Sodium vanadium manganese phosphate / carbon positive electrode material and preparation method and application thereof

Abstract

The invention relates to a vanadium-manganese-sodium phosphate / carbon positive electrode material and a preparation method and application thereof.The preparation method of the vanadium-manganese-sodium phosphate / carbon positive electrode material comprises the steps that a vanadium source, a phosphorus source and a manganese source are dissolved in deionized water respectively, and a vanadium source solution, a phosphorus source solution and a manganese source solution are obtained respectively; the method comprises the following steps: under the condition that the pH value is 4.00-6.00, dropwise adding a vanadium source solution and a manganese source solution into a phosphorus source solution respectively at the same time to carry out coprecipitation reaction, aging after dropwise adding, separating a solid product, and drying to obtain a vanadium manganese phosphate precursor; and mixing the vanadium manganese phosphate precursor, a carbon source, a sodium source and a reducing agent in an inert atmosphere, and carrying out solid-phase sintering reaction to obtain the vanadium manganese sodium phosphate / carbon positive electrode material. The prepared vanadium manganese sodium phosphate / carbon positive electrode material is high in purity, and has a proper vanadium and manganese ratio, excellent processing performance and good electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a sodium manganese vanadium phosphate / carbon positive electrode material and a preparation method and application thereof. Background Art

[0002] At present, reducing fossil fuel pollution, developing sustainable new energy, and corresponding efficient energy storage systems have become inevitable choices on the energy supply side.

[0003] Lithium-ion batteries have been widely used in portable electronic products, electric vehicles and other fields due to their advantages such as high energy density, high stability and long life. However, the low reserves and uneven distribution of lithium resources in the earth's crust limit the application of lithium-ion batteries in large-scale energy storage.

[0004] Sodium-ion batteries are considered an ideal large-scale energy storage technology due to their advantages such as high earth abundance of raw materials, good adaptability to high and low temperatures, and good safety. At present, research on sodium-ion batteries is mainly focused on the development of new high-energy density electrode materials and optimization of electrolyte systems. Among them, positive electrode materials have become a research hotspot for a long time because they are the key factor in the development of high-performance, low-cost sodium-ion batteries.

[0005] Among the existing cathode material systems, polyanion compound systems are considered to be the most commercially promising cathode material systems for sodium-ion batteries. Among the polyanion compound systems, sodium superion conductor (NASICON) phosphate system materials have excellent sodium ion conductivity, high structural stability and thermal stability, which have attracted widespread attention from many researchers.

[0006] As a typical NASICON type polyanion positive electrode material, sodium manganese vanadium phosphate has the advantages of high working voltage, high reversible capacity, high energy density, low cost and low toxicity, and is a promising positive electrode material for sodium ion batteries. However, the sodium manganese vanadium phosphate material generally obtained by the solid phase method has uneven element distribution in the sodium manganese vanadium phosphate material to a certain extent, and cannot form a uniform vanadium-manganese co-solution, which is manifested in the macroscopic performance of the sodium manganese vanadium phosphate material. The cycle performance and electrochemical performance of the sodium manganese vanadium phosphate material are deteriorated. Therefore, seeking a method for preparing sodium manganese vanadium phosphate materials with excellent performance has become a research hotspot. Summary of the invention

[0007] In order to solve at least one of the above technical problems, the present invention provides a sodium manganese vanadium phosphate / carbon positive electrode material and a preparation method and application thereof.

[0008] As one aspect, the present invention provides a method for preparing a sodium manganese vanadium phosphate / carbon positive electrode material, the preparation method comprising: dissolving a vanadium source, a phosphorus source and a manganese source in deionized water respectively to obtain a vanadium source solution, a phosphorus source solution and a manganese source solution respectively; wherein the molar ratio of the vanadium element in the vanadium source, the phosphorus element in the phosphorus source and the manganese element in the manganese source is (2-x):3:x, wherein 0.1<x<1.9, for example, x can be 0.3, 0.6, 0.9, 1.1, 1.3, 1.6, 1.7, etc.; in p Under the condition that the H value is 4.00-6.00, for example, the pH can be 4.10, 4.60, 4.90, 5.10, 5.30, 5.60, 5.70, etc., and the vanadium source solution and the manganese source solution are simultaneously dripped into the phosphorus source solution for co-precipitation reaction. After the dripping is completed, the solution is aged, the solid product is separated, and after drying, a vanadium manganese phosphate precursor is obtained; in an inert atmosphere, the vanadium manganese phosphate precursor, a carbon source, a sodium source and a reducing agent are mixed, and a solid phase sintering reaction is carried out to obtain a sodium vanadium manganese phosphate / carbon positive electrode material.

