An electrolyte for an anode-free sodium metal battery compatible with extremely low temperatures, a preparation method and applications thereof

Abstract

The application belongs to the technical field of sodium metal battery, and particularly relates to a negative-electrode-free sodium metal battery electrolyte compatible with extremely low temperature and a preparation method and application thereof. The negative-electrode-free sodium metal battery electrolyte compatible with extremely low temperature comprises a sodium salt and a mixed solvent, wherein the mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (6-9.5):(0.5-4); the first solvent is 1,2-dimethoxypropane, and the second solvent is dipropylene glycol dimethyl ether. The electrolyte exhibits an extremely low polarization voltage of 19.5 mV at -80 DEG C, and the first-cycle discharge specific capacity of a negative-electrode-free full battery corresponding to the electrolyte reaches 79.66 mAh / g at -60 DEG C, and the capacity retention rate is as high as 96.45% after 100 cycles.

Description

Technical Field

[0001] This invention belongs to the field of sodium metal battery technology, specifically relating to a low-temperature compatible, negative electrode-free sodium metal battery electrolyte, its preparation method, and its application. Background Technology

[0002] Sodium metal batteries have broad prospects for large-scale energy storage due to their high theoretical capacity and low cost. However, at low temperatures, the performance of traditional ester or ether electrolytes in sodium metal batteries deteriorates sharply due to problems such as decreased ionic conductivity, increased desolvation energy barrier, and interfacial instability. On the other hand, using cyclic ether solvents (such as DOL and THF) as low-temperature electrolytes often results in poor electrochemical stability due to their tendency to undergo ring-opening reactions.

[0003] Anode-less sodium batteries use layered oxide materials or polyanion electrodes as the positive electrode and copper or aluminum foil current collectors as the negative electrode. They typically use ethers as solvents, with sodium salts and other additives forming the electrolyte. In anode-less sodium batteries, the sodium metal is completely exposed in the electrolyte, causing significant side reactions such as gas production. Especially at extreme low temperatures, the sodium ion migration rate drops sharply, dendrite growth intensifies, the interface becomes unstable, and capacity decays rapidly, making it difficult to simultaneously achieve high ion transport and low interfacial polarization at extremely low temperatures.

[0004] This paper presents an electrolyte design strategy that enables sodium batteries to operate efficiently and stably at ultra-low temperatures, which is an effective way to solve the above problems. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a low-temperature compatible, electrodeless sodium metal battery electrolyte, its preparation method, and its applications. This invention specifically addresses the problems of slow ion transport, interface instability, and rapid capacity decay in existing electrolytes at ultra-low temperatures. It creatively provides a low-temperature compatible, electrodeless sodium metal battery electrolyte that exhibits an extremely low polarization voltage of 19.5 mV at -80℃. At -60℃, the electrolyte corresponds to a first-cycle discharge specific capacity of 79.66 mAh / g for a full battery without an electrode, and a capacity retention rate of 96.45% after 100 cycles. This overcomes the performance limitations of existing sodium batteries at ultra-low temperatures and is suitable for extreme environments such as polar regions and deep space.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: On the one hand, a sodium metal battery electrolyte compatible with extremely low temperatures without a negative electrode is provided, comprising a sodium salt and a mixed solvent, wherein the mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (6~9.5):(0.5~4); the first solvent is 1,2-dimethoxypropane and the second solvent is dipropylene glycol dimethyl ether.

[0007] Furthermore, a method for preparing the above-mentioned low-temperature compatible sodium metal battery electrolyte without a negative electrode is provided, comprising: The first solvent and the second solvent are mixed to obtain a mixed solvent; Under an inert atmosphere, sodium salt is added to the mixed solvent and stirred at room temperature until completely dissolved to obtain the low-temperature compatible sodium metal battery electrolyte without a negative electrode.

[0008] On the other hand, a sodium metal battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the aforementioned low-temperature compatible, negative electrode-free sodium metal battery electrolyte.

[0009] Compared with the prior art, the present invention has the following advantages: 1. Based on the systematic regulation of the solvation structure entropy of sodium ions, this invention creatively provides a low-temperature compatible, electrodeless sodium metal battery electrolyte. This electrolyte exhibits an extremely low polarization voltage of 19.5 mV at -80℃, and at -60℃, the electrolyte corresponds to a first-cycle discharge specific capacity of 79.66 mAh / g for a full battery without a negative electrode, and the capacity retention rate after 100 cycles is as high as 96.45%. This breakthrough overcomes the performance limitations of existing sodium batteries at ultra-low temperatures and is suitable for extreme environments such as polar regions and deep space.

