A positive electrode material, a preparation method thereof and a sodium ion battery

Abstract

This invention relates to the field of sodium-ion battery technology, specifically to a cathode material, its preparation method, and a sodium-ion battery. The cathode material comprises single-crystal particles, wherein the single-crystal particles satisfy δ≥75%; δ is L a / L b The proportion of single crystal particles <1.5, L a and L b These are the major and minor axes of the cross-section of the single crystal particle, respectively; and 1 / (δ 3 +δ 2 ) <I003 / I104<3 / (δ 3 +δ 2 This invention establishes a correlation between the relative peak intensity of I003 / I104 in XRD and the morphology of single-crystal particles, thereby restricting the selection of crystal faces of the particles, optimizing the morphology of single crystals, improving the geometric symmetry of single-crystal particles, ensuring the particle size distribution of single crystal particles, improving battery polarization, enhancing the structural stability of materials, and suppressing structural degradation, thereby improving the rate performance and cycle stability of cathode materials.

Description

Technical Field

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

[0002] Studies have shown that the particle size distribution of active materials is a crucial parameter in sodium-ion battery electrodes. The varying particle sizes result in asynchronous lithium insertion / extraction / sodium deintercalation processes. In the initial stages of discharge, sodium ion insertion primarily occurs on smaller particles. However, in the later stages, as the sodium ion insertion in smaller particles approaches saturation, the electrochemical reaction shifts between the surfaces of particles of different sizes, with sodium ion insertion mainly occurring on larger particles. This means that different active particle sizes lead to polarization during the charge-discharge process. Furthermore, irregular single-crystal particles generate greater volumetric stress, increasing the degree of phase transition and inducing intragranular cracks, ultimately leading to structural degradation.

[0003] To address the above issues, ensuring the particle size distribution of active materials and the geometric symmetry of single crystal particles is one of the key pathways to improve battery polarization, enhance material structural stability, and suppress structural degradation.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a cathode material that, by establishing a correlation between the relative peak intensity of I003 / I104 in XRD and the morphology of single-crystal particles, can ensure the particle size distribution of single-crystal particles, improve the geometric symmetry of single-crystal particles, thereby improving battery polarization, enhancing the structural stability of the material, and suppressing structural degradation.

[0006] The second objective of this invention is to provide a method for preparing a positive electrode material.

[0007] A third objective of this invention is to provide a sodium-ion battery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] This invention first provides a cathode material comprising single-crystal particles, wherein the single-crystal particles satisfy δ≥75%; where δ is L a / L b The proportion of single crystal particles <1.5, L a L is the major axis of the cross-section of the single crystal particle. b Let I be the minor axis of the cross-section of the single crystal particle; and the ratio of the diffraction peak intensity I003 of the 003 crystal plane to the diffraction peak intensity I104 of the I104 crystal plane of the cathode material, I003 / I104, satisfies: 1 / (δ 3+δ 2 )<I003 / I104<3 / (δ 3 +δ 2 )。

[0010] Further, the particle size distribution SPAN of the positive electrode material is (Dv90 - Dv10) / Dv50 < 1.3.

[0011] Further, the full width at half maximum FWHM of the diffraction peak of the 003 crystal plane of the positive electrode material 003 ≤0.13.

[0012] Further, the full width at half maximum FWHM of the diffraction peak of the 104 crystal plane of the positive electrode material 104 <0.15.

[0013] Further, the positive electrode material contains fluxing elements, and the fluxing elements include at least two of Bi, Ca, Co, Sr, Li, B, and F.

[0014] Further, the general formula of the positive electrode material is Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @M - O or Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @NaQ - F / O, where 0.98 ≤ x ≤ 1.05, 0.02 ≤ a ≤ 0.06, 0 ≤ α ≤ 0.1, M and Q are fluxing elements, M includes at least two of Bi, Ca, Co, Sr, Li, and B elements, and Q includes at least one of Bi, Ca, Co, Sr, Li, and B elements.

[0015] Further, the mass of element M accounts for 0.1% - 2% of the mass of Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @M - O in Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α by mass.

[0016] Furthermore, the sum of the masses of elements Q and F accounts for a certain percentage of the mass of Na. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @NaQ-F / O Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α 0.1% to 2% of the mass.

[0017] The present invention further provides a method for preparing a cathode material, comprising the following steps: mixing a Na source, a Cu source, an Fe source, a Ni source, a Mn source, a flux and water, then milling the mixture, followed by spray drying to obtain a spray-dried material; and sintering the spray-dried material to obtain the cathode material.

[0018] Furthermore, the flux includes at least two of the following: NaF, bismuth-containing compounds, calcium-containing compounds, cobalt-containing compounds, strontium-containing compounds, lithium-containing compounds, and boron-containing compounds.

