High-purity lithium metaphosphate, preparation method and application thereof

Abstract

The application discloses high-purity lithium metaphosphate and a preparation method and application thereof, and belongs to the technical field of lithium metaphosphate production. The preparation method comprises the following steps: mixing and reacting lithium salt and a phosphorus source to generate lithium dihydrogen phosphate solution; removing impurities and performing nanofiltration on the lithium dihydrogen phosphate solution to generate water; concentrating the obtained solid phase, and repeatedly removing impurities, nanofiltration and concentrating; collecting all liquid phases, and sequentially performing concentration crystallization, high-temperature transformation treatment and quenching treatment to prepare high-purity lithium metaphosphate. The preparation method is simple in process, stable in process and suitable for industrial production; the product is high in purity and stable in quality, and can be widely applied to the fields of battery materials, glass and ceramics.

Description

Technical Field

[0001] This application belongs to the field of lithium metaphosphate production technology, specifically, it relates to a high-purity lithium metaphosphate, its preparation method and application. Background Technology

[0002] Lithium metaphosphate (LiPO3), as a key inorganic phosphate material, has significant application value in lithium-ion battery electrolyte precursors (such as intermediates in the synthesis of lithium hexafluorophosphate), special glass additives, ceramic materials, and solid electrolytes. With the rapid development of the new energy industry and electrochemical energy storage technology, downstream industries have placed higher demands on the purity, crystal structure stability, and batch consistency of lithium metaphosphate products.

[0003] Currently, the main technologies for preparing lithium metaphosphate include solid-phase reaction, liquid-phase precipitation, and spray pyrolysis. Solid-phase reaction is a commonly used industrial method, typically involving mixing lithium sources such as lithium carbonate and lithium hydroxide with phosphates in a specific ratio and generating lithium metaphosphate through a solid-phase reaction at high temperatures. While this method has a relatively short process flow, it is highly dependent on the purity of the lithium source. When using low-grade lithium sources containing impurity ions such as sodium, potassium, calcium, and magnesium, these impurities readily participate in the reaction at high temperatures, forming secondary phases or solid solutions, leading to lattice distortion, decreased purity, and difficulty in controlling product consistency. Liquid-phase or solution-based methods primarily involve dissolving the lithium source in a phosphoric acid system, followed by evaporation, concentration, and thermal decomposition to prepare lithium metaphosphate. Although this method improves the uniformity of component mixing to some extent, obtaining high-purity products often requires complex pretreatment or purification of the solution system, and the evaporation and concentration process is energy-intensive, limiting production efficiency. Spray pyrolysis and similar vapor deposition technologies atomize lithium-phosphorus solutions and instantaneously decompose them at high temperatures to form powder. While this method can produce products with uniform particle size, it places stringent requirements on equipment materials during actual industrialization. Furthermore, in high-temperature gas-liquid reaction environments, products are prone to sticking to the walls and scaling, which seriously affects production continuity and increases equipment maintenance costs.

[0004] To improve product purity, existing technologies have explored two-step or multi-stage heat treatment processes. These include pre-preparing intermediate products (such as lithium pyrophosphate) followed by decomposition, or introducing auxiliary methods such as ion exchange and solvent washing to remove impurities. However, these improved solutions often suffer from lengthy processes, demanding operating conditions, and high energy consumption. Particularly in high-temperature sintering or spray tower environments, scaling caused by material deposition remains a persistent problem, limiting their application in low-cost, large-scale production.

[0005] In summary, existing lithium metaphosphate preparation processes generally suffer from drawbacks such as stringent requirements for lithium source purity, a lack of effective means to control impurity ions, and complex processes and equipment prone to scaling. How to achieve efficient and low-cost utilization of low-grade or high-impurity lithium sources while ensuring high product purity remains a pressing problem to be solved in this field. Summary of the Invention

[0006] The purpose of this application is to provide a high-purity lithium metaphosphate, its preparation method, and its application. This method directly uses a high-impurity, low-grade lithium source as raw material, efficiently preparing a high-purity, structurally stable lithium metaphosphate product without the need for complex deep purification pretreatment. This can further reduce the overall production cost of lithium metaphosphate, broaden the channels for the comprehensive utilization of lithium resources, and improve the performance of products in downstream new energy and new materials fields.

