Preparation method of rubidium or cesium electrolyte additive

Abstract

The invention provides a preparation method of a rubidium or cesium electrolyte additive. The preparation method comprises the following steps: S1, providing at least two solvents, and mixing the solvents to form a reaction solvent for later use; s2, taking a certain volume of reaction solvent, then adding rubidium salt or cesium salt, and fully stirring to completely dissolve the rubidium salt or cesium salt to prepare rubidium or cesium source feed liquid; s3, taking a certain volume of reaction solvent, then adding a lithium salt raw material, and fully stirring to completely dissolve the lithium salt raw material to prepare a lithium salt material liquid; s4, the rubidium or cesium source material liquid and the lithium salt material liquid are added into a reaction tank, stirring is conducted for a period of time, then filtering is conducted, an insoluble substance A and filtrate A are obtained, the insoluble substance A is composed of positive ions of rubidium or cesium and large-radius negative ions, and the insoluble substance A is precipitated due to the fact that the insoluble substance A has low solubility in a solvent; and S5, preparing a washing solution at a certain temperature, circularly washing the insoluble substance A according to a certain solid-to-liquid ratio, and drying the solid to obtain the rubidium or cesium electrolyte additive.

Description

Technical Field

[0001] This application relates to the field of electrolyte additive preparation, and more particularly to a method for preparing a rubidium or cesium electrolyte additive. Background Technology

[0002] With the rapid advancements in rechargeable battery technology, higher demands are being placed on their cycle performance and rate capability. Currently, limited by the current level of lithium iron phosphate (LFP) battery technology, some LFP batteries suffer from short lifespans and poor rate performance. Cesium hexafluorophosphate and rubidium tetrafluoroborate, containing rubidium / cesium compounds with large anionic radii, have significant potential as electrolyte additives to improve cell rate performance, extend the cycle life of LFP batteries, and enhance the low-temperature performance of electrolytes. However, there are currently no standardized process flows for these rubidium / cesium salts used in lithium-ion battery electrolytes. Most rubidium / cesium-containing electrolyte additives contain halogens, which means that traditional preparation methods not only require expensive rubidium / cesium halides as basic raw materials but also necessitate the addition of hazardous halogen-containing chemicals in a harsh anhydrous environment. Therefore, although rubidium / cesium additives significantly improve electrolyte performance, the lack of low-cost, high-efficiency preparation processes hinders their widespread adoption in the electrolyte field.

[0003] Rubidium / cesium compounds used as electrolyte additives often contain large-radius anions. Due to the large radius of rubidium / cesium ions, compounds formed with these large-radius anions often have high lattice energy, resulting in low solubility in water. This allows rubidium / cesium compounds containing large-radius anions, such as rubidium / cesium hexafluorophosphate and rubidium / cesium tetrafluoroborate, to be effectively separated from aqueous systems via ion exchange. However, ion exchange still has the following drawbacks: Because the production of raw materials such as sodium, potassium, and ammonium hexafluorophosphate and difluorophosphate has not yet reached a large-scale industrialization, their high cost still affects the cost of rubidium / cesium electrolyte additives. Although the corresponding lithium salt raw materials are widely used in the field of secondary batteries, and the production of lithium salt raw materials such as lithium hexafluorophosphate and lithium difluorophosphate has reached a large scale and has a lower cost, the hydrolysis of lithium salts will introduce a large number of impurities into the rubidium / cesium electrolyte additives prepared in pure aqueous phase systems. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems by providing a method for preparing rubidium or cesium electrolyte additives.

