Negative current collector of sodium metal battery without negative electrode, and preparation method and application of negative current collector

Abstract

The invention discloses a negative current collector of a negative-electrode-free sodium metal battery as well as a preparation method and application of the negative current collector, carbon spheres with spherical hollow cavities and open through holes are prepared, a current collector base material is coated with the carbon spheres to serve as the negative current collector, and the prepared negative current collector is used for preparing the negative-electrode-free sodium metal battery. The closed cavity in the hollow carbon sphere provides a confinement space for sodium storage, and the volume change in the circulation process can be effectively buffered. The open through holes in the shell of the hollow carbon sphere form a high-speed network for ion transmission, so that the surface migration kinetics of sodium ions is greatly improved, and uniform deposition is promoted. According to the negative current collector, the local current density is reduced synergistically, and sodium is guided to deposit in the sphere preferentially, so that the generation of dead sodium in the circulation process is reduced, and the coulombic efficiency of the negative-electrode-free sodium metal battery is improved.

Description

Technical Field

[0001] This invention relates to the field of sodium battery technology, and in particular to a negative electrode current collector for a negative electrodeless sodium metal battery, its preparation method, and its application. Background Technology

[0002] During the charging and discharging process of the battery, sodium ions reach the negative electrode through deposition, which differs from the insertion and extraction process in sodium-ion batteries. This significantly increases the battery's maximum mass capacity. Therefore, the theoretical capacity of a sodium metal battery negative electrode is equivalent to three times that of a graphite negative electrode in a lithium-ion battery. Furthermore, sodium is far more abundant in the Earth's crust than lithium, making it more competitive for large-scale applications.

[0003] However, prior to this, sodium was not the preferred anode material for commercially available rechargeable batteries. Similar to lithium metal anodes, sodium metal anodes also suffer from uneven deposition and stripping of sodium ions during battery cycling. This phenomenon causes volume expansion, resulting in some sodium failing to reach the current collector and becoming "dead sodium," thus increasing contact resistance. Meanwhile, some fresh sodium reacts with the electrolyte, continuously reducing the available electrolyte and ultimately leading to poor cycle performance. In anode-less metal batteries, the anode initially lacks any active lithium / sodium; the lithium / sodium source comes from the cathode material. Compared to metal batteries, this makes them more prone to problems such as low coulombic efficiency, poor cycle stability, and short circuits. Currently, for anode-less lithium batteries, by selecting appropriate lithium salts, solvents, or sacrificing cathode additives, thin and stable solid electrolyte interface layers have been successfully developed, significantly improving initial efficiency and cycle stability. Conversely, due to the high reactivity of metallic sodium, constructing a robust interface that simultaneously achieves favorable sodium ion transport and minimal sodium consumption remains a significant challenge for anode-free sodium batteries. Summary of the Invention

[0004] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a negative electrode current collector for a negative electrode-free sodium metal battery, its preparation method and application.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a negative electrode current collector for a sodium metal battery without a negative electrode, comprising a current collector substrate, a functional coating coated on the current collector substrate, wherein the functional coating comprises hollow carbon spheres with a total mass fraction of 10 and a mass ratio of (7-9):(0-2):1, a conductive material, and a binder; wherein the hollow carbon spheres are carbon spheres having spherical hollow cavities and open through holes, wherein the diameter of the hollow carbon spheres is 200-300nm, and the wall thickness of the hollow carbon spheres is 50-80nm.

[0006] The aforementioned sodium metal negative electrode current collector for a non-negative electrode battery has an active material loading of 2 mg / cm³ in the functional coating. 2 .

[0007] A method for preparing a negative electrode current collector for a sodium metal battery without a negative electrode, used to prepare the negative electrode current collector as described above, specifically includes the following steps: Step 1, Preparation of hollow carbon spheres: Ammonia, ethanol, and deionized water were mixed and stirred, and then tetrapropoxysilane, resorcinol, and formaldehyde were added. After stirring and reacting, spherical silica coated with phenolic resin was obtained. The spherical silica coated with phenolic resin was heated to 800°C in a nitrogen atmosphere and then annealed to carbonize the phenolic resin to obtain the product. The product was then subjected to silica template removal, washed, and dried to obtain hollow carbon spheres. Step 2: Put hollow carbon balls, binder, ultrapure water and anhydrous ethanol into a planetary ball mill and mix them into a uniform slurry. Coat the slurry onto the current collector substrate and dry the current collector substrate coated with slurry to obtain the negative electrode current collector.

