Composite lithium metal negative electrode material and preparation method thereof

Abstract

The application discloses a kind of composite lithium metal negative electrode material and preparation method thereof, it is related to electrochemical energy storage technical field, the method comprises: the three-dimensional porous carbon framework of pore size 50 to 500 nanometers is constructed, and 2 to 10 nanometer nitrogen-doped carbon layer is coated on its inner wall;Metal lithium is fused with lithium nitride to form lithium-rich melt;Capillary force is used to make molten lithium infiltrate into framework channel, in-situ generation and C-Li-N gradient interface phase;Lithium directional solidification is realized by programmed temperature cooling;Surface deposition 50 to 150 nanometer amorphous aluminum oxide passivation layer;Again, the final material is obtained by aging treatment.The application realizes lithium uniform loading, interface high ionic conductivity, structural integrity and high safety by the above technical scheme, significantly inhibits lithium dendrite growth, improves cycle stability and energy density consistency.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a composite lithium metal anode material and its preparation method. Background Technology

[0002] With the rapid development of high-energy-density lithium metal battery technology, composite lithium metal anode materials have become a key research direction for solid-state batteries and next-generation energy storage systems due to their significant potential in suppressing lithium dendrite growth, mitigating volume expansion during charge and discharge, and improving cycle stability. While lithium metal anodes theoretically possess extremely high specific capacity and the lowest electrochemical potential, they face serious interfacial side reactions, uncontrollable dendrite growth, and significant volume deformation in practical applications, necessitating control through structural design and interface engineering. Constructing a composite anode system that combines continuous electron / ion conduction, mechanical flexibility, and chemical stability is considered a crucial pathway to overcome these bottlenecks.

[0003] However, existing composite lithium metal anode materials still have significant shortcomings in terms of interface structure controllability, preparation safety, and composition stability. On the one hand, some methods rely on the in-situ reaction of high-temperature molten lithium with active additives to generate an interface-stable phase, although this can form... While high-conductivity ions are used, direct contact between strong oxidizing agents and liquid lithium is involved, posing a high operational hazard and complex side reaction pathways, making it difficult to precisely control the product composition and resulting in poor batch-to-batch consistency. On the other hand, although the strategy of using a carbon matrix to support lithium metal can provide a certain confined space, the interfacial bonding between lithium and the carbon framework is weak, making it prone to desorption or local collapse during repeated deposition / stripping. At the same time, the thickness and uniformity of the surface modification layer are limited by heat treatment conditions, making it difficult to achieve atomic-level precise construction and easily leading to excessively high local current density or a surge in interfacial impedance.

[0004] Furthermore, existing fabrication processes generally lack the ability to directionally control the microstructure, making it difficult to simultaneously achieve uniform lithium distribution, chemical stability of the interfacial phase, and mechanical integrity of the overall electrode. During long-term cycling, interfacial components may dissolve due to electrolyte erosion or crack due to stress accumulation, thereby accelerating lithium dendrite penetration and dead lithium formation, severely restricting the cycle life and safety performance of the battery. Summary of the Invention

[0005] The purpose of this invention is to provide a composite lithium metal anode material and its preparation method, so as to solve the problems of poor controllability of interface structure, low safety of preparation process, insufficient component stability and difficulty in precise control of microstructure in the existing composite lithium metal anode.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] On one hand, a composite lithium metal anode material, said material comprising:

[0008] A three-dimensional porous carbon framework matrix with a connected pore structure, a pore size distribution ranging from 50 nanometers to 500 nanometers, and a specific surface area ranging from 800 square meters per gram to 1200 square meters per gram.

[0009] A nitrogen-doped carbon layer is coated on the inner wall surface of the carbon skeleton, with a thickness of 2 nanometers to 10 nanometers and a nitrogen content of 6 atomic percent to 12 atomic percent, containing pyridine nitrogen and graphitic nitrogen functional groups.

[0010] Metallic lithium is uniformly filled within the porous framework channels, forming an in-situ interface with the nitrogen-doped carbon layer. A gradient interface phase dominated by C-Li-N, with a thickness of 3 to 8 nanometers;

[0011] A dense amorphous aluminum oxide passivation layer covers the outer surface of the material, with a thickness of 50 nanometers to 150 nanometers, a dielectric constant of 9 to 10, and a breakdown field strength of >5 megavolts per centimeter;

[0012] The composite lithium metal anode material also contains an ion-conducting phase formed by lithium nitride, and the overall structure has high electron / ion synergistic conduction capability, excellent interface stability and low volume expansion rate.

[0013] On the other hand, a method for preparing a composite lithium metal anode material includes the following steps:

[0014] Step S1: Provide a three-dimensional porous carbon framework matrix, wherein the three-dimensional porous carbon framework has a connected pore structure, the pore size distribution ranges from 50 nanometers to 500 nanometers, and the specific surface area is from 800 square meters per gram to 1200 square meters per gram. A nitrogen-doped carbon layer with a thickness of 2 nanometers to 10 nanometers is uniformly coated on the inner wall surface of the carbon framework by chemical vapor deposition process to form a composite conductive framework.

[0015] Step S2: Mix lithium metal blocks and lithium nitride powder in a mass ratio of 9:1 to 4:1, place them in a closed reaction chamber protected by an inert atmosphere, and heat them to melt at a temperature of 220 degrees Celsius to 260 degrees Celsius to form a homogenized lithium-rich melt, wherein the lithium nitride powder is uniformly dispersed in the liquid lithium as an ion-conducting phase precursor.