[0019] Furthermore, the bismuth-containing compound includes Bi2O3.

[0020] Furthermore, the calcium-containing compound includes at least one of CaCO3 and CaO.

[0021] Furthermore, the cobalt-containing compound includes at least one of CoO, Co3O4, and Co(OH)2.

[0022] Furthermore, the strontium-containing compound includes at least one of SrO and SrCO3.

[0023] Furthermore, the lithium-containing compound includes at least one of LiOH and Li2CO3.

[0024] Furthermore, the boron-containing compound includes at least one of H3BO3 / B2O3.

[0025] Furthermore, the rotational speed of the mill is 1800–2400 r / min.

[0026] Furthermore, the diaphragm pump frequency of the mill is 1 to 3 times / s.

[0027] Furthermore, the particle size Dv50 of the mixed material is 0.2–0.8 μm after milling.

[0028] Furthermore, the inlet air temperature of the spray dryer is 240–290°C, and the outlet air temperature is 100–140°C.

[0029] Furthermore, the sintering temperature is 940–1050°C, and the holding time is 12–21 hours.

[0030] Furthermore, the sintering process is followed by a pulverizing step.

[0031] The present invention also provides a sodium-ion battery, including a positive electrode material.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) This invention establishes the relationship between the relative peak intensity of I003 / I104 in XRD and the morphology of single crystal particles, thereby restricting the selection of crystal planes of particles, optimizing the morphology of single crystals, improving the geometric symmetry of single crystal particles, ensuring the particle distribution size of single crystal particles, thereby improving battery polarization, enhancing the stability of material structure, suppressing structural degradation, and improving the rate performance and cycle stability of cathode materials.

[0034] (2) The positive electrode material provided by the present invention has a small particle size distribution SPAN value, that is, the size distribution range of the positive electrode material is narrow and the uniformity is high.

[0035] (3) The cathode material provided by the present invention, by adding dual fluxing elements (dual fluxing agents), on the one hand, the dual fluxing elements form a transition phase with the main metal, change the solid solubility, which is more conducive to the growth of single crystal particles and improves the morphology of the first firing. On the other hand, it avoids the crystal face selection caused by a single flux to a certain extent, optimizes the morphology of the single crystal, and improves the geometric symmetry of the material.

[0036] (4) The positive electrode material provided by the present invention improves the roundness of the positive electrode material particles by adding dual fluxing elements (dual fluxing agents), reduces the stress and strain of the material during charging and discharging, improves the uniformity of sodium ion diffusion path, and enhances the rate performance and cycle stability of the positive electrode material.

[0037] (5) The positive electrode material provided by the present invention, by adding dual fluxing elements (dual fluxing agents), can obtain a uniform particle distribution size in one firing. The solid-phase diffusion of sodium ions between closely spaced particles is almost the same, reducing the polarization phenomenon in the charging and discharging process caused by the different sizes of active particles.

[0038] (6) The method for preparing the positive electrode material provided by the present invention adds a specific type of flux during the sand milling process. During the sand milling process, the flux and each raw material are more fully mixed and dispersed, which helps to generate a uniform low eutectic system during sintering, and improves the morphology. The sphericity and particle size distribution are significantly improved. To a certain extent, the stress and strain of the material during the charging and discharging process and the uniformity of the sodium ion diffusion path are reduced. The solid-phase diffusion of ions between close particles is almost the same, reducing the polarization phenomenon in the charging and discharging process caused by the different sizes of active particles, and improving the rate performance and cycle stability of the material. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 SEM image of the cathode material prepared in Example 1 of this invention;

[0041] Figure 2 L provided by the present invention a / L b A schematic diagram of the calculation method;

[0042] Figure 3 SEM image of the cathode material prepared in Comparative Example 1 provided by the present invention;

[0043] Figure 4 SEM image of the cathode material prepared in Comparative Example 7 provided by the present invention. Detailed Implementation

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0045] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0048] In a first aspect, the present invention provides a sodium-ion battery O3 phase layered oxide cathode material resistant to stress and strain. The cathode material comprises a plurality of single crystal particles, wherein the single crystal particles satisfy δ≥75%, including but not limited to any one of 75%, 76%, 78%, 80%, 82%, 83%, 85%, 86%, 88%, 89%, 90%, 92%, and 95%, or a range between any two.

[0049] Where δ is L a / L b The percentage (number percentage) of single crystal particles <1.5, L a L is the major axis of the cross-section of the single crystal particle. b The minor axis of the cross-section of the single crystal particle is given.

