Composite positive electrode material and preparation method thereof, positive plate and sodium ion battery

Abstract

The invention relates to a composite positive electrode material and a preparation method thereof, a positive plate and a sodium ion battery, the preparation method of the composite positive electrode material comprises the following steps: high-valence metal ions are doped in a layered oxide positive electrode material to obtain a first positive electrode material, and the high-valence metal ions are selected from at least one of Ru < 3 + >, Rh < 3 + >, Os < 4 + >, Ir < 4 + >, Ta < 5 + > or Nb < 5 + >; coating the surface of the first positive electrode material with a polyanionic positive electrode material to obtain a second positive electrode material; and sintering the second positive electrode material for 2-10 hours at the temperature of 250-350 DEG C in an oxygen-containing atmosphere to obtain the composite positive electrode material. By using the preparation method disclosed by the invention, the composite positive electrode material with lattice oxygen activation, sodium ion diffusion dynamic performance and structural stability synergistically improved can be obtained, so that the sodium ion battery has high capacity, high magnification and long cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite cathode material and its preparation method, a cathode sheet, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have become a promising electrochemical energy storage technology for large-scale energy storage systems and power batteries due to their advantages such as abundant sodium resources and low raw material costs. However, layered oxides, as commonly used cathode materials for sodium-ion batteries, still have the following core problems in practical industrial applications: (1) Poor structural stability: lattice slip and phase transition are prone to occur during high-rate charging and discharging, leading to capacity decay; (2) Low lattice oxygen utilization: lattice oxygen 2p orbital electrons are localized and cannot effectively participate in redox reactions; (3) Insufficient kinetic performance: sodium ions have high diffusion barriers in two-dimensional interlayers, resulting in severe polarization and limited rate performance. Summary of the Invention

[0003] Based on this, it is necessary to provide a composite cathode material and its preparation method, cathode sheet, and sodium-ion battery to address the above problems. Using the preparation method, a composite cathode material with synergistic improvement in lattice oxygen activation, sodium-ion diffusion kinetics, and structural stability can be obtained, thereby enabling sodium-ion batteries to have high capacity, high rate capability, and long cycle life.

[0004] A method for preparing a composite cathode material includes the following steps:

[0005] A first cathode material is obtained by doping a layered oxide cathode material with high-valence metal ions, wherein the high-valence metal ions are selected from Ru. 3+ ,Rh 3+ Os 4+ Ir 4+ Ta 5+ or Nb 5+ At least one of them;

[0006] A second cathode material is obtained by coating the surface of the first cathode material with a polyanionic cathode material.

[0007] In an oxygen-containing atmosphere, the second cathode material is sintered at a temperature of 250℃-350℃ for 2h-10h to obtain a composite cathode material.

[0008] In one embodiment, the step of doping the high-valence metal ions into the layered oxide cathode material includes: mixing the high-valence metal salt with the layered oxide cathode material, and then ball milling and sintering to obtain a first cathode material.

[0009] In one embodiment, the mass ratio of the high-valence metal salt to the layered oxide cathode material is 1:10 to 1:100;

[0010] And / or, the sintering step is carried out in an oxygen-containing atmosphere, heated to 300℃-800℃ at a heating rate of 1℃ / min-10℃ / min, and held for 1h-5h;

[0011] And / or, the high-valence metal salt is selected from chloride salts;

[0012] And / or, the chemical formula of the layered oxide cathode material is Na f M p O2, wherein M is selected from at least one of Fe, Co, Ni or Mn, 0 <f≤1,0<p≤1。

[0013] In one embodiment, the step of coating the surface of the first cathode material with the polyanionic cathode material includes: mixing the first cathode material with the raw material of the polyanionic cathode material, and then ball milling and sintering to obtain a second cathode material, wherein the raw material of the polyanionic cathode material includes anion source, metal source and sodium source.

[0014] In one embodiment, the mass ratio of the first cathode material to the raw material of the polyanionic cathode material is 1:1-10:1;

[0015] And / or, the sintering step is carried out in an inert atmosphere, heated to 300℃-800℃ at a heating rate of 1℃ / min-10℃ / min, and held for 1h-5h;

[0016] And / or, the anion source is selected from at least one of phosphate, pyrophosphate, sulfate, silicate, and phosphotungstenate;

[0017] And / or, the metal source is selected from at least one of ferric chloride, ferric sulfate, vanadium pentoxide, ammonium metavanadate, manganese sulfate, or manganese chloride;

[0018] And / or, the sodium source is selected from at least one of sodium carbonate and sodium hydroxide;

[0019] And / or, the raw materials of the polyanionic cathode material further include a carbon source, wherein the carbon source is selected from at least one of glucose and sucrose.

