A tungsten-doped composite positive electrode material, a positive electrode sheet, a sodium-ion battery and an electric device

Abstract

The application provides a tungsten-doped composite positive electrode material, a positive electrode sheet, a sodium ion battery and an electric device, and relates to the technical field of batteries.The particle structure of the composite positive electrode material is a core-shell structure, which comprises an inner core of layered oxide secondary particles with a material of O3 phase and an outer shell layer of sodium iron pyrophosphate crystal material coated on the surface of the inner core; and the interface between the inner core layer and the outer shell layer is enriched with tungsten elements.The composite positive electrode material provided by the application forms a tungsten element enrichment area on the interface between the core and the shell, forms a Ni-O-W-P charge bridge on the core-shell interface, can reduce the charge transfer resistance of the composite positive electrode material, is beneficial to the optimization of the fast charging performance of the battery, and provides material support for the wide application of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a tungsten-doped composite cathode material, cathode sheet, sodium-ion battery, and electrical equipment. Background Technology

[0002] Sodium is abundant and widely distributed, and compared to lithium-ion batteries, it is less prone to combustion and explosion, offering superior safety. Therefore, sodium-ion batteries have become a current research hotspot. With the increasing demand and higher requirements for batteries, fast charging performance has also become one of the key performance indicators for sodium-ion batteries.

[0003] Fast charging of sodium-ion batteries requires the rapid and reversible insertion of sodium ions into the lattice of the cathode material within a short period. This necessitates that the cathode material possess a good ion diffusion rate and low charge transfer resistance. However, fast-charging sodium-ion batteries require higher overpotentials and currents, increasing the risks of sodium deposition, sodium dendrite formation, and rapid deterioration of cycle performance. Therefore, compared to slow-charging sodium-ion batteries, fast-charging sodium-ion batteries place higher demands on the charge transfer resistance of the cathode material. Summary of the Invention

[0004] The purpose of this application is to provide a tungsten-doped composite cathode material, cathode sheet, battery and electrical device, wherein the tungsten-doped composite cathode material can significantly reduce the charge transfer resistance of the cathode material.

[0005] One of the purposes of this application is to provide a positive electrode.

[0006] Another objective of this application is to provide a sodium-ion battery.

[0007] One of the purposes of this application is to provide an electrical appliance.

[0008] In the first aspect, in order to solve the above problems, this application provides a tungsten-doped composite cathode material. The particle structure of the composite cathode material is a core-shell structure, including a core of layered oxide secondary particles of nickel O3 phase and an outer shell layer of sodium iron pyrophosphate crystals covering the surface of the core.

[0009] The interface between the core layer and the outer shell layer is enriched with tungsten.

[0010] Furthermore, in some embodiments of this application, the amount of tungsten doped in the composite cathode material is 0.5-2.0 wt%.

[0011] Furthermore, in some embodiments of this application, the tungsten element is doped into the core and / or the outer shell layer.

[0012] Furthermore, in some embodiments of this application, the tungsten element is incorporated into the composite cathode material as hexavalent tungsten ions.

[0013] Furthermore, in some embodiments of this application, the sodium iron pyrophosphate crystal is a whisker-shaped sodium iron pyrophosphate crystal.

[0014] Furthermore, in some embodiments of this application, the sodium iron pyrophosphate is partially intercalated into the core.

[0015] Furthermore, in some embodiments of this application, the charge transfer resistance of the composite cathode material is ≤46Ω / cm in an electrochemical impedance spectroscopy test at 25°C. 2 .

[0016] Furthermore, in some embodiments of this application, the exothermic peak of the composite cathode material in DSC testing is between 250-310°C.

[0017] Furthermore, in some embodiments of this application, the core has a size of 5-20 μm; the outer shell has a thickness of 200 nm-1 μm.

[0018] Furthermore, in some embodiments of this application, the chemical structural formula of the layered oxide is: Na x Ni y Fe z Mn a M (1-y-z-a) W b O2;

[0019] Where x ranges from 0.9 to 1; y ranges from 0.1 to 0.5; z ranges from 0.1 to 0.5; and a ranges from 0.1 to 0.5.

[0020] M is selected from at least one of titanium, copper, cerium, magnesium, aluminum, calcium, vanadium, and zinc.

[0021] Secondly, this application also provides a positive electrode sheet, comprising the tungsten-doped composite positive electrode material described in the first aspect.

[0022] Thirdly, this application also provides a sodium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator; the separator and the electrolyte are disposed between the positive electrode and the negative electrode.

[0023] The positive electrode is the positive electrode described in the second aspect.

[0024] Fourthly, this application also provides a battery module, including the sodium-ion battery described in the third aspect or including the positive electrode sheet described in the second aspect or the tungsten-doped composite positive electrode material described in the first aspect.

