PVDF-based composite solid electrolyte, preparation method and application thereof, and lithium battery

Abstract

This invention belongs to the field of lithium battery technology, specifically relating to a PVDF-based composite solid electrolyte, its preparation method and application, and lithium batteries. The composite solid electrolyte comprises a PVDF-based polymer, lithium salt, amide substances, nano-metal oxides, and residual organic solvents. The nano-metal oxides and amide substances jointly regulate the solvation structure of lithium ions, weakening the interaction between the solvent and lithium ions. [Li (residual solvent)] x ] + The interaction forces with the polymer create a weak interaction environment for lithium ions, promoting the Li-polymerization process. + The process facilitates the transport of ions and simultaneously transforms the solvent-derived electrode-electrolyte interface phase into an anion-dominant derived phase, thereby improving interface stability. On the other hand, the nano-metal oxides reduce the crystallinity of the PVDF polymer, inhibit spherulite formation, and densify the electrolyte membrane. This contributes to the construction of uniform and continuous ion transport channels, improves mechanical properties, effectively suppresses the growth of lithium dendrites, and enhances the cycle stability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a PVDF-based composite solid electrolyte, its preparation method and application, and lithium batteries. Background Technology

[0002] The rapid development of technologies such as electric vehicles, grid energy storage, and smart devices has continuously raised new expectations and requirements for the energy density and safety of rechargeable batteries. Lithium metal, with its high theoretical capacity of 3860 mAh / g and a minimum reduction potential of -3.04V (relative to the standard hydrogen electrode), is an ideal negative electrode for high-energy-density batteries. The combination of high-voltage ternary materials and lithium metal represents a development trend for high-energy-density lithium batteries. However, the extremely high electrochemical reactivity of lithium metal, lithium dendrite growth, and safety issues with commercial lithium battery electrolytes hinder the further development of lithium metal batteries (LMBs). Replacing liquid electrolytes (LE) and separators with solid-state electrolytes (SEs) that possess high ionic conductivity, high stability, and high mechanical properties holds promise for achieving solid-state lithium batteries that balance high safety and high energy density.

[0003] PVDF-based polymer electrolytes, primarily composed of polyvinylidene fluoride (PVDF) and its copolymers (PVDF-hexafluoropropylene, PVDF-trifluoroethylene), possess several desirable electrolyte properties, including a balance of mechanical strength and toughness, a wide voltage window, good thermal stability, high electrochemical stability, no adverse reactions with other materials, and good processability. However, solid-state electrolytes suffer from low ionic conductivity and high interfacial impedance at room temperature. In a system of PVDF-based polymer + lithium salt + a small amount of residual solvent, the residual solvent reacts with lithium ions (Li... + ) combine to form [Li (residual solvent)] x ] + The solvation structure ensures sufficient room-temperature ion transport in the system. However, [Li (residual solvent)] x ] + Due to the strong cation-dipole interaction and the strong dipole-dipole interaction with the polymer chain segments, the solvated structure exhibits poor interfacial stability between the positive and negative electrodes. Furthermore, the plasticizing effect of the residual solvent leads to a significant decrease in the mechanical properties of the electrolyte, making it difficult to suppress the growth of lithium dendrites and severely affecting the long-term cycling stability of the system. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a PVDF-based composite solid electrolyte, its preparation method and application, and lithium batteries. Lithium metal batteries assembled using the PVDF-based composite solid electrolyte of this invention exhibit high specific capacity, excellent rate performance, and good cycle stability.

[0005] This invention provides a PVDF-based composite solid electrolyte, comprising a PVDF-based polymer, and lithium salt, amide substances, nano-metal oxides and residual organic solvents dispersed in the PVDF-based polymer;

[0006] The amide compounds have the structural formula R-CO-NH2 or R-CO-NH-R', where R and R' are independently alkyl groups.

[0007] Preferably, the amide substance includes one or more of N-methylformamide, N-methylacetamide, N-methylpropionamide, formamide, acetamide, and propionamide.

[0008] Preferably, the molar ratio of the amide to the lithium salt is (1-8):1.

[0009] Preferably, the nano-metal oxide is a nano-single metal oxide, which includes one or more of titanium dioxide, zirconium dioxide, vanadium pentoxide, chromium trioxide, molybdenum trioxide, and tungsten trioxide.

