Sodium-ion battery electrolyte, preparation method and application thereof and sodium-ion battery

Abstract

The invention provides a sodium-ion battery electrolyte, a preparation method and application thereof and a sodium-ion battery. The sodium-ion battery electrolyte comprises a sodium salt electrolyte, a first ether solvent and a second ether solvent, wherein the solvation effect of the first ether solvent is stronger than that of the second ether solvent, and the volume ratio of the first ether solvent to the second ether solvent is (1-3): (1-3); the first ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; and the second ether solvent is at least one of trimethyl orthoformate, dimethyl formal, dimethoxyethane and 1, 1, 2-trimethoxyethane. According to the invention, sodium ion kinetics can be improved at low temperature, high rate and high cycle stability at room temperature can be maintained to-30 DEG C, and high capacity and rate capability can be shown at low temperature.

Description

Technical Field

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

[0002] With the continuous development of the transformation of energy structure, the trend of replacing fossil fuels with new energy is also gradually accelerating. At present, lithium-ion battery technology is relatively mature and has been widely used in many fields such as consumer electronic devices and electric vehicles. However, lithium mineral resources are relatively scarce and unevenly distributed in the earth's crust. In order to maintain the sustainable supply of new energy batteries, sodium, which is in the same main group as lithium, has received widespread attention. The abundance of sodium in the earth's crust is 2.83, and its distribution is more even. Therefore, the cost of sodium carbonate is much lower than that of lithium carbonate. The development of sodium-ion batteries can solve the problem of lithium resource shortage. In addition, a lot of experience and production line equipment in the development of lithium-ion batteries can be used in the research and development and production of sodium-ion batteries, which will help the rapid development of sodium-ion batteries.

[0003] Graphite is one of the most widely used negative electrode materials in lithium-ion batteries. Its special layered structure facilitates the insertion and removal of lithium ions during the battery's charge and discharge process. However, in sodium-ion batteries, sodium ions can be inserted into the interlayers of graphite together with ether electrolytes, such as diethylene glycol dimethyl ether (G2), which is a "co-intercalation" phenomenon, forming a ternary compound of "sodium ions-electrolyte-graphite". Since the co-intercalation process is that sodium ions are embedded in graphite together with solvents, the sodium ion desolvation step is omitted, so this electrochemical behavior can show excellent kinetics, making the sodium ion desolvation process smoother, which is directly reflected in the excellent cycle performance and rate performance exhibited by the sodium-ion battery of this system.

[0004] However, in low temperature environments, the difficulty of sodium ion deintercalation increases due to factors such as increased electrolyte viscosity, reduced ion conductivity, and slow electrode kinetics. The advantages of solvent co-intercalation behavior cannot be effectively utilized, which greatly reduces the capacity of sodium ion batteries, seriously affecting the overall performance of the battery and greatly limiting the scope of practical application. Therefore, in order to maintain the capacity of sodium ion batteries at low temperatures and the advantages of rapid deintercalation of co-intercalation behavior, the development of low-temperature and high-rate ether electrolytes is crucial for the development and large-scale application of sodium ion batteries. However, existing sodium ion battery electrolytes are difficult to operate stably at low temperatures (-30°C) and have poor rate performance at low temperatures.

[0005] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0006] In order to make up for the deficiencies of the prior art, a sodium ion battery electrolyte, a preparation method, an application thereof and a sodium ion battery are provided to solve the problem that the existing sodium ion battery electrolyte is difficult to operate stably at low temperature (-30°C) and has poor rate performance at low temperature.

[0007] The present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a sodium ion battery electrolyte, comprising: a sodium salt electrolyte, a first ether solvent, and a second ether solvent; wherein the solvation effect of the first ether solvent is stronger than that of the second ether solvent, and the volume ratio of the first ether solvent to the second ether solvent is 1-3:1-3; the first ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the second ether solvent is at least one of trimethyl orthoformate, dimethanol formal, dimethoxyethane, and 1,1,2-trimethoxyethane.

[0009] In a second aspect, the present invention provides a method for preparing the sodium ion battery electrolyte described in the first aspect, comprising the following steps: mixing a sodium salt electrolyte, a first ether solvent, and a second ether solvent in proportion to obtain the sodium ion battery electrolyte.

[0010] In a third aspect, the present invention provides a use of the sodium ion battery electrolyte described in the first aspect in a sodium ion battery, wherein the operating temperature range of the sodium ion battery electrolyte is 25 to -30°C.

