A three-dimensional polymer-modified interlayer for lithium-ion solid-state batteries and a method for preparing the same

Abstract

The present application relates to the technical field of lithium ion solid-state battery, in particular to a three-dimensional polymer modified interlayer for lithium ion solid-state battery and a preparation method thereof, comprising the following steps: adding polyacrylonitrile into N, N-dimethylformamide and stirring until completely dissolved, then adding modified polyamide acid-phosphonate copolymer and continuing to stir to obtain an electrospinning precursor solution, and electrospinning the electrospinning precursor solution to obtain a composite nanofiber membrane. The present application uses indium-containing heterocyclic modified diamine as the core monomer of polyamide acid-phosphonate copolymer, and the excellent lithium affinity activity of the core monomer can reduce the lithium deposition nucleation overpotential, promote the lithium dense dendrite-free deposition, and the indium-containing heterocyclic groups are uniformly dispersed in the three-dimensional framework through the crosslinking network of the modified polyamide acid-phosphonate copolymer, so that the contact interface between the interlayer and lithium metal forms a global uniform lithium affinity site, and the lithium atom concentrated deposition caused by the local lithium affinity activity difference is avoided.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion solid-state battery technology, specifically to a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries and its preparation method. Background Technology

[0002] Various types of rechargeable batteries have been developed, each using different materials to promote different chemical reactions to convert stored chemical energy into electrical energy. These include nickel-cadmium (Ni-Cd), nickel-metal hydride (NiMH), lead-acid, and lithium-ion (Li-ion). Compared with other rechargeable batteries, lithium-ion rechargeable batteries (hereinafter referred to as lithium-ion batteries) have the characteristics of high energy density, high cycle life, and no "memory effect".

[0003] Lithium-ion batteries typically consist of an anode (negative electrode), a cathode (positive electrode), and an electrolyte. The first generation of lithium-ion batteries used a liquid electrolyte solution. Currently, liquid electrolyte solutions have been replaced by polymer electrolytes, which are widely used in lithium-ion batteries. Solid electrolytes for lithium-ion batteries are under development and offer superior lifespan and energy density compared to other liquid and polymer electrolytes.

[0004] Optimizing the composition of the negative and positive electrodes is a key research focus for lithium-ion batteries. This can be used to combine with the solid electrolyte of lithium-ion batteries. For example, some lithium-ion batteries based on solid electrolytes use cathodes and anodes made of lithium cobalt oxide and lithium titanate, respectively. In addition, there are other cathodes and anodes. Other lithium-ion batteries based on solid electrolytes under development use anodes containing lithium metal. Solid-state lithium-ion batteries that use lithium metal as anodes are also called solid-state lithium metal batteries.

[0005] In solid-state lithium metal batteries, the lithium metal anode and the solid electrolyte are in direct contact. However, lithium metal anodes tend to generate lithium dendrites at the anode. Lithium dendrites are dendrites of lithium metal that grow from the surface of the lithium metal anode and penetrate into the solid electrolyte. Lithium dendrites cause various problems, such as reducing the performance of solid-state lithium metal batteries, including reducing the critical current density of solid-state lithium metal batteries. To address the problems mentioned in the background art, those skilled in the art propose a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries and its preparation method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries and a method for preparing the same, thereby solving the problems mentioned in the background section.

[0007] To achieve the aforementioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries includes the following steps:

[0009] S1. Add polyacrylonitrile to N,N-dimethylformamide and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution.

[0010] S2. Electrospin the electrospinning precursor solution in step S1 to obtain a composite nanofiber membrane. Vacuum dry the composite nanofiber membrane at 55-65℃ for 11-13h to form a three-dimensional polymer framework.

[0011] S3. Add the mixed solution to the three-dimensional polymer framework in step S2 and immerse it at room temperature for 0.5-1.5 hours to allow the mixed solution to penetrate into the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer.

[0012] The modified polyamic acid-phosphonate copolymer is prepared by the following steps:

[0013] S101. The modified diamine monomer is mixed into tetrahydrofuran. After adding the catalyst, the mixture is cooled to 0-3℃ to obtain a mixed solution. The mixture of pyromellitic dianhydride and dimethyl vinylphosphonate is added dropwise to the mixed solution. After the addition is complete, the temperature is raised to room temperature and reacted for 7-8 hours to form a polyamic acid-phosphonate prepolymer.

