CN114920271A - Method for preparing lithium hexafluorophosphate by dry method - Google Patents
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- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D15/00—Lithium compounds
- C01D15/005—Lithium hexafluorophosphate
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- C—CHEMISTRY; METALLURGY
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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Abstract
The invention belongs to the field of preparation of lithium hexafluorophosphate, and particularly relates to a method for preparing lithium hexafluorophosphate by a dry method. The method comprises the following steps: 1) mixing lithium fluoride powder and iodine in an open container by using foam glass as a carrier, placing the mixture below the foam glass carrier, heating, and then loading the lithium fluoride on the foam glass by adopting an iodine evaporation method to obtain a porous composite intermediate; 2) and placing the porous composite intermediate in a sealed reaction container, introducing phosphorus pentafluoride gas for reaction, obtaining a pre-product after the conversion of lithium fluoride is realized, placing the pre-product in an organic solvent for ultrasonic treatment, and collecting the precipitate at the bottom of the organic solvent to obtain the lithium hexafluorophosphate. The method has the advantages of the two conventional dry-method lithium hexafluorophosphate preparation processes by matching the template method, and simultaneously effectively overcomes the defects of the two conventional dry-method processes; the whole process flow is brief and efficient, the preparation efficiency is extremely high, and the purity of the obtained product can reach more than 99.5 percent.
Description
Technical Field
The invention belongs to the field of preparation of lithium hexafluorophosphate, and particularly relates to a method for preparing lithium hexafluorophosphate by a dry method.
Background
Lithium hexafluorophosphate (LiPF) 6 ) The lithium ion battery electrolyte lithium salt is a common and common lithium ion battery electrolyte lithium salt, and experiments prove that the lithium ion battery electrolyte lithium salt has the best comprehensive performance and the best using effect. For this reason, the production and preparation of lithium hexafluorophosphate has always been a focus of research.
The dry preparation is a traditional method for preparing lithium hexafluorophosphate, and the dry preparation comprises a gas-solid method and a hydrogen fluoride solvent method. The gas-solid method is more traditional and simpler, has higher production efficiency, directly leads high-temperature gas of phosphorus pentafluoride into a sealed container with lithium fluoride, and reacts under the conditions of high temperature and high pressure to obtain a lithium hexafluorophosphate product. The hydrogen fluoride solvent method is characterized in that lithium fluoride is placed in anhydrous hydrogen fluoride for porosification, and meanwhile, low-flow phosphorus pentafluoride gas is introduced for reaction, although the method overcomes the defects of low conversion rate and low product purity of the more traditional gas-solid method, the scheme utilizes the anhydrous hydrogen fluoride, so that the anhydrous hydrogen fluoride has strong volatility and corrosivity and strong hazard, great potential safety hazard exists in the production process, the reaction process needs to be carried out at low temperature, and the energy consumption is high.
Therefore, it is necessary to improve the existing preparation method and comprehensively improve the effect, efficiency and safety of the lithium hexafluorophosphate prepared by the dry method.
Disclosure of Invention
In order to solve the problems of low conversion rate, low product quality, high energy consumption, large potential safety hazard and the like of the conventional dry method for preparing lithium hexafluorophosphate, the invention provides a method for preparing lithium hexafluorophosphate by a dry method.
The invention aims to: firstly, the preparation efficiency of lithium hexafluorophosphate prepared by a dry method is improved; secondly, improving the purity of the obtained lithium hexafluorophosphate product; and thirdly, hydrogen fluoride is avoided, and the preparation safety is improved.
In order to achieve the purpose, the invention adopts the following technical scheme.
A method for dry-process preparation of lithium hexafluorophosphate, the method comprising: 1) mixing lithium fluoride powder and iodine in an open container by using foam glass as a carrier, placing the mixture below the foam glass carrier, heating, and then loading the lithium fluoride on the foam glass by adopting an iodine evaporation method to obtain a porous composite intermediate;
2) and (3) placing the porous composite intermediate in a sealed reaction container, introducing phosphorus pentafluoride gas for reaction, obtaining a pre-product after the conversion of lithium fluoride is realized, placing the pre-product in an organic solvent for ultrasonic treatment, and collecting the precipitate at the bottom of the organic solvent to obtain the lithium hexafluorophosphate.
