Zinc-based sodium-philic modified current collector, preparation method thereof and negative-electrode-free sodium metal battery

Abstract

The invention relates to the technical field of negative-electrode-free sodium metal batteries, in particular to a zinc-based sodium-philic modified current collector, a preparation method of the zinc-based sodium-philic modified current collector and a negative-electrode-free sodium metal battery with the zinc-based sodium-philic modified current collector. The current collector comprises a zinc foil substrate and a sodium-philic Zn-M intermetallic phase modification layer formed on the surface of the zinc foil substrate, M adopts one of Sb, Sn and Bi, the modification layer is generated in situ through magnetron sputtering of metal antimony on the zinc foil and annealing treatment, and the effect is the best when Sb is used as M metal. The preparation method has the beneficial effects that the alloy layer is subjected to reversible and non-cracking alloying / dealloying reaction in the sodium deposition / stripping process, a continuous conductive framework and a stable sodium-philic interface are kept, the sodium nucleation overpotential can be remarkably reduced, sodium is induced to be uniformly deposited on the surface of the current collector, and generation of dendritic crystals and dead sodium is inhibited; therefore, the coulombic efficiency, the cycle life and the safety of the negative-electrode-free sodium metal battery are improved.

Description

Technical Field

[0001] This invention relates to the field of sodium metal battery technology without negative electrode, and in particular to a zinc-based sodium-loving modified current collector, its preparation method, and a sodium metal battery without negative electrode having the current collector. Background Technology

[0002] Applications such as renewable energy grid connection, grid-side peak shaving, and new transportation modes place comprehensive demands on electrochemical energy storage systems, requiring high energy density, low cost, and long lifespan. While traditional lithium-ion batteries are technologically mature, their large-scale deployment faces bottlenecks due to uneven lithium resource distribution and cost pressures. In contrast, sodium-based batteries, built using sodium, an element more abundant in the Earth's crust, have natural advantages in resource endowment and material cost, and are therefore increasingly considered an important candidate technology for large-scale energy storage and medium-energy-density applications. Among various sodium-based systems, sodium metal batteries, using metallic sodium as the negative electrode, boast a capacity of nearly 1160 mAh·g. –1With its theoretical specific capacity and low electrode potential, sodium metal batteries possess the potential to construct high-energy-density batteries. However, the conventional design of excess sodium metal anodes not only increases the amount of active metal used and manufacturing costs, but also easily induces severe dendrite growth, dead sodium accumulation, and flammable electrolyte side reactions during cycling, leading to problems such as low coulombic efficiency, rapid capacity decay, and even safety accidents. To achieve a better balance between energy density and safety, anode-free sodium metal batteries have gradually become a research hotspot in recent years. These systems do not pre-place sodium metal or embedded anode materials during assembly; instead, they only use a metal current collector as the anode carrier. All available sodium ions originate from the cathode and electrolyte, and are deposited in situ on the current collector surface during the first charge. This anode-free configuration reduces the sodium metal processing steps, improves volumetric / mass energy density, and is expected to reduce total lifecycle costs and carbon footprint. However, due to the absence of an additional sodium metal buffer in the system, the sodium metal battery without a negative electrode is highly sensitive to the reversibility of the interface during each sodium deposition / stripping process. On the one hand, the solid electrolyte interface film continuously generated and repaired between the negative electrode current collector and the electrolyte continuously consumes the limited active sodium, leading to a gradual decrease in coulombic efficiency and cycle capacity. On the other hand, uneven ion / electron transport at the interface easily induces sodium to nucleate locally and then dendrite outward, forming dead sodium and safety hazards. Therefore, suppressing side reactions and achieving uniform sodium deposition are key challenges currently faced by the negative electrode-free system. In existing research, it is common to introduce sodium-loving metal or alloy coatings (such as Sn, Sb, Bi, Ag, etc.) onto conventional metal current collectors to reduce the sodium nucleation overpotential and guide its uniform deposition. This type of interface modification method has certain advantages in terms of cost and process, and has achieved positive results in sodium metal / negative electrode-free batteries. For example, in patent publication number CN 117747847 A, entitled "Composite Current Collector with Sodium-Favorable Interface and Its Preparation and Application in Electrode-less Sodium Batteries," a technical solution is disclosed that Cu, Fe, Ni, and Ti are used as matrices, and Sb, Bi, In, Ag, Pb, and Sn are combined with the matrices to form a sodium-favorable interface layer. However, these sodium-favorable coatings often undergo significant volume changes during repeated sodium alloying / dealloying processes, which easily leads to coating cracking, interface debonding, and repeated rupture and reconstruction of the SEI film. This weakens long-term sodium affinity and sodium deposition control capabilities, making it difficult to simultaneously achieve the long cycle life and process simplicity required for high-energy-density electrode-less sodium batteries. This is because the Cu, Fe, Ni and Ti commonly used as the matrix are high-melting-point metals (melting point greater than 1000℃). When magnetic sputtering or conventional heat treatment is used, the matrix can only serve as an inert physical support framework and cannot undergo bulk diffusion with sodium-loving substances such as Sb, Bi, In, Ag, Pb and Sn. This affects the adhesion of the sodium-loving interface layer of this type of current collector to the matrix and also affects the ability of the sodium-loving interface layer to induce uniform Na deposition.Therefore, how to construct a modified interface with a stable structure and long-term sodium affinity on a metal foil-based current collector with the simplest possible structure remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] To address the problems of insufficient affinity between traditional current collectors and sodium metal, difficulty in controlling sodium deposition morphology, and easy interface instability during cycling in existing anode-free sodium metal batteries, this invention proposes a zinc foil-based sodium-affinity modified current collector and its preparation method, and applies it to anode-free sodium metal batteries. The specific technical solution is as follows: A zinc-based sodium-loving current collector includes a zinc foil substrate and a sodium-loving interface layer composited on at least one surface of the zinc foil substrate; the sodium-loving interface layer is a metal-modified layer containing Zn-M intermetallic phases, wherein M is a metal element selected from Sb, Sn, and Bi; the sodium-loving interface layer is metallurgically bonded to the zinc foil substrate, and the sodium-loving interface layer forms a continuous and dense metal-modified layer on the surface of the zinc foil substrate, which is used to induce uniform deposition / stripping of sodium metal during battery charging / discharging.

