High-pressure-resistant sodium-ion battery electrolyte, preparation method and application thereof

Abstract

The application discloses a high-pressure-resistant sodium ion battery electrolyte and a preparation method and application thereof, and relates to the technical field of sodium ion batteries.The high-pressure-resistant sodium ion battery electrolyte comprises the following components in percentage by volume: 70-80% of a carbonate organic solvent and 20-30% of a diluent; and further comprises a conductive sodium salt, and the concentration of the conductive sodium salt is 1-2 mol / L.The application further comprises a preparation method and application of the high-pressure-resistant sodium ion battery electrolyte.The electrolyte uses a solvent with small polarity, which weakens the interaction between sodium ions and solvent molecules, thereby accelerating the desolvation of sodium ions at the electrode interface.The electrolyte obtained by the application has good compatibility with a layered oxide positive electrode and a sodium metal negative electrode, and overcomes the problems of continuous decomposition of a conventional sodium ion battery electrolyte and an interface, and is favorable for the sodium ion battery to have good cycle performance and rate performance under a high-pressure working state.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a high-voltage resistant sodium-ion battery electrolyte, its preparation method, and its application. Background Technology

[0002] Among numerous energy storage technologies, electrochemical energy storage systems, especially rechargeable secondary batteries, have attracted much attention due to their high energy transfer efficiency, long cycle life, low maintenance costs, and ease of modularization. With the large-scale application of lithium-ion batteries, concerns about lithium resources have spurred the rapid development of sodium-ion batteries as an alternative energy source. Sodium resources are abundant and widely distributed globally, and sodium-ion batteries have a similar structure and working principle to lithium-ion batteries. Therefore, the development of sodium-ion batteries shows great promise in the field of large-scale energy storage. P2-type layered oxides, as a representative material, are considered the most promising cathode material for sodium-ion batteries due to their low cost and high theoretical capacity. However, layered oxides undergo a large-volume P2-O2 phase transition at high voltages around 4.2V, and traditional electrolytes are not stable enough under high voltage, resulting in poor cycle performance, which severely restricts the commercial application of high-voltage cathode materials. Besides suppressing phase transitions through ion substitution or doping strategies, developing an electrolyte with high voltage resistance and good cycle stability is also an effective way to improve electrochemical performance.

[0003] In recent years, numerous studies have shown that high-concentration electrolytes not only increase the oxidative stability of the electrolyte bulk but also enhance the proportion of coordination contact ion pairs (CIPs) and ion aggregates (AGGs) in the electrolyte solvation structure. This is beneficial for the formation of inorganic-rich SEI and CEI. These advantages of high-concentration electrolytes significantly improve the cycle stability of sodium-ion batteries. However, in high-salt systems, as the concentration increases, the interaction forces between anions and cations also increase. Increased electrolyte viscosity leads to decreased ionic conductivity, resulting in poorer electrolyte wettability to the electrodes, i.e., poorer interfacial compatibility. Simultaneously, the increased use of conductive sodium salts will raise battery costs, hindering the commercial application of HCEs.

[0004] To address these issues, researchers have proposed the concept of locally high-concentration electrolyte solutions (LHCEs) and applied them to the field of lithium / sodium-ion batteries. This involves adding a diluent to a high-concentration electrolyte to reduce its concentration while maintaining a similar locally solvated structure. The diluent itself has a similar or wider electrochemical window to the high-concentration electrolyte, is insoluble in salts but miscible with solvents, forming an (ion-solvent) diluent state. To date, fluorinated ethers have been widely used as diluents in locally high-concentration electrolytes for lithium batteries, achieving good electrochemical performance. Therefore, to promote the development of locally high-concentration electrolytes for sodium-ion batteries, it is urgent to design a high-voltage-resistant locally high-concentration electrolyte to further improve the cycle stability of sodium-ion batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a high-voltage resistant sodium-ion battery electrolyte, its preparation method, and its application. This electrolyte is used to improve the electrochemical stability window of the electrolyte, further enhancing the cycle stability of sodium-ion batteries under high-voltage conditions. It effectively solves the problems of continuous decomposition at the interface, low cycle stability under high-voltage conditions, and high cost of conventional sodium-ion battery electrolytes in the prior art.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a high-voltage resistant sodium-ion battery electrolyte is provided, comprising the following volume percentage components: 70-80% carbonate organic solvent and 20-30% diluent; and further comprising conductive sodium salt, wherein the concentration of conductive sodium salt is 1-2 mol / L.

[0007] Furthermore, the high-voltage sodium-ion battery electrolyte comprises the following volume percentage components: 70% carbonate organic solvent and 30% diluent; it also includes a conductive sodium salt with a concentration of 1 mol / L.

