Composite lithium metal negative electrode material and preparation method thereof, negative electrode plate and solid-state battery

Abstract

The invention relates to the technical field of new energy, in particular to a composite lithium metal negative electrode material, a preparation method thereof, a negative electrode piece and a solid-state battery. The composite lithium metal negative electrode material comprises a lithium metal layer, a transition layer, a magnesium iodide functional layer and a graphite fluoride functional layer, the transition layer is located between the lithium metal layer and the magnesium iodide functional layer, the graphite fluoride functional layer is located on the side, away from the transition layer, of the magnesium iodide functional layer, and the transition layer comprises Li-Mg alloy. According to the composite lithium metal negative electrode material disclosed by the invention, the problem of interface contact between a solid electrolyte and an SEI (Solid Electrolyte Interphase) membrane can be dynamically relieved while the growth of lithium dendrites is inhibited, and the interface contact failure and rapid performance attenuation of an all-solid-state battery under zero pressure or low external pressure are improved; according to the composite lithium metal negative electrode material, the electrochemical performance of a solid-state battery can be remarkably improved on the whole, and the composite lithium metal negative electrode material also has good air stability and relatively low production cost.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to composite lithium metal anode materials and their preparation methods, anode sheets and solid-state batteries. Background Technology

[0002] In solid-state battery systems, uneven lithium deposition during long-term cycling leads to porosity at the solid-solid interface, resulting in higher interfacial impedance and polarization. Artificial SEI passivation layers effectively suppress lithium dendrite growth, reduce lithium-ion nucleation overpotential, and promote uniform lithium-ion nucleation, thus significantly improving ionic conductivity. However, traditional artificial passivation layers offer limited improvement to the solid-solid interface. Furthermore, the poor stability of lithium metal in air limits its practical application, increasing costs and impacting the performance of lithium metal anodes. Summary of the Invention

[0003] Based on this, the first aspect of this application provides a composite lithium metal anode material to solve the solid-state interface problem and improve the instability of lithium metal, the technical solution of which is as follows:

[0004] A composite lithium metal anode material includes a lithium metal layer, a transition layer, a magnesium iodide functional layer, and a fluorinated graphite functional layer. The transition layer is located between the lithium metal layer and the magnesium iodide functional layer, and the fluorinated graphite functional layer is located on the side of the magnesium iodide functional layer away from the transition layer. The transition layer comprises a Li-Mg alloy.

[0005] The second aspect of this application provides a method for preparing a composite lithium metal anode material, the technical solution of which is as follows:

[0006] A method for preparing a composite lithium metal anode material includes the following steps:

[0007] Magnesium iodide and an organic solvent are mixed to obtain a magnesium iodide solution;

[0008] The magnesium iodide solution is coated onto a lithium metal substrate and dried to form a lithium metal layer, a transition layer, and a magnesium iodide functional layer. The transition layer, which is located between the lithium metal layer and the magnesium iodide functional layer, comprises a Li-Mg alloy.

[0009] Fluorinated graphite is deposited on the side of the magnesium iodide functional layer away from the transition layer by magnetron sputtering, using fluorinated graphite as the target material, to form a fluorinated graphite functional layer.

[0010] A third aspect of this application provides a negative electrode sheet, which includes a current collector and a composite lithium metal negative electrode material located on the current collector. The composite lithium metal negative electrode material is prepared as described above, or by the preparation method of the composite lithium metal negative electrode material described above. The current collector is located on the side of the lithium metal layer away from the magnesium iodide functional layer.

[0011] A fourth aspect of this application provides a solid-state battery comprising a negative electrode, a positive electrode, and a solid electrolyte as described above, wherein the solid electrolyte is located between the negative electrode and the positive electrode.

