High-performance electrolyte additive, electrolyte and sodium ion battery

Abstract

The invention provides a high-performance electrolyte additive, an electrolyte and a sodium ion battery. The structural formula is at least one of azacyclo-sulfonate compounds: A-L-B, wherein the A group is selected from a five-membered or six-membered heterocyclic group containing at least one nitrogen atom; a group B: selected from a sulfonate group (-SO3R '), a sulfate group (-OSO3R'), a cyclic sulfonate, or a carboxylate group; and the group L is selected from a direct bond, a C1-C5 alkylene group, a C2-C5 alkenylene group, a C2-C5 alkynylene group or an oxygen-containing alkylene group. By adopting the high-performance electrolyte additive, the electrolyte and the sodium ion battery, good ionic conductivity and electrochemical stability can be achieved in a wide temperature range.

Description

Technical Field

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

[0002] With the rapid development of renewable energy and the increasing demand for energy storage, sodium-ion batteries have become an important supplement and alternative to lithium-ion batteries due to their advantages such as abundant sodium resources, low cost, and environmental friendliness. However, sodium-ion batteries still face many challenges in practical applications, especially problems such as poor electrode-electrolyte interface stability, short cycle life, insufficient high-temperature performance, and sodium dendrite growth, which seriously restrict their large-scale application.

[0003] Electrolytes, as a core component of batteries, directly affect their electrochemical and safety performance. Traditional electrolytes typically consist of sodium salts, organic solvents, and a small amount of functional additives, but they are prone to decomposition under high voltage or long-term cycling, leading to battery performance degradation. In particular, on the surface of the sodium metal anode, the unstable solid electrolyte interphase (SEI) film can exacerbate the growth of sodium dendrites, causing safety hazards such as battery short circuits.

[0004] To improve the stability and compatibility of electrolytes, functional additives are often introduced to regulate the electrode / electrolyte interface behavior. Commonly used additives include sulfur-containing compounds, fluorine-containing compounds, and some organic esters. However, in sodium-ion battery systems, these additives often exhibit problems such as uneven film formation, narrow electrochemical windows, or poor compatibility with sodium salts / solvents. Therefore, developing novel, efficient, and multifunctional electrolyte additives to achieve stable and dense SEI / CEI films, suppress dendrite growth, broaden the electrochemical window, and improve battery cycle stability has become a key issue in the current development of sodium-ion battery technology. Summary of the Invention

[0005] The purpose of this invention is to provide a high-performance electrolyte additive, electrolyte, and sodium-ion battery that exhibits good ionic conductivity, electrochemical stability, and rate cycling performance.

[0006] To achieve the above objectives, the present invention provides a high-performance electrolyte additive, having a structural formula of at least one of nitrogen-containing heterocyclic sulfonate compounds: ALB; in: Group A: Selected from five- or six-membered heterocyclic groups containing at least one nitrogen atom; Group B: Selected from sulfonate group (-SO3R'), sulfate group (-OSO3R'), cyclic sulfonate group, or carboxylic acid ester group; L group: selected from direct bonding, C1-C5 alkylene, C2-C5 alkenylene, C2-C5 alkyneene or oxyalkylene.

[0007] Preferably, the nitrogen-containing heterocyclic sulfonate compounds specifically include: Compound 1: 2-(pyridin-2-yl)ethyl methanesulfonate Compound 2: 2-(2-pyridyl)ethanesulfonic acid Compound 3: Methyl 3-(3-pyridyl)propynate .

[0008] Preferably, the A group specifically includes: pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, imidazoleyl, triazolyl, or their substituted derivatives.

[0009] Preferably, the B group specifically includes: ethyl sulfonate (–SO3CH2CH3), sulfonic acid (–SO3H), methyl ester (–COOCH3), methanesulfonate, and trifluoromethanesulfonate.

[0010] Preferably, the L group specifically includes: 1,2-ethylene (–CH2CH2–), methylene (–CH2–), or propynyl (-CH2C≡C--).

[0011] A high-performance electrolyte for a metal-ion battery comprises the following raw materials by mass percentage: 8-20 wt% sodium salt and 0.5-15 wt% electrolyte additives, with the balance being an organic solvent.

