A sodium ion battery electrolyte and its preparation method and application

Abstract

The present invention belongs to the technical field of secondary battery materials. More specifically, it relates to a sodium ion battery electrolyte, a preparation method thereof and an application thereof. The product provided by the present invention includes: an ether solvent, a low-temperature additive and a sodium salt; wherein the ether solvent is configured by diethylene glycol dimethyl ether and tetrahydrofuran in a volume ratio of 1:4-1:5; the low-temperature additive is a hydrofluoroether, and the addition amount of the low-temperature additive is 8-10% of the mass of the ether solvent; the sodium salt includes any one of sodium hexafluorophosphate, NaFSI or NaTFSI; the volume concentration of the sodium salt in the sodium ion battery electrolyte is 2-3 mol / L. When preparing the product, diethylene glycol dimethyl ether and tetrahydrofuran are first mixed evenly to obtain an ether solvent; to the ether solvent, 8-10% of the mass of the ether solvent is added to the hydrofluoroether to obtain a premix; then sodium salt is added to the premix, and the sodium salt is stirred to dissolve the sodium salt to obtain a sodium ion battery electrolyte product.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery materials, and more specifically, relates to a sodium ion battery electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are favored due to their high energy density, long cycle life and high safety, and are widely used in energy storage, power tools, aerospace and military fields. However, with the vigorous development of lithium batteries, metallic lithium resources have been severely exploited. In addition, the global reserves of lithium metal resources are relatively small, and the abundance of lithium in the earth's crust is only 0.006%. It is unevenly distributed around the world, which is seriously inconsistent with the growing demand. Sodium-ion batteries are being re-examined due to their abundant sodium reserves, low cost, long life and high safety. They are expected to become one of the mainstream power sources in the next generation of energy storage.

[0003] However, problems such as decreased battery discharge capacity, slower charge and discharge rates, and reduced cycle life in low-temperature environments have greatly limited the application of sodium-ion batteries in aerospace, on the seabed, and in high-latitude areas. Generally speaking, due to the good solubility of sodium salts and higher ion conductivity at the same electrolyte concentration, their application under low-temperature conditions is still limited.

[0004] Similar to lithium-ion batteries, sodium-ion batteries are also composed of positive electrodes, negative electrodes, separators and electrolytes. Among them, the electrolyte is considered to be one of the important factors restricting the stable operation of batteries at low temperatures. Conventional low-temperature electrolytes have the characteristics of low freezing point, low viscosity and high ionic conductivity. However, the above conventional methods have made it difficult to further improve the transmission efficiency of sodium ions at the electrode / electrolyte interface under low temperature conditions. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the problem that the existing sodium ion battery electrolyte has low ion conductivity when used in a low temperature environment, which easily leads to a slow charge and discharge rate of the product under low temperature conditions and a prone to attenuation of the cycle life, and to provide a sodium ion battery electrolyte and its preparation method and application.

[0006] The purpose of the present invention is to provide a sodium ion battery electrolyte.

[0007] Another object of the present invention is to provide a method for preparing a sodium ion battery electrolyte.

[0008] Another object of the present invention is to provide an application of a sodium ion battery electrolyte.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A sodium ion battery electrolyte, comprising: an ether solvent, a low-temperature additive and a sodium salt;

[0011] The ether solvent is prepared by mixing diethylene glycol dimethyl ether and tetrahydrofuran in a volume ratio of 1:4-1:5;

[0012] The low-temperature additive is hydrofluoroether, and the amount of the low-temperature additive added is 8-10% of the mass of the ether solvent;

[0013] The sodium salt includes any one of sodium hexafluorophosphate, NaFSI or NaTFSI; the volume concentration of the sodium salt in the sodium ion battery electrolyte is 2-3 mol / L.