[0009] In some embodiments of the present invention, the vanadium source includes at least one of vanadyl sulfate and vanadyl oxalate; and / or the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; and / or the manganese source includes at least one of manganese acetate, manganese sulfate, and manganese nitrate.

[0010] In some embodiments of the present invention, the vanadium source solution and the manganese source solution are simultaneously dripped into the phosphorus source solution at a dripping speed of 0.6 to 3 mL / min, for example, the dripping speed is 0.8 mL / min, 1.1 mL / min, 1.7 mL / min, 2.3 mL / min, 2.6 mL / min, 2.9 mL / min, etc.; and / or, the aging time is 3 to 6 h, for example, it can be 3.6 h, 3.9 h, 4.3 h, 4.9h, 5.1h, 5.6h, 5.9h, etc.; the temperature is 20-40°C, for example, it can be 23°C, 26°C, 29°C, 33°C, 36°C, 39°C, etc.; and / or the drying time is 6-8h, for example, it can be 6.1h, 6.3h, 6.8h, 7.3h, 7.6h, 7.9h, etc.; the temperature is 80-100°C, for example, it can be 81°C, 83°C, 86°C, 91°C, 93°C, 98°C, etc.

[0011] In some embodiments of the present invention, the sodium source includes at least one of sodium acetate, sodium carbonate, sodium nitrate, and sodium bicarbonate; and / or the carbon source includes at least one of glucose, sucrose, carbon nanotubes, and graphene; and / or the reducing agent includes at least one of citric acid and oxalic acid.

[0012] In some embodiments of the present invention, in the solid phase sintering reaction, the molar mass ratio of the vanadium manganese phosphate precursor, the sodium source and the reducing agent is 1:(3-5):(0.5-3), for example, it can be 1:3.1:0.6, 1:3.1:0.7, 1:3.6:1.9, 1:4.2:2.3, 1:4.6:2.6, 1:4.9:2.9, etc.; and / or, the temperature of the solid phase sintering reaction is 650-850°C, for example, it can be 668°C, 693°C, 713°C, 768°C, 816°C, 823°C, 839°C, etc.; the time is 6-15h, for example, it can be 6.6h, 7.2h, 8.3h, 9.8h, 11.8h, 12.6h, 13.9h, etc.

[0013] In some embodiments of the present invention, the preparation method further comprises: before the step of solid phase sintering reaction, sand milling and spray drying the mixture of vanadium manganese phosphate precursor, carbon source, sodium source and reducing agent.

[0014] In some embodiments of the present invention, the inlet air temperature of the spray drying process is 200-280°C, for example, it can be 208°C, 223°C, 243°C, 251°C, 267°C, 273°C, etc.; the outlet air temperature is 80-120°C, for example, it can be 83°C, 98°C, 112°C, 115°C, 117°C, 119°C, etc.

[0015] In some embodiments of the present invention, the amount of carbon source added satisfies that the carbon coating amount in the sodium manganese vanadium phosphate / carbon positive electrode material accounts for 1 to 5 wt.%, for example, it can be 1.3 wt.%, 1.9 wt.%, 2.1 wt.%, 2.8 wt.%, 3.2 wt.%, 3.9 wt.%, 4.3 wt.%, 4.6 wt.%, etc.; and / or, the pH value of 4.00 to 6.00 is achieved by adjusting the ammonia water.

[0016] As another aspect, the present invention provides a sodium manganese vanadium phosphate / carbon positive electrode material obtained by the above-mentioned preparation method.

[0017] As another aspect, the present invention provides a sodium manganese vanadium phosphate / carbon positive electrode material obtained by the above preparation method or the use of the above sodium manganese vanadium phosphate / carbon positive electrode material in the preparation of a secondary battery.

[0018] The technical solution of the embodiment of the present invention has the following advantages:

[0019] The preparation method of the sodium vanadium manganese phosphate / carbon positive electrode material in the embodiment of the present invention obtains the sodium vanadium manganese phosphate / carbon positive electrode material by combining a co-precipitation method and a solid phase sintering method; a vanadium manganese phosphate precursor is obtained by a co-precipitation reaction using a vanadium source solution, a manganese source solution and a phosphorus source solution, and then the vanadium manganese phosphate precursor, a sodium source, a carbon source and a reducing agent are mixed and solid-phase sintered to obtain a sodium vanadium manganese phosphate / carbon positive electrode material with high capacity and excellent rate performance.