[0008] Furthermore, the diluent is a fluorinated ether compound that is insoluble in sodium salts.

[0009] Furthermore, such as Figure 1 As shown, the fluorinated ether compounds insoluble in sodium salts are at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2-difluoroethyl) ether, and 2,2,2-trifluoroethyl ether.

[0010] Furthermore, the fluorinated ether compound insoluble in sodium salt is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0011] Furthermore, the carbonate organic solvent is at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, and fluoroethylene carbonate.

[0012] Furthermore, the carbonate organic solvent is fluoroethylene carbonate and methyl ethyl carbonate, with a volume ratio of fluoroethylene carbonate to methyl ethyl carbonate of 1:1-6.

[0013] Furthermore, the conductive sodium salt is at least one of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonylimide, and sodium bis(trifluoromethylsulfonyl)imide.

[0014] Furthermore, the conductive sodium salt is sodium hexafluorophosphate (NaPF6).

[0015] The preparation method of the above-mentioned high-voltage resistant sodium-ion battery electrolyte includes the following steps:

[0016] In an argon-protected glove box, carbonate organic solvents and diluents are mixed and stirred until homogeneous. Then, molecular sieves are added to remove water and purify the mixture, resulting in a mixed solution. The mixed solution is then mixed with conductive sodium salt and magnetically stirred for 2-4 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0017] Furthermore, the molecular sieve is a 4A molecular sieve.

[0018] Furthermore, after dehydration and purification using molecular sieves, the purity of carbonate organic solvents is ≥99.9%, and the water content is less than 10 ppm.

[0019] Furthermore, the oxygen and water content inside the glove box is <0.01ppm.

[0020] The application of the above-mentioned high-voltage resistant sodium-ion battery electrolyte in the preparation of sodium-ion batteries.

[0021] Furthermore, the positive electrode material of the sodium-ion battery is a layered oxide, and the negative electrode material is sodium metal.

[0022] The present invention has the following beneficial effects:

[0023] 1. The electrolyte of the present invention is used to improve the electrochemical stability window of the electrolyte, further enhance the cycle stability of sodium-ion batteries under high voltage conditions, and effectively solve the problems of continuous decomposition of electrolyte and interface, low cycle stability under high voltage conditions, and high cost in conventional sodium-ion battery technologies.

[0024] 2. The electrolyte of this invention uses a solvent with low polarity, which weakens the interaction between sodium ions and solvent molecules, thereby accelerating the desolvation of sodium ions at the electrode interface. Furthermore, the diluent increases the local concentration, resulting in excellent CEI formation at the interface, thus achieving long battery cycle life. The electrolyte obtained by this invention has good compatibility with layered oxide cathodes and sodium metal anodes, and overcomes the problem of continuous decomposition at the interface in conventional sodium-ion battery electrolytes, which is beneficial for sodium-ion batteries to have good cycle performance and rate performance under high-voltage operating conditions.

[0025] 3. Highly fluorinated ether compounds (such as TTE, HFE) are characterized by low polarity, low dielectric constant, and low viscosity. Due to the presence of numerous electron-withdrawing fluorine atoms, their solubility is reduced, making them more difficult to react with Na. + Direct solvation means that highly fluorinated ether compounds are miscible with conductive sodium salts. Compared to commercial sodium-ion battery electrolytes, the high-voltage resistant sodium-ion battery electrolyte provided by this invention features a locally high-concentration electrolyte formulation. The use of a diluent significantly reduces the electrolyte viscosity, facilitating thorough wetting of the positive and negative electrodes and the separator. Simultaneously, it promotes the formation of anion-dominated solvent shell structure, expanding the electrolyte's electrochemical stability window and effectively improving the cycle stability of sodium-ion batteries under high-voltage conditions. Attached Figure Description

[0026] Figure 1 The chemical structural formula of a fluorinated ether compound that is insoluble in sodium salt;

[0027] Figure 2 The cycle performance of coin cells assembled with sodium-ion battery electrolytes obtained in Example 1 and Comparative Examples 2-3;

[0028] Figure 3 Cycle performance of coin cells assembled with sodium-ion battery electrolytes obtained in Examples 1-5 and Comparative Example 3;

[0029] Figure 4 The rate performance of coin cells assembled with sodium-ion battery electrolytes obtained in Example 1 and Comparative Example 2 is shown. Detailed Implementation

[0030] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0031] Preparation of positive electrode material: P2 layered oxide powder, conductive carbon black and polyvinylidene fluoride were mixed in a mass ratio of 7.5:1.5:1, an appropriate amount of NMP was added, and the mixture was stirred in a ball mill for 0.5 h. Then it was evenly coated on aluminum foil. It was first dried in an 80°C forced-air drying oven for 0.5 h, and then vacuum dried in an 80°C vacuum drying oven for 12 h. After being taken out, it was cut into 10 mm circular electrode sheets using a slicer, weighed and placed in a glove box.

