A method for modifying a lithium negative electrode and a battery thereof

Abstract

The application discloses a modification method of a lithium-containing metal negative electrode, and the modification method comprises the following steps: adopting a passivation film containing a metal fluoride and alpha-PVDF-HFP to perform passivation treatment on the surface of the lithium-containing metal negative electrode, and obtaining the lithium-containing metal negative electrode with a passivation interface. The preparation method of the application overcomes the technical difficulties in the traditional method, i.e., various reagents are used to prepare a modified layer which is directly used for surface modification of the lithium negative electrode. The preparation of the passivation film promotes in-situ chemical conversion reaction of the lithium negative electrode, thereby promoting the modification of the lithium negative electrode. The modification method of the application can more uniformly improve the lithium negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery anode technology, specifically to a method for modifying a lithium anode and a battery thereof. Background Technology

[0002] Driven by the recent development of high-tech electronics and electric vehicles, all-solid-state lithium metal batteries (ASSLMBs) have emerged as candidates for the next generation of batteries. Compared with traditional lithium-ion batteries that use liquid organic electrolytes, highly safe solid-state electrolytes (SEs) can avoid the potential combustion risks associated with organic liquid electrolytes.

[0003] From the perspective of energy storage and conversion mechanisms, lithium metal, which achieves energy storage through conversion chemistry, has the lowest electrochemical potential (-3.04V compared to the standard hydrogen electrode) and the highest theoretical specific capacity (3860mAh g). -1 , or 2061mAh cm -3 Solid-state batteries, far surpassing graphite anodes which rely on intercalation chemistry for energy storage, are considered the "holy grail" and the ultimate choice for lithium-ion battery anodes. However, solid-state batteries still face many challenges. For lithium metal anodes in solid-state batteries: first, poor solid-solid interface contact leads to significant polarization during cycling; second, lithium dendrite growth causes internal short circuits and thermal runaway; and third, side reactions occur between the lithium anode and the electrolyte. Existing research has focused on modifying lithium anodes by preparing an artificial interface layer (SEI film) on the anode surface to improve conductivity and enhance the electrochemical performance of the metal anode.

[0004] However, existing methods for preparing artificial interface layers on metal anode surfaces still face certain technical challenges. First, the choice of raw materials affects the uniformity of dispersion in the final interface layer. If many types of raw materials are selected, solid reagents, with their rigid structures and inherent shapes, are easy to handle but prone to uneven distribution; liquid reagents have molecules with a certain degree of fluidity; and gaseous reagents typically require high-end equipment. These different characteristics of the raw materials may lead to poor uniformity of dispersion in the final interface layer, potentially resulting in suboptimal improvement. Second, existing methods for preparing interface layers still exhibit some degree of uneven lithium deposition, and lithium dendrites can still form during battery cycling. Third, there is still room for further improvement in the ionic conductivity of the obtained interface layer. Summary of the Invention

[0005] This invention addresses the problems in the prior art by first disclosing a passivation film and then using this passivation film to modify a lithium-containing metal anode. The passivation film promotes an in-situ chemical conversion reaction in the lithium-containing metal anode, thereby obtaining a modified anode that can solve the short-circuit problem caused by the formation and propagation of lithium dendrites during battery cycling. It also has high interface energy, which can improve the electrical performance of the battery. In addition, the passivation layer formed on the lithium-containing metal anode can reduce the side reactions between the lithium-containing metal anode and the electrolyte.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a passivation film comprising a metal fluoride and α-PVDF-HFP. The metal fluoride modulates the intensity of the α and β phases in PVDF-HFP, causing more of the β phase in PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) to transform into the α phase, and the metal fluoride also reduces the crystallinity of PVDF-HFP.

[0008] As a further embodiment, the raw materials for the passivation film include metal fluorides, PVDF-HFP, and low-boiling-point organic solvents. The raw material PVDF-HFP simultaneously contains both α and β phases.

[0009] As a further embodiment, the metal fluoride includes one or more of the following: CoF3 (cobalt trifluoride), MnF3 (manganese trifluoride), FeF3 (iron trifluoride), VF3 (vanadium trifluoride), VOF3 (vanadium trifluoride), TiF3 (titanium trifluoride), BiF3 (bismuth trifluoride), NiF2 (nickel fluoride), FeF2 (ferrous fluoride), CuF2 (copper fluoride), CuF (copper fluoride), SnF2 (stannous fluoride), and AgF (silver fluoride).

[0010] As a further embodiment, the metal fluoride includes CuF2. When the passivation film is used for a lithium-containing metal anode, Cu (copper) can provide better lithium nucleation sites, enabling better in-situ generation of Li-Cu microstructures on the lithium-containing metal anode, which can homogenize lithium deposition. Cu atoms act as diasterons to decompose the long-range ordered mode of the passivation interface, thereby helping the battery to exhibit higher capacity during cycling.

[0011] This invention provides a method for preparing the passivation film, the method comprising:

[0012] S1: Add metal fluoride and PVDF-HFP to a low-boiling-point organic solvent to obtain a homogeneous mixed solution. The main phase of PVDF-HFP in the mixed solution is the α phase (i.e., α-PVDF-HFP).

[0013] S2: Evaporate the low-boiling-point organic solvent in the mixed solution to obtain a passivation film.

[0014] As a further embodiment, the metal fluoride is used to regulate the intensity of the α and β phases in PVDF-HFP, promoting the conversion of the β phase into the α phase in PVDF-HFP.

[0015] As a further embodiment, the mass ratio of the metal fluoride to the low-boiling-point organic solvent in S1 is 0.5%-3%, and the concentration of PVDF-HFP in the mixed solution in S1 is 0.08g / mL-1.2g / mL.

[0016] As a further embodiment, the mass ratio of the metal fluoride to the low-boiling-point organic solvent in S1 is 0.8%-1.2%.

[0017] As a further step, the homogenization condition of the mixed solution in S1 is to stir at 40℃-60℃ for 1.5h-2.5h. Within this range, the intensity of the α and β phases in PVDF-HFP can be regulated by metal fluorides, ultimately obtaining PVDF-HFP dominated by the α phase.

[0018] As a further step, the low-boiling-point organic solvent in the evaporation mixture in step S2 is removed by vacuum drying at a temperature of 75°C-85°C for 20-30 hours. The selection of vacuum drying temperature and time is beneficial for removing the organic solvent. However, when the temperature is below 75°C or the drying time is less than 20 hours, the organic solvent may not completely evaporate from the passivation film. Conversely, when the temperature is above 85°C, the high temperature may damage the passivation film, thus hindering the modification of the lithium-containing metal anode.

