Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention relates to the technical field of batteries, and particularly discloses a sodium-ion battery electrolyte and a sodium-ion battery. The electrolyte provided by the invention enables the sodium ion battery to operate in a stable state, not only has relatively high safety, but also has relatively low capacity loss in a cycle process, can maintain good discharge capacity for a long time, is suitable for being applied to large-scale electrochemical energy storage occasions, and has wide application prospects. And the strict requirements of novel portable mobile equipment, electric automobiles and other emerging fields on the battery performance can be fully met.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to a sodium ion battery electrolyte and a sodium ion battery. Background Art

[0002] Today, the energy sector faces challenges primarily related to the increasing depletion of non-renewable fossil fuels and the irreversible pollution of the natural environment. Rechargeable batteries, as a renewable energy system, offer an effective solution to these challenges. Lithium-ion batteries are currently the most popular type of rechargeable battery. Their high energy density and operating voltage transcend the limitations of traditional secondary batteries, making them a highly convenient energy storage device widely used in various electronic products.

[0003] However, lithium is unevenly distributed in the Earth's crust, and the total amount of proven, mineable lithium ore is limited. This has led to high production costs for lithium-ion batteries, preventing them from fully meeting the needs of large-scale electrochemical energy storage. To overcome this constraint, sodium-ion batteries have been developed both domestically and internationally. Sodium, a cognate element of lithium with similar chemical properties, offers advantages such as low cost, abundant reserves, and widespread distribution. Sodium-ion batteries are the most suitable alternative to lithium-ion batteries and hold the greatest potential for future electrochemical energy storage applications. The electrolyte, a core component of sodium-ion batteries, transports and conducts ions between the positive and negative electrodes, serving as a pathway connecting the positive and negative electrode materials. The composition of the electrolyte influences parameters such as the cycling performance, initial charge and discharge efficiency, specific energy, safety, and rate capability of sodium-ion batteries, and also significantly impacts their production costs.

[0004] Regarding the above-mentioned related technologies, the inventors believe that although sodium-ion batteries have been verified in small-scale applications, due to the limitations of current technological levels, the cycle life of sodium-ion batteries is still relatively limited and cannot fully meet the needs of large-scale electrochemical energy storage. Summary of the Invention

[0005] In the related art, sodium ion batteries have limited cycle life and cannot fully meet the needs of large-scale electrochemical energy storage. To improve this defect, the present application provides a sodium ion battery electrolyte and a sodium ion battery.

[0006] In a first aspect, the present application provides a sodium ion battery electrolyte, which adopts the following technical solution: A sodium ion battery electrolyte comprises the following components by weight: 10-12% sodium salt, 6-10% additives, and the balance made up to 100% by solvent; the solvent comprises diethylene glycol dimethyl ether and carbonate, the sodium salt comprises sodium hexafluorophosphate, the additives comprise fluorine-containing phosphate esters, nitrile compounds, and modified nanotubes; the modified nanotubes are halloysite nanotubes having copolymer chain segments grafted onto their surfaces, and the copolymer chain segments contain nitrile groups.

[0007] By adopting the above technical solution, the present application selects diethylene glycol dimethyl ether and carbonate as solvents for the electrolyte. Carbonate can be compatible with both positive and negative electrode materials, has good electrochemical stability, and can be used in a wide temperature range. Diethylene glycol dimethyl ether as an ether solvent can improve the performance of the negative electrode and accelerate the storage of sodium ions. Although diethylene glycol dimethyl ether has the defect of being flammable, the fluorine-containing phosphate in the additive can play a flame retardant role, thereby overcoming the above defect, so that the advantages of these two electrolytes can be fully utilized in the same battery system. Fluorine-containing phosphate can also reduce the charge transfer resistance, inhibit the separation of electrolyte and solvent, and inhibit the polarization of the battery, which helps to maintain the stable operating state of the battery. Nitrile compounds and modified nanotubes both contain nitrile groups. Nitrile compounds are relatively easy to diffuse, and the copolymer chain segments on the surface of the modified nanotubes can accommodate a large number of nitrile groups. The synergistic cooperation of the two can make the nitrile groups evenly dispersed throughout the electrolyte. When the battery is running, the nitrile compounds and modified nanotubes can complex with the active ions of the positive electrode through the nitrile group, thereby shielding the active ions of the positive electrode and reducing the decomposition of the electrolyte by the positive electrode. Since carbonates themselves have good stability and the flammability disadvantage of diethylene glycol dimethyl ether has been overcome, the electrolyte is not easy to fail during the battery cycle. With the synergistic combination of fluorinated phosphates, nitrile compounds and modified nanotubes, as well as diethylene glycol dimethyl ether and carbonates, sodium ion batteries can operate in a stable state, not only with high safety, but also with less capacity loss during the cycle, and can maintain good discharge capacity for a long time, thus overcoming the defects in related technologies. It is suitable for application in large-scale electrochemical energy storage occasions and can fully meet the stringent requirements for battery performance in emerging fields such as new portable mobile devices and electric vehicles.

