PVDF (Polyvinylidene Fluoride) composite cellulose paper-based solid polymer electrolyte as well as preparation and application methods thereof

Abstract

The invention belongs to the technical field of solid-state lithium metal batteries, and particularly relates to a PVDF composite cellulose paper-based solid polymer electrolyte and a preparation and application method thereof, and the preparation method comprises the following steps: 1) mixing N-methylacetamide, lithium bis (trifluoromethanesulfonyl) imide and lithium nitrate; 2) mixing the product obtained in the step 1), polyvinylidene fluoride and a thermal initiator to obtain a low eutectic polymer electrolyte precursor; (3) soaking cellulose paper in the precursor obtained in the step (2), then taking out the cellulose paper, carrying out hot-pressing polymerization, and polymerizing polyvinylidene fluoride under the action of a thermal initiator; meanwhile, the eutectic solvent is encapsulated in situ in a cross-linked network structure of polyvinylidene fluoride. The preparation method has the advantages that the interface impedance is reduced and the ion transmission efficiency is improved by fusing the low viscosity, high conductivity and safety of the unique eutectic solvent system and the supporting effect of the cellulose paper, and the excellent interface stability also provides conditions for long-term stable circulation of the battery.

Description

Technical Field

[0001] This invention belongs to the field of solid-state lithium metal battery technology, and particularly relates to a PVDF composite cellulose paper-based solid polymer electrolyte and its preparation and application methods. Background Technology

[0002] In recent years, with the rapid development of electric vehicles, large-scale energy storage, and portable electronic devices, the demand for batteries with high energy density and high safety has become increasingly urgent. Lithium metal batteries are considered an ideal choice for next-generation high-energy-density energy storage systems due to their high theoretical specific capacity (3860 mAh / g) and low electrode potential (-3.04 V vs. SHE). However, the organic liquid electrolytes commonly used in traditional lithium-ion batteries have inherent safety risks such as easy leakage, flammability, and explosion, and it is difficult to suppress the uncontrollable growth of lithium dendrites, which seriously hinders the practical application of lithium metal batteries.

[0003] Solid-state electrolytes, especially polymer solid-state electrolytes, have become ideal candidates to replace liquid electrolytes due to their superior safety, good flexibility, and compatibility with electrode processing. Among them, polyvinylidene fluoride (PVDF)-based polymer electrolytes have attracted widespread attention due to their high dielectric constant, which facilitates lithium salt dissociation, and their good electrochemical stability. Therefore, solid-state electrolytes have enormous application potential in lithium-ion batteries, solid-state batteries, electrochemical sensors, and superconducting materials. However, existing solid-state electrolyte systems still face several serious challenges: First, the ionic conductivity is generally low. The ionic conductivity of traditional polymer electrolytes is typically below 10 at room temperature. -5 The S / cm ratio severely limits the battery's rate performance and low-temperature performance, making it unable to meet the demands for high power output in practical applications.

[0004] Second, poor solid-solid interface contact and excessively high impedance. Rigid or semi-rigid solid electrolytes have point-to-point contact with the electrodes, making it difficult to form a tight and complete interface like that of liquid electrolytes. This results in extremely high interface impedance and severe polarization, affecting the battery's capacity and cycle life.

[0005] Third, the ability to suppress lithium dendrites is insufficient. The growth of lithium dendrites can not only penetrate the electrolyte membrane or separator, causing short circuits, thermal runaway, or even violent explosions, but their repeated fracture and regeneration also consume active lithium and electrolyte, leading to low coulombic efficiency and rapid battery failure. This places extremely high demands on the mechanical strength (modulus) and electrochemical stability of solid-state electrolytes.

[0006] Fourth, poor interface stability. Polymer electrolytes, especially PVDF, have poor chemical / electrochemical compatibility with highly active lithium metal anodes, making them prone to side reactions and difficult to form a stable, dense solid electrolyte interphase (SEI) film, which exacerbates performance degradation during cycling.

