阅读说明：本技术 草酸硼酸锂及其衍生物的制备方法、电解液和二次电池 (Preparation method of lithium oxalate borate and derivatives thereof, electrolyte and secondary battery ) 是由 时迎华 赵文文 于 2020-05-26 设计创作，主要内容包括：本发明属于二次电池材料技术领域,具体涉及一种草酸硼酸锂及其衍生物的制备方法、电解液和二次电池。本发明草酸硼酸锂及其衍生物的制备方法中,所有的反应物均为有机物,溶剂为非水溶剂,可通过浓缩干燥得到纯度高的草酸硼酸锂及其衍生物,避免了氯离子浓度和游离酸偏高的问题,且反应过程中的原子经济性高、杂质少,无需事先合成反应原料,也不会产生HF等有害气体,在简化反应过程、节约生产成本的同时也提升了反应过程的安全性,对环境更加友好。本发明采用类似方法制备草酸硼酸锂及其衍生物,减少了设备投入、劳动力成本和能耗,具有良好的工业化应用前景。(The invention belongs to the technical field of secondary battery materials, and particularly relates to a preparation method of lithium oxalato borate and derivatives thereof, an electrolyte and a secondary battery. In the preparation method of the lithium oxalato borate and the derivatives thereof, all reactants are organic matters, the solvent is a non-aqueous solvent, and the high-purity lithium oxalato borate and the derivatives thereof can be obtained by concentration and drying, so that the problems of high chloride ion concentration and high free acid are solved, the atom economy in the reaction process is high, the impurities are few, the reaction raw materials do not need to be synthesized in advance, harmful gases such as HF (hydrogen fluoride) are not generated, the reaction process is simplified, the production cost is saved, the safety of the reaction process is improved, and the preparation method is more environment-friendly. The invention adopts a similar method to prepare the lithium oxalate borate and the derivatives thereof, reduces equipment investment, labor cost and energy consumption, and has good industrial application prospect.)

1. The preparation method of the lithium oxalato borate is characterized by comprising the following steps of:

providing oxalic acid, lithium tetrafluoroborate, a non-aqueous solvent and an organic auxiliary agent;

in the non-aqueous solvent, carrying out mixed reaction on the oxalic acid, the lithium tetrafluoroborate and the organic auxiliary agent to obtain a solution containing lithium oxalato borate;

concentrating and drying the solution containing the lithium oxalate borate to obtain the lithium oxalate borate;

the lithium oxalate borate is lithium difluoro oxalate borate and/or lithium bis (oxalate) borate.

2. The method for preparing lithium oxalato borate according to claim 1, wherein the structural formula of the organic auxiliary agent is shown in formula (I),

wherein R is₁、R₂、R₃、R₄Each independently selected from hydrogen atom, alkyl group with 1-10 carbon atoms, alkenyl group with 2-10 carbon atoms, alkynyl group with 2-10 carbon atoms, and C1-10 alkoxy, C6-20 aromatic group, or halogen group, and R₁、R₂、R₃、R₄At least one of the halogen groups is a halogen group, and the halogen atom in the halogen group is a chlorine atom, a bromine atom or an iodine atom.

3. The method for producing lithium oxalato borate according to claim 1, wherein the oxalic acid has a moisture content of 100ppm or less; and/or

In the step of carrying out mixed reaction on the oxalic acid and the lithium tetrafluoroborate and the organic auxiliary agent, the molar ratio of the oxalic acid to the lithium tetrafluoroborate is (0.5-3) to 1; and/or

In the step of carrying out mixed reaction on the oxalic acid, the lithium tetrafluoroborate and the organic auxiliary agent, the molar ratio of the organic auxiliary agent to the oxalic acid is (0.5-3) to 1; and/or

In the step of carrying out mixing reaction on the oxalic acid, the lithium tetrafluoroborate and the organic auxiliary agent, the temperature of the mixing reaction is 20-80 ℃; and/or

And in the step of carrying out mixing reaction on the oxalic acid, the lithium tetrafluoroborate and the organic auxiliary agent, the mixing reaction time is 1-6 h.

4. The method for producing lithium oxalatoborate according to any one of claims 1 to 3, wherein the mass of the nonaqueous solvent is 1 to 10 times the mass of the oxalic acid; and/or

The non-aqueous solvent is at least one selected from acetonitrile, 1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2, 5-dimethyltetrahydrofuran, 1, 4-dioxane, N-dimethylformamide, N-dimethylacetamide, formamide, dichloromethane, chloroform, diethyl ether, propyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl acetate, ethyl propionate, propyl acetate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, N-hexane, N-heptane, cyclohexane, benzene, toluene and xylene; and/or

The temperature of the concentration and drying is 20-100 ℃; and/or

The time for concentrating and drying is 1-8 h.

5. A preparation method of lithium oxalato borate derivatives is characterized by comprising the following steps:

providing lithium difluoro (oxalato) borate, a non-aqueous solvent, and a cyano-or isocyanate-group-containing silicon-based compound;

in the non-aqueous solvent, performing mixed reaction on the lithium difluoro oxalato borate and the cyano-group-or isocyanate-group-containing silicon-based compound, and concentrating and drying the obtained solution to obtain the lithium oxalato borate derivative;

the oxalic acid dinitrile lithium borate derivative is oxalic acid dinitrile lithium borate and oxalic acid diisocyanate lithium borate, the structural formulas of the oxalic acid dinitrile lithium borate derivative and the oxalic acid diisocyanate lithium borate derivative are respectively shown in a formula (II) and a formula (III),

6. the method for producing a lithium oxalato borate derivative according to claim 5, wherein the lithium difluorooxalato borate is produced by the method for producing lithium oxalato borate according to any one of claims 1 to 4; and/or

The silicon-based compound containing cyano or isocyanate groups is trimethylsilyl cyanide or trimethylsilyl isocyanate; and/or

In the step of carrying out mixed reaction on the lithium difluoro oxalate borate and the cyano-group or isocyanate-group-containing silicon-based compound, the molar ratio of the lithium difluoro oxalate borate to the cyano-group or isocyanate-group-containing silicon-based compound is 1 (2-3); and/or

In the step of carrying out mixed reaction on the lithium difluoro oxalate borate and the silicon-based compound containing the cyano group or the isocyanate group, the temperature of the mixed reaction is 0-60 ℃; and/or

In the step of carrying out mixing reaction on the lithium difluoro oxalate borate and the cyano-group or isocyanate-group-containing silicon-based compound, the mixing reaction time is 1h-6 h; and/or

The temperature of the concentration and drying is 20-100 ℃; and/or

The time for concentrating and drying is 1-8 h; and/or

The non-aqueous solvent is at least one selected from acetonitrile, 1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2, 5-dimethyltetrahydrofuran, 1, 4-dioxane, N-dimethylformamide, N-dimethylacetamide, formamide, dichloromethane, chloroform, diethyl ether, propyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl acetate, ethyl propionate, propyl acetate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, N-hexane, N-heptane, cyclohexane, benzene, toluene and xylene.

7. The lithium oxalato borate derivative is characterized in that the structural formulas of the lithium oxalato dinitrile borate and the lithium oxalato diisocyanate borate are respectively shown in a formula (II) and a formula (III),

8. an electrolyte additive comprising the lithium oxalato borate prepared by the method for preparing lithium oxalato borate according to any one of claims 1 to 4, or the lithium oxalato borate derivative prepared by the method for preparing a lithium oxalato borate derivative according to claim 5 or 6, or the lithium oxalato borate derivative according to claim 7.

9. An electrolyte comprising the electrolyte additive of claim 8.

10. A secondary battery comprising the electrolyte according to claim 9.

Technical Field

The invention belongs to the technical field of secondary battery materials, and particularly relates to a preparation method of lithium oxalato borate, a lithium oxalato borate derivative and a preparation method thereof, an electrolyte additive, an electrolyte and a secondary battery.

