Positive electrode material having core-shell structure, sodium-ion battery and preparation method for positive electrode material

Abstract

Provided in some embodiments of the present disclosure is a positive electrode material having a core-shell structure. The positive electrode material comprises an inner core and an outer shell that coats the inner core. The inner core comprises an O3-type material, the molecular formula of the O3-type material being NaxMO2, wherein x is any numerical value between 0.75 and 1. The outer shell comprises a P2-type material, the molecular formula of the P2-type material being Na2M2TeO6, wherein M in the O3-type material and the P2-type material is one or more of lithium, magnesium, aluminum, vanadium, titanium, chromium, iron, nickel, cobalt, manganese, copper, zinc, strontium, zirconium, lanthanum and bismuth. Further provided in some embodiments of the present disclosure are a sodium-ion battery and a preparation method for a positive electrode material.

Description

Core-shell structured positive electrode materials, sodium-ion batteries and their preparation methods Technical Field

[0001] This disclosure relates to a core-shell structured positive electrode material, a sodium-ion battery, and a method for preparing the positive electrode material. Background Technology

[0002] When preparing positive electrode materials for sodium-ion batteries, sodium-containing compounds are typically used as raw materials. However, this often results in residual sodium on the surface of the synthesized positive electrode material. Since sodium is a highly reactive element, its residue on the surface may lead to side reactions, affecting the performance of the positive electrode material and the stability of the battery. In some cases, additional post-cleaning treatment may be necessary to remove the residual sodium and maintain battery performance.

[0003] Therefore, how to provide positive electrode materials that reduce residual sodium on the surface is a topic that those skilled in the art are actively researching. Summary of the Invention

[0004] Some embodiments of this disclosure provide a core-shell structured positive electrode material, including a core and a shell covering the core. The core comprises an O3-type material, wherein the molecular formula of the O3-type material is Na. x MO2, where x is any value between 0.75 and 1. The outer shell contains a P2-type material with the molecular formula Na2M2TeO6. The M in both the O3-type and P2-type materials is one or more of lithium (Li), magnesium (Mg), aluminum (Al), vanadium (V), titanium (Ti), chromium (Cr), iron (Fe), nickel (Ni), cobalt (Co), manganese (Mn), copper (Cu), zinc (Zn), strontium (Sr), zirconium (Zr), lanthanum (La), and bismuth (Bi). By selecting a P2 / O3 composite material (core: O3-type material; outer shell: P2-type material) as the positive electrode material, the positive electrode material can combine the advantages of both O3-type and P2-type materials (O3-type material: high capacitance; P2-type material: good chemical stability, high charge / discharge rate, excellent structural stability, and good air storage stability). Meanwhile, since P2-type materials have a wider tolerance range for residual sodium on the surface, they can absorb more residual sodium from the surface of O3-type materials, thereby reducing the overall sodium content of the material system. Furthermore, the higher interfacial stability of P2-type materials and the reduction of residual sodium content in the entire system can reduce the occurrence of side reactions in the battery, further improving structural stability and thus enhancing battery safety and cycle stability.

[0005] In some implementations, the number of moles of the O3 type material is greater than or equal to the number of moles of the P2 type material.

[0006] In some embodiments, the molecular formula of the positive electrode material is yNa. x MO2·(1-y)Na2M2TeO6, where y is any value between 0.5 and 0.99.

[0007] In some embodiments, when the weight percentage of the positive electrode material is 100%, the weight percentage of sodium carbonate in the positive electrode material is 0% to 0.3%, and the weight percentage of sodium hydroxide in the positive electrode material is 0% to 0.1%.

[0008] In some embodiments, the molecular formula of the O3-type material includes NaNi. 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2, NaNi 0.5 Mn 0.5 O2, or combinations thereof.

[0009] In some embodiments, the molecular formula of the P2 type material includes Na2Ni2TeO6.

[0010] Some embodiments of this disclosure provide a sodium-ion battery, including: a negative electrode, a positive electrode, a separator, and a sodium-ion battery electrolyte. The positive electrode comprises the aforementioned positive electrode material. The separator is disposed between the negative electrode and the positive electrode.

[0011] Some embodiments of this disclosure provide a method for preparing a positive electrode material, including: providing an O3-type material and a P2-type material, wherein the molecular formula of the O3-type material is Na. x The molecular formula of the MO2 and P2 type materials is Na2M2TeO6, where x is any value between 0.75 and 1, and M is one or more of lithium, magnesium, aluminum, vanadium, titanium, chromium, iron, nickel, cobalt, manganese, copper, zinc, strontium, zirconium, lanthanum, and bismuth. A positive electrode material is obtained by heating a mixture of O3 and P2 type materials. This positive electrode material comprises a core and a shell covering the core. The core contains O3 type material, and the shell contains P2 type material. Heating a mixture of O3 and P2 type materials, instead of directly mixing and sintering the O3 and P2 type material precursors, improves the structural integrity of the positive electrode material.

