Single-crystal sodium-ion battery cathode material and preparation method thereof, and sodium-ion battery

Abstract

This invention relates to the field of sodium-ion batteries, and discloses a single-crystal sodium-ion battery cathode material and its preparation method, as well as a sodium-ion battery. The roundness R of the single-crystal particles of the cathode material and the size distribution concentration B of the single-crystal particles measured by SEM are also disclosed. P90 The following relationship is satisfied between them: 0.4 ≤ R / B P90 The ratio of agglomerated particles in the cathode material is ≤0.9; the proportion of agglomerated particles C in the cathode material is ≤5%. The monocrystalline sodium-ion cathode material satisfies a specific relationship between the roundness of the monocrystalline particles and the size distribution concentration of the monocrystalline particles, indicating that the cathode material can simultaneously take into account its own roundness and the inter-particle gradation relationship, thus having a high compaction density. When used in sodium-ion batteries, it can effectively improve the energy density, cycle stability and thermal stability of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, specifically to a single-crystal sodium-ion battery cathode material and its preparation method, and a sodium-ion battery. Background Technology

[0002] With the increasing scarcity of traditional energy sources and the growing severity of environmental pollution, the development of new clean energy sources has become a global consensus. In recent decades, lithium-ion batteries have been extensively researched due to their advantages such as high specific capacity and high energy density, and are widely used in various aspects of life, including new energy vehicles, large-scale energy storage, and portable mobile devices, profoundly impacting our lives. However, due to the limited reserves of lithium on Earth, accounting for only about 0.0065% of the Earth's crust and unevenly distributed globally, the price of raw materials for lithium-ion batteries has been rising continuously with their development, significantly limiting their potential for future applications. Sodium and lithium belong to the same group in the periodic table, have the same number of outermost electrons, and similar chemical properties. Furthermore, sodium is widely distributed in the Earth's crust, with an abundance of 2.74%, and its price is far lower than that of lithium-containing mineral raw materials, giving it a significant cost advantage over lithium-ion batteries. Therefore, sodium-ion batteries show great promise for applications in the energy storage field.

[0003] Currently, sodium-ion battery cathode materials that have received widespread attention from researchers mainly include layered metal oxides, Prussian blue compounds, and polyanionic compounds. Among them, transition metal oxides are considered the most promising sodium-ion battery cathode materials due to their high specific capacity and manufacturing process very similar to that of ternary lithium batteries. However, transition metal oxides also face problems due to their own structural composition, such as easy structural changes / phase transitions during sodium ion insertion / extraction, volume expansion, and large internal stress, resulting in poor cycle performance. Therefore, designing materials as more structurally stable single crystals can effectively improve the cycle performance and thermal stability of the materials and reduce gas generation during cycling. However, most of the reported single-crystal cathode materials have problems such as small single-crystal particle size, severe adhesion between particles (high agglomeration rate, poor independence), and low roundness of individual particles. This results in low compaction density of the final material, and the adhered particles are prone to breakage during cycling, exposing new interfaces and causing serious side reactions, thus preventing the full realization of the advantages of single-crystal materials.

[0004] Therefore, providing single-crystal sodium cathode materials with larger particle size, high roundness, suitable particle size distribution, and high compaction density is of great significance for improving material structure and cycle stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing monocrystalline cathode materials for sodium-ion batteries, such as small particle size, poor independence, and low particle roundness. This invention provides a monocrystalline sodium-ion cathode material, its preparation method, and a sodium-ion battery. The monocrystalline sodium-ion cathode material exhibits a specific relationship between the roundness of its monocrystalline particles and the concentration of their size distribution, indicating that the cathode material can simultaneously achieve both its own roundness and the gradation relationship between particles, thus possessing high compaction density. When used in sodium-ion batteries, it can effectively improve the energy density, cycle stability, and thermal stability of the sodium-ion battery.

[0006] To achieve the above objectives, the present invention provides a single-crystal sodium-ion cathode material, wherein the roundness R of the single-crystal particles of the cathode material and the size distribution concentration B of the single-crystal particles measured by SEM are... P90 The following relationship is satisfied between them: 0.4 ≤ R / B P90 ≤0.9;

[0007] The proportion of agglomerated particles in the cathode material is C≤5%.

[0008] A second aspect of the present invention provides a method for preparing a single-crystal sodium-ion cathode material, characterized in that the preparation method includes the following steps:

[0009] (1) A nickel-iron-manganese precursor, a sodium source, and optionally an M source are mixed and subjected to a first sintering and crushing process in an oxygen-containing atmosphere to obtain single-crystal sodium-ion cathode material process product I; or,

[0010] A precursor containing nickel, iron, manganese, and optionally M elements is mixed with a sodium source, and then subjected to a first sintering and crushing in an oxygen-containing atmosphere to obtain a single-crystal sodium-ion cathode material process product I.

[0011] (2) The single-crystal sodium ion cathode material process product I is mixed with a coating agent that optionally contains G element, and then sintered and crushed for the second time in an oxygen-containing atmosphere to obtain the single-crystal sodium ion cathode material.

[0012] The first sintering is a multi-stage sintering process, including: heating stage I, constant temperature stage I, heating stage II, and constant temperature stage II. The holding time t2 of constant temperature stage II is greater than the holding time t1 of constant temperature stage I, and the holding temperature T2 of constant temperature stage II is greater than the holding temperature T1 of constant temperature stage I.

[0013] A third aspect of the present invention provides a single-crystal sodium-ion cathode material prepared by the above-described preparation method.

[0014] A fourth aspect of the present invention provides a sodium-ion battery, characterized in that the sodium-ion battery comprises the above-mentioned monocrystalline sodium-ion cathode material.

[0015] Through the above technical solutions, the monocrystalline sodium-ion cathode material, its preparation method, and the sodium-ion battery provided by this invention achieve the following beneficial effects:

[0016] The monocrystalline sodium-ion cathode material provided by this invention satisfies a specific relationship between the roundness of its monocrystalline particles and the size distribution concentration of the monocrystalline particles obtained by SEM. Furthermore, the cathode material has a low agglomeration rate, indicating that the cathode material can simultaneously take into account its own roundness and the inter-particle gradation relationship, thereby having a high compaction density. When used in sodium-ion batteries, it can effectively improve the energy density, cycle stability, and thermal stability of sodium-ion batteries.