[0007] Despite researchers' attempts at various modification methods, such as adding inorganic fillers or using novel polymer matrices, achieving a synergistic balance between high ionic conductivity, excellent interfacial contact, superior lithium dendrite suppression, and long-term cycle stability has proven challenging. Therefore, developing a novel polymer solid electrolyte capable of simultaneously addressing these multiple challenges is crucial for the advancement of safe and high-performance solid-state lithium metal batteries. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, the present invention aims to provide a PVDF composite cellulose paper-based solid polymer electrolyte and its preparation and application methods. By introducing a unique eutectic solvent system composed of N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate, and combining it with polyvinylidene fluoride (PVDF) within a cellulose paper matrix, the problems of low ionic conductivity, poor solid-solid interface contact, and lithium dendrite suppression are synergistically solved. Ultimately, a solid electrolyte with high ionic conductivity, a wide electrochemical window, excellent interfacial stability, and long cycle life is obtained to meet the application requirements of high energy density and high safety solid-state lithium metal batteries.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a PVDF composite cellulose paper-based solid polymer electrolyte includes the following steps: 1) N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are mixed, with N-methylacetamide as a hydrogen bond donor, lithium bis(trifluoromethanesulfonyl)imide as a hydrogen bond acceptor and lithium nitrate as a stabilizer, to obtain a eutectic solvent through hydrogen bonding. 2) Mix the eutectic solvent, polyvinylidene fluoride and thermal initiator to obtain a eutectic polymer electrolyte precursor; 3) Cellulose paper is immersed in a low-eutectic polymer electrolyte precursor, then removed and subjected to hot-press polymerization. Under the action of a thermal initiator, polyvinylidene fluoride (PVDF) polymerizes; simultaneously, the low-eutectic solvent is in situ encapsulated within the cross-linked network structure of PVDF, yielding a PVDF composite cellulose paper-based polymer solid electrolyte. The low-eutectic system (DES) composed of N-methylacetamide (NMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is used as a polymer solid electrolyte for lithium metal batteries. Through unique intermolecular interactions, it simultaneously solves the core problems faced by traditional polymer electrolytes, such as low ionic conductivity, poor interfacial stability, and poor lithium metal compatibility.

[0010] In step 1), the mass ratio of N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide to lithium nitrate is (2.96~3.03):(2.94~2.97):(0.11~0.13).

[0011] In particular, an excessively high or low mass ratio of N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate will affect lithium-ion transport. When the content of lithium bis(trifluoromethanesulfonyl)imide is low, it cannot actively provide lithium ions during battery operation. When the content of lithium bis(trifluoromethanesulfonyl)imide is too high, the high concentration of lithium bis(trifluoromethanesulfonyl)imide will affect the lithium-ion transport rate, thereby affecting the cycle performance of the battery. In addition, when the content of lithium nitrate as a stabilizer is too low, the stability effect is not obvious. When the content of lithium nitrate is too high, it is not easy to dissolve and reduces the lithium-ion transport efficiency.

[0012] The mass ratio of polyvinylidene fluoride to eutectic solvent is (0.55~0.57):(9.95~10.02).

[0013] A mass ratio that is too high or too low for the eutectic solvent will significantly affect its physicochemical properties and application performance. Specifically, there are five aspects: first, a shift in the melting point of the eutectic solvent; second, a change in the viscosity of the eutectic solvent; third, a decrease in the solubility of the eutectic solvent; fourth, a decrease in ionic conductivity, affecting ion transport efficiency and thus battery performance; and fifth, a decrease in thermal and chemical stability, which in turn affects the stability of the eutectic solvent in use. Based on the above, the mass ratio of polyvinylidene fluoride to the eutectic solvent should be selected as (0.55~0.57):(9.95~10.02).

[0014] The thermal initiator is azobisisobutyronitrile or ammonium persulfate.

[0015] The amount of the thermal initiator is 0.8% to 0.9% of the mass of the eutectic solvent.

[0016] If the amount of thermal initiator is less than 0.8%, the polymerization reaction will be slow, the crosslinking density will be low, and incomplete solidification will occur. If the amount of thermal initiator is more than 0.9%, the polymerization reaction will be too fast, affecting uniformity and causing side reactions, which will affect the performance of PVDF composite cellulose paper-based polymer solid electrolyte.

[0017] The mass ratio of polyvinylidene fluoride to eutectic solvent is 56:1000.

[0018] The hot-press polymerization conditions are as follows: hot-press polymerization at 45~50MPa and 80~90℃ for 40~50min.

