Long-circulation electrolyte for sodium-ion battery and preparation method of long-circulation electrolyte

Abstract

The invention relates to the field of sodium ion battery energy storage, and provides a long-circulation electrolyte for a sodium ion battery and a preparation method thereof, and the long-circulation electrolyte comprises an organic ester solvent, a solute and an additive. The solute is a sodium salt with the concentration of 0.5-2.5 M; the solvent is a carbonic ester and / or ether mixed solution and an additive with the mass fraction of 0.1-25%. The electrolyte can form a stable solid electrolyte interface (SEI) on the surface of an electrode, so that the electrochemical performance of a battery is improved, meanwhile, the ionic conductivity of the electrolyte in a wide temperature range can be remarkably improved, and the electrochemical window of the electrolyte is effectively widened. The electrolyte can be applied to a sodium-ion battery system taking Prussian blue as a positive electrode, and the cycle performance of the sodium-ion battery system is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a long-cycle electrolyte for sodium ion batteries and a preparation method thereof. Background Art

[0002] In order to promote sustainable development, clean energy is the key to achieving sustainable economic, social and mitigation development. As the most popular electrochemical energy storage technology at present, lithium-ion batteries are widely used in new energy vehicles and portable electronic devices due to their high energy density and excellent cycle stability. However, the low content of lithium in the earth's crust (17 ppm) and its uneven distribution limit the practical application of lithium-ion batteries in large-scale energy storage. Sodium is expected to become a new large-scale energy storage technology after lithium-ion batteries due to its high abundance in the earth's crust, wide distribution and low price.

[0003] As an important component of the battery, the electrolyte of the sodium ion battery is responsible for transferring ions between the positive and negative electrodes, and plays an important role in the battery's rate, cycle life safety and self-discharge. Carbonate solvents are a commonly used solvent with a relatively higher dielectric constant than ether electrolytes, high salt solubility and good antioxidant capacity. However, during the battery cycle, the interfacial film formed by carbonate electrolytes is composed of organic components. Such films often have the characteristics of low mechanical strength and high resistance, which will cause the interfacial film to decompose during the charge and discharge process of the battery, thereby reducing the battery's charge and discharge efficiency and cycle stability. In the electrolyte, through the strategy of double salts, a stable interfacial film rich in inorganic substances can be constructed to improve the performance of the electrolyte.

[0004] The present invention introduces a new sodium salt, a traditional carbonate and an additive and mixes them in a specific ratio and applies them to a sodium ion battery system. Compared with a single salt electrolyte, the dual salt electrolyte exhibits a wider electrochemical window, higher ionic conductivity and better cycle stability. Summary of the invention

[0005] The purpose of the present invention is to improve the existing battery electrolyte to maintain good cycle stability in a wide temperature range, and to provide a long-cycle sodium ion battery electrolyte and a preparation method and application thereof.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: The sodium salt and the solvent are mixed to form a basic electrolyte, and then the additive is mixed with the basic electrolyte to form a sodium ion battery electrolyte suitable for a wide temperature range, wherein the sodium salt concentration is 0.7-2.0 mol / L.

[0007] The sodium salt is selected from any two combinations of sodium hexafluorophosphate (NaPF6), sodium difluorooxalatoborate (NaDFOB), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaOTf), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0008] The solvent is selected from at least one of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0009] The additive is at least one of fluoroethylene carbonate (FEC), 1,3,5-hydroxybenzene (THB), 1,3-propane sultone (PS), diethylene sulfate (DTD), methylene disulfonate (MMDS), vinyl carbonate (VC), 1-propylene-1, 3-sultone (PES), butyl sultone (BS), and tris(trimethylsilyl) phosphite (TMSP).

[0010] In the long-cycle sodium-ion battery electrolyte, the molar fraction of the sodium salt is 0.7~2.0 mol / L.

[0011] In the sodium ion battery electrolyte, the mass percentage of the sodium salt is 1-50%, the mass percentage of the solvent is 20-70%, and the mass percentage of the additive is 0.1-5%.

[0012] The present invention provides a method for preparing a long-cycle sodium ion battery electrolyte, comprising the following steps: Step 1: Under an argon atmosphere, pour a carbonate solvent into a beaker and mix thoroughly to obtain a pre-purified solution; Step 2: adding sodium salt to the pre-purified solution obtained in 1); Step 3: Add the molecular sieve to the pre-purified solution obtained in 2), let it stand for 4 hours, and finally remove the molecular sieve to obtain a purified solution; Step 4: dissolving the electrolyte additive into the purified solution obtained in 3), and mixing evenly to obtain a long-cycle sodium-ion battery electrolyte; Step 5: The molecular sieve is 3 Å or 4 Å molecular sieve.

[0013] The beneficial effects of the present invention are: The main purpose of the present invention is to overcome the shortcomings of the prior art and propose a long-cycle electrolyte for sodium ion batteries and a preparation method thereof. Compared with the prior art, the above technical solution proposed by the present invention can achieve the following beneficial effects: The present invention selects and uses various new sodium salts as the second sodium salt to introduce into the original electrolyte. The introduced sodium salt will decompose preferentially before the solvent is oxidized, forming an inorganic-rich interface film on the electrode surface. The stable interface film improves the battery's cycle performance. Compared with traditional carbonate electrolytes, the electrolyte proposed by the present invention has a wider electrochemical window, higher ionic conductivity and excellent cycle stability. It provides a feasible solution for long-cycle electrolytes for sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The electrolyte of Example 1 is at -40 o C. -30 o C. -20 o C. -10 o C. 10 o C. 30 o C. 50 o C. 70 o C. 90 o C of ionic conductivity.

