CN107720717B - Preparation method of lithium difluorophosphate - Google Patents
Preparation method of lithium difluorophosphate Download PDFInfo
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Abstract
A preparation method of lithium difluorophosphate has a synthesis principle that difluorophosphate and lithium hydroxide are in contact reaction in a non-aqueous solvent or difluorophosphate and lithium carbonate are in contact reaction in the non-aqueous solvent; the specific reaction equation comprises: HPO2F2+LiOH＝LiPO2F2+H2O; or 2HPO2F2+Li2CO3＝2LiPO2F2+H2O+CO2. The method takes difluorophosphoric acid and lithium carbonate or lithium hydroxide as main raw materials, does not use the commonly used lithium hexafluorophosphate in the prior art, and can reduce the reaction cost; in addition, harmful gases such as fluorine gas and the like are not used in the preparation process, the reaction process is easy to control, the safety coefficient is high, and the equipment cost is low; the reaction process is solid-liquid reaction, and the raw materials and the target product do not contain gas, so the purity of the raw materials and the product is easy to control and convenient to transport, and the utilization rate of the raw materials is high, thereby the cost can be reduced.
Description
Technical Field
The invention relates to a preparation method of difluorophosphate, in particular to a preparation method of lithium difluorophosphate.
Background
In recent years, lithium ion power batteries and energy storage batteries have become one of the research hotspots in the new energy field. Currently, the lithium ion power battery anode material mainly comprises lithium iron phosphate and nickel cobalt manganese ternary material, and the electrolyte is lithium hexafluorophosphate (LiPF)6) Mainly comprises a liquid electrolytic liquid system matched with a carbonate organic solvent.
And in the ternary positive electrode material system, a proper amount of lithium difluorophosphate (LiPO) is added2F2) The internal resistance of the battery can be reduced, and a protective film is formed on the positive electrode of the battery, so that the cycle performance of the battery is obviously improved; meanwhile, in a lithium iron phosphate anode system with high compaction density, lithium difluorophosphate is added into the electrolyte as electrolyte salt, so that the low-temperature performance of the battery is obviously improved. In addition, lithium difluorophosphate has high water tolerance, so that the lithium difluorophosphate has low requirements on production environment and is easy to carry out industrial production; and the possibility of adverse reaction during the application of the electrolyte to the battery is reduced. Lithium difluorophosphate is of particular interest because of the significant advantages mentioned above.
In the prior art, part of the preparation of lithium difluorophosphate is to prepare lithium difluorophosphate by using raw material gas generated by decomposition of lithium hexafluorophosphate. As disclosed in patent document cn200580043400.x, the raw material gas may be obtained by decomposing lithium hexafluorophosphate by contacting and reacting a raw material salt containing a carbonate and/or a phosphate with a raw material gas composed of P and F and optionally O. There are significant drawbacks to this approach. Firstly, because lithium hexafluorophosphate is used as a reaction raw material and the price of the lithium hexafluorophosphate is higher, the production cost is higher, and the lithium hexafluorophosphate is not suitable for mass production; and secondly, the contact reaction of raw material gas and raw material salt is carried out in the reaction process, and the gas is involved in the reaction of the raw materials, so that the yield of the reaction is reduced, the actual operation is relatively complex, and the adverse effect is brought to the actual production.
And the other part is to prepare lithium difluorophosphate by using the electrolyte of lithium hexafluorophosphate. For example, patent document CN200880007432.8 describes that lithium difluorophosphate is produced by using a lithium hexafluorophosphate electrolyte and a halide such as lithium chloride or lithium bromide as reaction raw materials and adding a small amount of water to provide oxygen atoms necessary for the reaction. This approach also has some inherent drawbacks. Firstly, the lithium hexafluorophosphate is used as a reaction raw material, so that the production cost is relatively high; secondly, the decomposition of lithium hexafluorophosphate in the electrolyte is not easy to control, and the lithium hexafluorophosphate can be decomposed into excessive high-activity phosphorus pentoxide due to the overhigh reaction temperature, so that the side reaction products are increased.