[0005] The technical solution of this application is implemented as follows: This invention provides a method for preparing a rubidium or cesium electrolyte additive, comprising the following steps: S1, providing at least two solvents to be mixed to form a reaction solvent for later use; S2, take a certain volume of reaction solvent, then add rubidium salt or cesium salt, stir thoroughly to completely dissolve it to prepare rubidium or cesium source solution, wherein the rubidium salt or cesium salt is rubidium sulfate or cesium sulfate; S3, take a certain volume of reaction solvent, then add lithium salt raw material, stir thoroughly to make it completely dissolved to prepare lithium salt solution; S4, the rubidium or cesium source solution and the lithium salt solution are added to the reaction tank, stirred for a period of time and then filtered to obtain insoluble matter A and filtrate A. Insoluble matter A is composed of rubidium or cesium cations and large-radius anions, which makes it have low solubility in the solvent and thus precipitates out. S5, prepare a washing solution at a certain temperature, and after circulating and washing the insoluble substance A according to a certain solid-liquid ratio, dry the solid to obtain a rubidium or cesium electrolyte additive.

[0006] As a further improvement, in step S1, the at least two solvents are selected from water, and at least one solvent selected from methanol, ethanol, propanol, ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, methyl ethyl carbonate, and dipropyl carbonate; preferably, the at least two solvents are selected from ethanol and water as reaction solvents, wherein the volume ratio of ethanol / water is 0.1-10:1.

[0007] As a further improvement, in step S2, the concentration of rubidium sulfate or cesium sulfate is 1-500 g / L.

[0008] As a further improvement, in step S3, the lithium salt raw material is selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium perchlorate, and the concentration of the lithium salt raw material is 1-500 g / L.

[0009] As a further improvement, in step S4, the volume ratio of the rubidium or cesium source solution and the lithium salt solution when mixed is 0.1-10:1.

[0010] As a further improvement, in step S5, the washing liquid is selected from one or more combinations of water, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, N-methylpyrrolidone, etc.; and the temperature of the washing liquid is 15-90℃.

[0011] As a further improvement, in step S5, the solid-liquid ratio of the insoluble substance A to the detergent is 1:1 to 1:40 g / mL.

[0012] As a further improvement, the preparation method further includes: S6, the filtrate A is used to obtain a solid product by evaporation and crystallization, and the evaporated solvent is collected by condensation and reflux and reused as the reaction solvent in step S1.

[0013] As a further improvement, the preparation method further includes: S7, the solid product from step 6 is selectively dissolved using a separating agent, and filtered to obtain insoluble substance B and filtrate B. Insoluble substance B is returned to the reaction tank in step S4.

[0014] As a further improvement, the preparation method further includes: S8, the filtrate B from step S7 is evaporated and crystallized to obtain crude lithium sulfate byproduct. The evaporated solvent is collected by condensation and reflux and reused as the separating agent in step S7.

[0015] As a further improvement, the preparation method further includes: in step S7, the separating agent is selected from one or more combinations of water, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and N-methylpyrrolidone.

[0016] As a further improvement, in step S5, the temperature for drying the solid is 25-100 °C.

[0017] As a further improvement, in step S6, the filtrate A is distilled under reduced pressure, and the evaporation and crystallization temperature is 60-200℃.

[0018] As a further improvement, in step S7, the solid-liquid ratio of the solid to the separating agent is 1:1 to 1:40 g / mL.

[0019] As a further improvement, in step S8, the filtrate B is distilled under reduced pressure, and the evaporation and crystallization temperature is 60-200℃.

[0020] The advantages or beneficial effects of the above technical solutions include at least the following: This invention prepares commonly used rubidium / cesium electrolyte additives based on the principle of ion exchange. It uses low-cost cesium sulfate as the cesium source, instead of specific, expensive rubidium / cesium sources such as rubidium / cesium fluoride as reactants. It eliminates the need for hazardous gases such as hydrogen fluoride and phosphorus pentafluoride, and does not require a harsh anhydrous environment, significantly simplifying the process and effectively reducing the cost of large-scale production. This breaks down the cost barrier for the widespread application of rubidium / cesium additives in the electrolyte industry. It provides a low-cost, high-efficiency, environmentally friendly, and scalable process route for preparing commonly used rubidium / cesium electrolyte additives.

[0021] This invention utilizes an organic solvent-water system to effectively suppress the hydrolysis of lithium salts, allowing lithium salt raw materials such as lithium hexafluorophosphate and lithium difluorophosphate, which are already in mass production, to be included in the raw material selection range of the ion exchange method, thus greatly reducing the production cost of the ion exchange method.

