Polymer solid electrolyte film with self-assembled polyester network as well as preparation method and application of polymer solid electrolyte film

Abstract

The invention provides a polymer solid electrolyte film with a self-assembled polyester network. The electrolyte film is composed of a nanocellulose film as a skeleton and polymer electrolyte slurry distributed in 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 (Polyethylene Glycol) and PVDF-HFP (Polyvinylidene Fluoride- The esterification reagent is 6FDA. The preparation method comprises the following steps: firstly preparing a polymer-lithium salt mixed solution, then adding an esterification reagent, and finally immersing a nanocellulose membrane for esterification reaction, thereby obtaining the solid electrolyte thin film. The prepared solid electrolyte film has ionic conductivity, stable interface and high and specific mechanical strength, and can solve the problem of practical application of a high-energy-density all-solid-state lithium metal battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery polymer electrolytes, and in particular relates to a polymer solid electrolyte film with a self-assembled polyester network, a preparation method and an application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are a type of secondary battery system developed in the last century. In 1991, after six years of research and development, Sony launched its first LIB product. This battery has a relatively simple structure and boasts high power density, high energy conversion efficiency, low-temperature startup, zero pollution, and lightweight. The main components of LIBs are the positive electrode, negative electrode, separator, and electrolyte.

[0003] The lithium metal anode has the highest theoretical specific capacity ( ) and the lowest potential (-3.040V vs standard hydrogen electrode) is considered to be a promising negative electrode for the next generation of lithium batteries. When it is combined with a nickel-rich layered oxide (NCM) positive electrode, the assembled lithium metal battery (LMB) is considered to be a satisfactory choice for achieving high energy density in electrochemical energy storage systems. Among them, the liquid electrolyte is an important component of the LMB. Most commercial LIBs currently used on the market are in the form of liquid electrolytes. The function of the liquid electrolyte is to transport Li2+ between the positive and negative electrodes. + The development of LMBs using traditional liquid electrolytes has been plagued by issues such as short cycle life, low efficiency, and serious safety hazards caused by dendrite growth during lithium deposition. Solid-state electrolytes (SSEs) offer the advantages of low flammability, high thermal stability, no leakage, and low explosion risk. Therefore, developing all-solid-state lithium metal batteries (ASSLMBs) with high safety, excellent performance, and superior energy density is an important approach to eliminating safety hazards and breaking through the bottleneck of liquid electrolyte LMBs.

[0004] After decades of research and exploration, solid electrolytes are mainly divided into inorganic solid electrolytes (ISE), polymer solid electrolytes (SPE) and composite polymer solid electrolytes (CPE). 、 and , has high ionic conductivity at room temperature (approx. ), and has good thermal stability and mechanical strength. However, its inherent high brittleness, poor interface contact and interface side reactions have severely limited its application in actual solid-state batteries. Solid polymer electrolytes (SPE), such as PEO, PVDF and PAN, have good flexibility, processability and interface compatibility with lithium metal negative electrodes, which help to improve the physical contact between the electrodes and alleviate interface problems. However, its ionic conductivity at room temperature is low (about to ), which is mainly limited by the high crystallinity of the polymer and the solubility and transport ability of the lithium salt in the polymer matrix. In addition, its mechanical strength and thermal stability often cannot meet the safety requirements of high-energy-density batteries. Although composite polymer solid electrolytes (CPE) combine the advantages of polymers and inorganic fillers, there are still many problems, such as the easy agglomeration of inorganic fillers leading to uneven dispersion, discontinuous ion conduction paths, poor interface contact causing increased impedance, decreased mechanical flexibility, and limited electrochemical stability, all of which seriously restrict its practical application in all-solid-state lithium batteries. Therefore, low ionic conductivity, inability to balance mechanical strength and flexibility, poor compatibility with electrodes, poor interface stability, and the imbalance between these are still important factors restricting the development of ASSLMB. Summary of the Invention

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

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A polymer solid electrolyte film with a self-assembled polyester network, the electrolyte film is composed of a nanocellulose membrane 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 agent, a catalyst, and a lithium salt; Wherein, the polymers are PEG and PVDF-HFP; and the esterification reagent is 6FDA.

