Modified current collector for a negative electrode-free sodium metal battery and method for preparing the same

Abstract

This invention discloses a modified current collector for a cathode-free sodium metal battery and its preparation method, belonging to the field of electrochemical energy storage device materials technology. The modified current collector comprises a metal substrate and an artificial solid electrolyte interface layer. The interface layer is an interpenetrating network structure composed of a porous ceramic coating and a permeable polymer coating. The porous ceramic coating contains two-dimensional MXene and cubic boron nitride nanoparticles, and the permeable polymer coating is multi-branched polyacrylic acid, whose molecular chains vertically penetrate the pores of the ceramic coating and chemically bond with the metal substrate. This invention utilizes the sub-nanometer rectification effect of MXene to homogenize the sodium ion flow, utilizes the high thermal conductivity and high modulus of cubic boron nitride to dissipate Joule heat and suppress dendrites, and combines this with the tenon-and-mortise anchoring effect of the polymer chains to solve the coating peeling problem. The modified current collector exhibits an interfacial peel strength ≥8.5 N / m and a cycle life exceeding 600 cycles, providing a high-safety and long-life solution for cathode-free sodium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of materials technology for electrochemical energy storage devices, and in particular to a modified current collector for a negative electrode-free sodium metal battery and its preparation method. Background Technology

[0002] As the global energy structure accelerates its transformation towards cleaner and lower-carbon energy sources, the large-scale energy storage and new energy vehicle industries have created an urgent demand for high-energy-density, low-cost rechargeable batteries. Electrodeless sodium metal batteries, by eliminating the pre-loading of negative electrode active material and using only the current collector as the carrier for sodium metal deposition / deposition, have a theoretical energy density far exceeding that of traditional sodium-ion batteries. Furthermore, sodium resources are abundant and widely distributed, making them a research hotspot for next-generation electrochemical energy storage technology.

[0003] However, the commercial application of anode-free sodium metal batteries still faces three major technological bottlenecks: First, the tip effect and sodium dendrite growth: Numerous micro-defects exist on the surface of the bare aluminum foil current collector, leading to uneven local electric field distribution during charging. Sodium ions preferentially nucleate unevenly at these defects and grow into needle-like and dendritic sodium dendrites. The continuous growth of these dendrites easily punctures the separator, causing internal short circuits, thermal runaway, or even explosions. Second, conventional modified coatings are prone to peeling and failure: Existing technologies often use layered stacking coatings of ceramic materials such as montmorillonite and boehmite for modification. The coating is easily delaminated and peeled off over a large area due to the approximately 300% volume expansion caused by repeated deposition / removal of sodium metal, relying only on weak van der Waals forces or physical adhesion between the coating and the aluminum foil substrate, thus losing its modification effect. Thirdly, local thermal runaway and the formation of dead sodium occur: the sodium metal deposition process is accompanied by significant Joule heating, while conventional ceramic modification materials (such as boehmite and alumina) have low thermal conductivity and cannot dissipate local heat in time, resulting in a sharp increase in interface temperature, accelerating electrolyte decomposition and drying, and the formation of "dead sodium", which significantly shortens the battery cycle life.

[0004] While existing technologies have proposed various coating schemes, such as montmorillonite / boehmite stacked coatings and carbon coatings, none of them can simultaneously solve the problems of coating delamination, dendrite growth, and heat accumulation, thus failing to meet the requirements for long-cycle operation. Therefore, developing a current collector modification technology for a cathodeless sodium metal battery that can simultaneously solve the problems of sodium dendrite growth, coating delamination, and localized thermal runaway has become crucial for promoting the industrialization of this field. Summary of the Invention

[0005] The purpose of this invention is to provide a modified current collector for a negative electrode-free sodium metal battery and its preparation method. By constructing an interpenetrating network artificial solid electrolyte interface layer with "skeleton support + flexible penetration", the invention synergistically achieves sodium ion flow homogenization, dendrite physical blocking, efficient Joule heat conduction, and strong interfacial bonding of the coating. This solves the defects of existing negative electrode-free sodium metal battery current collectors, such as severe sodium dendrite growth, easy peeling of modified coating, and frequent local thermal runaway, thereby improving the cycle life and safety of negative electrode-free sodium metal batteries.

