A sodium salt composition, a sodium ion battery electrolyte, application thereof, and a sodium ion battery

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium salt composition, a sodium ion battery electrolyte and application thereof, and a sodium ion battery. The sodium salt composition provided by the application comprises any five or more of sodium bistrifluoromethylsulfonimide, sodium hexafluorophosphate, sodium difluoro(oxalato)borate, sodium fluoroborate, sodium nitrate, sodium perchlorate and sodium difluorophosphate. The solvation configuration of the sodium ion battery electrolyte prepared by using the sodium salt composition is an aggregate with a multi-polar solvation shell, can form an inorganic matter-rich positive electrode surface solid electrolyte interface film (CEI) and a negative electrode surface solid electrolyte interface film (SEI), effectively protects the positive electrode and the negative electrode, and improves the cycle stability and rate performance of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium salt composition, a sodium-ion battery electrolyte and its application, and a sodium-ion battery. Background Technology

[0002] With the continuous development of human society, how to efficiently and safely develop and utilize energy has become a major challenge. The utilization of clean energy sources such as solar, wind, and tidal energy requires the development of large-scale energy storage technologies. Lithium-ion batteries, with their advantages of high energy density, low self-discharge, and long cycle life, are currently the preferred energy storage device in portable electronic devices and electric vehicles. However, in the application of large-scale energy storage, lithium-ion batteries still face the problem of lithium resource scarcity. Sodium-ion batteries work on a similar principle to lithium-ion batteries, and sodium resources on Earth are abundant. Sodium-ion batteries also have advantages such as low cost and good cycle life, making them a strong competitor in the field of large-scale energy storage. However, the high instability of the electrode / electrolyte interface during cycling severely hinders the development of sodium-ion batteries. In particular, an unstable positive electrode electrolyte interface (CEI) leads to continuous electrolyte side reactions, transition metal leaching, and rapid capacity decay, thereby reducing the cycle stability and rate performance of sodium-ion batteries. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a sodium salt composition, a sodium-ion battery electrolyte and its application, and a sodium-ion battery. The electrolyte prepared by the sodium salt composition is an aggregate with a multi-polar solvation shell, which can form a positive electrode surface solid electrolyte interphase (CEI) film and a negative electrode surface solid electrolyte interphase (SEI) film rich in inorganic matter, effectively protecting the positive and negative electrodes and improving the cycle stability and rate performance of the sodium-ion battery.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] The present invention provides a sodium salt composition comprising any five or more of sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium difluorooxalate borate, sodium fluoroborate, sodium nitrate, sodium perchlorate, and sodium difluorophosphate.

[0006] Preferably, the sodium salts in the sodium salt composition are of equal amount.

[0007] The present invention also provides a sodium-ion battery electrolyte, comprising a sodium salt composition, an organic solvent, and additives;

[0008] The sodium salt composition is the sodium salt composition described in the above technical solution;

[0009] The solvation configuration of the sodium-ion battery electrolyte is an aggregate with a multi-polar solvation shell;

[0010] The concentration of the sodium salt composition in the sodium-ion battery electrolyte is 0.5–0.8 mol / L;

[0011] The aggregates constitute 70-85% of the volume in the sodium-ion battery electrolyte.

[0012] Preferably, the organic solvent includes one or more of tetrahydrofuran, ethylene glycol dimethyl ether, and dioxolane.

[0013] Preferably, the additive includes one or more of ethylene carbonate, vinylene carbonate, propylene sulfite, and ethylene sulfate.

[0014] Preferably, the mass concentration of the additive in the sodium-ion battery electrolyte is 3-5%.

[0015] The present invention also provides the application of the sodium-ion battery electrolyte described in the above technical solution in sodium-ion batteries.

[0016] The present invention also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the sodium-ion battery electrolyte described in the above technical solution.

[0017] Preferably, the active material of the positive electrode includes layered oxides, Prussian blue compounds, or polyanionic compounds.

[0018] Preferably, the negative electrode comprises hard carbon, sodium metal, or sodium titanium phosphate.

[0019] This invention provides a sodium salt composition comprising any five or more of the following: sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium difluorooxalate borate, sodium fluoroborate, sodium nitrate, sodium perchlorate, and sodium difluorophosphate. In the electrolyte, organic solvent molecules arrange themselves around sodium ions to form a solvation shell. Each sodium salt in the sodium salt composition provided by this invention has a different solubility and varying ease of dissociation in the organic solvent. The addition of sodium salts with low solubility and strong coordination ability (such as NaNO3 and NaBF4) alters the solvation shell structure. Under the effect of multiple sodium salts, sodium salts with strong coordination with organic solvents (such as NaNO3 and NaBF4) enter the first solvation shell (the first tightly packed layer of solvent molecules formed by organic solvent molecules surrounding sodium ions). This increases the negative charge around the sodium ions, driving more sodium ions to approach each other. The aggregation of multiple sodium ions leads to an increase in the local concentration in the electrolyte. As the distance from the sodium ion core increases, the organic solvent molecules become less tightly packed, forming second, third, and other solvation shells. This results in the aggregation of multiple solvation shells, forming a large aggregate. This multipolar solvation structure, modulated by the solubility of different sodium salts, allows various anions to combine randomly (e.g., two TFSIs). - +1 BF4 - +1 DFOB - Or 1 NO3 - +1 TFSI - +1 PF6 - +1 BF4 - (Generally, there are four anions in total) enter the first solvation shell. Various anions migrate along with sodium ions during charging and discharging. Sodium ions undergo desolvation near the positive and negative electrode interfaces. In a multi-anion solvation shell, because different anions have different bond energies with sodium ions, this disordered state effectively reduces the desolvation energy of sodium ions, thereby enhancing the reaction kinetics at the positive and negative electrode interfaces. The anions then undergo redox reactions at the positive and negative electrode interfaces, forming inorganic compounds rich in F, S, B, N, and P (such as NaF, Na3N, SO3). - PO2 - BO -The presence of a solid electrolyte interphase (CEI) film on the positive electrode surface and a solid electrolyte interphase (SEI) film on the negative electrode surface effectively protects both the positive and negative electrodes, thereby improving the cycle stability and rate performance of sodium-ion batteries. The participation of multiple anionic groups in this electrolyte leads to greater diversity in the solvation structure. The involvement of anions weakens the interaction between sodium ions and solvent molecules, promoting sodium ion diffusion and the formation of stable interphase passivation layers (CEI, SEI). Compared to single-salt electrolytes, low-concentration electrolytes with multiple sodium salts exhibit enhanced cycle stability and rate performance.