[0017] Furthermore, the monocrystalline sodium-ion cathode material provided by this invention has a large particle size, and the monocrystalline particles have good independence and high roundness, which can effectively improve the material morphology and enhance the internal structural stability, so that the cathode material has high compaction density and thermal stability. When used in sodium-ion batteries, it can effectively improve the energy density, cycle stability and thermal stability of sodium-ion batteries.

[0018] In the preparation method of the single-crystal sodium-ion cathode material provided by the present invention, the solid-state reaction of the mixture of precursor material, sodium source and optional dopant is realized by adopting a multi-stage sintering method. This enables better particle growth of the cathode material in both stages of single-crystal growth during sintering, resulting in more rounded and regular cathode material particles. The obtained single-crystal cathode material has a rounded and regular morphology, uniform particle size, and less agglomeration and adhesion between particles, resulting in a high compaction density of the single-crystal cathode material.

[0019] Furthermore, the method for producing single-crystal sodium-ion cathode materials provided by this invention is simple, efficient, and suitable for large-scale production. Attached Figure Description

[0020] Figure 1 This is a SEM image of cathode material A1;

[0021] Figure 2 This is a SEM image of cathode material A2;

[0022] Figure 3 This is a SEM image of cathode material A3;

[0023] Figure 4 This is a SEM image of the cathode material D1;

[0024] Figure 5 This is a SEM image of the cathode material D2;

[0025] Figure 6These are the capacity retention curves for Example 1 (A1) and Comparative Example 1 (D1) after 80 cycles. Detailed Implementation

[0026] 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.

[0027] The first aspect of this invention provides a single-crystal sodium-ion cathode material, wherein the roundness R of the single-crystal particles of the cathode material and the size distribution concentration B of the single-crystal particles measured by SEM are... P90 The following relationship is satisfied between them: 0.40 ≤ R / B P90 ≤0.90;

[0028] The proportion of agglomerated particles in the cathode material is C≤5%.

[0029] In this invention, the inventors discovered that when the roundness R of the single-crystal particles of the cathode material is compared with the size distribution concentration B of the single-crystal particles measured by SEM, the yield of the cathode material is significantly higher than that of the cathode material. P90 When the above relationship is satisfied and the proportion C of agglomerated particles in the cathode material meets the above range, it indicates that the cathode material simultaneously considers the roundness of its particles and the gradation relationship between different single crystal particles. Furthermore, the agglomeration of particles in the cathode material is relatively small, which can effectively improve the compaction density of the material. When used to make electrode sheets, it has better filling properties, enabling the production of high-energy-density electrodes and improving the output characteristics of sodium-ion secondary batteries. The larger R is, the higher the particle roundness, requiring B... P90 The particle size distribution should also be larger to achieve high compaction performance. Conversely, if R is smaller, the particle size distribution should be slightly narrower, utilizing the inter-particle gaps to fill the gaps and achieve high-compaction material properties. When R and B... P90 When the ratio does not satisfy the above relationship, the performance of the cathode material deteriorates because the roundness of the single crystal particles does not match the gradation relationship between different particles.

[0030] In this invention, the agglomerated particles refer to secondary particles composed of no less than 5 primary particles. The agglomeration rate is obtained by SEM testing and calculation. Specifically, the agglomeration rate C = f / n × 100%, where f is the number of agglomerated particles in the cathode material; n is the total number of particles in the cathode material; wherein the total number of particles n includes the number of single crystal particles and the number of agglomerated particles.

[0031] Furthermore, 0.50 ≤ R / B P90 ≤0.80.

[0032] Furthermore, the proportion of agglomerated particles in the cathode material is C≤2%.

[0033] According to the present invention, the longest diagonal dimension D of the single crystal particles of the cathode material, as measured by SEM, is... c The projected area S satisfies the following relationship:

[0034] 0.55≤R=S / π(D c / 2) 2 ≤1.

[0035] In this invention, when the longest diagonal dimension D of the single crystal particle of the cathode material is measured by SEM... c The ratio between the projected area S and the projected area S satisfies the above relationship, and the closer the ratio is to 1, the higher the roundness of the material particles, and the easier it is for the material to obtain a higher compaction density.

[0036] In this invention, the projected area S of the single crystal particles of the cathode material, measured by SEM, is obtained using any commercially available graphic analysis software.

[0037] Furthermore, 0.60 ≤ R ≤ 1.

[0038] According to the present invention, the single crystal size D of the cathode material is measured by SEM. P90 D P10 With D P50 The following relationship must be satisfied:

[0039] 0.7≤B P90 =(D P90 -D P10 ) / D P50 ≤1.5.

[0040] Among them, D P10 In the SEM image of the cathode material, the particle size corresponding to a cumulative single-crystal particle size distribution percentage of 10% is shown; D P50 In the SEM image of the cathode material, the particle size corresponding to a cumulative single-crystal particle size distribution percentage of 50% is shown; D P90 The particle size is the percentage of cumulative single-crystal particle size distribution that corresponds to 90% in the SEM image of the cathode material.

[0041] In this invention, based on quantity, D P10 This indicates that 10% of the cathode material has a single crystal size smaller than D. P10 D P50 This indicates that 50% of the cathode material has a single crystal size smaller than D. P50 D P90 This indicates that 90% of the cathode materials have a single crystal size smaller than D. P90 .

[0042] In this invention, the D of a single particle in the cathode material, as measured by SEM, is... P This is the average of the longest and shortest diagonals of this particle.

[0043] In this invention, when the single crystal size of the cathode material measured by SEM satisfies the above relationship, it indicates that the cathode material has a suitable particle size distribution, and particles of different sizes can be better graded and filled, resulting in a higher compaction density of the material.

[0044] Furthermore, 0.9 ≤ B P90 ≤1.3.

[0045] According to the present invention, the average particle size D of the single crystal particles of the cathode material, as measured by SEM, is... PS The following relationship must be satisfied:

[0046] Among them, D c D is the longest diagonal of the single-crystal particles of the cathode material as measured by SEM; d is the shortest diagonal of the single crystal particles of the cathode material as measured by SEM; n is the total number of single crystal particles in the SEM of the cathode material.

[0047] In this invention, when the average particle size D of the single crystal particles of the cathode material is measured by SEM... PS Satisfying the above relationship indicates that the cathode material has a large particle size and a low specific surface area, which makes the cathode material exhibit better high-temperature storage and cycle performance as well as excellent processing performance.