[0016] Step S3: The composite conductive framework obtained in Step S1 is immersed in the lithium-rich melt prepared in Step S2. Driven by capillary force and wetting, the molten lithium spontaneously penetrates into the three-dimensional channels and undergoes an interfacial reaction with the nitrogen-doped carbon layer, generating in situ a composite conductive framework. A gradient interface phase dominated by C-Li-N is used to achieve uniform loading of lithium metal in the porous framework, thus obtaining the initial composite anode material.

[0017] Step S4: The initial composite anode material obtained in step S3 is subjected to programmed temperature-controlled cooling treatment at a cooling rate of 0.5 degrees Celsius per minute to 2 degrees Celsius per minute, so that lithium can be directionally solidified in the channels, suppressing the generation of grain boundary defects and microcracks, and maintaining the integrity of the interface phase.

[0018] Step S5: In an inert atmosphere glove box, an alumina passivation layer with a thickness of 50 nm to 150 nm is deposited on the surface of the initial composite negative electrode material using magnetron sputtering technology. The alumina passivation layer has a dense amorphous structure and is used to block electrolyte penetration and stabilize the electrode / electrolyte interface.

[0019] Step S6: The material obtained in step S5 is left to stand at a temperature of 60 degrees Celsius to 80 degrees Celsius for 12 to 24 hours to promote further reconstruction of the interface phase and stress release, so as to obtain the final composite lithium metal anode material.

[0020] Preferably, in step S1, the three-dimensional porous carbon skeleton is synthesized by a template method. An ordered macroporous structure formed by the self-assembly of silica nanospheres is used as a hard template. After being filled with phenolic resin and carbonized, the template is removed with hydrofluoric acid solution to obtain a carbon skeleton with periodically interconnected channels and a channel connectivity rate >98%.

[0021] Preferably, in step S1, the nitrogen content of the nitrogen-doped carbon layer is controlled between 6 atomic percent and 12 atomic percent. By introducing pyridine nitrogen and graphitic nitrogen functional groups, the adsorption capacity for lithium ions is enhanced, and the overpotential for lithium nucleation is reduced.

[0022] Preferably, in step S2, the average particle size of the lithium nitride powder is <100 nanometers. After ball milling, it is thoroughly mixed with the lithium metal block to ensure rapid dissolution and uniform distribution in the molten lithium phase during heating, thus avoiding local aggregation that could lead to uneven ion conduction.

[0023] Preferably, the immersion process in step S3 is carried out in a vacuum environment, with a vacuum degree ≥ Pa is used to remove residual gas in the channels, improve the penetration efficiency of molten lithium, and ensure that the lithium filling rate is >95%.

[0024] Preferably, in step S3, the interfacial reaction lasts for 10 to 30 minutes, and the reaction temperature is maintained at 240 degrees Celsius, which promotes the diffusion coupling of nitrogen atoms and lithium atoms in the nitrogen-doped carbon layer to generate a nitrogen-rich interfacial transition layer with a thickness of 3 to 8 nanometers.

[0025] Preferably, in step S4, the programmed temperature control cooling starts at 240 degrees Celsius and is divided into three stages: the first stage cools down to 180 degrees Celsius at a rate of 2 degrees Celsius per minute, the second stage cools down to 100 degrees Celsius at a rate of 1 degree Celsius per minute, and the third stage cools down to room temperature at a rate of 0.5 degrees Celsius per minute, so as to release thermal stress in a gradient and prevent lithium volume shrinkage from causing interface peeling.

[0026] Preferably, in step S5, the magnetron sputtering uses a high-purity alumina ceramic target, the sputtering power is 80 watts to 120 watts, the working pressure is 0.5 Pa to 1.5 Pa, the argon to oxygen flow ratio is 4:1, and the deposition rate is controlled at 0.8 nanometers per second to 1.2 nanometers per second to ensure that the alumina passivation layer is dense and free of pinholes.

[0027] Preferably, in step S5, the dielectric constant of the alumina passivation layer is 9 to 10, and the breakdown field strength is >5 MV per centimeter, which can effectively suppress electron leakage and guide the uniform transport of lithium ions.

[0028] Preferably, the aging treatment in step S6 is carried out in a dry argon atmosphere with a relative humidity of <1 ppm, which promotes... The interfacial chemical bonding between the phase and the alumina passivation layer forms a stable Li-Al-ON composite interface, which improves the overall mechanical strength.

[0029] Preferably, the process also includes electrochemical activation of the final composite lithium metal anode material, i.e., after assembling the half-cell, performing the first cycle at a current density of 0.1 mA per square centimeter, limiting the capacity to 1 mA per square centimeter, to form an initial solid electrolyte interface film and further optimize the interface ion transport characteristics.

[0030] Preferably, when the composite lithium metal anode material is used in an all-solid-state lithium battery system and is used in conjunction with a sulfide-based solid electrolyte, the interfacial contact impedance is <50 ohms / cm², the critical current density is >1.2 mA / cm², it can cycle stably for >500 cycles, and the capacity retention is >85%.

[0031] Preferably, when the composite lithium metal anode material is used in a pouch cell, the areal capacity density can reach 4 to 6 mAh per square centimeter, and the volume expansion rate is <8% after 100 cycles, which is significantly better than that of traditional lithium foil anodes.