[0020] The results of the examples show that, when combined with NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 The O2 cathode coin cell exhibited an excellent capacity retention of 89.48% after 250 cycles at a cutoff voltage of 4V and 0.5C (1C = 120mAh / g), while also demonstrating good cycle performance under both low and high temperature conditions. This invention provides valuable insights into the application of high-entropy, low-concentration electrolytes in sodium-ion batteries.

[0021] Furthermore, the cost of sodium salt is typically more than ten times that of solvent. The sodium-ion battery electrolyte provided by this invention has higher cycle stability and rate performance than single-salt electrolytes with the same sodium salt concentration. Therefore, under the same requirements for cycle stability and rate performance, the sodium salt concentration in the sodium-ion battery electrolyte provided by this invention is low, which can reduce the use of sodium salt and effectively reduce the cost of sodium-ion batteries, thereby facilitating the large-scale application of sodium-ion batteries in the field of energy storage. Attached Figure Description

[0022] Figure 1 The radial distribution function (solid line) and coordination number (dashed line) plots are calculated by molecular dynamics (MD) simulation based on the single salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1, where a is NTF and b is HEE electrolyte;

[0023] Figure 2 The solvation structure simulation diagrams are of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1.

[0024] Figure 3 Pie charts showing the solvation configuration distribution in the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1;

[0025] Figure 4 The wavenumber range is 550 to 1000 cm⁻¹ -1 Raman spectra (e) of the single-salt electrolyte (NTF) of Comparative Example 1, the HEE electrolyte of Example 1, and tetrahydrofuran (THF), and the Na NMR spectrum showing Na.+ Coordination environment diagram (f);

[0026] Figure 5 The anions and solvent in the HEE electrolyte prepared in Example 1, and Na + Binding energy diagram;

[0027] Figure 6 Calculated HOMO energy level diagram of anion molecules and solvent in the HEE electrolyte prepared in Example 1;

[0028] Figure 7 Aurbach coulomb efficiency plot (a) of Na||Cu battery assembled with single salt electrolyte (NTF) of Comparative Example 1 and HEE electrolyte of Example 1 and LSV curve of Na|| stainless steel half cell (b).

[0029] Figure 8 Tafel curves and exchange current density (i0) plots (c) of Na||Na batteries assembled with the single salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 at high overpotential, and Nyquist plots (d) of Na||Na batteries at NTF from 303 to 343 K.

[0030] Figure 9 The Nyquist plots (e) of the Na||Na battery in the HEE electrolyte of Example 1 from 303 to 343 K and the Na content of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown. + Desolvation energy diagram (f);

[0031] Figure 10 The cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 is shown in graph (a) at 0.5C and in the cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 in the voltage range of 2-4V. The cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 in the voltage range of 2-4.1V is shown in graph (b).

[0032] Figure 11 The Na||NaNMF battery assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 was tested at 18 mg·cm⁻¹. -2 Cyclic performance diagram of the positive electrode (c) and low-temperature (-20℃) performance diagram of the two electrolytes (d);

[0033] Figure 12 The high-temperature (40°C) performance graph (e) and the rate performance graph (f) of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown.

[0034] Figure 13TOF-SIMS 3D analysis diagram (a) and TOF-SIMS 2D surface mapping diagram (b) of secondary ion fragments on the NaNMF cathode after cycling with the HEE electrolyte of Example 1;

[0035] Figure 14 XPS spectra (c) and (d) of C1s and F1s on the NaNMF cathode after cycling with the HEE electrolyte of Example 1;

[0036] Figure 15 XPS spectra (e) and (f) of P 2p and S 2p on the NaNMF cathode after cycling with the HEE electrolyte of Example 1;

[0037] Figure 16 XPS spectra (g) and (h) of N1s and B1s on the NaNMF cathode after cycling with the HEE electrolyte of Example 1;

[0038] Figure 17 The in-situ EIS DRT calculation and charge / discharge curves of the Na||NaNMF batteries assembled with the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown in the figures for the 1st and 20th cycles, where a represents the 1st cycle with the single-salt electrolyte, b represents the 1st cycle with the HEE electrolyte, c represents the 20th cycle with the single-salt electrolyte, and d represents the 20th cycle with the HEE electrolyte.

[0039] Figure 18 The charge-discharge voltage curves (e) of the Na||NaNMF batteries assembled with the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 after 50 cycles, measured by GITT, and the corresponding DNA of the NaNMF cathode. + Figure (f);

[0040] Figure 19 NaNi prepared for application example 1 1 / 3 Mn 1 / 3 Fe 1 / 3 Characterization diagram of O2 (NaNMF), where af is the elemental distribution map of SEM, g is the SEM morphology map, and h is the XRD map. Detailed Implementation

[0041] The present invention provides a sodium salt composition comprising any five or more of sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium difluorooxalate borate, sodium fluoroborate, sodium nitrate, sodium perchlorate, and sodium difluorophosphate.