[0019] As a further step, deionized water is added to the homogeneous mixed solution in S1, with a volume ratio of 8:1 between the mixed solution and the deionized water. The mixture is then stirred at 40℃-60℃ for 25-35 minutes until homogeneous.

[0020] This invention provides a method for modifying a lithium-containing metal anode with a passivation film, wherein the modification method includes passivating the surface of the lithium-containing metal anode with the passivation film to obtain a lithium-containing metal anode with a passivated interface. The design of this invention is as follows: the modification method of this invention promotes in-situ chemical conversion reactions in the lithium-containing metal anode by preparing a passivation film, thereby obtaining a lithium-containing metal anode with higher interfacial energy and the ability to suppress lithium dendrite growth. Specifically, metal fluorides regulate the intensity of the α and β phases in PVDF-HFP, causing more of the β phase to transform into the α phase. The α phase is beneficial for improving the ion transport capacity of the lithium-containing metal anode. Furthermore, metal fluorides can reduce the crystallinity of PVDF-HFP, thereby promoting the reaction between PVDF-HFP and lithium metal, shortening the passivation time, and significantly reducing energy consumption. On this basis, the decomposition of metal fluorides generates metal on one hand, which is uniformly distributed on the surface of the lithium-containing metal anode, forming a lithiophilic structure with the lithium-containing metal anode. On the other hand, more LiF (lithium fluoride) is formed. LiF and the lithiophilic structure endow the lithium-containing metal anode with high coulombic efficiency and dendrite suppression ability, achieving effective protection of the lithium-containing metal anode.

[0021] As a further embodiment, the passivation treatment includes covering the surface of the lithium-containing metal anode with a passivation film, performing heat treatment, and separating the passivation film to obtain a lithium-containing metal anode with a passivated interface. In this invention, the lithium-containing metal anode includes a lithium metal anode and also includes a pre-lithiated anode. Specifically, the pre-lithiated anode is a pre-lithiated anode formed by bonding lithium metal sheets to the surface of graphite, silicon-carbon, or silicon-oxygen. The bonded lithium metal sheets have a thickness of 20 μm-50 μm.

[0022] As a further embodiment, the heat treatment temperature is 70℃-90℃; the heat treatment time is 1min-30min.

[0023] As a further embodiment, the heat treatment temperature is 70℃-90℃; the heat treatment time is 8min-12min.

[0024] As a better way to evaporate low-boiling-point organic solvents in a mixed solution, the mixed solution can be uniformly cast onto a clean glass plate, and most of the organic solvent can be evaporated at room temperature to obtain a passivation film. Then, the obtained passivation film can be dried in a vacuum drying oven at 80°C for 24 hours to remove residual organic solvents.

[0025] As a further embodiment, the heat treatment employs hot rolling, with a pressure of 20-30 kPa per unit area. This is beneficial for maintaining a tight adhesion between the passivation film and the lithium metal, thereby facilitating the modification of the lithium-containing metal anode surface by the passivation film.

[0026] The present invention provides a method for modifying a lithium-containing metal anode with the passivation film, comprising:

[0027] S1: Add metal fluoride and PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) to a low-boiling-point organic solvent to obtain a homogeneous mixed solution. The main phase of PVDF-HFP in the mixed solution is the α phase (i.e., α-PVDF-HFP).

[0028] S2: Evaporate the low-boiling-point organic solvent in the mixed solution to obtain a passivation film;

[0029] S3: A passivation film is applied to the surface of a lithium metal layer, followed by heat treatment. The passivation film is then separated to obtain a lithium-containing metal anode with a passivated interface.

[0030] S1: Add metal fluoride and PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) to a low-boiling-point organic solvent to obtain a homogeneous mixed solution. The main phase of PVDF-HFP in the mixed solution is the α phase (i.e., α-PVDF-HFP).

[0031] S2: Evaporate the low-boiling-point organic solvent in the mixed solution to obtain a passivation film;

[0032] S3: A passivation film is applied to the surface of a lithium-containing metal anode, followed by heat treatment. The passivation film is then separated to obtain a lithium-containing metal anode with a passivated interface.

[0033] As a further embodiment, the mass ratio of metal fluoride to low-boiling-point organic solvent in S1 is 0.5%-3%; the heat treatment temperature in S3 is 70℃-90℃; and the heat treatment time in S3 is 1min-30min. When the mass ratio of metal fluoride to low-boiling-point organic solvent is less than 0.5%, the metal fluoride promotes the conversion of a small portion of the β phase in the PVDF-HFP film into the α phase, and the main phase in the finally obtained PVDF-HFP is still dominated by the β phase. When the mass ratio of metal fluoride to low-boiling-point organic solvent is greater than 3%, the metal fluoride can change the crystallinity of PVDF-HFP, and the metal fluoride will trigger the deHF removal reaction of PVDF-HFP. This reaction will affect the metal fluoride, thereby affecting the modification of the lithium-containing metal anode by the interface layer. When the heat treatment temperature is below 70°C and the heat treatment time is less than 1 minute, it is not conducive to promoting the modification of the lithium-containing metal anode by the passivation film. On the one hand, a uniform passivation interface layer may not be formed on the surface of the lithium-containing metal anode, thus failing to complete the surface modification of the lithium-containing metal anode and affecting the rate performance of the battery. On the other hand, when the heat treatment temperature is above 90°C and the heat treatment time is above 30 minutes, the metal fluoride in the passivation film may react with the lithium metal of the lithium-containing metal anode to form a metal layer. The formation of a dense metal layer may affect the migration of lithium ions in the battery, resulting in a lower ionic conductivity of the battery. The lithium-containing metal anode obtained by the method of this invention has better electrical performance, suppresses lithium dendrites, and reduces side reactions between the electrolyte and the lithium-containing metal anode.

[0034] As a further refinement, in step S1, the mass ratio of metal fluoride to low-boiling-point organic solvent is 0.8%-1.2%; in step S3, the heat treatment temperature is 70℃-90℃; and in step S3, the heat treatment time is 8min-12min. When the mass ratio of metal fluoride to low-boiling-point organic solvent is 0.8%-1.2%, a good lithium deposition interface can be constructed, which is beneficial for the uniform deposition of metallic lithium and reduces the formation of lithium dendrites. With a heat treatment time within 8min-12min, the lithium-containing metal surface has more LiF after passivation, which to some extent inhibits lithium oxidation. Under the conditions of this invention, a more suitable passivation layer is formed on the surface of the lithium-containing metal anode, further improving the electrical performance of the lithium-containing metal anode, inhibiting lithium dendrites, and reducing side reactions between the electrolyte and the lithium-containing metal anode.

