CN111370760B - Composite solid electrolyte with wide electrochemical window and preparation method thereof - Google Patents

Abstract

The invention relates to the field of electrochemical energy storage, in particular to a wide electrochemical window composite solid electrolyte and a preparation method thereof. The composite solid electrolyte comprises polyacrylonitrile, lithium salt, ceramic filler and protective layer material, and the preparation method comprises the following steps: firstly, preparing precursor slurry of the composite electrolyte by ball milling or heating and stirring; then, coating the slurry on a clean glass plate by adopting a tape casting method, and drying to obtain the PAN-based composite solid electrolyte; and finally, preparing protective layer slurry, uniformly coating the protective layer slurry on one surface of the PAN-based composite solid electrolyte by a spin coating method or a tape casting forming method, and drying to obtain the composite solid electrolyte with the wide electrochemical window. The composite solid electrolyte of the invention has wide electrochemical window (0-4.5V vs. Li/Li) ⁺ ) The lithium ion battery has the advantages of thin thickness (5-300 mu m), good flexibility, simple preparation method and the like, and is suitable for the fields of lithium ion batteries, flow batteries and the like.

Description

A kind of wide electrochemical window composite solid electrolyte and its preparation method

technical field

The invention relates to the field of electrochemical energy storage, in particular to a wide electrochemical window composite solid electrolyte and a preparation method thereof.

Background technique

A new generation of batteries with high energy density and high safety is the key to the development of portable electronic products and electric vehicles, and has recently become the research focus of academia and industry. Lithium metal has extremely high energy density and the most negative potential, known as the crown of anode materials. In addition, traditional lithium-ion batteries use lithium iron phosphate as the positive electrode active material, but lithium iron phosphate has low potential and energy density, which cannot meet the current market demand for high energy density batteries. Using lithium metal negative electrode to replace traditional carbon material negative electrode and high-voltage ternary positive electrode to replace lithium iron phosphate positive electrode are currently the most potential solutions for realizing high energy density batteries. On the other hand, traditional lithium-ion batteries use flammable liquid electrolytes, which pose serious safety hazards. The use of solid electrolytes instead of traditional liquid electrolytes can effectively solve this problem. Moreover, since solid electrolytes usually have a high shear modulus, they can theoretically block the growth of lithium metal dendrites, and thus have the potential to make lithium metal negative electrodes practical.

Although there are many advantages, the current solid electrolytes usually have a narrow electrochemical window, which cannot be applied to both lithium metal anodes and high-voltage ternary cathodes. For example, oxide solid electrolyte perovskite-type LLTO and Nasicon-type LAGP have excellent positive electrode oxidation resistance, but they will be reduced by lithium metal and cannot be suitable for lithium metal negative electrode. As another example, polyethylene oxide (PEO) solid electrolyte has good compatibility with lithium metal, but the positive electrode has poor oxidation resistance and cannot be applied to ternary batteries.

Therefore, it is necessary to develop solid electrolytes with wide electrochemical windows to realize lithium metal ternary batteries with high energy density and high safety.

Contents of the invention

The purpose of the present invention is to provide a wide electrochemical window composite solid electrolyte and its preparation method, the composite solid electrolyte has a wide electrochemical window (0 ~ 4.5Vvs. Li/Li ⁺ ), thin thickness (5 ~ 300μm) and excellent flexibility. The preparation process is simple and easy to control, has strong operability and is suitable for large-scale production.

In order to achieve the above object, the present invention proposes the following technical solutions:

A composite solid electrolyte with a wide electrochemical window, the composition of the composite solid electrolyte is polyacrylonitrile, lithium salt, ceramic filler and protective layer material, wherein:

The ceramic filler is an inorganic non-metallic material that does not conduct electrons. The protective layer material includes a binder and a solid material that is stable in contact with lithium metal. The mass ratio of polyacrylonitrile to lithium salt is 1:0.001 to 1:10. Polyacrylonitrile The mass ratio of polyacrylonitrile to the ceramic filler is 1:20～1:0.01, and the mass ratio of polyacrylonitrile to the protective layer material is 1:1～1:0.0001; in the protective layer material, the adhesive and the solid in contact with lithium metal are stable The mass ratio between materials is 1:20～1:0.1.