[0050] Furthermore, the diffraction peak intensity I of the 003 crystal plane of the cathode material 003 The diffraction peak intensity of the I104 crystal plane I 104 The ratio I 003 / I 104 Satisfy: 1 / (δ) 3 +δ 2 ) 003 / I 104 <3 / (δ 3 +δ 2 ).

[0051] This invention establishes the I of XRD 003 / I 104 ​The relative peak intensity is related to the morphology of single crystal particles, thereby limiting the selection of crystal faces, optimizing the morphology of single crystals, improving the geometric symmetry of single crystal particles, ensuring the particle distribution size of single crystal particles, thereby improving battery polarization, enhancing material structural stability, suppressing structural degradation, and ensuring the consistency of sodium ion diffusion paths.

[0052] In some specific implementations, the size and number of single crystal particles are statistically analyzed based on CP electron microscopy images.

[0053] In some specific embodiments, the particle size distribution SPAN of the cathode material is (Dv90-Dv10) / Dv50 < 1.3, wherein the SPAN value includes, but is not limited to, any one of 1.29, 1.28, 1.26, 1.25, 1.23, 1.21, 1.20, 1.18, 1.16, 1.15, 1.13, 1.10, 1.05, and 1.00, or a range between any two. The cathode material provided by this invention has a small particle size distribution SPAN value, which indicates that the size distribution range of the cathode material is narrow and the uniformity is high.

[0054] In some specific embodiments, the full width at half maximum (FWHM) of the 003 crystal plane diffraction peak of the cathode material is... 003 ≤0.13, including but not limited to point values ​​of any one of 0.13, 0.129, 0.128, 0.125, 0.123, 0.120, 0.115, 0.110, 0.099, 0.095, 0.092, 0.090, and 0.080, or a range between any two.

[0055] In some specific embodiments, the full width at half maximum (FWHM) of the 104 crystal plane diffraction peak of the cathode material is... 104 <0.15, including but not limited to point values ​​of any one of 0.145, 0.140, 0.135, 0.130, 0.120, 0.110, 0.100, 0.095, 0.090, and 0.080, or a range between any two.

[0056] The narrow half-width at half-maximum (WHM) of the diffraction peaks provided by this invention indicates, on the one hand, that the crystal grain size distribution is narrow, limiting the possible broadening of diffraction peaks caused by fine powder; on the other hand, the narrow WHM reflects the degree of crystallization of the crystal material, further limiting the broadening of diffraction peaks caused by disordered changes in interplanar spacing due to lattice distortion.

[0057] In some specific embodiments, the cathode material contains fluxing elements, which include at least two of the elements Bi, Ca, Co, Sr, Li, B, and F, or three, four, or more of them.

[0058] In some specific embodiments, the general formula of the positive electrode material is Na. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @MO, where 0.98≤x≤1.05, 0.02≤a≤0.06, 0≤α≤0.1, and M is a fluxing element, including at least two of Bi, Ca, Co, Sr, Li, and B. x includes, but is not limited to, any one of the values ​​of 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, and 1.05, or a range between any two; a includes, but is not limited to, any one of the values ​​of 0.02, 0.03, 0.04, 0.05, and 0.06, or a range between any two. α satisfies the condition of equal positive and negative charges.

[0059] It is understandable that MO refers to oxides containing M. When preparing cathode materials, compounds containing M are added, and after subsequent sintering, oxides containing M are formed.

[0060] Alternatively, the general formula of the positive electrode material is Na. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @NaQ-F / O, where 0.98≤x≤1.05, 0.02≤a≤0.06, 0≤α≤0.1, F and Q are fluxing elements, and Q includes at least one of Bi, Ca, Co, Sr, Li and B. x includes, but is not limited to, any one of 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05 or a range between any two; a includes, but is not limited to, any one of 0.02, 0.03, 0.04, 0.05, 0.06 or a range between any two. α satisfies the condition of equal positive and negative charges.

[0061] It is understandable that fluxing elements (at least two of Bi, Ca, Co, Sr, Li, B, and F) can participate in the main cathode material (Na). x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α In crystal structures, the @ symbol is used here only for easy distinction and does not indicate that the two exist independently.

[0062] Adding the above-mentioned dual fluxing elements (dual fluxes), on the one hand, the dual fluxing elements form a transition phase with the matrix metal, changing the solid solubility, which is more conducive to the growth of single crystal particles and improving the morphology after the first firing. On the other hand, it can avoid the crystal plane preference caused by a single flux to a certain extent, optimize the single crystal morphology, and enhance the geometric symmetry of the material.

