Preparation method of lithium difluorophosphate for lithium secondary battery

Abstract

The invention relates to a method for preparing lithium difluorophosphate with high yield by using low-monovalent raw materials. More particularly, the present invention relates to a method for preparing a high-purity and high-yield lithium difluorophosphate salt without using a lithium hexafluorophosphate salt. Therefore, the lithium difluorophosphate salt prepared according to the present invention can be used in an electrolyte for a lithium secondary battery, and has the effects of electrochemical characteristics, output power, gas reduction, and the like when used in an electrolyte for a lithium secondary battery.

Description

Technical Field

[0001] The present invention relates to a method for preparing a lithium difluorophosphate salt with a high yield using a low unit price raw material. In addition, the present invention relates to a lithium difluorophosphate salt with reduced impurities. In particular, it relates to a method for preparing a lithium difluorophosphate salt with high purity and high yield without using a lithium hexafluorophosphate salt, and a high-purity lithium difluorophosphate salt prepared thereby. The lithium difluorophosphate salt prepared according to the present invention can be used in an electrolyte for a lithium secondary battery, and when used in an electrolyte for a lithium secondary battery, it has the effects of improving electrochemical characteristics, providing high output power, reducing gas, etc. Background Art

[0002] Lithium secondary batteries are widely used in small and advanced electronic devices such as mobile devices and laptop computers. As electric vehicles (EVs) become more popular, the development of medium and large lithium secondary batteries with high capacity and electrochemical stability is also underway.

[0003] With the increase in demand for medium and large lithium secondary batteries, the necessity for high-performance lithium secondary batteries is increasing, and a secondary battery with high output power, high energy density, gas reduction effect, and improved life is needed. Therefore, it is necessary to develop an electrolyte suitable for such a secondary battery, and thus multifunctional additives for improving the function of the electrolyte have begun to attract attention, especially the known lithium difluorophosphate salts help to improve the function of the electrolyte. According to this market impact, it is urgent to develop a high-purity lithium difluorophosphate salt that has a low preparation unit price and can improve the battery life. Summary of the invention

[0004] Technical issues

[0005] A well-known method for preparing lithium difluorophosphate is to use LiPF6, which is schematically shown in the following reaction formula 1.

[0006] Reaction 1:

[0007]

[0008] The reaction is characterized in that it is prepared by using lithium hexafluorophosphate (LiPF6) and various forms of siloxanes (Siloxane) without using water. However, the disadvantage of the method is that fluorosilane (SiF2(CH3)2) gas, a toxic substance, is produced as a by-product, and a large amount of acidic by-products remain in the product lithium difluorophosphate. In addition, the method uses expensive raw materials, such as lithium hexafluorophosphate (LiPF6) which is also used as a lithium secondary battery electrolyte together with siloxane (-Si(CH3)2O-), and has the disadvantage of high preparation unit price. Therefore, there is an urgent need for a preparation method of lithium difluorophosphate that is more economical than the existing preparation method and does not produce toxic by-products and is environmentally friendly.

[0009] To this end, the object of the present invention is to provide a novel preparation method for preparing lithium difluorophosphate salt by an environmentally friendly and economical method, which does not use expensive siloxanes and lithium hexafluorophosphate salt (LiPF6) and does not produce toxic fluorosilane gas.

[0010] Furthermore, another object of the present invention is to provide a high-purity lithium difluorophosphate salt.

[0011] Technical Solution

[0012] In order to solve the above problem, the present invention provides a method for preparing lithium difluorophosphate, which comprises:

[0013] Step 1) preparing a lithium dihalophosphate salt (LiPO2X2) of the following chemical formula 4 by reacting a phosphorus oxyhalide (POX3) compound of the following chemical formula 2, an oxidant (R1R2C=O) of the following chemical formula 3, and a lithium salt; and

[0014] Step 2) A lithium difluorophosphate salt (LiPO2F2) of the following Chemical Formula 1 is prepared by reacting a lithium dihalophosphate salt of Chemical Formula 4 with a fluoride salt of the following Chemical Formula 5.

[0015] Chemical formula 2:

[0016]

[0017] Chemical formula 3:

[0018]

[0019] Chemical formula 4:

[0020]

[0021] Chemical formula 5:

[0022] MF n

[0023] Chemical formula 1:

[0024]

[0025] In the chemical formula,

[0026] X is Cl, Br or I,

[0027] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0028] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0029] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N,

[0030] M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion,

[0031] n is 1 or 2.

