Method for constructing polymer electrolyte film by using sheet-shaped nanometer molybdenum carbide filler to inhibit lithium dendrite

Abstract

The application relates to a method for constructing a polymer electrolyte film by using a sheet-shaped nanometer molybdenum carbide filler to inhibit lithium dendrites, and relates to a method for preparing a solid-state lithium ion battery diaphragm. σ =7.27x10 ‑4 S.cm ‑1 The method can effectively reduce the bulk impedance and interface impedance of the polymer electrolyte film, form a stable solid-state electrolyte interface layer between the polymer electrolyte film and the anode, inhibit the formation of lithium dendrites and the influence of the lithium dendrites on the battery performance, and improve the charge-discharge specific capacity and capacity retention rate of the solid-state lithium ion battery. The application is applied to the field of solid-state lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of solid-state lithium-ion batteries, and particularly relates to a method for constructing a polymer electrolyte film with sheet-like nano-molybdenum carbide filler to suppress lithium dendrites. Background Technology

[0002] Lithium-ion batteries, with their high energy density, low self-discharge rate, long cycle life, and light weight, can meet the growing demands of consumers. Solid-state lithium-ion batteries, in particular, offer even higher energy density and safety, and have broader application prospects. Polymer electrolyte films can suppress lithium dendrite growth and improve battery safety and energy density. Ion transfer in polymer electrolyte films occurs in the amorphous regions of the polymer matrix. Compared to polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) has lower structural order and crystallinity, which is beneficial for the polymer's high ionic conductivity. However, the mechanical strength of PVDF-HFP is much lower than that of PVDF. Therefore, the PVDF / PVDF-HFP blend system is one of the most ideal polymer frameworks for solid polymer electrolyte films, but its low conductivity, low mechanical strength, and weak self-supporting ability still cannot meet the requirements of solid-state batteries. Since transition metal carbides are conductive, metal carbide / oxide heterojunction nanofillers can lower the energy barrier during lithium-ion migration, thereby increasing the effective carrier concentration at the electrode-electrolyte interface. Therefore, the addition of inorganic nanofillers in this application improves conductivity and enhances the mechanical and thermodynamic properties of the polymer electrolyte film. Summary of the Invention

[0003] The main objective of this invention is to provide a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrites, thereby overcoming the problems of unstable electrode-electrolyte interface and multiple lithium dendrites in existing batteries.

[0004] The method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites according to the present invention is carried out according to the following steps:

[0005] I. Preparation of sheet-like molybdenum carbide nanoparticles

[0006] Ammonium molybdate was added to deionized water and stirred for 5–15 min to obtain 0.1–0.6 mol·L⁻¹ water. -1 Solution A, set aside; add the carbon source to a 10%–20% dilute hydrochloric acid solution and stir for 30–40 min to obtain 0.5–1.5 mol·L⁻¹ -1Solution B; Add solution A to solution B, with a volume ratio of solution A to solution B of 1:1 to 1:2, stir at 150 to 200 rpm for 4 to 8 hours, then wash and filter repeatedly with deionized water and ethanol until pH = 6 to 7 to obtain a pale yellow solid; place the pale yellow solid in a tube furnace and keep it at 700 to 800℃ for 4 to 5 hours to obtain flake-shaped nano molybdenum carbide powder;

[0007] II. Preparation of Polymer Electrolyte Thin Films

[0008] Polyvinylidene fluoride-hexafluoropropylene and polyvinylidene fluoride were dissolved in dimethylformamide at a mass ratio of 1:1 to 1:4, and 0.01 to 0.05 mol·L⁻¹ was added to the slurry. -1 Melamine was stirred at 180–220 rpm for 12–16 h at room temperature, and 0.02–0.06 mol·L⁻¹ was added. -1 Flake-shaped molybdenum carbide nanoparticles were added to the slurry and stirred at 150–200 rpm for 12–16 h. Lithium salt was added and stirred again for 6–10 h. The slurry was cast onto a clean glass plate and dried at 80–120 °C for 60–80 min to obtain a black solid polymer electrolyte film.