[0008] Preferably, the modified nanotubes are prepared according to the following method: (1) adding vinyl alkoxysilane to an ethanol aqueous solution to obtain a silane solution for later use; adding a monomer to water to obtain a monomer dispersion for later use; in this step, the monomer includes acrylonitrile; (2) mixing the halloysite nanotubes and the silane solution, then adding hydrochloric acid for acidification, and heating the mixture to react to obtain an intermediate dispersion; (3) adding the monomer dispersion and the initiator to the intermediate dispersion, reacting the mixture in a water bath, cooling the mixture naturally after the reaction, and filtering and drying the product to obtain modified nanotubes.

[0009] By adopting the above technical solution, the present application first uses vinyl alkoxysilane to modify the halloysite nanotubes. The silanol groups on the surface of the halloysite nanotubes can undergo a condensation reaction with the vinyl alkoxysilane after hydrolysis, thereby grafting the vinyl group to the surface of the halloysite nanotubes. Subsequently, under the action of an initiator, a monomer represented by acrylonitrile undergoes a copolymerization reaction with the above-mentioned vinyl group, and a copolymer segment containing a nitrile group is further formed on the surface of the halloysite nanotubes, thereby obtaining a modified nanotube. The copolymer segment on the surface of the modified nanotubes can accommodate a large number of nitrile groups, and through synergistic cooperation with small molecule nitrile compounds, the nitrile groups can be evenly dispersed throughout the electrolyte, which helps to reduce the decomposition of the electrolyte by the positive electrode.

[0010] Preferably, in step (1) of preparing the modified nanotubes, the monomers used further include polyunsaturated fatty acids.

[0011] By adopting the above technical solution, polyunsaturated fatty acids have multiple double bonds that can participate in copolymerization, which can provide new branches for the copolymer chain segments, enhance the complexing effect of the modified nanotubes on the active ions of the positive electrode, and help reduce the decomposition of the electrolyte by the positive electrode.

[0012] Preferably, the polyunsaturated fatty acid molecule contains 3-5 carbon-carbon double bonds.

[0013] By adopting the above technical solution, the present application optimizes the number of carbon-carbon double bonds of polyunsaturated fatty acids, enhances the complexing effect of modified nanotubes on positive electrode active ions, and helps to reduce the decomposition of the electrolyte by the positive electrode.

[0014] Preferably, the additive further comprises 1,3-propane sultone.

[0015] By adopting the above technical solution, the LUMO energy of the 1,3-propane sultone molecule is low and has a higher reduction potential. Therefore, the 1,3-PS additive can also participate in the formation of a high-performance solid electrolyte film on the negative electrode surface, thereby improving the cycle stability of the sodium ion battery.

[0016] Preferably, the carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0017] By adopting the above technical solution, this application has selected specific types of carbonates. Ethylene carbonate and propylene carbonate have outstanding high-pressure resistance, good solubility, and a wide liquid range, making them ideal electrolyte solvents. When propylene carbonate replaces part of the ethylene carbonate, it creates a synergistic effect with 1,3-propane sultone, further improving the cycling stability of sodium-ion batteries.

[0018] Preferably, the carbonate further includes fluorine-containing ethylene carbonate.

