Positive electrode material and preparation method therefor, sodium ion battery and electrical apparatus

Abstract

The present disclosure belongs to the technical field of batteries. Specifically disclosed are a positive electrode material and a preparation method therefor, a sodium ion battery and an electrical apparatus. The positive electrode material comprises: Naa1(Nix1Fey1Mnz1Cun1Mm1M'p1)O2, M being selected from at least one element of Ca, Sr, Y, Sn, Ce and La, and M' being selected from at least one element of Co, Ti, V, Mg, B, Cr, Sb, Al, Zn, Zr, Nb, W and Li. A fitted straight line of the pressure Ti-micro-strain change △Ni of the positive electrode material satisfies △Ni=kTi, 0<k<0.016, wherein k is a slope, Ti is a pressure in MPa applied to the positive electrode material before a micro-strain is tested, and the micro-strain change △Ni is a difference between the micro-strain of the positive electrode material after applying the pressure Ti and the micro-strain of the positive electrode material without applying the pressure. Thus, the positive electrode material has a small micro-strain change, and excellent high voltage cycle stability.

Description

Positive electrode materials and their preparation methods, sodium-ion batteries and electrical devices Technical Field

[0001] This disclosure belongs to the field of battery technology, specifically relating to a cathode material and its preparation method, a sodium-ion battery, and an electrical device. Background Technology

[0002] In recent years, sodium-ion batteries have gained widespread attention and achieved rapid development due to their similar working principle to lithium-ion batteries, as well as the advantages of abundant sodium resources and low cost. Currently, sodium-ion batteries have been applied to a certain extent in start-stop power supplies, two-wheeled vehicles, and energy storage. Further improvements in energy density are expected, leading to wider application in the electric vehicle sector.

[0003] In sodium-ion battery systems, cathode materials are mainly classified into three types: layered oxides, polyanionic compounds, and Prussian blue compounds. Among them, layered oxides (Na... x MO2 materials, with their advantages of high energy density, good low-temperature performance, simple process and easy large-scale production, have been first applied in the low-to-mid-range passenger car and energy storage system markets.

[0004] With the continued decline in lithium prices, sodium-ion battery layered oxide materials have gradually lost their cost advantage. Improving the energy density and reducing the cost per watt-hour (WWh) of these materials has become a pressing issue. Currently, increasing the operating voltage is the most effective strategy for increasing energy density and reducing WWh; however, increasing the operating voltage exacerbates structural changes during cycling, leading to rapid degradation. Therefore, improving the structural stability of these sodium-ion battery layered oxide materials and enhancing their high-voltage cycling stability is the research topic of this disclosure. Summary of the Invention

[0005] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, this disclosure proposes a cathode material with small microscopic strain changes or good high-voltage cycling stability, a method for preparing the same, a sodium-ion battery, and an electrical device thereof.

[0006] The first aspect of this disclosure proposes a cathode material comprising: Na a1 (Ni x1 Fe y1 Mn z1 Cu n1 M m1 M' p1 O2 Formula 1

[0007] Where, 0.90 ≤ a1 ≤ 1.10, 0 ≤ x1 ≤ 0.5, 0 ≤ y1 ≤ 0.5, 0 ≤ z1 ≤ 0.5, 0 ≤ n1 ≤ 0.1, 0 < m1 ≤ 0.05, 0 ≤ p1 ≤ 0.05, and x1 + y1 + z1 + n1 + m1 + p1 = 1;

[0008] M is selected from at least one element of Ca, Sr, Y, Sn, Ce, and La;

[0009] M' is selected from at least one element of Co, Ti, V, Mg, B, Cr, Sb, Al, Zn, Zr, Nb, W, and Li;

[0010] The pressure T of the positive electrode material i - Microstrain change △N i The fitted straight line satisfies △N i = kT i , 0 < k < 0.016;

[0011] Where, k is the slope, and T i is the pressure applied to the positive electrode material in MPa before testing the microstrain. The microstrain change △N i is the difference between the microstrain of the positive electrode material after applying the pressure T i and the microstrain of the positive electrode material without applying the pressure.

[0012] Having the above composition, and the pressure T i - Microstrain change △N i The fitted straight line satisfies the above conditions, and this positive electrode material has high structural stability, tap density, and volume energy density.

[0013] In some embodiments, 0 < k < 0.012. When the k value is within this range, it indicates that the degree of microstrain change of the positive electrode material is weak, suggesting that the material structure is more stable, which can ensure the structural stability of the material during high-voltage charge-discharge tests and significantly improve the cycle performance.

[0014] In some embodiments, a1 is 0.90 to 1.05; in some other embodiments, a1 is 0.95 to 1.05; in some specific examples, a1 is 0.97 to 1.03.

[0015] In some embodiments, 0.01 ≤ m1 ≤ 0.05.

[0016] In some embodiments, 0.01 ≤ p1 ≤ 0.05.

[0017] In some embodiments, the median particle size D of the positive electrode material 50 is 3 μm to 10 μm; in some other embodiments, the median particle size D of the positive electrode material50 The median particle size D of the cathode material is 4μm to 9μm; in some specific embodiments, the median particle size D of the cathode material is... 50 The size is 5μm to 8μm. This is beneficial for improving the rate performance of sodium-ion batteries.

[0018] In some embodiments, the particle size distribution of the cathode material satisfies 1.1 < (D 90 -D 10 ) / D 50 <1.6; In other embodiments, the particle size distribution of the cathode material satisfies 1.2 < (D 90 -D 10 ) / D 50 <1.4. This facilitates a denser packing of cathode material particles, thereby further improving the energy density of sodium-ion batteries.

[0019] In some embodiments, the positive electrode material is an O3-type sodium-ion layered oxide.

[0020] The second aspect of this disclosure discloses a method for preparing a cathode material, comprising:

[0021] The precursor, sodium source, M source and optionally M' source are mixed to obtain a raw material mixture;

[0022] The raw material mixture is heated to T1℃ at a first heating rate v1, and then heated to T2℃ at a second heating rate v2, and held at the temperature for t time within the temperature range of T2-10℃ to T2+10℃ to obtain the positive electrode material, wherein v2 < v1.

[0023] The method disclosed above has a simple preparation process and is easy to implement for industrial production. By controlling the sintering process and introducing M element doping, a cathode material with small micro-strain and wide particle size distribution is prepared, which improves the structural stability and compaction density of the cathode material, thereby increasing the volumetric energy density of the cathode material.

[0024] In some embodiments, the difference between the first heating rate v1 and the second heating rate v2 is 1°C / min to 6°C / min.

