Process for the preparation of (difluorophosphoryloxy)trifluoroborates and use thereof

Abstract

The application discloses a preparation method and application of (difluorophosphoryloxy) trifluoroborate, and the preparation method comprises the following steps: using hexafluorophosphate, diboron trioxide and difluorophosphate as reaction raw materials to obtain a reaction product containing (difluorophosphoryloxy) trifluoroborate shown in formula (I) in a reaction solvent. The product is obtained through one-step reaction, the operation is simple, the reaction steps are few, the reaction conversion rate is high, the reaction process is free of by-products, the product is high in purity and good in quality, the production cost is low, and the application is suitable for industrialization.

Description

Technical Field

[0001] This invention relates to the field of electrolyte additive synthesis, and particularly to a novel method for preparing (difluorophosphoryloxy)trifluoroborate. Background Technology

[0002] Electrolyte additives are an indispensable component of lithium-ion or sodium-ion batteries. They are mainly responsible for building a stable electrode / electrolyte interface film to achieve electronic insulation and facilitate the transport of lithium or sodium ions. Under the influence of different additives and functional groups, the composition and structure of the battery interface film are changed, which ultimately affects the battery's cycle life, high-temperature storage, and low-temperature discharge performance.

[0003] Boron-containing additives, due to the electron-deficient effect of boron atoms, can dissolve inorganic lithium salts such as LiF on the surface of the interfacial film, thereby reducing the battery's internal resistance and improving its low-temperature performance. Phosphorus-containing additives, such as phosphate esters and phosphates, have strong interactions between their "P=O" functional groups and transition metal elements on the positive electrode surface, thus forming a stable positive electrode interfacial film. This improves the battery's storage and cycle performance. Furthermore, phosphorus-containing additives also have a certain flame-retardant effect in the electrolyte. Additives containing both phosphorus and boron can possess all of these advantages simultaneously, such as (difluorophosphoryloxy)trifluoroborate.

[0004] Patent CN102414902A discloses lithium (difluorophosphoryloxy)trifluoroborate and its synthesis method. It involves reacting lithium difluorophosphate with a boron trifluoride diethyl ether complex to obtain a product containing at least lithium (difluorophosphoryloxy)trifluoroborate. Using this as an electrolyte additive can improve the battery's room-temperature cycling performance and suppress impedance growth during cycling. However, lithium difluorophosphate has low solubility in most reaction solvents, requiring increased solvent usage during the reaction and resulting in high turbidity of the prepared lithium (difluorophosphoryloxy)trifluoroborate solution. Furthermore, using boron trifluoride as a raw material necessitates the removal of residual boron trifluoride in the reaction solution through vacuum distillation, significantly increasing reaction energy consumption and cost. Additionally, trace amounts of residual boron trifluoride in the product can degrade the battery's high-temperature performance.

[0005] Patent CN118545731A discloses a one-pot method for preparing (difluorophosphoryloxy)trifluoroborate, which involves adding lithium hexafluorophosphate, a siloxane compound, a boron trifluoride complex, and a reaction solvent into a reactor in a single step. While this method uses lithium hexafluorophosphate instead of lithium difluorophosphate as a raw material, avoiding solubility and sample turbidity issues during the reaction, the generated fluorosilanes increase the difficulty of waste treatment and also pose a risk of degrading the high-temperature performance of the battery.

[0006] Therefore, a method for preparing (difluorophosphoryloxy)trifluoroborate with low turbidity, high quality, no by-products, and low cost is proposed, which is beneficial to improving the quality of electrolytes and further improving the performance of lithium / sodium ion batteries. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a method for preparing (difluorophosphoryloxy)trifluoroborate products that reduces turbidity, improves product quality, is simple to operate, involves few reaction steps, has a high conversion rate, produces no byproducts, and has low production costs, making it suitable for industrial application.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing (difluorophosphoryloxy)trifluoroborate, the method comprising: reacting hexafluorophosphate, boron trioxide and difluorophosphate as raw materials in a reaction solvent to obtain a reaction product comprising the (difluorophosphoryloxy)trifluoroborate shown in formula (I), the reaction formula being as follows:

[0010]

[0011] In the formula, M is lithium or sodium.

[0012] The hexafluorophosphate described in this invention is selected from lithium hexafluorophosphate or sodium hexafluorophosphate.

[0013] The difluorophosphate described in this invention is selected from lithium difluorophosphate or sodium difluorophosphate.

[0014] The (difluorophosphoryloxy)trifluoroborate of the present invention is selected from lithium (difluorophosphoryloxy)trifluoroborate or sodium (difluorophosphoryloxy)trifluoroborate.

[0015] This invention uses hexafluorophosphate, boron trioxide, and difluorophosphate as raw materials to prepare (difluorophosphoryloxy)trifluoroborate. Hexafluorophosphate is a commonly used material in battery electrolytes with low cost, and a slight excess of hexafluorophosphate helps to shift the reaction forward. Excess hexafluorophosphate does not need to be removed; only the amount of hexafluorophosphate added as a salt needs to be reduced accordingly when preparing the electrolyte. Boron trioxide is more stable than boron trifluoride, making it easier to transport and store, and it can effectively avoid the residue of acidic gases in the product (difluorophosphoryloxy)trifluoroborate, thus promoting the improvement of battery high-temperature performance. Difluorophosphate plays a role in eliminating the byproduct (boron trifluoride) in the reaction, effectively preventing the generation of boron trifluoride acidic gas. This preparation method is not only simple to operate and has few reaction steps, but also has low production cost, making it suitable for industrial application. Moreover, the reaction process produces no byproducts, especially no acidic substances such as boron trifluoride and fluorosilanes (even a small amount of these acidic gases remaining in the electrolyte will significantly degrade the high-temperature performance of the battery).

