A method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability

Abstract

The application relates to a preparation method of an asymmetric quasi-solid-state electrolyte with enhanced interface stability, and relates to a preparation method of a quasi-solid-state electrolyte. The application aims to solve the problems of low ion conductivity, poor interface stability, narrow electrochemical window and short cycle life of a polymer solid-state electrolyte. The method comprises the following steps: I, preparing TiN nanofibers; II, preparing barium strontium titanate nanofibers; III, preparing a pouring liquid; and IV, preparing a solid-state electrolyte. The prepared asymmetric quasi-solid-state electrolyte with enhanced interface stability has an ion conductivity as high as 7.3*10 ‑4 S / cm, a lithium ion transference number of 0.74 and an electrochemical window as wide as 4.8 V; a LiFePO4||CSE||Li full battery assembled based on the electrolyte exhibits an initial discharge specific capacity of 140 mAh / g at a 1C rate, and the capacity retention rate is still more than 75% after 1000 cycles.

Description

Technical Field

[0001] This invention relates to a method for preparing a quasi-solid-state electrolyte. Background Technology

[0002] The development of electric vehicles, grid energy storage, and consumer electronics industries has intensified the global demand for lithium metal batteries with high energy density and long cycle life. Lithium metal batteries, with their higher theoretical specific capacity (3860 mAh / g) and lower redox potential (-3.04 V vs. standard hydrogen electrode), have become the next major research direction for lithium-ion batteries. However, electrolytes and separators struggle to suppress lithium dendrite growth. Dendrites piercing the separator and causing short circuits can lead to severe thermal runaway or even explosions, posing significant safety hazards and hindering the practical application of lithium metal batteries. As the link between the cathode and lithium metal anode, solid-state electrolytes (SSEs) combine the characteristics of being solvent-free and having high mechanical strength, making them a promising ideal alternative to liquid electrolytes.

[0003] Compared with inorganic solid electrolytes, polymer electrolytes have attracted much attention due to their excellent flexibility and film-forming processability. Using a solid-liquid hybrid system can further improve the interfacial contact between the electrolyte and the electrode, reduce interfacial impedance, and thus enhance battery performance. However, polymer electrolytes still face the following challenges: (1) insufficient mechanical strength, making it difficult to completely suppress lithium dendrite penetration; (2) low ionic conductivity, especially at room temperature compared to liquid electrolytes; and (3) limited electrochemical window, making them prone to decomposition under high pressure, leading to a decline in electrochemical performance. These problems limit the application potential of polymer electrolytes in high-performance batteries.

[0004] Currently, polymer materials such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), and PVDF-HFP copolymer (PVDF-HFP) are widely used as substrates for polymer electrolytes. However, existing polymer solid electrolytes suffer from problems such as low ionic conductivity, poor interfacial stability, narrow electrochemical window, and short cycle life. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of low ionic conductivity, poor interfacial stability, narrow electrochemical window and short cycle life of polymer solid electrolytes, and to provide a method for preparing an asymmetric quasi-solid electrolyte with enhanced interfacial stability.

[0006] A method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability is specifically carried out according to the following steps:

[0007] I. Preparation of TiN nanofibers:

[0008] ① Dissolve polyvinylpyrrolidone in a mixed solution of anhydrous ethanol and glacial acetic acid, stir magnetically until the polyvinylpyrrolidone is completely dissolved, then add tetrabutyl titanate and continue stirring until a homogeneous solution is formed, to obtain electrospinning precursor solution I.

[0009] ② Transfer the precursor solution I for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning, place the obtained fibers in an air atmosphere and heat them to 500℃~600℃. Calcinate them in an air atmosphere at 500℃~600℃ for a period of time to obtain TiO2 nanofibers. Place the TiO2 nanofibers in a tube furnace, introduce a mixture of ammonia / argon gas into the tube furnace, heat the tube furnace to 900℃~1000℃, and calcine them in an ammonia / argon mixed atmosphere at 900℃~1000℃ for a period of time to obtain TiN nanofibers.

[0010] II. Preparation of barium strontium titanate nanofibers:

[0011] ① Dissolve polyvinylpyrrolidone, barium acetate and strontium acetate in a mixed solution of anhydrous ethanol and glacial acetic acid. Stir magnetically until polyvinylpyrrolidone is completely dissolved. Then add tetrabutyl titanate and continue stirring until a homogeneous solution is formed to obtain electrospinning precursor solution II.

[0012] ② Transfer the precursor solution II for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning is completed, place the obtained fibers in the air and heat them to 800℃~1000℃. Calcine them for a period of time in an air atmosphere at a temperature of 800℃~1000℃ to obtain barium strontium titanate nanofibers.

[0013] III. Preparation of casting fluid:

[0014] ① Under ultrasonic conditions, barium strontium titanate nanofibers are dispersed in N,N-dimethylformamide, and then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added. The mixture is ultrasonically and magnetically stirred for a period of time to obtain casting liquid A.

