Gradient sodium-philic 3D porous current collector and preparation method and application thereof

Abstract

The invention discloses a gradient sodium-philic 3D porous current collector and a preparation method and application thereof, and relates to the technical field of battery materials. The 3D porous current collector comprises a base material, a sodium-philic layer on the surface of the base material and a stable layer on the surface of the sodium-philic layer; wherein the sodium-philic layer comprises a first sodium-philic layer which is electrochemically co-deposited or sequentially deposited and a second sodium-philic layer which is generated in situ when the sacrificial template is removed; the stabilizing layer is external to the second sodium-philic layer. The provided gradient sodium-philic 3D porous current collector is applied to a negative-electrode-free sodium battery and is used for enhancing initial and long-term sodium-philic performance and relieving volume expansion, so that long-term uniform and stable deposition of sodium ions on the current collector is realized, and finally, the coulombic efficiency of the negative-electrode-free sodium battery is improved and the cycle life of the negative-electrode-free sodium battery is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a 3D porous current collector with gradient sodium affinity and a preparation method and application thereof. BACKGROUND

[0002] The anode-free sodium battery has the advantages of good low-temperature performance, low cost and high energy density. The current collector is used in the anode-free sodium battery, which not only reduces the volume and weight of the battery to improve the energy density of the battery, but also simplifies the production process to reduce the cost. In the anode-free sodium battery, the "real anode" is sodium metal deposited on the anode current collector during the first charging process. However, the design of the anode-free increases the consumption of active Na, which leads to the easier breakage of the anode SEI. In addition, during the cycle of the battery, the uneven sodium deposition morphology is more likely to induce the formation of "dead Na", which leads to the reduction of the battery coulomb efficiency and the rapid decay of the capacity.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The present application aims to provide a 3D porous current collector with gradient sodium affinity and a preparation method and application thereof, so as to solve the above technical problems.

[0005] The present application is implemented as follows: In a first aspect, the embodiments of the present application provide a 3D porous current collector with gradient sodium affinity, which comprises a substrate, a sodium-affinity layer on the surface of the substrate, and a stabilization layer on the surface of the sodium-affinity layer. The sodium-affinity layer comprises a first sodium-affinity layer and a second sodium-affinity layer generated in situ when the sacrificial template is removed, which are electrochemically co-deposited or sequentially deposited; and the stabilization layer is outside the second sodium-affinity layer.

[0006] In a second aspect, the embodiments of the present application provide a preparation method of the 3D porous current collector as described above, which comprises the following preparation steps: A sacrificial template layer is prepared on the surface of the pretreated substrate, and a solidification treatment is performed to obtain a first substrate; A first sodium-affinity layer is prepared on the surface of the first substrate to obtain a second substrate; The second substrate is removed of the sacrificial template layer, and a second sodium-affinity layer is generated in situ to obtain a third substrate; The third substrate is subjected to a stabilization treatment to obtain a stabilization layer.

[0007] In a third aspect, the embodiments of the present application provide an anode-free sodium battery comprising the 3D porous current collector as described above or prepared by the preparation method as described above.

[0008] The present application has the following beneficial effects: The gradient sodium-philic 3D porous current collector provided by the embodiment of the present application is composed of a substrate-a first sodium-philic layer-sodium-philic metal oxide nanoparticles-a stable layer, which greatly enhances the initial sodium-philic property and long-term cycle stability of the current collector, thereby realizing long-term uniform and stable deposition of sodium ions on the current collector, and finally improving the coulombic efficiency and cycle life of the sodium battery without negative electrode. At the same time, the 3D porous framework structure can relieve the gas expansion caused by sodium deposition and the gas generated during the operation of the battery, reduce the safety risk, and further improve the cycle life of the battery.

