Heterogeneous functional electrolyte for anode-free sodium metal batteries, its preparation method, applications, and anode-free sodium metal batteries.

Abstract

This invention belongs to the field of anode-free sodium metal battery technology, specifically disclosing a heterogeneous functional electrolyte for anode-free sodium metal batteries, its preparation method, application, and the anode-free sodium metal battery itself. The heterogeneous functional electrolyte comprises a solution of an organic solvent, a sodium salt, and an insoluble additive. The additive is a material composed of component B, which has been pre-treated by plasma and ultrasonically assembled with component A. Component A is a fullerene; component B includes at least one of Zn-MOF, polydopamine, and tin dioxide. This invention innovatively uses a synergistic plasma-ultrasonic modified component containing components A and B as an additive, thus adapting to the charge-discharge characteristics of anode-free sodium metal batteries and significantly improving their high-temperature stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium metal battery technology without negative electrode, and particularly relates to an electrolyte additive for sodium metal battery without negative electrode. Background Technology

[0002] As the application of lithium-ion batteries continues to expand in consumer electronics, electric vehicles, and energy storage, the finite nature of lithium resources is becoming increasingly apparent. Against this backdrop, sodium-based batteries have attracted widespread attention due to their reliance on abundant sodium resources in the Earth's crust, demonstrating significant strategic value, particularly in cost-sensitive large-scale energy storage applications. However, sodium-ion batteries suffer from issues such as low specific capacity, which hinders their commercialization.

[0003] Electrodeless sodium metal batteries employ a unique structural design, eliminating the traditional sodium storage material on the negative electrode side and retaining only the current collector. During the initial charge, sodium metal is directly deposited on the surface of the current collector, and the battery operates as a sodium metal battery in subsequent cycles. This not only results in a higher operating voltage but also significantly improves mass and volumetric energy density due to the reduction in the use of inactive materials. However, compared to systems containing negative electrode active materials, the electrodeless structure consumes a large amount of active sodium from the positive electrode to form the solid electrolyte interphase (SEI) film during the initial charge-discharge process, accompanied by irreversible side reactions, leading to increased capacity loss and reduced cycle life. Furthermore, poor electrochemical performance at high temperatures has become a major obstacle to the commercialization of electrodeless sodium metal batteries. Therefore, developing an electrolyte with high chemical stability and excellent film-forming ability is crucial to improving the performance of electrodeless sodium metal batteries.

[0004] Currently, electrolyte design for this system largely follows the optimization strategies of conventional sodium batteries, lacking a systematic solution for structures without a negative electrode. For example, Chinese patent CN117638229A proposes a composite electrolyte additive that combines organic small molecules with inorganic sodium salts to improve performance; CN118554011A discloses an electrolyte system containing multiple sodium salts and solvents, aiming to improve interfacial stability; and CN19230941A reports a modified electrolyte based on hexagonal boron nitride nanodispersive phases for optimizing sodium deposition behavior.

[0005] Although the above technologies have improved the electrochemical performance of batteries to some extent, they still have significant limitations in terms of overall performance, and there is an urgent need to further explore more targeted electrolyte design and material innovation. Summary of the Invention

[0006] To address the problems of severe interfacial side reactions, unstable SEI film, uneven sodium deposition, and poor high-temperature performance in current electrodeless sodium metal battery electrolyte systems, the primary objective of this invention is to provide a heterogeneous functional electrolyte for electrodeless sodium metal batteries, which is designed to adapt to the physicochemical characteristics of electrodeless batteries and improve their cycle stability and high-temperature performance.

[0007] The second objective of this invention is to provide a method for preparing a heterogeneous functional electrolyte and its application in a sodium metal battery without a negative electrode.

[0008] A third objective of this invention is to provide a sodium metal battery without a negative electrode that includes the heterogeneous functional electrolyte.

[0009] Unlike conventional battery systems, in sodium metal batteries without a negative electrode, the current collector is directly exposed to the electrolyte, leading to intensified interfacial side reactions and rapid consumption of active sodium. Therefore, the electrolyte needs to possess higher chemical stability and an optimized solvation structure. To address this, this invention introduces functionalized additives to directionally regulate the electrolyte system. Specific improvements include:

[0010] A heterogeneous functional electrolyte for a negative electrode-free sodium metal battery is a solution containing an organic solvent, a sodium salt, and an insoluble additive.

