Pure ceramic lithium ion battery diaphragm and preparation method thereof

Abstract

The invention discloses a pure ceramic lithium ion battery diaphragm and a preparation method thereof, and belongs to the field of ceramic lithium ion battery diaphragms. The invention aims to overcome the defects of poor thermal stability, no flame-retardant effect and the like of a polymer material. Amphiphilic PVP, TBT and TEOS are adopted to form a three-dimensional network, in the electrostatic spinning process, PVP serves as a carrier, two precursors evenly form stable nanofibers, and the inorganic structure of the nanofibers is reserved through later calcination. The lithium ion battery diaphragm prepared by the method disclosed by the invention also has excellent thermal stability and flame retardance on the premise that the lithium ion battery diaphragm is porous. And no reaction is generated at an extremely high temperature and under the firing of an igniter, so that the safety of the lithium ion battery is greatly improved. And an electrochemical performance test shows that the composite material has excellent electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the field of ceramic lithium-ion battery diaphragms, and in particular relates to a pure ceramic lithium-ion battery diaphragm and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are developing rapidly in the energy field due to their advantages such as high energy density, low self-discharge rate and no memory effect.

[0003] Lithium-ion batteries (LIBs) have advantages in renewable resource storage due to their high energy density, long life, low self-discharge rate, and no memory effect. In addition, due to the above advantages, LIBs have been widely used in portable electronics and electric vehicles, becoming the most advanced electrochemical energy storage device today. However, commercial lithium-ion batteries still face many challenges and are increasingly unable to meet the growing electrochemical and safety requirements of portable electronic devices as well as high-end battery markets (including power batteries and specialty batteries).

[0004] As one of the important components of lithium batteries, the separator is a porous membrane located between the positive electrode and the negative electrode. The main function of the separator is to prevent the battery from short-circuiting due to the physical contact between the positive and negative electrodes, and also to store electrolytes for Li + Transport. Unlike electrode materials, traditional separators do not participate in electrochemical reactions, but their composition, microstructure, morphology, and other physicochemical properties directly affect the carrier transport properties, interfacial resistance, interaction with the electrolyte, and thermodynamic properties, which greatly affect the performance of lithium-based batteries.

[0005] Currently, most commercial lithium-ion battery separators are composites of polyethylene, polypropylene, and other different polyolefin materials. Some commercial separators are coated with inorganic coatings to improve the performance of the separators. Even if the mechanical strength of such separators is very good, when the temperature rises or combustion occurs, the separator will undergo serious dimensional changes, leading to danger. Although the modified separator has a certain improvement in high temperature resistance, it also sacrifices a large part of the electrochemical performance.

[0006] The lithium-ion battery separator prepared by electrospinning technology has high electrochemical performance. Most of the substrates are polymer materials. Even if inorganic materials are involved, they are only compounded with polymer materials by physical or chemical methods. To improve the performance of polymer materials, it is rare to fundamentally solve the shortcomings of polymer materials such as poor thermal stability and lack of flame retardant effect. While improving the shortcomings by other means, it will also have a great impact on the electrochemical performance. Summary of the invention

[0007] The present invention aims to solve the shortcomings of polymer-based materials as lithium-ion battery separators, and adopts a combination of electrostatic spinning and inorganic materials to prepare a pure inorganic ceramic lithium-ion battery separator. While solving the shortcomings of polymer-based lithium-ion battery separators, it can also have excellent electrochemical properties.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention uses polyvinyl pyrrolidone (PVP) as a solute, anhydrous ethanol as a solvent, acetic acid as an inhibitor, tetraethyl orthosilicate (TEOS) and tetrabutyl titanate (TBT) as inorganic fillers, uses amphiphilic PVP to form a three-dimensional network with TBT and TEOS, and uses PVP as a carrier to uniformly form stable nanofibers from the two precursors during electrospinning, and retains its inorganic structure after subsequent calcination. The preparation method of the pure ceramic lithium ion battery separator in the present invention is carried out according to the following steps:

[0010] Step 1, polyvinyl pyrrolidone (PVP), anhydrous ethanol and acetic acid are mixed and magnetically stirred until uniform;

[0011] Step 2, then add tetraethyl orthosilicate (TEOS), stir magnetically until uniform, then add tetrabutyl titanate (TBT), stir magnetically for 24h to 28h, electrospin to form a film, and dry;

[0012] Step 3: calcining and cooling to room temperature in the furnace to obtain the diaphragm.