[0004] Preferably, M is Sb, and the Zn-M intermetallic phase contained in the sodium-loving interface layer includes the Zn4Sb3 intermetallic phase.

[0005] Specifically, the Zn4Sb3 intermetallic phase is continuously distributed along the surface of the zinc foil substrate, forming a continuous alloyed interface layer covering the surface of the zinc foil substrate.

[0006] The thickness of the sodium-loving interface layer is 100nm~2000nm, preferably 300nm~1000nm, and more preferably 900nm.

[0007] The thickness of the zinc foil substrate is 10μm to 100μm, preferably 20μm to 50μm.

[0008] Regarding the aforementioned zinc-based sodium-loving current collector, this application also provides a method for its preparation, comprising the following steps: S1. Clean and dry the zinc foil substrate.

[0009] S2. In a vacuum magnetron sputtering apparatus, metal M is used as the target material to sputter and deposit on the surface of the zinc foil substrate from step S1, forming a metal M coating on the surface of the zinc foil substrate, wherein metal M is one of Sb, Sn, or Bi.

[0010] S3. The zinc foil substrate with the metal M coating formed on its surface in step S2 is heat-treated under an inert atmosphere to cause the metal M coating to undergo a solid-phase reaction with the zinc foil substrate, thereby forming a metal-modified layer containing Zn-M intermetallic phases in situ on the surface of the zinc foil substrate as a sodium-loving interface layer.

[0011] Specifically, in step S2, when using a vacuum magnetron sputtering device for sputtering deposition, it is carried out in a vacuum or inert atmosphere, and the magnetron sputtering power is 20~100W, the sputtering time is 1~20min, so as to obtain a metal M coating with a thickness of 100~2000nm.

[0012] Specifically, in step S3, the heat treatment temperature is 300~450℃, the holding time is 1~6h, the heating rate is 1~10℃ / min, and after the holding time is completed, the temperature is naturally cooled to room temperature under the protection of an inert atmosphere.

[0013] In a further preferred embodiment, the metal M used in step S2 is Sb, and when using a vacuum magnetron sputtering device for sputtering deposition, the magnetron sputtering power is 50W and the sputtering time is 5min; in step S3, the heat treatment temperature is 400℃, the holding time is 4h, and the heating rate is 5℃ / min, thereby forming an Sb modified layer with Zn4Sb3 as the main phase in situ on the zinc foil substrate surface as a sodium-loving interface layer.

