Artificial solid-electrolyte interphase layer and method of making the same

Abstract

The application discloses an artificial solid electrolyte interface layer and a preparation method thereof, and a preparation method of a composite piezoelectric film, and comprises the following steps: uniformly mixing an organic copolymer, an inorganic piezoelectric phase and a solvent to obtain a composite precursor solution, uniformly coating the composite precursor solution on an inert substrate, drying after coating is completed, and obtaining a composite film on the inert substrate; applying an electric field to the composite film, simultaneously, performing polarization treatment on the composite film, cooling to room temperature, and obtaining a composite piezoelectric film on the inert substrate. By constructing the composite piezoelectric film with residual polarization orientation on the surface of the negative electrode, the 'field-force coupling' response of the composite piezoelectric film under the action of the electric field and the stress is utilized, the dynamic negative feedback regulation of the lithium metal negative electrode interface electric field and the ion distribution is realized, and thus the dendrite growth is effectively inhibited, the deposition uniformity is improved, and the cycle stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery and functional interface material technology, specifically relating to an artificial solid electrolyte interface layer and its preparation method. Background Technology

[0002] Lithium metal is an ideal anode material for next-generation high-energy-density batteries due to its high theoretical specific capacity and the lowest redox potential. However, in actual charge-discharge cycles, the lithium metal anode interface has inherent defects: uneven local current density and ion flux (local concentration of ion flux) easily occur at the anode interface, which, while causing lithium dendrite formation and tip growth, is accompanied by problems such as the accumulation of "dead lithium", separator puncture, and internal short circuits, thus severely restricting the cycle stability and rate performance of the battery.

[0003] To address these issues, researchers have developed various modification strategies that have reduced interfacial side reactions and puncture risks to some extent. For example, inert coatings (such as Al2O3 or Li3PO4 coatings) can be constructed on the surface of lithium metal anodes using physical vapor deposition (PVD), atomic layer deposition (ALD), or solution coating processes to serve as artificial solid electrolyte interphase (SEI) layers, thereby suppressing dendrite growth and reducing interfacial side reactions. For instance, Li et al. (Adv. Mater. 2016, 28: 1853-1858) treated the lithium metal surface with polyphosphate to form a Li3PO4 coating, constructing a modified PPA-Li anode. This improved lithium-ion transport capacity and suppressed dendrite growth, achieving a modified PPA-Li anode with a performance of 0.5 mA / cm². 2 Stable cycling performance of 600 hours at current density. Chinese patent application CN 115732783 A utilizes plasma-enhanced chemical vapor deposition to induce a plasma reaction between a halide-rich organic liquid and a lithium metal anode, successfully preparing a composite lithium metal anode with a halide-rich artificial solid electrolyte interface (SEI) layer. This improves the cycle stability of the lithium metal battery at 1.0 mA / cm². 2 It can be stably cycled for 2300 hours at current density.

[0004] Currently, some progress has been made in optimizing electrolyte systems and improving the interfacial compatibility between electrolytes and lithium metal by adding inorganic filler particles to electrolytes or solid electrolyte matrices, thereby promoting the formation of stable and dense artificial solid electrolyte interphase (SEI) layers. Chinese patent application CN 118970046 A employs a lithium-loving modified titanium nitride nanotube array and a solid electrolyte interfacial film to form a hybrid conductor, promoting uniform lithium deposition and stripping within the nanotubes, effectively releasing stress, and improving the battery's electrochemical performance (at 0.2 mA / cm²). 2Stable cycling for 450 hours at current density). Chinese patent application CN111682257 A uses polyvinylidene fluoride and inorganic ionic conductor LAGP (Li 1.5 Al 0.5 Ge 1.5 (PO4)3) was blended with ionic liquid to prepare an organic-inorganic composite solid electrolyte film, which was then assembled into a lithium metal battery with an efficiency of 0.1 mA / cm². 2 It can be stably cycled for 2700 hours at current density.

[0005] However, existing modification strategies are still mainly based on passive barrier, lacking real-time, directional controllable adjustment capabilities when facing constantly changing electric fields and stresses during deposition, making it difficult to maintain uniform deposition under high current density or long cycle conditions. Therefore, there is an urgent need to develop an artificial solid electrolyte interface layer based on piezoelectric thin film materials, enabling it to achieve an adaptive and continuous negative feedback control mechanism during battery operation, thereby maintaining significant advantages in the safety and cycle stability of lithium metal batteries. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing composite piezoelectric thin films.

[0007] Another object of the present invention is to provide a composite piezoelectric film (artificial solid electrolyte interface layer).

[0008] Another objective of this invention is to provide a use of a composite piezoelectric film as an SEI film. By constructing a composite piezoelectric film with residual polarization orientation, the "field-force coupling" response generated by the composite piezoelectric film under electric field and stress is utilized to achieve dynamic negative feedback control of the electric field and ion distribution at the interface of the lithium metal anode (commercial lithium metal foil), thereby effectively suppressing dendrite growth, improving deposition uniformity and cycle stability, and providing a new technical approach for realizing high energy density and long life lithium metal batteries.

[0009] The objective of this invention is achieved through the following technical solution.