[0009] The gradient sodium-philic 3D porous current collector is applied in the sodium battery without negative electrode to enhance the initial and long-term sodium-philic property and relieve the volume expansion, thereby realizing long-term uniform and stable deposition of sodium ions on the current collector, and finally improving the coulombic efficiency and cycle life of the sodium battery without negative electrode. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0011] The rechargeable sodium metal battery has a wide application prospect in electrochemical energy storage due to its high theoretical capacity, low redox potential, and abundant Na resources. However, in actual application, the excessive use of Na metal in the negative electrode will reduce the energy density of the battery and further increase the production cost. In addition, the processing and forming of ultra-thin sodium metal negative electrode are also limited by the inherent properties of sodium. More importantly, the poor air stability of Na metal greatly limits the large-scale application of sodium metal batteries.

[0012] The gradient sodium-philic 3D porous current collector provided by the present application is applied in the sodium battery without negative electrode to enhance the initial and long-term sodium-philic property and relieve the volume expansion, thereby realizing long-term uniform and stable deposition of sodium ions on the current collector, and finally improving the coulombic efficiency and cycle life of the sodium battery without negative electrode. The specific embodiments are as follows: In a first aspect, the embodiments of the present application provide a gradient sodium-philic 3D porous current collector, which comprises a substrate, a sodium-philic layer on the surface of the substrate, and a stable layer on the surface of the sodium-philic layer. The sodium-philic layer comprises a first sodium-philic layer and a second sodium-philic layer generated in situ when the sacrificial template is removed, which are electrochemically co-deposited or sequentially deposited; and the stable layer is outside the second sodium-philic layer.

[0013] It should be noted that the sacrificial template is introduced to construct a long-range ordered, pore-size adjustable 3D macroporous framework to control the pores of the framework; the sodium-philic layer of the composition gradient structure greatly enhances the initial sodium-philic property and long-term cycle stability; the stable layer inhibits the excessive growth of the SEI on the current collector surface, improves the interface stability, prevents the active material from falling off, and enhances the overall conductivity.

[0014] In an optional embodiment, the first sodium-philic layer comprises at least one of sodium-philic metals Sn, In, Zn, Ag and Bi; Preferably, the sodium-philic metal comprises at least Sn, Ag and Bi; Preferably, the thickness of the first sodium-philic layer is 500 nm-1 μm.

[0015] It should be noted that the sodium-philic metal ions are reduced and deposited in the pores of the sacrificial template to form an Al-sodium-philic metal multi-alloy network wrapped by the template. By controlling the current density and deposition time, the gradient of the alloy composition can be adjusted. The first sodium-philic layer prepared by the embodiment of the present application is not a single sodium-philic metal layer, but a gradient structure prepared by electrochemical co-deposition or sequential deposition, which greatly enhances the initial sodium-philic property and long-term cycle stability.

[0016] In an optional embodiment, the second sodium-philic layer is a sodium-philic metal oxide layer; Preferably, the sodium-philic metal oxide is selected from at least one of tin oxide, indium oxide, zinc oxide, silver oxide and bismuth oxide.

[0017] It should be noted that the polystyrene microsphere template can be removed by burning during the heat treatment process, and the nanosilica sphere template can be removed by chemical etching.

[0018] If the template reagent is a mixture of polystyrene microspheres and silica nanospheres, after the chemical etching method is used to remove the nanosilica sphere template, low-temperature heat treatment is then performed to prepare the sodium-philic metal oxide layer.

[0019] During the heat treatment process, the sodium-philic metals such as Sn and Bi on the surface of the alloy can be slightly oxidized to form corresponding sodium-philic metal oxide nanoparticles. These oxide nanoparticles also have good sodium-philic property, can provide a large specific surface area and nucleation sites, form a micro-nano composite structure, and achieve the "super sodium-philic" property.

[0020] In an optional embodiment, the sacrificial template is selected from at least one of polystyrene microspheres and nanosilica spheres; Preferably, the particle size of the polystyrene microspheres and the nanosilica spheres is 200 nm-1 μm, respectively. And / or, the material of the substrate is aluminum or copper; And / or, the stable layer is an amorphous carbon layer with a thickness of 5-10 nm.

[0021] In a second aspect, embodiments of the present application provide a method for preparing a 3D porous current collector as described above, comprising the following preparation steps: A sacrificial template layer is prepared on the pretreated substrate surface, and a solidification treatment is performed to obtain a first substrate; A first sodium-philic layer is prepared on the surface of the first substrate to obtain a second substrate; The second substrate is removed of the sacrificial template layer while generating a second sodium-philic layer in situ to obtain a third substrate; A stable layer is prepared by performing a stabilization treatment on the third substrate.

