Sodium-ion battery high-voltage electrolyte, preparation method and sodium-ion battery

Abstract

The invention discloses an electrolyte, a preparation method and a sodium ion battery using the electrolyte. The electrolyte comprises an organic solvent, a functional cosolvent, a functional additive and conductive sodium salt, the organic solvent is composed of 1, 2-diethoxyethane and 1, 2-di-tert-butoxy ethane; the functional cosolvent is adiponitrile; the functional additive is p-nitroanisole; the conductive sodium salt is composed of sodium bis (fluorosulfonyl) imide and sodium hexafluorophosphate or sodium difluoro (oxalato) borate. The preparation method comprises the following steps: pretreating raw materials (dehydration and vacuum drying), proportionally mixing the organic solvent and the cosolvent in an inert atmosphere, adding the conductive sodium salt, stirring and dissolving, adding the functional additive, uniformly stirring, curing and filtering to obtain the electrolyte. Through unique collaborative design of non-fluorinated components, stable operation of the electrolyte under ultrahigh voltage and efficient regulation and control of an interface are realized.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a high-voltage electrolyte for sodium-ion batteries, its preparation method, and a sodium-ion battery. Background Technology

[0002] With the rapid development of renewable energy storage and electric vehicles, the demand for high-energy-density, low-cost, and long-life batteries is becoming increasingly urgent. Sodium-ion batteries (SIBs) are considered an important candidate for next-generation energy storage technology due to the abundance and low cost of sodium resources.

[0003] However, the energy density of existing sodium-ion batteries is generally lower than that of lithium-ion batteries, and one of the key limiting factors is the limited operating voltage of the positive electrode. Therefore, the industry is actively developing high-voltage positive electrode materials (such as NaNi). 0.6 Mn 0.2 Co 0.2 O2 / NMC622, phosphate Na3V2(PO4)3 / NVP). However, the application of these materials requires electrolytes with extremely high oxidation stability (typically >4.5 V vs. Na). + / Na), while also needing to achieve highly reversible sodium deposition / stripping on the negative electrode side (especially in anode-free sodium metal battery configurations) (coulombic efficiency >96%).

[0004] Currently, research on electrolytes for high-voltage sodium-ion batteries mainly focuses on the following categories, and each of these technical approaches has significant drawbacks:

[0005] Fluorinated additive route: Represented by the early introduction of fluoroethylene carbonate (FEC), which improves cycle stability by enhancing the negative electrode interface. However, this route still heavily relies on carbonate-based solvents, whose intrinsic antioxidant capacity is limited (typically <4.3V), making it difficult to meet higher voltage requirements. In addition, the synthesis of fluorinated compounds is complex and costly, and there are potential environmental pollution risks from perfluorinated and polyfluoroalkyl substances.

[0006] High-concentration / locally high-concentration electrolytes (HCE / LHCE): High-pressure compatibility is achieved by using extremely high concentrations of sodium salts (such as 5M sodium bis(fluorosulfonyl)imide (NaFSI)) to modulate the solvation structure. Although performance has improved, the system requires a huge amount of salt, resulting in extremely high cost. The high viscosity severely degrades wettability and ion mobility, and it often requires the use of fluorinated diluents, leading to poor environmental and economic benefits.

[0007] The novel salt-in-presalt (SIPS) paradigm utilizes liquid fluorinated precursors (such as PreTFSI) to dissolve sodium salts, creating an all-anionic coordination environment and achieving an ultra-wide electrochemical window. However, its drawbacks include the limitation of ionic conductivity to the extremely low solubility of the salt, resulting in poor rate performance, and the core solvent PreTFSI remains an expensive fluorinated organic compound, which is difficult to synthesize and poses environmental risks.

[0008] Non-fluorinated ether electrolytes: This route uses a mixed solvent of 1,2-diethoxyethane and 1,2-di-tert-butoxyethane, utilizing the steric hindrance effect of the latter to enhance antioxidant properties. Although the goal of non-fluorination is achieved, its interface control for sodium deposition in high-voltage anode-free systems remains insufficient. Furthermore, the DBE solvent synthesis steps are cumbersome, costly, and its low boiling point and volatility limit its long-term cycling stability and large-scale application prospects.

[0009] In summary, existing technological approaches suffer from fundamental flaws, such as difficulty in achieving a balance between high-pressure stability, interfacial reversibility, and environmental friendliness and cost.

[0010] Therefore, developing a novel electrolyte system that can simultaneously meet the requirements of ultra-high voltage stability, ultra-high coulombic efficiency, long cycle life, complete non-fluorination, and controllable cost has become the key to breaking through the practical application bottleneck of high-voltage sodium-ion batteries, especially anode-free sodium metal batteries. Summary of the Invention

[0011] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a high-voltage electrolyte for sodium-ion batteries, a preparation method thereof, and a sodium-ion battery, which realizes stable operation of the electrolyte under ultra-high voltage and efficient control of the interface.

