A one-step sodium-removed manganese-based phosphate cathode material, its preparation method and application

Abstract

This invention provides a one-step sodium-removed manganese-based phosphate cathode material, its preparation method, and its application. The chemical formula of the cathode material is Na. x VMn 1‑y M y (PO4)3 or Na x V 1‑y M y Mn(PO4)3; wherein, 2≤x≤4, 0.01≤y≤0.5; the M includes Ti 4+ Cr 3+ Y 3+ Zr 4+ Nb 5+ Mo 6+ Hf 4+ W 6+ The cathode material is a manganese-based phosphate cathode material in which M replaces part of the vanadium or manganese sites, and the cathode material exhibits one-step sodium ion deintercalation / intercalation kinetics. The one-step sodium-deintercalation manganese-based phosphate cathode material prepared by this invention has rapid sodium ion deintercalation / intercalation capability, excellent high-rate capacity and cycle stability, and effectively solves the problems of slow second-step sodium deintercalation kinetics and poor structural stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials technology, and in particular to a one-step sodium-desodium-based manganese phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, with their abundant and inexpensive sodium resources, better low-temperature performance, and improved safety, have become an effective complementary technology to lithium-ion batteries, showing broad application prospects in large-scale energy storage. Cathode materials, as one of the most crucial components of a battery, determine its capacity, rate performance, cycle performance, and safety. NASICON-type sodium vanadium phosphate cathode materials, with their advantages of three-dimensional ion diffusion channels, high operating voltage, high structural stability, and high safety, have become one of the best choices for large-scale energy storage applications. However, vanadium's high price and less-than-ideal environmental impact limit its widespread application. Due to manganese's advantages of higher operating voltage, lower price, and greater environmental friendliness, the development of manganese-based NASICON-type cathode materials has become a current research hotspot.

[0003] Taking Na₄VMn(PO₄)₃, which partially replaces vanadium with manganese, as an example, this material exhibits a higher operating voltage (3.6 V) and a cost reduction of over 35%. However, this cathode involves a two-step desodium removal reaction during charging. Specifically, the first Na… + Na detached from Na(2) site + Related to ion extraction, corresponding to V 3+ The oxidation of Na + It migrates in the 3D channel at a relatively fast diffusion rate. The second Na... + Sodium removal process and Mn 2+ It is related to oxidation, and in this process, Na + Migrating along the c-axis in the 1D channel, resulting in Na + The diffusion rate is relatively slow. This is mainly because, with the diffusion of Na... + During extraction, Na(2) sites preferentially form empty sites, while the filled Na(1) sites hinder the extraction of Na. + Diffusion between active Na(2) sites leads to two-step Na... + The ion diffusion coefficient of the desodium removal reaction is more than an order of magnitude lower than that of the first step, making it the rate-determining step in the entire desodium removal process and severely limiting the achievement of high capacity and high rate performance. Therefore, improving the kinetics of the second-step desodium removal reaction at the cathode is key to improving its electrochemical performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a one-step desodium-removed manganese-based phosphate cathode material, its preparation method, and its applications.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] On one hand, the present invention provides a one-step desodium-removed manganese-based phosphate cathode material, wherein the chemical formula of the cathode material is Na x VMn 1-y M y (PO4)3 or Na x V 1-y M y Mn(PO4)3;

[0007] Where 2≤x≤4, 0.01≤y≤0.5;

[0008] The M includes Ti 4+ Cr 3+ Y 3+ Zr 4+ Nb 5+ Mo 6+ Hf 4+ W 6+ The cathode material is any one or at least two of the following, wherein the cathode material is a manganese-based phosphate cathode material in which M replaces part of the vanadium or manganese sites, and the cathode material exhibits one-step sodium ion insertion / extraction kinetics.

[0009] On the other hand, the present invention provides a method for preparing the above-mentioned one-step sodium-free manganese-based phosphate cathode material, comprising the following steps:

[0010] Sodium source, M source, vanadium source, manganese source, phosphorus source, carbon source, and organic complexing agent are mixed in a mixed solvent as reactants, heated and stirred until a uniform and stable sol is formed, and then continuously dried to form a gel precursor; the obtained gel precursor is crushed and then subjected to high-temperature sintering treatment to obtain the cathode material.