[0048] Furthermore, 1.8μm≤D PS ≤5μm.

[0049] In this invention, the R, Dc, and D of the positive electrode material P90 D P10 D P50 B P90 and D PS The statistical results are obtained by randomly selecting approximately 300 single-crystal particles as samples from the SEM image. SEM testing requires random sampling of the cathode material and random selection of regions; the resulting SEM image should represent the average level of the cathode material. The diagonal values ​​of the major and minor axes of the single crystals can be obtained by any graphics analysis software or through manual measurement. The statistical results, Rc, Dd, are... P90 D P10 D P50 B P90 and D PS It can be obtained by any available statistical software.

[0050] According to the present invention, the particle size D of the positive electrode material is measured by a laser particle size analyzer. 10 It ranges from 2 to 4.5 μm.

[0051] According to the present invention, the particle size D of the positive electrode material is measured by a laser particle size analyzer. 50 It is 4-8μm.

[0052] According to the present invention, the particle size D of the positive electrode material is measured by a laser particle size analyzer. 90 It is 6-14μm.

[0053] According to the present invention, the particle size distribution K of the cathode material is measured by a laser particle size analyzer. 90 It is 1-1.5.

[0054] According to the present invention, the compaction density of the positive electrode material is 3.1-3.6 g / cm³. 3 .

[0055] In this invention, the cathode material has a high compaction density, thereby enabling the sodium-ion battery assembled from the cathode material to have a higher energy density.

[0056] Furthermore, the compaction density of the positive electrode material is 3.3-3.6 g / cm³. 3 .

[0057] According to the present invention, the positive electrode material has the composition shown in Formula I:

[0058] Na a Ni e Fe b Mn c T d O 2+f (Formula I)

[0059] Wherein, 0.95≤a≤1.1, 0.03≤b≤0.5, 0.03≤c≤0.5, 0≤d≤0.25, 0≤e≤0.50, -0.1≤f≤0.1;

[0060] T is selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, Sr, and Cu.

[0061] In one specific embodiment of the present invention, element T includes element M and element G; wherein element M includes a dopant element, and M is selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, Sr, and Cu. Element G includes a coating element, and G is selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, Sr, and Cu.

[0062] Furthermore, 0.96≤a≤1.08, 0.05≤b≤0.45, 0.05≤c≤0.45, 0.001≤d≤0.20, 0.05≤e≤0.45, and -0.08≤f≤0.08.

[0063] A second aspect of the present invention provides a method for preparing a single-crystal sodium-ion cathode material, wherein the preparation method includes the following steps:

[0064] (1) A nickel-iron-manganese precursor, a sodium source, and optionally an M source are mixed and subjected to a first sintering and crushing process in an oxygen-containing atmosphere to obtain single-crystal sodium-ion cathode material process product I; or,

[0065] A precursor containing nickel, iron, manganese, and optionally M elements is mixed with a sodium source, and then subjected to a first sintering and crushing in an oxygen-containing atmosphere to obtain a single-crystal sodium-ion cathode material process product I.

[0066] (2) The single-crystal sodium ion cathode material process product I is mixed with a coating agent that optionally contains G element, and then sintered and crushed for the second time in an oxygen-containing atmosphere to obtain the single-crystal sodium ion cathode material.

[0067] The first sintering is a multi-stage sintering process, including: heating stage I, constant temperature stage I, heating stage II, and constant temperature stage II. The holding time t2 of constant temperature stage II is greater than the holding time t1 of constant temperature stage I, and the holding temperature T2 of constant temperature stage II is greater than the holding temperature T1 of constant temperature stage I.

[0068] In this invention, the preparation method of the single-crystal sodium-ion cathode material employs a multi-stage sintering process to achieve a solid-state reaction between the precursor material, the sodium source, and optionally a dopant. This multi-stage sintering process allows for better single-crystal particle growth, resulting in more rounded and regular cathode material particles. The obtained single-crystal cathode material exhibits a rounded and regular morphology, uniform particle size, and minimal particle agglomeration and adhesion, resulting in a high compaction density. Furthermore, the addition of doping elements during the preparation process (i.e., solid-state synthesis) effectively promotes single-crystal growth and stabilizes the bulk structure of the material, leading to excellent physicochemical properties and electrochemical performance in the prepared sample.

[0069] Specifically, in the existing technology, the preparation of sodium ion single crystal cathode materials usually adopts a single heating program for sintering. The resulting single crystal particles have obvious edges and corners, poor roundness and regularity, or the single crystal particles are severely adhered to each other, have poor independence, and even still maintain a precursor-like morphology.

[0070] During their research, the inventors of this invention discovered that the solid-state reaction of a mixture of nickel-iron-manganese precursor, sodium source, and optionally M source, or a mixture of precursor containing nickel-iron-manganese and optionally M elements with sodium source, is divided into two stages: growth (stage I) and fusion (stage II). The growth stage is a low-temperature heating stage, in which the sodium source melts and penetrates into the precursor particles and undergoes a preliminary reaction, causing the fibers constituting the precursor to grow and become fuller, growing into fine primary particles. The fusion stage is a high-temperature isothermal stage, in which the sodium source further reacts with the fine primary particles, fusing them into larger particles. By controlling the sintering process of the first sintering stage of the material, the cathode material can achieve better particle growth in both stages of single crystal growth. Specifically, in the nucleation stage (isothermal stage I of the first sintering stage) of the reaction of a mixture of nickel-iron-manganese precursor, sodium source, and optional dopant M, or a mixture of precursor containing nickel-iron-manganese and optional M elements with sodium source, the primary particles formed by the fibers are made fuller and rounder. In the growth stage of isothermal sintering (isothermal stage II of the first sintering stage), the single crystal particles are more easily fused to form large single crystal particles. As a result, the obtained single crystal sodium ion cathode material has a round and regular morphology, uniform particle size, and less agglomeration and adhesion between particles, resulting in a high compaction density of the single crystal cathode material.

[0071] Furthermore, when the holding time and holding temperature of the isothermal stage I and isothermal stage II of the first sintering are controlled to meet the requirements of this invention, the resulting cathode material particles are more rounded and regular, with uniform particle size and less agglomeration and adhesion between particles, making it easier for the cathode material to obtain better compaction density and electrochemical performance.