[0022] In an optional embodiment, the dispersed sacrificial template reagent is closely arranged on the pretreated substrate surface by using a self-assembly method or a spin coating method to form a single-layer or double-layer ordered array of the sacrificial template layer; the sacrificial template layer is subjected to a solidification treatment at a temperature of 60-80°C to obtain a first substrate; Preferably, the concentration of the sacrificial template reagent is 1wt%-5wt% of an ethanol dispersion; Preferably, the pretreatment comprises ultrasonic cleaning in a cleaning agent for 15-50 min, and then the cleaned substrate is immersed in an alkaline solvent with a concentration of 0.5-1.5 M for 30 s to 1 min; Preferably, the cleaning agent is at least one selected from acetone, ethanol and deionized water; and the alkaline solvent is selected from sodium hydroxide or potassium hydroxide.

[0023] It should be noted that the cleaning agent is mainly used to remove oil stains and impurities on the substrate surface, and the substrate is sequentially cleaned with acetone, ethanol and deionized water. The alkaline solvent is mainly used to remove the natural oxide layer on the substrate surface.

[0024] After the alkaline solvent cleaning, the substrate surface is rinsed with deionized water to remove the residual alkaline solvent, and finally dried with nitrogen. In other embodiments of the present application, other drying methods can also be selected for drying the substrate according to actual needs.

[0025] The solidification treatment is beneficial to promote the drying and solidification of the sacrificial template reagent, and ensures the firm adhesion of the sacrificial template.

[0026] In an optional embodiment, when the first sodium-philic layer is prepared by the electrochemical codeposition method, the first electrolyte comprises a tin salt with a concentration of 0.1M-0.5M, a zinc salt with a concentration of 0.05M-0.1M, a bismuth salt with a concentration of 0.02M-0.05M, a sodium salt with a concentration of 0.5M-1.0M, and a complexing agent with a concentration of 0.06M-0.15M; and the first electrolyte is a mixed aqueous solution or an organic solution containing metal salts. The metal salts are all soluble salts, which are not particularly limited in the present application and can be selected from halide salts, nitrate salts, or sulfate salts of the corresponding metals according to actual needs.

[0027] Preferably, the pH of the electrolyte is 4-5; and the complexing agent is selected from any one of citric acid, sodium citrate, and potassium citrate. The electrolyte is in a weakly acidic environment, which can prevent the hydrolysis and precipitation of metal ions, and dilute sulfuric acid or acetic acid can be used to adjust the pH of the electrolyte, and the complexing agent is conducive to the uniform deposition.

[0028] Preferably, the first sodium-philic layer is prepared by using a constant current electrodeposition mode, wherein the working electrode is the first substrate, the counter electrode is made of platinum or graphite, and the reference electrode is a saturated calomel electrode. Preferably, the current density of the electrodeposition is 1mA / cm 2 -5mA / cm 2 , the deposition time is 30min-60min, and the temperature is 25℃-40℃. Preferably, the first sodium-philic layer is prepared by using a sequential deposition method, wherein the second electrolyte comprising a tin salt and a bismuth salt is deposited first, and then the third electrolyte comprising a zinc salt is deposited. Preferably, the second electrolyte comprises a tin salt with a concentration of 0.1M-0.5M, a bismuth salt with a concentration of 0.02M-0.05M, a sodium salt with a concentration of 0.5M-1.0M, and a complexing agent with a concentration of 0.06M-0.15M; and the third electrolyte comprises a zinc salt with a concentration of 0.05M-0.1M, a sodium salt with a concentration of 0.5M-1.0M, and a complexing agent with a concentration of 0.06M-0.15M.

[0029] It should be noted that, in the embodiments of the present application, the sequential deposition method first deposits Sn / Bi which is more sodium-philic, and then deposits Zn, which is conducive to enhancing the mechanical strength. In other embodiments, other types of sodium-philic metals can be selected according to actual needs.