[0010] Preferably, the mass ratio of the nano-metal oxide to the PVDF-based polymer is (0.03–0.2):1.

[0011] Preferably, the PVDF-based polymer includes PVDF homopolymer or PVDF copolymer, the PVDF copolymer includes binary copolymer or ternary copolymer, the binary copolymer includes poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), or poly(vinylidene fluoride-trifluorochloroethylene), and the ternary copolymer includes poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene).

[0012] Preferably, the lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalate borate, and lithium nitrate; the mass ratio of the lithium salt to the PVDF-based polymer is (0.6–1.2):1.

[0013] This invention also provides a method for preparing the PVDF-based composite solid electrolyte described in the above technical solution, comprising the following steps:

[0014] A precursor liquid is obtained by mixing PVDF-based polymers, lithium salts, amides, nano-metal oxides, and organic solvents.

[0015] The precursor liquid is cast to remove the organic solvent, thereby obtaining the PVDF-based composite solid electrolyte.

[0016] The present invention also provides the application of the PVDF-based composite solid electrolyte described in the above technical solution or the PVDF-based composite solid electrolyte obtained by the above preparation method in lithium batteries.

[0017] The present invention also provides a lithium battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the PVDF-based composite solid electrolyte described in the above technical solution or the PVDF-based composite solid electrolyte obtained by the above preparation method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention provides a PVDF-based composite solid electrolyte, comprising a PVDF-based polymer, and lithium salt, amide substances, nano-metal oxides and residual organic solvents dispersed in the PVDF-based polymer; wherein the amide substances have the structural formula R-CO-NH2 or R-CO-NH-R', where R and R' are independently alkyl groups.

[0020] The PVDF-based composite solid electrolyte of this invention comprises amide substances and nano-metal oxides, wherein the C=O in the amide substances can participate in [Li (residual solvent)]. x ] + The solvation structure of lithium ions is regulated by amino or imino groups, which provide hydrogen bond donors. Nanoscale metal oxides possess phase structures and abundant surface active sites. Amide substances and surface-defect-rich nanoscale metal oxides jointly regulate the solvation structure of lithium ions, weakening the interaction between the solvent and lithium ions. [Li (residual solvent)] x ] + The interaction forces with the polymer create a weak interaction environment for lithium ions, promoting the Li-polymerization process. + The transfer of ions is facilitated by the conversion of the solvent-derived electrode-electrolyte interface phase into an anion-dominant derived phase, thereby improving interface stability. On the other hand, the nano-metal oxide filler reduces the crystallinity of the PVDF polymer, inhibits spherulite formation, densifies the electrolyte membrane, and helps to construct a uniform and continuous ion transport channel, improving mechanical properties and effectively suppressing the growth of lithium dendrites, thus greatly improving the cycle stability of the battery.

[0021] The solid polymer electrolyte of this invention exhibits high ionic conductivity and good electrochemical stability at room temperature, and good compatibility with both positive and negative electrodes. Batteries assembled using the solid polymer electrolyte of this invention demonstrate high specific capacity and excellent rate performance, exhibiting superior cycle stability. The assembled ternary Li[Ni6Co2Mn2]O2 / lithium battery achieves over 300 cycles at 1C rate, with a specific capacity reaching 140 mAh g⁻¹. -1 . Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A photograph of the composite solid electrolyte prepared in Example 1;

[0024] Figure 2 A scanning electron microscope image of the composite solid electrolyte prepared in Example 1;

[0025] Figure 3 The stress-strain curve of the composite solid electrolyte prepared in Example 1;

[0026] Figure 4 The ionic conductivity-Arrhenius curve of the composite solid electrolyte prepared in Example 1;

[0027] Figure 5 Linear scan voltammetry curve of the steel sheet || Li battery with composite solid electrolyte prepared in Example 1;

[0028] Figure 6 The It curve and impedance diagrams before and after polarization of the Li||Li symmetric cell with composite solid electrolyte prepared in Example 1;

[0029] Figure 7 The voltage-time curve of the Li||Li symmetric cell with composite solid electrolyte prepared in Example 1 at constant current;

[0030] Figure 8 Rate cycling diagram of the button cell assembled in Application Example 1;

[0031] Figure 9 The cycling diagram of the button cell assembled in Application Example 1 at 1C;

[0032] Figure 10 The ionic conductivity-Arrhenius curve of the composite solid electrolyte prepared in Comparative Example 1;

[0033] Figure 11 SEM image of the composite solid electrolyte prepared in Comparative Example 1;

[0034] Figure 12 Cycling diagram of a coin cell assembled with the composite solid electrolyte prepared in Comparative Example 1 at 1C.