[0042] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0043] In one embodiment, the sodium salt includes any five or more of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium hexafluorophosphate (NaPF6), sodium difluorooxalate borate (NaDFOB), sodium fluoroborate (NaBF4), sodium nitrate (NaNO3), sodium perchlorate (NaClO4), and sodium difluorophosphate (NaDFP). In a specific embodiment, it is NaTFSI, NaPF6, NaDFOB, NaBF4, and NaNO3, or NaTFSI, NaClO4, NaDFOB, NaBF4, and NaNO3, or NaDFP, NaClO4, NaDFOB, NaBF4, and NaNO3.

[0044] In one embodiment, the sodium salts in the sodium salt composition are of equal amount.

[0045] The present invention also provides a sodium-ion battery electrolyte, comprising a sodium salt composition, an organic solvent, and additives;

[0046] The sodium salt composition is the sodium salt composition described in the above technical solution;

[0047] The solvation configuration of the sodium-ion battery electrolyte is an aggregate with a multi-polar solvation shell;

[0048] The concentration of the sodium salt composition in the sodium-ion battery electrolyte is 0.5–0.8 mol / L;

[0049] The aggregate has a volume percentage of 70-85% in the sodium-ion battery electrolyte.

[0050] In one embodiment, the organic solvent includes one or more of tetrahydrofuran, ethylene glycol dimethyl ether, and dioxolane, with tetrahydrofuran being a specific example.

[0051] In one embodiment, the additive includes one or more of ethylene carbonate, vinylene carbonate, propylene sulfite, and vinyl sulfate, with ethylene carbonate being a specific example. The main function of the additive in this invention is to form a stable SEI on the negative electrode surface, thereby enhancing the mechanical strength of the SEI.

[0052] In one embodiment, the concentration of the sodium salt composition in the sodium-ion battery electrolyte is 0.5 to 0.6 mol / L.

[0053] In this embodiment of the invention, the concentration of the sodium salt composition in the sodium-ion battery electrolyte is 0.5 mol / L, and the sodium salt composition is NaTFSI, NaPF6, NaDFOB, NaBF4 and NaNO3, wherein the concentration of each sodium salt is 0.1 mol / L.

[0054] In one embodiment, the aggregate has a volume percentage of 75-80% in the sodium-ion battery electrolyte.

[0055] In one embodiment, the mass concentration of the additive in the sodium-ion battery electrolyte is 3-5%, and in a specific embodiment it is 5%.

[0056] The solvation structure of an electrolyte refers to the interaction and arrangement between solvent and solute molecules in the electrolyte. This structure has a significant impact on the electrochemical performance of the electrolyte, including the battery's charge-discharge efficiency and cycle stability.

[0057] In the electrolyte, organic solvent molecules arrange themselves around sodium ions to form a solvation shell. The sodium salt compositions provided in this invention have different solubilities for each sodium salt and varying degrees of dissociation in the organic solvent. The addition of sodium salts with low solubility and strong coordination ability (such as NaNO3 and NaBF4) alters the solvation shell structure. Under the influence of multiple sodium salts, sodium salts with strong coordination with the organic solvent (such as NaNO3 and NaBF4) enter the first solvation shell (the first tightly packed layer of solvent molecules formed by organic solvent molecules surrounding sodium ions). This increases the negative charge around the sodium ions, driving more sodium ions to approach each other. The aggregation of multiple sodium ions leads to an increase in local concentration in the electrolyte. As the distance from the sodium ion core decreases, the arrangement of organic solvent molecules becomes less tight, forming second, third, and other solvation shells, resulting in the aggregation of multiple solvation shells into a large aggregate. This multipolar solvation structure, regulated by the solubility of different sodium salts, allows multiple anions to combine randomly (e.g., 2 TFSI). - +1 BF4 - +1 DFOB - Or 1 NO3 - +1 TFSI - +1 PF 6- +1 BF 4-(Generally, there are four anions in total) enter the first solvation shell. Various anions migrate along with sodium ions during charging and discharging. Sodium ions undergo desolvation near the positive and negative electrode interfaces. In a multi-anion solvent shell, due to the different bond energies between different anions and sodium ions, this disordered state effectively reduces the desolvation energy of sodium ions, thereby enhancing the reaction kinetics at the positive and negative electrode interfaces. Anions then undergo redox reactions at the positive and negative electrode interfaces, forming an inorganic-rich solid electrolyte interphase (CEI) film on the positive electrode surface and a solid electrolyte interphase (SEI) film on the negative electrode surface, effectively protecting the positive and negative electrodes and improving the cycle stability and rate performance of the sodium-ion battery. The participation of multiple anionic groups in this electrolyte leads to greater diversity in the solvation structure. The participation of anions reduces the interaction between sodium ions and solvent molecules, promoting sodium ion diffusion and the formation of stable interphase passivation layers (CEI, SEI). Compared to single-salt electrolytes, low-concentration electrolytes with multiple sodium salts exhibit enhanced cycle stability and rate performance.

[0058] The solid electrolyte interphase (CEI) film on the positive electrode surface is beneficial for Na + The diffusion of organic derivatives is located in the outer layer, which is conducive to the diffusion of Na. + The diffusion of these components ensures the toughness of the CEI. The presence of high-strength inorganic materials acts as a support, effectively protecting the integrity of the cathode particles. The uniform and coordinated composition of all components forms a stable CEI; the dense and uniform CEI facilitates charge transfer at the interface, thereby achieving long-term cycling performance.

