Sodium ion battery electrolyte and sodium ion secondary battery

Abstract

The invention provides a sodium ion battery electrolyte and a sodium ion secondary battery, the electrolyte comprises an electrolyte sodium salt and a solvent composition, the solvent composition comprises an organic solvent and a functional impregnating compound, and the functional impregnating compound is trifluoromethyl benzene. According to the invention, by introducing the trifluoromethyl benzene as a functional agent and an impregnating compound, the wettability of the electrolyte on the diaphragm is improved, the desolvation energy of sodium ions is reduced, and the battery performance is greatly improved. And due to the addition of trifluoromethyl benzene, the compatibility of sulfone and carbonic ester solvents and a carbon negative electrode is particularly improved. In addition, the action mechanism of the trifluoromethyl benzene serving as the functional impregnating compound is completely different from that of a common surfactant, fluoro-ether and fluorobenzene, and the trifluoromethyl benzene has a very strong application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a sodium-ion battery electrolyte and a sodium-ion secondary battery. Background Art

[0002] As the most efficient and convenient energy storage and conversion device, high-performance secondary batteries are crucial for establishing a clean energy system and achieving large-scale energy storage. Sodium-ion batteries are considered a beneficial supplement to lithium-ion batteries due to their advantages such as rich resources, wide distribution, and low cost, and are one of the ideal devices for large-scale energy storage applications. In recent years, the research and development of sodium-ion battery technology have received extensive attention from research groups around the world.

[0003] Currently, the electrolyte solvent system of sodium-ion batteries partially follows that of lithium-ion batteries. However, propylene carbonate, which is not commonly used in current lithium-ion batteries, has been widely used in sodium-ion batteries. Due to the poor wettability of propylene carbonate with the separator, wetting agents are often used in the propylene carbonate-based system to obtain better performance. For example, CN113906607A uses surfactants commonly used in lithium batteries to solve the wetting problem, and the surfactants are selected from anionic surfactants, cationic surfactants, non-ionic (hydrophilic) surfactants, and amphoteric (zwitterionic) surfactants. However, the surfactants used in this patent can only improve the wettability of the separator and do not have the functional role of participating in the sodium ion transport and / or insertion / extraction process. Summary of the Invention

[0004] Therefore, the object of the present invention is to provide a sodium-ion battery electrolyte system. By adding a new functional wetting agent, on the one hand, the wettability of the electrolyte to the separator is improved, and on the other hand, by combining with its solvent, the desolvation energy of sodium ions is reduced, thereby improving the battery performance.

[0005] The inventors of the present invention have found through long-term literature accumulation and in-depth research that trifluoromethylbenzene (CAS No.: 98-​​08-8) has good wettability with the separator and the electrode sheet and can be used as a wetting agent in the sodium-ion battery electrolyte; at the same time, the inventors unexpectedly found that trifluoromethylbenzene exhibits an appropriate electron-withdrawing effect in the sodium-ion battery electrolyte system, enabling it to combine with a solvent having a strong electron-donating group, reducing the interaction force between sodium ions and the strong electron-donating solvent, thereby reducing the desolvation energy of sodium ions and improving the rate performance and low-temperature performance of the battery, which are properties not possessed by existing common wetting agents. Based on the above findings, the inventors completed the present invention.

[0006] The first aspect of the present invention provides a sodium-ion battery electrolyte, which comprises: an electrolyte sodium salt and a solvent composition, and the solvent composition comprises an organic solvent and a functional wetting agent, wherein the functional wetting agent is trifluoromethylbenzene.

[0007] For the sodium-ion battery electrolyte provided by the present invention, the content of the functional wetting agent in the solvent composition is 0.01-15 wt%, preferably 0.5-15 wt%.

[0008] For the sodium-ion battery electrolyte provided by the present invention, the electrolyte sodium salt is selected from NaPF6, NaBF4, NaClO4; sodium salts of compounds containing fluorosulfonyl groups; sodium salts of compounds containing fluorosulfonates; sodium salts of oxalato borate compounds; sodium compounds containing tetrahedral anions such as tetra[3,5-bis(trifluoromethyl)phenyl]borate anion (B[3,5-(CF3)2C6H3] - 4), tris(pentafluorophenyl)borate anion (B(C6F5) - 4) and tetrakis(carboxylato)(trifluoromethyl) aluminate anion (Al[OC(CF3)3]-4), and one or more of them. Preferably, the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium difluorophosphate (NaDFP), sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and sodium bis(fluorosulfonyl)imide (NaFSI).