[0025] This application provides a tungsten-doped composite cathode material. The tungsten-doped composite cathode material has doped tungsten elements at the interface between the core and the outer shell, forming a Ni-OWP charge bridge with the layered oxide of the core and sodium iron pyrophosphate in the outer shell. This reduces the charge transfer resistance between the core and the outer shell, thereby reducing the charge transfer resistance of the cathode material. The charge transfer resistance of the composite cathode material provided in this application is reduced to 46 Ω / cm. 2 the following. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a scanning electron microscope image of the tungsten-doped composite cathode material provided in Example 1 of this application;

[0028] Figure 2 This is a partial distribution diagram of elements in the tungsten-doped composite cathode material provided in Example 1 of this application;

[0029] Figure 3 This is a DSC-TG curve of the tungsten-doped composite cathode material provided in Example 1 of this application. Detailed Implementation

[0030] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0032] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0033] The main factors affecting the charging rate of sodium-ion batteries include the ion diffusion rate and charge transfer resistance of the cathode material used. As the potential increases, the charge transfer resistance has a greater impact on the battery's fast-charging performance. Furthermore, to achieve fast charging, higher voltage and current chargers are used in sodium-ion battery charging. Therefore, reducing the charge transfer resistance of the cathode material has become one of the key challenges in the development of fast-charging sodium-ion batteries. In addition, as the potential and current increase, the cathode material is prone to polarization during charging, placing higher demands on its lattice stability. Because sodium ions have a large ionic radius, the cathode material is prone to expansion during sodium ion insertion and extraction, thus affecting its stability. The high voltage and high current of fast charging further exacerbate this defect. Therefore, fast-charging sodium-ion batteries place higher demands on the high-voltage cycle stability and charge transfer resistance of the cathode material. Based on this, this application provides a tungsten-doped composite cathode material. This composite cathode material uses a layered oxide of O3 phase coated with sodium iron pyrophosphate to suppress lattice distortion and stress changes during sodium ion insertion and extraction. Simultaneously, tungsten is doped into this composite cathode material to form a Ni-OWP charge bridge at the interface between the core and outer shell. This not only further improves the high-voltage stability of the composite cathode material but also reduces its interfacial impedance, resulting in superior high-potential cycle stability and charge transfer resistance, thus improving the battery's fast-charging performance. Specifically, the composite cathode material provided in this application has a core-shell structure, comprising a core of secondary particles of layered oxide containing nickel O3 phase and an outer shell of sodium iron pyrophosphate crystals coating the surface of the core.

[0034] The interface between the core layer and the outer shell layer is enriched with tungsten.

[0035] It should be noted that the "secondary particles" in this application refer to polycrystalline particles, that is, polycrystalline materials in the cathode material provided in this application whose core is an O3 phase layered oxide, with crystal interfaces between the individual crystals. The outer shell layer is a continuous or discontinuous outer shell layer grown on the surface of the core. It is preferably a continuous outer shell layer. It should be noted that the continuous outer shell layer mentioned in this application means that the sodium iron pyrophosphate crystal particles in the layered structure formed by the outer shell layer material are not distributed in an island-like manner, but rather form a network shell, an interconnected sheet-like shell, or a complete sphere or spheroidal shell.

[0036] It should be noted that, in this application, "at the interface between the core layer and the outer shell layer" refers to the surface where the secondary particles of the O3 phase layered oxide come into contact with or are near the contact of the sodium iron pyrophosphate crystal. When the sodium iron pyrophosphate crystal is partially embedded between the crystal interfaces of the secondary particles of the O3 phase layered oxide, "at the interface between the core layer and the outer shell layer" in this application also includes the surface where the embedded sodium iron pyrophosphate crystal contacts the crystal of the secondary particles of the O3 phase layered oxide and its vicinity.

[0037] Furthermore, the layered oxide containing nickel O3 phase in this application refers to the chemical structure with the general formula Na. α Ni β X γ O2 is a layered oxide of the O3 phase, wherein α ranges from 0.5 to 1; β ranges from 0.2 to 0.8; and γ ranges from 0.2 to 0.8. Other metallic elements X include iron, manganese, and may also include one or more of titanium, copper, cerium, magnesium, aluminum, calcium, vanadium, and zinc.

[0038] Preferably, the chemical structural formula of the layered oxide is: Na x Ni y Fe z Mn a M (1-y-z-a) W b O2; where x ranges from 0.95 to 1; y ranges from 0.3 to 0.34; z ranges from 0.3 to 0.34; a ranges from 0.3 to 0.34; and b ranges from 0.005 to 0.02.

[0039] In this application, the doped tungsten element is present at the interface between the core and the outer shell layer, and may also be present in the core and / or the existing outer shell layer. Preferably, the doped tungsten element is enriched at the interface between the core and the outer shell layer, forming a large number of Ni-OWP charge bridges at the interface, which can better reduce the interface resistance. In other embodiments, the elemental concentration of the doped tungsten element decreases sequentially from the interface between the core and the outer shell layer towards the core and / or the outer shell layer.

