Sodium-sulfur battery electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium metal batteries, and particularly discloses a sodium-sulfur battery electrolyte as well as a preparation method and application thereof. In the electrolyte, a main solvent is an ester polar solvent, a diluent is an amphiphilic fluorine-containing solvent, and a cosolvent is a common carbonic ester cosolvent; the amphiphilic fluorinated solvent is selected from one or more of 1, 1, 2, 2-tetrafluoroethyl methyl ether, hexafluoroisopropyl methyl ether or 1, 1, 2, 2-tetrafluoroethyl ethyl ether, and the amphiphilic fluorinated solvent is selected from one or more of hexafluoroisopropyl methyl ether, hexafluoroisopropyl methyl ether and 1, 1, 2, 2-tetrafluoroethyl ethyl ether. According to the invention, the amphiphilic fluorinated solvent is adopted as an electrolyte diluent, so that the capacity of the sodium-sulfur battery in an extreme environment can be effectively maintained, and the dissolution and shuttle effects of polysulfide are inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium metal batteries, and specifically discloses a sodium-sulfur battery electrolyte, a preparation method thereof, and applications thereof. Background Art

[0002] The growth of energy density of lithium-ion batteries is limited, and sulfur cathode materials have become the focus of researchers due to their advantages such as high theoretical specific capacity, environmental friendliness and low cost. Although lithium-sulfur batteries have developed rapidly, lithium resources are scarce. Sodium resources are abundant and inexpensive, so sodium-sulfur batteries have become a research hotspot. Na-S batteries have the advantages of high capacity, high charge and discharge efficiency, long cycle life, low cost and non-toxicity, making them suitable for large-scale markets, especially showing potential in energy storage and environmental protection applications. However, sodium-sulfur batteries have problems such as low sulfur conductivity, electrode structure collapse, polysulfide shuttle effect, unstable SEI interface and dendrite formation.

[0003] To address these issues, researchers have conducted extensive research on cathode structure, sodium metal anode modification, separator design, and electrolyte design. Existing technologies have improved battery cycling stability and Coulombic efficiency by optimizing coating thickness. Sulfur's low conductivity can be compensated by confining it within a porous conductive matrix, while also uniformly distributing ions to suppress Na dendrite growth. However, this technology involves complex and costly modification of the sodium metal anode.

[0004] In order to solve the problems existing in the above-mentioned prior art, another prior art can effectively reduce the solubility of polysulfides by increasing the salt concentration in the ether-based electrolyte, thereby improving battery performance. However, high-concentration electrolytes are often accompanied by problems of high viscosity and high density, which limits their feasibility in practical applications. To overcome this challenge, in recent years, people have tried to introduce diluents into high-concentration electrolytes to significantly reduce the viscosity of the electrolyte while maintaining a unique solvation structure, so that it has both excellent stability and operability. Although the fluorine-containing diluents used in the study can effectively regulate the properties of the electrolyte, the weakly polar fluorinated solvents used are all double-sided fluorinated solvents, with sodium-phobic chain segments on both sides, which are difficult to form coordination with sodium ions. Although they have a low freezing point and low viscosity, they are difficult to form coordination with sodium ions, thereby affecting the ion transport performance.

[0005] Therefore, the polysulfide shuttle effect and poor conductivity in extreme environments faced by traditional sodium-sulfur batteries have become technical challenges that need to be urgently solved in this research field. Summary of the Invention

[0006] In view of this, the present invention provides a sodium-sulfur battery electrolyte and a preparation method and application thereof.

[0007] In one aspect, the present invention provides a sodium-sulfur battery electrolyte.

[0008] A sodium-sulfur battery electrolyte comprising a sodium salt, a main solvent, a co-solvent and a diluent;

[0009] The main solvent is an ester polar solvent;

[0010] The diluent is an amphiphilic fluorinated solvent;

[0011] The cosolvent is a carbonate cosolvent;

[0012] The amphiphilic fluorinated solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl methyl ether, hexafluoroisopropyl methyl ether and 1,1,2,2-tetrafluoroethyl ethyl ether.