[0015] ② Under ultrasonic conditions, TiN nanofibers are dispersed in N,N-dimethylformamide, and then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added. The mixture is ultrasonically and magnetically stirred for a period of time to obtain casting liquid B.

[0016] IV. Preparation of solid electrolytes:

[0017] ① Place the casting liquid A under vacuum conditions to degas for a period of time, then cast it onto a clean glass plate, scrape it into a film with a scraper, and then place it in a forced-air drying oven to dry for a period of time to obtain the BST layer;

[0018] ② The casting liquid B is poured onto the BST layer, scraped into a film using a scraper, and then placed in a forced-air drying oven to dry for a period of time to obtain the TiN-BST bilayer asymmetric solid electrolyte, which is an asymmetric quasi-solid electrolyte that enhances interfacial stability.

[0019] The principles and advantages of this invention:

[0020] I. This invention uses PVDF-HFP and P(VDF-TrFE-CFE) as polymer substrates. PVDF-HFP exhibits significant advantages due to its excellent heat resistance and good mechanical strength. Meanwhile, poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CFE)) has a higher dielectric constant, which is more conducive to the dissociation of lithium salts, thereby achieving higher room temperature ionic conductivity. Mixing these two materials as a polymer matrix can not only achieve both high mechanical strength and high ionic conductivity, but also facilitate the manufacture of polymer electrolytes with high mechanical strength and high ionic conductivity, thus constructing high-performance lithium metal batteries.

[0021] II. This invention modifies the polymer by introducing barium strontium titanate (BST) nanofibers and titanium nitride (TiN) nanofibers, thereby reducing the polymer's crystallinity and improving the electrolyte's mechanical properties. A bilayer asymmetric solid electrolyte is prepared using a casting method, with the BST layer facing the positive electrode and the TiN layer facing the lithium metal negative electrode. The BST layer has a higher dielectric constant, which helps promote the dissociation of lithium salt in the electrolyte, significantly improving the electrolyte's ionic conductivity and broadening the electrochemical window. The TiN layer effectively suppresses side reactions between the electrolyte membrane and lithium metal, further improving the battery's cycle stability. Electrochemical performance tests show that the asymmetric quasi-solid electrolyte with enhanced interfacial stability prepared in this invention exhibits a high dielectric constant of 7.3 × 10⁻⁶. -4 The electrolyte exhibits an ionic conductivity of S / cm, a lithium-ion transference number of 0.74, and a wide electrochemical window of 4.8V. A LiFePO4||CSE||Li full cell assembled based on this electrolyte demonstrated an initial discharge specific capacity of 140 mAh / g at 1C rate, and retained over 75% of its capacity after 1000 cycles. This indicates that the asymmetric quasi-solid-state electrolyte with enhanced interfacial stability provided by this invention exhibits excellent performance in terms of cycle stability and lifespan, and has broad application prospects. Attached Figure Description

[0022] Figure 1The figures are electron microscope images and optical photographs; (a) is a surface electron microscope image of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, (b) is a cross-sectional electron microscope image of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, (c) is an optical photograph of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, (d) is a surface electron microscope image of the BST monolayer solid electrolyte prepared in Comparative Example 1, (e) is a cross-sectional electron microscope image of the BST monolayer solid electrolyte prepared in Comparative Example 1, (f) is an optical photograph of the BST monolayer solid electrolyte prepared in Comparative Example 1, (g) is a surface electron microscope image of the polymer solid electrolyte prepared in Comparative Example 2, (h) is a cross-sectional electron microscope image of the polymer solid electrolyte prepared in Comparative Example 2, and (i) is an optical photograph of the polymer solid electrolyte prepared in Comparative Example 2.

[0023] Figure 2 The XRD patterns are of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2.

[0024] Figure 3 The ionic conductivity and lithium-ion transference number of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2 are compared.

[0025] Figure 4 The electrochemical stability windows of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2 are shown.

[0026] Figure 5 The limiting current density of lithium symmetric batteries assembled using the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2.

[0027] Figure 6 The rate performance curves of LiFePO4||CSE||Li full cells assembled using the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2 are shown.

[0028] Figure 7The graph shows the cycling performance of LiFePO4||CSE||Li full cells assembled using the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2 at 1C rate. Detailed Implementation

[0029] Specific Implementation Method 1: This implementation method provides a method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability, specifically completed according to the following steps:

[0030] I. Preparation of TiN nanofibers:

[0031] ① Dissolve polyvinylpyrrolidone in a mixed solution of anhydrous ethanol and glacial acetic acid, stir magnetically until the polyvinylpyrrolidone is completely dissolved, then add tetrabutyl titanate and continue stirring until a homogeneous solution is formed, to obtain electrospinning precursor solution I.