[0007] In some specific embodiments, preferably, the mass ratio of PEG to PVDF-HFP is 2:1; The PEG is prepared by mixing PEG with a molecular weight of 2000Mn and PEG with a molecular weight of 6000Mn in a mass ratio of 1:1; the molecular weight of the PVDF-HFP is 13w mw; the purpose of using two PEGs with different molecular weights is to disrupt the chain segment arrangement during cross-linking and reduce its crystallinity.

[0008] Furthermore, the nanocellulose membrane has a thickness of 15 μm and an average pore size of 1 μm.

[0009] 4. The electrolyte membrane according to claim 1, wherein the solvent comprises any one of N-methyl-2-pyrrolidone, acetonitrile, DMSO, 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.

[0010] A method for preparing the above-mentioned electrolyte film comprises the following steps: S1. Taking the nanocellulose membrane, cutting it, and drying it to obtain a pretreated nanocellulose membrane; S2, mixing PEG and PVDF-HFP, adding a solvent, stirring to dissolve, then adding lithium salt, and continuing to stir to obtain a polymer-lithium salt mixed solution; S3, adding 6FDA to the polymer-lithium salt mixed solution of S2, stirring, then adding a catalyst, and continuing to stir the reaction to obtain an esterification reaction precursor solution; S4, immersing the pretreated nanocellulose membrane in S1 into the esterification reaction precursor solution in S3 to react, washing after the reaction is completed, and vacuum drying to obtain the electrolyte film.

[0011] Furthermore, in step S2, the amount of lithium salt added is 20-30 wt % of the mixed solution formed by PEG and PVDF-HFP.

[0012] 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.

[0013] Furthermore, the amount of 6FDA added in step S3 is the amount required for esterification reaction with the cellulose in the nanocellulose membrane and the total number of hydroxyl groups in PEG; the entire process of step S3 is carried out at room temperature, wherein, too high a temperature will cause PEG to react with 6FDA prematurely.

[0014] In some specific embodiments, preferably, the entire process of step S3 is performed at 80°C.

[0015] Furthermore, the reaction conditions in step S4 are: temperature 85-95° C., time 2.5-3.5 h; the cleaning is performed using isopropyl alcohol; and the vacuum drying temperature is 55-65° C.

[0016] In some specific embodiments, preferably, the reaction conditions in step S4 are: temperature 90° C., time 3 h; the cleaning is performed using isopropyl alcohol; and the vacuum drying temperature is 60° C.

[0017] Furthermore, in step S1, the drying temperature is 55-65° C., and the drying time is 4-6 hours.

[0018] In some specific embodiments, preferably, the drying temperature in step S1 is 60° C. and the drying time is 5 hours.

[0019] A lithium battery comprising the above-mentioned electrolyte film.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The thickness of the self-assembled film forming method of the present invention is highly controllable, and the prepared polymer solid electrolyte film with a self-assembled polyester network has high ionic conductivity (8×10 -4 S / cm), high lithium ion migration number ( t Li + =0.74), high voltage stability (4.8V), low lithium ion nucleation barrier (10.5mV), low activation energy (22.11Kj mol -1 ), maximum exchange current density (0.91mA cm -2 ).

[0021] The Li / Li symmetrical battery prepared by the method can survive a 500h long cycle without short circuit; the NCM811 / Li full battery prepared by the method has a high specific capacity (175mAh g) after 100 cycles. -1 ), high capacity retention (98%), high Coulombic efficiency (99.9%), and stable long-cycle performance. This further solves the problem of practical application of high-energy-density all-solid-state lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figures are the physical pictures and scanning electron microscope pictures of the nanocellulose membrane used in the examples.

[0023] Figure 2 The actual image and scanning electron microscope image of the solid electrolyte film prepared in Example 1; among them, a is the actual image, b is the image magnified 2000 times, and c is the image magnified 5000 times.

[0024] Figure 3 These are the XRD diffraction peak patterns of the solid electrolyte films prepared in Example 1 and Comparative Examples 1 and 2.

[0025] Figure 4 These are the TGA diffraction peak patterns of the solid electrolyte films prepared in Example 1 and Comparative Examples 1 and 2.

[0026] Figure 5 The mechanical strength curves of the solid electrolyte films prepared in Example 1, Comparative Examples 1, 2, and 3, and a 15µm thick nanocellulose membrane (15µm fiber membrane).

[0027] Figure 6 These are the Fourier transform infrared spectra of the solid electrolyte films prepared in Example 1 and Comparative Examples 1 and 2.