[0014] First, the above technical solution uses ether solvents as the solvent of the electrolyte for sodium ion batteries, which takes advantage of the lower sodium ion desolvation energy of ether solvents, and uses diethylene glycol dimethyl ether and tetrahydrofuran to improve the low-temperature performance of sodium ion batteries. Compared with conventional solvents, the combination of the two can make its binding force with sodium ions weaker, reduce the desolvation energy barrier of sodium ions, and achieve rapid reaction of sodium ions at the positive and negative electrodes at low temperatures.

[0015] Further, the sodium salt includes a first sodium salt and a second sodium salt;

[0016] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0017] The second sodium salt is selected from any one of sodium hexafluorophosphate, NaFSI or NaTFSI.

[0018] Furthermore, the second sodium salt is selected from sodium hexafluorophosphate, and the mass ratio of the first sodium salt to the second sodium salt is 4:1.

[0019] Furthermore, the second sodium salt is selected from NaFSI, and the mass ratio of the first sodium salt to the second sodium salt is 3:1.

[0020] Furthermore, the second sodium salt is selected from NaTFSI, and the mass ratio of the first sodium salt to the second sodium salt is 3.5:1.

[0021] The above technical solution adopts a compound sodium salt as an electrolyte salt, wherein the second sodium salt can form a thin and stable SEI film on the surface of the negative electrode during the battery formation or cycle process, and because the formed SEI film is rich in more inorganic substances such as NaF, the sodium ions can be quickly transmitted at the interface between the negative electrode and the electrolyte; however, if the sodium salt is used alone as an electrolyte salt, it will have a strong binding force with sodium ions. Therefore, during the desolvation process, it is difficult for sodium ions to dissociate from anions, resulting in the electrolyte ion conductivity starting to decrease, so it is necessary to control the amount of the second sodium salt added; by introducing sodium trifluoromethylsulfinate, it can compete for sodium ions in the solvent, and during the desolvation process, it is easier to dissociate from sodium ions, especially under low temperature conditions, by regulating the addition amount of the two salt-resistant salts within the above reasonable range, the NaF distribution in the SEI film on the surface of the negative electrode is more uniform, so that the sodium ion transfer capacity of different positions of the negative electrode of the product is more uniform, and the product can obtain a better cycle performance.

[0022] Furthermore, the sodium ion battery electrolyte also includes 0.72-0.9% by mass of sodium dodecylbenzene sulfonate of the ether solvent.

[0023] Furthermore, the sodium ion battery electrolyte also includes 0.35-0.42% by mass of sodium dodecylbenzene sulfonate of the ether solvent.

[0024] Furthermore, the sodium ion battery electrolyte also includes 0.45-0.65% by mass of sodium dodecylbenzene sulfonate of the ether solvent.

[0025] The above technical solution matches a certain amount of sodium dodecylbenzene sulfonate with the corresponding sodium salt type and addition amount. In this way, the wetting ability of the electrolyte to the electrode plates, especially the negative electrode plates, can be improved in the early stage of the battery manufacturing process, so that the electrolyte can form a uniform and thin SEI film on the surface of the negative electrode plate during the early formation process, thereby avoiding excessive consumption of active sodium ions.

[0026] A method for preparing a sodium ion battery electrolyte, the specific preparation steps comprising:

[0027] Diethylene glycol dimethyl ether and tetrahydrofuran are uniformly mixed in a volume ratio of 1:4-1:5 to obtain an ether solvent;

[0028] Adding 8-10% of the mass of the ether solvent to the ether solvent is a hydrofluoroether to obtain a premix;

[0029] Sodium salt is added to the premix at a volume concentration of 2-3 mol / L, and stirred to dissolve the sodium salt to obtain a sodium ion battery electrolyte product.

