Flame-retardant sodium-ion battery electrolyte and preparation method thereof

Abstract

The application discloses a kind of flame-retardant sodium-ion battery electrolyte and preparation method thereof, it is related to electrolyte preparation technical field, including precursor preparation, basic electrolyte preparation and flame-retardant electrolyte preparation.The application is by phosphorus-nitrogen-silicon hybrid oligomer precursor is added to the basic electrolyte that is composed of sulfone solvent, fluorinated ester and sodium salt, in vacuum condition is dispersed with gradient temperature ripening under low temperature high shear, it solves the problem that bulk phase flame-retardant additive and electrolyte compatibility is poor, easy to aggregate and settle and causes the problem of ion conductivity drop;By using formation stage electrode potential drive precursor in-situ electrochemical polymerization on positive and negative electrode surface, phosphorus-nitrogen-silicon hybrid nanometer interface film with ion conductivity and thermal response ceramicization characteristics is formed, solves the existing flame retardant only at high temperature decomposition and plays the role of passive lag problem and bulk phase flame-retardant and electrochemical performance inadaptable contradiction.

Description

Technical Field

[0001] This invention relates to the field of electrolyte preparation technology, specifically to a flame-retardant sodium-ion battery electrolyte and its preparation method. Background Technology

[0002] Sodium-ion batteries have broad application prospects in grid energy storage, low-speed electric vehicles, and residential energy storage due to the abundance and low cost of sodium resources. The electrolyte, as a key component of sodium-ion batteries, directly determines the reliability of the battery system. Currently, mainstream sodium-ion battery electrolytes use carbonate or ether solvents as the base, combined with sodium salts such as sodium perchlorate or sodium bis(fluorosulfonyl)imide. However, these organic electrolyte systems have low flash points and are easily flammable, which can exacerbate the spread of fire under thermal runaway conditions. Existing flame-retardant technologies mainly reduce flammability by adding phosphate ester flame retardants to the bulk phase, introducing fluorinated co-solvents, or using phosphazene additives, but all of these methods have inherent drawbacks.

[0003] In existing flame-retardant electrolytes, the compatibility between flame-retardant additives and the electrolyte matrix is ​​poor, resulting in poor dispersion stability, easy agglomeration and sedimentation, and decreased ion transport efficiency at low temperatures. At the same time, most flame retardants undergo irreversible reduction decomposition on the negative electrode surface, which destroys interfacial stability. Furthermore, existing flame-retardant systems are mostly passive and delayed protection, only functioning after the temperature reaches the decomposition threshold, making it difficult to pre-build a thermal stability barrier at the electrode interface. This results in a constant trade-off between flame-retardant function and electrochemical performance, making it impossible to achieve synergistic optimization across the entire temperature range. Summary of the Invention

[0004] The purpose of this invention is to provide a flame-retardant sodium-ion battery electrolyte and its preparation method, which solves the problems of poor compatibility between bulk flame-retardant additives and electrolytes, easy agglomeration and sedimentation, and the resulting decrease in ionic conductivity.

[0005] In a first aspect, embodiments of this application provide a method for preparing a flame-retardant sodium-ion battery electrolyte, comprising the following steps:

[0006] S1: Add a cyclotriphosphazene compound to an inert solvent, stir to dissolve, then add aminosilane dropwise, and then carry out a heated reaction. After the heated reaction is completed, remove the solvent and the byproduct hydrogen chloride by vacuum distillation to obtain the phosphorus nitrogen silicon hybrid oligomer precursor.

[0007] S2: Mix sulfone solvent with fluorinated ester, add sodium salt and stir to dissolve to obtain basic electrolyte;

[0008] S3: Add the phosphorus-nitrogen-silicon hybrid oligomer precursor to the basic electrolyte, disperse it under low temperature and high shear under vacuum conditions, and then ripen it by gradient heating to obtain a flame-retardant sodium-ion battery electrolyte.

[0009] In one embodiment, in S1, anhydrous tetrahydrofuran is selected as the inert solvent; the amount of the inert solvent is 150 mL to 250 mL; the amount of the cyclotriphosphazene compound is 0.05 mol to 0.10 mol; and the molar ratio of the cyclotriphosphazene compound to the aminosilane is 1:1.5 to 1:3.

[0010] In one embodiment, in S1, the cyclotriphosphazene compound is any one of hexachlorocyclotriphosphazene, phenoxycyclotriphosphazene, aminocyclotriphosphazene, and hydroxycyclotriphosphazene; the aminosilane is any one of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and phenylaminomethyltriethoxysilane.

