Vanadyl phosphate ammonium, a method for preparing the same, and a method for preparing a vanadium-phosphorus oxide compound using the same

Abstract

This invention provides ammonium vanadium oxyphosphate, its preparation method, and a method for preparing vanadium phosphorus oxides using it. The preparation method of ammonium vanadium oxyphosphate includes the following steps: adding a vanadium source and an ammonium source to phosphoric acid, reacting to form a precipitate, and filtering and washing to obtain ammonium vanadium oxyphosphate NH4(VOPO4)2. The preparation of ammonium vanadium oxyphosphate using this invention is simple and easy, and the prepared ammonium vanadium oxyphosphate has the advantages of good uniformity, good dispersibility, and high activity. This invention also discloses a method for preparing vanadium phosphorus oxides using ammonium vanadium oxyphosphate, including the following steps: reducing and calcining ammonium vanadium oxyphosphate to prepare vanadium pyrophosphate and / or vanadium phosphate, and then oxidizing and calcining to prepare vanadium oxyphosphate. This invention can prepare a variety of vanadium phosphorus oxides using ammonium vanadium oxyphosphate as a raw material. The vanadium oxyphosphate (VOPO4) prepared by this invention has high crystallinity and a large specific surface area (8-20m²). 2 / g), which is beneficial to improving the activity of the catalyst.

Description

Technical Field

[0001] This invention relates to materials technology, and more particularly to a vanadium oxyphosphate, its preparation method, and a method for preparing vanadium oxyphosphate compounds using the same. Background Technology

[0002] Human progress and development have been accompanied by the rapid depletion of fossil fuels; the burning of fossil fuels also leads to unavoidable environmental pollution. Among these, vehicle exhaust is a major cause of air pollution. Therefore, the development and application of electric vehicles (EVs) or hybrid electric vehicles (HEVs) and their corresponding power sources have rapidly progressed. In existing power battery systems, lithium-ion rechargeable batteries have an absolute advantage as a power source for EVs and HEVs due to their high volumetric and gravimetric energy ratios, high voltage, low self-discharge rate, lack of memory effect, and long cycle life.

[0003] Cathode materials are a crucial and core component of lithium-ion batteries. Currently, the most researched materials include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials. Lithium cobalt oxide is expensive and highly toxic, lithium manganese oxide has poor thermal stability, lithium nickel oxide has a complex synthesis process, lithium iron phosphate has low specific capacity and poor low-temperature performance, and ternary materials have poor safety. In contrast, lithium vanadium phosphate cathode materials not only have a theoretical specific capacity as high as 197 mAh·g⁻¹, but also good thermal stability, operating stably over a wide temperature range, thus becoming a major research direction for novel lithium-ion battery cathode materials.

[0004] Sodium-ion batteries are a new type of battery that has emerged in recent years. They have attracted widespread attention due to their advantages of good low-temperature performance, high rate performance, and good cycle performance. Among them, polyanion sodium battery materials have become the main sodium battery process route due to their advantages of good high-temperature stability and excellent cycle stability. These include sodium vanadium phosphate, sodium vanadium fluorophosphate (1111), and sodium vanadium fluorophosphate (3223).

[0005] In the production process of vanadium-based sodium / lithium battery cathode materials, the vanadium sources used are mainly vanadium phosphate, vanadium oxypyrophosphate ((VO)2P2O7), vanadium oxyphosphate (VOPO4), and other vanadium phosphate oxide compounds.

[0006] In recent years, numerous reports have covered the preparation methods of cathode materials, mainly including high-temperature solid-state method, carbothermal reduction method and sol-gel method.

[0007] For example, patent CN201410854493.5 describes a method for preparing vanadium oxyphosphate crystals. This method includes the following steps: (1) dissolving a vanadium source, a phosphorus source, and a carbon-containing organic compound in water to obtain a solution; (2) stirring the solution in a constant temperature water bath at 20–100°C; (3) adjusting the pH to 3–14; (4) heating the solution for 1–72 hours to obtain a gel; (5) vacuum drying to form an amorphous vanadium oxyphosphate precursor; and (6) sintering the solution at 300–750°C for 2–20 hours under an oxidizing atmosphere, followed by cooling to room temperature. The above-mentioned method for preparing vanadium oxyphosphate has problems such as complex reaction steps, the need for long-term drying of materials, high energy consumption, poor uniformity of the gel formed, and poor consistency of the prepared material.