[0008] In the above-mentioned method for preparing a negative electrode current collector for a sodium metal battery without a negative electrode, a conductive material is added in step 2. The total mass fraction of the hollow carbon spheres, conductive material, and binder is 10, and the mass ratio is (7-9):(0-2):1.

[0009] An application of a negative electrode current collector for a sodium-metal battery without a negative electrode, based on the above-described negative electrode current collector or a negative electrode current collector prepared by the above-described preparation method, wherein the negative electrode current collector is used to prepare a sodium-metal battery without a negative electrode.

[0010] The above-mentioned application of a negative electrode current collector in a sodium metal battery without a negative electrode uses an ether-based electrolyte system.

[0011] The above-mentioned application of a negative electrode current collector in a sodium metal battery without a negative electrode involves the following preparation method for the ether electrolyte system: NaPF6 is weighed using a balance with a water and oxygen content of less than 1 ppm in a glove box, dissolved in diethylene glycol dimethyl ether, and stirred on a magnetic stirrer until the solution is completely clear.

[0012] The beneficial effects of this invention are that the electrolyte preparation process is simple, and the use of diethylene glycol dimethyl ether, which has a large conductivity and a low electrolyte resistance, as a solvent can improve the transport rate of sodium ions in the electrolyte, thereby improving the charge and discharge efficiency.

[0013] This invention synthesizes carbon spheres that simultaneously possess hollow cavities and abundant pore structures. These spheres are used as negative electrode current collectors to provide a rapid channel for sodium ion transport, further improving the sodium ion transport rate, promoting uniform deposition, reducing dead sodium generation, and thus improving coulombic efficiency.

[0014] This invention combines the above-mentioned electrolyte, hollow carbon spherical electrode, and Prussian blue cathode to form a sodium-free metal full cell. With the cathode completely free of sodium, the full cell can still maintain a capacity of 87 mAh / g after 300 cycles, and the average coulombic efficiency is above 99%, thus improving cycle stability and coulombic efficiency. Attached Figure Description

[0015] Figure 1 This is a SEM image of the hollow carbon spheres in this invention; Figure 2 This is a cross-sectional SEM image of the hollow carbon spheres in this invention; Figure 3 This is a SEM image of the hollow carbon spherical electrode sheet without sodium deposition according to the present invention; Figure 4 This is a SEM image of the hollow carbon spherical electrode sheet after a certain amount of sodium has been deposited according to the present invention. Figure 5 This is a SEM image of the hollow carbon spherical electrode sheet after a large amount of sodium has been deposited according to the present invention; Figure 6 This invention is based on a current density of 10 mA / cm². 2 Cyclic performance of Na|| hollow carbon sphere half-cell; Figure 7 This invention is 5 mA / cm 2 Cyclic performance of Na@hollow carbon sphere || Na@hollow carbon sphere symmetric cells; Figure 8 This invention relates to the full-cell cycle performance of the sodium metal battery without a negative electrode. Detailed Implementation

[0016] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] This embodiment discloses a negative electrode current collector for a negative electrode-free sodium metal battery, improving the cycle stability and coulombic efficiency of the battery. The negative electrode current collector includes a current collector substrate, a functional coating coated on the substrate, and the functional coating comprising a conductive material in a mass ratio of 8:1:1, hollow carbon spheres, and a binder. The hollow carbon spheres are carbon spheres with spherical hollow cavities and open vias, with a diameter of 200-300 nm and a wall thickness of 60 nm. In this embodiment, the current collector substrate is copper foil, but it can also be aluminum foil, carbon-coated aluminum foil, or carbon-coated copper foil. On one hand, the closed internal cavity provides a confined space for sodium storage, effectively buffering volume changes during cycling. On the other hand, the open vias on the outer shell form a high-speed ion transport network, greatly improving the surface migration kinetics of sodium ions and promoting uniform deposition. This structure synergistically reduces local current density and guides sodium to preferentially deposit inside the spheres, thereby reducing the generation of dead sodium during cycling and improving the coulombic efficiency of the negative electrode-free sodium metal battery. Ultimately, the sodium metal anode based on this hollow carbon sphere current collector exhibits excellent structural stability and interfacial dynamics, and the half-cell can achieve a flow rate of 10 mA / cm². 2 It can stably cycle for over 1600 cycles at a current density, and the full battery still maintains a capacity of 87 mAh / g after 300 cycles (e.g., Figure 6 (As shown).

