Modified diaphragm applied to low-temperature negative-electrode-free sodium metal battery as well as preparation method and application of modified diaphragm

Abstract

The invention provides a modified diaphragm applied to a low-temperature negative-electrode-free sodium metal battery as well as a preparation method and application of the modified diaphragm, and relates to the technical field of negative-electrode-free sodium batteries. According to the invention, sodium vanadate is modified as a diaphragm coating, so that the mechanical stability and thermal stability of the diaphragm are improved, and the modified diaphragm also has the following advantages in other aspects: firstly, the modified layer has good electrolyte wettability, and can promote the uniformity of Na < + > flux, thereby inhibiting the formation of sodium dendrites; in addition, sodium vanadate has a larger interlayer spacing # imgabs0 #, provides a wider diffusion channel for Na < + >, is beneficial to improving the ion transmission rate, and is particularly beneficial to sodium ion diffusion under a low-temperature condition. And finally, the reversible oxidation reduction of V < 5 + > / V < 4 + > can reduce the migration potential barrier of Na < + >, so that a relatively high ion diffusion rate can still be kept at a low temperature, good dynamic performance is ensured, and the negative-electrode-free sodium metal battery can also stably work in a low-temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium batteries, and in particular to a modified diaphragm applied to a low-temperature negative electrode-free sodium metal battery, and a preparation method and application thereof. Background Art

[0002] In the past decade, the demand for low-cost, high-energy electrochemical storage devices has continued to grow. Sodium metal batteries have greatly promoted the development of rechargeable sodium metal battery systems due to their high theoretical energy density and low redox potential. However, sodium metal batteries also have some problems, such as the safety of direct use of sodium metal, the growth of sodium metal dendrites, the uncontrollable solid electrolyte membrane (SEI) formed by sodium metal and electrolyte, and the common use of sodium metal sheets directly as negative electrodes in battery systems, which limits the further improvement of their energy density. The negative electrode of the negative electrode-free sodium metal battery system uses copper foil or aluminum foil current collector to avoid the use of sodium metal, which improves the energy density of the battery on the one hand and improves the safety of the battery on the other.

[0003] However, during the operation of anode-free sodium metal batteries in low-temperature environments, the interfacial reaction kinetics are poor and the ion transport is slow, resulting in the formation of sodium metal dendrites and uneven deposition of sodium metal, causing the battery capacity to decay rapidly. Uneven sodium metal can also cause the shedding of sodium metal during repeated electroplating / stripping processes, resulting in the loss of active sodium metal, leading to lower coulombic efficiency (CE). This limits the practical application of low-temperature anode-free sodium metal batteries. As an important component of the battery, the diaphragm plays an important role in sodium ion transport, electrolyte solvation structure, and dendrite suppression. Therefore, designing an excellent modified diaphragm is critical to achieving low-temperature operation of anode-free sodium metal.

[0004] Currently, for negative electrode-free sodium batteries, Chinese patent publication number CN119275493A discloses negative electrode-free sodium metal batteries and their modified diaphragms, as well as the preparation and application of modified diaphragms. The modified diaphragms are prepared by magnetron sputtering titanium nitride, zinc nitride, and gallium nitride on the diaphragms. This preparation method has relatively high equipment requirements and high costs. In addition, the modified diaphragms are only suitable for maintaining battery operation at room temperature. The influence of the modified diaphragms on the solvation structure of the electrolyte and the performance of the battery at low temperatures need to be explored.

[0005] In addition, although there are related patents on sodium titanate as a diaphragm coating (CN108258172 A, CN108695476A), it is mainly used for high-temperature lithium batteries and has not been applied to low-temperature negative-electrode-free sodium metal batteries. Therefore, the present invention designs a modified diaphragm for low-temperature negative-electrode-free sodium metal batteries and its preparation method and application. Summary of the invention

[0006] The present invention provides a modified diaphragm for low-temperature negative electrode-free sodium metal battery and a preparation method and application thereof, the purpose of which is to solve the above-mentioned problems in the background technology.