[0035] Figure 13 The stress-strain curve of the composite solid polymer electrolyte prepared in Example 2;

[0036] Figure 14 The cycling diagram of the button cell assembled in Application Example 2 at 1C;

[0037] Figure 15 The stress-strain curve of the composite solid polymer electrolyte prepared in Example 3;

[0038] Figure 16 The cycling diagram of the button cell assembled in Application Example 3 at 1C;

[0039] Figure 17 Cycling diagram of a coin cell assembled from the composite solid electrolyte prepared in Comparative Example 2 at 1C. Detailed Implementation

[0040] This invention provides a PVDF-based composite solid electrolyte, comprising a PVDF-based polymer, and lithium salt, amide substances, nano-metal oxides and residual organic solvents dispersed in the PVDF-based polymer;

[0041] The chemical formula of the amide is R-CO-NH2 or R-CO-NH-R', where R and R' are independently alkyl groups.

[0042] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0043] In this invention, the PVDF-based composite solid electrolyte is based on a PVDF-based polymer, with lithium salt, amide molecules, and nano-metal oxides uniformly dispersed in the polymer matrix, and contains a small amount of residual solvent. The PVDF-based composite solid electrolyte of this invention exhibits high room-temperature ionic conductivity, excellent mechanical properties, and good electrochemical stability.

[0044] In this invention, the PVDF-based polymer preferably includes PVDF homopolymer or PVDF copolymer, and the PVDF copolymer preferably includes binary copolymer or ternary copolymer. The PVDF homopolymer shown is polyvinylidene fluoride, with the structural formula shown in I, and a weight-average molecular weight preferably of 50,000 to 2,000,000; the binary copolymer preferably includes poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), or poly(vinylidene fluoride-trifluorochloroethylene), with the structural formulas shown in Formulas II, III, and IV, respectively, and a weight-average molecular weight independently preferably of 50,000 to 2,000,000. When synthesizing the binary copolymer, the molar ratio of other comonomers to the vinylidene fluoride monomer is preferably (0. 0.1~0.2):1, the other comonomers include trifluoroethylene, hexafluoropropylene, or trifluorochloroethylene monomers; the terpolymer preferably includes poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene), with the structural formula shown in V, and a weight-average molecular weight preferably of 10,000~2,000,000. When synthesizing poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene), the molar ratio of trifluoroethylene monomer, trifluorochloroethylene monomer, and vinylidene fluoride monomer is preferably (0.01~0.1):(0.01~0.1):1. The PVDF-based polymer is the main material of the composite solid electrolyte, and is mainly composed of -CH2-CF2-, [Li (residual solvent)]. x ] + The solvation structure interacts with the PVDF chain to transport Li + The addition of comonomers can improve the flexibility and crystallinity of PVDF, and enhance the polymer's ability to promote lithium salt dissociation.

[0045]

[0046] In this invention, the lithium salt preferably includes one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium difluorooxalate borate (LiODFB), and lithium nitrate (LiNO3).

[0047] In this invention, the preferred mass ratio of lithium salt to PVDF-based polymer is (0.6–1.2):1, more preferably (0.65–1):1, and even more preferably (0.7–0.9):1, specifically 0.8:1. This mass ratio of lithium salt to PVDF polymer ensures that the ionic conductivity of the electrolyte meets the performance requirements of lithium batteries, while avoiding excessive residual solvent due to excessive lithium salt, which could lead to a decrease in the mechanical properties of the polymer electrolyte.

[0048] In this invention, the nano-metal oxide is preferably a nano-single metal oxide, which preferably includes one or more of titanium dioxide (TiO2), zirconium dioxide (ZrO2), vanadium pentoxide (V2O5), chromium trioxide (Cr2O3), molybdenum trioxide (MoO3), and tungsten trioxide (WO3). The tungsten trioxide is preferably in the form of nanosheets or nanorods, and the titanium dioxide is preferably in the form of nanoparticles.

