Fluorophenyl phosphonate esters, methods of making and use in sodium ion batteries

Abstract

This invention belongs to the field of sodium-ion batteries, and relates to a fluorophenylphosphonate, its preparation method, and its application in sodium-ion batteries. The fluorophenylphosphonate includes di(trifluoroisopropyl)phenylphosphonate or di(hexafluoroisopropyl)phenylphosphonate; the preparation steps are as follows: using fluoroalcohol and phenylphosphonyl dichloride as raw materials, triethylamine as an acid-binding agent, and diethyl ether as a reaction solvent, the fluorophenylphosphonate is prepared by a condensation substitution reaction. Sodium-ion batteries prepared using fluorophenylphosphonate exhibit high ionic conductivity and an electrochemical stability window. This phosphonate additive preferentially decomposes at the electrode interface, inducing the formation of a thin, dense, uniform electrode-electrolyte interface phase rich in NaF inorganic components, and giving the electrolyte excellent flame-retardant properties. Sodium-ion batteries assembled with positive electrode materials exhibit good rate performance and cycle stability, with a cycle life exceeding 5000 cycles at room temperature. Simultaneously, this electrolyte also exhibits excellent cycle performance at a high temperature of 60°C.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries and relates to battery electrolytes. Background Technology

[0002] With the increasing global demand for renewable energy storage, the development of high-performance, long-life, and safe sodium-ion batteries has become a cutting-edge research direction. The electrolyte, as a crucial component of sodium-ion batteries, not only performs ion transport but also directly participates in the formation of the electrode-electrolyte interface, significantly impacting the battery's electrochemical performance and safety. Currently, sodium-ion batteries commonly use carbonate-based solvents, such as ethylene carbonate (EC) and propylene carbonate (PC), which are also used in lithium-ion batteries. While these solvents possess high dielectric constants and good film-forming properties, they have two inherent drawbacks: poor interfacial compatibility with electrode materials and high flammability. During charge-discharge cycles, carbonate solvents undergo continuous oxidation / reduction decomposition on the electrode surface, leading to the formation of unstable solid-electrolyte (SEI) and cathode-electrolyte (CEI) interfaces. Furthermore, carbonate solvents have low flash points, making them highly susceptible to combustion or even explosion during thermal runaway, severely limiting the practical application of sodium-ion batteries. To address these issues, researchers have proposed various optimization strategies, including solvent system optimization, sodium salt screening, and the introduction of functional additives. Among them, electrolyte additives have become one of the most economical and efficient ways to improve interface stability and safety due to their advantages such as low dosage, significant effect, and no change to the main electrolyte formula.

[0003] Traditional phosphate esters (such as triethyl phosphate and trimethyl phosphate) are often used as flame retardant additives. This is because they decompose upon heating to generate phosphorus-containing free radicals, which can effectively capture hydrogen and hydroxyl radicals generated during combustion, thereby inhibiting the chain reaction. Furthermore, phosphate esters can promote dehydration and carbonization of materials, forming a dense carbonized layer that effectively isolates heat and oxygen from diffusion, reducing the generation of combustible gases and thus slowing down the combustion rate. Fluorinated reagents can provide fluorine free radicals during decomposition to quench the chain reaction and promote the formation of fluoride-rich SEI / CEI, making them ideal reagents that balance electrochemical performance and safety. Therefore, if the additive molecule contains both phosphorus and fluorine, the phosphorus-fluorine synergistic effect can potentially improve interfacial stability while imparting flame-retardant properties to the electrolyte system.

[0004] Patent CN 110518287 A discloses an electrolyte for a sodium-ion secondary battery, using phosphate esters and fluorinated ethers as flame retardants, combined with fluorinated additives to form a fluoride-rich SEI film. However, the combined use of multiple flame retardants and functional additives leads to a significant increase in electrolyte viscosity and a decrease in ionic conductivity. Furthermore, disordered competitive film formation causes increased interfacial impedance, resulting in battery performance loss, thus hindering its practical applicability. Patent CN 114039095 A discloses a flame-retardant sodium-ion battery electrolyte system. In addition to phosphate ester-based flame retardants and fluorinated film-forming additives, alkoxy functional additives are also added, effectively suppressing the increase in battery internal resistance caused by flame retardant additives and further improving electrochemical performance. However, this system still relies on the physical compounding of multiple additives, and there may be differences in interfacial compatibility between the components. Moreover, flammable carbonate solvents still constitute a large proportion, posing a safety hazard. Patent CN 112786968 A proposes a phosphate ester-based high-voltage flame-retardant lithium battery electrolyte, in which phosphate ester and lithium salt work together to form a stable solvation structure, solving the problem of incompatibility with graphite anode.

