Sodium metal negative electrode material for constructing hybrid solid electrolyte interface layer based on gas-liquid mixed plasma one-step method as well as preparation method and application of sodium metal negative electrode material

Abstract

The invention relates to the technical field of preparation of sodium metal electrode materials, and discloses a sodium metal negative electrode material for constructing a hybrid solid electrolyte interface layer based on a gas-liquid mixed plasma one-step method as well as a preparation method and application of the sodium metal negative electrode material. According to the method, sodium metal is used as a matrix, a sulfur hexafluoride gas source and a fluoroethylene carbonate liquid source are jointly used as plasma sources, a hybrid solid electrolyte interface layer is constructed in one step through plasma reaction, and the composite sodium metal electrode is obtained. The preparation method of the negative electrode material has the characteristics of simplicity, rapidness, high efficiency and easiness in control, and is favorable for promoting the development of an artificial solid electrolyte interface layer in a sodium metal battery. The hybrid solid electrolyte interface layer serves as a physical barrier and can directly isolate side reaction between metal sodium and electrolyte, and meanwhile, the excellent mechanical property of the hybrid solid electrolyte interface layer effectively inhibits growth of sodium dendrites. Therefore, the composite negative electrode shows good cycling stability, rate capability and high coulombic efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium metal electrode materials, in particular to the technical field of solid electrolyte interface layers (SEIs) in sodium metal batteries, and specifically relates to a sodium metal negative electrode material for constructing a hybrid solid electrolyte interface layer by a one-step gas-liquid hybrid plasma method, a preparation method thereof, and an application thereof. Background Art

[0002] With the proposal of the goals of "carbon peak" and "carbon neutrality", clean energy has developed rapidly. Sodium-ion batteries have gradually become an important energy storage device due to their high safety, relatively high energy density, long cycle life and other advantages. However, hard carbon, the currently widely used negative electrode material for sodium-ion batteries, has a low theoretical capacity and is difficult to meet the growing energy storage needs. Therefore, researchers have begun to actively explore materials to replace hard carbon.

[0003] Sodium metal, due to its extremely high theoretical capacity (1166 mAh / g) and extremely low redox potential (−2.71 V), has become an ideal choice for the negative electrode of sodium-ion batteries. However, the main challenges faced by sodium metal batteries include: volume expansion of metallic sodium during charge and discharge, growth of dendrites, and instability of the SEI. The SEI layer plays a crucial role in battery cycling. It can reduce the direct contact between sodium metal and the electrolyte and prevent side reactions from occurring. However, the naturally formed SEI layer is usually composed of an inorganic layer (such as Na 2 O, NaOH and Na 2 CO 3 ), and an organic layer (such as ROCO 2 Na, RONa and RCOO 2 Na). Although it can optimize the interface between sodium metal and the electrolyte, its structure is uneven and prone to cracking, leading to degradation and failure of battery performance. At the same time, the inorganic SEI layer has advantages in improving ionic conductivity and interface stability, but its rigidity is large and it is difficult to cope with the volume expansion of sodium metal and is prone to cracking and failure during long-term cycling. The organic component has good flexibility and can adapt to volume changes, but its stability is not as good as that of the inorganic SEI layer. Therefore, constructing a composite SEI layer with organic and inorganic components has become the focus of research.

[0004] Currently, researchers have tried to use different methods to prepare hybrid SEI layers, such as forming a layered structure through atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, or preparing a bilayer SEI by the soaking method. However, these methods are usually complex in process, time-consuming, and difficult to precisely control the thickness and uniformity of the interface layer, which limits their application in commercialization. At the same time, sodium flakes have the characteristics of high reaction activity and are prone to react with oxygen, water, etc., further limiting the interface modification of sodium-ion batteries.

[0005] Based on this, the present invention proposes a method for rapidly constructing a hybrid solid electrolyte interface layer by gas-liquid hybrid plasma-enhanced chemical vapor deposition. Under mild reaction conditions, this method can rapidly construct an SEI layer with excellent mechanical properties and ionic conductivity, regulate its chemical composition, thereby effectively inhibiting the growth of sodium dendrites, and improving the cycling stability of sodium metal electrodes, providing an effective solution for the next-generation high-energy-density sodium metal batteries. Summary of the Invention