[0016] To improve reactivity, shorten reaction time, and ensure that no unreacted boron trioxide residue remains in the reaction product, it is preferable to add hexafluorophosphate to the reaction apparatus in excess of the reaction equivalent. Excess hexafluorophosphate not only promotes the forward reaction but also does not need to be removed; the amount of hexafluorophosphate added as a salt only needs to be reduced accordingly when preparing the electrolyte. The molar ratio of hexafluorophosphate to boron trioxide is (1.5–3):1; preferably, the molar ratio is (1.5–2):1.

[0017] To improve reactivity, shorten reaction time, and ensure that no unreacted boron trioxide residue remains in the reaction product, it is preferable to add difluorophosphate to the reaction apparatus in excess of the reaction equivalence. Excess difluorophosphate not only promotes the forward reaction but also avoids the residue of acidic boron trifluoride gas. Furthermore, a slight excess of difluorophosphate in the product can improve battery performance in the electrolyte and does not require removal. However, excessive addition of difluorophosphate will lead to an increase in product turbidity. The molar ratio of difluorophosphate to boron trioxide is (0.5–1):1, preferably (0.5–0.8):1.

[0018] To improve reactivity, shorten reaction time, and ensure that no unreacted boron trioxide residue remains in the product, a chain alkyl alcohol is added as a catalyst. During the reaction, the chain alkyl alcohol reacts with boron trioxide to form a borate monoester intermediate. This intermediate has high solubility in the reaction solvent. After reacting with hexafluorophosphate to form (difluorophosphoryloxy)trifluoroborate, it releases the chain alkyl alcohol to continue catalyzing subsequent reactions. Therefore, adding a small amount of chain alkyl alcohol can significantly increase reactivity, shorten reaction time, and reduce product turbidity.

[0019] The chain alkyl alcohol is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, glycerol, and cyclohexanehexyl alcohol. The amount of the chain alkyl alcohol is 0.05-1.5% of the molar amount of boron trioxide, preferably 0.15-1.0%.

[0020] The reaction temperature of the present invention is sufficient to initiate the reaction to proceed to the right; preferably, the reaction temperature is 0–80°C.

[0021] The reaction time of the present invention is 0.5 to 24 hours; preferably, the reaction time is 0.5 to 10 hours.

[0022] The reaction solvent described in this invention can be any solvent capable of dissolving the reaction raw materials. Preferably, the reaction solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, diethyl ether, ethylene glycol dimethyl ether, acetonitrile, phenylacetonitrile, or propionitrile. More preferably, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, and methyl propionate. Because these preferred reaction solvents are commonly used solvents in lithium / sodium-ion battery electrolytes, the reaction product containing (difluorophosphoryloxy)trifluoroborate can be directly used in the preparation of the electrolyte without undergoing atmospheric or vacuum distillation to remove the solvent.

[0023] To obtain the (difluorophosphoryloxy)trifluoroborate product, the preparation method further includes the step of removing the reaction solvent and / or catalyst by atmospheric or vacuum distillation. Due to the solvation effect of (difluorophosphoryloxy)trifluoroborate, the (difluorophosphoryloxy)trifluoroborate product is a concentrated solution (containing the reaction solvent). Therefore, the reaction solvent of the present invention is preferably a commonly used organic solvent in electrolytes, so that the (difluorophosphoryloxy)trifluoroborate product (concentrated solution) can be directly used in the preparation of electrolytes.

[0024] During the experiment, the inventors of this invention discovered that two molecules of (difluorophosphoryloxy)trifluoroborate can generate one molecule of bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate.

[0025] The bis(difluorophosphoryloxy)trifluoroborate is selected from lithium bis(difluorophosphoryloxy)trifluoroborate or sodium bis(difluorophosphoryloxy)trifluoroborate.

[0026] The tetrafluoroborate is selected from lithium tetrafluoroborate or sodium tetrafluoroborate.

[0027] Taking lithium bis(difluorophosphoryloxy)trifluoroborate as an example, the reaction formula is as follows:

[0028]

[0029] The reaction is reversible and has relatively low forward reactivity. The main product is (difluorophosphoryloxy)trifluoroborate, with small amounts of bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate.

[0030] Specifically, based on the total mass of the product (excluding the solvent), the reaction product contains at least 70 wt% (difluorophosphoryloxy)trifluoroborate, preferably at least 80 wt% (difluorophosphoryloxy)trifluoroborate. A higher proportion of (difluorophosphoryloxy)trifluoroborate in the reaction product improves the overall performance of the battery, specifically reducing battery impedance and improving high-temperature cycling and high-temperature storage performance.

