Low-gas generating electrolyte for sodium-ion battery and low-gas generating sodium-ion battery

Abstract

The application discloses a low-gas electrolyte for a sodium ion battery and a low-gas sodium ion battery. The electrolyte is mainly composed of an organic solvent, a sodium salt and an additive, and further comprises an additive with the following general structure: the additive can improve the film formation of the electrolyte on the positive and negative electrodes of the sodium ion battery, has a good protection effect on the positive and negative electrodes, has good cycle performance when used in the sodium ion battery, can reduce the gas production of the sodium ion battery when used in a high-temperature environment, and widens the use temperature range of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to a low-gas-producing sodium-ion battery electrolyte and a sodium-ion battery, belonging to the field of sodium-ion battery technology. Background Technology

[0002] With the development of portable devices and new energy electric vehicles, lithium-ion batteries have been widely used. However, the increasing demand for lithium resources has led to persistently high prices for lithium-ion batteries, and frequent electric vehicle fires have created an urgent need for an economical and safe alternative or supplementary product. Due to the abundance and low cost of sodium, sodium-ion batteries have attracted widespread attention in recent years. Sodium-ion batteries, with their advantages of low cost and safety, are expected to be widely used in energy storage and low-speed small electric vehicles. However, current sodium-ion batteries produce a significant amount of gas at high temperatures, posing a risk of gas expansion during high-temperature use, which limits their application and development.

[0003] Therefore, optimizing the high-temperature cycle performance of sodium-ion batteries and reducing gas production under high-temperature use has become an important direction in this field. Chinese patent CN202111510524.1 discloses a high-temperature sodium-ion battery electrolyte. By introducing functional additives containing bis(trifluoromethyl) compounds into the electrolyte, an F-containing interfacial film can be formed on the positive and negative electrode surfaces, effectively improving the dissolution of organic components in the interfacial film at high temperatures, reducing the continuous decomposition of the electrolyte at the interface, and improving the high-temperature cycle performance of the battery. However, this invention cannot solve the gas production behavior of sodium-ion batteries at high temperatures.

[0004] Chinese patent CN 115275351 A discloses an overcharge prevention additive for sodium-ion batteries. By introducing diphenyl sulfone and its derivatives into the electrolyte, a protective film is formed on the surface of the positive electrode of the battery, which effectively suppresses gas production in sodium-ion batteries at high temperatures. However, this additive cannot provide good protection for the negative electrode, thus deteriorating the cycle life of the battery.

[0005] In summary, providing a novel sodium-ion battery electrolyte with relatively simple composition and low gas production, as well as a sodium-ion battery, has become a technical problem that needs to be solved. Summary of the Invention

[0006] To address the aforementioned shortcomings and deficiencies, one objective of this invention is to provide a sodium-ion battery electrolyte with low gas production.

[0007] Another object of the present invention is to provide a method for preparing the sodium-ion battery electrolyte described above.

[0008] Another object of the present invention is to provide a sodium-ion battery, wherein the sodium-ion battery uses the sodium-ion battery electrolyte described above.

[0009] On one hand, the present invention provides a sodium-ion battery electrolyte comprising a sodium salt, an organic solvent and additives, and a compound as shown in Formula I:

[0010]

[0011] R1 and R2 are independently selected from hydrogen atoms, C atoms, and C atoms. 1-4 Alkyl, C 1-4 alkenyl, C 1-4 alkynyl group, C 1-3 Alkoxy group, halogen atom, halogenated C 1-4 Alkyl, sulfonyl, cyano, amino, and carbonyl groups.

[0012] Specifically, compounds comprising the following structures: Formula II (1955-23-3), Formula III (58947-69-6), Formula IV (66414-40-2), Formula V (98453-74-8), and Formula VI (100130-34-5).

[0013]

[0014] In the electrolyte of the present invention, the compound represented by Formula I accounts for 0.1% to 2% of the total mass of the electrolyte.

[0015] In the sodium-ion battery electrolyte of the present invention, the water content of the sodium salt, organic solvent and additives is less than 15 ppm.