In the technical scheme of the invention, the advantages of two traditional dry preparation processes are combined, and the method has the advantages of simple process, high safety, high lithium fluoride conversion rate and high product purity. Specifically, in the technical scheme of the invention, lithium fluoride is loaded in a foam glass pore channel with a uniform porous structure in an iodine evaporation mode, and iodine is used as an adhesive to fix the lithium fluoride after contacting with the foam glass and condensing when meeting cold, so that the lithium fluoride is prevented from being lost. And in the subsequent process, a traditional gas-solid method scheme is adopted, the phosphorus pentafluoride gas is controlled to flow through the porous composite intermediate, due to the characteristics of the pore structure, the phosphorus pentafluoride gas and the lithium fluoride have more sufficient reaction time, the conversion rate of the lithium fluoride is improved, and meanwhile, the lithium fluoride is loaded on the pore structure, so that the lithium fluoride has a very large specific surface area, namely, a larger reaction area is actually provided, more effective and sufficient reaction can be realized, and the reaction efficiency is improved. Subsequent dissolution to remove iodine by specific organic solvent selection while ensuring that lithium hexafluorophosphate remains insoluble, separation of the support and product is achieved by a process of sonication. Therefore, for the technical scheme of the invention, the foam glass which has reaction inertia and unique structural characteristics in the whole reaction process and the iodine evaporation are taken as the core for realizing the whole scheme.
Preferably, the foam glass in the step 1) is open-cell foam silicon dioxide, and the open-cell rate is more than or equal to 50 percent;
the foam glass is in a plate shape and/or a sheet shape, and is arranged in the open container for closing the opening of the open container, so that iodine vapor flows to the foam glass.
Specifically, the foam glass can be prepared by adopting mesoporous silica, and the mesoporous silica has good reaction inertia, does not participate in the reaction and has a rich porous structure. The opening of the open container is closed by foam glass, so that the opening becomes a necessary path for iodine vapor to flow, and the stable loading of the lithium fluoride is realized. Meanwhile, the open container is adopted to form stable airflow, so that the generation of high-pressure conditions is avoided, and in addition, the foam glass can be kept at a relatively low temperature under the condition of not needing temperature reduction, so that the condensation of iodine vapor is effectively realized.
On the other hand, silica itself does not have very excellent thermal conductivity, and when a porous metal plate or a foam metal is adopted, not only impurities are easily introduced in a thermal diffusion mode, but also more importantly, the heat transfer efficiency of the silica is high, the downward surface of the carrier is easily led to play a role of a loading surface, and the temperature of the lower side surface is always kept low because the heat of the silica is quickly led out, so that iodine is easily condensed and the lithium fluoride powder is captured and bonded, and a large amount of adhesive load in a surface area can generate stacking, and the purity of an actual product is greatly reduced.
Preferably, the mesh number of the lithium fluoride powder in the step 1) is more than or equal to 200 meshes.
The lithium fluoride mesh size is too large to allow the iodine vapor stream to effectively move the lithium fluoride powder.
Preferably, the mass ratio of the lithium fluoride powder to the iodine in the step 1) is 1: (0.2-0.3); the volume ratio of the foam glass to the bulk volume of the mixed powder of lithium fluoride and iodine is 1: (0.02-0.05).
The mass ratio of the lithium fluoride to the iodine is controlled to ensure that enough iodine vapor can be generated to drive the lithium fluoride powder to rise, but the dosage of the iodine is not too large so as to avoid blocking a pore channel or leading the iodine to be wrapped outside the lithium fluoride, and further reducing the conversion rate or the conversion efficiency of the lithium fluoride. In addition, the loose volume ratio of the foam glass volume to the powder is controlled to ensure that the foam glass volume has enough content space for depositing lithium fluoride, and in addition, because the foam glass actually has a certain function of blocking gas circulation, the excessive volume of the foam glass generates a larger gas exchange obstruction, and finally the pressure at the inner side/lower side (i.e. the side for storing the powder relative to the position of the foam glass) of the container is increased, so that the vapor pressure is increased, and the sublimation of the iodine cannot be effectively realized.
Preferably, the heating temperature in the step 1) is controlled to be 45-75 ℃.
The iodine vapor airflow can be effectively and stably generated by controlling the heating temperature, and is used for carrying lithium fluoride and realizing the gluing effect. In the actual operation process, the temperature should be controlled to be more than or equal to 55 ℃ so as to avoid large-area condensation and deposition of the iodine on the lower side surface of the carrier.
Preferably, the flow rate of the phosphorus pentafluoride gas in the step 2) is controlled to be 200-500 mL/min.