Background

The lithium ion battery is a novel high-energy secondary battery which is developed in the 90 s, has the excellent performances of high energy density, small volume, light weight, high discharge rate, low self-discharge rate, long cycle life, no memory effect and the like, and is widely applied to the fields of digital products, power and energy storage.

With the continuous development of social demands, the service life, high and low temperature performance, safety performance, rate performance and the like of the lithium ion battery can not meet the requirements of power battery development. There are various ways to improve the performance of the power battery, wherein the structure and the property of the electrolyte lithium salt of the lithium ion battery play a crucial role in the electrochemical performance of the lithium ion battery. To date, a large number of novel lithium ion battery electrolyte lithium salts have been developed, and these novel lithium salts have better thermal stability and high and low temperature performance than commercial lithium hexafluorophosphate, but have some obvious disadvantages, such as low solubility, difficult synthesis, high price, corrosion of current collector, etc.

Lithium difluoro oxalate borate (LiODFB) is used as a new organic anion lithium salt, and compared with lithium tetrafluoroborate, LiODFB can form a more stable SEI film on the surface of a graphite negative electrode, so that the high-temperature cycle and high-temperature storage performance of the battery are improved. In addition, the SEI film formed by the LiODFB can prevent co-embedding of propylene carbonate on the surface of the negative electrode and prevent the structure of the SEI film from being damaged, so that low-viscosity propylene carbonate can be used for replacing ethylene carbonate in a LiODFB system, the viscosity of an electrolyte is reduced, the internal resistance of a battery is reduced, the lithium ion migration capacity is improved, and the low-temperature performance of the battery is further improved. Lithium bis (oxalato) borate (LiBOB) has the following advantages: the thermal stability is good, the thermal decomposition temperature is as high as 300 ℃, the safety of the battery can be improved to a certain extent, and the service temperature range of the battery can be widened; the LiBOB does not contain fluorine elements, so that hydrogen fluoride is not generated, the corrosion to electrode materials and a current collector is avoided, and the cycle life of the battery is prolonged; the LiBOB contains two oxalic acid units, a stable SEI film can be formed on the surface of the graphite cathode, the cathode film forming capability is strong, and the high-temperature performance of the battery can be effectively improved; the SEI film formed by the LiBOB can prevent the co-intercalation of the propylene carbonate on the surface of the negative electrode material and prevent the damage of the SEI film structure, so the LiBOB can be used in the electrolyte taking pure propylene carbonate as a solvent.

However, the existing method for preparing LiODFBThere are the following problems: the obtained LiODFB has low purity and a large amount of lithium tetrafluoroborate remains, so that waste of reaction raw materials and difficulty in subsequent separation and purification are caused; some methods require the use of AlCl₃Or SiCl₄As a reaction catalyst, impurity chloride ions are introduced and corrosive HF gas is generated, the yield of the method is low, the obtained crude product can be recrystallized for multiple times to obtain high-purity LiODFB, and the production cost is increased; in some methods, water is generated in the reaction process, which causes decomposition of LiODFB, reduces the reaction yield and product purity, and is not favorable for industrial production. In addition, the existing methods for preparing LiBOB also have some problems, such as: a large amount of water exists in the reaction system, the water can react with the LiBOB, and partial reaction raw materials are not completely reacted, so that the purity of the product is reduced; the reaction raw materials are difficult to obtain and need to be synthesized in advance, so that the production cost is increased; high synthesis energy consumption, low efficiency and the like, is not beneficial to industrial production, and influences the purity of the LiBOB product.

Therefore, the search for a preparation method of anhydrous lithium oxalate borate is one of the research focuses of the current novel electrolyte.

Disclosure of Invention

The invention aims to provide a preparation method of lithium oxalato borate, a lithium oxalato borate derivative and a preparation method thereof, an electrolyte additive, an electrolyte and a secondary battery, and aims to solve the technical problem of low product purity in the existing preparation process of lithium oxalato borate.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

the invention provides a preparation method of lithium oxalato borate, which comprises the following steps:

providing oxalic acid, lithium tetrafluoroborate, a non-aqueous solvent and an organic auxiliary agent;

in the non-aqueous solvent, carrying out mixed reaction on the oxalic acid, the lithium tetrafluoroborate and the organic auxiliary agent to obtain a solution containing lithium oxalato borate;

concentrating and drying the solution containing the lithium oxalate borate to obtain the lithium oxalate borate;

the lithium oxalate borate is lithium difluoro oxalate borate and/or lithium bis (oxalate) borate.

In another aspect, the present invention provides a method for preparing a lithium oxalato borate derivative, comprising the steps of:

providing lithium difluorooxalato borate, a non-aqueous solvent and a cyano-or isocyanate-group-containing silicon-based compound;

in the non-aqueous solvent, performing mixed reaction on the lithium difluoro oxalato borate and the cyano-group-or isocyanate-group-containing silicon-based compound, and concentrating and drying the obtained solution to obtain the lithium oxalato borate derivative;

the oxalic acid dinitrile lithium borate derivative is oxalic acid dinitrile lithium borate and oxalic acid diisocyanate lithium borate, the structural formulas of the oxalic acid dinitrile lithium borate derivative and the oxalic acid diisocyanate lithium borate derivative are respectively shown in a formula (II) and a formula (III),

the invention also provides a lithium oxalato borate derivative, which is oxalic acid dinitrile lithium borate and oxalic acid diisocyanate lithium borate, the structural formulas of which are respectively shown in the formulas (II) and (III),

in another aspect, the present invention provides an electrolyte additive, which comprises the lithium oxalato borate prepared by the above method for preparing lithium oxalato borate, or the lithium oxalato borate derivative prepared by the above method for preparing lithium oxalato borate derivative, or the above lithium oxalato borate derivative.

In still another aspect, the present invention provides an electrolyte, which includes the above electrolyte additive.

In a final aspect, the present invention provides a secondary battery comprising the above electrolyte.

According to the preparation method of the lithium oxalato borate, provided by the invention, the organic auxiliary agent is added to perform a mixing reaction with the oxalic acid and the lithium tetrafluoroborate, so that the oxalic acid with poor solubility in the non-aqueous solvent can be gradually dissolved to obtain a liquid containing the lithium oxalato borate, and then the liquid is concentrated and dried to obtain the lithium oxalato borate. In the preparation method, all reactants are organic matters, and the solvent is a non-aqueous solvent, so that the lithium oxalate borate with high purity can be obtained through concentration and drying, the problem of high chloride ion concentration and high free acid is solved, the atom economy in the reaction process is high, the impurities are few, the reaction raw materials do not need to be synthesized in advance, harmful gases such as HF and the like are not generated, the reaction process is simplified, the production cost is saved, the safety of the reaction process is improved, and the preparation method is more environment-friendly. In addition, the preparation method of the lithium oxalato borate provided by the invention can also be used as a previous step for preparing the lithium oxalato borate derivative, so that the effects of preparing various products by using a similar method and producing the various products by using the same set of instrument and equipment are realized, the equipment investment, the labor cost and the energy consumption are reduced, and the preparation method has a good industrial application prospect.

According to the preparation method of the lithium oxalate borate derivative, lithium difluoro oxalate borate is used as a raw material, and the lithium difluoro oxalate borate is reacted with a silicon-based compound containing cyano or isocyanate groups in a non-aqueous solvent, and then the lithium oxalate borate derivative is obtained through concentration and drying. The reactants in the preparation method are all organic matters, and the solvent is a non-aqueous solvent, so that the lithium oxalate borate derivative with high purity can be obtained through concentration and drying, the problem that the concentration of chloride ions and free acid are high is solved, the atom economy in the reaction process is high, the impurities are few, the reaction raw materials do not need to be synthesized in advance, harmful gases such as HF and the like are not generated, the reaction process is simplified, the production cost is saved, the safety of the reaction process is improved, and the preparation method is more environment-friendly.