[0006] To achieve the above objectives, the present invention provides a modified current collector for a negative electrode-free sodium metal battery, comprising a metal substrate and an artificial solid electrolyte phase interface layer formed on at least one surface of the metal substrate; The artificial solid electrolyte interface layer is an interpenetrating network structure composed of a discontinuous porous ceramic coating and a permeable polymer coating. The porous ceramic coating contains two-dimensional MXene and cubic boron nitride nanoparticles with fluorinated / hydroxyl functional groups on the surface. The permeable polymer coating is a multi-branched polyacrylic acid, whose molecular chain segments penetrate vertically through the pores of the porous ceramic coating, and whose functional groups at the bottom end form chemical bonds with the functional groups on the surface of the metal substrate.

[0007] Preferably, the metal substrate is an aluminum foil with a thickness of 8-15 μm.

[0008] Preferably, the mass ratio of two-dimensional MXene to cubic boron nitride nanoparticles is 1:5 to 1:20.

[0009] Preferably, the two-dimensional MXene is Ti3C2T. x .

[0010] Preferably, the porous ceramic coating has a porosity of 30% to 50% and a thickness of 1-3 μm.

[0011] Preferably, the molecular weight of the multi-branched polyacrylic acid is between 200,000 and 500,000; the carboxyl groups at the bottom of the multi-branched polyacrylic acid molecular chain form esterification bonds and hydrogen bonds with the hydroxyl groups on the surface of the metal substrate.

[0012] Preferably, the thickness of the artificial solid electrolyte phase interface layer is 2-4 μm, and the interfacial peel strength between the artificial solid electrolyte phase interface layer and the metal substrate is not less than 8.5 N / m.

[0013] The present invention also provides a modified current collector for a sodium metal battery without a negative electrode, comprising the following steps: S1. Two-dimensional MXene, cubic boron nitride nanoparticles and pore-forming agent are dispersed in deionized water and ultrasonicated to obtain a uniform ceramic slurry; the ceramic slurry is coated on the surface of a metal substrate and heated under vacuum until the pore-forming agent decomposes and volatilizes, forming a discontinuous porous ceramic coating in situ. S2. A multi-branched polyacrylic acid aqueous solution is coated on the surface of a discontinuous porous ceramic layer and left to stand so that it can penetrate into the pores of the discontinuous porous ceramic layer through capillary action and contact the surface of the metal substrate; then, vacuum heating is performed to crosslink and cure, forming an artificial solid electrolyte phase interface layer with an interpenetrating network structure, thus obtaining the target modified current collector.

[0014] Preferably, in step S1, the solid content of the ceramic slurry is 12wt%-18wt%; the pore-forming agent is ammonium bicarbonate, and the mixture is heated to 70°C.

[0015] Preferably, in step S2, the mass fraction of the multi-branched polyacrylic acid aqueous solution is 3%-5%; the crosslinking curing conditions are: vacuum baking at 80℃ for 2-3 hours.

[0016] The core principle of this invention lies in constructing three synergistic mechanisms: "sub-nanometer rectification, high thermal conductivity rigid armor, and tenon-and-mortise interpenetrating anchoring." This addresses the three major challenges of dendrite growth, coating peeling, and localized thermal runaway in anode-less sodium metal batteries from the source. The specific mechanisms are as follows: 1) Sub-nanometer ion rectification mechanism (MXene): Ti3C2T x The functional groups such as -F and -O on the surface of MXene have strong electronegativity, which form a polarized electric field in the interlayer. When disordered sodium ions approach, they are "queued and filtered" by the sub-nanometer interlayer gaps of MXene, forming a uniform laminar flow of sodium ions. This eliminates the concentration of local electric fields, inhibits the nucleation and growth of sodium dendrites from the source, and achieves a smooth and dense deposition of sodium metal.

[0017] 2) Thermal conductivity and rigid armor mechanism (cubic boron nitride): Cubic boron nitride is an ultra-hard ceramic material with a Young's modulus greater than 500 GPa, which can physically block the very few occasional tiny dendrites that are generated; at the same time, its thermal conductivity is as high as 100 W / (m·K), which can instantly and uniformly conduct the local Joule heat generated during sodium deposition to the entire aluminum foil substrate, avoid local overheating at the interface, and effectively inhibit electrolyte decomposition and the formation of "dead sodium".

