Ether-based electrolyte, high-first-effect sodium-ion battery and preparation method of high-first-effect sodium-ion battery

Abstract

The invention belongs to the technical field of sodium-ion batteries, and discloses an ether-based electrolyte, a high-first-effect sodium-ion battery and a preparation method of the high-first-effect sodium-ion battery, and the preparation method of the ether-based electrolyte comprises the following steps: mixing sodium salt, an ether solution and an additive to obtain the ether-based electrolyte; the ether solution is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or diethyl ether. The ether-based electrolyte prepared by the invention has excellent cycling stability and coulombic efficiency, the average coulombic efficiency is greatly improved, and when the ether-based electrolyte is applied to the sodium-ion battery, the sodium-ion battery still has the average coulombic efficiency exceeding 99% and excellent first-circle coulombic efficiency after being circulated for 100 circles.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to an ether-based electrolyte and a high-initial-efficiency sodium ion battery and a preparation method thereof. Background Art

[0002] With the continuous rise in global energy demand and the profound awakening of environmental awareness, the pursuit of efficient and sustainable energy storage has become an urgent and important mission for the scientific research community. As a potential alternative to lithium-ion batteries, sodium-ion batteries have attracted widespread attention worldwide due to their abundant resource base, economical cost advantages, and environmentally friendly characteristics. Their working mechanism is similar to that of lithium-ion batteries, relying on the insertion and deintercalation of metal ions between electrode materials to achieve stable charge and discharge cycles. However, compared with the maturity of lithium-ion battery technology and superior electrochemical performance, sodium-ion batteries still face many challenges in terms of the durability of positive electrode materials, electrolyte compatibility, and overall performance. Among the many technical difficulties that need to be overcome, the selection and optimization of electrolytes are recognized as one of the key paths to improving the performance of sodium-ion batteries. As a bridge for ion shuttles within the battery, the characteristics of the electrolyte are directly related to core indicators such as battery safety, cycle endurance, and energy density.

[0003] At present, ether-based electrolytes have stood out in the sodium-ion battery electrolyte system due to their low viscosity, high conductivity and excellent reduction stability on the negative electrode side, becoming a popular candidate. Unfortunately, ether-based electrolytes have insufficient antioxidant capacity under high voltage environments and are very likely to induce oxidative decomposition reactions, which not only weakens battery performance but also poses safety risks. Especially for the positive electrode materials of sodium-ion batteries, the introduction of fluorinated ether-based electrolytes is like a breath of fresh air, greatly improving their first-cycle coulombic efficiency (ICE) and significantly reducing the irreversible capacity loss during the first charge and discharge process, thereby improving the overall performance and cycle stability of the battery.

[0004] Therefore, it is of great significance to study an ether-based electrolyte and its preparation method that can improve the first-cycle coulombic efficiency, enhance the overall performance and cycle stability of the battery, as well as a sodium-ion battery with high first-cycle efficiency and its preparation method. Summary of the Invention

[0005] In view of this, the present invention provides an ether-based electrolyte and a high-initial-efficiency sodium-ion battery and a preparation method thereof, the purpose of which is to solve the problems of low initial efficiency on the positive electrode side, poor overall battery performance and poor cycle stability existing in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing an ether-based electrolyte, comprising the following steps: mixing a sodium salt, an ether solution and an additive to obtain an ether-based electrolyte;

[0008] The ether solution is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or ethyl ether.

[0009] Preferably, the sodium salt is sodium hexafluorophosphate, sodium trifluoromethanesulfonate or sodium perchlorate.

[0010] Preferably, the additive is fluoroethylene carbonate, vinylene carbonate or ethylene carbonate.

[0011] Preferably, the dosage ratio of the sodium salt, ether solution and additive is 1-5 mol:1 L:0.01-0.5 L.

[0012] Preferably, the mixing speed is 80-100 rpm, and the mixing time is 10-15 hours.

[0013] The present invention also provides an ether-based electrolyte prepared by the method for preparing the ether-based electrolyte.

