WO2022161438A1 - Boron-containing modified diaphragm and preparation method and application therefor, and battery including diaphragm - Google Patents

Abstract

Disclosed in the present disclosure are a boron-containing modified diaphragm and a preparation method and application therefor, and a battery including the diaphragm. The modified diaphragm is prepared by grafting boron with an electron-deficient effect to the surface and holes of a diaphragm base material by means of irradiation grafting. By means of the present invention, irradiation in-situ grafting technology, and high specific energy of rays generated by a radiation source are used, such that on the basis of guaranteeing original basic characteristics and morphology of a porous diaphragm to the greatest extent, a boron-containing compound is uniformly grafted to the surface of and the inside of holes of the porous diaphragm by means of in-situ grafting. The transport number of lithium ions can be increased, such that the energy efficiency of a lithium-ion secondary battery is improved, and a diaphragm is modified by using irradiation grafting technology, such that commercial prospects are provided for large-scale modified diaphragms.

Description

A boron-containing modified diaphragm, its preparation method and application, and a battery containing the diaphragm technical field

The invention relates to the field of polymer modified materials, in particular to a boron-containing modified diaphragm, a preparation method and application thereof, and a battery containing the diaphragm.

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, social and strategic significance, and has been widely used in mobile communications, It is very likely to become the most important power system in the fields of energy storage and electric vehicles.

In lithium-ion batteries, the main function of the separator is to prevent the contact between the positive and negative electrodes and allow ion conduction, which is an important part of the lithium-ion battery. Up to now, the separators used in commercial lithium-ion batteries are mainly polyolefin separator materials with microporous structure, 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 polyolefin separators can provide sufficient mechanical strength and chemical stability at room temperature, these polyolefin separators still have some disadvantages. Due to the poor wettability of common polyolefin separators in traditional liquid electrolytes, their liquid absorption capacity is low, which affects the cycle life of Li-ion batteries. In addition, the low Li-ion migration number of liquid electrolytes matched with polyolefin separators also fails to meet the demand for high-performance Li-ion batteries in emerging fields.

The lithium ion migration number is an important parameter of a lithium ion secondary battery. The higher the lithium-ion migration number, the higher the energy efficiency of the lithium-ion battery. When the Li-ion migration number approaches or reaches 1, the energy efficiency of the battery will be highest. This is because in the secondary battery, on the one hand, the migration of anions will lead to the consumption of battery energy; Concentration polarization, thereby reducing the energy efficiency of Li-ion batteries. In the existing electrolyte system, the lithium ion migration number is low (<0.3), which greatly affects the energy efficiency of the battery.

Usually, the modification of the diaphragm is not common. In the early years, a few literatures reported that the porous safety layer was formed by coating a uniform protective layer composed of inorganic ceramic microparticles on one or both sides of the diaphragm substrate. Sexual function diaphragm. However, the coating method also has unavoidable negative effects, such as a significant increase in the thickness of the separator, severe blockage of the porous structure, etc., and it is difficult for the current technology to modify the separator by modifying the ion transport channels on the separator. .

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention adopts the irradiation in-situ grafting technology, utilizes the high specific energy of the rays generated by the radiation source, on the basis of ensuring the original basic characteristics and morphology of the porous membrane as much as possible, through in-situ grafting. The grafting uniformly grafts the boron-containing monomer to the surface and the inside of the porous membrane. By modifying the ion transport path, the effective contact between ions and boron atoms is realized. The electron deficiency effect of boron atoms can be used as Lewis acid and anion. Coordination is carried out, thereby restricting the movement of anions. On the one hand, the lithium ion migration number is increased to improve the energy efficiency of lithium ion secondary batteries; on the other hand, the modification of the separator by using irradiation grafting technology provides a commercial prospect for large-scale modified separators.

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a boron-containing modified diaphragm, a preparation method and application thereof, and a battery containing the diaphragm.

