Preparation method of lithium hydrogen oxalate and lithium difluoro (oxalato) borate, and electrolyte

Abstract

The invention provides a preparation method of lithium hydrogen oxalate and lithium difluoro (oxalato) borate and an electrolyte. The preparation method of lithium hydrogen oxalate comprises the following steps: dissolving oxalic acid in water to obtain an oxalic acid solution; mixing an oxalic acid solution and a lithium source, and reacting at a first temperature to obtain a product; and adding a metal ion removal reagent into the product to carry out impurity removal treatment, and then carrying out first post-treatment. The preparation method of lithium difluoro (oxalato) borate comprises the following steps: dissolving lithium hydrogen oxalate and a boron trifluoride compound in an organic solvent to obtain a mixed solution; and adding trimethylchlorosilane into the mixed solution, carrying out a reaction at a second temperature, and then carrying out second post-treatment. The lithium hydrogen oxalate and the lithium difluoro (oxalato) borate prepared by the preparation method disclosed by the invention have extremely low metal impurity contents (less than 2.0 ppm and less than 1.0 ppm), and can greatly reduce the influence of metal ion impurities on the performance aspects of battery capacity, circulation, safety and the like when being used as electrolyte salt or an additive in a lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of material synthesis, and in particular to a compound applied to the field of new energy batteries, and more particularly to lithium hydrogen oxalate used as an electrolyte additive, a preparation method of lithium hydrogen oxalate, and a preparation method of lithium difluoro(oxalato)borate. Background Art

[0002] LiODFB (Lithium Difluoro(oxalato)borate) is a new type of electrolyte salt and is widely used in lithium-ion battery electrolytes. Its unique chemical structure gives it significant advantages in improving battery performance. LiODFB combines the characteristics of oxalate (C2O4²⁻) and fluoroborate (BF2⁻). It has high ionic conductivity, good thermal stability and electrochemical stability, and can form a stable solid electrolyte interface (SEI) film on the electrode surface. As an electrolyte additive, after LiODFB decomposes in the electrolyte, it can form a uniform and dense SEI film on the negative electrode surface, inhibit the further decomposition of the electrolyte, improve the antioxidant and reduction stability of the electrolyte, improve the cycle performance of the battery, reduce capacity attenuation, and enhance the high-temperature and low-temperature performance of the battery.

[0003] In addition, LiODFB can also be used as the main salt in the electrolyte or blended with other electrolyte salts (such as LiPF6) to provide high ionic conductivity, reduce the internal resistance of the battery, improve the rate performance of the battery, enhance the thermal stability of the electrolyte, and reduce side reactions at high temperatures. The gas generated during the decomposition of LiODFB is less, reducing the risk of battery swelling and thermal runaway. The formed SEI film has self-healing ability, which can prevent direct contact between the electrode and the electrolyte. After 1000 cycles, the capacity retention rate of the battery with LiODFB added can be increased by 10 - 20%. Under high-rate charge and discharge conditions, LiODFB can significantly reduce the polarization of the battery, improve the energy efficiency, and the temperature adaptability ranges from -20°C to 60°C. The LiODFB electrolyte exhibits excellent electrochemical performance.

[0004] The current preparation process of LiODFB uses oxalic acid, lithium oxalate, boron trifluoride and trimethylchlorosilane as raw materials. Among them, oxalic acid and lithium oxalate need to be dried separately, and part of the oxalic acid will sublimate during the drying process, causing harm to personnel and the environment. More importantly, due to the relatively high content of other metal ions in oxalic acid itself, the metal ions in commercially available oxalic acid / lithium oxalate are relatively high. For example, the iron ion is generally 20 ppm and the sodium ion is 30 - 50 ppm. The LiODFB prepared from these raw materials will cause the sodium, potassium, iron and other ions in the finished product to exceed the standard, and it is difficult to achieve a product with a total metal ion content of less than 1 ppm. Products with high impurity metal ions are harmful to battery performance.

[0005] For example, the reduction potential of metal impurity ions is lower than that of lithium ions. During the charging process, the metal impurity ions will first be embedded in the carbon negative electrode, occupying the positions where lithium ions are embedded, thus reducing the reversible capacity of the lithium-ion battery.

[0006] Metal impurities will accelerate the dissolution of the active material and the damage of the electrode structure, react with the electrolyte to produce corrosion and oxidation, damage the electrode structure, affect the insertion and extraction of lithium ions in the electrode, accelerate the pulverization and structural damage of the electrode material, and thus shorten the battery cycle life. Some substances formed by the reaction of metal impurities deposited on the battery surface will also cause an increase in the internal resistance of the battery and an increase in polarization. Metal impurities may cause abnormal heat accumulation during the charging or discharging process of the lithium battery, leading to battery thermal runaway and even battery explosion. Summary of the Invention

[0007] Based on the above problems, the object of the present invention is to provide a preparation method of lithium hydrogen oxalate and lithium difluorooxalate borate, and an electrolyte. The lithium hydrogen oxalate and lithium difluorooxalate borate prepared by the preparation method of the present invention have extremely low metal impurity contents (less than 2.0 ppm and less than 1.0 ppm respectively). When used as electrolyte salts or additives in lithium-ion batteries, it can greatly reduce their impact on battery performance such as capacity, cycle, and safety.