[0014] The present invention also provides a method for preparing a high-initial-efficiency sodium-ion battery containing the ether-based electrolyte, comprising the following steps:

[0015] 1) mixing sodium vanadium phosphate, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone to obtain a paste;

[0016] 2) coating the obtained paste slurry on aluminum foil, and then drying and rolling to obtain an electrode sheet;

[0017] 3) Assembling the electrode sheet, the separator, the sodium sheet and the electrolyte to obtain a sodium ion battery;

[0018] In the step 3), the electrolyte is the ether-based electrolyte.

[0019] Preferably, in step 1), the mass ratio of sodium vanadium phosphate, carbon nanotubes and polyvinylidene fluoride is 5-9:1-3:0.5-1.5; the amount ratio of sodium vanadium phosphate to N-methylpyrrolidone is 0.1-0.2g:1.25-2.5mL; the mixing speed is 200-600rpm, and the mixing time is 4-8h.

[0020] Preferably, in step 2), the coating thickness is 10 to 15 μm, the drying temperature is 80 to 120° C., the drying time is 43 to 53 hours, the rolling pressure is 5 to 15 MPa, and the rolling time is 5 to 15 minutes;

[0021] In the step 3), the assembly is performed in an argon atmosphere.

[0022] The present invention also provides a sodium ion battery prepared by the method for preparing a high-initial-efficiency sodium ion battery.

[0023] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0024] The ether-based electrolyte prepared by the present invention has excellent cycle stability and coulombic efficiency, and the average coulombic efficiency is greatly improved. When it is applied to sodium-ion batteries, the sodium-ion batteries still have an average coulombic efficiency of more than 99% and excellent first-cycle coulombic efficiency after 100 cycles.

[0025] The preparation method of the ether-based electrolyte of the present invention has a wide range of raw materials, is simple and easy to operate, can be produced on a large scale, is suitable for industrial application, and is applied to sodium ion batteries, greatly reducing the manufacturing cost of the batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] Figure 1 Schematic diagram of the preparation method of the ether-based electrolyte of the present invention;

[0028] Figure 2 This is a graph showing the cyclic voltammetry performance of the sodium ion battery obtained in Example 1 at a rate of 0.2 mV / s;

[0029] Figure 3 This is a cyclic voltammetry performance test diagram of the sodium ion battery obtained in Comparative Example 1 at a rate of 0.2 mV / s;

[0030] Figure 4 This is a cyclic voltammetry performance test diagram of the sodium ion battery obtained in Comparative Example 2 at a rate of 0.2 mV / s;

[0031] Figure 5 This is a test graph of efficiency-cycle number of the sodium ion batteries obtained in Example 1, Comparative Example 1 and Comparative Example 2 at a rate of 0.2C;

[0032] Figure 6 This is a voltage-specific capacity test diagram of the sodium ion battery obtained in Example 1 at a rate of 0.2C;

[0033] Figure 7This is a voltage-specific capacity test diagram of the sodium ion battery obtained in Comparative Example 1 at a rate of 0.2C;

[0034] Figure 8 This is a voltage-specific capacity test diagram of the sodium ion battery obtained in Comparative Example 2 at a rate of 0.2C;

[0035] Figure 9 This is a comparison chart of the first-cycle coulombic efficiency of sodium-ion batteries obtained with different electrolyte formulas at a rate of 0.2C. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing an ether-based electrolyte, comprising the following steps: mixing a sodium salt, an ether solution and an additive to obtain an ether-based electrolyte;

[0037] The ether solution is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or ethyl ether.

[0038] In the present invention, the preparation of the ether-based electrolyte is carried out in a glove box containing an argon atmosphere;

[0039] The ether-based electrolyte is preferably prepared by first preparing a mixed solution of sodium salt and ether solution, and then adding additives to the mixed solution to obtain the ether-based electrolyte; the concentration of the mixed solution is preferably 0-4 mol / L, more preferably 1-3 mol / L, and more preferably 2 mol / L.

[0040] In the present invention, the sodium salt is preferably sodium hexafluorophosphate, sodium trifluoromethanesulfonate or sodium perchlorate.

[0041] In the present invention, the additive is preferably fluoroethylene carbonate, vinylene carbonate or ethylene carbonate.

[0042] In the present invention, the usage ratio of the sodium salt, ether solution and additive is preferably 1-5 mol:1L:0.01-0.5L, more preferably 2-4 mol:1L:0.1-0.45L, and more preferably 2.5-3 mol:1L:0.2-0.3L.