[0040] The tungsten element is doped in the composite cathode material at a concentration of 0.5-2.0 wt%. For example, the tungsten element doping concentration in the composite cathode material can be any value within the range of 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%. Preferably, the tungsten element doping concentration in the composite cathode material is 1-1.5 wt%. The tungsten element doping concentration should not be too high or too low. Excessive tungsten element doping concentration will adversely affect the charge / discharge capacity of the cathode material; while excessively low tungsten element doping concentration will not significantly reduce the interface resistance.

[0041] It should be noted that the tungsten doping in the composite cathode material provided in this application can not only reduce the interfacial resistance of the cathode material, but also further improve the cycle stability of the cathode material, especially the high-potential cycle stability.

[0042] In this application, the tungsten element is incorporated into the composite cathode material as hexavalent tungsten ions.

[0043] The composite cathode material provided in this application exhibits a charge transfer resistance ≤46Ω / cm in electrochemical impedance spectroscopy testing at 25°C. 2 .

[0044] In other embodiments, the sodium iron phosphate pyrophosphate crystals in the outer shell layer of this application have a size of 2-20 nm in at least one dimension; and the sodium iron phosphate pyrophosphate crystals have a size of 500 nm-1 μm in at least one dimension, so that the sodium iron phosphate phosphate crystals can be inserted into the grain boundaries of the core, which can reduce the lattice distortion of the layered oxide, absorb the stress changes during the lattice distortion process, improve the cycle stability of the composite cathode material, and suppress the polarization of the composite cathode material at high potentials.

[0045] Specifically, the structure of the sodium iron pyrophosphate crystals in the composite cathode material provided in this application is sodium iron pyrophosphate whiskers, needle-shaped sodium iron pyrophosphate crystals, or plate-shaped sodium iron pyrophosphate crystals.

[0046] In this application, sodium iron pyrophosphate whiskers or needle-like sodium iron pyrophosphate crystals refer to structures in which the length of the sodium iron pyrophosphate crystal is much larger than its width and height, such as rod-shaped, needle-shaped, or whisker-shaped sodium iron pyrophosphate crystals with an aspect ratio of not less than 10; in this application, plate-like sodium iron pyrophosphate crystals refer to structures in which the thickness of the sodium iron pyrophosphate crystal is much smaller than its length and width, such as plate-like sodium iron pyrophosphate crystals with a thickness-to-length and width ratio of not less than 8.

[0047] Preferably, the sodium iron pyrophosphate crystals in the cathode material provided in this application are sodium iron pyrophosphate whiskers.

[0048] Sodium iron pyrophosphate whiskers, needle-like sodium iron pyrophosphate crystals, or plate-like sodium iron pyrophosphate crystals, especially sodium iron pyrophosphate whiskers, can better improve the high-potential cycling stability of composite cathode materials. The possible reason is that when needle-like, plate-like, or whisker-like sodium iron pyrophosphate crystals grow on the surface of a polycrystalline core, some of the crystals intrude into the layers of the layered oxide crystals, forming an intercalation structure. This not only suppresses the lattice distortion of the O3 phase layered oxide but also forms three-dimensional ion channels embedded in the core. Simultaneously, sodium iron pyrophosphate can preferentially adsorb Na⁺ in the high-voltage region (>3.8V), reducing the lattice strain of the O3 phase, thereby improving the cycling performance of the cathode material, especially in the high-voltage region (>3.8V). Furthermore, the applicant has found that the composite cathode material provided in this application also possesses excellent rate performance and charge / discharge capacity, especially at high potentials, exhibiting performance close to the full-potential capacity.

[0049] In some embodiments, the core has a size of 5-20 μm; the outer shell has a thickness of 200 nm-1 μm.

[0050] In some embodiments, the sodium iron pyrophosphate crystals are needle-like structures with an aspect ratio of 5-50; or

[0051] The sodium iron pyrophosphate crystals are plate-like structures with a thickness of 2-20 nm; or

[0052] The sodium iron pyrophosphate crystals have a whisker-like structure with an aspect ratio of 5-50.

[0053] In some embodiments, the sodium iron pyrophosphate phosphate accounts for 1%-20% of the content of the cathode material by mass fraction, preferably 3%-5%.

[0054] The chemical structural formula of sodium iron pyrophosphate used in this application is: Na4Fe(PO4)2(P2O7).

[0055] In some embodiments, the exothermic peak of the composite cathode material in the DSC test is between 280-310℃, indicating that the composite cathode material provided in this application has good thermal stability, which is beneficial to improving the safety performance of the battery.

[0056] To enable those skilled in the art to better implement this solution, this application also provides a method for preparing this tungsten-doped composite cathode material, including the following steps:

[0057] (1) Preparation of layered oxide precursors

[0058] Sodium, iron, nickel, manganese and tungsten sources are provided in a molar ratio of 1:0.33:0.33:0.33:0.01. The core raw material is mixed with the first solution and dispersion, and the Zeta potential is adjusted to above +35mV by adding the dispersion. The mixture is then ground and spray-dried to obtain layered oxide precursor particles.