One of the technical solutions of the present invention is a boron-containing modified diaphragm, which is prepared by introducing boron element with electron-deficient effect into the surface and holes of the diaphragm substrate by using irradiation grafting technology; the boron element is derived from unsaturated A boron-containing compound of a covalent molecule formed by a bond group and a sp2 hybridization of the boron atom.

The boron-containing compound having an unsaturated bond group and a covalent molecule formed by sp2 hybridization of boron atoms is 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxo One or more of cyclopentaborane, vinylboronic acid 2-methyl-2,4-pentanediol, vinylboronic acid methyliminodiacetate, and vinylboronic acid dibutyl ester.

The diaphragm base material is a single-layer or multi-layer composite film of polyolefin-based porous polymer film polyethylene or polypropylene, non-woven fabric and polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride , polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol and polyimide, and one or more of the blended and copolymerized polymers derived from the above-mentioned polymer materials.

The irradiation grafting method is one of a pre-irradiation grafting method, a co-irradiation grafting method and a peroxide method. The pre-irradiation grafting method is to irradiate the diaphragm under the condition of deoxygenation to generate relatively stable free radicals, and then graft with the de-aired monomer outside the radiation field at heating or room temperature; The irradiation-grafting method is to irradiate the diaphragm while the monomer is in direct contact; the peroxidation method is to pre-irradiate the diaphragm substrate in an oxygen atmosphere, and then graft it with the monomer.

The irradiation-grafted radiation source includes one of radioactive rays, a radiation source provided by acceleration and a neutron source.

Further, described radioactive rays include 1 kind in α-ray, β-ray and γ-ray, wherein the radioactive source of α-ray is a kind of ^241Am , ^239Pu and ^235U , the radioactive source of β-ray is ^3H , ¹⁴ One of C and ⁹⁰ Sr and the source of gamma rays are one of ⁶⁰ Co, ¹³⁷ Cs and ¹¹⁰ Sn.

Further, the radiation source provided by the acceleration includes one of an electron accelerator electron source and a heavily charged particle source.

Further, the neutron source includes one of an isotope neutron source, an accelerator neutron source and a reactor neutron source.

In the step (3), the irradiation dose is 10-100KGy, and the radiation dose is preferably 10-30KGy due to the radiation resistance and due effectiveness of the diaphragm base material.

The second technical solution of the present invention is the application of the boron-containing modified separator in the lithium ion secondary battery.

The third technical solution of the present invention is a lithium battery, which includes a positive electrode material and a negative electrode material, and the boron-containing modified separator is arranged between the positive electrode material and the negative electrode material.

Generally, the positive electrode active material involved in the positive electrode material can be reversibly occluded and released (intercalated and deintercalated) lithium ions

_{Lithium -} containing composite _oxides , _{spinel -} like oxides, Layered structure of metal chalcogenides, olivine structure, etc.

The positive electrode active material may specifically be 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 oxides, etc. Nickel composite oxides, lithium manganese nickel cobalt composite oxides, and materials with LiMPO ₄ (M=Fe, Mn, Ni) olivine crystal structure.

It is preferable to use a lithium-containing composite oxide with a layered structure or a spinel-like structure as the positive electrode active material, and lithium represented by LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1/2 Mn _1/2 O ₂ , etc. Manganese-nickel composite oxides, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ , etc., represented by lithium-manganese-nickel-cobalt composite oxides, or LiNi _1-xyz Co _x A _y Lithium-containing composite oxides such as Mg _z O ₂ (wherein, 0≤x≤1, 0≤y≤0.1, 0≤z≤0.1, and 0≤1-xyz≤1). In addition, a part of the constituent elements in the above-mentioned lithium-containing composite oxides also include lithium-containing composite oxides and the like substituted with additive elements such as Ge, Ti, Zr, Mg, Al, Mo, Sn, and the like.

