CN116031479B - Polymer solid electrolyte slurry and film for lithium ion battery, preparation method and application - Google Patents

Abstract

The invention relates to the field of solid lithium metal batteries, and discloses a polymer solid electrolyte slurry and a film of a lithium ion battery, a preparation method and application. The polymer solid electrolyte slurry consists of a continuous phase PVDF, a reinforcing phase pre-lithiated polyphenylene sulfide (PPS), lithium salt and an organic solvent; the single PVDF binder used in the process of manufacturing the battery core can be partially or completely replaced, so that the effects of increasing the lithium ion transmission efficiency, improving the interface contact and reducing the interface impedance are achieved. The polymer solid electrolyte membrane prepared based on the slurry improves the crystallinity of PVDF by adding pre-lithiated polyphenylene sulfide, and improves the mechanical property of the solid electrolyte membrane; the S-site channel on thioether bond is used for improving directional lithium ion migration and ionic conductivity, and meanwhile, the lithium ion rectification effect is achieved, and the growth of lithium dendrites is effectively inhibited.

Description

Lithium-ion battery polymer solid electrolyte slurry, membrane, preparation method and application

Technical field

The invention belongs to the field of lithium-ion battery materials and relates to a lithium-ion battery polymer solid electrolyte slurry, membrane, preparation method and application.

Background technique

Solid-state lithium-ion batteries have attracted much attention due to their high energy density, small size, safety, flexibility and deformability.

The key material of solid-state lithium-ion batteries is solid electrolyte, including polymer system (conductivity 10 ^-7 -10 ^-5 S/cm), oxide system (conductivity 10 ^-6 -10 ^-3 S/cm), sulfide system (conductivity 10 ^-3 -10 ^-2 S/cm); compared with traditional liquid electrolytes (conductivity 10 ^-2 S/cm), it has lower conductivity. Moreover, when used in batteries, due to the small solid/solid interface contact area of electrodes and electrolytes, the interface impedance is high, and the transmission of lithium ions between the interfaces is blocked. This directly leads to the high impedance and high rate of solid-state lithium batteries. Poor and unstable circulation limits its application.

Polymer solid-state electrolytes have good flexibility and easy processing properties, and have good contact with the electrode interface, which can reduce the interface resistance of solid-state batteries. In addition, the low density of the material can increase the energy density of the battery. In all-solid-state lithium metal anodes Batteries are receiving more and more attention. Common polymer solid electrolyte polyvinylidene fluoride (PVDF) polymers have attracted attention because of their stable electrochemical and mechanical properties and their ability to well dissociate lithium salts to improve their conductivity. However, it has a high degree of crystallinity and a high proportion of crystalline areas, which results in the inability to transport lithium ions quickly within the PVDF crystal structure. It has poor ion conductivity at room temperature, about 10 ^-5 S·cm ^-1 . Generally, it is achieved by using a gel. Chemical methods are used to improve its electrical conductivity, which in turn leads to a decrease in mechanical properties. Zhang et al. reported a solid electrolyte membrane based on PVDF–LiX with a conductivity of 2.03 × 10 ⁻⁴ S cm ⁻¹ at room temperature of 25 °C (X. Zhang, S. Wang, C. Xue, C. Xin, Y. Lin, Y. Shen, L. Li, C.-W. Nan, Adv. Mater. 2019, 31, 1806082.). Although this promotes the development of all-solid-state lithium metal batteries. However, PVDF-based solid electrolyte membranes still have problems with poor mechanical properties, thermal stability, and poor interface compatibility with electrodes, and their performance still needs to be further improved to meet the needs of commercial solid-state lithium battery production.

Contents of the invention

This invention aims at the problems of poor interface contact of the PVDF-based solid electrolyte, high solid/solid interface impedance, blocked transmission of lithium ions between the interfaces, low room temperature ionic conductivity, poor mechanical properties, etc. On the basis of improving the interface problems, the invention still needs to In order to meet the requirements of high capacity, high energy density and high safety, a solid electrolyte slurry is proposed that can partially or completely replace the single PVDF binder used in the process of making battery cells, thereby achieving Increase lithium ion transmission efficiency, improve interface contact, and reduce interface impedance.

In addition, in order to solve the problems of high crystallinity, low ionic conductivity and poor mechanical properties of PVDF, a solid electrolyte membrane and its preparation method are provided. By adding pre-lithiated polyphenylene sulfide, the crystallinity of PVDF is improved and the solid electrolyte is improved. Mechanical properties of the membrane; through the S-site channel on the thioether bond, it improves directional lithium ion migration and improves ionic conductivity. At the same time, it plays a lithium ion rectification effect and effectively inhibits the growth of lithium dendrites.

and the application of the above-mentioned solid electrolyte slurry and solid electrolyte membrane in lithium-ion secondary batteries.

