CN104577198A - Core/shell structure fiber film-based gel polymer electrolyte and preparation method thereof - Google Patents

Abstract

The invention relates to a polymer electrolyte, in particular to a microporous polymer electrolyte skeleton material prepared by coaxial electrospinning technology, and a method for preparing a gel-type polymer electrolyte using the skeleton material, belonging to the polymer lithium ion battery field. The preparation steps are: (1) preparation of core and shell electrospinning solutions; (2) preparation of core/shell structure nanofiber membranes by using coaxial electrospinning technology; (3) drying, cutting, lamination and pressing of nanofiber membranes to form Polymer gel electrolyte skeleton; (4) Activate and gel the skeleton material in the electrolyte in the glove box. The electrolyte framework material has super adsorption and retention for the electrolyte, and the prepared gel polymer electrolyte has high ionic conductivity, stable electrochemical window and good charge and discharge performance, and the interface with the lithium electrode It has good compatibility, meets the assembly requirements of commonly used button batteries, and can be applied to the preparation of secondary lithium ion batteries.

Description

Gel polymer electrolyte based on core/shell structure fiber membrane and its preparation method

technical field

The invention mainly relates to a microporous polymer electrolyte framework material prepared by coaxial electrospinning technology and a method for preparing a gel-type polymer electrolyte by using the framework material, belonging to the field of polymer lithium ion batteries.

Background technique

The polymer lithium-ion battery uses a polymer electrolyte with ion conductivity and a diaphragm function instead of a liquid electrolyte, and its working principle is basically the same as that of a liquid lithium-ion battery. During the charge and discharge process of the battery, lithium ions are intercalated and deintercalated between the positive and negative electrodes through the ion-conductive polymer electrolyte to realize the transformation from chemical energy to electrical energy. Compared with liquid lithium-ion batteries, polymer lithium-ion batteries have high energy density, do not have the problem of liquid leakage in liquid electrolyte batteries, improve the capacity of the battery, and can be made into large-area ultra-thin films to ensure the contact with the electrodes. Full contact between them is convenient for the development of electronic products towards miniaturization, light weight and thin film.

The microporous network is an important characteristic of the skeleton material in gel-type polymer electrolytes. Some typical methods for preparing polymer porous membranes include: extraction-activation method (Bellcore method), thermally induced phase separation method, controlled evaporation precipitation method, vapor phase Precipitation method, immersion precipitation method, self-assembly method, etc. generally require a large amount of organic solvents, which will cause environmental pollution, and the residual solvent in the film will affect its electrochemical and mechanical properties. In addition, these methods often have difficulty in controlling the size and uniformity of micropores in the electrolyte, resulting in low porosity and poor process reproducibility. Electrospinning is an effective method for fabricating fibrous membranes with nanometer to micrometer pore sizes. By controlling the parameters of the electrospinning process, polymer films with a porosity of 30%-90% can be prepared conveniently. In addition, the interconnected interfiber microporous structure can provide a large specific surface area and good ion transport channels, improve the affinity and stability of the polymer matrix and the electrolyte, and improve the high-current discharge performance and cycle performance of the battery.

In the gel polymer electrolyte, the polymer framework material absorbs the liquid electrolyte to form a gel state, the polymer mainly acts as a mechanical support, and lithium ions are mainly conducted through the adsorbed liquid electrolyte, so that its room temperature ionic conductivity can be close to that of the liquid electrolyte . At present, commercialized polymer lithium-ion batteries mainly use gel-type polymer electrolytes. For example, commercial gel polyelectrolytes for Sony mobile power supplies have been mass-produced. The main advantage is that the gel structure is stable, easy to cut and suitable for large-scale Manufactured, but its room temperature ionic conductivity needs to be further improved. At present, the preparation techniques of gel-type polyelectrolytes mainly include coating/casting method and emerging electrospinning method. The coating/casting method is relatively widely used, and its advantage is that it can guarantee high mechanical properties, but the electrical properties are relatively poor, and the obtained product is not a real "gel". The polymer electrolyte prepared by the electrospinning technology that has developed rapidly in recent years has a true "gel" property and has great advantages in electrical properties, but the current structural system rich in liquid small molecules leads to The significant decrease in mechanical properties has hindered commercial applications. Adding reinforcing agents, cross-linking and other methods to improve its mechanical properties, but the electrochemical properties will be lost. To solve this contradiction, it is necessary to develop new technical means.