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

For forming a positive electrode of a non-aqueous electrolyte secondary battery, for example, a conductive aid such as carbon black and acetylene black, or a binder such as polyvinylidene fluoride and polyethylene oxide are appropriately added to the above-mentioned positive electrode active material, A positive electrode mixture is prepared, and it is used by coating it on a strip-shaped molded body having a current collector such as aluminum foil as a core material. However, the manufacturing method of the positive electrode is not limited to the above example.

Commonly used negative electrode materials for lithium ion batteries can be used in the present invention. As the negative electrode active material related to the negative electrode, a compound capable of intercalating and deintercalating lithium metal and lithium can be used. For example, various materials such as alloys or oxides of aluminum, silicon, tin, and the like, carbon materials, and the like 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 bodies of organic polymer compounds, mesocarbon beads, and the like.

For forming the negative electrode of the non-aqueous electrolyte secondary battery, for example, a conductive aid such as carbon black and acetylene black, or a binder such as polyvinylidene fluoride and polyethylene oxide, etc. are appropriately added to the above-mentioned negative electrode active material, A negative electrode mixture is prepared and used after being coated on a belt-shaped molded body having a current collector such as copper foil as a core material. However, the manufacturing method of the negative electrode is not limited to the above example.

In the non-aqueous electrolyte secondary battery provided by the present invention, a non-aqueous solvent (organic solvent) is used as the non-aqueous electrolyte. Nonaqueous 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, thioesters (ethylene glycol sulfide, etc.) )Wait. Examples of the chain carbonate include low-viscosity polar chain carbonates represented by dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and aliphatic branched-chain carbonate-based compounds. A mixed solvent of cyclic carbonate (especially ethylene carbonate) and chain carbonate is particularly preferable. As ethers, dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1, 3-dioxolane (DOL), etc. are mentioned.

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

In addition, a fluorine-based solvent can also be used. Examples of the fluorine-based solvent 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 linear (perfluoroalkyl) alkyl ethers, that is, 2-tris Fluoromethyl hexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ether, 2-trifluoromethyl hexafluoropropyl propyl ether, 3-trifluoromethyl octafluorobutyl methyl ether, 3-trifluoro Methyl octafluorobutyl ether, 3-trifluoromethyl octafluorobutyl propyl ether, 4-trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ether, 4-trifluoro Methyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl dodecafluorohexyl ethyl ether, 5-trifluoromethyl dodecafluorohexyl propyl ether, 6-trifluoromethyl Fluoromethyl tetrafluoroheptyl methyl ether, 6-trifluoromethyl tetrafluoroheptyl ethyl ether, 6-trifluoromethyl tetrafluoroheptyl propyl ether, 7-trifluoromethyl hexafluorooctyl methyl ether ether, 7-trifluoromethyl hexafluorooctyl ether, 7-trifluoromethyl hexafluorooctyl propyl ether, etc.

Moreover, the said iso(perfluoroalkyl) alkyl ether and the (perfluoroalkyl) alkyl ether of the said linear structure can also be used together.

As the electrolyte salt used in the non-aqueous electrolyte solution, lithium salts such as lithium perchlorate, organoboron lithium salt, lithium salt of a 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), and the like. Among these lithium salts, fluorine-containing organolithium salts are particularly preferred. Fluorine-containing organic lithium salts are easily soluble in non-aqueous electrolytes 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 0.3 mol/L (mol/L) or more, more preferably 0.7 mol/L or more, preferably 1.7 mol/L or less, more preferably 1.2 mol/L or less . When the concentration of the electrolyte lithium salt is too low, the ion conductivity is too low, and when it is too high, there is a fear of precipitation of the electrolyte salt that is not completely dissolved.

In addition, various additives capable of improving the performance of a battery using the non-aqueous electrolyte may be added, and are not particularly limited.

The fourth technical solution of the present invention is a preparation method of a boron-containing modified diaphragm, which specifically includes the following steps:

(1) Preparation of boron-containing compound organic solution: adding boron-containing compound to an organic solvent outside the irradiation field, and stirring at a speed of 450-550r/min for 5.5-6.5h to obtain a boron-containing compound with a mass fraction of 10-100% The organic solution of the compound; wherein, when the organic solvent content is 0, a boron-containing compound with a mass fraction of 100% is obtained.