[0019] By employing this technical solution, the F ions in the fluorinated ethylene carbonate, which have a strong electron-withdrawing effect, are preferentially reduced to form a film during battery operation. This synergistic effect with the nitrile compound and modified nanotubes effectively reduces electrolyte decomposition. Furthermore, the film formed by the fluorinated ethylene carbonate effectively isolates the electrolyte from the hard carbon electrode, thereby suppressing side reactions in the electrolyte. This synergistic effect with other components in the electrolyte effectively extends the battery's lifespan.

[0020] Preferably, the nitrile compound includes at least one of succinonitrile, adiponitrile, and sulfonyldipropionitrile.

[0021] By adopting the above technical solution, the present application optimizes the type of nitrile compounds. The above-mentioned nitrile compounds can effectively reduce the decomposition of the electrolyte through the synergistic effect with fluorinated ethylene carbonate, which helps to improve the cycle stability of sodium ion batteries.

[0022] Preferably, the nitrile compound further comprises a nitrile organosilicon compound, and the nitrile organosilicon compound is prepared according to the following method: 2-Methyl-3-butenenitrile, hydrogenated silicone oil, chloroplatinic acid catalyst and isopropyl alcohol are mixed, and the mixture is heated and stirred under an argon atmosphere for reaction. After the reaction is completed, the mixture is cooled and then distilled under reduced pressure to obtain a nitrile-based organosilicon compound.

[0023] By adopting the above technical solution, the present application prepares an organosilicon compound containing a nitrile group through a hydrosilylation reaction. The nitrile organosilicon compound inherits the excellent thermal stability and low-temperature ion conductivity of the organosilicon compound, and has high electrical conductivity and is environmentally friendly. It can effectively reduce the decomposition of the electrolyte through a synergistic effect with fluorinated ethylene carbonate, which helps to fully improve the cycle stability of the sodium ion battery.

[0024] In a second aspect, the present application provides a sodium ion battery with a sodium ion battery electrolyte, which adopts the following technical solution.

[0025] A sodium ion battery containing a sodium ion battery electrolyte comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the electrolyte is any of the sodium ion battery electrolytes described above.

[0026] By adopting the above technical solution, the present application applies the above sodium ion battery electrolyte to the sodium ion battery to connect the positive electrode material and the negative electrode material. The carbonate selected in this application can be compatible with both the positive electrode material and the negative electrode material, and has good electrochemical stability, while diethylene glycol dimethyl ether can improve the negative electrode performance. Fluorine-containing phosphates can inhibit the polarization of the battery and help maintain the stability of the battery's operating state; nitrile compounds and modified nanotubes can complex with the active ions of the positive electrode through the nitrile group, thereby shielding the active ions of the positive electrode and reducing the decomposition of the electrolyte by the positive electrode. By using the above electrolyte, the sodium ion battery not only has higher safety, but also has less capacity loss during the cycle, can maintain good discharge capacity for a long time, is suitable for application in large-scale electrochemical energy storage occasions, and can fully meet the stringent requirements for battery performance in emerging fields such as new portable mobile devices and electric vehicles.

[0027] In summary, this application has the following beneficial effects: 1. The electrolyte of the present application enables sodium-ion batteries to operate in a stable state. It not only has high safety, but also has less capacity loss during the cycle and can maintain good discharge capacity for a long time. It is suitable for application in large-scale electrochemical energy storage occasions and can fully meet the stringent requirements of emerging fields such as new portable mobile devices and electric vehicles for battery performance.

[0028] 2. The copolymer chain segments on the surface of the modified nanotubes of the present application can accommodate a large number of nitrile groups. By cooperating with small molecule nitrile compounds, the nitrile groups can be evenly dispersed throughout the electrolyte, which helps to reduce the decomposition of the electrolyte by the positive electrode.

