A method for in-situ generation of solid electrolyte interface films for lithium metal batteries using two-dimensional titanium carbide and silk fibroin peptide modified layers.

Abstract

A method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a modified layer of two-dimensional titanium carbide and silk fibroin peptides addresses the problems of poor interfacial contact and easy side reactions between polymer electrolytes and lithium metal. The specific steps are as follows: acetylene black, two-dimensional titanium carbide, and silk fibroin peptides are mixed in a mass ratio of 1:1:1; an electrolyte slurry with a mass ratio of 5:2 to the above solids is added and stirred evenly; a 4 μm thick modified layer is prepared by a blade coating method; and the mixture is dried at 100°C to obtain an electrolyte film with the interface modified layer. This invention utilizes the fluorine terminals of two-dimensional titanium carbide and the amino nitrogen in silk fibroin peptides to generate a solid electrolyte interface film rich in lithium fluoride and lithium nitride in situ, effectively suppressing interfacial side reactions and alleviating lithium dendrite formation, thereby improving the cycle stability and electrochemical performance of lithium metal batteries. This invention is applicable to the field of lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal batteries, specifically relating to a method for in-situ generating a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer. Background Technology

[0002] Commercial lithium-ion primary batteries were developed in the late 1980s, with a specific energy of 100–200 Wh / kg. -1 and 200-300Wh / L -1 However, during battery cycling, the uncontrolled growth of lithium dendrites can lead to short circuits, fires, and even explosions. To date, the most significant problems facing lithium metal electrodes are incompatibility with the electrolyte interface and the growth of lithium dendrites:

[0003] (1) Unstable battery interface. During charging and discharging, a solid electrolyte interface film forms between the lithium anode and the polymer electrolyte. A stable solid electrolyte interface film allows lithium ions to move freely. An unstable solid electrolyte interface film will continuously break down and regenerate with battery cycling, leading to loss of active materials and deterioration of interface contact. Side reactions will result in low utilization of metallic lithium. (2) Uneven lithium deposition. The lithium deposition process includes ion transfer inside the battery and electron exchange in the external circuit. Usually, the latter occurs faster than the former. The transfer of ions on the electrode surface is essentially a diffusion process, and its inhomogeneity will lead to uneven current density distribution of lithium ions. In this way, lithium ions are deposited and nucleated in high current density areas, grow in protrusions with high-energy interfaces, and eventually form lithium dendrites. (3) Dendrite growth exacerbates the above problems and interface deterioration. The continuous growth of lithium dendrites damages the solid electrolyte interface film and hinders the electrochemical reaction. In summary, effectively controlling lithium ion deposition behavior and suppressing dendrite growth are the most urgent problems to be solved in the practical application of lithium batteries.

[0004] Interfacial modification of polymer electrolytes can perfectly solve the above problems. Lithium fluoride and lithium nitride are important materials for stabilizing solid electrolyte interfacial films. Lithium fluoride has the characteristics of high ionic conductivity, low diffusion energy, and high surface energy, playing a crucial role in regulating the uniform deposition of lithium ion flux. Solid electrolyte interfacial films rich in lithium nitride also play a role in inhibiting lithium dendrite growth.

[0005] As can be seen, a stable solid-state electrolyte interfacial film is equivalent to introducing a protective layer at the electrode / electrolyte interface. Therefore, controlling the stability of the electrode / electrolyte interface is crucial for improving the electrochemical performance of the battery. Summary of the Invention

[0006] This invention addresses the problems of severe interfacial side reactions and lithium dendrite growth in existing lithium metal batteries by proposing a method for in-situ generation of a solid electrolyte interfacial film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer. Compared to the polymer electrolyte before adding the interfacial layer, the polymer electrolyte film with the interfacial layer forms a stable solid electrolyte interfacial film, which not only suppresses the generation of interfacial side reactions but also has a positive effect on the cycle stability of the battery during subsequent cycling.

[0007] The purpose of this invention is to address the aforementioned problems by providing a method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer.

[0008] 1. A method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a modified layer of two-dimensional titanium carbide and silk fibroin peptide, characterized in that the modified layer comprises acetylene black, two-dimensional titanium carbide, silk fibroin peptide and polymer electrolyte precursor solution.

