Low-temperature aqueous sodium-ion battery electrolyte and preparation method thereof

Abstract

The invention discloses a low-temperature aqueous sodium-ion battery electrolyte and a preparation method thereof, and belongs to the technical field of sodium-ion batteries. The electrolyte comprises a sodium salt and a solvent system, the concentration of the sodium salt is 0.5-2.5 mol / L, and the solvent system is composed of water and a solvent with the dielectric constant larger than 30 and the freezing point lower than-20 DEG C. Particularly, the solvent system is composed of water and N, N-dimethylacetamide, the volume ratio of the water is 50-70 vol%, and the volume ratio of the N, N-dimethylacetamide is 30-50 vol%. By introducing the solvent with low freezing point and high dielectric constant, the conductivity of the electrolyte under the low temperature condition is effectively improved, the freezing point of the electrolyte is remarkably reduced, and the sodium ion battery assembled by the electrolyte can still keep excellent charge-discharge performance and cycle life under the low-temperature environment of-40 DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a low-temperature aqueous sodium ion battery electrolyte and a preparation method thereof. Background Art

[0002] In recent years, sodium-ion batteries have attracted widespread attention due to their low cost and wide distribution of sodium resources. They are regarded as a strong competitor to lithium-ion batteries and are expected to become an indispensable part of the future energy supply and storage system. The physical and chemical properties of sodium are similar to those of lithium, making sodium-ion batteries more cost-effective and safer in large-scale power station energy storage systems, and more competitive in certain application areas. Compared with traditional lead-acid batteries and zinc-manganese batteries, sodium-ion batteries not only have significant advantages in cycle life, energy density and cost, but also have outstanding progress in environmental protection and energy conservation, and are gradually entering the market.

[0003] However, sodium-ion batteries perform poorly in low-temperature environments. Low temperatures significantly slow down the diffusion rate of ions and reduce the migration speed of sodium ions, which leads to a decrease in the ionic conductivity of the electrolyte and a reduction in battery capacity. In extreme cases, the electrolyte may solidify, making the battery unable to work properly. Therefore, developing electrolytes suitable for low-temperature environments and improving the ionic conductivity of the electrolyte at low temperatures have become key research directions for improving the low-temperature performance of sodium-ion batteries. Summary of the invention

[0004] In order to solve the problem of reduced low-temperature performance or even failure of aqueous electrolyte systems in the prior art, the main purpose of the present invention is to provide a low-temperature aqueous sodium ion battery electrolyte, which improves the working performance of aqueous sodium ion batteries under low temperature conditions by optimizing the electrolyte formula and introducing organic additives.

[0005] Another object of the present invention is to provide a method for preparing the low-temperature aqueous sodium ion battery electrolyte, using sodium chloride as the sodium salt, water and N,N-dimethylacetamide with a high dielectric constant and a low freezing point as solvents, breaking the hydrogen bond network between water molecules by combining the carbonyl group of N,N-dimethylacetamide with the hydroxyl group of water, significantly reducing the freezing point of the electrolyte, and obtaining excellent low-temperature performance.

[0006] Another object of the present invention is to provide a high-performance aqueous sodium ion battery, which comprises the low-temperature aqueous sodium ion battery electrolyte.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] In a first aspect of the present invention, a low-temperature aqueous sodium ion battery electrolyte is provided, comprising a sodium salt and a solvent system;

[0009] The concentration of the sodium salt is 0.5 to 2.5 mol / L;

[0010] The solvent system consists of water and a solvent with a dielectric constant greater than 30 and a freezing point lower than -20°C.

[0011] The low-temperature aqueous sodium ion battery electrolyte of the present invention effectively improves the conductivity of the electrolyte under low-temperature conditions and significantly reduces the freezing point of the entire electrolyte system by introducing such solvents with low freezing points and high dielectric constants.

[0012] Preferably, the sodium salt is sodium chloride.

[0013] Preferably, the solvent system consists of water and N,N-dimethylacetamide, and in terms of volume percentage, the volume percentage of water is 50-70 vol%, and the volume percentage of N,N-dimethylacetamide is 30-50 vol%.

[0014] The operating temperature of the low-temperature aqueous sodium ion battery electrolyte is -40 to 25°C.

[0015] The second aspect of the present invention also provides a method for preparing the low-temperature aqueous sodium ion battery electrolyte, comprising the following steps: adding a sodium salt and a solvent system into a container respectively, magnetically stirring at a speed of 200 to 400 r / min for 8 to 16 hours, and then standing for 8 to 16 hours to obtain.

[0016] Preferably, the sodium salt and the solvent system are added to a container respectively, magnetically stirred at a speed of 300 r / min for 12 hours, and then left to stand for 12 hours.

[0017] The third aspect of the present invention also provides a high-performance aqueous sodium ion battery, which comprises the low-temperature aqueous sodium ion battery electrolyte.

