Sodium metal composite negative electrode material and preparation method and application thereof

Abstract

This invention discloses a sodium metal composite anode material, its preparation method, and its application. The sodium metal composite anode material comprises the following raw materials: a sodium metal matrix and tin-sulfur compounds and sodium salts composited within the bulk phase of the sodium metal matrix. The sodium metal composite anode material is prepared using a repeated folding-rolling process. During the repeated folding-rolling process, the tin-sulfur compounds react in situ with the sodium metal in the sodium metal matrix to generate a sodium-tin alloy / sodium sulfide interface network. The sodium salts are uniformly embedded within the sodium-tin alloy framework, thereby obtaining the sodium metal composite anode material. The added tin-sulfur compounds and sodium salts have a significant synergistic effect, jointly extending the deposition / exfoliation of sodium metal from the traditional two-dimensional surface to the three-dimensional bulk phase space. When this sodium metal composite anode material is applied to sodium metal batteries, it can effectively suppress dendrite growth and achieve excellent cycle stability and high-rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a sodium metal composite anode material, its preparation method, and its application. Background Technology

[0002] Sodium metal batteries are favored due to the abundance and low cost of sodium resources, as well as the extremely high theoretical specific capacity of sodium metal anodes (approximately 1166 mAh g⁻¹). -1 With its extremely low redox potential (-2.71 V vs. standard hydrogen electrode), it is considered a strong contender for the next generation of high-energy-density energy storage systems.

[0003] However, current sodium metal anode materials are still subject to many limitations in practical applications: (1) Sodium metal is subject to repeated electrochemical deposition (Na... + + e - → Na) and stripping (Na → Na + + e -(1) Dendrites are easily formed during the process. Dendrites may pierce the separator and cause a short circuit inside the battery, which may lead to serious safety hazards. At the same time, continuous side reactions will occur between sodium metal and electrolyte, which will cause the solid electrolyte interphase (SEI) layer to break repeatedly and expose fresh sodium surface. Subsequently, the solvent molecules and sodium salt in the electrolyte will undergo reduction decomposition on the newly exposed sodium surface, repair and form a new SEI layer, thereby accelerating electrolyte consumption and irreversible loss of active sodium, resulting in rapid decay of battery cycle life; (2) Sodium metal itself is soft and viscous, lacking an effective support skeleton. During the deposition / stripping process, sodium metal will undergo violent volume expansion and contraction. This volume effect is prone to cause electrode structure collapse, active material shedding and repeated breakage of SEI layer, further aggravating interface instability and capacity decay; (3) The interface modification strategies reported at present mainly focus on building alloy layer or artificial SEI layer on sodium metal surface. However, these strategies can usually only form two-dimensional interface layer and can only improve surface performance to a certain extent. They cannot fundamentally solve the problem of sodium metal bulk phase. The lack of ionic conductivity and structural support in the part means that traditional metal electrodes only have electronic conductivity. Their deposition / stripping process is restricted to a two-dimensional surface, which is prone to dendrite growth and local volume expansion due to uneven local current density. (4) In the existing research, the method of mechanically rolling metal powder (such as tin powder) onto the sodium metal surface can usually only form a two-dimensional alloy interface layer. The alloy layer thickness is limited, and the ability to alleviate volume expansion and improve interface stability is insufficient. Moreover, such methods often involve only a single alloying reaction and cannot build a three-dimensional conductive network inside the sodium metal bulk phase. It is also difficult to introduce additives with ionic conductivity to synergistically improve the interface and bulk phase performance. (5) In terms of interface SEI layer regulation, although conventional electrolyte additive strategies can improve the composition and structure of the SEI layer to a certain extent, the additives will be continuously consumed during the cycle and it is difficult to provide long-term stable interface protection. In addition, the SEI layer formed by electrolyte additives alone often has poor uniformity and cannot meet the requirements of high surface capacity, long cycle and high rate sodium metal batteries. Summary of the Invention

[0004] One of the objectives of this invention is to provide a sodium metal composite anode material that has excellent sodium affinity and mechanical strength, while effectively suppressing dendrite growth and making it less likely to cause battery short-circuit failure.

[0005] The second objective of this invention is to provide a method for preparing sodium metal composite anode materials that is simple, convenient, and inexpensive, making it suitable for large-scale production.

[0006] The third objective of this invention is to provide an application of a sodium metal composite anode material. When this sodium metal composite anode material is applied to a sodium metal battery, it not only has good compatibility with conventional cathode materials such as sodium vanadium phosphate, but also can be matched with high-voltage cathode systems, exhibiting excellent wide voltage window compatibility.

[0007] To achieve the above objectives, the solution of the present invention is: A sodium metal composite anode material includes the following raw materials: a sodium metal matrix and a tin-sulfur compound and a sodium salt composited within the bulk phase of the sodium metal matrix. The tin-sulfur compound reacts in situ with the sodium metal matrix during the rolling process to generate a sodium-tin alloy / sodium sulfide interface network with a three-dimensional continuous structure. The sodium-tin alloy / sodium sulfide interface network has a sodium-tin alloy framework with a three-dimensional continuous structure, and the sodium sulfide and the sodium salt are uniformly embedded in the sodium-tin alloy framework.

