Silane-based diluent-based sodium-sulfur battery electrolyte, preparation method and application thereof

Abstract

The application discloses a kind of sodium-sulfur battery electrolyte based on silane-based diluent and its preparation method and application, belong to sodium metal battery technical field.The concentration of sodium salt in the electrolyte is 1.0~4.0M, main solvent is ether polar solvent, diluent is weak polar silane-based solvent;Among them, weak polar silane-based solvent is one or more mixed in dimethyldimethoxysilane, dimethyldiethoxysilane, methyltriethoxysilane and tetraethyl silicate.The weak polar silane-based solvent of light weight is used as electrolyte diluent in the application, can effectively reduce the overall concentration of electrolyte, reduce the consumption of sodium salt;Sodium-sulfur battery electrolyte prepared with the diluent can effectively inhibit the dissolution and shuttle effect of polysulfide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium metal battery, and particularly relates to a sodium-sulfur battery electrolyte based on a silane-based diluent and a preparation method and application thereof. BACKGROUND

[0002] In recent years, the energy density of lithium ion batteries has reached a bottleneck. People pursue higher battery energy density and turn their attention to sulfur, which has lower cost and high theoretical capacity (1675 mAh·g -1 ). Metal lithium has low oxidation-reduction potential (-3.04 V vs. standard hydrogen electrode) and super-high theoretical capacity (3860 mAh·g -1 ), and becomes one of the most attractive negative electrode materials. Lithium-sulfur batteries have rapidly developed in the past decade, but lithium resources are scarce, with a crustal abundance of only 0.01 wt.%. Relatively, sodium resources are much more abundant, with a crustal abundance of 2.3 wt.%, and the price is 25 times lower than that of lithium. Therefore, room-temperature sodium-sulfur batteries are more ideal energy storage solutions.

[0003] Among many battery technologies, sodium-sulfur batteries have the advantages of easy availability of raw materials, high energy density, and low price, and are one of the most potential battery systems. However, sodium-sulfur batteries are still in the initial stage, and their commercialization faces more severe challenges than lithium-sulfur batteries: 1) Sodium polysulfide is generated in the charging and discharging process of sodium-sulfur batteries, and its dissolution in the electrolyte leads to a concentration difference between the positive and negative electrodes. This difference promotes sodium polysulfide to "shuttle" to the negative electrode with the electrolyte, and reacts with metal sodium, thereby causing loss of active material and loss of metal sodium. 2) In the charging and discharging process, sulfur and polysulfides have poor electronic conductivity, and their volume changes greatly. Therefore, in order to maintain fast electron transfer and good structural integrity, a high-conductivity host material needs to be used. 3) With the progress of electrochemical reaction, metal sodium continuously peels off and plating occurs on the electrode surface. However, due to uneven distribution of electrons and ions on the electrode surface, metal sodium nucleates and grows unevenly, and finally grows into sodium dendrites. The continuous growth of sodium dendrites may penetrate the separator, causing internal short circuit of the battery, and thus causing safety hazards.

[0004] In order to solve the above problems, researchers have done a lot of research work in the aspects of positive electrode structure design, sodium metal negative electrode modification, new type of separator design, electrolyte engineering, etc. For example, Zhao et al. used 5% fluorinated ethylene carbonate as an additive to add to 1.0M NaClO4-ethylene carbonate / propylene carbonate (EC / PC, V / V=1 / 1) electrolyte, and used carbon / sulfur composite material as cathode, to provide up to 1651 mAh·g -1The reversible capacity of the sodium-sulfur battery is improved. The solid electrolyte interface (SEI) is more effective, and the conversion between S and Na2S is more complete. Notably, the nucleophilic reaction between the carbonate electrolyte and sodium polysulfide occurs, and the cycle life of the sodium-sulfur battery using the carbonate electrolyte is significantly reduced in the case of a poor electrolyte. When the conventional dimethyl ether-based electrolyte is used, the sulfur positive electrode generates sodium polysulfide that is easily soluble in the electrolyte during the conversion process, and the "shuttle effect" occurs, resulting in loss of active material and passivation of the sodium metal negative electrode. Therefore, electrolyte engineering is considered to be an excellent solution to achieve long-life cycling of the sodium-sulfur battery. Compared with other improvement schemes, the development of a new electrolyte can better adapt to the existing production line and accelerate the industrialization of the sodium-sulfur battery. SUMMARY

