Polyimide-based composite solid electrolyte, preparation method and application

Abstract

The invention provides a polyimide-based composite solid electrolyte, a preparation method and application. The composite solid electrolyte comprises polyimide / cesium ion nanofibers; the polyimide / cesium ion nanofiber skeleton is filled with the polymer, the lithium salt and the inorganic filler. The composite solid electrolyte can inhibit the growth of lithium dendrites, improve the mechanical properties and reduce the crystallinity of the polymer. The composite solid electrolyte is used in a solid secondary battery, and the battery has excellent cycling stability and safety performance.

Description

Technical Field

[0001] This invention belongs to the field of secondary batteries, and particularly relates to electrolytes for solid-state batteries, specifically to a polyimide-based composite solid-state electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess the core advantages of high energy density and lightweight design, initially primarily meeting the power supply needs of various electronic components. In recent years, with the rapid iteration of end products such as electric vehicles and smartphones, lithium-ion batteries are evolving towards "three highs": high energy density, high power density, and high safety. Due to the inherent flammability of traditional liquid organic electrolytes, the risk of thermal runaway in high-energy-density lithium batteries exceeding 200Wh / kg increases significantly, making it difficult to fundamentally achieve a balance between energy density and safety. To address this core technological bottleneck, researchers have proposed a solution using solid-state electrolytes to replace traditional liquid electrolytes, aiming to fundamentally overcome the safety shortcomings of liquid lithium batteries.

[0003] In recent years, solid polymer-based electrolytes with excellent chemical stability and interfacial compatibility have become a research hotspot in this field. Among them, polyethylene oxide (PEO) has become one of the most promising polymer solid electrolyte materials due to its excellent interfacial adaptability (good flexibility, allowing for close bonding with positive and negative electrode materials) and lithium salt compatibility (efficient dissolution of bis(trifluoromethanesulfonyl)amino lithium salt). The lithium-ion conduction mechanism in polyethylene oxide (PEO) is mainly as follows: Li + Coordinated with the EO segment of PEO to form Li + -O coordination bonds; with repeated breaking / formation of coordination bonds, the solvation ligands of Li+ continuously change, Li + Jumping occurs due to the synergistic effect of the thermal motion of the EO chain segments. However, Li + Lithium ions are transported only in the amorphous regions of the PEO electrolyte, and not in the crystalline regions. Polyethylene oxide (PEO), with a crystallinity exceeding 60% at room temperature, has restricted chain segment movement; therefore, its ionic conductivity at room temperature is only 10. -6 ~10 -8 S / cm requires heating to above 60℃ to achieve a practical value of 10. -4 The lithium-ion transport capacity (S / cm) of polyethylene oxide (PEO) is insufficient for battery charging and discharging at room temperature. Furthermore, PEO readily induces lithium dendrite growth, which consumes lithium from the battery and punctures the solid electrolyte interphase (SEI) layer on the lithium anode surface. This can further penetrate the solid electrolyte, causing a short circuit between the positive and negative electrodes and triggering thermal runaway. Therefore, synergistically improving the lithium-ion transport capacity of PEO electrolyte and addressing the lithium dendrite growth problem are future research directions. Summary of the Invention

[0004] To address the shortcomings of the aforementioned polymer electrolytes, particularly polyethylene oxide (PEO) electrolytes, this invention provides a polyimide-based composite solid electrolyte, its preparation method, and its applications. This solid electrolyte comprises a polyimide / cesium ion nanofiber framework, along with a polymer, lithium salt, and inorganic filler filling the framework, forming a composite electrolyte. The polyimide / cesium ion nanofibers have a structure comprising two parts: polyimide nanofibers and cesium ions adsorbed on the surface of the polyimide nanofibers.

[0005] The inventors discovered that positively charged cesium ions attached to polyimide nanofibers can precipitate from the polyimide nanofibers and migrate to the lithium anode surface during charging and discharging. Since the reduction potential of cesium ions at lower concentrations is lower than that of lithium ions, cesium ions adsorb onto the lithium anode surface without being reduced. Therefore, positively charged cesium ions adsorb onto the tips of lithium dendrites on the anode. The cesium ions adsorbed at the tips of the lithium dendrites repel lithium ion deposition through electrostatic repulsion, thereby inhibiting further growth of lithium dendrites. Simultaneously, the inventors discovered that by adding cesium-containing polyimide nanofibers to the solid electrolyte, the crystallinity of polymers such as polyethylene oxide (PEO) electrolytes can be reduced, thereby improving the conduction of lithium ions in polymers such as PEO, thus ensuring that polymer solid electrolytes such as PEO can be used in secondary batteries at room temperature.