[0008] The sodium metal matrix is ​​sodium foil, and the tin sulfide compound is selected from at least one of tin disulfide (SnS2), tin sulfide (SnS), and tin trisulfide (Sn2S3).

[0009] The sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(trifluoromethanesulfonyl)imide (NaFSI), sodium perchlorate (NaClO4), and sodium trifluoromethanesulfonate (NaOTF).

[0010] The mass ratio of the tin-sulfur compound to the sodium salt is 1:0.5 to 1:1.5. If the proportion of the tin-sulfur compound is too high, it will lead to a relative deficiency of sodium salt and an incomplete ion-conducting network. If the proportion of the sodium salt is too high, it may increase the interfacial impedance due to excessive salt aggregation. The mass ratio of the tin-sulfur compound to the sodium metal matrix is ​​0.001 to 0.15:1. If the proportion of the tin-sulfur compound is too low, it will lead to a discontinuous three-dimensional alloy network, insufficient sodium-affinity nucleation and volume buffering effect. If the proportion of the tin-sulfur compound is too high, it will excessively consume active sodium and increase the brittleness of the electrode.

[0011] The thickness of the sodium metal composite anode material is 100 μm to 1 mm.

[0012] The sodium-tin alloy in the sodium-tin alloy / sodium sulfide interface network is selected from Na. 15 At least one of Sn4, Na9Sn4, NaSn and Na5Sn2.

[0013] A method for preparing a sodium metal composite anode material includes the following steps: Step 1: First, mix the tin-sulfur compound powder and sodium salt powder evenly in a certain proportion to obtain a mixed powder; Step 2: Then, the mixed powder obtained in Step 1 is evenly coated onto the surface of the sodium metal substrate; Step 3: Then, under the protection of inert gas, the sodium metal matrix coated with mixed powder obtained in step 2 is folded along the length direction, so that the mixed powder is sandwiched in the middle of the sodium metal matrix, and then put into a roller press for rolling to obtain the sodium metal matrix after the first rolling. Step 4: Then take out the sodium metal matrix after rolling, fold the sodium metal matrix again in a direction perpendicular to the previous fold, and put it into the rolling press for a second rolling to obtain the sodium metal matrix after the second rolling. The above process of processing the sodium metal matrix is ​​called the folding-rolling process. Step 5: Repeat the above folding-rolling process of the sodium metal matrix multiple times. During the repeated folding-rolling process, the tin sulfide compound reacts in situ with the sodium metal of the sodium metal matrix to generate a sodium-tin alloy / sodium sulfide interface network. That is, a sodium-tin alloy framework with a three-dimensional continuous structure is constructed inside the bulk phase of the sodium metal matrix, and the sodium salt is uniformly embedded in the sodium-tin alloy framework, thereby obtaining the sodium metal composite anode material.

[0014] The synthesis schematic diagram corresponding to the preparation method of this sodium metal composite anode material is shown below. Figure 1 As shown, during repeated folding and rolling processes, the mixed powder is gradually pressed into the bulk phase of the sodium metal matrix under mechanical force, and continuously contacts the fresh sodium surface during the cycle, promoting the sustained and thorough in-situ reaction. Due to the unique layered structure of tin-sulfur compounds, sodium atoms can directly diffuse into its lattice during rolling, undergoing an intercalation reaction, and subsequently undergoing a disorder transformation to form a disordered intermediate with a rock salt phase structure, which then undergoes a conversion reaction and an alloying reaction, ultimately producing a sodium-tin alloy and sodium sulfide.

[0015] In this sodium metal composite anode, through the forced mixing effect of the repeated folding-rolling process described above, the reaction products of tin-sulfur compounds (sodium-tin alloy and Na2S) and unreacted sodium salts are uniformly dispersed within the bulk phase of the sodium metal matrix. The sodium-tin alloy forms a three-dimensional continuous interpenetrating conductive network within the sodium metal bulk phase, providing an electronically conductive framework. Na2S, as a reaction product of tin-sulfur compounds and sodium metal, is uniformly dispersed in nanoparticle form and anchored within this three-dimensional alloy framework. The unreacted sodium salts are uniformly distributed as solid particles in the three-dimensional voids of the sodium-tin alloy framework, and can be activated to conduct ions after electrolyte injection. The sodium-tin alloy, Na2S, and sodium salts together construct an ion-electron dual-conductivity three-dimensional network, where Na2S and sodium salts provide ion transport channels, and the sodium-tin alloy provides the electronically conductive framework and structural support.