[0032] The present invention also provides a method for preparing lithium difluorophosphate, which comprises:

[0033] Step 1') preparing a difluorophosphate (MPO2F2) of the following chemical formula 6 by reacting a phosphorus oxyhalide (POX3) compound of the following chemical formula 2, an oxidant (R1R2C=O) of the following chemical formula 3, and a fluoride salt of the following chemical formula 5; and

[0034] Step 2') A lithium difluorophosphate salt (LiPO2F2) of the following Chemical Formula 1 is prepared by reacting the difluorophosphate salt of Chemical Formula 6 with a lithium salt.

[0035] Chemical formula 2:

[0036]

[0037] Chemical formula 3:

[0038]

[0039] Chemical formula 5:

[0040] MF n

[0041] Chemical formula 6:

[0042]

[0043] Chemical formula 1:

[0044]

[0045] In the chemical formula,

[0046] X is Cl, Br or I,

[0047] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0048] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0049] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N,

[0050] M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion,

[0051] n is 1 or 2.

[0052] The present invention also provides a method for preparing lithium difluorophosphate.

[0053] The method prepares a lithium difluorophosphate salt (LiPO2F2) of the following Chemical Formula 1 by reacting a phosphoryl fluoride (POF3) compound of the following Chemical Formula 7, an oxidizing agent (R1R2C=O) of the following Chemical Formula 3, and a lithium salt.

[0054] Chemical formula 7:

[0055]

[0056] Chemical formula 3:

[0057]

[0058] Chemical formula 1:

[0059]

[0060] In the chemical formula,

[0061] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0062] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0063] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N.

[0064] The present invention also provides a lithium difluorophosphate salt, which contains 0 to 500 ppm by weight of F - , 0 to 500 ppm by weight of Cl - , 0 to 500 ppm by weight of SO4 2- or 0~500 ppm by weight of PO4 3- .

[0065] Effects of the Invention

[0066] The preparation method according to the present invention does not use expensive lithium hexafluorophosphate (LiPF6) and siloxane, thus having the advantage of excellent economy. In addition, the preparation method according to the present invention has the effect of not producing toxic fluorosilane gas, being environmentally friendly, and being able to prepare lithium difluorophosphate with a high purity of more than 97% and a high yield of more than 80% through a relatively simple preparation method. The content of metal ion impurities and acidic ions such as hydrofluoric acid, hydrochloric acid, sulfuric acid, and phosphoric acid in the lithium difluorophosphate of the present invention is extremely low. Therefore, when used in an electrolyte for lithium secondary batteries, it has the advantage of improving electrical properties, output power, and gas reduction characteristics. DETAILED DESCRIPTION

[0067] The present invention is described in more detail below. The terms or words used in this specification and claims should not be interpreted as limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical ideas of the present invention based on the principle that the inventor can appropriately define the concepts of the terms in order to describe his own invention in the best way.

[0068] The existing method for commercial production of lithium difluorophosphate (LiPO2F2) is a method using lithium hexafluorophosphate (LiPF6). In most processes using lithium hexafluorophosphate (LiPF6), toxic gases such as hydrofluoric acid or fluorosilane are produced, so a separate purification device must be constructed. In addition, in the preparation method using lithium difluorophosphate (LiPO2F2), on the one hand, it is difficult to completely remove the hydrofluoric acid and fluorosilane produced as by-products. On the other hand, when lithium difluorophosphate containing such impurities is used to produce, store and circulate electrolytes, side reactions will occur over time and more impurities will be produced, resulting in a secondary problem of reduced purity. One of the by-products produced at this time is hydrofluoric acid. If hydrofluoric acid is dissolved in the electrolyte and injected into the battery, it may cause problems such as oxidation of the electrodes in the battery and the metal battery packaging container.

[0069] In addition, since lithium hexafluorophosphate (LiPF6) is the most widely used material that must be used in lithium secondary battery electrolytes, there is a problem that its price has skyrocketed as the demand for lithium secondary batteries increases. Therefore, in order to prepare lithium difluorophosphate (LiPO2F2) at a competitive price and high purity, it is urgent to develop a preparation technology that does not use lithium hexafluorophosphate (LiPF6).

