An electrolyte for a sodium metal battery without a negative electrode, a preparation method thereof, and an application thereof

Abstract

The present invention belongs to the technical field of sodium-ion battery electrolytes, and specifically discloses an anode-free sodium metal battery electrolyte, a preparation method thereof, and an application thereof. The anode-free sodium metal battery electrolyte includes an organic solvent, a sodium salt, and a sodium supplement additive; the sodium supplement additive includes at least one of sodium trimethylsilanolate and sodium amide. Through reasonable configuration, the electrolyte of the present invention forms a dense solid electrolyte interface film (SEI film) at the electrode-electrolyte interface of the anode-free sodium metal battery, effectively compensating for the irreversible loss of active sodium during the SEI formation stage, reducing the reversible capacity loss during the cycling process, and improving the cycling stability and safety of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery electrolytes, and particularly relates to an electrolyte for a sodium metal battery without a negative electrode, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing expansion of lithium-ion batteries in markets such as consumer electronics, electric vehicles, and energy storage, the limited nature of lithium resources has attracted people's attention. Sodium-based batteries have gradually received attention due to their reliance on the abundant sodium element on the earth, and they have important strategic significance in cost-sensitive applications such as energy storage. However, problems such as the low specific capacity of sodium-ion batteries have restricted their large-scale commercial applications.

[0003] In a sodium metal battery without a negative electrode, the traditional sodium-ion insertion material is omitted on the negative electrode side, and only the current collector is retained. Sodium metal is deposited on the surface of the current collector during the first charging process, and then it can operate as a sodium metal battery, providing a higher working voltage and significantly improving the mass and volume energy density by reducing the mass and volume of the battery. However, compared with an electrode with a negative electrode active material, during the first charge and discharge process of a sodium metal battery without a negative electrode, a large amount of active sodium from the positive electrode material is consumed on the negative electrode side to form a SEI film, and some side reactions also occur. These irreversible side reactions seriously reduce the charge and discharge capacity and cycle life of the battery. Therefore, how to design an electrolyte with high chemical stability and good sodium supplementation performance is extremely crucial for improving the performance of a sodium metal battery without a negative electrode.

[0004] However, for a sodium metal battery without a negative electrode, the prior art lacks a targeted improvement scheme for the sodium supplementation electrolyte. The optimization of its electrolyte mainly still follows the conventional electrolyte modification scheme. For example, the Chinese patent document with the publication number CN 117638229A discloses an electrolyte additive and an electrolyte for a sodium-ion battery without a negative electrode, and the specifically recorded electrolyte is a composite electrolyte of an organic small molecule additive and an inorganic sodium salt additive. Another example is that the Chinese patent document with the publication number CN 118554011A discloses an electrolyte for a sodium metal battery without a negative electrode and a sodium metal battery without a negative electrode. The modified electrolyte involved includes sodium salts, organic solvents, and additives, and the additives include one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and 2-methyltetrahydrofuran. Another example is that the Chinese patent document with the publication number CN 19230941A discloses a sodium metal battery without a negative electrode based on a hexagonal boron nitride modified electrolyte and a current collector, and the specifically recorded electrolyte is an organic electrolyte with a nano-dispersed phase.

[0005] In summary, although the prior art can improve the electrochemical performance of a sodium metal battery without a negative electrode, there is still a large room for improvement. Summary of the Invention

[0006] In view of the above existing deficiencies, the present invention provides an electrolyte for a sodium metal battery without a negative electrode, a preparation method thereof, and an application thereof. By adding a sodium supplement additive (sodium trimethylsilanolate and / or sodium amide) to the electrolyte, the irreversible active sodium loss in constructing a stable SEI film at the electrode-electrolyte interface is reduced, the reversible capacity loss during cycling is decreased, and the cycle stability and safety of the battery are improved.

[0007] To achieve the above object, the present invention provides an electrolyte for a sodium metal battery without a negative electrode, comprising an organic solvent, a sodium salt, and a sodium supplement additive; the sodium supplement additive comprises at least one of sodium trimethylsilanolate and sodium amide.

[0008] In response to the challenges of unstable SEI film and low first charging capacity faced by sodium metal batteries without a negative electrode, the present invention innovatively regulates the electrolyte system, specifically: by introducing a "self-sacrificial" sodium supplement additive (sodium trimethylsilanolate and / or sodium amide) through the design of the electrolyte system, during the first charging process of the battery, the positive electrode undergoes an oxidation reaction to release sodium ions, which directionally compensate for the active sodium consumed during the SEI formation stage and neutralize the sodium loss caused by other side reactions. This in-situ sodium supplement strategy can effectively meet the ion supply for sodium metal deposition and significantly improve the first charging capacity.