[0012] To achieve the above objectives, a first aspect of the present invention provides a high-voltage electrolyte for sodium-ion batteries, the high-voltage electrolyte comprising an organic solvent, a functional co-solvent, a functional additive, and a conductive sodium salt;

[0013] The organic solvent is composed of 1,2-diethoxyethane and 1,2-ditert-butoxyethane;

[0014] The functional co-solvent is adiponitrile;

[0015] The functional additive is p-nitroanisole;

[0016] The conductive sodium salt is composed of sodium difluorosulfonamide and sodium hexafluorophosphate or sodium difluorooxalate borate.

[0017] In some embodiments of the first aspect of this application, the concentration of sodium difluorosulfonamide is 0.6–1.2 mol / L, and the concentration of sodium hexafluorophosphate or sodium difluorooxalate borate is 0–0.6 mol / L;

[0018] The total molar concentration of sodium difluorosulfonamide and sodium hexafluorophosphate or sodium difluorooxalate borate is not greater than 1.2 mol / L.

[0019] In some embodiments of the first aspect of this application, the 1,2-diethoxyethane and 1,2-ditert-butoxyethane each account for 30 to 50 vol of the total volume of the organic solvent.

[0020] In some embodiments of the first aspect of this application, the volume ratio of 1,2-diethoxyethane to 1,2-ditert-butoxyethane is 1:0.6 to 1.7.

[0021] In some embodiments of the first aspect of this application, the mass fraction of the p-nitrobenzene is 0.5 to 3.0 wt%.

[0022] In some embodiments of the first aspect of this application, the adiponitrile accounts for 10 to 20 vol% of the total volume of the electrolyte.

[0023] To achieve the above objectives, a second aspect of the present invention provides a method for preparing a high-voltage electrolyte for a sodium-ion battery, the method comprising:

[0024] Step S1: Dehydrate and dry 1,2-diethoxyethane, 1,2-di-tert-butoxyethane and adiponitrile, and vacuum dry sodium difluorosulfonamide, sodium hexafluorophosphate or sodium difluorooxalate borate and p-nitrobenzene.

[0025] Step S2: Under an inert atmosphere, mix 1,2-diethoxyethane, 1,2-ditert-butoxyethane and adiponitrile in volume proportion;

[0026] Step S3: First add sodium difluorosulfonamide to the mixture and stir until it becomes transparent, then add sodium hexafluorophosphate or sodium difluorooxalate borate.

[0027] Step S4: Add dried p-nitroanisole to the mixture according to the mass ratio, and stir until homogeneous;

[0028] Step S5: The mixture is aged, then filtered to remove impurities and tested for quality to obtain the high-voltage electrolyte for sodium-ion batteries.

[0029] In some embodiments of the second aspect of this application, in step S2, the volume ratio of 1,2-diethoxyethane to 1,2-di-tert-butoxyethane is 1:0.6 to 1.7, and the amount of adiponitrile added accounts for 10 to 20 vol% of the total volume of the electrolyte; the dehydration and drying process uses molecular sieves to dehydrate to a moisture content of no more than 20 ppm, and the vacuum degree of the vacuum drying process is no higher than 10. -3 Pa;

[0030] In step S3, the concentration of sodium difluorosulfonamide is controlled to be 0.6–1.2 mol / L, the concentration of sodium hexafluorophosphate is controlled to be 0–0.6 mol / L, and the total salt concentration is not greater than 1.2 mol / L;

[0031] In step S4, the amount of p-nitroanisole added is controlled to be 0.5 to 3.0 wt% of the total mass of the electrolyte.

[0032] In some embodiments of the second aspect of this application, in step S1, the dehydration and drying process uses molecular sieves to dehydrate to a moisture content of no more than 20 ppm, and the vacuum drying process has a vacuum degree of no more than 10. -3 Pa;

[0033] In step S5, the aging process includes continuous stirring at 25°C for no less than 2 hours, followed by standing for no less than 12 hours; the filtration and impurity removal is carried out using a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm.

[0034] In step S5, the quality testing indicators include one or more of the following: moisture content, metal ion content, conductivity, oxidation stability, and pH value; after passing the quality test, nitrogen gas is introduced into the electrolyte and the electrolyte is sealed.

[0035] To achieve the above objectives, a third aspect of the present invention provides a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is the above-mentioned high-voltage electrolyte for sodium-ion batteries.

[0036] The advantages of this invention are as follows: First, through the steric hindrance effect of DBE, the anodic oxidation stability of the electrolyte is improved to >4.8 V, which can match the high-voltage positive electrode and effectively inhibit oxidative decomposition, resulting in excellent high-voltage stability. Second, multiple components synergistically construct a composite SEI layer rich in Na2O, polyimide network, and NaF in situ at the negative electrode, which has both high mechanical strength and fast ion transport capability, effectively inhibits dendrite growth, and has excellent interface performance. Third, the formed highly stable interface enables the anode-free sodium metal battery to retain >75% capacity after 500 cycles at 1C rate, with some embodiments reaching over 90%, resulting in a long battery cycle life. Fourth, the use of conventional chemicals is completely avoided, reducing environmental risks and raw material costs, and has good prospects for large-scale production. Fifth, the preparation process is carried out under an inert atmosphere, with simple steps and mild conditions, and strict pretreatment and filtration ensure the high purity and consistency of the electrolyte. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 The bar chart shows the first-efficiency and capacity retention rates of different embodiments of the sodium-ion battery high-voltage electrolyte of the present invention.