In addition, lithium difluorophosphate is produced by a hazardous gas such as fluorine gas. Which comprises the following steps: patent document CN201410537713.1 discloses that a mixed gas containing monofluorodioxy-phosphorus is obtained by reacting pyrophosphate with fluorine gas, and the mixed gas is introduced into an anhydrous hydrogen fluoride solution of lithium fluoride to react to obtain a lithium difluorophosphate product; in patent document CN201380050491.4, lithium fluoride is brought into contact with a phosphorus pentafluoride gas and reacted in the presence of a small amount of moisture to obtain lithium difluorophosphate. In the methods, because dangerous gases such as fluorine gas, phosphorus pentoxide and the like are used, the production danger coefficient is high; in order to ensure the production safety, the use of gas needs to be accurately controlled, so that the gas is prevented from leaking, and the production process is more complicated; in addition, because the gas participates in the reaction, it is difficult to ensure high raw material utilization rate.
Due to the above-mentioned drawbacks in the prior art, it is desirable to provide a new method for synthesizing lithium difluorophosphate, which can solve the problems in the prior art.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of lithium difluorophosphate, which is a solid-liquid reaction and has the advantages of low production cost, simple operation and high product yield.
A preparation method of lithium difluorophosphate is characterized in that the synthesis principle comprises the contact reaction of difluorophosphoric acid and lithium hydroxide in a non-aqueous solvent or the contact reaction of difluorophosphoric acid and lithium carbonate in the non-aqueous solvent; the non-aqueous solvent comprises a benign non-aqueous solvent of lithium difluorophosphate or a poor non-aqueous solvent of lithium difluorophosphate; the reaction equation includes:
HPO2F2+LiOH＝LiPO2F2+H2O；
or 2HPO2F2+Li2CO3＝2LiPO2F2+H2O+CO2。
Preferably, the purity of the difluorophosphoric acid is 96% or more, the purity of the lithium carbonate is 98% or more, and the purity of the lithium hydroxide is 98% or more.
Preferably, the purity of the difluorophosphoric acid is 99% or more, the purity of the lithium carbonate is 99% or more, and the purity of the lithium hydroxide is 99% or more.
A preparation method of lithium difluorophosphate, wherein a reaction solvent comprises a benign non-aqueous solvent of lithium difluorophosphate, and the preparation method comprises the following specific steps:
(1) and reflux reaction
a. Weighing lithium hydroxide and difluorophosphoric acid according to a proportion or weighing lithium carbonate and difluorophosphoric acid according to a proportion for later use;
b. adding the weighed lithium hydroxide or lithium carbonate into a benign non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture;
c. slowly dropwise adding the weighed difluorophosphoric acid into the mixture at the reaction temperature;
d. keeping the reaction temperature, and stirring at a constant speed for 2-10 hours to obtain a reaction product;
(2) mother liquor treatment
a. Filtering the reaction product to obtain filtrate;
b. adding a water removing agent into the filtrate, and uniformly stirring for 0.5-2 hours to obtain filtrate subjected to dehydration treatment;
c. and (3) concentrating, crystallizing and drying the filtrate after the dehydration treatment to obtain the final product lithium difluorophosphate.
Preferably, the benign non-aqueous solvent of lithium difluorophosphate comprises one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, alkyl alcohol or alkyl ketone.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.5 or more.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.5 to 1.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.5 to 0.6.
Preferably, the molar ratio of the lithium hydroxide to the difluorophosphoric acid is 1 or more.
Preferably, the molar ratio of lithium hydroxide to difluorophosphoric acid is 1 to 1.5.
Preferably, the molar ratio of lithium hydroxide to difluorophosphoric acid is 1 to 1.2.
Preferably, the water scavenger comprises: metallic lithium wire or phosphorus pentoxide.
Preferably, the method of concentration comprises rotary evaporation or falling film evaporation; the crystallization method comprises the steps of elution crystallization or cooling crystallization; the drying method comprises vacuum drying or boiling drying; the reaction temperature only ensures that the reaction occurs normally.
Preferably, the reaction temperature is 20 to 120 ℃.