[0013] Compared to existing technologies, the present invention uses an amphiphilic fluorinated solvent as a diluent. This amphiphilic fluorinated solvent has an exposed "-O-" group at one end, which can bind to sodium ions and improve the overall conductivity of the electrolyte. The other end is a fluoroalkyl group with weaker coordination ability, which allows sodium ions to combine with anions to form ion clusters. This reduces the desolvation energy barrier and facilitates the formation of a stable electrode-electrolyte interface layer on the surfaces of the sodium metal and sulfur positive electrodes. The sodium-sulfur battery electrolyte formulated in the present invention, using a sodium salt, a cosolvent, and a diluent, can simultaneously stabilize the sodium metal negative electrode and the sulfur positive electrode, effectively extending the service life of the sodium-sulfur battery.

[0014] Preferably, the sodium salt is selected from sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide and sodium hexafluorophosphate.

[0015] Preferably, the concentration of sodium salt in the electrolyte is 0.5M-1.5M.

[0016] Preferably, the ester polar solvent is methyl propionate.

[0017] Preferably, the volume ratio of the main solvent to the co-solvent and the diluent is 1:(0.5-1.5):(1.0-1.5).

[0018] More preferably, the carbonate cosolvent is selected from fluoroethylene carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate.

[0019] The second aspect of the present invention provides a method for preparing the sodium-sulfur battery electrolyte described in the aforementioned solution.

[0020] A method for preparing a sodium-sulfur battery electrolyte comprises the following steps: mixing a sodium salt, a main solvent, a co-solvent and a diluent to obtain the sodium-sulfur battery electrolyte.

[0021] The third aspect of the present invention provides the use of the sodium-sulfur battery electrolyte described in the above solution in a sodium-sulfur battery.

[0022] Preferably, the positive electrode of the sodium-sulfur battery is a sulfurized polyacrylonitrile positive electrode.

[0023] Preferably, the raw materials for preparing the sulfide polyacrylonitrile positive electrode include sulfide polyacrylonitrile, a conductive agent and a binder.

[0024] Preferably, the mass ratio of the sulfide polyacrylonitrile, the conductive agent and the binder is (75-95): (2.5-12.5):

[0025] (2.5-12.5).

[0026] Preferably, the preparation method of the sulfurized polyacrylonitrile comprises the following steps: mixing sulfur powder and polyacrylonitrile and then calcining to obtain the sulfurized polyacrylonitrile.

[0027] Further preferably, the mass ratio of the sulfur powder to polyacrylonitrile is 1:(3-5).

[0028] More preferably, the calcination is carried out in a nitrogen atmosphere, the calcination temperature is 300° C.-500° C., and the calcination time is 1 h-3 h.

[0029] More preferably, the particle size of the sulfide polyacrylonitrile is 100 nm-150 nm.

[0030] Further preferably, the conductive agent is selected from one or more of acetylene black, conductive carbon black, carbon nanotubes or graphene.

[0031] Further preferably, the binder is selected from one or more of styrene-butadiene rubber latex, polytetrafluoroethylene, carboxymethyl cellulose and polyvinylidene fluoride.

[0032] The beneficial technical effects of the present invention are as follows:

[0033] The present invention utilizes a lightweight, amphiphilic fluorinated solvent as an electrolyte diluent, effectively reducing the overall electrolyte concentration and sodium salt consumption. Furthermore, the diluent, combined with the ester primary solvent, significantly inhibits the dissolution and shuttling effects of polysulfides, fundamentally improving battery stability. Furthermore, the amphiphilic fluorinated solvent has a freezing point below -100°C, imparting excellent low-temperature freeze resistance to the electrolyte and effectively alleviating the high electrolyte viscosity problem of sodium-sulfur batteries in low-temperature environments.

[0034] The sodium-sulfur battery electrolyte provided by the present invention is used in combination with a sulfurized polyacrylonitrile positive electrode to enable the metal sodium-sulfur battery to have good electrochemical performance, and has important application prospects in the field of sodium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a graph showing the cycling stability test results of the sodium-sulfur battery at 25°C in Example 1.

[0036] Figure 2 This is a graph showing the cycling stability test results of the sodium-sulfur battery of Example 1 at -20°C.

[0037] Figure 3 Graph showing the electrochemical impedance spectroscopy results of the stainless steel-stainless steel battery at different temperatures in Example 1.

[0038] Figure 4 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Example 1 at 25°C.

[0039] Figure 5 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery of Example 1 at -20°C.

[0040] Figure 6 This is a graph showing the cycling stability test results of the sodium-sulfur battery at 25°C in Example 2.

[0041] Figure 7 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 4 at 25°C.

[0042] Figure 8 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 4 at -20°C.