[0011] In a fourth aspect, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode, the sodium ion battery electrolyte described in the first aspect, and a diaphragm.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The invention provides a sodium ion battery electrolyte, in particular an electrolyte matched with a sodium ion battery having a graphite negative electrode (graphite is used as a negative electrode active material). The invention selects a first ether solvent with strong solvation as a main solvent, matches a second ether solvent with weak solvation and a sodium salt electrolyte to form the sodium ion battery electrolyte, the second ether solvent with weak solvation in the system replaces the first ether solvent with strong solvation to perform partial desolvation behavior, improves the sodium ion dynamics in the co-intercalation stage at low temperature (as low as -30°C, the same below), maintains the advantages of high rate and high cycle stability of co-intercalation at room temperature, and also shows a high capacity retention rate and rate performance at -30°C, so that the sodium ion battery can operate stably at a low temperature of -30°C. Specifically, the first ether solvent with strong solvation has a stronger binding energy with sodium ions, and the partial desolvation process at low temperature becomes difficult; while the second ether solvent with weak solvation has a weaker binding energy with sodium ions, and can be partially desolvated with faster kinetics at low temperatures. The synergistic interaction between the two realizes the coordination of sodium ions with the two solvents, and at low temperatures, the solvated sodium ions partially remove the second ether solvent with weak solvation and then carry the first ether solvent with strong solvation into the negative electrode, thereby improving the sodium ion kinetics at low temperatures, maintaining high rate and high cycle stability at room temperature to -30°C, and also showing high capacity and rate performance at low temperatures.

[0014] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 are the electrostatic potential diagrams and binding energies of sodium ions binding to solvent molecules in the sodium ion battery electrolytes in Comparative Example 1 and Comparative Example 2 respectively calculated by density functional theory;

[0016] Figure 2 The charge and discharge curves of Example 4, Comparative Example 3 and Comparative Example 4 at 25°C, 0°C and -30°C are shown;

[0017] Figure 3 is the energy required for partial desolvation of the solvated sodium ions in Example 1 and Comparative Example 1 at room temperature (25° C.) and low temperature (−30° C.), calculated by density functional theory;

[0018] Figure 4 Schematic diagram of the co-intercalation of solvated sodium ions in Example 1 and Comparative Example 1;

[0019] Figure 5 The in-situ Raman spectra of the negative electrodes of Example 4 and Comparative Examples 3 and 4 during the charge and discharge process;

[0020] Figure 6The constant current intermittent titration curves of Example 4 and Comparative Example 3 at -30°C;

[0021] Figure 7 The rate performance of Example 4 at room temperature (25°C) and low temperature (-30°C);

[0022] Figure 8 Comparison of the capacity retention rates of Example 4 and Comparative Example 3 at different temperatures of 25, 0, -10, -20, and -30°C at a rate of 1C;

[0023] Fig. 9 The capacity change and cycle performance of Example 4 and Comparative Example 3 at different temperatures of 25, 0, -10, -20, and -30°C at a rate of 1C;

[0024] Fig.10 The cycle performance of Example 4 at room temperature (25°C) and low temperature (-30°C) at a rate of 1C. DETAILED DESCRIPTION

[0025] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0026] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0027] A sodium ion battery electrolyte is provided in a specific embodiment of the present invention, comprising: a sodium salt electrolyte, a first ether solvent, and a second ether solvent; wherein the solvation effect of the first ether solvent is stronger than that of the second ether solvent, and the volume ratio of the first ether solvent to the second ether solvent is 1-3:1-3; the first ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the second ether solvent is at least one of trimethyl orthoformate, dimethanol formal, dimethoxyethane, and 1,1,2-trimethoxyethane.

[0028] In some embodiments, the sodium salt electrolyte is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium difluorooxalatoborate and sodium tetrafluoroborate; more preferably, the sodium salt electrolyte is sodium hexafluorophosphate.

[0029] In some embodiments, the concentration of the sodium salt electrolyte in the sodium ion battery electrolyte is 0.5 to 2 mol / L; preferably, the concentration of the sodium salt electrolyte in the sodium ion battery electrolyte is 0.8 to 1.5 mol / L, and more preferably 1 mol / L.

[0030] In some embodiments, the first ether solvent is diethylene glycol dimethyl ether, and the second ether solvent is trimethyl orthoformate.

[0031] In some embodiments, the volume ratio of the first ether solvent to the second ether solvent is 1-2:2-3; more preferably, the volume ratio of the first ether solvent to the second ether solvent is 1:3.

