CN114957317B - Lithium cyanophosphate and preparation method and application thereof - Google Patents

Abstract

The present invention provides a lithium cyanophosphate, wherein the lithium cyanophosphate has a structure as shown in formula (I) or formula (II). The present invention designs a lithium cyanophosphate with a specific structure, which is a lithium salt compound with a novel structure. Moreover, the preparation method of the lithium cyanophosphate provided by the present invention, in particular, adopts a by-product precipitating agent, which can promote the synthesis of reaction intermediates, and adopts an inorganic lithium salt reactant, which can also promote the conversion of reaction intermediates to target products. The preparation method provided by the present invention has a simple synthesis process, a high yield, and low energy consumption, and is more suitable for industrial and large-scale production and application.

Description

Lithium cyanophosphate and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium ion battery electrolytes and relates to lithium cyanophosphate and a preparation method and application thereof.

Background Art

Lithium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work. During the charge and discharge process, Li ⁺ is intercalated and deintercalated back and forth between the two electrodes: during charging, Li ⁺ is deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharge, the opposite is true. Batteries generally use materials containing lithium elements as electrodes and are the representative of modern high-performance batteries. Lithium-ion batteries usually include positive electrodes, negative electrodes, diaphragms, electrolytes and shells. They have the advantages of high operating voltage, high specific energy, long cycle life, light weight, low self-discharge, no memory effect and high performance-price ratio. They have become the main choice of rechargeable power sources in high-power electric vehicles, artificial satellites, aerospace and other fields. With the widespread application of lithium-ion batteries in 3C, energy storage, power and other fields, how to improve their energy density has become the focus of current research. The way to achieve high energy density of batteries is to increase the capacity of positive and negative electrodes or to increase the operating voltage of the battery. The decomposition voltage of commercial carbonate electrolytes is 4.3V. When the voltage is higher than 4.3V, the electrolyte decomposes severely and is accompanied by a large amount of gas generation, which reduces the service life of the battery and causes safety problems.

In order to further broaden the working voltage of the electrolyte, nitriles are widely studied as electrolyte additives in the industry. Since the -C≡N bond energy in nitriles is relatively high, they are not easily oxidized and have good stability at the positive electrode. In addition, this type of compound has a strong coordination ability, can complex or adsorb metal ions, inhibit gas production at the negative electrode, and improve high-temperature cycle performance. However, as an electrolyte additive, the amount of nitrile added is usually less than 5%, and most of it is free in the electrolyte, resulting in a low content of nitrile additives that really work. Moreover, there are currently few reports on related compounds, and there are only some related literature on cyanophosphate chemicals.

Therefore, as downstream application industries gradually increase their requirements for the performance of lithium-ion batteries, further developing more types of lithium-ion electrolyte additives has become one of the urgent issues to be solved by many front-line researchers and scientific research companies in this field.

Summary of the invention

In view of this, the present invention provides a lithium cyanophosphate and a preparation method and application thereof, in particular, lithium cyanophosphate and a preparation method thereof. The lithium salt provided by the present invention has a novel structure, and the preparation and purification process is simple and feasible. The product can be used in lithium ion battery electrolyte additives, solid electrolytes, and diaphragm coating materials.

The present invention provides a lithium cyanophosphate, wherein the lithium cyanophosphate has a structure as shown in formula (I) or formula (II):

Wherein, R ₁ in formula (I) or formula (II) is independently selected from a haloalkylene group or an alkylene group;

The _R2 is selected from a haloalkylene group or an alkylene group.

Preferably, the lithium cyanophosphate is an additive for lithium ion batteries;

The lithium ion battery is specifically a lithium ion battery electrolyte;

The mass content of the lithium cyanophosphate in the electrolyte is 0.5% to 5%.

