Sodium-ion battery electrolytes and electrochemical devices
By using a specific ratio of zwitterionic additives and vinyl sulfate to form a monolayer structure in sodium-ion batteries, the problems of side reactions in the electrolyte catalyzed by high-voltage cathode materials and gas generation during high-temperature cycling were solved, thus improving the high-temperature performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ENVISION DYNAMICS TECH (JIANGSU) CO LTD
- Filing Date
- 2023-04-14
- Publication Date
- 2026-06-23
Smart Images
Figure CN116404252B_ABST
Abstract
Description
Technical Field
[0001] This invention provides a sodium-ion battery electrolyte and an electrochemical device. Background Technology
[0002] Currently, lithium-ion battery technology occupies a core position in energy storage and power batteries. Since its commercialization, lithium-ion battery technology has matured significantly. However, it also faces numerous challenges, such as the increasing scarcity of lithium resources and soaring material prices, forcing researchers to develop more economical and efficient alternative technologies. Lithium and sodium belong to the same Group I metals and have similar physical and chemical properties. However, sodium resources are far more abundant than lithium resources, and once the system is fully developed, its cost is expected to be lower than that of lithium resources within the next five years. Therefore, the development of sodium-ion batteries has received widespread attention from the industry in recent years.
[0003] Research on sodium-ion batteries still faces many challenges. In order to obtain an energy density system close to that of lithium-ion batteries, sodium-ion battery systems typically use high-voltage 4.0V layered ternary oxide cathode materials and hard carbon anode materials. On the one hand, in high-voltage cathode materials, highly chemically active transition metals can catalyze chemical side reactions in the electrolyte. On the other hand, at high temperatures, the main components of the anode SEI film, such as NaF and Na2CO3, have significantly higher solubility in carbonate solvents than lithium salts. This high solubility easily leads to damage to the SEI film, which is accompanied by repair, resulting in severe gas generation during high-temperature cycling.
[0004] Therefore, developing new electrolyte additives and mature sodium-ion battery electrolytes is crucial for the application of sodium-ion batteries. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to overcome the defects of existing sodium-ion batteries, such as the high chemical activity of transition metals in high-voltage cathode materials catalyzing chemical side reactions in the electrolyte and the serious gas generation during high-temperature cycling. The present invention provides a sodium-ion battery electrolyte and electrochemical device.
[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.
[0007] In a first aspect, the present invention provides a sodium-ion battery electrolyte containing 0.1% to 20% zwitterionic additives and 0.5% to 1 wt% ethylene sulfate; % represents the weight percentage of each component in the electrolyte.
[0008] The zwitterionic additive is shown in structural formula I:
[0009]
[0010] R1, R2, and R3 are independently alkyl, alkenyl, or alkynyl groups with 1 to 6 carbon atoms, containing 0 to 1 halogen atom, containing 0 to 1 carbonyl substituent, containing 0 to 1 ester substituent, or containing 0 to 1 aryl substituent, or cycloalkyl groups with 1 to 6 carbon atoms, or cycloalkenyl groups with 2 to 6 carbon atoms, and n is 1 to 3.
[0011] In a second aspect, the present invention provides an electrochemical device comprising the electrolyte as described above.
[0012] The positive and progressive effects of this invention are as follows:
[0013] In this invention, a specific amount of zwitterionic additive and vinyl sulfate are applied to the electrolyte to form a monolayer-like structure on the negative electrode surface through coulombic interactions. The monolayer structure can be uniformly adsorbed on the negative electrode interface, thus avoiding the dissolution of the negative electrode SEI film.
[0014] The electrolyte of this invention can effectively improve the capacity retention rate of batteries during high-temperature cycling and reduce the volume expansion rate during high-temperature storage. Detailed Implementation
[0015] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.
