Electrolyte additive, electrolyte and sodium ion battery

Abstract

The present invention belongs to the technical field of sodium ion batteries, and in particular relates to an electrolyte additive, an electrolyte, and a sodium ion battery, comprising an additive a and an additive b, wherein additive a is one or more of a first compound shown in Formula 1 and a second compound shown in Formula 2; wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, and R17 are independently selected from one of hydrogen, a halogen atom, a nitro group, an alkane group, an unsaturated hydrocarbon group, an alkoxy group, and an alkanoyl group, and the hydrogen in the alkane group, the unsaturated hydrocarbon group, the alkoxy group, and the alkanoyl group may be partially or completely substituted with one or more of a halogen atom, a cyano group, a carboxyl group, a nitro group, and a sulfonic acid group. The electrolyte additive of the present invention can effectively improve the cycle performance and high-temperature performance of the electrolyte.

Description

Technical Field

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

[0002] Sodium-ion batteries (SIBs) offer significant advantages, including low cost, non-toxicity, and abundant resources, making them highly competitive in replacing lithium-ion batteries in large-scale energy storage applications. However, their widespread application is hampered by poor rate and cycle performance, as well as low initial efficiency.

[0003] The electrolyte serves as the bridge connecting the positive and negative electrodes in sodium-ion batteries, impacting battery performance, including cycling, rate capability, and high-temperature storage. Of the three main electrolyte components, the sodium salt and solvent formulas have remained relatively unchanged. Additives, characterized by their low dosage and significant performance improvements, are key factors in enhancing sodium-ion battery performance and have become a research hotspot in recent years. However, existing electrolytes suffer from poor cycling and high-temperature performance. Summary of the Invention

[0004] One of the purposes of the present invention is to provide an electrolyte additive to address the deficiencies of the prior art, which can effectively improve the cycle performance and high-temperature performance of the electrolyte.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] An electrolyte additive, comprising an additive a and an additive b, wherein the additive a is one or more of a first compound shown in Formula 1 below and a second compound shown in Formula 2 below;

[0007]

[0008]

[0009] Wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16 and R17 are independently selected from one of H, a halogen atom, a nitro group, an alkyl group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms and an alkanoyl group having 2 to 10 carbon atoms, and the H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group, a nitro group and a sulfonic acid group.

[0010] Preferably, the additive b is one or more of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, propylene sulfite and 4-methylethylene sulfate.

[0011] Preferably, the additive a includes a first compound and a second compound, and the mass ratio of the first compound to the second compound is 2:1.

[0012] Preferably, the mass ratio of the additive a to the additive b is (1-5):(1-5).

[0013] Preferably, in the first compound, R1, R2 and R3 are halogen atoms, R4, R5, R6, R7, R8 and R9 are hydrogen atoms; in the second compound, R10, R11 and R12 are halogen atoms, R13, R14, R16 and R17 are hydrogen atoms, and R15 is a nitro group.

[0014] Preferably, R1, R2 and R3 in the first compound are fluorine atoms, and in the second compound, R10, R11 and R12 are fluorine atoms.

[0015] A second object of the present invention is to provide an electrolyte with excellent cycle performance and high temperature performance in order to address the deficiencies of the prior art.

[0016] In order to achieve the above object, the present invention adopts the following technical solutions:

[0017] An electrolyte comprises a sodium salt electrolyte, an organic solvent and the above-mentioned electrolyte additive, wherein the weight proportion of the sodium salt electrolyte is 10 to 16 parts, the weight proportion of the organic solvent is 80 to 90 parts, and the weight proportion of the electrolyte additive is 2 to 20 parts.

[0018] Preferably, the organic solvent includes a cyclic organic solvent and a chain organic solvent, the cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0019] Preferably, the sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalatoborate.

[0020] The third object of the present invention is to provide a sodium ion battery with excellent cycle performance and high temperature performance to address the shortcomings of the existing technology.

[0021] In order to achieve the above object, the present invention adopts the following technical solutions:

[0022] A sodium ion battery comprises the above-mentioned electrolyte.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the electrolyte additive of the present invention is used in a small amount in the electrolyte, but can greatly improve the performance of the electrolyte, and the electrolyte has excellent circulation and high-temperature storage performance. Among them, the main function of additive a is to form a stable interface film on the surface of the positive and negative electrodes, which can effectively inhibit the dissolution of the transition metal in the positive electrode into the electrolyte, thereby reducing the loss of active substances and the increase in resistance, thereby improving the cycle performance and high-temperature storage performance of the battery. Specifically, the first compound shown in Formula 1 of additive a is used, and the -CN functional group in the first compound can complex the transition metal ions in the positive electrode active material, inhibit the decomposition of the positive electrode material, and improve the stability of the electrode material; or the second compound shown in Formula 2 of additive a is used, and the -SO3 in the second compound is used. - The S atom in the formula is more electronegative than the C atom, so it has stronger reducing properties and can form a stable SEI film on the negative electrode surface in preference to carbonate. In addition, the complexation of the N atom in the second compound formula shown in Formula 2 with high-valent metal ions (Ni, Co, Mn, etc.) can effectively reduce the oxidation of the electrolyte by the positive electrode material, especially under high temperature conditions, and can inhibit the dissolution of metal ions caused by structural changes in the positive electrode material, thereby further improving the high temperature storage performance of the battery. In summary, the electrolyte additive of the present invention can significantly improve battery cycling and high temperature storage. The synergistic use of additive a and additive b forms a more uniform and dense SEI film with low membrane impedance, thereby further improving the cycling performance and high temperature storage performance of the sodium ion battery. DETAILED DESCRIPTION

[0024] 1. An electrolyte additive, comprising an additive a and an additive b, wherein the additive a is one or more of a first compound represented by Formula 1 and a second compound represented by Formula 2;

[0025]

[0026] Wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16 and R17 are independently selected from one of H, a halogen atom, a nitro group, an alkyl group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms and an alkanoyl group having 2 to 10 carbon atoms, and the H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group, a nitro group and a sulfonic acid group.

[0027] Preferably, the additive b is one or more of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, propylene sulfite and 4-methylethylene sulfate.

[0028] Preferably, the additive a includes a first compound and a second compound, and the mass ratio of the first compound to the second compound is 2:1.

[0029] Preferably, the mass ratio of the additive a to the additive b is (1-5):(1-5).

[0030] Preferably, in the first compound, R1, R2 and R3 are halogen atoms, R4, R5, R6, R7, R8 and R9 are hydrogen atoms; in the second compound, R10, R11 and R12 are halogen atoms, R13, R14, R16 and R17 are hydrogen atoms, and R15 is a nitro group.

[0031] Preferably, R1, R2 and R3 in the first compound are fluorine atoms, and in the second compound, R10, R11 and R12 are fluorine atoms.

[0032] 2. An electrolyte comprising a sodium salt electrolyte, an organic solvent and the above-mentioned electrolyte additive, wherein the weight proportion of the sodium salt electrolyte is 10 to 16 parts, the weight proportion of the organic solvent is 80 to 90 parts, and the weight proportion of the electrolyte additive is 2 to 20 parts.

[0033] The electrolyte of the present invention has excellent cycle performance and high-temperature performance.

[0034] Preferably, the organic solvent includes a cyclic organic solvent and a chain organic solvent, the cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0035] Preferably, the sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalatoborate.

[0036] 3. A sodium-ion battery comprising the aforementioned electrolyte. Specifically, a sodium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the electrolyte is any of the sodium-ion battery electrolytes described above.

[0037] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be further described in detail below in conjunction with specific implementation methods, but the implementation methods of the present invention are not limited thereto.

[0038] Example 1

[0039] The preparation method of the sodium ion battery is as follows:

[0040] 1) Positive Electrode Preparation: The cathode material Na₃V₂(PO₄)₃, the binder PVDF, and the conductive agent Super-P were dispersed in an organic solvent of NMP at a mass ratio of 90:4:6. The mixture was stirred in a vacuum mixer until stable and uniform, and then evenly coated onto a 12μm thick aluminum foil. The aluminum foil was air-dried at room temperature and then transferred to a 120°C forced air oven for drying for 1 hour. The resulting cathode sheet was then cold-pressed and die-cut.

[0041] 2) Anode Preparation: Spherical hard carbon, binder PVDF, and conductive agent Super-P were mixed in a mass ratio of 97:2:1, dispersed in NMP organic solvent, and evenly coated onto 15μm-thick aluminum foil. The foil was air-dried at room temperature and then transferred to a 120°C forced air oven for 1 hour. The negative electrode sheet was then cold-pressed and die-cut.

[0042] Electrolyte preparation:

[0043] 1) In a nitrogen-filled glove box (O<2 ppm, H<3 ppm), an organic solvent was prepared, wherein the organic solvent consisted of EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) in a weight ratio of 1:1:1;

[0044] 2) Slowly add NaPF6 to the organic solvent to prepare a sodium salt solution with a concentration of 1.12 mol / L;

[0045] 3) mixing a sodium salt solution, an organic solvent, and additives a and b in parts by weight of 14 parts, 83 parts, 1 part, and 2 parts to prepare an electrolyte;

[0046] Wherein, additive a is a mixture of a compound of formula I and a compound of formula II, wherein the weight ratio of the compound of formula I to the compound of formula II is 2:1, and its structure is shown below:

[0047]

[0048]

[0049] Preparation of sodium-ion batteries: The positive electrode, separator, and negative electrode are stacked in order and wound to obtain a bare battery cell. The cell is then encapsulated with an aluminum-plastic film as a shell, baked, injected with liquid, left to stand, formed, jig-shaped, sealed, and capacity tested to complete the preparation of the sodium-ion battery.

