A preparation method of lithium difluorooxalatoborate

Abstract

The present invention provides a preparation method of lithium difluorooxalate borate, belonging to the technical field of lithium battery electrolyte additives. The present invention obtains a bis(methylsilyl) oxalate compound by a substitution reaction between a methylchlorosilane compound and oxalic acid, and mixes the bis(methylsilyl) oxalate compound with lithium oxalate, a boron trifluoride complex and an organic solvent to obtain lithium difluorooxalate borate; wherein the bis(methylsilyl) oxalate compound is used as a raw material, has strong reaction activity, generates a stable methylfluorosilane gas byproduct while introducing oxalate into the system, and does not cause chloride ions and free acid residues; in addition, when the raw material is bis(trimethylsilyl) oxalate, even if there is a small amount of raw material residue, it can be used as a new multifunctional electrolyte additive, play a certain synergistic role, and can improve the compatibility between electrolytes. The whole process is simple, the product yield obtained by the reaction is high, the product purity is high, and the separation is easy, which is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of lithium battery electrolyte additives, and in particular to a preparation method of lithium difluorooxalatoborate. Background Art

[0002] As a new type of lithium salt, lithium difluorooxalatoborate combines half of the structure of lithium tetrafluoroborate and half of lithium bis(oxalatoborate), and has the advantages of both lithium salts. It not only inherits the stability of lithium bis(oxalatoborate) in high temperature environments, but also has the excellent performance of lithium tetrafluoroborate under low temperature conditions, thus achieving a wide range of operating temperature. At the same time, lithium difluorooxalatoborate has a high solubility in chain carbonate solvents, which improves the conductivity of the electrolyte. In addition, lithium difluorooxalatoborate also has good film-forming properties and cycle performance. These characteristics make it an ideal choice for lithium-ion battery electrolyte additives and have broad application prospects in the field of power batteries.

[0003] At present, the method for synthesizing lithium difluorooxalate borate is mainly to generate lithium difluorooxalate borate and lithium tetrafluoroborate by reacting lithium oxalate and boron trifluoride, and then remove the byproduct lithium tetrafluoroborate by recrystallization. However, lithium difluorooxalate borate and lithium tetrafluoroborate have similar physical properties, low separation yield, and are difficult to industrialize. Another synthesis method is to use lithium tetrafluoroborate and oxalic acid as raw materials, add chlorosilane and other additives to generate lithium difluorooxalate borate, but in actual operation, this method is prone to free acid and chlorine residues, which will affect product quality and reduce product purity.

[0004] Therefore, it is very necessary to provide a method with simple process, high product purity, complete reaction conversion rate and suitable for industrial production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing lithium difluorooxalatoborate, so as to solve the problems of difficult separation and low product purity in the current preparation method.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing lithium difluorooxalatoborate, comprising the following steps:

[0008] Mixing a methylchlorosilane compound, oxalic acid and a first solvent, and performing a substitution reaction under a first protective atmosphere to obtain a bis(methylsilyl)oxalate compound;

[0009] The bis(methylsilyl)oxalate, lithium oxalate, boron trifluoride complex and a second solvent are mixed, and reacted under a second protective atmosphere to obtain a crude lithium difluorooxalatoborate;

[0010] The crude lithium difluorooxalatoborate is recrystallized to obtain lithium difluorooxalatoborate.

[0011] Preferably, the methylchlorosilane compound includes dimethylchlorosilane or trimethylchlorosilane.

[0012] Preferably, the oxalic acid is anhydrous oxalic acid, and the molar ratio of the methylchlorosilane compound to oxalic acid is 2 to 2.5:1.

[0013] Preferably, the first solvent includes cyclohexane, acetonitrile, dimethyl carbonate, ethyl acetate or dichloromethane, and the usage ratio of the first solvent to oxalic acid is 100-1000mL:90g.

[0014] Preferably, the first protective atmosphere and the second protective atmosphere independently include argon, nitrogen, and helium.

[0015] Preferably, the temperature of the substitution reaction is 50-100° C. and the time is 12-48 hours.

[0016] Preferably, the boron trifluoride complex comprises one or more of boron trifluoride ethyl ether, boron trifluoride dimethyl carbonate or boron trifluoride acetonitrile.

[0017] Preferably, the molar ratio of the bis(methylsilyl)oxalate, lithium oxalate and boron trifluoride complex is 1-1.2:1-1.2:2-2.5.

[0018] Preferably, the second solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, butyl acetate, ethylene carbonate, propylene carbonate, tetrahydrofuran, acetonitrile and γ-butyrolactone; and the dosage ratio of the second solvent to lithium oxalate is 150-1000mL:102g.

[0019] Preferably, the reaction temperature is 50-100° C. and the reaction time is 3-12 hours.

