3 Ti _5/3 O ₄ , Lithium-manganese-nickel composite oxide, lithium-manganese-nickel-cobalt composite oxide; materials having an olivine-type crystal structure such as LiMPO ₄ (M=Fe, Mn, Ni), and the like.

In particular, lithium-containing composite oxides with a layered structure or a spinel structure are preferred, and lithium manganese nickel represented by LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1/2 Mn _1/2 O ₂ , etc. Composite oxides, lithium manganese nickel cobalt composite oxides represented by LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ , or LiNi _1-xyz Co _x Al _y Mg _z O ₂ (wherein, 0≤x≤1, 0≤y≤0.1, 0≤z≤0.1, 0≤1-xyz≤1) and other lithium-containing composite oxides. In addition, lithium-containing composite oxides in which some of the constituent elements of the above-mentioned lithium-containing composite oxides are replaced by additive elements such as Ge, Ti, Zr, Mg, Al, Mo, Sn, etc. are also included.

These positive electrode active materials may be used alone or in combination of two or more. For example, by using a lithium-containing composite oxide with a layered structure and a lithium-containing composite oxide with a spinel structure in combination, it is possible to achieve both a large capacity and an improvement in safety.

For constituting the positive electrode of the non-aqueous electrolyte secondary battery, for example, conductive aids such as carbon black and acetylene black are appropriately added to the above-mentioned positive electrode active material, or binders such as polyvinylidene fluoride and polyethylene oxide, etc., The positive electrode mixture is prepared and used after being coated on a belt-shaped molded body with a current collector such as aluminum foil as a core material. However, the production method of the positive electrode is not limited to the above example.

Generally, negative electrode materials used in lithium ion batteries can be used in the present invention. The negative electrode active material involved in the negative electrode can use a compound capable of intercalating and deintercalating lithium metal and lithium. For example, various materials such as alloys or oxides of aluminum, silicon, tin, and the like, and carbon materials can be used as the negative electrode active material. Examples of oxides include titanium dioxide and the like, and examples of carbon materials include graphite, pyrolytic carbons, cokes, glassy carbons, fired products of organic polymer compounds, mesocarbon beads, and the like.

For constituting the negative electrode of the non-aqueous electrolyte secondary battery, for example, conductive additives such as carbon black and acetylene black, or binders such as polyvinylidene fluoride and polyethylene oxide are appropriately added to the above-mentioned negative electrode active material, Negative electrode mixture is prepared and used after being coated on a strip-shaped molded body with a current collector such as copper foil as a core material. However, the production method of the negative electrode is not limited to the above example.

In the nonaqueous electrolyte secondary battery provided by the present invention, a nonaqueous solvent (organic solvent) is used as the nonaqueous electrolyte. Non-aqueous solvents include carbonates, ethers, and the like.

Carbonates include cyclic carbonates and chain carbonates. Cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfur esters (ethylene glycol sulfide, etc.) )Wait. Examples of chain carbonates include low-viscosity polar chain carbonates represented by dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and aliphatic branched-chain carbonates. A mixed solvent of cyclic carbonate (especially ethylene carbonate) and chain carbonate is particularly preferable.

Examples of ethers include dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), and the like.

In addition, in addition to the above-mentioned non-aqueous solvents, chain alkyl esters such as methyl propionate, chain phosphoric acid triesters such as trimethyl phosphate, etc.; nitrile solvents such as 3-methoxypropionitrile; Representative non-aqueous solvents (organic solvents) such as branched compounds having ether bonds.

In addition, fluorine-based solvents can also be used.