The composite solid electrolyte with a wide electrochemical window has a wide electrochemical window of 0-4.5Vvs.Li/Li ⁺ .

In the composite solid electrolyte with wide electrochemical window, the ceramic filler used in the composite solid electrolyte is boron nitride or zirconia.

In the composite solid electrolyte with a wide electrochemical window, the lithium salt used in the composite solid electrolyte is lithium perchlorate or lithium bistrifluoromethanesulfonimide.

In the composite solid electrolyte with wide electrochemical window, in the protective layer material of the composite solid electrolyte, the binder is polyvinylidene fluoride or polyacrylic acid, and the solid material is boron nitride or lithium fluoride.

The preparation method of the wide electrochemical window composite solid electrolyte, the specific steps are as follows:

(1) Mix polyacrylonitrile, lithium salt and ceramic filler in proportion, add solvent N,N-dimethylformamide or dimethyl sulfoxide, and then ball mill or heat and stir to obtain the precursor slurry of composite solid electrolyte, The solid content of the precursor slurry is 5-95wt%;

(2) Apply the slurry obtained in step (1) to a clean glass plate by tape casting, and heat and dry in a vacuum oven to obtain a polyacrylonitrile-based composite solid electrolyte;

(3) The adhesive is dissolved in the solvent N, N-dimethylformamide or dimethyl sulfoxide to form a solution of the adhesive, so that the concentration of the adhesive in the solution is 0.1 to 30 wt%, and the protective layer will be prepared The solid material is dispersed in the solution of the binder to form a protective layer slurry, and the protective layer slurry is evenly coated on one surface of the polyacrylonitrile-based composite solid electrolyte obtained in step (2), and after drying, the obtained This wide electrochemical window is compounded with a solid electrolyte.

In the preparation method of the wide electrochemical window composite solid electrolyte, in step (3), the protective layer slurry is coated on the surface of the polyacrylonitrile-based composite solid electrolyte by using a spin coating method or a tape casting method.

In the preparation method of the wide electrochemical window composite solid electrolyte, in step (3), the spin coating method refers to a coating method in which the sol, solution or suspension is evenly spread on the surface of the substrate by utilizing the centrifugal force generated by rotation .

In the preparation method of the wide electrochemical window composite solid electrolyte, in steps (2) and (3), the tape casting method refers to: first pour the precursor slurry out of the container, and apply it on the base tape by scraping with a scraper After being dried and solidified, the film that becomes the green belt is peeled off from the top, and then the green belt is punched or laminated according to the size and shape of the finished product.

In the preparation method of the wide electrochemical window composite solid electrolyte, in step (2), the heating and drying temperature in a vacuum oven is 30-150° C., and the time is 1-36 hours; in step (3), the drying is in a vacuum oven Keep warm at 30-150°C for 1-100 hours.

Design idea of the present invention is:

The polyacrylonitrile (PAN)-based solid electrolyte of the present invention has good mechanical properties and positive electrode oxidation resistance, but its negative electrode reduction resistance is poor, which greatly limits its practicability. The invention enables one surface of the PAN-based solid electrolyte to have excellent negative electrode stability through simple surface modification, thereby obtaining the wide electrochemical window composite solid electrolyte. It is worth noting that the surface-modified slurry can dissolve a small amount of PAN during the drying process, thereby eliminating the interface between the protective layer and the PAN-based solid electrolyte. Therefore, the wide electrochemical window composite solid electrolyte is a whole with good mechanical properties.

The present invention has following advantage and beneficial effect:

1. In the present invention, a PAN-based composite solid electrolyte is prepared by a tape casting method, and then a protective layer is coated on the surface of the electrolyte by a spin coating method or a tape casting method, and the wide electrochemical window composite solid electrolyte is successfully obtained. The composite solid electrolyte can be applied to both low-potential lithium metal negative electrodes and high-voltage ternary positive electrodes, and has great application potential in lithium-ion batteries, flow batteries and other fields.