[0032] A specific embodiment of the present invention also provides a method for preparing the above-mentioned sodium ion battery electrolyte, comprising the following steps: mixing a sodium salt electrolyte, a first ether solvent, and a second ether solvent in proportion to obtain the sodium ion battery electrolyte.

[0033] In some preferred embodiments, the preparation method comprises: stirring and mixing the first ether solvent and the second ether solvent for 10 minutes, then adding a sodium salt electrolyte, and mixing and stirring for 10 hours.

[0034] The specific embodiment of the present invention also provides the use of the above-mentioned sodium ion battery electrolyte in a sodium ion battery, and the operating temperature range of the sodium ion battery electrolyte is 25 to -30°C.

[0035] A specific embodiment of the present invention also provides a sodium ion battery, which includes a positive electrode, a negative electrode, the sodium ion battery electrolyte and a diaphragm, which are assembled in the order of positive electrode-electrolyte-diaphragm-electrolyte-negative electrode.

[0036] In the specific implementation of the present invention, the material and preparation method of the diaphragm are not limited, and methods familiar to those skilled in the art can be adopted. Preferably, the diaphragm is glass fiber.

[0037] In a specific embodiment of the present invention, the negative electrode preferably includes a negative electrode current collector and a negative electrode film covering the negative electrode current collector; the negative electrode current collector is not limited and can be made of materials well known to those skilled in the art.

[0038] In some embodiments, the negative electrode film includes a negative electrode active material and a binder; the negative electrode active material is preferably graphite.

[0039] The specific implementation of the present invention has no special restrictions on the type and source of the binder and the preparation method of the negative electrode active material, and corresponding materials well known to those skilled in the art can be used.

[0040] The specific implementation of the present invention has no special limitation on the material and preparation method of the positive electrode, and corresponding materials well known to those skilled in the art can be used. Preferably, the positive electrode is sodium metal.

[0041] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0042] Unless otherwise specified, the reagents and materials used in the implementation cases can be purchased commercially or prepared by conventional methods, and the instruments used can be purchased commercially.

[0043] Example 1

[0044] The sodium ion battery electrolyte provided in this embodiment includes sodium hexafluorophosphate (NaPF6), diethylene glycol dimethyl ether (G2) and trimethyl orthoformate (TMM); the concentration of NaPF6 is 1 mol / L; the volume ratio of G2:TMM is 1:3.

[0045] The preparation method of the above electrolyte comprises the following steps:

[0046] The G2 solvent was added to the TMM solvent and mixed, and the mixture was stirred for 10 minutes. Then, NaPF6 was dissolved in the mixed solvent and stirred for 10 hours to mix evenly to obtain a sodium ion battery electrolyte, which was recorded as SE-GT.

[0047] Example 2

[0048] The sodium ion battery electrolyte provided in this embodiment includes: NaPF6, G2 and TMM; the concentration of NaPF6 is 1 mol / L; the volume ratio of G2:TMM is 1:1.

[0049] Example 3

[0050] The sodium ion battery electrolyte provided in this embodiment includes: NaPF6, G2 and TMM; the concentration of NaPF6 is 1 mol / L; the volume ratio of G2:TMM is 3:1.

[0051] Example 4

[0052] The sodium ion battery of this embodiment comprises:

[0053] Step 1: Dry the negative electrode active material graphite at 120°C for 2h, weigh 900mg of graphite and 100mg of polyvinylidene fluoride binder respectively, grind them under an infrared lamp for 10min, pour them into a stirring bottle with a scale of 25×40mm, add 2.4mL of N-methylpyrrolidone, and stir at room temperature (25°C) for 4h to obtain the negative electrode slurry.

[0054] Step 2: Apply the negative electrode slurry obtained in step 1 on copper foil, first dry it in a forced air oven at 80°C, then transfer it to 120°C for vacuum drying for 3 hours, cut it into appropriate size to obtain a negative electrode sheet, and then place it in a vacuum oven for standby use.

[0055] Step three, assemble the negative electrode sheet prepared in step two, the liquid sodium ion battery electrolyte configured in Example 1, sodium metal (positive electrode sheet), and the separator (glass fiber) in the order of positive electrode sheet-electrolyte-separator-electrolyte-negative electrode sheet to obtain a sodium ion button half-cell.

[0056] Example 5

[0057] The difference between Example 5 and Example 4 is that the electrolyte is replaced with the sodium ion battery electrolyte configured in Example 2, and the remaining steps are the same as Example 4.