[0043] Figure 9 This is a graph showing the cycling stability test results of the sodium-sulfur battery at -20°C in Example 3.

[0044] Figure 10 This is a graph showing the cycling stability test results of the sodium-sulfur battery at -20°C in Comparative Example 5.

[0045] Figure 11 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 6 at 25°C.

[0046] Figure 12 This is the sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 6 at -20°C. DETAILED DESCRIPTION

[0047] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiment is only one embodiment of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] Example 1

[0049] This embodiment provides a sodium-sulfur battery, which specifically includes the following contents:

[0050] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl methyl ether, fluoroethylene carbonate, and methyl propionate solvents were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0051] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl methyl ether, 300 μL of the fluoroethylene carbonate, and 300 μL of the methyl propionate were mixed to obtain a sodium-sulfur battery electrolyte.

[0052] (3) Take 4 g of sulfur powder and 1 g of polyacrylonitrile, mix them evenly, calcine them at 450 °C for 3 h under a nitrogen atmosphere, and grind them to obtain sulfurized polyacrylonitrile powder.

[0053] (4) The vulcanized polyacrylonitrile powder is mixed with acetylene black, carboxymethyl cellulose and styrene-butadiene rubber latex in a ratio of 8:1:0.5:0.5 to obtain a vulcanized polyacrylonitrile slurry.

[0054] (5) The sulphurized polyacrylonitrile slurry was evenly coated on a carbon-coated aluminium foil and dried in a vacuum drying oven at 70° C. for 12 h to obtain a sulphurized polyacrylonitrile positive electrode material.

[0055] (6) The vulcanized polyacrylonitrile positive electrode material was punched into an electrode sheet with a diameter of 6 mm using a die punch and transferred to a glove box.

[0056] (7) The sodium-sulfur battery electrolyte is used as the battery electrolyte, a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 is used as the diaphragm, sodium metal is used as the negative electrode, and the sulfurized polyacrylonitrile positive electrode material is used as the positive electrode to assemble a sodium-sulfur battery.

[0057] Comparative Example 1

[0058] This comparative example provides a stainless steel-stainless steel battery, which specifically includes the following contents:

[0059] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl methyl ether, fluoroethylene carbonate, and methyl propionate solvents were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0060] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl methyl ether, 300 μL of the fluoroethylene carbonate, and 300 μL of the methyl propionate were mixed to obtain a sodium-sulfur battery electrolyte.

[0061] (3) The sodium-sulfur battery electrolyte was used as the battery electrolyte, and a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 was used as the diaphragm to assemble a stainless steel-stainless steel battery.

[0062] Comparative Example 2

[0063] This comparative example provides a sodium metal symmetrical battery, which specifically includes the following contents:

[0064] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, fluoroethylene carbonate, and methyl propionate solvent were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0065] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl methyl ether, 300 μL of the fluoroethylene carbonate, and 300 μL of the methyl propionate were mixed to obtain a sodium-sulfur battery electrolyte.

[0066] (3) The sodium-sulfur battery electrolyte was used as the battery electrolyte, and a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 was used as the diaphragm to assemble a sodium metal symmetrical battery.

[0067] Electrochemical performance tests were conducted on the sodium-sulfur battery in Example 1, the stainless steel-stainless steel battery in Comparative Example 1, and the sodium metal symmetrical battery in Comparative Example 2. The test results are shown in the figure below. Figure 1-4 shown.

[0068] in, Figure 1 The sulfur cathode loading is 2.93 mg cm -2 , the current density is 0.2A·g -1 , a graph showing the cycle stability test results of the sodium-sulfur battery in Example 1 at 50°C; Figure 2 The sulfur cathode loading is 2.93 mg / cm -2 , the current density is 0.2A·g -1 , the charge and discharge cut-off voltage is 0.2V-2.8V, and the cycle stability test results of the sodium-sulfur battery in Example 1 at -20°C; Figure 3 Graph showing the electrochemical impedance spectroscopy test results of the stainless steel-stainless steel battery in Comparative Example 1 under a frequency range of 100,000 Hz to 0.1 Hz; Figure 4 At 25°C, the current density is 1.0 mA·cm -2 , the deposition capacity is 1.0 mAh·cm -2The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 2 under the same conditions is shown in FIG. Figure 5 At -20℃, the current density is 0.2mA·cm -2 , the deposition capacity is 0.4 mAh·cm -2 Sodium deposition / stripping polarization curves of the sodium metal symmetric battery in Comparative Example 2 under the same conditions.