[0020] Beneficial effects of the present invention:

[0021] The present invention firstly carries out substitution reaction between methylchlorosilane compounds and anhydrous oxalic acid, and uses the generated bis(methylsilyl)oxalate compounds as raw materials to react with lithium oxalate and boron trifluoride complex in an organic solvent to obtain crude lithium difluorooxalate borate, and further obtains battery-grade lithium difluorooxalate borate by recrystallization. The reaction principle involved in the present invention is:

[0022] Li 2 C 2 O 4 +2BF 3 +(Me 3 Si) 2 C 2O 4 →2LiBF 2 C 2 O 4 +2Me 3 SiF↑

[0023] Li 2 C 2 O 4 +2BF 3 +(Me 2 SiH) 2 C 2 O 4 →2LiBF 2 C 2 O 4 +2Me 2 SiHF↑

[0024] The bis(methylsilyl)oxalate compounds prepared by the present invention have strong reaction activity, do not need additional auxiliary agents to promote the reaction, generate stable methylfluorosilane gas byproducts while introducing oxalate into the system, do not introduce chloride ions, and do not cause chloride ions and free acid residues; in addition, when the raw material is bis(trimethylsilyl)oxalate, even if there is a small amount of residue, it can be used as a new multifunctional electrolyte additive to play a certain synergistic role: it can remove trace water and HF generated at high temperature to build a stable CEI membrane; at the same time, lithium difluorooxalatoborate is an SEI membrane additive, and the two can be mixed together to build a stable positive and negative electrode membrane and improve the compatibility between electrolytes. The whole process is simple, the generated stable byproduct methylfluorosilane gas helps the reaction to move forward, the product yield obtained by the reaction is high, the product purity is high, and it is easy to separate, which is suitable for industrial production. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing lithium difluorooxalatoborate, comprising the following steps:

[0026] Mixing a methylchlorosilane compound, oxalic acid and a first solvent, and performing a substitution reaction under a first protective atmosphere to obtain a bis(methylsilyl)oxalate compound;

[0027] The bis(methylsilyl)oxalate compound, lithium oxalate, boron trifluoride complex and a second solvent are mixed, and reacted under a second protective atmosphere to obtain a crude lithium difluorooxalatoborate product;

[0028] The crude lithium difluorooxalatoborate is recrystallized to obtain lithium difluorooxalatoborate.

[0029] In the present invention, oxalic acid and a first solvent are preferably added to a reaction container under a first protective atmosphere, a methylchlorosilane compound is added under stirring, the temperature is increased, and a substitution reaction is performed to obtain a bis(methylsilyl)oxalate compound.

[0030] In the present invention, the first protective atmosphere preferably includes argon, nitrogen, helium, and more preferably includes argon.

[0031] In the present invention, the oxalic acid is preferably anhydrous oxalic acid, that is, oxalic acid with bound water removed.

[0032] In the present invention, the first solvent preferably includes cyclohexane, acetonitrile, dimethyl carbonate, ethyl acetate or dichloromethane, and is more preferably cyclohexane; the usage ratio of the first solvent to oxalic acid is preferably 100-1000mL:90g, and is more preferably 200-500mL:90g.

[0033] In the present invention, the methylchlorosilane compound preferably includes dimethylchlorosilane or trimethylchlorosilane; the molar ratio of the methylchlorosilane compound to oxalic acid is preferably 2 to 2.5:1, and more preferably 2 to 2.2:1; in a specific embodiment, the methylchlorosilane compound is used in excess to make the reaction more complete, and the excess methylchlorosilane compound is liquid and easy to separate from the solid product.

[0034] In the present invention, the temperature of the substitution reaction is preferably 50 to 100° C., more preferably 75° C., and the time is preferably 12 to 48 h, more preferably 24 h.

[0035] In the present invention, after the substitution reaction is carried out until no bubbles are generated, the reaction solution is quickly filtered, the obtained filtrate is subjected to rotary evaporation to remove the solvent, a large amount of white crystals are precipitated by cold, and the bis(methylsilyl)oxalate compound is obtained after drying.

[0036] In the present invention, the bis(methylsilyl)oxalate compound includes bis(dimethylsilyl)oxalate and / or bis(trimethylsilyl)oxalate; when the methylchlorosilane compound is dimethylchlorosilane, the obtained bis(methylsilyl)oxalate compound is bis(dimethylsilyl)oxalate, and when the methylchlorosilane compound is trimethylchlorosilane, the obtained bis(methylsilyl)oxalate compound is bis(trimethylsilyl)oxalate.

[0037] In the present invention, preferably, under a second protective atmosphere, a bis(methylsilyl)oxalate compound, lithium oxalate, a boron trifluoride complex and a second solvent are mixed to react, during which the escaped gas is preferably absorbed by a sodium hydroxide aqueous solution to obtain a crude lithium difluorooxalatoborate product.