[0016] In this invention, the sodium salt is one or more of sodium hexafluorophosphate (NaPF6), sodium difluorooxalate borate (NaODFB), and sodium bis(fluorosulfonyl)imide (NaFSI), preferably a mixed sodium salt of NaFSI, NaPF6, and NaODFB. NaPF6, the main solute in conventional sodium-ion electrolytes, has poor high-temperature stability and partially decomposes at high temperatures, increasing the gas production of sodium-ion batteries. NaFSI exhibits better stability at high temperatures, which is beneficial for improving the high-temperature performance of sodium-ion batteries. However, on the other hand, NaFSI can corrode the current collector during the cycling process of sodium-ion batteries, reducing their lifespan. Therefore, NaFSI cannot be used as a standalone sodium salt in a well-cycled sodium-ion battery electrolyte. NaODFB and NaPF6 can passivate the current collector during sodium-ion battery use, protecting it from NaFSI corrosion. Simultaneously, NaODFB can also form a high-quality SEI film on the negative electrode surface, further improving the high-temperature performance of the battery.

[0017] In this invention, the concentration of the sodium salt is 0.7-1.4 mol / L, preferably the concentration of NaPF6 is 0.2-1.1 mol / L, the concentration of NaODFB is 0.1-1.1 mol / L, and the concentration of NaFSI is 0.1-1 mol / L.

[0018] In this invention, the organic solvent is a mixture of carbonates and carboxylic acid esters. The carbonate solvent accounts for 80-100% by weight in the electrolyte solvent. Preferably, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP). The use of carbonate solvents and their concentration of over 80% of the total solvent volume in this invention is beneficial for achieving low gas production at high temperatures. Preferably, the organic solvent includes propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and ethyl butyrate. More preferably, by volume percentage, ethylene carbonate comprises 20-50%, propylene carbonate 10-40%, ethyl methyl carbonate 10-60%, and diethyl carbonate 0-20% in the organic solvent.

[0019] In this invention, the additive has a mass percentage of 2%-10%, and is preferably one or more of vinylene carbonate (VC), 1,3-propanesulfonate lactone (1,3-PS), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), succinic anhydride (SA), maleic anhydride (MAN), citrate anhydride (CA), succinic anhydride (SN), and adiponitrile (ADN).

[0020] On the other hand, the present invention also provides a method for preparing the above-mentioned low-gas-yield sodium-ion battery electrolyte, the steps of which are as follows:

[0021] The first step is to prepare a glove box with an argon atmosphere, water <1ppm, oxygen <1ppm. Under this environment, prepare the solvent required for the electrolyte in the required proportion and stir thoroughly.

[0022] The second step is to freeze the above mixed solvent at a low temperature for 4-12 hours, add sodium salt in the required proportion, and stir thoroughly for 1-4 hours.

[0023] The third step involves adding the additives and the compound shown in Formula I to the solvent according to the specified ratio, and then stirring thoroughly for 1-3 hours to obtain the desired sodium-ion battery electrolyte.

[0024] In the above preparation method, as a preferred approach, the freezing temperature is between -30°C and 0°C, which can effectively avoid the thermal decomposition and failure of certain substances in the electrolyte caused by the subsequent addition of sodium salt to generate heat.

[0025] Finally, the present invention also provides a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic casing, wherein the electrolyte is a sodium-ion battery electrolyte prepared by the above configuration method.

[0026] The positive electrode sheet includes a current collector, a positive electrode material, a conductive agent, and a binder.

[0027] The cathode materials include layered oxides containing sodium ions, polyanionic oxides containing sodium ions, and Prussian blue oxides containing sodium ions.

[0028] The negative electrode sheet comprises a negative electrode material, a current collector, a conductive agent, and a binder.

[0029] The negative electrode material includes artificial graphite, natural graphite and hard carbon, and preferably, the negative electrode material is hard carbon material.

[0030] The negative electrode current collector is made of aluminum foil or copper foil. Preferably, the negative electrode current collector is made of aluminum foil.

[0031] The sodium-ion battery prepared by the above method can be used under high temperature conditions, and the gas production is significantly reduced, which increases the upper limit of the operating temperature of the sodium-ion battery and extends its high-temperature service life.

[0032] In this invention, the above-mentioned technical features can be freely combined to form new technical solutions, provided they do not conflict with each other.

[0033] The beneficial effects of this invention are as follows:

[0034] The electrolyte additives in this invention contain multiple highly electronegative nitrogen atoms. Therefore, the HOMO energy level of these additives is higher than that of solvent molecules, allowing them to preferentially oxidize and decompose on the positive electrode surface to form a CEI film. Furthermore, the sulfate ester groups in the compound form a film on the negative electrode, resulting in a surface SEI film with excellent sodium ion conductivity, low impedance, and good stability, ensuring good cycle performance of the sodium-ion battery. This improves the stability of the interface between the positive and negative electrodes and the electrolyte, reducing side reactions between the electrodes and the electrolyte.