[0035] The present invention also provides a battery having a lithium-containing metal anode obtained by the modification method.

[0036] As a further embodiment, the battery includes a sulfide solid electrolyte battery.

[0037] The features and beneficial effects of this invention are as follows:

[0038] (1) The preparation method of the present invention overcomes the technical difficulties of using various reagents to prepare a modified layer for direct application to the surface modification of lithium metal anodes in traditional methods. The method of preparing a passivation film promotes the in-situ chemical conversion reaction of lithium metal anodes, thereby promoting the modification of lithium metal anodes. The modification method of the present invention can more uniformly improve lithium metal anodes.

[0039] (2) The lithium-containing metal anode obtained by the method of the present invention has better cycle stability and stable coulombic efficiency.

[0040] (3) The method of the present invention obtains lithium-containing metal anodes with high interface energy and effective ability to suppress lithium dendrites.

[0041] (4) The passivation layer formed on the surface of the lithium metal anode in this invention can reduce the side reactions between the lithium metal anode and the electrolyte, which is beneficial to improving the electrical performance of the lithium metal anode.

[0042] (5) Compared with other interface modification methods, the solid-phase passivation strategy of this invention provides a simple, efficient, and scalable method for lithium metal passivation by using passivation films with different compositions. This method can draw on excellent film-forming techniques to form passivation films that meet different needs. Simultaneously, existing roll-to-roll fabrication processes can be used to complete the passivation of lithium metal, greatly promoting the large-scale production of lithium metal batteries. Furthermore, this method can be further extended to applications of passivation modification of other alkali metal anodes. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the modification method of the present invention; wherein Figure 1 (a) shows the formation process of the passivation film. Figure 1 (b) is the solid-phase passivation process.

[0045] Figure 2 The images shown are X-ray diffraction patterns of embodiments and comparative examples of the present invention.

[0046] Figure 3 The images shown are physical representations of the passivation films used in the embodiments and comparative examples of this invention.

[0047] Figure 4The following are the electrical performance test results of LiCoO2 (lithium cobalt oxide) / LPSC (Li6PS5Cl, i.e., lithium-sulfur-phosphorus-chloride electrolyte) / Li (lithium) full cells with different CuF2 concentrations (Φ = 0.5wt%, 1wt%, 3wt%) and passivation times (t = 5min, 10min, 20min, 30min) in the passivation film of this invention. Figure 4 (a) shows the rate performance of passivation films with different concentrations of CuF2; Figure 4 (b) shows the charge-discharge curves of passivation films with different concentrations of CuF2 at a 2C rate; Figure 4 (c) is the first-cycle coulombic efficiency of passivation films with different concentrations of CuF2; Figure 4 (d) is the rate capability of passivation films with different passivation times; Figure 4 (e) shows the charge-discharge curves of passivation films with different passivation times at a 2C rate; Figure 4 (f) is the first-cycle coulomb efficiency of passivation films with different passivation times.

[0048] Figure 5 The surface composition of the lithium anode after solid-phase passivation in the embodiments and comparative examples of the present invention; wherein Figure 5 (a) is the electron energy spectrum (XPS) of the lithium anode; Figure 5 (b) is the electron energy spectrum (XPS) diagram of the lithium anode of the present invention; Figure 5 (c) is the electronic energy spectrum (XPS) of a comparative lithium anode.

[0049] Figure 6 The embodiments and comparative examples of this invention demonstrate the electrochemical performance of lithium deposition / stripping in symmetrical Li / LPSC / Li batteries at room temperature; wherein... Figure 6 (a) shows the embodiments and comparative examples of the present invention at 0.5 mA cm. -2 Constant current cycling stability at current density Figure 6 (b) is the critical current density of untreated Li at room temperature; Figure 6 (c) is the critical current density of the comparative example (PVDF-HFP@10min-Li) at room temperature; Figure 6 (d) is the critical current density of Example 2 at room temperature; Figure 6 (e) is the critical current density at room temperature in Example 6.

[0050] Figure 7 The electrical performance results of the embodiments and comparative examples of the present invention are shown below. Figure 7 (a) shows the rate performance (0.2-8C) of all-solid-state lithium metal batteries of LCO (lithium cobalt oxide) in the embodiments and comparative examples of the present invention. Figure 7 (b) is the charge-discharge curve of untreated Li; Figure 7(c) Charge-discharge curves of the comparative example of the present invention (PVDF-HFP@10min-Li); Figure 7 (d) is the charge-discharge curve of Embodiment 2 of the present invention; Figure 7 (e) is the charge-discharge curve of Embodiment 6 of the present invention.

[0051] Figure 8 The electrical performance of the embodiments and comparative examples of the present invention is shown below. Figure 8 (a) shows the discharge capacity and coulombic efficiency (area capacity of 1 mAh cm⁻¹) of the embodiments and comparative examples of the present invention at a 1C rate. -2 ), Figure 8 (b) shows the charge-discharge curves of the embodiments and comparative examples of the present invention after 50 cycles; Figure 8 (c) shows the charge-discharge curves of the embodiments and comparative examples of the present invention after 150 cycles; Figure 8 (d) shows the charge-discharge curves of the embodiments and comparative examples of the present invention after 300 cycles. Detailed Implementation

[0052] To facilitate understanding of the modification method of the lithium-containing metal anode of the present invention, a more comprehensive description of the modification method of the lithium-containing metal anode of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0053] Example 1:

[0054] Preparation of a 0.5 wt% CuF2-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 36.64 mg of CuF2 was added to the acetone. The mixture was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min to further mix. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0055] The prepared passivation film (0.5wt% CuF2-PVDF-HFP) was coated on the surface of lithium metal and hot rolled at 80°C on a rolling mill. The pressure per unit area during hot rolling was 25.6 kPa, and the passivation reaction time was 10 min to maintain the passivation film and lithium metal in close adhesion. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0056] Example 2:

[0057] Preparation of a 1 wt% CuF2-PVDF-HFP passivation film (Example 2 of this invention can also be expressed as CuF2-PVDF-HFP@10min): 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of CuF2 was added to the acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. Then, the solution was mechanically stirred at 50 °C for 30 min for further mixing. Afterward, the homogenized viscous mixture was cast onto a clean glass plate using a spatula, and most of the solvent acetone was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0058] The prepared passivation film (1wt% CuF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C using a rolling mill. The passivation reaction time was 10 min, followed by hot rolling. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface (CuF2-PVDF-HFP@10 min-Li).

