Sodium-ion positive electrode material, preparation method and application thereof, sodium-ion battery, sodium-ion battery pack and device

Abstract

This invention relates to the field of sodium-ion battery technology, and discloses a sodium-ion cathode material, its preparation method and application, a sodium-ion battery, a sodium-ion battery pack, and a device. The sodium-ion cathode material includes a matrix and a coating layer covering the matrix; the matrix has the composition shown in Formula I: Na 1‑x [Ni y Mn z M u Ti v O2 Formula I; the coating layer has the composition shown in Formula II: Na 2‑β Ti 6‑α M′ α O 13 Formula II. This sodium-ion cathode material possesses characteristics such as high ionic and electronic conductivity, strong structural stability, and strong chemical stability. Furthermore, using this composite cathode material in sodium-ion batteries can effectively improve the battery's electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion cathode material and its preparation method and application, a sodium-ion battery, a sodium-ion battery pack, and a device. Background Technology

[0002] The explosive growth of the new energy vehicle and large-scale energy storage markets, along with the significant increase in lithium-ion battery sales, has posed a severe challenge to the global lithium resource supply. Compared to lithium resources, sodium resources are abundant in the Earth's crust (2.4 wt%) and widely distributed, far exceeding the 0.0065 wt% of lithium resources. Therefore, in recent years, sodium-ion batteries have become a key energy storage system being developed in the new energy industry.

[0003] The cathode material is a crucial component in sodium-ion batteries, and currently, it mainly includes systems such as metal oxides, polyanionic compounds, Prussian blue-based materials, and organic materials. Among these, metal oxide cathode materials possess advantages such as high voltage plateau, high discharge capacity, and high powder compaction, making them a class of battery materials with significant development potential. The charge-discharge process of metal oxide cathode materials involves an insertion-extraction reaction. Due to the large radius of sodium ions, the volume expansion and contraction during charge-discharge are excessive, resulting in poor cycle performance and adversely affecting battery safety.

[0004] Therefore, there is an urgent need for a new composite cathode material for sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low ionic conductivity, poor structural stability, and poor chemical stability of existing sodium-ion battery cathode materials, and to provide a sodium-ion cathode material, its preparation method and application, a sodium-ion battery, a sodium-ion battery pack, and equipment. This sodium-ion cathode material has the characteristics of high ionic and electronic conductivity, strong structural stability, and strong chemical stability. At the same time, using this composite cathode material in sodium-ion batteries can effectively improve the electrochemical performance of the battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a sodium ion cathode material, the cathode material comprising a substrate and a coating layer covering the substrate;

[0007] The matrix has the composition shown in Formula I:

[0008] Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤x≤0.4, 0.2≤y≤0.6, 0.1≤z

[0009] ≤0.5, 0.1≤u≤0.5, 0≤v≤0.02, y+z+u+v=1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta;

[0010] The coating layer has the composition shown in II:

[0011] Na 2-β Ti 6-α M′ α O 13 Formula II, where 0 ≤ α < 0.6, -2 ≤ β < 1; M′ is selected from at least one of Li, Mg, Fe, Al, Ga, In, Ge, Y, Sc and Zr.

[0012] A second aspect of the present invention provides a method for preparing a sodium-ion cathode material, the method comprising the following steps:

[0013] A first sodium source, optionally an M′ source, a titanium source, and a solvent are mixed to obtain a first slurry; the first slurry is then subjected to a first drying and a first sintering to obtain a first sintered product; the first sintered product is then crushed and dried to obtain a coating layer.

[0014] The coating layer has the composition shown in Formula II:

[0015] Na 2-β Ti 6-α M′ α O 13 Formula II, where 0 ≤ α < 0.6, -2 ≤ β < 1; M′ is selected from at least one of Li, Mg, Fe, Al, Ga, In, Ge, Y, Sc and Zr;

[0016] (2) The second sodium source, nickel source, manganese source, M source and optional titanium source are mixed for the second time, and the resulting second mixture is subjected to a second drying and a second sintering in sequence to obtain the matrix;

[0017] The matrix has the composition shown in Formula I:

[0018] Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤x≤0.4, 0.2≤y≤0.6, 0.1≤z

[0019] ≤0.5, 0.1≤u≤0.5, 0≤v≤0.02, y+z+u+v=1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta;

[0020] (3) The coating layer and the substrate are mixed for a third time, and the resulting third mixture is heat-treated to obtain a composite cathode material;

[0021] The first sintering is carried out in a non-oxidizing gas.

[0022] The third aspect of this invention provides a sodium-ion cathode material prepared by the method provided in the second aspect.

[0023] The fourth aspect of this invention provides the application of the sodium-ion cathode material provided in the first or third aspect in a sodium-ion battery.

[0024] The fifth aspect of the present invention provides a sodium-ion battery comprising a positive electrode sheet made of a sodium-ion positive electrode material provided in the first or third aspect.

[0025] The sixth aspect of the present invention provides a sodium-ion battery pack comprising the sodium-ion battery provided in the fifth aspect.

[0026] A seventh aspect of the present invention provides an apparatus comprising the sodium-ion battery pack provided in the sixth aspect.

[0027] Through the above technical solutions, the sodium-ion cathode material, its preparation method and application, sodium-ion battery, sodium-ion battery pack, and equipment provided by the present invention achieve the following beneficial effects:

[0028] (1) The sodium ion cathode material provided by this invention, through Na 2-β Ti 6-α M′ α O 13 Coating can effectively improve the ionic and electronic conductivity and surface activity of the coating layer. At the same time, coating the coating layer on a specific substrate can significantly improve the structural stability and chemical stability of the composite cathode material.

[0029] (2) In the sodium-ion cathode material provided by the present invention, the coating layer is a pure phase coating containing specific doping elements. This ensures that the coating layer phase has high ionic conductivity and improves the electronic conductivity of the coating layer through element doping, thus avoiding the introduction of the coating layer from hindering the electron and ion channels of the matrix. Preferably, in the sodium-ion cathode material, the Ti element in the matrix is ​​distributed in a gradient, and the Ti element in the matrix is ​​more likely to react with Na2Ti6O contained in the coating layer. 13Na-Ti-O chemical bonds are formed between the phases, which further reduces the interfacial impedance while achieving tight coating.

[0030] (3) The method for preparing composite cathode material provided by the present invention involves heat-treating the coating layer in a non-oxidizing gas, which makes the coating layer and the substrate more tightly bonded, thereby improving the electrochemical performance of sodium-ion batteries made from sodium-ion cathode material; at the same time, the method simplifies the process flow and facilitates industrial production.