[0006] Specifically, the present invention provides a polyimide-based composite solid electrolyte comprising polyimide / cesium ion nanofibers; the polyimide / cesium ion nanofibers comprise two parts: polyimide nanofibers and cesium ions adsorbed on the surface of the polyimide nanofibers; the diameter of the polyimide nanofibers is 20~2000 nm; preferably 50~1000 nm; more preferably 100~500 nm.

[0007] The polyimide-based composite solid electrolyte uses polyimide / cesium ion nanofibers as a framework and also contains polymers, lithium salts, and inorganic fillers filled in the polyimide / cesium ion nanofiber framework.

[0008] The cesium ions are derived from cesium salts, selected from organic or inorganic cesium salts; specifically, they are selected from one or more of cesium acetate, cesium formate, cesium chloride, cesium nitrate, or cesium sulfate. Organic cesium salts are preferred, selected from one or more of cesium acetate and cesium formate, with cesium acetate being the most preferred.

[0009] The polymer is any one of polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride, and polyetherimide; the lithium salt is any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorooxalate)borate, and lithium bis(fluorosulfonyl)imide.

[0010] The inorganic filler is any one or more of silicon dioxide, aluminum oxide, zirconium dioxide, cerium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium titanium aluminum phosphate; preferably lithium lanthanum titanium oxide; more preferably a mixture of lithium lanthanum titanium oxide and silicon dioxide, wherein the weight ratio of the mixture is 1 to 5:1.

[0011] The thickness of the composite solid electrolyte is 5~500μm, preferably 5~200μm, more preferably 5~100μm, and can be prepared with the following thicknesses: 90μm, 80μm, 70μm, 60μm, 50μm, 40μm, 35μm, 30μm, 25μm, 20μm, 10μm.

[0012] In the composite solid electrolyte, polyimide / cesium ion nanofibers account for 5-50% of the total mass of the composite solid electrolyte, preferably 10-40%, and most preferably 20-30%.

[0013] This invention also provides a method for preparing a polyimide-based composite solid electrolyte, comprising the following steps: Step A: Polyamic acid anhydride and polyamine are condensed and polymerized in an organic solvent to obtain a precursor polyamic acid solution. Polyamic acid nanofibers are prepared by electrospinning and then subjected to heat treatment imidization at high temperature to dehydrate and cyclize the polyamic acid nanofibers to obtain polyimide nanofibers. Step B: The polyimide nanofibers obtained in Step A are immersed in an alkaline solution of a certain concentration to etch and open the ring. After washing with deionized water multiple times, they are dried. The washed and dried nanofibers are immersed in a cesium salt solution of a certain concentration for ion exchange. After washing with deionized water multiple times, they are dried to obtain polyimide / cesium ion nanofibers with cesium ions adsorbed on the surface. Step C: The polymer, lithium salt, inorganic filler and organic solvent are mixed in a certain proportion and stirred to obtain a mixed solution. Then the mixed solution is applied to the polyimide / cesium nanofibers obtained in step B in a certain way, and the solvent is removed by drying to obtain the composite solid electrolyte.

[0014] Furthermore, the polyimide mentioned in step A is any polyimide prepared by solution condensation polymerization of polyacid anhydrides and polyamines, and the high-temperature heat treatment temperature is 200℃~350℃, and the treatment time is 15min~3h.

[0015] Furthermore, the alkaline solution mentioned in step B is selected from any one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide; the concentration of the alkaline solution is 0.01~3 mol / L, preferably 0.05~1 mol / L, and most preferably 0.1~0.5 mol / L; the etching time of the alkaline solution is 10s to 10min, preferably 1~3min.

[0016] Furthermore, in step B, the drying temperature after etching the ring open is 40~80℃, and the drying time is 10~90min.

[0017] Furthermore, in step B, the cesium salt solution is any one or more of cesium acetate, cesium formate, cesium chloride, cesium nitrate, or cesium sulfate, with cesium acetate being preferred; the concentration of the cesium salt solution is 0.01~5 mol / L, preferably 0.05~2 mol / L, more preferably 0.1~1 mol / L, and most preferably 0.2 mol / L; the ion exchange time in step B is 20~100 min, preferably 30~80 min.

