A sodium metal negative electrode structure and preparation method thereof, and sodium ion battery

Abstract

The present invention provides a sodium metal negative electrode structure, a preparation method thereof, and a sodium ion battery. The sodium metal negative electrode structure comprises a sodium metal sheet and an artificial interface modification structure formed on the surface of the sodium metal sheet. The artificial interface modification structure comprises an evaporation structure formed on the surface of the sodium metal sheet by vacuum evaporation technology. The evaporation structure is made of at least one of a sodium alloy, an inorganic SEI film-forming agent, or a conductive metal element. The sodium alloy comprises sodium and metals and / or non-metals alloyed with sodium. The inorganic SEI film-forming agent can provide an effective inorganic component for the SEI layer. The modified structure formed by vacuum evaporation has good uniformity, stability, density, and adhesion, resulting in good interface stability for the sodium metal negative electrode structure, thereby improving the cycle life and capacity retention of the sodium ion battery.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and specifically relates to a sodium metal negative electrode structure and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Sodium-ion batteries (SIBs), due to their abundant resources, low cost, and environmental friendliness, have become a promising energy storage technology after lithium-ion batteries. However, SIBs face a number of challenges in their practical application, one of the most significant technical challenges being the stability of the sodium metal anode. Sodium metal exhibits high electrochemical reactivity and readily reacts with the electrolyte to form a dynamically unstable solid electrolyte interphase (SEI) layer in SIBs. This SEI layer exhibits poor mechanical stability and is prone to rupture and repeated regeneration during cycling, resulting in continuous depletion of active sodium and electrolyte. Furthermore, the growth of sodium dendrites can pose safety concerns. These factors collectively lead to battery performance degradation and shortened cycle life. Therefore, effectively improving the stability of the sodium metal anode and inhibiting its reaction with the electrolyte are key to improving the performance of SIBs.

[0003] Currently, common methods for solving the stability problem of sodium metal negative electrodes include using dynamic interface engineering, forming a protective coating on the surface of sodium metal with organic or inorganic materials, or optimizing the formation of the SEI layer by optimizing the electrolyte composition. Although these methods have improved the stability of the sodium metal negative electrode to a certain extent, there are still some problems that cannot be ignored: First, the stability of the modified layer is poor, and it is difficult to resist the mechanical stress and electrochemical reactions that may occur during the long-term cycle of the battery. For example, certain fluorides or phosphates may form a relatively rigid or unstable interface during the use of the battery, affecting ion migration and reducing the charge and discharge efficiency of the battery; second, the ionic conductivity of the modified layer is poor, which may lead to a decrease in the charge and discharge performance of the battery; third, although some alloying schemes can improve the stability of the negative electrode material, alleviate the sodium metal expansion problem, and improve the conductivity and cycle performance of the negative electrode, they still face the problems of phase separation, rapid capacity decay and low conductivity during the cycle. In addition, alloying in the existing technology usually adopts mechanical alloying or melting method. These alloying processes are often accompanied by different solubility and diffusion behavior of each element in the alloy, resulting in uneven structural changes or precipitation of the alloy during the battery cycle, thereby affecting the cycle stability of the battery. At the same time, certain alloying processes may not be able to fully optimize the interfacial reaction between the sodium metal negative electrode and the electrolyte, resulting in interface instability. Side reactions between the sodium metal and the electrolyte are still prone to occur, generating an unstable solid electrolyte interface layer, which affects the performance of the battery.

[0004] In summary, although some progress has been made in the research of sodium metal anodes, the above-mentioned existing technologies still have some limitations. In particular, there has been no significant breakthrough in how to effectively control the interaction between sodium metal and electrolyte, stabilize the formation of the SEI layer, and improve the ionic conductivity of the interfacial layer. Therefore, how to form a stable, long-lasting, and highly ionic conductive modified layer on the sodium metal surface has become the key to the development of sodium metal anode technology. Summary of the Invention

[0005] In order to solve all or part of the above technical problems, the present invention provides the following technical solutions:

[0006] One of the objectives of the present invention is to provide a sodium metal negative electrode structure, the sodium metal negative electrode structure comprising a sodium metal sheet and an artificial interface modification structure formed on the surface of the sodium metal sheet, the artificial interface modification structure comprising an evaporation structure, the evaporation structure being formed on the surface of the sodium metal sheet by vacuum evaporation technology;

[0007] The material of the evaporation structure includes at least one of a sodium alloy, an SEI inorganic film-forming agent or a conductive metal element, wherein the sodium alloy includes sodium and metals and / or non-metals alloyed with sodium; the SEI inorganic film-forming agent can provide an effective inorganic component for the SEI layer.

[0008] The SEI inorganic film-forming agent of the present invention refers to an agent that can serve as a component of the SEI layer and play an interface stabilizing role.

[0009] The present invention effectively isolates the sodium metal from direct contact with the electrolyte by forming an evaporation structure on the surface of the sodium metal sheet, slowing down the degradation of the SEI and improving the interfacial stability of the sodium metal. The evaporation structure can effectively inhibit the growth of sodium dendrites. When applied to solid-state sodium-ion batteries, the evaporation structure can improve the interfacial wettability between the sodium metal and the solid electrolyte. Sodium-ion batteries based on this sodium metal negative electrode structure have good cycle stability, capacity retention, and long service life.

[0010] In some embodiments, the metal alloyed with sodium includes one or more of Sn, Bi, Al, Zn, In, and Sb, but is not limited thereto. The non-metal alloyed with sodium includes, but is not limited to, Si. During the vacuum evaporation process, the metal and non-metal vaporize and deposit, and react with sodium to form a sodium alloy layer, thereby forming a negative electrode structure of a sodium metal sheet and a sodium alloy layer.

[0011] These sodium alloy layers have better mechanical strength and ductility than pure sodium metal. They can withstand the expansion and contraction of sodium metal during the charging and discharging process, reduce the rupture and shedding of the SEI layer, and make the battery have better structural stability during the cycle.