[0010] 2. This invention provides a low-temperature compatible sodium metal battery electrolyte without a negative electrode, comprising a sodium salt and a mixed solvent composed of 1,2-dimethoxypropane (DMP) and dipropylene glycol dimethyl ether (DMM). The electrolyte maintains a predominantly SSIP (solvent-separated ion pair) and CIP (contact ion pair) structure at -40°C, and retains high fluidity and low viscosity under ultra-low temperature conditions (-80°C). It features high ionic conductivity, low polarization voltage, and high interface stability under low-temperature conditions, effectively preventing dendrite formation.

[0011] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the fluidity test results of the electrolytes in Example 1 and the comparative examples under low temperature conditions of -60℃ to -80℃. Figure 2 This is a schematic diagram showing the in-situ viscosity test results of Example 1 and various comparative examples at temperatures ranging from 20°C to -100°C. Figure 3 The results of ionic conductivity tests for Example 1 and each comparative example are shown in the range of 25°C to -80°C. Figure 4 The results are Raman tests and peak fitting of the electrolytes in Example 1 and each comparative example. Figure 5 Characterization images of the electrolyte of Example 1 at different etching depths in XPS at -60°C; Figure 6 The results show the performance test results of the electrodeless full cell assembled with the electrolyte of Example 1. Figure 7 The voltage-time curves of Na||Na symmetric cells assembled with the electrolytes in Examples 1-5 were tested at -80°C. Figure 8 The Na||Al / C half-cell assembled with the electrolyte of Example 1 was deposited at low temperature at 0.5 mA h cm⁻¹. -2 Sodium morphology; Figure 9 The physicochemical properties of each component in Example 1 are shown. Detailed Implementation

[0013] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0014] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0015] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.

[0016] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0017] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0018] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0019] The technical principle employed in this invention is as follows: using 1,2-dimethoxypropane (DMP) as the main solvent and dipropylene glycol dimethyl ether (DMM) as the co-solvent, the synergistic effect of the α-methyl group of 1,2-dimethoxypropane and the hyperbranched structure of dipropylene glycol dimethyl ether is utilized to form a solvation environment with high configurational entropy, which promotes the solvation and rapid desolvation of sodium ions, reduces the desolvation energy barrier, and achieves efficient and stable operation of a cathode-free sodium metal battery from room temperature to ultra-low temperature.

[0020] On one hand, a low-temperature compatible sodium metal battery electrolyte without a negative electrode is provided, comprising a sodium salt and a mixed solvent, wherein the mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (6~9.5):(0.5~4); the first solvent is 1,2-dimethoxypropane (DMP), and the second solvent is dipropylene glycol dimethyl ether (DMM); the concentration of the sodium salt in the electrolyte is 0.5 M~1 M.

[0021] In some embodiments, the sodium salt is sodium hexafluorophosphate (NaPF6).

[0022] In some preferred embodiments, the low-temperature compatible, electrodeless sodium metal battery electrolyte is composed of sodium salt and a mixed solvent.

[0023] This invention preferably utilizes a low-temperature compatible, electrode-free sodium metal battery electrolyte composed solely of sodium salt and the aforementioned mixed solvent. A CIP / SSIP-dominated solvation structure is constructed using a methylated ether solvent (DMP) and a hyperbranched ether solvent (DMM). This solvation shell is stable and dynamic, exhibiting a low desolvation energy barrier, effectively promoting the formation of NaF-rich SEI / CEI and enhancing interfacial stability. Molecular dynamics simulations show that the mixed solvent system (PF-DMP / DMM) composed of sodium salt and the aforementioned mixed solvent exhibits stronger NaF-reactive properties at -60°C. + The solvation capability and performance test results show that the above-mentioned mixed solvent system corresponds to a first discharge specific capacity of 79.66 mAh / g for a full cell without a negative electrode at -60℃, and a capacity retention rate of 96.45% after 100 cycles at 0.1C. The electrolyte of the present invention can still maintain efficient ion transport and stable electrochemical performance at extremely low temperatures.