[0011] The molar ratio of sodium, manganese, vanadium, M, and phosphorus is (2-4):(1-x):1:x:3 or (2-4):1:(1-x):x:3, where 0.01≤x≤0.5; the carbon source and Na x VMn 1-y M y (PO4)3 or Na x V 1-y M y The mass ratio of Mn(PO4)3 is (0.01-0.1):1.

[0012] Preferably, the molar ratio of the organic complexing agent to all transition metal sources is (0.5-4):1.

[0013] Preferably, the organic complexing agent includes any one or at least two of ethylenediaminetetraacetic acid, oxalic acid, citric acid, and tartaric acid.

[0014] Preferably, the stirring conditions are: stirring time of 0.5-6 hours, stirring speed of 200-800 rpm, and stirring temperature of 60-120°C.

[0015] Preferably, the drying conditions are: drying temperature of 60-120℃ and drying time of 6-48h.

[0016] Preferably, the conditions for high-temperature sintering are: raising the temperature to 650-900℃ at a rate of 3-5℃ / min and holding for 4-12 hours; the high-temperature sintering atmosphere includes any one or at least two of argon, nitrogen, and argon-hydrogen.

[0017] Preferably, the organic solvent complexing agent includes any one or at least two of ethylenediaminetetraacetic acid, oxalic acid, citric acid, and tartaric acid.

[0018] Preferably, the mixed solvent is prepared by mixing an organic solvent and water in a volume ratio of (0-4):1.

[0019] Preferably, the organic solvent includes any one or at least two of ethanol, acetone, ethylene glycol, glycerol, isopropanol, tetrahydrofuran, and N,N-dimethylformamide.

[0020] Preferably, the M source includes M n+ The corresponding nitrate, oxalate, acetate, acetylacetone salt, oxide, or any one or at least two of them.

[0021] Preferably, the sodium source includes any one or at least two of sodium chloride, sodium phosphate, sodium acetate, sodium carbonate, and sodium hydroxide.

[0022] Preferably, the manganese source includes any one or at least two of manganese acetate, manganese nitrate, manganese oxide, manganese dioxide, and manganese acetylacetone.

[0023] Preferably, the vanadium source includes any one or at least two of vanadium pentoxide, ammonium metavanadate, vanadium chloride, vanadium trioxide, vanadium dioxide, sodium vanadate, vanadium acetylacetonate, and vanadium oxysulfate.

[0024] Preferably, when the vanadium source is a pentavalent vanadium source, the reaction raw materials also include a reducing agent; the reducing agent includes, but is not limited to, any one or at least two of ascorbic acid, oxalic acid, and citric acid.

[0025] Preferably, the phosphorus source includes any one or at least two of the following: ammonium dihydrogen phosphate, diamine hydrogen phosphate, ammonium phosphate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and phosphoric acid.

[0026] Preferably, the carbon source includes any one or at least two of citric acid, polyethylene glycol, starch, polyvinylpyrrolidone, glucose, sucrose, dopamine hydrochloride, graphene, and carbon nanotubes.

[0027] This invention provides an application of the above-mentioned cathode material, which is used in a sodium-ion battery.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] The one-step sodium-free manganese-based phosphate cathode material of this invention uses M to replace some vanadium sites or some manganese sites in the Na4VMn(PO4)3 crystal lattice structure, utilizing the M that replaces the vanadium or manganese sites. n+ The electronic structure, through spin-orbit coupling effect, regulates the local electronic structure, electronic state, and lattice structure of vanadium or manganese sites, thereby changing the working voltage and coordination environment of the vanadium and manganese active centers in the Na4VMn(PO4)3 cathode. This enables the Na4VMn(PO4)3 cathode material after partial substitution of vanadium or manganese sites by M, namely the one-step desodium-deintercalated manganese-based phosphate cathode material of this invention, to achieve a one-step rapid sodium insertion / extraction reaction.