[0049] In this invention, the size of the nano-metal oxide is preferably 1–100 nm. When the nano-metal oxide is in the form of particles, the size refers to the particle diameter; when it is a nanosheet, the size refers to the thickness; and when it is a nanorod, the size refers to the diameter of the circular cross-section. The nano-metal oxide has a phase structure, abundant surface active sites, low cost, and simple synthesis.

[0050] In this invention, the preferred mass ratio of the nano-metal oxide to the PVDF-based polymer is (0.03–0.2):1, more preferably (0.05–0.15):1, and even more preferably (0.05–0.1):1. The nano-metal oxide serves as a filler. The mass ratio of the nano-metal oxide to the PVDF-based polymer described in this invention effectively reduces the crystallinity of the polymer matrix, promotes lithium salt dissociation, and weakens the Li... + Solvation environment, improve Li + The transmission.

[0051] In this invention, the amide substances preferably include one or more of N-methylformamide, N-methylacetamide, N-methylpropionamide, formamide, acetamide and propionamide.

[0052] In this invention, the molar ratio of the amide to the lithium salt is preferably (1-8):1, more preferably (2-6):1, and even more preferably (3-5):1, specifically 5:1, 4:1, or 2:1. The molar ratio of the amide to the lithium salt in this invention allows the amide to participate in the [Li (residual solvent)] process. x ] + In the solvated structure, it competes with the residual solvent, weakens the binding of residual solvent molecules with lithium ions, and promotes the transport of the solvated structure in the chain segment through weak hydrogen bonding with the polymer chain.

[0053] In this invention, the organic solvent preferably includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0054] This invention also provides a method for preparing the PVDF-based composite solid electrolyte described in the above technical solution, comprising the following steps:

[0055] A precursor liquid is obtained by mixing PVDF-based polymers, lithium salts, amides, nano-metal oxides, and organic solvents.

[0056] The precursor liquid was cast to remove the organic solvent, resulting in a PVDF-based composite solid electrolyte.

[0057] This invention mixes PVDF-based polymers, lithium salts, amides, nano-metal oxides, and organic solvents to obtain a precursor fluid.

[0058] In this invention, the mass ratio of the organic solvent to the PVDF-based polymer is preferably (7-14):1, more preferably (8-12):1, and even more preferably (8.5-10):1.

[0059] In this invention, the mixing of the PVDF-based polymer, lithium salt, amide, nano-metal oxide, and organic solvent preferably includes: a first mixing of the nano-metal oxide and the organic solvent, followed by a second mixing of the resulting first mixture with the PVDF-based polymer, lithium salt, and amide. The first mixing is preferably performed under ultrasonic conditions, with the ultrasonic time preferably being 3–6 hours, which allows for preliminary dispersion of the nano-metal oxide filler. The second mixing is preferably performed under stirring conditions, preferably mechanical stirring, with the stirring speed preferably being 300–600 rpm, specifically 400 rpm or 500 rpm; the stirring time is preferably 6–18 hours, more preferably 8–15 hours, specifically 12 hours; and the stirring temperature is preferably 20–30°C, specifically 25°C. The stirring speed, temperature, and time specified in this invention ensure uniform mixing of the components.

[0060] After obtaining the precursor fluid, the present invention casts the precursor fluid to remove the organic solvent, thereby obtaining a PVDF-based composite solid electrolyte.

[0061] The present invention does not have any special requirements on the amount of precursor fluid poured; it can be selected according to the required electrolyte thickness.

[0062] In this invention, the casting is preferably carried out on a glass plate, and the removal of organic solvents is preferably achieved through drying, which is preferably carried out in an oven at a temperature of 50–80°C, specifically 60°C. The drying time is preferably 16–28 hours, more preferably 18–26 hours, and even more preferably 20–24 hours. During the drying process, the organic solvents are essentially removed, and due to intermolecular interactions, a small amount of organic solvent is retained in the electrolyte, resulting in a solid electrolyte. The drying temperature and time described in this invention yield an easily peelable film-like composite solid electrolyte.

[0063] The present invention also provides the application of the PVDF-based composite solid electrolyte described in the above technical solution or the PVDF-based composite solid electrolyte obtained by the above preparation method in lithium batteries.

[0064] The present invention also provides a lithium battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the PVDF-based composite solid electrolyte described in the above technical solution or the PVDF-based composite solid electrolyte obtained by the above preparation method.