[0011] The additive is a material in which component B is pre-treated by plasma and ultrasonically assembled with component A, wherein component A is fullerene; and component B includes at least one of Zn-MOF, polydopamine, and tin dioxide.

[0012] To adapt to the charging and discharging characteristics of a non-polar sodium metal battery, this invention innovatively uses a synergistic plasma-ultrasonic modified component containing component A and component B as an additive. This adapts to the charging and discharging characteristics of a non-polar sodium metal battery and can significantly improve the high-temperature stability of the non-polar sodium metal battery.

[0013] The electrolyte described in this invention, in conjunction with the heterogeneous additives, can optimize the sodium ion solvation structure, enhance the sodium affinity of the current collector surface, guide the uniform deposition and stripping of sodium ions, and reduce sodium loss caused by side reactions during the charge and discharge process of a negative electrode-free sodium-ion battery, thereby significantly improving the battery's cycle performance and high-temperature performance.

[0014] In this invention, the special control of the composition of components A and B, as well as the combination of plasma-ultrasound joint modification, are the key to synergistically improving the performance of electrolytes in negative electrode-free batteries.

[0015] In this invention, the Zn-MOF in component B is ZIF-8.

[0016] Preferably, component B comprises component B1 and component B2, wherein component B1 is Zn-MOF and component B2 is tin dioxide. Preferably, the weight ratio of component B1 to component B2 is 1:0.5~2. Preferably, the combination of this preferred component B and component A, in conjunction with the aforementioned modification process, can unexpectedly achieve synergy, thereby enhancing the performance of the negative electrode-free electrolyte.

[0017] In this invention, the weight ratio of component A to component B in the additive is 1:1 to 20; preferably 1:3 to 15; and more preferably 1:5 to 10.

[0018] The plasma treatment atmosphere is at least one of oxygen, argon, nitrogen or air, the plasma treatment power is 50~300 W, and the plasma treatment time is 5~30 min; more preferably, the plasma treatment power is 60~150 W, more preferably 80~120 W, and the plasma treatment time is 10~20 min.

[0019] The ultrasonic assembly power is 50~400 W, and the ultrasonic assembly time is 0.5~3 h; preferably, the ultrasonic assembly power is 100~300 W, more preferably 150~250 W, and the ultrasonic assembly time is 1.5~2.5 h.

[0020] In this invention, the organic solvent includes carbonate solvents and / or ether solvents;

[0021] Preferably, the carbonate solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate;

[0022] Preferably, the ether solvent is selected from at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0023] In this invention, the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium di(fluorooxalateborate).

[0024] In this invention, the concentration of sodium salt in the heterogeneous functional electrolyte is 0.5~1.5 mol / L, and more preferably 0.8~1 mol / L; the concentration of additive is 40~120 g / L, and more preferably 45~105 g / L.

[0025] The present invention also provides a method for preparing the heterogeneous functional electrolyte for a negative electrode-free sodium metal battery, wherein an organic solvent, a sodium salt, and an additive are mixed to obtain the electrolyte.

[0026] As an optional solution, the additive can be obtained by mixing component A and component B, and the mixing can be a solid-phase mixing or a liquid-phase mixing.

[0027] The present invention also provides an application of the heterogeneous functional electrolyte for the non-negative electrode sodium metal battery, which is used as an electrolyte to prepare a non-negative electrode sodium metal battery.

[0028] The present invention also provides a negative electrode-free sodium metal battery, characterized in that the electrolyte is a heterogeneous functional electrolyte for the negative electrode-free sodium metal battery.

[0029] Preferably, the active material in the positive electrode of the sodium metal battery without a negative electrode includes at least one of polyanionic compounds, transition metal oxides, and Prussian blue compounds;

[0030] The negative electrode of a sodium metal battery without a negative electrode is the current collector, preferably a carbon-coated aluminum foil.

[0031] In this invention, the sodium metal battery without a negative electrode, apart from containing the electrolyte described in this invention, can have conventional components and structural relationships.

