阅读说明：本技术 一种木浆纤维/纳米硫酸钡复合材料锂电池隔膜纸及制备方法 (Wood pulp fiber/nano barium sulfate composite material lithium battery diaphragm paper and preparation method thereof ) 是由 赵传山 李辉 李杰华 韩文佳 姜亦飞 于 2019-10-24 设计创作，主要内容包括：本发明涉及一种木浆纤维/纳米硫酸钡复合材料锂电池隔膜纸及其制备方法。本发明以木浆纤维为原料,采用高打浆度粘状打浆的方式,通过纸张制备工艺制备纤维基纸,将纳米纤维和纳米硫酸钡复合材料制备混合涂料,均匀的涂布于基纸两侧,并采用热压干燥的方式处理,再浸渍聚酰亚胺树脂溶液后,干燥制得锂电池隔膜纸。本发明的制备工艺成熟、方法简单,原料环保；以纳米纤维和纳米硫酸钡复合材料为涂层,填充隔膜基纸较大孔径,同时具有良好的润湿性和高温稳定性；以聚酰亚胺树脂为隔膜外层,提高锂电池隔膜的长时间高温热稳定性。本发明制备的锂电池隔膜纸,材料新型环保,便于产业化生产。(The invention relates to wood pulp fiber/nano barium sulfate composite material lithium battery diaphragm paper and a preparation method thereof. The preparation method comprises the steps of taking wood pulp fibers as raw materials, preparing fiber base paper through a paper preparation process by adopting a high-beating-degree viscous beating mode, preparing mixed coating from nano fibers and nano barium sulfate composite materials, uniformly coating the mixed coating on two sides of the base paper, treating the coated base paper in a hot-pressing drying mode, impregnating polyimide resin solution, and drying to obtain the lithium battery diaphragm paper. The preparation process is mature, the method is simple, and the raw materials are environment-friendly; the composite material of the nano-fiber and the nano-barium sulfate is used as a coating, and the larger aperture of the diaphragm base paper is filled, so that the composite material has good wettability and high-temperature stability; the polyimide resin is used as the outer layer of the diaphragm, so that the long-time high-temperature thermal stability of the lithium battery diaphragm is improved. The lithium battery diaphragm paper prepared by the invention is novel and environment-friendly in material and convenient for industrial production.)

1. The preparation method of the lithium battery separator paper is characterized by comprising the following steps:

(1) the virgin wood pulp fiber pulp is subjected to disintegration and pulping to prepare high-pulping-degree fiber pulp, and the prepared fiber pulp is prepared into 25g/m quantitative pulp by adopting a paper preparation process²～35g/m²The fiber-based paper of (1);

(2) uniformly mixing the nano-fiber and the nano-barium sulfate composite material according to a certain proportion to prepare a mixed coating, uniformly coating the mixed coating on two sides of the fiber base paper in the step (1), and performing hot-pressing drying to prepare a semi-finished lithium battery diaphragm paper;

(3) and (3) dissolving the polyimide resin with a solvent to prepare a polyimide resin solution with the mass percentage concentration of 5-10%, soaking the semi-finished lithium battery separator paper obtained in the step (2) in the polyimide resin solution for 10-30 s, and drying to obtain the finished lithium battery separator paper.

2. The method for preparing lithium battery separator paper according to claim 1, wherein the wood pulp fiber slurry in the step (1) is bleached softwood fiber, bleached hardwood fiber, or a mixed fiber slurry of two fibers mixed in proportion, which are prepared by a chemical method, a semi-chemical method, or a chemical-mechanical method;

preferably, the pulping mode in the step (1) is a sticky pulping mode;

further preferably, the beating degree of the wood pulp fiber slurry in the step (1) is 70-90 DEG SR;

more preferably, the paper making process in the step (1) is a low basis weight high-tightness tissue paper making process.

