A polymer solid electrolyte thin film with a self-assembled polyester network and a preparation method and application thereof

Abstract

The application provides a polymer solid-state electrolyte film with a self-assembled polyester network, which is composed of a nanocellulose film as a skeleton and a polymer electrolyte slurry distributed in the pores of the skeleton; the polymer electrolyte slurry is prepared by mixing a polymer, a solvent, an esterification reagent, a catalyst and a lithium salt; wherein the polymer is PEG and PVDF-HFP; and the esterification reagent is 6FDA. The solid-state electrolyte film is prepared by the following steps: firstly, preparing a polymer-lithium salt mixed solution; then, adding the esterification reagent; and finally, immersing the nanocellulose film to perform an esterification reaction. The prepared solid-state electrolyte film has the characteristics of ionic conductivity, interface stability and high mechanical strength, and can solve the problem of the high energy density all-solid-state lithium metal battery moving towards practical application.

Description

Technical Field

[0001] This invention belongs to the field of polymer electrolytes for lithium-ion batteries, specifically relating to a polymer solid electrolyte film with a self-assembled polyester network, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are a type of rechargeable battery system developed in the last century. In 1991, after six years of research and development, Sony launched its first LIB product. These batteries have a relatively simple structure and are characterized by high power density, high energy conversion efficiency, low-temperature start-up, no pollution, and light weight. The main components of LIBs include the positive electrode, negative electrode, separator, and electrolyte.

[0003] Lithium metal anodes have the highest theoretical specific capacity. The lowest potential (-3.040V vs. standard hydrogen electrode) is considered a promising anode for next-generation lithium-ion batteries. When combined with a nickel-rich layered oxide (NCM) cathode, the assembled lithium metal battery (LMB) is considered a satisfactory option for achieving high energy density in electrochemical energy storage systems. The liquid electrolyte is a crucial component of the LMB, and most commercially available LIBs currently use liquid electrolytes. The function of the liquid electrolyte is to transfer Li-24 atoms between the cathode and anode. + The development of lithium metal batteries (LMBs) using traditional liquid electrolytes has been hampered by problems such as short cycle life, low efficiency, and serious safety hazards caused by dendrite growth during lithium deposition. Solid-state electrolytes (SSEs), on the other hand, offer advantages such as low flammability, high thermal stability, no leakage, and low explosion risk. Therefore, developing all-solid-state lithium metal batteries (ASSLMBs) with high safety, good performance, and superior energy density is a crucial way to eliminate safety hazards and overcome the bottlenecks of liquid electrolyte LMBs.

[0004] After decades of research and exploration, solid-state electrolytes are mainly classified into inorganic solid-state electrolytes (ISE), polymer solid-state electrolytes (SPE), and composite polymer solid-state electrolytes (CPE). Inorganic solid-state electrolytes (ISE), such as... , and It has a high ionic conductivity (approximately) at room temperature. While possessing good thermal stability and mechanical strength, its inherent brittleness, poor interfacial contact, and interfacial side reactions severely limit its application in practical solid-state batteries. Solid polymer electrolytes (SPEs), such as PEO, PVDF, and PAN, exhibit good flexibility, processability, and interfacial compatibility with lithium metal anodes, which helps improve the physical contact between electrodes and alleviate interfacial problems. However, their ionic conductivity at room temperature is relatively low (approximately...). to The main limitations are the high crystallinity of the polymer and the solubility and transport capabilities of lithium salts within the polymer matrix. Furthermore, its mechanical strength and thermal stability often fail to meet the safety requirements of high-energy-density batteries. While composite polymer solid electrolytes (CPEs) combine the advantages of polymers and inorganic fillers, they still suffer from numerous problems. These include uneven dispersion due to inorganic filler agglomeration, discontinuous ion conduction pathways, increased impedance due to poor interfacial contact, decreased mechanical flexibility, and limited electrochemical stability. These issues severely restrict their practical application in all-solid-state lithium batteries. Therefore, low ionic conductivity, the inability to balance mechanical strength and flexibility, poor electrode compatibility, poor interfacial stability, and the imbalance among these factors remain significant constraints on the development of ASSLMBs. Summary of the Invention

