O3 type high-entropy sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses an O3-type high-capacity high-stability high-entropy sodium ion battery positive electrode material, which is characterized in that the molecular formula is NaaMxNyRzO2, M is a metal atom set for providing capacity, M is a FeNiCuCo or AlNiCuCo atom set, N is a metal atom set for increasing voltage, N is a ZnLiSb atom set, R is a metal atom set with a stable structure, R is a MnTiMg atom set, 0.8 < = a < = 1, 0.45 < = x < = 0.55, 0.1 < = y < = 0.2, 0.3 < = z < = 0.4. A metal atom set for providing capacity, a metal atom set for improving voltage and a metal atom set for stabilizing a structure are effectively combined together, so that the stability, the mechanical strength and the chemical activity of the material are enhanced, the diffusion degree of electrons / ions in the material is properly restrained, and the overall performance stability of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of high-entropy sodium-ion batteries, and particularly to a cathode material for a high-capacity and high-stability O3-type high-entropy sodium-ion battery. Background Art

[0002] As a new type of next-generation energy storage technology, sodium-ion batteries have higher sodium storage density and lower cost compared with traditional lithium-ion batteries. However, there are still some technical bottlenecks in current sodium-ion layered batteries, such as problems of operation stability, capacity limitation, and cycle life. High-entropy cathode materials are considered a new solution to solve these problems.

[0003] The structure of O3-type oxides consists of octahedrally coordinated metal ions and six-sided ring-shaped oxygen atoms, forming a layered structure. During charge and discharge processes, oxygen atoms need to receive or release charges, resulting in redox reactions of the oxides and thus achieving charge transfer. However, the O3-type structure has the Jahn-Teller effect, which is a physical effect commonly present in transition metal ions. This effect causes distortion of the octahedrally coordinated metal ions, making the crystal structure unstable. At the same time, when the oxide participates in the charge and discharge reaction, the position of the oxygen atoms may change, leading to further destruction of the crystal structure. This structural instability may cause problems such as easy structural cleavage and capacity attenuation of the material during cycling. Some studies have shown that O3-type oxides are prone to recombination and failure during cycling, limiting the long-term cycle service life of the battery. To solve this problem, researchers are looking for more stable cathode material structures, such as other structures like cobalt spin state matching. In addition, some researchers have also carried out optimization and improvement on the O3-type structure, such as methods of regulating oxygen vacancies and alloying, to improve performance indicators such as material stability and cycle service life.

[0004] High-entropy alloy materials refer to materials with a uniform composition composed of five or more elements, aiming to balance alloy components to provide higher entropy and better stability. The principle of the formation of high-entropy alloys is based on the spontaneous mixing in metastable solid solutions. Usually, the differences in the size and electronegativity between elements are factors that cause the preferential behavior of different atoms in the alloy. However, high-entropy alloys can overcome this behavior, thereby obtaining a more uniform composition and a higher entropy value. Compared with traditional single-composition cathode materials, high-entropy cathode materials have higher energy storage density, better chemical stability, and longer cycle life. For example, MgFeCoNiCu quinary hybrid materials and LiFeCoNiCuZn quinary hybrid materials belong to high-entropy alloy materials, which have high specific capacity and good electrochemical performance. In high-entropy cathode materials, the change of a single element is evenly dispersed into other elements, thereby reducing the limitations brought by a single element and expanding the operable range of the battery. However, due to the doping of multiple elements in high-entropy sodium-ion layered cathode materials, the overall performance stability of the battery is insufficient.

[0005] Based on the above situation, the present invention proposes an O3-type high-capacity and high-stable high-entropy sodium-ion battery cathode material and a preparation method thereof. Through the synergistic effect between multiple elements, the ion transport and chemical reaction of the material are promoted, so that it has both high capacity, high discharge voltage and cycle stability. Summary of the Invention

[0006] To solve the above problems, the purpose of the present invention is to provide an O3-type high-entropy sodium-ion battery cathode material. This high-entropy sodium-ion battery cathode material effectively combines the metal atom set that provides capacity, the metal atom set that increases voltage, and the metal atom set that stabilizes the structure. While enhancing the material stability, mechanical strength, and chemical activity, it also appropriately restricts the diffusion degree of electrons / ions in the material, improving the overall performance stability of the battery. A preparation method is also provided.

