Cellulose nanocrystal-based composite solid electrolyte film with one-dimensional core-shell structure and preparation method of cellulose nanocrystal-based composite solid electrolyte film

Abstract

The invention relates to a cellulose nanocrystal-based composite solid electrolyte film with a one-dimensional core-shell structure and a preparation method of the cellulose nanocrystal-based composite solid electrolyte film, and belongs to the technical field of solid electrolytes of lithium ion batteries. In order to solve the problems that an existing PVDF-HFP-based solid electrolyte is low in room-temperature ionic conductivity, poor in inorganic filler dispersity and poor in interfacial compatibility, the invention provides a preparation method of a one-dimensional core-shell structure composite solid electrolyte film based on a cellulose nanocrystal. A one-dimensional chain string type core-shell structure UiO-66 (at) CNC composite filler is constructed through an in-situ growth method, and the one-dimensional chain string type core-shell structure UiO-66 (at) CNC composite filler is introduced into a PVDF-HFP / LiTFSI matrix according to the content of 1-5 wt%. The obtained composite solid electrolyte membrane is excellent in room-temperature ionic conductivity, wide in electrochemical stable window, good in interface compatibility, capable of effectively inhibiting growth of lithium dendrites, uniform in film morphology, mild, simple and convenient in preparation process, easy to industrialize and suitable for all-solid-state lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology for lithium-ion batteries, and particularly relates to a one-dimensional core-shell structure composite solid electrolyte film based on cellulose nanocrystals and its preparation method. Background Technology

[0002] With the increasing demand for high-energy-density and high-safety rechargeable batteries from electric vehicles, large-scale energy storage, and portable electronic devices, traditional liquid lithium-ion batteries pose safety hazards such as thermal runaway and leakage due to the use of flammable organic electrolytes. All-solid-state lithium batteries, which use non-flammable solid electrolytes instead of liquid electrolytes, are considered a next-generation technology that fundamentally solves battery safety issues.

[0003] Among various solid electrolytes, polymer solid electrolytes, such as polyethylene oxide, polycarbonate, and polyvinylidene fluoride electrolytes, have attracted much attention due to their good flexibility, ease of processing, and interfacial contact with electrodes. Among these, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) based electrolytes show promising application prospects due to their high dielectric constant, good electrochemical stability, and mechanical strength. However, pure PVDF-HFP based solid electrolytes generally have low ionic conductivity at room temperature, typically below 10. -5 The low S / cm and lithium-ion transference number (LTM) below 0.3 severely limit its practical application performance. To improve its ionic conductivity, researchers often employ a composite strategy, introducing inorganic fillers such as Al₂O₃, SiO₂, and LLZO into a polymer matrix to form a composite solid electrolyte. However, traditional spherical or particulate inorganic fillers are often randomly dispersed in the polymer matrix, making it difficult to form continuous, fast ion transport channels, thus limiting the improvement in ionic conductivity. Furthermore, the poor interfacial compatibility between inorganic fillers and the polymer matrix easily leads to filler agglomeration, creating localized ion conduction "dead zones." Therefore, developing a novel filler with good compatibility with the polymer matrix and capable of constructing an efficient ion transport network, along with a corresponding preparation process, is crucial for obtaining high-performance PVDF-HFP-based composite solid electrolytes. Summary of the Invention

[0004] To address the problems of low room-temperature ionic conductivity, poor dispersibility of inorganic fillers, and poor interfacial compatibility in existing PVDF-HFP-based solid electrolytes, this invention provides a one-dimensional core-shell composite solid electrolyte film based on cellulose nanocrystals and its preparation method.

[0005] The technical solution of the present invention:

[0006] A method for preparing a one-dimensional core-shell composite solid electrolyte film based on cellulose nanocrystals includes the following steps:

[0007] Step 1: Using cellulose nanocrystals (CNC) with hydroxyl-rich surfaces as a one-dimensional template, UiO-66 nanoparticles are uniformly grown on the CNC surface through in-situ growth, forming a chain-like core-shell structured composite filler with CNC as the axis and UiO-66 as the shell. The specific method is as follows:

[0008] Cellulose nanocrystals, zirconium tetrachloride, and glacial acetic acid were ultrasonically dispersed in an organic solvent to obtain a mixed system. Terephthalic acid was dissolved in the organic solvent. The terephthalic acid solution was added dropwise to the mixed system at a certain dropping rate under continuous stirring. The reaction was carried out at 80°C for 24-36 hours. The reaction product was centrifuged, washed, and vacuum dried to obtain a one-dimensional chain-like core-shell structure UiO-66@CNC composite filler.