[0006] The present invention aims to solve various problems existing in the SEI layer in the sodium metal battery system, and proposes a preparation method of a composite sodium metal electrode with a hybrid SEI layer constructed by a gas-liquid hybrid plasma one-step method. By adjusting process parameters such as reaction time and radio frequency power, the generated SEI layer can achieve the effects of alleviating the volume expansion during sodium metal deposition and inhibiting the growth of sodium dendrites. A suitable SEI layer can accelerate the transport rate of sodium ions, thereby improving the charge-discharge performance of the battery; at the same time, it can effectively block the direct contact between sodium metal and the electrolyte, avoiding excessive decomposition of the electrolyte and electrode corrosion.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows: The present invention provides a preparation method of a sodium metal negative electrode material with a hybrid SEI layer constructed by a gas-liquid hybrid plasma one-step method. This method uses a sodium sheet as the substrate, and uses sulfur hexafluoride gas source and fluoroethylene carbonate liquid source as plasma sources together, and constructs a hybrid SEI layer through a vacuum plasma reaction in one step to finally obtain a composite sodium metal electrode. The present invention effectively realizes the construction of SEI on the sodium sheet by adopting vacuum plasma technology.

[0008] Preferably, the preparation method specifically includes the following steps: (1) Under a protective atmosphere, seal fluoroethylene carbonate (FEC) in a liquid source device, and at the same time seal the sodium sheet in a plasma device under a protective atmosphere; (2) Connect the plasma device and the liquid source device, and connect them to a plasma generator. Start the vacuum system to evacuate, and introduce sulfur hexafluoride (SF 6 through the liquid source device into the plasma device, and maintain the system at a certain vacuum degree; (3) Adjust the radio frequency power to excite the plasma. After ignition, sulfur hexafluoride (SF 6 reacts with the fluoroethylene carbonate (FEC) plasma on the surface of the sodium sheet; after reacting for a certain time, turn off the radio frequency power supply to form a composite sodium metal negative electrode (PFC@Na) with a hybrid SEI layer.

[0009] The following is a more preferred technical solution of the present invention: Preferably, in step (1), the fluoroethylene carbonate is battery-grade fluoroethylene carbonate (FEC), and more preferably the amount is 1-10 mL.

[0010] Preferably, in step (1), the gas source is sulfur hexafluoride.

[0011] Preferably, the sodium flakes may be conventional commercial sodium flakes, and the size of the sodium flakes is preferably 15 mm in diameter.

[0012] Preferably, in step (1), the plasma device consists of a quartz tube, a flange, and a copper ring.

[0013] Preferably, in step (2), the plasma device is evacuated to a vacuum degree of 10-20 Pa. More preferably, in step (2), after the gas source and the liquid source are introduced into the plasma device, the system maintains a vacuum degree of 15-20 Pa, more preferably 20 Pa.

[0014] Preferably, in step (2), the flow rate of sulfur hexafluoride gas is 5-30 scc / min, more preferably 20 scc / min.

[0015] Preferably, in step (2), the sulfur hexafluoride gas source is introduced into the liquid source, and the gas source and the liquid source are simultaneously introduced into the plasma device by bubbling.

[0016] Preferably, in step (3), the radio frequency power is 50-100 W, more preferably, the radio frequency power is 80-100 W, and more preferably, the radio frequency power is 90 W.

[0017] Preferably, in step (3), the plasma reaction time is 30-90 s, and more preferably, the plasma reaction time is 60 s. Too short a time and too low a power will result in SF 6 FEC and sodium metal will not have enough time to react. On the contrary, sodium metal will be damaged because it cannot withstand the violent reaction.

[0018] Preferably, the main components of the artificial hybrid solid electrolyte layer are NaF, Na 2 O,Na 2 CO 3 and organic fluorocarbon networks.

[0019] Preferably, the protective atmosphere includes at least one of argon and helium.

[0020] The present invention also provides a composite sodium metal electrode prepared by any of the above preparation methods and using a gas-liquid mixed plasma to construct a hybrid SEI layer in one step.

[0021] The present invention also provides an application of a composite sodium metal electrode prepared by any of the above preparation methods in the field of sodium ion batteries, which constructs a hybrid SEI layer by a one-step method of gas-liquid mixed plasma.

