A polyanion sodium electric positive electrode material and a preparation method and application thereof

Abstract

The application provides a polyanion sodium electric positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a polyanion source, a sodium source, a transition metal source and an organic solvent, then performing a solvothermal reaction to obtain a post-reaction liquid; the boiling point of the organic solvent is above 150 DEG C; precursor particles are separated from the post-reaction liquid to obtain precursor particles coated with the organic solvent, and then the precursor particles coated with the organic solvent are sintered to obtain the polyanion sodium electric positive electrode material. The preparation method of the application can realize uniform dispersion of the precursor at an atomic scale and prepare a nanoscale uniformly dispersed polyanion sodium electric positive electrode material, so that the electrochemical performance of a sodium ion battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a polyanionic sodium battery positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] The positive electrode material of a sodium ion battery includes a layered oxide positive electrode material, a polyanionic positive electrode material and a prussian blue type positive electrode material, wherein the polyanionic sodium battery positive electrode material is rich in types, controllable in cost, simple in synthesis process, has high chemical stability, thermal stability and electrochemical stability, and can achieve higher specific capacity and energy density. However, the polyanionic sodium battery positive electrode material generally has the defect of low electronic conductivity, and generally needs to be coated with carbon or have the grain size reduced to improve the electrochemical performance.

[0003] At present, the preparation process of the polyanionic sodium battery positive electrode material mainly includes a sol-gel method and a solid phase method. The sol-gel method first dissolves a precursor material in a solvent to form a liquid precursor, and then a sol and a gel are prepared through a series of processes, and finally an electrode product is obtained through calcination. For example, CN 116666608A discloses a high-entropy polyanionic sodium ion battery positive electrode material and a preparation method thereof, which includes the following steps: step one, mixing a sodium source, a transition metal source, a phosphorus source, a carbon source and water to obtain a uniformly dispersed solution through stirring various element sources, to obtain a first mixed system; step two, placing the first mixed system in an oil bath pot for heating and refluxing, obtaining a precursor through a sol-gel method, and drying the precursor; step three, performing first sintering on the dried precursor to obtain a second mixed system, and processing the second mixed system into a reduced particle size through a ball milling method; and step four, performing second sintering on the second mixed system after ball milling, and obtaining a high-entropy phosphate positive electrode material after the second sintering.

[0004] The solid phase method is to mix the precursor material uniformly and then directly perform high-temperature calcination to prepare an electrode material. For example, CN 114156452A discloses a sodium ion positive electrode material, a preparation method and an application thereof. The preparation method includes: mixing a sodium source, a manganese source, an aluminum source, a phosphorus source and a carbon source, and then sintering after mixing in a protective atmosphere to obtain the sodium ion positive electrode material; wherein the sodium ion positive electrode material includes an inner core and a carbon coating layer located on the surface of the inner core; the chemical formula of the inner core is Na4MnAl(PO4)3; the element molar ratio of manganese, aluminum and phosphorus in the manganese source, the aluminum source and the phosphorus source is consistent with the stoichiometric ratio of Na4MnAl(PO4)3, and a polyanionic compound Na4MnAl(PO4)3 is prepared through a solid phase method.

[0005] However, the sol-gel and solid-phase methods yield particles with large sizes and uneven size distributions, making it difficult to achieve stable battery performance. Therefore, there is a need to develop a method for preparing nanoscale polyanionic sodium cathode materials with uniform size distribution and ensuring that the electrode material has high conductivity, thereby exhibiting excellent electrochemical performance. Summary of the Invention

[0006] The purpose of this invention is to provide a polyanionic sodium cathode material, its preparation method, and its application. The preparation method is based on a pure oil phase system to prepare the polyanionic sodium cathode material, which can achieve uniform dispersion of the precursor at the atomic scale and prepare a nanoscale uniformly dispersed polyanionic sodium cathode material, thereby effectively improving the electrochemical performance of sodium-ion batteries.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a polyanionic sodium cathode material, the method comprising the following steps:

[0009] (1) Mix the polyanion source, sodium source, transition metal source and organic solvent, and then carry out a solvothermal reaction to obtain the reaction liquid;

[0010] The boiling point of the organic solvent is above 150°C;

[0011] (2) The precursor particles are separated from the reaction liquid in step (1) to obtain precursor particles coated with organic solvent. Then the precursor particles coated with organic solvent are sintered to obtain the polyanionic sodium cathode material.