[0010] A method for preparing a composite piezoelectric thin film includes the following steps:

[0011] S1, the organic copolymer, the inorganic piezoelectric phase, and the solvent are mixed uniformly to obtain a composite precursor solution. The organic copolymer is one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), and polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene terpolymer (P(VDF-TrFE-CTFE)). The inorganic piezoelectric phase includes modified bismuth titanate sodium. The ratio of the mass fraction of the organic copolymer, the mass fraction of the inorganic piezoelectric phase, and the volume fraction of the solvent is 1:(0.05~0.4):10, where mass fractions are in g and volume fractions are in mL. The modified bismuth titanate sodium is ion-doped bismuth titanate sodium.

[0012] In S1, the solvent is one or a mixture of N,N-dimethylformamide, N,N-dimethylacetamide, and tetrahydrofuran.

[0013] In S1, the ratio of the organic copolymer to the inorganic piezoelectric phase by mass is preferably 1:(0.1~0.25).

[0014] In S1, the method for preparing ion-doped sodium bismuth titanate includes: mixing Na source, Bi source, Ti source and W source uniformly to obtain a first mixture; pre-calcining the first mixture at 700~800℃ for 1~2h to obtain a precursor powder; mixing the precursor powder and a eutectic salt; holding the mixture at 800~900℃ for 1~3h; cooling to room temperature; washing the salt; and drying to obtain ion-doped sodium bismuth titanate. The ratio of Na in the Na source, Bi in the Bi source, Ti in the Ti source and W in the W source, by molar amount, is 0.5:4.5:(4-x):2x / 3, where 0.04≤x≤0.16; and the ratio of the precursor powder to the eutectic salt, by mass, is 1:(4~6).

[0015] In the above technical solution, the Na source is Na2CO3, the Bi source is Bi2O3, the Ti source is TiO2, and the W source is WO3.

[0016] In the above technical solution, the eutectic salt is a NaCl-KCl eutectic salt, which includes NaCl and KCl. By mass fraction, the ratio of NaCl to KCl in the NaCl-KCl eutectic salt is 1:(1~3).

[0017] S2, the composite precursor liquid is uniformly coated on an inert substrate. After coating, it is vacuum dried at 60~120℃ for 2~6h to obtain a composite film on the inert substrate.

[0018] In S2, the inert substrate is a glass sheet or a copper foil.

[0019] In S2, the coating method includes spin coating, casting, spraying, or blade coating.

[0020] In step S2, the thickness of the composite film is 10~20μm.

[0021] S3. An electric field is applied to the composite film, and the composite film is kept at 80~120℃ for 10~60min (for polarization treatment), and then cooled to room temperature to obtain a composite piezoelectric film with residual polarization orientation along the thickness direction on an inert substrate.

[0022] In S3, the electric field strength is 50~150mV / m.

[0023] In S3, the electric field is formed by a DC voltage.

[0024] The composite piezoelectric thin film obtained by the above preparation method.

[0025] The above-mentioned composite piezoelectric film is used as an SEI film (solid electrolyte interface film).

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The piezoelectric response of the composite piezoelectric film of the present invention as an SEI film can generate a periodic micro-electric field under charge and discharge volume changes or stress disturbances, so as to dynamically adjust the interface ion migration, make lithium deposition more uniform, thereby increasing the critical current density and extending the cycle life to 5000h.

[0028] 2. In the composite piezoelectric film prepared by this invention, the continuous phase of the organic copolymer PVDF-based material provides flexibility and electronic insulation, ensuring a dense adhesion between the film and the lithium metal surface; the inorganic piezoelectric phase has a high piezoelectric coefficient, which can significantly enhance the interface's response sensitivity to electric field and stress disturbances, forming an effective "field-force coupling" feedback. Excellent electrochemical stability is achieved through the synergy of the organic copolymer and the inorganic piezoelectric phase; the polarization voltage of the lithium metal symmetric battery based on the composite piezoelectric film remains stable at 90 mV during long-term cycling. Attached Figure Description

[0029] Figure 1 X-ray diffraction patterns of WO3-doped sodium titanate obtained in Example 1 and sodium titanate of Comparative Example 1 are shown.

[0030] Figure 2The images show the Raman spectra of WO3-doped sodium titanate obtained in Example 1 and sodium titanate of Comparative Example 1, where (a) is Comparative Example 1, (b) is Example 1-1, (c) is Example 1-2, (d) is Example 1-3, (e) is Example 1-4, and (f) is the Raman shift of the vibration peak as a function of the WO3 content.

[0031] Figure 3 The piezoelectric coefficient diagrams are for the WO3-doped sodium titanate obtained in Example 1 and the sodium titanate obtained in Comparative Example 1.

[0032] Figure 4 The lithium metal symmetric battery obtained in (a) Example 13 and the bare lithium symmetric battery obtained in (b) Example 14 were tested at 0.5 mA / cm. 2 Current density, 0.5 mAh / cm 2 Cyclic performance diagram under areal capacity conditions;

[0033] Figure 5 The lithium metal symmetric battery obtained in Example 9 operates at 0.5 mA / cm². 2 Current density, 0.5 mAh / cm 2 Cyclic performance diagram under areal capacity conditions;

[0034] Figure 6 The graphs show the cycle performance of the lithium metal full cell obtained in Example 16 and the bare lithium full cell obtained in Comparative Example 3. Detailed Implementation

[0035] This invention synthesizes a composite piezoelectric thin film by introducing an inorganic piezoelectric phase into an organic copolymer, and uses it as an artificial SEI film for the negative electrode. Utilizing a response mechanism, lithium dendrite growth is effectively suppressed, achieving active self-regulation and long-term stable operation of the lithium metal negative electrode interface, providing a feasible solution for high-energy-density, long-life lithium metal batteries.