[0008] To achieve the above object, the first aspect of the present invention provides a preparation method of lithium hydrogen oxalate, including the steps of: (1) Dissolving oxalic acid in water to obtain an oxalic acid solution; (2) Mixing the oxalic acid solution and a lithium source and reacting at a first temperature to obtain a product, and the molar ratio of oxalate ions in the oxalic acid solution to lithium ions in the lithium source is 1:0.9 - 1.0; (3) Adding a metal ion removal reagent to the product for impurity removal treatment, and then performing a first post-treatment.

[0009] The present invention controls the chemical reaction equivalent ratio of the oxalic acid solution and the lithium source to a certain value to prepare lithium hydrogen oxalate. Then, a metal ion removal reagent is added for impurity removal treatment. Through the complexation or adsorption of the metal ion removal reagent, metal ions such as sodium, potassium, and iron are combined to form a precipitate. Since lithium ions are relatively small and can easily pass through the pores of the precipitate, the purpose of separating lithium ions from other metal ions is achieved. Therefore, the lithium hydrogen oxalate prepared has a very low metal impurity content (less than 2.0 ppm). If used as an electrolyte salt or additive for lithium-ion batteries, the low impurity content has little impact on battery performance such as capacity, cycle, and safety.

[0010] As a technical solution of the present invention, the concentration of the oxalic acid solution is 10 - 80 wt.%, and the temperature at which oxalic acid is dissolved in water is 40 - 60 °C.

[0011] As a technical solution of the present invention, the first temperature is 80-100 °C, and the reaction time is 0.5-5.0 h.

[0012] As a technical solution of the present invention, the lithium source includes lithium hydroxide and / or lithium carbonate.

[0013] As a technical solution of the present invention, the chelating agent includes at least one of EDTA, activated carbon, and alumina.

[0014] As a technical solution of the present invention, the first post-treatment includes at least one of filtration, cooling crystallization, washing, and drying.

[0015] The lithium hydrogen oxalate prepared by the preparation method of lithium hydrogen oxalate provided by the second aspect of the present invention has a total metal ion content of <2.0 ppm. The impurity content is low, and when used as an electrolyte salt or additive for lithium ion batteries, it has little impact on battery performance such as capacity, cycle life, and safety.

[0016] The third aspect of the present invention provides a method for preparing lithium difluorooxalate borate, which includes the steps of: (1) Dissolving lithium hydrogen oxalate and a boron trifluoride compound in an organic solvent to obtain a mixed solution, where the lithium hydrogen oxalate is the lithium hydrogen oxalate prepared by the aforementioned preparation method of lithium hydrogen oxalate or the aforementioned lithium hydrogen oxalate; (2) Adding trimethylchlorosilane to the mixed solution and reacting at a second temperature, and then performing a second post-treatment.

[0017] The present invention uses lithium hydrogen oxalate with extremely low impurity content as the oxalic acid raw material, and reacts with a boron trifluoride compound and trimethylchlorosilane to prepare lithium difluorooxalate borate with extremely low impurity content. The total metal ions of the prepared lithium difluorooxalate borate are <1.0 ppm, and the content of low-metal ion impurities is extremely low. Therefore, when applied to batteries, it has little negative impact on the batteries. Moreover, this preparation method has a simple process, is environmentally friendly, and has a high yield.

[0018] As a technical solution of the present invention, the organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and the boron trifluoride compound includes boron trifluoride or a boron trifluoride carbonate complex.

[0019] As a technical solution of the present invention, the chemical reaction equivalent ratio of the lithium hydrogen oxalate, the boron trifluoride compound, and the trimethylchlorosilane is 1:0.95-1.40:1.0-1.5.

[0020] As a technical solution of the present invention, the second temperature is 10-90 °C, and the reaction is carried out at the second temperature for 1-8 h.

[0021] As a technical solution of the present invention, the second post-treatment includes at least one of filtration, cooling crystallization, washing, and drying.

[0022] The fourth aspect of the present invention provides the use of lithium hydrogen oxalate prepared by the aforementioned method for preparing lithium hydrogen oxalate, the aforementioned lithium hydrogen oxalate, or lithium difluorooxalatoborate prepared by the aforementioned method for preparing lithium difluorooxalatoborate as an electrolyte salt or an additive in a battery.