[0032] ② Transfer the precursor solution I for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning, place the obtained fibers in an air atmosphere and heat them to 500℃~600℃. Calcinate them in an air atmosphere at 500℃~600℃ for a period of time to obtain TiO2 nanofibers. Place the TiO2 nanofibers in a tube furnace, introduce a mixture of ammonia / argon gas into the tube furnace, heat the tube furnace to 900℃~1000℃, and calcine them in an ammonia / argon mixed atmosphere at 900℃~1000℃ for a period of time to obtain TiN nanofibers.

[0033] II. Preparation of barium strontium titanate nanofibers:

[0034] ① Dissolve polyvinylpyrrolidone, barium acetate and strontium acetate in a mixed solution of anhydrous ethanol and glacial acetic acid. Stir magnetically until polyvinylpyrrolidone is completely dissolved. Then add tetrabutyl titanate and continue stirring until a homogeneous solution is formed to obtain electrospinning precursor solution II.

[0035] ② Transfer the precursor solution II for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning is completed, place the obtained fibers in the air and heat them to 800℃~1000℃. Calcine them for a period of time in an air atmosphere at a temperature of 800℃~1000℃ to obtain barium strontium titanate nanofibers.

[0036] III. Preparation of casting fluid:

[0037] ① Under ultrasonic conditions, barium strontium titanate nanofibers are dispersed in N,N-dimethylformamide, and then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added. The mixture is ultrasonically and magnetically stirred for a period of time to obtain casting liquid A.

[0038] ② Under ultrasonic conditions, TiN nanofibers are dispersed in N,N-dimethylformamide, and then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added. The mixture is ultrasonically and magnetically stirred for a period of time to obtain casting liquid B.

[0039] IV. Preparation of solid electrolytes:

[0040] ① Place the casting liquid A under vacuum conditions to degas for a period of time, then cast it onto a clean glass plate, scrape it into a film with a scraper, and then place it in a forced-air drying oven to dry for a period of time to obtain the BST layer;

[0041] ② The casting liquid B is poured onto the BST layer, scraped into a film using a scraper, and then placed in a forced-air drying oven to dry for a period of time to obtain the TiN-BST bilayer asymmetric solid electrolyte, which is an asymmetric quasi-solid electrolyte that enhances interfacial stability.

[0042] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the mass ratio of polyvinylpyrrolidone to the volume ratio of the mixed solution of anhydrous ethanol and glacial acetic acid in step one ① is (1.5g~2.5g):(10mL~20mL); the volume ratio of anhydrous ethanol to glacial acetic acid in the mixed solution of anhydrous ethanol and glacial acetic acid in step one ① is 1:1; and the volume ratio of tetrabutyl titanate to the mixed solution of anhydrous ethanol and glacial acetic acid in step one ① is (4mL~5mL):(10mL~20mL). The other steps are the same as in Specific Implementation Method One.

[0043] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the electrospinning process parameters in step one (②) are as follows: using a No. 20 needle, a liquid supply rate of 1.5 mL / h to 2 mL / h, a voltage of 25 kV to 30 kV, and a distance of 12 cm to 18 cm between the needle and the electrode plate; in step one (②), the obtained fibers are placed in an air atmosphere and heated to 500°C to 600°C at a heating rate of 1°C / min to 2°C / min, and calcined in an air atmosphere at 500°C to 600°C for 3 to 4 hours. Other steps are the same as in Specific Implementation Method One or Two.

[0044] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one (②), the volume ratio of ammonia to argon in the ammonia / argon mixture is 1:1; in step one (②), the ammonia / argon mixture is introduced into the tube furnace, and the furnace is heated to 900°C to 1000°C at a heating rate of 5°C / min to 10°C / min, and calcined for 2 to 3 hours under the conditions of an ammonia / argon mixed atmosphere and a temperature of 900°C to 1000°C. The other steps are the same as in Specific Implementation Methods One to Three.

[0045] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in the following ways: In step two ①, the mass ratio of polyvinylpyrrolidone, barium acetate, and strontium acetate is (0.5g~0.7g):(2g~3g):(0.4g~0.5g); the mass ratio of polyvinylpyrrolidone to the volume ratio of the mixed solution of anhydrous ethanol and glacial acetic acid in step two ① is (0.5g~0.7g):(8mL~15mL); the mass ratio of polyvinylpyrrolidone to the volume ratio of tetrabutyl titanate in step two ① is (0.5g~0.7g):(3mL~3.5mL); and the volume ratio of anhydrous ethanol to glacial acetic acid in the mixed solution of anhydrous ethanol and glacial acetic acid in step two ① is 1:1. The other steps are the same as in Specific Implementation Methods One to Four.

[0046] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the electrospinning process parameters in step two (②) are as follows: using a No. 20 needle, a liquid supply rate of 1.5 mL / h to 2 mL / h, a voltage of 18 kV to 25 kV, and a distance of 12 cm to 18 cm between the needle and the electrode plate; in step two (②), the obtained fibers are placed in air and heated to 800°C to 1000°C at a heating rate of 5°C / min to 10°C / min, and calcined in air at a temperature of 800°C to 1000°C for 4 to 6 hours. Other steps are the same as in Specific Implementation Methods One to Five.

