Sulfide electrolyte filled interpenetrating porous network ultrathin interface layer and preparation method and application thereof

Abstract

The invention discloses a sulfide electrolyte filled interpenetrating porous network ultrathin interface layer as well as a preparation method and application thereof, and relates to the field of sulfide all-solid-state battery materials. Hydroxyl, carboxyl and amino in carboxymethyl chitosan can form hydrogen bonds and electrostatic interaction with fluorinated carbon chains of PVDF-HFP, toughness and environmental friendliness of the film are optimized, and excellent electrochemical stability of PVDF-HFP is reserved at the same time. Carrying out anti-solvent induced phase separation treatment on the film to form a uniform porous network structure; and finally, directionally depositing the sulfide electrolyte dispersion liquid into the porous network structure of the ultrathin film, accurately controlling the distribution of the electrolyte in a pore channel by using a spraying process, constructing a continuous lithium ion transmission channel, and drying to form the final composite ultrathin interface layer. The interface layer has the characteristics of ultrathin thickness and high ionic conductivity, and can effectively reduce the interface impedance and improve the interface stability and long cycle stability of the sulfide all-solid-state battery.

Description

Technical Field

[0001] The present invention relates to the field of sulfide all-solid-state battery materials, and specifically to an ultra-thin interface layer of an interpenetrating porous network filled with a sulfide electrolyte, a preparation method and an application thereof, and particularly to an ultra-thin interface layer of a PVDF-HFP composite bio-based interpenetrating porous network structure directional filled with a sulfide electrolyte, a preparation method and an application thereof. Background Art

[0002] With the development of new energy technologies, all-solid-state batteries have become a research hotspot for the next generation of energy storage devices due to their advantages such as high energy density, high safety, and no risk of leakage. Among them, sulfide electrolytes are widely used in all-solid-state battery systems due to their high ionic conductivity and excellent interface contact performance. However, compared with traditional liquid electrolytes, sulfide all-solid-state batteries still face many challenges in practical applications. Among them, the interface stability and cycle stability issues between the positive electrode material and the sulfide electrolyte are key factors affecting the performance of all-solid-state batteries. Due to the high chemical activity of sulfide electrolytes, side reactions are prone to occur when they come into contact with positive electrode materials such as high-nickel ternary materials, lithium-rich oxides, and lithium iron phosphate, resulting in increased interface impedance and degradation of the interface structure, which ultimately affects the long-term stable operation of the battery. In addition, the uneven contact between the sulfide electrolyte and the positive electrode active material particles may form a high impedance area, further reducing the rate performance and cycle life of the battery. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer and a preparation method and application thereof.

[0004] The objective of the present invention is achieved through the following technical solutions: <First aspect> The present invention provides a method for preparing an interpenetrating porous network ultra-thin interface layer filled with a sulfide electrolyte, comprising the following steps: The carboxymethyl chitosan-modified PVDF-HFP solution and the lithium salt solution are mixed evenly to obtain a precursor solution; The precursor solution is coated on a substrate, and an anti-solvent phase separation treatment and a drying treatment are performed to obtain an ultra-thin film with a porous structure having an interpenetrating network; The sulfide electrolyte slurry is uniformly deposited into the porous ultra-thin film structure, and dried to obtain the interface layer.

[0005] As an embodiment, the carboxymethyl chitosan-modified PVDF-HFP solution is a solution obtained by mixing a PVDF-HFP solution and a carboxymethyl chitosan solution.

[0006] As an embodiment, the ratio of solute to solvent in the carboxymethyl chitosan solution is (0.1-0.5) g: 20 mL.

[0007] As an embodiment, the solvent in the carboxymethyl chitosan solution is deionized water.

[0008] In some embodiments, the ratio of solute to solvent in the carboxymethyl chitosan solution is (0.2-0.3) g:20 mL.

[0009] As an embodiment, the ratio of solute to solvent in the PVDF-HFP solution is (0.5~2)g:10mL.