Examples of fluorine-based solvents include H(CF ₂ ) ₂ OCH ₃ , C ₄ F ₉ OCH ₃ , H(CF ₂ ) ₂ OCH ₂ CH ₃ , H(CF ₂ ) ₂ OCH ₂ CF ₃ , H( CF ₂ ) ₂ CH ₂ O(CF ₂ ) ₂ H, etc., or CF ₃ CHFCF ₂ OCH ₃ , CF ₃ CHFCF ₂ OCH ₂ CH ₃ and other straight-chain (perfluoroalkyl) alkyl ethers, that is, 2-tri Fluoromethyl hexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ethyl ether, 2-trifluoromethyl hexafluoropropyl propyl ether, 3-trifluoromethyl octafluorobutyl methyl ether, 3-trifluoromethyl Methyl octafluorobutyl ethyl ether, 3-trifluoromethyl octafluorobutyl propyl ether, 4-trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl Methyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl dodecafluorohexyl ethyl ether, 5-trifluoromethyl dodecafluorohexyl propyl ether, 6-trifluoromethyl Fluoromethyltetrafluoroheptylmethyl ether, 6-trifluoromethyltetrafluoroheptylethyl ether, 6-trifluoromethyltetrafluoroheptylpropyl ether, 7-trifluoromethylhexadecafluorooctylmethyl ether Ether, 7-trifluoromethyl hexadecafluorooctyl ethyl ether, 7-trifluoromethyl hexadecafluorooctyl propyl ether, etc.

In addition, the above-mentioned iso(perfluoroalkyl)alkyl ether and the above-mentioned straight-chain structure (perfluoroalkyl)alkyl ether may be used in combination.

As the electrolyte salt used in the non-aqueous electrolytic solution, lithium salts such as lithium perchlorate, organic boron lithium salt, lithium salt of fluorine-containing compound, and lithium imide salt are preferable.

Examples of such electrolyte salts include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₂ F ₄ (SO ₃ ) ₂ , LiN( C ₂ F ₅ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiC _n F _2n+1 SO ₃ (n≥2), LiN(RfOSO ₂ ) ₂ (wherein, Rf is a fluoroalkyl group), etc. Among these lithium salts, fluorine-containing organic lithium salts are particularly preferred. Fluorine-containing organic lithium salts are easily soluble in non-aqueous electrolytic solutions due to their high anionicity and easy separation into ions.

The concentration of the electrolyte lithium salt in the non-aqueous electrolyte, for example, is preferably above 0.3mol/L (mol/L), more preferably above 0.7mol/L, preferably below 1.7mol/L, more preferably below 1.2mol/L . When the concentration of the electrolyte lithium salt is too low, the ion conductivity is too small, and when it is too high, there is a concern that the incompletely dissolved electrolyte salt will precipitate out.

In addition, in the non-aqueous electrolytic solution, various additives that can improve the performance of the battery using it can also be added, and it is not particularly limited.

The benefits of the present invention are:

1. In the slurry made of sepiolite, anionic surfactant and dispersant (water and ethanol), there is no need to add thickener and binder, and the process is simple.

2. After the anionic surfactant is unbundled, the sepiolite forms a uniformly dispersed fibrous structure with a certain length-to-diameter ratio, which is evenly compounded on the surface of the basement membrane, which is not easy to drop powder, and improves the stress and thermal stability of the diaphragm Performance, thereby improving the overall safety performance of the diaphragm.

3. Sepiolite has a large specific surface area and strong adsorption capacity. It has good liquid absorption and liquid retention ability, which improves the cycle life of the battery.

4. Sodium lignosulfonate has a strong dispersion ability, suitable for dispersing solids in water medium, can be adsorbed on the surface of various solid particles, and can perform metal ion exchange.

Description of drawings

FIG. 1 is an SEM image of the sepiolite ceramic powder used in Example 1.

2 is the SEM image of the ceramic surface (left) and the PE surface (right) of the sepiolite composite ceramic membrane obtained in Example 1.

FIG. 3 is an SEM image of the cross-section of the ceramic diaphragm obtained in Example 1. FIG.