[0072] In one specific embodiment of the present invention, 3≤t2 / t1≤7.

[0073] In one specific embodiment of the present invention, 1 <T2 / T1≤2。

[0074] Furthermore, controlling the duration of the isothermal stage, particularly controlling the isothermal stage II isothermal time t2 to be 2-25h, preferably 8-15h, allows for a more complete sodium saturation reaction, making it easier for single crystal particles to fuse and form large single crystal particles. This results in a single-crystal sodium-ion cathode material with a rounded and regular morphology, uniform particle size, and less agglomeration and adhesion between particles, giving the single-crystal cathode material a high compaction density.

[0075] In one specific embodiment of the present invention, the isothermal time t1 of the isothermal stage I is 1-5h, preferably 2-4h.

[0076] In one specific embodiment of the present invention, the constant temperature T1 of the constant temperature stage I is 600-1000℃, preferably 650-900℃.

[0077] In one specific embodiment of the present invention, the constant temperature T2 of the constant temperature stage II is 600-1350℃, preferably 800-1100℃.

[0078] In this invention, in order to further improve the sintering capacity and reduce the time required before the material reacts, preferably, the heating rate v1 of heating stage I is greater than the heating rate v2 of heating stage II.

[0079] In one specific embodiment of the present invention, v1-v2 = 1-5℃ / min.

[0080] According to the present invention, the second sintering is a multi-stage sintering, including: a heating stage A, a isothermal stage A, a heating stage B, and an isothermal stage B, wherein the holding time t of the isothermal stage B is... B The holding time t is greater than that of the constant temperature stage A. A The heat preservation temperature T of the constant temperature stage B B The heat preservation temperature T is greater than that of the constant temperature stage A. A .

[0081] In this invention, a multi-stage sintering process is used to perform a second sintering on a mixture containing single-crystal sodium ion cathode material process product I and optional coating agent G, which can further improve the electron microscopic particle morphology of the cathode material, stabilize the surface structure of the material, reduce the deteriorating effect of fine powder particles on electrochemical performance, and further enhance the electrochemical performance of the cathode material.

[0082] In one specific embodiment of the present invention, 3≤t B / t A ≤8.

[0083] In one specific embodiment of the present invention, 1 <T B / T A ≤2.

[0084] Furthermore, in this invention, during the second sintering process, the duration of the isothermal stage is controlled, particularly the isothermal stage B, t. B The duration is 2-15 hours, preferably 6-12 hours.

[0085] In one specific embodiment of the present invention, the isothermal time t of the isothermal stage A A The duration is 1-5 hours, preferably 1-4 hours.

[0086] In one specific embodiment of the present invention, the isothermal temperature T of the isothermal stage A is... A The temperature range is 300-700℃, preferably 450-650℃.

[0087] In one specific embodiment of the present invention, the isothermal temperature T of the isothermal stage B is... B The temperature range is 500-1000℃, preferably 600-950℃.

[0088] According to the present invention, the holding temperature T of the isothermal stage B of the second sintering isothermal process is... B The holding temperature shall not exceed the holding temperature T2 of the isothermal stage II of the first sintering.

[0089] In this invention, preferably, the holding temperature T2 of the first sintering isothermal stage II is greater than or equal to the holding temperature T of the second sintering isothermal stage B. B .

[0090] Furthermore, the holding temperature T2 of the first sintering isothermal stage II is higher than the holding temperature T of the second sintering isothermal stage B. B Temperature ranges from 100 to 500°C, with a preferred range of 150 to 350°C.

[0091] In this invention, in order to further improve sintering capacity and reduce the time required before the material reacts, preferably, the heating rate v of the heating stage A is... A The heating rate v of the heating stage B is greater than the control temperature rise rate v. B .

[0092] In one specific embodiment of the present invention, v A -v B =1-5℃ / min.

[0093] In this invention, there is no particular limitation on the type of nickel-iron-manganese precursor, and conventional nickel-iron-manganese precursors in the art can be used.

[0094] In this invention, there is no particular limitation on the type of sodium source. Common sodium sources in the art can be used, such as at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium chloride, sodium fluoride, sodium sulfide, sodium sulfite, sodium bromide, and sodium iodide.

[0095] According to the present invention, the M source is selected from compounds containing the M element, preferably, the M-containing compound is selected from at least one of oxides, sulfides, hydroxides, oxyacids, carbonates, oxalates, phosphides, hydroxy oxides, nitrides and carbides containing the M element.

[0096] In this invention, a dopant M is added during the preparation of the cathode material. On the one hand, the M element can be embedded in the transition metal layer to stabilize the structure and suppress Mn. 3+ The resulting Jahn-Teller effect improves the cycling performance of the material; on the other hand, it can reduce the thickness of the transition metal oxide TMO6 octahedron, thereby increasing the interlayer spacing of sodium layers and improving the diffusion coefficient of sodium ions, which is conducive to the diffusion of sodium ions in the electrode material and improves the rate performance; at the same time, it also has a certain fluxing effect, which can synthesize single crystals at lower temperatures and shorter sintering times, which is conducive to improving production efficiency and reducing costs.

[0097] According to the present invention, the coating agent G is selected from compounds containing the element G, and preferably, the compound containing the element G is selected from at least one of oxides, sulfides, hydroxides, oxyacids, carbonates, oxalates, phosphides, hydroxy oxides, nitrides and carbides containing G.

[0098] In this invention, adding coating agent G during the preparation of the cathode material can effectively isolate the occurrence of side reactions, thereby stabilizing the surface and interface state of the material. Simultaneously, the coating can react with residual alkali on the surface at high temperatures, reducing the residual alkali level and improving the material's processing performance. A second sintering at a slightly higher temperature can repair internal defects in the single-crystal material, further enhancing its performance.

[0099] According to the present invention, the M element and the G element are each independently selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti and Cu.

[0100] In this invention, in step (1), the total molar amount of metal elements in the nickel-iron-manganese precursor [n(Ni)+n(Fe)+n(Mn)], the molar amount of Na element in the sodium source n(Na), and the molar amount of M element in the M source n(M) are such that: 0.95≤n(Na) / [n(Ni)+n(Fe)+n(Mn)+n(M)]≤1.1.

