Lithium salt-containing dual-additive sodium ion electrolyte and sodium ion battery

Abstract

The invention discloses a lithium salt-containing dual-additive sodium ion electrolyte and a sodium ion battery. The sodium ion battery electrolyte comprises a sodium salt, an ether organic solvent, an additive I and an additive II, wherein the additive I is lithium hexafluorophosphate; and the additive II is sodium perfluorooctanoate. According to the lithium salt-containing double-additive sodium ion electrolyte provided by the invention, the battery interface stability can be synergistically improved by virtue of lithium ions and perfluorooctanoic acid ions in the electrolyte, and the high-voltage oxidative decomposition resistance and ion transmission kinetics of an ether electrolyte are remarkably improved; in addition, when the electrolyte is applied to the sodium-ion battery, the electrochemical performance such as the rate, the cycle and the capacity of the battery can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a lithium salt-containing dual-additive sodium-ion electrolyte and a sodium-ion battery. Background Technology

[0002] The development of sodium-ion batteries is moving from demonstration applications to large-scale industrial implementation, with energy density becoming one of their core competitive advantages. The key to improving the energy density of sodium-ion batteries lies in using high-voltage cathode materials with operating voltages exceeding 4.0 V. However, highly promising ether-based electrolytes, such as dimethyl glycol ether (DME)-based electrolytes, have inherently weak resistance to oxidative decomposition, typically undergoing significant decomposition above 3.8 V, severely limiting their application. The core of this problem lies in the instability of the solid electrolyte interphase (CEI) film formed on the cathode surface at high voltages, which fails to form an effective passivation layer, leading to continuous electrolyte decomposition.

[0003] In existing technologies, methods to improve the high-voltage stability of ether electrolytes, such as constructing high-concentration electrolytes or designing novel solvent molecules, often face limitations such as high cost, complex processes, or sacrifice of kinetic performance. Adding conventional film-forming additives has limited effectiveness in ether systems, making it difficult to construct ideal CEI films that combine high stability and high ionic conductivity. Therefore, finding a simple and efficient method to simultaneously improve the antioxidant capacity of ether electrolytes and construct a stable positive electrode interface has become a key bottleneck. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a lithium salt-containing dual-additive sodium-ion electrolyte and a sodium-ion battery. This invention is based on a synergistic interface regulation strategy of lithium salt and fluorocarbon surfactant. Its core mechanism is: introducing lithium hexafluorophosphate to regulate the solvation structure of the electrolyte and improve the interfacial reaction of the electrolyte, ultimately forming a Li-containing electrolyte rich in inorganic components (NaF / LiF). + -Na + The composite inorganic component CEI is introduced, and simultaneously, sodium perfluorooctanoate (PFOA) anions are directionally adsorbed onto the positive electrode surface, participating in the construction of a hydrophobic fluorocarbon network during charging, further suppressing electrolyte decomposition under high voltage. This method effectively improves the stable voltage window of ether-based electrolytes in a simple way, and simultaneously optimizes interfacial ion transport kinetics and stability, providing a novel and effective solution for the development of high-performance ether-based sodium-ion batteries.

[0005] The present invention specifically adopts the following technical solution: On one hand, the present invention provides a lithium salt-containing dual-additive sodium ion electrolyte, wherein the sodium ion battery electrolyte comprises sodium salt, ether organic solvent, additive I and additive II; Additive I is lithium hexafluorophosphate; additive II is sodium perfluorooctanoate.

[0006] The chemical structure of the lithium hexafluorophosphate is shown in Formula I; the chemical structure of the sodium perfluorooctanoate is shown in Formula II.

[0007] .

[0008] In the technical solution of this invention, lithium hexafluorophosphate and sodium perfluorooctanoate are used as dual additives. They coexist in the electrolyte and improve the solvation structure and interfacial reaction of the electrolyte through synergistic effect, thereby effectively improving the electrode interface stability and ion transport rate.

[0009] Preferably, the lithium hexafluorophosphate has a mass percentage of 0.1%-5% in the electrolyte, such as 0.5%, 1%, 2%, 3%, 4% or 5%.