[0018] 3) Mortise and Tenon Interpenetrating Anchoring Mechanism (Multi-branched Polyacrylic Acid): Traditional double-layer coating structures resemble a "sandwich," with no chemical bonds between the layers, making them prone to disintegration under volume expansion. In this invention, the molecular chains of multi-branched polyacrylic acid penetrate vertically through the pores of the porous ceramic layer like "plant roots." The carboxyl groups at the bottom form strong esterification bonds and hydrogen bonds with the hydroxyl groups on the aluminum foil surface, firmly "rivet" the ceramic layer, polymer layer, and aluminum foil substrate together, forming an interpenetrating network structure similar to mortise and tenon joints. The interfacial peel strength is more than 7 times higher than that of traditional coatings, ensuring zero peeling of the coating under repeated volume expansion of sodium metal.

[0019] Based on the above mechanism, the modified current collector adopts an interpenetrating network structure design, which strongly bonds with the metal substrate without occupying additional internal space of the battery, ensuring smooth transport of sodium ions. The modified layer acts directly on the sodium deposition interface, which can truly reflect the interface ion distribution, heat accumulation and structural changes, realizing long-cycle, high-safety and stable operation of the negative electrode-free sodium metal battery.

[0020] Therefore, the modified current collector for a negative electrode-free sodium metal battery and its preparation method provided by the present invention have the following beneficial effects: (1) Suppress sodium dendrite growth from the source: The sodium ion flow is homogenized by the sub-nanometer ion rectification effect of MXene, and the sodium nucleation overpotential is reduced to 12.5mV, so as to achieve flat and dense deposition of sodium metal and completely solve the tip effect and dendrite growth problem of traditional current collectors.

[0021] (2) Super strong interface bonding, completely solving the problem of coating peeling: Through the penetration and chemical bonding of multi-branched polyacrylic acid, a tenon-and-mortise interpenetrating network structure is constructed, with an interface peeling strength of more than 8.5 N / m, which is 7 times higher than that of traditional coatings, and ensures zero peeling of the coating under the 300% volume expansion of sodium metal.

[0022] (3) High-efficiency thermal conduction and suppression of local thermal runaway: The introduction of highly thermally conductive cubic boron nitride nanoparticles can quickly and uniformly conduct local Joule heat at the interface, avoid the formation of hot zones, and significantly improve the thermal stability and cycle life of the battery.

[0023] (4) Excellent electrochemical performance: The sodium metal battery without negative electrode assembled using the modified current collector of this invention has a cycle life of more than 600 cycles at 1C rate and a capacity retention rate of 83.6%, which is far superior to the existing technical solutions.

[0024] (5) The preparation process is simple and can be mass-produced: The present invention adopts micro-gravure roller coating and solution penetration process, which is fully compatible with the existing aluminum foil coating production line. No new large-scale equipment is required, the production cost is low, and it has the potential for large-scale industrial production.

[0025] (6) High versatility: The modification ideas of this invention can be extended to other metal anode battery systems such as lithium metal batteries and potassium metal batteries, and have broad application prospects.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall layered structure of the modified current collector of the present invention; Figure 2 This is a schematic diagram of the interpenetrating network structure and tenon-and-mortise anchoring mechanism of the modified current collector of the present invention; Figure 3This is a comparison diagram of the interfacial peel strength of Examples 1-4 and Comparative Example 2 of the present invention; Figure 4 This is a comparison diagram of sodium nucleation overpotentials in Examples 1-4 and Comparative Examples 1-2 of the present invention; Figure 5 This is a comparison chart of the long-cycle performance of Examples 1-4 and Comparative Examples 1-2 of the present invention; Figure 6 Comparison of top-view SEM images of the negative electrode surface after 100 cycles of Examples 1-4 and Comparative Examples 1-2 of the present invention; Figure Labels 1. Metal substrate; 2. Discontinuous porous ceramic coating; 3. Penetrating polymer coating; 4. Multi-branched polyacrylic acid. Detailed Implementation

[0028] This invention provides a modified current collector for a negative electrode-free sodium metal battery, the structure of which is as follows: Figure 1 As shown, the device includes a metal substrate 1 and an artificial solid electrolyte interface layer formed on the surface of the metal substrate 1. The metal substrate 1 is an aluminum foil with a thickness of 8-15 μm, which serves as a carrier for sodium metal deposition and extraction in a negative electrode-free sodium metal battery, providing good conductivity and mechanical support. The artificial solid electrolyte interface layer has a total thickness of 2-4 μm and an interface peel strength of not less than 8.5 N / m. It exhibits no coating peeling or cracking under 300% volume expansion of sodium metal, and combines structural stability with ion transport properties.