[0019] In step 1), N-methylacetamide, which is heated and melted at 45-65°C, is mixed with lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate at 20-25°C and 100-120 kPa, and then magnetically stirred at a speed of 600-800 rpm for more than 12 hours. In step 2), at 20~25℃ and 100~120kPa, the eutectic solvent, polyvinylidene fluoride and thermal initiator are mixed and then magnetically stirred at a speed of 600~800 rpm for more than 12 hours. In step 3), the cellulose paper is immersed in a low co-soluble polymer electrolyte precursor at 20-25°C and 100-120 kPa for 10-15 minutes.

[0020] A PVDF composite cellulose paper-based solid polymer electrolyte prepared by the above preparation method, wherein the thickness of the PVDF composite cellulose paper-based solid polymer electrolyte is 30~35μm.

[0021] The PVDF composite cellulose paper-based solid polymer electrolyte is used to manufacture solid-state lithium metal batteries.

[0022] Preparation method of solid-state lithium metal battery: In an argon-filled glove box, place the negative electrode shell, spring sheet, gasket, and negative lithium electrode sheet in sequence. Cover the negative lithium electrode sheet with a solid polymer electrolyte, then place the positive electrode sheet in the box, cover with the positive electrode shell, and press the battery firmly. The positive electrode sheet is selected from either a lithium electrode sheet or an NCM811 electrode sheet.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention reduces interfacial impedance and improves ion transport efficiency by integrating the low viscosity, high conductivity, and safety of a unique eutectic solvent system with the support of cellulose paper. Its excellent interfacial stability also provides conditions for long-term stable battery cycling. Simultaneously, the unique flexibility of the cellulose paper base effectively solves the problem of poor electrode-electrolyte interface contact, further ensuring the battery's stable long-term cycling performance. Eutectic systems offer multiple innovative pathways for the development of lithium metal solid-state batteries. Their core value lies in: 1. Safety and cost: Most DES are non-flammable and use inexpensive raw materials, aligning with the development direction of high safety and low cost. 2. Interface engineering: Whether used as the electrolyte bulk or an in-situ interface layer, it can significantly improve solid-solid interface contact and reduce impedance. 3. Designability: Its physicochemical properties (such as electrochemical window, viscosity, and melting point) can be "customized."

[0024] 2. This invention mixes N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate. N-methylacetamide acts as a hydrogen bond donor, lithium bis(trifluoromethanesulfonyl)imide as a hydrogen bond acceptor, and lithium nitrate as a stabilizer. Through hydrogen bonding, a eutectic solvent is obtained. This unique eutectic solvent system can significantly improve the interfacial stability and ionic conductivity of the electrolyte. The eutectic solvent, polyvinylidene fluoride (PVDF), and a thermal initiator are mixed to obtain a eutectic polymer electrolyte precursor. Cellulose paper is immersed in the eutectic polymer electrolyte precursor, serving as a substrate and providing good support. Through hot-press polymerization, PVDF polymerizes under the action of the thermal initiator. Simultaneously, the eutectic solvent is in-situ encapsulated within the cross-linked network structure of PVDF, resulting in a PVDF composite cellulose paper-based polymer solid electrolyte. The PVDF composite cellulose paper-based polymer solid electrolyte prepared by this invention not only solves the problems of poor ionic conductivity and poor interfacial contact in existing solid-state batteries but also improves lithium-ion conductivity.

[0025] 3. The PVDF composite cellulose paper-based polymer solid electrolyte prepared by the method of this invention possesses non-flammability, high ionic conductivity, and a wide electrochemical window resistant to temperature changes. This is because the eutectic solvent is composed of a low-melting-point salt, lithium bis(trifluoromethanesulfonyl)imide, and a solvent, N-methylacetamide, whose melting point is much lower than that of traditional electrolyte solutions, allowing it to remain liquid over a wide temperature range. This characteristic not only endows the PVDF composite cellulose paper-based polymer solid electrolyte with high ionic conductivity but also ensures stable electrochemical performance under different temperature conditions, i.e., a wide electrochemical window. Simultaneously, the eutectic solvent exhibits high thermal stability and non-flammability, further avoiding flammability risks. Furthermore, during the polymerization of the eutectic polymer electrolyte precursor within the cellulose paper substrate, a solid network structure is formed. This network structure imparts higher mechanical strength than liquid electrolytes, effectively preventing leakage of the PVDF composite cellulose paper-based polymer solid electrolyte and improving battery safety. The eutectic solvent, composed of the hydrogen bond donor N-methylacetamide and the lithium bis(trifluoromethanesulfonyl)imide acceptor, possesses abundant ion conduction channels, and its ionic conductivity can reach the level of liquid electrolytes, i.e., 10. - 3 S / cm~10 -2 S / cm; its disruption of the polymer crystalline region enhances the chain segment mobility within the electrolyte, significantly contributing to the improvement of its ionic conductivity. Incorporating a eutectic solvent into the PVDF composite cellulose paper-based polymer electrolyte can significantly improve the conductivity of the solid electrolyte.

