Vanadium manganese sodium phosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a vanadium manganese sodium phosphate positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) placing a vanadium source, a phosphorus source and a manganese source in solvent water for a co-precipitation reaction, and then aging and drying to obtain a vanadium manganese phosphate precursor; and (2) uniformly mixing the vanadium manganese phosphate precursor, a sodium source, a carbon source and a reducing agent, drying and sintering to obtain the vanadium manganese sodium phosphate positive electrode material. According to the preparation method provided by the invention, the vanadium manganese sodium phosphate positive electrode material of which the manganese element content is reduced from inside to outside in a gradient manner is prepared by regulating and controlling the coprecipitation reaction conditions of the vanadium source, the phosphorus source and the manganese source, so that the Jahn-Teller effect of the manganese element and the dissolution of manganese ions are effectively inhibited, and the structural stability and the electrochemical stability of the positive electrode material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a sodium vanadium manganese phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Compared with traditional lithium ion batteries, sodium ion batteries have the characteristics of high safety and good high-low temperature adaptability, and sodium element has the advantages of low exploitation cost, wide distribution and rich reserves, so sodium ion batteries have the potential for large-scale application in the future.

[0003] The positive electrode material is the most important in the development of sodium ion batteries. Among the current positive electrode materials of sodium ion batteries, polyanion type positive electrode materials have attracted widespread attention due to their excellent sodium ion conductivity and structural stability. Sodium vanadium manganese phosphate is a polyanion type positive electrode material with a typical NASICON structure, and has the advantages of high working voltage, high reversible capacity, high energy density, low cost and low toxicity, and is a very promising positive electrode material for sodium ion batteries. However, the manganese element in the material is prone to dissolution due to Jahn-Teller effect during the change of valence, which leads to irreversible capacity loss and poor cycle performance of the positive electrode material.

[0004] Therefore, it is desirable to provide a new sodium vanadium manganese phosphate positive electrode material. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a sodium vanadium manganese phosphate positive electrode material and a preparation method and application thereof. The preparation method provided by the present application controls the conditions of the co-precipitation reaction of vanadium source, phosphorus source and manganese source, and prepares a sodium vanadium manganese phosphate positive electrode material with a gradient decrease in manganese element content from the inside to the outside, thereby effectively inhibiting the Jahn-Teller effect of manganese element and the dissolution of manganese ions, and improving the structural stability and electrochemical stability of the positive electrode material.

[0006] In a first aspect, the present application provides a preparation method of a sodium vanadium manganese phosphate positive electrode material, which comprises the following steps:

[0007] (1) placing vanadium source, phosphorus source and manganese source in solvent water to perform a co-precipitation reaction, and then aging and drying to obtain a sodium vanadium manganese phosphate precursor;

[0008] (2) mixing the sodium vanadium manganese phosphate precursor with a sodium source, a carbon source and a reducing agent, drying and sintering to obtain the sodium vanadium manganese phosphate positive electrode material.

[0009] The preparation method of the sodium vanadium manganese phosphate positive electrode material provided by the present application is simple in process and easy to mass produce.

[0010] As a preferred technical solution of the present invention, the method of subjecting the vanadium source, phosphorus source, and manganese source to coprecipitation reaction in solvent water in step (1) is as follows:

[0011] The aqueous solutions of the vanadium source and the manganese source are continuously introduced into the aqueous solution of the phosphorus source respectively for coprecipitation reaction, wherein the flow rate of the aqueous solution of the manganese source gradually decreases, and the flow rate of the aqueous solution of the vanadium source gradually increases.

[0012] The preparation method provided by the present invention prepares a sodium vanadium manganese phosphate cathode material with the content of manganese element gradually decreasing from inside to outside by regulating the conditions of the coprecipitation reaction of the vanadium source, phosphorus source, and manganese source, thereby effectively inhibiting the Jahn-Teller effect of the manganese element and the dissolution of manganese ions, and improving the structural stability and electrochemical stability of the cathode material. Specifically:

[0013] In the present invention, the vanadium source, phosphorus source, and manganese source are respectively dissolved in solvent water to obtain aqueous solutions of the vanadium source, manganese source, and phosphorus source with a certain concentration. Then, the aqueous solutions of the vanadium source and the manganese source are continuously introduced into the aqueous solution of the phosphorus source respectively for coprecipitation reaction, and during the reaction process, the flow rate of the aqueous solution of the manganese source is controlled to gradually decrease, and the flow rate of the aqueous solution of the vanadium source is controlled to gradually increase, so that the content of manganese element in the prepared sodium vanadium manganese phosphate precursor particles gradually decreases from inside to outside, and the content of vanadium element gradually increases. Furthermore, the content of manganese element in the finally prepared sodium vanadium manganese phosphate cathode particles gradually decreases from inside to outside, and the content of vanadium element gradually increases. By the high-concentration distribution of vanadium element on the outside of the particles, the structural stability of the product is improved, thereby effectively inhibiting the dissolution of manganese ions caused by the Jahn-Teller effect of the manganese element, so that the prepared sodium vanadium manganese phosphate cathode material has excellent structural stability and electrochemical stability.

[0014] As a preferred technical solution of the present invention, during the coprecipitation reaction, the total flow rate of the aqueous solutions of the vanadium source and the manganese source remains unchanged. The flow rate ratio m of the aqueous solution of the manganese source at the beginning of the reaction is 50% < m ≤ 100%, such as 60%, 70%, 80%, 90% or 100%, etc. During the reaction process, the flow rate ratio m decreases in a gradient manner, and the flow rate ratio m at the end of the reaction is 0 ≤ m < 50%, such as 0%, 10%, 20%, 30%, 40%, etc.

[0015] Under this condition, the content of manganese element in the prepared sodium vanadium manganese phosphate cathode material decreases in a gradient manner from inside to outside, and the content of vanadium element increases in a gradient manner, which more effectively improves the structural stability of the product, inhibits the dissolution of manganese, more effectively alleviates the irreversible capacity loss during the battery cycle process, and improves the electrochemical performance of the material.

[0016] As a preferred embodiment of the present invention, the molar ratio of vanadium in the vanadium source, manganese in the manganese source, and phosphorus in the phosphorus source is 2-n:n:3, wherein 0.1 < n < 1.9, and for example, it can be 1.8:0.2:3, 1.5:0.5:3, 1:1:3, 0.5:1.5:3, 0.2:1.8:3, etc.

[0017] By controlling the ratio of vanadium to manganese within the above-mentioned range, this invention enables the prepared sodium manganese vanadium phosphate cathode material to have a more stable structure and exhibit excellent electrochemical performance.

[0018] As a preferred technical solution of the present invention, the temperature of the coprecipitation reaction in step (1) is 20-50℃, such as 20℃, 30℃, 40℃, 50℃, etc., the time is 5-10h, such as 5h, 6h, 7h, 8h, 9h, 10h, etc., and the pH is 4-6.

[0019] This invention preferably utilizes ammonia water to adjust the pH within the range of 4-6, thereby ensuring the composition and proportion of the vanadium manganese phosphate precursor. If the pH is too low, some soluble acidic manganese phosphate may be generated, resulting in loss during washing and causing the precursor to differ from the target product; if the pH is too high, it will cause V and Mn to precipitate as hydroxides. Therefore, it is necessary to control the pH within the range of 4-6 to obtain the target vanadium manganese phosphate precursor.

[0020] As a preferred technical solution of the present invention, the aging temperature in step (1) is the same as the temperature of the coprecipitation reaction, and the aging time is 2-8h, for example 2h, 4h, 6h, 8h, etc.

[0021] As a preferred technical solution of the present invention, the drying in step (1) is to dry in a forced air at 80°C for 12 hours and then in a vacuum at 100°C for 8-12 hours, such as 8 hours, 10 hours, 12 hours, etc., to obtain the vanadium manganese phosphate precursor.

[0022] As a preferred embodiment of the present invention, the vanadium source is selected from vanadium oxysulfate (VOSO4) and / or vanadium oxyoxalate (VOC2O4).

[0023] As a preferred embodiment of the present invention, the manganese source is selected from at least one of manganese acetate (Mn(CH3COO)2), manganese sulfate (MnSO4), manganese nitrate (Mn(NO3)2), and manganese chloride (MnCl2).

[0024] As a preferred embodiment of the present invention, the phosphorus source is selected from 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).

[0025] As a preferred embodiment of the present invention, the molar ratio of the vanadium manganese phosphate precursor and the reducing agent is 1:(1-2), such as 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, etc.

[0026] As a preferred embodiment of the present invention, the molar ratio of the vanadium manganese phosphate precursor to the sodium source is 1:(3-5), for example, 1:3, 1:4, 1:5, etc.