[0011] In one embodiment, in S1, the molecular weight distribution of the phosphorus-nitrogen-silicon hybrid oligomer precursor is 1000 g / mol to 2000 g / mol, the phosphorus content is 12 wt% to 18 wt%, the nitrogen content is 8 wt% to 12 wt%, and the silicon content is 6 wt% to 10 wt%.

[0012] In one embodiment, in S1, the temperature of the aminosilane dropwise addition stage is 0°C to 5°C, the temperature of the heating reaction is 30°C to 60°C, and the reaction time is 4h to 8h.

[0013] In one embodiment, in S2, the volume ratio of sulfone solvent to fluorinated ester is 6:4 to 8:2, the concentration of sodium salt is 0.8 mol / L to 1.2 mol / L, and the stirring and dissolving temperature is 20°C to 30°C.

[0014] In one embodiment, in S2, the sulfone solvent is either sulfolane or dimethyl sulfoxide; the fluoroester is either ethylene fluorocarbonate or ethyl fluorocarbonate; and the sodium salt is either sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide.

[0015] In one embodiment, in S3, the amount of phosphorus-nitrogen-silicon hybrid oligomer precursor added is 1.0 wt% to 3.0 wt% of the total mass of the basic electrolyte;

[0016] The vacuum degree for low-temperature high-shear dispersion is 0.06MPa~0.10MPa, the temperature is 20℃~30℃, the rotation speed is 1500rpm~2500rpm, and the time is 20min~40min;

[0017] The gradient heating rate for aging was 1℃ / min to 3℃ / min, the aging temperature was 40℃ to 50℃, and the aging time was 10h to 14h.

[0018] In one embodiment, in S3, the vacuum degree of low-temperature high-shear dispersion is 0.08 MPa, the temperature is 25°C, the rotation speed is 2000 rpm, and the time is 30 min; the heating rate of gradient heating curing is 2°C / min, the curing temperature is 45°C, and the curing time is 12 h.

[0019] Secondly, this application provides a flame-retardant sodium-ion battery electrolyte, which is prepared using a flame-retardant sodium-ion battery electrolyte preparation method.

[0020] The beneficial effects of this invention are:

[0021] (1) This invention solves the problems of poor compatibility between bulk flame retardant additives and electrolytes, easy agglomeration and sedimentation, and decreased ionic conductivity by adding the phosphorus-nitrogen-silicon hybrid oligomer precursor to a basic electrolyte composed of sulfone solvents, fluorinated esters and sodium salts, and then dispersing it under vacuum conditions at low temperature and high shear and aging it with gradient temperature. This invention achieves uniform and stable dispersion of the flame retardant precursor in the electrolyte.

[0022] (2) This invention utilizes the electrode potential during the formation stage to drive the precursor to electrochemically polymerize in situ on the positive and negative electrode surfaces, forming a phosphorus-nitrogen-silicon hybrid nano-interface film with both ion conductivity and thermal response ceramicization characteristics. This solves the passive lag problem of existing flame retardants only playing a role after high-temperature decomposition and the contradiction between bulk flame retardancy and electrochemical performance. It realizes the intelligent response of room-temperature ion conductivity and high-temperature ceramicization barrier at the electrode interface and the decoupling optimization of flame retardant function and interface ion transport.

[0023] (3) This invention uses conventional industrial raw materials such as hexachlorocyclotriphosphazene and aminosilane to prepare precursors, and replaces the complex solid flame retardant membrane preparation process with precursor liquid injection and in-situ film formation process, which solves the problems of high raw material cost and complex process of high performance flame retardant electrolyte, and achieves compatibility with existing lithium-ion battery liquid injection process and low-cost preparation. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 This is a flowchart of the preparation process proposed in this invention;

[0026] Figure 2 The FTIR spectrum of the phosphorus-nitrogen-silicon hybrid oligomer precursor proposed in this invention;

[0027] Figure 3 This is the XPS P2p peak fitting spectrum of the negative electrode surface proposed in this invention;

[0028] Figure 4 The effect of precursor addition amount on electrolyte performance as proposed in this invention;

[0029] Figure 5 This is a comparison of all performance indicators of the embodiments and comparative examples proposed in this invention;

[0030] Figure 6 This invention provides a comprehensive comparison of raw material costs and electrochemical performance.

[0031] Figure 7 This invention provides a comparison of the 25℃ / 0.5C ambient temperature cycling performance.