The technical solution of the present invention is as follows:

A method for preparing lithium-ion battery polymer solid electrolyte slurry, which is characterized by including the following steps:

Step S1: Preparation of prelithiated polyphenylene sulfide powder. Mix polyphenylene sulfide particles, lithium chloride and tetrachloro-p-benzoquinone anionic complexing agent, and place them in an argon or nitrogen reactor and heat it to 200°C. -400℃, react for 2-5h, and then cool to room temperature with 1-2℃/min temperature control. The obtained product is washed with deionized water several times and filtered until neutral, and vacuum dried at 60℃ for 12-24h to obtain pre-lithium Polyphenylene sulfide powder A;

Step S2: Preparation of polymer solid electrolyte slurry, pre-mix the prelithiated polyphenylene sulfide powder A obtained in step S1 and polyvinylidene fluoride (PVDF) in a planetary mixer or kneader for 1-2 hours, Slowly add the organic solvent until the solid content is between 40-60%, and perform semi-dry kneading for 1-5 hours until the materials are evenly kneaded; add lithium salt, continue kneading for 1-5 hours, and then add the organic solvent until the solid content is 10-30%. Carry out high-speed dispersion and mixing with a dispersion speed of 2000-5000 rpm and a dispersion time of 1-2 hours to obtain solid electrolyte slurry B.

Further, the mass ratio of polyphenylene sulfide, lithium chloride and tetrachloro-p-benzoquinone described in step S1 is 100:5-15:15-50.

Further, the amounts of polyvinylidene fluoride (PVDF), prelithiated polyphenylene sulfide powder A, and lithium salt are 40-50 parts by weight, 10-20 parts by weight, and 20-40 parts by weight.

Further, the lithium salt is a double salt composed of LiBF ₄ and LiODFB, and the mass ratio of LiBF ₄ to LiODFB in the double salt is 1:1 to 1.5.

Further, the organic solvent is one or more of N,N-dimethylformamide, tetrahydrofuran, and N-methylpyrrolidone (NMP).

The ion battery polymer solid electrolyte slurry prepared by the described ion battery polymer solid electrolyte slurry preparation method.

The application of the ion battery polymer solid electrolyte slurry is characterized by completely or partially replacing a single PVDF binder with the binder used for the battery core pole pieces in the process of making the battery core.

A method for preparing a lithium-ion battery polymer solid electrolyte membrane based on the solid electrolyte slurry, which is characterized in that the solid electrolyte slurry B is coated into a film with a thickness of 25 μm-50 μm by using a doctor blade coating machine and a casting method. The solid electrolyte membrane is placed in a vacuum oven at a temperature of 60-100°C to dry for 10-24 hours, and finally the solid electrolyte membrane C is obtained.

The lithium ion battery polymer solid electrolyte membrane prepared by the method of the lithium ion battery polymer solid electrolyte membrane is characterized in that it is composed of continuous phase polyvinylidene fluoride (PVDF), reinforced phase prelithiated polyphenylene sulfide (PPS), It consists of lithium salt and organic solvent, in which the mass percentage of PVDF is 40%-50%, the mass percentage of pre-lithiated PPS is 10%-20%, and the mass percentage of lithium salt is 20-40%. The percentage content of organic solvent is 5-15%.

Further, in the lithium-ion battery polymer solid electrolyte membrane, the crystallinity of the continuous phase PVDF molecular structure is <72%; the linear crystallization zone of the polyphenylene sulfide is greater than 90%.

The application of the solid electrolyte membrane in the preparation of battery cells is characterized by being placed between the positive electrode and the negative electrode to produce a lithium metal negative electrode lithium ion battery or a negative electrode lithium ion battery.

Compared with the existing technology, the present invention has the following advantages

The prepared polymer solid electrolyte slurry can partially or completely replace the PVDF binder, reduce the contact resistance at the electrode/electrolyte interface, reduce the polarization internal resistance of the battery, and play a beneficial role in the cycle and stable performance of the battery.

The addition of reinforcing phase pre-lithiated polyphenylene sulfide can improve the mechanical strength of the PVDF solid electrolyte membrane and enhance the ionic conductivity. The chelating agent of pre-lithiated polyphenylene sulfide can chelate anions and prevent concentration polarization. , improve the directional migration of lithium ions along the sulfur (S) site channel to achieve the lithium ion rectification effect, thereby effectively inhibiting the growth of lithium dendrites.

The prepared polymer solid electrolyte membrane has the advantages of high decomposition voltage, large lithium ion migration number, and high ionic conductivity. It can effectively improve the electrochemical performance of lithium metal anode batteries to meet the requirements of commercial solid-state lithium battery applications.