[0031] The present invention also provides an electrolyte comprising (difluorophosphoryloxy)trifluoroborate, wherein the amount of (difluorophosphoryloxy)trifluoroborate in the electrolyte accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte. As an electrolyte additive, (difluorophosphoryloxy)trifluoroborate can reduce the initial impedance of the battery, improve high-temperature storage, high-temperature cycling, and low-temperature discharge performance, thus achieving a balance between high and low temperature performance of the battery.

[0032] Furthermore, the electrolyte also contains bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate.

[0033] Furthermore, the electrolyte satisfies the following conditions:

[0034] 1.5 ≤ a / b ≤ 9, and 1.0% ≤ c / a ≤ 5.0%.

[0035] Where a is the mass percentage of (difluorophosphoryloxy)trifluoroborate in the electrolyte, in %;

[0036] b represents the mass percentage of bis(difluorophosphoryloxy)trifluoroborate in the electrolyte, in %;

[0037] c represents the mass percentage of tetrafluoroborate in the electrolyte, expressed as a percentage.

[0038] Correlating the mass percentages of (difluorophosphoryloxy)trifluoroborate (a), bis(difluorophosphoryloxy)trifluoroborate (b), and tetrafluoroborate (c) in the electrolyte can comprehensively improve the battery's low impedance and high-temperature performance. When the value of a / b is too small, the battery's initial impedance is higher, while when the value of c / a is too large, the battery's high-temperature performance and cycle life are weaker. Therefore, properly adjusting the values ​​of a / b and c / a is crucial for maximizing the battery's overall performance.

[0039] The present invention also provides a secondary battery comprising (difluorophosphoryloxy)trifluoroborate, wherein the (difluorophosphoryloxy)trifluoroborate in the secondary battery is obtained by the above preparation method.

[0040] The present invention also provides a composition comprising (difluorophosphoryloxy)trifluoroborate, the composition comprising (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate, wherein, based on a total amount of (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate of 100 wt%, the content of (difluorophosphoryloxy)trifluoroborate is ≥70 wt%, the content of bis(difluorophosphoryloxy)trifluoroborate is ≤25 wt%, and the content of tetrafluoroborate is ≤5 wt%.

[0041] Furthermore, based on a total of 100wt% of (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate, and tetrafluoroborate, the content of (difluorophosphoryloxy)trifluoroborate is ≥80wt%, the content of bis(difluorophosphoryloxy)trifluoroborate is ≤17wt%, and the content of tetrafluoroborate is ≤3wt%.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] 1. This invention proposes a novel one-step method for preparing (difluorophosphoryloxy)trifluoroborate using hexafluorophosphate, boron trioxide, and difluorophosphate as raw materials. This method is not only simple to operate and involves fewer reaction steps, but also does not produce insoluble substances that would increase turbidity during the reaction process. Furthermore, the reaction process produces no byproducts, resulting in high product purity, good quality, and low production costs, making it suitable for industrial applications.

[0044] 2. This invention produces no byproducts during the reaction process, especially no acidic substances such as boron trifluoride and fluorosilanes (which would degrade the high-temperature performance of the battery). Therefore, the prepared (difluorophosphoryloxy)trifluoroborate lithium has high purity, which is more conducive to the high-temperature storage and high-temperature cycling performance of lithium-ion batteries. Attached Figure Description

[0045] Figure 1 The lithium salt No. 1 prepared in Example 1 of this invention 19 F-NMR spectrum, ■ represents the peak of lithium (difluorophosphoryloxy)trifluoroborate, ● represents the peak of lithium bis(difluorophosphoryloxy)trifluoroborate, Δ represents the peak of lithium tetrafluoroborate;

[0046] Figure 2 The lithium salt No. 1 prepared in Example 1 of this invention 31 P-NMR spectrum, ■ represents the peak of lithium (difluorophosphoryloxy)trifluoroborate, ● represents the peak of lithium bis(difluorophosphoryloxy)trifluoroborate;

[0047] Figure 3 The 2# control lithium salt prepared in Comparative Example 2 of this invention 19F-NMR spectrum, ■ represents the peak of lithium (difluorophosphoryloxy)trifluoroborate, ● represents the peak of lithium bis(difluorophosphoryloxy)trifluoroborate, Δ represents the peak of lithium tetrafluoroborate, ▲ represents the peak of silicon tetrafluoride.

[0048] Figure 4 The 2# control lithium salt prepared in Comparative Example 2 of this invention 31 In the P-NMR spectrum, ■ represents the peak of lithium (difluorophosphoryloxy)trifluoroborate, and ● represents the peak of lithium bis(difluorophosphoryloxy)trifluoroborate. Detailed Implementation

[0049] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0050] The structure and content of the products and control samples prepared in Examples 1-9 and Comparative Examples 1-4 of this invention were determined by 400M nuclear magnetic resonance fluorine spectroscopy (NMR spectroscopy). 19 F-NMR) and 400M nuclear magnetic resonance phosphorus spectrum (F-NMR) 31 Characterization was performed using P-NMR. The method involved adding a small amount of product to an NMR tube and diluting it with an appropriate amount of diethyl carbonate, ensuring the solution height did not exceed one-third of the NMR tube height. Since the NMR spectra of the same substance are essentially consistent and the peak position shifts are minimal under the same solvent conditions, detailed NMR spectra and results are only described in Example 1 and Comparative Example 2.