[0009] III. Preparation of cathode materials and battery assembly

[0010] Lithium iron phosphate, polyvinylidene fluoride, and acetylene black were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1 to 9:0.5:0.5. The slurry was coated on aluminum foil and dried in a vacuum oven at 100°C to 120°C for 20 to 26 hours. After cooling to room temperature, a lithium iron phosphate positive electrode was obtained. The negative electrode shell, the polymer electrolyte film obtained in step two, the lithium sheet, the nickel foam, and the positive electrode shell were assembled in an argon-filled glove box to obtain a solid-state lithium-ion battery.

[0011] This invention includes the following gain effects:

[0012] The present invention provides a simple preparation process for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite growth. The polymer electrolyte film prepared by this invention exhibits low cost, high mechanical stability, and certain flame retardancy. Furthermore, the solid polymer electrolyte film is easy to process, can mitigate lithium dendrite growth, and is lightweight, making it suitable for manufacturing flexible devices. The film preparation method primarily uses blade coating, which is suitable for large-area production and has excellent application prospects.

[0013] This invention employs a casting method followed by drying to prepare a solid polymer electrolyte film. The synthesis mechanism is as follows: Polyvinylidene fluoride (PVDF) possesses strong electron-withdrawing groups (CF) and a high dielectric constant of 8.5, which promotes the dissociation of lithium salts in the polymer matrix. Therefore, PVDF exhibits high solubility and excellent affinity for lithium salts. The larger molecular weight anions in lithium salts (TFSI...) - It is easier to form ion clusters, which can not only form special lithium-ion conduction channels, but also fix anions and prevent their free migration, thus avoiding a decrease in lithium-ion transference number. In addition, N,N-dimethylformamide (DMF) was chosen as the solvent of this invention due to its excellent polymer dissolution ability. The lone pair electrons on the oxygen atom give N,N-dimethylformamide strong intermolecular interaction forces, which can not only promote the dissociation of lithium salt, but also form complexes with lithium ions. This N,N-dimethylformamide and lithium salt complex has the characteristics of ionic liquid and locally has a high concentration of lithium ions, which is beneficial to improving ionic conductivity. CN in melamine and -CF3 in polyvinylidene fluoride / polyvinylidene fluoride-hexafluoropropylene synergistically enhance the Li3N and LiF in the electrolyte membrane and the negative electrode to form an SEI film, which helps to produce a complete and uniform SEI film, while the lone pair electrons on -N and -F become active sites for lithium-ion migration. In the solid film, the positively charged Mo and negatively charged carbon nanoparticles of the sheet-like molybdenum carbide nanoparticles jointly interfere with the migration of lithium ions in a uniform channel, forming uniform electric field lines. That is, the CN in melamine and the -CF3 in polyvinylidene fluoride / polyvinylidene fluoride-hexafluoropropylene are combined with the sheet-like molybdenum carbide nanoparticles, resulting in uniform and rapid deposition of lithium ions and avoiding the formation of dendritic lithium. Attached Figure Description

[0014] Figure 1 Scanning electron microscope image of sheet-like molybdenum carbide nanoparticles used in a method for constructing polymer electrolyte films to suppress lithium dendrites;

[0015] Figure 2 Scanning electron microscope (SEM) images and physical images of the sheet-like molybdenum carbide nanoparticle polymer electrolyte film used to construct a polymer electrolyte film for suppressing lithium dendrite formation.

[0016] Figure 3 A scanning electron microscope image of the lithium anode of a solid-state lithium-ion battery after 100 cycles, which is a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0017] Figure 4 X-ray diffraction patterns of sheet-like molybdenum carbide nanoparticles in Comparative Example 1 and Example 1, which are used to construct polymer electrolyte films to suppress lithium dendrites.