[0059] Furthermore, the cost of sodium salt is typically more than ten times that of solvent. The sodium-ion battery electrolyte provided by this invention has higher cycle stability and rate performance than single-salt electrolytes with the same sodium salt concentration. Therefore, under the same requirements for cycle stability and rate performance, the sodium salt concentration in the sodium-ion battery electrolyte provided by this invention is low, which can reduce the use of sodium salt and effectively reduce the cost of sodium-ion batteries, thereby facilitating the large-scale application of sodium-ion batteries in the field of energy storage.

[0060] As one embodiment, the preparation method of the sodium-ion battery electrolyte includes the following steps:

[0061] Sodium salt is dissolved in a mixed solution of organic solvent and additives in an inert atmosphere to obtain the sodium-ion battery electrolyte.

[0062] In one implementation, the inert atmosphere is argon.

[0063] Before dissolution, the present invention further includes: drying the sodium salt in an inert atmosphere or vacuum; the inert atmosphere is argon; the vacuum degree is 25 kPa; the drying temperature is 80-100°C, specifically 80-90°C in the embodiment; the drying time is 5-12 h, specifically 12 h in the embodiment.

[0064] Before dissolution, the present invention further includes: subjecting the organic solvent and additive to molecular sieve drying treatment, followed by filtration; the pore size of the molecular sieve used for the molecular sieve drying treatment is [missing information]. The drying time for the molecular sieve is 5 to 12 hours, and in a specific embodiment it is 10 to 12 hours; the pore size of the sieve used for filtration is 0.22 μm.

[0065] The present invention does not specifically limit the dissolution process; any dissolution process well known in the art can be used.

[0066] The present invention also provides the application of the sodium-ion battery electrolyte described in the above technical solution or the sodium-ion battery electrolyte prepared by the preparation method described in the above technical solution in sodium-ion batteries.

[0067] The present invention also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte of the sodium-ion battery is the sodium-ion battery electrolyte described in the above technical solution or the sodium-ion battery electrolyte prepared by the preparation method described in the above technical solution.

[0068] In one embodiment, the active material of the positive electrode includes layered oxides, Prussian blue compounds, or polyanionic compounds, with layered oxides being a specific example.

[0069] In one embodiment, the layered oxide includes sodium nickel manganese ferrite, specifically NaNi. 1 / 3 Mn 1 / 3Fe 1 / 3 O2; the polyanionic compound includes sodium vanadium phosphate (Na3V2(PO4)3) or sodium vanadium fluorophosphate (Na3V2(PO4)2F3); the Prussian blue compound is Na2Mn[Fe(CN)6].

[0070] As one implementation method, the NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 The preparation method of O2 includes the following steps: Na2CO3, NiO, Mn2O3, and Fe2O3 are mixed and ball-milled, dried, and then pulverized. The resulting powder is then calcined to obtain NaNi. 1 / 3 Mn 1 / 3Fe 1 / 3 O2.

[0071] In one embodiment, the Na₂CO₃, NiO, Mn₂O₃, and Fe₂O₃ were all purchased from Aladdin; the purity of the Na₂CO₃ was 99.9%; the purity of the NiO was 99%; the purity of the Mn₂O₃ was 98%; the purity of the Fe₂O₃ was 99%; the molar ratio of Na in Na₂CO₃, Ni in NiO, Mn in Mn₂O₃, and Fe in Fe₂O₃ was 1:1 / 3:1 / 3:1 / 3; the ball milling equipment was a planetary ball mill (MITR). ZQM-2L / 4L); the ball milling speed is 200-300 rpm, specifically 300 rpm in this embodiment; the ball milling time is 5-10 h, specifically 10 h in this embodiment; anhydrous ethanol is used as the medium for ball milling; the mass ratio of solid material to medium during ball milling is 1:5; the drying temperature is 50-70℃, specifically 55-65℃ in this embodiment; the drying time is 5-10 h, specifically 10 h in this embodiment; the pulverization is performed on a mortar; the particle size of the powder is 3-8 μm, specifically 5 μm in this embodiment; the calcination temperature is 850-1000℃, specifically 950℃ in this embodiment; the calcination time is 10-15 h, specifically 14 h in this embodiment; the calcination is carried out in air; after calcination, the product is cooled to 100℃, removed from the furnace, and immediately transferred to an argon-filled glove box, cooled to room temperature, and stored to avoid exposure to air.

[0072] In one embodiment, the negative electrode includes hard carbon, sodium metal, or sodium titanium phosphate, with sodium metal being used in a specific embodiment.

[0073] In one embodiment, the diaphragm comprises glass fiber, polypropylene (PP) or polyethylene (PE), with glass fiber being a specific example.

[0074] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0075] Example 1

[0076] NaTFSI, NaPF6, NaDFOB, NaBF4, and NaNO3 were dried at 80℃ for 12 hours under a vacuum of 25 kPa for later use. Tetrahydrofuran (THF) and ethylene carbonate (FEC) were then... After the molecular sieve was dried for 10 h, impurities were filtered out using a 0.22 μm pore size filter for later use. NaTFSI, NaPF6, NaDFOB, NaBF4, and NaNO3 were dissolved in a mixture of tetrahydrofuran (THF) and ethylene carbonate (FEC) to obtain a sodium-ion battery electrolyte (HEE electrolyte), wherein the concentration of each sodium salt was 0.1 mol / L, totaling 0.5 mol / L, and the mass concentration of ethylene carbonate in the sodium-ion battery electrolyte was 5%.