[0028] Figure 7This is a graph showing the electrochemical impedance spectroscopy (EIS) test results of a stainless steel / stainless steel symmetric battery assembled with solid electrolytes prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0029] Figure 8 This is a test diagram of the current-time curve of the solid electrolytes prepared in Example 1 and Comparative Examples 1, 2, and 3 after being assembled into a Li / Li symmetric battery and subjected to DC polarization.

[0030] Figure 9 This is a test diagram of the volt-ampere-current curve of the solid electrolyte prepared in Example 1 and Comparative Examples 1 and 2 after being assembled into a Li / stainless steel half-cell and subjected to DC polarization.

[0031] Figure 10 This is a test diagram of the lithium deposition voltage distribution curve of the Li / Cu half-cell assembled with the solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2.

[0032] Figure 11 This is a Tafel plot test diagram of the solid electrolyte prepared in Example 1 and Comparative Examples 1 and 2 assembled into a Li / Li symmetric battery.

[0033] Figure 12 Arrhenius curve test diagram of Li / Li symmetric battery assembled with solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2.

[0034] Figure 13 This is a constant current long cycle curve test diagram of a Li / Li symmetrical battery assembled with the solid electrolytes prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0035] Figure 14 Long cycle curves of NCM811 / Li full cells assembled with solid electrolytes prepared in Example 1 and Comparative Example 2; wherein, the full cell of Example 1 was tested at room temperature, and the full cell of Comparative Example 2 was tested at 60°C. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with specific examples so that those skilled in the art can more clearly understand the present invention. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and all reagents and consumables are commercially available products.

[0037] Example 1 This embodiment provides a polymer solid electrolyte film with a self-assembled polyester network, and the preparation process is as follows: S1. Take a nanocellulose membrane (thickness 15 µm, average pore size 1 µm), cut it, and dry it at 60°C for 5 h to remove moisture to obtain a pretreated nanocellulose membrane.

[0038] S2, polyethylene glycol (PEG, prepared by mixing 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, molecular weight of 13wmw) in a mass ratio of 2:1, adding N-methyl-2-pyrrolidone (NMP), stirring to dissolve, and then adding lithium bistrifluoromethylsulfonyl imide (LiTFSI, added in an amount of 25wt% of the mixed solution formed by PEG and PVDF-HFP), and continuing to stir for 2h to obtain a polymer-lithium salt mixed solution; S3. Add 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA, the amount added is the amount required for esterification reaction with the total number of hydroxyl groups in cellulose and PEG in the nanocellulose membrane) to the polymer-lithium salt mixed solution of S2 at 80°C, stir for 30 minutes, then add 5 mol% of 4-diaminopyridine, and continue stirring and reacting for 30 minutes to obtain an esterification reaction precursor solution; S4: Immerse the pretreated nanocellulose membrane in S1 in the esterification precursor solution in S3 for 3 hours at 90°C. After the reaction, rinse repeatedly with isopropyl alcohol and transfer to a vacuum oven at 60°C for 24 hours to remove the NMP solvent. After drying, the electrolyte film (designated PPEC) was obtained. Testing revealed a film thickness of 15 µm.

[0039] Comparative Example 1 This comparative example provides a solid electrolyte membrane prepared by a method essentially identical to that of Example 1, except that, in step S3, no catalyst was added, and step S4 was omitted. Instead, the nanofiber membrane was directly infiltrated with the mixed solution containing the esterification agent for 60 seconds, then transferred to a 60°C vacuum oven and allowed to stand for 24 hours. All other conditions remained unchanged, resulting in an unreacted polymer solid electrolyte membrane (designated PPEC Noreactive). Testing revealed a membrane thickness of 35 µm.

[0040] Comparative Example 2 This comparative example provides a solid electrolyte film prepared by a method essentially identical to that of Example 1, except that the PVDF-HFP was removed from step S2, and subsequent steps were omitted. Instead, the stirred mixed solution was directly infiltrated into a nanofiber separator for 60 seconds, then placed in a vacuum oven at 60°C for 24 hours to obtain a solid electrolyte film (designated PEG). Testing revealed a film thickness of 32 µm.

[0041] Comparative Example 3 This comparative example provides a solid electrolyte film prepared by a method essentially identical to that of Example 1, except that in step S3, 6FDA was replaced with a corresponding amount of 3,3',4,4'-biphenyltetracarboxylic acid (BPDA). The remaining steps remained unchanged, resulting in a polymer solid electrolyte film (designated PPEC-BPDA). Testing revealed a film thickness of 15 µm.