[0070] To this end, the inventors have attempted to develop a novel environmentally friendly and economical preparation method that does not use expensive siloxane and lithium hexafluorophosphate (LiPF6) and does not produce toxic fluorosilane gas. In the process, a method using a phosphorus oxyhalide (POX3) compound that can be easily obtained at a low price as a starting material was developed, and the present invention was completed. That is, the present invention can easily prepare phosphorus oxyhalide using an oxidant containing a carbonyl group (C=O), and can prepare lithium difluorophosphate in a simple, economical, environmentally friendly, high-purity and high-yield manner.

[0071] The present invention provides a method for preparing lithium difluorophosphate, which comprises:

[0072] Step 1) preparing a lithium dihalophosphate salt of the following chemical formula 4 by reacting a phosphorus oxyhalide compound of the following chemical formula 2, an oxidant of the following chemical formula 3, and a lithium salt; and

[0073] Step 2) preparing a lithium difluorophosphate salt of the following Chemical Formula 1 by reacting a lithium dihalophosphate salt of the following Chemical Formula 4 with a fluoride salt of the following Chemical Formula 5.

[0074] Chemical formula 2:

[0075]

[0076] Chemical formula 3:

[0077]

[0078] Chemical formula 4:

[0079]

[0080] Chemical formula 5:

[0081] MF n

[0082] Chemical formula 1:

[0083]

[0084] In the chemical formula,

[0085] X is Cl, Br or I,

[0086] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0087] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0088] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N,

[0089] M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion,

[0090] n is 1 or 2.

[0091] The method of the present invention is schematically shown in the following reaction formula 2.

[0092] Reaction 2:

[0093]

[0094] The present invention also provides a method for preparing lithium difluorophosphate, which comprises:

[0095] Step 1') preparing a difluorophosphate of the following Chemical Formula 6 by reacting a phosphorus oxyhalide (POX3) compound of the following Chemical Formula 2, an oxidant of the following Chemical Formula 3, and a fluoride salt of the following Chemical Formula 5; and

[0096] Step 2') A lithium difluorophosphate salt of the following Chemical Formula 1 is prepared by reacting a difluorophosphate salt of Chemical Formula 6 with a lithium salt.

[0097] Chemical formula 2:

[0098]

[0099] Chemical formula 3:

[0100]

[0101] Chemical formula 5:

[0102] MF n

[0103] Chemical formula 6:

[0104]

[0105] Chemical formula 1:

[0106]

[0107] In the chemical formula,

[0108] X is Cl, Br or I,

[0109] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0110] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0111] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N,

[0112] M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion,

[0113] n is 1 or 2.

[0114] The method of the present invention is schematically shown in the following reaction formula 3.

[0115] Reaction 3:

[0116]

[0117] The present invention also provides a method for preparing lithium difluorophosphate.

[0118] The method prepares a lithium difluorophosphate salt of the following Chemical Formula 1 by reacting a phosphoryl fluoride (POF3) compound of the following Chemical Formula 7, an oxidant of the following Chemical Formula 3, and a lithium salt.

[0119] Chemical formula 7:

[0120]

[0121] Chemical formula 3:

[0122]

[0123] Chemical formula 1:

[0124]

[0125] In the chemical formula,

[0126] R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4,

[0127] R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group,

[0128] R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N.

[0129] The method of the present invention is schematically shown in the following reaction formula 4.

[0130] Reaction 4:

[0131]

[0132] The present invention uses phosphoryl halide (POX3) instead of lithium hexafluorophosphate (LiPF6) to prepare lithium difluorophosphate, thereby inhibiting the generation of hydrofluoric acid or fluorosilane and not causing side reactions, thereby preparing high-purity lithium difluorophosphate (LiPO2F2).

[0133] A typical method of the existing method for preparing lithium difluorophosphate by oxidizing lithium hexafluorophosphate (LiPF6) is a method using expensive siloxane as an oxidant. The disadvantage of the method is that expensive reactants need to be used, and hydrofluoric acid and fluorosilane are produced as by-products and remain in the lithium difluorophosphate. Finally, in the process of removing the residual by-products (hydrofluoric acid and fluorosilane, etc.), a large yield loss occurs. And, in order to remove unreacted siloxane, a separate purification process is required. That is, the existing method for preparing lithium difluorophosphate has problems in terms of economy, the generation of toxic by-products and the purification treatment cost caused thereby, and the present invention has the advantage of not having these problems.