[0032] Beneficial effects

[0033] This invention innovatively modifies component B by plasma treatment and ultrasonic assembly with component A. This improves the physicochemical compatibility of components A and B, enhances their chemical interactions and coupling, effectively regulates the solvation structure of the electrolyte, induces the formation of a thin and robust SEI film rich in inorganic components, significantly improves the uniformity and reversibility of sodium deposition / stripping, improves the compatibility of anode-free sodium metal batteries, and thus improves the overall electrochemical performance of anode-free sodium metal batteries, especially in terms of significantly improved high-temperature cycling stability. Attached Figure Description

[0034] Figure 1 The first charge-discharge curves for Example 1 and Comparative Example 1 are shown below.

[0035] Figure 2 The first charge-discharge curves for Example 2 and Comparative Example 1 are shown below.

[0036] Figure 3 The first charge-discharge curves for Example 3 and Comparative Example 1 are shown below.

[0037] Figure 4 The charge-discharge cycle curves are for Examples 1, 2, 3 and Comparative Example 1; Detailed Implementation

[0038] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the implementation of the present invention without creative effort are all within the scope of protection of the present invention.

[0039] Example 1

[0040] Step 1: Preparation of Additive A

[0041] ZIF-8 nanoparticles were placed in a plasma reaction chamber, evacuated, and then purged with oxygen. The mixture was then plasma-treated at a radio frequency power of 100 W for 15 minutes. The treated ZIF-8 and fullerene (C60) were dispersed in toluene at a mass ratio of 5:1 and ultrasonically dispersed at a power of 200 W for 2 hours to allow for complete self-assembly. The solid product was separated by centrifugation, washed with toluene, and then vacuum-dried at 80 °C for 12 hours to obtain the ZIF-8@fullerene composite filler (additive A).

[0042] Step 2: Electrolyte preparation:

[0043] The electrolyte consists of an organic solvent, a sodium salt, and additives, and is prepared according to the following steps:

[0044] Organic solvent: diethylene glycol dimethyl ether;

[0045] Additive: ZIF-8@fullerene composite filler (additive A) obtained in step 1, with a concentration of 50 g / L;

[0046] Sodium salt: Sodium hexafluorophosphate, concentration 1 mol / L.

[0047] The specific preparation process of the electrolyte is as follows: Under a high-purity argon atmosphere (water content and oxygen content are both controlled at ≤0.01 ppm), the appropriate amount of sodium salt is accurately weighed and fully dissolved in an organic solvent to obtain the basic electrolyte; then, a specified amount of ZIF-8@fullerene composite filler is added to it, mixed evenly, and allowed to stand to ensure that the filler is evenly dispersed and free from agglomeration, thus obtaining the target electrolyte.

[0048] Performance testing

[0049] To evaluate the electrochemical performance of the prepared electrolyte, a sodium metal battery without a negative electrode was assembled and tested using it. The specific steps are as follows:

[0050] Carbon-coated aluminum foil was used as the negative electrode current collector, and was cut into 14 mm diameter discs using a cutting machine, with the carbon coating facing towards the positive electrode. The positive electrode active material was sodium vanadium phosphate (NVP), and its composition was NVP:conductive carbon black:PVDF = 8:1:1 (mass ratio). A porous single-layer polypropylene membrane was used as the separator. A 2032 coin cell was assembled in a glove box under a high-purity argon atmosphere (O2 and H2O content both <0.01 ppm).

[0051] Test 1: Performance at room temperature:

[0052] After battery assembly, the loading of the positive electrode active material in the NVP was 5.2 mg / cm³. 2 Electrochemical tests were conducted under the following conditions: voltage range 2.0-3.8V and test temperature 30℃. First, a constant current charge-discharge activation was performed at a current density of 10 mA / g, followed by a constant current charge-discharge cycle test at a current density of 100 mA / g to evaluate the electrochemical performance of the full cell.

[0053] Test 2: High Temperature Performance

[0054] Compared to Test 1, the difference is that the test temperature was changed to 60 ℃, while the other conditions are the same as Test 1.

[0055] Example 2

[0056] Compared with Example 1, the only difference is that the additive in step 1 is prepared by the following different steps: Preparation of additive B:

[0057] Polydopamine nanospheres were placed in a plasma reaction chamber, evacuated, and then purged with argon gas. The mixture was then plasma-treated at a radio frequency power of 80 W for 10 minutes. The treated polydopamine and fullerene (C70) were dispersed in ethanol at a mass ratio of 10:1 and ultrasonically dispersed at a power of 150 W for 1.5 hours to ensure complete composite formation. The solid product was separated by centrifugation, washed with ethanol, and then vacuum-dried at 60 °C for 8 hours to obtain the polydopamine / fullerene composite filler (additive B).