[0012] In some embodiments, the step of providing an O3-type material includes: mixing a first metal oxide and a first sodium-containing compound to obtain a first mixture; and heating the first mixture to sinter it into an O3-type material.

[0013] In some embodiments, the first metal oxide comprises Ni 0.45 Mn 0.4 Cu0.05 Ti 0.1 O x Ni 0.5 Mn 0.5 O x , or combinations thereof.

[0014] In some embodiments, the first sodium-containing compound comprises sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof.

[0015] In some embodiments, the step of heating the first mixture includes: heating to 600°C to 1000°C for 12 to 20 hours at a heating rate of 1°C / min to 10°C / min; and cooling at a cooling rate of 1°C / min to 3°C / min.

[0016] In some embodiments, after heating the first mixture, the O3 material is sieved to reduce the particle size of individual particles in the O3 material to 1 x 10⁻⁶. 2 nanometers to 1x10 4 nanometer.

[0017] In some embodiments, the step of providing a P2-type material includes: mixing a second metal oxide and a second sodium-containing compound to obtain a second mixture; and heating the second mixture to sinter it into a P2-type material.

[0018] In some embodiments, the second metal oxide comprises TeO2, NiO, or a combination thereof.

[0019] In some embodiments, the second sodium-containing compound comprises sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof.

[0020] In some embodiments, the step of heating the second mixture includes: heating to 500°C to 900°C for 4 to 16 hours at a heating rate of 1°C / min to 10°C / min; and cooling at a cooling rate of 1°C / min to 3°C / min.

[0021] In some embodiments, after the step of heating the second mixture, the P2 type material is crushed such that the individual particles in the P2 type material have a particle size of 1 nanometer to 999 nanometers.

[0022] In some embodiments, in the step of heating after mixing O3-type material and P2-type material, the molar ratio of O3-type material to P2-type material is 100:1 to 1:1.

[0023] In some embodiments, the heating step after mixing the O3 type material and the P2 type material includes: heating to 500°C to 900°C at a heating rate of 1°C / min to 10°C / min for 4 to 16 hours; and cooling at a cooling rate of 1°C / min to 3°C / min. Attached Figure Description

[0024] To make the above and other objects, features, advantages and embodiments disclosed herein more apparent and understandable, the accompanying drawings are described below:

[0025] Figure 1 is a flowchart of a method for preparing a positive electrode material according to some embodiments of the present disclosure.

[0026] Figure 2A shows the appearance of the O3 type material prepared according to point 1(2) of Example 1 under an electron microscope.

[0027] Figure 2B shows the appearance of the P2 type material prepared according to point 1(4) of Example 1 under an electron microscope.

[0028] Figure 2C shows the appearance of the P2 / O3 composite material prepared according to point 1(5) of Example 1 under an electron microscope.

[0029] Figure 2D shows the results of the half-cell electrochemical property test performed according to point 2 of Example 1. The positive electrode is either the O3 type material in point 1(2) of Example 1 or the P2 / O3 composite material in point 1(5) of Example 1.

[0030] Figure 2E shows the results of the full-cell electrochemical property test performed according to point 3 of Example 1, with the positive electrode using the P2 / O3 composite material obtained in point 1(5) of Example 1.

[0031] Figure 3A shows the appearance of the P2 / O3 composite material prepared according to point 1(5) of Example 2 under an electron microscope.

[0032] Figure 3B shows the results of the half-cell electrochemical property test performed according to point 2 of Example 2, with the positive electrode using the P2 / O3 composite material obtained in point 1(5) of Example 2. Detailed Implementation

[0033] The following describes several embodiments of this disclosure with reference to the accompanying drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details should not be used to limit this disclosure. That is, in some embodiments of this disclosure, these practical details are not essential and therefore should not be used to limit this disclosure. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner. Furthermore, for the reader's convenience, the dimensions of the components in the drawings are not drawn to scale.

[0034] It should be understood that relative terms such as “down” or “bottom” and “up” or “top” may be used herein to describe the relationship of one element to another, as illustrated in the accompanying drawings. It should be understood that relative terms are intended to include different orientations of the device beyond those shown in the figures. For example, if a device in one of the figures is flipped, an element described as being “down” to other elements will be oriented “up” to other elements. Thus, the exemplary term “down” can include both “down” and “up” orientations, depending on the specific orientation of the figure. Similarly, if a device in one of the figures is flipped, an element described as being “down” or “below” to other elements will be oriented “above” to other elements. Thus, the exemplary term “down” or “below” can include both “up” and “down” orientations.

