A negative electrode, a method for preparing the same, and a lithium metal battery including the same

Abstract

The application provides a negative electrode and a preparation method thereof and a lithium metal battery containing the same, and relates to the technical field of lithium metal batteries. The negative electrode comprises a negative electrode current collector and a composite functional layer, a lithiumophilic layer and a lithium seed layer which are sequentially stacked in the direction away from the negative electrode current collector; wherein the composite functional layer contains AlF3 and a lithium supplementing agent, and the mass fraction of the AlF3 is greater than that of the lithium supplementing agent. The negative electrode builds a gradient functional interface of the composite functional layer, the lithiumophilic layer and the lithium seed layer on the surface of the negative electrode current collector in sequence, realizes multi-dimensional synergistic regulation, significantly improves the first circle coulombic efficiency of the lithium ion battery using the negative electrode, greatly reduces the interface impedance, and makes the lithium deposition uniform and dense during the cycle process, thereby effectively solving the problems of dendrite growth, low coulombic efficiency and short cycle life of the conventional negative electrode caused by the lithium-averse property.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery technology, and in particular to a negative electrode, a method for preparing the same, and a lithium metal battery containing the same. Background Technology

[0002] With the development of new energy vehicles and the energy storage industry, traditional graphite anode batteries are gradually approaching their theoretical energy density limit, making it difficult to meet the ultra-high energy density requirements of future electric vehicles' long range and large-scale energy storage systems. Against this backdrop, lithium-free anode lithium metal batteries have attracted widespread attention due to their unique structural design. These batteries do not pre-deposit or place lithium metal sources on the anode side; instead, they directly use a current collector as the anode carrier. Lithium ions in the cathode migrate to the anode surface during the first charge and are deposited in situ to form a lithium metal layer. This approach significantly reduces the use of inactive materials (such as excess lithium metal), substantially reducing the mass and volume of the anode side, thereby effectively improving the overall energy density of the battery.

[0003] However, lithium-free anode structures also face numerous challenges in practical applications. Due to the lack of a stable lithium host on the anode side, lithium deposition on the current collector surface is often uneven, easily leading to lithium dendrite formation. The growth of lithium dendrites not only punctures the separator, causing internal short circuits and posing serious safety hazards, but also exacerbates side reactions between lithium and the electrolyte, resulting in the generation of "dead lithium" and the continuous consumption of reversible lithium, thus severely degrading the battery's coulombic efficiency and cycle life. Furthermore, conventional current collector materials (such as copper foil) have poor interfacial affinity with metallic lithium, resulting in high nucleation overpotentials during lithium deposition, further inducing uneven deposition and volume expansion. Therefore, how to effectively control lithium deposition / stripping behavior through reasonable interface design of the current collector surface has become a key technical challenge in current research on lithium-free anode lithium metal batteries. Existing technologies typically employ individual modifications using lithium-affinity metal layers, fluoride coatings, or lithium replenishing agents, but these methods struggle to simultaneously address lithium nucleation, interface stability, and lithium source compensation.

[0004] Therefore, it is of great significance to develop an anode that combines lithophile induction, stable SEI construction, and lithium replenishment functions.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a negative electrode in which an AlF3 / lithiogen composite functional layer, a lithiophilic layer, and a lithium seed layer are constructed on the negative electrode current collector. Through the synergistic effect of the gradient sequence structure of the multilayer structure, the first-cycle coulombic efficiency of lithium metal batteries using this negative electrode is significantly improved, and the interface impedance is greatly reduced. This effectively solves the problems of dendrite growth, low coulombic efficiency, and short cycle life caused by the lithiophilicity of conventional lithium-free negative electrodes.

[0007] The second objective of this invention is to provide a method for preparing a negative electrode.

[0008] A third objective of this invention is to provide a lithium metal battery.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention provides a negative electrode, comprising a negative electrode current collector and a composite functional layer, a lithiophilic layer, and a lithium seed layer sequentially stacked along a direction away from the negative electrode current collector; wherein: The material of the lithiophilic layer is selected from at least one of Mg, Zn and Ag; the composite functional layer contains AlF3 and a lithium supplementing agent, wherein the mass fraction of AlF3 is greater than the mass fraction of the lithium supplementing agent; Furthermore, the mass ratio of AlF3 to lithium supplement is 50~80:10~40.

[0010] Furthermore, the lithium replenishing agent includes at least one of Li2C2O4 and Li3N; And / or, the composite functional layer further includes a conductive agent and a binder; The mass ratio of AlF3, lithium supplement, conductive agent and binder is 50~80:10~40:5~15:5~15.

[0011] Furthermore, the conductive agent is selected from one or more of carbon black, carbon nanotubes, and graphene; And / or, the adhesive is selected from one or more of PVDF, PTFE, PAN, CMC and SBR; And / or, the negative electrode current collector is selected from any one of copper foil, composite copper foil, nickel foil, composite nickel foil, stainless steel foil, composite stainless steel foil, titanium foil, and composite titanium foil.

[0012] Furthermore, the thickness of the composite functional layer is 3~10μm; The thickness of the lithiophilic layer is 20~100nm; The thickness of the lithium seed layer is 0.5~2μm.

[0013] The present invention provides a method for preparing a negative electrode, comprising the following steps: S1: A composite functional layer is formed on the surface of the negative electrode current collector; S2: A lithiophilic layer is formed on the surface of the composite functional layer; S3: A lithium seed layer is formed on the surface of the lithiophilic layer; The steps of forming the lithiophilic layer and forming the lithium seed layer are carried out continuously in the same vacuum environment without breaking the vacuum in between.

[0014] Furthermore, the method for preparing the composite functional layer includes: coating a slurry containing AlF3, lithium supplement, conductive agent and binder onto the surface of the negative electrode current collector to obtain a wet film, and then drying it to form the composite functional layer.