[0020] Specifically, in the preparation method combining coprecipitation and solid phase sintering of the embodiment of the present invention, the coprecipitation method can not only use a vanadium source with low toxicity, but also make the vanadium-manganese ratio closer to the target value, and the solid phase sintering carbon coating effectively improves the electronic conductivity of the positive electrode material, and can inhibit the side reaction between the electrode active material and the electrolyte, ensure the rapid transmission of sodium ions, and effectively improve the rate performance of the material. The preparation process of the material is simple, the conductive carbon coating is uniform, the sodium vanadium manganese phosphate achieves an appropriate ratio of vanadium and manganese, and the obtained material has good cycle and rate performance, etc., and has broad application prospects.

[0021] In summary, the preparation method of the embodiment of the present invention combines coprecipitation and solid phase sintering to achieve stable and controllable preparation of positive electrode materials. The obtained positive electrode materials have the advantages of suitable vanadium and manganese ratio, high capacity, and good cycle and rate performance.

[0022] In addition, the preparation method of the embodiment of the present invention has the characteristics of low raw material cost and simple preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 This is a SEM image of the vanadium manganese phosphate precursor prepared in Example 1 of the present invention;

[0026] Figure 2 This is the XRD pattern of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 of the present invention;

[0027] Figure 3 This is a SEM image of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 of the present invention;

[0028] Figure 4The first charge-discharge curve of a half-cell assembled with the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 of the present invention and cycled at a rate of 0.1C;

[0029] Figure 5 This is a capacity-time diagram of a half-cell assembled with the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 of the present invention and cycled at a rate of 1C;

[0030] Figure 6 This is a half-cell rate performance diagram assembled using the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0033] According to an embodiment of one aspect of the present invention, a method for preparing a sodium manganese vanadium phosphate / carbon positive electrode material is provided, comprising the following steps:

[0034] (1) Dissolving a vanadium source, a phosphorus source, and a manganese source in deionized water respectively to prepare equal volumes of a vanadium source solution, a phosphorus source solution, and a manganese source solution, respectively; wherein the molar ratio of the vanadium element in the vanadium source, the phosphorus element in the phosphorus source, and the manganese element in the manganese source is (2-x):3:x; wherein 0.1<x<1.9;

[0035] (2) directly adding the phosphorus source solution obtained in step (1) into a reactor, and then dripping the vanadium source solution and the manganese source solution obtained in step (1) into the reactor dropwise for coprecipitation reaction, and fully stirring; at the same time, adjusting the pH value of the system by ammonia water to maintain it at 4.00-6.00; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 3-6 hours, and then filtering it by suction, then adding deionized water for washing and filtering it by suction, and repeating the above process three times; drying the material obtained by suction filtration at 80° C. for 8 hours, and then vacuum drying it at 100° C. for 6 hours; the obtained dry material is the vanadium manganese phosphate precursor;

[0036] (3) The dried material obtained in step (2) (i.e., the vanadium manganese phosphate precursor) is fully mixed with a carbon source, a sodium source and a reducing agent, and then spray-dried after sand milling for 2 to 5 hours; wherein the inlet air temperature of the spray drying is 200 to 280° C., and the outlet air temperature is 80 to 120° C. The spray-dried material is sintered at 650 to 850° C. for 6 to 15 hours under a nitrogen protective atmosphere, and then cooled to room temperature to obtain a sodium vanadium manganese phosphate / carbon positive electrode material.

[0037] In some embodiments of the present invention, in step (1), the vanadium source includes at least one of vanadyl sulfate (VOSO4) and vanadyl oxalate (VOC2O4).

[0038] In some embodiments of the present invention, in step (1), the phosphorus source includes at least one of phosphoric acid (H3PO4), ammonium dihydrogen phosphate (NH4H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), sodium dihydrogen phosphate (NaH2PO4), and disodium hydrogen phosphate (Na2HPO4).

[0039] In some embodiments of the present invention, in step (1), the manganese source includes at least one of manganese acetate (Mn(CH3COO)2), manganese sulfate (MnSO4), and manganese nitrate (Mn(NO3)2).

[0040] In some embodiments of the present invention, in step (2), the vanadium source solution prepared in step (1) and the manganese source solution prepared in step (1) are simultaneously and separately dripped into the phosphorus source solution prepared in step (1) at a dripping speed ranging from 0.6 to 3 mL / min.

[0041] In some embodiments of the present invention, in step (3), the sodium source includes at least one of sodium acetate (CH3COONa), sodium carbonate (Na2CO3), sodium nitrate (NaNO3) and sodium bicarbonate (NaHCO3).

[0042] In some embodiments of the present invention, in step (3), the carbon source comprises glucose (C6H 12 O6), sucrose (C 12 H 22 O 11 ), at least one of carbon nanotubes and graphene.