[0035] This paper will first describe the preparation method of the positive electrode material. Specifically, please refer to Figure 1, which shows the flow chart of a method 100 for preparing a core-shell structured positive electrode material according to some embodiments of this disclosure, including steps S110 to S120. In step S110, an O3-type material and a P2-type material are provided, wherein the molecular formula of the O3-type material is Na. x The molecular formula of the MO2 and P2 type materials is Na2M2TeO6, where x is any value between 0.75 and 1 (e.g., x is 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any value within the aforementioned range), and M is one or more of lithium, magnesium, aluminum, vanadium, titanium, chromium, iron, nickel, cobalt, manganese, copper, zinc, strontium, zirconium, lanthanum, and bismuth. In step S120, the O3 type material and the P2 type material are mixed and then heated to obtain the positive electrode material (or P2 / O3 composite material). The above steps will be described sequentially in the following description.

[0036] It is worth emphasizing that, compared to the method of directly mixing O3-type material precursors and P2-type material precursors and then sintering, some embodiments of this disclosure are designed with a step sequence of providing O3-type material and P2-type material separately and then sintering them together to form a P2 / O3 composite material. This ensures the integrity of O3 material and P2 material, improves the integrity of the P2 / O3 core-shell structure in the finished product, and thus improves the cycle stability of the battery.

[0037] In some embodiments, the molecular formula of the O3-type material contains NaNi 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2, NaNi 0.5 Mn 0.5 O2, or a combination thereof. In some embodiments, the molecular formula of the P2-type material contains Na2Ni2TeO6. It should be emphasized that, compared with the existing P2-type structure compound Na b (M a Mn 1-a )O2 (M is nickel or iron, 0.05 ≤ a ≤ 0.7, 0.67 ≤ b ≤ 0.78), by selecting Na2Ni2TeO6 as the shell of the P2 / O3 composite material in the positive electrode material, the structure and interface stability of the positive electrode material can be improved, and when combined with the O3 material, good electrochemical performance can be achieved. Specifically, due to the low surface residual sodium of this compound, the occurrence of unwanted side reactions can be reduced, the gas generation on the electrode surface can be reduced, and the interface impedance caused by gas generation can be reduced, thereby improving the interface stability. In addition, for the existing P2-type structure compound Na x TMO2 (TM is selected from at least one of Mn, Ti, V, Cr, and Fe, 0.2 < x < 0.5), V and Cr are less environmentally friendly, and there are problems of ion migration and dissolution for Mn and Fe elements. The positive electrode material formed by Ti element has a lower potential. Compared with Na x TMO2, Na2Ni2TeO6 can avoid the occurrence of the aforementioned problems.

[0038] In some embodiments, in step S110, the step of providing the O3-type material includes: mixing a first metal oxide and a first sodium-containing compound to obtain a first mixture; and heating the first mixture so that the first mixture is sintered into an O3-type material.

[0039] In some embodiments, the first metal oxide contains Ni 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O x , Ni 0.5 Mn 0.5 O x , or a combination thereof. In some embodiments, the first sodium-containing compound contains sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof. A person with ordinary skill can select appropriate first metal oxide and first sodium-containing compound according to actual application requirements.

[0040] In some embodiments, the step of heating the first mixture in step S110 includes: heating at a heating rate of 1°C / min to 10°C / min (1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any value in the aforementioned range) to 600°C to 1000°C (600°C, 700°C, 800°C, 900°C, 1000°C, or any value in the aforementioned range) for 12 hours to 20 hours (12 hours, 14 hours, 16 hours, 18 hours, 20 hours, or any value in the aforementioned range); and cooling at a cooling rate of 1°C / min to 3°C / min (1°C / min, 2°C / min, 3°C / min, or any value in the aforementioned range). Too rapid a heating rate, too high or too low a heating temperature, too long or too short a heating time, or too fast or too slow a cooling rate may reduce the structural integrity of the sintered O3 material.

[0041] In some embodiments, after heating the first mixture, the O3 material is sieved to reduce the particle size of individual particles in the O3 material to 1 x 10⁻⁶. 2 nanometers to 1x10 4 Nanoparticles (e.g., 1x10⁻⁶) 2 Nano, 2x10 2 Nano, 3x10 2 Nano, 4x10 2 Nano, 5x10 2 Nano, 6x10 2 Nano, 7x10 2 Nano, 8x10 2 Nano, 9x10 2 Nano, 1x10 3 Nano, 5x10 3 Nano, 1x10 4 (Number, or any value within the aforementioned range). By controlling the upper limit of the particle size of the O3-type material applied to the subsequent step S120, the uniformity of the O3-type material is ensured, thereby improving the structural stability of the positive electrode material.

[0042] In some embodiments, the step of providing the P2 type material in step S110 includes: mixing a second metal oxide and a second sodium-containing compound to obtain a second mixture; and heating the second mixture to sinter it into a P2 type material.