[0032] Figure 8 The effect of the process parameters proposed in this invention on electrolyte performance;

[0033] Figure 9 The XPS Si2p and N1s spectra of the negative electrode surface proposed in this invention;

[0034] Figure 10 This is an electron microscope scan image proposed in this invention. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0036] Existing sodium-ion battery electrolytes are mostly based on carbonate or ether solvents, combined with sodium salts such as sodium perchlorate or sodium bis(fluorosulfonyl)imide. However, such organic electrolyte systems have low flash points and are easily flammable, which can exacerbate the spread of fire under thermal runaway conditions. Although there have been attempts to reduce flammability by adding phosphate ester flame retardants or introducing fluorinated cosolvents, bulk flame retardants occupy the solvation sheath space and increase ion migration resistance, resulting in a sharp increase in electrolyte viscosity and a decrease in ionic conductivity at low temperatures. Moreover, most phosphate ester flame retardants undergo irreversible reduction decomposition on the surface of hard carbon anodes, destroying the stability of the solid electrolyte interfacial film and causing rapid capacity decay. Furthermore, existing flame retardants only function after the temperature reaches the decomposition threshold, which is a passive and delayed protection method. They cannot pre-build a thermal stability barrier at the electrode interface, nor can they simultaneously ensure ion conduction at room temperature and ceramic barrier at high temperature. This results in a trade-off between flame retardancy and electrochemical performance. At the same time, the synthesis routes for commercial high-purity phosphate esters, fluorophosphate esters, or phosphazene flame retardants are long and the purification costs are high, resulting in flame-retardant electrolytes being much more expensive than conventional electrolytes, which limits their commercial application in large-scale energy storage scenarios.

[0037] To address the aforementioned pain points of the prior art, this application provides a method for preparing a flame-retardant sodium-ion battery electrolyte and the flame-retardant sodium-ion battery electrolyte obtained by this method. By designing a phosphorus-nitrogen-silicon hybrid oligomer precursor, and utilizing the precursor liquid injection and in-situ electrochemical polymerization process during the battery formation stage, a hybrid nano-interface film with both ion conductivity and thermal responsive ceramic properties is formed on the electrode surface. This transfers the flame-retardant function from the electrolyte liquid phase to the electrode interface, achieving decoupling of flame retardancy and electrochemical transport performance. At the same time, conventional industrial raw materials are used to replace commercially available high-performance flame retardants, reducing preparation costs.

[0038] In terms of raw material and process design, this application uses cyclotriphosphazene compounds and aminosilanes as precursor backbone raw materials to prepare phosphorus-nitrogen-silicon hybrid oligomers through condensation reactions. These precursor molecules contain a phosphorus-nitrogen hybrid backbone, siloxane fragments, and terminal active groups. A basic electrolyte is prepared using sulfone solvents and fluorinated esters as co-solvents, and sodium difluorosulfonamide as the sodium salt, providing a wide-temperature-range ion transport environment. The precursor is added to the basic electrolyte at a predetermined mass fraction, and after low-temperature high-shear dispersion and gradient temperature ripening, the precursor is uniformly dispersed and fully associated with solvent molecules, resulting in a stable flame-retardant electrolyte. In terms of process control, this application establishes a standardized process system by optimizing the precursor addition amount, solvent ratio, dispersion, and ripening parameters to ensure stable electrolyte performance.

[0039] See appendix Figure 1 The complete process steps of this application are as follows:

[0040] S1: Precursor Preparation: A cyclotriphosphazene compound was added to an inert solvent and dissolved by stirring. An aminosilane was then added dropwise, followed by a heated reaction. After the reaction was complete, the solvent and the byproduct hydrogen chloride were removed by vacuum distillation to obtain a phosphorus-nitrogen-silicon hybrid oligomer precursor. The purpose of this step is to introduce siloxane fragments into the phosphorus-nitrogen backbone side chains through a condensation reaction, preparing a hybrid oligomer that combines phosphorus-nitrogen catalytic carbonization active centers with a high-temperature ceramic precursor, thus providing a reaction precursor for subsequent in-situ interfacial polymerization.

[0041] S2: Preparation of basic electrolyte: Sulfone solvent and fluorinated ester are mixed at a set volume ratio, sodium salt is added and stirred to dissolve at a set temperature to obtain the basic electrolyte. The purpose of this step is to prepare an electrolyte matrix with a wide temperature range and high ionic conductivity, providing a stable dispersion medium and ion transport channel for the flame retardant precursor.

[0042] S3: Flame-retardant electrolyte preparation: The phosphorus-nitrogen-silicon hybrid oligomer precursor is added to the base electrolyte and dispersed at low temperature and high shear under vacuum conditions, followed by gradient temperature curing to obtain a flame-retardant sodium-ion battery electrolyte. The purpose of this step is to uniformly disperse and associate the precursor in the base electrolyte, forming a stable flame-retardant electrolyte system, preventing precursor aggregation or sedimentation, and enabling the precursor to migrate to the electrode surface for in-situ polymerization during subsequent battery formation stages.