[0020] In one embodiment, the composite cathode material includes a layered oxide cathode material doped with high-valence metal ions and a polyanionic cathode material layer coated on the surface of the layered oxide cathode material doped with high-valence metal ions.

[0021] In one embodiment, the molecular formula of the layered oxide cathode material doped with high-valent metal ions is Na x M y A z O2, where M is selected from at least one of Fe, Co, Ni or Mn, and A is selected from Ru 3+ 、Rh 3+ 、Os 4+ 、Ir 4+ 、Ta 5+ or Nb 5+ ; at least one of them, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 0.1, and y and z satisfy the following conditions: when A is selected from Ru 3+ and / or Rh 3+ , y + z = 1; when A is selected from Os 4+ and / or Ir 4+ , y + 3 / 4z = 1; when A is selected from Ta 5+ and / or Nb 5+ , y + 3 / 5z = 1.

[0022] In one embodiment, the polyanionic cathode material layer is selected from at least one of sodium iron phosphate layer, sodium iron pyrophosphate layer or sodium tungstate phosphate layer.

[0023] A cathode sheet includes a current collector and a cathode active material layer disposed on the surface of the current collector, and the active material in the cathode active material layer is selected from the above composite cathode material.

[0024] A sodium ion battery uses the above cathode sheet.

[0025] In the present invention, first, metal ions with high catalytic activity and high valence states are introduced into the layered oxide cathode material, which can form a stable doping structure. These metal ions can have a strong interaction with lattice oxygen, regulate the electronic structure of lattice oxygen, promote the electrochemical activation of lattice oxygen, and at the same time, using excellent electronic regulation ability, further optimize the electronic conductivity and ion diffusion ability of the material; second, through in-situ coating technology, a polyanionic cathode material with a three-dimensional structure is coated on the surface of the first cathode material, which can improve the structural stability of the composite cathode material and further promote the role of sodium ion transport; third, by further sintering, a small amount of sodium in the lattice can be removed, reducing the initial sodium content in the composite cathode material, thereby increasing the bonding ratio of oxygen and other metals, and further enhancing the synergistic effect of oxygen and high-valent metals. Therefore, using the preparation method, a composite cathode material with synergistically improved lattice oxygen activation, sodium ion diffusion kinetics performance and structural stability can be obtained. Furthermore, when the composite cathode material is applied to a sodium ion battery, the sodium ion battery can have high capacity, high rate and long cycle life. Detailed Implementation

[0026] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0028] The method for preparing the composite cathode material provided by this invention includes the following steps:

[0029] S1, doping a high-valence metal ion into a layered oxide cathode material yields a first cathode material, wherein the high-valence metal ion is selected from Ru. 3+ ,Rh 3+ Os 4+ Ir 4+ Ta 5+ or Nb 5+ At least one of them;

[0030] S2, a polyanionic cathode material is coated on the surface of the first cathode material to obtain a second cathode material;

[0031] S3, In an oxygen-containing atmosphere, the second cathode material is sintered at a temperature of 250℃-350℃ for 2h-10h to obtain a composite cathode material.

[0032] In step S1, metal ions with high catalytic activity and high valence state are introduced into the layered oxide cathode material to form a stable doped structure. These metal ions can interact strongly with lattice oxygen, regulate the electronic structure of lattice oxygen, and promote the electrochemical activation of lattice oxygen. At the same time, the excellent electronic regulation capability is used to further optimize the electronic conductivity and ion diffusion capability of the material.

[0033] Specifically, these high-valence metal ions have high electronegativity and empty d orbitals, which can form strong covalent bonds (σ / π bonds) with the 2p orbitals of lattice oxygen. This can pull down the 2p orbitals of lattice oxygen, weaken the electronic localization of lattice oxygen, and thus activate the redox activity of lattice oxygen.

[0034] There are many ways to dop high-valence metal ions into layered oxide cathode materials. The present invention preferably uses a solid-state method to dop high-valence metal ions into layered oxide cathode materials. The steps include: mixing high-valence metal salts with the layered oxide cathode material, and then ball milling and sintering to obtain a first cathode material.