[0027] As a preferred embodiment of the present invention, the amount of carbon source is such that the carbon content in the sodium vanadium manganese phosphate cathode material is 1-5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, etc. That is, the present invention controls the amount of carbon source so that the carbon coating of the prepared sodium vanadium manganese phosphate cathode material is 1-5 wt%.

[0028] As a preferred technical solution of the present invention, the drying in step (2) is spray drying, with an inlet air temperature of 180-250℃, such as 180℃, 200℃, 220℃, 240℃, 250℃, etc.; and an outlet air temperature of 80-120℃, such as 80℃, 90℃, 100℃, 110℃, 120℃, etc.

[0029] As a preferred embodiment of the present invention, the sintering is carried out under the protection of an inert gas, wherein the inert gas is selected from nitrogen and / or argon; the sintering temperature is 700-850℃, for example 700℃, 750℃, 800℃, 850℃, etc.; the sintering time is 8-12h, for example 8h, 9h, 10h, 11h, 12h, etc.

[0030] As a preferred embodiment of the present invention, the sodium source is selected from at least one of sodium carbonate (Na2CO3), sodium nitrate (NaNO3), and sodium bicarbonate (NaHCO3).

[0031] As a preferred embodiment of the present invention, the carbon source is selected from glucose (C6H4O3). 12 O6), sucrose (C 12 H 22 O 11 ( ), carbon nanotubes and graphene, at least one of them.

[0032] As a preferred embodiment of the present invention, the reducing agent is selected from citric acid (C6H8O7) and / or oxalic acid (H2C2O4).

[0033] In a second aspect, the present invention provides a sodium vanadium manganese phosphate cathode material prepared by the preparation method described in the first aspect.

[0034] The sodium vanadium manganese phosphate cathode material prepared by this invention has manganese and vanadium elements distributed in a gradient from the inside to the outside, and has a carbon-coated structure. The content of manganese decreases from the inside to the outside, while the content of vanadium increases from the inside to the outside. Compared with sodium vanadium manganese phosphate cathode materials with uniform distribution of vanadium and manganese elements, the sodium vanadium manganese phosphate cathode material prepared by this invention can effectively suppress the Jahn-Teller effect of manganese and the dissolution of manganese ions, and has excellent structural stability and electrochemical stability.

[0035] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the sodium manganese vanadium phosphate positive electrode material described in the second aspect.

[0036] Fourthly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the positive electrode sheet described in the third aspect.

[0037] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art:

[0038] 1. The preparation process of this invention is simple. The structure of the product can be controlled by adjusting the conditions of the coprecipitation reaction, without the need for additional equipment.

[0039] 2. The preparation method provided by the present invention prepares sodium vanadium manganese phosphate cathode material with a decreasing manganese content from the inside to the outside by controlling the conditions of the co-precipitation reaction of vanadium source, phosphorus source and manganese source. This effectively suppresses the Jahn-Teller effect of manganese and the dissolution of manganese ions, and improves the structural stability and electrochemical stability of the cathode material. Attached Figure Description

[0040] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The graph shows the cycle performance of coin cells assembled with sodium manganese phosphate cathode materials prepared in Examples 1 and 7 of this invention at a 1C rate.

[0043] Figure 2 The graph shows the cycle performance of coin cells assembled with sodium manganese phosphate cathode materials prepared in Examples 2 and 8 of this invention at a 1C rate. Detailed Implementation

[0044] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0046] Example 1

[0047] This embodiment provides a sodium manganese vanadium phosphate cathode material and its preparation method, the preparation method including the following steps:

[0048] (1) Dissolve 1 mol vanadium oxalate, 1 mol manganese acetate and 3 mol phosphoric acid in deionized water to prepare 500 mL of vanadium source aqueous solution, manganese source aqueous solution and phosphorus source aqueous solution respectively, wherein the molar ratio of vanadium, manganese and phosphorus source elements is 1:1:3.

[0049] (2) The above-mentioned aqueous solution of phosphorus source was directly added to the reactor. The sum of the flow rates of the aqueous solutions of manganese source and vanadium source was fixed at 100 mL / h. A 10-hour flow ramp was set to linearly reduce the flow rate of the aqueous solution of manganese source from 80 mL / h at the beginning of feeding to 20 mL / h at the end of feeding. Similarly, a 10-hour flow ramp was set to linearly increase the flow rate of the aqueous solution of vanadium source from 20 mL / h at the beginning of feeding to 80 mL / h at the end of feeding. The co-precipitation reaction was thoroughly stirred, and the pH value of the system was adjusted to 4-6 by ammonia water. The resulting mixed slurry was aged for 5.5 h and then filtered. It was washed with 2 L of deionized water and then filtered again. The washing process was repeated three times. The material obtained by filtration was dried at 80℃ for 12 h by forced air drying and then vacuum dried at 100℃ for 8 h to obtain the vanadium manganese phosphate precursor.