[0010] In some embodiments, the ratio of solute to solvent in the PVDF-HFP solution is (1-1.5) g: 10 mL.

[0011] As an embodiment, the solvent in the PVDF-HFP solution is a polar solvent.

[0012] As an embodiment, the solvent in the PVDF-HFP solution is one or more of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran and acetone.

[0013] In some embodiments, the solvent in the PVDF-HFP solution is N-methylpyrrolidone.

[0014] As an embodiment, the solute in the lithium salt solution is lithium bis(trifluoromethylsulfonyl)imide or lithium dioxalatoborate.

[0015] As an embodiment, the solvent in the lithium salt solution is acetonitrile or tetrahydrofuran.

[0016] As an embodiment, the ratio of solute to solvent in the lithium salt solution is (0.2~0.8)g:5mL.

[0017] In some embodiments, the ratio of solute to solvent in the lithium salt solution is 0.5 g: 5 mL.

[0018] As an embodiment, the ratio of solute to solvent in the sulfide electrolyte slurry is (0.2~1.5)g:10mL.

[0019] In some embodiments, the ratio of solute to solvent in the sulfide electrolyte slurry is (0.5~1.0)g:10mL.

[0020] As an embodiment, the solute in the sulfide electrolyte slurry is lithium bis(oxalatoborate) or lithium bis(trifluoromethanesulfonyl)imide.

[0021] As an embodiment, the solvent in the sulfide electrolyte slurry is an ether solvent.

[0022] In some embodiments, the solvent in the sulfide electrolyte slurry is anisole.

[0023] As an embodiment, magnetic stirring is used to mix the solutions during the preparation of the precursor solution.

[0024] As an embodiment, the carboxymethyl chitosan-modified PVDF-HFP solution is prepared by mixing by magnetic stirring and ultrasonic treatment.

[0025] As an embodiment, the precursor solution is coated on the substrate to form a thin film with a thickness of 0.3-1.0 μm.

[0026] As an embodiment, the substrate is made of glass.

[0027] As an embodiment, the anti-solvent phase separation treatment is to immerse the substrate with the coated thin film in deionized water for phase separation.

[0028] As an embodiment, the anti-solvent phase separation treatment time is 0.8~1.2h.

[0029] As an embodiment, the deposition method is: spraying the sulfide electrolyte slurry onto a single side of the porous ultra-thin film structure by a spraying method.

[0030] As an embodiment, the spraying rate is 0.05-0.15 mL / min, and the spraying distance is 5-10 cm.

[0031] In some embodiments, the spraying rate is 0.1 mL / min and the spraying distance is 8 cm.

[0032] As an embodiment, the drying parameters are vacuum degree 0.05~0.09MPa and 40~80°C.

[0033] In some embodiments, the drying parameters are vacuum degree 0.08 MPa and 50-60°C.

[0034] <Second Aspect> The invention provides a sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer, comprising a porous skeleton formed by a PVDF-HFP polymer modified by carboxymethyl chitosan, lithium salt distributed in the skeleton, and sulfide distributed in the pores of the skeleton.

[0035] As an embodiment, the thickness of the interface layer is 0.5-5 μm.

[0036] In some embodiments, the thickness of the interface layer is 0.8-1.0 μm.

[0037] As an embodiment, the impedance of the interface layer is 17-20Ω, and the ionic conductivity is 8.0-9mS / cm.

[0038] In some embodiments, the impedance of the interface layer is 17.3-19.1Ω, and the ionic conductivity is 8.0-8.9 mS / cm.

[0039] <Third Aspect> The present invention provides an application of a sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer in an all-solid-state battery.

[0040] As an embodiment, the interface layer is used as an electrolyte layer.

