Polymer electrolyte for lithium metal battery and preparation method and application thereof

Abstract

The application discloses a polymer electrolyte for a lithium metal battery and a preparation method and application thereof, and relates to the technical field of battery electrolyte materials. + The desolvation energy barrier at the electrode interface is reduced, the ionic conductivity of the electrolyte is significantly enhanced, and the lithium ion can be guided to form a stable solid electrolyte interface film in cooperation with the lithium ion, so that the uniform lithium ion flow is achieved, the uncontrollable growth of lithium dendrites is significantly inhibited, the side reaction consumption of the electrolyte in the cycle process is greatly reduced, and the long-period stability of the battery is effectively ensured, and the application is suitable for large-scale popularization and application in lithium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, mainly to the field of lithium battery electrolyte materials technology, and specifically to a polymer electrolyte for lithium metal batteries, its preparation method and application. Background Technology

[0002] To meet the urgent demand for ever-increasing energy density of power batteries in cutting-edge fields such as electric vehicles and aerospace, the development of next-generation energy storage systems that break through the current technological bottlenecks of lithium-ion batteries is imperative. Against this backdrop, lithium metal batteries, which use lithium metal as the anode, are particularly advantageous due to the extremely high theoretical specific capacity (3860 mAhg) of their anode. -1 The extremely low electrochemical potential (-3.04 V vs. SHE) is considered a key factor in achieving a leap forward in battery energy density, particularly reaching 400 Wh / kg. -1 This is one of the key pathways to achieving the above goals. If it is matched with high-nickel ternary cathode materials, this combination is expected to build a battery platform with extremely high energy density.

[0003] High-nickel ternary cathode materials (such as NCM) are ideal primarily due to their high energy density. This stems from the high nickel content, which allows the battery to operate at higher voltages, thus increasing energy density. Simultaneously, these materials also exhibit good cycle performance and processability. Therefore, when combined with lithium metal anodes, the system demonstrates significant application potential in terms of energy density.

[0004] However, this promising battery system faces severe and unique challenges in its journey towards practical application, particularly when using polymer electrolyte systems, due to the presence of interfacial and bulk materials. On the negative electrode side, while the continuous consumption of liquid electrolyte is avoided between metallic lithium and the polymer electrolyte, poor physical contact at the solid-solid interface leads to high and uneven interfacial impedance. Simultaneously, the relatively slow transport kinetics of lithium ions in the polymer matrix, especially at room temperature, easily induces uneven lithium ion flux on the electrode surface, which can still lead to uncontrolled lithium dendrite growth, threatening battery safety. On the positive electrode side, the interfacial structure instability of high-nickel ternary materials at high voltages persists, and the relatively narrow electrochemical window (i.e., "narrow voltage window") of the polymer electrolyte may undergo electrochemical decomposition at high voltages, failing to effectively suppress side reactions such as transition metal ion dissolution and lattice oxygen loss at the positive electrode interface.

[0005] To address these challenges, researchers have dedicated themselves to developing high-performance polymer electrolyte systems, but these systems still have significant limitations. For example, classic polyethylene oxide (PEO)-based solid polymer electrolytes have relatively low room-temperature ionic conductivity (typically around 10). -7 ~10 -8The S / cm level severely limits the rate capability and low-temperature performance of batteries. While constructing composite systems through copolymerization, cross-linking, or the addition of nanofillers can reduce crystallinity and improve ionic conductivity and mechanical strength, it may also introduce new interfaces or sacrifice the material's flexibility and film-forming properties. Systems represented by gel electrolytes can improve conductivity, but their stability may deteriorate at high temperatures, leading to safety hazards similar to those of liquid electrolytes. Composite polymer electrolytes, considered an important development direction, face significant material design challenges in balancing multiple objectives such as high ionic conductivity, good mechanical properties, a wide electrochemical window, and interfacial compatibility with electrodes.