[0077] Example 2

[0078] The difference from Example 1 is that the sodium-ion battery electrolyte (HEE electrolyte) contains five sodium salts: NaTFSI, NaClO4, NaDFOB, NaBF4, and NaNO3, with each sodium salt having a concentration of 0.1 mol / L, totaling 0.5 mol / L.

[0079] Example 3

[0080] The difference from Example 1 is that the sodium-ion battery electrolyte (HEE electrolyte) contains five sodium salts, namely NaDFP, NaClO4, NaDFOB, NaBF4, and NaNO3, with each sodium salt having a concentration of 0.1 mol / L, totaling 0.5 mol / L.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that the five sodium salts in Example 1 are replaced with NaTFSI to obtain a single salt electrolyte NTF, wherein the concentration of NaTFSI is 0.5 mol / L.

[0083] Comparative Example 2

[0084] The difference from Example 1 is that the five sodium salts in Example 1 are replaced with NaPF6 to obtain a single-salt electrolyte NPF, wherein the concentration of NaPF6 is 0.5 mol / L.

[0085] Application Example 1

[0086] NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3Preparation of O2: A stoichiometric mixture of Na2CO3 (99.9% purity, Aladdin), NiO (99% purity, Aladdin), Mn2O3 (98% purity, Aladdin), and Fe2O3 (99% purity, Aladdin) (molar ratio of Na:Ni:Mn:Fe 1:1 / 3:1 / 3:1 / 3) was ball-milled in anhydrous ethanol at 300 rpm for 10 h using a planetary ball mill (MITRZQM-2L / 4L). The mass ratio of solid material to anhydrous ethanol during ball milling was 1:5. The resulting mixture was dried at 65℃ for 10 h and then ground in a mortar to obtain a powder with a particle size of 5 μm. The powder was then calcined in air at 950℃ for 14 h. At the end of calcination, when the temperature dropped to 100℃, the sample was removed from the furnace and immediately transferred to an argon-filled glove box to continue cooling to room temperature and stored.

[0087] With the NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 Using O2 as the positive electrode active material, sodium metal as the negative electrode, glass fiber as the separator, and the HEE electrolyte of Example 1 as the electrolyte, a Na||NaNMF battery is assembled.

[0088] A Na||Cu battery was assembled using Cu foil as the positive electrode, sodium metal as the negative electrode, glass fiber as the separator, and the HEE electrolyte from Example 1 as the electrolyte.

[0089] A Na|| stainless steel half-cell was assembled using a stainless steel gasket as the positive electrode, sodium metal as the negative electrode, glass fiber as the separator, and the HEE electrolyte of Example 1 as the electrolyte.

[0090] A Na||Na battery was assembled using sodium metal as the positive electrode, sodium metal as the negative electrode, glass fiber as the separator, and the HEE electrolyte from Example 1 as the electrolyte.

[0091] Comparative Application Example 1

[0092] The difference from Application Example 1 is that the HEE electrolyte in Example 1 is replaced with the single-salt electrolyte NTF in Comparative Example 1.

[0093] Performance testing

[0094] The morphology and microstructure of the samples were characterized by scanning electron microscopy (SEM, JSM 7800F, JEOL) and transmission electron microscopy (TEM, JEOL JEM-F200).

[0095] The chemical composition of the samples was determined by X-ray photoelectron spectroscopy (XPS, K-Alpha+, Thermo Fisher Scientific).

[0096] Raman spectra were recorded using a Renishaw inVia Raman microscope and a λ = 532 nm laser radiation.

[0097] Using Rigaku Miniflex II XRD instruments and Cu Kα radiation The crystallographic information of the synthesized product was examined by X-ray diffraction (XRD).

[0098] Standard checks were performed at a scan rate of 5° per minute, with scan angles ranging from 5° to 90°. 3D reconstructed images were obtained using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0099] In-situ electrochemical impedance spectroscopy (EIS) measurements were performed on an electrochemical workstation (Solartron, USA) and 2032 coin cells. The charge and discharge voltage range was 2–4 V at a 0.2C rate.

[0100] The EIS test frequency range is 1,000,000-0.1Hz, with an amplitude of 10mV. Prior to the in-situ EIS test, the battery was run through different cycles at a constant current density.

[0101] The DRT transformation was performed using MATLAB software, and all parameters remained consistent throughout the calculation process to ensure the consistency of the DRT results. The viscosity of the electrolyte was measured at 28°C using an MSKSFM-VT viscometer.

[0102] 23Na-NMR analysis of the electrolyte was performed using a Jeol ECZ500R 500MHz NMR spectrometer. Before testing, dimethyl sulfoxide (DMSO-d6) was thoroughly mixed with the electrolyte as a deuterating agent.

[0103] (1) Figure 1 The radial distribution function (solid line) and coordination number (dashed line) are plots calculated by molecular dynamics (MD) simulation based on the single salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1, where a is NTF and b is HEE electrolyte.

[0104] This invention uses molecular dynamics (MD) simulations to confirm the solvation structure of the HEE electrolyte and to elucidate its differences from the solvation structure of the single-salt electrolyte NTF. Figure 1 The radial distribution function indicates that, although the concentrations of each salt in the HEE electrolyte are lower than those in the single-salt electrolyte NTF, the anions of all five salts in the HEE electrolyte still enter the first solvation shell (dashed platform).

[0105] (2) Figure 2The diagram shows the solvation structure simulation of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1. Figure 3 Pie charts showing the solvation configuration distribution in the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1.