[0024] In some preferred embodiments, the mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (8~9.5):(0.5~2); in some preferred embodiments, the concentration of sodium salt in the electrolyte is 0.5 M.

[0025] In some further preferred embodiments, the volume ratio of the first solvent to the second solvent is 9:1.

[0026] Preferably, the electrolyte contains a mixture of methylated ether solvent DMP and hyperbranched ether solvent DMM at a volume ratio of (6~9.5):(0.5~4). As the proportion of DMM in the system increases, the polarization voltage shows a trend of first decreasing and then increasing. In a further preferred electrolyte, the mixture of methylated ether solvent DMP and hyperbranched ether solvent DMM at a volume ratio of 9:1 can exhibit the lowest nucleation overpotential and no obvious short circuit, with a polarization voltage as low as below 20 mV, and the highest cycle stability.

[0027] In some preferred embodiments, the low-temperature compatible, negative-electrode-free sodium metal battery electrolyte is compatible with temperatures down to -60°C.

[0028] The electrolyte of this invention remains liquid at ultra-low temperatures, with a polarization voltage of less than 20 mV, and features high capacity retention over long cycles.

[0029] On the other hand, a method for preparing the above-mentioned low-temperature compatible sodium metal battery electrolyte without a negative electrode is provided, comprising: The first solvent, 1,2-dimethoxypropane (DMP), and the second solvent, dipropylene glycol dimethyl ether (DMM), are mixed to obtain a mixed solvent. Under an inert atmosphere, sodium salt is added to the mixed solvent and stirred at room temperature until completely dissolved to obtain the low-temperature compatible sodium metal battery electrolyte without a negative electrode.

[0030] On another front, a sodium metal battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is a copper current collector or an aluminum current collector, the positive electrode active material is sodium vanadium phosphate (Na3V2(PO4)3, NVP), and the electrolyte is the aforementioned low-temperature compatible, negative electrode-free sodium metal battery electrolyte.

[0031] The electrolyte of this invention can achieve synergistic optimization of high ionic conductivity and low desolvation energy at low temperatures. It can be applied to battery systems that match high-load cathodes (such as NVP) and carbon-coated aluminum foil, and can operate stably in a temperature range of -80°C to 25°C.

[0032] The sodium metal battery described above, wherein the negative electrode-free sodium metal battery electrolyte compatible with extremely low temperatures can be compatible with temperatures down to -60°C.

[0033] It can be used for energy storage or detection equipment in extreme environments.

[0034] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.

[0035] Example 1 This embodiment provides a low-temperature compatible sodium metal battery electrolyte without a negative electrode, which is composed of NaPF6, 1,2-dimethoxypropane (DMP) and dipropylene glycol dimethyl ether (DMM); in the electrolyte, the volume ratio of DMP to DMM is 9:1, and the concentration of NaPF6 is 0.5 M.

[0036] This embodiment also provides a method for preparing the above-mentioned low-temperature compatible sodium metal battery electrolyte without a negative electrode, comprising: Step 1: Mix 90 mL of DMP and 10 mL of DMM to obtain a mixed solvent; Step 2: In an argon glove box, add NaPF6 to the above mixed solvent at a preset concentration and stir at room temperature until completely dissolved to obtain a sodium metal battery electrolyte without a negative electrode, labeled as PF-DMP / DMM.

[0037] Example 2 This embodiment provides a method for preparing a sodium metal battery electrolyte without a negative electrode that is compatible with extremely low temperatures. It is the same as in Example 1, except that the volumes of DMP and DMM are 95 mL and 5 mL, respectively.

[0038] Example 3 This embodiment provides a method for preparing a sodium metal battery electrolyte without a negative electrode that is compatible with extremely low temperatures. It is the same as in Example 1, except that the volumes of DMP and DMM are 80 mL and 20 mL, respectively.

[0039] Example 4 This embodiment provides a method for preparing a low-temperature compatible sodium metal battery electrolyte without a negative electrode, which is the same as in Example 1, except that the volumes of DMP and DMM are 60 mL and 40 mL, respectively.

[0040] Example 5 This embodiment provides a method for preparing a sodium metal battery electrolyte without a negative electrode that is compatible with extremely low temperatures. It is the same as in Example 1, except that the volumes of DMP and DMM are 70 mL and 30 mL, respectively.