[0043] In some embodiments of the present invention, in step (3), the reducing agent comprises citric acid (C6H 12 O6), oxalic acid (H2C2O4) or at least one of the following.

[0044] In some embodiments of the present invention, in step (3), the molar mass ratio of the vanadium manganese phosphate precursor to the reducing agent is 1:(0.5-3).

[0045] In some embodiments of the present invention, in step (3), the molar mass ratio of the vanadium manganese phosphate precursor to the sodium source is 1:(3-5).

[0046] In some embodiments of the present invention, in step (3), the molar mass ratio of the vanadium manganese phosphate precursor, the sodium source and the reducing agent is 1:(3-5):(0.5-3).

[0047] In some embodiments of the present invention, in step (3), the mass of the carbon source is calculated based on the ratio of the mass of the carbon source to the mass of the carbon coating being 1 to 5 wt.%.

[0048] In some embodiments of the present invention, in step (3), the sodium manganese vanadium phosphate / carbon positive electrode material refers to a carbon-coated sodium manganese vanadium phosphate positive electrode material.

[0049] According to an embodiment of another aspect of the present invention, there is provided a sodium manganese vanadium phosphate / carbon positive electrode material obtained by the above-mentioned preparation method.

[0050] According to another embodiment of the present invention, there is provided a sodium manganese vanadium phosphate / carbon positive electrode material obtained by the above preparation method or the use of the above sodium manganese vanadium phosphate / carbon positive electrode material in the preparation of a secondary battery.

[0051] In some embodiments of the present invention, the positive electrode sheet made of the above-mentioned sodium manganese vanadium phosphate / carbon positive electrode material, Super P conductive carbon, and polyvinylidene fluoride (PVDF) is used as the positive electrode of the sodium ion battery, and the metal sodium sheet is used as the counter electrode; 5Vol% fluoroethylene carbonate is added to the 1M NaClO4 / propylene carbonate solution as the electrolyte, and glass fiber is used as the diaphragm to assemble into a button battery in a glove box with a high-purity argon atmosphere.

[0052] Example 1

[0053] The method for preparing the sodium manganese vanadium phosphate / carbon positive electrode material of the embodiment of the present invention comprises the following steps:

[0054] (1) Dissolving vanadium oxysulfate (VOSO4), phosphoric acid (H3PO4), and manganese acetate (Mn(CH3COO)2) in deionized water to prepare equal volumes of vanadium source solution, phosphorus source solution, and manganese source solution, respectively; wherein the molar ratio of vanadium element in vanadium source vanadium oxysulfate (VOSO4), phosphorus element in phosphoric acid (H3PO4), and manganese element in manganese source manganese acetate (Mn(CH3COO)2) is 1:3:1;

[0055] (2) directly adding the phosphoric acid solution obtained in step (1) into a reactor, and then dripping the vanadyl sulfate solution and manganese acetate solution obtained in step (1) into the reactor dropwise at a dropping speed of 2 mL / min for a coprecipitation reaction, and fully stirring, while adjusting the pH value of the system to 4.5 by ammonia water; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 5.5 hours and then filtering it, then adding deionized water for washing and filtering it, and repeating the above process three times; drying the material obtained by suction filtration at 80° C. for 8 hours, and then vacuum drying it at 100° C. for 6 hours; the obtained dry material is the vanadium manganese phosphate precursor;

[0056] SEM image of vanadium manganese phosphate precursor Figure 1 As shown, the vanadium manganese phosphate precursor is composed of typical nanoparticle stacks.

[0057] (3) mixing the dried vanadium manganese phosphate precursor material obtained in step (2) with oxalic acid (H2C2O4), sodium carbonate (Na2CO3) and glucose (C6H 12 O6) are fully mixed, wherein the molar mass ratio of the vanadium manganese phosphate precursor and the reducing agent oxalic acid (H2C2O4) is 1:2, the molar mass ratio of the vanadium manganese phosphate precursor and the sodium source sodium carbonate (Na2CO3) is 1:4, and the carbon source glucose (C6H 12 The mass of O6) is calculated based on the carbon coating ratio of 3.0wt.%. The above mixture is sand-milled for 4.5 hours and then spray-dried. The inlet air temperature of the spray-drying is 220°C and the outlet air temperature is 100°C. The spray-dried material is sintered at 750°C for 10 hours under a nitrogen protective atmosphere and cooled to room temperature to obtain the sodium manganese vanadium phosphate / carbon positive electrode material;

[0058] XRD pattern of sodium manganese vanadium phosphate / carbon positive electrode material Figure 2 shown; according to Figure 2 It can be seen from the XRD spectrum that the sodium manganese vanadium phosphate / carbon cathode material prepared in step (3) is a typical Nasicon structure without obvious impurities, indicating that a relatively pure sodium manganese vanadium phosphate / carbon cathode material is obtained.