[0106] Depend on Figure 2 and Figure 3 It can be seen from the molecular simulation of the electrolyte as a whole that, unlike the single-salt electrolyte NTF, the anions in the HEE electrolyte aggregated, forming multiple anions that encapsulate Na. + Clusters. Combined Figure 1 The first plateau of the dashed lines in sections a and b corresponds to the coordination number. It can be observed that the proportion of small aggregates (AGGs) in the solvation configuration of the high-entropy electrolyte (HEE) is higher than that in the single-salt electrolyte (NTF). The lower AGG content in NTF leads to poor passivation of the organic-rich interfacial chemistry and electrochemical interface (CEI) derived from the single-salt electrolyte NTF, resulting in electrolyte consumption, low coulombic efficiency (CE), and irreversible capacity loss. In contrast, the high-entropy electrolyte (HEE) exhibits salt-dominated solvation interactions, where Na... + The surrounding solvation shell is mainly dominated by anions, resulting in anion-derived, inorganic, and robust CEI, which passivates THF solvent co-intercalation and further electrolyte decomposition, thereby achieving good cycling of the positive electrode.

[0107] (3) Figure 4 The wavenumber range is 550 to 1000 cm⁻¹ -1 Raman spectra (e) of the single-salt electrolyte (NTF) of Comparative Example 1, the HEE electrolyte of Example 1, and tetrahydrofuran (THF), and the Na NMR spectrum shown in 23Na NMR. + Coordination environment diagram (f).

[0108] Raman spectroscopy and nuclear magnetic resonance spectroscopy were used to further investigate the coordination behavior of each component in the two electrolytes. Figure 4 As shown in Figure e, a binding peak with the main solvent tetrahydrofuran (THF) exists in both NTF and HEE electrolytes, around 860. The solvation intensity was studied using NMR spectroscopy of 23Na liquid, where the chemical shift reflects the effect of the solvation environment on Na. + Shielding. The solvation shell of the high-entropy electrolyte (HEE) and Na... + Enhanced interactions between them, such as Figure 4 As shown in f in the figure. Compared with the displacement of NTF in a single-salt electrolyte, this indicates a high electron density due to strong solvation interactions, Na + The increased shielding indicates the aggregation state of anions in the high-entropy electrolyte.

[0109] (4) Figure 5 The anions and solvent in the HEE electrolyte prepared in Example 1, and Na + The binding energy diagram. Figure 6 The calculated HOMO energy level diagram is shown for the anion molecules and solvent in the HEE electrolyte prepared in Example 1.

[0110] To investigate the reasons for anion aggregation in high-entropy HEE electrolytes, Na... + The binding energies with each anion and solvent were simulated using the Vienna Atomic Number Simulation software package (VASP.5.4.4) in AIMD, employing the Projector Enhanced Wave (PAW) mode. The Perdew-Burke-Ernzerhof (PBE) function was used to describe the exchange correlation energy. Long-range van der Waals (vdW) dispersive interactions were performed using the DFT-D3 method developed by Grimme and his collaborators. The plane wave energy cutoff was set to 400 eV, and the Brillouin zone sampling was performed only at the Γ point. The results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the discovery of Na + -NO3 - The highest binding energy indicates that NaNO3 is the most difficult to dissociate in the solvent. Therefore, in the HEE electrolyte, each NO3-... - The presence of Na+ greater than 1 around the anion + Under the influence of charge, Na+ attracts other different anions to form aggregates with multiple solvated shells. These solvated shell aggregates, during charging and discharging, cause various anions to follow Na+. + They reach the positive electrode-electrolyte interface layer together and decompose to form CEI rich in various inorganic elements.

[0111] Depend on Figure 6 It can be seen that in the high-entropy HEE electrolyte system, NO 3- and BF 4- It will be the first to oxidize and decompose, forming CEI rich in N, B, and F-derived inorganic compounds.

[0112] (5) Figure 7 Aurbach coulomb efficiency plot (a) of Na||Cu battery assembled with single salt electrolyte (NTF) of Comparative Example 1 and HEE electrolyte of Example 1 and LSV curve of Na|| stainless steel half cell (b). Figure 8 Tafel curves and exchange current density (i0) plots (c) for Na||Na batteries assembled with the single salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 at high overpotentials, and Nyquist plots (d) for Na||Na batteries at NTF from 303 to 343 K. Figure 9The Nyquist plots (e) of the Na||Na battery in the HEE electrolyte of Example 1 from 303 to 343 K and the Na content of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown. + Desolvation energy diagram (f).

[0113] To investigate the reversibility of sodium metal intercalation / deintercalation in different electrolytes, the Aurbach method was used to test the coulombic efficiency (CE) of sodium / copper half-cells. The CE values ​​for the single-salt electrolyte NTF and the high-entropy electrolyte HEE were 93.84% and 97.71%, respectively. Figure 7 (a) This indicates that the high-entropy electrolyte (HEE) exhibits good reversibility of sodium metal intercalation / deintercalation.

[0114] Further, using the linear sweep voltammetry method at 1 mV·s -1 The oxidative stability of the two electrolytes was evaluated at a scan rate of [missing value]. Figure 7 In Figure b), when the voltage exceeds 4.25 V, the oxidation current density of the single-salt electrolyte NTF increases rapidly, indicating its weak oxidation stability. In contrast, the high-entropy electrolyte HEE also maintains a lower current density at 4.50 V, exhibiting a wider electrochemical window. Meanwhile, at high overpotentials, the exchange current densities of NTF and HEE electrolytes are 4.28 and 5.25 mA·cm⁻¹, respectively. -2 ( Figure 8 c). In Figure 8 d, Figure 9 China and Figure 9 In this study, the desolvation energies at the interfaces of two electrolytes in a symmetric Na||Na battery at 303–343 K were evaluated using electrochemical impedance spectroscopy (EIS). These energies can be calculated using the Arrhenius equation.