[0025] In some implementations, 3℃ / min≤v1≤6℃ / min, v2≤2℃ / min.

[0026] In some implementations, 500℃≤T1≤700℃.

[0027] In some implementations, 900℃≤T2≤1100℃.

[0028] In some implementations, 5h ≤ t ≤ 15h.

[0029] Under the above sintering conditions, the micro-strain changes of the cathode material can be reduced, which is beneficial to improving the structural stability and compaction density of the cathode material.

[0030] In some embodiments, the median particle size D of the precursor 50 The particle size is 3μm to 4μm. This is beneficial for obtaining cathode materials with suitable particle size, increasing the diffusion rate of sodium ions, and thus improving the electrochemical performance of the cathode material.

[0031] In some embodiments, the particle size distribution K of the precursor 90 Satisfy: 0.5 < K 90 =(D 90 -D 10 ) / D 50 <1.6.

[0032] In some embodiments, the tap density of the precursor is 1.40 g / cm³. 3 ~1.80g / cm 3 .

[0033] In some embodiments, the specific surface area of ​​the precursor is 10 m². 2 / g~30m 2 / g.

[0034] In some embodiments, the precursor includes: Ni x2 Fe y2 Mn z2 Cu n2 O a2 H b2 , where 0≤x2≤0.5, 0≤y2≤0.5, 0≤z2≤0.5, 0≤n2≤0.1, 1≤a2≤2, 0≤b2≤2, x2+y2+z2+n2=1.

[0035] When the current driving element meets the above conditions, it is beneficial to improve the energy density, rate performance and cycle life of sodium-ion batteries.

[0036] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxide. Therefore, the material is widely available and inexpensive.

[0037] In some embodiments, the M source includes at least one selected from oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M element; in other embodiments, the M source includes at least one selected from CaO, CaCO3, Ca3(PO4)2, CaF2, CaCl2, Ca(OH)2, CaSi2, Sr(OH)2, SrCO3, Sn(OH)4, Y2O3, La2O3, Ce2O3, and CeO2. Therefore, the materials are widely available and the cost is low.

[0038] In some embodiments, the M' source includes at least one of oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M' element; in other embodiments, the M' source includes at least one of Li2CO3, LiOH, Co(OH)2, V2O5, Cr2O3, ZrO, Zr(HPO4)2, ZrSi2, Al2O3, AlPO4, AlCl3, ZnO, TiO2, MgO, MgCO3, Mg2Si, Mg3(PO4)2, MgF2, MgCl2, Nb2O5, WO3, B2O3, Sb2O5, and Sb2O3. Therefore, the materials are widely available and the cost is low.

[0039] A third aspect of this disclosure provides a sodium-ion battery comprising the cathode material described in the first aspect of this disclosure or the cathode material prepared by the method described in the second aspect of this disclosure. Therefore, this sodium-ion battery exhibits excellent cycle stability.

[0040] This disclosure provides a fourth aspect of an electrical device, including the sodium-ion battery described in the third aspect of this disclosure. Therefore, the electrical device has a long service life. Attached Figure Description

[0041] Figure 1 is a SEM image of the precursor prepared in Example 1 of this disclosure.

[0042] Figure 2 is a SEM image of the cathode material prepared in Example 1 of this disclosure.

[0043] Figure 3 is a SEM image of the cathode materials prepared in Example 1 and Comparative Example 3 of this disclosure after being subjected to different pressures (0 MPa, 111 MPa, 333 MPa, 555 MPa).

[0044] Figure 4 is the XRD pattern of the precursor prepared in Example 1 of this disclosure.

[0045] Figure 5 is the XRD pattern of the cathode material prepared in Example 1 of this disclosure. Detailed Implementation

[0046] Embodiments of the present disclosure will be described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below by referring to the drawings are exemplary and intended to explain the present disclosure, and should not be construed as a limitation to the present disclosure.

[0047] A first aspect of the present disclosure provides a positive electrode material, comprising: Na a1 (Ni x1 Fe y1 Mn z1 Cu n1 M m1 M’ p1 )O2 Formula 1

[0048] In the formula, 0.90 ≤ a1 ≤ 1.10, 0 ≤ x1 ≤ 0.5, 0 ≤ y1 ≤ 0.5, 0 ≤ z1 ≤ 0.5, 0 ≤ n1 ≤ 0.1, 0 < m1 ≤ 0.05, 0 ≤ p1 ≤ 0.05, and x1 + y1 + z1 + n1 + m1 + p1 = 1;

[0049] M is selected from at least one element of Ca, Sr, Y, Sn, Ce, and La;

[0050] M’ is selected from at least one element of Co, Ti, V, Mg, B, Cr, Sb, Al, Zn, Zr, Nb, W, and Li;

[0051] The pressure T of the positive electrode material i - Microstrain change ΔN i The fitting straight line satisfies ΔN i = kT i , 0 < k < 0.016; <…>

[0052] Where k is the slope, and T i is the pressure applied to the positive electrode material before testing the microstrain, in MPa, and the microstrain change ΔN i is the difference between the microstrain of the positive electrode material after applying the pressure T i and the microstrain of the positive electrode material without applying the pressure.

[0053] In the present disclosure, the value of k reflects the degree of microstrain change of the positive electrode material under different pressure conditions. According to the value of k, the structural stability of the positive electrode material can be evaluated. The above positive electrode material of the present disclosure satisfies 0 < k < 0.016, has a relatively small degree of microstrain change, has better structural stability, and can ensure that the material maintains structural stability during high-voltage charge-discharge testing, greatly improving the cycle performance.

[0054] In some embodiments, 0 < k < 0.012, for example, it can be 0.001, 0.003, 0.005, 0.008, 0.01, or 0.011, etc. Among them, the value of k reflects the degree of microscopic strain change of the positive electrode material under different pressure conditions. The lower the k value, the weaker the degree of microscopic strain change of the positive electrode material as the pressure increases, indicating that the structure of the positive electrode material is more stable. The positive electrode material with a lower k value can ensure the structural stability of the positive electrode material during high-voltage charge and discharge tests, significantly improving the cycle performance.

