阅读说明：本技术 氮化硼涂覆的电池隔膜及其制备方法 (Boron nitride coated battery separator and method of making same ) 是由 陶晶 王志豪 王思双 陈瀚 于 2019-10-21 设计创作，主要内容包括：本发明公开了一种氮化硼涂覆的电池隔膜及其制备方法；所述电池隔膜包括基膜和涂覆于基膜单侧或双侧的氮化硼涂层,所述氮化硼涂层含有偶联剂接枝的氮化硼粉体。本发明采用在氮化硼粉体表面接枝偶联剂的方式,将氮化硼表面有机化,提高了氮化硼粉体与基膜界面亲和力,提高了涂层质量,进而改善了隔膜与电解液的浸润性；另外,在离子传输过程中,与偶联剂有机官能团亲和性高的离子更易于穿过其表面形成的孔道,因此本发明还同时提高了隔膜的离子电导率。(The invention discloses a boron nitride coated battery diaphragm and a preparation method thereof; the battery diaphragm comprises a base film and a boron nitride coating coated on one side or two sides of the base film, wherein the boron nitride coating contains coupling agent grafted boron nitride powder. According to the invention, the coupling agent is grafted on the surface of the boron nitride powder, so that the surface of the boron nitride is organized, the interfacial affinity of the boron nitride powder and a base film is improved, the coating quality is improved, and the wettability of a diaphragm and electrolyte is improved; in addition, in the ion transmission process, ions with high affinity with organic functional groups of the coupling agent can more easily penetrate through the pore channels formed on the surface of the ions, so that the ion conductivity of the diaphragm is improved simultaneously.)

1. A boron nitride coated battery separator comprises a base film and a boron nitride coating coated on one side or both sides of the base film, and is characterized in that: the boron nitride coating contains coupling agent grafted boron nitride powder.

2. The boron nitride coated battery separator of claim 1, wherein: the base film is a polyethylene film, a polypropylene film or a polyethylene and polypropylene composite film with the thickness of 5-40 mu m and the porosity of 30-80%.

3. The boron nitride coated battery separator of claim 1, wherein: the particle size of the boron nitride powder is 0.5-2 μm, and the thickness of the boron nitride coating is 0.5-5 μm.

4. The boron nitride coated battery separator of claim 1, wherein: the coupling agent comprises one or more of silane coupling agent, titanate coupling agent and perfluoro phenyl azide, and the mass ratio of the coupling agent to boron nitride is 1-10: 100.

5. The boron nitride coated battery separator according to any of claims 1 to 4, wherein: the boron nitride coating also contains alumina particles, and the mass ratio of the alumina particles to the boron nitride powder is 1-5: 5-9.

6. The method of making a boron nitride coated battery separator according to any of claims 1 to 5, wherein: the method comprises the following steps:

(1) mixing boron nitride powder with a coupling agent for a grafting reaction to prepare coupling agent grafted boron nitride powder;

(2) adding an auxiliary agent into the coupling agent grafted boron nitride powder prepared in the step (1), and mixing to prepare boron nitride coating slurry;

(3) conveying the base film into a coating device, and coating by using the boron nitride coating slurry prepared in the step (2);

(4) and (4) drying and rolling the battery diaphragm coated in the step (3) to obtain a finished product of the battery diaphragm coated with boron nitride.

7. The method of making a boron nitride coated battery separator according to claim 6, wherein: in the step (1), the specific steps of mixing the boron nitride powder and the coupling agent for grafting reaction are as follows: mixing and stirring boron nitride powder and a silane coupling agent or a titanate coupling agent, adding an initiator, and carrying out grafting reaction under an ice bath condition to obtain coupling agent grafted boron nitride powder; or mixing and stirring the boron nitride powder and the perfluorophenyl azide, and carrying out grafting reaction under the ultraviolet radiation condition to obtain the coupling agent grafted boron nitride powder.

8. The method of making a boron nitride coated battery separator according to claim 6, wherein: in the step (1), the boron nitride powder and the alumina particles are mixed according to a proportion and then mixed with a coupling agent for grafting reaction.

9. The method of making a boron nitride coated battery separator according to claim 6, 7 or 8, wherein: the boron nitride coating slurry is an aqueous slurry dispersed in water.

Technical Field

The invention belongs to the field of lithium battery diaphragm materials, and particularly relates to a boron nitride coated battery diaphragm and a preparation method thereof.