[0030] Meanwhile, the M introduced in this invention n+ Simultaneously inhibited Mn 3+ The Jahn-Teller distortion stabilizes the structural framework and significantly improves cycle life.

[0031] Therefore, the one-step sodium-desodium-based manganese phosphate cathode material prepared by this invention has rapid sodium ion deintercalation and deintercalation capabilities, excellent high-rate capacity and cycle stability, and effectively solves the problems of slow second-step sodium deintercalation kinetics and poor structural stability. Attached Figure Description

[0032] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the results shown in these drawings without creative effort.

[0033] Figure 1 The first charge-discharge curves of Example 3 and Comparative Example 2 at a rate of 0.1C are shown.

[0034] Figure 2 The dQm / dV curves corresponding to the first charge-discharge curves of Example 3 and Comparative Example 2 at 0.1C rate are shown.

[0035] Figure 3The constant current intermittent titration curves of Example 3 and Comparative Example 2 are shown below;

[0036] Figure 4 The XRD patterns are those of Example 3 and Comparative Example 2;

[0037] Figure 5 The graphs show the rate performance of Example 3 and Comparative Example 2.

[0038] Figure 6 This is a graph showing the cycling performance of Example 3 at a 10C rate. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0042] Sodium carbonate, vanadium pentoxide, manganese acetate, diamine hydrogen phosphate, chromium nitrate, oxalic acid, and glucose were weighed according to the elemental molar ratio of sodium:manganese:vanadium:chromium:phosphorus of 3.7:0.7:1:0.3:3, wherein the molar ratio of glucose to all transition metal sources was 1:1, and the molar ratio of oxalic acid to vanadium pentoxide was 1:1. The above raw materials were added sequentially to a mixed solvent of deionized water and ethanol in a volume ratio of 1:1, and heated and stirred at 80°C and 500 rpm for 3 hours until a uniform sol was formed. The synthesized sol was placed in a forced-air drying oven at 100°C for 12 hours to obtain the gel precursor.

[0043] The synthesized gel precursor was ground and then sintered in a tube furnace. The temperature was increased to 700℃ at a rate of 5℃ / min, and held at this temperature for 8 hours in an argon atmosphere to obtain Na. 3.7 Mn 0.7 VCr 0.3 (PO4)3 cathode material.

[0044] Example 2

[0045] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0046] Sodium acetate, ammonium metavanadate, ammonium dihydrogen phosphate, manganese nitrate, chromium acetylacetone, ascorbic acid, and sucrose were weighed according to the elemental molar ratio of sodium:manganese:vanadium:chromium:phosphorus of 4:1:0.7:0.3:3. The molar ratio of sucrose to all transition metal sources was 1:1, and the molar ratio of ascorbic acid to ammonium metavanadate was 1:2. The above raw materials were sequentially added to a mixed solvent of deionized water and isopropanol in a volume ratio of 1:0.5. The mixture was heated and stirred at 50°C for 500 rpm for 3 hours until a homogeneous sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 16 hours to obtain the gel precursor.

[0047] The synthesized gel precursor was ground and then sintered in a tube furnace. The temperature was increased to 650℃ at a rate of 3℃ / min and held at this temperature for 12 hours under a nitrogen atmosphere to obtain Na4MnV. 0.7 Cr 0.3 (PO4)3 cathode material.

[0048] Example 3

[0049] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0050] Sodium chloride, vanadium acetylacetonate, sodium phosphate, manganese acetate, zirconium oxychloride, and citric acid were weighed according to the elemental molar ratio of sodium:vanadium:manganese:zirconium:phosphorus of 3.6:1:0.8:0.2:3, wherein the molar ratio of citric acid to all transition metal element sources was 1.5:1. They were added sequentially to deionized water and heated and stirred at 80°C and 300 rpm for 3 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 12 hours to obtain the gel precursor.

[0051] The synthesized gel precursor was crushed and sintered in a tube furnace. The temperature was increased to 750°C at a rate of 5°C / min and held at this temperature for 12 hours in an argon atmosphere to obtain Na. 3.6 Mn 0.8 VZr 0.2 (PO4)3 cathode material.