[0006] More importantly, current research and optimization strategies for polymer electrolytes still fall short in simultaneously achieving effective protection for both high-voltage cathodes and highly active lithium metal anodes. For example, designs that enhance mechanical strength to suppress dendrite formation may conflict with the need to improve ionic conductivity or enhance interfacial contact with cathode particles. Modifications aimed at broadening the electrochemical window may have complex effects on lithium-ion transport kinetics or interfacial stability. The difficulty in achieving a balance between ionic conductivity, interfacial stability, electrochemical window, and overall practical feasibility reveals the multiple bottlenecks still facing current polymer electrolyte system design approaches.

[0007] Therefore, developing a novel polymer electrolyte system that can simultaneously and stably support high-nickel cathodes and lithium metal anodes, while ensuring efficient ion transport, constructing a robust, stable, and tightly connected physical and chemical protective layer at the solid-solid interface on both sides, and ensuring that the system has a sufficiently wide electrochemical window and thermal stability, is a core scientific problem and key technological breakthrough that needs to be addressed to move high-energy-density lithium metal batteries from concept to reality. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of poor ionic conductivity and interface stability when existing polymer electrolytes are used in high-nickel cathode and lithium metal anode batteries. This invention proposes a polymer electrolyte for lithium metal batteries, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention provides a polymer electrolyte for lithium metal batteries, which is prepared from the following raw materials in weight percentages: 20-25% polymer matrix, 1-5% organic acid functional monomer, 10-15% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 55-69% N,N-dimethylformamide (DMF).

[0010] The polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0011] The organic acid functional monomer is trifluoroacetic acid (TFA).

[0012] This invention discloses a polymer electrolyte for lithium metal batteries. By adding an appropriate amount of organic acid as a functional monomer to the electrolyte, it not only utilizes the weak coordination characteristics of organic acid, enabling it to actively insert and reconstruct lithium ions (Li₂O₃), but also... + The primary solvation sheath of Li promotes the transformation of the solvation structure from the traditional "solvent-dominated" to "anion-dominated" principle, effectively reducing the Li + The desolvation energy barrier at the electrode interface (lowers Li) + The polymer electrolyte of this invention improves the interfacial reaction kinetics by reducing migration resistance, promoting salt dissociation, and significantly enhancing the ionic conductivity of the electrolyte. Furthermore, after reduction and decomposition at the lithium metal anode interface, it synergistically interacts with lithium ions to guide the formation of a thin, dense, stable solid electrolyte interphase (SEI) film primarily composed of inorganic LiF. This SEI can both uniformly distribute lithium ion flow and significantly suppress the uncontrolled growth of lithium dendrites, while also greatly reducing the consumption of electrolyte by side reactions during cycling, effectively ensuring the long-term stability of the battery. The polymer electrolyte of this invention, through the addition of organic acid functional monomers, significantly improves the conductivity and interfacial stability of the polymer electrolyte, making it suitable for large-scale application in lithium metal batteries.

[0013] In polymer electrolytes, the polymer matrix serves as the matrix material, providing structural support, promoting ion transport, and inhibiting dendrite formation. Excessive polymer matrix can lead to over-crosslinking of polymer chains, reducing the flexibility of the electrolyte membrane; insufficient matrix can prevent the formation of continuous Li₂. + Transmission network; preferably, the polymer matrix has a weight percentage of 20-22%.

[0014] Preferably, the organic acid functional monomer has a weight percentage of 2-3%; the organic acid functional monomer can promote the dissociation of lithium salts in polymer electrolytes, thereby effectively reducing the lithium content. + The desolvation energy barrier at the electrode interface enhances the interfacial reaction kinetics; moreover, it can synergistically guide the formation of a stable solid electrolyte interfacial film with inorganic LiF as the main component, thereby significantly improving interfacial stability. If the amount is too large, the high polarity of the organic acid may affect the solvation structure of the electrolyte, which may lead to the excess organic acid competing with lithium salts (such as LiTFSI) in the electrolyte for solvation, reducing the stable components rich in inorganic substances (such as LiF, Li3N), resulting in a decrease in interfacial protection performance and exacerbating lithium dendrite growth; if the amount is too small, it may not be able to effectively participate in the solvation structure.