[0043] In this application, the cyclotriphosphazene compound is any one of hexachlorocyclotriphosphazene, phenoxycyclotriphosphazene, aminocyclotriphosphazene, and hydroxycyclotriphosphazene. This type of compound is widely available in industry, is a mature intermediate for flame retardants, and has controllable costs. The aminosilane is any one of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and phenylaminomethyltriethoxysilane. It is a common silane coupling agent and is widely used in coatings and composite materials. The sulfone solvent is any one of sulfolane and dimethyl sulfoxide. It has a high dielectric constant, which is beneficial for the dissociation of sodium salt. The fluorinated ester is any one of fluoroethylene carbonate and fluoroethyl methyl carbonate. It can help form a sodium fluoride-rich interface film. The sodium salt is any one of sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide. It has high thermal stability and a wide electrochemical window.

[0044] In this application, the molecular weight distribution of the phosphorus-nitrogen-silicon hybrid oligomer precursor is 1000 g / mol to 2000 g / mol, the phosphorus content is 12 wt% to 18 wt%, the nitrogen content is 8 wt% to 12 wt%, and the silicon content is 6 wt% to 10 wt%.

[0045] In some embodiments of this application, in step S1, anhydrous tetrahydrofuran is used as the inert solvent, the amount of cyclotriphosphazene compound is 0.05 mol to 0.10 mol, the amount of inert solvent is 150 mL to 250 mL, and the molar ratio of cyclotriphosphazene compound to aminosilane is 1:1.5 to 1:3; the temperature of the aminosilane dropwise addition stage is 0°C to 5°C, the temperature of the heated reaction is 30°C to 60°C, and the reaction time is 4 h to 8 h; if the scale of precursor synthesis is expanded, the amount of solvent can be increased proportionally to ensure that the reactants are fully dissolved; if it is necessary to increase the molecular weight of the precursor, the reaction time can be appropriately extended or the reaction temperature can be increased, but it is necessary to avoid excessively high temperature leading to an increase in side reactions.

[0046] In some embodiments of this application, the volume ratio of sulfone solvent to fluorinated ester in step S2 is 6:4 to 8:2, the concentration of sodium salt is 0.8 mol / L to 1.2 mol / L, and the stirring and dissolving temperature is 20°C to 30°C. If the application scenario requires high low-temperature ionic conductivity, the proportion of sulfone solvent can be appropriately increased. During winter production, the temperature can be appropriately raised to 30°C to accelerate the dissolution of sodium salt.

[0047] In some embodiments of this application, the amount of phosphorus-nitrogen-silicon hybrid oligomer precursor added in step S3 is 1.0wt% to 3.0wt% of the total mass of the basic electrolyte; the vacuum degree of low-temperature high-shear dispersion is 0.06MPa to 0.10MPa, the temperature is 20℃ to 30℃, the rotation speed is 1500rpm to 2500rpm, and the time is 20min to 40min; the heating rate of gradient heating and ripening is 1℃ / min to 3℃ / min, the ripening temperature is 40℃ to 50℃, and the ripening time is... The time interval is 10h to 14h; if the application scenario has extremely high safety requirements, the amount of precursor added can be increased to 3.0wt%; when the amount of material is large, a high speed of 2500rpm can be used, and when the amount of material is small, a speed of 1500rpm can be used; during the dispersion process, samples can be taken every 10min to observe the dispersion state, and the dispersion time can be adjusted according to the actual situation; if the equipment has high temperature control accuracy, a heating rate of 2℃ / min can be used; if the molecular weight of the precursor is large, the ripening temperature can be appropriately increased to 50℃ to promote the association reaction.

[0048] The preparation method of the flame-retardant sodium-ion battery electrolyte of this application is described in detail below with reference to specific embodiments. The raw materials in each embodiment are in accordance with the aforementioned ratio range, and the process steps are the same as the aforementioned complete process steps, with only some parameters differing.