[0018] Figure 5Infrared spectra of polymer electrolyte films of Comparative Example 1 and Example 1, which are used to construct polymer electrolyte films for suppressing lithium dendrites using sheet-like molybdenum carbide nanofillers. A is the infrared spectrum of the polymer electrolyte film of Comparative Example 1, and B is the infrared spectrum of the polymer electrolyte film of Example 1.

[0019] Figure 6 Thermogravimetric spectra of polymer electrolyte films in Comparative Example 1 and Example 1 are shown for a method of constructing polymer electrolyte films with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites. A is the thermogravimetric spectrum of polymer electrolyte film in Example 1, B is the thermogravimetric curve of polymer electrolyte film in Comparative Example 1, and C is the thermogravimetric curve of polymer electrolyte film without added molybdenum carbide nanofiller.

[0020] Figure 7 C1s plot of X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles, which is a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0021] Figure 8 N1s plot of X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles, as a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0022] Figure 9 S 2p plot of X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles, which is a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller as a method for suppressing lithium dendrites by a sheet-like molybdenum carbide nanofiller.

[0023] Figure 10 F1s plot of X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles, which is a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0024] Figure 11 Impedance curves of solid-state lithium-ion batteries at different cycle counts for a method of constructing polymer electrolyte films to suppress lithium dendrites using sheet-like molybdenum carbide nanofillers, as shown in Comparative Example 1. A is the impedance curve for 0 cycles, B is the impedance curve for 5 cycles, C is the impedance curve for 25 cycles, D is the impedance curve for 50 cycles, and E is the impedance curve for 100 cycles.

[0025] Figure 12 Example 1 shows a curve of current versus time during polarization in a solid-state lithium-ion battery, illustrating a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0026] Figure 13 Impedance diagrams of a solid-state lithium-ion battery before and after polarization are shown in Example 1 of a method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites. A is the impedance before polarization, B is the impedance after polarization, and the inset diagram is a fitted circuit diagram.

[0027] Figure 14 A curve showing the change of current over time during polarization in a solid-state lithium-ion battery, as a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller.

[0028] Figure 15 Impedance diagrams of a solid-state lithium-ion battery before and after polarization are shown in Comparative Example 1, which describes a method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites. A represents the impedance before polarization, and B represents the impedance after polarization. The inset diagram is a fitted circuit diagram.

[0029] Figure 16 The constant current polarization test curves of symmetrical cells in Comparative Example 1 and Example 1 are used to illustrate a method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites. A is the constant current polarization curve of the symmetrical cell without molybdenum carbide nanofiller, B is the constant current polarization curve of the symmetrical cell in Example 1, and C is the constant current polarization curve of the symmetrical cell in Comparative Example 1.

[0030] Figure 17 Electrochemical stability windows of polymer electrolyte films in Example 1, which is a method for constructing polymer electrolyte films to suppress lithium dendrites using sheet-like molybdenum carbide nanofillers, are shown in the following figures: A is without added molybdenum carbide, B is 1% molybdenum carbide from Example 1, C is 2% molybdenum carbide from Example 1, D is 4% molybdenum carbide from Example 1, E is 6% molybdenum carbide from Example 1, and F is 8% molybdenum carbide from Example 1.

[0031] Figure 18 The electrochemical stability window of the polymer electrolyte film in Comparative Example 1, which is a method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites, is as follows: A is 1% molybdenum carbide nanofiller of Comparative Example 1, B is 3% molybdenum carbide nanofiller of Comparative Example 1, C is 5% molybdenum carbide nanofiller of Comparative Example 1, and D is 7% molybdenum carbide nanofiller of Comparative Example 1.