[0050] Example 2

[0051] The difference from Example 1 is that the electrolyte includes the following raw materials in parts by weight: 14 parts of sodium salt electrolyte, 81 parts of organic solvent, 3 parts of additive a and 2 parts of additive b.

[0052] The rest is the same as in Example 1 and will not be described again here.

[0053] Example 3

[0054] The difference from Example 1 is that the electrolyte includes the following raw materials in parts by weight: 14 parts of sodium salt electrolyte, 79 parts of organic solvent, 5 parts of additive a and 2 parts of additive b.

[0055] The rest is the same as in Example 1 and will not be described again here.

[0056] Example 4

[0057] The difference from Example 1 is that the electrolyte includes the following raw materials in parts by weight: 14 parts of sodium salt electrolyte, 77 parts of organic solvent, 7 parts of additive a and 2 parts of additive b.

[0058] The rest is the same as in Example 1 and will not be described again here.

[0059] Example 5

[0060] The difference from Example 1 is that the first compound represented by Formula 1 and the second compound represented by Formula 2 are respectively:

[0061]

[0062] The rest is the same as in Example 1 and will not be described again here.

[0063] Example 6

[0064] The difference from Example 1 is that the additive a only includes the first compound of Formula 1, the structure of which is shown below:

[0065]

[0066] The rest is the same as in Example 1 and will not be described again here.

[0067] Example 7

[0068] The difference from Example 1 is that the additive a only includes the second compound of Formula 2, the structural formula of which is shown below:

[0069]

[0070] The rest is the same as in Example 1 and will not be described again here.

[0071] Example 8

[0072] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 1:1.

[0073] The rest is the same as in Example 1 and will not be described again here.

[0074] Example 9

[0075] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 1:2.

[0076] The rest is the same as in Example 1 and will not be described again here.

[0077] Example 10

[0078] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 1:3.

[0079] The rest is the same as in Example 1 and will not be described again here.

[0080] Example 11

[0081] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 1:5.

[0082] The rest is the same as in Example 1 and will not be described again here.

[0083] Example 12

[0084] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 3:1.

[0085] The rest is the same as in Example 1 and will not be described again here.

[0086] Example 13

[0087] The difference from Example 1 is that the additive a includes a first compound and a second compound, and the weight ratio of the first compound of Formula 1 to the second compound of Formula 2 is 5:1.

[0088] The rest is the same as in Example 1 and will not be described again here.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that the electrolyte includes the following raw materials in parts by weight: 14 parts of sodium salt electrolyte, 84 parts of organic solvent, and 2 parts of additive b.

[0091] The rest is the same as in Example 1 and will not be described again here.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that the electrolyte includes the following raw materials in parts by weight: 14 parts of sodium salt electrolyte, 84 parts of organic solvent, and 2 parts of additive a.

[0094] The rest is the same as in Example 1 and will not be described again here.

[0095] The electrolytes and sodium ion batteries prepared in the above examples and comparative examples were subjected to performance tests, and the test results are recorded in Tables 1 and 2.

[0096] 1. High temperature cycle life test

[0097] The sodium-ion battery was charged at 45°C at a constant current of 1C to 4.0V, then charged at a constant voltage to a cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.0V. This was counted as one charge-discharge cycle. The battery was then cycled 500 times under the above conditions. The capacity retention (%) of the sodium-ion battery after 500 cycles = (discharge capacity at the 500th cycle / initial discharge capacity) × 100%.

[0098] 2. High temperature storage performance test

[0099] Charge at room temperature with 1C constant current and constant voltage to 4.0V, cut off at 0.05C, then discharge with 1C constant current to 2.0V cut off, which is recorded as the initial capacity C0, and then store in a high-temperature test cabinet at 60℃ for 7 days; after leaving at room temperature for a few hours, discharge with 1C constant current to 2.0V, record the discharge capacity C1, and the charge percentage = C1 / C0; charge at room temperature with 1C constant current and constant voltage to 4.0V, cut off at 0.05C, then discharge with 1C constant current, cut off at 2.0V, and record the recovery capacity C2; the recovery percentage = C2 / C0.

