A sodium-ion battery electrolyte and a sodium-ion battery

Abstract

This invention relates to the field of sodium-ion battery technology, and discloses a sodium-ion battery electrolyte and a sodium-ion battery. The sodium-ion battery electrolyte includes an organic solvent, a sodium salt, and an additive; the additive includes additive A, which comprises sodium difluorooxalate borate and a compound with a sulfide structure; the compound with the sulfide structure is diallyl sulfide. The additive of this invention, through the synergistic effect of the sulfide-containing compound and sodium difluorooxalate borate, can effectively solve the interface problem and improve the cycle stability of the sodium-ion battery under high voltage.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion battery electrolyte and a sodium-ion battery. Background Technology

[0002] In recent years, lithium-ion batteries have become the most influential battery product on the market due to their advantages such as high energy density, high operating voltage, and good cycle stability, and are widely used in portable electronic products, electric vehicles, and energy storage. With the rapid development of these industries, the manufacturing scale of lithium-ion batteries has reached unprecedented heights. However, problems such as uneven distribution of lithium resources and soaring prices of lithium carbonate are becoming increasingly prominent, and relying solely on lithium-ion batteries can no longer meet the energy storage needs of new power systems.

[0003] Compared to lithium-ion batteries, sodium-ion batteries utilize abundant and evenly distributed sodium resources, completely unrestricted by resources or location. Researching sodium-ion batteries can avoid the bottlenecks in the battery industry caused by lithium resource shortages, and can gradually replace lead-acid batteries, which cause severe environmental pollution. Furthermore, sodium-ion batteries share similar working principles and manufacturing systems with lithium-ion batteries, allowing for the direct utilization of lithium-ion battery production and processing equipment to a certain extent, thus offering broad prospects for industrialization.

[0004] Among all sodium-ion battery cathode materials, layered oxide systems possess advantages such as low cost, environmental friendliness, ease of preparation, and high actual specific capacity, making them one of the cathode material systems most aligned with the development direction of sodium-ion batteries. They can meet the demand for high-energy-density rechargeable batteries in portable devices, electric vehicles, and other fields. For layered oxide cathodes, increasing the charging cut-off voltage is an effective way to improve capacity and energy density. However, under high voltage, the cathode material is prone to phase transitions, and side reactions at the electrode-electrolyte interface will degrade battery performance, rendering the battery unusable for recycling. Therefore, optimizing the electrolyte to improve the stability of the cathode structure under high voltage and solving the electrode-electrolyte interface problem has become a current research hotspot. However, the electrolyte additives and corresponding electrolyte formulations currently used are mostly based on and reference lithium-ion battery systems, and are not suitable for sodium-ion battery systems.

[0005] Therefore, there is an urgent need for a sodium-ion battery electrolyte and a sodium-ion battery to solve the above-mentioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the existing technical problems and provide a sodium-ion battery electrolyte and a sodium-ion battery.

[0007] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0008] A sodium-ion battery electrolyte, comprising an organic solvent, a sodium salt, and additives; the additives include additive A, which comprises sodium difluorooxalate borate and a compound containing a sulfide structure.

[0009] Preferably, the compound containing the sulfide structure is diallyl sulfide.

[0010] like Figure 1 The figure shows the molecular structure of diallyl sulfide in the additive of the present invention.

[0011] Preferably, the compound containing a sulfide structure accounts for 0.5 wt% to 3 wt% of the sodium-ion battery electrolyte; and the sodium difluorooxalate borate additive accounts for 0.1 wt% to 2 wt% of the sodium-ion battery electrolyte.

[0012] Preferably, the additive further includes additive B;

[0013] The additive B is at least one of fluorinated ethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sulfonate lactone (PS), methane disulfonate methylene ester (MMDS), adiponitrile (ADN), and succinic anhydride (SN).

[0014] The additive B accounts for 0.6 wt% to 5 wt% of the sodium-ion battery electrolyte by mass.