[0036] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] Source of raw materials used:

[0038] All the following raw materials were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] The purity of Na2CO3, Bi2O3, TiO2, WO3, MnO2, and Nb2O5 is 99.99%.

[0040] The purity of N,N-dimethylacetamide, N,N-dimethylformamide, and tetrahydrofuran was 99.00%.

[0041] The KH550 coupling agent and polyvinylpyrrolidone (PVP) have a purity of 99.99%, and the weight-average molecular weight of PVP is approximately 4.0 × 10⁻⁶. 4 g / mol;

[0042] Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), weight average molecular weight 1.0 × 10⁻⁶ 5 g / mol.

[0043] Example 1

[0044] A method for preparing a composite piezoelectric thin film includes the following steps:

[0045] S1. The organic copolymer is added to the solvent and stirred for 60 min until it is uniformly mixed to obtain a polymer solution. Then, an inorganic piezoelectric phase is added to the polymer solution and ultrasonically dispersed for 30 min (ultrasonic power is 300W) to obtain a homogeneous composite precursor solution. The organic copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the inorganic piezoelectric phase is modified sodium titanate, and the modified sodium titanate is ion-doped sodium titanate (WO3-doped sodium titanate). The mass fraction of the organic copolymer, the mass fraction of the inorganic piezoelectric phase and the volume fraction of the solvent are 1:0.25:10. The mass fraction is in g and the volume fraction is in mL. The solvent is N,N-dimethylacetamide.

[0046] A method for preparing ion-doped sodium bismuth titanate includes: mixing a Na source, a Bi source, a Ti source, and a W source, and wet ball milling them with ethanol for 8 hours until homogeneous to obtain a first mixture; pre-calcining the first mixture at 780°C for 2 hours in air (heating to 780°C at a rate of 5°C / min) to obtain a precursor powder; mixing the precursor powder with a eutectic salt (the eutectic salt is a NaCl-KCl eutectic salt, which is a mixture of NaCl and KCl, with a mass ratio of NaCl to KCl of 1:1); and holding the mixture at 900°C for 3 hours in air (heating to 900°C at a rate of 5°C / min). After cooling to room temperature, the salt was washed (washed by centrifugation three times with deionized water), dried at 80℃ for 12 hours, and then ground to obtain ion-doped sodium bismuth titanate, namely WO3-doped sodium bismuth titanate (named NBTW-100x, 0.04≤x≤0.16). The ratio of Na in the Na source, Bi in the Bi source, Ti in the Ti source, and W in the W source, by mass fraction, is 0.5:4.5:(4-x):2x / 3. The naming of sodium bismuth titanate with different x and ion doping in Example 1 is detailed in Table 1. The ratio of precursor powder to eutectic salt, by mass fraction, is 1:5. The Na source is Na2CO3, the Bi source is Bi2O3, the Ti source is TiO2, and the W source is WO3.

[0047] S2, the composite precursor liquid was uniformly coated onto an inert substrate (copper foil) using a scraping method. After coating, it was vacuum dried at 120°C for 2 hours to obtain a composite film with a thickness of 15±5μm on the inert substrate.

[0048] S3. Apply a DC voltage with an electric field strength of 150mV / m to the composite thin film, and simultaneously perform polarization treatment at 100℃ for 30min. Cool to room temperature of 20~25℃ to obtain a composite piezoelectric thin film with residual polarization orientation along the thickness direction on an inert substrate.

[0049] Table 1

[0050]

[0051] Example 2

[0052] A method for preparing a composite piezoelectric thin film includes the following steps:

[0053] S1. The organic copolymer is added to the solvent and stirred for 40 min until it is uniformly mixed to obtain a polymer solution. Then, an inorganic piezoelectric phase is added to the polymer solution and ultrasonically dispersed for 60 min (ultrasonic power is 300W) to obtain a homogeneous composite precursor solution. The organic copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the inorganic piezoelectric phase is modified sodium titanate, and the modified sodium titanate is sodium titanate treated with a surface coupling agent. The mass ratio of the organic copolymer, the inorganic piezoelectric phase and the solvent is 1:0.25:10. The mass part is in g and the volume part is in mL. The solvent is N,N-dimethylformamide.

[0054] A method for preparing surface-coupling agent-treated sodium bismuth titanate includes: dispersing sodium bismuth titanate (NBT) in a first solvent, adding KH550 coupling agent dropwise under magnetic stirring to obtain a reaction system, adjusting the pH of the reaction system to 4.5±0.5 with glacial acetic acid, stirring the reaction at 60℃ for 1 h to form an organic functional layer of KH550 coupling agent on the surface of sodium bismuth titanate, washing with deionized water by centrifugation, drying at 80℃ for 12 h, and grinding to obtain surface-coupling agent-treated sodium bismuth titanate (KH550 surface-modified sodium bismuth titanate). The first solvent is a mixture of anhydrous ethanol and deionized water, with a volume ratio of anhydrous ethanol to deionized water of 9:1; the mass ratio of sodium bismuth titanate to the volume ratio of the first solvent is 1:80 (mass parts in g, volume parts in mL); and the mass ratio of sodium bismuth titanate to KH550 coupling agent is 1:0.03.

