Highly fluorinated flame-retardant electrolyte additives, methods of making, and highly fluorinated flame-retardant electrolytes and their use in lithium batteries

Abstract

The application provides a highly fluorinated flame-retardant electrolyte additive, a preparation method, a highly fluorinated flame-retardant electrolyte and application thereof in lithium batteries, and the preparation method comprises the following steps: dissolving phosphorus trichloride in a solvent and cooling to 0-5 DEG C, then adding tert-butyl alcohol and stirring, then adding trifluoroalcohol and reacting to obtain intermediate product A; then, under a nitrogen atmosphere, adding the intermediate product A into a tert-butyl alcohol potassium solution in anhydrous dimethyl sulfoxide and reacting to obtain intermediate product B; finally, under a nitrogen atmosphere, adding dichloroalkane into the intermediate product B and reacting and purifying to obtain the highly fluorinated flame-retardant electrolyte additive. The flame-retardant electrolyte additive has good compatibility with lithium salt and organic solvent, and has high contents of fluorine and phosphorus flame-retardant elements. The additive can be used together with lithium salt and organic solvent to construct a flame-retardant electrolyte for lithium batteries, and can effectively reduce the flammability of the electrolyte and enhance the safety performance without sacrificing the efficiency and performance of the electrolyte.

Description

Technical Field

[0001] This invention relates to the fields of energy and new materials technology, and particularly to high-fluoride flame-retardant electrolyte additives, preparation methods, and high-fluoride flame-retardant electrolytes and their application in lithium batteries. Background Technology

[0002] Since their commercialization, lithium batteries have been widely used in mobile communications, energy storage, and other fields due to their high operating voltage, high energy density, and long cycle life. They are particularly important as a crucial component of electric bicycles and electric vehicles, providing convenience for safe travel in people's daily lives. However, with the large-scale expansion of lithium battery applications, spontaneous combustion and explosion accidents caused by lithium batteries have become increasingly common, seriously threatening personal and property safety. In recent years, research on the safety performance of lithium batteries has received increasing attention.

[0003] Currently, commercially available lithium-ion batteries primarily use liquid ester electrolytes such as ethylene carbonate. These materials have low flash points and are highly flammable. Under prolonged operation, the heat generated cannot be dissipated, potentially leading to thermal runaway, numerous short circuits within the battery, and even rapid combustion or explosion. Adding flame-retardant additives to lithium battery electrolytes can effectively improve their thermal stability and flame-retardant properties. Currently, the main flame-retardant additives include organophosphorus, nitrogen-based, silicon-based, and halogen-based additives. However, these traditional flame-retardant additives generally contain only one flame-retardant element in low concentrations, resulting in insufficient flame-retardant efficiency and performance. Furthermore, high concentrations of these traditional flame-retardant additives can also reduce the battery's electrochemical performance. Summary of the Invention

[0004] The purpose of this invention is to provide a highly fluorinated flame-retardant electrolyte additive that has a good synergistic flame-retardant effect and can improve the flame-retardant and safety performance of lithium battery electrolytes without affecting their efficiency and performance.

[0005] Another objective of this invention is to provide a method for preparing a highly fluorinated flame-retardant electrolyte additive. Based on a phosphorus-containing flame-retardant structure, a large number of fluorine atoms are introduced through reactions such as dehydrochlorination, thereby preparing a flame-retardant additive with excellent synergistic flame-retardant effect. The method has controllable parameters and is suitable for large-scale industrial production.

[0006] The third objective of this invention is to provide a highly fluorinated flame-retardant electrolyte that has good flame-retardant and safety properties.

[0007] The fourth objective of this invention is to provide a method for preparing a highly fluorinated flame-retardant electrolyte, which is simple to operate and has controllable parameters, and is suitable for large-scale industrial production.

[0008] The fifth objective of this invention is to provide the application of the aforementioned highly fluorinated flame-retardant electrolyte in the preparation of lithium batteries.

[0009] The technical problem solved by this invention is achieved by the following technical solution.

[0010] This invention proposes a highly fluorinated flame-retardant electrolyte additive, the structural formula of which is shown in Formula I:

[0011]

[0012] Wherein, R1 is any one of the following groups: -CH2-, -CH2-CH2-, -CH2-CH2-CH2-; R2 is any one of the following groups: -CH2-, -CH(CH3)-, -CH2-CH2, -CH2-CH2-CH2-.

[0013] This invention proposes a method for preparing a highly fluorinated flame-retardant electrolyte additive, comprising the following steps:

[0014] S1. Dissolve phosphorus trichloride in a solvent and cool to 0-5°C. Add tert-butanol dropwise and stir for 50-70 minutes. Then add trifluorool dropwise to react and obtain intermediate product A.