[0047] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in the following ways: In step three①, the mass ratio of barium strontium titanate nanofibers to the volume ratio of N,N-dimethylformamide is (50mg-60mg):(3mL-4mL); in step three①, the mass ratio of P(VDF-TrFE-CFE), PVDF-HFP, and LiFSI is (0.1g-0.2g):(0.1g-0.2g):(0.1g-0.3g); in step three①, the mass ratio of barium strontium titanate nanofibers to P(VDF-TrFE-CFE) is (50mg-60mg):(0.1g-0.2g); and the ultrasonic and magnetic stirring time in step three① is 10h-12h. Other steps are the same as in Specific Implementation Methods One to Six.

[0048] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in the following ways: In step three ②, the mass ratio of TiN nanofibers to the volume ratio of N,N-dimethylformamide is (25mg-30mg):(3mL-4mL); in step three ②, the mass ratio of P(VDF-TrFE-CFE), PVDF-HFP, and LiFSI is (0.1g-0.2g):(0.1g-0.2g):(0.1g-0.3g); in step three ②, the mass ratio of TiN nanofibers to P(VDF-TrFE-CFE) is (25mg-30mg):(0.1g-0.2g); and in step three ②, the ultrasonic and magnetic stirring time is 10h-12h. Other steps are the same as in Specific Implementation Methods One to Seven.

[0049] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the degassing time in step four① is 20 to 40 minutes; in step four①, a 500 μm doctor blade is used to scrape the film, which is then placed in a forced-air drying oven at a temperature of 50℃ to 60℃ for 2 to 3 hours to obtain the BST layer. Other steps are the same as in Specific Implementation Methods One to Eight.

[0050] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step four ②, a 500μm doctor blade is used to scrape the material into a film, which is then placed in a forced-air drying oven at a temperature of 50℃~60℃ for 10h~14h to obtain a TiN-BST bilayer asymmetric solid electrolyte. The other steps are the same as in Specific Implementation Methods One to Nine.

[0051] The beneficial effects of the present invention are verified using the following embodiments:

[0052] Example 1: A method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability, specifically comprising the following steps:

[0053] I. Preparation of TiN nanofibers:

[0054] ① Dissolve 2g of polyvinylpyrrolidone in a mixed solution of 7mL of anhydrous ethanol and 7mL of glacial acetic acid. Stir magnetically until the polyvinylpyrrolidone is completely dissolved. Then add 4.5mL of tetrabutyl titanate and continue stirring until a homogeneous solution is formed to obtain electrospinning precursor solution I.

[0055] ② Transfer the precursor solution I for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning, place the obtained fibers in an air atmosphere and heat them from room temperature to 550°C at a heating rate of 2°C / min. Then calcine them in an air atmosphere at 550°C for 3 hours to obtain TiO2 nanofibers. Place the TiO2 nanofibers in a tube furnace and introduce a mixture of ammonia and argon into the tube furnace. Heat the tube furnace from room temperature to 1000°C at a heating rate of 5°C / min. Calcine them in an ammonia / argon atmosphere at 1000°C for 2 hours to obtain TiN nanofibers.

[0056] The electrospinning process parameters described in step 1② are as follows: using a No. 20 needle, the liquid supply rate is 1.5 mL / h, the voltage is 27 kV, and the distance between the needle and the electrode is 15 cm.

[0057] In step 1②, the volume ratio of ammonia to argon in the ammonia / argon mixture is 1:1.

[0058] II. Preparation of barium strontium titanate nanofibers:

[0059] ① Dissolve 0.6g polyvinylpyrrolidone, 2.043g barium acetate and 0.410g strontium acetate in a mixed solution of 5mL anhydrous ethanol and 5mL glacial acetic acid. Stir magnetically until the polyvinylpyrrolidone is completely dissolved. Then add 3.4mL tetrabutyl titanate and continue stirring until a homogeneous solution is formed to obtain electrospinning precursor solution II.

[0060] ② Transfer the precursor solution II for electrospinning to a syringe, then install the syringe in an electrospinning machine for electrospinning. After electrospinning is completed, place the obtained fibers in the air and heat them from room temperature to 800°C at a heating rate of 5°C / min. Calcine them in the air atmosphere at 800°C for 4 hours to obtain barium strontium titanate nanofibers (BST nanofibers).

[0061] The electrospinning process parameters described in step 2② are as follows: using a No. 20 needle, a liquid supply rate of 1.5 / mLh, a voltage of 18kV, and a distance of 15cm between the needle and the electrode plate;

[0062] III. Preparation of casting fluid:

[0063] ① Under ultrasonic conditions, 56 mg of barium strontium titanate nanofibers were dispersed in 3 mL of N,N-dimethylformamide (DMF), and then 0.15 g of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CFE)), 0.15 g of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 0.2 g of lithium difluorosulfonylimide (LiFSI) were added. The mixture was ultrasonically and magnetically stirred for 12 h to obtain casting liquid A.