[0063] Moreover, the improvement of particle roundness brought by the addition of the dual fluxing elements (dual fluxes) can reduce the stress and strain during the charge and discharge process of the material, improve the consistency and uniformity of the sodium ion diffusion path, and enhance the rate performance and cycle stability of the material.

[0064] By adding the dual fluxing elements (dual fluxes), a uniform particle size distribution can be obtained after the first firing. The solid-phase diffusion of sodium ions between adjacent particles is almost the same, reducing the polarization phenomenon during the charge and discharge process caused by different sizes of active particles.

[0065] In some specific embodiments, the mass of element M accounts for Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @ in Na in M-O x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α 0.1% to 2% of the mass; including but not limited to any point value of 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2% or the range value between any two of them.

[0066] In some specific embodiments, the sum of the masses of element Q and element F accounts for Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @ in Na in NaQ-F / O x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-αThe mass is 0.1% to 2%, including but not limited to point values ​​of any one of 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, and 2%, or a range between any two.

[0067] It is understandable that Na, Cu, Fe, Ni, and Mn sources are used to form Na during the preparation of cathode materials. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α A flux is used to form MO or NaQ-F / O, wherein the mass of the M or Q element is the mass of the Na formed. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α 0.1% to 2% of the theoretical mass.

[0068] Secondly, the present invention provides a method for preparing the above-mentioned cathode material, which is also a process for improving the morphology of cathode material by using dual fluxes. Specifically, it includes the following steps: mixing Na source, Cu source, Fe source, Ni source, Mn source, flux and water, then sand milling, followed by spray drying to obtain spray-dried material; and sintering the spray-dried material to obtain the cathode material.

[0069] By adding dual fluxes during the sand milling process, and then sand milling and spray drying together with sodium source and transition metal oxide, uniformly dispersed flux spray particles are obtained. After solid-state sintering, the spray-dried material is used to obtain single crystal particles with improved morphology and high crystallinity.

[0070] The method for preparing cathode materials provided by this invention is simple to operate, has a short process, and is suitable for mass production. Furthermore, this method helps to ensure the particle size distribution and geometric symmetry of the single-crystal particles in the cathode material.

[0071] In some specific embodiments, the flux includes at least two of NaF, bismuth-containing compounds, calcium-containing compounds, cobalt-containing compounds, strontium-containing compounds, lithium-containing compounds, and boron-containing compounds.

[0072] This invention adds a specific type of flux during the sand milling process, which allows for more thorough mixing and dispersion between the flux and various raw materials. This helps to achieve uniform formation of the eutectic system during sintering, and improves the morphology. The sphericity and particle size distribution are significantly enhanced. To a certain extent, it reduces the stress and strain of the material during the charge and discharge process, ensures the uniformity of the sodium ion diffusion path, and makes the solid-phase diffusion of ions between close particles almost identical. This reduces the polarization phenomenon during the charge and discharge process caused by the difference in the size of active particles, and improves the rate performance and cycle stability of the material.

[0073] In some specific embodiments, the bismuth-containing compound includes Bi2O3.

[0074] In some specific embodiments, the calcium-containing compound includes at least one of CaCO3 and CaO.

[0075] In some specific embodiments, the cobalt-containing compound includes at least one of CoO, Co3O4, and Co(OH)2.

[0076] In some specific embodiments, the strontium-containing compound includes at least one of SrO and SrCO3.

[0077] In some specific embodiments, the lithium-containing compound includes at least one of LiOH and Li2CO3.

[0078] In some specific embodiments, the boron-containing compound includes at least one of H3BO3 / B2O3.

[0079] In some specific embodiments, the rotational speed of the mill is 1800 to 2400 r / min, including but not limited to any one of 1800 r / min, 1900 r / min, 2000 r / min, 2100 r / min, 2200 r / min, 2300 r / min, and 2400 r / min, or a range between any two.

[0080] In some specific embodiments, the frequency of the diaphragm pump in the mill is 1 to 3 times / s, for example, 1 time / s, 2 times / s or 3 times / s.

[0081] In some specific embodiments, the particle size Dv50 of the mixed material after milling is 0.2 to 0.8 μm, including but not limited to point values ​​of any one of 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, and 0.8 μm, or a range between any two.

[0082] In some specific embodiments, the inlet air temperature of the spray dryer is 240–290°C, including but not limited to any one of 240°C, 250°C, 260°C, 270°C, 280°C, and 290°C, or a range between any two. The outlet air temperature of the spray dryer is 100–140°C, including but not limited to any one of 100°C, 110°C, 120°C, 130°C, and 140°C, or a range between any two.