[0012] In addition, the sodium alloy layer (such as a sodium alloy layer containing Al and Si) can enhance the electrical conductivity of the negative electrode material, reduce the internal resistance, improve the charge and discharge efficiency, and improve the deposition / desorption efficiency of sodium, thereby making the negative electrode exhibit better electrochemical performance, which helps to improve the battery power density, especially in high-rate charge and discharge and long-cycle cycles.

[0013] In some embodiments, the SEI inorganic film-forming agent includes one or a combination of multiple of Na2O, NaF, Na2S, Si3N4, SiO2, and Al2O3, but is not limited thereto.

[0014] In some embodiments, the conductive metal element is formed by a sodium reactant chemically reacting with sodium during a vacuum evaporation process. The sodium reactant includes one or more of AgF and AlF3, but is not limited thereto. The reaction of AgF, AlF3 and sodium can generate Ag and Al metal elements. Ag is deposited on the surface of the sodium sheet to improve conductivity and inhibit dendrite growth, while Al is deposited on the surface of the sodium sheet to improve conductivity. At the same time, NaF is formed during the reaction. NaF is a stable component in the SEI, which helps passivate the negative electrode surface and reduce side reactions.

[0015] The inorganic compound can effectively disperse the current during the battery charge and discharge process, and more directly inhibit the formation of sodium dendrites, especially having obvious advantages in inhibiting the formation of sodium dendrites during high-rate charge and discharge.

[0016] In addition, some inorganic compounds (such as Na2O, NaF, Na2S) and other components can promote the uniform transmission of sodium ions at the interface.

[0017] The sodium alloy of the present invention can be an alloy formed by a metal / non-metal and sodium, such as Na-Sn, Na-Bi, Na-Al, Na-Zn, Na-In, Na-Sb, Na-Si, etc., or an alloy formed by two or more metals / non-metals and sodium.

[0018] In some embodiments, the evaporation structure includes a multi-layer stacked structure, which has at least two adjacent evaporation layers made of different materials, and the two evaporation layers are respectively formed of two different types of the sodium alloy, SEI inorganic film-forming agent or conductive metal element.

[0019] In some preferred embodiments, the multilayer stacked structure includes an alloy layer and a SEI inorganic film-forming agent layer arranged in sequence in a direction away from the sodium metal sheet, the material of the alloy layer is the sodium alloy, and the material of the SEI inorganic film-forming agent layer is the SEI inorganic film-forming agent.

[0020] In some embodiments, the evaporation structure includes a composite layer, and the material of the composite layer includes at least two of a sodium alloy, an SEI inorganic film-forming agent, or a conductive metal element.

[0021] In some preferred embodiments, the composite layer includes the sodium alloy and the SEI inorganic film-forming agent uniformly mixed.

[0022] Compared with the vapor deposition structure formed by simple metal or non-metal, or the vapor deposition structure formed by simple SEI inorganic film-forming agent, the multi-layer stacked structure and composite layer are significantly improved in promoting uniform transmission of sodium ions and inhibiting dendrite growth due to the good synergistic effect of sodium alloy and SEI inorganic film-forming agent.

[0023] In some embodiments, the thickness of the evaporation structure is 1~60 nm, preferably 2~10 nm. If the evaporation structure is thin, it is easy to cause problems such as insufficient interface protection, insufficient SEI mechanical strength, and insufficient alloy buffering capacity. If the evaporation structure is thicker, it is easy to cause ion migration to be blocked, electron tunneling effect to be limited, interface instability, and battery energy density to decrease. Although the evaporation structure can basically achieve the interface protection effect when it is 1~60 nm, after systematic research by the present invention, it is found that when the thickness of the evaporation structure is 2~10 nm, it can take into account interface protection, mechanical strength and battery energy density, and the overall performance is better.

[0024] A second object of the present invention is to provide a method for preparing a sodium metal negative electrode structure, wherein the sodium metal negative electrode structure comprises a sodium metal sheet and an artificial interface modification structure formed on the sodium metal sheet, wherein the artificial interface modification structure comprises a vapor deposition structure;

[0025] The preparation method comprises: in an environment with an oxygen content of less than 0.1 ppm, a humidity of less than 0.1 ppm, and a temperature of less than 20° C., using a vacuum evaporation method to form an evaporation structure on the surface of the sodium metal sheet by evaporating material;

[0026] The evaporation material includes at least one of a metal, a non-metal or an inorganic compound; the metal or non-metal can undergo an alloying reaction with sodium to form a sodium alloy; the inorganic compound includes an SEI inorganic film-forming agent and / or a sodium reactant; the SEI inorganic film-forming agent can provide an effective inorganic component for the SEI layer; and the sodium reactant can chemically react with sodium to generate a conductive metal element and an effective inorganic component for the SEI layer.

[0027] Because sodium metal expands and contracts during battery charge and discharge, the SEI layer can easily rupture or detach, affecting the battery's capacity retention and cycle stability. Vacuum evaporation technology creates a deposited structure that stabilizes the sodium negative electrode surface during battery operation, thereby maintaining the battery's cycle life and capacity retention. Vacuum evaporation technology precisely controls the thickness and composition of the deposited structure at a microscopic scale, resulting in a uniform, dense, and stable deposited structure. This avoids the problems of easy peeling and degradation, poor adhesion, and uneven thickness caused by mechanical stress or electrochemical reactions in modified layers formed by traditional coating methods or electrochemical deposition.

[0028] In addition, for the metals, non-metals and inorganic compounds mentioned in the present invention, the vacuum evaporation method can form an excellent quality evaporation layer on the surface of sodium metal. It is applicable to various types of materials and has good universality, which enables the interface modification of the sodium metal negative electrode surface to have diverse options to meet different application requirements.