[0015] In this process, lithium bis(trifluoromethanesulfonyl)imide releases lithium ions in the polymer electrolyte through its high degree of dissociation, forming coordination transport channels with the polymer chains. If the amount used is too large, excessive LiTFSI may accelerate the side reactions of lithium metal, leading to uneven SEI film or the generation of unstable organic decomposition products, consuming active lithium and reducing coulombic efficiency. If the amount used is insufficient, the lithium ion concentration is too low, which cannot effectively support the ion transport network, resulting in increased battery internal resistance and limited rate performance. Preferably, the weight percentage of lithium bis(trifluoromethanesulfonyl)imide is 12-13%.

[0016] In this polymer electrolyte, N,N-dimethylformamide (DMF) acts as a solvent, promoting the ionization and migration of lithium ions. Excessive DMF leads to an insufficient lithium-ion density in the electrolyte, causing excess DMF to react with the lithium metal anode, generating unstable organic compounds (such as hydrocarbons and CO2) and consuming active lithium, resulting in decreased coulombic efficiency. Conversely, insufficient DMF hinders lithium-ion ionization and migration, preventing the formation of continuous Li-ion bonds. + Transmission network; preferably, the N,N-dimethylformamide has a weight percentage of 62-66%.

[0017] To achieve the above objectives, the present invention further provides a method for preparing a polymer electrolyte for lithium metal batteries, comprising: uniformly mixing raw materials according to a formula, and reacting at 60-80°C for at least 2 hours.

[0018] This invention discloses a method for preparing a polymer electrolyte for lithium metal batteries. Through a heating reaction, organic acid functional monomers can be rapidly inserted into and reconstructed into lithium ions (Li). + The primary solvation sheath of Li facilitates a rapid shift in the solvation structure from the traditional "solvent-dominated" to "anion-dominated," thereby better reducing Li + The desolvation energy barrier at the electrode interface enhances the interfacial reaction kinetics, promotes salt dissociation, and improves the ionic conductivity of the electrolyte. The preparation method of this invention is simple, mild, and produces stable product performance, making it suitable for the industrial production of polymer electrolytes for lithium metal batteries.

[0019] Preferably, the reaction temperature is 65-75℃ and the reaction time is not less than 3 hours.

[0020] To achieve the above objectives, the present invention further provides an application of a polymer electrolyte for lithium metal batteries in lithium metal anode batteries; using the polymer electrolyte for lithium metal batteries of the present invention in lithium metal anode batteries can significantly improve the cycle performance and safety of the batteries.

[0021] Preferably, the positive electrode of the lithium metal anode battery is a nickel-containing ternary cathode material.

[0022] Preferably, the lithium metal anode battery is a Li||NCM811 battery.

[0023] Beneficial effects of the present invention

[0024] 1. The polymer electrolyte of this invention utilizes the weak coordination characteristics of organic acid functional monomers, enabling them to actively insert and reconstruct lithium ions (Li). + The primary solvation sheath of Li promotes the transformation of the solvation structure from the traditional "solvent-dominated" to "anion-dominated" principle, effectively reducing the Li + The desolvation energy barrier at the electrode interface (lowers Li) + (Migration resistance), improved interfacial reaction kinetics, promoted salt dissociation, and significantly enhanced the ionic conductivity of the electrolyte.

[0025] 2. The polymer electrolyte of the present invention can work synergistically with lithium ions after reduction and decomposition at the lithium metal anode interface to guide the formation of a thin and dense stable solid electrolyte interphase (SEI) film with inorganic LiF as the main component. This SEI can not only uniformly flow lithium ions and significantly suppress the uncontrollable growth of lithium dendrites, but also greatly reduce the consumption of electrolyte side reactions during cycling, effectively ensuring the long-term stability of the battery.

[0026] 3. The polymer electrolyte of this invention significantly improves the conductivity and interfacial stability of the polymer electrolyte by adding organic acid functional monomers, making it suitable for large-scale application in lithium metal batteries.

[0027] 4. The preparation method of the polymer electrolyte of the present invention is simple, mild, and produces stable product performance, making it suitable for the industrial production of polymer electrolytes for lithium metal batteries.