[0043] In some embodiments, the second metal oxide comprises TeO2, NiO, or a combination thereof. In some embodiments, the second sodium-containing compound comprises sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof. Those skilled in the art can typically select a suitable second metal oxide and a second sodium-containing compound based on the specific application requirements.

[0044] In some embodiments, the step of heating the second mixture in step S110 includes: heating at a rate of 1°C / min to 10°C / min (1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any value in the aforementioned range) to 500°C to 900°C (500°C, 600°C, 700°C, 800°C, 900°C, or any value in the aforementioned range) for 4 hours to 16 hours (4 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, or any value in the aforementioned range); and cooling at a rate of 1°C / min to 3°C / min (1°C / min, 2°C / min, 3°C / min, or any value in the aforementioned range). Too rapid a heating rate, too high or too low a heating temperature, too long or too short a heating time, or too fast or too slow a cooling rate may reduce the structural integrity of the sintered P2 material.

[0045] In some embodiments, after heating the second mixture, the process includes crushing the P2-type material so that the particle size of individual particles in the P2-type material is between 1 nanometer and 999 nanometers (e.g., 1 nanometer, 100 nanometer, 200 nanometer, 300 nanometer, 400 nanometer, 500 nanometer, 600 nanometer, 700 nanometer, 800 nanometer, 900 nanometer, 950 nanometer, 999 nanometer, or any value within the aforementioned range). By controlling the upper limit of the particle size of the P2-type material applied to the subsequent step S120, the uniformity of the P2-type material is ensured, thereby improving the structural stability of the positive electrode material.

[0046] In some embodiments, in step S120, after heating the mixture of O3-type and P2-type materials, the molar number of O3-type materials is greater than or equal to the molar number of P2-type materials. In some embodiments, in step S120, the molar ratio of O3-type to P2-type materials is between 100:1 and 1:1 (e.g., 100:1, 75:1, 50:1, 25:1, 1:1, or any value within the aforementioned range). If the molar ratio is too large, the proportion of O3 is too high, resulting in increased sodium residue; if the molar ratio is too small, the proportion of P2 is too high, limiting the maximum specific capacitance.

[0047] In some embodiments, step S120, which involves heating after mixing the O3-type material and the P2-type material, includes: heating at a rate of 1°C / min to 10°C / min (1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any value within the aforementioned range) to 500°C to 900°C (500°C, 600°C, 700°C, 800°C, 900°C, or any value within the aforementioned range) for 4 hours to 16 hours (4 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, or any value within the aforementioned range); and cooling at a rate of 1°C / min to 3°C / min (1°C / min, 2°C / min, 3°C / min, or any value within the aforementioned range). Too rapid a heating rate, too high or too low a heating temperature, too long or too short a heating time, or too fast or too slow a cooling rate may reduce the structural integrity of the sintered P2 / O3 material.

[0048] In some embodiments, when the weight percentage of the positive electrode material is 100%, the weight percentage of sodium carbonate in the positive electrode material is 0% to 0.3% (e.g., 0%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or any value within the aforementioned range), and the weight percentage of sodium hydroxide in the positive electrode material is 0% to 0.1% (e.g., 0%, 0.05%, 0.1%, or any value within the aforementioned range). In some embodiments, when using a titration method to estimate the surface sodium ion content of the positive electrode material, the surface sodium ion content is between 500 ppm and 1500 ppm, wherein the titration method includes: dissolving the positive electrode material in water and ethanol respectively; titrating the sodium carbonate in the water and the sodium hydroxide in the ethanol separately using hydrochloric acid; and estimating the surface sodium ion content based on the weight percentages of sodium carbonate and sodium hydroxide. It is worth emphasizing that, because the surface sodium ion content of the positive electrode material is lower than that of existing positive electrode materials, unwanted side reactions can be reduced and interface stability can be improved.

[0049] In some embodiments, the molar number of O3-type material in the positive electrode material is greater than or equal to the molar number of P2-type material. By controlling the molar relationship between O3 and P2 materials, it can be ensured that O3-type material acts as the main component of the P2 / O3 composite material, thus ensuring that the capacitance remains at a certain level. In some embodiments, the molecular formula of the positive electrode material is γNa. xMO2·(1-y)Na2M2TeO6, where y is any value between 0.5 and 0.99 (e.g., y is 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, or any value within the aforementioned range). Generally, those skilled in the art can adjust the value of y according to electrochemical performance requirements to obtain P2 / O3 composite materials with different electrochemical properties. In some embodiments, the molecular formula of the positive electrode material is 0.95NaNi. 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O20.05Na2Ni2TeO6 or 0.9NaNi 0.5 Mn 0.5 O2·0.1Na2Ni2TeO6. If the y value is too large, the proportion of O3 is too high, which increases the sodium residue. If the y value is too small, the proportion of P2 is too high, which limits the maximum specific capacitance.