[0038] In the present invention, the boron trifluoride complex preferably includes one or more of boron trifluoride ethyl ether, boron trifluoride dimethyl carbonate or boron trifluoride acetonitrile, and more preferably is a boron trifluoride dimethyl carbonate complex.

[0039] In the present invention, the molar ratio of the bis(methylsilyl)oxalate compound, lithium oxalate and boron trifluoride complex is preferably 1-1.2:1-1.2:2-2.5, and more preferably 1-1.05:1-1.05:2-2.1.

[0040] In the present invention, the second solvent preferably includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, butyl acetate, ethylene carbonate, propylene carbonate, tetrahydrofuran, acetonitrile and γ-butyrolactone, and further preferably includes one or more of dimethyl carbonate, ethyl acetate and acetonitrile; the dosage ratio of the second solvent to lithium oxalate is preferably 150-1000mL:102g, and further preferably 500mL:102g.

[0041] In the present invention, the reaction temperature is preferably 50 to 100° C., more preferably 50 to 80° C., and the reaction time is preferably 3 to 12 h, more preferably 8 to 12 h.

[0042] The reaction mechanism involved in the present invention is:

[0043] Li 2 C 2 O 4 +2BF 3 +(Me 3 Si) 2 C 2 O 4 →2LiBF 2 C 2 O 4 +2Me 3 SiF↑

[0044] Li 2 C 2 O 4 +2BF 3 +(Me 2 SiH) 2 C 2 O 4 →2LiBF 2 C 2 O 4 +2Me 2 SiHF↑

[0045] After the reaction is completed, the present invention preferably filters the reaction solution while hot, concentrates the filtrate, and cold precipitates to obtain a crude product of lithium difluorooxalatoborate.

[0046] In the present invention, the crude lithium difluorooxalatoborate is preferably recrystallized and dried in sequence to obtain lithium difluorooxalatoborate.

[0047] In the present invention, the recrystallization method is preferably to use dimethyl carbonate, diethyl carbonate, and ethyl acetate to redissolve the crude lithium difluorooxalatoborate, filter it, and then perform rotary evaporation to remove the solvent, and cold precipitate a large amount of white crystals.

[0048] In the present invention, the drying method is preferably vacuum drying, the drying temperature is preferably 100 to 150° C., and the drying time is preferably 8 to 24 hours, and more preferably 12 to 24 hours.

[0049] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0050] Example 1

[0051] Drying the oxalic acid to obtain anhydrous oxalic acid;

[0052] Under argon protection, 90 g of oxalic acid and 500 mL of cyclohexane were added to a flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser. 259.9 mL of trimethylsilyl chloride (5% excess) was added under stirring, and the temperature was raised to 75°C for substitution reaction. After reacting for 24 hours, the reaction solution was quickly filtered, and the filtrate was subjected to rotary evaporation to remove the solvent. A large amount of white crystals were obtained by cold precipitation. After drying, 208.6 g of bis(trimethylsilyl) oxalate was obtained, and the yield was 89%;

[0053] Under argon protection, 117.2 g of the above-mentioned bis(trimethylsilyl)oxalate, 51 g of lithium oxalate, 169.5 g of boron trifluoride carbonate dimethyl ester complex (boron trifluoride content is 40%) and 500 mL of dimethyl carbonate were added to a dry three-necked flask for reaction, heated to 60° C., and reacted for 8 hours, during which trimethylsilyl fluorogas escaped, which was absorbed by sodium hydroxide aqueous solution; after the reaction was completed, the reaction solution was filtered while hot, the filtrate was concentrated, and cold precipitation was performed to obtain a crude product of lithium difluorooxalatoborate;

[0054] The crude lithium difluorooxalatoborate was recrystallized and vacuum dried at 110° C. for 12 h to obtain 135.8 g of high-purity lithium difluorooxalatoborate with a purity of 99.97% and a yield of 95%.

[0055] Example 2

[0056] Drying the oxalic acid to obtain anhydrous oxalic acid;

[0057] Under argon protection, 90 g of oxalic acid and 500 mL of acetonitrile were added to a flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser. 227.7 mL of dimethylchlorosilane (5% excess) was added under stirring, and the temperature was raised to 80°C for substitution reaction. After reacting for 36 hours, the reaction solution was quickly filtered, and the filtrate was subjected to rotary evaporation to remove the solvent. A large amount of white crystals were obtained by cold precipitation. After drying, 193.6 g of bis(trimethylsilyl) oxalate was obtained, and the yield was 92%;