[0007] The present invention is realized through the following technical solutions:

[0008] An O3-type high-capacity and high-stable high-entropy sodium-ion battery cathode material, whose molecular formula is Na aMxNyRzO2, where M is a set of metal atoms that provides capacity, M is a set of FeNiCuCo or AlNiCuCo atoms, within the operating voltage range of the positive electrode, M is a set of electrochemically active metal atoms that transform between different oxidation states and participate in the intercalation and deintercalation of sodium ions to provide capacity. N is a set of metal atoms that raises the voltage, N is a set of ZnLiSb atoms, N can inhibit the ordering of sodium vacancies, effectively improve the kinetic characteristics of the electrode reaction, reduce the polarization phenomenon, and thus maintain a high voltage output during discharge. In addition, uneven charge distribution may lead to a decrease in the local potential. The N set of metal atoms can achieve charge compensation, optimize the charge distribution, and thus increase the overall potential and discharge voltage of the electrode. R is a set of metal atoms that stabilizes the structure, R is a set of MnTiMg atoms, which helps to maintain the integrity of the layered structure, reduce the structural collapse caused by volume changes, and thus improve the cycle stability of the battery, 0.8 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, 0.1 ≤ y ≤ 0.2, 0.3 ≤ z ≤ 0.4.

[0009] Its molecular formula is Na a Fe x1 Ni x2 Cu x3 Co x4 Zn y1 Li y2 Sb y3 Mn z1 Ti z2 Mg z3 O2, where, 0.8 ≤ a ≤ 1, 0.45 ≤ x1 + x2 + x3 + x4 ≤ 0.55, 0.1 ≤ y1 + y2 + y3 ≤ 0.2, 0.3 ≤ z1 + z2 + z3 ≤ 0.4.

[0010] Its molecular formula is Na 0.83 Fe 0.22 Ni 0.18 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 O2.

[0011] A preparation method of a high-entropy sodium-ion battery cathode material with O3 type, high capacity and high stability, comprising the following steps: Step 1), uniformly mixing the oxide precursors of Na, Fe, Ni, Cu, Co, Zn, Li, Sb, Mn, Ti, Mg in stoichiometric ratio, and taking out the mixed powder and pressing it into tablets; Step 2), pre-sintering the mixture obtained in Step 1) in an air atmosphere; Step 3), continuing to heat up on the basis of Step 2) for secondary sintering, and cooling to room temperature after holding for a period of time.

[0012] In Step 1), pre-sinter to 400-600 °C.

[0013] After pre-sintering, keep the temperature for 4-6 hours.

[0014] In Step 3), the temperature for continuous heating is 800-1000 °C.

[0015] In Step 3), the holding time is 14-16 hours.

[0016] The high-entropy cathode material of the present invention effectively combines the metal atom set that provides capacity, the metal atom set that raises the voltage, and the metal atom set that stabilizes the structure. The composition method can make the atoms have higher thermal motion energy, so it is more difficult to form a regular lattice in the crystal, and it presents a more chaotic state. Moreover, multiple elements will form a more complex network structure, which contains a large number of different bonding modes and coordination environments, thereby enhancing the characteristics of the material in terms of stability, mechanical strength, chemical activity, etc. In addition, compared with the existing high-entropy cathode materials, there are several more metal elements, which means that the migration and diffusion of ions are more complex. Although the diffusivity of ions / electrons in the material is further improved, due to the increase in elements, the chemical bonds with different ionic radii and bond energies are more complex and diverse. Therefore, it is also necessary to arrange different atom sets to appropriately constrain the diffusion degree while promoting the easy diffusion of electrons / ions in the material, so as to improve the overall performance stability of the battery.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] (1) The present invention uses various metal oxides as precursors, combines the advantages of multiple components, successfully prepares an O3 type high-entropy cathode material, and divides all elements into functional regions.

[0019] (2) Compared with the existing high-entropy materials, the present invention can exhibit more excellent cycling performance, high capacity (~133.5 mAh / g) and higher average discharge voltage (3.20 V) with about 10-40% reduction in nickel content. The cathode material obtained by this method can reach an energy density of 426.57 Wh / kg, reducing its raw material cost while optimizing the electrochemical performance. Description of the Drawings

[0020] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0021] Figure 1 XRD pattern of the Na 0.83 Fe 0.22 Ni 0.18 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.0 5Mg 0.025 O2 product;

[0022] Figure 2 XRD pattern of the Na 0.83 Fe 0.22 Ni 0.18 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.0 5Mg 0.025 Charge and discharge curve of the O2 product;

[0023] Figure 3 XRD pattern of the Na 0.83 Fe 0.22 Ni 0.18 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.0 5Mg 0.025 Cycle performance graph of the O2 product;

[0024] Figure 4 XRD pattern of the Na 0.83 Fe 0.2 Ni 0.2 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 O2 product;

[0025] Figure 5 For Na in Example 2 of the present invention 0.83 Fe 0.2 Ni 0.2 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 Charge and discharge curve diagram of the O2 product;

