Preparation method and application of sodium vanadium fluorophosphate and carbon-coated sodium vanadium fluorophosphate

Abstract

The application provides a preparation method of sodium vanadium fluorophosphate, which comprises the following steps: mixing a sodium source, a vanadium source, a phosphorus source and a fluorine source to form a first raw material, wherein the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the first raw material is a:b:c:d, wherein a, b, c and d are real numbers greater than 0, and a / c≤1.5, a / b<1.5, a / d<1, or a / c≥1.5, c / b<1 and c / d<2 / 3; the first raw material is treated to obtain a first precursor; and the first precursor is dried and calcined to obtain sodium vanadium fluorophosphate. The preparation method can be used to prepare sodium vanadium fluorophosphate with few impurities, high purity and excellent performance, and is helpful to the use of sodium vanadium fluorophosphate. The application further provides a preparation method and application of carbon-coated sodium vanadium fluorophosphate.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a preparation method of sodium vanadium fluorophosphate and carbon-coated sodium vanadium fluorophosphate and application thereof. BACKGROUND

[0002] Sodium vanadium fluorophosphate (Na3V2(PO4)2F3, NVOPF) as a typical sodium super ionic conductor (NASICON) has a stable three-dimensional framework structure, high theoretical specific capacity (128 mAh / g) and high working voltage, and has become a hotspot of electrode material research of sodium ion batteries. However, the sodium vanadium fluorophosphate prepared at present contains sodium vanadium phosphate (Na3V2(PO4)3) and other impurities, which directly reduces the discharge specific capacity and working voltage of the sodium vanadium fluorophosphate, and further reduces the energy density of the battery. Therefore, the preparation method of the sodium vanadium fluorophosphate needs to be improved to obtain sodium vanadium fluorophosphate with high purity and excellent performance. SUMMARY

[0003] Therefore, the application provides a preparation method of sodium vanadium fluorophosphate and carbon-coated sodium vanadium fluorophosphate and application thereof. The preparation method provided by the application can reduce the generation of sodium vanadium phosphate and other impurities, improve the purity of the sodium vanadium fluorophosphate, and thus obtain sodium vanadium fluorophosphate with excellent performance, which is beneficial to the use of the sodium vanadium fluorophosphate.

[0004] In a first aspect, the application provides a preparation method of sodium vanadium fluorophosphate, comprising:

[0005] The sodium source, the vanadium source, the phosphorus source and the fluorine source are mixed to form a first raw material, and the molar ratio of sodium elements, vanadium elements, phosphorus elements and fluorine elements in the first raw material is a:b:c:d, wherein a, b, c and d are real numbers greater than 0, and a, b, c and d satisfy: when a / c≤1.5, a / b<1.5, a / d<1, or when a / c≥1.5, c / b<1, c / d<2 / 3.

[0006] The first raw material is treated to obtain a first precursor;

[0007] The first precursor is dried and calcined to obtain sodium vanadium fluorophosphate.

[0008] Optionally, when a / c≤1.5, 1.36

[0009] Optionally, when a / c≤1.5, b is 2a / 3+e and d is a+3e, and e>0, or when a / c≥1.5, b is c+f and d is 1.5c+3f, and f>0.

[0010] Further, when a / c≤1.5, 2.5≤a≤3.5, 0.1≤e≤0.2, or when a / c≥1.5, 1.6

[0011] Further, when a / c≤1.5, 12.5≤a / e≤35, or when a / c≥1.5, 8.3

[0012] Optionally, the first raw material is treated to obtain the first precursor, including: the first raw material is treated by at least one of a solid phase method, a hydrothermal method, a sol-gel method, and a spray drying method to obtain the first precursor.

[0013] Optionally, the drying includes treatment at 100-120℃ for 1-3h.

[0014] Optionally, the calcination includes treatment at 300-400℃ for 1-5h, and then treatment at 600-800℃ for 10min-10h.

[0015] The preparation method of the sodium vanadium fluorophosphate provided in the application reduces the content of impurities in the sodium vanadium fluorophosphate by controlling the molar ratio of sodium, vanadium, phosphorus, and fluorine elements, thereby obtaining sodium vanadium fluorophosphate with high purity and excellent performance. The preparation method is simple in operation, short in preparation process, and high in preparation efficiency, which is conducive to the industrial production of sodium vanadium fluorophosphate and the use of sodium vanadium fluorophosphate.

[0016] In a second aspect, the application provides a preparation method of carbon-coated sodium vanadium fluorophosphate, including:

[0017] The sodium source, the vanadium source, the phosphorus source, the fluorine source, and the carbon source are mixed to form a second raw material, and the molar ratio of sodium, vanadium, phosphorus, and fluorine elements in the second raw material is a':b':c':d', wherein a', b', c', and d' are real numbers greater than 0, and a', b', c', and d' satisfy: when a' / c'≤1.5, a' / b' 1.5, c' / b' 2 / 3.

[0018] The second raw material is treated to obtain a second precursor;

[0019] The second precursor is dried and calcined to obtain carbon-coated sodium vanadium fluorophosphate.

[0020] The preparation method of the carbon-coated sodium vanadium fluorophosphate provided in the application reduces the content of impurities in the sodium vanadium fluorophosphate by controlling the molar ratio of sodium elements, vanadium elements, phosphorus elements and fluorine elements, and the carbon coating can also improve the conductivity of the sodium vanadium fluorophosphate, so that a material with high purity and excellent performance is obtained; and the preparation method is simple in operation, short in preparation process and high in preparation efficiency, which is conducive to the industrial production of the carbon-coated sodium vanadium fluorophosphate and the use of the carbon-coated sodium vanadium fluorophosphate.

[0021] In a third aspect, the application provides a battery pole piece, which comprises at least one of the sodium vanadium fluorophosphate prepared by the preparation method of the first aspect and the carbon-coated sodium vanadium fluorophosphate prepared by the preparation method of the second aspect.

[0022] The battery pole piece provided in the application uses the sodium vanadium fluorophosphate and / or the carbon-coated sodium vanadium fluorophosphate with high purity and excellent performance, so that the specific capacity and energy density of the battery pole piece can be improved, which is conducive to the use of the battery pole piece.

[0023] In a fourth aspect, the application provides a battery, which comprises the battery pole piece of the third aspect.

[0024] The battery provided in the application has high specific capacity and energy density of the battery pole piece, so that the battery has excellent electrochemical performance and is conducive to its use.

[0025] In a fifth aspect, the application provides an electric device, which comprises the battery of the fourth aspect.

[0026] The electric device provided in the application has excellent performance and strong product competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. The specific embodiments described herein are only used to explain the application and not to limit the application.

[0028] Figure 1 The preparation method flowchart of the sodium vanadium fluorophosphate provided in an embodiment of the application.

[0029] Figure 2 The preparation method flowchart of the carbon-coated sodium vanadium fluorophosphate provided in an embodiment of the application.

[0030] Figure 3 The cross-sectional schematic diagram of the positive electrode provided in an embodiment of the application.