The present invention also provides a method for preparing lithium cyanophosphate as described in any one of the above technical solutions, comprising the following steps:

1) mixing a compound having a structure of formula (1) and a hydrogen halide chelating agent to obtain a mixture A;

The compound having the structure of formula (2) and an organic solvent are mixed to obtain a mixture B;

Wherein, R ₁ is selected from haloalkylene or alkylene;

X is selected from halogen;

2) Mixing mixture A and mixture B again under low temperature conditions, and then heating them to continue the reaction, thereby obtaining a mixture containing a reaction intermediate;

3) The filtrate of the mixture containing the reaction intermediate obtained in the above step is filtered, mixed with water and an organic extractant, and the organic phase is separated to obtain an aqueous phase, and then an inorganic lithium salt solution is added to react again to obtain lithium cyanophosphate having a structure shown in formula (I) and/or formula (II).

Preferably, the hydrogen halide chelating agent includes one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine;

The molar ratio of the hydrogen halide chelating agent to the compound having the structure of formula (1) is (3-6): 1;

The organic solvent includes one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane;

The volume ratio of the organic solvent to the compound having the structure of formula (2) is 1:(1-10).

Preferably, the molar ratio of the compound having the structure of formula (1) to the compound having the structure of formula (2) is (1-3): (3-1);

By adjusting the molar ratio of the compound having the structure of formula (1) to the compound having the structure of formula (2), lithium cyanophosphate salts containing only formula (I) or (II) can be synthesized.

Preferably, the remixing is specifically, slowly dropping the mixture A of step 1) into the mixture B at low temperature and under stirring;

The slow dripping rate is 5-20 ml/h;

The temperature of the low temperature condition is -20 to 10°C;

The temperature of the continued reaction is 15-35°C.

Preferably, the continued reaction time is 5 to 20 hours;

The organic extractant includes one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane;

The inorganic lithium salt includes one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide and lithium acetate;

The concentration of the inorganic lithium salt solution is 0.001-1 mol/L.

Preferably, the cutoff condition for the second reaction is to react to neutrality;

After the second reaction, one or more steps of distillation, washing, separation and drying are further included;

The washing specifically comprises washing multiple times with an organic solvent insoluble in lithium cyanophosphate;

The organic solvent insoluble in lithium cyanophosphate includes one or more of methanol, ethanol, dichloromethane, n-hexane, petroleum ether and isopropanol.

The present invention also provides the use of the lithium cyanophosphate described in any one of the above technical solutions or the lithium cyanophosphate prepared by the preparation method described in any one of the above technical solutions in lithium ion batteries.

Preferably, the lithium-ion battery comprises a high-voltage lithium-ion battery;

The lithium-ion battery is specifically an electrolyte of a lithium-ion battery;

The lithium cyanophosphate is used as an additive for lithium ion battery electrolyte;

The mass content of the lithium cyanophosphate in the lithium ion battery electrolyte is 0.5% to 5%.

The present invention provides a lithium cyanophosphate, wherein the lithium cyanophosphate has a structure as shown in formula (I) or formula (II). Compared with the prior art, the present invention believes that the prior art only discloses a cyanophosphate ester compound, and the preparation method is loaded, and the product is not a lithium salt.

The present invention particularly designs a lithium cyanophosphate with a specific structure, which is a lithium salt compound with a novel structure. When the lithium cyanophosphate provided by the present invention is used for surface modification of the diaphragm, it can not only provide a large amount of cyano groups to inhibit the diffusion of transition metal ions to the negative electrode, but also improve the compatibility of the diaphragm with the electrolyte and increase its heat resistance.

The present invention also creatively provides a preparation method of the lithium cyanophosphate, in particular, the use of a by-product precipitating agent can promote the synthesis of the reaction intermediate, and the use of an inorganic lithium salt reactant can also promote the conversion of the reaction intermediate to the target product. The preparation method provided by the present invention has a simple synthesis process, a high yield, low energy consumption, and is more suitable for industrial and large-scale production and application.

The experimental results show that the present invention prepares lithium cyanophosphate with a specific structure, and the yield is 80%, and the purity after purification is >98%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a SEM image of lithium cyanoethyl phosphate prepared in Example 1 of the present invention;

FIG2 is an XRD diffraction pattern of lithium cyanoethyl phosphate prepared in Example 1 of the present invention;

FIG3 is an FT-IR spectrum of lithium cyanoethyl phosphate prepared in Example 1 of the present invention;

FIG4 is a ³¹ P NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent;

FIG5 is a ¹ H NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent;

FIG6 is a ¹³ C NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent;

FIG. 7 is a graph showing the cycling stability of lithium cyanoethyl phosphate prepared in Example 1 of the present invention for use in lithium ion batteries.