[0018] Furthermore, the polymer mentioned in step C is any one of polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride, and polyetherimide.

[0019] Furthermore, the lithium salt mentioned in step C is any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, and lithium bis(fluorosulfonyl)imide.

[0020] Furthermore, the inorganic filler mentioned in step C is any one or more of silicon dioxide, aluminum oxide, zirconium dioxide, cerium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium titanium aluminum phosphate, preferably lithium lanthanum titanium oxide.

[0021] Furthermore, the solvent mentioned in step C is any one or more of acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0022] Furthermore, the proportions of each substance in step C are as follows: 10-80 parts polymer, 5-40 parts lithium salt, and 0-40 parts inorganic filler; preferably, 10-50 parts polymer, 5-30 parts lithium salt, and 0-20 parts inorganic filler; more preferably, 20-40 parts polymer, 10-20 parts lithium salt, and 0-10 parts inorganic filler; and most preferably, 30 parts polymer, 15 parts lithium salt, and 5 parts inorganic filler.

[0023] Furthermore, the application method described in step C is spraying, scraping, or dipping.

[0024] Furthermore, the drying temperature in step C is 30~70℃; the drying time is 20~80min.

[0025] Furthermore, in step C, the polyimide / cesium ion nanofibers in the composite solid electrolyte account for 5-50% of the total mass of the composite solid electrolyte, preferably 10-40%, and most preferably 20-30%.

[0026] Furthermore, the thickness of the composite solid electrolyte obtained in step C is 5~500μm, preferably 5~200μm, more preferably 5~100μm, and can be prepared with the following thicknesses: 90μm, 80μm, 70μm, 60μm, 50μm, 40μm, 35μm, 30μm, 25μm, 20μm, 10μm.

[0027] The present invention also provides an application of polyimide / cesium ion nanofibers, which comprise two parts: polyimide nanofibers and cesium ions adsorbed on the surface of the polyimide nanofibers; the polyimide / cesium ion nanofibers are applied in solid-state secondary batteries.

[0028] Finally, the present invention also provides a solid-state battery comprising a positive electrode, a negative electrode, and a composite solid electrolyte disposed between the positive and negative electrodes, wherein the composite solid electrolyte comprises the aforementioned polyimide / cesium ion nanofibers, as well as polymers, lithium salts, and inorganic fillers.

[0029] Compared with the prior art, the present invention has the following superior technical effects: The composite solid electrolyte of this invention incorporates polyimide / cesium ion nanofibers, which adsorb monovalent cesium ions onto the surface of the polyimide nanofibers. During discharge, the cesium ions spontaneously migrate to the negative electrode surface and, through electrostatic repulsion, repel lithium ions from depositing at the tips of lithium dendrites. This effectively creates a shielding layer on the negative electrode surface, thus significantly inhibiting lithium dendrite growth.

[0030] The composite solid electrolyte of the present invention further enhances the polymer-based solid electrolyte by adding polyimide / cesium ion nanofibers, thereby improving the mechanical properties of the solid electrolyte and enhancing battery safety.

[0031] Meanwhile, the surface of polyimide / cesium ion nanofibers is rich in carboxylic acid groups, which can reduce the crystallinity of polymer-based solid electrolytes. Furthermore, the polyimide / cesium ion nanofibers provide long-range ordered transport channels for lithium ions. Therefore, the composite solid electrolyte of the present invention, by adding polyimide / cesium ion nanofibers, increases the area for lithium ion conduction, thereby accelerating the transport of lithium ions within the electrolyte.

[0032] This invention, by adding polyimide / cesium ion nanofibers, enables lithium batteries containing a solid electrolyte formed therefrom to exhibit excellent cycle stability and safety performance. Furthermore, the preparation process of the composite solid electrolyte of this invention is simple, low-cost, and easily industrialized. Attached Figure Description

[0033] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative examples are not intended to limit the embodiments. The term "illustrative" as used herein means "serving as an example, embodiment, or illustration." Any embodiment illustrated herein as "illustrative" is not necessarily to be construed as superior to or better than other embodiments.