[0009] Step 2: Preparation of precursor slurry:

[0010] PVDF-HFP polymer and lithium salt are dissolved in the organic solvent and stirred at a first temperature to obtain a homogeneous and transparent solution. The one-dimensional chain-like core-shell structure UiO-66@CNC composite filler obtained in step one is added to the homogeneous and transparent solution and stirred at a second temperature to obtain a uniform and stable precursor slurry.

[0011] Step 3: Film Formation and Post-treatment

[0012] The precursor slurry obtained in step two is cast into a film and then subjected to segmented vacuum drying to remove the solvent, resulting in a self-supporting composite solid electrolyte film.

[0013] Furthermore, in step one, the mass-to-volume ratio of cellulose nanocrystals, zirconium tetrachloride, glacial acetic acid, and organic solvent is 100-125 mg: 200-210 mg: 0.8-1.2 mL: 40-50 mL, and the mass-to-volume ratio of terephthalic acid to organic solvent is 210-230 mg: 40-50 mL; the organic solvent is N,N-dimethylformamide, and the molar ratio of zirconium tetrachloride to terephthalic acid is 1:1.5.

[0014] Furthermore, the mass-to-volume ratio of the cellulose nanocrystals, zirconium tetrachloride, glacial acetic acid, and organic solvent is 100 mg: 207 mg: 1.0 mL: 40 mL, and the mass-to-volume ratio of the terephthalic acid to the organic solvent is 230 mg: 40 mL.

[0015] Furthermore, in step one, the ultrasonic dispersion power is 400W and the ultrasonic time is 1h; the dropping speed is 2mL / min; the centrifugal washing is performed by centrifuging three times each with N,N-dimethylformamide and methanol, the centrifugation speed is 6000rpm and the centrifugation time is 5min; and the drying is performed by vacuum drying at 60℃ for 12h.

[0016] Furthermore, the lithium salt in step two is LiTFSI; the molecular weight of the PVDF-HFP is 400,000, and the mass ratio of the PVDF-HFP polymer to the lithium salt is 3:2.

[0017] Furthermore, in step two, the amount of the one-dimensional chain-like core-shell structure UiO-66@CNC composite filler added is 1~5wt% of the total solid mass of the precursor slurry; the mass concentration of the PVDF-HFP polymer in the precursor slurry is 10%.

[0018] Furthermore, in step two, the first temperature is 50°C and the stirring time is 6 hours, while the second temperature is 60°C and the stirring time is 12 hours.

[0019] Furthermore, the segmented vacuum drying described in step three involves first drying at 60°C for 4-6 hours, and then drying at 80°C for 2-4 hours.

[0020] A composite solid electrolyte film prepared by the preparation method provided by the present invention has a continuous and uniform PVDF-HFP polymer phase on its surface and a film thickness of 80~100μm.

[0021] A solid-state lithium battery includes a positive electrode, a negative electrode, and an electrolyte separator disposed between the positive and negative electrodes, wherein the electrolyte separator is the composite solid-state electrolyte film as described in claim 9.

[0022] The beneficial effects of this invention are:

[0023] This invention uses cellulose nanocrystals as a one-dimensional template, leveraging their one-dimensional nanostructure, abundant surface hydroxyl groups, and excellent dispersibility. Combined with an in-situ growth method, UiO-66 particles are uniformly coated onto their surface, successfully constructing a one-dimensional chain-like core-shell structure UiO-66@CNC composite filler. This cleverly combines the high ionic conductivity of MOF materials with the one-dimensional topology of CNC. Introducing this composite filler into a PVDF-HFP / LiTFSI matrix at an optimized content of 1-5 wt% significantly improves the overall performance of the composite solid electrolyte film, while also possessing the outstanding advantages of simple processing and easy industrialization.

[0024] The one-dimensional rigid framework provided by cellulose nanocrystals enables the UiO-66@CNC composite filler to effectively overlap within the PVDF-HFP matrix, constructing continuous rapid lithium-ion transport channels. Simultaneously, the inherent porous structure of UiO-66 provides additional lithium-ion transport sites, and the cellulose nanocrystals further reduce the crystallinity of the PVDF-HFP matrix, further promoting ion migration. The resulting composite solid-state electrolyte film exhibits significantly improved room-temperature ionic conductivity, reaching an optimal 4.42 × 10⁻⁶. -4 S / cm, satisfying ≥1×10 at room temperature -4Application requirements of S / cm.

[0025] The abundant hydroxyl functional groups on the surface of cellulose nanocrystals and the organic ligand properties of UiO-66 enable the composite filler to exhibit excellent interfacial affinity with the PVDF-HFP polymer matrix, effectively avoiding the agglomeration problem of traditional inorganic fillers, ensuring uniform dispersion of the filler, and enhancing the mechanical properties of the film. Simultaneously, the structural characteristics of the composite filler contribute to the formation of a more stable solid electrolyte interphase (SEI) film, broadening the electrochemical stability window to approximately 4.9V, and significantly improving interfacial compatibility with the lithium metal anode. Based on this electrolyte... Symmetric cells at 0.1 mA / cm 2 0.1mAh / cm 2 It can cycle stably for over 1400 hours under certain conditions and has excellent ability to suppress lithium dendrite growth.