DETAILED DESCRIPTION

In order to further understand the present invention, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

There is no particular restriction on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials of conventional purity in the field of lithium-ion battery electrolytes.

The present invention provides a lithium cyanophosphate, wherein the lithium cyanophosphate has a structure as shown in formula (I) or formula (II):

Wherein, R ₁ in formula (I) or formula (II) is independently selected from a haloalkylene group or an alkylene group;

The _R2 is selected from a haloalkylene group or an alkylene group.

In the present invention, the lithium cyanophosphate is preferably an additive for lithium ion batteries.

In the present invention, the lithium ion battery is preferably a lithium ion battery electrolyte.

In the present invention, the mass content of the lithium cyanophosphate in the lithium ion battery electrolyte is preferably 0.5% to 5%, more preferably 1% to 5%, and more preferably 2% to 4%.

The present invention provides a method for preparing lithium cyanophosphate according to any one of the above technical solutions, comprising the following steps:

1) mixing a compound having a structure of formula (1) and a hydrogen halide chelating agent to obtain a mixture A;

The compound having the structure of formula (2) and an organic solvent are mixed to obtain a mixture B;

Wherein, R1 is selected from haloalkylene or alkylene;

X is selected from halogen;

2) Mixing mixture A and mixture B again under low temperature conditions, and then heating them to continue the reaction, thereby obtaining a mixture containing a reaction intermediate;

3) The filtrate of the mixture containing the reaction intermediate obtained in the above step is filtered, mixed with water and an organic extractant, and the organic phase is separated to obtain an aqueous phase, and then an inorganic lithium salt solution is added to react again to obtain lithium cyanophosphate having a structure shown in formula (I) and/or formula (II).

The present invention firstly mixes a compound having a structure of formula (1) and a hydrogen halide chelating agent to obtain a mixture A;

The compound having the structure of formula (2) and an organic solvent are mixed to obtain a mixture B;

Wherein, R ₁ is selected from haloalkylene or alkylene;

X is selected from halogen;

In the present invention, the hydrogen halide chelating agent preferably includes one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine, more preferably triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine or pyridine.

In the present invention, the molar ratio of the hydrogen halide chelating agent to the compound having the structure of formula (1) is preferably (3-6):1, more preferably (3.5-5.5):1, and more preferably (4-5):1.

In the present invention, the organic solvent preferably includes one or more of toluene, n-hexane, petroleum ether, diethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane, and more preferably toluene, n-hexane, petroleum ether, diethyl ether, tert-methyl butyl ether, dichloromethane or dichloroethane.

In the present invention, the volume ratio of the organic solvent to the compound having the structure of formula (2) is preferably 1:(1-10), more preferably 1:(3-8), and more preferably 1:(5-6).

In the present invention, the molar ratio of the compound having the structure of formula (1) to the compound having the structure of formula (2) is preferably (1-3):(3-1), more preferably (1.4-2.6):(3-1), more preferably (1.8-2.2):(3-1), more preferably (3-1):(1.4-2.6), more preferably (3-1):(1.8-2.2).

In the present invention, the molar ratio of the compound having the structure of formula (1) to the compound having the structure of formula (2) is adjusted, and preferably a lithium cyanophosphate salt containing only formula (I) or (II) can be synthesized.

In the present invention, mixture A and mixture B are mixed again under low temperature conditions, and then the temperature is raised to continue the reaction to obtain a mixture containing a reaction intermediate.

In the present invention, the remixing is preferably performed by slowly dropping the mixture A in step 1) into the mixture B at low temperature and under stirring.

In the present invention, the slow dripping rate is preferably 5 to 20 ml/h, more preferably 8 to 17 ml/h, and more preferably 11 to 14 ml/h.