[0005] In view of this, the present invention provides a polymer solid electrolyte film with high ionic conductivity, stable interface, and high mechanical strength and a self-assembled polyester network, thereby solving the problem of bringing high energy density all-solid-state lithium metal batteries to practical application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A polymer solid electrolyte film with a self-assembled polyester network is disclosed, wherein the electrolyte film is composed of a nanocellulose membrane as a framework and a polymer electrolyte slurry distributed in the pores of the framework; the polymer electrolyte slurry is prepared by mixing a polymer, a solvent, an esterification agent, a catalyst, and a lithium salt.

[0008] The polymers are PEG and PVDF-HFP; the esterification agent is 6FDA.

[0009] In some specific embodiments, preferably, the mass ratio of PEG to PVDF-HFP is 2:1;

[0010] The PEG is composed of PEG with a molecular weight of 2000Mn and PEG with a molecular weight of 6000Mn mixed in a mass ratio of 1:1; the PVDF-HFP has a molecular weight of 13w mw; the purpose of using two different molecular weight PEGs is to disrupt their chain segment arrangement during crosslinking and reduce their crystallinity.

[0011] Furthermore, the nanocellulose membrane has a thickness of 15µm and an average pore size of 1µm.

[0012] 4. The electrolyte film according to claim 1, wherein the solvent comprises any one of N-methyl-2-pyrrolidone, acetonitrile, DMSO, and DME;

[0013] The catalyst includes any one of 4-diaminopyridine, 4-dimethylaminopyridine, triethylamine, and CDI;

[0014] The lithium salt includes any one of lithium bis(trifluoromethanesulfonyl)imide, LiFSI, LiBOB, LiDFOB, and LiPF6.

[0015] A method for preparing the above-mentioned electrolyte thin film includes the following steps:

[0016] S1. Take a nanocellulose membrane, cut it, and dry it to obtain a pretreated nanocellulose membrane;

[0017] S2. Mix PEG and PVDF-HFP, add solvent, stir to dissolve, then add lithium salt and continue stirring to obtain polymer-lithium salt mixed solution;

[0018] S3. Add 6FDA to the polymer-lithium salt mixed solution of S2, stir, then add the catalyst and continue stirring to obtain the esterification reaction precursor solution.

[0019] S4. The pretreated nanocellulose membrane from S1 is immersed in the esterification reaction precursor solution from S3 for reaction. After the reaction is completed, it is washed and dried under vacuum to obtain the electrolyte membrane.

[0020] Furthermore, in step S2, the amount of lithium salt added is 20-30 wt% of the mixed solution formed by PEG and PVDF-HFP.

[0021] In some specific embodiments, preferably, the amount of lithium salt added in step S2 is 25 wt% of the mixed solution formed by PEG and PVDF-HFP.

[0022] Furthermore, in step S3, the amount of 6FDA added is the amount required for the esterification reaction with the total number of hydroxyl groups in the cellulose and PEG in the nanocellulose membrane; the entire process of step S3 is carried out at room temperature, wherein excessively high temperature will cause the PEG to react with 6FDA prematurely.

[0023] In some specific embodiments, preferably, step S3 is performed at 80°C.

[0024] Furthermore, the reaction conditions in step S4 are: temperature 85~95℃, time 2.5~3.5h; the cleaning is performed using isopropanol; and the vacuum drying temperature is 55~65℃.

[0025] In some specific embodiments, preferably, the reaction conditions in step S4 are: temperature 90°C, time 3 hours; the cleaning is performed using isopropanol; and the vacuum drying temperature is 60°C.

[0026] Furthermore, in step S1, the drying temperature is 55~65℃ and the drying time is 4~6h.

[0027] In some specific embodiments, preferably, the drying temperature in step S1 is 60°C and the drying time is 5 hours.