[0050] Some embodiments of this disclosure also provide a sodium-ion battery, including a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a sodium-ion battery electrolyte. In some embodiments, the negative electrode may include a negative electrode material layer and a negative electrode current collector, wherein the negative electrode material layer may include, for example, carbon (e.g., hard carbon), metal oxides, alloys, or combinations thereof, and the negative electrode current collector may be, for example, copper foil or aluminum foil, wherein using aluminum foil can further reduce costs. In some embodiments, the positive electrode may include a positive electrode material layer and a positive electrode current collector, wherein the positive electrode material layer includes a metal oxide material (see the foregoing description of positive electrode materials for details).

[0051] The features and effects of this disclosure will be described in more detail below with reference to comparative examples and embodiments. It should be understood that, without departing from the scope of this disclosure, the materials used, their content and proportion, processing details, and processing procedures can be appropriately modified based on ordinary knowledge in the art. Therefore, this disclosure should not be interpreted as limiting by the embodiments described below.

[0052] <Example 1> Positive Electrode Material 1

[0053] 0.95 (NaNi) 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2)

[0054] 0.05(Na2Ni2TeO6)

[0055] 1. Preparation of positive electrode materials

[0056] (1) O3 phase mixing: The target molecular formula is set as NaNi 0.45 Mn 0.4 Cu0.05 Ti 0.1 O2, weigh out the first metal oxide (Ni) 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O x The first metal oxide and the first sodium-containing compound (sodium carbonate) are mixed in such a way that the molar ratio of the metal in the first metal oxide to the sodium in the first sodium-containing compound is 1:1. The first metal oxide and the first sodium-containing compound are then placed in a mixer and mixed evenly to obtain a first mixture.

[0057] (2) O3 phase sintering: The first mixture was placed in a box furnace under an oxygen atmosphere and heated to 900°C at a heating rate of 5°C / min for 15 hours, then cooled to room temperature (approximately 25°C) at a cooling rate of 2°C / min to obtain the initial O3 type material (since cooling to room temperature takes a long time, to save time, the initial O3 type material can be collected when it drops to approximately 100°C). Next, the initial O3 type material was passed through a 300-mesh sieve to obtain the O3 type material (NaNi). 0.45 Mn 0.4 Cu 0.05 Ti 0.1 The appearance of O2 and O3 type materials under an electron microscope is shown in Figure 2A, electron microscope image 212. They exhibit a layered structure, with individual particles having a diameter of less than 20 micrometers (including or equal to 20 micrometers) and an average particle size (here, the D50 particle size, i.e., the particle size at which the cumulative particle size distribution percentage is 50%) of approximately 3 micrometers.

[0058] (3) P2 phase mixing: Set the target molecular formula as Na2Ni2TeO6, weigh the second metal oxide (TeO2 and NiO) and the second sodium-containing compound (sodium carbonate) so that the molar ratio of the metal in the second metal oxide to the sodium in the second sodium-containing compound is 2:1, and put the second metal oxide and the second sodium-containing compound into a mixer and mix them evenly to obtain the second mixture.

[0059] (4) P2 phase sintering: The second mixture was placed in an oxygen-filled box furnace and heated to 600°C at a heating rate of 5°C / min for 5 hours, and then cooled to room temperature (approximately 25°C) at a cooling rate of 3°C / min to obtain the initial P2 type material (since cooling to room temperature takes a long time, to save time, the initial P2 type material can be collected when it drops to approximately 100°C). Next, the initial P2 type material was mechanically crushed until the particle size was less than 200 nanometers to obtain the P2 type material (Na2Ni2TeO6). The appearance of the P2 type material under an electron microscope is shown in Figure 2B, electron microscope image 214, which shows a layered structure.

[0060] (5) P2 / O3 composite: The target molecular formula is set to 0.95 (NaNi) 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2)0.05(Na2Ni2TeO6), weigh the O3 type material (NaNi) obtained at point (2). 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2) and the P2-type material (Na2Ni2TeO6) obtained in point (4) were used to make the molar ratio of O3-type material to P2-type material 0.95:0.05. Next, the O3-type material and P2-type material were mixed using a mixer. The resulting second mixture was placed in a box furnace under an oxygen atmosphere and heated to 810°C at a heating rate of 5°C / min for 4 hours. Then, it was cooled to room temperature at a cooling rate of 1°C / min to obtain the initial P2 / O3 composite material. Next, the initial P2 / O3 composite material was ground and crushed and passed through a 300-mesh sieve to obtain the P2 / O3 composite material. For the appearance of the P2 / O3 composite material under an electron microscope, please refer to the electron microscope image 220 in Figure 2C. The P2 / O3 composite material exhibits a clump-like aggregate structure, with individual particles having a particle size of less than 20 micrometers.