[0055] The method for obtaining sodium bismuth titanate (NBT) includes: mixing a Na source, a Bi source, and a Ti source, and wet ball milling them with ethanol for 8 hours until homogeneous to obtain a second mixture; pre-calcining the second mixture at 780℃ for 2 hours in air (heating to 780℃ at a rate of 5℃ / min) to obtain a precursor powder; and then mixing the precursor powder with a eutectic salt (the eutectic salt is a NaCl-KCl eutectic salt, which is a mixture of NaCl and KCl, with a NaCl to KCl ratio of 1:1 by mass). The mixture was stirred and kept at 900℃ for 3 hours in air (heating rate to 900℃ was 5℃ / min), cooled to room temperature, and the salt was washed (washed with deionized water by centrifugation three times). After drying at 80℃ for 12 hours, it was ground to obtain sodium bismuth titanate (NBT, powder). The ratio of Na in the Na source, Bi in the Bi source, and Ti in the Ti source was 0.5:4.5:4 by molar amount; the ratio of precursor powder to eutectic salt was 1:5 by mass; the Na source was Na2CO3, the Bi source was Bi2O3, and the Ti source was TiO2.

[0056] S2, The composite precursor liquid is uniformly coated onto an inert substrate (copper foil) using a casting method. After coating, it is vacuum dried at 100°C for 3 hours to obtain a composite film on the inert substrate. The thickness of the composite film is 15±5μm.

[0057] S3. Apply a DC voltage with an electric field strength of 150mV / m to the composite film, and simultaneously perform polarization treatment at 110℃ for 40min. Cool to room temperature of 20~25℃ to obtain a composite piezoelectric film (with residual polarization orientation along the thickness direction) on an inert substrate.

[0058] Example 3

[0059] A method for preparing a composite piezoelectric thin film includes the following steps:

[0060] S1. The organic copolymer is added to the solvent and stirred for 50 min until it is uniformly mixed to obtain a polymer solution. Then, an inorganic piezoelectric phase is added to the polymer solution and ultrasonically dispersed for 40 min (ultrasonic power is 300W) to obtain a homogeneous composite precursor solution. The organic copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the inorganic piezoelectric phase is modified sodium titanate, and the modified sodium titanate is sodium titanate coated with an organic shell. The mass fraction of the organic copolymer, the mass fraction of the inorganic piezoelectric phase and the volume fraction of the solvent are 1:0.25:10. The mass fraction is in g and the volume fraction is in mL. The solvent is tetrahydrofuran.

[0061] The method for preparing sodium bismuth titanate coated with an organic shell includes: dispersing sodium bismuth titanate (NBT) in a second solvent, adding polyvinylpyrrolidone (PVP) under magnetic stirring, stirring continuously at 60°C for 1 hour to uniformly coat the surface of sodium bismuth titanate with PVP to form an organic protective layer, centrifuging to obtain a solid, washing the solid three times with ethanol, drying at 80°C for 8 hours, and grinding to obtain sodium bismuth titanate coated with an organic shell (PVP). The second solvent is a mixture of anhydrous ethanol and deionized water, with a volume ratio of 1:1; the mass fraction of sodium bismuth titanate is in a volume ratio of 1:80 to the second solvent (g and mL); the mass fraction of sodium bismuth titanate is in a ratio of 1:0.02 to PVP; and the sodium bismuth titanate (NBT) is the same as that in Example 2.

[0062] S2, the composite precursor liquid was uniformly coated onto an inert substrate (glass slide) using a spin coating method (1200 rpm, 60 s). After coating, it was vacuum dried at 60 °C for 6 h to obtain a composite film on the inert substrate. The thickness of the composite film was 15 ± 5 μm.

[0063] S3. Apply a DC voltage with an electric field strength of 150mV / m to the composite film, and simultaneously perform polarization treatment at 90℃ for 30min. Cool to room temperature to obtain a composite piezoelectric film (with residual polarization orientation along the thickness direction) on an inert substrate.

[0064] Example 4

[0065] A method for preparing a composite piezoelectric thin film includes the following steps:

[0066] S1. The organic copolymer is added to the solvent and stirred for 45 min until it is uniformly mixed to obtain a polymer solution. Then, an inorganic piezoelectric phase is added to the polymer solution and ultrasonically dispersed for 50 min (ultrasonic power is 300W) to obtain a homogeneous composite precursor solution. The organic copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the inorganic piezoelectric phase is modified sodium titanate, and the modified sodium titanate is ion-doped sodium titanate (Mn / Nb-doped sodium titanate). The mass ratio of the organic copolymer, the inorganic piezoelectric phase and the solvent is 1:0.25:10. The mass part is in g and the volume part is in mL. The solvent is N,N-dimethylacetamide.

