Low-temperature-resistant double-salt-double-solvent electrolyte, preparation method and application of low-temperature-resistant double-salt-double-solvent electrolyte in sodium-ion battery

Abstract

The invention discloses a low-temperature-resistant double-salt-double-solvent electrolyte, a preparation method and application of the low-temperature-resistant double-salt-double-solvent electrolyte in a sodium-ion battery, and belongs to the technical field of new energy. The method comprises the following steps: dissolving two sodium salts in a chain organic solvent to obtain a double-salt-single-solvent electrolyte; and then adding an annular organic solvent into the double-salt-single-solvent electrolyte to obtain the low-temperature-resistant double-salt-double-solvent electrolyte. Through the synergistic effect of the double sodium salts, the electrolyte can still keep high ionic conductivity under a low-temperature condition; the cyclic molecular structure organic solvent is introduced as a cosolvent, so that the sodium ion transmission rate is accelerated; a double-salt-double-solvent electrolyte system promotes generation of an interfacial film rich in inorganic components on the surface of the hard carbon negative electrode, so that the coulombic efficiency and the cycling stability of the battery are improved; the sodium ion battery prepared from the double-salt-double-solvent electrolyte, a high-voltage positive electrode and a hard carbon negative electrode can be stably charged and discharged at-20 DEG C, and has excellent rate capability and long cycle life; the preparation process is simple, low in cost and applicable to large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology and relates to a low-temperature resistant dual-salt-dual-solvent electrolyte, its preparation method, and its application in sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries, with their significant advantages such as abundant sodium resources, low cost, and environmental friendliness, have shown broad application prospects in large-scale energy storage and low-speed electric vehicles. However, their commercialization process still faces many severe challenges, especially the problem of rapid performance degradation at low temperatures. When the ambient temperature is below zero, the viscosity of traditional ester-based electrolytes increases significantly, and the ionic conductivity decreases sharply. At the same time, the desolvation barrier at the electrode-electrolyte interface increases significantly, leading to a sharp deterioration in the battery's capacity and rate performance, making it almost impossible to operate normally at -20 °C and lower temperatures.

[0003] To overcome the bottleneck of low-temperature performance, existing technologies have explored various approaches. For example, using low-melting-point ether solvents can improve the low-temperature fluidity of electrolytes to some extent. However, single ether solvents have drawbacks such as poor oxidation resistance and a narrow electrochemical window. They are prone to decomposition under high-voltage conditions and are difficult to adapt to high-voltage cathode materials (such as layered oxides), resulting in poor battery cycle stability. In addition, existing research has also used ether-based electrolytes to improve the low-temperature performance of sodium-ion batteries. However, in electrolytes containing a single sodium salt, the electrode interface layer formed is difficult to meet the needs of both positive and negative electrodes and lacks stability, limiting the long-term cycle stability of sodium-ion batteries.

[0004] Currently, developing new electrolyte systems that combine excellent low-temperature performance and high-voltage resistance has become an urgent need to promote the application of sodium-ion batteries in cold-region energy storage and electric transportation. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a low-temperature resistant dual-salt-dual-solvent electrolyte, its preparation method, and its application in sodium-ion batteries. This invention aims to utilize a dual-salt electrolyte composed of sodium trifluoromethanesulfonate and sodium perchlorate, matched with a dual-solvent system composed of diethylene glycol dimethyl ether and tetrahydrofuran. Through the synergistic effect of the dual-salt electrolyte and the dual-solvent system, the low-temperature performance of the sodium-ion electrolyte is improved, its operating temperature range is broadened, and the problems of traditional sodium-ion battery electrolytes being unable to withstand high voltages and exhibiting rapid degradation of interfacial properties are solved. Sodium-ion batteries constructed using this electrolyte can achieve stable operation at -20 °C, demonstrating broad application potential.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a low-temperature resistant dual-salt-dual-solvent electrolyte, comprising dissolving two sodium salts in a chain-like organic solvent to obtain a dual-salt-single-solvent electrolyte; then adding a cyclic organic solvent to the dual-salt-single-solvent electrolyte to obtain a low-temperature resistant dual-salt-dual-solvent electrolyte. Specifically, the method includes the following steps:

[0008] The first step is to dissolve the two sodium salts in an organic solvent with a chain-like molecular structure to obtain a dual-salt-single-solvent electrolyte.