[0051] I. Preparation of Substances

[0052] Example 1

[0053] This embodiment provides the preparation of lithium trifluoroborate (difluorophosphoryloxy)trifluoroborate, specifically including the following steps:

[0054] S1. In a drying room with a dew point of -40°C, 500 ml of methyl ethyl carbonate and 0.05 mol (5.50 g, 99% purity) of lithium difluorophosphate were added to a reaction flask. The mixture was stirred thoroughly under a closed environment. Then, 0.15 mol (22.8 g, 99% purity) of lithium hexafluorophosphate and 0.1 mol (6.96 g, 99% purity) of boron trioxide were added. After reacting at 50°C for 6 hours, no insoluble matter was found in the reaction product, indicating that the boron trioxide had completely reacted, yielding a methyl ethyl carbonate solution containing lithium (difluorophosphoryloxy)trifluoroborate.

[0055] S2. Most of the solvent in the reaction product is removed by vacuum distillation. The vacuum distillation temperature is controlled at 60℃ and the time is controlled at 0.5h to obtain a concentrated product solution of lithium (difluorophosphoryloxy)trifluoroborate, which is designated as lithium salt #1.

[0056] The product is colorless and transparent, and its turbidity was measured to be 5.20 NTU using a turbidimeter.

[0057] Appendix Figure 1 and attached Figure 2 The following are given for lithium salt #1: 19 F-NMR and 31 p-NMR spectrum, from Figure 1 , Figure 2 It can be known that:

[0058] The NMR F-spectrum of lithium salt #1 is shown below:

[0059] Lithium trifluoroborate (difluorophosphoryloxy): δ = -92.71 ppm (d, J = 955.9 Hz), δ = -157.66 ppm (s)

[0060] Lithium bis(difluorophosphoryloxy)trifluoroborate: δ = -92.31 ppm (d, J = 962.9 Hz), δ = -151.18 ppm (s)

[0061] The NMR p-spectrum of lithium salt #1 is shown below:

[0062] (Difluorophosphoryloxy)trifluoroborate: δ=-27.92ppm(t,J=956.0Hz)

[0063] Lithium bis(difluorophosphoryloxy)trifluoroborate: δ = -29.30 ppm (t, J = 956.0 Hz)

[0064] Integrating the peak areas of the NMR F-spectrum reveals that the integrated area ratio of lithium (difluorophosphoryloxy)trifluoroborate (marked with "■"), lithium bis(difluorophosphoryloxy)trifluoroborate (marked with "●"), and lithium tetrafluoroborate (marked with "Δ") is 3.12:1.00:0.83. Converting this to a molar ratio, the ratio is 1:0.16:0.067, and further to a mass ratio, it is 1:0.25:0.033. Therefore, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #1 contains 77.8 wt% lithium (difluorophosphoryloxy)trifluoroborate, 19.5 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 2.7 wt% lithium tetrafluoroborate. Furthermore, the NMR F-spectrum results indicate no boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high calculation reliability.

[0065] Example 2

[0066] The operation in this embodiment is the same as in embodiment 1, except that the amount of lithium hexafluorophosphate added is increased from 0.15 mol to 0.25 mol. After reacting at 50°C for 4 hours, there are no insoluble substances in the reaction product, and a concentrated product solution of (difluorophosphoryloxy)trifluoroborate is obtained, which is designated as lithium salt #2.

[0067] The product is colorless and transparent, and its turbidity was measured to be 5.18 NTU using a turbidimeter.

[0068] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #2 contains 29.9 wt% unreacted lithium hexafluorophosphate, 55.3 wt% lithium (difluorophosphoryloxy)trifluoroborate, 12.9 wt% bis(difluorophosphoryloxy)trifluoroborate, and 1.90 wt% lithium tetrafluoroborate. Furthermore, the F-spectrum NMR results indicate the absence of boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0069] Example 3

[0070] The operation in this embodiment is the same as in embodiment 1, except that the amount of lithium difluorophosphate added is increased from 0.05 mol to 0.08 mol. After reacting at 50°C for 3 hours, there are no insoluble substances in the reaction product, and a concentrated product solution of lithium (difluorophosphoryloxy)trifluoroborate is obtained, which is designated as lithium salt #3.

[0071] The product is colorless and transparent, and its turbidity was measured to be 5.22 NTU using a turbidimeter.

[0072] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #3 contains 8.50 wt% unreacted lithium difluorophosphate, 72.2 wt% lithium (difluorophosphoryloxy)trifluoroborate, 16.8 wt% bis(difluorophosphoryloxy)trifluoroborate, and 2.47 wt% lithium tetrafluoroborate. Furthermore, the F-spectrum NMR results indicate the absence of boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0073] Example 4

[0074] The operation in this embodiment is the same as in embodiment 1, except that the reaction time is extended from 6 hours to 12 hours to obtain a concentrated product solution of (difluorophosphoryloxy)trifluoroborate, which is designated as lithium salt #4.

[0075] The product is colorless and transparent, and its turbidity was measured to be 5.21 NTU using a turbidimeter.

[0076] Integrating the area of ​​the F-spectrum NMR spectrum and calculating, it was found that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #4 contains 78.8 wt% lithium (difluorophosphoryloxy)trifluoroborate, 18.5 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 2.70 wt% lithium tetrafluoroborate. Furthermore, the F-spectrum NMR results indicate no boron trifluoride residue. Further area integration calculations using the P-spectrum showed consistent results and high reliability.