[0069] Depend on Figure 1 It can be seen that the first reversible specific capacity of the sulfurized polyacrylonitrile positive electrode is about 489 mAh g -1 , after 100 cycles, the capacity has almost no decay.

[0070] Depend on Figure 2 It can be seen that the first reversible specific capacity of the sulfurized polyacrylonitrile positive electrode is about 189 mAh g -1 After 100 cycles, the capacity has almost no attenuation, which improves the problem of low capacity and poor cycle performance of sodium-sulfur batteries in low temperature environments.

[0071] Depend on Figure 3 It can be seen that the electrolyte provided by the present invention has high ionic conductivity even at low temperatures.

[0072] Depend on Figure 4 It can be seen that the assembled Na metal symmetric battery has good cycling stability.

[0073] Depend on Figure 5 It can be seen that the polarization potential of the symmetrical battery remains stable after cycling for 250 h under low temperature conditions.

[0074] Example 2

[0075] This embodiment provides a sodium-sulfur battery, which specifically includes the following contents:

[0076] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, fluoroethylene carbonate, and methyl propionate solvent were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0077] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl methyl ether, 100 μL of the fluoroethylene carbonate, and 500 μL of the methyl propionate were mixed to obtain a sodium-sulfur battery electrolyte.

[0078] (3) Take 4 g of sulfur powder and 1 g of polyacrylonitrile, mix them evenly, calcine them at 450 °C for 3 h under a nitrogen atmosphere, and grind them to obtain sulfurized polyacrylonitrile powder.

[0079] (4) The vulcanized polyacrylonitrile powder is mixed with acetylene black, carboxymethyl cellulose and styrene-butadiene rubber latex in a ratio of 8:1:0.5:0.5 to obtain a vulcanized polyacrylonitrile slurry.

[0080] (5) The sulphurized polyacrylonitrile slurry was evenly coated on a carbon-coated aluminium foil and dried in a vacuum drying oven at 70° C. for 12 h to obtain a sulphurized polyacrylonitrile positive electrode material.

[0081] (6) The vulcanized polyacrylonitrile positive electrode material was punched into an electrode sheet with a diameter of 6 mm using a die punch and transferred to a glove box.

[0082] (7) The sodium-sulfur battery electrolyte is used as the battery electrolyte, a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 is used as the diaphragm, sodium metal is used as the negative electrode, and the sulfurized polyacrylonitrile positive electrode material is used as the positive electrode to assemble a sodium-sulfur battery.

[0083] The electrochemical performance test of the sodium-sulfur battery in Example 2 was carried out, and the test results were as follows: Figure 6 shown.

[0084] in, Figure 6 At 25°C, the current density is 0.2A·g -1 The graph shows the cycle stability test results of the sodium-sulfur battery in Example 2 under the conditions of .

[0085] Depend on Figure 6 It can be seen that the initial reversible specific capacity of the sulfide polyacrylonitrile positive electrode is about 433 mAh·g-1. After 100 cycles, the capacity is lower than that of Example 1 and decays faster.

[0086] Comparative Example 4

[0087] This comparative example provides a sodium metal symmetrical battery, which specifically includes the following contents:

[0088] (1) In a glove box filled with argon, fluoroethylene carbonate and methyl propionate solvents were used The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0089] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 500 μL of the fluoroethylene carbonate, and 500 μL of the methyl propionate were mixed to obtain an electrolyte solution.

[0090] (3) A sodium metal symmetrical battery was assembled using the electrolyte as the electrolyte of the battery and a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 as the diaphragm.

[0091] The electrochemical performance test of the sodium metal symmetrical battery in Comparative Example 4 was carried out, and the test results were as follows: Figure 7-8 shown.

[0092] in, Figure 7 At 25°C, the current density is 1.0 mA·cm -2 , the deposition capacity is 1.0 mAh·cm -2 The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 4 under the conditions of Figure 9 At -20℃, the current density is 0.2mA·cm -2 , the deposition capacity is 0.4 mAh·cm -2 Deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 4 under the same conditions.

[0093] Depend on Figure 7 It can be seen that the battery polarization potential is large, the polarization curve is tortuous, and a short circuit occurs around 115h.

[0094] Depend on Figure 8 It can be seen that the battery polarization potential is large, the polarization curve is tortuous, and a short circuit occurs after about 75 hours of cycling under low temperature conditions.