[0034] Figure 1 This is a schematic diagram of the ion exchange reaction between polyimide (PI) nanofibers and cesium acetate after the PI nanofibers are etched and opened by NaOH. The principle is to first use sodium hydroxide solution to destroy the imide ring structure of polyimide nanofibers, thus obtaining PI-COO-Na + Nanofibers are then subjected to an ion exchange reaction with a cesium acetate solution, ultimately resulting in cesium ions replacing sodium ions and complexing onto the polyimide.

[0035] Figure 2 The image shows the EDS spectrum of the polyimide / cesium ion nanofibers in Example 1.

[0036] Figure 3 The image shows the XPS spectrum of the polyimide / cesium ion nanofibers in Example 1.

[0037] Figure 4 This is a scanning electron microscope image of the polyimide / cesium ion nanofibers in Example 1.

[0038] Figure 5 This is a scanning electron microscope image of the surface of the composite solid electrolyte in Example 1.

[0039] Figure 6 A scanning electron microscope image of the lithium electrode surface of the solid-state battery of Example 1.

[0040] Figure 7 Scanning electron microscope (SEM) image of the lithium electrode surface used to prepare the solid-state battery of Comparative Example 1.

[0041] Figure 8 Scanning electron microscope (SEM) image of the lithium electrode surface used to prepare the solid-state battery of Comparative Example 2.

[0042] Figure 9 The images show the DSC spectra of the solid electrolytes in Example 1, Comparative Example 1, and Comparative Example 2.

[0043] Figure 10The stress-strain diagrams are shown for the solid electrolytes in Example 1, Comparative Example 1, and Comparative Example 2.

[0044] Figure 11 The diagram shows the number of cycles and discharge specific capacity for Preparation Example 1, Preparation Comparative Example 1, and Preparation Comparative Example 2. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Unless otherwise specified, the raw materials, components, methods, means, and other techniques or conditions used in the technical solutions of this invention are techniques or conditions well known to those skilled in the art or described in the literature in this field. Unless otherwise explicitly defined, the technical terms used in this invention are those commonly used in the art. Example 1

[0046] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath. The reaction conditions were controlled to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.1 mol / L sodium hydroxide solution for etching for 3 min. After washing three times with deionized water to remove the alkaline solution on the surface of the nanofibers, they were dried and then completely immersed in a 0.2 mol / L cesium acetate solution for ion exchange for 30 min. For the specific reaction process, please refer to the appendix. Figure 1 After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained. Their scanning electron microscope images are shown in the attached image. Figure 4 .

[0047] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, stirring to disperse and dissolve. Then, weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution, stirring with a magnetic rotor at 800 r / min for 12h to obtain a mixed solution; coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1), controlling the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 20% of the total mass of solid electrolyte; after drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. The surface scanning electron microscope image of this solid electrolyte can be found in the appendix. Figure 5 . Example 2

[0048] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.1 mol / L sodium hydroxide solution for etching for 3 min, followed by washing three times with deionized water to remove the alkaline solution from the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 0.2 mol / L cesium acetate solution for ion exchange for 30 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0049] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, and stir to disperse and dissolve. Then weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800 r / min for 12h. After the lithium salt and PEO are fully dissolved, add 5g of lithium lanthanum titanium oxide and stir for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1). Control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 20% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. Example 3

[0050] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Monomers hexafluorodianhydride (6FDA), 4,4'-diphenyl ether dianhydride (ODPA), and 4,4'-diaminodiphenyl ether (ODA) were selected and added to the reaction vessel at a molar ratio of dianhydride to diamine of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. Polyimide nanofibers were obtained by imidization treatment in a high-temperature furnace at 300℃. The polyimide nanofibers were completely immersed in a 0.5 mol / L lithium hydroxide solution for etching for 1 min, and then washed three times with deionized water to remove the alkaline solution on the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 1 mol / L cesium formate solution for ion exchange for 20 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0051] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 40g of polyethylene oxide and pour it into 1600ml of acetonitrile, and stir to disperse and dissolve. Then weigh 20g of lithium hexafluorophosphate and add it to the above solution. Stir with a magnetic rotor at 800 r / min for 12h. After the lithium salt and PEO are fully dissolved, add 3g of silicon dioxide and 4g of lithium lanthanum titanium oxide, and stir for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1). Control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 10% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. Example 4