[0049] Example 1

[0050] The specific steps of the flame-retardant sodium-ion battery electrolyte preparation method provided in this embodiment are as follows:

[0051] S1: Precursor preparation: 0.05 mol of hexachlorocyclotriphosphazene was placed in a three-necked flask, and 200 mL of anhydrous tetrahydrofuran was added as a solvent. After stirring and dissolving, the mixture was cooled to 0°C, and 0.10 mol of γ-aminopropyltriethoxysilane was slowly added dropwise, controlling the dropping rate to maintain the reaction temperature between 0°C and 5°C. After the addition was complete, the temperature was raised to 40°C and reacted for 6 hours. After the reaction was completed, the solvent and byproduct hydrogen chloride were removed by vacuum distillation to obtain a pale yellow viscous liquid, which is the precursor of phosphorus-nitrogen-silicon hybrid oligomers with a molecular weight distribution of 1000 g / mol to 2000 g / mol, a phosphorus content of approximately 15 wt%, a nitrogen content of approximately 10 wt%, and a silicon content of approximately 8 wt%.

[0052] S2: Preparation of basic electrolyte: Mix sulfolane and fluoroethylene carbonate at a volume ratio of 7:3, add sodium difluorosulfonamide, and stir at 25°C until completely dissolved to obtain the basic electrolyte, wherein the concentration of sodium difluorosulfonamide is 1.0 mol / L.

[0053] S3: Flame-retardant electrolyte preparation: The above phosphorus-nitrogen-silicon hybrid oligomer precursor was added to the basic electrolyte at 2.0 wt% of the total mass of the basic electrolyte. The mixture was placed in a planetary mixer and dispersed at low temperature and high shear for 30 min under vacuum of 0.08 MPa, temperature of 25℃ and rotation speed of 2000 rpm. The mixture was then transferred to a curing tank and heated to 45℃ at a heating rate of 2℃ / min under nitrogen protection. The mixture was then kept at this temperature for 12 h to obtain a uniform and stable flame-retardant sodium-ion battery electrolyte.

[0054] The precursor prepared in Example 1 was characterized by FTIR infrared spectroscopy, and the results are as follows: Figure 2 As shown, Figure 2 Middle, 3380cm -1 An absorption peak for the NH stretching vibration appears at 1210 cm⁻¹. -1 A characteristic absorption peak of the P=N skeleton appears at 1070 cm⁻¹. -1 An absorption peak for the Si-O-Si stretching vibration appears at 520 cm⁻¹. -1 The presence of P-Cl related absorption peaks confirms that the precursor molecule contains a phosphorus-nitrogen backbone and siloxane fragments.

[0055] Examples 2-8, Comparative Examples 1-3

[0056] The preparation steps of Examples 2-8 and Comparative Examples 1-3 were based on Example 1 (basic parameters: precursor addition 2.0 wt%; sulfolane to fluoroethylene carbonate volume ratio 7:3; aging temperature 45℃; dispersion time 30 min). Each example changed only one process parameter, and the other parameters were completely consistent with Example 1. Comparative Example 1 did not add a precursor, Comparative Example 2 added 2.0 wt% commercially available trimethyl phosphate as a flame retardant, and Comparative Example 3 added 2.0 wt% commercially available hexaphenoxycyclotriphosphazene as a flame retardant. Specific differences are shown in Table 1.

[0057] Table 1

[0058]

[0059] The electrolytes prepared in Examples 1-8 and Comparative Examples 1-3, and the assembled sodium-ion batteries, were subjected to performance testing. The test indicators included electrolyte self-extinguishing time, ionic conductivity at 25℃, ionic conductivity at -20℃, capacity retention after 500 cycles at room temperature, and capacity recovery rate after 7 days of high-temperature storage at 85℃. The results are shown in Table 2. Furthermore, the negative electrode of the battery assembled in Example 1 was characterized in multiple dimensions: X-ray photoelectron spectroscopy analysis results are shown below. Figure 3 and Figure 9 As shown, Figure 3 The P2p peak fitting spectrum shows a PN bonding peak at 133.5 eV and a PO bonding peak at 134.8 eV. Figure 9 The spectra of Si2p and N1s are shown. Si2p shows a Si-O bonding peak at 102.3 eV, while N1s shows a PN bonding peak at 400.1 eV. Scanning electron microscopy analysis results are as follows: Figure 10 As shown, Figure 10 In Figure 'a', the negative electrode surface of Comparative Example 1 (without flame retardant) is relatively smooth. Figure 10 In Example 2 (1.0 wt% precursor), a slight coating layer appeared on the surface. Figure 10 c represents Example 1 (2.0 wt% precursor), whose surface is covered by a uniform and dense hybrid interface film. Figure 10 In the middle d, which is comparative example 2 (trimethyl phosphate), obvious cracks and irregular agglomerates appeared on the surface.