[0018] Preferably, the positive electrode active material of the high performance aqueous sodium ion battery is Na2CoFe(CN)6, and the negative electrode active material of the high performance aqueous sodium ion battery is activated carbon.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention adds an organic solvent N,N-dimethylacetamide to a sodium salt (sodium chloride) solution to obtain a low-temperature aqueous sodium ion battery electrolyte. The carbonyl group of N,N-dimethylacetamide combines with the hydroxyl group of water to form a hydrogen bond, breaking the hydrogen bond network of water molecules, thereby lowering the freezing point of the electrolyte, maintaining a liquid state at -40°C, and having excellent ionic conductivity.

[0021] 2. The battery assembled from the low-temperature aqueous sodium ion battery electrolyte of the present invention has excellent rate performance and capacity retention rate, good charge and discharge performance, high cycle life, simple preparation process and convenient flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The freezing conditions of the electrolytes prepared in Comparative Example 1 and Examples 1-5 at different temperatures.

[0023] Figure 2 The figure shows the rate performance of the electrolyte prepared in Example 6 at -40°C.

[0024] Figure 3 The cycle performance of the electrolyte prepared in Example 6 at -40°C.

[0025] Figure 4 The actual application status of the battery assembled with the electrolyte prepared in Example 6 and Comparative Example 2. DETAILED DESCRIPTION

[0026] In order to more fully understand and demonstrate the technical solutions, purposes and advantages of the present invention, the technical effects produced by the present invention are further described in detail and completely in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all. It should be pointed out that for ordinary technicians in this field, other embodiments obtained without departing from the concept of the present invention all belong to the protection scope of the present invention.

[0027] Example 1

[0028] This embodiment provides a low-temperature electrolyte, and the preparation steps are as follows:

[0029] The composition of the mixed solvent is: 70 vol% of water, 30 vol% of N,N-dimethylacetamide, and NaCl dissolved in the mixed solvent at a molar concentration of 0.5 mol / L.

[0030] Preparation of low-temperature electrolyte: Weigh a certain amount of water into a sample bottle, and add N,N-dimethylacetamide and NaCl in sequence, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours.

[0031] Example 2

[0032] This embodiment provides a low-temperature electrolyte, and the preparation steps are as follows:

[0033] The composition of the mixed solvent is: 60 vol% of water, 40 vol% of N,N-dimethylacetamide, and NaCl dissolved in the mixed solvent at a molar concentration of 0.5 mol / L.

[0034] Preparation of low-temperature electrolyte: Weigh a certain amount of water into a sample bottle, and add N,N-dimethylacetamide and NaCl in sequence, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours.

[0035] Example 3

[0036] This embodiment provides a low-temperature electrolyte, and the preparation steps are as follows:

[0037] The composition of the mixed solvent is: 60 vol% of water, 40 vol% of N,N-dimethylacetamide, and NaCl dissolved in the mixed solvent at a molar concentration of 2 mol / L.

[0038] Preparation of low-temperature electrolyte: Weigh a certain amount of water into a sample bottle, and add N,N-dimethylacetamide and NaCl in sequence, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours.

[0039] Example 4

[0040] This embodiment provides a low-temperature electrolyte, and the preparation steps are as follows:

[0041] The composition of the mixed solvent is: 50 vol% of water and 50 vol% of N,N-dimethylacetamide, wherein NaCl is dissolved in the mixed solvent at a molar concentration of 0.5 mol / L.

[0042] Preparation of low-temperature electrolyte: Weigh a certain amount of water into a sample bottle, and add N,N-dimethylacetamide and NaCl in sequence, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours.

[0043] Example 5

[0044] This embodiment provides a low-temperature electrolyte, and the preparation steps are as follows:

[0045] The composition of the mixed solvent is: 50 vol% of water and 50 vol% of N,N-dimethylacetamide, wherein NaCl is dissolved in the mixed solvent at a molar concentration of 1.5 mol / L.

[0046] Preparation of low-temperature electrolyte: Weigh a certain amount of water into a sample bottle, and add N,N-dimethylacetamide and NaCl in sequence, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours.

[0047] Example 6

[0048] This embodiment provides an aqueous sodium ion battery, and the preparation steps are as follows:

[0049] Na2CoFe(CN)6, conductive agent acetylene black, and binder (PVDF) are mixed in a mass ratio of 7:2:1, ground with a mortar, and then an appropriate amount of organic solvent N-methyl-2-pyrrolidone (NMP) is added to the mixture, and then grinding is continued until uniform. The uniform slurry is coated on carbon paper using a four-sided coater, and then the coated electrode is transferred to a vacuum oven and vacuum dried at 90°C for 12 hours. The production process of the activated carbon (AC) negative electrode sheet is the same as that of the positive electrode sheet. The dried electrode sheet is cut and used for later use. Titanium foil is used as the pole ear, and the pole ear is assembled in the order of the pole ear, AC negative electrode sheet, Whatman diaphragm, Na2CoFe(CN)6 positive electrode sheet, and the pole ear. The low-temperature electrolyte prepared in Example 3 is directly dripped on the Whatman diaphragm, assembled into a battery, and left to stand for 4 hours to obtain an aqueous sodium ion battery.