[0059] (2) Preparation of sodium iron pyrophosphate precursor

[0060] The outer shell material is provided in a molar ratio of sodium source, iron source and phosphorus source of 4:3:4. The outer shell material and the second solution are stirred in a water bath at 40~90℃ for 4~48h to obtain a transparent sol-like sodium iron pyrophosphate precursor.

[0061] (3) The sodium iron pyrophosphate precursor and the layered oxide precursor particles are mixed at a mass ratio of 1:1.1~20 and ultrasonically dispersed for 2~8h. The mixture is then concentrated at 40~60℃ until the sodium iron pyrophosphate precursor increases in weight by 5-8%, so that the sodium iron pyrophosphate precursor is uniformly attached to the surface of the layered oxide precursor particles to obtain the composite material.

[0062] (4) Sintering

[0063] The composite material is vacuum dried for 8-24 hours, heated to 400-450℃ in the first sintering atmosphere, and sintered at that temperature for 4-8 hours. Then, the sintering atmosphere is adjusted to the second sintering atmosphere, and sintered at 500-700℃ for 4-8 hours, followed by annealing at 200-400℃ for 2-4 hours to obtain the cathode material of this application.

[0064] In step (1), the sodium source can be at least one of sodium carbonate, sodium hydroxide, and sodium dihydrogen phosphate. The iron source in step (1) can be at least one of ferric nitrate, ferric oxide, ferric phosphate, ferrous sulfate, ferrous oxalate dihydrate, and elemental iron. The nickel source in step (1) can be at least one of nickel hydroxide, nickel nitrate, and nickel sulfate. The manganese source in step (1) can be at least one of manganese oxide, manganese trioxide, manganese hydroxide, and manganese sulfate. The tungsten source in step (1) can be ammonium metatungstate, sodium tungstate, ammonium tungstate, tungsten acetate, and tungsten trioxide. The dopant in step (1) can be at least one of copper, vanadium, titanium, and aluminum. The first solution can be at least one of deionized water, ethylene glycol, N-methylpyrrolidone, and ethanol. The dispersion can be at least one of polyacrylic acid, ethylene glycol, and polyvinyl alcohol.

[0065] In step (2), the sodium source can be at least one of sodium carbonate, sodium hydroxide, and sodium dihydrogen phosphate. The iron source in step (2) can be at least one of ferric nitrate, ferric oxide, ferric phosphate, ferrous sulfate, ferrous oxalate dihydrate, and elemental iron. The second solution can be at least one of deionized water, ethylene glycol, N-methylpyrrolidone, and ethanol.

[0066] The first sintering atmosphere is a protective gas environment or a protective gas environment containing oxygen, preferably a 91.5~95% N2 + 5~8.5% O2 atmosphere; the second sintering atmosphere is a protective gas environment such as nitrogen, argon, helium, or a protective gas environment containing carbon dioxide and water vapor. Preferably, it is an N2 + 3~5% CO2 + 1~3% H2O atmosphere.

[0067] Preferably, the sodium source in step (1) can be the same as that in step (2) to reduce the introduction of more impurities.

[0068] Secondly, this application also provides a positive electrode sheet, comprising the positive electrode material described in the first aspect.

[0069] Thirdly, this application also provides a sodium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator; the separator and the electrolyte are disposed between the positive electrode and the negative electrode; the positive electrode is the positive electrode described in the second aspect.

[0070] The electrolyte can be a liquid electrolyte, a solid electrolyte, or other electrolytes. The separator can be a polymer separator or a polymer separator with a ceramic coating. The negative electrode may include a current collector and a coating applied to the surface of the current collector. The current collector may include a metal foil, such as aluminum foil or copper foil. The coating may include a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active material may be a carbon material or other material capable of sodium ion insertion / extraction. Similarly, the positive electrode may also include a current collector and a coating applied to the surface of the current collector. The coating may include the aforementioned positive electrode material and a binder.

[0071] Fourthly, this application also provides a battery device, including the sodium-ion battery described in the third aspect or including the positive electrode sheet described in the second aspect or the positive electrode material described in the first aspect.

[0072] The electrical device provided in this application includes a battery module composed of multiple batteries, used to provide power to the device. Exemplary examples of the electrical device include mobile communication equipment, computers, electric vehicles, electric trains, energy storage systems, etc.

[0073] To facilitate a better understanding of the innovative aspects of this application by those skilled in the art, the technical solutions of this application are further described in detail below with reference to embodiments. The embodiments of this application described in detail below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0074] Example 1

[0075] This embodiment provides a tungsten-doped composite cathode material, and the preparation method of the tungsten-doped composite cathode material is as follows:

[0076] (1) Preparation of layered oxide precursors

[0077] Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.285:0.015. The sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, ammonium metatungstate, and ethanol solution were added to a planetary ball mill. A 1 mol / L ammonium polyacrylate aqueous solution was added, and the Zeta potential was adjusted to +40 mV. The milling was carried out at 2000 rpm for 6 hours to obtain abrasive material. The abrasive material was then spray-dried to obtain spherical layered oxide precursors with an average particle size of D50: 5 μm. The spray-drying parameters were: 220-250℃, outlet air temperature: 80-100℃, atomization pressure: 0.3-0.5 MPa, nozzle diameter: 0.5 mm, and peristaltic pump-controlled feed rate: 10 mL / min.