[0018] This embodiment also discloses a method for preparing a negative electrode current collector for a negative electrodeless sodium metal battery, which specifically includes the following steps: Step 1, Preparation of hollow carbon spheres: 4 mL ammonia, 95 mL ethanol, and 15 mL deionized water were mixed together and stirred at 30°C for 5 minutes. Then, 10 mL tetrapropoxysilane was quickly added to the solution. After 30 minutes, 0.6 g resorcinol and 0.84 mL formaldehyde were added, and stirring was continued for 24 hours to obtain the product. The product was washed multiple times with deionized water and ethanol, centrifuged, and then dried in an oven overnight to obtain spherical SiO2 coated with phenolic resin. The SiO2 coated with phenolic resin was heated to 800°C at a heating rate of 5°C / min in a N2 environment. After reaching the temperature, it was annealed for 2 hours to carbonize the phenolic resin on the surface. Then, 6 mol / L concentrated hydrochloric acid or 10% HF acid solution was added under stirring to remove the silica template. The product was collected by centrifugation and washed multiple times with deionized water and ethanol. The product was then dried in an oven overnight to obtain hollow carbon spheres. Step 2: Hollow carbon spheres, Super P, and sodium carboxymethyl cellulose (CMC) were mixed at a mass ratio of 8:1:1. A certain amount of ultrapure water and anhydrous ethanol were added dropwise, and the mixture was then placed in a planetary ball mill to form a homogeneous slurry. The milling speed was 150 rpm, and the time was 6 hours. The slurry was then uniformly coated onto the surface of copper foil, with an active material loading of 2 mg / cm³. 2Then, the electrode loaded with active material is dried overnight in a vacuum oven at 60°C.

[0019] In step 2, the mass ratio of hollow carbon spheres, super P, and sodium carboxymethyl cellulose (CMC) can also be 7:2:1. Alternatively, conductive material (super P) can be omitted from the slurry in step 2, and the mass ratio of hollow carbon spheres to sodium carboxymethyl cellulose (CMC) in the slurry can be 9:1.

[0020] The SEM morphology of the hollow carbon spheres prepared in this embodiment is shown in the figure below. Figure 1-2 As shown, from Figure 2 As can be seen, the hollow carbon spheres have a diameter of 200-300 nm and an outer wall thickness of 60 nm. A top-view SEM image of the negative electrode current collector prepared by mixing hollow carbon spheres with conductive carbon black and a binder to form a slurry and coating it onto copper foil is shown below. Figure 3 As shown, from Figure 3 As can be seen, the hollow carbon spheres are evenly distributed and of uniform size.

[0021] The negative electrode current collector prepared in this embodiment can be used to prepare a sodium-metal battery without a negative electrode. The specific method for preparing a sodium-metal battery without a negative electrode includes: Step A, electrolyte preparation: Weigh 1.68g NaPF6 in a glove box where the water and oxygen content are both below 1ppm using a 0.01% balance, dissolve it in 10 mL of diethylene glycol dimethyl ether, and stir on a magnetic stirrer for 3 hours until the solution is completely clear.

[0022] Step B, Na2Fe x Mn (1-x) Fe(CN)6, Super P, and polyvinylidene fluoride (PVDF) were mixed evenly in a ratio of 8:1:1 (by mass), and an appropriate amount of NMP was added. After ball milling for 6 hours, the slurry was evenly coated onto aluminum foil and dried overnight in a vacuum oven.

[0023] Step C: When the water and oxygen content in the glove box is below 1 ppm, place the dried stainless steel electrode shell, electrode plates, and separator into the glove box, arranging them in the order of positive electrode shell, positive electrode plate, and separator. Add 35 μL of electrolyte, then add the negative electrode current collector, and finally cover with the negative electrode shell. Compact the mixture using a tablet press. After transferring the assembled battery out of the glove box, place it on a Newway battery rack for testing.