[0022] This invention optimizes the traditional washing process by using a hot detergent to purify the product, which can effectively achieve the physical desorption of impurities (cations and anions) and make the impurity content of the sample meet battery-grade standards.

[0023] This invention also includes a process design for by-product recovery. By utilizing the solubility difference between the product and the by-product, a suitable separating agent is selected. This effectively recovers rubidium / cesium resources that are slightly soluble in the solvent, and also recovers and enriches the crude lithium sulfate by-product. This further improves the economic added value of the process.

[0024] This invention also involves evaporation-condensation treatment of the solvents and separating agents involved in the process, ensuring that the solvents can be reused. Attached Figure Description

[0025] The accompanying drawings illustrate exemplary embodiments of the present application and, together with the description thereof, serve to explain the principles of the present application. These drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification.

[0026] Figure 1 A flowchart of the preparation method of the rubidium or cesium electrolyte additive provided in the embodiments of the present invention is shown.

[0027] Figure 2 The X-ray diffraction pattern of the cesium hexafluorophosphate electrolyte additive product prepared in Example 1 of the present invention is shown.

[0028] Figure 3 The product ion chromatography peak area integration results of the cesium hexafluorophosphate electrolyte additive prepared in Example 1 of the present invention are shown.

[0029] Figure 4 The Karl Fischer moisture content test curve of the cesium hexafluorophosphate electrolyte additive prepared in Example 1 of the present invention is shown.

[0030] Figure 5 The free acid autopotential titration curve of the cesium hexafluorophosphate electrolyte additive prepared in Example 2 of the present invention is shown.

[0031] Figure 6 The X-ray diffraction pattern of the rubidium tetrafluoroborate electrolyte additive product prepared in Example 2 of the present invention is shown.

[0032] Figure 7The results of the ion chromatography peak area integration of the rubidium tetrafluoroborate electrolyte additive prepared in Example 2 of the present invention are shown.

[0033] Figure 8 The Karl Fischer moisture content test curve of the rubidium tetrafluoroborate electrolyte additive prepared in Example 2 of the present invention is shown.

[0034] Figure 9 The free acid autopotential titration curve of the rubidium tetrafluoroborate electrolyte additive prepared in Example 2 of the present invention is shown. Detailed Implementation

[0035] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0036] It should be noted that, where there is no conflict, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] The names of the messages or information exchanged between multiple devices in the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of these messages or information.

[0038] Reference Figure 1 This invention provides a method for preparing a rubidium or cesium electrolyte additive, comprising the following steps: S1, providing at least two solvents to be mixed to form a reaction solvent for later use; S2, take a certain volume of reaction solvent, then add rubidium salt or cesium salt, stir thoroughly to make it completely dissolved to prepare rubidium or cesium source solution; S3, take a certain volume of reaction solvent, then add lithium salt raw material, stir thoroughly to make it completely dissolved to prepare lithium salt solution; S4, the rubidium or cesium source solution and the lithium salt solution are added to the reaction tank, stirred for a period of time and then filtered to obtain insoluble matter A and filtrate A. Insoluble matter A is composed of rubidium or cesium cations and large-radius anions, which makes it have low solubility in the solvent and thus precipitates out. S5, prepare a washing solution at a certain temperature, and after circulating and washing the insoluble substance A according to a certain solid-liquid ratio, dry the solid to obtain a rubidium or cesium electrolyte additive.