[0052] Example 4

[0053] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0054] Sodium acetate, vanadium acetylacetonate, sodium dihydrogen phosphate, manganese nitrate, zirconium acetylacetonate, glucose, and ascorbic acid were weighed according to the elemental molar ratio of sodium:vanadium:manganese:zirconium:phosphorus of 3.8:0.8:1:0.2:3. The molar ratio of glucose to all transition metal sources was 1:1, and the molar ratio of ascorbic acid to vanadium source was 2:1. The above raw materials were sequentially added to a 1:1 volume ratio of deionized water and acetone, and heated and stirred at 60°C for 400 rpm for 4.5 h until a homogeneous sol was formed. The synthesized sol was then dried in a forced-air drying oven at 60°C for 24 h to obtain the gel precursor.

[0055] The synthesized gel precursor was ground and sintered in a tube furnace. The temperature was increased to 650℃ at a rate of 3℃ / min and held at this temperature for 10 hours in an argon atmosphere to obtain Na. 3.8 MnV 0.8 Zr 0.2 (PO4)3 cathode material.

[0056] Example 5

[0057] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0058] Sodium hydroxide, vanadium chloride, diamine hydrogen phosphate, manganese acetylacetone, ammonium molybdate, and tartaric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:molybdenum:phosphorus of 3.2:1:0.8:0.2:3, wherein the molar ratio of tartaric acid to all transition metal sources was 2:1. The above raw materials were added sequentially to a mixed solvent of deionized water and tetrahydrofuran in a volume ratio of 4:1 and heated and stirred at 80°C and 500 rpm for 2 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 18 hours to obtain the gel precursor.

[0059] The synthesized gel precursor was ball-milled and then sintered in a tube furnace. The temperature was increased to 800℃ at a rate of 4℃ / min and held at this temperature for 6 hours under a nitrogen atmosphere to obtain Na. 3.2 Mn 0.8 VMo 0.2 (PO4)3 cathode material.

[0060] Example 6

[0061] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0062] Sodium hydroxide, vanadium chloride, diamine hydrogen phosphate, manganese acetylacetone, ammonium molybdate, and tartaric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:molybdenum:phosphorus of 3.4:0.8:1:0.2:3, wherein the molar ratio of tartaric acid to all transition metal sources was 2:1. The above raw materials were added sequentially to a mixed solvent of deionized water and tetrahydrofuran in a volume ratio of 4:1 and heated and stirred at 80°C and 500 rpm for 2 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 18 hours to obtain the gel precursor.

[0063] The synthesized gel precursor was ball-milled and then sintered in a tube furnace. The temperature was increased to 800℃ at a rate of 4℃ / min and held at this temperature for 6 hours under a nitrogen atmosphere to obtain Na. 3.4 MnV 0.8 Mo 0.2 (PO4)3 cathode material.

[0064] Example 7

[0065] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0066] Sodium acetate, vanadium pentoxide, sodium dihydrogen phosphate, manganese nitrate, yttrium acetylacetonate, citric acid, and ethylenediaminetetraacetic acid were weighed according to an elemental molar ratio of sodium:manganese:vanadium:yttrium:phosphorus of 3.7:0.7:1:0.3:3, wherein the molar ratio of citric acid, ethylenediaminetetraacetic acid, and all transition metal sources was 1:1:2. The above raw materials were added sequentially to a mixed solvent of deionized water and ethylene glycol in a volume ratio of 2:1 and heated and stirred at 60°C, a stirring rate of 300 rpm, and a stirring time of 4 h until a uniform sol was formed. The synthesized sol was placed in a forced-air drying oven and dried at 80°C for 12 h to obtain a gel precursor.

[0067] The synthesized gel precursor was ground and then sintered in a tube furnace. The temperature was increased to 800℃ at a rate of 5℃ / min, and held at this temperature for 8 hours in an argon atmosphere to obtain Na. 3.7 Mn 0.7 VY 0.3 (PO4)3 cathode material.