This patent uses coaxial electrospinning technology to design and prepare a polymer electrolyte framework material rich in microporous structure by selecting suitable core and shell polymers, and use this framework material to prepare gel-type polymer matter electrolyte. The shell polymer has good compatibility with the electrolyte and the lithium electrode, while the core polymer has good mechanical properties and can also provide ion transport channels. The two synergistically solve the problem of passivation of the interface between the polymer electrolyte and the lithium electrode, And problems such as poor mechanical properties, but also achieve higher liquid absorption and retention of polymer electrolytes, the prepared gel polymer electrolytes have high ionic conductivity, stable electrochemical window and good charge and discharge The performance can meet the assembly requirements of commonly used button batteries, and is suitable for the preparation of secondary lithium-ion batteries.

Contents of the invention

The purpose of the present invention is to provide a gel polymer electrolyte based on a core/shell structure nanofiber membrane and a preparation method thereof, the specific technical contents are as follows.

A microporous polymer electrolyte framework material prepared by coaxial electrospinning technology, and a method for preparing a gel-type polymer electrolyte using the framework material, are characterized in that they include the following components and steps:

Component 1: nanofiber core layer polymer, including polyacrylonitrile or polyvinylidene fluoride, with a content of 33% to 45wt% in the nanofiber. The core polymer should meet the requirements of mechanical reinforcement and ion transport pathway, meet the requirements of spinnability, and be incompatible with the shell polymer.

Component 2: nanofiber shell polymer, including polymethyl methacrylate or polyethylene oxide, with a content of 55% to 67wt% in the nanofiber. The shell polymer should have good affinity for lithium electrodes and electrolytes, satisfy spinnability, and be immiscible with the core polymer.

Component 3: a preferred electrolyte, including LiPF ₆ /DEC-EC (molar ratio 1:1) or LiPF ₆ /DMC-EC (molar ratio 1:1).

Step 1: Prepare the spinning solution for the core and shell polymers respectively, prepare a polymer nanofiber membrane with a core/shell structure by coaxial electrospinning technology, and dry it in a vacuum oven at 50°C for 8 hours;

Step II: cutting the nanofiber membrane obtained in step I into discs, stacking and compacting the discs, and drying them in a vacuum oven at 60°C for 20 hours to obtain a polymer gel electrolyte framework material;

Step Ⅲ: Place the skeleton material obtained in step Ⅱ in the electrolyte solution for activation and gelation in the glove box, blot the residual electrolyte solution on the surface with filter paper, obtain a transparent polymer gel electrolyte, and package it in an argon atmosphere spare.

See Figure 1 for the cutting, activation and gelation process of the polymer electrolyte framework material.

The core/shell structure porous polymer electrolyte skeleton material designed in this patent has good compatibility between the shell polymer and the electrolyte and lithium electrodes, while the core polymer has good mechanical properties and can also provide ion transmission channels. The two work together to solve the problems of passivation of the interface between the polymer electrolyte and the lithium electrode, and poor mechanical properties. Through the design of the core/shell structure, the advantages of different polymer materials can be fully utilized, the shortcomings of a single material can be avoided, and the nanoscale structural "composite" and functional complementarity can be realized. Compared with the common preparation method of gel-type polymer electrolyte—coating/casting method, the preparation process adopted by the present invention is simple, the ability to absorb and retain liquid electrolyte is stronger, and it has obvious advantages in electrochemical performance. The gel polymer electrolyte has high ionic conductivity, stable electrochemical window and good charge and discharge performance, can meet the assembly requirements of common button batteries, and is suitable for the preparation of secondary lithium ion batteries.