[0041] Comparative Example 1 This comparative example provides a sodium metal battery electrolyte without a negative electrode, composed of NaPF6 and 1,2-dimethoxypropane (DMP); the concentration of NaPF6 in the electrolyte is 0.5 M.

[0042] This embodiment also provides a method for preparing the above-mentioned negative electrode-free sodium metal battery electrolyte, including: In an argon glove box, NaPF6 was added to DMP at a preset concentration and stirred at room temperature until completely dissolved to obtain an electrolyte, labeled PF-DMP.

[0043] Comparative Example 2 This comparative example provides a sodium metal battery electrolyte without a negative electrode, composed of NaPF6 and dipropylene glycol dimethyl ether (DMM); the concentration of NaPF6 in the electrolyte is 0.5 M.

[0044] This embodiment also provides a method for preparing the above-mentioned negative electrode-free sodium metal battery electrolyte, including: In an argon glove box, NaPF6 was added to DMM at a preset concentration and stirred at room temperature until completely dissolved to obtain an electrolyte labeled PF-DMM.

[0045] Performance Evaluation 1. Low-temperature flow performance test The electrolytes of Example 1 and each comparative example were allowed to stand at -60℃ to -80℃ for 12 h, and their fluidity was observed. The results are as follows: Figure 1 As shown, both PF-DMM and PF-DMP solidify significantly at -60°C, while the PF-DMP / DMM of Example 1 remains liquid even at temperatures as low as -80°C.

[0046] 2. Viscosity test The in-situ viscosity test results of the electrolytes in Example 1 and the comparative examples at 20°C to -100°C are as follows: Figure 2 As shown, the test was conducted using a TA DHR-20 rotational rheometer with the following temperature program: starting temperature 25℃, ending temperature -100℃, and cooling rate 5℃ / min. The test results showed that as the test temperature decreased, the viscosity of the single-solvent electrolytes in each comparative example increased rapidly. However, the PF-DMP / DMM in Example 1 maintained low viscosity and high fluidity, remained liquid at -80℃, and showed no salt precipitation.

[0047] 3. Ionic conductivity test The ionic conductivity test results of Example 1 and each comparative example at 25 to -80°C are as follows: Figure 3 As shown, within a temperature range of 25 to -80°C, the ionic conductivity of PF-DMP / DMM in Example 1 is higher than that of the comparative example. Especially under extremely low temperature conditions, low temperature will reduce the ion migration rate of the electrolyte and increase battery polarization. However, electrolytes that can maintain high ionic conductivity under extremely low temperature conditions have a faster charge transport rate, which helps to reduce polarization voltage and improve rate performance and cycle stability.

[0048] 4. Raman test The Raman test and peak fitting results of the electrolytes in Example 1 and each comparative example are as follows: Figure 4 As shown, Raman spectroscopy results indicate that the PF-DMP / DMM in Example 1 still predominates in SSIP (solvent-separated ion pairs) and CIP (contact ion pairs) structures at -40°C, while the pure DMP or DMM in the comparative examples predominates in AGG (aggregate) structures. The SSIP / CIP structure is favorable for Na + The rapid desolvation and interfacial transport of PF-DMP / DMM are achieved, but the AGG structure increases the desolvation energy barrier and reduces ion migration efficiency. Therefore, PF-DMP / DMM can still maintain efficient ion transport at low temperatures, thus improving battery performance.

[0049] 5. XPS Test Characterization images of the electrolyte in Example 1 at different etching depths using XPS at -60°C are shown below. Figure 5 As shown, the electrolyte PF-DMP / DMM in Example 1 forms a NaF-rich interface layer with few organic components and high interface stability.

[0050] 6. Performance testing of a full battery without a negative electrode The performance test results of the electrodeless full cell assembled with the electrolyte in Example 1 are as follows: Figure 6 As shown, the assembly method includes: coating with a density of 10 mg / cm³. -2 The NVP was used as the positive electrode, and the carbon-coated aluminum foil was used as the negative electrode current collector. The N / P ratio was 0. The electrolyte used in each example or comparative example was used as the electrolyte. A sodium metal full cell without a negative electrode was assembled. The performance of the full cell was tested at -60°C, 0.05 C and 0.1C. The results showed that the PF-DMP / DMM corresponding negative electrode-free full cell of Example 1 had a first-cycle discharge specific capacity of 79.66 mAh / g and a capacity retention rate of 96.45% after 100 cycles at 0.1C.