[0007] In order to achieve the above-mentioned purpose, the embodiments of the present invention provide a modified diaphragm for low-temperature negative electrode-free sodium metal battery and its preparation method and application. The present invention uses sodium vanadate for modification as the diaphragm coating, which not only improves the mechanical stability and thermal stability of the diaphragm, but also has the following other advantages: first, the modified layer has good electrolyte wettability, which can promote Na + The uniformity of the flux can inhibit the formation of sodium dendrites. In addition, sodium vanadate has a larger interlayer spacing. for Na + Providing a wider diffusion channel is beneficial to improving the ion transmission rate, especially beneficial to the diffusion of sodium ions under low temperature conditions. 5+ / V 4+ The reversible redox reaction can reduce Na + The migration barrier enables the ion diffusion rate to remain high at low temperatures, thereby ensuring good kinetic performance, and the negative electrode-free sodium metal battery can also work stably in low temperature environments.

[0008] An embodiment of the present invention provides a modified diaphragm for low-temperature negative electrode-free sodium metal battery, comprising a base film and a sodium vanadate composite material coating coated on the surface of the base film;

[0009] The sodium vanadate composite material is prepared by mixing sodium vanadate and a binder in a certain proportion and grinding them, and then adding N-methylpyrrolidone.

[0010] Preferably, the base film comprises at least one of glass fiber, polydimethylsiloxane, polyimide, polypropylene PP, and polyethylene PE, and has a thickness of 10 to 200 μm.

[0011] Preferably, the binder includes at least one of polyvinylidene fluoride PVDF, polyacrylic acid PAA, polytetrafluoroethylene PTFE, and carboxymethyl cellulose CMC.

[0012] Preferably, the coating has a thickness of 2 to 20 μm.

[0013] Preferably, the mass ratio of the sodium vanadate to the binder is at least one of 9:1, 8:2, and 7:3.

[0014] Based on an overall concept of the invention, an embodiment of the present invention provides a method for preparing the above-mentioned modified diaphragm, wherein sodium vanadate and a binder are mixed and ground in proportion, a certain amount of N-methylpyrrolidone is added to form a slurry, the slurry is coated on a base film, and the modified diaphragm is obtained by drying.

[0015] Preferably, the drying is vacuum drying, the drying temperature is 60-120° C., and the time is 8-12 hours.

[0016] Preferably, the coating method includes at least one of gravure roller coating, dip coating, narrow coating or spray coating.

[0017] The embodiments of the present invention also provide the use of the modified diaphragm or the modified diaphragm obtained by the above-mentioned preparation method in a low-temperature negative electrode-free sodium metal battery.

[0018] Preferably, the negative electrode-free sodium metal battery further comprises a negative electrode current collector and a positive electrode active material; the positive electrode active material is selected from at least one of oxides, polyanions, Prussian blue, and organic positive electrode materials.

[0019] Mechanism description

[0020] Since sodium vanadate has a larger interlayer spacing for Na + Providing a wider diffusion channel is beneficial to improving the ion transmission rate, especially the diffusion of sodium ions under low temperature conditions. In addition, V 5+ / V 4+ The reversible redox reaction can reduce Na + The migration barrier of NaTiO2 can maintain a high ion diffusion rate at low temperature, thus ensuring good kinetic performance. + Migration is limited, and performance decreases significantly at low temperatures. Although sodium molybdate has good redox activity, its interlayer spacing is still not as large as that of sodium vanadate, resulting in poorer performance at low temperatures than sodium vanadate. + The migration is not only limited by the small interlayer spacing, but also by the Zr 4+ The lack of redox activity and poor electronic conductivity at low temperatures lead to their poor performance at low temperatures.