[0134] The present invention uses phosphorus oxyhalide instead of lithium hexafluorophosphate salt and uses a compound having a carbonyl group (C=O) as an oxidant, thereby stably preparing high-purity lithium difluorophosphate without generating fluorosilane byproducts and causing side reactions.

[0135] In the reaction formula 2, the step of reacting a phosphorus oxyhalide (POX3) compound with a compound having a carbonyl group (C=O) as an oxidant and a lithium salt, and the step of reacting a lithium dihalophosphate salt as a product of the step with a fluoride salt can be carried out by an in situ reaction, or by recovering the lithium dihalophosphate salt as an intermediate product and then reacting it with a fluoride salt.

[0136] In the reaction formula 3, the step of reacting a phosphorus oxyhalide (POX3) compound with a compound having a carbonyl group (C=O) and a fluoride salt as an oxidant, and the step of reacting a difluorophosphate as a product of the step with a lithium salt can be carried out by an in-situ reaction, or by recovering the difluorophosphate as an intermediate product and then reacting it with a lithium salt.

[0137] As the halide (X) of the phosphorus oxyhalide (POX3) compound used in the present invention, any one selected from chloride (Cl), bromide (Br) and iodide (I) can be used. The phosphorus oxyhalide (POX3) compound is preferably phosphorus oxychloride.

[0138] In the present invention, the compound of Chemical Formula 3 is a substance that oxidizes phosphoryl halide (POX3) or phosphoryl fluoride (POF3), and there is no limitation as long as it is a substance having a carbonyl group (C=O) and capable of oxidizing phosphoryl halide (POX3) or phosphoryl fluoride (POF3). Preferably, formaldehyde, formic acid, acetic acid, methyl acetate, ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, methylphenylformamide, acetamide, dimethylacetamide, cyanuric acid, cyanuric chloride, etc. can be cited.

[0139] In the present invention, the lithium salt is a substance that generates a lithium dihalophosphate salt or a lithium difluorophosphate salt, and is one or more selected from the group consisting of lithium acetate, lithium azide, lithium bicarbonate, lithium bisulfate, lithium carbonate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium cyanide, lithium dodecaborate, lithium hydride, lithium hydroxide, lithium nitrate, lithium oxalate, lithium oxide, lithium perchlorate, lithium sulfate, lithium sulfide, lithium amide, and mixtures thereof. The lithium salt is preferably lithium carbonate and / or lithium chloride.

[0140] In the present invention, MF of Chemical Formula 5 n The compound is a fluorinating agent in which the halogen of a phosphoryl halide (POX3) or a dihalophosphate is replaced by F, M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion, and n is 1 or 2.

[0141] The onium ion is an onium ion containing N or S.

[0142] The onium ion is preferably an ammonium ion.

[0143] The preparation of lithium difluorophosphate of the present invention can be carried out in a solvent.

[0144] The solvent may be preferably one or more selected from toluene, alkyl halides, nitriles, ethers, alcohols, esters, carbonate solvents, etc. Specifically, the solvent may include dimethoxyethane, ethyl acetate, butyl acetate, toluene, chloroform, dichloromethane, dichloroethane, tetrahydrofuran, acetonitrile, etc.

[0145] The preparation of lithium difluorophosphate of the present invention can be carried out at a temperature of 30° C. to 100° C. and can be carried out under an inert gas atmosphere such as nitrogen or argon. The preparation of lithium difluorophosphate can be carried out after mixing the reactants, preferably by stirring for 5 to 20 hours.

[0146] In order to prepare the lithium difluorophosphate of the present invention, the lithium salt can be reacted in an amount of 1 to 1.5 equivalents relative to 1 equivalent of phosphoryl halide or phosphoryl fluoride. The oxidant can be reacted in an amount of 1 to 1.5 equivalents relative to 1 equivalent of the phosphoryl halide or phosphoryl fluoride. When the lithium salt and the oxidant are used in the above content, lithium difluorophosphate can be prepared with high yield and high purity. In the present invention, in order to prepare high-purity lithium difluorophosphate, relative to 1 equivalent of phosphoryl halide, MF of Chemical Formula 5 n The reaction can be carried out in 2 to 8 equivalents.

[0147] The process of obtaining the product after the stepwise reaction may be a step of filtering the reaction solution and removing the reaction solvent, or a step of removing part of the reaction solvent and adding a blank solvent to the product to obtain crystals.