[0007] To achieve the above objectives, this application provides a method for preparing high-purity lithium metaphosphate, comprising the following steps: A lithium salt and a phosphorus source are mixed and reacted to generate a lithium dihydrogen phosphate solution. The lithium dihydrogen phosphate solution was subjected to impurity removal and nanofiltration to obtain a separated solid phase and liquid phase. The separated solid phase is concentrated and then subjected to repeated impurity removal, nanofiltration, and concentration processes. All liquid phases were collected and sequentially concentrated and crystallized, subjected to high-temperature transformation treatment and rapid cooling treatment to obtain high-purity lithium metaphosphate.

[0008] Furthermore, the lithium source includes at least one of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium oxide, lithium peroxide, lithium hydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, and lithium halides, and the phosphorus source includes at least one of orthophosphoric acid, metaphosphoric acid, and phosphorus pentoxide, and the lithium salt and phosphorus source are mixed in an equimolar ratio of lithium to phosphorus.

[0009] Furthermore, the reaction time after mixing lithium salt and phosphorus source is 60 min to 300 min, and the reaction temperature is 60℃ to 95℃.

[0010] Furthermore, the reagents used for impurity removal are PAC and / or hydrogen peroxide.

[0011] Furthermore, the membrane used for nanofiltration is a DK type nanofiltration membrane, a DL type nanofiltration membrane, or an NF270 type nanofiltration membrane, and the nanofiltration time is 30 min to 120 min.

[0012] Furthermore, the concentration and crystallization time is 60 min to 300 min, and the concentration and crystallization method is as follows: first concentrate and crystallize until the specific gravity of the solution is 1.4 to 2.0, and then cool to precipitate lithium dihydrogen phosphate crystals.

[0013] Furthermore, the temperature is increased to 200℃~350℃ at a rate of 3℃ / min~5℃ / min, and held for 1.5h~3h; Continue heating at a rate of 2℃ / min to 4℃ / min to 650℃ to 700℃, and hold at that temperature for 0.5h to 1.5h.

[0014] Furthermore, the quenching method involves cooling from 650°C to 700°C to 300°C to 450°C at a rate of 2°C / min to 15°C / min, or cooling from 650°C to 700°C to room temperature at a rate of 50°C / min to 100°C / min. On the other hand, this application also provides high-purity lithium metaphosphate prepared using the method provided in the first aspect. When the quenching process involves cooling from 650°C to 700°C to 300°C to 450°C at a rate of 2°C / min to 15°C / min, the obtained high-purity lithium metaphosphate is crystalline; when the quenching process involves cooling from 650°C to 700°C to room temperature at a rate of 50°C / min to 100°C / min, the obtained high-purity lithium metaphosphate is amorphous. By controlling the quenching rate, products with different microstructures can be obtained.

[0015] On the other hand, this application also provides an application of high-purity lithium metaphosphate, which can be used to prepare lithium iron phosphate cathode materials, optical glass, ceramic materials and solid electrolytes.

[0016] In summary, this application has the following beneficial effects: This application provides a high-purity lithium metaphosphate, its preparation method, and its applications. Unlike existing technologies that generally rely on high-purity lithium sources such as battery-grade lithium carbonate or lithium hydroxide, this application can directly utilize low-grade lithium sources containing high impurity components (such as sodium, potassium, calcium, and magnesium) as raw materials. Through reaction conversion and multi-stage impurity removal mechanisms within the phosphoric acid system, efficient conversion from high-impurity raw materials to high-purity products is achieved. This not only significantly reduces the stringent requirements for raw material purity and effectively avoids product quality degradation due to raw material fluctuations, but also broadens the utilization pathways of lithium resources and significantly reduces raw material procurement costs, demonstrating significant resource utilization value and economic advantages.