[0032] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0033] This invention achieves uniform construction of an electronic conduction network by constructing a three-dimensional porous carbon framework and introducing a nitrogen-doped carbon layer. Combined with molten lithium spontaneous infiltration technology, it enables a highly uniform distribution of lithium metal within the channels, avoiding the density unevenness problem caused by traditional pressing or coating processes.

[0034] This invention introduces lithium nitride as an ion-conducting phase precursor into the melt and utilizes its synergistic effect with a nitrogen-doped carbon layer to generate, in situ, lithium-rich... The gradient interface phase significantly improves the ionic conductivity and chemical stability of the interface, and effectively reduces the interfacial impedance.

[0035] This invention employs a programmed temperature-controlled cooling process to precisely control the solidification behavior of lithium, reducing microcracks and desorption caused by thermal stress concentration, and ensuring the long-term integrity of the electrode structure.

[0036] The amorphous alumina passivation layer deposited on the surface of this invention not only physically blocks electrolyte erosion, but also forms a stable composite passivation film through interface reconstruction, which greatly suppresses the occurrence of side reactions.

[0037] The entire preparation process of this invention does not require high temperature and high pressure or highly corrosive reagents. The operating conditions are mild, the safety is high, and it is easy to achieve continuous production, thus having good prospects for industrialization.

[0038] The composite lithium metal anode material prepared by this invention can maintain stable lithium deposition / stripping behavior under high current density, significantly suppressing the growth of lithium dendrites, extending battery cycle life, and alleviating volume deformation during charging and discharging, thereby improving battery safety performance and energy density consistency. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall technical solution architecture of the composite lithium metal anode material and its preparation method proposed in this invention;

[0040] Figure 2 This is a schematic diagram of the core principle framework of the synergistic effect of in-situ construction of gradient interface phase and ion conduction phase proposed in this invention;

[0041] Figure 3 This is a schematic diagram showing the relationship between the multi-level structure composition and functional layer distribution of the composite lithium metal anode material proposed in this invention.

[0042] Figure 4 This is a flowchart of the main process stages of the composite lithium metal anode material preparation method proposed in this invention. Detailed Implementation

[0043] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present invention and not to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the invention.

[0044] Example 1

[0045] Currently, with the rapid development of high-energy-density lithium metal battery technology, composite lithium metal anode materials have become a key research direction for solid-state batteries and next-generation energy storage systems due to their significant potential in suppressing lithium dendrite growth, mitigating volume expansion during charge and discharge, and improving cycle stability. Lithium metal anodes theoretically possess extremely high specific capacity and the lowest electrochemical potential, but in practical applications, they face serious interfacial side reactions, uncontrollable dendrite growth, and huge volume deformation, requiring control through structural design and interface engineering. Constructing a composite anode system that combines continuous electron / ion conduction, mechanical flexibility, and chemical stability is considered an important path to overcome these bottlenecks. However, existing composite lithium metal anode materials still have significant shortcomings in terms of interface structure controllability, preparation safety, and component stability. To address these technical problems, this invention proposes a composite lithium metal anode material and its preparation method, which can effectively solve the technical problems of poor interface structure controllability, low preparation process safety, insufficient component stability, and difficulty in precise microstructure control in existing composite lithium metal anodes. This invention is applied to a composite lithium metal anode material and its preparation method.

[0046] refer to Figure 4 The diagram shown illustrates the main process flow framework of the composite lithium metal anode material preparation method of this invention. The preparation method strictly follows six core steps, forming a tightly coupled process chain to ensure high consistency and repeatability of the final product in terms of microstructure, interfacial chemistry, and macroscopic properties. The entire process is carried out under an inert atmosphere, and all operations involving lithium metal are performed in an argon glove box with a dew point < -60 degrees Celsius and an oxygen content < 0.1 ppm to prevent the corrosion of lithium metal by moisture and oxygen.

[0047] In the above-mentioned method for preparing composite lithium metal anode materials, step S1 involves providing a three-dimensional porous carbon framework matrix. This three-dimensional porous carbon framework has a connected pore structure with a pore size distribution ranging from 50 nm to 500 nm and a specific surface area ranging from 800 m² / g to 1200 m² / g. A nitrogen-doped carbon layer with a thickness of 2 nm to 10 nm is uniformly coated onto the inner wall surface of the carbon framework using a chemical vapor deposition process, forming a composite conductive framework with high electronic conductivity and chemical stability. Specifically, the three-dimensional porous carbon framework is synthesized by a template method, using an ordered macroporous structure formed by the self-assembly of silica nanospheres as a hard template. The average particle size of the silica nanospheres is 300 nm, and after centrifugation and heat treatment, they form a face-centered cubic periodic macroporous array with a pore connectivity rate >98%. Subsequently, a phenolic resin precursor solution with a solid content of 20% was impregnated into the pores of the template under vacuum assistance and cured at 80°C for 12 hours. Then, carbonization was completed by heating to 900°C at a rate of 2°C per minute under a nitrogen atmosphere and holding at that temperature for 2 hours. Finally, the silica template was completely removed by etching with a 5% hydrofluoric acid solution at 60°C for 24 hours, yielding a carbon framework matrix with a three-dimensional interconnected network structure. The pore size distribution of this carbon framework, determined by mercury intrusion porosimetry, ranged from 50 nm to 500 nm, with a BET specific surface area of ​​1050 m² / g and a pore volume of 1.8 cm³ / g, meeting the requirements of synergistic high specific surface area and high porosity.