[0051] 7. Polarization Voltage Test Using two sodium plates as electrodes, Na||Na symmetric cells were assembled with the electrolytes from Examples 1-5. These Na||Na symmetric cells were tested at -80°C and a current density of 0.1 mA cm⁻¹. -2 The voltage-time graph of the test is as follows Figure 7 As shown, the results indicate that the electrolyte with 10% DMM volume percentage exhibits the lowest nucleation overpotential (polarization) and no significant short circuit occurs, demonstrating the highest cycle stability.

[0052] The polarization voltages of the electrolytes in Examples 1-5 corresponding to Na||Na symmetric cells are shown in Table 1. The test methods included using Na||Na symmetric cells at a current density of 0.1 mA cm⁻¹. -2Charge-discharge tests were conducted, and the results showed that the electrolyte polarization voltage of the present invention can be as low as below 20 mV.

[0053] Table 1. Polarization voltages of Na||Na symmetric cells corresponding to each electrolyte in Examples 1-5.

[0054] 8. Half-cell voltage-time test Sodium sheets and blank current collectors (Al / C) were added to the PF-DMP / DMM of Example 1, with a current density of 0.1 mAcm⁻¹. -2 Discharge was performed, with a discharge capacity of 0.5 Ma cm⁻¹. -2 Sodium deposition at low temperature (0.5 mA h cm⁻¹) in the assembled Na||Al / C half-cell was observed using SEM. -2 The morphology after sodium deposition is as follows: Figure 8 As shown, the sodium deposition thickness of PF-DMP / DMM is uniform, with no obvious grooves or unevenness on the surface, and no dendrite formation.

[0055] 9. Macroscopic physicochemical properties The physicochemical properties of each component in Example 1 are as follows: Figure 9 As shown, the components are diethylene glycol dimethyl ether (DIG), ethylene glycol dimethyl ether (EGDME), 1,2-dimethoxypropane (DMP), and dipropylene glycol dimethyl ether (DMM). The physicochemical properties include boiling point, melting point, flash point, and coordination parameters of each system, including sodium ion binding energy, electron-donating number (DN), and dielectric constant. It can be seen that DMP has the lowest sodium ion binding energy, and its α-methyl substitution structure helps to reduce the sodium ion binding energy. The combination of DMP and DMM, which also has a hyperbranched structure, helps to increase the configuration entropy, which is consistent with the aforementioned Raman spectroscopy test results. Furthermore, DMM and DMP have good fluidity at low temperatures, which is beneficial for ion transport and interface stability.

[0056] 10. Thermodynamic properties (solvation free energy ΔG) When evaluating the solvation thermodynamic parameters, incorporating the configuration entropy term into the calculation of solvation entropy reveals a significantly enhanced entropy increase effect in the mixed solvent system. This causes the solvation free energy ΔG_sol of the mixed system to shift more negatively across the entire temperature range of 200-400 K, while the change in ΔG_sol is smaller for the single solvent system. The results are shown in Table 2. Taking 298.15 K as an example, the ΔG_sol of the mixed solvent system increases from -10.741 kcal·mol⁻¹ when only vibrational entropy is considered. -1 Further reduced to -11.333 kcal·mol after including configurational entropy. -1This demonstrates superior solvation thermodynamics compared to the corresponding single-solvent system. Furthermore, as the temperature decreases, the contribution of the -TΔS_sol term to the free energy gradually increases, making the entropy-driven stabilization effect dominant at low temperatures, especially under cryogenic conditions. For example, at 213.15 K, the ΔG_sol of the mixed solvent system can reach -19.928 kcal·mol⁻¹. -1 This demonstrates stronger thermodynamic stability in solvation. In summary, the synergistic solvation effect exhibited by mixed solvents can thermodynamically rebalance the enthalpy and entropy terms, thereby making the solvation free energy more negative and increasing the degree of ion dissociation. This is particularly beneficial for maintaining high ion transport capacity under low-temperature conditions.

[0057] Table 2. Solvation free energy (ΔG) of electrolytes at room temperature and low temperature (-60℃)

[0058] 11. Coordination number of sodium ions Table 3. O / F ratio obtained from molecular dynamics simulations.