[0058] Under argon protection, 105.2 g of the above-mentioned bis(dimethylsilyl)oxalate, 51 g of lithium oxalate, 124 mL of boron trifluoride acetonitrile complex (boron trifluoride content of 62%) and 500 mL of acetonitrile were added to a dry three-necked flask, heated to 70° C., and reacted for 8 hours, during which dimethylfluorosilane gas escaped and was absorbed by sodium hydroxide aqueous solution; after the reaction was completed, the reaction solution was filtered while hot, the filtrate was concentrated, and cold precipitation was performed to obtain a crude product of lithium difluorooxalatoborate;

[0059] The crude lithium difluorooxalatoborate was recrystallized and vacuum dried at 110° C. for 12 h to obtain 128.5 g of high-purity lithium difluorooxalatoborate with a purity of 99.93% and a yield of 89%.

[0060] Example 3

[0061] Drying the oxalic acid to obtain anhydrous oxalic acid;

[0062] Under argon protection, 90 g of oxalic acid and 500 mL of dimethyl carbonate were added to a flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser. 259.9 mL of trimethylchlorosilane (5% excess) was added under stirring, and the temperature was raised to 75°C for substitution reaction. After reacting for 24 hours, the reaction solution was quickly filtered, and the filtrate was subjected to rotary evaporation to remove the solvent. A large amount of white crystals were obtained by cold precipitation. After drying, 211.0 g of bis(trimethylsilyl) oxalate was obtained, and the yield was 90%;

[0063] Under argon protection, 117.2 g of bis(trimethylsilyl)oxalate, 51 g of lithium oxalate, 125.5 mL of boron trifluoride ether complex (boron trifluoride content of 47%) and 500 mL of ethyl acetate were added to a dry three-necked flask, heated to 50° C., and reacted for 8 hours, during which trimethylsilyl fluorogas escaped, which was absorbed by sodium hydroxide aqueous solution; after the reaction, the reaction solution was filtered while hot, the filtrate was concentrated, and cold precipitation was performed to obtain a crude product of lithium difluorooxalatoborate;

[0064] The crude lithium difluorooxalatoborate was recrystallized and vacuum dried at 110° C. for 12 h to obtain 123.6 g of high-purity lithium difluorooxalatoborate with a purity of 99.90% and a yield of 86%.

[0065] As can be seen from the above embodiments, the present invention provides a method for preparing lithium difluorooxalate borate, using a bis(methylsilyl)oxalate ester compound obtained by substitution reaction of methylchlorosilane compounds and anhydrous oxalic acid as a raw material, reacting with lithium oxalate and a boron trifluoride complex in an organic solvent to obtain lithium difluorooxalate borate. The method of the present invention does not require the addition of other auxiliary agents, does not introduce chloride ions, thereby avoiding residual chloride ions and free acids, and generates a stable methylfluorosilane gas byproduct during the process, which does not require separation, and the product obtained by the reaction has a high yield and high product purity, and is suitable for industrial production.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing lithium difluorooxalatoborate, characterized in that: The following steps are involved: Mixing a methylchlorosilane compound, oxalic acid and a first solvent, and performing a substitution reaction under a first protective atmosphere to obtain a bis(methylsilyl)oxalate compound; The bis(methylsilyl)oxalate compound, lithium oxalate, boron trifluoride complex and a second solvent are mixed, and reacted under a second protective atmosphere to obtain a crude lithium difluorooxalatoborate product; The crude lithium difluorooxalatoborate is recrystallized to obtain lithium difluorooxalatoborate.

2. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The methylchlorosilane compound includes dimethylchlorosilane or trimethylchlorosilane.

3. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The oxalic acid is anhydrous oxalic acid, and the molar ratio of the methylchlorosilane compound to oxalic acid is 2 to 2.5:

1.

4. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The first solvent includes cyclohexane, acetonitrile, dimethyl carbonate, ethyl acetate or dichloromethane, and the usage ratio of the first solvent to oxalic acid is 100-1000mL:90g.

5. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The first protective atmosphere and the second protective atmosphere independently include argon, nitrogen, and helium.

6. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The temperature of the substitution reaction is 50-100° C., and the time is 12-48 hours.

7. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The boron trifluoride complex comprises one or more of boron trifluoride ethyl ether, boron trifluoride dimethyl carbonate or boron trifluoride acetonitrile.

8. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The molar ratio of the bis(methylsilyl)oxalate compound, lithium oxalate and boron trifluoride complex is 1-1.2:1-1.2:2-2.

5.

9. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The second solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, butyl acetate, ethylene carbonate, propylene carbonate, tetrahydrofuran, acetonitrile and γ-butyrolactone; the dosage ratio of the second solvent to lithium oxalate is 150-1000mL:102g.

10. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that: The reaction temperature is 50-100° C. and the reaction time is 3-12 hours.