2. The preparation process of the present invention is simple, rapid and high in yield, and is suitable for large-scale production.

Description of drawings

Figure 1 is a photo of the wide electrochemical window composite solid electrolyte prepared in Example 1. Among them, (a) is the surface of the protective layer, (b) is the surface without the protective layer, and (c) is the bending diagram.

2 is a scanning electron microscope (SEM) image of the wide electrochemical window composite solid electrolyte prepared in Example 1. Among them, (a) is the surface of the protective layer, (b) is the surface without the protective layer, and (c) is the section.

3 is the electrochemical impedance spectroscopy (EIS) of the wide electrochemical window composite solid electrolyte prepared in Example 1. In the figure, the abscissa Z' represents the real part of the impedance (Ω), and the ordinate Z" represents the imaginary part of the impedance (Ω).

Fig. 4 is the linear sweep voltammetry curve (LSV) of the wide electrochemical window composite solid electrolyte prepared in Example 1.

Detailed ways

In order to facilitate the understanding of the present invention, the following will describe the present invention more fully. However, the present invention can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

In the specific implementation process, the composition of the wide electrochemical window composite solid electrolyte of the present invention is polyacrylonitrile (PAN), lithium salt (for example: lithium perchlorate (LiClO ₄ ) or lithium bistrifluoromethanesulfonimide (LiTFSI )), ceramic fillers (such as: boron nitride (BN), zirconia (ZrO ₂ ), etc.) Vinyl fluoride (PVDF), polyacrylic acid (PAA), etc., and the solid material that is stable in contact with lithium metal can be boron nitride (BN), lithium fluoride (LiF, etc.), among them: polyacrylonitrile and lithium salt The mass ratio is 1:0.01～1:10 (preferably 1:0.3～1:1), the mass ratio of polyacrylonitrile to ceramic filler is 1:20～1:0.01 (preferably 1:4～1:0.05), The mass ratio of polyacrylonitrile to the protective layer material is 1:1 to 1:0.0001 (preferably 1:0.1 to 1:0.02); in the protective layer material, the mass between the adhesive and the solid material that is stable in contact with lithium metal The ratio is 1:20 to 1:0.1 (preferably 1:10 to 1:1). The preparation method of the wide electrochemical window composite solid electrolyte of the present invention comprises the following steps: firstly, the precursor slurry of the composite electrolyte is prepared by ball milling or heating and stirring; After drying, the polyacrylonitrile-based composite solid electrolyte is obtained; finally, the protective layer slurry is prepared, and it is uniformly coated on one surface of the obtained polyacrylonitrile-based composite solid electrolyte by spin coating or tape casting, and after drying That is, the wide electrochemical window composite solid electrolyte is obtained.

Hereinafter, the present invention will be described in further detail through examples and accompanying drawings.

Example 1:

The specific preparation process of the wide electrochemical window composite solid electrolyte in this example is as follows:

Weigh 0.1 g of nano-boron nitride (BN) and place it in 10 ml of N,N-dimethylformamide (DMF), sonicate for 48 hours, and then centrifuge to obtain exfoliated BN nanosheets. Weigh 0.5g of polyacrylonitrile (PAN), 0.25g of lithium perchlorate (LiClO ₄ ) and 0.05g of BN nanosheets, add 10ml of N,N-dimethylformamide (DMF), heat and stir at 80°C to make PAN , LiClO ₄ was completely dissolved, and the precursor slurry of the composite solid electrolyte was obtained. Then, the obtained slurry was coated on a clean glass plate by tape casting, and dried in a vacuum oven at 80° C. for 12 hours to obtain a PAN-BN composite solid electrolyte. Then weigh 0.5 g of BN nanosheets and 0.06 g of polyvinylidene fluoride (PVDF), add 10 ml of DMF, heat and stir to dissolve PVDF, and obtain a protective layer slurry. Finally, the BN-PVDF slurry was evenly coated on the surface of the PAN-BN composite solid electrolyte by spin coating method, and kept in a vacuum oven at 80°C for 12 hours to obtain the wide electrochemical window composite solid electrolyte. In addition, the composite solid electrolyte can be cut into discs of different sizes with a punch as required.

