Wide-temperature-range electrolyte for sodium battery

Abstract

The invention relates to a wide temperature range electrolyte for a sodium battery. The electrolyte comprises a sodium salt and an organic solvent, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis (fluorosulfonyl) imide, sodium bis (trifluoromethylsulfonyl) imide, sodium trifluoromethanesulfonate, sodium difluoro (oxalato) borate and sodium bis (oxalato) borate, and the organic solvent is one or more of 1, 2-diethoxyethane or 1, 2-diethoxyethane. The invention relates to a combination of 1, 2-diethoxyethane and tetrahydrofuran. The wide-temperature-range electrolyte provided by the invention has the advantages of high boiling point, low freezing point, low viscosity, high ionic conductivity and the like, and the solvation effect of the electrolyte solvent and sodium ions is weak, so that the desolvation energy barrier of the sodium ions is reduced, the desolvation energy and charge transfer resistance of the sodium ions on a positive and negative electrode interface are reduced, and the service life of the electrolyte is prolonged. The electrolyte can significantly improve the high and low temperature charge and discharge performance and cycle performance of the sodium battery, and can safely and stably operate in a wide temperature range of-70-60 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a wide-temperature range electrolyte for sodium batteries. Background Art

[0002] Currently, lithium batteries are widely used in digital products, electric vehicles, energy storage and other fields, but lithium batteries have disadvantages such as high cost, general low-temperature performance, poor rate performance, low lithium resource reserves and uneven distribution. Sodium batteries have a similar working principle to lithium batteries, and sodium resources are abundant, widely distributed, cheap and easy to obtain, so sodium batteries are considered to be an ideal supplement to lithium batteries. Especially in the fields of energy storage and low-speed electric vehicles, sodium batteries tend to replace lithium batteries.

[0003] With the application of sodium batteries in high-latitude and high-altitude areas and areas with large temperature differences between day and night, the electrochemical performance of existing sodium batteries under low temperature conditions faces challenges. At present, conventional sodium battery electrolytes generally have the disadvantages of high freezing point, high viscosity, and slow desolvation, which are key factors limiting the low-temperature performance of sodium batteries. When the temperature drops to 0°C, the viscosity of conventional electrolytes increases significantly, the ionic conductivity decreases, and the electrochemical performance of the battery is greatly attenuated; when the temperature drops to -40°C, the solidification of conventional electrolytes will cause the battery to be unable to charge and discharge normally. In addition, the strong solvation effect between the organic solvents of conventional electrolytes and sodium ions makes the desolvation energy of sodium ions at the positive and negative electrode interfaces high, the desolvation is slow, and the kinetics are poor, which limits the electrochemical performance of sodium batteries at low temperatures.

[0004] Therefore, the development of sodium battery electrolytes that can work normally under a wide temperature range, and sodium batteries using such electrolytes, is of great significance for the promotion and application of sodium batteries in fields such as energy storage and low-speed electric vehicles. Summary of the invention

[0005] The purpose of the present invention is to provide a wide temperature range electrolyte for sodium batteries to solve the problems existing in the above-mentioned prior art and enable the sodium batteries to achieve stable charging and discharging and stable cycling within the temperature range of -70 to 60°C.

[0006] To achieve the above-mentioned purpose, the present invention provides the following scheme: The present invention provides a wide temperature range electrolyte, the electrolyte composition includes sodium salt and organic solvent, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bis(oxalatoborate), the organic solvent is 1,2-diethoxyethane, or a combination of 1,2-diethoxyethane and tetrahydrofuran.

[0007] Further, when the organic solvent is a mixed solvent of 1,2-diethoxyethane and tetrahydrofuran in a volume ratio of 1:5 to 5:1, preferably, the organic solvent is a mixed solvent of 1,2-diethoxyethane and tetrahydrofuran in a volume ratio of 1:3 to 3:1.

[0008] Further, the concentration of the sodium salt in the electrolyte is 0.1 to 3 mol / L. Preferably, the concentration of the sodium salt in the electrolyte is 0.5 to 1.5 mol / L.