[0031] (4) Using the sodium-ion cathode material provided by the present invention in sodium-ion batteries can effectively improve the cycle life, rate capability and safety performance of the batteries. Attached Figure Description

[0032] Figure 1 This is a cross-sectional EDS line scan of the sodium-ion cathode material prepared in Example 1;

[0033] Figure 2 The XRD diffraction pattern of the coating layer C1 sample prepared in Example 1;

[0034] Figure 3 The XRD diffraction pattern of the sodium ion cathode material prepared in Comparative Example 1;

[0035] Figure 4 The image shows the XRD diffraction pattern of the sodium ion cathode material prepared in Example 10.

[0036] Figure 5 These are the DSC spectra of the sodium ion cathode materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] In this invention, unless otherwise specified, the terms "first," "second," and "third" do not indicate a sequential order, nor do they limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, "first" and "second" in "first sodium source" and "second sodium source" are only used to distinguish that these are not the same sodium source; similarly, "first," "second," and "third" in "first mixture," "second mixture," and "third mixture" are only used to distinguish that these are not the same mixture.

[0039] The first aspect of the present invention provides a sodium ion cathode material, the cathode material comprising a substrate and a coating layer covering the substrate;

[0040] The matrix has the composition shown in Formula I:

[0041] Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤x≤0.4, 0.2≤y≤0.6, 0.1≤z

[0042] ≤0.5, 0.1≤u≤0.5, 0≤v≤0.02, y+z+u+v=1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta;

[0043] The coating layer has the composition shown in Formula II:

[0044] Na 2-β Ti 6-α M′ α O 13 Formula II, where 0 ≤ α < 0.6, -2 ≤ β < 1; M′ is selected from at least one of Li, Mg, Fe, Al, Ga, In, Ge, Y, Sc and Zr.

[0045] In this invention, the sodium ion cathode material includes a coating layer of Na with a specific composition. 2-β Ti 6-α M′ α O 13 Both contain the same Na2Ti6O as the matrix. 13 The phase, and the coating layer Na2Ti6O 13 Na2Ti6O in the phase and matrix 13 The phases have the same crystal structure, and the Na-Ti-O chemical bonds that coexist in both phases can be organically combined to achieve a tight coating, ultimately resulting in a matrix containing Na+ and Na+ coated on the matrix. 2-β Ti 6-α M′ α O 13 The coated sodium-ion cathode material has high ionic and electronic conductivity, excellent structural stability and chemical stability.

[0046] In a specific embodiment of the present invention, in Formula I, -0.2 ≤ x ≤ 0.4, 0.2 ≤ y ≤ 0.5, 0.2 ≤ z ≤ 0.5, 0.2 ≤ u ≤ 0.5, 0.01 ≤ v ≤ 0.02, y + z + u + v = 1; M is selected from at least one of Fe, Cu, Nb, Co, V, and Cr.

[0047] In a preferred embodiment of the present invention, in Formula I, 0 ≤ x ≤ 0.35, 0.3 ≤ y ≤ 0.4, 0.2 ≤ z ≤ 0.4, 0.2 ≤ u ≤ 0.4, 0.01 < v ≤ 0.02, y + z + u + v = 1; M is selected from at least one of Fe, Cu, Nb, and V.

[0048] In a specific embodiment of the present invention, in Formula II, 0 < α < 0.5, -2 ≤ β < 1; M' is selected from at least one of Mg, Fe, Al, Y, and Zr.

[0049] In a preferred embodiment of the present invention, in Formula II, 0.01 ≤ α < 0.3, -2 ≤ β < 0.5; M' is selected from at least one of Fe, Mg, and Al.

[0050] In the present invention, in Formula II, the value of β depends on the valence state changes of each ion in Formula II to ensure the charge balance of the coating material.

[0051] According to the present invention, along the direction from the center to the surface of the substrate, the Ti element shows a gradient distribution, preferably a gradient increasing distribution.

[0052] In the present invention, by controlling the gradient distribution of the Ti element in the substrate, preferably, along the direction from the center to the surface of the substrate, the Ti element shows a gradient increasing distribution, that is, the content of the Ti element on the surface of the substrate is higher, which can ensure that the Ti element in the substrate is more likely to form a Na-Ti-O chemical bond with the phases containing Na2Ti6O in the coating layer, and further reduce the interface impedance on the premise of achieving a tight coating of the coating layer. 13 Under the premise of realizing the tight coating of the coating layer, further reduce the interface impedance.

[0053] Furthermore, along the direction from the center to the surface of the substrate, the increasing rate of the Ti element is 0.001 - 0.3 mol% / μm, preferably 0.001 - 0.2 mol% / μm, more preferably 0.001 - 0.1 mol% / μm.

[0054] In some embodiments of the present invention, preferably, the weight ratio of the substrate to the coating layer is 100:0.01-5, for example, 100:0.01, 100:0.05, 100:0.1, 100:0.5, 100:1, 100:3, 100:5, and any value within the range of any two values, preferably 100:0.05-3. At this preferred weight ratio, the coating layer can form a uniform coating of the substrate with relatively high coating density, effectively suppressing side reactions between the substrate and the electrolyte. Simultaneously, the coating layer thickness is not excessive, thus avoiding impacting the capacity and rate performance of the cathode material.

[0055] In some embodiments of the present invention, preferably, the thickness of the coating layer is 10-200 nm, more preferably 10-100 nm, and even more preferably 50-100 nm.

[0056] In some embodiments of the present invention, preferably, the average particle size D50 of the sodium ion cathode material is 2-30 μm, more preferably 4-12 μm.

[0057] In this invention, unless otherwise specified, the average particle size D50 parameter is measured using a laser particle size analyzer; the average particle size D50 parameter is measured using a laser particle size analyzer; and the thickness parameter is measured using a transmission electron microscope.

[0058] In some embodiments of the present invention, preferably, the sodium ion cathode material has an ionic conductivity of 10. -4 Up to 10 -3 S / cm, preferably 5×10 -4 Up to 10 -3 S / cm.

[0059] In some embodiments of the present invention, preferably, the electronic conductivity of the sodium ion cathode material is 10. -7 Up to 10 -6 S / cm, preferably 5×10 -7 Up to 10 -6 S / cm.

[0060] In this invention, unless otherwise specified, the ionic conductivity of the sodium ion cathode material is measured using an electrochemical workstation; the electronic conductivity of the sodium ion cathode material is measured using a powder resistance tester.

[0061] In this invention, the coating layer of the sodium ion cathode material is heat-treated in a non-oxidizing gas, which makes the coating layer and the substrate more tightly bonded, thereby improving the electrochemical performance of the sodium ion battery made from the sodium ion cathode material.

