A method for preparing a dual-salt-based anode-free sodium metal battery

Abstract

The application discloses a preparation method of an anode-free sodium metal battery based on double salt, relates to the technical field of sodium battery preparation, and comprises the following steps: MnO2 nanowires are coated with phenolic resin, carbonization is performed to obtain MnO2 nanowire templates, and the MnO2 nanowire templates are etched by using concentrated hydrochloric acid to remove the templates and obtain mesoporous carbon tubes; an electrolyte containing a NaBF4 additive is prepared; the mesoporous carbon tubes, conductive carbon black and a binder are mixed in proportion, and the mixed slurry is uniformly coated on the surface of treated copper foil, vacuum drying is performed to obtain a pole piece; the electrolyte is added after the positive electrode shell, the pole piece and the separator are placed in sequence, the negative electrode shell is capped on the top and compacted, and a prepared battery is obtained. The mesoporous carbon tube is used as a sodium carrier, more and more effective paths are provided for the surface diffusion of sodium ions, the ion and electron transmission rate is improved, the deposition and stripping reversibility of sodium is improved by adding a small amount of NaBF4, the cost is low, the safety is high, and the energy density of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium battery preparation, in particular to a preparation method of an anode-free sodium metal battery based on double salts. BACKGROUND

[0002] An anode-free sodium metal (AFNB) battery has higher energy density and lower safety hazards because there is no metal sodium anode in the initial battery manufacturing process, and is the most promising candidate to surpass the sodium metal battery. In the AFNB, the "true anode" is formed in-situ electrochemically during the first charging process; the Na formed on the anode side is encapsulated in an environment without air exposure, and since the active Na+ comes entirely from the positive electrode material, no Na is wasted. This not only simplifies the manufacturing process, but also improves the energy density of the AFNB. However, during the charging and discharging process of the AFNB, the active Na is consumed, and due to the large volume change of the deposited Na metal, and the high solubility of the SEI components (such as sodium alkyl carbonate), it is easy to cause the destruction and reconstruction of the solid electrolyte interface (SEI). This will cause rapid capacity decay. During repeated plating and stripping, uneven deposition morphology will also cause "dead Na", resulting in low coulombic efficiency (CE).

[0003] In view of these problems of the AFNB, different strategies have been used to deal with them, such as positive electrode pre-sodiumization, artificial SEI, current collector modification, etc. However, these strategies only solve the problem from a single perspective, and the macroscopic battery system needs a more systematic solution to optimize it, especially in such a system as the anode-free metal battery, which is extremely harsh in terms of active sodium consumption, and more "multi-party cooperation" is needed to effectively improve the battery performance. SUMMARY

[0004] In order to overcome the above-mentioned problems existing in the prior art, the application provides a preparation method of an anode-free sodium metal battery based on double salts.

[0005] The technical scheme adopted by the application to solve the technical problems is: a preparation method of an anode-free sodium metal battery based on double salts, comprising the following steps:

[0006] Step 1: preparing mesoporous carbon tubes: phenolic resin coating and carbonization are performed on MnO2 nanowires to obtain MnO2 nanowire templates, and the mesoporous carbon tubes are obtained by removing the MnO2 nanowire templates through concentrated hydrochloric acid etching;

[0007] Step 2: preparing an electrolyte containing a NaBF4 additive;

[0008] Step 3, anode-free sodium metal battery assembly: the mesoporous carbon tube, conductive carbon black and binder obtained in step 1 are mixed in proportion, and the mixed slurry is put into a ball mill to uniformly coat the surface of the treated copper foil, and the copper foil is vacuum dried to obtain a pole piece; after the positive shell, the pole piece and the separator are placed in order, the appropriate amount of electrolyte obtained in step 2 is added, and the negative shell is capped and compacted to obtain an assembled battery.

[0009] The preparation method of the above-mentioned anode-free sodium metal battery based on double salt, wherein the preparation process of the MnO2 nanowire in step 1 is as follows: MnSO4·H2O, KClO3 and CH3COOK are dissolved in deionized water, acetic acid is added, the mixed solution is poured into a reaction kettle, and a hydrothermal reaction is carried out at 160 DEG C, and the sample after reaction is extracted and washed to obtain MnO2 nanowire.

[0010] The preparation method of the above-mentioned anode-free sodium metal battery based on double salt, wherein the specific process of the MnO2 nanowire template preparation in step 1 is as follows: the MnO2 nanowire is dispersed in a mixture of ethanol and deionized water, tetrapropyl silane is added, formaldehyde, resorcinol and ethylenediamine are sequentially added after a certain interval, stirring is carried out at 30 DEG C for 24 hours, and after centrifugal washing and drying, carbonization is carried out at 800 DEG C in an argon atmosphere.

