Secondary battery and application

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a secondary battery and application. The secondary battery comprises a negative pole piece, wherein the negative pole piece comprises a carbon supporting substrate, a sodium alloy material and a coating; sodium alloy materials are arranged on the surface of the carbon supporting base body and in the pores of the carbon supporting base body, and the coating is arranged on the surface of the carbon supporting base body and comprises metal fluoride and carbon nanomaterials. The secondary battery has good conductivity and mechanical stability, the cycle life of a system can be effectively prolonged, sodium dendrites can be reduced in the charging process, and the secondary battery has better safety. According to the secondary battery, the carbon supporting matrix with a plurality of pores has good conductivity and mechanical stability, and the cycle life of a system can be effectively prolonged; and the sodium alloy material is distributed on the surface and pores of the carbon support matrix, so that the formation of sodium dendrites is reduced, and the safety of the secondary battery is improved.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and specifically relates to a secondary battery and its application. Background Art

[0002] As a promising energy storage method, sodium-ion batteries have gradually come into people's view. However, there is still a large room for improvement in the performance optimization of sodium-ion batteries. Compared with lithium ions, sodium ions have a larger ionic radius, and the diffusion rate of sodium ions in electrode materials is lower, which affects the rate performance and energy density of the battery. During the charge and discharge process of sodium-ion batteries, the electrode materials undergo volume changes, which easily damage the structure and affect the cycle stability and lifespan of the battery; dendrites are easily formed during the charging process, penetrating the separator and affecting battery safety. How to improve the conductivity and mechanical stability of sodium-ion batteries is of great significance for promoting the progress of sodium-ion battery technology. Summary of the Invention

[0003] The main purpose of this application is to provide a secondary battery and its application to solve the problems of poor conductivity and mechanical stability of existing sodium-ion batteries, as well as the easy generation of dendrites during the charging process.

[0004] To this end, this application provides the following technical solutions.

[0005] This application provides a secondary battery, including a negative electrode sheet, and the negative electrode sheet includes:

[0006] A carbon support matrix with a number of pores;

[0007] A sodium alloy material is provided on the surface of the carbon support matrix and in the pores of the carbon support matrix;

[0008] A coating is provided on the surface of the carbon support matrix, and the coating contains metal fluoride and carbon nanomaterials.

[0009] In one embodiment, the sodium alloy material distributed on the surface of the carbon support matrix forms a sodium alloy layer, the sodium alloy layer is between the carbon support matrix and the coating, and the thickness of the sodium alloy layer is 10 nm to 50 nm.

[0010] In one embodiment, the ratio of the thickness of the sodium alloy layer to the thickness of the coating is (1 to 3):1.

[0011] In one embodiment, the thickness of the coating is 10 nm to 50 nm.

[0012] In one embodiment, the sodium content in the sodium alloy material is 20 wt% to 90 wt%.

[0013] In one embodiment, the sodium alloy material includes at least one of sodium tin alloy, sodium lead alloy, sodium potassium alloy, sodium aluminum alloy, sodium lithium alloy, sodium copper alloy, sodium zinc alloy, and sodium bismuth alloy.

[0014] In one embodiment, the metal fluoride includes CoF 2 , NiF 2 and FeF 2 and at least one of them.

[0015] In one embodiment, the content of the metal fluoride in the coating is 5 wt% - 15 wt%.

[0016] In one embodiment, the porosity of the carbon support matrix is 10% - 65%.

[0017] The second aspect of the present application provides an electrical device including the above secondary battery.

[0018] The technical solution of the present application has the following advantages:

[0019] The secondary battery provided by the present application has good electrical conductivity and mechanical stability, can effectively improve the cycle life of the system, can reduce sodium dendrites during the charging process, and has better safety. The carbon support matrix with several pores in the secondary battery of the present application has good electrical conductivity and mechanical stability, and can effectively improve the cycle life of the system; the sodium alloy material is distributed on the surface and pores of the carbon support matrix, which helps to reduce the formation of sodium dendrites and improve the safety of the secondary battery. Specific Embodiments

[0020] The following embodiments are provided to better understand the present application further. It is not limited to the best embodiment, and does not limit the content and protection scope of the present application. Any product that is the same as or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior art features falls within the protection scope of the present application.

[0021] As analyzed in the background art, the existing sodium ion batteries have problems such as poor electrical conductivity and mechanical stability, and are prone to dendrite formation during the charging process. To solve these problems, the present application provides a secondary battery and its application.