[0023] The fifth aspect of the present invention provides an electrolyte solution, comprising a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes lithium hydrogen oxalate prepared by the aforementioned method for preparing lithium hydrogen oxalate, the aforementioned lithium hydrogen oxalate, or lithium difluorooxalatoborate prepared by the aforementioned method for preparing lithium difluorooxalatoborate, and the additive accounts for 0.01-10.0% of the mass of the electrolyte solution. Description of the Drawings

[0024] Figure 1 It is the IC spectrogram of lithium difluorooxalatoborate for Example 6. Detailed Embodiments

[0025] The present invention respectively provides a method for preparing lithium hydrogen oxalate and a method for preparing lithium difluorooxalatoborate. The content of metal ion impurities in lithium hydrogen oxalate prepared by the method for preparing lithium hydrogen oxalate of the present invention is very low, and the total amount of metal ions contained is <2.0 ppm. It can be used as a raw material to prepare lithium difluorooxalatoborate, or can be used as an electrolyte salt or an additive in a lithium-ion battery. When used as an electrolyte salt, lithium hydrogen oxalate can be used in mixture with other electrolyte salts (such as lithium hexafluorophosphate), and it can account for 0.1-10.0% of the total mass of the electrolyte salts. When used as an additive, lithium hydrogen oxalate can account for 0.01-5.0% of the mass of the electrolyte solution (including a non-aqueous organic solvent, an electrolyte salt, and an additive). The content of metal ion impurities in lithium difluorooxalatoborate prepared by the method for preparing lithium difluorooxalatoborate of the present invention is very low, and the total amount of metal ions contained is <1.0 ppm. It can be used as an electrolyte salt or an additive in a lithium-ion battery. When used as an electrolyte salt, lithium difluorooxalatoborate can be used alone or in mixture with other electrolyte salts (such as lithium hexafluorophosphate). When used in mixture, lithium difluorooxalatoborate can account for 1.0-25.0% of the total mass of the electrolyte salts. When used as an additive, lithium difluorooxalatoborate can account for 0.01-10.0% of the mass of the electrolyte solution (including a non-aqueous organic solvent, an electrolyte salt, and an additive).

[0026] The method for preparing lithium hydrogen oxalate of the present invention includes the following steps.

[0027] (1) Dissolve oxalic acid in water to obtain an oxalic acid solution.

[0028] (2) Mix the oxalic acid solution and the lithium source and react at a first temperature to obtain a product, wherein the molar ratio of oxalate ions in the oxalic acid solution to lithium ions in the lithium source is 1:0.9 - 1.0.

[0029] (3) Add a metal ion removal reagent to the product for impurity removal treatment, and then perform a first post-treatment.

[0030] Among them, the concentration of the oxalic acid solution is 10-80 wt.%, and as an example, the concentration can be but is not limited to 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.%. The oxalic acid may or may not contain crystal water, and further, the oxalic acid may be oxalic acid dihydrate. The temperature at which the oxalic acid is dissolved in water is 40-60 °C, and as an example, the temperature can be but is not limited to 40 °C, 42 °C, 44 °C, 46 °C, 48 °C, 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, 60 °C. The lithium source includes lithium hydroxide and / or lithium carbonate, that is, an alkaline lithium compound, and lithium hydroxide and / or lithium carbonate may or may not contain crystal water. The oxalic acid solution and the lithium source react at a first temperature, and the first temperature is 80-100 °C. As an example, the first temperature can be but is not limited to 80 °C, 82 °C, 84 °C, 86 °C, 88 °C, 90 °C, 92 °C, 94 °C, 96 °C, 98 °C, 100 °C. The reaction time is 0.5-5.0 h, and as an example, it can be but is not limited to 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h. After the reaction of the oxalic acid solution and the lithium source, a metal ion removing reagent is used to remove metal ion impurities. The impurity removal treatment includes mixing and stirring the product and the metal ion removing reagent for 0.4-4.0 h. As an example, the stirring time can be but is not limited to 0.4 h, 0.8 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h. The metal ion removing reagent includes at least one of EDTA, activated carbon, and alumina. Preferably, the metal ion removing reagent includes EDTA and activated carbon. Among them, EDTA can complex metal ions such as sodium, potassium, and iron to form complex precipitates, activated carbon can adsorb metal ions such as sodium, potassium, and iron, and alumina can also adsorb metal ion impurities such as sodium, potassium, and iron. Since lithium ions are relatively small and easily pass through the pores in the complex precipitate, activated carbon, or alumina, the lithium ions and other metal ions can be separated, and combined with the subsequent first post-treatment, other metal ions can be removed. The first post-treatment includes at least one of filtration, cooling crystallization, washing, and drying. Filtration can remove the complex precipitate, activated carbon adsorbing metal ions, and alumina, and the filtrate is taken for the first post-treatment. Filtration can be carried out by centrifugal stratification, vacuum filtration, or ordinary filtration. Cooling crystallization can be carried out at 10-20 °C. Washing can be carried out with an aqueous hydrochloric acid solution, saturated brine, or water and washed multiple times. Drying can be carried out with anhydrous sodium sulfate or in a vacuum drying oven.

[0031] In the preparation method of the present invention, the reaction equation between the oxalic acid solution and the lithium source can be shown as the following reaction formula.