[0015] Furthermore, the thickness of the wet film is 20~100μm; The drying process involves vacuum drying at 80°C for 10-14 hours.

[0016] Furthermore, the lithiophilic layer and lithium seed layer are formed by vapor deposition; Preferably, the steps of forming the lithiophilic layer and forming the lithium seed layer are carried out continuously while maintaining a vacuum state without breaking the vacuum, and are achieved by switching the evaporation source.

[0017] Furthermore, the vacuum level of the vacuum environment is ≤10. -5 Pa.

[0018] The present invention provides a lithium metal battery, wherein the lithium-ion battery includes the above-described negative electrode or the negative electrode prepared according to the above-described preparation method.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a negative electrode, comprising a negative electrode current collector and a composite functional layer, a lithiophilic layer, and a lithium seed layer sequentially stacked along a direction away from the negative electrode current collector; wherein: the lithiophilic layer is made of at least one of Mg, Zn, and Ag; the composite functional layer comprises AlF3 and a lithium supplement, wherein the mass fraction of AlF3 is greater than the mass fraction of the lithium supplement, and further, the mass ratio of AlF3 to Li3N is 50~80:10~40.

[0020] In the first charging stage, the pre-lithiated lithium seed layer of the negative electrode of the present invention can directly compensate for the active lithium consumed in the formation of SEI, effectively improving the first-cycle coulombic efficiency of the lithium metal battery. At the same time, after the lithiophilic layer and the lithium seed layer come into contact with each other, a Li-X (X=Mg, Zn, Ag) transition interface (alloyed region) is formed. Its flexible flow characteristics can eliminate local stress concentration in time and prevent the rigid LiF layer from cracking due to stress accumulation.

[0021] Furthermore, the composite functional layer containing AlF3 and a lithium replenishing agent forms an inorganic enriched interface phase containing LiF and a lithium replenishing agent in the interface region in contact with lithium. Specifically, during battery cycling, when Li... + Upon reaching the vicinity of AlF3, AlF3 undergoes an in-situ transformation reaction with metallic lithium (from lithium seed layer 4 or early deposited lithium) at their interface (AlF3 + 3Li). + +3e →3LiF+Al), the generated nanoscale LiF grains and Al together form a rigid framework with high mechanical strength in the composite functional layer 2. The generated LiF provides high interfacial mechanical stability and electronic barrier capability, while the lithium supplement provides lithium ion transport channels. Together, they alleviate the problems of limited ion transport in a single LiF layer and insufficient mechanical constraint on the interfacial region by a single lithium supplement layer.

[0022] Meanwhile, it is also important to clarify that the interface phase containing LiF and the lithium replenishing agent works in conjunction with the upper Li-X (X = Mg, Zn, Ag) transition interface: the former maintains ion transport and interface morphology stability, while the latter provides re-nucleation sites and protects the former from cracking due to stress accumulation; only when both are present can uniform lithium deposition be maintained and dead lithium accumulation reduced during the battery's initial deposition, deep stripping, and re-deposition cycles. In short, this invention, through the synergistic effect of the aforementioned layers, significantly improves the first-cycle coulombic efficiency of lithium metal batteries using this anode, substantially reduces interface impedance, and ensures uniform and dense lithium deposition during cycling, effectively solving the problems of dendrite growth, low coulombic efficiency, and short cycle life present in conventional lithium-free anodes.

[0023] The present invention provides a method for preparing a negative electrode. This method involves sequentially forming a composite functional layer, a lithiophilic layer, and a lithium seed layer on the surface of the negative electrode current collector, and ensuring that the latter two steps are completed continuously without breaking the vacuum. This avoids the oxidation of the lithiophilic layer and the deactivation of the lithium seed layer upon contact with air, thus ensuring the structural integrity and interfacial activity of each functional layer and achieving precise construction and synergistic effect of the gradient functional interface.

[0024] The lithium metal battery provided by the present invention uses the negative electrode as the negative electrode carrier, which can achieve uniform in-situ deposition of lithium during the first charge, and maintain interface stability, suppress dendrite growth, and compensate for the loss of active lithium during cycling, thereby improving the battery's first-cycle coulombic efficiency, cycle life and safety performance. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the negative electrode structure provided in Embodiment 1 of the present invention.

[0027] Icons: 1-Negative electrode current collector; 2-Composite functional layer; 3-Lithophilic layer; 4-Lithium seed layer. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] According to one aspect of the present invention, a negative electrode includes a negative electrode current collector 1 and a composite functional layer 2, a lithiophilic layer 3, and a lithium seed layer 4 sequentially stacked along a direction away from the negative electrode current collector 1; wherein: The composite functional layer 2 contains AlF3 and a lithium replenishing agent, wherein the mass fraction of AlF3 is greater than the mass fraction of the lithium replenishing agent.

[0030] Furthermore, the lithium supplement includes at least one of Li2C2O4 and Li3N.

[0031] The composite functional layer 2 further includes a conductive agent and a binder, and the mass ratio of AlF3, lithium supplementer, conductive agent and binder is 50~80:10~40:5~15:5~15. The negative electrode achieves multi-dimensional synergistic regulation of lithium deposition behavior by constructing a gradient functional interface of "negative electrode current collector 1, composite functional layer 2, lithiophilic layer 3, lithium seed layer 4".

[0032] Specifically, the composite functional layer 2 at the bottom layer contains AlF3 and a lithium replenishing agent, with their mass ratio controlled within the range of 50~80:10~40. This ensures that AlF3 transforms in situ into a LiF-rich solid electrolyte interface film upon contact with metallic lithium, utilizing the high mechanical strength of LiF to physically suppress lithium dendrite growth. Simultaneously, it leverages the advantages of the lithium replenishing agent (preferably Li3N) as a superionic conductor, significantly improving the interfacial lithium-ion transport kinetics. Furthermore, Li3N releases active lithium ions at its decomposition potential, compensating for irreversible lithium loss caused by SEI film formation and the formation of "dead lithium." The lithiophilic layer 3 in the middle provides high-density heterogeneous nucleation sites for lithium deposition, effectively reducing the nucleation overpotential and inducing lithium to transform from disordered island growth to uniform layered growth. The lithium seed layer 4 on the surface transforms the initially deposited heterogeneous interface into a homogeneous interface, effectively eliminating the initial nucleation barrier.