[0022] The present application provides a secondary battery, including a negative electrode sheet, and the negative electrode sheet includes:

[0023] a carbon support matrix with several pores; the sodium alloy material is disposed on the surface of the carbon support matrix and in the pores of the carbon support matrix;

[0024] a coating disposed on the surface of the carbon support matrix, and the coating contains a metal fluoride and a carbon nanomaterial.

[0025] During the charging process, sodium ions in the positive electrode material are continuously deposited on the surface of the sodium alloy material. Since the sodium alloy material itself has a low surface energy, it can promote the uniform diffusion of sodium ions and their deposition on the surface of the sodium alloy material, relieve sodium agglomeration, thereby reducing the formation of sodium dendrites and enhancing the safety of the battery. Compared with the conventional current collector in the prior art, such as copper foil, when sodium ions are deposited on the copper foil current collector, due to the uneven copper nucleation sites, the deposited sodium ions are prone to agglomerate to form sodium dendrites, leading to problems such as the penetration of the separator. The carbon-supported matrix with a number of pores can achieve high flexibility and mechanical properties. Using it as the carrier of the negative electrode sheet can improve conductivity and mechanical stability and increase the cycle life of the battery. The coating contains metal fluoride and carbon nanomaterials. The interface formed by the fluoride and the sodium alloy surface has a high Young's modulus, high sodium ion conductivity, low surface energy and strong sodium affinity, which helps to evenly distribute sodium ions, inhibit the formation of sodium dendrites, and reduce the side reaction between the sodium deposited on the sodium alloy surface and the electrolyte. The carbon nanomaterials can increase conductivity, promote the uniform deposition of sodium ions, and reduce dendrites. The combined action of the carbon nanomaterials and the metal fluoride can enhance the effect of uniform sodium ion deposition, and thus reduce dendrites.

[0026] The carbon-supported matrix, sodium alloy material and coating can endow the negative electrode sheet with high conductivity and low surface energy. Sodium ions from the positive electrode can be uniformly deposited on the negative electrode, slowing down the aggregation of sodium ions, inhibiting the formation of sodium dendrites, and improving the electrochemical performance of the battery. The negative electrode sheet of this application has good expandability and adaptability and can be adjusted and optimized according to different application requirements, thereby improving the battery performance.

[0027] In one embodiment, the sodium alloy material distributed on the surface of the carbon-supported matrix forms a sodium alloy layer, and the sodium alloy layer is located between the carbon-supported matrix and the coating. The thickness of the sodium alloy layer is 10 nm to 50 nm; for example, the thickness of the sodium alloy layer is one of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 12 nm to 35 nm, 15 nm to 25 nm, 35 nm to 45 nm. This can make the electron transport path appropriate and enable the sodium ions to be deposited more smoothly, enhancing the rate performance and cycle performance of the battery. In this embodiment, the sodium alloy layer is continuously distributed on the surface of the carbon-supported matrix, thus further increasing the transport rate of sodium ions on the surface of the carbon-supported matrix and enhancing the rate performance of the battery.

[0028] In one embodiment, the ratio of the thickness of the sodium alloy layer to that of the coating is (1 to 3):1. Additionally, the ratio of the thickness of the sodium alloy layer to that of the coating is one of or any range value of two of 1:1, 2:1, and 3:1. Controlling the ratio of the thickness of the sodium alloy layer and the coating in the present application to (1 to 3):1 can enable ions to have a suitable path, with both high electron conductivity and fast ion transport rate, improving the battery rate performance and cycle life.

[0029] In one embodiment, the thickness of the coating is 10 nm to 50 nm. For example, the thickness of the coating is one of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 15 nm to 30 nm, 18 nm to 45 nm, and 25 nm to 45 nm. This is beneficial for reducing the migration path of sodium ions, while also taking into account the electron conductivity of the coating, which is beneficial for the battery rate performance.

[0030] In one embodiment, the sodium content in the sodium alloy material is 20 wt% to 90 wt%, which can make the material have both ion conductivity and electron conductivity. For example, it can be one of or any range value of two of 20 wt%, 30 wt%, 50 wt%, 80 wt%, and 90 wt%. This can further improve the sodium ion transport rate and reduce the formation of sodium dendrites.

[0031] In one embodiment, the sodium alloy material includes at least one of sodium tin alloy, sodium lead alloy, sodium potassium alloy, sodium aluminum alloy, sodium lithium alloy, and sodium copper alloy. The above alloy materials have excellent ion conductivity and electron conductivity.

