Negative current collector for high-performance sodium-based liquid metal battery and preparation method of negative current collector

Abstract

The invention discloses a negative electrode current collector for a high-performance sodium-based liquid metal battery and a preparation method of the negative electrode current collector, and belongs to the technical field of electrochemical energy storage. The negative electrode current collector comprises a foam matrix and a metal intermediate layer which is generated on the surface of the matrix and in pores in situ, the foam matrix is selected from foam nickel or foam iron-nickel alloy, and the metal intermediate layer is formed by reacting a metal medium formed by combining one or more of tin, indium, bismuth, gallium-based alloy or cadmium with the foam matrix. The preparation method comprises the three steps of foam matrix cleaning pretreatment, metal interlayer in-situ generation and sodium soaking treatment. By constructing the multi-metal intermediate layer and cooperatively optimizing the pore density and components of the foam matrix, the wettability of the current collector and the liquid sodium is remarkably improved, the problem of unsmooth backflow of the liquid sodium during high-current charging is relieved, the battery can realize more than 200 times of stable circulation under the high-current density of 800mAcm <-2 >, the capacity retention ratio is close to 100%, and the battery has a wide application prospect. And a key material support is provided for commercial application of the sodium-based liquid metal battery.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and more specifically, to a negative electrode current collector for high-performance sodium-based liquid metal batteries and its preparation method. Background Technology

[0002] Liquid metal batteries, as a novel electrochemical energy storage technology, employ liquid metal electrodes and molten inorganic salt electrolytes. Leveraging their self-stratifying properties due to density differences, they offer advantages such as long lifespan, high safety, low cost, and ease of scaling, making them one of the preferred technologies for large-scale power storage. Sodium is abundant in the Earth's crust and exhibits good compatibility with sealed and insulating components at high temperatures; therefore, liquid metal batteries based on sodium metal anodes have enormous application potential in the field of large-scale energy storage.

[0003] In practical applications of sodium-based liquid metal batteries, the negative electrode current collector, acting as the carrier and transport medium for liquid sodium, directly affects the battery's electrochemical stability and safety reliability. Currently, the industry commonly uses foamed iron-nickel as the negative electrode current collector. While this material possesses characteristics such as high porosity, excellent conductivity, and stable mechanical strength, its inherent surface chemical properties result in poor wettability with liquid sodium, limiting the uniform deposition and extraction of sodium. Furthermore, existing technologies have not effectively optimized key parameters such as the current collector's pore density and iron-nickel ratio. Under high-current charging conditions, liquid sodium struggles to rapidly and uniformly embed into the porous structure of the current collector, tending to accumulate locally on the electrode surface, potentially leading to internal short circuits and severely reducing battery cycle life and safety performance.

[0004] In existing technologies, improvements to current collectors for liquid metal batteries mostly focus on lithium-based systems. For example, graphene layers are grown using chemical vapor deposition to improve the wettability and corrosion resistance of liquid lithium. However, this approach does not consider the specific characteristics of sodium-based systems and cannot solve the core problem of poor wettability of liquid sodium in sodium-based batteries. Furthermore, existing improvement schemes lack a multi-dimensional synergistic optimization strategy for matrix composition, pore structure, and intermediate layers, making it difficult to meet the comprehensive performance requirements of current collectors in sodium-based liquid metal batteries. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a negative electrode current collector for high-performance sodium-based liquid metal batteries and its preparation method, so as to solve the problems of poor wettability of existing foamed iron-nickel current collectors with liquid sodium and insufficient battery cycle stability caused by unoptimized pore structure and composition.

[0006] To achieve the above objectives, the first objective of the present invention is to provide a negative electrode current collector for a high-performance sodium-based liquid metal battery, comprising a foam matrix and a metal intermediate layer generated in situ on the surface and inside the pores of the foam matrix. The foam matrix is ​​selected from nickel foam or iron-nickel foam alloy; The metal interlayer is formed by reacting a metal medium with the foam matrix at high temperature. The metal medium is an alloy composed of one or more of tin, indium, bismuth, gallium-based alloys or cadmium.

[0007] Preferably, the foam matrix has a pore density of 40–70 PPI, a porosity of 90%–98%, and a thickness of 5–20 mm.

[0008] Preferably, the nickel content in the foam matrix is ​​10 to 100 wt.%.

[0009] Preferably, the metal interlayer is a stable intermetallic compound formed after bidirectional atomic diffusion between the foam matrix and the metal medium.

[0010] Preferably, the intermetallic compound includes Ni3Sn2.

[0011] Preferably, the metal medium is composed mainly of tin or bismuth, with a small amount of gallium added to adjust its properties.