[0039] Figure 2 This is a linear voltammetry (LSV) test curve of the high-voltage electrolyte for the sodium-ion battery of the present invention.

[0040] Figure 3 This is a comparison diagram of the surface elastic modulus distribution of the SEI film formed by the high-voltage electrolyte of the sodium-ion battery of the present invention (Example 5) and the existing DEBE electrolyte;

[0041] Figure 4 This is a schematic flowchart of the sodium-ion battery high-voltage electrolyte preparation method of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The abbreviations and key terms involved in this invention are defined as follows:

[0044] SIBs: Sodium-ion batteries;

[0045] NVP: Sodium vanadium phosphate, chemical formula Na3V2(PO4)3;

[0046] NMC622: Sodium lithium nickel manganese cobalt oxide, chemical formula NaNi 0.6 Mn 0.2 Co 0.2 O2;

[0047] FEC: Fluorinated vinyl carbonate;

[0048] PreTFSI: N,N-dimethyltrifluoromethanesulfonamide;

[0049] SIPS: an abbreviation for Salt-in-Presalt;

[0050] DME: 1,2-Dimethoxyethane (ethylene glycol dimethyl ether);

[0051] DEE: 1,2-diethoxyethane;

[0052] DBE: 1,2-Di-tert-butoxyethane;

[0053] DEBE: Non-fluorinated ether electrolyte;

[0054] BTFE: 2,2,2-trifluoroethyl ether;

[0055] NaFSI: Sodium bis(fluorosulfonyl)imide (sodium bis(fluorosulfonyl)imide);

[0056] PFAS: Perfluorinated and polyfluoroalkyl substances;

[0057] NaPF6: Sodium hexafluorophosphate;

[0058] NaBF2: Sodium difluorooxalate borate;

[0059] CEI: Positive Electrolyte Interface;

[0060] SEI: Solid electrolyte interface;

[0061] LUMO: Lowest unoccupied molecular orbital;

[0062] PVDF: Polyvinylidene fluoride;

[0063] M: moles per liter (mol / L), a unit of concentration;

[0064] ADN: Adiponitrile;

[0065] p-Nitroanisole: p-Nitroanisole;

[0066] NaFSI: Sodium difluorosulfonamide;

[0067] PTFE: Polytetrafluoroethylene;

[0068] Na2O: Sodium oxide;

[0069] Na2N: Sodium nitride;

[0070] ICE: Initial Coulomb efficiency (first efficiency).

[0071] In a first aspect, the present invention provides a high-voltage electrolyte for sodium-ion batteries, the electrolyte comprising an organic solvent, a functional co-solvent, a functional additive, and a conductive sodium salt.

[0072] The organic solvent consists of 1,2-diethoxyethane (DEE) and 1,2-di-tert-butoxyethane (DBE). DEE provides a good ion transport channel and moderate reducing activity, while DBE effectively inhibits the oxidative decomposition of solvent molecules under high pressure through the steric hindrance effect generated by its tert-butyl group. The volume of DEE accounts for 30% to 50% (30–50 vol%) of the total volume of the organic solvent, and the volume of DBE also accounts for 30% to 50% (30–50 vol%) of the total volume of the organic solvent. The volume ratio of DEE to DBE is 1:0.6 to 1:1.7, preferably 1:1.

[0073] The functional cosolvent is adiponitrile (ADN), which accounts for 10% to 20% of the total electrolyte volume. The strong polarity of ADN helps to promote the dissociation of sodium salt and improve the conductivity of the electrolyte. At the same time, ADN can be electrochemically reduced and polymerized on the negative electrode surface to form a three-dimensional polyimide / sodium cyanide network structure, thereby significantly enhancing the mechanical strength and stability of the solid electrolyte interface (SEI).

[0074] The functional additive is p-nitroanisole, which accounts for 0.5% to 3.0% (0.5–3.0 wt%) of the total electrolyte mass. p-nitroanisole has an extremely low LUMO energy level and can be preferentially reduced before the solvent and salt (reduction potential approximately 1.82 V vs. Na). + / Na), generating a continuous inorganic phase rich in sodium oxide (Na2O) in situ, serving as the framework of the SEI, optimizing Na + Improve the transmission path and reduce electrolyte consumption in subsequent cycles.

[0075] The conductive sodium salt is composed of sodium difluorosulfonamide (NaFSI) and sodium hexafluorophosphate (NaPF6). NaFSI is the main salt, with a concentration of 0.6 M to 1.2 M; NaPF6 is the auxiliary salt, with a concentration of 0 to 0.6 M, and the sum of the molar concentrations of the main salt NaFSI and the auxiliary salt NaPF6 does not exceed 1.2 M. This mixed salt system works synergistically to allow FSI to pass through. - It decomposes to form a flexible fluorinated interface layer, which can also pass through PF6. - Provide more Na + It also increases the content of dense NaF in the interface.