[0031] Figure 4 The XRD spectrum of Na3V2(PO4)2F3@C prepared in Examples 1-4 and Comparative Example 1.

[0032] Figure 5 TG curve of Na3V2(PO4)2F3@C prepared for Examples 1-4 and Comparative Example 1.

[0033] Figure 6 SEM image of Na3V2(PO4)2F3@C prepared for Examples 1-4 and Comparative Example 1.

[0034] Figure 7 Charge-discharge curve of a battery prepared from Na3V2(PO4)2F3@C prepared for Examples 1, 3 and 4 under 0.2C condition.

[0035] Figure 8 Charge-discharge curve of a battery prepared from Na3V2(PO4)2F3@C prepared for Examples 2 and Comparative Example 1 under 0.2C condition.

[0036] Figure 9 Cycle performance curve of a battery prepared from Na3V2(PO4)2F3@C prepared for Examples 1-4 and Comparative Example 1 under 1C condition.

[0037] Figure 10 Rate performance curve of a battery prepared from Na3V2(PO4)2F3@C prepared for Examples 1-4 and Comparative Example 1. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] Please refer to Figure 1 The flow chart of the preparation method of sodium vanadium fluorophosphate provided in an embodiment of the present application comprises:

[0040] S101: a sodium source, a vanadium source, a phosphorus source and a fluorine source are mixed to form a first raw material, and the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the first raw material is a:b:c:d, wherein a, b, c and d are real numbers greater than 0, and a, b, c and d satisfy: when a / c≤1.5, a / b<1.5, a / d<1, or when a / c≥1.5, c / b<1, c / d<2 / 3.

[0041] S102: the first raw material is treated to obtain a first precursor.

[0042] S103: the first precursor is dried and calcined to obtain sodium vanadium fluorophosphate.

[0043] In the related art, during the preparation of sodium vanadium fluorophosphate (Na3V2(PO4)2F3), sodium vanadium phosphate (Na3V2(PO4)3) and other impurities are generated. The specific capacity and potential platform of Na3V2(PO4)3 are lower than those of Na3V2(PO4)2F3, thereby causing the working voltage and discharge specific capacity of the material to decrease, and affecting the energy density of the battery made therefrom. By adjusting the molar ratio of sodium, vanadium, phosphorus and fluorine in the raw material, the excess of vanadium and fluorine in the raw material compensates for the loss of vanadium and fluorine during the preparation process, thereby reducing the generation of Na3V2(PO4)3 impurities, improving the purity of the prepared Na3V2(PO4)2F3, and ensuring the performance of Na3V2(PO4)2F3. The preparation method is simple, and only the proportion of each element in the raw material needs to be adjusted to significantly reduce the content of impurities and obtain Na3V2(PO4)2F3 with excellent performance. The preparation method is simple to operate, has a short preparation process and high preparation efficiency, is conducive to the industrial production of Na3V2(PO4)2F3, and is helpful to the use of Na3V2(PO4)2F3.

[0044] In S101, a first raw material is obtained by mixing sodium source, vanadium source, phosphorus source and fluorine source in a suitable proportion. Taking sodium as an example, the sodium in the first raw material comes from the sodium source, and can also come from other raw materials. The molar amount of sodium in the first raw material is the sum of the molar amounts of all sodium elements in the first raw material. Similarly, the molar amount of vanadium in the first raw material is the sum of the molar amounts of all vanadium elements in the first raw material, the molar amount of phosphorus in the first raw material is the sum of the molar amounts of all phosphorus elements in the first raw material, and the molar amount of fluorine in the first raw material is the sum of the molar amounts of all fluorine elements in the first raw material.

[0045] In the present application, the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the first raw material is a:b:c:d, a, b, c, d can be selected from any real number greater than 0 according to the needs. When a / c < 1.5, that is, the ratio of a to c is less than 3:2, the phosphorus element is excessive compared with the sodium element; when a / c > 1.5, that is, the ratio of a to c is greater than 3:2, the sodium element is excessive compared with the phosphorus element; when a / c = 1.5, that is, the ratio of a to c is 3:2, the sodium element and the phosphorus element satisfy the molar ratio of Na and P in Na3V2(PO4)2F3. When a / c ≤ 1.5, a / b < 1.5, a / d < 1, that is, the molar ratio of sodium element and vanadium element is less than 1.5, and the molar ratio of sodium element and fluorine element is less than 1, according to the molar ratio of Na and V in Na3V2(PO4)2F3 and the molar ratio of Na and F, it can be known that the vanadium element and the fluorine element in the first raw material are excessive. When a / c ≥ 1.5, c / b < 1, c / d < 2 / 3, that is, the molar ratio of phosphorus element and vanadium element is less than 1, and the molar ratio of phosphorus element and fluorine element is less than 2 / 3, according to the molar ratio of P and V in Na3V2(PO4)2F3 and the molar ratio of P and F, it can be known that the vanadium element and the fluorine element in the first raw material are excessive. Therefore, by making the vanadium element and the fluorine element in the first raw material excessive, the generation of Na3V2(PO4)3 impurities is avoided. It can be understood that when a / c = 1.5, the condition of c / b < 1 and c / d < 2 / 3 is also satisfied when the conditions of a / b < 1.5 and a / d < 1 are satisfied.

[0046] In an embodiment of the present application, when a / c≤1.5, 1.36

[0047] In an embodiment of the present application, when a / c≤1.5, b is 2a / 3+e, and d is a+3e, e>0. That is, when the molar ratio of sodium and vanadium is 3:2, the molar ratio of Na and V in Na3V2(PO4)2F3 is satisfied, and in the present application, b is 2a / 3+e, that is, the content of vanadium is increased by e, so that the vanadium is excessive relative to sodium, and the loss of vanadium in the preparation of Na3V2(PO4)2F3 is compensated; when the molar ratio of sodium and fluorine is 1:1, the molar ratio of Na and F in Na3V2(PO4)2F3 is satisfied, and in the present application, d is a+3e, that is, the content of fluorine is increased by 3e, so that the fluorine is excessive relative to sodium, and the loss of fluorine in the preparation of Na3V2(PO4)2F3 is compensated; at the same time, the amounts of vanadium and fluorine added relative to sodium are e and 3e respectively, that is, the amount of fluorine added relative to sodium is 3 times the amount of vanadium added relative to sodium, so as to further avoid the generation of Na3V2(PO4)3 impurities and improve the purity of the prepared Na3V2(PO4)2F3.

[0048] In an embodiment of the present application, when a / c≤1.5, 2.5≤a≤3.5, and 0

[0049] In an embodiment of the present application, when a / c≤1.5, 12.5≤a / e≤35, it is beneficial to reduce the generation of Na3V2(PO4)3impurities, and further improve the performance of Na3V2(PO4)2F3. Specifically, a / e can be but not limited to greater than or equal to 12.5, greater than or equal to 15, greater than or equal to 18, greater than or equal to 20, greater than or equal to 25, greater than or equal to 30, etc., and a / e can be but not limited to less than or equal to 20, less than or equal to 23, less than or equal to 25, less than or equal to 28, less than or equal to 30, less than or equal to 35, etc.