[0058] In step 2, the dosage of additive B was adjusted to 80 g / L; at the same time, the sodium salt was replaced with sodium difluorooxalate borate at a concentration of 0.8 mol / L, and other conditions were the same as in Example 1, and tests were conducted according to Test 1 and Test 2 of Example 1.

[0059] Example 3

[0060] The only difference from Example 1 is that in step 2, the organic solvent in the electrolyte is replaced with ethylene carbonate, and the concentration of additive A is increased to 100 g / L. Other conditions are the same as in Example 1, and tests are performed according to Test 1 and Test 2 of Example 1.

[0061] Example 4

[0062] Compared with Example 1, the only difference is that the additive in step 1 is prepared by the following different steps: Preparation of additive C:

[0063] Tin dioxide nanoparticles were placed in a plasma reaction chamber, evacuated, and then purged with oxygen. The mixture was then plasma-treated at a radio frequency power of 120 W for 20 minutes. The treated tin dioxide and fullerene (C60) were dispersed in N-methylpyrrolidone at a mass ratio of 8:1 and ultrasonically dispersed at a power of 250 W for 2.5 hours to stabilize the composite. The solid product was separated by centrifugation, washed with ethanol, and then vacuum-dried at 100 °C for 10 hours to obtain the SnO2 / fullerene composite filler (additive C).

[0064] All other operations and parameters are the same as in Example 1; and tests are performed according to Test 1 and Test 2 of Example 1.

[0065] Example 5

[0066] Compared with Example 1, the only difference is that in step 2, the additive is replaced with a mixture of additive A and additive C in a mass ratio of 1:1, while the total amount of additives remains unchanged (50 g / L). All other operations and parameters are the same as in Example 1, and tests are performed according to Test 1 and Test 2 of Example 1.

[0067] Comparative Example 1

[0068] Compared with Example 1, the only difference is that no additives were added to the electrolyte in step 2, and all other operations and parameters were the same as in Example 1; and tests were conducted according to Test 1 and Test 2 of Example 1.

[0069] Comparative Example 2

[0070] Compared with Example 1, the difference is that the additive was directly mixed with ZIF-8 and fullerene (C60) at a mass ratio of 5:1, and the plasma treatment and ultrasonic dispersion steps were omitted in the preparation process. Other conditions were the same as in Example 1. Tests were performed according to Test 1 and Test 2 of Example 1.

[0071] Comparative Example 3

[0072] Compared with Example 2, the difference is that the additive is made by directly mixing polydopamine nanospheres and fullerene (C70) at a mass ratio of 10:1. The plasma treatment and ultrasonic dispersion steps are omitted in the preparation process, and other conditions are the same as in Example 2.

[0073] Comparative Example 4

[0074] Compared with Example 1, the difference is that the additive is only untreated ZIF-8, and the amount of additive is the same as the total amount of additive in Example 1, while other conditions are the same as in Example 1. Tests were conducted according to Test 1 and Test 2 of Example 1.

[0075] Comparative Example 5

[0076] Compared with Example 1, the difference is that the additive is only untreated fullerene (C60), and the amount of additive is the same as the total amount of additive in Example 1, while other conditions are the same as in Example 1. Tests were conducted according to Test 1 and Test 2 of Example 1.

[0077] Comparative Example 6

[0078] Compared with Example 2, the difference is that the additive is only untreated polydopamine nanospheres, and the amount of additive is the same as the total amount of additive in Example 2, while other conditions are the same as in Example 2.

[0079] Comparative Example 7

[0080] Compared with Example 4, the difference is that the additive is only untreated tin dioxide nanoparticles, and the amount of additive is the same as the total amount of additive in Example 1, while other conditions are the same as in Example 4.

[0081] Comparative Example 8

[0082] Compared with Example 1, the difference is that in step 1, ZIF-8 is replaced by an equal weight of MIL-101(Cr), and the MIL-101(Cr)@fullerene composite filler is obtained through the treatment in step 1; other conditions are the same as in Example 1. And tests are performed according to Test 1 and Test 2 of Example 2.