[0026] The composite solid electrolyte membrane obtained by this invention exhibits a continuous and uniform PVDF-HFP polymer phase on its surface, with no obvious agglomeration defects at the interface, and the membrane thickness can be precisely controlled within 80~100μm. This film is suitable for all-solid-state lithium metal batteries, and solid-state lithium batteries assembled based on it exhibit high rate performance and long cycle stability, showing broad application prospects. The preparation method of this invention is based on a mature solution method, synthesizing the UiO-66@CNC composite filler via a hydrothermal / solvothermal method. The process conditions are mild, the operation is simple, and no complex and expensive equipment is required, demonstrating good potential for industrial production. Attached Figure Description

[0027] Figure 1 X-ray diffraction patterns of the one-dimensional chain-like core-shell structure UiO-66@CNC composite filler prepared in Example 1 and the UiO-66 nanoparticles prepared in Comparative Example 2;

[0028] Figure 2 Fourier transform infrared spectra of the composite solid electrolyte films prepared in Examples 1-3 and the polymer films prepared in Comparative Examples 1-2;

[0029] Figure 3 This is a low-magnification scanning electron microscope (SEM) image of the composite solid electrolyte film prepared in Example 1.

[0030] Figure 4 The images show high-magnification scanning electron microscope images and elemental distribution maps of the composite solid electrolyte film prepared in Example 1. A is an elemental overlay image, B is a fluorine elemental distribution map, C is a zirconium elemental distribution map, D is a sulfur elemental distribution map, and E is an oxygen elemental distribution map.

[0031] Figure 5 Lithium-solid electrolyte-stainless steel assembly using solid electrolyte films prepared in Example 2 and Comparative Example 1 Comparison of oxidative decomposition potential test results for button batteries;

[0032] Figure 6 Lithium-solid electrolyte-stainless steel assembly using solid electrolyte films prepared in Example 2 and Comparative Example 1 Comparison of lithium plating peeling test results for button batteries;

[0033] Figure 7 Stainless steel-solid electrolyte-stainless steel assembly using solid electrolyte films prepared in Examples 1-3 and Comparative Examples 1-2 Electrochemical impedance spectroscopy of a button cell;

[0034] Figure 8 Lithium-solid electrolyte-lithium iron phosphate assembled using the solid electrolyte films prepared in Example 2 and Comparative Examples 1-2 Comparison chart of rate test results for button batteries; Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0036] Example 1

[0037] This embodiment provides a method for preparing a one-dimensional core-shell structured composite solid electrolyte film based on cellulose nanocrystals. The specific steps are as follows:

[0038] Step 1: Preparation of one-dimensional chain-like core-shell structured UiO-66@CNC composite filler:

[0039] Weigh 0.1g of cellulose nanocrystals, 0.207g of zirconium tetrachloride, and 1mL of glacial acetic acid and add them to 40mL of DMF. Soak the mixture in a 400W ultrasonic bath for 1h to ensure thorough dispersion and obtain a mixed system. Dissolve 0.230g of terephthalic acid in 40mL of DMF and slowly add it dropwise to the mixed system at 2mL / min with continuous stirring. After the addition is complete, transfer the reaction system to an 80℃ oil bath for heating and stirring for 24h.

[0040] After the reaction was completed, the white solid product was collected by centrifugation and washed three times each with DMF and methanol by centrifugation. The centrifugation speed was 6000 rpm and the centrifugation time was 5 min. The precipitate was collected and dried in a vacuum drying oven at 60℃ for 12 h to obtain a one-dimensional chain-like core-shell structure UiO-66@CNC composite packing.

[0041] The cellulose nanocrystals used in this embodiment are rigid one-dimensional nanomaterials with a high aspect ratio. As a template, they can guide the directional growth of UiO-66 particles and effectively prevent their aggregation, thereby constructing a one-dimensional structure with continuous ion transport channels in the polymer matrix.

[0042] Step 2: Preparation of precursor slurry:

[0043] Weigh 0.500g of PVDF-HFP polymer and 0.340g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), add them to 4.0mL of DMF solvent, and stir magnetically at 50℃ for 6h to obtain a homogeneous and transparent solution; weigh 0.0085g of the one-dimensional chain-like structure UiO-66@CNC composite filler prepared in Example 1, add it to the obtained homogeneous and transparent solution, and continue to stir magnetically at 60℃ for 12h to obtain a uniform and stable precursor slurry, wherein the amount of one-dimensional chain-like structure UiO-66@CNC composite filler added accounts for 1wt% of the total solid mass of the precursor slurry.