[0059] Example 3:

[0060] Preparation of a 3wt% CuF2-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 219.84 mg of CuF2 was added to the acetone. The mixture was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min for further mixing. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0061] The prepared passivation film (3wt% CuF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0062] Example 4:

[0063] 1wt% CuF2-PVDF-HFP passivation film: 0.8 g PVDF-HFP was dissolved in 8 mL acetone, and 73.28 mg CuF2 was added to the acetone. The mixture was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min for further mixing. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0064] The prepared passivation film (1wt% CuF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 5 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0065] Example 5:

[0066] Preparation of a 1 wt% CuF2-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of CuF2 was added to the acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min for further mixing. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0067] The prepared passivation film (1wt% CuF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 20 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0068] Example 6:

[0069] Preparation of a 1 wt% CuF2-PVDF-HFP passivation film (Example 6 of this invention can also be represented as CuF2-PVDF-HFP@30min): 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of CuF2 was added to the acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. Then, the solution was mechanically stirred at 50 °C for 30 min for further mixing. Afterward, the homogenized viscous mixture was cast onto a clean glass plate using a spatula, and most of the solvent acetone was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0070] The prepared passivation film (1wt% CuF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C using a rolling mill. The passivation reaction time was 30 min, followed by hot rolling. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface (CuF2-PVDF-HFP@30 min-Li).

[0071] Example 7:

[0072] Preparation of a 1 wt% FeF3-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of FeF3 was added to the acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min for further mixing. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0073] The prepared passivation film (1wt% FeF3-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0074] Example 8: Preparation of a 1wt% NiF2-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of NiF2 was added to the acetone. The mixture was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min to further mix. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the solvent acetone was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0075] The prepared passivation film (1wt% NiF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0076] Example 9: Preparation of a 1 wt% SnF2-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of SnF2 was added to the acetone. The mixture was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min to further mix. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the solvent acetone was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0077] The prepared passivation film (1wt% SnF2-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0078] Example 10: Preparation of a 1 wt% AgF-PVDF-HFP passivation film: 0.8 g of PVDF-HFP was dissolved in 8 mL of acetone, and 73.28 mg of AgF was added to the acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min to further mix. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the solvent acetone was evaporated at room temperature to obtain the passivation film. Finally, the obtained film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0079] The prepared passivation film (1wt% AgF-PVDF-HFP) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10 min, and hot rolling was performed. The pressure per unit area during hot rolling was 25.6 kPa to ensure that the passivation film adhered tightly to the lithium metal. After the reaction was completed, the passivation film was separated to obtain lithium metal at the passivation interface.

[0080] Comparative Example 1:

[0081] Untreated Li metal.

[0082] Comparative Example 2:

[0083] PVDF-HFP passivation film (30 min): Dissolve 0.8 g PVDF-HFP in 8 mL acetone. Stir mechanically at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP is fully dissolved, add 1 mL deionized water at a volume ratio of 8:1. Then, further mix the solution by mechanical stirring at 50 °C for 30 min. Next, cast the homogenized viscous mixture onto a clean glass plate using a spatula, and evaporate most of the acetone solvent at room temperature to obtain the passivation film. Finally, dry the resulting film in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0084] The prepared passivation film (PVDF-HFP@30min) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 30min, and hot rolling was performed to maintain the passivation film and lithium metal in close adhesion. After the reaction was completed, the passivation film was separated to obtain lithium metal (PVDF-HFP@30min-Li) with passivated interface.

[0085] Comparative Example 3:

[0086] PVDF-HFP passivation film (10 min): 0.8 g PVDF-HFP was dissolved in 8 mL acetone. The solution was mechanically stirred at 50 °C for 2 h to obtain a homogeneous solution. After the PVDF-HFP was fully dissolved, 1 mL of deionized water was added at a volume ratio of 8:1. The solution was then mechanically stirred at 50 °C for 30 min for further mixing. The homogenized viscous mixture was then cast onto a clean glass plate using a spatula, and most of the acetone solvent was evaporated at room temperature to obtain the passivation film. Finally, the resulting film was dried in a vacuum drying oven at 80 °C for 24 h to remove residual free solvent.

[0087] The prepared passivation film (PVDF-HFP@10min) was vertically applied to the surface of lithium metal at 80°C on a rolling mill. The passivation reaction time was 10min, and hot rolling was performed to maintain the passivation film and lithium metal in close adhesion. After the reaction was completed, the passivation film was separated to obtain lithium metal (PVDF-HFP@10min-Li) with passivated interface.

[0088] We also used the lithium-containing metal anode modified by this invention in a battery and tested its electrical performance. Verification results analysis:

[0089] Table 1. Rate performance of lithium-containing metal anodes after treatment with CuF2-PVDF-HFP passivation films (Φ = 0.5, 1, 3) at Φ wt%.

[0090]

[0091] Table 2 Rate performance of lithium-containing metal anodes after different passivation times (t = 5, 10, 20, 30 min)

[0092]

[0093] Table 3. Element content of lithium surface after different passivation films.

[0094]

[0095] Table 4 Rate performance of LiCoO2 all-solid-state lithium metal batteries under different passivation methods

[0096]

[0097] Table 5 Cycle performance of LiCoO2 all-solid-state lithium metal batteries

[0098]

[0099]

[0100] Table 6 Electrical performance test results of embodiments of the present invention

[0101]

[0102] We successfully modified a lithium-containing metal anode using the preparation method of this invention, thereby obtaining a method that promotes in-situ chemical reactions in the lithium-containing metal anode through the preparation of a passivation film, thus modifying the anode. Specifically, we reduced the crystallinity of PVDF-HFP by using metal fluoride in a mixed solution, thereby accelerating the reaction time between PVDF-HFP and lithium metal and significantly reducing energy consumption. Furthermore, the metal fluoride can further regulate the intensity of the α and β phases in PVDF-HFP, ensuring that the α phase is the dominant phase, which is beneficial for improving the ion transport capacity of the lithium-containing metal anode. Additionally, the metal fluoride decomposes to generate metal, which is uniformly distributed on the surface of the lithium anode, forming a lithiophilic structure with the lithium-containing metal anode. Simultaneously, more LiF is formed. The LiF and the lithiophilic structure endow the lithium-containing metal anode with high coulombic efficiency and dendrite suppression ability, achieving effective protection of the lithium-containing metal anode. Therefore, the method of this invention prepares a lithium-containing metal anode with higher interfacial energy and the ability to suppress lithium dendrite growth.

[0103] We will further elaborate on the concept of this invention through the following content, and further optimize the solution of this invention by designing the conditions in the method, in order to obtain better method conditions. In this invention, lithium anode is selected as an example to further optimize the solution of this invention.