[0083] In some specific embodiments, the Na source, Cu source, Fe source, Ni source, Mn source, and flux are weighed according to the stoichiometric ratio. A certain amount of pure water with a solid content of 20-45% is weighed out. First, the Na source is dissolved in the pure water. Then, the Cu source, Fe source, Ni source, Mn source, and flux are premixed and slowly poured into the above-mentioned aqueous solution containing the sodium source, and then milled. After milling until the particle size meets the requirements, the resulting slurry is transferred to a spray drying tank for spray drying to obtain the spray-dried material.

[0084] In some specific embodiments, the sintering temperature is 940–1050°C, including but not limited to any one of 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1020°C, 1030°C, and 1050°C, or a range between any two. The sintering holding time is 12–21 hours, including but not limited to any one of 12 hours, 14 hours, 15 hours, 16 hours, 18 hours, 20 hours, and 21 hours, or a range between any two.

[0085] In some specific embodiments, the sintering process is followed by a pulverizing step. This pulverizing includes air jet milling.

[0086] Thirdly, the present invention provides a sodium-ion battery comprising the above-mentioned positive electrode material.

[0087] This sodium-ion battery exhibits excellent rate performance and cycle performance.

[0088] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0089] Example 1

[0090] The cathode material Na provided in this embodiment 1.025 Cu 0.04 (Ni 31 Fe34 Mn 35 ) 0.96 The preparation method of O2@BiCa-O includes the following steps: according to the chemical formula Na 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 Weigh out the Na source, Cu source, Fe source, Ni source, and Mn source respectively, and weigh out the amount of Na that is used for each source. 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of Bi₂O₃ (flux) is 0.8% based on Bi element and accounts for 0.8% of Na. 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 Theoretically, 0.3% CaCO3 (flux) was prepared based on elemental Ca content, and a certain amount of pure water with a solid content of 37.5% was also weighed. The Na source was dissolved in the pure water to obtain a sodium source solution. Then, a premix of Cu, Fe, Ni, Mn, Bi₂O₃, and CaCO₃ was slowly poured into the sodium source solution, and milled at 2200 rpm with a diaphragm pump at a frequency of 2 times / s. The particle size of the mixture was tested every half hour. When the particle size Dv₅₀ of the mixture reached 0.5 μm, the resulting slurry was transferred to the spray drying process. During spray drying, the feed rate was controlled at 15 Hz, the inlet air temperature at 260℃, and the outlet air temperature at 120℃ to obtain the spray-dried material. The spray-dried material was then sintered in a 500g pot, heated to 990℃ at a rate of 2℃ / min, held for 18 hours, and then slowly cooled to room temperature before air-jet pulverization to obtain the cathode material Na. 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 O2@BiCa-O.

[0091] See the SEM image of the cathode material. Figure 1 As shown. (Through) Figure 1 It can be seen that the cathode material is a single crystal particle.

[0092] Example 2

[0093] The cathode material Na provided in this embodiment 1.04 Cu 0.025 (Ni 31 Fe34 Mn 35 ) 0.975 The preparation method of O2@NaCa-F / O is basically the same as that in Example 1, except that: according to the chemical formula Na 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 Weigh out the Na, Cu, Fe, Ni, and Mn sources respectively, and weigh out the amount of Na... 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The theoretical mass of O2, calculated as Ca element, is 0.4% CaO (flux) and accounts for 0.4% of Na. 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The theoretical mass of O2 is 0.5% NaF (flux) based on the elemental charge of F.

[0094] Example 3

[0095] The cathode material Na provided in this embodiment 1.03 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@CaCo-O is basically the same as that in Example 1, except that: according to the chemical formula Na 1.03 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 Weigh out the Na, Cu, Fe, Ni, and Mn sources respectively, and weigh out the amount of Na... 1.03 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of O2, calculated as Ca element, is 0.2% CaO (flux) and accounts for a certain percentage of Na. 1.03 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of O2 is 1% Co(OH)2 (flux) based on the elemental Co.

[0096] Example 4

[0097] The cathode material Na provided in this embodiment 1.0 Cu 0.055 (Ni 31 Fe 34 Mn 35 ) 0.945 The preparation method of O2@CaSr-O is basically the same as that in Example 1, except that: according to the chemical formula Na 1.0 Cu 0.055 (Ni 31 Fe 34 Mn 35 ) 0.945 Weigh out the Na, Cu, Fe, Ni, and Mn sources respectively, and weigh out the amount of Na... 1.0 Cu 0.055 (Ni 31 Fe 34 Mn 35 ) 0.945 The theoretical mass of O2, calculated as Ca element, is 0.3% CaCO3 (flux) and accounts for a certain percentage of Na. 1.0 Cu 0.055 (Ni 31 Fe 34 Mn 35 ) 0.945 The theoretical mass of O2 is 1% SrCO3 (flux) based on the elemental Sr content.