[0016] In the sodium-ion battery electrolyte described in the first aspect of the present invention:
[0017] In a preferred embodiment, R1, R2, and R3 are all n-propyl groups, i.e., Formula I is compound 1:
[0018] In a preferred embodiment, R1, R2, and R3 are all methyl groups, i.e., Formula I is compound 2:
[0019] In a preferred embodiment, R1 and R2 are both methyl groups, and R3 is a methyl group. That is, Formula I is compound 3:
[0020] In a preferred embodiment, R1 and R2 are both methyl groups, and R3 is a cyclohexyl group. That is, Formula I is compound 4:
[0021] In a preferred embodiment, R1 and R2 are both methyl groups, and R3 is a benzyl group, i.e., Formula I is compound 5:
[0022] In this invention, the content of the zwitterionic additive is preferably 0.5% to 5%, for example 2%, 3% or 4%.
[0023] In this invention, the content of vinyl sulfate (DTD) is preferably 0.6-0.8 wt%, for example 0.7 wt%.
[0024] In this invention, the electrolyte may further include sodium salt.
[0025] The sodium salt content can be 6-18%, for example 12%, where % refers to the weight ratio of sodium salt in the electrolyte.
[0026] The sodium salt may include sodium hexafluorophosphate (NaPF6) and / or sodium bis(fluorosulfonyl)imide (NaFSI).
[0027] When the sodium salt is a mixture of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI), the weight ratio of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI) can be (0.8~1.2):1, for example 1:1.
[0028] When the sodium salt contains sodium hexafluorophosphate (NaPF6), the content of sodium hexafluorophosphate (NaPF6) can be 6 to 12 wt%, where % refers to the weight ratio of the sodium salt in the electrolyte.
[0029] Wherein, when the sodium salt contains sodium bis(fluorosulfonyl)imide (NaFSI), the content of sodium bis(fluorosulfonyl)imide (NaFSI) can be 0 to 6 wt%, where % refers to the weight ratio of the sodium salt in the electrolyte.
[0030] In this invention, the electrolyte may further include an organic non-aqueous solvent. The electrolyte of this invention is a non-aqueous electrolyte.
[0031] The organic non-aqueous solvent may be a carbonate.
[0032] The carbonates may include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC).
[0033] In this invention, when the electrolyte contains ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC), the volume ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) can be 2:2:4:2.
[0034] In this invention, preferably, the alkyl groups of R1, R2, and R3 that have 1 to 6 carbon atoms are independently alkyl groups with 1 to 4 carbon atoms. The alkyl groups with 1 to 4 carbon atoms can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl, preferably methyl, n-propyl, or n-butyl.
[0035] In this invention, preferably, the alkenyl groups with 1 to 6 carbon atoms in R1, R2, and R3 are independently alkenyl groups with 2 to 3 carbon atoms, such as vinyl or isopropenyl.
[0036] In this invention, preferably, the alkynyl group in R1, R2, and R3 has 1 to 6 carbon atoms.
[0037] In this invention, preferably, the cycloalkyl groups in R1, R2, and R3 with 3 to 10 carbon atoms are cycloalkyl groups with 4 to 10 carbon atoms; more preferably, they are cycloalkyl groups with 4 to 7 carbon atoms. The cycloalkyl groups with 3 to 10 carbon atoms are further preferably cyclobutyl, cyclopentyl, cyclohexyl, or cycloheptyl, with cyclohexyl being the most preferred.
[0038] In this invention, the halogens in R1, R2, and R3 are preferably F, Cl, Br, or I; Cl is more preferred.
[0039] In this invention, the aryl substituent in R1, R2, and R3 can be C 6-30 Aryl, for example C 6-14 Aryl, preferably C 6-10 Aryl, with phenyl being the preferred choice.
[0040] In this invention, preferably, when R1, R2, and R3 contain cycloalkyl or cycloalkenyl groups, the number of cyclic groups is 1 to 2.
[0041] In this invention, the ester substituent can be: In this case, Ra is an alkyl group with 1 to 6 carbon atoms or an alkenyl group with 2 to 6 carbon atoms.
[0042] Wherein, the alkyl group having 1 to 6 carbon atoms in Ra can be an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl, preferably methyl, n-propyl, or n-butyl.