[0032] There are differences in the ionic radii, reaction potentials, and electronegativities of sodium and potassium. During co - deposition, they can influence each other, reducing the nucleation over - potential of sodium deposition, enabling sodium to start depositing at a lower potential, and improving the charge - discharge efficiency of the battery. Using sodium - potassium alloy as the sodium alloy material, the formed SEI layer contains both sodium and potassium transport channels. This special SEI layer structure has good mechanical stability and ionic conductivity, can adapt to the volume change of the alloy negative electrode during charge - discharge, reduce the rupture and reconstruction of the SEI layer, and thus improve the cycle life of the battery. Sodium - zinc alloy can reduce the surface energy and diffusion barrier, providing favorable conditions for the migration of sodium ions, promoting the uniform deposition of sodium ions on the alloy surface, and being beneficial to improving the cycle performance of the battery. When the sodium alloy material includes sodium - tin alloy, the sodium - tin alloy reduces the surface energy, decreases the diffusion resistance of sodium ions on the alloy surface, increases the migration rate of sodium ions, enables sodium ions to be uniformly deposited at a lower over - potential, and enhances the electrochemical performance of the sodium metal negative electrode. When the sodium alloy material is sodium - bismuth alloy, the change in its surface energy helps the diffusion of sodium ions at the interface, enabling sodium ions to be more evenly distributed on the alloy surface, and then achieving uniform deposition and improving the charge - discharge performance of the battery.

[0033] In one embodiment, the metal fluoride includes CoF 2 , NiF 2 and FeF 2 or at least one of them. The above - mentioned metal fluorides can further enhance the uniform deposition of sodium ions. In one embodiment, the content of the metal fluoride in the coating is 5wt% - 15wt%. The content of the metal fluoride in the coating is one of 5wt%, 8wt%, 13wt%, 15wt%, 5wt% - 12wt%, 11wt% - 15wt%, 3wt% - 9wt%. When the metal fluoride in the coating is within the above range, it can reduce the corrosion of the sodium alloy material by the electrolyte and avoid hindering the transport of sodium ions, which is beneficial to improving the cycle and rate performance of the battery.

[0034] In one embodiment, the surface of the carbon nanomaterial includes at least one functional group among hydroxyl, carboxyl, sulfonic acid group, and amino group. The carbon nanomaterial includes carbon - based materials, such as carbon nanotubes, graphene, etc.; the carbon nanomaterial is preferably carbon nanotubes.

[0035] The oxygen atom in the hydroxyl group has a relatively high electronegativity and can form a certain electrostatic interaction with sodium ions, attracting the sodium ions to approach. The carboxyl group can dissociate hydrogen ions in the solution to form negatively charged carboxylate ions, which attract sodium ions through electrostatic attraction. At the same time, the oxygen atom in the carboxyl group forms a certain coordination interaction with sodium ions. The polarity of the sulfur-oxygen bond in the sulfonic acid group is very strong, and the sulfonic acid group is easily dissociated to form negatively charged sulfonate groups, which have a strong electrostatic attraction to sodium ions. The nitrogen atom in the amino group has lone pair electrons and can form a coordination bond with sodium ions, enhancing the affinity for sodium ions. The surface of the carbon nanomaterial includes at least one of the functional groups such as hydroxyl, carboxyl, sulfonic acid group, and amino group, which helps to further promote the uniform diffusion of sodium ions and reduce dendrites.

[0036] In one embodiment, the porosity of the carbon support matrix is 10% - 65%. This can ensure sufficient mechanical strength of the carbon support matrix while reducing the weight of the material, and at the same time helps the full infiltration of the electrolyte.

[0037] In one embodiment, the crystallinity of the carbon support matrix is 50% - 90%. This can enhance the electron conduction performance and stability under the action of the electric field of the carbon support matrix, and at the same time has good corrosion resistance.

[0038] In one embodiment, the thickness of the carbon support matrix is 0.1 mm - 0.8 mm. This can maintain the support strength and anti-breakage ability of the matrix structure, reduce polarization, decrease the internal resistance of the battery, and at the same time provide enough space to accommodate the electrolyte.

[0039] In one embodiment, the tensile strength of the carbon support matrix is 3000 Mpa - 5000 Mpa. This can enhance the anti-deformation ability of the electrode sheet.