[0098] Example 5

[0099] The cathode material Na provided in this embodiment 1.02 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@SrB-O is basically the same as that in Example 1, except that: according to the chemical formula Na 1.02 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 Weigh out the Na, Cu, Fe, Ni, and Mn sources respectively, and weigh out the amount of Na... 1.02 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of O2, calculated as Sr element, is 0.5% SrCO3 (flux) and accounts for a certain percentage of Na. 1.02 Cu 0.04 (Ni31 Fe 34 Mn 35 ) 0.96 O2 theoretical mass is 0.2% H3BO3 (flux) based on element B.

[0100] Example 6

[0101] The cathode material Na provided in this embodiment 1.01 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@SrLi-O is basically the same as that in Example 1, except that: according to the chemical formula Na 1.01 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 Weigh out the Na, Cu, Fe, Ni, and Mn sources respectively, and weigh out the amount of Na... 1.01 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of O2, calculated as Sr element, is 0.2% SrCO3 (flux) and accounts for a certain percentage of Na. 1.01 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The theoretical mass of O2 is 0.4% Li2CO3 (flux) based on the elemental composition of Li.

[0102] Example 7

[0103] The cathode material Na provided in this embodiment 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@BiCa-O is basically the same as that in Example 1, except that: the grinding is carried out at a speed of 2400 r / min and a diaphragm pump frequency of 3 times / s until the particle size Dv50 of the mixed material is 0.2 μm, and the inlet air temperature of spray drying is 240℃ and the outlet air temperature is 140℃.

[0104] Example 8

[0105] The cathode material Na provided in this embodiment 1.025 Cu 0.04 (Ni31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@BiCa-O is basically the same as that in Example 1, except that the sintering temperature is 940℃ and the holding time is 20h.

[0106] Comparative Example 1

[0107] The cathode material Na provided in this comparative example 1.03 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2 is basically the same as that in Example 3, except that the fluxing agents CaO and Co(OH)2 are not added.

[0108] SEM images of the cathode material prepared in this comparative example are shown below. Figure 3 As shown.

[0109] Comparative Example 2

[0110] The cathode material Na provided in this comparative example 0.95 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The preparation method of O2@NaCa-F / O is basically the same as that in Example 2, except that: according to the chemical formula Na 0.95 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 Weigh the Na source using O2.

[0111] Comparative Example 3

[0112] The cathode material Na provided in this comparative example 1.08 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The preparation method of O2@NaCa-F / O is basically the same as that in Example 2, except that: according to the chemical formula Na 1.08 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 Weigh the Na source using O2.

[0113] Comparative Example 4

[0114] The cathode material Na provided in this comparative example 1.04 Cu 0.015 (Ni 31 Fe 34 Mn 35 ) 0.985 The preparation method of O2@NaCa-F / O is basically the same as that in Example 2, except that: according to the chemical formula Na 1.04 Cu 0.015 (Ni 31 Fe 34 Mn 35 ) 0.985 O2 is used to weigh the Cu source.

[0115] Comparative Example 5

[0116] The cathode material Na provided in this comparative example 1.04 Cu 0.07 (Ni 31 Fe 34 Mn 35 ) 0.93 The preparation method of O2@NaCa-F / O is basically the same as that in Example 2, except that: according to the chemical formula Na 1.04 Cu 0.07 (Ni 31 Fe 34 Mn 35 ) 0.93 O2 is used to weigh the Cu source.

[0117] Comparative Example 6

[0118] The cathode material Na provided in this comparative example 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The preparation method of O2@NaCa-F / O is as follows:

[0119] According to the chemical formula Na 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975O2 sources Na, Cu, Fe, Ni, and Mn were weighed separately, and a certain amount of pure water was weighed according to a solid content of 37.5%. The Na source was dissolved in the pure water to obtain a sodium source solution. Then, the Cu, Fe, Ni, and Mn sources were premixed and slowly poured into the sodium source solution. The mixture was then milled at a speed of 2200 r / min and a diaphragm pump frequency of 2 times / s. The particle size of the mixture was tested every half hour. When the particle size Dv50 of the mixture reached 0.5 μm, the resulting slurry was transferred to the spray drying process. During spray drying, the feed rate was controlled at 15 Hz, the inlet air temperature at 260℃, and the outlet air temperature at 120℃ to obtain the spray-dried material.