[0012] This invention uses a high-boiling-point pure oil-phase organic solvent system to prepare polyanionic sodium cathode materials, instead of the traditional aqueous system. During solvothermal treatment, atomic-level dispersion can be achieved, which is beneficial to the formation of high-quality products during sintering. The sintered sample is composed of nanoscale particles with uniform size distribution, ensuring that the material has high conductivity and greatly improving the electrochemical performance of the polyanionic sodium cathode material.

[0013] Furthermore, this invention employs a high-boiling-point organic solvent system for solvothermal reaction, which can yield precursor particles coated with organic solvent. The residual organic solvent achieves in-situ carbon coating during subsequent sintering, further improving the conductivity of the material. At the same time, the preparation method described in this invention has high versatility and can prepare different types of polyanionic sodium cathode materials.

[0014] The boiling point of the organic solvent is above 150°C, for example, it can be 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the organic solvent in step (1) includes any one or a combination of at least two of fatty amines, fatty acids, chain olefins or phenyl ethers, and is preferably a combination of fatty amines and fatty acids.

[0016] Preferably, the fatty amine includes oleylamine and / or octadecylamine, with oleylamine being the most preferred.

[0017] Preferably, the fatty acid includes oleic acid.

[0018] Preferably, the chain olefin includes a straight-chain olefin of C15-C25, such as C15, C18, C20, C22 or C25, and preferably octadecene.

[0019] Preferably, the phenyl ether compound includes diphenyl ether.

[0020] Preferably, the organic solvent in step (1) includes any one or a combination of at least two of oleylamine, oleic acid, octadecylamine, octadecene, and diphenyl ether, and is preferably a combination of oleylamine and oleic acid.

[0021] This invention uses high-boiling-point organic solvents for preparation, especially oleylamine and / or oleic acid. Because oleylamine has reducing properties, it can effectively reduce ferric iron in the iron source; oleylamine or oleic acid has a high boiling point, can exist stably in solvothermal reactions, and can act as a capping agent to control the grain size at the nanoscale; and oleylamine or oleic acid has a certain surfactant effect, which can make the precursor materials uniformly dispersed in the solvent.

[0022] Preferably, the organic solvent in step (1) comprises aliphatic amines and fatty acids in a volume ratio of (2.5-10):1, such as 2.5:1, 3.5:1, 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1, 9.5:1 or 10:1, and more preferably oleylamines and oleic acid in a volume ratio of (2.5-5):1, such as 2.5:1, 3.5:1, 4.5:1 or 5:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] The present invention preferably uses oleylamine and oleic acid in a specific ratio. If there is too little oleylamine and too much oleic acid, the cost will be too high and the reaction process will be too violent, which will easily cause the reaction liquid to escape. If there is too much oleylamine and too little oleic acid, the precursors will not be mixed evenly during the reaction process, and high-quality cathode materials cannot be obtained in the subsequent sintering.

[0024] Preferably, the molar amount of organic solvent added in step (1) is 30-45 times the theoretical molar amount of the polyanionic sodium cathode material, for example, it can be 30 times, 35 times, 40 times or 45 times, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, conductive carbon is also added during the mixing process in step (1).

[0026] Preferably, the conductive carbon includes any one or a combination of at least two of carbon nanotubes, Super P, Ketjen Black, acetylene black, or graphene.

[0027] Preferably, the amount of conductive carbon added is 10-20 wt% of the theoretical amount of the polyanionic sodium cathode material, for example, it can be 10 wt%, 15 wt% or 20 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the polyanion source in step (1) includes any one or a combination of at least two of the following: phosphorus source, sulfur source, fluorine source, silicon source or boron source.

[0029] Preferably, the phosphorus source includes any one or a combination of at least two of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, or phosphoric acid.