[0005] It is evident that current technologies, in order to address the interfacial instability and flammability issues of traditional carbonate electrolyte systems in sodium-ion batteries, often employ a multi-component compounding strategy of "flame retardant + film-forming agent + functional additives." However, different additives often exhibit functional antagonism and excessively high total amounts, making it difficult to truly achieve a balance between safety and electrochemical performance. Therefore, seeking an electrolyte additive that can intrinsically integrate flame retardancy and interfacial film-forming regulation functions into a single structure at the molecular level, enabling sodium-ion batteries to achieve both high safety and electrochemical performance, is of significant practical importance. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a fluorophenylphosphonate, its preparation method, and its application in sodium-ion batteries. The integrated design of this invention avoids the problems associated with multi-component compounding, such as electrolyte viscosity, increased internal resistance, disordered film formation, and poor compatibility. It achieves both high-efficiency flame retardancy and stable SEI film construction with a lower addition amount, thus reconstructing the Na+... + Starting from the solvation structure level, this provides new design ideas for developing high-performance and high-safety sodium-ion battery electrolytes.

[0007] The technical solution of this invention is implemented as follows:

[0008] In a first aspect, the present invention provides a fluorophenylphosphonate, including di(trifluoroisopropyl)phenylphosphonate (TFP) or di(hexafluoroisopropyl)phenylphosphonate (HFP).

[0009] Furthermore, the structure of the fluorophenylphosphonate additive is as follows:

[0010] .

[0011] Secondly, this invention provides a method for synthesizing the two fluorophenylphosphonates mentioned above. In this invention, fluoroalcohols and phenylphosphonic dichloride are used as raw materials, triethylamine is used as an acid-binding agent, and diethyl ether is used as a reaction solvent. During the reaction, the acid-binding agent can neutralize the hydrogen chloride byproduct generated in situ, effectively suppressing side reactions in the system and improving the conversion rate of raw materials. By controlling the temperature and reacting in steps, both reaction selectivity and conversion completeness are taken into account. The post-processing is simple, the product purification effect is excellent, and the final product yield is excellent.

[0012] The synthetic route is as follows:

[0013] and

[0014] .

[0015] The synthesis steps are as follows:

[0016] (1) In the presence of an acid-binding agent, fluoroalcohol and phenylphosphonic dichloride undergo a substitution reaction under controlled temperature conditions, and the reaction solution is finally obtained after the reaction is complete; the condensation substitution reaction should be understood as the nucleophilic substitution reaction between fluoroalcohol and phenylphosphonic dichloride in a triethylamine acid-binding system;

[0017] (2) The reaction solution obtained in step (1) is subjected to solid-liquid separation, washing to remove impurities, drying to remove water, and then concentrated to remove solvent and purified by column chromatography to obtain the fluorophenylphosphonate. The post-treatment reaction should be understood as the whole process of purifying and refining reaction solution A to obtain the target final product.

[0018] Furthermore, the aforementioned fluoroalcohol is fluoroisopropanol; preferably, the fluoroisopropanol is selected from one of hexafluoroisopropanol and trifluoroisopropanol.

[0019] Furthermore, in step (1) above, the acid-binding agent is an organic base known to those skilled in the art that can neutralize hydrogen halides and catalyze nucleophilic substitution reactions, preferably triethylamine. When triethylamine is used, the reaction yield of fluoroalcohol and phenylphosphonic dichloride is high.

[0020] Furthermore, the molar ratio of the triethylamine used to the fluoroethanol is 1.0:1.0.

[0021] Further, in step (1) above, the amount of phenylphosphonic dichloride used is half the amount of fluoroalcohol, and the amount of fluoroalcohol used is in excess, so as to promote the complete conversion of phenylphosphonic dichloride. Preferably, the molar ratio of fluoroalcohol to phenylphosphonic dichloride is 1.0-2.0:1.0.

[0022] Furthermore, in step (1) above, the preferred temperature for the condensation substitution low-temperature reaction is 0-5℃ (ice-water bath). Within this temperature range, the condensation substitution reaction can proceed with high selectivity, while effectively avoiding side reactions caused by high temperature and improving the selectivity of raw material conversion.

[0023] Furthermore, in step (1) above, the low-temperature reaction time is preferably 20-25 h; after the low-temperature reaction is completed, the reflux temperature is preferably 35-45℃, and the reflux reaction time is preferably 1-3 h, so that the trace raw materials that have not been fully reacted in the system can fully react and maximize the conversion rate of raw materials.

[0024] The condensation substitution reaction in step (1) can be monitored by thin-layer chromatography or determined by the amount of solid byproducts generated in the system.

[0025] Furthermore, in step (2) above, the silica gel used for column chromatography purification is preferably 200-300 mesh, and pure petroleum ether is used as the eluent throughout the process. The elution selectivity is good, the product separation is high, and impurities in the crude product can be removed efficiently, resulting in a final product with excellent purity.

[0026] Thirdly, the present invention provides an electrolyte additive comprising the above-mentioned fluorophenylphosphonate.

[0027] Fourthly, the present invention provides a flame-retardant electrolyte for sodium-ion batteries, comprising the above-mentioned fluorophenylphosphonate, electrolyte sodium salt, and organic solvent.

[0028] Organic solvents include carbonate compounds, carboxylic acid esters such as ethylene glycol diacetate, and phosphate esters.