[0048] Furthermore, in the chemical vapor deposition process, acetonitrile was used as both the carbon and nitrogen source, high-purity nitrogen was used as the carrier gas at a flow rate of 100 standard cubic centimeters per minute, the reaction temperature was controlled at 750 degrees Celsius, and the deposition time was 30 minutes. Under these conditions, acetonitrile molecules undergo cleavage and recombination on the carbon framework surface, forming a uniformly coated nitrogen-doped carbon layer. X-ray photoelectron spectroscopy analysis showed that the nitrogen content of this nitrogen-doped carbon layer was 9 atomic percent, of which pyridine nitrogen accounted for 55%, graphitic nitrogen accounted for 40%, and the remainder was a small amount of pyrrole nitrogen. The introduction of pyridine nitrogen and graphitic nitrogen functional groups significantly enhanced the adsorption capacity for lithium ions and reduced the lithium nucleation overpotential. The mechanism of action is that pyridine nitrogen provides lone pairs of electrons, which, along with... Coordination bonds are formed; graphitic nitrogen promotes uniform nucleation of lithium atoms on the carbon surface by altering the local electron cloud density. The thickness of this nitrogen-doped carbon layer, measured by transmission electron microscopy, is 6 nanometers, and it exhibits a continuous, crack-free coating along the inner walls of the pores. See [link to documentation]. Figure 3 The schematic diagram shown is a multi-level structural composition and functional layer distribution relationship of the composite lithium metal anode material of the present invention. It clearly shows the layer-by-layer distribution relationship of the carbon skeleton matrix, nitrogen-doped carbon layer, gradient interface phase, lithium metal filler and outer surface alumina passivation layer.

[0049] In the above-mentioned method for preparing composite lithium metal anode materials, step S2 involves mixing lithium metal blocks and lithium nitride powder at a mass ratio of 9:1 to 4:1, placing the mixture in a sealed reaction chamber protected by an inert atmosphere, and heating it to melt at a temperature of 220°C to 260°C to form a homogenized lithium-rich melt. The lithium nitride powder serves as an ion-conducting phase precursor, uniformly dispersed in the liquid lithium. Specifically, the lithium nitride powder has an average particle size of <100 nanometers and is thoroughly mixed with high-purity lithium metal blocks (99.9% purity) at a mass ratio of 7:3 after being subjected to high-energy ball milling for 2 hours. The sealed reaction chamber is made of stainless steel, lined with polytetrafluoroethylene, and equipped with a magnetic stirring device and a precision temperature control system. The heating process was conducted under the protection of 99.999% high-purity argon gas, increasing the temperature from room temperature to 240 degrees Celsius at a rate of 1 degree Celsius per minute, and holding at this temperature for 30 minutes while continuously stirring at a speed of 200 rpm to ensure complete dissolution of lithium nitride powder in the molten lithium, forming a transparent, homogeneous, lithium-rich melt. Since the solubility of lithium nitride in liquid lithium increases with temperature, reaching 15% by mass at 240 degrees Celsius, the selected ratio ensured complete dissolution of all lithium nitride, preventing undissolved particles from causing uneven lithium filling in subsequent processes. The lithium-rich melt contains uniformly dispersed... The molecules will serve as a direct source of the ion-conducting phase during the subsequent percolation process, and will work synergistically with the nitrogen-doped carbon layer to generate an interface phase with high ionic conductivity in situ.

[0050] In the above-mentioned method for preparing composite lithium metal anode materials, in step S3, the composite conductive framework obtained in step S1 is immersed in the lithium-rich melt prepared in step S2. Driven by capillary force and wetting action, the molten lithium spontaneously penetrates into the three-dimensional channels and undergoes an interfacial reaction with the nitrogen-doped carbon layer, generating in situ a composite conductive framework. A gradient interface phase, primarily C-Li-N, is used to achieve uniform loading of lithium metal within a porous framework, yielding the initial composite anode material. Specifically, the immersion process is carried out under vacuum conditions, with a vacuum level not lower than [missing information]. To remove residual gas from the pores and improve the permeation efficiency of molten lithium, a vacuum pump is used. During operation, the composite conductive framework is first preheated to 240 degrees Celsius, then quickly transferred above the lithium-rich molten material already at 240 degrees Celsius, and the vacuum pump is started to evacuate to... The vacuum was maintained for 5 minutes, then slowly released, allowing molten lithium to spontaneously fill the pores under capillary pressure. Due to the excellent wettability of the nitrogen-doped carbon layer with a contact angle of <30 degrees to the molten lithium, the molten lithium could penetrate the entire three-dimensional network within 10 seconds. The interface reaction lasted for 20 minutes, with the reaction temperature maintained at 240 degrees Celsius, promoting diffusion coupling between nitrogen atoms and lithium atoms in the nitrogen-doped carbon layer, generating a nitrogen-rich interface transition layer with a thickness of 5 nanometers. This gradient interface phase, from the inside out, consists of a C-Li-N covalent bonded layer with a thickness of approximately 2 nanometers, a layer with a thickness of approximately 2.5 nanometers, and a layer of... The main phase layer and a small amount of material with a thickness of approximately 0.5 nanometers. The transition layer forms an electronically insulated but ionically conductive gradient structure, with an ionic conductivity reaching [value missing] at room temperature. Siemens' lithium content is on the order of centimeters. Scanning electron microscopy and energy dispersive spectroscopy analysis showed a lithium filling rate >95%, with highly uniform distribution and no obvious voids or aggregations. (See [reference needed]). Figure 2 The schematic diagram shown illustrates the core principle framework of the synergistic effect of in-situ construction of gradient interface phase and ion-conducting phase in this invention, which clearly reveals... Synergistic enhancement mechanism of ion-conducting phase and gradient interface phase.

