CN107302108B - Fire retardant siloxy fluoro cyclotriphosphazene and synthesis method thereof - Google Patents

Abstract

The invention discloses a fire retardant siloxy fluoro cyclotriphosphazene and a synthesis method thereof, wherein fluorinated cyclotriphosphazene is dissolved in an organic solvent, a siloxy compound and a catalyst are added for reaction for 0.5-72h, and fluorine atoms are replaced by siloxy groups to obtain the siloxy fluoro cyclotriphosphazene. The silicon-oxygen compound is potassium trimethylsilanolate, sodium trimethylsilanolate or lithium trimethylsilanolate. The synthesis method adopted by the invention has mild reaction conditions and good reaction controllability, and is convenient for industrial production; and the process flow is simple, reactants and solvents can be recycled, and the product purity and yield are high.

Description

A kind of flame retardant siloxy fluorine cyclotriphosphazene and its synthesis method

technical field

The invention belongs to the field of lithium ion batteries, and particularly relates to a flame retardant siloxy fluorocyclotriphosphazene and a synthesis method thereof.

Background technique

Phosphazene compounds are a class of organic-inorganic hybrid compounds whose backbones are alternately arranged by nitrogen and phosphorus, and can be divided into polyphosphazenes and cyclophosphazenes. Among them, chlorocyclotriphosphazene is the most representative compound among the cyclophosphazene compounds. Due to the strong reactivity of the chlorine atom, it is easily substituted by various nucleophiles. Therefore, using chlorocyclotriphosphazene as an intermediate, phosphazene derivatives with various organic functional groups can be synthesized.

At present, the most studied phosphazene derivatives are: hexaaniline cyclotriphosphazene, hexaethylamino cyclotriphosphazene, hexafluorocyclotriphosphazene, hexaisopropoxy cyclotriphosphazene, hexamethoxy cyclotriphosphazene Triphosphazene, hexaethoxy cyclotriphosphazene, hexa-n-propoxy cyclotriphosphazene. Phosphazene derivatives are mainly used as flame retardants.

However, as flame-retardant additives for lithium-ion battery electrolytes, the above-mentioned phosphazene derivatives have significant disadvantages. After research, it was found that hexaphenoxy cyclotriphosphazene, hexamethoxy cyclotriphosphazene, hexapropoxy cyclotriphosphazene, 1-ethoxy-1,3,3,5,5-pentafluorocyclotriphosphazene Phosphazene can not significantly improve the flash point of lithium-ion battery electrolyte, and the flame retardant temperature range is small, and the flame retardant performance varies widely with temperature, so it cannot completely prevent the battery from catching fire, burning or even explosion in the case of abuse. some security issues. In addition, the addition of flame retardant additives will have a greater negative impact on the battery performance of lithium batteries.

SUMMARY OF THE INVENTION

In order to overcome the above deficiencies, the present invention provides a method for synthesizing siloxy fluoro cyclotriphosphazene, and the prepared siloxy fluoro cyclotriphosphazene is used in high-performance lithium ion battery electrolyte additives.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for synthesizing siloxy fluorocyclotriphosphazene, comprising:

The fluorinated cyclotriphosphazene is dissolved in an organic solvent, a siloxy compound and a catalyst are added, and the reaction is carried out for 0.5-72 h to obtain the silyloxy fluorinated cyclotriphosphazene.

Preferably, the siloxy compound is potassium trimethylsiliconate, sodium trimethylsiliconate or lithium trimethylsiliconate.

Preferably, the catalyst is graphene, Raney nickel catalyst, palladium calcium carbonate, platinum oxide, ruthenium carbon, palladium carbon, aluminum-nickel alloy catalyst, rhodium carbon catalyst, anhydrous magnesium chloride or anhydrous ferric chloride.

Preferably, the material ratio of the fluorocyclotriphosphazene to the siloxy compound is 1:2-4:1.

Preferably, the reaction temperature is in the range of -30-120°C or 10-40°C.