[0062] A second aspect of this invention provides a method for preparing a sodium-ion cathode material, the method comprising the following steps:

[0063] (1) A first sodium source, optionally an M′ source, a titanium source and a solvent are mixed to obtain a first slurry; the first slurry is subjected to a first drying and a first sintering to obtain a first sintered product, and the first sintered product is subjected to a first crushing and drying to obtain a coating layer;

[0064] The coating layer has the composition shown in Formula II:

[0065] Na 2-β Ti 6-α M′ α O 13 Formula II, where 0 ≤ α < 0.6, -2 ≤ β < 1; M′ is selected from at least one of Li, Mg, Fe, Al, Ga, In, Ge, Y, Sc and Zr;

[0066] (2) The second sodium source, nickel source, manganese source, M source and optional titanium source are mixed for a second time, and the resulting second mixture is subjected to a second drying and a second sintering in sequence to obtain the matrix;

[0067] The matrix has the composition shown in Formula I:

[0068] Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤x≤0.4, 0.2≤y≤0.6, 0.1≤z

[0069] ≤0.5, 0.1≤u≤0.5, 0≤v≤0.02, y+z+u+v=1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta;

[0070] (3) The coating layer and the substrate are mixed for a third time, and the resulting third mixture is heat-treated to obtain the sodium ion cathode material;

[0071] The first sintering is carried out in a non-oxidizing gas.

[0072] In this invention, the preparation method described in the second aspect of the invention involves mixing a coating layer with a matrix having a specific composition and then subjecting the mixture to heat treatment to obtain the sodium-ion cathode material described in the first aspect of the invention. In this sodium-ion cathode material, the coating layer Na has a specific composition. 2-β Ti 6-α M′ α O 13Both contain the same Na2Ti6O as the matrix. 13 The phase, and the coating layer Na2Ti6O 13 Na2Ti6O in the phase and matrix 13 The phases have the same crystal structure, and the Na-Ti-O chemical bonds that coexist in both phases can be organically combined to achieve a tight coating, ultimately resulting in a matrix containing Na+ and Na+ coated on the matrix. 2-β Ti 6-α M′ α O 13 The coated sodium-ion cathode material has high ionic and electronic conductivity, excellent structural stability and chemical stability.

[0073] According to the present invention, the surface residual alkali content of the matrix is ​​≤2wt%.

[0074] In this invention, since the surface residual alkali is an inert layer, an excessively high residual alkali content will form a thick inert layer between the coating layer and the substrate, affecting the chemical bond between the substrate and the coating layer. In order to achieve a tight bond between the coating layer and the substrate, it is necessary to control the surface residual alkali content of the substrate to not exceed 2 wt%. Preferably, the surface residual alkali content of the substrate is controlled to be 0.1-1 wt%.

[0075] Furthermore, in this invention, performing the first sintering in a non-oxidizing gas to prepare the coating layer can reduce the Na content of the coating layer. 2-β Ti 6-α M′ α O 13 Ti 4+ The content of oxygen increases the amount of oxygen vacancies, thereby giving the coating material a certain degree of activity. During the process of coating the substrate, the coating material tends to bind more to the oxygen dangling bonds on the substrate surface, thereby improving the tightness of the coating material and the substrate, and improving the structural stability and cycle performance of the sodium ion cathode material.

[0076] In this invention, unless otherwise specified, the amount of each material fed is used entirely to generate the product. That is, the amounts of the first sodium source, M′ source, and titanium source fed satisfy the composition of Formula II; the amounts of the second sodium source, nickel source, manganese source, and M source fed satisfy the composition of Formula I.

[0077] In this invention, the non-oxidizing gas refers to a gas that does not contain oxygen. Preferably, the non-oxidizing gas includes, but is not limited to, nitrogen, helium, argon, and neon.

[0078] In this invention, the first mixing method in step (1) has a wide range of options, as long as the first sodium source, M′ source, titanium source and solvent are mixed evenly.

[0079] In this invention, in step (1), the types of the first sodium source, M′ source, and titanium source are subject to a wide range of selection, as long as the first sodium source, M′ source, and titanium source contain Na, M′, and Ti respectively. M′ is selected from at least one of Li, Mg, Fe, Al, Ga, In, Ge, Y, Sc, and Zr. Preferably, M′ is selected from at least one of Mg, Fe, Al, Y, and Zr. Preferably, the first sodium source, M′ source, and titanium source are each independently selected from at least one of oxides, hydroxides, nitrates, carbonates, and organic compounds containing Na, M′, and Ti.

[0080] In some embodiments of the present invention, preferably, in step (1), the amounts of the first sodium source, M' source and titanium source fed satisfy: n(Na):n(Ti):n(M')=(2-β):(6-α):α, where 0≤α<0.6, -2≤β<1.

[0081] In some preferred embodiments of the present invention, preferably, in step (1), 0≤α<0.6, -2≤β<1, where 0<α<0.5, -2≤β<1. More preferably, 0.01≤α<0.3, -2≤β<0.5.

[0082] In this invention, the first drying process aims to remove the solvent from the first slurry. Preferably, the equipment for the first drying includes, but is not limited to, a spray dryer, a blower oven, a vacuum oven, a freeze dryer, etc. In this invention, there are no particular limitations on the conditions for the first drying, as long as the solvent in the first slurry can be removed.

[0083] In some embodiments of the present invention, preferably, the solid content of the first slurry is 30-55 wt%. In the present invention, when the solid content of the first slurry is controlled to meet the above range, the materials in the slurry have good dispersibility, and the presence of excessive solvent avoids adverse effects on the matrix structure. For example, excessive solvent will cause sodium ions in the matrix to escape from the bulk phase.

[0084] In this invention, a wide range of solvents can be selected, as long as the solvent can dissolve the first sodium source, M′ source, and titanium source. Preferably, the solvent includes, but is not limited to, common solvents such as water, ethanol, ethylene glycol, and glycerol.

[0085] In this invention, the amount of solvent can be selected within a wide range, as long as the solid content in the first slurry meets the requirement of 30-55 wt%.

[0086] In some embodiments of the present invention, preferably, in step (1), the conditions for the first sintering include: a temperature of 500-1200℃, preferably 700-850℃; and a time of 4-10h, preferably 6-8h.

[0087] In this invention, when the conditions for the first sintering are controlled to meet the above-mentioned range, a pure-phase coating layer can be obtained, resulting in a coating layer with excellent crystallinity and structural stability. When used to coat a substrate, it can form a dense and uniform coating layer on the substrate surface, thereby significantly improving the charge-discharge capacity and cycle performance of the sodium-ion cathode material. Specifically, if the sintering temperature is too low or the sintering time is too short, impurity phases will appear in the coating layer. If the sintering temperature is too high or the sintering time is too long, the resulting coating layer will have excessive hardness and be difficult to break.

[0088] In some embodiments of the present invention, preferably, in step (1), the crushing process includes: crushing the first sintered product and the solvent at a weight ratio of 100:50-100.

[0089] In this invention, crushing the first sintered product according to the above method not only has higher crushing efficiency, but also enables the obtained coating layer to have excellent structural stability and dispersibility.

[0090] In this invention, there is no particular limitation on the type of solvent used in ball milling, as long as it can achieve uniform dispersion of the first sintered product.