[0065] The present invention does not have any special requirements for the composition of the positive and negative electrodes of the lithium battery. The positive and negative electrode materials of lithium batteries well known to those skilled in the art can be used. Specifically, the positive electrode active material is ternary Li[Ni6Co2Mn2]O2, the current collector is aluminum foil, the conductive agent is acetylene black, the binder is polytetrafluoroethylene, and the negative electrode is metallic lithium. The preferred mass ratio of Li[Ni6Co2Mn2]O2, acetylene black, and polytetrafluoroethylene is 8:1:1.

[0066] The present invention does not have any special requirements for the preparation method of the lithium battery; any lithium battery preparation method well known to those skilled in the art can be used.

[0067] The lithium battery of the present invention has excellent rate performance, high charge-discharge specific capacity, and excellent cycle stability.

[0068] To further illustrate the present invention, the PVDF-based composite solid electrolyte, its preparation method, its application, and lithium batteries provided by the present invention are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] (1) 0.01g of WO3 nanosheets were dispersed in 1.6g of N,N-dimethylacetamide and sonicated for 3h. Then, 0.2g of poly(vinylidene fluoride-hexafluoropropylene), 0.165g of lithium bis(trifluoromethanesulfonylimide) and 0.21g of N-methylacetamide were added and stirred at 400r / min for 12h at 25℃ to obtain the precursor fluid.

[0071] (2) The precursor liquid was poured onto a glass plate and placed in an oven at 60°C for 20 hours. The composite solid electrolyte was then obtained and cut into appropriate sizes for battery assembly.

[0072] Figure 1 A photograph of the composite solid electrolyte prepared in Example 1.

[0073] Figure 2 The image shows a SEM image of the composite solid electrolyte prepared in Example 1. Figure 2As can be seen from the data, the composite solid electrolyte prepared in Example 1 exhibits a dense and uniform structure on its surface, without obvious typical PVDF spherulites, indicating that the crystallinity of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) is suppressed.

[0074] Figure 3 The stress-strain curve of the composite solid polymer electrolyte prepared in Example 1 is shown below. Figure 3 As can be seen, the tensile strength and fracture strain of the composite solid polymer electrolyte prepared in Example 1 are 2.0 MPa and 180%, respectively, exhibiting good mechanical strength, which is beneficial to suppressing the growth of lithium dendrites.

[0075] Figure 4 The figure shows the ionic conductivity-Arrhenius curve for the composite solid electrolyte prepared in Example 1. The room temperature ionic conductivity of the composite solid electrolyte prepared in Example 1 is 9.6 × 10⁻⁶. -4 S·cm -1 With an activation energy of 0.11 eV, it demonstrates excellent ion transport capabilities and a low migration barrier.

[0076] The electrochemical window of the composite solid electrolyte prepared in Example 1 was tested, and the results are as follows: Figure 5 As shown, the oxidation potential is 4.57V, which can be matched with a ternary cathode.

[0077] The It curve and impedance before and after polarization of the Li||Li symmetric cell assembled from the composite solid electrolyte prepared in Example 1 were tested, and the results are as follows: Figure 6 As shown. From Figure 6 As can be seen, the lithium-ion transference number of the composite solid electrolyte prepared in Example 1 is 0.67 at room temperature.

[0078] The voltage-time curve of the Li||Li symmetric cell assembled from the composite solid electrolyte prepared in Example 1 was tested under constant current conditions, and the results are as follows: Figure 7 As shown. At 0.1 mAcm -2 and 0.1mAh cm -2 Under these conditions, the battery's polarization voltage was only 40mV, and no short circuit occurred after 1200 hours of stable cycling, indicating the interfacial stability of the lithium anode.

[0079] Application Example 1

[0080] A coin cell was assembled using the composite solid electrolyte prepared in Example 1 as the electrolyte. The positive electrode active material was ternary Li[Ni6Co2Mn2]O2, the current collector was aluminum foil, the conductive agent was acetylene black, and the binder was polytetrafluoroethylene. The mass ratio of the components of the positive electrode was Li[Ni6Co2Mn2]O2:acetylene black:polytetrafluoroethylene = 8:1:1; the negative electrode was lithium metal.

[0081] The obtained button cells were subjected to rate cycling tests, and the results are as follows: Figure 8 As shown, the obtained coin cell exhibits excellent rate performance, completing 5 cycles at different rates, and achieving 140 and 120 mAh g at high rates of 1C and 2C, respectively. -1 The discharge specific capacity remains at 170 mAh g after recovery at a low rate of 0.1C. -1 .

