CN106531929A - Drying process of ceramic coated bacterial cellulose porous thin film - Google Patents

Abstract

The invention provides a drying process for a ceramic-coated bacterial cellulose porous film, which is to dehydrate and dry the ceramic-coated bacterial cellulose film containing water, so as to obtain a ceramic-coated bacterial cellulose lithium-ion battery diaphragm with uniform thickness. The drying process of the ceramic-coated bacterial cellulose porous film of the invention has the characteristics of simple process, low energy consumption and suitable for large-scale production.

Description

A drying process for ceramic-coated bacterial cellulose porous film

technical field

The invention relates to the technical field of lithium-ion battery preparation, in particular to a drying process for a ceramic-coated bacterial cellulose porous film used for lithium-ion battery separators.

Background technique

The separator is the core component of the lithium-ion battery, which largely determines the performance, safety, service life and other important performance indicators of the lithium-ion battery. Compared with traditional lithium-ion batteries, the working environment of new lithium-ion power batteries is more complex, requiring higher power charging and discharging, higher safety and longer service life. Traditional lithium-ion battery separators cannot meet the performance requirements of power batteries. Therefore, the development of high-performance new power lithium-ion diaphragms has become an important field of technology competition in developed countries and regions in the automotive industry such as the United States, Europe, and Japan. Power lithium-ion battery diaphragm technology will have an important impact on the competition pattern of new energy vehicles in the world.

At present, almost all microporous separators widely used in the lithium-ion secondary battery industry use polyolefin microporous membranes. This method is mainly to obtain a semi-crystalline polymer film by melt extrusion, and then stretch it so that There are many micropores in the film, the manufacturing process does not require solvents, and the production rate is high. The polymer materials used are polypropylene (PP) and polyethylene (PE), which are one of the cheapest film materials. However, this kind of microporous membrane also has many disadvantages, such as the maximum crack aperture of the membrane is 0.4 μm, the widest is 0.04 μm, and the highest porosity is about 40%. Due to the low liquid absorption and the increase of lithium ion mobility, it is not conducive to the high current charge and discharge of the battery; at the same time, polypropylene has poor ductility and low surface energy, which is a difficult-to-stick plastic, which is not conducive to the adhesion of positive and negative electrodes. Junction, the interface between the separator and the electrode is not tightly combined, which affects the energy density of the battery; in addition, this method has complex equipment, high production costs, and expensive prices, and the production cost of the battery also increases accordingly. In addition, the thermal shrinkage of the traditional separator is relatively serious, and the melting temperature is low (PP is about 165 ^o C), these characteristics make the traditional separator unable to meet the safety requirements of the power battery.

In order to solve the above problems, countries and regions such as the United States and Japan are competing to develop high-performance power battery separators. In 2007, the United States developed a high-performance lithium-ion battery separator (Energain™) based on nanofiber spinning technology, which is specially used for power lithium-ion batteries. After using the diaphragm, the power of the battery can be increased by 15%-30%, the service life can be increased by 20%, and the safety of the battery can be greatly improved. German EVONIC company has developed a high-performance separator (SEPARION ^® ) specially used for power batteries. The safe temperature of this film reaches 210 ^o C, the thermal shrinkage rate is less than 1% (200 ^o C, 24h), and the wettability is significantly improved. , with excellent thermal and chemical stability. Teijin Technology Products Co., Ltd., a subsidiary of Japan's Teijin Group, announced on April 26, 2013 that the company has developed aramid nanofibers that can be mass-produced for the first time. The fibers have high quality and can provide reliable heat resistance and oxidation resistance. performance. The nanofibers are made of Teijinconex heat-resistant meta-aramid, which is proprietary to Teijin, and are uniform in size with a diameter of only a few hundred nanometers. It is reported that aramid nanofibers will be used in the manufacture of lithium-ion battery (LIBs) separators in the form of non-woven sheets, and the company will carry out commercial production of the fibers in 2014. According to reports, until now, Teijin's aramid nanofibers have only been produced in the laboratory, and the plates produced can maintain their shape at 300°C. The high temperature resistance and oxidation resistance of aramid nanofibers can enhance the safety of lithium-ion batteries for automobiles and static power storage, and ensure that the batteries can reduce the risk of fire in high-capacity, high-energy-density applications, which is more advantageous than traditional separators. Other characteristics of aramid nanofiber nonwoven sheets that can be applied to battery separators include: high porosity to facilitate smooth electrolyte flow, resulting in higher power output and fast charging capabilities; large surface area, nanofiber features, and high Porosity, when the ionic conductivity drops, still allows the electrolyte to effectively maintain the performance of the battery at low temperature; as a non-woven sheet, compared with traditional polyolefin-based separators, it enables faster electrolyte absorption and helps shorten The time it takes to get the electrolyte to pour into the battery, reducing the production cost of high-capacity batteries.