[0009] For the sodium-ion battery electrolyte provided by the present invention, the concentration of the electrolyte sodium salt in the electrolyte is 0.1-5 mol / L, preferably 0.5-2 mol / L.

[0010] For the sodium-ion battery electrolyte provided by the present invention, the solvent composition comprises one or more of carbonate solvents, carboxylate solvents, ether solvents, ionic liquids, nitrile solvents, and thio solvents, preferably a combination of carbonate solvents and ether solvents.

[0011] Among them, the carbonate solvent can be a cyclic carbonate solvent and / or a chain carbonate solvent. Preferably, the cyclic carbonate is ethylene carbonate and / or propylene carbonate; preferably, the chain carbonate is a carbonate synthesized from a straight-chain or branched-chain aliphatic monohydric alcohol with 3-8 carbon atoms and carbonic acid. In some embodiments of the present invention, the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and methyl ethyl carbonate.

[0012] The sodium-ion battery electrolyte provided by the present invention, wherein the carboxylic acid ester solvent can be a cyclic carboxylic acid ester solvent and / or a chain carboxylic acid ester solvent. Among them, the cyclic carboxylic acid ester can be γ-butyrolactone, and the chain carboxylic acid ester is a chain carboxylic acid ester with 3 to 8 carbon atoms. In some embodiments of the present invention, the chain carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, propyl propionate, and ethyl propionate.

[0013] The sodium-ion battery electrolyte provided by the present invention, wherein the ether solvent can be selected from one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0014] The sodium-ion battery electrolyte provided by the present invention, wherein the thio solvent can be selected from sulfone-containing compounds and sultone-containing compounds. In some embodiments of the present invention, the thio solvent is selected from one or more of 1,3-propylene glycol cyclic sulfate, 1,3-propane sultone, 1-propene 1,3-sultone, and sulfolane.

[0015] The other functional additives are selected from one or more of ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, allyl-1,3-sultone, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, vinylene sulfate, dimethyl sulfite, diethyl sulfite, and succinonitrile.

[0016] The second aspect of the present invention provides a sodium-ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The positive electrode sheet includes a sodium-containing positive electrode active material. Among them, the electrolyte is the sodium-ion battery electrolyte provided by the present invention.

[0017] For the sodium-ion secondary battery provided by the present invention, the material of the separator is one or more of polyethylene and polypropylene separators or glass fibers.

[0018] In the sodium-ion secondary battery of the present invention, the sodium-containing positive electrode active material can include one or more of layered transition metal oxides, polyanion compounds, or Prussian compounds. Preferably, the layered transition metal oxide includes NaMO2, and M includes one or more of Co, Ni, Fe, Mn, or V; preferably, the polyanion compound includes Na3V2(PO4)3 and / or NaFePO4; preferably, the Prussian blue compound includes Na2MnFe(CN)6.

[0019] In the sodium-ion secondary battery of the present invention, the negative electrode material of the negative electrode sheet may include one or more of carbon-based materials, alloy materials, compound materials, and metallic sodium. Preferably, the carbon-based material includes one or more of soft carbon, hard carbon, or soft-hard composite amorphous carbon; the alloy material includes one or more of tin / phosphorus / antimony / bismuth; the compound material includes one or more of sodium titanium phosphate / 2,5-benzoquinone-1,4-disodium.

[0020] By introducing trifluoromethylbenzene as a functional agent and wetting agent, the present invention improves the wettability of the electrolyte to the separator while reducing the desolvation energy of sodium ions, significantly improving the battery performance. The addition of trifluoromethylbenzene particularly improves the wettability of sulfone, propylene carbonate, and polyolefin separators (polypropylene, polyethylene). In addition, as a functional wetting agent, trifluoromethylbenzene has a completely different mechanism of action from common surfactants, fluoroethers, and fluorobenzenes (which do not coordinate with sodium ions), and has strong application prospects. Detailed implementation manners

[0021] The present invention will be further described in detail below in conjunction with the specific implementation manners. The examples given are only for clarifying the present invention and not for limiting the scope of the present invention.