The control of the flow rate of the phosphorus pentafluoride gas can improve the utilization rate of the phosphorus pentafluoride gas and ensure higher reaction efficiency.
Preferably, the phosphorus pentafluoride gas is introduced into the sealed reaction vessel, an air outlet end is arranged on the side opposite to the air inlet end, and the pressure in the sealed reaction vessel is controlled to be maintained at 1.15-1.25 atm.
In the step, nitrogen preheated to 45-50 ℃ can be introduced into the phosphorus pentafluoride gas for pre-purging, and a small amount of trace iodine simple substance attached to the surface of lithium fluoride can be taken away through pre-purging, so that the influence of the trace iodine simple substance on the contact reaction of the lithium fluoride and the phosphorus pentafluoride is avoided, and the yield and the purity of the product are improved. In addition, the pressure in the reaction container is controlled to control the sublimation of the iodine, so that the micro iodine attachments on the surface layer of the lithium fluoride can be effectively removed by influencing the vapor pressure and the like, and the lithium fluoride is prevented from falling and losing in the process because all the iodine is removed.
Preferably, the organic solvent in step 2) is an alcohol.
The alcohol can effectively dissolve the elemental iodine, the separation of the product and the carrier is realized, and meanwhile, the lithium hexafluorophosphate is insoluble in the alcohol, so that the extremely high-purity solid product can be directly obtained, the operations such as recrystallization and the like are not needed, and the production and preparation efficiency is greatly improved.
The invention has the beneficial effects that: 1) the template method has the advantages of the two existing dry-method lithium hexafluorophosphate preparation processes, and simultaneously effectively overcomes the defects of the two existing dry-method processes; 2) the whole process flow is brief and efficient, the preparation efficiency is extremely high, and the purity of the obtained product can reach more than 99.5 percent; 3) the scheme is green and pollution-free, the phosphorus pentafluoride tail gas can be recycled after trace iodine vapor is conveniently recovered and separated, and the recovery utilization rate of each material is high; 4) the whole process is safe, is suitable for popularization and use on a large scale, avoids the use of hydrogen fluoride and greatly reduces the cost.
Drawings
FIG. 1 is a schematic representation of the process of the present invention for lithium fluoride loading and conversion to lithium hexafluorophosphate.
Fig. 2 is a schematic diagram of the procedure of lithium fluoride loading and conversion to lithium hexafluorophosphate in comparative example 1.
Detailed Description
The invention is described in further detail below with reference to specific embodiments and the attached drawing figures. Those skilled in the art will be able to implement the invention based on these teachings. Furthermore, the embodiments of the present invention described in the following description are generally only a part of the embodiments of the present invention, and not all of the embodiments. Therefore, all other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "circumferential", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used merely for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., and "several" means one or more unless specifically limited otherwise.
In the present invention, unless otherwise explicitly stated or limited, the terms "mounted," "connected," "fixed," and the like are to be construed broadly, e.g., as being permanently connected, detachably connected, or integral; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be interconnected within two elements or in a relationship where two elements interact with each other unless otherwise specifically limited. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.
Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all those known to those skilled in the art.
Example 1
A method for dry-process preparation of lithium hexafluorophosphate, the method comprising: 1) the mesoporous silica plate with the aperture ratio of more than or equal to 50 percent is taken as a carrier, the aperture ratio of the mesoporous silica plate is 36-38 percent, and the plate area is 2 m 2 The thickness of the lithium fluoride powder is 0.15 m, the lithium fluoride powder is arranged at the opening of the top of a heating furnace with an open top end, and the lithium fluoride powder and the iodine particles with 200 meshes are mixed according to the mass ratio of 1: 0.25, 12 dm in total 3 The mixed powder is placed at the bottom of a heating furnace after being mixed, wherein iodine particles are uniformly paved at the bottom of the furnace, then lithium fluoride powder is uniformly paved, and then the mixture is heated to 65 ℃ and kept at a constant temperature until no powder is seen at the bottom of the furnace, namely a carrier is recovered to obtain a porous composite intermediate;
2) placing the porous composite intermediate in the middle of a sealed reaction vessel, wherein one end of the two sides of the plate surface is provided with a gas inlet, the other end is provided with a gas outlet, the gas inlet is filled with phosphorus pentafluoride gas at the rate of 16L/min for reaction for 28 h, the gas outlet is connected with a tail gas treatment device for collecting tail gas and condensing and recovering solid iodine, the rest tail gas can be heated again and enter the sealed reaction container for reaction, the pressure in the sealed reaction container is controlled to be 1.2 atm through the air exhaust rate of the air outlet, the lithium fluoride is converted to obtain the mesoporous silica plate loaded with the lithium hexafluorophosphate, the mesoporous silica plate loaded with the lithium hexafluorophosphate is placed in ethanol, and (3) completely immersing the lithium hexafluorophosphate-loaded mesoporous silica plate in ethanol, performing ultrasonic treatment, collecting precipitate at the bottom of the ethanol after no dust falls off, and obtaining the lithium hexafluorophosphate at the low temperature of 60 ℃.