[0029] In this invention, the artificial solid electrolyte interface layer is an interpenetrating network structure composed of a discontinuous porous ceramic coating 2 and a permeable polymer coating 3. The molecular chains of the permeable polymer coating 3 penetrate vertically through the pores of the porous ceramic coating, and the functional groups at its bottom end form chemical bonds with the functional groups on the surface of the metal substrate 1.

[0030] The porous ceramic coating is a composite porous layer containing two-dimensional MXene with fluorinated / hydroxyl functional groups on its surface and cubic boron nitride nanoparticles. This coating is formed by in-situ decomposition of a pore-forming agent, with a porosity of 30%~50% and a thickness of 1-3 μm. It provides permeation channels for polymer chains and ensures efficient transport of sodium ions. The two-dimensional MXene with fluorinated / hydroxyl functional groups on its surface is preferably Ti3C2T. x Two-dimensional MXene material. The penetrating polymer coating 3 is a multi-branched polyacrylic acid 4 with a molecular weight of 200,000 to 500,000. The functional groups at the bottom of the molecular chain form esterification bonds and hydrogen bonds with the surface of the metal substrate 1, achieving strong anchoring between the coating and the substrate. The mass ratio of two-dimensional MXene to cubic boron nitride nanoparticles is 1:5 to 1:20. This ratio can ensure the sub-nanometer rectification effect of MXene and give full play to the high modulus and high thermal conductivity of cubic boron nitride, synergistically achieving ion homogenization, dendrite suppression and thermal management functions.

[0031] like Figure 2 As shown, the molecular chains of multi-branched polyacrylic acid penetrate deeply into the pores of the porous ceramic coating through capillary action, and the bottom ends are chemically bonded to the metal substrate to form a tenon-and-mortise interpenetrating anchoring structure; the arrows indicate that the polymer chains penetrate the ceramic pores and anchor the metal substrate, realizing the integrated and firm bonding of the ceramic layer, polymer layer and metal substrate.

[0032] The present invention also provides a modified current collector for a sodium metal battery without a negative electrode, comprising the following steps: S1. Two-dimensional MXene, cubic boron nitride nanoparticles and pore-forming agent (ammonium bicarbonate) are dispersed in deionized water and sonicated for 30-60 min to obtain a uniform ceramic slurry with a solid content of 12wt%-18wt%. The ceramic slurry is coated on the surface of a metal substrate and heated under vacuum at 70℃ for 1-2 h until the pore-forming agent decomposes into ammonia, carbon dioxide and water volatilizes, forming a discontinuous porous ceramic coating in situ without any impurities.

[0033] S2. A 3%-5% (w / w) aqueous solution of multi-branched polyacrylic acid is coated onto the surface of a discontinuous porous ceramic layer. After standing for 3-5 minutes, the solution is allowed to penetrate into the pores of the discontinuous porous ceramic layer through capillary action and contact the surface of the metal substrate. Subsequently, the solution is vacuum heated at 80°C for 2-3 hours to crosslink and cure, forming an artificial solid electrolyte phase interface layer with an interpenetrating network structure, thus obtaining the target modified current collector.

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0035] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0036] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0037] Unless otherwise specified, the materials, reagents, instruments, and equipment used in this invention are all materials, reagents, instruments, and equipment routinely used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, without further explanation.

[0038] The component parameters used in the following examples or comparative examples are as follows: Ti3C2T with fluorinated / hydroxyl functional groups on the surface x MXene: 1-3 μm in diameter, 1-2 nm in thickness; Cubic boron nitride (c-BN) nanoparticles: particle size 50-100nm.

[0039] The performance of the current collectors obtained in the following embodiments and comparative examples was characterized using the following battery assembly and testing baseline conditions: Battery assembly: Using sodium vanadium phosphate (NVP) as the positive electrode active material, Celgard 2400 as the battery separator, and 1 mol / L NaClO4 / EC+DEC (volume ratio 1:1) as the electrolyte, a CR2032 button-type sodium metal battery without a negative electrode was assembled in an argon-protected glove box.

[0040] Electrochemical performance testing: All electrochemical performance tests were conducted at a constant temperature of 25℃ and a charge / discharge rate of 1C. The tests included sodium nucleation overpotential, initial coulombic efficiency, cycle life at 1C rate, and capacity retention.

[0041] Morphology characterization after cycling: After 100 cycles, the battery was disassembled under argon protection, the negative electrode current collector was removed, cleaned with DMC solvent, and the surface morphology of the negative electrode was observed using scanning electron microscopy (SEM) to evaluate the growth of sodium dendrites.

