Negative-electrode-free sodium metal battery electrolyte as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium-ion battery electrolyte, and particularly discloses negative-electrode-free sodium metal battery electrolyte as well as a preparation method and application thereof. The negative-electrode-free sodium metal battery electrolyte comprises an organic solvent, sodium salt and a sodium supplementing additive; the sodium supplementing additive comprises at least one of sodium trimethylsilanolate and sodium amide. According to the electrolyte disclosed by the invention, through reasonable configuration, a compact solid electrolyte interface film (SEI film) is formed on an electrode-electrolyte interface of the negative-electrode-free sodium metal battery, so that irreversible loss of active sodium in an SEI forming stage is effectively compensated, reversible capacity loss in a circulating process is reduced, and the circulating stability and safety of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrolytes, and in particular to a negative electrode-free sodium metal battery electrolyte, a preparation method thereof, and applications thereof. Background Art

[0002] As lithium-ion batteries expand their use in markets such as consumer electronics, electric vehicles, and energy storage, the limited availability of lithium resources is gaining attention. Sodium-based batteries, which rely on the abundant sodium element, are gaining increasing attention and hold strategic importance in cost-sensitive applications such as energy storage. However, issues such as the low specific capacity of sodium-ion batteries have hindered their large-scale commercial application.

[0003] Anode-free sodium metal batteries omit traditional sodium ion intercalation materials on the negative electrode side, retaining only the current collector. During the initial charge process, sodium metal is deposited on the current collector surface, and the battery can then operate as a sodium metal battery, providing a higher operating voltage and significantly improving the mass and volume energy density by reducing the mass and volume of the battery. However, compared to electrodes with negative electrode active materials, during the initial charge and discharge process of anode-free sodium metal batteries, the negative electrode side needs to consume a large amount of active sodium from the positive electrode material to form the SEI film, which is also accompanied by certain side reactions. These irreversible side reactions seriously reduce the battery's charge and discharge capacity and cycle life. Therefore, how to design an electrolyte with high chemical stability and good sodium replenishment performance is extremely critical to improving the performance of anode-free sodium metal batteries.

[0004] However, for sodium metal batteries without negative electrodes, the existing technology lacks targeted sodium-supplemented electrolyte improvement solutions. Its electrolyte optimization mainly follows the conventional electrolyte modification solution. For example, the Chinese patent document with publication number CN 117638229A discloses an electrolyte additive and electrolyte for sodium ion batteries without negative electrodes. The electrolyte specifically described is a composite electrolyte of an organic small molecule additive and an inorganic sodium salt additive. For another example, the Chinese patent document with publication number CN 118554011A discloses an electrolyte for sodium metal batteries without negative electrodes and a sodium metal battery without negative electrodes. The modified electrolyte involved includes sodium salt, organic solvent and additives. The additives include sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, and 2-methyltetrahydrofuran. One or more of the following: For example, Chinese patent document CN 19230941A discloses a negative electrode-free sodium battery based on a hexagonal boron nitride-modified electrolyte and a current collector. The electrolyte specifically described is an organic electrolyte with a nano-dispersed phase.

[0005] In summary, although the existing technology can improve the electrochemical performance of negative electrode-free sodium metal batteries, there is still much room for improvement. Summary of the Invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a negative electrode-free sodium metal battery electrolyte, a preparation method and application thereof. The present invention reduces the irreversible active sodium loss in the stable SEI film constructed at the electrode-electrolyte interface by adding sodium-supplementing additives (sodium trimethylsiliconate and / or sodium amide) to the electrolyte, reduces the reversible capacity loss during the cycle, and improves the battery cycle stability and safety.

[0007] In order to achieve the above object, the present invention provides a negative electrode-free sodium metal battery electrolyte, comprising an organic solvent, a sodium salt and a sodium supplement additive; the sodium supplement additive comprises at least one of sodium trimethylsilanol and sodium amide.

[0008] To address the challenges of SEI membrane instability and low first-charge capacity faced by anode-free sodium metal batteries, this invention innovatively modulates the electrolyte system. Specifically, through electrolyte system design, a "self-sacrificial" sodium-supplementing additive (sodium trimethylsiliconate and / or sodium amide) is introduced. During the battery's first charge, an oxidation reaction at the positive electrode releases sodium ions, specifically compensating for the active sodium consumed during the SEI formation phase and neutralizing sodium losses caused by other side reactions. This in-situ sodium-supplementing strategy effectively meets the ion supply for sodium metal deposition and significantly improves the first-charge 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 excessive additives leading to increased electrolyte viscosity.

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

[0011] According to one aspect of the present invention, 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.

[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 this concentration of organic solvent is to ensure that the electrolyte has appropriate fluidity and wettability.

[0013] According to one aspect of the present invention, the sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonylimide), and sodium bis(fluorooxalatoborate).

[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, thereby improving ionic conductivity.

