Sodium metal battery and electrolyte thereof

Abstract

The invention belongs to the field of batteries, and particularly relates to a sodium metal battery and an electrolyte thereof, and the electrolyte is a solution containing a formula 1 # imgabs0 # additive, a conductive sodium salt and an organic solvent; m is at least one of Cu, Fe and Ni. The additive in the formula 1 is innovatively used for the electrolyte of the metal sodium battery, so that a stable interface can be formed on the surface of a sodium metal negative electrode, the continuous side reaction of sodium metal and the electrolyte is inhibited, and the growth and non-uniform deposition of sodium dendrites are eliminated. Furthermore, the solid electrolyte interface (SEI) performance is optimized, so that the solid electrolyte interface can meet the application requirements of fast charging and long circulation.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium metal batteries, and in particular to the field of electrolytes for sodium metal batteries. Background Art

[0002] Sodium-based batteries have broad development prospects due to their price advantage. Compared with conventional sodium-ion batteries, sodium metal batteries use metallic sodium as the negative electrode, which has a higher specific capacity (1166mAh g -1 ) and a lower electrochemical potential (-2.71 V vs. SHE), making it an ideal research direction for sodium-based batteries. However, the high activity of the anode of sodium metal batteries leads to continuous side reactions with the electrolyte, forming a highly unstable solid electrolyte interface (SEI), which can cause uneven sodium deposition and severe dendrite growth, leading to battery failure.

[0003] The existing technology has proposed a variety of improvement strategies to address the above problems, such as constructing artificial SEI membranes, sodium-philic conductive frameworks, or electrolyte regulation to improve the stability of sodium metal negative electrodes. Among them, electrolyte regulation is very promising due to its high feasibility. The most commonly used regulation method is to introduce film-forming additives. Although this method has partially improved the performance, due to the high reactivity of the sodium metal battery negative electrode, the requirements for the electrolyte are more special. Conventional additives have the following limitations in sodium metal battery electrolytes: (1) Conventional additives are easily decomposed and consumed during the operation of the sodium metal battery, and their effects decrease after a cycle, making them unable to support long-term operation; (2) Existing additives have limited inhibitory effects on interfacial side reactions, making it difficult to balance ion flux uniformity and electrolyte compatibility; (3) Existing additive technologies are insufficient in synergistically optimizing the mechanical strength and ion conductivity of the SEI, resulting in high interfacial impedance and poor dynamic performance.

[0004] Therefore, there is an urgent need to develop a non-sacrificial, multifunctional electrolyte. The generated SEI can not only stably isolate sodium metal from direct contact with the electrolyte and inhibit the occurrence of side reactions, but also regulate the uniform deposition of sodium ions, while optimizing the interface components to improve the interface kinetics and meet the requirements of sodium metal batteries for electrolytes. Summary of the Invention

[0005] In response to the problems faced by sodium metal battery electrolytes, the first purpose of the present invention is to provide an electrolyte for a sodium metal battery, aiming to adapt to the high activity characteristics of sodium metal batteries and improve their fast charging stability.

[0006] The second object of the present invention is to provide the use of the electrolyte in the preparation of sodium metal batteries.

[0007] A third object of the present invention is to provide a sodium metal battery comprising the electrolyte.

[0008] Sodium metal batteries are different from lithium-ion batteries. They have problems such as low capacity density and difficulty adapting to fast charging application requirements. To address the problems faced by sodium metal batteries, the present invention provides the following solutions:

[0009] An electrolyte for a sodium metal battery, comprising an additive of formula 1, a conductive sodium salt, and an organic solvent;

[0010]

[0011] The M is at least one of Cu, Fe, and Ni.

[0012] To address the difficulty in adapting sodium metal batteries to fast-charging requirements due to their unique physicochemical characteristics, the present invention innovatively employs an additive of Formula 1 in the electrolyte of sodium metal batteries. This additive forms a stable interface on the surface of the sodium metal negative electrode, inhibiting persistent side reactions between the sodium metal and the electrolyte and eliminating sodium dendrite growth and uneven deposition. This in turn optimizes the solid electrolyte interface (SEI) performance, enabling the battery to meet fast-charging and long-cycle application requirements.

[0013] In the present invention, the additive of formula 1 comprises additive A and additive B in a weight ratio of 1:1 to 5 (more preferably 1:1.4 to 1.6);

[0014] Among them, the additive A is the formula 1 in which M is Cu; the additive B is the formula 1 in which M is Fe.

[0015] In the present invention, the additive of the combination of additive A and additive B can further improve the adaptability of the sodium metal battery based on the combination between the structures and the interaction between Fe-Cu, which helps to further enhance the fast charging and energy density of the sodium metal battery.