[0009] According to one aspect of the present invention, the concentration of the sodium supplement additive in the electrolyte is 0.1 - 0.5 mol / L. It should be noted that this concentration range can effectively compensate for sodium loss, form a stable SEI film, and avoid an increase in the viscosity of the electrolyte caused by excessive additives.

[0010] According to one aspect of the present invention, the organic solvent comprises at least one of carbonate organic solvents and ether organic solvents.

[0011] According to one aspect of the present invention, the carbonate organic solvents comprise at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate; the ether organic solvents comprise at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0012] According to one aspect of the present invention, the concentration of the organic solvent in the electrolyte is 60 - 90 wt%. It should be noted that the organic solvent at this concentration is to ensure that the electrolyte has appropriate fluidity and wettability.

[0013] According to one aspect of the present invention, the sodium salt comprises at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium difluoro(oxalato)borate.

[0014] According to one aspect of the present invention, the concentration of the sodium salt in the electrolyte is 0.5 - 1.5 mol / L. It should be noted that within this concentration range, sufficient sodium ion carriers can be ensured, improving the ionic conductivity.

[0015] Based on the same inventive concept, the present invention also provides a method for preparing the non-aqueous anode sodium metal battery electrolyte described above, comprising the following steps:

[0016] S1. Under an inert atmosphere condition, fully dissolve the sodium salt in an organic solvent to obtain a basic electrolyte;

[0017] S2. Add an additive to the basic electrolyte, mix evenly, and let it stand until no solid precipitates, to obtain the non-aqueous anode sodium metal battery electrolyte.

[0018] According to one aspect of the present invention, in step S1, the inert atmosphere is argon.

[0019] It should be noted that in the system of step S1, it is necessary to ensure the purity, moisture content, and oxygen content of the inert atmosphere.

[0020] Exemplarily, the inert atmosphere is a high-purity argon atmosphere, and the moisture content and oxygen content do not exceed 0.01 ppm.

[0021] Based on the same inventive concept, the present invention also provides a non-aqueous anode sodium metal battery, comprising a positive electrode, a separator, an electrolyte, and a current collector. The electrolyte is the non-aqueous anode sodium metal battery electrolyte described above or the non-aqueous anode sodium metal battery electrolyte prepared by the above-described preparation method.

[0022] According to one aspect of the present invention, the positive electrode is at least one of a polyanion compound, a transition metal oxide, and a Prussian blue compound; the current collector is a carbon-coated aluminum foil.

[0023] Advantages of the present invention:

[0024] (1) The sodium supplement additive of the present invention can participate in the construction of the SEI film during the first charge and discharge process as a sodium source, in-situ compensating for the irreversible loss of active sodium and significantly improving the electrochemical performance of the battery.

[0025] (2) The present invention provides support for solving the key problem of irreversible loss of active sodium during the initial charging process in a non-aqueous anode sodium metal battery by introducing a "self-sacrificing" type sodium supplement additive (sodium trimethylsilanolate and / or sodium amide) into the non-aqueous anode sodium metal battery electrolyte. Sodium amide exhibits significant electrochemical characteristics, with a theoretical specific capacity as high as 686 mAh·g -1, it is completely oxidized during the first charging process to release sodium ions, effectively compensating for the irreversible loss of active sodium. Its efficient sodium transfer optimizes the electrode surface kinetics; and its oxidation products are gaseous nitrogen, hydrogen, and soluble hydrazine, avoiding the residual "dead mass" in the battery and providing a key path for improving the energy density of the battery. The functionality of sodium trimethylsilanolate stems from the characteristics of the trimethylsilyl group in its molecule. During the first electrochemical cycle, it can efficiently remove hydrofluoric acid generated by side reactions of the electrolyte through the cleavage of the silicon-oxygen bond, generating trimethylfluorosilane ((CH3)3SiF) and oxygen, effectively removing by-products that are prone to corrode the electrode, and releasing sodium ions to achieve in-situ sodium supplementation of the electrode material, thereby promoting the formation of a thin, strong, and stable SEI film, enhancing the interfacial mechanical strength and chemical stability, and achieving a synergistic improvement in the electrochemical performance and cycle life of the battery. Brief Description of the Drawings

[0026] Figure 1 It is a comparative chart of the first charge-discharge curves of the batteries prepared from the electrolytes of Example 1 and Comparative Example 1 of the present invention;