[0030] In an optional embodiment, when the sacrificial template layer is prepared from polystyrene microspheres, low-temperature heat treatment is used to remove the sacrificial template layer. Preferably, when the sacrificial template layer is prepared from silica nanospheres, a chemical etching method is used to remove the sacrificial template layer. Preferably, when the low-temperature heat treatment is adopted, the second substrate is placed in a tube furnace, and heated to 350-450℃ at a rate of 2-5℃ / min under an air atmosphere, and kept for 1-2h; Preferably, when the chemical etching method is adopted, the etching solvent is 1.5-2M NaOH aqueous solution, the temperature is 50-60℃, and the time is 1-2h.

[0031] In an optional embodiment, the stabilizing treatment comprises carbon coating the third substrate by using a chemical vapor deposition method. Preferably, the temperature of the chemical vapor deposition method is 450-550℃, the gas introduced is acetylene / Ar mixed gas, the stabilizing treatment time is 10-20min, and the thickness of the carbon coating is 5-10nm.

[0032] It should be noted that the carbon coating prepared by the embodiment of the present application is an amorphous carbon layer; the carbon layer can inhibit excessive growth of SEI on the surface of the current collector, improve the interface stability, prevent the active material from falling off, and enhance the overall conductivity.

[0033] In a third aspect, the embodiments of the present application provide a negative-electrode-free sodium battery comprising the 3D porous current collector as described above or prepared by the preparation method as described above.

[0034] The features and performances of the present application are further described in detail below in combination with examples.

[0035] Example 1 The present embodiment provides a gradient sodium-friendly 3D porous current collector, which is prepared by the following steps: (1) Substrate pretreatment The 12μm aluminum foil substrate is sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 15min, and then the cleaned substrate is immersed in a 1M sodium hydroxide solution for 40s; The residual sodium hydroxide on the surface of the substrate is washed clean with deionized water, and finally dried with nitrogen, ready for use.

[0036] (2) Preparation of the first substrate The well-dispersed sacrificial template reagent is closely arranged on the surface of the substrate pretreated in step (1) by using a spin coating method to form a single-layer or double-layer ordered array of the sacrificial template layer; the sacrificial template layer is cured at a temperature of 70℃ to prepare the first substrate; wherein the sacrificial template reagent is 800nm polystyrene microspheres, and the concentration is 3wt% ethanol dispersion.

[0037] (3) Preparation of the second substrate The first sodium-philic layer is prepared on the surface of the sacrificial template layer of the first substrate prepared in step (2) by electrochemical co-deposition.

[0038] The electrolyte used in the electrochemical co-deposition comprises 0.3M tin chloride, 0.08M zinc chloride, 0.04M bismuth nitrate, 0.7M sodium sulfate and 0.10M sodium citrate, and the pH of the electrolyte is 4.5.

[0039] The first sodium-philic layer is prepared by constant current electrodeposition, wherein the working electrode is the first substrate, the counter electrode is made of platinum, and the reference electrode is a saturated calomel electrode; the current density for the electrodeposition is 3mA / cm 2 , the deposition time is 45min, the temperature is 30℃, and the thickness of the first sodium-philic layer is 800nm.

[0040] (4) Preparation of the third substrate The sacrificial template layer in the second substrate is removed by low-temperature heat treatment, and a second sodium-philic layer comprising tin oxide, bismuth oxide and zinc oxide is generated in situ to obtain the third substrate.

[0041] Specifically, the second substrate is placed in a tube furnace, heated to 400℃ at a rate of 5℃ / min in an air atmosphere, and kept at 400℃ for 1.5h.

[0042] (5) Preparation of the stable layer The third substrate is coated with a carbon coating layer by chemical vapor deposition to obtain the 3D porous current collector.

[0043] The temperature of the chemical vapor deposition is 500℃, the gas introduced is acetylene / Ar mixed gas, the stabilization treatment time is 15min, and the thickness of the carbon coating layer is 8nm.