[0095] Example 3

[0096] This embodiment provides a sodium-sulfur battery, which specifically includes the following contents:

[0097] (1) In a glove box filled with argon, fluoroethylene carbonate and methyl propionate solvents were used The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0098] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 500 μL of the fluoroethylene carbonate, and 500 μL of the methyl propionate were mixed to obtain an electrolyte solution.

[0099] (3) Take 4 g of sulfur powder and 1 g of polyacrylonitrile, mix them evenly, calcine them at 450 °C for 3 h under a nitrogen atmosphere, and grind them to obtain sulfurized polyacrylonitrile powder.

[0100] (4) The vulcanized polyacrylonitrile powder is mixed with acetylene black, carboxymethyl cellulose and styrene-butadiene rubber latex in a ratio of 8:1:0.5:0.5 to obtain a vulcanized polyacrylonitrile slurry.

[0101] (5) The sulphurized polyacrylonitrile slurry was evenly coated on a carbon-coated aluminium foil and dried in a vacuum drying oven at 70° C. for 12 h to obtain a sulphurized polyacrylonitrile positive electrode material.

[0102] (6) The vulcanized polyacrylonitrile positive electrode material was punched into an electrode sheet with a diameter of 6 mm using a die punch and transferred to a glove box.

[0103] (7) The sodium-sulfur battery electrolyte is used as the battery electrolyte, a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 is used as the diaphragm, sodium metal is used as the negative electrode, and the sulfurized polyacrylonitrile positive electrode material is used as the positive electrode to assemble a sodium-sulfur battery.

[0104] The electrochemical performance test of the sodium-sulfur battery in Example 3 was carried out, and the test results were as follows: Figure 9 shown.

[0105] in, Figure 9 The sulfur cathode loading is 2.93 mg / cm -2 , the current density is 0.2A·g -1 , the charge and discharge cut-off voltage is 0.2V-2.8V, and the cycle stability test results of the sodium-sulfur battery in Example 3 are shown at -20°C.

[0106] Depend on Figure 9 It can be seen that the first reversible specific capacity of the sulfurized polyacrylonitrile positive electrode is about 154 mAh g -1 After 100 cycles, the capacity decays to almost 0. The sodium-sulfur battery has low capacity and poor cycle performance in low-temperature environments.

[0107] Comparative Example 5

[0108] This comparative example provides a sodium-sulfur battery, which specifically includes the following contents:

[0109] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluoroethylene carbonate, and methyl propionate solvent were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0110] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 300 μL of the fluoroethylene carbonate, and 300 μL of the methyl propionate were mixed to obtain an electrolyte solution.

[0111] (3) Take 4 g of sulfur powder and 1 g of polyacrylonitrile, mix them evenly, calcine them at 450 °C for 3 h under a nitrogen atmosphere, and grind them to obtain sulfurized polyacrylonitrile powder.

[0112] (4) The vulcanized polyacrylonitrile powder is mixed with acetylene black, carboxymethyl cellulose and styrene-butadiene rubber latex in a ratio of 8:1:0.5:0.5 to obtain a vulcanized polyacrylonitrile slurry.

[0113] (5) The sulphurized polyacrylonitrile slurry was evenly coated on a carbon-coated aluminium foil and dried in a vacuum drying oven at 70° C. for 12 h to obtain a sulphurized polyacrylonitrile positive electrode material.

[0114] (6) The vulcanized polyacrylonitrile positive electrode material was punched into an electrode sheet with a diameter of 6 mm using a die punch and transferred to a glove box.

[0115] (7) A sodium-sulfur battery was assembled using the electrolyte as the electrolyte of the battery, a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 as the diaphragm, sodium metal as the negative electrode, and the sulfurized polyacrylonitrile positive electrode material as the positive electrode.

[0116] The electrochemical performance test of the sodium-sulfur battery in Comparative Example 5 was carried out, and the test results were as follows: Figure 10 shown.

[0117] in, Figure 10 The sulfur cathode loading is 2.93 mg / cm -2 , the current density is 0.2A·g -1 , the charge and discharge cut-off voltage is 0.2V-2.8V, and the cycle stability test results of the sodium-sulfur battery in Comparative Example 5 are shown at -20°C.

[0118] Depend on Figure 10 It can be seen that the first reversible specific capacity of the sulfurized polyacrylonitrile positive electrode is about 86 mAh g -1 After 100 cycles, the capacity cycle fluctuation is unstable, and the sodium-sulfur battery has low capacity and poor cycle performance under low temperature environment.