[0029] Furthermore, the aforementioned carbonate compounds include one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); carboxylic acid esters such as ethylene glycol diacetate are one or more of ethylene glycol diacetate (GDA), diethylene glycol diacetate (DGD), and triethylene glycol diacetate (TGD); and phosphate esters are one or more of trimethyl phosphate (TMP), triethyl phosphate (TEP), and trifluoroethyl phosphate (TFEP).

[0030] Furthermore, the aforementioned electrolyte sodium salt is one or more of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium difluorooxalate borate (NaDFOB), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaOTf), and sodium difluorosulfonylimide (NaFSI).

[0031] Furthermore, the aforementioned fluorophenylphosphonate additives include one of p-(trifluoroisopropyl)phenylphosphonate (TFP) and p-(hexafluoroisopropyl)phenylphosphonate (HFP).

[0032] Furthermore, the molar volume ratio of the above-mentioned electrolyte sodium salt to the organic solvent is 1-2 mol: 1L; the amount of the fluorophenyl phosphate additive is 5-50 wt% of the total mass of the electrolyte.

[0033] The preparation method of flame-retardant electrolyte for sodium-ion batteries includes the following steps:

[0034] 1) After drying organic solvents such as carbonate compounds, carboxylic acid esters such as ethylene glycol diacetate, and phosphate esters to remove water, select one or more of them and mix them to prepare an organic solvent;

[0035] 2) Under a dry, inert gas protective atmosphere, the electrolyte sodium salt and the fluorophenylphosphonate additive are added sequentially to the organic solvent and mixed evenly to prepare the flame-retardant electrolyte for sodium-ion batteries.

[0036] Further, in step 1), the organic solvents are all used after being dehydrated by passing them through a 4-Å molecular sieve; the method for preparing the organic solvents is to mix and stir one or more of the following: carbonate compounds, carboxylic acid esters such as ethylene glycol diacetate, and phosphate esters until the solution is clear and transparent.

[0037] Further, in step 2), the conditions for a dry inert atmosphere are H2O < 1 ppm and O2 < 1 ppm; the inert gases include argon, nitrogen, and helium; in step 1), the sodium electrolyte salt is first added and stirred until homogeneous to remove impurities and obtain a transparent solution; then, fluorophenylphosphonate additive is added and stirred until transparent.

[0038] Fifthly, the present invention provides a sodium-ion battery, comprising a positive electrode, a separator, a negative electrode, and the aforementioned flame-retardant electrolyte for sodium-ion batteries. The active material of the positive electrode includes any one of sodium vanadium phosphate (NVP), sodium iron pyrophosphate (NFP), sodium iron pyrophosphate (NFPP), sodium vanadium fluorophosphate (NVPF), sodium vanadium oxide phosphate (NVPOF), sodium ferrous sulfate (NFS), layered oxides, and organic carbonyl-based positive electrode materials. The negative electrode is a metallic sodium negative electrode and hard carbon.

[0039] Furthermore, the aforementioned sodium-ion batteries include coin-type sodium-ion batteries, pouch-type sodium-ion batteries, square sodium-ion batteries, or cylindrical sodium-ion batteries.

[0040] The present invention has the following beneficial effects:

[0041] 1. The fluorophenylphosphonate additive provided by this invention can preferentially participate in the coordination of sodium ions and weaken the coordination effect of the original solvent molecules, constructing a loosely reconstructed solvation structure. This solvation structure can optimize the film formation behavior at the electrode interface and facilitate the efficient desolvation of sodium ions at the electrolyte-electrode interface, helping to reduce the sodium ion desolvation energy barrier, thereby significantly improving the battery interface stability and electrochemical kinetic performance. In the flame-retardant electrolyte for sodium-ion batteries provided by this invention, the addition of phenylphosphonate flame retardant as an additive gives the electrolyte good thermal stability and flame-retardant properties.

[0042] 2. The flame-retardant electrolyte for sodium-ion batteries provided by this invention exhibits excellent high-temperature performance. The introduction of phenylphosphonate additives optimizes the electrolyte system, enhancing its high-temperature tolerance, inhibiting high-temperature electrolyte decomposition and battery short-circuit failure, and ensuring stable ion transport at high temperatures. The phenylphosphonate additives possess excellent thermal stability and interface regulation capabilities, making them suitable for use as high-temperature, long-cycle, high-safety sodium-ion battery electrolytes.

[0043] 3. The flame-retardant electrolyte for sodium-ion batteries provided by this invention has wide applicability and can be well matched with a variety of cathode materials, including polyanionic cathode materials such as NVP, NFP, NFPP, NVPF, NVPOF, and NFS, P2 layered oxide cathode materials, and organic carbonyl cathode materials.