[0014] Meanwhile, this application also provides a negative electrode-free sodium metal battery, which includes a positive electrode, a separator, and a negative electrode current collector sequentially compounded, and an electrolyte impregnating the positive electrode, separator, and negative electrode current collector. The negative electrode current collector adopts the above-mentioned zinc-based sodium-loving modified current collector. The negative electrode-free sodium metal battery does not have a pre-placed sodium metal negative electrode during assembly. All the active sodium in the battery comes from the positive electrode. During the first charging process, sodium is deposited in metallic form on the surface of the zinc-based sodium-loving modified current collector.

[0015] The beneficial effects of this invention are as follows: By introducing sodium-loving metal modification layers such as Sn, Bi, and Sb onto the surface of zinc foil and constructing an intermetallic interface layer in situ under annealing conditions, the sodium-loving metal modification layer and the zinc foil substrate have a strong bonding force. Furthermore, since the sodium-loving metal modification layer has a continuous and dense structure, as the negative electrode current collector of the negative electrodeless sodium battery, it undergoes reversible alloying / dealloying behavior during nanodeposition / stripping. The volume change in this process is mainly released in a buffered manner within the intermetallic phase of the modification layer, without causing large-area cracking or pulverization. It belongs to a non-pyrolysis alloying cross section, which can significantly reduce the sodium nucleation overpotential, induce sodium to nucleate and deposit uniformly on the interface, effectively suppress the formation of sodium dendrites, reduce the formation of dead sodium, and thus significantly improve the long-cycle performance of the negative electrodeless sodium battery. Attached Figure Description

[0016] Appendix Figure 1 This is a scanning electron microscope image of the zinc-based sodium-loving modified current collector of Example 1; Appendix Figure 2 The discharge capacity of the anode-free sodium battery assembled with the zinc-based sodium-loving modified current collector of Example 1 varies with the number of cycles at 300 mA / g. Appendix Figure 3 The curve showing the discharge capacity of the anode-free sodium battery assembled with the zinc-based sodium-loving modified current collector of Example 1 as a function of cycle number at 500 mA / g is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be noted that the following embodiments are used to further illustrate the invention, but do not limit the scope of the invention. Experimental steps not specified with specific conditions in the embodiments are generally performed under conventional conditions or according to the manufacturer's instructions.

[0018] Example 1: A 50 μm thick zinc foil (cleaned and dried) was used as the substrate for the negative electrode current collector. It was fixed on the substrate tray of a magnetron sputtering apparatus, and sputtered with antimony (Sb) as the target material in a vacuum or inert atmosphere. The sputtering power was 50 W for 5 min, forming an antimony coating approximately 900 nm thick on the zinc foil surface. The Sb-plated zinc foil substrate was then annealed at 400°C for 4 h in an inert atmosphere and naturally cooled to room temperature, allowing the antimony coating on the zinc foil substrate surface to react with the zinc foil substrate to form a zinc-antimony alloy modified layer. X-ray diffraction confirmed that this modified layer mainly consisted of the Zn₄Sb³ phase, uniformly adhered to the zinc foil substrate surface. Figure 1 The image shown is an electron microscope scan of the zinc-based sodium-loving modified current collector with a dense and uniform Zn4Sb3 modified layer obtained in this embodiment.

[0019] Example 2: The preparation method of this example is the same as that of Example 1, except that the sputtered metal target is replaced with Bi instead of Sb.

[0020] Example 3: The preparation method of this example is the same as that of Example 1, except that the sputtered metal target is replaced with Sn instead of Sb.

[0021] Comparative Example 1: The preparation method of this comparative example is the same as that of Example 1, except that no subsequent annealing heat treatment is performed after Sb is sputtered onto the zinc foil substrate.

[0022] Comparative Example 2: The preparation method of this comparative example is the same as that of Example 2, except that no subsequent annealing heat treatment is performed after Sb is sputtered onto the zinc foil substrate.

[0023] Comparative Example 3: The preparation method of this comparative example is the same as that of Example 3, except that no subsequent annealing heat treatment is performed after Sb is sputtered onto the zinc foil substrate.

[0024] Comparative Example 4: In this example, zinc foil without any modification treatment is used directly as the negative electrode current collector. That is, a raw bright zinc foil with a thickness of 50μm is used without sputtering coating or annealing treatment.