[0028] 5. The polymer electrolyte for lithium metal batteries of the present invention can be used in lithium metal anode batteries to significantly improve the cycle performance and safety of the batteries. Attached Figure Description

[0029] Figure 1 The images show the X-ray diffraction results of the polymer electrolyte and the reference electrolyte in Example 1 of this invention.

[0030] Figure 2 This is a graph showing the linear sweep voltammetry curves of the polymer electrolyte and the reference electrolyte in Example 1 of the present invention.

[0031] Figure 3 In Example 1 of this invention, the polymer electrolyte and the reference electrolyte... 7 Li and 19 The nuclear magnetic resonance spectrum test results of F are shown in the figure.

[0032] Figure 4The image shows the Raman spectra of the polymer electrolyte and the reference electrolyte in Example 1 of this invention.

[0033] Figure 5 This is a graph showing the ion transport number results of the polymer electrolyte and the reference electrolyte in Example 1 of the present invention.

[0034] Figure 6 The image shows a scanning electron microscope (SEM) image of the lithium metal surface in the battery assembled with the polymer electrolyte and the reference electrolyte in Example 1 of this invention (A is the polymer electrolyte in Example 1 of this invention; B is the reference electrolyte).

[0035] Figure 7 The graph shows the long-cycle test results of the battery assembled with the polymer electrolyte and the reference electrolyte in Example 1 under the conditions of 4.3V and 25°C.

[0036] Figure 8 The graph shows the long-cycle test results of the battery assembled with the polymer electrolyte and the reference electrolyte in Example 1 of this invention under conditions of 4.3V and 60°C. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0038] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available products.

[0039] Examples 1-5

[0040] A polymer electrolyte for lithium metal batteries is obtained by mixing polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), N,N-dimethylformamide (DMF), and trifluoroacetic acid (TFA) uniformly and then stirring and reacting at 70°C for 3 hours; the specific amounts of each raw material are shown in Table 1.

[0041] Table 1. Weight percentage of each raw material in Examples 1-5

[0042]

[0043] Examples 6-13

[0044] A polymer electrolyte for lithium metal batteries is obtained by mixing polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), N,N-dimethylformamide (DMF), and trifluoroacetic acid (TFA) uniformly and then stirring and reacting at 70°C for 3 hours; the specific amounts of each raw material are shown in Table 2.

[0045] Table 2. Weight percentage of each raw material in Examples 6-13

[0046]

[0047] Example 14

[0048] A polymer electrolyte for lithium metal batteries is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 60°C for 4 h.

[0049] Example 15

[0050] A polymer electrolyte for lithium metal batteries is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 80°C for 2 h.

[0051] Comparative Example 1

[0052] A reference electrolyte is obtained by mixing 25 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 62 wt% N,N-dimethylformamide (DMF) and stirring the mixture at 70°C for 3 h.

[0053] Comparative Example 2

[0054] A polymer electrolyte is obtained by mixing 24.5 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 0.5 wt% trifluoroacetic acid (TFA) and stirring the mixture at 70 °C for 3 h.

[0055] Comparative Example 3

[0056] A polymer electrolyte is obtained by mixing 19.5 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 5.5 wt% trifluoroacetic acid (TFA) and stirring the mixture at 70°C for 3 h.

[0057] Comparative Example 4

[0058] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 50°C for 3 h.

[0059] Comparative Example 5

[0060] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 90°C for 3 h.

[0061] Comparative Example 6

[0062] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 70 °C for 1.5 h.

[0063] Comparative Example 7

[0064] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride (PVDF), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and stirring the mixture at 70°C for 3 h.

[0065] Comparative Example 8

[0066] A polymer electrolyte is obtained by mixing 18 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 66 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 70°C for 3 h.

[0067] Comparative Example 9

[0068] A polymer electrolyte is obtained by mixing 27 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 57 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and then stirring the mixture at 70°C for 3 h.

[0069] Comparative Example 10

[0070] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 9 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 66 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and stirring the mixture at 70°C for 3 h.

[0071] Comparative Example 11

[0072] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 16 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 59 wt% N,N-dimethylformamide (DMF), and 3 wt% trifluoroacetic acid (TFA) and stirring the mixture at 70°C for 3 h.