Bacterial cellulose is extracellular cellulose produced by microorganisms (mainly bacteria), first discovered by British scientist Brown in 1886. Compared with plant cellulose, bacterial cellulose has many characteristics, such as high water holding capacity; under static culture conditions, it has high Young's modulus, high tensile strength and excellent shape maintenance ability; high crystallinity; ultrafine (nanoscale) fiber network structure; high void rate (>90%); high purity (over 99% is cellulose); high biocompatibility and good biodegradability; physical properties can be adjusted during biosynthesis Wait. Because bacterial cellulose has the above-mentioned excellent properties in terms of purity, liquid absorption, physical and mechanical properties, people attach great importance to its application research in various fields, and it also has a wide range of commercial application potential in lithium-ion battery separators.

However, several key technical problems need to be overcome to process bacterial cellulose wet film into lithium-ion battery separators: (1) the thickness of the cellulose separator should be less than 40 microns; (2) the thickness of the cellulose separator should be uniform; (3) the bacterial cellulose The separator should have a high porosity. The traditional freeze-drying, supercritical drying and other processes have the disadvantages of complicated process, high cost, and long drying cycle. However, direct drying of bacterial cellulose wet membrane membranes by hot pressing has the disadvantages of high energy consumption, small membrane porosity, and low ionic conductivity.

Wang Biao et al. conducted research on bacterial cellulose membrane gel polymer electrolytes for lithium batteries. They introduced lithium salt organic solutions into bacterial cellulose wet membranes by displacement method to prepare polymer gels. However, the battery performance of the polymer electrolyte gel membrane obtained by this method is not ideal. They also prepared a composite gel electrolyte membrane by adding silica particles to the bacterial cellulose gel membrane. However, since the silica particles were dispersed in the pores of the bacterial cellulose membrane, they could not effectively increase the Porosity, on the contrary, may reduce the amount of electrolyte adsorption, so the conductivity decreases instead. Jiang Fengjing et al. used an improved process to prepare ultra-thin bacterial cellulose membrane separators (dry films), but found that the prepared ultra-thin bacterial cellulose membranes had lower porosity, resulting in lower electrical conductivity than commercial separators.

In view of the problems existing in the above-mentioned key technologies, the inventor invented a ceramic-coated bacterial cellulose porous film with excellent lyophilicity, high porosity and ion conductivity, and excellent high temperature resistance for lithium-ion battery separators , and a preparation method thereof, the preparation method is simple and efficient, and the prepared bacterial cellulose porous film has the characteristics of high ion conductivity, high temperature resistance, and good battery performance, and can be used to prepare a high-performance, high temperature-resistant lithium-ion battery separator .

The present invention further proposes a fast and efficient drying method for the ceramic-coated bacterial cellulose porous film invented by the inventor before, so as to improve production efficiency and reduce production cost.

Contents of the invention

Aiming at the problems of slow drying speed and high energy consumption of ceramic-coated bacterial cellulose porous film, the present invention provides a fast and efficient drying method for ceramic-coated bacterial cellulose porous film to improve production efficiency and reduce production cost.

Technical scheme of the present invention is:

A drying process for ceramic-coated bacterial cellulose porous film, characterized in that: the drying process sequentially comprises three steps of cold pressing drying, hot pressing drying and hot air drying;

The cold pressing drying is characterized in that: the press used is a hydraulic press or an air press, the pressure is 0.1-1MPa, and the temperature is room temperature without heating;

The hot pressing drying is characterized in that: the press used is a hydraulic press or an air press, the pressure is 0.1~1MPa, the upper and lower pressing plates of the press have a heating function, and the hot pressing temperature is 80~120 ^o C;

The hot air drying is characterized in that: the hot air temperature is 80-150 ^o C, and the wind speed is greater than 2-12 m/s;

The drying process of the ceramic-coated bacterial cellulose porous film is characterized in that a conveyor belt is used to connect the three steps.