[0067] The method for preparing ion-doped sodium bismuth titanate includes: mixing Na, Bi, Ti, Mn, and Nb sources, and wet ball milling them with ethanol for 8 hours until homogeneous to obtain a first mixture; pre-calcining the first mixture at 780°C for 2 hours in air (heating rate to 780°C is 5°C / min) to obtain a precursor powder; mixing the precursor powder with a eutectic salt (the eutectic salt is a NaCl-KCl eutectic salt, which is a mixture of NaCl and KCl, with a mass ratio of NaCl to KCl of 1:1); and holding the mixture at 900°C in air. After 3 hours of heating (at a rate of 5℃ / min to 900℃), the mixture was cooled to room temperature, washed with deionized water (three centrifugal washes), dried at 80℃ for 12 hours, and then ground to obtain ion-doped sodium bismuth titanate. The ratio of Na in the Na source, Bi in the Bi source, Ti in the Ti source, Mn in the Mn source, and Nb in the Nb source, by molar percentage, was 0.5:4.5:3.9:0.06:0.04. The ratio of precursor powder to eutectic salt, by mass percentage, was 1:5. The Na source was Na₂CO₃, the Bi source was Bi₂O₃, the Ti source was TiO₂, the Mn source was MnO₂, and the Nb source was Nb₂O₅.

[0068] S2, The composite precursor liquid is uniformly coated onto an inert substrate (glass slide) by spraying. After coating, it is vacuum dried at 80°C for 3 hours to obtain a composite film on the inert substrate. The thickness of the composite film is 15±5μm.

[0069] S3. Apply a DC voltage with an electric field strength of 150mV / m to the composite film, and simultaneously perform polarization treatment at 80℃ for 25min. Cool to room temperature to obtain a composite piezoelectric film (with residual polarization orientation along the thickness direction) on an inert substrate.

[0070] Example 5

[0071] A method for preparing a modified lithium metal electrode includes: peeling the composite piezoelectric film obtained in "Examples 1-3" off an inert substrate and then directly rolling it onto the surface of a commercial lithium metal foil (the commercial lithium metal foil was purchased from KELOD New Energy Technology Co., Ltd., and the composite piezoelectric film on the surface of the commercial lithium metal foil serves as an artificial solid electrolyte interface layer) to obtain a modified lithium metal electrode, wherein the positive polarization surface of the composite piezoelectric film is far away from the surface of the commercial lithium metal foil.

[0072] Example 6

[0073] A method for preparing a modified lithium metal electrode is basically the same as that in Example 5, except that the composite piezoelectric film in this example is the composite piezoelectric film obtained in Example 2.

[0074] Example 7

[0075] A method for preparing a modified lithium metal electrode is basically the same as that in Example 6, except that the composite piezoelectric film in this example is the composite piezoelectric film obtained in Example 3.

[0076] Example 8

[0077] A method for preparing a modified lithium metal electrode is basically the same as that in Example 7, except that the composite piezoelectric film in this example is the composite piezoelectric film obtained in Example 4.

[0078] Comparative Example 1

[0079] A method for preparing a composite piezoelectric thin film includes the following steps:

[0080] S1. The organic copolymer is added to the solvent and stirred for 60 min until homogeneous to obtain a polymer solution. Then, an inorganic piezoelectric phase is added to the polymer solution and ultrasonically dispersed for 45 min (ultrasonic power of 300 W) to obtain a homogeneous composite precursor solution. The organic copolymer is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and the inorganic piezoelectric phase is sodium bismuth titanate (NBT). The mass ratio of the organic copolymer, the inorganic piezoelectric phase, and the solvent is 1:0.15:10. The mass part is in g, and the volume part is in mL. The solvent is N,N-dimethylacetamide. The sodium bismuth titanate (NBT) is the same as "sodium bismuth titanate (NBT)" in Example 2.

[0081] S2, the composite precursor liquid was uniformly coated onto an inert substrate (copper foil) using a spin coating method (1500 rpm, 60 s). After coating, it was vacuum dried at 90 °C for 4 h to obtain a composite film on the inert substrate. The thickness of the composite film was 15 ± 5 μm.

[0082] S3. Apply a DC voltage with an electric field strength of 150mV / m to the composite film, and simultaneously perform polarization treatment at 100℃ for 30min. Cool to room temperature to obtain a composite piezoelectric film (with residual polarization orientation along the thickness direction) on an inert substrate.

[0083] Comparative Example 2

[0084] A method for preparing a modified lithium metal electrode is basically the same as that in Example 5, except that the composite piezoelectric film in this comparative example is the composite piezoelectric film obtained in Comparative Example 1.

[0085] X-ray diffraction analysis was performed on the inorganic piezoelectric phase (WO3-doped sodium bismuth titanate) in Example 1 and the sodium bismuth titanate in Comparative Example 1. The results are as follows: Figure 1As shown. "NBTW-4" represents Example 1-1, "NBTW-8" represents Example 1-2, "NBTW-12" represents Example 1-3, "NBTW-16" represents Example 1-4, and "Pure NBTW" represents sodium bismuth titanate of Comparative Example 1; (a) shows XRD data, and (b) shows a magnified view. Figure 1 As shown in (a), the main phases of the inorganic piezoelectric phases (WO3-doped sodium bismuth titanate, NBTW-100x (0.04≤x≤0.16)) prepared in Examples 1-1 to 1-4 all correspond to the diffraction peaks of sodium bismuth titanate in Comparative Example 1. The diffraction peaks correspond to the strong peaks of the (111), (119), (020), (220), and (319) crystal planes of sodium bismuth titanate, respectively. This indicates that the inorganic piezoelectric phases (WO3-doped sodium bismuth titanate) prepared in Examples 1-1 to 1-4 are a single bismuth layered structure, and the strongest peak corresponding to the (119) crystal plane is consistent with the position of the characteristic peak of the bismuth layered structure of sodium bismuth titanate. Figure 1 (b) is Figure 1 In (a), a magnified view of 2θ near 30° shows that the diffraction peak corresponding to the (119) crystal plane gradually shifts to a lower angle with the increase of W source (WO3) content. This may be due to the W content in the W source. 6+ The doping increases the cell volume and causes the diffraction peaks to shift.