[0058] Example 6

[0059] The difference between Example 6 and Example 4 is that the electrolyte is replaced with the sodium ion battery electrolyte configured in Example 3, and the remaining steps are the same as Example 4.

[0060] Example 7

[0061] The difference between Example 7 and Example 4 is that the negative electrode active material graphite is replaced by hard carbon, and the remaining steps are the same as Example 4.

[0062] Example 8

[0063] The difference between Example 8 and Example 5 is that the negative electrode active material graphite is replaced by hard carbon negative, and the remaining steps are the same as Example 5.

[0064] Example 9

[0065] The difference between Example 9 and Example 6 is that the negative electrode active material graphite is replaced by hard carbon, and the remaining steps are the same as Example 6.

[0066] Example 10

[0067] The difference between Example 10 and Example 4 is that the negative electrode active material graphite is replaced by soft carbon, and the remaining steps are the same as those of Example 4.

[0068] Embodiment 11

[0069] The difference between Example 11 and Example 5 is that the negative electrode active material graphite is replaced by soft carbon, and the remaining steps are the same as Example 5.

[0070] Example 12

[0071] The difference between Example 12 and Example 6 is that the negative electrode active material graphite is replaced by soft carbon, and the remaining steps are the same as Example 6.

[0072] Comparative Example 1

[0073] The sodium ion battery electrolyte provided in this comparative example 1 includes: NaPF6 and G2; the concentration of NaPF6 is 1 mol / L.

[0074] The preparation method of the above electrolyte comprises the following steps:

[0075] NaPF6 was dissolved in G2 solvent and stirred for 10 hours to mix evenly, thereby obtaining a sodium ion battery electrolyte containing an ether solvent with a strong solvation effect, which was designated as BE-G2.

[0076] Comparative Example 2

[0077] The sodium ion battery electrolyte provided in this comparative example 2 includes: NaPF6 and TMM; the concentration of NaPF6 is 1 mol / L.

[0078] The preparation method of the above electrolyte comprises the following steps:

[0079] NaPF6 was dissolved in TMM solvent and stirred for 10 hours to mix evenly, thereby obtaining a sodium ion battery electrolyte containing an ether solvent with a weak solvation effect, which was recorded as BE-TMM.

[0080] Comparative Example 3

[0081] The difference between Comparative Example 3 and Example 4 is that the electrolyte prepared in Comparative Example 1 is selected, and the remaining steps are the same as those in Example 4.

[0082] Comparative Example 4

[0083] The difference between Comparative Example 4 and Example 4 is that the electrolyte prepared in Comparative Example 2 is selected, and the remaining steps are the same as those in Example 4.

[0084] Figure 1 The electrostatic potential diagram and binding energy of the sodium ions in the sodium ion battery electrolytes of Comparative Examples 1 and 2 respectively binding to the G2 and TMM solvent molecules calculated by density functional theory. Obviously, the binding energy of Comparative Example 1 of -2.69 eV is higher than that of Comparative Example 2 of -1.78 eV, that is, Comparative Example 1 and Comparative Example 2 belong to the electrolyte containing a strongly solvated ether solvent and the electrolyte containing a weakly solvated ether solvent, respectively.

[0085] Figure 2 The charge-discharge curves of Example 4, Comparative Example 3 and Comparative Example 4 at 25°C, 0°C and -30°C are shown. It can be seen that Comparative Example 3 has 111.6 mAh g -1 The capacity of Example 4 is 109.2 and 98.5 mAh g at room temperature and low temperature, respectively. -1 of higher capacity.

[0086] The energy required for partial desolvation of the solvated sodium ions in Example 1 and Comparative Example 1 at room temperature (25°C) and low temperature (-30°C) calculated by density functional theory is as follows: Figure 3 As shown, partial desolvation is required before the solvated sodium ions are co-embedded in graphite. Therefore, at room temperature and low temperature, the weakly solvated coordination in Example 1 is more easily partially desolvated to be embedded in graphite. In Comparative Example 1, since the coordinated solvent molecules are all strongly solvated ethers, it is difficult to partially desolvate at low temperatures, making embedding difficult, resulting in low temperature performance; Figure 4 Schematic diagram of the co-intercalation of solvated sodium ions in Example 1 and Comparative Example 1, revealing the mechanism of co-intercalation of sodium ions and solvent at low temperatures.