[0050] In an embodiment of the present application, when a / c≥1.5, 0.89

[0051] In an embodiment of the present application, when a / c≥1.5, b is c+f, and d is 1.5c+3f, and f>0. That is, when the molar ratio of phosphorus and vanadium is 1:1, it satisfies the molar ratio of P and V in Na3V2(PO4)2F3, and in the present application, b is c+f, that is, the content of vanadium is increased by f, so that the vanadium element is excessive relative to the phosphorus element, which compensates for the loss of vanadium in the preparation process of Na3V2(PO4)2F3; when the molar ratio of phosphorus and fluorine is 2:3, it satisfies the molar ratio of P and F in Na3V2(PO4)2F3, and in the present application, d is 1.5c+3f, that is, the content of fluorine is increased by 3e, so that the fluorine element is excessive relative to the sodium element, which compensates for the loss of fluorine in the preparation process of Na3V2(PO4)2F3; at the same time, the amounts of vanadium and fluorine added relative to the phosphorus element are f and 3f respectively, that is, the amount of fluorine added relative to the phosphorus element is 3 times the amount of vanadium added relative to the phosphorus element, so as to further avoid the generation of Na3V2(PO4)3impurities and improve the purity of the prepared Na3V2(PO4)2F3.

[0052] In an embodiment of the present application, when a / c≥1.5, 1.6

[0053] In an embodiment of the present application, when a / c≥1.5, 8.3

[0054] It can be understood that the sodium source, the vanadium source, the phosphorus source and the fluorine source respectively refer to materials capable of providing sodium elements, vanadium elements, phosphorus elements and fluorine elements. In an embodiment of the present application, the sodium source includes at least one of sodium fluoride, sodium carbonate, sodium oxalate, sodium sulfate and sodium metavanadate. In an embodiment of the present application, the vanadium source includes at least one of ammonium metavanadate, vanadium pentoxide, vanadium acetylacetonate, sodium metavanadate, vanadium trifluoride, vanadium tetrafluoride and vanadium oxytrifluoride. In an embodiment of the present application, the phosphorus source (such as a phosphate source) includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate. In an embodiment of the present application, the fluorine source includes at least one of sodium fluoride, ammonium fluoride, hydrofluoric acid, vanadium trifluoride, vanadium tetrafluoride and vanadium oxytrifluoride. In the present application, the purity of the sodium source, the vanadium source, the phosphorus source and the fluorine source can be greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, greater than or equal to 99.8%, greater than or equal to 99.9%, greater than or equal to 99.99% and the like.

[0055] In an embodiment of the present application, when the valence of vanadium element in the vanadium source is +5 or +4, the first raw material further comprises a reducing agent. In an embodiment of the present application, the reducing agent comprises at least one of citric acid, oxalic acid, glucose, fructose, ascorbic acid, carbon nanotubes, conductive carbon black (such as Super P, etc.), and graphene oxide. By adding the reducing agent, the +5 or +4 valence vanadium can be reduced to +3 valence vanadium, ensuring the preparation of Na3V2(PO4)2F3. In an embodiment of the present application, when a / c≤1.5, the molar ratio of sodium element and the reducing agent in the first raw material is greater than or equal to 3, and when a / c≥1.5, the molar ratio of phosphorus element and the reducing agent in the first raw material is greater than or equal to 2, so as to ensure the reduction of vanadium and the consumption of the reducing agent, and carbon coating is not generated.

[0056] In S102, the first raw material is treated to obtain the first precursor. In an embodiment of the present application, the first raw material is treated by at least one of a solid-phase method, a hydrothermal method, a sol-gel method, and a spray drying method to obtain the first precursor.

[0057] In an embodiment of the present application, the first raw material is treated by the solid-phase method to obtain the first precursor, comprising: ball milling the first raw material after adding a solvent to obtain the first precursor. Specifically, the medium for ball milling can be but is not limited to zirconium beads, and the solvent can be but is not limited to at least one of water, acetone, anhydrous ethanol, ethylene glycol, etc.

[0058] In an embodiment of the present application, the first raw material is treated by the hydrothermal method to obtain the first precursor, comprising: adding the first raw material to water and placing it in a hydrothermal reaction kettle, centrifuging after reacting at 150-220°C (such as 150°C, 160°C, 180°C, 200°C, 210°C, 215°C, etc.) for 10-15h (such as 10h, 11h, 12h, 13h, 14h, 15h, etc.) to obtain the first precursor. Specifically, the centrifugation can be but is not limited to centrifugation at 8000-15000rmp (such as 10000rmp, 12000rmp, 13000rmp, 14000rmp, etc.) for 2-10min (such as 3min, 5min, 8min, 9min, etc.).

[0059] In an embodiment of the present application, the first raw material is treated by the sol-gel method to obtain the first precursor, comprising: adding the first raw material to a solvent to obtain a gel-like first precursor. Specifically, the first raw material can be directly added to the solvent after mixing, or the weighed raw materials can be sequentially added to the solvent. The vanadium source and the reducing agent can be simultaneously added to the solvent, or the vanadium source can be added to the solvent first and then the reducing agent.

[0060] In an embodiment of the present application, the first raw material is processed by a spray drying method to obtain the first precursor, including: adding the first raw material into a solvent to form a first solution, and spray drying the first solution to obtain the first precursor. Specifically, the solvent can be, but is not limited to, at least one of water, acetone, anhydrous ethanol, ethylene glycol, etc.; the vanadium source and the reducing agent are added into the solvent at the same time, or the vanadium source is added into the solvent first and then the reducing agent is added. In an embodiment of the present application, the feeding temperature in the spray drying can be 180-220°C (such as 190°C, 200°C, 210°C, 215°C, etc.), the feeding speed can be 180-220 mL / h (such as 185 mL / h, 190 mL / h, 200 mL / h, 210 mL / h, etc.), and the fan frequency can be 70-90 HZ (such as 75 HZ, 80 HZ, 85 HZ, 90 HZ, etc.). The first precursor prepared by the spray drying can not be subjected to subsequent drying treatment, thereby saving the preparation process and improving the preparation efficiency.

[0061] In S103, the first precursor is dried and calcined to obtain the sodium vanadium fluorophosphate. Through drying, the solvent, water, etc. in the first precursor can be removed, and the solid content of the first precursor is improved. In the calcination process, the +3 valence vanadium can be produced under the action of the reducing agent to prepare Na3V2(PO4)2F3.

[0062] In an embodiment of the present application, the drying includes being treated at 100-120°C for 1-3h. Specifically, the drying temperature can be, but is not limited to, 100°C, 105°C, 108°C, 110°C, 115°C, 117°C or 120°C, etc., and the drying time can be, but is not limited to, 1h, 1.5h, 2h, 2.5h or 3h, etc. In the present application, the drying can be performed in a vacuum environment.