[0076] In this invention, sodium hexafluorophosphate (NaPF6) in the conductive sodium salt can also be replaced by sodium difluorooxalate borate (NaBF2), and the concentration of NaBF2 is set to be consistent with that of NaPF6.

[0077] The composition and function of the electrolyte of this invention are detailed in Table 1 below. This table systematically summarizes the core components, proportion ranges, and corresponding functions of the high-voltage electrolyte for sodium-ion batteries of this invention, clearly presenting the position and role of each component in the electrolyte system, providing key basis for electrolyte component design, performance regulation, and large-scale preparation.

[0078]

[0079] Table 1

[0080] The electrolyte of this invention can achieve precise performance control to adapt to different application scenarios based on the differences in the component ratios of four parts: organic solvent ratio, functional co-solvent content, functional additive dosage, conductive sodium salt ratio, and total concentration.

[0081] The following examples are designed based on different volume ratios of organic solvent (DEE / DBE), content of functional co-solvent (ADN), amount of functional additive (p-nitroanisole), ratio of conductive sodium salt (NaFSI / NaPF6), and total concentration in the general-purpose electrolyte:

[0082] Example 1:

[0083] Prepare the electrolyte according to the following proportions:

[0084] 1,2-Diethoxyethane (DEE): 40.0 vol%

[0085] 1,2-Di-tert-butoxyethane (DBE): 40.0 vol%

[0086] Adiponitrile (ADN): 20.0 vol%

[0087] p-Nitroanisole: 2.0 wt%

[0088] Sodium difluorosulfonamide (NaFSI): 1.0 M;

[0089] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0090] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0091] After the above components were mixed evenly, they were assembled into Al||NMC622 coin cells, and their electrochemical performance was tested. The initial coulombic efficiency (ICE) was 97.1% at the first charge-discharge cycle at 0.2C; after 500 cycles at 1C, the capacity retention reached 92.5%.

[0092] Example 2:

[0093] Prepare the electrolyte according to the following proportions:

[0094] 1,2-Diethoxyethane (DEE): 35.0 vol%

[0095] 1,2-Di-tert-butoxyethane (DBE): 50.0 vol%

[0096] Adiponitrile (ADN): 15.0 vol%

[0097] p-Nitroanisole: 1.5 wt%

[0098] Sodium difluorosulfonamide (NaFSI): 0.8 M;

[0099] Sodium hexafluorophosphate (NaPF6): 0.4 M.

[0100] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0101] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 96.6% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 89.0% after 500 cycles at 1 C rate.

[0102] Example 3:

[0103] Prepare the electrolyte according to the following proportions:

[0104] 1,2-Diethoxyethane (DEE): 50.0 vol%

[0105] 1,2-Di-tert-butoxyethane (DBE): 30.0 vol%

[0106] Adiponitrile (ADN): 20.0 vol%

[0107] p-Nitroanisole: 3.0 wt%

[0108] Sodium difluorosulfonamide (NaFSI): 1.2 M;

[0109] Sodium hexafluorophosphate (NaPF6): 0.0 M.

[0110] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0111] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 98.9% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 87.0% after 500 cycles at 1 C rate.

[0112] Example 4:

[0113] Prepare the electrolyte according to the following proportions:

[0114] 1,2-Diethoxyethane (DEE): 50.0 vol%

[0115] 1,2-Di-tert-butoxyethane (DBE): 35.0 vol%

[0116] Adiponitrile (ADN): 15.0 vol%

[0117] p-Nitroanisole: 0.5 wt%

[0118] Sodium difluorosulfonamide (NaFSI): 0.6 M;

[0119] Sodium hexafluorophosphate (NaPF6): 0.6 M.

[0120] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0121] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 95.0% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 88.5% after 500 cycles at 1 C rate.

[0122] Example 5:

[0123] Prepare the electrolyte according to the following proportions:

[0124] 1,2-Diethoxyethane (DEE): 45.0 vol%

[0125] 1,2-Di-tert-butoxyethane (DBE): 45.0 vol%

[0126] Adiponitrile (ADN): 10.0 vol%

[0127] p-Nitroanisole: 2.5 wt%

[0128] Sodium difluorosulfonamide (NaFSI): 1.0 M;

[0129] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0130] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0131] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 98.3% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 91.0% after 500 cycles at 1 C rate.

[0132] Example 6:

[0133] Prepare the electrolyte according to the following proportions:

[0134] 1,2-Diethoxyethane (DEE): 40.0 vol%

[0135] 1,2-Di-tert-butoxyethane (DBE): 40.0 vol%

[0136] Adiponitrile (ADN): 20.0 vol%

[0137] p-Nitroanisole: 1.0 wt%

[0138] Sodium difluorosulfonamide (NaFSI): 1.0 M;

[0139] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0140] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0141] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 99.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 88.8% after 500 cycles at 1 C rate.