[0032] Assembly of button batteries: Place the sodium sheet in the middle of the negative electrode shell, put in the separator (Whatman GF / D 1823-090 glass fiber filter membrane), add 160uL of electrolyte, then place the positive electrode material face down on the separator, then put in the gasket, spring and positive electrode shell, and finally press and assemble into a CR2032 battery using a battery sealing machine. After standing for 6 hours, test it.

[0033] Example 1

[0034] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0035] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 6:1:3 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0036] Example 2

[0037] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0038] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 5:2:3 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0039] Example 3

[0040] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0041] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 4:3:3 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0042] Example 4

[0043] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0044] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 2:6:2 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0045] Example 5

[0046] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0047] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 4:4:2 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0048] Example 6

[0049] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0050] In an argon-protected glove box, ethyl methyl carbonate (EMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) at a volume ratio of 6:4 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0051] Example 7

[0052] A high-voltage resistant sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0053] In an argon-protected glove box, ethyl methyl carbonate (EMC) / fluoroethylene carbonate (FEC) / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 6:1:3 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 2 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a high-voltage sodium-ion battery electrolyte.

[0054] Comparative Example 1

[0055] A sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0056] In an argon-protected glove box, ethyl methyl carbonate (EMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) with a volume ratio of 7:3 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a sodium-ion battery electrolyte.

[0057] Comparative Example 2

[0058] A sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0059] In an argon-protected glove box, ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC) at a volume ratio of 9:1 were mixed and stirred until homogeneous. Then, molecular sieves were added to remove water and purify the mixture to obtain a mixed solution. The mixed solution was then mixed with 1 mol / L of conductive sodium salt NaPF6 and magnetically stirred for 3 hours to obtain a sodium-ion battery electrolyte.

[0060] Comparative Example 3

[0061] A sodium-ion battery electrolyte, the preparation method of which includes the following steps:

[0062] Dissolve 1 mol / L NaClO4 in a 1:1 volume ratio of propylene carbonate (PC) / dimethyl carbonate (DMC), and then add 5% fluoroethylene carbonate (FEC) to obtain the sodium-ion battery electrolyte.

[0063] Experimental Example

[0064] The sodium-ion battery electrolytes obtained in Examples 1-7 and Comparative Examples 1-3 were assembled with layered oxides, separators, sodium metal sheets, gaskets, spring sheets, and positive and negative electrode shells into coin cells. Charge-discharge cycle tests were conducted at a rate of 1C in a voltage range of 2.2V-4.4V, and the results are shown in Table 1.

[0065] The sodium-ion battery electrolytes obtained in Example 1 and Comparative Examples 2-3 were assembled into coin cells with layered oxides, separators, sodium metal sheets, gaskets, spring contacts, and positive and negative electrode shells. Charge-discharge cycle tests were conducted at a 1C rate within a voltage range of 2.2V-4.4V. The results are as follows: Figure 2 As shown. Among them, Figure 2 In the table, from top to bottom, are Example 1, Comparative Example 2, and Comparative Example 3.

[0066] Similarly, the sodium-ion battery electrolytes obtained in Examples 1-5 and Comparative Example 3 were assembled into coin cells, and the test results are as follows: Figure 3 As shown. Among them, Figure 3 From top to bottom, the examples are Example 1, Example 3, Example 2, Example 5, Comparative Example 2, and Example 4.

[0067] The sodium-ion battery electrolytes obtained in Example 1 and Comparative Example 2 were assembled into coin cells with layered oxides, separators, sodium metal sheets, gaskets, springs, and positive and negative electrode shells. Charge-discharge cycle tests were conducted at a rate of 1C within a voltage range of 2.2V-4.4V. Rate performance was also tested at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, 20C, and 0.2C. The results are as follows: Figure 4 As shown. Among them, Figure 4 In the middle, from top to bottom are Example 1 and Comparative Example 2.

[0068] Table 1. Charge-discharge cycle test results

[0069]

[0070] As shown in Table 1, the proportions of fluoroethylene carbonate (FEC) and diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in the electrolyte of this invention have a significant impact on battery performance. When the proportion of fluoroethylene carbonate is controlled at 10% and the proportion of diluent is controlled at 30%, the prepared battery exhibits the best cycle performance.