[0026] 4. The PVDF composite cellulose paper-based polymer solid electrolyte of the present invention is soft and self-adaptive, enabling it to better fill the microscopic uneven areas on the electrode surface, thereby solving the problem of poor solid-solid interface contact between the solid electrolyte and the electrode and reducing interfacial impedance. Furthermore, this PVDF composite cellulose paper-based polymer solid electrolyte incorporates the characteristics of a low eutectic solvent. Its low viscosity and high conductivity effectively reduce ion migration resistance, thereby decreasing the internal resistance of the lithium metal battery and significantly improving the overall performance and charge / discharge efficiency of the lithium metal battery.

[0027] 5. The PVDF composite cellulose paper-based polymer solid electrolyte of this invention exhibits excellent interfacial compatibility and can suppress lithium dendrite growth. Its unique eutectic solvent system, with its low viscosity and structural characteristics, promotes a uniform electric field distribution in the lithium metal battery, effectively preventing uneven deposition of lithium ions on the lithium metal electrode surface, thereby reducing lithium dendrite formation, avoiding safety hazards such as short circuits and thermal runaway, and improving the safety and cycle life of the lithium metal battery. Simultaneously, under the action of N-methylacetamide and lithium bis(trifluoromethanesulfonyl)imide in its unique eutectic solvent system, the PVDF composite cellulose paper-based polymer solid electrolyte and the lithium metal battery electrode can synergistically electrochemically reduce and in situ construct a uniform, dense, and LiF-rich solid electrolyte interfacial film, namely an SEI film, which can effectively prevent direct contact between lithium metal and the cellulose paper-based polymer solid electrolyte, reducing side reactions. Its excellent mechanical modulus and high ionic conductivity further suppress lithium dendrite formation, further improving the cycle stability and lifespan of the lithium metal battery. Attached Figure Description

[0028] Figure 1 The Fourier transform infrared spectra of the PVDF composite cellulose paper-based polymer solid electrolyte and cellulose paper prepared in Example 1 are shown.

[0029] Figure 2 The image shows the surface SEM image of the PVDF composite cellulose paper-based polymer solid electrolyte prepared in Example 1.

[0030] Figure 3 The image shows a cross-sectional SEM image of the PVDF composite cellulose paper-based polymer solid electrolyte prepared in Example 1.

[0031] Figure 4 This is a visual representation of the flexibility of the PVDF composite cellulose paper-based polymer solid electrolyte prepared in Example 1.

[0032] Wherein, a is the visual image before folding, b is the visual image after one fold, c is the visual image after two folds, and d is the visual image after two folds unfolded.

[0033] Figure 5The impedance electrochemical test diagram shows the Li symmetric cell assembled using the PVDF composite cellulose paper-based polymer solid electrolyte prepared in Example 1.

[0034] Figure 6 The conductivity test results of the steel symmetric battery assembled in Application Example 1 at different temperatures are shown in the graph.

[0035] The illustration shows a partially enlarged view of the conductivity test results of the steel symmetric cell assembled in Example 1 at different temperatures.

[0036] Figure 7 Tafel curve of the Li symmetric cell assembled in Application Example 1.

[0037] Figure 8 The LSV curve of the Li-SS battery assembled in Application Example 1 is shown.

[0038] Figure 9 This is a long-cycle charge-discharge test diagram of the Li symmetric battery assembled in Application Example 1.

[0039] Figure 10 This is a long-cycle charge-discharge test diagram of a lithium metal full battery assembled in Application Example 1 using NCM811 as the positive electrode material.

[0040] Figure 11 This is a graph showing the GITT test data of a lithium metal full battery assembled in Application Example 1 using NCM8141 as the cathode material.

[0041] Figure 12 Impedance test diagrams of a lithium metal full cell assembled in Application Example 1 with NCM8141 as the positive electrode material after cycling at various temperatures.

[0042] Figure 13 Impedance test diagrams of the lithium symmetric battery assembled in Application Example 1 after different cycles.