[0009] The present application provides a sodium battery using the above-mentioned wide temperature range electrolyte, and the application temperature of the sodium battery is -70 to 60°C.

[0010] The sodium battery comprises: a positive electrode, a negative electrode, a separator and the above-mentioned wide temperature range electrolyte.

[0011] According to the above scheme, the positive electrode of the sodium battery is one or more of layered oxide type, polyanion type, Prussian blue type, Prussian white type and organic type sodium positive electrode. Preferably, the positive electrode is sodium vanadium phosphate.

[0012] According to the above scheme, the negative electrode is one or more of hard carbon, soft carbon, and metallic sodium.

[0013] According to the above solution, the separator is one or more of polypropylene film, polyethylene film and glass fiber.

[0014] The present invention discloses the following technical effects:

[0015] 1. The wide temperature range electrolyte provided by the present invention uses organic solvents 1,2-diethoxyethane and tetrahydrofuran with weak solvation characteristics, wherein 1,2-diethoxyethane is a chain ether, which combines with most sodium ions in the electrolyte, driving the sodium ions to be transported in the electrolyte, and at the same time, 1,2-diethoxyethane has a weak binding energy with sodium ions, that is, a weak solvation effect, so that the desolvation energy of sodium ions at the positive and negative electrode interfaces is low and the desolvation speed is fast, and the electrolyte has the advantages of high boiling point, low freezing point, low viscosity, high ionic conductivity, etc., which can significantly improve the charge and discharge performance and cycle stability of sodium batteries in a wide temperature range.

[0016] 2. The wide temperature range electrolyte provided by the present invention is obtained by compounding sodium salt and organic solvent. The sodium battery using the above electrolyte can form a stable SEI film rich in inorganic substances on the negative electrode side, isolate the adverse reactions at the electrode / electrolyte interface, improve the overall coulombic efficiency of the sodium battery, and enable the sodium battery to still have better electrochemical performance in a wide temperature range of -70 to 60°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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 labor.

[0018] Figure 1 This is an optical photograph of the electrolyte in Example 1 frozen at -70°C for 12 hours;

[0019] Figure 2 is the ionic conductivity of the electrolyte in Example 1 and Comparative Example 1 at different temperatures;

[0020] Figure 3 is the ionic conductivity of the electrolyte at different temperatures in Examples 2, 3 and Comparative Example 2;

[0021] Figure 4 is the cycle performance of the Na‖Na symmetric battery at -40°C in Example 4;

[0022] Figure 5 This is a scanning electron microscope photograph of the sodium metal surface of the Na‖Na symmetric battery in Example 4 after cycling at -40°C for 600 hours;

[0023] Figure 6 The cycling performance of the Na‖Na symmetric battery at -40°C in Comparative Example 3;

[0024] Figure 7 This is a graph of the 0.1C discharge specific capacity of the Na‖NVP battery in Example 5 at different temperatures;

[0025] Figure 8 The 0.1C charge and discharge curves of the Na‖NVP battery in Example 5 at different temperatures;

[0026] Fig. 9 The cycle performance diagram of the Na‖NVP battery in Example 5 at 0.5C cycle at different temperatures;

[0027] Fig.10 0.1C charge and discharge curve of the Na‖HC battery at -50°C in Example 6;

[0028] Fig.11 This is the cycle performance diagram of the Na‖HC battery in Example 6 at 1C cycle at -50°C. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] Example 1: Preparation of wide temperature range electrolyte

[0035] Under argon atmosphere, 0.001 mol NaPF 6 The precipitate was dissolved in 1 mL of a mixed organic solvent of 1,2-diethoxyethane / tetrahydrofuran (vol:vol=1:1) to obtain a wide temperature range electrolyte solution with a concentration of 1 mol / L.

[0036] The wide temperature range electrolyte obtained in Example 1 was placed in a -70°C low temperature box for 12 hours, and then taken out and tilted. It can be seen that the electrolyte is still liquid and has not solidified. Figure 1 shown.