[0068] Example 8

[0069] This embodiment provides a one-step method for preparing a sodium-removed manganese-based phosphate cathode material, specifically including the following steps:

[0070] Sodium citrate, sodium metavanadate, sodium phosphate, manganese acetylacetonate, yttrium oxalate nonahydrate, sucrose, and oxalic acid were weighed according to the elemental molar ratio of sodium:manganese:vanadium:yttrium:phosphorus of 4:1:0.7:0.3:3. The molar ratio of sucrose to all transition metal sources was 1:2, and the molar ratio of oxalic acid to ammonium metavanadate was 1:1. The above raw materials were sequentially added to a 1:1 volume ratio of deionized water and acetone and heated and stirred at 60°C for 500 rpm for 3 hours until a homogeneous sol was formed. The synthesized sol was then dried in a forced-air drying oven at 60°C for 24 hours to obtain the gel precursor.

[0071] The synthesized gel precursor was ground and then sintered in a tube furnace. The temperature was increased to 750℃ at a rate of 3℃ / min and held at this temperature for 8 hours in an argon atmosphere to obtain Na4MnV. 0.7 Y 0.3 (PO4)3 cathode material.

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing Na4MnV(PO4)3 cathode material, specifically including the following steps:

[0074] Sodium chloride, ammonium metavanadate, sodium dihydrogen phosphate, manganese acetate, and citric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:phosphorus of 4:1:1:3, wherein the molar ratio of citric acid to all transition metal sources was 1.5:1. These were then added sequentially to deionized water and heated and stirred at 80°C and 300 rpm for 3 hours until a homogeneous sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 12 hours to obtain the gel precursor.

[0075] The synthesized gel precursor was crushed and transferred to a tube furnace for sintering. The temperature was increased to 750℃ at a rate of 5℃ / min and held in an argon atmosphere for 12h to obtain Na4MnV(PO4)3 cathode material.

[0076] Comparative Example 2

[0077] This comparative example provides a method for preparing Na4MnV(PO4)3 cathode material, specifically including the following steps:

[0078] Sodium acetate, vanadium acetylacetonate, ammonium dihydrogen phosphate, manganese acetate, and citric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:phosphorus of 4:1:1:3, wherein the molar ratio of citric acid to all transition metal element sources was 1.5:1. They were then added sequentially to deionized water and heated and stirred at 80°C and 300 rpm for 3 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 12 hours to obtain the gel precursor.

[0079] The synthesized gel precursor was crushed and transferred to a tube furnace for sintering. The temperature was increased to 750℃ at a rate of 5℃ / min and held in an argon atmosphere for 12h to obtain Na4MnV(PO4)3 cathode material.

[0080] Comparative Example 3

[0081] This comparative example provides a method for preparing Na4MnV(PO4)3 cathode material, specifically including the following steps:

[0082] Sodium chloride, vanadium acetylacetonate, sodium phosphate, manganese acetate, and citric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:phosphorus of 4:1:1:3, wherein the molar ratio of citric acid to all transition metal sources was 1.5:1. They were then added sequentially to deionized water and heated and stirred at 100°C and 500 rpm for 2 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 100°C for 8 hours to obtain the gel precursor.

[0083] The synthesized gel precursor was crushed and transferred to a tube furnace for sintering. The temperature was increased to 750℃ at a rate of 5℃ / min and held in an argon atmosphere for 12h to obtain Na4MnV(PO4)3 cathode material.

[0084] Comparative Example 4

[0085] This comparative example provides a method for preparing Na4MnV(PO4)3 cathode material, specifically including the following steps:

[0086] Sodium chloride, vanadium acetylacetonate, sodium phosphate, manganese acetate, and citric acid were weighed according to an elemental molar ratio of sodium:vanadium:manganese:phosphorus of 4:1:1:3, wherein the molar ratio of citric acid to all transition metal source elements was 1.5:1. They were then added sequentially to deionized water and heated and stirred at 80°C and 300 rpm for 3 hours until a uniform sol was formed. The synthesized sol was then dried in a forced-air drying oven at 80°C for 12 hours to obtain the gel precursor.