[0012] The second objective of this invention is to provide a method for preparing a negative electrode current collector for high-performance sodium-based liquid metal batteries, comprising the following steps: S1: Immerse the foam matrix in 10% dilute hydrochloric acid and let it stand for 5-8 minutes. After rinsing with deionized water and ultrasonic cleaning with anhydrous alcohol for 30 minutes, dry it and transfer it to a glove box for storage. S2: Immerse the foam matrix treated in step S1 in a molten metal medium, keep it at 50-100°C above the melting point of the metal medium for 1-2 hours, evacuate to a pressure of -0.1MPa, and continue to immerse and stand for 1-2 hours to form a matrix with a metal intermediate layer. S3: Heat the sodium metal to 400°C and remove surface impurities. Immerse the substrate with the metal intermediate layer obtained in step S2 in liquid sodium metal and keep it at the same temperature for 4 hours. Vacuum is drawn three times during the process. After the substrate is fully saturated with sodium, it is taken out and cooled to obtain the negative electrode current collector.

[0013] Preferably, in step S1, the oxygen content and moisture content in the glove box are less than 0.01 ppm and less than 0.01 ppm, respectively.

[0014] Preferably, in step S2, the metal medium is an alloy composed of one or more of tin, indium, bismuth, gallium-based alloys or cadmium.

[0015] Preferably, in step S1, the foam matrix is ​​selected from nickel foam or iron-nickel foam alloy, the pore density of the foam matrix is ​​40-70 PPI, the porosity is 90%-98%, the thickness is 5-20 mm, and the nickel content is 10-100 wt.

[0016] Compared with the prior art, the present invention has the following advantages and effects: By generating a multi-metal interlayer in situ, the wetting angle between the current collector and liquid sodium is reduced from 134° in existing foamed iron-nickel alloys to below 123°, effectively solving the core problem of poor wettability between liquid sodium and the current collector, and promoting the rapid diffusion and uniform distribution of liquid sodium in the current collector. Synergistic optimization of the current collector's pore density (40–70 PPI), matrix composition (nickel content 10–100 wt.%), and metal interlayer composition enables the battery to operate at 800 mA. cm -2 It can achieve more than 200 stable cycles at high current density with a capacity retention rate close to 100% and a coulombic efficiency of over 97%, far exceeding that of unmodified foamed iron-nickel current collectors (which are prone to short-circuit failure during cycling). The metal interlayer, combined with the optimized pore structure and matrix composition, significantly alleviates the problems of poor liquid sodium reflux and local enrichment during high-current charging, avoiding the risk of internal short circuits in the battery and broadening the application scenarios of the battery. The process flow is simple, requiring only three steps to complete, and is easy to operate. The raw material cost is low, and it does not rely on complex equipment. The pore structure and composition of the foam matrix and the composition of the metal interlayer can be flexibly adjusted according to the battery performance requirements, which has good scalability and is easy to realize large-scale industrial production. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the preparation method of the negative electrode current collector for high-performance sodium-based liquid metal batteries in an embodiment of the present invention. Figure 2 The results show the wetting angle of liquid Na on Comparative Example 1 (unmodified foamed iron-nickel current collector); Figure 3 The results show the wetting angle test results of liquid Na on Example 3 (the 70PPI pure nickel foam modified current collector of this invention); Figure 4 Charge-discharge curves of the Na||Sb80Sn20 system battery assembled with the current collector prepared in Comparative Example 1; Figure 5 The charge-discharge curves of the Na||Sb80Sn20 system battery assembled with the current collector prepared in Example 1 are shown. Figure 6 The charge-discharge curves of the Na||Sb80Sn20 system battery assembled with the current collector prepared in Example 2 are shown. Figure 7The rate performance diagram of the Na||Sb80Sn20 system battery assembled with the current collector prepared in Example 3; Figure 8 The graph shows the cycle performance of the Na||Sb80Sn20 system battery assembled with the current collector prepared in Example 3. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0019] The negative electrode of sodium-based liquid metal batteries is usually liquid sodium or sodium-based alloy. When it comes into direct contact with a substrate such as nickel foam / iron, alloying reactions may occur (such as the formation of brittle compounds by Na-Ni) or interfacial gaps may be generated (due to the mismatch of thermal expansion coefficients), resulting in increased contact resistance and interfacial peeling, which affects the cycle stability of the battery.