[0010] Preferably, the sodium perfluorooctanoate in the electrolyte is 0.1%-2% by mass, for example, 0.5%, 1%, 1.5% or 2%.

[0011] Preferably, the ether solvent is selected from one or more of tetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0012] Preferably, the sodium salt is sodium hexafluorophosphate; the mass percentage of the sodium salt in the electrolyte is 10%-15%.

[0013] In another aspect, the present invention provides the application of the above-mentioned dual-additive sodium ion electrolyte in the preparation of sodium ion batteries.

[0014] In another aspect, the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a dual-additive sodium-ion electrolyte as described above.

[0015] In some specific embodiments, the positive electrode and the negative electrode are immersed in the dual-additive sodium ion electrolyte and separated by a membrane.

[0016] Preferably, the active material in the positive electrode is selected from any one of oxide-based positive electrode materials, polyanionic positive electrode materials, and Prussian blue positive electrode materials.

[0017] Specifically, the oxide-based cathode materials can include NaNiO2, NaCoO2, Na2NiFeMnO6, etc.

[0018] Specifically, examples of polyanionic cathode materials include Na3Fe2(PO4)P2O7, Na3V2(PO4)3, and Na4VMn(PO4)3.

[0019] Specifically, the Prussian blue cathode materials can include NaNiFe(CN)6, Na2MnFe(CN)6, Na2CoFe(CN)6, etc.

[0020] Preferably, the negative electrode is selected from any one of hard carbon, soft carbon, and sodium metal sheet.

[0021] Preferably, the diaphragm is selected from either a glass fiber diaphragm or a ceramic diaphragm.

[0022] In the technical solution of the present invention, thanks to the improvement of the electrolyte solvation structure and interfacial chemistry, the above-mentioned dual-additive sodium ion electrolyte applied to sodium ion batteries can effectively improve the interfacial stability and ion transport rate of the battery, thereby exhibiting excellent electrochemical performance such as rate capability, cycle life and capacity.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention employs lithium hexafluorophosphate and sodium perfluorooctanoate as synergistic additives, which can effectively improve the problem of easy oxidation and decomposition of ether electrolytes under high voltage. Specifically, the lithium ions in lithium hexafluorophosphate can effectively compete with sodium ions for coordination due to their strong interaction with anions and solvent molecules, thereby regulating the solvation structure and performance of the electrolyte, and thus controlling the interfacial reaction to guide the formation of Li. + -Na + A composite inorganic interface layer is formed; sodium perfluorooctanoate (PFOA), relying on its unique surface activity and solvent-repellent properties, oriented and participates in the construction of a dense organic fluorocarbon network on the cathode surface, reducing decomposition caused by solvent contact with the electrode interface. The two work synergistically to form a stable CEI layer with good ion transport at the cathode interface, effectively enhancing the antioxidant capacity of ether-based electrolytes, thus enabling them to be matched with high-voltage cathode materials and broadening the electrolyte selection for high-voltage sodium-ion batteries.

[0024] Thanks to the formation of a stable and dense interface structure, the continuous decomposition of the electrolyte caused by CEI rupture and shedding during battery cycling can be effectively mitigated. Simultaneously, the introduction of lithium ions enhances the battery's ion transport rate by regulating the electrolyte solvation structure. Therefore, batteries using this electrolyte not only exhibit excellent long-cycle stability and capacity retention, but also maintain low polarization and high capacity utilization even under high-rate charge-discharge conditions.

[0025] Furthermore, the embodiments of the present invention are simple in process, requiring only the addition of a small amount of functional additives to a conventional sodium salt-ether solvent system. This allows for the enhancement of the performance of ether electrolytes while leveraging their advantages, and is easily mass-produced. The electrolyte system exhibits good compatibility with sodium-ion battery electrode materials, improving the battery's overall electrochemical performance, including cycle life and capacity, providing a highly practical solution for developing high-performance sodium-ion batteries. Attached Figure Description

[0026] Figure 1 The cycling performance of the NFPP||Na battery assembled with the electrolyte in Example 1 of this invention and the NFPP||Na batteries assembled with the electrolytes in Comparative Examples 1-4 at a 2 C rate is compared.