[0043] In the present invention, the mixing speed is preferably 80 to 100 rpm, more preferably 85 to 95 rpm, more preferably 90 to 92 rpm, and the mixing time is preferably 10 to 15 h, more preferably 11 to 14 h, more preferably 12 to 13 h.

[0044] The present invention also provides an ether-based electrolyte prepared by the method for preparing the ether-based electrolyte.

[0045] The present invention also provides a method for preparing a high-initial-efficiency sodium-ion battery containing the ether-based electrolyte, comprising the following steps:

[0046] 1) mixing sodium vanadium phosphate, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone to obtain a paste;

[0047] 2) coating the obtained paste slurry on aluminum foil, and then drying and rolling to obtain an electrode sheet;

[0048] 3) Assembling the electrode sheet, the separator, the sodium sheet and the electrolyte to obtain a sodium ion battery;

[0049] In the step 3), the electrolyte is the ether-based electrolyte.

[0050] In the present invention, in the step 1), the mass ratio of sodium vanadium phosphate, carbon nanotubes and polyvinylidene fluoride is preferably 5-9:1-3:0.5-1.5, more preferably 6-8:1.5-2.5:0.75-1.25, and more preferably 6-8:1.75-2.25:1; the amount ratio of sodium vanadium phosphate to N-methylpyrrolidone is preferably 0.1-0.2 g:1.25-2.5 mL, more preferably 0.12-0.18 g:1.5-2.25 mL, and more preferably 0.13-0.17 g:1.625-2.125 mL.

[0051] In the present invention, in the step 1), sodium vanadium phosphate, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone are stirred before mixing, and the stirring is preferably manual stirring, and the manual stirring time is preferably 5 to 15 minutes, more preferably 8 to 14 minutes, and more preferably 10 to 12 minutes. Ball milling is preferably performed during the mixing process, and the ball milling speed is preferably 200 to 600 rpm, more preferably 300 to 550 rpm, and more preferably 400 to 500 rpm. The ball milling time is preferably 4 to 8 hours, more preferably 5 to 7.5 hours, and more preferably 5.5 to 6 hours. The ball milling is preferably performed on a planetary ball mill.

[0052] In the present invention, in step 2), the coating thickness is preferably 10 to 15 μm, more preferably 11 to 14 μm, and more preferably 12 to 13 μm;

[0053] The drying temperature is preferably 80-120°C, more preferably 90-110°C, more preferably 100-105°C, the drying time is preferably 43-53h, more preferably 45-50h, more preferably 47-48h, the drying is preferably vacuum drying, and the vacuum degree of vacuum drying is preferably 0.09-0.095MPa, more preferably 0.091-0.094MPa, more preferably 0.092-0.093MPa;

[0054] The rolling pressure is preferably 5 to 15 MPa, more preferably 7 to 13 MPa, more preferably 8 to 10 MPa, and the rolling time is preferably 5 to 15 min, more preferably 8 to 13 min, more preferably 10 to 12 min;

[0055] In step 3), the assembly is preferably performed in a glove box containing an argon atmosphere.

[0056] In the present invention, the diaphragm is preferably a glass fiber diaphragm produced by Whatman Company in the United Kingdom.

[0057] The present invention also provides a sodium ion battery prepared by the method for preparing a high-initial-efficiency sodium ion battery.

[0058] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] In the embodiment of the present invention, the sodium vanadium phosphate is untreated commercial sodium vanadium phosphate produced by Hefei Kejing Material Technology Co., Ltd.

[0060] Example 1

[0061] In a glove box containing an argon atmosphere, 2 mol of sodium hexafluorophosphate and 1 L of ethylene glycol dimethyl ether were mixed to obtain a mixed solution with a concentration of 2 mol / L. 10 mL of fluoroethylene carbonate was added to the obtained mixed solution, and the mixture was mixed at a speed of 100 rpm for 12 h to obtain an ether-based electrolyte.

[0062] 0.14 g of sodium vanadium phosphate, 0.04 g of carbon nanotubes, 0.02 g of polyvinylidene fluoride, and 1.75 mL of N-methylpyrrolidone were mixed and slowly stirred manually for 10 min. The mixture was then transferred to a planetary ball mill and ball-milled at 400 rpm for 6 h to obtain a paste-like slurry.