[0015] Figure 2 This is the charge and discharge curve of Example 1 at room temperature.

[0016] Figure 3 It is the long cycle diagram of Examples 1, 2, 3 and Comparative Example 1 at room temperature.

[0017] Figure 4 This is the electrochemical window of Example 1 at room temperature. DETAILED DESCRIPTION

[0018] The present invention further illustrates the technical solution of the present invention in detail with the following specific implementation cases, but the present invention is not limited to the following examples.

[0019] Abbreviations Sodium perchlorate: NaClO4 Sodium bis(fluorosulfonyl)imide: NaFSI Propylene carbonate: PC Ethyl Methyl Carbonate: EMC Diethyl carbonate: DEC Ethylene carbonate: VC.

[0020] Example 1. This embodiment provides a long-cycle sodium ion battery electrolyte, and its preparation method comprises the following steps: adding NaClO4 and NaFSI in a ratio of 8:2 to a PC, EMC, and DEC solvent mixed in a certain volume ratio, mixing them thoroughly, and then adding 1% VC of the total mass of the electrolyte to obtain the long-cycle sodium ion battery electrolyte of the present invention.

[0021] Example 2 This example provides an electrolyte, which is different from Example 1 in that the ratio of NaClO4 to NaFSI is 9:1.

[0022] Example 3 This example provides an electrolyte, which is different from Example 1 in that the ratio of NaClO4 to NaFSI is 7:3.

[0023] Comparative Example 1 This comparative example provides an electrolyte, which is different from Example 1 in that the ratio of NaClO4 to NaFSI is 1:0.

[0024] Comparative Example 2 This comparative example provides an electrolyte, which is different from Example 1 in that the ratio of NaClO4 to NaDFOB is 8:2.

[0025] Figure 1 For Example 1 at -40 o C. -30 o C. -20 o C. -10 o C. 10 o C. 30 o C. 50 o C. 70 o C. 90 o The variable temperature ionic conductivity at 40 °C proves that the long-life electrolyte has great application potential in this temperature range. Figure 2 is the charge and discharge curve of Example 1 at room temperature, Figure 3 The graphs of the production cycles of Examples 1, 2, 3 and Comparative Example 1 at room temperature demonstrate that the electrolyte has excellent cycle performance at room temperature. Figure 4 This is the LSV curve of Example 1 at room temperature, which proves that Example 1 has a wider electrochemical window.

[0026] The above embodiments are limited to further elaborating and illustrating the technical solution of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent replacement or partial modification made within the spirit and principle of the present invention shall be deemed to be within the protection scope of the present invention.

Claims

1. A long cycle electrolyte for sodium ion batteries, characterized in that: The invention comprises an inorganic sodium salt, a carbonate solvent and an additive, wherein the mass percentages are 1-50% of the sodium salt, 0.1-25% of the additive and 20-70% of the carbonate solvent, and the sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium difluorooxalatoborate (NaDFOB), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaOTf) and sodium bis(fluorosulfonyl)imide (NaFSI).

2. A long cycle electrolyte for sodium ion batteries according to claim 1, characterized in that: The sodium salt is sodium perchlorate (NaClO4) and sodium bis(fluorosulfonyl)imide (NaFSI), and the sodium salt concentration is 0.5~2.5 mol / L.

3. A long cycle electrolyte for sodium ion batteries according to claim 2, characterized in that: The sodium salt concentration is 0.7~2.0 mol / L.

4. A long cycle electrolyte for sodium ion batteries according to claim 3, characterized in that: The carbonate solvent includes at least one of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

5. A long cycle electrolyte for sodium ion batteries according to claim 4, characterized in that: The additive includes at least one of fluoroethylene carbonate (FEC), 1,3,5-hydroxybenzene (THB), 1,3-propane sultone (PS), diethylene sulfate (DTD), methylene methanedisulfonate (MMDS), vinyl carbonate (VC), 1-propylene-1, 3-sultone (PES), butyl sultone (BS), and tris(trimethylsilyl)phosphite (TMSP).

6. A method for preparing a long-cycle electrolyte for a sodium ion battery according to any one of claims 1 to 5, characterized in that: The preparation method thereof comprises the following steps: Step (1) under an argon atmosphere, pouring a carbonate solvent into a beaker and mixing thoroughly to obtain a pre-purified solution; Step (2) adding sodium salt to the pre-purified solution obtained in step (1); Step (3) adding the molecular sieve to the pre-purified solution obtained in step (2), standing for 4 hours, and finally removing the molecular sieve to obtain a purified solution; Step (4) dissolving the electrolyte additive into the purified solution obtained in step (3), and mixing them evenly to obtain a long-cycle sodium ion battery electrolyte.

7. The method for preparing a long-cycle electrolyte for a sodium ion battery according to claim 6, characterized in that: The molecular sieve is 3 Å or 4 Å molecular sieve.

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