[0044] 4. The flame-retardant electrolyte for sodium-ion batteries provided by this invention exhibits excellent rate performance and stable cycle life. The assembled Na||NFPP (8:1:1) battery induces the formation of a thin, dense, uniform solid-electrolyte interface phase rich in NaF inorganic components at the electrode interface. After 5500 cycles at 2 C at room temperature, the capacity retention rate is 90.09%. The assembled Na||NFPP (8:1:1) battery also demonstrates excellent high-temperature performance, showing no capacity decay after 500 cycles at 5 C; and can stably cycle over 2000 cycles at a high rate of 10 C with a capacity retention rate of 92.8%. This electrolyte possesses significant scientific research value and commercial application prospects.

[0045] 5. The flame-retardant electrolyte for sodium-ion batteries provided by this invention uses sodium hexafluorophosphate, sodium difluorooxalate borate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium difluorosulfonylimide, and sodium bis(trifluoromethanesulfonyl)imide as one or more of these sodium salts, which possess high oxidation decomposition potentials and are compatible with high-voltage cathode materials such as sodium vanadium fluorophosphate, sodium vanadium oxyphosphate, and sodium ferrous sulfate, thereby improving battery energy density. The preparation process of the flame-retardant electrolyte for sodium-ion batteries provided by this invention is simple and easy to implement, with no particularly demanding requirements for production equipment. It is highly compatible with existing industrial production processes and has excellent value for industrial mass production applications. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 The graph shows the cycling performance of the Na||NFPP (8:1:1) battery assembled with the electrolyte in Example 3 at 5 C rate and room temperature.

[0048] Figure 2 The rate performance of Na||NFPP (8:1:1) batteries assembled with electrolytes from Examples 3 and 4 at room temperature is shown in the graph.

[0049] Figure 3 To illustrate the flame retardant effects of Example 4 and Comparative Example 1, and the intrinsic flame retardancy of HFP;

[0050] Figure 4 This is a comparison of the ionic conductivity of the electrolytes in Example 4 and Comparative Example 1.

[0051] Figure 5 The graph shows the cycling performance of the Na||NFPP (8:1:1) batteries assembled in Example 4 and Comparative Example 1 at 2 C rate at room temperature.

[0052] Figure 6 The cycling performance of Na||NFPP (8:1:1) assembled in Example 4 and Comparative Example 1 at a high temperature of 60 °C and a 5 C rate is shown in the graph.

[0053] Figure 7 The cycling performance of Na||NFPP (8:1:1) assembled in Example 4 and Comparative Example 1 at a high temperature of 60 °C and a 10 C rate is shown in the graph.

[0054] Figure 8 The graph shows the cycling performance of the Na||NFPP pouch cell assembled in Example 4 at 2 C rate and room temperature.

[0055] Figure 9 The graph shows the cycling performance of the Na||NVP batteries assembled in Example 5 and Comparative Example 2 at 2 C rate and room temperature.

[0056] Figure 10 The charge-discharge curves of the Na||NVP batteries assembled in Example 5 and Comparative Example 2 at room temperature and 2 C rate are shown.

[0057] Figure 11 The cycling performance of the Na||NVP batteries assembled in Example 5 and Comparative Example 2 at 10 C rate at room temperature is shown in the graph.

[0058] Figure 12 Linear sweep voltammetry curves of the electrolyte in Example 6;

[0059] Figure 13 Rate performance of Na||NFPP (7:2:1) battery assembled with electrolyte in Example 6 at room temperature;

[0060] Figure 14 The graph shows the cycling performance of the Na||NFPP (7:2:1) battery assembled with the electrolyte in Example 6 at 1 C rate and room temperature.

[0061] Figure 15 Rate performance at room temperature of Na||NFPP (8:1:1) battery assembled with electrolyte in Example 6;

[0062] Figure 16 The linear sweep voltammetry curve d for the electrolyte in Example 7;

[0063] Figure 17 Rate performance at room temperature of Na||NFPP (7:2:1) battery assembled with electrolyte in Example 7;

[0064] Figure 18 The graph shows the cycling performance of the Na||NFPP (7:2:1) battery assembled with the electrolyte in Example 7 at 1 C rate and room temperature.

[0065] Figure 19 The cycling performance of the Na||NFPP (8:1:1) battery assembled with the electrolyte in Example 8 at a 0.5 C rate is shown in the graph.

[0066] Figure 20 The graph shows the cycling performance of the Na||NFPP (8:1:1) battery assembled with the electrolyte in Example 9 at a rate of 0.5 C. Detailed Implementation

[0067] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0068] Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0069] To further clarify the research and development objectives, complete technical solutions, and technical advantages of this invention, the following will elaborate on and specifically describe the technical solutions of this invention in conjunction with the accompanying drawings and specific implementation examples.

[0070] The fluorophenylphosphonate additives provided in the embodiments of the present invention include di(trifluoroisopropyl)phenylphosphonate or di(hexafluoroisopropyl)phenylphosphonate.

[0071] The sodium-ion battery provided in this embodiment of the invention includes a positive electrode, a separator, a negative electrode, and the flame-retardant electrolyte for sodium-ion batteries described above.

[0072] In some embodiments, the active material used in the positive electrode includes one of sodium vanadium phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium vanadium fluorophosphate, layered oxides, sodium vanadium oxide phosphate, and sodium ferrous sulfate.

