Na / SnF2 electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of electrode materials, in particular to a Na / SnF2 electrode and a preparation method and application thereof. The first purpose of the invention is to provide a preparation method of a Na / SnF2 electrode, which comprises the following steps: in a glove box protected by inert atmosphere, uniformly coating the surface of a sodium metal sheet with dried SnF2 powder to form a SnF2 layer, and then carrying out heating reaction to enable the SnF2 layer to completely react with Na to obtain the Na / SnF2 electrode. On one hand, a uniform, compact, mechanically firm and NaF-rich SEI protection layer is directly generated on the Na surface, and on the other hand, the metal Na and SnF2 are subjected to a chemical reaction to generate a sodium-tin alloy as a sodium-philic site to guide uniform deposition of sodium. The Na / SnF2 composite electrode prepared by the preparation method disclosed by the invention shows relatively small overpotential and excellent cycling stability in a symmetrical battery.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a Na / SnF2 electrode and a preparation method and application thereof. Background Art

[0002] Sodium has similar physical and chemical properties to lithium. On the one hand, Na has unique advantages such as its abundance in the earth's crust (≈2.74%) is much higher than that of lithium (≈0.0017%), its wide distribution, low cost, and ease of mining. On the other hand, sodium metal batteries have a high theoretical capacity (≈1166 mAh g -1 ), low redox potential (-2.714 V vs. standard hydrogen electrode), and high energy density make sodium metal anodes an ideal anode material for sodium-ion batteries (SIBs) as a novel energy storage system. However, the practical application of sodium metal anodes is hampered by several challenges, particularly the uncontrollable lithium dendrite formation and unstable solid electrolyte interphase (SEI) layer caused by uneven sodium deposition behavior. Specifically, sodium metal is highly reactive with liquid electrolytes and can spontaneously undergo chemical reactions, forming a fragile SEI layer on the surface. Furthermore, the huge volume expansion of the sodium anode during the sodium deposition / stripping process can generate mechanical stress, tearing the fragile native SEI layer, exposing fresh sodium to the electrolyte and further consuming the sodium metal. Worse still, sodium dendrites growing from cracks can penetrate the separator, leading to battery failure, which can also lead to battery safety issues. These obstacles ultimately lead to low Coulombic efficiency, short lifespan, and even safety hazards in sodium metal batteries (SMBs), causing internal short circuits, leading to thermal runaway, fire, and even explosion. Summary of the Invention

[0003] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a Na / SnF2 electrode and a preparation method and application thereof.

[0004] A first object of the present invention is to provide a method for preparing a Na / SnF2 electrode, comprising the following steps: in a glove box protected by an inert atmosphere, uniformly coating a surface of a sodium metal sheet with dry SnF2 powder to form a SnF2 layer, and then heating the sheet to react completely with Na to obtain a Na / SnF2 electrode.

[0005] Furthermore, the thickness of the SnF2 layer is 3-15 μm.

[0006] Furthermore, the reaction is heated at 70-90° C. for 5-9 hours.

[0007] Furthermore, the heating reaction is to place the sample on a polytetrafluoroethylene plate and heat it at 80° C. for 6 h.

[0008] Furthermore, the thickness of the sodium metal sheet is 0.30 mm.

[0009] Furthermore, SnF2 powder is evenly coated on the surface of the sodium metal sheet using a doctor blade coating method.

[0010] The second object of the present invention is to provide a Na / SnF2 electrode prepared by the above-mentioned preparation method.

[0011] The third object of the present invention is to provide an application of the Na / SnF2 electrode as described above, which is used as the negative electrode of a sodium metal battery.

[0012] The present invention uses an easy-to-use SnF2 precursor to modify Na metal, and a scraper coating method is used to precisely control the thickness of the in-situ formed metal fluoride heterogeneous protective layer. On the one hand, through the continuous in-situ reaction of SnF2 with the active metal Na, a uniform, dense and mechanically strong NaF-rich SEI protective layer is directly generated on the Na surface. On the other hand, the metal Na and SnF2 undergo a chemical reaction to generate a sodium-tin alloy as a sodium-philic site to guide the uniform deposition of sodium, that is, the SEI protective layer is a NaF / SnF2 heterogeneous, controllable and multifunctional artificial interface protective layer.

[0013] The reaction of SnF2 with metallic sodium produces a stable structure of NaSn alloy and NaF, promoting a synergistic effect and further improving performance. Specifically, the reaction produces Na-Sn alloy and NaF. Na-Sn alloy has a high ion diffusion coefficient, which can effectively promote Na + transport, reducing the Na nucleation overpotential, thus facilitating uniform sodium deposition; in the multi-component system, the NaSn alloy has a good inductive effect and sodium affinity, ensuring its close bonding and reliable stability during the Na deposition / stripping process. At the same time, the NaF-rich SEI has excellent mechanical strength, which can protect the electrode from electrolyte corrosion and inhibit the occurrence of side reactions, thereby effectively inhibiting the growth of sodium dendrites and maintaining the stability of the interface. In addition, the highly sodium-affinity SnF2 component and Na + The binding is strong, and the NaF in the SEI layer reduces the Na + The diffusion energy barrier of Na + The diffusion of NaSn alloy and NaF is inhibited, and the formation of Na dendrites is suppressed. The synergistic effect of the two components of NaSn alloy and NaF effectively promotes the electrochemical performance of the Na / SnF2 metal negative electrode. The Na / SnF2 composite electrode prepared by the present invention exhibits a small overpotential and excellent cycle stability in a symmetrical battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the XRD pattern of Na / SnF2 in Example 1;

[0015] Figure 2 is the SEM element distribution diagram of Na / SnF2 in Example 1;

[0016] Figure 3 The charge-discharge cycle performance of the bare Na and Na / SnF2 symmetric batteries in Application Example 1;

[0017] Figure 4 This is the rate performance of the bare Na and Na / SnF2 symmetric batteries in Application Example 2. DETAILED DESCRIPTION

[0018] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0019] Example 1

[0020] (1) SnF2 powder was placed in a vacuum drying oven at 100 °C for 24 h to remove surface moisture, and the dried powder was immediately transferred to an argon-filled glove box.