In the present invention, the temperature of the low temperature condition is preferably -20 to 10°C, more preferably -15 to 5°C, and even more preferably -10 to 0°C.

In the present invention, the temperature of the continued reaction is preferably 15 to 35°C, more preferably 19 to 31°C, and more preferably 23 to 27°C.

In the present invention, the continued reaction time is preferably 5 to 20 hours, more preferably 8 to 17 hours, and more preferably 11 to 14 hours.

In the present invention, the filtrate obtained by filtering the mixture containing the reaction intermediate obtained in the above steps is mixed with water and an organic extractant, and the organic phase is removed by separation to obtain an aqueous phase, and then an inorganic lithium salt solution is added to react again to obtain lithium cyanophosphate having a structure shown in formula (I) and/or formula (II).

In the present invention, the organic extractant preferably includes one or more of toluene, n-hexane, petroleum ether, diethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane, and more preferably toluene, n-hexane, petroleum ether, diethyl ether, tert-methyl butyl ether, dichloromethane or dichloroethane.

In the present invention, the inorganic lithium salt preferably includes one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide and lithium acetate, and more preferably lithium carbonate, lithium bicarbonate, lithium hydroxide or lithium acetate.

In the present invention, the concentration of the inorganic lithium salt solution is preferably 0.001-1 mol/L, more preferably 0.005-0.9 mol/L, more preferably 0.01-0.8 mol/L, more preferably 0.1-0.7 mol/L, more preferably 0.2-0.6 mol/L, more preferably 0.3-0.5 mol/L.

In the present invention, the cut-off condition for the second reaction is preferably to react to neutrality.

In the present invention, after the second reaction, it is preferred to include one or more steps of distillation, washing, separation and drying, and more preferably multiple steps of distillation, washing, separation and drying.

In the present invention, the washing is preferably performed multiple times using an organic solvent insoluble in lithium cyanophosphate.

In the present invention, the organic solvent insoluble in lithium cyanophosphate preferably includes one or more of methanol, ethanol, dichloromethane, n-hexane, petroleum ether and isopropanol, more preferably methanol, ethanol, dichloromethane, n-hexane, petroleum ether or isopropanol.

The present invention provides the use of the lithium cyanophosphate described in any one of the above technical solutions or the lithium cyanophosphate prepared by the preparation method described in any one of the above technical solutions in a lithium ion battery.

In the present invention, the lithium ion battery preferably includes a high voltage lithium ion battery.

In the present invention, the lithium ion battery is preferably an electrolyte of a lithium ion battery.

In the present invention, the lithium cyanophosphate is preferably used as an additive for lithium ion battery electrolyte.

In the present invention, the mass content of the lithium cyanophosphate in the lithium ion battery electrolyte is preferably 0.5% to 5%, more preferably 1% to 5%, and more preferably 2% to 4%.

The present invention is to complete and refine the overall preparation process, better ensure the structure and performance of the lithium cyanophosphate salt having formula (I) or (II), improve the efficiency of the preparation process and the performance of the lithium cyanophosphate electrolyte for lithium ion batteries, and the preparation method of the lithium cyanophosphate can specifically be the following steps:

1) adding a mixture A of a raw material 1 of the general formula (1-1) and a hydrogen halide chelating agent into a dropping funnel;

In the formula, _R1 represents a halogenated alkylene group or an alkylene group.

2) Adding a mixed solution B of a raw material 2 of the general formula (1-2) and an organic diluent solvent into a three-necked flask;

In the formula, X represents a halogen atom.

3) slowly adding the mixture A of step 1) dropwise to the mixture B of step 2) under low temperature and vigorous stirring;

4) slowly returning the mixed solution after the reaction in step 3) to 15-35° C. and continuing the reaction for 5-20 hours;

5) filtering and separating the mixed solution after the reaction in step 4), dissolving the filtrate in water, adding an organic extractant thereto, separating and removing the organic phase, and obtaining an aqueous phase solution containing the reaction intermediate;

6) adding a certain concentration of inorganic lithium salt solution to the aqueous solution of the reaction intermediate obtained in step 5) and reacting until neutral to obtain a mixed solution containing lithium cyanophosphate;

7) The solution containing lithium cyanophosphate in step 6) is subjected to reduced pressure distillation to remove the solvent, and then washed multiple times with an organic solvent insoluble in lithium cyanophosphate and centrifuged and dried to obtain pure lithium cyanophosphate of general formula (I) or (II).