[0015] Preferably, the organic solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, difluoroacetate, difluoroethyl acetate, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, acetonitrile, malononitrile, glutaronitrile, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, sulfolane, and dimethyl sulfoxide; the organic solvent accounts for 80 wt% to 90 wt% of the sodium-ion battery electrolyte by mass.

[0016] Preferably, the sodium salt comprises at least one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaOTf), sodium perchlorate, sodium tetrafluoroborate, and sodium nitrate; the sodium salt accounts for 5 wt% to 15 wt% of the mass percentage of the sodium-ion battery electrolyte.

[0017] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the sodium-ion battery electrolyte described above.

[0018] Specifically, the positive electrode and the negative electrode are immersed in sodium-ion battery electrolyte and separated by a separator.

[0019] Preferably, the positive electrode includes a positive electrode active material; the positive electrode active material is a layered oxide with the structural formula NaM. x O y M is at least one of iron, copper, nickel, cobalt, and manganese, 0.8≤x≤1.5, 1.5≤y≤2.5, and the values ​​of x and y satisfy the charge balance of the chemical formula.

[0020] More preferably, the positive electrode active material is NaFe. 0.5 Mn 0.5 O2, NaNi 0.3 Fe 0.4 Mn 0.3 O2, NaNi 0.33 Fe 0.34 Mn 0.33 O2, NaNi 0.25 Fe 0.5 Mn 0.25 O2, NaNi 0.2 Cu 0.1 Fe 0.4 Mn 0.3 O2, NaNi 0.25 Fe 0.4 Co 0.1 Mn 0.25 O2, NaNi 0.5 Fe 0.4 Mn 0.4 O 2.4 NaNi 0.4 Fe 0.2 Mn 0.3 O 1.8 At least one of them.

[0021] Preferably, the positive electrode further includes a conductive agent, which is at least one of carbon black, carbon nanotubes, and graphene.

[0022] Preferably, the negative electrode comprises at least one of hard carbon, soft carbon, expanded graphite, titanium-based materials, alloy materials, and organic materials.

[0023] Preferably, the negative electrode further includes a negative electrode current collector.

[0024] Preferably, the negative electrode current collector is aluminum foil or copper foil.

[0025] Preferably, the aluminum foil or copper foil is at least one of the following: aluminum foil or copper foil without other element doping, aluminum foil or copper foil with other element doping, and aluminum foil or copper foil with a coating layer on its surface.

[0026] This invention utilizes a compound with a sulfide structure and sodium difluorooxalate borate as additives. The sulfide structure in the sulfide-containing compound can undergo oxidation before other components in the electrolyte, forming a sulfur-rich positive electrode electrolyte interface (CEI) layer in situ. This effectively deactivates superoxide radicals generated at the positive electrode, suppressing interfacial side reactions and thus improving interfacial stability. Simultaneously, this CEI layer also inhibits the hydrolysis of hexafluorophosphate to HF, thereby suppressing the dissolution of transition metals and improving the stability of the positive electrode structure. Furthermore, the double bond structure in the sulfide-containing compound has strong reducing properties, enabling the formation of an SEI layer on the negative electrode surface. The fluorine component in sodium difluorooxalate borate further strengthens the CEI film formed at the positive electrode and also forms an SEI film at the negative electrode, reducing battery impedance and improving cycle performance. Therefore, this invention, through the synergistic effect of the sulfide-containing compound and sodium difluorooxalate borate, effectively solves interfacial problems and improves the cycle stability of sodium-ion batteries under high voltage.

[0027] Beneficial effects:

[0028] The additive of this invention can effectively solve interface problems and improve the cycle stability of sodium-ion batteries under high voltage through the synergistic effect of compounds with sulfide structures and sodium difluorooxalate borate. Attached Figure Description

[0029] Figure 1 The molecular structure of diallyl sulfide in the additive of this invention is shown. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0031] Example 1:

[0032] The preparation of a sodium-ion battery electrolyte and a sodium-ion battery includes the following steps:

[0033] (1) Preparation of sodium-ion battery electrolyte: The operation was carried out in an ultra-clean glove box under an argon atmosphere with moisture <0.01ppm and oxygen <0.01ppm. The sodium-ion battery electrolyte includes an organic solvent, sodium salt, and additives; after mixing the organic solvent, the sodium salt and additive B were added, and after complete dissolution, additive A was added and mixed evenly for later use.