The lithium oxalate borate derivative provided by the invention is two novel lithium salts, namely lithium oxalate dinitrile borate and lithium oxalate diisocyanate borate, and has the advantages of good thermal stability, high ionic conductivity and good application prospect.

The electrolyte additive provided by the invention comprises the lithium oxalate borate and the derivatives thereof prepared by the preparation method of the lithium oxalate borate and the derivatives thereof, or comprises the lithium oxalate borate derivatives. The reactants in the preparation method are all organic matters, the solvent is a non-aqueous solvent, and the obtained lithium oxalato borate and the derivatives thereof have high purity, good thermal stability and high ionic conductivity, so when the lithium oxalato borate and the derivatives thereof are used as the electrolyte additive, the increase of moisture and acidity of the electrolyte in the storage process can be effectively inhibited, and the stability and the safety of the electrolyte are improved.

The electrolyte provided by the invention comprises the electrolyte additive. The electrolyte additive can effectively inhibit the rising of moisture and acidity of the electrolyte in the storage process, so the electrolyte has good stability and safety.

The secondary battery provided by the invention comprises the electrolyte. The electrolyte can effectively improve the safety and stability of the obtained secondary battery, and experiments prove that the secondary battery has better normal-temperature cycle performance and high-temperature cycle performance and longer service life.

Detailed Description

In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, the term "and/or" describing an association relationship of associated objects means that there may be three relationships, for example, a and/or B, may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the description of the present invention, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight described in the embodiments of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.

In addition, unless the context clearly uses otherwise, an expression of a word in the singular is to be understood as including the plural of the word. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.

The embodiment of the invention provides a preparation method of lithium oxalato borate, which comprises the following steps:

s1, providing oxalic acid, lithium tetrafluoroborate, a non-aqueous solvent and an organic auxiliary agent;

s2, mixing oxalic acid, lithium tetrafluoroborate and an organic auxiliary agent in a non-aqueous solvent for reaction to obtain a solution containing lithium oxalato borate;

s3, concentrating and drying the solution containing the lithium oxalate borate to obtain the lithium oxalate borate;

the obtained lithium oxalate borate is lithium difluoro oxalate borate (LiODFB) and/or lithium bis oxalate borate (LiBOB).

In the preparation method of lithium oxalato borate provided by the embodiment of the invention, the organic auxiliary agent is added to perform a mixing reaction with oxalic acid and lithium tetrafluoroborate, so that oxalic acid with poor solubility in a non-aqueous solvent can be gradually dissolved to obtain a liquid containing lithium oxalato borate, and then the liquid is concentrated and dried to obtain the lithium oxalato borate. In the preparation method, all reactants are organic matters, and the solvent is a non-aqueous solvent, so that the lithium oxalate borate with high purity can be obtained through concentration and drying, the problem of high chloride ion concentration and high free acid is solved, the atom economy in the reaction process is high, the impurities are few, the reaction raw materials do not need to be synthesized in advance, harmful gases such as HF and the like are not generated, the reaction process is simplified, the production cost is saved, the safety of the reaction process is improved, and the preparation method is more environment-friendly. In addition, the preparation method of the lithium oxalato borate provided by the embodiment of the invention can also be used as a previous step for preparing the lithium oxalato borate derivative, so that the effects of preparing various products by a similar method and producing the various products by using the same set of instrument and equipment are realized, the equipment investment, the labor cost and the energy consumption are reduced, and the preparation method has a good industrial application prospect.

Specifically, in S1, in order to further reduce the moisture in the reaction system and reduce the free acid, in some embodiments, oxalic acid having a moisture content of 100ppm or less is selected. The oxalic acid raw material may be pretreated so that the water content is 100ppm or less. In some embodiments, the pretreatment may be performed as follows: the oxalic acid raw material is dried at the temperature of 50-100 ℃ under the vacuum condition until the water content of the oxalic acid is less than or equal to 100 ppm.

Non-aqueous solvents, i.e., solvents other than water. Since the lithium oxalato borate solution prepared by using the aqueous solvent is difficult to precipitate high-purity lithium oxalato borate through crystallization and has the problems of high chloride ion concentration and high free acid, the embodiment of the invention adopts the non-aqueous solvent to overcome the problems. In some embodiments, the non-aqueous solvent is selected from at least one of acetonitrile, 1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2, 5-dimethyltetrahydrofuran, 1, 4-dioxane, N-dimethylformamide, N-dimethylacetamide, formamide, dichloromethane, chloroform, diethyl ether, propyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl acetate, ethyl propionate, propyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, N-hexane, N-heptane, cyclohexane, benzene, toluene, xylene.

The organic adjuvant, used in the present example to completely dissolve oxalic acid, reacts with oxalic acid and lithium tetrafluoroborate. In some embodiments, the compound with the structural formula shown in formula (I) is selected as an organic auxiliary agent, so that the method has the advantages of obvious price advantage, good reaction effect, less impurities and mild reaction conditions; wherein R is₁、R₂、R₃、R₄Each independently selected from one of hydrogen atom, alkyl with 1-10 carbon atoms, alkenyl with 2-10 carbon atoms, alkynyl with 2-10 carbon atoms, alkoxy with 1-10 carbon atoms, aromatic group with 6-20 carbon atoms and halogen group, and R₁、R₂、R₃、R₄At least one of the halogen groups is a halogen group, the halogen atom in the halogen group is a chlorine atom, a bromine atom or an iodine atom,

further, in the structural formula of the organic auxiliary agent, R₁、R₂、R₃、R₄One substituent group is chlorine atom, and the other three substituent groups are respectively and independently selected from alkyl, alkenyl, alkynyl, alkoxy or aromatic groups.

In S2, R in the organic assistant is added to the non-aqueous solvent₄For example, the reaction formula of the mixed reaction of oxalic acid, lithium tetrafluoroborate and organic auxiliary agent is as follows:

in order to control the addition amount of reactants and the reaction, in some embodiments, oxalic acid may be mixed with a non-aqueous solvent, and only partial dissolution occurs due to poor solubility of oxalic acid, so that the system is a suspension; then adding a non-aqueous solution of lithium tetrafluoroborate into the suspension under the stirring condition, wherein the solid is in an incomplete dissolving state and the system is still the suspension; then adding the organic auxiliary agent and stirring, wherein the organic auxiliary agent is added preferably in a slow dropwise manner so as to safely and fully react. With the addition of the organic auxiliary agent, the suspended matters in the suspension are gradually dissolved, and HCl gas is discharged at the same time and can be absorbed by the inorganic alkaline water solution; after all the organic additives are added dropwise, the system is colorless and transparent.

Further, the inorganic base in the inorganic base aqueous solution for absorbing the HCl gas is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and potassium carbonate, preferably a saturated aqueous solution of sodium hydroxide, and has the advantages of low cost, readily available raw materials, and complete absorption.

In some embodiments, in the step of carrying out the mixed reaction of oxalic acid, lithium tetrafluoroborate and the organic auxiliary agent, the molar ratio of oxalic acid to lithium tetrafluoroborate is controlled to be (0.5-3):1, so that the reactants are completely reacted, and the generation of excessive impurities is reduced. Specifically, typical but non-limiting molar ratios of oxalic acid to lithium tetrafluoroborate are 20.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3: 1.