[0043] Figure 14 The conductivity test result of the steel symmetric cell assembled in Application Example 1 at 0°C is shown.

[0044] Figure 15 This is a graph showing the long-cycle charge-discharge test of a lithium metal full battery assembled in Application Example 1 using NCM811 as the positive electrode material at zero degrees Celsius. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0046] The technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased commercially or prepared by existing methods. Lithium bis(trifluoromethanesulfonyl)imide, i.e., LiTFSI, is mentioned.

[0047] A method for preparing a PVDF composite cellulose paper-based solid polymer electrolyte includes the following steps: 1) At 20~25℃ and 100~120kPa, N-methylacetamide that has been heated and melted at 45~65℃ is mixed with lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate, and then magnetically stirred at a speed of 600~800 rpm for more than 12 hours to obtain a eutectic solvent; wherein, the mass ratio of N-methylacetamide, lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate is (2.96~3.03):(2.94~2.97):(0.11~0.13).

[0048] 2) At 20-25℃ and 100-120 kPa, the eutectic solvent, polyvinylidene fluoride (PVDF), and thermal initiator are mixed and magnetically stirred at 600-800 rpm for at least 12 hours to obtain a eutectic polymer electrolyte precursor. The mass ratio of PVDF to the eutectic solvent is (0.55-0.57):(9.95-10.02), preferably 56:1000. The thermal initiator is azobisisobutyronitrile (AIB) or ammonium persulfate. The amount of thermal initiator is 0.8%-0.9% of the mass of the eutectic solvent.

[0049] 3) Cellulose paper is immersed in a low-eutectic polymer electrolyte precursor at 20-25℃ and 100-120 kPa for 10-15 minutes, then removed and subjected to hot-press polymerization. Under the action of a thermal initiator, polyvinylidene fluoride (PVDF) polymerizes; simultaneously, the low-eutectic solvent is encapsulated in situ within the cross-linked network structure of PVDF, yielding a PVDF composite cellulose paper-based polymer solid electrolyte. Renewable cellulose paper is selected. The hot-press polymerization conditions are: 45-50 MPa and 80-90℃ for 40-50 minutes.

[0050] The PVDF composite cellulose paper-based polymer solid electrolyte prepared by this invention not only reduces interfacial impedance and improves ion transport efficiency by combining the low viscosity, high conductivity, and safety of the unique eutectic solvent system with the supporting effect of cellulose paper, but also provides conditions for long-term stable cycling of the battery due to its excellent interfacial stability. At the same time, the unique softness of the cellulose paper base fully solves the problem of poor contact between the electrode and electrolyte interface, further ensuring the stable long-term cycling performance of the battery.

[0051] Example 1: A method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte includes the following steps: S1. N-methylacetamide, LiTFSI, and LiNO3 are mixed in a mass ratio of 3:2.95:0.12 to obtain a eutectic solvent, denoted as DES.

[0052] S2. Add 0.34g of polyvinylidene fluoride to 6.07g of DES and stir to mix evenly to obtain a mixture. Heat and stir the mixture until it is completely melted and LiTFSI is completely dissolved. Finally, add 0.05g of thermal initiator AIBN to obtain a low co-soluble polymer electrolyte precursor.

[0053] S3. The cellulose paper is soaked in a low-cosolubility polymer electrolyte precursor for wetting. Then, the cellulose paper soaked in the precursor is placed in a hot press and hot-pressed at a pressure of 45~50MPa and a temperature of 85℃ to obtain a PVDF composite cellulose paper-based polymer solid electrolyte with a thickness of 30μm.

[0054] Example 2: A method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte includes the following steps: S1. N-methylacetamide, LiTFSI and LiNO3 are mixed in a mass ratio of 2.96:2.94:0.13 to obtain a eutectic solvent, denoted as DES.

[0055] S2. Add 0.35g of polyvinylidene fluoride to 6.1g of DES and stir to mix evenly to obtain a mixture. Heat and stir the mixture until it is completely melted and LiTFSI is completely dissolved. Finally, add 0.0578g of thermal initiator AIBN to obtain a low co-soluble polymer electrolyte precursor.

[0056] S3. The cellulose paper is soaked in a low-cosolubility polymer electrolyte precursor for wetting. Then, the cellulose paper soaked in the precursor is placed in a hot press and hot-pressed at a pressure of 48 MPa and a temperature of 85°C to obtain a PVDF composite cellulose paper-based polymer solid electrolyte with a thickness of 31 μm.