3. The method for preparing lithium battery separator paper according to claim 1, wherein the nanofibers in step (2) are biomass nanofibers;

preferably, the biomass nanofibers comprise mechanically made nanofibers and/or chemically made nanofibers;

more preferably, the biomass nanofibers are softwood nanofibers, hardwood nanofibers and/or bacterial cellulose.

4. The preparation method of the lithium battery separator paper as claimed in claim 1, wherein in the step (2), the nano-fiber has a nano-scale size, a diameter of 20 to 50nm, an aspect ratio of 30 to 100: 1.

5. the method for preparing lithium battery separator paper as claimed in claim 1, wherein in the step (2), the nano barium sulfate composite material has a particle diameter size of nano level and a diameter of 20nm to 60 nm;

preferably, the nano barium sulfate composite material is prepared by any one or more than two methods of a grinding and grinding method, a chemical precipitation method, a micro-emulsion method, a super-heavy method or a micro-reactor method.

6. The method for preparing lithium battery separator paper as claimed in claim 1, wherein the mass percentage of the nano-fibers of the mixed coating in the step (2) is 30-70%, and the mass percentage of the nano-barium sulfate composite material is 30-70%.

7. The lithium battery of claim 1The preparation method of the pond diaphragm paper is characterized in that the coating weight of the mixed coating in the step (2) is 15g/m²～20g/m²The coating method is any one of gravure coating, slot coating, dip coating, spray coating, and spin coating.

8. The method for preparing lithium battery separator paper according to claim 1, wherein the hot-pressing drying in the step (2) is a hot-pressing drying mode of a hot press;

preferably, the hot pressing temperature is 100-130 ℃, and the hot pressing pressure is 3-5 MPa.

9. The method for preparing lithium battery separator paper according to claim 1, wherein the polyimide resin in step (3) is a soluble polyimide resin, and the solvent used is one or a mixture of two of strongly polar organic solvents DMA, DMF, NMP, dioxane, m-cresol, and chloroform.

10. The lithium battery separator paper prepared according to any one of claims 1 to 9, wherein the physical and chemical properties of the lithium battery separator paper are as follows: the quantitative ratio is 40-60 g/m²The pore diameter is 30 nm-100nm, the porosity is 40% -80%, the puncture strength is 300-600 gf, the contact angle of wetting liquid is 20-60 degrees, and the thermal shrinkage is less than 3% at the temperature of 200-300 ℃;

preferably, the heat shrinkage rate is less than 1.2% at 200 ℃ and less than 3% at 300 ℃.

Technical Field

The invention relates to wood pulp fiber/nano barium sulfate composite lithium battery diaphragm paper and a preparation method thereof, in particular to wood pulp fiber/nano barium sulfate composite lithium battery diaphragm paper which is excellent in wettability, high in thermal stability, high in film strength, simple in process, environment-friendly and pollution-free and a preparation method thereof, belonging to the technical field of papermaking and batteries.

Background

With the rapid development of science and technology, the application of batteries is increasingly wide. Lithium batteries, because of their high energy density, stable cycling characteristics, low discharge rates and high operating voltages, have been successfully used in portable electronic devices such as mobile phones, computers and cameras, and are expected to be used in electric vehicles and energy storage systems. The lithium battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator and the like. The diaphragm is the most important part with the technical content in the lithium battery component, and the chemical performance of the diaphragm has very important influence on the cycle performance, rate capability and safety performance of the battery. The diaphragm is isolated between the positive electrode and the negative electrode so as to prevent the internal short circuit of the battery caused by the physical contact of the two electrodes, and meanwhile, an ion transmission channel is provided, so that the free transfer of lithium ions during the charge and discharge of the battery is realized, and the current is formed. The battery separator must have good uniformity and insulating properties, good mechanical strength, excellent electrolyte wettability and thermal stability.