[0028] A lithium battery comprising the above-described electrolyte film.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The self-assembly film formation method of this invention offers highly controllable film thickness, and the prepared polymer solid electrolyte film with a self-assembled polyester network exhibits high ionic conductivity (8 × 10⁻⁶). -4 S / cm), high lithium-ion transport number ( t Li + =0.74), high voltage stability (4.8V), low lithium-ion nucleation barrier (10.5mV), and low activation energy (22.11KJ). mol -1 ), with a relatively large exchange current density (0.91mA) cm -2 ).

[0031] A Li / Li symmetric cell prepared using it did not exhibit short circuits after 500 hours of long cycling; an NCM811 / Li full cell prepared using it showed a high specific capacity (175 mAh g) after 100 cycles. -1 It boasts high capacity retention (98%), high coulombic efficiency (99.9%), and stable long-cycle performance. This further solves the challenge of bringing high-energy-density all-solid-state lithium metal batteries to practical applications. Attached Figure Description

[0032] Figure 1 The images shown are physical photos and scanning electron microscope images of the nanocellulose membrane used in the examples.

[0033] Figure 2 The images shown are physical images and scanning electron microscope images of the solid electrolyte film prepared in Example 1; where a is a physical image, b is a 2000x magnification image, and c is a 5000x magnification image.

[0034] Figure 3 The XRD diffraction peak patterns are those of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2.

[0035] Figure 4 The TGA diffraction peak patterns are those of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2.

[0036] Figure 5Mechanical strength curves of solid electrolyte films prepared in Examples 1, 1, 2, and 3, and 15µm thick nanocellulose membranes.

[0037] Figure 6 The Fourier transform infrared spectra of the solid electrolyte films prepared in Examples 1, 1, and 2 are shown.

[0038] Figure 7 The graph shows the electrochemical impedance spectroscopy (EIS) test results of stainless steel / stainless steel symmetric cells assembled with solid electrolytes prepared in Examples 1, 1, 2, and 3.

[0039] Figure 8 The current-time curves of the solid electrolytes prepared in Example 1, Comparative Examples 1, 2, and 3 after being assembled into Li / Li symmetric cells with DC polarization are shown in the test graphs.

[0040] Figure 9 The image shows the current-voltage curves of the solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 after being assembled into Li / stainless steel half-cells with DC polarization.

[0041] Figure 10 The graphs show the lithium deposition voltage distribution curves of the solid electrolytes prepared in Examples 1, 1, and 2 when assembled into Li / Cu half-cells.

[0042] Figure 11 The images show Tafel curves of Li / Li symmetric batteries assembled with the solid electrolytes prepared in Examples 1, 1, and 2.

[0043] Figure 12 The Arrhenius curves are obtained from the solid electrolytes prepared in Example 1, Comparative Examples 1 and 2, which are assembled into Li / Li symmetric cells.

[0044] Figure 13 The graph shows the constant current long cycle test curves of the solid electrolytes prepared in Example 1, Comparative Examples 1, 2, and 3 assembled into Li / Li symmetric batteries.

[0045] Figure 14 The long-cycle curves of NCM811 / Li full cells assembled with the solid electrolytes prepared in Example 1 and Comparative Example 2 are shown. The full cell in Example 1 was tested at room temperature, and the full cell in Comparative Example 2 was tested at 60°C. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and all reagents and consumables are commercially available products.

[0047] Example 1

[0048] This embodiment provides a polymer solid electrolyte film with a self-assembled polyester network, and its preparation process is as follows:

[0049] S1. Take a nanocellulose membrane (15µm thick, 1µm average pore size), cut it, and dry it at 60℃ for 5h to remove moisture, thus obtaining a pretreated nanocellulose membrane.

[0050] S2. Mix polyethylene glycol (PEG, which is a mixture of PEG with a molecular weight of 2000Mn and PEG with a molecular weight of 6000Mn in a mass ratio of 1:1) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, with a molecular weight of 13wmw) at a mass ratio of 2:1. Add N-methyl-2-pyrrolidone (NMP), stir to dissolve, and then add lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, the amount added is 25wt% of the mixed solution formed by PEG and PVDF-HFP). Continue stirring for 2 hours to obtain a polymer-lithium salt mixed solution.