[0015] S2. Under a nitrogen atmosphere, the intermediate product A is added dropwise to an anhydrous dimethyl sulfoxide solution of potassium tert-butoxide to react and obtain intermediate product B.

[0016] S3. Under a nitrogen atmosphere, dichloroalkane is added dropwise to the intermediate product B for reaction, and then purified to obtain the highly fluorinated flame-retardant electrolyte additive.

[0017] This invention proposes a highly fluorinated flame-retardant electrolyte, which, by mass percentage, comprises 3% to 20% lithium salt, 66% to 82% organic solvent, and 5% to 15% of the highly fluorinated flame-retardant electrolyte additive as described in claim 1.

[0018] This invention proposes a method for preparing a highly fluorinated flame-retardant electrolyte, comprising the following steps:

[0019] Weigh each component according to the mass percentage of the high-fluorinated flame-retardant electrolyte;

[0020] The lithium salt, the organic solvent, and the high-fluoride flame-retardant electrolyte additive are mixed and stirred for 1 to 6 hours to obtain the high-fluoride flame-retardant electrolyte.

[0021] This invention also proposes the application of the above-mentioned highly fluorinated flame-retardant electrolyte in the preparation of lithium batteries.

[0022] The beneficial effects of the high-fluoride flame-retardant electrolyte additive, its preparation method, and the high-fluoride flame-retardant electrolyte and its application in lithium batteries according to embodiments of the present invention are as follows:

[0023] 1. The high-fluoride flame-retardant electrolyte additive of the present invention incorporates high levels of phosphorus and fluorine elements, thereby achieving a good synergistic flame-retardant effect. Furthermore, this additive can significantly improve the flame-retardant and safety performance of lithium batteries even with relatively low addition amounts.

[0024] 2. The high-fluoride flame-retardant electrolyte additive of the present invention has good compatibility with lithium salts and organic solvents in the electrolyte, and therefore will not affect the viscosity, conductivity, battery cycle performance, etc. of the electrolyte. This electrolyte additive can be used with lithium salts and organic solvents to construct a high-fluoride flame-retardant electrolyte for lithium batteries.

[0025] 3. The high-fluoride flame-retardant electrolyte additive of the present invention is simple to synthesize and the reaction is easy to control, and has good application prospects in the fields of energy storage and electric vehicles. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The image shows the phosphorus NMR spectrum of the highly fluorinated flame-retardant electrolyte additive of Example 1 of this invention.

[0028] Figure 2 This is a flowchart illustrating the preparation process of the high-fluoride flame-retardant electrolyte additive of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0030] The following describes in detail the high-fluoride flame-retardant electrolyte additive, its preparation method, and the high-fluoride flame-retardant electrolyte and its application in lithium batteries according to embodiments of the present invention.

[0031] The present invention provides a highly fluorinated flame-retardant electrolyte additive, the structural formula of which is shown in Formula I:

[0032]

[0033] Wherein, R1 is any one of the following groups: -CH2-, -CH2-CH2-, -CH2-CH2-CH2-; R2 is any one of the following groups: -CH2-, -CH(CH3)-, -CH2-CH2, -CH2-CH2-CH2-.

[0034] This invention, based on a phosphorus-containing flame-retardant structure, introduces a large number of fluorine atoms through reactions such as dehydrochlorination, thereby achieving a good synergistic flame-retardant effect without affecting the efficiency and performance of the lithium battery electrolyte. The introduction of this highly fluorinated flame-retardant electrolyte additive effectively reduces the flammability of the electrolyte and enhances its safety performance.

[0035] Reference Figure 2 As shown, this invention provides a method for preparing a highly fluorinated flame-retardant electrolyte additive, comprising the following steps:

[0036] S1. Dissolve phosphorus trichloride in a solvent and cool to 0-5°C. Add tert-butanol dropwise and stir for 50-70 minutes. Then add trifluorool dropwise to react and obtain intermediate product A. Preferably, after dissolving phosphorus trichloride in the solvent, cool it in an ice-water bath. Then, slowly add tert-butanol dropwise through a constant-pressure dropping funnel while stirring in an ice bath. Then, add trifluorool dropwise through a constant-pressure dropping funnel and stop stirring to obtain intermediate product A.

[0037] Furthermore, in a preferred embodiment of the present invention, the molar ratio of phosphorus trichloride to tert-butanol is 1:0.8 to 1.2, and the solvent is selected from acetone, tetrahydrofuran, dichloromethane, and chloroform.