[0061] 2. Electrical testing of half-cells

[0062] In this experimental example, the positive electrode used either the O3 type material or the P2 / O3 composite material from point 1 of Example 1, and the negative electrode was metallic sodium. A 2032 type battery case was selected, and Whatman GF / F glass fiber was used as the separator. A coin cell was assembled in an environment where the water and oxygen content were both below 0.1 ppm. The electrochemical properties of the cells were tested at a charge-discharge rate of 1 coulomb within a voltage range of 2 volts to 4.2 volts. For detailed results, please refer to Figure 230 of Figure 2D.

[0063] As shown in Figure 230, compared to using O3-type materials as the positive electrode material, the discharge specific capacitance of the P2 / O3 composite material remains at a high level after 25 cycles. In other words, using P2 / O3 composite material as the positive electrode material can improve the discharge capacitance of the half-cell after several cycles and improve cycle stability.

[0064] 3. Electrical testing of the full battery

[0065] In this experimental example, the positive electrode uses the P2 / O3 composite material mentioned in point 1, the negative electrode is hard carbon, and a 2032 type battery casing is selected. Using 2400 (polypropylene, PP) as the separator, coin cells were assembled in an environment where the water and oxygen content were both below 0.1 ppm. The electrochemical properties were tested at a charge-discharge rate of 0.5 coulombs within a voltage range of 1.5 volts to 4.15 volts. For detailed results, please refer to Figure 240 of Figure 2E.

[0066] As shown in Figure 240, when the P2 / O3 composite material is used as the positive electrode material, even after more than 90 cycles, the discharge specific capacitance remains above 125 mAh / g, maintaining excellent electrochemical performance.

[0067] <Example 2> Positive Electrode Material 2

[0068] 0.9 (NaNi) 0.5 Mn 0.5 O2)·0.1(Na2Ni2TeO6)

[0069] 1. Preparation of positive electrode materials

[0070] (1) O3 phase mixing: The target molecular formula is set as NaNi 0.5 Mn 0.5 O2, weigh out the first metal oxide (Ni) 0.5 Mn 0.5 O x The first metal oxide and the first sodium-containing compound (sodium carbonate) are mixed in such a way that the molar ratio of the metal in the first metal oxide to the sodium in the first sodium-containing compound is 1:1. The first metal oxide and the first sodium-containing compound are then placed in a mixer and mixed evenly to obtain a first mixture.

[0071] (2) O3 phase sintering: The first mixture was placed in a box furnace under an oxygen atmosphere and heated to 950°C at a heating rate of 8°C / min for 12 hours, then cooled to room temperature (approximately 25°C) at a cooling rate of 1°C / min to obtain the initial O3 type material (since cooling to room temperature takes a long time, to save time, the initial O3 type material can be collected when it drops to approximately 100°C). Next, the initial O3 type material was passed through a 300-mesh sieve to obtain the O3 type material (NaNi). 0.5 Mn 0.5 O2).

[0072] (3) P2 phase mixing: Set the target molecular formula as Na2Ni2TeO6, weigh the second metal oxide (TeO2 and NiO) and the second sodium-containing compound (sodium carbonate) so that the molar ratio of the metal in the second metal oxide to the sodium in the second sodium-containing compound is 2:1, and put the second metal oxide and the second sodium-containing compound into a mixer and mix them evenly to obtain the second mixture.

[0073] (4) P2 phase sintering: The second mixture was placed in an oxygen-filled box furnace and heated to 700°C at a heating rate of 5°C / min for 6 hours, then cooled to room temperature (approximately 25°C) at a cooling rate of 2°C / min to obtain the initial P2 type material (since cooling to room temperature takes a long time, to save time, the initial P2 type material can be collected when it drops to approximately 100°C). Next, the initial P2 type material was subjected to airflow crushing until the particle size was less than 200 nanometers to obtain the P2 type material (Na2Ni2TeO6).

[0074] (5) P2 / O3 composite: The target molecular formula is set to 0.9 (NaNi) 0.5 Mn 0.5 O2)·0.1(Na2Ni2TeO6), weigh the O3 type material (NaNi) obtained at point (2). 0.5 Mn 0.5 The O2 and P2-type materials (Na2Ni2TeO6) obtained in point (4) were combined to make the molar ratio of O3-type material to P2-type material 0.9:0.1. Next, the O3-type material and P2-type material were mixed using a mixer. The resulting second mixture was placed in a box furnace under an oxygen atmosphere and heated to 900°C at a heating rate of 5°C / min for sintering for 5 hours. Then, it was cooled to room temperature at a cooling rate of 1°C / min to obtain the initial P2 / O3 composite material. Next, the initial P2 / O3 composite material was ground and crushed and passed through a 300-mesh sieve to obtain the P2 / O3 composite material. The appearance of the P2 / O3 composite material under an electron microscope is shown in electron microscope image 310 of Figure 3A. It exhibits a clump-like structure, with individual particles having a diameter of less than 20 micrometers.