[0009] 2. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin modified layer according to claim 1, characterized in that the mass ratio of acetylene black, two-dimensional titanium carbide and silk fibroin is 1-4:1-5:1-5.

[0010] The mass ratio of acetylene black, two-dimensional titanium carbide, and silk fibroin peptide is 1-4:1-5:1-5. The amino nitrogen in the silk fibroin peptide and the fluorine terminus in the two-dimensional titanium carbide react with lithium to form a solid electrolyte interface film rich in lithium nitride and lithium fluoride in situ. Furthermore, the amino groups in the silk fibroin peptide can form intermolecular hydrogen bonds with the hydroxyl terminus of the two-dimensional titanium carbide, thereby improving the mechanical properties of the modified layer and enhancing its resistance to lithium dendrite formation. Secondly, the lone pair electrons on the amino groups interact with lithium ions to form weak complexes, which can promote the decomposition of lithium salts. Moreover, the amino groups with lone pair electrons also exhibit lithiumophilicity, allowing lithium ions to diffuse uniformly at the interface, further inhibiting the formation of lithium dendrites.

[0011] 3. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin modified layer according to claim 1, characterized in that the mass ratio of acetylene black, two-dimensional titanium carbide and silk fibroin to polymer electrolyte precursor liquid is 1-9:2-25.

[0012] The mass ratio of the acetylene black, two-dimensional titanium carbide, and silk fibroin mixed solid to the polymer electrolyte precursor slurry is 1-9:2-25. Besides its ability to form lithium fluoride in situ using fluorine terminals, the two-dimensional layered morphology and conductivity of titanium carbide also play a crucial role in the modified layer. Furthermore, the components in the modified layer require the polymer electrolyte precursor slurry to provide a bridge for interconnection. If the content of the acetylene black, two-dimensional titanium carbide, and silk fibroin mixed solid is too high, it will consume excessive lithium ions to form a solid electrolyte interface film, leading to a decrease in battery capacity. Conversely, if the content of the acetylene black, two-dimensional titanium carbide, and silk fibroin mixed solid is too low, the SEI will not completely cover the interface, resulting in side reactions and rampant lithium dendrite growth at defect sites, leading to battery failure.

[0013] 4. A method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer, characterized in that the method is carried out according to the following steps:

[0014] I. Preparation of Polymer Electrolyte Precursor Solution

[0015] Methyl methacrylate, poly(vinylidene fluoride-hexafluoropropylene) copolymer, polyvinylidene fluoride, montmorillonite and lithium salt were dissolved in the organic solvent N,N-dimethylformamide in a mass ratio of 17-65:3-21:1-15:1-15:5-40. The mixtures were stirred evenly at room temperature and benzoyl peroxide was added for prepolymerization at 90°C.

[0016] II. Preparation of the Modified Layer

[0017] Acetylene black, two-dimensional titanium carbide and silk fibroin peptide were added to the solution obtained in step one in proportion and stirred at room temperature to obtain a homogeneous solution.

[0018] III. Preparation of Modified Polymer Electrolytes

[0019] The polymer electrolyte precursor solution obtained in step one was cast onto a glass plate using a solution casting method, vacuum dried for 4–18 hours, cooled to room temperature, and the modified layer obtained in step two was scraped onto the polymer electrolyte with a scraper, dried under the same conditions, and sliced ​​for later use.

[0020] IV. Battery Assembly

[0021] The modified polymer electrolyte obtained in step three is assembled, wherein the modified layer is brought into contact with the lithium sheet to obtain the lithium metal battery.