[0009] The organic solvent with the chain-like molecular structure is any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether.

[0010] The sodium salt is any two of sodium trifluoromethanesulfonate, sodium perchlorate, sodium hexafluorophosphate, or sodium tetrafluoroborate.

[0011] There are six possible combinations of sodium salts in the aforementioned dual-salt-single-solvent electrolyte. Regardless of the combination, the concentration requirements for each sodium salt are as follows: sodium trifluoromethanesulfonate concentration is 30~200 mg / mL. -1 The concentration of sodium perchlorate is 20~150 mg / mL. -1 The concentration of sodium hexafluorophosphate is 30~200 mg / mL. -1 The concentration of sodium tetrafluoroborate is 20~150 mg / mL. -1 .

[0012] The second step involves mixing the cyclic molecular structure of the organic solvent with the dual-salt-single-solvent electrolyte prepared in the first step to obtain the dual-salt-dual-solvent electrolyte.

[0013] The cyclic molecular structure organic solvent is at least one of tetrahydrofuran, 2-methyltetrahydrofuran, or 1,3-dioxolane.

[0014] In the aforementioned dual-salt-dual-solvent electrolyte, the molar ratio of the chain-structured organic solvent to the cyclic-structured organic solvent is 1:1 to 5:1.

[0015] A low-temperature resistant dual-salt-dual-solvent electrolyte is prepared using the method described above.

[0016] An application of a low-temperature resistant dual-salt-dual-solvent electrolyte is disclosed, which is used as an electrolyte in the preparation of low-temperature resistant, long-cycle-life sodium-ion batteries. Specifically, the low-temperature resistant dual-salt-dual-solvent electrolyte prepared in this invention is compatible with sodium-ion battery cathodes including at least one of sodium nickel manganate, sodium vanadium phosphate, sodium iron pyrophosphate, and sodium iron sulfate, and anodes including hard carbon.

[0017] Compared with existing technologies, this invention solves the problems of conventional ether-based electrolytes being intolerant to high voltages, difficult to adapt to high-voltage cathode materials, and the resulting electrode interface layer failing to meet the requirements of both positive and negative electrodes, resulting in insufficient stability and limiting the long-term cycle stability of sodium-ion batteries. Its beneficial effects are as follows:

[0018] (1) By synergistic effect of double sodium salts, the sodium ion solvation structure is optimized, the ion migration energy barrier at low temperature is reduced, and the electrolyte can still maintain high ionic conductivity under low temperature conditions.

[0019] (2) Introduce a low-viscosity, weakly coordinated cyclic molecular structure organic solvent as a co-solvent to reduce the viscosity of the system, alleviate low-temperature polarization, and accelerate the sodium ion transport rate.

[0020] (3) The dual-salt-dual-solvent electrolyte system promotes the formation of an interface film rich in inorganic components on the surface of the hard carbon anode, reduces the reduction of electrolyte on the surface of the hard carbon anode and irreversible sodium loss, and improves the coulombic efficiency and cycle stability of the battery.

[0021] (4) The sodium-ion battery prepared using this dual-salt-dual-solvent electrolyte with high-voltage positive electrode and hard carbon negative electrode can be stably charged and discharged at -20℃, and has excellent rate performance and long cycle life.

[0022] (5) The main components of the dual-salt-dual-solvent electrolyte are all commercial products. The preparation process is simple, the cost is low, and it can be applied to large-scale industrial production. Attached Figure Description

[0023] Figure 1 This is a test diagram of the electrochemical stability window of the dual-salt-dual-solvent electrolyte prepared in Example 1 of the present invention.

[0024] Figure 2 This is a graph showing the ionic conductivity of the dual-salt-dual-solvent electrolyte prepared in Example 1 of this invention.

[0025] Figure 3 The charge-discharge curves of a sodium-ion battery prepared using the dual-salt-dual-solvent electrolyte prepared in Example 1 of this invention, with sodium nickel iron manganate as the positive electrode and hard carbon as the negative electrode, are shown at -20 °C.

[0026] Figure 4 This is a cycle life diagram at -20 °C for a sodium-ion battery assembled using the dual-salt-dual-solvent electrolyte prepared in Example 1 of this invention, with sodium nickel iron manganate as the positive electrode and hard carbon as the negative electrode. Detailed Implementation

[0027] In view of the many shortcomings of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles. However, it should be understood that within the scope of this invention, the above-mentioned technical features of this invention and the technical features specifically described below (exemplary embodiments) can be combined with each other to constitute new or preferred technical solutions. Unless otherwise specified, the materials, reagents, etc., used in the following examples are commercially available.