[0051] In the above-mentioned method for preparing composite lithium metal anode materials, step S4 involves subjecting the initial composite anode material obtained in step S3 to programmed temperature-controlled cooling at a rate of 0.5°C to 2°C per minute. This allows lithium to solidify directionally within the pores, suppressing grain boundary defects and microcracks, and maintaining the integrity of the interface phase. Specifically, the programmed temperature-controlled cooling starts at 240°C and proceeds in three stages: the first stage cools to 180°C at a rate of 2°C per minute. During this stage, lithium is in a highly fluid state, and rapid cooling can suppress the formation of coarse grains. The second stage cools to 100°C at a rate of 1°C per minute. During this stage, lithium begins to crystallize, and a moderate cooling rate is beneficial for the formation of fine equiaxed crystals. The third stage cools to room temperature at a rate of 0.5°C per minute. This stage is a low-temperature contraction zone, and slow cooling can gradually release thermal stress, preventing interface peeling or microcracks caused by lithium volume contraction. The entire cooling process is carried out under argon positive pressure (0.1 MPa) protection to avoid localized oxidation caused by temperature fluctuations. Synchrotron radiation X-ray tomography revealed that the cooled lithium metal exhibited a dense, non-porous columnar crystal structure within the channels, with a grain size of <5 micrometers. The crystals were tightly bonded to the carbon skeleton interface, with no desorption or voids.

[0052] In the above-mentioned method for preparing composite lithium metal anode materials, step S5 involves depositing an alumina passivation layer with a thickness of 50 nm to 150 nm on the surface of the initial composite anode material using magnetron sputtering in an inert atmosphere glove box. The alumina passivation layer has a dense amorphous structure, which serves to block electrolyte penetration and stabilize the electrode / electrolyte interface. Specifically, the magnetron sputtering uses a high-purity alumina ceramic target with a purity of 99.99%, a sputtering power of 100 W, a working pressure of 1.0 Pa, argon gas at 40 standard cubic centimeters per minute, oxygen gas at 10 standard cubic centimeters per minute, an argon to oxygen flow rate ratio of 4:1, and a deposition rate controlled at 1.0 nm per second. During sputtering, the substrate temperature is maintained at room temperature, and the bias voltage is -50 V to enhance the film density. The obtained alumina passivation layer was confirmed by grazing incidence X-ray diffraction to be a completely amorphous structure with no diffraction peaks of any crystalline phase. Ellipsometry measurement showed its thickness to be 100 nm; its dielectric constant was 9.5, and its breakdown field strength was 5.2 MV / cm, effectively suppressing electron leakage and guiding uniform lithium-ion transport. This passivation layer covers the entire outer surface of the material, including edges and orifice areas, forming a continuous, pinhole-free physical barrier. See [link to relevant documentation]. Figure 1 The diagram shown is a schematic of the overall technical solution architecture of a composite lithium metal anode material and its preparation method proposed in this invention. The overall architecture clearly shows the complete technical path from carbon skeleton construction to surface passivation layer deposition.

[0053] In the above-mentioned method for preparing composite lithium metal anode materials, step S6 involves aging the material obtained in step S5 at a temperature of 60°C to 80°C for 12 to 24 hours to promote further reconstruction of the interface phase and stress release, thereby obtaining the final composite lithium metal anode material. Specifically, the aging treatment is carried out in a dry argon atmosphere with a relative humidity of <1 ppm, a temperature of 70°C, and a time of 18 hours. Under these conditions, Slow chemical bonding occurs at the interface between the phase and the alumina passivation layer, forming a stable Li-Al-ON composite interface with the following chemical composition: and The mixed phase, as confirmed by X-ray photoelectron spectroscopy depth profiling, shows that the composite interface is approximately 20 nanometers thick, significantly improving the overall mechanical strength and interfacial bonding energy. Simultaneously, the aging process promotes the relaxation of residual thermal stress, reducing the internal strain energy of the material by more than 30%, thereby enhancing the structural stability of the electrode during cycling.

[0054] To further optimize electrochemical performance, the final composite lithium metal anode material undergoes electrochemical activation treatment. Specifically, after assembling the half-cell, an initial cycle is performed at a current density of 0.1 mA / cm², limiting the capacity to 1 mA / cm², to form an initial solid electrolyte interface film and further optimize interfacial ion transport characteristics. The half-cell uses a lithium sheet as the counter electrode, a 1 mol / L lithium bis(trifluoromethanesulfonyl)imide solution in 1,3-dioxolane / ethylene glycol dimethyl ether as the electrolyte, and a glass fiber membrane as the separator. In the first cycle, the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether in the electrolyte is 1:1. Lithium ions undergo a reduction reaction on the passivation layer surface, generating a high-ion content... and The thin SEI film, with a thickness of about 10 nanometers, has a higher ionic conductivity than traditional SEI films, effectively reducing interfacial impedance.

