Preparation method and application of negative current collector of sodium metal battery

Abstract

The invention relates to the technical field of sodium metal battery negative electrode materials, and particularly provides a preparation method and application of a sodium metal battery negative electrode current collector. BiF3 buffer layer modification is carried out on the copper current collector through a simple coating method, the sodium ion conductivity can be improved through the conversion reaction of non-metallic elements and sodium and the alloying reaction of metallic elements and sodium, the active area of sodium deposition can be increased, and uniform deposition of sodium is promoted, so that dendritic crystal growth is inhibited. The average coulombic efficiency of the assembled sodium metal half cell is up to 99.78% even under the current density of 2mA / cm < 2 > and the high deposition capacity of 2mAh / cm < 2 >, so that the safety and the cycling stability of the sodium metal half cell are improved. In addition, the method is relatively simple to operate and relatively low in cost, and has the possibility of large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for sodium metal batteries, and in particular to the preparation and application of a negative electrode current collector for sodium metal batteries. Background Art

[0002] Due to its high theoretical specific capacity, low redox potential and low cost, it has become an ideal candidate material. In the negative electrode of sodium metal batteries, the current collector plays a key role. It not only provides an electron transfer path, but also directly affects the performance and stability of the battery. The most commonly used current collector materials for sodium metal batteries are metal foils or metal foams, such as copper / aluminum foil and foam copper / aluminum. Copper foil has good conductivity, can effectively promote the deposition and stripping process of sodium, and has high mechanical strength, making it suitable for use in the negative electrode of sodium metal batteries.

[0003] In current research, the high specific surface area of ​​the three-dimensional current collector can effectively reduce the local current density and improve the cycling stability of sodium metal. However, during the repeated deposition / stripping of sodium, the high surface area will lead to excessive consumption of sodium and electrolyte and reduced Coulomb efficiency. Therefore, it is necessary to modify the surface of the current collector with a buffer layer. The buffer layer is formed by the conversion reaction of non-metallic elements with sodium and the alloying reaction of metal elements with sodium, which can not only improve the sodium ion conductivity, but also increase the active area of ​​sodium deposition and improve the cycle life. Summary of the invention

[0004] The present invention provides a method for preparing a negative electrode current collector for a sodium metal battery and application thereof, aiming to solve the problems of poor safety and long-term cycle performance of the existing negative electrode current collector for a sodium metal battery caused by uneven charge distribution and uneven sodium deposition / stripping.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a negative electrode current collector of a sodium metal battery comprises modifying a copper foil with a buffer layer BiF3.

[0007] Further, the following steps are included:

[0008] (1) Cut the commercial copper foil into a size of 8cm*20cm;

[0009] (2) Cleaning the copper foil in an ethanol or acetone solution using ultrasonic waves and drying the copper foil;

[0010] (3) Preparation of BiF3 material;

[0011] (4) The BiF3 material prepared in step (3) is coated on the bare copper foil dried in step (2) by an electrode coating machine, and then placed in a vacuum drying oven for drying, thereby obtaining a copper foil modified with a buffer layer.

[0012] Furthermore, the slurry ratio of the BiF3 modified layer is 5:4:1, 7:2:1, 9:0.5:05, and the time is 10 to 24 hours, preferably 24 hours.

[0013] Furthermore, BiF3 accounts for 50%, 70%, and 90% respectively, Super P accounts for 40%, 20%, and 5% respectively, and PVDF accounts for 10%, 70%, and 5% respectively. The coating buffer layer in which BiF3 accounts for 70% is preferably selected.

[0014] Furthermore, a proper amount of N-methylpyrrolidone (NMP) was added.

[0015] Furthermore, the drying time of the copper foil coated with the BiF3 modification layer is 10 to 24 hours, preferably 12 hours.

[0016] The copper foil obtained by the above method is applied to sodium metal batteries, which can significantly improve the coulombic efficiency of the half-cell, as well as the safety and cycle stability of the full battery.