In the formula, R ₁ and R ₂ may be the same or different, and R ₁ and R ₂ represent a halogenated alkylene group or an alkylene group.

In the formula, _R1 represents a halogenated alkylene group or an alkylene group.

Specifically, the hydrogen halide chelating agent in step 1) is selected from one or a mixture of two or more of the following substances: triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine, pyridine, and the molar ratio of the hydrogen halide chelating agent to the raw material 1 is 3:1 to 6:1, preferably 3:1 to 4:1;

Specifically, the molar ratio of the raw material 1 in step 1) to the raw material 2 in step 2) is 1:3 to 3:1. Depending on the ratio of the raw material 1 to the raw material 2, lithium cyanophosphate containing only the general formula (I) or (II) can be synthesized respectively.

Specifically, the organic solvent described in step 2) is one or a mixture of two or more selected from the following substances: toluene, n-hexane, petroleum ether, ether, tert-methyl butyl ether, dichloromethane, dichloroethane, the volume ratio of the diluent to the raw material 2 is 1:1 to 10:1, preferably 2:1 to 3:1, and the dripping rate is 5 to 20 ml/h, preferably 10 to 15 ml/h.

Specifically, the low temperature reaction temperature of the reaction in step 3) is -20°C to 10°C, preferably -10°C to -5°C.

Specifically, the reaction temperature in step 4) is 15°C to 35°C, preferably 20°C to 30°C, and the reaction time is 5 to 20 hours, preferably 15 hours.

Specifically, the organic extractant in step 5) is one or a mixture of two or more selected from the following substances: toluene, n-hexane, petroleum ether, diethyl ether, tert-methyl butyl ether, dichloromethane, and dichloroethane.

Specifically, the inorganic lithium salt described in step 6) is one or a mixture of two or more selected from the following substances: lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium acetate, etc., with a concentration of 0.001 to 1 mol/L, preferably 0.1 to 0.5 mol/L.

Specifically, the organic solvent insoluble in lithium cyanophosphate in step 7) is one or a mixture of two or more selected from the following substances: methanol, ethanol, dichloromethane, n-hexane, petroleum ether, and isopropanol.

In the present invention, when a raw material 1 of the general formula (1-1) is mixed with a raw material 2 of the general formula (1-2), -OH in the raw material 1 and -X in the raw material 2 undergo a substitution reaction to obtain a reaction intermediate of the general formula (7-1) or (7-2); after the reaction intermediate is dissolved in water, the reaction intermediate undergoes a hydrolysis reaction to obtain a hydrolysis product of the general formula (7-3) or (7-4); when the hydrolysis product of the general formula (7-3) or (7-4) is reacted with an inorganic lithium salt, lithium cyanophosphate of the general formula (I) or (II) is obtained;

In the formula, R1 represents a halogenated alkylene group or an alkylene group.

In the formula, X represents a halogen atom.

In the formula, _R1 represents a halogenated alkylene group or an alkylene group, and X represents a halogen atom.

In the formula, R ₁ and R ₂ may be the same or different, R ₁ and R ₂ represent a halogenated alkylene group or an alkylene group, and X represents a halogen atom.

In the formula, _R1 represents a halogenated alkylene group or an alkylene group.

In the formula, R ₁ and R ₂ may be the same or different, and R ₁ and R ₂ represent a halogenated alkylene group or an alkylene group.

In the formula, R ₁ and R ₂ may be the same or different, and R ₁ and R ₂ represent a halogenated alkylene group or an alkylene group.

In the formula, _R1 represents a halogenated alkylene group or an alkylene group.

In the present invention, in order to obtain the above-mentioned compound, the ratio of raw material 1 to raw material 2 is precisely controlled to generate lithium cyanophosphate salts containing only general formula (1-3) or (1-4).