[0022] The present invention rapidly constructs a hybrid SEI layer on the surface of sodium metal by a one-step method of gas-liquid mixed plasma. So far, there has been no relevant report on the application of gas-liquid mixed plasma on the sodium metal negative electrode. By evacuating the system to a certain vacuum condition and adopting vacuum plasma technology, the present invention can effectively solve the problems of reaction with water, oxygen, etc. caused by the high reaction activity of sodium flakes, and thus can effectively react with gas sources and liquid sources to generate the target SEI. The SEI layer constructed by the present invention forms Na-F bonds through plasma reaction, can firmly adhere to the surface of the Na foil, establish a dense barrier, and effectively prevent the penetration of air and moisture. In addition, the NaF inorganic SEI layer can not only guide the uniform deposition of sodium ions, but its high Young's modulus can also prevent the SEI layer from cracking or falling off during the battery cycle, reduce the side reaction between metallic sodium and the electrolyte, and the outer layer of the organic fluorocarbon network can enhance the flexibility and mechanical stability of the SEI layer.

[0023] The effective combination of the inner sodium fluoride inorganic layer and the outer organic fluorocarbon network layer can effectively relieve the volume change during the sodium metal deposition process, ensuring the uniformity of Na + flow at the interface, thereby significantly inhibiting the formation of sodium dendrites. The sodium metal modified by this one-step method of gas-liquid mixed plasma exhibits more excellent electrochemical performance and higher safety, laying a solid foundation for the commercial application of sodium metal batteries.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a composite sodium metal electrode for constructing a hybrid SEI layer by a one-step method of gas-liquid plasma, its preparation method and application. The plasma enhanced chemical vapor deposition method for constructing the sodium metal negative electrode with a hybrid SEI layer is completed by a one-time reaction of gas and liquid source plasma with the surface of metallic sodium. During this process, the organic functional groups of the organic SEI layer spontaneously form an organic fluorocarbon network, thereby enhancing the flexibility and mechanical stability of the SEI layer; the inorganic SEI layer is mainly composed of NaF, Na 2 O, Na 2 CO 3 and can uniformly distribute Na + flow at the interface.

[0025] The preparation method of the PFC@Na anode material of the present invention has the characteristics of simplicity, rapidity, high efficiency, and easy control, which helps to promote the development of artificial SEI layers in sodium metal batteries. In applications, the hybrid SEI layer acts as a physical barrier, which can directly isolate the side reactions between metallic sodium and the electrolyte. At the same time, its excellent mechanical properties effectively inhibit the growth of sodium dendrites. Therefore, the composite anode prepared by the present invention exhibits good cycle stability, rate performance, and high Coulomb efficiency, solving the problems of unstable solid-liquid interface, large volume change, and sodium dendrite growth in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. Figure 1 is a schematic diagram of the one-step modification of sodium flakes by gas-liquid hybrid plasma in Example 5; FIG. Figure 2 is the XPS result in Example 5, Figure 2 in which (a)-(d) are the high-resolution XPS spectra of C 1s, F 1s, Na 1s, and O 1s in Example 3 respectively; FIG. Figure 3 is the cycle performance diagram of the button-type symmetric batteries assembled in Example 5 and Comparative Example 1 (3 mA / cm 2 current density, 3 mAh / cm 2 capacity); FIG. Figure 4 is the rate performance diagram of the button-type symmetric batteries assembled in Example 5 and Comparative Example 1 (0.5, 1, 2, 3, 4, 0.5 mA / cm 2 current density, 1 mAh / cm 2 capacity); FIG. Figure 5 is the Coulomb efficiency diagram of the button-type half batteries assembled in Example 5 and Comparative Example 1 (1 mA / cm 2 current density, 1 mAh / cm 2 capacity, 50 cycles); FIG. Figure 6 is the scanning electron microscope images of bare sodium and Example 5 before cycling and after 50 cycles of cycling, Figure 6 in which (a) and (b) are the scanning electron microscope images of bare sodium and Example 5 before cycling respectively, Figure 6 in which (c) and (d) are the scanning electron microscope images of bare sodium and Example 5 after cycling respectively. DETAILED DESCRIPTION OF THE INVENTION

[0027] To better clarify and understand the purpose, technical solution and advantages of the present invention, the following will further clearly, completely and detailedly describe the technical solution and implementation manner of the present invention through specific embodiments and in conjunction with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given. However, they are only a part of the embodiments of the present invention, not all of the embodiments. The specific implementation manners described are only for explaining and interpreting the present invention and do not limit the present invention. Based on the embodiments of the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0028] In the embodiments of the present invention, the experimental methods and conditions used are conventional methods and conventional conditions unless otherwise specified. The materials, reagents, or instrument devices used in the embodiments are conventional substances or devices known to those skilled in the art and can be obtained from commercial sources or prepared by conventional methods unless otherwise specified. The reaction conditions reflected in the content of the present invention can all achieve the reactions and obtain the products with the expected effects. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0029] Example 1

[0030] In an argon-filled glove box, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 Bringing in FEC vapor has little effect on the flow rate. The gas flow rate is generally selected as 20 sccm / min; reference can be made to Figure 1 As shown, SF was introduced 6 After bringing in FEC vapor, the system maintained a vacuum degree of 20 Pa. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted. The radio frequency power was adjusted to 100 W, and the vacuum degree inside the device was controlled at 20 Pa. After ignition, the plasma reacted with Na. After 30 s of reaction, a hybrid solid electrolyte interface layer (SEI) was formed. The radio frequency power supply was turned off to obtain the PFC@Na negative electrode.