[0014] S102. The polyamic acid-phosphonate prepolymer from step S101 is heated to 80-90℃ and kept at that temperature for 3-5 hours under an argon atmosphere to obtain a reaction system. After the reaction is completed, anhydrous calcium chloride is added to the reaction system to dry and remove water, thereby obtaining the modified polyamic acid-phosphonate copolymer.

[0015] Furthermore, the modified diamine monomer is prepared by the following steps:

[0016] S1011. Add the reaction raw materials to N,N-dimethylacetamide solvent and stir at 120-140℃ for 4-5 hours to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate.

[0017] S1012. After washing the precipitate obtained in step S1011 with methanol 3-5 times, purify the washed precipitate with sufficient eluent to obtain the modified diamine monomer.

[0018] Furthermore, in step S1, the ratio of polyacrylonitrile to modified polyamic acid-phosphonate copolymer by mass is 1:(0.33-0.41), and the ratio of the total mass of polyacrylonitrile to the mass of N,N-dimethylformamide is 1:(6.3-7.6).

[0019] Furthermore, in step S2, the concentration of the electrospinning precursor is controlled at 0.19-0.22 g / mL, and the electrospinning voltage is set to 20-23 kV.

[0020] Furthermore, the mixed solution in step S3 is a polyethylene oxide crosslinking solvent and a lithium salt, and the mass ratio of the three-dimensional polymer framework to the polyethylene oxide crosslinking solvent and the lithium salt is 1:(2.9-3.5):(0.58-0.77).

[0021] Furthermore, the catalyst in step S101 is pyridine, and the mass ratio of modified diamine monomer: pyromellitic dianhydride: dimethyl vinylphosphonate: pyridine is 1: (0.82-0.98): (0.25-0.35): (0.34-0.45), and the mass ratio of the total mass of the aforementioned four raw materials to the mass ratio of tetrahydrofuran solvent is 1: (5.7-6.5).

[0022] Furthermore, in step S101, the dropping rate of the mixed solution of pyromellitic dianhydride and dimethyl vinylphosphonate is 0.2-0.3 mL / min, and the volume ratio of the two in the mixed solution is 3:1.

[0023] Furthermore, in step S1011, the mass ratio of the reaction raw materials is 1:(0.74-0.93):(0.51-0.65):(1.12-1.35) for p-phenylenediamine, 5-hydroxyindole, indium trichloride, and anhydrous sodium carbonate, and the mass ratio of the total mass of the reaction raw materials to the mass ratio of N,N-dimethylacetamide solvent is 1:(3.3-3.9).

[0024] Furthermore, the eluent in step S1012 is tetrahydrofuran:methanol in a mass ratio of 6:1.

[0025] Furthermore, a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries is provided, wherein the three-dimensional polymer-modified intermediate layer is prepared according to the preparation method described above.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention uses indium-containing heterocyclic modified diamine as the core monomer of polyamic acid-phosphonate copolymer. Its excellent lithiophilic activity can reduce the overpotential for lithium deposition nucleation, promote dense lithium deposition without dendrites, and the indium-containing heterocyclic groups are uniformly dispersed in the three-dimensional framework through the cross-linking network of the modified polyamic acid-phosphonate copolymer, so that the contact interface between the intermediate layer and lithium metal forms uniform lithiophilic sites throughout the entire domain, avoiding the concentrated deposition of lithium atoms due to local differences in lithiophilic activity;

[0028] 2. This invention directly connects the lithiophilic interface and the three-dimensional framework through a modified polyamic acid-phosphonate copolymer. The phosphonate groups have excellent chemical inertness and strong polarity, which can enhance the interfacial bonding force between the intermediate layer and the lithium metal anode and solid electrolyte, eliminate interfacial gaps, and significantly reduce interfacial resistance. At the same time, the phosphonate groups can inhibit the occurrence of interfacial side reactions, prevent by-products from blocking ion channels, and ensure interfacial stability during battery cycling. The cross-linked network formed by copolymerization can fill the pores of the polyacrylonitrile three-dimensional framework, forming a continuous lithium-ion transport channel. At the same time, it firmly anchors the indium-containing heterocyclic groups within the framework, preventing functional components from falling off and failing, thus achieving a synergistic improvement in interfacial stability and ion conduction. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation process of the three-dimensional polymer-modified intermediate layer of the present invention;