[0104] In this project, we designed a solvent-free and highly efficient surface passivation method—solid-phase passivation (SPP). Benefiting from the reactivity between lithium metal and the passivation film, the lithium surface composition can be effectively adjusted, thereby suppressing dendrite growth. In the SPP method, the passivation film is pre-prepared independently on a glass substrate (e.g., ...). Figure 1 a). Then, the prepared passivation film is applied to the lithium metal surface, and a temperature of 80°C and vertical pressure are used to ensure close contact and interaction between the passivating agent molecules and the lithium metal surface (e.g., ...). Figure 1 (b) Under hot-pressing, passivating agent molecules undergo a solid-solid bonding reaction with lithium atoms. After a specific processing time, the passivation film substrate detaches, achieving effective passivation of the lithium metal surface. This invention improves upon traditional methods for preparing interface modification layers using raw material reagents. Traditional methods may result in poor uniformity of the obtained interface layer, leading to unsatisfactory final interface layer performance. In contrast, this invention promotes in-situ chemical reactions on the lithium metal surface through the passivation film, thereby adjusting the composition of the lithium surface and obtaining a high-interface-energy lithium anode.

[0105] In the method of this invention, the selection of the passivating agent for preparing the passivation film is crucial in the SPP method, and it typically needs to have a strong interaction with lithium metal. The poly(vinylidene fluoride-copoly-hexafluoropropylene) (PVDF-HFP) used in this invention is a widely used polymer. Due to its high density of polarizable fluorinated groups, it can induce a "LiF-rich" interfacial layer, which is beneficial for improving the mechanical strength and electrochemical stability of the interfacial layer. Based on this, CuF2 is used as a filler to prepare the CuF2-PVDF-HFP film. During the passivation reaction, CuF2 near the Li side can form a LiF-rich intermediate layer in situ (CuF2 + 2Li → 2LiF + Cu). This not only induces uniform Li deposition and inhibits dendrite formation, but also effectively improves the bonding ability of PVDF-HFP with the Li anode. This substitution reaction significantly improves the bonding strength and greatly shortens the passivation time.

[0106] We further investigated how the passivation film promotes in-situ chemical transformation of lithium metal. Based on the phase transformation method and natural evaporation method, we added different concentrations of CuF2 to PVDF-HFP to prepare two polymer passivation films: PVDF-HFP and CuF2-PVDF-HFP. X-ray diffraction (XRD) was used to characterize the crystal phases of the two passivating agents. Figure 2 XRD patterns of passivation films of CuF2, PVDF-HFP, and PVDF-HFP with different Φwt% CuF2 (Φ=0.5, 1, 3). Figure 2 In the diffraction pattern of CuF2, characteristic diffraction peaks appear at 2θ = 27.52°, 31.55°, and 33.56°, which matches the PDF card of 01-0771-1131, confirming it as a single-phase material. The XRD pattern of PVDF-HFP consists of crystalline peaks with broad background humps, indicating its semi-crystalline nature, and it can be found that PVDF-HFP has two crystalline phases, α and β. A large peak observed at 2θ = 19.7° corresponds to (100) and (200), confirming the formation of the β phase in PVDF-HFP. Small intensity peaks observed at 2θ = 18.2°, 26.7°, and 38.4° correspond to (100), (110), and (021), representing the α phase in PVDF-HFP. The results are consistent with those in the prior art, Badatya S. [1] The crystal structure of the original PVDF-HFP thin film was studied by X-ray diffraction. A large peak was observed at 2θ = 20.7°, corresponding to (100) and (200), confirming the formation of the β phase in PVDF-HFP; peaks at 2θ = 18.2°, 28.6°, and 38.0°, corresponding to (100), (110), and (021), confirmed the formation of the α phase in PVDF-HFP. [2]In pure PVDF-HFP, a diffraction peak was observed at 2θ = 18.3° and 26.7°, corresponding to (020) and (021), confirming that it is the α phase in PVDF-HFP. A diffraction peak was observed at 20.12°, corresponding to (110) and (200), confirming the formation of the β phase in PVDF-HFP. We also found that the intensity of the α phase in PVDF-HFP increased and the intensity of the β phase decreased in the XRD pattern of the embodiments of the present invention. We believe that CuF2 can regulate the intensity of the α and β phases in PVDF-HFP, promoting the conversion of more β phase into α phase. The α phase is beneficial for improving the ion transport capability of the lithium anode. Furthermore, Figure 2 The characteristic peaks of the polymer PVDF-HFP and the filler CuF2 are clearly visible in 3wt% CuF2-PVDF-HFP, indicating the presence of CuF2 in PVDF-HFP. Conversely, the peaks of CuF2 are not obvious at other concentrations, which is similar to the actual image of the passivation film. Figure 2 The passivation film of PVDF-HFP without CuF2 filler is white. After the introduction of CuF2, the color of the passivation film changes, gradually becoming blue-green with increasing concentration; a distinct blue-green color is observed in 3wt% CuF2-PVDF-HFP. With increasing CuF2 concentration, the position, intensity, and width of the diffraction peaks gradually change. Figure 2 XRD analysis clearly shows that, compared with the pure PVDF-HFP film, the CuF2-PVDF-HFP film reduces the β phase in the composite film and sharply increases the intensity of the α phase. Notably, the β phase in the passivation film has high polarity and continuously reacts with increasing CuF2 concentration. Therefore, the addition of CuF2 alters the crystallinity of PVDF-HFP, and the effect becomes more pronounced with increasing CuF2 concentration. This indicates that CuF2 may initiate the deHF removal reaction of PVDF-HFP, and this reaction affects CuF2, causing changes in the peak position of CuF2. This also verifies that the position, intensity, and width of the diffraction peaks gradually change with increasing CuF2 concentration in the XRD pattern. Therefore, in this invention, CuF2 enhances the ion transport capability of the lithium anode by adjusting the intensity of the α and β phases in PVDF-HFP.

[0107] Based on this, we further investigated how to control the conditions during the preparation process to further optimize the scheme of this invention. We first studied the effect of passivation films obtained with different amounts of CuF2 on the modification of the lithium anode. The decomposition of CuF2 generates Cu, which is uniformly distributed on the surface of the lithium anode, forming a Li-Cu microstructure. On the other hand, it forms more LiF. The LiF and Li-Cu microstructure endow the lithium metal anode with high coulombic efficiency and dendrite suppression ability, achieving effective protection of the lithium metal anode. Therefore, the amount of CuF2 added is particularly important for anode modification. When the concentration of CuF2 is low, it is insufficient to construct a good lithium deposition interface; conversely, a higher concentration of CuF2 will generate more LiF, and the ultra-low ionic conductivity of LiF also increases the overpotential of the battery. It is evident that selecting an appropriate concentration of CuF2 can not only achieve uniform lithium deposition and reduce lithium dendrites, but also improve the electrical performance of the lithium anode.