[0029] 3. This application utilizes fluorinated ethylene carbonate. By synergizing with nitrile compounds and modified nanotubes, fluorinated ethylene carbonate effectively reduces electrolyte decomposition. Furthermore, the film formed by fluorinated ethylene carbonate effectively isolates the electrolyte from the hard carbon electrode, thereby inhibiting side reactions in the electrolyte. This synergistic effect with other components in the electrolyte effectively extends the battery's lifespan. DETAILED DESCRIPTION

[0030] The present application is further described in detail below with reference to the Examples, Preparation Examples and Comparative Examples. The raw materials involved in the present application can all be obtained commercially.

[0031] Preparation example of modified nanotubes The following is an explanation using Preparation Example 1.

[0032] Preparation Example 1 In this preparation example, acrylonitrile and methyl acrylate are selected as monomers, and the molar ratio of acrylonitrile to methyl acrylate is 10:1.

[0033] In this preparation example, the modified nanotubes were prepared according to the following method: (1) Add 10 g of vinyl alkoxysilane to 1200 g of ethanol aqueous solution (containing 900 g of ethanol) to obtain a silane solution, which is set aside; add 150 g of monomer to 250 g of water to obtain a monomer dispersion, which is set aside; (2) 50 g of halloysite nanotubes and silane solution were mixed, and then hydrochloric acid was added for acidification, the pH was adjusted to 3.5, and the mixture was heated at 60° C. for 1 h to obtain an intermediate dispersion; (3) Adding the monomer dispersion and 1 g of ammonium persulfate initiator to the intermediate dispersion, reacting in a water bath at 70° C. for 4 h, cooling naturally after the reaction, and filtering and drying the product to obtain modified nanotubes.

[0034] Preparation Example 2 The difference between this preparation example and preparation example 1 is that the monomer further includes a polyunsaturated fatty acid, the molar ratio of the polyunsaturated fatty acid to acrylonitrile is 1:20, and the polyunsaturated fatty acid is linoleic acid.

[0035] Preparation Example 3 The difference between this preparation example and preparation example 2 is that linolenic acid is used as the polyunsaturated fatty acid.

[0036] Preparation Example 4 The difference between this preparation example and preparation example 2 is that arachidonic acid is used as the polyunsaturated fatty acid.

[0037] Preparation Example 5 The difference between this preparation example and preparation example 2 is that eicosapentaenoic acid is used as the polyunsaturated fatty acid.

[0038] Preparation Example of Nitrile Organosilicon Compound The following is an illustration of Preparation Example 6.

[0039] Preparation Example 6 In this preparation example, the nitrile organosilicon compound was prepared according to the following method: At room temperature, 12.77 g of 2-methyl-3-butenenitrile, 22.25 g of 1,1,3,3,3-pentamethyltrisiloxane, 5 mg of chloroplatinic acid catalyst and 3 mL of isopropanol were added to a 50 mL three-necked round-bottom flask in sequence, and then the mixture was heated to 90 ° C under an argon atmosphere and stirred for 48 hours. After the reaction, the system was cooled and distilled under reduced pressure to obtain a nitrile organosilicon compound. Example

[0040] Examples 1-3 The following description will be given using Example 1 as an example.

[0041] Example 1 In this embodiment, the solvent is composed of diethylene glycol dimethyl ether and carbonate in a weight ratio of 1:3, the carbonate is ethylene carbonate, the sodium salt is sodium hexafluorophosphate, the additive is composed of a nitrile compound and modified nanotubes, the nitrile compound is succinonitrile, and the modified nanotubes are prepared according to the method of Preparation Example 1.

[0042] This embodiment provides a sodium ion battery electrolyte, which includes the following components by weight percentage: 10% sodium salt, 6% additive, and the balance made up to 100% by solvent.

[0043] This embodiment also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte is the sodium-ion battery electrolyte of this embodiment. When assembling the sodium-ion battery, the positive electrode, separator, and negative electrode are stacked in sequence to obtain a sodium-ion battery cell. The battery prepared in the experiment was a 1.8Ah soft-pack battery. After drying the cell, 14g of the sodium-ion battery electrolyte was injected to obtain a sodium-ion battery.

[0044] The above positive electrode was prepared as follows: The active material, sodium vanadium phosphate, the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), were ground uniformly in a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone was then added and stirred to create a positive electrode slurry. The slurry was evenly applied to aluminum foil and placed in a forced-air oven. After drying, the copper foil was removed from the oven and rolled using a roller press to form the positive electrode.