[0115]

[0116] In the formula, Rct, A, R, and T represent resistance, the pre-exponential constant, the standard gas constant, and the absolute temperature, respectively. The activation energy is determined by temperature and Na. + The resistance is determined by resistance fitting during the solvent removal process. Na in HEE + The desolvation energy is 58.4 kJ·mol⁻¹. -1 It is significantly lower than the desolvation energy in NTF (67.4 kJ·mol⁻¹). -1 The significant reduction in the energy barrier demonstrates that the anion-enhanced solvation shell accelerates the Na+ process. + It played a crucial role in the transmission.

[0117] (6) Figure 10The cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 is shown in graph (a) at 0.5C and in the cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 in the voltage range of 2-4V. The cycling performance of Na||NaNMF batteries assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 in the voltage range of 2-4.1V is shown in graph (b).

[0118] Figure 11 The Na||NaNMF battery assembled using the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 was tested at 18 mg·cm⁻¹. -2 Cyclic performance of the positive electrode (c) and low-temperature (-20℃) performance of the two electrolytes (d).

[0119] Figure 12 The high-temperature (40°C) performance graph (e) and the rate performance graph (f) of the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown.

[0120] Using widely used O3-type NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 O2 was used as a cathode material in this study. 1 / 3Mn 1 / 3 Fe 1 / 3 O2 materials have an advantage in the cathode market due to their simple synthesis route, high capacity, and low cost. The electrochemical performance of two electrolytes was tested in a Na||NaNMF battery. At a voltage range of 2-4V and a rate of 0.5C, the high-entropy electrolyte (HEE) exhibited an excellent capacity retention of 89.48% after 250 cycles, superior to the single-salt electrolyte (NTF). Figure 10 (a). Meanwhile, when the cutoff voltage is increased to 4.1V ( Figure 10 In b), after 150 cycles, the high-entropy electrolyte (HEE) retained 88.36% of its capacity, which is significantly better than the single-salt electrolyte (NTF) (56.32%).

[0121] To verify its practical application value, the areal capacity of the positive electrode (18 mg·cm³) was increased. -2 Two electrolytes, NTF (non-nitrate electrolyte) and HEE (hydrochloric acid electrolyte), were tested. Figure 11 As shown in Figure c, the high-entropy electrolyte (HEE) retains 88.94% of its capacity after 100 cycles, while the single-salt electrolyte (NTF) shows a dramatic capacity decay. The high-entropy electrolyte (HEE) also exhibits excellent performance under both high and low temperature conditions, such as... Figure 11 d and Figure 12As shown in Figure e, at -20℃, the high-entropy electrolyte (HEE) retains 83.84% of its capacity after 200 cycles. Furthermore, it also exhibits good performance at a high temperature of 40℃. Rate testing of the two electrolytes shows that the high-entropy electrolyte (HEE) also demonstrates superior rate performance compared to the single-salt electrolyte (NTF). Figure 12 (f)

[0122] (7) Figure 13 The images show TOF-SIMS 3D analysis (a) and TOF-SIMS 2D surface mapping (b) of secondary ion fragments on the NaNMF cathode after cycling with the HEE electrolyte of Example 1.

[0123] Figure 14 XPS spectra (c) and (d) of C1s and F1s on the NaNMF cathode after cycling with the HEE electrolyte of Example 1.

[0124] Figure 15 XPS spectra (e) and (f) of P 2p and S 2p on the NaNMF cathode after cycling with the HEE electrolyte of Example 1.

[0125] Figure 16 XPS spectra (g) and (h) of N1s and B1s on the NaNMF cathode after cycling with the HEE electrolyte of Example 1.

[0126] To further investigate the distribution of CEI interface components on NaNMF, time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth analysis was employed. The TOF-SIMS depth distribution (normalized to maximum) of the high-entropy electrolyte (HEE) after 20 cycles on the NaNMF cathode surface was obtained, revealing various components within the depth-distributed CEI. For example... Figure 13 a and Figure 13 As shown in Figure b, TOF-SIMS analysis reveals that during the cycling process, the high-entropy electrolyte (HEE) forms inorganic compounds rich in F, S, B, N, and P (such as NaF, Na3N, SO42-) on the NaNMF cathode. 3- PO 2- BO - The CEI of the sample is relatively uniform, and the various components are distributed relatively evenly.

[0127] In addition, X-ray photoelectron spectroscopy (XPS) was used to determine the composition of CEI on the NaNMF cathode surface after high-entropy electrolyte (HEE) cycling. Figures 14-16 By analyzing the C1s spectra before and after etching ( Figure 14(c) It was found that the CEI composition formed by the high-entropy electrolyte (HEE) was uniform and did not change much before and after etching. This was confirmed by the F1s spectrum. Figure 14 As shown in d), the NaF content increased after 30 seconds of etching, indicating that multiple anions decomposed first in the early stage of CEI formation, forming a CEI rich in NaF. Meanwhile, observation of the S2p spectrum (…) Figure 15 In the middle f), the SN peak appeared 30s after etching, which also indicates that TFSI - Premature decomposition at the positive electrode interface is beneficial for the formation of a stable CEI. Analysis of the spectra of other inorganic elements shows that in P 2p (… Figure 15 (e), N 1s( Figure 16 (g) and B1s ( Figure 16 In the middle (h), inorganic substances rich in F, S, B, N, and P (such as NaF, Na3N, SO3) can be found after etching. - PO2 - BO - The presence of increases in both ( ) further confirms the relatively abundant inorganic elements within the CEI. In summary, the CEI structure formed by the high-entropy electrolyte (HEE) can be concluded to be: favorable for Na... + The diffusion of organic derivatives is located in the outer layer, which is conducive to the diffusion of Na. + The diffusion of these components ensures the toughness of the CEI. The presence of high-strength inorganic materials acts as a support, effectively protecting the integrity of the cathode particles. The uniform and coordinated composition of all components forms a stable CEI, thus achieving long-term cycle performance.