[0030] Preferably, the sulfur source includes any one or a combination of at least two of ammonium bisulfate, sodium bisulfate, sodium sulfate, sulfuric acid, or vanadium oxysulfate.

[0031] Preferably, the fluorine source includes any one or a combination of at least two of hydrofluoric acid, sodium fluoride, or ammonium fluoride.

[0032] Preferably, the silicon source includes sodium silicate and / or silicic acid.

[0033] Preferably, the boron source includes any one or a combination of at least two of sodium tetraborate, boric acid, or ammonium borate.

[0034] Preferably, the sodium source in step (1) includes any one or a combination of at least two of sodium oleate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium bisulfate, sodium sulfate, sodium fluoride, sodium oxalate, sodium acetate, sodium formate, sodium citrate, or sodium hydroxide, preferably sodium oleate.

[0035] Preferably, the transition metal source in step (1) includes any one or a combination of at least two of the following: iron source, vanadium source, titanium source or manganese source.

[0036] Preferably, the iron source includes any one or a combination of at least two of ferric acetylacetone, ferric nitrate, ferrous nitrate, ferric phosphate, ferrous phosphate, ferrous acetylacetone, ferrous oxalate, ferrous carbonate, ferric sulfate, or ferrous sulfate.

[0037] Preferably, the vanadium source includes any one or a combination of at least two of vanadium acetylacetonate, vanadium acetylacetonate oxyacetate, sodium metavanadate, ammonium metavanadate, sodium orthovanadate, vanadium oxalate, or vanadium oxysulfate.

[0038] Preferably, the titanium source includes any one or a combination of at least two of titanium acetylacetonate, metatitanic acid, titanium sulfate, titanium isopropoxide, tetraethyl titanate, or tetrabutyl titanate.

[0039] Preferably, the manganese source includes any one or a combination of at least two of manganese acetylacetonate, manganese carbonate, manganese sulfate, or manganese acetate.

[0040] Preferably, the mixing temperature in step (1) is 20-180℃, for example, it can be 20℃, 50℃, 80℃, 100℃, 125℃, 150℃ or 180℃, and the time is 5-300min, for example, it can be 10min, 30min, 50min, 70min, 100min, 125min, 150min, 175min, 200min, 225min, 250min, 275min or 300min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] Preferably, the temperature of the solvothermal reaction in step (1) is 180-300℃, for example, 180℃, 200℃, 250℃ or 300℃, and the time is 5-300min, for example, 10min, 30min, 50min, 70min, 100min, 125min, 150min, 175min, 200min, 225min, 250min, 275min or 300min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] Preferably, the solvothermal reaction includes two or three heating stages. When it includes two heating stages, the first holding stage heats up to 100-140°C, for example, 100°C, 120°C or 140°C, and then holds for 10-30 minutes, for example, 10 minutes, 20 minutes or 30 minutes. The second holding stage heats up to 250-270°C, for example, 250°C, 260°C or 270°C, and then holds for 30-60 minutes, for example, 30 minutes, 40 minutes, 50 minutes or 60 minutes, and then cools to room temperature.

[0043] Preferably, the solvothermal reaction includes two or three heating stages. When it includes three heating stages, the first holding stage heats up to 110-130°C, for example, 110°C, 120°C or 130°C, and then holds for 10-30 minutes, for example, 10 minutes, 20 minutes or 30 minutes. The second holding stage heats up to 170-190°C, for example, 170°C, 180°C or 190°C, and then holds for 10-30 minutes, for example, 10 minutes, 20 minutes or 30 minutes. The third holding stage heats up to 250-270°C, for example, 250°C, 260°C or 270°C, and then holds for 10-30 minutes, for example, 10 minutes, 20 minutes or 30 minutes, and then cools to room temperature.

[0044] Preferably, the method for separating the precursor particles in step (2) includes mixing the post-reaction liquid with an alcohol solvent, performing solid-liquid separation, and drying.