[0012] Preferably, the organic solvent includes carbonate solvents and phosphate solvents; The carbonate solvents are dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethylene carbonate (EC), and propylene carbonate (PC). The phosphate solvents are trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), dimethyl methylphosphonate (DMMP), and bis(2,2,2-trifluoroethyl)methyl phosphate (TFMP). Sodium salts include boron-containing sodium salts, sodium phosphate salts, and sulfonamide salts; The boron-containing sodium salt is selected from at least one of sodium difluorooxalate borate and sodium hexafluoroborate; The sodium phosphate salt is selected from at least one of sodium hexafluorophosphate and sodium difluorophosphate; The sulfonamide salt is selected from at least one of sodium bis(trifluoromethanesulfonamide)imide and sodium bis(fluorosulfonamide).

[0013] A sodium-ion battery, characterized in that it comprises a positive electrode, a sodium metal negative electrode, and a high-performance electrolyte for metal-ion batteries.

[0014] Therefore, this invention employs the aforementioned high-performance electrolyte additive, electrolyte, and sodium-ion battery. The prepared electrolyte, through the synergistic blending of multiple solvents and electrolyte salts, optimizes the solvation structure of the electrolyte, enabling it to possess high ionic conductivity at room temperature. Simultaneously, the introduction of phosphate ester solvents and specific sodium salts (such as boron-containing salts) effectively broadens the electrochemical window of the electrolyte, allowing it to operate stably at high voltages of 4.5V and above, exhibiting excellent rate cycling performance. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the ionic conductivity of Example 2; Figure 2 This is a schematic diagram of the electrochemical window in Example 2; Figure 3 This is a schematic diagram of the magnification in Example 2. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0018] Nitrogen-containing heterocycles with group A (such as pyridine, imidazole, triazole, etc.) possess lone pairs of electrons, making them excellent nucleophilic or coordination sites. On the positive electrode side, they can preferentially adsorb onto the surface of the positive electrode material (especially high-voltage positive electrodes), forming a physical barrier that inhibits the oxidative decomposition of the electrolyte under high voltage. They may also chelate dissolved transition metal ions (such as Mn) 3+ ,Fe 3+ This prevents them from migrating to the negative electrode and damaging the SEI film. On the negative electrode side (such as hard carbon), they can interact with defects or sodium ions on the negative electrode surface through nitrogen atoms, guiding the molecules to arrange in an orderly manner and laying the foundation for the reaction of B groups.

[0019] The length, rigidity, and chemical properties of the L-group linker directly affect the adsorption configuration, diffusion rate, and decomposition overpotential of the molecule. C1-C5 alkylene groups provide flexibility and appropriate chain length, influencing the compactness of the film layer. Propynyl groups (–CH2C≡C–) introduce an unsaturated triple bond; their π-electron cloud enhances the interaction with the electrode surface. Simultaneously, the triple bond itself may polymerize during electrochemical processes, forming a cross-linked, robust polymer interfacial film, significantly improving the mechanical and chemical stability of the SEI.

[0020] In the B group, sulfonates (–SO3R') have low bond energies for their S=O and SO bonds. At lower reduction potentials at the negative electrode (usually higher than the reduction potential of the electrolyte solvent), they preferentially undergo reductive decomposition, generating SEI film components rich in inorganic sulfides (such as Na2SO3, Na2S) or organic sulfonates. These SEIs are typically denser, have higher mechanical strength, and better ionic conductivity, effectively preventing solvent molecule co-intercalation and subsequent decomposition, thus improving first-efficiency and cycle stability. Sulfates (–OSO3R') function similarly to sulfonates and may also participate in film formation. The decomposition products of carboxylic esters (–COOR') may contain polyoxyethylene compounds or sodium salts, forming a more elastic organic layer that complements the inorganic layer, improving the toughness of the SEI.