(2) Cleaning and drying of the diaphragm substrate: cleaning the diaphragm substrate with acetone and drying at 55-65°C for 5.5-6.5h;

(3) adopt one of co-irradiation grafting reaction, pre-irradiation grafting reaction and peroxidation grafting reaction to carry out irradiation grafting, and the irradiation dose is 10-100KGy;

(4) Cleaning and drying after irradiation and grafting: The modified diaphragm obtained in step (3) is cleaned with ethanol, dried at 55-65° C. for 5.5-6.5 h, and the modified diaphragm containing boron is obtained after drying.

The co-irradiation grafting method is as follows: soak the diaphragm substrate treated in step (2) in an organic solution containing a boron compound and seal it, and pass in the inert gas argon to remove the dissolved oxygen therein (polymerization inhibition) , and then the co-irradiation grafting reaction was carried out by a radiation source.

The pre-irradiation grafting method is: pre-irradiating the diaphragm substrate treated in step (2) under an argon atmosphere, and then placing it in an organic solution containing a boron compound to carry out a graft reaction;

The peroxidation method is as follows: pre-irradiating the diaphragm substrate treated in step (2) under an oxygen atmosphere, and then placing it in an organic solution containing a boron compound to carry out a grafting reaction.

The boron-containing compound has an unsaturated bond group and the boron atom is sp2 hybridized to form a covalent molecule.

The organic solvent for dissolving boron-containing compounds is some small molecule alcohols, for example, methanol, ethanol, isopropanol, ethylpropanol, n-butanol, isobutanol, tert-butanol, etc.; or other small molecule solvents such as Acetone, chloroform, ethyl acetate, etc.

The technical solution has the following beneficial effects:

1. The present invention introduces boron element with electron-deficient effect in the diaphragm base material, and the electron-deficient effect of boron will interact with anions in the electrolyte, thereby promoting the dissociation of lithium salts, fixing anions, and improving lithium ion migration numbers; The lithium ion migration number of the invention is obviously higher than that of the common polyethylene separator, and the energy efficiency of the battery is effectively improved.

2. The present invention can directly introduce boron element into the porous diaphragm through the irradiation grafting method, the process operation is simple, no additional process is required, and it is favorable for commercial production. In addition, the radiation grafting method uses high-energy radiation to generate active sites (free radicals or ions) in the polymer, and then initiates the graft polymerization of monomers from the active sites. Compared with the common chemical grafting method, the irradiation grafting method has obvious advantages. This is because the interaction between the material and the ray produces various active particles such as free radicals and positive and negative ions. Since the energy absorption is independent of temperature, it is also related to the temperature. The molecular structure is irrelevant, so the substance can be uniformly "activated" by radiation, and the same can be achieved for substances with high chemical stability, which cannot be achieved by the usual chemical grafting method.

Description of drawings

The present invention will be further described below with reference to the accompanying drawings and embodiments.

FIG. 1 is the infrared spectrum of the modified diaphragm and the common commercial polyolefin diaphragm used in Examples 1-3.

Figures 2a and 2b are the SEM photos of the plane and the cross-section of the modified polyethylene separator and the elemental analysis photos of the energy dispersive spectrometer;

Figure 3 shows the actual amount of borane contained in Examples 1-3 measured by thermogravimetric analysis.

4a-4k are the AC impedance spectra and the steady-state current graphs of the lithium ion migration number measured by the steady-state amperometric method in Comparative Example 1 and Examples 11-20.

5 is a comparison curve of the rate performance of the battery of Example 21 using the modified separator of the present invention and the battery of Comparative Example 2 using the ordinary polyethylene separator.

FIG. 6 is a comparison of the cycle performance of the batteries obtained in Example 21 and Comparative Example 2. FIG.