[0108] The electrochemical performance of lithium anodes treated with Φwt% CuF2-PVDF-HFP passivation films (Φ=0.5, 1, 3) was investigated using LiCoO2(LCO) / LPSC / Li all-solid-state lithium metal batteries. Figure 4 As shown in (ac). Compared with untreated lithium foil, the solid-phase passivated lithium anode exhibits better rate performance in the battery, as shown in Table 1. Specifically, the lithium foil passivated with 1wt% CuF2-PVDF-HFP exhibits better rate performance, with higher discharge capacity and higher first-cycle coulombic efficiency. Figure 4 (b) shows the discharge capacity of different lithium sheets at 2C. The discharge capacity initially increases and then decreases with increasing CuF2 concentration. When the CuF2 mass ratio in the passivation film is 0.5wt%, 1wt%, and 3wt%, the discharge capacity is 93.55 mAh g. -1 102.47mAh g -1 and 86.26mAh g -1 We believe this is related to the mixed ionic / electronic conductor interface formed by the in-situ reaction of CuF2 and Li. The in-situ generated Li-Cu microstructure provides suitable lithium deposition sites, which can homogenize lithium deposition. Cu atoms act as diasteres to decompose the long-range ordered pattern of the passivation interface, thus exhibiting higher capacity during cycling. When the concentration of CuF2 is low, it is insufficient to construct a good lithium deposition interface. Conversely, higher concentrations of CuF2 produce more LiF, and the ultra-low ionic conductivity of LiF also increases the overpotential of the battery. We can... Figure 4As verified in (d), CuF2 can affect the electrical performance of lithium anode. We also found that when the concentration of CuF2 is higher, the cycle performance of the battery at 5C and 8C will decrease to a certain extent. We believe that this may be because the formation of dense nano-copper structure hinders the normal deposition of lithium ions. Therefore, after passivation with 3wt% CuF2-PVDF-HFP, the lithium sheet exhibits poor rate performance. Figure 4 (c) The first-cycle coulombic efficiency of different lithium sheets in LCO / Li batteries is shown. As expected, the first-cycle coulombic efficiency initially increases and then decreases with increasing CuF2 content in the passivation film. The coulombic efficiencies are 91.03%, 92.03%, and 90.02% when the CuF2 mass ratio is 0.5 wt%, 1 wt%, and 3 wt%, respectively. The passivated lithium metal anode of this invention achieves a high coulombic efficiency, far exceeding that of the untreated lithium metal anode, which has a coulombic efficiency of 88.83%. This demonstrates that the LiF-rich Cu multifunctional passivation layer formed on the lithium anode surface by the method of this invention can reduce side reactions between the exposed lithium metal and the solid electrolyte, thereby promoting high coulombic efficiency in the battery. We further prefer a CuF2 to low-boiling-point organic solvent ratio of 0.8 wt%–1.2 wt%.

[0109] Based on this, we selected a mass ratio of CuF2 to low-boiling-point organic solvent of 1 wt% to further study the optimization of passivation time on lithium anode modification. Passivation time can control the degree of modification of lithium anode by passivation film and is equally important in the preparation process. Figure 4 (d) shows the rate performance based on the solid-bonding time between the passivation film and lithium metal. When the passivation time is 5 min and 10 min, the battery can achieve stable rate cycling. The lithium metal after 10 min passivation exhibits higher rate performance, which is related to the formation of a uniform passivation interface layer on the lithium anode. When the passivation time is increased to 20 min or 30 min, the battery cannot achieve normal rate cycling and exhibits capacity decay due to greater polarization. We believe this may be due to the relatively dense nano-Cu layer and the low ionic conductivity of LiF at the interface. The capacity values ​​at different rates are shown in Table 2. Figure 4 (e) shows the discharge capacity of different lithium sheets at 2C. With the increase of passivation time, the discharge capacity first increases and then decreases. The discharge capacity is 98.12 mAh g at passivation times of 5 min, 10 min, 20 min and 30 min. -1 102.47mAh g -1 56.72mAh g -1 and 47.00mAh g -1 . Figure 4(f) shows the first-cycle coulombic efficiency of different lithium sheets in LCO / Li batteries. The coulombic efficiencies were 91.48%, 92.03%, 90.96%, and 90.72% at passivation times of 5 min, 10 min, 20 min, and 30 min, respectively. It is evident that the passivation time affects the passivation interface formed on the surface of the lithium anode, thus influencing the electrical performance of the lithium anode. We further optimized the passivation time of the passivation film to be 8 min–12 min.

[0110] We also conducted compositional analysis on the lithium anode obtained by this invention, using X-ray photoelectron spectroscopy (XPS) to detect the composition of the passivation interface layer on the surface of the lithium anode, such as... Figure 5 As shown, high-resolution XPS spectra were obtained for lithium sheets reacting with a CuF2-PVDF-HFP passivation film for 10 min (Example 2) and for lithium sheets reacting with a PVDF-HFP passivation film for 30 min (Comparative Example 2). The increased passivation time in the latter was due to the lower F content in the passivation film. In the lithium surface spectra after passivation with CuF2-PVDF-HFP@10 min (Example 2) and PVDF-HFP@30 min (Comparative Example 2), the peak at 284.8 eV, associated with imprecise carbon, was used to calibrate all spectra. The formation of lithium oxide is an unavoidable oxidation of the lithium sheet during the transfer process.

[0111] Specifically, after passivation with CuF2-PVDF-HFP@10min, the lithium surface consists of LiF, Li2O (lithium oxide), and Cu. After passivation with PVDF-HFP@30min, the lithium surface consists of LiF, Li2O, and Li2CO3. A LiF peak centered at 685.5 eV was detected on the lithium surface after both CuF2-PVDF-HFP@10min and PVDF-HFP@30min passivation, but their relative contents differed. The lithium surface after CuF2-PVDF-HFP@10min passivation showed more LiF, attributed to the decomposition of CuF2, with a relative content of 1.86%, significantly higher than that after PVDF-HFP@30min passivation. This also inhibited lithium oxidation to some extent (see Table 3). It is evident that CuF2 is beneficial for increasing LiF content while shortening passivation time. Furthermore, the lithium surface after CuF2-PVDF-HFP@10min passivation exhibits uniformly distributed nano-Cu, achieving a lithiophilic structure. The LiF passivation layer and the Li-Cu lithiophilic structure endow the lithium metal anode with high coulombic efficiency and dendrite suppression ability, thus achieving effective protection of the lithium metal anode.