[0148] The present invention provides a lithium difluorophosphate salt, which contains 0 to 500 ppm by weight of F - , 0 to 500 ppm by weight of Cl - , 0 to 500 ppm by weight of SO4 2- or 0~500 ppm by weight of PO4 3- .

[0149] The existing lithium difluorophosphate is prepared by using lithium hexafluorophosphate and silicic acid, and therefore contains a large amount of various acidic impurities.

[0150] In contrast, the lithium difluorophosphate salt of the present invention is prepared by a milder preparation method that does not produce acidic by-products. The lithium difluorophosphate salt as the final product may contain acidic impurities, especially F - , Cl - 、SO4 2 - or PO4 3- ions, and their contents are 0 wt ppm to 500 wt ppm respectively. - , Cl - 、SO4 2- or PO4 3-The content of the ions is preferably 0 wt ppm to 200 wt ppm, more preferably 0 wt ppm to 100 wt ppm, and further preferably 0 wt ppm to 50 wt ppm. The present invention is characterized in that the F - , Cl - 、SO4 2- and PO4 3- The sum of the ion contents is greater than 0 and less than 200 ppm by weight, more preferably greater than 0 and less than 150 ppm by weight.

[0151] When the lithium difluorophosphate salt with reduced impurities is used in an electrolyte for a lithium secondary battery, there is an advantage that electrical characteristics, output power, and gas reduction characteristics can be improved.

[0152] Embodiments of the present invention

[0153] Hereinafter, the preferred embodiments of the present invention are described in detail as follows. However, the present invention is not limited thereto. The following ppm is weight ppm.

[0154] Example

[0155] Example 1. Preparation of LiPO2F2 using formic acid in steps

[0156] 1. Preparation of LiPO2Cl2 using formic acid

[0157] Under a nitrogen atmosphere, 300 g of dimethoxyethane and 50 g (326 mmol) of phosphoryl chloride were quantitatively added to a flask equipped with a stirrer, a condenser and a thermometer, and the internal temperature was cooled to 5°C and stirred. Next, 14.5 g (342 mmol) of lithium chloride was added and stirred at low temperature. Then, 15.7 g (341 mmol) of formic acid was slowly added dropwise, the temperature was raised to 45°C, and the reaction was allowed to proceed for 5 hours. When the reaction was completed, the reaction solution was filtered and the solution was concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 43.6 g (310 mmol) of lithium dichlorophosphate as a white powder.

[0158] (yield 95%)

[0159] 2. Preparation of LiPO2F2 using LiPO2Cl2

[0160] Under a nitrogen atmosphere, add 300g of dimethoxyethane and 43.6g (310mmol) of lithium dichlorophosphate to a flask equipped with a stirrer, a condenser and a thermometer, and stir at room temperature. Next, add 45.8g (1237mmol) of ammonium fluoride, gradually raise the temperature to 80°C, and further react for 8 hours. When the reaction is complete, filter the reaction solution and concentrate the solution. Add 150g of toluene to the crude concentrate, filter the precipitated crystals, dry the filtered solid, and obtain 30g (279mmol) of lithium difluorophosphate as a white powder. (Yield 90%, purity 99%, impurity anion content: F is 18.4ppm, Cl is 4.4ppm, SO4 is 18.4ppm, PO4 is 12.2ppm)

[0161] Example 2. Preparation of in situ LiPO2F2 using formic acid

[0162] Under a nitrogen atmosphere, 300 g of dimethoxyethane and 50 g (326 mmol) of phosphoryl chloride were quantitatively added to a flask equipped with a stirrer, a condenser and a thermometer, and the internal temperature was cooled to 5 ° C and stirred. Next, 14.5 g (342 mmol) of lithium chloride was added and stirred at low temperature. Then, 15.7 g (341 mmol) of formic acid was slowly added dropwise, the temperature was raised to 45 ° C, and the reaction was carried out for 5 hours. After confirming that the bubble generation has ended, 45.8 g (1237 mmol) of ammonium fluoride was added, the temperature was gradually raised to 80 ° C, and the reaction was further carried out for 8 hours. When the reaction was completed, the reaction solution was filtered and the solution was concentrated. 150 g of toluene was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 30.6 g (284 mmol) of lithium difluorophosphate as a white powder. (yield 87%, purity 99%, impurity anion content: F is 20.3ppm, Cl is 5.2ppm, SO4 is 23.6ppm, PO4 is 15.1ppm)