[0012] Compared with traditional solutions, this application has the following advantages:

[0013] This application incorporates a magnesium iodide (MgI2) functional layer on a lithium metal layer, with a transition layer between the lithium metal layer and the MgI2 functional layer, and a fluorinated graphite (GF) functional layer on top of the MgI2 functional layer. The transition layer comprises a Li-Mg alloy, which dynamically fills the pores or voids caused by rapid lithium consumption and insufficient lithium diffusion at the battery cycle interface. The Li-Mg alloy is formed through a redox reaction between MgI2 and lithium metal; specifically, MgI2 reacts with lithium metal to generate Mg, and Mg and lithium form a solid solution, the Li-Mg alloy. Simultaneously, the fluorinated graphite functional layer acts as a barrier, isolating and blocking moisture and carbon dioxide (CO2) in the air from corroding the lithium metal and the hygroscopic MgI2. This allows for longer air stability in a dry environment, saving costs while improving the performance of the lithium anode. Furthermore, during battery cycling, some lithium ions from the positive electrode migrate to the GF surface and react with fluoride ions on the surface to form LiF. LiF and GF construct a more efficient lithium diffusion channel, providing abundant lithiophilic sites, which promotes the uniform nucleation of subsequent lithium ions to the lithium substrate via electromigration and diffusion, and inhibits the growth of lithium dendrites. Simultaneously, iodine ions (I₂) in MgI₂... - The migration that occurs under the influence of an electric field allows the metal anode material to pass through the pores between GF molecules and migrate to the GF surface, and further to the SEI interface layer between the GF and the solid electrolyte. This dynamically alleviates the interfacial contact problem between the solid electrolyte and the SEI film, improving the interfacial contact failure and rapid performance degradation of all-solid-state batteries under zero pressure or low external pressure. In summary, the composite lithium metal anode material of this application can significantly improve the overall electrochemical performance of solid-state batteries. Detailed Implementation

[0014] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0016] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0017] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0018] In this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0019] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0020] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0021] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0022] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0023] The first aspect of this application provides a composite lithium metal anode material. In one embodiment, the composite lithium metal anode material includes a lithium metal layer, a transition layer, a magnesium iodide functional layer, and a fluorinated graphite functional layer. The transition layer is located between the lithium metal layer and the magnesium iodide functional layer, and the fluorinated graphite functional layer is located on the side of the magnesium iodide functional layer away from the transition layer. The transition layer includes a Li-Mg alloy.

[0024] This embodiment features a magnesium iodide (MgI2) functional layer on a lithium metal layer, with a transition layer between the lithium metal layer and the MgI2 functional layer, and a fluorinated graphite (GF) functional layer on top of the MgI2 functional layer. The transition layer comprises a Li-Mg alloy, which dynamically fills the pores or voids caused by rapid lithium consumption and insufficient lithium diffusion at the battery cycle interface. The Li-Mg alloy is formed through a redox reaction between MgI2 and lithium metal; specifically, MgI2 reacts with lithium metal to generate Mg, and Mg and lithium form a solid solution of the Li-Mg alloy. Simultaneously, the fluorinated graphite functional layer acts as a barrier, isolating and blocking moisture and carbon dioxide (CO2) in the air from corroding the lithium metal and the hygroscopic MgI2. This allows for longer air stability in a dry environment, saving costs while improving the performance of the lithium anode. Furthermore, during battery cycling, some lithium ions from the positive electrode migrate to the GF surface and react with fluoride ions on the surface to form LiF. LiF and GF construct a more efficient lithium diffusion channel, providing abundant lithiophilic sites, which promotes the uniform nucleation of subsequent lithium ions to the lithium substrate via electromigration and diffusion, and inhibits the growth of lithium dendrites. Simultaneously, iodine ions (I₂) in MgI₂... - The migration that occurs under the influence of an electric field allows the metal anode material to pass through the pores between GF molecules and migrate to the GF surface, and further to the SEI interface layer between the GF and the solid electrolyte. This dynamically alleviates the interfacial contact problem between the solid electrolyte and the SEI film, improving the interfacial contact failure and rapid performance degradation of all-solid-state batteries under zero pressure or low external pressure. In summary, the composite lithium metal anode material of this embodiment can significantly improve the overall electrochemical performance of solid-state batteries.