[0042] Interface bonding performance testing: A universal testing machine was used to perform a 90° peel test on the modified current collector at a peel rate of 50 mm / min and a sample width of 20 mm. The interface peel strength (N / m) was recorded. Simultaneously, hundreds of repeated bending cycles simulating volume expansion (each cycle including bending and recovery) were performed to observe whether the coating peeled or cracked.

[0043] Thermal stability test: During battery charging, an infrared thermal imager is used to target the surface of the negative electrode current collector of the battery to monitor and record the highest interface temperature (°C) in real time, and to evaluate the formation of local hot spots.

[0044] Example 1 This embodiment provides a modified current collector for a negative electrode-free sodium metal battery, and its preparation method is as follows: (1) Preparation of pore-forming ceramic slurry: Ti3C2T with fluorinated / hydroxyl functional groups on the surface is used to form pore-forming ceramic slurry. x MXene, cubic boron nitride nanoparticles and ammonium bicarbonate pore-forming agent were dispersed in deionized water at a mass ratio of 1:10:1, with the solid content controlled at 15wt%. After magnetic stirring for 30 min, the mixture was ultrasonically treated for 45 min to obtain a uniform and stable ceramic slurry.

[0045] (2) Preparation of porous ceramic framework layer: Ceramic slurry was uniformly coated on one side of an aluminum foil with a thickness of 12 μm using a micro-gravure roller coating process, and the wet film thickness was controlled to be 5 μm. Then, it was dried in a vacuum drying oven at 70℃ for 1.5 h to completely decompose ammonium bicarbonate into ammonia, carbon dioxide and water, forming a discontinuous porous ceramic framework layer with a thickness of 2 μm and a porosity of 42% in situ.

[0046] (3) Polymer penetration and cross-linking curing: Prepare a 4% (w / w) aqueous solution of branched polyacrylic acid (PAA) with a molecular weight of 300,000. Coat the porous ceramic skeleton layer with this solution uniformly and let it stand for 4 min to allow it to penetrate deep into the aluminum foil substrate surface through capillary action. Then bake it in a vacuum drying oven at 80℃ for 2.5 h for cross-linking curing to obtain an artificial solid electrolyte phase interface layer with a total thickness of 3 μm, which is the modified current collector.

[0047] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The interface peel strength is 8.7 N / m. After 300 simulated volume expansion cycles, the coating remains intact without peeling or cracking. The sodium nucleation overpotential is 12.5 mV, the initial coulombic efficiency is 92.3%, and the capacity retention rate is 83.6% after 600 cycles at 1C rate. After 100 cycles, the battery was disassembled, and the negative electrode surface was smooth and dense with no visible sodium dendrites. The highest interface temperature during charging is 44.2℃, with no localized hot spots.

[0048] Example 2 This embodiment provides a modified current collector for high-porosity, electrodeless sodium metal batteries, and its preparation method is as follows: (1) Preparation of pore-forming ceramic slurry: Ti3C2T x MXene, cubic boron nitride nanoparticles and ammonium bicarbonate pore-forming agent were added to deionized water at a mass ratio of 1:5:4, with the solid content controlled at 12wt%. After magnetic stirring for 20 minutes, the mixture was ultrasonically treated for 30 minutes to obtain a uniform ceramic slurry.

[0049] (2) Preparation of porous ceramic skeleton layer: The slurry was coated on the surface of 12μm aluminum foil using a micro-gravure roller coating process, and the wet film thickness was controlled to be 6μm. Then, it was dried in a vacuum drying oven at 70℃ for 2h to completely decompose ammonium bicarbonate into ammonia, carbon dioxide and water, forming a discontinuous porous ceramic skeleton layer with a thickness of 2.5μm and a porosity of 48% in situ.

[0050] (3) Polymer penetration and cross-linking curing: Prepare a 3% (w / w) aqueous solution of multi-branched polyacrylic acid with a molecular weight of 250,000. After coating, let it stand for 5 min to allow it to fully penetrate, and then bake it in vacuum at 80℃ for 3 h to cross-link and cure it, thus obtaining an artificial solid electrolyte phase interface layer with a total thickness of 3.5 μm, which is the modified current collector.