[0017] Furthermore, the sodium metal half-cell uses a commercial sodium metal disc as the positive electrode and the electrolyte is 1M-NaPF6 inDIGLYME.

[0018] Furthermore, the sodium metal full battery uses commercial sodium vanadium phosphate as the positive electrode and deposits 3 mAh / cm 2 Sodium BiF3 modified copper foil was used as negative electrode.

[0019] The beneficial effects of the present invention are:

[0020] The sodium metal battery negative electrode current collector of the present invention uses an in-situ conversion method to convert BiF3 into a Bi and NaF mixed ion / electron conduction interface buffer layer on the surface of the copper current collector. The NaF phase in the buffer layer is conducive to Na + conduction, so that Na + The flux is homogenized, which promotes uniform deposition / stripping of sodium and improves the coulombic efficiency of the battery; it also improves the interface dynamics, which can effectively improve the cycle stability of the battery.

[0021] The coating method adopted by the present invention is simple, low in cost and has the possibility of large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 For a sodium metal half-cell at a current density of 1 mA / cm 2 , surface capacity is 1mAh / cm 2 Coulomb efficiency diagram below;

[0023] Figure 2 For a sodium metal half-cell at a current density of 2 mA / cm 2, surface capacity is 2mAh / cm 2 Coulomb efficiency diagram below;

[0024] Figure 3 This is a test diagram of the cycle performance of a sodium metal full battery;

[0025] Figure 4 This is the SEM image of BiF3@Cu foil after 50 cycles;

[0026] Figure 5 This is the SEM image of Cu foil after 50 cycles. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0028] Example 1

[0029] Cut the commercial copper foil into 8cm*20cm size, put it into a beaker filled with ethanol and then put it into an ultrasonic cleaner for cleaning, then dry it to get a clean and dust-free bare copper foil. Then weigh the chemicals according to the ratio of 50% BiF3, 40% Super P, and 10% PVDF, with the weights of 0.25g, 0.2g, and 0.05g respectively, then add an appropriate amount of NMP, stir for several hours, coat it on the bare copper foil, and put it into a vacuum drying oven for 12 hours for drying. Cut the dried coated copper foil into 12mm discs, recorded as BiF3-5.

[0030] Example 2

[0031] Cut the commercial copper foil into 8cm*20cm size, put it into a beaker filled with ethanol and then put it into an ultrasonic cleaner for cleaning, then dry it to get a clean and dust-free bare copper foil. Then weigh the chemicals according to the ratio of BiF3 accounting for 70%, Super P accounting for 20%, and PVDF accounting for 10%, with the weights of 0.35g, 0.1g, and 0.05g respectively, then add an appropriate amount of NMP, stir for several hours, coat it on the bare copper foil, and put it into a vacuum drying oven for 12 hours for drying. Cut the dried coated copper foil into 12mm discs, recorded as BiF3-7.

[0032] Example 3

[0033] Cut the commercial copper foil into 8cm*20cm size, put it into a beaker filled with ethanol and then put it into an ultrasonic cleaner for cleaning, then dry it to get a clean and dust-free bare copper foil. Then weigh the chemicals according to the ratio of BiF3 accounting for 90%, Super P accounting for 5%, and PVDF accounting for 5%, with the weights of 0.45g, 0.025g, and 0.025g respectively, then add an appropriate amount of NMP, stir for several hours, coat it on the bare copper foil, and put it into a vacuum drying oven for 12 hours for drying. Cut the dried coated copper foil into 12mm discs. Recorded as BiF3-9.

[0034] BiF3-7 and copper foil were used to assemble sodium metal half-cells and sodium metal full-cells, respectively, and the electrochemical performance was tested. The battery shell used in the sodium metal half-cell was a 2032-type button cell, with BiF3-7 and copper foil as the working electrodes, respectively, and a commercial sodium metal disc as the counter electrode. The electrolyte was 1M-NaPF6 in DIGLYME, and the separator was D-type glass fiber. When assembling the sodium metal full-cell, commercial sodium vanadium phosphate was used as the positive electrode material, and the negative electrode was deposited with 3mAh / cm 2 Sodium metal BiF3-7 and bare copper foil.