In the present invention, in order to obtain the above-mentioned compound, the organic solution dilutes the raw material 2, controls the reaction rate, and makes the reaction more complete, which can further improve the yield of the product compound.

In the present invention, in order to obtain the above-mentioned compound, a low temperature reaction is selected because the reaction is an exothermic reaction, and the temperature is -20°C to 10°C, preferably -10°C to -5°C.

In the present invention, in order to obtain the above-mentioned compound, an organic base is selected as a hydrogen halide chelating agent, and the organic base is triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine, pyridine, and the molar ratio of the hydrogen halide chelating agent to the general formula (1-2) is 3:1 to 6:1, preferably 3:1 to 4:1, which can further improve the yield of the product compound.

In the present invention, in order to obtain the above-mentioned compound, an organic base is selected as a hydrogen halide chelating agent, and the organic base is triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine, pyridine, and the molar ratio of the hydrogen halide chelating agent to the general formula (1-2) is 3:1 to 6:1, preferably 3:1 to 4:1, which can further improve the yield of the product compound.

In the present invention, in order to obtain the above-mentioned compound, the addition of dichloromethane in step (4) is beneficial to the precipitation of pyridine hydrochloride, which can further improve the yield of the product compound.

In the present invention, in order to obtain the above-mentioned high-purity lithium salt, the solvent in the lithium salt solution is removed by vacuum distillation, and an organic cleaning agent insoluble in lithium cyanophosphate is added for cleaning and centrifugation, and the hydrogen halide chelating agent, organic diluent and excess raw material 1 and raw material 2 are dissolved in organic cleaning. Specifically, one or a mixture of two or more of methanol, ethanol, dichloromethane, n-hexane, petroleum ether, and isopropanol can be used as the cleaning agent, and the obtained product is dried to obtain high-purity lithium cyanophosphate.

The above steps of the present invention provide a lithium cyanophosphate and a preparation method and application thereof. The present invention provides a lithium cyanophosphate with a specific structure, which is a lithium salt compound with a novel structure. When the lithium cyanophosphate provided by the present invention is used for surface modification of a diaphragm, it can not only provide a large amount of cyano groups to inhibit the diffusion of transition metal ions to the negative electrode, but also improve the compatibility of the diaphragm with the electrolyte and increase its heat resistance.

The present invention also creatively provides a preparation method of the lithium cyanophosphate, in particular, the use of a by-product precipitating agent can promote the synthesis of the reaction intermediate, and the use of an inorganic lithium salt reactant can also promote the conversion of the reaction intermediate to the target product. The preparation method provided by the present invention has a simple synthesis process, a high yield, low energy consumption, and is more suitable for industrial and large-scale production and application.

The experimental results show that the present invention prepares lithium cyanophosphate with a specific structure, and the yield is 80%, and the purity after purification is >98%.

In order to further illustrate the present invention, a lithium cyanophosphate provided by the present invention and its preparation method and application are described in detail in combination with the following examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The protection scope of the present invention is not limited to the following examples.

The reagents used in the following examples of the present invention are all commercially available products.

Example 1

(1) adding a mixed solution of 0.1 mol of 3-hydroxypropionitrile and 0.4 mol of triethylamine into a three-necked flask, and controlling the reaction temperature to be below -10°C;

(2) Mix 0.2 mol of POBr ₃ and 100 ml of petroleum ether and place them in a constant pressure dropping funnel;

(3) adding the mixed solution of step (1) dropwise to the mixed solution of step (2) at a rate of 10 ml/h;

(4) After the addition was complete, 50 ml of dichloroethane was added dropwise, and the reaction temperature was slowly raised to 20°C and reacted for 15 hours;

(5) adding 100 ml of dichloromethane to the solution after the reaction for extraction, filtering out triethylamine hydrochloride and distilling the filtrate under reduced pressure to obtain a crude reaction intermediate;

(6) Add the crude reaction intermediate to ice water to dissolve, then add dichloroethane and stir thoroughly, then use a separatory funnel to separate the liquid to obtain an aqueous phase (the product is extracted into the aqueous phase);

(7) adding 0.2 mol/L Li ₂ CO ₃ solution dropwise to the reaction intermediate aqueous solution, and reacting until the pH reaches 7.0 to obtain a mixed solution containing lithium cyanophosphate;

(8) The solution containing lithium cyanophosphate is subjected to reduced pressure distillation to remove the solvent, and then washed with methanol for multiple times, centrifuged, and dried to obtain pure lithium cyanophosphate.