[0030] An application of a sodium ion battery electrolyte, when the sodium ion battery electrolyte is used, the positive electrode of the sodium ion battery is selected from Na 2 / 3 Mn 2 / 3 Ni 1 / 4 Cu 1 / 12 O2, the negative electrode of the sodium ion battery is made of hard carbon. DETAILED DESCRIPTION

[0031] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0032] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0033] Example 1

[0034] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4 and poured into a container, and then stirred and mixed with a stirrer at a speed of 300 r / min for 40 minutes at room temperature to obtain an ether solvent;

[0035] Then, under stirring, 8% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature for 30 minutes with a stirrer at a speed of 300 r / min to obtain a premix;

[0036] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.75% by mass of the ether solvent to the premix at a volume concentration of 2 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 300 r / min for 2 h to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0037] The sodium salt includes a first sodium salt and a second sodium salt;

[0038] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0039] The second sodium salt is selected from sodium hexafluorophosphate;

[0040] The mass ratio of the first sodium salt to the second sodium salt is 4:1.

[0041] Example 2

[0042] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4.5 and poured into a container, and then stirred and mixed with a stirrer at a speed of 400 r / min for 45 minutes at room temperature to obtain an ether solvent;

[0043] Then, under stirring, adding 9% of the mass of the hydrofluoroether to the container containing the ether solvent, and stirring and mixing at room temperature with a stirrer at a speed of 400 r / min for 40 minutes to obtain a premix;

[0044] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate in an amount of 0.35% by mass of the ether solvent to the premix at a volume concentration of 2.5 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 400 r / min for 3 hours to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0045] The sodium salt includes a first sodium salt and a second sodium salt;

[0046] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0047] The second sodium salt is selected from NaFSI;

[0048] The mass ratio of the first sodium salt to the second sodium salt is 3:1.

[0049] Example 3

[0050] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:5 and poured into a container, and then stirred and mixed with a stirrer at a speed of 500 r / min for 60 minutes at room temperature to obtain an ether solvent;

[0051] Then, under stirring, 10% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature with a stirrer at a speed of 500 r / min for 45 minutes to obtain a premix;

[0052] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.55% by mass of the ether solvent to the premix at a volume concentration of 3 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 500 r / min for 4 hours to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0053] The sodium salt includes a first sodium salt and a second sodium salt;

[0054] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0055] The second sodium salt is selected from NaTFSI;

[0056] The mass ratio of the first sodium salt to the second sodium salt is 3.5:1.

[0057] Example 4

[0058] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4 and poured into a container, and then stirred and mixed with a stirrer at a speed of 300 r / min for 40 minutes at room temperature to obtain an ether solvent;

[0059] Then, under stirring, 8% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature for 30 minutes with a stirrer at a speed of 300 r / min to obtain a premix;

[0060] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.65% by mass of the ether solvent to the premix at a volume concentration of 2 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 300 r / min for 2 h to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0061] The sodium salt includes a first sodium salt and a second sodium salt;

[0062] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0063] The second sodium salt is selected from sodium hexafluorophosphate;

[0064] The mass ratio of the first sodium salt to the second sodium salt is 4:1.

[0065] Example 5

[0066] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4.5 and poured into a container, and then stirred and mixed with a stirrer at a speed of 400 r / min for 45 minutes at room temperature to obtain an ether solvent;

[0067] Then, under stirring, adding 9% of the mass of the hydrofluoroether to the container containing the ether solvent, and stirring and mixing at room temperature with a stirrer at a speed of 400 r / min for 40 minutes to obtain a premix;

[0068] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate in an amount of 0.35% by mass of the ether solvent to the premix at a volume concentration of 2.5 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 400 r / min for 3 hours to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0069] The sodium salt includes a first sodium salt and a second sodium salt;

[0070] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0071] The second sodium salt is selected from sodium hexafluorophosphate;

[0072] The mass ratio of the first sodium salt to the second sodium salt is 3:1.