[0030] Figure 2 This is a schematic diagram of the preparation process of the modified polyamic acid-phosphonate copolymer of the present invention;

[0031] Figure 3 This is a schematic diagram of the preparation process of the modified diamine monomer of the present invention;

[0032] Figure 4 This is an optical microscope image of the three-dimensional polymer-modified intermediate layer obtained in Example 1;

[0033] Figure 5 This is an optical microscope image of the three-dimensional polymer-modified intermediate layer prepared in Comparative Example 1.

[0034] Figure 6 The battery cycle performance test graphs obtained in Example 1, Example 2 and Comparative Example 1 are shown.

[0035] Figure 7 The current-time response curve of the battery obtained in Example 1;

[0036] Figure 8 The XRD phase analysis spectrum of the three-dimensional polymer-modified intermediate layer prepared in Example 1;

[0037] Figure 9 A high-magnification SEM image of the three-dimensional polymer framework obtained in Example 1;

[0038] Figure 10 The voltage response performance test curve of the battery prepared in Example 1 is shown. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Please see Figures 1-10 The present invention provides a technical solution:

[0041] Example 1:

[0042] A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries includes the following steps:

[0043] Weigh 1.0 g of p-phenylenediamine, 0.74 g of 5-hydroxyindole, 0.51 g of indium trichloride, and 1.12 g of anhydrous sodium carbonate. Add the above reaction raw materials to 11.12 g of N,N-dimethylacetamide solvent and stir at 120 °C for 4 h to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate. Wash the precipitate three times with methanol. Then, purify the washed precipitate with a sufficient amount of tetrahydrofuran-methanol eluent with a mass ratio of 6:1 to obtain the modified diamine monomer.

[0044] Weigh 1.0 g of modified diamine monomer, 0.82 g of pyromellitic dianhydride, 0.25 g of dimethyl vinylphosphonate, and 0.34 g of pyridine catalyst. Mix the modified diamine monomer and pyridine into 13.74 g of tetrahydrofuran solvent and cool to 0 °C to obtain a mixed solution. Prepare a mixture of pyromellitic dianhydride and dimethyl vinylphosphonate at a volume ratio of 3:1. Add the mixture dropwise to the mixed solution at a rate of 0.2 mL / min. After the addition is complete, heat to room temperature and react for 7 h to form a polyamic acid-phosphonate prepolymer. Heat the polyamic acid-phosphonate prepolymer to 80 °C under an argon atmosphere and hold for 3 h to obtain a reaction system. After the reaction is complete, add anhydrous calcium chloride to the reaction system to dry and remove water to obtain a modified polyamic acid-phosphonate copolymer.

[0045] Weigh 1.0 g of polyacrylonitrile and 0.33 g of the modified polyamic acid-phosphonate copolymer prepared above. Add the polyacrylonitrile to 6.3 g of N,N-dimethylformamide solvent and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution. Electrospin the electrospinning precursor solution at 20 kV to obtain a composite nanofiber membrane. Vacuum dry the composite nanofiber membrane at 55 °C for 11 h to form a three-dimensional polymer framework.

[0046] Weigh 2.9g of polyethylene oxide crosslinking solvent and 0.58g of lithium salt to prepare a mixed solution. Add the mixed solution dropwise to 1.0g of three-dimensional polymer framework and impregnate at room temperature for 0.5h to allow the mixed solution to fully penetrate the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer.