[0045] Preferably, the solid-liquid separation method includes centrifugation, wherein the centrifugation speed is 11000-13000 rpm, for example, 11000 rpm, 12000 rpm or 13000 rpm, and the centrifugation time is 3-10 min, for example, 3 min, 5 min, 7 min or 10 min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] Preferably, the drying includes a vacuum drying temperature of 40-60°C, for example, 40°C, 50°C or 60°C, for 1-3 hours, for example, 1 hour, 2 hours or 3 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the alcohol solvent includes ethanol.

[0048] Preferably, the sintering temperature in step (2) is 300-800℃, for example, 300℃, 400℃, 500℃, 600℃, 700℃ or 800℃, and the time is 1-30h, for example, 1h, 5h, 10h, 15h, 20h, 25h or 30h, and is carried out in a protective gas.

[0049] Preferably, in step (2), the sintering is first carried out at a temperature of 300-350°C, for example, 300°C, 325°C or 350°C, for 1-3 hours, for example, 1 hour, 2 hours or 3 hours, and then carried out at a temperature of 500-600°C, for example, 500°C, 550°C or 600°C, for 5-8 hours, for example, 5 hours, 6 hours, 7 hours or 8 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0051] (1) According to the formula, add the polyanion source, sodium source, transition metal source and conductive carbon to the organic solvent, stir at 20-180℃ for 5-300 min, and then solvothermal reaction at 180-300℃ for 5-300 min to obtain the reaction liquid.

[0052] The organic solvent has a boiling point above 150°C and includes any one or a combination of at least two of oleylamine, oleic acid, octadecylamine, octadecene, or diphenyl ether.

[0053] (2) Pour the reaction liquid from step (1) into an alcohol solvent, and after solid-liquid separation and drying, obtain the precursor particles coated with organic solvent. Then, sinter the precursor particles coated with organic solvent in a protective gas at a temperature of 300-800℃ for 1-30 hours to obtain the polyanionic sodium cathode material.

[0054] In a second aspect, the present invention provides a polyanionic sodium cathode material, which is prepared by the preparation method described in the first aspect.

[0055] Preferably, the polyanionic sodium cathode material includes sodium ferric sulfate, sodium ferric phosphate composite, sodium ferric fluorophosphate, sodium ferric phosphate, sodium vanadium phosphate, sodium ferric orthosilicate, or sodium ferric pentaborate.

[0056] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the polyanionic sodium cathode material as described in the second aspect.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The present invention uses a high-boiling-point organic solvent to prepare the precursor material, which can achieve atomic-level dispersion during solvent heat treatment, which is beneficial to the formation of high-quality products in the sintering process;

[0059] (2) The sample obtained after sintering in this invention is a nano-sized particle with uniform size distribution, which can greatly improve the electrochemical performance of polyanion sodium cathode material.

[0060] (3) The residual organic solvent in this invention can form in-situ carbon coating during sintering, which further improves the electrical conductivity of the material;

[0061] (4) The preparation method described in this invention has a wide range of applications and can be used to prepare polyanionic sodium electrode materials including sulfates, complex phosphates, fluorophosphates, phosphates, sodium iron phosphate, sodium vanadium phosphate, sodium iron orthosilicate or sodium iron pentaborate. Attached Figure Description

[0062] Figure 1 The image shows the XRD pattern of the polyanionic sodium cathode material described in Example 1 of this invention.

[0063] Figure 2 This is a TEM image of the polyanionic sodium cathode material described in Example 1 of the present invention;

[0064] Figure 3 The rate performance diagrams are for the coin half-cells made of the polyanionic sodium cathode material described in Examples 1 and 4 of this invention.

[0065] Figure 4 This is a cycle performance diagram of a coin cell made of the polyanionic sodium cathode material described in Example 1 of the present invention.

[0066] Figure 5 The image shows the XRD pattern of the polyanionic sodium cathode material described in Example 2 of this invention.

[0067] Figure 6 This is a TEM image of the polyanionic sodium cathode material described in Example 2 of the present invention;

[0068] Figure 7 The rate performance diagrams are for the coin half-cells made of the polyanionic sodium cathode material described in Examples 2 and 11 of this invention.

[0069] Figure 8 This is a cycle performance diagram of a coin cell made of the polyanionic sodium cathode material described in Example 2 of the present invention.