[0163] Example 3. Preparation of LiPO2F2 by dimethylformamide

[0164] 1. Preparation of NH4PO2F2 using dimethylformamide

[0165] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 24 g (328 mmol) of dimethylformamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to react for 18 hours. When the reaction was completed, it was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 36.1 g (303 mmol) of ammonium difluorophosphate as a white powder. (Yield 93%)

[0166] 2. Preparation of LiPO2F2 using NH4PO2F2

[0167] Under nitrogen atmosphere, add 300g of dimethoxyethane, 36.1g (303mmol) of ammonium difluorophosphate, 15.6g (211mmol) of lithium carbonate, and 5.1g (121mmol) of lithium chloride to a flask equipped with a stirrer, a condenser, and a thermometer, heat to 50°C, and react for 3 hours. When the reaction is completed, cool to room temperature, filter the reaction solution, and concentrate the solution. Add 150g of toluene to the crude concentrate, filter the precipitated crystals, dry the filtered solid, and obtain 29.8g (276mmol) of lithium difluorophosphate in the form of a white powder. (Yield 91%, purity 98%, impurity anion content: F is 21.3ppm, Cl is 6.0ppm, SO4 is 24.6ppm, PO4 is 13.9ppm)

[0168] Example 4. Preparation of in situ LiPO2F2 using dimethylformamide

[0169] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 24 g (328 mmol) of dimethylformamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to proceed for 18 hours. When the first reaction was completed, 15.6 g (211 mmol) of lithium carbonate and 5.1 g (121 mmol) of lithium chloride were quantitatively added, and stirring was maintained at 50°C for 3 hours. When the second reaction was completed, the reaction mixture was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 29.9 g (277 mmol) of lithium difluorophosphate as a white powder. (yield 85%, purity 99%, impurity anion content: F is 24.7ppm, Cl is 6.1ppm, SO4 is 28.4ppm, PO4 is 14.3ppm)

[0170] Example 5. Preparation of LiPO2F2 by acetamide

[0171] 1. Preparation of NH4PO2F2 using acetamide

[0172] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 19.4 g (328 mmol) of acetamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to react for 18 hours. When the reaction was completed, it was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 35.3 g (297 mmol) of ammonium difluorophosphate as a white powder. (Yield 91%)

[0173] 2. Preparation of LiPO2F2 using NH4PO2F2

[0174] Under nitrogen atmosphere, add 300g of dimethoxyethane, 35.3g (297mmol) of ammonium difluorophosphate, 15.6g (211mmol) of lithium carbonate, and 5.1g (121mmol) of lithium chloride to a flask equipped with a stirrer, a condenser, and a thermometer, heat to 50°C, and react for 3 hours. When the reaction is completed, cool to room temperature, filter the reaction solution, and concentrate the solution. Add 150g of toluene to the crude concentrate, filter the precipitated crystals, dry the filtered solid, and obtain 28.8g (267mmol) of lithium difluorophosphate as a white powder. (Yield 90%, purity 98%, impurity anion content: F is 27.4ppm, Cl is 6.9ppm, SO4 is 29.1ppm, PO4 is 15.5ppm)

[0175] Example 6. Preparation of in situ LiPO2F2 using acetamide

[0176] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 19.4 g (328 mmol) of acetamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to proceed for 18 hours. When the first reaction was completed, 15.6 g (211 mmol) of lithium carbonate and 5.1 g (121 mmol) of lithium chloride were quantitatively added, and the reaction was maintained at 50°C for 3 hours. When the second reaction was completed, the reaction mixture was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 28.8 g (267 mmol) of lithium difluorophosphate as a white powder. (yield 82%, purity 97%, impurity anion content: F is 32.4ppm, Cl is 7.4ppm, SO4 is 35.6ppm, PO4 is 16.8ppm)

[0177] Example 7. Preparation of LiPO2F2 by dimethylacetamide

[0178] 1. Preparation of NH4PO2F2 using dimethylacetamide

[0179] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 28.6 g (328 mmol) of dimethylacetamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to react for 18 hours. When the reaction was completed, it was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 33.7 g (283 mmol) of ammonium difluorophosphate as a white powder. (Yield 87%)