[0044] In this embodiment, the PVDF-HFP has a molecular weight of 400,000, which can form a flexible polymer support network, ensuring the extensibility and mechanical properties of the final solid electrolyte film.

[0045] Step 3: Film Formation and Post-treatment

[0046] The precursor slurry described in step two was poured into a flat polytetrafluoroethylene mold. A scraper was used to control the wet film thickness. The mold was then transferred to a vacuum drying oven and vacuum-dried at 60°C for 6 hours, followed by a slow increase to 80°C for another 2 hours to ensure complete and uniform solvent removal. After drying, the film was allowed to cool naturally to room temperature and carefully peeled off the mold to obtain a flexible, self-supporting composite solid electrolyte film with a thickness of 100 μm. This film was labeled SE-1. The obtained composite solid electrolyte film was cut into 19 mm diameter discs and stored in a dry environment for later use.

[0047] Example 2

[0048] This embodiment provides a method for preparing a one-dimensional core-shell structured composite solid electrolyte film based on cellulose nanocrystals. The specific steps are as follows:

[0049] Step 1: Preparation of one-dimensional chain-like core-shell structured UiO-66@CNC composite filler:

[0050] Weigh 0.1g of cellulose nanocrystals, 0.207g of zirconium tetrachloride, and 1mL of glacial acetic acid and add them to 40mL of DMF. Soak the mixture in a 400W ultrasonic bath for 1h to ensure thorough dispersion and obtain a mixed system. Dissolve 0.230g of terephthalic acid in 40mL of DMF and slowly add it dropwise to the mixed system at 2mL / min with continuous stirring. After the addition is complete, transfer the reaction system to an 80℃ oil bath for heating and stirring for 24h.

[0051] After the reaction was completed, the white solid product was collected by centrifugation and washed three times each with DMF and methanol by centrifugation. The centrifugation speed was 6000 rpm and the centrifugation time was 5 min. The precipitate was collected and dried in a vacuum drying oven at 60℃ for 12 h to obtain a one-dimensional chain-like core-shell structure UiO-66@CNC composite packing.

[0052] The cellulose nanocrystals used in this embodiment are rigid one-dimensional nanomaterials with a high aspect ratio. As a template, they can guide the directional growth of UiO-66 particles and effectively prevent their aggregation, thereby constructing a one-dimensional structure with continuous ion transport channels in the polymer matrix.

[0053] Step 2: Preparation of precursor slurry:

[0054] Weigh 0.500g of PVDF-HFP polymer and 0.340g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), add them to 4.0mL of DMF solvent, and stir magnetically at 50℃ for 6h to obtain a homogeneous and transparent solution; weigh 0.0260g of the one-dimensional chain-like structure UiO-66@CNC composite filler prepared in Example 1, add it to the obtained homogeneous and transparent solution, and continue to stir magnetically at 60℃ for 12h to obtain a uniform and stable precursor slurry, wherein the amount of one-dimensional chain-like structure UiO-66@CNC composite filler added accounts for 3wt% of the total solid mass of the precursor slurry.

[0055] In this embodiment, the PVDF-HFP has a molecular weight of 400,000, which can form a flexible polymer support network, ensuring the extensibility and mechanical properties of the final solid electrolyte film.

[0056] Step 3: Film Formation and Post-treatment

[0057] The precursor slurry described in step two was poured into a flat polytetrafluoroethylene mold. A scraper was used to control the wet film thickness. The mold was then transferred to a vacuum drying oven and vacuum-dried at 60°C for 6 hours, followed by a slow increase to 80°C for another 2 hours to ensure complete and uniform solvent removal. After drying, the film was allowed to cool naturally to room temperature and carefully peeled off the mold to obtain a flexible, self-supporting composite solid electrolyte film with a thickness of 100 μm. This film was labeled SE-3. The obtained composite solid electrolyte film was cut into 19 mm diameter discs and stored in a dry environment for later use.

[0058] Example 3

[0059] This embodiment provides a method for preparing a one-dimensional core-shell structured composite solid electrolyte film based on cellulose nanocrystals. The specific steps are as follows:

[0060] Step 1: Preparation of one-dimensional chain-like core-shell structured UiO-66@CNC composite filler:

[0061] Weigh 0.1g of cellulose nanocrystals, 0.207g of zirconium tetrachloride, and 1mL of glacial acetic acid and add them to 40mL of DMF. Soak the mixture in a 400W ultrasonic bath for 1h to ensure thorough dispersion and obtain a mixed system. Dissolve 0.230g of terephthalic acid in 40mL of DMF and slowly add it dropwise to the mixed system at 2mL / min with continuous stirring. After the addition is complete, transfer the reaction system to an 80℃ oil bath for heating and stirring for 24h.