Commercial separators currently used in lithium batteries are polyethylene separators, polypropylene separators, and composite separators thereof. Such separators have good chemical stability and mechanical strength and are widely used. However, such membranes have two inherent limitations: one is low porosity. The low porosity due to its semi-crystalline structure and melt-blown technology hinders the absorption of the liquid electrolyte by the separator, makes the separator have poor electrolyte wettability, results in low rate capability of the battery, and creates high ionic conduction resistance in the interfacial layers of the separator and the electrodes, compromising the safety of the lithium ion battery. Secondly, the thermal stability is poor. The melting point of polyethylene is about 130 c and the melting point of polypropylene is about 160 c, which causes such a separator to exhibit severe dimensional shrinkage at high temperature, and in the case where some dangerous behaviors occur, such as overcharge and high thermal shock, closed-cell behavior occurs in the PE layer as the temperature of the battery approaches the melting point of PE, ion transport paths are blocked, and thus electrochemical reaction is terminated, but if the temperature is continuously increased above the melting point of PP, the separator shrinks, and direct contact between electrodes is shorted, which may eventually lead to explosion of the battery.

In recent years, researchers have made many efforts to develop new materials for battery separators with high thermal stability and high electrolyte wettability. The current novel battery diaphragm materials mainly comprise the following materials:

(1) a nonwoven fabric-based separator. The nonwoven fabric is formed by orienting or randomly arranging organic fibers to form a porous film. The separator has better electrolyte wettability than the commercialized polyethylene and polypropylene separators. The non-woven fabric film presents a three-dimensional pore structure, and the structure can effectively improve the performances of electrolyte liquid absorption rate, electrolyte liquid retention rate, air permeability and the like. However, the lithium battery diaphragm has the problems of low film forming strength, large aperture size, uneven aperture range distribution and the like. The prepared lithium battery has the problems of low capacitance, low cyclic discharge rate and the like.

(2) An inorganic composite separator. The inorganic composite diaphragm is a porous composite film formed by coating a coating formed by an adhesive and inorganic nanoparticles on a diaphragm substrate, has excellent electrolyte wettability, can absorb and retain a large amount of electrolyte, has certain help for prolonging the service life of a battery, and still has excellent thermal dimensional stability, good cycle rate performance and safety performance under the condition of high temperature. However, the lithium battery diaphragm has the problems that the adhesive is not resistant to high temperature, the inorganic coating layer falls off at high temperature and the like, the preparation process is complex, the cost is high, and the large-scale production is not facilitated at the present stage.

(3) Polyimide material lithium battery diaphragm. The polyimide resin is a novel special insulating material, and the lithium battery diaphragm prepared from the polyimide resin has the characteristics of high strength, high modulus, high temperature resistance, radiation resistance, corrosion resistance and the like. At present, two methods are mainly used for preparing the lithium battery diaphragm by taking polyimide resin as a material, one method is to interweave polyamide fibers with an adhesive to form a porous membrane and then coat other materials to fill pores. The other is formed by directly coating polyimide resin, and the diaphragm has high strength, small pore size, narrow distribution range and poor wettability.