[0043] Among them, the alkenyl group with 2 to 6 carbon atoms in Ra can be an alkenyl group with 2 to 3 carbon atoms, such as vinyl or isopropenyl.
[0044] In this invention, n can be 2.
[0045] In the electrochemical device of the second aspect of the present invention:
[0046] The present invention also provides an electrochemical device comprising the electrolyte described above.
[0047] In this invention, the electrochemical device can generally be a conventional device in the art containing the sodium-ion battery electrolyte as described above, such as a battery or capacitor.
[0048] In some preferred embodiments, the electrochemical device is a sodium-ion battery. The sodium-ion battery typically includes a positive electrode, a negative electrode, an electrolyte, and a separator.
[0049] In a preferred embodiment, the compaction density of the positive electrode can be 3.25 g / cm³. 3 .
[0050] In a preferred embodiment, the positive electrode typically includes a positive electrode active material, a binder, and a conductive agent.
[0051] In this invention, the positive electrode can be prepared using conventional methods in the art. Preferably, the preparation method of the positive electrode includes the following steps: mixing the positive electrode active material, the binder and the conductive agent in N-methylpyrrolidone (NMP) and stirring under a vacuum mixer to obtain a positive electrode slurry; uniformly coating the positive electrode slurry onto an aluminum foil; drying the aluminum foil at room temperature and then transferring it to an oven for drying, followed by cold pressing and slitting to obtain the positive electrode.
[0052] The weight ratio of the positive electrode active material, the binder, and the conductive agent can be 95:2:3.
[0053] The positive electrode active material can be a conventional positive electrode active material used in sodium-ion batteries, such as NaNi. 0.33 Fe 0.33 Mn 0.34 O2.
[0054] The binder may be a conventional binder used in the field for the positive electrode of sodium-ion batteries, such as polyvinylidene fluoride (PVDF).
[0055] The conductive agent can be a conductive agent commonly used in the field for the positive electrode of sodium-ion batteries, such as acetylene black.
[0056] In a preferred embodiment, the compaction density of the negative electrode can be 1.5 g / cm³. 3 .
[0057] In a preferred embodiment, the negative electrode typically includes a negative electrode active material, a conductive agent, a binder, and a thickener.
[0058] In a preferred embodiment, the negative electrode typically comprises the negative electrode active material, the conductive agent, the binder, and the thickener.
[0059] In this invention, the negative electrode can be prepared using conventional methods in the art. Preferably, the preparation method of the negative electrode includes the following steps: mixing the negative electrode active material, the thickener, the binder, and the conductive agent in deionized water, and stirring evenly under a vacuum mixer to obtain a negative electrode slurry; uniformly coating the negative electrode slurry onto a negative electrode current collector copper foil; drying the copper foil at room temperature and then transferring it to an oven for drying, followed by cold pressing and slitting to obtain the negative electrode.
[0060] The weight ratio of the negative electrode active material, the conductive agent, the binder, and the thickener can be 96:2:1:1.
[0061] The negative electrode active material can be a negative electrode active material conventionally used in sodium-ion battery negative electrodes, such as hard carbon.
[0062] The conductive agent may be a conductive agent conventionally used in the field for the negative electrode of sodium-ion batteries, such as acetylene black.
[0063] The binder may be a conventional binder used in the field for the negative electrode of sodium-ion batteries, such as styrene-butadiene rubber (SBR).
[0064] The thickener can be a thickener conventionally used in the art for the negative electrode of sodium-ion batteries, such as sodium carboxymethyl cellulose (CMC-Na).
[0065] In a preferred embodiment, the amount of electrolyte can be selected according to the actual situation, for example, 3.0 g / Ah.
[0066] In the preferred embodiment described above, the separator can be a polyethylene film (PE).
[0067] In the preferred embodiment described above, the thickness of the isolation membrane can be 9 μm.