[0040] In one embodiment, the elastic modulus of the carbon support matrix is 200 Gpa - 250 Gpa. This can maintain the structural stability of the matrix. In addition, the elastic modulus of the material is related to its internal atomic structure and chemical bonds. A suitable elastic modulus range means that the bonding state between atoms is conducive to the movement of electrons.

[0041] In one embodiment, the carbon support matrix includes at least one of carbon paper, carbon cloth, and carbon foam. The above materials have excellent electrical conductivity and porosity, which are beneficial to the immersion of the electrolyte and the improvement of electronic conductivity, thereby improving the comprehensive performance of the battery. Preferably, carbon cloth is used as the carbon support matrix. Among them, the preparation process of the carbon cloth may include: dissolving an organic carbon source in an organic solvent to prepare a spinning solution; using a spinning technique to make the spinning solution into primary fibers; performing pre-oxidation treatment on the primary fibers; performing carbonization treatment on the pre-oxidized primary fibers under specific conditions to obtain carbon fibers; using an oxidant to perform surface oxidation treatment on the carbon fibers; coating a sizing agent on the surface of the treated carbon fibers; and weaving the carbon fibers coated with the sizing agent into a cloth to obtain carbon cloth. In the above preparation process, the organic carbon source can be one of polyacrylonitrile, polyvinyl alcohol, and pitch. Pre-oxidation is to stabilize the fiber structure and prevent it from breaking during subsequent processing. The temperature of the carbonization treatment is 1000°C to 1300°C, and the heating rate is 3°C / min to 7°C / min. The oxidant includes one of nitric acid, sulfuric acid, and polyphosphoric acid. The sizing agent includes an epoxy-based water-soluble sizing agent, and the epoxy-based water-soluble sizing agent includes one of polyamide epoxy resin, phenolic epoxy resin, and acrylic epoxy resin. Through the above preparation method, the prepared carbon cloth has a rich porosity, and at the same time has excellent flexibility and mechanical stability.

[0042] In another embodiment, the present application provides an electrical device including the above secondary battery.

[0043] Example 1

[0044] This example provides a secondary battery, including:

[0045] Preparation of the negative electrode sheet:

[0046] 1) Carbon cloth preparation: (Raw material preparation) High-purity (≥99%) polyacrylonitrile (PAN) powder with an average molecular weight of 150,000 is selected as the raw material and dissolved in dimethyl sulfoxide (DMSO) solvent to prepare a spinning solution with a mass fraction of 15%. Stir continuously at 60°C for 6 hours to ensure complete dissolution of PAN and uniform stability of the spinning solution, so as to obtain a high-quality spinning solution. (Spinning process) The wet spinning technique is adopted. The spinning solution is extruded through a spinneret with a pore diameter of 0.2 mm and enters a coagulation bath (formed by mixing water and dimethyl sulfoxide in a volume ratio of 7:3) to solidify into filaments. The spinning speed is controlled at 12 m / min, and at the same time, 1.5 times of air draft is applied in the spinning duct to make the fibers initially oriented during the solidification and stretching processes, obtaining as-spun fibers. (Pre-oxidation treatment) The as-spun fibers are pre-oxidized in an air-circulation oven. The temperature is raised from room temperature to 220°C at a heating rate of 2°C / min and held at 220°C for 90 minutes. During this process, the air flow rate is controlled at 10 L / min to ensure uniform heating of the fibers, causing the PAN molecules to undergo cyclization reactions to form a heat-resistant ladder structure. At the same time, the fiber color gradually changes from white to yellow, providing a suitable precursor structure for subsequent carbonization and initially affecting the crystallinity and pore structure of the fibers. (Carbonization process) The pre-oxidized fibers are placed in a high-temperature tubular furnace and carbonized under a nitrogen atmosphere (nitrogen purity ≥99.999%, flow rate of 200 mL / min). The temperature is raised from room temperature to 1250°C at a heating rate of 5°C / min and held at 1250°C for 70 minutes. During this process, non-carbon elements in the fibers gradually escape, and carbon atoms undergo rearrangement and crystallization. (Surface treatment) The carbonized fibers are surface-oxidized with a 5% nitric acid solution for 30 minutes at a temperature controlled at 60°C. (Sizing treatment) Epoxy-based water-soluble sizing agent is selected and prepared into a solution with a mass fraction of 8%. The fibers are sized at 40°C, and the sizing rate is controlled at 2%. The sized fibers are dried to remove excess moisture and solvents, making the sizing agent uniformly adhere to the fiber surface. (Weaving into cloth) The carbon fibers treated as above are woven in a plain weave pattern. The spacing between warp and weft yarns is set at 0.1 mm, and the interweaving frequency is 10 times / cm. By precisely controlling the weaving parameters, the carbon fibers are woven into carbon cloth with a thickness of 0.2 mm.