[0078] (2) Preparation of sodium iron pyrophosphate precursor

[0079] Ferrous oxalate dihydrate and sodium pyrophosphate were dissolved in 0.1 mol / L citric acid solution at a molar ratio of 3:1 and stirred in a water bath at 80°C for 4 hours to form a blue-green transparent sol, thus obtaining a nano-micelle-like sodium ferric pyrophosphate precursor.

[0080] (3) The layered oxide precursor was added to the transparent sol at a mass ratio of 1:10, ultrasonically dispersed for 30 min, and concentrated under reduced pressure at 50°C until the sol completely covered the particle surface; the sodium iron pyrophosphate precursor was uniformly attached to the surface of the layered oxide precursor particles to obtain the composite material.

[0081] (4) Sintering

[0082] The composite material was vacuum dried at 100℃ for 12 hours; then heated to 400℃ and sintered in a sintering atmosphere of 95% N2 + 5% O2 for 6 hours. Nitrogen gas was introduced to make the sintering atmosphere N2, and then the temperature was raised to 600℃ for 6 hours, followed by annealing at 300℃ for 2 hours to obtain the composite cathode material of this application: NaNi. 0.4 Fe 0.3 Mn 0.285 W 0.015 O2@1 / 11Na4Fe3(PO4)2(P2O7), its morphology and interface structure, DSC curve are as follows: Figures 1-3 As shown.

[0083] Example 2

[0084] This embodiment provides a cathode material, and the preparation method of the cathode material is as follows:

[0085] (1) Preparation of layered oxide precursors

[0086] Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.35:0.35:0.285:0.015. The sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, ammonium metatungstate, and ethanol solution were added to a planetary ball mill. A 1 mol / L ammonium polyacrylate ethanol solution was added, and the Zeta potential was adjusted to +40 mV. The mill was ground at 2000 rpm for 6 hours to obtain abrasive material. The abrasive material was then spray-dried to obtain spherical layered oxide precursors with an average particle size of D50: 6 μm. The spray-drying parameters were: 220-250℃, outlet air temperature: 80-100℃, atomization pressure: 0.3-0.5 MPa, nozzle diameter: 0.5 mm, and peristaltic pump-controlled feed rate: 10 mL / min.

[0087] (2) Preparation of sodium iron pyrophosphate precursor

[0088] Ferrous oxalate dihydrate and sodium pyrophosphate were dissolved in 0.1 mol / L citric acid solution at a molar ratio of 1:3 and stirred in a water bath at 80°C for 4 hours to form a blue-green transparent sol, thus obtaining a nano-micelle-like sodium ferric pyrophosphate precursor.

[0089] (3) The layered oxide precursor was added to the transparent sol at a mass ratio of 1:10, ultrasonically dispersed for 30 min, and concentrated under reduced pressure at 50°C until the sol completely covered the particle surface; the sodium iron pyrophosphate precursor was uniformly attached to the surface of the layered oxide precursor particles to obtain the composite material.

[0090] (4) Sintering

[0091] The composite material was vacuum dried at 100°C for 12 hours; then heated to 400°C and sintered for 4 hours, then heated to 750°C and sintered for 6 hours, and finally annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, thus obtaining the cathode material of this application.

[0092] NaNi 0.35 Fe 0.35 Mn 0.285 W 0.015 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0093] Example 3

[0094] This embodiment provides a cathode material, and the preparation method of the cathode material is as follows:

[0095] (1) Preparation of layered oxide precursors

[0096] Sodium carbonate, ferric phosphate, nickel oxide, manganese trioxide, and tungsten tetroxide were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.285:0.015. The sodium carbonate, ferric phosphate, nickel oxide, manganese trioxide, tungsten tetroxide, and ethanol solution were added to a planetary ball mill. Ammonium polyacrylate dispersant was added. The remaining steps were the same as step (1) in Example 1 to obtain a spherical layered oxide precursor with an average particle size of D50: 12 μm.

[0097] (2) Preparation of sodium iron pyrophosphate precursor

[0098] Sodium carbonate and ferric phosphate were dissolved in 0.1 mol / L citric acid solution at a molar ratio of 1:1.2 and stirred in a water bath at 80°C for 4 hours to form a blue-green transparent sol, thus obtaining a nano-micelle-like precursor of sodium iron pyrophosphate.

[0099] (3) The layered oxide precursor was added to the transparent sol at a mass ratio of 1:10, ultrasonically dispersed for 30 min, and concentrated under reduced pressure at 50°C until the sol completely covered the particle surface; the sodium iron pyrophosphate precursor was uniformly attached to the surface of the layered oxide precursor particles to obtain the composite material.