The lithium cyanophosphate prepared by the present invention is characterized.

See FIG. 1 , which is a SEM image of lithium cyanoethyl phosphate prepared in Example 1 of the present invention.

See FIG. 2 , which is an XRD diffraction pattern of lithium cyanoethyl phosphate prepared in Example 1 of the present invention.

See FIG. 3 , which is an FT-IR spectrum of lithium cyanoethyl phosphate prepared in Example 1 of the present invention.

See FIG. 4 , which is a ³¹ P NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent.

See FIG. 5 , which is a ¹ H NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent.

See FIG. 6 , which is a ¹³ C NMR graph of lithium cyanoethyl phosphate prepared in Example 1 of the present invention using deuterated DMSO as solvent.

The lithium cyanophosphate prepared by the present invention was subjected to electrochemical tests.

Lithium cyanophosphate was used as an electrolyte additive for lithium cobalt oxide/graphite soft-pack batteries, and the cycle performance of the lithium cobalt oxide/graphite soft-pack batteries at 3.0-4.45V and 1C rate charge and discharge was tested under a high temperature environment of 55°C. The conventional electrolyte mainly contained an organic solvent, a lithium salt and an additive. The organic solvent was composed of a cyclic carbonate solvent (PC, EC and FEC) and a linear carbonate (EMC). The weight ratio of PC:EC:EMC was 1:2:7, the amount of FEC was 6wt.% of the organic solvent, the concentration of lithium hexafluorophosphate in the organic solvent was 1mol/L, and the conventional additive was propane sultone in an amount of 2wt.%. Adding 2wt.% of lithium cyanophosphate to the conventional electrolyte additives gave the lithium ion battery electrolyte described in this embodiment.

See FIG. 7 , which is a graph showing the cycle stability of lithium cyanoethyl phosphate prepared in Example 1 of the present invention for use in lithium ion batteries.

Example 2

(1) Add 0.2 mol of a mixed solution of 4-hydroxyhexafluorobutyronitrile and 0.4 mol of diethylamine into a three-necked flask, and control the reaction temperature to be below -10°C;

(2) Mix 0.2 mol of POBr ₃ and 100 ml of ether and place in a constant pressure dropping funnel;

(3) adding the mixed solution of step (1) dropwise to the mixed solution of step (2) at a rate of 10 ml/h;

(4) After the addition was complete, 50 ml of dichloromethane was added dropwise, and the reaction temperature was slowly raised to 20°C and reacted for 15 hours;

(5) adding 100 ml of dichloromethane to the reaction solution for extraction, filtering out diethylamine hydrochloride and distilling the filtrate under reduced pressure to obtain a crude reaction intermediate;

(6) Add the crude reaction intermediate to ice water to dissolve, then add dichloromethane and stir thoroughly, then use a separatory funnel to separate the liquid to obtain an aqueous phase (the product is extracted into the aqueous phase);

(7) adding 0.2 mol/L Li ₂ CO ₃ solution dropwise to the reaction intermediate aqueous solution, and reacting until the pH reaches 7.0 to obtain a mixed solution containing lithium cyanophosphate;

(8) The solution containing lithium cyanophosphate is subjected to reduced pressure distillation to remove the solvent, and then washed with methanol for multiple times, centrifuged, and dried to obtain pure lithium cyanophosphate.