[0071] Adding fluoroethylene carbonate to the electrolyte significantly expands its electrochemical stability window. Comparing Example 1 and Comparative Example 1, without the addition of fluoroethylene carbonate (Comparative Example 1), the electrolyte exhibits poor oxidative stability, and the battery's initial charging voltage cannot reach 4.4V, making subsequent charge-discharge cycles impossible. After adding fluoroethylene carbonate (Example 1), the electrolyte's oxidative stability is significantly improved, demonstrating that fluoroethylene carbonate can significantly improve the electrolyte's high-voltage resistance.

[0072] Diluents play a crucial role in locally high-concentration electrolytes. Comparing Example 1 and Comparative Example 2, when no diluent is added (Comparative Example 2), there are more unsolvated free solvent molecules in the electrolyte, forming an interface dominated by organic matter at the electrolyte-electrode interface. This interface layer continuously decomposes during cycling, leading to poor battery cycle performance. Figure 2 As shown, the cycle retention rate was only 88.4%. However, in the electrolyte with added 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether diluent (Example 1), the number of free solvent molecules in the electrolyte decreased, forming a solvent shell structure dominated by anions. This structure may form an interface film dominated by inorganic matter at the interface. Therefore, the battery could still maintain a cycle retention rate of >95% after 100 cycles. However, when there was too much diluent or salt, such as when prepared according to the proportions in Examples 6 and 7, the electrolyte became noticeably turbid. This is a result of the immiscibility between the diluent and the salt.

[0073] Figure 2 Compared with Comparative Example 3, the electrolyte in Example 1 achieved a discharge specific capacity of 129.3 mAh g⁻¹ at a 1C rate in the first cycle. -1 The performance of the electrolyte far exceeds that of conventional electrolytes (Comparative Example 3). Moreover, after 100 battery cycles, the electrolyte of Example 1 achieved a capacity retention rate of 95.36%, compared to 87.25% for conventional electrolytes, significantly improving the electrochemical performance of the battery.

[0074] from Figure 3 It can be observed that, compared to other electrolyte ratios, when the volume percentage of diluent is 30% and the volume percentage of fluoroethylene carbonate is 10%, there are fewer free solvent molecules in the electrolyte than in other ratios. This allows for the formation of a solvent shell structure dominated by anions, resulting in optimal battery cycle performance. Figure 4 The rate performance of Example 1 and Comparative Example 2 shows that the electrolyte with a volume ratio of 6:1:3 still has 84 mAh g / L at a rate of 20C. -1 Its specific capacity far exceeds that of electrolyte without added diluent.

[0075] In summary, the high-voltage resistant sodium-ion battery electrolyte of the present invention, 1M NaPF6EMC:FEC:TTE (6:1:3), enables sodium-ion batteries using this electrolyte to achieve a discharge specific capacity of up to 129.3 mAh g at a current density of 1C under high voltage conditions of 2.2V-4.4V. -1 Furthermore, after 100 cycles, the capacity retention rate was 95.36%, and it still had 84 mAh g⁻¹ at a high current density of 20C. -1 The discharge specific capacity significantly improves the battery's cycle life and rate performance.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-voltage resistant sodium-ion battery electrolyte, characterized in that, It is composed of a carbonate organic solvent, a diluent, and a conductive sodium salt, with the volume percentages of the carbonate organic solvent and diluent being 70-80% and 20-30% respectively; the concentration of the conductive sodium salt is 1-2 mol / L; the carbonate organic solvent is fluoroethylene carbonate and methyl ethyl carbonate, with a volume ratio of 1:1-6; the diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, which is insoluble in sodium salt; and the high voltage is 2.2V-4.4V.

2. The high-voltage resistant sodium-ion battery electrolyte as described in claim 1, characterized in that, It comprises the following components by volume percentage: 70% carbonate organic solvent and 30% diluent; it also includes a conductive sodium salt with a concentration of 1 mol / L.

3. The high-voltage resistant sodium-ion battery electrolyte as described in claim 1, characterized in that, The conductive sodium salt is at least one of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonyl imide, and sodium bis(trifluoromethylsulfonyl)imide.

4. The method for preparing the high-voltage resistant sodium-ion battery electrolyte according to any one of claims 1-3, characterized in that, Includes the following steps: In an argon-protected glove box, carbonate organic solvents and diluents are mixed and stirred until homogeneous. Then, molecular sieves are added to remove water and purify the mixture, yielding a mixed solution. The mixed solution and conductive sodium salt are then mixed and magnetically stirred for 2-4 hours to obtain a high-voltage sodium-ion battery electrolyte.

5. The application of the high-voltage resistant sodium-ion battery electrolyte according to any one of claims 1-3 in the preparation of sodium-ion batteries.

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