Provides a simple and efficient method to prepare polymer solid electrolyte membranes. Through a simple blending method, the membrane production process is simple, the membrane formation is fast, and the efficiency is high. The conventional equipment used is easy to control and operate, so that polymers can be prepared in large quantities. Solid electrolytes and membranes meet the needs of commercial solid-state lithium battery production.

Description of the drawings

Figure 1 is a physical diagram of the polymer solid electrolyte membrane in Example 1;

Figure 2 is an SEM image of the polymer solid electrolyte membrane in Example 1;

Figure 3 is a tensile performance diagram of the polymer solid electrolyte of Example 1;

Figure 4 is a decomposition voltage (LSV) diagram of the polymer solid electrolyte of Example 1.

Implementation

The following examples are an illustration of the specific experimental operation part of the present invention. They are only used to illustrate the present invention and cannot be understood as limiting the present invention.

Example

First, mix 50g of polyphenylene sulfide particles, 5g of lithium chloride and 15g of tetrachloro-p-benzoquinone, place it in a reaction kettle that continuously supplies argon gas, raise the temperature to 220°C, react for 3 hours, and then control the cooling at 1°C/min. to room temperature, the obtained product was washed multiple times with deionized water, filtered until neutral, and vacuum dried at 60°C for 20 hours to obtain prelithiated polyphenylene sulfide powder A.

Put polyvinylidene fluoride (PVDF) into an oven to dry at 80°C for 24 hours, then take 50g PVDF and 9.2g pre-lithiated polyphenylene sulfide powder A, premix them in a planetary mixer for 2h, and slowly add 100 mL N- Methyl pyrrolidone (NMP), semi-dry knead for 2 hours, then add 33g of double salt composed of LiBF ₄ and LiODFB at a mass ratio of 1:1.2, continue kneading for 2 hours, then add 250 mL of organic solvent NMP, and set the dispersion speed to 3000 rpm/ minutes, dispersion time is 1 hour, and high-speed dispersion and mixing is performed to obtain solid electrolyte slurry B.

The solid electrolyte slurry B is coated on a blade coater into a thin film with a thickness of 30 μm, and then placed in a vacuum oven and dried at 100°C for 24 hours to obtain the polymer solid electrolyte membrane C, as shown in Figure 1. The surface of the solid electrolyte membrane can be observed using a scanning electron microscope (SEM), as shown in Figure 2. It can be observed that PPS is evenly distributed in the continuous phase of PVDF. The conductivity of the solid electrolyte membrane was measured using the AC impedance method to be 2.82×10 ^-4 S/cm. The tensile strength measured using an electronic universal testing machine is 6MPa, as shown in Figure 3. The lithium sheet/solid electrolyte membrane/steel sheet half-cell linear voltammetry test electrochemical window is 4.5V, and the linear voltammetry curve is shown in Figure 4.

In this case, a button cell is used for electrochemical testing, and solid electrolyte slurry B is used as the binder. The preparation of the positive electrode sheet is: the active material LFP, solid electrolyte slurry B, and conductive carbon superP are mixed according to the dry weight mass percentage of 94 ﹕2﹕4 Mix, add the organic solvent NMP, put it into a grinding tank and grind it for 40 minutes. Coat it on the aluminum foil of a scraper coater to form a single-sided positive electrode sheet with a thickness of 60 μm. Put it in an oven to dry at 60°C for 2 hours, and cut it with a cutting machine. The positive electrode piece has a diameter of 12 mm, and the negative electrode is a lithium metal negative electrode with a diameter of 15 mm. The solid electrolyte membrane prepared in this embodiment is used as a separator, and the solid electrolyte membrane is cut to a diameter of 19 mm. After the positive electrode sheet is dried in a vacuum oven at 100°C for 20 hours, place the solid electrolyte membrane between the positive electrode and the negative electrode in the glove box, and add 5 μL of lithium hexafluorophosphate commercial electrolyte to the positive and negative electrode sides to wet the electrode. The effect of the chip was tested, and the button battery was assembled, and a 0.2C rate charge and discharge test was performed on the charge and discharge tester. The discharge specific capacity was 149mAh/g.

The preparation methods of Examples 2-6 are the same as those of Example 1, except that the proportions of prelithiated polyphenylene sulfide, PVDF, and lithium salt are different. The proportions of prelithiated polyphenylene sulfide, PVDF, and lithium salt in specific embodiments 2-6 are detailed in Table 1.

Example

The preparation method of Example 7 is the same as that of Example 2, except that the negative electrode uses Cu without negative electrode metal, specifically copper foil treated with phosphoric acid and nitric acid.

The preparation method of this comparative example is the same as that of the above embodiment, except that the polymer electrolyte of PVDF and lithium salt of prelithiated polyphenylene sulfide powder is not added.

The electrochemical performance comparison of specific examples 1-7 and comparative examples is listed in Table 1.