[0025] The lithium metal layer can be lithium foil, lithium sheet, or lithium strip.

[0026] In addition to forming a Li-Mg alloy, the redox reaction between MgI2 and lithium metal also produces lithium iodide (LiI). In this embodiment, the transition layer also includes LiI.

[0027] The loading of magnesium iodide on the lithium metal layer is closely related to the cycle capacity retention. When the magnesium iodide loading is low, the generated Li-Mg alloy phase is insufficient to fill the porosity produced during cycling, and I⁻ migration is insufficient, leading to accelerated interfacial contact failure and exacerbated capacity decay. Optionally, the amount of magnesium iodide functional layer used satisfies the following requirement: per 1 cm2 The lithium metal layer is loaded with 0.01 mg to 0.1 mg of magnesium iodide. Experiments have verified that when the magnesium iodide loading m on the lithium metal layer is 0.02 mg / cm³, the optimal loading is achieved. 2 At that time, the capacity retention rate η after 100 cycles was 70.5%, and η increased rapidly with increasing m. When m ≥ 0.04 mg / cm², η was above 75%, and when m ≥ 0.05 mg / cm², η was above 75%. 2 Subsequently, the amount of Li-Mg alloy phase formation and I⁻ migration meet the cycling requirements, and η tends to stabilize, with η ≥ 80%, or even η ≥ 90%. Preferably, m ≥ 0.04 mg / cm². More preferably, m ≥ 0.05 mg / cm². 2 .

[0028] The thickness of the MgI2 functional layer and the GF functional layer are closely related to the cycle capacity retention and the container stability of the negative electrode. The average thickness of the MgI2 functional layer is d1, and the average thickness of the GF functional layer is d2. If d1 is too small, the amount of Li-Mg alloy phase formed is insufficient, resulting in poor pore filling; if d1 is too large, the ion transport path is prolonged, leading to an increase in overpotential and a decrease in coulombic efficiency. Optionally, the average thickness d1 of the magnesium iodide functional layer is 30 nm to 300 nm, preferably 50 nm to 250 nm. If d2 is too small, the barrier properties and LiF formation are insufficient, and the thickness is insufficient, resulting in inadequate barrier properties against water and CO2 and an inability to form a relatively stable ion channel and LiF interface. If d2 is too large, the excessive thickness of the GF layer leads to increased ion transport resistance and an increased proportion of its own resistance, resulting in an increase in the total interfacial impedance. Optionally, the average thickness d2 of the fluorinated graphite functional layer is 30 nm to 300 nm, preferably 50 nm to 250 nm.

[0029] To maintain an imbalance in the synergistic effect between the GF layer and the MgI2 inner layer, the average thickness ratio (d1 / d2) of the magnesium iodide functional layer to the fluorinated graphite functional layer can optionally be 1~2. When d1 / d2 = 1~2, the overall performance of the negative electrode is excellent (low interface impedance, high capacity retention, and long air stabilization time). Specifically, when d1 = 150 nm and d2 = 100 nm (d1 / d2 = 1.5), the capacity retention η after 100 cycles is 93%, the air stabilization time is 80 h, and the interface impedance is 50.5 Ω.

[0030] Fluorinated graphite (GF) has a porous structure with fluoride ions distributed on its surface. During battery cycling, some lithium ions from the cathode migrate to the GF surface and react with the fluoride ions to form LiF. LiF and GF construct a more efficient lithium diffusion channel, providing abundant lithiophilic sites. This promotes the uniform nucleation of subsequent lithium ions to the lithium substrate via electromigration and diffusion, inhibiting the growth of lithium dendrites. Simultaneously, iodine ions (I₂) in MgI₂... -The migration that occurs under the action of an electric field can pass through the pores between GF molecules and migrate to the GF surface, and further migrate to the SEI interface layer between the solid electrolyte and the solid electrolyte. This can dynamically alleviate the interface contact problem between the solid electrolyte and the SEI film, and improve the interface contact failure and rapid performance degradation of all-solid-state batteries under zero pressure or low external pressure.