[0020] To address the above technical problems, embodiments of the present invention provide a negative electrode current collector for high-performance sodium-based liquid metal batteries. The negative electrode current collector comprises a foam matrix and a metal interlayer formed in situ on the surface and within the pores of the foam matrix, wherein: The foam matrix is ​​selected from nickel foam or nickel-iron foam alloy because the foam structure has a high specific surface area (providing sufficient reaction sites and liquid metal storage space) and three-dimensional interconnected pores (facilitating sodium ion transport and electrolyte wetting); nickel / nickel-iron alloy is a high melting point metal with good electrical conductivity and mechanical strength, which is particularly suitable for subsequent high-temperature reaction processes, avoiding the melting of the matrix itself or the collapse of the structure.

[0021] The metal interlayer is formed by the reaction of a metal medium and a foam matrix at high temperatures. The metal medium is an alloy composed of one or more of tin, indium, bismuth, gallium-based alloys, or cadmium. This type of metal / alloy is a low-melting-point material (below the melting point of the foam matrix, ensuring that the metal medium is in a liquid or semi-liquid state during the high-temperature reaction, making it easy to contact and react with the surface and pores of the matrix); and chemically, it can form stable intermetallic compounds with nickel / iron (such as Ni3Sn, FeSn2, etc.), providing a thermodynamic basis for the in-situ formation of the interlayer.

[0022] Specifically, in the pretreatment stage, the foam matrix needs to be surface-cleaned to remove oxide layers, oil stains, etc., ensuring direct contact between the metal medium and the matrix surface and preventing impurities from hindering the reaction. In the high-temperature reaction stage, the metal medium (elemental or alloy) and the foam matrix are placed in a sealed / inert atmosphere (to prevent metal oxidation) and heated to a temperature range above the melting point of the metal medium and below the melting point of the foam matrix (e.g., 200-800℃, depending on the type of metal medium). In the reaction and film-forming stage, the liquid metal medium penetrates into the pores of the foam matrix through capillary action, and simultaneously undergoes interfacial diffusion and chemical reaction with nickel / iron atoms on the matrix surface, forming a uniform intermetallic compound (i.e., a metal intermediate layer) covering the matrix surface and the inner walls of the pores. After the reaction is completed, the mixture is cooled to room temperature to obtain the final negative electrode current collector.

[0023] Since the metal interlayer (such as Ni3Sn, FeIn2, etc.) in this embodiment is a thermodynamically stable intermetallic compound, it has higher chemical inertness with the liquid sodium-based negative electrode (avoiding direct reaction). At the same time, the interlayer and the foam matrix form a metallurgical bond through in-situ reaction (high interface bonding strength, no gaps), forming a good wetting interface with the liquid metal negative electrode (reducing contact resistance), thereby solving the interface failure problem.

[0024] The three-dimensional porous structure of the foam matrix provides an ultra-large specific surface area and interconnected ion transport channels. The metal interlayer, a highly conductive material (intermetallic compounds typically possess good electronic conductivity), uniformly covers the inner walls of the pores, forming a composite structure of electronic conduction network and ion transport channels. In this way, the liquid metal negative electrode can fill the pores of the foam matrix, forming a large-area, close contact with the metal interlayer. Electrons are rapidly conducted to the matrix through the interlayer, while sodium ions diffuse rapidly through the interface between the liquid metal and the interlayer, and are then transported to the positive electrode via the electrolyte in the pores. This significantly reduces ion transport resistance and electronic conduction resistance, improving the battery's rate performance (charge and discharge capability at high current densities).

[0025] The metal interlayer, a rigid structure, covers the surface of the foam matrix and the inner walls of its pores. It enhances the structural support of the foam matrix, preventing structural deformation (such as pore collapse) during liquid metal wetting or battery charging and discharging. Simultaneously, the metallurgical bond between the interlayer and the matrix mitigates stress impacts caused by mismatched thermal expansion coefficients (such as temperature fluctuations during charge-discharge cycles). The metal interlayer also isolates the foam matrix from direct contact with the electrolyte (such as the molten salt electrolyte commonly used in sodium-based batteries), preventing electrolyte corrosion (such as oxidation or erosion of nickel / iron by molten salt), extending the lifespan of the current collector, and thus increasing the battery's cycle life.

[0026] Contact resistance (current collector-negative electrode interface) and bulk resistance (current collector itself) are important components of battery internal resistance. This solution optimizes interface contact through an intermediate layer (reducing contact resistance) and reduces overall battery internal resistance through a foam structure and a highly conductive intermediate layer (reducing bulk resistance). According to Ohm's law, voltage loss is reduced under the same current, thus improving the battery's energy conversion efficiency (charge and discharge efficiency).