[0035] On the other hand, the present invention uses a specific ratio of sodium salts in the sodium-ion battery, which works synergistically with the electrolyte additives of the present invention to effectively improve the gas generation problem of sodium-ion batteries in high-temperature environments. This has a positive improvement effect on sodium-ion batteries used in high-temperature scenarios and further broadens the application scenarios of sodium-ion batteries. Therefore, the present invention has very important application value for low-cost sodium-ion applications. Detailed Implementation

[0036] The present invention will now be described in detail with reference to embodiments thereof. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. In fact, those skilled in the art will recognize that any modifications or alterations made to the present invention without departing from its scope or spirit will fall within the protection scope of the present invention.

[0037] The structural formulas of the specific additives used in the following examples are as follows:

[0038]

[0039] Raw materials and sources: T1, T2 and T3 were purchased from Aurora Fine Chemicals. In addition, the sodium salts, solvents and additives used in the examples were purchased from Suzhou Duoduo Chemical Reagent Co., Ltd.

[0040] Example 1

[0041] The low-gas-producing electrolyte used in the sodium-ion battery of this embodiment is composed of an organic solvent, sodium salt, and additives.

[0042] The organic solvent consists of the following volume percentages: 20% ethylene carbonate, 10% propylene carbonate, 60% methyl ethyl carbonate, and 10% diethyl carbonate.

[0043] The total concentration of the sodium salts is 1.4 M, NaPF6 is 0.2 M, NaFSI is 1.1 M, and NaODFB is 0.1 M.

[0044] The specific additive T1 accounts for 0.1% of the mass of the sodium-ion battery electrolyte, and the remaining additives account for 1.9% VC.

[0045] The preparation method of the electrolyte for the low-gas-yield sodium-ion battery in this embodiment is as follows:

[0046] In an argon-filled glove box (water and oxygen content <1ppm), the organic solvent of the formula amount is mixed and frozen at -30°C for 4 hours. The NaPF6, NaFSI and NaODFB of the formula amount are added to the mixture and stirred thoroughly for 1 hour. Finally, the VC and additive T1 of the formula amount are added and the mixture is stirred thoroughly for 3 hours to obtain the sodium-ion battery electrolyte.

[0047] The low-gas-producing sodium-ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte is the low-gas-producing sodium-ion battery electrolyte described above. A Prussian blue oxide containing sodium ions is used as the positive electrode; a hard carbon material is used as the negative electrode; and polyethylene (PE) material is used as the separator.

[0048] Example 2

[0049] The low-gas-producing electrolyte used in the sodium-ion battery of this embodiment is composed of an organic solvent, sodium salt, and additives.

[0050] The organic solvent consists of the following volume percentages: 50% ethylene carbonate, 40% propylene carbonate, and 10% methyl ethyl carbonate.

[0051] The total concentration of the sodium salts is 1.3M, NaPF6 is 1.1M, NaFSI is 0.1M, and NaODFB is 0.1M.

[0052] The specific additive T2 accounts for 2% of the mass of the sodium-ion battery electrolyte, and the remaining additives are 5% VC and 3% PS.

[0053] The preparation method of the electrolyte for the low-gas-yield sodium-ion battery in this embodiment is as follows:

[0054] In an argon-filled glove box (water and oxygen content <1ppm), the organic solvent of the formula is mixed and frozen at -30°C for 5 hours. The formula amounts of NaPF6, NaFSI, and NaODFB are added to the mixture and stirred thoroughly for 4 hours. Finally, the formula amounts of VC, PS, and T2 are added and the mixture is stirred thoroughly for 2 hours to obtain the sodium-ion battery electrolyte.

[0055] The sodium-ion battery was prepared in the same manner as in Example 1.

[0056] Example 3

[0057] The low-gas-producing electrolyte used in the sodium-ion battery of this embodiment is composed of organic solvent, sodium salt and additives.

[0058] The organic solvent consists of the following volume percentages: 20% ethylene carbonate, 20% propylene carbonate, and 60% methyl ethyl carbonate.

[0059] The total concentration of the sodium salts is 1.4 M, NaPF6 is 0.2 M, NaFSI is 0.1 M, and NaODFB is 1 M.

[0060] The specific additive T3 accounts for 1% of the mass percentage of the sodium-ion battery electrolyte, and the remaining additives are 1% VC and 1% PS.

[0061] The preparation method of the electrolyte for the low-gas-yield sodium-ion battery in this embodiment is as follows:

[0062] In an argon-filled glove box (water and oxygen content <1ppm), the organic solvent of the formula is mixed and frozen at -30°C for 5 hours. The formula amounts of NaPF6, NaFSI, and NaODFB are added to the mixture and stirred thoroughly for 2 hours. Finally, the formula amounts of VC, PS, and T3 are added and the mixture is stirred thoroughly for 2 hours to obtain the sodium-ion battery electrolyte.