[0042] Comparative Example 4 This comparative example provides a solid electrolyte membrane. Its preparation method is essentially the same as that of Example 1, except that, in step S1, a 30 µm-thick nanofiber separator is used. The remaining steps remain unchanged, resulting in a polymer solid electrolyte membrane. Testing revealed that the membrane had a thickness of 30 µm.

[0043] Furthermore, in order to understand the performance of the solid electrolyte films prepared above, the following experiments were conducted.

[0044] Each of the above solid electrolyte films was cut into small discs with a diameter of 16.5 mm and assembled into a stainless steel sheet (SS) | solid electrolyte | stainless steel sheet battery. The ionic conductivity of the solid electrolyte membranes was measured using electrochemical impedance spectroscopy (EIS) on an electrochemical workstation (CHI660c) with a frequency setting of 0.1 to 1 MHz and a perturbation amplitude of 5 mV. All these operations were performed in an argon-protected glove box. After battery assembly, galvanostatic charge / discharge tests and related electrochemical performance tests were performed on a LAND CT2001A. The ionic conductivity test results are shown in Table 1.

[0045] Table 1 Test results of ionic conductivity of prepared solid electrolyte films

[0046] As can be seen from Table 1, the solid electrolyte membranes obtained in Example 1 and Comparative Example 4 after esterification and cross-linking reaction have an ionic conductivity one order of magnitude lower than that in Example 1 and the mechanical strength is also affected to a certain extent, because the initial nanocellulose membrane of Comparative Example 4 is thicker, the ion transmission path is longer, and the cellulose sites inside it cannot be fully esterified, and a continuous path for ion transmission cannot be formed well.

[0047] The high ionic conductivity of Example 1 relative to Comparative Examples 1 and 2 indicates that the solid electrolyte membrane after the esterification cross-linking reaction has a richer and faster ion transmission path than the uncross-linked and basic PEO-based solid electrolyte membrane. At the same time, the esterification cross-linking reaction also gives Example 1 ultra-high mechanical strength. The high mechanical strength of Comparative Example 1 relative to Comparative Example 2 comes from the good film-forming properties of PVDF-HFP. The ultra-thin thickness of Example 1 relative to Comparative Examples 1 and 2 illustrates the high controllability of the thickness of the self-assembly film-forming method, and the thickness regulation is far superior to the traditional coating method; by comparing Example 1 and Comparative Example 3, it can be seen that after replacing the esterification reagent, the esterification reaction is still successfully carried out, and the thickness of the final film is still controllable and has high mechanical strength, but 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 the dissociation of lithium salts and improve t Li + At the same time, the polyester network formed by 6FDA induced the structural rearrangement of PVDF-HFP to form a β-rich phase, reducing the migration resistance and improving the ionic conductivity.

[0048] Furthermore, further tests were conducted on the raw materials and the prepared electrolyte films in the examples and comparative examples, and the results are shown in FIG. Figure 1-14 .

[0049] in, Figure 1 The figures are the physical pictures and scanning electron microscope pictures of the nanocellulose membrane used in the examples.

[0050] Figure 2 The actual image and scanning electron microscope image of the solid electrolyte film prepared in Example 1 (a is the actual image, b is the surface magnified 5000 times and the element distribution map, c is the cross-section magnified 2000 times and the element distribution map), Figure 2 It can be seen that the self-assembled polymer solid electrolyte membrane finally obtained is transparent and uniform, which shows that its internal structure has good uniformity and consistency from a macroscopic perspective. The surface SEM magnification image and the distribution map of each element also confirm its surface uniformity. The rich pores of the original cellulose membrane have been completely filled under the action of the esterification cross-linking reaction to form a uniform whole. The cross-sectional SEM image and element distribution map further prove the uniformity and globality of the esterification cross-linking reaction.

[0051] Figure 3The XRD diffraction peak patterns of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2, as well as the original nanofiber membrane and LiTFSI, show that Example 1 has the lowest crystallinity relative to Comparative Examples 1 and 2. This is attributed to the esterification and cross-linking of the polymer segments and cellulose disrupting the regular arrangement of the original polymer segments and reducing the overall crystallinity. Compared with the curve of the original LiTFSI, it can be seen that Example 1 has excellent solubility and dissociation degree for lithium salts, which also confirms the reason for its excellent ionic conductivity.