[0180] 2. Preparation of LiPO2F2 using NH4PO2F2

[0181] Under nitrogen atmosphere, add 300g of dimethoxyethane, 33.7g (283mmol) of ammonium difluorophosphate, 15.6g (211mmol) of lithium carbonate, and 5.1g (121mmol) of lithium chloride to a flask equipped with a stirrer, a condenser, and a thermometer, heat to 50°C, and react for 3 hours. When the reaction is completed, cool to room temperature, filter the reaction solution, and concentrate the solution. Add 150g of toluene to the crude concentrate, filter the precipitated crystals, dry the filtered solid, and obtain 27.5g (254mmol) of lithium difluorophosphate in the form of a white powder. (Yield 92%, purity 97%, impurity anion content: F is 35.3ppm, Cl is 7.6ppm, SO4 is 34.8ppm, PO4 is 21.1ppm)

[0182] Example 8. Preparation of in situ LiPO2F2 using dimethylacetamide

[0183] Under a nitrogen atmosphere, 300 g of dimethoxyethane, 28.6 g (328 mmol) of dimethylacetamide, and 48 g (1296 mmol) of ammonium fluoride were quantitatively added to a flask equipped with a stirrer, a condenser, and a thermometer, and the internal temperature was raised to 40°C and stirred. Next, 50 g (326 mmol) of phosphoryl chloride was slowly added dropwise, the temperature was raised to 50°C, and the reaction was allowed to proceed for 18 hours. When the first reaction was completed, 15.6 g (211 mmol) of lithium carbonate and 5.1 g (121 mmol) of lithium chloride were quantitatively added, and the reaction was maintained at 50°C for 3 hours. When the second reaction was completed, the reaction solution was cooled to room temperature, and then the reaction solution was filtered and concentrated. 150 g of hexane was added to the crude concentrate, the precipitated crystals were filtered, and the filtered solid was dried to obtain 28.1 g (260 mmol) of lithium difluorophosphate as a white powder. (yield 80%, purity 98%, impurity anion content: F is 42.2ppm, Cl is 8.5ppm, SO4 is 41.9ppm, PO4 is 23.3ppm)

[0184] Example 9. Preparation of LiPO2F2 using phosphoryl fluoride and formic acid

[0185] Under a nitrogen atmosphere, 300 g of dimethoxyethane and 50 g (481 mmol) of phosphoryl fluoride are quantitatively added to a flask equipped with a stirrer, a condenser and a thermometer, and the internal temperature is cooled to 5°C and stirred. Next, 13.1 g (505 mmol) of lithium fluoride is added and stirred at low temperature. Then, 23.2 g (505 mmol) of formic acid is slowly added dropwise, the temperature is raised to 45°C, and the reaction is carried out for 5 hours. When the reaction is completed, the reaction solution is filtered and the solution is concentrated. 150 g of hexane is added to the crude concentrate, the precipitated crystals are filtered, and the filtered solid is dried to obtain 46.7 g (433 mmol) of lithium difluorophosphate as a white powder. (Yield 90%, purity 99%, impurity anion content: F is 16.2 ppm, Cl is 2.1 ppm, SO4 is 13.3 ppm, PO4 is 10.5 ppm)

[0186] Table 1

[0187]

[0188] Industrial Applicability

[0189] The present invention relates to a method for preparing a difluorophosphate lithium salt with high purity and high yield without using a hexafluorophosphate lithium salt. According to the present invention, the difluorophosphate lithium salt can be prepared economically. In addition, the present invention provides a high-purity difluorophosphate lithium salt with reduced impurities. When the high-purity difluorophosphate lithium salt is used in an electrolyte for a lithium secondary battery, the electrochemical characteristics can be improved, high output power can be provided, and gas can be reduced.

Claims

1. A method for preparing lithium difluorophosphate, characterized in that: include: Step 1) preparing a lithium dihalophosphate salt of the following chemical formula 4 by reacting a phosphorus oxyhalide compound of the following chemical formula 2, an oxidant of the following chemical formula 3, and a lithium salt; as well as Step 2) preparing a lithium difluorophosphate salt of the following Chemical Formula 1 by reacting a lithium dihalophosphate salt of Chemical Formula 4 with a fluoride salt of the following Chemical Formula 5, Chemical formula 2: Chemical formula 3: Chemical formula 4: Chemical formula 5: MF n , Chemical formula 1: In the chemical formula, X is Cl, Br or I, R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4, R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group, R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N, M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion, n is 1 or 2.