[0073] Comparative Example 12

[0074] A polymer electrolyte is obtained by mixing 22 wt% polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62 wt% N,N-dimethylformamide (DMF), and 3 wt% pentafluoropropionic acid (PFA) and stirring the mixture at 70°C for 3 h.

[0075] Experimental example:

[0076] 1. X-ray diffraction test

[0077] The polymer electrolyte of Example 1 and the reference electrolyte of Comparative Example 1 were subjected to X-ray diffraction tests. The X-ray diffraction results are as follows: Figure 1 As shown.

[0078] Depend on Figure 1 The X-ray diffraction spectrum shows that, compared with the reference electrolyte, the peak intensity of the (020) crystal plane of the polymer electrolyte of the present invention is significantly reduced, indicating that the crystal structure of the polymer electrolyte is improved and there are more amorphous regions.

[0079] 2. Measurement of linear sweep voltammetric curves

[0080] The polymer electrolyte from Example 1 and the reference electrolyte were subjected to linear sweep voltammetry. The results of the linear sweep voltammetry are as follows: Figure 2 As shown.

[0081] Depend on Figure 2The linear sweep voltammetry results show that the oxidation window of the polymer electrolyte of the present invention is 5.04 V, while the reference electrolyte begins to undergo significant oxidative decomposition at 4.3 V. This proves that the addition of TFA in the present invention significantly improves the antioxidant capacity of the polymer electrolyte under high voltage.

[0082] 3. Nuclear magnetic resonance spectroscopy test

[0083] The polymer electrolyte from Example 1 and the reference electrolyte were subjected to nuclear magnetic resonance spectroscopy tests. 7 Li spectrum and 19 The F-spectral results are as follows Figure 3 As shown.

[0084] Depend on Figure 3 nuclear magnetic resonance spectrum 7 Li spectrum and 19 As can be seen from the F-spectrum, compared with the reference electrolyte, the polymer electrolyte of this invention... 7 Li NMR and 19 The F NMR signal clearly shifts towards the high field, indicating weak coordination of TFA molecules, suggesting that TFA participates in Li + The solvation structure was altered, changing the Li + The coordination environment.

[0085] 4. Raman spectroscopy test

[0086] Depend on Figure 4 Raman spectroscopy was used to study TFSI - Coordination states in the reference electrolyte and the polymeric electrolyte of this invention under extreme conditions. Quantitative analysis revealed that the polymeric electrolyte of this invention contains a significantly higher proportion of aggregates (aggregates - 40.2%) compared to the reference electrolyte (aggregates - 30.4%). This increased aggregation is associated with enhanced formation of an inorganic-rich SEI layer, contributing to improved interfacial stability.

[0087] 5. Ion transport number

[0088] A battery was prepared using the polymer electrolyte from Example 1 and a reference electrolyte as electrolytes for a Li||Li symmetric cell. The chronoampere and AC impedance of the battery were tested at a polarization voltage of 10 mV. The test results are as follows: Figure 5 As shown;

[0089] Depend on Figure 5 The ion transport number can be calculated; the ion transport number of the polymer electrolyte using this invention is 0.55, while the ion transport number of the reference electrolyte is only 0.35. This is due to the difference between TFA and Li. + The low binding energy of Li weakens its binding properties. + The overall binding strength with the solvent makes Li+ They are more easily desolvated and migrated under the influence of an electric field.

[0090] 6. Scanning electron microscope for lithium metal surface

[0091] The Li||Li symmetric cell assembled from the polymer electrolyte prepared in Example 1 and a reference electrolyte was tested at 1 mA cm⁻¹. -2 Scanning electron microscope (SEM) images of the lithium metal surface after the next cycle are shown below. Figure 6 As shown.

[0092] Depend on Figure 6 The comparison of lithium dendrite morphology on the lithium metal surface shows that the lithium metal surface deposited with the polymer electrolyte of the present invention is dense and flat, exhibiting a regular blocky morphology, while the lithium metal surface deposited with the reference electrolyte is thick and loose and porous. This indicates that the addition of TFA in the polymer electrolyte of the present invention suppresses unfavorable side reactions.