[0052] Figure 4 The TGA diffraction peak patterns of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2 show that Example 1 always maintains a lower weight loss rate than Comparative Examples 1 and 2 at an extreme high temperature of 400°C, and has excellent thermal stability.

[0053] Figure 5 The mechanical strength curves of the solid electrolyte films prepared in Example 1, Comparative Examples 1, 2, and 3, and a 15µm thick nanocellulose membrane (15µm fiber membrane).

[0054] Figure 6 The following are Fourier transform infrared spectra of the solid electrolyte films prepared in Example 1, Comparative Examples 1 and 2. The absorption peak weakened until it disappeared completely, indicating that the -OH groups in cellulose and PEG were almost completely involved in the esterification reaction; Peak splitting, The enhancement and low wavelength shift indicate that after 6FDA esterification and cross-linking, C=O forms a new hydrogen bond network, and the presence of certain ester groups in cellulose itself causes the C=O stretching vibration mode to change. The enhanced absorption of C=O of the original 6FDA indicates that more 6FDA has undergone esterification to form new C=O (ester group). Nearby enhancements, The esterification reaction forms more ester bonds, and after PEG / cellulose cross-linking, its CO vibration mode is restricted. The structural changes of PVDF-HFP are mainly reflected in Enhancement and In terms of absorption enhancement, the phase structure of PVDF-HFP is rearranged due to the influence of esterification and cross-linking, which reduces the crystallinity of the PVDF-HFP long-chain polymer and forms a rich β-phase structure, which is an important reason for its excellent ionic conductivity.

[0055] Figure 7The electrochemical impedance spectroscopy (EIS) test results of a stainless steel / stainless steel symmetrical battery assembled with solid electrolytes prepared in Example 1, Comparative Examples 1, 2, and 3 are shown in the figure. As can be seen from the figure, the polymer solid electrolyte cross-linked by 6FDA esterification in Example 1 has the smallest electrochemical impedance, that is, the highest ionic conductivity. After calculation, its ionic conductivity is as high as , and the other comparative examples maintain higher impedance due to higher crystallinity and poorer molecular control.

[0056] Figure 8 The current-time curve test diagram of the solid electrolyte prepared in Example 1, Comparative Examples 1, 2, and 3 after being assembled into a Li / Li symmetrical battery with DC polarization shows that: since the -CF3 of 6FDA and the -CF2- structure of PVDF-HFP can promote the dissociation of lithium salt, the higher t Li + (0.74). However, the lithium ion transference numbers of Comparative Examples 1, 2, and 3 are relatively low because they do not have the ability to dissociate lithium salts.

[0057] Figure 9 The volt-ampere-current curves of the solid electrolytes prepared in Example 1 and Comparative Examples 1 and 2 after DC polarization were assembled into Li / stainless steel half-cells show that the esterification reaction provides Example 1 with abundant ester groups, enhancing the high voltage stability (4.8V) of the polymer network. Furthermore, the high bond energy of the C-F bond of PVDF-HFP itself provides antioxidant capacity, enabling Example 1 to withstand higher voltages. However, Comparative Examples 1 and 2 contain a large number of carboxyl groups, resulting in lower withstand voltages and being easily oxidized and decomposed when paired with a high-voltage positive electrode.

[0058] Figure 10 The solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 are assembled into a Li / Cu half-cell lithium deposition voltage distribution curve test graph. It can be seen from the figure that: due to the uniform distribution of -CF3 structure in the polyester network formed by the esterification reaction of 6FDA, the electric field distribution at the interface and the higher ionic conductivity are optimized, and the nucleation barrier of lithium ions at the interface (10.5mV) is reduced, thereby having a smaller nucleation overpotential;.

[0059] Figure 11 The solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 are assembled into a Li / Li symmetric battery Tafel curve test diagram. It can be seen from the figure that the test results are consistent with Figure 10 The results show that Example 1 has a small nucleation overpotential and high ionic conductivity at the electrode interface and a large exchange current density at the interface (0.91 mA cm -2 ), which indicates that lithium ion transport at the interface is easier in Example 1.