[0059] SEM image of sodium manganese vanadium phosphate / carbon positive electrode material Figure 3 As shown, the cathode material exhibits a typical spherical morphology.

[0060] Example 2

[0061] The method for preparing the sodium manganese vanadium phosphate / carbon positive electrode material of the embodiment of the present invention comprises the following steps:

[0062] (1) dissolving vanadium oxysulfate (VOSO4), ammonium dihydrogen phosphate (NH4H2PO4), and manganese sulfate (MnSO4) in deionized water to prepare equal volumes of vanadium source solution, phosphorus source solution, and manganese source solution, respectively, wherein the molar ratio of vanadium element in vanadium source vanadium oxysulfate (VOSO4), phosphorus element in phosphorus source ammonium dihydrogen phosphate (NH4H2PO4), and manganese element in manganese sulfate (MnSO4) is 1.5:3:0.5;

[0063] (2) adding the ammonium dihydrogen phosphate solution obtained in step (1) directly into a reactor, and then dripping the vanadyl sulfate solution and manganese sulfate solution obtained in step (1) into the reactor dropwise at a dropping speed of 2.4 mL / min for coprecipitation reaction, and fully stirring, while adjusting the pH value of the system to 5.00 by ammonia water; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 5 hours and then filtering it by suction, then adding deionized water for washing and filtering it by suction, and repeating the above process three times; drying the material obtained by suction filtration at 80° C. for 8 hours, and then vacuum drying it at 100° C. for 6 hours; the obtained dry material is the vanadium manganese phosphate precursor;

[0064] (3) mixing the dried vanadium manganese phosphate precursor material obtained in step (2) with oxalic acid (H2C2O4), sodium acetate (CH3COONa) and sucrose (C 12 H 22 O 11 ) are fully mixed, wherein the molar mass ratio of the vanadium manganese phosphate precursor to the reducing agent oxalic acid (H2C2O4) is 1:2.5, the molar mass ratio of the vanadium manganese phosphate precursor to the sodium source sodium acetate (CH3COONa) is 1:3.5, and the carbon source sucrose (C 12 H 22 O 11 ) is calculated based on the carbon coating ratio of 2.0wt.%. The above mixture is sand-milled for 4 hours and then spray-dried. The inlet air temperature of the spray-drying is 240°C and the outlet air temperature is 105°C. The spray-dried material is sintered at 800°C for 8 hours under a nitrogen protective atmosphere and cooled to room temperature to obtain the sodium manganese vanadium phosphate / carbon positive electrode material.

[0065] Example 3

[0066] (1) dissolving vanadyl oxalate (VOC2O4), diammonium phosphate ((NH4)2HPO4), and manganese nitrate (Mn(NO3)2) in deionized water to prepare equal volumes of vanadium source solution, phosphorus source solution, and manganese source solution, respectively, wherein the molar ratio of vanadium element in the vanadium source vanadyl oxalate (VOC2O4), phosphorus element in the phosphorus source diammonium phosphate ((NH4)2HPO4), and manganese element in the manganese source manganese nitrate (Mn(NO3)2) is 0.5:3:1.5;

[0067] (2) directly adding the phosphoric acid solution obtained in step (1) into a reactor, and then dripping the vanadyl oxalate solution and manganese nitrate solution obtained in step (1) into the reactor dropwise at a dropping speed of 1.5 mL / min for coprecipitation reaction, and fully stirring, while adjusting the pH value of the system to 4.2 by ammonia water; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 3.5 hours and then filtering it, then adding deionized water for washing and filtering it, and repeating the above process three times; drying the material obtained by suction filtration at 80° C. for 8 hours, and then vacuum drying it at 100° C. for 6 hours; the obtained dry material is the vanadium manganese phosphate precursor;

[0068] (3) The dried vanadium manganese phosphate precursor obtained in step (2) is mixed with citric acid (C6H 12 O6), sodium bicarbonate (NaHCO3) and carbon nanotubes are fully mixed, wherein the vanadium manganese phosphate precursor and the reducing agent citric acid (C6H 12 The molar mass ratio of the precursor of manganese vanadium phosphate and the sodium source sodium bicarbonate (NaHCO3) is 1:1.5, the molar mass ratio of the precursor of manganese vanadium phosphate and the sodium source sodium bicarbonate (NaHCO3) is 1:4.5, and the mass of the carbon source carbon nanotubes is calculated based on the carbon coating amount of 3.5wt.%. The above mixture is sand milled for 3.5 hours and then spray dried. The inlet air temperature of the spray drying is 270°C and the outlet air temperature is 115°C. The spray dried material is sintered at 700°C for 12 hours under a nitrogen protective atmosphere and cooled to room temperature with the furnace to obtain the sodium manganese vanadium phosphate / carbon positive electrode material.