[0016] In steps 3 to 5, the roller gap is 0.02 mm to 1 mm, the roller speed is 0.05 m / min to 20 m / min, and the roller temperature is 20℃ to 80℃. If the roller gap is too small, it can cause excessive deformation or even cracking of the sodium metal; if the roller gap is too large, it will be difficult for the mixed powder to be pressed into the bulk phase of the sodium metal. If the roller speed is too fast, it will lead to uneven dispersion; if the roller speed is too slow, it will result in low efficiency. If the roller temperature is too high, it may trigger an excessive reaction; if the roller temperature is too low, the sodium metal will harden, making it unsuitable for processing.

[0017] In step 5, the folding-rolling process is repeated 18 to 50 times. If the number of repetitions is too few, the tin sulfide compound and sodium salt cannot be evenly dispersed into the bulk phase of sodium metal; if the number of repetitions is too many, the process time will be increased and the sodium metal may be overworked.

[0018] An application of a sodium metal composite anode material is to apply the sodium metal composite anode material to a sodium metal battery.

[0019] The sodium metal battery is assembled in the following order: CR2025 positive electrode steel shell, sodium metal composite negative electrode material, glass fiber separator, and sodium metal composite negative electrode material. The electrolyte of the sodium metal battery is a 1 M NaPF6 diethylene glycol dimethyl ether solution.

[0020] By adopting the above technical solution, the sodium metal composite anode material, its preparation method, and its application of the present invention have the following beneficial effects: 1. The sodium metal composite anode material provided by the present invention realizes the in-situ conversion-alloying reaction of tin-sulfur compounds and sodium metal through the rolling process, generating a sodium-tin alloy framework with a three-dimensional continuous structure that runs through the bulk phase of sodium metal. This three-dimensional alloy framework not only enables the uniform distribution and rapid transport of charge carriers inside the electrode, thereby avoiding the growth of sodium dendrites, but also serves as a stable framework structure to alleviate volume changes, maintain the structural integrity of the electrode during charge-discharge cycles, and significantly improve the cycle life of sodium metal batteries. 2. In the sodium metal composite anode material provided by this invention, the sodium salt is uniformly embedded in the sodium-tin alloy framework after being rolled. After the electrolyte is injected, the sodium salt is activated to conduct ions, forming an anion-derived ion-conducting network. At the same time, the sodium salt undergoes a chemical reduction reaction at the interface, forming a dense inorganic SEI layer, which can synergistically construct an ion-electron dual-conducting three-dimensional network with the sodium-tin alloy / sodium sulfide interface network. In particular, when different types of sodium salts are used, inorganic SEI layers rich in NaF, Na3N, Na2O, etc. can be formed, which have excellent interface stability, reduce interface impedance, and improve sodium ion conductivity. 3. The sodium metal composite anode material provided by this invention achieves functional reconstruction of the sodium metal bulk phase without relying on organic support materials such as conductive polymers. Unique Na2S nanoparticles are generated through the reaction path of tin-sulfur compound intercalation → disordering → conversion → alloying. These nanoparticles are uniformly dispersed in the sodium-tin alloy framework and form a mixed inorganic interface layer together with sodium salt derivatives. This structure extends the sodium metal deposition / exfoliation reaction from the traditional two-dimensional surface to the three-dimensional bulk phase region, significantly improving the uniformity of sodium deposition and the rate performance of the battery. 4. Overall, the sodium metal composite anode material provided by this invention exhibits a significant synergistic effect between tin-sulfur compounds and sodium salts, which is impossible to achieve with a single-component system. The three-dimensional sodium-tin alloy framework generated by the in-situ reaction of tin-sulfur compounds provides electronic conductivity pathways and structural support, while the sodium salt provides an ionic conductivity network and forms a stable inorganic-rich SEI layer after activation by the electrolyte. The two complement each other, jointly extending the deposition / stripping of sodium metal from the traditional two-dimensional surface to the three-dimensional bulk phase space. It is this dual synergistic mechanism of "electronic framework + ionic network" that enables this invention to maintain excellent cycle stability under harsh conditions of high-rate cycling, unlike the strategies in the prior art that rely solely on single alloying or single interface modification. 5. The sodium metal composite anode material provided by the present invention is prepared by physical rolling method. The process is simple, convenient and low cost. The uniform dispersion of tin sulfide compounds and sodium salt in sodium metal bulk phase can be achieved by repeated folding-rolling process. No organic solvents or high temperature treatment are required. It is green and environmentally friendly. The raw materials are all low-cost industrial products and are suitable for large-scale production. 6. The sodium metal composite anode material provided by this invention has excellent sodium affinity and mechanical strength. It not only has good compatibility with conventional cathode materials such as sodium vanadium phosphate, but also can be matched with high-voltage cathode systems, showing excellent wide voltage window compatibility. At the same time, it effectively suppresses dendrite growth and is less likely to cause battery short circuit failure. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the synthesis of the sodium metal composite anode material of the present invention; Figure 2 The physical characterization diagrams of the sodium metal composite anode material prepared in Example 1 are shown; (a) is a hardness test result diagram, and (b) is an optical photograph of the sodium metal composite anode material and ordinary sodium foil. Figure 3 The images show the SEM and EDS characterization of the cross-section of the sodium metal composite anode material prepared in Example 1. Figure 4 The image shows the XRD pattern of the sodium metal composite anode material prepared in Example 1. Figure 5The image shows a SEM image of the sodium metal composite anode material in the Na||Na symmetric cell composed of Example 1 after deposition / stripping cycles, where (a) is after sodium metal stripping and (b) is after sodium metal deposition. Figure 6 A comparison graph of voltage-time cycling performance of sodium metal batteries in Application Example 1 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 4 (corresponding to pure sodium metal material); Figure 7 EIS plots of sodium metal batteries of Application Example 1 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 4 (corresponding to pure sodium metal material) after different number of cycles; Figure 8 The graph shows the relationship between the number of cycles and the discharge specific capacity and coulombic efficiency of CR2016 coin cells using Example 5 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Example 6 (corresponding to pure sodium metal material). Figure 9 The rate performance test graphs of CR2016 coin cells are shown for Application Example 5 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 6 (corresponding to pure sodium metal material). Figure 10 The charge-discharge curves of CR2016 coin cells at different rates are shown for Application Example 5 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 6 (corresponding to pure sodium metal material). Figure 11 A comparison graph of the voltage-time cycling performance of sodium metal batteries for Application Example 1 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1), Application Example 2 (corresponding to the Na-Sn-S prepared in Example 1), and Application Example 3 (corresponding to the Na-sodium salt prepared in Example 2). Figure 12 The graphs show the cycle performance comparison of CR2016 coin cells using Application Example 5 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1), Application Example 7 (corresponding to the Na-Sn-S prepared in Example 1), and Application Example 8 (corresponding to the Na-sodium salt prepared in Example 2); where (a) is the relationship between the number of cycles and the discharge specific capacity at 1 C rate, and (b) is the relationship between the number of cycles and the discharge specific capacity at 10 C rate. Detailed Implementation