[0082] The obtained coin cells were subjected to a 1C long-cycle test, and the results are as follows: Figure 9 As shown, the obtained button cell retains 80% of its capacity after 300 cycles at 1C.

[0083] Comparative Example 1

[0084] A composite solid electrolyte was prepared using the method described in Example 1, but without the addition of WO3 nanosheets. The remaining process was the same as in Example 1, resulting in electrolyte Comparative Example 1.

[0085] Figure 10 The ionic conductivity-Arrhenius curve is shown for the composite solid electrolyte prepared in Comparative Example 1. The room temperature ionic conductivity of the electrolyte prepared in Comparative Example 1 is 7.7 × 10⁻⁶. -4 S·cm -1 The activation energy is 0.138 eV, the ionic conductivity is lower than that of Example 1, and the ion migration activation energy is greater.

[0086] Figure 11 The image shows the SEM image of the composite solid electrolyte prepared in Comparative Example 1. It can be seen that the electrolyte exhibits a distinct spherulite morphology, and the large diameter of the spherulites leads to numerous pores, which is detrimental to the continuous and uniform transport of lithium ions within the electrolyte. In contrast, in Example 1, the addition of WO3 nanosheets suppressed crystallinity, resulting in a denser electrolyte membrane surface.

[0087] Figure 12 The image shows the cycling performance of a coin cell assembled from the composite solid electrolyte prepared in Comparative Example 1 at 1C. Due to the porosity and uneven lithium-ion transport of the electrolyte, dendrite growth after 80 cycles leads to internal micro-short circuits and overcharging. Furthermore, the unstable solvation structure decomposes and the large ion migration activation energy causes the battery capacity to continuously decay after the start of cycling.

[0088] Example 2

[0089] (1) 0.01g of WO3 nanorods were dispersed in 1.4g of N,N-dimethylacetamide and sonicated for 3h. Then, 0.2g of poly(vinylidene fluoride-hexafluoropropylene), 0.165g of lithium bis(trifluoromethanesulfonylimide) and 0.136g of acetamide were added and stirred at 400r / min at 25℃ for 12h to obtain the precursor fluid.

[0090] (2) The precursor liquid was poured onto a glass plate and placed in an oven at 60°C for 24 hours. The composite solid electrolyte was then obtained and cut into appropriate sizes for battery assembly.

[0091] The composite solid electrolyte prepared in Example 2 has a room temperature ionic conductivity of 6.8 × 10⁻⁶. -4 S·cm -1 .

[0092] Figure 13 The stress-strain curve of the composite solid polymer electrolyte prepared in Example 2 is shown below. Figure 13 As can be seen, the tensile strength and fracture strain of the composite solid polymer electrolyte prepared in Example 2 are 2.5 MPa and 190%, respectively, which shows good mechanical strength and is beneficial to suppressing the growth of lithium dendrites.

[0093] Application Example 2

[0094] A coin cell was assembled using the composite solid electrolyte prepared in Example 2 as the electrolyte. The positive electrode active material was ternary Li[Ni6Co2Mn2]O2, the current collector was aluminum foil, the conductive agent was acetylene black, and the binder was polytetrafluoroethylene. The mass ratio of the components of the positive electrode was Li[Ni6Co2Mn2]O2:acetylene black:polytetrafluoroethylene = 8:1:1; the negative electrode was lithium metal.

[0095] The obtained coin cells were subjected to a 1C long-cycle test, and the results are as follows: Figure 14 As shown, the obtained button cell retains 85% of its capacity after 500 cycles at 1C.

[0096] Example 3

[0097] (1) 0.006 g of TiO2 nanoparticles were dispersed in 2 g of N,N-dimethylformamide and sonicated for 3 h. Then, 0.2 g of PVDF, 0.12 g of lithium bis(trifluoromethanesulfonylimide) and 0.049 g of acetamide were added and stirred at 500 r / min for 12 h at 25 °C to obtain the precursor liquid.

[0098] (2) The precursor liquid was poured onto a glass plate and placed in an oven at 60°C for 24 hours. The composite solid electrolyte was then obtained and cut into appropriate sizes for battery assembly.