[0055] The composite lithium metal anode material prepared above is applied to an all-solid-state lithium battery system, combined with, for example... When used in sulfide-based solid electrolytes, the interfacial contact impedance is <50 ohm² / cm², the critical current density is >1.2 mA / cm², and it can cycle stably for >500 cycles with a capacity retention of >85%. In pouch cells, the areal capacity density can reach 5 mAh / cm², and the volume expansion rate after 100 cycles is <8%, typically >25%, significantly superior to traditional lithium foil anodes. Its superior performance stems from the synergistic effect of its multi-layered structure: a three-dimensional porous carbon framework provides fast electron pathways and volume buffer space; nitrogen-doped carbon layers enhance lithium affinity and induce uniform nucleation; a gradient interfacial phase achieves high ionic conductivity and chemical stability; an alumina passivation layer blocks side reactions; and programmed cooling and aging treatment ensure structural integrity.

[0056] Example 2

[0057] Based on Example 1, this example provides an alternative method for preparing a three-dimensional porous carbon framework to verify the universality and scalability of the technical solution of the present invention. Specifically, the three-dimensional porous carbon framework is synthesized by cryo-casting instead of template method. The operation process is as follows: A graphene oxide aqueous dispersion with a concentration of 5 mg / mL is mixed with sodium carboxymethyl cellulose with a concentration of 1 mg / mL, wherein sodium carboxymethyl cellulose acts as a binder. After ultrasonic treatment for 30 minutes, the mixture is poured into a copper mold and placed on a cold stage at -40°C for directional freezing. Ice crystals grow along the direction perpendicular to the cold stage, forming a layered pore structure. Subsequently, the frozen sample is dried in a freeze dryer at -50°C and 10 Pa for 24 hours to obtain a porous aerogel precursor. Finally, the temperature is increased to 1000°C at 3°C ​​per minute and held for 1 hour in an argon atmosphere to complete thermal reduction and carbonization, obtaining a three-dimensional porous carbon framework with vertically oriented pores. The pore size distribution of the framework is 100 nm to 600 nm, the specific surface area is 950 m² / g, and the pore connectivity is >95%. The remaining preparation steps, namely steps S2 to S6, are exactly the same as in Example 1.

[0058] Testing revealed that the composite lithium metal anode material obtained in this embodiment has an interfacial impedance of 55 Ω·cm², a critical current density of 1.1 mA / cm², a capacity retention of 83% after 500 cycles, and a lithium filling rate of 93%. After 200 cycles at a current density of 0.5 mA / cm², the material maintains a coulombic efficiency of 99.2% and a volume expansion rate of 9.5%, slightly higher than Example 1, but still significantly better than traditional lithium foil. The performance difference mainly stems from the influence of channel orientation on lithium deposition behavior: while vertical channels facilitate vertical ion transport, their lateral confinement is weaker than that of the isotropic interconnected channels in Example 1, resulting in slightly higher local stress concentration. However, these results demonstrate that the core technologies of this invention—nitrogen-doped carbon layers, gradient interfacial phase construction, programmed cooling, and alumina passivation—have good adaptability to different carbon framework structures, further verifying the robustness and versatility of the technical solution of this invention.

[0059] Example 3

[0060] In this embodiment, to further verify the effect of nitrogen-doped carbon layer thickness on interface properties, we adjusted the thickness of the nitrogen-doped carbon layer in step S1. Specifically, the chemical vapor deposition time was shortened to 15 minutes, resulting in a nitrogen-doped carbon layer with a thickness of approximately 3 nanometers. Other conditions were the same as in Example 1. X-ray photoelectron spectroscopy analysis showed a nitrogen content of 7 atomic percent, with pyridine nitrogen accounting for 50% and graphitic nitrogen accounting for 45%. The remaining preparation steps were completely consistent with those in Example 1.

[0061] Electrochemical testing results showed that the material had a critical current density of 1.0 mA / cm², a volume expansion rate of 10% after 100 cycles, and a lithium filling rate of 92%. After 300 cycles at a current density of 1.0 mA / cm², the material maintained 88% capacity and had an interfacial impedance of 65 ohms / cm², slightly higher than the 50 ohms / cm² of Example 1 (6 nm thickness). Analysis indicated that while a thinner nitrogen-doped carbon layer could still induce uniform lithium nucleation, its buffering capacity against volume expansion and interfacial stability were slightly reduced, suggesting that a thickness in the 5-8 nm range was more beneficial for overall performance optimization.

[0062] Example 4

[0063] This embodiment aims to verify the effect of different lithium to lithium nitride ratios on material properties. In step S2, the mass ratio of lithium metal blocks to lithium nitride powder was adjusted to 9:1, i.e., a higher lithium content, while the remaining conditions were the same as in Example 1.

[0064] Test results show that the material has an interfacial impedance of 70 Ω·cm², a capacity retention of 90% after 500 cycles, a volume expansion rate of 9% after 100 cycles, and a lithium fill factor of 94%. The material exhibits excellent cycling stability at a low current density of 0.2 mA / cm², with a capacity retention of 90% after 500 cycles. However, at a high current density of 1.5 mA / cm², the interfacial ion transport capability is slightly insufficient, with a critical current density of 1.0 mA / cm². This indicates that a higher lithium content is beneficial for improving initial capacity and low-rate performance, but excessive lithium may dilute the interfacial ion-conducting phase, affecting ion transport efficiency at high rates.