Background

The diaphragm is used as a third electrode which is an important component of the lithium ion battery, and the quality of the diaphragm directly influences the capacity, internal resistance, service life and safety performance of the battery. The diaphragm mainly plays two roles in the battery, firstly, the positive electrode and the negative electrode of the battery are separated, the direct contact of positive and negative electrode materials is avoided, and the internal short circuit is prevented; and secondly, the lithium ion migration channel is used for ensuring that the lithium ions freely move between the positive electrode and the negative electrode. In terms of the two roles that a battery separator plays, it is required that it must satisfy the following requirements: the diaphragm must have electrochemical insulation to ensure effective isolation of the positive electrode and the negative electrode; the diaphragm must have certain aperture and aperture distribution, so as to ensure excellent permeability to ions; the diaphragm must have electrochemical stability and can resist electrolyte corrosion; the diaphragm has good wettability to the electrolyte, so that good liquid absorption capacity is ensured, and low internal resistance and high ionic conductivity are achieved; the diaphragm must have certain mechanical property, and the thickness of the diaphragm is also as small as possible along with the development of high energy density of the battery; the separator must have a certain thermodynamic stability to ensure the normal operation of the battery during the heat release of the charge-discharge reaction.

Because the polyolefin has stable chemical properties, higher mechanical strength and easy continuous production, the lithium ion battery diaphragm which is most used in the market at present is still a polyolefin diaphragm or a coating diaphragm which takes the polyolefin diaphragm as a base material. However, polyolefin is a non-polar material, and the electrolyte is composed of a polar organic solvent, so that the affinity between the polyolefin diaphragm and the electrolyte is insufficient, and on the other hand, the polyolefin diaphragm is limited by the performance of the polyolefin material, the thermal stability is poor, and the diaphragm shrinks due to heating in the operation process of the battery, so that the positive electrode and the negative electrode are short-circuited, the battery explodes, and the safety problem is caused. The ceramic coating process overcomes the defect of poor thermal stability of the polyolefin diaphragm, improves the wettability and puncture resistance of the diaphragm and electrolyte, and has comprehensively advanced the polyolefin diaphragm in performance. However, the ceramic coating can increase the thickness of the diaphragm and increase the internal resistance of the battery, so that the energy density of the battery is reduced, meanwhile, the interface intermiscibility of organic and inorganic materials of the ceramic composite diaphragm is poor, so that the problem of powder falling of the ceramic diaphragm is serious, and the heat resistance of the diaphragm is not obviously improved if the ceramic coating is not compact, but if the ceramic coating is too compact, the pores are blocked, so that the cycle performance and the rate performance of the battery are poor.

Based on the problems faced by the current polyolefin diaphragm and ceramic coating diaphragm, the diaphragm with an excellent coating needs to be developed urgently, the safety problem of the battery is solved, and meanwhile, the chemical stability of the lithium ion battery is ensured, the ionic conductivity is improved, and the cycle life is prolonged. Boron nitride is a material with no toxicity, high temperature resistance, corrosion resistance, high heat conductivity, high insulation and excellent performance, and consists of nitrogen atoms and boron atoms, wherein the chemical composition of the boron nitride is 43.6 percent of boron and 56.4 percent of nitrogen. Boron nitride is classified into hexagonal boron nitride, cubic boron nitride, and wurtzite boron nitride according to crystal form, wherein hexagonal boron nitride is the most common boron-nitrogen compound, has a graphite-like layered structure, and is in a bulk state. The hexagonal boron nitride has good electrical insulation, the dielectric constant is 4, and the hexagonal boron nitride has excellent thermal conductivity, is the material with the best thermal conductivity in ceramic materials, has stable chemical properties and no obvious melting point, and has the same expansion coefficient as quartz. Therefore, the boron nitride is taken as the lithium ion battery diaphragm coating material, and is a preferable scheme for solving the problems of poor safety, unstable cycle performance and the like of the diaphragm coated by ceramics such as alumina and the like in the prior art.

As boron nitride coating techniques for improving the overall performance of polyolefin and alumina ceramic coated membranes, for example, patent No. cn201410853236.x and patent No. CN201910317564.0 are known.

Patent CN201410853236.X discloses a diaphragm with an active nano boron nitride coating, wherein a polyolefin film and the active nano boron nitride coating coated on a base layer are adopted as a base material, so that the diaphragm has excellent heat resistance and mechanical properties, and has better liquid absorption/retention capacity and ion conductivity than the diaphragm with a traditional alumina coating. However, in the examples of this technique, there are disadvantages in terms of quality that the boron nitride powder cannot be sufficiently dispersed and easily settled by dispersing the dimethyl silicon oil with NMP as a solvent and using PVDF as a binder, and that the boron nitride cannot be sufficiently contacted due to poor adhesion of PVDF, resulting in a decrease in coating quality.