[0025] In this embodiment, Examples 1-3 and Comparative Examples 1-4 are used as negative electrode current collectors for the negative electrode-less sodium battery. The sodium battery is assembled using the following steps: Sodium iron pyrophosphate is used as the positive electrode active material. First, NFPP positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94:3:3 and stirred evenly to form a slurry. The obtained positive electrode slurry is uniformly coated on an aluminum foil current collector, vacuum dried at 120°C, and then rolled to obtain the positive electrode sheet (NFPP active material loading of approximately 10 mg / cm³). 2 Then, in a glove box filled with high-purity argon, using the aforementioned positive electrode as the positive electrode, Examples 1-3 and Comparative Examples 1-4 were used as negative electrode current collectors, respectively, with a 20 μm thick polypropylene microporous membrane, and a 1 mol / L sodium hexafluorophosphate (NaPF6) dimethoxyethane solution (DME, 1,2-dimethoxyethane) was added as the electrolyte. The cells were assembled in a CR2032 stainless steel button cell to form a sodium metal battery without a negative electrode. The assembly of the half-cells was the same as described above, except that the positive electrode material, sodium iron pyrophosphate, was replaced with a sodium metal sheet. During assembly, the water content and oxygen content were strictly controlled to be <1 ppm. All batteries were subjected to electrochemical testing after standing at 25°C for 12 hours.

[0026] Battery performance testing: All batteries were first charged to 3.9V at a constant current of 0.1C, then discharged to 1.5V at a constant current of 0.1C to determine the initial coulombic efficiency (i.e., the percentage of initial discharge capacity to initial charge capacity). Subsequently, constant current charge-discharge cycle tests were performed at room temperature (25°C) within a voltage window of 1.5–3.9V at a current density of 300 mA / g. The cycle life of each battery was tested, and cycle stability was evaluated by the discharge capacity retention rate (percentage of initial discharge capacity) after 300 cycles. Figure 2 , Figure 3 The figures show the discharge capacity of the anode-free sodium battery assembled with a zinc-based sodium-loving modified current collector having a dense and uniform Zn4Sb3 modified layer, prepared in Example 1, as a function of cycle number at 300 mA / g and 500 mA / g. The capacity retention rates after 1200 cycles were 83.97% and 86.88%, respectively, indicating a significant modification effect. The performance test results are shown in Table 1 below. Table 1 summarizes the initial discharge specific capacity, first charge-discharge coulombic efficiency, and capacity retention rate after 300 cycles for the anode-free sodium batteries assembled using Examples 1-3 and Comparative Examples 1-4 as anode current collectors.

[0027] sample Initial discharge specific capacity First Coulomb efficiency 300-cycle capacity retention Example 1 99.88 90.98% 89.62% Example 2 96.42 87.65% 81.32% Example 3 100.45 91.32% 86.23% Comparative Example 1 98.23 89.32% 43.23% Comparative Example 2 95.63 86.94% 23.23% Comparative Example 3 98.65 89.72% 47.43% Comparative Example 4 103.32 93.93% 21.23% Table 1 As shown in Table 1 above, the initial discharge specific capacity and initial coulombic efficiency of the battery samples prepared in Examples 1-3 and Comparative Examples 1-4 are comparable, but the differences in cycle stability are significant. Among them, Example 1 exhibits the best cycle performance, with a capacity still reaching 85% after 300 cycles, higher than Examples 2 and 3, and significantly higher than Comparative Examples 1-4. This indicates that the intermetallic interface layer generated by the reaction of various sodium-loving metal elements (Sb, Sn, Bi) with zinc can significantly improve the cycle life of the battery. Sb is particularly effective; the Zn4Sb3 alloy layer generated by its reaction with zinc has good sodium affinity, which can reduce the sodium nucleation overpotential and provide a uniform and stable deposition interface, thereby effectively suppressing dendrite growth and volume expansion.

[0028] Compared with Comparative Examples 1-4, Examples 2 and 3 also showed significant improvements in cycling performance, with capacity retention after 300 cycles only lower than Example 1. Among them, Comparative Examples 1-3, which did not undergo annealing treatment, had poor cycling performance, indicating that the modification effect of only sputtering to produce a metal layer without forming an alloy layer was limited; the bare zinc foil that underwent any treatment (Comparative Example 4) had the worst cycle life, with rapid capacity decay. Figure 2 and Figure 3 The results further demonstrate that the battery prepared in Example 1 maintains a stable capacity output at current densities of 300 mA / g and 500 mA / g, reflecting the significant advantages of the Zn4Sb3 modified current collector in long-term cycling at high current densities.