[0100] (4) Sintering

[0101] The composite material was vacuum dried at 100°C for 12 hours; then heated to 400°C and sintered for 4 hours, then heated to 750°C and sintered for 6 hours, and finally annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, thus obtaining the composite cathode material of this application.

[0102] NaNi 0.4 Fe 0.3 Mn 0.285 W 0.015 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0103] Example 4

[0104] This embodiment differs from Example 1 in that the amount of tungsten doping is changed. Specifically, in step (1), sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate are provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.29:0.01. The remaining steps are the same as in Example 1, resulting in a composite cathode material.

[0105] NaNi 0.4 Fe 0.3 Mn 0.29 W 0.01 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0106] Example 5

[0107] Compared to Example 1, in this embodiment, the mixing mass ratio of the layered oxide precursor particles and the sodium iron pyrophosphate precursor is adjusted to 1:20. The remaining steps are the same as in Example 1, resulting in the cathode composite material: NaNi. 0.4 Fe 0.3 Mn 0.285 W 0.015 O2@1 / 21Na4Fe3(PO4)2(P2O7).

[0108] Comparative Example 1

[0109] This comparative example, unlike Example 1 where the layered oxide does not contain Ni, specifically involves providing sodium carbonate, ferrous oxalate dihydrate, manganese trioxide, and sodium metatungstate in step (1) at a molar ratio of Na:Fe:Mn:W = 1:0.5:0.485:0.015. The remaining steps are the same as in Example 1, resulting in a composite cathode material: NaFe 0.5 Mn 0.485 W 0.015 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0110] Comparative Example 2

[0111] In Comparative Example 1, the composite material was vacuum dried at 100°C for 12 hours; then heated to 300°C and sintered in a nitrogen atmosphere for 4 hours, then heated to 550°C and sintered for 6 hours, and annealed at 200°C for 2 hours. The remaining steps were the same as in Example 1, and the positive electrode material of this application was obtained.

[0112] Comparative Example 3

[0113] Compared to Example 1, in this comparative example, the composite material was vacuum dried at 100°C for 12 hours; then heated to 300°C and sintered in a nitrogen atmosphere for 4 hours, then heated to 500°C and sintered for 12 hours, followed by annealing at 200°C for 2 hours. The remaining steps were the same as in Example 1, resulting in the cathode material of this application.

[0114] NaNi 0.4 Fe 0.3 Mn 0.285 W 0.015 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0115] Comparative Example 4

[0116] Compared to Example 1, this comparative example does not dope tungsten. Specifically, in step (1), sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, and manganese trioxide are provided in a molar ratio of Na:Ni:Fe:Mn = 1:0.4:0.3:0.3. The remaining steps are the same as in Example 1, resulting in a composite cathode material: NaNi 0.4 Fe 0.3 Mn 0.3 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0117] Comparative Example 5

[0118] This comparative example differs from Example 1 in that the amount of tungsten doping is changed. Specifically, in step (1), sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate are provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.297:0.003. The remaining steps are the same as in Example 1, resulting in a composite cathode material.

[0119] NaNi 0.4 Fe 0.3 Mn 0.297 W 0.003 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0120] Comparative Example 6

[0121] This comparative example differs from Example 1 in that the amount of tungsten doping is changed. Specifically, in step (1), sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate are provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.27:0.03. The remaining steps are the same as in Example 1, resulting in a composite cathode material.

[0122] NaNi 0.4 Fe 0.3 Mn 0.27 W 0.03 O2@1 / 11Na4Fe3(PO4)2(P2O7).

[0123] Comparative Example 7

[0124] Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.285:0.015. The sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, ammonium metatungstate, and an ethanol solution were added to a planetary ball mill. A 1 mol / L ammonium polyacrylate ethanol solution was added, and the Zeta potential was adjusted to +40 mV. The mill was ground at 2000 rpm for 2 hours to obtain abrasive material. The abrasive material was then spray-dried to obtain spherical sodium iron pyrophosphate phosphate precursors with an average particle size of D50: 10 μm. The spray-drying parameters were: 220-250℃, outlet air temperature: 80-100℃, atomization pressure: 0.3-0.5 MPa, nozzle diameter: 0.5 mm, and peristaltic pump-controlled feed rate: 10 mL / min.

[0125] (2) Sintering

[0126] The spherical layered oxide precursor was vacuum dried at 100°C for 12 hours; then heated to 400°C and sintered for 4 hours, then heated to 600°C and sintered for 6 hours, and finally annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, yielding O3 layered oxide: NaNi. 0.4 Fe 0.3 Mn 0.285 W 0.015 .

[0127] Comparative Example 8

[0128] (1) Preparation of layered oxide precursors

[0129] Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.285:0.015. Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, ammonium metatungstate, and ethanol solution were added to a planetary ball mill. The remaining steps were the same as in Example 1 to obtain a layered oxide precursor.