[0050] Comparative Example 1

[0051] The composition of the single-solvent electrolyte: water is used as the single solvent, wherein sodium sulfate is dissolved in water at a molar concentration of 1 mol / L. Preparation of the single-solvent electrolyte: weigh a certain amount of water and put it into a sample bottle, add sodium sulfate, then place it on a magnetic stirrer, stir it thoroughly at a speed of 300 r / min for 12 hours, and let it stand for 12 hours to obtain it.

[0052] Comparative Example 2

[0053] The commercial button battery is the AG3 button battery produced by Shenzhen Beidongli Technology Co., Ltd.

[0054] Figure 1 The electrolytes prepared in Comparative Example 1 and Examples 1-5 freeze at different temperatures. From left to right, they are Comparative Example 1, Examples 1 to 5. It can be seen that using N,N-dimethylacetamide as an additive can significantly improve the freezing point of the electrolyte. When the volume ratio of the additive is 40% and 50%, the electrolyte remains liquid at -40°C.

[0055] Table 1

[0056]

[0057] The test results of the ionic conductivity of the electrolytes prepared in Examples 1-5 and Comparative Example 1 at -40 to 25°C are shown in Table 1. It can be seen that the addition of N,N-dimethylacetamide reduces the ionic conductivity. When 40% by volume of N,N-dimethylacetamide and 2 mol / L of NaCl are added, the ionic conductivity at -40°C can be maintained at 1.1 mS·cm -1 .

[0058] The blue electric test system was used to test the charge and discharge performance of the aqueous sodium ion battery prepared in Example 6 at different temperatures. During the test, 1C = 150 mA -1 ,like Figure 2-4 As shown:

[0059] from Figure 2 It can be seen that when the current rate increases from 1C to 6C at -40°C, the battery can still maintain stable power supply. When the current density decreases from 6C to 1C, the battery specific capacity returns to the initial level, indicating that the aqueous sodium ion battery has excellent rate performance at -40°C.

[0060] from Figure 3 It can be seen that after 1000 cycles, the capacity retention rate of the battery is 97.8%. The excellent capacity retention rate indicates that the aqueous sodium ion battery has good cycle stability.

[0061] from Figure 4 It can be seen that the AG3 button battery of Comparative Example 2 fails at -40°C and cannot power the night light. However, the aqueous sodium ion battery prepared in Example 6 can still light up the LED at -40°C, proving that the low-temperature electrolyte of the present invention can be used in practice, has excellent electrochemical properties and long-term stability, and is a promising low-temperature electrolyte.

[0062] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-temperature aqueous sodium ion battery electrolyte, characterized in that: including a sodium salt and a solvent system; The concentration of the sodium salt is 0.5 to 2.5 mol / L; The solvent system consists of water and a solvent with a dielectric constant greater than 30 and a freezing point lower than -20°C.

2. The low-temperature aqueous sodium ion battery electrolyte according to claim 1, characterized in that The sodium salt is sodium chloride.

3. The low-temperature aqueous sodium ion battery electrolyte according to claim 1, characterized in that: The solvent system consists of water and N,N-dimethylacetamide. According to volume percentage, the volume percentage of water is 50-70 vol%, and the volume percentage of N,N-dimethylacetamide is 30-50 vol%.

4. The low-temperature aqueous sodium ion battery electrolyte according to claim 1, characterized in that: The operating temperature of the low-temperature aqueous sodium ion battery electrolyte is -40 to 25°C.

5. The method for preparing the low-temperature aqueous sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that: include: The sodium salt and the solvent system are added into a container respectively, and magnetically stirred at a speed of 200 to 400 r / min for 8 to 16 hours, and then allowed to stand for 8 to 16 hours to obtain the product.

6. The method for preparing a low-temperature aqueous sodium ion battery electrolyte according to claim 5, characterized in that: include: The sodium salt and the solvent system are added into the container respectively, and the mixture is magnetically stirred at a speed of 300 r / min for 12 hours, and then allowed to stand for 12 hours to obtain the product.

7. A high performance aqueous sodium ion battery, characterized in that: It comprises the low-temperature aqueous sodium ion battery electrolyte as described in any one of claims 1 to 4.

8. The high performance aqueous sodium ion battery according to claim 7, characterized in that: The positive electrode active material of the high-performance aqueous sodium ion battery is Na2CoFe(CN)6, and the negative electrode active material of the high-performance aqueous sodium ion battery is activated carbon.

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