[0070] Figure 9 The image shows the XRD pattern of the polyanionic sodium cathode material described in Example 3 of this invention.

[0071] Figure 10 This is a TEM image of the polyanionic sodium cathode material described in Example 3 of the present invention;

[0072] Figure 11 The rate performance diagrams are for the coin half-cells made of the polyanionic sodium cathode material described in Examples 3 and 13 of this invention.

[0073] Figure 12 This is a cycle performance diagram of a coin cell made of the polyanionic sodium cathode material described in Example 3 of the present invention. Detailed Implementation

[0074] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0075] Example 1

[0076] This embodiment provides a method for preparing a polyanionic sodium cathode material, wherein the polyanionic sodium cathode material is Na4Fe3(PO4)2(P2O7) / C / MWCNTs, wherein C is coated on the surface of Na4Fe3(PO4)2(P2O7), and MWCNTs are doped in Na4Fe3(PO4)2(P2O7). The preparation method includes the following steps:

[0077] (1) Add 2.3996g NaH2PO4 (20mmol), 5.2976g Fe(acac)3 (15mmol) and 0.328g MWCNTs (10wt% of polyanionic sodium cathode material) to a 250mL four-necked flask, then add 50mL oleylamine, and stir with a stirrer for 300min at 20℃ until the mixture is homogeneous;

[0078] (2) Under a flow rate of 0.5 L / min in N2 atmosphere, purge for 10 min, then heat to 120℃ and hold for 30 min, then heat to 250℃ and hold for 30 min. After holding, a homogeneous solution is obtained.

[0079] (3) After cooling the obtained solution to room temperature, pour it into a beaker containing 200 mL of ethanol. The prepared nanoparticles are uniformly precipitated. Then, the solid sample is obtained by centrifugation at 12000 rpm for 5 min. The obtained solid sample is placed in a vacuum dryer at 40 °C for 2 h to obtain nanoparticles uniformly coated with oleylamine.

[0080] (4) The dried solid sample is transferred to a tube furnace and pre-calcined at 300°C at a heating rate of 10°C / min under an Ar atmosphere for 1 hour. Then, it is pre-calcined at 550°C at a heating rate of 10°C / min for 10 hours. After cooling to room temperature in the furnace, the polyanionic sodium cathode material is obtained.

[0081] The XRD pattern of the polyanion sodium cathode material described in this embodiment is as follows: Figure 1 As shown, the TEM image is as follows Figure 2 As shown, the rate performance diagram of the fabricated coin cell is as follows. Figure 3 As shown in the figure, the cycle performance of the fabricated coin cell is as follows. Figure 4 As shown.

[0082] Example 2

[0083] This embodiment provides a method for preparing a polyanionic sodium cathode material, wherein the polyanionic sodium cathode material is Na2FePO4F / C / MWCNTs, wherein C is coated on the surface of Na2FePO4F, and MWCNTs are doped in Na2FePO4F. The preparation method includes the following steps:

[0084] (1) Add 0.5751g NH4H2PO4 (5mmol), 3.0444g sodium oleate (10mmol), 1.7659g Fe(acac)3 (5mmol) and 0.216g MWCNTs (20wt% of polyanionic sodium cathode material) to a 250mL four-necked flask, then add 50mL oleylamine, 15mL oleic acid and 172uL 49%HF (5mmol), and stir at 175℃ for 5min to mix evenly;

[0085] The volume ratio of oleylamine to oleic acid is 3.33:1;

[0086] (2) Under a flow rate of 0.5 L / min in N2 atmosphere, purge for 10 min, then heat to 180℃ and hold for 30 min, then heat to 250℃ and hold for 30 min. After holding, a homogeneous solution is obtained.

[0087] (3) After cooling the obtained solution to room temperature, pour it into a beaker containing 150 mL of ethanol. The prepared nanoparticles are uniformly precipitated. Then, the solid sample is obtained by centrifugation at 12000 rpm for 5 min. The obtained solid sample is placed in a vacuum dryer at 40 °C for 2 h to obtain nanoparticles uniformly coated with oleylamine and oleic acid.