[0064] ② Under ultrasonic conditions, 28 mg of TiN nanofibers were dispersed in 3 mL of N,N-dimethylformamide (DMF), and then 0.15 g of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene), 0.15 g of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 0.2 g of lithium difluorosulfonylimide (LiFSI) were added. The mixture was ultrasonically and magnetically stirred for 12 h to obtain casting solution B.

[0065] IV. Preparation of solid electrolytes:

[0066] ① Place the casting liquid A under vacuum for 30 minutes to degas, then cast it onto a clean glass plate, scrape it into a film using a 500μm scraper, and then dry it in a 55℃ forced-air drying oven for 2 hours to obtain the BST layer.

[0067] ② The casting liquid B is poured onto the BST layer, and a 500μm scraper is used to scrape it into a film. Then, it is placed in a 55℃ forced-air drying oven for 12h to obtain the TiN-BST bilayer asymmetric solid electrolyte, which is the asymmetric quasi-solid electrolyte (denoted as TiN-BST) that enhances the interfacial stability.

[0068] Comparing with Example 1: The preparation method of BST monolayer solid electrolyte is specifically carried out according to the following steps:

[0069] ① Under ultrasonic conditions, 28 mg of TiN nanofibers were dispersed in 3 mL of N,N-dimethylformamide (DMF), and then 0.15 g of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene), 0.15 g of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 0.2 g of lithium difluorosulfonylimide (LiFSI) were added. The mixture was ultrasonically and magnetically stirred for 12 h to obtain casting solution B.

[0070] ② Place the casting liquid B under vacuum conditions to degas for 30 minutes, then cast it onto a clean glass plate, scrape it into a film using a 750μm scraper, and then place it in a 55℃ forced-air drying oven to dry for 12 hours to obtain BST monolayer solid electrolyte (denoted as 10wt% BST).

[0071] Comparing with Example 2: The preparation method of the polymer solid electrolyte is specifically carried out according to the following steps:

[0072] ① Dissolve 0.15g of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene), 0.15g of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 0.2g of lithium difluorosulfonyl imide (LiFSI) in 3mL of N,N-dimethylformamide (DMF), and sonicate and magnetically stir for 12h to obtain casting liquid C;

[0073] ② Place the casting liquid C under vacuum for 30 minutes to degas, then cast it onto a clean glass plate, scrape it into a film using a 750μm scraper, and then dry it in a 55℃ forced-air drying oven for 12 hours to obtain the polymer solid electrolyte (denoted as Mixed polymer).

[0074] Figure 1 (a, d, g) show surface scanning electron microscope (SEM) images of the TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the electrolyte doped with 10 wt% BST nanofibers prepared in Control Example 1 (BST monolayer solid electrolyte), and the polymer electrolyte prepared in Control Example 2 (Mixed polymer), respectively. It can be observed that the electrolyte film surface after doping with inorganic fillers is smoother, with only a few small pores formed due to solvent evaporation during the drying process. Figure 1 (b, e, h) are cross-sectional electron micrographs of the electrolyte, showing that the film thickness is controlled between 40 and 50 μm, with a relatively dense internal structure and few pores, which is conducive to the effective transport of lithium ions inside. Among them, the TiN-BST film exhibits a distinct layered structure, reflecting the successful preparation of the bilayer structure. Figure 1 (c, f, i) are optical photographs of the TiN-BST bilayer asymmetric solid electrolyte, the electrolyte doped with 10 wt% BST nanofibers, and the polymer electrolyte, respectively. The electrolyte film without filler has high transparency, while the film doped with BST is uniformly white. The TiN-BST bilayer electrolyte exhibits black and white on its two sides, further verifying the successful preparation of the bilayer structure.

[0075] Figure 2 XRD patterns of three samples are shown. It can be observed that after doping with TiN and BST nanofibers, the characteristic crystallization peaks of the polymer become broader and less intense, indicating that its crystallization behavior is suppressed, thereby facilitating the rapid transport of lithium ions in the electrolyte. Furthermore, in the patterns, corresponding characteristic peaks appear at positions corresponding to the standard crystal cards PDF#06-0642 for TiN and PDF#89-0274 for BST, further confirming the successful doping of TiN and BST nanofibers into the electrolyte membrane.

[0076] Figure 3The ionic conductivity and lithium-ion transference number (LTU) of three solid-state electrolytes were demonstrated. After doping with BST nanofibers, both the ionic conductivity and LTU of the electrolyte were significantly improved. This indicates that the high dielectric constant of BST effectively promotes the dissociation of lithium salts, while the introduction of nanofibers constructs a continuous lithium-ion transport pathway within the electrolyte, thereby greatly enhancing ion mobility. Further employing a TiN-BST bilayer electrolyte, the ionic conductivity increased to 0.73 mS / cm, and the LTU was also significantly improved to 0.74. Surface doping with TiN nanofibers improved the electrochemical performance of the quasi-solid-state electrolyte and further optimized the overall ion transport characteristics of the electrolyte.