Detailed ways

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

Example 1

A boron-containing modified separator was prepared: 10 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 90 g of In water ethanol, the ethanol solution of borane with a mass fraction of 10% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene (PE) membrane was washed with acetone and dried at 60° C. for 6 h, then the polyethylene membrane was immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein was removed by inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Example 2

A boron-containing modified diaphragm was prepared: 20 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 80 g of In water ethanol, the ethanol solution of borane with a mass fraction of 20% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene septum was washed with acetone and dried at 60 °C for 6 h. The polyethylene membrane was then immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein was removed by passing through the inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Example 3

A boron-containing modified diaphragm was prepared: 30 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 70 g of In water ethanol, the ethanol solution of borane with a mass fraction of 30% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene septum was washed with acetone and dried at 60 °C for 6 h. The polyethylene membrane is then immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein is removed by passing through the inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Fig. 1 is the infrared spectrogram of the modified polyethylene separator prepared in Examples 1-3 and the common commercialized polyethylene separator. Compared with the common commercial polyethylene diaphragm, the modified polyethylene diaphragm has three distinct characteristic peaks, one is the stretching vibration peak of -CH ₃ at 1370 cm ^-1 ; the other is the BO stretching vibration peak at 1310 cm ^-1 ; One is the stretching vibration peak of CO at 1150 cm ^-1 . Moreover, there is no C=C peak near 1650 cm ^-1 , which can be judged that borane has been successfully grafted onto the polyethylene separator. It can also be seen from the infrared spectrum that with the increase of borane concentration, the peaks and peaks of stretching vibrations of -CH ₃ , BO and CO increase gradually, and the grafted proportions also increase gradually.

Figures 2a and 2b are the scanning electron microscope photos of the plane and the cross-section of the modified polyethylene separator and the photos of elemental analysis by energy dispersive spectrometer, respectively. It can be seen from Figure 2a that the elements C, O, and B are uniformly distributed on the surface of the polyolefin diaphragm. From Figure 2b, it can be seen that C, O, and B are uniformly distributed on the cross section of the polyolefin diaphragm. From this, it can be determined that boron The alkanes were successfully grafted on the ion transport channel.

Figure 3 shows the actual amount of borane contained in Examples 1-3 measured by thermogravimetric analysis. It can be clearly seen from the results in Figure 3 that compared with the original unmodified separator, the separator after grafting borane begins to lose weight at about 200 °C, and before reaching the temperature at which the separator itself decomposes, Examples 1-3 The weight loss is about 2.1%, 4.1% and 7.9% respectively, which is the mass of the actual grafted borane.

Example 4

A boron-containing modified diaphragm was prepared: 20 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 80 g of In water ethanol, the ethanol solution of borane with a mass fraction of 20% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene membrane was washed with acetone and dried at 60 °C for 6 h. The polyethylene membrane was then immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein was removed by passing through the inert gas argon (polymerization inhibition). It was placed in the radiation field and irradiated with γ-rays, and the irradiation dose was 30kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Example 5

A boron-containing modified diaphragm was prepared: 20 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 80 g of In water ethanol, the ethanol solution of borane with a mass fraction of 20% was obtained after stirring at a speed of 500 r/min for 6 h. The polyvinylidene fluoride-hexafluoropropylene film was washed with acetone and dried at 60 °C for 6 h. It is then immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein is removed by passing through the inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 h, and the modified polyvinylidene fluoride-hexafluoropropylene film was obtained after drying.