[0050] (3) The vanadium manganese phosphate precursor is thoroughly mixed with citric acid, sodium carbonate, and glucose, wherein the molar ratio of the vanadium manganese phosphate precursor to the reducing agent is 1:1.5, the molar ratio of the vanadium manganese phosphate precursor to the sodium source is 1:4, and the carbon source is added based on a carbon coating amount of 3 wt% in the sodium vanadium manganese phosphate cathode material. The above mixture is dispersed in water for 3 hours and then spray-dried. The inlet air temperature of the spray dryer is 200°C, and the outlet air temperature is 100°C. The spray-dried material is sintered at 800°C for 10 hours under a nitrogen protective atmosphere and then cooled to room temperature in the furnace to obtain the sodium vanadium manganese phosphate cathode material.

[0051] Example 2

[0052] This embodiment provides a sodium vanadium manganese phosphate cathode material and its preparation method. The preparation method is the same as that in Example 1. The difference between Example 1 and Example 1 is that in this embodiment, the molar ratio of vanadium, manganese and phosphorus source elements in step (1) is 1.2:0.8:3.

[0053] Example 3

[0054] This embodiment provides a sodium vanadium manganese phosphate cathode material and its preparation method. The preparation method is the same as that in Example 1. The difference between Example 1 and Example 1 is that in this embodiment, the flow rate of the aqueous solution of the manganese source in step (2) is 95 mL / h at the beginning of feeding and 5 mL / h at the end of feeding.

[0055] Example 4

[0056] This embodiment provides a sodium vanadium manganese phosphate cathode material and its preparation method. The preparation method is the same as that in Embodiment 1. The difference from Embodiment 1 is that the vanadium source is replaced with vanadium oxysulfate, the manganese source is replaced with manganese sulfate, the phosphorus source is replaced with diammonium hydrogen phosphate, the reducing agent is replaced with oxalic acid, the sodium source is replaced with sodium bicarbonate, and the carbon source is replaced with sucrose.

[0057] Example 5

[0058] This embodiment provides a sodium manganese vanadium phosphate cathode material and its preparation method, the preparation method including the following steps:

[0059] (1) Dissolve 1.8 mol vanadium oxalate, 0.2 mol manganese acetate and 3 mol phosphoric acid in deionized water to prepare 500 mL of vanadium source aqueous solution, manganese source aqueous solution and phosphorus source aqueous solution respectively, wherein the molar ratio of vanadium, manganese and phosphorus source elements is 1.8:0.2:3.

[0060] (2) The above-mentioned phosphorus source aqueous solution was directly added to the reactor. The sum of the flow rates of the manganese source aqueous solution and the vanadium source aqueous solution was fixed at 100 mL / h. A 10-hour flow ramp was set so that the flow rate of the manganese source aqueous solution linearly decreased from 100 mL / h at the beginning of feeding to 0 mL / h at the end of feeding. Similarly, a 10-hour flow ramp was set so that the flow rate of the vanadium source aqueous solution linearly increased from 0 mL / h at the beginning of feeding to 100 mL / h at the end of feeding. The co-precipitation reaction was thoroughly stirred, and the pH value of the system was adjusted to 4-6 by ammonia water. After aging the resulting mixed slurry for 8 hours, it was filtered. It was washed with 2 L of deionized water and then filtered again. The washing process was repeated three times. The material obtained by filtration was dried at 80℃ for 12 hours by forced air drying and then vacuum dried at 100℃ for 12 hours to obtain the vanadium manganese phosphate precursor.

[0061] (3) The vanadium manganese phosphate precursor is thoroughly mixed with citric acid, sodium carbonate, and glucose, wherein the molar ratio of the vanadium manganese phosphate precursor to the reducing agent is 1:1, the molar ratio of the vanadium manganese phosphate precursor to the sodium source is 1:5, and the carbon source is added based on a carbon coating amount of 5 wt% in the sodium vanadium manganese phosphate cathode material. The mixture is dispersed in water for 3 hours and then spray-dried. The inlet air temperature for spray drying is 250°C, and the outlet air temperature is 120°C. The spray-dried material is sintered at 700°C for 12 hours under a nitrogen protective atmosphere and then cooled to room temperature in the furnace to obtain the sodium vanadium manganese phosphate cathode material.