[0091] In this invention, the crushing equipment includes, but is not limited to, jaw crushers, roller mills, ball mills, air jet mills, mechanical mills, sand mills, colloid mills, etc.

[0092] In some embodiments of the present invention, preferably, the crushing results in an average particle size D50 of 10-200 nm for the coating layer, more preferably 10-100 nm, and even more preferably 50-100 nm.

[0093] In some embodiments of the present invention, preferably, the drying process includes: a temperature of 60-120°C and a time of 0.5-5 hours.

[0094] In some embodiments of the present invention, preferably, the dried product is pulverized.

[0095] In this invention, there is a wide range of options for the second mixing method in step (2), as long as the second sodium source, nickel source, manganese source and M source are mixed evenly.

[0096] In this invention, the types of the second sodium source, nickel source, manganese source, and M source are widely selectable, as long as the second sodium source, nickel source, manganese source, and M source contain Na, Ti, Mn, and M respectively. M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Ti, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm, and Ta. Preferably, M is selected from at least one of Fe, Cu, Nb, Co, V, and Cr. Preferably, in step (2), the second sodium source, nickel source, manganese source, and M source are each independently selected from at least one of oxides, hydroxides, carbonates, nitrates, and organic compounds containing Na, Ni, Mn, and M.

[0097] In this invention, the second drying is intended to remove moisture from the second mixture; wherein the drying equipment includes, but is not limited to, spray dryers, forced-air ovens, vacuum ovens, freeze dryers, etc.

[0098] In some embodiments of the present invention, preferably, the amounts of the second sodium source, nickel source, manganese source, M source and optional titanium source satisfy: n(Na):n(Ni):n(Mn):n(M):n(Ti)=(1-x):y:z:u:v, where -0.4≤x≤0.4, 0.2≤y≤0.6, 0.1≤z≤0.5, 0.1≤u≤0.5, 0≤v≤0.02, y+z+u+v=1.

[0099] In some preferred embodiments of the present invention, preferably, the amounts of the second sodium source, nickel source, manganese source, M source, and optionally titanium source satisfy: n(Na):n(Ni):n(Mn):n(M):n(Ti)=(1-x):y:z:u:v, where -0.2≤x≤0.4, 0.2≤y≤0.5, 0.2≤z≤0.5, 0.2≤u≤0.5, 0.01≤v≤0.02, y+z+u+v=1. More preferably, 0≤x≤0.35, 0.3≤y≤0.4, 0.2≤z≤0.4, 0.2≤u≤0.4, 0.01 <v≤0.02,y+z+u+v=1。

[0100] In some embodiments of the present invention, preferably, the second mixing includes the following steps: co-precipitating a nickel source, a manganese source, and an M source to obtain a precursor Ni. y Mn z M u (OH)2, the precursor Ni y Mn z M u (OH)2 is mixed with a titanium source (I) and then mixed with a second sodium source (II) to obtain a second mixture.

[0101] In this invention, the second mixing is carried out according to the above steps, that is, the precursor is first mixed with the titanium source, and then mixed with the second sodium source before the second sintering is performed. By controlling the second sintering time, the Ti element can be distributed in a gradient in the matrix. In particular, the Ti element is distributed in an increasing manner in the matrix along the direction from the center to the surface of the matrix.

[0102] In this invention, there are no particular limitations on the conditions for co-precipitation, and co-precipitation of nickel source, manganese source and M source can be achieved according to conventional conditions in the art.

[0103] In this invention, there are no particular limitations on the conditions for Mixing I and Mixing II, as long as it can be ensured that the precursor and the titanium source, as well as the mixture of the two and the second sodium source, can be fully and uniformly mixed.

[0104] In some embodiments of the present invention, preferably, the conditions for the second sintering include: a temperature of 600-1200°C, preferably 750-1200°C; and a time of 6-10 hours, preferably 8-10 hours.

[0105] In this invention, when the conditions for the second sintering are controlled to meet the above-mentioned range, it can ensure that the prepared matrix has excellent crystallinity and structural stability, thereby significantly improving the charge-discharge capacity and cycle performance of the sodium-ion cathode material containing the matrix material. Specifically, if the sintering temperature is too low or the sintering time is too short, the material reaction in the matrix will be incomplete, resulting in the appearance of impurity phases in the matrix. If the sintering temperature is too high or the sintering time is too long, it will cause the sodium ions in the matrix to volatilize, thereby affecting the electrochemical performance of the battery containing the prepared sodium-ion cathode material. In this invention, the third mixing method described in step (3) has a wide range of selection, as long as the coating layer and the matrix are mixed evenly.

[0106] In some embodiments of the present invention, preferably, in step (3), the heat treatment is performed in a non-oxidizing gas. In the present invention, controlling the heat treatment to be performed in a non-oxidizing gas is beneficial for the oxygen dangling bond bonding between the coating material and the substrate material surface, thereby making the bonding between the coating layer and the substrate tighter, and thus improving the cycle performance of the sodium-ion battery containing the sodium-ion cathode material.

[0107] In some embodiments of the present invention, preferably, in step (3), the conditions of the heat treatment include: a temperature of 200-600℃, preferably 400-600℃; and a time of 4-8h, preferably 6-8h.

[0108] In this invention, when the conditions for the heat treatment are controlled to meet the above-mentioned range, it can ensure that the substrate and the coating layer react fully and can be tightly bonded, thereby improving the cycle performance of the sodium-ion battery containing the sodium-ion cathode material.

[0109] In some embodiments of the present invention, preferably, the third mixing includes the following steps: directly mixing the coating layer and the matrix in the third mixing; or,

[0110] The coating layer and solvent are mixed and ball-milled to obtain a second slurry, and the second slurry is then mixed with the matrix in the third mixing process.

[0111] In this invention, there are no particular limitations on the conditions for ball milling, as long as the coating layer and solvent can be fully and uniformly mixed.

[0112] In this invention, there is no particular limitation on the amount of solvent used during ball milling, as long as the solid content of the second slurry obtained after ball milling is 30-55 wt%. In this invention, there is no particular limitation on the type of solvent used during ball milling, as long as uniform dispersion of the coating layer can be achieved.

[0113] In some embodiments of the present invention, preferably, in step (3), the weight ratio of the coating layer to the substrate is 0.01-5:100, for example, 0.01:100, 0.05:100, 0.1:100, 1:100, 3:100, 5:100, and any value within the range of any two values, preferably 0.05-3:100. At the preferred weight ratio, the coating layer can form a uniform coating of the substrate with relatively high coating density, effectively suppressing side reactions between the substrate and the electrolyte. Simultaneously, the coating layer thickness is not excessive, thus avoiding impacting the capacity and rate performance of the material. When the weight ratio is less than 0.01:100, the coating layer will not completely cover the substrate. The exposed parts that are not covered will still have side reactions with the electrolyte, causing a rapid deterioration in cycle performance. When the weight ratio is greater than 5:100, the coating layer on the substrate surface will be too thick, increasing the lithium ion transport path and affecting capacity and rate performance.