[0069] Example 4

[0070] (1) Dissolving vanadium sulfate (VOSO4), sodium dihydrogen phosphate (NaH2PO4), and manganese acetate (Mn(CH3COO)2) in deionized water to prepare equal volumes of vanadium source solution, phosphorus source solution, and manganese source solution, respectively; wherein the molar ratio of vanadium element in vanadium source vanadium sulfate (VOSO4), phosphorus element in phosphorus source sodium dihydrogen phosphate (NaH2PO4), and manganese element in manganese source manganese acetate (Mn(CH3COO)2) is 0.2:3:1.8;

[0071] (2) directly adding the sodium dihydrogen phosphate solution obtained in step (1) into a reactor, and then dripping the vanadium sulfate (VOSO4) solution and manganese acetate (Mn(CH3COO)2) solution obtained in step (1) into the reactor dropwise at a dropping speed of 0.8 mL / min for a coprecipitation reaction, and fully stirring, while adjusting the pH value of the system to 5.7 by ammonia water; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 5.5 h and then filtering it, then adding deionized water for washing and filtering it, and repeating the above process three times; drying the material obtained by suction at 80° C. for 8 h, and then vacuum drying it at 100° C. for 6 h; the obtained dry material is the vanadium manganese phosphate precursor;

[0072] (3) The dried vanadium manganese phosphate precursor obtained in step (2) is mixed with citric acid (C6H 12 O6), sodium nitrate (NaNO3) and graphene are fully mixed, wherein the vanadium manganese phosphate precursor and the reducing agent citric acid (C6H 12 The molar mass ratio of the precursor of manganese vanadium phosphate and the sodium source sodium nitrate (NaNO3) is 1:1, the molar mass ratio of the precursor of manganese vanadium phosphate and the sodium source sodium nitrate (NaNO3) is 1:4.8, and the mass of the carbon source graphene is calculated based on the carbon coating amount of 4.5wt.%. The above mixture is sand milled for 2.5 hours and then spray dried. The inlet air temperature of the spray drying is 210°C and the outlet air temperature is 85°C. The spray dried material is sintered at 625°C in a nitrogen protective atmosphere for 14 hours, and cooled to room temperature with the furnace to obtain the sodium manganese vanadium phosphate / carbon positive electrode material.

[0073] Example 5

[0074] (1) Dissolving vanadyl oxalate (VOC2O4), sodium dihydrogen phosphate (NaH2PO4), and manganese nitrate (Mn(NO3)2) in deionized water to prepare equal volumes of vanadium source solution, phosphorus source solution, and manganese source solution, respectively; wherein the molar ratio of the vanadium element in the vanadium source vanadyl oxalate (VOC2O4), the phosphorus element in the phosphorus source sodium dihydrogen phosphate (NaH2PO4), and the manganese element in the manganese source manganese nitrate (Mn(NO3)2) is 1.7:3:0.3;

[0075] (2) directly adding the sodium dihydrogen phosphate solution obtained in step (1) into a reactor, and then dripping the vanadyl oxalate (VOC2O4) solution and manganese nitrate (Mn(NO3)2) solution obtained in step (1) into the reactor dropwise at a dropping speed of 2.7 mL / min for coprecipitation reaction, and fully stirring, while adjusting the pH value of the system to 5.5 by ammonia water; aging the mixed solution containing the precipitate obtained after the coprecipitation reaction for 4 hours and then filtering it, then adding deionized water for washing and filtering it, and repeating the above process three times; drying the material obtained by suction filtration at 80° C. for 8 hours, and then vacuum drying it at 100° C. for 6 hours; the obtained dry material is the vanadium manganese phosphate precursor;