[0021] The above scheme of the present invention has the following beneficial effects:

[0022] (1) The present invention uses sodium vanadate to modify and prepare a diaphragm. The diaphragm can promote the migration of ions and the uniform deposition of sodium metal due to its excellent ion conductivity. In addition, sodium vanadate can provide additional sodium ions to improve the coulombic efficiency of the battery and extend the cycle life of the battery. The present invention compares the performance of sodium vanadate, sodium zirconate, sodium molybdate and sodium titanate in a negative electrode-free sodium metal battery under low temperature conditions. Compared with the coating modified by sodium titanate, sodium zirconate and sodium molybdate, the coating material modified by sodium vanadate in the present invention shows better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 : is a SEM image of the diaphragm of the embodiment of the present invention and the comparative example; wherein, Figure 1 a is the SEM image of the diaphragm of Comparative Example 1, Figure 1 b is a SEM image of the diaphragm of Example 1;

[0025] Figure 2 : is a performance diagram of the diaphragm assembled battery of the embodiment of the present invention and the comparative example; wherein, Figure 2 a is the coulombic efficiency diagram of the membrane-assembled sodium||copper half-cell of Example 1 and Comparative Example 1 at room temperature; Figure 2 b is the cycling performance diagram of the Na||Na symmetric battery assembled with the membranes of Example 1 and the comparative example at room temperature. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0027] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0028] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0029] In view of the existing problems, the present invention provides a modified diaphragm for low-temperature negative electrode-free sodium metal battery and a preparation method and application thereof.

[0030] An embodiment of the present invention provides a modified diaphragm for low-temperature negative electrode-free sodium metal battery, comprising a base film and a sodium vanadate composite material coating coated on the surface of the base film;

[0031] The sodium vanadate composite material is prepared by mixing sodium vanadate and a binder in a certain proportion and grinding them, and then adding N-methylpyrrolidone.

[0032] Preferably, the base film comprises at least one of glass fiber, polydimethylsiloxane, polyimide, polypropylene PP, and polyethylene PE, and has a thickness of 10 to 200 μm.

[0033] Preferably, the binder includes at least one of polyvinylidene fluoride PVDF, polyacrylic acid PAA, polytetrafluoroethylene PTFE, and carboxymethyl cellulose CMC.

[0034] Preferably, the coating has a thickness of 2 to 20 μm.

[0035] Preferably, the mass ratio of the sodium vanadate to the binder is at least one of 9:1, 8:2, and 7:3.

[0036] Based on an overall concept of the invention, an embodiment of the present invention provides a method for preparing the above-mentioned modified diaphragm, wherein sodium vanadate and a binder are mixed and ground in proportion, a certain amount of N-methylpyrrolidone is added to form a slurry, the slurry is coated on a base film, and the modified diaphragm is obtained by drying.

[0037] Preferably, the drying is vacuum drying, the drying temperature is 60-120° C., and the time is 8-12 hours.

[0038] Preferably, the coating method includes at least one of gravure roller coating, dip coating, narrow coating or spray coating.

[0039] The embodiments of the present invention also provide the use of the modified diaphragm or the modified diaphragm obtained by the above-mentioned preparation method in a low-temperature negative electrode-free sodium metal battery.

[0040] Preferably, the negative electrode-free sodium metal battery further comprises a negative electrode current collector and a positive electrode active material; the positive electrode active material is selected from at least one of oxides, polyanions, Prussian blue, and organic positive electrode materials.

[0041] The following is a detailed description through specific embodiments.