[0031] The composite lithium metal anode material of this embodiment can improve the solid-state interface problem while suppressing lithium dendrite growth, and the composite lithium metal anode material also has good air stability and low production cost.

[0032] A second aspect of this application provides a method for preparing a composite lithium metal anode material. In one embodiment, the method for preparing the composite lithium metal anode material includes the following steps:

[0033] S1. Mix magnesium iodide and organic solvent to obtain magnesium iodide solution.

[0034] Optionally, the organic solvent is selected from at least one of diethyl ether, ethylene glycol dimethyl ether, diethyl carbonate, fluoroethylene carbonate, tetrahydrofuran, acetone, and dimethyl sulfoxide. Optionally, the concentration of magnesium iodide in the magnesium iodide solution is 0.01 mol / L to 0.1 mol / L.

[0035] S2. Apply the magnesium iodide solution onto the lithium metal substrate and dry it to form a lithium metal layer, a transition layer, and a magnesium iodide functional layer, wherein the transition layer is located between the lithium metal layer and the magnesium iodide functional layer and includes a Li-Mg alloy.

[0036] Alternatively, the magnesium iodide solution can be applied by spraying.

[0037] Optionally, the concentration of magnesium iodide in the magnesium iodide solution and the amount of magnesium iodide solution applied can be adjusted to ensure that each cm 2 The lithium metal layer is loaded with 0.01 mg to 0.1 mg of magnesium iodide.

[0038] During the drying process of applying the magnesium iodide solution, MgI2 can undergo a redox reaction with lithium metal in the lithium metal substrate at the interface between the two to generate Mg and LiI. Mg will form a solid solution Li-Mg alloy with lithium. The Li-Mg alloy can dynamically fill the pores or voids caused by rapid lithium consumption and insufficient lithium diffusion at the interface during battery cycling. After the reaction, the remaining unreacted lithium metal constitutes the lithium metal layer, the reaction interface forms a transition layer, and the remaining unreacted MgI2 constitutes the MgI2 functional layer. At this time, the lithium metal layer and the MgI2 functional layer are separated by the transition layer and do not react.

[0039] S3. Using fluorinated graphite as the target material, fluorinated graphite is deposited on the magnesium iodide functional layer by magnetron sputtering to form a fluorinated graphite functional layer.

[0040] Optionally, the amount of magnesium iodide solution used for coating is adjusted so that the average thickness (d1) of the magnesium iodide functional layer is 30 nm to 300 nm. Optionally, the process parameters for depositing the fluorinated graphite are adjusted so that the average thickness (d2) of the fluorinated graphite functional layer is 30 nm to 300 nm. Optionally, the ratio of the average thickness of the magnesium iodide functional layer to the average thickness of the fluorinated graphite functional layer (d1 / d2) is 1 to 2. Wherein, d1 is the average thickness of the MgI2 functional layer after coating and drying, and d2 is the average thickness of the GF functional layer after magnetron sputtering.

[0041] A third aspect of this application provides a negative electrode sheet. In one embodiment, the negative electrode sheet includes a current collector and a composite lithium metal negative electrode material located on the current collector. The composite lithium metal negative electrode material is prepared as described above, or by the preparation method of the composite lithium metal negative electrode material described above. The current collector is located on the side of the lithium metal layer away from the magnesium iodide functional layer.

[0042] Optionally, the current collector is selected from copper foil.

[0043] A fourth aspect of this application provides a solid-state battery. In one embodiment, the solid-state battery includes a negative electrode, a positive electrode, and a solid electrolyte as described above, wherein the solid electrolyte is located between the negative electrode and the positive electrode.