[0057] Example 3: A method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte includes the following steps: S1. N-methylacetamide, LiTFSI and LiNO3 are mixed in a mass ratio of 3.03:2.97:0.11 to obtain a eutectic solvent, denoted as DES.

[0058] S2. Add 0.39g of polyvinylidene fluoride to 6.15g of DES and stir to mix evenly to obtain a mixture. Heat and stir the mixture until it is completely melted and LiTFSI is completely dissolved. Finally, add 0.06g of thermal initiator AIBN to obtain a low co-soluble polymer electrolyte precursor.

[0059] S3. The cellulose paper is soaked in a low-cosolubility polymer electrolyte precursor for wetting. Then, the cellulose paper soaked in the precursor is placed in a hot press and hot-pressed at a pressure of 46 MPa and a temperature of 80°C to obtain a PVDF composite cellulose paper-based polymer solid electrolyte with a thickness of 31.3 μm.

[0060] Example 4: A method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte includes the following steps: S1. N-methylacetamide, LiTFSI, and LiNO3 are mixed in a mass ratio of 3:2.95:0.12 to obtain a eutectic solvent, denoted as DES.

[0061] S2. Add 0.34g of polyvinylidene fluoride to 6.07g of DES and stir to mix evenly to obtain a mixture. Heat and stir the mixture until it is completely melted and LiTFSI is completely dissolved. Finally, add 0.05g of thermal initiator ammonium persulfate to obtain a low co-soluble polymer electrolyte precursor.

[0062] S3. The cellulose paper is soaked in a low-cosolubility polymer electrolyte precursor and then placed in a hot press for hot pressing polymerization at a pressure of 47 MPa and a temperature of 85°C to obtain a PVDF composite cellulose paper-based polymer solid electrolyte with a thickness of 32 μm.

[0063] Examples 1 to 3 of this invention all yielded PVDF composite cellulose paper-based polymer solid electrolytes with parallel effects. The following study uses the PVDF composite cellulose paper-based polymer solid electrolyte obtained in Example 1 as an example: I. Battery Assembly: The battery was assembled using the PVDF composite cellulose paper-based polymer solid electrolyte prepared in Example 1 as the electrolyte. Taking the CR2032 button battery as an example, in a glove box filled with argon gas, the negative electrode shell, spring, gasket, negative electrode lithium sheet are placed in sequence. The PVDF composite cellulose paper-based polymer solid electrolyte is then placed on the negative electrode lithium sheet, and the positive electrode lithium sheet is placed in. The positive electrode shell is then covered and the battery is pressed tightly to obtain the battery.

[0064] Figure 1 In the image, the orange curve represents the Fourier transform infrared spectrum of cellulose paper, and the red curve represents the Fourier transform infrared spectrum of the cellulose paper-based polymer solid electrolyte. (Observation...) Figure 1 The results show that the PVDF composite cellulose paper-based polymer solid electrolyte exhibits richer polar functional group characteristics, such as CO, C=O, and CH functional groups, compared to cellulose paper. This indicates that the eutectic polymer solid electrolyte precursor has been successfully combined with cellulose paper to form the PVDF composite cellulose paper-based polymer solid electrolyte.

[0065] Depend on Figure 2 It was found that cellulose paper has been successfully composited with PVDF to form a PVDF composite cellulose paper solid polymer electrolyte.

[0066] Depend on Figure 3 It was found that, under the premise of PVDF composite on the surface of cellulose paper, the interior is also fully impregnated and cured by eutectic solvent, and the thickness of PVDF composite cellulose paper-based polymer solid electrolyte is about 31.1 μm.

[0067] To illustrate the crucial role of the physical properties of PVDF composite cellulose paper-based polymer solid electrolyte in batteries, a visual demonstration of the PVDF composite cellulose paper-based polymer solid electrolyte membrane was presented.

[0068] Depend on Figure 4 The results showed that when the PVDF composite cellulose paper-based polymer solid electrolyte was folded in half and then folded again, the overall structure remained intact, and it also remained intact after being unfolded again. This indicates that the PVDF composite cellulose paper-based polymer solid electrolyte possesses great flexibility and mechanical properties. However, excellent thermal stability is paramount, especially under high-temperature conditions. Failure to maintain this stability could lead to significant changes in the dimensions of the battery electrolyte membrane, resulting in thermal runaway or catastrophic explosion.