Example 6

Preparation of a boron-containing modified diaphragm: adding 20 g of vinylboronic acid 2-methyl-2,4-pentanediol to 80 g of absolute ethanol outside the radiation field, and stirring at a speed of 500 r/min for 6 h to obtain 20% ethanol solution of borate ester. The polyethylene septum was washed with acetone and dried at 60 °C for 6 h. The polyethylene membrane was then immersed in an ethanolic solution of borane and sealed, and the dissolved oxygen therein was removed by passing through the inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Example 7

A boron-containing modified diaphragm was prepared: 20 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 80 g of In water ethanol, the ethanol solution of borane with a mass fraction of 20% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene diaphragm was washed with acetone and dried at 60° C. for 6 hours, then the polyethylene diaphragm was soaked in an ethanol solution of borane and sealed, and the dissolved oxygen therein was removed by passing in inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 100kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Example 8

Preparation of a boron-containing modified diaphragm: outside the radiation field, the polyethylene diaphragm was washed with acetone and dried at 60 °C for 6 h, and then the polyethylene diaphragm was placed in 4,4,5,5-tetramethyl-2- It is soaked in vinyl-1,3,2-dioxaborane and sealed, and the dissolved oxygen therein is removed by passing in inert gas argon (polymerization inhibition). It was placed in a radiation field and irradiated with γ-rays at a dose of 10kGy. After irradiation, the irradiated polyethylene membrane was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers. Then, it was dried at 60° C. for 6 hours, and the modified polyolefin membrane was obtained after drying.

Examples 1-8 The radiation grafting method used in the preparation of a boron-containing modified diaphragm is a co-radiation grafting method.

Example 9

A boron-containing modified diaphragm was prepared: 20 g of 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborane was added to 80 g of In water ethanol, the ethanol solution of borane with a mass fraction of 20% was obtained after stirring at a speed of 500 r/min for 6 h. The polyethylene septum was washed with acetone and dried at 60 °C for 6 h. Then, the polyethylene diaphragm was placed in the radiation field under the atmosphere of argon preservation and pre-irradiated with γ-rays, and the irradiation dose was 10 kGy. After the irradiation, the pre-irradiated polyethylene diaphragm was immersed in an ethanol solution of borate ester, and heated at 60 °C for 12 h. The polyethylene diaphragm after the grafting reaction was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers, and then dried at 60°C for 6 hours, and the modified polyolefin diaphragm was obtained after drying. The irradiation grafting method adopted in this embodiment is a pre-irradiation grafting method.

Example 10

Preparation of a boron-containing modified diaphragm: add 20 g of vinylboronic acid 2-methyl-2,4-pentanediol to 80 g of absolute ethanol outside the radiation field, and stir at a speed of 500 r/min for 6 h to obtain 20% ethanol solution of borate ester. The polyvinylidene fluoride-hexafluoropropylene was washed with acetone and dried at 60 °C for 6 h. Then, the polyethylene diaphragm was placed in a radiation field under an atmosphere of oxygen preservation and pre-irradiated with gamma rays, and the irradiation dose was 10 kGy. After the irradiation, the pre-irradiated polyethylene diaphragm was immersed in an ethanol solution of borate ester, and heated at 60 °C for 12 h. The polyethylene diaphragm after the grafting reaction was rinsed with a large amount of ethanol to remove unreacted monomers and homopolymers, and then dried at 60°C for 6 hours, and the modified polyolefin diaphragm was obtained after drying. The radiation grafting method used in this example is the peroxide method.

Example 11

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 1 is placed between the two metal lithium sheets.

Example 12

A simulated battery, comprising two metal lithium sheets, with the modified polyethylene separator prepared in Example 2 between the two metal lithium sheets.

Example 13

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 3 is located between the two metal lithium sheets.

Example 14

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 4 is located between the two metal lithium sheets.

Example 15

A simulated battery, comprising two metal lithium sheets, with the modified polyethylene separator prepared in Example 5 between the two metal lithium sheets.

Example 16

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 6 is located between the two metal lithium sheets.

Example 17

A simulated battery, comprising two metal lithium sheets, with the modified polyethylene separator prepared in Example 7 between the two metal lithium sheets.

Example 18

A simulated battery, comprising two metal lithium sheets, with the modified polyethylene separator prepared in Example 8 between the two metal lithium sheets.

Example 19

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 9 is arranged between the two metal lithium sheets.

Example 20

A simulated battery includes two metal lithium sheets, and the modified polyethylene separator prepared in Example 10 is placed between the two metal lithium sheets.