[0039] As a further improvement, in step S1, the at least two solvents are selected from water, and at least one solvent selected from methanol, ethanol, propanol, ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, methyl ethyl carbonate, and dipropyl carbonate. Preferably, the at least two solvents are selected from ethanol and water as reaction solvents. Rubidium / cesium compounds containing large-radius anions, such as rubidium / cesium hexafluorophosphate and rubidium / cesium tetrafluoroborate, can be effectively separated from aqueous systems by ion exchange. However, during the separation process, the hydrolysis of lithium salts leads to the introduction of a large number of impurities into the rubidium / cesium electrolyte additive prepared from a pure aqueous system. This invention creatively introduces a second solvent to suppress the hydrolysis of lithium salts. Therefore, it is necessary to adjust the ratio of the two solvents to effectively separate rubidium / cesium compounds on the one hand, and effectively suppress the hydrolysis of lithium salts on the other hand. Preferably, the volume ratio of ethanol to water is 0.1-10:1, more preferably, the volume ratio of ethanol to water is 0.5-0.9:1. In several embodiments, the volume ratios of ethanol to water are 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.81:1, 0.825:1, 0.83:1, 0.84:1, 0.85:1, and 0.9:1, respectively.

[0040] As a further improvement, in step S2, the rubidium salt or cesium salt is rubidium sulfate or cesium sulfate, and its concentration is 1-500 g / L. Preferably, the concentration of rubidium sulfate or cesium sulfate is 50-100 g / L.

[0041] As a further improvement, in step S3, the lithium salt raw material is selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium perchlorate, and the concentration of the lithium salt raw material is 1-500 g / L. Preferably, the concentration of the lithium salt raw material is 50-100 g / L.

[0042] As a further improvement, in step S4, the volume ratio of the rubidium or cesium source solution to the lithium salt solution is 0.1-10:1. Preferably, the volume ratio of the rubidium or cesium source solution to the lithium salt solution is 1-1.5:1.

[0043] As a further improvement, in step S5, the washing liquid is selected from one or more combinations of water, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, N-methylpyrrolidone, etc.; and the temperature of the washing liquid is 15-90℃.

[0044] As a further improvement, in step S5, the solid-liquid ratio of the insoluble substance A to the detergent is 1:1 to 1:40 g / mL. A small amount of Li remains adsorbed on the surface and between the crystal lattice of the rubidium / cesium precipitate.+ SO42 - Cl - Impurity ions. When the liquid-to-solid ratio is too low (<1:1), the washing liquid volume is too small, the impurity concentration quickly reaches saturation, and the desorption driving force decreases. Experiments show that when the liquid-to-solid ratio is ≥1:5, the secondary adsorption capacity of SO42 can be reduced to below 0.002%. Although cesium hexafluorophosphate and rubidium tetrafluoroborate are "poorly soluble," they are not absolutely insoluble (solubility in water at 25℃ is 0.3–0.8 g / 100 mL). When the liquid-to-solid ratio is >1:40, the total washing liquid volume is too large, the product begins to dissolve significantly, and the yield decreases by 2%–5%; at the same time, the energy consumption for evaporation recovery increases sharply. Therefore, preferably, the solid-to-liquid ratio of the insoluble substance A to the detergent is 1:5-1:10 g / mL. In several other embodiments, the solid-liquid ratio of the insoluble substance A to the detergent is 1:5 g / mL, 1:5.5 g / mL, 1:6 g / mL, 1:6.5 g / mL, 1:7 g / mL, 1:7.5 g / mL, 1:8 g / mL, 1:8.5 g / mL, 1:9 g / mL, and 1:9.5 g / mL.

[0045] As a further improvement, it also includes: S6, the filtrate A is used to obtain a solid product by evaporation and crystallization, and the evaporated solvent is collected by condensation and reflux and reused as the reaction solvent in step S1.

[0046] As a further improvement, it also includes: S7, the solid product from step 6 is selectively dissolved using a separating agent, and filtered to obtain insoluble substance B and filtrate B. Insoluble substance B is returned to the reaction tank in step S4.

[0047] As a further improvement, it also includes: S8, the filtrate B from step S7 is evaporated and crystallized to obtain crude lithium sulfate byproduct. The evaporated solvent is collected by condensation and reflux and reused as the separating agent in step S7.

[0048] As a further improvement, it further includes: in step S7, the separating agent is selected from one or more combinations of water, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and N-methylpyrrolidone.

[0049] As a further improvement, in step S5, the temperature for drying the solid is 25-100 °C.