[0044] The negative electrode used in this application is a lithium metal negative electrode modified with magnesium iodide (MgI2) and fluorinated graphite (GF). The fluorinated graphite (GF) used has a porous structure and fluoride ions distributed on its surface. During solid-state battery cycling (during the first formation of the solid-state battery), some lithium ions from the positive electrode migrate to the GF surface and react with fluoride ions on the fluorinated graphite (GF) surface to form LiF. LiF and GF construct a more efficient lithium diffusion channel, providing abundant lithiophilic sites, promoting the uniform nucleation of subsequent lithium ions to the lithium substrate via electromigration and diffusion, and inhibiting the growth of lithium dendrites. Simultaneously, iodide ions (I₂) in MgI2... - Under the influence of an electric field, the molecules migrate through the pores between GF molecules to the GF surface, and further migrate to the SEI interface layer between the GF and the solid electrolyte. At this point, the surface material of the negative electrode of the solid-state battery changes, specifically distributed as a lithium metal layer, a transition layer above the lithium metal layer, a magnesium iodide functional layer above the transition layer, a GF functional layer above the MgI2 functional layer, and lithium fluoride (LiF) and iodide ions (I-) above the GF functional layer. -This change can dynamically alleviate the interfacial contact problem between the solid electrolyte and the SEI membrane, and improve the interfacial contact failure and rapid performance degradation of all-solid-state batteries under zero pressure or low external pressure.

[0045] Optionally, the positive electrode sheet includes a positive electrode active material, which includes at least one of lithium iron phosphate positive electrode material, ternary nickel cobalt manganese positive electrode material, and lithium cobalt oxide positive electrode material.

[0046] Optionally, the solid electrolyte includes at least one of a sulfide solid electrolyte and a halide solid electrolyte. Optionally, the sulfide solid electrolyte includes Li 5.5 PS 4.5 Cl 1.5 Li7P3S 11 and Li 10 GeP2S 12 At least one of the following. The halide solid electrolyte includes Li3InCl6.

[0047] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0048] Example 1

[0049] This embodiment provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0050] Dissolution of S1 and MgI2

[0051] MgI2 was dissolved in ethylene glycol dimethyl ether in a glove box until fully dissolved, resulting in a completely dissolved MgI2 solution with a concentration of 0.01 mol / L.

[0052] Formation of S2 and MgI2 functional layers

[0053] Using copper foil as the current collector, metallic lithium is vapor-deposited onto the copper foil to form a lithium metal layer. The MgI2 solution obtained in S1 is uniformly sprayed onto the surface of the lithium metal layer, and after drying at 60°C, a MgI2 functional layer is formed, resulting in a Cu composite lithium metal material (MgI2@LiCu).

[0054] Subtracting the mass of the copper foil and lithium metal layer from the mass of the composite lithium metal material obtained in S2, the MgI2 loading is 5 mg. With the surface area of ​​the lithium metal layer being 100 cm², the MgI2 loading on the lithium metal layer is calculated to be 0.05 mg / cm².

[0055] The thickness (d1) of the MgI2 functional layer was measured to be 150 nm using scanning electron microscopy (SEM).

[0056] Formation of S3 and GF functional layers

[0057] Using MgI2@LiCu obtained from S2 as a substrate and GF as a target, a GF functional layer was magnetron sputtered onto MgI2@LiCu. The average thickness (d2) of the GF functional layer was 100 nm, resulting in a negative electrode (GF-MgI2@LiCu).

[0058] S4, Solid-state battery assembly

[0059] With NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS 4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to obtain the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to obtain the positive electrode. GF-MgI2@LiCu prepared by S3 was used as the negative electrode to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0060] Example 2

[0061] This embodiment provides a negative electrode sheet and its preparation method, which are basically the same as those in Example 1. The main difference is that the thickness of the MgI2 functional layer in S2 is 200 nm. Other differences are shown in Table 1.