[0060] Table 2

[0061]

[0062] Combining the data in Tables 1 and 2, the influence of each parameter on performance can be derived, as detailed in the following analysis:

[0063] 1. Effect of precursor addition amount (comparison of Example 1, Example 2, and Example 3)

[0064] See attached document Figure 4 In Table 1, Examples 2 and 3 only differed in the amount of precursor added: Example 2 had 1.0 wt%, and Example 3 had 3.0 wt%, while other parameters remained the same as Example 1 (2.0 wt%). Corresponding to the performance data in Table 2: Example 2 had a self-extinguishing time of 5.5 s, longer than Example 1's 3.5 s; an ionic conductivity of 8.3 mS / cm at 25°C, higher than Example 1's 8.0 mS / cm; a capacity retention rate of 94.2% after 500 cycles, higher than Example 1's 93.8%; and a high-temperature storage capacity recovery rate of 89.8%, lower than Example 1's 92.5%. Due to insufficient precursor content, the interfacial flame-retardant layer was thinner, resulting in decreased high-temperature barrier properties; however, the precursor's obstruction of bulk ion transport was reduced, leading to a slight increase in conductivity. Example 3 had a self-extinguishing time of 2.6 s, shorter than Example 1; an ionic conductivity of 7.5 mS / cm at 25°C, lower than Example 1; and a capacity retention rate of 92.5% after 500 cycles, lower than Example 1. Excessive precursor content increases dispersion difficulty, some incompletely associated precursors affect ion migration, and an excessively thick interfacial film increases interfacial impedance. 2.0 wt% is the optimal addition amount.

[0065] 2. Effect of solvent volume ratio (Comparison of Examples 1, 4, and 5)

[0066] See attached document Figure 2In Table 1, the solvent volume ratio for Example 4 is 6:4, and for Example 5 it is 8:2; other parameters are consistent with the 7:3 ratio for Example 1. Table 2 shows that in Example 4, due to the increased proportion of fluoroethylene carbonate, the ionic conductivity at 25°C is 7.4 mS / cm, and at -20°C it is 1.6 mS / cm, both lower than in Example 1. Because the viscosity of fluoroesters is higher than that of sulfolane, the increased proportion leads to an increase in the overall viscosity of the electrolyte, increasing the resistance to ion migration. In Example 5, with the increased proportion of sulfolane, the ionic conductivity at 25°C is 8.3 mS / cm, and at -20°C it is 2.1 mS / cm, both higher than in Example 1. Because sulfolane has a high dielectric constant, it facilitates the dissociation of sodium salts, and its relatively low viscosity facilitates ion transport. However, an excessively high proportion of sulfolane will slightly lower the flash point; a balance between flame retardancy and conductivity is necessary, and 7:3 is the optimal ratio.

[0067] 3. Effect of curing temperature (Comparison of Examples 1, 6, and 7)

[0068] See attached document Figure 8 In the left figure, Table 1 shows that the curing temperature for Example 6 was 40℃, and for Example 7 it was 50℃, with other parameters consistent with 45℃ in Example 1. Table 2 data shows that in Example 6, due to the lower curing temperature, the precursor and solvent molecules did not associate sufficiently, resulting in a longer self-extinguishing time (3.9s) than in Example 1, and a slightly lower ionic conductivity (7.9 mS / cm) at 25℃. Due to insufficient association, some precursors failed to migrate sufficiently to the electrode surface during battery formation, leading to a decrease in the density of the interfacial flame-retardant layer. Example 7, with its higher curing temperature, had a self-extinguishing time of 3.4s and an ionic conductivity of 8.0 mS / cm at 25℃, similar to Example 1. However, excessively high temperatures increase energy consumption and may cause slight decomposition of the fluorinated ester, leading to decreased long-term storage stability. 45℃ is the optimal curing temperature.

[0069] 4. The impact of dispersion time (comparison of Example 1 and Example 8)

[0070] See attached document Figure 8 As shown in the right figure, in Table 1, Example 8 only shortened the dispersion time to 20 min, while other parameters remained the same as Example 1's 30 min. In Table 2, Example 8's self-extinguishing time of 4.2 s was longer than Example 1's 3.5 s, and its ionic conductivity at 25°C of 7.7 mS / cm was lower than Example 1's 8.0 mS / cm. Due to insufficient dispersion time, the precursor locally agglomerated, with some areas having excessively high precursor concentrations and others having excessively low concentrations, affecting the uniformity of the interfacial flame-retardant layer. A dispersion time of 30 min was sufficient to uniformly disperse the precursor; further extending the dispersion time had limited performance improvement and instead increased energy consumption.

[0071] 5. Verify the necessity of key components / processes using comparative analysis.