[0130] (2) Mix and grind the layered oxide precursor and glucose at a mass ratio of 1:10; so that the glucose is uniformly attached to the surface of the layered oxide precursor particles to obtain the composite material.

[0131] (3) The composite material was vacuum dried at 100°C for 12 hours; then heated to 400°C and sintered for 4 hours, then heated to 600°C and sintered for 6 hours, and annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, and the cathode material in this application, NaNi, was obtained. 0.4 Fe 0.3 Mn 0.285 W 0.015 O2@1 / 11C.

[0132] Comparative Example 9

[0133] (1) Preparation of layered oxide precursors

[0134] Sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, and ammonium metatungstate were provided in a molar ratio of Na:Ni:Fe:Mn:W = 1:0.4:0.3:0.285:0.015. The sodium carbonate, ferrous oxalate dihydrate, nickel hydroxide, manganese trioxide, ammonium metatungstate, and ethanol solution were added to a planetary ball mill. Ammonium polyacrylate dispersant was added, and the Zeta potential was adjusted to above +40mV. The milling speed was 400 rpm, and the milling process was carried out for 24 hours to obtain wet abrasive. The wet abrasive was then spray-dried under the following conditions: inlet air temperature: 220-250℃, outlet air temperature: 80-100℃, atomization pressure: 0.3-0.5MPa, nozzle diameter: 0.5mm, and peristaltic pump-controlled feed rate: 10mL / min, to obtain spherical O3 layered oxide precursors with an average particle size of D50: 10μm.

[0135] (2) Sintering

[0136] The spherical O3 layered oxide precursor was vacuum dried at 100°C for 12 hours; then heated to 300°C and sintered for 4 hours, then heated to 600°C and sintered for 6 hours, and annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, and O3 layered oxide was obtained.

[0137] (3) Ferrous oxalate dihydrate and sodium pyrophosphate were dissolved in 1 mol / L citric acid solution at a molar ratio of 3:1 and stirred in a water bath at 60°C for 6 hours to form a blue-green transparent sol, thus obtaining a nano-micelle sodium pyrophosphate precursor. The sodium pyrophosphate precursor was concentrated and dried, then sintered at 400°C for 4 hours, then heated to 600°C for 6 hours, and annealed at 300°C for 2 hours. The sintering atmosphere was the same as in Example 1, thus obtaining sodium pyrophosphate.

[0138] (4) The layered oxide of O3 obtained in steps (2) and (3) and sodium iron pyrophosphate are mixed at a mass ratio of 10:1 and sintered at 400°C in a nitrogen atmosphere for 6 hours to form a composite cathode material of sodium iron pyrophosphate coated with O3.

[0139] To verify the superior performance of the cathode material provided in this application, the applicant used the composite cathode materials or cathode materials obtained in Examples 1-6 and Comparative Examples 1-9 as cathode active materials to prepare corresponding sodium-ion batteries. The specific preparation methods are as follows:

[0140] (1) Preparation of positive electrode sheet: The positive electrode material, conductive carbon black, polyvinylidene fluoride, and carbon nanotubes were mixed and stirred in a mass ratio of 95:1:3:1. N-methylpyrrolidone solvent was added to adjust the slurry to a solid content of 60% and a viscosity of 6000 mPa·s. The negative electrode slurry was transferred and coated onto a 15 μm thick carbon-coated aluminum foil using a transfer coating method. The coated electrode sheet was rolled to a thickness of 3 mg / cm.3 The compaction density is determined; the rolled electrode sheets are then die-cut into electrode sheets with a length of 48mm and a width of 38mm for later use.

[0141] (2) Preparation of negative electrode sheet: Hard carbon material, conductive carbon black, carboxymethyl cellulose, and styrene-butadiene rubber were mixed and kneaded in a mass ratio of 92:3:2:3. Deionized water was added to adjust the slurry to a solid content of 45% and a viscosity of 5000 mPa·s. The negative electrode slurry was transferred and coated onto a 15 μm thick carbon-coated aluminum foil using a transfer coating method. The coated electrode sheet was then rolled to a thickness of 1 mg / cm. 3 The compaction density is determined; the rolled electrode sheets are then die-cut into 50mm long and 40mm wide sheets for later use.

[0142] (3) Fabrication of sodium-ion batteries: The slit positive and negative electrode sheets are stacked on a stacking machine. The separator is made of PP / PE / PP three-layer material to form a soft-pack cell. Electrolyte (components: carbonate solvent and 1M sodium hexafluorophosphate) is injected, packaged, dried, and subjected to capacity testing to obtain a sodium-ion battery.

[0143] The sodium-ion batteries prepared above were subjected to morphology characterization tests, cycle performance tests, charge-discharge capacity tests, and rate performance tests; the specific test methods are as follows.

[0144] (1) High-potential cycling performance test

[0145] Using the Xinwei testing machine, the battery cells were cyclically tested at a 1C / 1C rate, with a voltage range of 2.5V-4.2V.