[0005] The present application aims to provide a silane-based diluent-based sodium-sulfur battery electrolyte and its preparation method and application. The electrolyte uses sodium salt as the solute, an ether-based polar solvent as the main solvent, and a low-polarity silane-based solvent as the diluent. The prepared local high-concentration electrolyte can simultaneously stabilize the metal sodium negative electrode and the sulfur positive electrode.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] One of the technical schemes of the present application: a silane-based diluent-based sodium-sulfur battery electrolyte is provided, the concentration of sodium salt in the electrolyte is 1.0-4.0 M, the main solvent is an ether-based polar solvent, and the diluent is a weakly polar silane-based solvent.

[0008] The weakly polar silane-based solvent is a mixture of one or more of dimethyldimethoxysilane (DMMS), dimethyldiethoxysilane (DEMS), methyltriethoxysilane (MTES), and tetraethyl orthosilicate (TEOS).

[0009] The density of the DMMS solvent at 25℃ is 0.848 g·cm -3 , and the dielectric constant (ε) is 3.70, which has poor solvation ability and good compatibility with sodium metal.

[0010] The density of the DEMS solvent at 25℃ is 0.84 g·cm -3 , and the dielectric constant (ε) is 3.22, which has poor solvation ability and good compatibility with sodium metal.

[0011] The density of the MTES solvent at 25℃ is 0.895 g·cm -3 , and the dielectric constant (ε) is 3.85, which has poor solvation ability and good compatibility with sodium metal.

[0012] The density of the TEOS solvent is 0.93 g·cm at 25 DEG C. -3 The dielectric constant (ε) is 4.10, and the solvent capacity is poor, which is not conducive to the dissolution of polysulfides and has good compatibility with sodium metal.

[0013] The ideal sodium-sulfur battery electrolyte should have high ionic conductivity, relatively low density, excellent electrode stability, and can effectively inhibit the dissolution of polysulfides. By increasing the salt concentration in the ether-based electrolyte, the dissolution of polysulfides can be effectively reduced, but high-concentration electrolyte has the disadvantages of high electrolyte viscosity and high density, which limits its practical application. By introducing a diluent into the high-concentration electrolyte, the unique solvation structure of the high-concentration electrolyte can be maintained, and the viscosity of the electrolyte can be significantly reduced, so it has attracted widespread attention. However, the diluent used in the current local high concentration is mostly fluorine-containing solvent, which has the problems of high density, high price, and can corrode the sodium metal negative electrode. By increasing the concentration, the dissolution of polysulfides can be effectively inhibited, but the economic benefit is significantly reduced. Therefore, the local high-concentration electrolyte based on the low-cost, low-density and environmentally friendly silane-based diluent provided by the present application can significantly reduce the overall cost, density and environmental toxicity of the electrolyte, and solve the problem of corrosion of fluorine-containing diluent on sodium metal, realizing long-life cycling of high-specific-energy sodium metal-sulfur batteries.

[0014] Preferably, the sodium salt is one or more of a mixture of sodium bisfluorosulfonylimide (NaFSI), sodium triflate (NaOTF), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), and sodium hexafluorophosphate (NaPF6).

[0015] Preferably, the ether-based polar solvent is ethylene glycol dimethyl ether (DME).

[0016] Preferably, the volume ratio of the main solvent to the diluent is 2:1 to 1:4.

[0017] The second technical scheme of the present application provides a preparation method of the sodium-sulfur battery electrolyte based on the silane-based diluent, and the steps include:

[0018] Mixing the sodium salt, the main solvent and the diluent to obtain the sodium-sulfur battery electrolyte based on the silane-based diluent.

[0019] The third technical scheme of the present application provides an application of the sodium-sulfur battery electrolyte based on the silane-based diluent in the preparation of a sodium-sulfur battery.

[0020] Preferably, the positive electrode of the sodium-sulfur battery is a sulfidized polyacrylonitrile positive electrode.

[0021] More preferably, the raw materials of the sulfidized polyacrylonitrile positive electrode include sulfidized polyacrylonitrile, a conductive agent and a binder.