Chinese patent document CN108172738A (application number: 201711368653.5) discloses a preparation method of cellulose-based lithium battery diaphragm base paper, which comprises the steps of dispersing polysulfonamide fibers into water to prepare the cellulose-based lithium battery diaphragm base paper; lignocellulosic pulp can be made in either of two ways. The first method comprises the following steps: pulping the cellulose pulp until the pulping degree is 40-92 SR to obtain the lignocellulose pulp. And the second method comprises the following steps: and (3) performing latency disintegration on the cellulose pulp to obtain lignocellulose pulp. Wherein, the cellulose pulp is of various types, such as one or more of bleached softwood kraft pulp, bleached hardwood kraft pulp and wood fiber mechanical pulp. Preparing mixed slurry, wherein the mass ratio of the polysulfonamide fibers to the lignocellulose in the mixed slurry is 1: (1-4), such as 1:2, 1:3, 1:4 or 1: 1; wherein adding nanocellulose to the mixed slurry comprises: in the first mode, 4-12 g of nano-cellulose is added into every 100g of mixed slurry, and the nano-cellulose is added into the mixed slurry; after the nano-cellulose is added into the mixed slurry, the total concentration of the total fiber in the mixed slurry is 2-10%. In the second mode, the nano-cellulose is coated on the wet paper of the cellulose-based lithium battery diaphragm according to the proportion of 4-12 g of nano-cellulose per 100g of mixed slurry. As for the nano-cellulose pulp in which the length of the nano-cellulose fiber is 150 nm-6 μm and the width of the nano-cellulose fiber is 2nm-100nm, for example, before the second mixed pulp is made into a wet cellulose-based lithium battery separator paper sheet, the second mixed pulp needs to be diluted with water to the mass concentration of 1% -4% so as to fully disperse the fibers, and the equipment used for making the paper sheet is a sheet maker or a paper machine. Sequentially carrying out double-sided squeezing, drying and press polishing on the cellulose-based lithium battery diaphragm wet paper to obtain cellulose-based lithium battery diaphragm base paper; when double-sided pressing is carried out, the pressure used for pressing each side is 3MPa to 10MPa, and the pressing time of each side is 2min to 10 min; the temperature used for drying is 80-105 ℃, the time used for drying is 5-20 min, and the temperature used for calendaringThe temperature is 100-120 ℃, and the pressure used for calendaring is 2-5 MPa. And carrying out post-treatment on the cellulose-based lithium battery diaphragm wet paper to obtain cellulose-based lithium battery diaphragm base paper. The thickness of the cellulose-based lithium battery diaphragm base paper is 20-60 mu m, and the quantitative content is 20g/m²-50g/m². The average void size inspection result in the physical property test of the cellulose-based lithium battery separator prepared by the method is 302 nm-473 nm.

Chinese patent document CN103545475A (application No. 201310518815.4) discloses a barium sulfate diaphragm for lithium ion batteries and a preparation method thereof, wherein the preparation method mainly comprises that the particle size of a barium sulfate medium coated on the surface layer of the battery diaphragm is 20 nm-300 nm. Mixing and stirring nano barium sulfate particles, a binder, a solvent and a dressing together, then coating the slurry on the front surface and the back surface of the lithium ion battery diaphragm to form a coating, and drying the coating to prepare the barium sulfate diaphragm; the lithium ion battery base diaphragm is a microporous diaphragm or a non-woven fabric diaphragm; the microporous diaphragm or the non-woven fabric diaphragm is made of one or more of PP, PE, polyvinyl alcohol, polyimide resin or polyethylene glycol terephthalate, the drying temperature is divided into four sections which are respectively 40-60 ℃, 60-80 ℃, 80-60 ℃ and 60-40 ℃, and the speed of the coating passing through the drying section is 5-59 meters per minute.

The battery emits heat during charge and discharge, and a large amount of heat is emitted particularly when short-circuiting or overcharging occurs. Therefore, when the temperature rises, the diaphragm should maintain the original integrity and a certain mechanical strength, continue to play a role in isolating the positive electrode and the negative electrode, and prevent the occurrence of short circuit, so the smaller the thermal shrinkage rate of the diaphragm is, the better the thermal stability is.

The air permeability of the lithium ion battery diaphragm is an important index of the diaphragm, and the better the air permeability is, the better the smoothness of lithium ions penetrating the diaphragm is, and the lower the resistance of the diaphragm is. It is determined comprehensively by the factors of the pore size and distribution of the membrane, the porosity, the shape of the pores, the tortuosity of the pores and the like. The aperture is generally required to be within the range of 10-100 nm, and when the aperture is less than 10nm, the lithium ion passing capacity is too small; the aperture is larger than 100nm, and the battery is easy to be short-circuited during the production of dendrite inside the battery.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the lithium battery diaphragm paper made of the wood pulp fiber/nano barium sulfate composite material and the preparation method thereof.