[0029] In addition, sodium metal is highly chemically active and readily reacts with substances such as water and oxygen to form sodium oxides or sodium hydrides, which can lead to surface instability. The present invention has found that controlling the water-oxygen content and ambient temperature within the above ranges can produce a negative electrode with a uniform, high-quality coating that meets electrode requirements. If the water-oxygen content and temperature are not strictly controlled, the sodium surface is easily oxidized, and the volatilization and migration of sodium prevent the stable deposition of the evaporated material. This means that subsequent operations cannot be performed, or the resulting negative electrode structure does not meet electrode requirements. Controlling the oxygen content to 0.01-0.1 ppm, the humidity to 0.01-0.1 ppm (i.e., the water content is 0.01-0.1 ppm), and the temperature to 13-20°C can achieve optimal evaporation results while balancing equipment conditions and costs.

[0030] In some embodiments, the metal includes one or a combination of multiple of Sn, Bi, Al, Zn, In, and Sb, but is not limited thereto.

[0031] In some embodiments, the non-metal includes Si, but is not limited thereto.

[0032] In some embodiments, the SEI inorganic film-forming agent includes one or a combination of multiple of Na2O, NaF, Na2S, Si3N4, SiO2, and Al2O3, but is not limited thereto.

[0033] In some embodiments, the sodium reactant includes one or a combination of AgF, AlF3, but is not limited thereto.

[0034] In some embodiments, the vacuum degree of the vacuum evaporation is 5×10 -4 ~1×10 -2Pa.

[0035] In some embodiments, the evaporation rate of the vacuum evaporation is 0.1~3 Å / s, preferably 0.2~0.8 Å / s. If the evaporation rate is too slow, the rotation of the substrate may not be able to compensate for the slow deposition rate, resulting in the deposition of the evaporation source on the substrate being locally too thick or too thin. If the evaporation rate is too fast, it may cause the evaporation source atoms / molecules to fail to fully migrate to the appropriate position on the substrate surface, forming a loose, rough or porous film structure, reducing the density and mechanical strength of the film; at the same time, the controllability of the process is reduced. In addition, deposition that is too slow or too fast may change the stress distribution within the deposited layer or between the deposited layer and the substrate, increase the risk of cracking the deposited layer, and affect the battery life.

[0036] In some embodiments, the voltage of the vacuum evaporation is 0.5-2 V, preferably 0.85-1.2 V.

[0037] In the embodiment where the evaporation material is the metal and / or non-metal, the voltage of the vacuum evaporation is preferably 0.95-1.2 V.

[0038] In the embodiment where the evaporation material is the SEI inorganic film-forming material and / or the sodium reactant, the voltage of the vacuum evaporation is preferably 0.85-1 V.

[0039] In some embodiments, the vapor deposition thickness is 1-60 nm, preferably 2-10 nm.

[0040] In some embodiments, during the vacuum evaporation, the distance between the sodium metal sheet and the evaporation material is 0.5-80 mm, preferably 25-40 mm.

[0041] In some embodiments, during the vacuum evaporation, the rotation speed of the sodium metal sheet is 0-30 rpm, such as 0.1-30 rpm, preferably 10-15 rpm.

[0042] In some embodiments, the vacuum evaporation method is single-source evaporation, multi-source sequential evaporation, or multi-source simultaneous evaporation.

[0043] In some embodiments, the single-source evaporation includes: selecting one of the evaporation materials for vacuum evaporation to form an evaporation structure on the sodium metal sheet.

[0044] In some embodiments, the multi-source sequential evaporation includes: sequentially evaporating at least two of metals and / or non-metals, SEI inorganic film-forming agents, or sodium reactants, so that the evaporated materials form a multi-layer stacked structure on the surface of the sodium metal sheet.

[0045] In some embodiments, the multi-source simultaneous evaporation includes: using at least two types of metals and / or non-metals, SEI inorganic film-forming agents or sodium reactants for simultaneous evaporation, so that at least two types of evaporation materials are simultaneously vaporized and deposited on the surface of the sodium metal sheet, thereby forming a composite layer.

[0046] In some embodiments, the evaporation material used in the multi-source sequential evaporation and the multi-source simultaneous evaporation includes at least one of the metals and / or non-metals, and also includes at least one of the SEI inorganic film-forming agents.

[0047] In some embodiments, the multi-source sequential evaporation includes: vaporizing and depositing at least one of the metals and / or non-metals and reacting with sodium to form a sodium alloy layer; vaporizing and depositing at least one of the SEI inorganic film-forming agents on the surface of the sodium alloy layer to form a SEI inorganic film-forming agent layer, thereby forming the multi-layer stacked structure.

[0048] In some embodiments, the multi-source simultaneous evaporation includes: simultaneously vaporizing and depositing at least one of the metals and / or non-metals and at least one of the SEI inorganic film-forming agents on the surface of the sodium metal sheet to form a composite layer in which the sodium alloy and the SEI inorganic film-forming agent are uniformly mixed.

[0049] A third object of the present invention is to provide a sodium metal negative electrode structure, wherein the sodium metal negative electrode structure is prepared by the method described in any one of the claims.

[0050] A fourth object of the present invention is to provide a negative electrode for a sodium ion battery, wherein the negative electrode for a sodium ion battery comprises any one of the sodium metal negative electrode structures described.

[0051] A fifth object of the present invention is to provide a sodium ion battery, wherein the sodium ion battery is a liquid sodium ion battery, the liquid sodium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator, and the negative electrode is the negative electrode for the sodium ion battery; or, the sodium ion battery is a solid-state sodium ion battery, the solid-state sodium ion battery includes a positive electrode, a negative electrode and a solid electrolyte, the solid electrolyte is an oxide solid electrolyte or a composite solid electrolyte, the negative electrode is the negative electrode for the sodium ion battery, and the vapor-deposited structure in the negative electrode is arranged in contact with the solid electrolyte.

[0052] The oxide solid electrolyte and composite solid electrolyte are types of solid electrolytes generally known in the art and will not be described in detail here.

[0053] For example, the oxide solid electrolyte may be a NaSICON type electrolyte, but is not limited thereto.

