NaBOB salt sodium-ion battery electrolyte based on dipole-dipole interaction and preparation method of NaBOB salt sodium-ion battery electrolyte

Abstract

The invention discloses a NaBOB salt sodium-ion battery electrolyte based on dipole-dipole interaction and a preparation method thereof.The NaBOB salt sodium-ion battery electrolyte comprises sodium salt, solvents and a film-forming additive, the sodium salt is sodium bis (oxalato) borate (NaBOB), and the solvents comprise the first solvent and the second solvent; the first solvent is one or more than two of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, 4-isopropyl phenyl diphenyl phosphate, diphenyl octyl phosphate and trioctyl phosphate; and the second solvent is one or more than two of 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether, tetrafluoropropanol, tri-(2, 2, 2-trifluoroethyl)-phosphate, 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether, bis (2, 2, 2-trifluoroethyl) ether and 1H, 1H, 5H octafluoropentyl 1, 1, 2, 2-tetrafluoroethyl ether. The method has the characteristics of high stability, good cyclicity and excellent safety.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to a NaBOB salt sodium ion battery electrolyte based on dipole-dipole action and a preparation method thereof. Background Art

[0002] Exploring efficient, safe, environmentally friendly, and low-cost energy storage systems that meet the requirements of a sustainable circular economy model is one of the great challenges facing mankind. Sodium-ion batteries have the advantages of high element abundance and low cost, and are considered to be an ideal choice for medium- and low-speed electric vehicles and large-scale energy storage.

[0003] However, traditional ester-based electrolytes are highly flammable, have poor thermal stability, and pose serious safety threats. To address these troubling challenges, several safe electrolytes have been extensively studied, such as aqueous systems, ionic liquids, phosphorus-based, and fluorine-based non-flammable electrolytes, to construct safe sodium-ion batteries (SIBs). However, the practical application of these electrolytes is hampered by various issues, such as unsatisfactory electrode-electrolyte interfaces, poor electrode compatibility, and high cost. Therefore, it is crucial to explore electrolytes with excellent comprehensive properties while improving safety and sodium storage performance.

[0004] Sodium bis(oxalatoborate) (NaBOB) is a low-cost, fluorine-free sodium salt with a high decomposition temperature (≥300°C) and better high-temperature stability than NaPF6. NaBOB can assist in the formation of a stable solid electrolyte interface (SEI) film in the electrolyte, effectively inhibiting the direct contact between the electrolyte and the electrode surface, and playing a role in inhibiting electrolyte corrosion and passivating aluminum foil. In 2020, Younesi et al. proposed a flame-retardant electrolyte based on NaBOB and trimethyl phosphate (TMP) as a single solvent, but this work failed to extend the application of the electrolyte to actual batteries. Phosphate electrolytes have the advantages of low cost, wide electrochemical window, and good salt solubility, and are the most promising flame-retardant electrolytes. However, low-concentration phosphate electrolytes cannot work with carbon-based anodes because they cannot form a stable and dense SEI film. In previous work, researchers prepared local high-concentration electrolytes (LHCEs) by adding inert diluents to local high-concentration electrolytes. LHCE has good electrochemical performance and good wettability. However, traditional hydrofluoroether diluents still have problems such as low boiling point, flammability and high cost. In addition, since low-polarity diluents are often not miscible with high-polarity HCE, few diluents can be used to form LHCE. Summary of the invention

[0005] The invention aims to provide a NaBOB salt sodium ion battery electrolyte based on dipole-dipole action and a preparation method thereof, which has the characteristics of high stability, good cyclability and excellent safety.