A preparation method of lithium difluorophosphate, wherein a reaction solvent is a poor non-aqueous solvent of lithium difluorophosphate, and the preparation method specifically comprises the following steps:
(1) crystallization reaction
a. Weighing lithium hydroxide and difluorophosphoric acid according to a proportion or weighing lithium carbonate and difluorophosphoric acid according to a proportion for later use;
b. adding the weighed lithium hydroxide or lithium carbonate into a poor non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture;
c. uniformly mixing the weighed difluorophosphoric acid and the poor non-aqueous solvent of the lithium difluorophosphate, and slowly dripping the mixture into the mixture at the reaction temperature;
d. keeping the reaction temperature, and stirring at a constant speed to obtain a reaction product;
(2) and separation of the product
a. Filtering the product to obtain a solid product;
b. and drying the solid product to obtain a final product.
Preferably, the poor non-aqueous solvent of lithium difluorophosphate comprises one or more of chain carbonates, cyclic carbonates, chain esters or cyclic esters.
Preferably, the poor non-aqueous solvent of lithium difluorophosphate comprises one or more of dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, dibutyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, gamma-butyrolactone or gamma-valerolactone.
Preferably, the poor non-aqueous solvent for lithium difluorophosphate comprises a carbonate-based solvent.
Preferably, the poor non-aqueous solvent for lithium difluorophosphate comprises a low boiling chain carbonate.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.5 or less.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.25 to 0.5.
Preferably, the molar ratio of the lithium carbonate to the difluorophosphoric acid is 0.4 to 0.5.
Preferably, the molar ratio of the lithium hydroxide to the difluorophosphoric acid is 1 or less.
Preferably, the molar ratio of lithium hydroxide to difluorophosphoric acid is from 0.5 to 1.
Preferably, the molar ratio of lithium hydroxide to difluorophosphoric acid is from 0.8 to 1.
Preferably, the reaction temperature is less than 200 ℃; the reaction time is 2-10 h.
Preferably, the reaction temperature is 30 to 120 ℃.
Preferably, the solvent is used in an amount such that the solid-to-liquid ratio is 5% to 50%.
Preferably, the difluorophosphoric acid is prepared by a chemical reaction, and the chemical reaction equation of the reaction comprises:
KH2PO4+2HSO3F＝HPO2F2+KHSO4+H2SO4；
H3PO4+2SO3+2CaF2＝HPO2F2+2HF+2CaSO4；
H3PO4+2POF3＝3HPO2F2；
POF3+HNO3＝HPO2F2+NO2F；
P2O3F4+H2O＝2HPO2F2；
or POF3+H2O＝HPO2F2+HF。
Preferably, the preparation method of the difluorophosphoric acid comprises the following steps: weighing fluorosulfonic acid under the protection of argon atmosphere, slowly adding potassium dihydrogen phosphate while stirring at a constant temperature of 5 ℃, and continuously stirring for 2 hours; after the reaction is finished, carrying out reduced pressure distillation to obtain colorless liquid difluorophosphoric acid.
Has the advantages that:
firstly, the method takes difluorophosphoric acid and lithium carbonate or lithium hydroxide as main raw materials, does not use the commonly used lithium hexafluorophosphate in the prior art, and can reduce the production cost. In addition, harmful gases such as fluorine gas and the like are not used in the preparation process, the reaction process is easy to control, the safety coefficient is high, and the equipment cost is low; the reaction process is a solid-liquid reaction, the raw materials and the target product do not contain gas, the purity of the raw materials and the product is easy to control, the raw materials and the product are convenient to transport, the utilization rate of the raw materials is high, and therefore the cost is reduced.
The lithium difluorophosphate can be completely dissolved in a benign non-aqueous solvent of the lithium difluorophosphate, the lithium carbonate or lithium hydroxide serving as a reaction raw material is almost insoluble in the lithium difluorophosphate, the lithium difluorophosphate is in a liquid state at normal temperature, the lithium carbonate or lithium hydroxide is controlled to be excessive in the reaction process, the only solute in the benign non-aqueous solvent of the lithium difluorophosphate is the lithium difluorophosphate serving as the reaction product, and the unreacted lithium carbonate or lithium hydroxide is removed after the reaction is finished, so that the separation of the product and the raw material can be realized. In the reflux reaction process, reactants can be fully contacted by continuously stirring, the reaction speed is accelerated, and the reaction time is saved; the carbon dioxide generated by the reaction can be discharged by continuously stirring, the utilization rate of raw materials is improved, the waste is reduced, and the cost is reduced. After the reaction is finished, unreacted lithium carbonate or lithium hydroxide can be removed through filtration, and then the solution is concentrated, crystallized and dried to obtain a reaction product lithium difluorophosphate, wherein the obtained product has high purity. The whole preparation method is simple to operate, high in safety coefficient, high in yield and good in development prospect.