[0083] Comparative Example 9

[0084] Compared with Example 2, the difference is that in step 1, polyaniline is used to replace polydopamine by an equal weight, and polyaniline@C70 composite filler is obtained after the treatment in step 1; other conditions are the same as in Example 2.

[0085] Comparative Example 10

[0086] Compared with Example 4, the difference is that in step 1, titanium dioxide is used to replace tin dioxide by the same weight, and titanium dioxide / fullerene composite filler is obtained through step 1. Other conditions are the same as in Example 4.

[0087] Comparative Example 11

[0088] Compared to Example 1, the only difference is that in step 1, ZIF-8 was not subjected to plasma treatment, but was directly subjected to ultrasonic treatment with C60. All other operations and parameters were the same as in Example 1. Tests were performed according to Test 1 and Test 2 of Example 2.

[0089] The test results under the test conditions of each case test 1 are as follows:

[0090] Table 1: Performance data at room temperature under Test 1

[0091]

[0092] Table 2: High-temperature performance data (60℃) under Test 2

[0093]

[0094] The data in Tables 1 and 2 show that plasma treatment of component B followed by ultrasonic assembly modification of component A improves the physicochemical compatibility of components A and B, enhances their chemical interactions and coupling relationship, effectively regulates the solvation structure of the electrolyte, induces the formation of a thin and robust SEI film rich in inorganic components, significantly improves the uniformity and reversibility of sodium deposition / stripping, improves the compatibility of anode-free sodium metal batteries, and thus improves the overall electrochemical performance of anode-free sodium metal batteries, especially in terms of a significant improvement in high-temperature cycling stability.

[0095] Furthermore, as can be seen from Examples 1 and 5, the performance can be further enhanced with the preferred combination of additives.

[0096] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A heterogeneous functional electrolyte for a sodium metal battery without a negative electrode, characterized in that, A solution containing organic solvents, sodium salts, and insoluble additives; The additive is a material in which component B is pre-treated by plasma and ultrasonically assembled with component A, wherein component A is fullerene; and component B includes at least one of Zn-MOF, polydopamine, and tin dioxide.

2. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in claim 1, characterized in that, In component B, the Zn-MOF is ZIF-8; Preferably, component B includes component B1 and component B2, wherein component B1 is Zn-MOF and component B2 is tin dioxide; preferably, the weight ratio of component B1 to component B2 is 1:0.5~2.

3. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in claim 1, characterized in that, In the additive, the weight ratio of component A to component B is 1:1 to 20; preferably 1:3 to 15; more preferably 1:5 to 10.

4. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in any one of claims 1 to 3, characterized in that, The atmosphere for plasma treatment is at least one of oxygen, argon, nitrogen, or air; the power of plasma treatment is 50-300 W; and the plasma treatment time is 5-30 min. The ultrasonic assembly power is 50~400 W, and the ultrasonic assembly time is 0.5~3 h; Further preferred, the plasma treatment power is 60~150W, preferably 80~120W, and the plasma treatment time is 10~20 min; the ultrasonic assembly power is 100~300W, preferably 150~250W, and the ultrasonic assembly time is 1.5~2.5 h.

5. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in claim 1, characterized in that, The organic solvents include carbonate solvents and / or ether solvents; Preferably, the carbonate solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate; Preferably, the ether solvent is selected from at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

6. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in claim 1, characterized in that, The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium di(fluorooxalateborate).

7. The heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in claim 1, characterized in that, In the heterogeneous functional electrolyte, the concentration of sodium salt is 0.5~1.5 mol / L; the concentration of additives is 40~120 g / L.

8. A method for preparing a heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in any one of claims 1 to 7, characterized in that, The organic solvent, sodium salt, and additives are mixed together to obtain the product.

9. The application of the heterogeneous functional electrolyte for a sodium metal battery without a negative electrode as described in any one of claims 1 to 7, characterized in that, It was used as an electrolyte in the preparation of a negative electrode-free sodium metal battery.

10. A sodium metal battery without a negative electrode, characterized in that, The electrolyte is the heterogeneous functional electrolyte for a negative electrode-free sodium metal battery as described in any one of claims 1 to 7; Preferably, the active material in the positive electrode of the sodium metal battery without a negative electrode includes at least one of polyanionic compounds, transition metal oxides, and Prussian blue compounds; The negative electrode of a sodium metal battery without a negative electrode is the current collector, preferably a carbon-coated aluminum foil.

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