[0047] 2) Preparation of sodium-potassium alloy: High-purity metallic sodium (purity ≥ 99.5%) and metallic potassium (purity ≥ 99.0%) are selected as raw materials and stored separately in sealed containers filled with inert gas (argon) to prevent reaction with air and moisture. Accurately weigh 500 g of sodium and potassium. Put metallic sodium and metallic potassium successively into a clean, dry stainless-steel reactor that has been pre-evacuated and filled with argon for protection inside. First, put in metallic sodium. After sealing the reactor, slowly heat it up to 100 °C and maintain this temperature for 30 minutes to fully melt the metallic sodium. Then, under the protection of argon, slowly add metallic potassium to the molten metallic sodium, and at the same time start the stirring device and stir at a speed of 200 revolutions per minute to ensure that the two metals are fully and evenly mixed. Throughout the process, the pressure inside the reactor is maintained slightly above atmospheric pressure (about 1.05 - 1.1 atmospheres) to prevent air from entering the reaction system. After the alloy mixing is completed, raise the temperature of the reactor to 150 °C and keep it at this temperature for 60 minutes to further volatilize and separate the impurities in the alloy. At the same time, by introducing a small amount of high-purity argon (argon flow rate is 10 - 15 milliliters per minute) into the reactor, using the stirring effect of the argon gas flow, promote the discharge of impurities and the homogenization of the alloy. After the refined sodium-potassium alloy solution reaches the expected purity and uniformity, lower the temperature of the reactor to about 100 °C to keep the alloy in good fluidity. Then, coat the alloy on the carbon cloth under the protection of argon.

[0048] 3) Then, carbon nanotubes and cobalt fluoride CoF with a mass ratio of 9:1 2 are mixed evenly and sprayed on the surface of the sodium-potassium alloy layer to obtain the negative electrode plate. The corresponding characteristics of the negative electrode plate are shown in Table 1.

[0049] Positive electrode plate: The layered metal oxide Na 0.8 MnO 2 is mixed with carbon nanotubes and PVDF in a mass ratio of 95:3.2:1.8, and a slurry is prepared using NMP as a solvent, coated on an aluminum foil current collector, dried, and cut to obtain the positive electrode plate.

[0050] Electrolyte: Sodium hexafluorophosphate is selected as the sodium salt, and the solvent (a mixed solvent formed by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) is prepared. The additive is 3% fluoroethylene carbonate. The concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L. Slowly add the weighed sodium hexafluorophosphate to the mixed solvent and stir to dissolve it fully. The stirring time is 2 h, then add fluoroethylene carbonate accounting for 3% of the total volume of the mixed solvent and continue stirring for 30 min to obtain the electrolyte. Assembly of the battery: Stack the positive electrode plate, negative electrode plate, and separator to obtain the core body, put the core body into an aluminum-plastic film, and inject the prepared electrolyte, and after baking and encapsulation treatment, the sodium-ion secondary battery is obtained.

[0051] Example 2-6

[0052] Examples 2-6 provide a secondary battery, which is different from Example 1 in that the concentration and viscosity of the spinning solution are adjusted to obtain carbon cloths with different porosities. The parameters of Examples 2-6 are shown in Table 1.

[0053] Examples 7-13

[0054] Examples 7-13 provide a secondary battery, which is different from Example 1 in that the diameter of the spinneret is adjusted to obtain carbon cloths with different thicknesses. The parameters of Examples 7-13 are shown in Table 1.

[0055] Examples 14-17

[0056] Examples 14-17 provide a secondary battery, which is different from Example 1 in that the coating amount of the sodium-potassium alloy, as well as the coating amounts of carbon nanotubes and cobalt fluoride CoF 2 are adjusted to obtain sodium alloy layers and coatings with different thicknesses. The parameters of Examples 14-17 are shown in Table 1.

[0057] Examples 18-20

[0058] Examples 18-20 provide a secondary battery, which is different from Example 1 in that the type of the sodium metal alloy is adjusted. The parameters of Examples 18-20 are shown in Table 1.

[0059] Examples 21-22

[0060] Examples 21-22 provide a secondary battery, which is different from Example 1 in that the type of the fluoride is adjusted. The parameters of Examples 21-22 are shown in Table 1.