[0027] Figure 2 It is a comparative chart of the first charge-discharge curves of the batteries prepared from the electrolytes of Example 2 and Comparative Example 1 of the present invention;

[0028] Figure 3 It is a comparative chart of the cycle capacity curves of the batteries prepared from the electrolytes of Examples 1-2 and Comparative Example 1 of the present invention. Detailed Embodiments

[0029] To make the present invention easier to understand, the present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below have the same meaning as understood by those of ordinary skill in the art; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0030] Example 1

[0031] A sodium metal battery electrolyte without a negative electrode is composed of an organic solvent, a sodium salt, and a sodium supplementation additive, specifically:

[0032] The organic solvent is diethylene glycol dimethyl ether;

[0033] The sodium supplementation additive is sodium trimethylsilanolate, with a concentration of 0.2 mol / L;

[0034] The sodium salt is sodium hexafluorophosphate with a concentration of 1 mol / L.

[0035] A method for preparing an electrolyte for a sodium metal battery without a cathode includes the following steps:

[0036] S1. Under the condition of a high-purity argon atmosphere (controlling the moisture and oxygen content to not exceed 0.01 ppm), dissolve the corresponding amount of sodium salt in an organic solvent to obtain a basic electrolyte.

[0037] S2. Add the corresponding amount of sodium supplement additive to the basic electrolyte, mix evenly, and let it stand to ensure that the sodium supplement additive is evenly dispersed and there is no precipitation, thereby obtaining an electrolyte for a sodium metal battery without a cathode.

[0038] Performance testing:

[0039] To verify the performance of the prepared electrolyte for a sodium metal battery without a cathode, the inventor assembled a sodium metal battery without a cathode using the following electrolyte for a sodium metal battery without a cathode, and then investigated the performance of the electrolyte for a sodium metal battery without a cathode by testing the performance of the obtained sodium metal battery without a cathode. Specifically, it includes:

[0040] Use a cutter to cut the carbon-coated aluminum foil into a sample piece with a diameter of 14 mm as the negative electrode current collector of the sodium metal battery without a cathode (the negative carbon layer faces the positive electrode direction), use sodium iron pyrophosphate (NFPP) as the positive electrode (the material composition ratio of the positive electrode material is NFPP: conductive carbon black: PVDF = 9:0.5:0.5) to assemble the battery, use a porous single-layer polypropylene membrane as the separator, and assemble a 2032 coin cell in a glove box (high-purity argon atmosphere, where the oxygen and water content is less than 0.01 ppm). Then, under the load of NFPP being 14.2 mg·cm -2 at a load of, in the voltage range of 1.5 - 3.9 V, first perform activation of constant current and constant voltage charge and discharge at a current density of 100 mA·g -1 (the cut-off current density is 5 mA·g -1 ), and then perform constant current charge and discharge testing on the full cell at a current density of 600 mA·g -1 (the test temperature is 30 °C).

[0041] Example 2

[0042] The difference between this example and Example 1 is: changing the type of sodium supplement additive, that is, replacing sodium trimethylsilanolate with sodium amide, and other steps and parameters are the same as those in Example 1.

[0043] Example 3

[0044] The difference between this example and Example 1 is: changing the type of sodium salt, that is, replacing sodium tetrafluoroborate with sodium hexafluorophosphate. Other steps and parameters are the same as those in Example 1.

[0045] Example 4

[0046] The difference between this example and Example 2 is: changing the type of sodium salt, that is, replacing sodium tetrafluoroborate with sodium hexafluorophosphate. Other steps and parameters are the same as those in Example 2.

[0047] Example 5

[0048] The difference between this example and Example 1 is: changing the type of organic solvent, that is, replacing diethylene glycol dimethyl ether with ethylene carbonate. Other steps and parameters are the same as those in Example 1.

[0049] Example 6

[0050] The difference between this example and Example 2 is: changing the type of organic solvent, that is, replacing diethylene glycol dimethyl ether with ethylene carbonate. Other steps and parameters are the same as those in Example 2.

[0051] Example 7

[0052] The difference between this example and Example 1 is: changing the type of organic solvent, that is, replacing diethylene glycol dimethyl ether with 2-methyltetrahydrofuran. Other steps and parameters are the same as those in Example 1.

[0053] Example 8

[0054] The difference between this example and Example 2 is: changing the type of organic solvent, that is, replacing diethylene glycol dimethyl ether with 2-methyltetrahydrofuran. Other steps and parameters are the same as those in Example 2.