[0041] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing an interpenetrating porous network ultra-thin interface layer filled with a sulfide electrolyte, the method having the following characteristics: 1) Modification of bio-based materials The present invention uses renewable biopolymer carboxymethyl chitosan to modify PVDF-HFP. The hydroxyl, carboxyl and amino groups in the carboxymethyl chitosan molecules can interact with the fluorinated carbon chains of PVDF-HFP through hydrogen bonds and electrostatic interactions, thereby improving its environmental friendliness while completely retaining the excellent electrochemical stability of PVDF-HFP itself.

[0042] 2) Construction of porous structure The modified film is subjected to anti-solvent induced phase separation treatment to form uniform, interconnected micro-nanoscale pores with a high specific surface area, creating favorable conditions for subsequent electrolyte filling and ion transport.

[0043] 3) Electrolyte deposition The sulfide electrolyte dispersion is precisely and directionally deposited into the porous network of the PVDF-HFP / carboxymethyl chitosan composite membrane by using a spraying process. By adjusting the spraying parameters, the electrolyte particles are ensured to fill the pores evenly, thereby improving the interface stability, reducing the interface impedance, and being in close contact with the positive electrode. A continuous lithium ion transmission channel is successfully constructed at the interface, and after drying, a composite ultra-thin interface layer is finally obtained.

[0044] The sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer prepared by the above method has outstanding performance advantages, as follows: 1) Efficient ion transmission The interpenetrating porous network structure provides an efficient channel for ion transmission, greatly improves the ion transmission capacity, effectively reduces the interface impedance, and makes the interface layer have a higher ionic conductivity, ensuring that lithium ions can be quickly transmitted at the interface.

[0045] 2) Good compatibility The composite interface layer significantly enhances the compatibility between the polymer membrane and the sulfide electrolyte, further promotes the conduction of ions, and improves the interface stability of the composite membrane.

[0046] 3) Ultra-thin design The interface layer adopts an ultra-thin design concept, which ensures the stability of the interface without significantly increasing the overall thickness of the battery, helping to maintain the high energy density of the battery. It is especially suitable for high-performance energy storage devices and power batteries.

[0047] 4) Application value The ultra-thin interface layer prepared by the present invention can effectively solve the long-standing interface problem between the positive electrode and the electrolyte of the sulfide all-solid-state battery, and significantly improve the interface stability and long-cycle stability of the battery. This innovative achievement provides an efficient and easily scalable solution for improving the performance of sulfide all-solid-state batteries, which is of vital importance to promoting the commercial application of all-solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 This is a SEM image of the interface layer prepared in Example 1 of the present invention, with a magnification of ×2000; Figure 2 This is a SEM image of the interface layer prepared in Example 1 of the present invention, with a magnification of ×10000; Figure 3 It is the electrochemical EIS impedance diagram of the sample of Example 1; Figure 4 It is the electrochemical EIS impedance diagram of the sample of Example 2; Figure 5 It is the electrochemical EIS impedance diagram of the sample of Comparative Example 1; Figure 6 This is the electrochemical EIS impedance diagram of the sample of Comparative Example 2. DETAILED DESCRIPTION

[0049] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0050] For ease of understanding, the abbreviations or nouns mentioned below are first explained: PVDF-HFP: polyvinylidene fluoride-hexafluoropropylene copolymer.