Lithium difluorophosphate as a reactant product and lithium carbonate or lithium hydroxide as a reaction raw material in a poor non-aqueous solvent of lithium difluorophosphate are not easy to dissolve, the difluorophosphate as the reaction raw material is liquid, the excess difluorophosphate is only controlled in the reaction process to ensure that the lithium carbonate or lithium difluorophosphate completely reacts, filter residue is obtained by filtering after the reaction is finished, and the separation of the product and the raw material is very easy to realize. In the crystallization reaction process, the difluorophosphoric acid is slowly dripped into the reaction solution, so that the utilization rate of raw materials is increased, the waste is reduced, and the cost is saved; continuously stirring after the dropwise adding is finished, so that reactants are fully contacted, and the reaction rate is accelerated; carbon dioxide generated by the reaction can be discharged by continuously stirring, the utilization rate of raw materials is improved, and the cost is saved. And after the reaction is finished, filtering to obtain filter residue, and drying and purifying the filter residue to obtain the final product lithium difluorophosphate, wherein the purity of the product is high, and the yield of the method is high.
Detailed Description
The present invention will be further described with reference to the following examples.
Examples 1 to 4
The reaction principle is that lithium carbonate and difluorophosphoric acid react in a benign non-aqueous solvent of lithium difluorophosphate, and the reaction equation is as follows: 2HPO2F2+Li2CO3＝2LiPO2F2+H2O+CO2。
The method comprises the following specific steps:
(1) and reflux reaction
①, weighing lithium carbonate and difluorophosphoric acid in proportion for later use, and ensuring the lithium carbonate to be excessive so as to avoid the solution obtained after the reaction is finished from containing unreacted difluorophosphoric acid, thereby causing the reduction of the purity of the product and the yield;
②, adding the weighed lithium carbonate into a proper amount of benign non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture, wherein the uniform mixture can stabilize the system, and the lithium carbonate can be uniformly dispersed in the solvent, and the using amount of the solvent is required to ensure that the reaction product lithium difluorophosphate can be completely dissolved;
③, slowly dripping the weighed difluorophosphoric acid into the mixture at the reaction temperature, keeping the mixture at the reaction temperature, and reacting the compound in the dripping process, thereby saving the reaction time and improving the efficiency;
④, keeping at reaction temperature, stirring at constant speed for 2-10 hours to obtain reaction product, the reaction time and reaction temperature are mutually influenced, the reaction temperature is high, the reaction speed is high, the reaction time is short, the reaction temperature is low, the yield is high, but the reaction time is long, stirring is ceaselessly to accelerate the reaction speed, the reaction time is saved, and simultaneously the carbon dioxide generated by the reaction can be discharged more quickly.
(2) Mother liquor treatment
a. Filtering the reaction product to obtain filtrate; filtering comprises pressure filtering or vacuum filtering;
b. adding a water removing agent into the filtrate, and uniformly stirring for 0.5-2 hours to obtain filtrate subjected to dehydration treatment; the dehydrator is uniformly dispersed in the system by uniform stirring, so that the dehydrator can fully contact with water in the system, the effect of full dehydration is achieved, and the purity of the product is improved; the water removing agent comprises metal lithium wires or phosphorus pentoxide;
c. concentrating, crystallizing and drying the filtrate after the dehydration treatment to obtain a final product lithium difluorophosphate; concentration includes rotary evaporation or falling film evaporation; the crystallization comprises dissolution crystallization or cooling crystallization; drying includes vacuum drying or boiling drying.