[0101] In this invention, in step (1), the total molar amount of metal elements in the precursor containing nickel, iron, manganese and optionally M elements and the amount of Na elements n(Na) in the sodium source are such that: 0.95≤n(Na) / [n(Ni)+n(Fe)+n(Mn)+n(M)]≤1.1.

[0102] In this invention, in step (2), the amounts of the single-crystal sodium-ion cathode material process product I and the coating agent G are such that the total molar amount of metal elements in the single-crystal sodium-ion cathode material process product I [n(Ni)+n(Fe)+n(Mn)+n(M)] and the molar amount of M element n(G) in the coating agent G satisfy: 0≤n(G):[n(Ni)+n(Fe)+n(Mn)+n(M)]≤0.1.

[0103] A third aspect of the present invention provides a sodium-ion battery single-crystal cathode material prepared by the above-described preparation method.

[0104] According to some embodiments of the present invention, the single-crystal cathode material is the same as or similar to the sodium-ion single-crystal cathode material described in the first aspect of the present invention, and will not be described again here.

[0105] A fourth aspect of the present invention provides a sodium-ion battery, wherein the sodium-ion battery contains the sodium-ion battery single-crystal cathode material described in the first or third aspect.

[0106] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0107] (1) Morphology test: Electron micrographs were obtained using a Hitachi S-4800 scanning electron microscope; among them, the particle size D PS D c D d Roundness (R), Aggregation rate (C) and (D) P90 D P10 D P50 Both the projected area S and the projected area S were obtained through SEM plotting.

[0108] (2) Particle size test: The volume distribution D was obtained by measuring the volumetric size using a Malvern 3000 laser particle size analyzer. 10 D 50 and D 90 ;

[0109] (3) Compacted density: The compacted density was obtained using a Mitsubishi compacted density tester;

[0110] (4) Electrochemical performance testing: CR2032 coin cell batteries were used for testing; Electrode preparation: Sodium-ion monocrystalline positive electrode material, conductive carbon, and binder were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a suitable mass ratio to form a uniform slurry. The slurry was coated onto aluminum foil and dried in an oven. It was then stamped into positive electrode sheets using a stamping machine. Battery assembly: In an argon-filled glove box, the positive electrode sheets, separator, negative electrode sheets, and electrolyte were assembled into CR2032 coin cells. Among them, sodium metal sheets were used for the negative electrode sheet; the separator used industry-standard PP / PE / glass fiber separators; the electrolyte was a mixture of NaPF6 and electrolyte additives such as ethylene carbonate (EC), diethyl carbonate (DEC), and vinylene carbonate (VC).

[0111] Example 1

[0112] (1) Sodium carbonate, nickel-iron-manganese precursor, calcium oxide, zinc oxide, strontium oxide and boron oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0113] (2) Mixture I was heated to T1 (700℃) at v1 (3.3)℃ / min under an oxygen atmosphere and held at t1 (2.5)h. Then it was heated to T2 (950)℃ at v2 (1)℃ / min and held at t2 (13)h. After natural cooling to room temperature, the mixture was crushed by an air jet mill to obtain process product I with a D50 of 5.5μm. Among them, v1-v2=2.3℃ / min, t2 / t1=5.2, T2 / T1=1.36.

[0114] (3) Alumina (as n(Al)) is mixed with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0115] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (4.5)℃ / min to T A (500)℃, heat preservation t A (2)h, and then with v B (2.5)℃ / min heating to T B (800)℃, heat preservation t B (8)h, naturally cooled to room temperature, and after crushing, a single-crystal sodium-ion cathode material A1 was obtained, in which v A -v B =2℃ / min, t B / t A =4,T B / T A=1.6.

[0116] The amounts of sodium carbonate, nickel-iron-manganese precursor, calcium oxide, zinc oxide, strontium oxide, boron oxide, and aluminum oxide used result in the following composition of the cathode material A1:

[0117] NaNi 0.309 Fe 0.309 Mn 0.309 Ca 0.019 Zn 0.009 Sr 0.019 B 0.006 Al 0.02 O2.

[0118] Example 2

[0119] (1) Sodium carbonate, nickel-iron-manganese precursor, zinc oxide, copper oxide, boron oxide, strontium oxide, yttrium oxide and calcium oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0120] (2) Mixture I was heated to T1 (650℃) at v1 (4.6)℃ / min and held at t1 (3h) under an oxygen atmosphere, then heated to T2 (980℃) at v2 (2)℃ / min and held at t2 (12h) before being naturally cooled to room temperature. The mixture was then crushed by an air jet mill to obtain process product I, D. 50 The value is 5.4 μm. Among them, v1-v2=2.6℃ / min, t2 / t1=4, T2 / T1=1.51.

[0121] (3) Alumina (as n(Al)) is mixed with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0122] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (5.5)℃ / min to T A (525)℃ constant temperature t A (2.5)h, and then with v B (3.5)℃ / min heating to T B (820)℃ heat preservation t B (9) After being naturally cooled to room temperature, the sodium-ion battery single-crystal cathode material A2 was obtained by crushing, wherein v A -v B =2℃ / min, t B / t A =3,T B / T A =1.56.

[0123] The amounts of sodium carbonate, nickel-iron-manganese precursor, zinc oxide, copper oxide, boron oxide, strontium oxide, yttrium oxide, calcium oxide, and aluminum oxide used result in the following composition of the cathode material A2:

[0124] NaNi 0.308 Fe 0.308 Mn 0.308 Zn 0.017 Cu 0.018 B 0.008 Sr 0.003 Y 0.002 Ca 0.008 Al 0.02 O2.

[0125] Example 3

[0126] (1) Sodium carbonate, nickel-iron-manganese precursor, copper oxide, yttrium oxide and boron oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0127] (2) Mixture I was heated to T1 (770) ℃ at v1 (3.5) ℃ / min under an oxygen atmosphere and held at that temperature for t1 (3.5) h. Then, it was heated to T2 (990) ℃ at v2 (2.2) ℃ / min and held for t2 (15) h. It was then naturally cooled to room temperature and crushed by an air jet mill to obtain process product I, D. 50 The value is 5.2 μm. Among them, v1-v2=1.3℃ / min, t2 / t1=4.29, T2 / T1=1.29.

