Preparation method of lithium mono / bis (trifluoroethoxy) phosphate mixture and application of lithium mono / bis (trifluoroethoxy) phosphate mixture in lithium ion battery

Abstract

The invention relates to a preparation method of a lithium mono / bis (trifluoroethoxy) phosphate mixture. The method comprises the following steps: 1) dispersing phosphorus pentoxide in an organic solvent I under the protection of an inert gas atmosphere, adding trifluoroethanol, reacting at 20-50 DEG C for 3-6 hours, adding water to hydrolyze a pyrophosphate intermediate after the reaction is finished, and concentrating to obtain mono / bis (trifluoroethoxy) phosphate; and 2) reacting the mono / bis (trifluoroethoxy) phosphate with lithium carbonate in an organic solvent II at 30-70 DEG C for 4-8 hours, and after the reaction is finished, performing post-treatment to obtain the lithium mono / bis (trifluoroethoxy) phosphate mixture. According to the method, phosphorus pentoxide and trifluoroethanol are adopted as raw materials, toxic and harmful chlorination reagents are not used, and the method has the advantages of being simple in process, environmentally friendly and the like. Meanwhile, when the compound is applied to the lithium ion battery as an electrolyte additive, the electrochemical performance of the battery can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically relating to a method for preparing a mixture of mono / ditrifluoroethoxy lithium phosphate and its application in lithium-ion batteries. The mixture of mono / ditrifluoroethoxy lithium phosphate is synthesized by direct esterification of phosphorus pentoxide (P2O5) with trifluoroethanol and then reacting it with lithium carbonate, and can be used as an electrolyte additive in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and lack of memory effect. With the increasing demands on lithium-ion battery performance, the development of high-performance electrolyte additives has become a research hotspot. Fluorinated organophosphorus compounds offer significant advantages as electrolyte additives for lithium-ion batteries. On the one hand, the strong electron-withdrawing effect of fluorine atoms can improve the thermal stability and oxidation resistance of the compounds; on the other hand, the presence of phosphorus-oxygen bonds gives them excellent film-forming properties, enabling the formation of stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) films on electrode surfaces.

[0003] Existing methods for synthesizing lithium fluoride phosphate additives are complex, using highly toxic or corrosive raw materials such as phosphorus oxychloride (POCl3), generating large amounts of corrosive HCl gas, requiring exhaust gas treatment equipment, which does not conform to the principles of green chemistry. Phosphorus pentoxide has high reactivity with common alcohols, but in fluorinated alcohol systems, the strong electron-withdrawing effect of fluorine leads to low reactivity and easily generates pyrophosphate ester byproducts. Both mono- and bis-trifluoroethoxyphosphate are lithium-ion battery electrolyte additives, each with its own focus. Mono-trifluoroethoxyphosphate can rapidly form a stable solid electrolyte interphase (SEI) film on the electrode surface, reducing electrolyte decomposition and improving battery cycle stability. Bis-trifluoroethoxyphosphate can optimize the SEI film structure, enhance its mechanical strength, inhibit lithium dendrite growth, and improve battery safety. Combining the two can leverage the advantages of rapid film formation and stable film structure, accelerating SEI film formation while ensuring film density and toughness, simultaneously improving battery cycle life and safety performance—an ideal combination balancing efficiency and stability. Therefore, it is of great significance to develop a mixture additive of mono / ditrifluoroethoxy lithium phosphate that has a simple synthesis process, is environmentally friendly, and has excellent performance.

[0004] Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a mixture of mono / ditrifluoroethoxy lithium phosphate and its preparation method. This method uses phosphorus pentoxide and trifluoroethanol as raw materials, avoiding the use of toxic and harmful chlorinating reagents, and has advantages such as simple process and environmental friendliness. Furthermore, this compound, when used as an electrolyte additive in lithium-ion batteries, can significantly improve the electrochemical performance of the battery.