[0031] Example 2

[0032] In an argon-filled glove box, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted. The radio frequency power was adjusted to 100 W, and the vacuum degree in the device was controlled at 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain the PFC@Na negative electrode.

[0033] Example 3

[0034] In an argon-filled glove box, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted. The radio frequency power was adjusted to 100 W, and the vacuum degree in the device was controlled at 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 90 s, the radio frequency power supply was turned off to obtain the PFC@Na negative electrode.

[0035] Example 4

[0036] In an argon-filled glove box, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted. The radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled at 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 30 s, the radio frequency power supply was turned off to obtain the PFC@Na negative electrode.

[0037] Example 5

[0038] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into a liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in a plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled to be 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PFC@Na negative electrode.

[0039] Example 6

[0040] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into a liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in a plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled to be 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 90 s, the radio frequency power supply was turned off to obtain a PFC@Na negative electrode.

[0041] Example 7

[0042] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into a liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in a plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 80 W, and the vacuum degree in the device was controlled to be 20 Pa. After glow discharge, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 30 s, the radio frequency power supply was turned off to obtain a PFC@Na negative electrode.

[0043] Example 8

[0044] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into a liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in a plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 80 W, and the vacuum degree in the device was controlled to be 20 Pa. After ignition, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PFC@Na negative electrode.

[0045] Example 9

[0046] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into a liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in a plasma equipment in the argon-filled glove box. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced with FEC vapor. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 80 W, and the vacuum degree in the device was controlled to be 20 Pa. After ignition, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 90 s, the radio frequency power supply was turned off to obtain a PFC@Na negative electrode.

[0047] Comparative Example 1

[0048] A commercial sodium sheet with a diameter of 15 mm was selected as the sodium metal negative electrode, and a sodium-sodium symmetric battery was assembled in a glove box with an argon atmosphere for electrochemical testing. The battery preparation adopted the battery preparation steps in the performance test part.

[0049] Comparative Example 2

[0050] In a glove box filled with argon gas, a 15-mm commercial sodium sheet was sealed in a plasma equipment. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Then, the plasma device was evacuated to 20 Pa and SF 6 was introduced. The radio frequency power supply switch was turned on, and the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled to be 20 Pa. After ignition, the plasma would react with Na to form an inorganic solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PF@Na negative electrode.

[0051] Comparative Example 3

[0052] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the glove box filled with argon gas. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and FEC vapor was introduced. The radio frequency power supply switch was turned on, the radio frequency power was adjusted, the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled at 20 Pa. After ignition, the plasma would react with Na to form an organic hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PC@Na negative electrode.

[0053] Comparative Example 4

[0054] In a glove box filled with argon gas, ethylene glycol dimethyl ether (DME) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the glove box filled with argon gas. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and SF 6 was introduced with DME vapor. The radio frequency power supply switch was turned on, the radio frequency power was adjusted, the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled at 20 Pa. After ignition, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PFE@Na negative electrode.

[0055] Comparative Example 5

[0056] In a glove box filled with argon gas, fluoroethylene carbonate (FEC) was loaded into the liquid source device. At the same time, a 15-mm commercial sodium sheet was sealed in the plasma equipment in the glove box filled with argon gas. Subsequently, the plasma device was transferred outside the glove box. Copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with wires. Subsequently, the plasma device was evacuated to 20 Pa and N 2 was introduced with FEC vapor. The radio frequency power supply switch was turned on, the radio frequency power was adjusted, the radio frequency power was adjusted to 90 W, and the vacuum degree in the device was controlled at 20 Pa. After ignition, the plasma would react with Na to form a hybrid solid electrolyte interface layer (SEI). After reacting for 60 s, the radio frequency power supply was turned off to obtain a PNC@Na negative electrode.