[0027] Figure 2 Linear sweep voltammetry curves of the electrolyte in Example 2 and the electrolyte in Comparative Example 5 of the present invention; Figure 3 Electrochemical impedance spectroscopy of the Na3Fe2(PO4)P2O7 (NFPP)||Na battery assembled with the electrolyte in Example 3 of the present invention and the NFPP||Na battery assembled with the electrolyte in Control Example 6. Figure 4 The rate performance of the NFPP||Na battery assembled with the electrolyte in Example 4 of the present invention and the NFPP||Na battery assembled with the electrolyte in Comparative Example 7 are compared at different current densities. Figure 5 The cycling performance of the NFPP||Na battery assembled with the electrolyte in Example 5 of this invention and the NFPP||Na battery assembled with the electrolyte in Comparative Example 8 is compared at a 10 C rate. Detailed Implementation

[0028] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0029] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0030] The main raw materials used in the preparation of the electrolyte and sodium-ion battery in the following examples and comparative examples are as follows: Additive I: Lithium hexafluorophosphate (Formula I).

[0031] Additive II: Sodium perfluorooctanoate (Formula II).

[0032] .

[0033] Organic solvents: diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), ethylene carbonate (EC), diethyl carbonate (DEC).

[0034] Sodium salt: NaPF6.

[0035] Sodium-ion battery cathode: Na3Fe2(PO4)P2O7 (NFPP).

[0036] Sodium-ion battery negative electrode: sodium metal sheet.

[0037] Sodium-ion battery separator: glass fiber separator.

[0038] Example 1: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DEGDME and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0039] NFPP, Ketjen black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. A sodium metal sheet was used as the negative electrode, glass fiber was used as the separator, and the prepared electrolyte was injected to assemble a CR2032 coin-type NFPP||Na battery. Charge-discharge cycle tests were performed at a 2 C rate using a LAND battery testing system, with a voltage range of 1.5-4 V.

[0040] Example 2: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0041] Using a sodium metal sheet as the negative electrode, a stainless steel sheet as the positive electrode, and glass fiber as the separator, and injecting the electrolyte prepared in Example 2, a CR2032 coin cell (denoted as a Na||SS cell) was assembled. Using an electrochemical workstation, the electrolyte was applied at 3.0 V to 6.0 V (vs. Na). + Within the voltage range of / Na), at 2.0 mV s -1The linear scan voltammetry curve of the battery was tested at a certain scan rate.

[0042] Example 3: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0043] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. A sodium metal sheet was used as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Example 3 was injected to assemble a CR2032 coin-type NFPP||Na battery. The electrochemical impedance spectroscopy of the battery was tested using an electrochemical workstation. The test frequency range was 10 Hz. -2 - 10 5 Hz, the disturbance signal is 10 mV.

[0044] Example 4: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0045] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Example 4, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge tests were conducted using a LAND battery testing system at different current densities, with a voltage range of 1.5-4 V.

[0046] Example 5: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0047] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Example 5, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 10 C rate using a LAND battery testing system, with a voltage range of 1.5-4 V.

[0048] Compare with Example 1: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in a mixed solvent with an EC:DEC volume ratio of 1:1 and stirred thoroughly. Then, 1% by mass of additive I and 1% by mass of additive II were added and stirred thoroughly for 24 h.

[0049] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 1, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 2 C rate using a LAND battery testing system, with a voltage range of 1.5-4 V.

[0050] Compare with Example 2: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DEGDME solvent and stirred thoroughly for 24 h.

[0051] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 2, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 2 C rate using a LAND battery testing system, with a voltage range of 1.5–4 V.

[0052] Compare with Example 3: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DEGDME solvent and stirred thoroughly. Then, 1% by mass of additive I was added and stirred thoroughly for 24 h.

[0053] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 3, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 2 C rate using a LAND battery testing system, with a voltage range of 1.5–4 V.