[0006] The present invention also provides the application of the above-mentioned method for preparing a mixture of mono / ditrifluoroethoxy lithium phosphate in lithium-ion batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a mixture of mono / ditrifluoroethoxy lithium phosphate, characterized by comprising the following steps: 1) Under the protection of an inert gas atmosphere (such as nitrogen, argon, etc.), phosphorus pentoxide is dispersed in organic solvent one, trifluoroethanol is added, and the reaction is carried out at 20-50℃ for 3-6 hours. After the reaction is completed, water is added to hydrolyze the pyrophosphate intermediate, and the solvent is removed by concentration to obtain mono / ditrifluoroethoxy phosphate. 2) React mono / ditrifluoroethoxyphosphate with lithium carbonate in organic solvent II at 30-70℃ for 4-8 hours. After the reaction is completed, post-treatment is performed to obtain a mixture of mono / ditrifluoroethoxyphosphate.

[0008] The reaction equation for the method of this invention is as follows: .

[0009] Specifically, in step 1), the molar ratio of phosphorus pentoxide to trifluoroethanol can be 1:(2.8-3.2). The reaction temperature can be 20-50℃, more preferably 40-45℃.

[0010] Specifically, in step 1), the trifluoroethanol can be added dropwise in stages, with each addition occurring at intervals of 5-15 minutes.

[0011] Furthermore, in step 1), the molar ratio of water added after the reaction to phosphorus pentoxide can be (0.5-1):1.

[0012] Furthermore, in step 1), the organic solvent is an aprotic organic solvent, which can be selected from at least one of toluene, cyclohexane, xylene, dichloromethane, etc. 200-500 ml of organic solvent can be added for every 1 mol of phosphorus pentoxide.

[0013] Specifically, in step 2), the molar ratio of monotrifluoroethoxyphosphate to bistrifluoroethoxyphosphate can be (0.8-1.2):1. The reaction temperature can be 30-70℃, more preferably 40-60℃.

[0014] Specifically, in step 2), the molar ratio of the mixture of mono / bis(trifluoroethoxy) phosphate to lithium carbonate can be 1:(1.5-1.7). In actual feeding, it is generally preferred that the molar ratio of mono(trifluoroethoxy) phosphate to lithium carbonate is 1:1, and the molar ratio of bis(trifluoroethoxy) phosphate to lithium carbonate is 1:0.5.

[0015] Furthermore, in step 2), the second organic solvent can be selected from at least one of anhydrous ethanol, anhydrous methanol, acetonitrile, etc.

[0016] In a further preferred embodiment, in step 2) of the above method, after the reaction is completed, the reaction solution is cooled to room temperature and filtered to remove unreacted lithium carbonate. The filtrate is concentrated to dryness by rotary evaporation under negative pressure and then dried to obtain a mixture of mono / ditrifluoroethoxy lithium phosphate.

[0017] The present invention provides a mixture of mono / ditrifluoroethoxy lithium phosphate prepared by the above method.

[0018] The present invention also provides the application of the above-mentioned mono / ditrifluoroethoxy lithium phosphate mixture as an electrolyte additive in the preparation of lithium-ion batteries.

[0019] Compared with the prior art, the beneficial effects of the method of the present invention are as follows: 1) The process of this invention is simple and environmentally friendly: This invention uses phosphorus pentoxide and trifluoroethanol to react directly, avoiding the use of toxic and harmful reagents such as phosphorus oxychloride in traditional methods, thus reducing environmental pollution.

[0020] 2) The reaction conditions of this invention are mild: the reaction is carried out at a low temperature, with low energy consumption, safe operation, and easy industrial production.

[0021] 3) Excellent product performance: Due to the strong electron-withdrawing effect of trifluoromethyl, the product of this invention has good thermal stability and electrochemical performance. As an electrolyte additive, it can significantly improve the cycle life and safety performance of lithium-ion batteries.