[0051] S3. At 80°C, 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA, the amount added is the amount required for esterification reaction with the total number of hydroxyl groups in the cellulose and PEG in the nanocellulose membrane) is added to the polymer-lithium salt mixed solution in S2. The mixture is stirred for 30 min, and then 5 mol% of 4-diaminopyridine is added. The mixture is stirred for another 30 min to obtain the esterification reaction precursor solution.

[0052] S4. At 90°C, the pretreated nanocellulose membrane from S1 was immersed in the esterification precursor solution from S3 and reacted for 3 hours. After the reaction, it was repeatedly washed with isopropanol and then transferred to 60°C for vacuum drying for 24 hours to remove NMP solvent. The resulting electrolyte membrane (named PPEC) was obtained after drying. The membrane thickness was measured to be 15µm.

[0053] Comparative Example 1

[0054] This comparative example provides a solid electrolyte membrane, the preparation method of which is basically the same as that of Example 1, except that: in step S3, no catalyst is added, and step S4 is not performed. The mixed solution containing the esterification reagent is directly impregnated into the nanofiber membrane for 60 seconds, and then transferred to a vacuum oven at 60°C and left to stand for 24 hours. All other steps remain unchanged, thus obtaining an unreacted polymer solid electrolyte membrane (named PPEC Noreactive). The membrane thickness was measured to be 35 µm.

[0055] Comparative Example 2

[0056] This comparative example provides a solid electrolyte film, the preparation method of which is basically the same as that of Example 1, except that: the PVDF-HFP is removed in step S2, and subsequent steps are omitted. The mixed solution after stirring is directly impregnated into the nanofiber membrane for 60 seconds, and then placed in a vacuum oven at 60°C for 24 hours to obtain the solid electrolyte film (named PEG). The film thickness was measured to be 32µm.

[0057] Comparative Example 3

[0058] This comparative example provides a solid electrolyte film, the preparation method of which is basically the same as that of Example 1, except that in step S3, 6FDA is replaced with the corresponding amount of 3,3',4,4'-biphenyltetracarboxylic acid di(BPDA), while the other steps remain unchanged. The resulting polymer solid electrolyte film (named PPEC-BPDA) has a thickness of 15µm.

[0059] Comparative Example 4

[0060] This comparative example provides a solid electrolyte film, the preparation method of which is basically the same as that of Example 1, except that: in step S1, a nanofiber membrane with a thickness of 30µm is used, while the other steps remain unchanged, resulting in a polymer solid electrolyte film. The film thickness was measured to be 30µm.

[0061] Furthermore, in order to understand the properties of the various solid electrolyte films prepared above, the following experiments were also conducted.

[0062] The solid electrolyte films were cut into small circular pieces with a diameter of 16.5 mm and assembled into stainless steel sheet (SS) | solid electrolyte | stainless steel sheet batteries. The ionic conductivity of the solid electrolyte films was tested using electrochemical impedance spectroscopy (EIS) on an electrochemical workstation (CHI660c), with a frequency range of 0.1–1 MHz and a perturbation amplitude of 5 mV. All operations were performed in a glove box under argon atmosphere protection. After battery assembly, constant current charge / discharge tests and related electrochemical performance tests were conducted on a LAND CT2001A. The test results of ionic conductivity are shown in Table 1.

[0063] Table 1. Test results of ionic conductivity of various prepared solid electrolyte films

[0064]

[0065] As shown in Table 1, the solid electrolyte membranes obtained by Example 1 and Comparative Example 4 after esterification and crosslinking reaction have lower ionic conductivity than Example 1. Due to the larger initial thickness of the nanocellulose membrane in Comparative Example 4, the ion transport path is longer, and the cellulose sites inside it cannot be fully esterified, so a continuous ion transport pathway cannot be formed well. Therefore, the mechanical strength is also affected to a certain extent.