The experimental parameters involved in the experimental procedure and the yields of the final products of examples 1-4 are specifically shown in table 1:
TABLE 1
From the above results, it is understood that the molar ratio of lithium carbonate to difluorophosphoric acid in example 4, in which lithium carbonate is excessive, was 0.55, and lithium difluorophosphate was prepared therefrom, and the yield of the final product was 94.12% at the maximum.
Examples 5 to 8
The reaction principle is that lithium hydroxide and difluorophosphoric acid react in a benign non-aqueous solvent of lithium difluorophosphate, and the reaction equation is as follows: HPO2F2+LiOH＝LiPO2F2+H2O；
The method comprises the following specific steps:
(1) and reflux reaction
①, weighing lithium hydroxide and difluorophosphoric acid in proportion for later use, ensuring the lithium hydroxide to be excessive to avoid the solution obtained after the reaction is finished containing unreacted difluorophosphoric acid, thereby reducing the purity of the product and the yield;
②, adding the weighed lithium hydroxide into a proper amount of benign non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture, wherein the uniform mixture can stabilize the system and ensure that the lithium hydroxide can be uniformly dispersed in the solvent, and the using amount of the solvent is ensured that the lithium difluorophosphate of the reaction product can be completely dissolved;
③, slowly dripping the weighed difluorophosphoric acid into the mixture at the reaction temperature, keeping the mixture at the reaction temperature, and reacting the compound in the dripping process, thereby saving the reaction time and improving the efficiency;
④, keeping at reaction temperature, stirring at constant speed for 2-10 hours to obtain reaction product, the reaction time and reaction temperature are mutually influenced, the reaction temperature is high, the reaction speed is high, the reaction time is short, the reaction temperature is low, the yield is high, but the reaction time is long, stirring is ceaselessly to accelerate the reaction speed, and the reaction time is saved.
(2) Mother liquor treatment
a. Filtering the reaction product to obtain filtrate; filtering comprises pressure filtering or vacuum filtering;
b. adding a water removing agent into the filtrate, and uniformly stirring for 0.5-2 hours to obtain filtrate subjected to dehydration treatment; the dehydrator is uniformly dispersed in the system by uniform stirring, so that the dehydrator can fully contact with water in the system, the effect of full dehydration is achieved, and the purity of the product is improved; the water removing agent comprises metal lithium wires or phosphorus pentoxide;
c. concentrating, crystallizing and drying the filtrate after the dehydration treatment to obtain a final product lithium difluorophosphate; concentration includes rotary evaporation or falling film evaporation; the crystallization comprises dissolution crystallization or cooling crystallization; drying includes vacuum drying or boiling drying.
The experimental parameters involved in the experimental procedure and the yields of the final products of examples 5-8 are specified in table 2:
TABLE 2
From the above results, it is understood that in example 8, in which the molar ratio of lithium hydroxide to difluorophosphoric acid is 1.1 and lithium hydroxide is in excess, lithium difluorophosphate is produced therefrom, and the yield of the final product is 88.24% at the maximum.
Examples 9 to 12
The reaction principle is that lithium carbonate and difluorophosphoric acid react in a poor non-aqueous solvent of lithium difluorophosphate, and the reaction equation is as follows: 2HPO2F2+Li2CO3＝2LiPO2F2+H2O+CO2。
The method comprises the following specific steps:
(1) crystallization reaction
①, weighing lithium carbonate and difluorophosphoric acid in proportion for later use, controlling the difluorophosphoric acid to be excessive, and enabling the lithium carbonate in the system to react completely, so that all insoluble solids in the final reaction system are lithium difluorophosphate to ensure the purity of the product;
②, adding the weighed lithium carbonate into a poor non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture, wherein the using amount of the poor non-aqueous solvent meets the requirement of uniform dispersion of lithium carbonate in the poor non-aqueous solvent, and simultaneously, since a part of unreacted difluorophosphate is dissolved in the solvent after the reaction is finished and the boiling point of the difluorophosphate is 115.9 ℃, the difluorophosphate is not easy to be removed by drying, the solubility of the difluorophosphate is reduced as much as possible in order to improve the purity of the product, namely the using amount of the solvent is increased as much as possible;
③, uniformly mixing the weighed difluorophosphoric acid and the poor non-aqueous solvent of the lithium difluorophosphate, and slowly dripping the mixture into the mixture at the temperature of between 30 and 120 ℃;
④, stirring at uniform speed for 2-10 hours at the same temperature to obtain reaction product, interacting reaction time and reaction temperature, high reaction speed, short reaction time, low reaction temperature, high yield, but long reaction time, stirring ceaselessly to accelerate reaction speed and save reaction time.