[0032] Figure 19 The specific capacity-efficiency graphs of solid-state lithium-ion batteries of Comparative Example 1 and Example 1, which are based on a method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrites, are shown at 1C and room temperature. A represents the charge-discharge specific capacity of Comparative Example 1, B represents the charge-discharge specific capacity of Example 1, C represents the charge-discharge specific capacity without the addition of molybdenum carbide nanofiller, and D represents the efficiency of Comparative Example 1. Figure 20The specific capacity-efficiency diagram of a solid-state lithium-ion battery in Comparative Example 1, which is a method for constructing a polymer electrolyte film to suppress lithium dendrites using sheet-like molybdenum carbide nanofiller, is shown at 2C and room temperature. A represents the charge-discharge specific capacity of Comparative Example 1, and B represents the efficiency of Comparative Example 1. Detailed Implementation

[0033] The reagents and testing instruments required in the preparation method of the present invention are shown in Tables 1-1 and 1-2 below;

[0034] Table 1-1 Reagents used in the experiment

[0035]

[0036]

[0037] Table 1-2 List of Instruments Used in the Experiment

[0038]

[0039] Comparative Example 1:

[0040] I. Preparation of sheet-like molybdenum carbide nanoparticles

[0041] 0.3 mol·L -1 Ammonium molybdate was added to deionized water and stirred for 10 min to obtain solution A, which was set aside for later use; 1 mol·L -1 Aniline was added to a 10% dilute hydrochloric acid solution and stirred for 30 minutes to obtain solution B; solution A was added to solution B and stirred for 4 hours, then washed and filtered repeatedly with deionized water and ethanol until pH=7, to obtain a pale yellow solid; the pale yellow solid was placed in a tube furnace and kept at 800℃ for 4 hours to obtain sheet-like nano-molybdenum carbide.

[0042] II. Preparation of Polymer Electrolyte Thin Films

[0043] Polyvinylidene fluoride-hexafluoropropylene and polyvinylidene fluoride were dissolved in N,N-dimethylformamide at a mass ratio of 1:4, and 0.01 mol·L⁻¹ was added to the slurry. -1 Melamine, stirred at room temperature for 12 hours, was added at 0.02 mol·L⁻¹. -1 Flake-shaped molybdenum carbide nanoparticles were added to the slurry and stirred for 12 hours. Lithium salt of 30% of the matrix mass was added and stirred again for 6 hours. The slurry was cast onto a clean glass plate and dried at 100°C for 70 minutes to obtain a black solid polymer electrolyte film.

[0044] III. Preparation of cathode materials and battery assembly

[0045] Lithium iron phosphate, polyvinylidene fluoride, and acetylene black were uniformly dispersed in N-methyl-2-pyrrolidone at a mass ratio of 8:1:1. The slurry was coated onto aluminum foil and dried in a vacuum oven at 100°C for 24 hours. After cooling to room temperature, lithium iron phosphate cathode was obtained.

[0046] Example 1: In step one, 1 mol·L -1 o-Toluidine was added to a 10% dilute hydrochloric acid solution and stirred for 30 min to obtain solution B. Other steps were the same as in Comparative Example 1. The polymer electrolyte film prepared in this way had an ionic conductivity of 5.70 × 10⁻⁶. -4 S·cm -1 The lithium-ion transference number is 0.42, the electrochemical stability window is 4.01V, and the initial cycle discharge specific capacity after being assembled into a solid-state lithium-ion battery is 105.3 mAh·g. -1 After 100 cycles, the average coulombic efficiency was 97.23%.

[0047] Example 2: The concentration of aniline in step one is 0.5 mol·L⁻¹ -1 Add to 10% dilute hydrochloric acid solution and stir for 30 minutes to obtain solution B. Other steps are the same as in Comparative Example 1.

[0048] Example 3: In step two, 10% by weight of lithium salt was added. The other steps were the same as in Comparative Example 1.

[0049] The polymer electrolyte film prepared in Comparative Example 1 has an ionic conductivity of 7.27 × 10⁻⁶. -4 S·cm -1 The lithium-ion transference number is 0.63, the electrochemical stability window is 4.23V, and the initial cycle discharge specific capacity after being assembled into a solid-state lithium-ion battery is 127.2 mAh·g. -1 After 100 cycles, the average coulombic efficiency was 98.11%. Compared with the polymer electrolyte film and solid-state lithium-ion battery prepared in Example 1, the polymer electrolyte film and solid-state lithium-ion battery prepared in Comparative Example 1 have the highest efficiency in terms of ionic conductivity, lithium-ion transference number, electrochemical stability window, initial discharge specific capacity, and average coulombic efficiency after 100 cycles.