The lithium battery diaphragm paper made of the wood pulp fiber/nano barium sulfate composite material and the preparation method thereof have the advantages of moderate aperture, excellent wettability, good air permeability, high film strength, high thermal stability, environmental protection and no pollution.

The technical scheme of the invention is as follows:

a preparation method of wood pulp fiber/nano barium sulfate composite material lithium battery diaphragm paper comprises the following steps:

(1) the virgin wood pulp fiber pulp is subjected to disintegration and pulping to prepare high-pulping-degree fiber pulp, and the prepared fiber pulp is prepared into 25g/m quantitative pulp by adopting a paper preparation process²～35g/m²The fiber-based paper of (1);

the wood fiber is pulped to generate a large amount of fine fibers, fiber gaps are filled, tightness is improved, and the aperture between the fibers is reduced, so that the aperture range is 1-30 mu m.

(2) Uniformly mixing the nano-fiber and the nano-barium sulfate composite material according to a certain proportion to prepare a mixed coating, uniformly coating the mixed coating on two sides of the fiber base paper in the step (1), and performing hot-pressing drying to prepare a semi-finished lithium battery diaphragm paper;

the mixed coating prepared from the nanofiber and nano barium sulfate composite material has good pore filling property, thermal stability and wettability, and can reduce the pore diameter of the fiber-based paper to be less than 100 nm; by using a hot-pressing drying mode, the coating can be filled into the fiber-based paper under a certain pressure, so that the inner and outer apertures of the lithium battery diaphragm paper are uniform.

(3) And (3) dissolving the polyimide resin with a solvent to prepare a polyimide resin solution with the mass percentage concentration of 5-10%, soaking the semi-finished lithium battery separator paper obtained in the step (2) in the polyimide resin solution for 10-30 s, and drying to obtain the finished lithium battery separator paper.

Semi-manufactured goods lithium cell diaphragm paper soaks in polyimide resin solution, can make lithium cell diaphragm paper keep higher heat stability under the long-time high temperature condition, can increase the combination between fibre base paper and the coating layer simultaneously, improves lithium cell diaphragm paper's physical strength, prevents that nanometer barium sulfate combined material from droing in the fibre paper base in electrolyte.

According to the invention, the wood pulp fiber pulp obtained by the step (1) is bleached softwood fiber, bleached hardwood fiber and mixed fiber pulp obtained by mixing the two fibers in proportion, wherein the bleached softwood fiber, the bleached hardwood fiber and the mixed fiber pulp are prepared by a chemical method, a semi-chemical method or a chemical-mechanical method.

According to the invention, the beating mode in the step (1) is preferably a sticky beating mode, and the sticky beating mode has the function of mainly brooming fibers.

According to the invention, the beating degree of the wood pulp fiber pulp in the step (1) is preferably 70-90 DEG SR;

preferably, according to the present invention, the paper making process is a low basis weight high-tightness tissue paper making process.

Compared with lithium battery base films prepared by other methods, the lithium battery diaphragm fiber base paper prepared by the low-basis-weight high-tightness tissue paper preparation process is simple in method, mature in process and convenient for large-scale production.

According to the present invention, preferably, the nanofibers in step (2) are biomass nanofibers.

Further preferably, the biomass nanofibers comprise mechanically produced nanofibers and/or chemically produced nanofibers.

More preferably, the biomass nanofibers are softwood nanofibers, hardwood nanofibers and/or bacterial cellulose.

According to the invention, preferably, in the step (2), the nano-fiber is nano-sized, the diameter is 20-50 nm, and the length-diameter ratio is 30-100: 1.

according to the invention, in the step (2), the nano barium sulfate composite material has a particle diameter size of nano level and a diameter of 20 nm-60 nm.

According to the invention, the nano barium sulfate composite material in the step (2) is prepared by any one or more than two methods of a grinding and grinding method, a chemical precipitation method, a micro-emulsion method, a super-heavy method or a micro-reactor method.