[0093] 7. Long-cycle testing of Li||NCM811 at ambient pressure of 4.3V and room temperature of 25℃

[0094] The Li||NCM811 battery assembled with the polymer electrolyte prepared in Example 1 and the reference electrolyte was subjected to cycle performance testing under the test conditions of cutoff voltage 4.3V (2.8-4.3V), 1C, and 25℃; the test results are as follows. Figure 7 As shown.

[0095] Depend on Figure 7 The results of long-term cycling tests of Li||NCM811 at ambient pressure of 4.3V and room temperature of 25°C show that the Li||NCM811 battery with polymer electrolyte of the present invention can stably cycle for more than 500 cycles, and the number of stable cycles with 80% capacity retention is 450. In contrast, the cycling performance of the Li||NCM811 battery using the reference electrolyte decays rapidly, and the number of cycles with 80% capacity retention is only 150.

[0096] 8. Long-cycle testing of Li||NCM811 at ambient pressure of 4.3V and room temperature of 60℃

[0097] The Li||NCM811 battery assembled with the polymer electrolyte prepared in Example 1 and the reference electrolyte was subjected to cycle performance testing under the test conditions of cutoff voltage 4.3 V (2.8-4.3 V), 1C, and 60°C; the test results are as follows. Figure 8 As shown.

[0098] Depend on Figure 8The results of long-term cycling tests of Li||NCM811 at ambient pressure of 4.3V and high temperature of 60°C show that the Li||NCM811 battery using the polymer electrolyte of this invention has a stable cycle count of 340 with 80% capacity retention; in contrast, the Li||NCM811 battery using the reference electrolyte exhibits rapid degradation in cycle performance, with only 160 cycles to maintain 80% capacity retention.

[0099] 9. The electrolytes in Examples 1-15 and Comparative Examples 1-12 were tested for the number of cycles with ion transport number and capacity retention of 80% (4.3V at ambient pressure, 25°C at room temperature, 1C; 4.3V at ambient pressure, 60°C at room temperature, 1C). The results are shown in Table 3.

[0100] Table 3 Performance test results of electrolytes in Examples 1-15 and Comparative Examples 1-12

[0101]

[0102] Analysis of the test results in Table 3 shows that the polymer electrolyte of the present invention has the best electrical performance when its composition is 22%wt polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), 13%wt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 62%wt N,N-dimethylformamide (DMF), and 3%wt trifluoroacetic acid (TFA). Any change in the proportion or type of each component, or the preparation process parameters, will lead to a significant decrease in the performance of the electrolyte.

[0103] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polymer electrolyte for lithium metal batteries, characterized in that, It is prepared from the following raw materials in weight percentages: 20-25% polymer matrix, 1-5% organic acid functional monomer, 10-15% lithium bis(trifluoromethanesulfonyl)imide and 55-69% N,N-dimethylformamide. The polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene; the organic acid functional monomer is trifluoroacetic acid.

2. The polymer electrolyte according to claim 1, characterized in that, The polymer matrix comprises 20-22% by weight.

3. The polymer electrolyte according to claim 1, characterized in that, The organic acid functional monomer has a weight percentage of 2-3%.

4. The polymer electrolyte according to claim 1, characterized in that, The weight percentage of the bis(trifluoromethanesulfonyl)imide lithium salt is 12-13%.

5. The polymer electrolyte according to claim 1, characterized in that, The N,N-dimethylformamide has a weight percentage of 62-66%.

6. A method for preparing a polymer electrolyte for lithium metal batteries according to any one of claims 1-5, characterized in that, include: After the raw materials are mixed evenly according to the formula, they are reacted at 60-80℃ for at least 2 hours.

7. The method for preparing the polymer electrolyte according to claim 6, characterized in that, The reaction temperature is 65-75℃, and the reaction time is not less than 3 hours.

8. The application of a polymer electrolyte for lithium metal batteries according to any one of claims 1-5 in lithium metal anode batteries.

9. The application according to claim 8, characterized in that, The positive electrode of the lithium metal anode battery uses a nickel-containing ternary cathode material.

10. The application according to claim 9, characterized in that, The lithium metal anode battery is a Li||NCM811 battery.

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