[0017] Furthermore, the preparation method provided in this application achieves impurity removal and product generation under relatively mild conditions through processes such as phosphoric acid system conversion, cyclic impurity removal, and concentration crystallization. The entire process is highly continuous, requiring no expensive and complex equipment or extreme reaction conditions, and is easy to operate and control, effectively solving problems such as equipment scaling and high maintenance costs in traditional processes. At the same time, the product quality is stable, with good batch repeatability, making it suitable for low-cost, large-scale industrial production.

[0018] Finally, the lithium metaphosphate product obtained by the preparation method of this application has high purity and low impurity content, which can meet the application requirements of high-end fields such as lithium-ion battery electrolyte precursors, optical glass and special ceramics. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the method for preparing high-purity lithium metaphosphate proposed in the embodiments of this application.

[0021] Figure 2 This is a test report for the high-purity lithium metaphosphate product prepared in the embodiments of this application.

[0022] Figure 3 This is the XRD pattern (crystalline state) of the high-purity lithium metaphosphate product prepared in Example 1 of this application.

[0023] Figure 4 This is the XRD pattern (crystalline state) of the high-purity lithium metaphosphate product prepared in Example 2 of this application.

[0024] Figure 5 This is the XRD pattern (amorphous state) of the high-purity lithium metaphosphate product prepared in Example 4 of this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] The limitations of existing lithium metaphosphate preparation technologies are primarily reflected in their extremely high dependence on the lithium source. Most mature processes require high-purity lithium salts such as battery-grade lithium carbonate or battery-grade lithium hydroxide as raw materials, making them unsuitable for low-grade lithium resources with high impurity content. When the lithium source contains common impurity ions such as sodium, potassium, calcium, and magnesium, these impurities readily combine with phosphorus and lithium components in the system during high-temperature reactions to form difficult-to-separate secondary phases, or even directly enter the lithium metaphosphate lattice to form stable defect structures. This ultimately leads to substandard product purity and decreased crystal structure stability, directly affecting the performance of downstream applications. Simultaneously, many existing processes suffer from lengthy procedures and multiple overlapping high-temperature treatment steps, resulting in high overall energy consumption and high investment and maintenance costs for supporting equipment, making it difficult to support low-cost, large-scale, stable industrial production.

[0027] Based on this, firstly, this application provides a method for preparing high-purity lithium metaphosphate, such as... Figure 1 As shown, it includes the following steps: S1. Lithium salt and phosphorus source are mixed and reacted to generate lithium dihydrogen phosphate solution.

[0028] In a specific embodiment, the lithium source includes at least one selected from anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium oxide, lithium peroxide, lithium hydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, and lithium halides. The phosphorus source includes at least one selected from orthophosphoric acid, metaphosphoric acid, and phosphorus pentoxide. The lithium salt and phosphorus source are mixed in an equimolar ratio of lithium to phosphorus. By selecting different lithium sources (such as industrial-grade lithium carbonate, lithium hydroxide, etc.), the dependence on the purity of raw materials is reduced.

[0029] In a specific embodiment, the reaction time after mixing lithium salt and phosphorus source is 60 min to 300 min, and the reaction temperature is 60℃ to 95℃.

[0030] S2. The lithium dihydrogen phosphate solution is subjected to impurity removal and nanofiltration to obtain a separated solid phase and liquid phase.

[0031] In a specific embodiment, the reagents for impurity removal are PAC and / or hydrogen peroxide. Hydrogen peroxide acts as an oxidant, removing any Fe that may be present in the solution. 2+ Oxidized into Fe, which is more easily precipitated 3+ PAC, as a flocculant, produces aluminum hydroxide colloids through hydrolysis, which, through adsorption bridging and charge neutralization, bind Fe... 3+ Heavy metal ions and some colloidal impurities (such as SiO2) are encapsulated and aggregated, forming large flocculent precipitates.

[0032] In specific embodiments, the nanofiltration membrane used is a DK-type nanofiltration membrane, a DL-type nanofiltration membrane, or an NF270-type nanofiltration membrane, and the nanofiltration time is 30 min to 120 min. Nanofiltration membranes possess unique pore size and charge characteristics, enabling them to retain divalent and multivalent ions (such as Ca²⁺). 2+ Mg 2+ Fe 3+ ) and colloids, allowing monovalent ions (such as Li) to... + Na + K + ( ) and solvent (water) pass through.