[0100] Table 1

[0101]

[0102] Table 2

[0103]

[0104] As can be seen from Tables 1 and 2 above, the electrolyte additives of the present invention effectively improve the cycling performance and high-temperature storage performance of the electrolyte compared to the electrolyte additives of Comparative Examples 1 and 2. Additive a in the electrolyte additives of the present invention can form a stable interfacial film on the positive and negative electrode surfaces, effectively inhibiting the dissolution of the positive electrode transition metal into the electrolyte, thereby reducing the loss of active material and the increase in resistance, thereby improving the cycling performance and high-temperature storage performance of the battery. At the same time, Additive b and Additive a act synergistically to form a more uniform and dense SEI film, reducing the membrane impedance and improving the cycling performance and high-temperature storage performance.

[0105] From the comparison of Examples 1-4, it can be concluded that when the weight ratio of additive a to additive b in the electrolyte additive is set to 1:2, the performance of the electrolyte is better, and the synergistic effect of the two is better. The capacity retention rate after 500 cycles at 25°C is as high as 93.5%, the capacity retention rate after 7 days of storage at 60°C is 95.6%, the capacity recovery rate is 99.7%, and the thickness expansion rate is only 0.7%.

[0106] By comparing Example 1 and Example 5, it can be concluded that when the first compound represented by Formula 1 and the second compound represented by Formula 2 in the additive a in the electrolyte additive are respectively:

[0107]

[0108] The prepared electrolyte has better performance. The fluorine atom in the first compound of Formula 1 in Example 1 can more effectively inhibit the loss of active substances in the electrolyte than the chlorine atom in the first compound of Formula 1 in Example 5, thereby improving the capacity retention rate and high-temperature storage performance of the electrolyte.

[0109] From the comparison of Examples 1, 6 and 7, it can be seen that when the additive a includes the first compound represented by Formula 1 and the second compound represented by Formula 2, the performance of the prepared electrolyte is better, and the effect achieved by combining the two is better.

[0110] By comparison of Examples 1 and 8-13, it can be concluded that when the weight ratio of the first compound of Formula 1 and the second compound of Formula 2 in the additive a is 2: 1, the performance of the prepared electrolyte is better, and the effect achieved by the compounding of the two is better. Specifically, it can be concluded from Examples 8-11 that when the weight ratio of the first compound of Formula 1 is 1 part, as the weight ratio of the second compound of Formula 2 increases, the capacity retention rate and high-temperature storage performance of the electrolyte decrease; it can be concluded from Examples 1 and 12-13 that as the weight ratio of the second compound of Formula 2 increases, the capacity retention rate and high-temperature storage performance of the electrolyte both decrease. When the weight ratio of the first compound of Formula 1 and the second compound of Formula 2 in the additive a is 2: 1, that is, Example 1, the performance of the prepared electrolyte is better, and the capacity retention rate and high-temperature storage performance achieve the best effect.

[0111] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. An electrolyte additive, characterized in that The method comprises an additive a and an additive b, wherein the additive a is one or more of a first compound shown in Formula 1 below and a second compound shown in Formula 2 below; wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R16, and R17 are independently selected from one of hydrogen, a halogen atom, a nitro group, an alkane group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, and an alkanoyl group having 2 to 10 carbon atoms, and hydrogen in the alkane group, the unsaturated hydrocarbon group, the alkoxy group, and the alkanoyl group may be partially or completely substituted with one or more of a halogen atom, a cyano group, a carboxyl group, a nitro group, and a sulfonic acid group; and R15 is a nitro group; The additive b is one or more of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, propylene sulfite and 4-methylethylene sulfate.

2. The electrolyte additive according to claim 1, characterized in that The additive a includes a first compound and a second compound, and the mass ratio of the first compound to the second compound is 2:

1.

3. The electrolyte additive according to claim 1 or 2, characterized in that The mass ratio of the additive a to the additive b is (1-5):(1-5).

4. The electrolyte additive according to claim 3, characterized in that In the first compound, R1, R2 and R3 are halogen atoms, R4, R5, R6, R7, R8 and R9 are hydrogen atoms; in the second compound, R10, R11 and R12 are halogen atoms, R13, R14, R16 and R17 are hydrogen atoms.

5. The electrolyte additive according to claim 4, characterized in that In the first compound, R1, R2 and R3 are fluorine atoms, and in the second compound, R10, R11 and R12 are fluorine atoms.

6. An electrolyte, characterized in that The electrolyte comprises a sodium salt electrolyte, an organic solvent and the electrolyte additive according to any one of claims 1 to 5, wherein the weight proportion of the sodium salt electrolyte is 10 to 16 parts, the weight proportion of the organic solvent is 80 to 90 parts, and the weight proportion of the electrolyte additive is 2 to 20 parts.

7. The electrolyte according to claim 6, characterized in that The organic solvent includes a cyclic organic solvent and a chain organic solvent. The cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate and butylene carbonate. The chain organic solvent is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

8. The electrolyte according to claim 6, characterized in that The sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalatoborate.

9. A sodium ion battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 6 to 8.

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