And (3) performing yield calculation and purity detection on the obtained lithium hexafluorophosphate, wherein the yield reaches 98.1% through detection, the purity of the product lithium hexafluorophosphate is about 99.61%, and the impurity components mainly comprise lithium fluoride and iodine.
Example 2
A method for dry-process preparation of lithium hexafluorophosphate, the method comprising:
1) the mesoporous silica plate with the aperture ratio of more than or equal to 50 percent is used as a carrier, the aperture ratio of the mesoporous silica plate is 36-38 percent, and the area of the plate is 2 m 2 The thickness of the lithium fluoride powder is 0.15 m, the lithium fluoride powder is arranged at the opening of the top of a heating furnace with an open top end, and the lithium fluoride powder and the iodine particles with 200 meshes are mixed according to the mass ratio of 1: 0.2, 6 dm in total 3 The mixed powder is placed at the bottom of a heating furnace after being mixed, wherein iodine particles are uniformly paved at the bottom of the furnace, then lithium fluoride powder is uniformly paved, and then the mixture is heated to 55 ℃ to keep constant temperature until no powder is seen at the bottom of the furnace, namely a porous composite intermediate is obtained by recovering a carrier;
2) placing a porous composite intermediate in the middle of a sealed reaction container, wherein one end of the two sides of the plate surface is provided with an air inlet, one end of the plate surface is provided with an air outlet, the air inlet is filled with phosphorus pentafluoride gas at 10L/min for reaction, the air outlet is connected with a tail gas treatment device for collecting tail gas and condensing and recycling solid iodine, the rest tail gas can be reheated and enters the sealed reaction container for reaction, the pressure in the sealed reaction container is controlled to be 1.15 atm through the air suction rate of the air outlet, a mesoporous silica plate loaded with lithium hexafluorophosphate is obtained after the conversion of lithium fluoride is realized, the mesoporous silica plate loaded with lithium hexafluorophosphate is placed in ethanol, the mesoporous silica plate loaded with lithium hexafluorophosphate is completely immersed in the ethanol and then subjected to ultrasonic treatment, precipitates at the bottom of the ethanol are collected after no dust falls, and lithium hexafluorophosphate is obtained at the low temperature of 60 ℃.
And (3) performing yield calculation and purity detection on the obtained lithium hexafluorophosphate, wherein the yield reaches 99.0% through detection, the purity of the product lithium hexafluorophosphate is about 99.81%, and the impurity components mainly comprise lithium fluoride and iodine.
Example 3
A method for dry-process preparation of lithium hexafluorophosphate, said method comprising: 1) the mesoporous silica plate with the aperture ratio of more than or equal to 50 percent is used as a carrier, the aperture ratio of the mesoporous silica plate is 36-38 percent, and the area of the plate is 2 m 2 The thickness of the lithium fluoride powder is 0.15 m, the lithium fluoride powder is arranged at the opening of the top of a heating furnace with an open top end, and the lithium fluoride powder and the iodine particles with 200 meshes are mixed according to the mass ratio of 1: 0.3, 15 dm in total 3 The mixed powder is placed at the bottom of a heating furnace after being mixed, wherein iodine particles are uniformly paved at the bottom of the furnace, then lithium fluoride powder is uniformly paved, and then the mixture is heated to 75 ℃ and kept at a constant temperature until no powder is seen at the bottom of the furnace, namely, a carrier is recovered to obtain a porous composite intermediate; 2) placing a porous composite intermediate in the middle of a sealed reaction container, wherein one end of the two sides of the plate surface of the porous composite intermediate is provided with a gas inlet, one end of the plate surface of the porous composite intermediate is provided with a gas outlet, the gas inlet is filled with phosphorus pentafluoride gas at 24L/min for reaction, the gas outlet is connected with a tail gas treatment device for collecting tail gas and condensing and recovering solid iodine, the rest tail gas can be heated again to enter the sealed reaction container for reaction, the pressure in the sealed reaction container is controlled to be 1.25 atm through the air suction rate of the gas outlet, a mesoporous silica plate loaded with lithium hexafluorophosphate is obtained after the conversion of lithium fluoride is realized, the mesoporous silica plate loaded with lithium hexafluorophosphate is placed in ethanol, the mesoporous silica plate loaded with lithium hexafluorophosphate is completely immersed in the ethanol and then subjected to ultrasonic treatment, precipitates at the bottom of the ethanol are collected after no dust falls, and lithium hexafluorophosphate is obtained at the low temperature of 60 ℃.