[0050] As a further improvement, in step S6, the filtrate A is distilled under reduced pressure, and the evaporation and crystallization temperature is 60-200℃.

[0051] As a further improvement, in step S7, the solid-liquid ratio of the solid to the separating agent is 1:1 to 1:40 g / mL.

[0052] As a further improvement, in step S8, the filtrate B is distilled under reduced pressure, and the evaporation and crystallization temperature is 60-200℃. Example 1: This embodiment uses cesium sulfate as the rubidium / cesium source and lithium hexafluorophosphate as the desired anionic compound to synthesize cesium hexafluorophosphate (CsPF6) electrolyte additive through the above technical solution, mainly including the following steps.

[0053] Preparation of reaction solvent: Mix 200 mL of ethanol and 240 mL of water thoroughly and use the mixture as the reaction solvent.

[0054] Preparation of cesium sulfate solution: Add 12.0 g of cesium sulfate to 120 mL of mixed solvent to prepare a 100 g / L cesium sulfate solution, and stir thoroughly with a glass rod for 10 min to ensure complete dissolution.

[0055] Preparation of lithium hexafluorophosphate solution: Weigh 10.0 g of lithium hexafluorophosphate in a nitrogen atmosphere and place it in a polytetrafluoroethylene beaker. Transfer it to air and quickly add 100 mL of reaction solvent. Stir thoroughly with a polytetrafluoroethylene stir bar for 10 min to completely dissolve it.

[0056] Ion exchange reaction: The above 120 mL cesium sulfate solution was quickly added to 100 mL lithium hexafluorophosphate solution, and the mixture was stirred continuously for 10 min using a polytetrafluoroethylene stir bar. After the reaction was completed, a solid-liquid mixture containing a transparent gelatinous precipitate was obtained.

[0057] Filtration of primary cesium hexafluorophosphate product: Install the vacuum filtration apparatus, check the tightness of the connection between the glass frit funnel and the filtration flask, and check for air leaks at the vacuum pump connection. Trim 0.22 μm filter paper to make it slightly smaller than the glass frit funnel, and add distilled water to moisten the filter paper. Slightly open the vacuum valve to ensure a tight connection between the filter paper and the funnel. Turn on the vacuum pump, pour in the solid-liquid mixture, and filter for at least 20 minutes until the solid and liquid are completely separated.

[0058] Solid-liquid separation: Transfer the filtrate to a 250 mL round-bottom flask. Set the water tank temperature of the rotary evaporator to 50°C. Attach the glass splash guard to the top of the round-bottom flask and then connect it to the rotary evaporator. Turn on the vacuum pump, circulate the water, and then evacuate the rotary evaporator to a vacuum before starting the rotation. After the ethanol has almost completely evaporated, adjust the temperature of the aqueous phase to 80°C and continue rotary evaporation until the liquid is completely evaporated. Collect the remaining solid byproducts in the flask. The evaporated liquid is collected by reflux and reused as a reaction solvent.

[0059] Washing solution preparation: Take 100 mL of ultrapure water and heat it to 80℃ to obtain the washing solution.

[0060] Primary product washing: Pour out the filtrate from the filtration flask and set it aside. Wash the filtration flask. Reinstall the cleaned filtration flask and check the airtightness of the filtration apparatus. Then slowly add 100 mL of the prepared washing solution and filter for more than 10 minutes until the solid and liquid are completely separated. Pour out the filtrate from the filtration flask and continue to use it as washing solution. Repeat the above steps 4 times. Close the filtration apparatus. When removing the solid from the funnel, remove the funnel from the filtration flask, hold the funnel tube with your left hand, invert it, and "slap" your left hand with your right hand to make the solid fall onto a clean watch glass along with the filter paper. Product drying: Transfer the solid product to a vacuum drying oven at 60℃ and dry for 12 h. After drying, grind the sample, put it into a sample bottle, label it, and store it in a dry and cool place.