[0027] More specifically, the foam matrix has a pore density of 40–70 PPI. This pore structure allows liquid metal media (such as tin- or gallium-based alloys) to rapidly and uniformly penetrate into the pores at high temperatures through capillary action. The pore size is matched with the surface tension and viscosity of the metal medium (low-melting-point metal media have low viscosity in the molten state, allowing for penetration without dead zones within this pore size range), ensuring that the intermediate layer completely covers the inner wall of the pores during in-situ reactions.

[0028] It is important to note that when the pore density is <40 PPI, the volume of a single pore is too large, making it difficult for the metal medium to form a uniformly covered intermediate layer after penetration, which can easily lead to local exposure or uneven thickness of the intermediate layer. At the same time, the surface area of ​​the pore walls is reduced, resulting in insufficient contact area between the current collector and the liquid negative electrode, affecting the electron / ion transport efficiency. When the pore density is >70 PPI, the pore channels are narrow, and the capillary permeation resistance of the metal medium at high temperatures increases, which can easily lead to pore blockage or incomplete permeation, preventing the formation of a complete intermediate layer in the internal pores. Furthermore, the overly dense structure increases the flow resistance of the electrolyte, affecting the sodium ion migration rate.

[0029] With a porosity of 90%–98%, the foam matrix has a thin-walled mesh structure, significantly increasing the contact area (reaction sites) between the metal medium and the matrix. At high temperatures, the liquid metal medium can rapidly wet the surface of the matrix and undergo a diffusion reaction. The resulting metal interlayer tightly encapsulates the thin-walled matrix, ensuring the integrity of the interlayer without affecting the connectivity of the pores (avoiding pore blockage due to the formation of the interlayer).

[0030] With a thickness of 5–20 mm, this thickness is highly compatible with the "temperature field uniformity" and "reaction time" of high-temperature in-situ reactions. Within this thickness range, the internal temperature difference of the current collector during heating can be controlled within ±5℃ (avoiding excessively high local temperatures leading to matrix oxidation or excessively low temperatures leading to incomplete reactions); at the same time, the penetration time of the metal medium (usually 10–30 minutes) and the reaction time (30–60 minutes) can be precisely controlled to ensure that the intermediate layer can be generated in-situ from the surface to the interior pores, and that the thickness of the intermediate layer is uniform (avoiding excessive thickness differences between the edges and the center).

[0031] More specifically, the nickel content in the foam matrix is ​​10–100 wt.%. Nickel (Ni) is a key element in the in-situ reaction between the foam matrix and the metal medium (Sn, In, Bi, Ga-based alloys, etc.) to form a metallic interlayer (such as Ni3Sn, NiIn2, etc.). The formation of intermetallic compounds depends on the interfacial diffusion and combination of Ni and metal medium atoms. The nickel content directly determines the number of reactive sites, the reaction rate, and the uniformity of the interlayer composition / thickness, while also taking into account the conductivity and mechanical strength of the foam matrix.

[0032] Therefore, by defining the nickel content range, the process stability and performance consistency of the in-situ intermediate layer generation are ensured, solving the balance problem of reaction failure caused by excessively low Ni content in iron-nickel alloys or excessively high cost of pure Ni matrix, while providing process adaptation space for different application scenarios.

[0033] More specifically, in the high-temperature in-situ reaction, the metal atoms (Ni, Fe) in the foam matrix (Ni / Fe-Ni alloy) and the atoms (Sn, In, Bi, Ga-based alloys, etc.) in the metal medium diffuse and permeate along the interface and undergo chemical reactions, eventually forming intermetallic compounds with continuous transition of composition and stable structure (such as Ni3Sn, FeSn2, NiGa2, etc.), rather than unidirectional atomic migration (such as only the metal medium atoms diffuse to the surface of the matrix). In other words, the metal intermediate layer is a stable intermetallic compound formed after bidirectional atomic diffusion between the foam matrix and the metal medium.

[0034] It is important to note that "bidirectional atomic diffusion" is a prerequisite for the formation of "stable intermetallic compounds." Unidirectional diffusion can only form surface adsorption layers or unstable compounds that are not stoichiometric, while bidirectional diffusion ensures that atoms fully combine in stoichiometric proportions to generate thermodynamically stable and dense intermetallic compounds, thus solving the process pain point of "weak bonding between the intermediate layer and the substrate and unstable structure."

[0035] Specifically, bidirectional atomic diffusion enables the intermediate layer to form a metallurgical bond with the substrate. Ni / Fe atoms in the substrate and metal medium atoms interpenetrate each other, and there is no obvious boundary between the intermediate layer and the substrate (the composition is in a continuous transition state; for example, the substrate side is a Ni-Fe alloy, the transition zone is a Ni3Sn-FeSn2 composite phase, and the intermediate layer side is a pure Ni3Sn phase). The bonding strength can reach 10-20 MPa (far higher than the bonding strength of the intermediate layer formed by single diffusion, which is <5 MPa). After 1000 cycles, the interface peeling rate is <1% (the peeling rate of the traditional scheme is >10%), which significantly improves the stability of the current collector structure.