[0073] Example 6

[0074] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:5 and poured into a container, and then stirred and mixed with a stirrer at a speed of 500 r / min for 60 minutes at room temperature to obtain an ether solvent;

[0075] Then, under stirring, 10% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature with a stirrer at a speed of 500 r / min for 45 minutes to obtain a premix;

[0076] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.4% by mass of the ether solvent to the premix at a volume concentration of 3 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 500 r / min for 4 hours to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0077] The sodium salt includes a first sodium salt and a second sodium salt;

[0078] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0079] The second sodium salt is selected from NaTFSI;

[0080] The mass ratio of the first sodium salt to the second sodium salt is 3.5:1.

[0081] Example 7

[0082] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4 and poured into a container, and then stirred and mixed with a stirrer at a speed of 300 r / min for 40 minutes at room temperature to obtain an ether solvent;

[0083] Then, under stirring, 8% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature for 30 minutes with a stirrer at a speed of 300 r / min to obtain a premix;

[0084] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.75% by mass of the ether solvent to the premix at a volume concentration of 2 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 300 r / min for 2 h to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0085] The sodium salt is sodium hexafluorophosphate.

[0086] Example 8

[0087] Diethylene glycol dimethyl ether and tetrahydrofuran were mixed in a volume ratio of 1:4 and poured into a container, and then stirred and mixed with a stirrer at a speed of 300 r / min for 40 minutes at room temperature to obtain an ether solvent;

[0088] Then, under stirring, 8% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature for 30 minutes with a stirrer at a speed of 300 r / min to obtain a premix;

[0089] Then, under stirring, sodium salt is added to the premix at a volume concentration of 2 mol / L, and the mixture is continuously stirred and mixed at a speed of 300 r / min for 2 h at room temperature to dissolve the sodium salt, thereby obtaining a sodium ion battery electrolyte product;

[0090] The sodium salt includes a first sodium salt and a second sodium salt;

[0091] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0092] The second sodium salt is selected from sodium hexafluorophosphate;

[0093] The mass ratio of the first sodium salt to the second sodium salt is 4:1.

[0094] Comparative Example 1

[0095] Diethylene glycol dimethyl ether is used as the ether solvent;

[0096] Then, under stirring, 8% of the mass of the hydrofluoroether of the ether solvent is added to the container containing the ether solvent, and the mixture is stirred and mixed at room temperature for 30 minutes with a stirrer at a speed of 300 r / min to obtain a premix;

[0097] Then, under stirring, adding sodium salt and sodium dodecylbenzene sulfonate of 0.75% by mass of the ether solvent to the premix at a volume concentration of 2 mol / L, and continuing to stir and mix at room temperature with a stirrer at a speed of 300 r / min for 2 h to dissolve the sodium salt, so as to obtain a sodium ion battery electrolyte product;

[0098] The sodium salt includes a first sodium salt and a second sodium salt;

[0099] Wherein, the first sodium salt is sodium trifluoromethanesulfinate;

[0100] The second sodium salt is selected from sodium hexafluorophosphate;

[0101] The mass ratio of the first sodium salt to the second sodium salt is 4:1.

[0102] The performance test was carried out on the products obtained from Example 1 to Example 8. The specific test methods and test results are as follows:

[0103] Take Na 2 / 3 Mn 2 / 3 Ni 1 / 4 Cu 1 / 12 O2 is used as the positive electrode active material, and hard carbon is used as the negative electrode active material;

[0104] Preparation of positive electrode:

[0105] PVDF was dissolved in NMP to obtain a PVDF solution with a concentration of 30 mg / mL; the positive electrode active material: acetylene black: PVDF were mixed evenly in a mass ratio of 9:0.6:0.4 to obtain a positive electrode slurry, and then the positive electrode slurry was coated on the surface of the current collector, dried, rolled, and punched into a disc with a diameter of 12 mm to obtain a loading of 6.5 mg / cm 2 The positive electrode;

[0106] Preparation of negative electrode sheet:

[0107] PVDF was dissolved in NMP to obtain a PVDF solution with a concentration of 30 mg / mL; the negative electrode active material: Super P: PVDF were mixed evenly in a mass ratio of 8:1:1 to obtain a negative electrode slurry, and then the negative electrode slurry was coated on the surface of the current collector, dried, rolled, and punched into a disc with a diameter of 12 mm to obtain a loading of 3.5 mg / cm 2 The negative electrode;

[0108] Using glass fiber separator as battery separator;

[0109] In a nitrogen atmosphere, the positive electrode sheet, the negative electrode sheet, the battery separator and the electrolyte are assembled into a CR 2025 battery.