[0021] The nitrogen atom of the pyridine ring in 2-(pyridin-2-yl)ethyl methanesulfonate possesses strong coordination ability and electron-donating properties. It preferentially and strongly chemisorbs onto the surface active sites of cathode materials (such as layered oxides). This forms a dense monomolecular protective film, acting like a "shield" to physically isolate the cathode active material from direct contact with the electrolyte. This significantly inhibits the oxidative decomposition of electrolyte solvents (especially carbonates) under high voltage, broadening the electrochemical window of the electrolyte. Sodium-ion cathode materials (such as NaNi...) x Mn x Co x O2) can dissolve transition metal ions (such as Mn) during the cycle. 3+ The nitrogen atoms in pyridine can effectively chelate (capture) these dissolved metal ions, preventing them from migrating to the negative electrode and damaging the SEI film. This is key to improving long-cycle performance. The reduction potential of ethyl sulfonate (–SO3C2H5) is typically higher than that of the main electrolyte solvent. Therefore, during the first charge (sodiumization) of the battery, it preferentially undergoes reduction on the surface of the negative electrode (e.g., hard carbon) before solvent molecules. Its decomposition products mainly include inorganic sodium salts (e.g., Na2SO3, Na2S, Na2O) and some organic sodium sulfonate salts. These components can form a dense, uniform, highly ionicly conductive, and mechanically strong solid electrolyte interface (SEI) film, effectively preventing further penetration and decomposition of the electrolyte solvent. This is beneficial for Na… + Rapid throughput reduces interfacial impedance and improves rate performance. It effectively buffers volume changes in the negative electrode material during cycling and inhibits the piercing growth of sodium dendrites. The methylene group, as a short-chain, flexible linker, efficiently couples the adsorption function of pyridine with the film-forming function of sulfonate esters. This ensures that after the pyridine groups are anchored on the electrode surface, the sulfonate ester groups can adhere to the electrode surface with appropriate spatial orientation, thereby achieving efficient and directional film formation.

[0022] 2-(2-pyridyl)ethanesulfonic acid contains a heterocyclic ring of aromatic nitrogen in its pyridine ring. The nitrogen atom has a lone pair of electrons, exhibiting strong electronegativity, which may preferentially adsorb or reduce it at the positive or negative electrode surface, altering the interfacial electric double layer structure and guiding the formation of a more uniform SEI. The nitrogen atom on the pyridine ring is a good coordination site; as a Lewis base, it can react with Na+. + A weak coordination interaction occurs, weakening the interaction between the solvent molecules and Na. + The strong binding of these molecules reduces the reduction tendency of solvent molecules on the negative electrode surface, thus improving the initial coulombic efficiency. This promotes the binding of anions (such as PF6) to the anode. - ClO4 - (etc.) enters the first solvated sheath layer, forming an anion-derived, inorganic-rich SEI. The sulfonic acid group (-SO3H) has a strong electron-withdrawing effect and acidity. It has a high reduction potential and preferentially decomposes on the negative electrode surface before the main solvent during battery formation. Its decomposition products (such as sulfites, sulfonates, etc.) are rich in sulfur and oxygen, and can participate in the construction of a robust, inorganic-rich SEI film. The inorganic components introduced by its decomposition can improve the ionic conductivity of the SEI and promote the formation of Na+. + Rapid transport. The ethane chain (-CH2-CH2-) provides suitable length and flexibility. It separates the "electron donor" (pyridine ring) and the "film-forming group" (sulfonic acid group), preventing interference between their electronic effects and allowing them to function independently and synergistically. The appropriate chain length ensures good solubility of the molecule in organic electrolytes.

[0023] The pyridine nitrogen atom in methyl 3-(3-pyridyl)propynate possesses a lone pair of electrons, which preferentially and efficiently capture HF and protic acids generated from the degradation of water and sodium salts in the electrolyte. This protects the positive electrode material and the fragile SEI film of the negative electrode from corrosion. The nitrogen atom can react with Na... + Weak coordination occurs, participating in and altering Na + The primary solvation sheath structure. This helps to reduce Na. + The desolvation barrier at the electrode interface enhances ion migration kinetics and improves rate performance. Ester groups (-COOCH3) provide inorganic components, optimizing membrane properties. Under reducing conditions, ester groups decompose to generate inorganic sodium salts such as Na2CO3 and ROCO2Na. These inorganic compounds are embedded in an organic framework constructed from alkyne bonds, forming an organic-inorganic composite SEI membrane, giving the membrane excellent ionic conductivity and mechanical strength. The polarity of the ester groups facilitates the dissolution and dispersion of the entire molecule in the electrolyte and improves the wettability of the electrolyte to the porous electrode. The reduction potential of alkyne bonds (-C≡C-) is higher than that of conventional electrolyte solvents. During the first charge of the battery, it undergoes reductive polymerization on the negative electrode surface, forming a dense organic polymer network rich in polyalkyne structures. This constitutes the flexible yet robust main framework of a high-quality SEI membrane.