[0033] S3. After concentrating the separated solid phase, repeat the impurity removal, nanofiltration, and concentration processes.

[0034] In this application, the separated solid phase (retentate) refers to a concentrated liquid rich in impurity ions. This liquid, once separated, can be recycled after concentration treatment according to this application or directly treated as waste liquid to recover any small amount of lithium salt that may be entrained, thereby improving the overall yield. The liquid phase (permeate) refers to a relatively pure lithium dihydrogen phosphate solution, which is the main material entering the concentration and crystallization process, in which most impurities have been removed. This application uses cyclic concentration, impurity removal, and nanofiltration steps to concentrate the obtained solid phase (retentate), followed by further chemical impurity removal and nanofiltration. The resulting product is a concentrated liquid further enriched with impurities. Through multiple cycles, impurities can be removed to the maximum extent, while the retained lithium salt is recovered, improving the raw material utilization rate.

[0035] S4. Collect all liquid phases and sequentially perform concentration and crystallization, high-temperature transformation treatment and rapid cooling treatment to obtain high-purity lithium metaphosphate.

[0036] In a specific embodiment, the concentration and crystallization time is 60-300 minutes. The concentration and crystallization method is as follows: first, concentrate and crystallize until the solution specific gravity is 1.4-2.0, then cool to precipitate lithium dihydrogen phosphate crystals. In this application, the permeate is further evaporated to make the solution supersaturated, and then cooled to precipitate lithium dihydrogen phosphate crystals. Then, the pure lithium dihydrogen phosphate crystals are heated for the first time, and lithium dihydrogen phosphate (LiH2PO4) gradually converts to lithium metaphosphate (LiPO3). Then, a second heating is performed at a high temperature of 650-700℃, where the molten lithium metaphosphate further reacts to form a more stable lithium metaphosphate melt. The high-temperature melt is rapidly cooled (quenched) so that the atoms in the melt do not have time to arrange themselves in an orderly manner to form crystals, thereby freezing its disordered structure and obtaining a transparent, glassy amorphous product. If the cooling rate is slower, crystalline lithium metaphosphate will form.

[0037] In a specific implementation, the high-temperature transformation treatment method includes: heating to 200℃~350℃ at a rate of 3℃ / min~5℃ / min and holding for 1.5h~3h; and continuously heating to 650℃~700℃ at a rate of 2℃ / min~4℃ / min and holding for 0.5h~1.5h.

[0038] In a specific implementation, the rapid cooling method is to cool from 650℃~700℃ to 300℃~450℃ at a rate of 2℃ / min~15℃ / min or to room temperature at a rate of 50℃ / min~100℃ / min.

[0039] In summary, step S1 of this application utilizes acid-base neutralization or metathesis reactions to convert lithium sources in different forms into a soluble lithium dihydrogen phosphate solution, transforming solid raw materials into a liquid-phase system. This ensures uniform mixing of lithium and phosphorus at the molecular level, avoiding the problem of uneven mixing in solid-phase methods. Step S2 uses hydrogen peroxide to remove difficult-to-precipitate Fe... 2+ Oxidized into easily precipitated Fe 3+ Alternatively, the hydrolytic flocculation of PAC (polyaluminum chloride) can be utilized to capture metal ions and colloidal impurities, forming large flocs through adsorption bridging and charge neutralization effects. Then, the pore size sieving and Donald's effect of nanofiltration membranes (DK / DL / NF270) can be used to retain divalent ions (such as Ca2+). 2+ Mg 2+ Fe 3+ ) and macromolecular organic matter, while allowing monovalent ions (Li) + Na + The solvent is permeated to achieve preliminary ion fractionation. Step S3 involves solid-liquid separation of the concentrated liquid retained in step S2 (containing flocculated impurities and some retained lithium salts). The solid phase is discharged as impurity residue or subjected to specific treatment, while part of the retained liquid is recycled. Step S4 involves evaporating the solvent to increase the concentration, and using cooling to achieve supersaturation of lithium dihydrogen phosphate to precipitate crystals. At the same time, the highly soluble monovalent impurities (Na+) are removed. + K + The sodium and potassium residues remain in the mother liquor, thus achieving "sodium and potassium removal". Then, the first step is to raise the temperature and dehydrate to ensure complete transformation of the intermediate phase. The second step is to melt and condense at high temperature to form lithium metaphosphate melt. Finally, the rapid cooling process uses the temperature difference to quickly cross the crystallization temperature range and inhibit crystal nucleus growth.