[0054] The composite solid electrolyte includes a polymer matrix, an electrolyte salt, and an inorganic filler. For example, the polymer matrix and electrolyte salt can be in a molar ratio of (18-6):1, and the inorganic filler can account for 5-40% by weight. The polymer matrix, electrolyte salt, and inorganic filler are known in the art and are not particularly limited in the present invention. The polymer matrix can include, for example, one or more of polyethylene oxide (PEO), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN), but is not limited thereto. The electrolyte salt can include, for example, one or more of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium trifluoromethanesulfonate (NaCF3SO3), but is not limited thereto. The inorganic filler can include, for example, one or more of barium titanate (BaTiO3), aluminum oxide (Al2O3), aluminum nitride (AlN), zinc oxide (ZnO), and silicon dioxide (SiO2), but is not limited thereto.

[0055] In some embodiments, the solid electrolyte is an oxide solid electrolyte, and the material of the contact interface between the evaporation structure and the solid electrolyte is a sodium alloy.

[0056] The present invention finds that the sodium alloy layer can improve the interfacial wettability between sodium metal and oxide solid electrolyte. Solid electrolyte and electrode are both rigid solids, and the contact interface is prone to microscopic pores or unevenness, resulting in a small actual contact area, obstructed ion transmission path, and a significant increase in interface resistance. In particular, the high hardness and rigidity of oxide solid electrolytes are prone to poor contact, poor interfacial chemical stability, and the interface problems caused by mechanical stress during the cycle are also more significant. Forming an alloy layer on the sodium metal negative electrode can reduce the formation of an interface modification layer on the metallic sodium negative electrode, while buffering volume changes, so that the contact between the electrode / electrolyte is changed from point contact to surface contact.

[0057] In some embodiments, the separator of the liquid sodium-ion battery can be a glass fiber filter paper membrane. The electrolyte of the liquid sodium-ion battery can include sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), and a solvent. The solvent can include one or more of propylene carbonate (PC), dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), but is not limited thereto. The electrolyte can also include 1-10 wt% of an additive, such as one or more of fluoroethylene carbonate (FEC), ethylene sulfite (ES), and vinylene carbonate (VC), but is not limited thereto.

[0058] In some embodiments, the positive electrode of the sodium ion battery may include a current collector and a positive electrode active material layer formed on the positive electrode, wherein the positive electrode active material layer includes an active material, carbon black (Super P), and polyvinylidene fluoride (PVDF) in a mass ratio of (70-90): (5-20): (5-10). The thickness of the positive electrode active material layer may be 25-50 μm. For example, the active material may include sodium nickel iron manganese oxide (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), sodium nickel iron manganate 424 (NaNi 0.4 Fe 0.2 Mn 0.4 O2), sodium iron phosphate pyrophosphate Na4Fe3(PO4)2(P2O7) or Prussian blue, but not limited thereto.

[0059] Compared with the prior art, the present invention has at least the following beneficial effects:

[0060] (1) The raw materials selected in the present invention have good compatibility with sodium metal. By forming an artificial interface modification layer on the surface of the sodium metal sheet, the direct contact between the sodium metal and the electrolyte is effectively isolated, the degradation of the SEI is slowed down, and the interfacial stability of the sodium metal is improved. The vapor deposition structure formed by these raw materials can effectively inhibit the growth of sodium dendrites. Sodium-ion batteries based on this sodium metal negative electrode structure have good cycle stability, capacity retention performance, and long service life.

[0061] (2) The present invention found that the alloy layer formed by evaporating metal / non-metal and sodium metal can improve the interfacial wettability between the sodium metal negative electrode and the oxide solid electrolyte, thereby improving the cycle stability and rate performance of the solid-state sodium ion battery.

[0062] (3) By optimizing the process conditions of vacuum evaporation technology and controlling the water-oxygen conditions, ambient temperature, evaporation voltage, and rate, the present invention successfully forms a high-quality evaporation layer on the sodium metal negative electrode that meets the requirements for electrode use. The evaporation layer has excellent uniformity, stability, density, and adhesion, solving the problems of uneven thickness and poor interlayer adhesion of the modified layer formed on the sodium negative electrode by coating and electrochemical deposition methods. In addition, the vacuum evaporation technology provided by the present invention has good universality, is applicable to a variety of evaporation materials, and is simple to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0064] Figure 1 Surface scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) of the artificial interface modification layer prepared in Example 1;

[0065] Figure 2 Surface scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) of the artificial interface modification layer prepared in Example 2;

[0066] Figure 3 1 is a comparison chart of the cycle performance of the symmetrical battery assembled in Example 1 and the symmetrical battery assembled in Comparative Example 1;

[0067] Figure 4 2 is a comparison chart of the cycle performance of the symmetrical battery assembled in Example 2 and the symmetrical battery assembled in Comparative Example 1;

[0068] Figure 5 3 is a charge-discharge curve diagram of the first three times of the full battery assembled in Example 3 at room temperature and 0.1 C current density;

[0069] Figure 6 is a cycling performance diagram of the full battery assembled in Example 6 at room temperature and 3 C current density;

[0070] Figure 7 is a surface scanning electron microscope (SEM) image of the artificial interface modification layer prepared in Example 7;

[0071] Figure 8 is a rate performance diagram of the full battery assembled in Example 7 at room temperature;

[0072] Figure 9 is a cycling performance diagram of the full battery assembled in Example 15 at room temperature and 1 C current density;

[0073] Figure 10 1 is a graph showing the first three charge and discharge curves of the full battery assembled in Example 16 at room temperature and a current density of 0.1 C. DETAILED DESCRIPTION

[0074] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art to employ the present invention in various ways in virtually any appropriate detailed embodiment.

[0075] In addition, unless otherwise specified, the various raw materials used in the following examples can be purchased from the market, etc., the various production and testing equipment used are also equipment known in the art, and the testing methods used are also conventional testing methods in the art.

[0076] Example 1

[0077] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0078] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.01 ppm, a humidity of 0.01 ppm, and a temperature of 18 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 1×10 -3 Pa, set the distance from the substrate stage to the evaporation source to 32 mm, and the substrate stage rotation speed to 10 rpm;

[0079] (2) Sn was selected as the evaporation material and placed in a crucible for single-source evaporation. It was evaporated at an average rate of 0.2 Å / s under an evaporation voltage of 1.2 V until an artificial interface modification structure with an evaporation thickness of 6 nm was formed, thereby obtaining a sodium metal negative electrode structure.