[0055] In this article, the pressure T of the positive electrode material i and the microscopic strain change △N i The method of fitting into a straight line includes:

[0056] Step 1: Measure n portions of the positive electrode material. Define the n portions of the positive electrode material as the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., the nth portion of the positive electrode material, where n is an integer greater than or equal to 5;

[0057] Step 2: Add the 1st portion of the positive electrode material, the 2nd portion of the positive electrode material,..., the nth portion of the positive electrode material into the mold respectively, and apply the 1st pressure, the 2nd pressure,..., the nth pressure that increase sequentially from small to large one by one. Then dissociate the obtained tablets to obtain the 1st sample, the 2nd sample,..., the nth sample respectively. The positive electrode material without applied pressure constitutes the initial sample;

[0058] Step 3: After calibrating the position of the goniometer and the width of the instrument of the X-ray powder diffractometer, use the X-ray powder diffractometer to perform X-ray diffraction tests on the initial sample, the 1st sample, the 2nd sample,..., the nth sample respectively to obtain X-ray diffraction data;

[0059] Step 4: According to the X-ray diffraction data, calculate the microscopic strains N0, N1, N2,..., N corresponding to the initial sample, the 1st sample, the 2nd sample,..., the nth sample n , and then calculate the microscopic strain change △N 1＝ N1 - N0, △N 2＝ N2 - N1,..., △N n＝ N n -N n-1 ;

[0060] Step 5: Make a scatter plot of the microscopic strain change and the pressure and fit a straight line, and determine the structural stability of the positive electrode material according to the slope of the fitted straight line.

[0061] It should be noted that the pressure applied to the positive electrode material must be within a reasonable range. In some embodiments, the pressure T1 of the positive electrode material is 50-150 MPa (e.g., 50 MPa, 80 MPa, 100 MPa, 120 MPa, or 150 MPa); in other embodiments, the pressure T1 of the positive electrode material is 80-120 MPa.

[0062] In some embodiments, the pressure T of the positive electrode material n The pressure is 150–900 MPa (e.g., 150 MPa, 200 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, or 900 MPa, etc.); in other embodiments, the pressure T of the positive electrode material is... n The pressure ranges from 160 to 600 MPa.

[0063] In some embodiments, the pressure T of the positive electrode material i With T i-1 The difference is 20 to 200 MPa (e.g., 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, 120 MPa, 140 MPa, 160 MPa, 180 MPa or 200 MPa, etc.); in other embodiments, the difference is 50 to 100 MPa, where i is an integer from 2 to n, and n is an integer greater than or equal to 5 (e.g., 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, etc.).

[0064] As an example, when n=7, the pressure T of the positive electrode material is... i and micro-strain change ΔN i The specific methods for fitting a line include:

[0065] Step 1: Treat the surface moisture of the positive electrode material, usually by drying it in a forced-air oven or vacuum oven at 150°C.

[0066] Step 2: Weigh the sample. Weigh the processed sample according to the following standards: For D 50 For samples ≤3μm, the sample size is 0.5–1.5 g; for samples ≤3μm D 50 For samples ≤7μm, the sample size is 1.5–3g; for D 50 For samples ≥7μm, take 3–5g. Transfer the weighed sample to the compaction mold and gently shake the mold to flatten the sample surface.

[0067] Step 3: Place the mold containing the sample into the equipment and slowly apply pressure to the specified pressure (specifically, 50MPa, 100MPa, 200MPa, 300MPa, 400MPa, 500MPa, or 600MPa). The pressure applied by the equipment / mold area equals the pressure. After standing for 30 seconds, remove the mold and demold the sample. Only one pressure point can be measured per sample preparation.

[0068] Step 4: Place the demolded positive electrode tablet into a mortar, gently separate the tablet and sieve it with a standard sieve to ensure that the tablet is completely pulverized without any flaky particles. Pack the processed sample into a bag, label it and store it.

[0069] Step 5: Perform instrument parameter calibration of the X-ray powder diffractometer. Use standard Si powder to calibrate the position of the goniometer and use standard LaB6 to calibrate the instrument width.

[0070] Under the determined test conditions, the position and width of the goniometer were calibrated. The standard materials (Si powder, LaB6) were prepared on the sample stage, the spectrum was acquired, the instrument was calibrated, and the data was saved.

[0071] Step 6: Prepare different compacted materials onto the sample stage, perform X-ray powder diffraction tests under defined conditions, and save the data for analysis; it is required that the samples prepared on the sample stage be flat and that the sample height be kept consistent each time.

[0072] Step 7: Import the test data into the refinement software for data processing.

[0073] (1) First, perform peak position processing, select the maximum peak value for processing, and ensure that the software can identify the position of all peaks;

[0074] (2) Perform phase identification using the PDF5+ database (International Diffraction Data Center), requiring the test data to be highly consistent with the card information;

[0075] (3) Add instrument width calibration data (external standard calibration width), select all crystal planes to calculate material micro-stress data using the Halder-Wagner method.

[0076] Step 8: Analyze the micro-strain data of the material calculated using the Halder-Wagner method.

[0077] Step 9: Perform scatter plot analysis on the micro-strain data and pressure, and determine the slope k.

[0078] In some embodiments, a1 is 0.90 to 1.05, for example, it can be 0.90, 0.93, 0.95, 0.98, 1, 1.03 or 1.05; in other embodiments, a1 is 0.95 to 1.05; in some specific embodiments, a1 is 0.97 to 1.03.

[0079] In some implementations, 0.01 ≤ m1 ≤ 0.05, for example, it can be 0.01, 0.02, 0.03, 0.04 or 0.05, etc.

[0080] In some implementations, 0.01 ≤ p1 ≤ 0.05, for example, it can be 0.01, 0.02, 0.03, 0.04 or 0.05, etc.

[0081] In some embodiments, the median particle size D of the cathode material 50 The particle size is 3μm to 10μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc.; in other embodiments, the median particle size D of the cathode material is... 50 The median particle size D of the cathode material is 4–9 μm; in some specific embodiments, the median particle size D of the cathode material is... 50 The median particle size D of the cathode material is 5μm to 8μm. 50 Within the aforementioned range, the sodium ion diffusion path is shortened, which is beneficial for improving the rate performance of sodium-ion batteries.

[0082] In some embodiments, the particle size distribution of the cathode material satisfies 1.1 < (D 90 -D 10 ) / D 50 <1.6, for example, it can be 1.2, 1.3, 1.4, 1.5 or 1.6, etc.; in other embodiments, the particle size distribution of the cathode material satisfies 1.2 < (D 90 -D 10 ) / D 50 <1.4. When the particle size distribution meets the above requirements, the cathode material particles can achieve a denser packing, which can further improve the energy density of sodium-ion batteries.