[0073] In some embodiments, the negative electrode is a metallic sodium negative electrode and hard carbon.

[0074] In some embodiments, the sodium-ion battery includes a coin cell sodium-ion battery, a pouch sodium-ion battery, a square sodium-ion battery, or a cylindrical sodium-ion battery.

[0075] The technical solution of the present invention will now be described with reference to specific embodiments:

[0076] Example 1

[0077] The preparation method of di(hexafluoroisopropyl)phenylphosphonate (HFP) in this embodiment is as follows:

[0078] ;

[0079] The experimental steps are as follows:

[0080] First, accurately weigh 11.76 g (0.07 mol) of hexafluoroisopropanol and place it in a flask containing 25 mL of diethyl ether. Add 9.7 mL (0.07 mol) of triethylamine under ice bath stirring. Dissolve 6.82 g (0.035 mol) of phenylphosphonic dichloride in 25 mL of diethyl ether and add it to a constant-pressure dropping funnel. Slowly add this mixture dropwise to the above system while continuously stirring. After the addition is complete, keep the system in an ice-water bath with continuous stirring for 24 h. During this process, a large amount of white solid can be observed to form. To ensure a more complete reaction, heat the reaction system to 40 °C and reflux for 2 h.

[0081] After the reaction was complete, the mixture was filtered and the filtrate was collected. The filter cake was washed with an appropriate amount of diethyl ether, and the washings were combined and added to the filtrate. The filtrate was dried overnight with anhydrous sodium sulfate to remove water. The low-boiling-point solvent was removed using a rotary evaporator to obtain the crude product, which was then purified by silica gel column chromatography using 200-300 mesh, with pure petroleum ether as the eluent. The target component was collected, and the solvent was removed by rotary evaporation to obtain a pure, pale yellow liquid product, namely HFP. The final product mass was 11.60 g, with a yield of 72.36%.

[0082] Example 2

[0083] The preparation method of di(hexafluoroisopropyl)phenylphosphonate (HFP) in this embodiment is as follows:

[0084] ;

[0085] The experimental steps are as follows:

[0086] First, accurately weigh 10.07 g (0.14 mol) of trifluoroisopropanol and place it in a flask containing 50 mL of diethyl ether. Add 19.46 mL (0.14 mol) of triethylamine under ice bath stirring. Dissolve 9.926 g (0.07 mol) of phenylphosphonic dichloride in 50 mL of diethyl ether and add it to a constant-pressure dropping funnel. Slowly add this mixture dropwise to the above system while continuously stirring. After the addition is complete, keep the system in an ice-water bath with continuous stirring for 24 h. During this process, a large amount of white solid can be observed to form. To ensure a more complete reaction, heat the reaction system to 42 °C and reflux for 2.5 h.

[0087] After the reaction was complete, the mixture was filtered and the filtrate was collected. The filter cake was washed with an appropriate amount of diethyl ether, and the washings were combined and added to the filtrate. The filtrate was dried overnight with anhydrous sodium sulfate to remove water. The low-boiling-point solvent was removed by rotary evaporation to obtain the crude product, which was then purified by 200-300 mesh silica gel column chromatography using pure petroleum ether as the eluent. The target component was collected, and the solvent was removed by rotary evaporation to obtain a pure, pale yellow liquid product, namely HFP. The final product mass was 16.57 g, with a yield of 74.48%.

[0088] Example 3

[0089] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaTFSI to organic solvent is 1 mol: 1 L, the organic solvent is an EC / PC mixed solvent with a volume ratio of 1:1, and 10 wt.% TFP of the total electrolyte mass is added.

[0090] The specific production steps are as follows:

[0091] Step S1: Prepare the solvent by adding 50 parts EC and then 50 parts PC, and stirring for 10 minutes until the mixture is homogeneous.

[0092] Step S2: Add sodium salt. Weigh NaTFSI according to the molar volume ratio of sodium salt to solvent of 1 mol: 1 L. After adding sodium salt to solvent, stir at a constant speed for 30 min until the mixture is uniform and a transparent solution is obtained.

[0093] Step S3: Add flame retardant additive. Select TFP and add it to the solvent at 10% of the total mass of the prepared electrolyte. Stir at a constant speed for 10 minutes until the solution is transparent.

[0094] The Na||NFPP battery assembled using the electrolyte described in Example 3 exhibits good long-cycle performance and rate performance. The Na||NFPP (8:1:1) battery retains 85.4% of its capacity after more than 4000 cycles at a current density of 5 C at room temperature. Figure 1 It exhibits excellent long cycle life. The average discharge specific capacity at rates of 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 3.0 C, 4.0 C, 5.0 C, 10.0 C, and 20.0 C is 98.1 mAh g⁻¹. -1 94.5 mAh g -1 89.4mAh g -1 85.7 mAh g -1 82.6 mAh g -1 80.1 mAh g -1 77.9 mAh g -1 76.1 mAh g -1 70.1 mAhg -1 and 59.2 mAh g -1 ( Figure 2 It exhibits excellent rate performance.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 3 is that no flame retardant additive TFP was added in this comparative example; the remaining components and steps are the same. Test data are shown in Table 1.