[0062] After the reaction was completed, the white solid product was collected by centrifugation and washed three times each with DMF and methanol by centrifugation. The centrifugation speed was 6000 rpm and the centrifugation time was 5 min. The precipitate was collected and dried in a vacuum drying oven at 60℃ for 12 h to obtain a one-dimensional chain-like core-shell structure UiO-66@CNC composite packing.

[0063] The cellulose nanocrystals used in this embodiment are rigid one-dimensional nanomaterials with a high aspect ratio. As a template, they can guide the directional growth of UiO-66 particles and effectively prevent their aggregation, thereby constructing a one-dimensional structure with continuous ion transport channels in the polymer matrix.

[0064] Step 2: Preparation of precursor slurry:

[0065] Weigh 0.500g of PVDF-HFP polymer and 0.340g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), add them to 4.0mL of DMF solvent, and stir magnetically at 50℃ for 6h to obtain a homogeneous and transparent solution; weigh 0.0442g of the one-dimensional chain-like structure UiO-66@CNC composite filler prepared in Example 1, add it to the obtained homogeneous and transparent solution, and continue to stir magnetically at 60℃ for 12h to obtain a uniform and stable precursor slurry, wherein the amount of one-dimensional chain-like structure UiO-66@CNC composite filler added accounts for 5wt% of the total solid mass of the precursor slurry.

[0066] In this embodiment, the PVDF-HFP has a molecular weight of 400,000, which can form a flexible polymer support network, ensuring the extensibility and mechanical properties of the final solid electrolyte film.

[0067] Step 3: Film Formation and Post-treatment

[0068] The precursor slurry described in step two was poured into a flat polytetrafluoroethylene mold. A scraper was used to control the wet film thickness. The mold was then transferred to a vacuum drying oven and vacuum-dried at 60°C for 6 hours, followed by a slow increase to 80°C for another 2 hours to ensure complete and uniform solvent removal. After drying, the film was allowed to cool naturally to room temperature and carefully peeled off the mold to obtain a flexible, self-supporting composite solid electrolyte film with a thickness of 100 μm. This film was labeled SE-5. The obtained composite solid electrolyte film was cut into 19 mm diameter discs and stored in a dry environment for later use.

[0069] Comparative Example 1

[0070] This comparative example does not add the one-dimensional chain-like UiO-66@CNC composite filler, but prepares pure polymer films based solely on PVDF-HFP and LiTFSI. The specific method is as follows:

[0071] Weigh 0.500 g of PVDF-HFP polymer and 0.340 g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), add to 4.0 mL of DMF solvent, and magnetically stir at 50 °C for 6 h to obtain a homogeneous and transparent solution. Pour the obtained homogeneous and transparent solution into a flat polytetrafluoroethylene mold, control the wet film thickness with a scraper, and then transfer the mold to a vacuum drying oven. First, vacuum dry at 60 °C for 6 h, then slowly raise the temperature to 80 °C and continue vacuum drying for 2 h to ensure complete and uniform removal of solvent. After drying, allow it to cool naturally to room temperature, and carefully peel it off from the mold to obtain a pure polymer film with a thickness of 100 μm. Mark this film as SE-0. Cut the obtained pure polymer film into 19 mm diameter discs and store them in a dry environment for later use.

[0072] Comparative Example 2

[0073] This comparative example uses UiO-66 nanoparticles as fillers to prepare polymer films. The specific method is as follows:

[0074] 0.360 g of zirconium tetrachloride was weighed and added to 30 mL of DMF, and treated in a 400 W ultrasonic bath for 30 min to ensure thorough mixing. 0.256 g of terephthalic acid and 0.8 mL of H2O were weighed and added to 30 mL of DMF, and stirred for 30 min to ensure thorough mixing. The zirconium tetrachloride / DMF solution was added to the terephthalic acid / DMF solution, and after stirring for 30 min, it was added to a polytetrafluoroethylene reactor and reacted at 120 °C for 24 h. After cooling to room temperature, the white solid precipitate was centrifuged and washed, and washed three times each with DMF and ethanol at 5000 rpm for 5 min. The precipitate was dried in a 60 °C vacuum drying oven for 12 h to obtain UiO-66 nanoparticle filler.

[0075] Weigh 0.500g of PVDF-HFP polymer and 0.340g of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), add them to 4.0mL of DMF solvent, and stir magnetically at 50℃ for 6h to obtain a homogeneous and transparent solution; weigh 0.0442g of the obtained UiO-66 nanoparticle filler, add it to the obtained homogeneous and transparent solution, and continue to stir magnetically at 60℃ for 12h to obtain a uniform and stable precursor slurry.