[0050] Performance tests were performed on the above comparative examples and embodiments. 1) Scanning electron microscopy (SEM) test. The surface morphology of the lithium sheet was observed using a scanning electron microscope (SEM). The instrument model was FEI sirion200, the accelerating voltage was 0.2-30kV, and the resolution was 20kV. The prepared samples were dried, quenched in liquid nitrogen, and the resulting samples were attached to a sample holder coated with conductive adhesive for testing.

[0051] 2) X-ray diffraction (XRD) analysis. The sheet-like molybdenum carbide nanostructure was analyzed using X-ray diffraction. The instrument was an X'Pert PRO, the target was a Cu target, the X-rays were CuKα rays, and the wavelength was [wavelength missing]. The current is 40mA, the voltage is 45kV, and the scanning angle is 20-80°. Before testing, the dry sample is evenly spread on the glass slide and then placed on the sample stage for testing.

[0052] 3) Fourier transform infrared (FT-IR) spectroscopy analysis. The optical properties of the thin film were measured and organic functional groups were identified using a T6 series ultraviolet spectrophotometer with a wavelength range of 300-900 nm.

[0053] 4) Thermogravimetric analysis (TG) test. This method, which measures the mass-temperature relationship of a substance under programmed temperature control, is used to test the thermal stability of polymer electrolyte films. The instrument model is TGA / SDTA851, and the heating rate is 10 g / min under N2 atmosphere. -1 Heating from room temperature to 600°C.

[0054] 5) X-ray photoelectron spectroscopy (XPS) analysis. The composition of the passivation layer (SEI) at the interface between the polymer electrolyte film and the lithium electrode was analyzed using XPS. The compositional changes and chemical states of elements in the solid electrolyte interface film generated under different polymer electrolyte films and cycling conditions were observed. The instrument was a Thermo Fisher ESCALAB Xi+, with the following parameters: aluminum / magnesium target (hν = 1486.6 eV), high-resolution pass voltage of 30 eV, step size of 0.05 eV, and C1s standard peak at 285 eV. Before testing, the solid-state lithium-ion battery was disassembled, and the side of the polymer electrolyte film in contact with the lithium electrode was used as the test surface. Experimental data were fitted using an XPSPEAK41.

[0055] 6) Interfacial impedance testing. Electrochemical impedance spectroscopy was used to test the interfacial impedance between the polymer electrolyte film and the electrode to determine the effect of the modified layer on the stability of the electrolyte-electrode interface. The electrochemical workstation was a CHI760E with a frequency of 0.01-100000Hz. Lithium iron phosphate half-cells were assembled and placed for different number of days for testing.

[0056] 7) Constant Current Polarization Test. The interfacial stability between the polymer electrolyte film and the electrode was tested using a constant current polarization method. The polymer battery was subjected to constant current charge and discharge at a constant current density. The voltage-time curve was used to determine the effectiveness of the interaction between the polymer electrolyte film surface modification layer and the lithium electrode interface. The instrument used was a LAND battery testing system CT2001A, with a current density of 0.05 mA·cm². -2 The battery assembly method is a lithium symmetric battery.

[0057] 8) Charge / Discharge Test. Charge / discharge tests yield many important parameters of the battery during cycling, such as charge / discharge specific capacity, charge / discharge efficiency, and voltage plateau. The instrument used is the LAND Battery Testing System CT2001A, with voltage settings of 2.6V-4.5V and -1.0-7.0V, and scan speeds of 0.2 mV·s. -1 and 2.0 mV·s -1 The polymer electrolyte film was assembled into a lithium iron phosphate half-cell for testing.