[0097] Example 4

[0098] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows:

[0099] The molar volume ratio of NaTFSI to organic solvent is 1 mol: 1 L. The organic solvent is a 1:1 volume ratio EC / PC mixed solvent, and 10 wt.% HFP of electrolyte is added.

[0100] This Example 4 is similar to Example 3 in its electrolyte preparation method, except that the flame retardant additive TFP in Example 3 is replaced with HFP, while the other components and preparation steps are the same.

[0101] The flame retardant additive HFP in Example 4 has excellent flame retardant properties and does not burn in an open flame environment. Figure 3 a). Applying HFP as a flame retardant additive to the electrolyte system can effectively improve the combustion characteristics of the electrolyte. The GF membrane, after being impregnated with the flame retardant electrolyte of Example 4, can be ignited upon contact with an open flame, but it can quickly self-extinguish after being removed from the heat source, with the self-extinguishing time shortened to 5 seconds. Figure 3 b).

[0102] The flame-retardant electrolyte system in Example 4 has an ionic conductivity of 5.73 mS·cm. -1 The value for Comparative Example 1 is 7.13 mS·cm. -1 ( Figure 4 After the introduction of HFP flame retardant components, the conductivity of the electrolyte decreases, but it still has excellent ion conduction performance, thus balancing the flame retardant safety and electrochemical performance of the electrolyte.

[0103] The average specific capacity of the Na||NFPP (8:1:1) battery assembled with this electrolyte at room temperature and at rates of 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 3.0 C, 4.0 C, 5.0 C, 10.0 C, 20.0 C, and 30.0 C was 108.8 mAh g⁻¹. -1 105.0 mAh g -1 99.7 mAh g -1 96.2 mAh g -1 92.8 mAh g -1 90.8 mAh g -1 89.3 mAh g -1 88.2 mAh g -1 83.4 mAh g -1 76.2 mAh g -1 and 64.8 mAh g -1 ( Figure 2 This indicates excellent rate performance. After cycling at a current density of 2 C for 5300 cycles, the capacity retention was 90.1% (…). Figure 5 It exhibits excellent long-term cycling stability.

[0104] Furthermore, the flame-retardant electrolyte for sodium-ion batteries in this embodiment exhibits excellent high-temperature electrochemical performance. In a Na||NFPP (8:1:1) battery assembled at 60°C, the electrolyte of Example 4 showed an initial discharge specific capacity close to 90 mAh g⁻¹ at a 5 C rate, with no capacity decay after 500 cycles; the electrolyte of Comparative Example 1 short-circuited after 132 cycles, and the membrane morphology showed obvious burning and sodium deposition. Figure 6 At a high rate of 10 C, the initial discharge specific capacity of this flame-retardant electrolyte is 88 mAh g⁻. 1 It can stably cycle for more than 2000 times with a capacity retention rate of 92.8%. Figure 7 ).

[0105] Example 4 further assembled a pouch cell for testing: using NFPP as the positive electrode (area loading 3.65 mg·cm⁻). 2 Surface capacity 0.43 mAh·cm⁻ 2 Using sodium metal as the negative electrode, it can stably cycle for over 600 cycles at a 2C rate at room temperature, with no significant decrease in discharge specific capacity. Figure 8 ).

[0106] In summary, the flame-retardant electrolyte system of Example 4 exhibits good interfacial compatibility, cycle stability, and safety performance in both half-cell and pouch cells, demonstrating significant practical application value.

[0107] Example 5

[0108] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaPF6 to organic solvent is 1 mol: 1 L, the organic solvent is an EC / EMC mixed solvent with a volume ratio of 1:1, and 10 wt.% HFP is added to the total electrolyte mass.

[0109] This embodiment 5 is similar to the assembly method of embodiment 3, except that the sodium salt in embodiment 4 is replaced with NaPF6, the organic solvent PC is replaced with EMC, and the flame retardant additive TFP is replaced with HFP. The remaining components and preparation steps are the same.

[0110] The Na||NVP battery assembled with this electrolyte exhibited stable long-cycle performance at room temperature: after 500 cycles at 2 C rate, the capacity retention was 87.59% ( Figure 9 ), corresponding charge and discharge curves ( Figure 10The results showed that the charge-discharge plateau and polarization of the battery changed very little during the 50, 100, 150, 200, and 250 cycles, indicating that the flame-retardant electrolyte and NVP cathode have good compatibility and can achieve stable long-cycle performance. Furthermore, the capacity retention rate was 73.13% after 500 cycles at a high rate of 10 C, and even after 1000 cycles, the capacity retention rate was still as high as 65.68%, demonstrating outstanding high-rate cycle tolerance. Figure 11 ).

[0111] Comparative Example 2:

[0112] The difference between this comparative example and Example 5 is that no flame retardant additive HFP was added in this comparative example; the remaining components and steps are the same. Test data are shown in Table 1.