The structure and performance of the wide electrochemical window composite solid electrolyte of this embodiment will be characterized as follows:

Figure 1 is a photo of the prepared wide electrochemical window composite solid electrolyte, (a), (b) and (c) are the surface of the protective layer, the surface without the protective layer, and the bending diagram, respectively. It can be seen from Figure 1(a) and (b) that the two surfaces of the composite electrolyte are very uniform. It can be seen from Figure 1(c) that the composite electrolyte has good flexibility. Figure 2(a) is the surface of the BN-PVDF protective layer. The protective layer is very dense and uniform, so it can effectively avoid the contact between PAN and lithium metal anode. It is worth mentioning that BN has a high shear modulus, which can effectively inhibit the growth of Li metal dendrites. Figure 2(b) is the surface of the wide electrochemical window composite electrolyte without a protective layer, and the surface is very uniform. Figure 2(c) is a cross-sectional view of the composite solid electrolyte, which shows that the thickness of the BN-PVDF protective layer is about 1.5 μm, and the total thickness of the composite electrolyte (including the protective layer) is only about 13.5 μm. More importantly, there is no clear boundary between the BN-PVDF protective layer and PAN-BN, indicating that the wide electrochemical window composite electrolyte is a whole. This is mainly because the solvent of the protective layer slurry can also dissolve PAN, so a small amount of PAN substrate can be dissolved during the drying process of the protective layer, thereby eliminating the interface between the two. Fig. 3 is the electrochemical impedance spectrum (EIS) of the prepared wide electrochemical window composite solid electrolyte, what this test uses is the button cell fixture, is lithium ion blocking electrode with stainless steel sheet, this composite solid electrolyte is sandwiched between two pieces In the middle of the stainless steel sheet, press it into a button battery, and measure the ESI curve in the frequency range of 0.1Hz to 7MHz. According to the thickness of the composite solid, the area of the stainless steel sheet and the internal resistance of the composite solid electrolyte (obtained by fitting the EIS data), the ionic conductivity of the composite electrolyte was calculated to be 0.1 mScm ^-1 . It can be seen from the linear sweep voltammetry curve in Fig. 4 that the electrochemical window of the composite solid electrolyte is 0-4.5Vvs. Li/Li ⁺ .

Example 2:

The specific preparation process of the wide electrochemical window composite solid electrolyte in this example is as follows:

Weigh 0.5g polyacrylonitrile (PAN), 1.0g lithium perchlorate (LiClO ₄ ) and 0.1g ZrO ₂ particles (particle size: ~100nm) and mix, add 15ml dimethyl sulfoxide (DMSO), heat at 60°C Stir to completely dissolve PAN and LiClO ₄ to obtain the precursor slurry of the composite solid electrolyte. Then the obtained slurry was coated on a clean glass plate by tape casting method, and dried in a vacuum oven at 60°C for 24 hours to obtain a PAN-ZrO ₂ composite solid electrolyte. Then weigh 0.5g of BN nanosheets (diameter: ~100nm) and 0.01g of polyvinylidene fluoride (PVDF), add 15ml of DMF, heat and stir to dissolve PVDF, and obtain the protective layer slurry. Finally, the tape casting method was used to uniformly coat the BN-PVDF slurry on the surface of the PAN-ZrO ₂ composite solid electrolyte, and keep it in a vacuum oven at 100°C for 6 hours to obtain the wide electrochemical window composite solid electrolyte. In addition, the composite solid electrolyte can be cut into discs of different sizes with a punch as required.