[0054] Compare with Example 4: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DEGDME solvent and stirred thoroughly. Then, 1% (w / w) of additive II was added and stirred thoroughly for 24 h.

[0055] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 4, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 2 C rate using a LAND battery testing system, with a voltage range of 1.5–4 V.

[0056] Compare with Example 5: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly for 24 h.

[0057] A CR2032 coin cell (denoted as Na||SS cell) was assembled using a sodium metal sheet as the negative electrode, a stainless steel sheet as the positive electrode, and a glass fiber separator, and injected with the electrolyte prepared in Comparative Example 5. An electrochemical workstation was used to measure the electrolyte from 3.0 V to 6.0 V (vs. Na). + Within the voltage range of / Na), at 2.0 mV s -1 The linear scan voltammetry curve of the battery was tested at a certain scan rate.

[0058] Compare with Example 6: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly for 24 h.

[0059] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. A CR2032 coin-type NFPP||Na battery was assembled using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 6. The electrochemical impedance spectroscopy of the battery was measured using an electrochemical workstation. The test frequency range was 10 Hz. -2 - 10 5 Hz, the disturbance signal is 10 mV.

[0060] Compare with Example 7: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly for 24 h.

[0061] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 7, a CR2032 coin-type NFPP||Na battery was assembled. Charge-discharge tests were conducted using a LAND battery testing system at different current densities, with a voltage range of 1.5–4 V.

[0062] Compare with Example 8: The electrolyte was prepared in an argon-filled glove box (H2O, O2 < 0.01 ppm) as follows: 1.0 M NaPF6 was dissolved in DME solvent and stirred thoroughly for 24 h.

[0063] NFPP, Ketjen Black, and PVDF were thoroughly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The slurry was evenly coated onto aluminum foil and dried to obtain an NFPP positive electrode sheet. Using this sodium metal sheet as the negative electrode, glass fiber as the separator, and the electrolyte prepared in Comparative Example 8, a coin-type NFPP||Na battery was assembled. Charge-discharge cycle tests were performed at a 10 C rate using a LAND battery testing system, with a voltage range of 1.5–4 V.

[0064] The NFPP||Na battery assembled using the electrolyte of Example 1 and the NFPP||Na batteries assembled using the electrolytes of Comparative Examples 1-4 were subjected to cycle testing at a current density of 2 C. Figure 1 When both additives were added to the ester-based electrolyte (Comparative Example 1), the assembled battery exhibited lower discharge specific capacity and cycle stability than the ether-based electrolyte without additives (Comparative Example 2). When the two additives were introduced into the ether-based electrolyte separately (Comparative Examples 3 and 4), the assembled battery showed improved discharge specific capacity and cycle stability compared to Comparative Example 2. When both additives were introduced into the ether-based electrolyte simultaneously (Example 1), the assembled battery exhibited higher capacity and excellent cycle stability, with a significantly better improvement effect than that of additives I or II alone. This indicates that adding lithium hexafluorophosphate and sodium perfluorooctanoate simultaneously to the ether-based electrolyte not only leverages the advantages of the ether-based electrolyte but also further enhances the electrochemical performance of the battery through their synergistic effect.

[0065] The Na||SS battery assembled using the electrolyte of Example 2 and the Na||SS battery assembled using the electrolyte of Control Example 5 were tested on an electrochemical workstation, and their linear sweep voltammetry curves were measured respectively. Figure 2 After the introduction of lithium hexafluorophosphate and sodium perfluorooctanoate additives, the oxidation potential of the electrolyte increased from 3.86 V to 4.82 V, which significantly improved the high-voltage stability of the electrolyte.

[0066] The electrochemical impedance spectroscopy (EIS) spectra of the NFPP||Na battery assembled using the electrolyte of Example 3 and the NFPP||Na battery assembled using the electrolyte of Control Example 6 were tested in an electrochemical workstation. Figure 3 The significant reduction in interface resistance of the NFPP||Na battery in Example 3 compared to the NFPP||Na battery in Comparative Example 6 demonstrates that the electrolyte described in the invention has better sodium ion transport kinetics, and the battery containing this electrolyte has lower charge transfer resistance and CEI resistance.