[0022] During battery assembly, the modified polymer electrolyte layer comes into contact with the lithium sheet. Utilizing the fluorine terminals of the two-dimensional titanium carbide in the modified layer and the amino nitrogen in the silk fibroin peptide, a solid electrolyte interface film rich in lithium fluoride and lithium nitride is formed in situ. Both lithium nitride and lithium fluoride are materials with good ion conductivity, providing efficient ion transport channels and promoting high-speed charging and discharging of the battery. Lithium nitride and lithium fluoride also have a wide electrochemical stability window, maintaining battery stability over a higher voltage range, allowing the battery to operate at higher voltages and energy densities. More importantly, lithium nitride and lithium fluoride effectively suppress lithium dendrite growth, reducing short circuits and safety hazards caused by lithium dendrites. Furthermore, the in-situ formed solid electrolyte interface film can uniformly cover the entire interface, significantly inhibiting lithium dendrite formation and tending to form spherical lithium deposits, solving the problems of instability and high interfacial impedance in solid electrolyte interface films.

[0023] The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a modified layer of two-dimensional titanium carbide and silk fibroin is characterized by the addition of an organic solvent when adding the polymer electrolyte precursor slurry and stirring it evenly. The acetylene black in the modified layer provides a soft contact interface between the polymer electrolyte and the lithium anode in the battery, effectively increasing interfacial contact and mitigating the high interfacial impedance caused by the solid-solid foundation. The two-dimensional titanium carbide in the modified layer generates lithium fluoride in-situ using its fluorine terminals; however, lithium fluoride has strong insulating properties, and the presence of only lithium fluoride in the solid electrolyte interface film can increase battery polarization. Therefore, the combined use of acetylene black, which also has conductive properties, with two-dimensional titanium carbide and silk fibroin enhances interfacial contact while forming a stable and dense solid electrolyte interface film in situ. However, when only the polymer electrolyte precursor slurry and the mixed solid of acetylene black, two-dimensional titanium carbide, and silk fibroin are present, the slurry viscosity is too high, resulting in an excessively thick modified layer. An excessively thick modified layer increases the ion transport path length in the electrolyte, thereby increasing ion transport resistance. Furthermore, an excessively thick modified layer will occupy internal battery space, reducing the volume of active materials available for charge storage and thus lowering the battery's energy density. Therefore, a certain amount of organic solvent needs to be added to control the consistency of the modified layer slurry.

[0024] Further specifying the method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a modified layer of two-dimensional titanium carbide and silk fibroin, the method is characterized in that the organic solvent is added at a rate of 20 drops / min to prevent the chemical from adhering to the wall and causing unevenness of the polymer electrolyte precursor solution, and the stirring time is 8-14 hours. The dropping rate and stirring are key factors in obtaining a uniform modified coating. The mixed solid of acetylene black, two-dimensional titanium carbide and silk fibroin, combined with the polymer electrolyte and modified coating, will prepare a uniform modified coating, making the in-situ generated solid electrolyte interface film uniform and dense, the lithium ion deposition current density uniform, eliminating lithium dendrites, and ensuring the safety and longevity of the lithium-ion solid-state battery.

[0025] The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer is characterized by the modified coating thickness being 1-10 μm. This thickness ensures the uniformity and smoothness of the modified layer, forming good polarization resistance, balancing current density, inducing the formation of a good solid electrolyte interface film, and enabling uniform lithium ion deposition to form a spherical lithium ion deposition morphology. An excessively thin modified layer increases the risk of electrolyte failure. An excessively thin modified layer cannot induce the formation of an effective solid electrolyte interface film as an interface barrier, making the electrolyte susceptible to damage from side reactions and other factors, which will shorten battery life or cause safety issues.

[0026] Further specifying the method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer, the method is characterized in that the vacuum drying temperature is 100-120℃. This vacuum drying temperature is higher than the boiling point of the solvent but much lower than the electrolyte decomposition temperature, allowing the solvent in the polymer electrolyte to completely evaporate into an all-solid electrolyte. During evaporation, micropores are formed, creating lithium-ion transport channels, improving the conductivity of the all-solid polymer electrolyte, and ensuring the stability of the polymer electrolyte.

[0027] The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer is characterized in that the two-dimensional titanium carbide is obtained by etching titanium aluminum carbide (Ti3AlC2) with hydrofluoric acid. During the reaction, the hydrofluoric acid first reacts with the surface aluminum oxide, and then with the metallic aluminum. The metallic aluminum can dissolve in the hydrofluoric acid to generate [AlF6]. 3- This process etches the aluminum in titanium carbide, forming a two-dimensional titanium carbide structure with a bellows-like structure.