Fig. 4 is a comparative picture of the ceramic diaphragm (left) and the PE base film (right) obtained before (4a) and after (4b) heat treatment (160°C) in Example 1.

detailed description

The following will be described in more detail through examples, but the protection scope of the present invention is not limited to these examples.

Example 1

At room temperature, weigh 0.5g of sodium lignosulfonate, add to 15ml of aqueous solution (the volume ratio of ethanol to deionized water is 1:1), ultrasonication for 5min, magnetic stirring for 1h; add 1.2g of sepiolite, ultrasonication After 30 minutes, continue magnetic stirring for 3 hours to obtain a ceramic slurry with a solid content of 10%. Coat one side of a 20cm×6m polyethylene diaphragm on a small coating machine, and obtain a composite ceramic diaphragm after drying.

Fig. 1 is the SEM image of the sepiolite body used in Example 1, it can be seen that the untreated sepiolite is in the form of fiber bundles. Figure 2 is a scanning electron micrograph of the composite ceramic diaphragm obtained in Example 1. It can be clearly observed from the photo that fibrous sepiolite is evenly dispersed on the surface of the polyolefin diaphragm; compared with Figure 1, the sepiolite structure can be found The unbundling of fiber bundles into fibers is due to the unbundling of sepiolite by the surfactant sodium lignosulfonate solution. At the same time, from the cross-sectional SEM image (Figure 3), we can clearly observe the two-layer structure of polyolefin and ceramic layer. The thickness of the polyolefin base film is 30um, and the thickness of the ceramic layer is about 4um. The polyolefin surface of the composite ceramic diaphragm maintains a good shape and structure of the base film.

The excellent thermal shrinkage resistance of the composite ceramic diaphragm obtained in the present invention can be visually reflected from Figure 4, which shows the composite ceramic diaphragm obtained before (4a) and after (4b) heat treatment (160°C for 0.5h) in Example 1 ( Left) and PE base film (right) comparison pictures. It can be seen that the thermal shrinkage resistance of the composite ceramic diaphragm obtained in the present invention is obviously better than that of commercial polyethylene diaphragms.

Example 2

At room temperature, weigh 0.5g of sodium lignosulfonate, add to 15ml of aqueous solution (the volume ratio of ethanol to deionized water is 1:1), ultrasonication for 5min, magnetic stirring for 1h; add 1.2g of sepiolite, ultrasonication After 30 minutes, continue magnetic stirring for 3 hours to obtain a ceramic slurry with a solid content of 10%. Double-sided coating is carried out on a 20cm×6m polyethylene diaphragm on a small coating machine, and a composite ceramic diaphragm is obtained after drying. The difference from Example 1 is that the double-sided coating reduces the curling of the separator and further ensures the thermal stability. At the same time, double-sided coating increases the overall thickness and mass of the separator. Therefore, both single-sided and double-sided coatings have their own advantages and disadvantages, and they need to be selected according to the actual battery system.

Example 3

At room temperature, weigh 0.5g of sodium lignosulfonate, add to 15ml of aqueous solution (the volume ratio of ethanol to deionized water is 1:1), ultrasonication for 5min, magnetic stirring for 1h; add 1.2g of sepiolite, ultrasonication After 30 minutes, continue magnetic stirring for 3 hours to obtain a ceramic slurry with a solid content of 10%. The diaphragm is made into a disc and immersed in the slurry directly, and the composite ceramic diaphragm is prepared by dip-coating method. After drying, the sepiolite composite ceramic diaphragm is obtained.

Example 4

A battery, comprising a positive electrode material and a negative electrode material, the composite ceramic diaphragm prepared in Example 1 is arranged between the positive electrode material and the negative electrode material.

Example 5

A battery, comprising a positive electrode material and a negative electrode material, between the positive electrode material and the negative electrode material is the composite ceramic diaphragm prepared in Example 2.

Example 6

A battery, comprising a positive electrode material and a negative electrode material, between the positive electrode material and the negative electrode material is the composite ceramic diaphragm prepared in Example 3.