[0087] The synthesized gel precursor was crushed and transferred to a tube furnace for sintering. The temperature was increased to 650℃ at a rate of 3℃ / min and held in an argon atmosphere for 10h to obtain Na4MnV(PO4)3 cathode material.

[0088] Electrochemical performance analysis was performed on the cathode materials provided in Example 3 and Comparative Example 2;

[0089] Battery manufacturing:

[0090] Using the positive electrode materials prepared in Example 3 and Comparative Example 2 as active materials, acetylene black as a conductive agent, and PVDF as a binder, respectively, the active material, acetylene black, and PVDF were uniformly mixed in an N-methyl-2-pyrrolidone solution at a mass ratio of 70:20:10 and ground for 20 min to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil and dried under vacuum at 80°C for 12 h. The dried aluminum foil coated with the positive electrode slurry was then cut into 12 mm diameter discs using a cutting machine to serve as the positive electrode of the sodium-ion battery. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and a mixed solution of 1.0 M sodium perchlorate and 5% polycarbonate as the electrolyte, CR2032 coin cells were assembled in an argon-filled glove box.

[0091] Electrochemical performance detection and analysis:

[0092] The assembled CR2032 coin cell was subjected to constant current charge-discharge tests at room temperature within a voltage window of 2.5–3.8 V. Figure 1 The figure shows the initial charge-discharge curves at a 0.1C rate. As can be seen from the figure, the electrode material prepared in Example 3 exhibits only one oxidation voltage plateau (~3.5V) in its charge-discharge curve at a 0.1C rate; while the electrode material prepared in Comparative Example 2 exhibits two oxidation voltage plateaus at a 0.1C rate, each at ~3.4V (corresponding to V...). 3+ / V 4+ ) and ~3.6V (corresponding to Mn 2+ / Mn 3+ The above results demonstrate that Zr substitution of some V or Mn successfully altered the local electronic coordination environment of V and Mn, promoting Na... + The diffusion and electron transport transform the two-step sodium desodium reaction into a one-step sodium desodium reaction, realizing a one-step sodium deintercalation / intercalation reaction mechanism.

[0093] Reference Figure 2 , Figure 2The figure shows the dQm / dV curves corresponding to the first charge-discharge curves at 0.1C rate. As can be seen from the figure, the dQm / dV curve of the electrode material prepared in Example 3 has only one pair of redox peaks, while the dQm / dV curve of the electrode material prepared in Comparative Example 2 has two pairs of redox peaks. This further illustrates that the electrode material prepared in Example 3 achieves a one-step sodium insertion / extraction reaction mechanism.

[0094] The electrode materials prepared in Example 3 and Comparative Example 2 were subjected to constant current intermittent titration performance tests. The performance test results are as follows: Figure 3 As can be seen from the figure, the sodium ion diffusion coefficient (D) of the electrode material prepared in Comparative Example 2 during the charging process is... Na + In the low-pressure area, it is approximately 5.03 × 10⁻⁶. -11 cm 2 ·s -1 In the high-voltage region, it is approximately 8.85 × 10⁻⁶. -12 cm 2 ·s -1 The electrode material prepared in Comparative Example 2 exhibits D during discharge overshoot. Na + In the high-voltage region, it is approximately 2.24 × 10⁻⁶. -11 cm 2 ·s -1 In the low-pressure area, it is approximately 4.34 × 10⁻⁶. -11 cm 2 ·s -1 The electrode material prepared in Example 3 has only a single charge-discharge platform, and during charging, D... Na + Approximately 1.01 × 10 -10 cm 2 ·s -1 During discharge, D Na + Approximately 9.36 × 10 -11 cm 2 ·s -1 As can be seen from the above, Zr doping significantly improves the Na+ content of the electrode material. + Diffusion kinetics.