[0040] Secondly, based on a general inventive concept, this application also provides high-purity lithium metaphosphate prepared using the preparation method described in the first aspect.

[0041] In a specific implementation, high-purity lithium metaphosphate is either crystalline or amorphous. When rapidly cooled to room temperature, it is amorphous lithium metaphosphate, and when heated again to 300°C or above, it forms crystalline lithium metaphosphate.

[0042] Thirdly, based on a general inventive concept, this application also provides applications of the high-purity lithium metaphosphate described in the second aspect, including applications in the preparation of lithium iron phosphate cathode materials, optical glass, ceramic materials, and solid electrolytes.

[0043] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments. All raw materials used in the embodiments of this application are industrial grade.

[0044] Example 1 This embodiment provides a method for preparing high-purity lithium metaphosphate, including the following steps: (1) After mixing 23.95g of anhydrous lithium hydroxide with 115.3g of phosphoric acid, the mixture was reacted at 60℃ for 60min to generate a lithium dihydrogen phosphate solution; (2) The lithium dihydrogen phosphate solution was purified by PAC, stirred for 30 min, and allowed to stand for 30 min. Then it was nanofiltered through a DK type nanofiltration membrane at an operating temperature of 25℃ and an operating pressure of 1.2 MPa to obtain nanofiltration liquid (permeate water (nanofiltration permeate)) and concentrate. After concentrating the concentrate, it was purified and nanofiltered three more times to obtain nanofiltration liquid and concentrate. All nanofiltration liquid was collected and concentrated for crystallization for 60 min until the specific gravity of the solution was 1.4. The solution was cooled to 25℃ at 2℃ / min under stirring and kept at the temperature for 2 h. After filtration, it was dried at 100℃ for 4 h to obtain lithium dihydrogen phosphate crystals.

[0045] (3) Lithium dihydrogen phosphate crystals were heated to 200℃ at a rate of 3℃ / min and held for 120 min, then heated to 650℃ at a rate of 3℃ / min and held for 60 min, and finally cooled to 300℃ at a rate of 10℃ / min to obtain crystalline high-purity lithium metaphosphate, the XRD pattern of which is shown in the figure. Figure 3 As shown. Unless otherwise specified, the parts in the following embodiments are consistent with those in Embodiment 1.

[0046] Example 2 This embodiment provides a method for preparing high-purity lithium metaphosphate, including the following steps: (1) After mixing 41.95g of lithium hydroxide monohydrate with 115.3g of metaphosphoric acid, the mixture was reacted at 95℃ for 300min to generate a lithium dihydrogen phosphate solution. (2) The lithium dihydrogen phosphate solution was purified by hydrogen peroxide and then subjected to nanofiltration through a DK type nanofiltration membrane at an operating temperature of 30°C and an operating pressure of 1.5 MPa to obtain nanofiltration liquid (product water) and concentrate. The concentrate was concentrated and then subjected to repeated purification, nanofiltration and concentration cycles. All nanofiltration liquid was collected and concentrated for crystallization for 300 min until the specific gravity of the solution was 2.0. After cooling, lithium dihydrogen phosphate crystals were precipitated.

[0047] (3) Lithium dihydrogen phosphate crystals were heated to 350℃ at a rate of 5℃ / min and held for 60 min, then heated to 700℃ at a rate of 3℃ / min and held for 30 min, and finally cooled to 450℃ at a rate of 8℃ / min to obtain crystalline high-purity lithium metaphosphate, the XRD pattern of which is shown in the figure. Figure 4 As shown.