Preferably, the fluorocyclotriphosphazene is hexafluorocyclotriphosphazene.

Preferably, the organic solvent is chlorobenzene, petroleum ether, pyridine, tetrahydrofuran, n-hexane, acetonitrile, benzonitrile, toluene, N,N-dimethylformamide (DMF), xylene or dimethylsulfone One or more mixtures of (DMSO ₂ ).

The present invention also provides the siloxy-fluoro cyclotriphosphazene prepared by any one of the above-mentioned methods, and the substitution of the siloxy group can be mono-substituted, partially-substituted or fully-substituted.

The present invention also provides the application of the above-mentioned siloxy fluorocyclotriphosphazene in the preparation of flame-retardant lithium ion batteries and electrolytes thereof.

The present invention also provides an electrolyte for a lithium ion battery, comprising: a flame retardant, the flame retardant being the above-mentioned siloxyfluorocyclotriphosphazene.

The beneficial effects of the present invention

(1) The viscosity of siloxy fluorocyclotriphosphazene is low, which ensures high conductivity of the electrolyte; it has four flame retardant elements N, P, F and Si, which have a synergistic effect, can reduce the amount of additives, and can Improve the flame retardant efficiency; the existence of F element helps to form an excellent SEI film at the electrode interface, improves the compatibility between the electrolyte and the active material, and the F element can also weaken the viscous force between molecules, making the migration resistance of molecules and ions reduce the viscosity and improve the conductivity of the electrolyte. Si element has temperature resistance characteristics and high thermal stability, which makes the electrolyte not only resistant to high temperature but also low temperature, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small. It has weather resistance and is not easily decomposed by ultraviolet light and ozone. Si element has better thermal stability, radiation resistance and weather resistance than other materials. Silicon has a lifespan of decades in the natural environment.

(2) compared with the prior art, the synthetic method adopted in the present invention has mild reaction conditions, good reaction controllability, and is convenient for industrialized production; the post-processing of the synthetic method only needs to perform suction filtration on the reacted material, and simple operations such as concentration are as follows: Products with higher quality and yield can be obtained without the need for repeated acid washing and alkali washing, thereby avoiding unnecessary losses caused by multiple washings and improving the yield. The invention has simple technological process, low energy consumption, recyclable reactants and solvents, and high product purity and yield.

(3) The preparation method of the present invention is simple, the synthesis efficiency is high, the practicability is strong, and it is easy to popularize.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Fig. 1 is the infrared spectrum of siloxyfluoro cyclotriphosphazene compounds.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, and/or combinations thereof.

In order to enable those skilled in the art to understand the technical solutions of the present invention more clearly, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

The invention provides a method for synthesizing siloxy fluoro cyclotriphosphazene, and the prepared siloxy fluoro cyclotriphosphazene is used as an electrolyte additive for high-performance lithium ion batteries.

For the siloxy fluoro cyclotriphosphazene compounds, the substitution of the siloxy group can be mono-substituted, partially-substituted or fully-substituted.

The present invention also provides a method for synthesizing siloxy fluorocyclotriphosphazene, comprising the following steps:

The fluorinated cyclotriphosphazene is dissolved in an organic solvent, a siloxy compound is added, a catalyst is selected, the reaction is carried out for 0.5-72 h, and the fluorine atom is replaced by a siloxy group to obtain a siloxy fluorine cyclotriphosphazene.

Preferably, the siloxy compound is potassium trimethylsiliconate, sodium trimethylsiliconate or lithium trimethylsiliconate. It is verified by experiments that the siloxylation effect of these three siloxy compounds is better.

In order to be able to improve the conversion rate of fluorocyclotriphosphazene, preferably, the material ratio of the fluorocyclotriphosphazene to the siloxy compound is 1:2-4:1.

Preferably, the catalyst is graphene, Raney nickel catalyst, palladium calcium carbonate, platinum oxide, ruthenium carbon, palladium carbon, aluminum-nickel alloy catalyst, rhodium carbon catalyst, anhydrous magnesium chloride, anhydrous ferric chloride and the like.