[0075] 2. Electrical testing of half-cells

[0076] In this experimental example, the positive electrode uses the P2 / O3 composite material from point 1 of Example 2. The electrochemical properties are tested using a half-cell assembly method, test conditions, and process that are substantially similar to the half-cell electrical test in point 2 of Example 1. For detailed results, please refer to Figure 3B, result figure 320.

[0077] As shown in Figure 320, when the P2 / O3 composite material of Example 2 is used as the positive electrode material, the discharge specific capacitance remains above 100 mAh / g even after more than 90 cycles, maintaining excellent electrochemical performance.

[0078] <Comprehensive Performance Evaluation>

[0079] To further analyze the differences between the O3-type material and the P2 / O3 composite material provided in the embodiments of this disclosure, and the differences between the P2 / O3 composite material provided in the embodiments of this disclosure and the positive electrode material of commercially available batteries, the following performance integration and comparison are further performed.

[0080] 1. Sodium residue

[0081] The O3-type material (NaNi) obtained at point 1(2) of Example 1 was selected. 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2), the P2 / O3 composite material obtained at point 1(5) of Example 1 (0.95 (NaNi) 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2)0.05(Na2Ni2TeO6)) and the P2 / O3 composite material obtained at point 1(5) of Example 2 (0.9(NaNi) 0.5 Mn 0.5 O2)·0.1(Na2Ni2TeO6)) were used as the test groups respectively.

[0082] To confirm the sodium carbonate content on the surface, the test group was placed in deionized water and stirred. Then, the sodium carbonate dissolved in the water was titrated with 0.1M dilute hydrochloric acid to estimate the sodium carbonate content on the surface of the test group.

[0083] To confirm the sodium hydroxide content on the surface, the test group was first placed in ethanol and stirred, and then the sodium hydroxide dissolved in the ethanol was titrated with 0.1M dilute hydrochloric acid to estimate the sodium hydroxide content on the surface of the test group.

[0084] Next, based on the calculated values ​​of sodium carbonate and sodium hydroxide, the sodium ion concentration on the surface of each test group was obtained, and the calculated results are shown in Table 1 below.

[0085] Table 1

[0086] Table 1 shows that, compared to the O3 type material, the sodium ion content remaining on the surface of both the P2 / O3 type materials in Example 1 and Example 2 is significantly reduced. Therefore, using the P2 / O3 type material as the positive electrode material of the battery can reduce battery side reactions caused by sodium ion residue, thereby improving battery safety.

[0087] 2. Battery performance

[0088] (1) Half-cell test

[0089] To confirm the O3-type materials, P2 / O3-type composite materials, and commercially available electrodes (NaNi) disclosed herein 1 / 3 Fe 1 / 3 Mn 1 / 3 The differences between O2) are summarized in Table 2. The performance parameters obtained by performing half-cell electrical tests on some groups in point 2 of Example 1 and point 2 of Example 2, as well as the performance parameters obtained by performing the same half-cell tests on commercially available electrode sets, are combined together. The commercially available electrode sets are those obtained by performing the same half-cell electrical tests on the half-cells in point 2 of Example 1 using commercially available electrodes as the positive electrode. The charge retention rate is the percentage of charging capacitor to discharging capacitor.

[0090] Table 2

[0091] Table 2 shows that, compared to commercially available electrodes, the half-cells prepared from the O3-type material of Example 1, the P2 / O3-type composite material of Example 1, and the P2 / O3-type composite material of Example 2 exhibit superior electrical performance in terms of capacitance retention rate, discharge capacitance after 100 cycles, and capacitance retention rate.

[0092] Furthermore, compared to O3-type materials, P2 / O3-type composite materials exhibit superior electrical performance (discharge capacitance and capacity retention) after 100 cycles when used as the positive electrode material. In other words, P2 / O3-type composite materials contribute to improved battery cycle stability.

[0093] (2) Full battery test

[0094] Table 3 summarizes the performance parameters obtained from the full-cell electrical tests performed using P2 / O3 composite material as the positive electrode material in point 3 of Example 1.

[0095] Table 3

[0096] Table 3 shows that the full cell prepared by the P2 / O3 composite material in Example 1 can still maintain a discharge capacitance of more than 120 mAh / g and a capacitance retention rate of more than 85% even after 100 cycles. It can maintain excellent electrical performance for a long time and exhibits good cycle stability.

[0097] Although the present disclosure has been described above with reference to embodiments, it is not intended to limit the present disclosure. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the appended claims.