[0142] Example 7:

[0143] Prepare the electrolyte according to the following proportions:

[0144] 1,2-Diethoxyethane (DEE): 50.0 vol%

[0145] 1,2-Di-tert-butoxyethane (DBE): 30.0 vol%

[0146] Adiponitrile (ADN): 20.0 vol%

[0147] p-Nitroanisole: 0.5 wt%

[0148] Sodium difluorosulfonamide (NaFSI): 0.8 M;

[0149] Sodium hexafluorophosphate (NaPF6): 0.4 M.

[0150] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0151] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 95.6% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 89.2% after 500 cycles at 1 C rate.

[0152] Example 8:

[0153] Prepare the electrolyte according to the following proportions:

[0154] 1,2-Diethoxyethane (DEE): 45.0 vol%

[0155] 1,2-Di-tert-butoxyethane (DBE): 45.0 vol%

[0156] Adiponitrile (ADN): 10.0 vol%

[0157] p-Nitroanisole: 2.0 wt%

[0158] Sodium difluorosulfonamide (NaFSI): 0.6 M;

[0159] Sodium hexafluorophosphate (NaPF6): 0.6 M.

[0160] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0161] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 96.3% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 89.5% after 500 cycles at 1 C rate.

[0162] Example 9:

[0163] Prepare the electrolyte according to the following proportions:

[0164] 1,2-Diethoxyethane (DEE): 30.0 vol%

[0165] 1,2-Di-tert-butoxyethane (DBE): 55.0 vol%

[0166] Adiponitrile (ADN): 15.0 vol%

[0167] p-Nitroanisole: 2.0 wt%

[0168] Sodium difluorosulfonamide (NaFSI): 1.0 M;

[0169] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0170] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0171] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 95.3% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 88.0% after 500 cycles at 1 C rate.

[0172] Example 10:

[0173] Prepare the electrolyte according to the following proportions:

[0174] 1,2-Diethoxyethane (DEE): 60.0 vol%

[0175] 1,2-Di-tert-butoxyethane (DBE): 25.0 vol%

[0176] Adiponitrile (ADN): 15.0 vol%

[0177] p-Nitroanisole: 1.5 wt%

[0178] Sodium difluorosulfonamide (NaFSI): 0.8 M;

[0179] Sodium hexafluorophosphate (NaPF6): 0.4 M.

[0180] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0181] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 96.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 87.5% after 500 cycles at 1 C rate.

[0182] Example 11:

[0183] Prepare the electrolyte according to the following proportions:

[0184] 1,2-Diethoxyethane (DEE): 55.0 vol%

[0185] 1,2-Di-tert-butoxyethane (DBE): 35.0 vol%

[0186] Adiponitrile (ADN): 10.0 vol%

[0187] p-Nitroanisole: 3.0 wt%

[0188] Sodium difluorosulfonamide (NaFSI): 1.2 M;

[0189] Sodium hexafluorophosphate (NaPF6): 0.0 M.

[0190] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0191] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 97.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 86.0% after 500 cycles at 1 C rate.

[0192] Example 12:

[0193] Prepare the electrolyte according to the following proportions:

[0194] 1,2-Diethoxyethane (DEE): 40.0 vol%

[0195] 1,2-Di-tert-butoxyethane (DBE): 50.0 vol%

[0196] Adiponitrile (ADN): 10.0 vol%

[0197] p-Nitroanisole: 2.5 wt%

[0198] Sodium difluorosulfonamide (NaFSI): 1.0 M;

[0199] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0200] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.2 M.

[0201] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 98.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 89.8% after 500 cycles at 1 C rate.

[0202] Example 13:

[0203] Prepare the electrolyte according to the following proportions:

[0204] 1,2-Diethoxyethane (DEE): 45.0 vol%

[0205] 1,2-Di-tert-butoxyethane (DBE): 45.0 vol%

[0206] Adiponitrile (ADN): 10.0 vol%

[0207] p-Nitroanisole: 2.5 wt%

[0208] Sodium difluorosulfonamide (NaFSI): 0.6 M;

[0209] Sodium hexafluorophosphate (NaPF6): 0.0 M.

[0210] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 0.6 M.

[0211] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 94.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 87.0% after 500 cycles at 1 C rate.

[0212] Example 14:

[0213] Prepare the electrolyte according to the following proportions:

[0214] 1,2-Diethoxyethane (DEE): 45.0 vol%

[0215] 1,2-Di-tert-butoxyethane (DBE): 45.0 vol%

[0216] Adiponitrile (ADN): 10.0 vol%

[0217] p-Nitroanisole: 2.5 wt%

[0218] Sodium difluorosulfonamide (NaFSI): 0.8 M;

[0219] Sodium hexafluorophosphate (NaPF6): 0.2 M.

[0220] In this embodiment of the invention, the total salt concentration (including NaFSI and NaPF6) is 1.0 M.

[0221] Tests showed that the battery using this electrolyte had an initial coulombic efficiency (ICE) of 96.8% during its first charge-discharge cycle at 0.2 C rate; and a capacity retention of 89.0% after 500 cycles at 1 C rate.

[0222] The above are 14 embodiments of the electrolyte of the present invention with different formulation ratios. Table 2 below summarizes the electrolyte composition ratios and corresponding key electrochemical performance data of the above 14 specific embodiments.