[0063] In an embodiment of the present application, the calcination comprises treating at 300-400°C (such as 320°C, 350°C, 360°C, 380°C, etc.) for 1-5h (such as 2h, 3h, 4h, 4.5h, 5h, etc.), and then treating at 600-800°C (such as 650°C, 700°C, 750°C, 790°C, etc.) for 10min-10h (such as 20min, 30min, 50min, 1h, 3h, 4h, 6h, 7h, 8h, 9h, 10h, etc.). In order to avoid the generation of impurities due to the volatilization of fluorine, the prior art uses a lower calcination temperature and a shorter calcination time. In the present application, the fluorine element and the vanadium element in the first raw material are in excess, so that the impurities generated due to the volatilization of fluorine can be reduced, and thus it is not necessary to reduce the calcination temperature and shorten the calcination time, thereby ensuring that the calcination is fully carried out to obtain Na3V2(PO4)2F3 with excellent performance. In an embodiment of the present application, the calcination is carried out under an inert gas to ensure the performance of the prepared Na3V2(PO4)2F3. Specifically, the inert gas can be, but is not limited to, argon. In the present application, the calcination can be carried out in a tube furnace (such as a general tube furnace, a microwave tube furnace, etc.) or a sintering furnace. In an embodiment of the present application, the calcination is carried out in a microwave tube furnace, which comprises treating at 300-400°C for 1-5h, and then treating at 600-800°C for 10min-60min. Since the microwave tube furnace has a high heating rate (about 20-50°C / min), the target temperature can be reached in a short time, rapid calcination can be achieved, and the loss of fluorine and vanadium can be avoided. In an embodiment of the present application, the heating rate in the calcination is 3-8°C / min (such as 4°C / min, 5°C / min, 6°C / min, 7°C / min, etc.) to heat to 300-400°C.

[0064] Please refer to Figure 2 The preparation method flowchart of the carbon-coated sodium vanadium fluorophosphate provided in an embodiment of the present application comprises the following steps:

[0065] S201: mixing a sodium source, a vanadium source, a phosphorus source, a fluorine source and a carbon source to form a second raw material, wherein the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the second raw material is a':b':c':d', wherein a', b', c' and d' are real numbers greater than 0, and a' and c' satisfy a' / c'≤1.5, a' / b'<1.5 and a' / d'<1, or c' and b' satisfy c' / b'<1 and c' / d'<2 / 3.

[0066] S202: obtaining a second precursor by treating the second raw material.

[0067] S203: obtaining the carbon-coated sodium vanadium fluorophosphate by drying and calcining the second precursor.

[0068] The preparation method of the carbon-coated sodium vanadium fluorophosphate (Na3V2(PO4)2F3@C) provided in the application controls the molar ratio of sodium elements, vanadium elements, phosphorus elements and fluorine elements, thereby reducing the content of impurities in the sodium vanadium fluorophosphate, and the carbon coating can improve the conductivity of the sodium vanadium fluorophosphate, so that a material with high purity and excellent performance is obtained. Moreover, the preparation method is simple to operate, has a short preparation process and high preparation efficiency, is conducive to the industrial production of the carbon-coated sodium vanadium fluorophosphate and the use of the carbon-coated sodium vanadium fluorophosphate. It can be understood that the carbon-coated sodium vanadium fluorophosphate provided in the application is only different from the preparation method of the sodium vanadium fluorophosphate in any of the above embodiments in that a carbon source is additionally added to the raw materials, so that a carbon coating layer can be formed on the surface of the sodium vanadium fluorophosphate after drying and sintering.

[0069] In S201, a second raw material is obtained by mixing sodium sources, vanadium sources, phosphorus sources, fluorine sources and carbon sources in appropriate proportions. Taking sodium elements as an example, the sodium elements in the second raw material come from the sodium sources, and can also come from other raw materials. The molar amount of sodium elements in the second raw material is the sum of the molar amounts of all sodium elements in the second raw material. Similarly, the molar amount of vanadium elements in the second raw material is the sum of the molar amounts of all vanadium elements in the second raw material, the molar amount of phosphorus elements in the second raw material is the sum of the molar amounts of all phosphorus elements in the second raw material, and the molar amount of fluorine elements in the second raw material is the sum of the molar amounts of all fluorine elements in the second raw material.

[0070] In this application, the molar ratio of sodium, vanadium, phosphorus, and fluorine in the second raw material is a':b':c':d', where a', b', c', and d' can be selected from any real numbers greater than 0 as needed. When a' / c' ≤ 1.5, meaning the ratio of a' to c' is less than 3:2, phosphorus is in excess compared to sodium; when a' / c' > 1.5, meaning the ratio of a' to c' is greater than 3:2, sodium is in excess compared to phosphorus; when a' / c' = 1.5, meaning the ratio of a' to c' is 3:2, sodium and phosphorus satisfy the molar ratio of Na and P in Na3V2(PO4)2F3. When a' / c' ≤ 1.5, a' / b' < 1.5, a' / d' < 1, meaning the molar ratio of sodium to vanadium is less than 1.5, and the molar ratio of sodium to fluorine is less than 1. Based on the molar ratios of Na to V and Na to F in Na3V2(PO4)2F3, it can be seen that vanadium and fluorine are in excess in the second raw material. When a' / c' ≥ 1.5, c' / b' < 1, c' / d' < 2 / 3, meaning the molar ratio of phosphorus to vanadium is less than 1, and the molar ratio of phosphorus to fluorine is less than 2 / 3. Based on the molar ratios of P to V and P to F in Na3V2(PO4)2F3, it can be seen that vanadium and fluorine are in excess in the second raw material. Therefore, by making the second raw material contain excess vanadium and fluorine, the formation of the Na3V2(PO4)3 impurity phase can be avoided. It is understandable that when a' / c' = 1.5, the conditions a' / b' < 1.5 and a' / d' < 1 are satisfied, and the conditions c' / b' < 1 and c' / d' < 2 / 3 are also satisfied.

[0071] In an embodiment of the present application, when a' / c'≤1.5, 1.36

[0072] In an embodiment of the present application, when a' / c'≤1.5, b' is 2a' / 3+e', d' is a'+3e', and e'>0. That is, when the molar ratio of sodium and vanadium is 3:2, the molar ratio of Na and V in Na3V2(PO4)2F3 is satisfied, and in the present application, b' is 2a' / 3+e', that is, the vanadium content is increased by e', so that the vanadium element is excessive relative to the sodium element, and the loss of vanadium in the preparation of Na3V2(PO4)2F3@C is compensated; when the molar ratio of sodium and fluorine is 1:1, the molar ratio of Na and F in Na3V2(PO4)2F3 is satisfied, and in the present application, d' is a'+3e', that is, the fluorine content is increased by 3e', so that the fluorine element is excessive relative to the sodium element, and the loss of fluorine in the preparation of Na3V2(PO4)2F3@C is compensated; at the same time, the amounts of vanadium and fluorine added relative to sodium are e' and 3e', respectively, that is, the amount of fluorine added relative to sodium is 3 times the amount of vanadium added relative to sodium, so as to further avoid the generation of Na3V2(PO4)3 impurities and improve the purity of the prepared Na3V2(PO4)2F3@C.