[0067] The NFPP||Na battery assembled using the electrolyte of Example 4 and the NFPP||Na battery assembled using the electrolyte of Comparative Example 7 were subjected to rate tests at different current densities, such as... Figure 4 Example 4 and Comparative Example 7 showed higher specific capacity at the same current density, further demonstrating that the electrolyte described in the invention has better sodium ion transfer kinetics and better rate performance.

[0068] The NFPP||Na battery assembled using the electrolyte of Example 5 and the NFPP||Na battery assembled using the electrolyte of Control Example 8 were subjected to long-cycle testing at a high current density of 10 C. Figure 5In Example 5, the NFPP||Na battery maintained excellent cycle stability (97.42% capacity retention) throughout 2100 cycles at a high current density of 10 C. In contrast, the NFPP||Na battery in Comparative Example 8, although retaining 94.01% capacity retention after the first 800 cycles, rapidly lost activity and its capacity decayed to 0 during subsequent charge and discharge cycles. This demonstrates that the electrolyte described in this invention not only forms a stable CEI and effectively suppresses electrolyte decomposition during battery charge and discharge, but also effectively improves the battery's transport kinetics, thereby improving the battery's high-rate cycle performance.

[0069] Therefore, as can be seen from the above embodiments and comparative examples, the lithium salt-containing dual-additive sodium ion electrolyte provided by the present invention further improves the battery's resistance to high-voltage decomposition, interface impedance, cycle life, rate capability, capacity, and other performance characteristics.

[0070] In summary, in this invention, thanks to the solvation behavior and interfacial chemistry of the two additives, lithium hexafluorophosphate and sodium perfluorooctanoate, their synergistic effect can simultaneously improve the battery transport kinetics and interfacial stability of the electrolyte, thereby enhancing the electrochemical performance of sodium-ion batteries, such as cycle life, rate capability, and capacity.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lithium salt-containing dual-additive sodium ion electrolyte, characterized in that, The sodium-ion battery electrolyte includes sodium salt, ether-based organic solvent, additive I, and additive II; Additive I is lithium hexafluorophosphate; additive II is sodium perfluorooctanoate.

2. The dual-additive sodium ion electrolyte according to claim 1, characterized in that, The lithium hexafluorophosphate has a mass percentage of 0.1%-5% in the electrolyte.

3. The dual-additive sodium ion electrolyte according to claim 1, characterized in that, The sodium perfluorooctanoate has a mass percentage of 0.1%-2% in the electrolyte.

4. The dual-additive sodium ion electrolyte according to claim 1, characterized in that, The ether solvent is selected from any one or more of tetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

5. The dual-additive sodium ion electrolyte according to claim 1, characterized in that, The sodium salt is sodium hexafluorophosphate; the mass percentage of the sodium salt in the electrolyte is 10%-15%.

6. The application of the dual-additive sodium ion electrolyte according to any one of claims 1-5 in the preparation of sodium ion batteries.

7. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the dual-additive sodium ion electrolyte as described in any one of claims 1-5.

8. The sodium-ion battery according to claim 7, characterized in that, The active material in the positive electrode is selected from any one of oxide-based positive electrode materials, polyanionic positive electrode materials, and Prussian blue positive electrode materials; Preferably, the oxide-based cathode material is selected from any one of NaNiO2, NaCoO2, and Na2NiFeMnO6; Preferably, the polyanionic cathode material is selected from any one of Na3Fe2(PO4)P2O7, Na3V2(PO4)3, and Na4VMn(PO4)3; Preferably, the Prussian blue cathode material is selected from any one of NaNiFe(CN)6, Na2MnFe(CN)6, and Na2CoFe(CN)6.

9. The sodium-ion battery according to claim 7, characterized in that, The negative electrode is selected from any one of hard carbon, soft carbon, and sodium metal sheets.

10. The sodium-ion battery according to claim 7, characterized in that, The diaphragm is selected from either glass fiber diaphragms or ceramic diaphragms.

Images