[0034] (2) Positive electrode (also known as positive electrode sheet) fabrication: Positive electrode active material sodium nickel manganese oxide (NaNi)0.3 Fe 0.4 Mn 0.3 The mass ratio of O2, polyvinylidene fluoride (PVDF) binder, and carbon black conductive agent is fixed at 96:2:2. The positive electrode active material sodium nickel iron manganese oxide (NiFeMnO), binder, and conductive agent are mixed according to their respective proportions. N-methylpyrrolidone (NMP) is added, and the mixture is stirred to prepare a positive electrode slurry. The mass fraction of NMP in the positive electrode slurry is 25 wt%. After double-sided coating, drying, and rolling, a positive electrode sheet is obtained and wound up for later use.

[0035] (3) Negative electrode (also known as negative electrode sheet) preparation: Hard carbon, thickener sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber latex (SBR), and conductive agent carbon black are dissolved in deionized water at a mass ratio of 94:1:2:3 and mixed evenly to prepare a negative electrode slurry. The mass fraction of deionized water in the negative electrode slurry is 43 wt%. After double-sided coating, drying, and rolling, the negative electrode sheet is obtained and wound up for later use.

[0036] (4) Sodium-ion battery assembly: The positive electrode, negative electrode and separator are assembled to obtain the battery cell. The battery cell is placed in the aluminum-plastic film shell, the electrolyte is injected and then sealed. After standing, formation, venting, resealing and capacity testing, a 6000mAh sodium-ion soft pack battery is obtained.

[0037] In this embodiment, the sodium-ion battery electrolyte includes the following raw materials: the total mass of organic solvent is 85g, including diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC) in a mass ratio of 2:5:3; the sodium salt is NaPF6, with a mass of 11.0g; the additives include additive A and additive B, where additive A is diallyl sulfide (0.5g) + sodium difluorooxalate borate (0.6g), and additive B is SN (2.0g).

[0038] Examples and Comparative Examples

[0039] Table 1 shows the electrolyte composition of the examples and comparative examples. The table records the electrolyte composition of Examples 1 to 6 and Comparative Examples 1 to 4. In Examples 2 to 6 and Comparative Examples 1 to 4, except for the electrolyte composition, the electrolyte preparation and battery manufacturing steps are the same as in Example 1.

[0040] Table 1. Electrolyte composition of the examples and comparative examples.

[0041]

[0042] In the table above, "Organic solvent and mass / g" records the mass ratio between different components in the organic solvent, and the total mass of the organic solvent is recorded in parentheses; "Sodium salt and mass / g" records the type of sodium salt used, and the mass of the sodium salt is recorded in parentheses; "Additives / g" records the composition of the additives, and the mass of the additives used is recorded in parentheses.

[0043] The electrolytes obtained in the examples and comparative examples were applied to sodium-ion batteries for performance testing.

[0044] The performance testing methods for sodium-ion batteries are as follows:

[0045] Initial Coulombic Efficiency Test: At room temperature (25°C), the sodium-ion battery was charged at a constant current of 0.05C to 2V and held for 30 minutes, yielding a charge of C1. It was then charged at a constant current of 0.1C to 3.8V and held for 150 minutes, yielding a charge of C2. After a second sealing process (evacuation), the battery was charged at a constant current of 0.5C to 4.4V and held for 5 minutes, yielding a charge of C3. Finally, it was discharged at a constant current of 0.5C to 2.0V, yielding a discharge charge of C4. This charge-discharge cycle was repeated 5 times. After each cycle, the battery was allowed to rest for 30 minutes. Initial Coulombic Efficiency