[0045] The above negative electrode was prepared as follows: Commercial hard carbon, acetylene black (a conductive agent), and polyvinylidene fluoride (PVDF) (a binder) were ground uniformly in a mass ratio of 8:1:1. An appropriate amount of NMP was then added and stirred to create a negative electrode material slurry. The slurry was evenly applied to copper foil and placed in a forced-air oven. After drying, the copper foil was removed from the oven and rolled using a roller press to produce the negative electrode.

[0046] As shown in Table 1, the main difference between Examples 1-3 is that the raw material ratios of the electrolyte are different.

[0047] Table 1 Raw material ratio of electrolyte Examples 3-7 As shown in Table 2, the difference between Examples 3-7 is that the preparation examples of the modified nanotubes are different.

[0048] Table 2 Preparation examples of modified nanotubes Example 8 The difference between this embodiment and embodiment 7 is that the additive further includes 1,3-propane sultone, and the weight of 1,3-propane sultone accounts for 2% of the total weight of the electrolyte.

[0049] Example 9 The difference between this embodiment and embodiment 8 is that the carbonate is prepared by mixing ethylene carbonate and propylene carbonate in a weight ratio of 1:1.

[0050] Example 10 The difference between this embodiment and embodiment 9 is that the carbonate is prepared by mixing ethylene carbonate, propylene carbonate and fluorinated ethylene carbonate in a weight ratio of 1:1:1, and the fluorinated ethylene carbonate is 4-fluoro-1,3-dioxolane-2-one (FEC).

[0051] Example 11 The difference between this embodiment and embodiment 10 is that the nitrile compound is prepared by mixing adiponitrile and disulfonyl propionitrile in a weight ratio of 1:1.

[0052] Example 12 This embodiment differs from Embodiment 10 in that the components of the electrolyte do not include 1,3-propane sultone.

[0053] Example 13 The difference between this embodiment and embodiment 10 is that the nitrile compound is prepared by mixing succinonitrile and a nitrile-based organosilicon compound in a weight ratio of 2:1, and the nitrile-based organosilicon compound is prepared according to the method of Preparation Example 6.

[0054] Comparative Example Comparative Example 1 This comparative example provides a sodium ion battery electrolyte, comprising the following components, by weight percentage: 12 wt% sodium hexafluorophosphate, 1% vinylene carbonate, 5 wt% additive A, 3 wt% additive B, with the remainder made up to 100% by solvent. The solvent is a carbonate ester, which is a mixture of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a weight ratio of 3:2:5.

[0055] In this comparative example, additive A is a derivative of hexafluorocyclotriphosphazene. The difference between additive A and hexafluorocyclotriphosphazene is that the fluorine atom connected to one of the phosphorus atoms is replaced by an ethoxy group. Additive B is o-dibromobenzene.

[0056] Comparative Example 2 This comparative example differs from Example 1 in that the solvent only includes diglyme.

[0057] Comparative Example 3 This comparative example differs from Example 1 in that the solvent only includes carbonate.

[0058] Comparative Example 4 The difference between this comparative example and Example 1 is that the additive does not include a fluorine-containing phosphate ester.

[0059] Comparative Example 5 The difference between this comparative example and Example 1 is that the additive does not include a nitrile compound.

[0060] Comparative Example 6 The difference between this comparative example and Example 1 is that the additive does not include a modified nanotube.

[0061] Performance detection test method The above sodium ion battery was subjected to a cycle test, and the steps were as follows: The above sodium ion battery was charged at 25°C to 3.9V with 0.5C constant current and constant voltage, and the cutoff current was 0.05C; then discharged to 2.0V with 0.5C constant current, and the initial discharge capacity Q0was recorded as the initial discharge capacity, and the environmental temperature was kept unchanged, and after 2500 cycles according to the same charge and discharge mode, the last discharge capacity Qwas recorded. 2500 The capacity retention rate was Q 2500 / Q0x 100%, and the results are shown in Table 3.

