High-voltage fast-charging electrolyte for sodium metal battery as well as preparation method and application of high-voltage fast-charging electrolyte

Abstract

The invention discloses a sodium metal battery high-voltage fast-charging electrolyte and a preparation method and application thereof, and belongs to the technical field of sodium metal batteries. The electrolyte comprises a sodium salt, an organic ester and linear ether hybrid solvent, the volume ratio of the organic ester solvent to the linear ether solvent in the electrolyte is (3-5): (5-7), and the concentration of the sodium salt is 0.5-1.5 mol L; the organic ester solvent is fluoroethylene carbonate (FEC); the linear ether solvent is one or two of diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME); and injecting the electrolyte into the sodium metal battery to obtain the high-voltage sodium metal battery. The high-voltage fast-charging electrolyte provided by the invention has a 5V electrochemical window, a sodium fluoride-rich solid electrolyte membrane with high ionic conductivity and strong mechanical property is formed in situ in the charging and discharging process, and continuous decomposition of a solvent can be inhibited, so that the energy density and the cycling stability of a battery are remarkably improved, and the fast-charging performance of the sodium metal battery is met.

Description

Technical Field

[0001] The present invention relates to an electrolyte suitable for a high-voltage fast-charge sodium metal battery, and in particular to a high-voltage fast-charge electrolyte for a sodium metal battery, a preparation method and an application thereof, and belongs to the technical field of sodium metal batteries. Background Art

[0002] With the rapid development of industry and technology, energy demand is growing, and the demand for efficient and sustainable energy storage and conversion technology is becoming more urgent. The invention and evolution of batteries, especially the emergence of modern rechargeable batteries, have greatly changed our lifestyle. They not only provide power for portable electronic devices, but also play an important role in electric vehicles, energy storage systems and other fields, becoming an indispensable energy storage and conversion tool in modern society.

[0003] Among many battery technologies, sodium metal batteries, as a new type of high energy density energy storage device, have received widespread attention in the field of new energy in recent years. Sodium metal batteries have the advantages of high theoretical specific capacity, abundant resources, and low cost. They are regarded as a strong competitor to lithium-ion batteries, especially in large-scale energy storage applications. However, the research and development and application of sodium metal batteries still face many challenges. Among them, the electrolyte, as an important component of the battery, is directly related to key indicators such as the battery's energy density, cycle life, and safety. However, traditional sodium metal battery electrolytes have problems such as poor stability and easy decomposition under high pressure conditions, which will cause the battery capacity to decay rapidly, severely limiting the application range and service life of sodium metal batteries.

[0004] At present, in order to solve this problem, researchers are constantly exploring new electrolyte formulas and preparation methods in order to improve the electrochemical stability of the electrolyte, broaden the electrochemical window, and enhance compatibility with the sodium metal negative electrode. For example, in the invention patent with application publication number CN 116072972 A and invention name A sodium ion electrolyte and its preparation method, different concentrations of ionic liquids are added to the electrolyte to achieve an electrolyte with a safer temperature; but due to the high viscosity of the ionic liquid, the fast charging performance of the battery is affected. For example, in the patent with application publication number CN 118198503 A and invention name A sodium ion battery fast charging electrolyte and sodium ion battery invention, the fast charging performance of the sodium battery is achieved by using chain ether as the main solvent and cyclic ether as the main solvent, but the voltage of the battery is not studied, which limits the development of high energy density sodium metal batteries. In addition, most high-voltage electrolytes use the method of solvent decomposition to form a film, so that the electrolyte is continuously decomposed to form a thicker solid electrolyte film, but it not only reduces the fast charging performance, but also reduces the cycle life of the battery.

[0005] Therefore, there is an urgent need to develop a high-voltage electrolyte with a simple preparation process, low cost, the ability to improve energy density and cycle stability, and meet the fast charging performance of the battery. Summary of the invention

[0006] The purpose of the present invention is to solve the problems in the prior art that the energy density of sodium metal high-voltage fast-charging electrolyte is not high and that conventional high-voltage electrolyte cannot meet its fast-charging performance, and to provide a sodium metal battery high-voltage fast-charging electrolyte and a preparation method and application thereof. The high-voltage fast-charging electrolyte forms a sodium fluoride-rich solid electrolyte membrane with high ionic conductivity and strong mechanical properties in situ during the charge and discharge process, which can inhibit the continuous decomposition of the solvent, thereby significantly improving the energy density and cycle stability of the battery and meeting the fast-charging performance of the sodium metal battery.