[0052] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.3 mol / L potassium hydroxide solution for etching for 0.5 min, followed by washing three times with deionized water to remove the alkaline solution from the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 2 mol / L cesium chloride solution for ion exchange for 60 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0053] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 40g of polyethylene oxide and pour it into 1600ml of acetonitrile, and stir to disperse and dissolve. Then weigh 30g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800 r / min for 12h. After the lithium salt and PEO are fully dissolved, add 15g of lithium titanium aluminum phosphate and stir for 16h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1). Control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 40% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. Example 5

[0054] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.2 mol / L sodium hydroxide solution for 2 min for etching, followed by washing three times with deionized water to remove the alkaline solution from the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 5 mol / L cesium nitrate solution for ion exchange for 80 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0055] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 50g of polyvinylidene fluoride and pour it into 2000ml of acetonitrile, and stir to disperse and dissolve. Then weigh 40g of lithium difluorosulfonylimide and add it to the above solution. Stir with a magnetic rotor at a speed of 800r / min for 12h. After the lithium salt and PEO are fully dissolved, add 10g of aluminum oxide and 10g of silicon dioxide, and stir for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1). Control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 5% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. Example 6

[0056] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) was added as solvent, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.1 mol / L sodium hydroxide solution for etching for 3 min, followed by washing three times with deionized water to remove the alkaline solution from the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 0.1 mol / L cesium sulfate solution for ion exchange for 40 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0057] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 35g of polyethylene oxide and pour it into 1400ml of acetonitrile, and stir to disperse and dissolve. Then weigh 25g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800r / min for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1), and control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 25% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained. Example 7

[0058] A polyimide / cesium ion nanofiber-based composite solid electrolyte is prepared by the following steps: (1) Preparation of polyimide / cesium ion nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to the reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The nanofibers were then subjected to imidization treatment in a high-temperature furnace at 300 °C to obtain polyimide nanofibers. The polyimide nanofibers were completely immersed in a 0.1 mol / L lithium hydroxide solution for etching for 3 min, followed by washing three times with deionized water to remove the alkaline solution on the surface of the nanofibers. After drying, the nanofibers were completely immersed in a 0.2 mol / L cesium acetate solution for ion exchange for 30 min. After washing with deionized water and drying, polyimide / cesium ion nanofibers were obtained.

[0059] (2) Preparation of polyimide / cesium ion nanofiber-based composite solid electrolyte: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, and stir to disperse and dissolve. Then weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800r / min for 12h. After the lithium salt and PEO are fully dissolved, add 2.5g of silica and 2.5g of lithium lanthanum titanium oxide, and stir for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide / cesium ion nanofiber membrane prepared in step (1). Control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 20% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide / cesium ion nanofiber-based composite solid electrolyte is obtained.

[0060] Comparative Example 1: A polyoxyethylene solid electrolyte, the preparation method of which includes the following steps: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, stirring to disperse and dissolve. Then, weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution, stirring with a magnetic rotor at 800r / min for 12h to obtain a mixed solution. The mixed solution is then coated onto a polytetrafluoroethylene (PTFE) plate by a scraper and dried at 60℃ for 12h to obtain a polyethylene oxide solid electrolyte.

[0061] Comparative Example 2: A polyimide nanofiber-based composite solid electrolyte, the preparation method of which includes the following steps: (1) Preparation of polyimide nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to a reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath. The reaction conditions were controlled to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The polyimide nanofibers were then obtained by imidization treatment in a high-temperature furnace at 300℃.

[0062] (2) Preparation of polyimide nanofiber-based composite solid electrolyte: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, and stir to disperse and dissolve. Then weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800 r / min for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide nanofiber membrane prepared in step (1), and control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 20% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide nanofiber-based composite solid electrolyte is obtained.

[0063] Comparative Example 3: A polyimide nanofiber-based composite solid electrolyte, the preparation method of which includes the following steps: (1) Preparation of polyimide nanofibers: Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were selected as monomers and added to a reaction vessel at a molar ratio of 1.01:1. N,N-dimethylformamide (DMF) solvent was added, and the reaction was stirred under an ice-water bath. The reaction conditions were controlled to prepare a polyamic acid solution with a solid content of 12%. Polyamic acid nanofibers were obtained by electrospinning at a voltage of 20 kV and a receiving distance of 18 cm. The polyimide nanofibers were then obtained by imidization treatment in a high-temperature furnace at 300℃.