[0120] Na is taken respectively 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 The theoretical mass of O2, calculated as Ca element, is 0.4% CaO (flux) and accounts for 0.4% of Na. 1.04 Cu 0.025 (Ni 31 Fe 34 Mn 35 ) 0.975 O2 theoretical mass is 0.5% NaF (flux) based on F element. The above spray-dried material is mixed evenly with CaO and NaF and then sintered in a 500g mortar. The temperature is increased to 990℃ at a rate of 2℃ / min and held for 18h. After that, it is slowly cooled to room temperature and then pulverized by airflow to obtain the positive electrode material.

[0121] Comparative Example 7

[0122] The cathode material Na provided in this comparative example 1.025 Cu 0.04 (Ni 31 Fe 34 Mn 35 ) 0.96 The preparation method of O2@Bi-O is basically the same as that in Example 1, except that CaCO3 is not added.

[0123] SEM images of the cathode material prepared in this comparative example are shown below. Figure 4 As shown.

[0124] The particle sizes Dv90, Dv10, Dv50, and particle size distribution SPAN (SPAN = (Dv90 - Dv10) / Dv50) of the cathode materials prepared in each embodiment and comparative example are shown in Table 1. Based on the CP electron microscopy images, the number of single-crystal particles in each cathode material meeting the following conditions was counted: L a L is the major axis of the cross-section of the single crystal particle. bLet L be the minor axis of the single crystal grain cross-section, and δ be L. a / L b The percentage of single-crystal particles with a density <1.5, and the δ values ​​of the single-crystal particles of the cathode materials prepared in each embodiment and comparative example are shown in Table 1. Wherein, L... a / L b The calculation method is as follows Figure 2 As shown, it is necessary to calculate the percentage of cases where δ < 1.5.

[0125] XRD tests were performed on the cathode materials prepared in each embodiment and each comparative example to obtain the full width at half maximum (FWHM) of the 003 crystal plane diffraction peak of the cathode materials. 003 The full width at half maximum (FWHM) of the 104 crystal plane diffraction peak 104 The ratio of the diffraction peak intensity I003 of the 003 crystal plane to the diffraction peak intensity I104 of the I104 crystal plane, I003 / I104, is shown in Table 1.

[0126] Table 1 Physicochemical and structural parameters of each cathode material

[0127]

[0128] The cathode materials prepared in each embodiment all satisfy the following relationship: 1 / (δ 3 +δ 2 ) <I003 / I104<3 / (δ 3 +δ 2 However, for proportions 1 to 7, the relation 1 / (δ) does not satisfy. 3 +δ 2 ) <I003 / I104<3 / (δ 3 +δ 2 ).

[0129] Using the positive electrode materials prepared in each embodiment and comparative example as positive electrode active materials, coin cells were fabricated according to the following method: A slurry of positive electrode active material: SP:PVDF was homogenized and coated at a mass ratio of 90:5:5, and cut into pieces with a diameter of [missing information]. The electrode was dried overnight and then transferred to a glove box (to obtain the positive electrode). A sodium metal sheet was used as the counter electrode, and the specifications of the sodium sheet used were as follows: 2032 coin cells were assembled in an Ar atmosphere-protected glove box using glass fiber as the separator and a NaPF6 solution with a sodium ion concentration of 1 mol / L (a mixture of EC and DMC in a volume ratio of 1:1) as the electrolyte. After assembly, the coin cells were placed at 25°C and tested using a Xinwei coin cell test cabinet. The test voltage ranged from 2.5 to 4.05 V. The cells were charged and discharged sequentially at 0.1C and 0.5C rates for three cycles, followed by a 1C cycle test for 100 cycles. The test results are shown in Table 2.

[0130] Table 2 Electrochemical performance test results of each battery

[0131]

[0132] As can be seen from Table 1, the coin cells assembled using the cathode materials of each embodiment have good rate performance and cycle performance.

[0133] Compared with Example 3, the addition of flux during the sand milling process significantly improved the performance of Comparative Example 1 compared to Example 3. The sand milling process allows for more thorough mixing and dispersion of the flux with the raw materials, which helps to achieve uniform formation of the eutectic system during sintering, and better improves the morphology. The sphericity and particle size distribution are significantly improved. To a certain extent, it reduces the stress and strain of the material during the charge and discharge process, and ensures the uniformity of the sodium ion diffusion path. The solid-phase diffusion of ions between close particles is almost the same, reducing the polarization phenomenon during the charge and discharge process caused by the difference in the size of active particles, and improving the rate performance and cycle stability of the material.

[0134] Compared with Example 2, Comparative Examples 2 to 5 show that the proportion of positive electrode material is a key indicator affecting material performance. In this case, even if flux is added, it is difficult to improve the performance.

[0135] Compared with Example 2, Comparative Example 6 found that adding flux during the high-mixing process made it difficult to achieve uniform dispersion of the flux, and the single crystal morphology of the sintered sample was not significantly improved, with a wider particle size distribution.