[0021] (2) A sodium metal block was taken out from the kerosene in the glove box and polished, and then pressed into a sodium metal sheet with a width of 50 mm, a length of 60 mm, and a thickness of 0.30 mm for use.

[0022] (3) 1g of SnF2 powder was placed on one end of a sodium metal sheet. The powder was then evenly coated on the surface of the sheet using a scraper. The adjustable scraper was adjusted to a thickness of 3 / 5 / 7 / 9 / 11 / 13 / 15 μm, respectively, to obtain SnF2 layers of varying thickness. The scraper-coated sample was placed on a polytetrafluoroethylene plate and heated at 80°C for 6 h to allow complete reaction between the SnF2 layer and the sodium. This resulted in a Na / SnF2 protective layer.

[0023] Figure 1 is the XRD pattern of Na / SnF2 in Example 1; Figure 2 is the SEM element distribution diagram of Na / SnF2 in Example 1; Figure 1 It can be seen that the XRD diffraction peaks of Na / SnF2 appear the diffraction peaks of NaF and Na9Sn4 compared with bare Na; Figure 2 It can be seen that the three elements Na, Sn and F are evenly distributed on the Na / SnF2 surface, indicating that the NaF / SnF2 heterogeneous artificial interface protective layer was successfully constructed by inducing the in situ reaction between Na and SnF2 layer.

[0024] Application Example 1

[0025] (4) In this application example, a Na / SnF2 composite negative electrode prepared by doctor blade coating with a thickness of 9 μm was selected for electrochemical testing to compare the charge and discharge cycle performance of bare Na||bare Na and Na / SnF2||Na / SnF2 symmetric batteries.

[0026] The specific operating conditions and results of the experiment are as follows:

[0027] Operating conditions: Symmetric cells were assembled in a glove box under argon conditions with O2<0.01ppm; H2O<0.01ppm, using bare Na||bare Na and Na / SnF2||Na / SnF2, a Whatman GF / D separator, 100μl NaClO4 in EC:PC=1:1+5wt% FEC electrolyte, and a CR2032 battery case.

[0028] See also Figure 3 In the application example 1, the symmetrical battery Na / SnF2||Na / SnF2 is at 0.5 mA cm -2 , 0.5mAh cm -2 Under these conditions, the overpotential is significantly smaller than that of bare Na||bare Na, and Na / SnF2||Na / SnF2 has excellent stable cycling performance.

[0029] Application Example 2

[0030] In this application example, a Na / SnF2 composite anode prepared by doctor blade coating with a thickness of 9 μm was used for electrochemical testing to compare the rate performance of bare Na||bare Na and Na / SnF2||Na / SnF2 symmetric cells.

[0031] The specific operating conditions and results of the experiment are as follows:

[0032] Operating conditions: Symmetric cells were assembled in a glove box under argon conditions with O2<0.01ppm and H2O<0.01ppm, using bare Na||bare Na and Na / SnF2||Na / SnF2, a Whatman GF / D separator, 100ul NaClO4 in EC:PC=1:1+5wt% FEC electrolyte, and a CR2032 battery case.

[0033] See also Figure 4 , for the symmetrical battery Na / SnF2||Na / SnF2 in Application Example 2 at a fixed capacity of 1 mAh cm -2The overpotential under different current density conditions is significantly lower than that of bare Na||bare Na, and Na / SnF2||Na / SnF2 has excellent and stable cycling performance. This shows that the Na / SnF2||Na / SnF2 symmetric battery has excellent cycling stability and can effectively inhibit the growth of sodium dendrites and stabilize the sodium metal anode.

[0034] Any matters not mentioned above shall be subject to the existing technology.

[0035] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a Na / SnF2 electrode, characterized in that: The steps include: In an inert atmosphere-protected glove box, dry SnF2 powder is evenly coated on the surface of a sodium metal sheet to form a SnF2 layer, which is then heated to react completely with Na to obtain a Na / SnF2 electrode.

2. The preparation method according to claim 1, wherein The thickness of the SnF2 layer is 3-15 μm.

3. The preparation method according to claim 1, wherein The reaction was heated at 70-90°C for 5-9h.

4. The preparation method according to claim 1, wherein The heating reaction was performed by placing the sample on a polytetrafluoroethylene plate and heating it at 80°C for 6 h.

5. The preparation method according to claim 1, wherein The thickness of the sodium metal sheet is 0.30 mm.

6. The preparation method according to claim 1, wherein The SnF2 powder was evenly coated on the surface of the sodium metal sheet using a doctor blade coating method.

7. A Na / SnF2 electrode prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the Na / SnF2 electrode according to claim 7, characterized in that: Used as the negative electrode of sodium metal batteries.

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