[0032]

[0033] Further, lithium hydrogen oxalate prepared as described above can be used in the present invention to prepare lithium difluoro(oxalato)borate. The preparation method of lithium difluoro(oxalato)borate may include the following steps.

[0034] (1) Dissolve lithium hydrogen oxalate and boron trifluoride compound in an organic solvent to obtain a mixed solution.

[0035] (2) Add trimethylchlorosilane to the mixed solution and react at a second temperature, and then perform a second post-treatment.

[0036] Among them, the boron trifluoride compound may include boron trifluoride or boron trifluoride carbonate complex. Preferably, the boron trifluoride compound is a boron trifluoride carbonate complex. Since boron trifluoride is a gas with high risk, adding boron trifluoride to a carbonate to form a boron trifluoride carbonate complex can reduce the risk. Boron trifluoride carbonate complex is a bulk chemical raw material, which is cheap and easily available. The carbonate may be one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate. The organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Preferably, the organic solvent is the same as the carbonate in the boron trifluoride carbonate complex to improve the solubility of the system. The chemical reaction equivalent ratio of lithium hydrogen oxalate, boron trifluoride compound, and trimethylchlorosilane is 1:0.95 - 1.40:1.0 - 1.5. As an example, the chemical reaction equivalent ratio can be, but is not limited to, 1:0.95:1.0, 1:0.95:1.3, 1:0.95:1.5, 1:1.00:1.0, 1:1.00:1.3, 1:1.00:1.5, 1:1.20:1.0, 1:1.20:1.3, 1:1.20:1.5, 1:1.40:1.0, 1:1.40:1.3, 1:1.40:1.5, 1:1.10:1.2, 1:1.30:1.1.4, 1:1.10:1.4.

[0037] In the preparation method of the present invention, the reaction equation of the oxalic acid solution and the lithium source may be as shown in the following reaction formula.

[0038]

[0040] Lithium hydrogen oxalate, boron trifluoride compounds and trimethylchlorosilane react at a second temperature, where the second temperature is 10 to 90 °C. As an example, the second temperature can be, but is not limited to, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C. The reaction is carried out at the second temperature for 1 to 8 h. As an example, it can be, but is not limited to, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h. The second post-treatment includes at least one of filtration, cooling crystallization, washing and drying. Filtration can be carried out by centrifugal stratification, vacuum filtration or ordinary filtration. Cooling crystallization can be carried out at 10 to 20 °C. Washing can be carried out with an aqueous hydrochloric acid solution, saturated brine or water and multiple washes. Drying can be carried out using anhydrous sodium sulfate or a vacuum drying oven.

[0041] To better illustrate the purpose, technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be construed as limitations of the present invention.

[0042] Part 1: Preparation of Lithium Hydrogen Oxalate Example 1 This example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0043] (1) In a 1000 ml reaction flask, add 250 g of deionized water and 200 g of oxalic acid dihydrate, and raise the temperature to 50 °C to obtain an oxalic acid solution.

[0044] (2) Add 66.6 g of lithium hydroxide monohydrate to the oxalic acid solution, raise the temperature to 90 °C and react for 3 h until completely dissolved and clarified to obtain a product.

[0045] (3) Add 0.1 g of EDTA and 2 g of activated carbon to the product, mix and stir for 2 h, then filter. Cool the filtrate to 10 °C for crystallization, then filter and dry to obtain 149.1 g of lithium hydrogen oxalate, and the yield is 98%.

[0046] The prepared lithium hydrogen oxalate was subjected to 1H NMR detection, and the 1H NMR data was: 1H NMR(400MHz,DMSO): δ11(s,1H). It is consistent with the target structure, indicating that lithium hydrogen oxalate was synthesized.

[0047] The prepared lithium hydrogen oxalate was subjected to metal ion detection, and the contents of each ion were as follows: K / 0.1 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0.1 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0.1 ppm, Al / 0.0 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0.1 ppm, and the total amount of metal ions was 1.2 ppm.

[0048] Example 2 This example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0049] (1) In a 1000 ml reaction flask, 660 g of deionized water and 200 g of oxalic acid dihydrate were added, and the temperature was raised to 50 °C to obtain an oxalic acid solution.

[0050] (2) 58.5 g of lithium carbonate was added to the oxalic acid solution, and the temperature was raised to 90 °C and reacted for 4 h until completely dissolved and clarified to obtain a product.

[0051] (3) 0.1 g of EDTA and 2 g of activated carbon were added to the product, mixed and stirred for 2 h, then filtered. The filtrate was cooled to 10 °C for crystallization, and then filtered and dried to obtain 149.4 g of lithium hydrogen oxalate, and the yield was 98%.

[0052] The prepared lithium hydrogen oxalate was subjected to 1H NMR detection, and the 1H NMR data was: 1H NMR(400 MHz, DMSO): δ11(s,1H). It was consistent with the target structure, indicating that lithium hydrogen oxalate was synthesized.