[0114] The third aspect of this invention provides a sodium-ion cathode material prepared by the preparation method provided in the second aspect.

[0115] The fourth aspect of this invention provides the application of the sodium-ion cathode material provided in the first or third aspect in a sodium-ion battery.

[0116] The fifth aspect of the present invention provides a sodium-ion battery comprising a positive electrode sheet made of a sodium-ion positive electrode material provided in the first or third aspect.

[0117] In some embodiments of the present invention, preferably, the sodium-ion battery retains ≥75% of its cycle life at 25°C and 80 cycles, more preferably 90-100%.

[0118] In some embodiments of the present invention, preferably, when the positive electrode is in a 4.2V charging state, the DSC heat dissipation temperature of the positive electrode is ≥280°C, and more preferably 290-350°C.

[0119] The sixth aspect of the present invention provides a sodium-ion battery pack comprising the sodium-ion battery provided in the fifth aspect.

[0120] A seventh aspect of the present invention provides an apparatus comprising the sodium-ion battery pack provided in the sixth aspect.

[0121] The present invention will be described in detail below through embodiments.

[0122] Ionic conductivity was measured using an electrochemical workstation.

[0123] The concentration gradient of Ti was measured using scanning electron microscopy (EDS).

[0124] Electronic conductivity was measured using a powder resistance meter via the four-probe method.

[0125] The residual alkali content was determined using a potentiometric titrator according to national standard methods.

[0126] The phase composition of the cathode material and the coating layer was determined using XRD diffraction according to national standard methods.

[0127] All raw materials used in the examples and comparative examples are commercially available products.

[0128] Preparation Example - Precursor Ni y Mn z M u Preparation of (OH)2

[0129] Nickel sulfate, manganese sulfate, and ferrous sulfate were mixed in proportions such that n(Ni):n(Mn):n(Fe) = 0.33:0.33:0.33, and then co-precipitated with ammonia and sodium hydroxide at 55°C for 46 hours. After washing and drying, the precursor Ni was obtained. 0.33 Fe 0.33 Mn 0.33 (OH)2.

[0130] Example 1

[0131] (1) Na2CO3, TiO2, Fe2O3 and water are mixed to obtain a slurry with a solid content of 50wt%, wherein the feed amounts of Na2CO3, TiO2 and Fe2O3 satisfy the following: n(Na):n(Ti):n(Fe)=2:5.9:0.1; the obtained slurry is processed in a spray dryer to obtain dried powder at a drying temperature of 110℃ for 0.5h. The powder is sintered at 800℃ for 6h under a nitrogen atmosphere to obtain the first sintered material. The first sintered material is then mixed with pure water (weight ratio of 100:100) and sand-milled in a sand mill for 4h to obtain the average particle size D. 50 The slurry was 50 nm thick, and the slurry was dried in a vacuum oven at 80°C for 2 hours to obtain powder. The powder was then pulverized by an air jet mill to obtain the coating layer C1.

[0132] The chemical composition of the coating layer C1 is Na2Ti. 5.9 Fe 0.1 O 13 Average particle size D 50 It is 100nm;

[0133] (2) Combine Na2CO3, Ni 0.33 Fe 0.33 Mn 0.33 The feed amounts of (OH)2 and TiO2 satisfy the following ratio: n(Na):[n(Ni)+n(Mn)+n(M)]:n(Ti)=1.03:0.99:0.01. Ni is first added to the mixture at 850 rpm in the mixing tank. 0.33 Fe 0.33 Mn 0.33 The mixture of (OH)2 and TiO2 was dry ball-milled for 4 hours; then Na2CO3 and Ni were mixed. 0.33 Fe 0.33 Mn 0.33 The mixture of (OH)2 and TiO2 was dry ball-milled for 4 h; the resulting second mixture was sintered in a muffle furnace at 950 °C for 8 h to obtain matrix B1;

[0134] The chemical composition of matrix B1 is Na. 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2;

[0135] (3) The above-mentioned coating layer C1 and substrate B1 are mixed in a high-speed mixer at a weight ratio of 1:100 for 20 minutes at 1000 rpm to obtain a third mixture; the above-mentioned third mixture is heat-treated in a muffle furnace under nitrogen atmosphere at 300°C for 4 hours to obtain sodium ion cathode material S1; wherein, sodium ion cathode material S1 is Na2Ti5.9 Fe 0.1 O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0136] Example 2

[0137] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0138] (1) Same as in Example 1, a coating layer C2 was prepared;

[0139] The chemical composition of the coating layer C2 is Na2Ti. 5.9 Fe 0.1 O 13 Average particle size D 50 It is 100nm;

[0140] (2) Combine Na2CO3, Ni 0.33 Fe 0.33 Mn 0.33 The feed amount of (OH)2 satisfies: n(Na):[n(Ni)+n(Mn)+n(M)]=1.03:1. The mixture is dry ball-milled in a mixing tank at 850 rpm for 4 h. The resulting second mixture is sintered in a muffle furnace at 950℃ for 8 h to obtain matrix B2.

[0141] The chemical composition of matrix B2 is Na. 1.03 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2;

[0142] (3) The above-mentioned coating layer C2 and substrate B2 are mixed in a high-speed mixer at a weight ratio of 1:100 for 20 minutes at 1000 rpm to obtain a third mixture; the above mixture is heat-treated in a muffle furnace under nitrogen atmosphere at 300°C for 4 hours to obtain sodium ion cathode material S2; wherein, sodium ion cathode material S2 is Na2Ti 5.9 Fe 0.1 O 13 Coated Na 1.03 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0143] Example 3

[0144] (1) Na2CO3, TiO2 and water are mixed to obtain a slurry with a solid content of 50wt%, wherein the feeding amounts of Na2CO3 and TiO2 satisfy the ratio of n(Na):n(Ti) = 2:6; the obtained slurry is processed in a spray dryer to obtain dried powder at a drying temperature of 110℃ for 0.5h; the powder is sintered at 800℃ for 6h under a nitrogen atmosphere to obtain the first sintered material; then the first sintered material is mixed with pure water (weight ratio of 100:100) and sand-milled in a sand mill for 4h to obtain the average particle size D. 50 The slurry was 50 nm thick, and the slurry was dried in a vacuum oven at 80°C for 2 hours to obtain powder. The powder was then pulverized by an air jet mill to obtain a coating layer C3.