[0113] Example 6

[0114] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaTFSI to organic solvent is 1 mol: 1 L, the organic solvent is GDA (ethylene glycol diacetate), and the flame-retardant additive is HFP, with a volume ratio of 8:2.

[0115] The preparation method of the flame-retardant electrolyte for sodium-ion batteries includes the following steps:

[0116] Step S1: Prepare the solvent by adding 80 parts of GDA and then 20 parts of HFP, stirring for 10-20 minutes until the mixture is homogeneous and the solution is clear and transparent;

[0117] Step S2: Add sodium salt, at a concentration of 1 mol / L. -1 Weigh out the molar concentration of NaTFSI, add sodium salt to the solvent, and stir at a constant speed for 20-30 minutes until the mixture is homogeneous. Remove impurities to obtain a transparent solution.

[0118] The sodium ion-based flame-retardant electrolyte prepared in this case has a decomposition voltage of 4.7 V. Figure 12 This material can be matched with high-voltage cathode materials. The assembled Na||NFPP (7:2:1) battery exhibits good rate and cycle performance at room temperature, with an average specific capacity of 103.3 mAh g⁻¹ at rates of 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 3.0 C, 4.0 C, and 5.0 C. -1 99.1 mAh g -1 93.5 mAh g -1 88.4 mAh g -1 81.9 mAh g -1 77.4 mAh g -1 73.3 mAh g-1 and 69.1 mAh g -1 ( Figure 13 Afterwards, it was cycled at a current density of 1 C, and the capacity showed no decay after more than 100 cycles. Figure 14 The assembled Na||NFPP (8:1:1) cells exhibited excellent rate performance at room temperature. Figure 15 ).

[0119] Example 7

[0120] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaTFSI to organic solvent is 1 mol: 1 L, and the volume ratio of organic solvent GDA to additive HFP is 6:4. The preparation steps in this embodiment are the same as in Example 6.

[0121] This electrolyte also has a high decomposition voltage of 4.7 V ( Figure 16 The assembled Na||NFPP (7:2:1) battery also exhibited good rate performance and cycle performance at room temperature, with an average specific capacity of 97.6 mAh g⁻¹ at rates of 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 3.0 C, 4.0 C, and 5.0 C. -1 93.4 mAh g -1 88.2 mAh g -1 83.5 mAh g -1 78.4 mAh g -1 75.0 mAh g -1 72.3 mAh g -1 and 70.0 mAh g -1 ( Figure 17 After cycling at a current density of 1 C for over 100 cycles, the capacity remained at 78.4 mAh g. -1 Similarly, there is no attenuation ( Figure 18 ).

[0122] Example 8

[0123] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaTFSI to organic solvent is 1.2 mol: 1 L, and the volume ratio of organic solvent GDA to additive HFP is 8: 2.

[0124] This embodiment is similar to the assembly method of Example 6, except that the molar volume ratio of sodium salt to organic solvent in Example 6 is 1.2 mol: 1L, while the other components and preparation steps are the same.

[0125] The Na||NFPP battery assembled using a flame-retardant electrolyte for sodium ions in this case study exhibits a first-cycle discharge capacity of 83.9 mAh g at room temperature and 0.5 C. -1 After 60 cycles, it still has 87.0 mAh g. -1 No capacity decay ( Figure 19 This electrolyte also has excellent cycle performance.

[0126] Example 9

[0127] A flame-retardant electrolyte formulation for sodium-ion batteries is as follows: the molar volume ratio of NaTFSI to organic solvent is 1.2 mol: 1 L, and the volume ratio of organic solvent GDA to additive HFP is 7:3.

[0128] In this embodiment, the preparation method of the electrolyte is the same as in Example 8.

[0129] The Na||NFPP battery assembled with this electrolyte exhibits a first-cycle discharge capacity of 81.6 mAh g at room temperature and 0.5 C. -1 After 60 cycles, the energy content is 83.8 mAh g. -1 The capacity also did not decrease ( Figure 20 ).

[0130] Implementation effect analysis

[0131] The assembly steps for preparing the battery using the electrolytes prepared in the above embodiments and comparative examples are as follows:

[0132] I. Preparation of Battery Electrodes

[0133] 1. Preparation of NFP / NFPP positive electrode sheet

[0134] Sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP) or NFP active material, conductive carbon (Super P Li), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1 or 7:2:1, with 1-methyl-2-pyrrolidone (NMP) as the solvent. After thorough mixing, the mixture was coated onto a 17 μm thick aluminum foil using a doctor blade and dried in a vacuum oven at 120 °C for 8 h. After drying, the electrodes were cut into circular sheets with a diameter of 13 mm using a die-cutting machine. The active material loading of the electrodes was 1.3-2.0 mg / cm³. -2 .

[0135] 2. Preparation of NVP positive electrode sheet

[0136] NVP, Super P Li, and PVDF were mixed at a mass ratio of 8:1:1, using NMP as a solvent. After thorough mixing, the mixture was coated onto a 17 μm thick aluminum foil using a doctor blade and dried in a vacuum oven at 120°C for 8 h. After drying, the foil was cut into circular electrodes with a diameter of 13 mm using a die-cutting machine. The active material loading of the electrodes was 1.3–2.0 mg / cm³. -2 .