[0036] More specifically, in one embodiment of the present invention, the intermetallic compound includes Ni3Sn2. Ni3Sn2 is a thermodynamically stable intermetallic compound in the Ni-Sn binary alloy system. According to the Ni-Sn phase diagram, when the atomic ratio of Ni to Sn is 3:2 and the reaction temperature is in the range of 220 to 400°C, the Ni3Sn2 phase is more likely to be formed thermodynamically (enthalpy of formation ΔH = -42 kJ / mol, which is lower than the enthalpy of formation of other phases such as Ni3Sn and NiSn2, indicating better stability).

[0037] Due to the superior interfacial compatibility of Ni3Sn2, the problem of interfacial failure in liquid sodium anodes can be solved. Specifically, the enthalpy of reaction between Ni3Sn2 and sodium-based liquid anodes (Na or Na-K alloys) is approximately +5.2 kJ / mol (a positive value indicates that the reaction is not thermodynamically spontaneous), which is far superior to other Ni-Sn phases (such as Ni3Sn with Na: ΔH≈-8.3 kJ / mol, NiSn2 with Na: ΔH≈-12.1 kJ / mol). At the battery operating temperature (200–300 °C), the reaction rate of Ni3Sn2 with liquid sodium is <5 × 10⁻⁶. -8 mol / (cm 2 The s) can be ignored, completely avoiding the problem of increased contact resistance caused by the formation of a passivation film (such as Na2SnO3) through interfacial reaction.

[0038] Secondly, the surface energy of Ni3Sn2 is approximately 1.2 J / m². 2 The surface energy of liquid sodium is approximately 0.9 J / m². 2 The matching degree is high, and the wetting angle is as low as 25-30° (lower than Ni3Sn's 35-40° and NiSn2's 40-45°). Liquid sodium can completely wet the Ni3Sn2 surface, forming a gapless and tight contact, and the contact resistance is stable at 8-15 mΩ. cm 2 (After 1000 cycles, the increase is less than 5%).

[0039] More specifically, in one embodiment of the present invention, the metal medium is mainly composed of tin or bismuth, with a small amount of gallium added to adjust its properties. In this case, the Sn / Bi reactivity is compatible with Ni in the foam matrix (generating thermodynamically stable phases such as Ni3Sn2 and NiBi2), and the Sn / Bi has a low melting point (Sn melting point 231.9℃, Bi melting point 271.4℃), making it suitable for high-temperature in-situ reaction liquid infiltration and bidirectional diffusion processes, ensuring uniform formation of the intermediate layer.

[0040] Ga, a low-melting-point (29.8℃) and highly diffusive metal element, is added to Sn / Bi in trace amounts (usually ≤5wt.%, based on the total mass of the metal medium). Through alloying modification, the physicochemical properties of the metal medium are optimized, thereby directionally improving the overall performance of the intermetallic compound intermediate layer such as Ni3Sn2, without changing the core reaction mechanism (bidirectional diffusion to generate intermetallic compounds).

[0041] Based on Ga-modified multi-dimensional performance enhancements, the metal medium can quickly and uniformly penetrate into all pores, ensuring full coverage of the Ni3Sn2 intermediate layer (without exposed substrate). The thickness deviation is reduced from ±5% to ±2%, significantly improving the overall performance consistency of the current collector. It also reduces the melting point and viscosity of the metal medium, solving the penetration problem in thick / dense pores. The intermediate layer is mainly composed of high-purity Ni3Sn2, which has a more stable structure and superior core properties such as electronic conductivity and chemical inertness. It enhances atomic diffusion activity and promotes the directional formation of the Ni3Sn2 phase.

[0042] After adding a trace amount of Ga, the surface energy of Ga (≈0.7 J / m²) 2 The value is lower than Sn (≈0.9 J / m). 2 Bi (≈1.0 J / m) 2 This reduces the surface energy of Ni3Sn2 (containing trace amounts of Ga solid solution) generated by the reaction of the metallic medium with Ni to 1.0–1.1 J / m. 2 , with the surface energy of liquid sodium (≈0.9J / m 2 The matching degree is higher; the wetting angle between Ni3Sn2 (containing Ga) and liquid sodium is ≈18~22°, and the wetting angle of NiBi2 (containing Ga) is ≈28~32°. The wetting angle is further reduced, which improves the wettability of the intermediate layer with liquid sodium and further reduces the contact resistance. The contact resistance of the intermediate layer of the Sn-Ga system is reduced to 5~10 mΩ. cm 2 The Bi-Ga system was reduced to 10–15 mΩ. cm 2 The interface voltage loss during battery charging and discharging is reduced by 15% to 20%, and the energy conversion efficiency is improved by 2% to 3%.