[0088] (4) The dried solid sample was transferred to a tube furnace and pre-calcined at 300°C at a heating rate of 10°C / min under an Ar atmosphere for 1 hour. Then, it was pre-calcined at 550°C at a heating rate of 10°C / min for 5 hours. After cooling to room temperature in the furnace, the polyanionic sodium cathode material was obtained.

[0089] The XRD pattern of the polyanion sodium cathode material described in this embodiment is as follows: Figure 5 As shown, the TEM image is as follows Figure 6 As shown, the rate performance diagram of the fabricated coin cell is as follows. Figure 7 As shown in the figure, the cycle performance of the fabricated coin cell is as follows. Figure 8 As shown.

[0090] Example 3

[0091] This embodiment provides a method for preparing a polyanionic sodium cathode material, wherein the polyanionic sodium cathode material is Na2Fe2(SO4)3 / C / MWCNTs, wherein C is coated on the surface of Na2Fe2(SO4)3, and MWCNTs are doped in Na2Fe2(SO4)3. The preparation method includes the following steps:

[0092] (1) Add 0.691g NH4HSO4 (6mmol), 1.218g sodium oleate (4mmol), 1.4127g Fe(acac)3 (4mmol) and 0.0892g MWCNTs (10wt% of polyanionic sodium cathode material) to a 250mL four-necked flask, then add 50mL oleylamine and 15mL oleic acid, and stir with a stirrer for 100min at 25℃ until the mixture is homogeneous;

[0093] The volume ratio of oleylamine to oleic acid is 3.33:1;

[0094] (2) Under a flow rate of 0.5 L / min in N2 atmosphere, purge for 10 min, then heat to 120℃ and hold for 30 min, then heat to 180℃ and hold for 30 min, and finally heat to 250℃ and hold for 30 min. After holding, a homogeneous solution is obtained.

[0095] (3) After cooling the obtained solution to room temperature, pour it into a beaker containing 125 mL of ethanol. The prepared nanoparticles are uniformly precipitated. Then, the solid sample is obtained by centrifugation at 12000 rpm for 5 min. The obtained solid sample is placed at 40℃ and vacuum dried for 2 h to obtain nanoparticles uniformly coated with oleylamine and oleic acid.

[0096] (4) The dried solid sample was transferred to a tube furnace and calcined at 370°C at a heating rate of 5°C / min under an Ar atmosphere for 10 hours. After cooling to room temperature in the furnace, the polyanionic sodium cathode material was obtained.

[0097] The XRD pattern of the polyanion sodium cathode material described in this embodiment is as follows: Figure 9 As shown, the TEM image is as follows Figure 10 As shown, the rate performance diagram of the fabricated coin cell is as follows. Figure 11 As shown in the figure, the cycle performance of the fabricated coin cell is as follows. Figure 12 As shown.

[0098] Example 4

[0099] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that MWCNTs are not added in step (1) to change the adaptability of the obtained polyanionic sodium cathode material.

[0100] The rate performance diagram of the coin half-cell made of the polyanion sodium cathode material described in this embodiment is shown in the figure below. Figure 3 As shown.

[0101] Example 5

[0102] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the oleylamine in step (1) is replaced by oleic acid.

[0103] Example 6

[0104] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the oleylamine in step (1) is replaced by octadecylamine.

[0105] Example 7

[0106] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the oleylamine in step (1) is replaced by octadecene.

[0107] Example 8

[0108] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the oleylamine in step (1) is replaced with diphenyl ether.

[0109] Example 9

[0110] This embodiment provides a method for preparing a polyanionic sodium cathode material. Except for step (1), where the volume of oleic acid is 10 mL and the volume ratio of oleylamine to oleic acid is 5:1, the preparation method is the same as in Example 2.

[0111] Example 10

[0112] This embodiment provides a method for preparing a polyanionic sodium cathode material. Except for step (1), where the volume of oleic acid is 20 mL and the volume ratio of oleylamine to oleic acid is 2.5:1, the preparation method is the same as in Example 2.