[0028] Example 1

[0029] 1) Sodium trifluoromethanesulfonate and sodium perchlorate were dissolved in diethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium trifluoromethanesulfonate was 70 mg / mL. -1 The concentration of sodium perchlorate is 70 mg / mL. -1 .

[0030] 2) Mix tetrahydrofuran with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of diethylene glycol dimethyl ether to tetrahydrofuran is 3:1.

[0031] Figure 1 This is a test chart of the electrochemical stability window of the dual-salt-dual-solvent electrolyte prepared in this embodiment, showing that this electrolyte can withstand a high voltage of 4.8 V.

[0032] Figure 2 This is a graph showing the ionic conductivity of the dual-salt, dual-solvent electrolyte prepared in Example 1 of this invention. Its ionic conductivity at -20°C reaches 2.4 mS / cm. -1 .

[0033] Figure 3 The charge-discharge curve of a sodium-ion battery assembled using the dual-salt-dual-solvent electrolyte prepared in Example 1 of this invention, with sodium nickel iron manganate as the positive electrode and hard carbon as the negative electrode, is shown at -20 °C. The battery's first-cycle discharge specific capacity is 112.83 mAhg. -1 The first lap coulomb efficiency was 75.14%.

[0034] Figure 4 This is a cycle life diagram at -20 °C for a sodium-ion battery assembled using the dual-salt-dual-solvent electrolyte prepared in Example 1 of this invention, with sodium nickel iron manganese oxide as the positive electrode and hard carbon as the negative electrode. The cycle life exceeds 250 cycles. In the application of this example, the electrolyte of the sodium-ion battery is the dual-salt-dual-solvent electrolyte prepared in this example, with sodium nickel iron manganese oxide as the positive electrode and hard carbon as the negative electrode.

[0035] Example 2

[0036] 1) Sodium trifluoromethanesulfonate and sodium hexafluorophosphate were dissolved in diethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium trifluoromethanesulfonate was 30 mg / mL. -1 The concentration of sodium hexafluorophosphate is 200 mg / mL. -1 .

[0037] 2) Mix tetrahydrofuran with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of diethylene glycol dimethyl ether to tetrahydrofuran is 3:1.

[0038] In this embodiment, the electrolyte of the sodium-ion battery is the dual-salt, dual-solvent electrolyte prepared in this embodiment, with sodium vanadium phosphate as the positive electrode and hard carbon as the negative electrode. The prepared battery has a first-cycle discharge specific capacity of 108 mAh g at -20 °C. -1 The first lap coulomb efficiency was 72.54%.

[0039] Example 3

[0040] 1) Sodium trifluoromethanesulfonate and sodium tetrafluoroborate were dissolved in triethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium trifluoromethanesulfonate was 200 mg / mL. -1 The concentration of sodium tetrafluoroborate is 50 mg / mL. -1 .

[0041] 2) Mix 1,3-dioxolane with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of triethylene glycol dimethyl ether to 1,3-dioxolane is 1:1.

[0042] In this embodiment, the electrolyte of the sodium-ion battery is the dual-salt, dual-solvent electrolyte prepared in this embodiment, with sodium iron pyrophosphate as the positive electrode and hard carbon as the negative electrode. The prepared battery has a cycle life of over 100 cycles at -20 °C and a capacity retention rate of 75%.

[0043] Example 4

[0044] 1) Sodium hexafluorophosphate and sodium tetrafluoroborate were dissolved in triethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium hexafluorophosphate was 120 mg / mL. -1 The concentration of sodium tetrafluoroborate is 20 mg / mL. -1 .

[0045] 2) Mix 1,3-dioxolane with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of triethylene glycol dimethyl ether to 1,3-dioxolane is 2:1.

[0046] In this embodiment, the electrolyte of the sodium-ion battery is the dual-salt, dual-solvent electrolyte prepared in this embodiment, with sodium iron sulfate as the positive electrode and hard carbon as the negative electrode. The prepared battery exhibits a discharge specific capacity of 70 mAh g⁻¹ under environmental conditions of -20 °C and a rate of 3C. -1 .