[0064] (2) Preparation of polyimide nanofiber-based composite solid electrolyte: First, weigh 30g of polyethylene oxide and pour it into 1200ml of acetonitrile, and stir to disperse and dissolve. Then weigh 15g of lithium bis(trifluoromethanesulfonyl)imide and add it to the above solution. Stir with a magnetic rotor at 800 r / min for 12h. After the lithium salt and PEO are fully dissolved, add 2.5g of nano-silica powder and 2.5g of lithium lanthanum titanium oxide, and stir for 12h to obtain a mixed solution. Coat the mixed solution onto the polyimide nanofiber membrane prepared in step (1), and control the ratio of solution to nanofiber membrane so that the mass of nanofiber membrane accounts for about 20% of the total mass of solid electrolyte. After drying at 60℃ for 12h, polyimide nanofiber-based composite solid electrolyte is obtained.

[0065] Preparation example: Solid-state battery fabrication: First, lithium iron phosphate (LFP) cathode sheets were prepared: 3.5g of lithium iron phosphate (LFP), 0.5g of polyvinylidene fluoride (PVDF), 0.5g of conductive carbon black (Super P), 0.3g of PEO, and 0.2g of lithium bis(trifluoromethanesulfonyl)imide were weighed and added to 8ml of N-methylpyrrolidone (NMP) to obtain a cathode slurry. The slurry was stirred for 15min using a high-speed homogenizer at 15000 r / min. The homogenized cathode slurry was then coated onto a carbon-coated aluminum foil current collector and dried at 80℃ to obtain an LFP cathode sheet. LFP cathode sheets with a diameter of 12cm and lithium sheets were cut as anodes and assembled with the solid electrolytes prepared in Examples 1-7 and Comparative Examples 1-3 to form button batteries. The solid batteries obtained were placed in an oven at 60℃ for 12h to ensure sufficient contact between the electrolyte and the positive and negative electrode interfaces before use, resulting in Preparation Examples 1-7 and Comparative Examples 1-3.

[0066] The above-described examples, comparative examples, preparation examples, and preparation comparative examples were evaluated using the following evaluation methods.

[0067] 1. EDS energy dispersive spectroscopy Using a scanning electron microscope (SEM) of model Sigma 360 from ZEISS GmbH, Germany, at a working voltage of 15 kV, energy dispersive spectroscopy (EDS) was performed on the polyimide / cesium ion nanofiber membrane in Example 1 with four elements: carbon, nitrogen, oxygen, and cesium. The EDS spectrum and elemental distribution table were obtained.

[0068] 2. XPS spectrum X-ray photoelectron spectroscopy (XPS) analysis was performed on the polyimide / cesium ion nanofiber membrane in Example 1 using a K-Alpha instrument from Thermo Fisher Scientific.

[0069] 3. Detection of lithium dendrites The button cell battery prepared in the above example was subjected to 100 constant current (0.05 mA) charge-discharge cycles, and then disassembled for lithium dendrite detection. The surface morphology of the lithium sheet was observed using a ZEISS Sigma 360 scanning electron microscope at an operating voltage of 15 kV.

[0070] 4. Detection of crystallinity Differential scanning calorimetry (DSC) was used to characterize the crystallinity of solid electrolytes. The working principle of DSC is based on the characteristic that substances release or absorb heat during physical or chemical reactions, which corresponds to melting and crystallization peaks in the DSC chart. The testing instrument and conditions were as follows: a DSC-200F3 differential scanning calorimeter manufactured by NETZSCH GmbH, Germany; nitrogen atmosphere; temperature range of -60 to 80 °C; and heating rate of 10 °C / min. -1 .

[0071] 5. Mechanical strength testing The mechanical properties of the material were obtained by testing it using a universal testing machine and recording its stress, strain, and Young's modulus. The solid electrolyte sample had dimensions of 2 mm × 28 mm, and the tensile speed was 20 mm / min. -1 .

[0072] 6. Cycle stability testing of solid-state batteries The LAND Blue Battery Testing System was used to perform charge-discharge cycle tests on the lithium iron phosphate-lithium metal (LFP / / Li) solid-state battery prepared in the example at a current density of 0.5C. The cycle stability of the solid-state battery was characterized by monitoring and recording the decay of the discharge specific capacity and the initial discharge specific capacity during the cycle.

[0073] The evaluation conclusions obtained using the above evaluation methods are as follows.