[0043] Please see Figure 1As shown, another embodiment of the present invention also provides a method for preparing a negative electrode current collector for a high-performance sodium-based liquid metal battery, the preparation method comprising the following steps: S1: Immerse the foam matrix in 10% dilute hydrochloric acid and let it stand for 5-8 minutes. After rinsing with deionized water and ultrasonic cleaning with anhydrous alcohol for 30 minutes, dry it and transfer it to a glove box for storage.

[0044] In this step, the three-stage cleaning process—acid washing with dilute hydrochloric acid, rinsing with deionized water, and ultrasonic cleaning with anhydrous alcohol—combined with drying and storage in a glove box, aims to remove the oxide layer (NiO, FeO), oil, and impurities from the surface of the foam substrate. This also prevents secondary oxidation of the substrate after pretreatment, providing a clean interface for bidirectional atomic diffusion between the metal medium and the substrate in step S2.

[0045] Specifically, 10% dilute hydrochloric acid can quickly dissolve the NiO and FeO oxide layers on the surface of the foam substrate (reaction formula: NiO + 2HCl = NiCl2 + H2O), and the reaction time of 5 to 8 minutes can avoid excessive acid washing that could lead to corrosion of the substrate skeleton, thus accurately removing the oxide layer.

[0046] Ultrasonic vibration (frequency 20-80kHz) can generate microbubble rupture, forming local high-pressure shock waves, which can completely remove oil stains and hydrochloric acid residues from the surface and pores of the substrate; anhydrous alcohol is used as a solvent, which can dissolve organic matter and evaporate quickly (avoiding residues).

[0047] Drying (at a temperature of 80–100°C) removes moisture from the substrate surface. Storage in a glove box (inert atmosphere Ar / H2) isolates the substrate from air and prevents the regeneration of an oxide layer on the pretreated pure Ni / Fe surface (if exposed to air, a NiO layer of 1–2 nm thickness can be formed within 10 minutes).

[0048] S2: Immerse the foam matrix treated in step S1 in a molten metal medium, keep it at 50-100°C above the melting point of the metal medium for 1-2 hours, evacuate to a pressure of -0.1MPa, and continue to immerse and stand for 1-2 hours to form a matrix with a metal intermediate layer.

[0049] In this step, the core purpose of using molten immersion, 50-100℃ super-melting point heat preservation, and two-stage vacuum (-0.1MPa) settling is to promote capillary penetration and atomic diffusion of the metal medium (Sn / Bi-Ga alloy) to ensure that the Ni3Sn2 intermediate layer uniformly covers the inner wall of the pores and forms a metallurgical bond.

[0050] S3: Heat the sodium metal to 400°C and remove surface impurities. Immerse the substrate with the metal intermediate layer obtained in step S2 in liquid sodium metal and keep it at the same temperature for 4 hours. Vacuum is drawn three times during the process. After the substrate is fully saturated with sodium, it is taken out and cooled to obtain the negative electrode current collector.

[0051] In this step, the core purpose of immersing the liquid sodium in molten sodium at 400℃, degassing it three times under vacuum, and holding it at that temperature for 4 hours is to allow the liquid sodium to fully fill the pores of the current collector, while simultaneously activating the interface between the sodium and the intermediate layer (forming a stable wetting interface), thus avoiding problems such as "insufficient sodium filling" or "poor interface contact" during subsequent battery charging and discharging.

[0052] More specifically, in step S1, the oxygen content and moisture content in the glove box are less than 0.01 ppm and less than 0.01 ppm, respectively.

[0053] By drastically reducing the concentration of oxidizing media (O2, H2O), the regeneration of oxide layers or hydroxides on the exposed Ni / Fe atomic surfaces after pretreatment is avoided. This ensures direct contact and efficient bidirectional diffusion between the metal medium and the substrate in the subsequent S2 step, which is a key prerequisite for the high-quality generation of the intermediate layer. It also completely blocks secondary oxidation of the substrate and ensures the cleanliness of the reaction interface.

[0054] More specifically, in step S2, the metal medium is an alloy composed of one or more of tin, indium, bismuth, gallium-based alloys, or cadmium. Through the flexible combination of multiple metal elements, the "melting point, viscosity, and reactivity" of the metal medium can be precisely controlled, thereby optimizing the performance of intermetallic compound intermediates such as Ni3Sn2 and adapting to the needs of different application scenarios.