[0062] Table 3 Capacity retention rate sample Capacity retention rate / % sample Capacity retention rate / % Example 1 82.8 Example 11 91.5 Example 2 83.5 Example 12 89.3 Example 3 85.1 Example 13 93.8 Example 4 85.4 Comparative Example 1 63.1 Example 5 85.7 Comparative Example 2 79.4 Example 6 86.3 Comparative Example 3 80.6 Example 7 86.9 Comparative Example 4 75.1 Example 8 88.2 Comparative Example 5 70.7 Example 9 89.5 Comparative Example 6 72.3 Example 10 91.7 / / In combination with Examples 1-3 and Comparative Example 1 and in combination with Table 3, it can be seen that the capacity retention rate measured in Examples 1-3 is significantly higher than that of Comparative Example 1, which is due to the synergistic cooperation of the fluorine-containing phosphate ester, the nitrile compound, and the modified nanotube, and the diethylene glycol dimethyl ether and the carbonate, the sodium ion battery of Examples 1-3 can operate in a stable state, not only has high safety, but also has less capacity loss during the cycle process, and can maintain good discharge capacity for a long time, thereby overcoming the defects in the related art, and is suitable for application in large-scale electrochemical energy storage occasions, and can fully meet the stringent requirements of new portable mobile devices, electric vehicles and other emerging fields for battery performance.

[0063] In combination with Example 1 and Comparative Examples 2-3 and in combination with Table 3, it can be seen that the capacity retention rate measured in Example 1 is higher than that of Comparative Examples 2-3, which is due to the fact that Comparative Examples 2-3 cannot exert the synergistic effect of diethylene glycol dimethyl ether and carbonate, resulting in limited cycle stability of the battery, and ultimately losing a lot of battery capacity during the cycle process.

[0064] It can be seen from the combination of Example 1 and Comparative Example 4 and Table 3 that the capacity retention measured in Example 1 is higher than that in Comparative Example 4, because the fluorine-containing phosphate ester can reduce the charge transfer resistance, inhibit the separation of electrolyte and solvent, and also inhibit the polarization of the battery, which helps to maintain the stable operation state of the battery. In the absence of fluorine-containing phosphate ester, other components cannot improve the cycle stability of the battery through the synergistic effect with fluorine-containing phosphate ester, so a lot of battery capacity is lost in long-term cycling.

[0065] It can be seen from the combination of Example 1 and Comparative Examples 5-6 and Table 3 that the capacity retention measured in Example 1 is higher than that in Comparative Examples 5-6, because Comparative Examples 5-6 cannot exert the synergistic effect of nitrile compounds and modified nanotubes, while nitrile compounds and modified nanotubes can complex with active ions of the positive electrode through nitrile groups, thereby shielding the active ions of the positive electrode and reducing the decomposition of the electrolyte by the positive electrode. In the absence of such synergistic effect, the cycle stability of the battery is poor, so a lot of battery capacity is lost in long-term cycling.

[0066] It can be seen from the combination of Examples 3-7 and Table 3 that after introducing polyunsaturated fatty acids into the copolymer segment on the surface of the modified nanotube, the number of branches of the copolymer increases with the increase in the number of double bonds contained in the polyunsaturated fatty acids, and the new branches enhance the complexing effect of the modified nanotube on the active ions of the positive electrode, which helps to reduce the decomposition of the electrolyte by the positive electrode.

[0067] It can be seen from the combination of Example 7, Example 8 and Table 3 that the capacity retention measured in Example 8 is higher, because the 1,3-propane sultone molecule has a low LUMO energy and a high reduction potential, so the 1,3-PS additive can also participate in the formation of a high-performance negative electrode surface solid-state electrolyte film, thereby improving the cycle stability of the sodium ion battery.

[0068] It can be seen from the combination of Example 8, Example 9 and Table 3 that the capacity retention measured in Example 9 is higher, because when propylene carbonate replaces part of the ethylene carbonate, it produces a synergistic effect with 1,3-propane sultone, which can further improve the cycle stability of the sodium ion battery.