[0063] The sodium-ion battery was prepared in the same manner as in Example 1.

[0064] Example 4

[0065] The low-gas-producing electrolyte used in the sodium-ion battery of this embodiment is composed of an organic solvent, sodium salt, and additives.

[0066] The organic solvent consists of the following volume percentages: 20% ethylene carbonate, 10% propylene carbonate, 20% methyl ethyl carbonate, and 20% diethyl carbonate.

[0067] The total concentration of the sodium salts is 0.7 M, NaPF6 is 0.3 M, NaFSI is 0.2 M, and NaODFB is 0.3 M.

[0068] The specific additive T2 accounts for 1% of the mass percentage of the sodium-ion battery electrolyte, and the remaining additives are 1% VC and 1% PS.

[0069] The preparation method of the electrolyte for the low-gas-yield sodium-ion battery in this embodiment is as follows:

[0070] In an argon-filled glove box (water and oxygen content <1ppm), the organic solvent of the formula is mixed and frozen at -30°C for 6 hours. The formula amounts of NaPF6, NaFSI, and NaODFB are added to the mixture and stirred thoroughly for 6 hours. Finally, the formula amounts of VC, PS, and T2 are added and the mixture is stirred thoroughly for 2 hours to obtain the sodium-ion battery electrolyte.

[0071] The sodium-ion battery was prepared in the same manner as in Example 1.

[0072] Example 5

[0073] The low-gas-producing electrolyte used in the sodium-ion battery of this embodiment is composed of an organic solvent, sodium salt, and additives.

[0074] The organic solvent is composed of the following volume percentages: 30% ethylene carbonate, 40% propylene carbonate, 20% methyl ethyl carbonate, and 10% diethyl carbonate.

[0075] The total concentration of the sodium salts is 1.2 M, NaPF6 is 0.2 M, NaFSI is 0.9 M, and NaODFB is 0.1 M.

[0076] The specific additive T1 accounts for 1% of the mass percentage of the sodium-ion battery electrolyte, and the remaining additives are 2% VC and 2% PS.

[0077] The preparation method of the electrolyte for the low-gas-yield sodium-ion battery in this embodiment is as follows:

[0078] In an argon-filled glove box (water and oxygen content <1ppm), the organic solvent of the formula is mixed and frozen at -30°C for 5 hours. The formula amounts of NaPF6, NaFSI, and NaODFB are added to the mixture and stirred thoroughly for 3 hours. Finally, the formula amounts of VC, PS, and T1 are added and the mixture is stirred thoroughly for 2 hours to obtain the sodium-ion battery electrolyte.

[0079] The sodium-ion battery was prepared in the same manner as in Example 1.

[0080] Comparative Example 1

[0081] The difference between this comparative example and Example 1 is that the electrolyte in this comparative example does not contain additive T1, and the electrolyte preparation and battery manufacturing method are the same as in Example 1.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 2 is that the solvent in this comparative example consists of 40% ethylene carbonate and 60% dimethyl carbonate, and the electrolyte preparation and battery manufacturing method are the same as in Example 2.

[0084] Comparative Example 3

[0085] The difference between this comparative example and Example 3 is that the sodium salt composition of this comparative example is 0.5M NaODFB, and the electrolyte preparation and battery manufacturing method are the same as in Example 3.

[0086] Comparative Example 4

[0087] The difference between this comparative example and Example 4 is that the electrolyte in this comparative example does not contain additive T2, and the electrolyte preparation and battery manufacturing method are the same as in Example 3.

[0088] Comparative Example 5

[0089] In this comparative example, the electrolyte additive is 4,4'-difluorodiphenyl sulfone (CAS No.: 383-29-9).

[0090]

[0091] The difference between this comparative example and Example 1 is that the additive T1 in this comparative example is replaced with an equal amount of 4,4'-difluorodiphenyl sulfone, and the electrolyte preparation and battery manufacturing method are the same as in Example 1.

[0092] The performance of the sodium-ion batteries obtained in the examples and comparative examples was tested at high temperatures. The test procedure was as follows: first, the initial battery volume V1 was measured; then, the battery was placed in a 45°C environment for 100 cycles, and the volume V2 was measured again. The difference between the two volumes (V2-V1) was the battery gas production data, and the capacity cycle retention rate was recorded. The test results are shown in Table 1.