[0015] Based on the same inventive concept, the present invention also provides a method for preparing any of the above-mentioned negative electrode-free sodium metal battery electrolytes, comprising the following steps: S1. Under inert atmosphere, fully dissolving the sodium salt in an organic solvent to obtain a basic electrolyte; S2. Adding additives to the basic electrolyte, mixing evenly, and standing until no solid is precipitated, thereby obtaining a negative electrode-free sodium metal battery electrolyte.

[0016] According to one aspect of the present invention, in step S1 , the inert atmosphere is argon.

[0017] It should be noted that, in the system in step S1, the purity, moisture and oxygen content of the inert atmosphere need to be ensured.

[0018] Exemplarily, the inert atmosphere is a high-purity argon atmosphere, and the moisture and oxygen contents do not exceed 0.01 ppm.

[0019] Based on the same inventive concept, the present invention also provides a negative electrode-free sodium metal battery, comprising a positive electrode, a separator, an electrolyte and a current collector, wherein the electrolyte is any of the negative electrode-free sodium metal battery electrolytes described above or the negative electrode-free sodium metal battery electrolyte prepared by the preparation method described above.

[0020] 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; and the current collector is a carbon-coated aluminum foil.

[0021] Beneficial effects of the present invention: (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 compensate for the irreversible loss of active sodium, and significantly improve the electrochemical performance of the battery.

[0022] (2) The present invention provides support for solving the key problem of irreversible loss of active sodium during the initial charge of anode-free sodium metal batteries by introducing a "self-sacrificial" sodium supplement additive (sodium trimethylsilanol and / or sodium amide) into the electrolyte of anode-free sodium metal batteries. Sodium amide exhibits remarkable electrochemical properties and a theoretical specific capacity of up to 686 mAh g -1During the first charge, it is completely oxidized to release sodium ions, effectively replenishing the irreversible loss of active sodium. Its efficient sodium transfer optimizes the electrode surface dynamics. Its oxidation products are gaseous nitrogen and hydrogen, as well as soluble hydrazine, which avoid residual "dead mass" in the battery and provide a key path for improving the battery's energy density. The functionality of sodium trimethylsiliconate stems from the properties of the trimethylsilyl group in its molecule. During the first electrochemical cycle, it can efficiently remove hydrofluoric acid produced by electrolyte side reactions by breaking the silicon-oxygen bond, generating trimethylfluorosilane ((CH3)3SiF) and oxygen, effectively removing byproducts that are prone to electrode corrosion. It also releases sodium ions to achieve in-situ sodium replenishment of the electrode material, thereby promoting the formation of a thin and strong SEI film, enhancing the mechanical strength and chemical stability of the interface, and achieving a synergistic improvement in the battery's electrochemical performance and cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a comparison chart of the first cycle charge and discharge curves of batteries prepared with the electrolytes of Example 1 of the present invention and Comparative Example 1; Figure 2 This is a comparison chart of the first cycle charge and discharge curves of batteries prepared with the electrolytes of Example 2 of the present invention and Comparative Example 1; Figure 3 This is a comparison chart of the cycle capacity curves of batteries prepared with the electrolytes of Examples 1-2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0024] To make the present invention easier to understand, the present invention is further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in this field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0025] Example 1 A negative electrode-free sodium metal battery electrolyte, comprising an organic solvent, a sodium salt, and a sodium-supplementing additive, specifically: The organic solvent is diethylene glycol dimethyl ether; The sodium supplement additive is sodium trimethylsilanol, with a concentration of 0.2 mol / L; The sodium salt is sodium hexafluorophosphate with a concentration of 1 mol / L.

[0026] A method for preparing an electrolyte for a negative electrode-free sodium metal battery comprises the following steps: S1. Under high-purity argon atmosphere (controlling the moisture and oxygen contents to not exceed 0.01 ppm), fully dissolving the corresponding amount of sodium salt in an organic solvent to obtain a basic electrolyte; S2. Adding a corresponding amount of a sodium supplement additive to the basic electrolyte, mixing evenly, and allowing to stand to ensure that the sodium supplement additive is evenly dispersed without precipitation, thereby obtaining a negative electrode-free sodium metal battery electrolyte.

[0027] Performance testing: In order to verify the performance of the prepared negative electrode-free sodium metal battery electrolyte, the inventors used the following negative electrode-free sodium metal battery electrolyte to assemble a negative electrode-free sodium metal battery, and then tested the performance of the obtained negative electrode-free sodium metal battery to examine the performance of the negative electrode-free sodium metal battery electrolyte. Specifically including: A carbon-coated aluminum foil was cut into 14 mm diameter sheets using a cutting machine as the negative electrode current collector for the anode-free sodium metal battery (the negative carbon layer faces the positive electrode). The battery was assembled using sodium ferric 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). A porous single-layer polypropylene membrane was used as the separator. 2032 button cells were assembled in a glove box (high-purity argon atmosphere, in which the oxygen and water content is less than 0.01 ppm). The full battery was then loaded with 14.2 mg cm-1 of NFPP. -2 Under the load, in the voltage range of 1.5-3.9 V, first use 100 mA·g -1 The first cycle of constant current and constant voltage charge and discharge was performed at a current density of 5 mA·g -1 ), and then at 600 mA·g -1 The full battery was subjected to constant current charge and discharge tests at a current density of 100 nm (all test temperatures were 30 °C).