[0076] The obtained precursor slurry was poured into a flat polytetrafluoroethylene mold. A scraper was used to control the wet film thickness. The mold was then transferred to a vacuum drying oven and vacuum-dried at 60°C for 6 hours, followed by a slow increase to 80°C for another 2 hours to ensure complete and uniform solvent removal. After drying, the film was allowed to cool naturally to room temperature and carefully peeled off the mold to obtain a pure polymer film with a thickness of 100 μm. This film was labeled SE-UiO. The obtained pure polymer film was cut into 19 mm diameter discs and stored in a dry environment for later use.

[0077] I. The structures of the composite solid electrolyte films prepared in Examples 1-3 and the polymer films prepared in Comparative Examples 1-2 were characterized.

[0078] (1) X-ray diffraction pattern analysis

[0079] The one-dimensional chain-like core-shell structure UiO-66@CNC composite filler prepared in Example 1 was characterized by X-ray diffraction, and the results are as follows: Figure 1As shown, the diffraction peak positions of UiO-66@CNC are basically consistent with the simulated standard spectrum of pure UiO-66 and the spectrum of UiO-66 particles synthesized in Comparative Example 2, with characteristic diffraction peaks of UiO-66 appearing at approximately 7.3°, 8.5°, and 25.7°. This indicates that UiO-66 grows uniformly and has a complete crystal structure during the in-situ growth process using cellulose nanocrystals as a substrate. Furthermore, no obvious characteristic peaks of cellulose crystals were observed in the spectrum of UiO-66@CNC, further confirming the formation of a unique core-shell composite structure with CNC as the axis and uniformly coated with UiO-66.

[0080] (2) Fourier transform infrared spectrum analysis

[0081] To investigate the internal chemical interactions of the composite films, Fourier transform infrared spectroscopy analysis was performed on SE-0, SE-1, SE-3, SE-5, and SE-UiO films. The results are as follows: Figure 2 As shown, the pure PVDF-HFP membrane (SE-0) at 760 cm⁻¹ -1 and 1183cm -1 A strong characteristic peak is observed at 840 cm⁻¹, corresponding to the nonpolar α-crystalline phase. However, after introducing one-dimensional chain-like UiO-66@CNC filler, the characteristic peak representing the polar β-crystalline phase in the composite film, especially in SE-3, is enhanced: specifically, at 840 cm⁻¹... -1 Absorption occurred at 760cm. -1 and 1183cm -1 The characteristic peaks of the α phase are relatively weakened. This indicates that the interaction between the filler and the polymer chains effectively induces the polymer matrix to transform from the α phase, which is unfavorable for ion transport, to the β phase, which is favorable for lithium ion coordination and transport. Increasing the β phase content enhances the polarity and mobility of the polymer chain segments, providing more pathways for lithium ion transport. The interaction between the lithium salt (LiTFSI) anion and the filler is key to improving the lithium ion transference number. Compared to SE-0, the SO2 asymmetric stretching vibration peak of LiTFSI in the composite film is located at 1330 cm⁻¹. -1 and 1180cm -1 Nearby, a shift towards lower wavenumbers occurred. This phenomenon indicates that Lewis acid sites (such as Zr) on the surface of the UiO-66@CNC filler... 4+ ) and TFSI - There are strong interactions between the anions. This interaction effectively promotes the dissociation of lithium salts and restricts the migration of anions, thereby helping to increase the lithium-ion transference number. This is an important microscopic mechanism by which the ionic conductivity of composite thin films is improved.

[0082] (3) Analysis of scanning electron microscope (SEM) images

[0083] The composite solid electrolyte film SE-3 prepared in Example 3 was characterized by scanning electron microscopy and elemental distribution analysis. The results are as follows: Figure 3 and Figure 4 As shown. From Figure 3 Low-magnification scanning electron microscope (SEM) images show that the thin film is dense and free of macroscopic defects. More importantly, Figure 4 The elemental distribution diagram clearly shows that the zirconium (Zr) signal points representing UiO-66 and the oxygen (O) signal points mainly representing CNC are highly overlapping in spatial location, and both are uniformly distributed in a dotted form throughout the observation area. This directly confirms the uniform dispersion of the UiO-66@CNC composite filler in the polymer matrix, and the tight core-shell structure relationship between UiO-66 and CNC. Simultaneously, fluorine (F, representing PVDF-HFP) and sulfur (S, representing LiTFSI) also exhibit continuous and uniform distribution, indicating that the preparation method of this invention yields a composite solid electrolyte film with uniform component distribution and stable structure.