[0073] In an embodiment of the present application, when a' / c'≤1.5, 2.5≤a'≤3.5, and 0

[0074] In an embodiment of the present application, when a' / c'≤1.5, 12.5≤a' / e'≤35, it is beneficial to reduce the generation of Na3V2(PO4)3impurities, and further improve the performance of Na3V2(PO4)2F3@C. Specifically, a' / e' can be but not limited to greater than or equal to 12.5, greater than or equal to 15, greater than or equal to 18, greater than or equal to 20, greater than or equal to 25, greater than or equal to 30, etc., and a' / e' can be but not limited to less than or equal to 20, less than or equal to 23, less than or equal to 25, less than or equal to 28, less than or equal to 30, less than or equal to 35, etc.

[0075] In an embodiment of the present application, when a' / c'≥1.5, 0.89

[0076] In an embodiment of the present application, when a' / c'≥1.5, b' is c'+f', d' is 1.5c'+3f', and f'>0. That is, when the molar ratio of phosphorus and vanadium is 1:1, the molar ratio of P and V in Na3V2(PO4)2F3 is satisfied, and in the present application, b' is c'+f', that is, the vanadium content is increased by f', so that the vanadium element is excessive relative to the phosphorus element, and the loss of vanadium in the preparation of Na3V2(PO4)2F3@C is compensated; when the molar ratio of phosphorus and fluorine is 2:3, the molar ratio of P and F in Na3V2(PO4)2F3 is satisfied, and in the present application, d' is 1.5c'+3f', that is, the fluorine content is increased by 3f', so that the fluorine element is excessive relative to the sodium element, and the loss of fluorine in the preparation of Na3V2(PO4)2F3@C is compensated; at the same time, the amounts of vanadium and fluorine added relative to the phosphorus element are f' and 3f', respectively, that is, the amount of fluorine added relative to the phosphorus element is 3 times the amount of vanadium added relative to the phosphorus element, so as to further avoid the generation of Na3V2(PO4)3 impurities and improve the purity of the prepared Na3V2(PO4)2F3@C.

[0077] In an embodiment of the present application, when a' / c'>1.5, 1.6

[0078] In an embodiment of the present application, when a / c≥1.5, 8.3

[0079] It can be understood that the sodium source, the vanadium source, the phosphorus source, the fluorine source and the carbon source respectively refer to materials capable of providing sodium elements, vanadium elements, phosphorus elements, fluorine elements and carbon elements. In an embodiment of the present application, the sodium source includes at least one of sodium fluoride, sodium carbonate, sodium oxalate, sodium sulfate and sodium metavanadate. In an embodiment of the present application, the vanadium source includes at least one of ammonium metavanadate, vanadium pentoxide, vanadium acetylacetonate, sodium metavanadate, vanadium trifluoride, vanadium tetrafluoride and vanadium oxytrifluoride. In an embodiment of the present application, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate. In an embodiment of the present application, the fluorine source includes at least one of sodium fluoride, ammonium fluoride, hydrofluoric acid, vanadium trifluoride, vanadium tetrafluoride and vanadium oxytrifluoride. In an embodiment of the present application, the carbon source includes at least one of citric acid, oxalic acid, glucose, fructose, sucrose and ascorbic acid. In the present application, the purity of the sodium source, the vanadium source, the phosphorus source, the fluorine source and the carbon source can be greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, greater than or equal to 99.8%, greater than or equal to 99.9%, greater than or equal to 99.99% and the like.

[0080] In an embodiment of the present application, when a' / c' ≤ 1.5, the molar ratio of sodium elements to carbon elements in the second raw material is 3: (1-4), and when a' / c' ≥ 1.5, the molar ratio of phosphorus elements to carbon elements in the second raw material is 2: (1-4), so as to ensure the formation of the carbon coating layer and improve the conductivity of Na3V2 (PO4) 2F3@C.

[0081] In an embodiment of the present application, when the valence of vanadium elements in the vanadium source is +5 or +4, the second raw material further includes a reducing agent. In an embodiment of the present application, the reducing agent includes at least one of citric acid, oxalic acid, glucose, fructose, ascorbic acid, carbon nanotubes, conductive carbon black (such as Super P and the like) and graphene oxide. By adding the reducing agent, the vanadium with +5 or +4 valence can be reduced to vanadium with +3 valence, so as to ensure the preparation of Na3V2 (PO4) 2F3@C. In an embodiment of the present application, when a' / c' ≤ 1.5, the molar ratio of sodium elements to reducing agents in the second raw material is greater than or equal to 3, and when a' / c' ≥ 1.5, the molar ratio of phosphorus elements to reducing agents in the second raw material is greater than or equal to 2, so as to ensure the reduction of vanadium and the consumption of the reducing agent, and the carbon coating is not generated. In the present application, when the carbon source has reducing property, it can also be used as a reducing agent at the same time, so as to avoid the addition of an extra reducing agent, reduce the amount of raw materials and reduce the preparation cost.

[0082] In S202, the second raw material is processed to obtain a second precursor. In an embodiment of the present application, the second raw material is processed to obtain the second precursor, including: the second raw material is processed by at least one of a solid phase method, a hydrothermal method, a sol-gel method and a spray drying method to obtain the second precursor. The specific process of the solid phase method, the hydrothermal method, the sol-gel method and the spray drying method is as described above, and will not be repeated here.

[0083] In S203, the second precursor is dried and calcined to obtain sodium vanadium fluorophosphate. Through drying, the solvent, water and the like in the second precursor can be removed, and the solid content of the second precursor is improved. In the calcination process, +3 valence vanadium can be produced under the action of a reducing agent to form Na3V2(PO4)2F3@C.

[0084] In an embodiment of the present application, the drying includes processing at 100-120°C for 1-3h. Specifically, the temperature of the drying can be but is not limited to 100°C, 105°C, 108°C, 110°C, 115°C, 117°C or 120°C, and the time of the drying can be but is not limited to 1h, 1.5h, 2h, 2.5h or 3h. In the present application, the drying can be carried out in a vacuum environment.