Those of ordinary skill in the art will know that when specific parameters of the present invention and components are changed within the following ranges, the same or similar technical effects as those of the above-described embodiments can still be obtained:

A composite ceramic diaphragm includes a polymer diaphragm substrate and a ceramic layer formed on the surface of the polymer diaphragm substrate. The polymer diaphragm substrate is selected from polyolefin porous polymers, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol , polyimide, and one or more of the blends and copolymers derived from the aforementioned polymers. The thickness of the ceramic layer is 500nm-10μm, preferably 300nm-30μm; the ceramic layer includes sepiolite fiber, the diameter of the sepiolite fiber is 100nm-500nm, and the length is 500nm-5μm; the composite ceramic The diaphragm was prepared by the following method:

Provide a mass ratio of 1%-30% anionic surfactant, 40-90% dispersant and 5%-30% fibrous sepiolite, adding the anionic surfactant to the dispersant Mix evenly, add the fibrous sepiolite and ultrasonically, continue magnetic stirring for 2 to 5 hours to unbundle the fibrous sepiolite into fibers to obtain a ceramic slurry, which is coated or impregnated on the The ceramic layer is formed on the surface of the polymer diaphragm substrate, and the composite ceramic diaphragm is obtained after drying. The anionic surfactant is at least one of sulfonate, carboxylate, sulfate ester salt and phosphate ester salt.

The above embodiments are only used to further illustrate a composite ceramic diaphragm of the present invention and its application, but the present invention is not limited to the embodiments, and any simple modification, equivalent change and Modifications all fall within the protection scope of the technical solutions of the present invention.

Claims (8)

1. a kind of composite ceramicses barrier film, it is characterised in that：The composite ceramicses barrier film includes membrane for polymer base material and formation In the ceramic layer of the membrane for polymer substrate surface, the thickness of the ceramic layer is 500nm-10 μm；The ceramic layer includes Sepiolite fibre, a diameter of 100nm-500nm of the sepiolite fibre, length are 500nm-5 μm；The composite ceramicses barrier film It is obtained by the following method：

Fibre bundle of the mass ratio for the anion surfactant, the dispersant of 40-90% and 5%-30% of 1%-30% is provided Shape meerschaum, by the anion surfactant mix homogeneously in the dispersant is added to, and adds the fiber bundle-like sea After afrodite ultrasound, continue 2～5h of magnetic agitation so that fiber bundle-like meerschaum solution beam obtains ceramic serosity into threadiness, it is described Ceramic serosity forms the ceramic layer by being coated or impregnated with the membrane for polymer substrate surface, obtains described after being dried Composite ceramicses barrier film.

2. composite ceramicses barrier film according to claim 1, it is characterised in that：The membrane for polymer base material is selected from polyolefin Class porous polymer, polyethylene glycol oxide, polyacrylonitrile, polymethyl methacrylate, Kynoar, Kynoar-hexafluoro One kind or number in propylene copolymer, polyvinyl alcohol, polyimides and blending, copolymerized polymer by derived from aforementioned polymer Kind.

3. composite ceramicses barrier film according to claim 1, it is characterised in that：The anion surfactant is sulfonic acid At least one in salt, carboxylate, sulfuric acid, phosphate ester salt.

4. composite ceramicses barrier film according to claim 3, it is characterised in that：The anion surfactant is lignin Sodium sulfonate.

5. composite ceramicses barrier film according to claim 1, it is characterised in that：The dispersant is ethanol water.

6. composite ceramicses barrier film according to claim 1, it is characterised in that：The ceramic size is coated or impregnated with described The single or double of membrane for polymer base material.

7. the application in the secondary battery of the composite ceramicses barrier film according to claim 1-6 any claim.

8. a kind of battery, including positive electrode, negative material, it is characterised in that：It is provided between positive electrode and negative material Composite ceramicses barrier film according to claim 1-7 any claim.