[0128] (3) Alumina (as n(Al)) is mixed with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0129] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (5) Temperature rise to T at ℃ / min A (580)℃, heat preservation t A (1.5)h, and then with v B (2.3)℃ / min heating to T B (700)℃, heat preservation t B (9.5)h, naturally cooled to room temperature, and then crushed to obtain single-crystal sodium-ion cathode material A3, wherein, v A -v B =2.7, t B / t A =6.3, T B / T A =1.2.

[0130] The amounts of sodium carbonate, nickel-iron-manganese precursor, copper oxide, yttrium oxide, boron oxide, and aluminum oxide used result in the following composition of the cathode material A3:

[0131] Na 1.000 Ni 0.310 Fe 0.310 Mn 0.318 Cu 0.028 Y 0.003 B 0.014 Al 0.024 O2.

[0132] Example 4

[0133] (1) Sodium carbonate, nickel-iron-manganese precursor, copper oxide, titanium oxide, boron oxide and aluminum oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0134] (2) Mixture I was heated to T1 (790℃) at v1 (5)℃ / min under an oxygen atmosphere and held at t1 (3)h. Then it was heated to T2 (1020)℃ at v2 (1.7)℃ / min and held at t2 (10)h. It was then naturally cooled to room temperature and crushed by an air jet mill to obtain process product I with a D50 of 5.3μm. Among them, v1-v2=3.3℃ / min, t2 / t1=3.3, T2 / T1=1.29.

[0135] (3) Alumina (as n(Al)) and magnesium oxide (as n(Mg)) are mixed with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0136] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (4.8)℃ / min heating to T A (450)℃, heat preservation t A (1.3)h, and then with v B (2) Temperature rise to T at ℃ / min B (650)℃, heat preservation t B (10)h, naturally cooled to room temperature, and then crushed to obtain a single-crystal sodium-ion cathode material A4, in which v A -v B = 2.8℃ / min, t B / t A =7.7, T B / T A =1.4.

[0137] The amounts of sodium carbonate, nickel-iron-manganese precursor, copper oxide, titanium oxide, boron oxide, aluminum oxide (total amount used in steps (1) and (3)), and magnesium oxide make the composition of cathode material A4 as follows:

[0138] Na 1.000 Ni 0.307 Fe0.307 Mn 0.307 Cu 0.037 Ti 0.005 B 0.006 Al 0.022 Mg 0.009 O2.

[0139] Example 5

[0140] (1) Sodium carbonate, nickel-iron-manganese precursor, zinc oxide, titanium oxide, boron oxide and tungsten oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0141] (2) Mixture I was heated to T1 (820℃) at v1 (4.4)℃ / min under an oxygen atmosphere and held at t1 (2)h. Then it was heated to T2 (1010)℃ at v2 (3)℃ / min and held at t2 (13)h. After natural cooling to room temperature, the mixture was crushed by an air jet mill to obtain process product I with a D50 of 5.6μm. Among them, v1-v2=1.4℃ / min, t2 / t1=6.5, T2 / T1=1.23.

[0142] (3) Titanium oxide (calculated as n(Ti)) is mixed with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0143] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (6) Temperature rise to T at ℃ / min A (500)℃, heat preservation t A (2.2)h, and then with v B (2.6)℃ / min heating to T B (750)℃, heat preservation t B (11)h, naturally cooled to room temperature, and then crushed to obtain a single-crystal sodium-ion cathode material A5, wherein, v A -v B = 3.4℃ / min, t B / t A =5,T B / T A =1.5.

[0144] The amounts of sodium carbonate, nickel-iron-manganese precursor, zinc oxide, titanium oxide (total amount used in steps (1) and (3)), boron oxide, tungsten oxide, and titanium oxide make the composition of cathode material A5 as follows:

[0145] Na 1.000 Ni 0.316 Fe 0.316 Mn 0.316 Zn 0.024 Ti 0.017 B0.009 W 0.003 O2.

[0146] Example 6

[0147] (1) Sodium carbonate, nickel-iron-manganese precursor, zinc oxide and zirconium oxide are mixed uniformly in a high-speed mixer in proportion to obtain mixture I;

[0148] (2) Mixture I was heated to T1 (860℃) at v1 (4)℃ / min under an oxygen atmosphere and held at t1 (2.5)h. Then it was heated to T2 (1000)℃ at v2 (1.5)℃ / min and held at t2 (14.5)h. After natural cooling to room temperature, the mixture was crushed by an air jet mill to obtain process product I with a D50 of 5.4μm. Among them, v1-v2=2.5℃ / min, t2 / t1=5.8, T2 / T1=1.16.

[0149] (3) Mix magnesium oxide (calculated as n(Mg)) with process product I in a high-speed mixer in a certain proportion to obtain mixture II;

[0150] (4) Mixture II was subjected to a second sintering under an oxygen atmosphere, with v A (5.3)℃ / min heating to T A (600)℃, heat preservation t A (2)h, and then with v B (1.7)℃ / min heating to T B (900)℃, heat preservation t B (7)h, naturally cooled to room temperature, and then crushed to obtain single-crystal sodium ion cathode material A6, wherein, v A -v B = 3.6℃ / min, t B / t A =3.5, T B / T A =1.5.

[0151] The amounts of sodium carbonate, nickel-iron-manganese precursor, zinc oxide, zirconium oxide, and magnesium oxide used result in the following composition for cathode material A6:

[0152] Na 1.000 Ni 0.308 Fe 0.308 Mn 0.308 Zn 0.028 Zr 0.037 Mg 0.01 O2.

[0153] Example 7

[0154] (1) Same as Example 1;

[0155] (2) Same as in Example 1;

[0156] (3) Same as Example 1;

[0157] (4) The holding time t of the isothermal stage A during the second sintering A The holding time t during the constant temperature stage B is 7 hours. B For 5 hours, t B / t A =0.71, thus obtaining cathode material A7.

[0158] Example 8

[0159] (1) Same as Example 1;

[0160] (2) Same as in Example 1;

[0161] (3) Same as Example 1;

[0162] (4) The holding temperature T of A during the second sintering isothermal stage A The holding temperature T during the constant temperature stage B is 800℃. B For 500℃, T B / T A =0.63, thus obtaining the positive electrode material A8.

[0163] Comparative Example 1

[0164] (1) Same as Example 1;

[0165] (2) Mixture I was heated to T1 (950℃) at v1 (3.3)℃ / min under an oxygen atmosphere, held at t1 (13)h, and naturally cooled to room temperature. Process product I was obtained by air jet milling with a D50 of 4.7μm.