[0026] Figure 6 For Na in Example 2 of the present invention 0.83 Fe 0.2 Ni 0.2 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 Cycling performance diagram of the O2 product;

[0027] Figure 7 For Na1Mn in Comparative Example 1 of the present invention 0.3 Ni 0.3 Fe 0.3 XRD diagram of the O2 product;

[0028] Figure 8 For Na1Mn in Comparative Example 1 of the present invention 0.3 Ni 0.3 Fe 0.3 Charge and discharge curve diagram of the O2 product;

[0029] Figure 9 For Na1Mn in Comparative Example 1 of the present invention 0.3 Ni 0.3 Fe 0.3 Cycling performance diagram of the O2 product. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example 1

[0032] According to Na 0.83 Fe 0.22 Ni 0.18Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 For the O₂ stoichiometry, weigh Na₂CO₃, Fe₂O₃, NiO, CuO, Co₂O₃, ZnO, Li₂CO₃, Sb₂O₅, Mn₂O₃, TiO₂, MgO and mix them in a ball mill at 500 revolutions per minute for 12 hours. Remove the mixed powder and press it into tablets, then pre-sinter it in an air atmosphere at 500 °C for 4 hours, then raise the temperature to 900 °C and sinter it in an air atmosphere for 14 hours, and then naturally cool it to room temperature. Use the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, polypropylene as the separator, and a solution of NaPF₆ in diglyme as the electrolyte to assemble a button battery and conduct charge-discharge tests. The current density is 12 mA / g, the voltage range is 2 - 4 V, the initial discharge capacity of the product can reach 133.5 mAh / g, the average discharge voltage is 3.20 V, the discharge specific energy is 426 Wh / kg, and the retention rate after 100 cycles is 87.2%.

[0033] Example 2

[0034] According to Na 0.83 Fe 0.2 Ni 0.2 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 For the O₂ stoichiometry, weigh Na₂CO₃, Mn₂O₃, NiO, Li₂CO₃ and mix them in a ball mill at 500 revolutions per minute for 12 hours. Remove the mixed powder and press it into tablets, then pre-sinter it in an air atmosphere at 500 °C for 4 hours, then raise the temperature to 900 °C and sinter it in an air atmosphere for 14 hours, and then naturally cool it to room temperature. Use the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, polypropylene as the separator, and a solution of NaPF₆ in diglyme as the electrolyte to assemble a button battery and conduct charge-discharge tests. The current density is 12 mA / g, the voltage range is 2 - 4 V, the initial discharge capacity of the product is 126.8 mAh / g, the average discharge voltage is 3.17 V, the discharge specific energy is 402 Wh / kg, and the retention rate after 100 cycles is 87.2%

[0035] Comparative Example 1

[0036] According to Na1Mn 0.3 Ni0.3 Fe 0.3 For the NaFeO₂ stoichiometry, weigh Na₂CO₃, Mn₂O₃, NiO, and Fe₂O₃ and mix them in a ball mill at 500 revolutions per minute for 12 hours. Remove the mixed powder and press it into tablets. Then, pre-sinter it in an air atmosphere at 500 °C for 4 hours, then raise the temperature to 900 °C and sinter it in an air atmosphere for 14 hours, and then naturally cool it to room temperature. Use the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, polypropylene as the separator, and a solution of NaPF₆ in diglyme as the electrolyte to assemble a button cell and conduct charge-discharge tests. The current density is 12 mA / g, the voltage range is 2 - 4 V. The initial discharge capacity of the product is 140.6 mAh / g, the average discharge voltage is 3.08 V, the discharge specific energy is 434.35 Wh / kg, and the retention rate after 100 cycles is 62.2%.

[0037] Comparative Example 2

[0038] According to the Na 0.83 Mn 0.4 Fe 0.3 Ni 0.275 Mo 0.025 For the stoichiometry, weigh Na₂CO₃, Mn₂O₃, NiO, and Fe₂O₃ and mix them in a ball mill at 500 revolutions per minute for 12 hours. Remove the mixed powder and press it into tablets. Then, pre-sinter it in an air atmosphere at 500 °C for 4 hours, then raise the temperature to 900 °C and sinter it in an air atmosphere for 14 hours, and then naturally cool it to room temperature. Use the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, polypropylene as the separator, and a solution of NaPF₆ in diglyme as the electrolyte to assemble a button cell and conduct charge-discharge tests. The current density is 12 mA / g, the voltage range is 2 - 4 V. The initial discharge capacity of the product is 115.7 mAh / g, the average discharge voltage is 3.10 V, the discharge specific energy is 415 Wh / kg, and the retention rate after 100 cycles is 70.5%.