[0055] Example 9

[0056] The difference between this example and Example 1 is: changing the type of sodium supplementation additive, that is, replacing sodium trimethylsilanolate (0.2 mol / L) with sodium trimethylsilanolate (0.1 mol / L) and sodium amide (0.1 mol / L). Other steps and parameters are the same as those in Example 1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is: no sodium supplementation additive is added. Other steps and parameters are the same as those in Example 1.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is: replacing the sodium supplementation additive in the electrolyte with trimethylsilanol. Other steps and parameters are the same as those in Example 1.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the sodium supplement additive in the electrolyte is replaced with sodium bis(trimethylsilyl)amide. Other steps and parameters are the same as those in Example 1.

[0063] Comparative Example 4

[0064] The difference between this comparative example and Example 1 is that no sodium salt is added to the electrolyte, and the sodium supplement additive is sodium trimethylsilanolate with a concentration of 1.2 mol·L -1 。

[0065] Results and analysis:

[0066] The relevant performance test results of the batteries prepared from the electrolytes of Examples 1-9 and Comparative Examples 1-4 are shown in Table 1 below:

[0067] Table 1:

[0068]

[0069] As can be seen from Table 1, the sodium supplement additives introduced into the electrolyte as additional sodium sources can effectively release sodium ions through oxidation reactions during the first charging process, compensate for the irreversible loss of active sodium caused by the formation of the SEI film and side reactions, and improve the first charge specific capacity and capacity retention rate of the battery. From Figure 1 and Figure 2 it can be seen that during the constant voltage charging process (charging cut-off voltage 3.9 V, cut-off current 5 mA·g -1 ), both sodium trimethylsilanolate and sodium amide exhibit excellent sodium supplement capabilities. Compared with Comparative Example 1 without a sodium supplement additive, the first charge-discharge specific capacities are 13.5% and 30.2% higher, respectively. In addition, comparing Examples 1-2 with Comparative Examples 2-3, the first charge-discharge specific capacities and capacity retention rates of Examples 1-2 are better than those of Comparative Examples 2-3, indicating the uniqueness, creativity, and superiority of the sodium supplement additives provided by the present invention. And from Comparative Example 4, it can be seen that sodium salts are crucial for maintaining ion transport and electrode stability. From Figure 3 it can be seen that the electrolyte system containing the sodium supplement additive can still maintain a high capacity retention rate after 30 cycles. This shows that the role of the additive is not limited to active sodium supplementation, but more importantly, it regulates the interfacial reaction kinetics between the electrode and the electrolyte, induces the formation of a thin, strong, and highly ion-conductive SEI film, inhibits side reactions, and further improves the electrochemical performance and cycle life of the battery.

[0070] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A negative electrode-free sodium metal battery electrolyte, characterized in that: The invention comprises an organic solvent, a sodium salt and a sodium supplement additive; the sodium supplement additive is sodium trimethylsiliconate or sodium trimethylsiliconate and sodium amide; and the concentration of the sodium supplement additive in the electrolyte is 0.1-0.5 mol / L.

2. The negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that: The organic solvent includes at least one of a carbonate organic solvent and an ether organic solvent.

3. The negative electrode-free sodium metal battery electrolyte according to claim 2, characterized in that: The carbonate organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate; the ether organic solvent includes at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

4. The negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that: The concentration of the organic solvent in the electrolyte is 60-90 wt %.

5. The negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that: The sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonylimide), and sodium bis(fluorooxalatoborate).

6. The negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that: The concentration of the sodium salt in the electrolyte is 0.5-1.5 mol / L.

7. The method for preparing a negative electrode-free sodium metal battery electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Under an inert atmosphere, fully dissolving the sodium salt in an organic solvent to obtain a basic electrolyte; S2. Adding a sodium supplement additive to the basic electrolyte, mixing evenly, and standing until no solid is precipitated, thereby obtaining a negative electrode-free sodium metal battery electrolyte.

8. A negative electrode-free sodium metal battery, characterized in that: The invention comprises a positive electrode, a separator, an electrolyte and a current collector, wherein the electrolyte is the negative electrode-free sodium metal battery electrolyte according to any one of claims 1 to 6 or the negative electrode-free sodium metal battery electrolyte prepared by the preparation method according to claim 7.

9. The negative electrode-free sodium metal battery according to claim 8, characterized in that: The positive electrode is at least one of a polyanion compound, a transition metal oxide, and a Prussian blue compound; and the current collector is a carbon-coated aluminum foil.

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