[0074] 1. From the appendix Figure 2 As can be seen from the EDS spectrum, cesium is uniformly distributed on the surface of polyimide nanofibers, with no obvious agglomeration and relatively uniform dispersion.

[0075] Meanwhile, the elemental distribution table was obtained through energy spectrum scanning as follows: Table 1. Elemental distribution of EDS energy spectrum scans in Example 1

[0076] 2. From the appendix Figure 3 It can be seen that the polyimide / cesium ion nanofiber membrane of Example 1 exhibits two characteristic peaks of Cs at 739.9 eV and 742.8 eV, corresponding to the 3d peaks of Cs, respectively. 3 / 2 Tracks and 3D 5 / 2 The orbital pattern indicates that cesium ions exist on the polyimide / cesium ion nanofiber membrane.

[0077] 3. From the appendix Figure 6-8It can be observed that the lithium anode surface of the polyimide / cesium ion nanofiber-based solid-state battery prepared in Example 1 is relatively smooth and flat, indicating that there are not many "dead lithium" formations during cycling, demonstrating a good lithium dendrite suppression effect. (See Appendix) Figure 6 The lithium anode surface of the PEO solid-state battery in Comparative Example 1 was very rough, and many non-uniform granular "dead lithium" particles were observed, indicating that a large number of lithium dendrites appeared during cycling. (See Appendix) Figure 7 The lithium anode surface of the polyimide nanofiber-based solid-state battery in Comparative Example 2 was somewhat rough, and the degree of "dead lithium" was between that in Example 1 and Comparative Example 2. (See Appendix) Figure 8 .

[0078] 4. From the appendix Figure 9 The DSC curves show that the PEO solid electrolyte in Comparative Example 1 exhibited a significant crystallization peak at around 55°C. However, neither the polyimide / cesium ion nanofiber membrane solid electrolyte in Example 1 nor the polyimide nanofiber membrane solid electrolyte in Comparative Example 2 showed a significant crystallization peak, and their crystallization temperatures were also significantly lower. This indicates that both polyimide / cesium ion-containing and polyimide solid electrolytes can reduce the crystallinity of polyethylene oxide solid electrolytes.

[0079] 5. From the appendix Figure 10 It can be seen that the PEO solid electrolyte in Comparative Example 1 has almost no mechanical properties, with a stress of only about 0.5 MPa; the PI / PEO solid electrolyte in Comparative Example 2 and the PI@Cs in Example 1... + The PI / PEO solid electrolyte exhibited excellent mechanical properties, with strain and stress of 55.8% and 7.4 MPa (PI / PEO electrolyte); and 70.3% and 6.5 MPa (PI@Cs electrolyte). + / PEO electrolyte).

[0080] 6. From the appendix Figure 11 It can be seen that, when performing charge-discharge cycle tests at a current density of 0.5 C, the solid-state battery prepared with the PEO electrolyte of Comparative Example 1 exhibits a low initial discharge specific capacity (19.9 mAh g⁻¹) in the initial state. -1 The initial discharge specific capacity of the solid-state battery prepared with the PI / PEO electrolyte in Comparative Example 2 was 141.1 mAh g⁻¹. -1 Preparation of PI@Cs in Example 1 + The initial discharge specific capacity of the solid-state battery with PEO electrolyte is 156.4 mAh g. -1 Furthermore, after 600 cycles, the PI@Cs prepared in Example 1... +Solid-state batteries with PI / PEO electrolytes still maintain a high discharge specific capacity and exhibit good cycle stability; however, solid-state batteries prepared with PI / PEO electrolytes in Comparative Example 2, due to the lack of lithium dendrite suppression effect, show a significant drop in capacity and short circuit after 484 cycles.

[0081] Table 2 Initial discharge specific capacity of Preparation Examples 1-7 and Comparative Examples 1-3 (unit: mAh g) -1 )

[0082] As can be seen from Table 2, the discharge specific capacity of the solid-state batteries prepared in Examples 1-7 is all above 150 mAh g. -1 The above, and the vast majority are in the range of 155 mAh g. -1 In the above examples, Preparation Example 2 and Preparation Example 7 achieved 160 mAh g⁻¹, respectively. -1 That's all. In contrast, the preparation of Comparative Example 103 was all within 150 mAh g⁻¹. -1 The following, especially Comparative Example 1, showed a concentration of only 19.9 mAh g. -1 This demonstrates that the polyimide / cesium ion nanofibers of the present invention, when used in solid electrolytes, exhibit superior technical effects compared to nanofibers without polyimide or containing only polyimide.