[0035] Optionally, when the high-valence metal salt is mixed with the layered oxide cathode material, the mass ratio is preferably 1:10 to 1:100, and can be selected from any value among 1:30, 1:60, 1:90, or 1:100, or any range between two. This mass ratio range ensures a sufficient high-valence metal-O network, thereby ensuring adequate lattice oxygen activation. Simultaneously, this ratio range also avoids excessive lattice distortion and crystal structure destruction caused by excessively high doping ratios, ensuring structural stability.

[0036] This invention does not impose any requirements on the selection of layered oxide cathode materials; for example, the chemical formula of the layered oxide cathode material is Na. f M p O2, wherein M is selected from at least one of Fe, Co, Ni or Mn, 0 <f≤1,0<p≤1。

[0037] Optionally, the high-valence metal salt is preferably a chloride salt with a low melting point, such as at least one of ruthenium trichloride, rhodium trichloride, osmium tetrachloride, iridium tetrachloride, tantalum pentachloride, or niobium tetrachloride, so as to better achieve the doping of high-valence metal ions.

[0038] Optionally, the sintering step is carried out in an oxygen-containing atmosphere, preferably in air. During sintering, the heating rate is preferably 1℃ / min-10℃ / min, which can be any value of 1℃ / min, 5℃ / min, or 10℃ / min, or any range between two values. The sintering temperature is preferably 300℃-800℃, which can be any value of 300℃, 600℃, or 800℃, or any range between two values. The sintering holding time is preferably 1h-5h, which can be any value of 1h, 3h, or 5h, or any range between two values. In this way, high-valence metal ions can be effectively doped into the layered oxide cathode material.

[0039] In step S2, an in-situ coating technique is used to coat the surface of the first cathode material with a polyanionic cathode material with a three-dimensional structure. This not only suppresses the phase transition of the layered oxide cathode material and improves the structural stability of the composite cathode material, but also allows the three-dimensional polyanionic cathode material to act as a sodium ion diffusion channel, further promoting sodium ion transport and reducing the sodium ion diffusion barrier.

[0040] There are many ways to coat the surface of the first cathode material with the polyanionic cathode material, and the present invention does not limit this. The present invention preferably mixes the first cathode material with the raw materials of the polyanionic cathode material, and then performs ball milling and sintering to obtain the second cathode material, wherein the raw materials of the polyanionic cathode material include anion source, metal source and sodium source.

[0041] Optionally, when mixing the raw materials of the first positive electrode material and the polyanionic positive electrode material, the mass ratio is preferably 1:1 to 10:1, and can be any value of 1:1, 5:1 or 10:1 or any range between the two, so as to ensure that the polyanionic positive electrode material layer is completely coated.

[0042] Optionally, the anion source is selected from at least one of phosphates, pyrophosphates, sulfates, silicates, and phosphotungstates, such as phosphoric acid, dihydrogen phosphate, hydrogen phosphate, pyrophosphate, dihydrogen pyrophosphate, hydrogen pyrophosphate, sulfuric acid, hydrogen sulfate, silicic acid, phosphotungstic acid, etc.; the metal source is selected from at least one of iron salts, vanadium salts, or manganese salts, such as ferric chloride, ferric sulfate, vanadium pentoxide, ammonium metavanadate, manganese sulfate, or manganese chloride; and the sodium source is selected from at least one of sodium carbonate and sodium hydroxide.

[0043] To improve the conductivity of the composite cathode material, a carbon source is added to the raw material of the polyanionic cathode material during in-situ coating. The carbon source can be selected from at least one of glucose or sucrose.

[0044] Optionally, the sintering step is carried out in an inert atmosphere, preferably in an atmosphere such as nitrogen or argon. During sintering, the heating rate is preferably 1℃ / min-10℃ / min, which can be any value of 1℃ / min, 5℃ / min, or 10℃ / min, or any range between two values. The sintering temperature is preferably 300℃-800℃, which can be any value of 300℃, 600℃, or 800℃, or any range between two values. The sintering holding time is preferably 1h-5h, which can be any value of 1h, 3h, or 5h, or any range between two values. This allows for a better formation of a three-dimensional network of polyanionic cathode material coating layer.

[0045] In step S3, further sintering of the second cathode material allows for the controlled volatilization of sodium ions, removing a small amount of sodium from the crystal lattice and reducing the initial sodium content in the composite cathode material. This reduces the bonding between sodium ions and lattice oxygen, increases the bonding ratio between lattice oxygen and other metals, and further weakens the electron localization of lattice oxygen, activating its redox activity. Simultaneously, the covalent bonds formed between the metal and lattice oxygen improve the stability of the lattice oxygen in the composite cathode material.