[0048] Example 3 This embodiment provides a method for preparing high-purity lithium metaphosphate, including the following steps: (1) After mixing 14.95g of lithium oxide with phosphorus pentoxide, the mixture was reacted at 75℃ for 150min to generate a lithium dihydrogen phosphate solution; (2) The lithium dihydrogen phosphate solution was purified by hydrogen peroxide and then subjected to nanofiltration through a DL-type nanofiltration membrane at an operating temperature of 25°C and an operating pressure of 1.0 MPa to obtain nanofiltration liquid (product water) and concentrate. The concentrate was concentrated and then subjected to repeated purification, nanofiltration and concentration cycles. All nanofiltration liquid was collected and concentrated and crystallized for 150 min until the specific gravity of the solution was 2.0. After cooling, lithium dihydrogen phosphate crystals were precipitated.

[0049] (3) The lithium dihydrogen phosphate crystals were heated to 200℃ at a rate of 5℃ / min and held for 90min, then heated to 650℃ at a rate of 4℃ / min and held for 60min, and finally cooled to room temperature at a rate of 100℃ / min to obtain amorphous high-purity lithium metaphosphate.

[0050] Example 4 This embodiment provides a method for preparing high-purity lithium metaphosphate, including the following steps: (1) After mixing 14.95g of lithium nitrate with 115.3g of phosphoric acid, the mixture was reacted at 85℃ for 200min to generate a lithium dihydrogen phosphate solution; (2) The lithium dihydrogen phosphate solution was purified by hydrogen peroxide and then subjected to nanofiltration through an NF270 nanofiltration membrane at an operating temperature of 25°C and an operating pressure of 1.4 MPa to obtain nanofiltration liquid (product water) and concentrate. The concentrate was concentrated and then subjected to repeated purification, nanofiltration and concentration cycles. All the nanofiltration liquid was collected and concentrated and crystallized for 200 min until the specific gravity of the solution was 1.8. After cooling, lithium dihydrogen phosphate crystals were precipitated.

[0051] (3) Lithium dihydrogen phosphate crystals were heated to 320℃ at a rate of 5℃ / min and held for 90 min, then heated to 660℃ at a rate of 4℃ / min and held for 60 min, and finally cooled to room temperature at a rate of 90℃ / min to obtain amorphous high-purity lithium metaphosphate, the XRD pattern of which is shown in the figure. Figure 5 As shown.

[0052] The elemental and impurity contents of the high-purity lithium metaphosphate obtained in Example 1 are shown in Table 1.

[0053] Table 1. Main element content and impurity index of lithium dihydrogen phosphate

[0054] Note: The main content of lithium dihydrogen phosphate is calculated using the impurity reduction method.

[0055] In summary, this application provides a method for preparing high-purity lithium metaphosphate from a high-impurity lithium source. This method employs a synergistic process of phosphoric acid system reaction conversion, PAC / hydrogen peroxide multi-stage impurity removal, and nanofiltration concentration cycle, combined with concentration crystallization, two-step high-temperature transformation, and rapid quenching, ultimately yielding a high-purity crystalline / amorphous lithium metaphosphate product. The specific process steps and their principles are as follows: First, a phosphoric acid system conversion process is performed to transform phosphorus into a highly water-soluble lithium salt, laying the chemical foundation for subsequent dissolution-crystallization purification. Subsequently, a multi-stage impurity removal process using PAC / hydrogen peroxide is employed, utilizing co-precipitation and adsorption bridging to remove Fe introduced from the lithium source. 3+ Heavy metals and some Si impurities are encapsulated and precipitated; at the same time, hydrogen peroxide encapsulates Fe. 2+ Oxidized to Fe 3 + This makes it easier for the flocs to capture, thus effectively removing impurities such as calcium, magnesium, and iron from the raw materials.

[0056] After impurity removal, the feed solution is concentrated and recycled via nanofiltration to remove highly soluble sodium salts (Na₂O₃). + The impurities, including trace amounts of residual monovalent impurities, are enriched in the mother liquor and removed through solid-liquid separation, further purifying the system. A subsequent concentration and crystallization step achieves effective removal of impurities and efficient generation of the target product.