[0145] The chemical composition of the coating layer C3 is Na2Ti6O. 13 Average particle size D 50 It is 100nm;

[0146] (2) Same as step (2) in Example 1, to prepare matrix B3;

[0147] The chemical composition of matrix B3 is Na. 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2;

[0148] (3) The above-mentioned coating layer C3 and substrate B3 are mixed in a high-speed mixer at a weight ratio of 1:100 for 20 min at 1000 rpm to obtain a third mixture; the above mixture is heat-treated in a muffle furnace under nitrogen atmosphere at 300℃ for 4 h to obtain sodium ion cathode material S3; wherein, sodium ion cathode material S3 is Na2Ti6O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0149] Example 4

[0150] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0151] (1) Same as in Example 1, a coating layer C4 was prepared;

[0152] (2) Combine Na2CO3, Ni 0.33 Fe 0.33 Mn 0.33The feed amounts of (OH)2 and TiO2 satisfy the following ratio: n(Na):[n(Ni)+n(Mn)+n(M)]:n(Ti)=1.03:0.99:0.01. Ni is first added to the mixture at 850 rpm in the mixing tank. 0.33 Fe 0.33 Mn 0.33 The mixture of (OH)2 and TiO2 was dry ball-milled for 4 hours; then Na2CO3 and Ni were mixed. 0.33 Fe 0.33 Mn 0.33 The mixture of (OH)2 and TiO2 was dry ball-milled for 4 h; the resulting second mixture was sintered in a muffle furnace at 950 °C for 10 h to obtain matrix B4;

[0153] The chemical composition of matrix B1 is Na. 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2;

[0154] (3) The above-mentioned coating layer C4 and substrate B4 are mixed in a high-speed mixer at a weight ratio of 1:100 for 20 min at 1000 rpm to obtain a third mixture; the above mixture is heat-treated in a muffle furnace under nitrogen atmosphere at 300℃ for 4 h to obtain sodium ion cathode material S4; wherein, sodium ion cathode material S4 is Na2Ti6O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0155] Example 5

[0156] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0157] (1) Same as in Example 1, a coating layer C5 was prepared;

[0158] (2) Same as in Example 1, matrix B5 was prepared;

[0159] (3) The above-mentioned coating layer C5 and substrate B5 are mixed in a high-speed mixer at a weight ratio of 1:100 for 20 minutes at 1000 rpm to obtain a third mixture; the above-mentioned third mixture is heat-treated in an oxygen atmosphere muffle furnace at 300°C for 4 hours to obtain sodium ion cathode material S5; wherein, sodium ion cathode material S5 is Na2Ti 5.9 Fe 0.1 O 13 Coated Na 1.03 Ni0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0160] Example 6

[0161] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0162] (1) Same as step (1) in Example 3, prepare the coating layer C6;

[0163] The chemical composition of the coating layer C6 is Na2Ti6O. 13 Average particle size D 50 It is 100nm;

[0164] (2) Same as step (2) in Example 2, prepare matrix B6;

[0165] The chemical composition of matrix B6 is Na. 1.03 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2;

[0166] (3) Similar to Example 1, the coating layer C6 was mixed with the substrate B6 and then subjected to heat treatment to obtain the sodium ion cathode material S6. The sodium ion cathode material S6 is Na2Ti6O. 13 Coated Na 1.03 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0167] Example 7

[0168] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0169] (1) Al2O3 was used to replace Fe2O3 to prepare the coating layer C7;

[0170] The chemical composition of the coating layer C7 is Na2Ti. 5.9 Al 0.1 O 13 Average particle size D 50 It is 100nm;

[0171] (2) Same as in Example 1, matrix B7 was prepared;

[0172] (3) Similar to Example 1, the coating layer C7 was mixed with the substrate B7 and then subjected to heat treatment to obtain the sodium ion cathode material S7. The sodium ion cathode material S7 is Na2Ti. 5.9 Al 0.1 O13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0173] Example 8

[0174] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0175] (1) Na2CO3, TiO2, MgO and water are mixed to obtain a slurry with a solid content of 50wt%, wherein the feed amounts of Na2CO3, TiO2 and MgO satisfy the following ratio: n(Na):n(Ti):n(Mg)=2.2:5.9:0.1; the obtained slurry is processed in a spray dryer to obtain dried powder at a drying temperature of 110℃ for 0.5h. The powder is sintered at 800℃ for 6h under a nitrogen atmosphere to obtain the first sintered material. The first sintered material is then mixed with pure water (weight ratio of 100:100) and sand-milled in a sand mill for 4h to obtain the average particle size D. 50 The slurry was 50 nm thick, and the slurry was dried in a vacuum oven at 80°C for 2 hours to obtain powder. The powder was then pulverized by an air jet mill to obtain a coating layer C8.

[0176] The chemical composition of the coating layer C8 is Na. 2.2 Ti 5.9 Mg 0.1 O 13 Average particle size D 50 It is 100nm;

[0177] (2) Same as in Example 1, substrate B8 was prepared;

[0178] (3) Unlike Example 1, the weight ratio of the coating layer C8 to the substrate B8 is 2:100, resulting in sodium ion cathode material S8, wherein the sodium ion cathode material S8 is Na2Ti 5.9 Fe 0.1 O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0179] Example 9

[0180] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0181] (1) Same as Example 1;

[0182] (2) Same as in Example 1;

[0183] (3) Unlike Example 1, the weight ratio of the coating layer C1 to the substrate B1 is 0.02:100, resulting in sodium ion cathode material S9, wherein the sodium ion cathode material S9 is Na2Ti. 5.9 Fe 0.1 O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0184] Example 10

[0185] Sodium-ion cathode materials were prepared according to the method in Example 1, specifically:

[0186] (1) Same as Example 1;

[0187] (2) Same as in Example 1;

[0188] (3) Unlike Example 1, the weight ratio of the coating layer C1 to the substrate B1 is 6:100, resulting in sodium ion cathode material S10, wherein the sodium ion cathode material S10 is Na2Ti 5.9 Fe 0.1 O 13 Coated Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0189] Comparative Example 1

[0190] Combine Na2CO3, Ni 0.33 Fe 0.33 Mn 0.33 The feed amounts of (OH)2 and TiO2 satisfy the following: n(Na):[n(Ni)+n(Mn)+n(M)]:n(Ti)=1.03:0.99:0.01. The mixture is dry ball-milled at 850 rpm for 4 hours in a mixing tank. The resulting mixture is then sintered in a muffle furnace at 950℃ for 8 hours to obtain the cathode material D1.

[0191] Among them, the chemical composition of D1 is Na 1.03 Ni 0.33 Fe 0.33 Mn 0.33 Ti 0.01 O2.

[0192] Comparative Example 2

[0193] Sodium-ion cathode materials were prepared according to the method in Example 1, with the following difference:

[0194] (1) The dried powder was sintered in an oxygen atmosphere to obtain a coating layer DC2.

[0195] The chemical composition of the coating layer DC2 is Na. 18 Ti 59 Fe 01 O 129 The average particle size is 100 nm.

[0196] (2) Same as in Example 1;

[0197] (3) Same as in Example 1; sodium ion cathode material DS2 was prepared.