[0044] Example 2 This example provides a gradient sodium-philic 3D porous current collector, and the preparation steps are the same as those of Example 1, except that: (3) Preparation of the second substrate The electrolyte used in the electrochemical co-deposition comprises 0.1M tin chloride, 0.05M zinc chloride, 0.02M bismuth nitrate, 0.5M sodium sulfate and 0.06M sodium citrate, and the pH of the electrolyte is 4.5.

[0045] Example 3 This example provides a gradient sodium-philic 3D porous current collector, and the preparation steps are the same as those of Example 1, except that: (3) Preparation of the second substrate The electrolyte during the electrochemical co-deposition comprises tin chloride with a concentration of 0.3 M, sodium sulfate with a concentration of 0.7 M, and sodium citrate with a concentration of 0.1 M; the pH of the electrolyte is 4.5.

[0046] Example 4 This example provides a 3D porous current collector with a gradient sodium affinity, and the preparation steps are the same as those of Example 1, except that: (3) Preparation of the second substrate The electrolyte during the electrochemical co-deposition comprises tin chloride with a concentration of 0.3 M, zinc chloride with a concentration of 0.08 M, sodium sulfate with a concentration of 0.7 M, and sodium citrate with a concentration of 0.1 M; the pH of the electrolyte is 4.5.

[0047] Example 5 This example provides a 3D porous current collector with a gradient sodium affinity, and the preparation steps are the same as those of Example 1, except that: (3) Preparation of the second substrate The electrolyte during the electrochemical co-deposition comprises tin chloride with a concentration of 0.3 M, bismuth nitrate with a concentration of 0.04 M, sodium sulfate with a concentration of 0.7 M, and sodium citrate with a concentration of 0.1 M; the pH of the electrolyte is 4.5.

[0048] Example 6 This example provides a 3D porous current collector with a gradient sodium affinity, and the preparation steps are the same as those of Example 1, except that: (3) Preparation of the second substrate The current density for the electrodeposition is 1 mA / cm 2 , the deposition time is 30 min, and the temperature is 50°C.

[0049] Example 7 This example provides a 3D porous current collector with a gradient sodium affinity, and the preparation steps are the same as those of Example 1, except that: (2) Preparation of the first substrate The sacrificial template reagent is silica nanospheres, and the concentration is 3 wt% in an ethanol dispersion.

[0050] (4) Preparation of the third substrate The sacrificial template layer is removed by a chemical etching method; the etching solvent is 1.0 M NaOH aqueous solution, the temperature is 50°C, and the time is 1 h.

[0051] Example 8 This example provides a 3D porous current collector with a gradient sodium affinity, and the preparation steps are the same as those of Example 1, except that: (2) Preparation of the first substrate The sacrificial template reagent is polystyrene microspheres and silica nanospheres, wherein the concentration of the polystyrene microspheres is 1.5 wt%, and the concentration of the silica nanospheres is 1.5 wt%.

[0052] (4) preparing a third substrate The silica nanospheres in the sacrificial template layer are removed by a chemical etching method; the etching solvent is 1.0 M NaOH aqueous solution, the temperature is 50°C, and the time is 1 h.

[0053] The polystyrene microspheres in the sacrificial template layer are removed by low-temperature heat treatment, and a second sodium-philic layer including tin oxide, bismuth oxide, and zinc oxide is generated in situ to obtain the third substrate.

[0054] Specifically, the second substrate is placed in a tube furnace, heated to 400°C at a rate of 5°C / min in an air atmosphere, and kept at 400°C for 1.5 h.

[0055] Example 9 This example provides a 3D porous current collector with a gradient sodium-philic property, and the preparation steps are the same as those in Example 1, except that: (1) substrate pretreatment The selected substrate is a copper foil.

[0056] Comparative Example 1 This comparative example provides a current collector, and the preparation steps are the same as those in Example 1, except that: Step (2) of preparing the first substrate is omitted, and the first sodium-philic layer is directly prepared on the surface of the pretreated substrate.

[0057] Comparative Example 2 This comparative example provides a current collector, and the preparation steps are the same as those in Example 1, except that: Step (5) of preparing the stable layer is omitted.