[0051] Example 1 This embodiment provides a method for preparing an ultra-thin interpenetrating porous network interface layer filled with a sulfide electrolyte, comprising the following steps: S1. Preparation of modified PVDF-HFP solution using carboxymethyl chitosan The PVDF-HFP solution and the carboxymethyl chitosan solution were mixed, magnetically stirred for 3 h at room temperature and ultrasonically treated for 45 min in a 40 kHz ultrasonic bath to form a uniform mixed solution, thereby obtaining a carboxymethyl chitosan-modified PVDF-HFP solution; S2. Preparation of precursor solution Add lithium borate oxalate solution to the modified PVDF-HFP solution, and stir magnetically for 2 h at room temperature to mix the solution evenly to obtain a precursor solution; S3. Preparation of interpenetrating network porous structure ultra-thin film by smearing and drying The precursor solution was uniformly coated on a glass substrate to form an ultra-thin film with a thickness of about 0.8 μm, and then the film was immersed in 100 mL of deionized water for 1 hour, and the anti-solvent effect was used to induce PVDF-HFP phase separation to form a connected porous structure film. The film was taken out of the water and dried in a 50°C vacuum drying oven (vacuum degree 0.08 MPa) for 12 hours to ensure the stability of the porous structure and remove residual moisture to obtain an interpenetrating network porous structure ultra-thin film; S4. Preparation of sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer Using the directional spraying method, the sulfide electrolyte slurry was evenly sprayed onto one side of the porous structure film, and the spraying rate was controlled to be 0.1 mL / min and the spraying distance was 8 cm to ensure that the electrolyte was evenly penetrated into the porous network structure. Then it was dried in a 60°C vacuum drying oven (vacuum degree 0.08 MPa) for 6 hours to remove the solvent, and finally a PVDF-HFP / carboxymethyl chitosan-sulfide electrolyte composite ultra-thin interface layer was formed with a thickness of about 1.0 μm and a porous structure with a pore size of about 50~200 nm. Figure 1 and Figure 2 shown.

[0052] It should be noted that in this embodiment, single-sided spraying is used to avoid leaving a residual covering layer of the sulfide electrolyte slurry on the surface of the porous structure film. However, in actual operation, some residue is inevitable. Therefore, the sulfide electrolyte layer on the surface of the sprayed side of the porous structure film does not exceed 300nm.

[0053] In this embodiment, the volumes of the PVDF-HFP solution, the carboxymethyl chitosan solution and the lithium bis(oxalate)borate solution are 5 mL, 10 mL and 2 mL respectively.

[0054] PVDF-HFP solution: 1.0 g of PVDF-HFP was dissolved in 10 mL of N-methylpyrrolidone (NMP) and magnetically stirred in a 70°C water bath for 5 hours until it was completely dissolved to form a uniform transparent solution with a concentration of about 8.86 wt.% (the density of NMP is 1.028 g / mL at 25°C).

[0055] Carboxymethyl chitosan solution: 0.2 g of carboxymethyl chitosan was dissolved in 20 mL of deionized water to prepare an aqueous solution, and magnetic stirring was performed at room temperature for 5 hours until a uniform carboxymethyl chitosan solution was formed. The mass fraction of carboxymethyl chitosan was about 0.99 wt.%.

[0056] Lithium dioxalate borate solution: 0.5 g of lithium dioxalate borate was dissolved in 5 mL of acetonitrile and magnetically stirred at room temperature for 30 min to form a uniform lithium dioxalate borate solution.

[0057] Sulfide electrolyte slurry: 0.5 g sulfide electrolyte Li 6 PS 5 Cl was added to 10 mL of anisole, an ether solvent, and ball-milled for 30 min under argon protection, followed by ultrasonic stirring for 30 min under argon protection to form a uniform electrolyte slurry.