[0037] Comparative Example 1

[0038] Under argon atmosphere, 0.001 mol NaPF 6The solution was dissolved in 1 mL of a mixed organic solvent of 1,2-dimethoxyethane / tetrahydrofuran (vol:vol=1:1) to obtain a comparative electrolyte solution with a concentration of 1 mol / L.

[0039] The wide temperature range electrolyte obtained in Example 1 and the electrolyte obtained in Comparative Example 1 were tested for ionic conductivity within the range of -70 to 20°C. The results are as follows: Figure 2 It can be found that even at a low temperature of -70°C, the wide temperature range electrolyte prepared by the present invention still has an ion conductivity of about 0.3 mS / cm, while the ion conductivity of the comparative electrolyte is only about 0.07 mS / cm.

[0040] Example 2: Preparation of wide temperature range electrolyte

[0041] Under argon atmosphere, 0.001 mol NaPF 6 The precipitate was dissolved in 1 mL of a mixed organic solvent of 1,2-diethoxyethane / tetrahydrofuran (vol:vol=1:3) to obtain a wide temperature range electrolyte solution with a concentration of 1 mol / L.

[0042] Example 3: Preparation of wide temperature range electrolyte

[0043] Under argon atmosphere, 0.001 mol NaPF 6 Dissolved in 1 mL of 1,2-diethoxyethane to obtain two wide temperature range electrolytes with a concentration of 1 mol / L.

[0044] Comparative Example 2

[0045] Under argon atmosphere, 0.001 mol NaPF 6 The electrolyte was dissolved in 1 mL of a mixed organic solvent of tetrahydrofuran to obtain a comparative electrolyte solution with a concentration of 1 mol / L.

[0046] The wide temperature range electrolytes obtained in Example 2 and Example 3 and the electrolyte obtained in Comparative Example 2 were tested for ionic conductivity within the range of -50 to 60°C. The results are as follows: Figure 3 It can be found that within a wide temperature range, the ionic conductivity of the wide temperature range electrolyte prepared by the present invention changes slowly as the temperature decreases, while the ionic conductivity of the comparative electrolyte drops sharply at -40°C, and the electrolyte performance is greatly affected by temperature changes.

[0047] Example 4: Symmetrical battery assembly

[0048] The sodium metal electrode loaded on the aluminum foil was used as the positive electrode and the negative electrode, the cut polypropylene film was used as the separator, and the wide temperature range electrolyte in Example 1 was used to assemble the Na||Na symmetric battery.

[0049] The battery was placed in a -40°C cryostat at 1 mA / cm 2 , 1mAh / cm 2 The battery can run stably for 600 hours. Figure 4 The battery was disassembled and the sodium metal electrode was characterized by scanning electron microscopy, as shown in Figure 5 As shown, the surface of the sodium metal is smooth and intact, and no side reactions occur.

[0050] Comparative Example 3

[0051] The sodium metal electrode loaded on the aluminum foil was used as the positive electrode and the negative electrode, the cut polypropylene film was used as the separator, and the electrolyte in Comparative Example 1 was used to assemble the Na||Na symmetric battery.

[0052] The battery was placed in a -40°C cryostat at 1 mA / cm 2 , 1mAh / cm 2 The battery was tested with a current of 10000A and a short circuit occurred after running for about 370 hours. Figure 4 This figure shows that the battery obtained in Comparative Example 3 is unstable in operation and has a shorter battery life than the battery obtained in Example 4.

[0053] Example 5: Na‖NVP battery assembly

[0054] Sodium vanadium phosphate, conductive agent and binder are mixed and ground in a mass ratio of 8:1:1, and a proper amount of N-methylpyrrolidone is added and mixed evenly. The mixture is loaded on aluminum foil and vacuum dried at 120°C for 10 hours. After drying, the mixture is cut into appropriate sizes and used as the positive electrode of a sodium battery.