[0033] Through the synergistic effect of the above-mentioned layers, the present invention significantly improves the first-cycle coulombic efficiency of lithium metal batteries using this negative electrode, greatly reduces the interface impedance, and ensures uniform and dense lithium deposition during cycling. This effectively solves the problems of dendrite growth, low coulombic efficiency, and short cycle life caused by the lithium-repellent properties of conventional lithium-free negative electrode current collector 1.

[0034] It should be noted that the working principles and synergistic mechanisms of each layer in this application are summarized as follows: (1) AlF3 / Li3N composite functional layer 2: In composite functional layer 2, AlF3 reacts with metallic lithium to form LiF in situ, blocking side reactions between the electrolyte and lithium and inhibiting lithium dendrite growth. Simultaneously, Li3N in composite functional layer 2 enhances interfacial ion transport capacity, reduces interfacial impedance, and decomposes to release active lithium during cycling, compensating for the loss of active lithium caused by side reactions and "dead lithium." Specifically, during battery cycling, when Li... + Upon reaching the vicinity of AlF3, AlF3 undergoes an in-situ transformation reaction with metallic lithium (from lithium seed layer 4 or early deposited lithium) at their interface (AlF3 + 3Li). + +3e →3LiF+Al), the resulting nanoscale LiF grains and Al together form a rigid framework with high mechanical strength within the composite functional layer 2. Simultaneously, LiF possesses low electronic conductivity and moderate ionic conductivity, which can force Li... + Electrons are concentrated in the Li3N phase to prevent local short circuits or precipitation of electrons inside the functional layer.

[0035] (2) Lithophilic layer 3: The AlF3 and the lithiophilic layer 3 can achieve spatial complementarity and dynamic synergistic regulation. Specifically, the surface lithiophilic layer 3 provides high-density heterogeneous nucleation sites, inducing uniform deposition of disordered lithium, while the underlying AlF3 transforms in situ into high-mechanical-strength LiF nanocrystals upon contact with metallic lithium, constructing a rigid framework with good mechanical stability on the surface of the negative electrode current collector 1. During battery cycling, when lithium deposition occurs, the lithiophilic layer 3 material guides the lithium ions above it. + The material is deposited uniformly downwards and anchored by the underlying AlF3 framework. The directional deposition channel guided by the lithiophilic layer 3 material can avoid the growth of lithium dendrites caused by excessive lithium ion flux.

[0036] In addition, after the Li-X (X=Mg, Zn, Ag) alloy is formed by cycling, its flexible flow can eliminate local stress concentration in time, preventing the rigid LiF layer from cracking due to stress accumulation (the rigid LiF layer can effectively suppress the tip penetration of lithium dendrites and prevent the flexible alloy layer from collapsing due to excessive deformation, thus causing local lithium depletion); the rigid-flexible interface formed by the two together blocks the two major failure paths of dendrite penetration and interface peeling during battery cycling from the root.

[0037] (3) Lithium seed layer 4: The lithium seed layer 4 enables the initial deposition to occur at the homogeneous lithium interface, reducing the nucleation barrier of the first deposition; this pre-lithiation layer can directly compensate for the active lithium consumed by the formation of SEI on the negative electrode side during the first charge of the positive electrode, effectively improving the first-cycle coulombic efficiency of the lithium metal battery.

[0038] When the above-mentioned negative electrode structure is prepared, when a lithium seed layer 4 is formed on the lithiophilic layer 3 by vacuum evaporation, the lithium in the lithium seed layer 4 and the magnesium in the lithiophilic layer 3 will undergo an alloying reaction at their interface to generate a Li-X (X=Mg, Zn, Ag) alloy solid solution (if the lithium seed layer 4 is not prepared by vacuum evaporation, this reaction will also occur during subsequent battery cycling to generate a Li-X (X=Mg, Zn, Ag) alloy). It should be clarified that the lithium in the lithium seed layer 4 is used to compensate for the loss of active lithium and is not directly used as the negative electrode active material. In the lithium metal battery using the negative electrode of this application, the negative electrode can essentially be understood as a lithium-free negative electrode, and its negative electrode active material (the active lithium deposited on the negative electrode current collector 1) is converted from the lithium ions released by the positive electrode.

[0039] When the above-mentioned negative electrode, positive electrode, and solid electrolyte are assembled into a battery, the overall charge-discharge mechanism of the battery cycle is as follows: During charging, lithium ions (Li) + Starting from the positive electrode, it sequentially passes through the lithium seed layer 4 (homogeneous epitaxy, zero barrier) and the lithiophilic layer 3 (lithiophilic induction, flux homogenization, in-situ generation of Li-X (X=Mg, Zn, Ag) alloy solid solution, serving as a buffer layer), and then migrates at high speed along the fast ion channel constructed by Li3N in the AlF3-Li3N composite functional layer 2, gaining electrons on the surface of the negative electrode current collector 1 and being reduced to dense layered metallic lithium.

[0040] During discharge, the process proceeds in reverse: metallic lithium is smoothly stripped into Li under the interfacial anchoring and diffusion enhancement of lithium-philic atoms. + AlF3 migrates out along the reverse channel of Li3N. At the same time, AlF3 reacts with lithium in Li-X (X=Mg, Zn, Ag) alloy to generate LiF and Al. The LiF and Al obtained by in-situ conversion have a rigid framework to resist volume shrinkage and maintain structural integrity.