[0065] Comparative Example 1

[0066] This comparative example aims to verify the effect of not introducing a nitrogen-doped carbon layer. In step S1, the chemical vapor deposition process was omitted, and an undoped three-dimensional porous carbon framework was used directly, with other conditions the same as in Example 1. The surface of this carbon framework contained only a small number of oxygen-containing functional groups and no pyridine nitrogen or graphitic nitrogen structures.

[0067] During the preparation process, the wettability of molten lithium within the carbon framework decreased significantly, with a contact angle >90 degrees, a filling rate of only about 70%, and uneven distribution. Test results showed that the material had an interfacial impedance >150 Ω·cm², a critical current density <0.5 mA / cm², a capacity retention of <60% after 500 cycles, and a volume expansion rate >25% after 100 cycles. The material exhibited significant capacity decay after 100 cycles at a current density of 0.5 mA / cm², with coulombic efficiency fluctuating between 85-92%, and significant lithium dendrite growth. These results indicate that the absence of a nitrogen-doped carbon layer leads to poor interfacial affinity, uneven lithium distribution, and weak dendrite suppression, severely restricting the cycle stability and safety of the battery.

[0068] Comparative Example 2

[0069] This comparative example aims to verify the effect of omitting the surface alumina passivation layer. In step S5, the alumina passivation layer is not deposited by magnetron sputtering, and other conditions are the same as in Example 1, with aging treatment performed directly.

[0070] Assembled all-solid-state battery tests revealed an interfacial contact impedance as high as 200 ohms per square centimeter, with a fill factor of 95%. At a current density of 0.8 mA per square centimeter, after 50 cycles, the material exhibited significant electrolyte decomposition and interfacial side reactions, with capacity retention rapidly dropping below 70% and volume expansion exceeding 15%. This indicates that the electrode surface, lacking passivation layer protection, is susceptible to electrolyte erosion, failing to form a stable electrode / electrolyte interface and severely impacting the battery's long-cycle performance and safety.

[0071] Comparative Example 3

[0072] This comparative example aims to verify the importance of the programmed temperature control cooling step. In step S4, a rapid cooling method is used, that is, the initial composite anode material is directly quenched from 240 degrees Celsius to room temperature at a cooling rate of approximately 50 degrees Celsius per minute. The remaining steps are the same as in Example 1.

[0073] After cooling, the material exhibited significant microcracks and interfacial delamination. Scanning electron microscopy revealed localized desorption between the lithium filler and the carbon framework. The material had an interfacial impedance of 120 Ω·cm² and a lithium filling rate of 90%. After 500 cycles, the capacity retention was 75%. In electrochemical testing, the material experienced accelerated volume expansion during cycling, reaching 20% ​​after 100 cycles, and the critical current density was only 0.8 mA / cm². These results indicate that uncontrolled cooling leads to thermal stress concentration, poor structural integrity, and severely impacts the electrode's mechanical stability and cycle life.

[0074] Traditional lithium foil has an interface impedance >300Ω·cm², a critical current density <0.3mA / cm², a capacity retention rate <50% after 500 cycles, and a volume expansion rate >30% after 100 cycles.

[0075] To more intuitively demonstrate the advantages of the technical solution of the present invention, the following is a systematic comparison of the key performance parameters of each embodiment and the comparative example, using a comparison chart of key performance parameters:

[0076] Materials Group Interfacial impedance (Ω·cm²) Critical current density (mA / cm²) Capacity retention rate after 500 cycles (%) Volume expansion rate (%) after 100 cycles Lithium filling rate (%) Example 1 <50 >1.2 >85 <8 >95 Example 2 55 1.1 83 9.5 93 Example 3 65 1.0 88 10 92 Example 4 70 1.0 90 9 94 Comparative Example 1 >150 <0.5 <60 >25 70 Comparative Example 2 200 0.8 <70 >15 95 Comparative Example 3 120 0.8 75 20 90 Traditional lithium foil >300 <0.3 <50 >30 -

[0077] As can be seen from the data in the table, the embodiments of the present invention are significantly superior to the comparative examples and traditional lithium foil anodes in terms of interfacial impedance, critical current density, cycle stability, and volume expansion control. This further confirms that the introduction of a nitrogen-doped carbon layer, the in-situ construction of a gradient interfacial phase, the programmed temperature-controlled cooling process, and the deposition of a surface alumina passivation layer are key technical features for improving the overall performance of the composite lithium metal anode material and its preparation method proposed in this invention. Each step works synergistically and is indispensable, jointly achieving a composite anode system with high ionic conductivity, structural integrity, interfacial stability, and high safety.

[0078] Through systematic comparison with the above embodiments and comparative examples, the technical advantages and necessity of the present invention have been fully verified. This solution not only exhibits excellent electrochemical and mechanical properties under ideal conditions, but also demonstrates good adaptability and stability under different structural parameters and process conditions, possessing clear prospects for industrial application.