[0083] In particle size distribution, D 50 Also known as the median particle size, it means that 50% of the volume of particles are smaller than or equal to this value, D. 90 This means that 90% of the volume of particles is smaller than or equal to this value, D 10 This means that 10% of the volume of particles are smaller than or equal to this value. (D) 10 D 50 D 90The measurement can be performed using a Malvern particle size analyzer: disperse the cathode material in a dispersant (pure water, ethanol, acetone or other surfactants), sonicate for 30 minutes, add the sample into the Malvern particle size analyzer, and start the test.

[0084] In some embodiments, the positive electrode material is an O3-type sodium-ion layered oxide, and its chemical composition may be Na. x MO2. Specifically, in O3-type sodium-ion layered oxides, transition metal oxide layers and sodium ion layers alternate, forming a sandwich-like structure. This can be characterized by XRD.

[0085] The second aspect of this disclosure discloses a method for preparing a cathode material, comprising:

[0086] S1: Mix the precursor, sodium source, M source and optionally M' source to obtain a raw material mixture.

[0087] In this step, there are no particular restrictions on the specific method of mixing the precursor, sodium source, M source, and optionally M' source; for example, a mixer can be used for mixing. It is understood that in this step, the addition of the M' source can be flexibly chosen as needed.

[0088] In some embodiments, the median particle size D of the precursor 50 The median particle size of the precursor is 3μm to 4μm, for example, it can be 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, or 4μm, etc. A median particle size of the precursor within this range is beneficial for obtaining cathode materials with suitable particle sizes, improving the diffusion rate of sodium ions, and thus enhancing the electrochemical performance of the cathode material.

[0089] In some embodiments, the particle size distribution K of the precursor 90 Satisfy: 0.5 < K 90 =(D 90 -D 10 ) / D 50 <1.6, for example, it can be 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5, etc. Having the above particle size distribution is beneficial to obtaining a cathode material with a suitable particle size distribution, thereby increasing the packing density of the cathode material, increasing its compaction density, and thus increasing the energy density of the battery.

[0090] In some embodiments, the tap density of the precursor is 1.40 g / cm³. 3 ~1.80g / cm 3 For example, it can be 1.40 g / cm³. 3 1.50g / cm 31.60g / cm 3 1.70g / cm 3 Or 1.80g / cm 3 This improves the compact packing effect of the cathode material, thereby increasing the energy density of the battery.

[0091] In this article, the tap density of the precursor refers to the mass per unit volume of the precursor powder in the container after tapping under specified conditions, which can be measured by the BT-30 tap density tester from Baxter Corporation.

[0092] In some embodiments, the specific surface area of ​​the precursor is 10 m². 2 / g~30m 2 / g, for example, can be 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g or 30m 2 / g etc. A specific surface area within this range ensures a denser precursor surface morphology and higher tap density, which is beneficial for increasing packing capacity and production capacity.

[0093] In this article, the specific surface area of ​​the precursor refers to the surface area per unit mass of the precursor, which was measured using a Tristar II3020 specific surface area analyzer from Micromertics, USA.

[0094] In some embodiments, the precursor includes: Ni x2 Fe y2 Mn z2 Cu n2 O a2 H b2 , where 0≤x2≤0.5, 0≤y2≤0.5, 0≤z2≤0.5, 0≤n2≤0.1, 1≤a2≤2, 0≤b2≤2, x2+y2+z2+n2=1.

[0095] Specifically, x² can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, etc.; y² can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, etc.; z² can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, etc. 0.35, 0.4, 0.45, or 0.5, etc.; n2 can be 0, 0.01, 0.03, 0.05, 0.08, or 0.1, etc.; a2 can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, etc.; b2 can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, etc.

[0096] In this paper, the preparation method of the precursor of the cathode material can be as follows:

[0097] (1) Prepare a mixed salt solution by mixing nickel, iron, manganese and copper salts with a concentration of 1.0 to 3.0 mol / L according to the molar ratio of Ni:Fe:Mn:Cu=x:y:z:n;

[0098] (2) The precursor slurry of the cathode material is synthesized by a continuous method under the protection of argon, nitrogen or other inert atmosphere by mixing salt solution, complexing agent and alkaline aqueous solution;

[0099] (3) The cathode material precursor slurry is filtered, washed and dried to obtain the cathode material precursor.

[0100] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxide. Therefore, the material is widely available and inexpensive.

[0101] In some embodiments, the M source includes at least one of oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M element; in other embodiments, the M source is at least one of CaO, CaCO3, Ca3(PO4)2, CaF2, CaCl2, Ca(OH)2, CaSi2, Sr(OH)2, SrCO3, Sn(OH)4, Y2O3, La2O3, Ce2O3, and CeO2. Therefore, the materials are widely available and the cost is low.

[0102] In some embodiments, the M' source includes at least one of oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M' element; in other embodiments, the M' source includes at least one of Li2CO3, LiOH, Co(OH)2, V2O5, Cr2O3, ZrO, Zr(HPO4)2, ZrSi2, Al2O3, AlPO4, AlCl3, ZnO, TiO2, MgO, MgCO3, Mg2Si, Mg3(PO4)2, MgF2, MgCl2, Nb2O5, WO3, B2O3, Sb2O5, and Sb2O3. Therefore, the materials are widely available and the cost is low.

[0103] S2: The raw material mixture is heated to T1℃ at a first heating rate v1, and then heated to T2℃ at a second heating rate v2, and held at the temperature for t time in the temperature range of T2-10℃ to T2+10℃ to obtain the positive electrode material, wherein v2 < v1.

[0104] In some embodiments, the difference between the first heating rate v1 and the second heating rate v2 is 1℃ / min to 6℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 6℃ / min.

[0105] In some implementations, 3℃ / min ≤ v1 ≤ 6℃ / min, and v2 ≤ 2℃ / min. Specifically, v1 can be 3℃ / min, 4℃ / min, 5℃ / min, or 6℃ / min, etc.; v2 can be 1℃ / min, 1.3℃ / min, 1.5℃ / min, 1.8℃ / min, or 2℃ / min, etc.

[0106] It is understandable that a faster heating rate will cause the surface of the cathode material to heat up quickly, while the interior heats up slowly, resulting in a rapid increase in the temperature difference between the inside and outside. This temperature difference leads to different reaction rates and crystallization rates in different regions of the cathode material, resulting in large structural differences and microscopic strain. Therefore, this disclosure employs a lower heating rate in the second heating process (T1-T2) where the reaction begins in the precursor and sodium source, allowing sufficient time for each region of the cathode material to reach thermal equilibrium, resulting in a more complete reaction, better structural uniformity, and lower microscopic stress.