[0077] Example 5

[0078] The operation in this embodiment is the same as in Example 1, except that the reaction solvent is replaced with diethyl carbonate and the reaction temperature is increased from 50°C to 70°C to obtain a concentrated product solution of (difluorophosphoryloxy)trifluoroborate, which is designated as lithium salt #5.

[0079] The product is colorless and transparent, and its turbidity was measured to be 5.22 NTU using a turbidimeter.

[0080] Integrating the peak area of ​​the NMR F-spectrum and calculating, it was found that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #5 contains 78.9 wt% lithium (difluorophosphoryloxy)trifluoroborate, 18.4 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 2.70 wt% lithium tetrafluoroborate. Furthermore, the NMR F-spectrum results indicate no boron trifluoride residue. Further area integration calculations using the P-spectrum showed consistent results and high reliability.

[0081] Example 6

[0082] The operation of this embodiment is the same as that of Example 1, except that in step S1, 0.001 mol (0.033 g) of methanol is added to the reaction flask as a reaction catalyst. After reacting at 50°C for 2 hours, there are no insoluble substances in the reaction product, indicating that boron trioxide has reacted completely. After step S2, a concentrated solution of lithium (difluorophosphoryloxy)trifluoroborate is obtained, which is designated as lithium salt #6.

[0083] The product is colorless and transparent, and its turbidity was measured to be 5.12 NTU using a turbidimeter.

[0084] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #6 contains 85.2 wt% lithium (difluorophosphoryloxy)trifluoroborate, 13.6 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 1.20 wt% lithium tetrafluoroborate. Furthermore, the F-spectrum NMR results indicate the absence of boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0085] Example 7

[0086] The operation of this embodiment is the same as that of embodiment 7, except that: in step S1, the amount of methanol added is increased to 0.0015 mol (0.05 g), and after reacting at 50°C for 1 h, there are no insoluble substances in the reaction product, indicating that boron trioxide has reacted completely. After step S2, a concentrated solution of lithium trifluoroborate (difluorophosphoryloxy) is obtained, which is designated as lithium salt #7.

[0087] The product is colorless and transparent, and its turbidity was measured to be 5.15 NTU using a turbidimeter.

[0088] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, assuming a total fluorinated lithium salt content of 100 wt%, lithium salt #7 contains 87.6 wt% lithium (difluorophosphoryloxy)trifluoroborate, 11.4 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 1.00 wt% lithium tetrafluoroborate. Furthermore, the F-spectrum NMR results indicate the absence of boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0089] Example 8

[0090] The operation in this embodiment is the same as in embodiment 1, except that lithium hexafluorophosphate is replaced with sodium hexafluorophosphate and lithium difluorophosphate is replaced with sodium difluorophosphate to obtain a product concentrate of sodium (difluorophosphoryloxy)trifluoroborate, which is designated as sodium salt #1.

[0091] The product is colorless and transparent, and its turbidity was measured to be 5.50 NTU using a turbidimeter.

[0092] Integrating and calculating the peak area of ​​the NMR F-spectrum reveals that, based on a total fluorine content of 100 wt%, sodium salt #1 contains 79.5 wt% sodium (difluorophosphoryloxy)trifluoroborate, 17.6 wt% sodium bis(difluorophosphoryloxy)trifluoroborate, and 2.90 wt% sodium tetrafluoroborate. Furthermore, the NMR F-spectrum results indicate no boron trifluoride residue. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0093] Comparative Example 1

[0094] This comparative example uses a lithium difluorophosphate and boron trifluoride methyl ethyl carbonate complex as a raw material to prepare a methyl ethyl carbonate solution containing lithium (difluorophosphoryloxy)trifluoroborate. The solution is then obtained by vacuum distillation, yielding a concentrated product of lithium (difluorophosphoryloxy)trifluoroborate. The specific steps include:

[0095] S1. In a drying room with a dew point of -40°C, 0.15 mol of lithium difluorophosphate (99% purity) and 0.15 mol of boron trifluorophosphate methyl ethyl carbonate complex (99% purity) were added to a reaction flask. 200 ml of methyl ethyl carbonate was added as a solvent. The system was stirred and mixed evenly under a closed environment. The reaction was carried out at 50°C for 12 h to obtain a methyl ethyl carbonate solution containing lithium (difluorophosphoryloxy)trifluoroborate. The solution contained a small amount of insoluble matter, which may be undissolved lithium difluorophosphate. The turbidity was analyzed by a turbidimeter and was 12.55 NTU. After filtration, a clear and transparent reaction product was obtained.

[0096] S2. Most of the solvent in the reaction product was removed by vacuum distillation. The vacuum distillation temperature was controlled at 60℃ and the time was controlled at 0.5h to obtain a concentrated product solution of lithium (difluorophosphoryloxy)trifluoroborate, which was designated as control lithium salt #1.

[0097] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, based on a total fluorinated lithium salt content of 100 wt%, the #1 control lithium salt contains 61.4 wt% lithium (difluorophosphoryloxy)trifluoroborate, 34.3 wt% lithium bis(difluorophosphoryloxy)trifluoroborate, and 4.3 wt% lithium tetrafluoroborate. Further area integration using the P-spectrum showed consistent results and high reliability.