[0041] Taking Mg as an example, throughout the charging and discharging process, Mg atoms suppress Li vacancy aggregation by extending the Sand time (depletion time), forming a dynamic and stable interface with the AlF3 / Li3N functional layer that combines rigidity and flexibility. This achieves efficient, uniform, and reversible insertion and extraction of lithium ions in the negative electrode. Specifically, in this invention, the lithiophilic layer 3 (thickness 20~100 nm) reacts in situ with the surface lithium seed layer 4 to form a β-phase Li-X (X=Mg, Zn, Ag) solid solution alloy, according to the Sand equation (… = (t0 (depletion time): the time required for the interfacial lithium concentration to drop to the critical point, D) eff (Diffusion coefficient: the rate at which lithium diffuses in the anode phase), the interfacial Li depletion time t0 and the effective diffusion coefficient of Li in the anode phase (D)eff They are strictly proportional (t0∝D) eff ). D of Li-X (X=Mg, Zn, Ag) alloys eff The higher current density compared to pure lithium allows for a longer sand time (t0). A longer t0 means that, at the same stripping current density, the Li concentration at the interface can be maintained for a longer period. Li vacancies are less likely to become supersaturated and nucleate at the interface, thus effectively suppressing the growth of micro-voids. This avoids interface stripping failure caused by void expansion at the lithium stripping interface, which leads to local contact loss, current concentration in the residual contact area, and consequently increased polarization and accumulation of "dead lithium".

[0042] Meanwhile, the in-situ Li-X (X=Mg, Zn, Ag) solid solution provides dynamic chemical anchoring at the lithium stripping interface due to the high mobility and continuous lithium-affinity adsorption of lithium-affin atoms in the lithium phase, preventing Li vacancies from agglomerating and forming nuclei at the interface, and giving the voids a self-repairing evolution path of "split-collapse". When the battery uses a sulfide solid electrolyte, the Li-X (X=Mg, Zn, Ag) solid solution further strengthens the contact between the negative electrode and the electrolyte layer through chemical bonding with sulfur.

[0043] The synergistic effect of the aforementioned diffusion kinetics and interfacial chemistry enables the gradient negative electrode of this invention to maintain a tight conformal interfacial contact throughout the charge-discharge cycle, thereby fundamentally blocking both the two major failure paths of "dendritic penetration" and "interfacial peeling".

[0044] In a preferred embodiment of the present invention, the lithium supplement includes at least one of Li2C2O4 and Li3N; In a preferred embodiment of the present invention, the composite functional layer 2 further includes a conductive agent and a binder; the mass ratio of AlF3, lithium supplement, conductive agent and binder is 50~80:10~40:5~15:5~15, preferably 70:15:10:5.

[0045] As an optional implementation, the mass ratio of AlF3, Li3N, conductive agent and binder is 50~80:10~40:5~15:5~15, for example, it can be 50:10:5:5, 80:40:15:15, or 70:15:10:5, or any combination of values ​​within this range.

[0046] In a preferred embodiment of the present invention, the conductive agent is selected from one or more of carbon black, carbon nanotubes, and graphene; In a preferred embodiment of the present invention, the adhesive is selected from one or more of PVDF, PTFE, PAN, CMC and SBR; In a preferred embodiment of the present invention, the negative electrode current collector 1 is selected from any one of copper foil, composite copper foil, nickel foil, composite nickel foil, stainless steel foil, composite stainless steel foil, titanium foil, and composite titanium foil.

[0047] In a preferred embodiment of the present invention, the thickness of the composite functional layer 2 is 3~10μm; the thickness of the lithiophilic layer 3 is 20~100nm; and the thickness of the lithium seed layer 4 is 0.5~2μm.

[0048] In a preferred embodiment, the thickness of the composite functional layer 2 of the present invention is 3~10 μm, which is beneficial to ensure interface stability and lithium replenishment capacity while taking into account ion transport dynamics; the thickness of the lithiophilic layer 3 is 20~100 nm, which can achieve a balance between providing sufficient lithiophilic nucleation sites and maintaining good electronic conductivity; the thickness of the lithium seed layer 4 is 0.5~2 μm, which can effectively eliminate the nucleation barrier of the first deposition and improve the initial coulombic efficiency, while avoiding the increase of inactive mass and the weakening of the advantages of the lithium-free anode structure due to excessive thickness.

[0049] According to one aspect of the present invention, a method for preparing a negative electrode includes the following steps: S1: A composite functional layer 2 is formed on the surface of the negative electrode current collector 1; S2: A lithiophilic layer 3 is formed on the surface of the composite functional layer 2; S3: A lithium seed layer 4 is formed on the surface of the lithiophilic layer 3; The steps of forming the lithiophilic layer 3 and the lithium seed layer 4 are carried out continuously in the same vacuum environment without breaking the vacuum in between.

[0050] The present invention provides a method for preparing a negative electrode. This method involves sequentially forming a composite functional layer 2, a lithiophilic layer 3, and a lithium seed layer 4 on the surface of the negative electrode current collector 1, and ensuring that the latter two steps are completed continuously without breaking the vacuum. This avoids the oxidation of the lithiophilic layer 3 and the deactivation of the lithium seed layer 4 upon contact with air, thus ensuring the structural integrity and interfacial activity of each functional layer and achieving the precise construction and synergistic effect of the gradient functional interface.

[0051] In a preferred embodiment of the present invention, the method for preparing the composite functional layer 2 includes: coating a slurry containing AlF3, Li3N, a conductive agent and a binder onto the surface of the negative electrode current collector 1 to obtain a wet film, and then drying it to form the composite functional layer 2.

[0052] In a preferred embodiment, the present invention coats a slurry containing AlF3, Li3N, a conductive agent and a binder onto the surface of the negative electrode current collector 1 and dries it into a film. This enables uniform loading and firm bonding of the composite functional layer 2 on the current collector, ensuring that it maintains structural stability and continuous function during subsequent evaporation and battery cycling.