[0058] Example 2 This embodiment provides a method for preparing an ultra-thin interpenetrating porous network interface layer filled with a sulfide electrolyte, comprising the following steps: S1. Preparation of modified PVDF-HFP solution using carboxymethyl chitosan The PVDF-HFP solution and the carboxymethyl chitosan solution were mixed, magnetically stirred for 3 h at room temperature and ultrasonically treated for 40 min in a 40 kHz ultrasonic bath to form a uniform mixed solution, thereby obtaining a carboxymethyl chitosan-modified PVDF-HFP solution; S2. Preparation of precursor solution Adding lithium bis(trifluoromethylsulfonyl)imide solution to the modified PVDF-HFP solution, and magnetically stirring for 2 h at room temperature to mix the solution evenly, thereby obtaining a precursor solution; S3. Preparation of interpenetrating network porous structure ultra-thin film by smearing and drying The precursor solution was uniformly coated on a glass substrate to form an ultra-thin film with a thickness of about 0.5 μm, and then the film was immersed in 80 mL of deionized water for 0.5 h, and the anti-solvent effect was used to induce PVDF-HFP phase separation to form a connected porous structure film. The film was taken out of the water and dried in a vacuum drying oven at 60 ° C for 18 h to ensure the stability of the porous structure and remove residual moisture to obtain an interpenetrating network porous structure ultra-thin film; S4. Preparation of sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer Using the spraying method, the sulfide electrolyte slurry was evenly sprayed onto one side of the porous film structure, and the spraying rate was controlled to 0.15 mL / min to ensure that the electrolyte was evenly filled into the porous network structure. It was then dried in a vacuum oven at 80 ° C for 8 hours to remove the solvent, and finally formed a PVDF-HFP / carboxymethyl chitosan-sulfide electrolyte composite ultra-thin interface layer with a thickness of about 0.8 μm and a porous structure with a pore size of about 50~200 nm.

[0059] In this embodiment, the volumes of the PVDF-HFP solution, the carboxymethyl chitosan solution and the lithium bis(oxalate)borate solution are 8 mL, 8 mL and 3 mL respectively.

[0060] PVDF-HFP solution: 1.8 g of PVDF-HFP was dissolved in 12 mL of N-methylpyrrolidone (NMP) and magnetically stirred in a water bath at 60°C for 4 h until it was completely dissolved to form a uniform transparent solution with a concentration of about 12.73 wt.%.

[0061] Carboxymethyl chitosan solution: 0.3 g of carboxymethyl chitosan was dissolved in 20 mL of deionized water to prepare an aqueous solution, and magnetic stirring was performed at room temperature for 4 hours until a uniform carboxymethyl chitosan solution was formed. The mass fraction of carboxymethyl chitosan was about 1.48 wt.%.

[0062] Lithium bis(trifluoromethylsulfonyl)imide solution: 0.5 g of lithium bis(trifluoromethylsulfonyl)imide was dissolved in 5 mL of tetrahydrofuran and magnetically stirred at room temperature for 40 min to form a uniform lithium bis(trifluoromethylsulfonyl)imide solution.

[0063] Sulfide electrolyte slurry: 1.0 g sulfide electrolyte Li 6 PS 5 Cl was added to 15 mL of anisole and ball-milled for 60 min under argon protection, followed by ultrasonic stirring for 40 min under argon protection to form a uniform electrolyte slurry.

[0064] Comparative Example 1 This comparative example is a method for preparing an ultra-thin interface layer of an interpenetrating porous network filled with sulfide electrolyte using unmodified PVDF-HFP. The steps are basically the same as those in Example 1, except that: Cancel step S1; In step S2, a precursor solution is prepared using a PVDF-HFP solution.

[0065] An unmodified PVDF-HFP interfacial layer with sulfide electrolyte directional filling was prepared, and the thickness was about 1 μm.

[0066] Comparative Example 2 This comparative example provides a method for preparing an interpenetrating porous network ultra-thin interface layer, that is, referring to Example 1, through steps S1, S2 and S3, an interpenetrating network porous structure ultra-thin film is prepared, and the thickness is about 0.8 μm.

[0067] Comparative Example 3 This comparative example provides a method for preparing an ultra-thin interface layer, and the steps are basically the same as those in Example 1, except that: The three solutions PVDF-HFP solution, carboxymethyl chitosan solution and lithium dioxalate borate solution in step S1 and step S2 are mixed together and then magnetically stirred to fully mix the solutions.

[0068] However, the subsequent steps did not form a porous structure film.

[0069] Performance Testing The electrochemical performance of the interface layers prepared in each embodiment and comparative example was tested.