Example 3:

The specific preparation process of the wide electrochemical window composite solid electrolyte in this example is as follows:

Weigh 0.1 g of nanometer boron nitride (BN) and place it in 10 ml of N,N-dimethylformamide (DMF), sonicate for 48 hours, and then centrifuge to obtain BN nanosheets. Weigh 0.5g of polyacrylonitrile (PAN), 0.6g of lithium bistrifluoromethanesulfonimide (LiTFSI) and 0.1g of the resulting BN nanosheets, add 30ml of dimethyl sulfoxide (DMSO), and heat and stir at 80°C Make PAN, LiClO ₄ dissolve completely. Then, the obtained slurry was coated on a clean glass plate by tape casting, and dried in a vacuum oven at 40° C. for 30 h to obtain a PAN-BN composite solid electrolyte. Then weigh 0.5g of LiF particles (particle size: ~1um) and 0.3g of polyvinylidene fluoride (PVDF), add 10ml of DMSO, heat and stir to dissolve PVDF, and obtain the protective layer slurry. Finally, the LiF-PVDF slurry was evenly coated on the surface of the PAN-BN composite solid electrolyte by spin coating method, and kept in a vacuum oven at 60°C for 50 hours to obtain the wide electrochemical window composite solid electrolyte. In addition, the composite solid electrolyte can be cut into discs of different sizes with a punch as required.

Example 4:

The specific preparation process of the wide electrochemical window composite solid electrolyte in this example is as follows:

Weigh 0.5g polyacrylonitrile (PAN), 0.1g lithium chloride (LiCl) and 0.2g silicon dioxide (SiO ₂ ) nanoparticles and mix them, add 30ml N,N-dimethylformamide (DMF), at 30 Heat and stir at ℃ to completely dissolve PAN and LiCl. Then, the obtained slurry was coated on a clean glass plate by tape casting method, and dried in a vacuum oven at 30° C. for 36 hours to obtain a PAN-SiO ₂ composite solid electrolyte. Then weigh 0.5 g of BN nanosheets prepared in Example 1 and 0.3 g of polyacrylic acid (PAA), add 10 ml of N-methylpyrrolidone (NMP), heat and stir to dissolve PAA, and obtain a protective layer slurry. Finally, the BN-PAA slurry was evenly coated on the surface of the PAN-SiO ₂ composite solid electrolyte by spin coating, and kept in a vacuum oven at 80°C for 12 hours to obtain the wide electrochemical window composite solid electrolyte. In addition, the composite solid electrolyte can be cut into discs of different sizes with a punch as required.

Example 5:

The specific preparation process of the wide electrochemical window composite solid electrolyte in this example is as follows:

Weigh 0.5g polyacrylonitrile (PAN), 1.0g lithium perchlorate (LiClO ₄ ) and 0.1g tin oxide (SnO ₂ ) and mix, add 10ml N-methylpyrrolidone (NMP), heat and stir at 50°C to make PAN , LiClO ₄ is completely dissolved. Then the obtained slurry was coated on a clean glass plate by tape casting, and dried in a vacuum oven at 60°C for 12 hours to obtain a PAN-SnO ₂ composite solid electrolyte. Then weigh 0.5g of the nanosheets prepared in BN Example 1 and 0.1g of polyvinylidene fluoride (PVDF), add 10ml of DMF, heat and stir to dissolve the PVDF, and obtain the protective layer slurry. Finally, the BN-PVDF slurry was evenly coated on the surface of the PAN-SnO ₂ composite solid electrolyte by spin coating method, and kept in a vacuum oven at 60°C for 10 hours to obtain the wide electrochemical window composite solid electrolyte. In addition, the composite solid electrolyte can be cut into discs of different sizes with a punch as required.

The results of the examples show that the composite solid electrolyte of the present invention has the advantages of wide electrochemical window (0-4.5Vvs.Li/Li ⁺ ), thin thickness (5-300μm), good flexibility and simple preparation method, and is suitable for lithium ion Batteries, flow batteries and other fields.