The ceramic-coated bacterial cellulose porous film obtained according to the above method has a porosity greater than 50%. It is very suitable for the preparation of lithium-ion battery separators. The drying process of the ceramic-coated bacterial cellulose porous film of the present invention has the remarkable characteristics of simple preparation process, low energy consumption, high efficiency and suitable for large-scale production.

Description of drawings

Fig. 1 is the process flow chart of the drying process of the ceramic-coated bacterial cellulose porous film described in the present invention.

Figure 2 is a comparison of battery charge and discharge performance between the ceramic-coated bacterial cellulose membrane prepared in the present invention and the commercial Celgard diaphragm. It can be seen that the battery capacity and high-rate sufficient electrical performance of the present invention are significantly better than Celgard commercial separators.

detailed description

Embodiments of the present invention will be described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Example 1:

First, put the ceramic-coated bacterial cellulose film on the conveyor belt and transfer it to the cold press, and the upper platen of the cold press moves downward to squeeze the ceramic-coated bacterial cellulose film with a pressure of 0.1 MPa. The mold closing time is For 1 minute, most of the water contained in the membrane was forced out of the membrane. The conveyor belt stops during mold closing. Then the pressing plate opens the mold (the upper pressing plate moves upward), the conveyor belt sends the film to the middle of the pressing plate of the hot press, and the upper pressing plate of the hot pressing machine moves downward to apply a pressure of 0.1 MPa to the ceramic-coated bacterial cellulose film. For 10 minutes, the temperature of the upper and lower platens is 80 ^o C, and the film is hot-pressed and dried. The conveyor belt stops during mold closing. Then the hot platen opens the mold (the upper platen moves upwards), and the conveyor belt sends the film to the air outlet of the hot air blower for hot air drying. The wind speed is 4m/s. The temperature of the hot air reaching the surface of the film is 150 ^oC , and the drying time is 2 minutes. During hot air drying, the conveyor belt stops.

The porosity of the ceramic-coated bacterial cellulose membrane prepared by the drying process is greater than 50%, and its performance on a lithium-ion battery is shown in FIG. 2 .

Example 2:

First, put the ceramic-coated bacterial cellulose film on the conveyor belt and transfer it to the cold press, and the upper platen of the cold press moves downward to squeeze the ceramic-coated bacterial cellulose film with a pressure of 1 MPa. The mold closing time is For 0.5 minutes, most of the water contained in the membrane was forced out of the membrane. The conveyor belt stops during mold closing. Then the pressing plate opens the mold (the upper pressing plate moves upward), the conveyor belt sends the film to the middle of the pressing plate of the hot press, and the upper pressing plate of the hot pressing machine moves downward to apply a pressure of 1 MPa to the ceramic-coated bacterial cellulose film. For 3 minutes, the temperature of the upper and lower platens is 120 ^o C, and the film is hot-pressed and dried. The conveyor belt stops during mold closing. Then the hot platen opens the mold (the upper platen moves upwards), and the conveyor belt sends the film to the air outlet of the hot air blower for hot air drying. The wind speed is 4m/s. The temperature of the hot air reaching the film surface is 80 ^oC , and the drying time is 1 minute. During hot air drying, the conveyor belt stops.

The porosity of the ceramic-coated bacterial cellulose membrane prepared by the drying process is greater than 50%, and its performance on a lithium-ion battery is shown in FIG. 2 .

Example 3:

First, put the ceramic-coated bacterial cellulose film on the conveyor belt and transfer it to the cold press, and the upper platen of the cold press moves downward to apply a pressure of 0.3 MPa to the ceramic-coated bacterial cellulose film for extrusion. The mold closing time is For 0.2 minutes, most of the water contained in the membrane was forced out of the membrane. The conveyor belt stops during mold closing. Then the pressing plate opens the mold (the upper pressing plate moves upward), the conveyor belt sends the film to the middle of the pressing plate of the hot press, and the upper pressing plate of the hot pressing machine moves downward to apply a pressure of 1 MPa to the ceramic-coated bacterial cellulose film. For 2 minutes, the temperature of the upper and lower platens is 100 ^o C, and the film is hot-pressed and dried. The conveyor belt stops during mold closing. Then the hot platen opens the mold (the upper platen moves upwards), and the conveyor belt sends the film to the air outlet of the hot air blower for hot air drying. The wind speed is 8m/s, the temperature of the hot air reaching the film surface is 100 ^oC , and the drying time is 0.5 minutes. During hot air drying, the conveyor belt stops.