[0061] Byproduct separation: Add 20 mL of deionized water to the solid byproduct in (6), stir for 10 min and filter to obtain crude cesium hexafluorophosphate. The solid product obtained by vacuum distilling the filtrate at 80°C using a rotary evaporator is crude lithium sulfate. The evaporated liquid is collected by condensation and reused as a separating agent.

[0062] Test Example 1: The X-ray diffraction pattern of the product prepared by the ion exchange process in this embodiment is as follows: Figure 2 As shown, the product is a single-phase cesium hexafluorophosphate and does not contain any other phases.

[0063] The cationic impurity detection of the product prepared by the ion exchange process in this embodiment is shown in Table 1. All data have been adjusted for pure water background. Since CsPF6 is commonly used as an additive in LiPF6 electrolyte systems, the cationic impurity detection items refer to the LiPF6 industry standard HG / T 4066-2015, including Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, and As. Except for Na, K, and Ca, all other impurities in the product are below the instrument's detection limit of 0.01 mg / L. The Na, K, and Ca contents in the product are only 0.0007%, 0.0035%, and 0.0002%, respectively, which meets the general requirements for use in battery-grade materials.

[0064] Table 1. Detection results of cationic impurities in cesium hexafluorophosphate products

[0065] The chromatographic peak area integral results of the product prepared by the ion exchange process in this embodiment are as follows: Figure 3 As shown in Figure 2, the results of the ion chromatography peak area integration analysis of the product SO4 are presented. 2- and Cl -The content is 0.0018% and 0.0001%, which meets the general usage requirements of general battery-grade materials.

[0066] Table 2 shows the results of the integrated analysis of the peak area in ion chromatography for the product.

[0067] The Karl Fischer moisture titration curve of the product prepared by the ion exchange process in this embodiment is as follows: Figure 4 As shown in Figure 3, the moisture content analysis results of the product are as follows. The moisture content of the product is 0.0061%, which meets the general usage requirements of general battery-grade materials.

[0068] Table 3. Karl Fischer moisture test results for the products.

[0069] The free acid titration curve of the product prepared by the ion exchange process in this embodiment is as follows: Figure 5 As shown in Figure 4, the product moisture content analysis results are presented. The calculated free acid content (calculated as HF) of the product is 0.0187%, which meets the general usage requirements for battery-grade materials. Table 4 Results of Free Acid Titration Analysis of the Product

[0070] Example 2: This embodiment uses rubidium sulfate as the rubidium / cesium source and lithium tetrafluoroborate as the desired anionic compound to synthesize rubidium tetrafluoroborate (RbBF4) electrolyte additive through the above technical solution, mainly including the following steps.

[0071] Preparation of reaction solvent: Mix 200 mL of ethanol and 240 mL of water thoroughly and use the mixture as the reaction solvent. Preparation of rubidium sulfate solution: Add 8.85 g of rubidium sulfate to 120 mL of mixed solvent to prepare a rubidium sulfate solution of 73.75 g / L. Stir thoroughly with a glass rod for 10 min to ensure complete dissolution. Preparation of lithium tetrafluoroborate solution: Weigh 7.24 g of lithium tetrafluoroborate in a nitrogen atmosphere and place it in a polytetrafluoroethylene beaker. Transfer it to air and quickly add 100 mL of reaction solvent. Stir thoroughly with a polytetrafluoroethylene stir bar for 10 min to completely dissolve it. Ion exchange reaction: The above 120 mL rubidium sulfate solution was quickly added to 100 mL lithium tetrafluoroborate solution, and the mixture was stirred continuously for 10 min using a polytetrafluoroethylene stir bar. After the reaction was completed, a solid-liquid mixture containing a transparent gel-like precipitate was obtained.