[0077] Assemble lithium-ion symmetric batteries:

[0078] The TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1 was cut into discs with a diameter of 14 mm and transferred to a glove box filled with argon gas. When assembling the battery, 2 μL of lithium electrolyte was dropped onto each side of the membrane to improve the interfacial contact between the electrode and the electrolyte. The electrolyte was a mixture of LiPF6 and FEC to EC, DEC and EMC, wherein the volume ratio of EC:DEC:EMC was 1:1:1, the concentration of LiPF6 in the electrolyte was 1 M, and the mass fraction of FEC was 5%.

[0079] The TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1 was assembled into a lithium symmetric battery. Both sides of the electrolyte were used as electrodes with lithium sheets of 10 mm in diameter. The battery assembly was carried out in a glove box filled with argon gas.

[0080] The BST monolayer solid electrolyte prepared in Comparative Example 1 and the polymer solid electrolyte prepared in Comparative Example 2 were assembled into lithium symmetric batteries according to the above method.

[0081] like Figure 4 As shown, the electrochemical stability window of the TiN-BST bilayer asymmetric solid electrolyte was tested using linear sweep voltammetry. The oxidation potential of the TiN-BST bilayer asymmetric solid electrolyte is 4.8 V, which meets the operating requirements of lithium battery cathode materials. Furthermore, the TiN-BST bilayer asymmetric solid electrolyte did not exhibit a significant reduction peak at 0 V, indicating its good resistance to reduction.

[0082] The limiting current density of the symmetrical lithium electrolyte was characterized by assembling lithium symmetric cells, such as... Figure 5 As shown, the limiting current density of the undoped quasi-solid electrolyte is 0.45 mA / cm². 2 After doping with BST nanofibers, the overpotential of the symmetric cell decreased, and the limiting current density increased to 0.65 mA / cm². 2TiN pairs can better suppress lithium dendrites and further increase the limiting current density to 1.4 mA / cm². 2 .

[0083] Figure 5 The TiN-BST double-layer is a lithium symmetric battery assembled using the TiN-BST double-layer asymmetric solid electrolyte prepared in Example 1; the 10wt% BST is a lithium symmetric battery assembled using the BST single-layer solid electrolyte prepared in Comparative Example 1; and the Mixed polymer is a lithium symmetric battery assembled using the polymer solid electrolyte prepared in Comparative Example 2.

[0084] Assemble a LiFePO4||CSE||Li full cell:

[0085] The TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1, the BST monolayer solid electrolyte prepared in Comparative Example 1, and the polymer solid electrolyte prepared in Comparative Example 2 were cut into discs with a diameter of 14 mm and transferred to a glove box filled with argon gas. When assembling the battery, 2 μL of lithium-ion electrolyte was dropped onto each side of the membrane to improve the interfacial contact between the electrode and the electrolyte. The electrolyte was a mixture of LiPF6 and FEC to EC, DEC and EMC, wherein the volume ratio of EC:DEC:EMC was 1:1:1, the concentration of LiPF6 in the electrolyte was 1 M, and the mass fraction of FEC was 5%.

[0086] The TiN-BST bilayer asymmetric solid electrolyte prepared in Example 1 was assembled into a quasi-solid-state lithium metal battery. The positive electrode was composed of lithium iron phosphate, superconducting carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10, and the negative electrode was a lithium metal sheet with a diameter of 14 mm. 4 μL of lithium hexafluorophosphate electrolyte was added to each side of the electrolyte. The battery was assembled in a glove box filled with argon gas.

[0087] LiFePO4||CSE||Li full cells were assembled using the BST monolayer solid electrolyte prepared in Comparative Example 1 and the polymer solid electrolyte prepared in Comparative Example 2, respectively, according to the above method.

[0088] Figure 6 and Figure 7 The TiN-BST double-layer is a LiFePO4||CSE||Li full cell assembled using the TiN-BST double-layer asymmetric solid electrolyte prepared in Example 1; the 10wt% BST is a LiFePO4||CSE||Li full cell assembled using the BST monolayer solid electrolyte prepared in Comparative Example 1; and the Mixed polymer is a LiFePO4||CSE||Li full cell assembled using the polymer solid electrolyte prepared in Comparative Example 2.

[0089] Figure 6 The rate performance of a battery assembled from a LiFePO4 cathode, a quasi-solid-state electrolyte, and a lithium metal anode was demonstrated. The unmodified quasi-solid-state electrolyte exhibited a discharge capacity of 150 mAh / g at 0.1C, but its discharge capacity rapidly decreased with increasing charge / discharge rate, reaching only 54 mAh / g and 30 mAh / g at 5C and 10C, respectively. However, after modification with BST nanofiber doping, the quasi-solid-state electrolyte exhibited improved rate performance due to its higher ionic conductivity and lithium-ion transference number. Furthermore, the reduction in interfacial side reactions resulted in a LiFePO4||CSE||Li full cell assembled using a TiN-BST bilayer asymmetric solid-state electrolyte, demonstrating a high discharge capacity of 160 mAh / g at 0.1C. Even at higher rates of 5C and 10C, the cell still maintained capacities of 97 mAh / g and 72 mAh / g, respectively, demonstrating rapid charge / discharge capabilities and fully proving the excellent rate performance of the modified quasi-solid-state electrolyte.