[0060] Figure 12 The solid electrolytes prepared in Example 1, Comparative Examples 1 and 2 are assembled into a Li / Li symmetric battery Arrhenius curve test diagram. It can be seen from the figure that: Here we further verify the transmission energy barrier of lithium ions inside the solid electrolyte. Since the -CF3 of the 6FDA cross-linked polyester network in Example 1 forms a three-dimensional ion channel that penetrates each other, the ionic conductivity is improved, and the polyester network induces the structural rearrangement of PVDF-HFP to form a β-rich phase, which reduces the migration resistance, giving Example 1 the lowest activation energy (22.11 Kj mol -1 ).

[0061] Figure 13 The solid electrolytes prepared in Example 1 and Comparative Examples 1, 2, and 3 are assembled into a constant current long cycle curve test diagram of a Li / Li symmetrical battery. It can be seen from the figure that Example 1 has a smaller polarization voltage than the comparative example while maintaining voltage stability for a long cycle. There is no short circuit phenomenon after 500 hours of cycling. However, Comparative Example 4, which has also undergone an esterification reaction, has a short circuit after 150 hours of cycling and the polarization voltage is too large and unstable. This shows that the polymer solid electrolyte that has undergone a 6FDA esterification cross-linking reaction has a regulating effect on the electrode interface. This is attributed to the uniformly distributed -CF3 structure in the polyester network formed by the 6FDA esterification reaction, which 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.

[0062] Figure 14 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, while the full cell in Comparative Example 2 was tested at 60°C. As can be seen from the figure, the self-assembled polyester network polymer solid electrolyte in Example 1 exhibits a higher specific capacity (175 mAh) after 100 cycles compared to the traditional PEO-based polymer solid electrolyte when paired with the NCM811 high-voltage cathode. g -1 ), high capacity retention rate (98%), high coulombic efficiency (99.9%), and excellent performance of stable long cycle.

[0063] Based on the above experiments, the polymer solid electrolyte film with a self-assembled polyester network prepared by the present invention has 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), low activation energy (22.11 Kj mol -1), the maximum exchange current density (0.91 mA cm -2 ), Li / Li symmetrical battery 500h long cycle without short circuit, NCM811 / Li full battery 100 cycles specific capacity (175 mAh g -1 ), capacity retention rate (98%), coulombic efficiency (99.9%) and stable long cycle.

[0064] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polymer solid electrolyte film having a self-assembled polyester network, characterized in that: The electrolyte film is composed of a nanocellulose membrane 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 agent, a catalyst, and a lithium salt; Wherein, the polymers are PEG and PVDF-HFP; and the esterification reagent is 6FDA.

2. The electrolyte membrane according to claim 1, wherein The mass ratio of PEG to PVDF-HFP is 2:1; The PEG is prepared by mixing PEG with a molecular weight of 2000Mn and PEG with a molecular weight of 6000Mn in a mass ratio of 1:1; and the molecular weight of the PVDF-HFP is 13w mw.

3. The electrolyte membrane according to claim 1, wherein The nanocellulose membrane has a thickness of 15 μm and an average pore size of 1 μm.

4. The electrolyte membrane according to claim 1, wherein 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.

5. A method for preparing the electrolyte film according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Taking the nanocellulose membrane, cutting it, and drying it to obtain a pretreated nanocellulose membrane; S2, mixing PEG and PVDF-HFP, adding a solvent, stirring to dissolve, then adding lithium salt, and continuing to stir to obtain a polymer-lithium salt mixed solution; S3, adding 6FDA to the polymer-lithium salt mixed solution of S2, stirring, then adding a catalyst, and continuing to stir the reaction to obtain an esterification reaction precursor solution; S4, immersing the pretreated nanocellulose membrane in S1 into the esterification reaction precursor solution in S3 to react, washing after the reaction is completed, and vacuum drying to obtain the electrolyte film.

6. The preparation method according to claim 5, 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.

7. The preparation method according to claim 5, characterized in that The amount of 6FDA added in step S3 is the amount required for esterification reaction with the cellulose in the nanocellulose membrane and the total number of hydroxyl groups in PEG; the entire process of step S3 is carried out at room temperature.

8. The preparation method according to claim 5, characterized in that The reaction conditions in step S4 are: temperature 85-95° C., time 2.5-3.5 h; the cleaning is performed using isopropyl alcohol; and the vacuum drying temperature is 55-65° C.

9. The preparation method according to claim 5, characterized in that In step S1, the drying temperature is 55-65° C., and the drying time is 4-6 hours.

10. A lithium battery, characterized in that: The lithium battery comprises the electrolyte film according to any one of claims 1 to 4.

Images