[0042] Example 1

[0043] A method for preparing a modified diaphragm for low-temperature negative electrode-free sodium metal batteries comprises mixing sodium vanadate and PVDF in a mass ratio of 9:1, grinding them, adding an appropriate amount of NMP to form a coating slurry, coating one side of the slurry on a commercial diaphragm with a coating thickness of 5 μm, and baking the diaphragm in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0044] Example 2

[0045] A method for preparing a modified diaphragm for low-temperature negative electrode-free sodium metal batteries comprises mixing sodium vanadate and PVDF in a mass ratio of 9:1, grinding them, adding an appropriate amount of NMP to form a coating slurry, coating one side of the slurry on a commercial diaphragm with a coating thickness of 2 μm, and baking the diaphragm in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0046] Example 3

[0047] A method for preparing a modified diaphragm for low-temperature negative electrode-free sodium metal batteries comprises mixing sodium vanadate and PVDF in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 10 μm, and baking the diaphragm in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0048] Example 4

[0049] A method for preparing a modified diaphragm for low-temperature negative electrode-free sodium metal batteries comprises mixing sodium vanadate and PVDF in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 20 μm, and baking the diaphragm in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0050] Example 5

[0051] A method for preparing a modified diaphragm for a low-temperature negative electrode-free sodium metal battery comprises the following steps: mixing sodium vanadate and PAA in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0052] Example 6

[0053] A method for preparing a modified diaphragm for low-temperature negative electrode-free sodium metal batteries comprises the following steps: mixing sodium vanadate and PTFE in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of alcohol to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0054] Example 7

[0055] A method for preparing a modified diaphragm for a low-temperature negative electrode-free sodium metal battery comprises the following steps: mixing sodium vanadate and CMC in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of water to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 h to obtain the modified diaphragm.

[0056] Comparative Example 1

[0057] In this comparative example, an unmodified commercial diaphragm was used.

[0058] Comparative Example 2

[0059] A method for preparing a modified diaphragm comprises mixing sodium zirconate and PVDF in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 hours to obtain the modified diaphragm.

[0060] Comparative Example 3

[0061] A method for preparing a modified diaphragm comprises mixing sodium titanate and PVDF in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 hours to obtain the modified diaphragm.

[0062] Comparative Example 4

[0063] A method for preparing a modified diaphragm comprises mixing sodium molybdate and PVDF in a mass ratio of 9:1, grinding the mixture, adding an appropriate amount of NMP to form a coating slurry, coating the mixture on one side of a commercial diaphragm with a coating thickness of 5 μm, and baking the mixture in a vacuum oven at 80° C. for 12 hours to obtain the modified diaphragm.

[0064] Performance testing and result analysis:

[0065] 1. The modified diaphragms of Comparative Example 1 and Example 1 were subjected to SEM analysis, and the results are as follows: Figure 1 As shown, the sodium vanadate of Example 1 is loaded on the base membrane in the form of nanorods, which is beneficial to the transmission of ions.

[0066] 2. Figure 2 a is the coulombic efficiency diagram of the sodium||copper half-cell assembled with the corresponding diaphragm of Example 1 of the present invention and Comparative Example 1 at room temperature, with 1 mol / L NaPF6 in diethylene glycol dimethyl ether (G2) as the electrolyte. It can be seen that after 300 cycles, the half-cell assembled with the diaphragm of Example 1 can still operate stably, and the coulombic efficiency is stable at about 99.5%. This indicates that the modified diaphragm of Example 1 can promote uniform deposition and stripping of sodium metal. Figure 2 b is the cycle performance diagram of the Na||Na symmetric battery assembled with the diaphragms of Example 1 and Comparative Example 1 at room temperature. -2 , the discharge capacity is 1 mAh cm -2 It can be seen that the symmetrical battery using the separator of Example 1 can run for 500 hours, while the separator of Comparative Example 1 can only run for 250 hours. This shows that the modified separator of the present invention inhibits the growth of sodium dendrites and improves its cycle life.