[0022] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0023] I. Preparation of Anode Materials Example 1 A method for preparing a sodium metal composite anode material includes the following steps: Step 1: First, mix SnS2 powder and NaPF6 powder at a mass ratio of 1:1 to obtain a mixed powder. Step 2: Then, the mixed powder obtained in Step 1 is evenly coated onto the surface of the sodium foil; Step 3: Then, in an argon glove box (O2 and H2O concentration <1 ppm), fold the sodium foil coated with mixed powder obtained in step 2 along its length so that the mixed powder is sandwiched in the middle of the sodium foil, and then put it into a roller press for rolling to obtain the sodium foil after the first rolling. Step 4: Then take out the rolled sodium foil, fold it again in a direction perpendicular to the previous fold, and put it into the rolling press for a second rolling process to obtain the second rolled sodium foil. The above sodium foil processing process is called the folding-rolling process. Step 5: Repeat the folding-rolling process of the sodium foil 28 times. During the repeated folding-rolling process, SnS2 reacts in situ with the sodium metal of the sodium foil to generate Na. 15 The Sn4 sodium-tin alloy / sodium sulfide interface network is a sodium-tin alloy framework with a three-dimensional continuous structure built inside the bulk phase of sodium foil, and sodium salts NaPF6 and Na2S are uniformly embedded in the sodium-tin alloy framework, thereby obtaining the sodium metal composite anode material, denoted as Na-Sn-S-sodium salt. In steps 3 to 5, the roller gap is 0.1 mm, the roller speed is 0.5 m / min, and the roller temperature is 25℃.

[0024] The sodium metal composite anode material has a three-dimensional continuous structure of sodium-tin alloy / sodium sulfide-sodium salt composite three-dimensional network, including a three-dimensional continuous sodium-tin alloy framework, and sodium salt and sodium sulfide are uniformly embedded in the sodium-tin alloy framework.

[0025] Comparative Example 1 A method for preparing a sodium metal composite anode material includes the following steps: Step 1: First, evenly spread SnS2 powder on the surface of sodium foil; Step 2: Then, in an argon glove box (O2 and H2O concentration <1 ppm), fold the sodium foil coated with SnS2 powder obtained in Step 1 along its length so that the SnS2 powder is sandwiched in the middle of the sodium foil, and then put it into a roller press for rolling to obtain the sodium foil after the first rolling. Step 3: Then take out the rolled sodium foil, fold it again in a direction perpendicular to the previous fold, and put it into the rolling press for a second rolling process to obtain the second rolled sodium foil. The above sodium foil processing process is called the folding-rolling process. Step 4: Repeat the folding-rolling process of the sodium foil 28 times. During the repeated folding-rolling process, SnS2 reacts in situ with the sodium metal of the sodium foil to generate Na. 15 The Sn4 sodium-tin alloy / sodium sulfide composite electrode is obtained by constructing a sodium-tin alloy framework with a three-dimensional continuous structure inside the bulk phase of sodium foil, thus obtaining the sodium metal composite negative electrode material, denoted as Na-Sn-S. In steps 2 to 4, the roll gap is 0.1 mm, the roll speed is 0.5 m / min, and the roll temperature is 25℃.