[0107] In some implementations, 500℃≤T1≤700℃, for example, can be 500℃, 550℃, 600℃, 650℃ or 700℃, etc.

[0108] In some implementations, 900℃≤T2≤1100℃, for example, can be 900℃, 950℃, 1000℃, 1050℃ or 1100℃.

[0109] In some implementations, 5h≤t≤15h, for example, it can be 5h, 8h, 10h, 12h or 15h.

[0110] Under the above sintering conditions, the micro-strain changes of the cathode material can be reduced, which is beneficial to improving the structural stability and compaction density of the cathode material.

[0111] This disclosure controls the degree of single crystallization by regulating the sintering process of the cathode material preparation, and simultaneously introduces M element doping with a radius close to that of sodium ions as a layer support to alleviate layer slippage, suppress crystal crack formation, and synergistically improve the structural stability of the cathode material. This results in a cathode material with stronger strain resistance and the ability to withstand greater Na+ ionization at greater depths. + The layer structure can still maintain stability during the insertion and extraction process, which improves the cycle stability of the cathode material under high voltage.

[0112] A third aspect of this disclosure provides a sodium-ion battery comprising the cathode material described in the first aspect of this disclosure or the cathode material prepared by the method described in the second aspect of this disclosure. Therefore, this sodium-ion battery exhibits excellent cycle stability.

[0113] It is understood that there are no particular restrictions on the specific type of sodium-ion battery; it can be a primary battery or a secondary battery. The shape of the sodium-ion battery can be cylindrical, square, or any other shape. According to the outer packaging, sodium-ion batteries can be hard-shell batteries, soft-pack batteries, etc.

[0114] Typically, a sodium-ion battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are fabricated into electrode assemblies using winding or stacking processes. The electrode assemblies and electrolyte are housed within an outer package. During the charging and discharging process of a sodium-ion battery, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through.

[0115] In some embodiments, the positive electrode sheet may include a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder. The positive current collector may include a metal foil, for example, aluminum foil. The positive active material may include the positive electrode material of the first aspect of this disclosure or the positive electrode material prepared by the method described in the second aspect of this disclosure. The conductive agent may include acetylene black, single-walled carbon nanotubes, and conventional materials in the art. The binder may be polyvinylidene fluoride (PVDF) and conventional materials in the art.

[0116] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material, a thickener, a conductive agent, and a binder. The negative electrode current collector may be a metal foil, for example, copper foil. The negative electrode active material may include artificial graphite, natural graphite, silicon-carbon based composite materials, sodium metal sheets, and other commonly used negative electrode active materials in the art. The thickener may be sodium carboxymethyl cellulose (CMC-Na) and other conventional materials in the art. The conductive agent may be acetylene black and other conventional materials in the art. The binder may be styrene-butadiene rubber and other conventional materials in the art.

[0117] In some embodiments, the separator may be a separator known in the art that can be used in sodium-ion batteries and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0118] This disclosure provides a fourth aspect of an electrical device, including the sodium-ion battery described in the third aspect of this disclosure. This electrical device possesses all the features and advantages of the sodium-ion battery described above, which will not be repeated here.

[0119] In some embodiments, the sodium-ion battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0120] The embodiments of this disclosure are described in detail below.

[0121] Example 1

[0122] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. The slurry was filtered, washed, and the filter cake was dried at 120℃ and then sieved to obtain the multi-component precursor A1. The particle size distribution of this precursor was K. 90 =(D90 -D 10 ) / D 50 =1.3.

[0123] S2: The multi-component precursor A1 prepared in S1, Na2CO3, and components C (CaO, Y2O3, B2O3) are mixed in a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture is heated to 600℃ at a rate of 6℃ / min in an oxidizing atmosphere, and then to 1050℃ at a rate of 1.5℃ / min. The mixture is held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material B1 is obtained.

[0124] Example 2

[0125] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. The slurry was filtered, washed, and the filter cake was dried at 120℃ and then sieved to obtain the multi-component precursor A2. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0126] S2: The multi-component precursor A2 prepared in S1, Na2CO3, and components C (CaO, Y2O3, B2O3) are mixed in a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture is heated to 600℃ at a rate of 6℃ / min in an oxidizing atmosphere, and then to 1000℃ at a rate of 1.5℃ / min. The mixture is held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material B2 is obtained.

[0127] Example 3

[0128] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor A3. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0129] S2: The multi-component precursor A3 prepared in S1, Na2CO3, and components C (CaO, Y2O3, B2O3) are mixed in a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture is heated to 600℃ at a rate of 6℃ / min in an oxidizing atmosphere, and then to 1100℃ at a rate of 1.5℃ / min. The mixture is held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material B3 is obtained.

[0130] Example 4

[0131] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor A4. The particle size distribution of this precursor is K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0132] S2: The multi-component precursor A4 prepared in S1 was mixed with Na2CO3 and components C (CaO, Y2O3, B2O3) at a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture was first heated to 600℃ at a heating rate of 6℃ / min in an oxidizing atmosphere, and then heated to 1050℃ at a heating rate of 0.5℃ / min. The mixture was held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material B4 was obtained.

[0133] Example 5

[0134] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor A5. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0135] S2: The multi-component precursor A5 prepared in S1 was mixed with Na2CO3 and components C (CaO, Y2O3, B2O3) at a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y)=1.01:1, where Na / Ca / Y / B=1.01:0.05:0.01:0.01. The mixture was first heated to 600℃ at a heating rate of 6℃ / min in an oxidizing atmosphere, and then heated to 1050℃ at a heating rate of 1.5℃ / min. The mixture was held at this temperature for 12h. After cooling, crushing, and sieving, O3-type single-crystal cathode material B5 was obtained.

[0136] Example 6

[0137] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor A6. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0138] S2: The multi-component precursor A6 prepared in S1 was mixed with Na2CO3 and components C (CaO, Y2O3, B2O3) at a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture was first heated to 600℃ at a heating rate of 3℃ / min in an oxidizing atmosphere, and then heated to 1050℃ at a heating rate of 1.5℃ / min. The mixture was held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material B6 was obtained.

[0139] Examples 7 to 21

[0140] Same as Example 1, with specific differences shown in Tables 1 and 2.

[0141] Comparative Example 1

[0142] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor AD1. The particle size distribution of this precursor is K. 90 =(D 90 -D10 ) / D 50 =1.3.

[0143] S2: The multi-component precursor AD1 prepared in S1 was mixed with Na2CO3 and components C (CaO, Y2O3, B2O3) in a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture was heated to 600℃ at a rate of 1℃ / min in an oxidizing atmosphere, and then to 1050℃ at a rate of 3℃ / min. The temperature was held for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material BD1 was obtained.