[0098] Comparative Example 2

[0099] This comparative example uses a lithium hexafluorophosphate, hexamethyldisiloxane, and boron trifluoride diethyl carbonate complex as raw materials to prepare a diethyl carbonate solution containing (difluorophosphoryloxy)trifluoroborate. The solution is then obtained by vacuum distillation, yielding a concentrated product of (difluorophosphoryloxy)trifluoroborate. The specific steps include:

[0100] S1. In a drying room with a dew point of -40°C, add 0.2 mol lithium hexafluorophosphate (99% purity), 0.4 mol hexamethyldisiloxane (99% purity), 0.2 mol boron trifluoride diethyl carbonate complex, and 200 mL diethyl carbonate to a reaction flask. Start stirring to mix the system evenly and react at 50°C for 6 h to obtain the reaction product (difluorophosphoryloxy)trifluoroborate.

[0101] S2. The reaction solvent and most of the residual fluorosilane gas in the reaction product were removed by vacuum distillation. The vacuum distillation temperature was controlled at 60℃ and the time was controlled at 0.5h to obtain a concentrated solution of (difluorophosphoryloxy)trifluoroborate, which was designated as control lithium salt #2.

[0102] The product is colorless and transparent, and its turbidity is 3.85 NTU when analyzed by a turbidimeter.

[0103] Appendix Figure 3 and attached Figure 4 The following are the reference lithium salts #2: 19 F-NMR and 31 p-NMR spectrum, from Figure 3 , Figure 4 It can be known that:

[0104] The NMR F-spectrum of control lithium salt #2 is shown below:

[0105] Lithium trifluoroborate (difluorophosphoryloxy): δ = -92.08 ppm (d, J = 953.5 Hz), δ = -156.71 ppm (s)

[0106] Lithium bis(difluorophosphoryloxy)trifluoroborate: δ = -91.72 ppm (d, J = 959.8 Hz), δ = -151.31 ppm (s)

[0107] Silicon tetrafluoride: δ = -165.52 ppm(s)

[0108] The NMR P-spectrum of reference lithium salt #2 is shown below:

[0109] (Difluorophosphoryloxy)trifluoroborate: δ = -26.91 ppm (t, J = 953.8 Hz)

[0110] Lithium bis(difluorophosphoryloxy)trifluoroborate: δ = -28.22 ppm (t, J = 963.1 Hz)

[0111] Integrating the area of ​​the F-spectrum NMR peaks and assuming a total fluorinated lithium salt content of 100 wt%, the proportions of lithium (difluorophosphoryloxy)trifluoroborate (marked with "■"), lithium bis(difluorophosphoryloxy)trifluoroborate (marked with "●"), and lithium tetrafluoroborate (marked with "Δ") in control lithium salt #2 were calculated to be 77.8 wt%, 19.5 wt%, and 2.7 wt%, respectively. Furthermore, the F-spectrum NMR results indicated the presence of residual silicon tetrafluoride (marked with "▲"). Further area integration using the P-spectrum revealed consistent results and high calculation reliability.

[0112] Comparative Example 3

[0113] The operation of this comparative example is the same as that of Example 1, except that lithium difluorophosphate is not added, and the reaction time is extended from 6h to 12h. After step S1, a methyl ethyl carbonate solution containing lithium (difluorophosphoryloxy)trifluoroborate is obtained. This solution contains insoluble matter, and the turbidity test shows 52.9 NTU. After filtration, 1.26g of insoluble matter is obtained, which is unreacted boron trioxide. After step S2, the filtrate is used to obtain a concentrated product solution of lithium (difluorophosphoryloxy)trifluoroborate, which is designated as control lithium salt #3.

[0114] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, based on a total fluorinated lithium salt content of 100 wt%, the #3 control lithium salt contains 16.0 wt% unreacted lithium hexafluorophosphate, 68.0 wt% lithium (difluorophosphoryloxy)trifluoroborate, 14.1 wt% bis(difluorophosphoryloxy)trifluoroborate, and 1.99 wt% lithium tetrafluoroborate. A small amount of boron trifluoride remains in the F-spectrum. Further area integration calculations using the P-spectrum show consistent results and high reliability.

[0115] Comparative Example 4

[0116] The procedure for this comparative example is the same as that for Comparative Example 1, except that lithium difluorophosphate is replaced with sodium difluorophosphate. After step S1, a methyl ethyl carbonate solution containing sodium difluorophosphate (difluorophosphoryloxy)trifluoroborate is obtained. This solution contains a small amount of insoluble matter, possibly undissolved sodium difluorophosphate. Analysis using a turbidimeter shows a turbidity of 15.20 NTU. After filtration, a clear and transparent reaction product is obtained. After step S2, the filtrate yields a concentrated product solution of sodium difluorophosphate (difluorophosphoryloxy)trifluoroborate, designated as control sodium salt #1.

[0117] Integrating and calculating the area of ​​the F-spectrum NMR peaks reveals that, based on a total fluorine content of 100 wt%, the No. 1 control sodium salt contains 65.5 wt% sodium difluorophosphoryloxytrifluoroborate, 30.9 wt% sodium bis(difluorophosphoryloxy)trifluoroborate, and 3.60 wt% sodium tetrafluoroborate. Further area integration using the P-spectrum showed consistent results and high reliability.