[0013] Furthermore, in step 1, the molecular weight of the PVP is 55,000 to 60,000.

[0014] Furthermore, in step 1, PVP, anhydrous ethanol and acetic acid are mixed in a mass ratio of 1.6:11:1.

[0015] Furthermore, in step 2, the mass ratio of PVP to TEOS is 1.6:6.

[0016] Furthermore, in step 2, the mass ratio of PVP to TBT is 1.6:1.

[0017] Furthermore, in step 2, the electrospinning parameters are: nozzle diameter is 16 mm, ambient temperature is room temperature, humidity is 25% to 45%, voltage is 13KV to 14KV, propulsion speed is 0.5ml / h to 0.6ml / h, and the distance between the nozzle and the collecting device is 15cm to 25cm.

[0018] Furthermore, in step 2, drying is performed at 60°C to 80°C.

[0019] Furthermore, in step 3, during the calcination process, the temperature is increased to 550° C. at a heating rate of 5° C. / min and kept at this temperature for 3 h to 5 h.

[0020] Furthermore, in steps 1 and 2, the speed of magnetic stirring is controlled at 400 r / min to 600 r / min.

[0021] A pure ceramic lithium-ion battery separator prepared by any of the above methods.

[0022] The battery separator of the present invention adopts the electrostatic spinning technology to prepare a pure ceramic lithium-ion battery separator for the first time. The characteristics of phase separation and the hydrophilic and hydrophobic ability between the three-dimensional network complex of polyvinyl pyrrolidone (PVP) / butyl titanate (TBT) / tetraethyl orthosilicate (TEOS) and the solvent, the hydrolysis and polycondensation of inorganic alcohol oxides and the slow evaporation during the electrostatic spinning process are utilized to form an electrostatically spun porous structure. Amorphous SIO2 is used as an adhesive to connect titanium dioxide nanocrystals to form a cross-linked network structure. The ceramic lithium-ion battery separator prepared by the present invention adopts the electrostatic spinning technology, combines the high porosity of the separator prepared by electrostatic spinning with the high temperature resistance and non-combustion advantages of inorganic materials, and greatly improves the safety of lithium-ion batteries during use.

[0023] The material structure in the electrospinning process of the present invention is as follows:

[0024]

[0025] The lithium-ion battery separator prepared by the method of the present invention has excellent thermal stability and flame retardancy while being porous. It will not react at extremely high temperatures or when burned by an igniter, thereby greatly improving the safety of the lithium-ion battery. After electrochemical performance testing, it was found that it has excellent electrochemical performance.

[0026] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the attached drawings are only provided for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a picture of the SiO2-TiO2 fiber diaphragm prepared in Example 1 under a scanning electron microscope;

[0028] Figure 2 This is a test diagram of the cycle performance of the SiO2-TiO2 fiber diaphragm prepared in Example 1;

[0029] Figure 3 This is a rate performance test chart of the SiO2-TiO2 fiber diaphragm prepared in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0031] Example 1: The preparation method of the pure ceramic lithium ion battery separator in this example is achieved by the following steps:

[0032] Step 1, take 1.6g PVP as solute, with a molecular weight of 58000; take 11g ethanol as solvent; take 1g acetic acid as inhibitor;

[0033] The solute, solvent and inhibitor were mixed and magnetically stirred at a speed of 500 r / min until the solute was dissolved and dispersed evenly. The stirring time was about 2 h.

[0034] Step 2: After the stirring is completed, 6 g of TEOS as an inorganic filler is added to the mixed solution, and magnetic stirring is performed at a speed of 500 r / min;

[0035] Then 1g TBT was added as another inorganic filler, and then magnetic stirring was performed at a speed of 500r / min until the viscosity of the solution increased. The stirring time was about 24h. During the stirring period, the three materials of PVP, TEOS and TBT formed a three-dimensional network.

[0036] After stirring, take a 5 ml syringe, replace the syringe needle with a No. 16 stainless steel nozzle and extract 5 ml of solution as the spinning solution;

[0037] The spinning solution is spun into a membrane using a high-voltage electrospinning machine. The spinning process is as follows:

[0038] The ambient temperature is room temperature, about 25°C, and the humidity is about 40%;

[0039] The silicone oil paper is spread on the drum of the high-pressure spinning machine and placed vertically on the propeller, which serves as a collecting device;

[0040] The syringe containing the spinning solution is placed on the propeller and fixed, and the distance between the 16-gauge stainless steel nozzle of the syringe and the collecting device is about 20 cm;

[0041] Starting device, voltage is 13KV, propeller propulsion speed is 2.5ml / min. ;

[0042] After the spinning solution is emptied, the spinning ends, and the spinning time is about 4 hours;

[0043] After spinning, the equipment was turned off, the silicone oil paper was removed from the drum, and the spun fiber membrane was removed from the silicone oil paper and placed in an oven for drying at 60°C overnight to remove residual solvent.