[0006] The present invention can be implemented by the following technical solutions: The invention discloses a NaBOB salt sodium ion battery electrolyte based on dipole-dipole action. The electrolyte comprises a sodium salt, a solvent and a film-forming additive. The sodium salt is sodium bis(oxalatoborate) (NaBOB). The solvent comprises a first solvent and a second solvent. The first solvent is one or more of trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), triphenyl phosphate (TPP), 4-isopropylphenyl diphenyl phosphate (IPPP), diphenyl octyl phosphate (DPOF) and trioctyl phosphate (TOP). The second solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), tetrafluoropropanol (TFP), tris-(2,2,2-trifluoroethyl)-phosphate (TFEP), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE) and 1H, 1H, 5H octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE). [sysucph1] The first solvent is a flame retardant organic solvent that can dissolve NaBOB, and the second solvent is an organic solvent that is miscible with the first solvent and has better reducing properties than the first solvent; the second solvent can weaken the first solvent phosphate ester salt and Na + The coordination strength of the second solvent is weakened, which is beneficial to reducing the desolvation energy barrier and accelerating the interfacial desolvation process; the anions of the second solvent and the first solvent can interact with each other by dipole-dipole to form a new solvation structure, thereby improving the reduction potential of phosphate as a whole.

[0007] Furthermore, the volume of the second solvent is 10-100%vt of the first solvent, preferably 20-70%vt. When the second solvent content is too little, the interaction range of the two solvents is small, and the free state of the first solvent is too much, which will still produce a strong reduction effect, resulting in the phenomenon of battery bloating; the conductivity decreases with the increase of the diluent content. When the second solvent content is too much, the electrolyte concentration is too low, which is not conducive to the cycle stability of the battery.

[0008] Furthermore, the concentration of the sodium salt is 0.1 to 1.0 mol / L. This depends on the solubility of the organic solvent for NaBOB, but too low a sodium salt concentration is not suitable for sodium ion batteries; too high a sodium salt concentration will also increase the amount of the second solvent used and increase costs.

[0009] Furthermore, the film-forming additive is one or more of fluoroethylene carbonate (FEC), difluoroethylene sulfate (DTD), propylene sulfate (TS), vinylene carbonate (VC), sodium difluorophosphate (NaPO2F2) and sodium difluorooxalate borate (NaDFOB). Fluoroethylene carbonate (FEC), sodium difluorophosphate (NaPO2F2) and sodium difluorooxalate borate (NaDFOB) can decompose on the electrode surface to form an inorganic NaF-rich SEI film; vinyl sulfate (DTD) and propylene sulfate (TS) can decompose on the electrode surface to form an inorganic Na2SO4-rich SEI film; vinylene carbonate (VC) decomposes on the negative electrode surface to generate CO2 and polymers, wherein CO2 further reacts with the negative electrode surface to reduce and decompose to form an inorganic SEI film containing Na2CO3.

[0010] Furthermore, the concentration of the film-forming additive is 0.01-10%wt, preferably 0.01-5%wt. Too little film-forming additive leads to incomplete film formation and unstable interface structure, causing a decrease in battery capacity and cycle life; too much film-forming additive may cause the interface film to be too thick, increase battery impedance, and affect battery performance.

[0011] Furthermore, the positive electrode material of the sodium ion battery is a polyanion material, such as sodium vanadium phosphate, sodium vanadium pyrophosphate, etc.

[0012] Furthermore, the negative electrode material of the sodium ion battery is hard carbon.

[0013] Another aspect of the present invention is to protect the preparation method of the above-mentioned NaBOB salt sodium ion battery electrolyte based on dipole-dipole action, comprising the following steps: S1. Preparation of a first purified solution: dissolving sodium salt NaBOB in a first solvent under protective atmosphere conditions to obtain a first purified solution; S2, preparation of a second purified solution: adding a second solvent to the first purified solution obtained in step S1, and mixing them uniformly to obtain a second purified solution; S3, mixing of electrolyte: dissolving the film-forming additive into the second purified solution obtained in step S2, and mixing evenly to obtain a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction.

[0014] Furthermore, the protective atmosphere [sysucph2] is argon or nitrogen. Specifically, the water content is ≤0.01 ppm, and the oxygen content is ≤0.01 ppm.

[0015] Furthermore, in steps S2 and S3, the uniform mixing method is shaking with an oscillator or heating and dissolving.