[0007] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a sodium metal battery high-voltage fast-charge electrolyte, the electrolyte comprising a sodium salt, an organic ester and a linear ether-based hybrid solvent, the volume ratio of the organic ester solvent to the linear ether-based solvent in the electrolyte is 3-5:5-7, and the concentration of the sodium salt is 0.5-1.5 mol / L; the organic ester solvent is fluoroethylene carbonate (FEC); the linear ether-based solvent is one or both of diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME).

[0008] Furthermore, the sodium salt is one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaOTF), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0009] The present invention also provides a method for preparing a sodium metal battery high-voltage fast-charge electrolyte, comprising the following steps: S1. Under argon atmosphere, place molecular sieves in organic esters and linear ether solvents respectively, let stand for 24 hours, then remove the molecular sieves to obtain a purified solvent; S2, the organic esters purified in the above step S1 and the linear ether solvent are fully mixed in a volume ratio of 3-5:5-7; S3. Dissolve the sodium salt in the mixed solution obtained in the above step S2, stir for 6 hours, and obtain a high-voltage fast-charge electrolyte after it is completely dissolved.

[0010] Furthermore, the molecular sieve is a 3Å molecular sieve.

[0011] The present invention also provides the use of the high-voltage fast-charge electrolyte prepared by the above preparation method in a sodium metal battery, and the above electrolyte is injected into the sodium metal battery to obtain a high-voltage sodium metal battery.

[0012] Furthermore, in the high-voltage sodium metal battery, the positive electrode is high-voltage resistant sodium vanadium fluorophosphate (NVPF) with a surface loading of 2 mg cm -2 ; The negative electrode is sodium metal with a thickness of 100μm; the diaphragm material is glass fiber.

[0013] The beneficial effects of the present invention are: 1) The high-voltage fast-charge electrolyte of the present invention forms a sodium fluoride-rich solid electrolyte membrane with high ionic conductivity and strong mechanical properties in situ during the charge and discharge process, which can inhibit the continuous decomposition of the solvent, thereby significantly improving the energy density and cycle stability of the battery and meeting the fast-charge performance of the sodium metal battery.

[0014] 2) The present invention realizes anion-enhanced solvation structure by compounding sodium salt with ester and ether hybrid solvents; by adjusting the ion-dipole interaction, a solvation sheath rich in anions is constructed, the proportion of inner layer anions is increased, the desolvation energy barrier is reduced, and the formation of a sodium fluoride-rich solid electrolyte membrane with high ionic conductivity and strong mechanical properties is promoted, thereby obtaining more excellent electrochemical properties of the electrolyte.

[0015] 3) The high-voltage electrolyte of the present invention has a simple preparation process, low cost and stable performance, which is of great significance for promoting the practical application of sodium metal batteries and promoting the further development of the new energy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The electrochemical window of Examples 1 to 6 of the present invention; Figure 2 The electrochemical windows of Embodiment 1 and Embodiments 7 to 11 of the present invention; Figure 3 This is a long cycle performance diagram of the Na||NVPF full battery assembled with the electrolytes of Examples 1 to 5 and Example 7 of the present invention at a rate of 20 C. DETAILED DESCRIPTION

[0017] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0018] Example 1: The present invention provides a sodium metal battery high-voltage fast-charge electrolyte, and the preparation process of the electrolyte is: fluoroethylene carbonate (FEC) is mixed with tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol dimethyl ether (DEGDME) in a volume ratio of 50%:30%:20%, and 1M sodium tetrafluoroborate (NaBF4) is added to the mixed FEC / TEGDME / DEGDME solution after uniform mixing, and then the solution is mixed uniformly at room temperature to finally obtain a high-voltage fast-charge electrolyte (named: TDF).

[0019] Example 2: The difference from Example 1 is that fluoroethylene carbonate (FEC) is mixed with tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol dimethyl ether (DEGDME) in a volume ratio of 30%:50%:20%.

[0020] Example 3: The difference from Example 1 is that fluoroethylene carbonate (FEC) is mixed with tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol dimethyl ether (DEGDME) in a volume ratio of 50%:20%:30%.

[0021] Example 4: The difference from Example 1 is that fluoroethylene carbonate (FEC) is mixed with tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol dimethyl ether (DEGDME) in a volume ratio of 40%:30%:30%.

[0022] Example 5: The difference from Example 1 is that 0.5 M NaBF4 is added to the mixed solution.

[0023] Example 6: The difference from Example 1 is that 1.5 M NaBF4 is added to the mixed solution.

[0024] Example 7: The present invention provides a sodium metal battery high-voltage fast-charge electrolyte, and the preparation process of the electrolyte is: fluoroethylene carbonate (FEC) and tetraethylene glycol dimethyl ether (TEGDME) are mixed in a volume ratio of 50%:50%, and 1M NaBF4 is added to the mixed FEC / TEGDME mixed solution after being mixed evenly, and then the solution is mixed evenly at room temperature to finally obtain a high-voltage fast-charge electrolyte (named: TF).