[0166] (3) Same as Example 1;

[0167] (4) Same as in Example 1, positive electrode material D1 was obtained.

[0168] The composition of the cathode material D1 is as follows:

[0169] Na 1.000 Ni 0.309 Fe 0.309 Mn 0.309 Ca 0.019 Zn 0.009 Sr 0.019 B 0.006 Al 0.02 O2.

[0170] Comparative Example 2

[0171] (1) Same as Example 1;

[0172] (2) During the first sintering process, the holding time t1 of the isothermal stage I is 7h, the holding time t2 of the isothermal stage II is 7h, and the rest is the same as in Example 1, to obtain process product I with D50 of 4.8μm; where t2 / t1=1.

[0173] (3) Same as Example 1;

[0174] (4) Same as in Example 1, positive electrode material D2 was obtained.

[0175] The composition of the cathode material D2 is as follows:

[0176] Na 1.000 Ni 0.309 Fe 0.309 Mn 0.309 Ca 0.019 Zn 0.009 Sr 0.019 B 0.006 Al 0.020 O2.

[0177] Comparative Example 3

[0178] (1) Same as Example 1;

[0179] (2) The holding temperature T1 of the isothermal stage I in the first sintering is 900℃, and the holding temperature T2 of the isothermal stage II is 600℃. T2 / T1=0.67, and process product I is obtained with D50 of 4.6μm.

[0180] (3) Same as Example 1;

[0181] (4) Same as in Example 1, positive electrode material D3 was obtained.

[0182] The composition of the cathode material D3 is as follows:

[0183] Na 1.000 Ni 0.309 Fe 0.309 Mn 0.309 Ca 0.019 Zn 0.009 Sr 0.019 B 0.006 Al 0.020 O2.

[0184] The physicochemical parameters of the cathode materials in the examples and comparative examples are shown in Table 1.

[0185] Table 1

[0186] unit μm μm μm μm μm μm ％ <![CDATA[g / cm 3 ]]> A1 2.3 1.5 1.9 273 1 1.8 3 1.11 1.10 0.63 3.31 0.57 A2 2.7 1.8 2.3 170 1 2.1 3.5 1.19 1.16 0.62 3.34 0.52 A3 2.7 1.9 2.3 162 1.2 2.2 3.7 1.14 1.23 0.63 3.35 0.55 A4 2.6 1.8 2.2 190 1.1 2 3.4 1.15 1.05 0.65 3.32 0.57 A5 2.9 2 2.5 151 1.2 2.2 3.8 1.18 1.32 0.62 3.32 0.53 A6 2.1 1.5 1.8 287 0.9 1.7 2.8 1.12 1.39 0.62 3.31 0.55 A7 2.1 1.5 1.8 291 1 1.8 3.2 1.22 2.06 0.58 3.27 0.47 A8 2 1.5 1.8 310 0.9 1.7 3 1.24 2.26 0.58 3.25 0.47 D1 1.7 1.1 1.4 435 0.6 1.2 2.4 1.50 6.90 0.50 2.90 0.33 D2 1.8 1.2 1.5 398 0.7 1.3 2.6 1.46 7.79 0.51 3.01 0.35 D3 1.7 1 1.4 421 0.6 1.4 2.7 1.50 6.89 0.49 2.95 0.33

[0187] Table 1 (continued)

[0188]

[0189] Figures 1-5 These are SEM images of the cathode materials A1-A3 prepared in Examples 1-3 of this invention, and the cathode materials D1 and D2 prepared in Comparative Examples 1-2. Figures 1-5 It can be seen that, compared with cathode materials A1-A3, cathode material D1 has poor single crystallization, smaller particles, severe agglomeration between particles, and poor independence. Cathode material D2 has poor single crystallization, with particles of varying sizes and severe adhesion. It is quite different from the cathode materials A1-A3 prepared in Examples 1-3.

[0190] The electrochemical performance of the battery is shown in Table 3.

[0191] Table 3

[0192]

[0193]

[0194] Figure 6 This is a graph showing the retention rates of cathode materials A1 and D1 after 80 cycles at high temperatures. Figure 6 It can be seen that the high-temperature 80-cycle retention rate of material A1 in Example 1 is 94.2%, while that of material D1 in Comparative Example 1 is only 80%. That is, the battery assembled using the cathode material provided by the present invention has superior electrochemical performance.

[0195] As can be seen from the results in Tables 2 and 3, the cathode material provided by the present invention has a good degree of single crystallization, uniform single crystal particle size, less adhesion, smooth surface, high compaction density and excellent processing performance; at the same time, when the cathode material provided by the present invention is assembled into a battery, it has excellent electrochemical performance.

[0196] 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 single-crystal sodium-ion cathode material, characterized in that, The roundness R of the single crystal particles of the cathode material and the size distribution concentration B of the single crystal particles measured by SEM are... P90 The following relationship is satisfied between them: 0.40 ≤ / B P90 ≤0.90; The proportion of agglomerated particles in the cathode material is C≤5%; The longest diagonal dimension D of the single crystal particles of the cathode material, as measured by SEM. c The projected area S satisfies the following relationship: 0.55≤ = / π( c / 2) 2 ≤1； The single crystal size D of the cathode material was measured by SEM. P90 D P10 With D P50 The following relationship must be satisfied: 0.7≤B P90 =(D P90 -D P10 ) / D P50 ≤1.5; D P10 In the SEM image of the cathode material, the particle size corresponding to a cumulative single-crystal particle size distribution percentage of 10% is shown; D P50 In the SEM image of the cathode material, the particle size corresponding to a cumulative single-crystal particle size distribution percentage of 50% is shown; D P90 The particle size corresponding to a cumulative single-crystal particle size distribution percentage of 90% in the SEM image of the cathode material; The cathode material has the composition shown in Formula I: Na a Ni e Fe b Mn c T d O 2+f (Equation I); Wherein, 0.95≤a≤1.1, 0.03≤b≤0.5, 0.03≤c≤0.5, 0≤d≤0.25, 0≤e≤0.50, -0.1≤f≤0.1; T is selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, Sr, and Cu.

2. The single-crystal sodium-ion cathode material according to claim 1, wherein, 0.50≤ / B P90 ≤0.80。 3. The single-crystal sodium-ion cathode material according to claim 1, wherein, The proportion of agglomerated particles in the cathode material is C≤2%.

4. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, 0.60≤R≤1。 5. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, 0.9≤B P90 ≤1.3。 6. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The average particle size D of the single crystal particles of the cathode material, as measured by SEM, is... PS The following relationship must be satisfied: 1.6μm≤ ≤8μm; where, D c D is the longest diagonal of the single-crystal particles of the cathode material as measured by SEM; d is the shortest diagonal of the single crystal particles of the cathode material as measured by SEM; n is the total number of single crystal particles in the SEM of the cathode material.

7. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein the average particle size D of the single-crystal particles of the cathode material, as measured by SEM, is... PS The following relationship must be satisfied: 1.8μm≤D PS ≤5μm.

8. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The particle size D of the positive electrode material was measured by a laser particle size analyzer. 10 It ranges from 2 to 4.5 μm.

9. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The particle size D of the positive electrode material was measured by a laser particle size analyzer. 50 It is 4-8μm.

10. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The particle size D of the positive electrode material was measured by a laser particle size analyzer. 90 It is 6-14μm.

11. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The particle size distribution K of the cathode material was measured by a laser particle size analyzer. 90 It is 1-1.

5.

12. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The compaction density of the positive electrode material is 3.1-3.6 g / cm³. 3 .

13. The single-crystal sodium-ion cathode material according to any one of claims 1-3, wherein, The compaction density of the positive electrode material is 3.3-3.6 g / cm³. 3 .

14. A method for preparing the single-crystal sodium-ion cathode material according to any one of claims 1-13, characterized in that, The preparation method includes the following steps: (1) The nickel-iron-manganese precursor, sodium source, and optionally M source are mixed and subjected to a first sintering and crushing in an oxygen-containing atmosphere to obtain single-crystal sodium-ion cathode material process product I; or, A precursor containing nickel, iron, manganese, and optionally M elements is mixed with a sodium source and subjected to a first sintering and crushing in an oxygen-containing atmosphere to obtain a single-crystal sodium-ion cathode material process product I. (2) The single-crystal sodium ion cathode material process product I is mixed with a coating agent that optionally contains G element, and then sintered and crushed for the second time in an oxygen-containing atmosphere to obtain the single-crystal sodium ion cathode material. The first sintering is a multi-stage sintering process, including: heating stage I, constant temperature stage I, heating stage II, and constant temperature stage II. The holding time t2 of constant temperature stage II is greater than the holding time t1 of constant temperature stage I, and the holding temperature T2 of constant temperature stage II is greater than the holding temperature T1 of constant temperature stage I.

15. The preparation method according to claim 14, wherein, 3≤t2 / t1≤7.

16. The preparation method according to claim 14, wherein, 1 <T2 / T1≤2。 17. The preparation method according to claim 14, wherein, t1 is 1-5h.

18. The preparation method according to claim 14, wherein, t1 is 2-4 hours.

19. The preparation method according to claim 14, wherein, t2 is 2-25h.

20. The preparation method according to claim 14, wherein, t2 is 8-15h.

21. The preparation method according to claim 14, wherein, T1 is 600-1000℃.

22. The preparation method according to claim 14, wherein, T1 is 650-900℃.

23. The preparation method according to claim 14, wherein, T2 is 600-1350℃.

24. The preparation method according to claim 14, wherein, T2 is 800-1100℃.

25. The preparation method according to claim 14, wherein, The heating rate v2 in heating stage II is less than the heating rate v1 in heating stage I.

26. The preparation method according to claim 14, wherein, v1-v2=1-5℃ / min.

27. The preparation method according to claim 14, wherein, The second sintering is a multi-stage sintering process, including: a heating stage A, a isothermal stage A, a heating stage B, and an isothermal stage B, wherein the holding time t of the isothermal stage B is... B The holding time t is greater than that of the constant temperature stage A. A The heat preservation temperature T of the constant temperature stage B B The heat preservation temperature T is greater than that of the constant temperature stage A. A。 28. The preparation method according to claim 27, wherein, The holding temperature T during the isothermal stage B of the second sintering isothermal process B The holding temperature shall not exceed the holding temperature T2 of the isothermal stage II of the first sintering.

29. The preparation method according to claim 27, wherein, The heating rate v of the heating stage B B The heating rate v is less than that of the heating stage A. A .

30. The preparation method according to claim 27, wherein, v A -v B =1-5℃ / min。 31. The preparation method according to claim 27, wherein, 3≤t B / t A ≤8。 32. The preparation method according to claim 27, wherein, 1<T B / T A ≤2。 33. The preparation method according to claim 27, wherein, t A It takes 1-5 hours.

34. The preparation method according to claim 27, wherein, t A For 1-4 hours.

35. The preparation method according to claim 27, wherein, t B It takes 2-15 hours.

36. The preparation method according to claim 27, wherein, t B It takes 6-12 hours.

37. The preparation method according to claim 27, wherein, T A The temperature ranges from 300 to 700℃.

38. The preparation method according to claim 27, wherein, T A The temperature ranges from 450 to 650℃.

39. The preparation method according to claim 27, wherein, T B The temperature ranges from 500 to 1000℃.

40. The preparation method according to claim 27, wherein, T B The temperature ranges from 600 to 950℃.

41. The preparation method according to any one of claims 14-40, wherein, The M source is selected from compounds containing the M element.

42. The preparation method according to any one of claims 14-40, wherein, The compound containing element M is selected from at least one of oxides, sulfides, hydroxides, oxyacids, carbonates, oxalates, phosphides, hydroxy oxides, nitrides, and carbides containing element M.

43. The preparation method according to any one of claims 14-40, wherein, The coating agent containing element G is selected from at least one of oxides, sulfides, hydroxides, oxyacids, carbonates, oxalates, phosphides, hydroxy oxides, nitrides, and carbides containing element G.

44. The preparation method according to any one of claims 14-40, wherein, The M element and the G element are each independently selected from at least one of V, Ta, Cr, La, Al, Ce, Y, Mg, Ni, Ba, Ra, Fe, Zr, Sn, Sb, Ca, Mn, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, Sr and Cu.

45. A single-crystal sodium-ion cathode material prepared by the preparation method according to any one of claims 14-44.

46. ​​A sodium-ion battery, characterized in that, The sodium-ion battery includes the monocrystalline sodium-ion cathode material as described in any one of claims 1-13 and 45.

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