[0062] Example 3

[0063] This embodiment provides a negative electrode sheet and its preparation method, which are basically the same as those in Example 1. The main difference is that the thickness of the MgI2 functional layer in S1 is 100 nm. Other differences are shown in Table 1.

[0064] Examples 4 to 12

[0065] The above embodiments provide negative electrode sheets and their preparation methods, which are basically the same as those in Embodiment 1. The main differences are shown in Table 1.

[0066] Comparative Example 1

[0067] This comparative example provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0068] S1 is the same as in Example 1.

[0069] S2, Same as Example 1.

[0070] S3, with NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS 4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to obtain the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to obtain the positive electrode. MgI2@LiCu prepared by S2 was used as the negative electrode to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0071] Comparative Example 2

[0072] This comparative example provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0073] S1. Using copper foil as the current collector, metallic lithium is vapor-deposited onto the copper foil to form a lithium metal layer. A GF functional layer is then magnetron sputtered onto the lithium metal layer, with an average thickness (d2) of 100 nm, to obtain the negative electrode (GF@LiCu).

[0074] S2, with NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS 4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to obtain the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to obtain the positive electrode. GF@LiCu prepared by S1 was used as the negative electrode to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0075] Comparative Example 3

[0076] This comparative example provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0077] S1. Using copper foil as the current collector, metallic lithium is vapor-deposited onto the copper foil to form a lithium metal layer, thus obtaining the negative electrode sheet.

[0078] S2, with NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS 4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to prepare the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to prepare the positive electrode sheet. The negative electrode sheet prepared by S1 was used to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0079] Comparative Example 4

[0080] This comparative example provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0081] S1. Same as in Example 1, but replace MgI2 with lithium iodide (LiI). Dissolve LiI in ethylene glycol dimethyl ether in a glove box until fully dissolved to obtain a completely dissolved LiI solution with a LiI concentration of 0.01 mol / L.

[0082] S2. Using copper foil as the current collector, metallic lithium is vapor-deposited onto the copper foil to form a lithium metal layer. The LiI solution obtained in S1 is uniformly sprayed onto the surface of the lithium metal layer, and after drying at 60°C, a LiI functional layer is formed, resulting in a composite lithium metal material (LiI@LiCu).

[0083] The mass of the composite lithium metal material obtained by the S2 method was subtracted from the mass of the copper foil and the lithium metal layer to obtain a LiI loading of 4 mg. With the surface area of ​​the lithium metal layer being 100 cm², the LiI loading on the lithium metal layer was calculated to be 0.04 mg / cm².

[0084] The thickness (d1) of the LiI functional layer was measured to be 150 nm using scanning electron microscopy (SEM).

[0085] S3. Using the LiI@LiCu obtained in S2 as a substrate and GF as a target, a GF functional layer is magnetron sputtered onto the LiI@LiCu. The average thickness (d2) of the GF functional layer is 100 nm. The negative electrode (GF-LiI@LiCu) is obtained.

[0086] S4, with NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to obtain the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to obtain the positive electrode. GF-LiI@LiCu prepared by S3 was used as the negative electrode to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0087] Comparative Example 5

[0088] This comparative example provides a negative electrode sheet and its preparation method, the steps of which are as follows:

[0089] S1 is the same as in Example 1.

[0090] S2, Same as Example 1.

[0091] S3. Using the MgI2@LiCu obtained in S2 as a substrate and graphene as a target, a graphene functional layer is magnetron sputtered onto the MgI2@Li. The average thickness (d2) of the graphene functional layer is 100 nm. This yields the negative electrode (C-MgI2@LiCu).