[0069] Figure 5 The EIS of a battery employing a PVDF composite cellulose paper-based polymer solid electrolyte was demonstrated. (Observation) Figure 5 The semicircles appearing at higher frequencies are correlated with charge transfer-related resistance values. Cellulose paper-based polymer solid electrolytes exhibit lower charge transfer resistance (Rct). This indicates that the PVDF composite cellulose paper-based polymer solid electrolyte exhibits lower resistance to Li... + Migration resistance is low, and the electrochemical reaction rate is fast. Furthermore, the temperature-dependent ionic conductivity of the PVDF composite cellulose paper-based polymer solid electrolyte was evaluated using EIS.

[0070] Depend on Figure 6The resistivity of the PVDF composite cellulose paper-based polymer solid electrolyte at 30℃ was found to be 4.69 Ω, and the ionic conductivity was 0.85 mS / cm. Furthermore, the ionic conductivity increased with increasing experimental temperature. The calculation of the ionic conductivity indicates that the PVDF composite cellulose paper-based polymer solid electrolyte exhibits good ion migration kinetics.

[0071] Depend on Figure 7 The superiority coefficient (j0) of the PVDF composite cellulose paper-based polymer solid electrolyte was found to be 0.135 mA / cm. 2 This indicates that the charge transfer kinetics of the PVDF composite cellulose paper-based polymer solid electrolyte are also good.

[0072] Depend on Figure 8 The LSV curves show that the PVDF composite cellulose paper-based polymer solid electrolyte has a wide electrochemical stability window, extending to 4.76V, indicating that the PVDF composite cellulose paper-based polymer solid electrolyte has great market application potential and can be used as an electrolyte for high-voltage batteries.

[0073] To further investigate the role of PVDF composite cellulose paper-based polymer solid electrolyte in stabilizing lithium metal anodes, this invention uses a 0.1 mA / cm²... 2 The current density and 0.1 mAh / cm 2 Continuous lithium-ion electroplating and stripping processes were performed at a capacity of [capacity value missing].

[0074] Depend on Figure 9 The results showed that the battery using the PVDF composite cellulose paper-based polymer solid electrolyte exhibited stable overpotential, and the polarization remained minimal even after 2200 hours of continuous use. Therefore, the PVDF composite cellulose paper-based polymer solid electrolyte achieved stable lithium plating and stripping.

[0075] To further investigate the role of PVDF composite cellulose paper-based polymer solid electrolyte in NCM811 full cells, this invention conducted cyclic charge-discharge tests on NCM811 full cells using PVDF composite cellulose paper-based polymer solid electrolyte at 0.1C.

[0076] Depend on Figure 10 The results show that the NCM811 full cell using PVDF composite cellulose paper-based polymer solid electrolyte has high cycle stability. The battery using PVDF composite cellulose paper-based polymer solid electrolyte can still maintain a high discharge specific capacity after 100 consecutive cycles at 0.1C.

[0077] Depend on Figure 11It was found that in the NCM811 full cell using PVDF composite cellulose paper-based polymer solid electrolyte, the electrolyte has a high diffusion coefficient D and exhibits excellent ion permeability and electrochemical performance.

[0078] Depend on Figure 12 The results show that, in the electrochemical impedance spectroscopy tests of the NCM811 full cell using PVDF composite cellulose paper-based polymer solid electrolyte at various cycling temperatures and after various cycling cycles, the battery using PVDF composite cellulose paper-based polymer solid electrolyte still maintains a relatively low impedance after various cycling temperatures and after various cycling cycles, indicating that it still maintains a low migration resistance to lithium ions under various cycling conditions and temperature conditions, and has a high electrochemical reaction rate retention rate.

[0079] Depend on Figure 13 The results show that in the electrochemical impedance spectroscopy test of the lithium symmetric battery assembled with PVDF composite cellulose paper-based polymer solid electrolyte under multiple cycle conditions, the solid electrolyte still maintains a relatively low electrochemical impedance under multiple cycle conditions, indicating that the electrolyte after the eutectic solvent and cellulose paper are combined still maintains a low migration resistance to lithium ions under various cycle conditions and temperature conditions, and the electrochemical reaction rate retention rate is high.