[0038] Further, in a preferred embodiment of the present invention, the trifluorool is selected from one of trifluoroethanol, 3,3,3-trifluoropropanol, and 4,4,4-trifluorobutanol. The trifluorool is added dropwise over a period of 0.5 to 1 hour, the reaction temperature does not exceed 30°C, and the reaction time is 12 to 16 hours. Preferably, the mass ratio of potassium trichloride to trifluorool is 1:1.45 to 1.47.

[0039] S2. Under a nitrogen atmosphere, intermediate product A is added dropwise to an anhydrous dimethyl sulfoxide solution of potassium tert-butoxide to react and obtain intermediate product B. The mass ratio of intermediate product A to potassium tert-butoxide is 1:2 to 2.2. The concentration of potassium tert-butoxide in the anhydrous dimethyl sulfoxide solution is 0.21 to 0.25 g / mL.

[0040] Furthermore, in a preferred embodiment of the present invention, the reaction temperature is 25–30°C and the reaction time is 3–5 h.

[0041] S3. Under a nitrogen atmosphere, dichloroalkane is added dropwise to the intermediate product B for reaction, and then purified to obtain the highly fluorinated flame-retardant electrolyte additive.

[0042] Furthermore, in a preferred embodiment of the present invention, the dichloroalkane is added for less than 1 hour, the reaction temperature is 25–50°C, and the reaction time is 1–4 hours.

[0043] The synthetic route of the high-fluoride flame-retardant electrolyte additive of the present invention is as follows:

[0044]

[0045] Wherein, R1 is any one of the following groups: -CH2-, -CH2-CH2-, -CH2-CH2-CH2-; R2 is any one of the following groups: -CH2-, -CH(CH3)-, -CH2-CH2, -CH2-CH2-CH2-.

[0046] This invention provides a highly fluorinated flame-retardant electrolyte, comprising, by mass percentage, 3%–20% lithium salt, 66%–82% organic solvent, and 5%–15% of the aforementioned highly fluorinated flame-retardant electrolyte additive. The highly fluorinated flame-retardant electrolyte additive prepared by this invention exhibits good compatibility with lithium salt and organic solvent, and has a high content of fluorine and phosphorus flame-retardant elements. It can effectively reduce the flammability of the electrolyte without sacrificing electrolyte efficiency and performance, thereby enhancing the safety performance of lithium battery electrolytes.

[0047] Furthermore, in a preferred embodiment of the present invention, the lithium salt is selected from lithium hexafluorophosphate and lithium difluorooxalate borate, and the organic solvent is a mixture of ethylene carbonate and dimethyl carbonate (EC / DMC), wherein the volume ratio of ethylene carbonate to dimethyl carbonate in the mixture is 1:1.

[0048] This invention provides a method for preparing a highly fluorinated flame-retardant electrolyte, comprising the following steps:

[0049] Weigh each component according to the mass percentage of the high-fluorinated flame-retardant electrolyte mentioned above.

[0050] The lithium salt, the organic solvent, and the high-fluoride flame-retardant electrolyte additive are mixed and stirred for 1 to 6 hours to obtain the high-fluoride flame-retardant electrolyte.

[0051] This invention provides the application of the above-mentioned highly fluorinated flame-retardant electrolyte in the preparation of lithium batteries.

[0052] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0053] Example 1

[0054] This embodiment provides a highly fluorinated flame-retardant electrolyte additive, which is prepared according to the following steps:

[0055] (1) Synthesis of intermediate products for high-fluorinated flame-retardant electrolyte additives:

[0056] 13.7 g of phosphorus trichloride and 200 mL of dichloromethane were added to a 500 mL flask and cooled to approximately 0 °C in an ice bath. Then, 100 mL of a 0.074 g / mL solution of tert-butanol in dichloromethane was slowly added dropwise through a constant-pressure dropping funnel over approximately 45 minutes. The mixture was stirred in an ice bath for one hour. Subsequently, 100 mL of a 0.02 g / mL solution of trifluoroethanol in dichloromethane was slowly added dropwise through a constant-pressure dropping funnel over approximately 30 minutes. After the addition was complete, the mixture was stirred and reacted for 12 hours. Finally, the mixture was heated to 47 °C, and impurities such as hydrogen chloride and dichloromethane were removed from the solution by reflux and rotary evaporation to obtain the intermediate product.