[0016] In the present invention, the content of the additive of formula 1 is 0.1 to 100 mg / mL; further, it can be 1 to 20 mg / mL; and more preferably, it is 5 to 10 mg / mL.

[0017] In the present invention, the conductive sodium salt is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, and sodium perchlorate.

[0018] In the present invention, the concentration of the conductive sodium salt is 0.5-5M; further, it can be 1-1.5M.

[0019] In the present invention, the organic solvent includes at least one of a carbonate solvent and an ether solvent.

[0020] In the present invention, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0021] The ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0022] Research in the present invention shows that the use of carbonate solvents can help further improve the compatibility between additives and metallic sodium, help further improve the interface structure and stability of metallic sodium battery pole pieces, and help further improve the fast charging stability of metallic sodium batteries.

[0023] The present invention also provides an application of the electrolyte, which is used as the electrolyte to prepare a sodium metal battery.

[0024] In the present invention, the sodium metal battery is a battery using metallic sodium and its alloys as negative electrode active materials.

[0025] The present invention also provides a sodium metal battery, comprising a battery core composed of a sodium metal negative electrode, a separator and a positive electrode sheet, which are compounded in sequence, and an electrolyte for soaking the battery core, wherein the electrolyte is the electrolyte described in the present invention.

[0026] The sodium metal battery of the present invention, in addition to comprising the electrolyte of the present invention, may have other components and structural relationships that are known.

[0027] For example, the positive electrode active material in the positive electrode of the present invention may be one or more of sodium manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron phosphate, and sodium manganese phosphate.

[0028] Beneficial effects

[0029] (1) The present invention provides an electrolyte suitable for sodium metal batteries, which can significantly improve the interfacial stability and electrochemical performance of the sodium metal negative electrode and inhibit side reactions and electrolyte consumption.

[0030] The sodium metal battery negative electrode has higher reactivity than the conventional sodium-based battery negative electrode. By introducing the planar molecules of the additive of formula 1, it is preferentially adsorbed on the sodium metal surface, blocking the direct contact between the electrolyte and the sodium metal negative electrode. As a result, the decomposition products of organic matter in the SEI after cycling are greatly reduced, and side reactions are reduced by more than 80%; dendrite growth is eliminated and sodium is deposited evenly; in addition, the nitrogen atoms of the additive of formula 1 enhance the sodium affinity of the sodium metal negative electrode interface and greatly reduce the nucleation overpotential; the electrostatic shielding effect of the metal atoms inhibits the growth of dendrite tips, and the sodium deposition surface is dense and smooth, with no pore structure; the SEI performance is optimized, and the interface dynamics are significantly improved.

[0031] (2) It is easy to achieve long-term stability and low-cost large-scale application. The electrolyte additive of the present invention has non-sacrificial function and long cycle life. It forms a dynamic molecular isolation layer through physical adsorption instead of sacrificial decomposition to improve battery performance, far exceeding traditional additives (such as FEC, Cs+ ) short-term effectiveness; in addition, the additive is added in a low amount in the electrolyte, is compatible with the existing electrolyte system, does not require complex process modification, and has controllable synthesis costs, making it suitable for large-scale production of high-energy-density sodium metal batteries.

[0032] (3) The introduction of additives with multiple different metal ions can form an alloyed SEI at the sodium metal negative electrode interface (for example, the simultaneous addition of additives A and B can form a copper-iron alloy layer at the sodium metal negative electrode interface), which can optimize the electron transfer path, reduce internal resistance, and improve mechanical stability and cycle life. This helps improve fast charging performance and low-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Graph showing the relationship between the cyclic coulombic efficiency and the number of cycles for the Na||Cu half-cells of Comparative Example 1 and Example 8;

[0034] Figure 2 Graph showing the relationship between specific capacity and cycle number at 5C and 10C rates for the full-cell Na@Cu||NVPF of Comparative Example 1 and Example 8; DETAILED DESCRIPTION

[0035] Example 1:

[0036] This embodiment 1 takes a button-type sodium half-cell as an example, and the specific preparation scheme is as follows:

[0037] (1) In a glove box filled with high-purity argon (water <0.01 ppm, oxygen <0.01 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) were uniformly mixed at a volume ratio of EC:DMC = 1:1, and water was removed through molecular sieves to obtain an electrolyte organic solvent;

[0038] (2) Also in the glove box, a certain amount of electrolyte salt NaPF6 was added to the above mixed solvent and stirred to obtain a basic electrolyte solution with a concentration of 1 mol / L;

[0039] (3) Add electrolyte additive A and additive B to the basic electrolyte obtained in (2) in a weight ratio of 1:1.5 and mix evenly until the liquid becomes clear and transparent. The total concentration of the additives (referring to the total concentration of additives A and additives B) is 10 mg / ml -1 After standing for four hours, a sodium metal battery electrolyte suitable for the sodium metal negative electrode was obtained.