[0063] The obtained paste slurry was evenly coated on aluminum foil with a thickness of 12 μm, and then the aluminum foil coated with the paste slurry was vacuum dried at 100°C and a vacuum degree of 0.093 MPa for 48 hours, and then roller pressed at a pressure of 10 MPa for 8 minutes to obtain an electrode sheet;

[0064] The obtained electrode sheet was cut into 12 mm × 12 mm electrode sheets, and the ether-based electrolyte, electrode sheet, glass fiber separator and sodium sheet with a size of 16 mm × 16 mm were assembled into a sodium ion battery in a glove box containing nitrogen.

[0065] Example 2

[0066] Replace "ethylene glycol dimethyl ether" in Example 1 with "diethylene glycol dimethyl ether", and the other steps are the same as in Example 1.

[0067] Example 3

[0068] The “ethylene glycol dimethyl ether” in Example 1 was replaced by “triethylene glycol dimethyl ether”, and the other steps were the same as those in Example 1.

[0069] Example 4

[0070] The “fluoroethylene carbonate” in Example 1 was replaced by “ethylene carbonate”, and the other steps were the same as those in Example 1.

[0071] Comparative Example 1

[0072] Delete "fluoroethylene carbonate" in Example 1, and the other steps are the same as in Example 1.

[0073] Comparative Example 2

[0074] The “ethylene glycol dimethyl ether” in Example 1 was replaced by “ethylene carbonate”, and the other steps were the same as in Example 1.

[0075] The performance of the sodium ion batteries prepared in Example 1 and Comparative Examples 1-2 was tested:

[0076] The sodium ion batteries obtained in Example 1 and Comparative Examples 1-2 were subjected to cyclic voltammetry performance tests at a rate of 0.2 mV / s. The results are shown in FIG. Figures 2-4 shown.

[0077] The sodium ion batteries obtained in Example 1 and Comparative Examples 1-2 were tested for efficiency-cycle number at a rate of 0.2C. The test results are as follows: Figure 5 shown.

[0078] The sodium ion batteries obtained in Example 1 and Comparative Examples 1-2 were tested for voltage-specific capacity at a rate of 0.2C. The test results are as follows: Figures 6-8 shown.

[0079] The cyclic voltammetry performance test of the sodium ion battery obtained in Example 1 at a rate of 0.2 mV / s is shown in the figure below: Figure 2 As shown in the figure, the cyclic voltammetry performance test of the sodium ion battery obtained in comparative example 1 at a rate of 0.2mV / s is shown in the figure Figure 3 As shown in the figure, the cyclic voltammetry performance test of the sodium ion battery obtained in comparative example 2 at a rate of 0.2mV / s is shown in the figure Figure 4 As shown. Figures 2-4 It can be seen that the ether-based electrolyte obtained in Example 1 can embed more Na at low voltage compared with the ether-based electrolyte obtained in Comparative Example 1. +Under the same number of cycles, the sodium ion battery obtained in Example 1 has better reversibility, smaller electrochemical polarization and better cycle stability, which also means that the addition of the additive (fluoroethylene carbonate) to the ether-based electrolyte obtained in Example 1 effectively improves the kinetic characteristics of the sodium ion battery. Compared with the ether-based electrolyte in Example 1, the electrolytes obtained in Comparative Examples 1 to 2 show a greater electrochemical polarization and worse reversibility.

[0080] The efficiency-cycle test graph of the sodium ion batteries obtained in Example 1, Comparative Example 1 and Comparative Example 2 at a rate of 0.2C is shown in the figure below: Figure 5 As shown. Figure 5 As shown, the sodium ion battery obtained in Example 1 has a coulombic efficiency of more than 99% even after 100 cycles at 0.2C, and has a first-cycle coulombic efficiency of up to 99.64%; the coulombic efficiency of the sodium ion battery obtained in Comparative Example 1 is always lower than 96%, which may be attributed to the severe oxidative decomposition of the electrolyte during the charging process; the sodium ion battery obtained in Comparative Example 2 has poor initial and average coulombic efficiency, and the coulombic efficiency is far less than 96%. This phenomenon is due to the good compatibility of the ether-based electrolyte with the electrode material and the low incidence of side reactions, while a serious irreversible phase change process occurs in the ester-based electrolyte.