[0118] By comparing Examples 1-7 of the present invention with Comparative Examples 1-3, the lithium (difluorophosphoryloxy)trifluoroborate products prepared by this process have low turbidity, no residual impurities such as fluorosilane and boron trifluoride that are harmful to battery performance, and the content of bis(difluorophosphoryloxy)trifluoroborate and lithium tetrafluoroborate in the products is lower, resulting in higher overall quality.

[0119] By comparing Examples 1 to 3 of the present invention, it can be seen that appropriately increasing the amount of lithium hexafluorophosphate and lithium difluorophosphate in the reaction system can promote the forward shift of the reaction and increase the reaction rate.

[0120] Comparing the reaction results of Examples 1 and 6-7 of this invention, it can be seen that adding a chain alkyl alcohol as a catalyst not only promotes complete reaction of the raw materials and increases the reaction yield, but also avoids the residue of boron trioxide, thus reducing the turbidity of the reaction product and eliminating the need for filtration, thereby simplifying the process. It also increases the reaction activity and significantly shortens the reaction time. Furthermore, with the increase of the catalyst dosage, the reaction rate further increases. This catalyst can be removed during subsequent distillation without affecting product quality.

[0121] II. Electrolyte

[0122] Preparation of basic electrolyte 1: In an argon-filled glove box (moisture < 5 ppm, oxygen < 10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of EC:EMC:DEC = 4:4:2. Then, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration reached 1.0 mol / L to obtain basic electrolyte 1.

[0123] Preparation of basic electrolyte 2: In an argon-filled glove box (moisture < 5 ppm, oxygen < 10 ppm), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of EC:EMC:PC = 7:10:1. Sodium hexafluorophosphate (NaPF6) was slowly added to the mixed solution until the molar concentration of NaPF6 was 1.0 mol / L, thus obtaining basic electrolyte 2.

[0124] Application Example 1

[0125] Add 1 wt% of lithium salt #1 to the base electrolyte 1 to obtain the electrolyte of this application example.

[0126] Application Example 2

[0127] Add 1 wt% of lithium salt #3 to the base electrolyte 1 to obtain the electrolyte of this application example.

[0128] Application Example 3

[0129] Add 1 wt% of lithium salt #4 to the base electrolyte 1 to obtain the electrolyte of this application example.

[0130] Application Example 4

[0131] Add 1 wt% of lithium salt #6 to the base electrolyte 1 to obtain the electrolyte of this application example.

[0132] Application Example 5

[0133] Add 1 wt% of lithium salt #7 to the base electrolyte 1 to obtain the electrolyte of this application example.

[0134] Application Example 6

[0135] Add 1 wt% of sodium salt #1 to the base electrolyte 2 to obtain the electrolyte of this application example.

[0136] Application Comparative Example 1

[0137] Add 1 wt% of control lithium salt #1 to the basic electrolyte 1 to obtain the comparative electrolyte for this application.

[0138] Application Comparative Example 2

[0139] Add 1 wt% of control lithium salt #2 to the base electrolyte 1 to obtain the comparative electrolyte for this application.

[0140] Application Comparative Example 3

[0141] Add 1 wt% of control lithium salt #3 to the basic electrolyte 1 to obtain the comparative electrolyte for this application.

[0142] Application Comparative Example 4

[0143] The base electrolyte 1 is left untreated to obtain the comparative electrolyte for this application.

[0144] Application Comparative Example 5

[0145] Add 1 wt% of control sodium salt #1 to the basic electrolyte 1 to obtain the comparative electrolyte for this application.

[0146] Application Comparative Example 6

[0147] The base electrolyte 2 is left untreated to obtain the comparative electrolyte for this application.

[0148] III. Electrochemical Performance Testing

[0149] The electrolytes used in Application Examples 1-5 and Comparative Examples 1-4 were respectively used to fabricate 1260mAh capacity soft-pack lithium-ion batteries. Each lithium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material is a ternary positive electrode (LiNi). 0.6 Co 0.2 Mn 0.2 O2, the negative electrode active material is high-capacity graphite. The preparation process is as follows: the positive electrode sheet, separator and negative electrode sheet are wound together into a core, sealed with aluminum-plastic film and then baked to ensure that the electrode moisture meets the requirements. After baking, the cell is injected with electrolyte, and after standing, formation, capacity testing and aging processes, the finished lithium-ion battery soft pack cell is obtained.

[0150] The electrolytes used in Application Example 6 and Comparative Examples 5-6 were respectively used to fabricate 1260mAh capacity sodium-ion batteries in soft-pack form. Each sodium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material is a ternary positive electrode (NaNi). 0.33 Fe 0.33 Mn 0.33 O2, with hard carbon as the negative electrode active material. The preparation process is as follows: the positive electrode, separator, and negative electrode are wound together into a core, sealed with aluminum-plastic film, and then baked to ensure that the electrode moisture content meets the requirements. After baking, the cell is injected with electrolyte, and after standing, formation, capacity testing, and aging processes, the finished sodium ion soft-pack cell is obtained.

[0151] The performance of the lithium-ion and sodium-ion batteries prepared above was tested (test voltage 2.8–4.2V), mainly including:

[0152] (1) 60℃ high temperature storage test: Charge the battery to 100% SOC and store it in an oven at 60±2℃ for 28 days. Test the volume before and after storage to obtain the volume expansion rate of the single cell before and after storage at 60℃; test the DCR value after storage at room temperature and calculate the percentage value of the initial DCR, which is recorded as the discharge DCR change rate.