[0072] See attached document Figure 5 and Figure 7In Table 1, Comparative Examples 1, 2, and 3 omit the key processes of this application or adopt bulk flame retardant alternatives, respectively. The necessity of these alternatives can be verified by the performance data in Table 2. Figure 5 This is a bar chart comparing all indicators of the examples and comparative examples. Figure 7 The cycling performance curves are for 25℃ / 0.5C ambient temperature.

[0073] Comparative Example 1, without the addition of a precursor, showed complete combustion of the electrolyte and a capacity retention rate of 96.5% after 500 cycles, which was higher than that of Example 1. However, its high-temperature storage capacity recovery rate of 76.8% was lower than that of Example 1, demonstrating that the electrolyte without flame retardant protection exhibited severe interfacial side reactions at high temperatures and insufficient long-term stability.

[0074] Comparative Example 2, with the addition of 2.0 wt% commercially available trimethyl phosphate as a bulk flame retardant, exhibited a self-extinguishing time of 9.2 s, an ionic conductivity of 0.5 mS / cm at -20℃, a capacity retention of 68.7% after 500 cycles, and a capacity recovery rate of 62.3% during high-temperature storage. This demonstrates that while the addition of phosphate to the bulk phase provides some flame retardancy, it severely disrupts the interfacial stability of the hard carbon anode, leading to deterioration in low-temperature performance and rapid capacity decay.

[0075] Comparative Example 3, with the addition of 2.0 wt% of commercially available hexaphenoxycyclotriphosphazene as a bulk flame retardant, exhibited a self-extinguishing time of 7.8 s, an ionic conductivity of 0.9 mS / cm at -20℃, a capacity retention rate of 79.2% after 500 cycles, and a high-temperature storage capacity recovery rate of 70.1%. This demonstrates that the addition of phosphazene-based flame retardants to the bulk phase also leads to a decrease in electrochemical performance, and the flame retardant efficiency is lower than that of the in-situ interface strategy proposed in this application.

[0076] To further verify the stability of the process, the parameters of Example 1 were repeated three times. The test results are shown in Table 3. The coefficient of variation was ≤3% for all of them, indicating that the parameter design in Table 1 has good repeatability and is suitable for industrial mass production.

[0077] Table 3

[0078]

[0079] The economic feasibility was verified by calculating the raw material cost of the flame-retardant electrolyte prepared in Example 1. The calculation results are shown in Table 4 and... Figure 6 . Figure 6The chart shows a comprehensive comparison of raw material costs and electrochemical performance. The cost of the flame-retardant electrolyte in this application is 2.4 yuan / L, the cost of the electrolyte with added trimethyl phosphate is 25 yuan / L, and the cost of the electrolyte with added hexaphenoxycyclotriphosphazene is 50 yuan / L. In terms of capacity retention after 500 cycles, the application achieves 93.8%, the trimethyl phosphate-added electrolyte achieves 68.7%, and the hexaphenoxycyclotriphosphazene-added electrolyte achieves 79.2%. Data shows that the precursor raw material cost of the flame-retardant electrolyte in this application is lower than that of commercially available high-performance flame retardants, and the overall cost increase compared to conventional non-flame-retardant electrolytes is controlled within 15%, meeting the cost constraints for large-scale energy storage applications.

[0080] Table 4

[0081]

[0082] Based on the data and analysis in Tables 1 to 4, the innovative points of the flame-retardant sodium-ion battery electrolyte preparation method of this application can be summarized into three points:

[0083] Design of phosphorus-nitrogen-silicon hybrid precursor and construction of in-situ polymerization interface: Phosphorus-nitrogen-silicon hybrid oligomer precursors were prepared by condensation reaction of hexachlorocyclotriphosphazene and aminosilane. The hybrid ceramic interface film was formed in-situ by electrochemical driving during the formation stage, which transferred the flame retardant function from the electrolytic liquid phase to the electrode interface, solved the contradiction between bulk flame retardancy and electrochemical performance, and achieved decoupling optimization of flame retardancy and ion transport.

[0084] Precise control of multi-stage process parameters: By optimizing key parameters such as precursor addition, solvent ratio, dispersion and aging temperature and time, a standardized process system is established to ensure stable electrolyte performance and avoid quality fluctuations caused by experience-based operation in traditional processes;

[0085] Industrial conventional raw material utilization and cost control: Using industrial conventional chemicals such as hexachlorocyclotriphosphazene and aminosilane as raw materials, commercial high-performance flame retardants can be replaced. The precursor preparation adopts normal temperature and pressure or mild heating conditions, without the need for high temperature and high pressure reactors, precious metal catalysts, or complex purification column chromatography. Energy consumption and equipment depreciation costs are extremely low, and the overall cost increase is controlled within 15%, which meets the economic requirements of large-scale energy storage applications.