[0039] Table 1 Performance Comparison of Products in Example 1, 2 and Comparative Example 1

[0040]

[0041] As can be seen from Table 1, Example 1 has obvious advantages over Example 2 in terms of discharge capacity, discharge voltage, and specific discharge energy while reducing the Ni content. From the XRD pattern, it can be seen that there is a certain amount of NiO impurity phase in Example 2. In Example 1, part of the Ni content was changed to Fe, reducing the NiO impurity phase, improving the low-potential plateau, raising the average discharge voltage (from 3.17 V to 3.20 V), and increasing the specific discharge capacity (from 126.8 mAh / g to 133.5 mAh / g), while maintaining good cycle stability. Although Comparative Example 1 exhibits a relatively high specific discharge capacity, it is due to the capacity contributed by a large amount of Ni, which greatly increases the production cost. Moreover, the specific discharge energy and cycle stability of the comparative example are far inferior to those of Example 1. The O3-type sodium-ion high-entropy cathode material proposed in the present invention uses multiple metal oxides as precursors, and such a composition makes the atomic arrangement in the material more disordered. In contrast, the atomic arrangement of ordinary layered cathode materials is more ordered and regular. The source of this difference is that the composition method of Example 1 can endow atoms with higher thermal motion energy, so it is more difficult to form a regular lattice in the crystal and presents a more disordered state. In addition, the multiple elements in Example 1 will form a more complex network structure, which contains a large number of different bonding modes and coordination environments, thereby enhancing the characteristics of the material in terms of stability, mechanical strength, and chemical activity. The multi-elements in Example 1 can improve the diffusivity of ions / electrons in the material because the chemical bonds between different elements often have different ionic radii and bond energies, making it easier for electrons / ions to diffuse in the material, thus improving the overall performance stability of the battery. In contrast, ordinary layered cathode materials are composed of only a few elements, and the ion / electron exchange between different elements is poor, and the charge diffusion is hindered, prone to accumulation and local reactions.

[0042] In summary, compared with the existing O3-type layered cathode materials and other types of high-entropy cathode materials, the present invention can exhibit excellent specific discharge energy, higher average discharge voltage, and cycle stability when reducing the nickel content by about 10 - 40%. The cathode material obtained by using this method can reach an energy density of 426 Wh / kg, reducing its raw material cost while increasing the energy density and maintaining excellent capacity retention.

[0043] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cathode material for an O3-type high-entropy sodium-ion battery, characterized in that, Its molecular formula is Na a MxNyRzO2, where M is a set of metal atoms providing capacity, M is a set of FeNiCuCo or AlNiCuCo atoms, N is a set of metal atoms for raising voltage, N is a set of ZnLiSb atoms, R is a set of metal atoms for stabilizing the structure, R is a set of MnTiMg atoms, 0.8 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, 0.1 ≤ y ≤ 0.2, 0.3 ≤ z ≤ 0.

4.

2. The cathode material for a high-entropy sodium-ion battery according to claim 1, wherein Its molecular formula is Na a Fe x1 Ni x2 Cu x3 Co x4 Zn y1 Li y2 Sb y3 Mn z1 Ti z2 Mg z3 O2, where 0.8 ≤ a ≤ 1, 0.45 ≤ x1 + x2 + x3 + x4 ≤0.55, 0.1 ≤ y1 + y2 + y3 ≤ 0.2, 0.3 ≤ z1 + z2 + z3 ≤ 0.

4.

3. The cathode material for a high-entropy sodium-ion battery according to claim 1, characterized in that, Its molecular formula is Na 0.83 Fe 0.22 Ni 0.18 Cu 0.05 Co 0.05 Zn 0.075 Li 0.025 Sb 0.05 Mn 0.275 Ti 0.05 Mg 0.025 O2。 4. The preparation method of the high-entropy sodium-ion battery cathode material according to claim 1, characterized in that, It includes the following steps: Step 1): Uniformly mix the oxide precursors of Na, Fe, Ni, Cu, Co, Zn, Li, Sb, Mn, Ti, and Mg in stoichiometric ratio, take out the mixed powder and press it into tablets; Step 2): Presinter the mixture obtained in Step 1) in an air atmosphere; Step 3): Based on Step 2), continue to raise the temperature for secondary sintering, keep the temperature for a period of time and then cool it to room temperature.

5. The preparation method according to claim 4, characterized in that In Step 1), presinter to 400 - 600 °C.

6. The preparation method according to claim 4, characterized in that, Keep the temperature for 4 - 6 hours after presintering.

7. The preparation method according to claim 4, characterized in that, In Step 3), the temperature for continuous heating is 800 - 1000 °C.

8. The preparation method according to claim 4, characterized in that, In Step 3), the holding time is 14 - 16 hours.

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