[0053] The prepared lithium hydrogen oxalate was subjected to metal ion detection, and the contents of each ion were as follows: K / 0.1 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0.1 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0.0 ppm, Al / 0.1 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0.1 ppm, and the total amount of metal ions was 1.2 ppm.

[0054] Example 3 This example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0055] (1) In a 1000 ml reaction flask, 250 g of deionized water and 200 g of oxalic acid dihydrate were added, and the temperature was raised to 50 °C to obtain an oxalic acid solution.

[0056] (2) 66.6 g of lithium hydroxide monohydrate was added to the oxalic acid solution, and the temperature was raised to 90 °C and reacted for 3 h until completely dissolved and clarified to obtain a product.

[0057] (3) Add 0.5 g of alumina to the product, mix and stir for 2 h, then filter. Cool the filtrate to 10 °C for crystallization, filter again, and dry to obtain 149.7 g of lithium hydrogen oxalate with a yield of 98.4%.

[0058] Perform 1H NMR detection on the prepared lithium hydrogen oxalate. The 1H NMR data are as follows: 1H NMR (400 MHz, DMSO): δ 11 (s, 1H). It is consistent with the target structure, indicating the synthesis of lithium hydrogen oxalate.

[0059] Perform metal ion detection on the prepared lithium hydrogen oxalate. The contents of each ion are as follows: K / 0.2 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0.1 ppm, Pb / 0.1 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0.1 ppm, Al / 0.2 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0.1 ppm, and the total amount of metal ions is 1.6 ppm.

[0060] Example 4 This example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0061] (1) In a 1000 ml reaction flask, add 250 g of deionized water and 200 g of oxalic acid dihydrate, and raise the temperature to 50 °C to obtain an oxalic acid solution.

[0062] (2) Add 66.6 g of lithium hydroxide monohydrate to the oxalic acid solution, raise the temperature to 90 °C, and react for 3 h until completely dissolved and clarified to obtain the product.

[0063] (3) Add 0.1 g of EDTA to the product, mix and stir for 2 h, then filter. Cool the filtrate to 10 °C for crystallization, filter again, and dry to obtain 150.1 g of lithium hydrogen oxalate with a yield of 98.8%.

[0064] Perform 1H NMR detection on the prepared lithium hydrogen oxalate. The 1H NMR data are as follows: 1H NMR (400 MHz, DMSO): δ 11 (s, 1H). It is consistent with the target structure, indicating the synthesis of lithium hydrogen oxalate.

[0065] Perform metal ion detection on the prepared lithium hydrogen oxalate. The contents of each ion are as follows: K / 0.1 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0.1 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0 ppm, Al / 0 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0.1 ppm, and the total amount of metal ions is 1.1 ppm.

[0066] Example 5 This example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0067] (1) In a 1000 ml reaction flask, add 250 g of deionized water and 200 g of oxalic acid dihydrate, and raise the temperature to 50 °C to obtain an oxalic acid solution.

[0068] (2) Add 66.6 g of lithium hydroxide monohydrate to the oxalic acid solution, raise the temperature to 90 °C and react for 4 h until completely dissolved and clarified to obtain a product.

[0069] (3) Add 2 g of activated carbon to the product, mix and stir for 2 h, then filter. Cool the filtrate to 10 °C for crystallization, then filter and dry to obtain 150.2 g of lithium hydrogen oxalate, and the yield is 98.8%.

[0070] The prepared lithium hydrogen oxalate was subjected to 1H NMR detection, and the 1H NMR data was: 1H NMR(400 MHz, DMSO): δ11(s, 1H). It is consistent with the target structure, indicating that lithium hydrogen oxalate was synthesized.

[0071] The prepared lithium hydrogen oxalate was subjected to metal ion detection, and the content of each ion was: K / 0.1 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0.0 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0.1 ppm, Al / 0.1 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0.1 ppm, and the total amount of metal ions was 1.2 ppm.

[0072] Comparative Example 1 This comparative example is for the preparation of lithium hydrogen oxalate, and its preparation method includes the following steps.

[0073] (1) In a 1000 ml reaction flask, add 250 g of deionized water and 200 g of oxalic acid dihydrate, and raise the temperature to 50 °C to obtain an oxalic acid solution.

[0074] (2) Add 66.6 g of lithium hydroxide monohydrate to the oxalic acid solution, raise the temperature to 90 °C and react for 3 h until completely dissolved and clarified to obtain a product. Filter the product, cool the filtrate to 10 °C for crystallization, then filter and dry to obtain 151.1 g of lithium hydrogen oxalate, and the yield is 99.3%.

[0075] The prepared lithium hydrogen oxalate was subjected to 1H NMR detection, and the 1H NMR data was: 1H NMR(400 MHz, DMSO): δ11(s, 1H). It is consistent with the target structure, indicating that lithium hydrogen oxalate was synthesized.