When the molar ratio of oxalic acid to lithium tetrafluoroborate is (0.5-3):1, the resulting product may be a mixture of lithium difluorooxalato borate and lithium bis-oxalato borate. Further, the kind of the obtained product can be controlled by adjusting the molar ratio of oxalic acid to lithium tetrafluoroborate. Wherein, when the molar ratio of the oxalic acid to the lithium tetrafluoroborate is 1 (1-2), preferably 1 (1-1.1), the obtained product is the lithium difluoro-oxalato-borate; when the molar ratio of oxalic acid to lithium tetrafluoroborate is (2-3):1, preferably (2-2.2):1, the product obtained is lithium bis (oxalato) borate.

In some embodiments, in the step of performing a mixing reaction of oxalic acid, lithium tetrafluoroborate and the organic auxiliary agent, the molar ratio of the organic auxiliary agent to oxalic acid is controlled to be (0.5-3):1, preferably (1-2):1, so that the reactants are completely reacted without generating excessive impurities. Specifically, typical, but not limiting, molar ratios of organic adjuvant to oxalic acid are 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3: 1.

In some embodiments, in the step of performing the mixing reaction of oxalic acid, lithium tetrafluoroborate and the organic auxiliary agent, the temperature of the mixing reaction is controlled to be 20 ℃ to 80 ℃, which is beneficial to the reaction and the complete reaction of the reactants. Specifically, typical, but not limiting, mixing reaction temperatures are 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃.

Further, when the target product is lithium bis (oxalato) borate, the molar ratio of oxalic acid to lithium tetrafluoroborate is controlled to be 1 (1-2), preferably 1 (1-1.1), the oxalic acid and the non-aqueous solvent are mixed, the lithium tetrafluoroborate is added into the suspension, the organic auxiliary agent is added into the suspension at room temperature, the reaction is carried out at room temperature for 1h-3h after the dripping of the organic auxiliary agent is finished, then the temperature is raised to 40-60 ℃ for continuous reaction for 1h-3h, and the reaction is more complete.

Further, when the target product is lithium difluoro-oxalato-borate, the molar ratio of oxalic acid to lithium tetrafluoroborate is controlled to be (2-3):1, preferably (2-2.2):1, and oxalic acid is mixed with a non-aqueous solvent, lithium tetrafluoroborate is added into the suspension, and the addition of an organic auxiliary agent is carried out at room temperature, and after the dropwise addition of the organic auxiliary agent is completed, the room temperature reaction is carried out for 1h-3h, then the temperature is raised to 40 ℃ -80 ℃ to continue the reaction for 1h-3h, so that the reaction is more complete.

In some embodiments, the oxalic acid, lithium tetrafluoroborate, and the organic auxiliary agent are dissolved in advance with a nonaqueous solvent, in which case the total mass of the nonaqueous solvent is required to be 1 to 10 times the mass of the oxalic acid.

And S3, concentrating and drying the solution containing the lithium oxalate borate obtained in the S2 to obtain the lithium oxalate borate.

In some embodiments, since the solution containing lithium oxalato borate may contain residual oxalic acid and other impurities, which may affect the purity of the obtained lithium oxalato borate product, the lithium oxalato borate and the organic base may be mixed and reacted to remove oxalic acid and other impurities in a precipitation manner before the concentration and drying steps.

Further, the organic base is at least one selected from the group consisting of triethylamine, diisopropylethylamine, triisopropylamine, pyridine, 2, 6-lutidine, 4-Dimethylaminopyridine (DMAP), morpholine, N-methylmorpholine, N-ethylmorpholine, piperidine, N-methylpiperidine, N-ethylpiperidine, imidazole, N-methylimidazole, N-ethylimidazole, 1, 8-diazabicycloundecen-7-ene (DBU), 1, 5-diazabicyclo [4.3.0] non-5-ene (DBN), triazamidine, guanidine and Tetramethylguanidine (TMG).

Further, the mass of the organic base accounts for 0.01-2%, preferably 0.01-1% of the mass of the oxalic acid, so that impurities such as oxalic acid and the like are fully precipitated and removed. In particular, typical but not limiting mass ratios are 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%.

Further, when the solution containing the lithium oxalate borate is mixed with the organic base for reaction, the temperature of the mixing reaction is controlled to be-20 ℃, which is beneficial to quickly forming a precipitate and removing redundant impurities. Specifically, typical, but not limiting, mixing reaction temperatures are-20 ℃, -15 ℃, -10 ℃, -5 ℃, 0 ℃,5 ℃, 10 ℃, 15 ℃, 20 ℃.

Furthermore, when the solution containing the lithium oxalate borate and the organic base are subjected to mixing reaction, the mixing reaction time is controlled to be 1-6 h, so that impurities such as oxalic acid and the like are fully precipitated. Specifically, typical, but not limiting, mixing reaction times are 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6 h.

In some embodiments, the method of concentrating and drying is as follows: the method comprises the steps of firstly, carrying out reduced pressure concentration on a solution containing lithium oxalate borate (or a solution obtained after the solution containing lithium oxalate borate is mixed with organic alkali to react and remove precipitates) to obtain a white solid, then, carrying out recrystallization on the white solid by using a non-aqueous solvent to obtain a white crystal, and then, carrying out vacuum drying on the white crystal to obtain a target product lithium difluoro-oxalato-borate and/or lithium bis-oxalato-borate.

Further, the temperature of the vacuum drying is controlled to be 20 ℃ to 100 ℃, preferably 30 ℃ to 60 ℃ to improve the efficiency of the vacuum drying. Specifically, typical but not limiting vacuum drying temperature is 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees.

Further, the time for vacuum drying is controlled to be 1h-8h, preferably 2h-6h, so that the crystals are fully dried. Specifically, typical, but not limiting, vacuum drying times are 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8 h.

The preparation method of lithium oxalato borate provided by the embodiment of the invention can be further used as a preparation method of lithium oxalato borate derivatives.

Correspondingly, the embodiment of the invention also provides a preparation method of the lithium oxalato borate derivative, which comprises the following steps:

s4, providing lithium difluoro oxalato borate, a non-aqueous solvent, and a silicon-based compound containing a cyano group or an isocyanate group;

s5, in a non-aqueous solvent, carrying out mixed reaction on lithium difluoro oxalato borate and a silicon-based compound containing a cyano group or an isocyanate group, and concentrating and drying the obtained solution to obtain a lithium oxalato borate derivative;

the lithium oxalate borate derivatives are oxalic acid dinitrile lithium borate (LiODCNB) and oxalic acid diisocyanate lithium borate (LiODNCOB), the structural formulas of which are respectively shown as a formula (II) and a formula (III),

according to the preparation method of the lithium oxalate borate derivative provided by the embodiment of the invention, lithium difluoro oxalate borate is used as a raw material, and is reacted with a silicon-based compound containing cyano or isocyanate groups in a non-aqueous solvent, and then the reaction product is concentrated and dried to obtain the lithium oxalate borate derivative. The reactants in the preparation method are all organic matters, and the solvent is a non-aqueous solvent, so that the lithium oxalate borate derivative with high purity can be obtained through concentration and drying, the problem that the concentration of chloride ions and free acid are high is solved, the atom economy in the reaction process is high, the impurities are few, the reaction raw materials do not need to be synthesized in advance, harmful gases such as HF and the like are not generated, the reaction process is simplified, the production cost is saved, the safety of the reaction process is improved, and the preparation method is more environment-friendly.

Specifically, in S4, lithium difluorooxalato borate can be prepared by a conventional method, and lithium difluorooxalato borate prepared by the method for preparing lithium oxalato borate provided by the embodiment of the present invention is preferably used, because all reactants in the method for preparing lithium oxalato borate provided by the embodiment of the present invention are organic substances, and the solvent is a non-aqueous solvent, the purity of lithium difluorooxalato borate is high, the impurities are few, and the problems of high chloride ion concentration and high free acid are avoided.