[0093] Table 1. Performance test results of sodium-ion batteries in the examples and comparative examples after 100 cycles at 45°C.

[0094]

[0095] As can be seen from the comparison of Example 1 and Comparative Examples 1 and 4, the additive T1 in this invention can improve the gas production of sodium-ion batteries without deteriorating the cycle performance.

[0096] A comparison of Example 2 and Comparative Example 2 shows that the specific solvent ratio in the electrolyte of the present invention can effectively improve the cycle and gas production of sodium-ion batteries.

[0097] A comparison of Example 3 and Comparative Example 3 shows that the specific sodium salt combination in the electrolyte of the present invention has a synergistic effect, which can effectively improve the cycle and gas production of sodium-ion batteries.

[0098] The cycling and gas production data from Example 1 and Comparative Example 5 show that the sodium-ion battery electrolyte of this invention exhibits not only low gas production but also good high-temperature cycling performance when used in high-temperature environments. This is because the additives in this invention not only protect the positive electrode but also form a low-resistance S-containing solid electrolyte film on the surface of the negative electrode, ensuring excellent cycling performance.

[0099] In summary, the low-gas-producing sodium-ion battery electrolyte of the present invention provides excellent high-temperature comprehensive performance for sodium-ion batteries.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, The sodium-ion battery electrolyte comprises sodium salt, organic solvent, and additives, as well as a compound as shown in Formula I: Equation I R1 and R2 are independently selected from hydrogen atoms, C atoms, and C atoms. 1-4 Alkyl, C 1-4 alkenyl, C 1-4 alkynyl group, C 1-3 Alkoxy group, halogen atom, halogenated C 1-4 The electrolyte contains alkyl, sulfonyl, cyano, amino, and carbonyl groups, and the compound represented by Formula I accounts for 0.1% to 2% of the total mass of the electrolyte. The sodium salt is one of sodium hexafluorophosphate (NaPF6), sodium difluorooxalate borate (NaODFB), and sodium difluorosulfonamide (NaFSI).

2. The sodium-ion battery electrolyte as described in claim 1, characterized in that, Formula I is selected from one or more compounds of Formulas II through VI. Formula II Formula III Formula IV Formula V Formula VI.

3. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The sodium salt is a mixed sodium salt of NaFSI, NaPF6 and NaODFB; the concentration of the sodium salt is 0.7-1.4 mol / L, the concentration of NaPF6 is 0.2-1.1 mol / L, the concentration of NaODFB is 0.1-1.1 mol / L, and the concentration of NaFSI is 0.1-1 mol / L.

4. The sodium-ion battery electrolyte according to any one of claims 1-3, characterized in that, The organic solvent is a mixture of carbonate and carboxylic acid ester, wherein the carbonate solvent accounts for 80-100% by weight in the electrolyte solvent, and the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

5. The sodium-ion battery electrolyte as described in claim 4, characterized in that, The organic solvent includes propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethyl butyrate. By volume percentage, ethylene carbonate accounts for 20-50%, propylene carbonate 10-40%, methyl ethyl carbonate 10-60%, and diethyl carbonate 0-20% in the organic solvent.

6. The sodium-ion battery electrolyte according to any one of claims 1-3, characterized in that, The additive has a mass percentage of 2%-10%, and the additive is one or more of vinylene carbonate (VC), 1,3-propanesulfonate lactone (1,3-PS), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), succinic anhydride (SA), maleic anhydride (MAN), citrate anhydride (CA), succinic anhydride (SN), and adiponitrile (ADN).

7. The method for preparing the sodium-ion battery electrolyte according to any one of claims 1-6, characterized in that, The steps are as follows: The first step is to prepare a glove box with an argon atmosphere, water <1ppm, oxygen <1ppm, and prepare the required solvent for the electrolyte in the required proportions under this environment and stir it thoroughly. The second step involves freezing the organic solvent at a low temperature for 4-12 hours, adding sodium salt in the required proportion, and stirring thoroughly for 1-4 hours. The third step involves adding the additives and the compound shown in Formula I to the solvent according to the specified ratio, and then stirring thoroughly for 1-3 hours or more to obtain the desired sodium-ion battery electrolyte.

8. The preparation method according to claim 7, characterized in that, The low-temperature environment is between -30°C and 0°C.

9. A sodium-ion battery, the sodium-ion battery comprising a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic casing, wherein the electrolyte is selected from the sodium-ion battery electrolyte as described in any one of claims 1-6 or the sodium-ion battery electrolyte prepared by the preparation method as described in any one of claims 7-8.

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