Comparative Example 1

A simulated battery consisting of two metal lithium sheets with a common commercial polyethylene separator between the two metal lithium sheets.

Lithium ion migration numbers of Examples 11-20 and Comparative Example 1 were tested by the steady state amperometric method. As shown in Fig. 4a, the lithium ion migration number of Comparative Example 1 was measured to be 0.17. As shown in Figures 4b-4k, the measured lithium ion migration numbers of Examples 11-20 were 0.32, 0.55, 0.47, 0.50, 0.44, 0.51, 0.38, 0.37, 0.41, and 0.40, respectively. It can be seen from the test results that the lithium ion migration number of the separator modified by the present invention is significantly higher than that of the ordinary polyethylene separator. The increase of the lithium ion migration number can avoid the concentration polarization of the electrolyte salt, prevent the formation of lithium dendrites, and at the same time can effectively improve the energy efficiency of the battery. Fig. 4h and Fig. 4i are the test results of Examples 17 and 18, respectively. From the test results, it can be seen that the method of irradiation graft modified diaphragm adopted in the present invention is also suitable for higher irradiation dose and higher borane concentration. The same applies. Fig. 4j and Fig. 4k are the test results of Examples 19 and 20, respectively. It can be seen from the test results that the pre-irradiation graft modification and the peroxidation graft modification method adopted in the present invention are equally applicable to the preparation of boron-containing modification. diaphragm.

Example 21

A battery includes a positive electrode material and a negative electrode material, and there is the modified polyethylene separator prepared in Example 2 between the positive electrode material and the negative electrode material.

Comparative Example 2

A battery includes a positive electrode material and a negative electrode material with a common commercial polyethylene separator between the positive electrode material and the negative electrode material.

The rate performance of the battery obtained in Example 21 and Comparative Example 2 was tested, as shown in FIG. 5 . It can be seen that due to the introduction of boron-containing borane, the modified separator obtained by using the present invention significantly increases the lithium ion migration number and realizes the rapid conduction of lithium ions. Therefore, the battery using this modified separator can be improved at high currents. Rate performance under charge and discharge conditions.

The cycle performances of the batteries obtained in Example 21 and Comparative Example 2 were tested, as shown in FIG. 6 . It can be seen that the cycle performance of the battery using the modified separator obtained by the present invention is significantly improved compared to the battery cycle performance using the conventional separator in the prior art.

Example 22

A battery includes a positive electrode material and a negative electrode material, and there is the modified separator prepared in Example 1 between the positive electrode material and the negative electrode material.

Example 23

A battery includes a positive electrode material and a negative electrode material, and there is the modified separator prepared in Example 3 between the positive electrode material and the negative electrode material.

Example 24

A battery includes a positive electrode material and a negative electrode material, and there is the modified separator prepared in Example 4 between the positive electrode material and the negative electrode material.

The above is only for the purpose of illustration, so the scope of implementation of the present invention cannot be limited accordingly, that is, the modifications made according to the scope of the patent of the present invention and the contents of the description should still fall within the scope of the present invention.

Industrial Applicability

The invention discloses a boron-containing modified diaphragm, a preparation method and application thereof, and a battery containing the diaphragm. The modified diaphragm grafts a boron element with electron-deficient effect to the surface of the diaphragm substrate through irradiation and grafting. made in the holes. The invention adopts the irradiation in-situ grafting technology, utilizes the high specific energy of the rays generated by the radiation source, and on the basis of ensuring the original basic characteristics and morphology of the porous membrane as much as possible, through the in-situ grafting to uniformize the boron-containing compound On the one hand, it can improve the lithium ion migration number, thereby improving the energy efficiency of lithium ion secondary batteries. Modified separators offer commercialization prospects with industrial applicability.