[0053] In a preferred embodiment of the present invention, the thickness of the wet film is 20~100μm.

[0054] As an optional implementation, the thickness of the wet film is 20~100μm, for example, it can be 20 μm, 40μm, 60μm, 80μm, 100μm, or any value between 20 and 100μm.

[0055] In a preferred embodiment of the present invention, the drying is performed by vacuum drying at 80°C for 10-14 hours.

[0056] In a preferred embodiment of the present invention, the lithiophilic layer 3 and the lithium seed layer 4 are formed by vapor deposition; Preferably, the steps of forming the lithiophilic layer 3 and the lithium seed layer 4 are carried out continuously while maintaining a vacuum state without breaking the vacuum, and are achieved by switching the evaporation source.

[0057] As a preferred embodiment, the lithiophilic layer 3 and the lithium seed layer 4 of the present invention are formed by vapor deposition, which is beneficial to obtaining a functional layer with precise thickness, clean interface and no solvent residue. By continuously vapor deposition by switching evaporation sources in the same vacuum environment, the oxidation of the lithiophilic layer 3 and the deactivation of the lithium seed layer 4 can be avoided, ensuring that the interface between the two layers is pure and tightly bonded, and ensuring the integrity and functional synergy of the gradient structure.

[0058] In a preferred embodiment of the present invention, the vacuum level of the vacuum environment is ≤10. -5 Pa.

[0059] In a preferred embodiment, the vacuum level of the present invention is controlled at ≤10. -5 Pa can effectively reduce the interference of residual gas on the evaporation process, ensuring the purity, density and interface quality of the lithiophilic layer 3 and the lithium seed layer 4, thereby improving the lithiophilicity, stability and electrochemical activity of the functional layer.

[0060] According to one aspect of the present invention, a lithium metal battery, the lithium-ion battery comprising the above-described negative electrode or the negative electrode prepared according to the above-described preparation method.

[0061] The lithium metal battery provided by the present invention uses the negative electrode as the negative electrode carrier, which can achieve uniform in-situ deposition of lithium during the first charge, and maintain interface stability, suppress dendrite growth, and compensate for the loss of active lithium during cycling, thereby improving the battery's first-cycle coulombic efficiency, cycle life and safety performance.

[0062] The technical solution of the present invention will be further described below with reference to the embodiments.

[0063] Example 1 Figure 1 This is a schematic diagram of the negative electrode structure provided in Embodiment 1 of the present invention; in, Figure 1 In the middle, 1 is the negative electrode current collector 1; Figure 1 Layer 2 is a composite functional layer 2; Figure 1 In the middle, layer 3 is a lithiophilic layer; Figure 1 In the middle, layer 4 is the lithium seed layer.

[0064] See Figure 1 This embodiment provides a negative electrode and its preparation method, the method is as follows: 1. Copper foil pretreatment: A 6 μm thick copper foil was selected as the negative electrode current collector 1. The copper foil was sequentially placed in acetone and anhydrous ethanol and ultrasonically cleaned for 15 min each to remove surface oil and oxide layer. The cleaned copper foil was then transferred to a vacuum oven and dried at 60 °C for 12 h. After drying, it was placed in an inert atmosphere glove box for later use.

[0065] 2. Preparation of composite slurry: Weigh the raw materials according to the following mass fractions: 70 wt% AlF3, 15 wt% Li3N, 10 wt% Super P conductive carbon, and 5 wt% PVDF binder. Add the above powders to N,N-dimethylformamide (DMF) solvent and stir continuously on a magnetic stirrer for 12 h until a uniformly dispersed, free-flowing black composite slurry is formed.

[0066] 3. Coating and drying of composite functional layer 2: The composite slurry was uniformly coated onto the pretreated copper foil surface using a doctor blade with a gap of 100 μm. After coating, the sample was dried in a vacuum environment at 80 °C for 12 h to completely remove the solvent and cure the adhesive. After drying, an AlF3 / Li3N composite functional layer 2 with a thickness of approximately 5 μm was formed on the copper foil surface.

[0067] 4. Preparation of lithiophilic layer 3: Transfer the dried sample into the thermal evaporation equipment chamber. Evacuate the system until the vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process and controlling the evaporation rate, metallic magnesium was deposited on the surface of the AlF3 / Li3N composite functional layer 2 to obtain a lithiophilic layer 3 with a thickness of approximately 50 nm.

[0068] 5. Preparation of lithium seed layer 4: While maintaining a high vacuum in the cavity, the evaporation source was directly switched to lithium metal, and the thermal evaporation process was continued to deposit lithium metal on the surface of the lithiophilic layer 3, thus obtaining a lithium seed layer 4 with a thickness of about 1 μm.

[0069] Thus, a gradient lithium-supplemented-lithophile anode is obtained, whose microstructure along the direction away from the anode current collector 1 is as follows: anode current collector 1, AlF3 / Li3N composite functional layer 2, lithiophile layer 3, and lithium seed layer 4.

[0070] Example 2 Except for the composition of the slurry in "Step 2, Preparation of Composite Slurry", which differs from that in Example 1, this embodiment is the same as the previous embodiment, as detailed below: Weigh the raw materials according to the following mass fractions: 350 wt% AlF3, 10 wt% Li3N, 15 wt% Super P conductive carbon, and 15 wt% PVDF binder. Add the above powders to N,N-dimethylformamide (DMF) solvent and stir continuously on a magnetic stirrer for 12 h until a uniformly dispersed, free-flowing black composite slurry is formed.

[0071] The mass ratio of AlF3 to Li3N is 50:10; the mass ratio of AlF3, Li3N, conductive agent and binder is 50:10:15:15.