[0058] Figure 1 Scanning electron microscope (SEM) image of molybdenum carbide nanoparticles used in a method for constructing polymer electrolyte films to suppress lithium dendrite formation. The SEM image shows that the molybdenum carbide nanoparticles are distinctly hexagonal in shape.

[0059] Figure 2 Scanning electron microscope (SEM) images and physical images of a polymer electrolyte film with sheet-like molybdenum carbide nanofiller used to construct a polymer electrolyte film for suppressing lithium dendrite formation. The sheet-like molybdenum carbide nanofiller is uniformly distributed, and the gray-black film is dense and flexible.

[0060] Figure 3 Scanning electron microscope (SEM) image of the lithium anode of a solid-state lithium-ion battery after 100 cycles, illustrating a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation, as shown in Example 1. The lithium anode surface of the solid-state lithium-ion battery in Example 1 shows almost no dendrites or bulk deposits. This indicates that the unique sheet-like structure facilitates uniform charge distribution, allowing for uniform deposition and nucleation of lithium ions on the anode surface. The positively charged Mo and negatively charged C in the sheet-like molybdenum carbide nanofiller contribute to the uniform migration of lithium ions, resulting in uniform lithium deposition on the anode during charging.

[0061] Figure 4 X-ray diffraction patterns of sheet-like molybdenum carbide nanoparticles in Comparative Example 1 and Example 1, illustrating a method for constructing polymer electrolyte films with sheet-like molybdenum carbide nanoparticles to suppress lithium dendrites. The peaks of the nanosheet-like molybdenum carbide at 34.52°, 37.91°, 39.61°, 52.37°, 61.76°, 69.57°, and 74.93° correspond to the (002), (020), (211), (022), (203), (231), and (223) crystal planes of hexagonal β-Mo₂C. The peaks of the nanoparticle-like molybdenum carbide at 34.42°, 37.87°, 39.49°, 52.05°, and 61.60° correspond to the (101), (020), (111), (121), and (002) crystal planes of orthorhombic α-Mo₂C.

[0062] Figure 5Infrared spectra of the polymer electrolyte films of Comparative Example 1 and Example 1, which are used to construct polymer electrolyte films for suppressing lithium dendrites using sheet-like molybdenum carbide nanofillers. 1137 cm⁻¹ -1 and 1197cm -1 The double peaks at 1354 cm⁻¹ represent the -CF₃ functional group in polyvinylidene fluoride / polyvinylidene fluoride-hexafluoropropylene. -1 The peak at 600 cm⁻¹ represents the symmetric stretching vibration of the CN bonds in melamine. -1 and 616cm -1 The bimodal distribution is attributed to the in-plane shear vibration of the NH bonds in melamine. The CN in melamine synergistically enhances the Li3N and LiF in the electrolyte membrane and negative electrode to form the SEI film, contributing to the formation of a complete and uniform SEI film. Simultaneously, the lone pairs of electrons on the -N and -F atoms become active sites for lithium-ion migration. The positively charged Mo and negatively charged carbon nanoparticles of the sheet-like molybdenum carbide in the solid film jointly interfere with lithium-ion migration in uniform channels, forming uniform electric field lines. In other words, the combination of CN in melamine, -CF3 in polyvinylidene fluoride / polyvinylidene fluoride-hexafluoropropylene, and sheet-like molybdenum carbide nanoparticles ensures uniform and rapid lithium-ion deposition, preventing the formation of dendritic lithium.

[0063] Figure 6 Thermogravimetric spectra of the polymer electrolyte films in Comparative Example 1 and Example 1, which illustrate a method for constructing polymer electrolyte films using sheet-like molybdenum carbide nanofillers to suppress lithium dendrite formation, are shown. The thermogravimetric curves reveal no mass loss up to 200°C, which is suitable for the operating temperature of lithium batteries.

[0064] Figure 7 The C1s plot of the X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles is shown in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. The peak at 288.6 eV corresponds to the C1s plot of lithium carbonate (Li₂CO₃).