[0022] 4) Multifunctional additive: The product of this invention has both flame retardancy and high voltage stability, and is suitable for next-generation lithium-ion batteries, especially high-nickel ternary cathode material batteries. Attached Figure Description

[0023] Figure 1 The mono / ditrifluoroethoxyphosphate prepared in Example 1 31P-NMR spectrum, test frequency: 400MHz, deuterated reagent: deuterated dimethyl sulfoxide. The phosphorus atom of monotrifluoroethoxyphosphate is affected by one trifluoroethoxy group, while the phosphorus atom of bistrifluoroethoxyphosphate is affected by two trifluoroethoxy groups simultaneously, further reducing the electron density and resulting in a larger chemical shift value. Therefore, there are two phosphorus absorption peaks, which correspond exactly to the spectrum. The figure shows that the phosphorus chemical shift value of bistrifluoroethoxyphosphate is -4.5102 ppm, and that of monotrifluoroethoxyphosphate is -12.1233 ppm, with a ratio of monotrifluoroethoxyphosphate to bistrifluoroethoxyphosphate of 1:0.9422. Figure 2 The mono / ditrifluoroethoxyphosphate prepared in Example 1 19 F NMR spectroscopy, test frequency: 400MHz, deuterated reagent: deuterated dimethyl sulfoxide. The -CF3 group in trifluoroethoxy has strong electron-withdrawing properties, reducing the electron cloud density around the fluorine atom. According to 19 In F NMR, a lower electron cloud density corresponds to a lower resonance frequency (a more negative chemical shift value). Monotrifluoroethoxyphosphate has three fluorine atoms at the same position, while bistrifluoroethoxyphosphate has six, resulting in two fluorine absorption peaks with a peak area ratio of 1:2, which corresponds exactly to the spectrum. The figure shows that the fluorine chemical shift value for monotrifluoroethoxyphosphate is -73.9590 ppm, and for bistrifluoroethoxyphosphate it is -74.0695 ppm. The peak area ratio for monotrifluoroethoxyphosphate and bistrifluoroethoxyphosphate is 1:1.8826. Detailed Implementation

[0024] This invention provides a method for preparing a mixture of mono / ditrifluoroethoxylithium phosphate. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the same result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The methods described in this invention have been described in detail through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0025] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing a mixture of mono / ditrifluoroethoxy lithium phosphate provided by the present invention.

[0026] In the following embodiments, all raw materials used are common commercially available products that can be directly purchased in the art or can be prepared according to conventional methods in the art. Operations not described in detail can be performed using conventional techniques in the art.

[0027] The phosphorus pentoxide used must be dried at 120℃ for 4 hours before use.

[0028] The trifluoroethanol and organic solvents used are controlled to have a moisture content of less than 50 ppm using 5A molecular sieves.

[0029] Example 1 Preparation of mono / ditrifluoroethoxyphosphates: Under nitrogen protection, in a 500 mL three-necked flask equipped with a stirrer, thermometer, and reflux condenser, 1 mol (142 g) of phosphorus pentoxide was suspended in 300 mL of anhydrous toluene. Then, 3 mol (300 g) of trifluoroethanol was slowly added dropwise in five portions (10 min apart), controlling the dropping rate to keep the reaction temperature below 50 °C. After the addition was complete, the reaction was stirred at 40 °C for 4 h, followed by the addition of 18 mL of 1 mol H₂O and continued hydrolysis at 40 °C for 30 min. The mixture was then filtered, concentrated, and 411 g of a pale yellow liquid was obtained. 31 p nuclear magnetic resonance spectrum ( 31 P NMR) and 19 F nuclear magnetic resonance spectrum ( 19 The product was characterized by F NMR, confirming its structure. The molar ratio of monotrifluoroethoxyphosphate to bistrifluoroethoxyphosphate was 1:0.94, the reaction yield was 93%, and the proportion of lithium pyrophosphate byproduct was <5%.