[0099] The composite solid electrolyte prepared in Example 3 has a room temperature ionic conductivity of 4.3 × 10⁻⁶. -4 S·cm -1 Compared with Examples 1 and 2, the electrolyte ionic conductivity is lower, mainly due to the lower amount of lithium salt and nano-metal oxide added.

[0100] Figure 15 The stress-strain curve is shown for the composite solid polymer electrolyte prepared in Example 3. The tensile strength and fracture strain of the composite solid polymer electrolyte prepared in Example 3 are 1.69 MPa and 150%, respectively.

[0101] Application Example 3

[0102] A coin cell was assembled using the composite solid electrolyte prepared in Example 3 as the electrolyte. The positive electrode active material was ternary Li[Ni6Co2Mn2]O2, the current collector was aluminum foil, the conductive agent was acetylene black, and the binder was polytetrafluoroethylene. The mass ratio of the components of the positive electrode was Li[Ni6Co2Mn2]O2:acetylene black:polytetrafluoroethylene = 8:1:1; the negative electrode was lithium metal.

[0103] The obtained coin cells were subjected to a 1C long-cycle test, and the results are as follows: Figure 16 As shown, the obtained button cell retains 80% of its capacity after 150 cycles at 1C.

[0104] Comparative Example 2

[0105] A composite solid electrolyte was prepared using the method described in Example 3, but without the addition of TiO2 nanoparticles. The remaining process was the same as in Example 3, resulting in electrolyte Comparative Example 2.

[0106] The composite solid electrolyte prepared in Comparative Example 2 has a room temperature ionic conductivity of 1.8 × 10⁻⁶. -4 S·cm -1 Compared to Example 3, the ionic conductivity is lower, mainly due to the low content of lithium salt and free amide molecules, the absence of nano-metal oxides, and the high crystallinity of the PVDF electrolyte, all of which are unfavorable for lithium-ion transport.

[0107] Figure 17 The image shows the cycling performance at 1C for a coin cell assembled from the composite solid electrolyte prepared in Comparative Example 2. The battery capacity degrades after 50 cycles due to low ionic conductivity and unstable solvation structure decomposition.

[0108] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A PVDF-based composite solid electrolyte, characterized in that, It includes PVDF-based polymers, as well as lithium salts, amides, nano-metal oxides and residual organic solvents dispersed in the PVDF-based polymers; The amides have the structural formula R-CO-NH2 or R-CO-NH-R', and include one or more of N-methylformamide, N-methylacetamide, N-methylpropionamide, formamide, acetamide, and propionamide. The nano-metal oxide is a nano-single metal oxide, which includes one or more of titanium dioxide, zirconium dioxide, vanadium pentoxide, chromium trioxide, molybdenum trioxide, and tungsten trioxide. The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

2. The PVDF-based composite solid electrolyte according to claim 1, characterized in that, The molar ratio of the amide to the lithium salt is (1~8):

1.

3. The PVDF-based composite solid electrolyte according to claim 1, characterized in that, The mass ratio of the nano-metal oxide to the PVDF-based polymer is (0.03~0.2):

1.

4. The PVDF-based composite solid electrolyte according to claim 1, characterized in that, The PVDF-based polymer includes PVDF homopolymers or PVDF copolymers, the PVDF copolymers include binary copolymers or ternary copolymers, the binary copolymers include poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-hexafluoropropylene), or poly(vinylidene fluoride-trifluorochloroethylene), and the ternary copolymers include poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene).

5. The PVDF-based composite solid electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalate borate, and lithium nitrate; the mass ratio of the lithium salt to the PVDF-based polymer is (0.6~1.2):

1.

6. The method for preparing the PVDF-based composite solid electrolyte according to any one of claims 1 to 5, characterized in that, Includes the following steps: A precursor liquid is obtained by mixing PVDF-based polymers, lithium salts, amides, nano-metal oxides, and organic solvents. The precursor liquid is cast and dried until the electrolyte becomes solid while retaining a small amount of organic solvent in the electrolyte, thus obtaining the PVDF-based composite solid electrolyte.

7. The application of the PVDF-based composite solid electrolyte according to any one of claims 1 to 5 or the PVDF-based composite solid electrolyte obtained by the preparation method according to claim 6 in lithium batteries.

8. A lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the PVDF-based composite solid electrolyte according to any one of claims 1 to 5 or the PVDF-based composite solid electrolyte obtained by the preparation method according to claim 6.

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