[0066] The high ionic conductivity of Example 1 compared to Comparative Examples 1 and 2 indicates that the solid electrolyte membrane after esterification and crosslinking has a richer and faster ion transport pathway than the uncrosslinked and basic PEO-based solid electrolyte membranes. Simultaneously, the esterification and crosslinking reaction also endows Example 1 with extremely high mechanical strength. The high mechanical strength of Comparative Example 1 compared to Comparative Example 2 stems from the excellent film-forming properties of PVDF-HFP. The ultra-thin thickness of Example 1 compared to Comparative Examples 1 and 2 demonstrates the high controllability of the thickness of the self-assembled film-forming method, which is far superior to traditional coating methods. Comparing Example 1 and Comparative Example 3, it can be seen that after replacing the esterification reagent, the esterification reaction still proceeds successfully, and the final film thickness remains controllable and possesses high mechanical strength. However, the ionic conductivity of Example 1 is far superior to that of Comparative Example 3. This is because the unique -CF3 functional group of 6FDA and the -CF2- structure of PVDF-HFP can promote lithium salt dissociation and improve... t Li + Meanwhile, the polyester network formed by 6FDA induces the structural rearrangement of PVDF-HFP to form a β-rich phase, reducing migration resistance and improving ionic conductivity.

[0067] Furthermore, further experiments were conducted on the raw materials and prepared electrolyte films used in the examples and comparative examples, and the results are shown in [the table below]. Figure 1-14 .

[0068] in, Figure 1 The images shown are physical photos and scanning electron microscope images of the nanocellulose membrane used in the examples.

[0069] Figure 2 The images shown are physical images and scanning electron microscope (SEM) images of the solid electrolyte film prepared in Example 1 (a is the physical image, b is a 5000x magnified surface image and elemental distribution map, c is a 2000x magnified cross-sectional image and elemental distribution map). Figure 2 It can be seen that the final self-assembled polymer solid electrolyte membrane is transparent and uniform, indicating good internal uniformity and consistency on a macroscopic level. The SEM magnification of the surface and the distribution map of each element also confirm the uniformity of the surface. The rich pores of the original cellulose membrane have been completely filled by the esterification and cross-linking reaction, forming a uniform whole. The SEM image and element distribution map of the cross section further prove the uniformity and globality of the esterification and cross-linking reaction.

[0070] Figure 3 The XRD diffraction peak patterns of the solid electrolyte films prepared in Examples 1, Comparative Examples 1 and 2, the original nanofiber film, and LiTFSI are shown in the figure. As can be seen from the figure, Example 1 has the lowest crystallinity compared to Comparative Examples 1 and 2. This is attributed to the fact that the esterification and crosslinking of polymer segments and cellulose disrupted the regular arrangement of the original polymer segments, reducing the overall crystallinity. Compared with the curve of the original LiTFSI, Example 1 has excellent solubility and dissociation for lithium salts, which also confirms the reason for its excellent ionic conductivity.

[0071] Figure 4 The TGA diffraction peak patterns of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2 are shown in the figure. As can be seen from the figure, Example 1 maintains a lower weight loss rate at the extreme high temperature of 400℃ compared with Comparative Examples 1 and 2, and has excellent thermal stability.

[0072] Figure 5 Mechanical strength curves of solid electrolyte films prepared in Examples 1, 1, 2, and 3, and 15µm thick nanocellulose membranes.

[0073] Figure 6 The Fourier transform infrared spectra of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2 are shown in the figures. The absorption peak weakened until it disappeared completely, indicating that the -OH groups in cellulose and PEG were almost entirely involved in the esterification reaction; while Peak splitting, The enhanced and low-wavelength shift indicates that after 6FDA esterification crosslinking, C=O forms a new hydrogen bond network, while the ester groups already present in cellulose cause a change in the C=O stretching vibration mode. After the reaction, The enhanced C=O absorption of the original 6FDA indicates that more 6FDA has undergone esterification to form new C=O (ester group). Nearby enhancement, The near-field weakening, the esterification reaction forming more ester bonds, and the CO vibrational mode being restricted after PEG / cellulose crosslinking. The structural changes in PVDF-HFP are mainly reflected in... Enhance and In terms of enhanced absorption, the phase structure of PVDF-HFP is rearranged due to the influence of esterification and crosslinking, which reduces the crystallinity of the long-chain polymer of PVDF-HFP and forms a rich β-phase structure, which is an important reason for its excellent ionic conductivity.