[0113] Example 11

[0114] This embodiment provides a method for preparing a polyanionic sodium cathode material. Except for step (1), in which the volume of oleic acid is 5 mL and the volume ratio of oleylamine to oleic acid is 10:1, the preparation method is the same as in Example 2.

[0115] The rate performance diagram of the coin half-cell made of the polyanion sodium cathode material described in this embodiment is shown in the figure below. Figure 7 As shown.

[0116] Example 12

[0117] This embodiment provides a method for preparing a polyanionic sodium cathode material. Except for step (1), in which the volume of oleic acid is 25 mL and the volume ratio of oleylamine to oleic acid is 2:1, the preparation method is the same as in Example 2.

[0118] Example 13

[0119] This embodiment provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as that in Example 3, except that MWCNTs are not added in step (1) to change the adaptability of the obtained polyanionic sodium cathode material.

[0120] The rate performance diagram of the coin half-cell made of the polyanion sodium cathode material described in this embodiment is shown in the figure below. Figure 11 As shown.

[0121] Comparative Example 1

[0122] This comparative example provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the volumetric amount of oleylamine in step (1) is replaced with ethanol.

[0123] In this comparative example, all the ethanol evaporated, making it impossible to separate the corresponding precursor particles.

[0124] Comparative Example 2

[0125] This comparative example provides a method for preparing a polyanionic sodium cathode material. The preparation method is the same as in Example 1, except that the volumetric amount of oleylamine in step (1) is replaced with water.

[0126] In this comparative example, a large amount of water evaporated, making it impossible to separate the corresponding precursor particles.

[0127] The polyanionic sodium cathode material, conductive agent (Super P), and binder (PVDF) obtained in the above examples and comparative examples were coated into a slurry in a ratio of 8:1:1. Button batteries were assembled in a glove box with water and oxygen levels below 0.01 ppm. In this case, metallic sodium was used as the negative electrode. The electrolyte used in Examples 3 and 13 was 1M NaClO4 in EC:PC (1:1 vol%) with 5% FEC. The electrolyte used in the other examples was 1M NaPF6 in EC:PC (1:1 vol%) with 5% FEC. The separator was a glass fiber membrane.

[0128] The prepared coin cells were subjected to cycle performance and rate performance tests under constant temperature of 30℃, with voltage window and current density as follows. Figure 3 , Figure 4 , Figure 7 , Figure 8 , Figure 11 and Figure 12 As shown in the figure, the test results are shown in Table 1:

[0129] Table 1

[0130]

[0131] As can be seen from Table 1:

[0132] As shown in Example 1, the present invention uses a pure-phase high-boiling-point organic solvent, which not only yields nanoscale particles with uniform size distribution, but also allows the organic solvent to act as a carbon source to coat the particle surface, thus preparing a high-performance polyanionic sodium cathode material. As shown in Examples 1 and 4, and Examples 3 and 13, the present invention preferably adds conductive carbon during the preparation process, thereby further improving the conductivity of the material. As shown in Examples 1 and 5-8, the type of organic solvent in the present invention affects the performance of the polyanionic sodium cathode material. As shown in Examples 2 and 9-12, the present invention preferably uses an oleylamine + oleic acid system, and the mass ratio of the two affects the uniformity of particle distribution, thereby affecting the performance of the product.

[0133] In summary, this invention provides a polyanionic sodium-ion battery cathode material, its preparation method, and its application. The preparation method is based on a pure oil phase system to prepare the polyanionic sodium-ion battery cathode material, which can achieve uniform dispersion of the precursor salt at the atomic scale and prepare a nanoscale uniformly dispersed polyanionic sodium-ion battery cathode material, thereby effectively improving the electrochemical performance of sodium-ion batteries.

[0134] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a polyanionic sodium cathode material, characterized in that, The preparation method includes the following steps: (1) Mix the polyanion source, sodium source, transition metal source and organic solvent, and then carry out a solvothermal reaction to obtain the reaction liquid; The boiling point of the organic solvent is above 150°C; The organic solvent includes any one or a combination of at least two of fatty amines, fatty acids, chain olefins or phenyl ethers; The fatty amines include oleylamine and / or octadecylamine; The fatty acids include oleic acid; The chain olefins include C15-C25 straight-chain olefins; The phenyl ether compounds include diphenyl ethers; (2) The precursor particles are separated from the reaction liquid in step (1) to obtain precursor particles coated with organic solvent. Then the precursor particles coated with organic solvent are sintered to obtain the polyanionic sodium cathode material. Conductive carbon was also added during the mixing process described in step (1).

2. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) is a combination of fatty amines and fatty acids.

3. The preparation method according to claim 1, characterized in that, The fatty amines include oleylamine.

4. The preparation method according to claim 1, characterized in that, The chain olefins include octadecene.

5. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) comprises aliphatic amines and fatty acids in a volume ratio of (2.5-10):

1.

6. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) includes oleylamine and oleic acid in a volume ratio of (2.5-5):

1.

7. The preparation method according to claim 1, characterized in that, The molar amount of organic solvent added in step (1) is 30-45 times the theoretical molar amount of the polyanionic sodium cathode material.

8. The preparation method according to claim 1, characterized in that, The conductive carbon includes any one or a combination of at least two of carbon nanotubes, Super P, Ketjen black, acetylene black, or graphene.

9. The preparation method according to claim 1, characterized in that, The amount of conductive carbon added is 10-20 wt% of the theoretical amount of the polyanionic sodium cathode material.

10. The preparation method according to claim 1, characterized in that, The polyanion source in step (1) includes any one or a combination of at least two of the following: phosphorus source, sulfur source, fluorine source, silicon source or boron source.

11. The preparation method according to claim 1, characterized in that, The sodium source in step (1) includes any one or a combination of at least two of sodium oleate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium bisulfate, sodium sulfate, sodium fluoride, sodium oxalate, sodium acetate, sodium formate, sodium citrate, or sodium hydroxide.

12. The preparation method according to claim 1, characterized in that, The transition metal source in step (1) includes any one or a combination of at least two of the following: iron source, vanadium source, titanium source or manganese source.

13. The preparation method according to claim 1, characterized in that, The mixing temperature in step (1) is 20-180℃ and the time is 5-300min.

14. The preparation method according to claim 1, characterized in that, The temperature of the solvothermal reaction in step (1) is 180-300℃ and the time is 5-300min.

15. The preparation method according to claim 1, characterized in that, The method for separating the precursor particles in step (2) includes mixing the reaction liquid with an alcohol solvent, solid-liquid separation, and drying.

16. The preparation method according to any one of claims 1-15, characterized in that, The sintering in step (2) is carried out at a temperature of 300-800℃ for 1-30 hours in a protective gas atmosphere.

17. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) According to the formula, add the polyanion source, sodium source, transition metal source and conductive carbon to the organic solvent, stir at 20-180℃ for 5-300 min, and then solvothermal reaction at 180-300℃ for 5-300 min to obtain the reaction liquid; The organic solvent has a boiling point above 150°C and includes any one or a combination of at least two of aliphatic amines, fatty acids, linear olefins, or phenyl ethers; the aliphatic amine includes oleylamine and / or octadecylamine; the fatty acid includes oleic acid; the linear olefin includes C15-C25 straight-chain olefins; and the phenyl ether includes diphenyl ether. (2) Pour the reaction liquid from step (1) into an alcohol solvent, and after solid-liquid separation and drying, obtain the precursor particles coated with organic solvent. Then, sinter the precursor particles coated with organic solvent in a protective gas at a temperature of 300-800℃ for 1-30h to obtain the polyanionic sodium cathode material.

18. A polyanionic sodium cathode material, characterized in that, The polyanionic sodium cathode material is prepared using the preparation method described in any one of claims 1-17.

19. The polyanionic sodium cathode material according to claim 18, characterized in that, The polyanionic sodium cathode material includes any one of composite sodium iron phosphate, sodium iron sulfate, sodium fluorophosphate, sodium iron phosphate, sodium vanadium phosphate, sodium iron orthosilicate, or sodium iron pentaborate.

20. A sodium-ion battery, characterized in that, The sodium-ion battery includes the polyanionic sodium-ion cathode material as described in claim 18 or 19.

Images