[0070] Ionic conductivity test: using Li 6 PS 5 Cl type sulfide electrolyte, first load 100 mg of sulfide electrolyte in the pressure battery mold, press at 1 ton pressure, hold pressure for 1 minute, then lay the prepared interface layer on the electrolyte, then load 100 mg of sulfide electrolyte, press at 1 ton pressure, hold pressure for 1 minute, use CHI660E electrochemical workstation, at room temperature in normal atmosphere, to perform AC impedance test (such as Figures 3 to 6 The ionic conductivity was calculated and the results are shown in Table 1.

[0071] Table 1 Electrochemical performance data of the interface layer

[0072] The interpenetrating porous network interface layer of the present invention has the characteristics of ultra-thinness and excellent interface compatibility, which can effectively reduce the interface impedance, and at the same time improve the interface ion conductivity by directional filling of sulfide electrolyte, optimize the lithium ion transmission channel, thereby significantly improving the rate performance and cycle life of the sulfide all-solid-state battery. The preparation method of the present invention has simple process, strong controllability, and is suitable for large-scale production, and has broad application prospects in the field of high energy density all-solid-state batteries.

[0073] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an ultra-thin interpenetrating porous network layer filled with sulfide electrolyte, characterized in that: The following steps are involved: The carboxymethyl chitosan-modified PVDF-HFP solution and the lithium salt solution are mixed evenly to obtain a precursor solution; The precursor solution is coated on a substrate, and an anti-solvent phase separation treatment and a drying treatment are performed to obtain an ultra-thin film with a porous structure having an interpenetrating network; The sulfide electrolyte slurry is uniformly deposited into the porous ultra-thin film structure, and dried to obtain the interface layer.

2. The preparation method according to claim 1, characterized in that: The carboxymethyl chitosan-modified PVDF-HFP solution is a solution obtained by mixing a PVDF-HFP solution and a carboxymethyl chitosan solution.

3. The preparation method according to claim 2, characterized in that: It also includes one or more of the following technical features: A. The ratio of solute to solvent in the carboxymethyl chitosan solution is (0.1-0.5) g: 20 mL; B. The solvent in the carboxymethyl chitosan solution is deionized water; C. The ratio of solute to solvent in the PVDF-HFP solution is (0.5-2) g: 10 mL; D. The solvent in the PVDF-HFP solution is one or more of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran and acetone.

4. The preparation method according to claim 1, characterized in that: It also includes one or more of the following technical features: A. The solute in the lithium salt solution is lithium bis(oxalatoborate) or lithium bis(trifluoromethylsulfonyl)imide, and the solvent is acetonitrile or tetrahydrofuran; B. The ratio of solute to solvent in the lithium salt solution is (0.2-0.8) g: 5 mL; C. The solute in the sulfide electrolyte slurry is lithium bis(oxalatoborate) or lithium bis(trifluoromethylsulfonyl)imide, and the solvent is an ether solvent; D. The ratio of solute to solvent in the sulfide electrolyte slurry is (0.2~1.5)g:10mL.

5. The preparation method according to claim 1, characterized in that: The precursor solution is coated on the substrate to form a thin film with a thickness of 0.3-1.0 μm.

6. The preparation method according to claim 1, characterized in that: The anti-solvent phase separation treatment is to immerse the substrate with the coated thin film in deionized water for phase separation.

7. The preparation method according to claim 1, characterized in that: The deposition method is: using a spraying method to spray the sulfide electrolyte slurry onto a single side of the porous ultra-thin film structure.

8. A sulfide electrolyte filled interpenetrating porous network ultra-thin interface layer, characterized in that: It is prepared according to the preparation method according to any one of claims 1 to 7.

9. The interface layer according to claim 8, characterized in that: It also includes one or more of the following technical features: A. The thickness of the interface layer is 0.5-5 μm; B. The impedance of the interface layer is 17-20Ω, and the ionic conductivity is 8.0-9mS / cm.

10. Use of the interface layer according to any one of claims 8 to 9 in an all-solid-state battery.

Images