[0061] Examples 23-24

[0062] Examples 23-24 provide a secondary battery, which is different from Example 1 in that the fluoride content is adjusted. The parameters of Examples 23-24 are shown in Table 1.

[0063] Examples 25-26

[0064] Examples 25-26 provide a secondary battery, which is different from Example 1 in that the sodium ratio in the sodium-potassium alloy raw material is adjusted to obtain sodium alloy materials with different sodium contents. The parameters of Examples 25-26 are shown in Table 1.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides a secondary battery, which is different from Example 1 in that a copper foil is used as the negative electrode plate.

[0067] Comparative Example 2

[0068] Comparative Example 2 provides a secondary battery, which is different from Example 1 in that the coating containing CoF 2 and carbon nanotube materials is removed.

[0069] The parameters of each example and comparative example are shown in Table 1.

[0070] Table 1 Parameters of Each Example and Comparative Example

[0071]

[0072]

[0073] Note: In the table, K represents the thickness ratio of the sodium alloy layer to the coating.

[0074] Test Example

[0075] This test example provides the performance of the batteries of each example and comparative example, which is as follows:

[0076] Test method for the initial efficiency of the battery: The voltage range is 1.5 - 4.00V. For the first charge: charge at a current rate of 0.33C to 4.00V, and then hold at 4.00V until the current drops to 0.05C, and record the capacity as C 1 ; For the first discharge: discharge at 0.33C to 1.5V, and record the capacity as C 2 . The initial efficiency is calculated by the following formula:

[0077]

[0078] Test method for the cycle performance of the battery: The voltage range is 1.5 - 4.00V, the rest time is 5 min, the current rate is 1C. For the charging stage, charge at a rate of 1C to 4.00V, and then hold at 4.00V until the current drops to 0.05C. For the discharging stage, discharge at 1C to 1.5V, and cycle 1000 times; It is calculated by the following formula:

[0079]

[0080] Test method for the rate performance of the battery: The voltage range is 1.5 - 4.00V. First, charge the secondary battery at a rate of 0.2C to full charge at 4.00V, then hold at 4.00V until the current drops to 0.05C, and rest for 5 min. Discharge at 1C to 1.5V, and the capacity is C 1 . Then charge at a rate of 0.2C to full charge at 4.00V, hold at 4.00V until the current drops to 0.05C, rest for 5 min, and discharge at 5C to 1.5V, and the capacity is C 2 . The rate performance is calculated by the following formula:

[0081]

[0082] The test results are shown in Table 2.

[0083] Test Results of Each Embodiment in Table 2

[0084]

[0085]

[0086] From the above results, it can be seen that the battery of the present application prepared with a specific negative electrode has a high initial efficiency, rate performance, and excellent cycle performance.

[0087] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A secondary battery, characterized in that: A negative electrode sheet is included, wherein the negative electrode sheet includes: A carbon support matrix having a plurality of pores; a sodium alloy material is arranged on the surface of the carbon support matrix and in the pores of the carbon support matrix; The coating is arranged on the surface of the carbon support substrate, and the coating comprises metal fluoride and carbon nanomaterial.

2. The secondary battery according to claim 1, characterized in that: The sodium alloy material distributed on the surface of the carbon support substrate forms a sodium alloy layer, the sodium alloy layer is between the carbon support substrate and the coating, and the thickness of the sodium alloy layer is 10nm-50nm.

3. The secondary battery according to claim 2, characterized in that: The ratio of the thickness of the sodium alloy layer to the thickness of the coating is (1-3):

1.

4. The secondary battery according to claim 1, characterized in that: The thickness of the coating is 10nm-50nm.

5. The secondary battery according to claim 1, characterized in that: The sodium content in the sodium alloy material is 20wt% to 90wt%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The sodium alloy material includes at least one of sodium-tin alloy, sodium-lead alloy, sodium-potassium alloy, sodium-aluminum alloy, sodium-lithium alloy, sodium-copper alloy, sodium-zinc alloy and sodium-bismuth alloy.

7. The secondary battery according to claim 1, characterized in that: The metal fluoride includes at least one of CoF2, NiF2 and FeF2.

8. The secondary battery according to claim 1, characterized in that: The content of the metal fluoride in the coating is 5wt% to 15wt%.

9. The secondary battery according to claim 1, characterized in that: The porosity of the carbon support matrix is ​​10% to 65%.

10. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 9.

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