[0035] The sodium metal half-cell assembled with BiF3-7 as the working electrode is denoted as BiF3@Cu foil, and the sodium metal half-cell with bare copper foil as the working electrode is denoted as Cu foil.

[0036] The full battery assembled by BiF3-7 copper foil deposited with sodium metal is denoted as Na∥∥BiF3@Cu foil, and the full battery assembled by bare copper foil deposited with sodium metal is denoted as Na∥∥Cu foil.

[0037] Figure 1 , 2 is the Coulomb efficiency diagram of the sodium metal half-cell at different current densities and different surface capacities.

[0038] It can be seen that at 1mA / cm 2 Current density, 1mAh / cm 2 Under the surface capacity, the coulombic efficiency of BiF3@Cu foil half-cell is very stable, and the average coulombic efficiency can reach 99.85%, which is much higher than that of Cu foil half-cell; even at 2mA / cm 2 Current density, 2mAh / cm 2 At high deposition capacity, the BiF3@Cu foil half-cell still cycles stably with a high average coulombic efficiency of 99.78%. It can be seen that the deposition / stripping effect of sodium on the copper foil coated with the BiF3 buffer layer is better, resulting in excellent and stable coulombic efficiency.

[0039] Figure 3The figure is a cycle performance diagram of a sodium metal full battery. The current density of the test is 1C (1C = 120mAh / g). It is not difficult to see that the sodium deposition on the copper foil modified with the BiF3 buffer layer is more uniform, making the full battery cycle performance of Na∥BiF3@Cu foil significantly better than that of Na∥Cu foil. This is due to the poor deposition and stripping effect of the bare copper foil. After the cycle, there is more and more "dead sodium" deposition on the bare copper foil, and the appearance of sodium dendrites, which eventually leads to battery failure.

[0040] BiF3-5 and BiF3-9 were tested and both had similar electrochemical properties to BiF3-7.

[0041] Figure 4 This is the SEM image of the BiF3@Cu foil half-cell after 50 cycles. It can be seen that the electrode surface remains flat without any dendrites, and sodium metal is evenly deposited on the BiF3 buffer layer. Figure 5 This is the SEM image of the Cu foil half-cell after 50 cycles. It can be seen that large and uneven sodium metal remains on the surface of the bare copper foil, which is the reason for the poor coulombic efficiency of the half-cell.

[0042] The sodium metal battery using the sodium metal battery negative electrode current collector of the present application has high safety, high coulombic efficiency and long cycle life.

Claims

1. A preparation and application of a negative electrode current collector for a sodium metal battery, characterized in that: The negative electrode current collector modified with BiF3 buffer layer was obtained by coating method.

2. The preparation of the negative electrode current collector of a sodium metal battery according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Clean the copper foil in ethanol or acetone solution using ultrasonic waves and dry the copper foil; (2) slurrying the prepared BiF3 active material; (3) The BiF3 active material slurry prepared in step (2) is coated on the bare copper foil dried in step (1) using an electrode coating machine, and then placed in a vacuum drying oven for drying, thereby obtaining a copper foil modified with a buffer layer.

3. The preparation of the negative electrode current collector of a sodium metal battery according to claim 1, characterized in that: The proportion of BiF3 active material during slurry preparation is 50% to 90%.

4. The preparation of the negative electrode current collector of a sodium metal battery according to claim 1, characterized in that: The slurry preparation time of BiF3 material is 12 to 24 hours.

5. The preparation of the negative electrode current collector of a sodium metal battery according to claim 1, characterized in that: The drying time after coating the BiF3 buffer layer is 12 to 24 hours.

6. The negative electrode current collector for a sodium metal battery and its application as claimed in claim 1 or the application of the negative electrode current collector for a sodium metal battery prepared by the preparation method according to any one of claims 2 to 5 in a sodium metal battery.

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