[0083] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

Claims

1. A polyimide-based composite solid electrolyte comprising polyimide / cesium ion nanofibers; the polyimide / cesium ion nanofibers comprising two parts: polyimide nanofibers and cesium ions adsorbed on the surface of the polyimide nanofibers; the diameter of the polyimide nanofibers being 20~2000 nm.

2. The polyimide-based composite solid electrolyte according to claim 1, characterized in that, The solid electrolyte is based on polyimide / cesium ion nanofibers and also contains polymers, lithium salts, and inorganic fillers filled in the polyimide / cesium ion nanofibers.

3. The polyimide-based composite solid electrolyte according to any one of claims 1 to 2, characterized in that, Cesium ions originate from cesium salts, which are selected from organic or inorganic cesium salts.

4. The polyimide-based composite solid electrolyte according to claim 3, characterized in that, Cesium salts are selected from one or more of cesium acetate, cesium formate, cesium chloride, cesium nitrate, or cesium sulfate.

5. The polyimide-based composite solid electrolyte according to claim 2, characterized in that, The polymer is any one of polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride, and polyetherimide; the lithium salt is any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorooxalate)borate, and lithium bis(fluorosulfonyl)imide.

6. The polyimide-based composite solid electrolyte according to claim 2, characterized in that, The inorganic filler is any one or more of silicon dioxide, aluminum oxide, zirconium dioxide, cerium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium titanium aluminum phosphate.

7. The polyimide-based composite solid electrolyte according to any one of claims 1 to 2, characterized in that, Polyimide / cesium ion nanofibers account for 5-50% of the total mass of the composite solid electrolyte.

8. The polyimide-based composite solid electrolyte according to any one of claims 1 to 2, characterized in that, The thickness of the composite solid electrolyte is 5~500μm.

9. A method for preparing a polyimide-based composite solid electrolyte, comprising the following steps: Step A: Polyamic acid anhydride and polyamine are condensed and polymerized in an organic solvent to obtain a precursor polyamic acid solution. Polyamic acid nanofibers are prepared by electrospinning and then subjected to heat treatment imidization at high temperature to dehydrate and cyclize the polyamic acid nanofibers to obtain polyimide nanofibers. Step B: The polyimide nanofibers obtained in Step A are immersed in an alkaline solution of a certain concentration to etch and open the ring. After washing with deionized water multiple times, they are dried. The washed and dried nanofibers are then immersed in a cesium salt solution of a certain concentration for ion exchange. After washing with deionized water multiple times, they are dried to obtain polyimide / cesium ion nanofibers with cesium ions adsorbed on the surface.

10. The method for preparing a polyimide-based composite solid electrolyte according to claim 9, characterized in that, The preparation method also includes: Step C: The polymer, lithium salt, inorganic filler and organic solvent are mixed in a certain proportion and stirred to obtain a mixed solution. Then the mixed solution is applied to the polyimide / cesium nanofibers obtained in step B in a certain way, and the solvent is removed by drying to obtain the composite solid electrolyte.

11. The method for preparing a polyimide-based composite solid electrolyte according to claim 9, characterized in that, The alkaline solution mentioned in step B is selected from any one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide; the concentration of the alkaline solution is 0.01~3 mol / L; and the etching time of the alkaline solution is 10s to 10min.

12. The method for preparing a polyimide-based composite solid electrolyte according to claim 9, characterized in that, The concentration of the cesium salt solution is 0.01~5 mol / L; the ion exchange time in step B is 20~100 min; the cesium salt is selected from organic or inorganic cesium salts.

13. The method for preparing a polyimide-based composite solid electrolyte according to claim 10, characterized in that, The weight ratio of each substance in step C is as follows: polymer 10~80 parts, lithium salt 5~40 parts, and inorganic filler 0~40 parts.

14. An application of a polyimide / cesium ion nanofiber, the polyimide / cesium ion nanofiber comprising the following two parts: polyimide nanofiber and cesium ions adsorbed on the surface of the polyimide nanofiber; the polyimide / cesium ion nanofiber being applied in a solid-state secondary battery.

15. A solid-state battery comprising a positive electrode, a negative electrode, and a polyimide-based composite solid electrolyte as described in any one of claims 1 to 8 disposed between the positive electrode and the negative electrode.

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