[0072] Filtration of rubidium tetrafluoroborate primary product: Install the vacuum filtration apparatus, check the connection between the glass frit funnel and the filtration flask for tightness, and check for air leaks at the vacuum pump connection. Trim the 0.22 μm filter paper to be slightly smaller than the glass frit funnel, and add distilled water to moisten the filter paper. Slightly open the vacuum valve to ensure a tight connection between the filter paper and the funnel. Turn on the vacuum pump, pour in the solid-liquid mixture, and filter for at least 20 minutes until the solid and liquid are completely separated. Solid-liquid separation: Transfer the filtrate to a 250 mL round-bottom flask. Set the water tank temperature of the rotary evaporator to 50°C. Attach the glass anti-splash bulb to the top of the round-bottom flask and then connect it to the rotary evaporator. Turn on the vacuum pump, circulate the water, and then evacuate the rotary evaporator to a vacuum before starting the rotation. After the ethanol has almost completely evaporated, adjust the temperature of the aqueous phase to 80°C and continue rotary evaporation until the liquid is completely evaporated. Collect the remaining solid byproducts in the flask. The evaporated liquid is collected by reflux and reused as a reaction solvent. Preparation of washing solution: Take 100 mL of ultrapure water and heat it to 80℃ to obtain the washing solution; Primary product washing: Pour out the filtrate from the filtration flask and set it aside. Wash the filtration flask. Reinstall the cleaned filtration flask and check the airtightness of the filtration apparatus. Then slowly add 100 mL of the prepared washing solution and filter for more than 10 minutes until the solid and liquid are completely separated. Pour out the filtrate from the filtration flask and continue to use it as washing solution. Repeat the above steps 4 times. Close the filtration apparatus. When removing the solid from the funnel, remove the funnel from the filtration flask, hold the funnel tube with your left hand, invert it, and "tap" your left hand with your right hand to make the solid fall onto a clean watch glass along with the filter paper. Product drying: Transfer the solid product to a vacuum drying oven at 60℃ and dry for 12 h. After drying, grind the sample, put it into a sample bottle, label it, and store it in a dry and cool place.

[0073] Byproduct separation: 20 mL of deionized water was added to the solid byproduct in the solid-liquid separation step, and after stirring for 10 min, the solid insoluble matter obtained by filtration was crude rubidium tetrafluoroborate. The solid product obtained by vacuum distillation of the filtrate at 80 °C using a rotary evaporator was crude lithium sulfate. The evaporated liquid was collected by condensation and reused as a separating agent.

[0074] Test Example 2: The X-ray diffraction pattern of the product prepared by the ion exchange process in this embodiment is as follows: Figure 6 As shown, the product is a single-phase rubidium tetrafluoroborate and does not contain any other phases.

[0075] The cationic impurity detection of the product prepared by the ion exchange process in this embodiment is shown in Table 5. All data have been adjusted for pure water background. Since RbBF4 is commonly used as an additive in LiPF6 electrolyte systems, the cationic impurity detection items refer to the LiPF6 industry standard HG / T 4066-2015, including Fe, K, Na, Ca, Cd, Cr, Cu, Mg, Ni, Pb, Zn, and As. Except for Na, K, and Ca, all other impurities in the product are below the instrument's detection limit of 0.01 mg / L. The Na, K, and Ca contents in the product are only 0.0006%, 0.0040%, and 0.0003%, respectively, meeting the general requirements for battery-grade materials.

[0076] Table 5 shows the results of cationic impurity detection in rubidium tetrafluoroborate products.

[0077] The chromatographic peak area integral results of the product prepared by the ion exchange process in this embodiment are as follows: Figure 7 As shown in Figure 6, the results of the ion chromatography peak area integration analysis of the product SO4 are presented. 2- and Cl - The content is 0.0016% and 0.0003%, which meets the general usage requirements of general battery-grade materials.

[0078] Table 6 shows the results of the integrated analysis of the peak area of ​​the product in ion chromatography.

[0079] The Karl Fischer moisture titration curve of the product prepared by the ion exchange process in this embodiment is as follows: Figure 8 As shown in Figure 7, the moisture content analysis results of the product are as follows. The moisture content of the product is 0.0065%, which meets the general usage requirements of general battery-grade materials.

[0080] Table 7 shows the Karl Fischer moisture test results for the products.