[0028] The hydrofluoric acid is prepared from lithium fluoride and hydrochloric acid, and this preparation method will improve experimental safety.

[0029] The etched two-dimensional titanium carbide was obtained by washing with distilled water and centrifuging. In the experiment, the etched aluminum, i.e., the generated soluble [AlF6], needs to be removed. 3- After washing, a pure two-dimensional titanium carbide with a bellows structure is obtained, which allows electrons to be evenly distributed on its surface while lithium ions can smoothly pass through the bellows gaps, increasing the conductivity of the electrolyte.

[0030] Further specifying the method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer, the silk fibroin peptide is characterized by being a hydrolyzed product of silk fibroin protein. Silk fibroin protein hydrolysis involves breaking the peptide bonds in the silk fibroin molecule, decomposing it into smaller polypeptides. When directly using silk fibroin to prepare the modified layer, it is difficult for silk fibroin to form a uniform and continuous film in the polymer electrolyte, resulting in defects or uneven ion transport paths in the battery. The low ionic conductivity of silk fibroin also limits the ion transport rate, leading to a decrease in battery performance. However, silk fibroin peptide, as a hydrolyzed product of silk fibroin protein, has more amino terminals and a smaller molecular weight, which can be used as a filler to reduce the crystallinity of the polymer electrolyte, accelerate the ion transport rate, and the more exposed amino groups are more conducive to the in-situ formation of lithium nitride.

[0031] Compared with existing technologies, this invention forms a uniform and dense solid electrolyte interface film in situ, which effectively reduces the interfacial impedance of polymer electrolytes, prevents the formation of lithium dendrites from affecting battery cycle performance and safety, and improves the charge / discharge specific capacity and capacity retention of all-solid-state lithium-ion batteries. Attached Figure Description

[0032] To more clearly illustrate the modified results of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0033] Figure 1 The bulk impedance diagram of the polymer electrolyte in Comparative Example 1 of this invention;

[0034] Figure 2 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 2 of the present invention;

[0035] Figure 3 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 3 of the present invention;

[0036] Figure 4 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 4 of the present invention;

[0037] Figure 5 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 5 of the present invention;

[0038] Figure 6 The polymer electrolyte bulk impedance diagram is shown in the embodiment of the present invention.

[0039] Figure 7 This is a SEM image of the polymer electrolyte of Comparative Example 1 of the present invention;

[0040] Figure 8 This is a SEM image of the polymer electrolyte in an embodiment of the present invention;

[0041] Figure 9 This is a SEM cross-sectional view of the polymer electrolyte of Comparative Example 1 of the present invention;

[0042] Figure 10 This is a SEM cross-sectional view of the polymer electrolyte in an embodiment of the present invention;

[0043] Figure 11 The stress-strain curve of the polymer electrolyte in Comparative Example 1 of this invention is shown.

[0044] Figure 12 The stress-strain curve of the polymer electrolyte in an embodiment of the present invention is shown.

[0045] Figure 13 The linear sweep voltammetry curve of the polymer electrolyte in Comparative Example 1 of this invention;

[0046] Figure 14 The linear sweep voltammetry curve of the polymer electrolyte in an embodiment of the present invention is shown below.

[0047] Figure 15 The in-situ impedance curve of the lithium iron phosphate half-cell assembled in Comparative Example 1 of this invention.

[0048] Figure 16 The in-situ impedance curve of the assembled lithium iron phosphate half-cell in an embodiment of the present invention;

[0049] Figure 17 The constant current polarization curve of the assembled lithium symmetric battery in Comparative Example 1 of this invention;

[0050] Figure 18 The constant current polarization curve of the assembled lithium symmetric battery in an embodiment of the present invention;

[0051] Figure 19 The figure shows the specific capacity-efficiency curve of the lithium iron phosphate half-cell assembled in Comparative Example 1 of the present invention. From top to bottom, the figure represents the coulombic efficiency and the charge / discharge specific capacity.

[0052] Figure 20 The figure shows the specific capacity-efficiency curves of the assembled lithium iron phosphate half-cell according to an embodiment of the present invention. From top to bottom, the figure represents the coulombic efficiency and the charge / discharge specific capacity.