[0144] Comparative Example 2

[0145] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor AD2. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0146] S2: The multi-component precursor AD2 prepared in S1, Na2CO3, and component C(B2O3) are heated to 600℃ at a heating rate of 6℃ / min in an oxidizing atmosphere, and then heated to 1050℃ at a heating rate of 1.5℃ / min. The temperature is held for 12 hours. After cooling, crushing, and sieving, O3-type single crystal cathode material BD2 is obtained.

[0147] Comparative Example 3

[0148] S1: Nickel sulfate, ferric sulfate, manganese sulfate, and copper sulfate are dissolved in a molar ratio of 30:32:34:4 to obtain a 2 mol / L mixed salt solution; sodium hydroxide is dissolved to prepare a 10 mol / L precipitant solution; and ammonia is dissolved to prepare an 8 mol / L complexing agent solution. 100 L of the mixed salt solution, precipitant solution, and complexing agent solution are introduced into a reactor in a parallel flow. Under a nitrogen atmosphere, the precipitate is continuously controlled to crystallize and grow until the median particle size D is reached. 50 The precursor slurry was grown to 3.5 μm. After filtration, washing, and drying the filter cake at 120℃, it was sieved to obtain the multi-component precursor AD3. The particle size distribution of this precursor was K. 90 =(D 90 -D 10 ) / D 50 =1.3.

[0149] S2: The multi-component precursor AD3 prepared in S1 was mixed with Na2CO3 and components C (CaO, Y2O3, B2O3) at a molar ratio of Na / (Ni+Fe+Mn+Cu+Ca+B+Y) = 1.01:1, where Na / Ca / Y / B = 1.01:0.02:0.01:0.01. The mixture was first heated to 600℃ at a heating rate of 6℃ / min in an oxidizing atmosphere, and then heated to 1050℃ at a heating rate of 6℃ / min. The mixture was held at this temperature for 12 hours. After cooling, crushing, and sieving, O3-type single-crystal cathode material BD3 was obtained.

[0150] The specific parameters of the above embodiments and comparative examples are shown in Tables 1 and 2.

[0151] Table 1. Composition of cathode material precursor and cathode material

[0152] Table 2 Experimental conditions

[0153] The test methods and results are as follows:

[0154] 1. Morphological testing:

[0155] This disclosure tests the scanning electron microscope (SEM) images of the precursors and O3-type single-crystal cathode materials prepared in the above embodiments and comparative examples, and provides exemplary SEM images of the precursor A1 and O3-type single-crystal cathode material B1 prepared in Example 1, as well as SEM images of the cathode materials prepared in Example 1 and Comparative Example 3 after applying different pressures (0 MPa, 111 MPa, 333 MPa, 555 MPa), the results of which are shown in Figures 1 to 3. As shown in Figure 1, the precursor A1 has a wide particle size distribution and a loose particle surface. As shown in Figure 2, the cathode material B1 has smooth single-crystal particles with a wide particle size distribution, with small particles filling the spaces between larger particles, exhibiting good gradation performance. Figure 3 shows a comparison of the particle morphology of Example 1 and Comparative Example 3 after applying different pressures (0 MPa, 111 MPa, 333 MPa, 555 MPa). It can be seen that the particle morphology of the sample from Example 1 remains basically intact with increasing pressure, without obvious cracks. However, with increasing pressure, obvious cracks can be observed on the particle surface of the sample from Comparative Example 3, and the degree of cracking is consistent with the micro-strain change ΔN in Table 3-2. i The data are directly proportional, which shows that the cathode material prepared in Example 1, which has a k value range defined by this disclosure, has stronger strain resistance and better crystal structure stability compared to the cathode material prepared in Comparative Example 3, which has a k value not within the range defined by this disclosure.

[0156] 2. Physical property testing:

[0157] This disclosure tested the XRD patterns of the precursors and O3-type single-crystal cathode materials in the above embodiments and comparative examples, and exemplarily provides XRD images of the precursor A1 and O3-type single-crystal cathode material B1 prepared in Example 1. The results are shown in Figures 4 and 5, respectively. As can be seen from Figure 4, the phase of the precursor A1 is (Ni 0.30 Fe 0.32 Mn 0.34 Cu 0.04 As can be seen from Figure 4, the phase of the sodium-ion battery single-crystal cathode material B1 disclosed herein is a sodium-ion battery O3-type layered oxide (O3-Na). 1.01 Ni 0.288 Fe 0.308 Mn 0.326 Cu 0.038 Ca 0.02 Y 0.01 B 0.01 O2).

[0158] 3. Microscopic strain testing:

[0159] This disclosure presents the O3-type single-crystal cathode material samples prepared in the above embodiments and comparative examples, which were subjected to fracturing tests under different pressures. The samples were also subjected to XRD fine-tuning analysis, and the micro-strain (i.e., lattice distortion) of the material was calculated.

[0160] Specifically, the following steps are included:

[0161] Step 1: Place the single-crystal sodium electrode material in a vacuum oven at 100-150℃ and dry it for 1-2 hours to treat the surface moisture.

[0162] Step 2: Weigh 3-5g of the processed sample and transfer it into the compaction mold. Gently shake the mold to make the sample surface flat.

[0163] Step 3: Place the mold containing the sample into the equipment and slowly pressurize it to different pressures (specifically 111MPa, 185MPa, 259MPa, 333MPa, 407MPa, 481MPa, 555MPa, etc.). After standing for 30 seconds, remove the mold and demold the sample. Only one pressure point can be measured at a time. After the measurement is completed, re-prepare the sample and test the next pressure point.

[0164] Step 4: Place the demolded positive electrode tablet into a mortar, gently separate the tablet and sieve it with a 300-400 mesh standard sieve to ensure that the tablet is completely pulverized without any flaky particles, and obtain a powder sample.

[0165] Step 5: Perform instrument parameter calibration for the X-ray powder diffractometer. Use standard Si powder to calibrate the goniometer position and standard LaB6 diameter to calibrate the instrument width. The procedure is as follows:

[0166] Test conditions: Voltage 40kV; Current 200mA; Step: 0.02°; Scan angle 5-120°; Acquisition time 45 minutes; Required peak intensity greater than 10000cps;

[0167] Under the determined test conditions, the position and width of the goniometer were calibrated respectively. The standard materials (Si powder, LaB6) were prepared on the sample stage, the spectrum was collected, the instrument was calibrated and the data was saved.