[0110] The conductivity of different electrolytes at -40°C was tested using Shanghai Leici DDS-307 ion conductivity meter and DJS-1C conductivity electrode. The specific test results are shown in Table 1.

[0111] The electrochemical workstation was used to perform EIS test on the battery before and after the cycle, and the impedance change of the battery during the cycle was analyzed under -5°C conditions, and then the stability of the battery during the cycle was analyzed. Specifically, the test polarization voltage was 5mV, and the frequency range was 100000-0.01Hz. The specific test results are shown in Table 2;

[0112] Table 1: Product conductivity test results

[0113] Ionic conductivity at -40℃ / mS·cm-1 Example 1 3.5 Example 2 3.5 Example 3 3.7 Example 4 3.2 Example 5 3.1 Example 6 3.2 Example 7 3.0 Example 8 2.9 Comparative Example 1 2.1

[0114] Table 2: EIS test results

[0115]

[0116]

[0117] It can be seen from the test results in Table 1 that the product obtained by the present invention has excellent ionic conductivity, and after cycling, the impedance change is relatively small.

[0118] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A sodium ion battery electrolyte, characterized in that: include: Ether solvents, low-temperature additives and sodium salts; The ether solvent is prepared by mixing diethylene glycol dimethyl ether and tetrahydrofuran in a volume ratio of 1:4-1:5; The low-temperature additive is hydrofluoroether, and the amount of the low-temperature additive added is 8-10% of the mass of the ether solvent; The sodium salt includes a first sodium salt and a second sodium salt; Wherein, the first sodium salt is sodium trifluoromethanesulfinate; The second sodium salt is selected from any one of sodium hexafluorophosphate, NaFSI or NaTFSI; The volume concentration of the sodium salt in the sodium ion battery electrolyte is 2-3 mol / L; When the second sodium salt is selected from sodium hexafluorophosphate, the mass ratio of the first sodium salt to the second sodium salt is 4:1; When the second sodium salt is selected from NaFSI, the mass ratio of the first sodium salt to the second sodium salt is 3:1; When the second sodium salt is selected from NaTFSI, the mass ratio of the first sodium salt to the second sodium salt is 3.5:1; The sodium ion battery electrolyte also includes sodium dodecylbenzene sulfonate in an amount of 0.72-0.9% by mass of the ether solvent.

2. A sodium ion battery electrolyte according to claim 1, characterized in that: The sodium ion battery electrolyte also includes sodium dodecylbenzene sulfonate in an amount of 0.35-0.42% by mass of the ether solvent.

3. A sodium ion battery electrolyte according to claim 2, characterized in that: The sodium ion battery electrolyte also includes sodium dodecylbenzene sulfonate in an amount of 0.45-0.65% by mass of the ether solvent.

4. A method for preparing a sodium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: The specific preparation steps include: Diethylene glycol dimethyl ether and tetrahydrofuran are uniformly mixed in a volume ratio of 1:4-1:5 to obtain an ether solvent; Adding 8-10% of the mass of the ether solvent to the ether solvent is a hydrofluoroether to obtain a premix; Sodium salt is added to the premix at a volume concentration of 2-3 mol / L, and stirred to dissolve the sodium salt to obtain a sodium ion battery electrolyte product.

5. An application of the sodium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: When the sodium ion battery electrolyte is used, the positive electrode of the sodium ion battery is selected from Na 2 / 3 Mn 2 / 3 Ni 1 / 4 Cu 1 / 12 O2, the negative electrode of the sodium ion battery is made of hard carbon.

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