(2) And separation of the product
a. Filtering the product to obtain filter residue; the main component of the filter residue is lithium difluorophosphate which is a reaction product, a small amount of solvent is arranged on the surface of the lithium difluorophosphate, and the lithium difluorophosphate needs to be purified through drying treatment; filtering comprises vacuum filtering or pressure filtering;
b. drying the solid product to obtain a final product; the solvent on the surface of the lithium difluorophosphate can be removed through drying treatment, and the lower the boiling point of the solvent is, the easier the solvent is to be removed through drying treatment; drying includes boiling drying or vacuum drying.
The experimental parameters involved in the experimental procedure and the yields of the final products for examples 9-12 are specifically shown in table 3:
TABLE 3
From the above results, it is understood that the molar ratio of lithium carbonate to difluorophosphoric acid in example 12, in which difluorophosphoric acid is in excess, was 0.45, and lithium difluorophosphate was produced therefrom, and the yield of the final product was 84.54% at the maximum.
Examples 13 to 16
The reaction principle is that lithium hydroxide and difluorophosphoric acid react in a poor non-aqueous solvent of lithium difluorophosphate, and the reaction equation is as follows: HPO2F2+LiOH＝LiPO2F2+H2O。
The method comprises the following specific steps:
(1) crystallization reaction
①, weighing lithium hydroxide and difluorophosphoric acid in proportion for later use, controlling the excess difluorophosphoric acid and controlling the excess difluorophosphoric acid to ensure that the lithium hydroxide in the system completely reacts, so that all insoluble solids in the final reaction system are lithium difluorophosphate to ensure the purity of the product;
②, adding the weighed lithium hydroxide into a poor non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture, wherein the using amount of the poor non-aqueous solvent meets the requirement of uniform dispersion of the lithium hydroxide in the poor non-aqueous solvent, and simultaneously, since a part of unreacted difluorophosphate is dissolved in the solvent after the reaction is finished and the boiling point of the difluorophosphate is 115.9 ℃, the difluorophosphate is not easy to remove by drying, the solubility of the difluorophosphate is reduced as much as possible in order to improve the purity of the product, namely the using amount of the solvent is as much as possible;
③, uniformly mixing the weighed difluorophosphoric acid and the poor non-aqueous solvent of the lithium difluorophosphate, and slowly dripping the mixture into the mixture at the temperature of 30-120 ℃, wherein the difluorophosphoric acid and the poor non-aqueous solvent are uniformly mixed firstly, and then a reaction system is dripped, so that the system can be quickly balanced, and the reaction rate is accelerated;
④, stirring at uniform speed for 2-10 hours at the same temperature to obtain reaction product, interacting reaction time and reaction temperature, high reaction speed, short reaction time, low reaction temperature, high yield, but long reaction time, stirring ceaselessly to accelerate reaction speed and save reaction time.
(2) And separation of the product
a. Filtering the product to obtain filter residue; the main component of the filter residue is lithium difluorophosphate which is a reaction product, a small amount of solvent is arranged on the surface of the lithium difluorophosphate, and the lithium difluorophosphate needs to be purified through drying treatment;
b. drying the solid product to obtain a final product; the solvent on the surface of lithium difluorophosphate can be removed by drying treatment, and the lower the boiling point of the solvent, the easier the solvent can be removed by drying treatment.
The experimental parameters involved in the experimental procedure and the yields of the final products for examples 13-16 are specifically shown in table 4:
TABLE 4
From the above results, it is understood that in example 16, in which the molar ratio of lithium hydroxide to difluorophosphoric acid was 0.9 and difluorophosphoric acid was in excess, lithium difluorophosphate was produced therefrom, and the yield of the final product was up to 82.15%.