[0030] Preparation of a mixture of mono / ditrifluoroethoxylithium phosphate: The mono / ditrifluoroethoxyphosphate mixture obtained above was transferred to a 500 mL three-necked flask equipped with a stirrer and thermometer. 1.5 mol (111 g) of lithium carbonate and 300 mL of anhydrous ethanol were added, and the mixture was stirred at 60 °C for 6 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and unreacted lithium carbonate was removed by filtration. The filtrate was concentrated to dryness by rotary evaporation under reduced pressure. The product was then dried under vacuum (60 °C, 12 h) to obtain 406 g of white solid mono / ditrifluoroethoxyphosphate mixture.

[0031] Electrochemical performance testing: The prepared mono / ditrifluoroethoxyphosphate mixture was added as an additive to the electrolyte of a lithium-ion battery, and its electrochemical performance was tested. Electrolyte formulation: 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate: methyl ethyl carbonate (EC:EMC=3:7, w / w), with 1 wt% additive added. Test battery: CR2032 coin cell, with NCM613 as the positive electrode and graphite as the negative electrode. Test conditions: The battery was subjected to charge-discharge cycle tests at 1C current, with a test voltage window of 2.8-4.3V, and temperatures of room temperature (25℃) and high temperature (55℃). The performance indicators of the lithium-ion battery using the mono / ditrifluoroethoxyphosphate mixture as an additive are shown in Table 1.

[0032] Comparative results show that the electrolyte with the product of this invention exhibits significantly better performance than traditional electrolytes. The electrolyte with the product of this invention demonstrates higher conductivity and thermal stability, resulting in significantly improved battery cycle performance and safety.

[0033] Example 2 Preparation of mono / ditrifluoroethoxyphosphates: Under nitrogen protection, in a 500 mL three-necked flask equipped with a stirrer, thermometer, and reflux condenser, 1 mol (142 g) of phosphorus pentoxide was suspended in 300 mL of anhydrous cyclohexane. Then, 3 mol (300 g) of trifluoroethanol was slowly added dropwise in five portions (10 min apart), controlling the dropping rate to keep the reaction temperature below 50 °C. After the addition was complete, the reaction was stirred at 40 °C for 4 h, followed by the addition of 18 mL of H₂O (1 mol) and continued hydrolysis at 40 °C for 30 min. The mixture was filtered, concentrated, and 407 g of a pale yellow liquid was obtained. 31 p nuclear magnetic resonance spectrum ( 31 P NMR) and 19 F nuclear magnetic resonance spectrum ( 19 The product was characterized by F NMR, confirming its structure. The molar ratio of monotrifluoroethoxyphosphate to bistrifluoroethoxyphosphate was 1:1.1, the reaction yield was 90%, and the proportion of lithium pyrophosphate byproduct was <5%.

[0034] Preparation of a mixture of mono / ditrifluoroethoxylithium phosphate: The mono / ditrifluoroethoxyphosphate mixture obtained above was transferred to a 500 mL three-necked flask equipped with a stirrer and thermometer. 1.5 mol (110 g) of lithium carbonate and 300 mL of anhydrous ethanol were added, and the mixture was stirred at 60 °C for 6 hours. After the reaction was completed, unreacted lithium carbonate was removed by filtration. The filtrate was concentrated to dryness under reduced pressure, and the product was dried under vacuum (60 °C, 12 h) to obtain 403 g of white solid mono / ditrifluoroethoxyphosphate mixture.

[0035] Comparative Example 1 Trifluoroethanol was not added in batches during the preparation of mono / ditrifluoroethoxy phosphates. The reaction temperature was raised to 100°C. Hydrolysis was carried out without adding water after the reaction was completed. The total yield of the product was 62%, and the proportion of pyrophosphate byproducts was as high as 35%.

[0036] Comparative Example 2 Electrochemical performance was tested under the same conditions using a conventional electrolyte (i.e., without the addition of the mono / ditrifluoroethoxy lithium phosphate mixture of the present invention as an additive), and the results are shown in Table 1.