[0080] Figure 1 The surface SEM image and surface energy spectrum (EDS) of the artificial interface modified structure prepared in this embodiment are as follows: Figure 1 As shown, the spectrum shows that the main elements Sn and Na are evenly distributed, that is, Sn reacts with sodium to form an artificial interface modification layer made of Sn-Na alloy during the vacuum evaporation process.

[0081] The sodium metal negative electrode structure is used to prepare sodium ion symmetric batteries and full batteries. The preparation method is as follows:

[0082] Preparation of symmetrical battery:

[0083] The sodium metal anode structure described above served as the working and counter electrodes, and a glass fiber filter paper membrane served as the separator. The electrolyte employed consisted of 1 mol / L sodium perchlorate (NaClO4) and a solvent consisting of ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio, with 2% fluoroethylene carbonate (FEC) added. The electrodes, separator, and electrolyte were assembled into a sodium-ion battery.

[0084] Preparation of full battery:

[0085] Preparation of the positive electrode: weigh NaNi according to the mass ratio of 80:10:10 1 / 3 Fe 1 / 3 Mn 1 / 3O2 positive electrode material, carbon black (SuperP) and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) and stirred at high speed for 4.5 hours to form a uniform conductive slurry, which was then coated on aluminum foil. The thickness of the coated active material was 40 μm. The positive electrode sheet was obtained after vacuum drying at 120°C for 12 hours.

[0086] The negative electrode is the sodium metal negative electrode prepared above;

[0087] The diaphragm is a glass fiber filter paper membrane;

[0088] The above-mentioned electrolyte components are used to assemble the above-mentioned positive electrode material and negative electrode into a sodium ion battery.

[0089] Example 2

[0090] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0091] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.1 ppm, a humidity of 0.01 ppm, and a temperature of 20 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 5×10 -3 Pa, set the distance from the substrate stage to the evaporation source to 30 mm, and the substrate stage rotation speed to 10 rpm;

[0092] (2) NaF was selected as the evaporation material and placed in a crucible for single-source evaporation. It was evaporated at an average rate of 0.5 Å / s under an evaporation voltage of 0.9 V until a NaF artificial interface modification structure with an evaporation thickness of 10 nm was formed, thereby obtaining a sodium metal negative electrode structure.

[0093] Figure 2 The surface SEM image and surface energy spectrum (EDS) of the artificial interface modified structure prepared in this embodiment are as follows: Figure 2 As shown, the spectrum shows that the main elements (F, Na) contained are evenly distributed.

[0094] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0095] Example 3

[0096] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0097] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.01 ppm, a humidity of 0.01 ppm, and a temperature of 13 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 1×10-3 Pa, set the distance from the substrate stage to the evaporation source to 40 mm, and the substrate stage rotation speed to 15 rpm;

[0098] (2) Na2S and Bi were selected as evaporation materials, and Na2S and Bi were placed in a crucible for dual-source evaporation in sequence. Bi was evaporated at an average rate of 0.6 Å / s under an evaporation voltage of 1.1 V until the evaporation thickness reached 2 nm to form the first modification layer; then Na2S was evaporated at an average rate of 0.8 Å / s under an evaporation voltage of 0.85 V until the evaporation thickness reached 6 nm to form the second modification layer. The first modification layer and the second modification layer constituted an artificial interface modification structure, thereby obtaining a sodium metal negative electrode structure.

[0099] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0100] Example 4

[0101] The only difference between Example 4 and Example 3 is that Example 4 uses only Bi as the evaporation material. Bi is placed in a crucible for single-source evaporation. Bi is evaporated at an average rate of 0.6 Å / s under an evaporation voltage of 1.1 V until the evaporation thickness reaches 8 nm, forming a modified structure. The remaining steps are the same as in Example 3 and are not repeated here.

[0102] Example 5

[0103] The only difference between Example 5 and Example 3 is that Example 5 uses only Na2S as the evaporation material, places Na2S in a crucible for dual-source sequential evaporation, and evaporates Na2S at an average rate of 0.8 Å / s under an evaporation voltage of 0.85 V until the evaporation thickness reaches 8 nm to form a modified structure. The rest is implemented in the same way as Example 3 and will not be repeated here.

[0104] Example 6

[0105] This embodiment is substantially the same as embodiment 2, with the only difference being that, in step (2), the vaporization is performed at an average rate of 0.1 Å / s at a vapor deposition voltage of 0.9 V until an artificial interface modification structure with a vapor deposition thickness of 5 nm is formed. The remaining steps are the same as those in embodiment 2 and will not be described in detail here.

[0106] Example 7

[0107] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0108] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.1 ppm, a humidity of 0.01 ppm, and a temperature of 16 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 5×10 -4 Pa, set the distance from the substrate stage to the evaporation source to 25 mm, and the substrate stage rotation speed to 10 rpm;

[0109] (2) In was selected as the evaporation material and placed in a crucible for single-source evaporation. It was evaporated at an average rate of 0.5 Å / s under an evaporation voltage of 1.1 V until an artificial interface modification layer with an evaporation thickness of 8 nm was formed, thereby obtaining a sodium metal negative electrode structure.

[0110] Figure 7 3 is a surface SEM scanning electron microscope image of the artificial interface modification structure prepared in this embodiment.

[0111] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0112] Example 8

[0113] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0114] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.01 ppm, a humidity of 0.01 ppm, and a temperature of 20 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 1×10 -3 Pa, set the distance from the substrate stage to the evaporation source to 40 mm, and the substrate stage rotation speed to 15 rpm;

[0115] (2) Na2O and Sn were selected as evaporation materials and placed in a crucible for dual-source simultaneous evaporation. Sn was evaporated at an average rate of 0.25 Å / s under a voltage of 1.1 V, and Na2O was evaporated at an average rate of 0.25 Å / s under a voltage of 1 V, forming an artificial interface modification layer with a total thickness of 3 nm to obtain a sodium metal negative electrode structure.