The non-aqueous solvent, which is used as a solvent for lithium difluorooxalato borate and the cyano-or isocyanate-group-containing silicon-based compound in the present example, is more favorable for precipitation of a high-purity tetrafluorooxalato phosphate derivative by crystallization because it does not contain water, and avoids the problem of a high free acid content. In some embodiments, the non-aqueous solvent is selected from at least one of acetonitrile, 1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2, 5-dimethyltetrahydrofuran, 1, 4-dioxane, N-dimethylformamide, N-dimethylacetamide, formamide, dichloromethane, chloroform, diethyl ether, propyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, methyl acetate, ethyl propionate, propyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, N-hexane, N-heptane, cyclohexane, benzene, toluene, xylene.

The silicon-based compound containing cyano or isocyanate group is used for reacting with the difluoro oxalic acid lithium borate to generate the oxalic acid lithium borate derivative bis oxalic acid dinitrile lithium borate and oxalic acid diisocyanate lithium borate. In some embodiments, the cyano-or isocyanate-containing silicon-based compound is trimethylsilylcyanide (Me)₃SiCN or trimethylsilyl isocyanate (Me)₃SiN ═ C ═ O). Wherein when the cyano-or isocyanate-containing silicon-based compound is Me₃SiCN timeThe obtained oxalic acid lithium borate derivative is oxalic acid dinitrile lithium borate; when the cyano-or isocyanate-containing silicon-based compound is Me₃When SiN ═ C ═ O, the obtained lithium oxalate borate derivative is lithium oxalate diisocyanate borate.

In S5, lithium difluoro-oxalato-borate and a cyano-group-or isocyanate-group-containing silicon-based compound are mixed and reacted in a non-aqueous solvent, and the obtained solution containing the lithium oxalato-borate derivative is concentrated and dried to obtain the lithium oxalato-borate derivative. Wherein when the cyano-or isocyanate-containing silicon-based compound is Me₃SiCN, the reaction formula of SiCN and lithium difluoro oxalato borate is shown as follows:

when the cyano-or isocyanate-containing silicon-based compound is Me₃When SiN ═ C ═ O, the reaction formula with lithium difluorooxalato borate is as follows:

in order to facilitate the control of the amount of the reactants and the reaction, in some embodiments, the lithium difluorooxalato borate and the cyano-or isocyanate-group-containing silicon-based compound may be dissolved in a non-aqueous solvent to obtain respective non-aqueous solutions, and then mixed to react. When mixing, the non-aqueous solution of the cyano-group-or isocyanate-group-containing silicon-based compound and the non-aqueous solvent is preferably added dropwise to the non-aqueous solution of lithium difluorooxalato borate and the non-aqueous solvent, and the gas is released and can be absorbed by the aqueous solution of an inorganic base; after completion of the dropwise addition, suspended solid matter was removed by static filtration to obtain a colorless transparent solution.

Furthermore, in the inorganic alkali aqueous solution for absorbing the gas released in the reaction process, the inorganic alkali is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and potassium carbonate, and preferably a saturated aqueous solution of sodium hydroxide, so that the method has the advantages of low cost, easily obtained raw materials and complete absorption.

In some embodiments, in the step of performing the mixing reaction of the lithium difluorooxalato borate and the cyano-group-or isocyanate-group-containing silicon-based compound, the molar ratio of the lithium difluorooxalato borate to the cyano-group-or isocyanate-group-containing silicon-based compound is controlled to be 1 (2-3), preferably 1 (2-2.2), so that the reactants are completely reacted and the generation of excessive impurities is reduced. Specifically, typical but non-limiting molar ratios of lithium difluorooxalato borate to cyano-or isocyanate-containing silicon-based compound are 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1: 3.

In some embodiments, in the step of performing the mixing reaction of the lithium difluoro (oxalato) borate and the cyano-group-or isocyanate-group-containing silicon-based compound, the temperature of the mixing reaction is controlled to be 0 ℃ to 60 ℃, so that the reaction is favorably performed and the reactants are completely reacted. Specifically, typical, but not limiting, mixing reaction temperatures are 0 ℃,5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃.

Further, the lithium difluoro oxalato borate is mixed with a non-aqueous solvent, a cyano-group-or isocyanate-group-containing silicon-based compound is mixed with a non-aqueous solvent, and the lithium difluoro oxalato borate is mixed with the cyano-group-or isocyanate-group-containing silicon-based compound at room temperature, the lithium difluoro oxalato borate and the cyano-group-or isocyanate-group-containing silicon-based compound are mixed, then room temperature reaction is carried out for a period of time, and then the temperature is increased to 40-60 ℃ for continuous reaction, so that the reaction is more complete.

In some embodiments, in the step of performing the mixing reaction of the lithium difluoro (oxalato) borate and the cyano-group-or isocyanate-group-containing silicon-based compound, the time of the mixing reaction is controlled to be 1h to 6h to ensure that the reactants are completely reacted. Specifically, typical, but not limiting, mixing reaction times are 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6 h.

Further, lithium difluoro oxalate borate and a silicon-based compound containing cyano or isocyanate group are mixed and then react for 1h-3h at room temperature, and then the temperature is raised to 40 ℃ to 60 ℃ to continue the reaction for 1h-3 h.

In some embodiments, the method of concentrating and drying is as follows: the method comprises the steps of firstly carrying out reduced pressure concentration on a solution containing the lithium oxalate borate derivative to obtain a white solid, then carrying out recrystallization on the white solid by using a non-aqueous solvent to obtain a white crystal, and then carrying out vacuum drying on the white crystal to obtain the target product lithium oxalate borate derivative.

Further, the temperature of the vacuum drying is controlled to be 20 ℃ to 100 ℃, preferably 30 ℃ to 60 ℃ to improve the efficiency of the vacuum drying. Specifically, typical but not limiting vacuum drying temperature is 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees.

Further, the time for vacuum drying is controlled to be 1h-8h, preferably 2h-6h, so that the crystals are fully dried. Specifically, typical, but not limiting, vacuum drying times are 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8 h.

Correspondingly, the embodiment of the invention provides a lithium oxalato borate derivative which is lithium oxalato dinitrile borate and lithium oxalato diisocyanate borate, the structural formulas of which are respectively shown as a formula (II) and a formula (III),

the lithium oxalate borate derivative provided by the embodiment of the invention is two novel lithium salts, namely lithium oxalate dinitrile borate and lithium oxalate diisocyanate borate, and has the advantages of good thermal stability, high ionic conductivity and good application prospect.

Correspondingly, the embodiment of the invention also provides an electrolyte additive, which comprises the lithium oxalate borate prepared by the preparation method of the lithium oxalate borate, or the lithium oxalate borate derivative prepared by the preparation method of the lithium oxalate borate derivative, or the lithium oxalate borate derivative.

The electrolyte additive provided by the embodiment of the invention comprises the lithium oxalate borate and the derivatives thereof prepared by the preparation method of the lithium oxalate borate and the derivatives thereof, or comprises the lithium oxalate borate derivatives. The reactants in the preparation method are all organic matters, the solvent is a non-aqueous solvent, and the obtained lithium oxalato borate and the derivatives thereof have high purity, good thermal stability and high ionic conductivity, so when the lithium oxalato borate and the derivatives thereof are used as the electrolyte additive, the increase of moisture and acidity of the electrolyte in the storage process can be effectively inhibited, and the stability and the safety of the electrolyte are improved.

Correspondingly, the embodiment of the invention also provides an electrolyte, which comprises the electrolyte additive.

The electrolyte provided by the embodiment of the invention comprises the electrolyte additive. The electrolyte additive can effectively inhibit the increase of moisture and acidity of the electrolyte in the storage process, so that the electrolyte provided by the embodiment of the invention has good stability and safety.