[0068] In this invention, the sodium-ion battery can be prepared using conventional methods in the art, preferably including the following steps: using a 9μm thick polyethylene film as a separator, the above-prepared positive electrode, separator, and negative electrode are stacked sequentially to obtain a bare cell, with the separator positioned between the positive and negative electrodes to provide isolation, then wrapped with an aluminum-plastic film, transferred to a vacuum oven to dry at 80°C, injected with the electrolyte as described above, and then sealed. After further processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, the finished soft-pack sodium-ion battery is obtained.
[0069] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.
[0070] Example 1
[0071] The specific structural formula and dosage of the zwitterionic additive in Example 1 are shown in Table 1.
[0072] In Example 1, in addition to the zwitterionic additives listed in Table 1, there is also an organic non-aqueous solvent, including ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC); ethylene sulfate (DTD); and sodium salts selected from sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI).
[0073] The volume ratio of the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) is 2:2:4:2; the amount of ethylene sulfate (DTD) is 0.5 wt%; the amount of NaPF6 is 6 wt%; the amount of NaFSI is 6 wt%, and % represents the weight percentage of each component in the electrolyte.
[0074] The electrolyte preparation method is as follows:
[0075] The electrolyte was prepared in a glove box with a nitrogen content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of 0.1 ppm. After thoroughly mixing the above solvents in the specified proportions, fully dried NaPF6 and NaFSI were added to the non-aqueous solvent, followed by the addition of a zwitterionic additive and vinyl sulfate, to prepare the non-aqueous electrolyte for sodium-ion batteries.
[0076] The preparation method of sodium-ion battery with electrolyte assembly is as follows: The positive electrode active material NaNi... 0.33 Fe 0.33 Mn 0.34 O2, conductive agent acetylene black, and binder polyvinylidene fluoride are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture is then coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet with a compacted density of 3.25 g / cm³. 3 .
[0077] Hard carbon (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were thoroughly mixed in a deionized water solvent system at a mass ratio of 96:2:1:1. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the negative electrode sheet with a compacted density of 1.5 g / cm³. 3 .
[0078] A diaphragm was obtained by using 9 μm thick polyethylene as the base membrane and coating the base membrane with a 3 μm thick nano-alumina coating.
[0079] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as an insulator. The stacked electrodes then form a bare cell.
[0080] After the bare cell is placed in an aluminum-plastic film and baked at 80°C to remove moisture, the corresponding electrolyte is injected and the cell is sealed (the amount of electrolyte can be 3.0g / Ah). Then, after processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, the finished soft-pack sodium-ion battery is obtained.
[0081] Examples 2-8
[0082] Examples 2-8 are also specific examples of sodium-ion battery electrolyte preparation. Except that the composition ratio of each component of the sodium-ion battery electrolyte is added as shown in Table 1, the rest are the same as in Example 1.
[0083] Comparative Example 1
[0084] Comparative Example 1 was identical to Example 1 except that the composition and ratio of the sodium-ion battery electrolyte were added as shown in Table 1.
[0085] Table 1. Types and amounts of additives in the electrolytes of the examples and comparative examples.
[0086]
[0087]
[0088] Effect Example
[0089] The lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-2 were subjected to performance tests on capacity retention during high-temperature cycling at 45°C and volume expansion rate after 30 days of storage at 60°C. The test methods are as follows:
[0090] 1. Capacity retention during high-temperature cycling at 45℃:
[0091] At 45℃, the sodium-ion battery was charged to 4.0V at a constant current of 0.5C, then charged at a constant voltage of 4.0V until the current was less than 0.05C. After resting for 30 minutes, it was discharged to 2.8V at a constant current of 1C. The discharge capacity of the sodium-ion battery at this point was measured, which is the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions, and the capacity retention rate after 1000 cycles was calculated. The capacity retention rate after cycling was calculated using the following formula.
[0092] Capacity retention rate (%) = (Discharge capacity after 1000 cycles / Discharge capacity after the first cycle) × 100%.