[0046] Optionally, the oxygen-containing atmosphere during sintering is preferably air. The sintering temperature can be any value among 250 °C, 300 °C, or 350 °C or a range value between any two of them, and the sintering time can be any value among 2 h, 5 h, or 10 h or a range value between any two of them.

[0047] In addition, in order to make the particle size of the composite cathode material more uniform, after sintering the second cathode material, ball milling and sieving treatments can be carried out in sequence, and the sieve mesh is preferably 400 mesh.

[0048] Therefore, using the preparation method described in the present invention, a composite cathode material with synergistically improved lattice oxygen activation, sodium ion diffusion kinetics performance, and structural stability can be obtained. Furthermore, when the composite cathode material is applied to a sodium-ion battery, the sodium-ion battery can have high capacity, high rate performance, and long cycle life.

[0049] Based on this, the present invention also provides a composite cathode material prepared by using the preparation method of the above composite cathode material. The composite cathode material includes a layered oxide cathode material doped with a high-valent metal ion and a polyanionic cathode material layer coated on the surface of the layered oxide cathode material doped with the high-valent metal ion.

[0050] Optionally, the molecular formula of the layered oxide cathode material doped with a high-valent metal ion is Na x M y A z O2, where M is selected from at least one of Fe, Co, Ni, or Mn, and A is selected from at least one of Ru 3+ 、Rh 3+ 、Os 4+ 、Ir 4+ 、Ta 5+ 或Nb 5+ ,0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 0.1. At the same time, y and z satisfy the following conditions: when A is selected from Ru 3+ 和 / 或Rh 3+ 时,y + z = 1;当A选自Os 4+ 和 / 或Ir 4+ 时,y + 3 / 4z = 1;当A选自Ta 5+ 和 / 或Nb 5+ 时,y + 3 / 5z = 1.

[0051] Optionally, the polyanionic cathode material layer is selected from at least one of a sodium iron phosphate layer, a sodium iron pyrophosphate layer, or a sodium tungstate phosphate layer.

[0052] The present invention also provides a positive electrode sheet, which includes a current collector and a positive electrode active material layer disposed on the surface of the current collector. The active material in the positive electrode active material layer is selected from the above composite cathode material.

[0053] It is understood that the positive electrode active material layer also includes binders and conductive agents. The selection of conductive agents and binders in this invention does not have special requirements; conventional selection and control are sufficient. For example, the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), or sodium carboxymethyl cellulose (CMC), and the conductive agent is selected from at least one of carbon nanotubes (CNT), conductive carbon black (SP), acetylene black, Ketjen black, or conductive graphite. Further details are omitted here.

[0054] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery uses the above-described positive electrode sheet.

[0055] It is understood that sodium-ion batteries also include negative electrode sheets, separators, and electrolytes. This invention does not have special requirements for the negative electrode sheets, separators, and electrolytes of sodium-ion batteries; conventional designs are sufficient. For example, the active material of the negative electrode sheet is selected from hard carbon materials, soft carbon materials, graphite, etc.; the conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite, etc.; the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc.; the separator is selected from polypropylene separators (PP), polyimide separators (PI), polyethylene separators (PE), ceramic-coated separators, etc.; the electrolyte contains sodium salts and organic solvents, wherein the sodium salt is selected from NaPF6, etc., and the organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), etc., which will not be elaborated further in this invention.

[0056] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0057] Example 1

[0058] IrCl4 and NaMn 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:100, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, and sintered for 2 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.596 Ni 0.398 Ir 0.008O2. Ammonium dihydrogen phosphate (NH4H2PO4), ferrous sulfate (FeSO4), and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% sucrose (by mass of the precursor) was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600℃ at a rate of 5℃ / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350℃ for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0059] The composite cathode material, Super P, MWCNT, and PVDF prepared above were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated electrode sheet was then rolled, slit, and sheeted to obtain the cathode sheet.

[0060] Hard carbon material, Super P, and CMC are mixed in a mass ratio of 97:1.5:1.5 to form a negative electrode slurry. Then, the negative electrode slurry is uniformly coated onto copper foil using a coating machine, and the coated electrode is rolled, slit, and sheeted to obtain the negative electrode sheet.

[0061] A ceramic-coated diaphragm was obtained by coating a 3μm thick Al2O3@BN composite ceramic coating on a 9μm thick PE base film, wherein the mass fraction of BN in the composite ceramic coating was 30wt%.