[0047] Example 5

[0048] 1) Sodium hexafluorophosphate and sodium perchlorate were dissolved in tetraethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium hexafluorophosphate was 30 mg / mL. -1 The concentration of sodium perchlorate is 150 mg / mL. -1 .

[0049] 2) Mix 2-methyltetrahydrofuran with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of tetraethylene glycol dimethyl ether to 2-methyltetrahydrofuran is 4:1.

[0050] In this embodiment, the electrolyte of the sodium-ion battery is the dual-salt, dual-solvent electrolyte prepared in this embodiment, with sodium nickel iron manganese oxide as the positive electrode and hard carbon as the negative electrode. The prepared battery has a cycle life of over 50 cycles at -10 °C and a capacity retention rate of 75%.

[0051] Example 6

[0052] 1) Sodium perchlorate and sodium tetrafluoroborate were dissolved in tetraethylene glycol dimethyl ether to obtain a dual-salt-single-solvent electrolyte. The concentration of sodium perchlorate was 20 mg / mL. -1 The concentration of sodium tetrafluoroborate is 150 mg / mL. -1 .

[0053] 2) Mix 2-methyltetrahydrofuran with the dual-salt-single-solvent electrolyte prepared in step 1) to obtain a dual-salt-dual-solvent electrolyte. The molar ratio of tetraethylene glycol dimethyl ether to 2-methyltetrahydrofuran is 5:1.

[0054] In this embodiment, the electrolyte of the sodium-ion battery is the dual-salt, dual-solvent electrolyte prepared in this embodiment, with sodium iron pyrophosphate as the positive electrode and hard carbon as the negative electrode. The prepared battery has a first-cycle discharge specific capacity of 100 mAh g at -10 °C. -1 The first lap coulomb efficiency is 75%.

[0055] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature resistant dual-salt-dual-solvent electrolyte, characterized in that, The preparation method includes the following steps: The first step involves dissolving two sodium salts in an organic solvent with a chain-like molecular structure to obtain a dual-salt-single-solvent electrolyte; the sodium salts are any two of sodium trifluoromethanesulfonate, sodium perchlorate, sodium hexafluorophosphate, or sodium tetrafluoroborate. The second step involves mixing the cyclic molecular structure of the organic solvent with the dual-salt-single-solvent electrolyte prepared in the first step to obtain the dual-salt-dual-solvent electrolyte. In the aforementioned dual-salt-dual-solvent electrolyte, the molar ratio of the chain-structured organic solvent to the cyclic-structured organic solvent is 1:1 to 5:

1.

2. The method for preparing a low-temperature resistant dual-salt-dual-solvent electrolyte according to claim 1, characterized in that, In the first step, the organic solvent with the chain-like molecular structure is any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether.

3. The method for preparing a low-temperature resistant dual-salt-dual-solvent electrolyte according to claim 1, characterized in that, In the first step, there are six possible combinations of sodium salts in the dual-salt-single-solvent electrolyte, and the concentration requirements for each sodium salt are as follows: sodium trifluoromethanesulfonate concentration is 30~200 mg / mL. -1 The concentration of sodium perchlorate is 20~150 mg / mL. -1 The concentration of sodium hexafluorophosphate is 30~200 mg / mL. -1 The concentration of sodium tetrafluoroborate is 20~150 mg / mL. -1 .

4. The method for preparing a low-temperature resistant dual-salt-dual-solvent electrolyte according to claim 1, characterized in that, In the second step, the cyclic molecular structure organic solvent is at least one of tetrahydrofuran, 2-methyltetrahydrofuran, or 1,3-dioxolane.

5. A low-temperature resistant dual-salt-dual-solvent electrolyte, characterized in that, The low-temperature resistant dual-salt-dual-solvent electrolyte is prepared by any one of the preparation methods described in claims 1-4.

6. An application of the low-temperature resistant dual-salt-dual-solvent electrolyte as described in claim 5, characterized in that, It is used as an electrolyte in sodium-ion batteries.

7. The application of the low-temperature resistant dual-salt-dual-solvent electrolyte according to claim 6, characterized in that, The positive electrode of the sodium-ion battery adapted to the low-temperature resistant dual-salt-dual-solvent electrolyte includes at least one of sodium nickel manganate, sodium vanadium phosphate, sodium iron pyrophosphate, and sodium iron sulfate, and the negative electrode is hard carbon.

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