[0116] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0117] Example 9

[0118] The only difference between this example and Example 8 is that in Example 9, only Sn was used as the evaporation material. Sn was placed in a crucible for single-source evaporation. Sn was evaporated at an average rate of 0.25 Å / s at a voltage of 1.1 V, resulting in a modified layer with a thickness of 3 nm. The remaining steps were carried out in the same manner as in Example 8 and are not further described here.

[0119] Example 10

[0120] The only difference between this example and Example 8 is that in Example 10, only Na2O was used as the evaporation material. This was placed in a crucible for single-source evaporation. Na2O was evaporated at an average rate of 0.25 Å / s at a voltage of 1 V, forming a modified layer with a thickness of 3 nm. The remaining steps were carried out in the same manner as in Example 8 and are not further described here.

[0121] Example 11

[0122] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0123] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.05 ppm, a humidity of 0.05 ppm, and a temperature of 18 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 1×10 -2 Pa, set the distance from the substrate stage to the evaporation source to 32 mm, and the substrate stage rotation speed to 12 rpm;

[0124] (2) Si was selected as the evaporation material and placed in a crucible for single-source evaporation. It was evaporated at an average rate of 0.3 Å / s under an evaporation voltage of 1.05 V until an artificial interface modification layer with an evaporation thickness of 4 nm was formed, thereby obtaining a sodium metal negative electrode structure.

[0125] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0126] Example 12

[0127] This embodiment provides a method for preparing a sodium metal negative electrode structure, which specifically includes the following steps:

[0128] (1) Vacuum evaporation of sodium sheets was performed in an environment with an initial oxygen content of 0.01 ppm, a humidity of 0.01 ppm, and a temperature of 20 °C: a 0.45 mm sodium sheet was placed on the substrate tray of the evaporation chamber, and the vacuum degree reached 1×10 -3 Pa, set the distance from the substrate stage to the evaporation source to 25 mm, and the substrate stage rotation speed to 15 rpm;

[0129] (2) AlF3 was selected as the evaporation material and placed in a crucible for single-source evaporation. It was evaporated at an average rate of 0.5 Å / s under an evaporation voltage of 0.85 V until an artificial interface modification structure with an evaporation thickness of 8 nm was formed, thereby obtaining a sodium metal negative electrode structure.

[0130] The sodium metal negative electrode structure prepared in this embodiment was made into a battery using the same method as in Example 1.

[0131] Example 13

[0132] The method for preparing the sodium metal negative electrode structure provided in Example 13 differs from that in Example 12 only in that the thickness of the interface modification layer is 1 nm. The rest of the steps are the same as in Example 12 and will not be described again.

[0133] Example 14

[0134] The method for preparing the sodium metal negative electrode structure provided in Example 14 differs from that in Example 12 only in that the thickness of the interface modification layer is 60 nm. The remaining steps are the same as in Example 12 and will not be described again.

[0135] Example 15

[0136] The method for preparing the sodium metal negative electrode structure in this embodiment is exactly the same as that in Example 2.

[0137] The only difference between this embodiment and embodiment 2 is that this embodiment uses a PEO-based solid electrolyte to assemble a battery. The preparation method of the solid electrolyte is as follows: PEO and NaTFSI are dissolved in anhydrous acetonitrile according to a certain stoichiometric ratio (EO:Na + =18:1) and 30 wt% ZnO filler was added. PEO and NaTFSI were vacuum dried at 60°C and 100°C, respectively. The mixture was stirred at room temperature for 5 hours to form a homogeneous solution, which was then slowly poured into a polytetrafluoroethylene mold. The solution was then air-dried for 6 hours to remove the solvent and cut into 19 mm diameter discs for later use.

[0138] Preparation of the positive electrode: weigh NaNi according to the mass ratio of 80:10:10 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, carbon black (SuperP) and polyvinylidene fluoride (PVDF), these three materials are dispersed in N-methylpyrrolidone (NMP), and are made into a uniform conductive slurry by high-speed dispersion stirring for 4.5 hours and coated on aluminum foil. The thickness of the coated active material is 40 μm, and the positive electrode sheet is obtained after vacuum drying at 120 ° C for 12 hours.

[0139] The prepared sodium metal negative electrode structure, solid electrolyte and positive electrode are assembled into a battery.

[0140] Example 16

[0141] Example 16 is substantially the same as Example 15, except that the battery of Example 16 uses a Na4Fe3(PO4)2(P2O7) positive electrode. The rest of the process is the same as Example 15 and will not be described again.

[0142] Example 17

[0143] Example 17 is basically the same as Example 15, except that the battery of Example 17 uses Na3Zr2Si2PO 12 (NaSICON type) solid electrolyte. The solid electrolyte preparation method is as follows: Na2CO3, ZrO2, SiO2, and NH4H2PO4 are weighed in a stoichiometric ratio, with an 8% excess of Na2CO3 and NH4H2PO4. The materials are placed in a ball mill containing zirconium dioxide balls, ethanol is added, and the mixture is ball milled at 800 rpm for 5 hours. The ball-milled material is dried and ground to a fine powder. The fine material is calcined in a high-temperature muffle furnace for 10 hours to fully react and obtain a precursor powder. The sintered precursor powder is ground to a fine powder and formed into 19 mm diameter discs using a tablet press. The embryo is cold isostatically pressed. Finally, the embryo is transferred to a high-temperature furnace and calcined at 1100°C to obtain the target electrolyte. The remaining steps are the same as in Example 15 and are not further described here.

[0144] Example 18

[0145] The method for preparing the sodium metal negative electrode structure in this embodiment is exactly the same as that in Example 1.

[0146] The only difference between this embodiment and embodiment 1 is that this embodiment uses Na3Zr2Si2PO 12 The solid electrolyte (NaSICON type) is prepared as follows: Na2CO3, ZrO2, SiO2, and NH4H2PO4 are weighed in a stoichiometric ratio, with an 8% excess of Na2CO3 and NH4H2PO4. The mixture is placed in a ball mill containing zirconium dioxide balls, ethanol is added, and the mixture is ball milled at 800 rpm for 5 hours. The milled material is then dried and ground to a fine powder. The fine material is calcined in a high-temperature muffle furnace for 10 hours to fully react and obtain a precursor powder. The sintered precursor powder is ground to a fine powder and pressed into 19 mm diameter discs using a tablet press. The embryo is then cold isostatically pressed. Finally, the embryo is transferred to a high-temperature furnace and calcined at 1100°C to obtain the target electrolyte.