[0223]

[0224] Table 2

[0225] As can be seen from the embodiments and data shown in Table 2, the sodium-ion battery electrolyte provided by the present invention exhibits excellent electrochemical performance under different component ratios.

[0226] Figure 1 This is a bar chart showing the first-efficiency and capacity retention rates of different embodiments of the sodium-ion battery high-voltage electrolyte of the present invention. Figure 1 As shown, the horizontal axis represents the numbers of the 14 embodiments, and the vertical axis corresponds to the initial coulombic efficiency (ICE) and the capacity retention rate after 500 cycles at 1 C rate, respectively. This visually presents the distribution of the core electrochemical performance of the electrolyte under different component ratios: the initial efficiency of all embodiments is consistently above 94.8%, with Embodiment 6 reaching as high as 99.8%, and Embodiments 3, 5, and 12 also exceeding 98%, indicating that the electrolyte of this invention forms SEI / CEI efficiently and has very few side reactions during the first charge-discharge process; the capacity retention rate is above 86.0%, with Embodiment 5 leading at 91.0%, and Embodiments 1 and 12 having capacity retention rates of 90.5% and 89.8%, respectively, reflecting the stability of the interface structure of the electrolyte during long-term cycling; at the same time, the chart clearly shows the influence of organic solvent ratio, functional cosolvent content, additive dosage, and salt concentration adjustment on performance, verifying the flexibility of electrolyte component design and the effectiveness of performance control, further confirming the feasibility of the "non-fluorinated solvent + functional precursor + synergistic film formation" technical solution.

[0227] Figure 2 This is a linear voltammetry (LSV) test curve of the high-voltage electrolyte for the sodium-ion battery of this invention. Figure 2 As shown, the horizontal axis represents the test potential (unit: V vs. Na). + The vertical axis represents the current intensity (unit: A), and the curves clearly show the electrochemical response characteristics of the electrolyte during the cathode and anodic scans: A significant reduction peak appears at 1.82 V during the cathode scan, corresponding to the preferential reduction reaction of the functional additive on nitrobenzene ether, verifying its design mechanism of "below solvent reduction potential, early film formation," and providing direct electrochemical evidence for the in-situ generation of an inorganic SEI layer rich in Na₂O; the oxidation current during the anodic scan only begins to increase significantly at ≥4.8 V, indicating that the oxidative stability of the electrolyte exceeds 4.8 V vs. Na. + / Na, far exceeding the 4.3 V voltage limit of traditional ether electrolytes, fully demonstrates that the steric hindrance effect of tert-butoxy groups in the organic solvent DBE can effectively suppress the dehydrogenation decomposition of solvent molecules at the high-voltage cathode interface, ensuring the compatibility of the electrolyte with high-voltage cathodes such as NMC622 and NVP, and laying a key foundation for stable cycling of the battery under ≥4.7 V conditions.

[0228] Figure 3 This is a comparison diagram of the surface elastic modulus distribution of the SEI film formed by the high-voltage electrolyte of the sodium-ion battery of the present invention (Example 5) and the existing DEBE electrolyte. Figure 3 As shown, the horizontal axis represents the test location on the SEI film surface (unit: μm), the left vertical axis represents the elastic modulus (unit: GPa), and the right vertical axis represents the stress (unit: GPa). The curves clearly show the differences in mechanical properties between the two types of SEI films: The SEI film formed by the electrolyte in Example 5 of this invention has a peak elastic modulus as high as 24.2 GPa, and it is generally uniformly distributed within the test range of 2.0 to 14.0 μm, with no obvious local attenuation, and an average value of about 5.1 GPa. This indicates that the film structure is dense, the mechanical properties are uniform, and it is strong and tough; while the SEI film formed by the existing DEBE electrolyte (1.0 M NaPF6 dissolved in DEE / DBE 1:1 mixture) has a discrete elastic modulus distribution, with an average value of only 0.7 GPa, which is less than 1 / 7 of that of the system of this invention, and its mechanical strength is significantly weak.

[0229] This difference confirms the SEI synergistic enhancement mechanism of the present invention: the polyimide mechanical framework generated by ADN reduction, the Na2O continuous phase guided by p-nitroanisole, and the NaF component provided by the NaFSI / NaPF6 mixed salt work synergistically to construct an inorganic-dominated, organic-inorganic composite high-performance SEI layer, which has an elastic modulus ≥5 GPa, effectively resisting volume changes and sodium dendrite puncture during sodium deposition, and providing key interfacial mechanical support for more than 500 long cycles at 1 C rate of the battery.

[0230] It should be noted that, regarding functional additives, the p-nitroanisole in the core component of this invention can be replaced by other nitro aromatic hydrocarbon compounds, such as m-nitrotoluene or o-nitrobenzaldehyde. These substitutes all contain nitro functional groups with low LUMO energy levels, which can preferentially undergo electrochemical reduction at a similar reduction potential to p-nitroanisole, thereby guiding the formation of an inorganic interface layer rich in Na2O, achieving the goal of optimizing the composition and function of the SEI.