[0085] In an embodiment of the present application, the calcination comprises treating at 300-400°C (such as 320°C, 350°C, 360°C, 380°C, etc.) for 1-5h (such as 2h, 3h, 4h, 4.5h, 5h, etc.), and then treating at 600-800°C (such as 650°C, 700°C, 750°C, 790°C, etc.) for 10min-10h (such as 20min, 30min, 50min, 1h, 3h, 4h, 6h, 7h, 8h, 9h, 10h, etc.). In order to avoid the generation of impurities due to the volatilization of fluorine, the prior art uses a lower calcination temperature and a shorter calcination time. In the present application, the second raw material is excessive in fluorine and vanadium elements, so that the impurities generated due to the volatilization of fluorine can be reduced, and thus it is not necessary to reduce the calcination temperature and shorten the calcination time, thereby ensuring the full calcination and obtaining Na3V2(PO4)2F3@C with excellent performance. In an embodiment of the present application, the calcination is carried out under an inert gas to ensure the performance of the prepared Na3V2(PO4)2F3@C. Specifically, the inert gas can be but is not limited to argon. In the present application, the calcination can be carried out in a tube furnace (such as a general tube furnace, a microwave tube furnace, etc.) or a sintering furnace. In an embodiment of the present application, the calcination is carried out in a microwave tube furnace, which comprises treating at 300-400°C for 1-5h, and then treating at 600-800°C for 10min-60min. Since the microwave tube furnace has a high heating rate (about 20-50°C / min), it can be heated to the target temperature in a short time to achieve rapid calcination, and the loss of fluorine and vanadium can also be avoided. In an embodiment of the present application, the heating rate in the calcination is 3-8°C / min (such as 4°C / min, 5°C / min, 6°C / min, 7°C / min, etc.) to heat to 300-400°C.

[0086] In an embodiment of the present application, the particle size D50 of the carbon-coated sodium vanadium fluorophosphate is 100-3000nm. Specifically, the particle size D50 of the carbon-coated sodium vanadium fluorophosphate can be but is not limited to 400nm, 500nm, 750nm, 1000nm, 1200nm, 1500nm, 1700nm, 2000nm, 2300nm, 2300nm or 2800nm, etc. The particle size D50 of the carbon-coated sodium vanadium fluorophosphate prepared in the present application is suitable, so that it has a suitable tap density, which is beneficial to the use of the carbon-coated sodium vanadium fluorophosphate.

[0087] In an embodiment of the present application, the mass content of carbon element in the carbon-coated sodium vanadium fluorophosphate is 5%-15%, which is helpful to improve the electronic conductivity. Specifically, the mass content of carbon element in the carbon-coated sodium vanadium fluorophosphate can be but is not limited to 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc.

[0088] The carbon-coated sodium vanadium fluorophosphate prepared in the application comprises sodium vanadium fluorophosphate and a carbon coating layer covering the sodium vanadium fluorophosphate. The carbon coating layer can improve the electronic conductivity of the sodium vanadium fluorophosphate, thereby improving the electrical performance of the material.

[0089] The application also provides a battery pole piece comprising at least one of the sodium vanadium fluorophosphate prepared in any of the above embodiments and the carbon-coated sodium vanadium fluorophosphate prepared in any of the above embodiments. The specific capacity and energy density of the battery pole piece provided by the application are beneficial to the use of the battery pole piece. The battery pole piece can be a positive electrode or a negative electrode, and the sodium vanadium fluorophosphate and the carbon-coated sodium vanadium fluorophosphate can be used as active materials in the electrode pole piece.

[0090] The following describes the electrode pole piece as a positive electrode. Please refer to Figure 3 FIG. 1 is a cross-sectional schematic view of a positive electrode provided by an embodiment of the application, wherein the positive electrode 100 comprises a positive electrode current collector 10 and a positive electrode active material layer 20 arranged on the surface of the positive electrode current collector 10, and the positive electrode active material layer 20 comprises the sodium vanadium fluorophosphate and / or the carbon-coated sodium vanadium fluorophosphate in any of the above embodiments. The material of the positive electrode current collector can be but is not limited to aluminum.

[0091] It can be understood that the sodium vanadium fluorophosphate and / or the carbon-coated sodium vanadium fluorophosphate are positive electrode active materials. In an embodiment of the application, the mass content of the positive electrode active material in the positive electrode active material layer is greater than or equal to 85%, thereby ensuring the electrochemical performance of the positive electrode. That is, the total mass content of the sodium vanadium fluorophosphate and the carbon-coated sodium vanadium fluorophosphate in the positive electrode active material layer is greater than or equal to 85%. Specifically, the mass content of the positive electrode active material in the positive electrode active material layer can be but is not limited to 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, etc.

[0092] In an embodiment of the application, the positive electrode active material layer can further comprise a positive electrode conductive agent. Specifically, the positive electrode conductive agent comprises at least one of conductive carbon black, acetylene black, carbon nanowire, graphite and graphene. In an embodiment of the application, the mass content of the positive electrode conductive agent in the positive electrode active material layer can be 0.1%-10%. Specifically, the mass content of the positive electrode conductive agent in the positive electrode active material layer can be but is not limited to 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0093] In an embodiment of the present application, the positive electrode active material layer can further include a positive electrode binder. Specifically, the positive electrode binder can include, but is not limited to, at least one of polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluoroelastomer, polyvinylpyrrolidone, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, polyethylene oxide, sodium carboxymethyl cellulose, and styrene butadiene rubber. In an embodiment of the present application, the mass content of the positive electrode binder in the positive electrode active material layer can be 0.5% to 5%. Specifically, the mass content of the positive electrode binder in the positive electrode active material layer can be, but is not limited to, 0.5%, 1%, 2%, 3%, 4%, or 5%, etc.

[0094] In the present application, the positive electrode active material can be dispersed in an organic solvent to form a positive electrode active slurry, the positive electrode active slurry can be coated on the surface of the positive electrode current collector, and the positive electrode can be prepared after drying. Specifically, at least one of a positive electrode conductive agent and a positive electrode binder can be further added to the positive electrode active slurry; and the organic solvent can include, but is not limited to, at least one of ethanol, toluene, xylene, anisole, acetonitrile, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, N-methyl pyrrolidone, acetone, etc.

[0095] The present application also provides a battery including the battery pole piece of any of the above embodiments. The battery provided by the present application has high specific capacity and energy density of the battery pole piece, which is beneficial to the excellent electrochemical performance of the battery.

[0096] In an embodiment of the present application, the battery pole piece is a positive electrode, and the battery includes the battery pole piece and a negative electrode. In an embodiment of the present application, the battery further includes a separator arranged between the battery pole piece and the negative electrode. In an embodiment of the present application, the battery further includes an electrolyte. At least part of the battery pole piece and at least part of the negative electrode are soaked in the electrolyte. The negative electrode, the separator, and the electrolyte are not particularly limited in the present application, and can include, but are not limited to, substances that can be used as a battery negative electrode, a separator, and an electrolyte in the art.

[0097] The present application provides an electric device including the battery of any of the above embodiments. The electric device provided by the present application has excellent performance and strong product competitiveness. The electric device of the present application can refer to a vehicle, an electronic device, an energy storage system, etc., and the above battery can be arranged in the electric device in the form of a single battery, a battery module, a battery pack, etc.

[0098] The effects of the technical solutions provided by the present application are further illustrated by specific embodiments below.

[0099] Embodiment 1

[0100] NaF (purity 99.9%), NH4F (purity 98%), NH4VO3 (purity 99.9%), NH4H2PO4 (purity 99%), C6H8O7·H2O (purity 99.8%) were weighed according to the molar ratio of 3:0.3:2.1:2:2.