The yield calculation and the purity detection are carried out on the obtained lithium hexafluorophosphate, the yield is up to 97.9 percent through detection, the purity of the product lithium hexafluorophosphate is about 99.54 percent, and the impurity components are mainly lithium fluoride and iodine.
Example 4
A method for dry-process preparation of lithium hexafluorophosphate, the method comprising: 1) the mesoporous silica plate with the aperture ratio of more than or equal to 50 percent is used as a carrier, the aperture ratio of the mesoporous silica plate is 36-38 percent, and the area of the plate is 2 m 2 The thickness is 0.15 m, the lithium fluoride powder is arranged at the opening of the top of a heating furnace with the top open, and the lithium fluoride powder and the iodine particles with the particle size of 200 meshes are mixed according to the mass ratio of 1: 0.25, 12 dm in total 3 The mixed powder is placed at the bottom of a heating furnace after being mixed, wherein iodine particles are uniformly paved at the bottom of the furnace, then lithium fluoride powder is uniformly paved, and then the mixture is heated to 65 ℃ and kept at a constant temperature until no powder is seen at the bottom of the furnace, namely, a carrier is recovered to obtain a porous composite intermediate; 2) placing a porous composite intermediate in the middle of a sealed reaction container, wherein one end of the two sides of the plate surface is provided with an air inlet, one end of the plate surface is provided with an air outlet, the air inlet is filled with phosphorus pentafluoride gas at 12L/min for reaction, the air outlet is connected with a tail gas treatment device for collecting tail gas and condensing and recycling solid iodine, the rest tail gas can be reheated and enters the sealed reaction container for reaction, the pressure in the sealed reaction container is controlled to be 1.15 atm through the air suction rate of the air outlet, a mesoporous silica plate loaded with lithium hexafluorophosphate is obtained after the conversion of lithium fluoride is realized, the mesoporous silica plate loaded with lithium hexafluorophosphate is placed in ethanol, the mesoporous silica plate loaded with lithium hexafluorophosphate is completely immersed in the ethanol and then subjected to ultrasonic treatment, precipitates at the bottom of the ethanol are collected after no dust falls, and lithium hexafluorophosphate is obtained at the low temperature of 60 ℃.
And (3) carrying out yield calculation and purity detection on the obtained lithium hexafluorophosphate, wherein the yield reaches 98.3% through detection, the purity of the product lithium hexafluorophosphate is about 99.75%, and the impurity components mainly comprise lithium fluoride and iodine.
Example 5
A method for dry-process preparation of lithium hexafluorophosphate, the method comprising: 1) the mesoporous silica plate with the aperture ratio of more than or equal to 50 percent is used as a carrier, the aperture ratio of the mesoporous silica plate is 36-38 percent, and the area of the plate is 2 m 2 A thickness of 0.15 m, providedPlacing the lithium fluoride powder and the iodine particles in a mass ratio of 1: 0.25, 12 dm in total 3 The mixed powder is placed at the bottom of a heating furnace after being mixed, wherein iodine particles are uniformly paved at the bottom of the furnace, then lithium fluoride powder is uniformly paved, and then the mixture is heated to 65 ℃ and kept at a constant temperature until no powder is seen at the bottom of the furnace, namely, a carrier is recovered to obtain a porous composite intermediate; 2) placing a porous composite intermediate in the middle of a sealed reaction container, wherein one end of the two sides of the plate surface of the porous composite intermediate is provided with a gas inlet, one end of the plate surface of the porous composite intermediate is provided with a gas outlet, the gas inlet is filled with phosphorus pentafluoride gas at 24L/min for reaction, the gas outlet is connected with a tail gas treatment device for collecting tail gas and condensing and recovering solid iodine, the rest tail gas can be heated again to enter the sealed reaction container for reaction, the pressure in the sealed reaction container is controlled to be 1.25 atm through the air suction rate of the gas outlet, a mesoporous silica plate loaded with lithium hexafluorophosphate is obtained after the conversion of lithium fluoride is realized, the mesoporous silica plate loaded with lithium hexafluorophosphate is placed in ethanol, the mesoporous silica plate loaded with lithium hexafluorophosphate is completely immersed in the ethanol and then subjected to ultrasonic treatment, precipitates at the bottom of the ethanol are collected after no dust falls, and lithium hexafluorophosphate is obtained at the low temperature of 60 ℃.