[0051] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The interfacial peel strength is 8.5 N / m. After 280 simulated volume expansion cycles, the coating remains intact without peeling or cracking. The sodium nucleation overpotential is 13.8 mV, and the initial coulombic efficiency is 91.7%. After 600 cycles at 1C, the capacity retention is 81.2%. After 100 cycles, the battery was disassembled, and the negative electrode surface was smooth and dense, with no visible sodium dendrites. The room temperature ionic conductivity is 1.2 × 10⁻⁶. -3 S / cm (9.8 × 10⁻⁶ in Example 1) -4 The maximum interface temperature during charging is 42.8℃, indicating superior thermal conductivity.

[0052] Example 3 This embodiment provides a modified current collector for an ultra-thin, electrodeless sodium metal battery, and its preparation method is as follows: (1) Preparation of pore-forming ceramic slurry: Ti3C2T x MXene, cubic boron nitride nanoparticles and ammonium bicarbonate pore-forming agent were added to deionized water at a mass ratio of 1:15:2, with the solid content controlled at 18wt%. After magnetic stirring for 40 min, the mixture was ultrasonically treated for 60 min to obtain a high-concentration ceramic slurry.

[0053] (2) Preparation of porous ceramic framework layer: The slurry was coated on the surface of 10μm aluminum foil using a high-precision micro-gravure roller coating process, and the wet film thickness was controlled to be 3μm. Vacuum drying at 70℃ for 1h resulted in the formation of an ultrathin discontinuous porous ceramic framework layer with a thickness of 1μm and a porosity of 35% in situ.

[0054] (3) Polymer penetration and cross-linking curing: Prepare a 5% (w / w) aqueous solution of multi-branched polyacrylic acid with a molecular weight of 400,000. After coating, let it stand for 3 minutes to allow rapid penetration. Cross-linking curing is performed by vacuum baking at 80℃ for 2 hours to obtain an ultrathin artificial solid electrolyte phase interface layer with a total thickness of 2 μm, which is the modified current collector.

[0055] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The interface peel strength is 8.6 N / m. After 290 simulated volume expansion cycles, the coating remains intact without peeling or cracking. The sodium nucleation overpotential is 14.2 mV, and the initial coulombic efficiency is 90.9%. After 600 cycles at 1C, the capacity retention rate is 79.5%. After 100 cycles, the battery was disassembled, and the negative electrode surface was smooth and dense with no visible sodium dendrites. Compared with Example 1, the cell volumetric energy density is increased by 6.2%. The highest interface temperature during charging is 45.1℃.

[0056] Example 4 The difference between this embodiment and embodiment 1 is that in step S2, a porous ceramic skeleton layer and an interpenetrating network interface layer are sequentially prepared on both sides of a 12μm aluminum foil using a micro-gravure roller coating process. The thickness of each modified layer is 1.5μm, the total modified layer thickness is 3μm, and the porosity is 40%.

[0057] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The interface peel strength is 8.8 N / m on one side. After 320 simulated volume expansion cycles, the coatings on both sides remain intact without peeling or cracking. The sodium nucleation overpotential is as low as 11.8 mV, and the initial coulombic efficiency is 93.1%. The capacity retention rate is 85.2% after 600 cycles at 1C rate. The synergistic effect of MXene and cubic boron nitride on both sides enhances ion rectification and thermal conductivity, resulting in more uniform sodium ion transport and significantly improved high-rate performance. After 400 cycles at 2C rate, the capacity retention rate is 78.3% (compared to only 72.5% in Example 1). The highest charging interface temperature is 43.5℃. After 100 cycles, the aluminum foil surfaces on both sides are smooth and dendrite-free, making it suitable for high-power sodium metal batteries without negative electrodes.

[0058] Comparative Example 1 Untreated 12μm electrolytic aluminum foil is used as the negative electrode current collector and is directly used in battery assembly without any coating modification.

[0059] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The sodium nucleation overpotential was 48.2 mV, and the initial coulombic efficiency was 76.5%. After 100 cycles at 1C, the capacity retention was only 12.8%. After 100 cycles, the battery was disassembled and dendrites were found to be clustered on the negative electrode surface, with a large amount of "dead sodium". The highest interface temperature during charging was 67.9℃, with obvious local hot spots.

[0060] Comparative Example 2 Modified aluminum foil was prepared using a traditional layered stacking coating process, and the preparation method is as follows: Montmorillonite and boehmite were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 1:2, and PVDF binder (10wt% solids content) was added and stirred until homogeneous to obtain a ceramic slurry. This slurry was coated onto a 12μm thick aluminum foil surface and vacuum dried at 80℃ to obtain a dense ceramic coating with a thickness of 3μm. The coating and the aluminum foil are bonded solely by physical adhesion, without an interpenetrating network structure or chemical bonding.