In some embodiments, the solvent in the electrolyte is a carbonate solvent, wherein the carbonate is a chain or cyclic carbonate. In some embodiments, at least one of Propylene Carbonate (PC), Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) is selected as a solvent of the electrolyte.

Further, the mass fraction of the carbonate solvent in the electrolyte is 70-90%.

In some embodiments, the electrolyte salt (i.e., the main salt) in the above electrolyte is lithium hexafluorophosphate.

Further, the mass percentage of lithium tetrafluoroborate in the electrolyte is 10% to 15%, and the mass percentage of lithium oxalato borate and the derivatives thereof prepared by the preparation method of lithium oxalato borate and the derivatives thereof provided by the embodiment of the invention or the above-mentioned lithium oxalato borate derivatives as additives in the electrolyte is 0.1% to 5%.

Correspondingly, the embodiment of the invention also provides a secondary battery, which comprises the electrolyte.

The secondary battery provided by the embodiment of the invention comprises the electrolyte. The electrolyte can effectively improve the safety and stability of the obtained secondary battery, and experiments prove that the secondary battery provided by the embodiment of the invention has better normal-temperature cycle performance and high-temperature cycle performance and longer service life.

Specifically, the secondary battery provided by the embodiment of the invention comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm. In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer on the surface thereof, and the components of the positive electrode active slurry for preparing the positive electrode active material layer include a positive electrode active material selected from Li, a conductive agent, and a binder₂TiO₃、LiCoO₂、LiMn₂O₄、LiFePO₄、LiNiO₂、LiNixCoyMnzO₂Or LiNixCoyAlzO₂And (x + y + z ═ 1), wherein the mass of the positive electrode active material accounts for 88-98% of the mass of the positive electrode active slurry.

In some embodiments, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer on the surface of the negative electrode current collector, the components of the negative electrode active slurry for preparing the negative electrode active material layer comprise a negative electrode active material, a conductive agent, a binder and a thickening agent, the negative electrode active material is selected from at least one of artificial graphite, mesocarbon microbeads and natural graphite coated or doped and modified, and the mass of the negative electrode active material accounts for 90-96% of the mass of the negative electrode active slurry.

It should be noted that the positive electrode current collector (or the negative electrode current collector) and the positive electrode active material layer (or the negative electrode active material layer) only provide a common positional relationship, that is, the positive electrode active slurry (or the negative electrode active slurry) is coated on the surface of the positive electrode current collector (or the negative electrode current collector) to form the positive electrode active material layer (or the negative electrode active material layer), and should not be construed as a limitation to the secondary battery provided in the embodiment of the present invention. According to the actual situation, the current collector and the active material may be changed according to the requirements for the battery performance, such as various ways of filling the mixed powder of the positive electrode active material (or the negative electrode active material) and the auxiliary agent in the hollow positive electrode current collector (or the hollow negative electrode current collector).

Furthermore, a solvent is required to be added when the positive electrode active slurry and the negative electrode active slurry are prepared, wherein the solvent is high-purity deionized water or N-methylpyrrolidone (NMP), the conductivity of the high-purity deionized water is less than or equal to 3us/cm, and the moisture content of the N-methylpyrrolidone is less than or equal to 100 ppm.

Further, the positive and negative electrode conductive agents are selected from at least one of conductive graphite, acetylene black and nano silver powder, and the mass of the positive and negative electrode conductive agents accounts for 1% -6% of the mass of the positive and negative electrode active slurry respectively.

Further, the positive and negative binders are selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, acrylic acid and styrene butadiene rubber, and the mass of the positive and negative binders accounts for 1% -6% of the mass of the positive and negative active slurry respectively.

Further, the negative electrode thickening agent is sodium carboxymethyl cellulose, and the mass of the negative electrode thickening agent accounts for 1% -4% of the mass of the negative electrode active slurry.

In some embodiments, the membrane may be a three-layer composite membrane with a thickness of 12 μm to 36 μm and a porosity of 30% to 65%.

In order to make the details and operation of the above-mentioned embodiments of the present invention clearly understood by those skilled in the art, and to make the methods for preparing lithium oxalato borate and its derivatives, the electrolyte and the secondary battery according to the embodiments of the present invention remarkably show the improved performance, the above-mentioned technical solutions are exemplified by a plurality of examples below.

Example 1

The embodiment provides a preparation method of LiODFB, which comprises the following steps:

(11) 18g of oxalic acid and 40ml of dimethyl carbonate were added to a 250ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of the dimethyl carbonate solution was put into a two-necked flask, the system was stirred at room temperature to obtain a suspension, and 46g of Me was added₃Adding 20ml dimethyl carbonate solution of SiCl (Me represents methyl) into two-neck bottle via dropping funnel, controlling dropping speed at 1 drop/second, releasing gas during dropping process and gradually dissolving insoluble substance, completely dissolving insoluble substance after all dropping process, and making the solution colorless and transparentContinuously stirring for 3h at room temperature, heating to 40 ℃, discharging a large amount of HCl gas, and reacting for 1h at 40 ℃. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(12) Cooling the system to 0 ℃, adding 100mg of triethylamine, keeping the temperature at 0 ℃, stirring for 1h, standing, settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solids. And (3) adding 60ml of dimethyl carbonate into the white solid by normal pressure filtration, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, separating out a large amount of white crystals, and placing the white crystals in a 40 ℃ oven for vacuum drying for 3 hours to obtain 25.8g of white powdery solid with the yield of 90%. In a glove box, 5mg of the obtained white powdery solid was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₂O₄BF₂[ODFB]^-136.83, the resulting white powdery solid was confirmed to be LiODFB.

Example 2

The embodiment provides a preparation method of LiODFB, which comprises the following steps:

(21) 18g of oxalic acid and 40ml of dimethyl carbonate were added to a 250ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of the dimethyl carbonate solution was put into a two-necked flask, the system was stirred at room temperature to obtain a suspension, and 46g of Me was added₃Adding 20ml of SiCl dimethyl carbonate solution into a two-mouth bottle through a dropping funnel, controlling the dropping speed to be 1 drop/second, releasing gas and gradually dissolving insoluble substances in the dropping process, completely dissolving the insoluble substances after all dropping is finished, enabling the solution to be colorless and transparent, continuously stirring at room temperature for 3 hours, then heating to 40 ℃, releasing a large amount of HCl gas, and keeping the temperature at 40 ℃ for reacting for 1 hour. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(22) Cooling the system to 0 ℃, adding 80mg of pyridine, keeping the temperature at 0 ℃, stirring for 1h, standing, settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solids. Normal pressure filtering directionAdding 60ml of dimethyl carbonate into the white solid, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, precipitating a large amount of white crystals, and placing the white crystals in a 40 ℃ oven for vacuum drying for 3 hours to obtain 26.5g of white powdery solid with the yield of 92%. In a glove box, 5mg of the obtained white powdery solid was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₂O₄BF₂[ODFB]^-136.83, the resulting white powdery solid was confirmed to be LiODFB.