The yield calculation and the purity detection are carried out on the obtained lithium hexafluorophosphate, the yield reaches 98.2 percent through detection, the purity of the product lithium hexafluorophosphate is about 99.58 percent, and the impurity components are mainly lithium fluoride and iodine.
Example 6
Based on example 1, the material ratio, the operation process and the parameters are the same as those of example 1, and only the following differences exist:
and in the step 2), introducing nitrogen preheated to 45 ℃ between the introduction of the phosphorus pentafluoride gas for 2 min for pre-purging, wherein the flow rate of the nitrogen is 16L/min. The remaining operating parameters and the like were the same as in example 1.
The yield of the obtained lithium hexafluorophosphate is calculated and the purity of the lithium hexafluorophosphate is detected to be 97.8 percent, the yield is slightly reduced, but the purity is further increased to 99.95 percent, and the main component of impurities is only lithium fluoride.
Example 7
Based on example 1, the material ratio, the operation process and the parameters are the same as those of example 1, and only the following differences exist: and 2) introducing nitrogen preheated to 50 ℃ between the introduction of the phosphorus pentafluoride gas in the step 2) for 2 min of pre-purging, wherein the nitrogen flow rate is 16L/min. The remaining operating parameters and the like were the same as in example 1.
The yield of the obtained lithium hexafluorophosphate is calculated and the purity of the lithium hexafluorophosphate is detected to be 97.7 percent, the yield is slightly reduced, but the purity is further increased to 99.96 percent, and the main component of impurities is only lithium fluoride.
It can be seen from the comparison of example 1, example 6 and example 7 that the yield of product shows a very slight decline after the pre-purging. But there is a more significant increase in product purity. Research and analysis show that during the deposition process of lithium fluoride, iodine vapor is condensed in pores of a carrier and used as a binder to adhere and fix lithium fluoride powder, but in the process, an extremely small amount of iodine is condensed on the outer surface of the lithium fluoride instead of the boundary between the lithium fluoride and the carrier, and is coated in the lithium fluoride during the subsequent reaction and conversion process of the lithium fluoride and phosphorus pentafluoride, and only the extremely small amount of iodine cannot be washed away in the subsequent ultrasonic treatment, so that the purity of the product is affected. And the high purification of lithium hexafluorophosphate can be realized while the product yield can be ensured by pre-purging the hot nitrogen. The lithium hexafluorophosphate prepared by the original scheme can basically meet the quality requirement of commercial lithium hexafluorophosphate HG/T4066-2008, but the quality of the lithium hexafluorophosphate obtained after nitrogen purging reaches the higher quality requirement of HG/T4066-2015, the lithium hexafluorophosphate product meeting the commercial requirement can be directly prepared in one step, and the operations such as purification and the like after the preparation by the conventional dry/wet method and other methods are not needed, so that the lithium hexafluorophosphate preparation method has great popularization and implementation values.
However, it should be noted that higher temperatures should not be used for purging. This is because higher temperature purging tends to cause some of the iodine as a "binder" to be carried away, resulting in a gradual decrease in product yield. Therefore, in order to control the yield and the product quality, at least the purging temperature of the nitrogen gas should be controlled between 45 ℃ and 55 ℃, and optimally, the purging temperature should be controlled between 45 ℃ and 50 ℃.
Comparative example 1
Based on example 1, the material ratio, the operation process and the parameters are the same as those of example 1, and only the following differences exist:
the mesoporous silica plate is replaced by the porous nichrome plate with the same specification as the carrier, and the specific surface area and the porosity of the porous nichrome plate are slightly higher than those of the mesoporous silica plate used in the example 1.