[0081] The free acid titration curve of the product prepared by the ion exchange process in this embodiment is as follows: Figure 9 As shown in Figure 8, the product moisture content analysis results are presented. The calculated free acid content (calculated as HF) of the product is 0.0192%, which meets the general usage requirements of typical battery-grade materials.

[0082] Table 8 shows the results of the free acid titration analysis of the product.

[0083] Those skilled in the art should understand that the above embodiments are merely for illustrative purposes and are not intended to limit the scope of this application. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of this application.

Claims

1. A process for the preparation of a rubidium or cesium electrolyte additive, characterized in that, The method comprises the following steps: S1, providing at least two solvents to be mixed to form a reaction solvent for standby; S2, taking a certain volume of the reaction solvent, then adding rubidium salt or cesium salt, and fully stirring to make it completely dissolved to configure a rubidium or cesium source solution, wherein the rubidium salt or cesium salt is rubidium sulfate or cesium sulfate; S3, taking a certain volume of the reaction solvent, then adding lithium salt raw material, and fully stirring to make it completely dissolved to configure a lithium salt solution; S4, adding the rubidium or cesium source solution and the lithium salt solution into a reaction tank, stirring for a period of time, and then filtering to obtain insoluble substance A and filtrate A, wherein the insoluble substance A is precipitated out due to the lower solubility of the rubidium or cesium cation and the large radius anion in the solvent; S5, configuring a washing liquid at a certain temperature, and then performing cyclic washing on the insoluble substance A according to a certain solid-liquid ratio, and then drying the solid to obtain a rubidium or cesium electrolyte additive.

2. The method of preparing a rubidium or cesium electrolyte additive according to claim 1, characterized in that, In step S1, the at least two solvents are selected from water, and at least one of methanol, ethanol, propanol, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, methyl ethyl carbonate, and dipropyl carbonate.

3. The method of claim 2, wherein the additive is prepared by the steps of: (a) dissolving a compound of formula (I) in a solvent; (b) adding a base to the solution; and (c) removing the solvent from the solution. In step S2, the concentration of the rubidium sulfate or cesium sulfate is 1-500 g / L, and the at least two solvents are selected from ethanol and water as the reaction solvent, wherein the volume ratio of ethanol / water is 0.1-10:

1.

4. The method of preparing a rubidium or cesium electrolyte additive according to claim 1, characterized in that, In step S3, the lithium salt raw material is selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, or lithium perchlorate, and the concentration of the lithium salt raw material is 1-500 g / L.

5. The method of preparing a rubidium or cesium electrolyte additive according to claim 1, wherein In step S4, the volume ratio of the rubidium or cesium source solution and the lithium salt solution is 0.1-10:1 when mixed.

6. The method of preparing a rubidium or cesium electrolyte additive according to claim 1, wherein In step S5, the washing liquid is selected from one or more than two combinations of water, methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and N-methyl pyrrolidone; and the temperature of the washing liquid is 15-90°C.

7. The process for the preparation of a rubidium or cesium electrolyte additive according to claim 6, characterized in that, In step S5, the solid-liquid ratio of the insoluble substance A and the washing liquid is 1:1-1:40 g / mL.

8. The method for preparing the rubidium or cesium electrolyte additive as described in claim 1, characterized in that, Further comprising: S6, the filtrate A is evaporated to obtain a solid product by crystallization, and the evaporated solvent is collected by condensation reflux to be reused as the reaction solvent in step S1.

9. The method of claim 8, wherein the additive is prepared by the steps of: a) dissolving a compound of formula (I) in a solvent; b) adding a base to the solution; and c) removing the solvent from the solution. Further comprising: S7, the solid product in step 6 is selectively dissolved by a separation agent, and then filtered to obtain insoluble substance B and filtrate B, and the insoluble substance B is returned to the reaction tank in step S4.

10. The method of preparing a rubidium or cesium electrolyte additive according to claim 9, wherein Further comprising: S8, the filtrate B in step S7 is evaporated to obtain a crude lithium sulfate byproduct by crystallization, and the evaporated solvent is collected by condensation reflux to be reused as the separation agent in step S7.

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