Through the above technical content, the following inventive effects can be obtained: the saturated liquid absorption rate of the polymer electrolyte skeleton material at room temperature is ≥870%, and the retention rate of the absorbed electrolyte after 15 days of storage is ≥86%; the lithium ion conductivity of the polymer electrolyte at room temperature is ≥4.4×10 ^-3 S·cm ^-1 , electrochemical window ≥ 4.5V, compared with pure component gel electrolyte, it has obvious advantages in charge and discharge stability and capacity retention.

Description of drawings

Fig. 1 Cutting, activation and gelation process of coaxial polymer electrolyte framework material.

Figure 2 is the first 50 cycle capacity curves of the core-shell gel electrolyte and the pure component electrolyte battery, the charge and discharge current is 0.1C, the abscissa is Cycle numbers, and the ordinate is Q/mAh.

Detailed ways:

The present invention is illustrated in detail by the following examples. The liquid absorption rate and liquid retention capacity are obtained by weighing method; the ionic conductivity is calculated by curve fitting measured by AC impedance method, and the test device is stainless steel/gel electrolyte/stainless steel system; the electrochemical stability window is scanned by linear voltammetry The test device is a stainless steel/gel electrolyte/metal lithium system; the relationship between battery capacity and cycle times is obtained from the constant current charge and discharge curve, and the charge and discharge current is 0.1C.

Example 1:

Component 1 is polyacrylonitrile with a molecular weight of 10 ⁵ g/mol (Mw), and the manufacturer is UK Courtaulds Co. Component 2 is polymethyl methacrylate with a molecular weight of 1.0-1.3×10 ⁵ g/mol (Mw), and the manufacturer is Aldrich Chemical Co. Component 3 is an electrolyte solution of 1 mol/L LiPF ₆ /DEC-EC (molar ratio is 1:1), and the manufacturer is Beijing Chemical Plant. The solvent used for the core layer and the shell layer spinning solution is N,N-dimethylformamide, wherein the concentration of the core layer spinning solution is 14wt%, and the concentration of the shell layer spinning solution is 20wt%. During the coaxial electrospinning process The flow rate ratio of the core spinning liquid to the shell spinning liquid is 0.5. The polymer fiber membrane obtained by electrospinning was dried in a vacuum oven at 50 °C for 8 h to remove residual moisture and solvent. Then it was cut into discs with a diameter of 22 mm, laminated and compacted, with a total weight of 78 mg, and vacuum-dried at 60° C. for 20 h to obtain an electrolyte framework material. Weigh the electrolyte according to the weight ratio of the framework material to the electrolyte of 1:15, soak the polymer framework material in the electrolyte solution at room temperature for 40 hours in an argon-filled glove box, and take out the remaining electrolyte solution on the surface with filter paper , to complete the activation and gelation to obtain a transparent polymer gel electrolyte.

The room temperature saturated liquid absorption rate of the polymer electrolyte skeleton material is 870%, and the retention rate of the absorbed electrolyte after 15 days of storage is 86.4%; the lithium ion conductivity of the polymer electrolyte at room temperature is 4.4×10 ^-3 S·cm ^-1 The window is 4.5V. A half-battery was assembled with a lithium metal sheet as the negative electrode and lithium cobalt oxide as the positive electrode. The constant current charge and discharge performance was tested. The charge and discharge current was 0.1C, and the capacity of the first 50 cycles was tested. It can be seen from Figure 2 that the polymer electrolyte material prepared in this example is significantly better than the pure PAN component gel electrolyte (comparative example) in terms of charge and discharge stability and capacity retention.

Example 2:

Component 1 is polyvinylidene fluoride, the molecular weight is 5.3×10 ⁵ g/mol (Mw), and the manufacturer is Aldrich Chemical Co. Component 2 is polyethylene oxide with a molecular weight of 10 ⁵ g/mol (Mw), and the manufacturer is Shanghai Liansheng Chemical Company. Component 3 is 1mol/L LIPF6/DMC-EC (molar ratio 1:1) electrolyte. The solvent used for the core layer and the shell layer spinning solution is N,N-dimethylformamide, wherein the concentration of the core layer spinning solution is 10wt%, and the concentration of the shell layer spinning solution is 16wt%. During the coaxial electrospinning process The flow rate ratio of the core spinning liquid to the shell spinning liquid is 0.7. The polymer fiber membrane obtained by electrospinning was dried in a vacuum oven at 50 °C for 8 h to remove residual moisture and solvent. Then it was cut into discs with a diameter of 24 mm, laminated and compacted, with a total weight of 85 mg, and vacuum-dried at 60° C. for 20 h to obtain an electrolyte framework material. Weigh the electrolyte according to the weight ratio of the framework material to the electrolyte of 1:20, soak the polymer framework material in the electrolyte solution at room temperature for 50 hours in an argon-filled glove box, and take out the remaining electrolyte solution on the surface with filter paper , to complete the activation and gelation to obtain a transparent polymer gel electrolyte.