Patent CN201910317564.0 discloses a preparation method of a hexagonal boron nitride ceramic mixed coating diaphragm, which comprises the steps of firstly dispersing boron nitride in deionized water for wetting and standby, adding a dispersant into polyvinylidene fluoride for dispersing, then grinding to form a pre-dispersion liquid for standby, then dispersing and stirring the wetted hexagonal boron nitride ceramic powder, the dispersant and the deionized water, then adding the pre-dispersion liquid for continuous stirring, adding a binder for stirring to obtain a mixed coating slurry dispersion liquid, and finally coating the mixed coating slurry dispersion liquid on a cut lithium ion battery diaphragm and drying to obtain the high-performance lithium ion battery mixed coating diaphragm. Although the technology adopts a water-based slurry system, the technology is more environment-friendly, but the coating slurry is prepared by using a mixing mode of organic/inorganic materials such as boron nitride and polyvinylidene fluoride, the dispersion uniformity of the slurry is difficult to achieve, and the uniformity of the coating quality is improved.

Disclosure of Invention

In view of the above, the present invention provides a boron nitride coated battery separator and a preparation method thereof, which can increase the interfacial affinity between boron nitride powder and a base film, improve the coating quality, improve the wettability between the separator and an electrolyte, and simultaneously improve the ionic conductivity.

In order to achieve the purpose, the invention provides the following technical scheme:

the invention provides a boron nitride coated battery diaphragm which comprises a base film and a boron nitride coating coated on one side or two sides of the base film, wherein the boron nitride coating contains coupling agent grafted boron nitride powder.

As a preferable technical scheme, the base film is a polyethylene film, a polypropylene film or a polyethylene and polypropylene composite film with the thickness of 5-40 μm and the porosity of 30-80%.

As a preferable technical scheme, the particle size of the boron nitride powder is 0.5-2 μm, and the thickness of the boron nitride coating is 0.5-5 μm.

As a preferable technical scheme, the coupling agent comprises one or more of a silane coupling agent, a titanate coupling agent and a perfluoro phenyl azide, and the mass ratio of the coupling agent to boron nitride is 1-10: 100.

As a preferable technical scheme, the boron nitride coating further contains alumina particles, and the mass ratio of the alumina particles to the boron nitride powder is 1-5: 5-9.

The invention also provides a preparation method of the boron nitride coated battery diaphragm, which comprises the following steps:

(1) mixing boron nitride powder with a coupling agent for a grafting reaction to prepare coupling agent grafted boron nitride powder;

(2) adding an auxiliary agent into the coupling agent grafted boron nitride powder prepared in the step (1), and mixing to prepare boron nitride coating slurry;

(3) conveying the base film into a coating device, and coating by using the boron nitride coating slurry prepared in the step (2);

(4) and (4) drying and rolling the battery diaphragm coated in the step (3) to obtain a finished product of the battery diaphragm coated with boron nitride.

As a preferred technical scheme, in the step (1), the specific steps of mixing the boron nitride powder and the coupling agent for grafting reaction are as follows: mixing and stirring boron nitride powder and a silane coupling agent or a titanate coupling agent, adding an initiator, and carrying out grafting reaction under an ice bath condition to obtain coupling agent grafted boron nitride powder; or mixing and stirring the boron nitride powder and the perfluorophenyl azide, and carrying out grafting reaction under the ultraviolet radiation condition to obtain the coupling agent grafted boron nitride powder.

As a preferable technical scheme, in the step (1), the boron nitride powder and the alumina particles are mixed according to a certain proportion and then mixed with a coupling agent for grafting reaction.

As a preferable embodiment, the boron nitride coating slurry is an aqueous slurry dispersed in water.

The invention has the beneficial effects that:

according to the invention, the coupling agent is grafted on the surface of the boron nitride powder, so that the surface of the boron nitride is organized, the interfacial affinity of the boron nitride powder and a base film is improved, the coating quality is improved, and the wettability of a diaphragm and electrolyte is improved; in addition, in the ion transmission process, ions with high affinity with organic functional groups of the coupling agent can more easily penetrate through the pore channels formed on the surface of the ions, so that the ion conductivity of the diaphragm is improved simultaneously.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is a schematic representation of coupling agent grafted boron nitride;

fig. 2 is a photograph of the membrane side of the boron nitride coated battery separator prepared in example 1.

Detailed Description

The present invention is further described with reference to the following drawings and specific examples so that those skilled in the art can better understand the present invention and can practice the present invention, but the examples are not intended to limit the present invention.