[0074] Figure 7The graph shows the electrochemical impedance spectroscopy (EIS) test results of stainless steel / stainless steel symmetric batteries assembled with solid electrolytes prepared in Examples 1, 1, 2, and 3. As can be seen from the graph, the 6FDA esterified crosslinked polymer solid electrolyte used in Example 1 has the lowest electrochemical impedance, which is also the highest ionic conductivity. Calculations show that its ionic conductivity is as high as... The other comparative examples maintain high impedance due to their higher crystallinity and poorer molecular regulation.

[0075] Figure 8 The figures show the current-time curves of Li / Li symmetric batteries assembled with solid electrolytes prepared in Examples 1, 1, 2, and 3 after DC polarization. As can be seen from the figures, the -CF3 structure of 6FDA and the -CF2- structure of PVDF-HFP promote lithium salt dissociation, thus giving Example 1 a higher current-time performance. t Li + (0.74). However, Comparative Examples 1, 2, and 3 did not have the ability to dissociate lithium salts, so their lithium ion transference numbers were low.

[0076] Figure 9 The figures show the DC polarization current curves of the solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 after being assembled into Li / stainless steel half-cells. As can be seen from the figures, the esterification reaction provides abundant ester groups for Example 1, which enhances the high voltage stability (4.8V) of the polymer network. The high bond energy of the CF bond in PVDF-HFP itself also provides antioxidant capacity, enabling Example 1 to withstand higher voltages. However, Comparative Examples 1 and 2 contain a large number of carboxyl groups, so they have lower voltage tolerance and are easily oxidized and decomposed when matched with a high-voltage positive electrode.

[0077] Figure 10 The figure shows the lithium deposition voltage distribution curves of the solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 assembled into Li / Cu half-cells. As can be seen from the figure, the uniformly distributed -CF3 structure in the polyester network formed by the 6FDA esterification reaction optimizes the electric field distribution and high ionic conductivity at the interface, reducing the nucleation barrier of lithium ions at the interface (10.5mV), thus resulting in a smaller nucleation overpotential.

[0078] Figure 11 The figures show the Tafel curves of the solid electrolytes prepared in Example 1, Comparative Examples 1 and 2, assembled into Li / Li symmetric batteries. As can be seen from the figures, the test results are similar to those in Example 2. Figure 10 With high correlation, Example 1 exhibits a small nucleation overpotential and high ionic conductivity at the electrode interface, as well as a large exchange current density (0.91 mA) at the interface. cm -2 The correlation is high, which indicates that lithium-ion transport at the interface is easier to achieve in Example 1.

[0079] Figure 12 The figures show Arrhenius curves of Li / Li symmetric batteries assembled with solid electrolytes prepared in Examples 1, 1, and 2. As can be seen from the figures, this further verifies the lithium-ion transport energy barrier within the solid electrolyte. In Example 1, the -CF3 atoms of the 6FDA crosslinked polyester network form interpenetrating three-dimensional ion channels, increasing ionic conductivity. Furthermore, the polyester network induces structural rearrangement of PVDF-HFP to form a β-rich phase, reducing migration resistance and giving Example 1 the lowest activation energy (22.11 KJ). mol -1 ).

[0080] Figure 13 The figures show the constant current long-cycle test curves of the solid electrolytes prepared in Examples 1, 1, 2, and 3 assembled into Li / Li symmetric batteries. As can be seen from the figures, Example 1, compared to the comparative examples, has a smaller polarization voltage while maintaining voltage stability over a long period of cycling, and no short circuit occurred after 500 hours of cycling. In contrast, Comparative Example 4, which also underwent esterification, experienced a short circuit after 150 hours of cycling, and the polarization voltage was too high and unstable. This indicates that the polymer solid electrolyte after 6FDA esterification crosslinking has a regulatory effect on the electrode interface. This is attributed to the fact that the uniformly distributed -CF3 structure in the polyester network formed by 6FDA esterification optimizes the electric field distribution at the interface, reduces the local current density peak, reduces the risk of lithium dendrite formation, and has good interface stability.