[0008] Therefore, there is an urgent need for a simple and easy method for preparing ammonium vanadium oxyphosphate, as well as for the further preparation of vanadium phosphate oxides from ammonium vanadium oxyphosphate. Summary of the Invention

[0009] The purpose of this invention is to address the problems of complex preparation methods, high energy consumption, and poor product uniformity in current methods for preparing vanadium oxyphosphate. This invention proposes a method for preparing vanadium oxyphosphate that is simple and easy to implement, and yields vanadium oxyphosphate with good uniformity, excellent dispersibility, and high activity.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing vanadium oxyphosphate, comprising the following steps:

[0011] Vanadium and ammonium sources are added to phosphoric acid, and a precipitate is formed by reaction. The precipitate is obtained by filtration and washing to obtain vanadium oxyphosphate NH4(VOPO4)2.

[0012] Furthermore, the vanadium source includes one or more of pentavalent vanadium sources, tetravalent vanadium sources, and trivalent vanadium sources.

[0013] Furthermore, the pentavalent vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, and ammonium polyvanadate.

[0014] Furthermore, the tetravalent vanadium source is one or more of vanadium dioxide, vanadium oxysulfate, vanadium oxyoxate, and vanadium oxydichloride.

[0015] Furthermore, the trivalent vanadium source is one or more of vanadium trioxide, vanadium sulfate, and vanadium trichloride.

[0016] Furthermore, the average valence state of vanadium in the vanadium source is 4.2-4.7, preferably 4.5. The vanadium source can be a mixture of a low-valence vanadium source and a high-valence vanadium source, such as vanadium tetroxide and vanadium pentoxide mixed in a molar ratio of 1:1; or pentavalent vanadium compounds can be used as raw materials, and a reducing agent can be used to quantitatively reduce vanadium to 4.5; or trivalent vanadium compounds can be used as raw materials, and an oxidizing agent can be used to quantitatively oxidize vanadium to 4.5.

[0017] Furthermore, the ammonium source is one or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium sulfate, ammonium chloride, ammonia, and ammonium carbonate.

[0018] Furthermore, the concentration of the phosphoric acid is 50-98%, preferably 70-98%. Unless otherwise specified, all percentages in this invention refer to mass percentages.

[0019] Furthermore, the reaction temperature is 50-100℃ and the reaction time is 1-10h; preferably, the reaction temperature is 60-90℃ and the reaction time is 1-6h.

[0020] Furthermore, the molar ratio of phosphorus in the phosphoric acid, ammonium ions in the ammonium source, and vanadium in the vanadium source is 1.0-1.5:0.5-2.0:1.0, preferably 1.0-1.3:0.5-1.5:1.0.

[0021] Furthermore, the washing process uses pure water and involves washing 1-6 times.

[0022] The reaction principle of this invention, vanadium oxyphosphate, is to utilize vanadium oxide with an average valence state of 4.5 as a vanadium source, reacting it with a phosphorus source and an ammonium source to obtain vanadium oxyphosphate. For example, vanadium tetroxide and vanadium pentoxide are mixed in a molar ratio of 1:1 and the following reaction is carried out:

[0023] V2O4+V2O5+4H3PO4+2NH4OH=2NH4(VOPO4)2+7H2O

[0024] For example, when vanadium trioxide and vanadium pentoxide are mixed in a molar ratio of 1:3, the following reaction occurs:

[0025] V2O3+3V2O5+8H3PO4+4NH4OH=4NH4(VOPO4)2+14H2O

[0026] The reaction process of this invention can also use pentavalent vanadium compounds as raw materials and quantitatively reduce vanadium to 4.5 valence using a reducing agent, or it can use trivalent vanadium compounds as raw materials and quantitatively oxidize vanadium to 4.5 valence using an oxidizing agent.

[0027] Another object of the present invention discloses a vanadium oxyphosphate prepared by the above preparation method.