[0065] Figure 8 The N1s plot of the X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles is shown in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. The peak at 398.9 eV belongs to the N1s phase of lithium nitride (Li3N). Lithium nitride is one of the fastest lithium-ion conductors, with an ionic conductivity of 10⁻⁶ at room temperature. 3 -10 4 S·cm -1 It can effectively improve the lithium-ion transport capacity of the solid electrolyte interface film and alleviate the lithium-ion concentration gradient on the cathode surface.

[0066] Figure 9The S 2p plot of the X-ray photoelectron spectroscopy (XPS) of the negative electrode-electrolyte interface of a solid-state lithium-ion battery after 100 cycles is shown in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. The peak at 170.0 eV corresponds to the S 2p plot of lithium sulfite (Li₂SO₃).

[0067] Figure 10 The F1s plot of the X-ray photoelectron spectroscopy (XPS) of a solid-state lithium-ion battery after 100 cycles is shown in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. The peak at 684.3 eV corresponds to the F1s of lithium fluoride (LiF). A dense and stable solid-state electrolyte interface film is formed between the polymer electrolyte film and the lithium anode interface. In the presence of lithium fluoride, metallic lithium tends to grow horizontally at the electrode-electrolyte interface, promoting the deposition of spherical lithium and ensuring battery safety during cycling.

[0068] Figure 11 Impedance plots of a solid-state lithium-ion battery at different cycle numbers are shown for Comparative Example 1, illustrating a method for constructing a polymer electrolyte film to suppress lithium dendrite formation using sheet-like molybdenum carbide nanofiller. After the first five cycles, the nanosheet molybdenum carbide induced a stable SEI film at the interface. From the 5th to the 100th cycle, the SEI film resistance remained stable. At the 5th and 25th cycles, the interfacial resistance remained almost constant, indicating stability during charge and discharge.

[0069] Figure 12 Example 1 shows a curve of current versus time during polarization in a solid-state lithium-ion battery, illustrating a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. Figure 13 Impedance diagrams of a solid-state lithium-ion battery before and after polarization, illustrating an example of a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. According to... Figure 12 and Figure 13 And formula t Li+ =I ss (ΔV-I0R0) / I0(ΔV-I ss R ss The calculated migration number for the comparative example is 0.42.

[0070] Figure 14 A curve showing the change of current over time during the polarization process of a solid-state lithium-ion battery, which is a comparative example of a method for constructing a polymer electrolyte film to suppress lithium dendrites using a sheet-like molybdenum carbide nanofiller. Figure 15 Impedance diagrams of a solid-state lithium-ion battery before and after polarization are shown in Comparative Example 1, illustrating a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. Based on... Figure 14 and Figure 15And formula t Li+ =I ss (ΔV-I0R0) / I0(ΔV-I ss R ss The calculated migration number for the comparative example is 0.63.

[0071] Figure 16 The constant current polarization test results of symmetric cells in Comparative Example 1 and Example 1 illustrate a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation. The lithium symmetric cell in Comparative Example 1 remained stable during 100 hours of cycling, and its polarization voltage was significantly lower than that in Example 1. This further confirms that molybdenum carbide nanofiller can effectively reduce the interfacial impedance of the polymer electrolyte film, reduce polarization, and thus improve the cycle performance of the battery.

[0072] Figure 17 The electrochemical stability window of the polymer electrolyte film in Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanoparticles to suppress lithium dendrites, is shown in the figure. The figure displays the electrochemical stability window (ESW) of solid polymer electrolyte films with different component contents. The polymer electrolyte film with 4% molybdenum carbide nanoparticles and 2% melamine has an ESW of 4.01 V.

[0073] Figure 18 The electrochemical stability window (ESW) of the polymer electrolyte film in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation, is shown in the figure. The ESW of the solid polymer electrolyte film with different component contents is also shown. The polymer electrolyte film with 5% sheet-like molybdenum carbide nanofiller and 2% melamine content has an ESW of 4.23 V.