[0057] During the heat treatment stage, a two-step heating process is employed to avoid the material directly entering the high-temperature section, which could lead to violent dehydration, splashing, or localized overheating and decomposition. This ensures complete transformation of the intermediate phase and uniform melt composition. Finally, a rapid quenching process cools the material to room temperature, preventing the disordered arrangement of atoms / molecules in the molten liquid from rearranging into a crystal lattice. This freezes the "short-range ordered, long-range disordered" structure of the high-temperature melt, ultimately yielding a transparent, glassy, ​​amorphous lithium metaphosphate. If the cooling rate is slower, reaching 300℃~450℃, a crystalline lithium metaphosphate product will be obtained.

[0058] The preparation method described in this application breaks through the dependence of existing technologies on high-purity lithium sources, significantly broadens the sources of raw materials, reduces production costs, and features a simple process flow, low equipment requirements, stable and controllable operation, making it easy to achieve large-scale industrial production. The prepared high-purity lithium metaphosphate can meet the application needs of high-end fields such as battery materials, special glass, and ceramics.

[0059] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0060] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are limited to all changes and modifications that include the preferred embodiments and fall within the scope of the embodiments of the present application.

[0061] Finally, it should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0062] This application uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing high-purity lithium metaphosphate, characterized in that, Includes the following steps: A lithium salt and a phosphorus source are mixed and reacted to generate a lithium dihydrogen phosphate solution. The lithium dihydrogen phosphate solution was subjected to impurity removal and nanofiltration to obtain a separated solid phase and liquid phase. The separated solid phase is concentrated and then repeatedly subjected to impurity removal, nanofiltration and concentration processes. All liquid phases were collected and sequentially concentrated and crystallized, subjected to high-temperature transformation treatment and rapid cooling treatment to obtain high-purity lithium metaphosphate.

2. The preparation method according to claim 1, characterized in that, The lithium source includes at least one of anhydrous lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium oxide, lithium peroxide, lithium hydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, and lithium halides. The phosphorus source includes at least one of orthophosphoric acid, metaphosphoric acid, and phosphorus pentoxide. The lithium salt and phosphorus source are mixed in a lithium-phosphorus molar ratio.

3. The preparation method according to claim 1, characterized in that, The reaction time for the lithium salt and phosphorus source mixture is 60 min to 300 min, and the reaction temperature is 60℃ to 95℃.

4. The preparation method according to claim 1, characterized in that, The reagents used for the impurity removal treatment are PAC and / or hydrogen peroxide.

5. The preparation method according to claim 1, characterized in that, The nanofiltration process uses a DK type nanofiltration membrane, a DL type nanofiltration membrane, or an NF270 type nanofiltration membrane, and the nanofiltration process takes 30 min to 120 min.

6. The preparation method according to claim 1, characterized in that, The concentration and crystallization time is 60 min to 300 min, and the concentration and crystallization method is as follows: first concentrate and crystallize until the specific gravity of the solution is 1.4 to 2.0, and then cool to precipitate lithium dihydrogen phosphate crystals.

7. The preparation method according to claim 1, characterized in that, The high-temperature transformation treatment method includes: Heat to 200℃~350℃ at a rate of 3℃ / min~5℃ / min, and hold for 1.5h~3h; Continue heating at a rate of 2℃ / min to 4℃ / min to 650℃ to 700℃, and hold at that temperature for 0.5h to 1.5h.

8. The preparation method according to claim 1, characterized in that, The rapid cooling method is to cool from 650℃~700℃ to 300℃~450℃ at a rate of 2℃ / min~15℃ / min or to room temperature at a rate of 50℃ / min~100℃ / min.

9. High-purity lithium metaphosphate prepared by the preparation method according to any one of claims 1-8.

10. The application of high-purity lithium metaphosphate according to claim 9, characterized in that, The high-purity lithium metaphosphate can be used to prepare lithium iron phosphate cathode materials, optical glass, ceramic materials, and solid electrolytes.

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