[0040] Example 2-11:

[0041] Sodium metal batteries and their compatible electrolytes were prepared according to the method of Example 1, except for the selection of electrolyte salts, solvent components, and electrolyte additives in the electrolyte. The other steps were the same as in Example 1. The battery electrolyte formulas in Examples 2-11 are shown in Table 1 below.

[0042] Comparative Examples 1-4:

[0043] Sodium metal batteries and their compatible electrolytes were prepared according to the method of Example 1, except for the selection of electrolyte salts, solvent components, and additives in the electrolyte. Other steps were the same as in Example 1. The battery electrolyte formulas in Comparative Examples 1-4 are shown in Table 1 below.

[0044] Table 1 Formula of battery electrolyte in Examples 1-11 and Comparative Examples 1-4

[0045] electrolyte salts Non-aqueous organic solvents electrolyte additives Example 1 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive A and Additive B (1:1.5) Example 2 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive A and Additive B (1:1) Example 3 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive A and Additive B (1:2) Example 4 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive A and Additive C (1:1.5) Example 5 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive A Example 6 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive B Example 7 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Additive C Example 8 1MNaFSI EC:DMC=1:1 <![CDATA[Additive A and Additive B (1:1.5) (a) > Example 9 <![CDATA[2MNaPF6]]> EC:DMC=1:1 <![CDATA[Additive A and Additive B (1:1.5) (b) > Example 10 <![CDATA[1MNaPF6]]> DME Additive A and Additive B (1:1.5) Example 11 <![CDATA[1MNaPF6]]> DEGDME Additive A and Additive B (1:1.5) Comparative Example 1 <![CDATA[1MNaPF6]]> EC:DMC=1:1 -- Comparative Example 2 <![CDATA[1MNaPF6]]> DME -- Comparative Example 3 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Fluoroethylene carbonate (FEC) Comparative Example 4 <![CDATA[1MNaPF6]]> EC:DMC=1:1 Cesium fluoride (CsF)

[0046] Note: Additive C is Formula 1 where M is Ni.

[0047] Unless otherwise stated, the total concentration of additives in each case was 10 mg ml -1 Wherein, (a): the total concentration of additives in the electrolyte is 15 mg ml -1 (b): The total concentration of additives in the electrolyte is 5 mg ml -1 .

[0048] experiment:

[0049] The performance test of the sodium metal battery electrolytes prepared in the above examples and comparative examples was completed through the following experiments.

[0050] 1. Electrode Preparation

[0051] The metal foil was cut into discs with a diameter of 13 mm, and then rinsed with dilute hydrochloric acid, deionized water, and alcohol in sequence and dried to obtain a metal foil electrode.

[0052] The positive electrode material (e.g., NVPF (sodium vanadium fluorophosphate)), PVDF, and acetylene black are mixed in a mass ratio of 7:2:1 and dispersed in NMP. The mixture is stirred at 3000 rpm using a homogenizer for approximately 20 minutes. The slurry is evenly coated on an aluminum foil surface using a doctor blade coating method and dried in an 80°C forced air drying oven for 12 hours. The dried electrode sheet is cut into 10 mm diameter discs using a sheet cutter. This produces the positive electrode sheet.

[0053] Graphite, PVDF, and acetylene black were mixed in a 7:2:1 mass ratio and dispersed in NMP. The mixture was stirred at 3000 rpm using a homogenizer for approximately 20 minutes. The slurry was evenly coated on the surface of copper foil using a doctor blade coating method and dried in an 80°C forced air oven for 12 hours. The dried electrode sheet was cut into 13 mm diameter discs using a sheet cutter. This produced the negative electrode sheet.

[0054] The sodium block was pressed to a thickness of about 0.5 mm and cut into discs with a diameter of 12 mm using a cutting machine to produce a sodium metal electrode.

[0055] 2. Battery assembly

[0056] Half-cell Na||Cu assembly: Copper foil was used as the positive electrode, sodium metal electrode as the negative electrode, PP and glass fiber as separators, and button cells were assembled in a glove box.

[0057] Symmetrical cell Na||Na assembly: copper foil is placed in a half-cell at 0.1 mA cm -2 Current pre-deposition 4 mAh cm -2 of metallic sodium, and the battery was used as a symmetrical battery for symmetrical battery cycle testing.