[0168] Step 6: Prepare different compacted materials onto the sample stage, perform X-ray powder diffraction tests under defined conditions, and save the data for analysis; ensure that the samples prepared on the sample stage are flat and that the sample height remains consistent each time.

[0169] Step 7: Import the test data into the refinement software for data processing:

[0170] (1) First, perform peak position processing, select the maximum peak value for processing, and ensure that the software can identify the position of all peaks;

[0171] (2) Perform phase identification. Use the PDF5+ database (International Centre for Diffraction Data) to determine the phases, and require that the test data be highly consistent with the card information.

[0172] (3) Add instrument width calibration data (external standard calibration width), and select all crystal planes to calculate the microstrain data of the material by the Halder-Wagner method.

[0173] Step 8: Analyze according to the microstrain (i.e., lattice distortion) data of the material calculated by the Halder-Wagner method. Compare the microstrain N i data at different pressures with the microstrain data N0 at a pressure of 0 MPa to obtain the change in microstrain △N i .

[0174] Step 9: Make a scatter plot and fitting analysis of the change in microstrain data at different pressures against the corresponding pressures to obtain the slope k value of the fitting line. According to the magnitude of the k value, it can be judged whether the structure is stable. The smaller the k value, the smaller the change in microstrain of the cathode material structure under different pressures, and the more stable the cathode material structure. Based on this, a rapid evaluation of the cathode material can be carried out to judge whether the cathode material structure is stable.

[0175] The change in microstrain data and the k value of the cathode material samples prepared in the above examples and comparative examples are specifically shown in Tables 3-1, 3-2, 3-3, and 3-4.

[0176] Table 3-1

[0177] Specific test data of some examples and comparative examples are shown in Tables 3-2, 3-3, and 3-4. [[ID=2​​​​​​4. Characterization of precursor and cathode material:

[0180] (1) Median particle size D 50 The particle size distribution was measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0181] (2) Particle size distribution of precursor K 90 K was calculated based on the precursor particle size results. 90 =(D 90 -D 10 ) / D 50 ;

[0182] (3) Precursor tap density: Measured using a BT-30 tap density tester from Baxter Corporation;

[0183] (4) Specific surface area of ​​precursor: measured by a Tristar II 3020 specific surface area tester from Micromertics, USA;

[0184] (5) Particle size distribution of cathode material: measured using a Mastersizer 3000 laser particle size analyzer from Malvern.

[0185] (6) Compacted density of positive electrode material: The density was measured using a Mitsubishi Chemical MCP-PD51 powder resistivity tester.

[0186] The specific test results are shown in Table 4.

[0187] Table 4

[0188] The above results show that the precursor K obtained by the method described in this disclosure 90 All are greater than 1 (except for K in Example 22) 90 The particle size distribution is relatively wide (less than 1). Figure 1 further shows that the precursor particles exhibit a wide size distribution; and the prepared cathode material also shows a wide size distribution, as shown in Figure 2. By comparing the examples and comparative examples in Table 4, it can be seen that the D of the precursor… 50 and particle size distribution K 90 When the value of K is within the preferred range, the sintered cathode material can still maintain a relatively wide particle size distribution. This cathode material with a wide particle size distribution has a high compaction density and volumetric energy density (corresponding to Table 5). In Example 21, the precursor K... 90 Outside of the preferred range, the prepared cathode material exhibits a lower compaction density.

[0189] 5. Electrochemical performance testing of cathode materials and batteries:

[0190] Battery preparation method: The positive electrode material prepared in each embodiment, acetylene black, and polyvinylidene fluoride (PVDF) are thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 95:3:2 to form a uniform slurry. This slurry is coated onto aluminum foil and dried at 120°C for 12 hours. Then, it is pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The loading of the positive electrode material is 15 mg / cm³. 2 .

[0191] Battery Assembly: In an Ar gas glove box with water and oxygen content both less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell and left to stand for 6 hours. The negative electrode used a 17 mm diameter, 1 mm thick metallic sodium sheet; the separator used a 25 μm thick Celgard 2325 porous membrane; and the electrolyte used was a 1 mol / L mixture of equal volumes of NaPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0192] Performance testing method: The button cell was electrochemically tested at 25°C using the Xinwei Battery Testing System, with a charge / discharge current density of 140 mA / g at 0.1C.

[0193] (1) Test method for specific capacity of 0.1C during the first charge and discharge cycle at 2.0-4.15V:

[0194] The prepared coin cells were subjected to charge-discharge tests at 25℃, 2.0-4.15V, and 0.1C to evaluate the specific capacity of the cathode material at the first charge-discharge at 0.1C.

[0195] (2) Average voltage test method for positive electrode materials:

[0196] The prepared coin cells were subjected to charge-discharge tests at 25℃, 2.0-4.15V, and 0.1C to evaluate the specific energy and specific capacity of the cathode material at the first discharge at 0.1C. The average voltage was calculated, i.e., specific energy / specific capacity.

[0197] (3) Ratio performance testing method:

[0198] The prepared coin cells were cycled twice at 25°C, 2.0–4.15 V, and 0.1C, and then cycled once each at 0.2C, 0.33C, 0.5C, and 1C. The rate performance of the multi-element cathode material was evaluated by the ratio of the initial discharge specific capacity at 0.1C to the discharge specific capacity at 1C. The initial discharge specific capacity at 0.1C was the discharge specific capacity of the coin cell in the first cycle, and the discharge specific capacity at 1C was the discharge specific capacity of the coin cell in the sixth cycle.

[0199] (4) Cycling performance test method:

[0200] The prepared coin cell was cycled twice at 25 °C, 2.0 - 4.15 V, and 0.1 C, and then cycled for 80 weeks at 1 C to evaluate the capacity retention rate of the material;

[0201] (5) Volume energy density test method:

[0202] Multiply the 0.1 C discharge specific capacity, average voltage obtained from the above methods (1) and (2) tests, and the tap density corresponding to each example in Table 3 to obtain the volume energy density.

[0203] The test results are shown in Table 5.

[0204] Table 5

[0205] According to the data in Table 5, by comparing Examples 1 - 21 and Comparative Examples 1 - 3, it can be seen that when the sintering regime in the positive electrode material is within the preferred range, the microstrain change of the material made therefrom is smaller, the k value is lower and meets the preferred range, the structure is more stable, and the retention rate after 80 cycles at 1 C can reach 94% under the high voltage of 2.0 - 4.15 V, which is greatly improved compared with the comparative examples, and the rate performance is also better;

[0206] By comparing Example 1, Example 5 and Example 20, it can be seen that when the Ca doping amount is within the preferred range, the microstrain change amount is smaller, and the k value meets the preferred conditions, having stronger anti-strain ability and more excellent structural stability. Therefore, when performing cyclic tests under the high voltage of 2.0 - 4.15 V, the retention rate after 80 cycles at 1 C can reach 94%; when the Ca doping amount exceeds the preferred range, its k value increases and exceeds the preferred range, the stability of the single crystal structure becomes poor, and the high voltage cycling performance is greatly reduced.