[0153] (2) 45℃ high temperature cycle test: The battery is cycled in an oven at 45±1℃ with a charge / discharge current of 1C / 1C. The discharge capacity is calculated every week. The cycle is stopped after 500 cycles, and the capacity retention rate after the cycle is calculated.

[0154] (3) -20℃ low temperature discharge: The battery is discharged to 80% of the lower limit voltage at a discharge current of 1C in an oven at -20±1℃. This is taken as the low temperature discharge capacity, and its percentage with the 1C discharge capacity at 25℃ is calculated and recorded as the low temperature discharge capacity retention rate.

[0155] Table 1 Electrochemical performance test results

[0156]

[0157]

[0158] As shown in Table 1 above, by comparing Application Examples 1-5 with Comparative Examples 1-3, and Application Example 6 with Comparative Example 5, it can be seen that the (difluorophosphoryloxy)trifluoroborate prepared by this invention, as an electrolyte additive, exhibits superior low impedance and improved high-temperature storage and low-temperature discharge performance. Furthermore, as the content of bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate in the (difluorophosphoryloxy)trifluoroborate decreases, its electrochemical performance is further enhanced.

[0159] Further comparison of application examples 1-5 and application comparative examples 1-3 shows that, due to the presence of fluorosilane residue in control lithium salt #2 and the presence of boron trifluoride residue in control lithium salt #3, both exhibit a certain degree of deterioration in high-temperature storage performance and high-temperature cycling performance.

Claims

1. A method for preparing a (difluorophosphoxy)trifluoroborate, characterized in that: The preparation method includes: reacting hexafluorophosphate, boron trioxide, and difluorophosphate as raw materials in a reaction solvent to obtain a reaction product containing the (difluorophosphoryloxy)trifluoroborate shown in formula (I), as follows: In the formula, M is lithium or sodium.

2. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 1, characterized in that: The reaction products, excluding the reaction solvent, contain at least 70 wt% (difluorophosphoryloxy)trifluoroborate.

3. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 1, characterized in that: The molar ratio of hexafluorophosphate to boron trioxide is (1.5-3):1, and the molar ratio of difluorophosphate to boron trioxide is (0.5-1):

1.

4. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 3, characterized in that: The molar ratio of hexafluorophosphate to boron trioxide is (1.5-2):1, and the molar ratio of difluorophosphate to boron trioxide is (0.5-0.8):

1.

5. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 1, characterized in that: A chain alkyl alcohol catalyst is added to the reaction, wherein the chain alkyl alcohol is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, glycerol, and cyclohexanehexanol.

6. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 5, characterized in that: The amount of the chain alkyl alcohol used is 0.05 to 1.5% of the molar amount of boron trioxide.

7. The method for preparing (difluorophosphoryloxy)trifluoroborate according to claim 1, characterized in that: The reaction solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, diethyl ether, ethylene glycol dimethyl ether, acetonitrile, phenylacetonitrile, or propionitrile.

8. An electrolyte comprising (difluorophosphoryloxy)trifluoroborate, characterized in that: The (difluorophosphoryloxy)trifluoroborate is obtained by the preparation method of any one of the (difluorophosphoryloxy)trifluoroborate according to claims 1-7, and the amount of (difluorophosphoryloxy)trifluoroborate in the electrolyte accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte.

9. The electrolyte containing (difluorophosphoryloxy)trifluoroborate according to claim 8, characterized in that: The electrolyte further comprises bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate, and the electrolyte satisfies the following conditions: 1.5 ≤ a / b ≤ 9, and 1.0% ≤ c / a ≤ 5.0%. Where a is the mass percentage of (difluorophosphoryloxy)trifluoroborate in the electrolyte, in %; b represents the mass percentage of bis(difluorophosphoryloxy)trifluoroborate in the electrolyte, in %; c represents the mass percentage of tetrafluoroborate in the electrolyte, expressed as a percentage.

10. A secondary battery comprising (difluorophosphoryloxy)trifluoroborate, characterized in that: The (difluorophosphoryloxy)trifluoroborate is obtained by the preparation method of any one of claims 1-7.

11. A composition comprising (difluorophosphoryloxy)trifluoroborate, characterized in that: The (difluorophosphoryloxy)trifluoroborate is obtained by the preparation method of (difluorophosphoryloxy)trifluoroborate according to any one of claims 1-7. The composition comprises (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate. The content of (difluorophosphoryloxy)trifluoroborate is calculated based on a total amount of (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate and tetrafluoroborate of 100 wt%. ≥70wt%, the content of bis(difluorophosphoryloxy)trifluoroborate is ≤25wt%, and the content of tetrafluoroborate is ≤5wt%; (difluorophosphoryloxy)trifluoroborate is selected from lithium (difluorophosphoryloxy)trifluoroborate or sodium (difluorophosphoryloxy)trifluoroborate, bis(difluorophosphoryloxy)trifluoroborate is selected from lithium (difluorophosphoryloxy)trifluoroborate or sodium (difluorophosphoryloxy)trifluoroborate, and tetrafluoroborate is selected from lithium tetrafluoroborate or sodium tetrafluoroborate.

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