[0098]

Symbol Explanation

Claims

1. A positive electrode material with a core-shell structure, characterized in that, include: The core contains an O3-type material, wherein the molecular formula of the O3-type material is Na. x MO2, where x is any value between 0.75 and 1; and The outer shell covering the core contains a P2-type material, wherein the molecular formula of the P2-type material is Na2M2TeO6, and the M in the O3-type material and the P2-type material is one or more of lithium, magnesium, aluminum, vanadium, titanium, chromium, iron, nickel, cobalt, manganese, copper, zinc, strontium, zirconium, lanthanum, and bismuth.

2. The positive electrode material according to claim 1, wherein the number of moles of the O3 type material is greater than or equal to the number of moles of the P2 type material.

3. The positive electrode material according to claim 2, wherein the molecular formula of the positive electrode material is yNa x MO2·(1-y)Na2M2TeO6, where y is any value between 0.5 and 0.

99.

4. The positive electrode material according to claim 1, wherein, when the weight percentage of the positive electrode material is 100%, the weight percentage of sodium carbonate in the positive electrode material is 0% to 0.3%, and the weight percentage of sodium hydroxide in the positive electrode material is 0% to 0.1%.

5. The positive electrode material according to claim 1, wherein the molecular formula of the O3 type material includes NaNi. 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O2, NaNi 0.5 Mn 0.5 O2, or combinations thereof.

6. The positive electrode material according to claim 1, wherein the molecular formula of the P2 type material includes Na2Ni2TeO6.

7. A sodium-ion battery, characterized in that, include: negative electrode; Positive electrode, comprising the positive electrode material according to claim 1; A separator is disposed between the negative electrode and the positive electrode; and Sodium-ion battery electrolyte.

8. A method for preparing a positive electrode material, characterized in that, include: O3-type and P2-type materials are provided, wherein the molecular formula of the O3-type material is Na. x MO2, the molecular formula of this P2 type material is Na2M2TeO6, where x is any value between 0.75 and 1, and M is one or more of lithium, magnesium, aluminum, vanadium, titanium, chromium, iron, nickel, cobalt, manganese, copper, zinc, strontium, zirconium, lanthanum, and bismuth; and The positive electrode material is obtained by heating the mixture of the O3 type material and the P2 type material. The positive electrode material includes a core and a shell covering the core. The core contains the O3 type material and the shell contains the P2 type material.

9. The method for preparing the positive electrode material according to claim 8, wherein the step of providing the O3-type material comprises: Mixing a first metal oxide and a first sodium-containing compound to obtain a first mixture; and The first mixture is heated so that it is sintered into the O3 type material.

10. The method for preparing the positive electrode material according to claim 9, wherein the first metal oxide comprises Ni. 0.45 Mn 0.4 Cu 0.05 Ti 0.1 O x Ni 0.5 Mn 0.5 O x , or combinations thereof.

11. The method for preparing the positive electrode material according to claim 9, wherein the first sodium-containing compound comprises sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof.

12. The method for preparing the positive electrode material according to claim 9, wherein the step of heating the first mixture comprises: Heating at a rate of 1°C / min to 10°C / min to 600°C to 1000°C for 12 to 20 hours; and Cool down at a rate of 1°C / minute to 3°C / minute.

13. The method for preparing the positive electrode material according to claim 9, wherein after the step of heating the first mixture, the method comprises sieving the O3-type material so that the particle size of individual particles in the O3-type material is 1x10⁻⁶. 2 nanometers to 1x10 4 nanometer.

14. The method for preparing the positive electrode material according to claim 8, wherein the step of providing the P2 type material comprises: Mixing a second metal oxide and a second sodium-containing compound yields a second mixture; and The second mixture is heated so that it is sintered into the P2 type material.

15. The method for preparing the positive electrode material according to claim 14, wherein the second metal oxide comprises TeO2, NiO, or a combination thereof.

16. The method for preparing the positive electrode material according to claim 14, wherein the second sodium-containing compound comprises sodium carbonate, sodium hydroxide, sodium acetate, sodium fluoride, or a combination thereof.

17. The method for preparing the positive electrode material according to claim 14, wherein the step of heating the second mixture comprises: Heating at a rate of 1°C / min to 10°C / min to 500°C to 900°C for 4 to 16 hours; and Cool down at a rate of 1°C / minute to 3°C / minute.

18. The method for preparing the positive electrode material according to claim 14, wherein after the step of heating the second mixture, the method comprises crushing the P2 type material such that the particle size of individual particles in the P2 type material is from 1 nanometer to 999 nanometers.

19. The method for preparing the positive electrode material according to claim 8, wherein in the step of heating after mixing the O3 type material and the P2 type material, the molar ratio of the O3 type material and the P2 type material is 100:1 to 1:

1.

20. The method for preparing the positive electrode material according to claim 8, wherein the step of heating after mixing the O3-type material and the P2-type material comprises: Heating at a rate of 1°C / min to 10°C / min to 500°C to 900°C for 4 to 16 hours; and Cool down at a rate of 1°C / minute to 3°C / minute.

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