[0095] The crystal structures of the electrode materials prepared in Example 3 and Comparative Example 2 were analyzed by XRD. Figure 4 The XRD patterns of Example 3 and Comparative Example 2 are shown. In the figures, the sharp diffraction peaks of both Example 3 and Comparative Example 2 indicate good crystallinity. Furthermore, it can be seen from the figures that the (116) peak of Example 3 gradually shifts to lower angles, while the (211) and (300) peaks gradually shift to higher angles, indicating that Zr substitution of some V or Mn leads to anisotropic changes in lattice parameters. On the one hand, Zr…4+ The ionic radius (r=0.72 Å) is greater than that of Mn. 2+ The ionic radius (r = 0.67 Å) increases the unit cell parameter; on the other hand, the Zr-O bond causes the unit cell parameter to shrink. Analysis showed that in Example 3, the Zr-O bond slightly decreased along the a-axis and b-axis, but significantly increased along the c-axis, indicating that Zr partial substitution of V or Mn is beneficial to Na. + The spread of.

[0096] To better demonstrate the impact of the one-step sodium insertion / extraction reaction mechanism on the electrochemical performance of the cathode material, the rate performance of the electrode materials prepared in Example 3 and Comparative Example 2 was tested, and the results are as follows: Figure 5 As shown in the figure, the electrode material prepared in Example 3 still maintains a discharge specific capacity of ~73 mAh·g at 15C. -1 This is significantly higher than the electrode material prepared in Comparative Example 2 (~50 mAh·g). -1 This demonstrates that the electrode material prepared in Example 3 has excellent high-rate capacity.

[0097] The electrode material prepared in Example 3 was subjected to cycle performance testing at a 10C rate, and the results are as follows: Figure 6 As shown in the figure, the electrode material prepared in Example 3 still retains a discharge specific capacity of ~69.7 mAh·g after 3000 cycles at 10C. -1 Its capacity retention rate was 92.7%. This indicates that the electrode material prepared in Example 3 has excellent cycle stability.

[0098] Matters not covered in this invention are common knowledge.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a one-step sodium-removed manganese-based phosphate cathode material, characterized in that, Includes the following steps: Sodium, zirconium, vanadium, manganese, phosphorus, carbon, and an organic complexing agent are mixed in a mixed solvent as reactants, heated and stirred until a uniform and stable sol is formed, and then continuously dried to form a gel precursor. The obtained gel precursor is then ground and subjected to high-temperature sintering to obtain the cathode material; the zirconium source includes Zr. 4+ The corresponding nitrate, oxalate, acetate, acetylacetone salt, oxide, or any one or at least two of them; The conditions for high-temperature sintering are: raising the temperature to 650-900℃ at a rate of 3-5℃ / min and holding for 4-12 hours; The high-temperature sintering atmosphere includes one or at least two of argon, nitrogen, and argon-hydrogen. The molar ratio of sodium, manganese, vanadium, zirconium, and phosphorus is 3.6:0.8:1:0.2:3; the carbon source and Na... 3.6 VMn 0.8 M 0.2 The mass ratio of (PO4)3 is (0.01-0.1):

1.

2. The method for preparing the cathode material as described in claim 1, characterized in that, The molar ratio of the organic complexing agent to all transition metal sources is (0.5-4):

1.

3. The method for preparing the cathode material as described in claim 1, characterized in that, The stirring conditions are as follows: stirring time is 0.5-6 hours, stirring speed is 200-800 rpm, and stirring temperature is 60-120℃.

4. The method for preparing the cathode material as described in claim 1, characterized in that, The drying conditions are: drying temperature of 60-120℃ and drying time of 6-48h.

5. The method for preparing the cathode material as described in claim 1, characterized in that, The organic complexing agent includes any one or at least two of ethylenediaminetetraacetic acid, oxalic acid, citric acid, and tartaric acid.

6. The method for preparing the cathode material as described in claim 1, characterized in that, The mixed solvent is prepared by mixing organic solvent and water in a volume ratio of (0-4):

1.

7. The method for preparing the cathode material as described in claim 6, characterized in that, The organic solvent includes any one or at least two of ethanol, acetone, ethylene glycol, glycerol, isopropanol, tetrahydrofuran, and N,N-dimethylformamide.

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