[0011] The preparation method of the above-mentioned anode-free sodium metal battery based on double salt, wherein step 2 is specifically as follows: NaBF4 is weighed in a glove box and transferred to a clean sample bottle with weighing paper, NaPF6 reference electrolyte is added, and the mixture is placed on a stirring table to be fully dissolved and uniformly mixed.

[0012] The preparation method of the above-mentioned anode-free sodium metal battery based on double salt, wherein the amount of the electrolyte added in step 3 is 35 microliters.

[0013] The preparation method of the above-mentioned anode-free sodium metal battery based on double salt, wherein the mesoporous carbon tube, conductive carbon black and binder are mixed in proportion, and then ultrapure water and ethanol are added.

[0014] The present application has the advantages that the present application only consumes sodium in the positive electrode and the electrolyte and stores in the form of metal, has low cost, high safety and is beneficial to improve the energy density of the battery; NaBF4 is used as an electrolyte additive, BF4 -The weakly coordinated anion, on the one hand, the weak coordination bond leads to improved solubility and reduced lattice energy. On the other hand, the weak coordination will reduce the ion pair, which is conducive to the formation of a loose solvation shell, and is conducive to the subsequent desolvation process. Finally, the favorable CEI / SEI is formed on the positive / negative electrode interface. In the current collector design, the hollow carbon tube Meso-CNT with ordered open mesoporous channels is used as a sodium carrier to improve the ion and electron transmission rate and provide a large number of effective paths for the surface diffusion of sodium ions. The anode-free sodium metal battery of the application can be stably cycled more than 200 cycles under the condition of poor sodium or even no sodium, and the capacity retention rate is more than 80%. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Fig. 1 is a schematic diagram of the morphology of the mesoporous carbon tube prepared in the application, wherein (a) is a SEM image of a single mesoporous carbon tube, (b) is a cross-sectional SEM image of the mesoporous carbon tube, (c) is a transmission electron microscope image of the mesoporous carbon tube, and (d) is a selected area electron diffraction image of the carbon tube;

[0016] Figure 2 Fig. 3 is a schematic diagram of the cycle performance of the symmetric battery of the application;

[0017] Figure 3 Fig. 4 is a schematic diagram of the charge-discharge curve of the full battery of the application;

[0018] Figure 4 Fig. 5 is a schematic diagram of the cycle performance of the full battery of the application. DETAILED DESCRIPTION

[0019] In order for those skilled in the art to better understand the technical solutions of the application, the application will be described in detail below in combination with the drawings and specific embodiments.

[0020] The embodiment discloses a preparation method of an anode-free sodium metal battery based on double salt. In the electrolyte design, double salt (NaPF6 / NaBF4) is used on the basis of ether solvent to simultaneously improve the positive / negative electrolyte interface. In the current collector design, hollow carbon tube (Meso-CNT) with ordered open mesoporous channels is used as a sodium carrier to improve the ion and electron transmission rate and provide a large number of effective paths for the surface diffusion of sodium ions. Finally, in the full battery composed of the Prussian blue (PB) positive electrode, it can be stably cycled more than 200 cycles (the capacity retention rate is more than 80%) under the condition of poor sodium or even no sodium. The specific steps are as follows.

[0021] Step 1: Preparation of mesoporous carbon tube (Meso-CNT).

[0022] 676 mg of MnSO4·H2O, 858 mg of KClO3, and 687 mg of CH3COOK were dissolved in 60 mL of deionized water, and then 3.2 mL of acetic acid was added. The mixture was poured into a reaction vessel and subjected to hydrothermal reaction at 160 °C for 8 h. After filtration and washing, the resulting sample yielded MnO2 nanowires. 0.17 g of MnO2 nanowires were dispersed in a mixture of 30 mL of ethanol and 70 mL of deionized water, and 7 mL of tetrapropoxysilane (TPOS) was added. After about ten minutes, 0.3 mL of formaldehyde, 0.2 g of resorcinol, and 0.3 mL of ethylenediamine were added sequentially to coat the nanowires with phenolic resin (RF). The mixture was stirred at 30 °C for 24 h, centrifuged, washed, dried, and then carbonized at 800 °C in a tube furnace under an argon atmosphere. The MnO2 nanowire template was removed by etching with 1 M concentrated hydrochloric acid. The morphology of the mesoporous carbon nanotubes prepared in this example is as follows. Figure 1 As shown, characterization by SEM and TEM reveals that, according to Figure 1 Figures a and b show that the diameter of the mesoporous carbon nanotubes is approximately 300 nm, and the wall thickness is approximately 50 nm. According to... Figure 1 As shown in C and D, no obvious lattice fringes were observed in the high-resolution transmission electron microscopy (HRTEM) images, and no obvious diffraction rings were found in the selected area electron diffraction. Therefore, it can be preliminarily determined that the material is in an amorphous state.