[0026] Comparative Example 2 A method for preparing a sodium metal composite anode material includes the following steps: Step 1: First, evenly spread NaPF6 powder on the surface of sodium foil; Step 2: Then, in an argon glove box (O2 and H2O concentration <1 ppm), fold the sodium foil coated with NaPF6 powder obtained in Step 2 along its length so that the NaPF6 powder is sandwiched in the middle of the sodium foil, and then put it into a roller press for rolling to obtain the sodium foil after the first rolling. Step 3: Then take out the rolled sodium foil, fold it again in a direction perpendicular to the previous fold, and put it into the rolling press for a second rolling process to obtain the second rolled sodium foil. The above sodium foil processing process is called the folding-rolling process. Step 4: Repeat the above folding-rolling process of sodium foil 28 times to obtain the sodium metal anode material, denoted as Na-sodium salt; In steps 2 to 4, the roll gap is 0.1 mm, the roll speed is 0.5 m / min, and the roll temperature is 25℃.

[0027] II. Application of Anode Materials Application Example 1 Sodium metal batteries (denoted as Na||Na symmetric batteries) were assembled in the following order: CR2025 positive electrode steel shell, sodium metal composite negative electrode material prepared in Example 1, glass fiber separator (model GF / C), and sodium metal composite negative electrode material prepared in Example 1. The sodium metal batteries were sealed and stored in an argon glove box at room temperature for more than 2 hours. The electrolyte of the sodium metal batteries was a 1 M NaPF6 diethylene glycol dimethyl ether solution.

[0028] Application Example 2 Sodium metal batteries (denoted as Na||Na symmetric batteries) were assembled in the following order: CR2025 positive electrode steel shell, sodium metal composite negative electrode material prepared in Comparative Example 1, glass fiber separator (model GF / C), and sodium metal composite negative electrode material prepared in Comparative Example 1. The sodium metal batteries were sealed and stored in an argon glove box at room temperature for more than 2 hours. The electrolyte of the sodium metal batteries was a 1 M diethylene glycol dimethyl ether solution of NaPF6.

[0029] Application Example 3 Sodium metal batteries (denoted as Na||Na symmetric batteries) were assembled in the following order: CR2025 positive electrode steel shell, sodium metal negative electrode material prepared in Comparative Example 2, glass fiber separator (model GF / C), and sodium metal negative electrode material prepared in Comparative Example 2. The sodium metal batteries were sealed and stored in an argon glove box at room temperature for more than 2 hours. The electrolyte of the sodium metal batteries was a 1 M diethylene glycol dimethyl ether solution of NaPF6.

[0030] Application Example 4 Sodium metal batteries (denoted as Na||Na symmetric batteries) are assembled in the following order: CR2025 positive electrode steel shell, pure sodium metal, glass fiber separator (model GF / C), and pure sodium metal. After sealing the sodium metal batteries, they are stored in an argon glove box and left at room temperature for more than 2 hours. The electrolyte for the sodium metal batteries is a 1 M diethylene glycol dimethyl ether solution of NaPF6.

[0031] Application Example 5 The CR2016 coin cell was assembled in the following order: CR2016 positive electrode steel shell, positive electrode sheet, glass fiber separator (model GF / C), and sodium metal composite negative electrode material prepared in Example 1. 90 μL of electrolyte was injected, and the cells were sealed and left at room temperature for more than 2 hours. The positive electrode sheet was a Prussian blue electrode sheet, and the electrolyte was a 1 M NaPF6 methyl ethyl carbonate / fluoroethylene carbonate (volume ratio of 7:3) mixed solution.

[0032] Application Example 6 The CR2016 coin cell was assembled in the following order: positive electrode steel shell, positive electrode sheet, glass fiber separator (model GF / C), and pure sodium metal. 90 μL of electrolyte was injected, and the cells were sealed and left at room temperature for more than 2 hours. The positive electrode sheet was a Prussian blue electrode sheet, and the electrolyte was a 1 M NaPF6 methyl ethyl carbonate / fluoroethylene carbonate (volume ratio of 7:3) mixed solution.

[0033] Application Example 7 The CR2016 coin cell was assembled in the following order: CR2016 positive electrode steel shell, positive electrode sheet, glass fiber separator (model GF / C), and sodium metal composite negative electrode material prepared in Comparative Example 1. 90 μL of electrolyte was injected, and the cells were sealed and left at room temperature for more than 2 hours. The positive electrode sheet was a Prussian blue electrode sheet, and the electrolyte was a 1 M NaPF6 methyl ethyl carbonate / fluoroethylene carbonate (volume ratio of 7:3) mixed solution.

[0034] Application Example 8 The CR2016 coin cell was assembled in the following order: CR2016 positive electrode steel shell, positive electrode sheet, glass fiber separator (model GF / C), and sodium metal composite negative electrode material prepared in Comparative Example 2. 90 μL of electrolyte was injected, and the cells were sealed and left at room temperature for more than 2 hours. The positive electrode sheet was a Prussian blue electrode sheet, and the electrolyte was a 1 M NaPF6 methyl ethyl carbonate / fluoroethylene carbonate (volume ratio of 7:3) mixed solution.