[0136] Compared with Example 1, the addition of a single flux in Comparative Example 7 can lead to a certain degree of preference for a particular crystal plane. That is, the addition of Bi alone leads to the increase in particle size and the obvious preference for the 003 crystal plane, resulting in a deterioration in the geometric symmetry of the material.

[0137] In summary, this invention establishes a correlation between the relative peak intensity of I003 / I104 in XRD and the morphology of single-crystal particles, thereby limiting the selection of crystal faces, optimizing the morphology of single crystals, improving the geometric symmetry of single-crystal particles, and ensuring the particle distribution size of single crystal particles. This improves battery polarization, enhances the structural stability of materials, suppresses structural degradation, and improves the rate performance and cycle stability of cathode materials.

[0138] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A positive electrode material, characterized in that, The cathode material comprises single-crystal particles, wherein the single-crystal particles satisfy δ≥75%; where δ is L a / L b The proportion of single crystal particles <1.5, L a L is the major axis of the cross-section of the single crystal particle. b The minor axis of the cross-section of the single crystal particle; Furthermore, the ratio of the diffraction peak intensity I003 of the 003 crystal plane to the diffraction peak intensity I104 of the I104 crystal plane of the cathode material, I003 / I104, satisfies: 1 / (δ 3 +δ 2 ) <I003 / I104<3 / (δ 3 +δ 2 ); The general formula of the positive electrode material is Na. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @MOorNa x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @NaQ- F / O, where 0.98≤x≤1.05, 0.02≤a≤0.06, 0≤α≤0.1, M and Q are fluxing elements, M includes at least two of Bi, Ca, Co, Sr, Li and B, and Q includes at least one of Bi, Ca, Co, Sr, Li and B.

2. The cathode material according to claim 1, characterized in that, The particle size distribution of the cathode material is SPAN = (Dv90 - Dv10) / Dv50 < 1.

3.

3. The positive electrode material according to claim 1, characterized in that, The full width at half maximum (FWHM) of the 003 crystal plane diffraction peak of the cathode material 003 ≤0.

13.

4. The positive electrode material according to claim 1, characterized in that, The full width at half maximum (FWHM) of the 104 crystal plane diffraction peak of the cathode material 104 <0.

15.

5. The cathode material according to claim 1, characterized in that, The mass of element M accounts for Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @In M-O, Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α is 0.1% - 2% of the mass.

6. The positive electrode material according to claim 1, characterized in that, The combined mass of elements Q and F accounts for a significant portion of Na. x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α @NaQ-F / O Na x Cu a (Ni 31 Fe 34 Mn 35 ) (1-a) O 2-α 0.1% to 2% of the mass.

7. The method for preparing the cathode material according to any one of claims 1 to 6, characterized in that, Includes the following steps: The Na source, Cu source, Fe source, Ni source, Mn source, flux, and water are mixed and milled, then spray-dried to obtain a spray-dried material; the flux includes at least two of NaF, bismuth-containing compounds, calcium-containing compounds, cobalt-containing compounds, strontium-containing compounds, lithium-containing compounds, and boron-containing compounds; The spray-dried material is sintered to obtain the positive electrode material.

8. The method for preparing the cathode material according to claim 7, characterized in that, The bismuth-containing compound includes Bi2O3; The calcium-containing compound includes at least one of CaCO3 and CaO; The cobalt-containing compound includes at least one of CoO, Co3O4, and Co(OH)2; The strontium-containing compound includes at least one of SrO and SrCO3; The lithium-containing compound includes at least one of LiOH and Li2CO3; The boron-containing compound includes at least one of H3BO3 / B2O3.

9. The method for preparing the cathode material according to claim 7, characterized in that, The rotational speed of the mill is 1800~2400 r / min.

10. The method for preparing the cathode material according to claim 7, characterized in that, The frequency of the diaphragm pump in the mill is 1 to 3 times / s.

11. The method for preparing the cathode material according to claim 7, characterized in that, The particle size Dv50 of the mixed material is 0.2~0.8μm after grinding.

12. The method for preparing the cathode material according to claim 7, characterized in that, The inlet air temperature of the spray dryer is 240~290℃, and the outlet air temperature is 100~140℃.

13. The method for preparing the cathode material according to claim 7, characterized in that, The sintering temperature is 940~1050℃, and the holding time is 12~21h.

14. The method for preparing the cathode material according to claim 7, characterized in that, The sintering process is followed by a crushing step.

15. A sodium-ion battery, characterized in that, Includes the cathode material as described in any one of claims 1 to 6.

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