[0037] Table 1. Data from Examples 1, 2 and Comparative Example 2 By comparing the performance indicators of the blank electrolyte (Comparative Example 2) and the electrolyte containing additives (Examples 1 and 2), the following conclusions can be drawn: 1) Significantly improved thermal stability. The thermal decomposition temperature of the blank electrolyte was 185℃. After adding the additive, the temperature of Example 1 increased to 212℃, and that of Example 2 further increased to 215℃, an increase of 15%~16%, indicating that the additive effectively enhanced the electrolyte's resistance to thermal decomposition.

[0038] 2) Electrochemical performance optimization. Cyclic capacity retention: After 200 cycles at room temperature, the blank electrolyte retained only 82.3%, while Examples 1 and 2 achieved 90.8% and 90.6%, respectively. After 200 cycles at 55°C, the blank electrolyte retained 75.9%, while Examples 1 and 2 improved to 86.7% and 86.9%, respectively, demonstrating superior performance at high temperatures. Initial coulombic efficiency: The blank electrolyte retained 84.5%, while Examples 1 and 2 both exceeded 89% (89.6% and 89.5%), indicating a significant improvement in energy utilization efficiency.

[0039] 3) Significant leap in flame retardant performance. Limiting Oxygen Index (LOI): The LOI of the blank electrolyte is 18% (flammable), while that of Examples 1 and 2 both exceed 33% (33% and 33.2%, respectively), requiring a higher oxygen concentration to burn, indicating a significant enhancement in flame retardancy. Combustion Time: The combustion time of the blank electrolyte is >60 seconds (easily sustains combustion), while that of Examples 1 and 2 is <10 seconds (difficult to sustain combustion, even approaching "self-extinguishing"), greatly reducing the risk of fire.

[0040] 4) The conductivity decreased slightly, but the impact was controllable. The room temperature conductivity decreased from 10.2 mS / cm in the blank to 9.7 mS / cm in Example 1 and 9.6 mS / cm in Example 2, a decrease of approximately 5%, which has an acceptable impact on the electrolyte's conductivity. In summary, the electrolyte containing additives has achieved breakthroughs in thermal stability, electrochemical cycling performance, and flame retardancy.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a mixture of mono / ditrifluoroethoxy lithium phosphate, characterized in that, Includes the following steps: 1) Under an inert gas atmosphere, phosphorus pentoxide was dispersed in organic solvent one, trifluoroethanol was added, and the reaction was carried out at 20-50℃ for 3-6 hours. After the reaction was completed, water was added to hydrolyze the pyrophosphate intermediate, and the mixture was concentrated to obtain mono / ditrifluoroethoxy phosphate. 2) React mono / ditrifluoroethoxyphosphate with lithium carbonate in organic solvent II at 30-70℃ for 4-8 hours. After the reaction is completed, post-treatment is performed to obtain a mixture of mono / ditrifluoroethoxyphosphate.

2. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 1), the molar ratio of phosphorus pentoxide and trifluoroethanol is 1:(2.8-3.2).

3. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 1), the trifluoroethanol is added dropwise in stages, with each addition occurring at intervals of 5-15 minutes.

4. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 1), the molar ratio of water to phosphorus pentoxide is (0.5-1):

1.

5. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 1), the organic solvent is selected from at least one of toluene, cyclohexane, xylene, and dichloromethane.

6. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 2), the molar ratio of monotrifluoroethoxyphosphate to bistrifluoroethoxyphosphate is (0.8-1.2):

1.

7. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 2), the molar ratio of the mixture of mono / bistrifluoroethoxyphosphate and lithium carbonate is 1:(1.5-1.7).

8. The method for preparing the mono / ditrifluoroethoxy lithium phosphate mixture as described in claim 1, characterized in that, In step 2), the organic solvent is selected from at least one of anhydrous ethanol, anhydrous methanol, and acetonitrile.

9. A mixture of mono / ditrifluoroethoxylithium phosphate prepared by any one of the methods described in claims 1 to 8.

10. The application of the mono / ditrifluoroethoxy lithium phosphate mixture of claim 9 as an electrolyte additive in the preparation of lithium-ion batteries.

Images