[0101] NH4VO3 was added into 30 ml deionized water, stirred uniformly at 85 ℃, then C6H8O7·H2O was added as reducing agent and carbon source, stirred to form a blue-green solution, then NaF, NH4F and NH4H2PO4 were added and stirred until the solvent evaporated to obtain a gel, then the gel was placed in a vacuum drying oven and dried at 110 ℃ for 1 h, then the slurry was ground to obtain a precursor powder. The precursor powder was placed in a porcelain boat and put into a tube furnace, heated to 350 ℃ at a rate of 5 ℃ / min under a flowing argon atmosphere, kept for 4 h, then calcined at 750 ℃ for 8 h, and then ground to obtain Na3V2(PO4)2F3@C.

[0102] Example 2

[0103] The same as Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 3:0.15:2.05:2:2.

[0104] Example 3

[0105] The same as Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 3:0.45:2.15:2:2.

[0106] Example 4

[0107] The same as Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 3:0.6:2.2:2:2.

[0108] Example 5

[0109] The same as Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 2.5:0.6:1.867:1.667:2.

[0110] Example 6

[0111] The same as Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 3:0.3:2.1:2.2:2.

[0112] Example 7

[0113] The same as Example 1 except that the molar ratio of Na2CO3, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3.65:3.3:2.1:2:2.

[0114] Example 8

[0115] The same as Example 1 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3:0.9:2.3:2:2.

[0116] Example 9

[0117] The same as Example 1 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3:0.3:2.1:2:1.05, Na3V2(PO4)2F3 is prepared.

[0118] Example 10

[0119] The same as Example 2 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3:0.15:2.05:2:1.025, Na3V2(PO4)2F3 is prepared.

[0120] Example 11

[0121] The same as Example 3 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3:0.45:2.15:2:1.075, Na3V2(PO4)2F3 is prepared.

[0122] Example 12

[0123] The same as Example 4 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 3:0.6:2.2:2:1.1, Na3V2(PO4)2F3 is prepared.

[0124] Example 13

[0125] The same as Example 5 except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7-H2O is 2.5:0.6:1.867:1.667:0.9335, Na3V2(PO4)2F3 is prepared.

[0126] Example 14

[0127] The same as Example 6, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7.H2O is 3:0.3:2.1:2.2:1.05, Na3V2(PO4)2F3 is prepared.

[0128] Example 15

[0129] The same as Example 7, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7.H2O is 1.65:3.3:2.1:2:1.05, Na3V2(PO4)2F3 is prepared.

[0130] Example 16

[0131] The same as Example 8, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7.H2O is 3:0.9:2.3:2:1.15, Na3V2(PO4)2F3 is prepared.

[0132] Example 17

[0133] The same as Example 9, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7.H2O is 3:0.3:2.1:2:1.05, Na3V2(PO4)2F3 is prepared.

[0134] Example 18

[0135] The same as Example 9, except that NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7.H2O is replaced by Na2CO3, NH4F, V2O5, NaH2PO4, C6H8O6 (ascorbic acid) respectively, and the molar ratio is 0.5:0.3:1.05:2:1.05.

[0136] Comparative Example 1

[0137] Each substance is weighed according to the molar ratio of NaF, NH4VO3, NH4H2PO4, C6H8O7.H2O is 3:2:2:2.

[0138] In 30 ml of deionized water, NH4VO3 was added, stirred uniformly at 85°C, then C6H8O7·H2O was added as a reducing agent and carbon source, stirred to form a blue-green solution, then NaF and NH4H2PO4 were added and stirred until the solvent evaporated to obtain a gel, then the gel was placed in a vacuum drying oven and dried at 110°C for 1 h, then the slurry was ground to obtain a precursor powder. The precursor powder was placed in a ceramic boat and placed in a tube furnace, heated to 350°C at 5°C / min under a flowing argon atmosphere, held for 4 h, then calcined at 750°C for 8 h, and then ground to obtain Na3V2(PO4)2F3@C.

[0139] Comparative Example 2

[0140] The same as Comparative Example 1, except that the molar ratio of NaF, NH4F, NH4VO3, NH4H2PO4, C6H8O7·H2O was 3:2:2:2:1, and Na3V2(PO4)2F3 was prepared.

[0141] Performance detection

[0142] The Na3V2(PO4)2F3@C or Na3V2(PO4)2F3 prepared in the examples and comparative examples was subjected to X-ray diffraction (XRD) test (test conditions: Cu target, scanning range 10°-80°, scanning speed 5° / min), wherein, compared with the comparative example, the product prepared in the example had fewer Na3V2(PO4)3 characteristic peaks and weaker peak intensity. Part of the XRD spectrum is shown in Figure 4 As shown in the figure, the diffraction peaks of Na3V2(PO4)2F3 in Na3V2(PO4)2F3@C prepared in Examples 1-4 were consistent with the diffraction peaks in the Na3V2(PO4)2F3 standard card (PDF #00-066-0372), corresponding to a tetragonal symmetry index in the P42 / mnm space group. Compared with the diffraction peaks in the Na3V2(PO4)3 standard card (PDF #00-062-0345), the Na3V2(PO4)3 characteristic peaks of Examples 1, 3 and 4 were fewer and had weaker peak intensity, and the Na3V2(PO4)3 characteristic peak intensity of Example 2 was slightly stronger than that of Examples 1, 3 and 4, but weaker than that of Na3V2(PO4)3 characteristic peak in Comparative Example 1, and the Na3V2(PO4)3 characteristic peak in Comparative Example 1 was obvious; therefore, the preparation method provided by the present application can reduce the generation of Na3V2(PO4)3 impurities in Na3V2(PO4)2F3.

[0143] The Na3V2(PO4)2F3@C prepared in Examples 1-4 and Comparative Example 1 was subjected to thermogravimetric analysis (TG) test, and the TG curve is shown in Figure 5TG test: 8 mg of Na3V2(PO4)2F3@C was tested under oxygen atmosphere at a temperature increasing rate of 5 ℃ / min, and the carbon material content was determined, and the results are shown in Table 1. It can be seen that the average content of carbon material in Na3V2(PO4)2F3@C prepared in Examples 1-4 and Comparative Example 1 is about 7.3 wt%, and the carbon content difference is not large, which will not greatly affect the comparison of the electrical performance test results.

[0144] The Na3V2(PO4)2F3@C prepared in the examples and Comparative Example 1 was subjected to scanning electron microscope (SEM) detection. Compared with Comparative Example 1, the Na3V2(PO4)2F3@C prepared in the examples had uniformly dispersed particles and relatively uniform particle size. Part of the SEM images are shown in Figure 6 It can be seen that the average particle size of Na3V2(PO4)2F3@C is about 1000 nm; compared with Comparative Example 1, the particle size of Na3V2(PO4)2F3@C prepared in Examples 1-4 is relatively uniform and the distribution is relatively dispersed; the Na3V2(PO4)2F3@C prepared in Examples 3 and 4 has more small particles and is prone to agglomeration, and compared with Examples 2-4, the particle size of Na3V2(PO4)2F3@C prepared in Example 1 is uniform and the dispersion is more uniform.