[0024] In this embodiment, after assembling the above-mentioned electrolyte, hollow carbon spherical electrode, and Prussian blue cathode into a sodium-free metal full cell, the full cell can maintain a capacity of 87 mAh / g after 300 cycles with a completely sodium-free negative electrode, and the average coulombic efficiency is above 99%, achieving improved cycle stability and coulombic efficiency (e.g., Figure 8 (As shown). The prepared battery operates at a current density of 5 mA / cm².2 The cycling performance of a symmetric cell composed of mesoporous carbon spherical electrodes after sodium deposition is stable for over 900 hours (e.g., Figure 7 (As shown).

[0025] The discharged battery was disassembled, the electrodes were removed, and SEM characterization was performed. Figure 4 This is a top-down SEM view of the electrode. It shows that after a certain amount of sodium is deposited, the mesoporous carbon spheres are filled with sodium, while the outer layers contain relatively little sodium. After depositing a large amount of sodium, the electrode is characterized by SEM, as shown below. Figure 5 As shown, after the carbon spheres are filled, sodium continues to spread along the surface in an island-like pattern without forming dendrites.

[0026] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and protection, and such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A negative electrode current collector for a sodium metal battery without a negative electrode, comprising a current collector substrate and a functional coating applied to the current collector substrate, characterized in that, The functional coating comprises hollow carbon spheres with a total mass fraction of 10 and a mass ratio of (7-9):(0-2):1, conductive material, and binder; the hollow carbon spheres are carbon spheres with spherical hollow cavities and open through holes, the diameter of the hollow carbon spheres is 200-300 nm, and the wall thickness of the hollow carbon spheres is 50-80 nm.

2. The negative electrode current collector for a sodium metal battery without a negative electrode according to claim 1, characterized in that, The active material loading in the functional coating is 2 mg / cm³. 2 .

3. A method for preparing a negative electrode current collector for a sodium metal battery without a negative electrode, characterized in that, The method for preparing the negative electrode current collector as described in any one of claims 1-2 specifically includes the following steps: Step 1, Preparation of hollow carbon spheres: Ammonia, ethanol, and deionized water were mixed and stirred, and then tetrapropoxysilane, resorcinol, and formaldehyde were added. After stirring and reacting, spherical silica coated with phenolic resin was obtained. The spherical silica coated with phenolic resin was heated to 800°C in a nitrogen atmosphere and then annealed to carbonize the phenolic resin to obtain the product. The product was then subjected to silica template removal, washed, and dried to obtain hollow carbon spheres. Step 2: Put hollow carbon balls, binder, ultrapure water and anhydrous ethanol into a planetary ball mill and mix them into a uniform slurry. Coat the slurry onto the current collector substrate and dry the current collector substrate coated with slurry to obtain the negative electrode current collector.

4. The method for preparing a negative electrode current collector for a sodium metal battery without a negative electrode according to claim 3, characterized in that, In step 2, a conductive material is also added. The total mass fraction of the hollow carbon spheres, conductive material, and binder is 10, and the mass ratio is (7-9):(0-2):

1.

5. An application of a negative electrode current collector in a sodium metal battery without a negative electrode, characterized in that, The negative electrode current collector is prepared based on the negative electrode current collector according to any one of claims 1-2 or the negative electrode current collector prepared based on the preparation method of any one of claims 3-4, and the negative electrode current collector is used to prepare a negative electrode-free sodium metal battery.

6. The application of the negative electrode current collector of a sodium metal battery without a negative electrode according to claim 5, characterized in that, The electrolyte in the non-negative electrode sodium metal battery adopts an ether-based electrolyte system.

7. The application of the negative electrode current collector of a sodium metal battery without a negative electrode according to claim 6, characterized in that, The preparation method of the ether electrolyte system is as follows: weigh NaPF6 in a glove box where the water and oxygen content are both below 1 ppm using a balance of 0.01%, dissolve it in diethylene glycol dimethyl ether, and stir on a magnetic stirrer until the solution is completely clear.

Images