[0022] More preferably, the mass ratio of the sulfidized polyacrylonitrile, the conductive agent and the binder is (75-95):(2.5-12.5):(2.5-12.5).

[0023] More preferably, the preparation step of the sulfidized polyacrylonitrile comprises mixing sulfur powder and polyacrylonitrile in a mass ratio of 1:4, calcining at 300-500℃ for 1-3h under nitrogen atmosphere, and grinding to a particle size of 100-150nm to obtain the sulfidized polyacrylonitrile.

[0024] More preferably, the conductive agent comprises at least one of Super P, acetylene black (AB), conductive carbon black, carbon nanotubes and graphene.

[0025] More preferably, the binder comprises at least one of styrene butadiene rubber (SBR) emulsion, polytetrafluoroethylene, carboxymethyl cellulose (CMC) and polyvinylidene fluoride.

[0026] The beneficial technical effects of the present application are as follows:

[0027] (1) The present application uses a light and weakly polar silane-based solvent as an electrolyte diluent, which can effectively reduce the overall concentration of the electrolyte and reduce the consumption of sodium salt.

[0028] (2) The sodium-sulfur battery electrolyte prepared by using a weakly polar silane-based solvent as a diluent can effectively inhibit the dissolution and shuttle effect of polysulfides.

[0029] (3) The inner layer of the electrode / electrolyte interface of the sodium metal-sulfur battery provided by the present application is rich in inorganic components, and the outer layer is a polymer layer. This multi-layer structure can promote the uniform deposition of sodium metal and inhibit the growth of sodium dendrites.

[0030] (4) The sodium-sulfur battery electrolyte based on the silane-based diluent provided by the present application has excellent electrochemical performance with the metal sodium-sulfur battery made of sulfidized polyacrylonitrile positive electrode, and has important application prospects in the field of sodium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The electrochemical impedance test results of the stainless steel-stainless steel battery in Example 1.

[0032] Figure 2 The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Example 1.

[0033] Figure 3 The cycle stability test results of the sodium-sulfur battery in Example 1.

[0034] Figure 4Scanning electron micrograph of sodium metal deposition onto carbon-coated aluminum foil in a sodium / aluminum (Na / Al) cell of Example 1.

[0035] Figure 5 Coulombic efficiency plot for a sodium / aluminum (Na / Al) cell of Example 1.

[0036] Figure 6 Sodium deposition / stripping polarization curve for a sodium metal symmetric cell of Example 2.

[0037] Figure 7 Sodium deposition / stripping polarization curve for a sodium metal symmetric cell of Example 3.

[0038] Figure 8 Sodium deposition / stripping polarization curve for a sodium metal symmetric cell of Example 4.

[0039] Figure 9 Coulombic efficiency plot for a sodium / aluminum (Na / Al) cell of Example 5.

[0040] Figure 10 Coulombic efficiency plot for a sodium / aluminum (Na / Al) cell of Example 6. DETAILED DESCRIPTION

[0041] Various illustrative embodiments of the present application are described in detail below. The detailed description is presented in terms of specific embodiments which include particular components, materials, and dimensions. Those skilled in the art will recognize that the application can be practiced with

[0042] Also, for ranges set forth herein (e.g., "between 1 and 5," "between 3 and 7," or, more generally, "between a lower limit and an upper limit"), ranges excluding the recited limits are also included (e.g., "between 1 and 5" includes 1 and 5, but not 1 and 5). Each intervening value of the recited range is also included (e.g., "between 1 and 5" includes 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, and 5.5). For ranges excluding the recited limits, the endpoints are specifically excluded. This means, for example, that a range of "between 1 and 5" excludes 1 and 5, but not 1 and 5. Unless otherwise stated, the limit for any numerical range to be within 10% of the stated range limits.

[0043] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. Unless otherwise indicated, all measurements are made in SI units.

[0044] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," and the like are open-ended terms that are intended to mean including, but not limited to.

[0045] Unless otherwise specified, "room temperature" in the examples of the present application means a temperature of 25 °C.

[0046] Example 1

[0047] (1) In an argon-filled glove box, DME, DMMS solvent was treated with molecular sieve dehydration, and NaFSI was dried at 80°C overnight.