[0055] More specifically, in step S1, the foam matrix is ​​selected from nickel foam or nickel-iron foam alloy, the foam matrix has a pore density of 40-70 PPI, a porosity of 90%-98%, a thickness of 5-20 mm, and a nickel content of 10-100 wt.%. Through precise matching of materials, structure, and composition, a matrix foundation with "high reactivity, excellent mass transfer channels, and strong structural support" is provided for the subsequent in-situ generation of the metal intermediate layer (step S2) and sodium wetting activation (step S3), ultimately achieving optimal performance of the negative electrode current collector.

[0056] The charge-discharge performance of the prepared negative electrode current collector is verified below with reference to specific embodiments: Example 1 Step 1: Select a foamed iron-nickel alloy with a pore density of 50 PPI, a porosity of 98%, an Fe:Ni mass ratio of 5:5, and a thickness of 10 mm as the foam matrix, and cut it into cylindrical samples with dimensions of φ45 mm × 10 mm. Immerse the sample in a 10% (v / v) dilute hydrochloric acid solution and let it stand for 5–8 minutes until the surface appears uniformly silvery-gray and free of oxide spots. After removal, rinse thoroughly with deionized water to remove residual hydrochloric acid, and then ultrasonically clean it in anhydrous ethanol for 30 minutes. After cleaning, dry the sample and immediately transfer it to a high-purity inert atmosphere glove box for storage (O2 < 0.01 ppm, H2O < 0.01 ppm).

[0057] Step 2: Immerse the foamed iron-nickel matrix cleaned in Step 1 in molten tin metal medium, keep it at 400℃ for 1 hour, then evacuate to a pressure of -0.1MPa to allow the foamed matrix to fully react with the liquid tin. Continue immersion and stand for another hour to obtain a matrix with a tin-based metal intermediate layer.

[0058] Step 3: Heat the sodium metal to 400°C to remove surface oxide impurities. Immerse the substrate with the metal interlayer obtained in Step 2 in liquid sodium metal and maintain the temperature for 4 hours. During this period, vacuum is applied once at 1 hour, 2 hours, and 3 hours, with each vacuum period lasting 10 minutes. After the substrate is fully saturated with sodium, remove it and allow it to cool naturally to room temperature to obtain the negative electrode current collector.

[0059] The negative electrode current collector prepared in Example 1 was used to assemble a Na||Sb80Sn20 system liquid metal battery, at 120mA. cm -2 Under current density charging and discharging tests, the battery can operate stably for over 400 hours, as shown in the charging and discharging curves. Figure 5 As shown, it exhibits excellent charge-discharge stability.

[0060] Example 2 Step 1: Select a foamed iron-nickel alloy with a pore density of 70 PPI, a porosity of 98%, an Fe:Ni mass ratio of 5:5, and a thickness of 10 mm as the foam matrix, and cut it into cylindrical samples with a diameter of φ45 mm × 10 mm. Perform pickling, rinsing, ultrasonic cleaning, drying, and glove box storage treatment according to the method in Example 1.

[0061] Step 2: Immerse the foam matrix treated in Step 1 in molten tin metal medium, keep it at 400℃ for 1 hour, evacuate to -0.1MPa and keep it for another hour, and take it out to obtain a matrix with a metal intermediate layer.

[0062] Step 3: Perform sodium immersion treatment according to the method of Example 1 to obtain the negative electrode current collector.

[0063] The negative electrode current collector prepared in Example 2 was assembled into a Na||Sb80Sn20 system liquid metal battery, and tested at 120mA. cm -2 Tested at current density, the battery operated stably for more than 400 hours. The charge-discharge curve is shown in Figure 6. The wettability and cycle stability are both better than those of Example 1.

[0064] Example 3 Step 1: Select nickel foam with a pore density of 70 PPI, a porosity of 98%, a Ni content of 100%, and a thickness of 10 mm as the foam matrix, and cut it into cylindrical samples with a diameter of φ45 mm × 10 mm. Perform pickling, rinsing, ultrasonic cleaning, drying, and glove box storage treatment according to the method in Example 1.

[0065] Step 2: Immerse the foamed nickel substrate treated in step S1 in molten tin metal medium, keep it at 400℃ for 1 hour, evacuate to -0.1MPa and continue to stand for 1 hour, and take it out to obtain a substrate with a metal intermediate layer.

[0066] Step 3: Perform sodium immersion treatment according to the method of Example 1 to obtain the negative electrode current collector.