Claims (14)

1. A boron-containing modified diaphragm is characterized in that: the modified diaphragm is prepared by grafting the boron element with electron-deficient effect into the surface and holes of the diaphragm base material by irradiation grafting technology.
2. The boron-containing modified diaphragm according to claim 1, wherein the boron element is derived from a boron-containing compound having an unsaturated bond group and a covalent molecule formed by sp2 hybridization of boron atoms.
3. The boron-containing modified diaphragm according to claim 1, wherein the boron-containing compound having an unsaturated bond group and a covalent molecule formed by sp2 hybridization of boron atoms comprises 4, 4, 5 ,5-Tetramethyl-2-vinyl-1,3,2-dioxolane, 2-methyl-2,4-pentanediol vinylboronic acid, methylimino vinylboronic acid One or more of diacetate and dibutyl vinylborate.
4. A boron-containing modified diaphragm according to claim 1, wherein the method of the irradiation grafting is one of a pre-irradiation grafting method, a co-irradiation grafting method and a peroxidation method.
5. The boron-containing modified diaphragm according to claim 1, wherein the irradiation dose of the irradiation graft is 10-100KGy.
6. Application of the boron-containing modified separator according to any one of claims 1-5 in a lithium ion secondary battery.
7. A battery, comprising a positive electrode material and a negative electrode material, is characterized in that: the boron-containing modified separator according to any one of claims 1-5 is arranged between the positive electrode material and the negative electrode material.
8. A method for preparing a boron-containing modified diaphragm, comprising the steps of:

   (1) Preparation of boron-containing compound organic solution: adding the boron-containing compound to the organic solvent, and stirring at a speed of 450-550r/min for 5.5-6.5h to obtain an organic solution with a mass fraction of 10-100% boron-containing compound;

   (2) Cleaning and drying the diaphragm substrate: wash the diaphragm substrate with acetone and dry at 55-65°C for 5.5-6.5h;

   (3) adopt one of co-irradiation grafting method, pre-irradiation grafting method and peroxidation method to carry out irradiation grafting, and the irradiation dose is 10-100KGy;

   (4) Cleaning and drying after irradiation and grafting: The modified diaphragm obtained in step (3) is cleaned with ethanol, dried at 55-65° C. for 5.5-6.5 hours, and the modified diaphragm containing boron is obtained after drying.
9. A kind of preparation method of boron-containing modified diaphragm according to claim 8, is characterized in that:

   The co-irradiation grafting method is as follows: placing the diaphragm substrate treated in step (2) in an organic solution containing a boron compound, and co-irradiating with a radiation source;

   Described pre-irradiation grafting method is: carry out pre-irradiation under the argon atmosphere by the membrane base material processed in step (2), then it is placed in the organic solution of boron-containing compound to carry out grafting reaction;

   The peroxidation method is as follows: pre-irradiating the diaphragm substrate treated in step (2) under an oxygen atmosphere, and then placing it in an organic solution containing a boron compound to carry out a grafting reaction.
10. The method for preparing a boron-containing modified diaphragm according to claim 8, wherein the boron-containing compound has an unsaturated bond group and the boron atom is sp2 hybridized to form a covalent molecule.
11. A separator for lithium batteries is characterized in that the separator contains boron element.
12. A separator for lithium batteries according to claim 11, characterized in that the boron-containing compound in the covalent molecule formed by the unsaturated bond group and the boron atom by sp2 hybridization is 4,4, 5,5-Tetramethyl-2-vinyl-1,3,2-dioxaborane, 2-methyl-2,4-pentanediol vinylboronic acid, methylidene vinylboronic acid One or more of aminodiacetate and dibutyl vinylborate.
13. A separator for lithium batteries according to claim 12, characterized in that the modified separator is prepared by grafting boron element with electron-deficient effect into the separator substrate by irradiation grafting technology.
14. A separator for lithium batteries according to claim 11, characterized in that the separator is a polyolefin-based porous polymer film polyethylene or polypropylene single-layer or multi-layer composite film, non-woven fabric and polyoxyethylene Ethylene, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol and polyimide, and blends and copolymers derived from the above polymer materials one or more of.

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