[0057] Performance Test

[0058] After the battery was stationary for 24 h, an electrochemical workstation was used to perform electrochemical tests on the batteries of Examples 1-9 and Comparative Examples 1-5. Battery preparation: The electrolyte was 1 mol / L NaPF 6 / DME (1:1 volume ratio, DME: dimethoxyethane), and the separator was Celgard 2500 type. The battery was assembled in the order of the positive electrode shell, sodium metal negative electrode material, electrolyte, separator, sodium metal negative electrode material, and negative electrode shell, and was tightly sealed with a fully automatic encapsulation machine. The electrochemical tests were all carried out at 30 °C, mainly including constant current charge and discharge tests and Coulomb efficiency tests. The long cycle performance of the battery was tested under the conditions of a current density of 3 mA / cm 2 and a capacity of 3 mAh / cm 2 . The rate performance of the battery was tested at current densities of 0.5, 1, 2, 3, 4, 0.5 mA / cm 2 and a fixed capacity of 1 mAh / cm 2 . The negative electrode materials of Examples 1-9 and Comparative Examples 1-5 were selected and paired with a copper positive electrode to form a sodium-copper battery. After cycling 100 times under the conditions of a current density of 1 mA / cm 2 and a capacity of 1 mAh / cm 2 , the Coulomb efficiency was tested.

[0059] Table 1 Summary of battery performance of Examples 1-9 and Comparative Examples 1-5

[0060] In the present invention, an inorganic-organic hybrid solid electrolyte layer was rapidly constructed on the surface of sodium metal by a one-step plasma gas-liquid mixing plasma method.

[0061] The inorganic sodium fluoride layer of the SEI layer can improve the thermodynamic stability of the sodium metal negative electrode and inhibit the growth of sodium dendrites. The stability of the SEI layer on the sodium negative electrode is related to the electrochemical performance of the sodium negative electrode. A rich inorganic SEI can make the electrochemical performance of the sodium negative electrode better, resulting in a smaller volume change of the SEI. The surface of NaF is sodium-philic, and Na electrodeposition is guided through the Na-NaF interaction; NaF generates a weak solvation environment by reducing the interaction between Na + and the solvent; NaF promotes the transport of Na + at the interface between the electrolyte and Na and promotes the reversible electrochemical reaction in the full battery.

[0062] Through Figure 2 , it can be seen from the high-resolution XPS spectra analysis of C 1s, F 1s, Na 1s, and O 1s of Example 5 that the organic fluorocarbon network layer of the SEI layer forms a covalent bond (C-F xIt adheres firmly to the surface of sodium metal and is connected to the SEI layer through chemical bonding and physical entanglement, achieving good connection between two different materials, namely sodium metal and the SEI layer. In addition to chemical bonding, the physical entanglement effect of the SEI layer also contributes to good adhesion. In short, FEC molecules bridge the two materials through chemical bonding and physical entanglement, enhancing the adhesion between the SEI layer and the sodium metal substrate. The organic SEI layer is flexible and elastic, enabling it to withstand the stress applied during the sodium plating / stripping process, thus avoiding a series of problems caused by the rupture of the SEI layer due to sodium dendrites.

[0063] Through Figure 6 , Figure 6 In (a) of [], it can be seen that the original sodium sheet has a more irregular planar structure, while Figure 6 In (b) of [], the plasma-modified sodium sheet is denser and smoother. Figure 6 In (c) of [] and Figure 6 In (d) of [], they are the SEM images of bare sodium and Example 5 after 50 cycles respectively. From the SEM images of bare sodium and Example 5 before and after cycling, it can be seen that the sodium dendrites formed in Example 5 after cycling are smoother and significantly fewer than those of bare sodium after cycling, indicating that PFC@Na can better resist the formation of sodium dendrites. Through Figure 3 From the cyclic performance graph of the coin-type symmetric battery of Example 5 and Comparative Example 1 in [], it can be seen that due to the construction of the hybrid SEI layer by the one-step gas-liquid mixed plasma method, the surface mechanical properties are more excellent, significantly inhibiting the growth of sodium dendrites, thus achieving a lower overpotential during long cycling and Figure 4 From the rate performance graph of the coin-type symmetric battery of Example 5 and Comparative Example 1 in [], it can be seen that Example 5 also shows a lower overpotential under high-rate conditions. Through Figure 5 From the Coulombic efficiency graph of the coin-type half-cells assembled in Example 5 and Comparative Example 1 in [], it can be seen that Example 5 with the hybrid SEI layer constructed by the one-step gas-liquid mixed plasma method also shows more excellent Coulombic efficiency.