Example 3

The embodiment provides a preparation method of LiODFB, which comprises the following steps:

(31) 18g of oxalic acid and 40ml of dimethyl carbonate were added to a 250ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of the dimethyl carbonate solution was put into a two-necked flask, the system was stirred at room temperature to obtain a suspension, and 46g of Me was added₃Adding 20ml of SiCl dimethyl carbonate solution into a two-mouth bottle through a dropping funnel, controlling the dropping speed to be 1 drop/second, releasing gas and gradually dissolving insoluble substances in the dropping process, completely dissolving the insoluble substances after all dropping is finished, enabling the solution to be colorless and transparent, continuously stirring at room temperature for 3 hours, then heating to 40 ℃, releasing a large amount of HCl gas, and keeping the temperature at 40 ℃ for reacting for 1 hour. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(32) Cooling the system to 0 ℃, adding 110mg of 2, 6-lutidine, keeping the temperature at 0 ℃, stirring for 1h, standing for settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solid. And (3) adding 60ml of dimethyl carbonate into the white solid by normal pressure filtration, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, separating out a large amount of white crystals, and placing the white crystals in a 40 ℃ oven for vacuum drying for 3 hours to obtain 27.3g of white powdery solid with the yield of 95%. In a glove box, the obtained white powdery solid 5mg was taken and added to 2ml of anhydrous acetonitrile to be completely dissolved, and an organic solvent was usedThe suspension was removed by filtration through a filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis results showed LC-MS (ESI) C₂O₄BF₂[ODFB]^-136.83, the resulting white powdery solid was confirmed to be LiODFB.

Example 4

The embodiment provides a method for preparing LiBOB, which comprises the following steps:

(41) 36g of oxalic acid and 100ml of dimethyl carbonate were added to a 500ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of dimethyl carbonate solution (A) is added into a two-neck flask, the system is stirred at room temperature to form a suspension, and 95g of Me is added₃Adding 50ml of SiCl dimethyl carbonate solution into a two-mouth bottle through a dropping funnel, controlling the dropping speed to be 1 drop/second, releasing gas and gradually dissolving insoluble substances in the dropping process, completely dissolving the insoluble substances after all dropping is finished, enabling the solution to be colorless and transparent, continuously stirring at room temperature for 3 hours, then heating to 40 ℃, releasing a large amount of HCl gas, keeping the temperature at 40 ℃, reacting for 1 hour, then heating to 60 ℃, and continuously reacting for 3 hours. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(42) Cooling the system to 0 ℃, adding 200mg of triethylamine, keeping the temperature at 0 ℃, stirring for 1h, standing, settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solids. And (3) adding 120ml of dimethyl carbonate into the white solid by normal pressure filtration, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, separating out a large amount of white crystals, and placing the white crystals in a 60 ℃ oven for vacuum drying for 3 hours to obtain 34.8g of white powdery solid with the yield of 90%. In a glove box, 5mg of the obtained white powdery solid was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₄O₈B[BOB]^-186.85, the white powdery solid obtained was confirmed to be LiBOB.

Example 5

The embodiment provides a method for preparing LiBOB, which comprises the following steps:

(51) 36g of oxalic acid and 100ml of dimethyl carbonate were added to a 500ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of dimethyl carbonate solution (A) is added into a two-neck flask, the system is stirred at room temperature to form a suspension, and 95g of Me is added₃Adding 50ml of SiCl dimethyl carbonate solution into a two-mouth bottle through a dropping funnel, controlling the dropping speed to be 1 drop/second, releasing gas and gradually dissolving insoluble substances in the dropping process, completely dissolving the insoluble substances after all dropping is finished, enabling the solution to be colorless and transparent, continuously stirring at room temperature for 3 hours, then heating to 40 ℃, releasing a large amount of HCl gas, keeping the temperature at 40 ℃, reacting for 1 hour, then heating to 60 ℃, and continuously reacting for 3 hours. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(52) Cooling the system to 0 ℃, adding 160mg of pyridine, keeping the temperature at 0 ℃, stirring for 1h, standing, settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solids. And (3) adding 120ml of dimethyl carbonate into the white solid by normal pressure filtration, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, separating out a large amount of white crystals, and placing the white crystals in a 60 ℃ oven for vacuum drying for 3 hours to obtain 35.6g of white powdery solid with the yield of 92%. In a glove box, 5mg of the obtained white powdery solid was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₄O₈B[BOB]^-186.85, the white powdery solid obtained was confirmed to be LiBOB.

Example 6

The embodiment provides a method for preparing LiBOB, which comprises the following steps:

(61) 36g of oxalic acid and 100ml of dimethyl carbonate were added to a 500ml two-necked flask, the solid was not completely dissolved with stirring at room temperature, and then 19g of LiBF was added₄80ml of dimethyl carbonate solution (A) is added into a two-neck flask, the system is stirred at room temperature to form a suspension, and 95g of Me is added₃Adding 50ml of SiCl dimethyl carbonate solution into a two-mouth bottle through a dropping funnel, controlling the dropping speed to be 1 drop/second, releasing gas and gradually dissolving insoluble substances in the dropping process, completely dissolving the insoluble substances after all dropping is finished, enabling the solution to be colorless and transparent, continuously stirring at room temperature for 3 hours, then heating to 40 ℃, releasing a large amount of HCl gas, keeping the temperature at 40 ℃, reacting for 1 hour, then heating to 60 ℃, and continuously reacting for 3 hours. The HCl gas produced by the reaction was absorbed by saturated aqueous solution of sodium hydroxide.

(62) Cooling the system to 0 ℃, adding 220mg of 2, 6-lutidine, keeping the temperature at 0 ℃, stirring for 1h, standing for settling, filtering at normal pressure, and concentrating the filtrate to separate out a large amount of white solid. And (3) adding 120ml of dimethyl carbonate into the white solid by normal pressure filtration, heating to 60 ℃ to completely dissolve the white solid, then cooling to room temperature to concentrate and crystallize, separating out a large amount of white crystals, and placing the white crystals in a 60 ℃ oven for vacuum drying for 3 hours to obtain 36.8g of white powdery solid with the yield of 95%. In a glove box, 5mg of the obtained white powdery solid was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₄O₈B[BOB]^-186.85, the white powdery solid obtained was confirmed to be LiBOB.

Example 7

The embodiment provides a preparation method of LiODCNB, which comprises the following steps:

adding 14.4g LiODFB and 50ml dimethyl carbonate into a 250ml double-mouth bottle, stirring the solid at room temperature to completely dissolve the solution to obtain a colorless transparent solution, and adding 20g Me₃50ml of SiCN dimethyl carbonate solution is added into a two-mouth bottle through a dropping funnel, the dropping speed is controlled to be 1 drop/second, and Me is added in the dropping process₃The SiF gas is discharged, the solution is colorless and transparent, and after all the SiF gas is completely dripped, the solution is continuously stirred for 3 hours at room temperature and then is heated to 40 ℃ for reaction for 1 hour. Standing at room temperature, filtering under normal pressure to remove suspended solid impurities to obtain colorless transparent solution, concentrating at room temperature under reduced pressure to obtain white solid, recrystallizing the white solid with 30ml dimethyl carbonate, and cooling to 40 deg.CVacuum drying for 3h gave 14.5g of the expected product in 92% yield. Reaction-derived Me₃The SiF gas was absorbed by a saturated aqueous solution of sodium hydroxide. In a glove box, 5mg of the target product was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₂O₄BC₂N₂[ODCNB]^-150.86, the target product is LiODCNB.

Example 8

This embodiment provides a method for preparing LiODNCOB, which includes the following steps:

to a 250ml two-necked flask were added 14.4g of LiODFB and 50ml of dimethyl carbonate, and the solid was completely dissolved in the solvent with stirring at room temperature to dissolve 24g of Me₃50ml of dimethyl carbonate solution containing SiN C O is added into a two-mouth bottle through a dropping funnel, the dropping speed is controlled to be 1 drop/second, gas is released during the dropping process, the solution is colorless and transparent, after all the dropping is finished, the stirring is continued for 3 hours at room temperature, and then the temperature is raised to 40 ℃ for reaction for 1 hour. Standing at room temperature and filtering under normal pressure to remove suspended solid impurities to obtain colorless transparent solution, concentrating at room temperature under reduced pressure to obtain white solid, recrystallizing the white solid with 30ml of dimethyl carbonate, and vacuum drying at 40 ℃ for 3h to obtain 17.7g of the target product with the yield of 93%. Reaction-derived Me₃The SiF gas was absorbed by a saturated aqueous solution of sodium hydroxide. In a glove box, 5mg of the target product was taken, added to 2ml of anhydrous acetonitrile to be completely dissolved, suspended matters were removed by filtration using an organic filter membrane, a small amount of the filtrate was injected using a syringe and analyzed by liquid chromatography-mass spectrometry (Thermo Fisher Scientific, non-high resolution), and the analysis result showed LC-MS (ESI) C₂O₄BN₂C₂O₂[ODNCOB]^-182.86, the target product was found to be LiODNCOB.