[0072] Example 3 Except for the composition of the slurry in "Step 2, Preparation of Composite Slurry", which differs from that in Example 1, this embodiment is the same as the previous embodiment, as detailed below: Weigh the raw materials according to the following mass fractions: 80 wt% AlF3, 10 wt% Li3N, 5 wt% Super P conductive carbon, and 5 wt% PVDF binder. Add the above powders to N,N-dimethylformamide (DMF) solvent and stir continuously on a magnetic stirrer for 12 h until a uniformly dispersed, free-flowing black composite slurry is formed.

[0073] The mass ratio of AlF3 to Li3N is 80:10; the mass ratio of AlF3, Li3N, conductive agent and binder is 80:10:5:5.

[0074] Example 4 Except for the thickness parameters of each layer, the steps in this embodiment are the same as those in Embodiment 1.

[0075] Specifically, the preparation method includes: 1. Copper foil pretreatment: Same as in Example 1; 2. Preparation of composite slurry: Same as in Example 1; 3. Coating and drying of composite functional layer 2: The composite slurry was uniformly coated onto the pretreated copper foil surface using a doctor blade with a gap of 30 μm. After coating, the sample was dried in a vacuum environment at 80 °C for 12 h to completely remove the solvent and cure the adhesive. After drying, an AlF3 / Li3N composite functional layer 2 with a thickness of approximately 3 μm was formed on the copper foil surface.

[0076] 4. Preparation of lithiophilic layer 3: Transfer the dried sample into the thermal evaporation equipment chamber. Evacuate the system until the vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process and controlling the evaporation rate, metallic magnesium was deposited on the surface of the AlF3 / Li3N composite functional layer 2 to obtain a lithiophilic layer 3 with a thickness of approximately 20 nm.

[0077] 5. Preparation of lithium seed layer 4: While maintaining a high vacuum in the cavity, the evaporation source was directly switched to lithium metal, and the thermal evaporation process was continued to deposit lithium metal on the surface of the lithiophilic layer 3, resulting in a lithium seed layer 4 with a thickness of approximately 0.5 μm.

[0078] Example 5 Except for the thickness parameters of each layer, the steps in this embodiment are the same as those in Embodiment 1.

[0079] Specifically, the preparation method includes: 1. Copper foil pretreatment: Same as in Example 1; 2. Preparation of composite slurry: Same as in Example 1; 3. Coating and drying of composite functional layer 2 The composite slurry was uniformly coated onto the pretreated copper foil surface using a doctor blade with a gap of 120 μm. After coating, the sample was dried in a vacuum environment at 80 °C for 12 h to completely remove the solvent and cure the adhesive. After drying, an AlF3 / Li3N composite functional layer 2 with a thickness of approximately 10 μm was formed on the copper foil surface.

[0080] 4. Preparation of lithiophilic layer 3: Transfer the dried sample into the thermal evaporation equipment chamber. Evacuate the system until the vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process and controlling the evaporation rate, metallic magnesium was deposited on the surface of the AlF3 / Li3N composite functional layer 2 to obtain a lithiophilic layer 3 with a thickness of approximately 100 nm.

[0081] 5. Preparation of lithium seed layer 4: While maintaining a high vacuum in the cavity, the evaporation source was directly switched to lithium metal, and the thermal evaporation process was continued to deposit lithium metal on the surface of the lithiophilic layer 3, thus obtaining a lithium seed layer 4 with a thickness of about 2 μm.

[0082] Comparative Example 1 This comparative example provides a lithium metal current collector without functional layer modification and its preparation method, which is used as a blank control group for the negative electrode of this invention.

[0083] 1. Copper foil pretreatment: A 6 μm thick copper foil was selected as the current collector substrate. The copper foil was sequentially placed in acetone and anhydrous ethanol and ultrasonically cleaned for 15 min each to remove surface oil and oxide layer. The cleaned copper foil was then transferred to a vacuum oven and dried at 60 °C for 12 h. After drying, it was placed in an inert atmosphere glove box for later use.

[0084] 2. Lithium layer preparation: The pretreated copper foil is transferred into the thermal evaporation equipment chamber, and a vacuum is drawn until the system vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process, metallic lithium was directly deposited on the surface of copper foil to obtain a lithium layer with a thickness of approximately 2 μm (i.e., without an intermediate functional layer). This yielded a simple negative electrode with a structure of "lithium layer / negative electrode current collector 1".

[0085] Comparative Example 2 This comparative example provides a lithium metal current collector that uses tin (Sn) instead of magnesium (Mg) as the lithiophilic intermediate layer to verify the irreplaceability of the lithiophilic layer 3.

[0086] 1. Copper foil pretreatment: Same as in Example 1.

[0087] 2. Coating and drying of composite functional layer 2: Same as in Example 1.

[0088] 3. Preparation of Sn lithiophilic layer 3: Transfer the dried sample into the chamber of the thermal evaporation equipment and evacuate to a vacuum level of ≤10. -5 Pa. Using a thermal evaporation process, metallic tin was deposited on the surface of the composite functional layer 2 to obtain a Sn layer with a thickness of approximately 50 nm (replacing the lithiophilic layer 3).

[0089] 4. Preparation of lithium seed layer 4: While maintaining a vacuum, the evaporation source was switched to lithium metal, and lithium metal was deposited on the surface of the Sn layer to obtain a lithium seed layer 4 with a thickness of approximately 1 μm. Thus, a negative electrode with the structure "lithium seed layer 4 / Sn lithiophilic layer 3 / AlF3-Li3N composite functional layer 2 / negative electrode current collector 1" was obtained.

[0090] Comparative Example 3 This comparative example provides a lithium metal current collector containing only a single AlF3 functional layer, without Li3N and the lithiophilic layer 3, to verify the necessity of Li3N and the lithiophilic layer 3 (corresponding to VELi-10μm@AlF3@Cu).