[0048] (2) 203.12 mg of NaFSI obtained in step (1) was fully dissolved in 156 μL of DME solvent obtained in step (1), and 283 μL of DMMS obtained in step (1) was added to obtain an electrolyte with a molar ratio of NaFSI:DME:DMMS of 1:1.5:2 (sodium salt concentration of 2.6 M).

[0049] (3) 4 g of sulfur powder and 1 g of polyacrylonitrile were mixed and calcined at 450°C for 3 h under a nitrogen atmosphere, and after grinding, sulfurized polyacrylonitrile powder (100-150 nm) was obtained.

[0050] (4) The sulfurized polyacrylonitrile powder obtained in step (3) was mixed with Super P, CMC, and SBR at a ratio of 8:1:0.5:0.5 to obtain a sulfurized polyacrylonitrile slurry.

[0051] (5) The slurry obtained in step (4) was uniformly coated on a carbon-coated aluminum foil, and dried at 80°C for 10 h in a vacuum drying oven to obtain a sulfurized polyacrylonitrile positive electrode material.

[0052] (6) The sulfurized polyacrylonitrile positive electrode material obtained in step (4) was punched into an electrode sheet with a diameter of 6 mm using a punch machine and transferred to a glove box.

[0053] (7) The solution obtained in step (2) was used as the electrolyte of the battery, and Glassfiber / A was used as the separator to assemble a stainless steel-stainless steel battery and perform electrochemical impedance testing at room temperature.

[0054] (8) The solution obtained in step (2) was used as the electrolyte of the battery, and Glassfiber / A was used as the separator to assemble a sodium metal symmetric battery and perform electrochemical performance testing at room temperature.

[0055] (9) The solution obtained in step (2) was used as the electrolyte of the battery, and Glassfiber / A was used as the separator, carbon-coated aluminum foil was used as the working electrode, and sodium was used as the counter electrode to assemble a Na / Al battery and perform sodium deposition testing at room temperature.

[0056] (10) The solution obtained in step (2) was used as the electrolyte of the battery, and Glassfiber / A was used as the separator, sodium metal was used as the negative electrode, and the sulfurized polyacrylonitrile positive electrode material obtained in step (6) was used as the positive electrode to assemble a sodium-sulfur battery and perform electrochemical performance testing at room temperature. ​

[0057] The results of the electrochemical impedance spectroscopy (25°C, frequency range 100000-0.1 Hz) of the stainless steel-stainless steel battery in Example 1 are shown in FIG. Figure 1 ,from Figure 1 It can be seen from the figure that the electrolyte has a high ionic conductivity.

[0058] Sodium deposition / stripping polarization curves of the sodium metal symmetric battery in Example 1 (25°C, current density of 0.5 mA·cm -2 , the deposition capacity is 0.5 mAh·cm -2 )See Figure 2 ,from Figure 2 It can be seen that the assembled sodium metal symmetric battery has good cycling stability.

[0059] The cycle stability test results of the sodium-sulfur battery in Example 1 are shown in Figure 3 , the positive and negative electrode surface capacity ratio is 4, and the current density is 0.2A·g -1 Under the conditions of 1.5 mol·L / min, the first reversible specific capacity of the polyacrylonitrile sulfide cathode is about 421 mAh·g -1 After 100 cycles, there is almost no capacity decay.

[0060] In the sodium / aluminum (Na / Al) battery of Example 1, the current density is 0.5 mA·cm -2 , the deposition amount is 2mAh·cm -2 The metallic sodium was deposited on the carbon-coated aluminum foil under the conditions of Figure 4 .from Figure 4 From the scanning electron microscope photos, it can be observed that the deposition of sodium metal is relatively smooth and uniform, indicating that the prepared electrolyte can achieve reversible deposition and stripping of metallic sodium.

[0061] The constant current charge and discharge method was used and the test was performed at 1.0 mA cm -2 Current density, 1.0 mAh cm -2 The coulombic efficiency of the sodium / aluminum (Na / Al) battery in Example 1 under the conditions of the deposition amount is shown in FIG. Figure 5 .

[0062] Example 2

[0063] Compared with Example 1, the difference is that the content of DMMS added in step (2) is different, and the electrolyte with a molar ratio of NaFSI:DME:DMMS of 1:1.5:3 (sodium salt concentration is 1.7 M) is obtained.