[0024] In one specific embodiment, the weight ratio of lithium salt, additives and solvent can be (0.8~2):(0.05~1.5):(7~10). Electrolytes prepared using the preferred composition ratio range are beneficial to further improve the electrochemical performance and safety performance of the battery.

[0025] Example 1 In the electrolyte of this embodiment, there are 1 part NaPF6, 0.5 parts 2-(pyridin-2-yl)ethyl methanesulfonate (purchased from Maclean, CAS No. 138428-37-2), and 8.5 parts organic solvent (a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a weight ratio of 2:7:1).

[0026] Preparation of high-performance electrolytes: In an argon-filled glove box with a moisture content of <0.01ppm and an oxygen content of <0.01ppm, ethylene carbonate, dimethyl carbonate, and diethyl carbonate are mixed in a mass ratio of 2:7:1 to obtain an organic solvent. Add NaPF6 to the organic solvent and stir for about 30 minutes until completely dissolved; Add 2-(pyridin-2-yl)ethyl methanesulfonate to the mixture in small amounts one at a time while stirring continuously until the additive is completely dissolved. Then, age the mixture for 12 hours and store it in a dark, anhydrous, oxygen-free environment below 40°C for later use.

[0027] Example 2 In Example 1, 2-(pyridin-2-yl)ethyl methanesulfonate was replaced with 0.5 parts of 2-(2-pyridinyl)ethanesulfonic acid (purchased from Aladdin Shanghai, CAS No. 68922-18-9), and the proportions of other components and the preparation method were the same as in Example 1.

[0028] Example 3 The preparation method is the same as in Example 1, except that the electrolyte formulation is modified to: 2 parts NaPF6, 7 parts methyl 3-(3-pyridyl)propynate (purchased from Maclean, CAS No. 78584-30-2), and 1 part organic solvent (a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a weight ratio of 2:7:1).

[0029] Example 4 The preparation method is the same as in Example 1, except that the electrolyte formulation is modified to: 1 part NaPF6, 1 part 2-(pyridin-2-yl)ethyl methanesulfonate (purchased from Maclean, CAS No. 138428-37-2), and 8 parts organic solvent (a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a weight ratio of 2:7:1).

[0030] Example 5 The preparation method is the same as in Example 1, except that the electrolyte formulation is modified to: 1 part NaPF6, 1 part 2-(2-pyridyl)ethanesulfonic acid (purchased from Shanghai Aladdin, CAS No. 68922-18-9), and 8 parts organic solvent (a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a weight ratio of 2:7:1).

[0031] Example 6 The preparation method is the same as in Example 1, except that the electrolyte formulation is modified to: 1 part NaPF6, 1 part methyl 3-(3-pyridyl)propynate (purchased from Maclean, CAS No. 78584-30-2), and 8 parts organic solvent (a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a weight ratio of 2:7:1).

[0032] Fabrication of NVPF electrodes: First, the active material (sodium vanadium fluorophosphate, NVPF), binder (polyvinylidene fluoride, PVDF), and conductive agent SP were weighed according to a mass ratio of 7:2:1, thoroughly ground, and mixed to prepare a mixed powder. Next, 2.5 mL of N-methylpyrrolidone (NMP) solvent was added to each gram of mixed powder, and the mixture was stirred to form a homogeneous slurry. Then, using a 150 μm thick coater, the slurry was uniformly coated onto the surface of carbon-coated aluminum foil. After coating, the aluminum foil was placed in a 60°C forced-air drying oven for preliminary drying to remove most of the solvent. The dried coating was cut to the required size and dried further at 60°C. The mass was then measured and recorded using a precision balance. Finally, the cut circular electrode sheets were placed in an 80°C vacuum oven and dried for at least 12 hours to obtain the final NVPF electrode sheet. After drying, the electrode sheet was quickly transferred to an argon glove box with an oxygen content below 0.1 ppm for storage to ensure material stability.

[0033] The preparation method of sodium-ion batteries specifically includes the following steps: (1) Assemble the electrolytes obtained in Examples 1-6 into batteries in the order of "stainless steel-separator-electrolyte-stainless steel", and test the ionic conductivity of the batteries. Figure 1 As shown.