[0067] 3. The modified diaphragms prepared in Examples 1 to 7 and the diaphragms in Comparative Examples 1 to 4 were applied to sodium metal||copper metal half-cells. The coulombic efficiencies of the half-cells are shown in Table 1 below:

[0068] Table 1

[0069] -20℃Na||Cu Coulombic efficiency (%) Example 1 99.7 Example 2 97.2 Example 3 96.3 Example 4 95.6 Example 5 99.5 Example 6 99.3 Example 7 99.6 Comparative Example 1 85.2 Comparative Example 2 88.5 Comparative Example 3 90.3 Comparative Example 4 91.7

[0070] It can be seen from Table 1 that after constructing a sodium vanadate coating on the commercial diaphragm, the coulombic efficiency of the half-cell at low temperature is improved. At the same time, the coulombic efficiency is higher than that of the sodium molybdate, sodium titanate and sodium zirconate modified diaphragms, indicating that the sodium vanadate coating can improve the sodium metal deposition / stripping behavior at low temperatures.

[0071] 4. The diaphragms of Examples 1 to 7 and Comparative Examples 1 to 4 are used as diaphragms for low-temperature negative electrode-free sodium metal batteries. The positive electrode material of the negative electrode-free sodium metal battery is sodium vanadium phosphate, the electrolyte is 1 mol / L NaPF6 in diethylene glycol dimethyl ether (G2), and the negative electrode current collector is carbon-coated aluminum foil. Table 2 shows the first cycle coulomb efficiency and capacity retention rate of 200 cycles of the negative electrode-free sodium metal battery using various embodiments and comparative examples at -20°C.

[0072] Table 2

[0073]

[0074] It can be seen from Table 2 that the diaphragm of Example 1 exhibits higher coulombic efficiency and better cycle stability in the low-temperature negative electrode-free sodium metal battery, which confirms that the sodium vanadate coating promotes the migration of sodium ions under low temperature conditions and is beneficial to the uniform deposition and stripping of sodium metal.

[0075] It can be seen from Tables 1 and 2 that when the coating thickness is 5 μm, the electrochemical performance of the battery is better. The type of binder has no significant effect on the coulombic efficiency of the half-cell when operating at low temperature, and the first cycle coulombic efficiency and cycle stability of the negative electrode-free sodium battery when operating at low temperature, which shows that the present invention has flexibility in the selection of binders.

[0076] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified diaphragm for low-temperature negative electrode-free sodium metal battery, characterized in that: It includes a base film and a sodium vanadate composite material coating coated on the surface of the base film; The sodium vanadate composite material is prepared by mixing sodium vanadate and a binder in a certain proportion and grinding them, and then adding N-methylpyrrolidone.

2. The modified diaphragm according to claim 1, characterized in that: The base film comprises at least one of glass fiber, polydimethylsiloxane, polyimide, polypropylene and polyethylene, and has a thickness of 10 to 200 μm.

3. The modified diaphragm according to claim 1, characterized in that: The binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, and carboxymethyl cellulose.

4. The modified diaphragm according to claim 1, characterized in that: The coating thickness is 2-20 μm.

5. The modified diaphragm according to claim 1, characterized in that: The mass ratio of the sodium vanadate to the binder is at least one of 9:1, 8:2, and 7:

3.

6. The method for preparing a modified diaphragm according to any one of claims 1 to 5, characterized in that: Sodium vanadate and a binder are mixed and ground in proportion, a certain amount of N-methylpyrrolidone is added to form a slurry, the slurry is coated on a base film, and the modified diaphragm is obtained by drying.

7. The preparation method according to claim 6, characterized in that: The drying is vacuum drying, the drying temperature is 60-120° C., and the time is 8-12 hours.

8. The preparation method according to claim 6, characterized in that: The coating method includes at least one of gravure roller coating, dip coating, narrow coating or spray coating.

9. Use of the modified diaphragm according to any one of claims 1 to 5 or the modified diaphragm obtained by the preparation method according to any one of claims 6 to 8 in a low-temperature negative electrode-free sodium metal battery.

10. The use according to claim 9, characterized in that: The negative electrode-free sodium metal battery also includes a negative electrode current collector and a positive electrode active material; the positive electrode active material is selected from at least one of oxides, polyanions, Prussian blue, and organic positive electrode materials.

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