[0080] Depend on Figure 14 The results show that in the steel symmetric battery assembled with PVDF composite cellulose paper-based polymer solid electrolyte, the cellulose paper exhibits better ionic conductivity at 0 degrees Celsius, indicating the superior electrochemical performance of the PVDF composite cellulose paper-based polymer solid electrolyte under the action of a eutectic solvent system at lower ambient temperatures.

[0081] Depend on Figure 15 The results show that the NCM811 full battery using PVDF composite cellulose paper-based polymer solid electrolyte has high stability in long-term charge-discharge cycles at zero degrees Celsius. The lithium metal battery using NCM811 as the positive electrode material with PVDF composite cellulose paper-based polymer solid electrolyte still maintains a high charge-discharge capacity after 60 consecutive cycles under dual conditions of 0.05C and zero degrees Celsius.

[0082] In summary, the PVDF composite cellulose paper-based polymer solid electrolyte prepared by this invention provides guidance for achieving stable cycle performance and high power density in solid-state batteries.

[0083] The cellulose paper-based polymer solid electrolyte prepared by this invention not only reduces interfacial impedance and improves ion transport efficiency by combining the low viscosity, high conductivity, and safety of the unique eutectic solvent system with the supporting effect of cellulose paper, but also provides conditions for long-term stable cycling of the battery due to its excellent interfacial stability. At the same time, the unique flexibility of cellulose paper fully solves the problem of poor contact between the electrode and electrolyte interface, further ensuring the stable long-term cycling performance of the battery.

[0084] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments.

Claims

1. A method for preparing a PVDF composite cellulose paper-based solid polymer electrolyte, characterized by, The method comprises the following steps: 1) mixing N-methyl acetamide, lithium bistrifluoromethanesulfonimide and lithium nitrate to obtain a eutectic solvent; 2) mixing the eutectic solvent, polyvinylidene fluoride and a thermal initiator to obtain a eutectic polymer electrolyte precursor; 3) immersing cellulose paper in the eutectic polymer electrolyte precursor, then taking out and performing thermal compression polymerization, under the action of the thermal initiator, polyvinylidene fluoride is polymerized; at the same time, the eutectic solvent is encapsulated in situ in the crosslinked network structure of polyvinylidene fluoride, to obtain a PVDF composite cellulose paper-based polymer solid electrolyte.

2. The method for preparing a PVDF composite cellulose paper-based solid polymer electrolyte according to claim 1, characterized in that, In step 1), the mass ratio of N-methyl acetamide, lithium bistrifluoromethanesulfonimide and lithium nitrate is (2.96-3.03):(2.94-2.97):(0.11-0.13).

3. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, The mass ratio of polyvinylidene fluoride and the eutectic solvent is (0.55-0.57):(9.95-10.02).

4. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, The thermal initiator is azobisdimethylvaleronitrile or ammonium persulfate.

5. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, The amount of the thermal initiator accounts for 0.8%-0.9% of the mass of the eutectic solvent.

6. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, The mass ratio of polyvinylidene fluoride and the eutectic solvent is 56:1000.

7. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, The thermal compression polymerization condition is 45-50 MPa, 80-90 ℃, and thermal compression polymerization for 40-50 min.

8. The method for preparing a PVDF composite cellulose paper-based polymer solid electrolyte according to claim 1, characterized in that, In step 1), at 20-25 ℃ and 100-120 kPa, the N-methyl acetamide heated and melted at 45-65 ℃ is mixed with lithium bistrifluoromethanesulfonimide and lithium nitrate, and then magnetically stirred at a speed of 600-800 rpm for more than 12 hours; In step 2), at 20-25 ℃ and 100-120 kPa, the eutectic solvent, polyvinylidene fluoride and the thermal initiator are mixed, and then magnetically stirred at a speed of 600-800 rpm for more than 12 hours; In step 3), the cellulose paper is immersed in the eutectic polymer electrolyte precursor at 20-25 ℃ and 100-120 kPa for 10-15 min.

9. A PVDF composite cellulose paper-based solid polymer electrolyte prepared according to the preparation method of any one of claims 1-8, characterized in that, The thickness of the PVDF composite cellulose paper-based solid polymer electrolyte is 30-35 μm.

10. A PVDF composite cellulose paper-based solid polymer electrolyte prepared according to the preparation method of any one of claims 1-8, characterized in that, The PVDF composite cellulose paper-based solid polymer electrolyte is used for manufacturing a solid-state lithium metal battery.

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