[0119] Comparative Example 6

[0120] This comparative example provides a sodium metal symmetrical battery, which specifically includes the following contents:

[0121] (1) In a glove box filled with argon, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluoroethylene carbonate, and methyl propionate solvent were used. The molecular sieve was used for dehydration treatment, and sodium bis(fluorosulfonyl)imide was kept at 80° C. and dried overnight.

[0122] (2) 203.12 mg of the sodium bis(fluorosulfonyl)imide, 400 μL of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 300 μL of the fluoroethylene carbonate, and 300 μL of the methyl propionate were mixed to obtain an electrolyte solution.

[0123] (3) A sodium metal symmetrical battery was assembled using the electrolyte as the electrolyte of the battery and a three-layer stacked diaphragm of GF-A (Whatman) and Celgard 2325 as the diaphragm.

[0124] The electrochemical performance test of the sodium metal symmetrical battery in Comparative Example 6 was carried out, and the test results were as follows: Figure 11-12 shown.

[0125] in, Figure 11 At 25°C, the current density is 1.0 mA·cm-2, and the deposition capacity is 1.0 mAh·cm -2 The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 6 is shown in FIG. Figure 12 At -20℃, the current density is 0.2mA·cm -2 , the deposition capacity is 0.4 mAh·cm -2 The sodium deposition / stripping polarization curve of the sodium metal symmetric battery in Comparative Example 6 is shown under the conditions of .

[0126] Depend on Figure 11 It can be seen that the first reversible specific capacity of the sulfurized polyacrylonitrile positive electrode is about 86 mAh g -1 After 100 cycles, the capacity cycle fluctuation is unstable, and the sodium-sulfur battery has low capacity and poor cycle performance under low temperature environment.

[0127] Depend on Figure 11 It can be seen that the short circuit of the sodium metal symmetric battery occurs around 300h.

[0128] Depend on Figure 12 It can be seen that the polarization potential of the sodium metal symmetric battery is large, the polarization curve is tortuous, and a short circuit occurs after about 150 hours of cycling under low temperature conditions.

[0129] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium-sulfur battery electrolyte, characterized in that: The electrolyte comprises sodium salt, a main solvent, a co-solvent and a diluent; The main solvent is an ester polar solvent; The diluent is an amphiphilic fluorinated solvent; The cosolvent is a carbonate cosolvent; The amphiphilic fluorinated solvent is selected from one or more of 1,1,2,2-tetrafluoroethyl methyl ether, hexafluoroisopropyl methyl ether or 1,1,2,2-tetrafluoroethyl ethyl ether.

2. The sodium-sulfur battery electrolyte according to claim 1, characterized in that The sodium salt is selected from sodium bis(trifluoromethylsulfonyl)imide, sodium trifluoromethanesulfonate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide and sodium hexafluorophosphate; and / or The concentration of the sodium salt is 0.5M-1.5M.

3. The sodium-sulfur battery electrolyte according to claim 1, characterized in that The ester polar solvent is methyl propionate.

4. The sodium-sulfur battery electrolyte according to claim 1, wherein The volume ratio of the main solvent to the co-solvent and the diluent is 1:(0.5-1.5):(1.0-1.5).

5. The method for preparing the sodium-sulfur battery electrolyte according to any one of claims 1 to 4, characterized in that: The steps include: The sodium salt, the main solvent, the auxiliary solvent and the diluent are mixed to obtain the sodium-sulfur battery electrolyte.

6. Use of the sodium-sulfur battery electrolyte according to any one of claims 1 to 4 or the sodium-sulfur battery electrolyte prepared according to claim 5 in a sodium-sulfur battery.

7. The use according to claim 6, characterized in that The positive electrode of the sodium-sulfur battery is a sulfurized polyacrylonitrile positive electrode.

8. The use according to claim 7, characterized in that The raw materials for preparing the sulfided polyacrylonitrile positive electrode include sulfided polyacrylonitrile, a conductive agent and a binder.

9. The use according to claim 8, characterized in that The mass ratio of the sulfide polyacrylonitrile, the conductive agent and the binder is (75-95):(2.5-12.5):(2.5-12.5).

10. The use according to claim 8, characterized in that The preparation method of the sulfurized polyacrylonitrile specifically comprises the following steps: mixing sulfur and polyacrylonitrile and then calcining to obtain the sulfurized polyacrylonitrile.

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