The room temperature saturated liquid absorption rate of the polymer electrolyte skeleton material is 1006%, and the retention rate of the absorbed electrolyte after 15 days of storage is 90.6%; the lithium ion conductivity of the polymer electrolyte at room temperature is 4.8×10 ^-3 S·cm ^-1 The window is 4.7V. A half-battery is assembled with a lithium metal sheet as the negative electrode and lithium cobalt oxide as the positive electrode, and the constant current charge and discharge performance is tested. The charge and discharge current is 0.1C, and the capacity of the first 50 cycles is tested. It can be seen from Figure 2 that the polymer electrolyte material prepared in this example is significantly better than the pure PAN component gel electrolyte (comparative example) in terms of charge and discharge stability and capacity retention.

Example 3:

Component 1 is polyacrylonitrile with a molecular weight of 10 ⁵ g/mol (Mw), and the manufacturer is UK Courtaulds Co. Component 2 is polyethylene oxide with a molecular weight of 10 ⁵ g/mol (Mw), and the manufacturer is Shanghai Liansheng Chemical Company. Component 3 is 1mol/L LIPF6/DEC-EC (molar ratio 1:1) electrolyte. The solvent used for the core layer and the shell layer spinning solution is N,N-dimethylformamide, wherein the concentration of the core layer spinning solution is 12wt%, and the concentration of the shell layer spinning solution is 18wt%. During the coaxial electrospinning process The flow rate ratio of the core spinning liquid to the shell spinning liquid is 0.8. The polymer fiber membrane obtained by electrospinning was dried in a vacuum oven at 50 °C for 8 h to remove residual moisture and solvent. Then it was cut into discs with a diameter of 20 mm, laminated and compacted, with a total weight of 70 mg, and vacuum-dried at 60° C. for 20 h to obtain an electrolyte framework material. Weigh the electrolyte solution according to the weight ratio of the framework material to the electrolyte solution of 1:18, soak the polymer framework material in the electrolyte solution at room temperature for 45 hours in a glove box filled with argon gas, and take out the residual electrolyte solution on the surface with filter paper , to complete the activation and gelation to obtain a transparent polymer gel electrolyte.

The room temperature saturated liquid absorption rate of the polymer electrolyte framework material is 1082%, and the retention rate of the absorbed electrolyte after 15 days of storage is 91.6%; the room temperature lithium ion conductivity of the polymer electrolyte is 4.4×10 ^-3 S·cm ^-1 , electrochemical The window is 5.0V. A half-battery was assembled with a lithium metal sheet as the negative electrode and lithium cobalt oxide as the positive electrode. The constant current charge and discharge performance was tested. The charge and discharge current was 0.1C, and the capacity of the first 50 cycles was tested. It can be seen from Figure 2 that the polymer electrolyte material prepared in this example is significantly better than the pure PAN component gel electrolyte (comparative example) in terms of charge and discharge stability and capacity retention.