[0053] Figure 21 The cycle impedance curve of the lithium iron phosphate half-cell assembled in Comparative Example 1 of this invention;

[0054] Figure 22 The cycle impedance curve of the assembled lithium iron phosphate half-cell according to an embodiment of the present invention;

[0055] Figure 23 This is a SEM image of the lithium sheet surface after cycling of the assembled lithium iron phosphate half-cell in Comparative Example 1 of the present invention.

[0056] Figure 24 This is a SEM image of the lithium sheet surface after cycling of a lithium iron phosphate half-cell assembled according to an embodiment of the present invention.

[0057] Figure 25 This is the N1s plot of the XPS solid electrolyte interface film formed in situ in Comparative Example 1 of the present invention;

[0058] Figure 26 This is the N1s plot of the XPS solid electrolyte interface film formed in situ according to an embodiment of the present invention;

[0059] Figure 27 This is the F1s plot of the XPS solid electrolyte interface film formed in situ in Comparative Example 1 of the present invention;

[0060] Figure 28 This is the F1s plot of the in-situ formed solid electrolyte interface film XPS in an embodiment of the present invention. Detailed Implementation

[0061] The following embodiments further illustrate the above-mentioned content of the present invention in detail. However, the subject matter of the present invention is not limited to the following embodiments, and all technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0062] Experimental drugs

[0063]

[0064] Experimental equipment

[0065]

[0066]

[0067] Comparative Example 1

[0068] 0.03 g of acetylene black solid powder was weighed into a weighing bottle and mixed thoroughly with the polymer electrolyte precursor slurry at a mass ratio of 2:5. N,N-dimethylformamide was added dropwise to adjust the concentration to an appropriate level. The mixture was then coated onto the surface of the polymer electrolyte film with a thickness of 50 μm and dried in an oven at 100 °C to obtain a polymer electrolyte with a 4 μm thick modified layer. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0069] Comparative Example 2

[0070] Acetylene black, two-dimensional titanium carbide, and silk fibroin powder in a mass ratio of 1:4:1 were weighed into a weighing bottle, and a polymer electrolyte precursor solution and N,N-dimethylformamide were added and mixed thoroughly. A 4 μm thick modified layer was prepared on the surface of the polymer electrolyte using a blade coating method. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0071] Comparative Example 3

[0072] Acetylene black, two-dimensional titanium carbide, and silk fibroin powder in a mass ratio of 1:1:4 were weighed into a weighing bottle, and a polymer electrolyte precursor solution and N,N-dimethylformamide were added and mixed thoroughly. A 4 μm thick modified layer was prepared on the surface of the polymer electrolyte using a blade coating method. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0073] Comparative Example 4

[0074] Acetylene black, two-dimensional titanium carbide, and silk fibroin powder in a mass ratio of 1:1:1 were weighed into a weighing bottle, and a polymer electrolyte precursor solution and N,N-dimethylformamide were added and mixed thoroughly. A 1 μm thick modified layer was prepared on the surface of the polymer electrolyte using a blade coating method. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0075] Comparative Example 5

[0076] Acetylene black, two-dimensional titanium carbide, and silk fibroin powder in a mass ratio of 1:1:1 were weighed into a weighing bottle, and a polymer electrolyte precursor solution and N,N-dimethylformamide were added and mixed thoroughly. A 10 μm thick modified layer was prepared on the surface of the polymer electrolyte using a blade coating method. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0077] Example

[0078] Acetylene black, two-dimensional titanium carbide, and silk fibroin powder in a mass ratio of 1:1:1 were weighed into a weighing bottle, and a polymer electrolyte precursor solution and N,N-dimethylformamide were added and mixed thoroughly. A 4 μm thick modified layer was prepared on the surface of the polymer electrolyte using a blade coating method. The prepared polymer electrolyte was then assembled into a lithium iron phosphate half-cell.

[0079] The drying method for the polymer electrolyte is exactly the same as that in Comparative Example 1.

[0080] Performance characterization was performed on the above embodiments and comparative examples.