[0047] Example 2:

[0048] A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries includes the following steps:

[0049] Weigh 1.0 g of p-phenylenediamine, 0.82 g of 5-hydroxyindole, 0.56 g of indium trichloride, and 1.20 g of anhydrous sodium carbonate. Add the above reaction raw materials to 12.53 g of N,N-dimethylacetamide solvent and stir at 128 °C for 4.3 h to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate. Wash the precipitate four times with methanol. Then, purify the washed precipitate with a sufficient amount of tetrahydrofuran-methanol eluent with a mass ratio of 6:1 to obtain the modified diamine monomer.

[0050] Weigh 1.0 g of modified diamine monomer, 0.88 g of pyromellitic dianhydride, 0.28 g of dimethyl vinylphosphonate, and 0.38 g of pyridine catalyst. Mix the modified diamine monomer and pyridine into 15.24 g of tetrahydrofuran solvent and cool to 1 °C to obtain a mixed solution. Prepare a mixture of pyromellitic dianhydride and dimethyl vinylphosphonate at a volume ratio of 3:1. Add the mixture dropwise to the mixed solution at a rate of 0.23 mL / min. After the addition is complete, heat to room temperature and react for 7.2 h to form a polyamic acid-phosphonate prepolymer. Heat the polyamic acid-phosphonate prepolymer to 83 °C under an argon atmosphere and hold for 3.5 h to obtain a reaction system. After the reaction is complete, add anhydrous calcium chloride to the reaction system to dry and remove water to obtain a modified polyamic acid-phosphonate copolymer.

[0051] Weigh 1.0 g of polyacrylonitrile and 0.36 g of the modified polyamic acid-phosphonate copolymer prepared above. Add the polyacrylonitrile to 6.8 g of N,N-dimethylformamide solvent and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution. Electrospin the electrospinning precursor solution at a voltage of 21 kV to obtain a composite nanofiber membrane. Vacuum dry the composite nanofiber membrane at 58 °C for 11.5 h to form a three-dimensional polymer framework.

[0052] Weigh 3.1g of polyethylene oxide crosslinking solvent and 0.65g of lithium salt to prepare a mixed solution. Add the mixed solution dropwise to 1.0g of three-dimensional polymer framework and impregnate at room temperature for 0.8h to allow the mixed solution to fully penetrate into the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer.

[0053] Example 3:

[0054] A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries includes the following steps:

[0055] Weigh 1.0 g of p-phenylenediamine, 0.88 g of 5-hydroxyindole, 0.61 g of indium trichloride, and 1.28 g of anhydrous sodium carbonate. Add the above reaction raw materials to 13.95 g of N,N-dimethylacetamide solvent and stir at 135 °C for 4.7 h to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate. Wash the precipitate four times with methanol. Then, purify the washed precipitate with a sufficient amount of tetrahydrofuran-methanol eluent with a mass ratio of 6:1 to obtain the modified diamine monomer.

[0056] Weigh 1.0 g of modified diamine monomer, 0.93 g of pyromellitic dianhydride, 0.32 g of dimethyl vinylphosphonate, and 0.42 g of pyridine catalyst. Mix the modified diamine monomer and pyridine into 16.82 g of tetrahydrofuran solvent and cool to 2 °C to obtain a mixed solution. Prepare a mixture of pyromellitic dianhydride and dimethyl vinylphosphonate at a volume ratio of 3:1. Add the mixture dropwise to the mixed solution at a rate of 0.27 mL / min. After the addition is complete, heat to room temperature and react for 7.7 h to form a polyamic acid-phosphonate prepolymer. Heat the polyamic acid-phosphonate prepolymer to 87 °C under an argon atmosphere and hold for 4.5 h to obtain a reaction system. After the reaction is complete, add anhydrous calcium chloride to the reaction system to dry and remove water to obtain a modified polyamic acid-phosphonate copolymer.

[0057] Weigh 1.0 g of polyacrylonitrile and 0.39 g of the modified polyamic acid-phosphonate copolymer prepared above. Add the polyacrylonitrile to 7.2 g of N,N-dimethylformamide solvent and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution. Electrospin the electrospinning precursor solution at a voltage of 22 kV to obtain a composite nanofiber membrane. Vacuum dry the composite nanofiber membrane at 62 °C for 12.5 h to form a three-dimensional polymer framework.