[0084] II. Electrochemical performance tests were conducted on the composite solid electrolyte films prepared in Examples 1-3 and the polymer films prepared in Comparative Examples 1-2.

[0085] (1) Analysis of LSV oxidation potential test results of the battery

[0086] To evaluate the high-pressure oxidation resistance of the composite solid electrolyte film, SE-3 and SE-0 films were used as electrolytes, stainless steel sheet SS was used as the working electrode, and lithium sheet was used as the counter electrode. The oxidation stability of SE-3 and SE-0 batteries was investigated by linear sweep voltammetry (LSV).

[0087] The results are as follows Figure 5 As shown, lithium metal was used as both the counter and reference electrodes, with a scan rate of 1 mV / s. Both curves maintained extremely low background currents in the ~3.0 V to ~4.0 V range. For the pure polymer film SE-0, the current began to rise sharply when the voltage reached approximately 4.3 V, indicating oxidative decomposition of the electrolyte. In contrast, the current of the SE-3 composite film prepared in this invention did not show a significant increase until the voltage reached approximately 4.9 V. This indicates that the introduction of one-dimensional chain-like UiO-66@CNC filler significantly broadened the electrochemical stability window of the composite solid electrolyte, increasing its upper limit of oxidation resistance by approximately 0.6 V. This enhancement can be attributed to the excellent thermodynamic stability of the UiO-66@CNC filler itself and its interaction with the polymer matrix, which jointly suppressed the decomposition of the electrolyte at high potentials. The wider electrochemical window allows this composite electrolyte to be compatible with high-voltage cathode materials, laying the foundation for constructing high-energy-density solid-state lithium batteries.

[0088] (2) Analysis of lithium plating peeling test results of batteries

[0089] To evaluate the interfacial compatibility between the composite solid electrolyte and the lithium metal anode, and its ability to suppress lithium dendrite formation, SE-3 and SE-0 films were used as electrolytes to assemble... Symmetrical cells undergo long-cycle testing. For example... Figure 6 As shown, at room temperature, for and The battery is subjected to 0.1 mA / cm 2 0.1mAh / cm 2 A constant current density was maintained, with each half-cycle deposition / dissolution time being 1 hour. Test results showed that the battery using the pure polymer electrolyte SE-0 had a high initial overpotential, and the voltage curve fluctuated more significantly during cycling, exhibiting obvious instability and large polarization. In contrast, the battery using the SE-3 composite electrolyte of this invention showed a significantly lower initial overpotential, and the voltage curve remained highly stable and symmetrical throughout a 1500-hour cycling process, with almost no overpotential increase. More importantly, the SE-3 battery did not exhibit any short-circuit phenomenon with a sudden voltage drop throughout the entire test. This fully demonstrates that the one-dimensional chain-like UiO-66@CNC composite solid-state electrolyte prepared by this invention can significantly reduce the interfacial impedance with lithium metal, form a stable solid electrolyte interfacial film (SEI), and effectively guide the uniform deposition of lithium ions, thereby greatly suppressing the growth of lithium dendrites and improving the cycle life and safety of solid-state lithium batteries.

[0090] (3) Analysis of Electrochemical Impedance Spectroscopy (EIS) Results of Batteries

[0091] Electrochemical impedance spectroscopy was used to accurately evaluate the ion conductivity of a series of samples. Each thin film sample was punched into a 19 mm diameter disc and sandwiched between two 15.8 mm diameter stainless steel (SS) blocking electrodes to assemble a symmetrical cell. The tests were conducted using an electrochemical workstation at room temperature (25°C) with a frequency range of 0.01 Hz to 1 MHz. The measured electrochemical impedance spectroscopy is shown below. Figure 7 As shown, the intersection point of the real axis (Z' axis) in the high-frequency region of the spectrum represents the bulk resistance (Rb) of the electrolyte. Figure 7As shown, the impedance value of sample SE-3 is closest to the origin, indicating that it has the lowest bulk resistance. Samples SE-1 and SE-5 are next, while the pure polymer film SE-0 has the highest bulk resistance. Notably, the bulk resistance of the SE-UiO sample using ordinary UiO-66 nanoparticles is significantly higher than that of the SE-3 sample using the one-dimensional chain-like UiO-66@CNC filler of this invention, directly demonstrating the unique advantage of the one-dimensional core-shell structure in enhancing ion transport dynamics.