[0028] Another object of the present invention discloses a method for preparing vanadium phosphate oxides using the above-mentioned vanadium oxyphosphate ammonium, comprising the following steps:

[0029] Vanadium oxyphosphate and / or vanadium phosphate are prepared by reduction and calcination of ammonium vanadium oxyphosphate.

[0030] Furthermore, the reduction calcination temperature is 400-1000℃, and the reduction calcination time is 1-20h; preferably, the reduction calcination temperature is 500-900℃, and preferably, the reduction calcination time is 1-10h.

[0031] Furthermore, when the reduction calcination temperature is 400-600℃, vanadium oxyphosphate is reduced and calcined to prepare vanadium pyrophosphate. In a reducing atmosphere, vanadium oxyphosphate is calcined at 400-600℃ to reduce vanadium to its tetravalent state, thus preparing vanadium pyrophosphate.

[0032] Furthermore, vanadium phosphate is prepared by reducing and calcining ammonium vanadium oxyphosphate at a reduction calcination temperature of 800-1000℃. In a reducing atmosphere, ammonium vanadium oxyphosphate is calcined at 800-1000℃ to reduce vanadium to its trivalent state, thus preparing vanadium phosphate.

[0033] Furthermore, when the reduction and calcination temperature is greater than 600°C and less than 800°C, the reduction and calcination of ammonium vanadium oxyphosphate yields a mixture of vanadium pyrophosphate and vanadium phosphate.

[0034] Furthermore, the reducing calcination atmosphere is one or more of ammonia, hydrogen, methane, and carbon monoxide.

[0035] Further, the above-mentioned vanadium pyrophosphate and / or vanadium phosphate are oxidized and calcined to prepare vanadium oxyphosphate (VOPO4).

[0036] Furthermore, the oxidation and calcination temperature is 300-700℃, and the oxidation and calcination time is 1-10h; preferably, the oxidation and calcination temperature is 400-500℃, and preferably, the oxidation and calcination time is 3-6h, to prepare vanadium oxyphosphate (VOPO4).

[0037] Furthermore, the oxidizing and calcining atmosphere is oxygen and / or air.

[0038] The vanadium oxyphosphate (VOPO4) can be used in the field of vanadium-based sodium / lithium-ion battery cathode materials.

[0039] The method for preparing vanadium oxyphosphate of the present invention has the following advantages compared with the prior art:

[0040] 1) This invention uses phosphorus source, vanadium source and ammonium source as raw materials to produce vanadium oxyphosphate NH4(VOPO4)2, forming uniform crystals. The material has good uniformity, uniform particle size distribution and high reactivity. The lithium vanadium phosphate prepared from it has excellent electrochemical performance.

[0041] 2) The reaction steps of this invention are simple, the reaction conditions are mild, and it is beneficial to control the reaction process;

[0042] 3) The raw materials involved in this invention (such as vanadium and phosphorus sources) are widely available, offer many choices, and are inexpensive;

[0043] 4) This invention first prepares ammonium vanadyl phosphate, then reduces and roasts it to obtain vanadyl pyrophosphate and / or vanadium phosphate, and finally oxidizes and roasts it to obtain vanadyl phosphate (VOPO4). That is, this invention can prepare various vanadium phosphate compounds using ammonium vanadyl phosphate as a raw material. The vanadyl phosphate (VOPO4) prepared by this invention has high crystallinity and a large specific surface area (8-20 μm²). 2 / g), which is beneficial to improving the activity of the catalyst. Attached Figure Description

[0044] Figure 1 The XRD diffraction pattern of the vanadium oxyphosphate prepared in Example 1 is shown.

[0045] Figure 2 The XRD diffraction pattern of vanadium oxyphosphate prepared in Example 4 is shown.

[0046] Figure 3 The image shows the SEM scan of the vanadium oxyphosphate prepared in Example 1.

[0047] Figure 4 The image shows the SEM scan of vanadium oxyphosphate prepared in Example 4. Detailed Implementation

[0048] The present invention will be further described below with reference to the embodiments:

[0049] Example 1

[0050] According to the molar ratio of phosphoric acid:ammonium metavanadate:VO2 = 1.5:1:1, ammonium metavanadate and vanadium dioxide were added to 70% phosphoric acid in one batch. The reaction temperature was controlled at 70℃, and the reaction was carried out for 4 hours. A precipitate was formed, filtered, and washed twice with pure water to obtain ammonium vanadium oxyphosphate. The product was analyzed by XRD. (See attached figure) Figure 1 Vanadium oxyphosphate was prepared. The XRD standard card code is 01-070-4618. The SEM scan of vanadium oxyphosphate is shown below. Figure 3 As shown, the material is a secondary sphere formed by primary particle aggregation, and the particle size distribution is uniform.