Example 3

(1) Add 0.2 mol of a mixed solution of 4-hydroxyhexafluorobutyronitrile and 0.4 mol of diethylamine into a three-necked flask, and control the reaction temperature to be below -10°C;

(2) Mix 0.4 mol of POBr ₃ and 100 ml of petroleum ether and place them in a constant pressure dropping funnel;

(3) adding the mixed solution of step (1) dropwise to the mixed solution of step (2) at a rate of 10 ml/h;

(4) After the addition was complete, 50 ml of dichloromethane was added dropwise, and the reaction temperature was slowly raised to 20°C and reacted for 15 hours;

(5) adding 100 ml of dichloromethane to the reaction solution for extraction, filtering out diethylamine hydrochloride and distilling the filtrate under reduced pressure to obtain a crude reaction intermediate;

(6) Add the crude reaction intermediate to ice water to dissolve, then add dichloromethane and stir thoroughly, then use a separatory funnel to separate the liquid to obtain an aqueous phase (the product is extracted into the aqueous phase);

(7) adding 0.2 mol/L Li ₂ CO ₃ solution dropwise to the reaction intermediate aqueous solution, and reacting until the pH reaches 7.0 to obtain a mixed solution containing lithium cyanophosphate;

(8) The solution containing lithium cyanophosphate is subjected to reduced pressure distillation to remove the solvent, and then washed with methanol for multiple times, centrifuged, and dried to obtain pure lithium cyanophosphate.

The above is a detailed introduction to a lithium cyanophosphate provided by the present invention and its preparation method and application. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims (8)

1. Application of lithium cyanophosphate as an additive to improve the cycle performance of lithium-ion batteries; The lithium cyanophosphate has a structure as shown in formula (II): The lithium ion battery comprises a lithium ion battery electrolyte; The mass content of the lithium cyanophosphate in the electrolyte is 0.5% to 5%. 2. A method for preparing lithium cyanophosphate for use as claimed in claim 1, characterized in that it comprises the following steps: 1) mixing a compound having a structure of formula (1) and a hydrogen halide chelating agent to obtain a mixture A; The hydrogen halide chelating agent is one or more of triethylamine, diethylamine, ethylenediamine, dipropylamine, tripropylamine, propylenediamine, n-butylamine and pyridine; The compound having the structure of formula (2) and an organic solvent are mixed to obtain a mixture B; Wherein, R ₁ is selected from ethylene; X is selected from halogen; 2) Mixing mixture A and mixture B again under low temperature conditions, and then heating them to continue the reaction, thereby obtaining a mixture containing a reaction intermediate; 3) The filtrate of the mixture containing the reaction intermediate obtained in the above step is filtered, mixed with water and an organic extractant, and the organic phase is separated to obtain an aqueous phase, and then an inorganic lithium salt solution is added to react again to obtain lithium cyanophosphate having a structure shown in formula (II). 3. The preparation method according to claim 2, characterized in that the molar ratio of the hydrogen halide chelating agent to the compound having the structure of formula (1) is (3-6):1. 4. The preparation method according to claim 2, characterized in that the organic solvent is one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane; The volume ratio of the organic solvent to the compound having the structure of formula (2) is 1:(1-10). 5. The preparation method according to claim 2, characterized in that the molar ratio of the compound having the structure of formula (1) to the compound having the structure of formula (2) is (1-3): (3-1). 6. The preparation method according to claim 2, characterized in that the remixing is specifically, under low temperature and stirring, the mixture A of step 1) is slowly added dropwise to the mixture B; The slow dripping rate is 5-20 ml/h; The temperature of the low temperature condition is -20 to 10°C; The temperature of the continued reaction is 15-35°C. 7. The preparation method according to claim 2, characterized in that the reaction time is 5 to 20 hours; The organic extractant is one or more of toluene, n-hexane, petroleum ether, ethyl ether, tert-methyl butyl ether, dichloromethane and dichloroethane; The inorganic lithium salt is one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide and lithium acetate; The concentration of the inorganic lithium salt solution is 0.001-1 mol/L. 8. The preparation method according to claim 2, characterized in that the cut-off condition for the second reaction is to react to neutrality; After the second reaction, one or more steps of distillation, washing, separation and drying are further included; The washing is performed multiple times using an organic solvent insoluble in lithium cyanophosphate; The organic solvent insoluble in lithium cyanophosphate is one or more of methanol, ethanol, dichloromethane, n-hexane, petroleum ether and isopropanol.