[0023] Step 2: Preparation of electrolyte containing NaBF4 additive.

[0024] Weigh 0.22 g of NaBF4 in a glove box and transfer it to a clean sample vial using weighing paper. Add 2 mL of reference electrolyte (a homogeneous and stable electrolyte system formed by dissolving sodium hexafluorophosphate (NaPF6) at a concentration of 1 mol / L in diethylene glycol dimethyl ether solvent). Place the vial on a stirring table to allow it to dissolve and mix thoroughly.

[0025] Step 3: Assemble the anode-free sodium metal battery.

[0026] Current collector: Commercial copper foil is cut into round pieces using an air press, soaked in ethanol and acetone respectively and ultrasonically treated to remove surface impurities and dust. After removing the ethanol and acetone solutions, the pieces are placed in an oven for vacuum drying and ready for use.

[0027] Electrode: Mix Meso-CNT, conductive carbon black (super P), and binder CMC in a certain proportion. Add a few drops of ultrapure water and ethanol as needed. Place the mixed slurry into a planetary ball mill and ball mill for 6 hours. After removing the slurry, coat it evenly onto the surface of copper foil and place it in a vacuum drying oven at 60 °C overnight.

[0028] Assembly of button cells: With the water and oxygen content in the glove box below 1 ppm, place the dried stainless steel electrode shells, electrodes, and separators into the glove box, arranging them in the order of positive electrode shell, electrodes, and separator. Add 35 μL of electrolyte, and finally place the negative electrode shell on top, pressing it firmly with a tablet press. After transferring the assembled batteries out of the glove box, they are placed on a Newway battery rack for testing.

[0029] The performance test results of the assembled battery are as follows: Figures 2-4 As shown, from Figure 2 It is known that symmetrical batteries can stably cycle for more than 3000 hours. Figures 3-4 As can be seen, after forming a full cell with the Prussian blue cathode, the charge-discharge curve shows that there is almost no significant capacity decay in the first three cycles. The full cell retains 85% of its capacity after 100 cycles and still retains 79% of its capacity after 200 cycles.

[0030] 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 spirit, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a dual-salt based anode-free sodium metal battery, characterized in that, It comprises the following steps: Step 1, preparation of mesoporous carbon tube: phenolic resin coating, carbonization of MnO2 nanowire to obtain MnO2 nanowire template, and removal of mesoporous carbon tube by etching with concentrated hydrochloric acid on the MnO2 nanowire template; Step 2, preparation of electrolyte containing NaBF4 additive; Step 3, anode-free sodium metal battery assembly: mixing the mesoporous carbon tube, conductive carbon black and binder obtained in step 1 in proportion, putting the mixed slurry into a ball mill, and uniformly coating the surface of the treated copper foil after spheroidizing, and vacuum drying the copper foil to obtain an electrode sheet; after placing the positive shell, electrode sheet and separator in order, adding an appropriate amount of electrolyte obtained in step 2, and compacting the negative shell on the top, a complete battery is obtained; The specific process of preparing the MnO2 nanowire template in step 1 is as follows: disperse MnO2 nanowires in a mixture of ethanol and deionized water, add tetrapropyl silane, then add formaldehyde, resorcinol and ethylenediamine at intervals, stir at 30℃ for 24 hours, centrifuge, wash and dry, and then carbonize at 800℃ in an argon atmosphere. The specific process of step 2 is as follows: weigh NaBF4 in a glove box and transfer it to a clean sample bottle with weighing paper, add NaPF6 reference electrolyte, and place it on a stirring table to fully dissolve and mix.

2. The method for preparing an anode-free sodium metal battery based on dual salts according to claim 1, characterized in that, The preparation process of MnO2 nanowires in step 1 is as follows: dissolve MnSO4・H2O, KClO3 and CH3COOK in deionized water, add acetic acid, pour the mixture into a reaction kettle, and perform hydrothermal reaction at 160℃, then perform suction filtration and washing on the reacted sample to obtain MnO2 nanowires.

3. The method for preparing an anode-free sodium metal battery based on dual salts according to claim 1, characterized in that, The amount of electrolyte added in step 3 is 35 microliters.

4. The method for preparing an anode-free sodium metal battery based on dual salts according to claim 1, characterized in that, In step 3, after mixing the mesoporous carbon tube, conductive carbon black and binder in proportion, add ultrapure water and ethanol.

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