[0076] The prepared lithium hydrogen oxalate was subjected to metal ion detection, and the contents of each ion were as follows: K / 0.2 ppm, Ca / 2.0 ppm, Fe / 1.0 ppm, Na / 1.0 ppm, Pb / 0.1 ppm, Ni / 1.0 ppm, Mg / 0.5 ppm, Cu / 0.2 ppm, Cd / 2.0 ppm, Cr / 1.0 ppm, Al / 2.0 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 1.0 ppm, and the total amount of metal ions was 12.2 ppm.

[0077] Part Two: Preparation of Lithium Difluorooxalatoborate Example 6 This example is for the preparation of lithium difluorooxalatoborate, and its preparation method includes the following steps.

[0078] (1) In a 1000 ml reaction flask, add 500 g of DMC, 40 g of lithium hydrogen oxalate prepared in Example 1, and 80 g of boron trifluoride dimethyl carbonate complex, and raise the temperature to 30 °C to obtain a mixed solution.

[0079] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h, then concentrate under vacuum, cool to 15 °C for crystallization, filtration, and drying to obtain 54.0 g of the product, with a yield of 90.2% and a purity of 99.87%.

[0080] The prepared lithium difluorooxalatoborate was subjected to 1H NMR detection, and the 1H NMR spectrum was as Figure 1 shown, which was consistent with the target structure, indicating that lithium difluorooxalatoborate was synthesized.

[0081] The prepared lithium difluorooxalatoborate was subjected to metal ion detection, and the contents of each ion were as follows: K / 0 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0 ppm, Ni / 0 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0 ppm, Cr / 0 ppm, Al / 0 ppm, Hg / 0 ppm, Zn / 0 ppm, As / 0.1 ppm, and the total amount of metal ions was 0.5 ppm.

[0082] Example 7 This example is for the preparation of lithium difluorooxalatoborate, and its preparation method includes the following steps.

[0083] (1) In a 1000 ml reaction flask, add 450 g of DEC, 40 g of lithium hydrogen oxalate prepared in Example 2, and 80 g of boron trifluoride dimethyl carbonate complex, and raise the temperature to 30 °C to obtain a mixed solution.

[0084] (2) Add 52 g of trimethylchlorosilane to the mixed solution and react at 65 °C for 4 h, then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 54.6 g of the product, with a yield of 91.2% and a purity of 99.80%.

[0085] Perform metal ion detection on the prepared lithium difluorooxalate borate. The contents of each ion are as follows: K / 0 ppm, Ca / 0 ppm, Fe / 0.1 ppm, Na / 0 ppm, Pb / 0.1 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0 ppm, Cr / 0 ppm, Al / 0 ppm, Hg / 0 ppm, Zn / 0.1 ppm, As / 0 ppm, and the total amount of metal ions is 0.6 ppm.

[0086] Example 8 This example is for the preparation of lithium difluorooxalate borate, and its preparation method includes the following steps.

[0087] (1) Add 500 g of DMC, 40 g of lithium hydrogen oxalate prepared in Example 3, and 80 g of boron trifluoride dimethyl carbonate complex to a 1000 ml reaction flask, and raise the temperature to 30 °C to obtain a mixed solution.

[0088] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h, then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 55.7 g of the product, with a yield of 93.0% and a purity of 99.82%.

[0089] Perform metal ion detection on the prepared lithium difluorooxalate borate. The contents of each ion are as follows: K / 0 ppm, Ca / 0.1 ppm, Fe / 0.1 ppm, Na / 0.1 ppm, Pb / 0.1 ppm, Ni / 0 ppm, Mg / 0 ppm, Cu / 0 ppm, Cd / 0.1 ppm, Cr / 0.1 ppm, Al / 0.1 ppm, Hg / 0 ppm, Zn / 0.1 ppm, As / 0 ppm, and the total amount of metal ions is 0.8 ppm.

[0090] Example 9 This example is for the preparation of lithium difluorooxalate borate, and its preparation method includes the following steps.

[0091] (1) Add 500 g of DMC, 40 g of lithium hydrogen oxalate prepared in Example 4, and 80 g of boron trifluoride dimethyl carbonate complex to a 1000 ml reaction flask, and raise the temperature to 30 °C to obtain a mixed solution.

[0092] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h. Then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 54.8 g of the product, with a yield of 91.5% and a purity of 99.84%.

[0093] Perform metal ion detection on the prepared lithium difluoro(oxalato)borate. The contents of each ion are as follows: K / 0.1 ppm, Ca / 0 ppm, Fe / 0.1 ppm, Na / 0.1 ppm, Pb / 0.1 ppm, Ni / 0 ppm, Mg / 0 ppm, Cu / 0 ppm, Cd / 0 ppm, Cr / 0.1 ppm, Al / 0 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0 ppm, and the total amount of metal ions is 0.7 ppm.

[0094] Example 10 This example is for the preparation of lithium difluoro(oxalato)borate, and its preparation method includes the following steps.

[0095] (1) In a 1000 ml reaction flask, add 500 g of DMC, 40 g of lithium hydrogen oxalate prepared in Example 5, and 80 g of boron trifluoride dimethyl carbonate complex, and raise the temperature to 30 °C to obtain a mixed solution.