[0081] 1) Impedance Measurement. The resistance of polymer electrolytes is an important standard for evaluating their performance and has a significant impact on the charge-discharge performance of batteries. Electrochemical impedance spectroscopy (EIS) was used to measure the resistance of polymer electrolytes. The instrument was a Shanghai Chenhua CHI760E electrochemical workstation with a frequency range of 0.01-100000Hz. Before testing, the polymer electrolyte was dried, and stainless steel (SS) sheets were used as inert electrodes to assemble stainless steel symmetrical blocking batteries for testing.

[0082] 2) Charge and discharge test. Charge and discharge tests are used to obtain many important parameters of the battery during cycling, such as charge / discharge specific capacity, charge / discharge efficiency, voltage plateau, etc. The instrument used is the LAND Battery Testing System CT2001A, with the voltage set at 2.6V-4.0V and the current rate at 0.5C. Polymer electrolytes are assembled into lithium iron phosphate half-cells for testing.

[0083] 3) 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.

[0084] 4) Constant Current Polarization Test. The interfacial stability between the polymer electrolyte 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 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.

[0085] 5) Scanning Electron Microscopy (SEM) Testing. The surface morphology of the lithium wafers 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 then the resulting samples were attached to a sample holder coated with conductive adhesive for testing.

[0086] 6) X-ray photoelectron spectroscopy (XPS) testing. XPS analysis was used to analyze the composition of the passivation layer (SEI) at the interface between the polymer electrolyte and the lithium electrode. The compositional changes and chemical states of each element in the solid electrolyte interfacial film generated under different polymer electrolytes 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 half-cell was disassembled, and the polymer electrolyte side in contact with the lithium electrode was used as the test surface. Experimental data were fitted using an XPSPEAK41.

[0087] Figure 1 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 1 of the present invention. The impedance of the polymer electrolyte is 10.9Ω.

[0088] Figure 2 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 2 of the present invention. The impedance of the polymer electrolyte is 14.6Ω.

[0089] Figure 3 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 3 of the present invention. The impedance of the polymer electrolyte is 9.8Ω.

[0090] Figure 4 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 4 of the present invention. The impedance of the polymer electrolyte is 7.5Ω.

[0091] Figure 5 This is the bulk impedance diagram of the polymer electrolyte in Comparative Example 5 of the present invention. The impedance of the polymer electrolyte is 12.8Ω.

[0092] Figure 6 This is a bulk impedance diagram of the polymer electrolyte according to an embodiment of the present invention. The impedance of the polymer electrolyte is approximately 6.1 Ω. The results show that introducing the modification layer can make the surface of the polymer electrolyte smoother and the contact between it and the lithium cathode tighter.

[0093] Figure 7 This is a SEM image of the polymer electrolyte of Comparative Example 1 of the present invention. Figure 8 This is a SEM surface image of the polymer electrolyte in an embodiment of the present invention. The polymer electrolyte in the embodiment exhibits a relatively uniform and dense morphology.

[0094] Figure 9 This is a SEM cross-sectional view of the polymer electrolyte of Comparative Example 1 of the present invention. Figure 10 This is a SEM cross-sectional image of the polymer electrolyte according to an embodiment of the present invention. The modified layer of the polymer electrolyte is 4 μm thick and has an interconnected network structure. The three-dimensional interconnecting pores are an effective conduction pathway for lithium ions.

[0095] Figure 11 This is the stress-strain curve of the polymer electrolyte in Comparative Example 1 of this invention. The tensile strength is 12.4 MPa.

[0096] Figure 12 This is the stress-strain curve of the polymer electrolyte in an embodiment of the present invention. The tensile strength reaches 16.6 MPa. This is due to the strong interaction between the polymer segments embedded in the two-dimensional titanium carbide, and further, after the introduction of silk fibroin peptides, the hydroxyl terminus of the two-dimensional titanium carbide can form intermolecular hydrogen bonds with the amino groups in the silk fibroin peptides, thereby further improving the tensile strength of the polymer electrolyte.

[0097] Figure 13 This is the linear sweep voltammetry curve of the polymer electrolyte in Comparative Example 1 of this invention. When the applied voltage reaches 4.45V, the corresponding current value changes.