[0058] Weigh 3.3g of polyethylene oxide crosslinking solvent and 0.71g of lithium salt to prepare a mixed solution. Add the mixed solution dropwise to 1.0g of three-dimensional polymer framework and immerse at room temperature for 1.2h to allow the mixed solution to fully penetrate the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer.

[0059] Example 4:

[0060] A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries includes the following steps:

[0061] Weigh 1.0 g of p-phenylenediamine, 0.93 g of 5-hydroxyindole, 0.65 g of indium trichloride, and 1.35 g of anhydrous sodium carbonate. Add the above reaction raw materials to 15.33 g of N,N-dimethylacetamide solvent and stir at 140 °C for 5 h to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate. Wash the precipitate 5 times with methanol. Then, purify the washed precipitate with a sufficient amount of tetrahydrofuran-methanol eluent with a mass ratio of 6:1 to obtain the modified diamine monomer.

[0062] Weigh 1.0 g of modified diamine monomer, 0.98 g of pyromellitic dianhydride, 0.35 g of dimethyl vinylphosphonate, and 0.45 g of pyridine catalyst. Mix the modified diamine monomer and pyridine into 18.07 g of tetrahydrofuran solvent and cool to 3 °C to obtain a mixed solution. Prepare a mixture of pyromellitic dianhydride and dimethyl vinylphosphonate at a volume ratio of 3:1. Add the mixture dropwise to the mixed solution at a rate of 0.3 mL / min. After the addition is complete, heat to room temperature and react for 8 h to form a polyamic acid-phosphonate prepolymer. Heat the polyamic acid-phosphonate prepolymer to 90 °C under an argon atmosphere and hold for 5 h to obtain a reaction system. After the reaction is complete, add anhydrous calcium chloride to the reaction system to dry and remove water to obtain a modified polyamic acid-phosphonate copolymer.

[0063] Weigh 1.0 g of polyacrylonitrile and 0.41 g of the modified polyamic acid-phosphonate copolymer prepared above. Add the polyacrylonitrile to 7.6 g of N,N-dimethylformamide solvent and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution. Electrospin the electrospinning precursor solution at a voltage of 23 kV to obtain a composite nanofiber membrane. Dry the composite nanofiber membrane under vacuum at 65 °C for 13 h to form a three-dimensional polymer framework.

[0064] Weigh 3.5g of polyethylene oxide crosslinking solvent and 0.77g of lithium salt to prepare a mixed solution. Add the mixed solution dropwise to 1.0g of three-dimensional polymer framework and immerse at room temperature for 1.5h to allow the mixed solution to fully penetrate the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer.

[0065] Comparative Example 1

[0066] Compared with Example 1, Comparative Example 1 omits steps S1011 and S1012, replaces the indium-containing heterocyclic modified diamine monomer with a conventional diamine monomer, and the remaining steps are exactly the same as in Example 1.

[0067] Comparative Example 2

[0068] Compared to Example 1, Comparative Example 2 omits steps S101 and S102, replaces the modified polyamic acid-phosphonate copolymer with a conventional polyamic acid crosslinking polymer, and the remaining steps are exactly the same as in Example 1.

[0069] Comparative Example 3

[0070] Compared to Example 1, Comparative Example 3 omits the modified polyamic acid-phosphonate copolymer in step S1, while the remaining steps are exactly the same as in Example 1.

[0071] Comparative Example 4

[0072] Comparative Example 4 uses a conventional intermediate layer (LLZO garnet type intermediate layer).

[0073] Through the aforementioned Examples 1-4 and Comparative Examples 1-4, eight different three-dimensional polymer modified intermediates were obtained. Performance tests were performed on each of the different three-dimensional polymer modified intermediates. Specifically, the eight three-dimensional polymer modified intermediate layers were cut into circular pieces with a diameter of 18 mm, and Li was synthesized using a solid-state synthesis method. 6.5 La3Zr 1.5 Ta 0.5 O 12 A solid electrolyte was sintered into a ceramic sheet. In an argon-filled glove box, a three-dimensional polymer-modified interlayer was sandwiched between the solid electrolyte and the lithium metal electrode to ensure tight contact. A symmetrical battery (Li|interlayer|LLZTO|interlayer|Li) was assembled. After sealing, the electrochemical performance of the eight batteries was tested. The specific test results are shown in Table 1 below.