[0064] Figure 6 The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Example 2 (25°C, current density of 1 mA·cm -2, deposition capacity of 1 mAh-cm -2 ). Figure 6 It is shown that the symmetric cell has a large polarization potential and a short circuit occurs at around 400 h.

[0065] Example 3

[0066] Compared with Example 1, the difference is that no diluent is added in step (2), and a high-concentration electrolyte with a molar ratio of NaFIS:DME of 1:1.5 (sodium salt concentration of 6.4 M) is obtained.

[0067] Figure 7 The sodium deposition / stripping polarization curve of the sodium metal symmetric cell in Example 3 (25°C, current density of 0.5 mA-cm -2 , deposition capacity of 0.5 mAh-cm -2 ). Figure 7 It is shown that the symmetric cell has a large polarization potential and a short circuit occurs at around 470 h.

[0068] Example 4

[0069] Compared with Example 1, the difference is that the diluent in step (2) is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and an electrolyte with the same molar ratio is obtained (sodium salt concentration of 2.2 M).

[0070] Figure 8 The sodium deposition / stripping polarization curve of the sodium metal symmetric cell in Example 4 (25°C, current density of 0.5 mA-cm -2 , deposition capacity of 0.5 mAh-cm -2 ). Figure 8 It is shown that the symmetric cell has a short circuit at around 540 h.

[0071] Example 5

[0072] Compared with Example 1, the difference is that the diluent in step (2) is 3-fluorotoluene, and an electrolyte with the same molar ratio is obtained (sodium salt concentration of 2.7 M).

[0073] Figure 9 The coulombic efficiency diagram of the sodium / aluminum (Na / Al) cell in Example 5 (1.0 mA-cm -2 current density, 1.0 mAh-cm -2 deposition capacity). Figure 9 It is shown that the coulombic efficiency of the cell is very low, and the highest is not more than 20%.

[0074] Example 6

[0075] Compared with Example 2, the difference is that the diluent in step (2) is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, to obtain an electrolyte with a molar ratio of NaFIS:DME:diluent of 1:1.5:3 (sodium salt concentration of 1.6 M).

[0076] Figure 10 The coulombic efficiency map of the sodium / aluminum (Na / Al) battery in Example 6 (1.0 mA·cm -2 Current density, 1.0 mA·cm -2 Deposited amount). Figure 10 It is shown that the battery has a high coulombic efficiency, but because the diluent has a side reaction with sodium metal, the coulombic efficiency decreases significantly.

[0077] The above-described examples are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A sodium-sulfur battery electrolyte based on a silane-based diluent, characterized in that: The sodium salt, the main solvent and the diluent are mixed to obtain the sodium-sulfur battery electrolyte based on the silane-based diluent; the concentration of the sodium salt in the sodium-sulfur battery electrolyte based on the silane-based diluent is 1.0-4.0 M, the main solvent is an ether polar solvent, and the diluent is a weakly polar silane-based solvent; The weakly polar silane-based solvent is a mixture of one or more of dimethyldimethoxysilane, dimethyldiethoxysilane, methyltriethoxysilane and tetraethyl silicate; The sodium salt is a mixture of one or more of sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide and sodium hexafluorophosphate; The ether polar solvent is ethylene glycol dimethyl ether; The volume ratio of the main solvent to the diluent is 2:1 to 1:

4.

2. Use of the sodium-sulfur battery electrolyte based on a silane-based diluent according to claim 1 in the preparation of a sodium-sulfur battery.

3. The use according to claim 2, characterized in that The positive electrode of the sodium-sulfur battery is a sulfurized polyacrylonitrile positive electrode.

4. The use according to claim 3, characterized in that The raw materials of the sulfided polyacrylonitrile positive electrode include sulfided polyacrylonitrile, a conductive agent and a binder.

5. The use according to claim 4, characterized in that The mass ratio of the sulfided polyacrylonitrile, the conductive agent and the binder is (75-95): (2.5-12.5): (2.5-12.5).

6. The use according to claim 4, characterized in that The preparation steps of the sulfide polyacrylonitrile include: mixing sulfur powder and polyacrylonitrile in a mass ratio of 1:4, calcining at 300-500° C. for 1-3 hours under a nitrogen atmosphere, and grinding to a particle size of 100-150 nm to obtain the sulfide polyacrylonitrile.

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