Table 1 Composition and electrochemical properties of polymer solid electrolytes in different embodiments

Example ingredients Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative example 1 negative electrode Lithium tablets Lithium tablets Lithium tablets Lithium tablets Lithium tablets Lithium tablets copper foil Lithium tablets PVDF 50g 50g 50g 50g 50g 60g 50g 50g PPS 9.2g 14.7g 20.75g 9.2g 14.7g 14.7g 14.7g 0g Li Yan 33g 33g 33g 33g 16.17g 16.17g 33g 33g Organic solvents NMP NMP NMP DMF NMP NMP NMP NMP 0.2C discharge specific capacity 149mAh/g 150mAh/g 140mAh/g 148mAh/g 145mAh/g 145mAh/g 150mAh/g 137mAh/g

Although the embodiments of the present invention have been described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. The preparation method of the lithium ion battery polymer solid electrolyte slurry is characterized by comprising the following steps:

step S1: preparing pre-lithiated polyphenylene sulfide powder, mixing polyphenylene sulfide particles, lithium chloride and a tetrachloro-p-benzoquinone anion complexing agent, placing the mixture in a reaction kettle of argon or nitrogen, heating to 200-400 ℃, reacting for 2-5 hours, then cooling to room temperature at a temperature of 1-2 ℃/min, washing the obtained product with deionized water for multiple times, filtering to neutrality, and vacuum-drying at 60 ℃ for 12-24 hours to obtain pre-lithiated polyphenylene sulfide powder A;

step S2: preparing polymer solid electrolyte slurry, namely premixing the pre-lithiated polyphenylene sulfide powder A obtained in the step S1 and polyvinylidene fluoride (PVDF) in a planetary mixer or a kneader for 1-2h, slowly adding an organic solvent until the solid content is 40-60%, and carrying out semi-dry kneading for 1-5h until the materials are uniformly kneaded; adding lithium salt, continuously kneading for 1-5h, then adding organic solvent until the solid content is 10-30%, and carrying out high-speed dispersion mixing, wherein the dispersion speed is 2000-5000 r/min, and the dispersion time is 1-2h, thus obtaining the solid electrolyte slurry B.

2. The method for preparing a solid electrolyte slurry according to claim 1, wherein the mass ratio of polyphenylene sulfide, lithium chloride and tetrachloro-p-benzoquinone in step S1 is 100:5-15:15-50; in the step S2, the dosage of the polyvinylidene fluoride (PVDF), the pre-lithiated polyphenylene sulfide powder A and the lithium salt is 40-50 parts by weight, 10-20 parts by weight and 20-40 parts by weight.

3. The method for producing a solid electrolyte slurry according to claim 1, wherein the lithium salt is LiBF ₄ And LiODFB, wherein LiBF is contained in the double salt ₄ With LiODFBThe mass ratio is 1:1-1.5.

4. The method for producing a solid electrolyte slurry according to claim 1, wherein the organic solvent is one or more of N, N-dimethylformamide, tetrahydrofuran, and N-methylpyrrolidone (NMP).

5. A lithium ion battery polymer solid electrolyte slurry prepared by the preparation method of any one of claims 1-4.

6. The use of the solid electrolyte slurry for lithium ion battery according to claim 5, wherein the binder for the electrode sheets in the process of manufacturing the cells completely or partially replaces the single PVDF binder.

7. The method for preparing the solid electrolyte membrane of the lithium ion battery based on the solid electrolyte slurry according to claim 5, wherein a doctor blade coater is adopted to coat the solid electrolyte slurry B into a solid electrolyte membrane with the thickness of 25-50 μm by using a tape casting method, and the solid electrolyte membrane is placed into a vacuum oven with the temperature of 60-100 ℃ to be dried for 10-24 hours, so that the solid electrolyte membrane C is finally obtained.

8. The solid electrolyte membrane for lithium ion battery prepared by the method for preparing the solid electrolyte membrane for lithium ion battery according to claim 7 is characterized by comprising continuous phase polyvinylidene fluoride (PVDF), reinforced phase pre-lithiated polyphenylene sulfide (PPS), lithium salt and organic solvent, wherein the weight percentage of PVDF is 40% -50%, the weight percentage of pre-lithiated PPS is 10% -20%, the weight percentage of lithium salt is 20-40%, the weight percentage of organic solvent is 5-15%, and the organic solvent is one or more of N, N-dimethylformamide, tetrahydrofuran and N-methylpyrrolidone (NMP).

9. The lithium ion battery polymer solid electrolyte membrane of claim 8, wherein the crystallinity of the continuous phase polyvinylidene fluoride (PVDF) is <72%; the linear crystallization area of the polyphenylene sulfide is more than 90%.

10. The use of the solid electrolyte membrane according to claim 9 for the preparation of a cell, wherein a metallic lithium negative lithium ion battery or a non-negative lithium ion battery is fabricated, placed between the positive electrode and the negative electrode.