[0092] S4, with NCM622:Li 5.5 PS 4.5 Cl 1.5 Carbon nanotube powder (CNTs) was mixed evenly at a mass ratio of 6:2:2 to form a mixed cathode powder, using Li... 5.5 PS 4.5 Cl 1.5 After being mixed with LiFSI at a mass ratio of 10:1, a mixed solid electrolyte powder was obtained. 100 mg of the mixed electrolyte powder was weighed and pressurized at 300 MPa for 1 min to obtain the solid electrolyte. 10 mg of the mixed positive electrode powder was weighed and pressurized at 300 MPa for 1 min to obtain the positive electrode. C-MgI2@LiCu prepared by S3 was used as the negative electrode to assemble a 2032 coin cell. The assembly process was carried out in a dry room (dew point < -40℃).

[0093] The electrochemical performance of the coin cells assembled in each embodiment and comparative example was tested. The test methods are as follows, and the test results are shown in Table 1.

[0094] Discharge capacity retention: The 2032 coin cells assembled in each embodiment and comparative example were charged to 4.2V at a constant current of 0.2C and then discharged to 2.8V at a constant current of 0.2C. This process was repeated 100 times, and the discharge capacity retention after 100 cycles was tested.

[0095] Air stability: After exposing the negative electrode sheets of each embodiment and comparative example to a dry environment for different times, X-ray diffraction analysis was performed to check whether LiOH was present on the XRD test surface, and the exposure time at which LiOH was detected was recorded. When H2O erodes the lithium metal surface to generate LiOH, "dead lithium" is easily generated during cycling, leading to rapid capacity and cycle life decay. If no LiOH is detected on the surface by XRD, it indicates good air stability and avoids H2O erosion of the lithium metal surface.

[0096] Interface impedance: The 2032 coin cells assembled in each embodiment and comparative example were tested by electrochemical impedance spectroscopy (EIS) after 10 cycles. The test frequency range was 1MHz to 10mHz, and the voltage amplitude was 5mV.

[0097] Table 1

[0098]

[0099] It is evident that the GF-MgI2@Li composite lithium metal anode material significantly improves the electrochemical performance of solid-state batteries. Specifically, the inner Li-Mg alloy phase fills the pores caused by lithium plating and stripping, reducing the rapid consumption of interfacial lithium. The self-generated LiF-GF in the outer layer provides good lithiophilicity and lithium diffusion channels, improves air stability, promotes uniform lithium ion deposition, and inhibits lithium dendrite growth. Furthermore, iodine ions dynamically fill the pores at the interface between the anode and the solid electrolyte under the drive of an electric field, improving the interfacial contact failure and rapid performance degradation of all-solid-state batteries under zero pressure or low external pressure. However, as shown in Example 4 and Comparative Example 2, with the reduction of MgI2, the battery interfacial impedance increases significantly, and the capacity retention rate drops sharply. The lack of dynamic regulation by MgI2 causes significant interfacial side reactions and physical contact losses, severely hindering charge transfer at the anode / electrolyte interface. Comparative Example 4, replacing MgI2 with LiI, resulted in a significant decrease in battery performance. This indicates that while the SEI layer maintains good physical contact with the solid electrolyte surface due to electromigration and iodine ion diffusion, the lack of magnesium to dynamically fill the voids between the lithium surface and the transition layer leads to significant interfacial resistance during lithium plating / stripping, resulting in sluggish reaction kinetics. Comparative Example 5, replacing fluorinated graphite with graphene, also showed a significant decrease in battery air stability. This was due to the absence of LiF's inhibition of H2O and suppression of lithium dendrite formation, leading to a capacity retention rate of only 78.3% after 100 cycles. In conclusion, only the synergistic effect of fluorinated graphite and magnesium iodide can significantly improve battery air stability, dynamically filling voids on the electrolyte, SEI, and lithium metal surfaces during cycling, thereby suppressing lithium dendrite formation and improving electrochemical performance.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite lithium metal anode material, characterized in that, It includes a lithium metal layer, a transition layer, a magnesium iodide functional layer, and a fluorinated graphite functional layer. The transition layer is located between the lithium metal layer and the magnesium iodide functional layer. The fluorinated graphite functional layer is located on the side of the magnesium iodide functional layer away from the transition layer. The transition layer includes a Li-Mg alloy.