[0086] Using the orthogonal phase structure of space group A21am as a model, for Figure 1 The XRD results were refined using Rietveld, and the data were simulated using the least squares method of GSAS. The refined parameters are shown in Table 2. According to the cell parameters (a, b, c, V, and b / a) of sodium bismuth titanate (NBT) and the inorganic piezoelectric phases (WO3-doped sodium bismuth titanate) obtained in Examples 1-1 to 1-4 in Table 2, the V value of WO3-doped sodium bismuth titanate increases with increasing WO3 content. This is because W... 6+ The radius is greater than Ti 4+ W 6+ The increase in cell volume is caused by the doping of WO3. In addition, the b / a value decreases slightly with the increase of WO3 content (the b / a ratio is related to orthogonal distortion, and the larger the b / a ratio, the higher the degree of distortion), indicating that the doping of WO3 reduces the degree of orthogonal distortion of sodium bismuth titanate.

[0087] Table 2

[0088]

[0089] To corroborate the Rietveld refinement results in Table 2, Raman spectroscopy was performed on the inorganic piezoelectric phase (WO3-doped sodium titanate) prepared in Example 1 (Examples 1-1 to 1-4) of this invention and the sodium titanate obtained in Comparative Example 1. The results are as follows: Figure 2 As shown. (a) is Comparative Example 1, (b) is Example 1-1, (c) is Example 1-2, (d) is Example 1-3, (e) is Example 1-4, and (f) is the functional relationship between the Raman shifts of the vibration peaks (v1~v6) and the WO3 content. After Lorentz fitting and peak segmentation processing ( Figure 2 In the text, "Lorentz fit" refers to the fitted data, and "observation" refers to the original data. The inorganic piezoelectric phase (WO3-doped sodium bismuth titanate) prepared in Example 1 can be divided into six peaks (v1~v6). Among them, the highest peak, v2, reflects the torsional bending vibration of the TiO6 octahedron and can be attributed to F. 2g Characteristics; peaks v1 and v3 are attributed to F respectively. 2μ and F 1μ It is activated by the distortion of the TiO6 octahedron. Located at 555 cm⁻¹. -1 E at the location g The vibration peak is related to symmetry, and it is prone to splitting under orthogonal distortion, splitting into a v4 peak (B). 2g ) and V5 peak (B 3g The v6 peak corresponds to the A peak of the TiO6 octahedron. 1g Tensile vibration. (From) Figure 2 From (a) to (e), it can be seen that as the WO3 content increases, E g The splitting degree of the vibrational peaks gradually decreases, and the v4 and v5 peaks gradually merge, indicating a weakening of orthorhombic lattice distortion. Furthermore, due to... Figure 2 As shown in (f), with the increase of WO3 content, the v2 and v3 peaks gradually approach each other, further indicating that the orthogonal distortion of bismuth titanate is weakening. This is consistent with the results of the b / a characteristic parameter in the Rietveld refinement.

[0090] The piezoelectric properties of the inorganic piezoelectric phases prepared in Examples 1-4 and Comparative Example 1 were tested, and the obtained piezoelectric coefficients (d) were measured. 33 As shown in Table 3, the inorganic piezoelectric phases prepared in "Examples 1-1" to "Examples 1-4" and Comparative Example 1 have the following d values: 33 Trend of change Figure 3 As shown. Figure 3 In the figures, "0.00" represents sodium bismuth titanate in Comparative Example 1, "0.04" represents the inorganic piezoelectric phase obtained in Examples 1-1, "0.08" represents the inorganic piezoelectric phase obtained in Examples 1-2, "0.12" represents the inorganic piezoelectric phase obtained in Examples 1-3, and "0.16" represents the inorganic piezoelectric phase obtained in Examples 1-4. Figure 3 It can be seen that as the WO3 doping content increases, the piezoelectric coefficient (d) of the resulting inorganic piezoelectric phase (WO3-doped sodium bismuth titanate) increases. 33 The value first increases and then decreases, reaching a maximum of 24.4 pC / N when x is 0.12 (Examples 1-3), approximately 1.8 times that of sodium bismuth titanate. This may be due to W 6+ The lattice distortion induced by doping promotes spontaneous polarization vector deflection, significantly improving the piezoelectric activity of the sodium bismuth titanate-based inorganic piezoelectric phase. When the WO3 content exceeds x=0.12 (i.e., excessive doping), the piezoelectric coefficient shows a decreasing trend, which may be attributed to the excessive W content. 6+ The introduction of this disrupts the structural regularity of the NBT-based inorganic piezoelectric phase, causing the originally ordered lattice arrangement to become disordered. This hinders the deflection of the spontaneous polarization vector, making it impossible to form a directional and stable polarization orientation, thereby weakening the piezoelectric response.