Preferably, the reaction temperature is -30-120°C.

Further preferably, the reaction temperature is 10-40°C.

Preferably, the fluorocyclotriphosphazene is hexafluorocyclotriphosphazene. Different fluorocyclotriphosphazene products can be prepared according to different raw materials.

In order to improve the reaction efficiency, preferably, the organic solvent is chlorobenzene, petroleum ether, pyridine, tetrahydrofuran, n-hexane, acetonitrile, benzonitrile, toluene, N,N-dimethylformamide (DMF), One or more mixtures of toluene or dimethyl sulfone (DMSO ₂ ).

Application of siloxy fluoro cyclotriphosphazene compound in preparing lithium ion battery electrolyte, specifically, the siloxy fluoro cyclotriphosphazene is used as a flame retardant for lithium ion battery electrolyte.

Wherein, the lithium ion battery electrolyte consists of four types of components: lithium salts, carbonate and/or ether organic solvents, phosphazene derivatives flame retardant additives and other functional additives, the phosphazene derivatives The flame retardant additive is siloxy pentafluorocyclotriphosphazene.

Wherein, the lithium salt is one of LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiBOB (lithium dioxalate borate) and LiN (CF ₃ SO ₂ ) ₂ or a mixture thereof .

The carbonate-based organic solvent is a cyclic carbonate-based compound and/or a chain carbonate-based compound.

The cyclic carbonate compound is one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL) and butylene carbonate. The chain carbonate compound is preferably selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), and a straight carbon number of 3-8. One or more of the carbonate derivatives synthesized from chain or branched aliphatic monoalcohols and carbonic acid.

The ether organic solvent is selected from tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane and diglyme one or more of them.

Other functional additives are one or more of the following compounds coexisting: biphenyl (BP), vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), propylene sulfite Esters, butenyl sulfite, 1,3-(1-propene) sultone, vinyl sulfite (ES), vinyl sulfate, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene and butylated cyanide .

The present invention adopts fluorinated cyclotriphosphazene, and replaces fluorine atoms with siloxy groups to obtain siloxy fluorinated cyclotriphosphazenes. Among them, the two flame retardant elements P and F in siloxyfluorocyclotriphosphazene are directly connected, which can increase the binding force between siloxyfluorocyclotriphosphazene and carbonate and/or ether organic solvents , reducing the volatility of carbonate organic solvents, thereby further improving the safety of the battery; P and Si are connected through an oxygen atom, which not only effectively reduces the release of flammable gases, but also increases the flash point of the additive. , thereby increasing the flash point of the electrolyte. The adopted phosphazene fluorinated ring structure effectively connects the four flame retardant elements together, which not only has no negative impact on the battery performance of the lithium battery, but can instead improve the battery cycle stability and battery capacity retention rate. It is found through experiments that the present invention adopts the phosphazene fluorinated ring structure to connect the four flame retardant elements together, and the flame retardant elements are compact, which not only reduces the usage amount of the flame retardant additives, makes the flame retardant effect excellent, but also improves the battery performance. The improved cycle stability and battery capacity retention rate are technical effects that cannot be expected by those skilled in the art.

Example 1:

Dissolve 49.8g of hexafluorocyclotriphosphazene crystals in 200ml of tetrahydrofuran to form a hexafluorocyclotriphosphazene solution, add 12.9g of potassium trimethylsiliconate and a small amount of graphene as a catalyst to the solution, stir until uniform, and at 10 The reaction was carried out at a temperature of ℃ for 20 hours. After filtration and vacuum distillation, the phosphazene derivative, siloxyfluorocyclotriphosphazene, was obtained with the following structural formula, and the yield was 95%. .