[0074] Table 1: Performance of the full battery in each implementation method

[0075]

[0076] As shown in Table 1, Examples 1-4 all possess a complete modified system consisting of an indium-containing heterocyclic modified diamine, a fluorinated polyamic acid, and a polyacrylonitrile three-dimensional framework. Their ionic conductivity, interfacial resistance, and cycle life are significantly better than those of Comparative Examples 1-4, demonstrating that this modified system effectively addresses the core challenges of lithium dendrite growth and low critical current density in the prior art. Comparative Example 1 (replacing the conventional diamine monomer and lacking the indium-containing heterocyclic group) has a cycle life of only 380 cycles, and its ionic conductivity and interfacial resistance are significantly worse than those of the Examples, proving that the indium-containing heterocyclic group is the key to improving lithium-affinity activity. Comparative Example 2 (replacing the conventional polyamic acid polymer and lacking the modified copolymer) exhibits the worst performance, with an ionic conductivity of only 0.31 mS / cm and an interfacial resistance as high as 358.7 Ω. cm 2The cycle life was only 45 cycles, which is insufficient for basic use. This indicates that the modified polyamic acid-phosphonate copolymer is crucial for ensuring interfacial stability and ion conduction. Comparative Example 3 (modified copolymer omitted) had a cycle life of only 210 cycles and an interfacial resistance of 189.2 Ω. cm 2 To further verify the irreplaceability of the modified copolymer, Comparative Example 4 uses a conventional LLZO garnet-type interlayer, whose ionic conductivity, interfacial resistance, and cycle life are far inferior to those of Examples 1-4. This directly proves that the modified interlayer of the present invention completely solves the pain points of slow ion conduction, high interfacial resistance, and short cycle life of conventional interlayers.

[0077] Figure 4 The image shown is an optical microscope image of the three-dimensional polymer-modified intermediate layer prepared in Example 1. The three-dimensional polymer-modified intermediate layer fiber in the middle exhibits a continuous, slender filamentous structure. The diameter of each fiber is uniform, with no obvious unevenness or breakage. This indicates that the electrospinning process is stable, the polymer components are uniformly dispersed, the rheological properties are well-adapted, and the fiber surface is smooth and clean, without bead-like protrusions, agglomerated particles, or obvious defects. This proves that the polymer matrix is ​​uniformly dispersed and no functional component agglomeration occurs, laying a structural foundation for the uniform exertion of lithiophilic activity and inhibition of lithium dendrites across the entire interface.

[0078] Figure 5 The image shows an optical microscope image of the three-dimensional polymer-modified intermediate layer prepared in Comparative Example 1. The fibers in the image have poor continuity, with local breaks and uneven thickness. Some areas show beaded protrusions or fiber adhesion. This is because Comparative Example 1 replaced the conventional diamine monomer, which lacked the coordination effect of indium-containing heterocycles and phosphonate groups, resulting in uneven dispersion of polymer components. The solution flow was unstable during electrospinning, which affected the fiber forming quality. The fiber surface was rough, and obvious particle agglomeration was visible. This further proves that conventional diamine monomers cannot achieve stable anchoring of functional components, resulting in a significant decrease in the regularity of the microstructure of the intermediate layer.

[0079] Figure 6 The graphs show the capacity retention-cycle count curves of the symmetrical batteries (Li|intermediate layer|LLZTO|intermediate layer|Li) prepared in Examples 1, 2, and Comparative Example 1 at a charge / discharge rate of 0.5C and a voltage range of 2.8–4.3V. The battery cycle performance test graphs demonstrate the capacity retention and coulombic efficiency changes of different samples within the 0.5C rate and 2.8–4.3V voltage range. Example 2 showed the highest initial specific capacity of 170 mAh g⁻¹. -1 It still maintains approximately 140 mAh g after 200 cycles. -1 The capacity decay is very slow, with a capacity retention of approximately 82%, exhibiting excellent cycling stability. Example 1 showed an initial specific capacity of approximately 110–120 mAh g. -1It remained stable at 100mAh g after 200 cycles. -1 The capacity retention rate was approximately 91%, but the absolute value of the specific capacity was significantly lower than that of Example 2, while the initial specific capacity of Comparative Example 1 was only about 70–80 mAhg. -1 The capacity fluctuates greatly and decays rapidly during cycling; after 200 cycles, only about 30–40 mAh g remains. -1 The capacity retention rate was less than 50%, indicating the worst stability. The coulombic efficiency of Example 2 remained stable in the range of 80%–90%, indicating good reversibility of the charge and discharge process and few side reactions. The coulombic efficiency of Example 1 remained stable in the range of 60%–70%, with weaker reversibility than Example 2. The coulombic efficiency of Comparative Example 1 fluctuated drastically, reflecting the presence of obvious irreversible or side reactions during the charge and discharge process.