[0146] (2) High-potential charge-discharge capacity test

[0147] Using a Xinwei testing machine, the battery cell was charged at 0.5C and discharged at 1C. The 1C discharge capacity was taken as the standard capacity, with a voltage range of 2.5V-4.2V. Using the 1C standard capacity, 2C and 30C currents were set. Charging to 4.2V at 0.5C and discharging to 2.5V at a 2C rate yielded the 2C capacity; charging to 4.2V at 0.5C and discharging to 2.5V at a 30C rate yielded the 30C capacity.

[0148] (3) Charge transfer resistance test

[0149] The electrochemical impedance spectroscopy of the battery was tested, and the charge transfer resistance was calculated; the frequency range used for the test was 0.01 Hz to 10 kHz.

[0150] (4) Elemental analysis test

[0151] The test was conducted using EDS-mapping, with a test voltage of 10KV and a scan speed of 30 seconds per frame.

[0152] The test results are shown in Table 1.

[0153] from Figure 1 It can be seen that the morphology of the coating layer on the surface of the cathode material provided in this application is a whisker-like structure. Therefore, the cathode material provided in this application has a core-shell structure, and its outer shell layer has a whisker-like crystal structure. Furthermore, from this application… Figure 2 The provided local elemental analysis shows that tungsten is present at the interface between the outer shell and the core of the composite cathode material provided in this application.

[0154] Table 1

[0155]

[0156] As shown in Table 1, after doping the core of the cathode material provided in this application with W, its interfacial transfer resistance decreases significantly, and its exothermic peak temperature also increases, resulting in a significant decrease in gas production in the battery based on this material; while W 6+ When the doping concentration is too low, it is difficult to form an effective Ni-OWP charge transport channel. Insufficient charge transport channel construction leads to high interfacial impedance and increased gas production, resulting in increased energy loss and reduced charge / discharge efficiency during charging and discharging. Capacity utilization is limited, and cycle stability decreases. Meanwhile, W... 6+ Excessive doping can lead to significant changes in the arrangement of atoms in the crystal lattice, causing lattice distortion and making it easy to generate impurity phases such as sodium tungstate. The presence of impurity phases can change the phase composition and structure of the material, occupy active sites, reduce sodium ion insertion / extraction channels, and the electrochemical activity of impurity phases differs from that of the host material, which can affect the overall performance of the battery. In addition, it can also reduce its conductivity, causing capacity decay and reduced thermal stability.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A tungsten-doped composite cathode material, characterized in that, The composite cathode material has a core-shell structure, comprising a core of O3 phase layered oxide secondary particles containing nickel and an outer shell of sodium iron pyrophosphate crystals covering the surface of the core. Tungsten is present at the interface between the kernel layer and the outer shell layer; The tungsten element is doped in the composite cathode material at a concentration of 0.5-2.0 wt%; the sodium iron pyrophosphate is partially intercalated into the core.

2. The tungsten-doped composite cathode material according to claim 1, characterized in that, The tungsten element is doped into the core and / or the outer shell layer.

3. The tungsten-doped composite cathode material according to claim 1, characterized in that, The tungsten element is incorporated into the composite cathode material as hexavalent tungsten ions.

4. The tungsten-doped composite cathode material according to any one of claims 1 to 3, characterized in that, The sodium ferric pyrophosphate crystals are whisker-shaped sodium ferric pyrophosphate crystals.

5. The tungsten-doped composite cathode material according to claim 1, characterized in that, The charge transfer resistance of the composite cathode material was ≤46Ω / cm in the electrochemical impedance spectroscopy test at 25℃. 2 .

6. The tungsten-doped composite cathode material according to claim 1, characterized in that, The exothermic peak of the composite cathode material in the DSC test is between 280-310℃.

7. The tungsten-doped composite cathode material according to claim 1, characterized in that, The core has a size of 5-20 μm; the outer shell has a thickness of 200 nm-1 μm.

8. The tungsten-doped composite cathode material according to claim 1, characterized in that, The chemical structural formula of the layered oxide is: Na x Ni y Fe z Mn a M (1-y-z-a) W b O2; Where x ranges from 0.95 to 1; y ranges from 0.1 to 0.5; z ranges from 0.1 to 0.5; a ranges from 0.1 to 0.5; and b ranges from 0.005 to 0.

02. M is selected from at least one of titanium, copper, cerium, magnesium, aluminum, calcium, vanadium, and zinc.

9. A positive electrode plate, characterized in that, Including the tungsten-doped composite cathode material as described in any one of claims 1 to 8.

10. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator; the separator and the electrolyte are disposed between the positive electrode and the negative electrode. The positive electrode is the positive electrode as described in claim 9.

11. A battery module, characterized in that, Includes the sodium-ion battery of claim 10, or the positive electrode sheet of claim 9, or the tungsten-doped composite positive electrode material of any one of claims 1 to 8.

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