[0058] Experimental Example The current collectors prepared or provided in each example are assembled into a negative electrode-free sodium ion battery, specifically: The active layer of the positive electrode sheet is composed of 95.1:2.0:2.4:0.5 sodium iron pyrophosphate, PVDF, conductive carbon black, and a dispersing agent; The electrolyte is 1M NaPF6-containing diethylene glycol dimethyl ether.

[0059] The first coulombic efficiency and cycle performance of the negative electrode-free sodium metal batteries prepared from each example and comparative example are tested, and the specific test method is as follows: Battery first coulombic efficiency test: after the assembled battery is stored for 10 h, it is charged to 3.5 V at 0.2 C constant current and constant voltage, and then stored for 0.5 h, and then discharged to 2.0 V at 0.5 C constant current, and the ratio of the battery discharge capacity to the charge capacity is calculated as CE; Cycle life test: after the assembled battery is stored for 10 h, it is charged to 3.5 V at 0.5 C constant current and constant voltage at room temperature 25 DEG C, and then stored for 0.5 h, and then discharged to 2.0 V at 1 C constant current, and the capacity retention rate is recorded after 100 cycles; Volume change test: after the battery after formation and capacity measurement is stored at room temperature 25 DEG C for 10 h, the initial volume of the battery is determined by the drainage method, and is recorded as V1; then it is put into a high-temperature room at 45 DEG C, and stored for 7D, and then taken out, and cooled to room temperature 25 DEG C, and then the volume after storage is determined by the drainage method, and is recorded as V2, and the volume change rate of 45 DEG C high-temperature storage for 7D is AV=(V2-V1) / V1*100%.

[0060] The test results are shown in Table 1.

[0061] Table 1 Electrochemical performance of each sodium-ion battery without negative electrode

[0062] In summary, the gradient sodium-philic 3D porous current collector provided by the embodiments of the present application is composed of aluminum (substrate)-zinc tin / bismuth alloy (first sodium-philic layer)-sodium-philic metal oxide nanoparticles / carbon (second sodium-philic layer / stable layer) in a composition gradient structure, which greatly enhances the initial sodium-philic property and long-term cycle stability of the current collector, thereby realizing long-term uniform and stable deposition of sodium ions on the current collector, and finally improving the coulombic efficiency and cycle life of the sodium battery without negative electrode. At the same time, the 3D porous framework structure can relieve the gas expansion caused by sodium deposition and the gas generated during the operation of the battery, reduce the safety risk, and further improve the cycle life of the battery.

[0063] The gradient sodium-philic 3D porous current collector is applied in the sodium battery without negative electrode to enhance the initial and long-term sodium-philic property and relieve the volume expansion, thereby realizing long-term uniform and stable deposition of sodium ions on the current collector, and finally improving the coulombic efficiency and cycle life of the sodium battery without negative electrode.

[0064] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A gradient sodium-philic 3D porous current collector, characterized in that, The 3D porous current collector comprises a substrate, a sodium-philic layer on the surface of the substrate, and a stable layer on the surface of the sodium-philic layer. The sodium-philic layer comprises a first sodium-philic layer prepared by electrochemical co-deposition or sequential deposition, and a second sodium-philic layer generated in situ when the sacrificial template is removed; and the stable layer is outside the second sodium-philic layer.

2. The 3D porous current collector of claim 1, wherein, The first sodium-philic layer comprises at least one of sodium-philic metals Sn, In, Zn, Ag and Bi. Preferably, the sodium-philic metals comprise at least Sn, Ag and Bi. Preferably, the thickness of the first sodium-philic layer is 500 nm-1 μm.

3. The 3D porous current collector of claim 1, wherein, The second sodium-philic layer is a sodium-philic metal oxide layer. Preferably, the sodium-philic metal oxide is at least one of tin oxide, indium oxide, zinc oxide, silver oxide and bismuth oxide.

4. The 3D porous current collector of claim 1, wherein, The sacrificial template is at least one of polystyrene microspheres and silica nanospheres. Preferably, the particle size of the polystyrene microspheres and the silica nanospheres is 200 nm-1 μm. Preferably, the substrate is made of aluminum or copper. Preferably, the stable layer is an amorphous carbon layer with a thickness of 5 nm-10 nm.