[0025] Example 8: The difference from Example 7 is that 1 M sodium trifluoromethanesulfonate (NaOTF) is added to the mixed solution to finally obtain a high-voltage fast-charge electrolyte (named: OTF).

[0026] Example 9: The difference from Example 7 is that 1 M sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) is added to the mixed solution to finally obtain a high-voltage fast-charge electrolyte (named: TFSI).

[0027] Example 10: The difference from Example 7 is that 1 M sodium bis(fluorosulfonyl)imide (NaFSI) is added to the mixed solution to finally obtain a high-voltage fast-charge electrolyte (named: FSI).

[0028] Example 11: The difference from Example 7 is that 1M sodium hexafluorophosphate (NaPF6) is added to the mixed solution to finally obtain a high-voltage fast-charge electrolyte (named: PF6).

[0029] Figure 1The electrochemical window obtained by linear sweep voltammetry test of the electrolytes of Examples 1 to 6; the experimental results show that the voltage window will increase as the amount of FEC added increases. It is found from Examples 1 and 5 to 6 that the electrochemical window at a concentration of 0.5 mol / L is the lowest, indicating that it is least resistant to high voltage. As the concentration of NaBF4 increases, the electrochemical windows at concentrations of 1 mol / L and 1.5 mol / L are almost the same. According to other parameters, such as ionic conductivity, the 1 mol / L concentration is the preferred embodiment.

[0030] Figure 2 The electrochemical windows obtained by linear sweep voltammetry test of the electrolytes of Examples 1 and 7 to 11; According to Examples 7 to 11, compared with different sodium salts, the electrolyte with NaBF4 has the widest electrochemical window, indicating the strongest antioxidant capacity. In addition, with the introduction of DEGDME, the TDF electrolyte has the highest antioxidant voltage (>5V).

[0031] Figure 3 The long cycle performance of Na||NVPF assembled with the electrolytes of Examples 1 to 5 and Example 7 at a rate of 20C; at a cut-off voltage of 4.5V and a high current density of 20C, it can still maintain 77.8 mAh g -1 The capacity is significantly higher than that of the TF electrolyte system, which is 59.93 mAh g -1 After 5000 cycles, the capacity retention rate is 84.8%.

[0032] The high-voltage fast-charge electrolyte of the present invention forms a sodium fluoride-rich solid electrolyte membrane with high ionic conductivity and strong mechanical properties in situ during the charge and discharge process, inhibiting the continuous decomposition of the solvent, thereby significantly improving the energy density and cycle stability of the battery and meeting the fast-charge performance of the sodium metal battery.

[0033] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A sodium metal battery high voltage fast charge electrolyte, characterized in that: The electrolyte includes a hybrid solvent of sodium salt, organic ester and linear ether, the volume ratio of organic ester solvent to linear ether solvent in the electrolyte is 3-5:5-7, and the concentration of sodium salt is 0.5-1.5 mol / L; the organic ester solvent is fluoroethylene carbonate (FEC); the linear ether solvent is one or two of diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME).

2. A sodium metal battery high-voltage fast-charge electrolyte according to claim 1, characterized in that: The sodium salt is one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaOTF), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

3. A method for preparing a sodium metal battery high-voltage fast-charge electrolyte according to claim 1 or 2, characterized in that: The following steps are involved: S1. Under argon atmosphere, place molecular sieves in organic esters and linear ether solvents respectively, let stand for 24 hours, then remove the molecular sieves to obtain a purified solvent; S2, the organic esters purified in the above step S1 and the linear ether solvent are fully mixed in a volume ratio of 3-5:5-7; S3. Dissolve the sodium salt in the mixed solution obtained in the above step S2, stir for 6 hours, and obtain a high-voltage fast-charge electrolyte after it is completely dissolved.

4. The preparation method according to claim 3, characterized in that: The molecular sieve is a 3Å molecular sieve.

5. Application of the high-voltage fast-charge electrolyte prepared by the preparation method according to claim 3 in a sodium metal battery, characterized in that: The electrolyte is injected into a sodium metal battery to obtain a high-voltage sodium metal battery.

6. The use according to claim 5, characterized in that: In the high-voltage sodium metal battery, the positive electrode is sodium vanadium phosphate (NVP) and high-voltage resistant sodium vanadium fluorophosphate (NVPF), with a surface loading of 2 mg cm -2 ; The negative electrode is sodium metal with a thickness of 100 μm; the separator material is glass fiber.

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