[0022] The materials and preparation methods used in the examples and comparative examples are described as follows.

[0023] Preparation of the positive electrode sheet:

[0024] Using O3-Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2 as the positive electrode active material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, mixing evenly according to a mass ratio of 90:6:4; adding N-methylpyrrolidone to make a slurry; coating the slurry on an aluminum foil, drying in vacuum at 120 °C overnight, and rolling to obtain the positive electrode sheet.

[0025] Preparation of the negative electrode sheet:

[0026] Using hard carbon as the negative electrode active material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, mixing evenly according to a mass ratio of 90:5:5; adding N-methylpyrrolidone to make a slurry; coating the slurry on an aluminum foil, drying in vacuum at 120 °C overnight, and rolling to obtain the negative electrode sheet.

[0027] Preparation of the electrolyte:

[0028] In a glove box filled with argon, according to the composition shown in Table 1, add sodium salts and solvents to prepare the electrolyte. The concentration of sodium salts in Examples 1-10 and Comparative Examples 1-6 is 1 mol / L.

[0029] Preparation of Sodium-Ion Secondary Battery

[0030] Assemble the matched positive and negative electrode sheets into an Ah-level battery cell, with the corresponding battery cell model being 26700 and the designed capacity of the battery cell being 3.2 Ah.

[0031] Testing Method: Test the electrochemical performance of the battery cells after formation and grading.

[0032] Capacity Retention Rate after 500 Cycles: The ratio of the capacity after 500 cycles at a 1C rate (constant voltage of 0.05C within the voltage range of 1.7 - 3.95V) to the initial capacity.

[0033] Discharge Retention Rate at 5C: That is, at a 5C current, the capacity intersects with the capacity at 1C.

[0034] Percentage of Discharge at -30°C to Room Temperature: The ratio of the discharge capacity at -30°C and 0.2C to the discharge capacity at room temperature.

[0035] Explanation of English Abbreviations in Table 1 is as follows:

[0036] DEC: Diethyl Carbonate; EC: Ethylene Carbonate; EP: Propyl Acetate; DEGDME: Diethylene Glycol Dimethyl Ether; PC: Propylene Carbonate; VC: Vinylene Carbonate; FB: Fluorobenzene; SUL: Sulfolane. The mass fractions of the additives and trifluoromethylbenzene are the mass fractions in the total solvent.

[0037]

[0038] As shown in Table 1, Examples 1 - 9 show the performance of the electrolyte added with the functional wetting agent trifluoromethylbenzene of the present invention. When the content of trifluoromethylbenzene is less than or equal to 15%, the battery has a high capacity retention rate (86% - 94%) after 500 cycles.

[0039] The comparison between Comparative Example 1 and Example 1 shows that the capacity retention rate of the battery in Comparative Example 1 without adding trifluoromethylbenzene is 83% after 500 cycles, the 5C capacity retention rate is 80%, and the room temperature retention rate at minus 30°C is 75%; which is much lower than the capacity retention rate of 92% after 500 cycles, the 5C capacity retention rate of 90%, and the room temperature retention rate of 85% at minus 30°C in Example 1.

[0040] In Example 2, when the system contains a solvent with poor compatibility with the carbon negative electrode (such as SUL), the battery still maintains a high capacity retention rate. Comparative Example 4 shows that the battery using a common wetting agent has a capacity retention rate of only 64% after 500 cycles. This indicates that trifluoromethylbenzene can improve the compatibility between the poor solvent SUL and the carbon negative electrode. Because trifluoromethylbenzene has a certain electron-withdrawing ability and combines with SUL with strong electron-donating ability, weakening the interaction between SUL and sodium ions, which is the manifestation of its functionality. The common wetting agent (such as fluorobenzene) does not have this effect. The comparison between Comparative Example 3 and Example 1 shows that the improvement of the battery cycling performance by the common wetting agent is lower than that of trifluoromethylbenzene.

[0041] The comparison between Example 3 and Comparative Example 6 shows that adding trifluoromethylbenzene can significantly enhance the performance of the PC-based electrolyte.

[0042] The results of Comparative Example 2 and Comparative Example 1 show that when the content of trifluoromethylbenzene is higher than 15%, the cycling performance of the battery deteriorates.