[0098] Figure 14 This is a linear sweep voltammetry curve of the polymer electrolyte in an embodiment of the present invention. When the applied voltage reaches 4.89V, the corresponding current value changes, which is higher than that of Comparative Example 1. The enhanced electrochemical stability can broaden the application range of polymer electrolytes in lithium metal batteries.

[0099] Figure 15 The figure shows the in-situ impedance curve of the lithium iron phosphate half-cell assembled in Comparative Example 1 of this invention. It can be seen from the figure that the impedance value of the solid electrolyte interface membrane is 225.8 Ω, and the impedance value changes significantly during cycling.

[0100] Figure 16 The in-situ impedance curves of the assembled lithium iron phosphate half-cell are shown in this embodiment of the invention. Before cycling, the impedance of the solid electrolyte interface film was only 89.8 Ω. The in-situ impedance change was small during cycling, indicating that the generated solid electrolyte interface film is dense, uniform, and more stable. The fluorine terminals on the two-dimensional titanium carbide surface and the amino nitrogen in the silk fibroin peptide spontaneously generate lithium fluoride and lithium nitride, respectively, in the in-situ reaction. The low conductivity and inherent electrochemical stability of lithium fluoride prevent side reactions between the polymer electrolyte and the lithium anode. Lithium nitride exhibits good stability to metallic lithium, providing a stable anode interface.

[0101] Figure 17 This is the constant current polarization curve of the lithium symmetric battery assembled in Comparative Example 1 of this invention. The current density is 0.1 mA cm⁻¹. -2 At that time, the battery polarization was 56mV.

[0102] Figure 18 The constant current polarization curves of the assembled lithium symmetric battery are shown in the embodiments of the present invention. At a current density of 0.1 mA cm⁻¹ -2At that time, the example exhibited excellent cycling performance with low polarization (45mV) and 200h, significantly lower than Example 1. The lithiophilicity of silk fibroin peptides is the main reason for its low polarization and promotion of uniform lithium-ion flux. The presence of lithium nitride during cycling maintains a uniform distribution of lithium ions at the interface, thereby preventing the growth of lithium dendrites.

[0103] Figure 19 The figure shows the specific capacity-efficiency curves of the lithium iron phosphate half-cell assembled in Comparative Example 1 of this invention. From top to bottom, the figures represent coulombic efficiency and charge / discharge specific capacity. At 0.5C and room temperature, the initial discharge specific capacity of the battery is 130.6 mAh g⁻¹. -1 And its capacity decays severely as the cycle continues.

[0104] Figure 20 The figure shows the specific capacity-efficiency curves of a lithium iron phosphate half-cell assembled according to an embodiment of the present invention. From top to bottom, the figures represent the coulombic efficiency and the charge / discharge specific capacity. The initial discharge specific capacity of the battery is 153.7 mAh g. -1 It still retains 137.5 mAh g after 100 cycles. -1 High capacity.

[0105] Figure 21 The impedance curves for the cycle number of the lithium iron phosphate half-cell assembled in Comparative Example 1 of this invention are shown. Figure 22 The diagram shows the cycle impedance curves of the assembled lithium iron phosphate half-cells according to embodiments of the present invention. In Comparative Example 1, the initial solid electrolyte interface membrane impedance was approximately 380 Ω. As cycling progressed, the impedance decreased slightly, but remained relatively high overall. In contrast, the solid electrolyte interface membrane impedance values ​​of the embodiments were lower than those of Comparative Example 1 before and after cycling.

[0106] Figure 23 This is a SEM image of the lithium sheet surface after cycling in Comparative Example 1 of this invention. To gain a deeper understanding of the effects of various modified layers, lithium-ion deposition kinetics were investigated after 30 cycles at 5C and room temperature. The presence of lithium dendrites was clearly observed in the lithium sheet of Comparative Example 1, indicating severe side reactions at the interface.

[0107] Figure 24 This is a SEM image of the lithium sheet surface after cycling of a lithium iron phosphate half-cell assembled according to an embodiment of the present invention. Due to the lower nucleation potential of this embodiment, lithium-ion deposition kinetics are easier during cycling. The lithium sheet surface is relatively smooth after cycling.