[0057] (2) Synthesis of HFFRA, a highly fluorinated flame-retardant electrolyte additive:

[0058] 4.694 g of potassium tert-butoxide was added to 20 mL of anhydrous dimethyl sulfoxide solution, stirred evenly at room temperature, and cooled to 10 °C. Then, under a nitrogen atmosphere, 9.844 g of intermediate product was slowly added dropwise to the above solution, with the temperature controlled at 25–30 °C. Then, under a nitrogen atmosphere, 1.878 g of dichloroethane was slowly added dropwise to the above solution through a constant pressure titration funnel, and the temperature was raised to 50 °C and reacted for 2 h. After purification, a highly fluorinated flame-retardant electrolyte additive was obtained.

[0059] The synthetic route and molecular structure of the target product are shown below:

[0060]

[0061] Example 2

[0062] This embodiment provides a highly fluorinated flame-retardant electrolyte, which is prepared according to the following method:

[0063] Ethylene carbonate and dimethyl carbonate were mixed uniformly at a volume ratio of 1:1 to obtain an organic solvent. Then, lithium hexafluorophosphate (concentration of 1.0 mol / L) and the high-fluorinated flame-retardant electrolyte additive HFFRA prepared in Example 1 were added. After stirring thoroughly for 1 hour, a high-fluorinated flame-retardant electrolyte was obtained. The HFFRA content in the high-fluorinated flame-retardant electrolyte was 5 wt%.

[0064] Example 3

[0065] This embodiment provides a highly fluorinated flame-retardant electrolyte, which is prepared according to the following method:

[0066] Ethylene carbonate and dimethyl carbonate were mixed uniformly at a volume ratio of 1:1 to obtain an organic solvent. Then, lithium hexafluorophosphate (concentration of 1.0 mol / L) and the high-fluorinated flame-retardant electrolyte additive HFFRA prepared in Example 1 were added. After stirring thoroughly for 1 hour, a high-fluorinated flame-retardant electrolyte was obtained. The content of HFFRA in the high-fluorinated flame-retardant electrolyte was 7.5 wt%.

[0067] Example 4

[0068] This embodiment provides a highly fluorinated flame-retardant electrolyte, which is prepared according to the following method:

[0069] Ethylene carbonate and dimethyl carbonate were mixed uniformly at a volume ratio of 1:1 to obtain an organic solvent. Then, lithium hexafluorophosphate (concentration of 1.0 mol / L) and the high-fluorinated flame-retardant electrolyte additive HFFRA prepared in Example 1 were added. After stirring thoroughly for 1 hour, a high-fluorinated flame-retardant electrolyte was obtained. The content of HFFRA in the high-fluorinated flame-retardant electrolyte was 10 wt%.

[0070] Example 5

[0071] This embodiment provides a highly fluorinated flame-retardant electrolyte, which is prepared according to the following method:

[0072] Ethylene carbonate and dimethyl carbonate were mixed uniformly at a volume ratio of 1:1 to obtain an organic solvent. Then, lithium hexafluorophosphate (concentration of 1.0 mol / L) and the high-fluorinated flame-retardant electrolyte additive HFFRA prepared in Example 1 were added. After stirring thoroughly for 1 hour, a high-fluorinated flame-retardant electrolyte was obtained. The content of HFFRA in the high-fluorinated flame-retardant electrolyte was 15 wt%.

[0073] Comparative Example 1

[0074] This comparative example provides an electrolyte solution by uniformly mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1 to obtain an organic solvent, then adding lithium hexafluorophosphate (concentration of 1.0 mol / L), and stirring thoroughly for 1 hour to obtain the electrolyte solution.

[0075] Experimental Example 1

[0076] This experimental example uses phosphorus nuclear magnetic resonance spectroscopy (NMR spectroscopy). 31 The structure of the highly fluorinated flame-retardant electrolyte additive prepared in Example 1 was characterized by P NMR.

[0077] like Figure 1The image shown is the NMR phosphorus spectrum of the highly fluorinated flame-retardant electrolyte additive prepared in Example 1 of this invention. From... Figure 1 It can be seen that, 31 The presence of only one characteristic peak in the 1P NMR results indicates the successful preparation of the final product HFFRA.

[0078] Experimental Example 2

[0079] This experiment tested the combustion performance of the highly fluorinated flame-retardant electrolytes of Examples 2-5 and the electrolyte of Comparative Example 1. The test results are shown in Table 1.