[0034] ; σ represents ionic conductivity, in mS·cm -1 L represents the distance between the two stainless steel electrodes, in cm, which is the thickness of the separator; R represents the battery's internal resistance, in Ω; S is the effective contact area between the electrolyte and the electrode, in cm.

[0035] (2) Assemble the batteries using the electrolytes obtained in Examples 1-6 in the order of "stainless steel-separator-electrolyte-sodium sheet", and perform linear sweep voltammetry tests on the batteries. Figure 2 As shown.

[0036] Table 1. Voltamperometric tests of electrolytes prepared in Examples 1-6

[0037] As shown in Table 1, the electrolyte in the examples exhibits higher ionic conductivity and better stability in NVPF batteries.

[0038] (3) Stack the positive electrode, separator, and negative electrode in sequence; The electrolytes prepared in Examples 1-6 were assembled into pouch cells in the order of "positive electrode-separator-electrolyte-sodium sheet" and the rate and cycle performance of the cells were tested.

[0039] Table 2. Electrolyte ratio and cycle performance tests obtained in Examples 1-6

[0040] As shown in Table 2, the electrolyte used in the embodiments can effectively improve the overcharge resistance and high-temperature storage performance of sodium-ion batteries in NVPF batteries, while also maintaining low-temperature discharge performance and cycle performance. Figure 3 As shown.

[0041] Table 3. Rate testing of electrolytes prepared in Examples 1-6

[0042] As shown in Table 3, the electrolyte of the embodiment has higher capacity in NVPF batteries at different rates, especially at a high rate of 5C, where the improvement is most obvious compared to the comparative ratio, showing superior battery rate performance.

[0043] Therefore, the present invention uses the above-mentioned high-performance electrolyte additive, electrolyte, and sodium-ion battery to prepare an electrolyte that has good ionic conductivity and electrochemical performance at room temperature, and is suitable for wide-temperature-range batteries and electrochemical devices.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-performance electrolyte additive, characterized in that, The structural formula is at least one of the following: ALB; in: Group A: Selected from five- or six-membered heterocyclic groups containing at least one nitrogen atom; B group: selected from sulfonate group, sulfate group, cyclic sulfonate group, or carboxylic acid ester group; L group: selected from direct bonding, C1-C5 alkylene, C2-C5 alkenylene, C2-C5 alkyneene or oxyalkylene.

2. The high-performance electrolyte additive according to claim 1, characterized in that, Nitrogen heterocyclic sulfonates specifically include: Compound 1: 2-(pyridin-2-yl)ethyl methanesulfonate Compound 2: 2-(2-pyridyl)ethanesulfonic acid Compound 3: Methyl 3-(3-pyridyl)propynate 。 3. The high-performance electrolyte additive according to claim 1, characterized in that, The A group specifically includes: pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, imidazolyl, triazolyl, or their substituted derivatives.

4. The high-performance electrolyte additive according to claim 1, characterized in that, The B group specifically includes: ethyl sulfonate, sulfonic acid group, methyl ester group, methanesulfonate group, and trifluoromethanesulfonate group.

5. The high-performance electrolyte additive according to claim 1, characterized in that, The L group specifically includes: 1,2-ethylene, methylene, or propynyl.

6. A high-performance electrolyte for a metal-ion battery, characterized in that, The raw materials comprise the following percentages by mass: 8-20 wt% sodium salt and 0.5-15 wt% electrolyte additive as described in claim 1, with the balance being organic solvent.

7. The high-performance electrolyte for a metal-ion battery according to claim 6, characterized in that, Organic solvents include carbonate solvents and phosphate solvents; The carbonate solvent is dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene carbonate, or propylene carbonate. The phosphate ester solvents are trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, and bis(2,2,2-trifluoroethyl)methyl phosphate; Sodium salts include boron-containing sodium salts, sodium phosphate salts, and sulfonamide salts; The boron-containing sodium salt is selected from at least one of sodium difluorooxalate borate and sodium hexafluoroborate; The sodium phosphate salt is selected from at least one of sodium hexafluorophosphate and sodium difluorophosphate; The sulfonamide salt is selected from at least one of sodium bis(trifluoromethanesulfonamide)imide and sodium bis(fluorosulfonamide).

8. A sodium-ion battery, characterized in that, It includes a positive electrode, a sodium metal negative electrode, and a high-performance electrolyte for a metal-ion battery as described in claim 6.

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