Experimental example 1

Dissolving lithium hexafluorophosphate in a carbonate solvent to make the concentration of the lithium hexafluorophosphate be 1.0mol/L, wherein the carbonate solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 3:5:2, the mass fraction of the mixed solvent is 70-90%, and the mixed solvent is used as a control sample electrolyte and is numbered as (1);

dissolving lithium hexafluorophosphate in a carbonate solvent to enable the concentration of the lithium hexafluorophosphate to be 1.0mol/L, wherein the carbonate solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 3:5:2, and the mass fraction of the carbonate solvent is 70-90%; adding the LiODFB obtained in the example 1 into the mixed solution of the lithium hexafluorophosphate and the carbonic ester in a glove box (the water content and the oxygen content in the glove box are lower than 1ppm) in an argon atmosphere to obtain an electrolyte containing the LiODFB, wherein the LiODFB accounts for 1% of the mass of the electrolyte and is numbered as (2);

dissolving lithium hexafluorophosphate in a carbonate solvent to enable the concentration of the lithium hexafluorophosphate to be 1.0mol/L, wherein the carbonate solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 3:5:2, and the mass fraction of the carbonate solvent is 70-90%; respectively adding the LiBOB obtained in example 4 into the mixed solution of lithium hexafluorophosphate and carbonic ester in a glove box (the water content and the oxygen content in the glove box are lower than 1ppm) in an argon atmosphere to obtain an electrolyte containing the LiBOB, wherein the mass of the LiBOB accounts for 1 percent of the mass of the electrolyte, and the serial number is (3);

dissolving lithium hexafluorophosphate in a carbonate solvent to enable the concentration of the lithium hexafluorophosphate to be 1.0mol/L, wherein the carbonate solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 3:5:2, and the mass fraction of the carbonate solvent is 70-90%; adding the LiODCNB obtained in example 7 into the mixed solution of lithium hexafluorophosphate and carbonate in a glove box (the water and oxygen content in the glove box is lower than 1ppm) in an argon atmosphere to obtain an electrolyte containing the LiODCNB, wherein the LiODCNB accounts for 1% of the mass of the electrolyte, and the electrolyte is numbered as (4);

dissolving lithium hexafluorophosphate in a carbonate solvent to enable the concentration of the lithium hexafluorophosphate to be 1.0mol/L, wherein the carbonate solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to the mass ratio of 3:5:2, and the mass fraction of the carbonate solvent is 70-90%; LiODNCOB obtained in example 8 was added to the mixed solution of lithium hexafluorophosphate and carbonate in a glove box (containing water and oxygen in an amount of less than 1ppm) under an argon atmosphere to obtain an electrolyte solution containing LiODNCOB in an amount of 1% by mass based on the mass of the electrolyte solution, and the electrolyte solution was numbered as (5);

the prepared electrolytes (1) to (5) are sealed and stored in a glove box, a small amount of the electrolytes are respectively placed in a fluorination bottle, and the water content and the acidity are tested after the electrolytes are placed for 1 month at room temperature, wherein the specific data are shown in table 1.

Table 1 electrolyte moisture and acidity test results

Electrolyte numbering	Additive agent	Addition quality (%)	Moisture (ppm)	Acidity (ppm)
					(1)	\	\	82	126
(2)	LiODFB	1	75	130
					(3)	LiBOB	1	78	124
(4)	LiODCNB	1	54	112
					(5)	LiODNCOB	1	42	74

The results in table 1 show that LiODFB obtained in example 1 of the present invention has a function of reducing the moisture of the electrolyte, and that liodbs obtained in example 4 of the present invention, LiODCNB obtained in example 7 of the present invention, and liodcob obtained in example 8 of the present invention all have a function of reducing the moisture and acidity of the electrolyte, wherein the LiODCNB and LiODCNB have a more significant effect of reducing the moisture and acidity of the electrolyte, and can improve the stability of the electrolyte and improve the safety of the battery to a certain extent.

Experimental example 2

This experimental example has made CR2032 type button lithium ion battery, and the battery includes: stainless steel battery case, gasket, spring plate, positive electrode material, negative electrode material, separator material, and electrolytes (1) to (4) prepared in experimental example 1.

Wherein, the commonly used nickel cobalt lithium manganate (LiNi) is used_0.6Co_0.2Mn_0.2O₂NCM622 for short) as a positive electrode active substance, artificial graphite as a negative electrode active substance, and a positive electrode active slurry obtained by mixing 96% of the positive electrode active substance, 2% of PVDF as a binder and 2% of Super S as conductive carbon black in mass ratio. And coating the obtained positive active slurry on an aluminum foil in a dust-free room, wherein the thickness of the aluminum foil is 0.06-0.20mm, and thus obtaining the positive pole piece. 96% of negative electrode active slurry by massMixing the material, 2% of CMC/SBR adhesive and 2% of Super S conductive carbon black, and coating the obtained negative active slurry on copper foil in a dust-free room to obtain a negative pole piece with the thickness of 0.06-0.20 mm. And (3) placing the positive pole piece and the negative pole piece obtained by coating into an air-blowing drying oven, drying for 12 hours at the temperature of 80 ℃, stamping and slicing the dried pole pieces, drying for 24 hours in a vacuum drying oven at the temperature of 130 ℃, transferring into a glove box (the content of water and oxygen in the glove box is lower than 1ppm), weighing and calculating the mass of an active substance, and finally preparing a 2032 button cell in the glove box. The button cell adopts the mode of assembly from bottom to top, is positive pole shell, anodal, diaphragm, negative pole, gasket, shell fragment, negative pole shell in proper order to reduce shell fragment and gasket and cause positive negative pole piece dislocation at rotatory in-process.

The electrolyte solutions (1) to (5) prepared in experimental example 1 were used to fill the above-described button cells, and the obtained button cells were (a), (b), (c), (d), and (e) in this order. To maintain the consistency of the experiment, all button cells used the same volume of electrolyte. And dropwise adding the electrolyte between the layers of the button cell by using a syringe. And then carrying out charge and discharge tests on the prepared battery, and carrying out electrochemical performance tests on the assembled button battery by using a LAND charge and discharge test system. The battery test voltage is 3.0-4.3V, the capacity retention rate of the battery is tested after the battery is subjected to constant current charge-discharge circulation for 200 weeks at room temperature and 45 ℃ respectively, and the specific data are shown in Table 2.

TABLE 2 Battery capacity retention test results

As can be seen from the test results in table 2, the electrolyte containing LiODFB obtained in example 1 of the present invention, liobb obtained in example 4 of the present invention, LiODCNB obtained in example 7 of the present invention, and LiODCNB obtained in example 8 of the present invention can effectively improve the normal temperature cycle performance and the high temperature cycle performance of the battery, and the LiODCNB and LiODCNB have better effects on improving the normal temperature cycle performance and the high temperature cycle performance of the battery. Therefore, the preparation method of the lithium oxalate borate and the derivatives thereof, and the corresponding lithium oxalate borate derivatives lithium oxalate dinitrile borate and lithium oxalate diisocyanate borate which are used as electrolyte additives can improve the safety of the battery, improve the normal-temperature and high-temperature cycle performance of the battery and have multiple functions.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.