[0092] (4) Analysis of battery rate test results

[0093] To comprehensively evaluate the practical application performance of composite solid electrolytes, SE-3, SE-0, and SE-UiO films were used as electrolytes, lithium metal as the anode, and lithium iron phosphate as the cathode. Using this as the positive electrode, an all-solid-state coin cell was assembled, and its rate performance was tested. The results are as follows: Figure 8 As shown. The battery is first activated at a 0.1C rate, then cycled five times each at 0.2C, 0.5C, 1C, and 2C rates, finally returning to a 0.1C rate. Figure 8 As shown, the battery using the pure polymer electrolyte SE-0 exhibits a sharp capacity decay with increasing rate, almost losing its capacity at 2C. The battery using the ordinary UiO-66 composite electrolyte SE-UiO shows some improvement, but the effect is still limited. In contrast, the battery using the SE-3 composite electrolyte of this invention demonstrates superior rate performance: its initial specific capacity at 0.1C reaches 158.7 mAh / g, and its capacity retention (relative to 0.1C capacity) at high rates of 0.2C, 0.5C, 1C, and 2C is as high as 98%, 92.3%, 84.8%, and 71.77%, respectively, significantly better than the two comparative examples. Most importantly, when the test rate returns from 2C to 0.1C, the capacity of the SE-3 battery recovers to over 99% of its initial value. This result fully demonstrates that the one-dimensional chain-like UiO-66@CNC composite solid-state electrolyte provided by this invention can significantly improve lithium-ion transport kinetics and interface stability, enabling all-solid-state batteries to possess excellent fast charge / discharge capabilities and cycle reversibility.

Claims

1. A method for preparing a one-dimensional core-shell structured composite solid electrolyte thin film based on cellulose nanocrystals, characterized in that, Includes the following steps: Step 1: Preparation of one-dimensional chain-like core-shell structured UiO-66@CNC composite filler: Cellulose nanocrystals, zirconium tetrachloride, and glacial acetic acid were ultrasonically dispersed in an organic solvent to obtain a mixed system. Terephthalic acid was dissolved in the organic solvent, and the terephthalic acid solution was added dropwise to the mixed system at a certain dropping rate under continuous stirring. The reaction was carried out at 80°C for 24-36 hours. The reaction product was centrifuged, washed, and vacuum dried to obtain a one-dimensional chain-like core-shell structure UiO-66@CNC composite filler. Step 2: Preparation of precursor slurry: PVDF-HFP polymer and lithium salt are dissolved in the organic solvent and stirred at a first temperature to obtain a homogeneous and transparent solution. The one-dimensional chain-like core-shell structure UiO-66@CNC composite filler obtained in step one is added to the homogeneous and transparent solution and stirred at a second temperature to obtain a uniform and stable precursor slurry. Step 3: Film Formation and Post-treatment The precursor slurry obtained in step two is cast into a film and then subjected to segmented vacuum drying to remove the solvent, resulting in a self-supporting composite solid electrolyte film.

2. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of cellulose nanocrystals, zirconium tetrachloride, glacial acetic acid, and organic solvent in step one is 100-125 mg: 200-210 mg: 0.8-1.2 mL: 40-50 mL; the organic solvent is N,N-dimethylformamide.

3. The preparation method according to claim 1 or 2, characterized in that, The mass-to-volume ratio of terephthalic acid to organic solvent in step one is 210~230mg:40~50mL, and the molar ratio of zirconium tetrachloride to terephthalic acid is 1:1.

5.

4. The preparation method according to claim 3, characterized in that, The ultrasonic dispersion in step one has a power of 400W and an ultrasonic time of 1h; the dropping rate is 2mL / min; the centrifugal washing is performed by centrifuging three times each with N,N-dimethylformamide and methanol, with a centrifugation speed of 6000rpm and a centrifugation time of 5min; and the drying is performed by vacuum drying at 60℃ for 12h.

5. The preparation method according to claim 4, characterized in that, The lithium salt in step two is LiTFSI; the molecular weight of the PVDF-HFP is 400,000, and the mass ratio of the PVDF-HFP polymer to the lithium salt is 3:

2.

6. The preparation method according to claim 4, characterized in that, The amount of the one-dimensional chain-like core-shell structure UiO-66@CNC composite filler added in step two is 1~5wt% of the total solid mass of the precursor slurry; the mass concentration of the PVDF-HFP polymer in the precursor slurry is 10%.

7. The preparation method according to claim 6, characterized in that, Step 2: The first temperature is 50℃ and the stirring time is 6 hours; the second temperature is 60℃ and the stirring time is 12 hours.

8. The preparation method according to claim 7, characterized in that, The segmented vacuum drying described in step three involves first drying at 60°C for 4-6 hours, and then drying at 80°C for 2-4 hours.

9. A composite solid electrolyte film prepared by the preparation method according to any one of claims 1-8, characterized in that, The surface of the composite solid electrolyte membrane exhibits a continuous and uniform PVDF-HFP polymer phase, and the film thickness is 80~100μm.

10. A solid-state lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte separator disposed between the positive and negative electrodes, characterized in that, The electrolyte membrane is the composite solid electrolyte film as described in claim 9.

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