[0080] Figure 7 The current-time response curve of the battery obtained in Example 1 shows that in the initial stage (t≈0), the current drops rapidly from the initial value I0 (approximately 0.0005A), which corresponds to the rapid charging of the double layer on the electrode surface and the interface charge transfer process, belonging to the non-diffusion-controlled transient response. In the middle stage (t≈0-3000s), the rate of current decrease slows down, entering the diffusion-controlled stage. In the later stage (t≈3000-7000s), the current tends to stabilize and approaches the steady-state current I. s (Close to 0A) indicates that the concentration gradient inside the electrode has reached equilibrium, the diffusion flux matches the external current, and the system has entered a quasi-steady state.

[0081] Figure 8 The XRD phase analysis spectrum of the three-dimensional polymer-modified intermediate layer prepared in Example 1 is shown, in which polyacrylonitrile (PAN) is at 17°. There is a sharp and strong diffraction peak within 18°, and at 29°... There is also a relatively weak characteristic peak within 30°, indicating that pure PAN has good crystallinity, regular molecular chain arrangement, and clear crystalline structure. The modified polyamide-phosphate copolymer has a weaker characteristic peak within 19°. There is only one broad and diffuse diffraction peak within 20°, and subsequent peaks are also very weak, indicating that the copolymer has low crystallinity, small crystal region size, or irregular molecular chain arrangement, mainly in an amorphous or low-crystallinity state. The diffraction peaks of the composite film (polymer / PAN) are the superposition of the former two, retaining the PAN peaks at 17°. The characteristic peaks within 18° also exhibit the broad peak characteristics of copolymers, but the characteristic peak intensity of PAN decreases and the peak shape becomes broader. This indicates that after blending, the crystallization of PAN is suppressed, and the crystallinity of the composite system is between that of pure PAN and pure copolymers, reflecting that the interaction between the two polymers at the molecular scale has changed the original crystal structure.

[0082] Figure 9The image shows a high-magnification SEM image of the three-dimensional polymer framework prepared in Example 1. The fibers in the image exhibit a continuous, slender filamentous structure with a uniform diameter of approximately 0.8–1.2 μm, which is micron-sized. The fibers are randomly interwoven and stacked to form a three-dimensional network structure with high porosity. This structure is conducive to material transport and permeation. The fiber surface is smooth and there are no obvious bead-like protrusions or breakage defects, indicating that the spinning process is stable and the rheological properties of the polymer material are well adapted.

[0083] Figure 10 The voltage response performance test curve of the battery prepared in Example 1 is shown in the low current density stage (0.1-0.5 mA). cm -2 The small voltage fluctuation amplitude (polarization voltage approximately) and symmetrical curve indicate that the battery has low interfacial impedance, good reversibility of lithium deposition / stripping, and stable interfacial contact between the solid electrolyte and the electrode at low current. In the high current density stage (1-10 mA)... cm -2 The voltage fluctuation amplitude increased sharply (the polarization voltage reached a maximum of 0.8V), and the curve symmetry deteriorated, indicating that the interface polarization increased significantly under high current. This may be due to insufficient ionic conductivity of the solid electrolyte, increased interfacial contact resistance, or a surge in local impedance caused by lithium dendrite growth. In the final stage, the voltage deviated significantly and fluctuated erratically, indicating that the battery was close to failure (such as lithium dendrites penetrating the electrolyte or irreversible side reactions occurring at the interface).