2. A method for preparing lithium difluorophosphate, characterized in that: include: Step 1') preparing a difluorophosphate of the following Chemical Formula 6 by reacting a phosphorus oxyhalide compound of the following Chemical Formula 2, an oxidant of the following Chemical Formula 3, and a fluoride salt of the following Chemical Formula 5; and Step 2') preparing a lithium difluorophosphate salt of the following Chemical Formula 1 by reacting a difluorophosphate salt of Chemical Formula 6 with a lithium salt, Chemical formula 2: Chemical formula 3: Chemical formula 5: MF n , Chemical formula 6: Chemical formula 1: In the chemical formula, X is Cl, Br or I, R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4, R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group, R1 and R2 can together form a ring having 2 to 5 carbon atoms, which ring can contain one or more heteroatoms O or N, M is H, Li, Na, K, Ca, Zn, Sb, Rb, Cs or an onium ion, n is 1 or 2.

3. A method for preparing lithium difluorophosphate, characterized in that: The method comprises the steps of preparing a lithium difluorophosphate salt of the following chemical formula 1 by reacting a phosphoryl fluoride compound of the following chemical formula 7, an oxidant of the following chemical formula 3, and a lithium salt, Chemical formula 7: Chemical formula 3: Chemical formula 1: In the chemical formula, R1 and R2 are each independently H, C1-10 alkyl, phenyl, OH, OR3, NH2, NHR4, NR5R6, ONa, OK or ONH4, R3, R4, R5 and R6 are each independently a C1-10 alkyl group or a phenyl group, R1 and R2 can together form a ring having 2 to 5 carbon atoms, which can contain one or more heteroatoms O or N.

4. The method for preparing the lithium difluorophosphate according to claim 1, 2 or 3, characterized in that: The oxidizing agent of Chemical Formula 3 is at least one selected from the group consisting of formaldehyde, formic acid, acetic acid, methyl acetate, ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, methylphenylformamide, acetamide, dimethylacetamide, cyanuric acid and cyanuric chloride.

5. The method for preparing lithium difluorophosphate according to claim 1, 2 or 3, characterized in that: The lithium salt is one or more selected from the group consisting of lithium acetate, lithium azide, lithium bicarbonate, lithium bisulfate, lithium carbonate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium cyanide, lithium dodecorate, lithium hydride, lithium hydroxide, lithium nitrate, lithium oxalate, lithium oxide, lithium perchlorate, lithium sulfate, lithium sulfide or lithium amide and mixtures thereof.

6. The method for preparing lithium difluorophosphate according to claim 1, 2 or 3, characterized in that: The preparation of lithium difluorophosphate is carried out in a solvent.

7. The method for preparing lithium difluorophosphate according to claim 6, characterized in that: The solvent is one or more selected from the group consisting of toluene, alkyl halides, nitriles, ethers, alcohols, esters and carbonates.

8. The method for preparing lithium difluorophosphate according to claim 1 or 2, characterized in that: 1 to 1.5 equivalents of lithium salt are reacted with respect to 1 equivalent of phosphorus oxyhalide.

9. The method for preparing lithium difluorophosphate according to claim 3, characterized in that: 1 to 1.5 equivalents of the lithium salt are reacted with respect to 1 equivalent of phosphoryl fluoride.

10. The method for preparing lithium difluorophosphate according to claim 1 or 2, characterized in that: The oxidizing agent is reacted in an amount of 1 to 1.5 equivalents relative to 1 equivalent of the phosphorus oxyhalide.

11. The method for preparing lithium difluorophosphate according to claim 3, characterized in that: The oxidizing agent is reacted in an amount of 1 to 1.5 equivalents relative to 1 equivalent of phosphoryl fluoride.

12. The method for preparing lithium difluorophosphate according to claim 1 or 2, characterized in that: Relative to 1 equivalent of phosphorus oxyhalide, 2 to 8 equivalents of MF n to react.

13. A lithium difluorophosphate salt, characterized in that Contains 0-500 ppm by weight of F - , 0 to 500 ppm by weight of Cl - , 0 to 500 ppm by weight of SO4 2- or 0~500 ppm by weight of PO4 3- .

14. The lithium difluorophosphate salt according to claim 13, characterized in that F - , Cl - 、SO4 2- and PO4 3- The sum of the ion contents is greater than 0 and less than or equal to 200 ppm by weight.

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