[0090] Figure 7 The cycling performance of the quasi-solid-state battery at 1C rate was demonstrated. The unmodified polymer electrolyte had an initial discharge specific capacity of approximately 124 mAh / g, which rapidly decreased after 100 cycles, and the capacity retention dropped below 50% after 200 cycles. The quasi-solid-state electrolyte modified with BST nanofibers showed enhanced performance, exhibiting an initial discharge specific capacity of 135 mAh / g at 1C. However, due to poor interfacial stability, the capacity retention did not exceed 60% after 300 cycles. With the addition of a TiN functional layer, the LiFePO4||CSE||Li full cell assembled using the TiN-BST bilayer asymmetric solid-state electrolyte maintained a high initial discharge specific capacity (140 mAh / g) and retained a capacity of 107 mAh / g after 1000 cycles, with a capacity retention greater than 75%. This indicates that the electrochemical performance of the quasi-solid-state electrolyte was effectively improved after TiN nanofiber doping modification, and the assembled battery exhibited excellent cycling performance and discharge capacity.

Claims

1. A method of making an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability, characterized in that The preparation method is specifically completed according to the following steps: I. Preparation of TiN nanofiber: ①, polyvinylpyrrolidone is dissolved in a mixed solution of anhydrous ethanol and glacial acetic acid, magnetic stirring until polyvinylpyrrolidone is completely dissolved, then tetrabutyl titanate is added and stirring is continued until a uniform solution is formed, to obtain an electrospinning precursor solution I; ②, the electrospinning precursor solution I is transferred to a syringe, and the syringe is installed in the electrospinning machine for electrospinning, after electrospinning is completed, the obtained fiber is placed in air atmosphere, heated to 500-600 DEG C, calcined at 500-600 DEG C in air atmosphere for a period of time, to obtain TiO2 nanofiber; the TiO2 nanofiber is placed in a tube furnace, a mixture of ammonia / argon gas is introduced into the tube furnace, the tube furnace is heated to 900-1000 DEG C, and calcined at 900-1000 DEG C in the mixed atmosphere of ammonia / argon for a period of time, to obtain TiN nanofiber; II. Preparation of barium strontium titanate nanofiber: ①, polyvinylpyrrolidone, barium acetate and strontium acetate are dissolved in a mixed solution of anhydrous ethanol and glacial acetic acid, magnetic stirring until polyvinylpyrrolidone is completely dissolved, then tetrabutyl titanate is added and stirring is continued until a uniform solution is formed, to obtain an electrospinning precursor solution II; ②, the electrospinning precursor solution II is transferred to a syringe, and the syringe is installed in the electrospinning machine for electrospinning, after electrospinning is completed, the obtained fiber is placed in air, heated to 800-1000 DEG C, calcined at 800-1000 DEG C in air atmosphere for a period of time, to obtain barium strontium titanate nanofiber; III. Preparation of pouring liquid: ①, under ultrasonic conditions, the barium strontium titanate nanofiber is dispersed in N,N-dimethylformamide, then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added, ultrasonic and magnetic stirring for a period of time, to obtain pouring liquid A; ②, under ultrasonic conditions, the TiN nanofiber is dispersed in N,N-dimethylformamide, then P(VDF-TrFE-CFE), PVDF-HFP and LiFSI are added, ultrasonic and magnetic stirring for a period of time, to obtain pouring liquid B; IV. Preparation of solid electrolyte: ①, the pouring liquid A is placed in a vacuum condition for a period of time, then cast on a clean glass plate, using a scraper to scrape it into a film, then placed in a blast drying oven for a period of time, to obtain a BST layer; ②, the pouring liquid B is poured on the BST layer, using a scraper to scrape it into a film, then placed in a blast drying oven for a period of time, to obtain a TiN-BST double-layer asymmetric solid electrolyte, which is an asymmetric quasi-solid-state electrolyte for enhancing interface stability.

2. The method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability according to claim 1, characterized in that... The volume ratio of the polyvinylpyrrolidone to the mixed solution of anhydrous ethanol and glacial acetic acid in step 1 1 is (1.5g-2.5g):(10mL-20mL); the volume ratio of anhydrous ethanol to glacial acetic acid in the mixed solution of anhydrous ethanol and glacial acetic acid in step 1 1 is 1:1; the volume ratio of the tetrabutyl titanate to the mixed solution of anhydrous ethanol and glacial acetic acid in step 1 1 is (4mL-5mL):(10mL-20mL).