Example 2:

49.8 g of hexafluorocyclotriphosphazene crystals were dissolved in 300 ml of n-hexane to form a hexafluorocyclotriphosphazene solution, 12.9 g of potassium trimethylsiliconate and an appropriate amount of Raney nickel were added to the solution as catalysts, stirred until uniform, and added to the solution. The reaction was carried out at a temperature of 40 °C for 10 h, and the phosphazene derivative, siloxyfluorocyclotriphosphazene, was obtained after filtration and distillation under reduced pressure, and the yield was 96%.

Example 3:

49.8g of hexafluorocyclotriphosphazene crystals were dissolved in 200ml of chlorobenzene to form a hexafluorocyclotriphosphazene solution, 12.9g of potassium trimethylsiliconate and a small amount of graphene were added to the solution as catalysts, stirred until uniform, and placed in the solution. The reaction was carried out at a temperature of 30 °C for 15 h, and the phosphazene derivative siloxyfluorocyclotriphosphazene was obtained after filtration and distillation under reduced pressure, and the yield was 95%.

Example 4:

This example is the same as Example 1, except that tetrahydrofuran is changed to petroleum ether, and potassium trimethylsilanolate is changed to sodium trimethylsiliconate to obtain phosphazene derivative siloxy fluorocyclotriphosphazene , the yield was 97%.

Example 5:

This example is the same as Example 1, except that tetrahydrofuran is changed to pyridine, and potassium trimethylsilanolate is changed to sodium trimethylsiliconate to obtain a phosphazene derivative, siloxyfluorocyclotriphosphazene, Yield was 96%.

Example 6:

This example is the same as Example 1, except that tetrahydrofuran is changed to DMF, and potassium trimethylsilanolate is changed to sodium trimethylsiliconate to obtain a phosphazene derivative, siloxyfluorocyclotriphosphazene, Yield was 97%.

Example 7:

This example is the same as Example 1, except that tetrahydrofuran is changed to acetonitrile, and potassium trimethylsilanolate is changed to lithium trimethylsiliconate to obtain a phosphazene derivative, siloxyfluorocyclotriphosphazene, Yield was 96%.

Example 8:

This example is the same as Example 1, except that tetrahydrofuran is changed to benzonitrile, and potassium trimethylsilanolate is changed to lithium trimethylsiliconate to obtain phosphazene derivative siloxyfluorocyclotriphosphine Nitrile in 97% yield.

Example 9:

This example is the same as Example 1, except that tetrahydrofuran is changed to a mixture of tetrahydrofuran and petroleum ether, and potassium trimethylsilanolate is changed to lithium trimethylsiliconate to obtain a phosphazene derivative siloxy fluoride. Cyclotriphosphazene in 95% yield.

Experimental Examples 1 to 32 Flame Retardant Effect

The present invention, as a phosphazene derivative type flame retardant, is different from the previous type of flame retardant in that the siloxyfluoro cyclotriphosphazene contains element Si. The element Si has temperature resistance characteristics and high thermal stability, which makes the electrolyte not only resistant to high temperature but also low temperature, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small. It has weather resistance and is not easily decomposed by ultraviolet light and ozone. Si element has better thermal stability, radiation resistance and weather resistance than other materials. Silicon has a lifespan of decades in the natural environment.

The present invention lists the component compositions of 32 kinds of flame-retardant electrolyte solutions and the test data of the self-extinguishing time of each electrolyte solution in tabular form, and the specific data is as follows in Table 1.

Table 1 Composition and self-extinguishing time of various electrolytes

Available from Table 1, the electrolyte in the present invention is added with siloxy pentafluorocyclotriphosphazene flame retardant additive, which can significantly improve the flame retardant performance of the electrolyte. As in the electrolyte in Experimental Example 18, its organic solvent is the volume of The ratio of EC/DEC/EMC is 1:1:1, which contains 0.3mol/L LiClO ₄ , 0.2mol/L VC and 6% siloxy pentafluorocyclotriphosphazene flame retardant additive, which can achieve completely no flame retardancy. Combustible effect (self-extinguishing time is 0s), the mass fraction of flame retardant additives in the electrolyte generally reaches 10-40% in the prior art to have a better non-flammable effect, but the flame retardant with a higher mass fraction is flame retardant. Additives will increase the viscosity of the electrolyte, affect the conductivity of the electrolyte, and then affect the battery performance of the lithium battery.