[0091] Table 3

[0092]

[0093] Examples 9-13

[0094] The method for assembling a lithium metal symmetric battery includes: in a glove box, assembling the battery in the following order from bottom to top: negative electrode shell (bottom shell), first modified lithium metal electrode (composite piezoelectric film facing up), separator, second modified lithium metal electrode (composite piezoelectric film facing down), gasket, spring sheet, and positive electrode shell (top cover) (with electrolyte added during the process), and then sealing it at 0.5 MPa using a button cell packaging machine to ensure no electrolyte leakage, thus obtaining a CR2032 type button cell symmetric battery as a lithium metal symmetric battery. The modified lithium metal electrode is one of the modified lithium metal electrodes obtained in Examples 5-8 and Comparative Example 2. The correspondence between the modified lithium metal electrodes of different examples and the lithium metal symmetric battery is shown in Table 4. The separator is a PP separator with a diameter of 18 mm. The electrolyte includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and a solvent. The concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in the electrolyte is 1 mol / L. The solvent is a mixture of 1,3-dioxolane (DOL) and dimethyl ethylene glycol (DME) in a volume ratio of 1:1. The volume of the electrolyte is 20 μL to ensure that the electrolyte completely wets the separator and the composite piezoelectric film. The glove box is an argon environment, and the contents of water and oxygen are both ≤0.1 ppm.

[0095] Table 4

[0096]

[0097] Example 14

[0098] The method for assembling a bare lithium symmetric battery is basically the same as the method for assembling a lithium metal symmetric battery in Example 9, except that the "modified lithium metal electrode" is replaced with commercial lithium metal foil (bare lithium anode, purchased from KELU New Energy Technology Co., Ltd.).

[0099] Example 15

[0100] Cyclic stability test: The symmetric cell was placed in a constant temperature environment of 25℃ for 12 hours to complete interface wetting, and then its electrochemical performance was tested. The electrochemical performance test conditions were as follows: at 0.5 mA / cm 2 Current density, 0.5 mAh / cm 2 At the given capacity, a constant current charge-discharge cycle test was conducted with a charge-discharge time of 1 hour (i.e., 0.5 hours of charging and 0.5 hours of discharging). The symmetric battery was either a lithium metal symmetric battery or the bare lithium symmetric battery obtained in Example 14, with the lithium metal symmetric battery being one of the lithium metal symmetric batteries obtained in Examples 9-13. The cycle life of the lithium metal symmetric batteries obtained in Examples 9-13 is shown in Table 5, and the cycle stability test results of the lithium metal symmetric battery obtained in Example 13 are shown in Table 5. Figure 4 As shown in (a), the cycle stability test results of the bare lithium symmetric battery obtained in Example 14 are as follows: Figure 4 As shown in (b), the cycle stability test results of the lithium metal symmetric battery obtained in Example 9 are as follows: Figure 5 As shown.

[0101] Depend on Figure 4 It can be seen that at 0.5 mA / cm 2 Current density, 0.5 mAh / cm 2 Under the given areal capacity conditions, compared to the bare lithium symmetric battery obtained in Example 14, the lithium metal symmetric battery obtained in Example 13 (a symmetric battery assembled from the modified lithium metal electrode of Comparative Example 2) exhibited more stable cycle performance, with a cycle life of 1000 h. (See Table 5 and...) Figure 5 It can be seen that the modified lithium metal electrode obtained in Example 5 is based on the composite piezoelectric thin film obtained in "Examples 1-3" (with the optimal piezoelectric coefficient (d)). 33 The lithium metal symmetric battery prepared from the sample and assembled in Example 9 exhibited the best cycle stability, with a cycle life of up to 5000 h; and the polarization voltage of the lithium metal symmetric battery obtained in Example 9 remained stable at 90 mV throughout the long cycle. The cycle lives of the lithium metal symmetric batteries obtained in Examples 10-12 were 2580, 2800, and 3200 h, respectively.

[0102] Table 5

[0103]

[0104] Example 16

[0105] The method for assembling lithium metal full cells is basically the same as the "method for assembling lithium metal symmetric cells" in Example 9, except that the "second modified lithium metal electrode" is replaced with a commercially available positive electrode. The commercially available positive electrode was purchased from KELU New Energy Technology Co., Ltd., and the positive electrode material in the commercially available positive electrode is high-voltage NCM811 (LiNi). 0.8 Co 0.1 Mn 0.1 O2) materials.

[0106] Comparative Example 3

[0107] The method for assembling bare lithium-ion full cells is basically the same as the "method for assembling lithium metal symmetric cells" in Example 9, the only difference being that the "second modified lithium metal electrode" is replaced with a commercially available cathode. The commercially available cathode was purchased from KELU New Energy Technology Co., Ltd., and the cathode material in the commercially available cathode is high-voltage NCM811 (LiNi). 0.8 Co 0.1 Mn 0.1 O2) material. The "first modified lithium metal electrode" was replaced with a commercial lithium metal foil (purchased from KELU New Energy Technology Co., Ltd.)

[0108] Example 17

[0109] Cycle stability tests were conducted on the lithium metal full cell obtained in Example 16 and the bare lithium full cell obtained in Comparative Example 3. The test conditions were as follows: the full cells were cycled at a constant temperature of 25°C, a voltage window of 3~4.3V, and a current density of 1C (1C = 220mA / g). The full cells were either the lithium metal full cell obtained in Example 16 or the bare lithium full cell obtained in Comparative Example 3. The results are as follows: Figure 6 As shown, "lithium anode based on Examples 1-3" corresponds to the lithium metal full cell obtained in Example 16, and "bare lithium anode" corresponds to the bare lithium full cell obtained in Example 3.