[0035] III. Characterization of Anode Materials 1. Physical properties The sodium metal composite anode material prepared in Example 1 was subjected to hardness testing, optical imaging, and thickness measurement. The results are as follows: Figure 2 As shown. Figure 2 As shown in (a), the Shore hardness of pure sodium metal is about 27.5 HA, while the hardness of the sodium metal composite anode material is significantly increased to about 69 HA, indicating that the sodium metal composite anode material has higher mechanical strength. Figure 2 The optical photograph in (b) shows that the surface of the sodium metal composite anode material is smooth and silvery-gray.

[0036] 2. SEM and EDS characterization The cross-section of the sodium metal composite anode material prepared in Example 1 was observed by scanning electron microscopy (SEM) and characterized by energy dispersive spectroscopy (EDS). The results are as follows: Figure 3 As shown. Figure 3 The SEM images show that the sodium-tin alloy is densely and uniformly distributed in the sodium metal bulk phase. The EDS surface distribution map shows that Sn, S, P, and F elements are uniformly distributed throughout the bulk phase region, confirming that the repeated folding-rolling process realizes the reaction product of tin-sulfur compounds (Na). 15 Sn4 and Na2S) are uniformly dispersed with sodium salts in the sodium metal bulk phase.

[0037] 3. XRD characterization The sodium metal composite anode material prepared in Example 1 was characterized by X-ray diffraction (XRD), and the results are as follows: Figure 4 As shown. In addition to the characteristic diffraction peaks of sodium metal (PDF#22-0948), the XRD pattern of the composite anode also shows peaks similar to those of Na. 15The diffraction peaks corresponding to Sn4 (PDF#31-1327) and NaPF6 (PDF#07-0292) confirm the in-situ formation of sodium-tin alloy and sodium sulfide.

[0038] 4. SEM characterization The sodium metal battery constructed in Application Example 1 was tested at 1 mA cm⁻¹. -2 20mAh cm -2 Repeated electrochemical deposition (Na) under these conditions + + e - → Na) and stripping (Na → Na + + e - After the process, the battery was disassembled, and the sodium metal composite anode material after the reaction was observed by SEM. The results are as follows: Figure 5 As shown in (a), a sodium-tin alloy framework with a clearly visible three-dimensional continuous structure is subsequently deposited, resulting in a dense and smooth surface with no dendrite growth observed (e.g.). Figure 5 (b) indicates that the sodium metal deposition / stripping reaction is reversible.

[0039] IV. Electrochemical Performance Testing 1. Constant current charge-discharge tests were performed on the sodium metal batteries corresponding to Example 1 (Na-Sn-S-sodium salt prepared in Example 1) and Application Example 4 (pure sodium metal material) using the battery testing system, with a current density of 5 mA cm⁻¹. -2 The surface capacity is 20mAh cm -2 The obtained voltage-time cycling performance is as follows: Figure 6 As shown: The sodium metal battery in Application Example 1 has a stable cycle time of over 2500 hours, and the overpotential remains stable during the cycle; while the pure sodium metal symmetric battery shows a sharp change in polarization and a short circuit after about 200 hours.

[0040] 2. Electrochemical impedance spectroscopy (EIS) tests were performed on sodium metal batteries corresponding to Example 1 (the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 4 (the pure sodium metal material) after different number of cycles. The results are as follows: Figure 7 As shown. The charge transfer impedance (corresponding to the Nyquist semicircle diameter) of the sodium metal battery in Application Example 1 remained at a low level throughout the cycling process and did not increase significantly with the number of cycles, indicating low interfacial impedance and a stable SEI layer. In contrast, the charge transfer impedance of the sodium metal battery corresponding to pure sodium was significantly higher than that of the sodium metal battery in Application Example 1, and continued to increase with the number of cycles, indicating severe side reactions at the pure sodium interface, continuous thickening of the SEI layer, and obstruction of ion transport.

[0041] 3. Charge-discharge tests were conducted on CR2016 coin cells using the battery testing system corresponding to Case 5 (Na-Sn-S-sodium salt prepared in Example 1) and Application Example 6 (pure sodium metal material). The test conditions were: the loading of Prussian blue active material in the positive electrode was 3 mAh cm⁻¹. -2 The voltage range is 2.0 V to 4.2 V, and the capacity is 1 C (1 C = 143 mAh g). -1 The measured cycle performance is as follows: Figure 8 As shown. The initial discharge specific capacity of the battery is 140 mAh g. -1 After 200 cycles, the capacity retention rate is 85%, and the coulombic efficiency is stable at over 99.6%; the capacity retention rate of pure sodium metal full cell is only 20.4% after 200 cycles under the same conditions.