[0062] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6. Then, 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. The concentration of sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was 12 mS / cm (25℃).

[0063] The battery adopts a full tab design, with positive electrode, negative electrode and separator stacked alternately in the order of "positive electrode-separator-negative electrode" and wound into a bare cell; after flattening and shaping the end face, the current collector end face is laser welded to bring out the full tab; then it is put into the casing, injected with electrolyte and sealed, and finally made into a 32700 cylindrical battery.

[0064] Example 2

[0065] The only difference between Example 2 and Example 1 is that RuCl3 and NaMn are used. 0.6 Ni 0.4O2 was mixed at a mass ratio of 1:10, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 650 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.57 Ni 0.38 Ru 0.05 O2. Phosphoric acid, ammonium metavanadate, and sodium hydroxide were uniformly mixed in a molar ratio of 1:1:1 as a precursor. 10% (by weight of the precursor) of sucrose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 700°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 300°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0066] Example 3

[0067] The only difference between Example 3 and Example 1 is that RhCl3 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.588 Ni 0.392 Rh 0.02 O2. Phosphotungstic acid, manganese chloride, and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% (by weight of the precursor) of sucrose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 250°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0068] Example 4

[0069] The only difference between Example 4 and Example 1 is that OsCl4 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 700 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.591 Ni0.394 Os 0.02 O2. Ammonium dihydrogen pyrophosphate, manganese sulfate, and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0070] Example 5

[0071] The only difference between Example 5 and Example 1 is that TaCl5 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:50, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.596 Ni 0.398 Ta 0.01 O2. Pyrophosphate, vanadium pentoxide, and sodium carbonate were uniformly mixed in a molar ratio of 2:1:1 as a precursor. 10% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350°C for 5 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0072] Example 6

[0073] The only difference between Example 6 and Example 1 is that NbCl5 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 600 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.593 Ni 0.395 Ta 0.02O2. Ammonium bisulfate, vanadium pentoxide, and sodium carbonate were uniformly mixed in a molar ratio of 2:1:1 as a precursor. 5% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 300°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0074] Comparative Example 1

[0075] The only difference between Comparative Example 1 and Example 1 is that AlCl3 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 700 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.588 Ni 0.392 Al 0.02 O2. Ammonium dihydrogen pyrophosphate, manganese sulfate, and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0076] Comparative Example 2

[0077] The only difference between Comparative Example 2 and Example 1 is that TiCl4 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 700 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.592 Ni 0.394 Ti 0.02O2. Ammonium dihydrogen pyrophosphate, manganese sulfate, and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0078] Comparative Example 3

[0079] The only difference between Comparative Example 3 and Example 1 is that VCl5 and NaMn are used. 0.6 Ni 0.4 O2 was mixed at a mass ratio of 1:20, and 20 ml of anhydrous ethanol was added dropwise. The mixture was ball-milled at 500 r / min for 2 h. Then, in an air atmosphere, the temperature was increased to 700 °C at a rate of 5 °C / min, and sintered for 5 h to obtain the first cathode material. The molecular formula of the first cathode material is NaMn. 0.594 Ni 0.396 V 0.02 O2. Ammonium dihydrogen pyrophosphate, manganese sulfate, and sodium carbonate were uniformly mixed in a molar ratio of 2:2:1 as a precursor. 5% (by weight of the precursor) of glucose was added, along with the first cathode material at a mass ratio of 4:1 to the precursor. The mixture was ball-milled at 500 rpm for 2 hours. Then, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 5°C / min, and sintered for 5 hours to obtain the second cathode material. The second cathode material was then sintered at 350°C for 2 hours in an air atmosphere. After cooling, it was ball-milled through a 400-mesh sieve to obtain the composite cathode material.

[0080] Comparative Example 4

[0081] The only difference between Comparative Example 4 and Example 1 is that the second cathode material is directly ball-milled through a 400-mesh sieve without undergoing a sintering step to obtain the composite cathode material.

[0082] Comparative Example 5

[0083] The only difference between Comparative Example 5 and Example 1 is that the second cathode material was sintered at 200°C for 5 hours in an air atmosphere, and after cooling, it was ball-milled through a 400-mesh sieve to obtain a composite cathode material.

[0084] Comparative Example 6

[0085] The only difference between Comparative Example 6 and Example 1 is that the second cathode material was sintered at 500°C for 2 hours in an air atmosphere, and after cooling, it was ball-milled through a 400-mesh sieve to obtain a composite cathode material.