[0061] The test was conducted under the aforementioned unified benchmark conditions, and the results are as follows: The interface peel strength was only 1.1 N / m, and the coating peeled off over a large area after 50 simulated volume expansion cycles; the sodium nucleation overpotential was 31.7 mV, and the initial coulombic efficiency was 84.1%; after 200 cycles at 1C, the capacity retention rate was 35.2%; after 100 cycles, the battery was disassembled, and the coating on the negative electrode surface cracked, with dendrite penetration in some areas; the highest interface temperature during charging was 58.6℃.

[0062] The performance comparison of Examples 1-4 and Comparative Examples 1-2 is summarized in Table 1.

[0063] Table 1: Summary of performance comparison between Examples 1-4 and Comparative Examples 1-2

[0064] The following analysis is based on the attached diagram and test results: (1) Interface combined with performance analysis As shown in Table 1 and Figure 3 As shown, the interfacial peel strengths of Examples 1-4 of the present invention reached 8.7 N / m, 8.5 N / m, 8.6 N / m, and 8.8 N / m, respectively, while the peel strength of the traditional layered coating in Comparative Example 2 was only 1.1 N / m. This significant improvement is attributed to the "mortise and tenon" interpenetrating network structure constructed in this invention: multi-branched polyacrylic acid molecular chains vertically penetrate the pores of the porous ceramic framework, and their bottom carboxyl groups form esterification bonds and hydrogen bonds with the hydroxyl groups on the aluminum foil surface, achieving a leap from physical adsorption to chemical bonding. In contrast, the coating of Comparative Example 2 relies solely on the physical adhesion of the PVDF binder, resulting in weak interfacial bonding. After 300 simulated volume expansion cycles, the coating peeled off over a large area, while the coating of the embodiments of the present invention remained intact, without peeling or cracking, after 300 cycles.

[0065] (2) Sodium nucleation overpotential analysis As shown in Table 1 and Figure 4As shown, the sodium nucleation overpotential in Comparative Example 1 is as high as 48.2 mV, indicating that sodium ions have difficulty nucleating at defects and the process is uneven. Comparative Example 2 has an overpotential of 31.7 mV, which is an improvement but still relatively high. The sodium nucleation overpotentials in Examples 1-4 of this invention are as low as 12.5 mV, 13.8 mV, 14.2 mV, and 11.8 mV, respectively. This is because the -F and -O functional groups on the MXene surface have strong electronegativity, forming a polarized electric field in the sub-nanometer interlayer. This "rectifies" and filters the disordered sodium ion flow, forming a uniform laminar flow, thereby significantly reducing the nucleation barrier and suppressing dendrite nucleation and growth at the source.

[0066] (3) Long-cycle performance analysis As shown in Table 1 and Figure 5 As shown, at a 1C rate, Comparative Example 1 exhibits rapid capacity decay after less than 100 cycles, with capacity retention of only 4.2% and 8.3% after 600 cycles. In contrast, Examples 1-4 of this invention demonstrate excellent cycling stability: Example 1 maintains a capacity retention of 83.6% after 600 cycles, Example 2 81.2%, Example 3 79.5%, and Example 4 85.2%. This is attributed to three synergistic mechanisms: MXene's ion rectification suppresses dendrites; cubic boron nitride's rigid armor physically blocks dendrites and dissipates Joule heat; and the interpenetrating network structure ensures the coating does not peel off during long-term volume expansion. These three mechanisms collectively guarantee interface stability and long cycle life.

[0067] (4) Analysis of interface temperature and negative electrode morphology As shown in Table 1 and Figure 6 As shown, the SEM top-view comparison of the negative electrode surface after 100 cycles reveals the following: Comparative Example 1 exhibits dendrite clusters and a large amount of "dead sodium" on its surface; Comparative Example 2 shows a cracked coating with localized dendrite penetration; while the negative electrode surfaces of Examples 1-4 of this invention are all smooth and dense, with no visible sodium dendrites. This is attributed to the high thermal conductivity of cubic boron nitride, which instantly and uniformly conducts the deposited Joule heat to the entire aluminum foil substrate, preventing the formation of localized hot zones. During charging, the highest interface temperature in Comparative Example 1 reached 67.9℃, and in Comparative Example 2 it was 58.6℃, while the highest temperatures in Examples 1-4 of this invention were 44.2℃, 42.8℃, 45.1℃, and 43.5℃, respectively, significantly lower than the comparative examples, demonstrating its excellent thermal management capabilities.