The porosity of the ceramic-coated bacterial cellulose membrane prepared by the drying process is greater than 50%, and its performance on a lithium-ion battery is shown in FIG. 2 .

Example 4:

First, put the ceramic-coated bacterial cellulose film on the conveyor belt and transfer it to the cold press. The upper platen of the cold press moves downward to apply a pressure of 0.8 MPa to the ceramic-coated bacterial cellulose film. The mold closing time is At 0.6 minutes, most of the water contained in the membrane was forced out of the membrane. The conveyor belt stops during mold closing. Then the pressing plate opens the mold (the upper pressing plate moves upward), the conveyor belt sends the film to the middle of the pressing plate of the hot press, and the upper pressing plate of the hot pressing machine moves downward to apply a pressure of 0.8 MPa to the ceramic-coated bacterial cellulose film. For 5 minutes, the temperature of the upper and lower platens is 90 ^o C, and the film is hot-pressed and dried. The conveyor belt stops during mold closing. Then the hot platen opens the mold (the upper platen moves upwards), and the conveyor belt sends the film to the air outlet of the hot air blower for hot air drying. The wind speed is 12m/s. The temperature of the hot air reaching the surface of the film is 120 ^oC , and the drying time is 1 minute. During hot air drying, the conveyor belt stops.

The porosity of the ceramic-coated bacterial cellulose membrane prepared by the drying process is greater than 50%, and its performance on a lithium-ion battery is shown in FIG. 2 .

Example 5:

First, put the ceramic-coated bacterial cellulose film on the conveyor belt and transfer it to the cold press. The upper platen of the cold press moves downward to apply a pressure of 0.3 MPa to the ceramic-coated bacterial cellulose film. The mold closing time is For 1 minute, most of the water contained in the membrane was forced out of the membrane. The conveyor belt stops during mold closing. Then the pressing plate opens the mold (the upper pressing plate moves upward), the conveyor belt sends the film to the middle of the pressing plate of the hot press, and the upper pressing plate of the hot pressing machine moves downward to apply a pressure of 0.3 MPa to the ceramic-coated bacterial cellulose film. For 1 minute, the temperature of the upper and lower platens is 120 ^o C, and the film is hot-pressed and dried. The conveyor belt stops during mold closing. Then the hot platen opens the mold (the upper platen moves upwards), and the conveyor belt sends the film to the air outlet of the hot air blower for hot air drying. The wind speed is 6 m/s. The temperature of the hot air reaching the surface of the film is 120 ^oC , and the drying time is 1 minute. During hot air drying, the conveyor belt stops.

The porosity of the ceramic-coated bacterial cellulose membrane prepared by the drying process is greater than 50%, and its performance on a lithium-ion battery is shown in FIG. 2 .

Claims (5)

1. a kind of drying process of ceramic coatings Bacterial cellulose porous membrane, it is characterised in that：Drying process includes dry, three steps of hot-pressing drying and hot air drying of colding pressing successively.

2. drying of colding pressing according to claim 1, it is characterised in that：Press used is that hydraulic pressure is extruded or air pressure press, and pressure is 0.1 ~ 1MPa, and temperature is room temperature, without the need for heating.

3. hot-pressing drying according to claim 1, it is characterised in that：Press used is hydraulic press or air pressure press, and pressure is 0.1 ~ 1MPa, and upper and lower two block pressur plate of press has heating function, and hot pressing temperature is 80 ~ 120^oC。

4. hot air drying according to claim 1, it is characterised in that：Hot blast temperature is 80 ~ 150^oC, wind speed are more than 4m/s.

5. the drying process of a kind of ceramic coatings Bacterial cellulose porous membrane according to claim 1, it is characterised in that：Three steps are connected using a conveyer belt.