[0080] Table 1 Combustion Test of High-Fluoride Flame-Retardant Electrolyte

[0081] electrolyte Electrolyte composition HFFRA content (wt%) Extinguishing time after ignition (s / g) 1 <![CDATA[LiPF6 / EC / DMC]]> 0 70 2 <![CDATA[LiPF6 / EC / DMC / HFFRA]]> 5 32 3 <![CDATA[LiPF6 / EC / DMC / HFFRA]]> 7.5 28 4 <![CDATA[LiPF6 / EC / DMC / HFFRA]]> 10 23 5 <![CDATA[LiPF6 / EC / DMC / HFFRA]]> 15 15

[0082] As can be seen from Table 1, the high-fluoride flame-retardant electrolyte additive prepared in this invention has been successfully introduced into the electrolyte, and the self-extinguishing performance and safety performance of the electrolyte have significantly improved with the increase of the amount of high-fluoride flame-retardant electrolyte additive.

[0083] Experimental Example 3

[0084] In this experiment, the high-fluoride flame-retardant electrolytes of Examples 2-5 and the electrolyte of Comparative Example 1 were used in 2032 button batteries, and the cycle performance of the batteries was tested. The specific steps included:

[0085] First, the lithium sheet, Celgard 2325 separator, and the required positive electrode material LiFePO4 were assembled separately. Then, 80–100 mL of the highly fluorinated flame-retardant electrolyte from Examples 2–5 and the electrolyte from Comparative Example 1 were added respectively. The entire assembly process was completed in a glove box, and the electrochemical test of this half-cell was conducted at a rate of 0.2C. The results are shown in Table 2.

[0086] Table 2 Battery Cycle Performance Tests for High-Fluoride Flame-Retardant Electrolytes

[0087]

[0088] As can be seen from the battery cycle performance test in Table 2, the introduction of high-fluoride flame-retardant electrolyte additives not only does not affect the internal reaction of the electrolyte, but also helps to stabilize the battery capacity.

[0089] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a highly fluorinated flame-retardant electrolyte additive, characterized in that, The structural formula of the highly fluorinated flame-retardant electrolyte additive is shown in Formula I: Formula I Wherein, R1 is any one of the following groups: -CH2-, -CH2-CH2-, -CH2-CH2-CH2-; R2 is any one of the following groups: -CH2-, -CH(CH3)-, -CH2-CH2, -CH2-CH2-CH2-; Includes the following steps: S1. Dissolve phosphorus trichloride in a solvent and cool to 0~5℃. Add tert-butanol dropwise and stir for 50~70 min. Then add trifluorool dropwise to react and obtain intermediate product A. S2. Under a nitrogen atmosphere, the intermediate product A is added dropwise to an anhydrous dimethyl sulfoxide solution of potassium tert-butoxide to react and obtain intermediate product B. S3. Under a nitrogen atmosphere, dichloroalkane is added dropwise to the intermediate product B for reaction and purification to obtain the highly fluorinated flame-retardant electrolyte additive. The dropwise addition time of the dichloroalkane is less than 1 hour, the reaction temperature is 25~50℃, and the reaction time is 1~4 hours.

2. The preparation method according to claim 1, characterized in that, In step S1, the solvent is selected from acetone, tetrahydrofuran, dichloromethane, and chloroform, and the molar ratio of phosphorus trichloride and tert-butanol is 1:0.8~1.

2.

3. The preparation method according to claim 1, characterized in that, In step S1, the trifluorool is selected from one of trifluoroethanol, 3,3,3-trifluoropropanol, and 4,4,4-trifluorobutanol. The trifluorool is added dropwise over a period of 0.5 to 1 hour, the reaction temperature does not exceed 30°C, and the reaction time is 12 to 16 hours.

4. The preparation method according to claim 1, characterized in that, In step S2, the reaction temperature is 25~30℃ and the reaction time is 3~5h.

5. A highly fluorinated flame-retardant electrolyte, characterized in that, The electrolyte comprises, by weight percentage, 3% to 20% lithium salt, 66% to 82% organic solvent, and 5% to 15% high-fluoride flame-retardant electrolyte additive as described in claim 1.

6. The highly fluorinated flame-retardant electrolyte according to claim 5, characterized in that, The lithium salt is selected from lithium hexafluorophosphate and lithium difluorooxalate borate, and the organic solvent is a mixture of ethylene carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate to dimethyl carbonate in the mixture is 1:

1.

7. A method for preparing a highly fluorinated flame-retardant electrolyte, characterized in that, Includes the following steps: Weigh each component according to the mass percentage of the high-fluoride flame-retardant electrolyte according to any one of claims 5 to 6; The lithium salt, the organic solvent, and the high-fluoride flame-retardant electrolyte additive are mixed and stirred for 1-6 hours to obtain the high-fluoride flame-retardant electrolyte.

8. The application of the high-fluoride flame-retardant electrolyte according to any one of claims 5 to 6 in the preparation of lithium batteries.

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