[0110] Depend on Figure 6 As can be seen, the lithium metal full battery obtained in Example 16 has an initial discharge specific capacity of 190.0 mAh / g at a current density of 1C, and a discharge specific capacity of 154.5 mAh / g after 400 cycles, still maintaining a capacity retention of 81.3%. This indicates that the lithium metal full battery obtained in Example 16 has good cycle stability. In contrast, the bare lithium full battery obtained in Comparative Example 3 has an initial discharge specific capacity of 179.8 mAh / g at a current density of 1C, and a discharge specific capacity of 110.6 mAh / g after 113 cycles, with a capacity retention of only 61.5%, exhibiting poor cycle stability.

[0111] The continuous phase based on the organic copolymer PVDF of this invention imparts excellent electronic insulation and interfacial compliance to the composite piezoelectric film; the inorganic piezoelectric phase provides a high piezoelectric coefficient (d). 33 The artificial solid electrolyte interface (SEI) layer can respond to local electric field and stress changes during electrochemical deposition, forming an effective "field-force coupling" feedback, thereby dynamically suppressing electric field concentration and dendrite growth. The synergistic effect of the organic copolymer base and the inorganic piezoelectric phase enables the SEI layer to have both "field-force negative feedback" and "electric field regulation" functions, possessing excellent polarization retention, electrochemical stability, and active regulation capability to suppress dendrites. After polarization treatment, the composite piezoelectric film forms and maintains a stable residual polarization orientation along the thickness direction, enabling it to respond quickly to local electric field changes during electrochemical deposition. When micro-protrusions or electric field concentrations appear on the surface of commercial lithium metal foil, the SEI layer will generate a local reverse potential opposite to the direction of the applied electric field at the corresponding location, and superimpose additional piezoelectric stress, thereby weakening the local overpotential at the tip, regulating the interface ion migration behavior, breaking the positive feedback chain of "dendrite-electrodeposition", and changing the lithium deposition process from tip-preferential growth to a uniform and dense surface deposition morphology. Therefore, the modified lithium metal electrode based on composite piezoelectric thin film can achieve an adaptive and continuous negative feedback control mechanism during battery operation, showing significant advantages in safety and cycle stability compared to traditional passive protective layers.

[0112] Based on Examples 1-3, adjusting the organic copolymer, solvent, coating method, electric field strength, and parameter values ​​within the scope of the invention can achieve the same technical effects as Examples 1-3.

[0113] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite piezoelectric thin film, characterized in that, Includes the following steps: S1, the organic copolymer, the inorganic piezoelectric phase, and the solvent are mixed uniformly to obtain a composite precursor solution. The organic copolymer is one or more of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-trifluoroethylene copolymer, and PVDF-trifluoroethylene-chlorotrifluoroethylene terpolymer. The inorganic piezoelectric phase includes modified sodium bismuth titanate. The ratio of the mass fraction of the organic copolymer, the mass fraction of the inorganic piezoelectric phase, and the volume fraction of the solvent is 1:(0.05~0.4):10, where mass fractions are in g and volume fractions are in mL. The modified sodium bismuth titanate is ion-doped sodium bismuth titanate. S2, the composite precursor liquid is uniformly coated on an inert substrate. After coating, it is vacuum dried at 60~120℃ for 2~6h to obtain a composite film on the inert substrate. S3. An electric field is applied to the composite film, and the composite film is kept at 80~120℃ for 10~60min and cooled to room temperature to obtain a composite piezoelectric film with residual polarization orientation along the thickness direction on an inert substrate.

2. The preparation method according to claim 1, characterized in that, In S1, the solvent is one or a mixture of N,N-dimethylformamide, N,N-dimethylacetamide, and tetrahydrofuran.

3. The preparation method according to claim 1, characterized in that, In S1, the method for preparing ion-doped sodium bismuth titanate includes: mixing Na source, Bi source, Ti source and W source uniformly to obtain a first mixture; pre-calcining the first mixture at 700~800℃ for 1~2h to obtain a precursor powder; mixing the precursor powder and a eutectic salt; holding the mixture at 800~900℃ for 1~3h; cooling to room temperature; washing the salt; and drying to obtain ion-doped sodium bismuth titanate. The ratio of Na in the Na source, Bi in the Bi source, Ti in the Ti source and W in the W source, by molar amount, is 0.5:4.5:(4-x):2x / 3, where 0.04≤x≤0.16; and the ratio of the precursor powder to the eutectic salt, by mass, is 1:(4~6).

4. The preparation method according to claim 1, characterized in that, The eutectic salt is a NaCl-KCl eutectic salt, which includes NaCl and KCl. By mass, the ratio of NaCl to KCl in the NaCl-KCl eutectic salt is 1:(1~3).

5. The preparation method according to claim 1, characterized in that, The inert substrate is a glass sheet or copper foil.

6. The preparation method according to claim 1, characterized in that, In S2, the coating method includes spin coating, casting, spraying, or blade coating.

7. The preparation method according to claim 1, characterized in that, The thickness of the composite film is 10~20μm.

8. The preparation method according to claim 1, characterized in that, In S3, the electric field strength is 50~150mV / m; the electric field is formed by a DC voltage.

9. The composite piezoelectric thin film obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the composite piezoelectric film as a solid electrolyte interface film as described in claim 9.

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