[0087] Figure 5 The in-situ Raman spectra of the negative electrodes of Example 4 and Comparative Examples 3 and 4 during the charge and discharge process show that graphite can be observed at 1580 cm -1 The G peak at 1600 cm-1 gradually moves to 1600 cm-2 during the sodiumization process. -1 The phenomenon of shift represents the co-embedding behavior of the solvent and the sodium ions, and the potential at which the shift occurs represents the difficulty of co-embedding, that is, comparative example 4 is at a disadvantage in the diffusion process.

[0088] The constant current intermittent titration curves of Example 4 and Comparative Example 3 at -30°C are as follows: Figure 6 As shown, the overpotential of Example 4 at low temperature is significantly lower than that of Comparative Example 3, and the ion diffusion coefficient is higher, which further proves that the performance of Comparative Example 3 is deteriorated due to the slow kinetics of the partial desolvation process at low temperature.

[0089] The rate performance of Example 4 at room temperature (25°C) and low temperature (-30°C) is as follows Figure 7 As shown in Figure 1, the excellent rate performance at room temperature is also reflected at low temperature. Even at a high rate of 5C, there is a capacity retention rate of about 60%, bringing the fast kinetics advantage of ether co-intercalation to a low temperature environment. The capacity retention rate comparison and capacity change of Example 4 and Comparative Example 3 at different temperatures of 25, 0, -10, -20, and -30°C at a rate of 1C are shown in Figure 1. Figure 8 , 9 As shown, it can be clearly seen that the improved Example 4 has a huge advantage at low temperatures. Even at a 1C rate at -30°C, it can maintain 90% of the capacity, which is much higher than the 30% of Comparative Example 3. Fig.10 The cycle performance of Example 4 at room temperature (25°C) and low temperature (-30°C) at a rate of 1C is shown. It can stably cycle for more than 500 cycles at low temperature.

[0090] In summary, the specific embodiments of the present invention prepare sodium ion battery electrolytes with strongly solvating ether solvents and weakly solvating ether solvents, and successfully achieve high-rate and long-cycle operation of graphite electrode materials at low temperatures (-30°C) by optimizing the partial desolvation process, which provides a new understanding of the co-intercalation mechanism of graphite electrodes in sodium ion batteries, provides design ideas for sodium ion batteries used in extreme climates, and provides new ideas for other low-temperature battery fields.

[0091] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A sodium ion battery electrolyte, characterized in that: include: Sodium salt electrolyte, a first ether solvent, and a second ether solvent; wherein the solvating effect of the first ether solvent is stronger than that of the second ether solvent, and the volume ratio of the first ether solvent to the second ether solvent is 1-3:1-3; the first ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the second ether solvent is at least one of trimethyl orthoformate, dimethanol formal, dimethoxyethane and 1,1,2-trimethoxyethane.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The sodium salt electrolyte is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium perchlorate, sodium difluorooxalatoborate and sodium tetrafluoroborate; preferably, the sodium salt electrolyte is sodium hexafluorophosphate.

3. The sodium ion battery electrolyte according to claim 1, characterized in that The concentration of the sodium salt electrolyte in the sodium ion battery electrolyte is 0.5 to 2 mol / L; preferably, the concentration of the sodium salt electrolyte in the sodium ion battery electrolyte is 0.8 to 1.5 mol / L, and more preferably 1 mol / L.

4. The sodium ion battery electrolyte according to claim 1, characterized in that The first ether solvent is diethylene glycol dimethyl ether, and the second ether solvent is trimethyl orthoformate.

5. The sodium ion battery electrolyte according to claim 1, characterized in that The volume ratio of the first ether solvent to the second ether solvent is 1-2:2-3.

6. The sodium ion battery electrolyte according to claim 1, characterized in that The volume ratio of the first ether solvent to the second ether solvent is 1:

3.

7. A method for preparing a sodium ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: mixing a sodium salt electrolyte, a first ether solvent and a second ether solvent in proportion to obtain the sodium ion battery electrolyte.

8. Use of the sodium ion battery electrolyte according to any one of claims 1 to 6 in a sodium ion battery, characterized in that: The operating temperature range of the sodium ion battery electrolyte is 25 to -30°C.

9. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, the sodium ion battery electrolyte according to any one of claims 1 to 5, and a diaphragm.

10. The sodium ion battery according to claim 9, characterized in that: The negative electrode comprises a negative electrode current collector and a negative electrode film covered on the negative electrode current collector; the negative electrode film comprises a negative electrode active material and a binder; the negative electrode active material is graphite; the positive electrode is sodium metal, and the separator is glass fiber.

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