[0081] Figure 14 The figures show the long-cycle curves of NCM811 / Li full cells assembled with the solid electrolytes prepared in Example 1 and Comparative Example 2; the full cell in Example 1 was tested at room temperature, and the full cell in Comparative Example 2 was tested at 60°C. As can be seen from the figures, the self-assembled polyester network polymer solid electrolyte of Example 1 exhibits a higher specific capacity (175 mAh) after 100 cycles compared to the conventional PEO-based polymer solid electrolyte when matched with the high-voltage NCM811 cathode. g -1 It boasts excellent performance including high capacity retention (98%), high coulombic efficiency (99.9%), and stable long-cycle operation.

[0082] Based on the above experimental verifications, the polymer solid electrolyte film with a self-assembled polyester network prepared by this invention possesses the following characteristics: High ionic conductivity, high lithium-ion transference number ( t Li + =0.74), high voltage stability (4.8V), low lithium-ion nucleation barrier (10.5 mV), and low activation energy (22.11 KJ). mol -1), with a relatively large exchange current density (0.91 mA) cm -2 The Li / Li symmetric cell did not experience a short circuit after 500 hours of long-term cycling, and the NCM811 / Li full cell had a specific capacity of 175 mAh after 100 cycles. g -1 It has a capacity retention rate (98%), a coulombic efficiency (99.9%), and is stable over long cycles.

[0083] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polymer solid electrolyte film possessing a self-assembled polyester network, characterized in that, The electrolyte membrane is obtained by immersing a nanocellulose membrane as a framework in an esterification reaction precursor solution prepared by mixing a polymer, solvent, esterification reagent, catalyst, and lithium salt, and reacting at 85~95℃. The polymers are PEG and PVDF-HFP; the esterification agent is 6FDA; The mass ratio of PEG to PVDF-HFP is 2:1; the amount of 6FDA added is the amount required for esterification reaction with the total number of hydroxyl groups in the cellulose and PEG in the nanocellulose membrane; The PEG is composed of PEG with a molecular weight of 2000Mn and PEG with a molecular weight of 6000Mn mixed in a mass ratio of 1:1; the PVDF-HFP has a molecular weight of 13w mw.

2. The electrolyte film according to claim 1, characterized in that, The solvent includes any one of N-methyl-2-pyrrolidone, acetonitrile, DMSO, and DME; The catalyst includes any one of 4-diaminopyridine, 4-dimethylaminopyridine, triethylamine, and CDI; The lithium salt includes any one of lithium bis(trifluoromethanesulfonyl)imide, LiFSI, LiBOB, LiDFOB, and LiPF6.

3. A method for preparing an electrolyte thin film according to any one of claims 1 or 2, characterized in that, Includes the following steps: S1. Take a nanocellulose membrane, cut it, and dry it to obtain a pretreated nanocellulose membrane; S2. Mix PEG and PVDF-HFP, add solvent, stir to dissolve, then add lithium salt and continue stirring to obtain polymer-lithium salt mixed solution; S3. Add 6FDA to the polymer-lithium salt mixed solution of S2, stir, then add the catalyst and continue stirring to obtain the esterification reaction precursor solution. S4. The pretreated nanocellulose membrane from S1 is immersed in the esterification reaction precursor solution from S3 for reaction. After the reaction is completed, it is washed and dried under vacuum to obtain the electrolyte membrane.

4. The preparation method according to claim 3, characterized in that, In step S2, the amount of lithium salt added is 20-30 wt% of the mixed solution formed by PEG and PVDF-HFP.

5. The preparation method according to claim 3, characterized in that, The reaction conditions in step S4 are: temperature 85~95℃, time 2.5~3.5h; the cleaning is performed using isopropanol; the vacuum drying temperature is 55~65℃.

6. The preparation method according to claim 3, characterized in that, In step S1, the drying temperature is 55~65℃ and the drying time is 4~6h.

7. A lithium battery, characterized in that, The lithium battery contains the electrolyte film as described in any one of claims 1 or 2.

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