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries, characterized in that, Includes the following steps: S1. Add polyacrylonitrile to N,N-dimethylformamide and stir until completely dissolved. Then add the modified polyamic acid-phosphonate copolymer and continue stirring to obtain an electrospinning precursor solution. S2. Electrospin the electrospinning precursor solution in step S1 to obtain a composite nanofiber membrane. Vacuum dry the composite nanofiber membrane at 55-65℃ for 11-13h to form a three-dimensional polymer framework. S3. Add the mixed solution to the three-dimensional polymer framework in step S2 and immerse it at room temperature for 0.5-1.5 hours to allow the mixed solution to penetrate into the pores of the three-dimensional polymer framework and form a gel-like three-dimensional polymer modified intermediate layer. The modified polyamic acid-phosphonate copolymer is prepared by the following steps: S101. The modified diamine monomer is mixed into tetrahydrofuran. After adding the catalyst, the mixture is cooled to 0-3℃ to obtain a mixed solution. The mixture of pyromellitic dianhydride and dimethyl vinylphosphonate is added dropwise to the mixed solution. After the addition is completed, the temperature is raised to room temperature and reacted for 7-8 hours to form a polyamic acid-phosphonate prepolymer. S102. The polyamic acid-phosphonate prepolymer in step S101 is heated to 80-90℃ and kept at that temperature for 3-5 hours under an argon atmosphere to obtain a reaction system. After the reaction is completed, anhydrous calcium chloride is added to the reaction system to dry and remove water, thereby obtaining the modified polyamic acid-phosphonate copolymer. The modified diamine monomer is prepared by the following steps: S1011. Add the reaction raw materials to N,N-dimethylacetamide solvent and stir at 120-140℃ for 4-5 hours to obtain a reaction solution. Cool the reaction solution to room temperature and filter it. Add the filtrate dropwise to deionized water to precipitate the precipitate. S1012. After washing the precipitate obtained in step S1011 with methanol 3-5 times, purify the washed precipitate with sufficient eluent to obtain the modified diamine monomer. In step S1011, the mass ratio of the reactants is 1:(0.74-0.93):(0.51-0.65):(1.12-1.35) for p-phenylenediamine, 5-hydroxyindole, indium trichloride, and anhydrous sodium carbonate, and the mass ratio of the total mass of the reactants to the N,N-dimethylacetamide solvent is 1:(3.3-3.9).

2. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, In step S1, the ratio of polyacrylonitrile to modified polyamic acid-phosphonate copolymer by mass is 1:(0.33-0.41), and the ratio of the total mass of polyacrylonitrile to the mass of N,N-dimethylformamide is 1:(6.3-7.6).

3. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, In step S2, the concentration of the electrospinning precursor is controlled at 0.19-0.22 g / mL, and the electrospinning voltage is set to 20-23 kV.

4. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, The mixed solution in step S3 is a polyethylene oxide crosslinking solvent and a lithium salt, with the mass ratio of the three-dimensional polymer framework to the polyethylene oxide crosslinking solvent and the lithium salt being 1:(2.9-3.5):(0.58-0.77).

5. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, The catalyst in step S101 is pyridine, and the mass ratio of modified diamine monomer: pyromellitic dianhydride: dimethyl vinylphosphonate: pyridine is 1: (0.82-0.98): (0.25-0.35): (0.34-0.45). The mass ratio of the total mass of the above four raw materials to the mass ratio of tetrahydrofuran solvent is 1: (5.7-6.5).

6. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, In step S101, the dropping rate of the mixed solution of pyromellitic dianhydride and dimethyl vinylphosphonate is 0.2-0.3 mL / min, and the volume ratio of the two in the mixed solution is 3:

1.

7. The method for preparing a three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries according to claim 1, characterized in that, The eluent in step S1012 is tetrahydrofuran:methanol in a mass ratio of 6:

1.

8. A three-dimensional polymer-modified intermediate layer for lithium-ion solid-state batteries, characterized in that, The three-dimensional polymer-modified intermediate layer is prepared by the method according to any one of claims 1-7.

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