It can also be seen from this table 1 that different organic solvents and other functional additives have different effects on the flame retardant properties of the electrolyte. , when the content of flame retardant additives is small, it can play a completely non-flammable effect.

Experimental example 33 Battery capacity effect of lithium ion battery

The electrolyte solution described in Experimental Example 18 was injected into a commercial LiMn ₂ O ₄ /graphite lithium-ion battery for charge and discharge experiments. It is concluded that after the battery is cycled for 20 weeks, the capacity retention rate of the battery without the flame retardant additive is 90%, and the capacity retention rate of the battery containing the flame retardant additive is 94%.

The electrolyte solution described in Experimental Example 24 was injected into a commercial LiMn ₂ O ₄ /graphite lithium-ion battery for charge and discharge experiments. It was concluded that after 20 cycles of battery cycle, the capacity retention rate of the battery without flame retardant additive was 89%, and the capacity retention rate of the battery containing flame retardant additive was 93%.

The flame retardant additives in the prior art can reduce the flammability of the electrolyte, but most of the flame retardant additives have a large negative impact on the performance of lithium batteries, and a few flame retardant additives will also reduce the battery performance of lithium batteries. After the flame retardant additives in this application are added, under the premise of ensuring excellent flame retardant effect, adding a small amount of flame retardant additives not only has no negative impact on the battery performance of lithium batteries, but can improve the battery cycle stability and battery capacity. The retention rate can be used as a safety additive in practical batteries, which is a technical effect that cannot be achieved by conventional flame retardant additives for lithium battery electrolytes in the prior art. When the content of the flame retardant additive is high, it will affect the conductivity of the electrolyte, the cycle stability of the battery and the battery capacity retention rate.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (10)

1. A synthetic method of siloxy fluoro cyclotriphosphazene is characterized by comprising the following steps:

dissolving fluorinated cyclotriphosphazene in an organic solvent, adding a siloxy compound and a catalyst, and reacting for 0.5-72h to obtain siloxy fluoro cyclotriphosphazene;

the siloxy compound is potassium trimethylsilanolate, sodium trimethylsilanolate or lithium trimethylsilanolate.

2. The method of claim 1, wherein the catalyst is graphene, raney nickel catalyst, palladium calcium carbonate, platinum oxide, ruthenium carbon, palladium carbon, aluminum nickel alloy catalyst, rhodium carbon catalyst, anhydrous magnesium chloride, or anhydrous iron chloride.

3. The method of claim 1, wherein the ratio of the amount of species of fluorocyclotriphosphazene to siloxy compound is from 1:2 to 4: 1.

4. The process of claim 1, wherein the reaction temperature is in the range of-30 to 120 ℃.

5. The method of claim 4, wherein the reaction temperature is in the range of 10 to 40 ℃.

6. The method of claim 1, wherein the fluorocyclotriphosphazene is hexafluorocyclotriphosphazene.

7. The method of claim 1, wherein the organic solvent is chlorobenzene, petroleum ether, pyridine, tetrahydrofuran, N-hexane, acetonitrile, benzonitrile, toluene, N-Dimethylformamide (DMF), xylene, or Dimethylsulfone (DMSO)₂) One or more mixtures thereof.

8. A siloxy fluorocyclotriphosphazene prepared by the process of any one of claims 1 to 7, wherein the substitution of the siloxy groups is partial or full.

9. The use of the siloxy fluorocyclotriphosphazene according to claim 8 in the preparation of a flame retardant lithium ion battery electrolyte.

10. A lithium ion battery electrolyte, comprising: a flame retardant which is the siloxy fluorocyclotriphosphazene of claim 9.

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