[0028] Example 2 The difference between this embodiment and embodiment 1 is that the type of sodium supplement additive is changed, that is, sodium trimethylsiliconate is replaced by sodium amide. The other steps and parameters are the same as those in embodiment 1.

[0029] Example 3 The difference between this embodiment and embodiment 1 is that the type of sodium salt is changed, that is, sodium tetrafluoroborate is replaced by sodium hexafluorophosphate. Other steps and parameters are the same as those in embodiment 1.

[0030] Example 4 The difference between this embodiment and embodiment 2 is that the type of sodium salt is changed, that is, sodium tetrafluoroborate is replaced by sodium hexafluorophosphate. The other steps and parameters are the same as those in embodiment 2.

[0031] Example 5 The difference between this embodiment and embodiment 1 is that the type of organic solvent is changed, that is, diethylene glycol dimethyl ether is replaced with ethylene carbonate. Other steps and parameters are the same as those in embodiment 1.

[0032] Example 6 The difference between this embodiment and embodiment 2 is that the type of organic solvent is changed, that is, diethylene glycol dimethyl ether is replaced with ethylene carbonate. Other steps and parameters are the same as those in embodiment 2.

[0033] Example 7 The difference between this embodiment and embodiment 1 is that the type of organic solvent is changed, that is, diethylene glycol dimethyl ether is replaced with 2-methyltetrahydrofuran. Other steps and parameters are the same as those in embodiment 1.

[0034] Example 8 The difference between this embodiment and embodiment 2 is that the type of organic solvent is changed, that is, diethylene glycol dimethyl ether is replaced with 2-methyltetrahydrofuran. Other steps and parameters are the same as those in embodiment 2.

[0035] Example 9 This example differs from Example 1 in that the type of sodium supplement additive is changed, i.e., sodium trimethylsiliconate (0.2 mol / L) is replaced with sodium trimethylsiliconate (0.1 mol / L) and sodium amide (0.1 mol / L). Other steps and parameters are the same as in Example 1.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that no sodium supplement additive is added. Other steps and parameters are the same as those in Example 1.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that the sodium supplement in the electrolyte is replaced with trimethylsilanol. The other steps and parameters are the same as those in Example 1.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that the sodium supplement in the electrolyte is replaced with sodium bis(trimethylsilyl)amide. The other steps and parameters are the same as those in Example 1.

[0039] Comparative Example 4 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 trimethylsilanol with a concentration of 1.2 mol·L -1 .

[0040] Results and Analysis: The relevant performance test results of the batteries prepared with the electrolytes of Examples 1 to 9 and Comparative Examples 1 to 4 are shown in Table 1 below: Table 1:

[0041] As shown in Table 1, the sodium supplement additives introduced into the electrolyte as an additional sodium source can effectively release sodium ions through oxidation reactions during the first charge process, compensating for the irreversible active sodium loss caused by the SEI film formation process and side reactions, thereby improving the battery's first charge specific capacity and capacity retention rate. 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 ), sodium trimethylsiliconate and sodium amide both showed excellent sodium supplementation capabilities. Compared with the comparative example 1 without sodium supplementation additives, the first charge and discharge specific capacities were 13.5% and 30.2% higher, respectively. In addition, compared with Example 1-2 and Comparative Example 2-3, the first charge and discharge specific capacity and capacity retention rate of Example 1-2 were better than those of Comparative Example 2-3, indicating the uniqueness, creativity and superiority of the sodium supplementation additive provided by the present invention. And it can be seen from Comparative Example 4 that sodium salt is crucial to maintaining ion transport and electrode stability. By 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 replenishing active sodium. It also regulates the reaction kinetics of the electrode-electrolyte interface, induces the formation of a thin and strong SEI film with high ionic conductivity, inhibits the occurrence of side reactions, and further improves the electrochemical performance and cycle life of the battery.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

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 supplementing additive; the sodium supplementing additive comprises at least one of sodium trimethylsilanol and sodium amide.

2. The negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that: The concentration of the sodium supplement additive in the electrolyte is 0.1-0.5 mol / L.

3. 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.

4. The negative electrode-free sodium metal battery electrolyte according to claim 3, 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.

5. 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 %.

6. 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).

7. 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.

8. The method for preparing a negative electrode-free sodium metal battery electrolyte according to any one of claims 1 to 7, 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.

9. 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 7 or the negative electrode-free sodium metal battery electrolyte prepared by the preparation method according to claim 8.

10. The negative electrode-free sodium metal battery according to claim 9, 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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