[0042] 4. Rate performance tests were conducted on the CR2016 coin cells using the battery testing system corresponding to Case 5 (the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 6 (the pure sodium metal material). Charge and discharge were performed at rates of 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, respectively. Figure 9 As shown. The discharge specific capacities of Application Example 5 are 153, 149, 142, 139, and 127 mAh g, respectively. -1 When the rate of change returns to 1 C, the capacity recovers to 140mAh g. -1 The pure sodium metal full cell in Application Example 6 exhibits a lower discharge capacity at high rates. Figure 10 The charge-discharge curves of CR2016 coin cells in Application Example 5 (corresponding to the Na-Sn-S-sodium salt prepared in Example 1) and Application Example 6 (corresponding to pure sodium metal material) at different rates are shown. It is shown that the full cell of Application Example 5 maintains a significant voltage plateau at different rates and the increase in polarization is small.

[0043] 5. Using the battery testing system, constant current charge-discharge tests were performed on the sodium metal batteries corresponding to Example 1 (Na-Sn-S-sodium salt prepared in Example 1), Example 2 (Na-Sn-S prepared in Example 1), and Example 3 (Na-sodium salt prepared in Example 2), with a current density of 5 mA cm⁻¹. -2 The surface capacity is 5mAh cm -2 ,like Figure 11As shown, the sodium metal battery in Application Example 2 (sodium metal composite anode material with only SnS2 added) exhibited a high overpotential in the early stages of cycling, and the polarization gradually increased after approximately 200 hours of cycling, while the interface stability gradually decreased. The battery short-circuited after approximately 340 hours of cycling. Compared to Application Example 1, its cycle life was significantly shortened, indicating that while the three-dimensional alloy framework formed solely by tin-sulfur compounds has some effect, it lacks the ion-conducting network and stable SEI layer provided by sodium salts. During long-term cycling, interfacial side reactions gradually accumulate, ultimately leading to performance degradation.

[0044] In Application Example 3 (sodium metal anode containing only NaPF6), the sodium metal battery experienced a short circuit after only about 300 hours of stable cycling. Compared to Application Example 1, its cycle life was even shorter, indicating that the SEI layer formed solely by sodium salt could not provide sufficient mechanical support. Lacking the support of a three-dimensional alloy framework, sodium dendrites quickly pierced the SEI layer, leading to battery failure.

[0045] 6. Long-cycle charge-discharge tests were conducted on CR2016 coin cells using the battery testing system corresponding to Case 5 (Na-Sn-S-sodium salt prepared in Example 1), Application Example 7 (Na-Sn-S prepared in Example 1), and Application Example 8 (Na-sodium salt prepared in Example 2). The test conditions were: the loading of Prussian blue active material in the positive electrode was 3 mAh cm⁻¹. -2 The voltage range is 2.0 V to 4.2 V, and the 1 C (1 C = 143 mAh g) is used. -1 The measured cycle performance is as follows: Figure 12 As shown in (a), at a 1 C rate, the initial discharge specific capacity of the full cell using Example 5 (Na-Sn-S-sodium salt) is 140 mAh g. -1 After 200 cycles, the capacity retention rate was 85%, and the coulombic efficiency remained stable at over 99.6%. However, the full cell of Application Example 7 (sodium metal composite anode material with only SnS2 added) showed significant capacity decay after 200 cycles, with a capacity retention rate of only 62%. The full cell of Application Example 8 (sodium metal anode material with only NaPF6 added) had the worst cycle stability, with a capacity retention rate of 48% after 200 cycles.

[0046] 7. Further utilize the battery testing system to conduct long-cycle charge-discharge tests on the CR2016 coin cells corresponding to Case 5, Application Example 7, and Application Example 8 at a high rate of 10 C. The test conditions are: the loading of Prussian blue active material in the positive electrode is 4 mg cm⁻¹. -2 The voltage range is 2.0 V to 4.2 V, and the measured cycle performance is as follows: Figure 12 As shown in (b), at an ultra-high current density of 10 C, the full cell using Example 5 (Na-Sn-S-sodium salt) still maintains 111 mAh g⁻¹.-1 The initial discharge specific capacity was [value missing], and the capacity retention rate was 94% after 3000 cycles. In contrast, the full cell using Example 7 (sodium metal composite anode material with only SnS2 added) retained 102 mAh g⁻¹. -1 The initial discharge specific capacity was [not specified], and after 3000 cycles, the capacity retention was only 53%. The full cell of Application Example 8 (containing only a sodium metal anode with NaPF6) retained 93 mAh g⁻¹. -1 The initial discharge specific capacity is insufficient to function properly after less than 2000 cycles at a high rate of 10 C, and the capacity rapidly decays to near zero.