Claims (7)

1. A wide electrochemical window composite solid electrolyte, characterized in that the composition of the composite solid electrolyte is polyacrylonitrile, lithium salt, ceramic filler and protective layer material, wherein: The mass ratio of polyacrylonitrile to lithium salt is 1:0.001 to 1:10, the mass ratio of polyacrylonitrile to ceramic filler is 1:20 to 1:0.01, and the mass ratio of polyacrylonitrile to protective layer material The mass ratio is 1:1～1:0.0001; the protective layer material includes an adhesive and a solid material that is stable in contact with lithium metal, and the mass ratio between the adhesive and the solid material that is stable in contact with lithium metal is 1:20～1:0.1; The ceramic filler is boron nitride or zirconia, the lithium salt is lithium perchlorate or lithium bistrifluoromethanesulfonimide, the binder is polyvinylidene fluoride or polyacrylic acid, and the solid material is boron nitride or lithium fluoride; The specific steps of the preparation method of the wide electrochemical window composite solid electrolyte are as follows: (1) Mix polyacrylonitrile, lithium salt and ceramic filler in proportion, add solvent N,N-dimethylformamide or dimethyl sulfoxide, and then ball mill or heat and stir to obtain the precursor slurry of composite solid electrolyte, The solid content of the precursor slurry is 5-95wt%; (2) coating the precursor slurry of the composite solid electrolyte obtained in step (1) on a clean glass plate by tape casting, and placing it in a vacuum oven for heating and drying to obtain a polyacrylonitrile-based composite solid electrolyte; (3) The adhesive is dissolved in the solvent N, N-dimethylformamide or dimethyl sulfoxide to form a solution of the adhesive, so that the concentration of the adhesive in the solution is 0.1 to 30 wt%, and the protective layer will be prepared The solid material is dispersed in the solution of the binder to form a protective layer slurry, and the protective layer slurry is evenly coated on one surface of the polyacrylonitrile-based composite solid electrolyte obtained in step (2), and after drying, the obtained This wide electrochemical window is compounded with a solid electrolyte. 2. The wide electrochemical window composite solid electrolyte according to claim 1, characterized in that the composite solid electrolyte has a wide electrochemical window of 0-4.5 Vvs. Li/Li ⁺ . 3. A method for preparing the wide electrochemical window composite solid electrolyte according to any one of claims 1 to 2, wherein the specific steps are as follows: (1) Mix polyacrylonitrile, lithium salt and ceramic filler in proportion, add solvent N,N-dimethylformamide or dimethyl sulfoxide, and then ball mill or heat and stir to obtain the precursor slurry of composite solid electrolyte, The solid content of the precursor slurry is 5-95wt%; (2) coating the precursor slurry of the composite solid electrolyte obtained in step (1) on a clean glass plate by tape casting, and placing it in a vacuum oven for heating and drying to obtain a polyacrylonitrile-based composite solid electrolyte; (3) The adhesive is dissolved in the solvent N, N-dimethylformamide or dimethyl sulfoxide to form a solution of the adhesive, so that the concentration of the adhesive in the solution is 0.1 to 30 wt%, and the protective layer will be prepared The solid material is dispersed in the solution of the binder to form a protective layer slurry, and the protective layer slurry is evenly coated on one surface of the polyacrylonitrile-based composite solid electrolyte obtained in step (2), and after drying, the obtained This wide electrochemical window is compounded with a solid electrolyte. 4. according to the preparation method of the wide electrochemical window composite solid electrolyte of claim 3, it is characterized in that, in step (3), adopt spin-coating method or casting method, the protective layer slurry is coated on polyacrylonitrile on the surface of the composite solid electrolyte. 5. According to the preparation method of the wide electrochemical window composite solid electrolyte according to claim 4, it is characterized in that, in step (3), the spin coating method refers to: using the centrifugal force generated by rotation to uniformly coat the sol, solution or suspension Coating method that spreads onto the surface of the substrate. 6. According to the preparation method of the wide electrochemical window composite solid electrolyte according to claim 4, it is characterized in that, in steps (2) and (3), the tape casting method refers to: first, the precursor slurry is poured out from the container , is scraped and coated on the base tape by a scraper, after drying and curing, it is peeled off to become a film of a green tape, and then the green tape is punched or laminated according to the size and shape of the finished product. 7. According to the preparation method of the wide electrochemical window composite solid electrolyte according to claim 4, it is characterized in that, in step (2), the temperature of heating and drying in the vacuum oven is 30～150 ℃, and the time is 1～36h; step ( In 3), drying is carried out in a vacuum oven at 30-150° C. for 1-100 hours.

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