[0198] Comparative Example 3

[0199] Sodium-ion cathode materials were prepared according to the method in Example 1, with the following difference:

[0200] (1) The feed amounts of Na2CO3, TiO2, and Fe2O3 satisfy the following ratio: n(Na):n(Ti):n(Fe)=2:2.9:0.1. The dried powder is sintered under an oxygen atmosphere to obtain the coating layer DC3.

[0201] The chemical composition of the coating layer DC3 is Na2Ti. 2.9 Fe 0.1 O7 has an average particle size of 100 nm.

[0202] (2) Same as in Example 1;

[0203] (3) Same as in Example 1; sodium ion cathode material DS3 was prepared.

[0204] Table 1

[0205]

[0206] a This refers to a matrix that is not Ti-doped.

[0207] b This refers to a matrix doped with Ti, but without a gradient distribution of Ti.

[0208] Table 1 (continued)

[0209]

[0210]

[0211] a This refers to a matrix that is not Ti-doped.

[0212] bThis refers to a matrix doped with Ti, but the Ti is not distributed in a gradient.

[0213] Table 1 (continued)

[0214]

[0215] a This refers to a matrix that is not Ti-doped.

[0216] b This refers to a matrix doped with Ti, but without a gradient distribution of Ti.

[0217] Table 1 (continued)

[0218]

[0219]

[0220] a This refers to a matrix that is not Ti-doped.

[0221] b This refers to a matrix doped with Ti, but without a gradient distribution of Ti.

[0222] Table 1 (continued)

[0223]

[0224] a This refers to a matrix that is not Ti-doped.

[0225] b This refers to a matrix doped with Ti, but without a gradient distribution of Ti.

[0226] The particle size, ionic conductivity, electronic conductivity, and volume impedance of the sodium ion cathode materials prepared in the examples and comparative examples were tested, and the results are shown in Table 2.

[0227] Table 2

[0228]

[0229]

[0230] Test case

[0231] The cathode materials prepared in the examples and comparative examples were subjected to initial charge-discharge performance and cycle performance tests.

[0232] Button cells are prepared according to the following steps:

[0233] 95g of positive electrode material, 2.5g of acetylene black and 2.5g of polyvinylidene fluoride (PVDF) were mixed, coated on aluminum foil and dried. The mixture was then stamped with a pressure of 100MPa to obtain a positive electrode sheet with a diameter of 12mm and a thickness of 120μm. The positive electrode sheet was then placed in a vacuum drying oven and dried at 120℃ for 12h.

[0234] The negative electrode uses a Na metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator uses a polyethylene porous membrane with a thickness of 25 μm; the electrolyte uses an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 mol / L NaPF6 as the electrolyte.

[0235] The positive electrode, separator, negative electrode, and electrolyte are assembled into a 2025 type button cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0236] Test conditions:

[0237] The assembled 2025 coin cells were left to stand for 12 hours. The initial charge-discharge capacity parameters were measured in a coin cell test cabinet at 25℃ and 0.1C@2.0-4.0V. Then, the rate performance parameters were tested sequentially at 0.1C and 1C rates, and the cycle performance was tested after 80 cycles at 1C. After two 0.1C charge-discharge cycles, the coin cells were recharged to 4.2V. The positive electrode was then removed and placed in a differential thermal-gravimetric analyzer (DSC) for testing. The results are shown in Table 3.

[0238] Table 3

[0239] 0.1C discharge (mAh / g) 1C discharge (mAh / g) 80-week cycle retention rate DSC peak temperature (°C) Example 1 152 145 93％ 295 Example 2 146 134 89％ 294 Example 3 149 140 92％ 296 Example 4 145 132 90％ 290 Example 5 148 142 91％ 294 Example 6 141 128 89％ 281 Example 7 148 143 93％ 295 Example 8 146 140 94％ 307 Example 9 147 140 91％ 292 Example 10 132 125 93％ 300 Comparative Example 1 132 115 85％ 270 Comparative Example 2 140 120 87％ 280 Comparative Example 3 135 110 87％ 272

[0240] Figure 1 This is a cross-sectional EDS line scan of the sodium-ion cathode material S1 prepared in Example 1, obtained by... Figure 1 It can be seen that Ti elements are distributed in a gradient in the matrix of the cathode material and the coating layer is doped with Fe elements.

[0241] Figure 2 The XRD diffraction pattern of the coated layer C1 sample prepared in Example 1 shows that the coated layer C1 is Na2Ti6O. 13 Pure phase of structure.

[0242] Figure 3 The XRD diffraction pattern of the cathode material prepared in Comparative Example 1 shows that the cathode material is a pure phase with a NaFeO2 structure.

[0243] Figure 4The XRD diffraction pattern of the cathode material prepared in Example 10 shows that, in addition to the main phase of NaFeO2, Na2Ti6O2 is also present in the cathode material. 13 The diffraction peaks of the structure indicate the presence of Na2Ti6O on the surface of the cathode material. 13 The cladding layer of the structure.

[0244] Figure 5 The above are DSC spectra of the positive electrode sheets prepared from the sodium-ion positive electrode materials of Example 1 and Comparative Example 1 at a charging state of 4.2V. Figure 2 It can be seen that the thermal stability of the positive electrode sheet made from the sodium ion positive electrode material of Example 1 with a nano-coating layer on the surface is significantly better than that of the positive electrode sheet made from the sodium ion positive electrode material of Comparative Example 1 without a coating layer, indicating that the safety performance of the sodium ion positive electrode material provided in Example 1 is better than that of the sodium ion positive electrode material of Comparative Example 1.

[0245] As can be seen from the results in Table 3, compared with Comparative Examples 1-3, the sodium-ion battery with positive electrode sheet made of sodium-ion positive electrode material from Examples 1-10 has higher charge-discharge capacity and cycle performance, and the positive electrode sheet has a higher thermal runaway temperature, which means that thermal runaway of the positive electrode material will only occur at higher ambient temperatures, making the battery more reliable.

[0246] Furthermore, the coating layer of the sodium-ion cathode material in Example 1 contains doped elements and the Ti element in the matrix is ​​distributed in a gradient. When this sodium-ion cathode material is used in a sodium-ion battery, the charge-discharge capacity, cycle performance and heat release temperature are further improved.

[0247] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A sodium-ion cathode material, characterized in that, The positive electrode material includes a matrix and a coating layer covering the matrix; The matrix has the composition shown in Formula I: Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤ x ≤0.4, 0.2≤ y ≤0.6, 0.1≤ z ≤0.5, 0.1≤ u ≤0.5, 0.01≤ v ≤0.02, y + z + u+v =1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta; In this embodiment, the Ti element exhibits a gradient-increasing distribution along the direction from the center of the matrix to its surface. The coating layer has the composition shown in Formula II: Na 2-β Ti 6-α M′ α O 13 Equation II, where 0 < α <0.6, -2≤β<1; M′ is selected from at least one of Mg, Fe and Al.