[0076] (3) mixing the dried vanadium manganese phosphate precursor material obtained in step (2) with oxalic acid (H2C2O4), sodium carbonate (Na2CO3) and glucose (C6H 12 O6) are fully mixed, wherein the molar mass ratio of the vanadium manganese phosphate precursor to the reducing agent oxalic acid (H2C2O4) is 1:0.75, the molar mass ratio of the vanadium manganese phosphate precursor to the sodium source sodium carbonate (Na2CO3) is 1:3.3, and the carbon source glucose (C6H 12The mass of O6 is calculated based on the carbon coating ratio of 4.0wt.%. The above mixture is sand-milled for 3 hours and then spray-dried. The inlet air temperature of the spray-drying is 250°C and the outlet air temperature is 95°C. The spray-dried material is sintered at 675°C for 13 hours under a nitrogen protective atmosphere and cooled to room temperature to obtain the sodium manganese vanadium phosphate / carbon positive electrode material.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing sodium manganese vanadium phosphate / carbon positive electrode material by a traditional solid phase method, which specifically comprises the following steps:

[0079] 0.5 mol of vanadium pentoxide (V2O5), 1 mol of manganese dioxide (MnO2), 3 mol of sodium dihydrogen phosphate (NaH2PO4), 2 mol of oxalic acid (H2C2O4) and glucose (C6H 12 O6) is dissolved in deionized water and mixed, wherein the mass of glucose is calculated based on the carbon coating amount of the sodium manganese vanadium phosphate / carbon positive electrode material being 3.0wt%, the fully mixed material is sand milled for 4.5 hours and then spray dried, the inlet air temperature of the spray drying is 220°C, and the outlet air temperature is 100°C, the spray dried material is sintered at 750°C in nitrogen protective gas for 10 hours to obtain the sodium manganese vanadium phosphate / carbon positive electrode material.

[0080] Performance Testing

[0081] (1) Preparation of positive electrode for sodium ion battery

[0082] The sodium manganese vanadium phosphate / carbon positive electrode materials prepared in Examples 1 to 5 and Comparative Example 1 were used as positive electrode active materials and were mixed with Super P conductive carbon and polyvinylidene fluoride (PVDF) at a ratio of 8:1:1 to obtain positive electrode active slurry, which was then coated on an aluminum foil current collector to prepare a positive electrode sheet; wherein the surface density of the active material was 5 mg / cm 2 .

[0083] (2) Assembly of button batteries

[0084] The different positive electrode sheets obtained in step (1) are used as positive electrodes for sodium ion batteries.

[0085] A metal sodium sheet was used as a counter electrode, 5 Vol% ethylene carbonate was added to a 1 M NaClO4 / propylene carbonate solution as an electrolyte, and glass fiber was used as a separator. A button cell was assembled in a glove box with a high-purity argon atmosphere.

[0086] (3) Performance testing

[0087] The method of performance testing is as follows: the assembled button cell is subjected to electrochemical performance testing, wherein the voltage window is 2.5 to 3.8V.

[0088] (4) Results of performance testing

[0089] ① The first charge and discharge curve of the half-cell assembled with the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 at a cycle rate of 0.1C is as follows: Figure 4 As shown; the capacity-time diagram of the half-cell assembled with the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 at a cycle rate of 1C is as follows Figure 5 As shown; the half-cell rate performance diagram of the sodium manganese vanadium phosphate / carbon positive electrode material assembled in Example 1 is as shown Figure 6 The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 1 as a positive electrode active material is calculated as 115 mAh / g, the discharge capacity of the battery at 0.1C is 108.7 mAh / g, the battery is cycled 50 times at 1C rate, the capacity retention rate is 97.4%, and the discharge capacity at 10C rate is 54 mAh / g. The results are listed in Table 1.

[0090] ② The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 2 as a positive electrode active material is calculated as 115 mAh / g, the discharge capacity of the battery at 0.1C is 106 mAh / g, the battery is cycled 50 times at a rate of 1C, the capacity retention rate is 95.4%, and the discharge capacity at a rate of 10C is 38 mAh / g. The results are listed in Table 1.

[0091] ③ The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 3 as a positive electrode active material is calculated as 115 mAh / g, the discharge capacity of the battery at 0.1C is 102 mAh / g, the battery is cycled 50 times at a rate of 1C, the capacity retention rate is 93.2%, and the discharge capacity at a rate of 10C is 41 mAh / g. The results are listed in Table 1.

[0092] ④ The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 4 as a positive electrode active material is calculated as 117 mAh / g, the discharge capacity of the battery at 0.1C is 101 mAh / g, the battery is cycled 50 times at a rate of 1C, the capacity retention rate is 89.7%, and the discharge capacity at a rate of 10C is 47 mAh / g. The results are listed in Table 1.

[0093] ⑤ The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Example 5 as a positive electrode active material is calculated as 115 mAh / g, the discharge capacity of the battery at 0.1C is 101 mAh / g, the battery is cycled 50 times at a rate of 1C, the capacity retention rate is 91.3%, and the discharge capacity at a rate of 10C is 49 mAh / g. The results are listed in Table 1.