[0112] The electrochemical performance of Li / Li symmetric batteries was studied using LPSC electrolyte under different test conditions to further explain the suppression effect of lithium dendrites on lithium sheets under solid-state passivation in all-solid-state batteries. Figure 6(be) shows the critical current density (CCD) test results at room temperature, evaluating the performance of untreated lithium anodes, PVDF-HFP, and CuF2-PVDF-HFP passivated lithium anodes in the battery. The maximum current density before voltage drop due to short circuit caused by lithium dendrite growth is shown. The current density was increased incrementally during constant current testing, with the deposition / stripping time fixed at 0.5 h. The untreated lithium anode was used in a lithium symmetric battery, achieving a current density of 1.5 mA cm⁻¹. -2 Premature short circuits occurred at certain current densities. Furthermore, the critical current densities of the lithium-ion wafer after PVDF-HFP passivation for 10 min were 1.7 mA cm⁻¹. -2 Furthermore, it still exhibits relatively regular voltage behavior after a soft short circuit. This indicates that fluorides possess high interfacial energy at the lithium / electrolyte interface, effectively suppressing dendrite formation. In addition, based on the PVDF-HFP passivation film, a relatively long passivation time is required to achieve good passivation performance. The critical current densities of the lithium sheets passivated with CuF2-PVDF-HFP@10min and CuF2-PVDF-HFP@30min were 3.7 mA cm⁻¹, respectively. -2 and 2.7mA cm -2 Compared to PVDF-HFP-based passivation films, CuF2-PVDF-HFP achieves a shorter passivation time and a higher critical current density. We believe this is related to the increased number of lithium-phobic LiF interfaces and the Li-Cu electronic conductivity structure generated in situ by CuF2. After 30 minutes of passivation, the CuF2-PVDF-HFP passivation film produces a dense nano-Cu structure on the lithium surface, which to some extent hinders lithium-ion deposition, resulting in more irregular voltage behavior. Therefore, introducing CuF2 into a PVDF-HFP-based passivation film can shorten the passivation time, consume less energy, and the constructed LiF-rich Cu lithium-phobic passivation layer can better suppress dendrite formation.

[0113] Inspired by the significant improvement in CCD performance, a comparative evaluation of the constant current cycling stability of Li / LPSC / Li symmetric batteries with LPSC solid electrolyte was conducted. Figure 6 a. Lithium-ion symmetric cells with untreated lithium anodes at room temperature and lithium anodes passivated by CuF2-PVDF-HFP@10 min were compared at 0.5 mA cm⁻¹. -2 Its long-cycle stability. (By...) Figure 6(a) It can be seen that the initial overpotential of the untreated lithium anode is about 9 mV, which gradually increases with cycling, exhibiting uneven lithium deposition. Furthermore, a short circuit was observed after approximately 200 h of cycling. In contrast, the lithium anode passivated with CuF2-PVDF-HFP@10 min can stably maintain stripping and deposition, with cycling times exceeding 1000 h. The CuF2-PVDF-HFP@10 min passivated lithium anode showed an overpotential of approximately 11 mV, which did not increase significantly with cycling. The PVDF-HFP@10 min passivated lithium anode showed a slight increase in polarization after 300 h, but still maintained stable cycling. We believe that the solid-phase passivation interface layer has high structural and compositional uniformity, and LiF has a high interface energy to Li, which can effectively suppress the growth of Li dendrites. The introduced electronically conductive Cu can reduce the Li plating overpotential, resulting in excellent long-term stability of the battery.

[0114] Based on this, in order to further verify the differences in electrical performance between the lithium anode, untreated lithium, and comparative examples of the present invention, we further selected Example 2 (1wt% CuF2, passivation time of 10 min) in the preferred system of the present invention and Example 6 (1wt% CuF2, passivation time of 30 min) in the non-preferred system of the present invention as examples for further comparative study. We constructed an all-solid-state lithium metal battery using a lithium anode, LPSC electrolyte, and LCO cathode.

[0115] Rate performance, as a key metric, demonstrates the potential to achieve higher power densities. Figure 7 The rate performance of all-solid-state lithium metal batteries after passivation of lithium sheets is shown for untreated lithium sheets (Comparative Example 1), PVDF-HFP@10min (Comparative Example 3), and CuF2-PVDF-HFP@10min (Example 2) and CuF2-PVDF-HFP@30min (Example 6) with CuF2 introduced. The current rate was gradually increased from 0.2C (0.1 mA cm⁻¹) to 0.5C, 1C, 2C, 5C, 8C, and finally back to 0.5C. All batteries were tested between 2.8V and 4.2V, and the detailed values ​​are shown in Table 4. The solid-phase passivated lithium sheets of this invention, when applied to batteries, all exhibited gradually optimized rate performance, especially CuF2-PVDF-HFP@10min-Li (Example 2), which retained 32.08% of its capacity at 8C. For the best-performing CuF2-PVDF-HFP@10min-Li, even with a low charge / discharge rate of 0.2C in the initial cycling phase, the battery exhibits minimal polarization and a reversible specific capacity of 125.31 mAh g⁻¹. -lWhen the rate of change is increased sequentially to 0.5C, 1C, 2C, 5C, and 8C, the reversible specific capacity released by the battery decreases to 119.16 mAh g, respectively. -l 114.06mAh g -l 102.47mAh g -l 92.36mAh g -l and 80.77mAh g -l After 5 charge-discharge cycles at each current density, the reversible specific capacity of the CuF2-PVDF-HFP@10min-Li (Example 2) was reduced to 0.5C, and the reversible specific capacity of the battery recovered to 117.38 mAh g. -1 Compared to the discharge specific capacity at 0.5C, the capacity retention rate reaches 98.50%. This demonstrates that under high-rate conditions, the lithium anode of this invention undergoes almost no irreversible reactions during battery charging and discharging, resulting in excellent battery performance. It also indicates that the in-situ protective layer formed by this passivation method can effectively suppress lithium dendrite growth, achieving uniform lithium metal deposition and exhibiting strong high-current tolerance. In contrast, the PVDF-HFP@10min-Li (Comparative Example 3) passivation film, with its shorter passivation time, forms less LiF protective layer, failing to prevent side reactions between lithium metal and the electrolyte, resulting in greater polarization at high currents and lower battery capacity. Therefore, the preparation method of this invention, with its in-situ chemical conversion on the surface of the lithium anode, can improve the electrical performance of the lithium anode.