[0044] Step 3: Spread the dried fiber membrane on a ceramic plate and place it in a muffle furnace.

[0045] The muffle furnace was set to a heating rate of 5°C / min at room temperature to calcine the fiber membrane, and the final temperature was set to 550°C.

[0046] After the calcination is completed, the heat is kept warm, and the whole process takes about 6 hours.

[0047] After the insulation time is over, the muffle furnace is closed to cool down. After the temperature of the muffle furnace drops to room temperature, the fiber membrane is taken out to obtain the final product, namely, the SiO2-TiO2 fiber diaphragm.

[0048] The image of the SiO2-TiO2 fiber diaphragm prepared by the method of this embodiment under a scanning electron microscope is as follows: Figure 1 As shown, there are Figure 1 It can be seen that the microscopic morphology of SiO2-TiO2 fiber membrane was observed using a scanning electron microscope (AproeC, Thermoscientific, USA). The sample was treated with gold spraying, and the scanning electron microscope image of the sample was analyzed using NanoMeasure software to obtain the size and distribution of the fiber diameter in the fiber membrane sample.

[0049] The cycle performance test diagram of the SiO2-TiO2 fiber diaphragm prepared by the method of this embodiment is shown in the figure Figure 2 As shown, there are Figure 2 It can be seen that the cycle and rate performance of button batteries assembled with Celgard membrane and SiO2-TiO2 fiber membrane were tested using a battery testing system (CT-4008T, Shenzhen Xinwei Electronics Co., Ltd.). In a water-free glove box filled with argon (Ar), the button full battery was assembled in the order of positive electrode shell / NCM523 positive electrode / fiber membrane / Li negative electrode / steel sheet / shrapnel / foam nickel / negative electrode shell. The assembled battery was left for 24 hours, the charge and discharge rate was 0.5C, the working voltage was 3.0-4.2V, and it was cycled 150 times.

[0050] The rate performance test diagram of the SiO2-TiO22 fiber diaphragm prepared by the method of this embodiment is shown in the figure Figure 3 As shown, there are Figure 3It can be seen that according to the assembly method introduced in the cycle performance, a lithium-ion full battery was obtained. The assembled button full battery was tested for high-rate discharge performance, charged at a rate of 0.1C, and discharged at discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 0.1C for 7 times, with an operating voltage of 3.0-4.2V.

Claims

1. A method for preparing a pure ceramic lithium-ion battery separator, characterized in that: The steps include: Step 1, polyvinyl pyrrolidone (PVP), anhydrous ethanol and acetic acid are mixed and magnetically stirred until uniform; Step 2, then add tetraethyl orthosilicate (TEOS), stir magnetically until uniform, then add tetrabutyl titanate (TBT), stir magnetically for 24h to 28h; Step 3: calcining and cooling to room temperature in the furnace to obtain the diaphragm.

2. The method according to claim 1, characterized in that: The molecular weight of PVP is 55,000 to 60,000.

3. The method according to claim 1, characterized in that: The mass ratio of PVP, anhydrous ethanol and acetic acid is 1.6:11:

1.

4. The method according to claim 1, characterized in that: The mass ratio of PVP to TEOS is 1.6:

6.

5. The method according to claim 1, characterized in that: The mass ratio of PVP to TBT is 1.6:

1.

6. The method according to claim 1, characterized in that: During the calcination process, the electrospinning parameters are: nozzle diameter is 16 mm, ambient temperature is room temperature, humidity is 25% to 45%, voltage is 13 KV to 14 KV, propulsion speed is 0.5 ml / h to 0.6 ml / h, and the distance between the nozzle and the collecting device is 15 cm to 25 cm.

7. The method according to claim 1, characterized in that: Dry at 60℃~80℃.

8. The method according to claim 1, characterized in that: The temperature was raised to 550°C at a heating rate of 5°C / min and kept at this temperature for 3 h to 5 h.

9. The method according to claim 1, characterized in that: In steps 1 and 2, the speed of magnetic stirring is controlled at 400 r / min to 600 r / min.

10. A pure ceramic lithium ion battery separator prepared by the method according to any one of claims 1 to 9.

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