[0016] The present invention discloses a NaBOB salt sodium ion battery electrolyte based on dipole-dipole action and a preparation method thereof, which has the following beneficial effects: The present invention adds a mixed solvent system of a first solvent and a second solvent to a low-concentration phosphate electrolyte, adjusts the interface solvation structure of the electrolyte through the dipole-dipole effect between the first solvent and the second solvent, and the second solvent weakens the interaction between the first solvent phosphate ester salt and Na + The coordination strength of the second solvent is weakened, which is beneficial to reducing the desolvation energy barrier, accelerating the interfacial desolvation process, and preventing the phosphate from staying on the electrode surface and being reduced and decomposed. On the other hand, the interaction between the second solvent and the first solvent becomes stronger, thereby increasing the reduction potential of the phosphate as a whole, that is, the stability of the electrolyte system. In addition, the uncoordinated second solvent can be reduced at the negative electrode before the first solvent, forming a stable SEI film, which prevents the free phosphate from directly contacting the negative electrode interface and continuously decomposing to produce gas, so the bulging phenomenon disappears. This design significantly improves the safety, stability and cycle performance of the electrolyte.

[0017] In addition, the electrolyte of the present invention enables low-concentration or even ultra-low-concentration NaBOB-based phosphate electrolytes to be truly applied to actual batteries, and the soft-pack batteries based on the electrolyte have excellent electrochemical properties, which is conducive to the commercial development of new sodium salt NaBOB-based flame-retardant electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Cycling performance curves of HC / / NFPP soft-pack batteries assembled with the electrolytes of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0020] The invention discloses a NaBOB salt sodium ion battery electrolyte based on dipole-dipole action. The electrolyte comprises a sodium salt, a solvent and a film-forming additive. The sodium salt is sodium bis(oxalatoborate) (NaBOB). The solvent comprises a first solvent and a second solvent. The first solvent is one or more of trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), triphenyl phosphate (TPP), 4-isopropylphenyl diphenyl phosphate (IPPP), diphenyl octyl phosphate (DPOF) and trioctyl phosphate (TOP). The second solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), tetrafluoropropanol (TFP), tris-(2,2,2-trifluoroethyl)-phosphate (TFEP), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE) and 1H,1H,5H octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE).

[0021] Furthermore, the volume of the second solvent is 10-100% vt of the first solvent, preferably 20-70% vt.

[0022] Furthermore, the concentration of the sodium salt is 0.1 to 1.0 mol / L.

[0023] Furthermore, the film-forming additive is one or more of fluoroethylene carbonate (FEC), diethylene sulfate (DTD), propylene sulfate (TS), vinylene carbonate (VC), sodium difluorophosphate (NaPO2F2) and sodium difluorooxalatoborate (NaDFOB).

[0024] Furthermore, the concentration of the film-forming additive is 0.01 to 10% wt, preferably 0.01 to 5% wt.

[0025] Furthermore, the positive electrode material of the sodium ion battery is a polyanion material, such as sodium vanadium phosphate, sodium vanadium pyrophosphate, and the like.

[0026] Furthermore, the negative electrode material of the sodium ion battery is hard carbon.

[0027] Another aspect of the present invention is to protect the preparation method of the above-mentioned NaBOB salt sodium ion battery electrolyte based on dipole-dipole action, comprising the following steps: S1. Preparation of a first purified solution: dissolving sodium salt NaBOB in a first solvent under protective atmosphere conditions to obtain a first purified solution; S2, preparation of a second purified solution: adding a second solvent to the first purified solution obtained in step S1, and mixing them uniformly to obtain a second purified solution; S3, mixing of electrolyte: dissolving the film-forming additive into the second purified solution obtained in step S2, and mixing evenly to obtain a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction.

[0028] Furthermore, the protective atmosphere is argon or nitrogen. Specifically, the water content is ≤0.01 ppm, and the oxygen content is ≤0.01 ppm.

[0029] Furthermore, in steps S2 and S3, the uniform mixing is achieved by shaking with a shaker or heating to dissolve.

[0030] Embodiment 1: First, 0.4 mol / L NaBOB was dissolved in TMP solvent to prepare 1 ml electrolyte; then 0.5 ml diluent TFEP was added; finally, 2% FEC and 3% VC were added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.27 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium pyrophosphate (NFPP), and the negative electrode material is hard carbon (HC).

[0031] Example 2 First, 0.38 mol / L NaBOB was dissolved in TEP solvent to prepare 1 ml electrolyte; then 0.6 ml diluent TFP was added; finally, 2% TS and 3% VC were added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.24 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium pyrophosphate (NFPP), and the negative electrode material is hard carbon (HC).