[0062] Example 6

[0063] This embodiment provides a sodium manganese vanadium phosphate cathode material and its preparation method, the preparation method including the following steps:

[0064] (1) Dissolve 0.2 mol vanadium oxalate, 1.8 mol manganese acetate and 3 mol phosphoric acid in deionized water to prepare 500 mL of vanadium source aqueous solution, manganese source aqueous solution and phosphorus source aqueous solution respectively, wherein the molar ratio of vanadium, manganese and phosphorus source elements is 0.2:1.8:3.

[0065] (2) The above-mentioned phosphorus source aqueous solution was directly added to the reactor. The sum of the flow rates of the manganese source aqueous solution and the vanadium source aqueous solution was fixed at 100 mL / h. A 10-hour flow ramp was set to linearly reduce the flow rate of the manganese source aqueous solution from 51 mL / h at the beginning of feeding to 49 mL / h at the end of feeding. Similarly, a 10-hour flow ramp was set to linearly increase the flow rate of the vanadium source aqueous solution from 49 mL / h at the beginning of feeding to 51 mL / h at the end of feeding. The co-precipitation reaction was thoroughly stirred, and the pH value of the system was adjusted to 4-6 by ammonia water. The resulting mixed slurry was aged for 2 hours and then filtered. It was washed with 2 L of deionized water and then filtered again. The washing process was repeated three times. The material obtained by filtration was dried at 80℃ for 12 hours by forced air drying and then vacuum dried at 100℃ for 12 hours to obtain the vanadium manganese phosphate precursor.

[0066] (3) The vanadium manganese phosphate precursor is thoroughly mixed with citric acid, sodium carbonate, and glucose, wherein the molar ratio of the vanadium manganese phosphate precursor to the reducing agent is 1:2, the molar ratio of the vanadium manganese phosphate precursor to the sodium source is 1:3, and the carbon source is added based on a carbon coating amount of 1 wt% in the sodium vanadium manganese phosphate cathode material. The mixture is dispersed in water for 3 hours and then spray-dried. The inlet air temperature for spray drying is 180°C, and the outlet air temperature is 80°C. The spray-dried material is sintered at 850°C for 8 hours under a nitrogen protective atmosphere and then cooled to room temperature in the furnace to obtain the sodium vanadium manganese phosphate cathode material.

[0067] Example 7

[0068] This embodiment provides a sodium vanadium manganese phosphate cathode material and its preparation method. The preparation method is the same as that in Example 1. The difference between Example 1 and Example 1 is that in this embodiment, the flow rates of the aqueous solutions of the manganese source and the aqueous solutions of the vanadium source are both 50 mL / h during the co-precipitation reaction in step (2), that is, there is no flow ramp throughout the process.

[0069] Example 8

[0070] This embodiment provides a sodium vanadium manganese phosphate cathode material and its preparation method. The preparation method is the same as that in Example 2. The difference between Example 2 and Example 2 is that in this embodiment, the flow rates of the aqueous solutions of the manganese source and the aqueous solutions of the vanadium source are both 50 mL / h during the co-precipitation reaction in step (2), that is, there is no flow ramp throughout the process.

[0071] Application examples

[0072] In this application example, the sodium manganese vanadium phosphate cathode materials prepared in Examples 1-8 are used as cathode active materials to prepare cathode plates and assemble coin cells:

[0073] A mixture of sodium manganese vanadium phosphate cathode material, Super P conductive carbon, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 was mixed with NMP solvent and coated onto aluminum foil to a thickness of 250 μm. The mixture was first dried at 80 °C for 5 h, followed by further drying at 120 °C for 12 h to obtain the cathode sheet. The active material loading of the cathode was 5 mg / cm³. 2 ;

[0074] A button cell was assembled in a glove box under a high-purity argon atmosphere using a sodium metal sheet as the counter electrode, 5 vol% fluoroethylene carbonate (FEC) as the electrolyte, a 1 M NaClO4 solution of ethylene carbonate (EC): propylene carbonate (PC) in a 1:1 (vol ratio) atmosphere, and glass fiber as the separator.

[0075] Performance testing

[0076] Performance testing was conducted using an electrochemical workstation with a voltage window of 2.2-3.8V. After the battery was activated at 0.1C for 3 cycles, a 1C cycle test was performed.