[0059] The ratio of sodium ion-solvent coordination (Na-O) and sodium ion-anion coordination (Na-F) obtained from molecular dynamics simulations (expressed as the oxygen-fluorine ratio (O / F), which is defined as the ratio of oxygen atoms (from solvent molecules) to fluorine atoms (from PF6) in the first coordination shell of the sodium ion. - The O / F ratio, which directly reflects the relative contributions of solvent and anions to the coordination of sodium ions: a higher O / F value indicates a more pronounced solvent-dominated solvent sheath, which is beneficial for ion dissociation and transport. As shown in Table 3, the simulation methods included molecular dynamics (MD) simulations using the Gromacs program and the Universal Amber Force Field (GAFF), with a simulation chamber size of 50 × 50 × 50 Å. 3The appropriate electrolyte salts / solvents were filled using the Packmol program. The structures were first pre-relaxed using energy minimization calculations, and then annealed in the range of 0-298.15 K with a time step of 1 ps until equilibrium was reached. The entire process lasted 100 ps, ​​and the final MD simulation ran for a total of 1 ns at a simulation temperature of 298.15 K. It was observed that at room temperature, the O / F ratios of the single-solvent electrolytes PF-DMM and PF-DMP were 5.71 and 6.91, respectively, but decreased significantly at low temperatures: for PF-DMM, the ratio decreased from 5.71 at 25 °C to 1.55 at –60 °C; for PF-DMP, the ratio decreased from 6.91 to 2.80. This reduction indicates that the binding of anions is enhanced at low temperatures, and since the solvation environment is mainly composed of anions, this enhanced binding usually leads to a decrease in ionic conductivity (due to suppressed ion mobility). In contrast, the PF-DMP / DMM electrolyte has an oxygen / fluorine ratio of 26.33 at 25°C and remains as high as 3.17 at -60°C. This higher oxygen / fluorine ratio, especially at low temperatures, indicates stronger solvation ability. At the same time, the reduced binding effect of anions helps to accelerate ion dissociation and transport rates, bridging the gap between macroscopic conductivity and microscopic solvation behavior. This demonstrates that the electrolyte system of the present invention exhibits superior ionic conductivity at low temperatures.

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium metal battery electrolyte for ultra-low temperature compatible, without a negative electrode, characterized in that, It includes a sodium salt and a mixed solvent, wherein the mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (6~9.5):(0.5~4); the first solvent is 1,2-dimethoxypropane and the second solvent is dipropylene glycol dimethyl ether.

2. The low-temperature compatible sodium metal battery electrolyte without a negative electrode according to claim 1, characterized in that, The mixed solvent is composed of a first solvent and a second solvent in a volume ratio of (8~9.5):(0.5~2); the concentration of sodium salt in the electrolyte is 0.5 M~1 M.

3. The low-temperature compatible sodium metal battery electrolyte without a negative electrode according to claim 2, characterized in that, The concentration of sodium salt in the electrolyte is 0.5 M.

4. The low-temperature compatible sodium metal battery electrolyte without a negative electrode according to claim 1, characterized in that, The sodium salt is sodium hexafluorophosphate.

5. The sodium metal battery electrolyte for ultra-low temperature compatibility according to claim 1, characterized in that, The electrolyte for the low-temperature compatible, electrodeless sodium metal battery is composed of sodium salt and a mixed solvent.

6. The low-temperature compatible sodium metal battery electrolyte without a negative electrode according to claim 1, characterized in that, The aforementioned low-temperature compatible, electrodeless sodium metal battery electrolyte is compatible with temperatures down to -60°C.

7. A method for preparing the low-temperature compatible sodium metal battery electrolyte as described in claim 1, characterized in that, include: The first solvent and the second solvent are mixed to obtain a mixed solvent; Under an inert atmosphere, sodium salt is added to the mixed solvent and stirred at room temperature until completely dissolved to obtain the low-temperature compatible sodium metal battery electrolyte without a negative electrode.

8. A sodium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the low-temperature compatible sodium metal battery electrolyte without a negative electrode as described in any one of claims 1 to 6, or the low-temperature compatible sodium metal battery electrolyte without a negative electrode prepared by the preparation method described in claim 7.

9. The sodium metal battery according to claim 8, characterized in that, The negative electrode is a copper current collector or an aluminum current collector, and the positive electrode active material is sodium vanadium phosphate.

Images