[0128] (8) Figure 17 The in-situ EIS DRT calculations and charge / discharge curves of Na||NaNMF batteries assembled with the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 are shown for the 1st and 20th cycles, where a represents the 1st cycle with the single-salt electrolyte, b represents the 1st cycle with the HEE electrolyte, c represents the 20th cycle with the single-salt electrolyte, and d represents the 20th cycle with the HEE electrolyte.

[0129] Figure 18 The charge-discharge voltage curves (e) of the Na||NaNMF batteries assembled with the single-salt electrolyte (NTF) of Comparative Example 1 and the HEE electrolyte of Example 1 after 50 cycles, measured by GITT, and the corresponding DNA of the NaNMF cathode. + Figure (f).

[0130] To analyze the complex evolution of the electrode-electrolyte interface during charging and discharging, in-situ electrochemical impedance spectroscopy (in-situ EIS) was performed. Figure 17This study further explores this issue by analyzing the relaxation time (DRT) distribution. DRT is a model-free method that separates the complex and highly overlapping physical and chemical processes of an electrochemical system by converting EIS from frequency to time constant. It is evident that the mid-to-low frequency semicircles in the in-situ EIS spectrum exhibit dynamic evolution during charge and discharge, which can be attributed to the continuous reaction and phase transition between the cathode and electrolyte during charge and discharge. Three distinct relaxation times can be identified in the DRT results, located between 10⁻⁴ and 10⁻³, 10⁻¹ and 1, and 10 to 10², labeled τ₁, τ₂, and τ₃. The peak area of ​​the DRT represents the impedance value of a specific electrochemical process. The high-frequency τ₁ and mid-frequency τ₂ symbolize different interfacial transition responses and charge transfer evolution during CEI formation in the NaNMF electrode, respectively. The rightward shift of the τ₁ peak during charge and discharge indicates the continuous reaction between the cathode and electrolyte, representing the irreversible process of CEI formation. τ₂ represents the electrochemical kinetics related to charge transfer at the electrode-electrolyte interface. τ3 represents the mass transfer of the electrolyte in the pores at the electrode, which will not be analyzed here. Firstly, analyzing the DRT results at τ1, the single-salt electrolyte NTF shows a strong signal during the first charge-discharge cycle, indicating a strong reaction at the interface; while in the high-entropy electrolyte HEE, the τ1 signal is lower during the first charge-discharge cycle, indicating a more stable reaction at the interface. During the 20th charge-discharge cycle, the high-entropy electrolyte shows a stronger signal at τ1, indicating the formation of a stable and dense CEI after cycling, effectively ensuring cycle stability. Secondly, at τ2, the peak value of the single-salt electrolyte NTF increases progressively during cycling. In contrast, the high-entropy electrolyte HEE tends to be stable, indicating that a dense and uniform CEI facilitates charge transfer at the interface. Intermittent galvanostatic titration (GITT) and the calculated sodium ion diffusion coefficient (DNa) are also analyzed. + The results showed that the DNA in the positive electrode cyclic in NaTFSI / SUL:OTE:FEC was... + Significantly higher ( Figure 18 The results (e, f) confirm the rapid interfacial diffusion kinetics and strong structural stability during the charge-discharge process of high-entropy electrolyte HEE.

[0131] (9) Figure 19 NaNi prepared for application example 1 1 / 3 Mn 1 / 3 Fe 1 / 3 Characterization diagram of O2 (NaNMF), where af is the elemental distribution map of SEM, g is the SEM morphology map, and h is the XRD map.

[0132] Depend on Figure 19 It can be seen that the NaNi prepared using Example 1 1 / 3 Mn1 / 3 Fe 1 / 3 O2 is an O3-type layered oxide cathode material.

[0133] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, Includes sodium salt compositions, organic solvents, and additives; The sodium salt composition comprises NaTFSI, NaPF6, NaDFOB, NaBF4 and NaNO3, or NaTFSI, NaClO4, NaDFOB, NaBF4 and NaNO3, or NaDFP, NaClO4, NaDFOB, NaBF4 and NaNO3; the amount of each sodium salt in the sodium salt composition is the same. The solvation configuration of the sodium-ion battery electrolyte is an aggregate with a multi-polar solvation shell; The concentration of the sodium salt composition in the sodium-ion battery electrolyte is 0.5 mol / L; The aggregate has a volume percentage of 70-85% in the sodium-ion battery electrolyte; The organic solvent is tetrahydrofuran; The additive is ethylene carbonate.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The additive has a mass concentration of 3-5% in the sodium-ion battery electrolyte.

3. The application of the sodium-ion battery electrolyte according to claim 1 or 2 in sodium-ion batteries.

4. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the sodium-ion battery electrolyte as described in claim 1 or 2.

5. The sodium-ion battery according to claim 4, characterized in that, The active material of the positive electrode includes layered oxides, Prussian blue compounds, or polyanionic compounds.

6. The sodium-ion battery according to claim 4, characterized in that, The negative electrode includes hard carbon, sodium metal, or sodium titanium phosphate.

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