Example 17
Weighing 98.17g of fluorosulfonic acid under the protection of argon atmosphere, stirring at constant speed at the constant temperature of 5 ℃, slowly adding 70.06g of monopotassium phosphate, and continuing to stir for 2 hours; after completion of the reaction, distillation was carried out at 50 ℃ under reduced pressure under a vacuum of 8mm Hg to give a clear colorless fraction with a yield of about 86.16%.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the examples shown herein, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that several modifications and decorations within the scope of the invention are possible to those skilled in the art without departing from the principle of the invention.
Claims (10)
1. A preparation method of lithium difluorophosphate is characterized in that the synthesis principle comprises the contact reaction of difluorophosphoric acid and lithium hydroxide in a non-aqueous solvent or the contact reaction of difluorophosphoric acid and lithium carbonate in the non-aqueous solvent; the non-aqueous solvent comprises a benign non-aqueous solvent of lithium difluorophosphate or a poor non-aqueous solvent of lithium difluorophosphate; the reaction equation includes:
HPO2F2+LiOH＝LiPO2F2+H2O；
or 2HPO2F2+Li2CO3＝2LiPO2F2+H2O+CO2。
2. The method for preparing lithium difluorophosphate according to claim 1, wherein the purity of difluorophosphate is 96% or more, the purity of lithium carbonate is 98% or more, and the purity of lithium hydroxide is 98% or more.
3. The method for preparing lithium difluorophosphate according to claim 1 or 2, wherein the reaction solvent is a benign non-aqueous solvent of lithium difluorophosphate, and the method comprises the following steps:
(1) and reflux reaction
①, weighing lithium hydroxide and difluorophosphoric acid in proportion or lithium carbonate and difluorophosphoric acid in proportion for later use;
②, adding the weighed lithium hydroxide or lithium carbonate into a benign non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture;
③, slowly dripping the weighed difluorophosphoric acid into the mixture at the reaction temperature;
④, keeping the temperature at the reaction temperature, and stirring at a constant speed for 2-10 hours to obtain a reaction product;
(2) mother liquor treatment
a. Filtering the reaction product to obtain filtrate;
b. adding a water removing agent into the filtrate, and uniformly stirring for 0.5-2 hours to obtain filtrate subjected to dehydration treatment;
c. and (3) concentrating, crystallizing and drying the filtrate after the dehydration treatment to obtain the final product lithium difluorophosphate.
4. The method of claim 3, wherein the benign non-aqueous solvent of lithium difluorophosphate comprises one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, alkyl alcohol, and alkyl ketone.
5. The method for preparing lithium difluorophosphate according to claim 3, wherein the molar ratio of lithium carbonate to difluorophosphate is 0.5 or more.
6. The method for preparing lithium difluorophosphate according to claim 3, wherein the molar ratio of lithium hydroxide to difluorophosphate is 1 or more.
7. The method for preparing lithium difluorophosphate according to claim 1 or 2, wherein the reaction solvent is a poor non-aqueous solvent for lithium difluorophosphate, and the method comprises the following specific steps:
(1) crystallization reaction
①, weighing lithium hydroxide and difluorophosphoric acid in proportion or lithium carbonate and difluorophosphoric acid in proportion for later use;
②, adding the weighed lithium hydroxide or lithium carbonate into a poor non-aqueous solvent of lithium difluorophosphate, and stirring to obtain a uniform mixture;
③, uniformly mixing the weighed difluorophosphoric acid and the poor non-aqueous solvent of the lithium difluorophosphate, and slowly dripping the mixture into the mixture at the reaction temperature;
④, keeping the temperature at the reaction temperature, and stirring at a constant speed to obtain a reaction product;
(2) and separation of the product
a. Filtering the product to obtain a solid product;
b. and drying the solid product to obtain a final product.
8. The method of claim 7, wherein the non-aqueous solvent comprises a chain carbonate, a cyclic carbonate, a chain ester, or a cyclic ester.
9. The method of claim 7, wherein the molar ratio of lithium carbonate to difluorophosphoric acid is less than 0.5.
10. The method of claim 7, wherein the molar ratio of lithium hydroxide to difluorophosphoric acid is less than 1.
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