[0096] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h. Then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 54.9 g of the product, with a yield of 91.7% and a purity of 99.88%.

[0097] Perform metal ion detection on the prepared lithium difluoro(oxalato)borate. The contents of each ion are as follows: K / 0.1 ppm, Ca / 0.1 ppm, Fe / 0 ppm, Na / 0 ppm, Pb / 0 ppm, Ni / 0.1 ppm, Mg / 0 ppm, Cu / 0.1 ppm, Cd / 0 ppm, Cr / 0.1 ppm, Al / 0 ppm, Hg / 0.1 ppm, Zn / 0.1 ppm, As / 0 ppm, and the total amount of metal ions is 0.7 ppm.

[0098] Comparative Example 2 This comparative example is for the preparation of lithium difluoro(oxalato)borate, and its preparation method includes the following steps.

[0099] (1) In a 1000 ml reaction flask, add 500 g of DMC, 40 g of lithium hydrogen oxalate prepared in Comparative Example 1, and 80 g of boron trifluoride dimethyl carbonate complex, and raise the temperature to 30 °C to obtain a mixed solution.

[0100] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h, then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 55.0 g of the product, with a yield of 91.9% and a purity of 93.67%.

[0101] Perform metal ion detection on the prepared lithium difluoro(oxalato)borate. The contents of each ion are as follows: K / 0.5 ppm, Ca / 0.1 ppm, Fe / 1.0 ppm, Na / 0 ppm, Pb / 1.0 ppm, Ni / 0.1 ppm, Mg / 0.1 ppm, Cu / 0.1 ppm, Cd / 0.1 ppm, Cr / 0.1 ppm, Al / 1.0 ppm, Hg / 0.1 ppm, Zn / 1.0 ppm, As / 0.1 ppm, and the total amount of metal ions is 5.3 ppm.

[0102] Comparative Example 3 This comparative example is for the preparation of lithium difluoro(oxalato)borate, and its preparation method includes the following steps.

[0103] (1) In a 1000 ml reaction flask, add 500 g of DMC, 40 g of lithium oxalate, and 80 g of boron trifluoride dimethyl carbonate complex, and raise the temperature to 30 °C to obtain a mixed solution.

[0104] (2) Add 45 g of trimethylchlorosilane to the mixed solution and react at 50 °C for 3 h, then concentrate under vacuum, cool down to 15 °C for crystallization, filtration, and drying to obtain 53.8 g of the product, with a yield of 89.9% and a purity of 90.57%.

[0105] Perform metal ion detection on the prepared lithium difluoro(oxalato)borate. The contents of each ion are as follows: K / 1.0 ppm, Ca / 1.0 ppm, Fe / 1.0 ppm, Na / 1.0 ppm, Pb / 1.0 ppm, Ni / 1.0 ppm, Mg / 2.0 ppm, Cu / 1.0 ppm, Cd / 1.0 ppm, Cr / 1.0 ppm, Al / 2.0 ppm, Hg / 1.0 ppm, Zn / 1.0 ppm, As / 1.0 ppm, and the total amount of metal ions is 16.0 ppm.

[0106] Part Three: Applications of Lithium Hydrogen Oxalate and Lithium Difluoro(Oxalato)Borate in Batteries 1.1 Preparation of non-aqueous electrolyte: In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 86.5 g of a mixed solvent obtained by uniformly mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 2:3 was used as an organic solvent. Then, 1 g of lithium difluorooxalate borate prepared in Examples 6 - 10 and Comparative Examples 2 - 3 was added respectively to obtain a mixed solution. The mixed solution was sealed and packaged and placed in a freezer (-4°C) for 2 h and then taken out. In a glove box filled with nitrogen (O2 < 1 ppm, H2O < 1 ppm), 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution. After mixing evenly, non-aqueous electrolytes 1 - 7# were prepared.

[0107] 1.2 Preparation of the positive electrode sheet: The ternary material LiNi 0.5 Co 0.2 Mn 0.3 Zr 0.03 O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNT) were mixed evenly in a mass ratio of 96.5:1.5:1:1 to form a lithium-ion battery positive electrode paste with a certain viscosity. After coating both sides of the aluminum foil and drying and rolling, a positive electrode sheet was obtained, and a lithium-ion battery positive electrode sheet that met the requirements was made.

[0108] 1.3 Preparation of the negative electrode sheet: Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) were made into a paste in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and the mixed paste was coated on both sides of the copper foil. After drying and rolling, a negative electrode sheet was obtained, and a lithium-ion battery negative electrode sheet that met the requirements was made.

[0109] 1.4 Preparation of the lithium-ion battery: The positive electrode sheet, negative electrode sheet, and separator prepared according to the above process were made into a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, a length of 60 mm, and a total capacity of 2 Ah through a stacking process. After vacuum baking at 75°C for 10 h and injecting non-aqueous electrolytes 1 - 7# respectively, and standing for 24 h, lithium-ion batteries 1 - 7# were completed.