[0032] Example 3 First, 0.3 mol / L NaBOB was dissolved in TBP solvent to prepare 1 ml electrolyte; then 0.5 ml diluent HFE was added; finally, 2% NaDFOB and 2TS% were added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.20 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium phosphate (NVP), and the negative electrode material is hard carbon (HC).

[0033] Example 4 First, 0.5 mol / L NaBOB was dissolved in TPP solvent to prepare 1 ml electrolyte; then 0.2 ml diluent TTE was added; finally, 2% DTD and 5 VC% were added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.42 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium pyrophosphate (NFPP), and the negative electrode material is hard carbon (HC).

[0034] Example 5 First, 0.38 mol / L NaBOB was dissolved in TEP solvent to prepare 1 ml electrolyte; then 0.6 ml diluent TFP was added; finally, 2% TS was added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.24 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium phosphate (NVP), and the negative electrode material is hard carbon (HC).

[0035] Example 6 First, 0.38 mol / L NaBOB was dissolved in TEP solvent to prepare 1 ml electrolyte; then 0.5 ml diluent TFEP was added; finally 3 VC% was added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.24 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium phosphate (NVP), and the negative electrode material is hard carbon (HC).

[0036] Comparative Example 1 First, 0.4 mol / L NaBOB was dissolved in TMP solvent to prepare 1 ml electrolyte; then 2% FEC and 3% VC were added to the mixed electrolyte and mixed evenly to obtain the electrolyte. The final concentration of the electrolyte was 0.26 mol / L. The positive electrode material of the sodium ion battery is sodium vanadium pyrophosphate (NFPP), and the negative electrode material is hard carbon (HC).

[0037] The above electrolyte was used to make 1 Ah soft pack batteries, and the separator used was glass fiber (Whatman GF / F). The cycle performance of the HC / / NFPP soft pack battery made in this application example is shown in Figure 2. Figure 1 After 100 weeks of cycle testing, the capacity retention rate of the soft-pack battery of Comparative Example 1 without adding a stabilizing diluent was only 54.79%; the capacity retention rate of the soft-pack battery of Example 1 with adding a stabilizing diluent was as high as 94.90%, and the cycle stability was greatly improved.

[0038] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction, comprising a sodium salt, a solvent and a film-forming additive, characterized in that: The sodium salt is sodium bis(oxalatoborate) (NaBOB), the solvent includes a first solvent and a second solvent, the first solvent is one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, 4-isopropylphenyl diphenyl phosphate, diphenyl octyl phosphate, and trioctyl phosphate. The second solvent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, tetrafluoropropanol, tris-(2,2,2-trifluoroethyl)-phosphate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and 1H,1H,5H octafluoropentyl 1,1,2,2-tetrafluoroethyl ether.

2. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The volume of the second solvent is 10-100%vt of the first solvent.

3. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The concentration of the sodium salt is 0.1-1.0 mol / L.

4. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The film-forming additive is one or more of fluoroethylene carbonate, vinyl sulfate, propylene sulfate, vinylene carbonate, sodium difluorophosphate and sodium difluorooxalatoborate.

5. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The concentration of the film-forming additive is 0.01 to 10%wt.

6. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The positive electrode material of the sodium ion battery is a polyanion material.

7. The NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 1, characterized in that: The negative electrode material of the sodium ion battery is hard carbon.

8. A method for preparing a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction as claimed in any one of claims 1 to 7, characterized in that The following steps are involved: S1. Preparation of a first purified solution: dissolving sodium salt NaBOB in a first solvent under protective atmosphere conditions to obtain a first purified solution; S2, preparation of a second purified solution: adding a second solvent to the first purified solution obtained in step S1, and mixing them uniformly to obtain a second purified solution; S3, mixing of electrolyte: dissolving the film-forming additive into the second purified solution obtained in step S2, and mixing evenly to obtain a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction.

9. The method for preparing a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 8, characterized in that: The protective atmosphere is argon or nitrogen.

10. The method for preparing a NaBOB salt sodium ion battery electrolyte based on dipole-dipole interaction according to claim 9, characterized in that: In steps S2 and S3, the uniform mixing is performed by shaking with a shaker or heating and dissolving.

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