[0137] 3. Preparation of NVPF / NVPOF / NFS positive electrode sheets

[0138] NVPF, NVPOF or NFS, Super P Li, and PVDF were mixed at a mass ratio of 7:2:1, using NMP as a solvent. After thorough mixing, the mixture was coated onto a 17 μm thick aluminum foil using a doctor blade and dried in a vacuum oven at 120°C for 8 h. After drying, the foil was cut into circular electrodes with a diameter of 13 mm using a die-cutting machine. The active material loading of the electrodes was 1.3–2.0 mg / cm³. -2 .

[0139] 4. Preparation of hard carbon negative electrode sheet

[0140] Hard carbon, Super P Li, and PVDF were mixed at a mass ratio of 0.85:0.1:0.05, using NMP as a solvent. After thorough mixing, the mixture was coated onto a 17 μm thick copper foil using a doctor blade and dried overnight at 60°C in a vacuum oven. After drying, the coated electrodes were cut into circular sheets with a diameter of 13 mm using a die-cutting machine. The active material loading of the electrodes was 0.8–2 mg / cm³. -2 .

[0141] II. Battery Assembly

[0142] The positive electrode material is one or more of the materials mentioned above, the negative electrode material is sodium metal or hard carbon, the current collector is aluminum foil or copper foil, the separator is glass fiber (Whatman, pore size 2.7 μm), and the electrolyte volume is 100-120 μL. A sodium-ion battery is assembled. All operations during battery assembly are performed in a glove box (O2 and H2O < 1 ppm). The battery performance test results are shown in Table 1.

[0143] Table 1. Performance of assembled batteries in Examples 3-9 and Comparative Examples 1-2

[0144]

[0145] As shown in Table 1, the examples exhibited superior cycle stability compared to the control group in both carbonate and carboxylic acid ester electrolytes, indicating that adding a certain amount of fluorinated phenylphosphonate can significantly improve the room temperature and high temperature cycle stability of sodium-ion batteries.

[0146] 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 fluorophenylphosphonate, characterized in that: Including di(trifluoroisopropyl)phenylphosphonate or di(hexafluoroisopropyl)phenylphosphonate; The structural formula of the bis(trifluoroisopropyl)phenylphosphonate is: ; The structural formula of the di(hexafluoroisopropyl)phenylphosphonate is: .

2. The method for preparing the fluorophenylphosphonate according to claim 1, characterized in that, The steps are as follows: using fluoro alcohol and phenylphosphonic dichloride as raw materials, triethylamine as an acid-binding agent, and diethyl ether as a reaction solvent, fluorophenylphosphonate is prepared by condensation substitution reaction.

3. The method for preparing fluorophenylphosphonate according to claim 2, characterized in that, The steps are as follows: (1) In the presence of an acid-binding agent, fluoroalcohols and phenylphosphonic dichloride undergo a substitution reaction in a solvent. After the reaction is complete, the mixture is heated and refluxed to obtain a reaction solution. (2) The reaction solution in step (1) is separated into solid and liquid, washed to remove impurities and dried to obtain crude product. The crude product is purified by column chromatography to obtain fluorophenylphosphonate.

4. The method for preparing fluorophenylphosphonate according to claim 2 or 3, characterized in that: In step (1), the fluorinated alcohol is fluorinated isopropanol, and the acid-binding agent is an organic base that undergoes a catalytic nucleophilic substitution reaction with hydrogen halide.

5. The method for preparing fluorophenylphosphonate according to claim 4, characterized in that: The fluoroisopropanol is hexafluoroisopropanol or trifluoroisopropanol; the acid-binding agent is triethylamine or pyridine.

6. The method for preparing fluorophenylphosphonate according to claim 4, characterized in that: The molar ratio of the fluoroalcohol, phenylphosphonic dichloride, and acid-binding agent is 1-2:1:1-2; the temperature of the substitution reaction is 0-5℃ and the time is 20-25h; the temperature of the reflux reaction is 35-45℃ and the time is 1-3h.

7. The method for preparing fluorophenylphosphonate according to claim 5, characterized in that: When the fluoroalcohol is hexafluoroisopropanol, the fluorophenyl phosphonate obtained is di(hexafluoroisopropyl)phenylphosphonate; when the fluoroalcohol is trifluoroisopropanol, the fluorophenyl phosphate obtained is di(trifluoroisopropyl)phenylphosphonate.

8. An electrolyte additive, characterized in that: It includes the fluorophenylphosphonate of claim 1.

9. A flame-retardant electrolyte for sodium-ion batteries, characterized in that: It includes the fluorophenylphosphonate as described in claim 1, the electrolyte sodium salt, and the organic solvent.

10. A sodium-ion battery, characterized in that: It includes a positive electrode, a separator, a negative electrode, and the flame-retardant electrolyte for sodium-ion batteries as described in claim 9.

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