[0094] ⑥ The theoretical capacity of the sodium manganese vanadium phosphate / carbon positive electrode material prepared in Comparative Example 1 as the positive electrode active material is calculated as 115 mAh / g, the discharge capacity of the battery at 0.1C is 92 mAh / g, the battery is cycled 50 times at a rate of 1C, the capacity retention rate is 82.1%, and the discharge capacity at a rate of 10C is 22 mAh / g. The results are listed in Table 1.

[0095] Table 1 Battery performance test results prepared from sodium manganese vanadium phosphate / carbon positive electrode materials of Examples 1 to 5 and Comparative Example 1

[0096]

[0097] In summary, the preparation method of the sodium vanadium manganese phosphate / carbon positive electrode material in the embodiment of the present invention combines the co-precipitation method and the solid phase sintering method. First, the vanadium source solution and the manganese source solution are simultaneously dripped into the phosphorus source solution to obtain a vanadium manganese phosphate precipitate through a co-precipitation reaction; the vanadium manganese phosphate precipitate is filtered, washed and dried to obtain a vanadium manganese phosphate precursor; the vanadium manganese phosphate precursor is sand-milled, sprayed and sintered with a sodium source, a carbon source and a reducing agent to obtain a carbon-coated sodium vanadium manganese phosphate / carbon positive electrode material; the prepared carbon-coated sodium vanadium manganese phosphate / carbon positive electrode material has high purity, a suitable ratio of vanadium and manganese, excellent processing performance and good electrochemical performance.

[0098] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0099] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing sodium manganese vanadium phosphate / carbon positive electrode material, characterized in that: The preparation method comprises: Dissolving a vanadium source, a phosphorus source and a manganese source in deionized water respectively to obtain a vanadium source solution, a phosphorus source solution and a manganese source solution; The molar ratio of the vanadium element in the vanadium source, the phosphorus element in the phosphorus source and the manganese element in the manganese source is (2-x):3:x, wherein 0.1<x<1.9; Under the condition of pH value of 4.00-6.00, the vanadium source solution and the manganese source solution are simultaneously dripped into the phosphorus source solution for coprecipitation reaction, and after the dripping is completed, the solution is aged, the solid product is separated, and the solid product is dried to obtain a vanadium manganese phosphate precursor; In an inert atmosphere, a vanadium manganese phosphate precursor, a carbon source, a sodium source and a reducing agent are mixed and subjected to a solid phase sintering reaction to obtain a sodium vanadium manganese phosphate / carbon positive electrode material.

2. The preparation method according to claim 1, characterized in that: The vanadium source includes at least one of vanadyl sulfate and vanadyl oxalate; And / or, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; And / or, the manganese source includes at least one of manganese acetate, manganese sulfate and manganese nitrate.

3. The preparation method according to claim 1 or 2, characterized in that: The vanadium source solution and the manganese source solution are simultaneously dripped into the phosphorus source solution at a dropping speed of 0.6 to 3 mL / min; And / or, the aging time is 3 to 6 hours and the temperature is 20 to 40° C.; And / or, the drying time is 6 to 8 hours and the temperature is 80 to 100°C.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The sodium source includes at least one of sodium acetate, sodium carbonate, sodium nitrate and sodium bicarbonate; And / or, the carbon source includes at least one of glucose, sucrose, carbon nanotubes, and graphene; And / or, the reducing agent includes at least one of citric acid and oxalic acid.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the solid phase sintering reaction, The molar mass ratio of the vanadium manganese phosphate precursor, the sodium source and the reducing agent is 1:(3-5):(0.5-3); And / or, the temperature of the solid phase sintering reaction is 650-850° C., and the time is 6-15 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The preparation method further comprises: Before the solid phase sintering reaction step, the mixture of vanadium manganese phosphate precursor, carbon source, sodium source and reducing agent is subjected to sand milling and spray drying.

7. The preparation method according to claim 6, characterized in that: The spray drying process has an air inlet temperature of 200-280°C and an air outlet temperature of 80-120°C.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The amount of the carbon source added is such that the carbon coating in the sodium manganese vanadium phosphate / carbon positive electrode material accounts for 1 to 5 wt.%; And / or, the pH value of 4.00 to 6.00 is achieved by adjusting with ammonia water.

9. A sodium manganese vanadium phosphate / carbon positive electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the sodium manganese vanadium phosphate / carbon positive electrode material obtained by the preparation method according to any one of claims 1 to 8 or the sodium manganese vanadium phosphate / carbon positive electrode material according to claim 9 in the preparation of a secondary battery.

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