[0079] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite lithium metal anode material, characterized in that, include: A three-dimensional porous carbon framework matrix with a connected pore structure, a pore size distribution ranging from 50 nanometers to 500 nanometers, and a specific surface area ranging from 800 square meters per gram to 1200 square meters per gram. A nitrogen-doped carbon layer is coated on the inner wall surface of the carbon skeleton, with a thickness of 2 nanometers to 10 nanometers and a nitrogen content of 6 atomic percent to 12 atomic percent, containing pyridine nitrogen and graphitic nitrogen functional groups. Metallic lithium is uniformly filled within the porous framework channels, forming an in-situ interface with the nitrogen-doped carbon layer. A gradient interface phase dominated by C-Li-N, with a thickness of 3 to 8 nanometers; A dense amorphous aluminum oxide passivation layer covers the outer surface of the material, with a thickness of 50 nanometers to 150 nanometers, a dielectric constant of 9 to 10, and a breakdown field strength of >5 megavolts per centimeter; The composite lithium metal anode material also contains an ion-conducting phase formed by the introduction of lithium nitride.

2. A method for preparing a composite lithium metal anode material, characterized in that, The preparation method for the composite lithium metal anode material according to claim 1 includes the following specific steps: Step S1: Provide a three-dimensional porous carbon framework matrix, wherein the three-dimensional porous carbon framework has a connected pore structure, the pore size distribution ranges from 50 nanometers to 500 nanometers, and the specific surface area is from 800 square meters per gram to 1200 square meters per gram. A nitrogen-doped carbon layer with a thickness of 2 nanometers to 10 nanometers is uniformly coated on the inner wall surface of the carbon framework by chemical vapor deposition process to form a composite conductive framework with high electronic conductivity and chemical stability. Step S2: Mix lithium metal blocks and lithium nitride powder in a mass ratio of 9:1 to 4:1, place them in a closed reaction chamber protected by an inert atmosphere, and heat them to melt at a temperature of 220 degrees Celsius to 260 degrees Celsius to form a homogenized lithium-rich melt, wherein the lithium nitride powder is uniformly dispersed in the liquid lithium as an ion-conducting phase precursor. Step S3: The composite conductive framework obtained in Step S1 is immersed in the lithium-rich melt prepared in Step S2. Driven by capillary force and wetting, the molten lithium spontaneously penetrates into the three-dimensional channels and undergoes an interfacial reaction with the nitrogen-doped carbon layer, generating in situ a composite conductive framework. A gradient interface phase dominated by C-Li-N is used to achieve uniform loading of lithium metal in the porous framework, thus obtaining the initial composite anode material. Step S4: The initial composite anode material obtained in step S3 is subjected to programmed temperature-controlled cooling treatment at a cooling rate of 0.5 degrees Celsius per minute to 2 degrees Celsius per minute, so that lithium can be directionally solidified in the channels, suppressing the generation of grain boundary defects and microcracks, and maintaining the integrity of the interface phase. Step S5: In an inert atmosphere glove box, an alumina passivation layer with a thickness of 50 nm to 150 nm is deposited on the surface of the initial composite negative electrode material using magnetron sputtering technology. The alumina passivation layer has a dense amorphous structure and is used to block electrolyte penetration and stabilize the electrode / electrolyte interface. Step S6: The material obtained in step S5 is left to stand at a temperature of 60 degrees Celsius to 80 degrees Celsius for 12 to 24 hours to promote further reconstruction of the interface phase and stress release, so as to obtain the final composite lithium metal anode material.

3. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S1, the three-dimensional porous carbon skeleton is synthesized by a template method. An ordered macroporous structure formed by the self-assembly of silica nanospheres is used as a hard template. After being filled with phenolic resin and carbonized, the template is removed with hydrofluoric acid solution to obtain a carbon skeleton with periodically interconnected channels and a channel connectivity rate of >98%. The nitrogen content of the nitrogen-doped carbon layer is 6 atomic percent to 12 atomic percent, and it contains pyridine nitrogen and graphitic nitrogen functional groups.

4. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S2, the average particle size of the lithium nitride powder is <100 nanometers. After ball milling, it is mixed with the lithium metal block to ensure complete dissolution and uniform distribution in the molten lithium phase during heating.

5. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S3, the immersion process is carried out in a vacuum environment, with a vacuum degree > Pa, to achieve a lithium filling rate >95%.

6. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S3, the interfacial reaction lasts for 10 to 30 minutes, the reaction temperature is maintained at 240 degrees Celsius, and a nitrogen-rich interfacial transition layer with a thickness of 3 to 8 nanometers is generated.

7. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S4, the programmed temperature control cooling starts at 240 degrees Celsius and is divided into three stages: the first stage cools down to 180 degrees Celsius at a rate of 2 degrees Celsius per minute, the second stage cools down to 100 degrees Celsius at a rate of 1 degree Celsius per minute, and the third stage cools down to room temperature at a rate of 0.5 degrees Celsius per minute.

8. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S5, the magnetron sputtering uses a high-purity alumina ceramic target, with a sputtering power of 80 watts to 120 watts, a working pressure of 0.5 Pa to 1.5 Pa, an argon to oxygen flow ratio of 4:1, and a deposition rate controlled at 0.8 nanometers per second to 1.2 nanometers per second.

9. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S5, the dielectric constant of the alumina passivation layer is 9 to 10, and the breakdown field strength is >5 megavolts per centimeter.

10. The method for preparing the composite lithium metal anode material according to claim 2, characterized in that: In step S6, the aging treatment is carried out in a dry argon atmosphere with a relative humidity of <1ppm to promote the formation of a Li-Al-ON composite interface between the Li3N phase and the alumina passivation layer.

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