[0231] Secondly, the functional cosolvent adiponitrile (ADN) of this invention can also be replaced with other dinitrile compounds, such as glutaronitrile or sebaconitrile. They also exert a strong polar effect through the cyano group in their molecules, promoting the dissociation of the salt and participating in the construction of a nitride-based polymer network, thereby enhancing the mechanical strength of the SEI.

[0232] Finally, the organic solvent 1,2-di-tert-butoxyethane (DBE), which provides the key steric hindrance effect, can be replaced by other sterically hindered ether solvents, such as diisopropoxyethane. These solvents can also enhance antioxidant properties by protecting the ether oxygen bond through the steric shielding of the alkyl chain.

[0233] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte. Figure 4 A schematic flowchart of the electrolyte preparation method is shown, such as... Figure 4 As shown, the preparation method specifically includes the following steps:

[0234] S1: Raw material pretreatment.

[0235] In this embodiment of the invention, the raw material pretreatment specifically includes the following aspects:

[0236] 1,2-diethoxyethane (DEE), 1,2-di-tert-butoxyethane (DBE), and adiponitrile (ADN) were dehydrated in a 4 Å molecular sieve (dehydration time not less than 48 h) and their moisture content was controlled to be no more than 20 ppm.

[0237] Sodium difluorosulfonamide (NaFSI), sodium hexafluorophosphate (NaPF6), or sodium difluorooxalate borate (NaBF2) were subjected to a vacuum of ≤10 at 120°C. -3 Vacuum drying is carried out under Pa conditions (preferably for 24 hours).

[0238] p-Nitroanisole was vacuum dried at 60°C (preferably for 12 hours) to ensure the purity and dryness of the raw material.

[0239] S2: Solvent mixing.

[0240] In an argon glove box (O2 / H2O ≤ 0.1 ppm), weigh and mix 30~50 vol% DEE, 30~50 vol% DBE and 10~20 vol% ADN by volume ratio.

[0241] The volume ratio of DEE to DBE is 1:0.6~1.7 (preferably 1:1), and the total volume of DEE and DBE is 60~100 vol%, ensuring that the total proportion of the solvent system is 100%.

[0242] S3: The main salt dissolves.

[0243] Transfer the mixed solvent to the reaction vessel and start the magnetic stirrer at 300 rpm. First, add NaFSI in batches until the concentration is 0.6~1.2 M. Stir until completely transparent, then add NaPF6 (or NaBF2) until the concentration is 0~0.6 M, and control the total salt concentration to ≤1.2 M.

[0244] During stirring, the stirring temperature needs to be maintained at 25±2℃ to avoid local overheating that could lead to salt decomposition.

[0245] S4: Add additives.

[0246] The dried p-nitroanisole was slowly added to the electrolyte at a ratio of 0.5~3.0 wt%, and the stirring speed was reduced to 150 rpm to avoid introducing air bubbles that would affect the uniformity of the electrolyte.

[0247] S5: Stir and cook.

[0248] In a sealed reactor, stir continuously at 25°C for no less than 2 hours, followed by a standing and ripening time of no less than 12 hours to allow the additives to fully pre-react and ensure film formation effect.

[0249] S6: Filtration and impurity removal, and quality inspection.

[0250] Under argon protection, the matured electrolyte is filtered under pressure using a 0.22μm polytetrafluoroethylene (PTFE) filter membrane to remove impurity particles, and the filtrate is transferred to a drying storage tank.

[0251] The electrolyte needs to undergo quality testing after filtration to remove impurities. The testing includes the following aspects:

[0252] The electrolyte moisture content was ≤15 ppm as determined by the Karl Fischer method.

[0253] The content of metal ions such as Fe and Cu was ≤1 ppm as determined by ICP-MS.

[0254] The conductivity at 25℃ was ≥8 mS / cm, and the oxidation stability was >4.8 V vs. Na. + / Na, pH value is 6.5~7.5.

[0255] S7: Nitrogen-filled encapsulation.

[0256] High-purity nitrogen (nitrogen purity ≥ 99.999%) is introduced into the qualified electrolyte, which is then sealed in an aluminum-plastic bag and stored at -20℃ in the dark to prevent the electrolyte from decomposing or absorbing moisture.

[0257] Thirdly, the present invention provides a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is the above-mentioned high-voltage electrolyte for sodium-ion batteries.

[0258] The advantages of this invention are as follows: First, through the steric hindrance effect of DBE, the anodic oxidation stability of the electrolyte is improved to >4.8 V, which can match the high-voltage positive electrode and effectively inhibit oxidative decomposition, resulting in excellent high-voltage stability. Second, multiple components synergistically construct a composite SEI layer rich in Na2O, polyimide network, and NaF in situ at the negative electrode, which has both high mechanical strength and fast ion transport capability, effectively inhibits dendrite growth, and has excellent interface performance. Third, the formed highly stable interface enables the anode-free sodium metal battery to retain >75% capacity after 500 cycles at 1C rate, with some embodiments reaching over 90%, resulting in a long battery cycle life. Fourth, the use of conventional chemicals is completely avoided, reducing environmental risks and raw material costs, and has good prospects for large-scale production. Fifth, the preparation process is carried out under an inert atmosphere, with simple steps and mild conditions, and strict pretreatment and filtration ensure the high purity and consistency of the electrolyte.