[0091] 1. Copper foil pretreatment: Same as in Example 1.

[0092] 2. Preparation of a single AlF3 layer: A pure AlF3 layer was deposited on the pretreated copper foil surface by thermal evaporation or magnetron sputtering, with the thickness controlled at about 5 μm (comparable to the thickness of composite functional layer 2 in Example 1).

[0093] 3. Preparation of lithium seed layer 4: While maintaining a vacuum, metallic lithium was deposited on the surface of the AlF3 layer to obtain a lithium seed layer 4 with a thickness of approximately 1 μm. Thus, a negative electrode with the structure "lithium seed layer 4 / AlF3 layer / negative electrode current collector 1" (without Li3N, without Mg) was obtained.

[0094] Comparative Example 4 This comparative example provides a negative electrode and its preparation method, the method being as follows: 1. Copper foil pretreatment: Same as in Example 1.

[0095] 2. Preparation of a single AlF3 layer: A pure AlF3 layer was deposited on the pretreated copper foil surface by thermal evaporation or magnetron sputtering, with the thickness controlled at about 5 μm (comparable to the thickness of composite functional layer 2 in Example 1).

[0096] 3. Preparation of lithiophilic layer 3: Transfer the dried sample into the thermal evaporation equipment chamber. Evacuate the system until the vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process and controlling the evaporation rate, metallic magnesium was deposited on the surface of a single AlF3 layer to obtain a lithiophilic layer 3 with a thickness of approximately 50 nm.

[0097] Preparation of lithium seed layer 4: While maintaining a vacuum, metallic lithium is deposited on the surface of the lithiophilic layer 3 to obtain a lithium seed layer 4 with a thickness of approximately 1 μm. Thus, a negative electrode with the structure "lithium seed layer 4 / lithophilic layer 3 / AlF3 layer / negative electrode current collector 1" is obtained.

[0098] Comparative Example 5 This embodiment provides a negative electrode and its preparation method, the method being as follows: 1. Copper foil pretreatment: Same as in Example 1.

[0099] 2. Preparation of a single-layer Li3N layer: A pure Li3N layer was deposited on the pretreated copper foil surface by thermal evaporation or magnetron sputtering, with the thickness controlled at about 5 μm (comparable to the thickness of composite functional layer 2 in Example 1).

[0100] 3. Preparation of lithiophilic layer 3: Transfer the dried sample into the thermal evaporation equipment chamber. Evacuate the system until the vacuum level reaches and is maintained at ≤10. -5 Pa. Using a thermal evaporation process and controlling the evaporation rate, metallic magnesium was deposited on the surface of a monolayer Li3N to obtain a lithiophilic layer 3 with a thickness of approximately 50 nm.

[0101] Preparation of lithium seed layer 4: While maintaining a vacuum, metallic lithium is deposited on the surface of the lithiophilic layer 3 to obtain a lithium seed layer 4 with a thickness of approximately 1 μm. Thus, a negative electrode with the structure "lithium seed layer 4 / lithophilic layer 3 / Li3N layer / negative electrode current collector 1" is obtained.

[0102] Comparative Example 6 This embodiment provides a negative electrode and its preparation method, the method being as follows: 1. Copper foil pretreatment: Same as in Example 1.

[0103] 2. Preparation of lithiophilic layer 3: The pretreated copper foil is transferred into the thermal evaporation equipment chamber. A vacuum is then drawn until the system vacuum level reaches and is maintained at ≤10. -5 Pa. A lithium-affinity layer with a thickness of approximately 50 nm was prepared by using a thermal evaporation process and controlling the evaporation rate to deposit metallic magnesium on the surface of copper foil.

[0104] 3. Preparation of Li3N layer: A pure Li3N layer was deposited on the surface of the lithiophilic layer 3 by thermal evaporation or magnetron sputtering, with the thickness controlled at approximately 2.5 μm.

[0105] 4. Preparation of AlF3 layer: A pure AlF3 layer was deposited on the surface of a monolayer Li3N layer using thermal evaporation or magnetron sputtering, with the thickness controlled at approximately 2.5 μm.

[0106] 5. Preparation of lithium seed layer 4: While maintaining a vacuum, metallic lithium was deposited on the surface of the AlF3 layer to obtain a lithium seed layer 4 with a thickness of approximately 1 μm. Thus, the structure obtained is "lithium seed layer 4 / lithophile layer 3 / Li3N layer / AlF3 layer / negative electrode current collector 1" (with a clear interface between the AlF3 layer and the Li3N layer).

[0107] Experimental Example 1 To verify the technical effect of the negative electrode of the present invention, the negative electrodes prepared in Examples 1-5 and Comparative Examples 1-6 were assembled into test batteries for electrochemical performance testing.

[0108] Specifically, each current collector was cut into 12mm diameter discs, with NCM811 as the positive electrode, and the positive electrode surface capacity was controlled at 4~5mAh cm⁻¹. -², Assemble CR2032 button cells in an argon atmosphere glove box.

[0109] The test methods and conditions are as follows: 1. Cycle life 0.2C: The cycle life is defined as the number of cycles when the capacity decays to 80% of the initial capacity under constant current charge and discharge at a rate of 0.2C, with a voltage range of 2.8~4.3V. 2. Capacity retention rate: After 400 cycles at 0.2C, calculate the ratio of the discharge capacity to the discharge capacity of the 3rd cycle; 3. Impedance: Electrochemical impedance spectroscopy (EIS) was used with a frequency range of 100kHz to 10mHz and an amplitude of 5mV. After the initial charge to 4.3V, the sample was left to stand for 2 hours before testing. The interface impedance (Rct) was obtained by fitting an equivalent circuit.

[0110] See Table 1 for specific test results.