[0207] From the above results, it can be seen that the positive electrode material of the sodium ion battery provided by the present disclosure is a copper-based multi-component continuous process precursor with particle size distributions K 90 and D 50 within the preferred range, which is mixed with the first dopant M and the second dopant M' in a preferred ratio, and calcined by controlling the sintering regime (heating rate, holding temperature) within the preferred range to obtain a single crystal positive electrode material. Through microstrain testing of this positive electrode material, the results show that the positive electrode material prepared under such preferred conditions has a small microstrain change amount, a low k value and meets the preferred conditions (0 < k < 0.012), showing excellent anti-strain ability, greatly improving the structural stability of the positive electrode material, and showing excellent cycling stability and rate performance in the high voltage cycling test at 2.0 - 4.15 V, greatly improving the problem of poor cycling stability of the sodium ion layered oxide positive electrode material under high voltage.

[0208] In the description of this disclosure, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0209] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0210] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A cathode material, wherein, include: Na a1 (Ni x1 Fe y1 Mn z1 Cu n1 M m1 M’ p1 )O2 Formula 1 In the formula, 0.90≤a1≤1.10, 0≤x1≤0.5, 0≤y1≤0.5, 0≤z1≤0.5, 0≤n1≤0.1, 0<m1≤0.05, 0≤p1≤0.05, x1+y1+z1+n1+m1+p1=1; M is selected from at least one element from Ca, Sr, Y, Sn, Ce, and La; M' is selected from at least one element from Co, Ti, V, Mg, B, Cr, Sb, Al, Zn, Zr, Nb, W, and Li; The pressure T of the positive electrode material i -Microscopic strain change ΔN i The fitted straight line satisfies △N i =kT i 0 <k<0.016; Where k is the slope, T i The pressure applied to the cathode material in MPa before testing microstrain, and the microstrain change ΔN i Is the applied pressure T i The difference between the microstrain of the cathode material after pressure is applied and the microstrain of the cathode material before pressure is applied.

2. The cathode material according to claim 1, wherein, 0<k<0.012。 3. The cathode material according to claim 1, wherein, a1 is 0.90~1.05, 0.01≤m1≤0.05, 0.01≤p1≤0.

05.

4. The cathode material according to claim 3, wherein, a1 ranges from 0.95 to 1.

05.

5. The cathode material according to claim 3 or 4, wherein, a1 ranges from 0.97 to 1.

03.

6. The cathode material according to claim 1, wherein, The median particle size D of the cathode material 50 The size ranges from 3μm to 10μm.

7. The cathode material according to claim 6, wherein, The median particle size D of the cathode material 50 The size ranges from 4μm to 9μm.

8. The cathode material according to claim 6 or 7, wherein, The median particle size D of the cathode material 50 The size ranges from 5μm to 8μm.

9. The cathode material according to claim 1, wherein, The particle size distribution of the cathode material satisfies 1.1 < (D 90 -D 10 ) / D 50 <1.

6.

10. The cathode material according to claim 9, wherein, The particle size distribution of the cathode material satisfies 1.2 < (D 90 -D 10 ) / D 50 <1.

4.

11. The cathode material according to claim 1, wherein, The cathode material is an O3-type sodium-ion layered oxide.

12. A method for preparing the cathode material according to any one of claims 1 to 11, wherein, include: The precursor, sodium source, M source and optionally M' source are mixed to obtain a raw material mixture; The raw material mixture is heated to T1℃ at a first heating rate v1, and then heated to T2℃ at a second heating rate v2, and held at the temperature for t time within the temperature range of T2-10℃ to T2+10℃ to obtain the positive electrode material, wherein v2 < v1.

13. The method according to claim 12, wherein, The difference between the first heating rate v1 and the second heating rate v2 is 1℃ / min to 6℃ / min.

14. The method according to claim 12, wherein, 3℃ / min≤v1≤6℃ / min, v2≤2℃ / min.

15. The method according to claim 12, wherein, At least one of the following conditions must be met: 500℃≤T1≤700℃; 900℃≤T2≤1100℃; 5h≤t≤15h.

16. The method according to claim 12, wherein, The precursor satisfies at least one of the following conditions: The median particle size D of the precursor 50 The size is 3μm to 4μm; The particle size distribution K of the precursor 90 Satisfy: 0.5 < K 90 =(D 90 -D 10 ) / D 50 <1.6; The tap density of the precursor is 1.40 g / cm³. 3 ~1.80g / cm 3 ; The specific surface area of ​​the precursor is 10m². 2 / g~30m 2 / g.

17. The method according to claim 12, wherein, The precursor includes: Ni x2 Fe y2 Mn z2 Cu n2 O a2 H b2 Where, 0≤x²≤0.5, 0≤y²≤0.5, 0≤z²≤0.5, 0≤n²≤0.1, 1≤a²≤2, 0≤b²≤2, x²+y²+z²+n²=1.

18. The method according to claim 12, wherein, At least one of the following conditions must be met: The sodium source includes at least one of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxide; The M source includes at least one of oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M element, preferably including at least one of CaO, CaCO3, Ca3(PO4)2, CaF2, CaCl2, Ca(OH)2, CaSi2, Sr(OH)2, SrCO3, Sn(OH)4, Y2O3, La2O3, Ce2O3, and CeO2; The M' source includes at least one of oxides, carbonates, phosphates, fluorides, chlorides, hydroxides, and silicides containing the M' element, preferably including at least one of Li2CO3, LiOH, Co(OH)2, V2O5, Cr2O3, ZrO, Zr(HPO4)2, ZrSi2, Al2O3, AlPO4, AlCl3, ZnO, TiO2, MgO, MgCO3, Mg2Si, Mg3(PO4)2, MgF2, MgCl2, Nb2O5, WO3, B2O3, Sb2O5, and Sb2O3.

19. A sodium-ion battery, wherein, The cathode material includes any one of claims 1 to 11 or the cathode material prepared by any one of claims 12 to 18.

20. An electrical appliance, wherein, Including the sodium-ion battery as described in claim 19.

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