[0029] Of course, the above are only preferred embodiments of the present invention and are not intended to limit the scope of application of the present invention. Therefore, any equivalent changes made to the principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A zinc-based sodium-loving current collector, characterized in that: Includes a zinc foil substrate and a sodium-loving interface layer laminated to at least one surface of the zinc foil substrate; The sodium-loving interface layer is a metal-modified layer containing Zn-M intermetallic phases, wherein M is a metal element selected from Sb, Sn, and Bi. The sodium-loving interface layer is metallurgically bonded to the zinc foil substrate, and the sodium-loving interface layer forms a continuous and dense metal modification layer on the surface of the zinc foil substrate, which is used to induce uniform deposition / stripping of sodium metal during battery charging / discharging.

2. The zinc-based sodium-loving current collector according to claim 1, characterized in that: M is Sb, and the Zn-M intermetallic phase contained in the sodium-loving interface layer includes the Zn4Sb3 intermetallic phase.

3. The zinc-based sodium-loving current collector according to claim 2, characterized in that: The Zn4Sb3 intermetallic phase is continuously distributed along the surface of the zinc foil substrate, forming a continuous alloyed interface layer covering the surface of the zinc foil substrate.

4. A zinc-based sodium-loving current collector according to any one of claims 1 to 3, characterized in that: The thickness of the sodium-loving interface layer is 100nm~2000nm.

5. A zinc-based sodium-loving current collector according to any one of claims 1 to 3, characterized in that: The thickness of the zinc foil substrate is 10μm to 100μm.

6. A method for preparing a zinc-based sodium-loving current collector as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Clean and dry the zinc foil substrate; S2. In a vacuum magnetron sputtering apparatus, metal M is used as a target to sputter and deposit on the surface of the zinc foil substrate in step S1, forming a metal M coating on the surface of the zinc foil substrate, wherein metal M is one of Sb, Sn, and Bi. S3. The zinc foil substrate with the metal M coating formed on its surface in step S2 is heat-treated under an inert atmosphere to cause the metal M coating to undergo a solid-phase reaction with the zinc foil substrate, thereby forming a metal-modified layer containing Zn-M intermetallic phases in situ on the surface of the zinc foil substrate as a sodium-loving interface layer.

7. The method for preparing a zinc-based sodium-loving current collector according to claim 6, characterized in that: In step S2, when sputtering deposition is performed using a vacuum magnetron sputtering device, it is carried out in a vacuum or inert atmosphere, and the magnetron sputtering power is 20~100W, the sputtering time is 1~20min, so as to obtain a metal M coating with a thickness of 100~2000nm.

8. The method for preparing a zinc-based sodium-loving current collector according to claim 6, characterized in that: In step S3, the heat treatment temperature is 300~450℃, the holding time is 1~6h, the heating rate is 1~10℃ / min, and after the holding time is completed, the heat treatment is naturally cooled to room temperature under the protection of an inert atmosphere.

9. A method for preparing a zinc-based sodium-loving current collector according to any one of claims 6 to 8, characterized in that: The metal M used in step S2 is Sb. When using a vacuum magnetron sputtering device for sputtering deposition, the magnetron sputtering power is 50W and the sputtering time is 5min. In step S3, the heat treatment temperature is 400℃, the holding time is 4h, and the heating rate is 5℃ / min, so as to form an Sb modified layer with Zn4Sb3 as the main phase in situ on the zinc foil substrate as a sodium-loving interface layer.

10. A sodium metal battery without a negative electrode, characterized in that: The present invention comprises a positive electrode, a separator, and a negative electrode current collector sequentially combined, and an electrolyte in which the positive electrode, the separator, and the negative electrode current collector are impregnated, wherein the negative electrode current collector is a zinc-based sodium-loving modified current collector as described in any one of claims 1-5. The sodium metal battery without a negative electrode does not have a pre-installed sodium metal negative electrode during assembly. All the active sodium in the battery comes from the positive electrode. During the first charging process, sodium is deposited in metallic form on the surface of the zinc-based sodium-loving modified current collector.

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