[0147] Preparation of the positive electrode: weigh NaNi according to the mass ratio of 80:10:10 1 / 3 Fe 1 / 3 Mn1 / 3 O2 positive electrode material, carbon black (SuperP) and polyvinylidene fluoride (PVDF), these three materials are dispersed in N-methylpyrrolidone (NMP), and are made into a uniform conductive slurry by high-speed dispersion stirring for 4.5 hours and coated on aluminum foil. The thickness of the coated active material is 40 μm, and the positive electrode sheet is obtained after vacuum drying at 120 ° C for 12 hours.

[0148] The prepared sodium metal negative electrode structure, solid electrolyte and positive electrode are assembled into a battery.

[0149] Comparative Example 1

[0150] Comparative Example 1 provides a counter cell: a pure sodium metal sheet is used as the working electrode and counter electrode, and a glass fiber filter paper membrane is used as the separator. The electrolyte used includes 1 mol / L sodium perchlorate (NaClO4) and a solvent consisting of ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio, with 2% fluoroethylene carbonate (FEC) added thereto. The electrodes, separator, and electrolyte are assembled into a sodium-ion battery.

[0151] Comparative Example 1 also provides a full battery, which differs from the full battery of Example 1 only in that Comparative Example 1 uses a simple sodium sheet as the negative electrode.

[0152] Comparative Example 2

[0153] The preparation method of the sodium metal negative electrode structure provided in Comparative Example 2 differs from that in Example 5 only in that the average evaporation rate is 3.6 Å / s. The remaining steps are the same as in Example 5 and are not further described here.

[0154] Comparative Example 3

[0155] The sodium ion solid-state battery provided in Comparative Example 3 differs from the sodium ion solid-state battery of Example 15 only in that a simple sodium metal sheet is used as the negative electrode in Comparative Example 3. The remaining steps are the same as in Example 15 and are not described again here.

[0156] Comparative Example 4

[0157] The sodium ion solid-state battery provided in Comparative Example 4 differs from the sodium ion solid-state battery of Example 17 only in that Comparative Example 4 uses a simple sodium metal sheet as the negative electrode. The remaining steps are the same as in Example 17 and are not described again here.

[0158] Comparative Example 5

[0159] The preparation method of the sodium metal negative electrode structure provided in Comparative Example 5 differs from that in Example 17 only in that the thickness of the interface modification layer is 0.1 nm. The rest of the steps are the same as in Example 17 and will not be described again.

[0160] Comparative Example 6

[0161] The preparation method of the sodium metal negative electrode structure provided in Comparative Example 6 differs from that in Example 17 only in that the thickness of the interface modification layer is 500 nm. The remaining steps are the same as those in Example 17 and are not further described here.

[0162] The performance of the batteries prepared in the above embodiments and comparative examples was tested:

[0163] Figure 3 3 is a comparison chart of the cycle performance of the symmetrical battery assembled in Example 1 and the symmetrical battery assembled in Comparative Example 1. Figure 4 3 is a comparison chart of the cycle performance of the symmetrical battery assembled in Example 2 and the symmetrical battery assembled in Comparative Example 1. Figure 5 3 is a charge-discharge curve diagram of the first three times of the full battery assembled in Example 3 at room temperature and 0.1 C current density. Figure 6 This is a cycling performance diagram of the full battery assembled in Example 6 at room temperature and 3 C current density. Figure 8 This is a rate performance diagram of the full battery assembled in Example 7 at room temperature. Figure 9 This is a cycling performance diagram of the full battery assembled in Example 15 at room temperature and 1 C current density. Figure 10 1 is a graph showing the first three charge and discharge curves of the full battery assembled in Example 16 at room temperature and a current density of 0.1 C.

[0164] Table 1 Performance of the sodium ion battery symmetric cells prepared in Examples 1-14 and Comparative Examples 1-2

[0165]

[0166] Table 2 Relevant performance of symmetrical solid-state sodium ion batteries prepared in Examples 15-18 and Comparative Examples 3-6

[0167]

[0168] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and are not intended to limit the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0169] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0170] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for the elements of the embodiments without departing from the spirit and scope of the present invention. Additionally, many modifications may be made to adapt specific circumstances or materials to the teachings of the present invention without departing from the scope of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for carrying out the present invention, but rather to include all embodiments within the scope of the appended claims. Furthermore, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another.

Claims

1. A sodium metal negative electrode structure, characterized in that: The sodium metal negative electrode structure includes a sodium metal sheet and an artificial interface modification structure formed on the surface of the sodium metal sheet. The artificial interface modification structure includes a vapor deposition structure. The thickness of the vapor deposition structure is 1-60 nm. The vapor deposition structure is formed on the surface of the sodium metal sheet by vacuum deposition technology. The vacuum degree of the vacuum deposition is 5×10 -4 ~1×10 -2 Pa, voltage is 0.5~2 V, evaporation rate is 0.1~3 Å / s; The material of the evaporation structure includes at least one of a sodium alloy, an SEI inorganic film-forming agent or a conductive metal element, wherein the sodium alloy includes sodium and metals and / or non-metals alloyed with sodium; the SEI inorganic film-forming agent can provide an effective inorganic component for the SEI layer.

2. The sodium metal negative electrode structure according to claim 1, characterized in that: The metal includes one or a combination of multiple of Sn, Bi, Al, Zn, In, and Sb.

3. The sodium metal negative electrode structure according to claim 1, characterized in that: The non-metal includes Si.

4. The sodium metal negative electrode structure according to claim 1, wherein: The SEI inorganic film-forming agent includes one or a combination of multiple of Na2O, NaF, Na2S, Si3N4, SiO2, and Al2O3.