[0055] The sodium metal electrode loaded on the aluminum foil was used as the negative electrode, the cut polypropylene film was used as the separator, the positive electrode prepared as above was matched, and the wide temperature range electrolyte in Example 1 was used to assemble the Na||NVP battery.

[0056] The Na||NVP battery obtained in Example 5 was subjected to charge and discharge tests at different temperatures. Figure 7 This is the 0.1C discharge capacity diagram of Na‖NVP battery at different temperatures. Figure 8 The charge and discharge curves of Na‖NVP battery at 0.1C at different temperatures are shown below. Fig. 9 for Na‖

[0057] The cycle performance diagram of NVP battery at 0.5C cycle at different temperatures. It can be seen that at -40℃, the discharge capacity of Na‖NVP battery is 63mAh / g; even at a low temperature of -60℃, the discharge capacity of Na‖NVP battery is still 42mAh / g; Na‖NVP battery cycles 100 times in a wide temperature range, and the capacity retention rate can reach more than 95%, with excellent cycle performance.

[0058] Example 6: Na‖HC battery assembly

[0059] Hard carbon, conductive agent and binder are mixed and ground in a mass ratio of 8:1:1, and a proper amount of N-methylpyrrolidone is added and mixed evenly. The mixture is loaded on aluminum foil and vacuum dried at 120°C for 10 hours. After drying, the mixture is cut into appropriate sizes to obtain hard carbon electrodes.

[0060] The sodium metal electrode loaded on aluminum foil was used as the negative electrode, the cut polypropylene film was used as the diaphragm, the hard carbon electrode prepared as above was matched, and the 1 mol / L 1,2-diethoxyethane / tetrahydrofuran (vol:vol=1:3) wide temperature range electrolyte in Example 2 was used to assemble the Na‖HC battery.

[0061] The Na||HC battery obtained in Example 6 was subjected to a cycle test at -50°C. Fig.10 This is the first cycle charge and discharge curve of 0.1C. Fig.11 This is a cycle performance diagram of 5 cycles at 0.1C and then a long cycle at 1C. It can be seen that the 0.1C charging capacity of the hard carbon negative electrode is still 275mAh / g at -50°C, and the 1C cycle retention rate is close to 100%, with excellent low-temperature effect, indicating that the wide temperature range electrolyte provided by the present invention has a good application effect in the field of sodium batteries, which is of great significance to promoting the application of sodium batteries in a wide temperature range.

[0062] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0063] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A wide temperature range electrolyte for sodium batteries, characterized in that: The electrolyte composition comprises sodium salt and an organic solvent, and the organic solvent is 1,2-diethoxyethane, or a combination of 1,2-diethoxyethane and tetrahydrofuran.

2. The electrolyte according to claim 1, characterized in that When the organic solvent is selected from a combination of 1,2-diethoxyethane and tetrahydrofuran, the volume ratio thereof is a mixed solvent of 1:5 to 5:

1.

3. The electrolyte according to claim 1, characterized in that The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, and sodium bis(oxalatoborate).

4. The electrolyte according to claim 3, characterized in that The concentration of the sodium salt in the electrolyte is 0.1 to 3 mol / L.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The application temperature of the electrolyte is -70 to 60°C.

6. Application of a wide temperature range electrolyte in a sodium battery, characterized in that: The wide temperature range sodium battery comprises: a positive electrode, a separator, a negative electrode and the electrolyte according to claims 1 to 4.

7. The use of the wide temperature range electrolyte in sodium batteries according to claim 6, characterized in that: The positive electrode is one or more of layered oxide type, polyanion type, Prussian blue type, Prussian white type and organic type sodium positive electrode.

8. The use of the wide temperature range electrolyte in sodium batteries according to claim 6, characterized in that: The negative electrode is one or more of hard carbon, soft carbon, and metallic sodium.

9. The use of the wide temperature range electrolyte in sodium batteries according to claim 6, characterized in that: The application temperature of sodium batteries is -70~60℃.

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