3. The method of claim 1, wherein the non-symmetric quasi-solid-state electrolyte is prepared by the steps of: (a) mixing the electrolyte solution with the polymer solution; (b) adding the mixed solution to the porous separator; and (c) drying the mixed solution to form the non-symmetric quasi-solid-state electrolyte. The process parameters of electrospinning in step 2 1 are as follows: using a 20-gauge needle, the liquid supply speed is 1.5mL / h-2mL / h, the voltage is 25kV-30kV, and the distance between the needle and the electrode plate is 12cm-18cm; in step 2 1, the obtained fiber is placed in an air atmosphere, and heated to 500°C-600°C at a heating rate of 1°C / min-2°C / min, and calcined under the condition of air atmosphere and 500°C-600°C for 3h-4h.

4. The method for preparing an asymmetric quasi-solid-state electrolyte with enhanced interfacial stability according to claim 1, characterized in that... The volume ratio of ammonia to argon in the mixed gas of ammonia / argon in step 2 1 is 1:1; in step 2 1, the mixed gas of ammonia / argon is introduced into the tube furnace, and the tube furnace is heated to 900°C-1000°C at a heating rate of 5°C / min-10°C / min, and calcined under the condition of mixed atmosphere of ammonia / argon and 900°C-1000°C for 2h-3h.

5. The method of claim 1, wherein the non-symmetric quasi-solid-state electrolyte is prepared by the steps of: a) mixing the electrolyte solution with the polymer solution; b) adding the mixed solution to the porous separator; c) drying the mixed solution to form the non-symmetric quasi-solid-state electrolyte. The mass ratio of the polyvinylpyrrolidone, barium acetate and strontium acetate in step 2 1 is (0.5g-0.7g):(2g-3g):(0.4g-0.5g); the volume ratio of the polyvinylpyrrolidone to the mixed solution of anhydrous ethanol and glacial acetic acid in step 2 1 is (0.5g-0.7g):(8mL-15mL); the volume ratio of the polyvinylpyrrolidone to the tetrabutyl titanate in step 2 1 is (0.5g-0.7g):(3mL-3.5mL); the volume ratio of anhydrous ethanol to glacial acetic acid in the mixed solution of anhydrous ethanol and glacial acetic acid in step 2 1 is 1:

1.

6. The method of claim 1, wherein the non-symmetric quasi-solid-state electrolyte is prepared by the steps of: a) mixing the electrolyte solution with the polymer solution; b) adding the mixed solution to the porous separator; c) drying the mixed solution to form the non-symmetric quasi-solid-state electrolyte. The process parameters of electrospinning in step 2 1 are as follows: using a 20-gauge needle, the liquid supply speed is 1.5mL / h-2mL / h, the voltage is 25kV-30kV, and the distance between the needle and the electrode plate is 12cm-18cm; in step 2 1, the obtained fiber is placed in an air atmosphere, and heated to 500°C-600°C at a heating rate of 1°C / min-2°C / min, and calcined under the condition of air atmosphere and 500°C-600°C for 3h-4h.

7. The method of claim 1, wherein the method further comprises The mass-to-volume ratio of the barium strontium titanate nanofiber described in step three ① to N,N-dimethylformamide is (50 mg-60 mg):(3 mL-4 mL); the mass ratio of P(VDF-TrFE-CFE), PVDF-HFP and LiFSI described in step three ① is (0.1 g-0.2 g):(0.1 g-0.2 g):(0.1 g-0.3 g); the mass ratio of the barium strontium titanate nanofiber to P(VDF-TrFE-CFE) described in step three ① is (50 mg-60 mg):(0.1 g-0.2 g); the ultrasonic and magnetic stirring time described in step three ① is 10 h-12 h.

8. The method of claim 1, wherein the method further comprises The mass-to-volume ratio of the TiN nanofiber described in step three ② to N,N-dimethylformamide is (25 mg-30 mg):(3 mL-4 mL); the mass ratio of P(VDF-TrFE-CFE), PVDF-HFP and LiFSI described in step three ② is (0.1 g-0.2 g):(0.1 g-0.2 g):(0.1 g-0.3 g); the mass ratio of the TiN nanofiber to P(VDF-TrFE-CFE) described in step three ② is (25 mg-30 mg):(0.1 g-0.2 g); the ultrasonic and magnetic stirring time described in step three ② is 10 h-12 h.

9. The method of claim 1, wherein the method further comprises The defoaming time described in step four ① is 20 min-40 min; a 500 μm spatula is used to scrape it into a film in step four ①, which is then placed in a blast drying oven at a temperature of 50 ℃-60 ℃ for drying for 2 h-3 h to obtain a BST layer.

10. The method of claim 1, wherein the method further comprises A 500 μm spatula is used to scrape it into a film in step four ②, which is then placed in a blast drying oven at a temperature of 50 ℃-60 ℃ for drying for 10 h-14 h to obtain a TiN-BST double-layer asymmetric solid-state electrolyte.

Images