2. The composite lithium metal anode material according to claim 1, characterized in that, The amount of the magnesium iodide functional layer meets the following requirement: per 1cm 2 The lithium metal layer is loaded with 0.01 mg to 0.1 mg of magnesium iodide.

3. The composite lithium metal anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The average thickness of the magnesium iodide functional layer is 30 nm to 300 nm; preferably 50 nm to 250 nm; (2) The average thickness of the fluorinated graphite functional layer is 30nm~300nm; preferably 50nm~250nm.

4. The composite lithium metal anode material according to claim 3, characterized in that, The average thickness ratio of the magnesium iodide functional layer to the fluorinated graphite functional layer is 1~2.

5. A method for preparing a composite lithium metal anode material, characterized in that, Includes the following steps: Magnesium iodide and an organic solvent are mixed to obtain a magnesium iodide solution; The magnesium iodide solution is coated onto a lithium metal substrate and dried to form a lithium metal layer, a transition layer, and a magnesium iodide functional layer. The transition layer, which is located between the lithium metal layer and the magnesium iodide functional layer, comprises a Li-Mg alloy. Fluorinated graphite is deposited on the side of the magnesium iodide functional layer away from the transition layer by magnetron sputtering, using fluorinated graphite as the target material, to form a fluorinated graphite functional layer.

6. The method for preparing the composite lithium metal anode material according to claim 5, characterized in that, Adjust the concentration of magnesium iodide in the magnesium iodide solution and adjust the amount of magnesium iodide solution used for coating, so that each 1 cm 2 The lithium metal layer is loaded with 0.01 mg to 0.1 mg of magnesium iodide.

7. The method for preparing the composite lithium metal anode material according to claim 5, characterized in that, Includes at least one of the following features: (1) Adjust the amount of magnesium iodide solution used to coat the magnesium iodide functional layer so that the average thickness of the magnesium iodide functional layer is 30nm~300nm; (2) Adjust the process parameters for depositing the fluorinated graphite so that the average thickness of the fluorinated graphite functional layer is 30nm~300nm.

8. The method for preparing the composite lithium metal anode material according to claim 7, characterized in that, The average thickness ratio of the magnesium iodide functional layer to the fluorinated graphite functional layer is 1 to 2.

9. The method for preparing the composite lithium metal anode material according to any one of claims 5 to 8, characterized in that, Includes at least one of the following features: (1) The organic solvent is selected from at least one of diethyl ether, ethylene glycol dimethyl ether, diethyl carbonate, fluoroethylene carbonate, tetrahydrofuran, acetone and dimethyl sulfoxide; (2) The concentration of magnesium iodide in the magnesium iodide solution is 0.01 mol / L to 0.1 mol / L.

10. A negative electrode sheet, characterized in that, The present invention includes a current collector and a composite lithium metal anode material located on the current collector, wherein the composite lithium metal anode material is as described in any one of claims 1 to 4, or is prepared by the method for preparing the composite lithium metal anode material according to any one of claims 5 to 9, wherein the current collector is located on the side of the lithium metal layer away from the magnesium iodide functional layer.

11. A solid-state battery, characterized in that, It includes the negative electrode, the positive electrode, and the solid electrolyte as described in claim 10, wherein the solid electrolyte is located between the negative electrode and the positive electrode.

12. The solid-state battery according to claim 11, characterized in that, Includes at least one of the following features: (1) The positive electrode sheet includes a positive electrode active material, which includes at least one of lithium iron phosphate positive electrode material, ternary nickel cobalt manganese positive electrode material and lithium cobalt oxide positive electrode material; (2) The solid electrolyte includes at least one of sulfide solid electrolyte and halide solid electrolyte.

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