According to the invention, the mass percent of the nano-fiber in the mixed coating in the step (2) is preferably 30-70%, and the mass percent of the nano barium sulfate composite material is preferably 30-70%.

According to the invention, the coating weight of the mixed coating in the step (2) is 15g/m²～20g/m²The coating method is any one of gravure coating, slot coating, dip coating, spray coating, and spin coating.

According to the invention, the hot-pressing drying in the step (2) is preferably a hot-pressing drying mode of a hot press.

More preferably, the hot pressing temperature is 100 ℃ to 130 ℃ and the hot pressing pressure is 3MPa to 5 MPa.

According to the invention, the polyimide resin in the step (3) is preferably a soluble polyimide resin, and the solvent used is one or a mixture of two of strong polar organic solvents DMA, DMF, NMP, dioxane, m-cresol and chloroform.

The invention discloses a wood pulp fiber/nano barium sulfate composite material lithium battery diaphragm paper, which has the following physical and chemical indexes: the quantitative ratio is 40-60 g/m²The pore diameter is 30 nm-100nm, the porosity is 40% -80%, the puncture strength is 300-600 gf, the contact angle of wetting liquid is 20-60 degrees, and the thermal shrinkage is less than 3% at the temperature of 200-300 ℃.

Preferably: the thermal shrinkage rate of the lithium battery diaphragm paper is less than 1.2% at 200 ℃ and less than 3% at 300 ℃.

Advantageous effects

1. The aperture of the lithium battery diaphragm paper prepared by the invention is in the range of 30 nm-100nm, and the size is moderate; the wetting angle is 20-60 degrees, and the liquid absorption property is good; the heat shrinkage rate is less than 3 percent after 60 minutes at the temperature of 200-300 ℃, and the high-temperature-resistant material has good long-time high-temperature resistance. The problems of improper pore diameter, poor wettability, no high temperature resistance and the like in the current lithium battery diaphragm are solved. The paper is rich in raw material resources, environment-friendly and safe, the paper preparation process is adopted in the manufacturing method, the method is simple, the cost is low, and the industrialization is facilitated.

2. The invention selects the wood pulp fiber as the raw material, the wood pulp fiber resource is rich, the cost is low, the dispersion is easy in water, and the finished paper is uniform; the wood pulp fibers are subjected to high devillicate fibrillation after pulping treatment, and the fibers can be combined through hydrogen bonds to form a base paper structure with higher strength; the wood pulp fiber has high thermal stability and good wettability.

3. Selecting a nano-fiber and nano-barium sulfate composite material as a mixed coating. The nano-fiber is prepared from plant fiber, has all the characteristics of the plant fiber, and can be combined with fiber-based paper through hydrogen bonds as a coating; the nano barium sulfate composite material has good high-temperature stability but poor hydrophilicity, and the two nano materials are mixed, so that the coating has good surface binding property, and the wettability and the thermal stability of the lithium battery diaphragm are obviously improved; the mixed coating prepared from the nanofiber and nano barium sulfate composite material is coated on two sides of the fiber-based paper, and the coating can be filled in the fiber-based paper under pressure in a hot-pressing drying mode to reduce the pores among the fiber-based paper, so that the inner and outer pore diameters of the battery diaphragm are uniform, and the pore diameter range of the battery diaphragm is reached.

4. Polyimide resin is selected to impregnate the semi-finished lithium battery diaphragm paper, so that the long-time thermal stability of the paper can be improved, and the lithium battery can continue to work at high temperature; the polyimide resin plays a role of an adhesive, the physical strength of the lithium battery diaphragm paper is improved, and the mixed coating layer is prevented from falling off due to long-time soaking in electrolyte.

Detailed description of the invention

The technical solution of the present invention is further described with reference to the following examples, but the scope of the present invention is not limited thereto.