[0108] Figure 25 This is the N1s plot of the XPS solid electrolyte interface film formed in situ in Comparative Example 1 of the present invention. Figure 26This is the N1s spectrum of the XPS film formed in situ as a solid electrolyte interface membrane in an embodiment of the present invention. The peak position of lithium nitride in the N1s spectrum is 397.2 eV. The lithium nitride content in this embodiment is significantly higher than that in Comparative Example 1. The amino nitrogen in the silk fibroin peptide is converted into lithium nitride in situ during cycling. As a superionic conductor, lithium nitride plays an important role in improving ionic conductivity, reducing interfacial resistance, and preventing lithium dendrite growth.

[0109] Figure 27 This is the F1s plot of the in-situ formed solid electrolyte interface film XPS of Comparative Example 1 of the present invention. Figure 28 This is the F1s spectrum of the XPS film formed in situ as a solid electrolyte interface membrane in an embodiment of the present invention. The 684.8 eV in the F1s spectrum belongs to lithium fluoride, and the lithium fluoride content in this embodiment is significantly higher than in Comparative Example 1. The fluorine termini in the two-dimensional titanium carbide generate lithium fluoride in situ during cycling. Lithium fluoride, with its high interfacial stability, can block interfacial side reactions.

Claims

1. A method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer, characterized in that... The method is performed according to the following steps: I. Preparation of Polymer Electrolyte Precursor Solution Methyl methacrylate, poly(vinylidene fluoride-hexafluoropropylene) copolymer, polyvinylidene fluoride, montmorillonite and lithium salt in a mass ratio of 17~65:3~21:1~15:1~15:5~40 were dissolved in the organic solvent N,N-dimethylformamide, stirred evenly at room temperature, and benzoyl peroxide was added for prepolymerization at 90 °C to obtain a polymer electrolyte precursor solution. II. Preparation of the Precursor Solution for the Modified Layer Take a portion of the polymer electrolyte precursor solution obtained in step one, add acetylene black, two-dimensional titanium carbide, and silk fibroin peptide in a mass ratio of 1:1:1, and then add the organic solvent N,N-dimethylformamide. Stir at room temperature to obtain a uniform modified layer precursor solution. The two-dimensional titanium carbide is obtained by etching titanium aluminum carbide with hydrofluoric acid, which is prepared by lithium fluoride and hydrochloric acid. The etched two-dimensional titanium carbide is collected after washing with distilled water and centrifugation. III. Preparation of Interfacial Films The remaining polymer electrolyte precursor solution obtained in step one was cast onto a glass plate using a casting method. After vacuum drying at 100-120 °C for 4-18 h and cooling to room temperature, a polymer electrolyte was obtained. Then, the modified layer precursor solution obtained in step two was coated onto the polymer electrolyte with a scraper and vacuum dried at 100-120 °C for 4-18 h to obtain a modified layer with a thickness of 4 µm on the surface of the polymer electrolyte. This resulted in the in-situ generation of a solid electrolyte interface film for lithium metal batteries using two-dimensional titanium carbide and silk fibroin modified layers. IV. Battery Assembly The interface film obtained in step three is assembled, wherein the modified layer of the interface film is brought into contact with the lithium sheet to obtain the lithium metal battery.

2. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer according to claim 1, characterized in that, In step two, the total mass ratio of acetylene black, two-dimensional titanium carbide, and silk fibroin peptide to the polymer electrolyte precursor solution obtained in step one is 1-9: 2-25.

3. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer according to claim 1, characterized in that, The organic solvent described in step two is added dropwise at a rate of 20 drops / min, and the stirring time is 8-14 h.

4. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer according to claim 1, characterized in that, The vacuum drying temperature described in step three is 100-120 ℃.

5. The method for in-situ generation of a solid electrolyte interface film for lithium metal batteries using a two-dimensional titanium carbide and silk fibroin peptide modified layer according to claim 1, characterized in that, The silk fibroin peptides mentioned above are hydrolyzed products of silk fibroin protein.

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