[0145] The Na3V2(PO4)2F3@C prepared in Examples 1-8 and Comparative Example 1 was added to deionized water in a mass ratio of 8:1:1 with carbon black and polyvinylidene fluoride, respectively, and then stirred in a vacuum stirrer to form a stable and uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil and dried at 105 ℃ for 6 h to obtain a positive electrode. A metal sodium sheet with a suitable size was cut and used as a negative electrode. 1 mol of NaPF6 was dissolved in 1 L of a mixed solvent of propylene carbonate and fluoroethylene carbonate (volume ratio of propylene carbonate to fluoroethylene carbonate is 100:6) to obtain an electrolyte. In a glove box, under an argon atmosphere, the above-mentioned positive electrode, glass fiber separator and the above-mentioned negative electrode were alternately stacked and the above-mentioned electrolyte was injected to form a button cell. After assembling each battery, it was placed at 25 ℃ for 12 h, and the following tests were performed on a Land-2001A battery test system:

[0146] The batteries were tested for charge-discharge cycle at 25℃ with a current of 1C rate, the voltage range was 2V-4.5V, the first circle discharge specific capacity of each battery was recorded, and the capacity retention rate after 50 cycles was recorded; the discharge capacity of each battery at different rates such as 0.2C, 0.5C, 1C, 2C, 5C was tested at 25℃, the voltage range was 2V-4.5V, wherein the first circle discharge specific capacity was equal to the ratio of the first circle discharge capacity of each battery to the mass of the positive active material in the battery, the capacity retention rate after 50 cycles was equal to the ratio of the discharge capacity after 50 cycles to the first circle discharge capacity, and the detection results were shown in Table 1; Figure 7 and Figure 8 The charge-discharge curve of the battery made of Na3V2(PO4)2F3@C of Example 1-4, Comparative Example 1 under 0.2C condition was shown, Figure 9 The cycle performance curve of the battery made of Na3V2(PO4)2F3@C of Example 1-4, Comparative Example 1 under 1C condition was shown, Figure 10 The rate performance curve of the battery made of Na3V2(PO4)2F3@C of Example 1-4, Comparative Example 1 was shown.

[0147] Table 1 Performance detection results

[0148]

[0149]

[0150] Because Na3V2(PO4)3 appeared a voltage platform of about 3.4V(vs.Na + / Na) on the charge-discharge curve. Figure 7 , Figure 8 It can be seen that the 0.2C charge-discharge curve had a charge-discharge platform around 3.4V, wherein compared with Comparative Example 1, the charge-discharge platform of Example 1-4 was obviously shorter, which indicated that the content of Na3V2(PO4)3 impurity phase in Na3V2(PO4)2F3@C was less, i.e. the purity of Na3V2(PO4)2F3@C was higher; and compared with Example 2, the charge-discharge platform of Example 1, 3-4 was shorter, and the purity of Na3V2(PO4)2F3@C was higher.

[0151] From Figure 9 , Figure 10As can be seen from Table 1, compared with Comparative Example 1, the Na3V2(PO4)3 impurity phase content in the Na3V2(PO4)2F3@C prepared in Examples 1-8 is less, the discharge specific capacity and capacity retention of the prepared battery are at a high level, and the cycle performance is excellent. Among them, the discharge specific capacity of the battery prepared in Example 1 after 50 cycles at a current density of 1C is 117.5 mAh / g, the capacity retention is 99.0%, the discharge specific capacities at current densities of 0.2C, 0.5C, 1C, 2C and 5C are 124.0 mAh / g, 121.5 mAh / g, 119.1 mAh / g, 115.8 mAh / g and 110.0 mAh / g respectively, and excellent performance is shown in the cycle and high rate. Therefore, the preparation method provided in the application can prepare a sodium vanadium fluorophosphate with less impurity phase content and high purity, and a carbon-coated sodium vanadium fluorophosphate, which is beneficial to its use.

[0152] The above-described examples only express several embodiments of the application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the application. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the application, which all belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A method for producing sodium vanadium fluorophosphate, characterized by, Comprising: a sodium source, a vanadium source, a phosphorus source and a fluorine source are mixed to form a first raw material, the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the first raw material is a:b:c:d, wherein a, b, c, d are real numbers greater than 0, a, b, c, d satisfy: when a / c≤1.5, a / b<1.5, a / d<1, or when a / c≥1.5, c / b<1, c / d<2 / 3; The first precursor is obtained after the first raw material is treated; The sodium vanadium fluorophosphate is obtained after the first precursor is dried and calcined.

2. The production method according to claim 1, wherein When a / c≤1.5, 1.36<a / b<1.5, 0.83<a / d<1, or when a / c≥1.5, 0.89<c / b<1, 0.55<c / d<2 / 3.

3. The production method according to claim 1, wherein When a / c≤1.5, b is 2a / 3+e, d is a+3e, e>0, or when a / c≥1.5, b is c+f, d is 1.5c+3f, f>0.

4. The production method according to claim 3, wherein When a / c≤1.5, 2.5≤a≤3.5, 0.1≤e≤0.2, or when a / c≥1.5, 1.6<c<2.4, 0.1≤f≤0.

2.

5. The production method according to claim 3, wherein When a / c≤1.5, 12.5≤a / e≤35, or when a / c≥1.5, 8.3<c / f<23.

4.

6. The production method according to claim 1, wherein The first precursor is obtained after the first raw material is treated. The first precursor is obtained after the first raw material is treated by at least one of a solid phase method, a hydrothermal method, a sol-gel method and a spray drying method.

7. The production method according to claim 1, wherein The drying comprises treating at 100℃-120℃ for 1h-3h; The calcining comprises treating at 300℃-400℃ for 1h-5h, and then treating at 600℃-800℃ for 10min-10h.

8. A method for preparing carbon-coated sodium vanadium fluorophosphate, characterized in that, Comprising: a sodium source, a vanadium source, a phosphorus source, a fluorine source and a carbon source are mixed to form a second raw material, the molar ratio of sodium element, vanadium element, phosphorus element and fluorine element in the second raw material is a’ :b’ :c’ :d’, wherein a’, b’, c’, d’ are real numbers greater than 0, a’, b’, c’, d’ satisfy: when a’ / c’≤1.5, a’ / b’<1.5, a’ / d’<1, or when a’ / c’≥1.5, c’ / b’<1, c’ / d’<2 / 3; The second precursor is obtained after the second raw material is treated; The carbon-coated sodium vanadium fluorophosphate is obtained after the second precursor is dried and calcined.

9. A battery electrode sheet, characterized by, At least one of the sodium vanadium fluorophosphate prepared by the preparation method of any one of claims 1-7 and the carbon-coated sodium vanadium fluorophosphate prepared by the preparation method of claim 8.

10. A battery, characterized by The battery pole piece of claim 9 is included.

11. An electrical device, characterized by The battery of claim 10 is included.

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