[0068] In summary, the modified current collector prepared by this invention exhibits an interfacial bonding strength that is more than 7 times higher than that of traditional coatings, completely solving the coating peeling problem caused by sodium metal volume expansion; the sodium nucleation overpotential is significantly reduced, inhibiting sodium dendrite growth at its source; and the interfacial thermal conductivity is greatly improved, effectively preventing localized thermal runaway. Furthermore, the battery assembled with the modified current collector has a cycle life exceeding 600 cycles, far superior to existing technologies.

[0069] Therefore, the modified current collector for anode-free sodium metal batteries based on sub-nanometer rectification and interpenetrating network structure and its preparation method of the present invention can be directly applied to various metal anode battery systems such as anode-free sodium metal batteries, lithium metal batteries, and potassium metal batteries, and is particularly suitable for scenarios such as new energy vehicle power batteries and large-scale energy storage power stations with high requirements for energy density and safety. The preparation process of this modified current collector is fully compatible with existing aluminum foil coating production lines, requiring no additional large-scale equipment, resulting in low production costs and the potential for large-scale industrial production. Furthermore, the modified current collector of the present invention can be integrated with a battery thermal management system to achieve dynamic control of the battery's operating state by real-time monitoring of interface temperature changes, further improving battery safety and lifespan.

[0070] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A modified current collector for a sodium metal battery without a negative electrode, characterized in that: It includes a metal substrate and an artificial solid electrolyte phase interface layer formed on at least one surface of the metal substrate; The artificial solid electrolyte interface layer is an interpenetrating network structure composed of a discontinuous porous ceramic coating and a permeable polymer coating. The porous ceramic coating contains two-dimensional MXene and cubic boron nitride nanoparticles with fluorinated / hydroxyl functional groups on the surface. The permeable polymer coating is a multi-branched polyacrylic acid, whose molecular chain segments penetrate vertically through the pores of the porous ceramic coating, and whose functional groups at the bottom end form chemical bonds with the functional groups on the surface of the metal substrate.

2. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: The metal substrate is an aluminum foil with a thickness of 8-15μm.

3. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: The mass ratio of two-dimensional MXene to cubic boron nitride nanoparticles is 1:5 to 1:

20.

4. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: Two-dimensional MXene is Ti3C2T x .

5. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: The porous ceramic coating has a porosity of 30% to 50% and a thickness of 1-3 μm.

6. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: The molecular weight of multi-branched polyacrylic acid ranges from 200,000 to 500,000; the carboxyl groups at the bottom of the multi-branched polyacrylic acid molecular chain form esterification bonds and hydrogen bonds with the hydroxyl groups on the surface of the metal substrate.

7. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that: The thickness of the artificial solid electrolyte phase interface layer is 2-4 μm, and the interfacial peel strength between the artificial solid electrolyte phase interface layer and the metal substrate is not less than 8.5 N / m.

8. A method for preparing a modified current collector for a negative electrode-free sodium metal battery as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Two-dimensional MXene, cubic boron nitride nanoparticles and pore-forming agent are dispersed in deionized water and ultrasonicated to obtain a uniform ceramic slurry; the ceramic slurry is coated on the surface of a metal substrate and heated under vacuum until the pore-forming agent decomposes and volatilizes, forming a discontinuous porous ceramic coating in situ. S2. A multi-branched polyacrylic acid aqueous solution is coated on the surface of a discontinuous porous ceramic layer and left to stand so that it can penetrate into the pores of the discontinuous porous ceramic layer through capillary action and contact the surface of the metal substrate; then, vacuum heating is performed to crosslink and cure, forming an artificial solid electrolyte phase interface layer with an interpenetrating network structure, thus obtaining the target modified current collector.

9. The method for preparing a modified current collector for a negative electrode-free sodium metal battery according to claim 8, characterized in that: In step S1, the solid content of the ceramic slurry is 12wt%-18wt%; the pore-forming agent is ammonium bicarbonate, and the slurry is heated to 70℃.

10. The method for preparing a modified current collector for a negative electrode-free sodium metal battery according to claim 8, characterized in that: In step S2, the mass fraction of the multi-branched polyacrylic acid aqueous solution is 3%-5%; the cross-linking curing conditions are: vacuum baking at 80℃ for 2-3 hours.

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