2. The sodium-ion cathode material according to claim 1, wherein, In Equation I, -0.2 ≤ x ≤0.4, 0.2≤ y ≤0.5, 0.2≤ z ≤0.5, 0.2≤ u ≤0.5, 0.01≤ v ≤0.02, y + z + u+v =1; M is selected from at least one of Fe, Cu, Nb, Co, V and Cr.

3. The sodium-ion cathode material according to claim 1 or 2, wherein, In Equation II, 0 < α <0.5, -2≤β<1.

4. The sodium-ion cathode material according to claim 1 or 2, wherein, The rate of increase of Ti element along the direction from the center of the matrix to its surface is 0.001-0.3 mol% / μm.

5. The sodium-ion cathode material according to claim 4, wherein, The rate of increase of Ti element along the direction from the center of the matrix to its surface is 0.001-0.2 mol% / μm.

6. The sodium-ion cathode material according to claim 1 or 2, wherein, The weight ratio of the substrate to the coating layer is 100:0.01-5; And / or, the thickness of the coating layer is 10-200 nm; And / or, the average particle size D50 of the cathode material is 2-30µm.

7. The sodium-ion cathode material according to claim 6, wherein, The weight ratio of the substrate to the coating layer is 100:0.05-3; And / or, the thickness of the coating layer is 10-100 nm; And / or, the average particle size D50 of the cathode material is 4-12µm.

8. The sodium-ion cathode material according to claim 1 or 2, wherein, The positive electrode material has an ionic conductivity of 10. -4 Up to 10 -3 S / cm; And / or, the electronic conductivity of the positive electrode material is 10. -7 Up to 10 -6 S / cm.

9. The sodium-ion cathode material according to claim 8, wherein, The positive electrode material has an ionic conductivity of 5 × 10⁻⁶. -4 Up to 10 -3 S / cm; And / or, the electronic conductivity of the positive electrode material is 5 × 10⁻⁶. -7 Up to 10 -6 S / cm.

10. A method for preparing the sodium-ion cathode material according to any one of claims 1-9, characterized in that, The preparation method includes: (1) The first sodium source, M′ source, titanium source and solvent are mixed for the first time to obtain the first slurry; the first slurry is subjected to the first drying and the first sintering in sequence to obtain the first sintered product, and the first sintered product is crushed and dried in sequence to obtain the coating layer; The coating layer has the composition shown in Formula II: Na 2-β Ti 6-α M′ α O 13 Equation II, where 0 < α <0.6, -2≤β<1; M′ is selected from at least one of Mg, Fe, and Al; (2) The second sodium source, nickel source, manganese source, M source and titanium source are mixed for the second time, and the resulting second mixture is subjected to a second drying and a second sintering in sequence to obtain the matrix; The matrix has the composition shown in Formula I: Na 1-x [Ni y Mn z M u Ti v O2 formula I, where -0.4≤ x ≤0.4, 0.2≤ y ≤0.6, 0.1≤ z ≤0.5, 0.1≤ u ≤0.5, 0.01≤ v ≤0.02, y + z + u+v =1; M is selected from at least one of Fe, Mg, Al, Cu, Zn, Zr, Nb, Co, Y, V, Sc, Cr, W, La, Mo, Os, Pr, Re, Ru, Sr, Sm and Ta; (3) The coating layer and the substrate are mixed for a third time, and the resulting third mixture is heat-treated to obtain the sodium ion cathode material; The first sintering is carried out in a non-oxidizing gas.

11. The preparation method according to claim 10, wherein, In step (1), the solid content of the first slurry is 30-55 wt%; And / or, the conditions for the first sintering include: a temperature of 500-1200℃; and a time of 4-10h; And / or, the crushing step includes: crushing the first sintered product and the solvent at a weight ratio of 100:50-100; And / or, the drying conditions include: a temperature of 60-120°C and a time of 0.5-5 hours; And / or, the average particle size D50 of the coating layer is 10-200 nm.

12. The preparation method according to claim 11, wherein, The conditions for the first sintering include: a temperature of 700-850℃ and a time of 6-8 hours; And / or, the average particle size D50 of the coating layer is 10-100 nm.

13. The preparation method according to claim 10 or 11, wherein, The second mixing includes the following steps: co-precipitating a nickel source, a manganese source, and an M source to obtain a precursor Ni. y Mn z M u (OH)2, the precursor Ni y Mn z M u (OH)2 is mixed with a titanium source (I) and then mixed with a second sodium source (II) to obtain a second mixture.

14. The preparation method according to claim 10 or 11, wherein, The conditions for the second sintering include: a temperature of 600-1200℃ and a time of 6-10 hours; And / or, the surface residual alkali content of the matrix is ​​≤2wt%.

15. The preparation method according to claim 14, wherein, The conditions for the second sintering include: a temperature of 750-1200℃ and a time of 8-10 hours; And / or, the surface residual alkali content of the matrix is ​​0.1-1 wt%.

16. The preparation method according to claim 10 or 11, wherein, The heat treatment is carried out in a non-oxidizing gas; And / or, the conditions for the heat treatment include: a temperature of 200-600℃; and a time of 4-8h.

17. The preparation method according to claim 16, wherein, The heat treatment conditions include: a temperature of 400-600℃ and a time of 6-8 hours.

18. The preparation method according to claim 10 or 11, wherein, The third mixing includes the following steps: directly mixing the coating layer and the matrix in the third mixing.

19. The preparation method according to claim 10 or 11, wherein, The third mixing includes the following steps: mixing the coating layer and the solvent and ball milling them to obtain a second slurry, and then mixing the second slurry with the matrix in the third mixing.

20. The preparation method according to claim 19, wherein, The solid content of the second slurry is 30-55 wt%.

21. The preparation method according to claim 10 or 11, wherein, The weight ratio of the coating layer to the substrate is 0.01-5:

100.

22. The preparation method according to claim 10 or 11, wherein, The weight ratio of the coating layer to the substrate is 0.05-3:

100.

23. A sodium-ion cathode material prepared by the preparation method according to any one of claims 10-22.

24. The application of the sodium-ion cathode material according to any one of claims 1-9 and 23 in sodium-ion batteries.

25. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode sheet made of the sodium-ion positive electrode material as described in any one of claims 1-9 and 23.

26. The sodium-ion battery according to claim 25, wherein, The sodium-ion battery retains ≥75% efficiency after 80 cycles at 25°C. And / or, in the 4.2V charging state, the DSC heat dissipation temperature of the positive electrode is ≥280℃.

27. The sodium-ion battery according to claim 26, wherein, The sodium-ion battery retains 90-100% of its efficiency at 25°C and 80 cycles. And / or, in the 4.2V charging state, the DSC heat dissipation temperature of the positive electrode is 290-350°C.

28. A sodium-ion battery pack, characterized in that, The sodium-ion battery pack comprises the sodium-ion battery according to any one of claims 25-27.

29. An apparatus comprising the sodium-ion battery pack of claim 28.

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