[0116] exist Figure 8 In our study, we constructed an all-solid-state lithium metal battery using an LCO cathode / lithium anode and an LPSC electrolyte, and further investigated the cycle performance and corresponding coulombic efficiency of the lithium metal anode under solid-state passivation. Figure 8 The results show that CuF2-PVDF-HFP@10min-Li at 1C (lithium anode current density of 1 mA cm⁻¹) -2 At 55°C, it can maintain 95.75 mAh g during 300 cycles. -1 The treated lithium metal exhibits a high discharge capacity and a coulombic efficiency of 99.96%, with a capacity retention of up to 82.19%. In contrast, untreated lithium metal exhibits a significantly lower discharge capacity, with a discharge capacity of only 39.26 mAh g⁻¹ after 300 cycles. -1The capacity retention rate was 50.09%. We believe this is because untreated lithium metal reacts with LPSC, and the side reactions intensify with each cycle. This not only consumes lithium metal but also increases polarization, severely impacting battery performance. Similar to untreated lithium metal, the weaker LiF protective layer of PVDF-HFP@10min-Li cannot completely prevent side reactions, resulting in low capacity; after 300 cycles, its discharge capacity was only 44.92 mAh g⁻¹. -1 The capacity retention rate was 50.23%. In contrast, CuF2-PVDF-HFP@30min-Li (Example 6) had a dense interface layer that affected the normal deposition of lithium ions. After a long period of cycling, lithium ions accumulated on the interface layer, which may cause short circuits. Figure 8 (bc) and Table 5 show the charge-discharge curves and their specific discharge capacities of four different lithium anodes after 50, 150, and 300 cycles. The discharge capacities of CuF2-PVDF-HFP@10min-Li in the all-solid-state lithium metal battery at 50, 150, and 300 cycles are 105.10 mAh g⁻¹. -1 97.59mAh g -1 and 95.75mAh g -1 The discharge capacities of untreated lithium metal in an all-solid-state lithium metal battery at 50, 150, and 300 cycles were 59.19 mAh g. -1 46.55mAh g -1 and 39.26mAh g -1 Therefore, the solid-phase passivation prepared by this invention provides the lithium anode with more stable cycling, which is expected to enable its application in lithium metal batteries.

[0117] We also compared the differences in electrical performance of different metal fluorides when used in batteries, and the results are shown in Table 6. Table 6 uses electrolytes to study Li / Li symmetric batteries. First, the lithium anode of the present invention can be used in different battery systems, and we can see from Table 6 that Example 2 is significantly better than Examples 7-10. It can be seen that the lithium anode has better electrical performance when the metal fluoride is CuF2, and we further prefer CuF2 as the metal fluoride.

[0118] In summary, we propose a simple, efficient, and scalable method to achieve uniform lithium-ion conduction at the lithium / solid electrolyte interface by using passivation films with different compositions, while simultaneously addressing the short-circuit problem caused by lithium dendrite formation and propagation. Our research shows that by introducing CuF2 into the PVDF-HFP passivation film and enabling its reaction with metallic lithium, a LiF-rich Li-Cu microstructure passivation layer can be effectively formed, thereby reducing the interfacial resistance and exhibiting a record-breaking CCD of 3.7 mA cm⁻¹ at room temperature. -2 The introduction of CuF2 shortens the reaction time between the PVDF-HFP-based passivation film and lithium metal, consuming less energy. Simultaneously, the electronically conductive Cu can reduce the overpotential of Li plating, achieving more stable cycling. Thanks to this solid-phase passivation layer, the Li / LPSC / Li symmetric cell achieves a cycling speed of 0.5 mA cm⁻¹. -2 Excellent cycle stability exceeding 1000 hours can be achieved at high current densities (1C, 1.0 mA cm⁻¹). The all-solid-state LCO / Li battery achieves this at high current densities. -2 The battery exhibits excellent electrochemical performance with long-term durability (>300 cycles) and a capacity retention of 82.19%. This invention provides a new approach for the rational design of artificial passivation layers with controllable composition on lithium metal anodes, which can be implemented in conjunction with other strategies, greatly promoting the large-scale production of lithium metal batteries.

[0119] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0120] References:

[0121] [1] Badatya S, Kumar A, Sharma C, et al. Transparent flexible graphenequantum dot-(PVDF-HFP) piezoelectric nanogenerator[J]. Materials Letters, 2021,290.

[0122] [2]Dash S,Mohanty H S,Ravikant,et al.Ferroelectric ceramic dispersionto enhance the beta phase of polymer for improving dielectric andferroelectric properties of the composites[J].Polymer Bulletin,2021,78(9):5317-5336。

Claims

1. A method for modifying a lithium-containing metal anode, characterized in that, The modification method includes: S1: Add metal fluoride and PVDF-HFP to a low-boiling-point organic solvent to obtain a homogeneous mixed solution. The main phase of PVDF-HFP in the mixed solution is the α phase. S2: Evaporate the low-boiling-point organic solvent in the mixed solution to obtain a passivation film; S3: Cover the surface of the lithium-containing metal anode with a passivation film, perform heat treatment, and separate the passivation film to obtain a lithium-containing metal anode with a passivation interface; In S1, the mass ratio of metal fluoride to low-boiling-point organic solvent is 0.5%-3%; the concentration of PVDF-HFP in the mixed solution is 0.08 g / mL-1.2 g / mL. The heat treatment in S3 is hot rolling, and the pressure of hot rolling is 20kPa-30kPa; The heat treatment temperature in S3 is 70℃-90℃; the heat treatment time in S3 is 1min-30min.

2. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The metal fluoride is used to regulate the intensity of the α and β phases in PVDF-HFP, and to promote the conversion of the β phase into the α phase in PVDF-HFP.

3. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The mass ratio of metal fluoride to low-boiling-point organic solvent in S1 is 0.8%-1.2%.

4. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The heat treatment temperature in S3 is 70℃-90℃; the heat treatment time in S3 is 8min-12min.

5. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The low-boiling-point organic solvent in the S2 evaporation mixture is carried out in a vacuum drying oven at a temperature of 75℃-85℃.

6. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, Deionized water needs to be added to the homogeneous mixed solution in S1. The volume ratio of the mixed solution to the deionized water is 8:1, and the solution is mixed evenly.

7. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The metal fluoride includes one or more of CoF3, MnF3, FeF3, VF3, VOF3, TiF3, BiF3, NiF2, FeF2, CuF2, CuF, SnF2, and AgF.

8. The method for modifying a lithium-containing metal anode according to claim 1, characterized in that, The metal fluoride includes CuF2.

9. A battery, characterized in that, The battery comprises a lithium-containing metal anode obtained by the modification method according to any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The battery includes a sulfide solid electrolyte battery.

Images