[0081] The voltage-specific capacity test diagram of the sodium ion battery obtained in Example 1 at a rate of 0.2C is shown in FIG. Figure 6 As shown in the voltage-specific capacity test diagram of the sodium ion battery obtained in Comparative Example 1 at a rate of 0.2C, Figure 7 As shown in the voltage-specific capacity test diagram of the sodium ion battery obtained in comparative example 2 at a rate of 0.2C, Figure 8 As shown. Figures 6-8 As shown, compared with the ether-based electrolyte obtained in Comparative Example 1 and the ester-based electrolyte obtained in Comparative Example 2, the ether-based electrolyte obtained in Example 1 exhibits a more stable voltage platform and smaller voltage polarization at a rate of 0.2C. The voltage-specific capacity also further reflects that the addition of the additive leads to a larger specific capacity and smaller capacity decay of the electrolyte. The different sodium intercalation and deintercalation mechanisms in the ether-based electrolyte and the ester-based electrolyte also enable the ether-based electrolyte to achieve a higher initial coulombic efficiency and better electrochemical performance.

[0082] The comparison of the first cycle coulombic efficiency of sodium ion batteries obtained with different electrolyte formulas at a rate of 0.2C is shown in the figure below. Figure 9 As shown. Figure 9 It can be seen that the 2MNaPF6-DME-1%FEC electrolyte system obtained in Example 1 has the highest first-cycle coulombic efficiency compared with the electrolyte systems obtained in Comparative Examples 1 and 2.

[0083] The above is only 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 within the scope of protection of the present invention.

Claims

1. A method for preparing an ether-based electrolyte, characterized in that: The method comprises the following steps: mixing sodium salt, ether solution and additives to obtain ether-based electrolyte; The ether solution is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or ethyl ether.

2. The method for preparing an ether-based electrolyte according to claim 1, wherein: The sodium salt is sodium hexafluorophosphate, sodium trifluoromethanesulfonate or sodium perchlorate.

3. The method for preparing an ether-based electrolyte according to claim 2, wherein: The additive is fluoroethylene carbonate, vinylene carbonate or ethylene carbonate.

4. The method for preparing an ether-based electrolyte according to claim 2 or 3, characterized in that: The dosage ratio of the sodium salt, ether solution and additive is 1-5 mol:1 L:0.01-0.5 L.

5. The method for preparing an ether-based electrolyte according to claim 4, characterized in that: The mixing speed is 80-100 rpm, and the mixing time is 10-15 hours.

6. The ether-based electrolyte prepared by the method for preparing an ether-based electrolyte according to any one of claims 1 to 5.

7. A method for preparing a high-first-efficiency sodium-ion battery comprising the ether-based electrolyte according to claim 6, characterized in that: The steps include: 1) mixing sodium vanadium phosphate, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone to obtain a paste; 2) coating the obtained paste slurry on aluminum foil, and then drying and rolling to obtain an electrode sheet; 3) Assembling the electrode sheet, the separator, the sodium sheet and the electrolyte to obtain a sodium ion battery; In the step 3), the electrolyte is the ether-based electrolyte according to claim 6.

8. The method for preparing a high first-efficiency sodium ion battery according to claim 7, characterized in that: In the step 1), the mass ratio of sodium vanadium phosphate, carbon nanotubes and polyvinylidene fluoride is 5-9:1-3:0.5-1.5; the amount ratio of sodium vanadium phosphate to N-methylpyrrolidone is 0.1-0.2g:1.25-2.5mL; the mixing speed is 200-600rpm, and the mixing time is 4-8h.

9. The method for preparing a high first-efficiency sodium ion battery according to claim 8, wherein: In the step 2), the coating thickness is 10 to 15 μm, the drying temperature is 80 to 120° C., the drying time is 43 to 53 hours, the roller pressure is 5 to 15 MPa, and the roller pressing time is 5 to 15 minutes; In the step 3), the assembly is performed in an argon atmosphere.

10. A sodium ion battery prepared by the method for preparing a high first-efficiency sodium ion battery according to any one of claims 7 to 9.

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