[0077] The test results are shown in Table 1 and Figures 1-2 As shown, where, Figure 1 The graph shows the cycle performance of coin cells assembled with sodium manganese phosphate cathode materials prepared in Examples 1 and 7 at a 1C rate. Figure 2 The graph shows the cycling performance of coin cells assembled with sodium manganese phosphate cathode materials prepared in Examples 2 and 8 at a 1C rate.

[0078] The results in Table 1 are shown below:

[0079] Table 1

[0080]

[0081] From Table 1 and Figures 1-2 It can be observed that the sodium vanadium manganese phosphate cathode material prepared by this invention has excellent cycle stability.

[0082] The comparison between Examples 1 and 7, and between Examples 2 and 8, reveals that the manganese content in the sodium vanadium manganese phosphate cathode material prepared by the flow ramp method decreases from the inside to the outside in a gradient distribution, exhibiting superior cycle stability.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0084] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily 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 invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a sodium manganese vanadium phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) Place a vanadium source, a phosphorus source, and a manganese source in solvent water for coprecipitation reaction, then age and dry to obtain a manganese vanadium phosphate precursor; (2) Mix the manganese vanadium phosphate precursor with a sodium source, a carbon source, and a reducing agent, dry and sinter to obtain the sodium manganese vanadium phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The method for placing the vanadium source, the phosphorus source, and the manganese source in solvent water for coprecipitation reaction in step (1) is: Continuously introduce the aqueous solution of the vanadium source and the aqueous solution of the manganese source into the aqueous solution of the phosphorus source respectively for coprecipitation reaction, wherein the flow rate of the aqueous solution of the manganese source gradually decreases, and the flow rate of the aqueous solution of the vanadium source gradually increases; Preferably, during the coprecipitation reaction, the total flow rate of the aqueous solution of the vanadium source and the aqueous solution of the manganese source remains unchanged, the flow rate ratio m of the aqueous solution of the manganese source at the start of the reaction is 50% < m ≤ 100%, the flow rate ratio m decreases gradually during the reaction, and the flow rate ratio m at the end of the reaction is 0 ≤ m < 50%; Preferably, the molar ratio of vanadium element in the vanadium source, manganese element in the manganese source, and phosphorus element in the phosphorus source is 2 - n : n : 3, where 0.1 < n < 1.

9.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the coprecipitation reaction in step (1) is 20 - 50°C, the time is 5 - 10 h, and the pH is 4 - 6; And / or, the temperature of the aging in step (1) is the same as the temperature of the coprecipitation reaction, and the aging time is 2 - 8 h; And / or, the drying in step (1) is to dry in a blast at 80°C for 12 h and then dry in vacuum at 100°C for 8 - 12 h.

4. The preparation method according to any one of claims 1-3, characterized in that, The vanadium source is selected from vanadyl sulfate and / or oxalic acid vanadyl; And / or, the manganese source is selected from at least one of manganese acetate, manganese sulfate, manganese nitrate, and manganese chloride; And / or, the phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

5. The preparation method according to any one of claims 1-4, characterized in that, The molar ratio of the manganese vanadium phosphate precursor to the reducing agent is 1 : (1 - 2); And / or, the molar ratio of the manganese vanadium phosphate precursor to the sodium source is 1 : (3 - 5); And / or, the amount of the carbon source is such that the carbon content in the sodium manganese vanadium phosphate cathode material is 1 - 5 wt%.

6. The preparation method according to any one of claims 1-5, characterized in that, The drying in step (2) is spray drying, the inlet air temperature is 180 - 250°C, and the outlet air temperature is 80 - 120°C; And / or, the sintering is carried out under the protection of an inert gas, the sintering temperature is 700 - 850°C, and the sintering time is 8 - 12 h.

7. The preparation method according to any one of claims 1-6, characterized in that, The sodium source is selected from at least one of sodium carbonate, sodium nitrate, and sodium bicarbonate; And / or, the carbon source is selected from at least one of glucose, sucrose, carbon nanotubes, and graphene; And / or, the reducing agent is selected from citric acid and / or oxalic acid.

8. The sodium manganese vanadium phosphate cathode material prepared by the preparation method according to any one of claims 1 - 7.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes the sodium manganese vanadium phosphate cathode material according to claim 8.

10. A sodium-ion battery, characterized in that, The sodium ion battery includes the positive electrode sheet according to claim 9.

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