5. The sodium metal negative electrode structure according to claim 1, wherein: The conductive metal element is formed by a chemical reaction between a sodium reactant and sodium during a vacuum evaporation process, wherein the sodium reactant includes one or a combination of AgF and AlF3.

6. The sodium metal negative electrode structure according to claim 1, characterized in that: The evaporation structure includes a multi-layer stacked structure, which has at least two adjacent evaporation layers made of different materials. The two evaporation layers are respectively formed of two different types of the sodium alloy, SEI inorganic film-forming agent or conductive metal element.

7. The sodium metal negative electrode structure according to claim 1, characterized in that: The evaporation structure includes a composite layer, and the material of the composite layer includes at least two of a sodium alloy, an SEI inorganic film-forming agent, or a conductive metal element.

8. The sodium metal negative electrode structure according to claim 6, characterized in that: The multi-layer stacked structure includes an alloy layer and an SEI inorganic film-forming agent layer sequentially arranged in a direction away from the sodium metal sheet. The alloy layer is made of the sodium alloy, and the SEI inorganic film-forming agent layer is made of the SEI inorganic film-forming agent.

9. The sodium metal negative electrode structure according to claim 7, characterized in that: The composite layer includes the sodium alloy and the SEI inorganic film-forming agent uniformly mixed.

10. A method for preparing a sodium metal negative electrode structure, characterized in that: The sodium metal negative electrode structure includes a sodium metal sheet and an artificial interface modification structure formed on the sodium metal sheet, wherein the artificial interface modification structure includes an evaporation structure; The preparation method comprises: in an environment with an oxygen content of less than 0.1 ppm, a humidity of less than 0.1 ppm, and a temperature of less than 20°C, using a vacuum evaporation method to form an evaporation structure with a thickness of 1 to 60 nm on the surface of the sodium metal sheet; wherein the vacuum degree of the vacuum evaporation is 5×10 -4 ~1×10 -2 Pa, voltage is 0.5~2 V, evaporation rate is 0.1~3 Å / s; The evaporation material includes at least one of a metal, a non-metal or an inorganic compound; the metal or non-metal can undergo an alloying reaction with sodium to form a sodium alloy; the inorganic compound includes an SEI inorganic film-forming agent and / or a sodium reactant; the SEI inorganic film-forming agent can provide an effective inorganic component for the SEI layer; and the sodium reactant can chemically react with sodium to generate a conductive metal element and an effective inorganic component for the SEI layer.

11. The preparation method according to claim 10, characterized in that: The metal includes one or a combination of multiple of Sn, Bi, Al, Zn, In, and Sb.

12. The preparation method according to claim 10, characterized in that: The non-metal includes Si; and / or the SEI inorganic film-forming agent includes one or a combination of multiple of Na2O, NaF, Na2S, Si3N4, SiO2, and Al2O3.

13. The preparation method according to claim 10, characterized in that: The sodium reactant includes one or a combination of AgF and AlF3.

14. The preparation method according to claim 10, wherein: During the vacuum evaporation, the distance between the sodium metal sheet and the evaporation material is 0.5-80 mm, and the rotation speed of the sodium metal sheet is 0-30 rpm.

15. The preparation method according to claim 10, characterized in that: The vacuum evaporation method includes single-source evaporation, multi-source sequential evaporation, or multi-source simultaneous evaporation. The single-source evaporation includes: selecting one of the evaporation materials for vacuum evaporation to form an evaporation structure on the sodium metal sheet. The multi-source sequential evaporation includes: using at least two types of metals and / or non-metals, SEI inorganic film-forming agents, or sodium reactants for sequential evaporation, so that the evaporation materials form a multi-layer stacked structure on the surface of the sodium metal sheet. The multi-source simultaneous evaporation includes: using at least two types of metals and / or non-metals, SEI inorganic film-forming agents, or sodium reactants for simultaneous evaporation, so that at least two types of evaporation materials are simultaneously vaporized and deposited on the surface of the sodium metal sheet, thereby forming a composite layer.

16. The preparation method according to claim 15, characterized in that: The evaporation material used in the multi-source sequential evaporation and the multi-source simultaneous evaporation includes at least one of the metals and / or non-metals, and also includes at least one of the SEI inorganic film-forming agents.

17. The preparation method according to claim 16, characterized in that The multi-source sequential evaporation includes: vaporizing and depositing at least one of the metals and / or non-metals and reacting with sodium to form a sodium alloy layer; vaporizing and depositing at least one of the SEI inorganic film-forming agents and forming an SEI inorganic film-forming agent layer on the surface of the sodium alloy layer, thereby forming the multi-layer stacked structure.

18. The preparation method according to claim 16, characterized in that The multi-source simultaneous evaporation includes: simultaneously vaporizing and depositing at least one of the metals and / or non-metals and at least one of the SEI inorganic film-forming agents on the surface of the sodium metal sheet, thereby forming a composite layer of a uniform mixture of the sodium alloy and the SEI inorganic film-forming agent.

19. A sodium metal negative electrode structure, characterized in that: It is prepared by the method according to any one of claims 10 to 18.

20. A negative electrode for a sodium ion battery, characterized in that: The negative electrode for a sodium ion battery comprises the sodium metal negative electrode structure according to any one of claims 1 to 9 and 19.

21. A sodium ion battery, characterized in that: The sodium ion battery is a liquid sodium ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode is the negative electrode for the sodium ion battery according to claim 20; Alternatively, the sodium ion battery is a solid-state sodium ion battery, which includes a positive electrode, a negative electrode and a solid electrolyte, wherein the solid electrolyte is an oxide solid electrolyte or a composite solid electrolyte, and the negative electrode is the negative electrode for the sodium ion battery according to claim 20, and the vapor-deposited structure in the negative electrode is arranged in contact with the solid electrolyte.

22. The sodium ion battery according to claim 21, characterized in that: The solid electrolyte is an oxide solid electrolyte, and the material of the contact interface between the evaporation structure and the solid electrolyte is a sodium alloy.

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