[0058] Full cell Na@Cu||NVPF assembly: Copper foil was placed in a half cell at 0.1 mA cm -2 Current pre-deposition 2 mAh cm -2 The sodium metal was removed and used as the negative electrode. The positive electrode was NVPF@Al, with PP and glass fiber as separators. Before testing, the battery was activated at 0.1C for three cycles, with a test voltage range of 2V to 4.3V.

[0059] 3. Test Method

[0060] The battery charge and discharge cycle tests were all conducted at a constant temperature of 25°C. Before the test, both the half-cell and the symmetrical cell were charged at 0.1 mA cm -2 The current is pre-activated for 5 cycles within the test range.

[0061] 4. Test Results

[0062] Table 2 Performance and cycle test results of half-cell Na||Cu of Examples 1-11 and Comparative Examples 1-4

[0063]

[0064]

[0065] Table 3 Performance and cycle test results of full-cell Na@Cu||NVPF of Examples 1-11 and Comparative Examples 1-4

[0066]

[0067] In summary, the present invention uses the additive of Formula 1 as an additive to the sodium metal battery electrolyte and systematically studies its effect on the cycling performance of Na||Cu half-cells and full-cells. In particular, it studies its effect on the long-term cycling stability of the sodium metal anode in the Na||Cu half-cell.

[0068] Compared to an electrolyte without additives, the additives in Formula 1 can form a molecular isolation layer on the surface of the sodium metal anode. The additives in Formula 1 can be uniformly adsorbed on the surface of the sodium anode before the electrolyte solvent, thereby isolating the electrolyte and reducing side reactions. The sodium-philic nitrogen and metal atoms in the additives can regulate the uniform deposition of sodium. Their two-dimensional sheet-like structure allows them to expand and contract with the changes in the anode surface, effectively adapting to volume changes and improving the stability of the anode interface. The simultaneous introduction of multiple additives in Formula 1 can form an alloy phase interface at the anode interface, further enhancing battery performance, such as fast charging.

[0069] The results show that the Na||Cu half-cell and full-cell assembled with the electrolyte prepared with the additive of formula 1 provided by the present invention can significantly improve the long-cycle stability. -1 After 300 cycles at the same current density, the capacity retention rate can be maintained at more than 99.5%. In terms of charge and discharge rate, the electrolyte prepared by the additive of formula 1 also has certain advantages over traditional additives such as FEC. The discharge capacity at 10C at the 120th cycle can still reach 103.2mAh mg -1 .

[0070] It can be seen from Example 1 and Comparative Examples 1 to 4 that the use of the additives of the present invention can be compatible with sodium metal batteries, which helps to optimize the interface and improve the high-rate performance of the battery.

[0071] It can be seen from Examples 1 to 3 and Examples 5 to 6 that the use of the additives A and B in combination of the present invention as additives can help further improve the interfacial effect, help further improve the adaptability of the electrolyte to the sodium metal battery, and help further improve the high rate performance.

[0072] In addition, it can be seen from Examples 1, 4, and 7 that when M is Cu and Fe, better sodium metal battery adaptability can be obtained, which helps to improve the high-rate performance of the sodium metal battery.

[0073] It can be seen from Example 1 and Examples 8 to 11 that both ester solvents and ether solvents can achieve good effects.

Claims

1. An electrolyte for a sodium metal battery, characterized in that A solution comprising an additive of formula 1, a conductive sodium salt, and an organic solvent; The M is at least one of Cu, Fe, and Ni.

2. The electrolyte of the sodium metal battery according to claim 1, wherein The additive of formula 1 comprises additive A and additive B in a weight ratio of 1:1 to 5; Among them, the additive A is the formula 1 in which M is Cu; the additive B is the formula 1 in which M is Fe.

3. The electrolyte of the sodium metal battery according to claim 1 or 2, characterized in that The content of the additive of formula 1 is 0.1-100 mg / mL.

4. The electrolyte of the sodium metal battery according to claim 1, wherein The conductive sodium salt is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate and sodium perchlorate.

5. The electrolyte of the sodium metal battery according to claim 1 or 4, characterized in that The concentration of the conductive sodium salt is 0.5-5M.

6. The electrolyte of the sodium metal battery according to claim 1, wherein The organic solvent includes at least one of a carbonate solvent and an ether solvent.

7. The electrolyte of the sodium metal battery according to claim 6, wherein The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; The ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

8. Use of the electrolyte according to any one of claims 1 to 7, characterized in that: It is used as the electrolyte to prepare sodium metal batteries.

9. The use of the electrolyte according to claim 8, characterized in that The sodium metal battery is a battery using metallic sodium and its alloys as negative electrode active materials.

10. A sodium metal battery comprising a battery cell comprising a sodium metal negative electrode, a separator, and a positive electrode sheet, which are sequentially composited, and an electrolyte for soaking the battery cell, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 7.

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