[0043] This embodiment is only a preferred embodiment of the present invention, which is only used to explain the present invention rather than limit the present invention. Modifications, substitutions, changes, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A sodium ion battery electrolyte comprising: An electrolyte sodium salt and a solvent composition, wherein the solvent composition comprises an organic solvent and a functional wetting agent, wherein the functional wetting agent is trifluoromethylbenzene.

2. The sodium ion battery electrolyte according to claim 1, wherein The content of the functional wetting agent in the solvent composition is 0.01 to 15 wt %, preferably 0.5 to 15 wt %.

3. The sodium ion battery electrolyte according to claim 1 or 2, wherein in, The electrolyte sodium salt is selected from one or more of NaPF6, NaBF4, NaClO4; sodium salts of fluorine-containing sulfonyl compounds; sodium salts of fluorine-containing sulfonate compounds; sodium salts of oxalato borate compounds; sodium compounds containing tetrahedral anions such as tetrakis[3,5-bis(trifluoromethyl)phenylborate anion, tris(pentafluorophenyl)borate anion and tetracarboxyl(trifluoromethyl)aluminate anion; Preferably, the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium bistrifluoromethylsulfonyl imide and sodium bisfluorosulfonyl imide.

4. The sodium ion battery electrolyte according to any one of claims 1 to 3, wherein The concentration of the electrolyte sodium salt in the electrolyte solution is 0.1 to 5 mol / L, preferably 0.5 to 2 mol / L.

5. The sodium ion battery electrolyte according to any one of claims 1 to 4, wherein The organic solvent includes one or more of a carbonate solvent, a carboxylate solvent, an ether solvent, and a sulfur-based solvent, and is preferably a combination of a carbonate solvent and an ether solvent. Preferably, the carbonate solvent is a cyclic carbonate solvent and / or a chain carbonate solvent; Preferably, the cyclic carbonate is ethylene carbonate and / or propylene carbonate; preferably, the chain carbonate is a carbonate synthesized from a linear or branched aliphatic monoalcohol having 3 to 8 carbon atoms and carbonic acid; Preferably, the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate and methyl ethyl carbonate. Preferably, the carboxylate solvent is a cyclic carboxylate solvent and / or a chain carboxylate solvent, wherein the cyclic carboxylate is γ-butyrolactone, and the chain carbonate is a chain carboxylate with a carbon number of 3 to 8; preferably, the chain carboxylate is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, propyl propionate and ethyl propionate. Preferably, the ether solvent is selected from one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. Preferably, the sulfur-based solvent is selected from sulfone-containing compounds and sultone-containing compounds; preferably, the sulfur-based solvent is selected from one or more of 1,3-propylene glycol cyclic sulfate, 1,3-propane sultone, 1-propylene 1,3-sultone and sulfolane.

6. The sodium ion battery electrolyte according to any one of claims 1 to 5, wherein The organic solvent includes propylene carbonate and / or a sulfone-containing compound.

7. The sodium ion battery electrolyte according to any one of claims 1 to 6, wherein The electrolyte further comprises one or more other functional additives selected from the group consisting of vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, propenyl-1,3-sultone, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, vinyl sulfate, dimethyl sulfite, diethyl sulfite and succinonitrile.

8. A sodium ion secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material containing sodium ions, wherein: The electrolyte is the sodium ion battery electrolyte according to any one of claims 1 to 7.

9. The sodium ion secondary battery according to claim 8, wherein The material of the diaphragm is one or more of polyethylene and polypropylene diaphragms or glass fiber.

10. The sodium ion secondary battery according to claim 8, wherein The positive electrode active material containing sodium ions includes one or more of a layered transition metal oxide, a polyanion compound or a Prussian compound; preferably, the layered transition metal oxide includes NaMO2, and M includes one or more of Co, Ni, Fe, Mn or V; preferably, the polyanion compound includes Na3V2(PO4)3 and / or NaFePO4; preferably, the Prussian compound includes Na2MnFe(CN)6; Preferably, the negative electrode material of the negative electrode sheet includes one or more of carbon-based materials, alloy materials, compound materials and metallic sodium; preferably, the carbon-based material includes one or more of soft carbon, hard carbon or soft and hard composite amorphous carbon; the alloy material includes one or more of tin / phosphorus / antimony / bismuth; the compound material includes one or more of sodium titanium phosphate 2,5-benzoquinone-1,4 disodium.

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