[0074] Figure 19 The specific capacity-efficiency diagrams of solid-state lithium-ion batteries from Comparative Example 1 and Example 1, which illustrate a method for constructing polymer electrolyte films using sheet-like molybdenum carbide nanofillers to suppress lithium dendrite formation, are shown at 1C and room temperature. The solid-state lithium-ion battery of Comparative Example 1 exhibits a discharge specific capacity of 127.2 mAh·g⁻¹ during its first cycle. -1 After 100 cycles, the concentration was 133.2 ± 5 mAh·g. -1 The capacity retention was close to 100%, and the average coulombic efficiency was 98.11%. In comparison, the solid-state lithium-ion battery in Example 1 had an initial cycle specific capacity of 105.3 mAh·g. -1 After 100 cycles, the capacity retention rate was 98%, and the average coulombic efficiency was 97.23%, which significantly improved the cycle stability of the battery.

[0075] Figure 20The specific capacity-efficiency diagram of a solid-state lithium-ion battery in Comparative Example 1, which describes a method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation, is shown at 2C and room temperature. The solid-state lithium-ion battery in Comparative Example 1 underwent 500 cycles at a high current density of 2C, maintaining a capacity retention of 51.6% and an average coulombic efficiency of 99.33%.

Claims

1. A method for constructing a polymer electrolyte film using sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation, characterized in that... A method for constructing a polymer electrolyte film with sheet-like molybdenum carbide nanofiller to suppress lithium dendrite formation is carried out according to the following steps: I. Preparation of sheet-like molybdenum carbide nanoparticles Ammonium molybdate was added to deionized water and stirred for 5–15 min to obtain a concentration of 0.1–0.6 mol / L. -1 Solution A is prepared for later use; o-toluidine or aniline is added as a carbon source to a 10%–20% dilute hydrochloric acid solution and stirred for 30–40 min to obtain a concentration of 0.5–1.5 mol / L. -1 Solution B; Add solution A to solution B, stir at 150~200 rpm for 4~8 h, then wash and filter repeatedly with deionized water and ethanol until pH=6~7 to obtain a pale yellow solid; place the pale yellow solid in a tube furnace and keep it at 700~800 ℃ for 4~5 h to obtain sheet-like nano molybdenum carbide. II. Preparation of Polymer Electrolyte Thin Films Polyvinylidene fluoride (PVDF)-hexafluoropropylene (HCF) and PVDF were mixed in a mass ratio of 1:1 to 1:4 and then dissolved in dimethylformamide. The mass-to-volume ratio of the PVDF-HCF and PVDF mixture to dimethylformamide was 1:5 to 1:10 to obtain a slurry. Melamine was then added to the slurry at a concentration of 0.01 to 0.05 mol·L⁻¹. -1 Stir at 180–220 rpm for 12–16 h at room temperature to obtain a slurry; then, adjust the concentration to 0.02–0.06 mol·L⁻¹. -1 Flake-shaped molybdenum carbide nanoparticles are added to the slurry and stirred at 150-200 rpm for 12-16 h to obtain the slurry. 10%-50% of the matrix mass of lithium salt is added and stirred again for 6-10 h. The mixture is then cast onto a clean glass plate and dried at 80-120 ℃ for 60-80 min to obtain a black solid polymer electrolyte film.

2. A battery assembled from a polymer electrolyte film using a sheet-like molybdenum carbide nanofiller prepared by the preparation method of claim 1.

3. The battery according to claim 2, characterized in that... The battery assembly method is as follows: Lithium iron phosphate, polyvinylidene fluoride, and acetylene black were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1~9:0.5:0.

5. The slurry was coated onto aluminum foil and dried in a vacuum oven at 100 ℃~120 ℃ for 20~26 h. After cooling to room temperature, a lithium iron phosphate positive electrode was obtained. The solid-state lithium-ion battery was assembled in a glove box filled with argon gas in the following order: negative electrode shell, nickel foam, lithium sheet, polymer electrolyte film obtained in step two, positive electrode, and positive electrode shell.

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