[0086] In summary, the specific implementation method of this application demonstrates the innovation, stability and practicality of the process through a complete logical chain of parameter design, performance testing, pattern analysis and application verification. It not only solves the technical pain points of electrochemical performance deterioration and high cost caused by the addition of liquid phase in traditional flame-retardant electrolysis, but also meets the comprehensive requirements of sodium-ion batteries for wide temperature range, long cycle and high safety, and has broad promotion value.

[0087] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a flame-retardant sodium-ion battery electrolyte, characterized in that, Includes the following steps: S1: A cyclotriphosphazene compound is added to an inert solvent, dissolved by stirring, and then aminosilane is added dropwise. The reaction is then carried out at a higher temperature. After the reaction is complete, the solvent and the byproduct hydrogen chloride are removed by vacuum distillation to obtain a phosphorus-nitrogen-silicon hybrid oligomer precursor. The phosphorus-nitrogen-silicon hybrid oligomer precursor has a molecular weight distribution of 1000 g / mol to 2000 g / mol, a phosphorus content of 12 wt% to 18 wt%, a nitrogen content of 8 wt% to 12 wt%, and a silicon content of 6 wt% to 10 wt%. S2: Mix a sulfone solvent with a fluorinated ester, add a sodium salt and stir to dissolve, to obtain a basic electrolyte; the sulfone solvent is any one of sulfolane and dimethyl sulfoxide; the fluorinated ester is any one of fluoroethylene carbonate and fluoroethyl methyl carbonate; the sodium salt is any one of sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide. S3: The phosphorus-nitrogen-silicon hybrid oligomer precursor is added to the basic electrolyte and dispersed under low temperature and high shear under vacuum conditions, followed by gradient heating and aging to obtain a flame-retardant sodium-ion battery electrolyte. The amount of phosphorus-nitrogen-silicon hybrid oligomer precursor added is 1.0wt% to 3.0wt% of the total mass of the basic electrolyte. The vacuum degree of the low temperature and high shear dispersion is 0.06MPa to 0.10MPa, the temperature is 20℃ to 30℃, the rotation speed is 1500rpm to 2500rpm, and the time is 20min to 40min. The heating rate of the gradient heating and aging is 1℃ / min to 3℃ / min, the aging temperature is 40℃ to 50℃, and the aging time is 10h to 14h.

2. The method for preparing the flame-retardant sodium-ion battery electrolyte according to claim 1, characterized in that, In step S1, the inert solvent is anhydrous tetrahydrofuran; the amount of the inert solvent is 150 mL to 250 mL; the amount of the cyclotriphosphazene compound is 0.05 mol to 0.10 mol; and the molar ratio of the cyclotriphosphazene compound to aminosilane is 1:1.5 to 1:

3.

3. The method for preparing the flame-retardant sodium-ion battery electrolyte according to claim 1, characterized in that, In S1, the cyclotriphosphazene compound is any one of hexachlorocyclotriphosphazene, phenoxycyclotriphosphazene, aminocyclotriphosphazene, and hydroxycyclotriphosphazene; the aminosilane is any one of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and phenylaminomethyltriethoxysilane.

4. The method for preparing the flame-retardant sodium-ion battery electrolyte according to claim 1, characterized in that, In step S1, the temperature of the aminosilane dropwise addition stage is 0°C to 5°C, the temperature of the heating reaction is 30°C to 60°C, and the reaction time is 4h to 8h.

5. The method for preparing the flame-retardant sodium-ion battery electrolyte according to claim 1, characterized in that, In S2, the volume ratio of sulfone solvent to fluorinated ester is 6:4 to 8:2, the concentration of sodium salt is 0.8 mol / L to 1.2 mol / L, and the stirring and dissolving temperature is 20℃ to 30℃.

6. The method for preparing the flame-retardant sodium-ion battery electrolyte according to claim 1, characterized in that, In step S3, the vacuum degree of the low-temperature high-shear dispersion is 0.08 MPa, the temperature is 25°C, the rotation speed is 2000 rpm, and the time is 30 min; the heating rate of the gradient heating and ripening is 2°C / min, the ripening temperature is 45°C, and the ripening time is 12 h.

7. A flame-retardant sodium-ion battery electrolyte, characterized in that, The electrolyte is prepared using the method described in any one of claims 1 to 6 for flame-retardant sodium-ion batteries.

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