[0046] =C4 / (C1+C2+C3)×100%

[0047] Room temperature cycling test: The sodium-ion battery was charged at 25°C with a constant current of 1C to 4.4V, then charged with a constant voltage until the current ≤0.05C, allowed to stand for 10 minutes, and then discharged with a constant current of 1C to 2V. This constitutes one charge-discharge cycle. Then, 200 cycles were performed using the same method. The capacity retention rate (%) of the sodium-ion battery after n cycles = (discharge capacity in the nth charge-discharge cycle / discharge capacity in the first charge-discharge cycle) × 100%, where n is the number of charge-discharge cycles. The test results of the initial coulombic efficiency, capacity retention rate after 200 charge-discharge cycles, and discharge voltage plateau of the sodium-ion batteries prepared with the electrolytes of each embodiment and comparative example are shown in Table 2.

[0048] Negative electrode transition metal ion content test: The sodium-ion battery after 200 cycles was disassembled to obtain the negative electrode sheet. The surface of the electrode sheet was rinsed with DEC 3-5 times. The resulting material was then dried in a vacuum oven at 60℃ for 2 hours. After grinding, digestion, and sample preparation, ICP testing was performed according to the corresponding ion detection method. Five parallel samples were tested for the negative electrode sheet of each battery, and the average value was taken.

[0049] Table 2 shows the electrical performance and ICP test results of sodium-ion batteries prepared with sodium-ion battery electrolytes from each embodiment and comparative example.

[0050]

[0051]

[0052] As shown in Table 2, the sodium-ion battery using the sodium-ion battery electrolyte disclosed in the embodiments of this invention exhibits significantly improved performance compared to the comparative product. Compared to sodium-ion battery electrolytes that do not contain additives or only contain diallyl sulfide or sodium difluorooxalate borate, the simultaneous addition of diallyl sulfide and sodium difluorooxalate borate for synergistic compounding in the sodium-ion battery electrolyte can generate a stable CEI and SEI interface layer, effectively suppressing the dissolution of transition metal ions and improving the cycle stability of the sodium-ion battery under high voltage.

[0053] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that: The sodium-ion battery electrolyte includes an organic solvent, a sodium salt, and an additive; the additive includes additive A, which includes sodium difluorooxalate borate and a compound containing a sulfur ether structure; the compound containing a sulfur ether structure is diallyl sulfide. The compound containing a sulfide structure accounts for 0.5 wt% to 3 wt% of the sodium-ion battery electrolyte; the sodium difluorooxalate borate additive accounts for 0.1 wt% to 2 wt% of the sodium-ion battery electrolyte.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that: The additives also include additive B; The additive B is at least one of fluorinated ethylene carbonate, difluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propanesulfonate lactone, methanedisulfonate, adiponitrile, and succinate. The additive B accounts for 0.6 wt% to 5 wt% of the sodium-ion battery electrolyte by mass.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that: The organic solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, difluoroacetate, difluoroethyl acetate, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, acetonitrile, malononitrile, glutaronitrile, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, sulfolane, and dimethyl sulfoxide; the organic solvent accounts for 80wt% to 90wt% of the mass percentage of the sodium-ion battery electrolyte.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that: The sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium perchlorate, sodium tetrafluoroborate, and sodium nitrate; the sodium salt accounts for 5 wt% to 15 wt% of the mass percentage of the sodium-ion battery electrolyte.

5. A sodium-ion battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that: It also includes the sodium-ion battery electrolyte according to any one of claims 1-4.

6. A sodium-ion battery according to claim 5, characterized in that: The positive electrode includes a positive electrode active material; the positive electrode active material is a layered oxide with the structural formula NaM. x O y M is at least one of iron, copper, nickel, cobalt, and manganese, 0.8≤x≤1.5, 1.5≤y≤2.5, and the values ​​of x and y satisfy the charge balance of the chemical formula.

7. A sodium-ion battery according to claim 6, characterized in that: The positive electrode also includes a conductive agent, which is at least one of carbon black, carbon nanotubes, and graphene.

8. A sodium-ion battery according to claim 5, characterized in that: The negative electrode includes at least one of hard carbon, soft carbon, expanded graphite, alloy materials, and organic materials.

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