[0259] In summary, the sodium-ion battery high-voltage electrolyte, its preparation method, and the sodium-ion battery provided by this invention achieve stable long-cycle operation at high voltage through a unique non-fluorinated synergistic film formation and steric hindrance stabilization mechanism. Simultaneously, they offer the advantages of environmental friendliness and cost control, demonstrating broad prospects for industrial application. This will provide a solid technical foundation for promoting the commercialization of next-generation high-energy-density, low-cost sodium metal batteries.

[0260] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-voltage electrolyte for sodium-ion batteries, characterized in that, The high-voltage electrolyte includes an organic solvent, a functional co-solvent, a functional additive, and a conductive sodium salt; The organic solvent is composed of 1,2-diethoxyethane and 1,2-ditert-butoxyethane; The functional co-solvent is adiponitrile; The functional additive is p-nitroanisole; The conductive sodium salt is composed of sodium difluorosulfonamide and sodium hexafluorophosphate or sodium difluorooxalate borate.

2. The sodium-ion battery high-voltage electrolyte according to claim 1, characterized in that, The concentration of sodium difluorosulfonamide is 0.6–1.2 mol / L, and the concentration of sodium hexafluorophosphate or sodium difluorooxalate borate is 0–0.6 mol / L. The total molar concentration of sodium difluorosulfonamide and sodium hexafluorophosphate or sodium difluorooxalate borate is not greater than 1.2 mol / L.

3. The sodium-ion battery high-voltage electrolyte according to claim 1, characterized in that, The 1,2-diethoxyethane and 1,2-ditert-butoxyethane each account for 30-50 vol of the total volume of the organic solvent.

4. The sodium-ion battery high-voltage electrolyte according to claim 3, characterized in that, The volume ratio of 1,2-diethoxyethane to 1,2-ditert-butoxyethane is 1:0.6 to 1.

7.

5. The sodium-ion battery high-voltage electrolyte according to claim 1, characterized in that, The mass fraction of the p-nitroanisole is 0.5–3.0 wt%.

6. The sodium-ion battery high-voltage electrolyte according to claim 1, characterized in that, The adiponitrile accounts for 10-20 vol% of the total volume of the electrolyte.

7. A method for preparing a high-voltage electrolyte for a sodium-ion battery as described in any one of claims 1 to 6, characterized in that, The preparation method includes: Step S1: Dehydrate and dry 1,2-diethoxyethane, 1,2-di-tert-butoxyethane and adiponitrile, and vacuum dry sodium difluorosulfonamide, sodium hexafluorophosphate or sodium difluorooxalate borate and p-nitrobenzene. Step S2: Under an inert atmosphere, mix 1,2-diethoxyethane, 1,2-ditert-butoxyethane and adiponitrile in volume proportions. Step S3: First add sodium difluorosulfonamide to the mixture and stir until it becomes transparent, then add sodium hexafluorophosphate or sodium difluorooxalate borate. Step S4: Add dried p-nitroanisole to the mixture according to the mass ratio, and stir until homogeneous; Step S5: The mixture is aged, then filtered to remove impurities and tested for quality to obtain the high-voltage electrolyte for sodium-ion batteries.

8. The method for preparing the high-voltage electrolyte for sodium-ion batteries according to claim 7, characterized in that: In step S2, the volume ratio of 1,2-diethoxyethane to 1,2-di-tert-butoxyethane is 1:0.6–1.7, and the amount of adiponitrile added accounts for 10–20 vol% of the total electrolyte volume; the dehydration and drying process uses molecular sieves to dehydrate to a moisture content of no more than 20 ppm, and the vacuum degree of the vacuum drying process is no higher than 10. -3 Pa; In step S3, the concentration of sodium difluorosulfonamide is controlled to be 0.6–1.2 mol / L, the concentration of sodium hexafluorophosphate is controlled to be 0–0.6 mol / L, and the total salt concentration is not greater than 1.2 mol / L; In step S4, the amount of p-nitroanisole added is controlled to be 0.5 to 3.0 wt% of the total mass of the electrolyte.

9. The method for preparing the high-voltage electrolyte for sodium-ion batteries according to claim 7, characterized in that: In step S1, the dehydration and drying process uses molecular sieves to dehydrate to a moisture content of no more than 20 ppm, and the vacuum drying process has a vacuum degree of no more than 10. -3 Pa; In step S5, the aging process includes continuous stirring at 25°C for no less than 2 hours, followed by standing for no less than 12 hours; the filtration and impurity removal is carried out using a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm. In step S5, the quality testing indicators include one or more of the following: moisture content, metal ion content, conductivity, oxidation stability, and pH value; after passing the quality test, nitrogen gas is introduced into the electrolyte and the electrolyte is sealed.

10. A sodium-ion battery, characterized in that, The electrolyte of the sodium-ion battery is the high-voltage electrolyte of the sodium-ion battery as described in any one of claims 1 to 6.

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