5. A method of producing a 3D porous current collector according to any one of claims 1 to 4, characterized in that, The preparation method comprises the following steps: A sacrificial template layer is prepared on the surface of the pretreated substrate and is subjected to a curing treatment to obtain a first substrate; A first sodium-philic layer is prepared on the surface of the first substrate to obtain a second substrate; The second substrate is removed of the sacrificial template layer, and a second sodium-philic layer is generated in situ to obtain a third substrate; The third substrate is subjected to a stabilization treatment to obtain a stable layer.

6. The production method according to claim 5, wherein The self-assembly method or the spin coating method is used to arrange the dispersed sacrificial template reagent closely on the surface of the pretreated substrate to form a single-layer or double-layer ordered array of the sacrificial template layer; the sacrificial template layer is subjected to a curing treatment at a temperature of 60-80°C to obtain the first substrate. Preferably, the concentration of the sacrificial template reagent is 1wt%-5wt% of an ethanol dispersion. Preferably, the pretreatment comprises ultrasonic cleaning in a cleaning agent for 15-50 min, and then the cleaned substrate is immersed in an alkaline solvent with a concentration of 0.5M-1.5M for 30 s to 1 min. Preferably, the cleaning agent is at least one of acetone, ethanol and deionized water; and the alkaline solvent is sodium hydroxide or potassium hydroxide.

7. The preparation method according to claim 5, characterized in that, When the first sodium-philic layer is prepared by the electrochemical co-deposition method, the first electrolyte comprises a tin salt with a concentration of 0.1M-0.5M, a zinc salt with a concentration of 0.05M-0.1M, a bismuth salt with a concentration of 0.02M-0.05M, a sodium salt with a concentration of 0.5M-1.0M and a complexing agent with a concentration of 0.06M-0.15M. Preferably, the pH of the electrolyte is 4-5; and the complexing agent is any one of citric acid or sodium citrate. Preferably, the first sodium-philic layer is prepared by the constant current electrodeposition mode, in which the working electrode is the first substrate, the counter electrode is made of platinum or graphite, and the reference electrode is a saturated calomel electrode. Preferably, the current density for the electrodeposition is 1 mA / cm 2 - 5 mA / cm 2 , the deposition time is 30 min - 60 min; the temperature is 25°C - 40°C; Preferably, when the first sodium-philic layer is prepared by the sequential deposition method, a second electrolyte comprising a tin salt and a bismuth salt is first deposited, and then a third electrolyte comprising a zinc salt is deposited. Preferably, the second electrolyte comprises a tin salt with a concentration of 0.1M-0.5M, a bismuth salt with a concentration of 0.02M-0.05M, a sodium salt with a concentration of 0.5M-1.0M and a complexing agent with a concentration of 0.06M-0.15M; and the third electrolyte comprises a zinc salt with a concentration of 0.05M-0.1M, a sodium salt with a concentration of 0.5M-1.0M and a complexing agent with a concentration of 0.06M-0.15M.

8. The preparation method according to claim 5, characterized in that, When the sacrificial template layer is made of polystyrene microspheres, the sacrificial template layer is removed by low-temperature heat treatment; When the sacrificial template layer is made of silica nanospheres, the sacrificial template layer is removed by chemical etching; Preferably, when the low-temperature heat treatment is used, the second substrate is placed in a tube furnace, heated to 350℃-450℃ at a rate of 2℃ / min-5℃ / min in air atmosphere, and kept for 1h-2h; Preferably, when the chemical etching is used, the etching solvent is 1.5M-2M NaOH aqueous solution, the temperature is 50℃-60℃, and the time is 1h-2h.

9. The preparation method according to claim 5, characterized in that, The stabilization treatment comprises carbon coating of the third substrate by chemical vapor deposition; Preferably, the temperature of the chemical vapor deposition is 450℃-550℃, the gas is acetylene / Ar mixed gas, the stabilization treatment time is 10min-20min, and the thickness of the carbon coating is 5nm-10nm.

10. A negative electrode-free sodium battery, characterized by, The 3D porous current collector comprises the 3D porous current collector according to any one of claims 1-4 or is prepared by the method according to any one of claims 5-9.

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