[0093] 2. Volume expansion rate after 30 days of storage at 60℃:
[0094] At 25°C, the sodium-ion battery was charged at a constant current of 0.5C to 4.0V, and then charged at a constant voltage to a current of 0.05C. The volume of the sodium-ion battery was measured and recorded as V0. The fully charged battery was then stored in a 60°C oven for 30 days, and the volume after storage was measured and recorded as V1. The volume expansion rate of the sodium-ion battery relative to its initial volume before storage was calculated using the following formula:
[0095] Volume expansion rate (%) = (V1-V0) / V0×100%.
[0096] The test results are shown in Table 2 below.
[0097] Table 2
[0098]
[0099] From the results of Examples 4 to 8, it can be seen that when the amount of additive is 2%, Example 1 using Compound 1 has the best overall performance, with the best high-temperature cycling performance and better storage gas generation performance.
[0100] The results from Examples 4 to 8 show that the optimal addition amount of the additive is 0.5% to 5%, which exhibits good performance in both high-temperature cycling and storage gas generation.
[0101] From the comparison of Comparative Example 1 and Examples 4-6, it can be seen that as the amount of additive gradually increases, the high-temperature cycling and storage gas generation performance will first improve and then deteriorate, indicating that the cell performance will be unsatisfactory when it exceeds a certain value.
[0102] The results of Comparative Example 2 and Example 7 show that when the amount of additive exceeds the above range, it will have a deteriorating effect on performance.
[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A sodium-ion battery electrolyte, characterized in that, It contains 0.1% to 20% zwitterionic additives and 0.5% to 1 wt% ethylene sulfate; % represents the weight percentage of each component in the electrolyte; The zwitterionic additive is shown in structural formula I: R1, R2, and R3 are independently alkyl, alkenyl, or alkynyl groups with 1 to 6 carbon atoms, containing 0 to 1 halogen atom, containing 0 to 1 carbonyl substituent, containing 0 to 1 ester substituent, or containing 0 to 1 aryl substituent, or cycloalkyl or cycloalkenyl groups with 3 to 10 carbon atoms, and n is 1 to 3.
2. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The additive shown in Formula I is 3. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The content of the zwitterionic additive is 0.5% to 5%.
4. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The content of the vinyl sulfate is 0.6-0.8 wt%.
5. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The electrolyte comprises sodium hexafluorophosphate and / or sodium bis(fluorosulfonyl)imide.
6. The sodium-ion battery electrolyte as described in claim 5, characterized in that, When the electrolyte contains sodium hexafluorophosphate, the content of sodium hexafluorophosphate is 6-12 wt%, where % refers to the weight ratio of sodium salt in the electrolyte; When the electrolyte contains sodium bis(fluorosulfonyl)imide, the content of sodium bis(fluorosulfonyl)imide is 0-6 wt%, where % refers to the weight ratio of the sodium salt in the electrolyte.
7. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The electrolyte includes ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate.
8. The sodium-ion battery electrolyte as described in claim 7, characterized in that, The volume ratio of the ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate is 2:2:4:
2.
9. The sodium-ion battery electrolyte as described in claim 1, characterized in that, The structural formula of the zwitterionic additive satisfies one or more of the following conditions: a. The alkyl groups in R1, R2, and R3 that have 1 to 6 carbon atoms are independently alkyl groups that have 1 to 4 carbon atoms; b. In R1, R2, and R3, the alkenyl groups with 1 to 6 carbon atoms are independently alkenyl groups with 2 to 3 carbon atoms; c. In R1, R2, and R3, the number of carbon atoms is 1–6, and the ynthyl group is... d. Cycloalkyl groups with 3 to 10 carbon atoms in R1, R2, and R3 are cycloalkyl groups with 4 to 10 carbon atoms; e. The halogens mentioned in R1, R2, and R3 are F, Cl, Br, or I; f. In R1, R2, and R3, the aryl substituent is C 6-30 Aryl; g. In R1, R2, and R3, when cycloalkyl or cycloalkenyl groups are present, the number of cyclic groups is 1 to 2; hn is 2.
10. An electrochemical device comprising a sodium-ion battery electrolyte as described in any one of claims 1 to 9.