[0051] Example 2

[0052] According to the formula of phosphoric acid (concentration 80%): ammonium dihydrogen phosphate: VO2: V2O5 = 1:1:1:0.5 (molar ratio), the four components were mixed in an 80℃ water bath and reacted for 5 hours to form a precipitate. The precipitate was filtered and washed three times with pure water to obtain ammonium vanadium oxyphosphate. The product was analyzed by XRD, and the results confirmed that the prepared product was ammonium vanadium oxyphosphate.

[0053] Example 3

[0054] According to the formula of phosphoric acid (concentration 90%): ammonium sulfate: VO2: V2O5 = 2:0.5:1:0.5 (molar ratio), the four components were mixed and reacted in a 90℃ water bath for 3 hours to form a precipitate. The precipitate was filtered and washed three times with pure water to obtain ammonium vanadium oxyphosphate. The product was analyzed by XRD, and the results confirmed that the prepared product was ammonium vanadium oxyphosphate.

[0055] Example 4

[0056] The preparation of vanadium oxyphosphate compounds using the vanadium oxyphosphate prepared in Example 1 includes the following steps: vanadium oxyphosphate is placed in an ammonia atmosphere and calcined at 700°C for 2 hours to obtain vanadium phosphate, and then oxidized and calcined at 400°C in an air atmosphere for 4 hours to obtain vanadium oxyphosphate VOPO4.

[0057] The products were analyzed by XRD, see attached. Figure 2 Vanadium oxyphosphate was prepared. The SEM scan of vanadium oxyphosphate is shown below. Figure 4 As shown, after oxidation and calcination, the material exhibits a uniform particle distribution and a significantly improved crystallinity compared to the precursor, with a specific surface area of ​​10 m². 2 / g.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for the preparation of a vanadium phosphorus oxide compound, characterized in that, Includes the following steps: Vanadium source and ammonium source are added to phosphoric acid, and a precipitate is formed by reaction. The precipitate is filtered and washed to obtain vanadium oxyphosphate ammonium NH4(VOPO4)2. The reaction temperature is 60-90℃ and the reaction time is 1-6h. The vanadium source has an average vanadium valence of 4.5, and the vanadium source includes one or more of pentavalent vanadium sources, tetravalent vanadium sources, and trivalent vanadium sources; The molar ratio of phosphorus in the phosphoric acid, ammonium ions in the ammonium source, and vanadium in the vanadium source is 1.0-1.5:0.5-2.0:1.0, and the mass percentage content of the phosphoric acid is 70-98%. Vanadium oxyphosphate ammonium phosphate was reduced and calcined to prepare vanadium oxyphosphate pyrophosphate and / or vanadium phosphate. When the reduction and calcination temperature is 400-600℃, vanadium oxyphosphate is prepared by reduction and calcination of ammonium vanadium oxyphosphate. Vanadium phosphate is prepared by reducing and calcining ammonium vanadium oxyphosphate at a reduction and calcination temperature of 800-1000℃. When the reduction calcination temperature is greater than 600°C and less than 800°C, the reduction calcination of ammonium vanadium oxyphosphate yields a mixture of vanadium pyrophosphate and vanadium phosphate.

2. The method for preparing vanadium phosphorus oxides according to claim 1, characterized in that, The ammonium source is one or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium sulfate, ammonium chloride, ammonia, and ammonium carbonate.

3. The method for preparing vanadium phosphorus oxides according to claim 1, characterized in that, Includes the following steps: Vanadium oxyphosphate is prepared by oxidative calcination of the vanadium pyrophosphate and / or vanadium phosphate.

4. The method of claim 3, wherein the vanadium phosphorus oxide compound is prepared by the process of claim 1 or 2. The oxidation and calcination temperature is 300-700℃, and the oxidation and calcination time is 1-10h.

Images