[0110] Performance tests were carried out on lithium-ion batteries 1 - 7#, and the test results are shown in Table 1. The test conditions are as follows.

[0111] Place the battery in an environment of 25°C, charge it at a constant current of 0.1C to 4.2V, then charge it at a constant voltage of 4.2V until the current drops to 0.05C, record the charging capacity C1, then discharge it at a constant current of 0.5C to 2.5V, and record the discharge capacity C0. Then place the battery in an environment of 25°C, charge it at a constant current of 1.0C to 4.2V, then charge it at a constant voltage until the current drops to 0.05C, and then discharge it at a constant current of 1.0C to 2.5V. Repeat this cycle, and record the discharge capacity of the first cycle and the last cycle.

[0112] Capacity retention rate = (battery capacity C1 after 500 cycles / initial battery capacity C0) * 100% Table 1 Electrochemical performance test results of each example

[0113] From the results in Table 1, it can be seen that when lithium difluorooxalate borate prepared using lithium hydrogen oxalate after impurity removal treatment with a metal ion removal reagent is used in a lithium-ion battery, the performance of the battery can be significantly improved.

[0114] In addition, based on the comparison between lithium-ion battery 1# and lithium-ion batteries 3 - 5#, it can be seen that compared with alumina, when the metal ion removal reagent is EDTA or activated carbon, the metal impurity content of the prepared lithium hydrogen oxalate and lithium difluorooxalate borate is lower, and the performance of the battery is better.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only the embodiments listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing lithium hydrogen oxalate, characterized in that: Includes steps: (1) dissolving oxalic acid in water to obtain an oxalic acid solution; (2) mixing the oxalic acid solution and the lithium source and reacting them at a first temperature to obtain a product, wherein the molar ratio of oxalate ions in the oxalic acid solution to lithium ions in the lithium source is 1:0.9-1.0; (3) Adding a metal ion removal agent to the product for impurity removal treatment, and then performing a first post-treatment.

2. The method for preparing lithium hydrogen oxalate according to claim 1, characterized in that: Includes at least one of the following features ① to ⑤: ① The concentration of the oxalic acid solution is 10-80wt.%, and the temperature at which the oxalic acid is dissolved in water is 40-60°C; ② The first temperature is 80-100°C, and the reaction time is 0.5-5.0h; ③ The lithium source includes lithium hydroxide and / or lithium carbonate; ④ The metal ion removal agent includes at least one of EDTA, activated carbon and alumina; ⑤ The first post-treatment includes at least one of filtration, cooling crystallization, washing and drying.

3. The lithium hydrogen oxalate prepared by the method for preparing lithium hydrogen oxalate according to any one of claims 1 to 2, characterized in that: The total amount of metal ions contained is less than 2.0 ppm.

4. A method for preparing lithium difluorooxalatoborate, characterized in that: Includes steps: (1) dissolving lithium hydrogen oxalate and a boron trifluoride compound in an organic solvent to obtain a mixed solution, wherein the lithium hydrogen oxalate is the lithium hydrogen oxalate prepared by the method for preparing lithium hydrogen oxalate according to any one of claims 1 to 2 or the lithium hydrogen oxalate according to claim 3; (ii) adding trimethylsilyl chloride to the mixed solution and reacting the mixture at a second temperature, and then performing a second post-treatment.

5. The method for preparing lithium difluorooxalatoborate according to claim 4, characterized in that: The organic solvent includes at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and the boron trifluoride compound includes boron trifluoride or boron trifluoride carbonate complex.

6. The method for preparing lithium difluorooxalatoborate according to claim 4, characterized in that: The chemical reaction equivalent ratio of the lithium hydrogen oxalate, the boron trifluoride compound and the trimethylsilyl chloride is 1:0.95~1.40:1.0~1.

5.

7. The method for preparing lithium difluorooxalatoborate according to claim 4, characterized in that: The second temperature is 10-90° C., and the reaction is carried out at the second temperature for 1-8 hours.

8. The method for preparing lithium difluorooxalatoborate according to claim 4, characterized in that: The second post-treatment comprises at least one of filtration, cooling crystallization, washing and drying.

9. Use of the lithium hydrogen oxalate prepared by the method for preparing lithium hydrogen oxalate according to any one of claims 1 to 2, the lithium hydrogen oxalate according to claim 3, or the lithium difluoro oxalatoborate prepared by the method for preparing lithium difluoro oxalatoborate according to any one of claims 4 to 8 as an electrolyte salt or additive in a battery.

10. An electrolyte comprising a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive comprises lithium hydrogen oxalate prepared by the method for preparing lithium hydrogen oxalate according to any one of claims 1 to 2, the lithium hydrogen oxalate according to claim 3, or lithium difluoro oxalatoborate prepared by the method for preparing lithium difluoro oxalatoborate according to any one of claims 4 to 8, and the additive accounts for 0.01 to 10.0% of the mass of the electrolyte.

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