[0086] The performance of sodium-ion batteries from Examples 1-6 and Comparative Examples 1-6 was tested, and the results are shown in Tables 1 and 2.

[0087] Table 1

[0088]

[0089] Table 2

[0090]

[0091] 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.

[0092] The embodiments described above are merely illustrative of several implementations of the present invention, 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 the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a composite cathode material, characterized in that, Includes the following steps: A first cathode material is obtained by doping a layered oxide cathode material with high-valence metal ions, wherein the high-valence metal ions are selected from Ru. 3+ ,Rh 3+ Os 4+ Ir 4+ Ta 5+ or Nb 5+ At least one of them; A second cathode material is obtained by coating the surface of the first cathode material with a polyanionic cathode material. In an oxygen-containing atmosphere, the second cathode material is sintered at a temperature of 250℃-350℃ for 2h-10h to obtain a composite cathode material.

2. The method for preparing the composite cathode material according to claim 1, characterized in that, The step of doping the high-valence metal ions into the layered oxide cathode material includes: mixing the high-valence metal salt with the layered oxide cathode material, and then ball milling and sintering to obtain a first cathode material.

3. The method for preparing the composite cathode material according to claim 2, characterized in that, The mass ratio of the high-valence metal salt to the layered oxide cathode material is 1:10-1:100; And / or, the sintering step is carried out in an oxygen-containing atmosphere, heated to 300℃-800℃ at a heating rate of 1℃ / min-10℃ / min, and held for 1h-5h; And / or, the high-valence metal salt is selected from chloride salts; And / or, the chemical formula of the layered oxide cathode material is Na f M p O2, wherein M is selected from at least one of Fe, Co, Ni or Mn, 0 <f≤1,0<p≤1。 4. The method for preparing the composite cathode material according to claim 1, characterized in that, The step of coating the surface of the first cathode material with the polyanionic cathode material includes: mixing the first cathode material with the raw materials of the polyanionic cathode material, and then ball milling and sintering to obtain the second cathode material, wherein the raw materials of the polyanionic cathode material include anion source, metal source and sodium source.

5. The method for preparing the composite cathode material according to claim 4, characterized in that, The mass ratio of the raw materials of the first positive electrode material to the polyanionic positive electrode material is 1:1-10:1; And / or, the sintering step is carried out in an inert atmosphere, heated to 300℃-800℃ at a heating rate of 1℃ / min-10℃ / min, and held for 1h-5h; And / or, the anion source is selected from at least one of phosphate, pyrophosphate, sulfate, silicate, and phosphotungstenate; And / or, the metal source is selected from at least one of ferric chloride, ferric sulfate, vanadium pentoxide, ammonium metavanadate, manganese sulfate, or manganese chloride; And / or, the sodium source is selected from at least one of sodium carbonate and sodium hydroxide; And / or, the raw materials of the polyanionic cathode material further include a carbon source, wherein the carbon source is selected from at least one of glucose and sucrose.

6. A composite cathode material prepared using the method for preparing the composite cathode material according to any one of claims 1-5, characterized in that, The composite cathode material includes a layered oxide cathode material doped with high-valence metal ions and a polyanionic cathode material layer coated on the surface of the layered oxide cathode material doped with high-valence metal ions.

7. The composite cathode material according to claim 6, characterized in that, The molecular formula of the high-valent metal ion-doped layered oxide cathode material is Na x M y A z O2, where M is selected from at least one of Fe, Co, Ni or Mn, and A is selected from Ru 3+ 、Rh 3+ 、Os 4+ 、Ir 4+ 、Ta 5+ or Nb 5+ at least one of them, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 0.1, and y and z satisfy the following conditions: when A is selected from Ru 3+ and / or Rh 3+ , y + z = 1; when A is selected from Os 4+ and / or Ir 4+ , y + 3 / 4z = 1; when A is selected from Ta 5+ and / or Nb 5+ , y + 3 / 5z = 1.

8. The composite cathode material according to claim 6, characterized in that, The polyanionic cathode material layer is selected from at least one of sodium iron phosphate layer, sodium iron pyrophosphate layer, or sodium phosphotungstenate layer.

9. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode active material layer disposed on the surface of the current collector, wherein the active material in the positive electrode active material layer is selected from the composite positive electrode material according to any one of claims 6-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery uses the positive electrode as described in claim 9.

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