The yield of the obtained lithium hexafluorophosphate is calculated and the purity of the lithium hexafluorophosphate is detected, the yield of the product is up to 96.2 percent and is reduced to some extent, the purity of the product is obviously reduced to 91.72 percent, and the main components of impurities comprise lithium fluoride, iodine and partial metal diffusion components.
As shown in fig. 1 and fig. 2, the lithium fluoride load and the transition from phosphorus pentafluoride to lithium hexafluorophosphate under purge of the embodiment 1 of the present invention are shown in fig. 1, which can almost completely realize the transition, and the temperature of the upper and lower surfaces of the mesoporous silica plate is detected immediately after step 1) is finished, the temperature of the lower surface of the mesoporous silica plate in the embodiment 1 reaches about 49 ℃, so that iodine cannot be effectively condensed and deposited, and the temperature of the upper surface is substantially equivalent to the room temperature, while the temperature of the lower surface of the porous nichrome plate in the comparative example 1 is only slightly higher than the room temperature, and is about 38 to 41 ℃, which can meet the requirement of iodine deposition.
Due to the temperature difference, when porous metal carriers such as a porous nichrome plate and the like are adopted, part of lithium fluoride particles are adhered and fixed on the lower side surface of the carrier by iodine simple substances and are coated in a large amount, so that reaction transformation cannot be effectively realized, and the purity of the finally obtained product is remarkably reduced.
Therefore, in the technical solution of the present invention, the carrier needs to be selected in consideration of the structural characteristics such as porosity of the carrier, chemical properties such as reaction inertness, and other physical characteristics such as thermal conductivity. After a number of experiments, foamed silica, especially open-cell mesoporous silica plates, is the most preferred choice.
Claims (8)
1. A method for dry-process preparation of lithium hexafluorophosphate, the method comprising: 1) mixing lithium fluoride powder and iodine in an open container by using foam glass as a carrier, placing the mixture below the foam glass carrier, heating, and then loading the lithium fluoride on the foam glass by adopting an iodine evaporation method to obtain a porous composite intermediate; 2) and placing the porous composite intermediate in a sealed reaction container, introducing phosphorus pentafluoride gas for reaction, obtaining a pre-product after the conversion of lithium fluoride is realized, placing the pre-product in an organic solvent for ultrasonic treatment, and collecting the precipitate at the bottom of the organic solvent to obtain the lithium hexafluorophosphate.
2. The method for preparing lithium hexafluorophosphate by a dry method according to claim 1, wherein the foam glass in step 1) is open-cell foam silica, and the open-cell content is not less than 50%; the foam glass is in a plate shape and/or a sheet shape, and is arranged in the open container for closing the opening of the open container, so that iodine vapor flows to the foam glass.
3. The method for preparing lithium hexafluorophosphate by a dry method according to claim 1, wherein the mesh number of the lithium fluoride powder in step 1) is not less than 200 meshes.
4. The method for preparing lithium hexafluorophosphate by the dry method according to claim 1 or 3, wherein the mass ratio of the lithium fluoride powder to iodine in step 1) is 1: (0.2 to 0.3); the volume ratio of the foam glass to the bulk volume of the mixed powder of lithium fluoride and iodine is 1: (0.02-0.05).
5. The method for preparing lithium hexafluorophosphate by a dry method according to claim 4, wherein the heating temperature in step 1) is controlled to be 45-75 ℃.
6. The method for dry-process preparation of lithium hexafluorophosphate according to claim 1, wherein the flow rate of the phosphorus pentafluoride gas in step 2) is controlled to 5-12L/min per square meter of plate surface area.
7. The method for preparing lithium hexafluorophosphate according to claim 1 or 6, wherein the phosphorus pentafluoride gas is introduced into the sealed reaction vessel, an air outlet end is arranged on the side opposite to the air inlet end, and the pressure in the sealed reaction vessel is controlled to be maintained at 1.15-1.25 atm.
8. The method for preparing lithium hexafluorophosphate by dry process according to claim 1, wherein the organic solvent in step 2) is alcohol.
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| WO2023226243A1 (en) * | 2022-05-26 | 2023-11-30 | 福建省龙德新能源有限公司 | Method for preparing lithium hexafluorophosphate by dry method |
| CN117446833A (en) * | 2023-09-20 | 2024-01-26 | 山东立中新能源材料有限公司 | Preparation method of sodium hexafluorophosphate for sodium battery |
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| CN114920271B (en) | 2023-03-03 |
| WO2023226243A1 (en) | 2023-11-30 |
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