[0047] The above comparison of battery performance over long cycles clearly reveals the synergistic nature of SnS2 and sodium salt: When only SnS2 is added, although the sodium metal anode forms a three-dimensional sodium-tin alloy framework (an auxiliary electronic conductivity network), it lacks an activatable ionic conductivity network (generated by NaPF6 after electrolyte wetting and dissolution). At high rates, Na… + The inability to respond and replenish in a timely manner led to Na + Rapid transport at the electrode / electrolyte interface and within the bulk phase is difficult, and the sharp increase in polarization leads to zero capacity. While the addition of NaPF6 alone allows the sodium metal anode to form a certain ionic conductive network, it lacks a supporting framework, resulting in rapid electrode structure collapse and short-circuit failure at high rates. Only when SnS2 and sodium salt are present simultaneously does the in-situ reaction of tin-sulfur compounds generate a three-dimensional sodium-tin alloy framework, providing a stable electronic conductive network and supporting framework. The sodium salt, after activation by the electrolyte, provides a bulk ionic conductive network. Together, they construct a sodium metal electrode matrix with high ionic and electronic conductivity, allowing the deposition / stripping reaction of sodium metal to proceed uniformly and rapidly in the three-dimensional bulk space, rather than being limited to the two-dimensional surface. Thanks to this, full cells assembled using the Na-Sn-S-sodium salt system can still cycle stably at an ultra-high rate of 10 C, achieving a high-rate, long-cycle stability that is unattainable by full cells assembled using either a single SnS2 system or a single sodium salt system.

[0048] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A sodium metal composite anode material, characterized in that: The material includes the following raw materials: a sodium metal matrix and tin-sulfur compounds and sodium salts composited within the bulk phase of the sodium metal matrix. The tin-sulfur compounds react in situ with the sodium metal matrix during the rolling process to generate a sodium-tin alloy / sodium sulfide interface network with a three-dimensional continuous structure. The sodium-tin alloy / sodium sulfide interface network has a sodium-tin alloy framework with a three-dimensional continuous structure, and the sodium sulfide and the sodium salt are uniformly embedded in the sodium-tin alloy framework.

2. The sodium metal composite anode material according to claim 1, characterized in that: The sodium metal matrix is ​​sodium foil, the tin-sulfur compound is selected from at least one of SnS2, SnS and Sn2S3, and the sodium salt is selected from at least one of NaPF6, NaTFSI, NaFSI, NaClO4 and NaOTF.

3. The sodium metal composite anode material according to claim 1, characterized in that: The mass ratio of the tin-sulfur compound to the sodium salt is 1:0.5 to 1:1.

5.

4. The sodium metal composite anode material according to claim 1, characterized in that: The thickness of the sodium metal composite anode material is 100 μm to 1 mm.

5. The sodium metal composite anode material according to claim 1, characterized in that: The sodium-tin alloy in the sodium-tin alloy / sodium sulfide interface network is selected from Na. 15 At least one of Sn4, Na9Sn4, NaSn and Na5Sn2.

6. A method for preparing a sodium metal composite anode material as described in claim 1, characterized in that: Includes the following steps: Step 1: First, mix the tin-sulfur compound powder and sodium salt powder evenly in a certain proportion to obtain a mixed powder; Step 2: Then, the mixed powder obtained in Step 1 is evenly coated onto the surface of the sodium metal substrate; Step 3: Then, under the protection of inert gas, the sodium metal matrix coated with mixed powder obtained in step 2 is folded along the length direction, so that the mixed powder is sandwiched in the middle of the sodium metal matrix, and then put into a roller press for rolling to obtain the sodium metal matrix after the first rolling. Step 4: Then take out the sodium metal matrix after rolling, fold the sodium metal matrix again in a direction perpendicular to the previous fold, and put it into the rolling press for a second rolling to obtain the sodium metal matrix after the second rolling. The above process of processing the sodium metal matrix is ​​called the folding-rolling process. Step 5: Repeat the above folding-rolling process of the sodium metal matrix multiple times. During the repeated folding-rolling process, the tin sulfide compound reacts in situ with the sodium metal of the sodium metal matrix to generate a sodium-tin alloy / sodium sulfide interface network. That is, a sodium-tin alloy framework with a three-dimensional continuous structure is constructed inside the bulk phase of the sodium metal matrix, and the sodium salt is uniformly embedded in the sodium-tin alloy framework, thereby obtaining the sodium metal composite anode material.

7. The method for preparing a sodium metal composite anode material according to claim 6, characterized in that: In steps 3 to 5, the gap between the rollers is 0.02 mm to 1 mm, the speed of the rollers is 0.05 m / min to 20 m / min, and the temperature of the rollers is 20℃ to 80℃.

8. The method for preparing a sodium metal composite anode material according to claim 6, characterized in that: In step 5, the folding-rolling process is repeated 18 to 50 times.

9. An application of a sodium metal composite anode material, characterized in that: This refers to applying the sodium metal composite negative electrode material as described in claim 1 to a sodium metal battery.

10. The application of the sodium metal composite anode material according to claim 9, characterized in that: The sodium metal battery is assembled in the following order: CR2025 positive electrode steel shell, sodium metal composite negative electrode material, glass fiber separator, and sodium metal composite negative electrode material. The electrolyte of the sodium metal battery is a 1 M NaPF6 diethylene glycol dimethyl ether solution.

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