Comparative example:

In order to compare with the example of the gel polymer electrolyte based on the core/shell structure nanofiber membrane, pure polyacrylonitrile was used to prepare the nanofiber membrane without the core/shell structure, the molecular weight was 10 ⁵ g/mol (Mw), and the production The manufacturer is UK Courtaulds Co. The concentration of the spinning solution was 14wt%, and other electrospinning parameters were kept the same as in Example 1. The polymer fiber membrane obtained by electrospinning was dried in a vacuum oven at 50 °C for 8 h to remove residual moisture and solvent. Then it was cut into discs with a diameter of 22 mm, laminated and compacted, with a total weight of 78 mg, and vacuum-dried at 60° C. for 20 h to obtain an electrolyte framework material. Select 1mol/L LIPF6/DEC-EC (molar ratio is 1:1) electrolyte, weigh the electrolyte according to the weight ratio of the skeleton material and the electrolyte as 1:15, and put the polymer in a glove box filled with argon. The skeleton material was soaked in the electrolyte solution at room temperature for 40 hours, and the residual electrolyte solution on the surface was blotted with filter paper to complete activation and gelation, and a transparent polymer gel electrolyte was obtained.

The room temperature saturated liquid absorption rate of the polyacrylonitrile fiber membrane electrolyte skeleton material is 675%, and the retention rate of the absorbed electrolyte after 15 days of storage is 84.3%; the lithium ion conductivity of the polymer electrolyte at room temperature is 1.7×10 ^-3 S·cm ^-1 , the electrochemical window is 5.2V. Compared with the examples of the present invention, the advantages of the gel polymer electrolyte based on the core/shell structure nanofibrous membrane can be highlighted.

Claims (8)

1. A gel polymer electrolyte based on core/shell structure nanofibrous membrane and preparation method thereof, is characterized in that, comprises following components and steps: Component 1: nanofiber core polymer; Component 2: nanofiber shell polymer; Component 3: preferred electrolyte; Step 1: Prepare the spinning solution for the core and shell polymers respectively, prepare a polymer nanofiber membrane with a core/shell structure by coaxial electrospinning technology, and dry it in a vacuum oven at 50°C for 8 hours; Step II: cutting the nanofiber membrane obtained in step I into discs, stacking and compacting the discs, and drying them in a vacuum oven at 60°C for 20 hours to obtain a polymer gel electrolyte framework material; Step Ⅲ: Place the skeleton material obtained in step Ⅱ in the electrolyte solution for activation and gelation in the glove box, blot the residual electrolyte solution on the surface with filter paper, obtain a transparent polymer gel electrolyte, and package it in an argon atmosphere spare. 2. a kind of gel polymer electrolyte based on core/shell structure nanofiber membrane and preparation method thereof according to claim 1, wherein, the nanofiber core layer polymer described in component 1 is polyacrylonitrile or The content of polyvinylidene fluoride in the nanofiber is 33%~45wt%. 3. a kind of gel polymer electrolyte based on core/shell structure nanofiber membrane and preparation method thereof according to claim 1, wherein, the nanofiber shell polymer described in component 2 is polymethacrylic acid Methyl ester or polyethylene oxide, the content in the nanofiber is 55%~67wt%. 4. A kind of gel polymer electrolyte based on core/shell structure nanofiber membrane and preparation method thereof according to claim 1, wherein, the preferred electrolyte described in component 3 comprises LiPF ₆ /DEC-EC (molar ratio is l:1) or LiPF ₆ /DMC-EC (molar ratio is l:1). 5. A kind of gel polymer electrolyte based on core/shell structure nanofiber membrane and preparation method thereof according to claim 1, wherein, the concentration of the core layer polymer spinning solution in step I is controlled at 10 ~ 14wt%, The concentration of the shell polymer spinning solution is controlled at 16-20wt%. 6. A gel polymer electrolyte based on a core/shell structure nanofiber membrane and a preparation method thereof according to claim 1, wherein the flow rate ratio of the core layer spinning solution to the shell layer spinning solution in step I is 0.5 ~0.8. 7. A gel polymer electrolyte based on a core/shell structure nanofiber membrane and a preparation method thereof according to claim 1, wherein the total weight of the stacked skeleton material in step II is controlled between 70 and 85 mg, The disc diameter is 20~24mm. 8. A gel polymer electrolyte based on a core/shell structure nanofiber membrane and a preparation method thereof according to claim 1, wherein, during the activation and gelation of the polymer electrolyte skeleton material in step III, the skeleton material The weight ratio to the electrolyte is 1:15~1:20, and the overall time for activation and gelation is 40~50h.