[0069] It can be seen from the combination of Example 9, Example 10 and Table 3 that the capacity retention measured in Example 10 is higher, because the fluorine-containing ethylene carbonate has a strong electron-withdrawing F ion, which is often reduced to a film during battery operation, and can effectively reduce the decomposition of the electrolyte through the synergistic effect with nitrile compounds and modified nanotubes. In addition, the film formed by the fluorine-containing ethylene carbonate can well isolate the electrolyte and the hard carbon electrode, thereby inhibiting the side reactions of the electrolyte, and can effectively prolong the service life of the battery through the synergistic effect with other components in the electrolyte.

[0070] It can be seen in combination with Examples 10-12 and in combination with Table 3 that dinitrile, adiponitrile, sulfuryl dinitrile can effectively reduce the decomposition of the electrolyte by synergistic effect with fluoro-containing ethylene carbonate, and improve the cycle stability of the sodium ion battery. When these nitrile compounds are not used in combination with 1,3-propane sultone, the cycle stability of the battery is poor.

[0071] It can be seen in combination with Example 10, Example 13 and in combination with Table 3 that the capacity retention rate measured in Example 13 is higher, which is due to the nitrile group organosilicon compound inherits the excellent thermal stability and low temperature ion conductivity of the organosilicon compound, and the high conductivity, environmental friendliness, can effectively reduce the decomposition of the electrolyte by synergistic effect with fluoro-containing ethylene carbonate, and help to fully improve the cycle stability of the sodium ion battery.

[0072] The above examples are only an explanation of the present application, not a limitation of the present application, and those skilled in the art can make modifications to the examples of the present application without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A sodium ion battery electrolyte, characterized in that The electrolyte comprises the following components by weight percentage: 10-12% sodium salt, 6-10% additives, and the balance made up to 100% by solvent; the solvent comprises diethylene glycol dimethyl ether and carbonate, the sodium salt comprises sodium hexafluorophosphate, and the additives comprise fluorine-containing phosphate esters, nitrile compounds, and modified nanotubes; The modified nanotubes are halloysite nanotubes with copolymer chain segments grafted onto their surfaces, and the copolymer chain segments contain nitrile groups.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The modified nanotubes are prepared according to the following method: (1) Adding vinyl alkoxysilane to an ethanol aqueous solution to obtain a silane solution, which is set aside; adding a monomer to water to obtain a monomer dispersion, which is set aside; in this step, the monomer includes acrylonitrile; (2) mixing the halloysite nanotubes and the silane solution, then adding hydrochloric acid for acidification, and heating the mixture to react to obtain an intermediate dispersion; (3) Adding monomer dispersion and initiator to the intermediate dispersion, reacting under water bath heating conditions, cooling naturally after the reaction, filtering and drying the product to obtain modified nanotubes.

3. The sodium ion battery electrolyte according to claim 2, characterized in that In the step (1) of preparing the modified nanotubes, the monomers used further include polyunsaturated fatty acids.

4. The sodium ion battery electrolyte according to claim 3, characterized in that The polyunsaturated fatty acid molecules contain 3-5 carbon-carbon double bonds.

5. The sodium ion battery electrolyte according to claim 1, characterized in that The additive also includes 1,3-propane sultone.

6. The sodium ion battery electrolyte according to claim 5, characterized in that The carbonate includes at least one of ethylene carbonate and propylene carbonate.

7. The sodium ion battery electrolyte according to claim 6, characterized in that The carbonate esters also include fluorine-containing ethylene carbonate.

8. The sodium ion battery electrolyte according to claim 7, characterized in that The nitrile compound includes at least one of succinonitrile, adiponitrile, and sulfonyldipropionitrile.

9. The sodium ion battery electrolyte according to claim 8, characterized in that The nitrile compound also includes a nitrile organosilicon compound, which is prepared according to the following method: 2-Methyl-3-butenenitrile, hydrogenated silicone oil, chloroplatinic acid catalyst and isopropyl alcohol are mixed, and the mixture is heated and stirred under an argon atmosphere for reaction. After the reaction is completed, the mixture is cooled and then distilled under reduced pressure to obtain a nitrile-based organosilicon compound.

10. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the electrolyte is the sodium ion battery electrolyte according to any one of claims 1 to 9.

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