[0064] From the above table analysis, it can be seen that when the radio frequency power is outside 90 W, such as 100 W in Examples 1-3 and 80 W in Examples 7-9, although SEI@Na can be formed, its electrochemical performance, such as cycle stability, overpotential, or Coulombic efficiency, is slightly inferior to that of Examples 4-6. At the same time, by comparing Examples 1-9, it can be seen that when the reaction time is outside 60 s, such as 30 s in Examples 1, 4, 7 and 90 s in Examples 3, 6, 9, although SEI@Na can also be formed, its electrochemical performance, such as cycle stability, overpotential, or Coulombic efficiency, is slightly inferior to that of Examples 2, 5, 8. This shows that maintaining the radio frequency power at 90 W and the ignition reaction time at 60 s are the optimized conditions, indicating that SEI@Na formed within this range has good cycle stability and can inhibit the growth of sodium dendrites. The experimental data of Comparative Examples 1-5 show that PFC@Na formed within the same time range has better electrochemical performance, thus demonstrating the superiority of the one-step method of gas-liquid hybrid plasma to construct a hybrid SEI layer in the present invention.

[0065] The present invention rapidly constructs a hybrid SEI layer in situ on the surface of sodium metal by the one-step method of gas-liquid hybrid plasma. The effective combination of the inorganic inner layer and the organic outer layer can alleviate the volume change during the sodium metal deposition process and improve the Na + conductivity at the uniform interface and inhibit the formation of sodium dendrites. Therefore, the sodium sheet modified by plasma shows more excellent electrochemical performance and safety, providing the possibility for the commercial application of sodium metal batteries. Electrochemical tests show that the sodium metal negative electrode material modified by the one-step method of gas-liquid hybrid plasma of the present invention has good cycle stability.

[0066] The SEI layer formed by the one-step method of gas-liquid hybrid plasma of the present invention has good mechanical strength and electrochemical stability and can inhibit the growth of sodium dendrites. It has broad application prospects in fields such as small mobile electronic devices, electric vehicles, solar power generation, and aerospace.

[0067] The above-described embodiments are only preferred solutions of the present invention and do not impose any form of limitation on the present invention. There are other variations and modifications without exceeding the technical solutions described in the claims.

Claims

1. A method for preparing a sodium metal negative electrode material based on a one-step method of constructing a hybrid solid electrolyte interface layer using a gas-liquid mixed plasma, characterized in that: The method uses a sodium sheet as a matrix, utilizes a sulfur hexafluoride gas source and a fluoroethylene carbonate liquid source as plasma sources, and constructs a hybrid solid electrolyte interface layer in one step through a plasma reaction to obtain a composite sodium metal electrode.

2. According to claim 1, a method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma, characterized in that: The fluoroethylene carbonate is fluoroethylene carbonate of battery-grade concentration.

3. According to claim 1, a method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma, characterized in that: The reaction radio frequency power is 50-100 W, the vacuum degree is 15-20 Pa, and the reaction time is 30-90 seconds.

4. According to claim 3, a method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma, characterized in that: The RF power is 80-100 W, the vacuum degree is 20 Pa, and the reaction time is 30-60 seconds.

5. According to claim 4, a method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma, characterized in that: The RF power was 90 W, the vacuum degree was 20 Pa, and the reaction time was 60 s.

6. A method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma according to any one of claims 1 to 5, characterized in that: The steps include: (1) sealing the liquid source into a liquid source device under a protective atmosphere, and sealing the sodium sheet in a plasma device; (2) connecting the plasma device and the liquid source device to the plasma generator, then evacuating the plasma device, introducing the gas source and bringing the liquid source into the plasma device; (3) Adjusting the RF power and reacting for a certain period of time after ignition to form a composite sodium metal electrode with a hybrid solid electrolyte interface layer.

7. The method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma according to claim 6, characterized in that: In step (2), the gas flow rate is 5-30 scc / min.

8. The method for preparing a sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on a gas-liquid mixed plasma according to claim 6, characterized in that: In step (2), the vacuum degree of the plasma device is 15-20 Pa.

9. A sodium metal negative electrode material prepared by the preparation method according to any one of claims 1 to 8, wherein a hybrid solid electrolyte interface layer is constructed by a one-step method based on gas-liquid mixed plasma.

10. Use of the sodium metal negative electrode material with a hybrid solid electrolyte interface layer constructed by a one-step method based on gas-liquid mixed plasma according to claim 9 in the field of batteries.

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