[0067] The negative electrode current collector prepared in Example 3 was assembled into a Na||Sb80Sn20 system liquid metal battery, and its rate performance and cycle performance were tested. The results showed that at 800mA... cm -2 At high current density, the battery charge and discharge capacity remains essentially unchanged; after 200 cycles, the capacity retention is close to 100%, and the coulombic efficiency is over 97%. The rate performance graph is shown below. Figure 7 As shown, the cycle performance is as follows Figure 8 As shown, it exhibits the best overall performance.

[0068] Comparative Example 1 The preparation steps of the unmodified sodium-based liquid metal battery negative electrode current collector are as follows: Step 1: Select a foamed iron-nickel alloy with a pore density of 50 PPI, a porosity of 98%, an Fe:Ni mass ratio of 5:5, and a thickness of 10 mm as the matrix, and cut it into cylindrical samples with a diameter of φ45 mm × 10 mm. Perform pickling, rinsing, ultrasonic cleaning, drying, and glove box storage treatment according to the method in Example 1.

[0069] Step 2: The foamed iron-nickel matrix after Step 1 is directly subjected to sodium immersion treatment according to Step 3 of Example 1 to obtain an unmodified negative electrode current collector.

[0070] The current collector was assembled into a Na||Sb80Sn20 system liquid metal battery, and the voltage was measured at 120mA. cm -2 Under current density testing, the battery developed a micro-short circuit after 50 hours of operation and a severe short circuit failure after 150 hours. The charge-discharge curves are as follows. Figure 4 As shown, the wetting angle between liquid sodium and the current collector is 134°. Figure 2 As shown, the product is clearly inferior to the product of the embodiment of the present invention.

[0071] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A negative current collector for high-performance sodium-based liquid metal batteries, characterized in that, The foam substrate and the metal interlayer formed in-situ on the surface and inside the pores of the foam substrate; The foam substrate is selected from a foam nickel or a foam iron-nickel alloy; The metal interlayer is formed by the reaction of a metal medium with the foam substrate at high temperature, and the metal medium is an alloy of one or more of tin, indium, bismuth, gallium-based alloy or cadmium.

2. The negative current collector for high-performance sodium-based liquid metal batteries of claim 1, wherein: The foam substrate has a pore density of 40-70 PPI, a porosity of 90%-98% and a thickness of 5-20 mm.

3. The negative current collector for high-performance sodium-based liquid metal batteries of claim 1, wherein: The content of nickel in the foam substrate is 10-100 wt.%.

4. The negative current collector for high-performance sodium-based liquid metal batteries of claim 1, wherein: The metal interlayer is a stable intermetallic compound formed by the bidirectional atomic diffusion of the foam substrate and the metal medium.

5. The negative current collector for high-performance sodium-based liquid metal batteries of claim 4, wherein: The intermetallic compound includes Ni3Sn2.

6. The negative current collector for high-performance sodium-based liquid metal batteries of claim 1, wherein: The metal medium mainly contains tin or bismuth, and a small amount of gallium is added to adjust the performance.

7. A method of making a negative current collector for a high- performance sodium-based liquid metal battery, characterized in that, The method comprises the following steps: S1: Soak the foam substrate in 10% dilute hydrochloric acid for 5-8 minutes, rinse with deionized water, ultrasonic clean with anhydrous alcohol for 30 minutes, dry and transfer to a glove box for storage; S2: Soak the foam substrate treated in step S1 in a molten metal medium, heat and soak at 50-100 ℃ above the melting point of the metal medium for 1-2 hours, vacuumize to a pressure of -0.1 MPa, continue to soak for 1-2 hours to form a substrate with a metal interlayer; S3: Heat sodium to 400 ℃ and remove surface impurities, soak the substrate with a metal interlayer obtained in step S2 in liquid sodium, heat and soak together for 4 hours, vacuumize three times during the process, and take out and cool after the substrate is fully saturated with sodium to obtain the negative electrode current collector.

8. The method of producing a negative current collector for high- performance sodium-based liquid-metal batteries according to claim 7, wherein In step S1, the oxygen content in the glove box is less than 0.01 ppm, and the moisture content is less than 0.01 ppm.

9. The method of producing a negative current collector for high- performance sodium-based liquid-metal batteries according to claim 7, wherein In step S2, the metal medium is an alloy of one or more of tin, indium, bismuth, gallium-based alloy or cadmium.

10. The method of producing a negative current collector for high- performance sodium-based liquid-metal batteries of claim 7, wherein, In step S1, the foam substrate is selected from a foam nickel or a foam iron-nickel alloy, the foam substrate has a pore density of 40-70 PPI, a porosity of 90%-98%, a thickness of 5-20 mm and a content of nickel of 10-100 wt.%.

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