[0111] Table 1. Electrochemical performance test results of each example and comparative example in this experiment:

[0112] As shown in Table 1, Examples 1 through 5 all exhibited excellent cycle stability and low interface impedance. Among them, Example 1 had the best overall performance, with higher cycle life and capacity retention than the other examples, and the lowest interface impedance. The performance of Example 4 was second only to Example 1, indicating that appropriately reducing the thickness of each layer has the potential to save materials and simplify the process. However, excessive thinning (such as the low Li3N ratio in Example 2) or increasing the thickness (such as in Example 5) will lead to a decrease in performance, indicating that the thickness and composition ratio of each functional layer need to be matched within a reasonable range.

[0113] Compared to all comparative examples, Examples 1-5 exhibit significant advantages in cycle life, capacity retention, and interfacial impedance. Comparative Examples 1-3 represent bare copper foil, Sn-substituted lithiophilic layer 3, and AlF3 monolayer modification, respectively. All three showed shorter cycle life and higher interfacial impedance, demonstrating that single modification or inappropriate lithiophilic material selection cannot solve the multiple failure problems faced by the lithium-free anode current collector 1. Comparative Example 3 shows that performance drops sharply after Sn replaces Mg, verifying that the dynamic self-repair mechanism of the Mg-Li system through the formation of a continuous BCC solid solution is irreplaceable by other lithiophilic metals. Comparative Examples 4-5 further show that omitting either AlF3 or Li3N, even with lithiophilic layer 3 and lithium seed layer 4 retained, still results in a cycle life far lower than all other examples, proving an irreplaceable synergistic relationship between AlF3 and Li3N. The mechanically strengthened interface provided by AlF3 and the fast ion conduction and lithium replenishment functions provided by Li3N must coexist to achieve a synergistic effect. Although AlF3 and Li3N coexist in Comparative Example 6, they are arranged in a layered stacking manner, and their performance is significantly worse than that of Examples 1-5. This indicates that the two components must be uniformly mixed in the same functional layer in order to achieve the synchronous coupling of the "conduction-lithium replenishment-protection" function in space and time.

[0114] In summary, this invention achieves functional synergy among layers by constructing a gradient functional interface consisting of a negative electrode current collector 1, an AlF3-Li3N composite functional layer 2, a lithiophilic layer 3, and a lithium seed layer 4. In-situ conversion of AlF3 to LiF constructs a high-modulus SEI framework, providing interface strengthening and dendrite suppression. Li3N provides a fast ion conduction channel and built-in lithium replenishment function. The lithiophilic layer 3 induces uniform lithium nucleation and forms a dynamically self-healing Li-X (X=Mg, Zn, Ag) solid solution. The lithium seed layer 4 eliminates the heterogeneous nucleation barrier. This four-layer structure collectively achieves full-process control of lithium deposition / stripping behavior, effectively solving the problems of short cycle life and low coulombic efficiency in lithium metal batteries without lithium negative electrodes caused by poor interface affinity, uneven lithium deposition, and continuous loss of active lithium.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode, characterized in that, It includes a negative electrode current collector (1) and a composite functional layer (2), a lithiophilic layer (3), and a lithium seed layer (4) stacked sequentially along a direction away from the negative electrode current collector (1); wherein: The material of the lithiophilic layer (3) is selected from at least one of Mg, Zn and Ag; The composite functional layer (2) contains AlF3 and a lithium supplement, wherein the mass fraction of AlF3 is greater than the mass fraction of the lithium supplement.

2. The negative electrode according to claim 1, characterized in that, The lithium supplementer in the composite functional layer (2) includes at least one of Li2C2O4 and Li3N; The composite functional layer (2) also includes a conductive agent and a binder; The mass ratio of AlF3, lithium supplement, conductive agent and binder is 50~80:10~40:5~15:5~15.

3. The negative electrode according to claim 2, characterized in that, The conductive agent is selected from one or more of carbon black, carbon nanotubes, and graphene; The adhesive is selected from one or more of PVDF, PTFE, PAN, CMC and SBR; The negative electrode current collector (1) is selected from any one of copper foil, composite copper foil, nickel foil, composite nickel foil, stainless steel foil, composite stainless steel foil, titanium foil, and composite titanium foil.

4. The negative electrode according to claim 1, characterized in that, The thickness of the composite functional layer (2) is 3~10μm; The thickness of the lithiophilic layer (3) is 20~100nm; The thickness of the lithium seed layer (4) is 0.5~2μm.

5. A method for preparing a negative electrode, characterized in that, Includes the following steps: S1: A composite functional layer (2) is formed on the surface of the negative electrode current collector (1); S2: A lithiophilic layer (3) is formed on the surface of the composite functional layer (2); S3: A lithium seed layer (4) is formed on the surface of the lithiophilic layer (3); The steps of forming the lithiophilic layer (3) and forming the lithium seed layer (4) are carried out continuously in the same vacuum environment without breaking the vacuum in between.

6. The preparation method according to claim 5, characterized in that, The method for preparing the composite functional layer (2) includes: coating a slurry containing AlF3, lithium supplement, conductive agent and binder onto the surface of the negative electrode current collector (1) to obtain a wet film, and then drying it to form the composite functional layer (2).

7. The preparation method according to claim 6, characterized in that, The thickness of the wet film is 20~100μm; The drying process involves vacuum drying at 80°C for 10-14 hours.

8. The preparation method according to claim 5, characterized in that, The lithiophilic layer (3) and the lithium seed layer (4) are formed by vapor deposition. The steps of forming the lithiophilic layer (3) and the lithium seed layer (4) are carried out continuously under the condition of maintaining a vacuum state and not breaking the vacuum, and are achieved by switching the evaporation source.

9. The preparation method according to claim 5, characterized in that, The vacuum level of the vacuum environment is ≤10. -5 Pa.

10. A lithium metal battery, characterized in that, Includes the negative electrode according to any one of claims 1 to 4 or the negative electrode prepared according to any one of claims 5 to 9.

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